Regulation of ovine and porcine stearoyl coenzyme A desaturase gene promoters by fatty acids and sterols

Stearoyl CoA desaturase (SCD) is responsible for converting SFA into MUFA and plays an important role in regulating the fatty acid composition of tissues. Although the number of SCD isoforms differs among species, SCD-1 is the predominant isoform expressed in the major lipogenic tissues of all species studied. The SCD-1 gene promoter region has been cloned for several species, including the human, mouse, pig, and recently, the cow. In this study, we cloned and partially characterized the ovine SCD promoter region. Sequence alignment showed a high degree of similarity with published bovine (94%) and porcine (92%) sequences. This included a highly conserved PUFA response region, which was also similar to that found in the human SCD and mouse SCD-1 promoters. Previous studies have indicated that there may be species differences in the regulation of SCD promoter activity by fatty acids. Using promoter-reporter gene (luciferase) constructs transfected into both HEK 293 and McA-RH7777 cells (kidney- and liver-derived cell lines, respectively), we showed the activity of the SCD promoter from 4 different species (mouse, human, pig, and sheep) to be reduced in a dose-dependent manner by addition of unsaturated fatty acids to the media, with linoleic acid being more potent than oleic acid after a 24-h treatment at 60 μM. This effect was dependent on the presence of the PUFA response region. In each of the species studied, the PUFA response region of the SCD promoter was shown to have an active sterol response element, which responded to treatment of cells with sterol or overexpression of the truncated active form of sterol regulatory element binding protein-1c. Thus, any species differences in previously reported regulation of SCD expression by fatty acids are not due to differences in promoter structure between species, but are more likely to depend on the cell type being studied or the relative concentrations and distribution of sterol regulatory element binding proteins or other transcription factors.