Molecular cloning and expression of the rat β₁-adrenergic receptor gene

Using the sequence homology approach for cloning related genes within the G-protein-coupled receptor gene family, we have cloned the gene for the rat β₁-adrenergic receptor (β₁-AR). The rat β₁-adrenergic receptor gene was isolated from a λ EMBL3 rat genomic DNA library using the hamster β₂-adrenergic receptor (β₂-AR) coding sequence as a probe under low stringency hybridization conditions. The rat β₁-AR gene encodes a protein of 466 amino acids that contains one consensus site for N-linked glycosylation (Asn-p15) and three consensus sites for cAMP-dependent protein kinase phosphorylation (der-296, Ser-301, and Ser-401). The encoded rat β₁-AR is 98 and 91% similar at the amino acid level with the human β₁-AR in the transmembrane domains and in the overall sequence, respectively. Genomic Southern blot and gene dosage analyses indicate that the rat β₁-AR gene is a single copy gene. The tissue distribution of the rat β₁-AR mRNA was highest in the pineal gland with other brain regions and peripheral tissues, including the heart, expressing the mRNA at moderate levels. The bacteriophage clone containing the rat β₁-AR gene with its natural promoter was co-transfected with the selectable marker (pRSVneo) conferring neomycin resistance into β₁-AR-deficient mouse L cells. Analyses of the selected transfectant demonstrates efficient expression of the β₁-AR gene and functional receptor. ¹²⁵I-Labeled iodocyanopindolol bound transfectant membranes with an affinity of K(D) = 24 pm; the β₁-AR-selective antagonist ICI 89,406 displaced iodocyanopindolol binding with a K(i) ~ 140 times lower than that for the β₂-AR-selective antagonist ICI 118,551. In addition, in the transfectant cell line, adenylylcyclase was stimulated by β-adrenergic receptor agonists with the rank order of potency of isoproterenol > norepinephrine = epinephrine, consistent with properties expected of the β₁-AR subtype.