Interferon-gamma-induced MD-2 protein expression and lipopolysaccharide (LPS) responsiveness in corneal epithelial cells is mediated by Janus tyrosine kinase-2 activation and direct binding of STAT1 protein to the MD-2 promoter

J Biol Chem. 2011 Jul 8;286(27):23753-62. doi: 10.1074/jbc.M111.219345. Epub 2011 May 13.

Abstract

The inability of epithelial cells from the cornea and other tissues to respond to LPS is reportedly due to low expression of the TLR4 co-receptor MD-2. We generated MD-2(-/-) bone marrow chimeras, and showed that MD-2 expression on non-myeloid cells was sufficient to mediate LPS-induced corneal inflammation. As IFN-γ is produced during Pseudomonas aeruginosa corneal infection, we examined the role of this cytokine on MD-2 expression by primary human corneal epithelial (HCE) cells and HCE cell lines. Exogenous IFN-γ was found to induce MD-2 mRNA, MD-2 cell surface expression, and LPS responsiveness as determined by p65 translocation to the nucleus and production of IL-6, CXCL1, and CXCL8/IL-8. Incubation with either the AG490 JAK2 inhibitor or with STAT1 siRNA blocked STAT1 phosphorylation and MD-2 transcription. Furthermore, EMSA analysis demonstrated that STAT1 binds to the MD-2 promoter, indicating that STAT1 is an MD-2 transcription factor. Together, these findings demonstrate that IFN-γ induces MD-2 expression and LPS responsiveness in HCE cells by JAK-2-dependent STAT1 activation and direct binding to the MD-2 promoter. Furthermore, given our findings on LPS-induced corneal inflammation, it is likely that IFN-γ-induced MD-2 expression by corneal epithelial cells contributes to the host response in vivo, determining the extent of tissue damage and bacterial clearance.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line, Transformed
  • Cytokines / biosynthesis
  • Cytokines / genetics
  • Enzyme Activation / genetics
  • Epithelial Cells / metabolism*
  • Epithelial Cells / microbiology
  • Epithelium, Corneal / metabolism*
  • Epithelium, Corneal / microbiology
  • Gene Expression Regulation / genetics
  • Humans
  • Interferon-gamma / genetics
  • Interferon-gamma / metabolism*
  • Janus Kinase 2 / genetics
  • Janus Kinase 2 / metabolism*
  • Keratitis / genetics
  • Keratitis / metabolism
  • Keratitis / microbiology
  • Lipopolysaccharides / metabolism*
  • Lymphocyte Antigen 96 / genetics
  • Lymphocyte Antigen 96 / metabolism*
  • Mice
  • Mice, Knockout
  • Pseudomonas Infections / genetics
  • Pseudomonas Infections / metabolism*
  • Pseudomonas aeruginosa / metabolism*
  • Response Elements*
  • STAT1 Transcription Factor / genetics
  • STAT1 Transcription Factor / metabolism*

Substances

  • Cytokines
  • LY96 protein, human
  • Lipopolysaccharides
  • Ly96 protein, mouse
  • Lymphocyte Antigen 96
  • STAT1 Transcription Factor
  • STAT1 protein, human
  • Stat1 protein, mouse
  • Interferon-gamma
  • JAK2 protein, human
  • Jak2 protein, mouse
  • Janus Kinase 2