BENE, a Novel Raft-associated Protein of the MAL Proteolipid Family, Interacts with Caveolin-1 in Human Endothelial-like ECV304 Cells

Abstract

The MAL proteolipid, an integral protein present in glycolipid- and cholesterol-enriched membrane (GEM) rafts, is an element of the machinery necessary for apical sorting in polarized epithelial Madin-Darby canine kidney cells. MAL was the first member identified of an extended family of proteins that have significant overall sequence identity. In this study we have used a newly generated monoclonal antibody to investigate an unedited member of this family, named BENE, which was found to be expressed in endothelial-like ECV304 cells and normal human endothelium. Human BENE was characterized as a proteolipid protein predominantly present in GEM rafts in ECV304 cells. Coimmunoprecipitation experiments revealed that BENE interacted with caveolin-1. Confocal immunofluorescence and electron microscopic analyses indicated that BENE mainly accumulated into intracellular vesicular/tubular structures that partially colocalize with internal caveolin-1. In response to cell surface cholesterol oxidation, BENE redistributed to the dilated vesicular structures that concentrate most of the caveolin-1 originally on the cell surface. After cessation of cholesterol oxidation, a detectable fraction of the BENE molecules migrated to the plasmalemma accompanying caveolin-1 and then returned progressively to its steady state distribution. Together, these features highlight the BENE proteolipid as being an element of the machinery for raft-mediated trafficking in endothelial cells.