The 3′-untranslated region of the β2-adrenergic receptor mRNA regulates receptor synthesis

Abstract

β2-Adrenergic receptors (β2-ARs) are low abundance integral membrane proteins that mediate the effects of catecholamines at the cell surface. Post-transcriptional regulation of β2-AR is dependent, in part, on sequences within the 5′- and 3′-untranslated regions (UTRs) of the receptor mRNA. In this work, we demonstrate that 3′-UTR sequences regulate the translation of the receptor mRNA. Deletion of the 3′-UTR sequences resulted in 2-2.5-fold increases in receptor expression. The steady-state levels of β2-AR mRNA did not change significantly in the presence or absence of the 3′-UTR, suggesting that the translation of the receptor mRNA is suppressed by 3′-UTR sequences. Introduction of the receptor 3′-UTR sequences into the 3′-UTR of a heterologous reporter gene (luciferase) resulted in a 70% decrease in reporter gene expression without significant changes in luciferase mRNA levels. Sucrose density gradient fractionation of cytoplasmic extracts from Chinese hamster ovary cells transfected with full-length receptor cDNA demonstrated that the receptor transcripts were distributed between polysomal and non-polysomal fractions. Deletion of 3′-UTR sequences from the receptor cDNA resulted in a clear shift in the distribution of receptor mRNA toward the polysomal fractions, favoring increased translation. The 3′-UTR sequences of the receptor mRNA were sufficient to shift the distribution of luciferase mRNA from predominantly polysomal fractions toward non-polysomal fractions in cells transfected with the chimeric luciferase construct. Taken together, our results provide the first evidence for translational control of β2-AR expression by 3′-UTR sequences. Presumably, this occurs by affecting the receptor mRNA localization.