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J. Biol. Chem., Vol. 280, Issue 37, 32521-32530, September 16, 2005

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Dominant Negative Mechanism Underlies Autosomal Dominant Stargardt-like Macular Dystrophy Linked to Mutations in ELOVL4^*

Celene Grayson1 and Robert S. Molday, A Canada Research Chair in Vision and Macular Degeneration¶2

From the Department of Biochemistry and Molecular Biology and ^¶Department of Ophthalmology and Visual Sciences, Centre for Macular Research, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada

ELOVL4 (elongation of very long chain fatty acids 4) is a member of the ELO family of proteins involved in the biosynthesis of very long chain fatty acids. Protein truncation mutations in ELOVL4 have been identified in patients with autosomal dominant Stargardt-like macular degeneration. To determine whether a dominant negative mechanism is responsible for the autosomal dominant inheritance pattern of this disease, we studied the subcellular localization and interaction of wild type and mutant ELOVL4 in COS-7 and HEK 293T cultured cells by immunofluorescence and co-immunoprecipitation. Wild type ELOVL4 containing an endoplasmic reticulum retention sequence was localized to the endoplasmic reticulum as expected. In contrast, disease-associated C-terminal truncation ELOVL4 mutants accumulated as large inclusions exhibiting aggresome-like characteristics in a juxtanuclear position within COS-7 cells. When the wild type and mutant proteins were co-expressed incultured cells, wild type ELOVL4 co-purified with mutant ELOVL4 on an immunoaffinity column and co-localized with the mutant protein in aggresome-like inclusions adjacent to the nucleus. These results indicate that wild type and mutant ELOVL4 form a complex that exhibits an abnormal subcellular localization found for individually expressed mutant ELOVL4. From these studies, we conclude that disease-linked C-terminal truncation mutants of ELOVL4 exert a dominant negative effect on wild type ELOVL4, altering its subcellular localization. This dominant negative mechanism contributes to the autosomal dominant inheritance of Stargardt-like macular dystrophy.

Received for publication, March 29, 2005 , and in revised form, July 8, 2005.

^* This work was supported by NEI, National Institutes of Health, Grant EY 02422, Canadian Institutes for Health Research Grant MT 5822, and the Macula Vision Research Foundation. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Recipient of Foundation Fighting Blindness, Canada, the Michael Smith Foundation for Health Research, and the Arthur and June Willms Postdoctoral Fellowships.

² To whom correspondence should be addressed: Dept. of Biochemistry and Molecular Biology, 2350 Health Sciences Mall, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada. Tel.: 604-822-6173; Fax: 604-822-5227; E-mail: molday{at}interchange.ubc.ca.

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