Solving the IRAK-4 enigma: application of kinase-dead knock-in mice.
Interleukin-1 receptor-associated kinase (IRAK-4) is an essential component of the signal transduction complex downstream of the interleukin (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 has been controversial. In order to investigate the role of IRAK-4 kinase function in vivo, we generated "knock-in" mice where the wild-type IRAK-4 gene is replaced with a mutant gene encoding kinase-deficient IRAK-4 protein (IRAK-4 KD). IRAK-4 kinase is 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 demonstrated lack of cellular responsiveness to stimulation with IL-1beta or Toll-like receptor 4 (TLR4) and TLR7 agonists. IRAK-4 KD cells were severely impaired in NF-kappaB, JNK, and p38 activation in response to IL-1beta or TLR7 ligand. In addition, activation of JNK and p38 was affected in lipopolysaccharide (LPS)-stimulated IRAK-4 KD macrophages. As a consequence, IL-1 receptor/TLR4/TLR7-mediated production of cytokines and chemokines was 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-1R-, TLR4-, and TLR7-mediated induction of inflammatory responses.
Koziczak-Holbro
M
M
Novartis Institutes for BioMedical Research, Postfach 4002, Basel, Switzerland. magdalena.koziczak@novartis.com
Joyce
C
C
Glück
A
A
Kinzel
B
B
Müller
M
M
Gram
H
H
D000818:Animals; D005786:Gene Expression Regulation; D006801:Humans; D053592:Interleukin-1 Receptor-Associated Kinases / Q000235:genetics / Q000378:metabolism*; D053583:Interleukin-1beta / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D015398:Signal Transduction; D051193:Toll-Like Receptors / Q000378:metabolism; D014158:Transcription, Genetic / Q000235:genetics
D053583:Interleukin-1beta; D051193:Toll-Like Receptors; D053592:Interleukin-1 Receptor-Associated Kinases; C507774:Irak4 protein, mouse