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Quantitative assessment of promoter hypermethylation during breast cancer development
Ulrich Lehmann1, Florian Länger, Henning Feist
1Institute of Pathology, Medizinische Hochschule Hannover, Carl-Neuberg-Strasse 1, D-30625 Hannover, Germany. lehmann.ulrich@mh-hannover.de
Abstract:
The aberrant methylation of cytosine residues in the promoter region of growth regulatory genes is now widely recognized as an additional mechanism for gene inactivation in cancer cells. In this study we analyzed the methylation status of four growth regulatory genes (p16, RASSF1A, cyclinD2, 14-3-3zeta) during breast cancer progression. For this purpose invasive and noninvasive tumor cell populations as well as hyperplastic cell proliferations were isolated from a series of archival breast tissue specimens (n = 57) using laser-assisted microdissection. A new real-time polymerase chain reaction-based assay was used for the sensitive and quantitative determination of the cell-specific methylation status. We found that aberrant promoter methylation was already prevalent in pure intraductal carcinoma with different frequencies and different methylation levels for the four genes analyzed. For RASSF1A and 14-3-3zeta promoter methylation was also demonstrated in epithelial hyperplasia and intraductal papillomas. By contrast, aberrant methylation of cyclinD2 and p16 was restricted to cancerous epithelium. Increased methylation of the cyclinD2 gene was significantly associated with a higher van Nuys grade. Furthermore, when intraductal and invasive tumor cells were compared, significant quantitative changes in the methylation level were detected primarily within the cyclinD2 gene. These results demonstrate that promoter methylation is an early and frequent event in breast cancer development, but displays great quantitative and gene-specific differences, and changes in a gene-specific manner during tumor progression.
Insights
Aberrant promoter methylation of growth regulatory genes is an early event in breast cancer development. Methylation patterns differ between genes and change during tumor progression, offering insights into cancer evolution.
Area of Science:
- Oncology
- Molecular Biology
- Epigenetics
Background:
- Aberrant methylation of cytosine residues in promoter regions of growth regulatory genes is a known mechanism for gene inactivation in cancer.
- Understanding the role of epigenetic modifications in breast cancer progression is crucial for developing targeted therapies.
Purpose of the Study:
- To analyze the methylation status of four key growth regulatory genes (p16, RASSF1A, cyclinD2, 14-3-3zeta) throughout breast cancer progression.
- To investigate the prevalence and quantitative changes in promoter methylation in different stages of breast cancer, from hyperplasia to invasive carcinoma.
Main Methods:
- Utilized laser-assisted microdissection to isolate pure invasive, noninvasive tumor cell populations, and hyperplastic cell proliferations from archival breast tissue specimens (n=57).
- Employed a novel real-time polymerase chain reaction (PCR)-based assay for sensitive and quantitative determination of cell-specific methylation status.
Main Results:
- Aberrant promoter methylation was prevalent in intraductal carcinoma, with varying frequencies and levels across the four genes.
- Methylation of RASSF1A and 14-3-3zeta was observed in pre-cancerous lesions (epithelial hyperplasia, intraductal papillomas), while cyclinD2 and p16 methylation was specific to cancerous epithelium.
- Increased cyclinD2 methylation correlated significantly with higher van Nuys grade, and quantitative methylation changes were most prominent in cyclinD2 between intraductal and invasive tumors.
Conclusions:
- Promoter methylation is an early and frequent event in breast cancer development.
- Methylation patterns exhibit significant gene-specific quantitative differences and evolve during tumor progression.
- These findings highlight the dynamic role of epigenetic alterations in the multi-step process of breast cancer development.