VIP36, A NOVEL COMPONENT OF GLYCOLIPID RAFTS AND EXOCYTIC CARRIER VESICLES IN EPITHELIAL-CELLS

In simple epithelial cells, apical and basolateral proteins and lipids in transit to the cell surface are sorted in the trans-Golgi network. We have recently isolated detergent-insoluble complexes from Madin - Darby canine kidney cells that are enriched in glycosphingolipids, api cal cargo and a subset of the proteins of the exocytic carrier vesicle s. The vesicular proteins are thought to be involved in protein sortin g and include VIP21-caveolin. The vesicular protein VIP36 (36 kDa vesi cular integral membrane protein) has been purified froma CHAPS-insolub le residue and a cDNA encoding VIP36 has been isolated. The N-terminal 31 kDa luminal/exoplasmic domain of the encoded protein shows homolog y to leguminous plant lectins. The transiently expressed protein is lo calized to the Golgi apparatus, endosomal and vesicular structures and the plasma membrane, as predicted for a protein involved in transport between the Golgi and the cell surface. It is diffusely localized on the plasma membrane but can be redistributed by antibody modulation in to caveolae and clathrin-coated pits. Wespeculate that VIP36 binds to sugar residues of glycosphingolipids and/or glycosylphosphatidyl-inosi tol anchors and might provide a link between the extracellular/luminal face of glycolipid rafts and the cytoplasmic protein segregation mach inery.