Neutral/alkaline and acid ceramidase activities are actively released by murine endothelial cells

Ceramidases (CDase(s)) play a key role in sphingolipid metabolism by hydrol yzing ceramide into sphingosine. Here we report that murine endothelial cel ls, macrophages, and human fibroblasts are all able to release acid as well as neutral/alkaline CDase activities in the culture medium. Endothelial ce lls were characterized by the highest specific activity of cellular as well as secreted CDases, The release of both enzymatic activities was reduced b y protein synthesis inhibitor cycloheximide but was unaffected by the block ing of RNA transcription with actinomycin D, The discharge of acid and neut ral/alkaline CDases was also diminished by brefeldin A, a fungal metabolite which disrupts Golgi apparatus. Remarkably, treatment of endothelial cells with bradykinin resulted in a significant increase of neutral/alkaline but not acid CDase release. This report represents the first evidence for the existence of constitutive and regulated release of CDase activities by endo thelial cells. In view of the known ability of these cells to secrete sphin gomyelinase, this finding suggests that CDase may participate in extracellu lar sphingomyelin metabolism which is presently known to have a role in ath erogenesis and could be involved in other physiological or pathological eve nts. (C) 2000 Academic Press.