Synergetic Contributions of Viral VP1, VP3, and 3C to Activation of the AKT-AMPK-MAPK-MTOR Signaling Pathway for Seneca Valley Virus-Induced Autophagy.

Seneca Valley virus (SVV), a member of the Picornaviridae family, can activate autophagy via the PERK and ATF6 unfolded protein response pathways and facilitate viral replication; however, the precise molecular mechanism that regulates SVV-induced autophagy remains unclear. Here, we revealed that SVV infection inhibited the phosphorylation of mechanistic target of rapamycin kinase (MTOR) and activated phosphorylation of the serine/threonine kinase AKT. We observed that activating AMP-activated protein kinase (AMPK), extracellular signal-regulated kinase (ERK), mitogen-activated protein kinase (MAPK), and p38 MAPK signaling by SVV infection promoted autophagy induction and viral replication; additionally, the SVV-induced autophagy was independent of the ULK1 complex. We further evaluated the role of viral protein(s) in the AKT-AMPK-MAPK-MTOR pathway during SVV-induced autophagy and found that VP1 induced autophagy, as evidenced by puncta colocalization with microtubule-associated protein 1 light chain 3 (LC3) in the cytoplasm and enhanced LC3-II levels. This might be associated with the interaction of VP1 with sequestosome 1 and promoting its degradation. In addition, the expression of VP1 enhanced AKT phosphorylation and AMPK phosphorylation, while MTOR phosphorylation was inhibited. These results indicate that VP1 induces autophagy by the AKT-AMPK-MTOR pathway. Additionally, expression of VP3 and 3C was found to activate autophagy induction via the ERK1/2 MAPK-MTOR and p38 MAPK-MTOR pathway. Taken together, our data suggest that SVV-induced autophagy has finely tuned molecular mechanisms in which VP1, VP3, and 3C contribute synergistically to the AKT-AMPK-MAPK-MTOR pathway. IMPORTANCE Autophagy is an essential cellular catabolic process to sustain normal physiological processes that are modulated by a variety of signaling pathways. Invading virus is a stimulus to induce autophagy that regulates viral replication. It has been demonstrated that Seneca Valley virus (SVV) induced autophagy via the PERK and ATF6 unfolded protein response pathways. However, the precise signaling pathway involved in autophagy is still poorly understood. In this study, our results demonstrated that viral proteins VP1, VP3, and 3C contribute synergistically to activation of the AKT-AMPK-MAPK-MTOR signaling pathway for SVV-induced autophagy. These findings reveal systemically the finely tuned molecular mechanism of SVV-induced autophagy, thereby facilitating deeper insight into the development of potential control strategies against SVV infection.