SV-40 large T antigen reversibly inhibits expression of tyrosinase, TRP-1, TRP-2 and Mitf, but not Pax-3, in conditionally immortalized mouse melanocytes.
Transformation of mouse melanocytes with a variety of exogenous oncogenes or chemical carcinogens frequently results in irreversible loss of pigmentation. We have infected mouse melanocytes with a temperature-sensitive mutant of the simian virus 40 (SV40) large tumour antigen to study the molecular mechanisms underlying depigmentation during melanocyte transformation. The results show that, out of six cell lines analyzed at the permissive temperature of the oncoprotein, three epidermal and two dermal melanocyte clones remained pigmented and retained the ability to synthesize melanin and to express the melanocyte-specific genes, including tyrosinase, tyrosinase related protein-1, tyrosinase related protein-2 and Mitf. In contrast, one dermal melanocyte clone (DMEL-3) gradually depigmented. This depigmentation was characterized by enhanced growth and down-regulation of melanocyte-specific gene expression. When the oncogene was inactivated by culture at the non-permissive temperature, the pigmented phenotype in DMEL-3 cells could be rescued, and there was a corresponding time-dependent increase in melanocyte-specific gene expression. After extended passage, this rescue could not be achieved. Our results provide direct evidence for the role of the SV40 large T antigen in melanocyte de-differentiation. Expression of Pax-3, a transcription factor implicated in melanocyte differentiation, was unaltered during the SV40-initiated de-differentiation, and de-differentiated melanocytes expressed normal levels of Pax-3 message. We speculate on the mechanism by which the oncoprotein might be regulating Mitf gene expression and of the role of Pax-3 in this process.
Prince
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Department of Anatomy and Cell Biology, University of Cape Town, Observatory, 7925, Cape Town, South Africa.
Illing
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Kidson
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D016475:3T3 Cells; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000378:metabolism*; D015152:Blotting, Northern; D015139:Blotting, Southern; D015153:Blotting, Western; D002460:Cell Line; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors*; D007370:Interferon Type I / Q000037:antagonists & inhibitors*; D019746:Intramolecular Oxidoreductases / Q000037:antagonists & inhibitors*; D008543:Melanins / Q000096:biosynthesis / Q000378:metabolism; D008544:Melanocytes / Q000378:metabolism* / Q000821:virology; D008546:Melanoma, Experimental; D051379:Mice; D008810:Mice, Inbred C57BL; D051739:Microphthalmia-Associated Transcription Factor; D014442:Monophenol Monooxygenase / Q000037:antagonists & inhibitors*; D000072041:PAX3 Transcription Factor; D051761:Paired Box Transcription Factors; D010858:Pigmentation / Q000502:physiology; D011257:Pregnancy Proteins / Q000037:antagonists & inhibitors*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012867:Skin / Q000166:cytology; D013696:Temperature; D014157:Transcription Factors
D000952:Antigens, Polyomavirus Transforming; D004268:DNA-Binding Proteins; D007370:Interferon Type I; D008543:Melanins; D051739:Microphthalmia-Associated Transcription Factor; C497235:Mitf protein, mouse; D000072041:PAX3 Transcription Factor; D051761:Paired Box Transcription Factors; D011257:Pregnancy Proteins; D014157:Transcription Factors; C020947:interferon tau; C068686:Pax3 protein, mouse; D014442:Monophenol Monooxygenase; D019746:Intramolecular Oxidoreductases; C042501:dopachrome isomerase