Lymphotoxin Signaling Is Initiated by the Viral Polymerase in HCV-linked Tumorigenesis

Abstract

Exposure to hepatitis C virus (HCV) typically results in chronic infection that leads to progressive liver disease ranging from mild inflammation to severe fibrosis and cirrhosis as well as primary liver cancer. HCV triggers innate immune signaling within the infected hepatocyte, a first step in mounting of the adaptive response against HCV infection. Persistent inflammation is strongly associated with liver tumorigenesis. The goal of our work was to investigate the initiation of the inflammatory processes triggered by HCV viral proteins in their host cell and their possible link with HCV-related liver cancer. We report a dramatic upregulation of the lymphotoxin signaling pathway and more specifically of lymphotoxin-β in tumors of the FL-N/35 HCV-transgenic mice. Lymphotoxin expression is accompanied by activation of NF-κB, neosynthesis of chemokines and intra-tumoral recruitment of mononuclear cells. Spectacularly, IKKβ inactivation in FL-N/35 mice drastically reduces tumor incidence. Activation of lymphotoxin-β pathway can be reproduced in several cellular models, including the full length replicon and HCV-infected primary human hepatocytes. We have identified NS5B, the HCV RNA dependent RNA polymerase, as the viral protein responsible for this phenotype and shown that pharmacological inhibition of its activity alleviates activation of the pro-inflammatory pathway. These results open new perspectives in understanding the inflammatory mechanisms linked to HCV infection and tumorigenesis.

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

“…This is typically the outcome of HCV infections, where chronic inflammation is associated with many adverse effects, notably, liver fibrosis, cirrhosis, and HCC. We along with others have previously reported that NS5B, the HCV RNA-dependent RNA polymerase, induces expression of proinflammatory cytokines (12,13). Double-stranded RNA, generated by viral RNA polymerases during replication and transcription of viral genomes, is a common PAMP recognized by the immune system during infection by RNA viruses.…”

“…It has previously been reported that the HCV core and NS3 proteins induce expression of proinflammatory cytokines through as yet to be identified mechanisms (9,10). More recently, we along with others have shown that NS5B, the HCV RNA-dependent RNA polymerase, activates innate immune signaling through the production of small RNA species that are recognized by intracellular receptors and give rise to cytokine production, including type I interferons (11)(12)(13). Thus, expression of viral gene products fuels the persistence of inflammatory signaling.…”

“…(i) NS5B catalytic site mutant. The point mutation G317V (34) was introduced in the GDD motif of the NS5B protein as previously described (12).…”

“…Despite lack of overt inflammation in this model of constitutive transgene expression, we have recently described the role of viral proteins and, more specifically, of the viral polymerase, in triggering inflammatory signaling during hepatocarcinogenesis driven by the HCV transgene (12). NS5B, the HCV RNAdependent RNA polymerase, synthesizes double-stranded RNA of cellular origin that triggers innate immune responses in hepatocytes and leads to production of type I IFN and other inflammatory cytokines (12,13,(39)(40)(41)(42).…”

Oxidative stress and hepatic Nox proteins in chronic hepatitis C and hepatocellular carcinoma

“…Recently, a dramatic upregulation in lymphotoxin-β levels was identified in tumors from HCV transgenic mice, which was accompanied by activation of NF-κB, elevated chemokines, and intra-tumoral recruitment of mononuclear cells (200) (Figure 3B). Inactivation of IKKβ reduced the tumor rate in these animals (200).…”