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  • Title: Polyunsaturated fatty acids suppress sterol regulatory element-binding protein 1c promoter activity by inhibition of liver X receptor (LXR) binding to LXR response elements.
    Author: Yoshikawa T, Shimano H, Yahagi N, Ide T, Amemiya-Kudo M, Matsuzaka T, Nakakuki M, Tomita S, Okazaki H, Tamura Y, Iizuka Y, Ohashi K, Takahashi A, Sone H, Osuga Ji J, Gotoda T, Ishibashi S, Yamada N.
    Journal: J Biol Chem; 2002 Jan 18; 277(3):1705-11. PubMed ID: 11694526.
    Abstract:
    Previous studies have demonstrated that polyunsaturated fatty acids (PUFAs) suppress sterol regulatory element-binding protein 1c (SREBP-1c) expression and, thus, lipogenesis. In the current study, the molecular mechanism for this suppressive effect was investigated with luciferase reporter gene assays using the SREBP-1c promoter in HEK293 cells. Consistent with previous data, the addition of PUFAs to the medium in the assays robustly inhibited the SREBP-1c promoter activity. Deletion and mutation of the two liver X receptor (LXR)-responsive elements (LXREs) in the SREBP-1c promoter region eliminated this suppressive effect, indicating that both LXREs are important PUFA-suppressive elements. The luciferase activities of both SREBP-1c promoter and LXRE enhancer constructs induced by co-expression of LXRalpha or -beta were strongly suppressed by the addition of various PUFAs (arachidonic acid > eicosapentaenoic acid > docosahexaenoic acid > linoleic acid), whereas saturated or mono-unsaturated fatty acids had minimal effects. Gel shift mobility and ligand binding domain activation assays demonstrated that PUFA suppression of SREBP-1c expression is mediated through its competition with LXR ligand in the activation of the ligand binding domain of LXR, thereby inhibiting binding of LXR/retinoid X receptor heterodimer to the LXREs in the SREBP-1c promoter. These data suggest that PUFAs could be deeply involved in nutritional regulation of cellular fatty acid levels by inhibiting an LXR-SREBP-1c system crucial for lipogenesis.
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