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Tumor suppressor p53 down-regulates tissue-specific expression of tyrosinase gene in human melanoma cell lines
1Department of Surgical Oncology, University of Illinois at Chicago, USA.
Abstract:
Tyrosinase, the key gene in melanin pigment synthesis, is tissue-specifically expressed in melanocytic cells. Expression of this gene is regulated by various hormones, carcinogens, and environmental factors. The molecular basis underlying tyrosinase gene regulation is still not clear. In this report, we present the effects of tumor suppressor p53 protein in tyrosinase gene expression and melanin synthesis in human melanoma. After stable transfection of wild type p53 expression plasmid into a highly pigmented melanoma cell line, overexpression of wt p53 suppressed the pigmentation of the melanoma cells. The loss of pigmentation was associated with the loss of endogenous tyrosinase expression at the activity and mRNA levels. In order to determine whether the p53 repression of tyrosinase mRNA involved modulation of tyrosinase promoter activity, transient transfection approaches involving p53 expression plasmid and construct containing chloramphenicol acetyl transferase (CAT) reporter gene linked to 270 bp tissue-specific tyrosinase promoter have been used. p53 specifically repressed CAT gene expression from the tyrosinase promoter and not from the Rous sarcoma virus promoter. These data suggest that in human melanoma p53 down-regulates the tissue-specific expression of tyrosinase gene and subsequent melanin synthesis.
Insights
The tumor suppressor p53 protein reduces melanin synthesis in human melanoma. Overexpression of wild type p53 suppresses tyrosinase gene expression and pigmentation in melanoma cells.
Area of Science:
- Molecular Biology
- Cancer Research
- Biochemistry
Background:
- Tyrosinase is the key gene for melanin pigment synthesis, crucial for melanocytic cell function.
- Melanin synthesis regulation is complex, influenced by hormones, carcinogens, and environmental factors.
- The precise molecular mechanisms governing tyrosinase gene regulation remain incompletely understood.
Purpose of the Study:
- To investigate the role of the tumor suppressor p53 protein in regulating tyrosinase gene expression.
- To determine the impact of p53 on melanin synthesis in human melanoma cells.
- To elucidate the molecular mechanisms by which p53 influences tyrosinase expression.
Main Methods:
- Stable transfection of wild type p53 expression plasmid into a human melanoma cell line.
- Assessing pigmentation, tyrosinase activity, and mRNA levels post-transfection.
- Transient transfection assays using a chloramphenicol acetyltransferase (CAT) reporter gene linked to the tyrosinase promoter to evaluate promoter activity.
Main Results:
- Overexpression of wild type p53 led to suppressed pigmentation in melanoma cells.
- The loss of pigmentation correlated with decreased tyrosinase activity and mRNA levels.
- p53 specifically repressed the tyrosinase promoter activity, but not the Rous sarcoma virus promoter, indicating a targeted effect.
Conclusions:
- In human melanoma, the p53 protein acts as a down-regulator of tissue-specific tyrosinase gene expression.
- p53-mediated suppression of tyrosinase leads to reduced melanin synthesis.
- These findings provide insights into the molecular basis of tyrosinase gene regulation and its role in melanoma.