Chapter 9 - Suppression of Innate Antiviral Immunity after Hepatitis C Virus Infection: Role of the Unfolded Protein Response and Autophagy

Abstract

Autophagy, a conserved “self-eating” process aimed at maintaining cellular homeostasis, has diverse functions in host–pathogen interactions. Many viruses, including hepatitis C virus (HCV), have evolved strategies to subvert the host autophagic machinery and enhance their own replication. Nevertheless, the underlying mechanism for the role of autophagy in HCV replication and whether autophagy modulates the innate immunity in HCV infection are still poorly understood. In a recent study, we showed that infection of hepatoma Huh7 cells with cell culture-derived HCVcc perturbs the autophagy pathway, which proceeds to fusion of the autophagosome with a lysosome, through the unfolded protein response (UPR), to promote HCV RNA replication. Deregulation of the UPR and autophagy by gene silencing or interference with complete autolysosome formation with inhibitors such as chloroquine and Bafilomycin A1 impeded HCV RNA replication. Interruption of the UPR and autophagy concurred with upregulation of the HCV pathogen-associated molecular pattern (PAMP) RNA-mediated cytoplasmic retinoic acid-inducible gene-I signaling and interferon beta (IFN-β)-mediated antiviral responses. With the battery of UPR and autophagy inducers, we demonstrated that activated UPR–autophagy signaling downregulates HCV PAMP RNA-mediated innate immunity even in a context without HCV infection. Moreover, disruption of the autophagic flux by chloroquine or individual knockdown of lysosome-associated membrane protein 2 and RAS-related GTP-binding protein 7, which are critical for fusion of autophagosomes with lysosomes, mitigated UPR- and autophagy-mediated suppression of innate antiviral immunity. Our results manifest that the UPR and autophagy machinery acts as a negative regulator in innate immunity, thus stimulating HCV replication. Our study will also benefit the development of efficacious anti-HCV therapeutic and intervention approaches targeting and/or modifying the UPR and autophagy signaling pathway.