Three members of the ghrelin receptor family were characterized in parallel: the ghrelin
receptor, the neurotensin receptor 2 and the orphan receptor GPR39. In transiently
transfected COS-7 and human embryonic kidney 293 cells, all three receptors displayed a
high degree of ligand-independent signaling activity. The structurally homologous motilin
receptor served as a constitutively silent control; upon agonist stimulation, however, it
signaled with a similar efficacy to the three related receptors. The constitutive activity of the …