CXCR2 chemokine receptor antagonism enhances DOP opioid receptor function via allosteric regulation of the CXCR2-DOP receptor heterodimer.

Opioid agonists have a broad range of effects on cells of the immune system, including modulation of the inflammatory response, and opioid and chemokine receptors are co-expressed by many white cells. Hetero-oligomerization of the human DOP opioid and chemokine CXCR2 receptors could be detected following their co-expression by each of co-immunoprecipitation, three different resonance energy transfer techniques and the construction of pairs of individually inactive but potentially complementary receptor G-protein alpha subunit fusion proteins. Although DOP receptor agonists and a CXCR2 antagonist had no inherent affinity for the alternative receptor when either receptor was expressed individually, use of cells that expressed a DOP opioid receptor construct constitutively, and in which expression of a CXCR2 receptor construct could be regulated, demonstrated that the CXCR2 antagonist enhanced the function of DOP receptor agonists only in the presence of CXCR2.

Novel pharmacological applications of G-protein-coupled receptor-G protein fusions.

Single, bi-functional polypeptides consisting of a G-protein-coupled receptor (GPCR) linked directly to a G protein alpha subunit have been employed for a number of years to study many aspects of signal initiation, including the roles of post-translational modifications, effects of mutations in both receptor and G protein and in the de-orphanisation of novel G-protein-coupled receptors. Recently, they have been used to improve signal-to-background in ligand assay screens and to study both agonist-directed signal trafficking and distinct conformational states of receptors. As well as such novel concepts in pharmacology, G-protein-coupled receptor-G protein fusions have recently been employed to examine receptor homo-dimerisation and hetero-dimerisation and are beginning to be used to explore allosteric effects within GPCR hetero-dimers.