Chromosome instability, chromosome transcriptome, and clonal evolution of tumor cell populations

A Paradoxical Role for Somatic Chromosomal Mosaicism and Chromosome Instability in Cancer: Theoretical and Technological Aspects

Somatic chromosomal mosaicism, chromosome instability, and cancer are intimately linked together. Addressing the role of somatic genome variations (encompassing chromosomal mosaicism and instability) in cancer yields paradoxical results. Firstly, somatic mosaicism for specific chromosomal rearrangement causes cancer per se. Secondly, chromosomal mosaicism and instability are associated with a variety of diseases (chromosomal disorders demonstrating less severe phenotypes, complex diseases), which exhibit cancer predisposition. Chromosome instability syndromes may be considered the best examples of these diseases. Thirdly, chromosomal mosaicism and instability are able to result not only in cancerous diseases but also in non-cancerous disorders (brain diseases, autoimmune diseases, etc.). Currently, the molecular basis for these three outcomes of somatic chromosomal mosaicism and chromosome instability remains incompletely understood. Here, we address possible mechanisms for the aforementioned scenarios using a system analysis model. A number of theoretical models based on studies dedicated to chromosomal mosaicism and chromosome instability seem to be valuable for disentangling and understanding molecular pathways to cancer-causing genome chaos. In addition, technological aspects of uncovering causes and consequences of somatic chromosomal mosaicism and chromosome instability are discussed. In total, molecular cytogenetics, cytogenomics, and system analysis are likely to form a powerful technological alliance for successful research against cancer.

CDK2 inhibition disorders centrosome stoichiometry and alters cellular outcomes in aneuploid cancer cells

Cyclin-dependent Kinase 2 (CDK2) inhibition prevents supernumerary centrosome clustering. This causes multipolarity, anaphase catastrophe and apoptotic death of aneuploid cancers. This study elucidated how CDK2 antagonism affected centrosome stoichiometry. Focused ion beam scanning electron microscopy (FIB-SEM) and immunofluorescent imaging were used. Studies interrogated multipolar mitosis after pharmacologic or genetic repression of CDK2. CDK2/9 antagonism with CYC065 (Fadraciclib)-treatment disordered centrosome stoichiometry in aneuploid cancer cells, preventing centrosome clustering. This caused ring-like chromosomes or multipolar cancer cells to form before onset of cell death. Intriguingly, CDK2 inhibition caused a statistically significant increase in single centrioles rather than intact centrosomes with two centrioles in cancer cells having chromosome rings or multipolarity. Statistically significant alterations in centrosome stoichiometry were undetected in other mitotic cancer cells. To confirm this pharmacodynamic effect, CDK2 but not CDK9 siRNA-mediated knockdown augmented cancer cells with chromosome ring or multipolarity formation. Notably, engineered gain of CDK2, but not CDK9 expression, reversed emergence of cancer cells with chromosome rings or multipolarity, despite CYC065-treatment. In marked contrast, CDK2 inhibition of primary human alveolar epithelial cells did not confer statistically significant increases of cells with ring-like chromosomes or multipolarity. Hence, CDK2 antagonism caused differential effects in malignant versus normal alveolar epithelial cells. Translational relevance was confirmed by CYC065-treatment of syngeneic lung cancers in mice. Mitotic figures in tumors exhibited chromosome rings or multipolarity. Thus, CDK2 inhibition preferentially disorders centrosome stoichiometry in cancer cells. Engaging this disruption is a strategy to explore against aneuploid cancers in future clinical trials.

Gene dosage compensation: Origins, criteria to identify compensated genes, and mechanisms including sensor loops as an emerging systems-level property in cancer

The gene dosage compensation hypothesis presents a mechanism through which the expression of certain genes is modulated to compensate for differences in the dose of genes when additional chromosomes are present. It is one of the means through which cancer cells actively cope with the potential damaging effects of aneuploidy, a hallmark of most cancers. Dosage compensation arises through several processes, including downregulation or overexpression of specific genes and the relocation of dosage-sensitive genes. In cancer, a majority of compensated genes are generally thought to be regulated at the translational or post-translational level, and include the basic components of a compensation loop, including sensors of gene dosage and modulators of gene expression. Post-translational regulation is mostly undertaken by a general degradation or aggregation of remaining protein subunits of macromolecular complexes. An increasingly important role has also been observed for transcriptional level regulation. This article reviews the process of targeted gene dosage compensation in cancer and other biological conditions, along with the mechanisms by which cells regulate specific genes to restore cellular homeostasis. These mechanisms represent potential targets for the inhibition of dosage compensation of specific genes in aneuploid cancers. This article critically examines the process of targeted gene dosage compensation in cancer and other biological contexts, alongside the criteria for identifying genes subject to dosage compensation and the intricate mechanisms by which cells orchestrate the regulation of specific genes to reinstate cellular homeostasis. Ultimately, our aim is to gain a comprehensive understanding of the intricate nature of a systems-level property. This property hinges upon the kinetic parameters of regulatory motifs, which we have termed "gene dosage sensor loops." These loops have the potential to operate at both the transcriptional and translational levels, thus emerging as promising candidates for the inhibition of dosage compensation in specific genes. Additionally, they represent novel and highly specific therapeutic targets in the context of aneuploid cancer.

miR-18a expression correlates with ATM and p53 levels and poor prognosis in lymphomas

microRNAs (miRNAs) are non-coding, endogenous, small-molecule RNAs. They are involved in cell proliferation, differentiation, apoptosis, and metabolism. Additionally, they play an essential role in the development and progression of various malignancies. Recent research has revealed that miR-18a plays an important role in cancer development. However, its role in lymphoma is not yet fully understood. In this study, we investigated the clinicopathological characteristics and potential functional roles of miR-18a in lymphomas. First, we predicted the potential downstream genes of miR-18a using miRTarBase software and subjected these downstream genes to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses to determine the potential mechanisms of action of these genes. We found that these target genes were closely related to cellular senescence, the p53 signaling pathway, and other signaling pathways. From the predicted downstream target genes, ATM and p53 were selected as the target genes; their deletion in patients with lymphoma was detected using the fluorescence in situ hybridization technique. The results showed that some patients with lymphoma have a deletion of the ATM and p53 genes. In addition, the deletion rates of ATM and p53 were positively correlated with the expression of miR-18a. Next, the expression levels of miR-18a and the deletion rates of ATM and p53 were used for correlation and prognostic analyses with patient clinical information. The findings revealed a significant difference in disease-free survival (DFS) between patients with lymphoma with ATM deletion and those with a normal ATM gene expression (p < 0.001). Moreover, a significant difference in overall survival (OS) and DFS between patients with p53 deletion and those with normal p53 expression was observed (p < 0.001). The results indicate that the deletion of ATM and p53 downstream of miR-18a is closely associated with the development of lymphoma. Thus, these biomarkers may serve as key prognostic biomarkers for lymphomas.

Telomere attrition and genomic instability in unexplained recurrent pregnancy loss in humans: A preliminary study

Genome instability is defined as an elevated rate of DNA damage and mutations as a result of exposure to potential direct and indirect mutagens. This current investigation was designed to elucidate the genomic instability among couples experiencing unexplained recurrent pregnancy loss (uRPL). A cohort of 1272 individuals with history of unexplained RPL with normal karyotype was retrospectively screened for levels of intracellular ROS production, baseline genomic instability and telomere functionality. The experimental outcome was compared with 728 fertile control individuals. In this study, it was perceived that individuals with uRPL exhibited higher intracellular oxidative stress, along with higher basal levels of genomic instability as compared with the fertile controls. This observation elucidates the role of genomic instability as well as involvement of telomeres in cases of uRPL. It was also observed that higher oxidative stress might be associated with DNA damage and telomere dysfunction resulting in genomic instability among subjects with unexplained RPL. This study highlighted the assessment of genomic instability status in individuals experiencing uRPL.

Chromosomal instability in adult-type diffuse gliomas

Chromosomal instability (CIN) is a fundamental property of cancer and a key underlying mechanism of tumorigenesis and malignant progression, and has been documented in a wide variety of cancers, including colorectal carcinoma with mutations in genes such as APC. Recent reports have demonstrated that CIN, driven in part by mutations in genes maintaining overall genomic stability, is found in subsets of adult-type diffusely infiltrating gliomas of all histologic and molecular grades, with resulting elevated overall copy number burden, chromothripsis, and poor clinical outcome. Still, relatively few studies have examined the effect of this process, due in part to the difficulty of routinely measuring CIN clinically. Herein, we review the underlying mechanisms of CIN, the relationship between chromosomal instability and malignancy, the prognostic significance and treatment potential in various cancers, systemic disease, and more specifically, in diffusely infiltrating glioma subtypes. While still in the early stages of discovery compared to other solid tumor types in which CIN is a known driver of malignancy, the presence of CIN as an early factor in gliomas may in part explain the ability of these tumors to develop resistance to standard therapy, while also providing a potential molecular target for future therapies.

Mathematical modeling for mutator phenotype and clonal selection advantage in the risk analysis of lung cancer

Cancer is one of the leading diseases for human mortality. Although substantial research works have been conducted to investigate the initiation and progression of cancer disease, it is still an active debate regarding the function of mutations conferring a clone advantage and the importance of mutator phenotypes caused by the mutation of stability genes. To address this issue further, we develop a mathematical model based on the incidence data of non-small cell lung cancer and small cell lung cancer from the Surveillance Epidemiology and End Results registry in the USA. The key biological parameters have been analyzed to investigate the potential effective measures for inhibiting the risk of lung cancer. Although the first event is the gene mutation that leads to clonal expansion of cells for lung cancer, the simulation results show that the clonal advantage of cancer cells alone is insufficient to cause tumorigenesis. Our analysis suggests that mutations in genes that keep genetic stability are critical in the development of lung cancer. This implies that mutator phenotype is an important indicator for the diagnosis of lung cancer, which can enable early detection and treatment to reduce the risk of lung cancer effectively. Furthermore, the parameter analysis indicates that it would be highly effective to control the risk of lung cancer by inhibiting the transformation rate from the normal cells to mutated cells and the clonal expansion of cells with fewer gene mutations.

The Dynamic Instability of the Aneuploid Genome

Proper partitioning of replicated sister chromatids at each mitosis is crucial for maintaining cell homeostasis. Errors in this process lead to aneuploidy, a condition in which daughter cells harbor genome imbalances. Importantly, aneuploid cells often experience DNA damage, which in turn could drive genome instability. This might be the product of DNA damage accumulation in micronuclei and/or a consequence of aneuploidy-induced replication stress in S-phase. Although high levels of genome instability are associated with cell cycle arrest, they can also confer a proliferative advantage in some circumstances and fuel tumor growth. Here, we review the main consequences of chromosome segregation errors on genome stability, with a special focus on the bidirectional relationship between aneuploidy and DNA damage. Also, we discuss recent findings showing how increased genome instability can provide a proliferation improvement under specific conditions, including chemotherapeutic treatments.

Understanding Retinoblastoma Post-Translational Regulation for the Design of Targeted Cancer Therapies

Simple Summary

Rb1 is a regulator of cell cycle progression and genomic stability. This review focuses on post-translational modifications, their effect on Rb1 interactors, and their role in intracellular signaling in the context of cancer development. Finally, we highlight potential approaches to harness these post-translational modifications to design novel effective anticancer therapies.

Abstract

The retinoblastoma protein (Rb1) is a prototypical tumor suppressor protein whose role was described more than 40 years ago. Together with p107 (also known as RBL1) and p130 (also known as RBL2), the Rb1 belongs to a family of structurally and functionally similar proteins that inhibits cell cycle progression. Given the central role of Rb1 in regulating proliferation, its expression or function is altered in most types of cancer. One of the mechanisms underlying Rb-mediated cell cycle inhibition is the binding and repression of E2F transcription factors, and these processes are dependent on Rb1 phosphorylation status. However, recent work shows that Rb1 is a convergent point of many pathways and thus the regulation of its function through post-translational modifications is more complex than initially expected. Moreover, depending on the context, downstream signaling can be both E2F-dependent and -independent. This review seeks to summarize the most recent research on Rb1 function and regulation and discuss potential avenues for the design of novel cancer therapies.

MYC dosage compensation is mediated by miRNA-transcription factor interactions in aneuploid cancer

We hypothesize that dosage compensation of critical genes arises from systems-level properties for cancer cells to withstand the negative effects of aneuploidy. We identified several candidate genes in cancer multiomics data and developed a biocomputational platform to construct a mathematical model of their interaction network with micro-RNAs and transcription factors, where the property of dosage compensation emerged for MYC and was dependent on the kinetic parameters of its feedback interactions with three micro-RNAs. These circuits were experimentally validated using a genetic tug-of-war technique to overexpress an exogenous MYC, leading to overexpression of the three microRNAs involved and downregulation of endogenous MYC. In addition, MYC overexpression or inhibition of its compensating miRNAs led to dosage-dependent cytotoxicity in MYC-amplified colon cancer cells. Finally, we identified negative correlation of MYC dosage compensation with patient survival in TCGA breast cancer patients, highlighting the potential of this mechanism to prevent aneuploid cancer progression.

The unfolded protein response links tumor aneuploidy to local immune dysregulation

Aneuploidy is a chromosomal abnormality associated with poor prognosis in many cancer types. Here, we tested the hypothesis that the unfolded protein response (UPR) mechanistically links aneuploidy and local immune dysregulation. Using a single somatic copy number alteration (SCNA) score inclusive of whole‐chromosome, chromosome arm, and focal alterations in a pan‐cancer analysis of 9,375 samples in The Cancer Genome Atlas (TCGA) database, we found an inverse correlation with a cytotoxicity (CYT) score across disease stages. Co‐expression patterns of UPR genes changed substantially between SCNA^low and SCNA^high groups. Pathway activity scores showed increased activity of multiple branches of the UPR in response to aneuploidy. The PERK branch showed the strongest association with a reduced CYT score. The conditioned medium of aneuploid cells transmitted XBP1 splicing and caused IL‐6 and arginase 1 transcription in receiver bone marrow‐derived macrophages and markedly diminished the production of IFN‐γ and granzyme B in activated human T cells. We propose the UPR as a mechanistic link between aneuploidy and immune dysregulation in the tumor microenvironment.

Suv420 enrichment at the centromere limits Aurora B localization and function

Centromere structure and function are defined by the epigenetic modification of histones at centromeric and pericentromeric chromatin. The constitutive heterochromatin found at pericentromeric regions is highly enriched for H3K9me3 and H4K20me3. Although mis-expression of the methyltransferase enzymes that regulate these marks, Suv39 and Suv420, is common in disease, the consequences of such changes are not well understood. Our data show that increased centromere localization of Suv39 and Suv420 suppresses centromere transcription and compromises localization of the mitotic kinase Aurora B, decreasing microtubule dynamics and compromising chromosome alignment and segregation. We find that inhibition of Suv420 methyltransferase activity partially restores Aurora B localization to centromeres and that restoration of the Aurora B-containing chromosomal passenger complex to the centromere is sufficient to suppress mitotic errors that result when Suv420 and H4K20me3 is enriched at centromeres. Consistent with a role for Suv39 and Suv420 in negatively regulating Aurora B, high expression of these enzymes corresponds with increased sensitivity to Aurora kinase inhibition in human cancer cells, suggesting that increased H3K9 and H4K20 methylation may be an underappreciated source of chromosome mis-segregation in cancer. This article has an associated First Person interview with the first author of the paper.

CDKN2A Deletion in Melanoma Excludes T Cell Infiltration by Repressing Chemokine Expression in a Cell Cycle-Dependent Manner

T-cell-mediated immune response is the prerequisite for T-cell-based immunotherapy. However, the limitation of T-cell infiltration in solid tumors restricted the therapeutic effect of T-cell-based immunotherapy. The present study screened the molecular and genetic features of The Cancer Genome Atlas (TCGA)-skin cutaneous melanoma (SKCM) cohort, revealing that T-cell infiltration negatively correlated with genome copy number alteration. The analysis of the TCGA-SKCM cohort indicated that the copy number of CDKN2A was significantly decreased in patients with low T-cell infiltration. The results were validated in the other two melanoma cohorts (DFCI, Science 2015, and TGEN, Genome Res 2017). Besides, the immunohistochemistry analysis of CDKN2A and CD8 expression in 5 melanoma in situ and 15 invasive melanoma patients also showed that CD8 expression was decreased in the patients with low CDKN2A expression and there was a positive correlation between CDKN2A and CD8 expression in these patients. Interestingly, the CDKN2A deletion group and the group with low expression of T-cell markers shared similar gene and pathway alteration as compared with the normal CDKN2A group and the group with high expression of T-cell markers, especially the chemokine pathway. Further mechanistic study indicated that CDKN2A enhanced T cell recruitment and chemokine expression possibly through modulating MAPK and NF-κB signaling pathways in a cell cycle–dependent manner. Finally, we also found that CDKN2A deletion negatively correlated with the expression of T-cell markers in many other cancer types. In conclusion, CDKN2A deletion could inhibit T cell infiltration by inhibiting chemokine expression in a cell cycle dependent manner.

Insights into Hepatitis B Virus DNA Integration-55 Years after Virus Discovery

Hepatitis B virus (HBV), which was discovered in 1965, is a threat to global public health. HBV infects human hepatocytes and leads to acute and chronic liver diseases, and there is no cure. In cells infected by HBV, viral DNA can be integrated into the cellular genome. HBV DNA integration is a complicated process during the HBV life cycle. Although HBV integration normally results in replication-incompetent transcripts, it can still act as a template for viral protein expression. Of note, it is a primary driver of hepatocellular carcinoma (HCC). Recently, with the development of detection methods and research models, the molecular biology and the pathogenicity of HBV DNA integration have been better revealed. Here, we review the advances in the research of HBV DNA integration, including molecular mechanisms, detection methods, research models, the effects on host and viral gene expression, the role of HBV integrations in the pathogenesis of HCC, and potential treatment strategies. Finally, we discuss possible future research prospects of HBV DNA integration.

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HBV DNA integration is associated with hepatocarcinogenesis via multiple mechanisms

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HBV double-stranded linear DNA (dslDNA) is the dominant substrate for integration into the host genome

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The insertion sites of HBV DNA integration occur throughout the whole host genome using the NHEJ or MMEJ DNA repair pathway

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HBV DNA integration should be used as a clinical indicator for disease monitoring and treatment of patients with HBV infection

Aneuploidy and gene expression: is there dosage compensation?

Aneuploidy (i.e., abnormal chromosome number) is the leading cause of miscarriage and congenital defects in humans. Moreover, aneuploidy is ubiquitous in cancer. The deleterious phenotypes associated with aneuploidy are likely a result of the imbalance in the levels of gene products derived from the additional chromosome(s). Here, we summarize the current knowledge on how the presence of extra chromosomes impacts gene expression. We describe studies that have found a strict correlation between gene dosage and transcript levels as wells as studies that have found a less stringent correlation, hinting at the possible existence of dosage compensation mechanisms. We conclude by peering into the epigenetic changes found in aneuploid cells and outlining current knowledge gaps and potential areas of future investigation.

Aneuploidy in yeast: Segregation error or adaptation mechanism?

Aneuploidy is the loss or gain of chromosomes within a genome. It is often detrimental and has been associated with cell death and genetic disorders. However, aneuploidy can also be beneficial and provide a quick solution through changes in gene dosage when cells face environmental stress. Here, we review the prevalence of aneuploidy in Saccharomyces, Candida, and Cryptococcus yeasts (and their hybrid offspring) and analyse associations with chromosome size and specific stressors. We discuss how aneuploidy, a segregation error, may in fact provide a natural route for the diversification of microbes and enable important evolutionary innovations given the right ecological circumstances, such as the colonisation of new environments or the transition from commensal to pathogenic lifestyle. We also draw attention to a largely unstudied cross link between hybridisation and aneuploidy. Hybrid meiosis, involving two divergent genomes, can lead to drastically increased rates of aneuploidy in the offspring due to antirecombination and chromosomal missegregation. Because hybridisation and aneuploidy have both been shown to increase with environmental stress, we believe it important and timely to start exploring the evolutionary significance of their co-occurrence.

HNRNPL Restrains miR-155 Targeting of BUB1 to Stabilize Aberrant Karyotypes of Transformed Cells in Chronic Lymphocytic Leukemia

Aneuploidy and overexpression of hsa-miR-155-5p (miR-155) characterize most solid and hematological malignancies. We recently demonstrated that miR-155 sustains aneuploidy at early stages of in vitro cellular transformation. During in vitro transformation of normal human fibroblast, upregulation of miR-155 downregulates spindle checkpoint proteins as the mitotic checkpoint serine/threonine kinase budding uninhibited by benzimidazoles 1 (BUB1), the centromere protein F (CENPF) and the zw10 kinetochore protein (ZW10), compromising the chromosome alignment at the metaphase plate and leading to aneuploidy in daughter cells. Here we show that the heterogeneous nuclear ribonucleoprotein L (HNRNPL) binds to the polymorphic marker D2S1888 at the 3′UTR of BUB1 gene, impairs the miR-155 targeting, and restores BUB1 expression in chronic lymphocytic leukemia. This mechanism occurs at advanced passages of cell transformation and allows the expansion of more favorable clones. Our findings have revealed, at least in part, the molecular mechanisms behind the chromosomal stabilization of cell lines and the concept that, to survive, tumor cells cannot continuously change their genetic heritage but need to stabilize the most suitable karyotype.

Transcriptional Aneuploidy Responses of Brassica rapa-oleracea Monosomic Alien Addition Lines (MAALs) Derived From Natural Allopolyploid B. napus

Establishing the whole set of aneuploids, for one naturally evolved allopolyploid species, provides a unique opportunity to elucidate the transcriptomic response of the constituent subgenomes to serial aneuploidy. Previously, the whole set of monosomic alien addition lines (MAALs, C1-C9) with each of the nine C subgenome chromosomes, added to the extracted A subgenome, was developed in the context of the allotetraploid Brassica napus donor “Oro,” after the restitution of the ancestral B. rapa (RBR Oro) was realized. Herein, transcriptomic analysis using high-throughput technology was conducted to detect gene expression alterations in these MAALs and RBR. Compared to diploid RBR, the genes of all of the MAALs showed various degrees of dysregulated expressions that resulted from cis effects and more prevailing trans effects. In addition, the trans-effect on gene expression in MAALs increased with higher levels of homology between the recipient A subgenome and additional C subgenome chromosomes, instead of gene numbers of extra chromosomes. A total of 10 trans-effect dysregulated genes, among all pairwise comparisons, were mainly involved in the function of transporter activity. Furthermore, highly expressed genes were more prone to downregulation and vice-versa, suggesting a common trend for transcriptional pattern responses to aneuploidy. These results provided a comprehensive insight of the impact of gene expression of individual chromosomes, in one subgenome, on another intact subgenome for one allopolyploid with a long evolutionary history.

Detecting Chromosome Instability in Cancer: Approaches to Resolve Cell-to-Cell Heterogeneity

Chromosome instability (CIN) is defined as an increased rate of chromosome gains and losses that manifests as cell-to-cell karyotypic heterogeneity and drives cancer initiation and evolution. Current research efforts are aimed at identifying the etiological origins of CIN, establishing its roles in cancer pathogenesis, understanding its implications for patient prognosis, and developing novel therapeutics that are capable of exploiting CIN. Thus, the ability to accurately identify and evaluate CIN is critical within both research and clinical settings. Here, we provide an overview of quantitative single cell approaches that evaluate and resolve cell-to-cell heterogeneity and CIN, and discuss considerations when selecting the most appropriate approach to suit both research and clinical contexts.

p53 mediates hydroxyurea resistance in aneuploid cells of colon cancer

Aneuploidy refers to aberrancies in cellular chromosome count, which is prevalent in most human cancers. Chemotherapy is an effective cancer treatment; however, the development of drug resistance is a major concern of conventional chemotherapy. The chemotherapy agent hydroxyurea (HU) targets proliferating cells and has long been applied to treat various human cancers. It remains elusive whether aneuploidy affects the drug sensitivity of hydroxyurea. By generating an inducible aneuploidy model, we found that aneuploid colon cancer cells were resistant to HU treatment compared to euploid controls. Surprisingly, further analyses showed that the HU resistance was dependent on the expression of wild type p53. Activation of the p53 pathway in aneuploidy cells reduced cell proliferation but generated resistance of tumor cells to HU treatment. HU resistance was abrogated in aneuploid cells if p53 was absent but re-gained when inducing proliferation repression in cells by serum deprivation. Our results demonstrate that the HU resistance developed in aneuploid colon cancer cells is mediated by wild type p53 and indicates the prognostic value of combining karyotypic and p53 status in clinical cancer treatment.

Chromosome instability in tumor cells due to defects in Aurora B mediated error correction at kinetochores

We characterized a panel of cancer cells and found that they exhibited chromosome instability (CIN) that was associated with high frequencies of aberrant kinetochore:microtubule attachments. Failure to resolve these defective attachments before anaphase onset can lead to missegregation of chromosomes. Aurora B kinase is concentrated at the inner centromere where it contributes to multiple kinetochore functions, one of which is in error-correction. Analysis of several CIN cell lines showed that many aspects of Aurora B kinase functions were normal. Furthermore, the amount and activity of Aurora B kinase was not reduced at the kinetochores of CIN cells that were examined. However, phosphorylation of a centromeric biosensor for Aurora B in OVCAR10, MCF7 and U2OS cells was consistently reduced relative to non CIN cells. This suggested a localized problem with Aurora B’s ability to phosphorylate substrates important for error correction. This possibility was supported by our ability to improve error correction and reduce the frequency of lagging chromosome in CIN cells by directing endogenous Aurora B to the region of centromere that was tested by the biosensor. Our studies suggest that the kinetochores of CIN cells have a defect that limits accessibility of Aurora B to substrates that are important for error-correction.

New Cell Cycle Inhibitors Target Aneuploidy in Cancer Therapy

Aneuploidy is a hallmark of cancer. Defects in chromosome segregation result in aneuploidy. Multiple pathways are engaged in this process, including errors in kinetochore-microtubule attachments, supernumerary centrosomes, spindle assembly checkpoint (SAC) defects, and chromosome cohesion defects. Although aneuploidy provides an adaptation and proliferative advantage in affected cells, excessive aneuploidy beyond a critical level can be lethal to cancer cells. Given this, enhanced chromosome missegregation is hypothesized to limit survival of aneuploid cancer cells, especially when compared to diploid cells. Based on this concept, proteins and pathways engaged in chromosome segregation are being exploited as candidate therapeutic targets for aneuploid cancers. Agents that induce chromosome missegregation and aneuploidy now exist, including SAC inhibitors, those that alter centrosome fidelity and others that are under active study in preclinical and clinical contexts. This review explores the therapeutic potentials of such new agents, including the benefits of combining them with other antineoplastic agents.

Engaging Anaphase Catastrophe Mechanisms to Eradicate Aneuploid Cancers

Cancer cells often have supernumerary centrosomes that promote genomic instability, a pathognomonic feature of cancer. During mitosis, cancer cells with supernumerary centrosomes undergo bipolar cell division by clustering centrosomes into two poles. When supernumerary centrosome clustering is antagonized, cancer cells are forced to undergo multipolar division leading to death of daughter cells. This proapoptotic pathway, called anaphase catastrophe, preferentially eliminates aneuploid cancer cells and malignant tumors in engineered mouse models. Anaphase catastrophe occurs through the loss or inhibition of the centrosomal protein CP110, a direct cyclin-dependent kinase 1 (CDK1) and CDK2 target. Intriguingly, CP110 is repressed by the KRAS oncoprotein. This sensitizes KRAS-driven lung cancers (an unmet medical need) to respond to CDK2 inhibitors. Anaphase catastrophe-inducing agents like CDK1 and CDK2 antagonists are lethal to cancer cells with supernumerary centrosomes, but can relatively spare normal cells with two centrosomes. This mechanism is proposed to provide a therapeutic window in the cancer clinic following treatment with a CDK1 or CDK2 inhibitor. Taken together, anaphase catastrophe is a clinically tractable mechanism that promotes death of neoplastic tumors with aneuploidy, a hallmark of cancer. Mol Cancer Ther; 17(4); 724-31. ©2018 AACR.

Polo-like kinase 4 inhibition produces polyploidy and apoptotic death of lung cancers

Polo-like kinase 4 (PLK4) is a serine/threonine kinase regulating centriole duplication. CFI-400945 is a highly selective PLK4 inhibitor that deregulates centriole duplication, causing mitotic defects and death of aneuploid cancers. Prior work was substantially extended by showing CFI-400945 causes polyploidy, growth inhibition, and apoptotic death of murine and human lung cancer cells, despite expression of mutated KRAS or p53. Analysis of DNA content by propidium iodide (PI) staining revealed cells with >4N DNA content (polyploidy) markedly increased after CFI-400945 treatment. Centrosome numbers and mitotic spindles were scored. CFI-400945 treatment produced supernumerary centrosomes and mitotic defects in lung cancer cells. In vivo antineoplastic activity of CFI-400945 was established in mice with syngeneic lung cancer xenografts. Lung tumor growth was significantly inhibited at well-tolerated dosages. Phosphohistone H3 staining of resected lung cancers following CFI-400945 treatment confirmed the presence of aberrant mitosis. PLK4 expression profiles in human lung cancers were explored using The Cancer Genome Atlas (TCGA) and RNA in situ hybridization (RNA ISH) of microarrays containing normal and malignant lung tissues. PLK4 expression was significantly higher in the malignant versus normal lung and conferred an unfavorable survival (P < 0.05). Intriguingly, cyclin dependent kinase 2 (CDK2) antagonism cooperated with PLK4 inhibition. Taken together, PLK4 inhibition alone or as part of a combination regimen is a promising way to combat lung cancer.

Hsa-miR-155-5p drives aneuploidy at early stages of cellular transformation

Hsa-miR-155-5p (miR-155) is overexpressed in most solid and hematological malignancies. It promotes loss of genomic integrity in cancer cells by targeting genes involved in microsatellite instability and DNA repair; however, the link between miR-155 and aneuploidy has been scarcely investigated. Here we describe a novel mechanism by which miR-155 causes chromosomal instability. Using osteosarcoma cells (U2OS) and normal human dermal fibroblast (HDF), two well-established models for the study of chromosome congression, we demonstrate that miR-155 targets the spindle checkpoint proteins BUB1, CENP-F, and ZW10, thus compromising chromosome alignment at the metaphase plate. In U2OS cells, exogenous miR-155 expression reduced the recruitment of BUB1, CENP-F, and ZW10 to the kinetochores which resulted in defective chromosome congression. In contrast, during in vitro transformation of HDF by enforced expression of SV40 Large T antigen and human telomerase (HDF_LT/hTERT), inhibition of miR-155 reduced chromosome congression errors and aneuploidy at early passages. Using live-cell imaging we observed that miR-155 delays progression through mitosis, indicating an activated mitotic spindle checkpoint, which likely fails to reduce aneuploidy. Overall, this study provides insight into a mechanism that generates aneuploidy at early stages of cellular transformation, pointing to a role for miR-155 in chromosomal instability at tumor onset.

New Insights in the Cytogenetic Practice: Karyotypic Chaos, Non-Clonal Chromosomal Alterations and Chromosomal Instability in Human Cancer and Therapy Response

Recently, non-clonal chromosomal alterations previously unappreciated are being proposed to be included in cytogenetic practice. The aim of this inclusion is to obtain a greater understanding of chromosomal instability (CIN) and tumor heterogeneity and their role in cancer evolution and therapy response. Although several genetic assays have allowed the evaluation of the variation in a population of cancer cells, these assays do not provide information at the level of individual cells, therefore limiting the information of the genomic diversity within tumors (heterogeneity). The karyotype is one of the few available cytogenetic techniques that allow us not only to identify the chromosomal alterations present within a single cell, but also allows us to profile both clonal (CCA) and non-clonal chromosomal alterations (NCCAs). A greater understanding of CIN and tumor heterogeneity in cancer could not only improve existing therapeutic regimens but could also be used as targets for the design of new therapeutic approaches. In this review we indicate the importance and significance of karyotypic chaos, NCCAs and CIN in the prognosis of human cancers.

Key rates for the grades and transformation ability of glioma: model simulations and clinical cases

Tumor progression to higher grade is a fundamental property of cancer. The malignant advancement of the pathological features may either develop during the later stages of cancer growth (natural evolution) or it may necessitate new mutations or molecular events that alter the rates of growth, dispersion, or neovascularization (transformation). Here, we model the pathological and radiological features of grades 2-4 gliomas at the times of diagnosis and death and study grade development and the progression to higher grades. We perform a retrospective review of clinical cases based on model predictions. Simulations uncover two unusual patterns of glioma progression, which are supported by clinical cases: (1) some grades 2 and 3 gliomas lack the ability of progression to higher grades, and (2) grade 3 glioma may evolve to GBM in a few weeks. All 13 gliomas that recurred at the same grade carry either the IDH1-R132H or the ATRX mutation. All (five of five) grade 3 tumors are 1p/19q co-deleted, IDH1-R132H mutated and ATRX wt. Furthermore, three of seven grade 2 gliomas are both IDH1-R132H mutated and ATRX mutated. Simulations replicate the good prognosis of secondary GBM. The results support the hypothesis that constant rates of dispersion, proliferation, and angiogenesis prescribe either a natural evolution or the inability to progress to higher grades. Furthermore, the accrual of molecular events that change a tumor's ability to infiltrate, proliferate or neovascularize may transform the glioma either into a more aggressive tumor at the same grade or elevate its grade.

Chromosome instability drives phenotypic switching to metastasis

Chromosome instability (CIN) is the most striking feature of human cancers. However, how CIN drives tumor progression to metastasis remains elusive. Here we studied the role of chromosome content changes in generating the phenotypic dynamics that are required for metastasis. We isolated epithelial and mesenchymal clones from human carcinoma cell lines and showed that the epithelial clones were able to generate mesenchymal variants, which had the potential to further produce epithelial revertants autonomously. The successive acquisition of invasive mesenchymal and then epithelial phenotypes recapitulated the steps in tumor progression to metastasis. Importantly, the generation of mesenchymal variants from clonal epithelial populations was associated with subtle changes in chromosome content, which altered the chromosome transcriptome and influenced the expression of genes encoding intercellular junction (IJ) proteins, whereas the loss of chromosome 10p, which harbors the ZEB1 gene, was frequently detected in epithelial variants generated from mesenchymal clones. Knocking down these IJ genes in epithelial cells induced a mesenchymal phenotype, whereas knocking down the ZEB1 gene in mesenchymal cells induced an epithelial phenotype, demonstrating a causal role of chromosome content changes in phenotypic determination. Thus, our studies suggest a paradigm of tumor metastasis: primary epithelial carcinoma cells that lose chromosomes harboring IJ genes acquire an invasive mesenchymal phenotype, and subsequent chromosome content changes such as loss of 10p in disseminated mesenchymal cells generate epithelial variants, which can be selected for to generate epithelial tumors during metastatic colonization.

Development-associated immunophenotypes reveal the heterogeneous and individualized early responses of adult B-acute lymphoblastic leukemia

B cell acute lymphoblastic leukemia (B-ALL) exhibits phenotypes reminiscent of normal stages of B-cell development. As demonstrated by flow cytometry, the immunophenotypes are able to determine the stages of B cell development. Multicolor flow cytometry (MFC) is more accurate at identifying cell populations. In this study, 9-color panels, including CD10, CD19, CD20, CD22, CD34, CD79a, CD179a, and IgM, which are sequentially expressed during B cell development, were designed to detect the leukemia cell subpopulations in adult B-ALL patients. In 23 patients at diagnosis, 192 heterogeneous subpopulations of leukemia cells were detected. Compared with their counterparts at diagnosis and after the 1st course of induction therapy, the responses of the subpopulations were also heterogeneous. In the CD10 population, the residual B cell subpopulations in the BCR/ABL patients were obviously reduced compared to those in the BCR/ABL patients. New subpopulations were detected in 22 of 23 patients and were primarily located in the CD34CD10 populations. Subpopulations of clonal evolution were heterogeneous after induction therapy. Our results suggest that the subpopulations in B-ALL patients should be dynamically monitored by development-associated immunophenotyping before, during, and after induction therapy and to predict the prognosis of the disease.

Systemic Chromosome Instability Resulted in Colonic Transcriptomic Changes in Metabolic, Proliferation, and Stem Cell Regulators in Sgo1-/+ Mice

Colon cancer is the second most lethal cancer and is predicted to claim 49,700 lives in the United States this year. Chromosome instability (CIN) is observed in 80% to 90% of colon cancers and is thought to contribute to colon cancer progression and recurrence. To investigate the impact of CIN on colon cancer development, we developed shugoshin-1 (Sgo1) haploinsufficient (-/+) mice, an animal model focusing on mitotic error-induced CIN. In this study, we analyzed signature changes in the colonic transcriptome of Sgo1(-/+) mice to examine the molecular events underlying the altered carcinogenesis profiles in Sgo1(-/+) mice. We performed next-generation sequencing of normal-looking colonic mucosal tissue from mice treated with the carcinogen azoxymethane after 24 weeks. Transcriptome profiling revealed 349 hits with a 2-fold expression difference threshold (217 upregulated genes, 132 downregulated genes, P < 0.05). Pathway analyses indicated that the Sgo1-CIN tissues upregulated pathways known to be activated in colon cancer, including lipid metabolism (z score 4.47), Notch signaling (4.47), insulin signaling (3.81), and PPAR pathways (3.75), and downregulated pathways involved in immune responses including allograft rejection (6.69) and graft-versus-host disease (6.54). Notably, stem cell markers were also misregulated. Collectively, our findings demonstrate that systemic CIN results in transcriptomic changes in metabolism, proliferation, cell fate, and immune responses in the colon, which may foster a microenvironment amenable to cancer development. Therefore, therapeutic approaches focusing on these identified pathways may be valuable for colon cancer prevention and treatment.

Selective advantage of trisomic human cells cultured in non-standard conditions

An abnormal chromosome number, a condition known as aneuploidy, is a ubiquitous feature of cancer cells. A number of studies have shown that aneuploidy impairs cellular fitness. However, there is also evidence that aneuploidy can arise in response to specific challenges and can confer a selective advantage under certain environmental stresses. Cancer cells are likely exposed to a number of challenging conditions arising within the tumor microenvironment. To investigate whether aneuploidy may confer a selective advantage to cancer cells, we employed a controlled experimental system. We used the diploid, colorectal cancer cell line DLD1 and two DLD1-derived cell lines carrying single-chromosome aneuploidies to assess a number of cancer cell properties. Such properties, which included rates of proliferation and apoptosis, anchorage-independent growth, and invasiveness, were assessed both under standard culture conditions and under conditions of stress (i.e., serum starvation, drug treatment, hypoxia). Similar experiments were performed in diploid vs. aneuploid non-transformed human primary cells. Overall, our data show that aneuploidy can confer selective advantage to human cells cultured under non-standard conditions. These findings indicate that aneuploidy can increase the adaptability of cells, even those, such as cancer cells, that are already characterized by increased proliferative capacity and aggressive tumorigenic phenotypes.

Consequences of aneuploidy in sickness and in health

A link between aneuploidy and miscarriage or cancer in humans has been known for a long time. However, only in recent years the development of experimental models of whole-chromosome aneuploidy has allowed investigators to take a closer look at how aneuploidy affects individual cells. Collectively, recent studies using these models have shown that aneuploidy induces transcriptomic and proteomic changes, chromosomal instability, and adaptation. In this article, we discuss the findings from these recent studies and present current and emerging models on how aneuploidy may be deleterious in certain contexts, but beneficial in others.

A relay race on the evolutionary adaptation spectrum

Adaptation is the process in which organisms improve their fitness by changing their phenotype using genetic or non-genetic mechanisms. The adaptation toolbox consists of varied molecular and genetic means that we posit span an almost continuous "adaptation spectrum." Different adaptations are characterized by the time needed for organisms to attain them and by their duration. We suggest that organisms often adapt by progressing the adaptation spectrum, starting with rapidly attained physiological and epigenetic adaptations and culminating with slower long-lasting genetic ones. A tantalizing possibility is that earlier adaptations facilitate realization of later ones.

Genomic instability: Crossing pathways at the origin of structural and numerical chromosome changes

Genomic instability leads to a wide spectrum of genetic changes, including single nucleotide mutations, structural chromosome alterations, and numerical chromosome changes. The accepted view on how these events are generated predicts that separate cellular mechanisms and genetic events explain the occurrence of these types of genetic variation. Recently, new findings have shed light on the complexity of the mechanisms leading to structural and numerical chromosome aberrations, their intertwining pathways, and their dynamic evolution, in somatic as well as in germ cells. In this review, we present a critical analysis of these recent discoveries in this area, with the aim to contribute to a deeper knowledge of the molecular networks leading to adverse outcomes in humans following exposure to environmental factors. The review illustrates how several technological advances, including DNA sequencing methods, bioinformatics, and live-cell imaging approaches, have contributed to produce a renewed concept of the mechanisms causing genomic instability. Special attention is also given to the specific pathways causing genomic instability in mammalian germ cells. Remarkably, the same scenario emerged from some pioneering studies published in the 1980s to 1990s, when the evolution of polyploidy, the chromosomal effects of spindle poisons, the fate of micronuclei, were intuitively proposed to share mechanisms and pathways. Thus, an old working hypothesis has eventually found proper validation.

Conceptual models for the initiation of hepatitis B virus-associated hepatocellular carcinoma

Although chronic hepatitis B virus (HBV) infection is a known risk factor for the development of hepatocellular carcinoma (HCC), the steps involved in the progression from normal liver to HCC are poorly understood. In this review, we apply five conceptual models, previously proposed by Vineis et al. to explain carcinogenesis in general, to explore the possible steps involved in the initiation and evolution of HBV-associated HCC. Available data suggest that the most suitable and inclusive model is based on evolution of hepatocyte subpopulations. In this evolutionary model, HCC-associated changes are driven by selection and subsequent clonal expansion of phenotypically altered hepatocyte subpopulations in the microenvironment of the HBV-infected liver. This model can incorporate the wide range of mechanisms proposed to play a role in the initiation of HCC including oncogenic HBV proteins, integration of HBV DNA and chronic inflammation of the liver. The model may assist in the early prevention, detection and treatment of HCC and may guide future studies of the initiation of HBV-associated HCC.

Clonal Evolution and Blast Crisis Correlate with Enhanced Proteolytic Activity of Separase in BCR-ABL b3a2 Fusion Type CML under Imatinib Therapy

Unbalanced (major route) additional cytogenetic aberrations (ACA) at diagnosis of chronic myeloid leukemia (CML) indicate an increased risk of progression and shorter survival. Moreover, newly arising ACA under imatinib treatment and clonal evolution are considered features of acceleration and define failure of therapy according to the European LeukemiaNet (ELN) recommendations. On the basis of 1151 Philadelphia chromosome positive chronic phase patients of the randomized CML-study IV, we examined the incidence of newly arising ACA under imatinib treatment with regard to the p210BCR-ABL breakpoint variants b2a2 and b3a2. We found a preferential acquisition of unbalanced ACA in patients with b3a2 vs. b2a2 fusion type (ratio: 6.3 vs. 1.6, p = 0.0246) concurring with a faster progress to blast crisis for b3a2 patients (p = 0.0124). ESPL1/Separase, a cysteine endopeptidase, is a key player in chromosomal segregation during mitosis. Separase overexpression and/or hyperactivity has been reported from a wide range of cancers and cause defective mitotic spindles, chromosome missegregation and aneuploidy. We investigated the influence of p210BCR-ABL breakpoint variants and imatinib treatment on expression and proteolytic activity of Separase as measured with a specific fluorogenic assay on CML cell lines (b2a2: KCL-22, BV-173; b3a2: K562, LAMA-84). Despite a drop in Separase protein levels an up to 5.4-fold increase of Separase activity under imatinib treatment was observed exclusively in b3a2 but not in b2a2 cell lines. Mimicking the influence of imatinib on BV-173 and LAMA-84 cells by ESPL1 silencing stimulated Separase proteolytic activity in both b3a2 and b2a2 cell lines. Our data suggest the existence of a fusion type-related feedback mechanism that posttranslationally stimulates Separase proteolytic activity after therapy-induced decreases in Separase protein levels. This could render b3a2 CML cells more prone to aneuploidy and clonal evolution than b2a2 progenitors and may therefore explain the cytogenetic results of CML patients.

Chromosome mis-segregation and cytokinesis failure in trisomic human cells

Cancer cells display aneuploid karyotypes and typically mis-segregate chromosomes at high rates, a phenotype referred to as chromosomal instability (CIN). To test the effects of aneuploidy on chromosome segregation and other mitotic phenotypes we used the colorectal cancer cell line DLD1 (2n = 46) and two variants with trisomy 7 or 13 (DLD1+7 and DLD1+13), as well as euploid and trisomy 13 amniocytes (AF and AF+13). We found that trisomic cells displayed higher rates of chromosome mis-segregation compared to their euploid counterparts. Furthermore, cells with trisomy 13 displayed a distinctive cytokinesis failure phenotype. We showed that up-regulation of SPG20 expression, brought about by trisomy 13 in DLD1+13 and AF+13 cells, is sufficient for the cytokinesis failure phenotype. Overall, our study shows that aneuploidy can induce chromosome mis-segregation. Moreover, we identified a trisomy 13-specific mitotic phenotype that is driven by up-regulation of a gene encoded on the aneuploid chromosome.

DOI:http://dx.doi.org/10.7554/eLife.05068.001

The DNA in a human cell is divided between forty-six structures called chromosomes. Before a cell divides, it copies every chromosome so that each daughter cell will have the same DNA as the parent cell. These chromosomes align in the center of the cell and then the matching chromosomes are separated and pulled to opposite ends.

However, in some cases the separation process does not work properly, which can produce cells that either have too many, or too few, chromosomes. Abnormal numbers of chromosomes within cells—called aneuploidy—is a leading cause of miscarriage and birth defects in humans. Aneuploidy is also a common feature of cancer cells.

It is common for the chromosomes in cancer cells to be distributed unequally when the cell divides. This phenomenon is known as chromosomal instability, but the link between aneuploidy and chromosomal instability in cancer cells is not fully understood.

Here, Nicholson et al. used live-cell imaging techniques to analyze healthy human cells and cancer cells that had either the normal forty-six chromosomes, or a defined extra chromosome. Nicholson et al. found that when the cells divided, the chromosomes in the cells that had an extra copy of chromosome 7 or 13 were more prone to distributing chromosomes unequally, compared to cells with a normal number of chromosomes.

Nicholson et al. also observed that the cells with an extra chromosome 13 were unable to properly divide into two. These cells had increased levels of a protein called Spartin—which is important for the last stage in cell division—and this was responsible for the failure to produce two daughter cells.

These findings show that aneuploidy can cause chromosomal instability in human cells. Furthermore, Nicholson et al. have identified a defect in cell division that is specifically caused by the presence of an extra chromosome 13 in human cells. A future challenge will be to determine how, and to what extent, different chromosomes can affect chromosome stability. This could be useful in the development of therapies against cancer cells with aneuploidy.

DOI:http://dx.doi.org/10.7554/eLife.05068.002

Link between aneuploidy and chromosome instability

Aneuploidy is widely acknowledged as a leading cause of miscarriage and birth defects in humans, and is generally known to be deleterious to the survival of individual cells. However, aneuploidy is also ubiquitous in cancer and is found to arise as an adaptive response in certain contexts. This dichotomy of aneuploidy has attracted the interest of researchers for over a century, but many studies have reached conflicting conclusions. The emergence of new technology has allowed scientists to revisit the aneuploidy problem and has fueled a number of recent studies aimed at understanding the effects of aneuploidy on cell physiology. Here, we review these studies, in light of previous observations and knowledge, specifically focusing on the effects of aneuploidy on cellular homeostasis, chromosome stability, and adaptation.

Step-wise and punctuated genome evolution drive phenotype changes of tumor cells

The pattern of genome evolution can be divided into two phases: the step-wise continuous phase (step-wise clonal evolution, stable dominant clonal chromosome aberrations (CCAs), and low frequency of non-CCAs, NCCAs) and punctuated phase (marked by elevated NCCAs and transitional CCAs). Depending on the phase, system stresses (the diverse CIN promoting factors) may lead to the very different phenotype responses. To address the contribution of chromosome instability (CIN) to phenotype changes of tumor cells, we characterized CCAs/NCCAs of HeLa and HEK293 cells, and their derivatives after genotoxic stresses (a stable plasmid transfection, ectopic expression of cancer-associated CHI3L1 gene or treatment with temozolomide) by conventional cytogenetics, copy number alterations (CNAs) by array comparative genome hybridization, and phenotype changes by cell viability and soft agar assays. Transfection of either the empty vector pcDNA3.1 or pcDNA3.1_CHI3L1 into 293 cells initiated the punctuated genome changes. In contrast, HeLa_CHI3L1 cells demonstrated the step-wise genome changes. Increased CIN correlated with lower viability of 293_pcDNA3.1 cells but higher colony formation efficiency (CFE). Artificial CHI3L1 production in 293_CHI3L1 cells increased viability and further contributed to CFE. The opposite growth characteristics of 293_CHI3L1 and HeLa_CHI3L1 cells were revealed. The effect and function of a (trans)gene can be opposite and versatile in cells with different genetic network, which is defined by genome context. Temozolomide treatment of 293_pcDNA3.1 cells intensified the stochastic punctuated genome changes and CNAs, and significantly reduced viability and CFE. In contrast, temozolomide treatment of HeLa_CHI3L1 cells promoted the step-wise genome changes, CNAs, and increased viability and CFE, which did not correlate with the ectopic CHI3L1 production. Thus, consistent coevolution of karyotypes and phenotypes was observed. CIN as a driving force of genome evolution significantly influences growth characteristics of tumor cells and should be always taken into consideration during the different experimental manipulations.

Molecular pathways: regulation and targeting of kinetochore-microtubule attachment in cancer

Kinetochores are large protein structures assembled on centromeric DNA during mitosis that bind to microtubules of the mitotic spindle to orchestrate and power chromosome movements. Deregulation of kinetochore-microtubule (KT-MT) attachments has been implicated in driving chromosome instability and cancer evolution; however, the nature and source of KT-MT attachment defects in cancer cells remain largely unknown. Here, we highlight recent findings suggesting that oncogene-driven changes in kinetochore regulation occur in glioblastoma multiforme (GBM) and possibly other cancers exhibiting chromosome instability, giving rise to novel therapeutic opportunities. In particular, we consider the GLE2p-binding sequence domains of BubR1 and the newly discovered BuGZ, two kinetochore-associated proteins, as candidate therapeutic targets for GBM.

Differentiation of hESCs into Mesodermal Subtypes: Vascular-, Hematopoietic- and Mesenchymal-lineage Cells

To date, studies on the application of mesodermally derived mesenchymal-, hematopoietic- and vascular-lineage cells for cell therapy have provided either poor or insufficient data. The results are equivocal with regard to therapeutic efficiency and yield. Since the establishment of human embryonic stem cells (hESCs) in 1998, the capacity of hESCs to differentiate into various mesodermal lineages has sparked considerable interest in the regenerative medicine community, a group interested in generating specialized cells to treat patients suffering from degenerative diseases. Even though hESCs are sensitive, effective methods for guiding the differentiation of hESCs into specific mesodermal cell types are still being developed. In addition, to understand the functional properties of hESC derivatives, numerous animal model studies have been performed by many research groups over the last decade. In this review, we describe and summarize the protocols currently used for differentiation of hESCs into multiple mesodermal lineages and their therapeutic efficiency in different animal models. Furthermore, we discuss the technical hurdles associated with each protocol and the safety of hESC derivatives for therapeutic applications. Technical improvement of the methods used to produce hESC derivatives for therapeutic use in patients with degenerative diseases should remain an objective of future studies, as should the development of effective and stable induction systems.

Unstable genomes elevate transcriptome dynamics

The challenge of identifying common expression signatures in cancer is well known, however the reason behind this is largely unclear. Traditionally variation in expression signatures has been attributed to technological problems, however recent evidence suggests that chromosome instability (CIN) and resultant karyotypic heterogeneity may be a large contributing factor. Using a well-defined model of immortalization, we systematically compared the pattern of genome alteration and expression dynamics during somatic evolution. Co-measurement of global gene expression and karyotypic alteration throughout the immortalization process reveals that karyotype changes influence gene expression as major structural and numerical karyotypic alterations result in large gene expression deviation. Replicate samples from stages with stable genomes are more similar to each other than are replicate samples with karyotypic heterogeneity. Karyotypic and gene expression change during immortalization is dynamic as each stage of progression has a unique expression pattern. This was further verified by comparing global expression in two replicates grown in one flask with known karyotypes. Replicates with higher karyotypic instability were found to be less similar than replicates with stable karyotypes. This data illustrates the karyotype, transcriptome, and transcriptome determined pathways are in constant flux during somatic cellular evolution (particularly during the macroevolutionary phase) and this flux is an inextricable feature of CIN and essential for cancer formation. The findings presented here underscore the importance of understanding the evolutionary process of cancer in order to design improved treatment modalities.

Suppression of genome instability in pRB-deficient cells by enhancement of chromosome cohesion

Chromosome instability (CIN), a common feature of solid tumors, promotes tumor evolution and increases drug resistance during therapy. We previously demonstrated that loss of the retinoblastoma protein (pRB) tumor suppressor causes changes in centromere structure and generates CIN. However, the mechanism and significance of this change was unclear. Here, we show that defects in cohesion are key to the pRB loss phenotype. pRB loss alters H4K20 methylation, a prerequisite for efficient establishment of cohesion at centromeres. Changes in cohesin regulation are evident during S phase, where they compromise replication and increase DNA damage. Ultimately, such changes compromise mitotic fidelity following pRB loss. Remarkably, increasing cohesion suppressed all of these phenotypes and dramatically reduced CIN in cancer cells lacking functional pRB. These data explain how loss of pRB undermines genomic integrity. Given the frequent functional inactivation of pRB in cancer, conditions that increase cohesion may provide a general strategy to suppress CIN.

Multi-layered cancer chromosomal instability phenotype

Whole-chromosomal instability (W-CIN) – unequal chromosome distribution during cell division – is a characteristic feature of a majority of cancer cells distinguishing them from their normal counterparts. The precise molecular mechanisms that may cause mis-segregation of chromosomes in tumor cells just recently became more evident. The consequences of W-CIN are numerous and play a critical role in carcinogenesis. W-CIN mediates evolution of cancer cell population under selective pressure and can facilitate the accumulation of genetic changes that promote malignancy. It has both tumor-promoting and tumor-suppressive effects, and their balance could be beneficial or detrimental for carcinogenesis. The characterization of W-CIN as a complex multi-layered adaptive phenotype highlights the intra- and extracellular adaptations to the consequences of genome reshuffling. It also provides a framework for targeting aggressive chromosomally unstable cancers.

MMTV-Espl1 transgenic mice develop aneuploid, estrogen receptor alpha (ERα)-positive mammary adenocarcinomas

Separase, a protease encoded by the ESPL1 gene, cleaves the chromosomal cohesin during mitosis. Separase protein and transcripts are overexpressed in a wide range of human cancers (Meyer et al., Clin Cancer Res 2009; 15: 2703-2710). To investigate the physiological consequence of Separase overexpression in animals, we have generated a transgenic MMTVEspl1 mouse model that overexpresses Separase protein in the mammary glands. MMTV-Espl1 mice in a C57BL/6 genetic background develop aggressive, highly aneuploid, and estrogen receptor alpha positive (ERα+) mammary adenocarcinomas with an 80% penetrance. The mammary tumors caused by overexpression of Separase, alone or combined with p53 heterozygosity, in mammary epithelium mimic several aspects of the most aggressive forms of human breast cancer, including high levels of genetic instability, cell cycle defects, poor differentiation, distant metastasis, and metaplasia. Histopathologically, MMTV-Espl1 tumors are highly heterogeneous showing features of both luminal as well as basal subtypes of breast cancers, with aggressive disease phenotype. In addition to aneuploidy, Separase overexpression results in chromosomal instability (CIN) including premature chromatid separation (PCS), lagging chromosomes, anaphase bridges, micronuclei, centrosome amplification, multi nucleated cells, gradual accumulation of DNA damage, and progressive loss of tumor suppressors p53 and cadherin gene loci. These results suggest that Separase overexpressing mammary cells are not only susceptible to chromosomal missegregation-induced aneuploidy but also other genetic instabilities including DNA damage and loss of key tumor suppressor gene loci, which in combination can initiate tumorigenesis and disease progression.

Tumor-specific chromosome mis-segregation controls cancer plasticity by maintaining tumor heterogeneity

Aneuploidy with chromosome instability is a cancer hallmark. We studied chromosome 7 (Chr7) copy number variation (CNV) in gliomas and in primary cultures derived from them. We found tumor heterogeneity with cells having Chr7-CNV commonly occurs in gliomas, with a higher percentage of cells in high-grade gliomas carrying more than 2 copies of Chr7, as compared to low-grade gliomas. Interestingly, all Chr7-aneuploid cell types in the parental culture of established glioma cell lines reappeared in single-cell-derived subcultures. We then characterized the biology of three syngeneic glioma cultures dominated by different Chr7-aneuploid cell types. We found phenotypic divergence for cells following Chr7 mis-segregation, which benefited overall tumor growth in vitro and in vivo. Mathematical modeling suggested the involvement of chromosome instability and interactions among cell subpopulations in restoring the optimal equilibrium of tumor cell types. Both our experimental data and mathematical modeling demonstrated that the complexity of tumor heterogeneity could be enhanced by the existence of chromosomes with structural abnormality, in addition to their mis-segregations. Overall, our findings show, for the first time, the involvement of chromosome instability in maintaining tumor heterogeneity, which underlies the enhanced growth, persistence and treatment resistance of cancers.

Individual karyotypes at the origins of cervical carcinomas

Background

In 1952 Papanicolaou et al. first diagnosed and graded cervical carcinomas based on individual “abnormal DNA contents” and cellular phenotypes. Surprisingly current papilloma virus and mutation theories of carcinomas do not mention these individualities. The viral theory holds that randomly integrated, defective genomes of papilloma viruses, which are often untranscribed, cause cervical carcinomas with unknown cofactors 20–50 years after infection. Virus-free carcinomas are attributed to mutations of a few tumor-suppressor genes, especially the p53 gene. But the paradox of how a few mutations or latent defective viral DNAs would generate carcinomas with endless individual DNA contents, degrees of malignancies and cellular phenotypes is unsolved. Since speciation predicts individuality, we test here the theory that cancers are autonomous species with individual clonal karyotypes and phenotypes. This theory postulates that carcinogens induce aneuploidy. By unbalancing mitosis genes aneuploidy catalyzes chain reactions of karyotypic evolutions. Most such evolutions end with non-viable karyotypes but a few become new cancer karyotypes. Despite congenitally unbalanced mitosis genes cancer karyotypes are stabilized by clonal selections for cancer-specific autonomy.

Results

To test the prediction of the speciation theory that individual carcinomas have individual clonal karyotypes and phenotypes, we have analyzed here the phenotypes and karyotypes of nine cervical carcinomas. Seven of these contained papilloma virus sequences and two did not. We determined phenotypic individuality and clonality based on the morphology and sociology of carcinoma cells in vitro. Karyotypic individuality and clonality were determined by comparing all chromosomes of 20 karyotypes of carcinomas in three-dimensional arrays. Such arrays list chromosome numbers on the x-axis, chromosome copy numbers on the y-axis and the number of karyotypes arrayed on the z-axis. We found (1) individual clonal karyotypes and phenotypes in all nine carcinomas, but no virus-specific markers, (2) 1-to-1 variations between carcinoma-specific karyotypes and phenotypes, e.g. drug-resistance and cell morphology, (3) proportionality between the copy numbers of chromosomes and the copy numbers of hundreds of over- and under-expressed mRNAs, (4) evidence that tobacco-carcinogens induce cervical carcinomas via aneuploidy, consistent with the speciation theory.

Conclusions

Since the individual clonal karyotypes of nine carcinomas correlated and co-varied 1-to-1 with complex individual transcriptomes and phenotypes, we have classical genetic and functional transcriptomic evidence to conclude that these karyotypes encode carcinomas - much like the clonal karyotypes that encode conventional species. These individual karyotypes explain the individual “DNA contents”, the endless grades of malignancies and the complex individual transcriptomes and phenotypes of carcinomas.