Transcription of the β2‐adrenergic receptor gene in rat liver is regulated during early postnatal development by an upstream repressor element

: As early postnatal development of the male rat proceeds, there is a decline in transcription of the beta2-adrenergic receptor gene in liver which is associated with a decline in beta2-adrenergic receptor mediated glucose mobilization. In this study, primary cultures of rat hepatocytes transiently transfected with fusion genes containing various segments of beta2-adrenergic receptor gene 5'-flanking DNA fused to a promoterless luciferase reporter gene were used to identify genetic elements that might control beta2-adrenergic receptor gene expression during the first 10 days of postnatal life. We found that 261 bp of beta2-adrenergic receptor gene 5'-flanking region (-372 to -95, start of translation is +1) was sufficient to direct high luciferase expression in fetal day 18 hepatocytes and therefore included the beta2-adrenergic receptor gene promoter. Luciferase activities in fetal day 18 hepatocytes transfected with pbeta2AR(-372/-95), pbeta2AR(-1,335/-95) and pbeta2AR(-3,349/-95) were fourfold greater than that in either postnatal day 5 or postnatal day 10 hepatocytes transfected with the same fusion genes. By use of gel mobility shift assays, we observed increased protein binding to a 50 bp segment (-372 to -323) of the beta2-adrenergic receptor gene 5'-flanking region with nuclear extracts prepared from postnatal day 5 and postnatal day 10 hepatocytes compared to fetal day 18 hepatocytes. These findings suggest the presence of a regulatory element in the 5'-flanking region of the beta2-adrenergic receptor gene that appears to be involved in suppression of transcription of the beta2-adrenergic receptor gene in liver during early postnatal development.