Constitutive activity of the melanocortin-4 receptor is maintained by its N-terminal domain and plays a role in energy homeostasis in humans.
The melanocortin-4 receptor (MC4R), a centrally expressed G protein-coupled receptor (GPCR), is essential for the maintenance of long-term energy balance in humans. Mutations in MC4R are the most common genetic cause of obesity. Since activation of this receptor leads to a decrease in food intake, MC4R is also a major therapeutic target for the treatment of obesity. Control of MC4R activity in vivo is modulated by the opposing effects of the anorexigenic agonist alpha-melanocyte-stimulating hormone (alpha-MSH) and the orexigenic antagonist agouti-related protein (AGRP). In addition, experiments in vitro have demonstrated that the human MC4R has an intrinsic constitutive activity on which AGRP also acts as an inverse agonist. The physiological role of this constitutive activity in the control of energy balance as well as the domain of the protein implicated in its maintenance are unknown. By systematically studying functional defects in naturally occurring MC4R mutations from obese patients, we defined a cluster of N-terminal mutations that selectively impair the constitutive activity of the receptor. Further characterization of this domain demonstrated that it functions as a tethered intramolecular ligand that maintains the constitutive activity of MC4R and may provide novel avenues for the design of drugs targeting this receptor. Our results also suggest that the tonic satiety signal provided by the constitutive activity of MC4R may be required for maintaining long-term energy homeostasis in humans.
Gladstone Institute of Cardiovascular Disease, UCSF, San Francisco, California 94143-0540, USA.
Supriya
S
Srinivasan
Cecile
C
Lubrano-Berthelier
Cedric
C
Govaerts
Franck
F
Picard
Pamela
P
Santiago
Bruce R
BR
Conklin
Christian
C
Vaisse
D054369:Agouti-Related Protein; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D015195:Drug Design; D004435:Eating; D004734:Energy Metabolism; D006706:Homeostasis; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D008024:Ligands; D051379:Mice; D008969:Molecular Sequence Data; D009765:Obesity / Q000235:genetics / Q000378:metabolism; D017354:Point Mutation; D017433:Protein Structure, Secondary; D011506:Proteins / Q000378:metabolism; D044105:Receptor, Melanocortin, Type 4 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015290:Second Messenger Systems / Q000502:physiology; D015533:Transcriptional Activation; D000521:alpha-MSH / Q000378:metabolism
C515198:AGRP protein, human; D054369:Agouti-Related Protein; C515199:Agrp protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D008024:Ligands; D011506:Proteins; D044105:Receptor, Melanocortin, Type 4; D000521:alpha-MSH; D000242:Cyclic AMP