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Low Grade Amplification of MDM2 Gene in a Subset of Human Breast Cancers without p53 Alterations
1Division of Clinical Genetics, Department of Medical Genetics, Biomedical Research Center, Osaka University Medical School, 2-2 Yamadaoka, Suita 565, Japan.
Abstract:
MDM2 protein is thought to bind to p53 tumor suppressor protein leading to inhibition of p53-mediated transactivation. Amplification of the MDM2 gene has been frequently observed in human sarcoma, and relevant overexpression of the MDM2 protein is assumed to contribute to tumorigenesis through inactivation of the p53 function. In order to determine whether MDM2 amplification plays a role in the development of human breast cancer without genetic alteration of p53, we analyzed, MDM2 gene amplification by quantitative hybridization and genetic alteration of p53, in 32 primary tumors and 26 metastatic lymph nodes. Low grade amplification of the MDM2 gene (2-6 fold) was observed in four cases, none of which showed even subtle genetic alterations of p53 or loss of alleles on 17p. Moreover, in three of the four cases with MDM2 gene amplification, the level of gene amplification in the metastatic lymph nodes was slightly higher than that in the primary tumors. These results, taken together with previous findings, suggest that a subset of breast cancers without genetic alteration of p53 may also arise by inactivation of the p53 function through interaction with the overexpressed MDM2 protein induced by gene amplification.
Insights
MDM2 gene amplification may drive breast cancer development by inactivating the p53 tumor suppressor protein. This occurs even without p53 genetic alterations, suggesting a new pathway in breast cancer progression.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- MDM2 protein inhibits the p53 tumor suppressor, a key factor in preventing cancer.
- MDM2 gene amplification is linked to sarcoma development by inactivating p53.
- The role of MDM2 amplification in breast cancer, particularly when p53 is unaltered, requires investigation.
Purpose of the Study:
- To investigate MDM2 gene amplification in human breast cancer without p53 genetic alterations.
- To determine if MDM2 amplification contributes to breast cancer development and progression.
Main Methods:
- Quantitative hybridization was used to analyze MDM2 gene amplification.
- Genetic alterations of the p53 gene were assessed in primary tumors and metastatic lymph nodes.
- 32 primary breast tumors and 26 metastatic lymph nodes were analyzed.
Main Results:
- Low-grade MDM2 gene amplification (2-6 fold) was detected in four breast cancer cases.
- None of the cases with MDM2 amplification showed p53 genetic alterations or 17p allele loss.
- MDM2 amplification levels were higher in metastatic lymph nodes compared to primary tumors in three cases.
Conclusions:
- MDM2 gene amplification can inactivate p53 function in breast cancer, even without p53 genetic mutations.
- This mechanism suggests a subset of breast cancers may develop due to MDM2 overexpression induced by gene amplification.
- Findings highlight a potential therapeutic target in breast cancer treatment by addressing MDM2-p53 interactions.
