RIP2 mediates LPS-induced p38 and IkappaBalpha signaling including IL-12 p40 expression in human monocyte-derived dendritic cells.
IL-12, the critical factor for the generation of the Th1 type immune response, is produced by dendritic cells (DC) upon stimulation with LPS. Different signal pathways mediate LPS-induced expression of IL-12 and involve PI3K, MAPK and the transcription factor NF-kappaB. Here, we show that the kinase Raf is involved in the expression of IL-12 in human DC stimulated by LPS. We demonstrate that Raf regulates the expression of the IL-12 subunit p40 not via the kinase MEK, the major effector of Raf in growth factor-dependent signaling, but via the receptor-interacting protein 2 (RIP2) using specific inhibitors for MAPK pathways. RIP2 is a kinase participating in LPS/Toll-like receptor 4 signaling. Knockdown of RIP2 by siRNA inhibited LPS-dependent expression of IL-12 p40. In addition, knockdown of RIP2 reduced phosphorylation of p38 MAPK, ERK and IkappaBalpha, which are known upstream regulators of IL-12 production. Thus, in human DC LPS stimulates a signal cascade that involves the Raf-dependent activation of RIP2 leading to expression of IL-12 p40.
Usluoglu
Nurguel
N
Institute of Medical Virology, University of Zurich, Zurich, Switzerland.
Pavlovic
Jovan
J
Moelling
Karin
K
Radziwill
Gerald
G
D015153:Blotting, Western; D002478:Cells, Cultured; D003713:Dendritic Cells / Q000276:immunology* / Q000378:metabolism; D015870:Gene Expression / Q000276:immunology; D006801:Humans; D020672:I-kappa B Proteins / Q000276:immunology* / Q000378:metabolism; D053762:Interleukin-12 Subunit p40 / Q000096:biosynthesis*; D008070:Lipopolysaccharides / Q000276:immunology; D009000:Monocytes / Q000166:cytology / Q000276:immunology; D000072000:NF-KappaB Inhibitor alpha; D034741:RNA, Small Interfering; D053475:Receptor-Interacting Protein Serine-Threonine Kinase 2 / Q000276:immunology* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000276:immunology*; D014162:Transfection; D048051:p38 Mitogen-Activated Protein Kinases / Q000276:immunology* / Q000378:metabolism
D020672:I-kappa B Proteins; D053762:Interleukin-12 Subunit p40; D008070:Lipopolysaccharides; C000606204:NFKBIA protein, human; D034741:RNA, Small Interfering; D000072000:NF-KappaB Inhibitor alpha; C506253:RIPK2 protein, human; D053475:Receptor-Interacting Protein Serine-Threonine Kinase 2; D048051:p38 Mitogen-Activated Protein Kinases