Analysis of subcellular location of bestrophin in transfected RPE cell lines

Best macular dystrophy is an autosomal dominant disease leading to macular degeneration and subsequent impaired vision. The disease has juvenile onset and affects the retinal pigment epithelium and adjacent photoreceptors. There are histopathological similarities between Best macular dystrophy (BMD) and age-related macular degeneration (AMD) with accumulation of lipofuscin in the outer retina. Recently, we identified the gene VMD2 causing Best macular dystrophy. The VMD2 gene has unknown function and there are no similarities between the VMD2 product, called bestrophin, and other proteins with known function. In order to gain more knowledge about the function of bestrophin we investigated its subcellular localization. DNA constructs encoding the bestrophin protein fused to the green fluorescent protein (GFP) or a c-myc tag were transiently expressed in COS-7 cells or retinal pigment epithelium cells. The observed pattern of bestrophin fusion protein was spotted and mainly perinuclear, well corresponding to the endoplasmic reticulum (ER), which was also suggested when counterstaining with an ER probe. Probes for other organelles had a different localization pattern compared to bestrophin. In conclusion, the results indicate that bestrophin is located to the endoplasmic reticulum.