Characterization of the promoter region of the rat CCAAT/enhancer-binding protein alpha gene and regulation by thyroid hormone in rat immortalized brown adipocytes.
CCAAT/enhancer binding proteins (C/EBP) are a family of transcription factors with a highly conserved basic/leucine zipper (bZIP) domain that has been implicated in the transcriptional control of genes involved in cell growth and differentiation. We have previously demonstrated that the expression of C/EBPalpha and C/EBPbeta genes is regulated by thyroid hormone in rat liver during development. The aim of the present study was to explore the molecular mechanisms underlying the control of C/EBPalpha gene expression by thyroid hormone. To achieve this goal, we isolated and characterized a genomic clone containing 1171 bp of the 5'-flanking region of the rat C/EBPalpha gene. This fragment was an active promoter in MB492 cells, an immortalized brown adipocyte cell line that expresses the endogenous C/EBPalpha gene in a T3-dependent manner. Sequence analysis suggested the presence of three thyroid hormone response elements, TRE-1 (-602/-589), TRE2 (-411/-396), and TRE3 (-376/-350). The results of deletion, mutagenesis, and gel mobility shift analysis disclosed that only TRE-1, an ER2-type response element, represented a functional T3 response element. Our results demonstrate that T3 is a factor that positively regulates C/EBPalpha gene expression in a direct fashion.
Menéndez-Hurtado
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Instituto de Investigaciones Biomédicas, Consejo Superior de Investigaciones Cientificas-Universidad Autónoma de Madrid, Spain.
Santos
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Pérez-Castillo
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D002001:Adipose Tissue, Brown / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000235:genetics*; D002461:Cell Line, Transformed; D003001:Cloning, Molecular; D017353:Gene Deletion; D005786:Gene Expression Regulation / Q000187:drug effects*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D011401:Promoter Regions, Genetic; D051381:Rats; D011988:Receptors, Thyroid Hormone / Q000378:metabolism; D020218:Response Elements; D014162:Transfection; D014284:Triiodothyronine / Q000494:pharmacology*
D022763:CCAAT-Enhancer-Binding Protein-alpha; D011988:Receptors, Thyroid Hormone; D014284:Triiodothyronine