Cleavage of Atg3 protein by caspase-8 regulates autophagy during receptor-activated cell death

PubMed ID: 22644571Autophagy is an evolutionarily conserved mechanism contributing to cell survival under stress conditions including nutrient and growth factor deprivation. Connections and cross-talk between cell death mechanisms and autophagy is under investigation. Here, we describe Atg3, an essential regulatory component of autophagosome biogenesis, as a new substrate of caspase-8 during receptormediated cell death. Both, tumor necrosis factor a and tumor necrosis factor-related apoptosis inducing ligand induced cell death was accompanied by Atg3 cleavage and this event was inhibited by a pan-caspase inhibitor (zVAD) or a caspase-8-specific inhibitor (zIETD). Indeed, caspase-8 overexpression led to Atg3 degradation and this event depended on caspase-8 enzymatic activity. Mutation of the caspase-8 cleavage site on Atg3 abolished its cleavage both in vitro and in vivo, demonstrating that Atg3 was a direct target of caspase-8. Autophagy was inactive during apoptosis and blockage of caspases or overexpression of a noncleavable Atg3 protein reestablished autophagic activity upon death receptor stimulation. In this system, autophagy was important for cell survival since inhibition of autophagy increased cell death. Therefore, Atg3 provides a novel link between apoptosis and autophagy during receptoractivated cell death. © Springer Science+Business Media, LLC 2012.1449 107T153Acknowledgments pcDNA-HA-caspase-8 and pcDNA3-caspase-8-C377S-HA (mutant caspase-8) plasmids were kindly provided by Nesrin Ozoren and Gabriel Nunez. This work was supported by The Scientific and Technological Research Council of Turkey (TUBI-TAK) 1001 grant (Project No. 107T153), EMBO Strategical Development and Installations Grant (EMBO-SDIG, Project No. 1449) and Sabanci University. D.G. is a recipient of Turkish Academy of Sciences (TUBA) GEBIP Award. O. O. and D. O. A. are recipients of TUBITAK-2218 postdoctoral scholarship. -