A host cell RNA-binding protein, Staufen1, has a role in hepatitis C virus replication before virus assembly.

Staufen1 is a dsRNA-binding protein involved in the regulation of translation and the trafficking and degradation of cellular RNAs. Staufen1 has also been shown to stimulate translation of human immunodeficiency virus type 1 (HIV-1) RNA, regulate HIV-1 and influenza A virus assembly, and there is also indication that it can interact with hepatitis C virus (HCV) RNA. To investigate the role of Staufen1 in the HCV replication cycle, the effects of small interfering RNA knockout of Staufen1 on HCV strain JFH-1 replication and the intracellular distribution of the Staufen1 protein during HCV infection were examined. Silencing Staufen1 in HCV-infected Huh7 cells reduced virus secretion by around 70 %, intracellular HCV RNA levels by around 40 %, and core and NS3 proteins by around 95 and 45 %, respectively. Staufen1 appeared to be predominantly localized in the endoplasmic reticulum at the nuclear periphery in both uninfected and HCV-infected Huh7 cells. However, Staufen1 showed significant co-localization with NS3 and dsRNA, indicating that it may bind to replicating HCV RNA that is associated with the non-structural proteins. Staufen1 and HCV core protein localized very closely to one another during infection, but did not appear to overlap, indicating that Staufen1 may not bind to core protein or localize to the core-coated lipid droplets, suggesting that it may not be directly involved in HCV virus assembly. These findings indicate that Staufen1 is an important factor in HCV replication and that it might play a role early in the HCV replication cycle, e.g. in translation, replication or trafficking of the HCV genome, rather than in virion morphogenesis.