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Hepatic Expression of the SPOT 14 (S14) Paralog S14-Related (Mid1 Interacting Protein) Is Regulated by Dietary Carbohydrate

Departments of Biochemistry, Molecular Biology, and Biophysics (N.G.T., H.C.T.) and Medicine (L.B.A., G.W.A., C.N.M.), University of Minnesota, Minneapolis, Minnesota 55455

Address all correspondence and requests for reprints to: Cary N. Mariash, M.D., Professor of Medicine, MMC 101, 420 Delaware Street SE, Minneapolis, Minnesota 55455. E-mail: mariasc{at}umn.edu.

The Spot 14 (S14) gene is rapidly up-regulated by signals that induce lipogenesis such as enhanced glucose metabolism and thyroid hormone administration. Previous studies in S14 null mice show that S14 is required for normal lipogenesis in the lactating mammary gland, but not the liver. We speculated that the lack of a hepatic phenotype was due to the expression of a compensatory gene. We recently reported that this gene is likely an S14 paralog that we named S14-Related (S14-R). S14-R is expressed in the liver, but not in the mammary gland. If S14-R compensates for the absence of S14 in the liver, we hypothesized that, like S14, S14-R expression should be glucose responsive. Here, we report that hepatic S14-R mRNA levels increase with high-carbohydrate feeding in mice or within 2 h of treating cultured hepatocytes with elevated glucose. A potential carbohydrate response element (ChoRE) was identified at position –458 of the S14-R promoter. Deletion of or point mutations within the putative S14-R ChoRE led to 50–95% inhibition of the glucose response. Gel-shift analysis revealed that the glucose-activated transcription complex carbohydrate responsive element-binding protein/Max-like protein X (Mlx) binds to the S14-R ChoRE. Finally, S14-R glucose induction is completely blocked when a dominant-negative form of Mlx is overexpressed in primary hepatocytes. In conclusion, our results indicate that the S14-R gene is a glucose-responsive target of carbohydrate responsive element-binding protein/Mlx and suggest that the S14-R protein is a compensatory factor, at least partially responsible for the normal liver lipogenesis observed in the S14 null mouse.