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Phosphoinositide-specific phospholipase C (PLC) plays a significant role in transmembrane signaling. In response to extracellular stimuli such as hormones, growth factors, and neurotransmitters, PLC hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) to generate the secondary messengers inositol 1,4,5-triphosphate (IP3) and diacylglycerol (DAG). At least four families of PLCs have been identified: PLCβ, PLCγ, PLCδ and PLCε. PLC activity is largely regulated by phosphorylation. For example, phosphorylation of PLCβ3 at Ser1105 by PKA or PKC inhibits activity, whereas phosphorylation of PLCγ at Tyr 771, 783, and 1245 by both receptor (EGFR) and nonreceptor tyrosine kinases (Syk) results in activation. In addition, members of the PLCβ subfamily are activated by the α- or β/γ-subunits of heterotrimeric G-proteins and play an important role in GPCR signaling cascades.