Evidence for Negative Binding Cooperativity within CCR5-CCR2b Heterodimers

Abstract

It is well established that most G protein-coupled receptors are able to form homo-and heterodimers, although the functional consequences of this process often remain unclear. CCR5 is a chemokine receptor that plays an important role in inflammatory diseases and acts as a major coreceptor for human immunodeficiency viruses. CCR5 was previously shown to homodimerize and heterodimerize with CCR2b, a closely related receptor. In the present study, we have analyzed the functional consequences of this dimerization process, in terms of ligand binding, stimulation of intracellular cascades, and internalization. Bioluminescence resonance energy transfer and coimmunoprecipitation assays demonstrated that CCR5 and CCR2b heterodimerize with the same efficiency as they homodimerize. In contrast to what has been reported previously, no cooperative signaling was observed after costimulation of the two receptors by their respective ligands. However, we observed that CCR5-specific ligands that are unable to compete for monocyte chemoattractant protein (MCP-1) binding on cells expressing CCR2b alone efficiently prevented MCP-1 binding when CCR5 and CCR2b were coexpressed. The extent of this cross-competition was correlated with the amount of CCR5 expressed in cells, as determined by fluorescence-activated cell sorting analysis. Similar observations were made for the CCR2b-selective ligand MCP-1 that competed efficiently for macrophage inflammatory protein-1␤ binding on cells expressing both receptors. Internalization assays did not allow us to demonstrate cointernalization of the receptors in response to agonist stimulation. Together, our observations suggest that CCR5 and CCR2b form homo-and heterodimers with similar efficiencies and that a receptor dimer can only bind a single chemokine.

RANTES Modulates the Release of Glutamate in Human Neocortex

“…The coupling of the receptors to different transducing pathways, PLC/IP 3 under basal conditions and adenylyl cyclase/PKA under depolarizing conditions, may have a number of explanations. For instance, it was shown that the chemokine receptors exist as homodimers or heterodimers and that the dimer composition can direct the coupling to different transducing pathways (Mellado et al, 2001;El-Asmar et al, 2005;Springael et al, 2005).…”

International Union of Basic and Clinical Pharmacology. LXVII. Recommendations for the Recognition and Nomenclature of G Protein-Coupled Receptor Heteromultimers

“…In a recent study, the group of Parmentier elegantly demonstrated that binding of the CCR2 radioligand 125 I-monocyte chemoattractant protein-1 could be partially inhibited by the selective CCR5 agonist macrophage inflammatory protein-1␤, the maximal inhibition being correlated with the expected amount of CCR2-CCR5 heterodimers in the cell (El-Asmar et al, 2005). Conversely, binding of the CCR5 radioligand could also be partially inhibited by a CCR2 specific agonist, further demonstrating a negative cooperativity between the two binding sites in a CCR2-CCR5 heterodimer.…”

Chemokines in Wound Healing and as Potential Therapeutic Targets for Reducing Cutaneous Scarring

“…Although they may function as monomers, it is now well established that many chemokine receptors also act as dimers or higher order oligomers. 172 In fact, all tested chemokine receptors form oligomers in a ligand-independent manner, [173][174][175][176][177] and heterodimers can form even between CC and CXC subclasses. 172 Another relevant phenomenon is that of crosstalk between different receptors.…”