Phospholipases and PI 3-Kinase Activity
Phosphoglycerides are the starting point for the generation of several critical signaling second messengers produced by PI 3-Kinase and Phospholipase A, C or D (PLA, PLC or PLD). There are many phosphoglycerides, only PIP2 (phosphatidylinositol 4,5-bisphosphate) is shown, and a few others are described here (see table). PIP2 is the substrate for PI 3-Kinase and PLC. PI 3-Kinase phosphorylates PIP2 to produce PIP3, which is in turn the substrate for the lipid phosphatase PTEN. PLC hydrolyzes PIP2 to produce DAG (diacylglycerol) and IP3 (inositol 1,4,5-trisphosphate). PC is the substrate for the PLAs and for PLD, which produce lyso-PC and arachidonic acid, or PA and choline, respectively. PLA isoforms recognize different sites on PC; PLA1 removes the external fatty acid, while PLA2 cleaves off the internal. All of the end products of PI 3-Kinase and the phospholipases are critical second messengers which stimulate downstream signal transduction pathways, or are key building blocks for other important biological processes.
| Phosphogyceride | Abbreviation | Headgroup |
| Pl 4,5-biphosphate | PIP2 | Inositol 4.5-bisphosphate |
| Pl 3,4,5-triphosphate | PIP3 | Inositol 4.5-trisphosphate |
| Phosphatidylcholine | PC | choline |
| Phosphatidic acid | PA | OH |
