Phosphatidylinositol 3-kinases (PI3Ks) are a family of lipid kinases whose biological function is to phosphorylate the 3-hydroxyl group of phosphoinositide. It is proved that PI3K-dependent signaling pathway contributes to many cellular processes such as cell growth, proliferation, differentiation, motility, survival and intracellular trafficking, which might be involved in oncogenesis under certain situation. When a growth factor or ligand binds to the tyrosine kinase receptors (RTK), the PI3K is activated by G protein-coupled receptors. PI3Ks family is generally divided into Class I, Class II, and Class III according to their primary structure, regulation, and in vitro lipid substrate specificity. Class I PI3Ks are heterodimeric molecules composed of a regulatory subunit (p85) and a catalytic subunit (p110). The regulatory subunit of PI3K could be further divided in to six subtypes: p85-α, p85-β, p55-γ, p150,p101 and p87. P85α is the most highly expressed regulatory subunit than the others. And the catalytic subunit could also further divided into four subtypes: p110-α, p110-β, p110-γ and p110-δ. The α and β isoforms of p110 are expressed in all kinds of cells, whereas δ is only found in leukocytes. The regulatory subunit p101 and catalytic subunit p110γ comprise a complex which is classified as Class IB PI3K. Other collocations of regulatory and catalytic subunits are called Class IA PI3Ks. However, class II is structurally different from Class I. There are three catalytic isoforms of Class II PI3Ks: PI3K-C2α, -C2β, and -C2γ, but no regulatory subunit. Class III is structurally similar to Class I for the reason that it is composed of a catalytic (Vps34) and a regulatory subunit (p150). Functionally, class I PI3Ks catalyze the production of phosphatidylinositol 3-phosphate (PtdIns-3,4-P), phosphatidylinositol (3,4)-bisphosphate (PtdIns-3,4-P2), and phosphatidylinositol (3,4,5)-triphosphate (PtdIns-3,4,5-P3). Class II is related to the production of PtdIns-3-P and PtdIns-3,4-P2, while class III specifically catalyzes the production of PtdIns-3,4-P2 [3-5].
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