title: Inhibition of the mitogen-activated protein kinase pathway triggers B16 melanoma cell differentiation.
abstract: In B16 melanoma cells, mitogen-activated protein (MAP) kinases are activated during cAMP-induced melanogenesis (Englaro, W., Rezzonico, R., Durand-Clément, M., Lallemand, D., Ortonne, J. P., and Ballotti, R. (1995) J. Biol. Chem. 270, 24315-24320). To establish the role of the MAP kinases in melanogenesis, we studied the effects of a specific MAP kinase kinase (MEK) inhibitor PD 98059 on different melanogenic parameters. We showed that PD 98059 inhibits the activation of MAP kinase extracellular signal-regulated kinase 1 by cAMP, but does not impair the effects of cAMP either on the morphological differentiation, characterized by an increase in dendrite outgrowth, or on the up-regulation of tyrosinase that is the key enzyme in melanogenesis. On the contrary, PD 98059 promotes by itself cell dendricity and increases the tyrosinase amount and activity. Moreover, down-regulation of the MAP kinase pathway by PD 98059, or with dominant negative mutants of p21(ras) and MEK, triggers a stimulation of the tyrosinase promoter activity and enhances the effect of cAMP on this parameter. Conversely, activation of the MAP kinase pathway, using constitutive active mutants of p21(ras) and MEK, leads to an inhibition of basal and cAMP-induced tyrosinase gene transcription. These results demonstrate that the MAP kinase pathway activation is not required for cAMP-induced melanogenesis. Furthermore, the inhibition of this pathway induces B16 melanoma cell differentiation, while a sustained activation impairs the melanogenic effect of cAMP-elevating agents.
authors.affiliation: INSERM U-385, Faculté de médecine, Avenue de Valombrose, 06107 Nice Cedex 2, France.
authors.forename: W
authors.initials: W
authors.lastname: Englaro
authors.forename: C
authors.initials: C
authors.lastname: Bertolotto
authors.forename: R
authors.initials: R
authors.lastname: Buscà
authors.forename: A
authors.initials: A
authors.lastname: Brunet
authors.forename: G
authors.initials: G
authors.lastname: Pagès
authors.forename: J P
authors.initials: JP
authors.lastname: Ortonne
authors.forename: R
authors.initials: R
authors.lastname: Ballotti
mesh_terms: D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005419:Flavonoids / Q000494:pharmacology*; D008156:Luciferases / Q000378:metabolism; D008546:Melanoma, Experimental / Q000473:pathology*; D051379:Mice; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D014442:Monophenol Monooxygenase / Q000378:metabolism; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D004791:Enzyme Inhibitors; D005419:Flavonoids; D047428:Protein Kinase Inhibitors; D011993:Recombinant Fusion Proteins; D005576:Colforsin; D000242:Cyclic AMP; D008156:Luciferases; D014442:Monophenol Monooxygenase; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D013755:Tetradecanoylphorbol Acetate; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one