GPR6  G protein-coupled receptor 6, also known as GPR6, is a protein which in humans is encoded by the "GPR6" gene. GPR6 is a member of the G protein-coupled receptor family of transmembrane receptors. It has been reported that GPR6 is both constitutively active but in addition is further activated by sphingosine-1-phosphate. GPR6 up-regulates cyclic AMP levels and promotes neurite outgrowth.