SIGNAL-TRANSDUCTION OF INTERLEUKIN-2 IN HUMAN NATURAL-KILLER-CELLS - INVOLVEMENT OF THE P56(LCK) TYROSINE KINASE

Despite numerous reports, the role of the protein tyrosine kinase p56( kk) in IL-2 signal transduction has remained controversial. We show he re, using IL-2-dependent human natural killer cell lines, that p56(kk) is regulated by IL-2 in two different ways: (1) IL-2 induces a rapid increase of p56(kk) kinase activity as assessed in vitro; and (2) foll owing IL-2 stimulation, p56(kk) undergoes phosphorylation on serine re sidues that is reflected by a modification of its electrophoretic mobi lity in SDS-PAGE. Furthermore, dose response experiments, and blocking studies performed with anti-IL-2R alpha antibodies, indicated that bi nding of IL-2 to the IL-2R beta chain was sufficient to produce these modifications of p56(kk). In contrast, activation of the CD2 pathway s timulated the kinase activity of p56(kk), but did not induce a signifi cant shift in NK cells, as opposed to T lymphocytes. Western blot anal yses, and immunoprecipitations of cell lysates from P-32-preloaded NK cells demonstrated that seven major proteins are tyrosine phosphorylat ed in response to IL-2. These phosphoproteins, with apparent molecular weights of 190, 150, 120, 110, 85, 65 and 56, which may not all be p5 6(kk) substrates, undergo phosphorylation and dephosphorylation with d ifferent kinetics. Furthermore, pp120 was identified as rasGAP, by Wes tern blot and immunoprecipitation experiments. rasGAP and some of its co-precipitating molecules become phosphorylated in response to IL-2, presumably by p56(kk), which would thus provide a link between IL-2R a nd downstream events critical for NK cell proliferation and function.