Biased Signaling in Naturally Occurring Mutations in Human Melanocortin-3 Receptor Gene

Abstract

The melanocortin-3 receptor (MC3R) is primarily expressed in the hypothalamus and plays an important role in the regulation of energy homeostasis. Recently, some studies demonstrated that MC3R also signals through mitogen-activated protein kinases (MAPKs), especially extracellular signal-regulated kinases 1 and 2 (ERK1/2). ERK1/2 signaling is known to alter gene expression, potentially contributing to the prolonged action of melanocortins on energy homeostasis regulation. In the present study, we performed detailed functional studies on 8 novel naturally occurring MC3R mutations recently reported, and the effects of endogenous MC3R agonist, α-melanocyte stimulating hormone (MSH), on ERK1/2 signaling on all 22 naturally occurring MC3R mutations reported to date. We found that mutants D158Y and L299V were potential pathogenic causes to obesity. Four residues, F82, D158, L249 and L299, played critical roles in different aspects of MC3R function. α-MSH exhibited balanced activity in Gs-cAMP and ERK1/2 signaling pathways in 15 of the 22 mutant MC3Rs. The other 7 mutant MC3Rs were biased to either one of the signaling pathways. In summary, we provided novel data about the structure-function relationship of MC3R, identifying residues important for receptor function. We also demonstrated that some mutations exhibited biased signaling, preferentially activating one intracellular signaling pathway, adding a new layer of complexity to MC3R pharmacology.

Functions of DPLIY motif and helix 8 of human melanocortin-3 receptor

“…NDP-MSH was reported to induce ERK1/2 phosphorylation in HEK293 cells transfected with WT MC3R in a very fast and potent pattern, peaking at only 5 min with an EC 50 of 3.3 ± 1.5 nM ( Chai et al 2007 ). These data suggest these mutants were biased receptors, supporting two recent studies on biased signaling at the MC3R ( Montero-Melendez et al 2015 ; Yang et al 2015 ).…”

“…The MC4R plays an undisputed role in human obesity pathogenesis since mutations in MC4R have been characterized as the most common monogenic form of obesity in human ( Farooqi et al 2003 ; Hinney et al 2013; Tao 2009 ). However, the role of MC3R in human obesity pathogenesis is more controversial (reviewed in ( Tao 2010b )), although some MC3R mutations (such as I183N and I335S) have been recognized as possible genetic contributors for morbid obesity ( Lee et al 2007 ; Lee et al 2002 ; Mencarelli et al 2008 ; Rached et al 2004 ; Tao 2007 ; Tao and Segaloff 2004 ; Yang et al 2015 ; Yang and Tao 2012 ).…”

“…We generated 20 mutants and studied the cell surface expression, ligand binding and signaling properties of the mutant receptors. Since MC3R activation has also been reported to stimulate ERK1/2 phosphorylation ( Begriche et al 2012 ; Chai et al 2007 ) (one report suggested that the MC3R does not activate ERK1/2 ( Daniels et al 2003 )), and we and others recently reported biased signaling in the MC3R ( Huang and Tao 2014 ; Montero-Melendez et al 2015 ; Yang et al 2015 ), the ERK1/2 signaling pathway of the hMC3R was also investigated.…”

Identification and pharmacological analyses of eight naturally occurring caprine melanocortin-1 receptor mutations in three different goat breeds

“…In the mouse MC1R, a mutant receptor constitutively active in the cAMP pathway is not active in both basal and a-MSH induced ERK1/2 signaling, also representing a case of biased signaling (Benned-Jensen et al, 2011). Of note, biased signaling has been reported for MC4R and MC3R mutants (Breit et al, 2011;He and Tao, 2014;Mo and Tao, 2013;Mo et al, 2012;Yang et al, 2015), including biased constitutive signaling (Tao, 2014).…”

Polymorphisms and mutations in the melanocortin-3 receptor and their relation to human obesity

“…Certain variants, such as A260V, have decreased protein synthesis or accelerated protein degradation (Class I). Others, such as T280S, demonstrate significantly reduced cell surface expression, which expectedly results in decreased ligand binding, and nearly abolished signaling (Class II) [19, 55, 56]. Mutations such as D158Y have preserved translocation to the cell surface, but inherent defects in ligand binding lead to poor signaling (Class III) [19, 55].…”