Critical role of CREBH-mediated induction of TGF-β2 by HCV infection in fibrogenic responses in hepatic stellate cells

Abstract

Mechanisms of hepatic fibrogenesis induced by Hepatitis C virus (HCV), one of the leading causes of liver fibrosis, are not fully understood. We studied transcriptional up-regulation of transforming growth factor β (TGF-β), especially TGF-β2, which is mediated via the activation of liver-enriched transcription factor CREBH triggered by HCV infection and its functional significance for induction of profibrogenic phenotypes via interaction of HCV-infected cells with hepatic stellate cells (HSC). Compared to TGF-β1, expression of TGF-β2 mRNA was induced faster and to a higher level upon HCV infection. Serum TGF-β2 levels in hepatitis C patients were higher compared to those in healthy individuals and were positively correlated with hepatic fibrosis stages, F0-F2. TGF-β2 promoter activity was decreased and increased, respectively, by silencing and over-expression of CREBH. CREBH-recognition sites were identified in the TGF-β2 promoter. CREBH binding to the promoter and its increase in cells expressing HCV Core-NS2 were shown by gel mobility shift and chromatin immunoprecipitation, respectively. The active form of CREBH was detectable in HCV-infected chimeric mice with human livers and cells expressing HCV proteins. Involvement of CREBH in HCV-induced fibrogenic response was further demonstrated in the CREBH null-mutant mouse model. Fibrogenic phenotypes were assessed using co-cultures of HCV-infected cells and HSC. Expressions of fibrogenic factors and TGF-β1 increasing in the co-cultures was prevented by TGF-β2- or CREBH silencing. Conclusion: CREBH was identified as a key positive regulator of TGF-β2 transcription in HCV-infected cells. TGF-β2 released from the infected cells potentially contributes to cross-induction of TGF-β in an autocrine manner via its own signaling pathway, leading to an increase in fibrogenic responses in adjacent HSC. This article is protected by copyright. All rights reserved.

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