guanosine-triphosphate and Neoplasms

To search more therapeutic strategies for Ras-mutant tumors, regulators of the Ras superfamily involved in the GTP/GDP (guanosine triphosphate/guanosine diphosphate) cycle have been well concerned for their anti-tumor potentials. GTPase activating proteins (GAPs) provide the catalytic group necessary for the hydrolysis of GTPs, which accelerate the switch by cycling between GTP-bound active and GDP-bound inactive forms. Inactivated GAPs lose their function in activating GTPase, leading to the continuous activation of downstream signaling pathways, uncontrolled cell proliferation, and eventually carcinogenesis. A growing number of evidence has shown the close link between GAPs and human tumors, and as a result, GAPs are believed as potential anti-tumor targets. The present review mainly summarizes the critically important role of GAPs in human tumors by introducing the classification, function and regulatory mechanism. Moreover, we comprehensively describe the relationship between dysregulated GAPs and the certain type of tumor. Finally, the current status, research progress, and clinical value of GAPs as therapeutic targets are also discussed, as well as the challenges and future direction in the cancer therapy.

Topics: GTP Phosphohydrolases; GTPase-Activating Proteins; Guanosine Diphosphate; Guanosine Triphosphate; Humans; Neoplasms; ras GTPase-Activating Proteins

Tissue transglutaminase (TG2) is a member of the transglutaminase family that catalyzes Ca

Topics: Epithelial-Mesenchymal Transition; GTP-Binding Proteins; Guanosine Triphosphate; Humans; Neoplasms; Protein Glutamine gamma Glutamyltransferase 2; Transglutaminases

After decades of efforts, we have recently made progress into targeting KRAS mutations in several malignancies. Known as the 'holy grail' of targeted cancer therapies, KRAS is the most frequently mutated oncogene in human malignancies. Under normal conditions, KRAS shuttles between the GDP-bound 'off' state and the GTP-bound 'on' state. Mutant KRAS is constitutively activated and leads to persistent downstream signaling and oncogenesis. In 2013, improved understanding of KRAS biology and newer drug designing technologies led to the crucial discovery of a cysteine drug-binding pocket in GDP-bound mutant KRAS G12C protein. Covalent inhibitors that block mutant KRAS G12C were successfully developed and sotorasib was the first KRAS G12C inhibitor to be approved, with several more in the pipeline. Simultaneously, effects of KRAS mutations on tumour microenvironment were also discovered, partly owing to the universal use of immune checkpoint inhibitors. In this review, we discuss the discovery, biology, and function of KRAS in human malignancies. We also discuss the relationship between KRAS mutations and the tumour microenvironment, and therapeutic strategies to target KRAS. Finally, we review the current clinical evidence and ongoing clinical trials of novel agents targeting KRAS and shine light on resistance pathways known so far.

Topics: Antineoplastic Agents; Cysteine; Guanosine Triphosphate; Humans; Immune Checkpoint Inhibitors; Mutation; Neoplasms; Proto-Oncogene Proteins p21(ras); Tumor Microenvironment

Innate immunity is regulated by a broad set of evolutionary conserved receptors to finely probe the local environment and maintain host integrity. Besides pathogen recognition through conserved motifs, several of these receptors also sense aberrant or misplaced self-molecules as a sign of perturbed homeostasis. Among them, self-nucleic acid sensing by the cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) pathway alerts on the presence of both exogenous and endogenous DNA in the cytoplasm. We review recent literature demonstrating that self-nucleic acid detection through the STING pathway is central to numerous processes, from cell physiology to sterile injury, auto-immunity and cancer. We address the role of STING in autoimmune diseases linked to dysfunctional DNAse or related to mutations in DNA sensing pathways. We expose the role of the cGAS/STING pathway in inflammatory diseases, neurodegenerative conditions and cancer. Connections between STING in various cell processes including autophagy and cell death are developed. Finally, we review proposed mechanisms to explain the sources of cytoplasmic DNA.

Topics: Adenosine Triphosphate; Adult; Autoimmune Diseases; Autophagy; Cytokines; Cytoplasm; DNA; Guanosine Triphosphate; Humans; Immunity, Innate; Infant; Inflammation; Interferon Type I; Membrane Proteins; Mitochondria; Neoplasms; Neurodegenerative Diseases; NF-kappa B; Nucleotides, Cyclic; Nucleotidyltransferases; Signal Transduction

GTPase-activating protein (GAP) is a negative regulator of GTPase protein that is thought to promote the conversion of the active GTPase-GTP form to the GTPase-GDP form. Based on its ability to regulate GTPase proteins and other domains, GAPs are directly or indirectly involved in various cell requirement processes. We reviewed the existing evidence of GAPs regulating regulated cell death (RCD), mainly apoptosis and autophagy, as well as some novel RCDs, with particular attention to their association in diseases, especially cancer. We also considered that GAPs could affect tumor immunity and attempted to link GAPs, RCD and tumor immunity. A deeper understanding of the GAPs for regulating these processes could lead to the discovery of new therapeutic targets to avoid pathologic cell loss or to mediate cancer cell death.

Topics: Animals; GTP Phosphohydrolases; GTPase-Activating Proteins; Guanosine Triphosphate; Humans; Neoplasms; Regulated Cell Death

Growing cells increase multiple biosynthetic processes in response to the high metabolic demands needed to sustain proliferation. The even higher metabolic requirements in the setting of cancer provoke proportionately greater biosynthesis. Underappreciated key aspects of this increased metabolic demand are guanine nucleotides and adaptive mechanisms to regulate their concentration. Using the malignant brain tumour, glioblastoma, as a model, we have demonstrated that one of the rate-limiting enzymes for guanosine triphosphate (GTP) synthesis, inosine monophosphate dehydrogenase-2 (IMPDH2), is increased and IMPDH2 expression is necessary for the activation of de novo GTP biosynthesis. Moreover, increased IMPDH2 enhances RNA polymerase I and III transcription directly linking GTP metabolism to both anabolic capacity as well as nucleolar enlargement historically observed as associated with cancer. In this review, we will review in detail the basis of these new discoveries and, more generally, summarize the current knowledge on the role of GTP metabolism in cancer.

Topics: Cell Proliferation; Cellular Reprogramming; Guanosine Triphosphate; Humans; IMP Dehydrogenase; Neoplasms

The RAS genes encode for members of a large superfamily of guanosine-5'-triphosphate (GTP)-binding proteins that control diverse intracellular signaling pathways to promote cell proliferation. Somatic mutations in the RAS oncogenes are the most common activating lesions found in human cancers. These mutations invariably result in the gain-of-function of RAS by impairing GTP hydrolysis and are frequently associated with poor responses to standard cancer therapies. In this review, we summarize key findings of past and present landmark studies that have deepened our understanding of the RAS biology in the context of oncogenesis. We also discuss how emerging areas of research could further bolster a renewed global effort to target the largely undruggable oncogenic RAS and/or its activated downstream effector signaling cascades to achieve better treatment outcomes for RAS-mutant cancer patients.

Topics: Animals; Autophagy; Cell Transformation, Neoplastic; Guanosine Triphosphate; Humans; Mutation; Neoplasms; ras Proteins; Signal Transduction

Oncogenic rat sarcoma (Ras) is linked to the most fatal cancers such as those of the pancreas, colon, and lung. Decades of research to discover an efficacious drug that can block oncogenic Ras signaling have yielded disappointing results; thus, Ras was considered "undruggable" until recently. Inhibitors that directly target Ras by binding to previously undiscovered pockets have been recently identified. Some of these molecules are either isolated from natural products or derived from natural compounds. In this review, we described the potential of these compounds and other inhibitors of Ras signaling in drugging Ras. We highlighted the modes of action of these compounds in suppressing signaling pathways activated by oncogenic Ras, such as mitogen-activated protein kinase (MAPK) signaling and the phosphoinositide-3-kinase (PI3K) pathways. The anti-Ras strategy of these compounds can be categorized into four main types: inhibition of Ras-effector interaction, interference of Ras membrane association, prevention of Ras-guanosine triphosphate (GTP) formation, and downregulation of Ras proteins. Another promising strategy that must be validated experimentally is enhancement of the intrinsic Ras-guanosine triphosphatase (GTPase) activity by small chemical entities. Among the inhibitors of Ras signaling that were reported thus far, salirasib and TLN-4601 have been tested for their clinical efficacy. Although both compounds passed phase I trials, they failed in their respective phase II trials. Therefore, new compounds of natural origin with relevant clinical activity against Ras-driven malignancies are urgently needed. Apart from salirasib and TLN-4601, some other compounds with a proven inhibitory effect on Ras signaling include derivatives of salirasib, sulindac, polyamine, andrographolide, lipstatin, levoglucosenone, rasfonin, and quercetin.

Topics: Antineoplastic Agents; Cell Membrane; Down-Regulation; Drug Discovery; Guanosine Triphosphate; Neoplasms; ras Proteins

The crystal structure of RAS was first solved 25 years ago. In spite of tremendous and sustained efforts, there are still no drugs in the clinic that directly target this major driver of human cancers. Recent success in the discovery of compounds that bind RAS and inhibit signaling has fueled renewed enthusiasm, and in-depth understanding of the structure and function of RAS has opened new avenues for direct targeting. To succeed, we must focus on the molecular details of the RAS structure and understand at a high-resolution level how the oncogenic mutants impair function. Structural networks of intramolecular communication between the RAS active site and membrane-interacting regions on the G-domain are disrupted in oncogenic mutants. Although conserved across the isoforms, these networks are near hot spots of protein-ligand interactions with amino acid composition that varies among RAS proteins. These differences could have an effect on stabilization of conformational states of interest in attenuating signaling through RAS. The development of strategies to target these novel sites will add a fresh direction in the quest to conquer RAS-driven cancers. Clin Cancer Res; 21(8); 1810-8. ©2015 AACR. See all articles in this CCR Focus section, "Targeting RAS-Driven Cancers."

Topics: Allosteric Regulation; Animals; Antineoplastic Agents; Binding Sites; Catalytic Domain; Guanosine Triphosphate; Humans; Molecular Targeted Therapy; Mutation; Neoplasms; Oncogene Protein p21(ras); Protein Binding; Protein Isoforms; Signal Transduction

Ras proteins play a major role in human cancers but have not yielded to therapeutic attack. Ras-driven cancers are among the most difficult to treat and often excluded from therapies. The Ras proteins have been termed "undruggable," based on failures from an era in which understanding of signaling transduction, feedback loops, redundancy, tumor heterogeneity, and Ras' oncogenic role was poor. Structures of Ras oncoproteins bound to their effectors or regulators are unsolved, and it is unknown precisely how Ras proteins activate their downstream targets. These knowledge gaps have impaired development of therapeutic strategies. A better understanding of Ras biology and biochemistry, coupled with new ways of targeting undruggable proteins, is likely to lead to new ways of defeating Ras-driven cancers.

Topics: Animals; Guanosine Diphosphate; Guanosine Triphosphate; Humans; Mice; Neoplasms; Oncogene Protein p21(ras); Protein Processing, Post-Translational; Proto-Oncogene Proteins p21(ras); Retroviridae Infections; Signal Transduction; Tumor Virus Infections

Ras proteins, particularly their active GTP-bound forms (Ras·GTP), were thought "undruggable" owing to the absence of apparent drug-accepting pockets in their crystal structures. Only recently, such pockets have been found in the crystal structures representing a novel Ras·GTP conformation. We have conducted an in silico docking screen targeting a pocket in the crystal structure of M-Ras(P40D)·GTP and obtained Kobe0065, which, along with its analogue Kobe2602, inhibits binding of H-Ras·GTP to c-Raf-1. They inhibit the growth of H-rasG12V-transformed NIH3T3 cells, which are accompanied by downregulation of not only MEK/ERK but also Akt, RalA, and Sos, indicating the blockade of interaction with multiple effectors. Moreover, they exhibit antitumor activity on a xenograft of human colon carcinoma carrying K-rasG12V. The nuclear magnetic resonance structure of a complex of the compound with H-Ras(T35S)·GTP confirms its insertion into the surface pocket. Thus, these compounds may serve as a novel scaffold for the development of Ras inhibitors with higher potency and specificity.

Topics: Animals; Antineoplastic Agents; Drug Discovery; Enzyme Inhibitors; Guanosine Triphosphate; Humans; Neoplasms; ras Proteins; Small Molecule Libraries

Physical processes in living cells were not taken into consideration among the essentials of biological activity, regardless of the fact that they establish a state far from thermodynamic equilibrium. In biological system chemical energy is transformed into the work of physical forces for various biological functions. The energy transformation pathway is very likely connected with generation of the endogenous electrodynamic field as suggested by experimentally proved electrodynamic activity of biological systems connected with mitochondrial and microtubule functions. Besides production of ATP and GTP (adenosine and guanosine triphosphate) mitochondria form a proton space charge layer, strong static electric field, and water ordering around them in cytosol - that are necessary conditions for generation of coherent electrodynamic field by microtubules. Electrodynamic forces are of a long-range nature in comparison with bond and cohesive forces. Mitochondrial dysfunction leads to disturbances of the electromagnetic field; its power and coherence may be diminished, and frequency spectrum altered. Consequently, defective electrodynamic interaction forces between cancer and healthy cells may result in local invasion of cancer cells. Further deformation of interaction forces connected with experimentally disclosed spatial disarrangement of the cytoskeleton and disordered electrodynamic field condition metastatic process. Cancer therapeutic strategy targeting mitochondria may restore normal physiological functions of mitochondria and open the apoptotic pathway. Apoptosis of too much damaged cancer cells was observed. Considerable experience with DCA (dichloroacetate) cancer treatment in humans was accumulated. Clinical trials should assess DCA therapeutic potential and collect data for development of novel more effective drugs for mitochondrial restoration of various cancers.

Topics: Adenosine Triphosphate; Cell Transformation, Neoplastic; Dichloroacetic Acid; Electrophysiological Phenomena; Energy Metabolism; Guanosine Triphosphate; Humans; Microtubules; Mitochondria; Neoplasms

Rac GTPases are crucial signaling regulators in eukaryotic cells, acting downstream of many cell surface receptors. They play essential roles in diverse cellular functions including cytoskeleton dynamics, cell motility, cell survival and apoptosis. Their activities are controlled by a tightly regulated GDP/GTP cycle coupled with an alternation between cytoplasm and membrane compartments. Aberrant Rac signaling is found in some human cancers as a result of changes in the GTPase itself or in its regulation loops. This review highlights recent findings regarding the molecular and functional aspects of Rac that mediate tumorigenic transformation and metastasis. It also describes the cellular mechanisms that potentially explain the complex role of Rac in tumorigenesis. Finally, it discusses approaches for modulating Rac function as a potential anticancer strategy.

Topics: Animals; Antineoplastic Agents; Guanosine Diphosphate; Guanosine Triphosphate; Humans; Mice; Mice, Knockout; NADPH Oxidases; Neoplasm Invasiveness; Neoplasm Metastasis; Neoplasms; Neovascularization, Pathologic; rac GTP-Binding Proteins

Hungary is among the leading countries in Europe regarding the mortality and incidence of different types of tumours. Therefore, developing effective therapies is especially important in this country. Investigation of tumour formation and progression on the molecular level is required to develop possible therapeutical targets. Such targets can be proteins with tumour suppressor function, which inhibit intracellular signalling processes that under pathophysiological conditions can lead to uncontrolled cell proliferation and tumour formation. Protein e3B1/Abi-1, which belongs to the family of Abl-interactors, was isolated recently as a possible tumour suppressor. As a partner of Abl kinase, its role has been investigated in the development and progression of some types of leukemias, however, more and more experimental data suggest that it is a general suppressor protein. According to the latest results, e3B1/Abi-1 via the Ras small G-protein has an essential role in the regulation of cell proliferation, and via Rac activation it can affect actin remodelling, cell adhesion and migration. Cell proliferation is important in tumour development, while cell adhesion and migration has a role in metastasis formation. The latest results showed deletion of the gene encoding protein e3B1/Abi-1 in prostate cancer, loss of its expression during the progression of some types of leukemias, and there are data on the effect of imatinib mesylate (Gleevec or outside USA Glivec, Novartis), one of the newest drugs in leukemia treatment, on the phosphorylation of e3B1/Abi-1 as well. This report summarizes the data published on protein e3B1/Abi-1, with special interest in practical implications.

Topics: Adaptor Proteins, Signal Transducing; Animals; Cytoskeletal Proteins; Enzyme Activation; ErbB Receptors; Guanosine Triphosphate; Humans; Neoplasms; Tumor Suppressor Proteins

Septins are an evolutionarily conserved group of GTP-binding and filament-forming proteins that belong to the large superclass of P-loop GTPases. While originally discovered in yeast as cell division cycle mutants with cytokinesis defects, they are now known to have diverse cellular roles which include polarity determination, cytoskeletal reorganization, membrane dynamics, vesicle trafficking, and exocytosis. Septin proteins form homo- and hetero-oligomeric polymers which can assemble into higher-order filaments. They are also known to interact with components of the cytoskeleton, ie actin and tubulin. The precise role of GTP binding is not clear but a current model suggests that it is associated with conformational changes which alter binding to other proteins. There are at least 12 human septin genes, and although information on expression patterns is limited, most undergo complex alternative splicing with some degree of tissue specificity. Nevertheless, an increasing body of data implicates the septin family in the pathogenesis of diverse disease states including neoplasia, neurodegenerative conditions, and infections. Here the known biochemical properties of mammalian septins are reviewed in the light of the data from yeast and other model organisms. The data implicating septins in human disease are considered and a model linking these data is proposed. It is posited that septins can act as regulatable scaffolds where the stoichiometry of septin associations, modifications, GTP status, and the interactions with other proteins allow the regulation of key cellular processes including polarity determination. Derangements of such septin scaffolds thus explain the role of septins in disease states.

Topics: Animals; Communicable Diseases; Cytokinesis; Cytoskeleton; Diptera; GTP Phosphohydrolases; Guanosine Triphosphate; Humans; Invertebrates; Mammals; Models, Biological; Neoplasms; Nervous System Diseases; Signal Transduction; Yeasts

Ras mutation is observed in 20-30% of human malignancies. Ras proteins belong to the family of G-proteins, which are able to bind and hydrolyze guanosine triphosphate reversibly. They are responsible for signal transduction within cell. Ras undergoes several steps of posttranslational modification, but only farmesylation is necessary for its biologic activity. The crucial enzyme of farnesylation - farnesyltransferase (FT-ase) has become a major target for the development of new anticancer agents--farnesyltransferase inhibitors (FTI). Mutation of Ras results in the abrogation of its normal GTP-ase activity and subsequently it causes a permanent activation of Ras with uncontrolled growth and proliferation of cells. Recently published trials revealed, that FTI are highly effective in several malignant disorders, including myeloid leukemias. FTI are bioavailable after oral administration and have an acceptable toxicity profile. No enhanced myelosuppression effect was noted. It was observed, that FTI may increase cytotoxic effect of some antineoplastic drugs and radiotherapy. It seems that these agents are an interesting and promising therapeutic option for patients, who were resistant to conventional chemotherapy. The benefits of ambulatory drug administration may improve the quality of life in oncological patients. The II phase trials with FTI are under way and we hope, that these agents will find an unquestionable position in treatment of patients with malignancies.

Topics: Alkyl and Aryl Transferases; Antineoplastic Agents; Farnesyltranstransferase; Genes, ras; GTP-Binding Proteins; Guanosine Triphosphate; Humans; Imidazoles; Neoplasms; Piperidines; Point Mutation; Pyridines; Quinolones; Signal Transduction

Topics: Animals; Antimetabolites; Antineoplastic Agents; Cell Line, Tumor; Guanosine Triphosphate; Humans; Ligands; Neoplasms; Ribavirin; Signal Transduction

Benzamide riboside (BR) is a nucleoside prodrug that is phosphorylated to its 5'-monophosphate (BRMP) and then converted to its active metabolite, BAD (benzamide adenine dinucleotide), an analogue of NAD by the action of NMN adenylyltransferase (NMNAT). BAD is a potent, reversible, and noncompetitive inhibitor of inosine 5'-monophosphate dehydrogenase (IMPDH) resulting in depletion of guanylates (GTP and dGTP). IMPDH inhibitors such as BR induce differentiation and apoptosis as a consequence of GTP depletion. Tiazofurin (TR) and selenazofurin (SR) require similar metabolism by NMNAT. NMNAT is the rate-limiting step in the synthesis of NAD and NAD analogues. BR- and TR-sensitive leukemic cells contain high NMNAT activity, whereas resistant clones have greatly downregulated NMNAT activity (<0.1% of wild type). Perhaps the applicability of BR and analogues could be enhanced if combined with NMNAT gene expression in BR-resistant leukemic blasts. NAD has important regulatory role in repair of DNA damage and cell growth since it is a substrate for poly(ADP-ribose) polymerase (PARP). PARP appears to direct short-patch base excision repair and induce p53 upregulation leading to apoptosis. BR inhibits PARP at high concentrations when assayed in permeabilized leukemic cells. Several other IMPDH inhibitors (TR, mycophenolic acid, and ribavirin) exhibit similar PARP inhibitory activity. Although this inhibition was reversible, it was not prevented by the addition of guanosine, GTP, or its nonhydrolyzable analog gamma-S-GTP. Therefore, it can be concluded that IMPDH inhibitors directly inhibit PARP. Presumably, the shared IMP-NAD active site of IMPDH has a similar architecture to the NAD-binding pocket of PARP.

Topics: Antineoplastic Agents; Apoptosis; Cell Differentiation; Cell Survival; Enzyme Inhibitors; Guanosine Triphosphate; Humans; IMP Dehydrogenase; Neoplasms; Nicotinamide-Nucleotide Adenylyltransferase; Nucleosides; Tumor Cells, Cultured

Benzamide riboside (BR) after anabolism to an analogue of NAD, was shown to inhibit the activity of NAD-dependent enzymes such as inosine 5'-monophosphate dehydrogenase (IMPDH), the rate limiting enzyme in de novo guanylate biosynthesis, and malate dehydrogenase which is involved in the citric cycle and respiratory chain. BR exhibits strong anti-carcinogenic effects due to growth retardation and due to induction of apoptosis and necrosis. Apoptosis is ascribed to the inhibition of IMPDH because cell death can be blocked by restoring intracellular guanylate metabolism by the addition of guanosine. It is shown here, however, that also survival-relevant genes such as cdc25A, akt, bcl-2 and transferrin receptor become repressed by BR, whereas the expression level of the apoptosis enforcing gene c-myc persists. Even though BR-mediated growth retardation still allows BR to induce apoptosis, rapamycin-mediated cell cycle block and cell contact inhibition prevent cell death, it strongly suggests that BR induces a type of c-Myc-dependent apoptosis. At high concentrations BR induces DNA double strand breaks by yet to be determined mechanisms that occur hours before necrosis can be detected. This is accompanied by a dramatic decrease of intracellular ATP. The artificial restoration of ATP by addition of adenosine or sufficient provision of an energy source such as glucose prevents BR-promoted necrosis and favors apoptosis. This observation may be of clinical relevance.

Topics: Apoptosis; Cell Division; DNA Damage; Enzyme Inhibitors; Female; Gene Expression; Glucose; Guanosine Triphosphate; HL-60 Cells; Humans; IMP Dehydrogenase; Necrosis; Neoplasms; Nucleosides; Tumor Cells, Cultured

Over the last decades, knowledge on the genetic defects involved in tumor formation and growth has increased rapidly. This has launched the development of novel anticancer agents, interfering with the proteins encoded by the identified mutated genes. One gene of particular interest is ras, which is found mutated at high frequency in a number of malignancies. The Ras protein is involved in signal transduction: it passes on stimuli from extracellular factors to the cell nucleus, thereby changing the expression of a number of growth regulating genes. Mutated Ras proteins remain longer in their active form than normal Ras proteins, resulting in an overstimulation of the proliferative pathway. In order to function, Ras proteins must undergo a series of post-translational modifications, the most important of which is farnesylation. Inhibition of Ras can be accomplished through inhibition of farnesyl transferase, the enzyme responsible for this modification. With this aim, a number of agents, designated farnesyl transferase inhibitors (FTIs), have been developed that possess antineoplastic activity. Several of them have recently entered clinical trials. Even though clinical testing is still at an early stage, antitumor activity has been observed. At the same time, knowledge on the biochemical mechanisms through which these drugs exert their activity is expanding. Apart from Ras, they also target other cellular proteins that require farnesylation to become activated, e.g. RhoB. Inhibition of the farnesylation of RhoB results in growth blockade of the exposed tumor cells as well as an increase in the rate of apoptosis. In conclusion, FTIs present a promising class of anticancer agents, acting through biochemical modulation of the tumor cells.

Topics: Alkyl and Aryl Transferases; Animals; Antineoplastic Agents; Enzyme Inhibitors; Farnesyltranstransferase; Genes, ras; Guanosine Triphosphate; Humans; Neoplasms; ras Proteins; rho GTP-Binding Proteins; Signal Transduction

The concept of Molecular Science of the Living Organism was described, where the living state is explained as the purposive flows of the quantum mechanically controlled chemical reaction systems which support the homeostasis of the living organism. In the 21st century, the post genomic sequence era, the concept may be a self-evident truth. Molecular Science of the Living Organism was presented in the case of G-proteins: i.e., the atomically controlled mechanism of 1. the carcinogenesis which originates from the point mutation of ras p21, 2. the activation of a receptor protein at the cell membrane, especially in the case of bacteriorhodopsin, 3. the activation of an inactive G-protein by the activated receptor protein.

Topics: Alkyl and Aryl Transferases; Bacteriorhodopsins; Computational Biology; Genes, ras; GTP-Binding Proteins; GTPase-Activating Proteins; Guanosine Diphosphate; Guanosine Triphosphate; Humans; Neoplasms; Point Mutation; Protein Conformation; Protons

RhoB is a small GTPase that regulates actin organization and vesicle transport. It is required for signalling apoptosis in transformed cells that are exposed to farnesyltransferase inhibitors, DNA-damaging agents or taxol. Genetic analysis in mice indicates that RhoB is dispensable for normal cell physiology, but that it has a suppressor or negative modifier function in stress-associated processes, including cancer.

Topics: Actins; Alkyl and Aryl Transferases; Animals; Antineoplastic Agents; Apoptosis; Cell Adhesion; Cell Division; DNA Damage; Enzyme Induction; Enzyme Inhibitors; Farnesyltranstransferase; Guanosine Triphosphate; Humans; Mice; Multigene Family; Neoplasm Proteins; Neoplasms; Paclitaxel; Protein Prenylation; Protein Processing, Post-Translational; ras Proteins; rhoB GTP-Binding Protein; Signal Transduction; Stress, Physiological

As a result of its transforming abilities, activated Ras is expressed in a great number of cancers. The ras mutation frequency varies between 95% in pancreatic cancer and 5% in breast cancer. In leukemia, the highest frequency (30%) is found in acute myeloid leukemia. The presence of ras mutations has been correlated with a poor prognosis and negative clinical outcome. This suggests that mutated Ras activates mechanisms, which favor tumor growth, enhance the metastatic capacity of tumors or modulate tumor-specific immune responses. Several new functions of Ras, such as downregulation of major histocompatibility complex molecules, upregulation of certain cytokines, growth factors and degradative enzymes have been uncovered in the last decade. Additionally, mutated Ras can also serve as a primary target for the development of immunotherapy or drug therapy. This review will discuss the mechanisms by which Ras expressing tumors are able to evade destruction by the immune system and enhance their growth and metastatic potential. It will further elaborate on the attempts to develop successful immunotherapy and drug therapy targeting Ras expressing tumors.

Topics: Alkyl and Aryl Transferases; Animals; Antigen Presentation; Antineoplastic Agents; Cell Adhesion Molecules; Cell Transformation, Neoplastic; Cytokines; Drug Design; Endopeptidases; Enzyme Activation; Farnesyltranstransferase; Fungal Proteins; Fusion Proteins, bcr-abl; Genes, ras; Growth Substances; Guanosine Triphosphate; Humans; Immune System; Immunotherapy; Leukemia; Mice; Models, Biological; Mutation; Neoplasm Metastasis; Neoplasm Proteins; Neoplasms; Neurofibromin 1; Oligonucleotides, Antisense; Proteins; Proto-Oncogene Proteins p21(ras); Reoviridae Infections; Repressor Proteins; Signal Transduction; SOS1 Protein; T-Lymphocyte Subsets

Inosine 5 -monophosphate dehydrogenase (IMPDH) is a rate-limiting enzyme for the synthesis of GTP and dGTP. Two isoforms of IMPDH have been identified. IMPDH Type I is ubiquitous and predominantly present in normal cells, whereas IMPDH Type II is predominant in malignant cells. IMPDH plays an important role in the expression of cellular genes, such as p53, c-myc and Ki-ras. IMPDH activity is transformation and progression linked in cancer cells. IMPDH inhibitors, tiazofurin, selenazofurin, and benzamide riboside share similar mechanism of action and are metabolized to their respective NAD analogues to exert antitumor activity. Tiazofurin exhibits clinical responses in patients with acute myeloid leukemia and chronic myeloid leukemia in blast crisis. These responses relate to the level of the NAD analogue formed in the leukemic cells. Resistance to tiazofurin and related IMPDH inhibitors relate mainly to a decrease in NMN adenylyltransferase activity. IMPDH inhbitors induce apoptosis. IMPDH inhitors are valuable probes for examining biochemical functions of GTP as they selectively reduce guanylate concentration. Incomplete depletion of cellular GTP level seems to down-regulate G-protein function, thereby inhibit cell growth or induce apoptosis. Inosine 5'-monophosphate dehydrogenase (IMPDH, EC 1.1.1.205) catalyzes the dehydrogenation of IMP to XMP utilizing NAD as the proton acceptor. Studies have demonstrated that IMPDH is a rate-limiting step in the de novo synthesis of guanylates, including GTP and dGTP. The importance of IMPDH is central because dGTP is required for the DNA synthesis and GTP plays a major role not only for the cellular activity but also for cellular regulation. Two isoforms of IMPDH have been demonstrated. IMPDH Type I is ubiquitous and predominately present in normal cells, whereas the IMPDH Type II enzyme is predominant in malignant cells. Although guanylates could be salvaged from guanine by the enzyme hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8), the level of circulating guanine is low in dividing cells and this route is probably insufficient to satisfy the needs of guanylates in the cells.

Topics: Antineoplastic Agents; Apoptosis; cdc25 Phosphatases; Clinical Trials as Topic; Clinical Trials, Phase I as Topic; Clinical Trials, Phase II as Topic; Drug Resistance, Neoplasm; Enzyme Inhibitors; Female; Guanosine Triphosphate; HL-60 Cells; Humans; IMP Dehydrogenase; Leukemia, Myeloid; Neoplasms; Nucleosides; Organoselenium Compounds; Ovarian Neoplasms; Protein Tyrosine Phosphatases; Ribavirin; Ribonucleosides; RNA, Messenger; Time Factors; Tumor Cells, Cultured

Topics: Antimetabolites, Antineoplastic; Deoxyguanine Nucleotides; Guanosine Triphosphate; Humans; IMP Dehydrogenase; Inosine Monophosphate; Leukemia; Neoplasms; Purines; Ribavirin; Signal Transduction

Intensified adenosine triphosphate (ATP) degradation following therapeutic hyperthermia is often observed in solid tumors. As a result, accumulation of purine catabolites can be expected together with formation of protons at several stages during degradation to the final product, uric acid. Proton formation in turn can contribute to the development of heat-induced acidosis. Furthermore, oxidation of hypoxanthine and xanthine may result in generation of reactive oxygen species, which may lead to DNA damage, lipid peroxidation and protein denaturation, thus also contributing to heat-induced cytotoxicity. In hyperthermia experiments a tumor-size-dependent, significant increase in the levels of the following catabolites has been demonstrated: [symbol: see text] [IMP + GMP] (sum of guanosine and inosine monophosphate levels), inosine, hypoxanthine, xanthine and uric acid, along with a drop in ATP and guanosine triphosphate (GTP) levels. These data suggest that formation of reactive oxygen species and protons during purine degradation may indeed play a significant role in the antitumor effect of hyperthermia.

Topics: Adenosine Triphosphate; Animals; Guanosine Monophosphate; Guanosine Triphosphate; Humans; Hyperthermia, Induced; Inosine Monophosphate; Models, Biological; Neoplasms; Neoplasms, Experimental; Purines; Ribonucleotides

Topics: DNA; DNA Mutational Analysis; DNA, Neoplasm; Enzyme Activation; Genes, ras; GTP Phosphohydrolases; GTP-Binding Proteins; GTPase-Activating Proteins; Guanosine Triphosphate; Humans; Neoplasms; Polymerase Chain Reaction; Protein Binding; Proteins; Proto-Oncogene Proteins p21(ras); ras GTPase-Activating Proteins; Signal Transduction

Topics: Animals; Cell Wall; GTP-Binding Proteins; Guanosine Triphosphate; Microtubules; Morphogenesis; Neoplasms; Nucleic Acids; Oncogenes; Phospholipids; Polyamines; Protein Biosynthesis; Spores, Bacterial; Spores, Fungal

Topics: Adenosine Triphosphate; Animals; Biological Transport; Blood Cells; Cell Transformation, Neoplastic; Cyclic AMP; Cyclic GMP; Female; Guanosine Triphosphate; Humans; Kidney; Liver; Male; Neoplasms; Neoplasms, Experimental; Nucleotides, Cyclic; Rats; Receptors, Cell Surface

RAS proteins regulate most aspects of cellular physiology. They are mutated in 30% of human cancers and 4% of developmental disorders termed Rasopathies. They cycle between active GTP-bound and inactive GDP-bound states. When active, they can interact with a wide range of effectors that control fundamental biochemical and biological processes. Emerging evidence suggests that RAS proteins are not simple on/off switches but sophisticated information processing devices that compute cell fate decisions by integrating external and internal cues. A critical component of this compute function is the dynamic regulation of RAS activation and downstream signaling that allows RAS to produce a rich and nuanced spectrum of biological outputs. We discuss recent findings how the dynamics of RAS and its downstream signaling is regulated. Starting from the structural and biochemical properties of wild-type and mutant RAS proteins and their activation cycle, we examine higher molecular assemblies, effector interactions and downstream signaling outputs, all under the aspect of dynamic regulation. We also consider how computational and mathematical modeling approaches contribute to analyze and understand the pleiotropic functions of RAS in health and disease.

Topics: Guanosine Triphosphate; Humans; Neoplasms; ras Proteins; Signal Transduction

Early cancer screening enables timely detection of carcinogenesis, and aids in prompt clinical intervention. Herein, we report on the development of a simple, sensitive, and rapid fluorometric assay based on the aptamer probe (aptamer beacon probe, ABP) for monitoring the energy-demand biomarker adenosine triphosphate (ATP), an essential energy source that is released into the tumor microenvironment. Its level plays a significant role in risk assessment of malignancies. The operation of the ABP for ATP was examined using solutions of ATP and other nucleotides (UTP, GTP, CTP), followed by monitoring of ATP production in SW480 cancer cells. Then, the effect of a glycolysis inhibitor, 2-deoxyglucose (2-DG), on SW480 cells was investigated. The stability of predominant ABP conformations in the temperature range of 23-91 °C and the effects of temperature on ABP interactions with ATP, UTP, GTP, and CTP were evaluated based on quenching efficiencies (QE) and Stern-Volmer constants (

Topics: Adenosine Triphosphate; Aptamers, Nucleotide; Biosensing Techniques; Deoxyglucose; Glycolysis; Guanosine Triphosphate; Neoplasms; Uridine Triphosphate

KRAS mutations are major drivers of various cancers. Recently, allele-specific inhibitors of the KRAS G12C mutant were developed that covalently modify the thiol of Cys12, thereby trapping KRAS in an inactive GDP-bound state. To study the mechanism of action of the covalent inhibitors in both in vitro and intracellular environments, we used real-time NMR to simultaneously observe GTP hydrolysis and inhibitor binding. In vitro NMR experiments showed that the rate constant of ARS-853 modification is identical to that of GTP hydrolysis, indicating that GTP hydrolysis is the rate-limiting step for ARS-853 modification. In-cell NMR analysis revealed that the ARS-853 reaction proceeds significantly faster than that in vitro, reflecting acceleration of GTP hydrolysis by endogenous GTPase proteins. This study demonstrated that the KRAS covalent inhibitor is as effective in the cell as in vitro and that in-cell NMR is a valuable validation tool for assessing the pharmacological properties of the drug in the intracellular context.

Topics: Guanosine Triphosphate; Humans; Magnetic Resonance Spectroscopy; Mutation; Neoplasms; Proto-Oncogene Proteins p21(ras)

KRas is the most frequently mutated protein of the three Ras isoforms in various cancer types. KRas mutations (i.e. G12C) are present in approximately 30% of human cancers. Based on our previously reported KRas G12C inhibitor LLK-10, we designed a series of quinazoline analogues with a trifluoromethacrylic acid warhead as covalent inhibitor of KRas G12C. The pharmacological activities of these compounds were assessed against a panel of KRas G12C mutated cancer cells (i.e. H358 and H23). Among them, K20 showed that highest antiproliferative potency with an average IC

Topics: Animals; Guanosine Triphosphate; Humans; Mice; Mice, Nude; Mutation; Neoplasms; Piperazines; Proto-Oncogene Proteins p21(ras); Quinazolines

Topics: Animals; Antineoplastic Agents; Guanosine Triphosphate; Humans; Mice; Mice, Nude; Mutation; Neoplasms; Proto-Oncogene Proteins p21(ras); Quinazolines

Aberrant activation of EGFR due to overexpression or mutation is associated with poor prognosis in many types of tumors. Here we show that blocking the sorting system that directs EGFR to plasma membrane is a potent strategy to treat EGFR-dependent tumors. We find that EGFR palmitoylation by DHHC13 is critical for its plasma membrane localization and identify ARF6 as a key factor in this process. N-myristoylated ARF6 recognizes palmitoylated EGFR via lipid-lipid interaction, recruits the exocyst complex to promote EGFR budding from Golgi, and facilitates EGFR transporting to plasma membrane in a GTP-bound form. To evaluate the therapeutic potential of this sorting system, we design a cell-permeable peptide, N-myristoylated GKVL-TAT, and find it effectively disrupts plasma membrane localization of EGFR and significantly inhibits progression of EGFR-dependent tumors. Our findings shed lights on the underlying mechanism of how palmitoylation directs protein sorting and provide an potential strategy to manage EGFR-dependent tumors.

Topics: ADP-Ribosylation Factors; Cell Membrane; ErbB Receptors; Guanosine Triphosphate; Humans; Lipids; Neoplasms; Protein Transport

The glycolytic enzyme lactate dehydrogenase A (LDHA) is frequently overexpressed in cancer, which promotes glycolysis and cancer. The oncogenic effect of LDHA has been attributed to its glycolytic enzyme activity. Here we report an unexpected noncanonical oncogenic mechanism of LDHA; LDHA activates small GTPase Rac1 to promote cancer independently of its glycolytic enzyme activity. Mechanistically, LDHA interacts with the active form of Rac1, Rac1-GTP, to inhibit Rac1-GTP interaction with its negative regulator, GTPase-activating proteins, leading to Rac1 activation in cancer cells and mouse tissues. In clinical breast cancer specimens, LDHA overexpression is associated with higher Rac1 activity. Rac1 inhibition suppresses the oncogenic effect of LDHA. Combination inhibition of LDHA enzyme activity and Rac1 activity by small-molecule inhibitors displays a synergistic inhibitory effect on breast cancers with LDHA overexpression. These results reveal a critical oncogenic mechanism of LDHA and suggest a promising therapeutic strategy for breast cancers with LDHA overexpression.

Topics: Animals; GTP Phosphohydrolases; Guanosine Triphosphate; Isoenzymes; L-Lactate Dehydrogenase; Lactate Dehydrogenase 5; Mice; Neoplasms

Heterotrimeric G-proteins (Gαβγ) are the main transducers of signals from GPCRs, mediating the action of countless natural stimuli and therapeutic agents. However, there are currently no robust approaches to directly measure the activity of endogenous G-proteins in cells. Here, we describe a suite of optical biosensors that detect endogenous active G-proteins with sub-second resolution in live cells. Using a modular design principle, we developed genetically encoded, unimolecular biosensors for endogenous Gα-GTP and free Gβγ: the two active species of heterotrimeric G-proteins. This design was leveraged to generate biosensors with specificity for different heterotrimeric G-proteins or for other G-proteins, such as Rho GTPases. Versatility was further validated by implementing the biosensors in multiple contexts, from characterizing cancer-associated G-protein mutants to neurotransmitter signaling in primary neurons. Overall, the versatile biosensor design introduced here enables studying the activity of endogenous G-proteins in live cells with high fidelity, temporal resolution, and convenience.

Topics: Amino Acid Motifs; Animals; Bioluminescence Resonance Energy Transfer Techniques; Biosensing Techniques; Cells, Cultured; GTP-Binding Protein alpha Subunits, Gq-G11; Guanine Nucleotide Exchange Factors; Guanosine Triphosphate; HEK293 Cells; HeLa Cells; Heterotrimeric GTP-Binding Proteins; Humans; Mice; Mice, Inbred C57BL; Mutation; Neoplasms; Neurons; Receptors, G-Protein-Coupled; Signal Transduction; Urinary Bladder Neoplasms

The most frequently mutated oncogene in cancer is KRAS, which uses alternative fourth exons to generate two gene products (KRAS4A and KRAS4B) that differ only in their C-terminal membrane-targeting region

Topics: Allosteric Regulation; Animals; Cell Line, Tumor; Enzyme Activation; Glycolysis; Guanosine Triphosphate; Hexokinase; Humans; In Vitro Techniques; Isoenzymes; Lipoylation; Male; Mice; Mitochondria; Mitochondrial Membranes; Neoplasms; Protein Binding; Protein Transport; Proto-Oncogene Proteins p21(ras)

Topics: Gene Expression Regulation; Guanosine Diphosphate; Guanosine Triphosphate; Humans; Neoplasms; Oncogenes; ras Proteins; Signal Transduction

Topics: Animals; Antineoplastic Agents; Biomarkers, Tumor; Cell Line, Tumor; Enzyme Inhibitors; Extracellular Signal-Regulated MAP Kinases; Genetic Predisposition to Disease; Guanosine Triphosphate; HEK293 Cells; Humans; Mice, Inbred BALB C; Mice, Nude; Mitogen-Activated Protein Kinase Kinases; Mutation; Neoplasms; Neurofibromin 1; Phenotype; Protein Tyrosine Phosphatase, Non-Receptor Type 11; Proto-Oncogene Proteins B-raf; Proto-Oncogene Proteins p21(ras); raf Kinases; Signal Transduction; SOS1 Protein; Tumor Burden; Xenograft Model Antitumor Assays

A mutated KRAS protein is frequently observed in human cancers. Traditionally, the oncogenic properties of KRAS missense mutants at position 12 (G12X) have been considered as equal. Here, by assessing the probabilities of occurrence of all KRAS G12X mutations and KRAS dynamics we show that this assumption does not hold true. Instead, our findings revealed an outstanding mutational bias. We conducted a thorough mutational analysis of KRAS G12X mutations and assessed to what extent the observed mutation frequencies follow a random distribution. Unique tissue-specific frequencies are displayed with specific mutations, especially with G12R, which cannot be explained by random probabilities. To clarify the underlying causes for the nonrandom probabilities, we conducted extensive atomistic molecular dynamics simulations (170 μs) to study the differences of G12X mutations on a molecular level. The simulations revealed an allosteric hydrophobic signaling network in KRAS, and that protein dynamics is altered among the G12X mutants and as such differs from the wild-type and is mutation-specific. The shift in long-timescale conformational dynamics was confirmed with Markov state modeling. A G12X mutation was found to modify KRAS dynamics in an allosteric way, which is especially manifested in the switch regions that are responsible for the effector protein binding. The findings provide a basis to understand better the oncogenic properties of KRAS G12X mutants and the consequences of the observed nonrandom frequencies of specific G12X mutations.

Topics: DNA Mutational Analysis; Genes, ras; Guanosine Diphosphate; Guanosine Triphosphate; Humans; Hydrophobic and Hydrophilic Interactions; Ligands; Markov Chains; Molecular Conformation; Molecular Dynamics Simulation; Mutation; Mutation, Missense; Neoplasms; Principal Component Analysis; Probability; Proto-Oncogene Proteins p21(ras)

Despite years of study, the structural or dynamical basis for the differential reactivity and oncogenicity of Ras isoforms and mutants remains unclear. In this study, we investigated the effects of amino acid variations on the structure and dynamics of wild type and oncogenic mutants G12D, G12V, and G13D of H- and K-Ras proteins. Based on data from µs-scale molecular dynamics simulations, we show that the overall structure of the proteins remains similar but there are important differences in dynamics and interaction networks. We identified differences in residue interaction patterns around the canonical switch and distal loop regions, and persistent sodium ion binding near the GTP particularly in the G13D mutants. Our results also suggest that different Ras variants have distinct local structural features and interactions with the GTP, variations that have the potential to affect GTP release and hydrolysis. Furthermore, we found that H-Ras proteins and particularly the G12V and G13D variants are significantly more flexible than their K-Ras counterparts. Finally, while most of the simulated proteins sampled the effector-interacting state 2 conformational state, G12V and G13D H-Ras adopted an open switch state 1 conformation that is defective in effector interaction. These differences have implications for Ras GTPase activity, effector or exchange factor binding, dimerization and membrane interaction. Proteins 2017; 85:1618-1632. © 2017 Wiley Periodicals, Inc.

Topics: Amino Acid Sequence; Guanosine Triphosphate; Humans; Ligands; Mutant Proteins; Mutation; Neoplasms; Protein Binding; Protein Conformation; Proto-Oncogene Proteins p21(ras); ras Proteins

Melanoma progression is associated with increased invasion and, often, decreased levels of microphthalmia-associated transcription factor (MITF). Accordingly, downregulation of MITF induces invasion in melanoma cells; however, little is known about the underlying mechanisms. Here, we report for the first time that depletion of MITF results in elevation of intracellular GTP levels and increased amounts of active (GTP-bound) RAC1, RHO-A and RHO-C. Concomitantly, MITF-depleted cells display larger number of invadopodia and increased invasion. We further demonstrate that the gene for guanosine monophosphate reductase (GMPR) is a direct MITF target, and that the partial repression of GMPR accounts mostly for the above phenotypes in MITF-depleted cells. Reciprocally, transactivation of GMPR is required for MITF-dependent suppression of melanoma cell invasion, tumorigenicity and lung colonization. Moreover, loss of GMPR accompanies downregulation of MITF in vemurafenib-resistant BRAF

Topics: Animals; Cell Line, Tumor; Disease Models, Animal; Disease Progression; Ectopic Gene Expression; Extracellular Matrix; Female; Gene Expression Regulation, Neoplastic; GMP Reductase; Guanosine Triphosphate; Heterografts; Humans; Intracellular Space; Melanocytes; Melanoma; Melanoma, Experimental; Mice; Microphthalmia-Associated Transcription Factor; Neoplasm Invasiveness; Neoplasm Metastasis; Neoplasms; rho GTP-Binding Proteins

Small nucleolar RNAs (snoRNAs) are conserved noncoding RNAs best studied as ribonucleoprotein (RNP) guides in RNA modification. To explore their role in cancer, we compared 5,473 tumor-normal genome pairs to identify snoRNAs with frequent copy number loss. The SNORD50A-SNORD50B snoRNA locus was deleted in 10-40% of 12 common cancers, where its loss was associated with reduced survival. A human protein microarray screen identified direct SNORD50A and SNORD50B RNA binding to K-Ras. Loss of SNORD50A and SNORD50B increased the amount of GTP-bound, active K-Ras and hyperactivated Ras-ERK1/ERK2 signaling. Loss of these snoRNAs also increased binding by farnesyltransferase to K-Ras and increased K-Ras prenylation, suggesting that KRAS mutation might synergize with SNORD50A and SNORD50B loss in cancer. In agreement with this hypothesis, CRISPR-mediated deletion of SNORD50A and SNORD50B in KRAS-mutant tumor cells enhanced tumorigenesis, and SNORD50A and SNORD50B deletion and oncogenic KRAS mutation co-occurred significantly in multiple human tumor types. SNORD50A and SNORD50B snoRNAs thus directly bind and inhibit K-Ras and are recurrently deleted in human cancer.

Topics: Animals; Cell Line, Tumor; Clustered Regularly Interspaced Short Palindromic Repeats; Female; Gene Deletion; Gene Expression Regulation, Neoplastic; Guanosine Triphosphate; Humans; Mice, Inbred NOD; Mutation; Neoplasms; Prenylation; ras Proteins; RNA, Small Nucleolar; RNA, Untranslated; Xenograft Model Antitumor Assays

In the present study we determined the relative contribution of two processes to breast cancer progression: (1) Intrinsic events, such as activation of the Ras pathway and down-regulation of p53; (2) The inflammatory cytokines TNFα and IL-1β, shown in our published studies to be highly expressed in tumors of >80% of breast cancer patients with recurrent disease.. Using MCF-7 human breast tumor cells originally expressing WT-Ras and WT-p53, we determined the impact of the above-mentioned elements and cooperativity between them on the expression of CXCL8 (ELISA, qRT-PCR), a member of a "cancer-related chemokine cluster" that we have previously identified. Then, we determined the mechanisms involved (Ras-binding-domain assays, Western blot, luciferase), and tested the impact of Ras + TNFα on angiogenicity (chorioallantoic membrane assays) and on tumor growth at the mammary fat pad of mice and on metastasis, in vivo.. Using RasG12V that recapitulates multiple stimulations induced by receptor tyrosine kinases, we found that RasG12V alone induced CXCL8 expression at the mRNA and protein levels, whereas down-regulation of p53 did not. TNFα and IL-1β potently induced CXCL8 expression and synergized with RasG12V, together leading to amplified CXCL8 expression. Testing the impact of WT-Ras, which is the common form in breast cancer patients, we found that WT-Ras was not active in promoting CXCL8; however, TNFα has induced the activation of WT-Ras: joining these two elements has led to cooperative induction of CXCL8 expression, via the activation of MEK, NF-κB and AP-1. Importantly, TNFα has led to increased expression of WT-Ras in an active GTP-bound form, with properties similar to those of RasG12V. Jointly, TNFα + Ras activities have given rise to increased angiogenesis and to elevated tumor cell dissemination to lymph nodes.. TNFα cooperates with Ras in promoting the metastatic phenotype of MCF-7 breast tumor cells, and turns WT-Ras into a tumor-supporting entity. Thus, in breast cancer patients the cytokine may rescue the pro-cancerous potential of WT-Ras, and together these two elements may lead to a more aggressive disease. These findings have clinical relevance, suggesting that we need to consider new therapeutic regimens that inhibit Ras and TNFα, in breast cancer patients.

Topics: Animals; Cell Line, Tumor; Chick Embryo; Female; Gene Expression Regulation, Neoplastic; Guanosine Triphosphate; Humans; Interleukin-1beta; Interleukin-8; MAP Kinase Signaling System; MCF-7 Cells; Mice; Neoplasm Metastasis; Neoplasms; Neovascularization, Pathologic; NF-kappa B; Protein Binding; Protein Interaction Domains and Motifs; Proto-Oncogene Proteins p21(ras); Signal Transduction; Transcription Factor AP-1; Transcription, Genetic; Tumor Necrosis Factor-alpha; Tumor Suppressor Protein p53

There is an increasing number of disease-associated Gα mutations identified from genome-wide sequencing campaigns or targeted efforts. Albright's Hereditary Osteodystrophy (AHO) was the first inherited disease associated with loss-of-function mutations in a G protein (Gαs) and other studies revealed gain-of-function Gα mutations in cancer. Here we attempted to solve the apparent quandary posed by the fact that the same mutation in two different G proteins appeared associated with both AHO and cancer. We first confirmed the presence of an inherited Gαs-R265H mutation from a previously described clinical case report of AHO. This mutation is structurally analogous to Gαo-R243H, an oncogenic mutant with increased activity in vitro and in cells due to rapid nucleotide exchange. We found that, contrary to Gαo-R243H, Gαs-R265H activity is compromised due to greatly impaired nucleotide binding in vitro and in cells. We obtained equivalent results when comparing another AHO mutation in Gαs (D173N) with a counterpart cancer mutation in Gαo (D151N). Gαo-R243H binds nucleotides efficiently under steady-state conditions but releases GDP much faster than the WT protein, suggesting diminished affinity for the nucleotide. These results indicate that the same disease-linked mutation in two different G proteins affects a common biochemical feature (nucleotide affinity) but to a different grade depending on the G protein (mild decrease for Gαo and severe for Gαs). We conclude that Gαs-R265H has dramatically impaired nucleotide affinity leading to the loss-of-function in AHO whereas Gαo-R243H has a mild decrease in nucleotide affinity that causes rapid nucleotide turnover and subsequent hyperactivity in cancer.

Topics: Amino Acid Sequence; Amino Acid Substitution; Chromogranins; Female; GTP-Binding Protein alpha Subunits, Gi-Go; GTP-Binding Protein alpha Subunits, Gs; Guanosine Triphosphate; HEK293 Cells; Humans; Male; Models, Molecular; Molecular Sequence Data; Mutant Proteins; Mutation; Neoplasms; Pedigree; Protein Subunits; Pseudohypoparathyroidism; Recombinant Proteins; Sequence Homology, Amino Acid; Structural Homology, Protein

Aberrant signaling by oncogenic mutant rat sarcoma (Ras) proteins occurs in ∼15% of all human tumors, yet direct inhibition of Ras by small molecules has remained elusive. Recently, several small-molecule ligands have been discovered that directly bind Ras and inhibit its function by interfering with exchange factor binding. However, it is unclear whether, or how, these ligands could lead to drugs that act against constitutively active oncogenic mutant Ras. Using a dynamics-based pocket identification scheme, ensemble docking, and innovative cell-based assays, here we show that andrographolide (AGP)--a bicyclic diterpenoid lactone isolated from Andrographis paniculata--and its benzylidene derivatives bind to transient pockets on Kirsten-Ras (K-Ras) and inhibit GDP-GTP exchange. As expected for inhibitors of exchange factor binding, AGP derivatives reduced GTP loading of wild-type K-Ras in response to acute EGF stimulation with a concomitant reduction in MAPK activation. Remarkably, however, prolonged treatment with AGP derivatives also reduced GTP loading of, and signal transmission by, oncogenic mutant K-RasG12V. In sum, the combined analysis of our computational and cell biology results show that AGP derivatives directly bind Ras, block GDP-GTP exchange, and inhibit both wild-type and oncogenic K-Ras signaling. Importantly, our findings not only show that nucleotide exchange factors are required for oncogenic Ras signaling but also demonstrate that inhibiting nucleotide exchange is a valid approach to abrogating the function of oncogenic mutant Ras.

Topics: Andrographis; Animals; Anti-Inflammatory Agents; Binding Sites; Computer Simulation; Diterpenes; Guanosine Triphosphate; Models, Chemical; Neoplasms; Plant Preparations; Protein Structure, Tertiary; Proto-Oncogene Proteins p21(ras); ras Guanine Nucleotide Exchange Factors; Rats

Cytoplasmic filamentous rods and rings (RR) structures were identified using human autoantibodies as probes. In the present study, the formation of these conserved structures in mammalian cells and functions linked to these structures were examined.. Distinct cytoplasmic rods (∼3-10 µm in length) and rings (∼2-5 µm in diameter) in HEp-2 cells were initially observed in immunofluorescence using human autoantibodies. Co-localization studies revealed that, although RR had filament-like features, they were not enriched in actin, tubulin, or vimentin, and not associated with centrosomes or other known cytoplasmic structures. Further independent studies revealed that two key enzymes in the nucleotide synthetic pathway cytidine triphosphate synthase 1 (CTPS1) and inosine monophosphate dehydrogenase 2 (IMPDH2) were highly enriched in RR. CTPS1 enzyme inhibitors 6-diazo-5-oxo-L-norleucine and Acivicin as well as the IMPDH2 inhibitor Ribavirin exhibited dose-dependent induction of RR in >95% of cells in all cancer cell lines tested as well as mouse primary cells. RR formation by lower concentration of Ribavirin was enhanced in IMPDH2-knockdown HeLa cells whereas it was inhibited in GFP-IMPDH2 overexpressed HeLa cells. Interestingly, RR were detected readily in untreated mouse embryonic stem cells (>95%); upon retinoic acid differentiation, RR disassembled in these cells but reformed when treated with Acivicin.. RR formation represented response to disturbances in the CTP or GTP synthetic pathways in cancer cell lines and mouse primary cells and RR are the convergence physical structures in these pathways. The availability of specific markers for these conserved structures and the ability to induce formation in vitro will allow further investigations in structure and function of RR in many biological systems in health and diseases.

Topics: Animals; Biosynthetic Pathways; Cell Cycle; Cell Line; Cytidine Triphosphate; Cytoplasmic Structures; Embryonic Stem Cells; Enzyme Inhibitors; Guanosine Triphosphate; Humans; IMP Dehydrogenase; Mammals; Mice; Neoplasms; Time Factors

Aberrant cell division is a hallmark of cancer, but the molecular circuitries of this process in tumor cells are not well understood. Here, we used a high-throughput proteomics screening to identify novel molecular partners of survivin, an essential regulator of mitosis overexpressed in cancer. We found that survivin associates with the small GTPase Ran in an evolutionarily conserved recognition in mammalian cells and Xenopus laevis extracts. This interaction is regulated during the cell cycle, involves Ran-GTP, requires a discrete binding interface centered on Glu65 in survivin, and is independent of the Ran effector Crm1. Disruption of a survivin-Ran complex does not affect the assembly of survivin within the chromosomal passenger complex or its cytosolic accumulation, but it inhibits the delivery of the Ran effector molecule TPX2 to microtubules. In turn, this results in aberrant mitotic spindle formation and chromosome missegregation in tumor, but not normal, cells. Therefore, survivin is a novel effector of Ran signaling, and this pathway may be preferentially exploited for spindle assembly in tumor cells.

Topics: Animals; Binding Sites; Cell Cycle; Cell Cycle Proteins; Fibroblasts; Guanosine Triphosphate; HeLa Cells; Humans; Inhibitor of Apoptosis Proteins; Mice; Microtubule-Associated Proteins; Microtubules; Neoplasm Proteins; Neoplasms; NIH 3T3 Cells; Nuclear Proteins; Nucleotides; Ovum; Protein Binding; Proteomics; ran GTP-Binding Protein; Spindle Apparatus; Survivin; Xenopus

In addition to their role in nucleotide homeostasis, members of the Nucleoside Diphosphate Kinase (NDPK) family have been implicated in tumor metastasis, cell migration and vesicle trafficking. Although its role in most cases depends on nucleotide catalysis, a precise understanding of how the catalytic activity of NDPK supports its function in diverse processes is lacking. Here we report that wild type, but not catalytically inactive (H118C) NDPKB, undergoes dynamic self-assembly into ordered 20-25 nm diameter filaments in vitro. Self-assembly is nucleoside triphosphate dependent, GTP being most effective at promoting polymer formation. In addition, polymerization appears to depend on formation of the phosphoryl-Histidine intermediate of the enzyme, suggesting a previously unappreciated conformational change in NDPK during its catalytic cycle. We hypothesize that the observed nucleotide-dependent self-assembly property of NDPKB may reflect a key feature of NDPK enzymes that enables their function in diverse processes.

Topics: Biological Transport; Cell Movement; Guanosine Triphosphate; Homeostasis; Humans; Neoplasm Metastasis; Neoplasm Proteins; Neoplasms; NM23 Nucleoside Diphosphate Kinases; Protein Structure, Quaternary

Galectin-3 (Gal-3) is a pleiotropic beta-galactoside-binding protein expressed at relatively high levels in human neoplasms. Its carbohydrate recognition domain (CRD) contains a hydrophobic pocket that can accommodate the farnesyl moiety of K-Ras. Binding of K-Ras to Gal-3 stabilizes K-Ras in its active (GTP-bound) state. Gal-3, which does not interact with N-Ras, was nevertheless shown to reduce N-Ras-GTP in BT-549 cells by an unknown mechanism that we explored here. First, comparative analysis of various cancer cell lines (glioblastomas, breast cancer cells and ovarian carcinomas) showed a positive correlation between low N-Ras-GTP/high K-Ras-GTP phenotype and Gal-3 expression levels. Next we found that epidermal growth factor-stimulated GTP loading of N-Ras, but not of K-Ras, is blocked in cells expressing high levels of Gal-3. Activation of Ras guanine nucleotide releasing proteins (RasGRPs) by phorbol 12-myristate 13-acetate (PMA) or downregulation of Gal-3 by Gal-3 shRNA increased the levels of N-Ras-GTP in Gal-3 expressing cells. We further show that the N-terminal domain of Gal-3 interacts with and inhibits RasGRP4-mediated GTP loading on N-Ras and H-Ras proteins. Growth of BT-549 cells stably expressing the Gal-3 N-terminal domain was strongly attenuated. Overall, these experiments demonstrate a new control mechanism of Ras activation in cancer cells whereby the Gal-3 N-terminal domain inhibits activation of N-Ras and H-Ras proteins.

Topics: Animals; Blotting, Western; Cricetinae; Epidermal Growth Factor; Galectin 3; Genes, ras; Guanosine Triphosphate; Humans; Immunoprecipitation; Neoplasms; ras Guanine Nucleotide Exchange Factors; ras Proteins; Rats; RNA, Small Interfering; Tetradecanoylphorbol Acetate; Tumor Cells, Cultured

The microtubule-associated protein TOGp, which belongs to a widely distributed protein family from yeasts to humans, is highly expressed in human tumors and brain tissue. From purified components we have determined the effect of TOGp on thermally induced tubulin association in vitro in the presence of 1 mm GTP and 3.4 m glycerol. Physicochemical parameters describing the mechanism of tubulin polymerization were deduced from the kinetic curves by application of the classical theoretical models of tubulin assembly. We have calculated from the polymerization time curves a range of parameters characteristic of nucleation, elongation, or steady state phase. In addition, the tubulin subunits turnover at microtubule ends was deduced from tubulin GTPase activity. For comparison, parallel experiments were conducted with colchicine and taxol, two drugs active on microtubules and with tau, a structural microtubule-associated protein from brain tissue. TOGp, which decreases the nucleus size and the tenth time of the reaction (the time required to produce 10% of the final amount of polymer), shortens the nucleation phase of microtubule assembly. In addition, TOGp favors microtubule formation by increasing the apparent first order rate constant of elongation. Moreover, TOGp increases the total amount of polymer by decreasing the tubulin critical concentration and by inhibiting depolymerization during the steady state of the reaction.

Topics: Animals; Brain; Brain Chemistry; Guanosine Triphosphate; Humans; Kinetics; Microtubule-Associated Proteins; Microtubules; Models, Molecular; Neoplasms; Swine; Tubulin

Interaction of the Eph family of receptor protein tyrosine kinases and their ligands, ephrin family members, induces bi-directional signaling via cell-cell contacts. High expression of B-type ephrin is associated with high invasion potential of tumors, however, the mechanism by which ephrin-B promotes cancer cell invasion is poorly understood. We show that interaction of ephrin-B1 with the Eph receptor B2 (EphB2) significantly enhances processing of the extracellular domain of ephrin-B1, which is regulated by the C-terminus. Matrix metalloproteinase-8 (MMP-8) is the key protease that cleaves ephrin-B1, and the C-terminus of ephrin-B1 regulates activation of the extracellular release of MMP-8 without requirement of de novo protein synthesis. One possible mechanism by which ephrin-B1 regulates the exocytosis of MMP-8 is the activation of Arf1 GTPase, a critical regulator of membrane trafficking. In support of this hypothesis, activation of ephrin-B1 increased GTP-bound Arf1, and the secretion of MMP-8 was reduced by expression of a dominant-negative mutant of Arf1. Expression of ephrin-B1 promoted the invasion of cancer cells in vivo, which required the C-terminus of ephrin-B1. Our results suggest a novel function of the C-terminus of ephrin-B1 in activating MMP-8 secretion, which promotes the invasion of cancer cells.

Topics: ADP-Ribosylation Factor 1; Enzyme Activation; Ephrin-B1; Exocytosis; Gene Expression Regulation, Neoplastic; Guanosine Triphosphate; Humans; Matrix Metalloproteinase 8; Neoplasm Invasiveness; Neoplasm Proteins; Neoplasms; Protein Structure, Tertiary; Protein Transport; U937 Cells

To investigate the unregulated Ras activation associated with cancer, we developed and validated a mathematical model of Ras signaling. The model-based predictions and associated experiments help explain why only one of two classes of activating Ras point mutations with in vitro transformation potential is commonly found in cancers. Model-based analysis of these mutants uncovered a systems-level process that contributes to total Ras activation in cells. This predicted behavior was supported by experimental observations. We also used the model to identify a strategy in which a drug could cause stronger inhibition on the cancerous Ras network than on the wild-type network. This system-level analysis of the oncogenic Ras network provides new insights and potential therapeutic strategies.

Topics: Antineoplastic Agents; Cell Line; Cell Line, Tumor; Cell Transformation, Neoplastic; Computer Simulation; Extracellular Signal-Regulated MAP Kinases; Genes, ras; GTP Phosphohydrolases; GTPase-Activating Proteins; Guanosine Diphosphate; Guanosine Triphosphate; Humans; Mathematics; Metabolic Networks and Pathways; Models, Biological; Neoplasms; Phosphorylation; Point Mutation; ras Proteins; Signal Transduction

RalGEFs were recently shown to be critical for Ras-mediated transformed and tumorigenic growth of human cells. We now show that the oncogenic activity of these proteins is propagated by activation of one RalGEF substrate, RalA, but blunted by another closely related substrate, RalB, and that the oncogenic signaling requires binding of the RalBP1 and exocyst subunit effector proteins. Knockdown of RalA expression impeded, if not abolished, the ability of human cancer cells to form tumors. RalA was also commonly activated in a panel of cell lines from pancreatic cancers, a disease characterized by activation of Ras. Activation of RalA signaling thus appears to be a critical step in Ras-induced transformation and tumorigenesis of human cells.

Topics: Animals; ATP-Binding Cassette Transporters; Carrier Proteins; Cell Line; Cell Line, Tumor; Cell Proliferation; Cell Transformation, Neoplastic; Gene Expression; GTPase-Activating Proteins; Guanosine Triphosphate; Humans; Mice; Mice, SCID; Neoplasm Transplantation; Neoplasms; Pancreatic Neoplasms; Protein Binding; Protein Transport; Proto-Oncogene Proteins p21(ras); ral GTP-Binding Proteins; ral Guanine Nucleotide Exchange Factor; rho GTP-Binding Proteins; RNA, Small Interfering; Transfection; Vesicular Transport Proteins

Topics: Animals; Brain; Carrier Proteins; Cell Line; Cell Nucleolus; Cell Nucleus; GTP-Binding Proteins; Guanosine Triphosphate; Humans; Neoplasms; Nuclear Proteins; Rats; Stem Cells; Tumor Suppressor Protein p53

Embryonic stem (ES) cells are pluripotent cells derived from early mammalian embryos. Their immortality and rapid growth make them attractive sources for stem cell therapies; however, they produce tumours (teratomas) when transplanted, which could preclude their therapeutic usage. Why ES cells, which lack chromosomal abnormalities, possess tumour-like properties is largely unknown. Here we show that mouse ES cells specifically express a Ras-like gene, which we have named ERas. We show that human HRasp, which is a recognized pseudogene, does not contain reported base substitutions and instead encodes the human orthologue of ERas. This protein contains amino-acid residues identical to those present in active mutants of Ras and causes oncogenic transformation in NIH 3T3 cells. ERas interacts with phosphatidylinositol-3-OH kinase but not with Raf. ERas-null ES cells maintain pluripotency but show significantly reduced growth and tumorigenicity, which are rescued by expression of ERas complementary DNA or by activated phosphatidylinositol-3-OH kinase. We conclude that the transforming oncogene ERas is important in the tumour-like growth properties of ES cells.

Topics: 3T3 Cells; Amino Acid Sequence; Animals; Cell Division; Cell Transformation, Neoplastic; Cloning, Molecular; Embryo, Mammalian; Genes, ras; Guanosine Diphosphate; Guanosine Triphosphate; Mice; Molecular Sequence Data; Neoplasms; Oncogene Protein p21(ras); Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-raf; Pseudogenes; Stem Cells

Tissue transglutaminase (tTGase, tTG) is known as being implicated in the intracellular cross-linking of proteins occurring in a growing series of physiological conditions including--just to mention the most relevant ones--programmed cell death (apoptosis), cell adhesion, growth, spreading and differentiation, tumor growth, metastasis, cell adhesion, proliferation, differentiation, extra cellular matrix (ECM) stabilization. In the current work we investigated tTG activity and expression of "normal" and potential transformed cytosolic tTG antigens in mammalian cells. Most cell lines studied showed low tTG activity, which in all cases could be enhanced considerably by treating cell cytosol homogenates with trypsin. The results suggested the existence -in transformed cells- of inactive types of tTGase. We purified cytosolic tTG antigens from these cells utilizing a GTP-agarose resin, and we can therefore conclude that "normal" molecular weight (mw) tTG antigens, but also high molecular weight (hmw) and low molecular weight (lmw) tTG antigens from transformed cells, retain GTP-binding ability. The initial results from our study also allowed us to hypothesize that transformed hmw- and lmw- tTG antigens should not be considered as the result of post-translational modifications of normal mw, cytosolic tTG. The potentially low or absent transamidating functionality of cytosolic tTG species in transformed mammalian cells could be responsible for decreased or even abolished programmed cell death, whereas the unaffected GTP-binding functionality of such proteins in these cells might lead to increased signal transduction and possibly proliferation.

Topics: 3T3 Cells; Animals; Antibodies, Monoclonal; Blotting, Western; Cell Transformation, Neoplastic; Chromatography, Affinity; Cytosol; Electrophoresis, Polyacrylamide Gel; Guanosine Triphosphate; Humans; Immunohistochemistry; Isoenzymes; Mammals; Mice; Molecular Weight; Neoplasms; Phenotype; Transglutaminases

Topics: Animals; Antineoplastic Agents; Apoptosis; Chromatography, High Pressure Liquid; Clinical Trials as Topic; Down-Regulation; Guanosine Triphosphate; History, 20th Century; Humans; Ischemia; Kidney Neoplasms; Leukemia; Models, Biological; Neoplasms; Ribavirin; Signal Transduction; Time Factors; Tumor Cells, Cultured

The synthesis and biological activity of selenophenfurin (5-beta-D-ribofuranosylselenophene-3-carboxamide, 1), the selenophene analogue of selenazofurin, are described. Glycosylation of ethyl selenophene-3-carboxylate (6) under stannic chloride-catalyzed conditions gave 2- and 5-glycosylated regioisomers, as a mixture of alpha- and beta-anomers, and the beta-2,5-diglycosylated derivative. Deprotected ethyl 5-beta-D-ribofuranosylselenophene-3-carboxylate (12 beta) was converted into selenophenfurin by ammonolysis. The structure of 12 beta was determined by 1H- and 13C-NMR, crystallographic, and computational studies. Selenophenfurin proved to be antiproliferative against a number of leukemia, lymphoma, and solid tumor cell lines at concentrations similar to those of selenazofurin but was more potent than the thiophene and thiazole analogues thiophenfurin and tiazofurin. Incubation of K562 cells with selenophenfurin resulted in inhibition of IMP dehydrogenase (IMPDH) (76%) and an increase in IMP pools (14.5-fold) with a concurrent decrease in GTP levels (58%). The results obtained confirm the hypothesis that the presence of heteroatoms such as S or Se in the heterocycle in position 2 with respect to the glycosidic bond is essential for both cytotoxicity and IMP dehydrogenase inhibitory activity in this type of C-nucleosides.

Topics: Animals; Antineoplastic Agents; Cell Division; Computer Simulation; Crystallography, X-Ray; Enzyme Inhibitors; Guanosine Triphosphate; Humans; IMP Dehydrogenase; Inosine Monophosphate; Leukemia; Lymphoma; Magnetic Resonance Spectroscopy; Mice; Models, Molecular; Molecular Structure; Neoplasms; Organoselenium Compounds; Ribavirin; Ribonucleosides; Tumor Cells, Cultured

A cancer-specific form of NADH oxidase inhibited or stimulated by 1 or 100 microM capsaicin (8-methyl-N-vanillyl-6-noneamide) is present in sera from cancer patients. The capsaicin-inhibited NADH oxidase activity appears to be absent from sera of individuals free of cancer. The capsaicin-inhibited activity is present both in freshly collected sera and in sera stored frozen for varying periods of time. For the latter, an assay was carried out under renaturing conditions in the presence of NADH and reduced glutathione followed by dilute hydrogen peroxide. Inhibition was half maximal at about 1 microM capsaicin. The capsaicin-inhibited activity was found in sera over a broad spectrum of cancer patients including patients with solid cancers (e.g., breast, prostate, lung, ovarian) as well as with leukemias and lymphomas.

Topics: Capsaicin; Chloromercuribenzoates; Enzyme Activation; Enzyme Inhibitors; Guanosine Diphosphate; Guanosine Triphosphate; Humans; Kinetics; Multienzyme Complexes; NADH, NADPH Oxidoreductases; Neoplasms; p-Chloromercuribenzoic Acid

LU103793 (NSC D-669356) is a new synthetic derivative of Dolastatin 15, an antiproliferative compound which was isolated from the mollusk Dolabella auricularia. Like Dolastatin 15, LU103793 is highly cytotoxic in vitro (IC50 = 0.1 nM). To investigate the mechanism of action of LU103793, we used a combination of biochemical and cellular methods. Turbidity assays with bovine brain microtubules demonstrated that LU103793 inhibits microtubule polymerization in a concentration-dependent manner (IC50 = 7 microM). Treatment with this compound also induced depolymerization of preassembled microtubules. Cell cycle analysis of tumor cell lines treated with LU103793 indicated a block in the G2-M phase. At the cellular level, it induced depolymerization of microtubules in interphase cells and development of abnormal spindles and chromosome distribution in mitotic cells. Although these effects are very similar to the cellular alterations caused by vinblastine, LU103793 does not inhibit vinblastine binding to unpolymerized tubulin in vitro. Our results suggest that LU103793 exerts its cytotoxic activity primarily through disruption of microtubule organization.

Topics: Adenocarcinoma; Amino Acid Sequence; Antineoplastic Agents; Breast Neoplasms; Cell Cycle; Cell Division; Chromosomes, Human; Colonic Neoplasms; Drug Interactions; Guanosine Triphosphate; HeLa Cells; Humans; Hydrolysis; Microtubules; Mitosis; Molecular Sequence Data; Neoplasms; Oligopeptides; Tubulin; Tumor Cells, Cultured; Vinblastine

ras oncoproteins and ras-related proteins constitute a large family of the small GTP-binding protein family. The rab branch of the ras superfamily is involved in the intracellular transport along the secretory and endocytic pathway in eukaryotic cells. We here demonstrate that a member of the rab branch, the rab2 protein, is frequently overexpressed in peripheral blood mononuclear cells from patients with solid neoplasms. Moreover, this expression is shown to be greatly modified during the course of therapy. Our results provide strong evidence for the implication of a small GTP-binding protein in immunological events associated with neoplastic diseases. The precise cellular population involved as well as the potential prognostic value of this process remains to be determined.

Topics: Antineoplastic Agents; Electrophoresis, Polyacrylamide Gel; Female; GTP-Binding Proteins; Guanosine Triphosphate; Humans; Interleukin-2; Leukocytes, Mononuclear; Male; Neoplasm Proteins; Neoplasms; Prospective Studies; rab2 GTP-Binding Protein; Urogenital Neoplasms

A substitution of Gly for Val at position 19, which corresponds to oncogenic Gly13-->Val mutation of ras p21, was introduced in a low Mr GTP-binding protein, ram p25. The protein was expressed in cytosolic fraction of Escherichia coli and purified by using specific antibody raised against ram p25. The mutated protein had no guanine nucleotide-binding activity although [Val13]ras p21 was reported to have. The analysis of guanine nucleotide composition of the purified [Val19]ram p25 revealed that the protein was free of nucleotide whereas the normal ram p25 bound about 1 mol of GDP per mol of protein. These results strongly suggested that some part(s) of variable regions as well as the consensus regions are important for the biochemical properties of ram p25.

Topics: Amino Acid Sequence; Base Sequence; Cloning, Molecular; Escherichia coli; Genes, ras; Glycine; GTP Phosphohydrolases; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Diphosphate; Guanosine Triphosphate; Humans; Kinetics; Molecular Sequence Data; Molecular Weight; Multigene Family; Mutagenesis, Site-Directed; Neoplasms; Oligodeoxyribonucleotides; Peptide Fragments; rab GTP-Binding Proteins; rab27 GTP-Binding Proteins; Recombinant Proteins; Sequence Homology, Amino Acid; Trypsin; Valine

The crystal structure at 2.7 A resolution of the normal human c-H-ras oncogene protein lacking a flexible carboxyl-terminal 18 residue reveals that the protein consists of a six-stranded beta sheet, four alpha helices, and nine connecting loops. Four loops are involved in interactions with bound guanosine diphosphate: one with the phosphates, another with the ribose, and two with the guanine base. Most of the transforming proteins (in vivo and in vitro) have single amino acid substitutions at one of a few key positions in three of these four loops plus one additional loop. The biological functions of the remaining five loops and other exposed regions are at present unknown. However, one loop corresponds to the binding site for a neutralizing monoclonal antibody and another to a putative "effector region"; mutations in the latter region do not alter guanine nucleotide binding or guanosine triphosphatase activity but they do reduce the transforming activity of activated proteins. The data provide a structural basis for understanding the known biochemical properties of normal as well as activated ras oncogene proteins and indicate additional regions in the molecule that may possibly participate in other cellular functions.

Topics: Amino Acid Sequence; Antibodies, Monoclonal; Binding Sites; Catalysis; Crystallization; Epitopes; Escherichia coli; GTP Phosphohydrolases; Guanosine Diphosphate; Guanosine Triphosphate; Neoplasms; Phosphates; Protein Conformation; Proto-Oncogene Proteins; Proto-Oncogene Proteins p21(ras); Recombinant Proteins; X-Ray Diffraction

Topics: GTP-Binding Proteins; Guanosine Triphosphate; Humans; Neoplasms; Protein Conformation; Proto-Oncogene Proteins; Proto-Oncogene Proteins p21(ras)

The accumulation, metabolism, and retention of mercaptopurine (MP) was studied in four human neoplastic cell lines (three acute leukemia lines Molt-4, CCRF-CEM, and HL-60; and one Burkitt's lymphoma line, Wilson), each of which was sensitive to MP. Two cell lines resistant to MP (WilsonR and CCRF-CEMR) were also studied. The cell lines were incubated for 3 h in 10 microM [14C]MP and then placed in drug-free media for an additional 3 h. Cell samples were obtained at regular intervals, and the intracellular MP metabolites were measured in the acid-soluble fractions by anion-exchange high-pressure liquid chromatography. MP accumulated progressively within cells during the 3-h drug exposure period and declined rapidly when the cells were placed in drug-free media. Over 80% of the intracellular MP was present in the form of three nucleotide metabolites, MP ribose monophosphate, thioxanthosine monophosphate, and thioguanosine monophosphate. MP ribose monophosphate was found in greatest amount, accounting for 59-85% of the intracellular metabolite pool. Thioxanthosine monophosphate thioguanosine monophosphate were detected in lesser amounts. Study of leukemic cells obtained from patients demonstrated a similar pattern of MP accumulation, metabolism, and retention, although the overall amounts of the various metabolites formed were less. In contrast, there was essentially no MP nucleotide metabolite formation in the two MP-resistant cell lines. A more complete understanding of the cellular pharmacokinetics of MP in human neoplastic cells is likely to lead to a more rational use of the drug in the clinical setting.

Topics: Adenosine Triphosphate; Cell Line; Chromatography, High Pressure Liquid; Guanosine Triphosphate; Humans; Kinetics; Leukemia; Mercaptopurine; Neoplasms; Nucleotides; Phosphoribosyl Pyrophosphate

As many as 40 distinct oncogenes of viral and cellular origin have been identified to date. Many of these genes can be grouped into functional classes on the basis of their effects on cellular phenotype. These groupings suggest a small number of mechanisms of action of the oncogene-encoded proteins. Some data suggest that, in the cytoplasm, these proteins may regulate levels of critical second messenger molecules; in the nucleus, these proteins may modulate the activity of the cell's transcriptional machinery. Many of the gene products can also be related to a signaling pathway that determines the cell's response to growth-stimulating factors. Because some of these genes are expressed in nongrowing, differentiated cells, the encoded proteins may in certain tissues mediate functions that are unrelated to cellular growth control.

Topics: Animals; Birds; Cell Nucleus; Cell Transformation, Neoplastic; Chickens; Cytoplasm; Deltaretrovirus; DNA Tumor Viruses; Drosophila; Epidermal Growth Factor; Growth Substances; Guanosine Triphosphate; Humans; Mutation; Neoplasms; Oncogenes; Platelet-Derived Growth Factor; Polyomavirus; Proto-Oncogenes; Rats; Repetitive Sequences, Nucleic Acid; Retroviridae; Simian virus 40; Transcription, Genetic

An unusual isozyme of lactate dehydrogenase (LDH; L-lactate:NAD+ oxidoreductase, EC 1.1.1.27), LDHk, has been described in cells transformed by the Kirsten murine sarcoma virus (KiMSV). This isozyme appears to contain one or more subunits encoded by the transforming gene of KiMSV and is readily distinguished from other isozymes of LDH. Specifically, it is more basic than other LDH isozymes, has an apparent subunit structure of (35,000)4(22,000)1, is essentially inactive if assayed under a normal atmosphere, and is strongly inhibited by GTP and various related compounds. We have examined human cancer and normal tissue controls for expression of an activity like LDHk. In 11 out of 16 human carcinomas, LDHk activity was increased 10- to 500-fold over the level seen in adjoining nontumor tissue. In contrast, other LDH isozymes were increased by only 2- to 5-fold.

Topics: Aerobiosis; Breast Neoplasms; Colonic Neoplasms; Female; Guanosine Triphosphate; HeLa Cells; Humans; Isoenzymes; L-Lactate Dehydrogenase; Neoplasms; Reference Values

Topics: Aged; alpha-Fetoproteins; Animals; Carcinoembryonic Antigen; Female; Ferritins; Guanosine Triphosphate; Humans; Isoenzymes; Male; Mice; Middle Aged; Neoplasms