GPR83 Engages Endogenous Peptides from Two Distinct Precursors to Elicit Differential SignalingS

PEN is an abundant neuropeptide that activates G protein-coupled receptor 83 (GPR83), which is considered a novel therapeutic target due to its roles in regulation of feeding-, reward-, and anxietyrelated behaviors. Themajor formof PEN in the brain is 22 residues in length. Previous studies have identified shorter forms of PEN in mouse brain and neuroendocrine cells; these shorter forms were named PEN18, PEN19, and PEN20, with the number reflecting the length of the peptide. The C-terminal five residues of PEN20 are identical to the C-terminus of a procholecystokinin (proCCK)- derived peptide, named proCCK56-62, that is present in mouse brain. ProCCK56-62 is highly conserved across species, although it has no homology to the bioactive cholecystokinin domain. ProCCK56-62 and a longer form, proCCK56-63, were tested for their ability to engage GPR83. Both peptides bind GPR83 with high affinity, activate second messenger pathways, and induce ligand-mediated receptor endocytosis. Interestingly, the shorter PEN peptides, ProCC56-62 and ProCCK56-63, differentially activate signal transduction pathways. Whereas PEN22 and PEN20 facilitate receptor coupling to Gai, PEN18, PEN19, and ProCCK peptides facilitate coupling to Gas. Furthermore, the ProCCK peptides exhibit dose-dependent Ga subtype selectivity in that they facilitate coupling to Gas at low concentrations and Gai at high concentrations. These data demonstrate that peptides derived from two distinct peptide precursors can differentially activate GPR83 and that GPR83 exhibits Ga subtype preference depending on the nature and concentration of the peptide. These results are consistent with the emerging idea that endogenous neuropeptides function as biased ligands.