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J. Exp. Med.,
Volume 187, Number 12, June 15, 1998 2073-2079
By







From the * R.W. Johnson Pharmaceutical Research Institute, San Diego, California 92121; and the Interleukin (IL)-1 is a proinflammatory cytokine with pleiotropic effects in inflammation. IL-1
binding to its receptor triggers a cascade of signaling events, including activation of the stress-activated mitogen-activated protein (MAP) kinases, c-Jun NH2-terminal kinase (JNK) and p38
MAP kinase, as well as transcription factor nuclear factor
R.W. Johnson Pharmaceutical Research Institute, Raritan, New Jersey 08869
B (NF-
B). IL-1 signaling results in
cellular responses through induction of inflammatory gene products such as IL-6. One of the
earliest events in IL-1 signaling is the rapid interaction of IL-1 receptor-associated kinases,
IRAK and IRAK-2, with the receptor complex. The relative roles of IRAK and IRAK-2 in
IL-1 signaling pathways and subsequent cellular responses have not been previously determined. To evaluate the importance of IRAK in IL-1 signaling, IRAK-deficient mouse fibroblast cells were prepared and studied. Here we report that IL-1-mediated activation of JNK,
p38, and NF-
B were all reduced in embryonic fibroblasts deficient in IRAK expression. In
addition, IL-6 production in response to IL-1 was also dramatically reduced in IRAK-deficient embryonic fibroblasts and in skin fibroblasts prepared from IRAK-deficient mice. Our results
demonstrate that IRAK plays an essential proximal role in coordinating multiple IL-1 signaling
pathways for optimal induction of cellular responses.
B
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