title: Negative regulation of human growth hormone gene expression by insulin is dependent on hypoxia-inducible factor binding in primary non-tumor pituitary cells.
abstract: Insulin controls growth hormone (GH) production at multiple levels, including via a direct effect on pituitary somatotrophs. There are no data, however, on the regulation of the intact human (h) GH gene (hGH1) by insulin in non-tumor pituitary cells, but the proximal promoter region (nucleotides -496/+1) responds negatively to insulin in transfected pituitary tumor cells. A DNA-protein interaction was also induced by insulin at nucleotides -308/-235. Here, we confirmed the presence of a hypoxia-inducible factor 1 (HIF-1) binding site within these sequences (-264/-259) and investigated whether HIF-1 is associated with insulin regulation of "endogenous" hGH1. In the absence of primary human pituitary cells, transgenic mice expressing the intact hGH locus in a somatotroph-specific manner were generated. A significant and dose-dependent decrease in hGH and mouse GH RNA levels was detected in primary pituitary cell cultures from these mice with insulin treatment. Increasing HIF-1α availability with a hypoxia mimetic significantly decreased hGH RNA levels and was accompanied by recruitment of HIF-1α to the hGH1 promoter in situ as seen with insulin. Both inhibition of HIF-1 DNA binding by echinomycin and RNA interference of HIF-1α synthesis blunted the negative effect of insulin on hGH1 but not mGH. The insulin response is also sensitive to histone deacetylase inhibition/trichostatin A and associated with a decrease in H3/H4 hyperacetylation in the proximal hGH1 promoter region. These data are consistent with HIF-1-dependent down-regulation of hGH1 by insulin via chromatin remodeling specifically in the proximal promoter region.
authors: Department of Physiology, Division of Endocrine and Metabolic diseases, University of Manitoba, Winnipeg, Manitoba, Canada.
authors: Hana
authors: H
authors: Vakili
authors: Yan
authors: Y
authors: Jin
authors: Peter A
authors: PA
authors: Cattini
mesh_terms: D000818:Animals; D001483:Base Sequence; D002843:Chromatin / Q000378:metabolism; D005260:Female; D005786:Gene Expression Regulation; D019382:Human Growth Hormone / Q000096:biosynthesis*; D006801:Humans; D006946:Hyperinsulinism / Q000378:metabolism; D000860:Hypoxia / Q000378:metabolism*; D051793:Hypoxia-Inducible Factor 1 / Q000378:metabolism; D007328:Insulin / Q000378:metabolism*; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D008969:Molecular Sequence Data; D010902:Pituitary Gland / Q000378:metabolism*; D011485:Protein Binding; D012313:RNA / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid
chemical_list: D002843:Chromatin; D051793:Hypoxia-Inducible Factor 1; D007328:Insulin; D019382:Human Growth Hormone; D012313:RNA