title: Microphthalmia associated transcription factor is a target of the phosphatidylinositol-3-kinase pathway.
abstract: In B16 melanoma cells, cyclic adenosine monophosphate inhibits the phosphatidylinositol-3-kinase and the phosphatidylinositol-3-kinase inhibitor, LY294002, stimulates melanogenesis. However, the molecular mechanisms, by which phosphatidylinositol-3-kinase inhibition increases melanogenesis remained to be identified. In this study, we show that LY294002 up-regulates the expression of the melanogenic enzymes, tyrosinase and Tyrp1, through a transcriptional mechanism that involves microphthalmia associated transcription factor, a basic helix-loop-helix transcription factor, which plays a key role in melanocyte survival and differentiation. Further, we observe that LY294002 increases the intracellular content of microphthalmia associated transcription factor, thereby demonstrating that microphthalmia associated transcription factor is also a convergence point of the phosphatidylinositol-3-kinase signaling pathway. Finally, our results indicate that LY294002 controls microphthalmia associated transcription factor at the transcriptional level through distal regulatory element that remain to be identified. Interestingly, we have recently reported that cAMP-elevating agents, through a phosphatidylinositol-3-kinase/AKT inhibition and a glycogen synthase kinase 3beta activation, may stimulate microphthalmia associated transcription factor binding to its target sequence, suggesting that inhibition of the phosphatidylinositol-3-kinase is implicated in the stimulation of melanogenesis at different levels. Thus, the results presented in this report strengthen the importance of the phosphatidylinositol-3-kinase pathway in the regulation of melanogenesis and emphasize the complexity of the cyclic adenosine monophosphate signaling that controls melanocyte differentiation and melanogenesis.
authors: INSERM U385, Biologie et Physiopathologie de la Peau, Nice, France.
authors: Mehdi
authors: M
authors: Khaled
authors: Lionel
authors: L
authors: Larribere
authors: Karine
authors: K
authors: Bille
authors: Jean-Paul
authors: JP
authors: Ortonne
authors: Robert
authors: R
authors: Ballotti
authors: Corine
authors: C
authors: Bertolotto
mesh_terms: D000818:Animals; D002867:Chromones / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology; D008543:Melanins / Q000096:biosynthesis; D008544:Melanocytes / Q000166:cytology / Q000378:metabolism*; D008545:Melanoma; D008562:Membrane Glycoproteins / Q000235:genetics; D051379:Mice; D051739:Microphthalmia-Associated Transcription Factor; D014442:Monophenol Monooxygenase / Q000235:genetics; D009025:Morpholines / Q000494:pharmacology; D010088:Oxidoreductases; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011401:Promoter Regions, Genetic / Q000502:physiology; D012878:Skin Neoplasms; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology; D014407:Tumor Cells, Cultured
chemical_list: D002867:Chromones; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D008543:Melanins; D008562:Membrane Glycoproteins; D051739:Microphthalmia-Associated Transcription Factor; D014442:Monophenol Monooxygenase; D009025:Morpholines; D010088:Oxidoreductases; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D014157:Transcription Factors; C497235:Mitf protein, mouse; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C079621:Tyrp1 protein, mouse