Human adenovirus type 5 induces cell lysis through autophagy and autophagy-triggered caspase activity

Oncolytic adenoviruses, such as Delta-24-RGD, are promising therapies for patients with brain tumor. Clinical trials have shown that the potency of these cancer-selective adenoviruses should be increased to optimize therapeutic efficacy. One potential strategy is to increase the efficiency of adenovirus-induced cell lysis, a mechanism that has not been clearly described. In this study, for the first time, we report that autophagy plays a role in adenovirus-induced cell lysis. At the late stage after adenovirus infection, numerous autophagic vacuoles accompany the disruption of cellular structure, leading to cell lysis. The virus induces a complete autophagic process from autophagosome initiation to its turnover through fusion with the lysosome although the formation of the autophagosome is sufficient for virally induced cell lysis. Importantly, downmodulation of autophagy genes (ATG5 or ATG10) rescues the infected cells from being lysed by the virus. Moreover, autophagy triggers caspase activity via the extrinsic FADD/caspase 8 pathway, which also contributes to adenovirus-mediated cell lysis. Therefore, our study implicates autophagy and caspase activation as part of the mechanism for cell lysis induced by adenovirus and suggests that manipulation of the process is a potential strategy to optimize clinical efficacy of oncolytic adenoviruses.