A thyroid hormone response unit formed between the promoter and first intron of the carnitine palmitoyltransferase-Ialpha gene mediates the liver-specific induction by thyroid hormone.
Carnitine palmitoyltransferase-I (CPT-I) catalyzes the rate-controlling step of fatty acid oxidation. CPT-I converts long-chain fatty acyl-CoAs to acylcarnitines for translocation across the mitochondrial membrane. The mRNA levels and enzyme activity of the liver isoform, CPT-Ialpha, are greatly increased in the liver of hyperthyroid animals. Thyroid hormone (T3) stimulates CPT-Ialpha transcription far more robustly in the liver than in non-hepatic tissues. We have shown that the thyroid hormone receptor (TR) binds to a thyroid hormone response element (TRE) located in the CPT-Ialpha promoter. In addition, elements in the first intron participate in the T3 induction of CPT-Ialpha gene expression, but the CPT-Ialpha intron alone cannot confer a T3 response. We found that deletion of sequences in the first intron between +653 and +744 decreased the T3 induction of CPT-Ialpha. Upstream stimulatory factor (USF) and CCAAT enhancer binding proteins (C/EBPs) bind to elements within this region, and these factors are required for the T3 response. The binding of TR and C/EBP to the CPT-Ialpha gene in vivo was shown by the chromatin immunoprecipitation assay. We determined that TR can physically interact with USF-1, USF-2, and C/EBPalpha. Transgenic mice were created that carry CPT-Ialpha-luciferase transgenes with or without the first intron of the CPT-Ialpha gene. In these mouse lines, the first intron is required for T3 induction as well as high levels of hepatic expression. Our data indicate that the T3 stimulates CPT-Ialpha gene expression in the liver through a T3 response unit consisting of the TRE in the promoter and additional factors, C/EBP and USF, bound in the first intron.
Jackson-Hayes
Loretta
L
Department of Pharmacology, College of Medicine, University of Tennessee Health Science Center, Memphis 38163, USA.
Song
Shulan
S
Lavrentyev
Eduard N
EN
Jansen
Michelle S
MS
Hillgartner
F Bradley
FB
Tian
Liquin
L
Wood
Philip A
PA
Cook
George A
GA
Park
Edwards A
EA
D000818:Animals; D001483:Base Sequence; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000378:metabolism; D002334:Carnitine O-Palmitoyltransferase / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D017931:DNA Primers; D024202:Electrophoretic Mobility Shift Assay; D004790:Enzyme Induction; D005786:Gene Expression Regulation / Q000502:physiology*; D007438:Introns; D008099:Liver / Q000201:enzymology*; D008156:Luciferases / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D011401:Promoter Regions, Genetic; D011988:Receptors, Thyroid Hormone / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D014284:Triiodothyronine / Q000502:physiology*
D022763:CCAAT-Enhancer-Binding Protein-alpha; D017931:DNA Primers; D011988:Receptors, Thyroid Hormone; D014157:Transcription Factors; D014284:Triiodothyronine; D008156:Luciferases; D002334:Carnitine O-Palmitoyltransferase