A DDX5 S480A polymorphism is associated with increased transcription of fibrogenic genes in hepatic stellate cells

Abstract

We recently identified a missense single nucleotide polymorphism (SNP) in DDX5 (rs1140409, p.S480A) that enhances the risk of developing cirrhosis. DDX5 is an ATP-dependent RNA helicase and transcriptional modulator. We hypothesized that the activity of DDX5 in regulating fibrogenic gene transcription in hepatic stellate cells (HSCs) is altered by the S480A SNP. To test this, we employed two approaches: 1) transient overexpression of DDX5 cDNA or siRNA knockdown of endogenous DDX5, with replacement by either DDX5 wild type (WT) or SNP cDNA, or 2) stable expression of exogenous DDX5 WT and SNP in HSC lines. WT DDX5 mRNA in HSCs was inversely correlated with gene expression for α2(I) collagen, tissue inhibitor of metalloproteinase-1, and transforming growth factor-α1. Stable DDX5 SNP-expressing cells had higher basal and transforming growth factor-α1-stimulated expression and enhanced promoter activities of fibrogenic genes. DDX5 variant-expressing cells also had higher Smad3 and AP-1-responsive reporter activities. In a one-hybrid GAL4 system, co-expression of the DDX5 SNP variant with chimeras of GAL4 DNA binding domain linked to JunD or Sp1 displayed higher transactivation of a GAL4-responsive reporter than that of DDX5 WT. Increased fibrogenic gene expression in DDX5 SNP-expressing cells was associated with reduced recruitment of DDX5 homodimers to responsive promoters, but there was no difference in the recruitment of the co-repressor HDAC1 (histone deacetylase 1). These data suggest that DDX5 is a repressor of fibrogenic genes in HSCs through interaction with transcriptional complexes. The enhanced fibrogenic activity of the DDX5 risk variant is linked to a reduced repressive function toward these target genes. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.