Effects of IL-1 receptor-associated kinase (IRAK) expression on IL-1 signaling are independent of its kinase activity

Interleukin-1 (IL-1) stimulates the association of the IL-1 receptor-associ ated protein kinase (IRAK) with the heterodimer of IL-1RI and IL-1RAcP via the adapter protein MyD88. In the receptor complex IRAK becomes heavily pho sphorylated and concomitantly activated. Here we show that overexpression o f a kinase-inactive mutant of IRAK (K239S) inhibits neither IL-1-stimulated activation of the transcription factor NF-kappa B, nor that of the c-Jun N -terminal kinase nor IL-2 production in murine EL-4 cells, but enhances the se effects in a manner comparable to wild type IRAK. This strongly suggests that the intrinsic kinase activity is not required for downstream signalin g via IRAK. (C) 1999 Federation of European Biochemical Societies.