CHARACTERIZATION OF AN INTERLEUKIN-2 (IL-2)-INDUCED TYROSINE-PHOSPHORYLATED 116-KDA PROTEIN ASSOCIATED WITH THE IL-2 RECEPTOR BETA-SUBUNIT

In this paper we have extended previous results on interleukin-2 recep tor (IL2-R) signal transduction and focused on the interleukin-2 (IL-2 )-stimulated tyrosine phosphorylation of a 116-kDa protein (p116) obse rved in IL-2 responsive cells. This protein exhibited rapid and transi ent phosphorylation kinetics in both human T-lymphocytes and the YT ce ll line, attaining maximum tyrosine phosphorylation within 5 min of st imulation with IL-2. Tyrosine phosphorylated p116 co-purified with act ivated IL-2 receptor beta-chain (IL2-Rbeta) when IL2-R complexes were covalently stabilized with the membrane-permeable cleavable cross-link ing agent dithiobis(succimidyl propionate) prior to detergent cell lys is and immunoprecipitation with monoclonal anti-IL2-Rbeta antibodies. Under these conditions comparable amounts of tyrosine-phosphorylated p 116 were immuno-precipitated with either anti-IL2-Rbeta antibodies or antiphosphotyrosine antibodies, suggesting that a major portion of tyr osine phosphorylated p116 is associated with the IL2-Rbeta subunit. Fu rthermore, unphosphorylated p116 was also associated with unactivated IL2-Rbeta, based on the observation that p116 from unstimulated YT cel ls underwent tyrosine phosphorylation in IL2-Rbeta immune-complex tyro sine kinase assay as demonstrated by anti-phosphotyrosine immunoblotti ng. The presence of tyrosine kinase activity in affinity-purified IL2- Rbeta complexes supports the notion of a preformed receptor-kinase com plex. The co-association of both p116 and tyrosine kinase activity wit h the IL2-Rbeta supports the critical role of the beta-chain in IL2-R signal transduction and suggests that p116 may have a role in the dyna mics of IL2-R activation.