27 February 2012
Background: Receptor heteromers are macromolecular complexes containing at least two different receptor subunits, resulting in distinct pharmacology.
Results: The observed α 1AAR-CXCR2 heteromer recruits β-arrestin strongly upon activation with norepinephrine, in contrast to α 1AAR alone.
Conclusion: Heteromerization with CXCR2 dramatically changes α 1AAR pharmacology, revealing the potential for heteromer-specific biased agonism.
Significance: Such heteromer-specific novel pharmacology has important implications for drug discovery.
We have provided the first evidence for specific heteromerization between the α 1A-adrenoceptor (α 1AAR) and CXC chemokine receptor 2 (CXCR2) in live cells. α 1AAR and CXCR2 are both expressed in areas such as the stromal smooth muscle layer of the prostate. By utilizing the G protein-coupled receptor (GPCR) heteromer identification technology on the live cell-based bioluminescence resonance energy transfer (BRET) assay platform, our studies in human embryonic kidney 293 cells have identified norepinephrine-dependent β-arrestin recruitment that was in turn dependent upon co-expression of α 1AAR with CXCR2. These findings have been supported by co-localization observed using confocal microscopy. This norepinephrine-dependent β-arrestin recruitment was inhibited not only by the α 1AR antagonist Terazosin but also by the CXCR2-specific allosteric inverse agonist SB265610. Furthermore, Labetalol, which is marketed for hypertension as a nonselective β-adrenoceptor antagonist with α 1AR antagonist properties, was identified as a heteromer-specific-biased agonist exhibiting partial agonism for inositol phosphate production but essentially full agonism for β-arrestin recruitment at the α 1AAR-CXCR2 heteromer. Finally, bioluminescence resonance energy transfer studies with both receptors tagged suggest that α 1AAR-CXCR2 heteromerization occurs constitutively and is not modulated by ligand. These findings support the concept of GPCR heteromer complexes exhibiting distinct pharmacology, thereby providing additional mechanisms through which GPCRs can potentially achieve their diverse biological functions. This has important implications for the use and future development of pharmaceuticals targeting these receptors.