Regulation of glucose-6-phosphatase gene expression in cultured hepatocytes and H4IIE cells by short-chain fatty acids: role of hepatic nuclear factor-4alpha.

Mechanisms underlying dietary nutrient regulation of glucose-6-phosphatase (Glc-6-Pase) gene expression are not well understood. Here we investigated the effects of short-chain fatty acids on the expression of this gene in primary cultures of rat hepatocytes and H4IIE hepatoma cells. Propionate, butyrate, valerate, and caproate induced severalfold increases in the expression of Glc-6-Pase mRNA. In reporter gene assays, propionate, valerate, caproate, and also octanoate increased Glc-6-Pase promoter activity by 6-16-fold. Butyrate, by itself, had little or no effect on promoter activity, but it induced a robust increase (45-fold) in promoter activity in cells co-transfected with a plasmid expressing the transcription factor HNF-4alpha (alpha isoforms of hepatic nuclear factor 4). HNF-4alpha also enhanced promoter activity induced by other short-chain fatty acids. A dominant negative form of HNF-4alpha abrogated the fatty acid-induced promoter activity, a finding that accentuates a role for HNF-4alpha in the transcription process studied here. In cells transfected with HNF-4alpha, short-chain fatty acids and trichostatin A, an inhibitor of histone deacetylase, synergistically enhanced promoter activity, suggesting that hyperacetylation of histones is an important component of the transactivation of the Glc-6-Pase gene promoter by HNF-4alpha. Region-751/-466 of this promoter contains seven putative HNF-4alpha-binding motifs. Binding of HNF-4alpha to this region was confirmed by electrophoretic mobility shift and chromatin immunoprecipitation assays, indicating that HNF-4alpha is recruited to the Glc-6-Pase gene promoter during short-chain fatty acid-induced transcription from this promoter.