G protein activation via chemokine (C-X-C motif) receptor 4 and _1b-adrenoceptor is ligand and heteromer-dependent

It is unknown whether heteromerization between chemokine (C-X-C motif) receptor 4 (CXCR4), atypical chemokine receptor 3 (ACKR3) and alpha(1b)-adrenoceptor (alpha(1b)-AR) influences effects of the CXCR4/ACKR3 agonist chemokine (C-X-C motif) ligand 12 (CXCL12) and the noncognate CXCR4 agonist ubiquitin on agonist-promoted G protein activation. We provide biophysical evidence that both ligands stimulate CXCR4-mediated Gai activation. Unlike CXCL12, ubiquitin fails to recruit b-arrestin. Both ligands differentially modulate the conformation of CXCR4:ACKR3 heterodimers and its propensity to hetero-trimerize with alpha(1b)-AR. CXCR4:ACKR3 heterodimerization reduces the potency of CXCL12, but not of ubiquitin, to activate Gai. Ubiquitin enhances phenylephrine-stimulated alpha(1b)-AR-promoted Gaq activation from hetero-oligomers comprising CXCR4. CXCL12 enhances phenylephrine-stimulated alpha(1b)-AR-promoted Gaq activation from CXCR4:alpha(1b)-AR heterodimers and reduces phenylephrine-stimulated alpha(1b)-AR-promoted Gaq activation from ACKR3 comprising heterodimers and trimers. Our findings suggest heteromer and ligand-dependent functions of the receptor partners.