Complete List of Publications

Key Publications

MRAP2 regulates ghrelin receptor signaling and hunger sensing

Srisai D, Yin TC, Lee AA, Rouault AAJ, Pearson NA, Grobe JL, Sebag JA.

Nat Commun. 2017 Sep 28;8(1):713.

Ghrelin is the only known circulating orexigenic hormone. It is primarily secreted by the stomach and acts at its receptor, the growth hormone secretagogue receptor 1a (GHSR1a), in the hypothalamus to signal hunger and promote food intake. The melanocortin receptor accessory protein 2 (MRAP2) was previously shown to regulate energy homeostasis through the modulation of the activity of the melanocortin-4 receptor and prokineticin receptors. In this study we identify MRAP2 as a partner of ghrelin-GHSR1a signaling. We show that MRAP2 interacts with GHSR1a and potentiates ghrelin-stimulated signaling both in vitro and in vivo. We demonstrate that in the absence of MRAP2, fasting fails to activate agouti-related protein neurons. In addition, we show that the orexigenic effect of ghrelin is lost in mice lacking MRAP2. Our results suggest that MRAP2 is an important modulator of the energy homeostasis machinery that operates through the regulation of multiple GPCRs throughout the hypothalamus.Melanocortin receptor accessory protein 2 (MRAP2) is an adaptor protein that contributes to melanocortin-4 receptor and prokineticin receptor 1 signalling. Here the authors show that MRAP2 also regulates ghrelin receptor signalling in the hypothalamus and starvation sensing in mice.

Regions of MRAP2 required for the inhibition of orexin and prokineticin receptor signaling.

Rouault AAJ, Lee AA, Sebag JA.

Biochim Biophys Acta. 2017 Sep 19. 

The Melanocortin Receptor Accessory Protein 2 (MRAP2) regulates the activity of several GPCRs involved in the control of food intake and energy expenditure. While MRAP2 was originally thought to exclusively interact with melanocortin receptors we have recently shown that it interacts with and inhibits the trafficking and signaling of the prokineticin receptor 1 (PKR1). In this study we demonstrate a new role of MRAP2 in the regulation of the orexin receptor 1 (OX1R) and identify the specific regions of MRAP2 required for the regulation of OX1R and PKR1. Importantly, like MC4R and PKRs, OX1R is predominately expressed in the brain where it regulates food intake. By demonstrating that MRAP2 modulates the activity of OX1R we further establish the critical role of MRAP2 in the control of energy homeostasis.

Melanocortin Receptor Accessory Proteins (MRAPs): Functions in the Melanocortin System and Beyond.

Alix A.J. Rouault, Dinesh K. Srinivasan, Terry C. Yin, Abigail A. Lee, Julien A. Sebag

Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease, May 9, 2017

G-protein coupled receptors (GPCRs) are regulated by numerous proteins including kinases, G-proteins, β-arrestins and accessory proteins. Several families of GPCR accessory proteins like Receptor Activity Modifying Proteins, Receptor Transporting Proteins and Melanocortin Receptor Accessory Proteins (MRAPs) have been identified as regulator of receptor trafficking, signaling and ligand specificity. The MRAP family contains two members, MRAP1 and MRAP2, responsible for the formation of a functional ACTH receptor and for the regulation of energy homeostasis respectively. Like all known GPCR accessory proteins, MRAPs are single transmembrane proteins, however, they form a unique structure since they assemble as an anti-parallel homodimer. Moreover, the accepted idea that MRAPs are specific regulators of melanocortin receptors was recently challenged by the discovery that MRAP2 inhibits the activity of prokineticin receptors. Recent studies are starting to explain the role of the unusual structure of MRAPs and to illustrate the importance of MRAP2 for the maintenance of both energy and glucose homeostasis.

The Melanocortin Receptor Accessory Protein 2 promotes food intake through inhibition of the Prokineticin Receptor-1.

Chaly AL, Srisai D1, Gardner EE, Sebag JA.

eLife, February 1, 2016

The Melanocortin Receptor Accessory Protein 2 (MRAP2) is an important regulator of energy homeostasis and its loss causes severe obesity in rodents. MRAP2 mediates its action in part through the potentiation of the MC4R, however, it is clear that MRAP2 is expressed in tissues that do not express MC4R, and that the deletion of MRAP2 does not recapitulate the phenotype of Mc4r KO mice. Consequently, we hypothesized that other GPCRs involved in the control of energy homeostasis are likely to be regulated by MRAP2. In this study we identified PKR1 as the first non-melanocortin GPCR to be regulated by MRAP2. We show that MRAP2 significantly and specifically inhibits PKR1 signaling. We also demonstrate that PKR1 and MRAP2 co-localize in neurons and that Mrap2 KO mice are hypersensitive to PKR1 stimulation. This study not only identifies new partners of MRAP2 but also a new pathway through which MRAP2 regulates energy homeostasis. ​

G-protein-independent coupling of MC4R to Kir7.1 in hypothalamic neurons.

Ghamari-Langroudi M, Digby GJ, Sebag JA, Millhauser GL, Palomino R, Matthews R, Gillyard T, Panaro BL, Tough IR, Cox HM, Denton JS, Cone RD.

Nature, Apr 2, 2015

The regulated release of anorexigenic α-melanocyte stimulating hormone (α-MSH) and orexigenic Agouti-related protein (AgRP) from discrete hypothalamic arcuate neurons onto common target sites in the central nervous system has a fundamental role in the regulation of energy homeostasis. Both peptides bind with high affinity to the melanocortin-4 receptor (MC4R); existing data show that α-MSH is an agonist that couples the receptor to the Gαs signalling pathway, while AgRP binds competitively to block α-MSH binding and blocks the constitutive activity mediated by the ligand-mimetic amino-terminal domain of the receptor. Here we show that, in mice, regulation of firing activity of neurons from the paraventricular nucleus of the hypothalamus (PVN) by α-MSH and AgRP can be mediated independently of Gαs signalling by ligand-induced coupling of MC4R to closure of inwardly rectifying potassium channel, Kir7.1. Furthermore, AgRP is a biased agonist that hyperpolarizes neurons by binding to MC4R and opening Kir7.1, independently of its inhibition of α-MSH binding. Consequently, Kir7.1 signalling appears to be central to melanocortin-mediated regulation of energy homeostasis within the PVN. Coupling of MC4R to Kir7.1 may explain unusual aspects of the control of energy homeostasis by melanocortin signalling, including the gene dosage effect of MC4R and the sustained effects of AgRP on food intake.

Developmental control of the melanocortin-4 receptor by MRAP2 proteins in zebrafish.

Sebag JA, Zhang C, Hinkle PM, Bradshaw AM, Cone RD.

Science, July 19, 2013

The melanocortin-4 receptor (MC4R) is essential for control of energy homeostasis in vertebrates. MC4R interacts with melanocortin receptor accessory protein 2 (MRAP2) in vitro, but its functions in vivo are unknown. We found that MRAP2a, a larval form, stimulates growth of zebrafish by specifically blocking the action of MC4R. In cell culture, this protein binds MC4R and reduces the ability of the receptor to bind its ligand, α-melanocyte-stimulating hormone (α-MSH). A paralog, MRAP2b, expressed later in development, also binds MC4R but increases ligand sensitivity. Thus, MRAP2 proteins allow for developmental control of MC4R activity, with MRAP2a blocking its function and stimulating growth during larval development, whereas MRAP2b enhances responsiveness to α-MSH once the zebrafish begins feeding, thus increasing the capacity for regulated feeding and growth.

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