Phosphatidylinositol phosphates, or phosphoinositides, are intracellular signaling lipids. Seven different phosphoinositides have been identified in mammals, each distinguished by the number and/or position of the phosphate groups on the inositol ring. The inositol can be mono-, di-, or triphosphorylated, with the remaining phosphoinositides being isomers of these three forms. Phosphoinositides regulate a variety of signal transduction processes, thus playing a number of important roles in the cell, such as actin cytoskeletal reorganization, membrane transport, and cell proliferation. They may also affect protein localization, aggregation, and activity by acting as secondary messengers. The ability of the cell to recognize the different types of phosphoinositides as different cellular signals means that their synthesis and metabolism must be tightly regulated. Synthesis begins with the attachment of an inositol phosphate head group to diacylglycerol via a phospholipase C enzyme, creating a phosphoinositide. Conversion between the different types of phosphoinositides is then done by a number of specific phosphoinositide kinases and phosphatases, which add (kinase) and remove (phosphatase) phosphates from the inositol ring. The specific localization and regulation of the phosphoinositide kinases and phosphatases thus controls the activity of the phosphoinositides. While the phosphoinositides are always located in the membrane, their particular kinases and phosphatases may be found in the cytoplasm or in the membrane of the cell or cell organelles.

Phosphatidylinositol Phosphate Metabolism References