title: Stimulation of melanoblast pigmentation by 8-methoxypsoralen:the involvement of microphthalmia-associated transcription factor, the protein kinase a signal pathway, and proteasome-mediated degradation.
abstract: In this study, we used melb-a melanoblasts as a model to study mechanisms involved in stimulating melanocyte function in vitiliginous skin following exposure to 8-methoxypsoralen (8MOP). Melanin content and tyrosinase activity increased 3- and 7-fold, respectively, in melanoblasts treated with 8MOP for 6 d compared with untreated controls. The intracellular signal pathways involved in 8MOP-induced effects on melanoblasts were investigated, particularly the roles of protein kinase A and protein kinase C. Forskolin, a protein kinase A activator, mimicked and enhanced the 8MOP stimulation of melanoblast pigmentation whereas a protein kinase C activator, 1-oleoyl-2-acetylglycerol, had no effect, indicating that the protein kinase A pathway is involved rather than the protein kinase C pathway. Those observations were confirmed using inhibitors of the protein kinase A or protein kinase C pathways. Western blot and semiquantitative reverse transcriptase polymerase chain reaction were performed to assess the protein and mRNA expression levels of microphthalmia-associated transcription factor and tyrosinase in melanoblasts treated with 8MOP for 3 h, 6 h, 1 d, 3 d, or 6 d. Incubation with 8MOP stimulated microphthalmia-associated transcription factor protein and mRNA levels within 3 h, but, in contrast, tyrosinase mRNA and protein levels did not increase following 8MOP treatment until 1 d after treatment. The proteasome inhibitor lactacystin blocked the proteasome-mediated proteolysis of tyrosinase, and its effect on proteasomal function was enhanced by 8MOP. Taken together, these results show that 8MOP functions by initially stimulating levels of microphthalmia-associated transcription factor expression via activation of the protein kinase A pathway, which thereby stimulates tyrosinase expression and function and eventually leads to dramatic increases in melanin production by melanoblasts.
authors.affiliation: Pigment Cell Biology Section, Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Tie Chi
authors.initials: TC
authors.lastname: Lei
authors.forename: Victoria
authors.initials: V
authors.lastname: Virador
authors.forename: Ken-Ichi
authors.initials: K
authors.lastname: Yasumoto
authors.forename: Wilfred D
authors.initials: WD
authors.lastname: Vieira
authors.forename: Kazutomo
authors.initials: K
authors.lastname: Toyofuku
authors.forename: Vincent J
authors.initials: VJ
authors.lastname: Hearing
mesh_terms: D000818:Animals; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression / Q000187:drug effects / Q000502:physiology; D008543:Melanins / Q000378:metabolism; D008544:Melanocytes / Q000166:cytology / Q000502:physiology*; D008730:Methoxsalen / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D051739:Microphthalmia-Associated Transcription Factor; D014442:Monophenol Monooxygenase / Q000235:genetics / Q000378:metabolism; D009097:Multienzyme Complexes / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D012333:RNA, Messenger / Q000032:analysis; D015398:Signal Transduction / Q000502:physiology*; D012880:Skin Pigmentation / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology
chemical_list: D004268:DNA-Binding Proteins; D008543:Melanins; D051739:Microphthalmia-Associated Transcription Factor; C497235:Mitf protein, mouse; D009097:Multienzyme Complexes; D012333:RNA, Messenger; D014157:Transcription Factors; D005576:Colforsin; D014442:Monophenol Monooxygenase; D017868:Cyclic AMP-Dependent Protein Kinases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D008730:Methoxsalen