Elucidation of CXCR7-Mediated Signaling Events and Inhibition of CXCR4-Mediated Tumor Cell Transendothelial Migration by CXCR7 Ligands

Abstract

CXCR7 binds chemokines CXCL11 (I-TAC) and CXCL12 (SDF-1) but does not act as a classical chemoattractant receptor. Using CCX771, a novel small molecule with high affinity and selectivity for CXCR7, we found that, although CXCR7 is dispensable for “bare filter” in vitro chemotaxis, CXCR7 plays an essential role in the CXCL12/CXCR4-mediated transendothelial migration (TEM) of CXCR4+CXCR7+ human tumor cells. Importantly, although CXCL11 is unable to stimulate directly the migration of these cells, it acts as a potent antagonist of their CXCL12-induced TEM. Furthermore, even though this TEM is driven by CXCR4, the CXCR7 ligand CCX771 is substantially more potent at inhibiting it than the CXCR4 antagonist AMD3100, which is more than 100 times weaker at inhibiting TEM when compared with its ability to block bare filter chemotaxis. Far from being a “silent” receptor, we show that CXCR7 displays early hallmark events associated with intracellular signaling. Upon cognate chemokine binding, CXCR7 associates with β-arrestin2, an interaction that can be blocked by CXCR7-specific mAbs. Remarkably, the synthetic CXCR7 ligand CCX771 also potently stimulates β-arrestin2 recruitment to CXCR7, with greater potency and efficacy than the endogenous chemokine ligands. These results indicate that CXCR7 can regulate CXCL12-mediated migratory cues, and thus may play a critical role in driving CXCR4+CXCR7+ tumor cell metastasis and tissue invasion. CXCR7 ligands, such as the chemokine CXCL11 and the newly described synthetic molecule CCX771, may represent novel therapeutic opportunities for the control of such cells.

β-arrestin- but not G protein-mediated signaling by the “decoy” receptor CXCR7

“…However, we did observe recruitment of β-arrestin to the plasma membrane upon treatment with both ligands in HEK293 cells transiently transfected with CXCR7 and GFP-labeled β-arrestin2 (Fig. 1A), consistent with recent reports of ligand-dependent interactions between these two molecules (15,16). Notably, we did not observe such recruitment in mock transfected HEK293 cells, which express endogenous CXCR4, an alternate receptor for SDF-1α (Fig.…”

“…It has also been proposed that CXCR7 acts as a coreceptor for CXCR4 (11,13), as the two receptors form heterodimers in the context of overexpression in transiently transfected cells. It has also been proposed that ligand binding to CXCR7 may result in crosstalk with CXCR4 mediated by intracellular signaling molecules (15). More recently, it has been demonstrated that CXCR7 interacts with β-arrestin in a liganddependent manner (15)(16)(17), resulting in ligand internalization, but without any assessment of changes in signaling.…”

“…It has also been proposed that ligand binding to CXCR7 may result in crosstalk with CXCR4 mediated by intracellular signaling molecules (15). More recently, it has been demonstrated that CXCR7 interacts with β-arrestin in a liganddependent manner (15)(16)(17), resulting in ligand internalization, but without any assessment of changes in signaling. Given these findings we set out to test whether CXCR7 can signal through β-arrestins to determine whether this receptor acts as an endogenous β-arrestin-biased receptor.…”

DNA methylation regulates the expression of CXCL12 in rheumatoid arthritis synovial fibroblasts

“…9,45 Recent studies found an association between CXCR7 and the adaptor protein b-arrestin2. [47][48][49] Interactions of arrestins with different receptors have been shown to facilitate activation of the MAPK cascade, a signaling pathway, which is known to regulate also MMPs. 50 High production of MMPs by RASFs has been identified as a major mechanism of joint destruction in RA.…”

In Vivo Invasion of Head and Neck Squamous Cell Carcinoma Cells Does Not Require Macrophages

“…CXCR7 is unlikely to be mediating the invasion response to CXCL12, since AMD3100 does not inhibit CXCR7 signaling as measured by ␤-arrestin recruitment. 44 The mechanism by which CXCR4 transactivates EGFR for invasion in vivo is likely to be due to EGFR ligand release, since the ADAM17 inhibitor TAPI-2 blocked CXCL12-induced invasion. However, EGF-induced invasion was not inhibited by TAPI-2 at 0.5 mol/L, indicating that EGFinduced invasion does not involve relay of EGFR ligand signaling.…”