Depletion of p31 promotes sensitivity to antimitotic drugs

Antimitotic spindle poisons are among the most important chemotherapeutic agents available. However, precocious mitotic exit by mitotic slippage limit the cytotoxicity of spindle poisons. The MAD2-binding protein p31 is implicated in the silencing the spindle-assembly checkpoint after all kinetochores are attached to spindles. In this study, we reported that the levels of p31 and MAD2 in different cell lines are closely linked with the susceptibility to mitotic slippage. Downregulation of p31 increased the sensitivity of multiple cancer cell lines to spindle poisons including nocodazole, vincristine, and Taxol. In the absence of p31, lower concentrations of spindle poisons were required to induce mitotic block. The delay in checkpoint silencing was induced by an accumulation of mitotic checkpoint complexes. The increase in the duration of mitotic block after p31 depletion resulted in a dramatic increase in mitotic cell death upon challenge with spindle poisons. Significantly, cells that are normally prone to mitotic slippage and resistant to spindle disruption-mediated mitotic death were also sensitized after p31 depletion. These results highlighted the importance of p31 in checkpoint silencing and its potential as a target for antimitotic therapies. –––––––––––––––––––––––––––––––––––––––– Mitotic exit is driven by anaphase-promoting complex/cyclosome (APC/C), which mediates the destruction of substrates including cyclin B and securin (1). Although phosphorylation by CDK1 and binding to CDC20 are involved in APC/C activation, complete activation is initiated only when all the chromosomes have achieved proper bipolar spindle attachment. Unattached kinetochores or the absence of tension between the paired kinetochores activates the spindleassembly checkpoint (2). Essential components of the checkpoint include a diffusible complex containing MAD2, BUBR1, BUB3, and CDC20 (called the mitotic checkpoint complex or MCC), which promotes the inhibition of APC/C–CDC20 by MAD2 (3). Binding to CDC20 requires a conformational change in MAD2 from an open (O-MAD2) to a closed conformation (C-MAD2) (4). Several mechanisms have been implicated in switching off the checkpoint after it is satisfied. In mammalian cells, there is compelling evidence that MAD2 is neutralized by binding to a protein called p31 (also called MAD2L1BP) (5). While overexpression of p31 disrupts the http://www.jbc.org/cgi/doi/10.1074/jbc.M112.364356 The latest version is at JBC Papers in Press. Published on April 27, 2012 as Manuscript M112.364356