Identification of differentially expressed genes in breast cancer tissues and cells

Breast cancer, is the second leading cause of cancer related deaths among women in developed countries, and the incidence of morbidity and mortality is rising in developing countries. The purpose of this project was to utilize the differential display technique to identify genetic changes in normal versus malignant breast tissue. It was also used in a defined cell culture system having differential cellular characteristics, to identify genes that may be responsible for different biological behavior of these cell lines. Messenger RNA from normal, breast cancer tissues, and breast tissues from reduction mamoplasty yielded fifty-nine differentially expressed bands representing differentially expressed genes. Northern hybridization analysis proved negative, suggesting that these genes may represent low abundant message. mRNA from two clones; one tumorigenic, and the other non-tumorigenic in nude mice; obtained by stable transfection of galectin-3 gene in a non-tumorigenic BT 549 breast cell line, was analyzed by differential display. Galectin-3, a calcium independent carbohydrate binding protein has been shown to be involved in many biological processes, but its exact function is still unclear. A 607 bp fragment was differentially expressed by the tumorigenic clone, and DNA sequence of which revealed a 93% homology with the human Line 1 retrotransposon (Ll). Ll is a poly-A mobile element, and its insertion into functional genes has been implicated in human diseases, including breast cancer, however its role in breast cancer is not clear. To determine the locale and expression of galectin-3 and L1 in normal versus tumor tissues, immunohistochemical analysis of breast carcinoma specimens, fibrocystic, normal breast tissues, and the tumorigenic clone of BT 549, 11-9-1-4, was performed. L1 and galectin-3 was found to be co-localized, and the imrnuno-staining was most intense in tumor tissue, and was minimal in normal tissue. Staining was significantly correlated with disease progression and tumor recurrence, suggesting that the expression of galectin-3 and L1 may represent a new mechanism by which breast tumor cells acquire aggressive phenotype. However, the interaction of L1 and galectin-3, if any, and their influence on tumor development and progression remains to be determined