Guanylate-binding protein 1 acts as a pro-viral factor for the life cycle of hepatitis C virus

Viral infections trigger the expression of interferons (IFNs) and interferon stimulated genes (ISGs), which are crucial to modulate an antiviral response. The human guanylate binding protein 1 (GBP1) is an ISG and exhibits antiviral activity against several viruses. In a previous study, GBP1 was described to impair replication of the hepatitis C virus (HCV). However, the impact of GBP1 on the HCV life cycle is still enigmatic.To monitor the expression and subcellular distribution of GBP1 and HCV we performed qPCR, Western blot, CLSM and STED microscopy, virus titration and reporter gene assays.In contrast to previous reports, we observed that HCV induces the expression of GBP1. Further, to induce GBP1 expression, the cells were stimulated with IFN gamma. GBP1 modulation was achieved either by overexpression of GBP1-Wt or by siRNA-mediated knockdown. Silencing of GBP1 impaired the release of viral particles and resulted in intracellular HCV core accumulation, while overexpression of GBP1 favored viral replication and release. CLSM and STED analyses revealed a vesicular distribution of GBP1 in the perinuclear region. Here, it colocalizes with HCV core around lipid droplets, where it acts as assembly platform and thereby favors HCV morphogenesis and release.Collectively, our results identify an unprecedented function of GBP1 as a pro-viral factor. As such, it is essential for viral assembly and release acting through tethering factors involved in HCV morphogenesis onto the surface of lipid droplets. Morphogenesis and release of the hepatitis C virus (HCV) are still not fully understood. Here we describe a novel so far unprecedented pro-viral function of the interferon stimulated gene (ISG) human guanylate binding protein 1 (GBP1). In contrast to the supposed antiviral effect, we observe that GBP1 favors morphogenesis and release of HCV by acting as an assembly platform on the surface of lipid droplets. This extends our knowledge about the functions of GBP1 and the life cycle of HCV and should be considered for curative approaches targeting innate immunity.