title: Microphthalmia-associated transcription factor (MITF) is required but is not sufficient to induce the expression of melanogenic genes.
abstract: Microphthalmia-associated transcription factor (MITF) plays a pivotal role in melanocyte survival and differentiation. Nevertheless, until now it has not been possible to show that MITF regulates the expression of the endogenous tyrosinase or Tyrp1. Further, a direct involvement of MITF in the regulation of melanin synthesis, a key parameter of melanocyte differentiation, remains to be demonstrated. In the present report, using recombinant adenovirus encoding the wild-type or a dominant negative form of MITF, as well as stable cell lines expressing tetracycline inducible wild-type MITF, we reassessed the role of MITF in melanocyte differentiation and in the regulation of melanin synthesis. Immunofluorescence studies, as well as Western blot analyses, show that infection of B16 mouse melanoma cells or human melanocytes with adenovirus encoding wild-type MITF does not increase the expression of the endogenous melanogenic enzymes. However, infection with the MITF dominant negative mutant inhibits the expression of endogenous tyrosinase and Tyrp1 proteins and blocks cAMP-induced melanin synthesis. Thus, MITF is required but does not seem to be sufficient to induce the expression of melanogenic enzymes and we show for the first time a direct involvement of MITF in the regulation of melanin pigment synthesis. As a whole, our data point to the existence of still unknown regulatory mechanisms that co-operate or synergize with MITF to control melanogenic gene expression and melanin synthesis. The identification of such mechanisms will greatly improve our understanding of the melanocyte differentiation processes.
authors.affiliation: Faculté de Médecine, Biologie et Physiopathologie de la Peau, Nice cedex, France.
authors.forename: Cédric
authors.initials: C
authors.lastname: Gaggioli
authors.forename: Roser
authors.initials: R
authors.lastname: Buscà
authors.forename: Patricia
authors.initials: P
authors.lastname: Abbe
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Ortonne
authors.forename: Robert
authors.initials: R
authors.lastname: Ballotti
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D000242:Cyclic AMP / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000502:physiology*; D015870:Gene Expression; D005822:Genetic Vectors; D006801:Humans; D008543:Melanins / Q000096:biosynthesis*; D008544:Melanocytes / Q000201:enzymology / Q000378:metabolism*; D008545:Melanoma / Q000378:metabolism; D008562:Membrane Glycoproteins; D051379:Mice; D051739:Microphthalmia-Associated Transcription Factor; D014442:Monophenol Monooxygenase / Q000378:metabolism; D010088:Oxidoreductases; D011506:Proteins / Q000378:metabolism; D013752:Tetracycline / Q000494:pharmacology; D014157:Transcription Factors / Q000502:physiology*; D015854:Up-Regulation
chemical_list: D004268:DNA-Binding Proteins; C497234:MITF protein, human; D008543:Melanins; D008562:Membrane Glycoproteins; D051739:Microphthalmia-Associated Transcription Factor; C497235:Mitf protein, mouse; D011506:Proteins; D014157:Transcription Factors; D000242:Cyclic AMP; D010088:Oxidoreductases; C489799:TYRP1 protein, human; C079621:Tyrp1 protein, mouse; C064056:tyrosinase-related protein-1; D014442:Monophenol Monooxygenase; D013752:Tetracycline