Hyeon-Ok Jin

Activating transcription factor 4 and CCAAT/enhancer-binding protein-β negatively regulate the mammalian target of rapamycin via Redd1 expression in response to oxidative and endoplasmic reticulum stress

Regulation of mRNA translation in mammalian cells involves the coordinated control of mammalian target of rapamycin (mTOR) signaling. At present, limited information is available on the potential relevance of mTOR regulation, although translation inhibition during oxidative and endoplasmic reticulum (ER) stress is clearly important. In this study, we show that activating transcription factor 4 (ATF4) and CCAAT/enhancer-binding protein-beta (C/EBP-beta) negatively regulate mTOR via Redd1 expression in response to oxidative and ER stress. Oxidative and ER stress conditions induce rapid and significant activation of ATF4 downstream of eIF2alpha phosphorylation, which is responsible for Redd1 expression. In our experiment, overexpression of ATF4 was associated with reduced mTOR activity via Redd1 expression, whereas suppression of ATF4 levels with small interfering RNA led to the recovery of decreased mTOR activity mediated by downregulation of Redd1 during oxidative and ER stress. We additionally identified Redd1 as a downstream effector of C/EBP-beta stimulated by ATF4 activated under the stress conditions examined. RNA interference studies provided further evidence of the requirement of C/EBP-beta for Redd1 expression. We conclude that the Redd1 gene is transactivated by the ATF4 and C/EBP family of transcription factors, leading to mTOR inhibition in response to oxidative and ER stress.

Anti-Apoptotic Effects of Caspase Inhibitors on Rat Intervertebral Disc Cells

BACKGROUND Apoptosis is thought to be a critical component of disc degeneration. Two main pathways of Fas-mediated apoptosis have been identified: Type I, which is the death-inducing signaling complex pathway, and Type II, which is the mitochondrial pathway. The apoptotic pathway for anulus fibrosus cells, which is phenotypically different from that of nucleus pulposus cells, has not been elucidated to our knowledge. The ultimate initiators or executioners of apoptosis are caspases. There are also inhibitors of caspases, which have the potential of being used as anti-apoptotic therapeutic agents. We therefore undertook this study to determine (1) the apoptotic pathway of anulus fibrosus cells and (2) the anti-apoptotic potential of caspase inhibitors. METHODS Rat anulus fibrosus cells were isolated, cultured, and placed in either 0% (apoptosis-promoting condition) or 10% (normal control) fetal bovine serum. We identified and quantified the presence of apoptotic cell death, caspase activities, and loss of mitochondrial membrane potential. In addition, we examined the cells for the expression of Fas, procaspases, and cytochrome-c. Finally, we analyzed the degree of anti-apoptotic effects of caspase inhibitors on the cells in 1% fetal bovine serum. RESULTS The percentage of apoptosis and Fas expression in the cells incubated in 0% fetal bovine serum were increased compared with those in the cells incubated in 10% fetal bovine serum (both p < 0.001). Caspase-8, 9, and 3 activities were increased and expression of procaspases was decreased in the 0% fetal bovine serum compared with those in the 10% fetal bovine serum (all p < 0.001). In contrast, the loss of mitochondrial membrane potential and cytochrome-c release into the cytosol were unchanged in the 0% fetal bovine serum. Pancaspase and caspase-8 inhibitors reduced apoptotic cell death (p < 0.001 and p < 0.05, respectively), but caspase-9 inhibitor did not reduce apoptotic cell death. CONCLUSIONS Our results suggest that, unlike nucleus pulposus cells, anulus fibrosus cells are Fas Type-I cells, which undergo apoptosis through the death-inducing signaling complex. We also found that apoptosis of intervertebral disc cells can be attenuated by caspase inhibitors.

Up‐regulation of Bak and Bim via JNK downstream pathway in the response to nitric oxide in human glioblastoma cells

Nitric oxide (NO) is a chemical messenger implicated in neuronal damage associated with ischemia neurodegenerative disease and excitotoxicity. In the present study, we examined the biological effects of NO and its mechanisms in human malignant glioblastoma cells. Addition of a NO donor, S‐nitroso‐N‐acetyl‐penicillamine (SNAP), induced apoptosis in U87MG human glioblastoma cells, accompanied by opening mitochondrial permeability transition pores, release of cytochrome c and AIF, and subsequently by caspase activation. NO‐induced apoptosis occurred concurrently with significantly increased levels of the Bak and Bim. Treatment with SNAP resulted in sustained activation of JNK and its downstream pathway, c‐Jun/AP‐1. The expression of dominant‐negative (DN)‐JNK1 and DN‐c‐Jun suppressed the activation of AP‐1, the induction of Bak and Bim, and the SNAP‐induced apoptosis. In addition, de novo protein synthesis was required for the initiation of apoptosis in that the protein synthesis inhibitor, cycloheximide (CHX), inhibited NO‐induced apoptotic cell death as well as up‐regulation of Bak and Bim. These results suggest that NO activates an apoptotic cascade, involving sustained JNK activation, AP‐1 DNA binding activity, and subsequent Bak and Bim induction, followed by cytochrome c and AIF releases and caspases cascade activation, resulting in human malignant brain tumor cell death. J. Cell. Physiol. 206: 477–486, 2006.

Sulindac and its metabolites inhibit invasion of glioblastoma cells via down‐regulation of Akt/PKB and MMP‐2

Non‐steroidal anti‐inflammatory drug (NSAID), sulindac has chemopreventive and anti‐tumorigenic properties, however, the molecular mechanism of this inhibitory action has not been clearly defined. The Akt/protein kinase B, serine/threonine kinase is well known as an important mediator of many cell survival signaling pathways. In the present study, we demonstrate that down‐regulation of Akt is a major effect of anti‐invasiveness property of sulindac and its metabolites in glioblastoma cells. Myristoylated Akt (MyrAkt) transfected U87MG glioblastoma cells showed increase invasiveness, whereas DN‐Akt transfected cells showed decrease invasiveness indicating that Akt potently promoted glioblastoma cell invasion. MMP‐2 promoter and enzyme activity were up‐regulated in Akt kinase activity dependent manner. Sulindac and its metabolites down‐regulated Akt phosphorylation, inhibited MMP‐2 production, and significantly inhibited invasiveness of human glioblastoma cells. In addition, sulindac and LY294002, a selective inhibitor of phosphoinositide 3‐kinase (PI3K), synergistically inhibited the invasion of glioblastoma cells. Furthermore, only celecoxib showed Akt phosphorylation reduction and an anti‐invasivness in glioblastoma cells, whereas aspirin, ketoprofen, ketorolac, and naproxen did not. In conclusion, our results provide evidence that down‐regulation of Akt pathway and MMP‐2 may be one of the mechanisms by which sulindac and its metabolites inhibit glioblastoma cell invasion.

Arsenic trioxide sensitizes CD95/Fas‐induced apoptosis through ROS‐mediated upregulation of CD95/Fas by NF‐κB activation

CD95/Fas is a cell surface protein that belongs to the tumor necrosis factor receptor family. Signals through CD95/Fas are able to induce apoptosis in sensitive cells. Therefore, modalities to regulate the CD95/Fas expression level in tumor cells are called for. In the present study, we show that sublethal doses of arsenic trioxide (As2O3) sensitized CD95/Fas‐induced apoptosis in human cervical cancer cells, and the sensitizing effects resulted from As2O3‐mediated increase in the expression of the CD95/Fas. N‐acetyl‐L‐cysteine, a specific scavenger of reactive oxygen species, abrogated As2O3‐induced upregulation of CD95/Fas and enhancement of CD95/Fas‐mediated apoptosis. Furthermore, inhibition of NF‐κB by transient transfection of IκBα supersuppressor blocked the increase of CD95/Fas expression following As2O3 treatment. Antisense oligonucleotide of CD95/Fas and ZB4, an antibody that blocks the binding of CD95/Fas ligand to CD95/Fas, reduced the amount of As2O3‐sensitized CD95/Fas‐induced apoptosis, demonstrating the specificity of CD95/Fas‐binding ligands in the As2O3‐sensitized CD95/Fas‐induced apoptosis. These findings demonstrate that sensitization of human cervical cancer cells to CD95/Fas‐mediated apoptosis by As2O3 can be partly due to induction of ROS and subsequent upregulation of CD95/Fas gene expression by NF‐κB activation.

Histone Deacetylase Inhibitors Sensitize Human Non-small Cell Lung Cancer Cells to Ionizing Radiation Through Acetyl p53-Mediated c-myc Down-Regulation

Introduction: Histone deacetylase inhibitors (HDACIs) induce growth arrest and apoptosis in cancer cells. In addition to their intrinsic anticancer properties, HDACIs modulate cellular responses to ionizing radiation (IR). We examined the molecular mechanism(s) associated with the radiosensitizing effects of HDACIs in human lung cancer cells. Methods: Lung cancer cells were pretreated with the appropriate concentrations of suberoylanilide hydroxamic acid or trichostatin A. After 2 hours, cells were irradiated with various doses of &ggr;-IR, and then we performed 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, fluorescence-activated cell sorting analysis, clonogenic assay, and Western blotting to detect cell viability or apoptosis and changes of specific proteins expression levels. Results: In this study, we showed that HDACIs (including suberoylanilide hydroxamic acid and trichostatin A) and IR synergistically trigger cell death in human non-small cell lung cancer cells. Cell viability and clonogenic survival were markedly decreased in cultures cotreated with HDACIs and IR. Interestingly, p53 acetylation at lysine 382 was significantly increased, and c-myc expression simultaneously down-regulated in cotreated cells. Radiosensitization by HDACIs was inhibited on transfection with small interfering RNA against p53 and c-myc overexpression, supporting the involvement of p53 and c-myc in this process. Furthermore, c-myc down-regulation and apoptotic cell death coinduced by IR and HDACI were suppressed in cells transfected with mutant K382R p53 and C135Y p53 displaying loss of acetylation at lysine 382 and DNA-binding activity, respectively. Conclusions: Our results collectively demonstrate that the degree of radiosensitization by HDACIs is influenced by acetyl p53-mediated c-myc down-regulation.

Sorafenib induces apoptotic cell death in human non-small cell lung cancer cells by down-regulating mammalian target of rapamycin (mTOR)-dependent survivin expression.

Sorafenib, a multikinase inhibitor, is emerging as a promising targeted agent that may possess antitumor activity against a broad range of cancers. The mechanism by which sorafenib induces lung cancer cell death and apoptosis, however, is not understood. In the present study, we provide evidence that sorafenib acts through inhibition of mammalian target of rapamycin (mTOR) to down-regulate survivin and promote apoptotic cell death in human non-small cell lung cancer (NSCLC) cells. Sorafenib induced ATF4-mediated Redd1 expression, leading to mTOR inhibition-the upstream signal for down-regulation of survivin. Overexpression of survivin reduced sorafenib-induced apoptosis, whereas silencing survivin using small interfering RNA (siRNA) enhanced it, supporting the interpretation that down-regulation of survivin is involved in sorafenib-induced cell death in human NSCLC cells. Furthermore, sorafenib abolished the induction of survivin that normally accompanies IGF-1-stimulated mTOR activation. We further found that Redd1-induced mTOR down-regulation and ATF4/CHOP-induced expression of the TRAIL receptor DR5 associated with sorafenib treatment helped sensitize cells to TRAIL-induced apoptosis. Our study suggests that sorafenib mediates apoptotic cell death in human NSCLC cells through Redd1-induced inhibition of mTOR and subsequent down-regulation of survivin, events that are associated with sensitization to TRAIL-induced apoptotic cell death.

Activation of Epidermal Growth Factor Receptor and Its Downstream Signaling Pathway by Nitric Oxide in Response to Ionizing Radiation

Epidermal growth factor receptor (EGFR) is activated by ionizing radiation (IR), but the molecular mechanism for this effect is unknown. We have found that intracellular generation of nitric oxide (NO) by NO synthase (NOS) is required for the rapid activation of EGFR phosphorylation by IR. Treatment of A549 lung cancer cells with IR increased NOS activity within minutes, accompanied by an increase of NO. 2-Phenyl-4,4,5,5,-tetramethylimidazolline-1-oxyl-3-oxide, an NO scavenger, and NG-monomethyl-l-arginine, an NOS inhibitor, abolished the increase in intracellular NO and activation of EGFR by IR. In addition, an NO donor alone induced EGFR phosphorylation. Transient transfection with small interfering RNA for endothelial NOS reduced IR-induced NO production and suppressed IR-induced EGFR activation. Overexpression of endothelial NOS increased IR-induced NO generation and EGFR activation. These results indicate a novel molecular mechanism for EGFR activation by IR-induced NO production via NOS. (Mol Cancer Res 2008;6(6):996–1002)

Sulindac-derived reactive oxygen species induce apoptosis of human multiple myeloma cells via p38 mitogen activated protein kinase-induced mitochondrial dysfunction

Non-steroidal anti-inflammatory drugs are well known to induce apoptosis of cancer cells independent of their ability to inhibit cyclooxygenase-2, but the molecular mechanism for this effect has not yet been fully elucidated. The purpose of this study was to elucidate the potential signaling components underlying sulindac-induced apoptosis in human multiple myeloma (MM) cells. We found that sulindac induces apoptosis by promoting ROS generation, accompanied by opening of mitochondrial permeability transition pores, release of cytochrome c and apoptosis inducing factor from mitochondria, followed by caspase activation. Bcl-2 cleavage and down-regulation of the inhibitor of apoptosis proteins (IAPs) family including cIAP-1/2, XIAP, and survivin, occurred downstream of ROS production during sulindac-induced apoptosis. Forced expression of survivin and Bcl-2 blocked sulindac-induced apoptosis. Most importantly, sulindac-derived ROS activated p38 mitogen-activated protein kinase and p53. SB203580, a p38 mitogen-activated protein kinase inhibitor, and RNA inhibition of p53 inhibited the sulindac-induced apoptosis. Furthermore, p53, Bax, and Bak accumulated in mitochondria during sulindac-induced apoptosis. All of these events were significantly suppressed by SB203580. Our results demonstrate a novel mechanism of sulindac-induced apoptosis in human MM cells, namely, accumulation of p53, Bax, and Bak in mitochondria mediated by p38 MAPK activation downstream of ROS production.

Diarsenic and tetraarsenic oxide inhibit cell cycle progression and bFGF- and VEGF-induced proliferation of human endothelial cells.

Arsenic trioxide (As2O3, diarsenic oxide) has recently been reported to induce apoptosis and inhibit the proliferation of various human cancer cells derived from solid tumors as well as hematopoietic malignancies. In this study, the in vitro effects of As2O3 and tetraasrsenic oxide (As4O6) on cell cycle regulation and basic fibroblast growth factor (bFGF)‐ or vascular endothelial growth factor (VEGF)‐stimulated cell proliferation of human umbilical vein endothelial cells (HUVEC) were investigated. Significant dose‐dependent inhibition of cell proliferation was observed when HUVEC were treated with either arsenical compound for 48 h, and flow cytometric analysis revealed that these two arsenical compounds induced cell cycle arrest at the G1 and G2/M phases—the increases in cell population at the G1 and G2/M phase were dominantly observed in As2O3‐ and As4O6‐treated cells, respectively. In both arsenical compounds‐treated cells, the protein levels of cyclin A and CDC25C were significantly reduced in a dose‐dependent manner, concomitant to the reduced activities of CDK2‐ and CDC2‐associated kinase. In G1‐synchronized HUVEC, the arsenical compounds prevented the cell cycle progression from G1 to S phase, which was stimulated by bFGF or VEGF, through the inhibition of growth factor‐dependent signaling. These results suggest that arsenical compounds inhibit the proliferation of HUVEC via G1 and G2/M phase arrest of the cell cycle. In addition, these inhibitory effects on bFGF‐ or VEGF‐stimulated cell proliferation suggest antiangiogenic potential of these arsenical compounds.