Abstract
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.
Original language | English |
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Pages (from-to) | 13956-61 |
Number of pages | 6 |
Journal | Proceedings of the National Academy of Sciences of the United States of America |
Volume | 96 |
Issue number | 24 |
DOIs | |
Publication status | Published - 23 Nov 1999 |
Externally published | Yes |
Keywords
- Animals
- Cell Line
- Cell Line, Transformed
- DNA-Binding Proteins/metabolism
- Enzyme Activation
- Enzyme Inhibitors/pharmacology
- Humans
- Imidazoles/pharmacology
- Interferon-gamma/metabolism
- Intracellular Signaling Peptides and Proteins
- Janus Kinase 2
- Lipopolysaccharides/pharmacology
- MAP Kinase Signaling System
- Macrophages/cytology
- Mitogen-Activated Protein Kinases/metabolism
- Phosphorylation
- Protein Serine-Threonine Kinases/metabolism
- Protein-Tyrosine Kinases/metabolism
- Proto-Oncogene Proteins
- Pyridines/pharmacology
- Rabbits
- Recombinant Fusion Proteins/metabolism
- STAT1 Transcription Factor
- Serine/metabolism
- Trans-Activators/metabolism
- Transcription, Genetic/drug effects
- Tumor Necrosis Factor-alpha/immunology
- Ultraviolet Rays
- p38 Mitogen-Activated Protein Kinases