McGraw D W, Forbes S L, Kramer L A, Liggett S B
Department of Medicine and Department of Pharmacology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267, USA.
J Clin Invest. 1998 Dec 1;102(11):1927-32. doi: 10.1172/JCI4862.
Cellular expression of the beta2-adrenergic receptor (beta2AR) is controlled in part by a 19-amino acid peptide that regulates mRNA translation. This peptide is encoded by a short open reading frame, termed the 5' leader cistron (5'LC), which is 102 bp upstream of the beta2AR 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 peptide. Allele frequencies were 0.37 for Arg and 0.63 for Cys. To determine if these variants altered beta2AR expression, COS-7 cells were transfected with polymorphic constructs consisting of 1,989 bp encompassing the 5'LC and the beta2AR coding block exactly as found in the human gene. beta2AR density, as determined by [125I]CYP radioligand binding, was 72% higher in cells transfected with the 5'LC-Cys19 construct as compared with those transfected with the 5'LC-Arg19 construct and 110% higher when a cotransfection technique with a luciferase construct was used to control for transfection efficiency. Levels of the two mRNA transcripts were not different, confirming in vitro studies that the upstream peptide regulates receptor expression at the translational level. In human airway smooth muscle cells that natively express beta2AR, receptor expression was approximately twofold higher in those bearing the Cys versus the Arg polymorphism, confirming the phenotype in a relevant cell type. Linkage disequilibrium was observed between the 5'LC-Cys polymorphism and the beta2AR coding block polymorphisms Arg16 and Gln27 (P < 0.0001), although several different haplotypes were identified. Thus, beta2AR expression in the human population is controlled by a common polymorphism of this 5'LC, and may be responsible for interindividual variation in betaAR responsiveness.
β2 - 肾上腺素能受体（β2AR）的细胞表达部分受一种调节mRNA翻译的19个氨基酸的肽控制。该肽由一个短开放阅读框编码，称为5'前导顺反子（5'LC），位于β2AR编码区上游102 bp处。在176名正常受试者中，我们发现了一个单核苷酸多态性，导致该肽第19位出现精氨酸（以前称为野生型）或半胱氨酸。精氨酸等位基因频率为0.37，半胱氨酸为0.63。为了确定这些变体是否改变β2AR的表达，将包含5'LC和β2AR编码区的1989 bp多态性构建体（与人基因中完全相同）转染到COS - 7细胞中。通过[125I]CYP放射性配体结合测定，与转染5'LC - Arg19构建体的细胞相比，转染5'LC - Cys19构建体的细胞中β2AR密度高72%；当使用荧光素酶构建体的共转染技术来控制转染效率时，β2AR密度高110%。两种mRNA转录本的水平没有差异，这证实了体外研究中上游肽在翻译水平调节受体表达的结果。在天然表达β2AR的人气道平滑肌细胞中，携带半胱氨酸多态性的细胞中受体表达比携带精氨酸多态性的细胞高约两倍，这在相关细胞类型中证实了该表型。尽管鉴定出了几种不同的单倍型，但观察到5'LC - Cys多态性与β2AR编码区多态性Arg16和Gln27之间存在连锁不平衡（P < 0.0001）。因此，人群中β2AR的表达受这种5'LC常见多态性的控制，可能是βAR反应性个体差异的原因。
