Asymmetrical ligand-induced cross-regulation of chemokine (C-X-C motif) receptor 4 by α(1)-adrenergic receptors at the heteromeric receptor complex

Recently, we reported that chemokine (C-X-C motif) receptor (CXCR)4 and atypical chemokine receptor 3 regulate α(1)-adrenergic receptors (α(1)-AR) through the formation of hetero-oligomeric complexes. Whether α(1)-ARs also regulate chemokine receptor function within such heteromeric receptor complexes is unknown. We observed that activation of α(1b)-AR within the α(1b)-AR:CXCR4 heteromeric complex leads to cross-recruitment of β-arrestin2 to CXCR4, which could not be inhibited with AMD3100. Activation of CXCR4 did not cross-recruit β-arrestin2 to α(1b)-AR. A peptide analogue of transmembrane domain 2 of CXCR4 interfered with α(1b)-AR:CXCR4 heteromerization and inhibited α(1b)-AR-mediated β-arrestin2 cross-recruitment. Phenylephrine (PE) induced internalization of CXCR4 in HEK293 cells co-expressing CXCR4 and α(1b)-AR and of endogenous CXCR4 in human vascular smooth muscle cells (hVSMC). The latter was detectable despite blockade of CXCR4 with the neutralizing antibody 12G5. hVSMC migrated towards CXCL12 and PE, but not towards a combination of CXCL12 and PE. PE inhibited CXCL12-induced chemotaxis of hVSMC (IC(50): 77 ± 30 nM). Phentolamine cross-inhibited CXCL12-induced chemotaxis of hVSMC, whereas AMD3100 did not cross-inhibit PE-induced chemotaxis. These data provide evidence for asymmetrical cross-regulation of CXCR4 by α(1)-adrenergic receptors within the heteromeric receptor complex. Our findings provide mechanistic insights into the function of α(1)-AR:CXCR4 heteromers and suggest alternative approaches to modulate CXCR4 in disease conditions.