Data from p31^comet Induces Cellular Senescence through p21 Accumulation and Mad2 Disruption

<div>Abstract<p>Functional suppression of spindle checkpoint protein activity results in apoptotic cell death arising from mitotic failure, including defective spindle formation, chromosome missegregation, and premature mitotic exit. The recently identified p31^comet protein acts as a spindle checkpoint silencer via communication with the transient Mad2 complex. In the present study, we found that p31^comet overexpression led to two distinct phenotypic changes, cellular apoptosis and senescence. Because of a paucity of direct molecular link of spindle checkpoint to cellular senescence, however, the present report focuses on the relationship between abnormal spindle checkpoint formation and p31^comet-induced senescence by using susceptible tumor cell lines. p31^comet-induced senescence was accompanied by mitotic catastrophe with massive nuclear and chromosomal abnormalities. The progression of the senescence was completely inhibited by the depletion of p21^{<i>Waf1/Cip1</i>} and partly inhibited by the depletion of the tumor suppressor protein p53. Notably, p21^{<i>Waf1/Cip1</i>} depletion caused a dramatic phenotypic conversion of p31^comet-induced senescence into cell death through mitotic catastrophe, indicating that p21^{<i>Waf1/Cip1</i>} is a major mediator of p31^comet-induced cellular senescence. In contrast to wild-type p31^comet, overexpression of a p31 mutant lacking the Mad2 binding region did not cause senescence. Moreover, depletion of Mad2 by small interfering RNA induced senescence. Here, we show that p31^comet induces tumor cell senescence by mediating p21^{<i>Waf1/Cip1</i>} accumulation and Mad2 disruption and that these effects are dependent on a direct interaction of p31^comet with Mad2. Our results could be used to control tumor growth. (Mol Cancer Res 2009;7(3):371–82)</p></div>