Ecotropic murine leukemia virus receptor is physically associated with caveolin and membrane rafts

We used a Sindbis virus expression system to stably express a chimeric ecotropic murine leukemia virus (MLV) receptor gene, CAT1, fused to green fluorescent protein (gfp) in BHK cells. The chimeric gene was expressed on the cell surface and functioned as an MLV receptor. Using gfp as an epitope tag, we found that CATI cross-immunoprecipitated with caveolin, a cellular protein associated non-clathrin-coated endocytic vesicles. Biochemical studies showed that CATI copurified with caveolin in a detergent-insoluble membrane fraction that forms cholesterol-rich "rafts" on the cell surface. Disruption of rafts by methyl-beta -cyclodextrin, a drug that extracts cholesterol, reduced susceptibility to MLV without decreasing surface CATI. The results indicate that association of the MLV receptor with cholesterol-rich rafts is important for an early step in virus infection.