Abstract 659: Overexpression of TPX2 accelerates cell cycle progression in melanoma and is an indicator of response to Aurora A kinase inhibitors

Abstract

Abstract There is a tremendous need to identify more effective treatments for metastatic melanoma. In order to detect genetic changes in melanoma that might facilitate the development of novel therapies, we performed aCGH in melanoma cell lines and tumors and identified that Targeting Protein for Xklp2 (TPX2) was the most commonly amplified gene on 20q11.21, a region of frequent gain. Gene expression profiling studies also demonstrated overexpression of TPX2, suggesting a previously unknown role in the development of melanoma. TPX2 is a microtubule-associated protein that regulates bipolar spindle assembly and centrosome replication; the TPX2 - Aurora A interaction is essential for accurate segregation of chromosome and mitosis progression. We evaluated a potential role for TPX2 overexpression in melanoma using TPX2 overexpressing melanoma cell lines as a model. TPX2 overexpressing cell lines display accelerated cell cycle progression, increased CDK1/CDK2 activity, cyclin A/B1 levels, and constitutive activation and overexpression of Aurora A. We depleted TPX2 using shRNA to further dissect its role in melanoma. In unsynchronized cells, TPX2 depletion causes prolonged mitotic arrest accompanied by persistent activation of the spindle-assembly checkpoint (SAC) and caspase-3, and subsequent caspase-dependent cell death. In contrast, with G1/S synchronization, TPX2 depletion decreases S phase entry and delays S-G2-M phase transition followed by marked cell death. Accordingly, TPX2 depletion was associated with decreased CDK1 activity but not CDK2 activity, and activation of caspase and low activation of the SAC. Our data demonstrate that TPX2 overexpression is required for increased CDK1-cyclinB1 activity, thus accelerating cell cycle progression. Accordingly, TPX2-overexpressing melanoma cell lines are dependent on TPX2 for proliferation, whereas non-overexpressing cell lines and melanocytes are not. Additionally, TPX2-overexpressing cell lines are 3-10 time more sensitive to an Aurora A kinase inhibitor (VX680) than non-overexpressing cell line, suggesting that TPX2-activating Aurora A kinase could become a novel therapeutic target for treatment of melanoma with highly expressed TPX2, Finally, TPX2-IHC staining demonstrated that a significantly increased expression of TPX2 in primary and metastatic melanoma as compared to begin nevi, suggesting it is a marker of progression. Thus, we have identified TPX2 as a novel gene upregulated in melanoma. Overexpression of TPX2 may be a marker of tumors sensitive to Aurora A inhibitors allowing patient stratification for optimal therapeutic selection. 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 659.