Physical interaction with Ephrin B1 promotes CXCR4 intracellular localization and oncogenic potential

Chemokine receptor 4 (CXCR4) is a member of the chemokine receptor family, exclusively activated by the chemokine CXCL12. While CXCR4 regulates numerous physiological processes associated with cell migration and embryogenesis, its overexpression has been involved in various cancer types. Studies suggest that intracellular CXCR4 rather than CXCL12-induced signaling at the plasma membrane contributes to its pro-tumorigenic functions. Given the role of GPCR-interacting proteins in their trafficking and subcellular localization, we characterized the CXCR4 interactome using an affinity purification coupled to mass spectrometry (AP-MS) strategy. The most abundant protein identified in the CXCR4 interactome is Ephrin B1, a member of the Ephrin protein family that shares several functions with CXCR4, such as the regulation of cell migration and proliferation. Further studies showed that the interaction between CXCR4 and Ephrin B1 is direct and enhanced upon CXCR4 activation by CXCL12. They also indicated that Ephrin B1 prevents CXCR4 N-glycosylation, decreases CXCR4 cell surface expression, and consistently inhibits CXCL12-induced CXCR4 coupling to G_αi1-3 and recruitment of β-arrestins 1 and 2. Conversely, Ephrin B1 signals to Erk1/2 through CXCR4 activation and mediates the decrease in Death Receptor 5 expression elicited by intracellular CXCR4. Collectively, these findings identify Ephrin B1 as a potential regulator of CXCR4-driven tumorigenic signaling.