guanosine-triphosphate and Carcinogenesis

RHOA is a member of RHO family small GTPases. Over the past 2 decades, numerous biochemical and cell biological studies on RHOA have demonstrated signalings such as activation of RHO-associated coiled-coil forming kinases through guanine nucleotide exchange and GTP hydrolysis, cellular responses such as actin fiber formation and myocin activation, biological consequences such as cell motility and cytokineses, etc. There have also been a plenty of active discussion on the roles of RHOA in tumorigenesis, primarily based on gain- and loss-of-function experiments. However, cell-type-specific functions of RHOA have only recently been delineated by conditional gene targeting strategies. Furthermore, very little information had been available on human cancer genetics until we and others recently reported frequent somatic RHOA mutations in a distinct subtype of T-cell-type malignant lymphoma called angioimmunoblastic T-cell lymphoma (AITL), and other T-cell lymphoma with AITL-like features. The RHOA mutations were very specific to these types of lymphoma among hematologic malignancies, and a single hotspot, glycine at the 17th position, was affected by the replacement with valine (G17V). Remarkably, G17V RHOA did not bind GTP, and moreover, it inhibited the GTP binding to wild-type RHOA. How G17V RHOA contributes to T-cell lymphomagenesis needs to be clarified.

Topics: Animals; Carcinogenesis; Guanosine Triphosphate; Humans; Lymphoma, T-Cell; Mutation, Missense; Protein Binding; rhoA GTP-Binding Protein

Metabolic reprogramming is a hallmark of cancer. Metabolic rate-limiting enzymes and oncogenic c-Myc (Myc) play critical roles in metabolic reprogramming to affect tumourigenesis. However, a systematic assessment of metabolic rate-limiting enzymes and their relationship with Myc in human cancers is lacking.. Multiple Pan-cancer datasets were used to develop the transcriptome, genomic alterations, clinical outcomes and Myc correlation landscapes of 168 metabolic rate-limiting enzymes across 20 cancers. Real-time quantitative PCR and immunoblotting were, respectively, used to examine the mRNA and protein of inosine monophosphate dehydrogenase 1 (IMPDH1) in human colorectal cancer (CRC), azoxymethane/dextran sulphate sodium-induced mouse CRC and spontaneous intestinal tumours from APC. We explored the global expression patterns, dysregulation profiles, genomic alterations and clinical relevance of 168 metabolic rate-limiting enzymes across human cancers. Importantly, a series of enzymes were associated with Myc, especially top three upregulated enzymes (TK1, RRM2 and IMPDH1) were positively correlated with Myc in multiple cancers. As a proof-of-concept exemplification, we demonstrated that IMPDH1, a rate-limiting enzyme in GTP biosynthesis, is highly upregulated in CRC and promotes CRC growth in vitro and in vivo. Mechanistically, IMPDH2 stabilizes IMPDH1 by decreasing the polyubiquitination levels of IMPDH1, and Myc promotes the de novo GTP biosynthesis by the transcriptional activation of IMPDH1/2. Finally, we confirmed that the Myc-IMPDH1/2 axis is dysregulated across human cancers.. Our study highlights the essential roles of metabolic rate-limiting enzymes in tumourigenesis and their crosstalk with Myc, and the Myc-IMPDH1/2 axis promotes tumourigenesis by altering GTP metabolic reprogramming. Our results propose the inhibition of IMPDH1 as a viable option for cancer treatment.

Topics: Animals; Carcinogenesis; Guanosine Triphosphate; Humans; IMP Dehydrogenase; Mice; Proto-Oncogene Proteins c-myc

Transcription initiation factor 90 (TIF-90), an alternatively spliced variant of TIF-IA, differs by a 90 base pair deletion of exon 6. TIF-90 has been shown to regulate ribosomal RNA (rRNA) synthesis by interacting with polymerase I (Pol I) during the initiation of ribosomal DNA (rDNA) transcription in the nucleolus. Recently, we showed that TIF-90-mediated rRNA synthesis can play an important role in driving tumorigenesis in human colon cancer cells. Here we show that TIF-90 binds GTP at threonine 310, and that GTP binding is required for TIF-90-enhanced rRNA synthesis. Overexpression of activated AKT induces TIF-90 T310, but not a GTP-binding site (TIF-90 T310N) mutant, to translocate into the nucleolus and increase rRNA synthesis. Complementing this result, treatment with mycophenolic acid (MPA), an inhibitor of GTP production, dissociates TIF-90 from Pol I and hence abolishes AKT-increased rRNA synthesis by way of TIF-90 activation. Thus, TIF-90 requires bound GTP to fulfill its function as an enhancer of rRNA synthesis. Both TIF variants are highly expressed in colon cancer cells, and depletion of TIF-IA expression in these cells results in significant sensitivity to MPA-inhibited rRNA synthesis and reduced cell proliferation. Finally, a combination of MPA and AZD8055 (an inhibitor of both AKT and mTOR) synergistically inhibits rRNA synthesis, in vivo tumor growth, and other oncogenic activities of primary human colon cancer cells, suggesting a potential avenue for the development of therapeutic treatments by targeting the regulation of rRNA synthesis by TIF proteins.

Topics: Carcinogenesis; Cell Line, Tumor; Cell Proliferation; Colonic Neoplasms; DNA, Ribosomal; Guanosine Triphosphate; HCT116 Cells; Humans; Ribosomes; RNA Polymerase I; RNA, Ribosomal; Signal Transduction; Transcription Factors; Transcription, Genetic

Macroautophagy (hereafter referred to as autophagy) plays essential roles in cellular and organismal homeostasis. Transcription factor EB (TFEB) is a master regulator of autophagy and lysosome biogenesis. It is not fully understood how the function of TFEB in autophagy pathway is regulated. Here, we show that Rac1 GTPase is a negative modulator of autophagy by targeting TFEB. Mechanistically, Rac1 reduces autophagy flux by repressing the expressing of autophagy genes. Further investigation revealed that under nutrient-rich conditions, mammalian target of rapamycin (mTOR) phosphorylates TFEB to facilitate the interaction between Rac1 and TFEB. Biochemical dissection uncovered that guanosine 5'-triphosphate (GTP)-bound form of Rac1 selectively interacts with phosphorylated TFEB. This inhibitory interaction prevents the dephosphorylation and nucleus translocation of TFEB, which hampers the transcriptional activation of autophagy-related genes. Furthermore, Rac1-TFEB axis appeared to be important for tumorigenesis, as overexpression of dephosphorylated mutant of TFEB was able to delay the tumor growth driven by Rac1 overexpression. Together, this study not only elucidates a previously uncharacterized autophagy regulation mechanism involving Rac1 and TFEB under physiological and pathological conditions but also suggests a strategy to treat cancers that are driven by Rac1 overexpression.

Topics: Animals; Autophagy; Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; Carcinogenesis; Gene Expression Regulation; Guanosine Triphosphate; HeLa Cells; Hep G2 Cells; Humans; Mice, SCID; rac1 GTP-Binding Protein; Signal Transduction; Xenograft Model Antitumor Assays

The C-terminal guanine nucleotide exchange factor (GEF) module of Trio (TrioC) transfers signals from the Gα

Topics: Binding Sites; Carcinogenesis; Cell Line, Tumor; Crystallography, X-Ray; GTP-Binding Protein alpha Subunits, Gq-G11; Guanosine Triphosphate; HEK293 Cells; Humans; Melanoma; Models, Molecular; Mutation; Protein Binding; Protein Domains; Rho Guanine Nucleotide Exchange Factors; rhoA GTP-Binding Protein; Signal Transduction; Uveal Neoplasms

Ras-related C3 botulinum toxin substrate 1 (Rac1) plays critical roles in the maintenance of cell morphology by cycling between inactive guanosine diphosphate (GDP)-bound and active guanosine triphosphate (GTP)-bound states. Rac1 P29S mutant is known to strongly promote oncogenesis by facilitating its intrinsic GDP dissociation and thereby increasing the level of the GTP-bound state. Here, we used solution nuclear magnetic resonance spectroscopy to investigate the activation mechanism of the oncogenic P29S mutant. We demonstrate that the conformational landscape is markedly altered in the mutant, and the preexisting equilibrium is shifted toward the conformation with reduced affinity for Mg

Topics: Amino Acid Substitution; Binding Sites; Carcinogenesis; Cations, Divalent; Cloning, Molecular; Coenzymes; Escherichia coli; Gene Expression; Genetic Vectors; Glutathione Transferase; Guanosine Diphosphate; Guanosine Triphosphate; Humans; Kinetics; Magnesium; Models, Molecular; Mutation; Neoplasm Proteins; Nuclear Magnetic Resonance, Biomolecular; Protein Binding; Protein Conformation, alpha-Helical; Protein Conformation, beta-Strand; Protein Interaction Domains and Motifs; rac1 GTP-Binding Protein; Recombinant Fusion Proteins; Thermodynamics

While cellular GTP concentration dramatically changes in response to an organism's cellular status, whether it serves as a metabolic cue for biological signaling remains elusive due to the lack of molecular identification of GTP sensors. Here we report that PI5P4Kβ, a phosphoinositide kinase that regulates PI(5)P levels, detects GTP concentration and converts them into lipid second messenger signaling. Biochemical analyses show that PI5P4Kβ preferentially utilizes GTP, rather than ATP, for PI(5)P phosphorylation, and its activity reflects changes in direct proportion to the physiological GTP concentration. Structural and biological analyses reveal that the GTP-sensing activity of PI5P4Kβ is critical for metabolic adaptation and tumorigenesis. These results demonstrate that PI5P4Kβ is the missing GTP sensor and that GTP concentration functions as a metabolic cue via PI5P4Kβ. The critical role of the GTP-sensing activity of PI5P4Kβ in cancer signifies this lipid kinase as a cancer therapeutic target.

Topics: Adenosine Triphosphate; Amino Acid Sequence; Animals; Carcinogenesis; Cell Proliferation; Crystallography, X-Ray; Guanosine Triphosphate; HEK293 Cells; Humans; Hydrolysis; Intracellular Space; Kinetics; Mice; Molecular Sequence Data; Mutant Proteins; Phosphatidylinositol Phosphates; Phosphotransferases (Alcohol Group Acceptor); Protein Binding; Proteomics; Signal Transduction