Activated PI3K phosphorylates phosphatidylinositol (PI) 4-phosphate and PI 4,5-bisphosphate (PIP2) to generate PI 3,4-bisphosphate and PI 3,4,5-triphosphate (PIP3) and these second messengers recruit other signaling proteins containing plecstrin homology (PH) domain. Products of PI3K are involved in the regulation of PLC-gamma 1 and VAV activation. The PH domain of PLC-gamma 1 binds to PIP3 and is targeted to the membrane. PIP3 binds to the PH domain of VAV2/VAV3 and increases it activity and PI3K may also strongly stimulate VAV activity by converting an inhibitory regulator VAV to an activator (Toker & Cantley 1997, Fischer et al. 1998, Falasca et al. 1998).