Pharmacoperones as Novel Therapeutics for Diverse Protein Conformational Diseases.

After synthesis, proteins are folded into their native conformations aided by molecular chaperones. Dysfunction in folding caused by genetic mutations in numerous genes causes protein conformational diseases. Membrane proteins are more prone to misfolding due to their more intricate folding than soluble proteins. Misfolded proteins are detected by the cellular quality control systems, especially in the endoplasmic reticulum, and proteins may be retained there for eventual degradation by the ubiquitin-proteasome system or through autophagy. Some misfolded proteins aggregate, leading to pathologies in numerous neurological diseases. In vitro, modulating mutant protein folding by altering molecular chaperone expression can ameliorate some misfolding. Some small molecules known as chemical chaperones also correct mutant protein misfolding in vitro and in vivo. However, due to their lack of specificity, their potential as therapeutics is limited. Another class of compounds, known as pharmacological chaperones (pharmacoperones), binds with high specificity to misfolded proteins, either as enzyme substrates or receptor ligands, leading to decreased folding energy barriers and correction of the misfolding. Because many of the misfolded proteins are misrouted but do not have defects in function per se, pharmacoperones have promising potential in advancing to the clinic as therapeutics, since correcting routing may ameliorate the underlying mechanism of disease. This review will comprehensively summarize this exciting area of research, surveying the literature from in vitro studies in cell lines to transgenic animal models and clinical trials in several protein misfolding diseases.

Pharmacology of orange-spotted grouper (Epinephelus coioides) melanocortin-5 receptor and its modulation by Mrap2.

The mammalian melanocortin-5 receptors (MC5Rs) are involved in various functions, including exocrine gland secretion, glucose uptake, adipocyte lipolysis, and immunity. However, the physiological role of fish Mc5r is rarely studied. Melanocortin-2 receptor accessory protein 2 (MRAP2) modulates pharmacological properties of melanocortin receptors. Herein, to lay the foundation for future physiological studies, we cloned the orange-spotted grouper (Epinephelus coioides) mc5r, with a 1008 bp open reading frame and a predicted protein of 334 amino acids. Grouper mc5r had abundant expression in the brain, skin, and kidney. Four ligands could bind to grouper Mc5r and dose-dependently increase intracellular cAMP levels. Grouper Mrap2 did not affect binding affinity or potency of Mc5r; however, grouper Mrap2 decreased cell surface expression and maximal binding of Mc5r. Mrap2 also significantly decreased the maximal response to a superpotent agonist but not the endogenous agonist. This study provided new data on fish Mc5r pharmacology and its regulation by Mrap2.

Melanocortin-5 Receptor: Pharmacology and Its Regulation of Energy Metabolism.

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.

Regulation of melanocortin-5 receptor pharmacology by two isoforms of MRAP2 in ricefield eel (Monopterus albus).

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.

Regulation of melanocortin-1 receptor pharmacology by melanocortin receptor accessory protein 2 in orange-spotted grouper (Epinephelus coioides).

Melanocortin-1 receptor (MC1R) has important roles in regulating pigmentation and inflammation. Melanocortin receptor accessory protein 2 (MRAP2) modulates trafficking, ligand binding, and signaling of mammalian melanocortin receptors. However, the effect of MRAP2 on fish MC1R has not been extensively studied. Herein, we cloned the orange-spotted grouper (Epinephelus coioides) mc1r, which had a 972 bp open reading frame encoding a putative protein of 323 amino acids. Grouper mc1r was mainly expressed in the brain, skin, testis, spleen, head kidney, and kidney. EcoMC1R showed high constitutive activities in both Gs-cAMP and ERK1/2 pathways, which could be differentially modulated by grouper MRAP2 (EcoMRAP2). Three agonists, including α-melanocyte-stimulating hormone (MSH), ß-MSH, and ACTH, could bind to EcoMC1R and dose-dependently increase intracellular cAMP production. EcoMRAP2 had no effect on the IC50 in binding assay or EC50 in cAMP assay; however, it dose-dependently decreased the cell surface expression and maximal response to the three agonists. EcoMRAP2 increased basal ERK1/2 activation but did not alter α-MSH-stimulated ERK1/2 activation. This study extends the knowledge base of fish MC1R pharmacology and its regulation by MRAP2.

Alanine Scanning Mutagenesis of the DRYxxI Motif and Intracellular Loop 2 of Human Melanocortin-4 Receptor.

The melanocortin-4 receptor (MC4R) is a member of the G-protein-coupled receptor (GPCR) superfamily, which has been extensively studied in obesity pathogenesis due to its critical role in regulating energy homeostasis. Both the Gs-cAMP and ERK1/2 cascades are known as important intracellular signaling pathways initiated by the MC4R. The DRYxxI motif at the end of transmembrane domain 3 and the intracellular loop 2 (ICL2) are thought to be crucial for receptor function in several GPCRs. To study the functions of this domain in MC4R, we performed alanine-scanning mutagenesis on seventeen residues. We showed that one residue was critical for receptor cell surface expression. Eight residues were important for ligand binding. Mutations of three residues impaired Gs-cAMP signaling without changing the binding properties. Investigation on constitutive activities of all the mutants in the cAMP pathway revealed that six residues were involved in constraining the receptor in inactive states and five residues were important for receptor activation in the absence of an agonist. In addition, mutations of four residues impaired the ligand-stimulated ERK1/2 signaling pathway without affecting the binding properties. We also showed that some mutants were biased to the Gs-cAMP or ERK1/2 signaling pathway. In summary, we demonstrated that the DRYxxI motif and ICL2 were important for MC4R function.

Structural Complexity and Plasticity of Signaling Regulation at the Melanocortin-4 Receptor.

The melanocortin-4 receptor (MC4R) is a class A G protein-coupled receptor (GPCR), essential for regulation of appetite and metabolism. Pathogenic inactivating MC4R mutations are the most frequent cause of monogenic obesity, a growing medical and socioeconomic problem worldwide. The MC4R mediates either ligand-independent or ligand-dependent signaling. Agonists such as α-melanocyte-stimulating hormone (α-MSH) induce anorexigenic effects, in contrast to the endogenous inverse agonist agouti-related peptide (AgRP), which causes orexigenic effects by suppressing high basal signaling activity. Agonist action triggers the binding of different subtypes of G proteins and arrestins, leading to concomitant induction of diverse intracellular signaling cascades. An increasing number of experimental studies have unraveled molecular properties and mechanisms of MC4R signal transduction related to physiological and pathophysiological aspects. In addition, the MC4R crystal structure was recently determined at 2.75 Å resolution in an inactive state bound with a peptide antagonist. Underpinned by structural homology models of MC4R complexes simulating a presumably active-state conformation compared to the structure of the inactive state, we here briefly summarize the current understanding and key players involved in the MC4R switching process between different activity states. Finally, these perspectives highlight the complexity and plasticity in MC4R signaling regulation and identify gaps in our current knowledge.

PPAR-δ Activation Ameliorates Diabetes-Induced Cognitive Dysfunction by Modulating Integrin-linked Kinase and AMPA Receptor Function.

An estimated 9% of the American population experiences type II diabetes mellitus (T2DM) due to diet or genetic predisposition. Recent reports indicate that patients with T2DM are at increased risk for cognitive dysfunctions, as observed in conditions like Alzheimer's disease (AD). In addition, AD is the leading cause of dementia, highlighting the urgency of developing novel therapeutic targets for T2DM-induced cognitive deficits. The peroxisome proliferator activated receptor-δ (PPAR-δ) is highly expressed in the brain and has been shown to play an important role in spatial memory and hippocampal neurogenesis. However, the effect of PPAR-δ agonists on T2DM-induced cognitive impairment has not been explored. In this study, the effects of GW0742 (a selective PPAR-δ agonist) on hippocampal synaptic transmission, plasticity, and spatial memory were investigated in the db/db mouse model of T2DM. Oral administration of GW0742 for 2 weeks significantly improved hippocampal long-term potentiation. In addition, GW0742 effectively prevented deficits in hippocampal dependent spatial memory in db/db mice. PPAR-δ-mediated improvements in synaptic plasticity and behavior were accompanied by a significant recovery in hippocampal α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor-mediated synaptic transmission. Our findings suggest that activation of PPAR-δ might ameliorate T2DM-induced impairments in hippocampal synaptic plasticity and memory.

Orange-spotted grouper melanocortin-4 receptor: Modulation of signaling by MRAP2.

Melanocortin-4 receptor (MC4R) and melanocortin receptor accessory protein 2 (MRAP2) play important roles in the melanocortin system, and interaction of MC4R and MRAP2 is suggested to play pivotal role in energy balance of vertebrates. Orange-spotted grouper (Epinephelus coioides) is a widely cultured marine fish with high economic value in Asia. To explore potential interaction between grouper MC4R and MRAP2, herein we cloned grouper mc4r and mrap2. Grouper mc4r consisted of a 981 bp ORF encoding a putative protein of 327 amino acids, while the grouper mrap2 consisted of a 696 bp ORF encoding a putative protein of 232 amino acids. Sequence and phylogenetic analysis revealed that the grouper MC4R and MRAP2 were highly homologous at amino acid levels to several teleost MC4Rs and MRAP2s, respectively. qRT-PCR results showed that both mc4r and mrap2 were expressed primarily in the central nervous system. In the periphery, these genes were expressed more widely in male fish. The cloned grouper MC4R was functional, exhibiting high constitutive activity in cAMP pathway, capable of binding to three peptide agonists and increasing intracellular cAMP production dose-dependently. MRAP2 significantly decreased basal and agonist-stimulated cAMP signaling. MRAP2 also increased basal ERK1/2 activation but decreased ligand-induced stimulation when expressed at high levels. These data will facilitate future investigation of these molecules in regulating diverse physiological processes in orange-spotted grouper.

Characterization of channel catfish (Ictalurus punctatus) melanocortin-3 receptor reveals a potential network in regulation of energy homeostasis.

The melanocortin-3 receptor (MC3R) is known to be involved in regulation of energy homeostasis, regulating feed efficiency and nutrient partitioning in mammals. Its physiological roles in non-mammalian vertebrates, especially economically important aquaculture species, are not well understood. Channel catfish (Ictalurus punctatus) is the main freshwater aquaculture species in North America. In this study, we characterized the channel catfish MC3R. The mc3r of channel catfish encoded a putative protein (ipMC3R) of 367 amino acids. We transfected HEK293T cells with ipMC3R plasmid for functional studies. Five agonists, including adrenocorticotropin, α-melanocyte stimulating hormone (α-MSH), ß-MSH, [Nle4, D-Phe7]-α-MSH, and D-Trp8-γ-MSH, were used in the pharmacological studies. Our results showed that ipMC3R bound ß-MSH with higher affinity and D-Trp8-γ-MSH with lower affinity compared with human MC3R. All agonists could stimulate ipMC3R and increase intracellular cAMP production with sub-nanomolar potencies. The extracellular signal-regulated kinases 1 and 2 (ERK1/2) activation could also be triggered by ipMC3R. The ipMC3R exhibited constitutive activities in both cAMP and ERK1/2 pathways, and Agouti-related protein served as an inverse agonist at ipMC3R, potently inhibiting the high basal cAMP level. Moreover, we showed that melanocortin receptor accessory protein 2 (MRAP2) preferentially modulated ipMC3R in cAMP production rather than ERK1/2 activation. Our study will assist further investigation of the physiological roles of the ipMC3R, especially in energy homeostasis, in channel catfish.

Pharmacology of the giant panda (Ailuropoda melanoleuca) melanocortin-3 receptor.

The melanocortin-3 receptor (MC3R) is a member of the G protein-coupled receptor superfamily that plays a critical role in controlling energy balance and metabolism. Although pharmacological characterization of MC3R has been reported previously in several other species, there is no report on the MC3R from giant panda (Ailuropoda melanoleuca). This ancient species is known as a 'living fossil' and is among the most endangered animals in the world. Giant panda survive on a specialized diet of bamboo despite possessing a typical carnivorous digestive system. We report herein the molecular cloning and pharmacological characterization of amMC3R. Homology and phylogenetic analysis showed that amMC3R was highly homologous (>85%) to several other mammalian MC3Rs. Using human MC3R (hMC3R) as a control, the binding of five agonists, [Nle4, D-Phe7]-α-melanocyte stimulating hormone (NDP-MSH), α-, ß-, γ-, and D-Trp8-γ-MSH, was investigated, as well as Gs-cAMP and pERK1/2 signaling. The results showed that amMC3R bound NDP- and D-Trp8-γ-MSH with the highest affinity, followed by α-, ß-, and γ-MSH, with the same rank order as hMC3R. When stimulated with agonists, amMC3R displayed increased intracellular cAMP and activation of pERK1/2. These data suggest that the cloned amMC3R was a functional receptor. The availability of amMC3R and knowledge of its pharmacological functions will assist further investigation of its role in controlling energy balance and metabolism.

Expression of estrogen receptors in female rainbow trout (Oncorhynchus mykiss) during first ovarian development and under dense rearing condition.

To study the expression of four estrogen receptor genes (erα1, erα2, erß1, erß2) of female rainbow trout (Oncorhynchus mykiss) during first ovarian development, trouts were sampled from different ovarian stages. Serum E2 (estradiol) was measured by ELISA and estrogen receptors mRNA expression were examined by qRT-PCR. Our results showed a close association between increased erα1 and vitellogenin mRNA expression during ovarian maturation and increased erα2 mRNA expression in mature ovarian stages. Correlation analysis revealed that a negative relationship between serum E2 and ovarian erß1 (or hepatic erß2), but ovarian erß2 mRNA expression was relatively unchanged during first ovarian development. Trout were also reared in different densities as stocking density 1, 2 and 3 (SD1, 4.6-31.1 kg/m3; SD2, 6.6-40.6 kg/m3; SD3, 8.6-49.3 kg/m3) to elucidate effects of high density on estrogen receptor expression. Histology observation showed ovarian development of trout in higher densities were retard with a relatively early stage and fewer vitellogenin accumulation. Trout in high densities showed significantly decreased serum E2, erα mRNA expression and increasing trends of erß mRNA expression. A noticeable increase of ovarian erß2 mRNA expression was seen in trout when density is approaching to 50 kg/m3. In conclusion, we may hypothesize that increased erß mRNA expression triggered by high density result in decreased erα mRNA expression and vitellogenesis. As a result, ovarian development in higher densities was retard.

Biased signaling initiated by agouti-related peptide through human melanocortin-3 and -4 receptors.

The neural melanocortin receptors (MCRs), melanocortin-3 and -4 receptors (MC3R and MC4R), have been increasingly recognized as important regulators of energy homeostasis. The orexigenic agouti-related peptide (AgRP), initially identified as an endogenous antagonist for both neural MCRs, has been suggested to be a biased agonist of MC4R independent of its antagonizing effects. In the present study, we sought to determine the potential of AgRP to regulate the activation of intracellular kinases, including extracellular signal-regulated kinase 1 and 2 (ERK1/2), AKT and AMP-activated protein kinase (AMPK), through neural MCRs. We showed that AgRP acted as a biased agonist in human MC3R (hMC3R), decreasing cAMP activity of constitutively active mutant (F347A) hMC3R but stimulating ERK1/2 activation in both wide type and F347A hMC3Rs. AgRP-stimulated ERK1/2 phosphorylation through MC3R was abolished by protein kinase A (PKA) inhibitor H-89 but not Rp-cAMPS, whereas AgRP-initiated ERK1/2 activation through MC4R was inhibited by phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin and LY294002. Both NDP-MSH and AgRP treatment induced significant AKT phosphorylation in GT1-7 cells but not in MC3R- or MC4R-transfected HEK293T cells. The phosphorylated AMPK levels in both GT1-7 cells and HERK293T cells transfected with neural MCRs were significantly decreased upon stimulation with NDP-MSH but not with AgRP. In summary, we provided novel data for AgRP-initiated multiple intracellular signaling pathways, demonstrating biased agonism of AgRP in both neural MCRs, leading to a better understanding of neural MCR pharmacology.

Pharmacological chaperones for the misfolded melanocortin-4 receptor associated with human obesity.

The melanocortin-4 receptor (MC4R) plays a vital role in regulating energy homeostasis. Mutations in the MC4R cause early-onset severe obesity. The majority of loss of function MC4R mutants are retained intracellularly, many of which are not terminally misfolded and can be stabilized and targeted to the plasma membrane by different chaperones. Some of the mutants might be functional once coaxed to the cell surface. Molecular chaperones and chemical chaperones correct the misfolding of some mutant MC4Rs. However, their therapeutic application is very limited due to their non-specific mechanism of action and, for chemical chaperone, high dosage needed to be effective. Several pharmacological chaperones have been identified for the MC4R and Ipsen 5i and Ipsen 17 are the most potent and efficacious. Here we provide a comprehensive review on how different approaches have been applied to rescue misfolded MC4R mutants. This article is part of a Special Issue entitled: Melanocortin Receptors - edited by Ya-Xiong Tao.

Biased signaling at neural melanocortin receptors in regulation of energy homeostasis.

The global prevalence of obesity highlights the importance of understanding on regulation of energy homeostasis. The central melanocortin system is an important intersection connecting the neural pathways controlling satiety and energy expenditure to regulate energy homeostasis by sensing and integrating the signals of external stimuli. In this system, neural melanocortin receptors (MCRs), melanocortin-3 and -4 receptors (MC3R and MC4R), play crucial roles in the regulation of energy homeostasis. Recently, multiple intracellular signaling pathways and biased signaling at neural MCRs have been discovered, providing new insights into neural MCR signaling. This review attempts to summarize biased signaling including biased receptor mutants (both naturally occurring and lab-generated) and biased ligands at neural MCRs, and to provide a better understanding of obesity pathogenesis and new therapeutic implications for obesity treatment.

Hydrogen sulfide cytoprotective signaling is endothelial nitric oxide synthase-nitric oxide dependent.

Previous studies have demonstrated that hydrogen sulfide (H2S) protects against multiple cardiovascular disease states in a similar manner as nitric oxide (NO). H2S therapy also has been shown to augment NO bioavailability and signaling. The purpose of this study was to investigate the impact of H2S deficiency on endothelial NO synthase (eNOS) function, NO production, and ischemia/reperfusion (I/R) injury. We found that mice lacking the H2S-producing enzyme cystathionine γ-lyase (CSE) exhibit elevated oxidative stress, dysfunctional eNOS, diminished NO levels, and exacerbated myocardial and hepatic I/R injury. In CSE KO mice, acute H2S therapy restored eNOS function and NO bioavailability and attenuated I/R injury. In addition, we found that H2S therapy fails to protect against I/R in eNOS phosphomutant mice (S1179A). Our results suggest that H2S-mediated cytoprotective signaling in the setting of I/R injury is dependent in large part on eNOS activation and NO generation.

Effects of fasting, temperature, and photoperiod on preproghrelin mRNA expression in Chinese perch.

Preproghrelin, a gut/brain peptide, plays an important role in the regulation of food intake and energy homeostasis in teleost and mammals. In the present study, we obtained the full-length preproghrelin cDNA in Chinese perch. The preproghrelin messenger RNA (mRNA) tissue expression showed that level was much higher in stomach and pituitary than in other tissues. The fasting study showed, after gastric emptying (3-6 h), short-term fasting (6-12 h) increased preproghrelin expression in the stomach. While in the pituitary, fasting reduced preproghrelin expression at 1, 3, 12, and 48 h, presenting state fluctuation of self-adjustment. The temperature study showed that the mRNA expression of preproghrelin was the highest in the brain at 26 °C and highest in the stomach at 32 °C, respectively, with different optimum temperature in these two tissues, reflecting spatiotemporal differences of regulation by central nervous system and peripheral organs. The photoperiod study showed that normal light (11 h of lightness and 13 h of darkness) led to highest preproghrelin expression, both in the brain and in the stomach, than continuous light or continuous dark, proving food intake is adapted to natural photoperiod or normal light in this study. These results all indicated that tissue-specific preproghrelin expression of Chinese perch could be significantly affected by environmental factors. Short-term fasting of 6 h after gastric emptying, 26 °C, and normal light led to higher preproghrelin expression, which indicated potential appetite increase in Chinese perch.

Nitrite therapy improves left ventricular function during heart failure via restoration of nitric oxide-mediated cytoprotective signaling.

RATIONALE: Nitric oxide (NO) bioavailability is reduced in the setting of heart failure. Nitrite (NO2) is a critically important NO intermediate that is metabolized to NO during pathological states. We have previously demonstrated that sodium nitrite ameliorates acute myocardial ischemia/reperfusion injury. OBJECTIVE: No evidence exists as to whether increasing NO bioavailability via nitrite therapy attenuates heart failure severity after pressure-overload-induced hypertrophy. METHODS AND RESULTS: Serum from patients with heart failure exhibited significantly decreased nitrosothiol and cGMP levels. Transverse aortic constriction was performed in mice at 10 to 12 weeks. Sodium nitrite (50 mg/L) or saline vehicle was administered daily in the drinking water postoperative from day 1 for 9 weeks. Echocardiography was performed at baseline and at 1, 3, 6, and 9 weeks after transverse aortic constriction to assess left ventricular dimensions and ejection fraction. We observed increased cardiac nitrite, nitrosothiol, and cGMP levels in mice treated with nitrite. Sodium nitrite preserved left ventricular ejection fraction and improved left ventricular dimensions at 9 weeks (P<0.001 versus vehicle). In addition, circulating and cardiac brain natriuretic peptide levels were attenuated in mice receiving nitrite (P<0.05 versus vehicle). Western blot analyses revealed upregulation of Akt-endothelial nitric oxide-nitric oxide-cGMP-GS3Kß signaling early in the progression of hypertrophy and heart failure. CONCLUSIONS: These results support the emerging concept that nitrite therapy may be a viable clinical option for increasing NO levels and may have a practical clinical use in the treatment of heart failure.

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

The melanocortin-1 receptor (MC1R) belongs to the family of seven transmembrane G protein-coupled receptors and plays a central role in animal coat color. We have sequenced the full coding region of 954bp of the MC1R gene in 72 goats of three breeds with different coat colors and identified five missense mutations (K226E, F250V, G255D, V265I, and C267W) and one silent mutation (A61A), among which two haplotypes with complete linkage disequilibrium (A61A and F250V, G255D and V265I) were found. We performed detailed functional studies on the six single and two double mutations in transiently transfected HEK293T cells. We found that none of the mutants had decreased cell surface expression. However, all the mutants except A61A had decreased constitutive activities in the cAMP pathway. Five mutations (F250V, G255D, G267W, A61A/F250V, G255D/V265I) exhibited significant defects in ligand binding and consequent agonist-induced cAMP signaling and ERK1/2 activation. Additionally, K226E, with normal ligand binding affinity and cAMP signaling, showed a significant defect in ERK1/2 activation, exhibiting biased signaling. Co-expression studies showed that the five defective mutants did not affect wild-type MC1R signaling, hence they were not dominant negative. In summary, we provided detailed data of these goat MC1R mutations leading to a better understanding of the role of MC1R mutation and coat color in goats.

Molecular cloning and pharmacological characterization of giant panda (Ailuropoda melanoleuca) melanocortin-4 receptor.

The melanocortin-4 receptor (MC4R) is critical in regulating mammalian food intake and energy expenditure. Giant panda (Ailuropoda melanoleuca), famous as the living fossil, is an endangered species endemic to China. We are interested in exploring the functions of the giant panda MC4R (amMC4R) in regulating energy homeostasis and report herein the molecular cloning and pharmacology of the amMC4R. Sequence analysis revealed that amMC4R was highly homologous (>88%) at nucleotide and amino acid sequences to several mammalian MC4Rs. Western blot revealed that the expression construct myc-amMC4R in pcDNA3.1 was successfully constructed and expressed in HEK293T cells. With human MC4R (hMC4R) as a control, pharmacological characteristics of amMC4R were analyzed with binding and signaling assays. Four agonists, including [Nle(4), D-Phe(7)]-α-melanocyte stimulating hormone (NDP-MSH), α- and ß-MSH, and a small molecule agonist, THIQ, were used in binding and signaling assays. We showed that amMC4R bound NDP-MSH with the highest affinity followed by THIQ, α-MSH, and ß-MSH, with the same ranking order as hMC4R. Treatment of HEK293T cells expressing amMC4R with different concentrations of agonists resulted in dose-dependent increase of intracellular cAMP levels, with similar EC50s for the four agonists. The results suggested that the cloned amMC4R encoded a functional MC4R. The availability of amMC4R and its binding and signaling properties will facilitate the investigation of amMC4R in regulating food intake and energy homeostasis.