Addendum to Scheduled Presentations ANIMAL SCIENCES

THE ROLE OF NOTCH 1 EXPRESSION IN MAMMARY EPITHELIAL CELLS ON THE SECRETION OF GROWTH FACTORS AND CYTOKINES Malignant tumors thrive in their microenvironment by secreting factors that affect the growth of cells around them and/or cytokine release from the immune cells sent to destroy them. In mammary gland tumorigenesis, the enhanced expression of Notch in tumor cells has been shown to play an active role in progression. Using the CellTiter96â AQueous One Solution Cell Proliferation Assay (MTS assay), supernatants from Notch 1 expressing cells were tested on immortal HC11 mammary epithelial cells to determine the role of any secreted growth factors on cell proliferation. In addition, enzyme linked immunoassays (ELISAs) were used to quantify interferon gamma release from activated T cells grown in the presence of these supernatants. Data obtained from the MTS assays suggest a trend toward a reductionin the proliferative capacity of HC11 cells exposed to these supernatants. To distinguish whether the decrease in metabolic activity detected by the MTS assay is due to actual growth reduction or death of a subpopulation of cells, we perform cell death assays using two different markers of cell death. The assays confirm that growth arrest and not death is responsible for the decreased bioreduction of the MTS tetrazolium compound. FACScan data from the cell death assays also indicate an interesting decrease in the size of cells grown in supernatant versus medial control. This is an important avenue for further study. ELISA results show a decrease in interferon gamma release from activated T cells grown in supernatant from Notch 1 expressing cells. Currently, we are attempting to identify the secreted factors responsible for these effects. Overall, the data suggests a novel mechanism in which Notch 1 expression may contribute to breast cancer progression through the secretion of factors that help tumor cells escape immunosurveillance and regulate growth of neighboring cells.