XAF1基因对顺铂诱导肺腺癌A549细胞凋亡作用的研究

目的:通过顺铂诱导人肺腺癌细胞A549的凋亡,研究X染色体连锁凋亡抑制蛋白相关因子1(X-linked inhibitor of apoptosis protein associated factor-1,XAF1)基因在A549细胞中的表达情况,初步探讨该基因在凋亡中的作用。方法:采用4μg/mL浓度的顺铂处理A549细胞,MTT法检测细胞的增殖抑制率;AnnexinⅤ/7-AAD检测A549细胞凋亡情况;RT-PCR和蛋白质印迹法分别检测A549凋亡后XAF1mRNA和蛋白的表达;Caspase-3试剂盒检测A549细胞凋亡后Caspase-3的活性。结果:用4μg/mL浓度顺铂处理A549细胞2、12和24h后,A549细胞增殖抑制率分别为(3.40±0.65)%、(8.31±0.73)%和(14.72±0.24)%,与对照组(1.03±0.28)%相比均明显增高,P值分别为0.004、0.000和0.000,细胞增殖抑制率随时间增加而增强;A549细胞凋亡率分别为(4.35±0.95)%、(9.69±2.60)%和(22.35±1.24)%,与对照组(1.39±0.21)%相比均明显增加,P值分别为0.006、0.005和0.000,细胞凋亡率随顺铂作用时间延长而增加;实验组XAF1mRNA表达水平分别为(0.199±0.029)、(0.654±0.093)和(1.216±0.101),对照组为(0.091±0.020),XAF1mRNA表达水平随作用时间的延长呈增加趋势,P值分别为0.006、0.001和0.000;实验组XAF1蛋白表达水平分别为(0.322±0.041)、(0.508±0.014)和(0.901±0.014),对照组为(0.124±0.007),XAF1蛋白表达水平随作用时间的延长呈增加趋势,P值分别为0.001、0.000和0.000;Caspase-3活性(A405nm)分别为(34.745±3.781)、(69.524±3.096)和(94.787±5.429),对照组为(21.914±1.962),Caspase-3活性随顺铂作用时间的延长而增加。结论:顺铂诱导A549细胞凋亡可以引起XAF1表达增加,且随细胞凋亡水平的提高而增加,提示XAF1可能参与顺铂诱导人肺腺癌A549细胞的凋亡过程。     

地塞米松预处理人肺腺癌 A549 细胞对顺铂抗肿瘤活性的影响

目的：探讨地塞米松（dexamethasone,DEX）预处理人肺腺癌A549细胞后,对化疗药物顺铂（cispla—tin,DDP）抗肿瘤活性的影响。方法：以不同浓度（500、1000nmol／L）DEX预先作用于人肺腺癌A549细胞12h后,再用不同浓度（1．25、2．5、5u/ml）DDP处理。流式细胞术测定细胞凋亡,细胞计数观察细胞生长密度、形态。结果：DEX对A549细胞增殖有抑制作用。DDP能够明显抑制A549细胞增殖,促进其凋亡。DEX预处理后DDP干预A549细胞的增殖抑制作用较单一用DDP增强,且随着DEX浓度的增加,其对化疗药物DDP凋亡抑制作用的影响增强。结论：DEX预处理对顺铂诱导的人肺腺癌A549细胞的凋亡具有明显的促进作用,能增强DDP的抗肿瘤活性。     

姜黄素对耐顺铂人肺腺癌细胞Survivin表达及其化疗敏感性的影响

目的:探讨姜黄素(Cur)对耐顺铂(DDP)人肺腺癌细胞A549/DDP Survivin表达及其化疗敏感性的影响。方法:以非毒性剂量(10μmol/L)的姜黄素作用于A549/DDP细胞,采用RT-PCR和免疫组化SABC法分别检测Survivin mRNA和蛋白的表达,MTT法检测A549/DDP细胞对DDP的半效抑制浓度IC50、耐药指数和细胞生长抑制率,流式细胞术检测细胞凋亡率。结果:Cur能使A549/DDP细胞Survivin mRNA相对表达水平由(79.17±5.96)%下调至(57.8±9.8)%,P=0.014;而蛋白表达强度也由1.174±0.059降至1.009±0.072,P=0.023。A549/DDP细胞对DDP IC50及耐药指数分别由(206.77±9.19)μmol/L和10.90降低至(160.80±3.91)μmol/L和7.42,P值分别为0.041和0.035;细胞凋亡率由7.1%增至17.7%,Cur和DDP联合应用后凋亡率达40.61%,P=0.012。结论:Cur下调A549/DDP细胞Survivin表达,可能与部分解除Survivin导致的细胞凋亡抑制有关。     

重组人肿瘤坏死因子相关凋亡诱导配体蛋白(rhTRAIL) 逆转人肺腺癌细胞A549/ CDDP耐顺铂效应的初步研究

 目的 探讨重组人可溶性肿瘤坏死因子相关诱导配体蛋白(rhTRAIL)对人肺腺癌细胞A549／CDDP耐顺铂的逆转效应。方法 以顺铂(CDDP)联合不同浓度的rhTRAIL处理A549／CDDP，以四氮唑噻蓝盐(MTT)比色法检测顺铂的半效抑制浓度IC50并计算耐药逆转倍数RI。结果 rhTRAIL体外可明显降低A549／CDDP对CDDP的IC50提高耐药逆转倍数。结论 rhTRAIL体外可较大程度逆转A549／CDDP细胞对CDDP的耐药性，有望成为抗耐药性肺癌的一种新的生物制剂。     

Amorphigenin联合顺铂对人肺腺癌A549/DDP细胞的协同抗肿瘤作用

背景与目的 Amorphigenin是从紫穗槐属植物的种子中分离提取的鱼藤酮类化合物,研究发现amorphigenin对多种肿瘤细胞具有增殖抑制作用。本研究拟探讨amorphigenin对人肺腺癌耐顺铂细胞株A549/DDP的抗肿瘤作用及其可能的分子机制。方法采用CCK-8法测定A549/DDP细胞的增殖;克隆形成实验测定A549/DDP细胞的克隆形成;流式细胞术检测细胞的凋亡率;Western blot技术检测caspase-3、PARP和LRP蛋白的表达。结果Amorphigenin可抑制A549/DDP细胞的增殖48 h[半数抑制浓度（half maximal inhibitory concentra-tion, IC50）]为（2.19±0.92）μmol/L、抑制克隆形成及诱导细胞凋亡。此外,Amorphigenin与顺铂联合可协同地抑制A549/DDP细胞生长和促进凋亡;降低耐药蛋白LRP蛋白的表达。结论 Amorphigenin可抑制A549/DDP细胞增殖和促进细胞凋亡;amorphigenin可能是通过抑制耐药蛋白LRP蛋白表达,进而与顺铂对A549/DDP细胞产生协同抑制作用。     

氧化铁磁性纳米颗粒介导wt-p53基因对肺腺癌细胞增殖和凋亡的影响

目的：探讨氧化铁磁性纳米颗粒介导野生型p53基因（wild type p53,wt-p53）对耐顺铂人肺腺癌细胞A549/DDP增殖抑制和凋亡诱导的作用。方法：氧化铁磁性纳米颗粒介导wt-p53转染肺腺癌细胞A549/DDP作为实验组,以纳米颗粒介导空载体pcDNA3转染作为阴性对照组,脂质体介导wt-p53转染作阳性对照组。MTT法和绘制生长曲线观察基因转染对A549/DDP细胞增殖抑制作用,荧光显微镜、流式细胞术观察其对A549/DDP细胞诱导凋亡作用,RT-PCR检测其对A549/DDP细胞Bax mRNA表达的影响。结果：氧化铁磁性纳米颗粒介导wt-p53对人肺腺癌细胞A549/DDP增殖有持续的抑制作用,而以脂质体介导wt-p53对增殖抑制作用持续时间短暂;纳米颗粒介导wt-p53对人肺腺癌细胞A549/DDP诱导凋亡作用明显强于以脂质体载体;同时介导wt-p53上调Bax mRNA表达水平的作用也明显强于以脂质体载体。结论：氧化铁磁性纳米颗粒介导wt-p53转染对人肺腺癌细胞A549/DDP有持续的增殖抑制和诱导凋亡的作用。     

卡铂联合TRAIL对肺癌A549细胞增殖和凋亡的影响

目的:观察卡铂联合TNF相关凋亡诱导配体(TRAIL)对人肺腺癌细胞A549增殖和凋亡的影响。方法:经20、40、80 μg/mL卡铂和100 ng/μL TRAIL单用或联用处理后,用MTS法检测A549细胞的增殖能力,在光镜下观察细胞形态学变化;并采用流式细胞术检测细胞凋亡情况;RT-PCR和Western blot法检测死亡受体4(DR4)、死亡受体5(DR5)、Survivin和X连锁凋亡抑制蛋白基因(XIAP)mRNA与蛋白表达的变化。结果:卡铂和TRAIL单用或联用均可浓度依赖性抑制A549细胞的增殖,诱导其凋亡,两药联用比单用卡铂时抑制率和凋亡率更高(P<0.05)。单用卡铂或TRAIL可使A549细胞数减少,漂浮细胞增多,出现明显的凋亡形态变化,且明显降低Survivin和XIAP的mRNA和蛋白表达水平(P均<0.05);但对A549细胞DR4和DR5 mRNA表达均无明显影响,而单用卡铂或TRAIL却能升高A549细胞DR5蛋白的表达(P<0.05)。与单用组相比,TRAIL与卡铂联用A549细胞凋亡形态变化更明显,可明显降低A549细胞Survivin和XIAP mRNA和蛋白的表达水平及升高DR5蛋白表达水平(P<0.05)。结论:卡铂与TRAIL联用可协同抑制肺癌细胞A549细胞增殖,促进其凋亡,且与卡铂能够增加A549细胞DR5蛋白的表达和降低Survivin及XIAP的表达相关。     

曲古抑素A对耐顺铂人肺腺癌细胞株凋亡影响及其机制的探讨

目的:探讨曲古抑素A(TSA)诱导耐顺铂(DDP)人肺腺癌A549/DDP细胞株凋亡的作用及机制。方法:荧光染色检测细胞凋亡,蛋白质印迹法分析cFLIP、Caspase-8、Caspase-3和聚腺苷二磷酸核糖聚合酶(PARP)蛋白表达的变化,同时比色法测定Caspase-8活性。结果:曲古抑素A能诱导凋亡A549/DDP细胞株凋亡,随着浓度增加,其凋亡率逐渐增加。蛋白质印迹法结果显示,TSA处理细胞后,cFLIP蛋白水平下降,Pro-caspase-8减少,提示该酶被激活,促使Bid蛋白切割。Procaspase-3减少,提示酶被激活。PARP蛋白减少,切割的条带逐渐增加,提示PARP活性增加,促进细胞凋亡。比色法结果显示TSA对Caspase-8活性和cFLIP的影响具有浓度和时间依赖性。结论:TSA可以通过降低cFLIP水平激活Caspase-8诱导A549/DDP细胞凋亡。     

全反式维甲酸与顺铂联合对肺腺癌A549细胞株增殖与凋亡影响的观察

目的:体外观察全反式维甲酸(ATRA)联合顺铂(DDP)抑制肺腺癌细胞株A549增殖及诱导其凋亡的作用.方法:应用四甲基偶氮唑盐比色法(MTT)测定A549细胞生长抑制率,荧光定量RT-PCR法测定A549细胞维甲酸受体-β(RARβ)mRNA、血管内皮细胞生长因子(VEGF)mRNA的转录情况.结果:应用DDP(5、 10 和 50 mg/L)之后,与对照组相比,可以显著抑制A549细胞的增殖作用,且随着药物浓度的增加,其抑制作用增强,P＜0.05;ATRA+DDP联合用药组的细胞增殖抑制作用较单独应用DDP有更高的抑制强度,与DDP组相比,ATRA+DDP组增加了RARβ的表达,抑制了VEGF的表达,A549细胞的凋亡率增加,P＜0.05.结论:全反式维甲酸联合顺铂能更有效抑制A549细胞的增殖,增加非小细胞肺癌对顺铂化疗的敏感性.     

PDCD5蛋白联合顺铂对A549细胞凋亡影响研究

目的通过重组人程序性细胞死亡分子5(rhPDCD5)蛋白与顺铂单独或联合作用于肺腺癌A549细胞,探讨rhPDCD5联合顺铂对细胞凋亡的影响,并探讨其可能的作用机制。方法采用MTT法分别检测不同浓度的rhPDCD5蛋白(5、10、15和30mg/L)、不同浓度的顺铂(2.5、5、10、20和40mg/L)及20mg/L顺铂、15mg/L rhPDCD5蛋白单独/联合作用24h后对人肺腺癌A549细胞的增殖抑制率;采用流式细胞仪检测对照组、rhPDCCD5组(15mg/L)、顺铂组(20mg/L)及联合用药组细胞凋亡;蛋白质印迹法测检测各组间细胞中Caspase-3表达。结果 MTT结果显示,与对照组相比,不同浓度rhPDCD5蛋白作用于A549细胞,对细胞增殖抑制率的作用不明显,F=0.114,P=0.949;随着顺铂浓度的增高,抑制作用逐步增强,药物剂量与细胞增殖抑制率呈正相关,F=88.564,P<0.01;联合用药组较单药组细胞表现出更强的抑制作用,F=1 258.284,P<0.01。流式细胞仪检测结果显示,对照组凋亡率为(7.77±0.15)%,rhPDCD5组为(9.37±0.31)%,顺铂组为(23.13±0.35)%,rhPDCD5+顺铂组为(31.33±0.45)%,组间比较差异有统计学意义,F=3 458.747,P<0.01。蛋白质印迹法结果显示,单用rhPDCD5组较对照组cleaved Caspase-3表达上调不明显,顺铂组及联合用药组cleaved Caspase-3表达上调,且联合用药组表达上调最明显,F=92.734,P<0.01。结论 rhPDCD5蛋白单独应用对A549细胞的增殖及凋亡作用不明显;rhPDCD5蛋白可明显增加顺铂抑制A549细胞增殖、诱导细胞凋亡的作用,其机制可能是通过激活Caspase-3信号通路促进顺铂诱导A549细胞凋亡,增加顺铂的化疗敏感性,在治疗肺腺癌中联合用药可能会具有较大的应用潜力。     

Lovastatin sensitized human glioblastoma cells to TRAIL-induced apoptosis

Synergy study with chemotherapeutic agents is a common in vitro strategy in the search for effective cancer therapy. For non-chemotherapeutic agents, efficacious synergistic effects are uncommon. Here, we have examined two non-chemotherapeutic agents for synergistic effects: lovastatin and Tumor Necrosis Factor (TNF)-related apoptosis-inducing ligand (TRAIL) for synergistic effects; on three human malignant glioblastoma cell lines, M059K, M59J, and A172. Cells treated with lovastatin plus TRAIL for 48 h showed 50% apoptotic cell death, whereas TRAIL alone (1,000 ng/ml) did not, suggesting that lovastatin sensitized the glioblastoma cells to TRAIL attack. Cell cycle analysis indicated that lovastatin increased G₀–G₁ arrest in these cells. Annexin V study demonstrated that apoptosis was the predominant mode of cell death. We conclude that the combination of lovastatin and TRAIL enhances apoptosis synergistically. Moreover, lovastatin sensitized glioblastoma cells to TRAIL, suggesting a new strategy to treat glioblastoma.     

Intrinsic susceptibility to radiation-induced apoptosis of human lymphocyte subpopulations

PURPOSE: With the aim to evaluate intrinsic radiosensitivity, the susceptibility of lymphocyte subpopulations to radiation-induced apoptosis was determined. The investigated parameters included measurement reliability, phenotypic variance, intra- and inter-individual variability, and correlations between radiation-induced and spontaneous apoptosis. METHODS AND MATERIALS: Quiescent lymphocytes of 63 healthy volunteers, sampled up to four times over a 1-year period were gamma-irradiated in vitro. Subsequent apoptosis (annexin V) was measured for T4-, T8-, and B-lymphocyte subpopulations using 6-color flow cytometry. Spontaneous apoptosis was measured and radiosensitivity was quantified from the dose-effect curves. RESULTS: After thawing and short-term culture, both spontaneous apoptosis as well as radiation-induced apoptosis (radiosensitivity) differed among the three lymphocyte subpopulations, with T4 being most resistant, and B most sensitive. Spontaneous and radiation-induced apoptosis were correlated in all cell types, and variance between individuals was considerably higher than variance within individuals for both. A small but highly significant increase of both spontaneous and radiation-induced apoptosis was observed with age for T8, but not for T4 and B. Radiosensitivity of T8 and B proved to be sex-independent, whereas female T4 lymphocytes were less radiosensitive than those from males. T4 and T8 radiosensitivities were loosely correlated, and neither of them was related to B radiosensitivity. CONCLUSION: Tendency to spontaneous and radiation-induced apoptosis of lymphocyte subpopulations differs among individuals. In addition, depending on the cell types, age and sex are factors influencing these parameters.     

Bortezomib sensitizes primary human esthesioneuroblastoma cells to TRAIL-induced apoptosis

TNF-related apoptosis-inducing ligand (TRAIL), a promising novel anti-cancer cytokine of the TNF superfamily, and Bortezomib, the first-in-class clinically used proteasome inhibitor, alone or in combination have been shown to efficiently kill numerous tumor cell lines. However, data concerning primary human tumor cells are very rare. Using primary esthesioneuroblastoma cells we analyzed the anti-tumor potential and the mechanism employed by Bortezomib in combination with TRAIL for the treatment of this rare but aggressive tumor. Expression of components of the TRAIL pathway was analyzed in tumor specimens and isolated primary tumor cells at the protein level. Cells were treated with TRAIL, Bortezomib, and a combination thereof, and apoptosis induction was quantified. Clonogenicity assays were performed to elucidate the long-term effect of this treatment. Despite expressing all components of the TRAIL pathway, freshly isolated primary esthesioneuroblastoma cells were completely resistant to TRAIL-induced apoptosis. They could, however, be very efficiently sensitized by subtoxic doses of Bortezomib. The influence of Bortezomib on the TRAIL pathway was analyzed and showed upregulation of TRAIL death receptor expression, enhancement of the TRAIL death-inducing signaling complex (DISC), and downregulation of anti-apoptotic proteins of the TRAIL pathway. Of clinical relevance, TRAIL-resistant primary tumor cells could be repeatedly sensitized by Bortezomib, providing the basis for repeated clinical application schedules. This is the first report on the highly synergistic induction of apoptosis in primary esthesioneuroblastoma cells by Bortezomib and TRAIL. This combination, therefore, represents a promising novel therapeutic option for esthesioneuroblastoma.     

Heritability of susceptibility to ionizing radiation-induced apoptosis of human lymphocyte subpopulations

PURPOSE: To evaluate the heritability of intrinsic radiosensitivity, the induction of apoptosis in lymphocyte subpopulations was determined on samples from related individuals belonging to large kindred families. METHODS AND MATERIALS: Quiescent lymphocytes from 334 healthy individuals were gamma-irradiated in vitro. Apoptosis was determined 18 h after irradiation by eight-color flow cytometry. Radiosensitivity was quantified from dose-effect curves. Intrafamilial correlations and heritability were computed for 199 father-mother-offspring trios using the programs SOLAR (Sequential Oligogenic Linkage Analysis Routines) and SAGE (Statistical Analysis for Genetic Epidemiology). Segregation analyses were conducted using SAGE. RESULTS: Marked differential susceptibility of naive and memory T lymphocytes was demonstrated. Also, although age and gender were significant covariates, their effects only accounted for a minor part of the inter-individual variation. Parent-offspring and sib-sib correlations were significant for the radiosensitivity of B cells, T4, and T8 and of effector memory T4 and T8 subpopulations. In the T4-effector memory subpopulation, the phenotype showed correlations most consistent with dominant or additive genetic effects, and the results of the segregation analysis were consistent with the contribution of a bi-allelic dominant locus. CONCLUSIONS: Heritability was demonstrated for the susceptibility to ionizing radiation-induced apoptosis of lymphocyte populations, and the segregation of the T4-effector memory radiosensitivity phenotype was consistent with a simple mendelian transmission model involving one major gene.     

Securin depletion sensitizes human colon cancer cells to fisetin-induced apoptosis

Securin is highly-expressed in various tumors including those of the colon. In this study, the role of securin in the anticancer effects of fisetin on human colon cancer cells was investigated. Fisetin-induced apoptosis in HCT116 cells as indicated by TUNEL assay, Annexin V-FITC/PI double staining, Ser15-phosphorylation of p53, and cleavages of procaspase-3 and PARP. These effects were enhanced in HCT116 securin-null cells or in wild-type cells in which securin was knockdown by siRNA, but attenuated when wild-type or non-degradable securin was reconstituted. Moreover, fisetin did not induce apoptosis in HCT116 p53-null and HT-29 p53-mutant cells. Knockdown of securin in HCT116 p53-null cells potentiated fisetin-induced cytotoxicity by induction of apoptosis. Our results provide the first evidence to support that securin depletion sensitizes human colon cancer cells to fisetin-induced apoptosis.     

Leucine-rich protein 130 contributes to apoptosis resistance of human hepatocarcinoma cells

LRP130 is a ubiquitous protein involved in cellular homeostasis, microtubule alteration, and transactivation of a few multidrug resistance genes. Its role in resistance to apoptosis in HepG2 and HUH7 hepatocarcinoma cells was investigated. Using shRNA-producing lentiviruses to down-regulate the LRP130 gene, we showed that i) LRP130 did not affect the capacity of hepatocarcinoma cells to extrude drugs since LRP130 down-regulation was insufficient to significantly reduce P-glycoprotein production in these cells, and ii) the expression of 11 apoptosis-related genes measured by PCR-array was significantly reduced. Interestingly, six of these genes encode extrinsic pathway proapoptotic proteins whose expression was higher in LRP130-non producing than in LRP130-producing HepG2 cells. Fluorescence microscopy confirmed this new anti-apoptotic role of LRP130, which is strengthened by a significantly reduced cytochrome c oxidase activity in LRP130-down-regulated hepatocarcinoma cells.     

Ibulocydine sensitizes human cancers to radiotherapy by induction of mitochondria-mediated apoptosis

Background and purpose

Ibulocydine (IB), a novel prodrug of CDK inhibitor, has been reported to have anti-cancer effect in human hepatoma cells. In order to address its feasibility as a radiosensitizer to improve radiotherapeutic efficacy for human cancers, this study was designed.

Material and methods

Human cancer cells of lung and colon were treated with IB and/or radiotherapy (RT). The cellular effects were assessed by CCK-8, clonogenic, flow cytometric, and western blotting assays. In vivo radiotherapeutic efficacy was evaluated using the xenograft mouse model.

Results

Combined treatment of IB and RT significantly reduced viability and survival fraction of the cells. Apoptotic cell death accompanied with activation of caspases, decrease in Bcl-2/Bax expression, loss of mitochondrial membrane potential (MMP) leading to release of cytochrome c into cytosol was observed. Recovery of Bcl-2 expression level by introducing Bcl-2 expressing plasmid DNA compromised the loss of MMP and apoptosis induced by IB and RT. In vivo therapeutic efficacy of combined treatment was verified in the xenograft mouse model, in which tumor growth was markedly delayed by RT with IB.

Conclusions

IB demonstrated the property of sensitizing human cancer cells to RT by induction of mitochondria-mediated apoptosis, suggesting that IB deserves to be applied for chemoradiotherapy.     

Inhibition of apoptosis in human breast cancer as related to prognosis

Breast tumorigenesis proceeds through an accumulation of specific genetic alterations. Breast malignant transformation is dependent on not only the rate of cell production but also on apoptosis, a genetically programmed process of autonomous cell death. It may also be important in the overall growth dynamics of neoplastic cells, both in the natural history and when they are exposed to chemotherapy or radiation. This study evaluated the biological and clinical implications of spontaneous apoptosis in human breast cancer. Apoptosis was measured in 8 normal breast tissues and 91 human breast cancer samples by Apoptag end labeling method. We found there was a significant inhibition of spontaneous apoptosis in breast cancer cells compared with normal breast epithelium. In 91 breast cancer samples, apoptotic index (AI) was strongly associated with lymph node metastasis; Low apoptosis of tumor cells was more frequent in poorly differentiated tumors and has a poor outcome.     

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.     

Buthionine sulfoximine sensitizes antihormone-resistant human breast cancer cells to estrogen-induced apoptosis

Introduction  

Estrogen deprivation using aromatase inhibitors is one of the standard treatments for postmenopausal women with estrogen receptor (ER)-positive breast cancer. However, one of the consequences of prolonged estrogen suppression is acquired drug resistance. Our group is interested in studying antihormone resistance and has previously reported the development of an estrogen deprived human breast cancer cell line, MCF-7:5C, which undergoes apoptosis in the presence of estradiol. In contrast, another estrogen deprived cell line, MCF-7:2A, appears to have elevated levels of glutathione (GSH) and is resistant to estradiol-induced apoptosis. In the present study, we evaluated whether buthionine sulfoximine (BSO), a potent inhibitor of glutathione (GSH) synthesis, is capable of sensitizing antihormone resistant MCF-7:2A cells to estradiol-induced apoptosis.