CAPRIN1 Is Required for Control of Viral Replication Complexes by Interferon Gamma.

Replication complexes (RCs), formed by positive-strand (+) RNA viruses through rearrangements of host endomembranes, protect their replicating RNA from host innate immune defenses. We have shown that two evolutionarily conserved defense systems, autophagy and interferon (IFN), target viral RCs and inhibit viral replication collaboratively. However, the mechanism by which autophagy proteins target viral RCs and the role of IFN-inducible GTPases in the disruption of RCs remains poorly understood. Here, using murine norovirus (MNV) as a model (+) RNA virus, we show that the guanylate binding protein 1 (GBP1) is the human GTPase responsible for inhibiting RCs. Furthermore, we found that ATG16L1 mediates the LC3 targeting of MNV RC by binding to WIPI2B and CAPRIN1, and that IFN gamma-mediated control of MNV replication was dependent on CAPRIN1. Collectively, this study identifies a novel mechanism for the autophagy machinery-mediated recognition and inhibition of viral RCs, a hallmark of (+) RNA virus replication. Replication complexes provide a microenvironment important for (+) RNA virus replication and shield it from host immune response. Previously we have shown that interferon gamma (IFNG) disrupts the RC of MNV via evolutionarily conserved autophagy proteins and IFN-inducible GTPases. Elucidating the mechanism of targeting of viral RC by ATG16L1 and IFN-induced GTPase will pave the way for development of therapeutics targeting the viral replication complexes. Here, we have identified GBP1 as the sole GBP targeting viral RC and uncovered the novel role of CAPRIN1 in recruiting ATG16L1 to the viral RC.