The activated form of the Lck tyrosine protein kinase in cells exposed to hydrogen peroxide is phosphorylated at both Tyr-394 and Tyr-505.
Members of the Src family of non-receptor tyrosine protein kinases are known to be inhibited by the intramolecular association between a phosphorylated carboxyl-terminal tyrosine residue and the SH2 domain. We have previously shown that exposure of cells to H2O2 strongly activates Lck, a lymphocyte-specific Src family kinase, by inducing phosphorylation on Tyr-394, an absolutely conserved residue within the activation loop of the catalytic domain. Here we show that Lck that has been activated by H2O2 is simultaneously phosphorylated at both the carboxyl-terminal tyrosine (Tyr-505) and Tyr-394. Thus, dephosphorylation of Tyr-505 is not a prerequisite for either phosphorylation of Lck at Tyr-394 or catalytic activation of the kinase. These results indicate that activation of Lck by phosphorylation of Tyr-394 is dominant over any inhibition induced by phosphorylation of Tyr-505. We propose that these results may be extended to all Src family members.
Hardwick
J S
JS
Molecular Biology and Virology Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA. hardwick@biomail.ucsd.edu
Sefton
B M
BM
D000818:Animals; D015153:Blotting, Western; D002384:Catalysis; D004789:Enzyme Activation; D005347:Fibroblasts / Q000187:drug effects / Q000201:enzymology; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D019169:Jurkat Cells; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D013601:T-Lymphocytes / Q000187:drug effects / Q000201:enzymology; D014443:Tyrosine / Q000378:metabolism*
D014443:Tyrosine; D006861:Hydrogen Peroxide; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck)