Microphthalmia Associated Transcription Factor Is a Target of the Phosphatidylinositol-3-Kinase Pathway

• Published in: Journal of investigative dermatology Vol. 121; no. 4; pp. 831 - 836
• Main Authors: Khaled, Mehdi, Larribere, Lionel, Bille, Karine, Ortonne, Jean-Paul, Ballotti, Robert, Bertolotto, Corine
• Format: Journal Article
• Language: English
• Published: Danvers, MA Elsevier Inc 01.10.2003; Nature Publishing; Elsevier Limited; Nature Publishing Group
• Subjects: Animals; Biological and medical sciences; Cancer; Chromones - pharmacology; cyclic adenosine monophosphate; Dermatology; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Enzyme Inhibitors - pharmacology; Gene Expression Regulation, Enzymologic - drug effects; Gene Expression Regulation, Enzymologic - physiology; Investigative techniques, diagnostic techniques (general aspects); Life Sciences; Medical sciences; Melanins - biosynthesis; Melanocytes - cytology; Melanocytes - metabolism; Melanoma; Membrane Glycoproteins - genetics; Mice; Microphthalmia-Associated Transcription Factor; Monophenol Monooxygenase - genetics; Morpholines - pharmacology; Oxidoreductases; Pathology. Cytology. Biochemistry. Spectrometry. Miscellaneous investigative techniques; Phosphatidylinositol 3-Kinases - antagonists & inhibitors; Phosphatidylinositol 3-Kinases - metabolism; phosphatidylinositol-3-kinase; Promoter Regions, Genetic - physiology; Skin Neoplasms; Transcription Factors - genetics; Transcription Factors - metabolism; Transcription, Genetic - drug effects; Transcription, Genetic - physiology; Tumor Cells, Cultured; tyrosinase; TYRP1; microphthalmia associated transcription factor; cyclic adenosine monophosphate; tyrosinase; phosphatidylinositol-3-kinase; TYRP1; Vertebrata; Mammalia; Mouse; cyclic adenosine monophosphate/microphthalmia associated transcription factor/phosphatidylinositol-3-kinase/tyrosinase/ TYRP1; Enzyme; Transferases; Animal; Rodentia; Malignant melanoma; Transcription factor; Tumor cell; 1-Phosphatidylinositol 3-kinase
• ISSN: 0022-202X; 1523-1747
• DOI: 10.1046/j.1523-1747.2003.12420.x

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 3β 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.