IRAK4 kinase activity is redundant for interleukin-1 (IL-1) receptor-associated kinase phosphorylation and IL-1 responsiveness.
Interleukin-1 (IL-1) stimulation leads to the recruitment of interleukin-1 receptor-associated kinase (IRAK) to the IL-1 receptor, where IRAK is phosphorylated, ubiquitinated, and eventually degraded. Kinase-inactive mutant IRAK is still phosphorylated in response to IL-1 stimulation when it is transfected into IRAK-deficient cells, suggesting that there must be an IRAK kinase in the pathway. The fact that IRAK4, another IRAK family member necessary for the IL-1 pathway, is able to phosphorylate IRAK in vitro suggests that IRAK4 might be the IRAK kinase. However, we now found that the IRAK4 kinase-inactive mutant had the same ability as the wild-type IRAK4 in restoring IL-1-mediated signaling in human IRAK4-deficient cells, including NFkappaB-dependent reporter gene expression, the activation of NFkappaB and JNK, and endogenous IL-8 gene expression. These results strongly indicate that the kinase activity of human IRAK4 is not necessary for IL-1 signaling. Furthermore, we showed that the kinase activity of IRAK4 was not necessary for IL-1-induced IRAK phosphorylation, suggesting that IRAK phosphorylation can probably be achieved either by autophosphorylation or by trans-phosphorylation through IRAK4. In support of this, only the impairment of the kinase activity of both IRAK and IRAK4 efficiently abolished the IL-1 pathway, demonstrating that the kinase activity of IRAK and IRAK4 is redundant for IL-1-mediated signaling. Moreover, consistent with the fact that IRAK4 is a necessary component of the IL-1 pathway, we found that IRAK4 was required for the efficient recruitment of IRAK to the IL-1 receptor complex.
Qin
Jinzhong
J
Department of Immunology, Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
Jiang
Zhengfan
Z
Qian
Youcun
Y
Casanova
Jean-Laurent
JL
Li
Xiaoxia
X
D015152:Blotting, Northern; D015153:Blotting, Western; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D019040:E-Selectin / Q000378:metabolism; D004789:Enzyme Activation; D005347:Fibroblasts / Q000378:metabolism; D017930:Genes, Reporter; D005816:Genetic Complementation Test; D006801:Humans; D007375:Interleukin-1 / Q000378:metabolism*; D053592:Interleukin-1 Receptor-Associated Kinases; D016209:Interleukin-8 / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases; D008156:Luciferases / Q000378:metabolism; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation; D016328:NF-kappa B / Q000378:metabolism; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism / Q000502:physiology*; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D017472:Receptors, Interleukin-1 / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection; D025801:Ubiquitin / Q000378:metabolism
D019040:E-Selectin; D007375:Interleukin-1; D016209:Interleukin-8; D016328:NF-kappa B; D017472:Receptors, Interleukin-1; D025801:Ubiquitin; D008156:Luciferases; D017853:Phosphotransferases (Alcohol Group Acceptor); C507773:IRAK4 protein, human; D053592:Interleukin-1 Receptor-Associated Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases