Activation Of PI3K/Akt Pathway Limits JNK-mediated Apoptosis During EV71 Infection

Enterovirus 71(EV71) is one of the most important pathogens causing emerging infectious disease in humans and representing a major public health concern, particularly in the Asia-Pacific region. EV71 is a single, positive-stranded RNA virus that belongs to the Enterovirus genus of the Picornaviridae Family. During infection, the 7.4-kb genome of EV71 encodes a single polyprotein that is proteolytically cleaved into four structural proteins(VP1, VP2, VP3 and VP4) and seven nonstructural proteins(2A, 2B, 2C, 3A, 3B, 3C and 3D). Apoptosis is frequently induced to inhibit virus replication during infection of Enterovirus 71(EV71). On the contrary, anti-apoptotic pathway, such as PI3K/Akt pathway, is simultaneously exploited by EV71 to accomplish the viral life cycle. The relationship that EV71-induced apoptosis and PI3K/Akt signaling pathway remains to be elucidated.In this study, we demonstrated that EV71 infection altered Bax conformation and triggered its redistribution from the cytosol to mitochondria in RD cells. Subsequently, cytochrome c was released from mitochondria to cytosol. We also found that c-Jun NH2-terminal kinase(JNK) was activated during EV71 infection. The JNK specific inhibitor significantly inhibited Bax activation and cytochrome c release, suggesting that EV71-induced apoptosis was involved into a JNK-dependent manner. Meanwhile, EV71-induced Akt phosphorylation involved a PI3K-dependent mechanism. Inhibition of the PI3K/Akt pathway enhanced JNK phosphorylation and the JNK-mediated apoptosis upon EV71 infection. Moreover, PI3K/Akt pathway phosphorylated apoptosis signal-regulating kinase 1(ASK1) and negatively regulated the ASK1 activity. Knockdown of ASK1 significantly decreased JNK phosphorylation, which implied that ASK1 phosphorylation by Akt inhibited ASK1-mediated JNK activation. Collectively, these data reveal that activation of the PI3K/Akt pathway limits JNK-mediated apoptosis by phosphorylating and inactivating ASK1 during EV71 infection.In summary, this study found that EV71 infection activates the PI3K/Akt signal pathway and JNK signal pathway at the early stage of infection. At the same time, activated Akt phospholates the ASK1 to down-regulat the kinase activity as the infetion proceeding. The release of cytochrome c from mitochondria to cytosol is inhibited and the tralocation of Bax protein from cytosol to mitochondria is blocked. Evently, the earyl apoptosis of EV71-infected cells was significantly inhibited. These results suggest that the activation of early PI3K/Akt survival pathway suppresses EV71-induced JNK activation and JNK-mediated apo-ptosis through phosphorylation of ASK1 in RD cells.