Bahouth S W, Cui X, Beauchamp M J, Park E A
Department of Pharmacology, College of Medicine, The University of Tennessee, 874 Union Avenue, Memphis, TN 38163, USA.
J Mol Cell Cardiol. 1997 Dec;29(12):3223-37. doi: 10.1006/jmcc.1997.0549.
Transcription of the rat gene for the beta1-adrenergic receptor (beta1-AR) is stimulated by thyroid hormone (T3) in ventricular myocytes. To identify the domains involved in the regulation of beta1-AR gene transcription by T3, three kb of 5'-flanking sequence of the rat beta1-AR gene were ligated to a luciferase reporter gene and transiently transfected into ventricular myocytes. By generating deletions in the rat beta1-AR promoter, a region between -125 and -100 was found to mediate a three-fold induction by T3. This element was able to confer T3 responsiveness to a neutral promoter driving the luciferase reporter gene. Through site directed mutagenesis of this region, it was determined that the T3 responsive element (TRE) was organized as a direct repeat separated by five nucleotides in which the 5'-most AGGTCG half-site was between nucleotides -105 to -102 and the 3'-most AGGTCA half-site between nucleotides -116 and -113. Both the thyroid hormone receptor isoforms alpha and beta bound to the oligomer representing the sequences between -125 and -100 most efficiently as heterodimers with the retinoid X receptor. This TRE is unusual in that it is a direct repeat separated by five nucleotides which is located 3' to the transcriptional start site.
甲状腺激素（T3）可刺激心室肌细胞中大鼠β1 - 肾上腺素能受体（β1 - AR）基因的转录。为了确定参与T3对β1 - AR基因转录调控的结构域，将大鼠β1 - AR基因的3 kb 5'侧翼序列与荧光素酶报告基因连接，并瞬时转染到心室肌细胞中。通过对大鼠β1 - AR启动子进行缺失突变，发现 - 125至 - 100之间的区域介导了T3的三倍诱导作用。该元件能够赋予驱动荧光素酶报告基因的中性启动子T3反应性。通过对该区域进行定点诱变，确定T3反应元件（TRE）组织为一个由五个核苷酸隔开的直接重复序列，其中最靠近5'端的AGGTCG半位点位于 - 105至 - 102核苷酸之间，最靠近3'端的AGGTCA半位点位于 - 116至 - 113核苷酸之间。甲状腺激素受体亚型α和β都以与视黄酸X受体的异二聚体形式最有效地结合到代表 - 125至 - 100之间序列的寡聚体上。这个TRE的不同寻常之处在于它是一个由五个核苷酸隔开的直接重复序列，位于转录起始位点的3'端。
