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The Role of PTEN in Hormon Refractory Breast Cancer
PTEN is a tumor suppressor gene that is the second most frequently mutated gene in human cancers behind p53. Many cancers, including breast cancer, have a reduction or loss of PTEN expression brought about through loss of heterozygosity (LOH) and/or epigenetic silencing mechanisms or harbor loss of function mutations in the phosphatase catalytic domain . In breast cancer, this loss correlates highly with lymph node metastasis and poor prognosis, as well as resistance to current chemotherapies. However, phenotypic effects of PTEN inactivation in human cancer cells remain poorly defined. We hypothesize that loss of PTEN expression promotes a malignant phenotype in non-tumorigenic mammary epithelial cells which may result in altered therapeutic responses. To evaluate the biological and clinical relevance of these mutations, we propose to generate in vitro model systems using human somatic cell knock-out technologies. This knock-out technology involving targeted homologous recombination will enable us to delete PTEN expression in the non-tumorigenic mammary epithelial cell lines, MCF10A and IMEC. Following the generation of the PTEN-null cell lines, comparisons will be made against their isogenic parental control cells. These isogenic cell line pairs, which differ only in their PTEN status, will enable us to test our hypothesis via the following specific aims: 1) to define changes in PI3K/AKT signal transduction in PTEN-null human mammary epithelial cells, 2) to define changes in transformation, cell migration, and cell invasion in PTEN-null human mammary epithelial cells, and 3) to determine the role of PTEN loss in response to chemotherapy and radiation therapy in human mammary epithelial cells. Generation of PTEN-null human mammary epithelial cells will yield insight into the molecular pathways involved in the initiation and/or progression of cancer, and most importantly, will aid in defining more precise chemotherapeutic and radiation treatment strategies.
Normal cell growth is regulated by a delicate balance of positive and negative factors. However, a shift in the balance may release a cell from its normal growth controls, allowing it to acquire malignant characteristics. One such shift may be the increased activation of the PI3K/AKT signaling cascade, an important growth-promoting pathway in the cell. The PTEN protein is a factor that acts at an early step along the PI3K/AKT pathway and aids in regulating pathway activation, which in turn maintains the cell within its normal growth parameters. Many cancers, including breast cancer, have a reduction or loss of PTEN protein expression. T his loss correlates highly with lymph node metastasis and poor prognosis. Therefore, we hypothesize that loss of PTEN expression in mammary epithelial cells shifts this delicate balance of growth regulation and facilitates the progression towards tumor advancement. We propose to generate novel human breast cell lines that will enable us to evaluate the biological and clinical relevance of PTEN loss. To create these cell lines, we begin with non-tumorigenic mammary epithelial cells that have normal PTEN expression. Using sophisticated gene targeting technology, we then delete the PTEN gene from these cells to create a model system that recapitulates the complete loss of PTEN protein expression seen in breast cancer cells. Following the generation of the PTEN-null cell lines, comparisons will be made against their isogenic parental control cells. These cell lines are “isogenic” because they differ only in their PTEN status, which therefore allows for the unambiguous study of PTEN function. These isogenic pairs will enable us to test our hypothesis that the loss of PTEN protein expression in mammary epithelial cells promotes the development and progression of breast cancer. Our goals are to first, define changes in the PI3K/AKT signaling pathway in PTEN-null human mammary epithelial cells; second, to define the tumorigenic characteristics that the PTEN-null human mammary epithelial cells may acquire, and finally to determine the role of PTEN loss in response to current chemo and radiation therapies used for breast cancer treatment. The g eneration of PTEN-null human mammary epithelial cells will yield insight into the molecular pathways involved in the initiation and progression of breast cancer, and most importantly will aid in defining more effective treatment strategies against this devasting illness .