Abstract 2038: Aurora A and BRCA1 cooperate to control cytokinesis failure leading to aneuploidy in ovarian cystadenoma cells

Abstract

Abstract Aneuploidy, defined by a chromosome number that is not a multiple of the haploid number, is a hallmark of cancer. In order to study the mechanism of aneuploidy development in ovarian cancer, we used cell strains derived from benign ovarian cystadenomas, the benign counterparts of the type of ovarian cancer that develops in BRCA1 mutation carriers. The cells were transfected with SV40 Large T Antigen, conferring the equivalent of a p53 mutation, which is present in nearly all cancers that develop in BRCA1 mutation carriers. These cells are not immortal and invariably reach crisis after up to 50 population doublings in vitro. We previously showed that this crisis event, which is not triggered by telomere attrition, is associated with a cell cycle arrest at the M phase, and that decreased BRCA1 expression allows cells to overcome this crisis event, resulting in tetraploidy and subsequent aneuploidy. The finding that cells recovering from crisis undergo sudden changes in their ploidy status strongly suggests that such recovery is characterized by initiation of a new cell cycle without first completing cytokinesis. We used time-lapse photography to test this hypothesis. Such studies revealed that a significant proportion of cells treated with siRNA against BRCA1 recovered from a cell cycle arrest during the mitotic phase without undergoing cytokinesis, resulting in bi-nucleation. We further hypothesized that Aurora A plays a role in regulating this process, in part, by acting as an upstream regulator of BRCA1 expression. Here we show that Aurora A protein and kinase activity are both up-regulated while levels of BRCA1 expression are down-regulated in cells as they age in culture. Levels of BRCA1 expression increased upon knockdown of Aurora A kinase, further suggesting an inverse relationship between expression levels of these proteins. Inhibition of Aurora A prevented recovery from mitotic arrest as evidenced by an increase in BubR1 and Mad2, two components of the mitotic checkpoint complex and a decrease in Cdc27, a component of the anaphase promoting complex. Genomic DNA profiles of cells treated with siRNA against Aurora A showed decreased tetraploidy and microscopic examination showed decreased multinucleation. Time-lapse photography of cells approaching crisis, treated with siRNA against Aurora A showed that the M phase arrest was prolonged compared to controls and invariably led to apoptosis in contrast to cells treated with siRNA against BRCA1. Down regulation of Aurora A in a younger cells, not approaching crisis, did not induce a mitotic arrest. We conclude that decreased BRCA1 expression in cells approaching crisis leads to recovery from a mitotic arrest without completion of cytokinesis, leading to tetraploidy and subsequent aneuploidy. Although decreased Aurora A expression does not induce a mitotic arrest, it prevents recovery from such arrest, resulting in cell death from apoptosis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2038. doi:1538-7445.AM2012-2038