Étude des mécanismes d'action du récepteur de chimiokine CXCR7/ACKR3

The recently discovered chemokine receptor CXCR7 was found to bind CXCL12, a chemokine previously thought to be an exclusive ligand of the CXCR4 chemokine receptor (Balabanian et al., 2005). It appears that those two receptors are expressed in similar cell types. Considering its roles as a co-receptor for the cellular entry of HIV and also its potent roles in cancer, CXCR4 has now become an interesting target for the development of new therapeutic molecules. AMD3100, a CXCR4 antagonist now approved for hematopoïetic stem cell mobilization, was also found to bind the CXCR7 chemokine receptor (Kalatskaya et al., 2009). In fact, AMD3100 acts as a CXCR7 agonist by inducing β-arrestin recruitement to the receptor. These new findings prompt investigators to reevaluate the selectivity of a therapeutic molecule developed to target exclusively the CXCR4 receptor, TC14012, as an anti-HIV drug. Using BRET technology, our results demonstrate that TC14012 is also capable of binding the CXCR7 chemokine receptor. As does AMD3100, TC14012 acts as an agonist on CXCR7. However, as opposed to CXCR4, the two molecules induce β-arrestin recruitment. We observe that it the spatial rearrangement of the CXCR4 and CXCR7 bodies that is responsible for these opposite effects. Functional selectivity is defined when different ligands bind a single receptor, and each ligand preferentially activates intracellular signaling pathways in favors of others. In addition to the CXCL12 chemokine, CXCR7 also has an other natural ligand, the CXCL11 chemokine. The fact that CXCR7 has two endogenous ligands highlights the concept of functional selectivity. It was discovered that even if a structural resemblance exists between chemokines, they can have diverging roles on intracellular signaling. This is thought to be due, at least in part, to distinct conformational change in the receptor (Zidar et al., 2009). We observed that there is indeed a difference in behavior in the receptor when it is complexed-bound to its endogenous ligands CXCL11 or CXCL12, and β-arrestine. Using directed mutagenesis of the E/DRY/LAIV motif of the CXCR7 receptor, we identified the arginine residue to be necessary for the CXCR7/β-arrestin interaction, upon stimulation with CXCL11, but not CXCL12. As opposed to CXCL12, we show that upon CXCL11 stimulation, CXCR7 significantly delays surface recycling. Additionally, we observed that this delay is completely abrogated by the substitution of arginine residue (R) at position 3.50 within the highly conserve motif E/DRYLAIV of the receptor with an alanine (A) (CXCR7-R142A). Also, we observed that in absence of β-arrestin, the degradation of the CXCL11 chemokine was less efficient. Take together, we demonstrate that β-arrestin recruitment to CXCR7 and cell surface expression of CXCR7 is ligand specific. Arginine residue (R) at position 3.50 within the highly conserve motif E/DRYLAIV of the CXCR7 receptor is important for cell surface expression and β-arrestin recruitment in response to CXCL11. In summary, our study highlights the concept of functional selectivity between CXCR7 and its two ligands CXCL11 and CXCL12.

Keyphrases: Cxcr7, Cxcr4, Cxcl12, Cxcl11, Beta-arrestine, Tc14012, Amd3100, Trafficking intracellulaire, Bret