title: Regulation of human delta-6 desaturase gene transcription: identification of a functional direct repeat-1 element.
abstract: The rate-limiting step in 20:4(n-6) and 22:6(n-3) synthesis is the desaturation of 18:2(n-6) and 18:3(n-3) by Delta-6 desaturase. In this report, we demonstrate that n-6 and n-3 PUFAs suppressed the hepatic expression of rodent Delta-6 desaturase by inhibiting the rate of Delta-6 desaturase gene transcription. In contrast, consumption of the peroxisome proliferator-activated receptor (PPAR)alpha activator WY 14,643 significantly enhanced the transcription of hepatic Delta-6 desaturase by more than 500%. Transfection reporter assays with HepG2 cells revealed that the PUFA response region for the human Delta-6 desaturase gene involved the proximal promoter region of -283/+1 human Delta-6 desaturase gene, while the WY 14,643 response element (RE) was identified as an imperfect direct repeat (DR-1) located at -385/-373. The WY 14,643 induction of the human Delta-6 desaturase promoter activity was dependent upon the expression of PPARalpha. Electrophoretic mobility shift assays revealed that nuclear proteins extracted from HepG2 cells expressing PPARalpha specifically interacted with the -385/-373 DR-1 sequence of the human Delta-6 desaturase gene. The interaction was eliminated by the unlabeled PPARalpha RE of the rat acyl-CoA oxidase gene, and the protein-DNA complex was super-shifted by treatment with anti-PPARalpha. The -385/-373 sequence also interacted with a mixture of in vitro translated PPARalpha-retinoic acid receptor X (RXR)alpha, but by themselves neither PPARalpha nor RXRalpha could bind to the Delta-6 desaturase DR-1. These data indicate that the 5'-flanking region of the human Delta-6 desaturase gene contains a DR-1 that functions in the regulation of human Delta-6 desaturase gene transcription, and thereby plays a role in the synthesis of 20- and 22-carbon polyenoic fatty acids.
authors.affiliation: Pennington Biomedical Research Center, Louisiana State University, 6400 Perkins Road, Baton Rouge 70808, USA.
authors.forename: Chongren
authors.initials: C
authors.lastname: Tang
authors.forename: Hyekung P
authors.initials: HP
authors.lastname: Cho
authors.forename: Manabu T
authors.initials: MT
authors.lastname: Nakamura
authors.forename: Steven D
authors.initials: SD
authors.lastname: Clarke
mesh_terms: D000818:Animals; D044943:Fatty Acid Desaturases / Q000096:biosynthesis / Q000235:genetics*; D005231:Fatty Acids, Unsaturated / Q000096:biosynthesis / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D008024:Ligands; D050602:Linoleoyl-CoA Desaturase; D008297:Male; D011401:Promoter Regions, Genetic; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear; D012091:Repetitive Sequences, Nucleic Acid; D020218:Response Elements / Q000235:genetics; D013230:Stearoyl-CoA Desaturase / Q000096:biosynthesis / Q000097:blood / Q000235:genetics*; D014157:Transcription Factors; D014158:Transcription, Genetic
chemical_list: D005231:Fatty Acids, Unsaturated; D008024:Ligands; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D044943:Fatty Acid Desaturases; D013230:Stearoyl-CoA Desaturase; C533241:FADS2 protein, human; D050602:Linoleoyl-CoA Desaturase; C474452:delta 6-desaturase, rat