STRUCTURAL DOMAINS OF INTERLEUKIN-2 RECEPTOR-BETA CRITICAL FOR SIGNAL-TRANSDUCTION - KINASE ASSOCIATION AND NUCLEAR COMPLEX-FORMATION

The structural domains of interleukin-2 receptor beta (IL-2R beta) wer e examined, characterizing the protein domains, associated phosphoprot eins and nuclear complexes of IL-2-induced signal transduction. A seri es of IL-2R beta cytoplasmic deletion mutants were constructed and tra nsfected into a murine pre-B-cell line, Ba/F3. The proliferative respo nse of characterized clones was determined. A minimal linear cytoplasm ic sequence required for proliferation and a sequence motif (PQPLXP) n eeded along with Box1-Box2 for IL-2-induced proliferation were identif ied, Anti-phosphotyrosine Western-blot analysis of a stimulated biolog ically active clone showed several IL-2-induced tyrosylphosphorylated proteins with molecular masses ranging from 45 to 116 kDa. In vitro ki nase studies of biologically active clone-receptor complexes showed a 116 kDa protein (p116) to be the major tyrosine-phosphorylated compone nt. The presence of the p116 kinase in the receptor complex correlates with IL-2-induced proliferation. An IL-2-inducible p116 kinase has re cently been characterized as a Jak kinase family member and named Jak3 . Nuclear complexes were formed with the GRR oligomer only when the IL -2R beta mutant supported proliferation. This led us to conclude that Box1-Box2 and PQPLXP motifs associate with Jak3 and that this associat ion is an essential element in the IL-2 signal-transduction pathway cu lminating in the formation of a nuclear complex.