Coordinate regulation of TPL-2 and NF-κB signaling in macrophages by NF-κB1 p105.
The role of IκB kinase (IKK)-induced proteolysis of NF-κB1 p105 in innate immune signaling was investigated using macrophages from Nfkb1(SSAA/SSAA) mice, in which the IKK target serines on p105 are mutated to alanines. We found that the IKK/p105 signaling pathway was essential for TPL-2 kinase activation of extracellular signal-regulated kinase (ERK) mitogen-activate protein (MAP) kinase and modulated the activation of NF-κB. The Nfkb1(SSAA) mutation prevented the agonist-induced release of TPL-2 from its inhibitor p105, which blocked activation of ERK by lipopolysaccharide (LPS), tumor necrosis factor (TNF), CpG, tripalmitoyl-Cys-Ser-Lys (Pam(3)CSK), poly(I · C), flagellin, and R848. The Nfkb1(SSAA) mutation also prevented LPS-induced processing of p105 to p50 and reduced p50 levels, in addition to decreasing the nuclear translocation of RelA and cRel. Reduced p50 in Nfkb1(SSAA/SSAA) macrophages significantly decreased LPS induction of the IκBζ-regulated Il6 and Csf2 genes. LPS upregulation of Il12a and Il12b mRNAs was also impaired although specific blockade of TPL-2 signaling increased expression of these genes at late time points. Activation of TPL-2/ERK signaling by IKK-induced p105 proteolysis, therefore, induced a negative feedback loop to downregulate NF-κB-dependent expression of the proinflammatory cytokine interleukin-12 (IL-12). Unexpectedly, TPL-2 promoted soluble TNF production independently of IKK-induced p105 phosphorylation and its ability to activate ERK, which has important implications for the development of anti-inflammatory drugs targeting TPL-2.
Division of Immune Cell Biology, MRC National Institute for Medical Research, Mill Hill, London, United Kingdom.
Huei-Ting
HT
Yang
Stamatia
S
Papoutsopoulou
Monica
M
Belich
Christine
C
Brender
Julia
J
Janzen
Thorsten
T
Gantke
Matt
M
Handley
Steven C
SC
Ley
D019943:Amino Acid Substitution; D000818:Animals; D002478:Cells, Cultured; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000276:immunology; D005786:Gene Expression Regulation; D051550:I-kappa B Kinase / Q000235:genetics / Q000276:immunology*; D053765:Interleukin-12 Subunit p35 / Q000235:genetics; D053762:Interleukin-12 Subunit p40 / Q000235:genetics; D008070:Lipopolysaccharides / Q000276:immunology; D020930:MAP Kinase Kinase Kinases / Q000276:immunology*; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D016328:NF-kappa B / Q000276:immunology*; D052002:NF-kappa B p50 Subunit / Q000235:genetics* / Q000276:immunology*; D011518:Proto-Oncogene Proteins / Q000276:immunology*; D012333:RNA, Messenger / Q000235:genetics; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000276:immunology; D048069:Tumor Necrosis Factors / Q000276:immunology
C508859:Il12a protein, mouse; D053765:Interleukin-12 Subunit p35; D053762:Interleukin-12 Subunit p40; D008070:Lipopolysaccharides; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D048069:Tumor Necrosis Factors; D051550:I-kappa B Kinase; D048049:Extracellular Signal-Regulated MAP Kinases; D020930:MAP Kinase Kinase Kinases; C489843:Map3k8 protein, mouse