Interleukin-1 receptor-associated kinase and TRAF-6 mediate the transcriptional regulation of interleukin-2 by interleukin-1 via NFkappaB but unlike interleukin-1 are unable to stabilise interleukin-2 mRNA.

Interleukin-1 receptor-associated kinase, IRAK, has been shown to activate NFkappaB in response to interleukin-1. We have explored the involvement of IRAK in regulation of the interleukin-2 gene in the murine thymoma cell line EL4.NOB-1 by examining its effect on interleukin-2 promoter-linked reporter gene expression, interleukin-2 gene transcription and interleukin-2 protein production. Cells transfected with IRAK displayed high levels of phosphorylated IRAK, increased interleukin-2 promoter-linked reporter gene expression (which was dependent on NFkappaB) and interleukin-2 gene transcription. IRAK was unable, however, to increase interleukin-2 protein production. Overexpression of TRAF-6 induced similar responses and again failed to increase interleukin-2 protein production. A dominant negative TRAF-6 inhibited reporter gene expression and interleukin-2 protein production in response to both interleukin-1 and IRAK transfection. Interleukin-1 treatment and IRAK or TRAF-6 transfection increased interleukin-2 mRNA production. Only interleukin-1 treatment stabilised the induced transcripts with 50% being detectable at 20 h post induction. The interleukin-2 mRNA induced in IRAK- or TRAF-6-transfected cells was depleted by >90% at 6 h post induction. These data implicate IRAK and TRAF-6 in transcriptional regulation of interleukin-2 gene expression via NFkappaB, and provide direct evidence that IRAK lies upstream from TRAF-6. Neither IRAK nor TRAF-6 participates in stabilisation of interleukin-2 mRNA which is required for interleukin-2 protein production.