Abstract 2913: Autophagy resulting from specific ablation of the proapoptotic function of cytochrome c

Apoptosis and autophagy are two evolutionarily conserved and sometimes mutually exclusive cell death regulatory mechanisms. The balance and cross talk between these two processes determine cell fate and have an important role in therapeutic response to anticancer agents. It has been shown that apoptosis can cross talk with autophagy through the actions of the Bcl-2 family proteins. For example, Bcl-2 inhibits autophagy by interacting with Beclin-1, the master regulator of autophagy. However, the underlying mechanisms by which apoptosis and autophagy regulate each other remain unclear. In this study, we investigated whether cytochrome c (cyto c), a critical regulator of the mitochondrial apoptotic pathway, is involved in regulating autophagy. A cyto c mutant (K72A) that retains its normal electron transfer function but fails to bind to Apaf-1 was knocked into HCT116 colorectal cancer cells by homologous recombination. Although the mutant cyto c can still be released from the mitochondria into the cytosol in response to apoptosis induction, caspase activation and other execution steps of apoptosis were inhibited. Remarkably, a significant increase in autophagy was observed in the cyto c-knockin cells, as indicated by formation of GFP-LC3 puncta and increased conversion of LC3-I into LC3-II. Furthermore, knockdown of Beclin-1 by siRNA suppressed autophagy in the cyto c-knockin cells. These results indicate that the execution steps of apoptosis downstream of cytochrome c release, including formation of apoptosome and activation of caspases, can inhibit autophagy. Autophagy can be unleashed when apoptosis is initiated, but fails to be executed. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2913.