P56(LCK) - A TRANSDUCING PROTEIN THAT BINDS TO SH2 CONTAINING PROTEINS AND TO PHOSPHOTYROSINE-CONTAINING PROTEINS

In T lymphocytes, several proteins are rapidly phosphorylated on tyros ine after stimulation. In this study we examine the ability of tyrosin e phosphorylated proteins from Jurkat T cells stimulated by CD2 or T c ell receptor (TcR)-CD3 to interact with the src homology 2 (SH2) domai ns from p56(lck) (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-phosph orylated at least on two sites, can interact in vitro with the SH2 fro m Lck, phospholipase C (PLC)-gamma 1, p85 (the regulatory subunit of p hosphatidyl-inositol-3 kinase (PI3K)) and Nck and with the full length Grb2. These data give additional support to the idea that Lck is an i mportant signal transducing molecule in lymphocytes.