Hepatocyte nuclear factor (HNF)-4 alpha-driven epigenetic silencing of the human PED gene

Overexpression of PED (also known as PEA15) determines insulin resistance and impaired insulin secretion and may contribute to progression toward type 2 diabetes. Recently, we found that the transcription factor hepatocyte nuclear factor (HNF)-4 alpha binds to PED promoter and represses its transcription. However, the molecular details responsible for regulation of PED gene remain unclear. Here we used gain and loss of function approaches to investigate the hypothesis that HNF-4 alpha controls chromatin remodelling at the PED promoter in human cell lines. HNF-4 alpha production and binding induce chromatin remodelling at the -250 to 50 region of PED, indicating that remodelling is limited to two nucleosomes located at the proximal promoter. Chromatin immunoprecipitation assays also revealed concomitant HNF-4 alpha-induced deacetylation of histone H3 at Lys9 and Lys14, and increased dimethylation of histone H3 at Lys9. The latter was followed by reduction of histone H3 Lys4 dimethylation. HNF-4 alpha was also shown to target the histone deacetylase complex associated with silencing mediator of retinoic acid and thyroid hormone receptor, both at the PED promoter, and at GRB14 and USP21 regulatory regions, leading to a reduction of mRNA levels. Moreover, HNF-4 alpha silencing and PED overexpression were accompanied by a significant reduction of hepatic glycogen content. These results show that HNF-4 alpha serves as a scaffold protein for histone deacetylase activities, thereby inhibiting liver expression of genes including PED. Dysregulation of these mechanisms may lead to upregulation of the PED gene in type 2 diabetes.