The p7 viroporin of the hepatitis C virus contributes to liver inflammation by stimulating production of Interleukin-1β

Abstract

Hepatitis C is one of the most widespread infectious diseases worldwide and hepatitis C virus (HCV)-induced chronic inflammation is highly associated with progredient liver damage. It was shown that HCV infection increases levels of pro-inflammatory cytokines via activation of NOD-like receptor (NLRP3) inflammasomes, yet the underlying mechanism is still under question. We propose modulation of intracellular pH by p7, a 63 residue ion channel produced by the hepatitis C virus as a possible pathomechanism for hepatitis C-associated inflammation. Recombinant constructs corresponding to HCV genotypes 1-4 were expressed in HEK 293 and RAW 264.7 cells and changes of intracellular pH were monitored using pH-sensitive fluorescent probes as well as production of inflammatory cytokines. Presence of p7 induced general loss of vesicular acidity as well as producing a significant increase in the levels of interleukin-1β (IL-1β). Effects showed a genotype-dependent pattern of IL-1β production, in agreement with the pH-response profile of p7 channels corresponding to hepatitis C genotypes. Lowering the pH of the extracellular medium increased activity of p7 channels as well as production of IL-1β for genotypes 1, 3, and 4, but less for genotype 2. Our data are in agreement with the hypothesis that p7 activity can trigger intracellular signaling cascades that are involved in HCV-associated cytopathy.

The NS1 Protein of Influenza A Virus Participates in Necroptosis by Interacting with MLKL and Increasing Its Oligomerization and Membrane Translocation

“…Furthermore, NLRP3 inflammasome activation following severe acute respiratory syndrome coronavirus (SARS-CoV) infection leads to excessive IL-1␤ production, resulting in pulmonary damage, edema, and death (40). A similar association between the activation of NLRP3 and increased pathogenesis has been reported for HIV-1 (41), hepatitis C virus (HCV) (42,43), and Sindbis virus (44). Our finding that NS1 of IAV interacts with MLKL, resulting in inflammasome activation and increased IL-1␤ processing and release, may fit into the finding that NS1 activates necroptosis and inflammasome pathways to benefit IAV pathogenesis through excessive IL-1␤ production and a strong inflammatory response.…”

Viroporins and inflammasomes: A key to understand virus-induced inflammation

“…In LPS-primed macrophages, p7 increased levels of IL-1β in a genotype dependent manner. Treatment of J o u r n a l P r e -p r o o f transfected cells with rimantadine abolished p7-induced effects completely, in agreement with the pH-response profile of p7 channels, concluding that p7 with its proton conductance activity can provide the second signal required for inflammasome activation [78,111].…”

“…Recently several studies have linked activation of NLRP3 inflammasomes and production of the inflammatory cytokine IL-1β to viral infections such as influenza A virus (IAV), J o u r n a l P r e -p r o o f hepatitis C virus (HCV) and encephalomyocarditis virus (EMCV) [78][79][80] as summarized in Figure 3.…”

“…The ion channel was also reported to cause global loss of organelle acidity upon expression [31]. Reports have shown that IL-1β levels are higher in HCV induced liver diseases than in other forms of liver damage, however the mechanism by which HCV infection activates NLRP3 is still under investigation [17,78,109]. Furthermore, introduction of HCV viroporin p7 RNA into THP-1 cells was sufficient to cause IL-1β secretion [110].…”

“…When p7 constructs of different genotypes were expressed in human embryonic kidney (HEK-293) cells, as well as in murine macrophage (RAW 264.7) cells [50,78], the effects of extracellular concentrations of H + concentration and the channel blocker rimantadine on cytokine production were demonstrated [78]. In LPS-primed macrophages, p7 increased levels of IL-1β in a genotype dependent manner.…”