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Wang W, Tian Y, Shi X, Ma Q, Xu Y, Yang G, Yi W, Shi Y, Zhou N. N-glycosylation of the human neuropeptide QRFP receptor (QRFPR) is essential for ligand binding and receptor activation. J Neurochem 2021; 158:138-152. [PMID: 33655503 DOI: 10.1111/jnc.15337] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2020] [Revised: 02/23/2021] [Accepted: 02/24/2021] [Indexed: 11/29/2022]
Abstract
The newly identified pyroglutamylated RFamide peptide (QRFP) signaling system has been shown to be implicated in regulating a variety of physiological processes. G-protein-coupled receptors (GPCRs) are preferentially N-glycosylated on extracellular domains. The human QRFP receptor QRFPR (GPR103) possesses three N-glycosylation consensus sites, two located on the N-terminal domain (N5 and N19) and one on the first extracellular loop (ECL1) (N106); however, to date, their role in QRFPR expression and signaling has not been established. Here, we combined mutants with glutamine substitution of the critical asparagines of the consensus sites with glycosidase PNGase F and N-glycosylation inhibitor tunicamycin to study the effect of N-glycosylation in the regulation of QRFPR cell surface expression and signaling. Western blot analysis performed with site-directed mutagenesis revealed that two asparagines at N19 in the N-terminus and N106 in ECL1, but not N5 in the N-terminus, served as sites for N-glycosylation. Treatment with PNGase F and tunicamycin resulted in a reduction in both two-protein species, ~43 kDa and ~85 kDa in size, by 2-4 kDa. Analysis with confocal microscopy and quantitative ELISA showed that N-glycosylation of QRFPR is not essentially required for targeting the cell membrane. However, further binding assay and functional assays demonstrated that removal of N-glycosylation sequons or treatment with tunicamycin led to significant impairments in the interaction of receptor with QRFP26 and downstream signaling. Thus, our findings suggest that for the human QRFP receptor (QRFPR), N-glycosylation is not important for cell surface expression but is a pre-requisite for ligand binding and receptor activation.
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Affiliation(s)
- Weiwei Wang
- Institute of Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, China
| | - Yanan Tian
- Institute of Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, China
| | - Xiaoliu Shi
- Institute of Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, China
| | - Qiang Ma
- Institute of Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, China
| | - Yue Xu
- Institute of Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, China
| | - Gangjie Yang
- Institute of Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, China
| | - Wen Yi
- Institute of Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, China
| | - Ying Shi
- Institute of Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, China
| | - Naiming Zhou
- Institute of Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, China
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Patwardhan A, Cheng N, Trejo J. Post-Translational Modifications of G Protein-Coupled Receptors Control Cellular Signaling Dynamics in Space and Time. Pharmacol Rev 2021; 73:120-151. [PMID: 33268549 PMCID: PMC7736832 DOI: 10.1124/pharmrev.120.000082] [Citation(s) in RCA: 75] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
G protein-coupled receptors (GPCRs) are a large family comprising >800 signaling receptors that regulate numerous cellular and physiologic responses. GPCRs have been implicated in numerous diseases and represent the largest class of drug targets. Although advances in GPCR structure and pharmacology have improved drug discovery, the regulation of GPCR function by diverse post-translational modifications (PTMs) has received minimal attention. Over 200 PTMs are known to exist in mammalian cells, yet only a few have been reported for GPCRs. Early studies revealed phosphorylation as a major regulator of GPCR signaling, whereas later reports implicated a function for ubiquitination, glycosylation, and palmitoylation in GPCR biology. Although our knowledge of GPCR phosphorylation is extensive, our knowledge of the modifying enzymes, regulation, and function of other GPCR PTMs is limited. In this review we provide a comprehensive overview of GPCR post-translational modifications with a greater focus on new discoveries. We discuss the subcellular location and regulatory mechanisms that control post-translational modifications of GPCRs. The functional implications of newly discovered GPCR PTMs on receptor folding, biosynthesis, endocytic trafficking, dimerization, compartmentalized signaling, and biased signaling are also provided. Methods to detect and study GPCR PTMs as well as PTM crosstalk are further highlighted. Finally, we conclude with a discussion of the implications of GPCR PTMs in human disease and their importance for drug discovery. SIGNIFICANCE STATEMENT: Post-translational modification of G protein-coupled receptors (GPCRs) controls all aspects of receptor function; however, the detection and study of diverse types of GPCR modifications are limited. A thorough understanding of the role and mechanisms by which diverse post-translational modifications regulate GPCR signaling and trafficking is essential for understanding dysregulated mechanisms in disease and for improving and refining drug development for GPCRs.
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Affiliation(s)
- Anand Patwardhan
- Department of Pharmacology and the Biomedical Sciences Graduate Program, School of Medicine, University of California, San Diego, La Jolla, California
| | - Norton Cheng
- Department of Pharmacology and the Biomedical Sciences Graduate Program, School of Medicine, University of California, San Diego, La Jolla, California
| | - JoAnn Trejo
- Department of Pharmacology and the Biomedical Sciences Graduate Program, School of Medicine, University of California, San Diego, La Jolla, California
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Wang T, Nakagawa S, Miyake T, Setsu G, Kunisue S, Goto K, Hirasawa A, Okamura H, Yamaguchi Y, Doi M. Identification and functional characterisation of N-linked glycosylation of the orphan G protein-coupled receptor Gpr176. Sci Rep 2020; 10:4429. [PMID: 32157140 PMCID: PMC7064540 DOI: 10.1038/s41598-020-61370-y] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2019] [Accepted: 02/26/2020] [Indexed: 12/13/2022] Open
Abstract
G-protein-coupled receptors (GPCRs) are important drug targets with diverse therapeutic applications. However, there are still more than a hundred orphan GPCRs, whose protein functions and biochemical features remain unidentified. Gpr176 encodes a class-A orphan GPCR that has a role in circadian clock regulation in mouse hypothalamus and is also implicated in human breast cancer transcriptional response. Here we show that Gpr176 is N-glycosylated. Peptide-N-glycosidase treatment of mouse hypothalamus extracts revealed that endogenous Gpr176 undergoes N-glycosylation. Using a heterologous expression system, we show that N-glycosylation occurs at four conserved asparagine residues in the N-terminal region of Gpr176. Deficient N-glycosylation due to mutation of these residues reduced the protein expression of Gpr176. At the molecular function level, Gpr176 has constitutive, agonist-independent activity that leads to reduced cAMP synthesis. Although deficient N-glycosylation did not compromise this intrinsic activity, the resultant reduction in protein expression was accompanied by attenuation of cAMP-repressive activity in the cells. We also demonstrate that human GPR176 is N-glycosylated. Importantly, missense variations in the conserved N-glycosylation sites of human GPR176 (rs1473415441; rs761894953) affected N-glycosylation and thereby attenuated protein expression and cAMP-repressive activity in the cells. We show that N-glycosylation is a prerequisite for the efficient protein expression of functional Gpr176/GPR176.
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Affiliation(s)
- Tianyu Wang
- Department of Systems Biology, Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyō-ku, Kyoto, 606-8501, Japan
| | - Shumpei Nakagawa
- Department of Systems Biology, Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyō-ku, Kyoto, 606-8501, Japan
| | - Takahito Miyake
- Department of Systems Biology, Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyō-ku, Kyoto, 606-8501, Japan
| | - Genzui Setsu
- Department of Systems Biology, Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyō-ku, Kyoto, 606-8501, Japan
| | - Sumihiro Kunisue
- Department of Systems Biology, Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyō-ku, Kyoto, 606-8501, Japan
| | - Kaoru Goto
- Department of Systems Biology, Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyō-ku, Kyoto, 606-8501, Japan
| | - Akira Hirasawa
- Department of Genomic Drug Discovery Science, Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyō-ku, Kyoto, 606-8501, Japan
| | - Hitoshi Okamura
- Department of Systems Biology, Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyō-ku, Kyoto, 606-8501, Japan.,Laboratory of Molecular Brain Science, Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyō-ku, Kyoto, 606-8501, Japan
| | - Yoshiaki Yamaguchi
- Department of Systems Biology, Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyō-ku, Kyoto, 606-8501, Japan
| | - Masao Doi
- Department of Systems Biology, Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyō-ku, Kyoto, 606-8501, Japan.
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Wu Y, Zhao X, Chen L, Wang J, Duan Y, Li H, Lu L. Transcriptomic Analyses of the Hypothalamic-Pituitary-Gonadal Axis Identify Candidate Genes Related to Egg Production in Xinjiang Yili Geese. Animals (Basel) 2020; 10:E90. [PMID: 31935822 PMCID: PMC7023467 DOI: 10.3390/ani10010090] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2019] [Revised: 12/26/2019] [Accepted: 01/02/2020] [Indexed: 12/22/2022] Open
Abstract
The study was conducted to investigate the transcriptomic differences of the hypothalamic-pituitary-gonadal axis between Xinjiang Yili geese with high and low egg production and to find candidate genes regulating the egg production of Xinjiang Yili geese. The 8 selected Xinjiang Yili Geese with high or low egg production (4 for each group) were 3 years old, with good health, and under the same feeding condition. High-throughput sequencing technology was used to sequence cDNA libraries of the hypothalami, pituitary glands, and ovaries. The sequencing data were compared and analyzed, and the transcripts with significant differences were identified and analyzed with bioinformatics. The study showed that the transcriptome sequencing data of the 24 samples contained a total of 1,176,496,146 valid reads and 176.47 gigabase data. Differential expression analyses identified 135, 56, and 331 genes in the hypothalami, pituitary glands, and ovaries of Xinjiang Yili geese with high and low egg production. Further annotation of these differentially expressed genes in the non-redundant protein sequence database (Nr) revealed that 98, 52, and 309 genes were annotated, respectively. Through the annotations of GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) databases, 30 candidate genes related to the egg production of Xinjiang Yili geese were preliminarily selected. The gap junction, focal adhesion, and ECM-receptor interaction signaling pathways were enriched with the hypothalamic, pituitary, and ovarian differentially expressed genes, and the calcium signaling pathway was enriched with the pituitary and ovarian differentially expressed genes. Thus, these pathways in the hypothalamic-pituitary-gonadal axis may play an important role in regulating egg production of Xinjiang Yili geese. The results provided the transcriptomic information of the hypothalamic-pituitary-gonadal axis of Xinjiang Yili geese and laid the theoretical basis for revealing the molecular mechanisms regulating the egg-laying traits of Xinjiang Yili geese.
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Affiliation(s)
- Yingping Wu
- College of Animal Science, Xinjiang Agricultural University, Urumqi 830000, China; (Y.W.); (X.Z.); (J.W.); (Y.D.)
| | - Xiaoyu Zhao
- College of Animal Science, Xinjiang Agricultural University, Urumqi 830000, China; (Y.W.); (X.Z.); (J.W.); (Y.D.)
| | - Li Chen
- Institute of Animal Husbandry and Veterinary Science, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China;
| | - Junhua Wang
- College of Animal Science, Xinjiang Agricultural University, Urumqi 830000, China; (Y.W.); (X.Z.); (J.W.); (Y.D.)
| | - Yuqing Duan
- College of Animal Science, Xinjiang Agricultural University, Urumqi 830000, China; (Y.W.); (X.Z.); (J.W.); (Y.D.)
| | - Haiying Li
- College of Animal Science, Xinjiang Agricultural University, Urumqi 830000, China; (Y.W.); (X.Z.); (J.W.); (Y.D.)
| | - Lizhi Lu
- Institute of Animal Husbandry and Veterinary Science, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China;
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Rodrigues AR, Sousa D, Almeida H, Gouveia AM. Cell surface targeting of the Melanocortin 5 Receptor (MC5R) requires serine-rich terminal motifs. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2017; 1864:1217-1226. [PMID: 28396017 DOI: 10.1016/j.bbamcr.2017.04.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Revised: 04/05/2017] [Accepted: 04/07/2017] [Indexed: 01/11/2023]
Abstract
The Melanocortin 5 Receptor (MC5R) is a cell surface receptor that belongs to the class of G-protein coupled receptors (GPCRs), which comprises an intracellular carboxylic domain, seven transmembrane helices and an extracellular amino terminal. Over the last few years, MC5R has been implicated in the regulation of lipid metabolism in exocrine glands, muscle and even in adipose tissue and its function is quite dependent on its correct cell membrane targeting. In this context, the purpose of this work was to study the role of MC5R N-terminus in the receptor trafficking from the endoplasmic reticulum (ER) through the Golgi complex to the plasma membrane. Analysis of N-terminal deleted forms of MC5R revealed that the first 21 amino acids contain the information responsible for the receptor cell surface expression and the removal of further amino acids interfere with the receptor synthesis. In this setting, several mutant forms of the receptor were created by site directed mutagenesis of the MC5R first 21 amino acids and their presence at the plasma membrane was assessed. We have found that two small motifs, constituted by residues Ser4/Ser5 and Ser17/Glu18, are clearly involved in the correct targeting of MC5R to the cell surface. Fluorescence microscopy analysis has revealed that MC5R constructs with mutations in those residues are mainly retained at the ER/Golgi complex. Furthermore, the homodimerization ability of the receptor is maintained in these mutant forms, suggesting that other mechanisms are involved in the regulation of the anterograde transport of MC5R by those N-terminal domains.
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Affiliation(s)
- A R Rodrigues
- Departamento de Biomedicina-Unidade de Biologia Experimental, Faculdade de Medicina da Universidade do Porto, Porto, Portugal; I3S - Instituto de Investigação e Inovação em Saúde, IBMC - Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal
| | - D Sousa
- I3S - Instituto de Investigação e Inovação em Saúde, IPATIMUP, Universidade do Porto, Porto, Portugal
| | - H Almeida
- Departamento de Biomedicina-Unidade de Biologia Experimental, Faculdade de Medicina da Universidade do Porto, Porto, Portugal; I3S - Instituto de Investigação e Inovação em Saúde, IBMC - Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal
| | - A M Gouveia
- Departamento de Biomedicina-Unidade de Biologia Experimental, Faculdade de Medicina da Universidade do Porto, Porto, Portugal; I3S - Instituto de Investigação e Inovação em Saúde, IBMC - Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal; Faculdade de Ciências da Nutrição e Alimentação, Universidade do Porto, Porto, Portugal.
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6
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Coleman JLJ, Ngo T, Smith NJ. The G protein-coupled receptor N-terminus and receptor signalling: N-tering a new era. Cell Signal 2017; 33:1-9. [PMID: 28188824 DOI: 10.1016/j.cellsig.2017.02.004] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2017] [Accepted: 02/06/2017] [Indexed: 01/22/2023]
Abstract
G protein-coupled receptors (GPCRs) are a vast family of membrane-traversing proteins, essential to the ability of eukaryotic life to detect, and mount an intracellular response to, a diverse range of extracellular stimuli. GPCRs have evolved with archetypal features including an extracellular N-terminus and intracellular C-terminus that flank a transmembrane structure of seven sequential helices joined by intracellular and extracellular loops. These structural domains contribute to the ability of a GPCR to be correctly synthesised and inserted into the cell membrane, to interact with its cognate ligand(s) and to couple with signal-transducing heterotrimeric G proteins, allowing the activated receptor to selectively modulate a number of signalling cascades. Whilst well known for its importance in receptor translation and trafficking, the GPCR N-terminus is underexplored as a participant in receptor signalling. This review aims to discuss and integrate recent advances in knowledge of the vital roles of the GPCR N-terminus in receptor signalling.
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Affiliation(s)
- James L J Coleman
- Molecular Pharmacology Group, Victor Chang Cardiac Research Institute, Darlinghurst, NSW 2010, Australia; St Vincent's Clinical School, University of New South Wales, Darlinghurst, NSW 2010, Australia.
| | - Tony Ngo
- Molecular Pharmacology Group, Victor Chang Cardiac Research Institute, Darlinghurst, NSW 2010, Australia; St Vincent's Clinical School, University of New South Wales, Darlinghurst, NSW 2010, Australia
| | - Nicola J Smith
- Molecular Pharmacology Group, Victor Chang Cardiac Research Institute, Darlinghurst, NSW 2010, Australia; St Vincent's Clinical School, University of New South Wales, Darlinghurst, NSW 2010, Australia.
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7
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Fridmanis D, Roga A, Klovins J. ACTH Receptor (MC2R) Specificity: What Do We Know About Underlying Molecular Mechanisms? Front Endocrinol (Lausanne) 2017; 8:13. [PMID: 28220105 PMCID: PMC5292628 DOI: 10.3389/fendo.2017.00013] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/14/2016] [Accepted: 01/16/2017] [Indexed: 11/13/2022] Open
Abstract
Coincidentally, the release of this Research Topic in Frontiers in Endocrinology takes place 25 years after the discovery of the adrenocorticotropic hormone receptor (ACTHR) by Mountjoy and colleagues. In subsequent years, following the discovery of other types of mammalian melanocortin receptors (MCRs), ACTHR also became known as melanocortin type 2 receptor (MC2R). At present, five types of MCRs have been reported, all of which share significant sequence similarity at the amino acid level, and all of which specifically bind melanocortins (MCs)-a group of biologically active peptides generated by proteolysis of the proopiomelanocortin precursor. All MCs share an identical -H-F-R-W- pharmacophore sequence. α-Melanocyte-stimulating hormone (α-MSH) and adrenocorticotropic hormone (ACTH) are the most extensively studied MCs and are derived from the same region. Essentially, α-MSH is formed from the first 13 amino acid residues of ACTH. ACTHR is unique among MCRs because it binds one sole ligand-ACTH, which makes it a very attractive research object for molecular pharmacologists. However, much research has failed, and functional studies of this receptor are lagging behind other MCRs. The reason for these difficulties has already been outlined by Mountjoy and colleagues in their publication on ACTHR coding sequence discovery where the Cloudman S91 melanoma cell line was used for receptor expression because it was a "more sensitive assay system." Subsequent work showed that ACTHR could be successfully expressed only in endogenous MCR-expressing cell lines, since in other cell lines it is retained within the endoplasmic reticulum. The resolution of this methodological problem came in 2005 with the discovery of melanocortin receptor accessory protein, which is required for the formation of functionally active ACTHR. The decade that followed this discovery was filled with exciting research that provided insight into the molecular mechanisms underlying the action of ACTHR. The purpose of this review is to summarize the advances in this fascinating research field.
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Affiliation(s)
| | - Ance Roga
- Latvian Biomedical Research and Study Centre, Riga, Latvia
| | - Janis Klovins
- Latvian Biomedical Research and Study Centre, Riga, Latvia
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Sivanesan D, Beauchamp C, Quinou C, Lee J, Lesage S, Chemtob S, Rioux JD, Michnick SW. IL23R (Interleukin 23 Receptor) Variants Protective against Inflammatory Bowel Diseases (IBD) Display Loss of Function due to Impaired Protein Stability and Intracellular Trafficking. J Biol Chem 2016; 291:8673-85. [PMID: 26887945 DOI: 10.1074/jbc.m116.715870] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2016] [Indexed: 01/19/2023] Open
Abstract
Genome-wide association studies as well as murine models have shown that the interleukin 23 receptor (IL23R) pathway plays a pivotal role in chronic inflammatory diseases such as Crohn disease (CD), ulcerative colitis, psoriasis, and type 1 diabetes. Genome-wide association studies and targeted re-sequencing studies have revealed the presence of multiple potentially causal variants of the IL23R. Specifically the G149R, V362I, and R381Q IL23Rα chain variants are linked to protection against the development of Crohn disease and ulcerative colitis in humans. Moreover, the exact mechanism of action of these receptor variants has not been elucidated. We show that all three of these IL23Rα variants cause a reduction in IL23 receptor activation-mediated phosphorylation of the signal-transducing activator of transcription 3 (STAT3) and phosphorylation of signal transducing activator of transcription 4 (STAT4). The reduction in signaling is due to lower levels of cell surface receptor expression. For G149R, the receptor retention in the endoplasmic reticulum is due to an impairment of receptor maturation, whereas the R381Q and V362I variants have reduced protein stability. Finally, we demonstrate that the endogenous expression of IL23Rα protein from V362I and R381Q variants in human lymphoblastoid cell lines exhibited lower expression levels relative to susceptibility alleles. Our results suggest a convergent cause of IL23Rα variant protection against chronic inflammatory disease.
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Affiliation(s)
- Durga Sivanesan
- From the Department of Biochemistry, University of Montreal, Montreal, Quebec H3C 3J7, Canada, University of Ottawa, Department of Biochemistry, Microbiology, and Immunology, Ottawa, Ontario K1H 8M5, Canada
| | - Claudine Beauchamp
- University of Montreal and the Montreal Heart Institute, Research Center, Montreal, Quebec H1T 1C8, Canada
| | - Christiane Quinou
- CHU Sainte-Justine, Research Centre, Montreal, Quebec H3T 1C5, Canada, and
| | - Jonathan Lee
- University of Ottawa, Department of Biochemistry, Microbiology, and Immunology, Ottawa, Ontario K1H 8M5, Canada
| | - Sylvie Lesage
- Centre of Recherche Hospital Maisonneuve-Rosemont, Department of Microbiology, Infection, and Immunology, University of Montreal, Montreal, Quebec H1T 2M4, Canada
| | - Sylvain Chemtob
- CHU Sainte-Justine, Research Centre, Montreal, Quebec H3T 1C5, Canada, and
| | - John D Rioux
- University of Montreal and the Montreal Heart Institute, Research Center, Montreal, Quebec H1T 1C8, Canada
| | - Stephen W Michnick
- From the Department of Biochemistry, University of Montreal, Montreal, Quebec H3C 3J7, Canada,
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Trempel F, Kajiura H, Ranf S, Grimmer J, Westphal L, Zipfel C, Scheel D, Fujiyama K, Lee J. Altered glycosylation of exported proteins, including surface immune receptors, compromises calcium and downstream signaling responses to microbe-associated molecular patterns in Arabidopsis thaliana. BMC PLANT BIOLOGY 2016; 16:31. [PMID: 26822404 PMCID: PMC4730752 DOI: 10.1186/s12870-016-0718-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Accepted: 01/19/2016] [Indexed: 05/10/2023]
Abstract
BACKGROUND Calcium, as a second messenger, transduces extracellular signals into cellular reactions. A rise in cytosolic calcium concentration is one of the first plant responses after exposure to microbe-associated molecular patterns (MAMPs). We reported previously the isolation of Arabidopsis thaliana mutants with a "changed calcium elevation" (cce) response to flg22, a 22-amino-acid MAMP derived from bacterial flagellin. RESULTS Here, we characterized the cce2 mutant and its weaker allelic mutant, cce3. Besides flg22, the mutants respond with a reduced calcium elevation to several other MAMPs and a plant endogenous peptide that is proteolytically processed from pre-pro-proteins during wounding. Downstream defense-related events such flg22-induced mitogen-activated protein kinase activation, accumulation of reactive oxygen species and growth arrest are also attenuated in cce2/cce3. By genetic mapping, next-generation sequencing and allelism assay, CCE2/CCE3 was identified to be ALG3 (Asparagine-linked glycosylation 3). This encodes the α-1,3-mannosyltransferase responsible for the first step of core oligosaccharide Glc3Man9GlcNAc2 glycan assembly on the endoplasmic reticulum (ER) luminal side. Complementation assays and glycan analysis in yeast alg3 mutant confirmed the reduced enzymatic function of the proteins encoded by the cce2/cce3 alleles - leading to accumulation of M5(ER), the immature five mannose-containing oligosaccharide structure found in the ER. Proper protein glycosylation is required for ER/Golgi processing and trafficking of membrane proteins to the plasma membrane. Endoglycosidase H-insensitivity of flg22 receptor, FLS2, in the cce2/cce3 mutants suggests altered glycan structures in the receptor. CONCLUSION Proper glycosylation of MAMP receptors (or other exported proteins) is required for optimal responses to MAMPs and is important for immune signaling of host plants.
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Affiliation(s)
- Fabian Trempel
- Leibniz Institute of Plant Biochemistry, Weinberg 3, D-06120, Halle/Saale, Germany.
| | - Hiroyuki Kajiura
- The International Center for Biotechnology, Osaka University, 2-1 Yamada-oka, Suita-shi, Osaka, 565, Japan.
| | - Stefanie Ranf
- Current address: Phytopathology, TUM School of Life Sciences, Weihenstephan, Technische Universität München, Emil-Ramann-Str. 2, D-85350, Freising-Weihenstephan, Germany.
| | - Julia Grimmer
- Current address: Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Weinbergweg 22, D-06120, Halle, Germany.
| | - Lore Westphal
- Leibniz Institute of Plant Biochemistry, Weinberg 3, D-06120, Halle/Saale, Germany.
| | - Cyril Zipfel
- The Sainsbury Laboratory, Norwich Research Park, Norwich, NR4 7UH, UK.
| | - Dierk Scheel
- Leibniz Institute of Plant Biochemistry, Weinberg 3, D-06120, Halle/Saale, Germany.
| | - Kazuhito Fujiyama
- The International Center for Biotechnology, Osaka University, 2-1 Yamada-oka, Suita-shi, Osaka, 565, Japan.
| | - Justin Lee
- Leibniz Institute of Plant Biochemistry, Weinberg 3, D-06120, Halle/Saale, Germany.
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10
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Maben ZJ, Malik S, Jiang LH, Hinkle PM. Dual Topology of the Melanocortin-2 Receptor Accessory Protein Is Stable. Front Endocrinol (Lausanne) 2016; 7:96. [PMID: 27486435 PMCID: PMC4947873 DOI: 10.3389/fendo.2016.00096] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Accepted: 07/05/2016] [Indexed: 01/02/2023] Open
Abstract
Melanocortin 2 receptor accessory protein (MRAP) facilitates trafficking of melanocortin 2 (MC2) receptors and is essential for ACTH binding and signaling. MRAP is a single transmembrane domain protein that forms antiparallel homodimers. These studies ask when MRAP first acquires this dual topology, whether MRAP architecture is static or stable, and whether the accessory protein undergoes rapid turnover. To answer these questions, we developed an approach that capitalizes on the specificity of bacterial biotin ligase, which adds biotin to lysine in a short acceptor peptide sequence; the distinct mobility of MRAP protomers of opposite orientations based on their N-linked glycosylation; and the ease of identifying biotin-labeled proteins. We inserted biotin ligase acceptor peptides at the N- or C-terminal ends of MRAP and expressed the modified proteins in mammalian cells together with either cytoplasmic or endoplasmic reticulum-targeted biotin ligase. MRAP assumed dual topology early in biosynthesis in both CHO and OS3 adrenal cells. Once established, MRAP orientation was stable. Despite its conformational stability, MRAP displayed a half-life of under 2 h in CHO cells. The amount of MRAP was increased by the proteasome inhibitor MG132 and MRAP underwent ubiquitylation on lysine and other amino acids. Nonetheless, when protein synthesis was blocked with cycloheximide, MRAP was rapidly degraded even when MG132 was included and all lysines were replaced by arginines, implicating non-proteasomal degradation pathways. The results show that although MRAP does not change orientations during trafficking, its synthesis and degradation are dynamically regulated.
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Affiliation(s)
- Zachary J. Maben
- Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, NY, USA
| | - Sundeep Malik
- Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, NY, USA
| | - Liyi H. Jiang
- Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, NY, USA
| | - Patricia M. Hinkle
- Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, NY, USA
- *Correspondence: Patricia M. Hinkle,
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Malik S, Dolan TM, Maben ZJ, Hinkle PM. Adrenocorticotropic Hormone (ACTH) Responses Require Actions of the Melanocortin-2 Receptor Accessory Protein on the Extracellular Surface of the Plasma Membrane. J Biol Chem 2015; 290:27972-85. [PMID: 26424796 DOI: 10.1074/jbc.m115.668491] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2015] [Indexed: 01/26/2023] Open
Abstract
The melanocortin-2 (MC2) receptor is a G protein-coupled receptor that mediates responses to ACTH. The MC2 receptor acts in concert with the MC2 receptor accessory protein (MRAP) that is absolutely required for ACTH binding and signaling. MRAP has a single transmembrane domain and forms a highly unusual antiparallel homodimer that is stably associated with MC2 receptors at the plasma membrane. Despite the physiological importance of the interaction between the MC2 receptor and MRAP, there is little understanding of how the accessory protein works. The dual topology of MRAP has made it impossible to determine whether highly conserved and necessary regions of MRAP are required on the intracellular or extracellular face of the plasma membrane. The strategy used here was to fix the orientation of two antiparallel MRAP molecules and then introduce inactivating mutations on one side of the membrane or the other. This was achieved by engineering proteins containing tandem copies of MRAP fused to the amino terminus of the MC2 receptor. The data firmly establish that only the extracellular amino terminus (Nout) copy of MRAP, oriented with critical segments on the extracellular side of the membrane, is essential. The transmembrane domain of MRAP is also required in only the Nout orientation. Finally, activity of MRAP-MRAP-MC2-receptor fusion proteins with inactivating mutations in either MRAP or the receptor was rescued by co-expression of free wild-type MRAP or free wild-type receptor. These results show that the basic MRAP-MRAP-receptor signaling unit forms higher order complexes and that these multimers signal.
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Affiliation(s)
- Sundeep Malik
- From the Department of Pharmacology and Physiology, University of Rochester Medical Center Rochester, New York 14642
| | - Terrance M Dolan
- From the Department of Pharmacology and Physiology, University of Rochester Medical Center Rochester, New York 14642
| | - Zachary J Maben
- From the Department of Pharmacology and Physiology, University of Rochester Medical Center Rochester, New York 14642
| | - Patricia M Hinkle
- From the Department of Pharmacology and Physiology, University of Rochester Medical Center Rochester, New York 14642
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12
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Jackson DS, Ramachandrappa S, Clark AJ, Chan LF. Melanocortin receptor accessory proteins in adrenal disease and obesity. Front Neurosci 2015; 9:213. [PMID: 26113808 PMCID: PMC4461818 DOI: 10.3389/fnins.2015.00213] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2014] [Accepted: 05/28/2015] [Indexed: 12/02/2022] Open
Abstract
Melanocortin receptor accessory proteins (MRAPs) are regulators of the melanocortin receptor family. MRAP is an essential accessory factor for the functional expression of the MC2R/ACTH receptor. The importance of MRAP in adrenal gland physiology is demonstrated by the clinical condition familial glucocorticoid deficiency type 2. The role of its paralog melanocortin-2-receptor accessory protein 2 (MRAP2), which is predominantly expressed in the hypothalamus including the paraventricular nucleus, has recently been linked to mammalian obesity. Whole body deletion and targeted brain specific deletion of the Mrap2 gene result in severe obesity in mice. Interestingly, Mrap2 complete knockout (KO) mice have increased body weight without detectable changes to food intake or energy expenditure. Rare heterozygous variants of MRAP2 have been found in humans with severe, early-onset obesity. In vitro data have shown that Mrap2 interaction with the melanocortin-4-receptor (Mc4r) affects receptor signaling. However, the mechanism by which Mrap2 regulates body weight in vivo is not fully understood and differences between the phenotypes of Mrap2 and Mc4r KO mice may point toward Mc4r independent mechanisms.
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Affiliation(s)
- David S Jackson
- Centre for Endocrinology, William Harvey Research Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London London, UK
| | - Shwetha Ramachandrappa
- Centre for Endocrinology, William Harvey Research Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London London, UK
| | - Adrian J Clark
- Centre for Endocrinology, William Harvey Research Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London London, UK
| | - Li F Chan
- Centre for Endocrinology, William Harvey Research Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London London, UK
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13
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Arrat H, Lukas TJ, Siddique T. ACTH (Acthar Gel) Reduces Toxic SOD1 Protein Linked to Amyotrophic Lateral Sclerosis in Transgenic Mice: A Novel Observation. PLoS One 2015; 10:e0125638. [PMID: 25955410 PMCID: PMC4425507 DOI: 10.1371/journal.pone.0125638] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Accepted: 03/12/2015] [Indexed: 12/11/2022] Open
Abstract
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease with a complex etiology and pathology that makes the development of new therapies difficult. ACTH has neurotrophic and myotrophic effects, but has not been tested in an ALS mouse model. The G93A-SOD1 mouse model of ALS was used to test the ability of this drug to delay ALS-like symptoms. We showed that within a specific dose range, ACTH significantly postponed the disease onset and paralysis in the mouse model. To our surprise and of greater significance is that ACTH significantly reduced the levels of soluble SOD1 in the spinal cord and CNS tissues of G93A-SOD1 treated mice as well as cultured fibroblasts.
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Affiliation(s)
- Hasan Arrat
- Department of Neurology, Northwestern University, Feinberg School of Medicine, Chicago, IL, 60611, United States of America
| | - Thomas J. Lukas
- Department of Pharmacology, Northwestern University, Feinberg School of Medicine, Chicago, IL, 60611, United States of America
- * E-mail: (TS); (TJL)
| | - Teepu Siddique
- Department of Neurology, Northwestern University, Feinberg School of Medicine, Chicago, IL, 60611, United States of America
- * E-mail: (TS); (TJL)
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14
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Abstract
The purpose of this article is to review fundamentals in adrenal gland histophysiology. Key findings regarding the important signaling pathways involved in the regulation of steroidogenesis and adrenal growth are summarized. We illustrate how adrenal gland morphology and function are deeply interconnected in which novel signaling pathways (Wnt, Sonic hedgehog, Notch, β-catenin) or ionic channels are required for their integrity. Emphasis is given to exploring the mechanisms and challenges underlying the regulation of proliferation, growth, and functionality. Also addressed is the fact that while it is now well-accepted that steroidogenesis results from an enzymatic shuttle between mitochondria and endoplasmic reticulum, key questions still remain on the various aspects related to cellular uptake and delivery of free cholesterol. The significant progress achieved over the past decade regarding the precise molecular mechanisms by which the two main regulators of adrenal cortex, adrenocorticotropin hormone (ACTH) and angiotensin II act on their receptors is reviewed, including structure-activity relationships and their potential applications. Particular attention has been given to crucial second messengers and how various kinases, phosphatases, and cytoskeleton-associated proteins interact to ensure homeostasis and/or meet physiological demands. References to animal studies are also made in an attempt to unravel associated clinical conditions. Many of the aspects addressed in this article still represent a challenge for future studies, their outcome aimed at providing evidence that the adrenal gland, through its steroid hormones, occupies a central position in many situations where homeostasis is disrupted, thus highlighting the relevance of exploring and understanding how this key organ is regulated. © 2014 American Physiological Society. Compr Physiol 4:889-964, 2014.
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Affiliation(s)
- Nicole Gallo-Payet
- Division of Endocrinology, Department of Medicine, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, and Centre de Recherche Clinique Étienne-Le Bel of the Centre Hospitalier Universitaire de Sherbrooke (CHUS), Sherbrooke, Quebec, Canada
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15
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Watanabe I, Zhu J, Recio-Pinto E, Thornhill WB. The Degree of N-glycosylation Affects the Trafficking and Cell Surface Expression Levels of Kv1.4 Potassium Channels. J Membr Biol 2014; 248:187-96. [DOI: 10.1007/s00232-014-9756-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2014] [Accepted: 11/11/2014] [Indexed: 02/04/2023]
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16
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Denhez B, Lizotte F, Guimond MO, Jones N, Takano T, Geraldes P. Increased SHP-1 protein expression by high glucose levels reduces nephrin phosphorylation in podocytes. J Biol Chem 2014; 290:350-8. [PMID: 25404734 DOI: 10.1074/jbc.m114.612721] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Nephrin, a critical podocyte membrane component that is reduced in diabetic nephropathy, has been shown to activate phosphotyrosine signaling pathways in human podocytes. Nephrin signaling is important to reduce cell death induced by apoptotic stimuli. We have shown previously that high glucose level exposure and diabetes increased the expression of SHP-1, causing podocyte apoptosis. SHP-1 possesses two Src homology 2 domains that serve as docking elements to dephosphorylate tyrosine residues of target proteins. However, it remains unknown whether SHP-1 interacts with nephrin and whether its elevated expression affects the nephrin phosphorylation state in diabetes. Here we show that human podocytes exposed to high glucose levels exhibited elevated expression of SHP-1, which was associated with nephrin. Coexpression of nephrin-CD16 and SHP-1 reduced nephrin tyrosine phosphorylation in transfected human embryonic kidney 293 cells. A single tyrosine-to-phenylalanine mutation revealed that rat nephrin Tyr(1127) and Tyr(1152) are required to allow SHP-1 interaction with nephrin. Overexpression of dominant negative SHP-1 in human podocytes prevented high glucose-induced reduction of nephrin phosphorylation. In vivo, immunoblot analysis demonstrated that nephrin expression and phosphorylation were decreased in glomeruli of type 1 diabetic Akita mice (Ins2(+/C96Y)) compared with control littermate mice (Ins2(+/+)), and this was associated with elevated SHP-1 and cleaved caspase-3 expression. Furthermore, immunofluorescence analysis indicated increased colocalization of SHP-1 with nephrin in diabetic mice compared with control littermates. In conclusion, our results demonstrate that high glucose exposure increases SHP-1 interaction with nephrin, causing decreased nephrin phosphorylation, which may, in turn, contribute to diabetic nephropathy.
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Affiliation(s)
- Benoit Denhez
- From the Research Center of the Centre Hospitalier Universitaire de Sherbrooke and Division of Endocrinology, Departments of Medicine, Université de Sherbrooke, Sherbrooke, Québec J1H 5N4, Canada
| | - Farah Lizotte
- From the Research Center of the Centre Hospitalier Universitaire de Sherbrooke and Division of Endocrinology, Departments of Medicine, Université de Sherbrooke, Sherbrooke, Québec J1H 5N4, Canada
| | - Marie-Odile Guimond
- From the Research Center of the Centre Hospitalier Universitaire de Sherbrooke and Division of Endocrinology, Departments of Medicine, Université de Sherbrooke, Sherbrooke, Québec J1H 5N4, Canada
| | - Nina Jones
- the Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada, and
| | - Tomoko Takano
- the McGill University Health Center, Montreal, Québec H3H 2R9, Canada
| | - Pedro Geraldes
- From the Research Center of the Centre Hospitalier Universitaire de Sherbrooke and Division of Endocrinology, Departments of Medicine, Université de Sherbrooke, Sherbrooke, Québec J1H 5N4, Canada,
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17
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García-Borrón JC, Abdel-Malek Z, Jiménez-Cervantes C. MC1R, the cAMP pathway, and the response to solar UV: extending the horizon beyond pigmentation. Pigment Cell Melanoma Res 2014; 27:699-720. [PMID: 24807163 DOI: 10.1111/pcmr.12257] [Citation(s) in RCA: 128] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2014] [Accepted: 05/01/2014] [Indexed: 12/20/2022]
Abstract
The melanocortin 1 receptor (MC1R) is a G protein-coupled receptor crucial for the regulation of melanocyte proliferation and function. Upon binding melanocortins, MC1R activates several signaling cascades, notably the cAMP pathway leading to synthesis of photoprotective eumelanin. Polymorphisms in the MC1R gene are a major source of normal variation of human hair color and skin pigmentation, response to ultraviolet radiation (UVR), and skin cancer susceptibility. The identification of a surprisingly high number of MC1R natural variants strongly associated with pigmentary phenotypes and increased skin cancer risk has prompted research on the functional properties of the wild-type receptor and frequent mutant alleles. We summarize current knowledge on MC1R structural and functional properties, as well as on its intracellular trafficking and signaling. We also review the current knowledge about the function of MC1R as a skin cancer, particularly melanoma, susceptibility gene and how it modulates the response of melanocytes to UVR.
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Affiliation(s)
- Jose C García-Borrón
- Department of Biochemistry and Molecular Biology, School of Medicine, University of Murcia, Murcia, Spain; Instituto Murciano de Investigación Biomédica (IMIB), El Palmar, Murcia, Spain
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18
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Rodrigues AR, Sousa D, Almeida H, Gouveia AM. Structural determinants regulating cell surface targeting of melanocortin receptors. J Mol Endocrinol 2013; 51:R23-32. [PMID: 23907004 DOI: 10.1530/jme-13-0055] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Melanocortin receptors (MCRs) belong to the G-protein-coupled receptor family of transmembrane proteins. They recognize specific ligands named melanocortins that are mainly produced in the pituitary and hypothalamus. Newly synthesized MCRs at the endoplasmic reticulum are subjected to quality control mechanisms that screen for the correct structure, folding or processing, essential for their proper cell surface expression. Some motifs, located at the N- or C-terminus or even on transmembrane and in loop regions, have been implicated in these biological processes. This article reviews these specific domains and the role of accessory proteins and post-translation modifications in MCRs' targeting to cell surface. Additionally, promising approaches involving pharmacological stabilization of misfolded and misrouted mutant MCRs, which improve their forward transport, are reported. Understanding the MCRs' structural determinants fundamental for their proper cell surface integration is essential for correcting abnormalities found in some diseases.
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Affiliation(s)
- A R Rodrigues
- Department of Experimental Biology, Faculty of Medicine, University of Porto, Alameda Prof. Hernâni Monteiro, 4200-319 Porto, Portugal Instituto de Biologia Molecular e Celular (IBMC), University of Porto, Porto, Portugal IPATIMUP, Institute of Molecular Pathology and Immunology Faculty of Nutrition and Food Sciences, University of Porto, Porto, Portugal
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19
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Agulleiro MJ, Sánchez E, Leal E, Cortés R, Fernández-Durán B, Guillot R, Davis P, Dores RM, Gallo-Payet N, Cerdá-Reverter JM. Molecular characterization and functional regulation of melanocortin 2 receptor (MC2R) in the sea bass. A putative role in the adaptation to stress. PLoS One 2013; 8:e65450. [PMID: 23724142 PMCID: PMC3664627 DOI: 10.1371/journal.pone.0065450] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2011] [Accepted: 04/25/2013] [Indexed: 01/11/2023] Open
Abstract
The activation of melanocortin 2 receptor (MC2R) by ACTH mediates the signaling cascade leading to steroid synthesis in the interrenal tissue (analogous to the adrenal cortex in mammals) of fish. However, little is known about the functional regulation of this receptor in fish. In this work described, we cloned sea bass MC2R from a liver cDNA. SbMC2R requires the melanocortin 2 receptor accessory protein (MRAP) for its functional expression. Dietary cortisol but not long-term stress protocols downregulated interrenal sbMC2R expression. Data suggest the existence of a negative feedback on interrenal sbMC2R expression imposed by local or systemic glucocorticoids. This feedback could be involved in long-term stress adaptation by regulating interrenal sensitivity to ACTH. ACTH-induced MC2R activation stimulates hepatic lipolysis, suggesting that ACTH may mediate stress-induced effects upstream of cortisol release.
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MESH Headings
- Adaptation, Biological/genetics
- Adrenocorticotropic Hormone/pharmacology
- Amino Acid Sequence
- Animals
- Bass/genetics
- Bass/metabolism
- CHO Cells
- Cloning, Molecular
- Cricetulus
- Fasting
- Gene Expression
- Gene Expression Regulation/drug effects
- Lipid Metabolism/drug effects
- Liver/drug effects
- Liver/metabolism
- Molecular Sequence Data
- Organ Specificity/genetics
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Receptor, Melanocortin, Type 2/agonists
- Receptor, Melanocortin, Type 2/chemistry
- Receptor, Melanocortin, Type 2/genetics
- Receptor, Melanocortin, Type 2/metabolism
- Sequence Alignment
- Stress, Physiological/genetics
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Affiliation(s)
- Maria Josep Agulleiro
- Department of Fish Physiology and Biotechnology, Instituto de Acuicultura de Torre de la Sal, Consejo Superior de Investigaciones Científicas (IATS-CSIC), Castellón, Spain
| | - Elisa Sánchez
- Department of Fish Physiology and Biotechnology, Instituto de Acuicultura de Torre de la Sal, Consejo Superior de Investigaciones Científicas (IATS-CSIC), Castellón, Spain
| | - Esther Leal
- Department of Fish Physiology and Biotechnology, Instituto de Acuicultura de Torre de la Sal, Consejo Superior de Investigaciones Científicas (IATS-CSIC), Castellón, Spain
| | - Raúl Cortés
- Department of Fish Physiology and Biotechnology, Instituto de Acuicultura de Torre de la Sal, Consejo Superior de Investigaciones Científicas (IATS-CSIC), Castellón, Spain
| | - Begoña Fernández-Durán
- Department of Fish Physiology and Biotechnology, Instituto de Acuicultura de Torre de la Sal, Consejo Superior de Investigaciones Científicas (IATS-CSIC), Castellón, Spain
| | - Raúl Guillot
- Department of Fish Physiology and Biotechnology, Instituto de Acuicultura de Torre de la Sal, Consejo Superior de Investigaciones Científicas (IATS-CSIC), Castellón, Spain
| | - Perry Davis
- Department of Biological Sciences, University of Denver, Denver, Colorado, United States of America
| | - Robert M. Dores
- Department of Biological Sciences, University of Denver, Denver, Colorado, United States of America
| | - Nicole Gallo-Payet
- Department of Medicine, University of Sherbrooke, Sherbrooke, Québec, Canada
| | - José Miguel Cerdá-Reverter
- Department of Fish Physiology and Biotechnology, Instituto de Acuicultura de Torre de la Sal, Consejo Superior de Investigaciones Científicas (IATS-CSIC), Castellón, Spain
- * E-mail:
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20
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Kay EI, Botha R, Montgomery JM, Mountjoy KG. hMRAPa increases αMSH-induced hMC1R and hMC3R functional coupling and hMC4R constitutive activity. J Mol Endocrinol 2013; 50:203-15. [PMID: 23296982 DOI: 10.1530/jme-12-0221] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Human melanocortin 2 receptor accessory protein (hMRAPa) is hypothesised to have functions beyond promoting human melanocortin 2 receptor (hMC2R) functional expression. To understand these potential functions, we exogenously co-expressed hMRAPa-FLAG with each of the five hMCR subtypes in HEK293 cells and assessed hMCR subtype coupling to adenylyl cyclase. We also co-expressed each HA-hMCR subtype with hMRAPa-FLAG to investigate their subcellular localisation. hMRAPa-FLAG enhanced α-melanocyte stimulating hormone (α-MSH)-stimulated hMC1R and hMC3R but reduced NDP-α-MSH-stimulated hMC5R, maximum coupling to adenylyl cyclase. hMRAPa-FLAG specifically increased hMC4R constitutive coupling to adenylyl cyclase despite not co-localising with the HA-hMC4R in the cell membrane. hMRAPa-FLAG co-localised with HA-hMC1R or HA-hMC3R in the perinuclear region, in cytoplasmic vesicles and at the plasma membrane, while it co-localised with HA-hMC2R, HA-hMC4R and HA-hMC5R predominantly in cytoplasmic vesicles. These diverse effects of hMRAPa indicate that hMRAPa could be an important modulator of the central and peripheral melanocortin systems if hMRAPa and any hMCR subtype co-express in the same cell.
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Affiliation(s)
- Emma I Kay
- Department of Physiology, Faculty of Medical and Health Sciences, University of Auckland, Auckland 1142, New Zealand
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21
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Kay EI, Botha R, Montgomery JM, Mountjoy KG. hMRAPa specifically alters hMC4R molecular mass and N-linked complex glycosylation in HEK293 cells. J Mol Endocrinol 2013; 50:217-27. [PMID: 23307947 DOI: 10.1530/jme-12-0220] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Human melanocortin 2 receptor accessory protein 1(hMRAPa) is essential for human melanocortin 2 receptor (hMC2R)-regulated adrenal steroidogenesis. hMRAPa enhances hMC2R N-linked glycosylation and maturation, promotes hMC2R cell surface expression and enables ACTH to bind and activate the MC2R. However, hMRAPa is predicted to have functions beyond its critical role in hMC2R activity. It is more widely expressed than the hMC2R and it has been shown to co-immunoprecipitate with all other hMCR subtypes and other G-protein-coupled receptors, when these are co-expressed with each receptor in heterologous cells. The physiological relevance of hMRAPa interactions with these receptors is unknown. We hypothesised that hMRAPa could influence post-translational processing and maturation of these receptors, similar to its actions on the hMC2R. Here we used co-immunoprecipitation and western blotting techniques to characterise effects of hMRAPa-FLAG co-expression on the maturation of each HA-tagged hMCR subtype and the HA-tagged human calcitonin receptor-like receptor (hCL), co-expressed in HEK293 cells. While hMRAPa-FLAG interacted with all five HA-hMCR subtypes and the HA-hCL, it only altered HA-hMC4R molecular mass. This altered HA-hMC4R molecular mass was due to a change in endoglycosidase H-resistant complex N-linked glycosylation, which we observed for HA-hMC4R in both intracellular and cell surface fractions. This effect was specific to the HA-hMC4R as hMRAPa did not alter the molecular mass of any of the other receptors that we examined. In conclusion, the specific effects of hMRAPa on hMC4R molecular mass and complex N-linked glycosylation provide evidence in support of a role for MRAPα in hMC4R functions.
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Affiliation(s)
- Emma I Kay
- Department of Physiology, Faculty of Medical and Health Sciences, University of Auckland, Auckland 1142, New Zealand
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22
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Dreses-Werringloer U, Vingtdeux V, Zhao H, Chandakkar P, Davies P, Marambaud P. CALHM1 controls the Ca²⁺-dependent MEK, ERK, RSK and MSK signaling cascade in neurons. J Cell Sci 2013; 126:1199-206. [PMID: 23345406 DOI: 10.1242/jcs.117135] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Calcium homeostasis modulator 1 (CALHM1) is a Ca(2+) channel controlling neuronal excitability and potentially involved in the pathogenesis of Alzheimer's disease (AD). Although strong evidence indicates that CALHM1 is required for neuronal electrical activity, its role in intracellular Ca(2+) signaling remains unknown. In the present study, we show that in hippocampal HT-22 cells, CALHM1 expression led to a robust and relatively selective activation of the Ca(2+)-sensing kinases ERK1/2. CALHM1 also triggered activation of MEK1/2, the upstream ERK1/2-activating kinases, and of RSK1/2/3 and MSK1, two downstream effectors of ERK1/2 signaling. CALHM1-mediated activation of ERK1/2 signaling was controlled by the small GTPase Ras. Pharmacological inhibition of CALHM1 permeability using Ruthenium Red, Zn(2+), and Gd(3+), or expression of the CALHM1 N140A and W114A mutants, which are deficient in mediating Ca(2+) influx, prevented the effect of CALHM1 on the MEK, ERK, RSK and MSK signaling cascade, demonstrating that CALHM1 controlled this pathway via its channel properties. Importantly, expression of CALHM1 bearing the natural P86L polymorphism, which leads to a partial loss of CALHM1 function and is associated with an earlier age at onset in AD patients, showed reduced activation of ERK1/2, RSK1/2/3, and MSK1. In line with these results obtained in transfected cells, primary cerebral neurons isolated from Calhm1 knockout mice showed significant impairments in the activation of MEK, ERK, RSK and MSK signaling. The present study identifies a previously uncharacterized mechanism of control of Ca(2+)-dependent ERK1/2 signaling in neurons, and further establishes CALHM1 as a critical ion channel for neuronal signaling and function.
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Affiliation(s)
- Ute Dreses-Werringloer
- Litwin-Zucker Research Center for the Study of Alzheimer's Disease, The Feinstein Institute for Medical Research, Manhasset, New York, USA
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Abreu AP, Noel SD, Xu S, Carroll RS, Latronico AC, Kaiser UB. Evidence of the importance of the first intracellular loop of prokineticin receptor 2 in receptor function. Mol Endocrinol 2012; 26:1417-27. [PMID: 22745195 DOI: 10.1210/me.2012-1102] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Prokineticin receptors (PROKR) are G protein-coupled receptors (GPCR) that regulate diverse biological processes, including olfactory bulb neurogenesis and GnRH neuronal migration. Mutations in PROKR2 have been described in patients with varying degrees of GnRH deficiency and are located in diverse functional domains of the receptor. Our goal was to determine whether variants in the first intracellular loop (ICL1) of PROKR2 (R80C, R85C, and R85H) identified in patients with hypogonadotropic hypogonadism interfere with receptor function and to elucidate the mechanisms of these effects. Because of structural homology among GPCR, clarification of the role of ICL1 in PROKR2 activity may contribute to a better understanding of this domain across other GPCR. The effects of the ICL1 PROKR2 mutations on activation of signal transduction pathways, ligand binding, and receptor expression were evaluated. Our results indicated that the R85C and R85H PROKR2 mutations interfere only modestly with receptor function, whereas the R80C PROKR2 mutation leads to a marked reduction in receptor activity. Cotransfection of wild-type (WT) and R80C PROKR2 showed that the R80C mutant could exert a dominant negative effect on WT PROKR2 in vitro by interfering with WT receptor expression. In summary, we have shown the importance of Arg80 in ICL1 for PROKR2 expression and demonstrate that R80C PROKR2 exerts a dominant negative effect on WT PROKR2.
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Affiliation(s)
- Ana Paula Abreu
- Division of Endocrinology, Diabetes, and Hypertension, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA
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24
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Zhu J, Yan J, Thornhill WB. N-glycosylation promotes the cell surface expression of Kv1.3 potassium channels. FEBS J 2012; 279:2632-44. [PMID: 22613618 DOI: 10.1111/j.1742-4658.2012.08642.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The voltage-gated potassium channel Kv1.3 plays an essential role in modulating membrane excitability in many cell types. Kv1.3 is a heavily glycosylated membrane protein. Two successive N-glycosylation consensus sites, N228NS and N229ST, are present on the S1-S2 linker of rat Kv1.3. Our data suggest that Kv1.3 contains only one N-glycan and it is predominantly attached to N229 in the S1-S2 extracellular linker. Preventing N-glycosylation of Kv1.3 significantly decreased its surface protein level and surface conductance density level, which were ∼ 49% and ∼ 46% respectively of the level of wild type. Supplementation of N-acetylglucosamine (GlcNAc), l-fucose or N-acetylneuraminic acid to the culture medium promoted Kv1.3 surface protein expression, whereas supplementation of d-glucose, d-mannose or d-galactose did not. Among the three effective monosaccharides/derivatives, adding GlcNAc appeared to reduce sialic acid content and increase the degree of branching in the N-glycan of Kv1.3, suggesting that the N-glycan structure and composition had changed. Furthermore, the cell surface half-life of the Kv1.3 surface protein was increased upon GlcNAc supplementation, indicating that it had decreased internalization. The GlcNAc effect appears to apply mainly to membrane proteins containing complex type N-glycans. Thus, N-glycosylation promotes Kv1.3 cell surface expression; supplementation of GlcNAc increased Kv1.3 surface protein level and decreased its internalization, presumably by a combined effect of decreased branch size and increased branching of the N-glycan.
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Affiliation(s)
- Jing Zhu
- Department of Biological Sciences and Center for Cancer, Genetic Diseases and Gene Regulation, Fordham University, Bronx, NY, USA
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Roy S, Roy SJ, Pinard S, Agulleiro MJ, Cerdá-Reverter JM, Parent JL, Gallo-Payet N. The C-terminal domains of melanocortin-2 receptor (MC2R) accessory proteins (MRAP1) influence their localization and ACTH-induced cAMP production. Gen Comp Endocrinol 2012; 176:265-74. [PMID: 22366472 DOI: 10.1016/j.ygcen.2012.02.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/30/2011] [Revised: 02/01/2012] [Accepted: 02/05/2012] [Indexed: 01/13/2023]
Abstract
ACTH binding to the human melanocortin-2 receptor (MC2R) requires the presence of the MC2R accessory protein1 isoforms, MRAPα or MRAPβ. This study evaluated the role of the isoform-specific C-terminal domains of MRAP with regard to their cellular localization, topology, interaction with MRAP2 and cAMP production. When stably expressed in HEK293/FRT cells or in B16-G4F mouse melanoma cells (an MSH receptor-deficient cell clone), MRAPα and MRAPdCT (truncated MRAP1, N-terminal only) localized mainly around the nuclear envelope and within dense intracellular endosomes, while MRAPβ exhibited a strong localization at the plasma membrane, and partially with rapid recycling endosomes. MRAPβ and MRAPdCT both exhibited dual-topology (N(cyto)/C(exo) and N(exo)/C(cyto)) at the plasma membrane whereas MRAPα exhibited only N(cyto)/C(exo) topology at the plasma membrane while adopting dual-topology in intracellular compartments. Both MRAPα and MRAP2 colocalized in intracellular compartments, as opposed to weak colocalization between MRAPβ and MRAP2. MRAP2 and MC2R enhanced the expression of MRAP1 isoforms and vice versa. Moreover, in both HEK293/FRT and B16-G4F cells, ACTH failed to activate MC2R unless MRAP1 was present. MRAP1 expression enhanced MC2R cell-surface expression as well as concentration-dependent cAMP accumulation. In the presence of human or zebrafish MC2R, MRAPβ induced the highest cAMP accumulation while MRAPdCT induced the lowest. Together, the present findings indicate that the C-terminal domains of MRAP dictate their intracellular localization in addition to regulating ACTH-induced cAMP production. These preferential localizations suggest that MRAPα is involved in MC2R targeting to the plasma membrane, while MRAPβ may enhance ACTH-MC2R coupling to cAMP production.
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Affiliation(s)
- Simon Roy
- Service d'Endocrinologie, Département de Médecine, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, Québec, Canada J1H 5N4
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Roy S, Roy SJ, Pinard S, Taillefer LD, Rached M, Parent JL, Gallo-Payet N. Mechanisms of melanocortin-2 receptor (MC2R) internalization and recycling in human embryonic kidney (hek) cells: identification of Key Ser/Thr (S/T) amino acids. Mol Endocrinol 2011; 25:1961-77. [PMID: 21920850 DOI: 10.1210/me.2011-0018] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
ACTH is the most important stimulus of the adrenal cortex. The precise molecular mechanisms underlying the ACTH response are not yet clarified. The functional ACTH receptor includes melanocortin-2 receptor (MC2R) and MC2R accessory proteins (MRAP). In human embryonic kidney 293/Flp recombinase target cells expressing MC2R, MRAP1 isoforms, and MRAP2, we found that ACTH induced a concentration-dependent and arrestin-, clathrin-, and dynamin-dependent MC2R/MRAP1 internalization, followed by intracellular colocalization with Rab (Ras-like small guanosine triphosphate enzyme)4-, Rab5-, and Rab11-positive recycling endosomes. Preincubation of cells with monensin and brefeldin A revealed that 28% of the internalized receptors were recycled back to the plasma membrane and participated in total accumulation of cAMP. Moreover, certain intracellular Ser and Thr (S/T) residues of MC2R were found to play important roles not only in plasma membrane targeting and function but also in promoting receptor internalization. The S/T residues T131, S140, T204, and S280 were involved in MRAP1-independent cell-surface MC2R expression. Other mutants (S140A, S208A, and S202D) had lower cell-surface expressions in absence of MRAPβ. In addition, T143A and T147D drastically impaired cell-surface expression and function, whereas T131A, T131D, and S280D abrogated MC2R internalization. Thus, the modification of MC2R intracellular S/T residues may positively or negatively regulate its plasma membrane expression and the capacity of ACTH to induce cAMP accumulation. Mutations of T131, T143, T147, and S280 into either A or D had major repercussions on cell-surface expression, cAMP accumulation, and/or internalization parameters, pointing mostly to the second intracellular loop as being crucial for MC2R expression and functional regulation.
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Affiliation(s)
- Simon Roy
- Service d'Endocrinologie, Département de Médecine, Université de Sherbrooke, Québec, Canada
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Romero-Fernandez W, Borroto-Escuela DO, Perez Alea M, Garcia-Mesa Y, Garriga P. Altered trafficking and unfolded protein response induction as a result of M3 muscarinic receptor impaired N-glycosylation. Glycobiology 2011; 21:1663-72. [DOI: 10.1093/glycob/cwr105] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
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28
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Roy S, Pinard S, Chouinard L, Gallo-Payet N. Adrenocorticotropin hormone (ACTH) effects on MAPK phosphorylation in human fasciculata cells and in embryonic kidney 293 cells expressing human melanocortin 2 receptor (MC2R) and MC2R accessory protein (MRAP)β. Mol Cell Endocrinol 2011; 336:31-40. [PMID: 21195128 DOI: 10.1016/j.mce.2010.12.030] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/16/2010] [Revised: 12/20/2010] [Accepted: 12/21/2010] [Indexed: 11/15/2022]
Abstract
Adrenocorticotropin hormone (ACTH) exerts trophic effects on adrenocortical cells. We studied the phosphorylation of mitogen-activated proteins kinases (MAPKs) in human embryonic kidney cells stably expressing the ACTH receptor, MC2R, and its accessory protein MRAPβ and in primary cultures of human adrenal fasciculata cells. ACTH induced a maximal increase in p44/p42(mapk) and of p38 MAPK phosphorylation after 5min. Neither the overexpression of wild-type arrestin2, arrestin3 or their respective dominant negative forms affected p44/p42(mapk) phosphorylation. However, preincubation with the recycling inhibitors brefeldin A and monensin attenuated both cAMP accumulation and p44/p42(mapk) phosphorylation proportionally. Cyclic AMP-related PKA inhibitors (H89, KI(6-22)) and Rp-cAMPS decreased p44/p42(mapk) phosphorylation but not ACTH-mediated cAMP production. The selective Epac1/2 activator, 8-pCPT-2'-O-MecAMP, did not modify the effect of ACTH. Thus, cAMP/PKA, but not cAMP/Epac1/2 pathways, or arrestin-coupled internalization of MC2R is involved in ACTH-induced p44/p42(mapk) phosphorylation by human MC2R. Together, ACTH binding to MC2R stimulates PKA-dependent p44/p42(mapk) phosphorylation.
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Affiliation(s)
- Simon Roy
- Service d'Endocrinologie, Département de Médecine, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, Québec, Canada J1H 5N4
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Herraiz C, Sánchez-Laorden BL, Jiménez-Cervantes C, García-Borrón JC. N-glycosylation of the human melanocortin 1 receptor: occupancy of glycosylation sequons and functional role. Pigment Cell Melanoma Res 2011; 24:479-89. [PMID: 21410905 DOI: 10.1111/j.1755-148x.2011.00848.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The melanocortin 1 receptor (MC1R), a major determinant of skin pigmentation and phototype, mediates the actions of α-melanocyte-stimulating hormone on melanocytes and is critical for melanocyte proliferation and differentiation. MC1R has two putative N-glycosylation targets, Asn15 and Asn29. It has been shown that MC1R is a glycoprotein with an unusual sensitivity to endoglycosidase H digestion. However, the occupancy and functional importance of each specific glycosylation sequon remains unknown. We demonstrate that MC1R is N-glycosylated at Asn15 and Asn29, with structurally and functionally different glycan chains. N-glycosylation is not necessary for high affinity agonist binding or functional coupling but has a strong effect on the availability of MC1R molecules on the plasma membrane, most likely by a combination of improved forward trafficking and decreased internalization. Finally, we found that MC1R variants exhibit different degrees of glycosylation which do not show a simple correlation with their functional status or intracellular trafficking.
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Affiliation(s)
- Cecilia Herraiz
- Department of Biochemistry and Molecular Biology, School of Medicine, University of Murcia, Murcia, Spain
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Use of chimeric melanocortin-2 and -4 receptors to identify regions responsible for ligand specificity and dependence on melanocortin 2 receptor accessory protein. Eur J Pharmacol 2011; 660:94-102. [PMID: 21211532 DOI: 10.1016/j.ejphar.2010.10.113] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2010] [Revised: 10/15/2010] [Accepted: 10/31/2010] [Indexed: 01/07/2023]
Abstract
The melanocortin 2 (MC(2)) receptor differs from other melanocortin family members in its pharmacological profile and reliance on an accessory protein, MC(2) receptor accessory protein (MRAP), for surface expression and signal transduction. To identify features of the MC(2) receptor responsible for these characteristics, we created chimeras between MC(2) and MC(4) receptors and expressed these in CHO cells, where MRAP is essential for trafficking and signaling by MC(2) but not MC(4) receptors. Replacing the first transmembrane segment of the MC(2) receptor with the corresponding region from the MC(4) receptor allowed some surface expression in the absence of an accessory protein, while ACTH-induced cAMP production remained entirely MRAP-dependent. On the other hand, replacing the last two transmembrane domains, third extracellular loop and C-terminal tail of the MC(4) receptor with the corresponding regions from the MC(2) receptor resulted in MRAP-dependent signaling. Surprisingly, replacing the second and third transmembrane domains and the intervening first extracellular loop of MC(2) receptors with MC(4) sequences generated a chimera (2C2) that responded to both adrenocorticotropic hormone (ACTH) and to the potent MSH analog 4-norleucine-7-d-phenylalanine-α-melanocyte stimulating hormone (NDP-α-MSH), which does not activate native MC(2) receptors. The 2C2 chimeric receptor was able to respond to NDP-α-MSH without MRAP, but MRAP shifted the EC50 value for NDP-α-MSH to the left and caused constitutive activity. These results identify the first transmembrane domain as important for surface expression and regions from the second to third transmembrane segments of the MC(2) receptor as important for MRAP dependent-signal transduction and ligand specificity.
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Sebag JA, Hinkle PM. Regulation of G protein-coupled receptor signaling: specific dominant-negative effects of melanocortin 2 receptor accessory protein 2. Sci Signal 2010; 3:ra28. [PMID: 20371771 DOI: 10.1126/scisignal.2000593] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs), which constitute the largest family of membrane proteins, mediate responses to diverse physiological stimuli. The presence of melanocortin 2 receptors (MC2Rs) on the plasma membrane requires the presence of either MC2R accessory protein (MRAP) or MRAP2, which are homologous accessory proteins. Here, we show that, whereas MRAP was essential for activation of MC2R signaling, MRAP2 was an endogenous inhibitor that competed with MRAP for binding to MC2R and decreased the potency of adrenocorticotropic hormone (ACTH), the endogenous agonist for MC2Rs, in stimulating the production of adenosine 3',5'-monophosphate (cAMP). ACTH bound with high affinity to MC2Rs in the presence of MRAP, but not MRAP2. The ability of MRAP and MRAP2 to influence ligand-binding affinity was specific to MC2R, because these proteins had little effect on the binding of NDP-alpha-melanocyte-stimulating hormone to MC4R or on its stimulation of cAMP responses. These results demonstrate that the balance of stimulatory and inhibitory accessory proteins can control the sensitivity of a GPCR to its natural agonist.
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Affiliation(s)
- Julien A Sebag
- Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, NY 14642, USA
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