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Drugs targeting microtubules rely on the mitotic checkpoint to arrest cell proliferation. The prolonged mitotic arrest induced by such drugs is followed by a G1 arrest. Here, we follow for several weeks the fate of G1-arrested human cells after treatment with nocodazole. We find that a small fraction of cells escapes from the arrest and resumes proliferation. These escaping cells experience reduced DNA damage and p21 activation. Cells surviving treatment are enriched for anti-apoptotic proteins, including Triap1. Increasing Triap1 levels allows cells to survive the first treatment with reduced DNA damage and lower levels of p21; accordingly, decreasing Triap1 re-sensitizes cells to nocodazole. We show that Triap1 upregulation leads to the retention of cytochrome c in the mitochondria, opposing the partial activation of caspases caused by nocodazole. In summary, our results point to a potential role of Triap1 upregulation in the emergence of resistance to drugs that induce prolonged mitotic arrest., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

Improperly attached chromosomes activate the mitotic checkpoint that arrests cell division before anaphase. Cells can maintain an arrest for several hours but eventually will resume proliferation, a process we refer to as adaptation. Whether adapting cells bypass an active block or whether the block has to be removed to resume proliferation is not clear. Likewise, it is not known whether all cells of a genetically homogeneous population are equally capable to adapt. Here, we show that the mitotic checkpoint is operational when yeast cells adapt and that each cell has the same propensity to adapt. Our results are consistent with a model of the mitotic checkpoint where adaptation is driven by random fluctuations of APC/C Cdc20 , the molecular species inhibited by the checkpoint. Our data provide a quantitative framework for understanding how cells overcome a constant stimulus that halts cell cycle progression., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Background: The spindle assembly checkpoint (SAC) arrests cells when kinetochores are unattached to spindle microtubules. The signaling pathway is initiated at the kinetochores by one SAC component, Mad2, which catalyzes the initial steps of the cascade via the conformational dimerization of its open and closed conformers. Away from kinetochores, the dimerization surface of Mad2 has been proposed, based on data in vitro, to either interact with SAC activators or inactivators and thus to contribute to SAC activation or silencing. Here, we analyze its role in vivo., Results: To analyze the putative pathway downstream of the kinetochores, we used two complementary approaches: we activated the SAC ectopically and independently from kinetochores, and we separated genetically the kinetochore-dependent and independent pools of Mad2. We found that the dimerization surface is required also downstream of kinetochores to mount a checkpoint response., Conclusion: Our results show that away from kinetochores the dimerization surface is required for stabilizing the end-product of the pathway, the mitotic checkpoint complex. Surprisingly, downstream of kinetochores the surface does not mediate Mad2 dimerization. Instead, our results are consistent with a role of Mad3 as the main interactor of Mad2 via the dimerization surface., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The spindle assembly checkpoint (SAC) restricts mitotic exit to cells that have completed chromosome-microtubule attachment. Cdc20 is a bifunctional protein. In complex with SAC proteins Mad2, BubR1, and Bub3, Cdc20 forms the mitotic checkpoint complex (MCC), which binds the anaphase-promoting complex (APC/C) and inhibits its mitotic exit-promoting activity. When devoid of SAC proteins, Cdc20 serves as an APC/C coactivator and promotes mitotic exit. During mitotic arrest, Cdc20 is continuously degraded via ubiquitin-dependent proteolysis and resynthesized. It is believed that this cycle keeps the levels of Cdc20 below a threshold above which Cdc20 would promote mitotic exit. We report that p31(comet), a checkpoint antagonist, is necessary for mitotic destabilization of Cdc20. p31(comet) depletion stabilizes the MCC, super-inhibits the APC/C, and delays mitotic exit, indicating that Cdc20 proteolysis in prometaphase opposes the checkpoint. Our studies reveal a homeostatic network in which checkpoint-sustaining and -repressing forces oppose each other during mitotic arrest and suggest ways for enhancing the sensitivity of cancer cells to antitubulin chemotherapeutics., (Copyright © 2011 Elsevier Inc. All rights reserved.)