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

Abstract

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 α 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. This effect was observed for both enkephalin- and alkaloid-based opioid agonists, and the effective concentrations of the CXCR2 antagonist reflected CXCR2 receptor occupancy. Entirely equivalent results were obtained in cells in which the native DOP opioid receptor was expressed constitutively and in which expression of the isolated CXCR2 receptor could be induced. These results indicate that a CXCR2 receptor antagonist can enhance the function of agonists at a receptor for which it has no inherent direct affinity by acting as an allosteric regulator of a receptor that is a heterodimer partner for the CXCR2 receptor. These results have novel and important implications for the development and use of small-molecule therapeutics.

Growth Hormone Secretagogues and Growth Hormone Releasing Peptides Act As Orthosteric Super-Agonists but Not Allosteric Regulators for Activation of the G Protein Gαo1 by the Ghrelin Receptor

“…Such data have resulted in the generation of a complex model that evokes the necessity of the ghrelin receptor's existing as a dimer and in which the various positive and negative allosteric effects on the action of ghrelin may be explained by the growth hormone secretagogues and growth hormone releasing peptides binding in distinct ways to the individual protomers of the ghrelin receptor dimer (Holst et al, 2005;Schwartz and Holst, 2006). This is intriguing because there are a growing number of instances in which ligands with highly selective affinity and/or potency for one GPCR can affect the pharmacology, function, and/or cellular distribution of a second GPCR for which they have no inherent direct affinity if the two GPCRs form a heterodimer (El-Asmar et al, 2005;Ellis et al, 2006;Parenty et al, 2008), and this has been discussed in terms of allosteric effects across the heterodimer interface (Milligan and Smith, 2007). However, such effects are substantially more challenging to explore for potential GPCR homo-dimers unless a mutated receptor, designed to alter its affinity to pharmacological agents, is paired with the corresponding wild-type receptor to generate an asymmetric homodimer or pseudo heterodimer that has distinct pharmacology at each protomer (Damian et al, 2006;Sartania et al, 2007).…”

Molecular Pharmacology ofδ-Opioid Receptors

“…The CXCR2-DOPr hetero-oligomerization was shown in HEK293 cells using different resonance energy transfer techniques as well as coimmunoprecipitation. In this particular case, the blockade of CXCR2 with an antagonist increased DOPr-mediated G protein activation, without affecting the binding properties of opioid ligands (Parenty et al, 2008). Therefore, although CXCR4 provides a dominant negative effect and a suppression of the signaling of DOPr, CXCR2 rather acts as an allosteric regulator able to enhance the effect of DOPr agonists.…”

Evidence for activity-regulated hormone-binding cooperativity across glycoprotein hormone receptor homomers

“…45). Such allosteric behaviour is also responsible for the gain of opioid receptor function observed when treating a chemokine-opioid receptor heteromer with a chemokine receptor antagonist 46 . These considerations extend beyond the field of chemokine receptors and may be patho-physiologically important 47,48 .…”