Phosphoinositide 3-kinases (PI3Ks) are lipid kinases that catalyze the phosphorylation of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂) to generate the second messenger phosphatidylinositol (3,4,5)-trisphosphate (PI(3,4,5)P₃). The production of PI(3,4,5)P₃ facilitates the recruitment and activation of pleckstrin homology (PH) domain–containing proteins at the plasma membrane, thereby initiating downstream signaling cascades essential for cellular proliferation, survival, and migration.
PI3Ks are divided into three major classes, among which Class I PI3Ks are most prominently implicated in cancer biology. Class I enzymes comprise four distinct catalytic isoforms: PI3Kα, PI3Kβ, PI3Kδ, and PI3Kγ.
Class IA PI3Ks, the subclass most commonly associated with oncogenic signaling, function as heterodimeric lipid kinases composed of a catalytic p110 subunit (p110α, p110β, or p110δ, encoded by PIK3CA, PIK3CB, and PIK3CD, respectively) and a regulatory p85 subunit.
The PI3K signaling pathway plays a central role in diverse biological processes, including cell cycle progression, cellular growth, survival, actin cytoskeletal rearrangement, migration, and intracellular vesicular trafficking.