Genetic analysis of the role of the PI3K-Akt pathway in lipopolysaccharide-induced cytokine and tissue factor gene expression in monocytes/macrophages.
LPS stimulation of monocytes/macrophages induces the expression of genes encoding proinflammatory cytokines and the procoagulant protein, tissue factor. Induction of these genes is mediated by various signaling pathways, including mitogen-activated protein kinases, and several transcription factors, including Egr-1, AP-1, ATF-2, and NF-kappaB. We used a genetic approach to determine the role of the phosphatidylinositol-3-kinase (PI3K)-protein kinase B (Akt) pathway in the regulation of LPS signaling and gene expression in isolated macrophages and in mice. The PI3K-Akt pathway is negatively regulated by the phosphatase and tensin homologue (PTEN). We used peritoneal exudate cells from Pik3r1-deficient mice, which lack the p85alpha regulatory subunit of PI3K and have reduced PI3K activity, and peritoneal macrophages from PTEN(flox/flox)/LysMCre mice (PTEN(-/-)), which have increased Akt activity. Analysis of LPS signaling in Pik3r1(-/-) and PTEN(-/-) cells indicated that the PI3K-Akt pathway inhibited activation of the ERK1/2, JNK1/2, and p38 mitogen-activated protein kinases and reduced the levels of nuclear Egr-1 protein and phosphorylated ATF-2. Modulating the PI3K-Akt pathway did not affect LPS-induced degradation of IkappaBalpha or NF-kappaB nuclear translocation. LPS induction of TNF-alpha, IL-6, and tissue factor gene expression was increased in Pik3r1(-/-) peritoneal exudate cells and decreased in PTEN(-/-) peritoneal macrophages compared with wild-type (WT) cells. Furthermore, LPS-induced inflammation and coagulation were enhanced in WT mice containing Pik3r1(-/-) bone marrow compared with WT mice containing WT bone marrow and in mice lacking the p85alpha subunit in all cells. Taken together, our results indicate that the PI3K-Akt pathway negatively regulates LPS signaling and gene expression in monocytes/macrophages.
Luyendyk
James P
JP
Department of Immunology, The Scripps Research Institute, La Jolla, CA 92037, USA.
Schabbauer
Gernot A
GA
Tencati
Michael
M
Holscher
Todd
T
Pawlinski
Rafal
R
Mackman
Nigel
N
D000818:Animals; D001202:Ascitic Fluid / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D002478:Cells, Cultured; D016207:Cytokines / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics*; D015536:Down-Regulation / Q000276:immunology; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000276:immunology*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000276:immunology; D017737:Macrophages, Peritoneal / Q000201:enzymology / Q000276:immunology / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009000:Monocytes / Q000201:enzymology / Q000276:immunology / Q000378:metabolism*; D051059:PTEN Phosphohydrolase / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics; D019869:Phosphatidylinositol 3-Kinases / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D013925:Thromboplastin / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics*; D015854:Up-Regulation / Q000276:immunology
D016207:Cytokines; D008070:Lipopolysaccharides; D013925:Thromboplastin; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D051059:PTEN Phosphohydrolase