G protein activation via chemokine (C-X-C motif) receptor 4 and α1b -adrenoceptor is ligand and heteromer-dependent

Abstract

It is unknown whether heteromerization between chemokine (C-X-C motif) receptor 4 (CXCR4), atypical chemokine receptor 3 (ACKR3) and α_1b -adrenoceptor (α_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 Gαi activation. Unlike CXCL12, ubiquitin fails to recruit β-arrestin. Both ligands differentially modulate the conformation of CXCR4:ACKR3 heterodimers and its propensity to hetero-trimerize with α_1b -AR. CXCR4:ACKR3 heterodimerization reduces the potency of CXCL12, but not of ubiquitin, to activate Gαi. Ubiquitin enhances phenylephrine-stimulated α_1b -AR-promoted Gαq activation from hetero-oligomers comprising CXCR4. CXCL12 enhances phenylephrine-stimulated α_1b -AR-promoted Gαq activation from CXCR4:α_1b -AR heterodimers and reduces phenylephrine-stimulated α_1b -AR-promoted Gαq activation from ACKR3 comprising heterodimers and trimers. Our findings suggest heteromer and ligand-dependent functions of the receptor partners.

Keywords: CXCL12; GPCR heteromers; Gαi; Gαq; atypical chemokine receptor 3; ubiquitin.