OBJECTIVE The chemokine-like receptor 1(CMKLR1,Chem R23) is a functional receptor for chemerin,the chemerin-derived nonapeptide(C9),and the amyloid β peptide 1-42(Aβ_(42)).Because these peptides share little sequence homology,studies were conducted to investigate their pharmacological properties and regulation at CMKLR1.METHODS Cells expressing CMKLR1 were incubated with Aβ_(42) before stimulation with a strong agonist,the C9 peptide.Calcium mobilization,c AMP inhibition and MAP kinase activation were measured.Intramolecular FRET were determined using CMKLR1 constructs with an ECFP attached to the C-terminus and a Fl As H binding motif embedded in the first intracellular loop(IL1).RESULTS Binding of both Aβ_(42) and the C9 peptide induced CMKLR1 internalization,but only the Aβ_(42)-induced receptor internalization involved clathrin-coated pits.Likewise,Aβ_(42) but not C9 stimulated β-arrestin 2 translocation to plasma membranes.A robust Ca~(2+)flux was observed following C9 stimulation,whereas Aβ_(42) was ineffective even at micromolar concentrations.Despite its low potency in calcium mobilization assay,Aβ_(42) was able to alter C9-induced Ca~(2+) flux in dose-dependent manner:a potentiation effect at 100 pmol·L~(-1) of Aβ_(42) was followed by a suppression at 10 nmol·L~(-1) and further potentiation at 1 μmol·L~(-1).This unusual and biphasic modulatory effect was also seen in the C9-induced ERK phosphorylation but the dose curve was opposite to that of Ca~(2+) flux and c AMP inhibition,suggesting a reciprocal regulatory mechanism.Intramolecular FRET assay confirmed that Aβ_(42) modulates CMKLR1 rather than its downstream signaling pathways.CONCLUSION These findings suggest Aβ_(42) as an allosteric modulator that can both positively and negatively regulate the activation state of CMKLR1 in a manner that differs from existing allosteric modulatory mechanisms. OBJECTIVE The chemokine-like receptor 1 (CMKLR1, Chem R23) is a functional receptor for chemerin, the chemerin-derived nonapeptide (C9), and the amyloid β peptide 1-42 (Aβ_ (42) homology, studies were conducted to investigate their pharmacological properties and regulation at CMKLR1.METHODS Cells expressing CMKLR1 were incubated with Aβ_ (42) before stimulation with a strong agonist, the C9 peptide.Calcium mobilization, c AMP inhibition and MAP kinase activation were measured. Intramolecular FRET were determined using CMKLR1 constructs with an ECFP attached to the C-terminus and a Fl As H binding motif embedded in the first intracellular loop (IL1) .RESULTS Binding of both Aβ_ (42) and the C9 peptide induced CMKLR1 internalization, but only the Aβ_ (42) -induced receptor internalization involved clathrin-coated pits. Liverwise, Aβ_ (42) but not C9 stimulated β-arrestin 2 translocation to plasma membranes. A robust Ca 2+ flux was observed following C9 stim (42) was ineffective even at micromolar concentrations. Both its low potency in calcium mobilization assay, Aβ - (42) was able to alter C9-induced Ca 2+ flux in dose-dependent manner: a potentiation effect at 100 pmol·L -1 of Aβ_ (42) was followed by a suppression at 10 nmol·L -1 and further potentiation at 1 μmol·L -1. This unusual and biphasic modulatory effect was also seen in the C9-induced ERK phosphorylation but the dose curve was opposite to that of Ca ~ (2+) flux and c AMP inhibition, suggesting a reciprocal regulatory mechanism. Intramolecular FRET assay confirmed that Aβ - (42) modulates CMKLR1 rather than its downstream signaling pathways. CONCLUSION These findings suggest Aβ_ (42) as an allosteric modulator that can both positively and negatively regulate the activation state of CMKLR1 in a different manner from existing allosteric modulatory mechanisms.