维生素E琥珀酸酯通过内质网应激诱导胃癌SGC-7901细胞凋亡的研究

目的:探讨内质网应激在维生素E琥珀酸酯(vitamin E succinate,VES)诱导人胃癌SGC-7901细胞凋亡过程中的作用。方法:分别采用Western blotting和RT-PCR检测VES不同剂量(0、5、10和20μg/ml)处理SGC-7901细胞24 h和20μg/ml VES处理SGC-7901细胞不同时间对内质网应激标志物葡萄糖调节蛋白(glucose regulative protein,GRP)GRP78、GRP94和内质网应激凋亡途径关键因子C/EBP同源蛋白(C/EBP-homologous protein,CHOP)的蛋白和mRNA表达的影响;进一步采用RNA瞬时干扰阻断CHOP的表达后用20μg/ml VES作用SGC-7901细胞24 h,采用DAPI染色法观察细胞凋亡的改变。结果:20μg/ml VES组在mRNA水平卜均诱导GRP78、GRP94和CHOP的表达增加;在蛋白水平上20μg/ml VES显著增加GRP78和CHOP的表达,GRP94表达先降低,而后又升高;阻断CHOP后VES诱导的细胞凋亡由46.3%降低为27.9%(P0.05)。结论:内质网应激可能参与了VES诱导的SGC-7901细胞凋亡。     

Vitamin E succinate-induced apoptosis of SGC-7901 cells via endoplasmic reticulum stress

目的:探讨内质网应激在维生素E琥珀酸酯(vitamin E succinate,VES)诱导人胃癌SGC-7901细胞凋亡过程中的作用.方法:分别采用Western blotting和RT-PCR检测VES不同剂量(0、5、10和20μg/ml)处理SGC-7901细胞24 h和20 μ g/ml VES处理SGC-7901细胞不同时间对内质网应激标志物葡萄糖调节蛋白(glucose regulative protein,GRP)G RP78、GRP94和内质网应激凋亡途径关键因子C/EBP同源蛋白(C/EBP-homologous protein,CHOP)的蛋白和mRNA表达的影响;进一步采用RNA瞬时干扰阻断CHOP的表达后用20 μg/ml VES作用SGC-7901细胞24h,采用DAPI染色法观察细胞凋亡的改变.结果:20μg/ml VES组在mRNA水平上均诱导GRP78、GRP94和CHOP的表达增加;在蛋白水平上20 μg/ml VES显著增加GRP78和CHOP的表达,GRP94表达先降低,而后又升高;阻断CHOP后VES诱导的细胞凋亡由46.3％降低为27.9％ (P＜0.05).结论:内质网应激可能参与了VES诱导的SGC-7901细胞凋亡.     

内质网应激在芹菜素诱导胃癌细胞凋亡中的作用

目的:探讨内质网应激在芹菜素诱导人胃癌SGC-7901细胞凋亡中的作用。方法:采用Western blot方法检测不同剂最(0、20、40、60、80μmol/L)芹菜素作用48 h和60μmol/L芹菜素作用不同时间(0、12、24、48 h)后对胃癌SGC-7901细胞中内质网应激标志物葡萄糖调节蛋白(glucose regulative protein,GRP)GRP78、GRP94和内质网应激凋亡途径关键因子C/EBP同源蛋白(C/EBP-homologousprotein,CHOP)表达的影响;并用DAPI荧光染色和流式细胞仪检测10 mmol/L内质网应激抑制剂4-苯丁酸(4-phenylbutyrie acid,PBA)加入前后细胞凋亡情况的变化。结果:芹菜素可以诱导GRP78、GRP94蛋白的表达,并随着剂量和时间的增加蛋白表达量也呈增加趋势,但芹菜素不能诱导CHOP蛋白的表达;荧光染色和流式细胞术结果显示4-PBA与20μmol/L芹菜素联合作用组的细胞凋亡率明显增加,与20μmol/L芹菜素组及溶剂对照组间的差异具有统计学意义(P0.05或P0.01)。结论:内质网应激在芹菜素诱导人胃癌SGC-7901细胞凋亡中可能对细胞起到保护作用。     

Roles of endoplasmic reticulum stress in apigenin-induced apoptosis in human gastric cancer SGC-7901 cells

目的:探讨内质网应激在芹菜素诱导人胃癌SGC-7901细胞凋亡中的作用.方法:采用Western blot方法检测不同剂量(0、20、40、60、80μmol/L)芹菜素作用48 h和60μmol/L芹菜素作用不同时间(0、12、24、48 h)后对胃癌SGC-7901细胞中内质网应激标志物葡萄糖调节蛋白(glucose regulative protein,GRP)GRP78、GRP94和内质网应激凋亡途径关键因子C/EBP同源蛋白(C/EBP-homologous protein,CHOP)表达的影响;并用DAPI荧光染色和流式细胞仪检测10 mmol/L内质网应激抑制剂4-苯丁酸(4-phenylbutyric acid,PBA)加入前后细胞凋亡情况的变化.结果:芹菜素可以诱导GRP78、GRP94蛋白的表达,并随着剂量和时间的增加蛋白表达量也呈增加趋势,但芹菜素不能诱导CHOP蛋白的表达;荧光染色和流式细胞术结果显示4-PBA与20μmol/L芹菜素联合作用组的细胞凋亡率明显增加,与20μmol/L芹菜素组及溶剂对照组间的差异具有统计学意义(P＜0.05或P＜0.01).结论:内质网应激在芹菜素诱导人胃癌SGC-7901细胞凋亡中可能对细胞起到保护作用.     

衣霉素通过上调TRAIL-R2增加胃癌细胞对TRAIL的敏感性

目的:研究衣霉素(tunicamycin,TM)上调胃癌细胞对肿瘤坏死因子相关凋亡诱导配体(TNF-related apoptosis-inducing ligand,TRAIL)诱导凋亡敏感性的作用机制。方法:采用碘化丙啶染色的FCM法检测TM(1μmol/L)与TRAIL(100μg/L)单独或联合作用3、6、16、24和36h时对SGC-7901细胞凋亡率的影响;FCM法检测TM处理前后细胞表面TRAIL受体1(TRAIL receptor1,TRAIL-R1)、-R2、-R3和-R4的表达情况;实时荧光定量-PCR法检测TRAIL-R2mRNA的表达情况;蛋白质印迹法检测葡萄糖调节蛋白78(glucose-regulated protein 78kDa,GRP78)和CCAAT/增强子结合蛋白同源蛋白(CCAAT/enhancer-binding protein homologous protein,CHOP)的表达水平;RT-PCR检测X盒结合蛋白(X-box binding protein1,XBP1)mRNA的剪接情况。结果:TM单独作用引起的SGC-7901细胞的凋亡率低,TM和TRAIL联合作用能有效提高SGC-7901细胞的凋亡率;TM能明显上调SGC-7901细胞表面TRAIL-R2的表达水平,而对TRAIL-R1、-R3和-R4却无明显影响;TRAIL-R2mRNA的表达水平随TM作用时间延长而相应升高;GRP78蛋白的上调和XBP-1mRNA的剪接活化证实了TM可诱导未折叠蛋白反应(unfolded protein response,UPR)的发生;CHOP蛋白的表达水平也在TM作用后上调。结论:TM通过诱导UPR上调TRAIL-R2的表达,从而增加胃癌细胞对TRAIL的敏感性,CHOP介导了TRAIL-R2的上调作用。     

奥沙利铂通过上调死亡受体表达增强TRAIL诱导胃癌细胞凋亡的实验研究

目的:研究奥沙利铂对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、采用流式细胞仪检测细胞凋亡,采用Western blot检测DR5蛋白表达.结果:100ng/ml的TRAIL导致轻度的增殖抑制,诱导不超过5%的细胞凋亡;TRAIL(100ng/ml)联合奥沙利铂(23.44μg/ml)引起明显的细胞增殖抑制和细胞凋亡(P＜0.05),TRAIL没有明显改变死亡受体5(DR5)的表达,而23.44 μg/ml奥沙利铂作用胃癌细胞24小时后,明显上调了DR5的表达.结论:奥沙利铂通过上调DR5的表达增强TRAIL诱导的胃癌细胞凋亡.     

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。     

内质网应激对乳腺癌细胞5-FU化疗敏感性影响的观察

目的:探讨内质网应激(endoplasmic reticulum stress,ERS)状态对乳腺癌细胞5-氟尿嘧啶(5-FU)化疗敏感性的影响。方法:MTS试验比较乳腺癌MCF-7细胞及其衍生的5-FU耐受细胞(MCF-7/5-FU)对5-FU的敏感性,电子显微镜观察MCF-7及MCF-7/5-FU细胞中的内质网含量情况,Real-time RT-PCR法检测MCF-7及MCF-7/5-FU细胞中基础水平的内质网应激标志的表达情况,5-FU刺激MCF-7和MCF-7/5-FU细胞后,Real-time RT-PCR法检测内质网应激标志的表达变化以反映内质网的应激状态。结果:耐药细胞MCF-7/5-FU对5-FU的耐药指数为16。相比于亲本细胞MCF-7细胞,MCF-7/5-FU细胞中的内质网含量明显更为丰富。GRP94和CHOP在MCF-7/5-FU中的表达量分别是MCF-7中表达量的2.1(t=9.288,P=0.003)和1.8倍(t=6.057,P=0.008)。比较最高剂量5-FU诱导和未加5-FU时CHOP和GRP94的表达量。在MCF-7细胞中,分别上调12.23(t=15.082,P=0.001)和2.54倍(t=6.196,P=0.038);在MCF-7/5-FU细胞中,分别上调5.45(t=15.451,P=0.003)和2.38倍(t=7.218,P=0.007)。比较在5-FU刺激下72和0h时CHOP以及GRP94的表达量。在MCF-7细胞中,分别上调12.04(t=15.093,P=0.001)和3.15(t=4.540,P=0.032)倍;在MCF-7/5-FU细胞中,分别上调4.20(t=4.363,P=0.005)和1.88倍(t=2.875,P=0.041)。说明5-FU能以剂量依赖性和时间依赖性上调CHOP和GRP94的表达,且在MCF-7细胞中诱导上调更为明显。结论:内质网应激参与乳腺癌细胞对5-FU化疗的敏感性,轻度的应激参与化疗耐受,而较强的应激则有利于化疗效果。     

重组人TRAIL蛋白联合顺铂对人卵巢癌细胞生长及凋亡的影响

背景与目的：研究发现肿瘤坏死因子的相关凋亡诱导配体(tumor necrosis factor-related apoptosis inducing ligand,TRAIL)可以增强化疗药物对肿瘤细胞的杀伤作用。本研究旨在探讨TRAIL与顺铂联合应用对体外培养的卵巢癌细胞SKOV3和OVCAR3生长凋亡的影响及可能的诱导机制。方法：利用MTT法和流式细胞仪检测在顺铂和重组人TRAIL蛋白共同作用下,SKOV3和OVCAR3细胞的增殖抑制效应及细胞凋亡程度;并应用实时荧光定量聚合酶链反应(real-time fluorescent quantitative polymerase chain reaction,RTFQ-PCR)检测药物处理后TRAIL死亡受体DR4、DR5的mRNA表达水平;同时用蛋白[质]印迹法(Western blot)检测DR4、DR5的蛋白表达水平。结果：SKOV3和OVCAR3细胞均对TRAIL蛋白敏感,随着TRAIL蛋白浓度的升高,细胞的生长抑制率可达64%;而TRAIL与顺铂联合用药对两种细胞的抑制率均达到92%以上,对细胞的增殖抑制呈现高效协同作用,与单独用药组比较差异有统计学意义(P<0.05);TRAIL和顺铂联合组两种细胞凋亡率分别为(31.50±0.79)%和(36.60±1.31)%,显著高于单独用药组;RTFQ-PCR和Western blot检测结果显示,SKOV3和OVCAR3细胞在TRAIL与顺铂联合用药后,死亡受体DR4、DR5表达水平均显著上调。结论：在体外,TRAIL与化疗药物顺铂联用能明显抑制卵巢癌细胞增殖,诱导肿瘤细胞凋亡。TRAIL能明显增强顺铂对卵巢癌细胞的敏感性,其诱导机制可能与死亡受体DR4、DR5表达水平上调有关。     

Oligomycin A enhances apoptotic effect of TRAIL through CHOP‐mediated death receptor 5 expression

Development of resistance to TNF‐related apoptosis‐inducing ligand (TRAIL) in tumor cells is one of the important problems in cancer treatment. Despite the previous report demonstrating that oligomycin suppressed TNF‐induced apoptosis, in our screening of small molecules enhancing cancer cell death to TRAIL, oligomycin A (OMA) was found to enhance TRAIL‐induced apoptosis in HeLa cells. CCAAT/enhancer‐binding protein homologous protein (CHOP) was found to directly bind to death receptor 5 (DR5) promoter through endoplasmic reticulum stress (ER‐stress) signaling and sensitize the cells to TRAIL. Among ER‐stress associated proteins, OMA triggered the inositol‐requiring enzyme 1 (IRE1) signaling pathway, leading to X‐binding protein 1 (XBP1) splicing, CHOP expression and DR5 upregulation. In contrast, small‐interfering RNA (siRNA) of CHOP reduced the number of apoptotic cells in response to the co‐treatment of TRAIL and OMA. Collectively, our data suggest that OMA enhances apoptotic death of cervical cancer cells to TRAIL through upregulation of CHOP‐mediated DR5 expression following ER‐stress. © 2011 Wiley Periodicals, Inc.     

Inhibition of MEK sensitizes human melanoma cells to endoplasmic reticulum stress-induced apoptosis

Past studies have shown that activation of mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK)/ERK is a common cause for resistance of melanoma cells to death receptor-mediated or mitochondria-mediated apoptosis. We report in this study that inhibition of the MEK/ERK pathway also sensitizes melanoma cells to endoplasmic reticulum (ER) stress-induced apoptosis, and this is mediated, at least in part, by caspase-4 activation and is associated with inhibition of the ER chaperon glucose-regulated protein 78 (GRP78) expression. Treatment with the ER stress inducer tunicamycin or thapsigargin did not induce significant apoptosis in the majority of melanoma cell lines, but resistance to these agents was reversed by the MEK inhibitor U0126 or MEK1 small interfering RNA (siRNA). Induction of apoptosis by ER stress when MEK was inhibited was caspase dependent with caspase-4, caspase-9, and caspase-3 being involved. Caspase-4 seemed to be the apical caspase in that caspase-4 activation occurred before activation of caspase-9 and caspase-3 and that inhibition of caspase-4 by a specific inhibitor or siRNA blocked activation of caspase-9 and caspase-3, whereas inhibition of caspase-9 or caspase-3 did not inhibit caspase-4 activation. Moreover, overexpression of Bcl-2 inhibited activation of caspase-9 and caspase-3 but had minimal effect on caspase-4 activation. Inhibition of MEK/ERK also resulted in down-regulation of GRP78, which was physically associated with caspase-4, before and after treatment with tunicamycin or thapsigargin. In addition, siRNA knockdown of GRP78 increased ER stress-induced caspase-4 activation and apoptosis. Taken together, these results seem to have important implications for new treatment strategies in melanoma by combinations of agents that induce ER stress and inhibitors of the MEK/ERK pathway.     

Baicalein overcomes tumor necrosis factor-related apoptosis-inducing ligand resistance via two different cell-specific pathways in cancer cells but not in normal cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is one of the most promising candidates for new cancer therapeutics. A current problem is that some cancers still remain resistant to TRAIL. We show for the first time that a naturally occurring flavonoid, baicalein, overcomes TRAIL resistance in cancer cells. The combination of baicalein and TRAIL effectively induced apoptosis in TRAIL-resistant colon cancer SW480 cells. Baicalein up-regulated the expression of death receptor 5 (DR5) among TRAIL receptors at the mRNA and protein levels. Suppression of this up-regulation with small interfering RNA (siRNA) efficiently reduced the apoptosis induced by TRAIL and baicalein, suggesting that the sensitization was mediated through DR5 induction. Moreover, baicalein also overcame TRAIL resistance with DR5 up-regulation in prostate cancer PC3 cells. Of note, the combination of TRAIL and baicalein hardly induced apoptosis in normal human cells, such as blood cells and hepatocytes. Baicalein increased DR5 promoter activity, and this enhanced activity was diminished by mutation of a CCAAT/enhancer-binding protein homologous protein (CHOP)-binding site in SW480 cells. In SW480 cells, CHOP siRNA blocked both functions of baicalein. CHOP expression was induced by baicalein in SW480 cells; however, in PC3 cells, baicalein scarcely induced CHOP and mutation of the CHOP-binding site did not abrogate the DR5 promoter activation by baicalein. Interestingly, baicalein induced reactive oxygen species (ROS) and a ROS scavenger prevented DR5 expression and TRAIL sensitization in PC3 but not SW480 cells. These results indicate that, using two different pathways, baicalein exposes cancer surveillance of TRAIL and overcomes TRAIL resistance in cancer cells.     

ROS and CHOP are critical for dibenzylideneacetone to sensitize tumor cells to TRAIL through induction of death receptors and downregulation of cell survival proteins

Because tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) selectively kills tumor cells, it is being tested in cancer patients. Unfortunately, patients develop resistance to the cytokine, therefore, agents that can sensitize cells to TRAIL are urgently needed. In this study, we investigated whether dibenzylideneacetone (DBA) can sensitize cancer cells to TRAIL and potentiates TRAIL-induced apoptosis. As indicated by accumulation of the membrane phospholipid phosphatidylserine, DNA breaks, intracellular esterase activity, and activation of caspase-8, -9, and -3, we concluded that DBA potentiated TRAIL-induced apoptosis in colon cancer cells. DBA also converted TRAIL resistant-cells to TRAIL-sensitive. When examined for the mechanism, we found that DBA decreased the expression of antiapoptotic proteins and decoy receptor-2 and increased proapoptotic proteins. DBA also induced both death receptor (DR)-5 and DR4. Knockdown of DR5 and DR4 by small interfering RNA (SiRNA) reduced the sensitizing effect of DBA on TRAIL-induced apoptosis. In addition, DBA increased the expression of CHOP proteins. Knockdown of CHOP by siRNA decreased the induction of DBA-induced DR5 expression and apoptosis. Induction of receptors by DBA, however, was p53-independent, as deletion of p53 had no effect on receptor induction. We observed that DBA-induced induction of DR5 and DR4 was mediated through generation of reactive oxygen species (ROS), as N-acetylcysteine blocked the induction of death receptors and suppression of cell survival proteins by DBA. Overall, our results show that DBA potentiates TRAIL-induced apoptosis through downregulation of cell survival proteins and upregulation of death receptors via activation of ROS and CHOP mediated pathways.     

Prospective impact of 5-FU in the induction of endoplasmic reticulum stress, modulation of GRP78 expression and autophagy in Sk-Hep1 cells

Hepatocellular carcinoma (HCC) is one of the most aggressive malignant diseases and is highly resistant to conventional chemotherapy. Therefore, HCC requires more effective prevention and treatment strategies. 5-fluorouracil (5-FU) remains the most widely used chemotherapeutic drug for the treatment of gastrointestinal, breast, head and neck, and ovarian cancers. In pursuit of a novel effective strategy, we have evaluated the potential of 5-FU to promote endoplasmic reticulum (ER) stress and autophagy in Sk-Hep1 HCC cells. We found that 5-FU profoundly induces ER stress in Sk-Hep1 cells and upregulates p53 and activates CHOP/GADD153 and caspase-12. Activation of CHOP/GADD153 and caspase-12 promotes mitochondrial cell death in Sk-Hep1 cells followed by ER stress. Changes in calcium homeostasis and the protein folding machinery cause stress in the ER, leading to apoptotic cell death. Stress in the ER activates autophagy to remove the misfolded protein aggregates and recover from the stress environment. Our study demonstrates that 5-FU-induced ER stress suppresses autophagy and also downregulates GRP78 expression. Activation of autophagy followed by ER stress facilitates the cell survival response. Therefore, the inhibition of protective autophagy may provide a useful pharmacological target. Taken together, these results indicate that 5-FU-induced ER stress activates the mitochondrial apoptotic cell death pathway by downregulating GRP78 and protective autophagy proteins in Sk-Hep1 cells, raising the possibility of using 5-FU as a therapeutic agent to target human HCC.     

Tunicamycin enhances tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis in human prostate cancer cells

Death receptor 5 (DR5/TRAIL-R2) is an apoptosis-inducing membrane receptor for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL/Apo2L). In this study, we showed that tunicamycin, a naturally occurring antibiotic, is a potent enhancer of TRAIL-induced apoptosis through up-regulation of DR5 expression. Tunicamycin significantly sensitized PC-3, androgen-independent human prostate cancer cells, to TRAIL-induced apoptosis. The tunicamycin-mediated enhancement of TRAIL-induced apoptosis was markedly blocked by a recombinant human DR5/Fc chimeric protein. Tunicamycin and TRAIL cooperatively activated caspase-8, -10, -9, and -3 and Bid cleavage and this activation was also blocked in the presence of the DR5/Fc chimera. Tunicamycin up-regulated DR5 expression at the mRNA and protein levels in a dose-dependent manner. Furthermore, the tunicamycin-mediated sensitization to TRAIL was efficiently reduced by DR5 small interfering RNA, suggesting that the sensitization was mediated through induction of DR5 expression. Tunicamycin increased DR5 promoter activity and this enhanced activity was diminished by mutation of a CHOP-binding site. In addition, suppression of CHOP expression by small interfering RNA reduced the tunicamycin-mediated induction of DR5. Of note, tunicamycin-mediated induction of CHOP and DR5 protein expression was not observed in normal human peripheral blood mononuclear cells. Moreover, tunicamycin did not sensitize the cells to TRAIL-induced apoptosis. Thus, combined treatment with tunicamycin and TRAIL may be a promising candidate for prostate cancer therapy.