Limited impact of multiple 5′ single-nucleotide polymorphisms on the transcriptional control of the human β 2 -adrenoceptor gene

The human β 2 -adrenoceptor (β 2 -AR) is subject to agonist-induced down-regulation. The degree of down-regulation is associated with certain single-nucleotide polymorphisms (SNPs) through yet unknown mechanisms. The 5′-leader sequence of the β 2 -AR gene contains several SNPs that are in strong linkage disequilibrium. The −367 T/C polymorphism, in particular, has been shown to affect transcriptional activity in reporter gene assays. In the present study we analysed the impact of this −367 SNP on the transcription rate of the β 2 -AR gene in the context of the complete natural locus. Taking advantage of the additional full disequilibrium with the +79 SNP in the β 2 -AR coding sequence, allele-specific transcript quantification was performed in PBMCs of six −367 heterozygous mild asthmatic patients. Our data are in line with the reported impact of the −367 SNP and give no indication of additional haplotype-related effects on β 2 -AR transcription. We further show that the −367 SNP affects the binding of a yet unidentified transcription factor complex, whose binding activity is not modulated by pharmacological compounds that induce or down-regulate β 2 -AR expression, suggesting a role in constitutive steady state expression rather than in inducible expression. As the β 2 -AR allele with a higher transcription rate associates with stronger agonist-induced down-regulation, it is not likely that the −367 SNP is causally related to the degree of down-regulation.