Ribonucleotide reductase M2 promotes RNA replication of hepatitis C virus by protecting NS5B protein from hPLIC1-dependent proteasomal degradation

Hepatitis C virus (HCV) establishes a chronic infection that can lead to cirrhosis and hepatocellular carcinoma. The HCV life cycle is closely associated with host factors that promote or restrict viral replication, the characterization of which could help to identify potential therapeutic targets. To this end, here we performed a genome-wide microarray analysis and identified ribonucleotide reductase M2 (RRM2) as a cellular factor essential for HCV replication. We found that RRM2 is up-regulated in response to HCV infection in quiescent hepatocytes from humanized chimeric mouse livers. To elucidate the molecular basis of RRM2 expression in HCV-infected cells, we used HCV-infected hepatocytes from chimeric mice and hepatoma cells infected with the HCV strain JFH1. Both models exhibited increased RRM2 mRNA and protein expression levels. Moreover, siRNA-mediated silencing of RRM2 suppressed HCV replication and infection. Of note, RRM2 and RNA polymerase nonstructural protein 5B (NS5B) partially co-localized in cells and co-immunoprecipitated, suggesting that they might interact. RRM2 knockdown reduced NS5B expression, which depended on the protein degradation pathway, as NS5B RNA levels did not decrease and NS5B protein stability correlated with RRM2 protein levels. We also found that RRM2 silencing decreased levels of hPLIC1 (human homolog 1 of protein linking integrin-associated protein and cytoskeleton), a ubiquitin-like protein that interacts with NS5B and promotes its degradation. This finding suggests that there is a dynamic interplay between RRM2 and the NS5B–hPLIC1 complex that has an important function in HCV replication. Together, these results identify a role of host RRM2 in viral RNA replication.