Phosphoinositide-specific phospholipase C (PLC) plays a critical role in the initiation of receptor mediated signal transduction through the generation of the two second messengers, inositol 1,4,5-triphosphate and diacylglycerol from phosphatidylinositol 4,5-bisphosphate.There are many mammalian PLC isozymes, including PLC (beta)1, PLC (beta)2, PLC (beta)3, PLC (beta)4, PLC (gamma)1, PLC (gamma)2, PLC ?1, PLC ?2 and PLC e. After stimulation of the collagen receptor glycoprotein VI in human platelets, PLC (gamma)2 associates with several tyrosine-phosphorylated proteins (Syk, SLP-76, Lyn, linker for activation of T cells (LAT) and the FcR (gamma) chain), which bind to its C-terminal SH2 domain. PLC (gamma)1 associates with Syk in B cells, but PLC (gamma)2 does not associate with Syk in platelets. The C-terminal SH2 domain is involved in the regulation of PLC (gamma)2. In addition, Btk can induce PLC (gamma)2 tyrosine phosphorylation and initiate calcium moblization in CD72-stimulated B lymphocytes.