Stat1 combines signals derived from IFN-gamma and LPS receptors during macrophage activation.
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.
Kovarik
P
P
Vienna Biocenter, Institute of Microbiology and Genetics, Dr Bohr-Gasse 9, A-1030 Vienna, Austria.
Stoiber
D
D
Novy
M
M
Decker
T
T
D000818:Animals; D000906:Antibodies / Q000276:immunology; D000918:Antibody Specificity / Q000276:immunology; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D004789:Enzyme Activation; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism / Q000494:pharmacology; D018950:Lipopolysaccharide Receptors / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000378:metabolism / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008934:Mitogens / Q000494:pharmacology; D010766:Phosphorylation; D011817:Rabbits; D017471:Receptors, Interferon / Q000378:metabolism*; D050794:STAT1 Transcription Factor; D012486:Salmonella typhimurium / Q000502:physiology; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D015534:Trans-Activators / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism; D000096743:Interferon gamma Receptor
D000906:Antibodies; D004268:DNA-Binding Proteins; D007371:Interferon-gamma; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D008934:Mitogens; D017471:Receptors, Interferon; D050794:STAT1 Transcription Factor; D012694:Serine; D015534:Trans-Activators; D014443:Tyrosine; D000096743:Interferon gamma Receptor; C494079:STAT1 protein, human; C494080:Stat1 protein, mouse