Abstract A large number of patients are resistant to taxane-based chemotherapy. Functional mitotic checkpoints are essential for taxane sensitivity. Thus, mitotic regulators are potential markers for therapy response and could be targeted for anticancer therapy. In this study we identified a novel function of Ubiquitin Specific processing Protease-7 (USP7) that interacts and cooperates with protein Daxx in regulation of mitosis and taxane resistance. Depletion of USP7 impairs mitotic progression, stabilizes cyclin B and reduces stability of the mitotic E3 ubiquitin ligase, Checkpoint with Forkhead and RING finger (CHFR). Consequently, cells with depleted of USP7 accumulate Aurora A kinase, a CHFR substrate, thus elevating multipolar mitoses. We further show that these effects are independent from the USP7 substrate p53. Thus, USP7 and Daxx are necessary to regulate proper execution of mitosis, partially via regulation of CHFR and Aurora A kinase stability. Results from colony formation assay, in silico analysis across the NCI60 platform and in breast cancer patients suggest that USP7 levels inversely correlate with response to taxanes, pointing at the USP7 protein as a potential predictive factor for taxane response in cancer patients. In addition, we demonstrated that inhibition of Aurora A attenuates USP7-mediated taxane resistance, suggesting that combinatorial drug regimens of Taxol and Aurora A inhibitors may improve the outcome of chemotherapy response in cancer patients resistant to taxane treatment. Finally our study offers novel insights on USP7 inhibition as cancer therapy. Citation Format: Serena Giovinazzi, Viacheslav M. Morozov, Matthew K. Summers, William C. Reinhold, Alexander M. Ishov. USP7 and Daxx regulate mitosis progression and taxane sensitivity by affecting stability of Aurora A kinase. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 573. doi:10.1158/1538-7445.AM2013-573