Regulation of melanogenesis induced by 5-methoxypsoralen without ultraviolet light in murine melanoma cells.
Melanogenesis in melanoma cells can be enhanced by psoralens in the absence of UV light. Melanin biosynthesis is regulated by a number of melanocyte-specific proteins, including tyrosinase, DOPAchrome tautomerase (DCT), and tyrosinase-related protein-1 (TRP-1, gp75). To get more insight on the molecular mechanisms involved in psoralens-induced melanogenesis, we determined tyrosinase and DCT activities as well as mRNA and protein levels of tyrosinase, DCT, and TRP-1 in S91 mouse melanoma cells treated by 5-MOP. High concentration of 5-MOP (5 x 10(-5) M) induced a time-dependent increase of tyrosinase activity and melanin content, which was correlated to an increase of both mRNA and protein levels of tyrosinase. These results demonstrate that the 5-MOP stimulation of melanogenesis is related to increased tyrosinase synthesis. In addition, 5-MOP stimulated TRP-1 synthesis and induced a dose-dependent decrease of DCT activity without any modification in the expression of the protein. We explored then the signalling pathways involved in 5-MOP-induced melanogenesis and, particularly, the role of cyclic AMP and protein kinase C (PKC). A small stimulation of cyclic AMP production was observed in presence of 5-MOP. Furthermore, 1-oleoyl-2-acetylglycerol (OAG), a PKC activator, potentiated the 5-MOP stimulation of tyrosinase activity, while calphostin, a specific PKC inhibitor, inhibited the 5-MOP induction of tyrosinase activity. Phorbol-myristate acetate (PMA), described as a strong activator of PKC, inhibited also the effect of 5-MOP when used at long term. Taken together, these results demonstrate that in murine melanoma cells 5-MOP stimulates melanogenesis by increasing activity and synthesis of tyrosinase. Tyrosinase and TRP-1 expression are coordinately regulated by 5-MOP. Furthermore, a negative correlation between melanogenesis and DCT activity was observed under 5-MOP stimulation. At least, PKA and PKC systems appear to play an important role in the melanogenic effect of 5-MOP.
INSERM U.385, Faculté de Médecine, Nice, France.
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Mengeaud
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JP
Ortonne
D000078223:5-Methoxypsoralen; D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism; D019746:Intramolecular Oxidoreductases; D007535:Isomerases / Q000235:genetics / Q000378:metabolism; D008543:Melanins / Q000096:biosynthesis*; D008546:Melanoma, Experimental / Q000378:metabolism*; D008562:Membrane Glycoproteins; D008730:Methoxsalen / Q000031:analogs & derivatives* / Q000494:pharmacology; D051379:Mice; D014442:Monophenol Monooxygenase / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases; D011493:Protein Kinase C / Q000378:metabolism; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014466:Ultraviolet Rays
D008543:Melanins; D008562:Membrane Glycoproteins; D011506:Proteins; D012333:RNA, Messenger; D000078223:5-Methoxypsoralen; D000242:Cyclic AMP; D010088:Oxidoreductases; C079621:Tyrp1 protein, mouse; C064056:tyrosinase-related protein-1; D014442:Monophenol Monooxygenase; D011493:Protein Kinase C; D007535:Isomerases; D019746:Intramolecular Oxidoreductases; C042501:dopachrome isomerase; D008730:Methoxsalen