| Abstrakt: |
Generation and attenuation of lipid second messengers are key processes in cellular signalling. Receptor‐mediated increase in 1,2‐diacylglycerol (DG) levels is attenuated by DG kinase and DG lipase. We here report a novel mechanism of DG attenuation by phospholipase D (PLD), which also precludes the production of another (putative) second messenger, phosphatidic acid (PA). In the presence of an alcohol, PLD converts phosphatidylcholine (PC) into a phosphatidylalcohol (by transphosphatidylation) rather than into PA. We found in bradykinin‐stimulated human fibroblasts that PLD mediates transphosphatidylation from PC (donor) to the endogenous ‘alcohol’ DG (acceptor), yielding bis(1,2‐diacylglycero)‐3‐sn‐phosphate (bisphosphatidic acid; bisPA). This uncommon phospholipid is thus a condensation product of the phospholipase C (PLC) and PLD signalling pathways, where PLC produces DG and PLD couples this DG to a phosphatidyl moiety. Long‐term phorbol ester treatment blocks bradykinin‐induced activation of PLD and consequent bisPA formation, thereby unveiling rapid formation of DG. BisPA formation is rapid (15 s) and transient (peaks at 2–10 min) and is also induced by other stimuli capable of raising DG and activating PLD simultaneously, e.g. endothelin, lysophosphatidic acid, fetal calf serum, phorbol ester, dioctanoylglycerol or bacterial PLC. This novel metabolic route counteracts rapid accumulation of receptor‐induced DG and PA, and assigns for the first time a physiological role to the transphosphatidylation activity of PLD, that is signal attenuation. |
