Activation of phospholipase Cγ by PI 3-kinase-induced PH domain-mediated membrane targeting

Signaling via growth factor receptors frequently results in the concomitant activation of phospholipase Cγ (PLCγ) and phosphatidylinositol (PI) 3-kinase. While it is well established that tyrosine phosphorylation of PLCγ is necessary for its activation, we show here that PLCγ is regulated additionally by the lipid products of PI 3-kinase. We demonstrate that the pleckstrin homology (PH) domain of PLCγ binds to phosphatidylinositol 3,4,5-trisphosphate [PdtIns(3,4,5)P3], and is targeted to the membrane in response to growth factor stimulation, while a mutated version of this PH domain that does not bind PdtIns(3,4,5)P3 is not membrane targeted. Consistent with these observations, activation of PI 3-kinase causes PLCγPH domain-mediated membrane targeting and PLCγ activation. By contrast, either the inhibition of PI 3-kinase by overexpression of a dominant-negative mutant or the prevention of PLCγ membrane targeting by overexpression of the PLCγ PH domain prevents growth factor-induced PLCγ activation. These experiments reveal a novel mechanism for cross-talk and mutual regulation of activity between two enzymes that participate in the control of phosphoinositide metabolism.