INHIBITION OF PHORBOL ESTER-STIMULATED ARACHIDONIC-ACID RELEASE BY ALKYLGLYCEROLS

Although synthetic analogs of alkylglycerol (AG), such as dodecylglyce rol, possess potent biological activities, their mechanism of action h as not been determined. We recently detected substantial amounts of AG in unstimulated MDCK cells (Warne, T.R. and Robinson, M. (1991) Anal. Biochem. 198, 302-307) raising the possibility that the endogenous co mpound may act as a biological mediator. In this study, we examined th e effects of synthetic AG on the release elf arachidonic acid and arac hidonate metabolites (AA) from Madin Darby canine kidney (MDCK) cells in response to 12-O-tetradecanylphorbol-13-acetate (TPA) in order to c haracterize its effects on this signalling pathway. Treatment of MDCK with AG potently inhibited the release of AA during subsequent stimula tion with TPA. Dodecylglycerol, the most effective of a series of alky glycerols tested, was active at concentrations as low as 3 mu M. The s n-1 and sn-3 forms of AG were found to be equally potent inhibitors. T he effects of AG on AA release were not the result of arachidonic acid redistribution among cellular lipids and were independent of the phos pholipid source of the released AA. AG did not inhibit the release of AA from MDCK cells when bradykinin was used as a stimulus, indicating selectivity for the effects produced by phorbol esters. These results show that AG can function as a potent and specific inhibitor of TPA-me diated AA release. The ability of AG to regulate this signalling pathw ay in intact MDCK cells, together with its natural occurrence, suggest s a potential bioregulatory role for the endogenous compound as an inh ibitor of protein kinase C.