Lee Yong J, Song Jae J, Kim Jin H, Kim Hyeong-Reh Choi, Song Young K
Department of Surgery and Cancer Institute, School of Medicine, University of Pittsburgh, PA 15213, USA.
Exp Cell Res. 2004 Feb 1;293(1):129-43. doi: 10.1016/j.yexcr.2003.09.015.
Tumor necrosis factor-related apoptosis inducing ligand (TRAIL/APO-2L), a member of the tumor necrosis factor (TNF) gene family, is considered as one of the most promising cancer therapeutic agents due to its ability to selectively kill tumor cells. Although microenvironments of solid tumors (hypoxia, nutrient deprivation, and low pH) often affect the effectiveness of chemotherapy, few studies have been reported on the relationship between tumor microenvironments and TRAIL. In this study, we investigated whether low extracellular pH affects TRAIL-induced apoptotic death. When human prostate carcinoma DU145 cells were treated with 200 ng/ml His-tagged TRAIL for 4 h, the survival was approximately 10% at pH 6.3-6.6 and 61.3% at pH 7.4. Similar results were observed in human colorectal carcinoma CX-1 cell line. The TRAIL-mediated activation of caspase, cytochrome c release, and poly (ADP-ribose) polymerase (PARP) cleavage was promoted at low extracellular pH. Immunoprecipitation followed by western blot analysis shows that low extracellular pH enhances the association of truncated Bid with Bax during treatment with TRAIL. Western blot analysis also shows that the low extracellular pH-enhanced TRAIL cytotoxicity does not involve modulation of the levels of TRAIL receptors (DR4, DR5, and DcR2), FLIP, inhibitor of apoptosis (IAP), and Bcl-2. Overexpression of Bcl-2 effectively prevented low extracellular pH-augmented TRAIL cytotoxicity. Taken together, we propose that TRAIL-mediated cytotoxicity is greatly enhanced in low pH environments by promoting caspase activation.
肿瘤坏死因子相关凋亡诱导配体（TRAIL/APO-2L）是肿瘤坏死因子（TNF）基因家族的成员之一，因其能够选择性杀死肿瘤细胞而被认为是最有前景的癌症治疗药物之一。尽管实体瘤的微环境（缺氧、营养剥夺和低pH值）常常影响化疗效果，但关于肿瘤微环境与TRAIL之间关系的研究报道较少。在本研究中，我们调查了低细胞外pH值是否会影响TRAIL诱导的凋亡死亡。当用人前列腺癌DU145细胞用200 ng/ml的His标签TRAIL处理4小时时，在pH 6.3 - 6.6时细胞存活率约为10%，在pH 7.4时为61.3%。在人结肠直肠癌CX-1细胞系中也观察到了类似结果。在低细胞外pH值下，TRAIL介导的半胱天冬酶激活、细胞色素c释放和聚（ADP-核糖）聚合酶（PARP）裂解得到促进。免疫沉淀后进行蛋白质印迹分析表明，低细胞外pH值增强了TRAIL处理期间截短的Bid与Bax的结合。蛋白质印迹分析还表明，低细胞外pH值增强的TRAIL细胞毒性不涉及TRAIL受体（DR4、DR5和DcR2）、FLIP、凋亡抑制蛋白（IAP）和Bcl-2水平的调节。Bcl-2的过表达有效地阻止了低细胞外pH值增强的TRAIL细胞毒性。综上所述，我们提出在低pH环境中，通过促进半胱天冬酶激活，TRAIL介导的细胞毒性会大大增强。
