Chromosomal instability and cancer: a complex relationship with therapeutic potential

Spindle microtubule dysfunction and cancer predisposition

Chromosome segregation and spindle microtubule dynamics are strictly coordinated during cell division in order to preserve genomic integrity. Alterations in the genome that affect microtubule stability and spindle assembly during mitosis may contribute to genomic instability and cancer predisposition, but directly testing this potential link poses a significant challenge. Germ-line mutations in tumor suppressor genes that predispose patients to cancer and alter spindle microtubule dynamics offer unique opportunities to investigate the relationship between spindle dysfunction and carcinogenesis. Mutations in two such tumor suppressors, adenomatous polyposis coli (APC) and Shwachman-Bodian-Diamond syndrome (SBDS), affect multifunctional proteins that have been well characterized for their roles in Wnt signaling and interphase ribosome assembly, respectively. Less understood, however, is how their shared involvement in stabilizing the microtubules that comprise the mitotic spindle contributes to cancer predisposition. Here, we briefly discuss the potential for mutations in APC and SBDS as informative tools for studying the impact of mitotic spindle dysfunction on cellular transformation.

WT1 interacts with MAD2 and regulates mitotic checkpoint function

Tumour suppressors safeguard the fidelity of the mitotic checkpoint by transcriptional regulation of genes that encode components of the mitotic checkpoint complex (MCC). Here we report a new role for the tumour suppressor and transcription factor, WT1, in the mitotic checkpoint. We show that WT1 regulates the MCC by directly interacting with the spindle assembly checkpoint protein, MAD2. WT1 colocalizes with MAD2 during mitosis and preferentially binds to the functionally active, closed-conformer, C-MAD2. Furthermore, WT1 associates with the MCC containing MAD2, BUBR1 and CDC20, resulting in prolonged inhibition of the anaphase-promoting complex/cyclosome (APC/C) and delayed degradation of its substrates SECURIN and CYCLIN B1. Strikingly, RNA interference-mediated depletion of WT1 leads to enhanced turnover of SECURIN, decreased lag time to anaphase and defects in chromosome segregation. Our findings identify WT1 as a regulator of the mitotic checkpoint and chromosomal stability.

Chromosomal instability selects gene copy-number variants encoding core regulators of proliferation in ER+ breast cancer

Chromosomal instability (CIN) is associated with poor outcome in epithelial malignancies, including breast carcinomas. Evidence suggests that prognostic signatures in estrogen receptor-positive (ER(+)) breast cancer define tumors with CIN and high proliferative potential. Intriguingly, CIN induction in lower eukaryotic cells and human cells is context dependent, typically resulting in a proliferation disadvantage but conferring a fitness benefit under strong selection pressures. We hypothesized that CIN permits accelerated genomic evolution through the generation of diverse DNA copy-number events that may be selected during disease development. In support of this hypothesis, we found evidence for selection of gene amplification of core regulators of proliferation in CIN-associated cancer genomes. Stable DNA copy-number amplifications of the core regulators TPX2 and UBE2C were associated with expression of a gene module involved in proliferation. The module genes were enriched within prognostic signature gene sets for ER(+) breast cancer, providing a logical connection between CIN and prognostic signature expression. Our results provide a framework to decipher the impact of intratumor heterogeneity on key cancer phenotypes, and they suggest that CIN provides a permissive landscape for selection of copy-number alterations that drive cancer proliferation.

Genomic instability, driver genes and cell selection: Projections from cancer to stem cells

Cancer cells and stem cells share many traits, including a tendency towards genomic instability. Human cancers exhibit tumor-specific genomic aberrations, which often affect their malignancy and drug response. During their culture propagation, human pluripotent stem cells (hPSCs) also acquire characteristic genomic aberrations, which may have significant impact on their molecular and cellular phenotypes. These aberrations vary in size from single nucleotide alterations to copy number alterations to whole chromosome gains. A prominent challenge in both cancer and stem cell research is to identify "driver aberrations" that confer a selection advantage, and "driver genes" that underlie the recurrence of these aberrations. Following principles that are already well-established in cancer research, candidate driver genes have also been suggested in hPSCs. Experimental validation of the functional role of such candidates can uncover whether these are bona fide driver genes. The identification of driver genes may bring us closer to a mechanistic understanding of the genomic instability of stem cells. Guided by terminologies and methodologies commonly applied in cancer research, such understanding may have important ramifications for both stem cell and cancer biology. This article is part of a Special Issue entitled: Stress as a fundamental theme in cell plasticity.

STAG2 promotes error correction in mitosis by regulating kinetochore-microtubule attachments

Mutations in the STAG2 gene are present in ∼20% of tumors from different tissues of origin. STAG2 encodes a subunit of the cohesin complex, and tumors with loss-of-function mutations are usually aneuploid and display elevated frequencies of lagging chromosomes during anaphase. Lagging chromosomes are a hallmark of chromosomal instability (CIN) arising from persistent errors in kinetochore-microtubule (kMT) attachment. To determine whether the loss of STAG2 increases the rate of formation of kMT attachment errors or decreases the rate of their correction, we examined mitosis in STAG2-deficient cells. STAG2 depletion does not impair bipolar spindle formation or delay mitotic progression. Instead, loss of STAG2 permits excessive centromere stretch along with hyperstabilization of kMT attachments. STAG2-deficient cells display mislocalization of Bub1 kinase, Bub3 and the chromosome passenger complex. Importantly, strategically destabilizing kMT attachments in tumor cells harboring STAG2 mutations by overexpression of the microtubule-destabilizing enzymes MCAK (also known as KIF2C) and Kif2B decreased the rate of lagging chromosomes and reduced the rate of chromosome missegregation. These data demonstrate that STAG2 promotes the correction of kMT attachment errors to ensure faithful chromosome segregation during mitosis.

Analysis of centromere signal patterns in breast cancer cells with chromosomal instability using image cytometry combined with centromere fluorescence in situ hybridization

Fluorescence in situ hybridization (FISH) with centromeric probes is a method used to detect chromosomal instability (CIN), a hallmark of most cancers. However, no studies thus far have investigated the relationship between centromeric FISH signals and the cell cycle in cancer cells. In this study, the chromosome content in each cell cycle phase was evaluated with respect to the number of centromeric FISH signals in two breast cancer cell lines and eight surgically resected breast cancer specimens using image cytometry. Variations in chromosome number were detected at each phase of the cell cycle but were not associated with proliferative capacity in the cell lines. Furthermore, the chromosome doubling frequency differed in each cell line and clinical specimen. These results reveal two aspects of centromeric FISH signal variation in breast cancers that exhibit CIN, and suggest that chromosome doubling is a remarkable occurrence that may increase the heterogeneity of tumors.

Chemogenetic evaluation of the mitotic kinesin CENP-E reveals a critical role in triple-negative breast cancer

Breast cancer patients with tumors lacking the three diagnostic markers (ER, PR, and HER2) are classified as triple-negative (primarily basal-like) and have poor prognosis because there is no disease-specific therapy available. To address this unmet medical need, gene expression analyses using more than a thousand breast cancer samples were conducted, which identified elevated centromere protein E (CENP-E) expression in the basal-a molecular subtype relative to other subtypes. CENP-E, a mitotic kinesin component of the spindle assembly checkpoint, is shown to be induced in basal-a tumor cell lines by the mitotic spindle inhibitor drug docetaxel. CENP-E knockdown by inducible shRNA reduces basal-a breast cancer cell viability. A potent, selective CENP-E inhibitor (PF-2771) was used to define the contribution of CENP-E motor function to basal-like breast cancer. Mechanistic evaluation of PF-2771 in basal-a tumor cells links CENP-E-dependent molecular events (e.g., phosphorylation of histone H3 Ser-10; phospho-HH3-Ser10) to functional outcomes (e.g., chromosomal congression defects). Across a diverse panel of breast cell lines, CENP-E inhibition by PF-2771 selectively inhibits proliferation of basal breast cancer cell lines relative to premalignant ones and its response correlates with the degree of chromosomal instability. Pharmacokinetic-pharmacodynamic efficacy analysis in a basal-a xenograft tumor model shows that PF-2771 exposure is well correlated with increased phospho-HH3-Ser10 levels and tumor growth regression. Complete tumor regression is observed in a patient-derived, basal-a breast cancer xenograft tumor model treated with PF-2771. Tumor regression is also observed with PF-2771 in a taxane-resistant basal-a model. Taken together, CENP-E may be an effective therapeutic target for patients with triple-negative/basal-a breast cancer.

Meta-analysis of the global gene expression profile of triple-negative breast cancer identifies genes for the prognostication and treatment of aggressive breast cancer

Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype lacking expression of estrogen and progesterone receptors (ER/PR) and HER2, thus limiting therapy options. We hypothesized that meta-analysis of TNBC gene expression profiles would illuminate mechanisms underlying the aggressive nature of this disease and identify therapeutic targets. Meta-analysis in the Oncomine database identified 206 genes that were recurrently deregulated in TNBC compared with non-TNBC and in tumors that metastasized or led to death within 5 years. This ‘aggressiveness gene list' was enriched for two core functions/metagenes: chromosomal instability (CIN) and ER signaling metagenes. We calculated an ‘aggressiveness score' as the ratio of the CIN metagene to the ER metagene, which identified aggressive tumors in breast cancer data sets regardless of subtype or other clinico-pathological indicators. A score calculated from six genes from the CIN metagene and two genes from the ER metagene recapitulated the aggressiveness score. By multivariate survival analysis, we show that our aggressiveness scores (from 206 genes or the 8 representative genes) outperformed several published prognostic signatures. Small interfering RNA screen revealed that the CIN metagene holds therapeutic targets against TNBC. Particularly, the inhibition of TTK significantly reduced the survival of TNBC cells and synergized with docetaxel in vitro. Importantly, mitosis-independent expression of TTK protein was associated with aggressive subgroups, poor survival and further stratified outcome within grade 3, lymph node-positive, HER2-positive and TNBC patients. In conclusion, we identified the core components of CIN and ER metagenes that identify aggressive breast tumors and have therapeutic potential in TNBC and aggressive breast tumors. Prognostication from these metagenes at the mRNA level was limited to ER-positive tumors. However, we provide evidence that mitosis-independent expression of TTK protein was prognostic in TNBC and other aggressive breast cancer subgroups, suggesting that protection of CIN/aneuploidy drives aggressiveness and treatment resistance.

Genetics and epigenetics of adrenocortical tumors

Adrenocortical tumors are common neoplasms. Most are benign, nonfunctional and clinically irrelevant. However, adrenocortical carcinoma is a rare disease with a dismal prognosis and no effective treatment apart from surgical resection. The molecular genetics of adrenocortical tumors remain poorly understood. For decades, molecular studies relied on a small number of samples and were directed to candidate-genes. This approach, based on the elucidation of the genetics of rare genetic syndromes in which adrenocortical tumors are a manifestation, has led to the discovery of major dysfunctional molecular pathways in adrenocortical tumors, such as the IGF pathway, the Wnt pathway and TP53. However, with the advent of high-throughput methodologies and the organization of international consortiums to obtain a larger number of samples and high-quality clinical data, this paradigm is rapidly changing. In the last decade, genome-wide expression profile studies, microRNA profiling and methylation profiling allowed the identification of subgroups of tumors with distinct genetic markers, molecular pathways activation patterns and clinical behavior. As a consequence, molecular classification of tumors has proven to be superior to traditional histological and clinical methods in prognosis prediction. In addition, this knowledge has also allowed the proposal of molecular-targeted approaches to provide better treatment options for advanced disease. This review aims to summarize the most relevant data on the rapidly evolving field of genetics of adrenal disorders.

Tumor cell plasticity: the challenge to catch a moving target

Every cancer cell is "different"--within one and the same tumor, between different lesions originating from the same tumor, among different patients suffering from the same tumor type, and certainly between different tumor types. The complexity of tumor development, with its genetic, phenotypic and functional heterogeneity and plasticity within tumors and between primary tumors and metastases, underlies the unpredictable influences and stimuli of a tumor-associated inflammatory microenvironment, immune response, mechanical and metabolic stress, therapy-induced inflammation or interaction with microbiota. The stochastic and context dependent nature of these factors accounts for the difficulties to investigate the impact of resulting cell plasticity on tumor development, and justifies the challenge to prevent tumor recurrence. The emerging concept of cell plasticity and reciprocity (to change the phenotype by processing signals from the environment) throws more light on the actual complexity of tumor heterogeneity than can be expected solely from a unidirectional, classical cancer stem cell (CSC) model. To date, it remains widely unclear to what extent cell plasticity impacts tumor development, and it is difficult to assess by current methods. As a high tumor plasticity is likely to predict a poor outcome for patients, the future therapeutic challenge will be the development of personalized treatment strategies to predict and finally prevent cell plasticity in patients.

STK31 is a cell-cycle regulated protein that contributes to the tumorigenicity of epithelial cancer cells

Serine/threonine kinase 31 (STK31) is one of the novel cancer/testis antigens for which its biological functions remain largely unclear. Here, we demonstrate that STK31 is overexpressed in many human colorectal cancer cell lines and tissues. STK31 co-localizes with pericentrin in the centrosomal region throughout all phases of the cell cycle. Interestingly, when cells undergo mitosis, STK31 also localizes to the centromeres, central spindle, and midbody. This localization behavior is similar to that of chromosomal passenger proteins, which are known to be the important players of the spindle assembly checkpoint. The expression of STK31 is cell cycle-dependent through the regulation of a putative D-box near its C-terminal region. Ectopically-expressed STK31-GFP increases cell migration and invasive ability without altering the proliferation rate of cancer cells, whereas the knockdown expression of endogenous STK31 by lentivirus-derived shRNA results in microtubule assembly defects that prolong the duration of mitosis and lead to apoptosis. Taken together, our results suggest that the aberrant expression of STK31 contributes to tumorigenicity in somatic cancer cells. STK31 might therefore act as a potential therapeutic target in human somatic cancers.

Chromosomal instability portends superior response of rectal adenocarcinoma to chemoradiation therapy

BACKGROUND

Persistent chromosome segregation errors represent a conspicuous feature of human neoplasms. It is widely accepted that this chromosomal instability is associated with poor prognosis; however, its effect on therapeutic response is a matter of conjecture.

METHODS

Here, the role of chromosome segregation errors in the response of patients with rectal adenocarcinoma to chemoradiation therapy (CRT) was examined. Pretreatment samples from 62 patients were surveyed for evidence of chromosome mis-segregation and mis-segregation frequency was correlated to the pathological response to CRT as determined by the tumor regression grade after surgical resection of irradiated tumors.

RESULTS

Surprisingly, it was found that errors in chromosome segregation predicted enhanced pathological response of rectal adenocarcinoma to CRT (odds ratio, 3.9; P = .02). Furthermore, tumor response inversely correlated with the frequency of cells that exhibited segregation errors during anaphase (correlation coefficient, 0.94; P < .05). Strikingly, elevated chromosome mis-segregation combined with decreased levels of the DNA damage repair protein Mre11 portended a markedly enhanced response (odds ratio, 54.0; P = .008).

CONCLUSIONS

The results of the current study demonstrate that chromosomal instability is a favorable predictor of response to CRT in patients with locally invasive rectal adenocarcinoma. Therefore, the authors propose that downstream structural damage to chromosomes resulting from segregation errors potentiates the effect of DNA-damaging therapies and synergizes with deficiencies in the DNA repair machinery. This work identifies a novel mechanistic marker that foretells treatment response to CRT and suggests that concomitant targeting of whole-chromosome segregation and DNA repair may constitute an effective therapeutic strategy.

DNA-PKcs activates the Chk2-Brca1 pathway during mitosis to ensure chromosomal stability

The catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) is known to have a critical role in DNA double-strand break repair. We have previously reported that DNA-PKcs is activated when cells enter mitosis and functions in mitotic spindle assembly and chromosome segregation. Here we report that DNA-PKcs is the upstream regulator of the Chk2-Brca1 pathway, which impacts microtubule dynamics, kinetochore attachment and chromosomal segregation in mitosis. Downstream from Chk2, Brca1 promotes monoubiquitination of γ-tubulin to inhibit microtubule nucleation and growth. We found that DNA-PKcs is essential for mitotic Chk2 phosphorylation at Thr68. As in Chk2- and Brca1-deficient cells, loss of DNA-PKcs resulted in chromosome misalignment and lagging during anaphase owing to elevation in microtubule dynamics. Importantly, these mitotic aberrations in DNA-PKcs-defective cells were alleviated by the overexpression of phosphomimetic Chk2 or Brca1 mutant proteins but not their wild-type counterparts. Taken together, these results demonstrate that DNA-PKcs regulates mitotic spindle organization and chromosomal instability via the Chk2-Brca1 signaling pathway.

Overview of cyclins D1 function in cancer and the CDK inhibitor landscape: past and present

INTRODUCTION

Intensive efforts, over the last decade, have been made to inhibit the kinase activity of cyclins that act as mediators during cell-cycle progression. Activation of the cyclin D1 oncogene, often by amplification or rearrangement, is a major driver of multiple types of human tumors including breast and squamous cell cancers, B-cell lymphoma, myeloma and parathyroid adenoma.

AREAS COVERED

In this review, the authors summarize the activity of cyclins and cyclin-dependent kinases in cell-cycle progression and transcription. They focus on cyclin D1/CDK4/CDK6, a central mediator in the transition from G1 to S phase. Furthermore, the authors discuss the first generation of pan-cyclin-dependent kinase inhibitors that failed to meet expectation and discuss, in detail, the second generation of highly specific cyclin D1/CDK4/CDK6 inhibitors that are proving to be more efficacious.

EXPERT OPINION

The mechanism by which cyclin D1 drives tumorigenesis may be dependent on kinase and kinase-independent functions. Further evidence is necessary to delineate the roles of cyclin D1 in early pre-neoplastic lesions where its overexpression may promote genomic instability in a kinase-independent manner.

Proteomics of differential extraction fractions enriched for chromatin-binding proteins from colon adenoma and carcinoma tissues

BACKGROUND

Altered nuclear and genomic structure and function are hallmarks of cancer cells. Research into nuclear proteins in human tissues could uncover novel molecular processes in cancer. Here, we examine biochemical tissue fractions containing chromatin-binding (CB) proteins in the context of colorectal cancer (CRC) progression.

METHODS

CB protein-containing fractions were biochemically extracted from human colorectal tissues, including carcinomas with chromosomal instability (CIN), carcinomas with microsatellite instability (MIN), and adenomas. The CB proteins were subjected to label-free LC-MS/MS and the data were analyzed by bioinformatics.

RESULTS

Over 1700 proteins were identified in the CB fraction from colonic tissues, including 938 proteins associated with nuclear annotation. Of the latter, 169 proteins were differential between adenomas and carcinomas. In this adenoma-versus-carcinoma comparison, apart from specific changes in components of the splicing and protein translational machineries, we also identified significant changes in several proteins associated with chromatin-directed functions. Furthermore, several key cell cycle proteins as well as those involved in cellular stress were increased, whereas specific components of chromosome segregation and DNA recombination/repair systems were decreased.

CONCLUSIONS

Our study identifies proteomic changes at the subnuclear level that are associated with CRC and may be further investigated. This article is part of a Special Issue entitled: Biomarkers: A Proteomic Challenge.

JNK signaling is needed to tolerate chromosomal instability

Chromosomal instability (CIN), as a common feature of tumors, represents a potential therapeutic target if ways can be found to specifically cause apoptosis in unstably dividing cells. We have previously shown that if signaling through the JNK pathway is reduced, apoptosis is triggered in models of chromosomal instability induced by loss of the spindle checkpoint. Here we identify components upstream and downstream of JNK that are able to mediate this effect, and test the involvement of p53 and DNA damage in causing apoptosis when JNK signaling is reduced in CIN cells. We show that cell cycle progression timing has a strong effect on the apoptosis seen when JNK signaling is reduced in genetically unstable cells: a shortened G 2 phase enhances the apoptosis, while lengthening G 2 rescues the JNK-deficient CIN cell death phenotype. Our findings suggest that chromosomal instability represents a significant stress to dividing cells, and that without JNK signaling, cells undergo apoptosis because they lack a timely and effective response to DNA damage.

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.

Cancer quasispecies and stem-like adaptive aneuploidy

In this paper we develop a theoretical frame to understand self-regulation of aneuploidy rate in cancer and stem cells. This is accomplished building upon quasispecies theory, by leaving its formal mathematical structure intact, but by drastically changing the meaning of its objects. In particular, we propose a novel definition of chromosomal master sequence, as a sequence of physically distinct whole or fragmented chromosomes, whose length is taken to be the sum of the copy numbers of each whole or fragmented chromosome. This fundamental change in the functional objects of quasispecies theory allows us to show that previously measured aneuploidy rates in cancer populations are already close to a formally derived aneuploid error threshold, and that any value of aneuploidy rate larger than the aneuploid error threshold would lead to a loss of fitness of a tumor population. Finally, we make a phenomenological analysis of existing experimental evidence to argue that single clone cancer cells, derived from an aneuploid cancer subpopulation, are capable of self-regulating their aneuploidy rate and of adapting it to distinct environments, namely primary and metastatic microenvironments. We also discuss the potential origin of this self-regulatory ability in the wider context of developmental and comparative biology and we hypothesize the existence of a diversification factor, i.e. a cellular mechanism that regulates adaptation of aneuploidy rates, active in all embryo, adult and cancer stem cells.

Selective inhibition of pancreatic ductal adenocarcinoma cell growth by the mitotic MPS1 kinase inhibitor NMS-P715

Most solid tumors, including pancreatic ductal adenocarcinoma (PDAC), exhibit structural and numerical chromosome instability (CIN). Although often implicated as a driver of tumor progression and drug resistance, CIN also reduces cell fitness and poses a vulnerability that can be exploited therapeutically. The spindle assembly checkpoint (SAC) ensures correct chromosome-microtubule attachment, thereby minimizing chromosome segregation errors. Many tumors exhibit upregulation of SAC components such as MPS1, which may help contain CIN within survivable limits. Prior studies showed that MPS1 inhibition with the small molecule NMS-P715 limits tumor growth in xenograft models. In cancer cell lines, NMS-P715 causes cell death associated with impaired SAC function and increased chromosome missegregation. Although normal cells appeared more resistant, effects on stem cells, which are the dose-limiting toxicity of most chemotherapeutics, were not examined. Elevated expression of 70 genes (CIN70), including MPS1, provides a surrogate measure of CIN and predicts poor patient survival in multiple tumor types. Our new findings show that the degree of CIN70 upregulation varies considerably among PDAC tumors, with higher CIN70 gene expression predictive of poor outcome. We identified a 25 gene subset (PDAC CIN25) whose overexpression was most strongly correlated with poor survival and included MPS1. In vitro, growth of human and murine PDAC cells is inhibited by NMS-P715 treatment, whereas adipose-derived human mesenchymal stem cells are relatively resistant and maintain chromosome stability upon exposure to NMS-P715. These studies suggest that NMS-P715 could have a favorable therapeutic index and warrant further investigation of MPS1 inhibition as a new PDAC treatment strategy.

Meiotic double-strand breaks uncover and protect against mitotic errors in the C. elegans germline

In sexually reproducing multicellular organisms, genetic information is propagated via the germline, the specialized tissue that generates haploid gametes. The C. elegans germline generates gametes in an assembly line-like process-mitotic divisions under the control of the stem cell niche produce nuclei that, upon leaving the niche, enter into meiosis and progress through meiotic prophase [1]. Here, we characterize the effects of perturbing cell division in the mitotic region of the C. elegans germline. We show that mitotic errors result in a spindle checkpoint-dependent cell-cycle delay, but defective nuclei are eventually formed and enter meiosis. These defective nuclei are eliminated by programmed cell death during meiotic prophase. The cell death-based removal of defective nuclei does not require the spindle checkpoint but instead depends on the DNA damage checkpoint. Removal of nuclei resulting from errors in mitosis also requires Spo11, the enzyme that creates double-strand breaks to initiate meiotic recombination. Consistent with this, double-strand breaks are increased in number and persist longer in germlines with mitotic defects. These findings reveal that the process of initiating meiotic recombination inherently selects against nuclei with abnormal chromosomal content generated by mitotic errors, thereby ensuring the genomic integrity of gametes.

Centrosome dysfunction contributes to chromosome instability, chromoanagenesis, and genome reprograming in cancer

The unique ability of centrosomes to nucleate and organize microtubules makes them unrivaled conductors of important interphase processes, such as intracellular payload traffic, cell polarity, cell locomotion, and organization of the immunologic synapse. But it is in mitosis that centrosomes loom large, for they orchestrate, with clockmaker's precision, the assembly and functioning of the mitotic spindle, ensuring the equal partitioning of the replicated genome into daughter cells. Centrosome dysfunction is inextricably linked to aneuploidy and chromosome instability, both hallmarks of cancer cells. Several aspects of centrosome function in normal and cancer cells have been molecularly characterized during the last two decades, greatly enhancing our mechanistic understanding of this tiny organelle. Whether centrosome defects alone can cause cancer, remains unanswered. Until recently, the aggregate of the evidence had suggested that centrosome dysfunction, by deregulating the fidelity of chromosome segregation, promotes and accelerates the characteristic Darwinian evolution of the cancer genome enabled by increased mutational load and/or decreased DNA repair. Very recent experimental work has shown that missegregated chromosomes resulting from centrosome dysfunction may experience extensive DNA damage, suggesting additional dimensions to the role of centrosomes in cancer. Centrosome dysfunction is particularly prevalent in tumors in which the genome has undergone extensive structural rearrangements and chromosome domain reshuffling. Ongoing gene reshuffling reprograms the genome for continuous growth, survival, and evasion of the immune system. Manipulation of molecular networks controlling centrosome function may soon become a viable target for specific therapeutic intervention in cancer, particularly since normal cells, which lack centrosome alterations, may be spared the toxicity of such therapies.

Sirtuin-3 (SIRT3) and the Hallmarks of Cancer

Sirtuins (SIRT1-SIRT7), the mammalian homologs of the silent information regulator 2 (Sir2) in Saccharomyces cerevisiae, have been a major focus of study in the scientific community this past decade because of their emerging role in cancer biology and other age-related diseases. Emerging functions for this unique family of enzymes include roles in genomic stability, angiogenesis, metabolism, and anoikis. Here, we review recent developments on the role of sirtuins in cancer with a particular focus on SIRT3 and its role in the hallmarks of cancer and as a potential drug target for cancer treatment.

Overexpression of CENP-H as a novel prognostic biomarker for human hepatocellular carcinoma progression and patient survival

Centromere protein H (CENP-H) has been shown to be significantly upregulated in many types of cancers and is associated with disrupted cell cycle regulation, cell proliferation and genetic instability. The aim of the present study was to explore the expression and localization of CENP-H in hepatocellular carcinoma (HCC) and determine whether its overexpression is a prognostic biomarker for HCC. Reverse transcription-polymerase chain reaction (pcr), real-time qPCR and western blotting were used to compare CENP-H expression at the mRNA and protein levels in HCC samples and corresponding adjacent non-cancerous samples. CENP-H protein levels were determined in 60 paired paraffin-embedded HCC tissues using immunohistochemistry (IHC), and the correlation with clinicopathological features and patient prognosis was analyzed. In addition, an immunofluorescence assay was performed to test the expression and localization of CENP-H protein in HCC cells. Results showed that levels of CENP-H mRNA and protein were higher in HCC samples than in the corresponding adjacent non-cancerous samples. In 60 paired paraffin-embedded tissues, CENP-H was upregulated in the HCC samples (38/60, 63.3%) relative to the adjacent non-cancerous samples (21/60, 35%, P=0.003), and a higher level of upregulation was associated with tumor size (P=0.032); higher histological grade (P=0.001); more advanced TNM stage (P=0.002) and Chinese clinical stage (P=0.008); and poorer prognosis. In addition, consistent with the results of IHC, the immunofluorescence assay showed that CENP-H was localized in the nucleus of Hep3B cells. CENP-H was overexpressed in HCC, and its level of upregulation was an independent prognostic indicator, suggesting that CENP-H may be an effective therapeutic strategy for the treatment of HCC.

Development of a Drosophila cell-based error correction assay

Accurate transmission of the genome through cell division requires microtubules from opposing spindle poles to interact with protein super-structures called kinetochores that assemble on each sister chromatid. Most kinetochores establish erroneous attachments that are destabilized through a process called error correction. Failure to correct improper kinetochore-microtubule (kt-MT) interactions before anaphase onset results in chromosomal instability (CIN), which has been implicated in tumorigenesis and tumor adaptation. Thus, it is important to characterize the molecular basis of error correction to better comprehend how CIN occurs and how it can be modulated. An error correction assay has been previously developed in cultured mammalian cells in which incorrect kt-MT attachments are created through the induction of monopolar spindle assembly via chemical inhibition of kinesin-5. Error correction is then monitored following inhibitor wash out. Implementing the error correction assay in Drosophila melanogaster S2 cells would be valuable because kt-MT attachments are easily visualized and the cells are highly amenable to RNAi and high-throughput screening. However, Drosophila kinesin-5 (Klp61F) is unaffected by available small molecule inhibitors. To overcome this limitation, we have rendered S2 cells susceptible to kinesin-5 inhibitors by functionally replacing Klp61F with human kinesin-5 (Eg5). Eg5 expression rescued the assembly of monopolar spindles typically caused by Klp61F depletion. Eg5-mediated bipoles collapsed into monopoles due, in part, to kinesin-14 (Ncd) activity when treated with the kinesin-5 inhibitor S-trityl-L-cysteine (STLC). Furthermore, bipolar spindles reassembled and error correction was observed after STLC wash out. Importantly, error correction in Eg5-expressing S2 cells was dependent on the well-established error correction kinase Aurora B. This system provides a powerful new cell-based platform for studying error correction and CIN.

Posttranslational modifications of the retinoblastoma tumor suppressor protein as determinants of function

The retinoblastoma tumor suppressor protein (pRB) plays an integral role in G1-S checkpoint control and consequently is a frequent target for inactivation in cancer. The RB protein can function as an adaptor, nucleating components such as E2Fs and chromatin regulating enzymes into the same complex. For this reason, pRB's regulation by posttranslational modifications is thought to be critical. pRB is phosphorylated by a number of different kinases such as cyclin dependent kinases (Cdks), p38 MAP kinase, Chk1/2, Abl, and Aurora b. Although phosphorylation of pRB by Cdks has been extensively studied, activities regulated through phosphorylation by other kinases are just starting to be understood. As well as being phosphorylated, pRB is acetylated, methylated, ubiquitylated, and SUMOylated. Acetylation, methylation, and SUMOylation play roles in pRB mediated gene silencing. Ubiquitinylation of pRB promotes its degradation and may be used to regulate apoptosis. Recent proteomic data have revealed that pRB is posttranslationally modified to a much greater extent than previously thought. This new information suggests that many unknown pathways affect pRB regulation. This review focuses on posttranslational modifications of pRB and how they influence its function. The final part of the review summarizes new phosphorylation sites from accumulated proteomic data and discusses the possibilities that might arise from this data.

Cyclins and cell cycle control in cancer and disease

Cyclin D1 overexpression is found in more than 50% of human breast cancers and causes mammary cancer in transgenic mice. Dysregulation of cyclin D1 gene expression or function contributes to the loss of normal cell cycle control during tumorigenesis. Recent studies have demonstrated that cyclin D1 conducts additional specific functions to regulate gene expression in the context of local chromatin, promote cellular migration, and promote chromosomal instability. It is anticipated that these additional functions contribute to the pathology associated with dysregulated cyclin D1 abundance. This article discusses evidence that examines the functional roles that cyclin D1 may play in cancer with an emphasis on other cyclin family members that also may contribute to cancer and disease in a similar fashion.

Plasticity of tumour and immune cells: a source of heterogeneity and a cause for therapy resistance?

Immunotherapies, signal transduction inhibitors and chemotherapies can successfully achieve remissions in advanced stage cancer patients, but durable responses are rare. Using malignant melanoma as a paradigm, we propose that therapy-induced injury to tumour tissue and the resultant inflammation can activate protective and regenerative responses that represent a shared resistance mechanism to different treatments. Inflammation-driven phenotypic plasticity alters the antigenic landscape of tumour cells, rewires oncogenic signalling networks, protects against cell death and reprogrammes immune cell functions. We propose that the successful combination of cancer treatments to tackle resistance requires an interdisciplinary understanding of these resistance mechanisms, supported by mathematical models.

Three-dimensional nuclear telomere architecture changes during endometrial carcinoma development

Endometrioid or type-I endometrial carcinoma (EC) develops from hyperproliferative glandular pathologies. Inactivation of the tumor suppressor gene PTEN is frequently associated with type-I EC. Using a previously characterized Pten heterozygous (Pten+/-) mouse model, this study investigates the three-dimensional (3D) telomere profiles during progression from hyperplastic lesions to EC to test the hypothesis that altered 3D telomere profiles can be detected prior to Pten loss in early hyperproliferative lesions. We used immunohistochemistry and 3D-telomere fluorescent in-situ hybridization to investigate Pten expression, telomere length and signal distribution, average number and spatial distribution of telomeres and formation of telomere aggregates in uterine glandular epithelial cells from wildtype and Pten+/- mice. Pten showed nuclear and cytoplasmic localization in WT, predominantly cytoplasmic staining in simple hyperplasia (SH) and was markedly reduced in atypical hyperplasia (AH). Telomere length in glandular epithelial cells does not shorten with age. The average number of telomeres per nucleus was not different in WT and Pten+/- mice indicating the lack of substantial numeric chromosome aberrations during EC development. We observed telomere aggregates in lesions of AH and EC. SH lesions in Pten+/- mice differed from normal glandular epithelium by an increased relative number of shorter telomeres and by a telomere signal distribution indicative of a heterogeneous cell population. Our study revealed that alterations in the nuclear 3D telomere architecture are present in early proliferative lesions of mouse uterine tissues indicative of EC development. The changes in telomere length distribution and nuclear signal distribution precede the loss of Pten.

Posttranslational modifications regulate HIPK2, a driver of proliferative diseases

The serine/threonine kinase homeodomain-interacting protein kinase (HIPK2) is a tumor suppressor and functions as an evolutionary conserved regulator of signaling and gene expression. This kinase regulates a surprisingly vast array of biological processes that range from the DNA damage response and apoptosis to hypoxia signaling and cell proliferation. Recent studies show the tight control of HIPK2 by hierarchically occurring posttranslational modifications such as phosphorylation, small ubiquitin-like modifier modification, acetylation, and ubiquitination. The physiological function of HIPK2 as a regulator of cell proliferation and survival has a downside: proliferative diseases. Dysregulation of HIPK2 can result in increased proliferation of cell populations as it occurs in cancer or fibrosis. We discuss various models that could explain how inappropriate expression, modification, or localization of HIPK2 can be a driver for these proliferative diseases.

The motor protein KIF14 inhibits tumor growth and cancer metastasis in lung adenocarcinoma

The motor protein kinesin superfamily proteins (KIFs) are involved in cancer progression. The depletion of one of the KIFs, KIF14, might delay the metaphase-to-anaphase transition, resulting in a binucleated status, which enhances tumor progression; however, the exact correlation between KIF14 and cancer progression remains ambiguous. In this study, using loss of heterozygosity and array comparative genomic hybridization analyses, we observed a 30% loss in the regions surrounding KIF14 on chromosome 1q in lung adenocarcinomas. In addition, the protein expression levels of KIF14 in 122 lung adenocarcinomas also indicated that approximately 30% of adenocarcinomas showed KIF14 down-regulation compared with the expression in the bronchial epithelial cells of adjacent normal counterparts. In addition, the reduced expression of KIF14 mRNA or proteins was correlated with poor overall survival (P = 0.0158 and <0.0001, respectively), and the protein levels were also inversely correlated with metastasis (P<0.0001). The overexpression of KIF14 in lung adenocarcinoma cells inhibited anchorage-independent growth in vitro and xenograft tumor growth in vivo. The overexpression and silencing of KIF14 also inhibited or enhanced cancer cell migration, invasion and adhesion to the extracellular matrix proteins laminin and collagen IV. Furthermore, we detected the adhesion molecules cadherin 11 (CDH11) and melanoma cell adhesion molecule (MCAM) as cargo on KIF14. The overexpression and silencing of KIF14 enhanced or reduced the recruitment of CDH11 in the membrane fraction, suggesting that KIF14 might act through recruiting adhesion molecules to the cell membrane and modulating cell adhesive, migratory and invasive properties. Thus, KIF14 might inhibit tumor growth and cancer metastasis in lung adenocarcinomas.

PARI overexpression promotes genomic instability and pancreatic tumorigenesis

Treatment options for patients with pancreatic ductal adenocarcinoma (PDAC) remain limited. Therapeutic targets of interest include mutated molecules that predispose to pancreatic cancer such as KRAS and TP53. Here, we show that an element of the homologous recombination pathway of DNA repair, the PARP-binding protein C12orf48/PARI (PARPBP), is overexpressed specifically in pancreatic cancer cells where it is an appealing candidate for targeted therapy. PARI upregulation in pancreatic cancer cells or avian DT40 cells conferred DNA repair deficiency and genomic instability. Significantly, PARI silencing compromised cancer cell proliferation in vitro, leading to cell-cycle alterations associated with S-phase delay, perturbed DNA replication, and activation of the DNA damage response pathway in the absence of DNA damage stimuli. Conversely, PARI overexpression produced tolerance to DNA damage by promoting replication of damaged DNA. In a mouse xenograft model of pancreatic cancer, PARI silencing was sufficient to reduce pancreatic tumor growth in vivo. Taken together, our findings offered a preclinical proof-of-concept for PARI as candidate therapeutic target to treat PDAC.

Reduced life- and healthspan in mice carrying a mono-allelic BubR1 MVA mutation

Mosaic Variegated Aneuploidy (MVA) syndrome is a rare autosomal recessive disorder characterized by inaccurate chromosome segregation and high rates of near-diploid aneuploidy. Children with MVA syndrome die at an early age, are cancer prone, and have progeroid features like facial dysmorphisms, short stature, and cataracts. The majority of MVA cases are linked to mutations in BUBR1, a mitotic checkpoint gene required for proper chromosome segregation. Affected patients either have bi-allelic BUBR1 mutations, with one allele harboring a missense mutation and the other a nonsense mutation, or mono-allelic BUBR1 mutations combined with allelic variants that yield low amounts of wild-type BubR1 protein. Parents of MVA patients that carry single allele mutations have mild mitotic defects, but whether they are at risk for any of the pathologies associated with MVA syndrome is unknown. To address this, we engineered a mouse model for the nonsense mutation 2211insGTTA (referred to as GTTA) found in MVA patients with bi-allelic BUBR1 mutations. Here we report that both the median and maximum lifespans of the resulting BubR1^+/GTTA mice are significantly reduced. Furthermore, BubR1^+/GTTA mice develop several aging-related phenotypes at an accelerated rate, including cataract formation, lordokyphosis, skeletal muscle wasting, impaired exercise ability, and fat loss. BubR1^+/GTTA mice develop mild aneuploidies and show enhanced growth of carcinogen-induced tumors. Collectively, these data demonstrate that the BUBR1 GTTA mutation compromises longevity and healthspan, raising the interesting possibility that mono-allelic changes in BUBR1 might contribute to differences in aging rates in the general population.

Aging is the main risk factor for the majority of chronic diseases and the leading cause of death and disability in humans. Humans age at different rates, but the molecular genetic basis underlying this phenomenon remains largely unknown. Efforts to understand how we age have focused on genetic changes that extend lifespan or underlie progeroid disorders. One potential progeroid disorder, MVA syndrome, has been associated with mutations in the mitotic regulator BUBR1. Although MVA syndrome is rare due to its recessive nature, individuals carrying heterozygous BUBR1 mutations associated with MVA would be much more prevalent. However, whether such carriers are asymptomatic or at risk of developing aspects of MVA syndrome later in life is unknown. To investigate this, we engineered mice to carry an analogous mutation to the human MVA BUBR1 nonsense mutation 2211insGTTA. We find that these mice have a reduced lifespan and develop several age-related phenotypes at an accelerated rate. These findings suggest that bi-allelic integrity of BUBR1 is a key determinant of healthspan and longevity, and provide a conceptual framework for elucidating differences in aging rates among humans.

High level of chromosomal aberration in ovarian cancer genome correlates with poor clinical outcome

OBJECTIVES

Structural aberration in chromosomes characterizes almost all human solid cancers and analysis of those alterations may reveal the history of chromosomal instability. However, the clinical significance of massive chromosomal abnormality in ovarian high-grade serous carcinoma (HGSC) remains elusive. In this study, we addressed this issue by analyzing the genomic profiles in 455 ovarian HGSCs available from The Cancer Genome Atlas (TCGA).

METHODS

DNA copy number, mRNA expression, and clinical information were downloaded from the TCGA data portal. A chromosomal disruption index (CDI) was developed to summarize the extent of copy number aberrations across the entire genome. A Cox regression model was applied to identify factors associated with poor prognosis. Genes whose expression was associated with CDI were identified by a 2-stage multivariate linear regression and were used to find enriched pathways by Ingenuity Pathway Analysis.

RESULTS

Multivariate survival analysis showed that a higher CDI was significantly associated with a worse overall survival in patients. Interestingly, the pattern of DNA copy number alterations across all the chromosomes was similar between tumors with high and low CDI, suggesting they did not arise from different mechanisms. We also observed that expression of several genes was highly correlated with the CDI, even after adjusting for local copy number variation. We found that molecular pathways involving DNA damage response and mitosis were significantly enriched in these CDI-correlated genes.

CONCLUSION

Our results provide a new insight into the role of chromosomal rearrangement in the development of HGSC and the promise of applying CDI in risk-stratifying HGSC patients, perhaps for different clinical managements. The genes whose expression is correlated with CDI are worthy of further study to elucidate the mechanism of chromosomal instability in HGSC.

Alisertib (MLN8237) an investigational agent suppresses Aurora A and B activity, inhibits proliferation, promotes endo-reduplication and induces apoptosis in T-NHL cell lines supporting its importance in PTCL treatment

Peripheral T-cell lymphomas (PTCL) are a diverse group of rare non-Hodgkin lymphomas (NHL) that carry a poor prognosis and are in need of effective therapies. Alisertib (MLN8237) an investigational agent that inhibits Aurora A Ser/Thr kinase has shown activity in PTCL patients. Here we demonstrate that aurora A and B are highly expressed in T-cell lymphoma cell lines. In PTCL patient samples aurora A was positive in 3 of 24 samples and co-expressed with aurora B. Aurora B was positive in tumor cells in 22 of 32 samples. Of the subtypes of PTCL, aurora B was over-expressed in PTCL (NOS) [73%], T-NHL [100%], ALCL (Alk-Neg) [100%] and AITL [100%]. Treatment with MLN8237 inhibited PTCL cell proliferation in CRL-2396 and TIB-48 cells with an IC50 of 80-100nM. MLN8237 induced endo-reduplication in a dose and time dependent manner in PTCL cell lines leading to apoptosis demonstrated by flow cytometry and PARP-cleavage at concentrations achieved in early phase clinical trials. Moreover, inhibition of HisH3 and aurora A phosphorylation was dose dependent and strongly correlated with endo-reduplication. The data provide a sound rationale for aurora inhibition in PTCL as a therapeutic modality and warrants clinical trial evaluation.

Diagnostic role of chromosomal instability in melanoma

Early diagnosis gives melanoma patients the best chance for long term survival. However discrimination of an early melanoma from an unusual/atypical benign nevus can represent a significant challenge. There are no current pathological markers to definitively define malignant potential in these indeterminate lesions. Thus, there is a need for improved diagnostic tools. Chromosomal instability (CIN) is a hallmark of cancer and is markedly prevalent in melanoma. Advances in genomics have opened the door for the development of molecular tools to better segregate benign and malignant lesions. This paper focuses on CIN in melanoma and the role of current diagnostic approaches.

Aneuploid human colonic epithelial cells are sensitive to AICAR-induced growth inhibition through EGFR degradation

Trisomy for chromosome 7 is frequently observed as an initiating event in sporadic colorectal cancer. Although unstable chromosome numbers and recurrent aneuploidies drive a large fraction of human cancers, targeted therapies selective to pre-neoplastic trisomic cells are non-existent. We have previously characterized a trisomy 7 cell line (1CT+7) spontaneously derived from normal diploid human colonic epithelial cells that aberrantly expresses the epidermal growth factor receptor (EGFR, chromosome 7p11). Recent studies identified AICAR (5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside) as a pharmacological inhibitor of aneuploid murine fibroblast proliferation. Here, we report that AICAR induces profound cytostatic and metabolic effects on 1CT+7 cells, but not on their isogenic diploid counterpart. Dose-response experiments indicate that 1CT+7 cells are fourfold preferentially sensitive to AICAR compared to diploid cells. Unexpectedly, treatment of 1CT+7 cells with AICAR led to a reversible 3.5-fold reduction (P=0.0025) in EGFR overexpression. AICAR-induced depletion of EGFR protein can be abrogated through inhibition of the proteasome with MG132. AICAR also heavily promoted EGFR ubiquitination in cell-based immunoprecipitation assays, suggesting enhanced degradation of EGFR protein mediated by the proteasome. Moreover, treatment with AICAR reduced EGFR protein levels in a panel of human colorectal cancer cells in vitro and in xenograft tumors in vivo. Our data collectively support the pharmacological compound AICAR as a novel inhibitor of EGFR protein abundance and as a potential anticancer agent for aneuploidy-driven colorectal cancer.

First-principles density-functional theory calculations of electron-transfer rates in azurin dimers

The HeLa cell line is one of the most popular cell lines in biomedical research, despite its well-known chromosomal instability. We compared the genomic and transcriptomic profiles of 4 different HeLa batches and showed that the gain and loss of genomic material varies widely between batches, drastically affecting basal gene expression. Moreover, different pathways were activated in response to a hypoxic stimulus. Our study emphasizes the large genomic and transcriptomic variability among different batches, to the point that the same experiment performed with different batches can lead to distinct conclusions and irreproducible results. The HeLa cell line is thought to be a unique cell line but it is clear that substantial differences between the primary tumour and the human genome exist and that an indeterminate number of HeLa cell lines may exist, each with a unique genomic profile.