SPOT-14 PROTEIN FUNCTIONS AT THE PRETRANSLATIONAL LEVEL IN THE REGULATION OF HEPATIC-METABOLISM BY THYROID-HORMONE AND GLUCOSE

''Spot 14'' protein appears rapidly in nuclei of hepatocytes exposed t o glucose and thyroid hormone. Exposure of glucose- and T-3-treated he patocytes to a spot 14 antisense oligonucleotide inhibited induction o f mRNAs encoding malic enzyme, ATP citrate lyase, fatty acid synthase, liver-type pyruvate kinase, phosphoenolpyruvate carboxykinase, and ty pe I deiodinase but not hydroxymethylglutaryl-CoA reductase, cytochrom e c, and actin mRNAs. Induction of spot 14, ATP citrate-lyase, and fat ty acid synthase polypeptides, but not propionyl-CoA carboxylase and m itochondrial pyruvate carboxylase, was inhibited. Antisense treatment of hepatocytes transfected with a reporter controlled by a glucose- an d T-3-inducible fragment of the pyruvate kinase gene promoter inhibite d reporter activity, as did cotransfection of the reporter and a spot 14 antisense plasmid. Spot 14 protein acts in the induction of mRNAs c oding for key lipogenic (malic enzyme, ATP citrate-lyase, fatty acid s ynthase), glycolytic (pyruvate kinase), and gluconeogenic enzymes (pho sphoenolpyruvate carboxykinase), as well as the diet responsive type I deiodinase, but not those involved in mitochondrial respiration (cyto chrome c) or cholesterol synthesis (hydroxymethylglutaryl-CoA reductas e). Transfection experiments indicated that these effects are mediated at the transcriptional level. The protein functions in the activation of genes involved in metabolic switching between the fasted and fed s tates in liver.