Human PI3Ka is composed of two subunits: the catalytic subunit p110a, and a regulatory subunit,p85a . After cell stimulation, PI3Ka is recruited to the membrane and activated by binding, through an SH2 domain (nSH2) of p85, to phosphotyrosine motifs of activated membrane receptors or their phosphorylated substrates. In vitro, phosphorylated peptides carrying the cognate sequences (pY-pep) also activate the enzyme. The PIP3 lipids produced by activated PI3Ks act as membrane docking sites for pleckstrin homology domain (PH)-containing proteins such as the AKT serine/threonine kinases (also known as protein kinase B, PKB) and the 3-phosphoinositide-dependent protein kinase-1 (PDK1) . Through this activity, class I PI3Ks link cell-surface receptors including epidermal growth factor receptor, insulin-like growth factor receptor,and platelet growth factor receptor to signaling networks that control cell growth, proliferation,survival,apoptosis, differentiation, motility, migration, and adhesion