Evidence for a role for the phosphotyrosine-binding domain of Shc in interleukin 2 signaling

Stimulation via the T-cell growth factor interleukin 2 (IL-2) leads to tyrosine phosphorylation of Shc, the interaction of Shc with Grb2, and the Ras GTP/GDP exchange factor, mSOS. Shc also coprecipitates with the IL-2 receptor (IG-2R), and therefore, may link IL-2R to Ras activation. We have further characterized the Shc-IL-2R interaction and have made the following observations. (i) Among the two phosphotyrosine-interaction domains present in Shc, the phosphotyrosine-binding (PTB) domain, rather than its SH2 domain, interacts with the tyrosine-phosphorylated IL-2R beta chain. Moreover, the Shc-PTB domain binds a phosphopeptide derived from the IL-2R beta chain (corresponding to residues surrounding Y338, SCFTNQGpYFF) with high affinity. (ii) In vivo, mutant IL-2R beta chains lacking the acidic region of IL-2R beta (which contains Y338) fail to phosphorylate Shc. Furthermore, when wild type or mutant Shc proteins that lack the PTB domain were expressed in the IL-2-dependent CTLL-2O cell line, an intact Shc-PTB domain was required for Shc phosphorylation by the IL-2R, which provides further support for a Shc-PTB-IL-2R interaction in vivo. (iii) PTB and SH2 domains of Shc associate with different proteins in IL-2- and T-cell-receptor-stimulated lysates, suggesting that Shc, through the concurrent use of its two different phosphotyrosine-binding domains, could assemble multiple protein complexes. Taken together, our in vivo and in vitro observations suggest that the PTB domain of Shc interacts with Y338 of the IL-2R and provide evidence for a functional role for the Shc-PTB domain in IL-2 signaling.