Polymorphisms of the 5 ' leader cistron of the human beta(2)-adrenergic receptor regulate receptor expression

Cellular expression of the beta(2)-adrenergic receptor (beta(2)AR) is contr olled in part by a 19-amino acid peptide that regulates mRNA translation. T his peptide is encoded by a short open reading frame, termed the 5' leader cistron (5'LC), which is 102 bp upstream of the beta(2)AR coding block. In 176 normal subjects we found a single nucleotide polymorphism resulting in either Arg (previously denoted wild-type) or Cys at position 19 of this pep tide. Allele frequencies were 0.37 for Arg and 0.63 for Cys. To determine i f these variants altered beta(2)AR expression, COS-7 cells were transfected with polymorphic constructs consisting of 1,989 bp encompassing the 5'LC a nd the beta(2)AR coding block exactly as found in the human gene. beta(2)AR density, as determined by [I-125]CYP radioligand binding, was 72% higher i n cells transfected with the 5'LC-Cys19 construct as compared with those tr ansfected with the 5'LC-Arg19 construct and 110% higher when a cotransfecti on technique with a luciferase construct was used to control for transfecti on efficiency. Levels of the two mRNA transcripts were not different, confi rming in vitro studies that the upstream peptide regulates receptor express ion at the translational level. In human airway smooth muscle cells that na tively express beta(2)AR, receptor expression was approximately twofold hig her in those bearing the Cys versus the Arg polymorphism, confirming the ph enotype in a relevant cell type. Linkage disequilibrium was observed betwee n the 5'LC-Cys polymorphism and the beta(2)AR coding block polymorphisms Ar g16 and Gln27 (P < 0.0001), although several different haplotypes were iden tified. Thus, beta(2)AR expression in the human population is controlled by a common polymorphism of this 5'LC, and may be responsible for interindivi dual variation in beta AR responsiveness.