MAPK mediates RAS-induced chromosome instability

The two sides of chromosomal instability: drivers and brakes in cancer

Chromosomal instability (CIN) is a hallmark of cancer and is associated with tumor cell malignancy. CIN triggers a chain reaction in cells leading to chromosomal abnormalities, including deviations from the normal chromosome number or structural changes in chromosomes. CIN arises from errors in DNA replication and chromosome segregation during cell division, leading to the formation of cells with abnormal number and/or structure of chromosomes. Errors in DNA replication result from abnormal replication licensing as well as replication stress, such as double-strand breaks and stalled replication forks; meanwhile, errors in chromosome segregation stem from defects in chromosome segregation machinery, including centrosome amplification, erroneous microtubule-kinetochore attachments, spindle assembly checkpoint, or defective sister chromatids cohesion. In normal cells, CIN is deleterious and is associated with DNA damage, proteotoxic stress, metabolic alteration, cell cycle arrest, and senescence. Paradoxically, despite these negative consequences, CIN is one of the hallmarks of cancer found in over 90% of solid tumors and in blood cancers. Furthermore, CIN could endow tumors with enhanced adaptation capabilities due to increased intratumor heterogeneity, thereby facilitating adaptive resistance to therapies; however, excessive CIN could induce tumor cells death, leading to the "just-right" model for CIN in tumors. Elucidating the complex nature of CIN is crucial for understanding the dynamics of tumorigenesis and for developing effective anti-tumor treatments. This review provides an overview of causes and consequences of CIN, as well as the paradox of CIN, a phenomenon that continues to perplex researchers. Finally, this review explores the potential of CIN-based anti-tumor therapy.

DNA replication stress and mitotic catastrophe mediate sotorasib addiction in KRASG12C-mutant cancer

BACKGROUND

Sotorasib is the first KRAS^G12C inhibitor approved by the US Food and Drug Administration for treating KRAS^G12C-mutant non-small-cell lung cancer (NSCLC). Clinical trials on the therapeutic use of sotorasib for cancer have reported promising results. However, KRAS^G12C-mutant cancers can acquire resistance to sotorasib after treatment. We incidentally discovered that sotorasib-resistant (SR) cancer cells are addicted to this inhibitor. In this study, we investigated the mechanisms underlying sotorasib addiction.

METHODS

Sotorasib-resistant cells were established using KRAS^G12C-mutant pancreatic cancer and NSCLC cell lines. Cell viability in the presence or absence of sotorasib and in combination with multiple inhibitors was assessed through proliferation assay and annexin V/propidium iodide (PI) flow cytometry assays. The mechanisms underlying drug addiction were elucidated through 5-bromo-2'-deoxyuridine (BrdU) incorporation assay, immunofluorescence staining, time-lapse microscopy, and comet assay. Furthermore, a subcutaneous xenograft model was used to demonstrate sotorasib addiction in vivo.

RESULTS

In the absence of sotorasib, the sotorasib-resistant cells underwent p21^Waf1/^Cip1-mediated cell cycle arrest and caspase-dependent apoptosis. Sotorasib withdrawal resulted in robust activation of mitogen-activated protein kinase (MAPK) pathway, inducing severe DNA damage and replication stress, which activated the DNA damage response (DDR) pathway. Persistent MAPK pathway hyperactivation with DDR exhaustion led to premature mitotic entry and aberrant mitosis, followed by micronucleus and nucleoplasmic bridge formation. Pharmacologic activation of the MAPK pathway with a type I BRAF inhibitor could further enhance the effects of sotorasib withdrawal on sotorasib-resistant cancer cells both in vitro and in vivo.

CONCLUSIONS

We elucidated the mechanisms underlying the sotorasib addiction of cancer cells. Sotorasib addiction appears to be mediated through MAPK pathway hyperactivity, DNA damage, replication stress, and mitotic catastrophe. Moreover, we devised a therapeutic strategy involving a type I BRAF inhibitor to strengthen the effects of sotorasib addiction; this strategy may provide clinical benefit for patients with cancer.

A pan-cancer compendium of chromosomal instability

Chromosomal instability (CIN) results in the accumulation of large-scale losses, gains and rearrangements of DNA¹. The broad genomic complexity caused by CIN is a hallmark of cancer²; however, there is no systematic framework to measure different types of CIN and their effect on clinical phenotypes pan-cancer. Here we evaluate the extent, diversity and origin of CIN across 7,880 tumours representing 33 cancer types. We present a compendium of 17 copy number signatures that characterize specific types of CIN, with putative aetiologies supported by multiple independent data sources. The signatures predict drug response and identify new drug targets. Our framework refines the understanding of impaired homologous recombination, which is one of the most therapeutically targetable types of CIN. Our results illuminate a fundamental structure underlying genomic complexity in human cancers and provide a resource to guide future CIN research.

The MAP kinase inhibitor PD98059 reduces chromosomal instability in the autoimmune encephalomyelitis SJL/J-mouse model of multiple sclerosis

Multiple sclerosis (MS), a disease in which the immune system attacks nerve cells, has been associated with both genetic and environmental risk factors. We observed increased micronucleus (MN) formation in SJL/J mouse experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Most of these MN were due to chromosomal loss. Increased activation of MAP kinases, which leads to disruption of the mitotic spindle and improper segregation of chromosomes, is associated with MS. MAP kinase inhibitors, such as PD98059, may therefore be beneficial for MS. In the EAE model, PD98059 treatment reduced adverse effects, including MN formation, lipid peroxidation, and GSH oxidation. Interventions that mitigate chromosomal instability may have therapeutic value in MS.

An Integrative Morphomolecular Classification System of Gastric Carcinoma With Distinct Clinical Outcomes

A robust morphomolecular classification system for gastric carcinoma is required. A 4-tier morphologic classification is proposed, including diffuse, intestinal, tubular, and lymphoid types. A tissue microarray for mismatch repair immunohistochemistry and Epstein-Barr virus (EBV) in situ hybridization were performed in 329 gastric carcinomas. DNA flow cytometry was used to detect aneuploidy in formalin-fixed paraffin-embedded samples. Lymphoid histology was the third most common histologic pattern at our institute and strongly associated with EBV infection and PMS2/MLH1-deficiency (both P<0.001). HER2 overexpression and SATB2 expression more frequently occurred in intestinal histology (both P<0.001). Loss of ARID1A expression was strikingly associated with lymphoid histology (P<0.001) and negative E-cadherin expression was correlated with diffuse histology (P=0.001). Programmed death-ligand 1 expression was most frequently present in lymphoid-type gastric carcinoma than other histologic subtypes and correlated with the molecular features of PMS2/MLH1-deficiency and EBV infection (all P<0.001). Aneuploidy was detected in 53% of gastric carcinomas and was highly correlated with intestinal type and the least with the lymphoid type (P<0.001). Notably, lymphoid-type gastric carcinoma showed the best outcome, whereas tubular type showed the worst survival rate (P<0.001). We integrated aneuploidy with morphologic patterns to propose a morphomolecular classification scheme, which served as a successful and independent prognostic factor in multivariate 5-year disease-free survival analysis (P<0.001). Overall, we describe an integrated morphomolecular classification system for gastric carcinomas to effectively predict patient outcomes. This system is cost-effective and reliable and can help select target therapeutics and facilitate clinical management.

Genome instability in multiple myeloma

Multiple myeloma (MM) is an incurable plasma cell malignancy characterized by clonal proliferation of plasma cells and a heterogenous genomic landscape. Copy number and structural changes due to chromosomal instability (CIN) are common features of MM. In this review, we describe how primary and secondary genetic events caused by CIN can contribute to increased instability across the genome of malignant plasma cells; with a focus on specific driver genomic events, and how they interfere with cell-cycle checkpoints, to prompt accelerated proliferation. We also provide insight into other forms of CIN, such as chromothripsis and chromoplexy. We evaluate how the tumor microenvironment can contribute to a further increase in chromosomal instability in myeloma cells. Lastly, we highlight the role of certain mutational signatures in leading to high mutation rate and genome instability in certain MM patients. We suggest that assessing CIN in MM and its precursors states may help improve predicting the risk of progression to symptomatic disease and relapse and identifying future therapeutic targets.

Endocrine disruptors from the environment affecting breast cancer

Evaluation of carcinogenic substances from the environment is a challenge for scientists. Recently, a novel approach based on 10 key characteristics of human carcinogens classified by the International Agency for Research on Cancer (IARC) has emerged. Carcinogenesis depends on different mechanisms and factors, including genetic, infectious (bacteria, viruses) and environmental (chemicals) factors. Endocrine disruptors are exogenous chemicals that can interfere and impair the function of the endocrine system due to their interaction with estrogen receptors or their estrogen signaling pathways inducing adverse effects in the normal mammary development, originating cancer. They are heterogeneous chemicals and include numerous synthetic substances used worldwide in agriculture, industry and consumer products. The most common are plasticizers, such as bisphenol A (BPA), pesticides, such as dichlorodiphenyltrichloroethane, and polychlorinated biphenyls (PCBs). Xenoestrogens appear to serve an important role in the increased incidence of breast cancer in the United States and numerous other countries. Several studies have demonstrated the role of organochlorine xenoestrogens in breast cancer. Therefore, the overall cumulative exposure of women to estrogens results in an increased risk for this type of cancer. Factors like lifestyle and diet also serve a role in the increased incidence of this disease. The aim of the present study was to analyze these chemical compounds based on the key characteristics given by the IARC, with a special focus on breast cancer, to establish whether these compounds are carcinogens, and to create a model for future analysis of other endocrine disruptors.

Genomic landscape of platinum resistant and sensitive testicular cancers

While most testicular germ cell tumours (TGCTs) exhibit exquisite sensitivity to platinum chemotherapy, ~10% are platinum resistant. To gain insight into the underlying mechanisms, we undertake whole exome sequencing and copy number analysis in 40 tumours from 26 cases with platinum-resistant TGCT, and combine this with published genomic data on an additional 624 TGCTs. We integrate analyses for driver mutations, mutational burden, global, arm-level and focal copy number (CN) events, and SNV and CN signatures. Albeit preliminary and observational in nature, these analyses provide support for a possible mechanistic link between early driver mutations in RAS and KIT and the widespread copy number events by which TGCT is characterised.

RAS/MAPK signaling functions in oxidative stress, DNA damage response and cancer progression

Mitogen-activated protein kinase (MAPK) signaling pathways organize a great constitution network that regulates several physiological processes, like cell growth, differentiation, and apoptotic cell death. Due to the crucial importance of this signaling pathway, dysregulation of the MAPK signaling cascades is involved in the pathogenesis of various human cancer types. Oxidative stress and DNA damage are two important factors which in common lead to carcinogenesis through dysregulation of this signaling pathway. Reactive oxygen species (ROS) are a common subproduct of oxidative energy metabolism and are considered to be a significant physiological modulator of several intracellular signaling pathways including the MAPK pathway. Studies demonstrated that the MAP kinases extracellular signal-regulated kinase (ERK) 1/2 and p38 were activated in response to oxidative stress. In addition, DNA damage is a partly common circumstance in cell life and may result in mutation, cancer, and even cell death. Recently, accumulating evidence illustrated that the MEK/ERK pathway is associated with the suitable performance of cellular DNA damage response (DDR), the main pathway of tumor suppression. During DDR, the MEK/ERK pathway is regularly activated, which contributes to the appropriate activation of DDR checkpoints to inhibit cell division. Therefore, the aim of this review is to comprehensively discuss the critical function of MAPK signaling in oxidative stress, DNA damage, and cancer progression.

Perspective: Potential Impact and Therapeutic Implications of Oncogenic PI3K Activation on Chromosomal Instability

Genetic activation of the class I PI3K pathway is very common in cancer. This mostly results from oncogenic mutations in PIK3CA, the gene encoding the ubiquitously expressed PI3Kα catalytic subunit, or from inactivation of the PTEN tumour suppressor, a lipid phosphatase that opposes class I PI3K signalling. The clinical impact of PI3K inhibitors in solid tumours, aimed at dampening cancer-cell-intrinsic PI3K activity, has thus far been limited. Challenges include poor drug tolerance, incomplete pathway inhibition and pre-existing or inhibitor-induced resistance. The principle of pharmacologically targeting cancer-cell-intrinsic PI3K activity also assumes that all cancer-promoting effects of PI3K activation are reversible, which might not be the case. Emerging evidence suggests that genetic PI3K pathway activation can induce and/or allow cells to tolerate chromosomal instability, which-even if occurring in a low fraction of the cell population-might help to facilitate and/or drive tumour evolution. While it is clear that such genomic events cannot be reverted pharmacologically, a role for PI3K in the regulation of chromosomal instability could be exploited by using PI3K pathway inhibitors to prevent those genomic events from happening and/or reduce the pace at which they are occurring, thereby dampening cancer development or progression. Such an impact might be most effective in tumours with clonal PI3K activation and achievable at lower drug doses than the maximum-tolerated doses of PI3K inhibitors currently used in the clinic.

Copy number signatures and mutational processes in ovarian carcinoma

The genomic complexity of profound copy number aberrations has prevented effective molecular stratification of ovarian cancers. Here, to decode this complexity, we derived copy number signatures from shallow whole-genome sequencing of 117 high-grade serous ovarian cancer (HGSOC) cases, which were validated on 527 independent cases. We show that HGSOC comprises a continuum of genomes shaped by multiple mutational processes that result in known patterns of genomic aberration. Copy number signature exposures at diagnosis predict both overall survival and the probability of platinum-resistant relapse. Measurement of signature exposures provides a rational framework to choose combination treatments that target multiple mutational processes.

Copy number signatures and mutational processes in ovarian carcinoma

The genomic complexity of profound copy number aberrations has prevented effective molecular stratification of ovarian cancers. Here, to decode this complexity, we derived copy number signatures from shallow whole-genome sequencing of 117 high-grade serous ovarian cancer (HGSOC) cases, which were validated on 527 independent cases. We show that HGSOC comprises a continuum of genomes shaped by multiple mutational processes that result in known patterns of genomic aberration. Copy number signature exposures at diagnosis predict both overall survival and the probability of platinum-resistant relapse. Measurement of signature exposures provides a rational framework to choose combination treatments that target multiple mutational processes.

Copy number signatures and mutational processes in ovarian carcinoma

The genomic complexity of profound copy number aberrations has prevented effective molecular stratification of ovarian cancers. Here, to decode this complexity, we derived copy number signatures from shallow whole-genome sequencing of 117 high-grade serous ovarian cancer (HGSOC) cases, which were validated on 527 independent cases. We show that HGSOC comprises a continuum of genomes shaped by multiple mutational processes that result in known patterns of genomic aberration. Copy number signature exposures at diagnosis predict both overall survival and the probability of platinum-resistant relapse. Measurement of signature exposures provides a rational framework to choose combination treatments that target multiple mutational processes.

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

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

The E2F activators control multiple mitotic regulators and maintain genomic integrity through Sgo1 and BubR1

The E2F1, E2F2, and E2F3a transcriptional activators control proliferation. However, how the E2F activators regulate mitosis to maintain genomic integrity is unclear. Centrosome amplification (CA) and unregulated spindle assembly checkpoint (SAC) are major generators of aneuploidy and chromosome instability (CIN) in cancer. Previously, we showed that overexpression of single E2F activators induced CA and CIN in mammary epithelial cells, and here we show that combined overexpression of E2F activators did not enhance CA. Instead, the E2F activators elevated expression of multiple mitotic regulators, including Sgo1, Nek2, Hec1, BubR1, and Mps1/TTK. cBioPortal analyses of the TCGA database showed that E2F overexpression in lobular invasive breast tumors correlates with overexpression of multiple regulators of chromosome segregation, centrosome homeostasis, and the SAC. Kaplan-Meier plots identified correlations between individual or combined overexpression of E2F1, E2F3a, Mps1/TTK, Nek2, BubR1, or Hec1 and poor overall and relapse-free survival of breast cancer patients. In MCF10A normal mammary epithelial cells co-overexpressing E2Fs, transient Sgo1 knockdown induced CA, high percentages of premature sister chromatid separation, chromosome losses, increased apoptosis, and decreased cell clonogenicity. BubR1 silencing resulted in chromosome losses without CA, demonstrating that Sgo1 and BubR1 maintain genomic integrity through two distinct mechanisms. Our results suggest that deregulated activation of the E2Fs in mammary epithelial cells is counteracted by activation of a Sgo1-dependent mitotic checkpoint.

Chromosomal Instability in Gastric Cancer Biology

Gastric cancer (GC) is the fifth most common cancer in the world and accounts for 7% of the total cancer incidence. The prognosis of GC is dismal in Western countries due to late diagnosis: approximately 70% of the patients die within 5 years following initial diagnosis. Recently, integrative genomic analyses led to the proposal of a molecular classification of GC into four subtypes, i.e.,microsatellite-instable, Epstein-Barr virus–positive, chromosomal-instable (CIN), and genomically stable GCs. Molecular classification of GC advances our knowledge of the biology of GC and may have implications for diagnostics and patient treatment. Diagnosis of microsatellite-instable GC and Epstein-Barr virus–positive GC is more or less straightforward. Microsatellite instability can be tested by immunohistochemistry (MLH1, PMS2, MSH2, and MSH6) and/or molecular-biological analysis. Epstein-Barr virus–positive GC can be tested by in situ hybridization (Epstein-Barr virus encoded small RNA). However, with regard to CIN, testing may be more complicated and may require a more in-depth knowledge of the underlying mechanism leading to CIN. In addition, CIN GC may not constitute a distinct subgroup but may rather be a compilation of a more heterogeneous group of tumors. In this review, we aim to clarify the definition of CIN and to point out the molecular mechanisms leading to this molecular phenotype and the challenges faced in characterizing this type of cancer.

Reduced levels of Dusp3/Vhr phosphatase impair normal spindle bipolarity in an Erk1/2 activity-dependent manner

Dual specificity phosphatase-3 (Dusp3/Vhr) regulates cell cycle progression by counteracting the effects of mitogen-activated protein kinases (Mapk) Erk1/2 and Jnk. Despite the known upregulation of Dusp3 at M phase in mammalian cells, its mitotic functions are poorly characterized. Here, we report that loss of Dusp3 by RNAi leads to the formation of multipolar spindles in human mitotic cancer cells in an Erk1/2-dependent manner. In the phosphatase-silenced cells, the normal bipolar spindle structure was restored by chemical inhibition of Erk1/2 and ectopic overexpression of Dusp3. We propose that at M phase Dusp3 keeps Erk1/2 activity in check to facilitate normal mitosis.

Oncogenic KRAS triggers MAPK-dependent errors in mitosis and MYC-dependent sensitivity to anti-mitotic agents

Oncogenic KRAS induces cell proliferation and transformation, but little is known about its effects on cell division. Functional genetic screens have recently revealed that cancer cell lines expressing oncogenic KRAS are sensitive to interference with mitosis, but neither the mechanism nor the uniformity of anti-mitotic drug sensitivity connected with mutant KRAS expression are yet clear. Here, we report that acute expression of oncogenic KRAS in HeLa cells induces mitotic delay and defects in chromosome segregation through mitogen-activated protein kinase (MAPK) pathway activation and de-regulated expression of several mitosis-related genes. These anomalies are accompanied by increased sensitivity to anti-mitotic agents, a phenotype dependent on the transcription factor MYC and its downstream target anti-apoptotic protein BCL-XL. Unexpectedly, we find no correlation between KRAS mutational status or MYC expression levels and anti-mitotic drug sensitivity when surveying a large database of anti-cancer drug responses. However, we report that the co-existence of KRAS mutations and high MYC expression predicts anti-mitotic drug sensitivity. Our findings reveal a novel function of oncogenic KRAS in regulating accurate mitotic progression and suggest new avenues to therapeutically target KRAS-mutant tumours and stratify patients in ongoing clinical trials of anti-mitotic drugs.

Signal transduction in cancer

Cancer is driven by genetic and epigenetic alterations that allow cells to overproliferate and escape mechanisms that normally control their survival and migration. Many of these alterations map to signaling pathways that control cell growth and division, cell death, cell fate, and cell motility, and can be placed in the context of distortions of wider signaling networks that fuel cancer progression, such as changes in the tumor microenvironment, angiogenesis, and inflammation. Mutations that convert cellular proto-oncogenes to oncogenes can cause hyperactivation of these signaling pathways, whereas inactivation of tumor suppressors eliminates critical negative regulators of signaling. An examination of the PI3K-Akt and Ras-ERK pathways illustrates how such alterations dysregulate signaling in cancer and produce many of the characteristic features of tumor cells.

Role of NEK2A in human cancer and its therapeutic potentials

Chromosome instability (CIN) has been identified as a common feature of most human cancers. A number of centrosomal kinases are thought to cause CIN in cancer cells. Part of those centrosomal kinases exhibit elevated expression in a wide variety of tumours and cancer cell lines. Additionally, critical roles in many aspects of cancer cell growth, proliferation, metastasis, and drug resistance have been assigned to some of these centrosomal kinases, such as polo-like kinase 1 (PLk1) and Aurora-A kinase. Recent studies from our group and others revealed that a centrosomal kinase, Never in Mitosis (NIMA) Related Kinase 2A (NEK2A), is frequently upregulated in multiple types of human cancers. Uncontrolled activity of NEK2A activates several oncogenic pathways and ABC transporters, thereby leading to CIN, cancer cell proliferation, metastasis, and enhanced drug resistance. In this paper, we highlight recent findings on the aberrant expression and functional significance of NEK2A in human cancers and emphasize their significance for therapeutic potentials.

E2F activators signal and maintain centrosome amplification in breast cancer cells

Centrosomes ensure accurate chromosome segregation by directing spindle bipolarity. Loss of centrosome regulation results in centrosome amplification, multipolar mitosis and aneuploidy. Since centrosome amplification is common in premalignant lesions and breast tumors, it is proposed to play a central role in breast tumorigenesis, a hypothesis that remains to be tested. The coordination between the cell and centrosome cycles is of paramount importance to maintain normal centrosome numbers, and the E2Fs may be responsible for regulating these cycles. However, the role of E2F activators in centrosome amplification is unclear. Because E2Fs are deregulated in Her2(+) cells displaying centrosome amplification, we addressed whether they signal this abnormal process. Knockdown of E2F1 or E2F3 in Her2(+) cells decreased centrosome amplification without significantly affecting cell cycle progression, whereas the overexpression of E2F1, E2F2, or E2F3 increased centrosome amplification in MCF10A mammary epithelial cells. Our results revealed that E2Fs affect the expression of proteins, including Nek2 and Plk4, known to influence the cell/centrosome cycles and mitosis. Downregulation of E2F3 resulted in cell death and delays/blocks in cytokinesis, which was reversed by Nek2 overexpression. Nek2 overexpression enhanced centrosome amplification in Her2(+) breast cancer cells silenced for E2F3, revealing a role for the E2F activators in maintaining centrosome amplification in part through Nek2.

Constitutive ERK1/2 activation contributes to production of double minute chromosomes in tumour cells

Double minute chromosomes (DMs) are extrachromosomal cytogenetic structures found in tumour cells. As hallmarks of gene amplification, DMs often carry oncogenes and drug-resistance genes and play important roles in malignant tumour progression and drug resistance. The mitogen-activated protein kinase (MAPK) signalling pathway is frequently dysregulated in human malignant tumours, which induces genomic instability, but it remains unclear whether a close relationship exists between MAPK signalling and DMs. In the present study, we focused on three major components of MAPK signalling, ERK1/2, JNK1/2/3 and p38, to investigate the relationship between MAPK and DM production in tumour cells. We found that the constitutive phosphorylation of ERK1/2, but not JNK1/2/3 and p38, was closely associated with DMs in tumour cells. Inhibition of ERK1/2 activation in DM-containing and ERK1/2 constitutively phosphorylated tumour cells was able to markedly decrease the number of DMs, as well as the degree of amplification and expression of DM-carried genes. The mechanism was found to be an increasing tendency of DM DNA to break, become enveloped into micronuclei (MNs) and excluded from the tumour cells during the S/G₂ phases of the cell cycle, events that accompanied the reversion of malignant behaviour. Our study reveals a linkage between ERK1/2 activation and DM stability in tumour cells.

Synergistic effect of EMS1-shRNA and sorafenib on proliferation, migration, invasion and endocytosis of SMMC-7721

To investigate the synergistic effect of EMS1-PSilencer4.1-shRNA (EMS1-shRNA) and sorafenib on biological behaviors of HCC cell line SMMC-7721. EMS1-shRNA was constructed and transfected into SMMC-7721 cells. Decreased levels of EMS1/cortactin were tested in RT-QPCR and Western blot assay. Proliferation, migration, invasion, and endocytosis of SMMC-7721 were tested through CCK8 assay, scratch test, transwell invasion assay and transferrin endocytosis assay, respectively. Raf-1 was detected by Western blot assay. HCC xenograft model was prepared to observe tumor growth. Animals were euthanized and their subcutaneous lesions were weighed. Then the tissues were fixed and paraffin sections were prepared. Cortactin and PCNA (a proliferation marker) were then detected by immunohistochemistry. As compared with untreated group, the levels of EMS1 gene and cortactin protein in EMS1-shRNA-transfected group were significantly reduced; Among EMS1-shRNA-transfected group, sorafenib-treated group and combined group, the levels of proliferation at 48 h were reduced to 83.69, 57.18, 41.94 %; the levels of migration were reduced to 49.69, 60.83, and 21. 67 %; the levels of invasion were reduced to 42.97, 53.65, 18.18 %; the levels of endocytosis were reduced to 37.15, 97.95 % (p > 0.05), 20.68 % (p < 0.05, respectively). Western blot assay showed levels of Raf-1 were reduced to 68.56, 59.09, 21.90 %. The tumor volume and weight of nude mice HCC xenograft tumors were reduced significantly either (p < 0.05, respectively). Immunohistochemistry showed levels of cortactin and PCNA were reduced to 35.69, 93.84, 23.68 and 87.69, 43.84, 33.68 % in each group, respectively. The biological behaviors of SMMC-7721 were inhibited in the presence of EMS1-shRNA and sorafenib both alone and in combination. The combination of the agents improved the curative effect over either single agent, showing synergetic effect.

Cdk4 and nek2 signal binucleation and centrosome amplification in a her2+ breast cancer model

Centrosome amplification (CA) is a contributor to carcinogenesis, generating aneuploidy, and chromosome instability. Previous work shows that breast adenocarcinomas have a higher frequency of centrosome defects compared to normal breast tissues. Abnormal centrosome phenotypes are found in pre-malignant lesions, suggesting an early role in breast carcinogenesis. However, the role of CA in breast cancers remains elusive. Identification of pathways and regulatory molecules involved in the generation of CA is essential to understanding its role in breast tumorigenesis. We established a breast cancer model of CA using Her2-positive cells. Our goal was to identify centrosome cycle molecules that are deregulated by aberrant Her2 signaling and the mechanisms driving CA. Our results show some Her2+ breast cancer cell lines harbor both CA and binucleation. Abolishing the expression of Cdk4 abrogated both CA and binucleation in these cells. We also found the source of binucleation in these cells to be defective cytokinesis that is normalized by downregulation of Cdk4. Protein levels of Nek2 diminish upon Cdk4 knockdown and vice versa, suggesting a molecular connection between Cdk4 and Nek2. Knockdown of Nek2 reduces CA and binucleation in this model while its overexpression further enhances centrosome amplification. We conclude that CA is modulated through Cdk4 and Nek2 signaling and that binucleation is a likely source of CA in Her2+ breast cancer cells.

Myocardin related transcription factors are required for coordinated cell cycle progression

Myocardin related transcription factors A and B (MRTFs) activate serum response factor-driven transcription in response to Rho signaling and changes in actin dynamics. Myocardin and MRTFs have been implicated in anti-proliferative effects on a range of cell types. The precise mechanisms, however, remained elusive. We employed double knockdown of MRTF-A and MRTF-B in NIH 3T3 fibroblasts to evaluate its effects on cell cycle progression and proliferation. We show that transient depletion of MRTFs conveys a modest anti-proliferative effect and impinges on normal cell cycle progression, resulting in significantly shortened G 1 phase and slightly extended S and G 2 phase under normal growth conditions. Under serum-starved conditions we observed aberrant entry into the S and G 2 phases without subsequent cell division. This was accompanied by downregulation of cyclin-CDK inhibitors p27Kip1, p18Ink4c and 19Ink4d as well as upregulation of p21Waf1 and cyclin D1. Extended knockdown led to increased formation of micronuclei, while cells stably depleted of MRTFs tend to become aneuploid and polyploid. Thus, MRTFs are required for accurate cell cycle progression and maintenance of genomic stability in fibroblast cells.

Human endogenous retroviral K element encodes fusogenic activity in melanoma cells

INTRODUCTION AND HYPOTHESIS

Nuclear atypia with features of multi nuclei have been detected in human melanoma specimens. We found that the K type human endogenous retroviral element (HERV K) is expressed in such cells. Since cellular syncytia can form when cells are infected with retroviruses, we hypothesized that HERV K expressed in melanoma cells may contribute to the formation of multinuclear atypia cells in melanoma.

EXPERIMENTS AND RESULTS

We specifically inhibited HERV K expression using RNA interference (RNAi) and monoclonal antibodies and observed dramatic reduction of intercellular fusion of cultured melanoma cells. Importantly, we identified loss of heterozygosity (LOH)of D19S433 in a cell clone that survived and proliferated after cell fusion.

CONCLUSION

Our results support the notion that proteins encoded by HERV K can mediate intercellular fusion of melanoma cells, which may generate multinuclear cells and drive the evolution of genetic changes that provide growth and survival advantages.

Cancer cell micronucleus: an update on clinical and diagnostic applications

Micronucleus (MN) is the small nucleus that forms whenever a chromosome or its fragment is not incorporated into one of the daughter nuclei during cell division. Any form of genotoxic stress due to extraneous or internal factors leads to formation of a MN, which serves as an indicator of chromosomal instability. Chromosomal damage and formation of MN are believed to play a significant role in the pathogenesis of many malignancies. Studies have shown that MN assay can be used as a tool for risk prediction, screening, diagnosis, prognosis and as a treatment-response indicator in cancers. With the advancements in technology, greater details are becoming available regarding the molecular events in carcinogenesis. The micronuclei (MNi) in the cancer cells are now being used as tools to understand the pathogenetics of the malignancies. However, despite large number of studies on MNi in lymphocytes or exfoliated cells of cancer patients, the data regarding a cancer cell MN remain scarce. This review article tries to unleash some of the mysteries related to the formation of MN inside the cancer cell. Also, it discusses the possible effects and the events post MN formation in the cancer cell.

EGFR gene variants are associated with specific somatic aberrations in glioma

A number of gene variants have been associated with an increased risk of developing glioma. We hypothesized that the reported risk variants may be associated with tumor genomic instability. To explore potential correlations between germline risk variants and somatic genetic events, we analyzed matched tumor and blood samples from 95 glioma patients by means of SNP genotyping. The generated genotype data was used to calculate genome-wide allele-specific copy number profiles of the tumor samples. We compared the copy number profiles across samples and found two EGFR gene variants (rs17172430 and rs11979158) that were associated with homozygous deletion at the CDKN2A/B locus. One of the EGFR variants (rs17172430) was also associated with loss of heterozygosity at the EGFR locus. Our findings were confirmed in a separate dataset consisting of matched blood and tumor samples from 300 glioblastoma patients, compiled from publically available TCGA data. These results imply there is a functional effect of germline EGFR variants on tumor progression.

Expanding applications of chemical genetics in signal transduction

Chemical genetics represents an expanding collection of techniques applied to a variety of signaling processes. These techniques use a combination of chemical reporters and protein engineering to identify targets of a signaling enzyme in a global and non-directed manner without resorting to hypothesis-driven candidate approaches. In the last year, chemical genetics has been applied to a variety of kinases, revealing a much broader spectrum of substrates than had been appreciated. Here, we discuss recent developments in chemical genetics, including insights from our own proteomic screen for substrates of the kinase ERK2. These studies have revealed that many kinases have overlapping substrate specificity, and they often target several proteins in any particular downstream pathway. It remains to be determined whether this configuration exists to provide redundant control, or whether each target contributes a fraction of the total regulatory effect. From a general perspective, chemical genetics is applicable in principle to a broad range of posttranslational modifications (PTMs), most notably methylation and acetylation, although many challenges remain in implementing this approach. Recent developments in chemical reporters and protein engineering suggest that chemical genetics will soon be a powerful tool for mapping signal transduction through these and other PTMs.

The G1 phase Cdks regulate the centrosome cycle and mediate oncogene-dependent centrosome amplification

Because centrosome amplification generates aneuploidy and since centrosome amplification is ubiquitous in human tumors, a strong case is made for centrosome amplification being a major force in tumor biogenesis. Various evidence showing that oncogenes and altered tumor suppressors lead to centrosome amplification and aneuploidy suggests that oncogenes and altered tumor suppressors are a major source of genomic instability in tumors, and that they generate those abnormal processes to initiate and sustain tumorigenesis. We discuss how altered tumor suppressors and oncogenes utilize the cell cycle regulatory machinery to signal centrosome amplification and aneuploidy.

Mutant K-ras promotes carcinogen-induced murine colorectal tumourigenesis, but does not alter tumour chromosome stability

K-ras (KRAS) mutations are observed in around 40% of human colorectal adenomas and carcinomas. Previously, we developed and characterized a strain of transgenic mice with inducible intestinal epithelial expression of K-ras{Val12} via a Cre/LoxP system. To evaluate the influence of mutant K-ras on carcinogen-induced colorectal tumourigenesis, we induced neoplastic alterations in the large intestines of wild-type and K-ras{Val12} mice using the colon-selective carcinogen 1,2-dimethylhydrazine (DMH), which has been widely used to induce colorectal tumours that are histopathologically similar to those observed in humans. K-ras{Val12} expression significantly promoted DMH-induced colorectal tumourigenesis: the average lifespan of the mice decreased from 38.52 ± 1.97 weeks for 40 control mice to 32.42 ± 2.17 weeks for 26 K-ras{Val12} mice (mean ± SEM, p < 0.05) and the abundance of large intestinal tumours increased from 2.27 ± 0.15 per control mouse to 3.85 ± 0.20 in K-ras{Val12} mice (mean ± SEM, p < 0.01). Adenomas from DMH-treated K-ras{Val12} mice showed significantly higher proportions of Ki-67-positive proliferating cells (10.9 ± 0.69%) compared with those from DMH-treated wild-type mice (7.77 ± 0.47%) (mean ± SEM, p < 0.01) and a mild increase in apoptotic nuclei staining for cleaved caspase-3 (1.94 ± 0.21% compared with 1.15 ± 0.14%, mean ± SEM, p < 0.01). In the adenomas from DMH-treated K-ras{Val12} mice, K-ras{Val12} transgene recombination and expression were confirmed, with immunohistochemical evidence of strong Erk/MapK and mild PI3K/Akt pathway activation compared with adenomas from DMH-treated wild-type mice. Microarray hybridization and clustering analysis demonstrated different expression profiles in adenomas from DMH-treated wild-type and DMH-treated K-ras{Val12} mice, indicating involvement of different molecular mechanisms including Erk/MapK and PI3K/Akt signalling in K-ras{Val12}-expressing adenomas. Array-comparative genomic hybridization analysis showed chromosome stability in both cohorts, with only a very few tiny alterations observed in one adenoma from a DMH-treated K-ras{Val12} mouse. Taken together, these data show that mutant K-ras significantly promotes DMH-induced colorectal tumourigenesis, resulting in distinct changes in cell signalling and proliferation, but does not alter chromosome stability in the tumours.

p38α MAPK is a MTOC-associated protein regulating spindle assembly, spindle length and accurate chromosome segregation during mouse oocyte meiotic maturation

P38αMAPK (p38α) is usually activated in response to various stresses and plays a role in the inhibition of cell proliferation and tumor progression, but little is known about its roles in meiotic spindle assembly. In this study, we characterized the dynamic localization of p38α and explored its function in mouse oocyte meiotic maturation. P38α specifically colocalized with γ-tubulin and Plk1 at the center of MTOCs and spindle poles. Depletion of p38α by specific morpholino injection resulted in severely defective spindles and misaligned chromosomes probably via MK2 dephosphorylation. Notably, depletion of p38α led to significant spindle pole defects, spindle elongation, non-tethered kinetochore microtubules and increased microtubule tension. The disruption of spindle stability was coupled with decreased γ-tubulin and Plk1 at MTOCs. Overexpression of Eg5, a conserved motor protein, also caused spindle elongation and its morpholino injection almost completely rescued spindle elongation caused by p38α depletion. In addition, p38α-depletion decreased BubR1 and interfered with spindle assembly checkpoint (SAC), which resulted in aneuploid oocytes. Together, these data indicate that p38α is an important component of MTOCs, which regulates spindle assembly and spindle length, as well as stabilizes the spindle and spindle poles. Perturbed SAC and abnormal microtubule tension may be responsible for the misaligned chromosomes and high aneuploidy in p38α-depleted mouse oocytes.

The Ras oncogene signals centrosome amplification in mammary epithelial cells through cyclin D1/Cdk4 and Nek2

Centrosome amplification (CA) contributes to carcinogenesis by generating aneuploidy. Elevated frequencies of CA in most benign breast lesions and primary tumors suggest a causative role for CA in breast cancers. Clearly, identifying which and how altered signal transduction pathways contribute to CA is crucial to breast cancer control. Although a causative and cooperative role for c-Myc and Ras in mammary tumorigenesis is well documented, their ability to generate CA during mammary tumor initiation remains unexplored. To answer that question, K-Ras(G12D) and c-Myc were induced in mouse mammary glands. Although CA was observed in mammary tumors initiated by c-Myc or K-Ras(G12D), it was detected only in premalignant mammary lesions expressing K-Ras(G12D). CA, both in vivo and in vitro, was associated with increased expression of the centrosome-regulatory proteins, cyclin D1 and Nek2. Abolishing the expression of cyclin D1, Cdk4 or Nek2 in MCF10A human mammary epithelial cells expressing H-Ras(G12V) abrogated Ras-induced CA, whereas silencing cyclin E1 or B2 had no effect. Thus, we conclude that CA precedes mammary tumorigenesis, and interfering with centrosome-regulatory targets suppresses CA.

Extracellular-regulated kinase-mitogen-activated protein kinase cascade: unsolved issues

This review point out several aspects regarding the mitogen-activated protein kinase (MAPK)/extracellular-regulated kinase (Erk) network, which are still pending issues in the understanding how this pathway integrate information to drive cell fates. Focusing on the role of Erk during cell cycle, it has to be underlined that Erk downstream effectors, which are required for mitosis progression and contribute to aneuploidy during tumorigenesis, remain to be determined. In addition to the identity of the terminal enzymes or effectors of Erk, it has to be stressed that the dynamic nature of the Erk signal is itself a key factor in cell phenotype decisions. Development of biophotonics strategies for monitoring the Erk network at the spatiotemporal level in living cells, as well as computational and hypothesis-driven approaches, are called to unravel the principles by which signaling networks create biochemical and biological specificities. Finally, Erk dynamics might also be impacted by other post-translational modification than phosphorylation, such as O-GlcNAcylation.

Multipolar mitosis of tetraploid cells: inhibition by p53 and dependency on Mos

Tetraploidy can constitute a metastable intermediate between normal diploidy and oncogenic aneuploidy. Here, we show that the absence of p53 is not only permissive for the survival but also for multipolar asymmetric divisions of tetraploid cells, which lead to the generation of aneuploid cells with a near-to-diploid chromosome content. Multipolar mitoses (which reduce the tetraploid genome to a sub-tetraploid state) are more frequent when p53 is downregulated and the product of the Mos oncogene is upregulated. Mos inhibits the coalescence of supernumerary centrosomes that allow for normal bipolar mitoses of tetraploid cells. In the absence of p53, Mos knockdown prevents multipolar mitoses and exerts genome-stabilizing effects. These results elucidate the mechanisms through which asymmetric cell division drives chromosomal instability in tetraploid cells.

Cdk2 and Cdk4 regulate the centrosome cycle and are critical mediators of centrosome amplification in p53-null cells

The two mitotic centrosomes direct spindle bipolarity to maintain euploidy. Centrosome amplification-the acquisition of > or =3 centrosomes-generates multipolar mitoses, aneuploidy, and chromosome instability to promote cancer biogenesis. While much evidence suggests that Cdk2 is the major conductor of the centrosome cycle and that it mediates centrosome amplification induced by various altered tumor suppressors, the role played by Cdk4 in a normal or deregulated centrosome cycle is unknown. Using a gene knockout approach, we report that Cdk2 and Cdk4 are critical to the centrosome cycle, since centrosome separation and duplication are premature in Cdk2(-)(/)(-) mouse embryonic fibroblasts (MEFs) and are compromised in Cdk4(-)(/)(-) MEFs. Additionally, ablation of Cdk4 or Cdk2 abrogates centrosome amplification and chromosome instability in p53-null MEFs. Absence of Cdk2 or Cdk4 prevents centrosome amplification by abrogating excessive centriole duplication. Furthermore, hyperactive Cdk2 and Cdk4 deregulate the licensing of the centrosome duplication cycle in p53-null cells by hyperphosphorylating nucleophosmin (NPM) at Thr199, as evidenced by observations that ablation of Cdk2, Cdk4, or both Cdk2 and Cdk4 abrogates that excessive phosphorylation. Since a mutant form of NPM lacking the G(1) Cdk phosphorylation site (NPM(T199A)) prevents centrosome amplification to the same extent as ablation of Cdk2 or Cdk4, we conclude that the Cdk2/Cdk4/NPM pathway is a major guardian of centrosome dysfunction and genomic integrity.

Identification of a kinase profile that predicts chromosome damage induced by small molecule kinase inhibitors

Kinases are heavily pursued pharmaceutical targets because of their mechanistic role in many diseases. Small molecule kinase inhibitors (SMKIs) are a compound class that includes marketed drugs and compounds in various stages of drug development. While effective, many SMKIs have been associated with toxicity including chromosomal damage. Screening for kinase-mediated toxicity as early as possible is crucial, as is a better understanding of how off-target kinase inhibition may give rise to chromosomal damage. To that end, we employed a competitive binding assay and an analytical method to predict the toxicity of SMKIs. Specifically, we developed a model based on the binding affinity of SMKIs to a panel of kinases to predict whether a compound tests positive for chromosome damage. As training data, we used the binding affinity of 113 SMKIs against a representative subset of all kinases (290 kinases), yielding a 113x290 data matrix. Additionally, these 113 SMKIs were tested for genotoxicity in an in vitro micronucleus test (MNT). Among a variety of models from our analytical toolbox, we selected using cross-validation a combination of feature selection and pattern recognition techniques: Kolmogorov-Smirnov/T-test hybrid as a univariate filter, followed by Random Forests for feature selection and Support Vector Machines (SVM) for pattern recognition. Feature selection identified 21 kinases predictive of MNT. Using the corresponding binding affinities, the SVM could accurately predict MNT results with 85% accuracy (68% sensitivity, 91% specificity). This indicates that kinase inhibition profiles are predictive of SMKI genotoxicity. While in vitro testing is required for regulatory review, our analysis identified a fast and cost-efficient method for screening out compounds earlier in drug development. Equally important, by identifying a panel of kinases predictive of genotoxicity, we provide medicinal chemists a set of kinases to avoid when designing compounds, thereby providing a basis for rational drug design away from genotoxicity.

Endogenous expression of Hras(G12V) induces developmental defects and neoplasms with copy number imbalances of the oncogene

We developed mice with germline endogenous expression of oncogenic Hras to study effects on development and mechanisms of tumor initiation. They had high perinatal mortality, abnormal cranial dimensions, defective dental ameloblasts, and nasal septal deviation, consistent with some of the features of human Costello syndrome. These mice developed papillomas and angiosarcomas, which were associated with Hras(G12V) allelic imbalance and augmented Hras signaling. Endogenous expression of Hras(G12V) was also associated with a higher mutation rate in vivo. Tumor initiation by Hras(G12V) likely requires augmentation of signal output, which in papillomas and angiosarcomas is achieved via increased Hras-gene copy number, which may be favored by a higher mutation frequency in cells expressing the oncoprotein.

Raf kinase inhibitor protein: mechanism of loss of expression and association with genomic instability

Aims:

Raf kinase inhibitory protein (RKIP; also known as PEBP, for phosphatidylethanolamine-binding protein) is an endogenous inhibitor of the Raf– MAPK kinase (MEK)–MAP kinase pathway. It has emerged as a significant metastasis suppressor in a variety of human cancers including colorectal cancer (CRC) and was recently shown to regulate the spindle checkpoint in cultured cells. This study aims at correlating RKIP expression with chromosomal instability in colorectal cancer samples and identifies possible mechanisms of RKIP loss.

Methods:

Chromosomal instability was assessed using metaphase-based comparative genomic hybridisation (CGH) and loss of heterozygosity (LOH) in 65 cases with microsatellite stable CRC and correlated with RKIP expression. Methyl-specific PCR was used on DNA extracted from 82 cases with CRC to determine CpG methylation status at the RKIP promoter and the results correlated with RKIP protein expression.

Results:

We demonstrate for the first time that in microsatellite stable (MSS) CRC, the number of chromosomal losses is inversely proportional to RKIP expression levels. We also show that methylation of the RKIP promoter is a major mechanism by which RKIP expression is silenced in CRC.

Conclusions:

RKIP loss by hypermethylation of its promoter could have a significant influence on colorectal cancer aneuploidy, which might explain its association with metastatic progression.

Role of extracellular signal-regulated kinase (ERK) signaling in nucleotide excision repair and genotoxicity in response to As(III) and Pb(II)

Arsenic and lead can induce genetic injuries and epigenetic signaling pathways in cultured mammalian cells. To test whether signaling pathways affect the extent of genetic injuries, we explored the impacts of extracellular signal-regulated kinase 1 and 2 (ERK) on nucleotide excision repair (NER), cytotoxicity, and genotoxicity following sodium arsenite [As(III)] and lead acetate [Pb(II)]. Sustained ERK activation was observed in human cells exposed to As(III) and Pb(II). As(III) inhibited the cellular NER synthesis capability; conversely, Pb(II) stimulated it. ERK activation contributed to the As(III)-induced NER inhibition and micronucleus formation. In contrast, this signal was required for inducing cellular NER activity and preventing mutagenesis following Pb(II). ERK activation by Pb(II) was dependent on protein kinase C (PKCα) that also exhibited anti-mutagenicity. Enforced expression of ERK signaling markedly elevated the cellular NER activity, which was suppressed by As(III). Nonetheless, ERK activation could counteract the cytotoxicity caused by these two metals. Together, the results indicate that pro-survival ERK signaling exhibits dual and opposing impacts on NER process following As(III) and Pb(II) exposures. The findings also suggest that ERK is an important epigenetic signaling in the determination of metal genotoxicity.

The G2 p38-mediated stress-activated checkpoint pathway becomes attenuated in transformed cells

When human cells are stressed during G2, they are delayed from entering mitosis via a checkpoint mediated by the p38 kinase, and this delay can be modeled by the selective activation of p38 with anisomycin. Here, we report, on the basis of live-cell studies, that 75 nM anisomycin transiently (1 hr) activates p38 which, in turn, rapidly and completely blocks entry into mitosis for at least 4 hr in all primary, telomerase- or spontaneously immortalized (p53+ and pRB+) human cells. However, the same treatment does not delay entry into mitosis in cancer cells, or the delay in entering mitosis is shortened, even though it induces a similar transient and comparable (or stronger) activation of p38. Because the primary substrate of p38, the MK2 kinase, is also transiently (1-2 hr) activated by anisomycin in both normal and cancer cells, checkpoint disruption in transformed cells occurs downstream of MK2. Finally, observations on isogenic lines reveal that the duration of the stress checkpoint is shortened in cells lacking both p53 and pRb and that the constitutive expression of an active H-Ras oncogene in these cells further attenuates the checkpoint via an ERK1/2-dependent manner. Thus, transformation leads to attenuation of the p38-mediated stress checkpoint. This outcome is likely selected for during transformation because it confers the ability to outgrow normal cells under stressful in vitro (culture) or in vivo (tumor) environments. Our data caution against using cancer cells to study how p38 produces a G2 arrest.

Overexpression of Eg5 causes genomic instability and tumor formation in mice

Proper chromosome segregation in eukaryotes is driven by a complex superstructure called the mitotic spindle. Assembly, maintenance, and function of the spindle depend on centrosome migration, organization of microtubule arrays, and force generation by microtubule motors. Spindle pole migration and elongation are controlled by the unique balance of forces generated by antagonistic molecular motors that act upon microtubules of the mitotic spindle. Defects in components of this complex structure have been shown to lead to chromosome missegregation and genomic instability. Here, we show that overexpression of Eg5, a member of the Bim-C class of kinesin-related proteins, leads to disruption of normal spindle development, as we observe both monopolar and multipolar spindles in Eg5 transgenic mice. Our findings show that perturbation of the mitotic spindle leads to chromosomal missegregation and the accumulation of tetraploid cells. Aging of these mice revealed a higher incidence of tumor formation with a mixed array of tumor types appearing in mice ages 3 to 30 months with the mean age of 20 months. Analysis of the tumors revealed widespread aneuploidy and genetic instability, both hallmarks of nearly all solid tumors. Together with previous findings, our results indicate that Eg5 overexpression disrupts the unique balance of forces associated with normal spindle assembly and function, and thereby leads to the development of spindle defects, genetic instability, and tumors.

Spindle assembly checkpoint and centrosome abnormalities in oral cancer

Like many solid tumours, oral squamous cell carcinomas (OSCC) invariably exhibit chromosomal instability (CIN) leading to aneuploidy. The mechanisms responsible for CIN in OSCC, however, are largely unknown. This study examined the fidelity of the spindle checkpoint, together with the number, structure and function of centrosomes in a series of well-characterised aneuploid immortal OSCC-derived cell lines that harbour p53 and p16(INK4A) defects. The spindle checkpoints were fully functional in 2 of 7 cell lines and attenuated in the remaining 5 cell lines. Overexpression of the spindle checkpoint protein, Cdc20, was observed in 2 of the cell lines with attenuated checkpoints. Defects in centrosome number, size and localisation were detected in 5 of the cell lines. Clonal cell populations contained cells with both normal and abnormal numbers of centrosomes, suggesting that the control of centrosome number may be inherently unstable in OSCC-derived cell lines. Centrosomal abnormalities were then examined in tissue samples of oral epithelial dysplasias and carcinomas. Abnormal centrosomes were detected in all the tissues examined albeit in a low percentage of cells (<1% to >5%). The percentage of cells containing centrosome abnormalities was significantly higher in the carcinomas than in the dysplasias (p<0.02) and in the poorly differentiated SCCs relative to their moderately differentiated (p<0.04) and well-differentiated (p<0.01) counterparts. We suggest that the genetic alterations associated with the development of the immortal phenotype, together with spindle checkpoint and centrosome defects, are responsible, albeit in part, for the complex karyotypes observed in OSCC. The presence of centrosome abnormalities in oral dysplasias raises the possibility that such defects might contribute to malignant progression.

Repression of sestrin family genes contributes to oncogenic Ras-induced reactive oxygen species up-regulation and genetic instability

Oncogenic mutations within RAS genes and inactivation of p53 are the most common events in cancer. Earlier, we reported that activated Ras contributes to chromosome instability, especially in p53-deficient cells. Here we show that an increase in intracellular reactive oxygen species (ROS) and oxidative DNA damage represents a major mechanism of Ras-induced mutagenesis. Introduction of oncogenic H- or N-Ras caused elevated intracellular ROS, accumulation of 8-oxo-2'-deoxyguanosine, and increased number of chromosome breaks in mitotic cells, which were prevented by antioxidant N-acetyl-L-cysteine. By using Ras mutants that selectively activate either of the three major targets of Ras (Raf, RalGDS, and phosphatidylinositol-3-kinase) as well as dominant-negative Rac1 and RalA mutants and inhibitors of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinases kinase-1 and p38 MAPKs, we have shown that several Ras effectors independently mediate ROS up-regulation. Introduction of oncogenic RAS resulted in repression of transcription from sestrin family genes SESN1 and SESN3, which encode antioxidant modulators of peroxiredoxins. Inhibition of mRNAs from these genes in control cells by RNA interference substantially increased ROS levels and mutagenesis. Ectopic expression of SESN1 and SESN3 from lentiviral constructs interfered with Ras-induced ROS increase, suggesting their important contribution to the effect. The stability of Ras-induced increase in ROS was dependent on a p53 function: in the p53-positive cells displaying activation of p53 in response to Ras, only transient (4-7 days) elevation of ROS was observed, whereas in the p53-deficient cells the up-regulation was permanent. The reversion to normal ROS levels in the Ras-expressing p53-positive cells correlated with up-regulation of p53-responsive genes, including reactivation of SESN1 gene. Thus, changes in expression of sestrins can represent an important determinant of genetic instability in neoplastic cells showing simultaneous dysfunctions of Ras and p53.

Unscheduled overexpression of human WAPL promotes chromosomal instability

Previously, we have isolated and characterized a novel human gene termed human WAPL that has the characteristics of an oncogene in uterine cervical cancer. WAPL is inducible by human papillomavirus (HPV) E6 and E7 oncoproteins. On the other hand, recent studies have revealed that WAPL regulates sister chromatid resolution by controlling the association of cohesin and chromatin. However, the effects of WAPL overexpression on cervical carcinogenesis are still unclear. Here, we show that WAPL overexpression induces generation of multinucleated cells. In addition, WAPL-overexpressing cells demonstrated increases in chromatid breaks in comparison with control cells. These results were obtained even in HPV-negative cell lines. High frequent premature sister separation by disregulation of cohesin may lead to these results. Thus, our study suggests that unscheduled overexpression of WAPL disturbs mitosis and cytokinesis, and contributes to tumor progression by induction of chromosomal instability (CIN).