Phosphoinositide 3-kinase (PI3K) phosphorylates phosphatidylinositol (PI), PI-4-phosphate and PI-4,5-bisphosphate to catalyze the production of PI-3,4,5-triphosphate. Growth factors and hormones activate PI3K to coordinate various cellular events, such as cell growth, cell cycle entry, cell migration and cell survival. This PI3K activation is reversed by PTEN. In cancers caused by the loss of PTEN activity, PI3K is constituitively active and promotes cell proliferation. PI3Ks are composed of a catalytic subunit and a regulatory subunit. Various isoforms of the catalytic subunit (p110a, p110b and p110d) associate with regulatory subunits (p85a and p85b) with the exception of p110g which interacts with a unique p101 regulatory subunit.
