Differential Desensitization of Homozygous Haplotypes of the β₂-Adrenergic Receptor in Lymphocytes

Abstract

Single-nucleotide polymorphisms of the ␤ 2 -adrenergic receptor gene and its 5Ј promoter have been associated with differences in receptor function and desensitization. Linkage disequilibrium may account for inconsistencies in reported effects of isolated polymorphisms. Therefore, we have investigated the three most common homozygous haplotypes of the ␤ 2 -adrenergic receptor (position 19 [Cys/Arg] of the 5Ј leader cistron and positions 16 [Arg/Gly] and 27 [Gln/Glu] of the receptor) for putative differences in agonistinduced desensitization. Lymphocytes of well defined nonasthmatic, nonallergic subjects homozygous for the haplotype CysGlyGln, ArgGlyGlu, or CysArgGln were isolated. Desensitization of (Ϫ)-isoproterenol-induced cyclic adenosine monophosphate (cAMP) accumulation and ␤ 2 -adrenergic receptor sequestration and downregulation were measured in relation to ␤ 2 -adrenergic receptor-mediated inhibition of IFN-␥ and interleukin-5 production. We observed that lymphocytes of individuals bearing the CysGlyGln haplotype were more susceptible to desensitization of the ␤-agonist-induced cAMP response than those of individuals with the ArgGlyGlu or CysArgGln haplotype. The haplotype-dependent desensitization of ␤-agonistinduced cAMP response was not associated with haplotype-dependent ␤ 2 -adrenergic receptor sequestration or downregulation. In addition, our data suggest reduced inhibition, in lymphocytes of subjects with the CysGlyGln haplotype, of interleukin-5 production induced by treatment with antibodies to the T-cell receptor-CD3 complex and to costimulatory molecule CD28 (␣CD3/␣CD28). This is the first study demonstrating haplotype-related differences in agonistinduced ␤ 2 -adrenergic receptor desensitization in primary human cells. This haplotype-related desensitization of the ␤ 2 -adrenergic receptor in lymphocytes might have consequences regarding the regulation of helper T-cell type 2 inflammatory responses.

Effects of In Utero and Childhood Tobacco Smoke Exposure and β2-Adrenergic Receptor Genotype on Childhood Asthma and Wheezing

“…The promoter Arg19Cys SNP is in strong linkage disequilibrium with the coding SNPs Arg16Gly and Glu27Gln, and 3 common haplotypes (Cys19-Gly16-Gln27, Arg19-Gly16-Glu27, and Cys19-Arg16-Gln27) exist. 13 Because the MAF for Ile164 is very low (∼1%) and the alleles at the Arg19Cys locus could be predicted from the diplotypes estimated from Arg16Gly and Glu27Gln genotypes, it was not necessary to genotype Arg19Cys and Thr164Ile SNPs.…”

“…These inconsistencies may have resulted from conducting experiments on different cell lines (eg, airway smooth muscle, respiratory epithelium, lymphocyte, mast cell, macrophage) with pleiotropic effects of the SNPs on these cells. [13][14][15][16] Because these SNPs are tightly linked, some researchers have also argued that assessment of individual SNP effects without considering haplotypes in previous studies may have resulted in inconsistent associations between these SNPs and agonist-promoted β2AR desensitization. Given the haplotype distributions, the Arg16 allele is carried in the Cys19-Arg16-Gln27 haplotype (Arg16-Gln27 diplotype in this study).…”

“…Furthermore, for examining joint effects of exposures and the genetic variants, such intraethnic substructure would have to be related to both factors, which is unlikely. Because the associations between the SNPs and exposures showed similar results by ethnicity and the joint effects of Arg16Gly and maternal smoking during pregnancy showed similar magnitude of associations by ethnicity, our analytic approach of conducting pooled analyses adjusting for ethnicity is unlikely to introduce a bias that could account for the findings.The modifying role of smoking on the association between ADRB2 Arg16Gly and asthma/ wheeze was reported previously for adults, 7 and existing data suggest that both smoking and these functional SNPs modulate β2AR density and activity 13,23 ; therefore, our analyses were based on specified a priori hypotheses. In this setting, we do not consider it appropriate to disregard previous information on the biology of β2AR expression and to adjust the P values for testing a set of selected a priori hypotheses.…”

“…The promoter Arg19Cys SNP is in strong linkage disequilibrium with the coding SNPs Arg16Gly and Glu27Gln, and 3 common haplotypes (Cys19-Gly16-Gln27, Arg19-Gly16-Glu27, and Cys19-Arg16-Gln27) exist. 13 Because the MAF for Ile164 is very low (∼1%) and the alleles at the Arg19Cys locus could be predicted from the diplotypes estimated from Arg16Gly and Glu27Gln genotypes, it was not necessary to genotype Arg19Cys and Thr164Ile SNPs.Previous in vitro and in vivo studies provided conflicting data on the functional significance of these SNPs. These inconsistencies may have resulted from conducting experiments on different cell lines (eg, airway smooth muscle, respiratory epithelium, lymphocyte, mast cell, macrophage) with pleiotropic effects of the SNPs on these cells.…”

Pharmacogenetics of the human beta-adrenergic receptors

“…87 Oostendorp et al 88 used human lymphocytes and measured desensitization to isoproterenol-induced cAMP accumulation; ADRB2 Haplotype 2 showed significantly greater desensitization as compared to Haplotypes 1 or 3 (the Thr164Ile polymorphism was not genotyped in this work). The authors suggest that the differential haplotype effect may be important for the regulation of type 2 helper cells in asthma inflammation.…”