Bestrophin, the product of the Best vitelliform macular dystrophy gene (VMD2), localizes to the basolateral plasma membrane of the retinal pigment epithelium

Best vitelliform macular dystrophy is a dominantly inherited, early onset, macular degenerative disease that exhibits some histopathologic similaritie s to age-related macular degeneration. Although the vitelliform lesion is c ommon in the fundus of individuals with Best disease, diagnosis is based on a reduced ratio of the light peak to dark trough in the electrooculogram. Recently, the VMD2 gene on chromosome 11q13, encoding the protein bestrophi n, was identified. The function of bestrophin is unknown. To facilitate stu dies of bestrophin, we produced both rabbit polyclonal and mouse monoclonal antibodies that proved useful for Western blotting, immunoprecipitation, a nd immunocytochemistry. To characterize bestrophin, we initially probed the retinal pigment epithelium (RPE)-derived cell lines ARPE-19, D407, and RPE -J. All of the cell lines expressed bestrophin mRNA by reverse transcriptio n-PCR, but not on Western blots. Bestrophin in human RPE partitioned in the detergent phase during Triton X-114 extraction and could be modified by bi otin in intact cells, indicative of a plasma membrane localization. Immunoc ytochemical staining of macaque and porcine eyes indicated that bestrophin is localized at the basolateral plasma membrane of RPE cells. When expresse d in RPE-J cells by adenovirus-mediated gene transfer, bestrophin again was determined by confocal microscopy and cell surface biotinylation to be a b asolateral plasma membrane protein. The basolateral plasma membrane localiz ation of bestrophin suggests the possibility that bestrophin plays a role i n generating the altered electrooculogram of individuals with Best disease.