Critical Role of CREBH-Mediated Induction of Transforming Growth Factor β2 by Hepatitis C Virus Infection in Fibrogenic Responses in Hepatic Stellate Cells

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 beta (TGF-beta), especially TGF-beta 2, which is mediated by activation of liver-enriched transcription factor cAMP-responsive element-binding protein, hepatocyte specific (CREBH) triggered by HCV infection and its functional significance for induction of profibrogenic phenotypes by interaction of HCV-infected cells with hepatic stellate cells (HSCs). Compared to TGF-beta 1, expression of TGF-beta 2 mRNA was induced faster and to a higher level upon HCV infection. Serum TGF-beta 2 levels in hepatitis C patients were higher compared to those in healthy individuals and were positively correlated with hepatic fibrosis stages F0-F2. TGF-beta 2 promoter activity was decreased and increased, respectively, by silencing and overexpression of CREBH. CREBH recognition sites were identified in the TGF-beta 2 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 HSCs. Expressions of fibrogenic factors and TGF-beta 1 increasing in the co-cultures was prevented by TGF-beta 2- or CREBH silencing. Conclusion: CREBH was identified as a key positive regulator of TGF-beta 2 transcription in HCV-infected cells. TGF-beta 2 released from infected cells potentially contributes to cross-induction of TGF-beta in an autocrine manner through its own signaling pathway, leading to an increase in fibrogenic responses in adjacent HSCs.