Cell type specific localization of sphingomyelin biosynthesis

We have studied the incorporation of [C-14]serine and of [H-3]sphingosine i nto sphingomyelin in the presence or absence of brefeldin A (BFA) in three different cell types. Administration of BFA (1 mu g/ml) to fibroblasts for 24 h increased the incorporation of label into sphingomyelin 1.5-3 fold com pared with untreated controls. In contrast, BFA strongly decreased sphingom yelin biosynthesis (4-5 fold) in cerebellar neurons as well as in neuroblas toma cells. The effect of BFA on glycosphingolipid formation, however, was similar in all three cell types studied: an increased labeling of the precu rsor glycolipids GlcCer, LacCer, GM3 and GD3 was paralleled by a decreased formation of complex gangliosides, GM1, GD1a, GT1b and GQ1b, Our data there fore suggest that in neuronal cells sphingomyelin synthesis, like the forma tion of complex gangliosides, is localized primarily distal to the BFA bloc k, in a post-Golgi compartment, most probably the trans-Golgi network, wher eas in fibroblasts sphingomyelin biosynthesis is mainly localized prior to the BFA block, in the Golgi apparatus, as has been shown for LacCer, GlcCer , GM3 and GD3 synthases, (C) 2000 Federation of European Biochemical Societ ies. Published by Elsevier Science B.V. All rights reserved.