Hepatocyte nuclear factor 1 and the glucocorticoid receptor synergistically activate transcription of the rat insulin-like growth factor binding protein-1 gene

Mol Endocrinol. 1997 Nov;11(12):1822-31. doi: 10.1210/mend.11.12.0021.

Abstract

The insulin-like growth factor (IGF) binding proteins (IGFBPs) are a family of proteins that bind IGF-I and IGF-II and modulate their biological activities. IGFBP-1 is distinctive among the IGFBPs in its rapid regulation in response to metabolic and hormonal changes. The synthetic glucocorticoid, dexamethasone, increases IGFBP-1 mRNA abundance and gene transcription in rat liver and in H4-II-E rat hepatoma cells. A glucocorticoid response element (GRE) located at nucleotide (nt) -91/-77 is required for dexamethasone to stimulate rat IGFBP-1 promoter activity in transient transfection assays in H4-II-E cells. In addition to the GRE, three accessory regulatory sites [a putative hepatocyte nuclear factor-1 (HNF-1) site (nt -62/-50), an insulin-response element (nt -108/-99), and an upstream site (nt -252/-236)] are involved in dexamethasone stimulation under some, but not all, circumstances. The present study begins to address the mechanism by which transcription factors bound to the putative HNF-1 site act synergistically with the glucocorticoid receptor (GR) bound to the GRE. In gel shift assays, HNF-1alpha and HNF-1beta in H4-II-E extracts bind to the palindromic HNF-1 site. Both half-sites are required. Overexpression of HNF-1beta enhances dexamethasone-stimulated promoter activity. Both the HNF-1 site and the GRE must be intact for stimulation to occur. By contrast, overexpression of HNF-1alpha does not enhance dexamethasone-stimulated promoter activity, although, as also observed with overexpression of HNF-1beta, it inhibits basal promoter activity. Thus, the synergistic effects of HNF-1beta and the GR on dexamethasone-stimulated promoter activity require that they are bound to the HNF-1 site and the GRE, respectively, and may involve protein-protein interactions between the transcription factors, or between them and the basal transcription machinery or a steroid receptor coactivator. Synergy between the ubiquitously expressed GR and HNF-1, which is developmentally regulated and expressed in a limited number of tissues, provides a possible mechanism for tissue- and development-specific regulation of glucocorticoid action.

MeSH terms

  • Animals
  • Carrier Proteins / drug effects
  • Carrier Proteins / genetics*
  • Cell Nucleus / genetics
  • Cell Nucleus / metabolism
  • DNA-Binding Proteins*
  • Dexamethasone / pharmacology
  • Drug Synergism
  • Electrophoresis, Polyacrylamide Gel
  • Hepatocyte Nuclear Factor 1
  • Hepatocyte Nuclear Factor 1-alpha
  • Hepatocyte Nuclear Factor 1-beta
  • Nuclear Proteins*
  • Pregnancy Proteins / drug effects
  • Pregnancy Proteins / genetics*
  • Promoter Regions, Genetic / drug effects
  • Protein Binding / genetics
  • Rats
  • Receptors, Glucocorticoid / genetics*
  • Receptors, Glucocorticoid / physiology*
  • Transcription Factors / biosynthesis
  • Transcription Factors / genetics*
  • Transcription Factors / physiology*
  • Transcriptional Activation / drug effects*
  • Tumor Cells, Cultured

Substances

  • Carrier Proteins
  • DNA-Binding Proteins
  • Hepatocyte Nuclear Factor 1-alpha
  • Hnf1a protein, rat
  • Nuclear Proteins
  • Pregnancy Proteins
  • Receptors, Glucocorticoid
  • Transcription Factors
  • pregnancy-associated alpha 1-glycoprotein, rat
  • Hepatocyte Nuclear Factor 1
  • Hepatocyte Nuclear Factor 1-beta
  • Dexamethasone