One lipid, multiple functions: how various pools of PI(4,5)P2 are created in the plasma membrane

Phosphatidylinositol 4,5-bisphosphate [PI(4,5)P-2] is a minor lipid of the inner leaflet of the plasma membrane that controls the activity of numerous proteins and serves as a source of second messengers. This multifunctionality of PI(4,5)P-2 relies on mechanisms ensuring transient appearance of PI(4,5)P-2 clusters in the plasma membrane. One such mechanism involves phosphorylation of PI(4)P to PI(4,5)P-2 by the type I phosphatidylinositol-4-phosphate 5-kinases (PIP5KI) at discrete membrane locations coupled with PI(4)P delivery/synthesis at the plasma membrane. Simultaneously, both PI(4)P and PI(4,5)P-2 participate in anchoring PIP5KI at the plasma membrane via electrostatic bonds. PIP5KI isoforms are also selectively recruited and activated at the plasma membrane by Rac1, talin, or AP-2 to generate PI(4,5)P-2 in ruffles and lamellipodia, focal contacts, and clathrin-coated pits. In addition, PI(4,5)P-2 can accumulate at sphingolipid/cholesterol-based rafts following activation of distinct membrane receptors or be sequestered in a reversible manner due to electrostatic constrains posed by proteins like MARCKS.