Department of Anatomy and Cell Biology and Mitochondria Hub Regulation Center, College of Medicine, Dong-A University, Busan, Republic of Korea.
Int J Oncol. 2012 Oct;41(4):1443-54. doi: 10.3892/ijo.2012.1585. Epub 2012 Aug 7.
The Bcl-2 protein is known to exert not only anti-apoptotic but also anti-autophagic activities. Numerous studies have demonstrated that etoposide, which is one of the most widely used cancer chemotherapy agents, induces apoptotic cell death. However, the exact molecular mechanism leading to cell death by etoposide remains to be resolved. This study aimed to dissect the mode of cell death induced by etoposide in Hep3B hepatoma cells. Furthermore, this study was conducted to examine whether etoposide overcomes the resistance conferred by Bcl-2 in Hep3B hepatoma cells. We observed that Hep3B cells treated with etoposide show not only apoptotic but autophagic phenotypes. Autophagy inhibition by 3-methyladenine (3MA) and caspase inhibition by zVAD-fmk effectively decreased autophagic and apoptotic phenotypes, respectively. However, either zVAD-fmk or 3MA only partially prevented cell death. These data indicate that etoposide concomitantly induces autophagic cell death and apoptosis in Hep3B cells. Importantly, etoposide can effectively induce cell death in Bcl-2-overexpressing Hep3B cells. Conversely, staurosporine, which exclusively induces apoptosis in Hep3B cells, did not efficiently induce cell death in Bcl‑2‑overexpressing Hep3B cells. Staurosporine-treated Hep3B cells also showed an autophagic phenotype. While autophagy is cell death-inducing in Hep3B cells treated with etoposide, it is cytoprotective in Hep3B cells treated with staurosporine. To this end, we observed that etoposide-induced mixed type of programmed cell death is associated with the dissociation of Bcl-2 from Beclin-1. Taken together, etoposide induces a mixed type of programmed cell death and overcomes the resistance conferred by Bcl-2 in Hep3B hepatoma cells.
Bcl-2 蛋白不仅具有抗细胞凋亡作用，还具有抗细胞自噬作用。大量研究表明，依托泊苷是最广泛使用的癌症化疗药物之一，可诱导细胞凋亡。然而，依托泊苷导致细胞死亡的确切分子机制仍有待解决。本研究旨在剖析依托泊苷诱导 Hep3B 肝癌细胞死亡的方式。此外，本研究还旨在研究依托泊苷是否能克服 Hep3B 肝癌细胞中 Bcl-2 带来的耐药性。我们观察到，用依托泊苷处理的 Hep3B 细胞不仅表现出凋亡表型，还表现出自噬表型。用 3-甲基腺嘌呤（3MA）抑制自噬和用 zVAD-fmk 抑制半胱天冬酶可分别有效减少自噬和凋亡表型。然而，zVAD-fmk 或 3MA 只能部分阻止细胞死亡。这些数据表明，依托泊苷可同时诱导 Hep3B 细胞发生自噬性细胞死亡和凋亡。重要的是，依托泊苷能有效诱导过表达 Bcl-2 的 Hep3B 细胞发生细胞死亡。相反，只在 Hep3B 细胞中诱导凋亡的 staurosporine 不能有效诱导过表达 Bcl-2 的 Hep3B 细胞发生细胞死亡。staurosporine 处理的 Hep3B 细胞也表现出自噬表型。虽然自噬在依托泊苷处理的 Hep3B 细胞中是细胞死亡诱导因素，但在 staurosporine 处理的 Hep3B 细胞中却是细胞保护因素。为此，我们观察到，依托泊苷诱导的混合性程序性细胞死亡与 Bcl-2 从 Beclin-1 上解离有关。总之，依托泊苷诱导混合性程序性细胞死亡，并克服了 Hep3B 肝癌细胞中 Bcl-2 带来的耐药性。
