The Epstein-Barr Virus-encoded G Protein-coupled Receptor BILF1 Hetero-oligomerizes with Human CXCR4, Scavenges Gαi Proteins, and Constitutively Impairs CXCR4 Functioning

Cells express distinct G protein-coupled receptor (GPCR) subtypes on their surface, allowing them to react to a corresponding variety of extracellular stimuli. Cross-regulation between different ligand-GPCR pairs is essential to generate appropriate physiological responses. GPCRs can physically affect each other's functioning by forming heteromeric complexes, whereas cross-regulation between activated GPCRs also occurs through integration of shared intracellular signaling networks. Human herpesviruses utilize virally encoded GPCRs to hijack cellular signaling networks for their own benefit. Previously, we demonstrated that the Epstein-Barr virus-encoded GPCR BILF1 forms heterodimeric complexes with human chemokine receptors. Using a combination of bimolecular complementation and bioluminescence resonance energy transfer approaches, we now show the formation of hetero-oligomeric complexes between this viral GPCR and human CXCR4. BILF1 impaired CXCL12 binding to CXCR4 and, consequently, also CXCL12-induced signaling. In contrast, the G protein uncoupled mutant BILF1-K(3.50)A affected CXCL12-induced CXCR4 signaling to a much lesser extent, indicating that BILF1-mediated CXCR4 inhibition is a consequence of its constitutive activity. Co-expression of G alpha(i1) with BILF1 and CXCR4 restored CXCL12-induced signaling. Likewise, BILF1 formed heteromers with the human histamine H-4 receptor (H4R). BILF1 inhibited histamine-induced G alpha(i)-mediated signaling by H4R, however, without affecting histamine binding to this receptor. These data indicate that functional cross-regulation of G alpha(i)-coupled GPCRs by BILF1 is at the level of G proteins, even though these GPCRs are assembled in hetero-oligomeric complexes.