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The histone methyltransferase ASH1 orchestrates fibrogenic gene transcription during myofibroblast transdifferentiation.

Perugorria MJ, Wilson CL, Zeybel M, Walsh M, Amin S, Robinson S, White SA, Burt AD, Oakley F, Tsukamoto H, Mann DA, Mann J

BACKGROUND AND AIMS: Transdifferentiation of hepatic stellate cells (HSCs) to a myofibroblast-like phenotype is a pivotal event that drives liver fibrosis. HSC transdifferentiation requires coordinated global changes in gene expression. Here we have investigated epigenetic regulators that orchestrate HSC transdifferentiation. METHODS: Expression profiling of epigenetic regulators was carried out in primary quiescent HSC and myofibroblasts by qRT-PCR. Recruitment of histone modifying enzymes (MLL5, Set1 and ASH1) to fibrogenic genes was determined by chromatin immunoprecipitation (ChIP). Functional studies on ASH1 were carried out by depletion of the protein by siRNA. Function of the ASH1 regulator, MeCP2, was determined in myofibroblastic HSC. RESULTS: The lysine 4 Histone 3 (H3K4) methyltransferases MLL5, Set1 and ASH1 were highly up-regulated during HSC transdifferentiation. H3K4 trimethylation at 5' end of the gene is a signature of active transcription. ASH1, but not MLL5 or Set1, was recruited to the regulatory regions of αSMA, collagen I, TIMP1 and TGFβ1. Depletion of ASH1 in HSC-derived myofibroblasts caused broad suppression of fibrogenic gene expression. We also discovered that MeCP2 positively regulates ASH1 expression. CONCLUSIONS: We identify ASH1 as a key transcriptional activator component of the MeCP2 epigenetic relay pathway that orchestrates coordinated induction of multiple pro-fibrogenic genes. (HEPATOLOGY 2012.).


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April, 2012


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