TY - JOUR T1 - BubR1 Is Required for a Sustained Mitotic Spindle Checkpoint Arrest in Human Cancer Cells Treated with Tubulin-Targeting Pyrrolo-1,5-Benzoxazepines JF - Molecular Pharmacology JO - Mol Pharmacol SP - 419 LP - 430 DO - 10.1124/mol.107.039024 VL - 73 IS - 2 AU - Lisa M. Greene AU - Giuseppe Campiani AU - Mark Lawler AU - D. Clive Williams AU - Daniela M. Zisterer Y1 - 2008/02/01 UR - http://molpharm.aspetjournals.org/content/73/2/419.abstract N2 - Intrinsic or acquired resistance to chemotherapy is a major clinical problem that has evoked the need to develop innovative approaches to predict and ultimately reverse drug resistance. A prolonged G2M arrest has been associated with apoptotic resistance to various microtubule-targeting agents (MTAs). In this study, we describe the functional significance of the mitotic spindle checkpoint proteins, BubR1 and Bub3, in maintaining a mitotic arrest after microtubule disruption by nocodazole and a novel series of MTAs, the pyrrolo-1,5-benzoxazepines (PBOXs), in human cancer cells. Cells expressing high levels of BubR1 and Bub3 (K562, MDA-MB-231, and HeLa) display a prolonged G2M arrest after exposure to MTAs. On the other hand, cells with low endogenous levels of mitotic spindle checkpoint proteins (SK-BR-3 and HL-60) transiently arrest in mitosis and undergo increased apoptosis. The phosphorylation of BubR1 correlated with PBOX-induced G2M arrest in four cell lines tested, indicating an active mitotic spindle checkpoint. Gene silencing of BubR1 by small interfering RNA interference reduced PBOX-induced G2M arrest without enhancing apoptotic efficacy. Further analysis demonstrated that PBOX-treated BubR1-depleted cells were both mononucleated and multinucleated with a polyploid DNA content, suggesting a requirement for BubR1 in cytokinesis. Taken together, these results suggest that BubR1 contributes to the mitotic checkpoint induced by the PBOXs. The American Society for Pharmacology and Experimental Therapeutics ER -