TLR2- and TLR4-dependent activation of STAT1 serine phosphorylation in murine macrophages is protein kinase C-delta-independent.
Engagement of Toll-like receptor (TLR) proteins activates multiple signal transduction pathways. Previous studies demonstrated that TLR2 and TLR4 engagement leads to rapid phosphorylation of the transcription factor STAT1 at serine 727 (Ser-727 STAT1) in murine macrophages. Only TLR4 engagement induced STAT1 phosphorylation at tyrosine 701, although this response was delayed compared with Ser-727 STAT1 phosphorylation. Unlike other cell types, the p38 mitogen-activated protein kinase was necessary, but not sufficient, for TLR-induced phosphorylation of Ser-727 STAT1 in macrophages. We and others had previously shown that Ser-727 STAT1 phosphorylation could be blocked by rottlerin, an inhibitor of protein kinase C-delta (PKC-delta). Here we report that peritoneal exudate macrophages from PKC-delta-deficient mice can be activated through TLR2 and TLR4 to elicit rapid phosphorylation of Ser-727 STAT1, which was blocked by both rottlerin and the p38 inhibitor SB203580, but not by the pan-PKC inhibitor bisindoylmaleamide. Furthermore, both normal and PKC-delta-deficient macrophages secreted comparable amounts of IL-6, IP-10, and RANTES following TLR engagement. In contrast, IFN-gamma-induced STAT1 serine phosphorylation was independent of both PKC-delta and p38. Overall, these studies demonstrate that a PKC-delta-independent signaling pathway downstream of both TLR2 and TLR4 is necessary for Ser-727 STAT1 phosphorylation in primary murine macrophages.
Shoenfelt
Joanna L
JL
Division of Pulmonary and Critical Care Medicine and Mucosal Biology Research Center, University of Maryland School of Medicine, Baltimore, USA.
Fenton
Matthew J
MJ
D000098:Acetophenones / Q000494:pharmacology; D000818:Animals; D001578:Benzopyrans / Q000494:pharmacology; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004926:Escherichia coli / Q000276:immunology; D007093:Imidazoles / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D017737:Macrophages, Peritoneal / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010766:Phosphorylation; D010768:Phosphoserine / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051745:Protein Kinase C-delta / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology; D050794:STAT1 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D051195:Toll-Like Receptor 2 / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000378:metabolism*
D000098:Acetophenones; D001578:Benzopyrans; D016207:Cytokines; D004791:Enzyme Inhibitors; D007093:Imidazoles; D008070:Lipopolysaccharides; D011725:Pyridines; D050794:STAT1 Transcription Factor; C494080:Stat1 protein, mouse; C493486:Tlr2 protein, mouse; C493487:Tlr4 protein, mouse; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D010768:Phosphoserine; C085746:rottlerin; D051745:Protein Kinase C-delta; C093642:SB 203580