Chromosomal Instability In Cancer Research Articles

Prolonged mitosis causes separase deregulation and chromosome nondisjunction

During mitotic chromosome segregation, the protease separase severs cohesin between sister chromatids. A probe for separase activity has shown that separase undergoes abrupt activation shortly before anaphase onset, after being suppressed throughout metaphase; however, the relevance of this control remains unclear. Here, we report that separase activates precociously, with respect to anaphase onset, during prolonged metaphase in multiple types of cancer cell lines. The artificial extension of metaphase in chromosomally stable diploid cells leads to precocious activation and, subsequently, to chromosomal bridges in anaphase, which seems to be attributable to incomplete cohesin removal. Conversely, shortening back of a prolonged metaphase restores the activation of separase and ameliorates anaphase bridge formation. These observations suggest that retarded metaphase progression affects the separase activation profile and its enzymatic proficiency. Our findings provide an unanticipated etiology for chromosomal instability in cancers and underscore the relevance of swift mitotic transitions for fail-safe chromosome segregation.

Abstract IA16: Cancer evolution, immune evasion and metastasis

Abstract Increasing evidence supports complex subclonal relationships in solid tumours, manifested as intratumour heterogeneity. Parallel evolution of subclones, with distinct somatic events occurring in the same gene, signal transduction pathway or protein complex, suggests constraints to tumour evolution that might be therapeutically exploitable. Data from TRACERx, a longitudinal lung cancer evolution study will be presented. Drivers of tumour heterogeneity change during the disease course and contribute to the temporally distinct origins of lung cancer driver events. APOBEC driven mutagenesis appears to be enriched in subclones in multiple tumour types. Oncogene, tumour suppressor gene and drug induced DNA replication stress are found to drive APOBEC mutagenesis. Phylogenetic tracking detects minimal residual disease and clonal evolution of disease from primary to metastatic sites, presenting opportunities for drug development. On-going chromosomal instability, manifested as Mirrored Subclonal Allelic Imbalance (MSAI) is found to be a major driver of intratumour heterogeneity across cancer types, contributing to parallel evolution and selection. The finding of subclonal driver events, evidence of ongoing selection within subclones, combined with genome instability driving cell-to-cell variation is likely to limit the efficacy of targeted monotherapies, suggesting the need for new approaches to drug development and clinical trial design and integration of cancer immunotherapeutic approaches. Multiple adaptive mechanisms to neo-antigen evolution have been found in TRACERx that emphasise the role of cancer chromosomal instability driving immune evasion and HLA/MHC loss and loss of clonal neo-antigens as well as epigenetic repression of neo-antigens. The clonal neo-antigenic architecture may act as a tumour vulnerability, targeting multiple clonal neo-antigens present in each tumour to mitigate resistance and treatment failure. Citation Format: Charles Swanton. Cancer evolution, immune evasion and metastasis [abstract]. In: Proceedings of the AACR Virtual Special Conference on Tumor Heterogeneity: From Single Cells to Clinical Impact; 2020 Sep 17-18. Philadelphia (PA): AACR; Cancer Res 2020;80(21 Suppl):Abstract nr IA16.

Origins and Consequences of Chromosomal Instability: From Cellular Adaptation to Genome Chaos-Mediated System Survival.

When discussing chromosomal instability, most of the literature focuses on the characterization of individual molecular mechanisms. These studies search for genomic and environmental causes and consequences of chromosomal instability in cancer, aiming to identify key triggering factors useful to control chromosomal instability and apply this knowledge in the clinic. Since cancer is a phenomenon of new system emergence from normal tissue driven by somatic evolution, such studies should be done in the context of new genome system emergence during evolution. In this perspective, both the origin and key outcome of chromosomal instability are examined using the genome theory of cancer evolution. Specifically, chromosomal instability was linked to a spectrum of genomic and non-genomic variants, from epigenetic alterations to drastic genome chaos. These highly diverse factors were then unified by the evolutionary mechanism of cancer. Following identification of the hidden link between cellular adaptation (positive and essential) and its trade-off (unavoidable and negative) of chromosomal instability, why chromosomal instability is the main player in the macro-cellular evolution of cancer is briefly discussed. Finally, new research directions are suggested, including searching for a common mechanism of evolutionary phase transition, establishing chromosomal instability as an evolutionary biomarker, validating the new two-phase evolutionary model of cancer, and applying such a model to improve clinical outcomes and to understand the genome-defined mechanism of organismal evolution.

Pervasive chromosomal instability and karyotype order in tumour evolution.

Chromosomal instability in cancer consists of dynamic changes to the number and structure of chromosomes1,2. The resulting diversity in somatic copy number alterations (SCNAs) may provide the variation necessary for tumour evolution1,3,4. Here we use multi-sample phasing and SCNA analysis of 1,421 samples from 394 tumours across 22tumour types to show that continuous chromosomal instability results in pervasive SCNA heterogeneity. Parallel evolutionary events, which cause disruption in the same genes (such as BCL9,MCL1, ARNT (also known as HIF1B), TERT and MYC) within separate subclones, were present in 37% of tumours. Most recurrent lossesprobably occurred before whole-genome doubling, that was foundas a clonal event in 49% of tumours. However, loss of heterozygosity at the human leukocyte antigen (HLA) locus and loss of chromosome 8p to a single haploid copy recurred at substantial subclonal frequencies, even in tumours with whole-genome doubling, indicating ongoing karyotype remodelling. Focal amplifications that affected chromosomes 1q21 (which encompasses BCL9,MCL1 and ARNT), 5p15.33 (TERT), 11q13.3 (CCND1), 19q12 (CCNE1) and 8q24.1 (MYC) were frequently subclonal yet appeared to be clonal within single samples. Analysis of an independent series of 1,024 metastatic samples revealed that 13 focal SCNAs were enriched in metastatic samples, including gains in chromosome 8q24.1 (encompassing MYC) in clear cell renal cellcarcinoma and chromosome 11q13.3 (encompassing CCND1) in HER2+ breast cancer. Chromosomal instability may enable the continuous selection of SCNAs, which are established as ordered events that often occur in parallel, throughout tumour evolution.

The role of Anaphase Promoting Complex activation, inhibition and substrates in cancer development and progression.

The Anaphase Promoting Complex (APC), a multi-subunit ubiquitin ligase, facilitates mitotic and G1 progression, and is now recognized to play a role in maintaining genomic stability. Many APC substrates have been observed overexpressed in multiple cancer types, such as CDC20, the Aurora A and B kinases, and Forkhead box M1 (FOXM1), suggesting APC activity is important for cell health. We performed BioGRID analyses of the APC coactivators CDC20 and CDH1, which revealed that at least 69 proteins serve as APC substrates, with 60 of them identified as playing a role in tumor promotion and 9 involved in tumor suppression. While these substrates and their association with malignancies have been studied in isolation, the possibility exists that generalized APC dysfunction could result in the inappropriate stabilization of multiple APC targets, thereby changing tumor behavior and treatment responsiveness. It is also possible that the APC itself plays a crucial role in tumorigenesis through its regulation of mitotic progression. In this review the connections between APC activity and dysregulation will be discussed with regards to cell cycle dysfunction and chromosome instability in cancer, along with the individual roles that the accumulation of various APC substrates may play in cancer progression.

3D genome organization contributes to genome instability at fragile sites

Common fragile sites (CFSs) are regions susceptible to replication stress and are hotspots for chromosomal instability in cancer. Several features were suggested to underlie CFS instability, however, these features are prevalent across the genome. Therefore, the molecular mechanisms underlying CFS instability remain unclear. Here, we explore the transcriptional profile and DNA replication timing (RT) under mild replication stress in the context of the 3D genome organization. The results reveal a fragility signature, comprised of a TAD boundary overlapping a highly transcribed large gene with APH-induced RT-delay. This signature enables precise mapping of core fragility regions in known CFSs and identification of novel fragile sites. CFS stability may be compromised by incomplete DNA replication and repair in TAD boundaries core fragility regions leading to genomic instability. The identified fragility signature will allow for a more comprehensive mapping of CFSs and pave the way for investigating mechanisms promoting genomic instability in cancer.

ER-Directed TREX1 Limits cGAS Recognition of Micronuclei

Chromosomal instability in cancer results in the formation of nuclear aberrations termed micronuclei. Spontaneous loss of micronuclear envelope integrity exposes DNA to the cytoplasm, leading to chromosome fragmentation and innate immune activation. Despite connections to cancer genome evolution and anti-tumor immunity, the mechanisms underlying damage and immune sensing of micronuclear DNA are poorly understood. Here, we use a novel method for the purification of micronuclei and live-cell imaging to show that the ER-associated nuclease TREX1 inhibits cGAS sensing of micronuclei by stably associating with and degrading micronuclear DNA upon micronuclear envelope rupture. We identify a TREX1 mutation, previously associated with autoimmune disease, that untethers TREX1 from the ER, disrupts TREX1 localization to micronuclei, alleviates micronuclear DNA damage, and enhances cGAS recognition of micronuclei. Together, these results establish ER-directed resection of micronuclear DNA by TREX1 as a critical regulator of cytosolic DNA sensing in chromosomally unstable cells and provide a mechanistic basis for the importance of TREX1 ER-tethering in preventing autoimmunity.

Histone stress: an unexplored source of chromosomal instability in cancer?

Ploidy is stably maintained in most human somatic cells by a sequential and tight coordination of cell cycle events. Undesired whole genome doublings or duplications are frequent in tumours and have been quite recently described as macro-evolutionary events associated with poor prognosis. In vitro and in vivo studies suggest that polyploidy can favour genome instability, facilitate the formation and progression of tumours, and modify their sensitivity to chemotherapeutic agents. Stress is strongly related to changes in ploidy and whole genome doublings. In this review, we summarize different mechanisms that promote polyploidization, describe a new type of stress able to trigger WGDs in S. cerevisiae, histone stress, and provide some examples and theoretical scenarios that support that cancer cells might suffer from this type of stress. We finally highlight some results showing that the kinase Swe1 (Wee1 in humans) has a role in sensing histone levels before cells enter mitosis, thereby avoiding their undesired consequences on chromosome segregation and ploidy control.

Chromosomal Instability Promotes cGAS‐Mediated Cytosolic DNA Response in Metastatic Cancer

Recent implication of chromosomal instability (CIN) in metastatic cancer cells has pointed to the frequency of chromosome missegregation as a key difference between primary and metastatic tumors. Understanding the cellular response therefore aids development of treatments to prevent metastasis. Chromosome missegregation creates micronuclei of double stranded DNA (dsDNA) fragments that are prone to rupture in the cytoplasm. The cGAS‐STING pathway responds to cytosolic dsDNA by activating inflammatory response pathways, a reaction useful to protect against viruses. Dimerization of cGAS, induced by dsDNA binding, catalyzes synthesis of cyclic GAMP (cGAMP) from ATP and GTP. Activation of cGAS results in upregulation of IFN‐β and NF‐κB stimulated immune response pathways. Cytosolic dsDNA associated with CIN has been proposed to induce cGAS‐STING mediated immune mimicry in cancer cells, allowing tumors to flourish in otherwise lethal environments. The Pingry School SMART Team, in conjunction with MSOE Center for BioMolecular Modeling, is using 3‐D modeling and printing technology to further examine the binding of cytosolic dsDNA to cGAS and the resultant production of the signaling molecule, cGAMP, by the enzyme. Stimulation of a cGAS‐STING inflammatory response due to CIN in cancer may contribute to the metastatic transition of primary tumor cells. The Pingry School SMART Team aims to utilize the cGAS structural model to better understand the role of this protein in responding to CIN and its link to metastasis through cytosolic dsDNA induced immune response.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

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.

Abstract P3-09-01: MYC dysregulates mitotic spindle function in triple-negative breast cancer creating a dependency on TPX2

Abstract Tumors that overexpress the MYC oncogene, including most receptor triple-negative breast cancers, frequently demonstrate aneuploidy, numerical chromosome alterations associated with highly aggressive cancers. Aneuploidy is also associated with rapid tumor evolution and poor patient outcome. We identify that MYC overexpression induces reversible defects in microtubule nucleation and mitotic spindle assembly, in TNBCs and other epithelial cells, promoting chromosome segregation defects, micronuclei and chromosomal instability (CIN). High TPX2 expression is permissive for mitotic spindle assembly and chromosome segregation in cells with MYC overexpression; whereas TPX2 depletion blocks mitotic progression, induces cell death and prevents tumor growth. Attenuating MYC expression reverses mitotic defects, even in established breast tumor cell lines, implicating an ongoing role for high MYC in the persistence of CIN in cancers. Our studies implicate the MYC oncogene as a regulator of spindle assembly and identify a new MYC-TPX2 synthetic-lethal interaction in TNBC that could represent a future therapeutic strategy in MYC-overexpressing cancers. Moreover, our studies suggest that blocking MYC activity can attenuate the emergence of CIN and tumor evolution. Citation Format: Goga A, Rohrberg J, Corella A, Taileb M, Kilinc S, Jokisch M-L, Camarda R, Zhou A, Balakrishnan S, Chang AN, Klein-Connolly H. MYC dysregulates mitotic spindle function in triple-negative breast cancer creating a dependency on TPX2 [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-09-01.

Chromosome 17 centromere amplification and chromosomal instability (CIN) in breast cancer: Pathogenic and therapeutic implications.

Chromosomal instability (CIN) is present in variable degrees in a significant percentage (up to 90%) of cancers and often portends adverse outcomes. However, it has not been incorporated in clinical practice as a prognostic marker due to the lack of standardization and proof of clinical utility of assays to measure it, as well as uncertainties regarding optimal cut-offs. Amplification of the centromeric region of chromosome 17 as measured by In Situ Hybridization (ISH) of the CEP17 probe is used clinically as part of the ISH assay for HER2 status determination in breast cancer in cases with intermediate (2+) result of HER2 protein expression by immunohistochemistry. CEP17 amplification concerns the centromeric area and rarely extends beyond it to involve polysomy of the whole chromosome. The association of CEP17 amplification with generalized CIN remains uncertain. Such association, if confirmed, could be an opportunity for a practical and clinically validated test of CIN in breast cancer. This paper explores the association of CIN with centromere 17 amplification and with centromere function in general, as well as the pathophysiology of centromeres/kinetochore function during mitosis that underlies their relationship with CIN in cancer and in breast cancer in particular.

Tolerance of Chromosomal Instability in Cancer: Mechanisms and Therapeutic Opportunities.

Chromosomal instability (CIN) is the result of ongoing changes in the number (aneuploidy) and structure of chromosomes. CIN is induced by chromosome missegregation in mitosis and leads to karyotypic diversity within the cancer cell population, thereby adding to intratumor heterogeneity. Regardless of the overall pro-oncogenic function of CIN, its onset is typically detrimental for cell fitness and thus tumors must develop CIN-tolerance mechanisms in order to propagate. There is overwhelming genetic and functional evidence linking mutations in the tumor suppressor TP53 with CIN-tolerance. However, the pathways leading to p53 activation following chromosome missegregation remain controversial. Recently, additional mechanisms have been identified in CIN-surveillance, resulting in a more complex network of pathways acting independently or in cooperation with p53. Tolerance might also be achieved by modifying aspects of the cancer cell physiology in order to attenuate CIN or by adaptation to the consequences of aneuploid karyotypes. In this review, we summarize the current knowledge about p53-dependent and -independent mechanisms of CIN-tolerance in cancer, the adaptations observed in CIN cells buffering CIN levels, its consequences for cellular homeostasis, and the potential of exploiting these adaptations in order to design new cancer therapies.

Abstract 1461: Targeting mitotic kinases in breast cancers in Latinas

Abstract African Americans and Latino women (Latinas) in the US have higher risks of developing molecular subtypes of breast cancer that associate with poor-prognosis, including hormone receptor-negative (HR-): triple-negative (ER-PR-Her2-), and Her2-positive breast cancer relative to whites. These women also present with higher-stage breast tumors relative to whites. We specifically study Puerto Rican women, a population in which breast cancers are the primary cause of cancer-related death, and who display a higher frequency of HR- breast tumors than other Latinas. We propose that chromosome instability (CIN) is a principal contributor to poor prognosis of breast cancers in African Americans and Latinas, since HR- breast cancers accumulate the highest CIN of all breast cancer subtypes. CIN in cancers correlates with poor clinical outcomes and centrosome amplification (CA) -defined as the presence of 3 or more centrosomes within a cell-, and defective mitosis are two principal drivers of CIN. Albeit CA correlates with invasion, metastasis, poor clinical outcomes, and HR- subtypes, molecular mechanisms responsible for CA in breast cancers are still unknown. We have identified MPS1 and NEK2 as centrosomes/mitotic kinases that drive CA/CIN in HR- breast cancer cells, and that can potentially be targeted to curb the malignant behavior of the most aggressive breast cancer subtypes affecting ethnic minorities. MPS1 and NEK2 are upregulated in HR- breast tumors and are co-overexpressed in several predictive signatures of poor prognosis subtypes and metastasis. Our preliminary data indicated that these kinases are overexpressed in over 60% breast cancers from Puerto Rican women and that they are exclusively co-upregulated in basal breast cancers. Our preliminary data also showed that these two mitotic kinases can significantly influence epithelial-to-mesenchymal transition (EMT) and invasion -activities never described for mitotic kinases. Also, although inactivating NEK2 suppresses S phase, inhibition of MPS1 reduces survival of breast cancer cells. Because inhibitors are available for MPS1 and NEK2, it would be feasible to target these kinases to combat metastatic HR- breast cancers. Our work will allow the identification of pathways influenced by mitotic regulators in breast cancer cells driving invasion and metastasis and will provide potential prognostic markers for high-risk breast tumors in various ethnic/racial groups, including African American and Latinas (including Puerto Rican women). Citation Format: Yainyrette Rivera-Rivera, Mihaela Marina, Jamie King, Miyoung Lee, Harold I. Saavedra. Targeting mitotic kinases in breast cancers in Latinas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1461.

Determinants and clinical implications of chromosomal instability in cancer.

Aberrant chromosomal architecture, ranging from small insertions or deletions to large chromosomal alterations, is one of the most common characteristics of cancer genomes. Chromosomal instability (CIN) underpins much of the intratumoural heterogeneity observed in cancers and drives phenotypic adaptation during tumour evolution. Thus, an urgent need exists to increase our efforts to target CIN as if it were a molecular entity. Indeed, CIN accelerates the development of anticancer drug resistance, often leading to treatment failure and disease recurrence, which limit the effectiveness of most current therapies. Identifying novel strategies to modulate CIN and to exploit the fitness cost associated with aneuploidy in cancer is, therefore, of paramount importance for the successful treatment of cancer. Modern sequencing and analytical methods greatly facilitate the identification and cataloguing of somatic copy-number alterations and offer new possibilities to better exploit the dynamic process of CIN. In this Review, we describe the principles governing CIN propagation in cancer and how CIN might influence sensitivity to immune-checkpoint inhibition, and survey the vulnerabilities associated with CIN that offer potential therapeutic opportunities.

Centrosome aberrations and chromosome instability contribute to tumorigenesis and intra-tumor heterogeneity.

Centrosomes serve as the major microtubule organizing centers in cells and thereby contribute to cell shape, polarity, and motility. Also, centrosomes ensure equal chromosome segregation during mitosis. Centrosome aberrations arise when the centrosome cycle is deregulated, or as a result of cytokinesis failure. A long-standing postulate is that centrosome aberrations are involved in the initiation and progression of cancer. However, this notion has been a subject of controversy because until recently the relationship has been correlative. Recently, it was shown that numerical or structural centrosome aberrations can initiate tumors in certain tissues in mice, as well as invasion. Particularly, we will focus on centrosome amplification and chromosome instability as drivers of intra-tumor heterogeneity and their consequences in cancer. We will also discuss briefly the controversies surrounding this theory to highlight the fact that the role of both centrosome amplification and chromosome instability in cancer is highly context-dependent. Further, we will discuss single-cell sequencing as a novel technique to understand intra-tumor heterogeneity and some therapeutic approaches to target chromosome instability.

The Role of Chromosomal Instability in Cancer and Therapeutic Responses.

Cancer is one of the leading causes of death, and despite increased research in recent years, control of advanced-stage disease and optimal therapeutic responses remain elusive. Recent technological improvements have increased our understanding of human cancer as a heterogeneous disease. For instance, four hallmarks of cancer have recently been included, which in addition to being involved in cancer development, could be involved in therapeutic responses and resistance. One of these hallmarks is chromosome instability (CIN), a source of genetic variation in either altered chromosome number or structure. CIN has become a hot topic in recent years, not only for its implications in cancer diagnostics and prognostics, but also for its role in therapeutic responses. Chromosomal alterations are mainly used to determine genetic heterogeneity in tumors, but CIN could also reveal treatment efficacy, as many therapies are based on increasing CIN, which causes aberrant cells to undergo apoptosis. However, it should be noted that contradictory findings on the implications of CIN for the therapeutic response have been reported, with some studies associating high CIN with a better therapeutic response and others associating it with therapeutic resistance. Considering these observations, it is necessary to increase our understanding of the role CIN plays not only in tumor development, but also in therapeutic responses. This review focuses on recent studies that suggest possible mechanisms and consequences of CIN in different disease types, with a primary focus on cancer outcomes and therapeutic responses.

Role of chromosomal instability in cancer progression.

Cancer cells often display chromosomal instability (CIN), a defect that involves loss or rearrangement of the cell's genetic material - chromosomes - during cell division. This process results in the generation of aneuploidy, a deviation from the haploid number of chromosomes, and structural alterations of chromosomes in over 90% of solid tumours and many haematological cancers. This trait is unique to cancer cells as normal cells in the body generally strictly maintain the correct number and structure of chromosomes. This key difference between cancer and normal cells has led to two important hypotheses: (i) cancer cells have had to overcome inherent barriers to changes in chromosomes that are not tolerated in non-cancer cells and (ii) CIN represents a cancer-specific target to allow the specific elimination of cancer cells from the body. To exploit these hypotheses and design novel approaches to treat cancer, a full understanding of the mechanisms driving CIN and how CIN contributes to cancer progression is required. Here, we will discuss the possible mechanisms driving chromosomal instability, how CIN may contribute to the progression at multiple stages of tumour evolution and possible future therapeutic directions based on targeting cancer chromosomal instability.

Abstract 5713: PIGN gene expression aberration weakens chromosomal stability via altering its interaction with the spindle assembly checkpoint protein complex during leukemogenesis

Abstract Previous studies have linked increased frequency of glycosylphosphatidylinositol-anchor protein (GPI-AP) deficiency with genomic instability and the risk of carcinogenesis. Recently, Phosphatidylinositol Glycan Anchor Biosynthesis; Class N (PIGN), a gene participating in GPI-AP synthesis, was suggested as a cancer chromosomal instability suppressor in a colon cancer model. We investigated the association of PIGN with genomic instability and leukemogenesis. A Random Forest analysis of the gene expression array data from 55 MDS patients (GSE4619) demonstrated a significant (p = 0.0007) correlation (Pearson r =-0.4068) between GPI-anchor biosynthesis gene expression and genomic instability, in which PIGN was ranked as the third most important in predicting risk of MDS progression. We observed that PIGN gene expression aberrations (increased transcriptional activity but diminished to no protein production) were associated with increased frequency of GPI-AP deficiency in leukemic cells during leukemic transformation/progression. The PIGN gene expression aberrations were attributed to partial intron retentions between exons 14 and 15 resulting in frameshifts and premature termination which were confirmed by examining the RNA-seq data from a group of AML patients (phs001027.v1.p1). PIGN gene expression aberration correlated with the elevation of genomic instability marker expression that was independent of the TP53 regulatory pathway. PIGN protein expression suppression/elimination caused a similar pattern of genomic instability that was rescued by PIGN restoration. Furthermore, PIGN bound to the spindle assembly checkpoint proteins and regulated their expression during the cell cycle. In conclusion, PIGN gene is crucial in the regulation of mitotic integrity to maintain chromosomal stability and prevents leukemic transformation/progression. Citation Format: Jeffrey J. Pu, Emmanuel K. Teye, Abigail Sido, Yuka I. Kawasawa, Ping Xin, Niklas K. Finnberg, Wafik S. El-Deiry, Sara Shimko. PIGN gene expression aberration weakens chromosomal stability via altering its interaction with the spindle assembly checkpoint protein complex during leukemogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5713. doi:10.1158/1538-7445.AM2017-5713

Mislocalization of centromeric histone H3 variant CENP-A contributes to chromosomal instability (CIN) in human cells.

Chromosomal instability (CIN) is a hallmark of many cancers and a major contributor to tumorigenesis. Centromere and kinetochore associated proteins such as the evolutionarily conserved centromeric histone H3 variant CENP-A, associate with centromeric DNA for centromere function and chromosomal stability. Stringent regulation of cellular CENP-A levels prevents its mislocalization in yeast and flies to maintain genome stability. CENP-A overexpression and mislocalization are observed in several cancers and reported to be associated with increased invasiveness and poor prognosis. We examined whether there is a direct relationship between mislocalization of overexpressed CENP-A and CIN using HeLa and chromosomally stable diploid RPE1 cell lines as model systems. Our results show that mislocalization of overexpressed CENP-A to chromosome arms leads to chromosome congression defects, lagging chromosomes, micronuclei formation and a delay in mitotic exit. CENP-A overexpressing cells showed altered localization of centromere and kinetochore associated proteins such as CENP-C, CENP-T and Nuf2 leading to weakened native kinetochores as shown by reduced interkinetochore distance and CIN. Importantly, our results show that mislocalization of CENP-A to chromosome arms is one of the major contributors for CIN as depletion of histone chaperone DAXX prevents CENP-A mislocalization and rescues the reduced interkinetochore distance and CIN phenotype in CENP-A overexpressing cells. In summary, our results establish that CENP-A overexpression and mislocalization result in a CIN phenotype in human cells. This study provides insights into how overexpression of CENP-A may contribute to CIN in cancers and underscore the importance of understanding the pathways that prevent CENP-A mislocalization for genome stability.