Glucocorticoid-independent repression of tumor necrosis factor (TNF) alpha-stimulated interleukin (IL)-6 expression by the glucocorticoid receptor: a potential mechanism for protection against an excessive inflammatory response

J Biol Chem. 2011 Jun 3;286(22):19297-310. doi: 10.1074/jbc.M110.193672. Epub 2011 Apr 7.

Abstract

TNFα signaling and cytokine levels play a crucial role in cervical immunity and the host response to infections. We investigated the role of liganded and unliganded glucocorticoid receptor (GR) in IL-6 and IL-8 gene regulation in response to TNFα in the End1/E6E7 immortalized human endocervical epithelial cell line. In the absence of glucocorticoids, both decreasing GR protein levels by an siRNA strategy and results with the GR antagonist RU486 suggest a role for the unliganded GR in reduction of TNFα-induced IL-6 and IL-8 mRNA levels in End1/E6E7 cells. Moreover, GR-dependent repression of endogenous IL-6 mRNA as well as a minimal IL-6 promoter-reporter gene is also demonstrated in COS-1 cells in the absence of GR ligand, suggesting a transcriptional mechanism that is not cell-specific. TNFα induced recruitment of both the unliganded GR and GR-interacting protein type 1 (GRIP-1) to the IL-6 promoter. This, together with GRIP-1 overexpression studies, suggests a function for GRIP-1 as a GR co-repressor in this context. TNFα was shown to induce phosphorylation of the unliganded human GR at Ser-226 but not Ser-211, unlike dexamethasone, which induced hyperphosphorylation at both serine residues. Ser-226 is shown to be required for the ligand-independent GR-mediated repression of IL-6 in response to TNFα. Taken together, these results support a model whereby the unliganded GR attenuates TNFα-stimulated IL-6 transcription by a mechanism involving selective phosphorylation and recruitment of the unliganded GR and GRIP-1 to the IL-6 promoter. These findings suggest the presence of a novel autoregulatory mechanism that may prevent overproduction of IL-6 in the endocervix, possibly protecting against negative effects of excessive inflammation.

MeSH terms

  • Animals
  • COS Cells
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism
  • Chlorocebus aethiops
  • Epithelial Cells / metabolism*
  • Gene Expression Regulation*
  • Hormone Antagonists / pharmacology
  • Humans
  • Inflammation / genetics
  • Inflammation / metabolism
  • Interleukin-6 / biosynthesis*
  • Interleukin-6 / genetics
  • Mifepristone / pharmacology
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism
  • Phosphorylation / drug effects
  • Phosphorylation / genetics
  • Promoter Regions, Genetic
  • Receptors, Glucocorticoid / genetics
  • Receptors, Glucocorticoid / metabolism*
  • Transcription, Genetic*
  • Tumor Necrosis Factor-alpha / genetics
  • Tumor Necrosis Factor-alpha / metabolism*
  • Tumor Necrosis Factor-alpha / pharmacology

Substances

  • Carrier Proteins
  • GRIP1 protein, human
  • Hormone Antagonists
  • IL6 protein, human
  • Interleukin-6
  • Nerve Tissue Proteins
  • Receptors, Glucocorticoid
  • Tumor Necrosis Factor-alpha
  • Mifepristone