ERK/ribosomal S6 kinase (RSK) signaling positively regulates death receptor 5 expression through co-activation of CHOP and Elk1.
ABSTRACT Death receptor 5 (DR5) is a death domain-containing transmembrane receptor that triggers apoptosis upon binding to its ligand or when overexpressed. Its expression is induced by certain small molecule drugs, including celecoxib, through mechanisms that have not been fully elucidated. The current study has revealed a novel ERK/ribosomal S6 kinase (RSK)-dependent mechanism that regulates DR5 expression primarily using celecoxib as a DR5 inducer. Both C/EBP homologous protein (CHOP) and Elk1 are required for celecoxib-induced DR5 expression based on promoter deletion and mutation analysis and siRNA-mediated gene silencing results. Co-expression of both CHOP and Elk1 exhibited enhanced effects on increasing DR5 promoter activity and DR5 expression, indicating that CHOP and Elk1 co-operatively regulate DR5 expression. Because Elk1 is an ERK-regulated protein, we accordingly found that celecoxib increased the levels of phosphorylated ERK1/2, RSK2, and Elk1. Inhibition of either ERK signaling with a MEK inhibitor or ERK1/2 siRNA, or RSK2 signaling with an RSK2 inhibitor or RSK2 siRNA abrogated DR5 up-regulation by celecoxib as well as other agents. Moreover, these inhibitions suppressed celecoxib-induced CHOP up-regulation. Thus, ERK/RSK-dependent, CHOP and Elk1-mediated mechanisms are critical for DR5 induction. Additionally, celecoxib increased CHOP promoter activity in an ATF4-dependent manner, and siRNA-mediated blockade of ATF4 abrogated both CHOP induction and DR5 up-regulation, indicating that ATF4 is involved in celecoxib-induced CHOP and DR5 expression. Collectively, we conclude that small molecules such as celecoxib induce DR5 expression through activating ERK/RSK signaling and subsequent Elk1 activation and ATF4-dependent CHOP induction.
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ABSTRACT: Jellyfish eggs neither undergo apparent cortical reaction nor show any significant change in the membrane potential at fertilization, but nevertheless show monospermy. Utilizing the perfectly transparent eggs of the hydrozoan jellyfish Cytaeis uchidae, here we show that the polyspermy block is accomplished via a novel mechanism: a collaboration between Ca(2+) and mitogen-activated protein kinase (MAPK). In Cytaeis, adhesion of a sperm to the animal pole surface of an egg was immediately followed by sperm-egg fusion and initiation of an intracellular Ca(2+) rise from this site. The elevated Ca(2+) levels lasted for several minutes following the sperm-egg fusion. The Ca(2+) rise proved to be necessary and sufficient for a polyspermy block, as inhibiting a Ca(2+) rise with EGTA promoted polyspermy, and conversely, triggering a Ca(2+) rise by inositol 1,4,5-trisphosphate (IP3) or excess K(+) immediately abolished the egg's capacity for sperm-egg fusion. A Ca(2+) rise at fertilization or by artificial stimulations evoked dephosphorylation of MAPK in eggs. The eggs in which phosphorylated MAPK was maintained by injection of mRNA for MAPK kinase kinase (Mos), like intact eggs, exhibited a Ca(2+) rise at fertilization or by IP3 injection, and shut down the subsequent sperm-egg fusion. However, the Mos-expressing eggs became capable of accepting sperm following the arrest of Ca(2+) rise. In contrast, addition of inhibitors of MAPK kinase (MEK) to unfertilized eggs caused MAPK dephosphorylation without elevating Ca(2+) levels, and prevented sperm-egg fusion. Rephosphorylation of MAPK by injecting Mos mRNA after fertilization recovered sperm attraction, which is known to be another MAPK-dependent event, but did not permit subsequent sperm-egg fusion. Thus, it is possible that MAPK dephosphorylation irreversibly blocks sperm-egg fusion and reversibly suppresses sperm attraction. Collectively, our data suggest that both the fast and late mechanisms dependent on Ca(2+) and MAPK, respectively, ensure a polyspermy block in jellyfish eggs.Developmental Biology 05/2014; · 3.87 Impact Factor
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ABSTRACT: Although tumor necrosis factor–related apoptosis-inducing ligand (TRAIL) has shown efficacy in a phase 2 clinical trial, development of resistance to TRAIL by tumor cells is a major roadblock. We investigated whether quercetin, a flavonoid, can sensitize human ovarian cancer cells to TRAIL. Results indicate that quercetin sensitized cancer cells to TRAIL. The quercetin induced expression of death receptor DR5 but did not affect expression of DR4 in cancer cells. The induction of DR5 was mediated through activation of JNK and through up-regulation of a transcription factor CCAAT enhancer-binding protein homologous protein (CHOP); as silencing of these signaling molecules abrogated the effect of quercetin. Upregulation of DR5 was mediated through the generation of reactive oxygen species (ROS), as ROS scavengers reduced the effect of quercetin on JNK activation, CHOP up-regulation, DR induction, TRAIL sensitization, downregulated the expression of cell survival proteins and up-regulated the proapoptotic proteins. Furthermore, the combination of quercetin with TRAIL was found to be mediated inhibition of tumor growth of human SKOV-3 xenograft was associated with induction of apoptosis, activation of caspase-3, CHOP and DR5 in vivo. Overall, our data suggest that quercetin enhances apoptotic death of ovarian cancer cells to TRAIL through upregulation of CHOP-induced DR5 expression following ROS mediated ER-stress. This article is protected by copyright. All rights reserved.Cancer Science 03/2014; · 3.48 Impact Factor
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ABSTRACT: Natural chalcones have been proved to inhibit cancer cells with therapeutic potential, but the underlying molecular mechanism is still largely unexplored. Here, we identified a novel chalcone, 2'-hydroxy-4',5'-dimethoxychalcone (HDMC) and demonstrated that HDMC induced apoptosis in various nonsmall cell lung cancer cells. Further study showed that HDMC elevated cellular reactive oxygen species (ROS) levels, thus inducing expressions of ATF4 and C/EBP homologous protein (CHOP). Then, death receptor 5 (DR5) was upregulated through ATF4-CHOP axis and eventually resulted in apoptosis. We also found that downregulation of c-FLIPL contributed to HDMC-induced apoptosis. In conclusion, HDMC induces apoptosis in human nonsmall cell lung cancer cells via activation of DR5 signaling pathway, and ROS-mediated ATF4-CHOP axis is involved in the process. Our results further supported the potential for HDMC to be developed as a new antitumor agent for cancer therapy or chemoprevention. © 2013 IUBMB Life, 2013.International Union of Biochemistry and Molecular Biology Life 04/2013; · 2.79 Impact Factor