Down-regulation of the mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase gene by insulin: the role of the forkhead transcription factor FKHRL1.
Normal physiological responses to carbohydrate shortages cause the liver to increase the production of ketone bodies from the acetyl-CoA generated from fatty acid oxidation. This allows the use of ketone bodies for energy, thereby preserving the limited glucose for use by the brain. This adaptative response is switched off by insulin rapidly inhibiting the expression of the mitochondrial 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase (HMGCS2) gene, which is a key control site of ketogenesis. We decided to investigate the molecular mechanism of this inhibition. In the present study, we show that FKHRL1, a member of the forkhead in rhabdosarcoma (FKHR) subclass of the Fox family of transcription factors, stimulates transcription from transfected 3-hydroxy-3-methylglutaryl-CoA synthase promoter-luciferase reporter constructs, and that this stimulation is repressed by insulin. An FKHRL1-responsive sequence AAAAATA, located 211 bp upstream of the HMGCS2 gene transcription start site, was identified by deletion analysis. It binds FKHRL1 in vivo and in vitro and confers FKHRL1 responsiveness on homologous and heterologous promoters. If it is mutated, it partially blocks the effect of insulin in HepG2 cells, both in the absence and presence of overexpressed FKHRL1. These results suggest that FKHRL1 contributes to the regulation of HMGCS2 gene expression by insulin.
Nadal
Alícia
A
Department of Biochemistry and Molecular Biology, School of Pharmacy, University of Barcelona, Avda. Diagonal, 643, E-08028 Barcelona, Spain.
Marrero
Pedro F
PF
Haro
Diego
D
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002843:Chromatin / Q000378:metabolism; D002867:Chromones / Q000494:pharmacology; D004272:DNA, Mitochondrial / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015536:Down-Regulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005227:Fatty Acids / Q000378:metabolism; D000071161:Forkhead Box Protein O1; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D017930:Genes, Reporter; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D006904:Hydroxymethylglutaryl-CoA Synthase / Q000235:genetics* / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D008156:Luciferases / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology* / Q000235:genetics; D009025:Morpholines / Q000494:pharmacology; D009154:Mutation; D009419:Nerve Tissue Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation; D000077191:Wortmannin
D000730:Androstadienes; D002843:Chromatin; D002867:Chromones; D004272:DNA, Mitochondrial; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D005227:Fatty Acids; D000071161:Forkhead Box Protein O1; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D006904:Hydroxymethylglutaryl-CoA Synthase; D007328:Insulin; D008156:Luciferases; D009025:Morpholines; D009419:Nerve Tissue Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D014157:Transcription Factors; D000077191:Wortmannin; C085126:FOXO1 protein, human; C499517:FOXO3 protein, human; C499515:FOXO3 protein, rat; C074639:Foxo1 protein, rat; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one