INVOLVEMENT OF PHOSPHOLIPASE-D ACTIVATION IN ENDOTHELIN-1-INDUCED RELEASE OF ARACHIDONIC-ACID IN OSTEOBLAST-LIKE CELLS

In a previous study, we have shown that endothelin-1 (ET-1) activates phospholipase D independently from protein kinase C in osteoblast-like MC3T3-E1 cells. II is well recognized that phosphatidylycholine hydro lysis by phospholipase D generates phosphatidic acid, which can be fur ther degraded by phosphatidic acid phosphohydrolase to diacylglycerol. In the present study, we investigated the role of phospholipase D act ivation in ET-1-induced arachidonic acid release and prostaglandin E(2 ) (PGE(2)) synthesis in osteoblast-like MC3T3-E1 cells. ET-1 stimulate d arachidonic acid release dose-dependently in the range between 0.1 n M and 0.1 mu M Propranolol, an inhibitor of phosphatidic acid phosphoh ydrolase, significantly inhibited the ET-1-induced arachidonic acid re lease in a dose dependent manner as well as the ET-1-induced diacylgly cerol formation. 1,6-bis-(cyclohexyloxyminocarbonylamino) -hexane (RHC -80267), an inhibitor of diacylglycerol lipase, significantly suppress ed the ET-1-induced arachidonic acid release. The pretreatment with pr opranolol and RHC-80267 also inhibited the ET-1-induced PGE(2) synthes is. These results strongly suggest that phosphatidylcholine hydrolysis by phospholipase D is involved in the arachidonic acid release induce d by ET-1 in osteoblast-like cells. (C) 1997 Wiley-Liss, Inc.