Abstract
The hepatitis C virus (HCV) nonstructural (NS) protein 5A is a multifunctional protein that plays a central role in viral replication and assembly. Antiviral agents directly targeting NS5A are currently in clinical development. Although the elucidation of the mechanism of action (MOA) of NS5A inhibitors has been the focus of intensive research, a detailed understanding of how these agents exert their antiviral effect is still lacking. In this study, we observed that the downregulation of NS5A hyperphosphorylation is associated with the actions of NS5A inhibitors belonging to different chemotypes. NS5A is known to recruit the lipid kinase phosphatidylinositol 4-kinase IIIα (PI4KIIIα) to the HCV-induced membranous web in order to generate phosphatidylinositol 4-phosphate (PI4P) at the sites of replication. We demonstrate that treatment with NS5A inhibitors leads to an impairment in the NS5A-PI4KIIIα complex formation that is paralleled by a significant reduction in PI4P and cholesterol levels within the endomembrane structures of HCV-replicating cells. A similar decrease in PI4P and cholesterol levels was also obtained upon treatment with a PI4KIIIα-targeting inhibitor. In addition, both the NS5A and PI4KIIIα classes of inhibitors induced similar subcellular relocalization of the NS5A protein, causing the formation of large cytoplasmic NS5A-containing clusters previously reported to be one of the hallmarks of inhibition of the action of PI4KIIIα. Because of the similarities between the effects induced by treatment with PI4KIIIα or NS5A inhibitors and the observation that agents targeting NS5A impair NS5A-PI4KIIIα complex formation, we speculate that NS5A inhibitors act by interfering with the function of the NS5A-PI4KIIIα complex.