Activation of Phospholipase C2 by Tyrosine Phosphorylation

Phospholipase C2 (PLC2) has been implicated in collagen-induced signal transduction in platelets and antigen-dependent signaling in B-lymphocytes. It has been suggested that tyrosine kinases activate PLC2. We expressed the full-length cDNA for human PLC2 in bacteria and purified the recombinant enzyme. The recombinant enzyme was Ca2-dependent with optimal ac-tivity in the range of 1 to 10 M Ca2. In vitro phosphorylation experiments with recombinant PLC2 and recombinant Lck, Fyn, and Lyn tyrosine kinases showed that phosphorylation of PLC2 led to activation of the recombinant enzyme. Using site-directed mutagenesis, we investigated the role of specific tyrosine residues in activation of PLC2. A mutant form of PLC2, in which all three tyrosines at positions 743, 753, and 759 in the SH2-SH3 linker region were replaced by phenylalanines, exhibited decreased Lck