RNase L Triggers Autophagy in Response to Viral Infections

Abstract

Autophagy is a programmed homeostatic response to diverse types of cellular stress that disposes of long-lived proteins, organelles, and invading microbes within double-membraned structures called autophagosomes. The 2=,5=-oligoadenylate/ RNase L system is a virus-activated host RNase pathway that disposes of or processes viral and cellular single-stranded RNAs. Here we report that activation of RNase L during viral infections induces autophagy. Accordingly, infections with encephalomyocarditis virus or vesicular stomatitis virus led to higher levels of autophagy in wild-type mouse embryonic fibroblasts (MEF) than in RNase L-null MEF. Similarly, direct activation of RNase L with a 2=,5=-oligoadenylate resulted in p62(SQSTM1) degradation, LC3BI/LC3BII conversion, and appearance of autophagosomes. To determine the effect of RNase L-mediated autophagy on viral replication, we compared viral yields in wild A utophagy (or "self-eating") is an essential and ancient cellular process for degrading and recycling components of longlived proteins, organelles, and microbial invaders (7,22). These materials are sequestered in the cytoplasm within double-membrane vesicles termed autophagosomes that fuse with lysosomes, causing the contents to be degraded. While autophagy is often induced in response to viral infections, the impact of autophagy on pathogenesis and virus replication can be unpredictable. For instance, intracerebral injection of Sindbis virus in mice induced autophagy, causing degradation of viral proteins while promoting viral clearance and protecting against virus-mediated neuronal cell death (32). However, while animal survival was enhanced by autophagy there was no effect on virus replication. There is also a complex, reciprocal relationship between autophagy and the mammalian immune system (22). The fact that many viruses have evolved strategies for countering and/or subverting autophagy supports a role for autophagy in the host antiviral response (31, 43). As an example of cross talk between autophagy and the innate immune response, autophagy mediates cellular recognition of some single-strand RNA (ssRNA) viruses, leading to alpha interferon (IFN-␣) induction in plasmacytoid dendritic cells (20). In addition, downstream events in IFN-regulated pathways regulate the autophagocytic process itself. For instance, PKR is an IFNinducible serine/threonine protein kinase that inhibits translation by phosphorylating eIF2␣ and that promotes autophagocytic degradation of HSV-1 (37, 38). Effects of PKR on both translation and autophagy are blocked by the HSV-1 neurovirulence gene product ICP34.5, which redirects protein phosphatase 1␣ to dephosphorylate eIF2␣. Here we implicate a second IFN-regulated pathway, the 2=,5=-oligoadenylate (OAS)/RNase L system (3, 34), in the control of autophagy.OASs are IFN-inducible pathogen recognition receptors (PRR) that produce 2=,5=-linked oligonucleotides of the formula p x 5=A(2=p5=A) n (x ϭ 1 to 3; n Ն 2) (2-5A) from ATP in response to viral double-stranded RNA (dsRNA) (15). The ...

RNase L Induces Autophagy via c-Jun N-terminal Kinase and Double-stranded RNA-dependent Protein Kinase Signaling Pathways

“…Addendum-While this work was under review, Chakrabarti et al (65) reported that RNase L triggers autophagy in response to viral infections, consistent with our data described here.…”

Antimicrobial Autophagy: A Conserved Innate Immune Response in Drosophila

“…Herpes simplex virus type 1 can antagonize autophagy via the viral protein ICP34.5, and mice more easily clear ICP34.5-mutant viruses compared to wild type viruses, again suggesting a détente between autophagy and viruses [66]. More recent data suggest that autophagy can control other viruses such as human immunodeficiency virus (HIV), encephalomyocarditis virus and human papilloma virus in mammalian cells in certain contexts, although the in vivo significance has not been assessed [67–69]. Since Drosophila are infected by viruses and are a genetically tractable model, flies are well suited for probing the interactions between viruses and autophagy.…”

Oncolytic viruses as therapeutic cancer vaccines

“…OVs such as Ad [54,79-81], HSV [70,82,83], reovirus [84-86], influenza virus [87], VSV and encephalomyocarditis virus [88] induce autophagy in cancer cells. Autophagy enhances tumor immunogenicity by two mechanisms.…”