Stat1 combines signals derived from IFN-gamma and LPS receptors during macrophage activation

EMBO J. 1998 Jul 1;17(13):3660-8. doi: 10.1093/emboj/17.13.3660.

Abstract

Complete activation of macrophages during immune responses results from stimulation with the activating cytokine interferon-gamma (IFN-gamma) and a second stimulus, usually a microbial product. Bacterial infection of macrophages, or treatment with bacterial lipopolysaccharide (LPS), resulted in rapid Stat1 phosphorylation on Ser727 (S727) independently of concomitant tyrosine phosphorylation. IFN-gamma also caused rapid phosphorylation of S727. In both situations, S727 phosphorylation was reduced by pre-treatment of cells with the serine kinase inhibitor H7. When macrophages were treated sequentially or simultaneously with LPS and IFN-gamma, the pool of molecules phosphorylated on both Tyr701 (Y701) and S727 was strongly increased. Consistently, Stat1-dependent transcription in response to IFN-gamma was significantly enhanced if the cells were pre-treated with bacterial LPS. The relative amount of S727-phosphorylated Stat1 in the non-tyrosine phosphorylated fraction was considerably smaller than that in the tyrosine-phosphorylated fraction. No evidence was found for an effect of S727 phosphorylation on the phosphorylation of Y701 by IFN-gamma. Thus, serine and tyrosine phosphorylation of Stat1 are caused independently of each other, but the serine kinase may recognize tyrosine-phosphorylated Stat1 preferentially in the course of an IFN-gamma response. The data suggest Stat1 to be a convergence point for immunological stimuli in a macrophage proinflammatory response.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies / immunology
  • Antibody Specificity / immunology
  • Cell Line
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / immunology
  • DNA-Binding Proteins / metabolism*
  • Enzyme Activation
  • Humans
  • Interferon gamma Receptor
  • Interferon-gamma / metabolism
  • Interferon-gamma / pharmacology
  • Lipopolysaccharide Receptors / metabolism*
  • Lipopolysaccharides / metabolism
  • Lipopolysaccharides / pharmacology
  • Macrophages / drug effects
  • Macrophages / metabolism*
  • Mice
  • Mitogens / pharmacology
  • Phosphorylation
  • Rabbits
  • Receptors, Interferon / metabolism*
  • STAT1 Transcription Factor
  • Salmonella typhimurium / physiology
  • Serine / metabolism
  • Signal Transduction*
  • Trans-Activators / genetics
  • Trans-Activators / immunology
  • Trans-Activators / metabolism*
  • Transcription, Genetic
  • Tumor Cells, Cultured
  • Tyrosine / metabolism

Substances

  • Antibodies
  • DNA-Binding Proteins
  • Lipopolysaccharide Receptors
  • Lipopolysaccharides
  • Mitogens
  • Receptors, Interferon
  • STAT1 Transcription Factor
  • STAT1 protein, human
  • Stat1 protein, mouse
  • Trans-Activators
  • Tyrosine
  • Serine
  • Interferon-gamma