title: Functional status and relationships of melanocortin 1 receptor signaling to the cAMP and extracellular signal-regulated protein kinases 1 and 2 pathways in human melanoma cells.
abstract: Melanocortin 1 receptor (MC1R), a major determinant of skin phototype frequently mutated in melanoma, is a Gs protein-coupled receptor that regulates pigment production in melanocytes. MC1R stimulation activates cAMP synthesis and the extracellular signal-regulated (ERK) ERK1 and ERK2. In human melanocytes, ERK activation by MC1R relies on cAMP-independent transactivation of the c-KIT receptor. Thus MC1R functional coupling to the cAMP and ERK pathways may involve different structural requirements giving raise to biased effects of skin cancer-associated mutations. We evaluated the impact of MC1R mutations on ERK activation, cAMP production and agonist binding. We found that MC1R mutations impair cAMP production much more often than ERK activation, suggesting less stringent requirements for functional coupling to the ERK pathway. We examined the crosstalk of the cAMP and ERK pathways in HBL human melanoma cells (wild-type for MC1R, NRAS and BRAF). ERK activation by constitutively active upstream effectors or pharmacological inhibition had little effect on MC1R-stimulated cAMP synthesis. High cAMP levels were compatible with normal ERK activation but, surprisingly, the adenylyl cyclase activator forskolin abolished ERK activation by MC1R, most likely by a cAMP-independent mechanism. These results indicate little crosstalk of the cAMP and ERK pathways in HBL melanoma cells. Finally, we studied cAMP accumulation in a panel of 22 human melanoma cell lines stimulated with MC1R agonists or forskolin. cAMP synthesis was often inhibited, even in cells wild-type for MC1R and NRAS. Therefore, the cAMP pathway is more frequently impaired in melanoma than could be predicted by the MC1R or NRAS genotype.
authors.affiliation: Department of Biochemistry and Molecular Biology, School of Medicine, University of Murcia, Campus de Espinardo, Murcia, Spain.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Herraiz
authors.forename: Fabrice
authors.initials: F
authors.lastname: Journé
authors.forename: Ghanem
authors.initials: G
authors.lastname: Ghanem
authors.forename: Celia
authors.initials: C
authors.lastname: Jiménez-Cervantes
authors.forename: José C
authors.initials: JC
authors.lastname: García-Borrón
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D045744:Cell Line, Tumor; D000242:Cyclic AMP / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D020935:MAP Kinase Signaling System; D008545:Melanoma; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics / Q000378:metabolism; D044102:Receptor, Melanocortin, Type 1 / Q000235:genetics / Q000378:metabolism*; D015290:Second Messenger Systems
chemical_list: D008565:Membrane Proteins; D044102:Receptor, Melanocortin, Type 1; D000242:Cyclic AMP; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; C535150:MAPK1 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020558:GTP Phosphohydrolases; C579846:NRAS protein, human