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Regulation of Tyrosinase mRNA in Mouse Melanoma Cells by α -Melanocyte–Stimulating Hormone

Journal of Investigative Dermatology, ISSN: 0022-202X, Vol: 107, Issue: 5, Page: 689-693
1996
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Cloudman S-91 mouse melanoma cells respond to α -melanocyte–stimulating hormone) by demonstrating marked increase in tyrosinase activity (O-diphenol-O 2 oxidoreductase EC 1.14.18 1). This increase is the result of increased levels of tyrosinase mRNA with a subsequent increased in tyrosinase abundance. Our studies were carried out to determine the effect of melanocyte-stimulating hormone on tyrosinase gene transcription and to measure the kinetics of the hormone–induced increase in tyrosinase mRNA. When melanoma cells were exposed continuously to melanocyte-stimulating hormone for 6 d, a large but transient increase in both tyrosinase mRNA abundance and enzyme activity were observed. The maximum increase in tyrosinase mRNA occurred 60 h after melanocyte-simulating hormone stimulation and was followed by decline in message levels even though cells were continuously exposed to hormone. Results of nuclear run-off transcription assays showed that melanocyte-stimulating hormone caused a slow increase in the rate of transcription of the tyrosinase gene with a maximal 6-fold stimulation occurring at 48 h. In cells treated with the ribonucleic acid synthesis inhibitor, 5,6-dichloro-1- β -D-ribofuranosyl-benzimidazole, tyrosinase mRNA levels decayed with a half-life of 4–5 h. This decay rate was unaffected by treatment of cells with melanocyte-stimulating hormone, indicating that the hormone does not act to stabilize tyrosinase ribonucleic acid, inhibition of protein synthesis by treatment with cycloheximide had no effect on the melanocyte-stimulating hormone-induced increase in tyrosinase messenger ribonucleic acid levels suggesting that ongoing protein synthesis is not required for, at least, the initial stimulation of tyrosinase gene transcription by melanocyte-stimulating hormone.

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