Phosphatidylinositol-4,5-bisphosphate

The phosphatidylinositol-4,5-bisphosphates (PIP2) are phospholipids of the cell membrane. They occur on the cytosolic side of the cell membrane. PIP2 play an important role in the transmission of extracellular signals in the cell (e.g. in the signal transduction pathway of the activated B cell) and control the processes of endocytosis.

Activation of various receptors located in the cell membrane leads to activation of the enzyme phospholipase C (PLC). PLC hydrolytically cleaves PIP2 into diacylglycerols (DAG) and inositol-1,4,5-trisphosphate (IP3). DAG and IP3 can contribute as so-called "second messengers" to the transmission of the signal in the cell.

Phosphoinositide-3-kinases (PI3K) convert PIP2 into phosphatidylinositol-3,4,5-triphosphate(PIP3). The reverse reaction of PIP3 to PIP2 is performed by the phosphatase PTEN.