Tag: Rabbit polyclonal to ZNF268.

STAT1 is an essential transcription factor for macrophage activation by IFN-γ

STAT1 is an essential transcription factor for macrophage activation by IFN-γ and requires phosphorylation of the C-terminal Ser727 for transcriptional activity. was confirmed by using cells expressing an SB203580-resistant p38 MAPK. Cobicistat In such cells STAT1 Ser727 phosphorylation in response to UV irradiation was found to be SB203580 insensitive. Targeted disruption of the gene encoding a kinase downstream of p38 MAPK with a key role in LPS-stimulated TNF-α 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 by β and p38MAPKα but not by MAPK-activated protein kinase 2. Janus kinase 2 activity previously reported to be required for IFN-γ-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. Signal transducers and activators of transcription (STATs) cause rapid transcriptional responses to cytokines (1 2 The prototype of this protein family STAT1 lies at the heart of the immediate response to interferons (IFN). Targeted disruption of the STAT1 gene obstructs the IFN “system” and causes a loss of natural immunity to microbial pathogens (3 4 In the case of bacteria this is largely attributable to an impairment of macrophage activation by the Th1 cytokine IFN-γ. In a normal situation IFN-γ activates STAT1 by triggering phosphorylation at two distinct sites. IFN-γ receptor-associated Janus kinases 1 and 2 (JAK1 and JAK2) phosphorylate Tyr701 and induce SH2 domain-mediated STAT1 dimerization followed by nuclear translocation and Cobicistat binding to γ-interferon activation site DNA sequences (1 5 The C-terminal Ser727 within a potential mitogen-activated protein kinase (MAPK) consensus PMSP motif is phosphorylated by (a) hitherto unknown kinase(s). This event strongly increases the transcription factor activity of STAT1 (6). In fact STAT1 mutated to alanine at position 727 is unable to mediate interferon responses (7 8 Relevant to the biology of macrophages S727 can serve to feed IFN-γ-independent signals into STAT1. For example macrophage-activating components of bacterial Rabbit polyclonal to ZNF268. cell walls like lipopolysaccharide (LPS) strongly activate a STAT1 Ser727 kinase independently of Tyr701 phosphorylation. Concomitantly the presence of IFN-γ and LPS increases the efficiency of Ser727 phosphorylation over that of IFN-γ alone and thus produces a large pool of STAT1 molecules phosphorylated on both Tyr701 and Ser727 (9). The presence of bacterial signals thus enhances the synthesis of an arsenal of antimicrobial proteins that occurs upon IFN-γ-mediated macrophage activation because it promotes transcription of STAT1 Cobicistat target genes over that induced by IFN-γ alone. STAT1 Ser727 phosphorylation contributes to the antibacterial strategies of the innate immune system therefore. An open question remains whether LPS-derived signals target the same STAT1 Ser727 kinase that is also stimulated by IFN-γ. The treatment of macrophages with LPS causes activation of all three major groups of MAPKs (10 11 These are the extracellular signal-regulated kinases (ERK1 and ERK2) as well as the c-Jun kinases (JNKs) and the p38 MAPK isoenzymes. Although ERKs are usually referred to as growth factor-stimulated MAPKs JNKs and p38 MAPK are classical stress-activated kinases stimulated by a plethora of signals such as proinflammatory cytokines like TNF-α or IL-1 UV irradiation microbial infection osmotic Cobicistat stress and others (12). Proteins such as transcription factors translation initiation factors or heat shock proteins that are targets of MAPK Cobicistat pathways and orchestrate a cellular growth factor or stress response may be direct substrates of ERKs JNKs or p38 MAPK or alternatively may be phosphorylated by kinases that are their substrates. Several protein Cobicistat kinase substrates of MAPKs have been identified and are targets of the ERK1/2 pathway {MAPK-activated kinase [MAPKAP-K1/ribosomal S6 kinase (RSK)] (13 14 the p38 MAPK.