Inhibition of arachidonic acid release and cytosolic phospholipase A 2α activity by d- erythro-sphingosine

Abstract

Sphingolipid metabolites such as sphingosine 1-phosphate (S1P) and ceramide can mediate many cellular events including apoptosis, stress responses and growth arrest. Although ceramide stimulates arachidonic acid metabolism in several cells, the effects of sphingosine and its endogenous analogs have not been established. We investigated the effects of d- erythro-sphingosine and its metabolites on arachidonic acid release in the two cells and on the activity of cytosolic phospholipase A 2α. C2-Ceramide ( N-acetyl- d- erythro-sphingosine, 100 μM) alone stimulated [ 3H]arachidonic acid release and enhanced the ionomycin-induced release from the prelabeled PC12 cells and L929 cells. In contrast, exogenous addition of d- erythro-sphingosine inhibited the responses in a concentration-dependent manner in the two cell lines. d- erythro-sphingosine, d- erythro- N,N-dimethylsphingosine ( d- erythro-DMS) and d- erythro-dihydrosphingosine ( d- erythro-DHS) significantly inhibited mastoparan-, but not Na 3VO 4-, stimulated arachidonic acid release in PC12 cells. d- erythro-S1P and dl- threo-DHS showed no effect on the responses. Production of prostaglandin F 2α was also enhanced by C2-ceramide (20 μM) and suppressed by d- erythro-sphingosine (10 μM) in PC12 cells. An in vitro study revealed that d- erythro-sphingosine, d- erythro-DMS and d- erythro-DHS directly inhibited cytosolic phospholipase A 2α activity. These findings suggest that ceramide and d- erythro-analogs of sphingosine have opposite effects on phospholipase A 2 activity and thus regulate arachidonic acid release from cells.