leupeptins and Colonic-Neoplasms

All-trans retinoic acid (ATRA) is a promising therapeutic agent, but exhibits low efficacy against human cancers. We investigated the effect of sphingosine-1-phosphate (S1P) on ATRA activity in human colon cancer HT-29 cells. S1P antagonized ATRA activity on HT-29 cell proliferation and retinoic acid receptor beta (RARβ) expression. S1P treatment or transient co-transfection with SphK2 expression vector antagonized ATRA-induced RARβ promoter activity. Proteasome inhibition prevented S1P-induced modulation of ATRA activity. Overall, S1P antagonized ATRA's inhibitory effects by down-regulating RARβ expression, likely via the proteasome-dependent pathway. Decreasing S1P production or inhibiting SphK2 activity could enhance the efficacy of retinoids in cancer treatments.

Topics: Cell Proliferation; Colonic Neoplasms; Down-Regulation; HT29 Cells; Humans; Leupeptins; Lysophospholipids; Proteasome Inhibitors; Receptors, Retinoic Acid; Sphingosine; Tretinoin

rhTRAIL is a therapeutic agent, derived from the TRAIL cytokine, which induces apoptosis in cancer cells by activating the membrane death receptors 4 and 5 (DR4 and DR5). Here, we investigated each receptor's contribution to rhTRAIL sensitivity and rhTRAIL resistance. We assessed whether agonistic DR4 or DR5 antibodies could be used to circumvent rhTRAIL resistance, alone or in combination with various chemotherapies.. Our study was performed in an isogenic model comprised of the SW948 human colon carcinoma cell line and its rhTRAIL resistant sub-line SW948-TR. Effects of rhTRAIL and agonistic DR4/DR5 antibodies on cell viability were measured using MTT assays and identification of morphological changes characteristic of apoptosis, after acridine orange staining. Sensitivity to the different death receptor ligands was stimulated using pretreatment with the cytokine IFN-gamma and the proteasome inhibitor MG-132. To investigate the mechanisms underlying the changes in rhTRAIL sensitivity, alterations in expression levels of targets of interest were measured by Western blot analysis. Co-immunoprecipitation was used to determine the composition of the death-inducing signalling complex at the cell membrane.. SW948 cells were sensitive to all three of the DR-targeting agents tested, although the agonistic DR5 antibody induced only weak caspase 8 cleavage and limited apoptosis. Surprisingly, agonistic DR4 and DR5 antibodies induced equivalent DISC formation and caspase 8 cleavage at the level of their individual receptors, suggesting impairment of further caspase 8 processing upon DR5 stimulation. SW948-TR cells were cross-resistant to all DR-targeting agents as a result of decreased caspase 8 expression levels. Caspase 8 protein expression was restored by MG-132 and IFN-gamma pretreatment, which also re-established sensitivity to rhTRAIL and agonistic DR4 antibody in SW948-TR. Surprisingly, MG-132 but not IFN-gamma could also increase DR5-mediated apoptosis in SW948-TR.. These results highlight a critical difference between DR4- and DR5-mediated apoptotic signaling modulation, with possible implications for future combinatorial regimens.

Topics: Antibodies, Monoclonal; Apoptosis; Carcinoma; Cell Line, Tumor; Colonic Neoplasms; Death Domain Receptor Signaling Adaptor Proteins; Drug Evaluation, Preclinical; Drug Resistance, Neoplasm; Enzyme Inhibitors; Humans; Leupeptins; Proteasome Inhibitors; Receptors, TNF-Related Apoptosis-Inducing Ligand; Signal Transduction; TNF-Related Apoptosis-Inducing Ligand

The development of intratumoral hypoxia, a hallmark of rapidly progressing solid tumors, renders tumor cells resistant to chemotherapy and radiation therapy. We have recently shown that inhibition of aldose reductase (AR), an enzyme that catalyzes the reduction of lipid aldehydes and their glutathione conjugates, prevents human colon cancer cell growth in culture as well as in nude mouse xenografts by inhibiting the NF-κB-dependent activation of oxidative stress-mediated inflammatory and carcinogenic markers. However, the role of AR in mediating hypoxic stress signals is not known. We therefore investigated the molecular mechanisms by which AR inhibition prevents the hypoxia-induced human colon cancer cells growth and invasion. Our results indicate that AR inhibition by the pharmacological inhibitor fidarestat or ablation by AR-specific siRNA prevents hypoxia-induced proliferation of HT29, SW480, and Caco-2 colon cancer cells. Furthermore, hypoxia-induced increase in the level of HIF-1α in colon cancer cells was significantly decreased by AR inhibition. During hypoxic conditions, treatment of HT29 cells with the AR inhibitor fidarestat significantly decreased the expression of vascular endothelial growth factor, a down target of HIF-1α, at both mRNA and protein levels and also prevented the activation of PI3K/AKT, GSK3β, Snail, and lysyl oxidase. Furthermore, inhibition of hypoxia-induced HIF-1α protein accumulation by AR inhibition was abolished in the presence of MG132, a potent inhibitor of the 26 S proteasome. In addition, AR inhibition also prevented the hypoxia-induced inflammatory molecules such as Cox-2 and PGE2 and expression of extracellular matrix proteins such as MMP2, vimentin, uPAR, and lysyl oxidase 2. In conclusion, our results indicate that AR mediates hypoxic signals, leading to tumor progression and invasion.

Topics: Aldehyde Reductase; Caco-2 Cells; Cell Hypoxia; Colonic Neoplasms; Cyclooxygenase 2; Cysteine Proteinase Inhibitors; Dinoprostone; Gene Expression Regulation, Neoplastic; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Humans; Hypoxia-Inducible Factor 1, alpha Subunit; Imidazolidines; Leupeptins; Matrix Metalloproteinase 2; Neoplasm Invasiveness; Phosphatidylinositol 3-Kinases; Proteasome Endopeptidase Complex; Proteasome Inhibitors; Protein-Lysine 6-Oxidase; Proto-Oncogene Proteins c-akt; RNA, Messenger; RNA, Neoplasm; Vascular Endothelial Growth Factor A; Vimentin

Carbonyl reduction is a central metabolic process that controls the level of key regulatory molecules as well as xenobiotics. Carbonyl reductase 3 (CBR3; SDR21C2), a member of the short-chain dehydrogenase/reductase (SDR) superfamily, has been poorly characterized so far, and the regulation of its expression is a complete mystery. Here, we show that CBR3 expression is regulated via Nrf2, a key regulator in response to oxidative stress. In human cancer cell lines, CBR3 mRNA was expressed differentially, ranging from very high (A549, lung) to very low (HT-29, colon; HepG2, liver) levels. CBR3 protein was highly expressed in SW-480 (colon) cells but was absent in HCT116 (colon) and HepG2 cells. CBR3 mRNA could be induced in HT-29 cells by Nrf2 agonists [sulforaphane (SUL, 7-fold) and diethyl maleate (DEM, 4-fold)] or hormone receptor ligand Z-guggulsterone (5-fold). Aryl hydrocarbon receptor agonist B[k]F failed to induce CBR3 mRNA after incubation for 8 h but elevated CBR3 levels after 24 h, most likely mediated by B[k]F metabolites that can activate Nrf2 signaling. Inhibition of Nrf2-activating upstream kinase MEK/ERK by PD98059 weakened DEM-mediated induction of CBR3 mRNA. Proteasome inhibitors MG-132 (5 μM) and bortezomib (50 nM) dramatically increased the level of CBR3 mRNA, obviously because of the increase in the level of Nrf2 protein. While siRNA-mediated knockdown of Nrf2 led to a decrease in the level of CBR3 mRNA in A549 cells (30% of control), Keap1 knockdown increased the level of CBR3 mRNA expression in HepG2 (9.3-fold) and HT-29 (2.7-fold) cells. Here, we provide for the first time evidence that human CBR3 is a new member of the Nrf2 gene battery.

Topics: Alcohol Oxidoreductases; Animals; Cell Line; Cell Line, Tumor; Colonic Neoplasms; Cricetinae; Enzyme Inhibitors; Flavonoids; Gene Expression; Gene Expression Regulation; Humans; Hydroquinones; Leupeptins; Maleates; NAD(P)H Dehydrogenase (Quinone); NF-E2-Related Factor 2; Oxidative Stress; Proteasome Inhibitors; RNA, Messenger; Transfection

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) triggers the apoptotic cascade in various colon cancer cell lines after binding to the membrane receptors DR4 and DR5. However, not all cancer cell lines are sensitive to the therapeutic recombinant human TRAIL (rhTRAIL). To investigate the causes of TRAIL resistance in colon cancer cell lines, models have been developed, mostly in mismatch repair-deficient cells. These cells are prone to mutations in genes containing tandem repeat, including pro-apoptotic protein Bax. We therefore investigated the mechanism underlying TRAIL resistance acquisition in a mismatch repair-proficient colon carcinoma cell line. The TRAIL-resistant cell line SW948-TR was established from the TRAIL-sensitive cell line SW948 by continuous exposure to rhTRAIL, and exhibited 140-fold less sensitivity to rhTRAIL in a cell viability assay. Resistance was stable for over a year in the absence of rhTRAIL. Both cell lines had similar TRAIL receptor cell membrane expression levels. Treatment with the protein synthesis inhibitor cycloheximide sensitized SW948-TR to rhTRAIL-induced apoptosis, indicating that the functionality of the TRAIL receptors was maintained. In SW948-TR, procaspase 8 protein levels but not mRNA levels were notably lower than in SW948. Downregulation of c-FLIP with short interfering RNA (siRNA) sensitized SW948-TR cells to rhTRAIL while caspase 8 siRNA decreased rhTRAIL sensitivity in SW948, indicating the importance of the caspase 8/c-FLIP ratio. Proteasome inhibition with MG132 did not restore basic procaspase 8 levels but stabilized cleaved caspase 8 in rhTRAIL-treated SW948-TR cells. Altogether, our results suggest that colon cancer cells can acquire rhTRAIL resistance by primarily reducing the basal procaspase 8/c-FLIP ratio and by increasing active caspase 8 degradation after rhTRAIL treatment. Proteasome inhibitors can effectively overcome acquired rhTRAIL resistance in mismatch repair-proficient colon cancer cells.

Topics: Antineoplastic Agents; Apoptosis; Carcinoma; CASP8 and FADD-Like Apoptosis Regulating Protein; Caspase 8; Cell Line, Tumor; Cell Survival; Colonic Neoplasms; Cycloheximide; Cysteine Proteinase Inhibitors; DNA Mismatch Repair; Dose-Response Relationship, Drug; Down-Regulation; Drug Resistance, Neoplasm; Enzyme Activation; Humans; Inhibitory Concentration 50; Leupeptins; Phenotype; Proteasome Endopeptidase Complex; Proteasome Inhibitors; Protein Synthesis Inhibitors; Recombinant Proteins; RNA Interference; Time Factors; TNF-Related Apoptosis-Inducing Ligand

Conjugated secondary bile acids promote human colon cancer cell proliferation by activating EGF receptors (EGFR). We hypothesized that bile acid-induced EGFR activation also mediates cell survival by downstream Akt-regulated activation of NF-kappaB. Deoxycholyltaurine (DCT) treatment attenuated TNF-alpha-induced colon cancer cell apoptosis, and stimulated rapid and sustained NF-kappaB nuclear translocation and transcriptional activity (detected by NF-kappaB binding to an oligonucleotide consensus sequence and by activation of luciferase reporter gene constructs). Both DCT-induced NF-kappaB nuclear translocation and attenuation of TNF-alpha-stimulated apoptosis were dependent on EGFR activation. Inhibitors of nuclear translocation, proteosome activity, and IkappaBalpha kinase attenuated NF-kappaB transcriptional activity. Cell transfection with adenoviral vectors encoding a non-degradable IkappaBalpha 'super-repressor' blocked the actions of DCT on both NF-kappaB activation and TNF-alpha-induced apoptosis. Likewise, transfection with mutant akt and treatment with a chemical inhibitor of Akt attenuated effects of DCT on NF-kappaB transcriptional activity and TNF-alpha-induced apoptosis. Chemical inhibitors of Akt and NF-kappaB activation also attenuated DCT-induced rescue of H508 cells from ultraviolet radiation-induced apoptosis. Collectively, these observations indicate that, downstream of EGFR, bile acid-induced colon cancer cell survival is mediated by Akt-dependent NF-kappaB activation. These findings provide a mechanism whereby bile acids increase resistance of colon cancer to chemotherapy and radiation.

Topics: Active Transport, Cell Nucleus; Apoptosis; Bile Acids and Salts; Cell Line, Tumor; Cell Nucleus; Cell Survival; Chromones; Colonic Neoplasms; ErbB Receptors; Humans; I-kappa B Kinase; Leupeptins; Morpholines; Mutation; NF-kappa B; Nitriles; Peptides; Proto-Oncogene Proteins c-akt; Sulfones; Taurodeoxycholic Acid; Tumor Necrosis Factor-alpha; Ultraviolet Rays

Protein homeostasis relies on a balance between protein synthesis and protein degradation. The ubiquitin-proteasome system is a major catabolic pathway for protein degradation. In this respect, proteasome inhibition has been used therapeutically for the treatment of cancer. Whether inhibition of protein degradation by proteasome inhibitor can repress protein translation via a negative feedback mechanism, however, is unknown. In this study, proteasome inhibitor MG-132 lowered the proliferation of colon cancer cells HT-29 and SW1116. In this connection, MG-132 reduced the phosphorylation of mammalian target of rapamycin (mTOR) at Ser2448 and Ser2481 and the phosphorylation of its downstream targets 4E-BP1 and p70/p85 S6 kinases. Further analysis revealed that MG-132 inhibited protein translation as evidenced by the reductions of (35)S-methionine incorporation and polysomes/80S ratio. Knockdown of raptor, a structural component of mTOR complex 1, mimicked the anti-proliferative effect of MG-132. To conclude, we demonstrate that the inhibition of protein degradation by proteasome inhibitor represses mTOR signaling and protein translation in colon cancer cells.

Topics: Adaptor Proteins, Signal Transducing; Antineoplastic Agents; Colonic Neoplasms; Cysteine Proteinase Inhibitors; Humans; Leupeptins; Phosphorylation; Polyribosomes; Proteasome Inhibitors; Protein Biosynthesis; Protein Kinases; Protein Synthesis Inhibitors; Proteins; Regulatory-Associated Protein of mTOR; TOR Serine-Threonine Kinases

The ubiquitin-proteasome system (UPS) and lysosome-dependent macroautophagy (autophagy) are two major intracellular pathways for protein degradation. Blockade of UPS by proteasome inhibitors has been shown to activate autophagy. Recent evidence also suggests that proteasome inhibitors may inhibit cancer growth. In this study, the effect of a proteasome inhibitor MG-132 on the proliferation and autophagy of cultured colon cancer cells (HT-29) was elucidated. Results showed that MG-132 inhibited HT-29 cell proliferation and induced G(2)/M cell cycle arrest which was associated with the formation of LC3(+) autophagic vacuoles and the accumulation of acidic vesicular organelles. MG-132 also increased the protein expression of LC3-I and -II in a time-dependent manner. In this connection, 3-methyladenine, a Class III phosphoinositide 3-kinase inhibitor, significantly abolished the formation of LC3(+) autophagic vacuoles and the expression of LC3-II but not LC3-I induced by MG-132. Taken together, this study demonstrates that inhibition of proteasome in colon cancer cells lowers cell proliferation and activates autophagy. This discovery may shed a new light on the novel function of proteasome in the regulation of autophagy and proliferation in colon cancer cells.

Topics: Adenine; Autophagy; Cell Division; Cell Line, Tumor; Cell Proliferation; Colonic Neoplasms; Cysteine Proteinase Inhibitors; Cytoplasmic Vesicles; G2 Phase; Humans; Leupeptins; Microtubule-Associated Proteins; Proteasome Inhibitors; Vacuoles

The present study was to see whether echinomycin-induced apoptosis would be NF-kappaB-dependent and if so, whether echinomycin would activate or inhibit NF-kappaB as well as resultant chemokine IL-8 expression. In HT-29 cells echinomycin activated NF-kappaB in time-dependent manner. EMSA in the presence of antibodies specific for p50 and p65 subunits indicated that echinomycin-induces the translocation of p50-p65 heterodimeric subunits of NF-kappaB. Levels of IkappaB were detected at initial echinomycin treatment and thereafter decreased, faintly seen after a 6h treatment. In contrast p-IkappaB levels were clearly detected throughout 6-24h of echinomycin treatment, albeit initially fainted. To clarify the role of NF-kappaB on IL-8 expression in echinomycin-mediated apoptosis of HT-29 cells, ELISA plus RT-PCR clearly showed that IL-8 production is inducible by echinomycin treatment. Using a specific inhibitor, IL-8 regulation at echinomycin treatment in HT-29 cells occurred via both caspase-3 and NF-kappaB-dependent signal pathway. To confirm whether two different pathways (NF-kappaB and caspase) would be coupled, only NF-kappaB inhibitor (PDTC) and caspase-3 specific inhibitor (Z-DEVD-FMK) together significantly attenuated echinomycin-initiated apoptosis of HT-29 cells, pretreatment of HT-29 cells with PDTC rarely affected echinomycin-induced caspase-3 activation. So echinomycin-induced apoptosis in HT-29 cells occurs via NF-kappaB activation independent of caspase-3 activation modulating the resultant-linked key chemokine IL-8 expression and echinomycin-induced apoptosis is NF-kappaB-dependant and directly related to NF-kappaB activation, consequently regulating IL-8 expression.

Topics: Antibiotics, Antineoplastic; Apoptosis; Caspase 3; Caspase Inhibitors; Cell Line, Tumor; Colonic Neoplasms; Cysteine Proteinase Inhibitors; Echinomycin; Enzyme Activation; Humans; I-kappa B Kinase; Interleukin-8; Leupeptins; NF-kappa B; Protein Subunits; Signal Transduction

Curcumin (diferuloylmethane) is the major active ingredient of turmeric (Curcuma longa) used in South Asian cuisine for centuries. Curcumin has been shown to inhibit the growth of transformed cells and to have a number of potential molecular targets. However, the essential molecular targets of curcumin under physiologic conditions have not been completely defined. Herein, we report that the tumor cellular proteasome is most likely an important target of curcumin. Nucleophilic susceptibility and in silico docking studies show that both carbonyl carbons of the curcumin molecule are highly susceptible to a nucleophilic attack by the hydroxyl group of the NH(2)-terminal threonine of the proteasomal chymotrypsin-like (CT-like) subunit. Consistently, curcumin potently inhibits the CT-like activity of a purified rabbit 20S proteasome (IC(50) = 1.85 micromol/L) and cellular 26S proteasome. Furthermore, inhibition of proteasome activity by curcumin in human colon cancer HCT-116 and SW480 cell lines leads to accumulation of ubiquitinated proteins and several proteasome target proteins, and subsequent induction of apoptosis. Furthermore, treatment of HCT-116 colon tumor-bearing ICR SCID mice with curcumin resulted in decreased tumor growth, associated with proteasome inhibition, proliferation suppression, and apoptosis induction in tumor tissues. Our study shows that proteasome inhibition could be one of the mechanisms for the chemopreventive and/or therapeutic roles of curcumin in human colon cancer. Based on its ability to inhibit the proteasome and induce apoptosis in both HCT-116 and metastatic SW480 colon cancer cell lines, our study suggests that curcumin could potentially be used for treatment of both early-stage and late-stage/refractory colon cancer.

Topics: Animals; Apoptosis; Caspase 3; Caspase 7; Cell Growth Processes; Colonic Neoplasms; Curcumin; Dose-Response Relationship, Drug; Female; HCT116 Cells; Humans; Leupeptins; Mice; Models, Molecular; Poly(ADP-ribose) Polymerases; Protease Inhibitors; Proteasome Endopeptidase Complex; Proteasome Inhibitors; Xenograft Model Antitumor Assays

We examined the effect of celecoxib on the expression of T-cell factors (TCFs) to clarify the mechanism by which celecoxib suppress beta-catenin/TCF-dependent transcriptional activity without reducing the level of beta-catenin protein, using HCT-116 cells. Celecoxib suppressed the expression of TCF-1 and TCF-4 in a time-dependent manner. Pretreatment of cells with the proteasome inhibitor MG132 inhibited the loss of TCF-1 and TCF-4 induced by celecoxib, suggesting that celecoxib induced the proteasome-dependent degradation of TCF-1 and TCF-4. Beta-catenin/TCF-dependent transcriptional activity was significantly decreased after the treatment with celecoxib for 6 h and the pretreatment of the cells with MG132 attenuated the effect of celecoxib. Further, celecoxib also suppressed the expression of TCF-1 and TCF-4 in another colon cancer cell line, DLD-1. Our results suggest that TCF-1 and TCF-4 degradation may involve the inhibition of the Wnt/beta-catenin signaling pathway induced by celecoxib.

Topics: Anti-Inflammatory Agents, Non-Steroidal; beta Catenin; Celecoxib; Cell Line, Tumor; Colonic Neoplasms; Cysteine Proteinase Inhibitors; Humans; Leupeptins; Proteasome Inhibitors; Pyrazoles; Sulfonamides; T Cell Transcription Factor 1; TCF Transcription Factors; Transcription Factor 7-Like 2 Protein; Transcription, Genetic; Wnt Proteins

p53 regulates apoptosis and the cell cycle through actions in the nucleus and cytoplasm. Altering the subcellular localization of p53 can alter its biological function. Therefore, small molecules that change the localization of p53 would be useful chemical probes to understand the influence of subcellular localization on the function of p53. To identify such molecules, a high-content screen for compounds that increased the localization of p53 to the nucleus or cytoplasm was developed, automated, and conducted. With this image-based assay, we identified ellipticine that increased the nuclear localization of GFP-mutant p53 protein but not GFP alone in Saos-2 osteosarcoma cells. In addition, ellipticine increased the nuclear localization of endogenous p53 in HCT116 colon cancer cells with a resultant increase in the transactivation of the p21 promoter. Increased nuclear p53 after ellipticine treatment was not associated with an increase in DNA double stranded breaks, indicating that ellipticine shifts p53 to the nucleus through a mechanism independent of DNA damage. Thus, a chemical biology approach has identified a molecule that shifts the localization of p53 and enhances its nuclear activity.

Topics: Active Transport, Cell Nucleus; Cell Line, Tumor; Colonic Neoplasms; Cyclin-Dependent Kinase Inhibitor p21; DNA Damage; Drug Evaluation, Preclinical; Ellipticines; Green Fluorescent Proteins; Humans; Leupeptins; Osteosarcoma; Recombinant Fusion Proteins; Thapsigargin; Tumor Suppressor Protein p53

The efficacy of adenovirus vector-based cancer gene therapy is controversial. Its uptake by cells in many cases requires the major receptor for adenoviruses, the coxsackievirus and adenovirus receptor (CAR). Low transduction is believed to be one of the main barriers as the expression of CAR on tumor cells is frequently reduced. Increasing CAR expression on tumor cells thus offers a promising opportunity for more effective adenovirus based treatment. Expression of CAR in 62 cases of colon tumor specimens were examined with immunohistochemistry. To modify the CAR expression, the effects of proteasome inhibitor MG132 on CAR expression of colon cancer cell lines were determined by flow cytometry, RT-PCR, and western blot. To evaluate adenovirus transfer, we further used rAd.EGFP, rAd.p53, and oncolytic adenovirus to infect target cells. The CAR expression was significantly decreased in colon carcinomas, both in primary tumors and lymphonode metastasis. Though the deregulation of CAR occurred in early disease and showed no relationship with TNM stage, when primary tumors are more than 5 cm in diameter, this deregulation becomes more frequent. More importantly, proteasome inhibitor MG-132 could enhance CAR expression in colon carcinoma cell line lovo, accompanied with enhanced adenovirus transfer, target gene expression, and oncolysis. These data provide a rational basis for evaluation of CAR expression in tumors and pretreatment with CAR conditioner prior to adenovirus vector-based gene therapy.

Topics: Blotting, Western; Cell Line, Tumor; Colonic Neoplasms; Coxsackie and Adenovirus Receptor-Like Membrane Protein; Cysteine Proteinase Inhibitors; Flow Cytometry; Gene Expression Regulation, Neoplastic; Genetic Therapy; Humans; Immunohistochemistry; Leupeptins; Receptors, Virus; Reverse Transcriptase Polymerase Chain Reaction

Inhibition of proteasome has been emerging as a promising approach in pathway-directed cancer therapy. Bone morphogenetic protein (BMP) signalling, which is known to be regulated by the ubiquitin-proteasome pathway in osteoblasts, plays a crucial role in the suppression of gastrointestinal carcinogenesis. Here we sought to elucidate the anti-mitogenic effect of a proteasome inhibitor in relation to BMP signalling in colon cancer.. The effects of the proteasome inhibitor MG-132 on proliferation of SW1116 and HT-29 colon cancer cells were determined by [(3)H]-thymidine incorporation and colony-formation assay. The involvement of BMP signalling in the action of MG-132 was elucidated by western blot, real-time PCR, immunofluorescence and RNA interference.. MG-132 significantly suppressed the proliferation of colon cancer SW1116 and HT-29 cells. In this regard, MG-132 activated BMP signalling and this was manifested as an increase in Smad1/5/8 phosphorylation and upregulation of p21(Waf1/Cip1) and p27(Kip1) expression. Knockdown of BMP receptor II abolished Smad1/5/8 phosphorylation, the induction of p21(Waf1/Cip1) and p27(Kip1) and inhibition of cell proliferation induced by MG-132. Further analysis revealed that MG-132 upregulated the expression of BMP1 and BMP2, which are secreted members of the BMP superfamily. Moreover, the expression of Smad6, an intracellular inhibitor of BMP signalling, was suppressed by MG-132.. These findings suggest that inhibition of proteasome suppresses the proliferation of colon cancer cells via activation of BMP signalling. They also demonstrate a novel aspect of proteasome function in the regulation of colon cancer cell proliferation.

Topics: Adenocarcinoma; Antineoplastic Agents; Blotting, Western; Bone Morphogenetic Proteins; Cell Line, Tumor; Colonic Neoplasms; Cysteine Proteinase Inhibitors; Fluorescent Antibody Technique; Gene Expression Regulation; Humans; Leupeptins; Phosphorylation; Polymerase Chain Reaction; RNA Interference; Signal Transduction

Several food polyphenols act as chemopreventers by reducing the incidence of many types of cancer, especially in colon epithelia. In this study, we have investigated whether the flavonoid quercetin can modulate cell proliferation and survival by targeting key molecules and/or biological processes responsible for tumor cell properties. The effect of quercetin on the expression of Ras oncoproteins was specifically studied using systems of either constitutive or conditional expression of oncogenic RAS in human epithelial cells. Our findings suggest that quercetin inhibits cell viability as well as cancer cell properties like anchorage-independent growth. These findings were further supported at the molecular level, since quercetin treatment resulted in a preferential reduction of Ras protein levels in cell lines expressing oncogenic Ras proteins. Notably, in cells that only express wild-type Ras or in those where the oncogenic Ras allele was knocked out, quercetin had no evident effects upon Ras levels. We have shown that quercetin drastically reduces half-life of oncogenic Ras but has no effect when the cells are treated with a proteasome inhibitor. Moreover, in Ha-RAS-transformed cells, quercetin induces autophagic processes. Since quercetin downregulates the levels of oncogenic Ras in cancer cells, we propose that this flavonoid could act as a chemopreventive agent for cancers with frequent mutations of RAS genes.

Topics: Autophagy; Cell Proliferation; Cell Transformation, Neoplastic; Colon; Colonic Neoplasms; Genes, ras; Humans; Leupeptins; Oncogene Protein p21(ras); Quercetin; ras Proteins; Tumor Cells, Cultured

Experimental data suggest therapeutic advantage from selective disruption of the hypoxia response. We recently found that the proteasome inhibitor bortezomib decreases tumor carbonic anhydrase IX (CAIX) expression in colon cancer patients and herein report a companion laboratory study to test if this effect was the result of hypoxia-inducible factor (HIF) inhibition. Human cervical (SiHa and Me180) and colon (RKO) carcinoma cell lines were treated with bortezomib or the structurally unrelated proteasome inhibitor MG132 in normoxic and hypoxic conditions in vitro. Two different in vivo experiments investigated bortezomib effects after single dose (2 mg/kg, 24 h) or longer exposure in severe combined immunodeficient mice bearing SiHa xenografts. Treatment with either drug produced accumulation of HIF-1alpha in vitro but strongly inhibited the production of CAIX and vascular endothelial growth factor (VEGF) under hypoxia. This correlated with more than 10-fold reduction in HIF-1 transcriptional activity under hypoxic conditions. A similar effect of bortezomib was seen in vivo, using the nitroimidazole probe EF5 to define regions of tumor hypoxia and a triple immunofluorescence technique to measure the spatial distributions of HIF-1alpha and CAIX. Plasma VEGF levels decreased by approximately 90% during treatment with bortezomib, indicating that this agent can potently inhibit the hypoxia response in tumors.

Topics: Antigens, Neoplasm; Antineoplastic Agents; Boronic Acids; Bortezomib; Carbonic Anhydrase IX; Carbonic Anhydrases; Carcinoma, Squamous Cell; Caspase 3; Cell Hypoxia; Cell Line, Tumor; Cell Nucleus; Colonic Neoplasms; E1A-Associated p300 Protein; Enzyme Activation; Female; Humans; Hypoxia-Inducible Factor 1, alpha Subunit; Leupeptins; Male; Prostatic Neoplasms; Protease Inhibitors; Protein Binding; Pyrazines; Uterine Cervical Neoplasms; Vascular Endothelial Growth Factor A; Xenograft Model Antitumor Assays

Targeting the ubiquitin-proteasome degradation pathway has become a promising approach for cancer therapy. Previous studies have shown that proteasome inhibition leads to apoptosis in various cancer cells. The mechanism by which apoptosis occurs are not fully understood and can be cell type and/or inhibitor specific. In this study, we investigated the mechanism of mitochondrial activation by proteasome inhibitors in colon cancer cells. We found that Bax activation and mitochondria translocation were required for apoptosis induced by multiple proteasome inhibitors. In contrast, reactive oxygen species did not seem to be induced by MG132 or bortezomib and antioxidants had no effects on MG132-induced apoptosis. In contrast, treatment with MG132 or bortezomib induced a significant accumulation of p53 and PUMA. Genetic deletion of either p53 or PUMA led to a marked suppression of apoptosis induced by these inhibitors, accompanied with reduced Bax activation and cytochrome c release. Consistently, inhibition of translation by cycloheximide could also effectively abolish the accumulation of p53 and PUMA and suppress MG132-induced Bax activation and apoptosis. These findings thus strongly indicate the critical involvement of p53-, PUMA-, and Bax-mediated mitochondrial activation in proteasome inhibitor-induced apoptosis in colon cancer cells.

Topics: Animals; Apoptosis; Apoptosis Regulatory Proteins; bcl-2-Associated X Protein; Boronic Acids; Bortezomib; Caspase Inhibitors; Caspases; Cell Nucleus; Colonic Neoplasms; Cysteine Proteinase Inhibitors; Cytochromes c; Humans; Leupeptins; Mice; Mitochondria; Proteasome Inhibitors; Protein Transport; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-bcl-2; Pyrazines; Reactive Oxygen Species; Tumor Cells, Cultured; Tumor Suppressor Protein p53

Heat shock protein (Hsp) 70B' is a human Hsp70 chaperone that is strictly inducible, having little or no basal expression levels in most cells. Using siRNAs to knockdown Hsp70B' and Hsp72 in HT-29, SW-480, and CRL-1807 human colon cell lines, we have found that the two are regulated coordinately in response to stress. We also have found that proteasome inhibition is a potent activator of Hsp70B'. Flow cytometry was used to assay Hsp70B' promoter activity in HT-29eGFP cells in this study. Knockdown of both Hsp70B'- and Hsp72-sensitized cells to heat stress and increasing concentrations of proteasome inhibitor. These data support the conclusion that Hsp72 is the primary Hsp70 family responder to increasing levels of proteotoxic stress, and Hsp70B' is a secondary responder. Interestingly ZnSO4 induces Hsp70B' and not Hsp72 in CRL-1807 cells, suggesting a stressor-specific primary role for Hsp70B'. Both Hsp70B' and Hsp72 are important for maintaining viability under conditions that increase the accumulation of damaged proteins in HT-29 cells. These findings are likely to be important in pathological conditions in which Hsp70B' contributes to cell survival.

Topics: Antineoplastic Agents; Cell Survival; Colon; Colonic Neoplasms; Cysteine Proteinase Inhibitors; Hot Temperature; HSP70 Heat-Shock Proteins; HSP72 Heat-Shock Proteins; HT29 Cells; Humans; Leupeptins; Promoter Regions, Genetic; Proteasome Endopeptidase Complex; Proteasome Inhibitors; RNA Interference; RNA, Small Interfering; Stress, Physiological; Time Factors; Transfection; Up-Regulation

The purpose of this study was to investigate whether proteasome inhibition acts as a thermal sensitizing agent to induce tumor cell death in a colon cancer cell line.. HT-29 colon cancer cells were exposed to hyperthermia (43 degrees C) in the presence of proteasome inhibition for 1 h. Viable cell mass and apoptosis were measured by MTT and annexin V staining, respectively. Protein levels were determined by Western blot analysis.. A significant synergistic effect on cell viability with proteasome inhibition was noted under hyperthermic conditions compared to hyperthermia alone (p < 0.05). Increases in phosphorylated ERK and decreases in HSP27 levels were observed in the cells exposed to proteasome inhibition at 43 degrees C. Pretreatment with an inhibitor of ERK yielded an additional increase in apoptosis when used in combination with proteasome inhibition and hyperthermia. Decreased expression of HSP27 by siRNA also resulted in increased thermally induced apoptotic cell death.. Thermal sensitization through proteasome inhibition may represent a novel approach to increase the efficacy of hyperthermia as an anticancer modality.

Topics: Antineoplastic Agents; Apoptosis; Blotting, Western; Butadienes; Cell Proliferation; Cell Survival; Colonic Neoplasms; Cysteine Proteinase Inhibitors; Dose-Response Relationship, Drug; Drug Synergism; Electrophoresis, Polyacrylamide Gel; Enzyme Inhibitors; Heat-Shock Proteins; HT29 Cells; Humans; Hyperthermia, Induced; Leupeptins; Nitriles; Protease Inhibitors; Proteasome Inhibitors; RNA, Small Interfering

The synergistic interaction between proteasome inhibitors and tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a promising approach to induce cell death in tumor cells. However, the molecular and biochemical mechanisms of this synergism have been proven to be cell type specific. We therefore focused our investigation on TRAIL-resistant colon carcinoma cells in this study. DNA fragmentation, mitochondrial membrane depolarization and increased caspase-3-like enzyme activity was exclusively induced only by combined treatment with proteasome inhibitors (epoxomicin, MG132, bortezomib/PS-341) and TRAIL. The expression level of anti-apoptotic proteins (XIAP, survivin, Bcl-2, Bcl-XL), regulated by NF-kappaB transcription factor, was not effected by any of these treatments. TRAIL alone induced only partial activation of caspase-3 (p20), while the combination of TRAIL and proteasome inhibition led to the full proteolytic activation of caspase-3 (p17). Only the combination treatment induced marked membrane depolarization and the release of cytochrome c, HtrA2/Omi and Smac/DIABLO. Apoptosis-inducing factor (AIF) was not released in any of these conditions. These results are consistent with a model where the full activation of caspase-3 by caspase-8 is dependent on the release of Smac/DIABLO in response to the combined treatment. This molecular mechanism, independent of the inhibition NF-kappaB activity, may provide rationale for the combination treatment of colon carcinomas with proteasome inhibitors and recombinant TRAIL or agonistic antibody of TRAIL receptors.

Topics: Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Apoptosis Regulatory Proteins; Boronic Acids; Bortezomib; Caspase 3; Caspase 8; Colonic Neoplasms; Drug Synergism; Enzyme Activation; Humans; Intracellular Signaling Peptides and Proteins; Leupeptins; Mitochondria; Mitochondrial Proteins; Oligopeptides; Protease Inhibitors; Proteasome Inhibitors; Pyrazines; TNF-Related Apoptosis-Inducing Ligand

Proteasome inhibitors can resensitize cells that are resistant to tumor necrosis factor-related apoptotic-inducing ligand (TRAIL)-mediated apoptosis. However, the underlying mechanisms of this effect are unclear. To characterize the mechanisms of interaction between proteasome inhibitors and TRAIL protein, we evaluated the effects of combined treatment with the proteasome inhibitors bortezomib and MG132 and TRAIL protein on two TRAIL-resistant human colon cancer cell lines, DLD1-TRAIL/R and LOVO-TRAIL/R. Both bortezomib and MG132 in combination with TRAIL enhanced apoptotosis induction in these cells, as evidenced by enhanced cleavage of caspases 8, 9, and 3, Bid, poly(ADP-ribose) polymerase and by the release of cytochrome C and Smac. Subsequent studies showed that combined treatment with bortezomib or MG132 resulted in an increase of death receptor (DR) 5 and Bik at protein levels but had no effects on protein levels of DR4, Bax, Bak, Bcl-2, Bcl-XL or Flice-inhibitory protein (FLIP). Moreover, c-Jun N-terminal kinase (JNK) is activated by these proteasome inhibitors. Blocking JNK activation with the JNK inhibitor SP600125 attenuated DR5 increase, but enhancement of apoptosis induction and increase of Bik protein were not affected. However, bortezomib-mediated TRAIL sensitization was partially blocked by using siRNA to knockdown Bik. Thus, our data suggests that accumulation of Bik may be critical for proteasome inhibitor-mediated resensitization of TRAIL.

Topics: Apoptosis; Apoptosis Regulatory Proteins; bcl-2-Associated X Protein; bcl-X Protein; BH3 Interacting Domain Death Agonist Protein; Boronic Acids; Bortezomib; Caspases; Cell Proliferation; Colonic Neoplasms; Cysteine Proteinase Inhibitors; Cytochromes c; Drug Resistance, Neoplasm; Humans; Intracellular Signaling Peptides and Proteins; Leupeptins; Membrane Glycoproteins; Membrane Proteins; Mitochondrial Proteins; Poly(ADP-ribose) Polymerases; Proto-Oncogene Proteins c-bcl-2; Pyrazines; Receptors, TNF-Related Apoptosis-Inducing Ligand; Receptors, Tumor Necrosis Factor; RNA, Small Interfering; TNF-Related Apoptosis-Inducing Ligand; Tumor Cells, Cultured; Tumor Necrosis Factor-alpha

Apo2L/TRAIL (tumor necrosis factor-related apoptosis inducing ligand (TRAIL), also known as Apo2L) is a potentially important anticancer agent awaiting clinical trials. Unfortunately, however, some cancer cells exhibit resistance to Apo2L/TRAIL, which could limit the use of this potentially promising anticancer agent. Although the molecular basis of the inherent or acquired resistance to Apo2L/TRAIL remains unclear, previous studies indicate that Bax deficiency can confer resistance to Apo2L/TRAIL. Proteasome inhibition is also emerging as a promising therapeutic strategy to manage human malignancies. Here, we report that proteasome inhibitor MG132 upregulates Apo2L/TRAIL death receptor 5 expression in both Bax-proficient and -deficient HCT116 cells. MG132 effectively cooperated with Apo2L/TRAIL to induce apoptosis in both Bax-proficient and -deficient cells that was coupled with caspases-8 and -3 activation and Bid cleavage. Although both agents in combination also induced cytochrome c and Smac release from mitochondria into cytosol and activated caspase-9 in Bax-proficient cells, their effects on these events were significantly diminished in Bax-deficient cells. These results suggest that Bax is not absolutely required for death receptor 5-dependent apoptotic signals and MG132 by upregulating DR5 effectively cooperates with Apo2L/TRAIL to overcome Bax deficiency-induced resistance to Apo2L/TRAIL. Our results have important clinical implications in that the use of Apo2L/TRAIL and proteasome inhibitors in combination could prove to be a novel therapeutic strategy to manage the Apo2L/TRAIL-resistant tumors.

Topics: Antineoplastic Agents; Apoptosis; Apoptosis Regulatory Proteins; bcl-2-Associated X Protein; Cell Line, Tumor; Colonic Neoplasms; Drug Interactions; Humans; Leupeptins; Membrane Glycoproteins; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-bcl-2; Receptors, TNF-Related Apoptosis-Inducing Ligand; Receptors, Tumor Necrosis Factor; Time Factors; TNF-Related Apoptosis-Inducing Ligand; Tumor Necrosis Factor-alpha; Up-Regulation

The p53 oncosuppressor protein is subject to negative regulation by MDM2, which efficiently inhibits its activity through an autoregulatory loop. In response to stress, however, p53 undergoes post-translational modifications that allow the protein to escape MDM2 control, accumulate, and become active. Recent studies have shown that, following DNA damage, the HIPK2 serine/threonine kinase binds and phosphorylates p53, inducing p53 transcriptional activity and apoptotic function. Here, we investigated the role of HIPK2 in the activation of p53 in the presence of MDM2. We found that HIPK2 rescues p53 transcriptional activity overcoming MDM2 inhibition, and that restoration of this p53 function induces apoptosis. Recovery of p53-dependent apoptosis is achieved by preventing p53 nuclear export and ubiquitination mediated by MDM2 in vitro and in vivo following genotoxic stress. These results shed new light on the mechanisms by which the HIPK2/p53 pathway promotes apoptosis and suppression of tumorigenesis.

Topics: Adenocarcinoma; Antineoplastic Agents; Apoptosis; Blotting, Western; Carrier Proteins; Cell Line, Tumor; Cell Nucleus; Cisplatin; Colonic Neoplasms; Cysteine Proteinase Inhibitors; DNA Damage; Humans; Leupeptins; Luciferases; Lung Neoplasms; Nuclear Proteins; Osteosarcoma; Precipitin Tests; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-mdm2; Transcriptional Activation; Tumor Suppressor Protein p53; Ubiquitin

Enhancing apoptosis to remove abnormal cells has potential in reversing cancerous processes. Caspase-3 activation generally accompanies apoptosis and its substrates include enzymes responsible for DNA fragmentation and isozymes of protein kinase C (PKC). Recent data, however, question its obligatory role in apoptosis. We have examined whether modulation of PKC activity induces apoptosis in COLO 205 cells and the role of caspase-3. Proliferation ([3H]thymidine) and apoptosis (DNA fragmentation and FACS) of COLO 205 cells were measured in response to PKC activation and inhibition. Caspase-3 activity was assayed and the effects of its inhibition with Ac-DEVD-cmk, and the effect of other protease inhibitors, on apoptosis were determined. PKC activation and inhibition both reduced DNA synthesis and induced DNA fragmentation. As PKC inhibitors induced DNA fragmentation more rapidly than PKC activators and failed to block activator effects, we conclude that it is PKC down-regulation (i.e., inhibition) after activator exposure that mediates apoptosis. Increases in caspase-3 activity occurred during apoptosis but apoptosis was not blocked by caspase inhibition. By contrast, the cysteine protease inhibitor, E-64d, blocked apoptosis. Cysteine proteases not of the caspase family may either act more closely to the apoptotic process than caspases or lie on an alternative, more active pathway.

Topics: Aged; Alkaloids; Amino Acid Chloromethyl Ketones; Aprotinin; Benzophenanthridines; Benzyl Compounds; Caspase 3; Caspases; Cell Division; Cell Transformation, Neoplastic; Colonic Neoplasms; Cysteine Endopeptidases; Cysteine Proteinase Inhibitors; Dipeptides; DNA; DNA Fragmentation; Down-Regulation; Humans; Hydrocarbons, Fluorinated; Leucine; Leupeptins; Male; Pepstatins; Phenanthridines; Protein Kinase C; Pyridines; Tumor Cells, Cultured

Colorectal cancer (CRC) is the second leading cause of cancer death in the USA. Accumulation of beta-catenin protein is nearly ubiquitous in colon adenomas and cancers, presumably due to mutations in the APC or beta-catenin genes that inhibit proteasome-dependent degradation of beta-catenin protein. Substantial clinical, epidemiological, and animal evidence indicate that sulindac and other non-steroidal anti-inflammatory drugs (NSAIDs) prevent the development of CRC. The mechanisms by which sulindac exerts its potent growth inhibitory effects against colon tumor cells are incompletely understood, but down-regulation of beta-catenin has been suggested as one potential mechanism. The goal of this study was to determine the mechanism of beta-catenin protein down-regulation by sulindac metabolites. Treatment of human colon cancer cell lines with apoptotic concentrations of sulindac metabolites (sulindac sulfide, sulindac sulfone) induced a dose- and time-dependent inhibition of beta-catenin protein expression. Inhibition of proteasome activity with MG-132 partially blocked the ability of sulindac sulfide and sulindac sulfone to inhibit beta-catenin protein expression. Pretreatment with the caspase inhibitor z-VAD-fmk blocked morphological signs of apoptosis as well as caspase cleavage, and also partially prevented beta-catenin degradation by sulindac metabolites. These effects occurred in cells with bi-allelic APC mutation (SW480), with wild-type APC but mono-allelic beta-catenin mutation (HCT116) and in cells that lack expression of either COX-1 or -2 (HCT15). These results indicate that loss of beta-catenin protein induced by sulindac metabolites is COX independent and at least partially due to reactivation of beta-catenin proteasome degradation and partially a result of caspase activation during the process of apoptosis.

Topics: Adenomatous Polyposis Coli; Antineoplastic Agents; Apoptosis; beta Catenin; Caspase 3; Caspase Inhibitors; Caspases; Cell Nucleus; Colonic Neoplasms; Cysteine Endopeptidases; Cysteine Proteinase Inhibitors; Cytoskeletal Proteins; Down-Regulation; Enzyme Inhibitors; Humans; Leupeptins; Multienzyme Complexes; Proteasome Endopeptidase Complex; Signal Transduction; Sulindac; Trans-Activators; Tumor Cells, Cultured

Growth-inhibitory effects on DS19 mouse erythroleukemia cells were seen in the micromolar concentration range with allicin and S-allylmercaptocysteine and in the millimolar range with allyl butyrate, allyl phenyl sulfone, and S-allyl cysteine. Increased acetylation of histones was induced by incubation of cells with the allyl compounds at concentrations similar to those that resulted in the inhibition of cell proliferation. The induction of histone acetylation by S-allylmercaptocysteine was also observed in Caco-2 human colon cancer cells and T47D human breast cancer cells. In contrast to the effect on histone acetylation, there was a decrease in the incorporation of phosphate into histones when DS19 cells were incubated with 25 microM S-allylmercaptocysteine. Histone deacetylase activity was inhibited by allyl butyrate, but there was little or no effect with the allyl sulfur compounds examined in this study. A similar degree of downregulation of histone deacetylase and histone acetyltransferase was observed when DS19 cells were incubated with S-allylmercaptocysteine or allyl isothiocyanate. The induction of histone acetylation by S-allylmercaptocysteine was not blocked by a proteasome inhibitor. The mechanism by which S-allylmercaptocysteine induces histone acetylation remains to be characterized. It may be related in part to metabolism to allyl mercaptan, which is a more effective inhibitor of histone deacetylase.

Topics: Acetylation; Acetyltransferases; Allyl Compounds; Animals; Antineoplastic Agents; Breast Neoplasms; Colonic Neoplasms; Cysteine; Disulfides; Electrophoresis, Polyacrylamide Gel; Female; Histone Acetyltransferases; Histone Deacetylases; Histones; Humans; Leukemia, Erythroblastic, Acute; Leupeptins; Mice; Saccharomyces cerevisiae Proteins; Sulfinic Acids; Tumor Cells, Cultured

We have shown previously that rats can be cured from induced peritoneal colon carcinomatosis by injections of apoptotic bodies derived from tumor cells and interleukin 2. This curative treatment generated a tumor-specific cytotoxic T-cell response associated with a humoral response. Autoantibodies from sera of cured rats strongly recognized a Mr 67,000 protein from apoptotic bodies and weakly reacted with a protein of Mr approximately 97,000 in PROb parental cells. We now show that these autoantibodies are directed against BARD1, originally identified as a protein interacting with the product of the breast cancer gene 1, BRCA1. We demonstrate that the Mr 67,000 antigen is a cleaved form of BARD1 present in apoptotic bodies derived from rat and human colon and mammary carcinoma cell lines. Moreover, we show that the cleavage site of BARD1 is located NH2 terminally but downstream of the RING domain essential for BARD1 and BRCA1 protein interaction. In vitro studies using [35S]methionine-labeled human BARD1 and apoptotic cellular extracts derived from SW48 carcinoma cells indicate that BARD1 proteolysis occurs at an early stage of apoptosis and in a cell cycle-dependent manner. This hydrolysis is inhibited by EGTA, and the calpain inhibitor I, N-acetyl-leu-leu-norleucinal, but not by several caspases inhibitors, suggesting that BARD1 is hydrolyzed by the calcium-dependent cysteine proteases, calpains. Thus, the highly immunogenic form of cleaved BARD1 could contribute to the antitumoral response mediated by apoptotic bodies.

Topics: Amino Acid Sequence; Animals; Antibodies, Monoclonal; Apoptosis; Autoantigens; Blotting, Western; BRCA1 Protein; Breast Neoplasms; Calpain; Carrier Proteins; Cell Cycle; Cell Fractionation; Cloning, Molecular; Colonic Neoplasms; Cysteine Proteinase Inhibitors; DNA, Complementary; Egtazic Acid; Enzyme Inhibitors; Gene Library; Humans; Leupeptins; Mammary Neoplasms, Animal; Mice; Molecular Sequence Data; Precipitin Tests; Protein Binding; Protein Structure, Tertiary; Rats; Sequence Homology, Amino Acid; Tumor Cells, Cultured; Tumor Suppressor Proteins; Ubiquitin-Protein Ligases

The proteasome is a multiprotein complex involved in the degradation of ubiquitinated proteins. Three proteasome inhibitors, calpain inhibitor I, lactacystin and MG132, induced apoptosis in several human malignant glioma cell lines. Although proteasome inhibitors induced p53 accumulation in a cell line retaining wild-type p53 activity, p53 activity was dispensable for apoptosis since transdominant-negative p53 abrogated p53-dependent p21 induction but did not modulate apoptosis. Further, p21 was induced by higher concentrations of proteasome inhibitors in a p53-independent manner both in p53 wild-type and in p53 mutant cell lines. Although there was a strong G2/M arrest in response to proteasome inhibition in glioma cells, this G2/M arrest was also observed in p21(-/-) colon carcinoma cells, suggesting that p21 is dispensable for the G2/M arrest associated with proteasome inhibition. Interestingly, the p21(-/-) cells were more resistant to protease inhibitors than parental p21(+/+) cells. In summary, our data indicate that proteasome inhibition induces a p21-independent G2/M arrest and p53-independent apoptosis in human malignant glioma cells.

Topics: Acetylcysteine; Apoptosis; Cell Cycle; Cell Division; Cell Survival; Colonic Neoplasms; Cyclin-Dependent Kinase Inhibitor p21; Cyclins; Cysteine Endopeptidases; Cysteine Proteinase Inhibitors; Enzyme Inhibitors; Glioma; Glycoproteins; Humans; Kinetics; Leupeptins; Multienzyme Complexes; Proteasome Endopeptidase Complex; Serine Proteinase Inhibitors; Tumor Cells, Cultured; Tumor Suppressor Protein p53

Enterocyte-like differentiated HT-29 colon carcinoma cells were shown to contain far higher intracellular levels of activity of lysosomal cathepsins B, D, and L than their undifferentiated counterparts. In the latter, inhibition of lysosomal functions by leupeptin or ammonium chloride led to a marked increase in the cell-associated activity of the three cathepsins. High levels of pro-cathepsins B, D, and L were found in the culture media of both HT-29 cell populations. Ammonium chloride and chloroquine, which are known to impair the mannose-6-phosphate-dependent trafficking of lysosomal-targeted proteins, did not increase the secretion of the three cathepsins in either undifferentiated or differentiated cultures of HT-29 cells. Analyses by cell fractionation revealed heterogeneities with regard to the density and the content of lysosomal cathepsins between the two cell populations. Leupeptin induced the accumulation of mature lysosomal cathepsins B and L in light density organelles in undifferentiated HT-29 cells. Altogether, these data demonstrate that (1) the expression and subcellular distribution of cathepsins B, D, and L in HT-29 cells are influenced by their state of enterocytic differentiation, (2) the segregation of lysosomal cathepsins is largely inefficient in this tumor cell line and does not increase upon differentiation, and (3) the mannose-6-phosphate-receptor-dependent pathway plays a minor role in the sorting of the three cathepsins, both in undifferentiated and enterocytic-differentiated HT-29 cells.

Topics: Ammonium Chloride; Cathepsin B; Cathepsin D; Cathepsin L; Cathepsins; Cell Differentiation; Colon; Colonic Neoplasms; Cysteine Endopeptidases; Cysteine Proteinase Inhibitors; Endopeptidases; HT29 Cells; Humans; Leupeptins; Lysosomes; Mannosephosphates

Intestinal epithelial cells express a low level of HLA class II molecules constitutively, with elevated levels seen in the setting of mucosal inflammation including inflammatory bowel disease. The ability of intestinal epithelial cells to act as antigen presenting cells for alphabeta CD4(+) T lymphocytes was examined through a molecular analysis of the HLA class II antigen processing pathway. We have shown that intestinal epithelial cells contain abundant constitutive levels of the cathepsin proteases proven to function in HLA class II mediated antigen presentation. Activation of these cells by gamma-IFN induced the expression of invariant chain and HLA-DM alphabeta, thus facilitating the formation of compact, SDS-stable HLA- DR alphabeta heterodimers. Using HLA-DR-restricted T cells and retroviral mediated gene transfer of HLA-DR alleles into the intestinal epithelial cell lines HT-29 and T84, we demonstrated efficient antigen processing and presentation to CD4(+) T lymphocytes in the presence of the proinflammatory cytokine gamma-IFN. The class II processing pathway and presentation in the presence of gamma-IFN was indistinguishable from that observed with a conventional antigen presenting cell. Antigen processing also occurred in intestinal epithelial cells in the absence of gamma-IFN, and in contrast to that seen after stimulation with gamma-IFN, required high concentration of antigen and was not inhibited by the protease inhibitor leupeptin. These data suggest the use of two distinct pathways of HLA class II antigen processing in enterocytes with differential immunomodulatory properties in the presence or absence of mucosal inflammation.

Topics: Cathepsin B; Cathepsin H; Cathepsin L; Cathepsins; CD4-Positive T-Lymphocytes; Colonic Neoplasms; Cysteine Endopeptidases; Dimerization; DNA Primers; Endopeptidases; Histocompatibility Antigens Class II; HLA-D Antigens; HLA-DQ Antigens; HLA-DR Antigens; Humans; Interferon-gamma; Intestinal Mucosa; Leupeptins; Polymerase Chain Reaction; Protease Inhibitors; Recombinant Proteins; Transfection; Tumor Cells, Cultured

Cathepsin B, a thiol protease, has been reported to be involved in cancer progression and metastasis. The suppressive effects of two kinds of protease inhibitors, leupeptin and dietary camostate (FOY-305), on tumorigenesis and progression in 1, 2-dimethylhydrazine (DMH)-induced rat colon neoplasm were examined in relation to tissue cathepsin B activity. Male Donryu rats were treated with leupeptin or FOY-305 during or after the administration of DMH. There were no significant differences in average tumor numbers among all DMH-treated groups. However, the percentage of small tumors was significantly higher in the group in which leupeptin was supplied during DMH administration. This trend was not recognized in the FOY-305-treated groups. The ratio of cathepsin B activity in the tumors to that in the tumor-bearing tissue (T/Tb) was significantly increased with increasing tumor size (P = 0.009). The cathepsin B activity levels in the tumor-bearing mucosa in the groups which received leupeptin or FOY-305 following DMH treatment were both significantly lower than that in the group which received neither protease inhibitor (P = 0.046 and P = 0.0067, respectively). The results obtained indicate that leupeptin may have suppressed tumor growth by lowering the tissue cathepsin B activity.

Topics: 1,2-Dimethylhydrazine; Animals; Carcinogens; Cathepsin B; Colonic Neoplasms; Dimethylhydrazines; Esters; Gabexate; Guanidines; Leupeptins; Male; Protease Inhibitors; Rats

When the human colon cancer cells HT-29 undergo enterocytic differentiation, they correctly process their N-glycans, whereas their undifferentiated counterpart are unable to process Man9-8-GlcNAc2 species, the natural substrate of alpha-mannosidase I. As this enzyme is fully active in both HT-29 cell populations, we hypothesize that N-glycoproteins are unable to reach the cis Golgi, the site where alpha-mannosidase I has been localized. We have demonstrated this point by using 1-deoxymannojirimycin, leupeptin, and monensin. In the presence of 1-deoxymannojirimycin, a specific inhibitor of alpha-mannosidase I, differentiated HT-29 cells, as expected, accumulate Man9-8-GlcNAc2 species, whereas in undifferentiated HT-29 cells these compounds continue to be rapidly degraded. In contrast, the use of leupeptin, a specific inhibitor of thiol and serine proteases, leads to the accumulation of these oligosaccharides in undifferentiated HT-29 cells. Monensin, a carboxylic ionophore that perturbs distal Golgi functions, is unable to stabilize these compounds. Therefore, we conclude that N-linked glycoproteins in undifferentiated HT-29 cells rapidly egress from the exocytic pathway to a leupeptin-sensitive degradative compartment without entering a monensin-sensitive compartment. These results favor the hypothesis that a direct pathway should exist between the rough endoplasmic reticulum and a leupeptin-sensitive degradative compartment in undifferentiated HT-29 cells. The emergence of this new pathway could explain why protein stability and N-glycan processing may vary as a function of the state of cell differentiation.

Topics: 1-Deoxynojirimycin; alpha-Mannosidase; Biological Transport; Cell Differentiation; Colon; Colonic Neoplasms; Glucosamine; Humans; In Vitro Techniques; Leupeptins; Mannosidases; Membrane Glycoproteins; Monensin; Polysaccharides; Protein Processing, Post-Translational; Tumor Cells, Cultured

HT-29 cells derived from a human colonic adenocarcinoma, can express a typical intestinal differentiation. Undifferentiated HT-29 cells accumulate N-linked glycoproteins substituted with unprocessed carbohydrate chains before to degrade them. Conversely, carbohydrate chains of N-linked glycoproteins are classically processed in differentiated HT-29 cells. The instability of N-linked glycoproteins in undifferentiated HT-29 cells is due to their rapid delivery from the endoplasmic reticulum to a compartment with lysosomal characteristics. This catabolitic pathway involves a bypass of the Golgi apparatus.

Topics: Adenocarcinoma; Cell Transformation, Neoplastic; Colonic Neoplasms; Drug Stability; Glycoproteins; Humans; Leupeptins; Polysaccharides; Protein Processing, Post-Translational; Tumor Cells, Cultured