PI3Kα plays a specific role in apoptosis in human colon cancer cells. Injection of neutralizing antibodies specific to PI3Kα into adenocarcinoma cells induced apoptosis, a response that was reverted by treating cells with caspase inhibitor. It was also shown that PI3Kα mediatedphosphorylation of the p85α adapter reduces the lipid kinase activity of the heterodimer and this gives hints for PI3K-dependent signaling events not requiring production of 3’-phosphorylated phosphoinositides. PI3Kα is a key regulator of the initiation of keratinocytedifferentiation. A decrease in PI3K activity results in a loss of keratinocyte adhesion to the extracellular membrane and the initiation of early phase differentiation. The PI3Kα catalytic and regulatory subunits are coexpressed in Sf9 insect cells. The catalytic subunit carries a GST-Tag and the heterodimer was purified by affinity chromatography. The GST-Tag facilitates the protein’s application in typical GST pull-down assays.
Phosphoinositide 3-kinases (PI3Ks) phosphorylate phosphatidylinositols (PIs) at their 3´-OH position generating lipid second messengers and thereby regulate numerous biological processes including cell growth, differentiation, survival, proliferation, migration and metabolism. On the basis of structural similarities and substrate specificity, the PI3K family can be subdivided into three classes termed I, II, and III. All human class I members are heterodimers consistingof a catalytic subunit (MW approx. 110kD) and a noncatalytic subunit (MW 50, 55, 85, or 101kD) and are known to phosphorylate phosphatidylinositol (PI), phosphatidylinositol-4-mono-phosphate (PIP) and phosphatidylinositol-4,5-bisphosphate (PIP2) in vitro. The class I members can be further subdivided into class IA and IB PI3Ks. Class IA exists in three isoforms p110α, p110β and p110δ) whereas the only class IB member is termed p110γ. Class IA PI3Ks are activated by adaptor proteins such as Ras or BCAP, or tyrosine-kinase-associated receptors including antigen, co-stimulatory and cytokine receptors (e.g. CD19, CD28, Insulin receptor, EGFR, and PDGFR). p110γ is activated by G-protein-coupledreceptors (GPCRs). Effectors of class I PI3Ks are pleckstrin-homology domain proteins such as Akt/PKB, BTK, TEC, ITK, BAM32, and small GTPases (e.g. Cdc42, Rac, or Ras). The action of PI3Ks is regulated by the phosphatidylinositol- 3,4,5-trisphosphate phosphatases SHIP and PTEN.
Note: Human p110 alpha differs from the bovine enzyme in only 2 positions, K532R and S535C. Both lie in the PIK domain of the enzyme (aa 525-696) and are not expected to interfere with binding of p85 (aa 31-108) or Ras (aa 173-292) or with catalytic function(aa 699-1064).
Activity: ~ 3nmol/mg/min using phosphatidylinositol as the substrate.
