MAPK inhibitors and siRNAs differentially affect cell death and ROS levels in arsenic trioxide-treated human pulmonary fibroblast cells

Arsenic trioxide (ATO; As2O3) induces cell death in various types of cancer cells including lung cancer via increasing reactive oxygen species (ROS) and regulating mitogen-activated protein kinase (MAPK) signaling cascades. However, little is known about the relationship between ATO and MAPK signaling in normal lung cells. Here, we investigated the effects of MAPK inhibitors and siRNAs on ATO-treated human pulmonary fibroblast (HPF) cells in relation to cell growth, cell death, ROS and glutathione (GSH) levels. ATO induced cell growth inhibition and death in HPF cells and it increased ROS levels including O2?- and GSH depleted cell number. None of the MAPK (MEK, JNK and p38) inhibitors affected cell growth inhibition and cell death by ATO. The MEK inhibitor decreased O2?- levels in ATO-treated HPF cells whereas JNK and p38 inhibitors generally increased ROS levels including O2?- in these cells. None of these inhibitors altered the ATO-induced GSH depletion. Moreover, ERK siRNA did not change HPF cell growth and death by ATO whereas JNK and p38 siRNAs enhanced cell growth inhibition and death. In addition, JNK and p38 siRNAs increased ROS levels and GSH depletion in ATO-treated HPF cells. In conclusion, MAPK inhibitors changed ROS levels in ATO-treated HPF cells, but did not affect cell growth inhibition and death. siRNAs targeting JNK and p38 showing an increase in ROS levels and GSH depletion in ATO-treated HPF cells augmented cell growth inhibition and death.     

PPARgamma ligands enhance TRAIL-induced apoptosis through DR5 upregulation and c-FLIP downregulation in human lung cancer cells

Peroxisome proliferator-activated receptor gamma (PPARgamma) ligands are potential chemo-preventive agents. Many studies have shown that PPARy ligands induce apoptosis in various types of cancer cells including lung cancer cells. Some PPAR gamma ligands have been shown to downregulate c-FLIP expression and thus enhance tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in some cancer cell lines. In the current study, we further show that PPARy ligands induced the expression of death receptor 5 (DR5) and increased DR5 distribution at the cell surface in addition to reducing c-FLIP levels in human lung cancer cells. These agents cooperated with TRAIL to enhance induction of apoptosis in human lung cancer cells. Both overexpression of c-FLIP and knockdown of DR5 abrogated PPARgamma ligand's ability to enhance TRAIL-induced apoptosis. Thus, it appears that not only c-FLIP downregulation but also DR5 upregulation contribute to PPARy ligand-mediated enhancement of TRAIL-induced apoptosis in human lung cancer cells. Both the PPARgamma antagonist GW9662 and silencing PPARgamma expression failed to diminish PPARgamma ligand-induced DR5 upregulation or c-FLIP downregulation, indicating that PPARy ligands modulate the expression of DR5 and c-FLIP through a PPARy-independent mechanism. Collectively, we conclude that PPARy ligands exert PPARy-independent effects on inducing DR5 expression and downregulating c-FLIP levels, leading to enhancement of TRAIL-induced apoptosis.     

Proteasome inhibition by MG132 induces growth inhibition and death of human pulmonary fibroblast cells in a caspase-independent manner

MG132 as a proteasome inhibitor that can induce apoptotic cell death in various cell types including lung cancer cells. We investigated the cellular effects of MG132 on human pulmonary fibroblast (HPF) cells in relation to cell growth inhibition and death, and described the molecular mechanisms of MG132 in HPF cell death. This agent dose-dependently inhibited the growth of HPF cells with an IC50 of approximately 20 μM at 24 h and induced cell death accompanied by the loss of mitochondrial membrane potential (MMP; ?Ψm) and an increase in caspase-3 and -8 activities. MG132 increased intracellular ROS levels and GSH-depleted cell numbers. However, all the tested caspase inhibitors intensified HPF growth inhibition by MG132 and caspase-9 inhibitor also enhanced cell death and MMP (?Ψm) loss. Moreover, the administration of Bcl-2 siRNA augmented HPF cell death by MG132 whereas p53, Bax, caspase-3 and -8 siRNAs did not strongly affect cell death. In addition, each caspase inhibitor and siRNA differently affects ROS levels including O2?- regardless of cell growth inhibition and cell death levels. Caspase-8 and -9 inhibitors increased the number of GSH-depleted cells in MG132-treated HPF cells. In conclusion, MG132 induced growth inhibition and death in HPF cells in a caspase-independent manner. The growth inhibition and death of HPF cells by MG132 and/or each caspase inhibitor or apoptosis-related siRNA were not tightly related to the changes in ROS levels.     

Induction and regulation of tumor necrosis factor-related apoptosis-inducing ligand/Apo-2 ligand-mediated apoptosis in renal cell carcinoma

The lack of effective therapy for disseminated renal cell carcinoma (RCC) has stimulated the search for novel treatments including immunotherapeutic strategies. However, poor therapeutic responses and marked toxicity associated with immunological agents has limited their use. The tumor necrosis factor family member tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)/Apo-2 ligand induces apoptosis in a variety of tumor cell types, while having little cytotoxic activity against normal cells. In this study the activation and regulation of TRAIL-induced apoptosis and TRAIL receptor expression in human RCC cell lines and pathologic specimens was examined. TRAIL induced caspase-mediated apoptotic death of RCC cells with variable sensitivities among the cell lines tested. Compared with TRAIL-sensitive RCC cell lines (A-498, ACHN, and 769-P), the TRAIL-resistant RCC cell line (786-O) expressed lesser amounts of the death-inducing TRAIL receptors, and greater amounts of survivin, an inhibitor of apoptosis. Incubation of 786-O with actinomycin D increased the expression of the death-inducing TRAIL receptors and, concomitantly, decreased the intracellular levels of survivin, resulting in TRAIL-induced apoptotic death. The link between survivin and TRAIL regulation was confirmed when an increase in TRAIL resistance was observed after overexpression of survivin in the TRAIL-sensitive, survivin-negative RCC line A-498. These findings, along with our observation that TRAIL receptors are expressed in RCC tumor tissue, suggest that TRAIL may be useful as a therapeutic agent for RCC and that survivin may partially regulate TRAIL-induced cell death.     

T and B leukemic cell lines exhibit different requirements for cell death: correlation between caspase activation, DFF40/DFF45 expression, DNA fragmentation and apoptosis in T cell lines but not in Burkitt's lymphoma.

The execution phase of apoptosis occurs through the activation and function of caspases which cleave key substrates that orchestrate the death process. Here, we have compared the sensitivity of various T and B cell lines to death receptor or staurosporine-induced apoptosis. First, we found a lack of correlation between death receptor expression and sensitivity to Fas or Trail. By contrast, a correlation between caspase activation, DNA fragmentation and cell death in T cell lines was evidenced. Among T cells, CEM underwent apoptosis in response to CH11 but were resistant to Trail in agreement with the absence of Trail receptors (DR4 and DR5) on their surface. The B cell line SKW 6.4 was sensitive to CH11 and staurosporine but resistant to Trail. As B cell lines expressed significant levels of DR4 and DR5, resistance to Trail in SKW 6.4 is likely due to the expression of the decoy receptor DcR1. Burkitt's lymphoma such as RPMI 8866 and Raji did not exhibit DNA fragmentation in response to CH11, Trail or staurosporine but showed long-term caspase-dependent loss of viability upon effector treatment. The B cell lines used in this study express very weak or undetectable levels of DFF40 and relatively high levels of DFF45. Interestingly, cytosolic extracts from RPMI 88.66 but not other B lymphoma exhibit altered levels of cytochrome c-dependent caspase activation. Taken together, our results show that: (1) death receptor expression does not correlate with sensitivity to apoptosis; (2) the very low ratio of DFF40 vs. DFF45 is unlikely to explain by itself the lack of DNA fragmentation observed in certain B cell lines; and (3) a defective cytochrome c-dependent caspase activation might account at least in part for the insensitivity of certain Burkitt's lymphoma (RPMI 88.66) to apoptosis. Thus it seems that resistance of Burkitt's lymphoma to apoptosis is not governed by a general mechanism, but is rather multifactorial and differs from one cell line to another.     

Fatty acid synthase: a novel target for antiglioma therapy

High levels of fatty acid synthase (FAS) expression have been observed in several cancers, including breast, prostate, colon and lung carcinoma, compared with their respective normal tissue. We present data that show high levels of FAS protein in human and rat glioma cell lines and human glioma tissue samples, as compared to normal rat astrocytes and normal human brain. Incubating glioma cells with the FAS inhibitor cerulenin decreased endogenous fatty acid synthesis by approximately 50%. Cell cycle analysis demonstrated a time- and dose-dependent increase in S-phase cell arrest following cerulenin treatment for 24 h. Further, treatment with cerulenin resulted in time- and dose-dependent decreases in glioma cell viability, as well as reduced clonogenic survival. Increased apoptotic cell death and PARP cleavage were observed in U251 and SNB-19 cells treated with cerulenin, which was independent of the death receptor pathway. Overexpressing Bcl-2 inhibited cerulenin-mediated cell death. In contrast, primary rat astrocytes appeared unaffected. Finally, RNAi-mediated knockdown of FAS leading to reduced FAS enzymatic activity was associated with decreased glioma cell viability. These findings suggest that FAS might be a novel target for antiglioma therapy.     

Expression of cellular FLICE inhibitory protein, caspase-8, and protease inhibitor-9 in Ewing sarcoma and implications for susceptibility to cytotoxic pathways.

PURPOSE: Ewing sarcoma is a common pediatric bone tumor with an unfavorable prognosis for metastatic or recurrent disease. Cellular immunotherapy may provide new treatment options and depends on the cytolytic death receptor and perforin/granzyme pathways. Expression of death receptor pathway inhibitor cellular FLICE inhibitory protein (cFLIP), initiator caspase-8, and granzyme B inhibitor protease inhibitor-9 (PI-9) have been reported to determine susceptibility to cell- and chemotherapy-mediated killing in several tumor types. Here, we have studied their in vitro and in vivo expression in Ewing sarcoma and the implications for susceptibility to cytotoxicity. EXPERIMENTAL DESIGN: Ewing sarcoma cell lines (n = 8) were tested for cFLIP, PI-9, and caspase-8 expression. Functional significance was tested by anti-Fas antibody (death receptor pathway) or natural killer cell (perforin/granzyme pathway) treatment. Immunohistochemistry was done on 28 sections from 18 patients. In half of the cases, sequential material, including metastases, was available. RESULTS: Although all tested Ewing sarcoma cell lines expressed cFLIP, resistance to CD95/Fas-mediated apoptosis was only observed in two cell lines lacking caspase-8 expression. PI-9 was expressed at low levels in four of eight Ewing sarcoma cell lines, but positive cell lines remained susceptible to perforin/granzyme-mediated killing. In primary Ewing sarcoma, including metastases, cFLIP was abundantly expressed in 18 of 18 patients. Caspase-8 was expressed in all patients but showed more intertumoral and intratumoral variation in both intensity and heterogeneity of staining. PI-9, in contrast, was undetectable. CONCLUSIONS: The expression patterns of cFLIP, caspase-8, and the absence of PI-9 provide a rationale to preferentially exploit the perforin/granzyme pathway in cytotoxic therapies against Ewing sarcoma.     

DcR2 (TRAIL-R4) siRNA and adenovirus delivery of TRAIL (Ad5hTRAIL) break down in vitro tumorigenic potential of prostate carcinoma cells

High levels of decoy receptor 2 (DcR2; TRAIL-R4) expression are correlated with TRAIL resistance in prostate cancer cells. In addition, upregulation of TRAIL death receptor (DR4 and DR5) expression, either by ionizing radiation or chemotherapy, can sensitize cancer cells to TRAIL. Considering more than half of human cancers are TRAIL resistant, modulation of surface TRAIL receptor expression appears to be an attractive treatment modality to counteract TRAIL resistance. In this study, three siRNA duplexes targeting DcR2 receptor were tested. Ad5hTRAIL infections were performed to overexpress human full-length TRAIL to induce cell death, and the in vitro tumorigenic potential of prostate cancer cells was assessed using colony-forming assays on soft agar. The DU145 and LNCaP prostate cancer cell lines, which express high levels of DcR2, were resistant to Ad5hTRAIL-induced death. Downregulation of surface DcR2 expression by siRNA sensitized these prostate cancer cell lines to Ad5hTRAIL. In addition, DcR2 siRNA-mediated knockdown of DcR2, followed by Ad5hTRAIL infection, dramatically reduced the in vitro tumorigenic potential of prostate cancer cells. Collectively, our results suggest the potential for combining receptor-specific siRNA with TRAIL in the treatment of certain cancers.     

TRAIL, FasL and a blocking anti-DR5 antibody augment paclitaxel-induced apoptosis in human non-small-cell lung cancer.

Lung carcinoma is one of the most frequent causes of malignancy-related mortality in the world. Paclitaxel (PA) is an antineoplastic agent used in the treatment of non-small-cell lung cancer (NSCLC) and possesses a single-agent response rate approaching 25%. PA kills tumor cells by inducing both cellular necrosis and apoptosis. Fas and Trail receptors (DR4 and DR5) are TNF family members and act as death signal transduction proteins in the apoptosis cascade. Despite the importance of PA in lung cancer treatment, the function of Fas, DR4 and DR5 in PA-induced apoptosis, as well as the effect of their respective ligands FasL and TRAIL alone or in combination with PA, remains poorly understood. We show here that 10 microM PA induces a significant 10- to 57-fold increase in primary lung cancer cell apoptosis and is associated with 20-215% increases in caspase-3 activity in various NSCLC cell types. All the lung cancer cells express Fas, FasL, DR4 and DR5; however PA did not significantly modify their levels. We provide here the first time evidence that TRAIL is a potent inducer of apoptosis in multiple NSCLC cell lines. Noticeably, CH11, the Fas receptor cross-linking and the antagonistic anti-DR5 antibody enhance considerably the spontaneous apoptotic rate in 3 out of 5 cell types. The combination treatments, FasL+PA, TRAIL+PA or PA+anti-DR5 antibody, greatly enhance PA-apoptotic effect in most cell lines. These data suggest that the use of new combination treatment with PA and ligands targeting Fas or TRAIL receptors would be particularly efficacious.     

Molecular mechanisms of ginsenoside Rh2-mediated G1 growth arrest and apoptosis in human lung adenocarcinoma A549 cells

Ginsenoside Rh2 (Rh2), a purified ginseng saponin, has been shown to have antiproliferative effects in certain cancer cell types. However, the molecular mechanisms of Rh2 on cell growth and death have not been fully clarified. In this study, the antiproliferative effect of Rh2 in human lung adenocarcinoma A549 cells was investigated. Treatment of A549 cells with 30 g/ml Rh2 resulted in G₁ phase arrest, followed by progression to apoptosis. This Rh2-mediated G₁ arrest was accompanied by downregulation of the protein levels and kinase activities of cyclin-D1, cyclin-E and Cdk6, and the upregulation of pRb2/p130. In addition, Rh2-induced apoptosis was confirmed by TUNEL assay and DNA fragmentation analysis. Administration of Rh2 caused an increase in the expression levels of TRAIL-RI (DR4) death receptor but did not alter the levels of other death receptors or Bcl-2 family molecules. Furthermore, the Rh2-induced apoptosis was significantly inhibited by DR4:Fc fusion protein, which inhibits TRAIL-DR4-mediated apoptosis. In addition, caspase-2, caspase-3 and caspase-8 were highly activated upon Rh2 treatment. Inhibitors of caspase-2, caspase-3 and caspase-8 markedly prevented the cell death induced by Rh2. Inhibitor of caspase-8 significantly inhibited the activation of caspase-2, caspase-3 and caspase-8. These observations indicate that multiple G₁-related cell cycle regulatory proteins are regulated by Rh2 and contribute to Rh2-induced G₁ growth arrest. The increase in the expression level of DR4 death receptor may play a critical role in the initiation of Rh2-triggered apoptosis, and the activation of the caspase-8/caspase-3 cascade acts as the executioner of the Rh2-induced death process.     

Sulindac sulfide-induced apoptosis involves death receptor 5 and the caspase 8-dependent pathway in human colon and prostate cancer cells

Sulindac is the most extensively investigated clinically relevant chemopreventive nonsteroidal anti-inflammatory drug. Sulindac sulfide is one of the major metabolites of sulindac that is believed to mediate its antitumorigenic effects by inducing apoptosis. Recent evidence suggests that sulindac sulfide engages the mitochondrial pathway involving caspase 9 and Bax to mediate its apoptotic effects [Zhang et al., Science (Wash. DC), 290: 989-992, 2000]. In this report, we demonstrate that sulindac sulfide also engaged the membrane death receptor (DR) pathway to mediate apoptosis. Sulindac sulfide up-regulated DR5 and activated the proximal caspase 8 in various different colon and prostate cancer cell lines. Sulindac sulfide specifically up-regulated the DR5 levels but had no effect on the levels of other DRs including DR4, Fas, and tumor necrosis factor receptor 1. To further delineate the role of DR5 in sulindac sulfide-induced apoptosis, we used JCA-1 prostate cancer cells that are deficient in mounting a Fas and tumor necrosis factor receptor 1-dependent apoptotic response but are proficient in mediating DR5-dependent apoptosis. JCA-1 cells were stably transfected with dominant-negative Fas-associated death domain to block the flow of apoptotic signals originating from the endogenous DR5, and sulindac sulfide-induced apoptosis was investigated. Our results indicated that by blocking the DR5-dependent apoptotic pathway, dominant-negative Fas-associated death domain did indeed inhibit sulindac sulfide-induced apoptosis. Furthermore, exogenous tumor necrosis factor-related apoptosis-inducing ligand, the ligand for DR5, also potentiated sulindac sulfide-induced apoptosis in all of the cell lines tested, thereby further supporting the involvement of DR5 in sulindac sulfide-induced apoptosis. Thus, our results demonstrate that sulindac sulfide also engages the membrane DR pathway involving DR5 and proximal caspase 8 to induce apoptosis.     

Death receptor signals to mitochondria

Apoptosis is the best-characterized form of programmed cell death (PCD) and is of fundamental importance in tissue homeostasis. In mammalian systems, there are two major pathways that are involved in the initiation of apoptosis: the "extrinsic" death receptor pathway and the "intrinsic" mitochondrial pathway. Although these pathways act independently to initiate the death machinery in some cellular systems, in many cell types, including numerous tumor cells, there is delicate coordination and cross talk between the extrinsic and intrinsic pathways, which leads to the activation of the executioner caspase cascade. Additionally, there appears to be a fine balance between the caspase-mediated arm of death receptor signaling that engages mitochondria and the caspase-independent arm that promotes vacuole proliferation in many cells. Here, we review our current knowledge about the layers of complexity that are posed by the interactions between death receptor-induced pathways and how they influence mitochondria to regulate cellular life and death decisions.     

紫杉醇提高胃癌MGC803细胞对TRAIL的敏感性

目的：研究紫杉醇对TRAIL诱导胃癌细胞凋亡的影响,探讨死亡受体5（DR5）在TRAIL诱导细胞凋亡中的作用。方法：采用MTT法测定细胞活力,流式细胞仪检测细胞凋亡,western blot检测蛋白表达。结果：在MGC803细胞中,100ng/ml的TRAIL导致轻度的增殖抑制和细胞凋亡,TRAIL（100ng/ml）联合紫杉醇（3.41g/ml）引起明显的增殖抑制和细胞凋亡（P〈0.05）。TRAIL单药没有改变死亡受体5（DR5）的表达,而3.41g/ml紫杉醇作用MGC803细胞后明显上调了DR5的表达。结论：紫杉醇通过上调DR5的表达增强TRAIL诱导的胃癌MGC803细胞凋亡。     

Proteasome Inhibitors Diminish c-Met Expression and Induce Cell Death in Non-Small Cell Lung Cancer Cells

Non-small cell lung cancer (NSCLC) is the most common type of lung cancer and accounts for 85% of all lung carcinomas. The hepatocyte growth factor receptor (c-Met) has been considered as a potential therapeutic target for NSCLC. Proteasome inhibition induces cell apoptosis and has been used as a novel therapeutic approach for treating diseases including NSCLC; however, the effects of different proteasome inhibitors on NSCLC have not been fully investigated. The aim of this study is to determine a precise strategy for treating NSCLC by targeting c-Met using different proteasome inhibitors. Three proteasome inhibitors, bortezomib, MG132, and ONX 0914, were used in this study. Bortezomib (50 nM) significantly reduced c-Met levels and cell viability in H1299 and H441 cells, while similar effects were observed in H460 and A549 cells when a higher concentration (~100 nM) was used. Bortezomib decreased c-Met gene expression in H1299 and H441 cells, but it had no effect in A549 and H460 cells. MG-132 at a low concentration (0.5 µM) diminished c-Met levels in H441 cells, while neither a low nor a high concentration (~20 µM) altered c-Met levels in A549 and H460 cells. A higher concentration of MG-132 (5 µM) was required for decreasing c-Met levels in H1299 cells. Furthermore, MG-132 induced cell death in all four cell types. Among all the four cell lines, H441 cells expressed higher levels of c-Met and appeared to be the most susceptible to MG-132. MG-132 decreased c-Met mRNA levels in both H1299 and H441 cells. ONX 0914 reduced c-Met levels in H460, H1299, and H441 cells but not in A549 cells. c-Met levels were decreased the most in H441 cells treated with ONX 0914. ONX 0914 did not alter cell viability in H441; however, it did induce cell death among H460, A549, and H1299 cells. This study reveals that different proteasome inhibitors produce varied inhibitory effects in NSCLS cell lines.     

H-Ras regulation of TRAIL death receptor mediated apoptosis

TNF-related apoptosis-inducing ligand (TRAIL) induces apoptosis through the death receptors (DRs) 4 and/or 5 expressed on the cell surface. Multiple clinical trials are underway to evaluate the antitumor activity of recombinant human TRAIL and agonistic antibodies to DR4 or DR5. However, their therapeutic potential is limited by the high frequency of cancer resistance. Here we provide evidence demonstrating the role of H-Ras in TRAIL receptor mediated apoptosis. By analyzing the genome wide mRNA expression data of the NCI60 cancer cell lines, we found that H-Ras expression was consistently upregulated in TRAIL-resistant cell lines. By contrast, no correlation was found between TRAIL sensitivity and K-Ras expression levels or their mutational profiles. Notably, H-Ras upregulation associated with a surface deficiency of TRAIL death receptors. Selective inhibition of H-Ras activity in TRAIL-resistant cells restored the surface expression of both DR4 and DR5 without changing their total protein levels. The resulting cells became highly susceptible to both TRAIL and agonistic DR5 antibody, whereas K-Ras inhibition had little or no effect on TRAIL-induced apoptosis, indicating H-Ras plays a distinct role in the regulation of TRAIL death receptors. Further studies are warranted to determine the therapeutic potential of H-Ras-specific inhibitors in combination with TRAIL receptor agonists.