Thyroid hormone induces β1-adrenergic receptor gene transcription through a direct repeat separated by five nucleotides

Transcription of the rat gene for the beta(1)-adrenergic receptor (beta(1)-AR) is stimulated by thyroid hormone (T-3) in ventricular myocytes. To identify the domains involved in the regulation of beta(1)-AR gene transcription by T-3. three kb of 5'-flanking sequence of the rat beta(1)-AR gene were ligated to a luciferase reporter gene and transiently transfected into ventricular myocytes, By generating deletions in the rat beta(1)-AR promoter. a region between -125 and -100 was found to mediate a three-fold induction by T-3. This element was able to confer T-3 responsiveness to a neutral promoter driving the luciferase reporter gene. Through site directed mutagenesis of this region, it was determined that the T-3 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. (C) 1997 Academic Press Limited.