Abstract
Interleukin‐1 (IL‐1) stimulates the association of the IL‐1 receptor‐associated protein kinase (IRAK) with the heterodimer of IL‐1RI and IL‐1RAcP via the adapter protein MyD88. In the receptor complex IRAK becomes heavily phosphorylated and concomitantly activated. Here we show that overexpression of a kinase‐inactive mutant of IRAK (K239S) inhibits neither IL‐1‐stimulated activation of the transcription factor NF‐κB, nor that of the c‐Jun N‐terminal kinase nor IL‐2 production in murine EL‐4 cells, but enhances these effects in a manner comparable to wild type IRAK. This strongly suggests that the intrinsic kinase activity is not required for downstream signaling via IRAK.

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