5–Bp–Deletion Mutant ELOVL4 Protein Causes Altered Localization of the Wild Type ELOVL4 Protein in COS–7 Cells– Probable Mechanism Underlying Stargardt’s–Like Macular Degeneration

Abstract

Abstract: : Purpose: To understand the mechanism underlying Stargardt's–like macular dystrophy (STGD3), an autosomal dominant macular degeneration due to mutations in the gene ELOVL4. We studied the intracellular fate of the mutant and wild type ELOVL4 proteins in COS–7 cells co–expressing these proteins Methods: Wild type and 5–bp–deletion mutant ELOVL4 proteins carrying N–terminal GFP and/or V5 tags, were expressed in COS–7 cells. Expression and cellular localization were characterized by immunolabeling, confocal microscopy, and western blot analysis with appropriate antibodies. Localization of these proteins was further characterized using specific organelle markers and treatment with nocodozole Results: Immuno fluorescence analysis of COS–7 cells expressing 5–bp–deletion mutant ELOVL4 protein and cells co–expressing both the wild type and 5–bp–deletion mutant ELOVL4 proteins showed localization to cytoplasmic, perinuclear aggregate. Localization of the wild type protein is indistinguishable from the localization of the mutant protein. This suggests that the wild type and mutant proteins may interact with each other and form juxtra nuclear aggregates. We further investigated and found that these aggregates accumulate near golgi and share several features with aggresomes. Conclusions: In presence of the 5–bp–deletion mutant ELOVL4 protein, the wild type protein gets recruited into perinuclear cytoplasmic inclusions that resemble aggresomes. Altered localization of the wild type ELOVL4 protein in the presence of the mutant protein may explain the mechanism underlying macular degeneration in patients with mutations in the ELOVL4 gene.

Keywords: proteins encoded by disease genes • retinal degenerations: cell biology • genetics