Figure 12.

The multiple functions of PtdIns(4,5)P₂ in the plasma membrane. A: this lipid serves as a precursor of the second messengers, Ins(1,4,5)P₃ and DG upon PLC activation, or of PtdIns(3,4,5)P₃ during PI3K action. It can also be dephosphorylated by 5-phosphatases to PtdIns4P. B: in addition to this “precursor” role, PtdIns(4,5)P₂ can 1) regulate the activity of enzymes such as PLCδ1 or PLD; 2) contribute to the recruitment of endocytic clathrin adaptors; 3) anchor the actin cytoskeleton to the PM; 4) help dock secretory vesicles and presynatptic vesicles to the membrane during exocytosis; and 5) maintain or regulate the active conformation of a variety of ion channels and transporters. C: polarized or localized distribution of PtdIns(4,5)P₂ and PtdIns(3,4,5)P₃ play important roles in establishing and/or maintaining polarity, such as in directional migration, in local events, such as in phagocytosis, or in polarized epithelial cells that form barriers between their luminal and basolateral sides.