BRCT Domains and Breast Cancer Predisposition
MCC - Dr. Alvaro Monteiro
PSM - Dr. Jaime Matta
This U56 pilot project was funded in December, 2009. In women, breast carcinoma is the most common invasive cancer worldwide, accounting for 20% of all malignancies. DNA repair is a critical defense system in the human body aimed at protecting the integrity and stability of the genome by its protection from the harmful effects of cancer-causing agents. A significant step in identifying individuals at increased risk for cancer was the isolation of highly penetrant tumor suppressor genes responsible for hereditary cancer syndromes. Thus, prevention strategies need to shift from identification of unique inactivating mutations with strong effects to estimating the results of small effects in a large number of variants in a pathway or in a network. Mutations in BRCA1, a DNA repair gene, account for 40-45% of all hereditary cases and for ~80% of cases in families with multiple breast and ovarian cancers. However, the current evidence suggests that susceptibility to most sporadic cancers result from a multiplicative effect of moderate risk variants in more than one gene. Recent results have led to the proposal that the DNA Damage Response (DDR) acts as an anti-cancer barrier in tumorigenesis. A protein domain called BRCT (BRCA1 C-terminal domain), which recognizes phosphopeptides, is present in a variety of proteins involved in the DDR. Therefore, our general hypothesis to be tested here is that breast cancer risk in individuals without mutations in BRCA1 or BRCA2 can be at least partly attributable to diminished DNA repair capacity (DRC) regulated by BRCT genes. To test this hypothesis we will accomplish the following specific aims:
To determine the extent to which BRCT genes show changes in expression levels in breast tumors and the extent to which these changes correlate to diminished DNA repair capacity in lymphocytes from breast cancer patients. We will compare expression levels in all BRCT genes in the human genome in twenty nine breast tumor samples and sixty nine normal tissue samples obtained by microarray expression analysis. We will identify which tumor samples show significant changes in BRCT genes and will determine the extent to which they correlate to DNA repair capacity measured in lymphocytes from the same patients by means of a phenotypic assay.
To validate the findings from Aim 1 in a genetically-defined system of isogenic cell lines. We will use RNA interference or overexpression of the BRCT genes, identified in the previous aim, to generate pairs of isogenic breast cancer cell lines in which the only variable is the expression of the gene to be tested. Using this defined system we will perform DNA repair capacity assays and assess the status of DNA damage checkpoints in these cells.
This proposal is significant because understanding the role of BRCT genes in breast carcinoma will provide insights into their effects on treatment and prognosis and open up the possibility of a mechanism-based, targeted strategy in cancer treatment based on a combination of DNA repair genotypes and tumor characteristics. It may provide a rationale for developing new patient-based medicine that optimizes the selection of chemotherapeutic agents and radiotherapy protocols based on DNA repair and other cancer susceptibility genes in a Hispanic population that may have unique pharmacogenomics and pharmacogenetic features. This study may also reveal genes that may be polymorphic in the population and lead to the identification of single nucleotide analysis (SNPs) that could form the basis for a genotyping tests to improve risk assessment in Hispanic women.