response to IL-1b of WT and IRAK4 kinase dead mouse embryonic fibroblasts

IRAK-4 is an essential component of the signal transduction complex downstream of the IL-1- and Toll-like receptors. Though regarded as the first kinase in the signaling cascade, the role of IRAK-4 kinase activity versus its scaffold function is still controversial. In order to investigate the role of IRAK-4 kinase function in vivo, knock-in mice were generated by replacing the wild type IRAK-4 gene with a mutant gene encoding kinase deficient IRAK-4 protein (IRAK-4 KD). Analysis of embryonic fibroblasts and macrophages obtained from IRAK-4 KD mice with a number of experimental techniques demonstrated that they greatly lack responsiveness to stimulation with IL-1b or a Toll-like receptor 7 (TLR7) agonist. One of the techniques used, microarray analysis, identified IRAK-4 kinase-dependent IL-1b response genes in mouse embryonic fibroblasts and revealed that the induction of IL-1b-responsive mRNAs was largely ablated in IRAK-4 KD cells. In summary, our results suggest that IRAK-4 kinase activity plays a critical role in IL-1R/TLR7-mediated induction of inflammatory responses.

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Koziczak-Holbro M, Joyce C, Glück A, Kinzel B, Müller M, Tschopp C, Mathison JC, Davis CN, Gram H