P56lck: a transducing protein that binds to SH2 containing proteins and to phosphotyrosine containing proteins.

In T lymphocytes, several proteins are rapidly phosphorylated on tyrosine after stimulation. In this study we examine the ability of tyrosine phosphorylated proteins from Jurkat T cells stimulated by CD2 or T cell receptor (TcR)-CD3 to interact with the src homology 2 (SH2) domains from p56lck (Lck). Our data show that the patterns are different depending on the stimulation. The specificity of the interactions was assessed by blocking experiments with high affinity phosphotyrosine [Y(P)] peptides. Phosphorylation experiments suggest that one or several kinases are able to interact with the SH2 from Lck. On the other hand, full length Lck overexpressed in Sf9 cells, which is tyrosine-phosphorylated at least on two sites, can interact in vitro with the SH2 from Lck, phospholipase C (PLC)-gamma 1, p85 (the regulatory subunit of phosphatidyl-inositol-3 kinase (PI3K)) and Nck and with the full length Grb2. These data give additional support to the idea that Lck is an important signal transducing molecule in lymphocytes.