Interleukin-1 (IL-1)-receptor-associated kinase (IRAK) is an indispensable signalling molecule for host-defence responses initiated by a variety of ligands that bind to members of the Toll/IL-1 receptor family. Here we report a novel splice variant of mouse IRAK-1, IRAK-1-S, which is generated by utilizing a new splicing acceptor site within exon 12. IRAK-1-S cDNA is shorter than the originally reported IRAK-1 (IRAK-1-W) cDNA by 271 nucleotides, and the subsequent frameshift causes a premature termination of translation after 23 amino acids, which are unique to the IRAK-1-S protein. To elucidate the physiological function of IRAK-1-S, we overexpressed it in 293T cells and studied the effects on the IL-1 signalling cascade. As it lacks the C-terminal region of IRAK-1-W that has been reported to contain the TRAF6 (tumour necrosis factor receptor-associated factor 6) binding domain, IRAK-1-S was unable to bind TRAF6 protein, which is a proposed downstream signalling molecule. However, IRAK-1-S overexpressed in 293T cells induced constitutive activation of nuclear factor-κB (NF-κB) and c-Jun N-terminal kinase (JNK) independent of stimulation by IL-1, as did IRAK-1-W. To clarify the mechanism of NF-κB activation by IRAK-1-S in the absence of binding to TRAF6, we demonstrated that IRAK-1-S binds to IRAK-1-W through its death domain; the findings suggested that overexpressed IRAK-1-S may bind endogenous IRAK-1-W and activate TRAF6 through IRAK-1-W. These results also indicate that this novel variant may play roles in the activation of NF-κB and JNK by IL-1 and other ligands whose signal transduction is dependent on IRAK-1 under physiological conditions.
- alternative splicing
- death domain
- IL-1-receptor-associated kinase (IRAK)
- IL-1 signalling
- c-Jun N-terminal kinase (JNK)
- nuclear factor-κB (NF-κB)
The novel nucleotide sequence data reported will appear in the DDBJ, EMBL, GenBank® and GSDB Nucleotide Sequence Databases under accession numbers AB088370 (cDNA sequence covering the whole coding region of IRAK-1-S) and AB088390 (genomic sequence covering introns 11—12 of mouse IRAK-1).
Abbreviations used: EMSA, electrophoretic mobility-shift assay; HA, haemagglutinin; IL-1, interleukin-1; IL-1R, IL-1 receptor; IRAK, IL-1-receptor-associated kinase; IRAK-1-W, mouse full-length IRAK-1 reported originally (aa 1—710); IRAK-1-S, novel splice variant of IRAK-1; IRAK-1-W-ΔN, N-terminally truncated IRAK-1-W (aa 34—710 of IRAK-1-W); JNK, c-Jun N-terminal kinase; NF-κB, nuclear factor κB; RT-PCR, reverse transcription—PCR; TAK, transforming growth factor-β-activated kinase; TLR, Toll-like receptor; TNF, tumour necrosis factor; TRAF6, TNF-receptor-associated factor 6.
- The Biochemical Society, London ©2003