Assessment of agonism at G-protein coupled receptors by phosphatidic acid and lysophosphatidic acid in human embryonic kidney 293 cells

Several different molecular species of phosphatidic acid (PA) bind to a G-p rotein coupled receptor (GPCR) to induce activation of the p42/p44 mitogen- activated protein kinase (p42/p44 MAPK) pathway in HEK 293 cells. PA is act ive at low nanomolar concentrations and the response is sensitive to pertus sis toxin (which uncouples GPCRs from G(i o)). The de-acylated product of P A, lysophosphatidic acid (LPA), which binds to members of the endothelial d ifferentiation gene (EDG) family of receptors also stimulated p42/p44 MAPK in a pertussis toxin sensitive manner, but with an similar to 100-1000 fold lower potency compared with the different molecular species of PA. RT-PCR using gene-specific primers showed that HEK 293 cells express EDG2 and PSP2 4, the latter being a lipid binding GPCR out with the EDG cluster. We concl ude that PA is a novel high potency GPCR agonist.