Abstract
Dietary polyunsaturated fat is known to suppress expression of fatty acid synthase (FAS), a central enzyme in de novo lipogenesis. The sterol regulatory element-binding protein (SREBP) has recently been shown to be involved in this suppression. We previously reported that the first 2.1 kb of the FAS promoter are sufficient for transcriptional induction by a high carbohydrate diet as well as suppression by polyunsaturated fat in transgenic mice. Here, we first examined the DNA sequences responsible for SREBP-mediated suppression of FAS promoter activity by polyunsaturated fatty acids (PUFA) in vivo. Feeding polyunsaturated fat prevented both the low-level activation of the −278 FAS promoter which contains the −150 sterol response element (SRE), as well as the maximal activation of the longer −444 FAS promoter. We observed that ectopic expression of the activated form of SREBP in liver prevented PUFA-mediated suppression of both the endogenous FAS and FAS promoter-reporter transgene expression. We also found that the promoter region required for PUFA suppression in vivo is located between −278 to −131, where SREBP functions. Using HepG2 cells, we further examined the specific FAS promoter elements required for PUFA suppression. We found that the −150 SRE, as well as the –65 E-Box, contribute to PUFA suppression of the FAS promoter, at least in vitro.—Moon, Y. S., M-J. Latasa, M. J. Griffin, and H. S. Sul. Suppression of fatty acid synthase promoter by polyunsaturated fatty acids. J. Lipid Res. 2002. 43: 691–698.
Highlights
Dietary polyunsaturated fat is known to suppress expression of fatty acid synthase (FAS), a central enzyme in de novo lipogenesis
We demonstrated that binding of sterol regulatory element binding protein (SREBP) to the Ϫ150 sterol response element (SRE) is responsible for low-level induction, whereas occupancy of the Ϫ332 E-box by upstream stimulatory factor (USF) is necessary for high-level activation of the FAS promoter
We found that two upstream 5Ј-regions of the FAS promoter are required for carbohydrate/insulin regulation in vivo: one at Ϫ278 to Ϫ131 that accounts for a low level induction, and the other at Ϫ444 to Ϫ278 for maximal induction [13]
Summary
Production of transgenic mice and plasmids construction Transgenic mice containing Ϫ2,100 to ϩ67 of the rat FAS gene linked to the CAT reporter gene have been described previously [12]. The reporter gene constructs for Ϫ278-FAS-LUC and Ϫ278(Ϫ65)-FAS-LUC containing the Ϫ278/ϩ67 of the rat FAS promoter fused to the LUC reporter plasmid pGL2-basic (Promega) in the absence or presence of the mutation of Ϫ65/Ϫ60, were generated by ligating the BsaHI–XhoI fragment from Ϫ2,100-CAT [8] or Ϫ2,100(Ϫ65)-CAT plasmids, respectively, to the pGL2basic vector after digestion with SmaI and XhoI. The reporter gene constructs for Ϫ125-FAS-LUC and Ϫ125(Ϫ65)-FAS-LUC containing the Ϫ125/ϩ67 of the rat FAS promoter fused to the LUC reporter plasmid pGL2-basic (Promega) in the absence or presence of the mutation of Ϫ65/Ϫ60, were generated by ligating the XmaI–XhoI fragment from Ϫ2,100-CAT or Ϫ2,100(Ϫ65)CAT plasmids, respectively, to the pGL2basic vector after digestion with the same restriction enzymes
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