INTERLEUKIN-2 STIMULATION INDUCES TYROSINE PHOSPHORYLATION OF P120-CBL AND CRKL AND FORMATION OF MULTIMOLECULAR SIGNALING COMPLEXES IN T-LYMPHOCYTES AND NATURAL-KILLER-CELLS

Interleukin (IL)-2, a major growth and differentiation factor far T ly mphocytes, was found to induce tyrosine phosphorylation of the proto-o ncogene products p120-Cbl and CrkL in IL-2-dependent cell lines, We es tablished that, in unstimulated lymphocytes, the Src homology 2 (SH2) and SH3 domain-containing protein Grb2 and the p85 subunit of phosphat idylinositol 3-kinase, associate constitutively with Cbl via their SPP S domains, Furthermore, IL-2 stimulation increased the level of intera ction of phosphorylated Cbl with the p85 SH2 domains, and we provide e vidence that the preformed Cbl-Grb2 complex recruits the phosphorylate d p52 Shc adaptor protein, In addition, we demonstrate that the SH2-SH 3-SH3 adaptor protein CrkL is tyrosine-phosphorylated in an IL-2-depen dent manner and, via its SH2 domain, associates with a large proportio n of phosphorylated Cbl, We also show that p85 is preassociated with t he CrkL SH3 domain, Furthermore, the association of CrkL and p85 is in creased after IL-2 treatment by a mechanism involving intermediary tyr osine-phosphorylated proteins that remain to be identified, Our result s show that CrkL associates independently with Cbl or p85 and suggest that it salse participates in larger complexes containing Cbl and p85. Although the precise roles of Cbl and CrkL remain to be elucidated, t heir tyrosine phosphorylation, in addition to the multiple protein int eractions described here, strongly suggest that Cbl and CrkL may play pivotal roles in the early steps of IL-2 signal transduction.