Hepatitis C virus non-structural proteins modulate cellular kinases for increased cytoplasmic abundance of host factor HuR and facilitate viral replication

Host protein HuR translocation from nucleus to cytoplasm following infection is crucial for the life cycle of several RNA viruses including hepatitis C virus (HCV), a major causative agent of hepatocellular carcinoma. HuR assists the assembly of replication-complex on the viral-3 & PRIME;UTR, and its depletion hampers viral replication. Although cytoplasmic HuR is crucial for HCV replication, little is known about how the virus orchestrates the mobilization of HuR into the cytoplasm from the nucleus. We show that two viral proteins, NS3 and NS5A, act co-ordinately to alter the equilibrium of the nucleo-cytoplasmic movement of HuR. NS3 activates protein kinase C (PKC)-& delta;, which in-turn phosphorylates HuR on S318 residue, triggering its export to the cytoplasm. NS5A inactivates AMP-activated kinase (AMPK) resulting in diminished nuclear import of HuR through blockade of AMPK-mediated phosphorylation and acetylation of importin-& alpha;1. Cytoplasmic retention or entry of HuR can be reversed by an AMPK activator or a PKC-& delta; inhibitor. Our findings suggest that efforts should be made to develop inhibitors of PKC-& delta; and activators of AMPK, either separately or in combination, to inhibit HCV infection. Author summaryHepatitis C virus is a major human pathogen, which exploits cellular machinery for its propagation in liver cells. The cytoplasmic availability of cellular components is crucial for their direct influence on processes involving the viral RNA, which lacks any nuclear history. Our results establish the involvement of viral proteins, NS3 and NS5A in achieving increased cytoplasmic abundance of a host factor HuR, an RNA binding protein (RBP) critical for HCV replication. This is achieved via direct post-translational modification of HuR and indirect regulation of its nuclear carrier by coercing two host kinases, PKC-& delta; and AMPK-& alpha;. RBPs are emerging as novel targetable candidates for gene regulation. Similar studies with other RBPs and targeting protein modifications, in place of whole protein knockdown, could usher in a revolutionary strategy to neutralize emerging RNA virus-based diseases, while preserving their cellular functions.