Advanced fluorescence microscopy reveals disruption of dynamic CXCR4 dimerization by subpocket-specific inverse agonists

Ali Işbilir, Jan Möller, Marta Arimont, Vladimir Bobkov, Cristina Perpiñá-Viciano, Carsten Hoffmann, Asuka Inoue, Raimond Heukers, Chris de Graaf, Martine J. Smit, Paolo Annibale, Martin J. Lohse

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

Although class A G protein-coupled receptors (GPCRs) can function as monomers, many of them form dimers and oligomers, but the mechanisms and functional relevance of such oligomerization is ill understood. Here, we investigate this problem for the CXC chemokine receptor 4 (CXCR4), a GPCR that regulates immune and hematopoietic cell trafficking, and a major drug target in cancer therapy. We combine single-molecule microscopy and fluorescence fluctuation spectroscopy to investigate CXCR4 membrane organization in living cells at densities ranging from a few molecules to hundreds of molecules per square micrometer of the plasma membrane. We observe that CXCR4 forms dynamic, transient homodimers, and that the monomer-dimer equilibrium is governed by receptor density. CXCR4 inverse agonists that bind to the receptor minor pocket inhibit CXCR4 constitutive activity and abolish receptor dimerization. A mutation in the minor binding pocket reduced the dimer-disrupting ability of these ligands. In addition, mutating critical residues in the sixth transmembrane helix of CXCR4 markedly diminished both basal activity and dimerization, supporting the notion that CXCR4 basal activity is required for dimer formation. Together, these results link CXCR4 dimerization to its density and to its activity. They further suggest that inverse agonists binding to the minor pocket suppress both dimerization and constitutive activity and may represent a specific strategy to target CXCR4.

Original languageEnglish
Pages (from-to)29144-29154
Number of pages11
JournalProceedings of the National Academy of Sciences of the United States of America
Volume117
Issue number46
Early online date4 Nov 2020
DOIs
Publication statusPublished - 17 Nov 2020

Keywords

  • basal activity
  • chemokine receptor
  • dimerization
  • GPCR
  • microscopy

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