IRAK-4 kinase activity is required for interleukin-1 (IL-1) receptor- and toll-like receptor 7-mediated signaling and gene expression.
IRAK-4 is an essential component of the signal transduction complex downstream of the IL-1- and Toll-like receptors. Although regarded as the first kinase in the signaling cascade, the role of IRAK-4 kinase activity versus its scaffold function is still controversial. 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). IRAK-4 kinase was rendered inactive by mutating the conserved lysine residues in the ATP pocket essential for coordinating ATP. Analyses of embryonic fibroblasts and macrophages obtained from IRAK-4 KD mice demonstrate lack of cellular responsiveness to stimulation with IL-1beta or a Toll-like receptor 7 (TLR7) agonist. IRAK-4 kinase deficiency prevents the recruitment of IRAK-1 to the IL-1 receptor complex and its subsequent phosphorylation and degradation. IRAK-4 KD cells are severely impaired in NFkappaB, JNK, and p38 activation in response to IL-1beta or TLR7 ligand. As a consequence, IL-1 receptor/TLR7-mediated production of cytokines and chemokines is largely absent in these cells. Additionally, microarray analysis identified IL-1beta response genes and revealed that the induction of IL-1beta-responsive mRNAs is largely ablated in IRAK-4 KD cells. In summary, our results suggest that IRAK-4 kinase activity plays a critical role in IL-1 receptor (IL-1R)/TLR7-mediated induction of inflammatory responses.
Koziczak-Holbro
Magdalena
M
Novartis Institutes for BioMedical Research, CH-4002 Basel, Switzerland.
Joyce
Claire
C
Glück
Anton
A
Kinzel
Bernd
B
Müller
Matthias
M
Tschopp
Claude
C
Mathison
John C
JC
Davis
Christopher N
CN
Gram
Hermann
H
D000818:Animals; D002460:Cell Line; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D007249:Inflammation / Q000235:genetics / Q000378:metabolism; D053592:Interleukin-1 Receptor-Associated Kinases / Q000172:deficiency / Q000378:metabolism*; D008264:Macrophages / Q000166:cytology / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D017472:Receptors, Interleukin-1 / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D051199:Toll-Like Receptor 7 / Q000819:agonists / Q000235:genetics / Q000378:metabolism*
D008562:Membrane Glycoproteins; D046912:Multiprotein Complexes; D012333:RNA, Messenger; D017472:Receptors, Interleukin-1; C477038:Tlr7 protein, mouse; D051199:Toll-Like Receptor 7; D053592:Interleukin-1 Receptor-Associated Kinases; C507774:Irak4 protein, mouse