Chemokine and opioid peptide scavenging through constitutive and ligand-induced release of ACKR3-bearing extracellular vesicles
Atypical chemokine receptors (ACKRs) are non-signaling GPCRs that regulate ligand availability, with ACKR3 functioning as a dual scavenger of chemokines and opioid peptides. Here, we demonstrate that following ligand stimulation, besides the canonical internalization, ACKR3 is released on extracellular vesicles (EVs). ACKR3 was also found on EVs released under basal conditions, although to a lesser extent. These observations were confirmed across multiple cellular contexts, including endogenous systems. Mechanistically, basal and ligand-induced EV release are independent of GRKs and {beta}-arrestin but each relies on distinct trafficking routes and C-terminal determinants. Ligand-induced EV release is associated with plasma membrane localization and receptor recycling pathways. In contrast, basal EV release is governed by intracellular sorting processes and influenced by receptor ubiquitination and RAMP3. Functionally, EV-associated ACKR3 retains high-affinity ligand binding, enabling sequestration of CXCL12 and opioid peptides and thereby attenuating their signaling through CXCR4 and MOR. We also show that the release on EVs, in particular under basal conditions, is observed for other receptors such as KOR, CXCR4 and several ACKRs. Collectively, these findings establish EVs as regulators in chemokine and opioid systems and as a previously underappreciated dimension of ACKR3 and more broadly GPCR biology.