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Focus on Apical Polarity to Develop Breast Cancer Prevention Strategies
Risk and Prevention, Epidemiology
Background: Breast cancer chemoprevention is currently limited to anti-hormonal agents with an efficiency restricted to estrogen-responsive tissues and serious potential side effects. We propose that the identification and correction of lesions prior to proliferation would help develop additional preventive strategies. It has been shown that normal tissue architecture maintains breast differentiation and can silence genetic aberrations. We have postulated that changes in epithelial architecture may be a source to detect early neoplastic events. We have found that alterations in apical polarity occur in normal looking tissue and increase with the stage of breast neoplasia. Loss of apical polarity primes cells to enter the cell cycle and is accompanied with changes in the expression of cell proliferation and DNA repair genes, which suggests that the architectural organization of the apical pole is paramount to maintain cell quiescence and genome stability. Hypothesis: The alteration of apical polarity is essential for neoplastic development and restoring and/or maintaining apical polarity may be sufficient to stop cancer development. Specific aims: (1) determine the effect of epidemiological factors involved in increased breast cancer risk and of potential chemopreventive dietary compounds on the maintenance of apical polarity; (2) identify the correlation between changes in apical polarity and alterations in the expression of proliferation and DNA repair genes on sections of breast biopsies; (3) decipher the mechanism by which loss of apical polarity primes cells for cell cycle entry. Study design: In Aim 1, cultures of polarized breast acini will be treated with ratios of fatty acids and siRNA for circadian gene PER1 to mimic conditions that increase breast cancer risk. Conversely, apical polarity impaired-breast acini will be incubated with linoleic acid that has potential chemopreventive action. Resulting effects on the organization of apical polarity markers and the expression of proliferation and DNA repair genes will be assessed via statistical analyses. In Aim 2, serial sections of archival tissue biopsies of normal looking epithelium from patients with or without detectable benign lesions will be used to determine the association between specific changes in apical polarity markers and the expression of proliferation and DNA repair genes. In Aim 3, the expression of apical polarity markers and apical polarity-dependent proliferation genes will be altered in breast acini and the effect on differentiation and cell behavior will be determined. Potential outcomes/benefits of the research: This project should confirm the importance of apical polarity loss in very early stages of breast cancer development, and establish statistically significant maps of genomic and architectural changes that will become the source of screens for the detection of harmful pre-neoplastic lesions and of high throughput screens of chemopreventive agents.
The eradication of breast cancer will require the development of strategies for very early detection of changes in the breast tissue that enable cancer development, and for the discovery of harmless agents that counteract such changes. We are proposing that focusing on early changes in the architecture of the breast epithelium, in tissues that appear normal looking by usual histological analysis, will permit the establishment of novel cancer prevention strategies. The organization of cells into well-differentiated structures, like the breast glandular structures (or acini), has been shown to override changes in the genome, thus demonstrating the predominance of tissue architecture in the control of cell behavior. We have identified that the loss of organization of the side of breast epithelial cells in contact with the lumen (referred to as apical polarity) occurs very early during breast cancer development (e.g., hyperplasia). Certain alterations in the expression or distribution of proteins that are apical polarity markers in luminal cells are even seen in normal looking breast epithelium. Using cell culture systems that mimic the formation of breast acini, we have further shown that alteration of apical polarity is sufficient to sensitize cells to enter the cell cycle and alter the expression of genes that control proliferation and repair of the genome. Several of these genes have also been associated with breast cancer development. Thus, the loss of apical polarity may be a determinant factor in the initiation of breast neoplastic diseases. Our goals are to ascertain the importance of apical polarity loss in the development of breast neoplasia by testing the influence of risk factors and potential chemopreventive agents on this aspect of tissue architecture using cell cultures that mimic the formation of breast acini, and by determining the correlation between specific alterations in apical polarity and changes in the expression of genes that control proliferation and DNA repair on archival biopsy sections of normal looking breast tissues. In addition, we will identify which apical polarity marker(s) is predominantly responsible for changes in gene expression that promote the initiation of proliferation. Upon completion of this project we will have produced statistically significant tissue maps that combine alterations in apical polarity and gene expression and will be the basis for the development of high throughput screens of agents with potential protective effects. In addition, one or more apical polarity markers identified as major players in the control cell cycle entry in this research project could become targets for the development of in vivo detection methods for preneoplastic stages of breast cancer.