Limited impact of multiple 5′ single-nucleotide polymorphisms on the transcriptional control of the human β2-adrenoceptor gene

The human beta(2)-adrenoceptor (beta(2)-AR) is subject to agonist-induced down-regulation. The degree of downregulation is associated with certain single-nucleotide polymorphisms ( SNPs) through yet unknown mechanisms. The 5'-leader sequence of the beta(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 beta(2)-AR gene in the context of the complete natural locus. Taking advantage of the additional full disequilibrium with the + 79 SNP in the beta(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 beta(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 beta(2)-AR expression, suggesting a role in constitutive steady state expression rather than in inducible expression. As the beta(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.