Single nucleotide polymorphism (-468 gly to ala) at the promoter region of sterol regulatory element-binding protein-1c associates with genetic defect of fructose-induced hepatic lipogenesis

To evaluate the genetic susceptibility to metabolic disorders induced by high fructose diet, we investigated the metabolic characteristics in 10 strains of inbred mice and found that they were separated into CBA and DBA groups according to the response to high fructose diet. The hepatic mRNA expression of the sterol regulatory element-binding protein-1 (SREBP-1) in CBA/JN was remarkably enhanced by high fructose diet but not in DBA/2N. Similar results were observed in primary hepatocytes after exposure to fructose. The nucleotide sequence at - 468 bp from the putative starting point of the SREBP-1c gene was adenine in the DBA group while it was guanine in the CBA group. In hepatocytes from CBA/JN, the activity of CBA-SREBP-1c promoter was significantly increased by 2.4- and 2.2-fold, in response to 30 mM fructose or 10 nM insulin, respectively, whereas the activity of DBA-SREBP-1c promoter responded to insulin but not to fructose. In hepatocytes from DBA/2N, both types of SREBP-1c promoter activities in response to insulin were attenuated. Furthermore, electrophoretic mobility shift assay revealed an unidentified nuclear protein bound to the oligonucleotides made from the region between - 453 to - 480 bp of the SREBP-1c promoter of CBA/JN but not to the probe from DBA/2N. Thus, in DBA/2N, the reduced mRNA expression of SREBP-1 after fructose refeeding appeared to associate with two independent mechanisms, 1) loss of binding of unidentified proteins to the region between - 453 to - 480 bp of the SREBP-1c promoter and 2) impaired insulin stimulation of SREBP-1c promoter activity.