Regulation of human delta-6 desaturase gene transcription: identification of a functional direct repeat-1 element

• Published in: Journal of lipid research Vol. 44; no. 4; pp. 686 - 695
• Main Authors: Tang, Chongren, Cho, Hyekung P, Nakamura, Manabu T, Clarke, Steven D
• Format: Journal Article
• Language: English
• Published: United States Elsevier 01.04.2003
• Subjects: Animals; Fatty Acid Desaturases - biosynthesis; Fatty Acid Desaturases - genetics; Fatty Acids, Unsaturated - biosynthesis; Fatty Acids, Unsaturated - physiology; Gene Expression Regulation, Enzymologic; Humans; Ligands; Linoleoyl-CoA Desaturase; liver; Male; peroxisome proliferator-activated receptor α; polyunsaturated fatty acids; Promoter Regions, Genetic; Rats; Rats, Sprague-Dawley; Receptors, Cytoplasmic and Nuclear; Repetitive Sequences, Nucleic Acid; Response Elements - genetics; Stearoyl-CoA Desaturase - biosynthesis; Stearoyl-CoA Desaturase - blood; Stearoyl-CoA Desaturase - genetics; Transcription Factors; Transcription, Genetic
• ISSN: 0022-2275
• DOI: 10.1194/jlr.M200195-JLR200

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.