Abstract 1068: Cooperation between BRCA1 and Aurora A kinase regulates in vitro crisis in epithelial cells derived from benign ovarian tumors

Abstract

Abstract Aneuploidy, as defined by a chromosome number that is not a multiple of the haploid number, is a hallmark of cancer. We used an in vitro cell culture model where explants of benign epithelial ovarian tumors (cystadenomas) were transfected with an expression vector for SV40 Large T Antigen, allowing bypass of senescence due, in part, to p53 and Rb inhibition by this antigen. We previously showed that such cells eventually reach a crisis event that is associated with a cell cycle arrest at the M phase and is independent of telomere attrition. Cells that recover from this event do not complete cytokinesis and become polyploid, which is a precursor to aneuploidy. Decreased BRCA1 expression facilitates abrogation of mitotic arrest, leading to increased rates of aneuploidy. We hypothesized that Aurora A plays a role in regulating this ploidy-associated crisis event by acting as an upstream regulator of BRCA1 expression. Here we show that Aurora A kinase activity and expression is up-regulated in cells approaching crisis. Over-expression of Aurora A resulted in decreased levels of BRCA1, resulting in increased tetraploidy and aneuploidy, secondary to cells overcoming a ploidy-associated crisis. Levels of BRCA1 expression increased upon knockdown of Aurora A kinase using siRNA, further suggesting an inverse relationship between expression levels of these two proteins. Inhibition of Aurora A in cultured ovarian cystadenomas approaching crisis led to decreased cell proliferation and a concomitant decrease in tetraploidy. We tested the hypothesis that this was associated with an increase in crisis-related apoptosis by knocking down Aurora A kinase using siRNA technologies in cells approaching crisis, followed by western blotting using antibodies against PARP and cleaved CASPASE 7 fragment. The results indeed showed increased levels of these two protein fragments upon Aurora A knockdown, indicating activation of a caspase-regulated apoptotic pathway. Our findings suggest a novel role for Aurora A's influence on BRCA1 expression levels in cells approaching ploidy dependent crisis. This may, in part, explain the increased rate of near polyploidy associated with high grade ovarian carcinomas and may provide insights into the mechanism underlying aneuploidy development in epithelial cancers in general. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1068.