Stress-induced phosphorylation of STAT1 at Ser727 requires p38 mitogen-activated protein kinase whereas IFN-gamma uses a different signaling pathway.
STAT1 is an essential transcription factor for macrophage activation by IFN-gamma and requires phosphorylation of the C-terminal Ser727 for transcriptional activity. In macrophages, Ser727 phosphorylation in response to bacterial lipopolysaccharide (LPS), UV irradiation, or TNF-alpha occurred through a signaling path sensitive to the p38 mitogen-activated protein kinase (p38 MAPK) inhibitor SB203580 whereas IFN-gamma-mediated Ser727 phosphorylation was not inhibited by the drug. Consistently, SB203580 did not affect IFN-gamma-mediated, Stat1-dependent transcription but inhibited its enhancement by LPS. Furthermore, LPS, UV irradiation, and TNF-alpha caused activation of p38 MAPK whereas IFN-gamma did not. An essential role for p38 MAPK activity in STAT1 Ser727 phosphorylation was confirmed by using cells expressing an SB203580-resistant p38 MAPK. In such cells, STAT1 Ser727 phosphorylation in response to UV irradiation was found to be SB203580 insensitive. Targeted disruption of the mapkap-k2 gene, encoding a kinase downstream of p38 MAPK with a key role in LPS-stimulated TNF-alpha production and stress-induced heat shock protein 25 phosphorylation, was without a significant effect on UV-mediated Ser727 phosphorylation. The recombinant Stat1 C terminus was phosphorylated in vitro by p38MAPKalpha and beta but not by MAPK-activated protein kinase 2. Janus kinase 2 activity, previously reported to be required for IFN-gamma-mediated Ser727 phosphorylation, was not needed for LPS-mediated Ser727 phosphorylation, and activation of Janus kinase 2 did not cause the appearance of STAT1 Ser727 kinase activity. Our data suggest that STAT1 is phosphorylated at Ser727 by a stress-activated signaling pathway either through p38 MAPK directly or through an unidentified kinase downstream of p38MAPK.
Kovarik
P
P
Vienna Biocenter, Institute of Microbiology and Genetics, Dr. Bohr-Gasse 9, A-1030 Vienna, Austria.
Stoiber
D
D
Eyers
P A
PA
Menghini
R
R
Neininger
A
A
Gaestel
M
M
Cohen
P
P
Decker
T
T
D000818:Animals; D002460:Cell Line; D002461:Cell Line, Transformed; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D007371:Interferon-gamma / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D053614:Janus Kinase 2; D008070:Lipopolysaccharides / Q000494:pharmacology; D020935:MAP Kinase Signaling System; D008264:Macrophages / Q000166:cytology / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D011725:Pyridines / Q000494:pharmacology; D011817:Rabbits; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D050794:STAT1 Transcription Factor; D012694:Serine / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology / Q000494:pharmacology; D014466:Ultraviolet Rays; D048051:p38 Mitogen-Activated Protein Kinases; D000099190:MAP-Kinase-Activated Kinase 2
D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D007093:Imidazoles; D007371:Interferon-gamma; D047908:Intracellular Signaling Peptides and Proteins; D053614:Janus Kinase 2; D008070:Lipopolysaccharides; D020928:Mitogen-Activated Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D011725:Pyridines; D011993:Recombinant Fusion Proteins; D050794:STAT1 Transcription Factor; D012694:Serine; D015534:Trans-Activators; D014409:Tumor Necrosis Factor-alpha; D048051:p38 Mitogen-Activated Protein Kinases; D000099190:MAP-Kinase-Activated Kinase 2; C494079:STAT1 protein, human; C507924:JAK2 protein, human; C093642:SB 203580