title: Atrophic macular degeneration mutations in ELOVL4 result in the intracellular misrouting of the protein.
abstract: Elongation of very long chain fatty acids 4 (ELOVL4) is a novel member of the ELO family of genes that are involved in fatty acid metabolism. ELOVL4 encodes a putative transmembrane protein of 314 amino acids that carries a possible endoplasmic reticulum (ER) retention/retrieval signal (KXKXX) at the C-terminus. Two distinct mutations, a 5-bp deletion and a complex mutation from the same region in exon 6 of this gene, have been reported so far and are associated with autosomal dominant atrophic macular degeneration (adMD/STGD3). Both of these deletions could result in C-terminal truncation and loss of the ER retention signal in the mutant protein. We expressed the wild-type and mutant proteins in COS-7 and CHO cells to study the intracellular distribution of ELOVL4 and to identify possible implications of the above mutations in its localization. Immunofluorescence analysis of these proteins along with organelle marker antibodies revealed predominant ER localization for wild-type ELOVL4. Targeted deletion of the dilysine motif at the C-terminus of the protein resulted in the loss of ER localization. Immunoelectron microscopy and immunofluorescence analysis revealed a similar ER localization pattern for the protein in human photoreceptors. These data indicate that ELOVL4 is an ER-resident protein, which supports its suggested function in fatty acid elongation. We also demonstrate that the localization of both mutant proteins was dramatically changed from an ER to a Golgi distribution. Our observations suggest that the consequences of defective protein trafficking could underlie the molecular mechanism associated with degeneration of the macula in the patients with adMD/STGD3.
authors.affiliation: Kellogg Eye Center, Ophthalmology, University of Michigan, 1000 Wall Street, Ann Arbor, MI 48105, USA.
authors.forename: Rajesh
authors.initials: R
authors.lastname: Ambasudhan
authors.forename: XiaoFei
authors.initials: X
authors.lastname: Wang
authors.forename: Monica M
authors.initials: MM
authors.lastname: Jablonski
authors.forename: Debra A
authors.initials: DA
authors.lastname: Thompson
authors.forename: Pamela S
authors.initials: PS
authors.lastname: Lagali
authors.forename: Paul W
authors.initials: PW
authors.lastname: Wong
authors.forename: Paul A
authors.initials: PA
authors.lastname: Sieving
authors.forename: Radha
authors.initials: R
authors.lastname: Ayyagari
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D020126:Brefeldin A / Q000494:pharmacology; D016466:CHO Cells; D019556:COS Cells; D006224:Cricetinae; D004247:DNA / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005136:Eye Proteins / Q000235:genetics* / Q000378:metabolism*; D005456:Fluorescent Dyes / Q000494:pharmacology; D017353:Gene Deletion; D005799:Genes, Dominant; D006056:Golgi Apparatus / Q000378:metabolism; D049452:Green Fluorescent Proteins; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D008164:Luminescent Proteins / Q000378:metabolism; D008239:Lysine / Q000737:chemistry; D008268:Macular Degeneration / Q000235:genetics* / Q000473:pathology; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D015739:Nocodazole / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012160:Retina / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions; D014162:Transfection
chemical_list: C418975:ELOVL4 protein, human; D005136:Eye Proteins; D005456:Fluorescent Dyes; D008164:Luminescent Proteins; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D020126:Brefeldin A; D004247:DNA; D008239:Lysine; D015739:Nocodazole