title: Delayed ERK activation by ceramide reduces melanin synthesis in human melanocytes.
abstract: Sphingolipid metabolites regulate many aspects of cell growth and differentiation. However, the effects of sphingolipids on the growth and melanogenesis of human melanocytes are not known. In the present study, we investigated the effects of sphingolipid metabolites and the possible signalling pathways involved in human melanocytes. Our data show that C(2)-ceramide inhibits cell growth in a dose-dependent manner, whereas sphingosine-1-phosphate (SPP) has no effect. Moreover, we observed that the melanin content of the cells was significantly decreased by C(2)-ceramide. The pigmentation-inhibiting effect of C(2)-ceramide at 1-10 microM was stronger than that of kojic acid, tested at 1-100 microM. The tyrosinase activity of cell extracts was reduced by C(2)-ceramide treatment. However, in the cell-free system, C(2)-ceramide could not suppress tyrosinase, whereas kojic acid directly inhibited tyrosinase. These results suggest that C(2)-ceramide decreases the pigmentation of melanocytes indirectly regulating tyrosinase. Furthermore, we found that C(2)-ceramide decreased the protein expression of microphthalmia-associated transcription factor (MITF), which is required for tyrosinase expression. To identify the signalling pathway of ceramide, we studied the ability of C(2)-ceramide to influence extracellular signal-regulated protein kinase (ERK) and Akt/protein kinase B (PKB) activation. C(2)-ceramide induced a delayed activation of ERK ( > 1 h) and a much later activation of Akt/PKB ( > 3 h) in human melanocytes. In addition, the specific inhibition of the ERK and the Akt signalling pathways by PD98059 and LY294002, respectively, increased melanin synthesis. Thus, it seems that sustained ERK and Akt activation may lead to the suppression of cell growth and melanogenesis.
authors.affiliation: Department of Dermatology and Artificial Organ Laboratory of Clinical Research Institute, Seoul National University College of Medicine, 28 Yongon-Dong, Chongno-Gu, Seoul 110-744, Republic of Korea.
authors.forename: Dong-Seok
authors.initials: DS
authors.lastname: Kim
authors.forename: Sook-Young
authors.initials: SY
authors.lastname: Kim
authors.forename: Jin-Ho
authors.initials: JH
authors.lastname: Chung
authors.forename: Kyu-Han
authors.initials: KH
authors.lastname: Kim
authors.forename: Hee-Chul
authors.initials: HC
authors.lastname: Eun
authors.forename: Kyoung-Chan
authors.initials: KC
authors.lastname: Park
mesh_terms: D000293:Adolescent; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis; D004268:DNA-Binding Proteins / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008246:Lysophospholipids; D008543:Melanins / Q000096:biosynthesis*; D008544:Melanocytes / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism*; D051739:Microphthalmia-Associated Transcription Factor; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D014442:Monophenol Monooxygenase / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011753:Pyrones / Q000494:pharmacology; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D014157:Transcription Factors / Q000096:biosynthesis
chemical_list: D002867:Chromones; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D005419:Flavonoids; D008246:Lysophospholipids; C497234:MITF protein, human; D008543:Melanins; D051739:Microphthalmia-Associated Transcription Factor; D009025:Morpholines; C064769:N-acetylsphingosine; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D011753:Pyrones; D014157:Transcription Factors; C060506:sphingosine 1-phosphate; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C011890:kojic acid; D004247:DNA; D014442:Monophenol Monooxygenase; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D013110:Sphingosine; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one