Functional consequences of a novel mutation in ELOVL4 causing macular dystrophy

Abstract

Abstract: : Purpose: ELOVL4 belongs to fatty acid elongase (ELO) family of genes. Members of the ELOVL4 family share common structural features, including multiple putative membrane–spanning domains, a single histidine cluster motif and putative dilysine motifs thought to signal ER retention. A 5–bp deletion of human ELOVL4 causes autosomal dominant stargardt like macular dystrophy (STGD3). This deletion results in a frame–shift and loss of C–terminal 51 amino acids that include the dilysine ER targeting signal. The goals of this study were to identify novel mutation, and determine the subcellular localization and functional consequences of wild type and mutant ELOVL4 in the cultured cells. Methods: Mutation screening of ELOVL4 gene was conducted in a family with macular dystrophy. Both wild type and mutant ELOVL4 cDNAs were cloned in a pEGFPC1 expression vector. The resultant recombinant constructs express EGFP–ELOVL4 fusion proteins and were used for mammalian cell transfection study. Biochemical and microscopic analysis were performed to investigate expression and localization of fusion proteins. Results: A C817G mutation resulting in ELOVL 270 stop was identified in a Dutch family with autosomal dominant macular dystrophy. We expressed EGFP–ELOVL4 proteins in mammalian cultured cells. Wild type protein was localized in the ER compartment. In contrast, the truncated mutant protein (which has no ER retention signal) appeared to be mislocalized to other compartments within transfected cells. Cells expressing mutant ELOVL4 underwent apoptotic cell death. Conclusions: We have identified a novel mutation in ELOVL4 causing autosomal dominant macular dystrophy. Wild type ELOVL4 is localized to ER, as predicted from its primary sequence. Mutant ELOVL4 has a different localization and causes apoptotic death. The above results could be an explanation of the photoreceptor cell degeneration in patients with STGD3 .

Keywords: apoptosis/cell death • gene/expression