Phosphatidylinositol phosphate 5-kinase Iβ recruits AP-2 to the plasma membrane and regulates rates of constitutive endocytosis

Overexpression of phosphatidylinositol phosphate 5-kinase (PIP5KI) isoforms alpha, beta, or gamma in CV-1 cells increased phosphatidylinositol 4,5-bisphosphate (PIP2) levels by 35, 180, and 0%, respectively. Endocytosis of transferrin receptors, association of AP-2 proteins with membranes, and the number of clathrin-coated pits at the plasma membrane increased when PIP2 increased. When expression of PIP5KIbeta was inhibited with small interference RNA in HeLa cells, expression of PIP5KIalpha was also reduced slightly, but PIP5KIgamma expression was increased. PIP2 levels and internalization of transferrin receptors dropped 50% in these cells; thus, PIP5KIgamma could not compensate for loss of PIP5KIbeta. When expression of PIP5Kalpha was reduced, expression of both PIP5KIbeta and PIP5KIgamma increased and PIP2 levels did not change. A similar increase of PIP5KIalpha and PIP5KIbeta occurred when PIP5KIgamma was inhibited. These results indicate that constitutive endocytosis in CV-1 and HeLa cells requires (and may be regulated by) PIP2 produced primarily by PIP5KIbeta.