Department of Pharmacology and Chemical Biology, University of Pittsburgh Cancer Institute, University of Pittsburgh, Pittsburgh, Pennsylvania 15213, USA.
Cancer Res. 2011 May 15;71(10):3625-34. doi: 10.1158/0008-5472.CAN-10-4475. Epub 2011 Mar 28.
Autophagy is an evolutionarily conserved stress response mechanism that often occurs in apoptosis-defective cancer cells and can protect against cell death. In this study, we investigated how apoptosis and autophagy affect each other in cancer cells in response to chemotherapeutic treatment. We found that specific ablation of the proapoptotic function of cytochrome c, a key regulator of mitochondria-mediated apoptosis, enhanced autophagy following chemotherapeutic treatment. Induction of autophagy required Beclin 1 and was associated with blockage of Beclin 1 cleavage by caspase 8 at two sites. To investigate the role of Beclin 1 cleavage in the suppression of autophagy and cell survival, a caspase-resistant mutant of Beclin 1 was knocked into HCT116 colon cancer cells. Beclin 1 mutant knockin resulted in markedly increased autophagy and improved long-term cell survival after chemotherapeutic treatment but without affecting apoptosis and caspase activation. Furthermore, Beclin 1 mutant tumors were significantly less responsive to chemotherapeutic treatment than were wild-type tumors. These results show that chemotherapy-induced apoptosis inhibits autophagy at the execution stage subsequent to cytochrome c release through caspase 8-mediated cleavage of Beclin 1. If apoptosis fails to execute, autophagy is unleashed due to lack of Beclin 1 cleavage by caspases and can contribute to cancer cell survival and therapeutic resistance. Therefore, Beclin 1 may be a useful target for inhibiting autophagy to sensitize chemotherapy.
自噬是一种进化上保守的应激反应机制，通常发生在凋亡缺陷的癌细胞中，可以防止细胞死亡。在这项研究中，我们研究了在化疗治疗下，凋亡和自噬如何在癌细胞中相互影响。我们发现，细胞色素 c（线粒体介导的凋亡的关键调节剂）的促凋亡功能的特异性缺失增强了化疗后的自噬。自噬的诱导需要 Beclin 1，并且与 caspase 8 在两个位点对 Beclin 1 切割的阻断有关。为了研究 Beclin 1 切割在抑制自噬和细胞存活中的作用，将 Beclin 1 的一种 caspase 抗性突变体敲入到 HCT116 结肠癌细胞中。Beclin 1 突变体的敲入导致自噬明显增加，并在化疗后长期细胞存活得到改善，但不影响凋亡和 caspase 激活。此外，Beclin 1 突变体肿瘤对化疗的反应明显低于野生型肿瘤。这些结果表明，化疗诱导的凋亡通过 caspase 8 介导的 Beclin 1 切割抑制细胞色素 c 释放后执行阶段的自噬。如果凋亡未能执行，则由于缺乏 caspase 对 Beclin 1 的切割，自噬被释放，并有助于癌细胞的存活和治疗抵抗。因此，Beclin 1 可能是一个有用的靶点，通过抑制自噬来增强化疗的敏感性。
