Teressa Paulsen, University of Utah
Life Sciences
Breast cancer is still the most common cancer among women regardless of race or ethnicity. The focus of our research is to uncover the mechanism breast cancer cells use to escape the inherent limitations of the telomere and obtain immortality. The protective end of a chromosome, the telomere, degrades with each cellular division. The cellular response to telomere dysfunction is to activate programmed cell death. Therefore, this type of damage normally limits the proliferative potential of the cell and subsequently carcinogenesis.
We have developed a novel tool to determine how breast cancer cells survive telomere loss. In our system Cre recombinase induces recombination between sister chromatids at a site adjacent to a telomere. The chromatids subsequently form a dicentric chromosome and the endogenous telomeres are lost as an acentric chromosome. The dicentric chromosome forms a bridge and breaks during mitosis and each daughter cell inherits a chromosome missing a single telomere. Additionally, our assay induces expression of a fluorescent protein only after telomere loss. Since the broken end cannot be fixed by typical DNA repair, cells predominantly die. Cells that do survive, however, can be isolated by fluorescence activated cell sorting and analyzed to characterize the genetic pathway mediating survival. The proteins involved in these pathways may represent novel targets for cancer therapy.
We are currently testing our telomere loss assay in a breast cancer cell line that models tumor-initiating cells associated with the poorest prognosis in patients. Using phase contrast microscopy and time-lapse imaging we have confirmed that dicentric bridges are generated in mouse embryonic stem cells, in mouse embryonic fibroblasts, and in the developing mouse embryo. Furthermore, in mouse embryos the dicentric bridges break and cells only fluoresce following Cre expression.