Activation of Autophagy by α-Herpesviruses in Myeloid Cells Is Mediated by Cytoplasmic Viral DNA through a Mechanism Dependent on Stimulator of IFN Genes

Abstract

Autophagy has been established as a player in host defense against viruses. The mechanisms by which the host induces autophagy during infection are diverse. In the case of herpes simplex virus type 1 (HSV-1), dsRNA dependent protein kinase (PKR) is essential for induction of autophagy in fibroblasts through phosphorylation of eukaryotic initiation factor 2α (eIF2α). HSV-1 counteracts autophagy via ICP34.5, which dephosphorylates eIF2α and inhibits Beclin 1. Investigation of autophagy during HSV-1 infection has largely been conducted in permissive cells, but recent work suggests the existence of an eIF2α-independent autophagy-inducing pathway in non-permissive cells. To clarify and further characterize the existence of a novel autophagy-inducing pathway in non-permissive cells, we examined different HSV and cellular components in murine myeloid cells for their role in autophagy. We demonstrate that HSV-1-induced autophagy does not correlate with phosphorylation of eIF2α, is independent of functional PKR, and is not antagonized by ICP34.5. Autophagy was activated independent of viral gene expression but required viral entry. Importantly, we found that the presence of genomic DNA in the virion was essential for induction of autophagy and, conversely, that transfection of HSV-derived DNA induced LC3 II formation, a marker of autophagy. This occurred through a mechanism dependent on STING, an essential component for the IFN response to intracellular DNA. Finally we observed that HSV-1 DNA was present in the cytosol devoid of capsid material following HSV-1 infection of DCs. Thus, our data suggest that HSV-1 genomic DNA induces autophagy in non-permissive cells in a STING dependent manner.

A Proautophagic Antiviral Role for the Cellular Prion Protein Identified by Infection with a Herpes Simplex Virus 1 ICP34.5 Mutant

“…Astrocytes may utilize autophagy in several strategies to promote cellular and host defense, which HSV-1 ICP34.5 governs to different extents, depending on the cell type infected (33,43,44,57,76,77). First, in electron micrographs we frequently observed virus particles adjacent to phagophores and inside completed autophagosomes, suggesting that xenophagic degradation of virus particles may be a defense mechanism of astrocytes that would also reduce virus release to neighboring neurons.…”

Role of the DNA Sensor STING in Protection from Lethal Infection following Corneal and Intracerebral Challenge with Herpes Simplex Virus 1

“…There is clear evidence, however, that in addition to stimulating the IFN-driven antiviral response, STING-dependent responses also stimulate the xenophagy pathway that promotes the clearance of intracellular pathogens (60). Indeed, STING is critical for the HSV-induced autophagy response, at least in bone marrow-derived dendritic cells (BMDCs) (61). Notably, STING transcription is low in cornea and brain tissues but high in antigen-presenting cells, cells that undergo significant autophagic flux (62,63).…”

Activation and Regulation of DNA-Driven Immune Responses

“…This is in contrast to the TLR9 pathway, where autophagy appears to facilitate the delivery of the DNA PAMP to the TLR9-containing endosomal compartment (8). It was previously described that cytosolic DNA is a trigger of autophagy (101,102) (Fig. 2C), and the first demonstration of the involvement of this basic catabolic process in the regulation of the DNA-activated pathway was provided by Saitoh and associates (103).…”