RT Journal Article
SR Electronic
T1 Signaling and Ligand Binding by Recombinant Neuromedin U Receptors: Evidence for Dual Coupling to Gα<sub>q/11</sub> and Gα<sub>i</sub> and an Irreversible Ligand-Receptor Interaction
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 1544
OP 1556
DO 10.1124/mol.104.002337
VO 66
IS 6
A1 Paul J. Brighton
A1 Philip G. Szekeres
A1 Alan Wise
A1 Gary B. Willars
YR 2004
UL http://molpharm.aspetjournals.org/content/66/6/1544.abstract
AB The neuropeptide neuromedin U (NmU) shows considerable structural conservation across species. Within the body, it is widely distributed and in mammals has been implicated in physiological roles, including the regulation of feeding, anxiety, pain, blood flow, and smooth muscle contraction. Human NmU-25 (hNmU-25) and other NmU analogs were recently identified as ligands for two human orphan G protein-coupled receptors, subsequently named hNmU-R1 and hNmU-R2. These receptors have approximately 50% amino acid homology, and, at least in mammalian species, NmU-R1 and NmU-R2 are expressed predominantly in the periphery and central nervous system, respectively. Here, we have characterized signaling mediated by hNmU-R1 and hNmU-R2 expressed as recombinant proteins in human embryonic kidney 293 cells, particularly to define their G protein coupling and the activation and regulation of signal transduction pathways. We show that these receptors couple to both Gαq/11 and Gαi. Activation of either receptor type causes a pertussis toxin-insensitive activation of both phospholipase C and mitogen activated-protein kinase and a pertussis toxin-sensitive inhibition of adenylyl cyclase with subnanomolar potency for each. Activation of phospholipase C is sustained, but despite this capacity for prolonged receptor activation, repetitive application of hNmU-25 does not cause repetitive intracellular Ca2+ signaling by either recombinant receptors or those expressed endogenously in isolated smooth muscle cells from rat fundus. Using several strategies, we show this to be a consequence of essentially irreversible binding of hNmU-25 to its receptors and that this is followed by ligand internalization. Despite structural differences between receptors, there were no apparent differences in their activation, coupling, or regulation.