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Biomedical subjects

Gen Sheng Wu

Publications and source records attributed to Gen Sheng Wu.

13 recordsLinked to original sources
PubMed2006

Tumor necrosis factor-related apoptosis-inducing ligand is required for tumor necrosis factor alpha-mediated sensitization of human breast cancer cells to chemotherapy.

Tumor necrosis factor alpha (TNFalpha) induces apoptosis and sensitizes cancer cells to chemotherapy, but the mechanism underlying its sensitization is not fully understood. Here, we report that TNFalpha-mediated sensitization of cancer cells to chemotherapy involves activation of the TRAIL pathway. We show that the combined treatment of breast cancer cells with TNFalpha and Adriamycin significantly increases cell death compared with the treatment with either agent alone. The combined treatment activated both death receptor and mitochondrial apoptotic pathways, whereas Adriamycin alone activated only the mitochondrial pathway, and TNFalpha failed to activate either. Furthermore, we show that TNFalpha induces TRAIL through a transcriptional mechanism. Using reporter gene assays in conjunction with chromatin immunoprecipitation assays, we show that TRAIL induction by TNFalpha is regulated via both nuclear factor-kappaB and Sp1 binding sites. Importantly, down-regulation of TRAIL by small interfering RNA silencing decreased TNFalpha-mediated Adriamycin-induced caspase activation and apoptosis, and thus enhanced breast cancer cell resistance to Adriamycin. Collectively, our results suggest that induction of TRAIL by TNFalpha is critical for sensitization of breast cancer cells to chemotherapy.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2006

Mitogen-activated protein kinase phosphatase-1 is required for cisplatin resistance.

Mitogen-activated protein kinase (MAPK) phosphatase (MKP)-1 is a member of the MKP family that negatively regulates MAPK signaling. MKP-1 has been implicated in cell survival in response to stressful stimuli, including anticancer treatment, but its role in cisplatin resistance is not fully understood. Here, we show that cisplatin induces MKP-1 in several human cancer cell lines. Induction of MKP-1 by cisplatin was through the transcriptional mechanism regulated by extracellular signal-regulated kinase (ERK). Overexpression of MKP-1 rendered human lung cancer cells resistant to cisplatin. Conversely, down-regulation of MKP-1 by small interfering RNA silencing sensitized human lung cancer cells to cisplatin-induced cell death. Using primary mouse embryonic fibroblasts (MEF) from MKP-1 knockout mice, we show that induction of MKP-1 by cisplatin correlates with inactivation of c-Jun NH(2)-terminal kinase (JNK) but not ERK and p38. Furthermore, apoptosis induced by cisplatin was significant in MKP-1(-/-) MEFs, whereas such change was minimal in MKP-1(+/+) MEFs. More importantly, cisplatin-induced cell death is inhibited by blocking JNK but not ERK and p38 activities. Collectively, our results establish a critical role of JNK in cisplatin-induced apoptosis and suggest that MKP-1 is required for cisplatin resistance.

Animals↗
PubMed2006

The role of mitogen-activated protein kinase phosphatase-1 in oxidative damage-induced cell death.

Mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1) is a member of the MAPK phosphatase family that functions as a negative regulator of MAPK signaling. MKP-1 is induced by oxidative stress, but the role of its induction in cell death is not fully understood. Here, we show that hydrogen peroxide (H(2)O(2)) induces MKP-1 and activates MAPKs. Induction of MKP-1 by H(2)O(2) correlated with inactivation of p38 and c-Jun-NH(2)-kinase (JNK). Overexpression of MKP-1 increased cell resistance to H(2)O(2)-induced death. Furthermore, we show by small interfering RNA silencing that down-regulation of MKP-1 increases phosphorylated p38 and JNK and subsequent cell death induced by H(2)O(2). More importantly, primary embryonic fibroblasts from mice lacking MKP-1 had a higher level of phosphorylated p38 and JNK and were more sensitive to H(2)O(2)-induced cell death compared with corresponding cells with MKP-1, indicating that p38 and JNK pathways may play important roles in H(2)O(2)-mediated cell death. Thus, these results suggest that activation of MKP-1 is a survival mechanism against oxidative damage.

Breast Neoplasms↗
PubMed2006

Stochastic cancer progression driven by non-clonal chromosome aberrations.

Cancer research has previously focused on the identification of specific genes and pathways responsible for cancer initiation and progression based on the prevailing viewpoint that cancer is caused by a stepwise accumulation of genetic aberrations. This viewpoint, however, is not consistent with the clinical finding that tumors display high levels of genetic heterogeneity and distinctive karyotypes. We show that chromosomal instability primarily generates stochastic karyotypic changes leading to the random progression of cancer. This was accomplished by tracing karyotypic patterns of individual cells that contained either defective genes responsible for genome integrity or were challenged by onco-proteins or carcinogens that destabilized the genome. Analysis included the tracing of patterns of karyotypic evolution during different stages of cellular immortalization. This study revealed that non-clonal chromosomal aberrations (NCCAs) (both aneuploidy and structural aberrations) and not recurrent clonal chromosomal aberrations (CCAs) are directly linked to genomic instability and karyotypic evolution. Discovery of "transitional CCAs" during in vitro immortalization clearly demonstrates that karyotypic evolution in solid tumors is not a continuous process. NCCAs and their dynamic interplay with CCAs create infinite genomic combinations leading to clonal diversity necessary for cancer cell evolution. The karyotypic chaos observed within the cell crisis stage prior to establishment of the immortalization further supports the ultimate importance of genetic aberrations at the karyotypic or genome level. Therefore, genomic instability generated NCCAs are a key driving force in cancer progression. The dynamic relationship between NCCAs and CCAs provides a mechanism underlying chromosomal based cancer evolution and could have broad clinical applications.

Animals↗
PubMed2005

DR5 knockout mice are compromised in radiation-induced apoptosis.

DR5 (also called TRAIL receptor 2 and KILLER) is an apoptosis-inducing membrane receptor for tumor necrosis factor-related apoptosis-inducing ligand (also called TRAIL and Apo2 ligand). DR5 is a transcriptional target of p53, and its overexpression induces cell death in vitro. However, the in vivo biology of DR5 has remained largely unexplored. To better understand the role of DR5 in development and in adult tissues, we have created a knockout mouse lacking DR5. This mouse is viable and develops normally with the exception of having an enlarged thymus. We show that DR5 is not expressed in developing embryos but is present in the decidua and chorion early in development. DR5-null mouse embryo fibroblasts expressing E1A are resistant to treatment with TRAIL, suggesting that DR5 may be the primary proapoptotic receptor for TRAIL in the mouse. When exposed to ionizing radiation, DR5-null tissues exhibit reduced amounts of apoptosis compared to wild-type thymus, spleen, Peyer's patches, and the white matter of the brain. In the ileum, colon, and stomach, DR5 deficiency was associated with a subtle phenotype of radiation-induced cell death. These results indicate that DR5 has a limited role during embryogenesis and early stages of development but plays an organ-specific role in the response to DNA-damaging stimuli.

Animals↗
PubMed2004

p53 Transactivates the phosphatase MKP1 through both intronic and exonic p53 responsive elements.

The tumor suppressor p53 protein can negatively regulate mitogen-activated protein kinase (MAPK) signaling via the induction of MAPK phosphatases. We have recently described that MKP1, a member of the MAPK phosphatase family, is transcriptionally regulated by p53 via a p53 responsive element located in the second intron of the MKP1 gene. Here, we identify an additional p53 responsive element located in the third exon of the MKP1 gene. We demonstrated in reporter gene assays that p53 binds to this exonic element and transactivates MKP1. Furthermore, we showed that this exonic responsive element could be bound by p53 both in vitro and in vivo as demonstrated by gel shift and ChIP assays, respectively. Mutation of either exonic or intronic site resulted in a ~50% decrease in luciferase reporter activity, and loss of both sites completely abrogated p53-dependent transcription of MKP1. These results suggest that each element sufficiently confers p53 responsiveness and that both elements are required for its full activation. Thus, our results provide the mechanism by which p53 controls transcription of the MKP1 gene.

Carcinoma↗
PubMed2004

The functional interactions between the p53 and MAPK signaling pathways.

The p53 tumor suppressor protein exerts its growth inhibitory activity by activating and interacting with diverse signaling pathways. As a downstream target, p53 protein is phosphorylated and activated by a number of protein kinases in response to stressful stimuli. As an upstream activator, activated p53 acts as a transcription factor to induce and/or suppress a number of genes whose expression leads to the activation of diverse signaling pathways. p53 protein can also interact with a number of proteins, resulting in an increase or decrease in p53 activity itself. The activation of p53 leads to many outcomes in cells, including cell cycle arrest and apoptosis. It has become clear that the p53 protein can functionally interact with the mitogen-activated protein kinase (MAPK) pathways, including the stress-activated protein kinase [SAPK/c-Jun N-terminal protein kinase (JNK)], the p38 mitogen-activated protein kinase (MAPK), and the extracellular signal related kinase (ERK). Upon exposure to stressful stimuli, MAP kinases phosphorylate and activate p53, leading to p53-mediated cellular responses. Recent studies have suggested a role of p53 as an upstream activator to regulate MAPK signaling via the transcriptional activation of members of the dual specificity phosphatase family. Because both the p53 and MAPK signaling pathways are altered in the majority of human tumors, understanding their functional interaction may provide new insights into the deregulated cell proliferation and survival that is characteristic of cancer.

Animals↗
PubMed2003

The phosphatase MKP1 is a transcriptional target of p53 involved in cell cycle regulation.

The tumor suppressor p53 protein suppresses cell growth by inducing cell cycle arrest or apoptosis. Despite the fact that p53-dependent p21-mediated G1 arrest induced by DNA damage is well defined, the role of p53 in the cell cycle in response to the MAKP signaling remains to be determined. Here we show that MKP1, a member of the dual specificity protein phosphatase family capable of inactivating MAPKs, is a transcriptional target of p53. MKP1 mRNA and protein levels were increased upon p53 activation in several well defined p53-regulated cell systems. p53 bound to a consensus p53 binding site located in the second intron of the MKP1 gene and transactivated MKP1 in reporter gene assays. Inhibition of phosphatase activity impaired p53-mediated G1 arrest in arrested human glioblastoma GM cells in response to growth factor stimuli. Importantly conditional expression of MKP1 prevented arrested human cancer cells from entering into the cell cycle. Thus, these results provide a novel mechanism by which p53 controls the cell cycle in response to the MAPK signaling in the absence of DNA damage and suggest that p53 may negatively control the MAKP pathway via MKP1.

Binding Sites↗
PubMed2002

Induction of apoptosis by the new anticancer drug XK469 in human ovarian cancer cell lines.

XK469, a synthetic quinoxaline phenoxypropionic acid derivative, has been found to have selective activity against a broad panel of solid tumors including several drug-resistant cell lines and has been approved for phase I clinical evaluation. Recent studies suggested that XK469 is a selective topoisomerase IIbeta inhibitor, but the mechanism of XK469-induced cell death remains unknown. Here we investigate the ability of XK469 to induce apoptosis of human cancer cells. In the human ovarian cancer cell line PA1, XK469 caused the release of cytochrome c, activation of caspases including caspases 9, 7 and 3, cleavage of PARP, and subsequently cell death. Moreover, Bcl2 and Bax were cleaved in XK469 treated cells. PA1 cells expressing the dominant negative-caspase 9 were less sensitive to XK469. Importantly, in these PA1 cells expressing DN-casp 9, the activation of caspases including caspases 3, 7 and 9, and cleavage of Bax and Bcl2 were inhibited, suggesting that the activation of the mitochondrial pathway is required for XK469-induced anticancer activity. These results indicate that the induction of apoptosis by XK469 may account for its anti-tumor activity and such activity is required for the activation of the mitochondrial pathway. Thus, our study defines a possible mechanism, at least in part, underlying XK469-induced anti-cancer activity.

Antineoplastic Agents↗
PubMed2002

Caspase 9 is required for p53-dependent apoptosis and chemosensitivity in a human ovarian cancer cell line.

The p53 gene suppresses tumor cell growth by inducing cell cycle arrest or apoptosis. Loss of its apoptosis activity has been implicated not only in tumor development but also in chemoresistance. We previously reported that targeting p53 for degradation by the human HPV E6 gene in the ovarian cancer cell line PA1 leads to an increase in the chemoresistant phenotype. Here we investigate the relationship between loss of p53-dependent caspase activation and chemosensitivity. In PA1-neo cells with wild-type p53, the activation of caspases including caspases 9, 8, 7 and 3 and cleavage of PARP were detected following adriamycin or etoposide treatment, whereas no such changes were observed in PA1-E6 cells whose p53 is degraded, suggesting that loss of p53 impairs caspase activation. Importantly, we showed that loss of caspase activation in PA1-E6 cells correlates with increased cell survival. Moreover, PA1 cells overexpressing a dominant negative caspase 9 were found to have decreased caspase-dependent apoptosis, as compared with vector control cells. Furthermore, these dominant negative caspase 9 expressing cells were resistant to chemotherapeutic agent-induced killing. Our results suggest that caspase 9 may be an important target for anticancer drug development. Thus, identifying novel compounds that can activate caspase 9 may be a strategy for overcoming a defect in the p53 apoptosis pathway.

Antineoplastic Agents↗
PubMed2002

Identification of a novel synthetic triterpenoid, methyl-2-cyano-3,12-dioxooleana-1,9-dien-28-oate, that potently induces caspase-mediated apoptosis in human lung cancer cells.

Lung cancer continues to be the leading cause of cancer-related death in the United States. Therefore, new agents targeting prevention and treatment of lung cancer are urgently needed. In the present study, we demonstrate that a novel synthetic triterpenoid methyl-2-cyano-3,12-dioxooleana-1,9-dien-28-oate (CDDO-Me) is a potent inducer of apoptosis in human non-small cell lung carcinoma (NSCLC) cells. The concentrations required for a 50% decrease in cell survival (IC50) ranged from 0.1 to 0.3 microM. CDDO-Me induced rapid apoptosis and triggered a series of effects associated with apoptosis including a rapid release of cytochrome c from mitochondria, activation of procaspase-9, -7, -6, and -3, and cleavage of poly(ADP-ribose) polymerase and lamin A/C. Moreover, the caspase-3 inhibitor Z-DEVD-FMK and the pan caspase inhibitor Z-VAD-FMK suppressed CDDO-Me-induced apoptosis. These results indicate that CDDO-Me induced apoptosis in human NSCLC cells via a cytochrome c-triggered caspase activation pathway. CDDO-Me did not alter the level of Bcl-2 and Bcl-xL proteins, and no correlation was found between cell sensitivity to CDDO-Me and basal Bcl-2 expression level. Furthermore, overexpression of Bcl-2 did not protect cells from CDDO-Me-induced apoptosis. These results suggest that CDDO-Me induces apoptosis in NSCLC cells irrespective of Bcl-2 expression level. In addition, no correlation was found between cell sensitivity to CDDO-Me and p53 status, suggesting that CDDO-Me induce a p53-independent apoptosis. Our results demonstrate that CDDO-Me may be a good candidate for additional evaluation as a potential therapeutic agent for human lung cancers and possibly other types of cancer.

Apoptosis↗