Background：

G protein-coupled receptors (GPRs)， also known as seven transmembrane receptors， heptahelical receptors or 7TM receptors， comprise a superfamily of proteins that play a role in many different stimulus-response pathways. G protein coupled receptors translate extracellular signals into intracellular signals (G protein activation) and they respond to a variety of signaling molecules， such as hormones and neurotransmitters. GPR146 (G protein-coupled receptor 146)， also known as PGR8， is a 333 amino acid multi-pass transmembrane protein that belongs to the G-protein coupled receptor 1 family. Characterized as an orphan receptor for which its endogenous ligand has yet to be identified， GPR146 is thought to play a role in signaling events throughout the cell.