TRANSPORT OF PROTEOLIPID PROTEIN TO THE PLASMA-MEMBRANE DOES NOT DEPEND ON GLYCOSPHINGOLIPID COTRANSPORT IN OLIGODENDROCYTE CULTURES

The possibility that transport of proteolipid protein (PLP) from its s ite of synthesis to the plasma membrane is dependent on cotransport wi th (sulfo)galactocerebrosides was investigated in primary cultured oli godendrocytes and Chinese hamster ovary (CHO) cells expressing PLP. Su lfation was inhibited by growing oligodendrocytes in the presence of a competitive inhibitor of this process, sodium chlorate, Under these c ircumstances, sulfatide synthesis was inhibited by 85%., Nevertheless, PLP was still delivered to the plasma membrane in quantitative amount s, Furthermore, when PLP was expressed in CHO cells, which normally sy nthesize very low amounts of galactosyl ceramide (GalCer) and no sulfa tide, PLP was transported to the plasma membrane, Moreover; in CHO cel ls coexpressing PLP and ceramide galactosyl transferase, PLP cell surf ace labeling was unaltered, Noting that it has been demonstrated that proteins destined for the apical surface of epithelial cells colocaliz e with glycolipid-enriched microdomains, we isolated detergent-insolub le membrane complexes from cultured oligodendrocytes, We found, howeve r, that most of the PLP is present in the detergent-soluble fraction a nd, furthermore, that PLP could not be chased into or out of the insol uble fraction, Taken together, these data make it very likely that in oligodendrocytes PLP transport takes place irrespective of the presenc e of glycosphingolipids GalCer and sulfatide, (C) 1998 Wiley-Liss, Inc .