Negative regulation of human growth hormone gene expression by insulin is dependent on hypoxia-inducible factor binding in primary non-tumor pituitary cells

J Biol Chem. 2012 Sep 28;287(40):33282-92. doi: 10.1074/jbc.M112.380949. Epub 2012 Jul 25.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Base Sequence
  • Chromatin / metabolism
  • Female
  • Gene Expression Regulation
  • Human Growth Hormone / biosynthesis*
  • Humans
  • Hyperinsulinism / metabolism
  • Hypoxia / metabolism*
  • Hypoxia-Inducible Factor 1 / metabolism
  • Insulin / metabolism*
  • Male
  • Mice
  • Mice, Transgenic
  • Models, Biological
  • Molecular Sequence Data
  • Pituitary Gland / metabolism*
  • Protein Binding
  • RNA / metabolism
  • Sequence Homology, Nucleic Acid

Substances

  • Chromatin
  • Hypoxia-Inducible Factor 1
  • Insulin
  • Human Growth Hormone
  • RNA