Interfering with mitosis for cancer treatment is an old concept that has proven highly successful in the clinics. Microtubule poisons are used to treat patients with different types of blood or solid ...cancer since more than 20 years, but how these drugs achieve clinical response is still unclear. Arresting cells in mitosis can promote their demise, at least in a petri dish. Yet, at the molecular level, this type of cell death is poorly defined and cancer cells often find ways to escape. The signaling pathways activated can lead to mitotic slippage, cell death, or senescence. Therefore, any attempt to unravel the mechanistic action of microtubule poisons will have to investigate aspects of cell cycle control, cell death initiation in mitosis and after slippage, at single‐cell resolution. Here, we discuss possible mechanisms and signaling pathways controlling cell death in mitosis or after escape from mitotic arrest, as well as secondary consequences of mitotic errors, particularly sterile inflammation, and finally address the question how clinical efficacy of anti‐mitotic drugs may come about and could be improved.
Arresting cells in mitosis is very successful as cancer treatment, but it remains unclear how clinical responses are achieved. This review discusses mechanisms controlling cell death in mitosis, and how clinical efficacy of anti‐mitotic drugs comes about and could be improved.
The Ser-Thr kinase mammalian target of rapamycin (mTOR) controls cell growth and metabolism by stimulating glycolysis and synthesis of proteins and lipids. To further understand the central role of ...mTOR in cell physiology, we used quantitative phosphoproteomics to identify substrates or downstream effectors of the two mTOR complexes. mTOR controlled the phosphorylation of 335 proteins, including CAD (carbamoyl-phosphate synthetase 2, aspartate transcarbamylase, and dihydroorotase). CAD catalyzes the first three steps in de novo pyrimidine synthesis. mTORC1 indirectly phosphorylated CAD-S1859 through S6 kinase (S6K). CAD-S1859 phosphorylation promoted CAD oligomerization and thereby stimulated de novo synthesis of pyrimidines and progression through S phase of the cell cycle in mammalian cells. Thus, mTORC1 also stimulates the synthesis of nucleotides to control cell proliferation.
Centrosomes, the main microtubule-organizing centers in animal cells, are replicated exactly once during the cell division cycle to form the poles of the mitotic spindle. Supernumerary centrosomes ...can lead to aberrant cell division and have been causally linked to chromosomal instability and cancer. Here, we report that an increase in the number of mature centrosomes, generated by disrupting cytokinesis or forcing centrosome overduplication, triggers the activation of the PIDDosome multiprotein complex, leading to Caspase-2-mediated MDM2 cleavage, p53 stabilization, and p21-dependent cell cycle arrest. This pathway also restrains the extent of developmentally scheduled polyploidization by regulating p53 levels in hepatocytes during liver organogenesis. Taken together, the PIDDosome acts as a first barrier, engaging p53 to halt the proliferation of cells carrying more than one mature centrosome to maintain genome integrity.
The PIDDosome is often used as the alias for a multi-protein complex that includes the p53-induced death domain protein 1 (PIDD1), the bipartite linker protein CRADD (also known as RAIDD) and the ...pro-form of an endopeptidase belonging to the caspase family, i.e. caspase-2. Yet, PIDD1 variants can also interact with a number of other proteins that include RIPK1 (also known as RIP1) and IKBKG (also known as NEMO), PCNA and RFC5, as well as nucleolar components such as NPM1 or NCL. This promiscuity in protein binding is facilitated mainly by autoprocessing of the full-length protein into various fragments that contain different structural domains. As a result, multiple responses can be mediated by protein complexes that contain a PIDD1 domain. This suggests that PIDD1 acts as an integrator for multiple types of stress that need instant attention. Examples are various types of DNA lesion but also the presence of extra centrosomes that can foster aneuploidy and, ultimately, promote DNA damage. Here, we review the role of PIDD1 in response to DNA damage and also highlight novel functions of PIDD1, such as in centrosome surveillance and scheduled polyploidisation as part of a cellular differentiation program during organogenesis.
Centrosome amplification results into genetic instability and predisposes cells to neoplastic transformation. Supernumerary centrosomes trigger p53 stabilization dependent on the PIDDosome (a ...multiprotein complex composed by PIDD1, RAIDD and Caspase‐2), whose activation results in cleavage of p53’s key inhibitor, MDM2. Here, we demonstrate that PIDD1 is recruited to mature centrosomes by the centriolar distal appendage protein ANKRD26. PIDDosome‐dependent Caspase‐2 activation requires not only PIDD1 centrosomal localization, but also its autoproteolysis. Following cytokinesis failure, supernumerary centrosomes form clusters, which appear to be necessary for PIDDosome activation. In addition, in the context of DNA damage, activation of the complex results from a p53‐dependent elevation of PIDD1 levels independently of centrosome amplification. We propose that PIDDosome activation can in both cases be promoted by an ANKRD26‐dependent local increase in PIDD1 concentration close to the centrosome. Collectively, these findings provide a paradigm for how centrosomes can contribute to cell fate determination by igniting a signalling cascade.
SYNOPSIS
The PIDDosome is a Caspase‐2‐activating platform assembling in response to two stimuli: genotoxic stress and supernumerary centrosomes. Here, both triggers are shown to rely on centrosomal localization of PIDD1, highlighting the centrosome’s capability to influence cell fate.
Centriolar distal appendage protein ANKRD26 is the centrosomal PIDD1 receptor.
The centrosome recruits the PIDD1 precursor, which undergoes subsequent autoproteolysis.
Clustering of PIDD1‐positive extra‐centrosomes is required for PIDDosome activation.
P53‐dependent PIDD1 transactivation leads to centrosome‐dependent PIDDosome activation even in the absence of extra‐centrosomes.
ANKRD26‐dependent PIDD1 recruitment is involved in p53 activation both upon genotoxic stress and in the presence of supernumerary centrosomes.
Cell death on extended mitotic arrest is considered arguably most critical for the efficacy of microtubule-targeting agents (MTAs) in anticancer therapy. While the molecular machinery controlling ...mitotic arrest on MTA treatment, the spindle assembly checkpoint (SAC), appears well defined, the molecular components executing cell death, as well as factors connecting both networks remain poorly understood. Here we conduct a mini screen exploring systematically the contribution of individual BCL2 family proteins at single cell resolution to death on extended mitotic arrest, and demonstrate that the mitotic phosphorylation of BCL2 and BCLX represent a priming event for apoptosis that is ultimately triggered by NOXA-dependent MCL1 degradation, enabling BIM-dependent cell death. Our findings provide a comprehensive model for the initiation of apoptosis in cells stalled in mitosis and provide a molecular basis for the increased efficacy of combinatorial treatment of cancer cells using MTAs and BH3 mimetics.
53BP1 acts at the crossroads between DNA repair and p53‐mediated stress response. With its interactors p53 and USP28, it is part of the mitotic surveillance (or mitotic stopwatch) pathway (MSP), a ...sensor that monitors the duration of cell division, promoting p53‐dependent cell cycle arrest when a critical time threshold is surpassed. Here, we show that Polo‐like kinase 1 (PLK1) activity is essential for the time‐dependent release of 53BP1 from kinetochores. PLK1 inhibition, which leads to 53BP1 persistence at kinetochores, prevents cytosolic 53BP1 association with p53 and results in a blunted MSP. Strikingly, the identification of CENP‐F as the kinetochore docking partner of 53BP1 enabled us to show that measurement of mitotic timing by the MSP does not take place at kinetochores, as perturbing CENP‐F‐53BP1 binding had no measurable impact on the MSP. Taken together, we propose that PLK1 supports the MSP by generating a cytosolic pool of 53BP1 and that an unknown cytosolic mechanism enables the measurement of mitotic duration.
Synopsis
Following an abnormally extended mitosis, cells activate p53 via 53BP1. Surprisingly, 53BP1 kinetochore localization is dispensable for this process, whereas PLK1 activity, a negative regulator of 53BP1 localization, appears to be essential.
53BP1 kinetochore localization is dispensable for the mitotic surveillance (or mitotic stopwatch) pathway (MSP).
PLK1 is required for the MSP.
PLK1 activity promotes 53BP1 kinetochore dynamics and 53BP1‐p53 complex formation.
Following an abnormally extended mitosis, cells activate p53 via 53BP1. Surprisingly, 53BP1 kinetochore localization is dispensable for this process, whereas PLK1 activity, a negative regulator of 53BP1 localization, appears to be essential.
Unscheduled increases in ploidy underlie defects in tissue function, premature aging, and malignancy. A concomitant event to polyploidization is the amplification of centrosomes, the main microtubule ...organization centers in animal cells. Supernumerary centrosomes are frequent in tumors, correlating with higher aggressiveness and poor prognosis. However, extra centrosomes initially also exert an onco-protective effect by activating p53-induced cell cycle arrest. If additional signaling events initiated by centrosomes help prevent pathology is unknown. Here, we report that extra centrosomes, arising during unscheduled polyploidization or aberrant centriole biogenesis, induce activation of NF-κB signaling and sterile inflammation. This signaling requires the NEMO-PIDDosome, a multi-protein complex composed of PIDD1, RIPK1, and NEMO/IKKγ. Remarkably, the presence of supernumerary centrosomes suffices to induce a paracrine chemokine and cytokine profile, able to polarize macrophages into a pro-inflammatory phenotype. Furthermore, extra centrosomes increase the immunogenicity of cancer cells and render them more susceptible to NK-cell attack. Hence, the PIDDosome acts as a dual effector, able to engage not only the p53 network for cell cycle control but also NF-κB signaling to instruct innate immunity.
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.
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•Cells arrested by nocodazole accumulate DNA damage but recover growth after G1 arrest•When treated for a second time, cells accumulate less DNA damage and recover faster•The expression of about 100 proteins, including Triap1, is altered•Increased Triap1 expression decreases DNA damage and accounts for the faster recovery
Antimitotic drugs impair microtubule dynamics and cause cells to arrest in mitosis or die due to DNA damage. Pavani et al. show that a fraction of cells escapes the arrest and restores proliferation and, when treated a second time, can repress cell death and decrease the extent of DNA damage.
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