CERAMIDE TRANSPORT FROM ENDOPLASMIC-RETICULUM TO GOLGI-APPARATUS IS NOT VESICLE-MEDIATED

Ceramide (Cer) transfer from the endoplasmic reticulum (ER) to the Gol gi apparatus was measured under conditions that block vesicle-mediated protein transfer. This was done either in intact cells by reducing th e incubation temperature to 15 degrees C, or in streptolysin O-permeab ilized cells by manipulating the intracellular environment. In both ca ses, Cer transfer was not inhibited, as demonstrated by the biosynthes is of ceramide monohexosides and sphingomyelin (SM) de novo from metab olically (with [C-14]serine) labelled Cer. This assay is based on the knowledge that Cer is synthesized, starting from serine and palmitoyl- CoA, at the ER, whereas glycosphingolipids and SM are synthesized in t he (early) Golgi apparatus. Formation of [C-14]glycosphingolipids and [C-14]SM was observed under conditions that block vesicle-mediated ves icular stomatitis virus glycoprotein transport. These results indicate that [C-14]Cer is transferred from ER to Golgi by a non-vesicular mec hanism.