Abstract A71: Cdk2, Mad2, and the tetraploidy checkpoint in paclitaxel-induced endoreduplication.

Abstract

Abstract The classic chemotherapeutic, paclitaxel, causes endoreduplication in cells, but the mechanism and cellular characteristics that promote this genome doubling are poorly understood. In studying the chromosomal instability of tumor cell lines from mice with mammary expression of a constitutively active Cyclin D1-Cdk2 fusion protein, we noticed an increased rate of this paclitaxel induced endoreduplication. Further studies have shown that this effect is specifically due to the kinase activity of Cdk2 and that increased Cdk2 activity causes of upregulation of the mitotic checkpoint protein, Mad2. While increased Mad2 expression alone has previously been shown to cause mitotic defects and genome doubling, it does not appear to be the culprit in this situation. We instead found that normalization of Mad2 levels through short hairpin RNA-mediated knockdown further increased the rate of endoreduplication in the presence of paclitaxel. It was seen that while exposure to the spindle poison further elevated Mad2 levels, long-term treatment led to an overall decrease in protein expression. This presumably allows cells to escape mitotic arrest and enter G1 phase, potentially triggering the somewhat controversial p53-mediated tetraploidy checkpoint. Indeed, stable knock-down of p53 cooperates with increased Cdk2 activity to create a very high rate of endoreduplication. These findings raise intriguing questions about the consequences of using one of the world's most widely used chemotherapeutic agents in patients with increased Cdk2 activity. Future studies will investigate whether this increased rate of endoreduplication worsens treatment outcome by eliciting chromosomal instability or improves it by generating cells that are unviable in the long-term. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A71.