Promoter Analysis of the Rat b1-Adrenergic Receptor Gene Identifies Sequences Involved in Basal Expression

The b1-adrenergic receptor (b1-AR) mediates several functions of catecholamines in the heart, including the stimulation of heart rate and contractility. The expression of the rat b1-AR gene was assessed by transiently transfecting chimeric genes containing the b1-AR promoter, driving the luciferase reporter gene into various cell lines. b1-AR/luciferase vectors containing 3 kb of the 59-flanking region and extending to 2126 relative to the start site of translation were expressed at high levels in ventricular myocytes, SK-N-MC cells, and HepG2 cells. The addition of 26 nucleotides from 2125 to 2100 to the 23311 b1-AR/luciferase chimeric gene reduced expression in myo-cytes and SK-N-MC cells while eliminating expression in HepG2 cells. This element is located 125 base-pairs 39 to the transcriptional start site. The mutation of four nucleotides be-tween 2121 and 2118 diminished the inhibitory effect of this element. The inhibitory activity of the 2125 to 2100 sequence was completely dependent on promoter context and position-ing. In addition to this 39 element, sequences between 23311 and 22740 in the 59-flanking region of the b1-AR gene were required for the full transcriptional suppression. Using DNase I footprinting and gel mobility assays, it was determined that within the 26-bp region, rat heart nuclear proteins bound to tw