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John P Murnane - One of the best experts on this subject based on the ideXlab platform.
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mechanisms of telomere loss and their consequences for Chromosome Instability
Frontiers in Oncology, 2012Co-Authors: Keiko Muraki, Kristine Nyhan, Limei Han, John P MurnaneAbstract:The ends of Chromosomes in mammals, called telomeres, are composed of a 6 base pair repeat sequence, TTAGGG, which is added on by the enzyme telomerase. In combination with a protein complex called shelterin, these telomeric repeat sequences form a cap that protects the ends of Chromosomes. Due to insufficient telomerase expression, telomeres shorten gradually with each cell division in human somatic cells, which limits the number of times they can divide. The extensive cell division involved in cancer cell progression therefore requires that cancer cells must acquire the ability to maintain telomeres, either through expression of telomerase, or through an alternative mechanism involving recombination. It is commonly thought that the source of many Chromosome rearrangements in cancer cells is a result of the extensive telomere shortening that occurs prior to the expression of telomerase. However, despite the expression of telomerase, tumor cells can continue to show Chromosome Instability due to telomere loss. Dysfunctional telomeres in cancer cells can result from oncogene-induced replication stress, which results in double-strand breaks (DSBs) at fragile sites, including telomeres. DSBs near telomeres are especially prone to Chromosome rearrangements, because telomeric regions are deficient in DSB repair. The deficiency in DSB repair near telomeres is also an important mechanism for ionizing radiation-induced replicative senescence in normal human cells. In addition, DSBs near telomeres can result in Chromosome Instability in mouse embryonic stem cells, suggesting that telomere loss can contribute to heritable Chromosome rearrangements. Consistent with this possibility, telomeric regions in humans are highly heterogeneous, and Chromosome rearrangements near telomeres are commonly involved in human genetic disease. Understanding the mechanisms of telomere loss will therefore provide important insights into both human cancer and genetic disease.
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telomere dysfunction and Chromosome Instability
Mutation Research, 2012Co-Authors: John P MurnaneAbstract:The ends of Chromosomes are composed of a short repeat sequence and associated proteins that together form a cap, called a telomere, that keeps the ends from appearing as double-strand breaks (DSBs) and prevents Chromosome fusion. The loss of telomeric repeat sequences or deficiencies in telomeric proteins can result in Chromosome fusion and lead to Chromosome Instability. The similarity between Chromosome rearrangements resulting from telomere loss and those found in cancer cells implicates telomere loss as an important mechanism for the Chromosome Instability contributing to human cancer. Telomere loss in cancer cells can occur through gradual shortening due to insufficient telomerase, the protein that maintains telomeres. However, cancer cells often have a high rate of spontaneous telomere loss despite the expression of telomerase, which has been proposed to result from a combination of oncogene-mediated replication stress and a deficiency in DSB repair in telomeric regions. Chromosome fusion in mammalian cells primarily involves nonhomologous end joining (NHEJ), which is the major form of DSB repair. Chromosome fusion initiates Chromosome Instability involving breakage-fusion-bridge (B/F/B) cycles, in which dicentric Chromosomes form bridges and break as the cell attempts to divide, repeating the process in subsequent cell cycles. Fusion between sister chromatids results in large inverted repeats on the end of the Chromosome, which amplify further following additional B/F/B cycles. B/F/B cycles continue until the Chromosome acquires a new telomere, most often by translocation of the end of another Chromosome. The Instability is not confined to a Chromosome that loses its telomere, because the Instability is transferred to the Chromosome donating a translocation. Moreover, the amplified regions are unstable and form extrachromosomal DNA that can reintegrate at new locations. Knowledge concerning the factors promoting telomere loss and its consequences is therefore important for understanding Chromosome Instability in human cancer.
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telomere loss as a mechanism for Chromosome Instability in human cancer
Cancer Research, 2010Co-Authors: John P MurnaneAbstract:Cancer cells commonly have a high rate of telomere loss, even when expressing telomerase, contributing to Chromosome Instability and tumor cell progression. This review addresses the hypothesis that this high rate of telomere loss results from a combination of four factors. The first factor is an increase in the frequency of double-strand breaks (DSB) at fragile sites in cancer cells due to replication stress. The second factor is that telomeres are fragile sites. The third factor is that subtelomeric regions are highly sensitive to DSBs, so that DSBs near telomeres have an increased probability of resulting in Chromosome Instability. The fourth factor is that cancer cells may be deficient in Chromosome healing, the de novo addition of telomeres to the sites of DSBs, a mechanism that prevents Chromosome Instability resulting from DSBs near telomeres. Understanding these factors and how they influence telomere loss will provide important insights into the mechanisms of Chromosome Instability and the development of novel approaches for anti-cancer therapy. Cancer Res; 70(11); 4255–9. ©2010 AACR.
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Telomeres and Chromosome Instability.
DNA repair, 2006Co-Authors: John P MurnaneAbstract:Genomic Instability has been proposed to play an important role in cancer by accelerating the accumulation of genetic changes responsible for cancer cell evolution. One mechanism for Chromosome Instability is through the loss of telomeres, which are DNA-protein complexes that protect the ends of Chromosomes and prevent Chromosome fusion. Telomere loss can occur as a result of exogenous DNA damage, or spontaneously in cancer cells that commonly have a high rate of telomere loss. Mouse embryonic stem cells and human tumor cell lines that contain a selectable marker gene located immediately adjacent to a telomere have been used to investigate the consequences of telomere loss. In both cell types, telomere loss is followed by either the addition of a new telomere on to the end of the broken Chromosome, or sister chromatid fusion and prolonged breakage/fusion/bridge (B/F/B) cycles that result in DNA amplification and large terminal deletions. The regions amplified by B/F/B cycles can then be transferred to other Chromosomes, either through the formation of double-minute Chromosomes that reintegrate at other sites, or through end-to-end fusions between Chromosomes. B/F/B cycles eventually end when a Chromosome acquires a new telomere by one of several mechanisms, the most common of which is translocation, which can involve either nonreciprocal transfer or duplication of all or part of an arm of another Chromosome. Telomere acquisition involving nonreciprocal translocations results in the loss of a telomere on the donor Chromosome, which subsequently becomes unstable. In contrast, translocations involving duplications do not destabilize the donor Chromosome, although they result in allelic imbalances. Thus, the loss of a single telomere can generate a wide variety of Chromosome alterations commonly associated with human cancer, not only on the Chromosome that originally lost its telomere, but other Chromosomes as well. Factors promoting spontaneous telomere loss and the resulting B/F/B cycles are therefore likely to be important in generating the karyotypic changes associated with human cancer.
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telomeres Chromosome Instability and cancer
Nucleic Acids Research, 2006Co-Authors: Susan M Bailey, John P MurnaneAbstract:Telomeres are composed of repetitive G-rich sequence and an abundance of associated proteins that together form a dynamic cap that protects Chromosome ends and allows them to be distinguished from deleterious DSBs. Telomere-associated proteins also function to regulate telomerase, the ribonucleoprtotein responsible for addition of the species-specific terminal repeat sequence. Loss of telomere function is an important mechanism for the Chromosome Instability commonly found in cancer. Dysfunctional telomeres can result either from alterations in the telomere-associated proteins required for end-capping function, or from alterations that promote the gradual or sudden loss of sufficient repeat sequence necessary to maintain proper telomere structure. Regardless of the mechanism, loss of telomere function can result in sister chromatid fusion and prolonged breakage/fusion/bridge (B/F/B) cycles, leading to extensive DNA amplification and large terminal deletions. B/F/B cycles terminate primarily when the unstable Chromosome acquires a new telomere, most often by translocation of the ends of other Chromosomes, thereby providing a mechanism for transfer of Instability from one Chromosome to another. Thus, the loss of a single telomere can result in on-going Instability, affect multiple Chromosomes, and generate many of the types of rearrangements commonly associated with human cancer.
Kirk J. Mcmanus - One of the best experts on this subject based on the ideXlab platform.
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Reduced SKP1 Expression Induces Chromosome Instability through Aberrant Cyclin E1 Protein Turnover.
Cancers, 2020Co-Authors: Laura L. Thompson, Allison K. Baergen, Zelda Lichtensztejn, Kirk J. McmanusAbstract:Chromosome Instability (CIN), or progressive changes in Chromosome numbers, is an enabling feature of many cancers; however, the mechanisms giving rise to CIN remain poorly understood. To expand our mechanistic understanding of the molecular determinants of CIN in humans, we employed a cross-species approach to identify 164 human candidates to screen. Using quantitative imaging microscopy (QuantIM), we show that silencing 148 genes resulted in significant changes in CIN-associated phenotypes in two distinct cellular contexts. Ten genes were prioritized for validation based on cancer patient datasets revealing frequent gene copy number losses and associations with worse patient outcomes. QuantIM determined silencing of each gene-induced CIN, identifying novel roles for each as Chromosome stability genes. SKP1 was selected for in-depth analyses as it forms part of SCF (SKP1, CUL1, FBox) complex, an E3 ubiquitin ligase that targets proteins for proteolytic degradation. Remarkably, SKP1 silencing induced increases in replication stress, DNA double strand breaks and chromothriptic events that were ascribed to aberrant increases in Cyclin E1 levels arising from reduced SKP1 expression. Collectively, these data reveal a high degree of evolutionary conservation between human and budding yeast CIN genes and further identify aberrant mechanisms associated with increases in chromothriptic events.
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Detecting Chromosome Instability in Cancer: Approaches to Resolve Cell-to-Cell Heterogeneity.
Cancers, 2019Co-Authors: Chloe C. Lepage, Claire R. Morden, Michaela C. L. Palmer, Mark W Nachtigal, Kirk J. McmanusAbstract: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.
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abstract 3587 multiplexed nuclear area and micronucleus screening identifies skp1 as a human Chromosome Instability gene
Cancer Research, 2016Co-Authors: Laura H Thompson, Zelda Lichtensztejn, Allison K. Baergen, Kirk J. McmanusAbstract:Chromosome Instability (CIN) is defined as an increase in the rate at which whole Chromosomes or large chromosomal fragments are gained or lost. It is hallmark of cancer that occurs frequently in both solid and liquid tumors. In addition, CIN is associated with highly aggressive tumors, the acquisition of multi-drug resistance, tumor recurrence and poor patient prognosis. Despite this, the majority of human CIN genes have yet to be elucidated, highlighting the need for studies aimed at identifying the defective genes that underlie CIN. In this study we utilized two complementary, image-based approaches capable of detecting CIN-associated phenotypes following RNAi-based silencing of candidate CIN genes. The first assay involves quantifying nuclear areas following silencing, where changes in mean nuclear area relative to controls act as a surrogate marker of CIN. The second approach monitors micronucleus (MN) formation where increases in the number of micronuclei are indicative of DNA damage or the mitotic defects that underlie CIN. These assays were employed in a high-content screen of 164 human candidate CIN genes in two unrelated cell lines, HT1080 and hTERT. In HT1080, the nuclear area and MN enumeration assays identified 88 and 96 putative CIN genes, respectively. In hTERT, the nuclear area and MN assays identified 112 and 19 putative CIN genes, respectively. Promising putative CIN genes such as SKP1 were identified and prioritized for subsequent validation based on the number of assays that identified the gene, and the strength of the CIN phenotype. Preliminary data collected through Western blotting, mitotic Chromosome spreads and flow cytometry, provides evidence to support the validation of SKP1 as a bona fide human CIN gene. Identification and characterization of human CIN genes will provide critical insights into CIN and tumorigenesis, as well as identify potential targets that could be exploited in novel, precision medicine approaches for superior cancer treatment. Citation Format: Laura Thompson, Allison Baergen, Zelda Lichtensztejn, Kirk McManus. Multiplexed nuclear area and micronucleus screening identifies SKP1 as a human Chromosome Instability gene. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3587.
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chromatid cohesion defects may underlie Chromosome Instability in human colorectal cancers
Proceedings of the National Academy of Sciences of the United States of America, 2008Co-Authors: Kirk J. Mcmanus, Karen Wing Yee Yuen, Marcelo Reis, Giovanni Parmigiani, Dong Shen, I J Barrett, Yasaman NouhiAbstract:Although the majority of colorectal cancers exhibit Chromosome Instability (CIN), only a few genes that might cause this phenotype have been identified and no general mechanism underlying their function has emerged. To systematically identify somatic mutations in potential CIN genes in colorectal cancers, we determined the sequence of 102 human homologues of 96 yeast CIN genes known to function in various aspects of Chromosome transmission fidelity. We identified 11 somatic mutations distributed among five genes in a panel that included 132 colorectal cancers. Remarkably, all but one of these 11 mutations were in the homologs of yeast genes that regulate sister chromatid cohesion. We then demonstrated that down-regulation of such homologs resulted in chromosomal Instability and chromatid cohesion defects in human cells. Finally, we showed that down-regulation or genetic disruption of the two major candidate CIN genes identified in previous studies (MRE11A and CDC4) also resulted in abnormal sister chromatid cohesion in human cells. These results suggest that defective sister chromatid cohesion as a result of somatic mutations may represent a major cause of Chromosome Instability in human cancers.
D Garciacruz - One of the best experts on this subject based on the ideXlab platform.
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Chromosome Instability induced in vitro with mitomycin c in five seckel syndrome patients
American Journal of Medical Genetics Part A, 2003Co-Authors: Lucina Bobabillamorales, Alfredo Coronarivera, Roman J Coronarivera, Christopher Buenrostro, Teresa A Garciacobian, Enrique Coronarivera, Jose Maria Cantugarza, D GarciacruzAbstract:Seckel syndrome (SS) is an autosomal recessive entity characterized by proportionate pre- and post-natal growth retardation, microcephaly, typical facial appearance with beak-like protrusion, and severe mental retardation. A heterogeneous basis for SS was proposed since around 25% of SS patients have hematological anomalies, suggesting a subgroup of SS with Chromosome Instability and hematological disorders. Chromosome Instability induced by mitomycin C (MMC) has been observed in previous reports. The purpose of this study is to report cytogenetic features in five patients with SS. The patients had low birth weight (mean 1,870 g), short stature (SD = 6.36), microcephaly (OFC, SD = 8.1), typical facial appearance, and multiple articular dislocations. None of them had anemia at the time of examination. In all cases their parents were healthy and non-consanguineous. Lymphocytes of SS patients and a control group (n = 9) matched by age and sex were cultured with and without MMC, and harvested at 72 and 96 hr. Chromosomal aberrations (chromatid and chromosomal gaps and breaks, deletions, fragments, and exchanges) were scored in 100 metaphases per culture. A statistical increase of chromosomal aberrations was observed in 96 hr MMC cultures in all patients (40.2% vs. 2.8%). Sister chromatid exchanges were also performed with no differences between groups. Clinical and cytogenetic findings support the idea that SS may correspond to a Chromosome Instability syndrome. © 2003 Wiley-Liss, Inc.
Vladimir Larionov - One of the best experts on this subject based on the ideXlab platform.
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Novel screen for anti-cancer drugs that elevate Chromosome Instability (CIN) using human artificial Chromosome (HAC).
Oncotarget, 2018Co-Authors: Natalay Kouprina, Yves Pommier, Vladimir LarionovAbstract:Human artificial Chromosomes (HACs) bearing functional kinetochores have been exploited as promising systems for gene delivery and expression and in studies of different epigenetic modifications on kinetochore structure and function. The HAC-based technology has been also used to develop drug screening and assessment strategies to manipulate the CIN (Chromosome Instability) phenotype in cancer cells. More recently, we designed a new protocol for systematic analysis of compounds specifically targeting telomeres and telomerase. This approach used two isogenic cell lines containing a circular HAC (lacking telomeres) and a linear HAC (containing telomeres): compounds that target telomerase or telomeres should preferentially induce loss of the linear HAC but not the circular HAC. This platform enables identification and ranking of compounds that greatly increase Chromosome mis-segregation rates as a result of telomere dysfunction and may expedite the development of new therapeutic strategies for cancer treatment.
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abstract 2737 quantitative assessment of Chromosome Instability induced through chemical disruption of mitotic progression
Cancer Research, 2016Co-Authors: Sarine Markossian, Vladimir Larionov, Alexei Arnaoutov, Nakhle S Saba, Mary DassoAbstract:Most solid tumors are aneuploid, carrying an abnormal number of Chromosomes, and they missegregate whole Chromosomes in a phenomenon termed Chromosome Instability (CIN). CIN is associated with poor prognosis in many cancer types, and targeting of CIN is an attractive strategy for anti-cancer therapeutics. The mechanisms causing CIN and its contributions to tumor initiation and growth are not well defined, partly because there is no straightforward, quantitative assays for CIN in human cells. To address this problem, we have developed the first Human Artificial Chromosome (HAC)-based quantitative live-cell assay for mitotic Chromosome segregation in mammalian cells, with which we can easily score the rates of CIN within one cell division under different experimental conditions. We have constructed a HAC encoding copies of enhanced green fluorescent protein (eGFP) fused to the destruction box (DB) of hSecurin, a substrate of the anaphase promoting complex/cyclosome (APC/C) ubiquitin ligase, which becomes active during anaphase to catalyze the proteolysis of critical mitotic target proteins. This HAC also contains tet operator (tetO) arrays and sequences encoding the tetracycline repressor fused to monomeric cherry fluorescent protein (tetR-mCherry). We have produced human U2OS cells (U2OS-Phoenix) carrying this HAC, in which we monitor HAC segregation in two ways: First, APC/C degrades the DB-eGFP fusion expressed from the HAC at anaphase onset, and DB-eGFP re-accumulates in the daughter cells after G1 phase, when APC/C becomes inactive. Daughter cells that do not obtain a copy of the HAC will thus be GFP negative in the subsequent interphase. Second, because tetR-mCherry binds to the tetO arrays, the HAC itself could be followed by live imaging. Following the HAC by live cell imaging experiments, we show that U2OS-Phoenix cells have low inherent levels of CIN, but HAC missegregation is markedly increased by treatment with Reversine, an inhibitor of Mps1, and microtubule agents Nocodazole and Paclitaxel. In summary, we have developed new assays to score CIN levels in human cells and have shown that CIN levels increase upon chemical disruption of mitotic progression, which makes our assays ideal for chemical screens. Citation Format: Sarine Markossian, Alexei Arnaoutov, Nakhle S. Saba, Vladimir Larionov, Mary Dasso. Quantitative assessment of Chromosome Instability induced through chemical disruption of mitotic progression. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2737.
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quantitative assessment of Chromosome Instability induced through chemical disruption of mitotic progression
Cell Cycle, 2016Co-Authors: Sarine Markossian, Vladimir Larionov, Alexei Arnaoutov, Nakhle S Saba, Mary DassoAbstract:Most solid tumors are aneuploid, carrying an abnormal number of Chromosomes, and they frequently missegregate whole Chromosomes in a phenomenon termed Chromosome Instability (CIN). While CIN can be provoked through disruption of numerous mitotic pathways, it is not clear which of these mechanisms are most critical, or whether alternative mechanisms could also contribute significantly in vivo. One difficulty in determining the relative importance of candidate CIN regulators has been the lack of a straightforward, quantitative assay for CIN in live human cells: While gross mitotic abnormalities can be detected visually, moderate levels of CIN may not be obvious, and are thus problematic to measure. To address this issue, we have developed the first Human Artificial Chromosome (HAC)-based quantitative live-cell assay for mitotic Chromosome segregation in human cells. We have produced U2OS-Phoenix cells carrying the alphoid(tetO)-HAC encoding copies of eGFP fused to the destruction box (DB) of anaphase promoting complex/cyclosome (APC/C) substrate hSecurin and sequences encoding the tetracycline repressor fused to mCherry (TetR-mCherry). Upon HAC missegregation, daughter cells that do not obtain a copy of the HAC are GFP negative in the subsequent interphase. The HAC can also be monitored live following the TetR-mCherry signal. U2OS-Phoenix cells show low inherent levels of CIN, which can be enhanced by agents that target mitotic progression through distinct mechanisms. This assay allows direct detection of CIN induced by clinically important agents without conspicuous mitotic defects, allowing us to score increased levels of CIN that fall below the threshold required for discernable morphological disruption.
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development of a novel hac based gain of signal quantitative assay for measuring Chromosome Instability cin in cancer cells
Oncotarget, 2016Co-Authors: Jung-hyun Kim, William C Earnshaw, Natalay Kouprina, Hiroshi Masumoto, Nikolay V. Goncharov, Vadim Kumeiko, Nicholas C.o. Lee, Hee-sheung Lee, Vladimir LarionovAbstract:// Jung-Hyun Kim 1 , Hee-Sheung Lee 1 , Nicholas C. O. Lee 1 , Nikolay V. Goncharov 1,2 , Vadim Kumeiko 2 , Hiroshi Masumoto 3 , William C. Earnshaw 4 , Natalay Kouprina 1 and Vladimir Larionov 1 1 Developmental Therapeutics Branch, National Cancer Institute, NIH, Bethesda, MD, USA 2 School of Biomedicine, Far Eastern Federal University, A. V. Zhirmunsky Institute of Marine Biology, FEB RAS, Vladivostok, Russia 3 Laboratory of Cell Engineering, Department of Human Genome Research, Kazusa DNA Research Institute, Kisarazu, Japan 4 Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, Scotland Correspondence to: Vladimir Larionov, email: // Keywords : Chromosome Instability, CIN, human artificial Chromosome, HAC, anticancer drugs Received : November 04, 2015 Accepted : January 29, 2016 Published : March 02, 2016 Abstract Accumulating data indicates that Chromosome Instability (CIN) common to cancer cells can be used as a target for cancer therapy. At present the rate of Chromosome mis-segregation is quantified by laborious techniques such as coupling clonal cell analysis with karyotyping or fluorescence in situ hybridization (FISH). Recently, a novel assay was developed based on the loss of a non-essential human artificial Chromosome (HAC) carrying a constitutively expressed EGFP transgene (“loss of signal” assay). Using this system, anticancer drugs can be easily ranked on by their effect on HAC loss. However, it is problematic to covert this “loss of signal” assay into a high-throughput screen to identify drugs and mutations that increase CIN levels. To address this point, we re-designed the HAC-based assay. In this new system, the HAC carries a constitutively expressed shRNA against the EGFP transgene integrated into human genome. Thus, cells that inherit the HAC display no green fluorescence, while cells lacking the HAC do. We verified the accuracy of this “gain of signal” assay by measuring the level of CIN induced by known antimitotic drugs and added to the list of previously ranked CIN inducing compounds, two newly characterized inhibitors of the centromere-associated protein CENP-E, PF-2771 and GSK923295 that exhibit the highest effect on Chromosome Instability measured to date. The “gain of signal” assay was also sensitive enough to detect increase of CIN after siRNA depletion of known genes controlling mitotic progression through distinct mechanisms. Hence this assay can be utilized in future experiments to uncover novel human CIN genes, which will provide novel insight into the pathogenesis of cancer. Also described is the possible conversion of this new assay into a high-throughput screen using a fluorescence microplate reader to characterize chemical libraries and identify new conditions that modulate CIN level.
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Systematic over-expression screens for Chromosome Instability identify conserved dosage Chromosome Instability genes in yeast and human tumors
bioRxiv, 2016Co-Authors: Supipi Duffy, Yi Kan Wang, Erin B. Styles, Tejomayee Singh, Sohrab P. Shah, Vladimir Larionov, Brenda J AndrewsAbstract:Somatic copy number amplifications (SCNAs) and gene over-expression are common features of many cancers. To determine the role of gene over-expression on genome stability, we performed functional genomic screens in the budding yeast for Chromosome Instability, a defining characteristic of cancer that can be targeted by therapeutics. Over-expression of 245 yeast genes increases Chromosome Instability by influencing processes such as Chromosome segregation and DNA damage repair. Testing candidate human homologs, which were highly recurrently altered in tumors lead to the identification of 2 genes, Tdp1 and Taf12 that contribute to CIN in human cells when over-expressed. Rhabdomyosarcoma lines with higher levels of Tdp1 also show Chromosome Instability and can be partially rescued by siRNA-mediated knockdown of Tdp1. Using synthetic dosage lethality screens in yeast, we identified candidate target genes that will specifically target tumors with high levels of Tdp1. We demonstrate the utility of functional genetic screens in model organisms to broaden the spectrum of CIN genes, to identify novel genes relevant to Chromosome Instability in humans and to identify candidate gene targets that can be leveraged to selectively kill tumors over-expressing specific genes.
Kenji Fukasawa - One of the best experts on this subject based on the ideXlab platform.
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centrosome amplification Chromosome Instability and cancer development
Cancer Letters, 2005Co-Authors: Kenji FukasawaAbstract:During mitosis, two centrosomes form spindle poles and direct the formation of bipolar mitotic spindles, which is an essential event for accurate Chromosome segregation into daughter cells. The presence of more than two centrosomes (centrosome amplification), severely disturbs mitotic process and cytokinesis via formation of more than two spindle poles, resulting in an increased frequency of Chromosome segregation errors (Chromosome Instability). Destabilization of Chromosomes by centrosome amplification aids acquisition of further malignant phenotypes, hence promoting tumor progression. Centrosome amplification occurs frequently in almost all types of cancer, and is considered as the major contributing factor for Chromosome Instability in cancer cells. Upon cytokinesis, each daughter cell receives one centrosome, and thus centrosome must duplicate once, and only once, before the next mitosis. If centrosomes duplicate more than once within a single cell cycle, centrosome amplification occurs, which is frequently seen in cells harboring mutations in some tumor suppressor proteins such as p53 and BRCA1. The recent studies have provided critical information for understanding how loss of these proteins allows multiple rounds of centrosome duplication. In this review, how centrosome amplification destabilizes Chromosomes, how loss of certain tumor suppressor proteins leads to centrosome amplification, and the role of centrosome amplification in cancer development will be discussed.
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centrosome hyperamplification in human cancer Chromosome Instability induced by p53 mutation and or mdm2 overexpression
Oncogene, 1999Co-Authors: Patrick E Carroll, Masaru Okuda, Henning F Horn, Paul W Biddinger, Peter J Stambrook, Lyon L Gleich, Y Q Li, Pheruza Tarapore, Kenji FukasawaAbstract:We have previously reported that loss of p53 tumor suppressor protein results in centrosome hyperamplification, which leads to aberrant mitosis and Chromosome Instability. Since p53 is either deleted or mutated in human cancers at a high frequency, we investigated whether human cancers showed centrosome hyperamplification. Screening of advanced stage breast ductal carcinomas and squamous cell carcinomas of the head and neck (SCCHN) revealed that centrosome hyperamplification is frequent in both tumor types. Moreover, through the analyses of p53 in SCCHN samples by direct sequencing and by loss-of-heterozygosity test, we found that p53 mutations correlated with occurrence of centrosome hyperamplification. However, in some cases, we observed centrosome hyperamplification in tumors that retained wild-type p53. These tumors contained high levels of Mdm2. Since Mdm2 can inactivate p53 through physical association, we investigated whether Mdm2 overexpression induced centrosome hyperamplification. We found that Mdm2 overexpression, like loss of p53, induced centrosome hyperamplification and Chromosome Instability in cultured cells.
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Centrosome hyperamplification in human cancer: Chromosome Instability induced by p53 mutation and/or Mdm2 overexpression
Oncogene, 1999Co-Authors: Patrick E Carroll, Masaru Okuda, Henning F Horn, Paul W Biddinger, Peter J Stambrook, Lyon L Gleich, Pheruza Tarapore, Kenji FukasawaAbstract:We have previously reported that loss of p53 tumor suppressor protein results in centrosome hyperamplification, which leads to aberrant mitosis and Chromosome Instability. Since p53 is either deleted or mutated in human cancers at a high frequency, we investigated whether human cancers showed centrosome hyperamplification. Screening of advanced stage breast ductal carcinomas and squamous cell carcinomas of the head and neck (SCCHN) revealed that centrosome hyperamplification is frequent in both tumor types. Moreover, through the analyses of p53 in SCCHN samples by direct sequencing and by loss-of-heterozygosity test, we found that p53 mutations correlated with occurrence of centrosome hyperamplification. However, in some cases, we observed centrosome hyperamplification in tumors that retained wild-type p53. These tumors contained high levels of Mdm2. Since Mdm2 can inactivate p53 through physical association, we investigated whether Mdm2 overexpression induced centrosome hyperamplification. We found that Mdm2 overexpression, like loss of p53, induced centrosome hyperamplification and Chromosome Instability in cultured cells.