Chicken ovalbumin upstream-promoter transcription factor and E-box-binding proteins enhance thyroid-hormone responsiveness of the malic enzyme gene in avian hepatocytes.
In chick embryo hepatocytes (CEH), stimulation of malic enzyme transcription by 3,3',5-tri-iodothyronine (T3) is mediated by a liver-specific and T3-inducible DNase I hypersensitive region (-3910 to -3640 bp) in the malic enzyme gene. Previous studies have shown that this region contains a cluster of five T3 response elements (T3REs), referred to as a T3 response unit (T3RU), plus three accessory elements that enhance T3 responsiveness conferred by the T3RU. Here we report the identification of two additional accessory elements within the -3910 to -3640 bp region. Each element augments T3 regulation of malic enzyme transcription in CEH. One element, designated region G (-3681/-3666 bp), contains a single nuclear-hormone-receptor half-site that binds the orphan receptor chicken ovalbumin upstream-promoter transcription factor. The other element, designated region H (-3655/-3646 bp), contains an E-box motif that binds proteins of unknown identity. Stimulation of T3RE function by region G or region H does not require the presence of additional malic enzyme sequences. In contrast with the stimulatory effects of regions G and H on T3 responsiveness in CEH, neither of these elements is effective in modulating T3 responsiveness in chick embryo fibroblasts (CEF). Instead, region H functions as a T3-insensitive repressor of transcription in CEF. These results indicate that chicken ovalbumin upstream-promoter transcription factor and E-box-binding proteins interact with nuclear T3 receptors to enhance T3 regulation of malic enzyme transcription in CEH and that alterations in region G and region H activities contribute to diminished T3 regulation of malic enzyme transcription in CEF relative to CEH. As the pattern of protein binding to regions G and H varies substantially between CEH and CEF, the mechanism for cell-type-dependent differences in region G and region H activity may involve alterations in protein binding to these T3 accessory elements.
Wang
Yutong
Y
Department of Biochemistry and Molecular Pharmacology, School of Medicine, P.O. Box 9142, West Virginia University, Morgantown, WV 26506-9142, USA.
Zhang
Yanqiao
Y
Hillgartner
F Bradley
FB
D000818:Animals; D001665:Binding Sites; D051836:COUP Transcription Factors; D002478:Cells, Cultured; D002642:Chick Embryo; D004247:DNA; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D005786:Gene Expression Regulation / Q000235:genetics; D022781:Hepatocytes / Q000201:enzymology*; D008291:Malate Dehydrogenase / Q000235:genetics*; D009154:Mutation; D011987:Receptors, Steroid; D012689:Sequence Homology, Nucleic Acid; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic / Q000235:genetics; D014284:Triiodothyronine / Q000494:pharmacology*
D051836:COUP Transcription Factors; D004268:DNA-Binding Proteins; D011987:Receptors, Steroid; D014157:Transcription Factors; D014284:Triiodothyronine; D004247:DNA; D008291:Malate Dehydrogenase