Association of the Glucocorticoid Receptor With STAT3, C/EBPbeta, and the Hormone-Responsive Element Within the Rat Haptoglobin Gene Promoter During the Acute Phase Response

IUBMB Life. 2010 Mar;62(3):227-36. doi: 10.1002/iub.313.

Abstract

Upregulation of haptoglobin (Hp) expression in the rat during the acute phase (AP) response is the result of synergistic effects of IL-6-, IL-1beta-, and corticosterone-activated signaling pathways. IL-6 signaling terminates in cis-trans interactions of the Hp gene hormone-responsive element (HRE) with transcription factors STAT3 and C/EBPbeta. The aim of this study was to examine the unresolved molecular mechanism of glucocorticoid action. A 3-fold rise in serum corticosterone at 2 and 4 h of the AP response induced by turpentine administration preceded a 2.3-fold increase in the rate of Hp gene transcription at 12 h that was accompanied by a 4.8-fold increase in glucocorticoid receptor (GR), the appearance of an 86-kDa STAT3 isoform and 3.9-, 1.9-, and 1.7-fold increased amounts of 91-kDa STAT3, 35- and 42-kDa C/EBPbeta isoforms in the nucleus. These events resulted in 4.6- and 2.5-fold increased Hp levels in the liver and serum at 24 h. HRE affinity chromatography and immunoblot analysis revealed that maximal occupancy of the HRE with GR, STAT3, and C/EBPbeta at 12 h correlated with increased transcriptional activity of the Hp gene. Coimmunoprecipitation experiments showed that activated GR established de novo interaction with STAT3 isoforms while GR-C/EBPbeta interactions observed during basal transcription increased during the AP response. Computer analysis of the HRE disclosed two potential GR-binding sites: one overlapping STAT3, another adjacent to a C/EBPbeta-binding site. This finding and the experimental results suggest that activated GR through direct interactions with STAT3 and C/EBPbeta, participates in Hp gene upregulation as a transcriptional coactivator.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acute-Phase Reaction / genetics*
  • Animals
  • Base Sequence
  • CCAAT-Enhancer-Binding Protein-beta / genetics*
  • Corticosterone / blood
  • Gene Expression Regulation
  • Haptoglobins / genetics*
  • Hormones / pharmacology
  • Liver / metabolism
  • Male
  • Molecular Sequence Data
  • Promoter Regions, Genetic
  • Rats
  • Rats, Wistar
  • Receptors, Glucocorticoid / genetics*
  • Response Elements / physiology*
  • STAT3 Transcription Factor / genetics*
  • Turpentine
  • Up-Regulation

Substances

  • CCAAT-Enhancer-Binding Protein-beta
  • Haptoglobins
  • Hormones
  • Receptors, Glucocorticoid
  • STAT3 Transcription Factor
  • Stat3 protein, rat
  • Corticosterone
  • Turpentine