NOD1 Participates in the Innate Immune Response Triggered by Hepatitis C Virus Polymerase

Abstract

Hepatitis C virus (HCV) triggers innate immunity signaling in the infected cell. Replication of the viral genome is dispensable for this phenotype, and we along with others have recently shown that NS5B, the viral RNA-dependent RNA polymerase, synthesizes double-stranded RNA (dsRNA) from cellular templates, thus eliciting an inflammatory response, notably via activation of type I interferon and lymphotoxin ␤. Here, we investigated intracellular signal transduction pathways involved in this process. Using HepaRG cells, a model that largely recapitulates the in vivo complexities of the innate immunity receptor signaling, we have confirmed that NS5B triggered increased expression of the canonical pattern recognition receptors (PRRs) specific for dsRNA, namely, RIG-I, MDA5, and Toll-like receptor 3 (TLR3). Unexpectedly, intracellular dsRNA also led to accumulation of NOD1, a receptor classically involved in recognition of bacterial peptidoglycans. NOD1 activation, confirmed by analysis of its downstream targets, was likely due to its interaction with dsRNA and was independent of RIG-I and mitochondrial antiviral signaling protein (MAVS/IPS-1/Cardif/VISA) signaling. It is likely to have a functional significance in the cellular response in the context of HCV infection since interference with the NOD1 pathway severely reduced the inflammatory response elicited by NS5B. IMPORTANCEIn this study, we show that NOD1, a PRR that normally senses bacterial peptidoglycans, is activated by HCV viral polymerase, probably through an interaction with dsRNA, suggesting that NOD1 acts as an RNA ligand recognition receptor. In consequence, interference with NOD1-mediated signaling significantly weakens the inflammatory response to dsRNA. These results add a new level of complexity to the understanding of the cross talk between different classes of pattern recognition receptors and may be related to certain complications of chronic hepatitis C virus infection.

Characterization of Pattern Recognition Receptor Expression and Functionality in Liver Primary Cells and Derived Cell Lines

“…1) and IRF1, 3, and 7, the transcription factors involved in TLR signaling, were detected in almost all tested cells. Similarly, expression of NOD1 and NOD2 (previously described to be functional in hepatocytes [27,28]) was barely detectable at basal level, but RIP2, a NOD adaptor protein was detected in almost all cells tested (Fig. 1).…”

The expression patterns of immune response genes in the Peripheral Blood Mononuclear cells of pregnant women presenting with subclinical or clinical HEV infection are different and trimester-dependent: A whole transcriptome analysis

“…Though NOD1 and NOD2 members of the NLR family are activated by specific bacterial peptides [44], similar to dengue [45] and RSV [46], we report HEV-induced NLR activation. In the light of increased expression of NOD1 in hepatitis C patients [47] and the involvement of NOD1 through interaction with dsRNA in hepatocytes infected in-vitro or in-vivo with HCV [48], current observations with PBMCs need to be extended to hepatocytes.…”

NOD1 and NOD2 in inflammatory and infectious diseases

“…However, ssRNA is unable to activate NOD1 26 . Rather, at least in vitro in a hepatocyte cell line, synthetic dsRNA (polyI:C) or dsRNA generated by the RNA polymerase of hepatitis C virus induces NOD1 expression and interacts with NOD1, resulting in activation of downstream signaling pathways 27 . Interestingly, this interaction occurred independently of the LRR, but requires an intact NBD for full activity 27 .…”

“…Rather, at least in vitro in a hepatocyte cell line, synthetic dsRNA (polyI:C) or dsRNA generated by the RNA polymerase of hepatitis C virus induces NOD1 expression and interacts with NOD1, resulting in activation of downstream signaling pathways 27 . Interestingly, this interaction occurred independently of the LRR, but requires an intact NBD for full activity 27 . Similarly, zebrafish NOD1 overexpressed in the carp fish cell line epithelioma papulosum cyprinid (EPC) was capable of binding to the dsRNA virus, spring viremia of carp virus (SVCV), as well as polyI:C that was CARD‐dependent, suggesting perhaps the involvement of an intermediary protein for this interaction 28 …”