DNA-Damage Response during Mitosis Induces Whole-Chromosome Missegregation
TL;DR: It is shown that when DNA damage is induced during mitosis, the DDR unexpectedly induces errors in the segregation of entire chromosomes, thus linking structural and numerical chromosomal instabilities.
Abstract: Many cancers display both structural (s-CIN) and numerical (w-CIN) chromosomal instabilities. Defective chromosome segregation during mitosis has been shown to cause DNA damage that induces structural rearrangements of chromosomes (s-CIN). In contrast, whether DNA damage can disrupt mitotic processes to generate whole chromosomal instability (w-CIN) is unknown. Here we show that activation of the DNA damage response (DDR) during mitosis selectively stabilizes kinetochore-microtubule (k-MT) attachments to chromosomes through Aurora-A and Plk1 kinases, thereby increasing the frequency of lagging chromosomes during anaphase. Inhibition of DDR proteins, ATM or Chk2, abolishes the effect of DNA damage on k-MTs and chromosome segregation, whereas activation of the DDR in the absence of DNA damage is sufficient to induce chromosome segregation errors. Finally, inhibiting the DDR during mitosis in cancer cells with persistent DNA damage suppresses inherent chromosome segregation defects. Thus, DDR during mitosis inappropriately stabilizes k-MTs creating a link between s-CIN and w-CIN.
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TL;DR: An improved understanding of the tumour-intrinsic processes that inhibit essential immune surveillance processes, such as phagocytosis and innate immune sensing, could pave the way for the development of highly effective combination immunotherapy strategies that modulate both innate and adaptive antitumour immune responses.
Abstract: Cancer immunotherapies targeting adaptive immune checkpoints have substantially improved patient outcomes across multiple metastatic and treatment-refractory cancer types. However, emerging studies have demonstrated that innate immune checkpoints, which interfere with the detection and clearance of malignant cells through phagocytosis and suppress innate immune sensing, also have a key role in tumour-mediated immune escape and might, therefore, be potential targets for cancer immunotherapy. Indeed, preclinical studies and early clinical data have established the promise of targeting phagocytosis checkpoints, such as the CD47-signal-regulatory protein α (SIRPα) axis, either alone or in combination with other cancer therapies. In this Review, we highlight the current understanding of how cancer cells evade the immune system by disrupting phagocytic clearance and the effect of phagocytosis checkpoint blockade on induction of antitumour immune responses. Given the role of innate immune cells in priming adaptive immune responses, an improved understanding of the tumour-intrinsic processes that inhibit essential immune surveillance processes, such as phagocytosis and innate immune sensing, could pave the way for the development of highly effective combination immunotherapy strategies that modulate both innate and adaptive antitumour immune responses.
454 citations
TL;DR: These multipronged effects distinguish CIN as a central driver of tumor evolution and as a genomic source for the crosstalk between the tumor and its microenvironment, in the course of immune editing and evasion.
355 citations
TL;DR: A detailed analysis of cell cycle control mechanisms and their role in cancer can be found in this article, where the authors reveal how these dependencies can be best exploited in cancer treatment and how to best exploit these dependencies.
Abstract: Cancer is a group of diseases in which cells divide continuously and excessively. Cell division is tightly regulated by multiple evolutionarily conserved cell cycle control mechanisms, to ensure the production of two genetically identical cells. Cell cycle checkpoints operate as DNA surveillance mechanisms that prevent the accumulation and propagation of genetic errors during cell division. Checkpoints can delay cell cycle progression or, in response to irreparable DNA damage, induce cell cycle exit or cell death. Cancer-associated mutations that perturb cell cycle control allow continuous cell division chiefly by compromising the ability of cells to exit the cell cycle. Continuous rounds of division, however, create increased reliance on other cell cycle control mechanisms to prevent catastrophic levels of damage and maintain cell viability. New detailed insights into cell cycle control mechanisms and their role in cancer reveal how these dependencies can be best exploited in cancer treatment.
270 citations
TL;DR: Findings suggest that the relationship between CIN, aneuploidy and cancer is more complex than what was previously anticipated and a working hypothesis is proposed to reconcile the conflicting observations regarding the role of aneuPLoidsy and CIN in tumorigenesis.
Abstract: Genomic instability (GIN) is a hallmark of cancer cells that facilitates the acquisition of mutations conferring aggressive or drug-resistant phenotypes during cancer evolution. Chromosomal instability (CIN) is a form of GIN that involves frequent cytogenetic changes leading to changes in chromosome copy number (aneuploidy). While both CIN and aneuploidy are common characteristics of cancer cells, their roles in tumor initiation and progression are unclear. On the one hand, CIN and aneuploidy are known to provide genetic variation to allow cells to adapt in changing environments such as nutrient fluctuations and hypoxia. Patients with constitutive aneuploidies are more susceptible to certain types of cancers, suggesting that changes in chromosome copy number could positively contribute to cancer evolution. On the other hand, chromosomal imbalances have been observed to have detrimental effects on cellular fitness and might trigger cell cycle arrest or apoptosis. Furthermore, mouse models for CIN have led to conflicting results. Taken together these findings suggest that the relationship between CIN, aneuploidy and cancer is more complex than what was previously anticipated. Here we review what is known about this complex menage a trois, discuss recent evidence suggesting that aneuploidy, CIN and GIN together promote a vicious cycle of genome chaos. Lastly, we propose a working hypothesis to reconcile the conflicting observations regarding the role of aneuploidy and CIN in tumorigenesis.
209 citations
Cites background from "DNA-Damage Response during Mitosis ..."
...To close the loop, it has been recently shown that activating the DNA damage response during mitosis by DNA-damaging drugs or ionizing radiation resulted in increased chromosome missegregation through stabilization of kinetochore-microtubule interactions by Aurora A and PLK1 kinases [121]....
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TL;DR: It is concluded that ongoing CIN is common in colorectal cancer organoids, and proposed that CIN levels and the tolerance for mitotic errors shape aneuploidy landscapes and karyotype heterogeneity.
Abstract: Chromosome segregation errors cause aneuploidy and genomic heterogeneity, which are hallmarks of cancer in humans. A persistent high frequency of these errors (chromosomal instability (CIN)) is predicted to profoundly impact tumor evolution and therapy response. It is unknown, however, how prevalent CIN is in human tumors. Using three-dimensional live-cell imaging of patient-derived tumor organoids (tumor PDOs), we show that CIN is widespread in colorectal carcinomas regardless of background genetic alterations, including microsatellite instability. Cell-fate tracking showed that, although mitotic errors are frequently followed by cell death, some tumor PDOs are largely insensitive to mitotic errors. Single-cell karyotype sequencing confirmed heterogeneity of copy number alterations in tumor PDOs and showed that monoclonal lines evolved novel karyotypes over time in vitro. We conclude that ongoing CIN is common in colorectal cancer organoids, and propose that CIN levels and the tolerance for mitotic errors shape aneuploidy landscapes and karyotype heterogeneity.
148 citations
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TL;DR: It is shown that ATM is held inactive in unirradiated cells as a dimer or higher-order multimer, with the kinase domain bound to a region surrounding serine 1981 that is contained within the previously described ‘FAT’ domain.
Abstract: The ATM protein kinase, mutations of which are associated with the human disease ataxia-telangiectasia, mediates responses to ionizing radiation in mammalian cells. Here we show that ATM is held inactive in unirradiated cells as a dimer or higher-order multimer, with the kinase domain bound to a region surrounding serine 1981 that is contained within the previously described 'FAT' domain. Cellular irradiation induces rapid intermolecular autophosphorylation of serine 1981 that causes dimer dissociation and initiates cellular ATM kinase activity. Most ATM molecules in the cell are rapidly phosphorylated on this site after doses of radiation as low as 0.5 Gy, and binding of a phosphospecific antibody is detectable after the introduction of only a few DNA double-strand breaks in the cell. Activation of the ATM kinase seems to be an initiating event in cellular responses to irradiation, and our data indicate that ATM activation is not dependent on direct binding to DNA strand breaks, but may result from changes in the structure of chromatin.
3,411 citations
"DNA-Damage Response during Mitosis ..." refers background in this paper
...To this end, we exposed cells to chloroquine, an independent activator of ATM kinase (18)....
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TL;DR: KU-55933 is a novel, specific, and potent inhibitor of the ATM kinase, which did not potentiate the cytotoxic effects of ionizing radiation on ataxia-telangiectasia cells, nor did it affect their cell cycle profile after DNA damage.
Abstract: The serine/threonine protein kinase ATM signals to cell cycle and DNA repair components by phosphorylating downstream targets such as p53, CHK2, NBS1, and BRCA1. Mutation of ATM occurs in the human autosomal recessive disorder ataxia-telangiectasia, which is characterized by hypersensitivity to ionizing radiation and a failure of cells to arrest the cell cycle after the induction of DNA double-strand breaks. It has thus been proposed that ATM inhibition would cause cellular radio- and chemosensitization. Through screening a small molecule compound library developed for the phosphatidylinositol 3′-kinase–like kinase family, we identified an ATP-competitive inhibitor, 2-morpholin-4-yl-6-thianthren-1-yl-pyran-4-one (KU-55933), that inhibits ATM with an IC50 of 13 nmol/L and a Ki of 2.2 nmol/L. KU-55933 shows specificity with respect to inhibition of other phosphatidylinositol 3′-kinase–like kinases. Cellular inhibition of ATM by KU-55933 was demonstrated by the ablation of ionizing radiation-dependent phosphorylation of a range of ATM targets, including p53, γH2AX, NBS1, and SMC1. KU-55933 did not show inhibition of UV light DNA damage induced cellular phosphorylation events. Exposure of cells to KU-55933 resulted in a significant sensitization to the cytotoxic effects of ionizing radiation and to the DNA double-strand break-inducing chemotherapeutic agents, etoposide, doxorubicin, and camptothecin. Inhibition of ATM by KU-55933 also caused a loss of ionizing radiation-induced cell cycle arrest. By contrast, KU-55933 did not potentiate the cytotoxic effects of ionizing radiation on ataxia-telangiectasia cells, nor did it affect their cell cycle profile after DNA damage. We conclude that KU-55933 is a novel, specific, and potent inhibitor of the ATM kinase.
1,197 citations
"DNA-Damage Response during Mitosis ..." refers background in this paper
...KU55933, an inhibitor of activated ATM kinase (16), completely abolished the effects of doxorubicin on k-MT stability in metaphase cells (Fig....
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TL;DR: A mechanism by which errors in mitotic chromosome segregation generate DNA breaks via the formation of structures called micronuclei is identified, which potentially lead to mutations and chromosome rearrangements that can integrate into the genome.
Abstract: The involvement of whole-chromosome aneuploidy in tumorigenesis is the subject of debate, in large part because of the lack of insight into underlying mechanisms. Here we identify a mechanism by which errors in mitotic chromosome segregation generate DNA breaks via the formation of structures called micronuclei. Whole-chromosome-containing micronuclei form when mitotic errors produce lagging chromosomes. We tracked the fate of newly generated micronuclei and found that they undergo defective and asynchronous DNA replication, resulting in DNA damage and often extensive fragmentation of the chromosome in the micronucleus. Micronuclei can persist in cells over several generations but the chromosome in the micronucleus can also be distributed to daughter nuclei. Thus, chromosome segregation errors potentially lead to mutations and chromosome rearrangements that can integrate into the genome. Pulverization of chromosomes in micronuclei may also be one explanation for 'chromothripsis' in cancer and developmental disorders, where isolated chromosomes or chromosome arms undergo massive local DNA breakage and rearrangement.
1,072 citations
TL;DR: Evidence for impaired replication fork progression and increased DNA replication stress in CIN+ colorectal cancer (CRC) cells relative to CIN− CRC cells is found, with structural chromosome abnormalities precipitating chromosome missegregation in mitosis.
Abstract: Cancer chromosomal instability (CIN) results in an increased rate of change of chromosome number and structure and generates intratumour heterogeneity. CIN is observed in most solid tumours and is associated with both poor prognosis and drug resistance. Understanding a mechanistic basis for CIN is therefore paramount. Here we find evidence for impaired replication fork progression and increased DNA replication stress in CIN(+) colorectal cancer (CRC) cells relative to CIN(-) CRC cells, with structural chromosome abnormalities precipitating chromosome missegregation in mitosis. We identify three new CIN-suppressor genes (PIGN (also known as MCD4), MEX3C (RKHD2) and ZNF516 (KIAA0222)) encoded on chromosome 18q that are subject to frequent copy number loss in CIN(+) CRC. Chromosome 18q loss was temporally associated with aneuploidy onset at the adenoma-carcinoma transition. CIN-suppressor gene silencing leads to DNA replication stress, structural chromosome abnormalities and chromosome missegregation. Supplementing cells with nucleosides, to alleviate replication-associated damage, reduces the frequency of chromosome segregation errors after CIN-suppressor gene silencing, and attenuates segregation errors and DNA damage in CIN(+) cells. These data implicate a central role for replication stress in the generation of structural and numerical CIN, which may inform new therapeutic approaches to limit intratumour heterogeneity.
724 citations
"DNA-Damage Response during Mitosis ..." refers background in this paper
...However, cancer cells often encounter DNA damage during mitosis secondary to checkpoint slippage with persistence of premitotic damage (3)...
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...However, it was recently shown that premitotic replication stress, which leads to DNA damage that can persist into mitosis, is also a feature of colorectal cell lines with w-CIN (3)....
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...Anaphase spindles can also exhibit bridged chromatin (3, 11) such that DNA, from the same chromosome or from nondisjoined sister chromatids, is stretched toward opposite spindle poles (Fig....
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TL;DR: It is demonstrated that the initial activation of PLK1 is a primary function of aurora A, and that Bora/aurora-A-dependent phosphorylation is a prerequisite for PLK 1 to promote mitotic entry after a checkpoint-dependent arrest.
Abstract: Polo-like kinase-1 (PLK1) is an essential mitotic kinase regulating multiple aspects of the cell division process. Activation of PLK1 requires phosphorylation of a conserved threonine residue (Thr 210) in the T-loop of the PLK1 kinase domain, but the kinase responsible for this has not yet been affirmatively identified. Here we show that in human cells PLK1 activation occurs several hours before entry into mitosis, and requires aurora A (AURKA, also known as STK6)-dependent phosphorylation of Thr 210. We find that aurora A can directly phosphorylate PLK1 on Thr 210, and that activity of aurora A towards PLK1 is greatly enhanced by Bora (also known as C13orf34 and FLJ22624), a known cofactor for aurora A (ref. 7). We show that Bora/aurora-A-dependent phosphorylation is a prerequisite for PLK1 to promote mitotic entry after a checkpoint-dependent arrest. Importantly, expression of a PLK1-T210D phospho-mimicking mutant partially overcomes the requirement for aurora A in checkpoint recovery. Taken together, these data demonstrate that the initial activation of PLK1 is a primary function of aurora A.
664 citations
"DNA-Damage Response during Mitosis ..." refers background in this paper
...Here, we show that activation of the DNA-damage response (DDR) during mitosis selectively stabilizes kinetochore–microtubule (k-MT) attachments to chromosomes through Aurora-A and PLK1 kinases, thereby increasing the frequency of lagging chromosomes during anaphase....
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...Yet, there was an increase in the levels of phospho–Centromere protein A (pCENP-A), which is also phosphorylated by Aurora-A kinase (Supplementary Fig....
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...Upon DNA damage, CHK1 and CHK2 inhibit mitotic entry by deregulating Pololike kinase 1 (PLK1) whose subsequent activation by AuroraA is required for checkpoint recovery (1, 2)....
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...Tubulin-specific DM1α (Sigma-Aldrich), anti-centromere (CREST; Dartmouth College, Hanover, NH), HEC1/NDC80-specific (Novus Biologicals), anti–γ-H2AX (Novus Biologicals), GFP-specific (William Wickner, Dartmouth College, Hanover, NH), anti-pCHK2 S19 and S33/35 (Cell Signaling Technology), anti-CHK2 (Cell Signaling Technology), anti–pPLK1-Thr210 (Cell Signaling Technology), anti–pAurora-A antibodies were used at dilutions of 1:1,000 (1:10,000 for anti-GFP antibody)....
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...Collectively, these results suggest that the DDR signals through Aurora-A and PLK1 to increase k-MT stability in response to mitotic DNA damage....
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