Abstract P1-03-05: Separase Over Expression Co-Operates with Loss of p53 in Promoting Aberrant Proliferation, Delayed Involution and Accumulation of DNA Damage in the Mouse Mammary Epithelium

Abstract

Background: Aneuploidy is a common feature of human tumors, often correlating with poor prognosis. Several proteins involved in the mitotic spindle checkpoint are thought to play a major role in aneuploidy suppression. Specifically, the cohesin proteins that regulate sister chromatid separation and Separase, the endopeptidase that cleaves Rad21 to remove cohesion and allow timely cell cycle progression are thought to play key roles in maintaining normal cellular ploidy and preventing accumulation of abnormal cellular karyotypes. Studies using a transplant model showed that over expression of Separase in diploid mouse mammary epithelial cells resulted in the rapid accumulation of aneuploidy, and when transplanted in mice, there was rapid development of mammary tumors. It was also shown before that a sub set of human breast cancers show significant over expression of Separase, suggesting a possible role of Separase in the development and/or progression of breast cancer. Material and Methods: Using genetically engineered mouse models we studied the direct effect of Separase over expression in the mouse mammary epithelium. Two separate mammary gland specific promoters, WAP and MMTV, were used to drive Separase expression in the mouse mammary gland. The role of loss of p53 combined with over expression of Separase was studied by crossing the Tg-MMTV and WAP-Separase mice with p53 knockout mice in the same genetic background. Results: We found that over expression of Separase in the mouse mammary epithelium resulted in aberrant proliferation as early as day one lactation. The increase in proliferation was more acute in a p53 heterozygous background. Also, the Separase over expressing mice showed a significant delay in involution compared to wild type mammary epithelium and an accumulation of DNA damage. In a p53 heterozygous background, some of these mice developed spontaneous mammary tumors over a period of 7-12 months. Ongoing studies are evaluating the histopathological nature of these mammary tumors. Discussion: Previous studies suggested that Separase is over expressed in a sub set of human breast cancers. An understanding of the specific biological pathways involved in the initiation and progression of cancer in the mammary epithelium from aberrant expression of Separase can establish Separase as a novel diagnostic marker for breast cancer screening. Our studies suggest that Separase over expression in the mammary epithelium results in accumulation of aberrant proliferation and delayed involution post lactation, as well as results in the accumulation of DNA damage. These factors combined with loss of a key tumor suppressor like p53 can lead to genetic instability and breast cancer development. Further classification of the sub type of breast cancer in this animal model using array analysis can help establish Separase as a new prognostic marker in breast cancer research. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P1-03-05.