title: Characterization of density-dependent regulation of the tyrosinase gene promoter: role of protein kinase C.
abstract: The rate-limiting step in melanogenesis is catalyzed by tyrosinase, a multifunctional enzyme encoded by the albino locus. We have previously reported that depletion of protein kinase C by long-term treatment of B16 mouse melanoma cells with phorbol dibutyrate (PDBu) prevented cell density-dependent melanogenesis. This was accompanied by a lack of induction of tyrosinase protein and mRNA. We report here the effect of PDBu on the functional activity of the mouse tyrosinase promoter by reporter gene assay and its effect on the binding of nuclear proteins from B16 cells to the "M-box" region of the mouse tyrosinase promoter. Short-term PDBu treatment of B16 cells transfected with a mouse tyrosinase promoter-luciferase construct resulted in increased reporter gene activity, while long-term PDBu treatment inhibited reporter gene activity. Using an oligonucleotide containing the M-box and its flanking residues in electrophoretic mobility shift assays, we found a density-dependent change in the pattern of DNA-protein complexes. One complex was found to be negatively regulated by long-term PDBu treatment. Competition experiments with various mutated oligonucleotides demonstrated that both the M-box and flanking residues are important for nuclear protein binding. The complex whose formation was inhibited by long-term PDBu treatment was shown to contain the basic helix-loop-helix leucine zipper protein microphthalmia-associated transcription factor (MITF). These results suggest that chronic PDBu treatment might inhibit tyrosinase expression (and subsequent melanogenesis) by affecting the amount or function of MITF.
authors.affiliation: Department of Biochemistry and Molecular Biology, Marshall University School of Medicine, Huntington, West Virginia 25755, USA.
authors.forename: H
authors.initials: H
authors.lastname: Mahalingam
authors.forename: A
authors.initials: A
authors.lastname: Watanabe
authors.forename: M
authors.initials: M
authors.lastname: Tachibana
authors.forename: R M
authors.initials: RM
authors.lastname: Niles
mesh_terms: D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D017930:Genes, Reporter; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism*; D008156:Luciferases / Q000096:biosynthesis; D008546:Melanoma, Experimental; D051379:Mice; D008969:Molecular Sequence Data; D014442:Monophenol Monooxygenase / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D011493:Protein Kinase C / Q000378:metabolism*; D051571:Protein Kinase C-alpha; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D004268:DNA-Binding Proteins; D007527:Isoenzymes; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D015240:Phorbol 12,13-Dibutyrate; D008156:Luciferases; D014442:Monophenol Monooxygenase; C496628:PRKCA protein, human; C496630:Prkca protein, mouse; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha