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Mutations and defective expression of the WAF1 p21 tumour-suppressor gene in malignant melanomas
M J Vidal1, F Loganzo, A R de Oliveira
1Laboratory of Mammalian Cell Transformation, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
Abstract:
The WAF1 gene, located on chromosome 6p, encodes a M(r) 21,000 protein (p21) that can arrest cell growth by associating with and inhibiting cyclin-dependent kinase complexes that are necessary for cells to exit Gr. Transcriptional activation of WAF1 can be accomplished by increasing levels of p53 protein induced by various cellular stresses, including DNA damage. Metastatic melanomas are paradoxical in that most overexpress wild-type p53 protein, yet cell growth is not inhibited. Thus, it is possible that lack of growth suppression in melanomas is due, in part, to mutations in the WAF1 gene. Therefore, we examined the entire coding region of the WAF1 gene in 24 metastatic melanoma cell lines and three normal melanocyte lines by single-strand conformation polymorphism (SSCP) analysis and direct DNA sequencing. We similarly examined the DNA from lymphoblastoid cell lines, derived from nine individuals belonging to seven melanoma-prone families, in which haplotypes of markers on 6p cosegregate with melanoma for germline mutations in the WAF1 gene. Results indicate that (i) mutation of the WAF1 gene is an infrequent event in individuals with sporadic melanoma or predisposed to familial melanoma and (ii) the uncontrolled growth of melanoma cells is not due to mutation of the WAF1 gene. However, expression studies found a wide variation in the level of p21 protein in melanoma cells, suggesting that aberrant regulation of p21 may play a role in melanoma development. Moreover, there was no predictable relationship between p21 expression and p53 expression, indicating that other, p53-independent, pathways may be important for the regulation of p21 in melanoma cells.
Insights
Melanoma cells often overexpress p53 but continue to grow, suggesting WAF1 gene mutations might cause this. However, this study found WAF1 gene mutations are rare in melanoma, and p21 protein levels vary, indicating other regulatory pathways are involved.
Area of Science:
- Molecular Biology
- Cancer Genetics
- Cell Cycle Regulation
Background:
- The WAF1 gene encodes p21, a protein that inhibits cyclin-dependent kinases to arrest cell growth.
- WAF1 is transcriptionally activated by p53, a tumor suppressor often overexpressed in metastatic melanomas.
- Melanoma's uncontrolled growth despite wild-type p53 suggests potential defects in WAF1 or its regulation.
Purpose of the Study:
- To investigate mutations in the WAF1 gene as a cause for uncontrolled melanoma cell growth.
- To explore the role of WAF1 gene and p21 protein in melanoma development.
- To understand the relationship between p53 and p21 expression in melanoma cells.
Main Methods:
- Single-strand conformation polymorphism (SSCP) analysis and direct DNA sequencing of the WAF1 gene coding region.
- Examination of WAF1 in 24 metastatic melanoma cell lines, 3 normal melanocyte lines, and lymphoblastoid cell lines from melanoma-prone families.
- Analysis of p21 and p53 protein expression levels in melanoma cells.
Main Results:
- WAF1 gene mutations were infrequent in both sporadic and familial melanoma cases.
- The uncontrolled proliferation of melanoma cells is not attributable to WAF1 gene mutations.
- Significant variation in p21 protein levels was observed in melanoma cells, independent of p53 levels.
Conclusions:
- WAF1 gene mutations do not appear to be a primary driver of uncontrolled growth in metastatic melanoma.
- Aberrant regulation of p21 protein, potentially through p53-independent pathways, may contribute to melanoma development.
- Further research into p53-independent regulatory mechanisms of p21 is warranted for understanding melanoma pathogenesis.