Mutations and aneuploidy: co-conspirators in cancer?

Cellular and molecular mechanisms of plasticity in cancer

Cancer cells are plastic - they can assume a wide range of distinct phenotypes. Plasticity is integral to cancer initiation and progression, as well as to the emergence and maintenance of intratumoral heterogeneity. Furthermore, plastic cells can rapidly adapt to and evade therapy, which poses a challenge for effective cancer treatment. As such, targeting plasticity in cancer holds tremendous promise. Yet, the principles governing plasticity in cancer cells remain poorly understood. Here, we provide an overview of the fundamental molecular and cellular mechanisms that underlie plasticity in cancer and in other biological contexts, including development and regeneration. We propose a key role for high-plasticity cell states (HPCSs) as crucial nodes for cell state transitions and enablers of intra-tumoral heterogeneity.

Tools used to assay genomic instability in cancers and cancer meiomitosis

Genomic instability is a defining characteristic of cancer and the analysis of DNA damage at the chromosome level is a crucial part of the study of carcinogenesis and genotoxicity. Chromosomal instability (CIN), the most common level of genomic instability in cancers, is defined as the rate of loss or gain of chromosomes through successive divisions. As such, DNA in cancer cells is highly unstable. However, the underlying mechanisms remain elusive. There is a debate as to whether instability succeeds transformation, or if it is a by-product of cancer, and therefore, studying potential molecular and cellular contributors of genomic instability is of high importance. Recent work has suggested an important role for ectopic expression of meiosis genes in driving genomic instability via a process called meiomitosis. Improving understanding of these mechanisms can contribute to the development of targeted therapies that exploit DNA damage and repair mechanisms. Here, we discuss a workflow of novel and established techniques used to assess chromosomal instability as well as the nature of genomic instability such as double strand breaks, micronuclei, and chromatin bridges. For each technique, we discuss their advantages and limitations in a lab setting. Lastly, we provide detailed protocols for the discussed techniques.

Somatic Sex: On the Origin of Neoplasms With Chromosome Counts in Uneven Ploidy Ranges

Stable aneuploid genomes with nonrandom numerical changes in uneven ploidy ranges define distinct subsets of hematologic malignancies and solid tumors. The idea put forward herein suggests that they emerge from interactions between diploid mitotic and G0/G1 cells, which can in a single step produce all combinations of mono-, di-, tri-, tetra- and pentasomic paternal/maternal homologue configurations that define such genomes. A nanotube-mediated influx of interphase cell cytoplasm into mitotic cells would thus be responsible for the critical nondisjunction and segregation errors by physically impeding the proper formation of the cell division machinery, whereas only a complete cell fusion can simultaneously generate pentasomies, uniparental trisomies as well as biclonal hypo- and hyperdiploid cell populations. The term "somatic sex" was devised to accentuate the similarities between germ cell and somatic cell fusions. A somatic cell fusion, in particular, recapitulates many processes that are also instrumental in the formation of an abnormal zygote that involves a diploid oocyte and a haploid sperm, which then may further develop into a digynic triploid embryo. Despite their somehow deceptive differences and consequences, the resemblance of these two routes may go far beyond of what has hitherto been appreciated. Based on the arguments put forward herein, I propose that embryonic malignancies of mesenchymal origin with these particular types of aneuploidies can thus be viewed as the kind of flawed somatic equivalent of a digynic triploid embryo.

Linking stem cells to chromosomal instability

The discovery of a stem cell population in human neoplasias has given a new impulse to the study of the origins of cancer. The tissue compartment in which transformation first occurs likely comprises stem cells, since these cells need to consolidate the short-term and long-term requisites of tissue renewal. Because of their unique role, stem cells have a combination of characteristics that makes them susceptible to genetic damage, transformation, and tumor initiation. One type of genetic damage in particular, chromosomal instability, might affect the stem cell compartment, because it induces an ongoing cycle of DNA damage and alters cellular programming. Here, we will discuss some of the recently described links between SC, chromosomal instability, and carcinogenesis, and outline some of the consequences for oncoimmunology.

Extreme intratumour heterogeneity and driver evolution in mismatch repair deficient gastro-oesophageal cancer

Mismatch repair deficient (dMMR) gastro-oesophageal adenocarcinomas (GOAs) show better outcomes than their MMR-proficient counterparts and high immunotherapy sensitivity. The hypermutator-phenotype of dMMR tumours theoretically enables high evolvability but their evolution has not been investigated. Here we apply multi-region exome sequencing (MSeq) to four treatment-naive dMMR GOAs. This reveals extreme intratumour heterogeneity (ITH), exceeding ITH in other cancer types >20-fold, but also long phylogenetic trunks which may explain the exquisite immunotherapy sensitivity of dMMR tumours. Subclonal driver mutations are common and parallel evolution occurs in RAS, PIK3CA, SWI/SNF-complex genes and in immune evasion regulators. MSeq data and evolution analysis of single region-data from 64 MSI GOAs show that chromosome 8 gains are early genetic events and that the hypermutator-phenotype remains active during progression. MSeq may be necessary for biomarker development in these heterogeneous cancers. Comparison with other MSeq-analysed tumour types reveals mutation rates and their timing to determine phylogenetic tree morphologies.

The role of DNA image cytometry in screening oral potentially malignant lesions using brushings: A systematic review

It is believed that the majority of oral cancers develop from oral potentially malignant lesions (OPML). Though they can be easily detected during screening, risk stratification is difficult. During screening clinicians often find it difficult to distinguish OPMLs from benign lesions, and predicting OPML at risk of malignant transformation is particularly challenging. DNA aneuploidy has been known to be a marker of malignancy in a number of sites including the oral cavity. We performed a systematic review to evaluate the effectiveness of DNA-ICM using brushings in differentiating OPMLs from benign/inflammatory lesions during screening and in predicting malignant transformation. MEDLINE, Pubmed, EMBASE electronic databases were systematically searched using a combination of keywords and subject headings. A total of 11 articles satisfied our inclusion criteria. These studies reported a wide range of sensitivity (16-96.4%) and specificity (90-100%) due to the differences in study design, definitions of high risk or low risk lesions and DNA-ICM protocol used. No long-term longitudinal studies were identified to assess the role of DNA-ICM using brushings in predicting malignant transformation. No studies evaluated the role of DNA-ICM in community screening settings. A number of studies combined DNA-ICM with other techniques like cytology or argyrophilic nucleolar organizer region counts leading to improved test results. In spite of DNA aneuploidy being accepted as a marker of malignancy, there is limited evidence of DNA-ICM using brushings being successful as an adjunct oral cancer screening tool. Longitudinal studies and large community screening studies need to be undertaken to draw stronger conclusion.

Defective Nuclear Lamina in Aneuploidy and Carcinogenesis

Aneuploidy, loss or gain of whole chromosomes, is a prominent feature of carcinomas, and is generally considered to play an important role in the initiation and progression of cancer. In high-grade serous ovarian cancer, the only common gene aberration is the p53 point mutation, though extensive genomic perturbation is common due to severe aneuploidy, which presents as a deviant karyotype. Several mechanisms for the development of aneuploidy in cancer cells have been recognized, including chromosomal non-disjunction during mitosis, centrosome amplification, and more recently, nuclear envelope rupture at interphase. Many cancer types including ovarian cancer have lost or reduced expression of Lamin A/C, a structural component of the lamina matrix that underlies the nuclear envelope in differentiated cells. Several recent studies suggest that a nuclear lamina defect caused by the loss or reduction of Lamin A/C leads to failure in cytokinesis and formation of tetraploid cells, transient nuclear envelope rupture, and formation of nuclear protrusions and micronuclei during the cell cycle gap phase. Thus, loss and reduction of Lamin A/C underlies the two common features of cancer—aberrations in nuclear morphology and aneuploidy. We discuss here and emphasize the newly recognized mechanism of chromosomal instability due to the rupture of a defective nuclear lamina, which may account for the rapid genomic changes in carcinogenesis.

Integrating the DNA damage and protein stress responses during cancer development and treatment

During evolution, cells have developed a wide spectrum of stress response modules to ensure homeostasis. The genome and proteome damage response pathways constitute the pillars of this interwoven 'defensive' network. Consequently, the deregulation of these pathways correlates with ageing and various pathophysiological states, including cancer. In the present review, we highlight: (1) the structure of the genome and proteome damage response pathways; (2) their functional crosstalk; and (3) the conditions under which they predispose to cancer. Within this context, we emphasize the role of oncogene-induced DNA damage as a driving force that shapes the cellular landscape for the emergence of the various hallmarks of cancer. We also discuss potential means to exploit key cancer-related alterations of the genome and proteome damage response pathways in order to develop novel efficient therapeutic modalities. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

New biological research and understanding of Papanicolaou's test

The development of the Papanicolaou smear test by Dr. George Nicholas Papanicolaou (1883-1962) is one of the most significant achievements in screening for disease and cancer prevention in history. The Papanicolaou smear has been used for screening of cervical cancer since the 1950s. The test is technically straightforward and practical and based on a simple scientific observation: malignant cells have an aberrant nuclear morphology that can be distinguished from benign cells. Here, we review the scientific understanding that has been achieved and continues to be made on the causes and consequences of abnormal nuclear morphology, the basis of Dr. Papanicolaou's invention. The deformed nuclear shape is caused by the loss of lamina and nuclear envelope structural proteins. The consequences of a nuclear envelope defect include chromosomal numerical instability, altered chromatin organization and gene expression, and increased cell mobility because of a malleable nuclear envelope. HPV (Human Papilloma Virus) infection is recognized as the key etiology in the development of cervical cancer. Persistent HPV infection causes disruption of the nuclear lamina, which presents as a change in nuclear morphology detectable by a Papanicolaou smear. Thus, the causes and consequences of nuclear deformation are now linked to the mechanisms of viral carcinogenesis, and are still undergoing active investigation to reveal the details. Recently a statue was installed in front of the Papanicolaou's Cancer Research Building to honor the inventor. Remarkably, the invention nearly 60 years ago by Dr. Papanicolaou still exerts clinical impacts and inspires scientific inquiries.

Downregulation of tyrosine threonine kinase inhibits tumor growth via G2/M arrest in human endometrioid endometrial adenocarcinoma

Endometrial cancer is the most common gynecologic malignancy, about 80% of which is endometrial endometrioid carcinoma. Dysregulation of spindle assembly checkpoint plays a vital role in endometrial endometrioid carcinoma tumorigenesis and progression. The purpose of this study was to explore how tyrosine threonine kinase, a spindle assembly checkpoint-related protein, promotes the endometrial endometrioid carcinoma progression. We found that both messenger RNA and protein levels of tyrosine threonine kinase in endometrial endometrioid carcinoma tissues are higher than those in normal endometrial tissues, and its expression is associated with tumor stages. Genetic depletion of tyrosine threonine kinase by RNA interference in two endometrial endometrioid carcinoma cell lines significantly inhibits cell proliferation and induces apoptosis. Mechanistically, depletion of tyrosine threonine kinase induces G2/M cell cycle arrest and triggers caspase-dependent cell apoptosis. Collectively, tyrosine threonine kinase is significantly upregulated in endometrial endometrioid carcinoma, and downregulation of tyrosine threonine kinase can suppress endometrial endometrioid carcinoma cell proliferation and promote apoptosis via G2/M cell cycle arrest. Our study demonstrates that tyrosine threonine kinase can be a potential therapeutic target for endometrial endometrioid carcinoma treatment.

Nuclear envelope structural defect underlies the main cause of aneuploidy in ovarian carcinogenesis

BACKGROUND

The Cancer Atlas project has shown that p53 is the only commonly (96 %) mutated gene found in high-grade serous epithelial ovarian cancer, the major histological subtype. Another general genetic change is extensive aneuploidy caused by chromosomal numerical instability, which is thought to promote malignant transformation. Conventionally, aneuploidy is thought to be the result of mitotic errors and chromosomal nondisjunction during mitosis. Previously, we found that ovarian cancer cells often lost or reduced nuclear lamina proteins lamin A/C, and suppression of lamin A/C in cultured ovarian epithelial cells leads to aneuploidy. Following up, we investigated the mechanisms of lamin A/C-suppression in promoting aneuploidy and synergy with p53 inactivation.

RESULTS

We found that suppression of lamin A/C by siRNA in human ovarian surface epithelial cells led to frequent nuclear protrusions and formation of micronuclei. Lamin A/C-suppressed cells also often underwent mitotic failure and furrow regression to form tetraploid cells, which frequently underwent aberrant multiple polar mitosis to form aneuploid cells. In ovarian surface epithelial cells isolated from p53 null mice, transient suppression of lamin A/C produced massive aneuploidy with complex karyotypes, and the cells formed malignant tumors when implanted in mice.

CONCLUSIONS

Based on the results, we conclude that a nuclear envelope structural defect, such as the loss or reduction of lamin A/C proteins, leads to aneuploidy by both the formation of tetraploid intermediates following mitotic failure, and the reduction of chromosome (s) following nuclear budding and subsequent loss of micronuclei. We suggest that the nuclear envelope defect, rather than chromosomal unequal distribution during cytokinesis, is the main cause of aneuploidy in ovarian cancer development.

Chromosomal disruption and rearrangements during murine sarcoma development converge to stable karyotypic formation kept by telomerase overexpression

BACKGROUND

Tumor initiation presents a complex and unstable genomic landscape; one of the earliest hallmark events of cancer, and its progression is probably based on selection mechanisms under specific environments that lead to functional tumor cell speciation. We hypothesized that viable tumor phenotypes possess common and highly stable karyotypes and their proliferation is facilitated by an attuned high telomerase activity. Very few investigations have focused on the evolution of common chromosomal rearrangements associated to molecular events that result in functional phenotypes during tumor development.

RESULTS

We have used cytogenetic, flow cytometry and cell culture tools to investigate chromosomal rearrangements and clonality during cancer development using the murine sarcoma TG180 model, and also molecular biology techniques to establish a correlation between chromosome instability and telomerase activity, since telomeres are highly affected during cancer evolution. Cytogenetic analysis showed a near-tetraploid karyotype originated by endoreduplication. Chromosomal rearrangements were random events in response to in vitro conditions, but a stable karyotypic equilibrium was achieved during tumor progression in different in vivo conditions, suggesting that a specific microenvironment may stabilize the chromosomal number and architecture. Specific chromosome aberrations (marker chromosomes) and activated regions (rDNAs) were ubiquitous in the karyotype, suggesting that the conservation of these patterns may be advantageous for tumor progression. High telomerase expression was also correlated with the chromosomal rearrangements stabilization.

CONCLUSIONS

Our data reinforce the notion that the sarcoma cell evolution converges from a highly unstable karyotype to relatively stable and functional chromosome rearrangements, which are further enabled by telomerase overexpression.

Tissue Regeneration in the Chronically Inflamed Tumor Environment: Implications for Cell Fusion Driven Tumor Progression and Therapy Resistant Tumor Hybrid Cells

The biological phenomenon of cell fusion in a cancer context is still a matter of controversial debates. Even though a plethora of in vitro and in vivo data have been published in the past decades the ultimate proof that tumor hybrid cells could originate in (human) cancers and could contribute to the progression of the disease is still missing, suggesting that the cell fusion hypothesis is rather fiction than fact. However, is the lack of this ultimate proof a valid argument against this hypothesis, particularly if one has to consider that appropriate markers do not (yet) exist, thus making it virtually impossible to identify a human tumor cell clearly as a tumor hybrid cell. In the present review, we will summarize the evidence supporting the cell fusion in cancer concept. Moreover, we will refine the cell fusion hypothesis by providing evidence that cell fusion is a potent inducer of aneuploidy, genomic instability and, most likely, even chromothripsis, suggesting that cell fusion, like mutations and aneuploidy, might be an inducer of a mutator phenotype. Finally, we will show that "accidental" tissue repair processes during cancer therapy could lead to the origin of therapy resistant cancer hybrid stem cells.

Revisiting tumour aneuploidy - the place of ploidy assessment in the molecular era

Chromosome instability (CIN) is gaining increasing interest as a central process in cancer. CIN, either past or present, is indicated whenever tumour cells harbour an abnormal quantity of DNA, termed 'aneuploidy'. At present, the most widely used approach to detecting aneuploidy is DNA cytometry - a well-known research assay that involves staining of DNA in the nuclei of cells from a tissue sample, followed by analysis using quantitative flow cytometry or microscopic imaging. Aneuploidy in cancer tissue has been implicated as a predictor of a poor prognosis. In this Review, we have explored this hypothesis by surveying the current landscape of peer-reviewed research in which DNA cytometry has been applied in studies with disease-appropriate clinical follow up. This area of research is broad, however, and we restricted our survey to results published since 2000 relating to seven common epithelial cancers (those of the breast; endometrium, ovary, and uterine cervix; oesophagus; colon and rectum; lung; prostate; and bladder). We placed particular emphasis on results from multivariate analyses to pinpoint situations in which the prognostic value of aneuploidy as a biomarker is strong compared with that of existing indicators, such as clinical stage, histological grade, and specific molecular markers. We summarize the implications of our findings for the prognostic use of ploidy analysis in the clinic and for the theoretical understanding of the role of CIN in carcinogenesis.

Quantitative multigene FISH on breast carcinomas identifies der(1;16)(q10;p10) as an early event in luminal A tumors

In situ detection of genomic alterations in cancer provides information at the single cell level, making it possible to investigate genomic changes in cells in a tissue context. Such topological information is important when studying intratumor heterogeneity as well as alterations related to different steps in tumor progression. We developed a quantitative multigene fluorescence in situ hybridization (QM FISH) method to detect multiple genomic regions in single cells in complex tissues. As a “proof of principle” we applied the method to breast cancer samples to identify partners in whole arm (WA) translocations. WA gain of chromosome arm 1q and loss of chromosome arm 16q are among the most frequent genomic events in breast cancer. By designing five specific FISH probes based on breakpoint information from comparative genomic hybridization array (aCGH) profiles, we visualized chromosomal translocations in clinical samples at the single cell level. By analyzing aCGH data from 295 patients with breast carcinoma with known molecular subtype, we found concurrent WA gain of 1q and loss of 16q to be more frequent in luminal A tumors compared to other molecular subtypes. QM FISH applied to a subset of samples (n = 26) identified a derivative chromosome der(1;16)(q10;p10), a result of a centromere-close translocation between chromosome arms 1q and 16p. In addition, we observed that the distribution of cells with the translocation varied from sample to sample, some had a homogenous cell population while others displayed intratumor heterogeneity with cell-to-cell variation. Finally, for one tumor with both preinvasive and invasive components, the fraction of cells with translocation was lower and more heterogeneous in the preinvasive tumor cells compared to the cells in the invasive component. © 2014 The Authors Genes, Chromosomes & Cancer Published by Wiley Periodicals, Inc.

Multinucleation during C. trachomatis infections is caused by the contribution of two effector pathways

Chlamydia trachomatis is an obligate intracellular bacterial pathogen and the second leading cause of sexually transmitted infections in the US. Infections cause significant morbidity and can lead to serious reproductive sequelae, including an epidemiological link to increased rates of reproductive cancers. One of the overt changes that infected cells exhibit is the development of genomic instability leading to multinucleation. Here we demonstrate that the induction of multinucleation is not conserved equally across chlamydial species; C. trachomatis L2 caused high levels of multinucleation, C. muridarum intermediate levels, and C. caviae had very modest effects on multinucleation. Our data show that at least two effector pathways together cause genomic instability during infection leading to multinucleation. We find that the highly conserved chlamydial protease CPAF is a key effector for one of these pathways. CPAF secretion is required for the loss of centrosome duplication regulation as well as inducing early mitotic exit. The second effector pathway involves the induction of centrosome position errors. This function is not conserved in three chlamydial species tested. Together these two pathways contribute to the induction of high levels of genomic instability and multinucleation seen in C. trachomatis infections.

Biomarkers in melanoma: Stage III and IV disease

The prognosis associated with Stage III melanoma is variable (17-65% 5-year survival) and primarily influenced by the number of lymph nodes involved, the presence of ulceration in a primary lesion, and the tumor burden present in each lymph node. In patients with metastatic (Stage IV) melanoma, the prognosis remains dismal (6-18% 5-year survival) and is influenced primarily by the sites (and extent) of metastatic involvement. Serum lactate dehydrogenase is the only prognostic biomarker useful in metastatic melanoma and it has been incorporated into the 2002 American Joint Committee on Cancer tumor, node, metastasis staging system. In this review, the known prognostic factors in Stage III and IV melanoma are reviewed. Selected investigational therapies and associated biomarkers are also discussed.

Side population cells as prototype of chemoresistant, tumor-initiating cells

Classically, isolation of CSCs from tumors exploits the detection of cell surface markers associated with normal stem cells. Invariable expression of these cell surface markers in almost all proliferating tumor cells that albeit impart specific functionality, the universality, and clinical credibility of CSC phenotype based on markers is still dubious. Side Population (SP) cells, as defined by Hoechst dye exclusion in flow cytometry, have been identified in many solid tumors and cell lines and the SP phenotype can be considered as an enriched source of stem cells as well as an alternative source for the isolation of cancer stem cells especially when molecular markers for stem cells are unknown. SP cells may be responsible for the maintenance and propagation of tumors and the proportion of SP cells may be a predictor of patient outcome. Several of these markers used in cell sorting have emerged as prognostic markers of disease progression though it is seen that the development of new CSC-targeted strategies is often hindered by poor understanding of their regulatory networks and functions. This review intends to appraise the experimental progress towards enhanced isolation and drug screening based on property of acquired chemoresistance of cancer stem cells.

Discovery and mechanistic study of a small molecule inhibitor for motor protein KIFC1

Centrosome amplification is observed in many human cancers and has been proposed to be a driver of both genetic instability and tumorigenesis. Cancer cells have evolved mechanisms to bundle multiple centrosomes into two spindle poles to avoid multipolar mitosis that can lead to chromosomal segregation defects and eventually cell death. KIFC1, a kinesin-14 family protein, plays an essential role in centrosomal bundling in cancer cells, but its function is not required for normal diploid cell division, suggesting that KIFC1 is an attractive therapeutic target for human cancers. To this end, we have identified the first reported small molecule inhibitor AZ82 for KIFC1. AZ82 bound specifically to the KIFC1/microtubule (MT) binary complex and inhibited the MT-stimulated KIFC1 enzymatic activity in an ATP-competitive and MT-noncompetitive manner with a Ki of 0.043 μM. AZ82 effectively engaged with the minus end-directed KIFC1 motor inside cells to reverse the monopolar spindle phenotype induced by the inhibition of the plus end-directed kinesin Eg5. Treatment with AZ82 caused centrosome declustering in BT-549 breast cancer cells with amplified centrosomes. Consistent with genetic studies, our data confirmed that KIFC1 inhibition by a small molecule holds promise for targeting cancer cells with amplified centrosomes and provided evidence that functional suppression of KIFC1 by inhibiting its enzymatic activity could be an effective means for developing cancer therapeutics.

Chlamydia induces anchorage independence in 3T3 cells and detrimental cytological defects in an infection model

Chlamydia are gram negative, obligate intracellular bacterial organisms with different species causing a multitude of infections in both humans and animals. Chlamydia trachomatis is the causative agent of the sexually transmitted infection (STI) Chlamydia, the most commonly acquired bacterial STI in the United States. Chlamydial infections have also been epidemiologically linked to cervical cancer in women co-infected with the human papillomavirus (HPV). We have previously shown chlamydial infection results in centrosome amplification and multipolar spindle formation leading to chromosomal instability. Many studies indicate that centrosome abnormalities, spindle defects, and chromosome segregation errors can lead to cell transformation. We hypothesize that the presence of these defects within infected dividing cells identifies a possible mechanism for Chlamydia as a cofactor in cervical cancer formation. Here we demonstrate that infection with Chlamydia trachomatis is able to transform 3T3 cells in soft agar resulting in anchorage independence and increased colony formation. Additionally, we show for the first time Chlamydia infects actively replicating cells in vivo. Infection of mice with Chlamydia results in significantly increased cell proliferation within the cervix, and in evidence of cervical dysplasia. Confocal examination of these infected tissues also revealed elements of chlamydial induced chromosome instability. These results contribute to a growing body of data implicating a role for Chlamydia in cervical cancer development and suggest a possible molecular mechanism for this effect.

Nuclear DNA-Content in Mesenchymal Lesions in Dogs: Its Value as Marker of Malignancy and Extent of Genomic Instability

DNA-aneuploidy may reflect the malignant nature of mesenchymal proliferations and herald gross genomic instability as a mechanistic factor in tumor genesis. DNA-ploidy and -index were determined by flow cytometry in canine inflammatory or neoplastic mesenchymal tissues and related to clinico-pathological features, biological behavior and p53 gene mutational status. Half of all sarcomas were aneuploid. Benign mesenchymal neoplasms were rarely aneuploid and inflammatory lesions not at all. The aneuploidy rate was comparable to that reported for human sarcomas with significant variation amongst subtypes. DNA-ploidy status in canines lacked a relation with histological grade of malignancy, in contrast to human sarcomas. While aneuploidy was related to the development of metastases in soft tissue sarcomas it was not in osteosarcomas. No relation amongst sarcomas was found between ploidy status and presence of P53 gene mutations. Heterogeneity of the DNA index between primary and metastatic sarcoma sites was present in half of the cases examined. Hypoploidy is more common in canine sarcomas and hyperploid cases have less deviation of the DNA index than human sarcomas. The variation in the presence and extent of aneuploidy amongst sarcoma subtypes indicates variation in genomic instability. This study strengthens the concept of interspecies variation in the evolution of gross chromosomal aberrations during cancer development.

Loss of A-type lamin expression compromises nuclear envelope integrity in breast cancer

Through advances in technology, the genetic basis of cancer has been investigated at the genomic level, and many fundamental questions have begun to be addressed. Among several key unresolved questions in cancer biology, the molecular basis for the link between nuclear deformation and malignancy has not been determined. Another hallmark of human cancer is aneuploidy; however, the causes and consequences of aneuploidy are unanswered and are hotly contested topics. We found that nuclear lamina proteins lamin A/C are absent in a significant fraction (38%) of human breast cancer tissues. Even in lamin A/C–positive breast cancer, lamin A/C expression is heterogeneous or aberrant (such as non-nuclear distribution) in the population of tumor cells, as determined by immunohistology and immunofluorescence microscopy. In most breast cancer cell lines, a significant fraction of the lamin A/C– negative population was observed. To determine the consequences of the loss of lamin A/C, we suppressed their expression by shRNA in non-cancerous primary breast epithelial cells. Down-regulation of lamin A/C in breast epithelial cells led to morphological deformation, resembling that of cancer cells, as observed by immunofluorescence microscopy. The lamin A/C–suppressed breast epithelial cells developed aneuploidy as determined by both flow Cytometry and fluorescence in situ hybridization. We conclude that the loss of nuclear envelope structural proteins lamin A/C in breast cancer underlies the two hallmarks of cancer aberrations in nuclear morphology and aneuploidy.

Mitotic centromere-associated kinesin (MCAK): a potential cancer drug target

The inability to faithfully segregate chromosomes in mitosis results in chromosome instability, a hallmark of solid tumors. Disruption of microtubule dynamics contributes highly to mitotic chromosome instability. The kinesin-13 family is critical in the regulation of microtubule dynamics and the best characterized member of the family, the mitotic centromere-associated kinesin (MCAK), has recently been attracting enormous attention. MCAK regulates microtubule dynamics as a potent depolymerizer of microtubules by removing tubulin subunits from the polymer end. This depolymerizing activity plays pivotal roles in spindle formation, in correcting erroneous attachments of microtubule-kinetochore and in chromosome movement. Thus, the accurate regulation of MCAK is important for ensuring the faithful segregation of chromosomes in mitosis and for safeguarding chromosome stability. In this review we summarize recent data concerning the regulation of MCAK by mitotic kinases, Aurora A/B, Polo-like kinase 1 and cyclin-dependent kinase 1. We propose a molecular model of the regulation of MCAK by these mitotic kinases and relevant phosphatases throughout mitosis. An ever-increasing quantity of data indicates that MCAK is aberrantly regulated in cancer cells. This deregulation is linked to increased malignance, invasiveness, metastasis and drug resistance, most probably due to increased chromosomal instability and remodeling of the microtubule cytoskeleton in cancer cells. Most interestingly, recent observations suggest that MCAK could be a novel molecular target for cancer therapy, as a new cancer antigen or as a mitotic regulator. This collection of new data indicates that MCAK could be a new star in the cancer research sky due to its critical roles in the control of genome stability and the cytoskeleton. Further investigations are required to dissect the fine details of the regulation of MCAK throughout mitosis and its involvements in oncogenesis.

BRCA1 loss induces GADD153-mediated doxorubicin resistance in prostate cancer

BRCA1 plays numerous roles in the regulation of genome integrity and chemoresistance. Although BRCA1 interaction with key proteins involved in DNA repair is well known, its role as a coregulator in the transcriptional response to DNA damage remains poorly understood. In this study, we show that BRCA1 plays a central role in the transcriptional response to genotoxic stress in prostate cancer. BRCA1 expression mediates apoptosis, cell-cycle arrest, and decreased viability in response to doxorubicin treatment. Xenograft studies using human prostate carcinoma PC3 cells show that BRCA1 depletion results in increased tumor growth. A focused survey of BRCA1-regulated genes in prostate carcinoma reveals that multiple regulators of genome stability and cell-cycle control, including BLM, FEN1, DDB2, H3F3B, BRCA2, CCNB2, MAD2L1, and GADD153, are direct transcriptional targets of BRCA1. Furthermore, we show that BRCA1 targets GADD153 promoter to increase its transcription in response to DNA damage. Finally, GADD153 depletion significantly abrogates BRCA1 influence on cell-cycle progression and cell death in response to doxorubicin treatment. These findings define a novel transcriptional pathway through which BRCA1 orchestrates cell fate decisions in response to genotoxic insults, and suggest that BRCA1 status should be considered for new chemotherapeutic treatment strategies in prostate cancer.

Centromere fission, not telomere erosion, triggers chromosomal instability in human carcinomas

The majority of sporadic carcinomas suffer from a kind of genetic instability in which chromosome number changes occur together with segmental defects. This means that changes involving intact chromosomes accompany breakage-induced alterations. Whereas the causes of aneuploidy are described in detail, the origins of chromosome breakage in sporadic carcinomas remain disputed. The three main pathways of chromosomal instability (CIN) proposed until now (random breakage, telomere fusion and centromere fission) are largely based on animal models and in vitro experiments, and recent studies revealed several discrepancies between animal models and human cancer. Here, we discuss how the experimental systems translate to human carcinomas and compare the theoretical breakage products to data from patient material and cancer cell lines. The majority of chromosomal defects in human carcinomas comprises pericentromeric breaks that are captured by healthy telomeres, and only a minor proportion of chromosome fusions can be attributed to telomere erosion or random breakage. Centromere fission, not telomere erosion, is therefore the most probably trigger of CIN and early carcinogenesis. Similar centromere–telomere fusions might drive a subset of congenital defects and evolutionary chromosome changes.

Nuclear envelope structural defects cause chromosomal numerical instability and aneuploidy in ovarian cancer

BACKGROUND

Despite our substantial understanding of molecular mechanisms and gene mutations involved in cancer, the technical approaches for diagnosis and prognosis of cancer are limited. In routine clinical diagnosis of cancer, the procedure is very basic: nuclear morphology is used as a common assessment of the degree of malignancy, and hence acts as a prognostic and predictive indicator of the disease. Furthermore, though the atypical nuclear morphology of cancer cells is believed to be a consequence of oncogenic signaling, the molecular basis remains unclear. Another common characteristic of human cancer is aneuploidy, but the causes and its role in carcinogenesis are not well established.

METHODS

We investigated the expression of the nuclear envelope proteins lamin A/C in ovarian cancer by immunohistochemistry and studied the consequence of lamin A/C suppression using siRNA in primary human ovarian surface epithelial cells in culture. We used immunofluorescence microscopy to analyze nuclear morphology, flow cytometry to analyze cellular DNA content, and fluorescence in situ hybridization to examine cell ploidy of the lamin A/C-suppressed cells.

RESULTS

We found that nuclear lamina proteins lamin A/C are often absent (47%) in ovarian cancer cells and tissues. Even in lamin A/C-positive ovarian cancer, the expression is heterogeneous within the population of tumor cells. In most cancer cell lines, a significant fraction of the lamin A/C-negative population was observed to intermix with the lamin A/C-positive cells. Down regulation of lamin A/C in non-cancerous primary ovarian surface epithelial cells led to morphological deformation and development of aneuploidy. The aneuploid cells became growth retarded due to a p53-dependent induction of the cell cycle inhibitor p21.

CONCLUSIONS

We conclude that the loss of nuclear envelope structural proteins, such as lamin A/C, may underlie two of the hallmarks of cancer--aberrations in nuclear morphology and aneuploidy.

High levels of the Mps1 checkpoint protein are protective of aneuploidy in breast cancer cells

Most human cancers are aneuploid and have chromosomal instability, which contrasts to the inability of human cells to normally tolerate aneuploidy. Noting that aneuploidy in human breast cancer correlates with increased expression levels of the Mps1 checkpoint gene, we investigated whether these high levels of Mps1 contribute to the ability of breast cancer cells to tolerate this aneuploidy. Reducing Mps1 levels in cultured human breast cancer cells by RNAi resulted in aberrant mitoses, induction of apoptosis, and decreased ability of human breast cancer cells to grow as xenografts in nude mice. Remarkably, breast cancer cells that survive reductions in levels of Mps1 have relatively less aneuploidy, as measured by copies of specific chromosomes, compared with cells that have constitutively high levels of Mps1. Thus, high levels of Mps1 in breast cancer cells likely contribute to these cells tolerating aneuploidy.

Phenotypic consequences of aneuploidy in Arabidopsis thaliana

Aneuploid cells are characterized by incomplete chromosome sets. The resulting imbalance in gene dosage has phenotypic consequences that are specific to each karyotype. Even in the case of Down syndrome, the most viable and studied form of human aneuploidy, the mechanisms underlying the connected phenotypes remain mostly unclear. Because of their tolerance to aneuploidy, plants provide a powerful system for a genome-wide investigation of aneuploid syndromes, an approach that is not feasible in animal systems. Indeed, in many plant species, populations of aneuploid individuals can be easily obtained from triploid individuals. We phenotyped a population of Arabidopsis thaliana aneuploid individuals containing 25 different karyotypes. Even in this highly heterogeneous population, we demonstrate that certain traits are strongly associated with the dosage of specific chromosome types and that chromosomal effects can be additive. Further, we identified subtle developmental phenotypes expressed in the diploid progeny of aneuploid parent(s) but not in euploid controls from diploid lineages. These results indicate long-term phenotypic consequences of aneuploidy that can persist after chromosomal balance has been restored. We verified the diploid nature of these individuals by whole-genome sequencing and discuss the possibility that trans-generational phenotypic effects stem from epigenetic modifications passed from aneuploid parents to their diploid progeny.

CDK5RAP2 regulates centriole engagement and cohesion in mice

Centriole duplication occurs once per cell cycle, ensuring that each cell contains two centrosomes, each containing a mother-daughter pair of tightly engaged centrioles at mitotic entry. Loss of the tight engagement between mother and daughter centrioles appears to license the next round of centriole duplication. However, the molecular mechanisms regulating this process remain largely unknown. Mutations in CDK5RAP2, which encodes a centrosomal protein, cause autosomal recessive primary microcephaly in humans. Here we show that CDK5RAP2 loss of function in mice causes centriole amplification with a preponderance of single, unpaired centrioles and increased numbers of daughter-daughter centriole pairs. These results indicate that CDK5RAP2 is required to maintain centriole engagement and cohesion, thereby restricting centriole replication. Early in mitosis, amplified centrosomes assemble multipolar spindles in CDK5RAP2 mutant cells. Moreover, both mother and daughter centrioles are amplified and the excess mother centrioles template multiple primary cilia in CDK5RAP2 mutant cells.

Functional importance of RASSF1A microtubule localization and polymorphisms

Ras association domain family protein 1A (RASSF1A) is one of the more heavily methylated genes in human cancers. In addition to promoter-specific methylation, RASSF1A polymorphisms have been identified in cancer patients. RASSF1A is a tumor suppressor protein involved in death receptor-dependent apoptosis and it is localized to microtubules. Currently, the biological importance of RASSF1A microtubule localization and the functional consequences of RASSF1A polymorphisms is not understood. In this study, we have investigated both RASSF1A microtubule association and polymorphisms. Loss of RASSF1A microtubule association resulted in the nuclear appearance of RASSF1A and the loss of association with α-, γ- and β-tubulin. Moreover, the loss of microtubule localization of RASSF1A resulted in enhanced tumor-promoting potential, as determined by a xenograft transplantation model in nude mice. It is surprising that, several RASSF1A polymorphisms also lost the ability to associate with α-, γ- and β-tubulin and lost the ability to prevent tumor formation in a xenograft nude mouse model when compared with wild-type RASSF1A. Our results demonstrate a role for RASSF1A microtubule localization in eliciting its tumor suppressor function. In addition, some RASSF1A polymorphisms lack the tumor suppressor function of RASSF1A and, if present in patients, may be tumorigenic.

MCAK regulates chromosome alignment but is not necessary for preventing aneuploidy in mouse oocyte meiosis I

Errors in chromosome segregation in mammalian oocytes lead to aneuploid eggs that are developmentally compromised. In mitotic cells, mitotic centromere associated kinesin (MCAK; KIF2C) prevents chromosome segregation errors by detaching incorrect microtubule-kinetochore interactions. Here, we examine whether MCAK is involved in spindle function in mouse oocyte meiosis I, and whether MCAK is necessary to prevent chromosome segregation errors. We find that MCAK is recruited to centromeres, kinetochores and chromosome arms in mid-meiosis I, and that MCAK depletion, or inhibition using a dominant-negative construct, causes chromosome misalignment. However, the majority of oocytes complete meiosis I and the resulting eggs retain the correct number of chromosomes. Moreover, MCAK-depleted oocytes can recover from mono-orientation of homologous kinetochores in mid-meiosis I to segregate chromosomes correctly. Thus, MCAK contributes to chromosome alignment in meiosis I, but is not necessary for preventing chromosome segregation errors. Although other correction mechanisms may function in mammalian meiosis I, we speculate that late establishment of kinetochore microtubules in oocytes reduces the likelihood of incorrect microtubule-kinetochore interactions, bypassing the requirement for error correction.

Centromere-localized breaks indicate the generation of DNA damage by the mitotic spindle

Most carcinomas present some form of chromosome instability in combination with spindle defects. Numerical instability is likely caused by spindle aberrations, but the origin of breaks and translocations remains elusive. To determine whether one mechanism can bring about both types of instability, we studied the relationship between DNA damage and spindle defects. Although lacking apparent repair defects, primary Dido mutant cells formed micronuclei containing damaged DNA. The presence of centromeres showed that micronuclei were caused by spindle defects, and cell cycle markers showed that DNA damage was generated during mitosis. Although the micronuclei themselves persisted, the DNA damage within was repaired during S and G2 phases. DNA breaks in Dido mutant cells regularly colocalized with centromeres, which were occasionally distorted. Comparable defects were found in APC mutant cell lines, an independent system for spindle defects. On the basis of these results, we propose a model for break formation in which spindle defects lead to centromere shearing.

Pericentrin in cellular function and disease

Pericentrin is an integral component of the centrosome that serves as a multifunctional scaffold for anchoring numerous proteins and protein complexes. Through these interactions, pericentrin contributes to a diversity of fundamental cellular processes. Recent studies link pericentrin to a growing list of human disorders. Studies on pericentrin at the cellular, molecular, and, more recently, organismal level, provide a platform for generating models to elucidate the etiology of these disorders. Although the complexity of phenotypes associated with pericentrin-mediated disorders is somewhat daunting, insights into the cellular basis of disease are beginning to come into focus. In this review, we focus on human conditions associated with loss or elevation of pericentrin and propose cellular and molecular models that might explain them.

Centrosomes and myeloma; aneuploidy and proliferation

Multiple myeloma is the second most common hematological malignancy in the United States. The disease is characterized by an accumulation of clonal plasma cells. Clinically, patients present with anemia, lytic bone lesions, hypercalcaemia, or renal impairment. The genome of the malignant plasma cells is extremely unstable and is typically aneuploid and characterized by a complex combination of structure and numerical abnormalities. The basis of the genomic instability underlying myeloma is unclear. In this regard, centrosome amplification is present in about a third of myeloma and may represent a mechanism leading to genomic instability in myeloma. Centrosome amplification is associated with high-risk features and poor prognosis. Understanding the underlying etiology of centrosome amplification in myeloma may lead to new therapeutic avenues.

Loss of GATA6 leads to nuclear deformation and aneuploidy in ovarian cancer

A prominent hallmark of most human cancer is aneuploidy, which is a result of the chromosomal instability of cancer cells and is thought to contribute to the initiation and progression of most carcinomas. The developmentally regulated GATA6 transcription factor is commonly lost in ovarian cancer, and the loss of its expression is closely associated with neoplastic transformation of the ovarian surface epithelium. In the present study, we found that reduction of GATA6 expression with small interfering RNA (siRNA) in human ovarian surface epithelial cells resulted in deformation of the nuclear envelope, failure of cytokinesis, and formation of polyploid and aneuploid cells. We further discovered that loss of the nuclear envelope protein emerin may mediate the consequences of GATA6 suppression. The nuclear phenotypes were reproduced by direct suppression of emerin with siRNA. Thus, we conclude that diminished expression of GATA6 leads to a compromised nuclear envelope that is causal for polyploidy and aneuploidy in ovarian tumorigenesis. The loss of emerin may be the basis of nuclear morphological deformation and subsequently the cause of aneuploidy in ovarian cancer cells.

Isolation and characterization of a spontaneously immortalized bovine retinal pigmented epithelial cell line

BACKGROUND

The Retinal Pigmented Epithelium (RPE) is juxtaposed with the photoreceptor outer segments of the eye. The proximity of the photoreceptor cells is a prerequisite for their survival, as they depend on the RPE to remove the outer segments and are also influenced by RPE cell paracrine factors. RPE cell death can cause a progressive loss of photoreceptor function, which can diminish vision and, over time, blindness ensues. Degeneration of the retina has been shown to induce a variety of retinopathies, such as Stargardt's disease, Cone-Rod Dystrophy (CRD), Retinitis Pigmentosa (RP), Fundus Flavimaculatus (FFM), Best's disease and Age-related Macular Degeneration (AMD). We have cultured primary bovine RPE cells to gain a further understanding of the mechanisms of RPE cell death. One of the cultures, named tRPE, surpassed senescence and was further characterized to determine its viability as a model for retinal diseases.

RESULTS

The tRPE cell line has been passaged up to 150 population doublings and was shown to be morphologically similar to primary cells. They have been characterized to be of RPE origin by reverse transcriptase PCR and immunocytochemistry using the RPE-specific genes RPE65 and CRALBP and RPE-specific proteins RPE65 and Bestrophin. The tRPE cells are also immunoreactive to vimentin, cytokeratin and zonula occludens-1 antibodies. Chromosome analysis indicates a normal diploid number. The tRPE cells do not grow in suspension or in soft agar. After 3H thymidine incorporation, the cells do not appear to divide appreciably after confluency.

CONCLUSION

The tRPE cells are immortal, but still exhibit contact inhibition, serum dependence, monolayer growth and secrete an extra-cellular matrix. They retain the in-vivo morphology, gene expression and cell polarity. Additionally, the cells endocytose exogenous melanin, A2E and purified lipofuscin granules. This cell line may be a useful in-vitro research model for retinal maculopathies.

Hydrophobic bile acids, genomic instability, Darwinian selection, and colon carcinogenesis

Sporadic colon cancer is caused predominantly by dietary factors. We have selected bile acids as a focus of this review since high levels of hydrophobic bile acids accompany a Western-style diet, and play a key role in colon carcinogenesis. We describe how bile acid-induced stresses cause cell death in susceptible cells, contribute to genomic instability in surviving cells, impose Darwinian selection on survivors and enhance initiation and progression to colon cancer. The most likely major mechanisms by which hydrophobic bile acids induce stresses on cells (DNA damage, endoplasmic reticulum stress, mitochondrial damage) are described. Persistent exposure of colon epithelial cells to hydrophobic bile acids can result in the activation of pro-survival stress-response pathways, and the modulation of numerous genes/proteins associated with chromosome maintenance and mitosis. The multiple mechanisms by which hydrophobic bile acids contribute to genomic instability are discussed, and include oxidative DNA damage, p53 and other mutations, micronuclei formation and aneuploidy. Since bile acids and oxidative stress decrease DNA repair proteins, an increase in DNA damage and increased genomic instability through this mechanism is also described. This review provides a mechanistic explanation for the important link between a Western-style diet and associated increased levels of colon cancer.

A survivin-ran complex regulates spindle formation in tumor cells

Aberrant cell division is a hallmark of cancer, but the molecular circuitries of this process in tumor cells are not well understood. Here, we used a high-throughput proteomics screening to identify novel molecular partners of survivin, an essential regulator of mitosis overexpressed in cancer. We found that survivin associates with the small GTPase Ran in an evolutionarily conserved recognition in mammalian cells and Xenopus laevis extracts. This interaction is regulated during the cell cycle, involves Ran-GTP, requires a discrete binding interface centered on Glu65 in survivin, and is independent of the Ran effector Crm1. Disruption of a survivin-Ran complex does not affect the assembly of survivin within the chromosomal passenger complex or its cytosolic accumulation, but it inhibits the delivery of the Ran effector molecule TPX2 to microtubules. In turn, this results in aberrant mitotic spindle formation and chromosome missegregation in tumor, but not normal, cells. Therefore, survivin is a novel effector of Ran signaling, and this pathway may be preferentially exploited for spindle assembly in tumor cells.

Mdm2 promotes genetic instability and transformation independent of p53

Mdm2, a regulator of the tumor suppressor p53, is frequently overexpressed in human malignancies. Mdm2 also has unresolved, p53-independent functions that contribute to tumorigenesis. Here, we show that increased Mdm2 expression induced chromosome/chromatid breaks and delayed DNA double-strand break repair in cells lacking p53 but not in cells with a mutant form of Nbs1, a component of the Mre11/Rad50/Nbs1 DNA repair complex. A 31-amino-acid region of Mdm2 was necessary for binding to Nbs1. Mutation of conserved amino acids in the Nbs1 binding domain of Mdm2 inhibited Mdm2-Nbs1 association and prevented Mdm2 from delaying phosphorylation of H2AX and ATM-S/TQ sites, repair of DNA breaks, and resolution of DNA damage foci. Similarly, the mutation of eight amino acids in the Mdm2 binding domain of Nbs1 inhibited Mdm2-Nbs1 interaction and blocked the ability of Mdm2 to delay DNA break repair. Both Nbs1 and ATM, but not the ubiquitin ligase activity of Mdm2, were necessary to inhibit DNA break repair. Only Mdm2 with an intact Nbs1 binding domain was able to increase the frequency of chromosome/chromatid breaks and the transformation efficiency of cells lacking p53. Therefore, the interaction of Mdm2 with Nbs1 inhibited DNA break repair, leading to chromosome instability and subsequent transformation that was independent of p53.

Aneuploidy and RAS mutations are mutually exclusive events in the development of well-differentiated thyroid follicular tumours

OBJECTIVE

Follicular thyroid tumours present several genetic alterations such as aneuploidy, RAS mutations and PAX8/PPARgammarearrangements. The molecular basis of aneuploidy remains undefined in the majority of human cancers. It has been proposed that mutations in RAS oncogenes could be related to chromosomal instability, although this issue remains controversial. The aim of our study was to investigate the correlation between aneuploidy, RAS mutations and PAX8/PPARgamma gene rearrangement in thyroid follicular tumours.

DESIGN

Ploidy status was determined by flow cytometry in 111 thyroid lesions (42 follicular thyroid adenomas, 27 follicular thyroid carcinomas, 19 follicular variants of papillary thyroid carcinoma, 20 poorly differentiated thyroid carcinomas and 3 anaplastic thyroid carcinomas). RAS mutations and PAX8/PPARgamma fusion gene were investigated in 101 and 87 of these samples, respectively.

RESULTS

Altogether, 12 of 50 (24%) diploid tumours presented RAS mutation which contrasts with 3 of 51 (5.9%; P = 0.0124) RAS mutations in the group of aneuploid tumours. The aneuploid tumours harbouring RAS mutations were two poorly differentiated carcinomas and one follicular variant of papillary thyroid carcinoma with poorly differentiated areas. None of the tumours with RAS mutations expressed the PAX8/PPARgamma fusion gene. Three of five (60%) follicular thyroid adenomas and 1 of 7 (14%) follicular thyroid carcinomas, with the PAX8/PPARgamma fusion gene, were aneuploid.

CONCLUSIONS

Our data suggest that aneuploidy and RAS mutations are mutually exclusive events in the development of well-differentiated thyroid follicular tumours.

Somatic loss of BRCA1 and p53 in mice induces mammary tumors with features of human BRCA1-mutated basal-like breast cancer

Women carrying germ-line mutations in BRCA1 are strongly predisposed to developing breast cancers with characteristic features also observed in sporadic basal-like breast cancers. They appear as high-grade tumors with high proliferation rates and pushing borders. On the molecular level, they are negative for hormone receptors and ERBB2, display frequent TP53 mutations, and express basal epithelial markers. To study the role of BRCA1 and P53 loss of function in breast cancer development, we generated conditional mouse models with tissue-specific mutation of Brca1 and/or p53 in basal epithelial cells. Somatic loss of both BRCA1 and p53 resulted in the rapid and efficient formation of highly proliferative, poorly differentiated, estrogen receptor-negative mammary carcinomas with pushing borders and increased expression of basal epithelial markers, reminiscent of human basal-like breast cancer. BRCA1- and p53-deficient mouse mammary tumors exhibit dramatic genomic instability, and their molecular signatures resemble those of human BRCA1-mutated breast cancers. Thus, these tumors display important hallmarks of hereditary breast cancers in BRCA1-mutation carriers.

Acrylamide effects on kinesin-related proteins of the mitotic/meiotic spindle

The microtubule (MT) motor protein kinesin is a vital component of cells and organs expressing acrylamide (ACR) toxicity. As a mechanism of its potential carcinogenicity, we determined whether kinesins involved in cell division are inhibited by ACR similar to neuronal kinesin [Sickles, D.W., Brady, S.T., Testino, A.R., Friedman, M.A., and Wrenn, R.A. (1996). Direct effect of the neurotoxicant acrylamide on kinesin-based microtubule motility. Journal of Neuroscience Research 46, 7-17.] Kinesin-related genes were isolated from rat testes [Navolanic, P.M., and Sperry, A.O. (2000). Identification of isoforms of a mitotic motor in mammalian spermatogenesis. Biology of Reproduction 62, 1360-1369.], their kinesin-like proteins expressed in bacteria using recombinant DNA techniques and the effects of ACR, glycidamide (GLY) and propionamide (a non-neurotoxic metabolite) on the function of two of the identified kinesin motors were tested. KIFC5A MT bundling activity, required for mitotic spindle formation, was measured in an MT-binding assay. Both ACR and GLY caused a similar concentration-dependent reduction in the binding of MT; concentrations of 100 microM ACR or GLY reduced its activity by 60%. KRP2 MT disassembling activity was assayed using the quantity of tubulin disassembled from taxol-stabilized MT. Both ACR and GLY inhibited KRP2-induced MT disassembly. GLY was substantially more potent; significant reductions of 60% were achieved by 500 microM, a comparable inhibition by ACR required a 5 mM concentration. Propionamide had no significant effect on either kinesin, except KRP2 at 10 mM. This is the first report of ACR inhibition of a mitotic/meiotic motor protein. ACR (or GLY) inhibition of kinesin may be an alternative mechanism to DNA adduction in the production of cell division defects and potential carcinogenicity. We conclude that ACR may act on multiple kinesin family members and produce toxicities in organs highly dependent on microtubule-based functions.

Rbm15 modulates Notch-induced transcriptional activation and affects myeloid differentiation

RBM15 is the fusion partner with MKL in the t(1;22) translocation of acute megakaryoblastic leukemia. To understand the role of the RBM15-MKL1 fusion protein in leukemia, we must understand the normal functions of RBM15 and MKL. Here, we show a role for Rbm15 in myelopoiesis. Rbm15 is expressed at highest levels in hematopoietic stem cells and at more moderate levels during myelopoiesis of murine cell lines and primary murine cells. Decreasing Rbm15 levels with RNA interference enhances differentiation of the 32DWT18 myeloid precursor cell line. Conversely, enforced expression of Rbm15 inhibits 32DWT18 differentiation. We show that Rbm15 alters Notch-induced HES1 promoter activity in a cell type-specific manner. Rbm15 inhibits Notch-induced HES1 transcription in nonhematopoietic cells but stimulates this activity in hematopoietic cell lines, including 32DWT18 and human erythroleukemia cells. Moreover, the N terminus of Rbm15 coimmunoprecipitates with RBPJkappa, a critical factor in Notch signaling, and the Rbm15 N terminus has a dominant negative effect, impairing activation of HES1 promoter activity by full-length-Rbm15. Thus, Rbm15 is differentially expressed during hematopoiesis and may act to inhibit myeloid differentiation in hematopoietic cells via a mechanism that is mediated by stimulation of Notch signaling via RBPJkappa.

Molecular karyotyping and aneuploidy detection in Arabidopsis thaliana using quantitative fluorescent polymerase chain reaction

Certain cellular processes are sensitive to changes in gene dosage. Aneuploidy is deleterious because of an imbalance of gene dosage on a chromosomal scale. Identification, classification and characterization of aneuploidy are therefore important for molecular, population and medical genetics and for a deeper understanding of the mechanisms underlying dosage sensitivity. Notwithstanding recent progress in genomic technologies, limited means are available for detecting and classifying changes in chromosome dose. The development of an inexpensive and scalable karyotyping method would allow rapid detection and characterization of both simple and complex aneuploid types. In addition to the problem of karyotyping, genomic and molecular genetic studies of aneuploids and polyploids are complicated by multiple heterozygous combinations possible at loci present in more than two copies. Quantitative scoring of allele genotypes would enable large-scale population genetic experiments in polyploids, and permit genetic analyses on bulked populations in diploid species. Here, we demonstrate that quantitative fluorescent-polymerase chain reaction (QF-PCR) can be used to simultaneously genotype and karyotype aneuploid and polyploid Arabidopsis thaliana. Comparison of QF-PCR with flow cytometric determination of nuclear DNA content indicated near perfect agreement between the methods, but complete karyotype resolution was only possible using QF-PCR. A complex karyotype, determined by QF-PCR, was validated by comparative genomic hybridization to microarrays. Finally, we screened the progeny of tetraploid individuals and found that more than 25% were aneuploid and that our artificially induced tetraploid strain produced fewer aneuploid individuals than a tetraploid strain isolated from nature.

Expression and genomic profiling of colorectal cancer

Colorectal cancer still represents a paradigm for the elucidation of the cellular, genetic and molecular mechanisms that underly solid tumor initiation, progression to malignancy, and metastasis to distal organ sites. The relative ease with which pathological specimens can be obtained by either surgery or endoscopy from different stages of tumor progression has facilitated the application of omics technologies to allow the genome-wide analysis both at the RNA (gene expression) and DNA (aneuploidy) levels. Here, we have reviewed the multiplicity of studies appeared to date in the scientific literature on the expression and genomic analysis of colorectal cancer, and attempted an integration of the profiling data generated and made available in the public domain. This approach is likely to pinpoint specific chromosomal loci and the corresponding genes which (i) play rate-limiting roles in colorectal cancer, (ii) represent putative diagnostic and prognostic markers for the accurate prediction of clinical outcome and response to treatment, and (iii) encompass potential therapeutic targets. Moreover, cross-species data mining and integration of the human colorectal cancer profiles with those obtained from mouse models of intestinal tumorigenesis will even more contribute to the elucidation of highly conserved pathways and cellular functions underlying malignancy in the GI tract. Notwithstanding the above promises, tumor heterogeneity, limited cohort sizes, and methodological differences among experimental and bioinformatic approaches still poses main obstacles towards the optimal utilization and integration of omics profiles.