Detection of receptor ligands by monitoring selective stabilization of a Renilla luciferase-tagged constitutively active mutant G-protein-coupled receptor

摘要

class="enumerated" style="list-style-type:decimal">The wild-type β2-adrenoceptor and a constitutively active mutant of this receptor were C-terminally tagged with luciferase from the sea pansy Renilla reniformis.C-terminal addition of Renilla luciferase did not substantially alter the levels of expression of either form of the receptor, the elevated constitutive activity of the mutant β2-adrenoceptor nor the capacity of isoprenaline to elevate cyclic AMP levels in intact cells expressing these constructs.Treatment of cells expressing constitutively active mutant β2-adrenoceptor-Renilla luciferase with antagonist/inverse agonist ligands resulted in upregulation of levels of this polypeptide which could be monitored by the elevated luciferase activity.The pEC50 for ligand-induced luciferase upregulation and ligand affinity to bind the receptor were highly correlated.Similar upregulation could be observed following sustained treatment with agonist ligands.These effects were only observed at a constitutively active mutant of the β2-adrenoceptor. Co-expression of the wild-type β2-adrenoceptor C-terminally tagged with the luciferase from Photinus pyralis did not result in ligand-induced upregulation of the levels of activity of this luciferase.Co-expression of the constitutively active mutant β2-adrenoceptor-Renilla luciferase and an equivalent mutant of the α1b-adrenoceptor C-terminally tagged with green fluorescent protein allowed pharmacological selectivity of adrenoceptor antagonists to be demonstrated.This approach offers a sensitive and convenient means, which is amenable to high throughput analysis, to monitor ligand binding to a constitutively active mutant receptor.As no prior knowledge of receptor ligands is required this approach may be suitable to identify ligands at orphan G protein-coupled receptors.