Abstract
Tyrosine phosphorylation of multiple proteins, including the receptor itself, is an initial event in IL-2 signaling and leads to recruitment of SH2 or PTB domain-containing proteins to the receptor. In this study, we have used subdomains of the IL-2 receptor β chain (IL-2Rβ) expressed in Escherichia coli as GST fusion proteins to identify the tyrosine residues that could be phosphorylated by p56 lck, one of the critical tyrosine kinases activated by IL-2. We report that recombinant p56 lck phosphorylates in vitro tyrosine residues within the IL-2Rβ chain but not those within the IL-2Rγ chain. p56 lck phosphorylates tyrosine residues 355, 358 and 361 but not 338 of the IL-2Rβ chain acidic subdomain. Interestingly, phosphorylation of Tyr-358 appears to require the presence of either Tyr-355 or Tyr-361. p56 lck also phosphorylates very efficiently the two tyrosines present in the IL-2Rβ chain C-terminal region, Tyr-392 and Tyr-510. We also investigated the association of p56 lck with the IL-2Rβ chain which was found to depend on a short stretch of the IL-2Rβ chain acidic subdomain, and to be independent of the presence of its tyrosine residues.
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