Background：

Catalyzes the phosphorylation of phosphatidylinositol 4-phosphate (PtdIns4P) to form phosphatidylinositol 4，5-bisphosphate (PtdIns(4，5)P2). PtdIns(4，5)P2 is involved in a variety of cellular processes and is the substrate to form phosphatidylinositol 3，4，5-trisphosphate (PtdIns(3，4，5)P3)， another second messenger. The majority of PtdIns(4，5)P2 is thought to occur via type I phosphatidylinositol 4-phosphate 5-kinases given the abundance of PtdIns4P. Participates in a variety of cellular processes such as vesicle mediated transport， cell adhesion， cell polarization and cell migration. Together with PIP5K1A is required for phagocytosis， but they regulate different types of actin remodeling at sequential steps. Promotes particle attachment by generating the pool of PtdIns(4，5)P2 that induces controlled actin depolymerization to facilitate Fc-gamma-R clustering. Mediates RAC1-dependent reorganization of actin filaments. Required for synaptic vesicle transport. Controls the plasma membrane