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Modulation of MC2R and MRAP Isoform Expression in Transient and Stable Conditions Cell surface detection of Myc-MC2R using anti-c-Myc antibodies (A and C) and MRAP constructions using anti-Flag antibodies (B and D) was measured by cell surface ELISA as described in Materials and Methods. A, 293/FRT transfected with pEGFP (substracted background OD) or stable 293/FRT/Myc-MC2R cells transiently transfected with pEGFP (control), pcDNA3/MRAP, or pcDNA3/MRAP were assayed for c-Myc detection. B, Epitope-tagged MRAP constructions were expressed transiently from pcDNA5/FRT/GOI vectors in 293/FRT cells (shown) or stable 293/FRT/Myc-MC2R cells (data not shown; similar results) and tested for Flag epitope detection. C, Stable 293/FRT (control), 293/FRT/MRAP, and 293/FRT/MRAP cells were transiently transfected with pEGFP (substracted background OD) or pcDNA3/Myc-MC2R and assayed for c-Myc epitope detection. D, Stable 293/FRT (control), 293/FRT/Flag-MRAP, 293/FRT/MRAP-Flag, 293/FRT/Flag-MRAP, and 293/FRT/MRAP-Flag cells were assayed for cell surface Flag epitope detection. Results represent the mean SEM of three experiments, each performed in triplicate. *, P 0.05; **, P 0.01; and ***, P 0.001, compared with control or indicated conditions.
Source publication
The ACTH receptor [melanocortin-2 receptor (MC2R)] is the smallest known G protein-coupled receptor (GPCR). Herein, human MC2R accessory protein (MRAP) isoforms alpha and beta, cloned from a human fetal adrenal gland, were expressed with c-Myc-tagged MC2R (Myc-MC2R) in 293/Flp recombinase target site cells by homologous recombination. Although inse...
Contexts in source publication
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... trans- fected with native untagged MRAP or MRAP, ELISA measurements indicated that cell surface MC2R ex- pression increased by 1.9 0.2-fold in MRAP-trans- fected cells (P 0.01) compared with 2.8 0.2-fold in MRAP-transfected cells (P 0.001) over basal Myc- MC2R density in control cells (P 0.01; difference between MRAP transfected cells, n 4) (Fig. ...
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... the functional properties of MRAP and MRAP, 10 MRAP constructions were created, consisting of Flag and 6xHis epitope tags fused to N-and/or C termini of MRAP and MRAP (Table 2, and supplemental data 1 published as sup- plemental data on The Endocrine Society's Journals Online web site at http://mend.endojournals.org). As illustrated in Fig. 5B, in transient overexpression con- ditions, Flag-MRAP in 293/FRT cells was poorly de- tected at the cell surface in comparison with MRAP- Flag, with MRAP-Flag being significantly detected over control cells and over Flag-MRAP (P 0.001, n 3). On the other hand, Flag-MRAP and MRAP- Flag were both significantly detected at the cell sur- ...
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... being significantly detected over control cells and over Flag-MRAP (P 0.001, n 3). On the other hand, Flag-MRAP and MRAP- Flag were both significantly detected at the cell sur- face compared with control cells and compared with Flag-MRAP control (P 0.05 each). Results were similar when 6xHis-tagged MRAP isoforms were as- sayed (data not shown). Fig. 5A, cell sur- face Myc-MC2R expression was increased by 1.5-fold in 293/FRT/MRAP cells compared with MRAP cells (P 0.05). In individual MRAP isoform stable isogenic cells, the level of membrane detection of all MRAP constructions was low, nearing the limit of detection. However, the level of MRAP-Flag was higher than Flag-MRAP (P 0.05). ...
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... 0.05). In individual MRAP isoform stable isogenic cells, the level of membrane detection of all MRAP constructions was low, nearing the limit of detection. However, the level of MRAP-Flag was higher than Flag-MRAP (P 0.05). MRAP-Flag was also higher than Flag-MRAP (P 0.001) and higher than MRAP-Flag when isogenic cell lines are compared (P 0.05) (Fig. 5D). Together, these results indicate that MRAP isoforms enhance Myc-MC2R cell surface expression compared with its basal level and that MRAP is less potent than MRAP in this process. Furthermore, lower expression of proteins in MRAP isoform stable isogenic cells did not reveal the same pattern of cell surface expression for MRAP isoforms ...
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... and suitable model in comparison with tran- sient overexpression in a small percentage of cells. Therefore, to avoid artifactual misinterpretation due to the overexpression of MC2R or MRAP isoforms in transiently transfected cells, the following studies were conducted using stable bicistronic isogenic cell lines. All the data described in Fig. 5 were validated by immunofluorescence observations and ELISA mea- surements (supplemental data 2 published as supple- mental data on The Endocrine Society's Journals On- line web ...
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... both planes, MC2R appeared both in the cytoplasm and at the plasma membrane (Fig. 6, panels A, E, I, and M). Comparison of panels A and E with panels I and M reveal that expression of MC2R was more intense at the cell membrane when com- bined with MRAP expression rather than with MRAP. These latter results are consistent with the data reported in Fig. 5, A and D, and are supported by cell surface expression of the proteins quantified in ELISA experiments (Fig. 6Q). However, as shown in the merged images and magnification insets, red and green fluorescent labels were not superimposed (Fig. 6, C and G; and magnification of the merged images, Fig. 6, panels D, H, L, and P, arrows). These ...
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... and magnification insets, red and green fluorescent labels were not superimposed (Fig. 6, C and G; and magnification of the merged images, Fig. 6, panels D, H, L, and P, arrows). These immuno- fluorescence data were also supported by ELISA mea- surements. As shown in Fig. 6R, MRAP C termini were hardly present at the cell membrane; however, as in Fig. 5D, MRAP appeared more abundant than MRAP. Thus, whereas MC2R was found in high con- centration at the cell surface, MRAP isoforms were expressed at low levels and appeared in the vicinity of MC2R, rather than superimposed with ...
Citations
... The MRAP family comprises two accessory proteins that generate distinct phenotypes by regulating different melanocortin receptors in vivo. MRAP1 was originally identified as an accessory partner for maintaining proper translocation and ACTH stimulation of MC2R signaling for steroidogenesis in the adrenal gland (Metherell et al., 2005;Roy, Rached, & Gallo-Payet, 2007). MRAP2 was subsequently discovered in 2009 from cDNA panel of human tissues (Chan et al., 2009). ...
The discovery of G-protein coupled receptor (GPCR) accessory proteins has fundamentally redefined the pharmacological concept of GPCR signaling, demonstrating a more complex molecular basis for receptor specificity on the plasma membrane and impressionable downstream intracellular cascades. GPCR accessory proteins not only contribute to the proper folding and trafficking of receptors, but also exhibit selectable receptor preferences. The melanocortin receptor accessory proteins (MRAP1 and MRAP2) as well as receptor activity-modifying proteins (RAMPs) are two well-known single transmembrane partners for the regulation of the melanocortin receptors (MC1R-MC5R) and the glucagon receptor (GCGR), respectively. Especially, MRAP family participates in the pathological control of multiple endocrine disorders and RAMPs contribute to the endogenous regulation of glucose homeostasis. However, the precise mechanisms by which the MRAP and RAMP proteins regulate receptor signaling at the atomic resolution remain unknown. Recent progress made in the determination of RAMP2-bound GCGR complexes published on Cell (Krishna Kumar et al., 2023) unraveled the importance of RAMP2 for the promotion of extracellular receptor dynamics leading to cytoplasmic surface inactivation. Moreover, the new findings on Cell Research (Luo et al., 2023) of the adrenocorticotropic hormone (ACTH)-bound MC2R–Gs–MRAP1 complex disclosed the essential role of MRAP1 for MC2R activation and specificity of ligand recognition. In this article, we reviewed a series of key findings of MRAP proteins in the last decade, and the recent structural investigation of MRAP-MC2R and RAMP-GCGR functional complex and the expanded identification of new GPCR partners of MRAP proteins. In-depth understanding of GPCR modulation by single transmembrane accessory proteins will provide valuable insights for the therapeutic drug development to treat multiple GPCR associated human disorders.
... 2,3 MRAP1 was initially discovered to facilitate the trafficking of melanocortin receptor 2 (MC2R) to the plasma membrane after translation and is required for MC2R activity. [4][5][6] The N-terminus of MRAP1 was further proven to be a prerequisite for the activation of MC2R. 4,7,8 MRAP1 was reported to exist as an anti-parallel homodimer with the two copies of MRAP1 inserted into the membrane in 'N-terminus out' and 'Cterminus out' orientations, respectively, which appears to be the functional conformation of MRAP1 to bind MC2R. ...
G protein-coupled receptors (GPCRs) are regulated by various downstream proteins, of which the melanocortin receptor accessory protein 1 (MRAP1) is closely involved in the regulation of melanocortin receptor 2 (MC2R). Assisted by MRAP1, MC2R responds to adrenocorticotropic hormone (ACTH) and stimulates glucocorticoid biogenesis and cortisol secretion. MC2R activation plays an essential role in the hypothalamic-pituitary-adrenal (HPA) axis that regulates stress response, while its dysfunction causes glucocorticoid insufficiency- or cortisol excess-associated disorders. Here, we present a cryo-electron microscopy (cryo-EM) structure of the ACTH-bound MC2R–Gs–MRAP1 complex. Our structure, together with mutagenesis analysis, reveals a unique sharp kink at the extracellular region of MRAP1 and the ‘seat-belt’ effect of MRAP1 on stabilizing ACTH binding and MC2R activation. Mechanisms of ACTH recognition by MC2R and receptor activation are also demonstrated. These findings deepen our understanding of GPCR regulation by accessory proteins and provide valuable insights into the ab initio design of therapeutic agents targeting MC2R.
... MCRs have been shown to interact with small single transmembrane proteins, melanocortin-2 receptor accessory proteins (MRAPs, including MRAP1 and MRAP2) [28][29][30][31] (reviewed in [32,33]). MRAP1 was first identified as the specific chaperone for MC2R, essential for MC2R forward trafficking [28,29,33,34]. Human (h) MRAP1 mutations account for~20% of familial glucocorticoid deficiency cases [28,35]. ...
The neural melanocortin receptors (MCRs), melanocortin-3 and -4 receptors (MC3R and MC4R), have crucial roles in regulating energy homeostasis. The melanocortin-2 receptor accessory proteins (MRAPs, MRAP1 and MRAP2) have been shown to regulate neural MCRs in a species-specific manner. The potential effects of MRAP1 and MRAP2 on canine neural MCRs have not been investigated before. Herein, we cloned canine (c) MC3R and identified one canine MRAP2 splice variant, MRAP2b, with N-terminal extension of cMRAP2a. Canine MC3R showed higher maximal responses to five agonists than those of human MC3R. We further investigated the modulation of cMRAP1, cMRAP2a, and cMRAP2b, on cMC3R and cMC4R pharmacology. For the cMC3R, all MRAPs had no effect on trafficking; cMRAP1 significantly decreased Bmax whereas cMRAP2a and cMRAP2b significantly increased Bmax. Both MRAP1 and MRAP2a decreased Rmaxs in response to α-MSH and ACTH; MRAP2b only decreased α-MSH-stimulated cAMP generation. For the MC4R, MRAP1 and MRAP2a increased cell surface expression, and MRAP1 and MRAP2a increased Bmaxs. All MRAPs had increased affinities to α-MSH and ACTH. MRAP2a increased ACTH-induced cAMP levels, whereas MRAP2b decreased α-MSH- and ACTH-stimulated cAMP production. These findings may lead to a better understanding of the regulation of neural MCRs by MRAP1 and MRAP2s.
... Melanocortin-2 receptor (MC2R) accessory protein (MRAP) was initially discovered as an essential partner for MC2R by assisting in MC2R trafficking from the endoplasmic reticulum to the cell surface [112][113][114]. MRAP2, a subsequently discovered homolog of MRAP, exhibits similar functions to MRAP in adrenal differentiation and proliferation [115]. ...
As the most recent melanocortin receptor (MCR) identified, melanocortin-5 receptor (MC5R) has unique tissue expression patterns, pharmacological properties, and physiological functions. Different from the other four MCR subtypes, MC5R is widely distributed in both the central nervous system and peripheral tissues and is associated with multiple functions. MC5R in sebaceous and preputial glands regulates lipid production and sexual behavior, respectively. MC5R expressed in immune cells is involved in immunomodulation. Among the five MCRs, MC5R is the predominant subtype expressed in skeletal muscle and white adipose tissue, tissues critical for energy metabolism. Activated MC5R triggers lipid mobilization in adipocytes and glucose uptake in skeletal muscle. Therefore, MC5R is a potential target for treating patients with obesity and diabetes mellitus. Melanocortin-2 receptor accessory proteins can modulate the cell surface expression, dimerization, and pharmacology of MC5R. This minireview summarizes the molecular and pharmacological properties of MC5R and highlights the progress made on MC5R in energy metabolism. We poInt. out knowledge gaps that need to be explored in the future.
... Melanocortin-2 receptor accessory protein 1 (MRAP1), first identified as low molecular weight protein from fat tissue [28], was the first MC2R accessory protein identified, as the specific molecular chaperone for MC2R in regulating receptor expression, ligand binding, and signaling [29][30][31][32]. MRAP1 mutations account for ~20% of familial glucocorticoid deficiency cases [29,33]. ...
... MRAP1 mutations account for ~20% of familial glucocorticoid deficiency cases [29,33]. There are two alternatively spliced isoforms of human (h) MRAP1, hMRAP1a and hMRAP1b, with similar effects on MC2R trafficking and signaling [29,30]. MRAP1a and MRAP1b are widely expressed, but their distribution patterns are distinct [29,34]. ...
The neural melanocortin receptors (MCRs), melanocortin-3 and -4 receptors (MC3R and MC4R), play essential non-redundant roles in the regulation of energy homeostasis. Interaction of neural MCRs and melanocortin-2 receptor accessory proteins (MRAPs, MRAP1 and MRAP2) is suggested to play pivotal roles in MC3R and MC4R signaling. In the present study, we identified two new human (h) MRAP2 splice variants, MRAP2b (465 bp open reading frame) and MRAP2c (381 bp open reading frame). Human MRAP2s are different in C-termini. We investigated the effects of five isoforms of MRAPs, hMRAP1a, hMRAP1b, hMRAP2a, hMRAP2b, and hMRAP2c, on MC3R and MC4R pharmacology. At the hMC3R, hMRAP1a and hMRAP2c increased and hMRAP1b decreased the cell surface expression. hMRAP1a increased affinity to ACTH. Four MRAPs (hMRAP1a, hMRAP1b, hMRAP2a, and hMRAP2c) decreased the maximal responses in response to α-MSH and ACTH. For hMC4R, hMRAP1a, hMRAP2a, and hMRAP2c increased the cell surface expression of hMC4R. Human MRAP1b significantly increased affinity to ACTH while MRAP2a decreased affinity to ACTH. Human MRAP1a increased ACTH potency. MRAPs also affected hMC4R basal activities, with hMRAP1s increasing and hMRAP2s decreasing the basal activities. In summary, the newly identified splicing variants, hMRAP2b and hMRAP2c, could regulate MC3R and MC4R pharmacology. The two MRAP1s and three MRAP2s had differential effects on MC3R and MC4R trafficking, binding, and signaling. These findings led to a better understanding of the regulation of neural MCRs by MRAP1s and MRAP2s.
... Melanocortin-2 receptor accessory protein 2 (MRAP2), together with MRAP1, are single-transmembrane proteins and involved in regulating protein expression, binding, and signaling of MCRs (Asai et al., 2013;Cerdá-Reverter et al., 2013;Chan et al., 2009;Sebag et al., 2013). MRAP1 primarily chaperones MC2R to the plasma membrane and is also involved in both ACTH binding and ACTH-induced cAMP generation (Roy et al., 2007;Webb and Clark, 2010). MRAP1 mutations are responsible for about 20 % of familial glucocorticoid deficiency (Metherell et al., 2005). ...
The melanocortin-5 receptor (MC5R) has been implicated in the regulation of exocrine gland secretion, immune regulation, and muscle fatty acid oxidation in mammals. Melanocortin-2 receptor accessory protein 2 (MRAP2) can modulate trafficking, ligand binding, and signaling of melanocortin receptors. To explore potential interaction between ricefield eel (Monopterus albus) MC5R and MRAP2s (maMC5R, maMRAP2X1, and maMRAP2X2), herein we studied the pharmacological characteristics of maMC5R and its modulation by maMRAP2s expressed in the human embryonic kidney cells. Three agonists, α-melanocyte-stimulating hormone (α-MSH), ACTH (1-24), and [Nle⁴, D-Phe⁷]-α-MSH, could bind to maMC5R and induce intracellular cAMP production dose-dependently. Compared with human MC5R (hMC5R), maMC5R displayed decreased maximal binding but higher binding affinity to α-MSH or ACTH (1-24). When stimulated with α-MSH or ACTH (1-24), maMC5R showed significantly lower EC50 and maximal response than hMC5R. Two maMRAP2s had no effect on cell surface expression of maMC5R, whereas they significantly increased maximal binding. Only maMRAP2X2 significantly decreased the binding affinity of ACTH (1-24). Both maMRAP2X1 and maMRAP2X2 significantly reduced maMC5R efficacy but did not affect ligand sensitivity. The availability of maMC5R pharmacological characteristics and modulation by maMRAP2s will assist the investigation of its roles in regulating diverse physiological processes in ricefield eel.
... Examples of the physiological processes regulated by MCRs include inflammation and immunoregulation in MC1Rexpressing neutrophils, monocytes, macrophages, dendritic cells, and B lymphocytes; corticosteroid production in MC2R-expressing adrenocortical cells; energy homeostasis and control of inflammation in MC3R-expressing monocytes, B lymphocytes, and macrophages; neuroprotection in MC4Rexpressing cells within the brain and spinal cord; and immunomodulatory functions in MC5R-expressing B and T lymphocytes, mast cells, and macrophages in peripheral tissues [5,[11][12][13]. MC2R is unique among MCRs in that it binds only to certain ACTH peptides and requires accessory proteins that are essential for binding and receptor trafficking from the endoplasmic reticulum to the cell surface [2,[13][14][15][16][17]. As such, a-MSH (ACTH 1-13 ) does not activate MC2R, and animal studies have confirmed that it is not capable of stimulating corticosteroid secretion [18,19]. ...
... These data are supported by prior studies that observed the binding and functional activity of various MCR agonists [1][2][3][4][5][6][7][8][9][10][11][12][13] MC1R > MC4R > MC3R > MC5R ACTH [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] MC1R > MC3R > MC4R > MC5R ACTH MC1R > MC4R > MC3R > MC5R N25D-ACTH MC1R > MC3R > MC4R > MC5R hACTH MC1R > MC4R > MC3R > MC5R pACTH MC1R > MC3R > MC4R > MC5R ACTH: adrenocorticotropic hormone; h: human; MCR: melanocortin receptor; N25D: N-25 deamidated; p: porcine. [ [36][37][38][39]. ...
Purpose:
To compare the binding and agonistic activity of Acthar® Gel and synthetic melanocortin receptor (MCR) agonists and examine how the activity of select agonists affects the in vivo production of corticosterone.
Materials and methods:
In vitro binding was determined using concentration-dependent displacement of the ligand [125I]Nle4, D-Phe7-α-melanocyte-stimulating hormone (α-MSH) on cells expressing MC1R, MC3R, MC4R, or MC5R. Functional activity was determined using a time-resolved fluorescence cyclic adenosine monophosphate (cAMP) assay in cells expressing MC1R, MC2R, MC3R, MC4R, or MC5R. In vivo corticosterone analyses were performed by measuring plasma corticosterone levels in Sprague Dawley rats.
Results:
Acthar Gel and synthetic MCR agonists exhibited the highest binding at MC1R, lowest binding at MC5R, and moderate binding at MC3R and MC4R. Acthar Gel stimulated the production of cAMP in all 5 MCR-expressing cell lines, with MC2R displaying the lowest level of full agonist activity, 3-, 6.6-, and 10-fold lower than MC1R, MC3R, and MC4R, respectively. Acthar Gel was a partial agonist at MC5R. The synthetic MCR agonists induced full activity at all 5 MCRs, with the exception of α-MSH having no activity at MC2R. Acthar Gel treatment had less of an impact on in vivo production of corticosterone compared with synthetic ACTH1-24 depot.
Conclusions:
Acthar Gel bound to and activated each MCR tested in this study, with partial agonist activity at MC5R and the lowest level of full agonist activity at MC2R, which distinguished it from synthetic MCR agonists. The minimal activity of Acthar Gel at MC2R corresponded to lower endogenous corticosteroid production.
... There is also no data on the affinities of the MRAP dimer for the receptor. Roy et al provided immunofluorescent imaging data to support the existence of non-complexed MC2R and MRAP in transfected cells (30). If there is free MC2R on the cell surface this would form a reservoir of "spare" receptor that was incapable of responding to ACTH. ...
Glucocorticoid production in mammals is principally regulated by the action of the pituitary hormone adrenocorticotropin (ACTH) acting on its cognate membrane receptor on the zona fasciculata cells of the adrenal cortex. The receptor for ACTH consists of two essential components, a small seven transmembrane domain G protein-coupled receptor of the melanocortin receptor subgroup known as the melanocortin 2 receptor (MC2R) and a small single transmembrane domain protein that adopts a antiparallel homodimeric form and which is known as the melanocortin 2 receptor accessory protein (MRAP). MRAP is essential for the trafficking of the MC2R to the cell surface as well as being required for receptor responsiveness to ACTH at physiological concentrations—probably by facilitating ACTH binding, but possibly also by supporting G protein interaction with the MC2R. A number of studies have shown that ACTH stimulates the expression of functional receptor at the cell surface and the transcription of both MC2R and MRAP mRNA. However, the time course of these transcriptional effects differs such that MRAP is expressed relatively rapidly whereas MC2R transcription responds much more slowly. Furthermore, recent data suggests that MRAP protein is turned over with a short half-life whereas MC2R has a significantly longer half-life. These findings imply that these two ACTH receptor proteins have distinct trajectories and that it is likely that MRAP-independent MC2R is present at the cell surface. In such a situation newly transcribed and translated MRAP could enable the rapid recruitment of functional receptor at the plasma membrane without the need for new MC2R translation. This may be advantageous in circumstances of significant stress in that the potentially complex and perhaps inefficient process of de novo MC2R translation, folding, post-translational modification and trafficking can be avoided.
... Human MRAP has two isoforms produced by alternative splicing, MRAP-α (19 kDa) and MRAP-β (11.5 kDa), which differ in the C-terminus. The functional difference between the two isoforms is unclear although differences have been reported in ACTH binding capacity and cAMP generation have been reported (35). Interestingly, MRAP can form unique antiparallel transmembrane homodimers, which together with its paralogue MRAP2 are as yet the only group of proteins known to do so in eukaryotic cells. ...
The melanocortin-2-receptor (MC2R), also known as the ACTH receptor, is a critical component of the hypothalamic-pituitary-adrenal axis. The importance of MC2R in adrenal physiology is exemplified by the condition familial glucocorticoid deficiency (FGD), a potentially fatal disease characterised by isolated cortisol deficiency. MC2R mutations cause ~25% of cases. The discovery of a MC2R accessory protein MRAP, mutations of which account for ~20% of FGD, has provided insight into MC2R trafficking and signalling. MRAP is a single transmembrane domain accessory protein highly expressed in the adrenal gland and essential for MC2R expression and function. Mouse models helped elucidate the action of ACTH. The Mc2r knockout (Mc2r−/−) mice was the first mouse model developed to have adrenal insufficiency with deficiencies in glucocorticoid, mineralocorticoid and catecholamines. We recently reported the generation of the Mrap-/- mice which better mimics the human FGD phenotype with isolated glucocorticoid deficiency alone. The adrenal glands of adult Mrap−/− mice were grossly dysmorphic with a thickened capsule, deranged zonation and deranged WNT4/beta-catenin and sonic hedgehog (SHH) pathway signalling. Collectively, these mouse models of FGD highlight the importance of ACTH and MRAP in adrenal progenitor cell regulation, cortex maintenance and zonation.
... The functional expression of MC2R requires an adrenal-specific factor named MC2R accessory protein (MRAP) [10]. This single-transmembrane domain protein assists MC2R trafficking to the plasma membrane but is also involved in both ACTH binding [11,12] and ACTH-induced cAMP production [11]. Specific details of the structure-activity relationship between receptor and accessory protein are unknown [13,14] but it has been suggested that MC2R may require MRAP interaction to form a high affinity-binding pocket to ACTH or may assist MC2R to bind to the Gs subunit of the heterodimeric G protein complex [15]. ...
... The functional expression of MC2R requires an adrenal-specific factor named MC2R accessory protein (MRAP) [10]. This single-transmembrane domain protein assists MC2R trafficking to the plasma membrane but is also involved in both ACTH binding [11,12] and ACTH-induced cAMP production [11]. Specific details of the structure-activity relationship between receptor and accessory protein are unknown [13,14] but it has been suggested that MC2R may require MRAP interaction to form a high affinity-binding pocket to ACTH or may assist MC2R to bind to the Gs subunit of the heterodimeric G protein complex [15]. ...
Melanocortin 4 receptor (MC4R), a canonical melanocyte-stimulating hormone receptor, is the main responsible for monogenic obesity in humans. Previous studies in fish and avian species showed that MC4R becomes an adrenocorticotropic hormone (ACTH) receptor after interaction with the melanocortin 2 receptor accessory protein 2 (MRAP2). We show that human MC4R behaves in a similar way through its interaction with MRAP2. This evolutionary conservation of MRAP2-induced ligand selectivity supports a physiological role for the interaction with MC4R. Both proteins are co-expressed in the same hypothalamic neurons, providing an anatomical substrate and molecular mechanism for the central therapeutic actions of ACTH in the treatment of infantile spasms. These neurons may link the effects of stress on the energy balance independently of glucocorticoid secretion. The complex MC4R-MRAP2 throws new light on the action of ACTH and, by extension, on the relay of stress-related information to additional biological systems.
