The PI(4,5)P2 cycle or simply PIP2 cycle (also known as PI cycle in past) is one of the important signalling cascades underlying many cellular functions including GPCR signaling, cytokinesis,[1] endocytosis,[2] and apoptosis.[3]
PIP2 cycle involves steps of chemical reactions characterized by various enzymes. First hydrolysis of PIP2 molecules by activated phospholipase C leads to formation of diacylglycerol and inositol trisphosphate. These two are themselves important second messengers.[4] Diacylglycerol further converted into phosphatidic acid (PA) by DAGK enzyme. Furthermore, CDP-diacylglycerol synthetase uses CTP to create cytidine diphosphate diacylglycerol from PA.[5][6] Generated CDP-DAG then condensed to PI by phosphatidylinositol synthase.[7] This PI is then phosphorylated to PI4P and back to PIP2 via action of PI4K and PIP5K[8]