Biomedical subjects

Devasis Chatterjee

Publications and source records attributed to Devasis Chatterjee.

7 recordsLinked to original sources

PubMed2006

Stat3 cleavage by caspases: impact on full-length Stat3 expression, fragment formation, and transcriptional activity.

Stat3 and its isoforms belong to a family of cytoplasmic transcription factors that affect the synthesis of various proteins. Caspases are cysteinyl-aspartate proteases that function under apoptotic and non-apoptotic conditions. We now report that, in addition to transcriptional splicing, Stat3 fragmentation can be mediated by caspases. Caspase activation in DU145 cells was achieved by staurosporine (STS) exposure, and Western analysis revealed a reduction in full-length Stat3 (fl-Stat3) expression that was caspase-mediated. This proteolytic relationship was further studied by exposing purified Stat3 protein to a mixture of active caspases under cell-free conditions. This demonstrated that caspases directly cleaved Stat3 and Stat3 cleavage was accompanied by the apparent formation of cleavage fragment(s). Stat3 cleavage fragments, reflecting multiple caspase cleavage sites, also were observed in vitro following STS exposure in DU145 cells and in HEK293T cells transfected to express Stat3 truncation mutants. The impact of cleavage on Stat3 transcriptional activity next was assessed and revealed that cleavage of fl-Stat3 was accompanied by reductions in Stat3-DNA binding, Stat3-driven reporter protein (luciferase) activity, and the expression of selected Stat3-dependent genes. Further, reduced Stat3 expression correlated with increased sensitivity to apoptotic stimuli. In concomitant experiments, reporter activity was assessed in Stat3 truncation mutant-expressing HEK293T cells and revealed that, under non-apoptotic conditions, expression of different Stat3 fragments induced differential effects on Stat3-driven luciferase activity. These findings demonstrate that fl-Stat3 undergoes proteolytic processing by caspases that reduces its expression and leads to the formation of cleavage fragments that may modulate Stat3 transcriptional activity.

Amino Acid Chloromethyl Ketones↗

PubMed2005

Stat3 dimerization regulated by reversible acetylation of a single lysine residue.

Upon cytokine treatment, members of the signal transducers and activators of transcription (STAT) family of proteins are phosphorylated on tyrosine and serine sites within the carboxyl-terminal region in cells. We show that in response to cytokine treatment, Stat3 is also acetylated on a single lysine residue, Lys685. Histone acetyltransferase p300-mediated Stat3 acetylation on Lys685 was reversible by type I histone deacetylase (HDAC). Use of a prostate cancer cell line (PC3) that lacks Stat3 and PC3 cells expressing wild-type Stat3 or a Stat3 mutant containing a Lys685-to-Arg substitution revealed that Lys685 acetylation was critical for Stat3 to form stable dimers required for cytokine-stimulated DNA binding and transcriptional regulation, to enhance transcription of cell growth-related genes, and to promote cell cycle progression in response to treatment with oncostatin M.

Acetylation↗

PubMed2004

Inhibition of the Raf-MEK1/2-ERK1/2 signaling pathway, Bcl-xL down-regulation, and chemosensitization of non-Hodgkin's lymphoma B cells by Rituximab.

Rituximab (Rituxan, IDEC-C2B8) has been shown to sensitize non-Hodgkin's lymphoma (NHL) cell lines to chemotherapeutic drug-induced apoptosis. Rituximab treatment of Bcl-2-deficient Ramos cells and Bcl-2-expressing Daudi cells selectively decreases Bcl-(xL) expression and sensitizes the cells to paclitaxel-induced apoptosis. This study delineates the signaling pathway involved in rituximab-mediated Bcl-(xL) down-regulation in Ramos and Daudi NHL B cells. We hypothesized that rituximab may interfere with the extracellular signal-regulated kinase (ERK) 1/2 pathway, leading to decreased Bcl-(xL) expression. Rituximab (20 microg/mL) inhibited the kinase activity of mitogen-activated protein kinase kinase (MEK) 1/2 and reduced the phosphorylation of the components of the ERK1/2 pathway (Raf-1, MEK1/2, and ERK1/2) and decreased activator protein-1 DNA binding activity and Bcl-(xL) gene expression. These events occurred with similar kinetics and were observed 3 to 6 hours after rituximab treatment. Rituximab-mediated effects were corroborated by using specific inhibitors of the ERK1/2 pathway, which also reduced Bcl-(xL) levels and sensitized the NHL B cells to paclitaxel-induced apoptosis. Previous findings implicated a negative regulatory role of the Raf-1 kinase inhibitor protein (RKIP) on the ERK1/2 pathway. Rituximab treatment of NHL B cells significantly up-regulated RKIP expression, thus interrupting the ERK1/2 signaling pathway through the physical association between Raf-1 and RKIP, which was concomitant with Bcl-(xL) down-regulation. These novel findings reveal a signaling pathway triggered by rituximab, whereby rituximab-mediated up-regulation of RKIP adversely regulates the activity of the ERK1/2 pathway, Bcl-(xL) expression, and subsequent chemosensitization of drug-refractory NHL B cells. The significance of these findings is discussed.

Amino Acid Sequence↗

PubMed2004

Mechanistic and antineoplastic evaluation of taurolidine in the DU145 model of human prostate cancer.

Taurolidine (TRD) was designed in the 1970s as a broad-spectrum antibiotic and is used clinically at high doses without systemic toxicity. We have found that this agent possesses cytotoxic activity in human tumor cell lines and antineoplastic activity in mice bearing i.p. human tumor xenografts. We now report the mechanism by which TRD induces cell death in DU145 human prostate tumor cells. The IC50 (3 days) of TRD in this model was 16.8+/-1.1 microM. Cytotoxicity was associated with DNA debris and increased membrane phosphatidylserine externalization, both suggesting the induction of apoptosis. This was confirmed by the ability of TRD to induce PARP cleavage in these cells, an effect prevented by coexposure to the pan-caspase inhibitor zVAD-FMK. TRD exposure also resulted in the appearance of cytochrome c in the cytoplasm, procaspase 9 activation within 2 h of drug exposure and procaspase 8 activation 4 h after exposure. Parallel experiments revealed that cytochrome c appearance in the cytoplasm was not blocked by preexposure to zVAD-FMK, while activation of both procaspase 9 and procaspase 8 was prevented. Finally, antineoplastic activity was assessed in mice bearing subcutaneous xenografts of DU145 cells. Initial studies quantitated the toxicity of three i.p. injections of TRD, administered as one injection on three alternate days per week, at doses ranging from 500 to 700 mg/kg per injection. The 500 mg/kg dose produced about 7% mortality after three cycles and effectively inhibited tumor growth. Thus, TRD induced mitochondrial-mediated apoptosis in DU145 human prostate tumor cells and this effect could be exploited for therapeutic advantage.

Animals↗

PubMed2004

RKIP sensitizes prostate and breast cancer cells to drug-induced apoptosis.

Cancer cells are more susceptible to chemotherapeutic agent-induced apoptosis than their normal counterparts. Although it has been demonstrated that the increased sensitivity results from deregulation of oncoproteins during cancer development (Evan, G. I., and Vousden, K. H. (2001) Nature 411, 342-348; Green, D. R., and Evan, G. I. (2002) Cancer Cell 1, 19-30), little is known about the signaling pathways leading to changes in the apoptotic threshold in cancer cells. Here we show that low RKIP expression levels in tumorigenic human prostate and breast cancer cells are rapidly induced upon chemotherapeutic drug treatment, sensitizing the cells to apoptosis. We show that the maximal RKIP expression correlates perfectly with the onset of apoptosis. In cancer cells resistant to DNA-damaging agents, treatment with the drugs does not up-regulate RKIP expression. However, ectopic expression of RKIP resensitizes DNA-damaging agent-resistant cells to undergo apoptosis. This sensitization can be reversed by up-regulation of survival pathways. Down-regulation of endogenous RKIP by expression of antisense and small interfering RNA (siRNA) confers resistance on sensitive cancer cells to anticancer drug-induced apoptosis. Our studies suggest that RKIP may represent a novel effector of signal transduction pathways leading to apoptosis and a prognostic marker of the pathogenesis of human cancer cells and tumors after treatment with clinically relevant chemotherapeutic drugs.

Androgen-Binding Protein↗

PubMed2004

Raf-1 kinase inhibitor protein: structure, function, regulation of cell signaling, and pivotal role in apoptosis.

The acquisition of resistance to conventional therapies such as radiation and chemotherapeutic drugs remains the major obstacle in the successful treatment of cancer patients. Tumor cells acquire resistance to apoptotic stimuli and it has been demonstrated that conventional therapies exert their cytotoxic activities primarily by inducing apoptosis in the cells. Resistance to radiation and chemotherapeutic drugs has led to the development of immunotherapy and gene therapy approaches with the intent of overcoming resistance to drugs and radiation as well as enhancing the specificity to eliminate tumor cells. However, cytotoxic lymphocytes primarily kill by apoptosis and, therefore, drug-resistant tumor cells may also be cross-resistant to immunotherapy. To evade apoptosis, tumor cells have adopted various mechanisms that interfere with the apoptotic signaling pathways and promote constitutive activation of cellular proliferation and survival pathways. Thus, modifications of the antiapoptotic genes in cancer cells are warranted for the effectiveness of conventional therapies as well as novel immunotherapeutic approaches. Such modifications will avert the resistant phenotype of the tumor cells and will render them susceptible to apoptosis. Current studies, both in vitro and preclinically in vivo, have been aimed at the modification and regulation of expression of apoptosis-related gene products and their activities. A novel protein designated Raf-1 kinase inhibitor protein (RKIP) has been partially characterized. RKIP is a member of the phosphatidylethanolamine-binding protein family. RKIP has been shown to disrupt the Raf-1-MEK1/2 [mitogen-activated protein kinase-ERK (extracellular signal-regulated kinase) kinase-1/2]-ERK1/2 and NF-kappaB signaling pathways, via physical interaction with Raf-1-MEK1/2 and NF-kappaB-inducing kinase or transforming growth factor beta-activated kinase-1, respectively, thereby abrogating the survival and antiapoptotic properties of these signaling pathways. In addition, RKIP has been shown to act as a signal modifier that enhances receptor signaling by inhibiting G protein-coupled receptor kinase-2. By regulating cell signaling, growth, and survival through its expression and activity, RKIP is considered to play a pivotal role in cancer, regulating apoptosis induced by drugs or immune-mediated stimuli. Overexpression of RKIP sensitizes tumor cells to chemotherapeutic drug-induced apoptosis. Also, induction of RKIP by drugs or anti-receptor antibodies sensitizes cancer cells to drug-induced apoptosis. In this review, we discuss the discovery, structure, function, and significance of RKIP in cancer.

Amino Acid Sequence↗

PubMed2004

Reduction of 9-nitrocamptothecin-triggered apoptosis in DU-145 human prostate cancer cells by ectopic expression of 14-3-3zeta.

A promising family of anticancer agents, the camptothecins, is noted for their ability to induce apoptosis specifically in malignant cells. However, a major obstacle for successful cancer treatment by these and other chemotherapeutic agents is the intrinsic or acquired resistance to drug treatment. Resistance to 9NC6, a camptothecin derivative, has been modeled in vitro using a human prostate cancer cell line. To elucidate the mechanism for acquired 9NC resistance, we have used a subtractive cloning approach to identify genes whose altered expression level is reflective of 9NC resistance or susceptibility. Differential gene expression was compared between wild-type human prostate cancer cell line, DU-145, and a 9NC-resistant subline, RC1. Results were confirmed by Northern and Western blot analyses. In this report, we focus on one gene, 14-3-3zeta. An expression vector of a full-length myc-epitope-tagged 14-3-3zeta cDNA was constructed and used for transfection into DU-145 cells. We consistently observed that 14-3-3zeta message and protein levels were dramatically increased in 9NC resistant cells. The expression levels of other 14-3-3 family members were unaffected. Strikingly, ectopic overexpression of 14-3-3zeta in wild-type 9NC-susceptible prostate cancer cells decreased 9NC-induced apoptosis. Our results suggest a novel direct or indirect role of 14-3-3zeta in mediating resistance of DU-145 cells to the topoisomerase I inhibitor, 9NC. We are currently exploring whether this represents a more general pathway for drug resistance as well.

14-3-3 Proteins↗