Association of STAT1, STAT3 and STAT5 proteins with the IL-2 receptor involves different subdomains of the IL-2 receptor β chain

Upon IL-2 stimulation of T lymphocytes, the IL-2 receptor (IL-2R) becomes phosphorylated on specific tyrosine residues which serve as docking sites for proteins containing SH2 or phosphotyrosine binding domains. To study the interaction of the IL-2R beta chain with Shc and STAT proteins, subdomains of the IL-2R beta chain were expressed as tyrosine-phosphorylated glutathione S-transferase fusion proteins and used to pull-down interacting proteins from Kit 225 cell lysates. These experiments provide direct biochemical evidence that binding to the IL-2R of the adaptor protein Shc requires phosphorylation of Tyr-338 in the IL-2R beta acidic subdomain. In addition, we report that STAT proteins that are activated by IL-2, i.e. STAT1, STAT3 and STAT5, indeed associate with the IL-2R beta chain. Both the A and B isoforms of STAT5 were found to associate with Tyr-510 of the IL-2R beta C-terminal region, depending on its phosphorylation. In contrast, STAT1 and STAT3 associated with the IL-2R beta chain through its acidic subdomain. These results indicate that the interaction between IL-2R beta and STAT1 or 3 does not require either phosphorylation of the receptor or even the presence of tyrosine residues of IL-2R beta. Thus, the IL-2R recruits STAT proteins through different modes of interaction.