Activation of the c-Jun NH2-terminal kinase pathway by coronavirus infectious bronchitis virus promotes apoptosis independently of c-Jun

Mitogen-activated protein kinases (MAPKs) are conserved protein kinases that regulate a variety of important cellular signaling pathways. Among them, c-Jun N-terminal kinases (JNK) are known to be activated by various environmental stresses including virus infections. Previously, activation of the JNK pathway has been detected in cells infected with several coronaviruses. However, detailed characterization of the pathway as well as its implication in host-virus interactions has not been fully investigated. Here we report that the JNK pathway was activated in cells infected with the avian coronavirus infectious bronchitis virus (IBV). Of the two known upstream MAPK kinases (MKK), MKK7, but not MKK4, was shown to be responsible for IBV-induced JNK activation. Moreover, knockdown and overexpression experiments demonstrated that JNK served as a pro-apoptotic protein during IBV infection. Interestingly, pro-apoptotic activity of JNK was not mediated via c-Jun, but involved modulation of the anti-apoptotic protein B-cell lymphoma 2 (Bcl2). Taken together, JNK constitutes an important aspect of coronavirus-host interaction, along with other MAPKs.