Atg5 is required for adenovirus-induced autophagy in cancer cells

3357

Pathogen infection induces autophagy in eukaryotic cells. In the case of viruses, autophagy is a double-edged sword that can either facilitate or impede replication. On one hand, autophagy reduces the replication capability of the herpes viruses. On the other hand, the RNA virus poliovirus uses autophagosomes to form replication complexes. Recently we characterized the autophagy induced by the oncolytic adenovirus Delta-24-RGD in brain tumor stem cells. In this study we showed infection of glioma cells with replication deficient adenoviral vectors did not trigger autophagy, showing that infection is necessary but not sufficient for adenoviral-induced autophagy. Our data revealed that autophagy inducers, such as rapamycin and LY294,002, works together with the virus to enhance autophagy as analyzed by acridine orange staining of the acidic vacuoles. Importantly, treatment with rapamycin did not modify Delta-24-RGD replication significantly. Taken together these observations indicate that autophagy does not compromise adenovirus replication. However, autophagy inhibitors, such as 3-Methyladenine, inhibit autophagy and, when used together with adenoviruses, significantly impairs adenoviral replication as assessed by measuring viral titers. Importantly a series of E1A and E1B replication competent adenoviruses induced consistently more autophagy in U-87 MG cells, with high basal levels of ATG5, than in U-251 MG cells expressing low levels of ATG5. Notably, infection of ATG5 -/- MEFS resulted in a significant decrease of autophagy. Our data indicate that autophagy is in the pathway of adenoviral replication and place Atg5 as a required event for the induction of autophagy. These results are relevant for the understanding of the molecular events controlling autophagy in cancer cells and may favor the development of novel therapeutic tools, including oncolytic adenoviruses, targeting autophagy in apoptosis-resistant cells.