Regulation of Apical Polarity in Breast Cancer

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DESCRIPTION (provided by applicant): Cancer is associated with alterations in tissue organization and function. Notably, the alteration of tissue polarity may be determinant for the progression of epithelial cancers. In the mammary gland, baso-apical tissue polarity is illustrated by the asymmetrical distribution of membrane proteins between the basal pole of cells in contact with the basement membrane, and the apical pole of cells that delineates the lumen of the epithelial structures or acini. Alterations in basal polarity accompany the invasive phenotype. Although alterations in apical polarity have been frequently reported in breast cancer, little is known regarding the control mechanisms, and the consequences as well as diagnosis and prognosis values of such alterations. Tight junctions are adhesion complexes that play a critical role in the establishment and maintenance of apical polarity. Our preliminary results show that the distribution of tight junction organizer ZO-1 is altered in invasive carcinomas and in certain types of carcinoma in situ, confirming literature reports that suggest that loss of apical polarity accompany tumor progression. In addition, we have evidence to show that DNA methylation is a major mechanism of epigenetic control of apical polarity. The long-term hypothesis is that the identification of genes involved in the control of apical polarity will bring invaluable information for the diagnosis and prognosis of breast neoplasias, and the establishment of new strategies to help prevent breast cancer progression. 2 aims are proposed: (1) to identify statistically significant genes that are potential regulators of apical polarity using Affymetrix microarray analysis of three-dimension (3D) culture of non-neoplastic mammary epithelial SI cells that form phenotypically normal breast acini in the presence of matrigel, and apical polarity-impaired acini upon DNA-hypomethylation by 5-azacytidine, culture in collagen I, or treatment with a gap junction blocker. Genes showing altered expression in all models of apical polarity-impaired acini compared to controls will be selected using 3 different model-based statistical analyses of the microarray data. The influence of the selected genes on the control of apical polarity (CAP genes) will be investigated by altering their expression in polarized and apical polarity-impaired structures formed by different breast cell models. (2) To explore the distribution of known apical polarity markers and the expression profile of CAP genes on archival biopsies of normal and neoplastic breast tissues and relate the expression profile of CAP genes to alterations in the distribution of apical polarity markers and tumor progression. Non-neoplastic, pre-malignant and pre-invasive breast lesions will be immunostained for a series of tight junction and subapical CRB complex proteins and the correlation between the distribution patterns of these apical markers and histological grade or tissue criteria for apical polarity loss will be assessed. CAP genes expression in non-invasive and invasive breast lesions will be compared to histological classification and distribution maps of apical markers. This project should bring a better knowledge of the involvement of apical polarity loss in breast cancer progression and identify novel markers for prognosis-related studies and targets to prevent tumor progression.