Phosphatidylinositol 3-kinase (PI 3-kinase), is a phosphoinositide-specific protein kinase that plays a central role in mitogenic signal transduction leading to cellular regulation, cell growth and differentiation, and oncogenesis. PI 3-kinase associates with, and is activated by a wide range of tyrosine kinase receptors including EGF, PDGF, CSF-1, erbB-3 and insulin receptor, non-receptor protein-tyrosine kinases of the src family (e.g. pp60src), and crk and abl proto-oncogene products. PI 3-kinase is involved in signal transduction in terminally differentiated, activated cells like platelets and neutrophils.