Unraveling the Molecular Mechanisms Underlying Spontaneous Multipolar Mitosis Through CIN-seq.

Glioblastoma (GB) is the most frequent human brain tumor and is associated with a poor prognosis. Multipolar mitosis and spindles have occasionally been observed in cultured glioblastoma cells and in glioblastoma tissues, but their mode of origin and relevance have remained unclear. In the present study, we investigated a novel GB cell line (SGB4) exhibiting mitotic aberrations and established a functional link between cytokinesis failure, centrosome amplification, multipolar mitosis and aneuploidy in glioblastoma. Long-term live cell imaging showed that >3% of mitotic SGB4 cells underwent multipolar mitosis (tripolar>tetrapolar>pentapolar). A significant amount of daugther cells generated by multipolar mitosis were viable and completed several rounds of mitosis. Pedigree analysis of mitotic events revealed that in many cases a bipolar mitosis with failed cytokinesis occurred prior to a multipolar mitosis. Additionally, we observed that SGB4 cells were also able to undergo a bipolar mitosis after failed cytokinesis. Colchicine-induced mitotic arrest and metaphase spreads demonstrated that SGB4 cells had a modal chromosome number of 58 ranging from 23 to 170. Approximately 82% of SGB4 cells were hyperdiploid (47-57 chromosomes) or hypotriploid (58-68 chromosomes). In conclusion, SGB4 cells passed through multipolar cell divisions and generated viable progeny by reductive mitoses. Our results identified cytokinesis failure occurring before and after multipolar or bipolar mitoses as important mechanisms to generate chromosomal heterogeneity in glioblastoma cells.

Mitotic index and multipolar mitosis in routine histologic sections as prognostic markers of pancreatic cancers: A clinicopathological study.

Introduction: Chromosomal instability (CIN) is the predominant form of genomic instability in cancers, characterized by both numerical and structural alterations of chromosomes. CIN is crucial for the most threatening aspect of cancers: their ability to evolve, allowing them to circumvent immune detection, metastasize, develop resistance to therapies, and lead to treatment failure. At the same time, the CIN phenotype could provide valuable targets for cancer therapy. We developed a multiplex FISH (miFISH) method to study heterogeneity and ongoing CIN in cancer cells. The objective of our research was to determine whether high-grade aneuploidy develops through sequential or abrupt changes in chromosomal content, a question previously unexplored due to the absence of comprehensive methods for simultaneously detecting different forms of ongoing CIN on a single-cell level. Experimental Procedure: Sequential hybridizations of miFISH panels allow the assessment of up to 35 probes per single cell. Each panel was designed to include the centromeric probe and gene-specific probes on the p- and q-arm for a given chromosome. This approach was applied to colorectal cancer cell lines (with and without microsatellite instability) and colorectal cancer samples. A total of 10000-25000 targets were collected from each slide. Analysis was done by counting of signals in mononucleated cells, binucleated/dividing cells and metaphase spreads. Results: The simultaneous evaluation of centromeric and gene-specific sets of miFISH probes led to unprecedented insights into the patterns of distribution of chromosomal content among individual cells, and, especially, in dividing cells. We compared different forms of ongoing CIN: structural rearrangements, formation of micronuclei with whole chromosomes or chromosomal fragments, non-disjunctions of chromosomes, grossly asymmetrical cell divisions, including divisions with ploidy changes and multipolar mitoses. We observed that gradual changes in chromosomal/genomic content occur primarily due to frequent structural rearrangements, less frequent chromosome or fragment losses in micronuclei, and very rare single chromosome non-disjunctions. Of note, grossly abnormal cell divisions, characterized by massive non-disjunctions and structural rearrangements, occur with relatively high frequency. The same patterns of chromosomal heterogeneity and instability have been observed in cancer cell lines and in tumor samples. Conclusions: The novel miFISH approach applied to studies of chromosomal instability in colorectal cancers and cell lines revealed multiple paths leading to chromosomal diversification of cancer cell populations. Grossly abnormal cell divisions are likely to contribute to high-level aneuploidies and ploidy changes, and could underlie the rapid evolution of cancer under selective pressure. Citation Format: Anna Roschke, Darawalee Wangsa, Nina Gutzeit, Richard Korshkov, Tim Thoerner, Kerstin Heselmeyer-Haddad, Paul Meltzer. Novel miFISH single-cell approach gives new insights into chromosomal instability and evolution of colorectal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3890.

Micronuclei are small, independent cytoplasmic structures containing nuclear material. They typically form during cell division due to DNA damage or division abnormalities, serve as biomarkers of genetic damage, and are closely associated with chromosomal instability (CIN). Emerging evidence suggests that micronuclei actively promote and exacerbate CIN, with significant implications in disease pathology and potential therapeutic applications. This review provides a comprehensive overview of micronuclei by exploring their origins, formation mechanisms, and functional consequences, and detailing the fate of micronuclei post-formation, which is essential for elucidating their role in genomic instability and potential therapeutic implications. Furthermore, micronuclei can contribute to extreme chromosomal shattering and genomic instability. These processes are increasingly recognized as critical contributors to disease progression, particularly in cancer. Although micronuclei have traditionally been viewed as markers of genomic instability, recent evidence suggests that they may also serve functional roles. Their potential use as treatments for certain diseases appears theoretically feasible; however, challenges remain in selectively targeting cells to induce the formation of favorable micronuclei and maintain optimal immune responses. Addressing these questions could open new avenues for therapeutic interventions.

The CpG Island Methylator Phenotype and Chromosomal Instability Are Inversely Correlated in Sporadic Colorectal Cancer

Role of genomic instability in arsenic-induced carcinogenicity. A review

Long-range regulators of gene expression are emerging as promising new biomarkers and therapeutic targets for human diseases including cancer. As current breast cancer biomarkers have limited power for predicting disease progression and response to therapy, we have explored the potential of long-range regulators of non-coding RNAs to be useful in the prognostication of breast cancer. HOTAIR is a long non-coding RNA that is overexpressed, promotes metastasis, and is predictive of poor prognosis in breast cancer. Here we describe a long-range transcriptional enhancer of the HOTAIR gene that binds several hormone receptors and associated transcription factors, interacts with the HOTAIR promoter and augments HOTAIR transcription. This enhancer is dependent on FOXA1 and FOXM1 transcription factors and functionally interacts with a novel alternate HOTAIR promoter. Analysis of breast cancer gene expression data indicates that HOTAIR is co-expressed with FOXA1 and FOXM1 in HER2-enriched tumours, and these factors enhance the prognostic power of HOTAIR in this subtype of breast cancer. The combination of HOTAIR and FOXM1 also enables better predictions of response to endocrine therapy for ER+ breast cancer. FOXM1 is a member of the recently described chromosome instability module and consistent with this, the expression of HOTAIR and FOXM1 is associated with increased frequency of copy number alterations and somatic non-synonymous mutations. Our study corroborates the importance of enhancers in breast cancer, elucidates the transcriptional regulation of HOTAIR, suggests HOTAIR as a novel biomarker of patient response to endocrine therapy, and implicates HOTAIR in chromosome instability. Citation Format: Michael J. Milevskiy, Fares Al-Ejeh, Jodi M. Saunus, Korinne S. Northwood, Amy E. McCart-Reed, Eloise Dray, Kenneth Nephew, Peter J. Bailey, Joshua A. Betts, Andrew Stone, Julia M W Gee, Annette M. Shewan, Juliet D. French, Stacey L. Edwards, Susan J. Clark, Sunil R. Lakhani, Melissa A. Brown. Long-range regulation of HOTAIR identifies novel biomarkers of breast cancer outcome and suggests a role in genome instability. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1980.

Cancer cells often have unstable genomes and increased centrosome and chromosome numbers, which play an important part of malignant transformation in the most recent models tumorigenesis. However, very little is known about divisional failures in cancer cells that may lead to chromosomal and centrosomal amplifications. We show here that cancer cells often failed at cytokinesis due to decreased phosphorylation of the myosin regulatory light chain (MLC), a key regulatory component of cortical contraction during division. Reduced MLC phosphorylation was associated with high expression of myosin phosphatase and/or reduced myosin light chain kinase levels. Furthermore, expression of phosphomimetic MLC largely prevented cytokinesis failure in the tested cancer cells. When myosin light chain phosphorylation was restored to normal levels by phosphatase knockdown multinucleation, and multipolar mitosis were both markedly reduced, resulting in enhanced genome stabilization. Furthermore, both overexpression of myosin phosphatase or inhibition of the myosin light chain kinase (MLCK) in nonmalignant cells can recapitulate some of the mitotic defects of cancer cells, including multinucleation and multipolar spindles, indicating these changes are sufficient to reproduce the cytokinesis failures we see in cancer cells. These results for the first time define the molecular defects leading to divisional failure in cancer cells.

Analysis of centrosome number and structure has become one means of assessing the potential for aberrant chromosome segregation and aneuploidy in tumor cells. Centrosome amplification directly causes multipolar catastrophic mitoses in mouse embryonic fibroblasts (MEFs) deficient for the tumor suppressor genes Brca1 or Trp53. We observed supernumerary centrosomes in cell lines established from aneuploid, but not from diploid, colorectal carcinomas; however, multipolar mitoses were never observed. This discrepancy prompted us to thoroughly characterize the centrosome abnormalities in these and other cancer cell lines with respect to both structure and function. The most striking result was that supernumerary centrosomes in aneuploid colorectal cancer cell lines were unable to nucleate microtubules, despite the presence of gamma-tubulin, pericentrin, PLK1, and AURKA. Analysis by scanning electron microscopy revealed that these supernumerary structures are devoid of centrioles, a result significantly different from observations in aneuploid pancreatic cancer cell lines and in Trp53 or Brca1 deficient MEFs. Thus, multipolar mitoses are dependent upon the ability of extra gamma-tubulin containing structures to nucleate microtubules, and this correlated with the presence of centrioles. The assessment of centrosome function with respect to chromosome segregation must therefore take into consideration the presence of centrioles and the capacity to nucleate microtubules. The patterns and mechanisms of chromosomal aberrations in hematologic malignancies and solid tumors are fundamentally different. The former is characterized by specific chromosome translocations, whose consequence is the activation of oncogenes. Most carcinomas, however, reveal variations in the nuclear DNA content. The observed genomic imbalances and gross variations in chromosome number can result from unequal chromosome segregation during mitotic cell division. It is therefore fundamental to elucidate mechanisms involved in distribution of the genome to daughter cells. Prior to cell division, the centrosome organizes microtubules and the mitotic spindle. Deciphering the consequences of alterations in centrosome number, structure, and function is an important step towards understanding how a diploid genome is maintained. Although extra centrosomes have now been observed in carcinomas and were correlated with aneuploidy, a careful functional investigation of these structures and their role in generating chromosome imbalances may lead to the identification of distinct mechanistic pathways of genomic instability. Understanding these pathways will also be important in determining whether they are potential molecular targets of therapeutic intervention.

Telomere Dysfunction and DNA Damage Checkpoints in Diseases and Cancer of the Gastrointestinal Tract

Morphology based scoring of chromosomal instability and its correlation with cell viability

The role of chromosomal instability (CI) in oncogenesis is very well described in solid tumours, but there are a lack of studies on haematology malignancy, especially with multiple morphological markers. The study aims to analyze seven morphological markers of CI- chromatin bridges (CB), multipolar mitosis (MPM), nuclear budding (NB), micronuclei (MN), nuclear heterogeneity (NH), laggards, chromatin strings (CS) in bone marrow aspirate (BMA) and biopsy of acute leukaemia (AL), and myelodysplastic syndrome (MDS). It is a retrospective cross-sectional analytical study where BMA and biopsy were reviewed for CI markers. We compared CI markers in five categories. CI markers were further correlated with clinical manifestations and outcomes of patients. The study included 54 samples of 37 patients. Overall, the median (IQR) of markers were as follows: MN 3.5 (1,7), NB 5 (1,18), MPM 1 (0,4), CB 1(0,2), Laggards 0 (0,1), and CS 2.5 (0,6). NH was noted in 65.4% of samples. All CI markers except laggards were significantly increased in B-ALL, AML, and MDS compared to other categories. Many CI markers were significantly raised with a few clinical features. The MN, MPM, Laggard, and NH markers were significantly increased in the dead patients compared to those who survived. The study, one of the first to analyze multiple CI markers, revealed that the CI markers were significantly increased in AL and MDS patients and significantly associated with clinical manifestations and outcomes. Morphology markers of CI are valuable and cost-effective in diagnostic strategy, type of malignancies, and assessing prognosis.

Cancer is a genetic disease. Cancer cells contain various mutations, which includes SNPs to chromosomal aberrations. Together, these changes are referred to as genome instability. Genetic instability is one of the common characteristics of colorectal cancer. In colorectal cancer three major types of genetic instability have been reported. They are chromosomal translocations, microsatellite instability (MSI), and chromosome instability (CIN). Microsatellite instability occurs due to variations in DNA mismatch repair genes, while chromosomal instability is distinguished by major chromosomal alterations occurring at cell division and usually involves β‐catenin and Adenomatous polyposis coli protein (APC) mutations. This chapter summarizes the major molecular mechanisms leading to genomic and microsatellite instability and tumorigenesis.

High-grade serous ovarian cancer (HGSC) is the most common and lethal form of ovarian cancer, accounting for over 70% of ovarian cancer cases. HGSC mortality is largely driven by early and diffuse transcoelomic spread from the primary site throughout the peritoneal cavity, resulting in roughly three-quarters of cases presenting with advanced stage disease at time of diagnosis. Following detachment from the primary tumor, disseminated ovarian cancer cells are spread by the peritoneal fluid and ascites where they must adapt to their new microenvironment to survive and successfully form metastases. Crucial to this spread is the formation of multicellular aggregates containing both cancer and non-malignant stromal cells, which enhance cancer cell survival and are associated with poor clinical outcome. While most studies on HGSC multicellular aggregates have focused on ovarian cancer cells alone, the interactions between ovarian cancer cells and other non-malignant cells have yet to be fully elucidated. Prior work by our group have shown that stromal-progenitor cells, termed carcinoma-associated mesenchymal stem/stromal cells (CA-MSCs), enhance HGSC metastasis through direct cellular interaction and formation of heterocellular CA-MSC:cancer cell complexes. Here we demonstrate CA-MSCs enhance metastasis by preferentially donating their mitochondria to cancer cells with the least amount of endogenous mitochondria content (‘mito poor’ cancer cells), increasing their ability to survive and driving tumor heterogeneity at the metastatic site in vivo. Mito poor cancer cells were shown to have decreased proliferative capacity, increased sensitivity to platinum-based chemotherapy and display decreased oxidative phosphorylation (OXPHOS) compared to ‘mito rich’ cancer cells. Primary patient-derived CA-MSCs rescue this vulnerable phenotype by increasing proliferation, chemoresistance and OXPHOS in mito poor cancer cells. These findings were validated in a fully autologous system using CA-MSCs and cancer cells derived from the same patient to prevent confounding effects of cellular response to foreign organelle/DNA. Through lentiviral knockdown of the mitochondrial motor protein MIRO1 we further demonstrate mitochondrial transfer is necessary for CA-MSC-mediated rescue of mito poor cancer cells. Further, we developed a haplotype-specific quantification of mitochondrial DNA to differentiate CA-MSC from endogenous cancer cell mitochondria which was used to quantify the amount of CA-MSC mitochondrial donation and demonstrate donated mitochondria persist in cancer cells up to 14 days. Importantly, CA-MSC mitochondrial donation occurred in vivo and was associated with decreased survival in an orthotopic ovarian cancer murine model. Genomic barcoding was used to quantify tumor cell clonal heterogeneity; using this system we demonstrate CA-MSC mitochondrial donation significantly enhance tumor cell heterogeneity at the metastatic site in vivo. Collectively, we report CA-MSC mitochondrial transfer as a driver of HGSC progression, heterogeneity and metastasis. Citation Format: Leonard G. Frisbie, Catherine A. Pressimone, Roja Baruwal, Geyon L. Garcia, Zanib Javed, Claudette St. Croix, Simon Watkins, Michael Calderone, Huda I. Atiya, Nadine Hempel, Alexander Pearson, Lan G. Coffman. Carcinoma-associated mesenchymal stem cells promote high-grade serous ovarian cancer metastasis and drive tumor heterogeneity at the metastatic site through direct mitochondrial transfer [abstract]. In: Proceedings of the AACR Special Conference on Ovarian Cancer; 2023 Oct 5-7; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_2):Abstract nr B085.

Polyploid cancer cells exhibit chromosomal instability (CIN), which is associated with tumorigenesis and therapy resistance. The mechanisms that induce polyploidy and how these mechanisms contribute to CIN are not fully understood. Here we evaluate CIN in human cells that become polyploid through an experimentally induced endoreplication cycle. When these induced endoreplicating cells (iECs) returned to mitosis, it resulted in aneuploidy in daughter cells. This aneuploidy resulted from multipolar divisions, chromosome missegregation, and failure in cytokinesis. The iECs went through several rounds of division, ultimately spawning proliferative cells of reduced ploidy. iECs have reduced levels of the kinesin-14 HSET, which likely accounts for the multipolar divisions, and overexpression of HSET reduced spindle multipolarity. However, HSET overexpression had only mild effects on CIN, suggesting that additional defects must contribute to genomic instability in dividing iECs. Overall our results suggest that transient endoreplication cycles generate a diverse population of proliferative aneuploid cells that have the potential to contribute to tumor heterogeneity.