Association of MAD2 expression with mitotic checkpoint competence in hepatoma cells

Spindle assembly checkpoint competence in aneuploid canine malignant melanoma cell lines

The spindle assembly checkpoint (SAC) is a surveillance mechanism that prevents unequal segregation of chromosomes during mitosis. Abnormalities in the SAC are associated with chromosome instability and resultant aneuploidy. This study was performed to evaluate the SAC competence in canine malignant melanoma (CMM) using four aneuploid cell lines (CMeC1, CMeC2, KMeC, and LMeC). After treatment with nocodazole, a microtubule disrupting agent, CMeC1, KMeC, and LMeC cells were arrested in M phase, whereas CMeC2 cells were not arrested, and progressed into the next cell cycle phase without cytokinesis. Chromosome spread analysis revealed a significantly increased rate of premature sister chromatid separation in CMeC2 cells. Expression of the phosphorylated form of the SAC regulator, monopolar spindle 1 (Mps1), was lower in CMeC2 cells than in the other CMM cell lines. These results indicate that the SAC is defective in CMeC2 cells, which may partially explain aneuploidy in CMM. Thus, CMeC2 cells may be useful for further studies of the SAC mechanism in CMM and in determining the relationship between SAC incompetence and aneuploidy.

Defective mitosis-linked DNA damage response and chromosomal instability in liver cancer

Hepatocellular carcinoma (HCC), the most common form of liver cancer, represents a health problem in hepatic viruses-eradicating era because obesity, type 2 diabetes, and nonalcoholic steatohepatitis (NASH) are considered emerging pathogenic factors. Metabolic disorders underpin mitotic errors that lead to numerical and structural chromosome aberrations in a significant proportion of cell divisions. Here, we review that genomically unstable HCCs show evidence for a paradoxically DNA damage response (DDR) which leads to ongoing chromosome segregation errors. The understanding of DDR induced by defective mitoses is crucial to our ability to develop or improve liver cancer therapeutic strategies.

Examining the key genes and pathways in hepatocellular carcinoma development from hepatitis B virus‑positive cirrhosis

To identify the key genes and pathways in the development of hepatocellular carcinoma (HCC) from hepatitis B virus (HBV)-positive liver cirrhosis, differentially expressed genes (DEGs) between HCC and liver cirrhosis tissue samples from the GSE17548 gene expression profile dataset were screened. A total of 1,845 DEGs were identified, including 1,803 upregulated and 42 downregulated genes. Gene Ontology, Kyoto Encyclopedia of Genes and Genomes (KEGG) and protein-protein interaction (PPI) network analyses were performed. It was identified that the ‘cell cycle’ and ‘progesterone-mediated oocyte maturation’ KEGG pathways were significantly enriched in the DEGs. In addition, the high expression of the hub genes from the PPI network (including cyclin dependent kinase 1, cyclin B1, cyclin B2, mitotic arrest deficient 2 like 1, BUB1 mitotic checkpoint serine/threonine kinase and cyclin A2; P=0.00116, 0.00021, 0.04889, 0.00222, 0.00015 and 0.00647, respectively) was associated with a decrease in overall survival for patients with HCC as identified using survival and expression data from The Cancer Genome Atlas. The identified hub genes and pathways may help to elucidate the molecular mechanisms of HCC progression from HBV-positive liver cirrhosis. Additionally, they may be useful as therapeutic targets or serve as novel biomarkers for HCC prognosis prediction.

Induction of Chromosome Instability by Activation of Yes-Associated Protein and Forkhead Box M1 in Liver Cancer

BACKGROUND & AIMS

Many different types of cancer cells have chromosome instability. The hippo pathway leads to phosphorylation of the transcriptional activator yes-associated protein 1 (YAP1, YAP), which regulates proliferation and has been associated with the development of liver cancer. We investigated the effects of hippo signaling via YAP on chromosome stability and hepatocarcinogenesis in humans and mice.

METHODS

We analyzed transcriptome data from 242 patients with hepatocellular carcinoma (HCC) to search for gene signatures associated with chromosomal instability (CIN); we investigated associations with overall survival time and cancer recurrence using Kaplan-Meier curves. We analyzed changes in expression of these signature genes, at mRNA and protein levels, after small interfering RNA-mediated silencing of YAP in Sk-Hep1, SNU182, HepG2, or pancreatic cancer cells, as well as incubation with thiostrepton (an inhibitor of forkhead box M1 [FOXM1]) or verteporfin (inhibitor of the interaction between YAP and TEA domain transcription factor 4 [TEAD4]). We performed co-immunoprecipitation and chromatin immunoprecipitation experiments. We collected liver tissues from mice that express a constitutively active form of YAP (YAP^S127A) and analyzed gene expression signatures and histomorphologic parameters associated with chromosomal instability. Mice were given injections of thiostrepton and livers were collected and analyzed by immunoblotting, immunohistochemistry, histology, and real-time polymerase chain reaction. We performed immunohistochemical analyses on tissue microarrays of 105 HCCs and 7 nontumor liver tissues.

RESULTS

Gene expression patterns associated with chromosome instability, called CIN25 and CIN70, were detected in HCCs from patients with shorter survival time or early cancer recurrence. TEAD4 and YAP were required for CIN25 and CIN70 signature expression via induction and binding of FOXM1. Disrupting the interaction between YAP and TEAD4 with verteporfin, or inhibiting FOXM1 with thiostrepton, reduced the chromosome instability gene expression patterns. Hyperplastic livers and tumors from YAP^S127A mice had increased CIN25 and CIN70 gene expression patterns, aneuploidy, and defects in mitosis. Injection of YAP^S127A mice with thiostrepton reduced liver overgrowth and signs of chromosomal instability. In human HCC tissues, high levels of nuclear YAP correlated with increased chromosome instability gene expression patterns and aneuploidy.

CONCLUSIONS

By analyzing cell lines, genetically modified mice, and HCC tissues, we found that YAP cooperates with FOXM1 to contribute to chromosome instability. Agents that disrupt this pathway might be developed as treatments for liver cancer. Transcriptome data are available in the Gene Expression Omnibus public database (accession numbers: GSE32597 and GSE73396).

Proline-rich acidic protein 1 (PRAP1) is a novel interacting partner of MAD1 and has a suppressive role in mitotic checkpoint signalling in hepatocellular carcinoma

Loss of mitotic checkpoint of cells contributes to chromosomal instability and leads to carcinogenesis. Mitotic arrest deficient 1 (MAD1) is a key component in mitotic checkpoint signalling. In this study, we identified a novel MAD1 interacting partner, proline-rich acidic protein 1 (PRAP1), using yeast-two hybrid screening, and investigated its role in mitotic checkpoint signalling in hepatocellular carcinoma (HCC). We demonstrated the physical interaction of PRAP1 with MAD1 and of PRAP1 with MAD1 isoform MAD1β, using a co-immunoprecipitation assay. Moreover, stable expression of PRAP1 in mitotic checkpoint-competent HCC cells, BEL-7402 and SMMC-7721, induced impairment of the mitotic checkpoint (p < 0.01), formation of chromosome bridges (p < 0.01) and aberrant chromosome numbers (p < 0.001). Interestingly, ectopic expression PRAP1 in HCC cells led to significant under-expression of MAD1. In human HCC tumours, 40.4% (23/57) of HCCs showed under-expression of PRAP1 protein as compared with their corresponding non-tumorous livers; up-regulation of MAD1 protein was significantly associated with down-regulation of PRAP1 (p = 0.030). Our data revealed that PRAP1 is a protein interacting partner of MAD1 and that PRAP1 is able to down-regulate MAD1 and suppress mitotic checkpoint signalling in HCC.

Genetic instability: tipping the balance

Tumor cells typically contain a genome that is highly divergent from the genome of normal, non-transformed cells. This genetic divergence is caused by a number of distinct changes that the tumor cell acquires during its transformation from a normal cell into a tumorigenic counterpart. Changes to the genome include mutations, deletions, insertions, and also gross chromosomal aberrations, such as chromosome translocations and whole chromosome gains or losses. This genetic disorder of the tumor cell has complicated the identification of crucial driver mutations that cause cancer. Moreover, the large genetic divergence between different tumors causes them to behave very differently, and makes it difficult to predict response to therapy. In addition, tumor cells are genetically unstable and frequently acquire new mutations and/or gross chromosomal aberrations as they divide. This is beneficial for the overall capacity of a tumor to adapt to changes in its environment, but newly acquired genetic alterations can also compromise the genetic dominance of the tumor cell and thus affect tumor cell viability. Here, we review the mechanisms that can cause gross chromosomal aberrations, and discuss how these affect tumor cell viability.

Let's huddle to prevent a muddle: centrosome declustering as an attractive anticancer strategy

Nearly a century ago, cell biologists postulated that the chromosomal aberrations blighting cancer cells might be caused by a mysterious organelle-the centrosome-that had only just been discovered. For years, however, this enigmatic structure was neglected in oncologic investigations and has only recently reemerged as a key suspect in tumorigenesis. A majority of cancer cells, unlike healthy cells, possess an amplified centrosome complement, which they manage to coalesce neatly at two spindle poles during mitosis. This clustering mechanism permits the cell to form a pseudo-bipolar mitotic spindle for segregation of sister chromatids. On rare occasions this mechanism fails, resulting in declustered centrosomes and the assembly of a multipolar spindle. Spindle multipolarity consigns the cell to an almost certain fate of mitotic arrest or death. The catastrophic nature of multipolarity has attracted efforts to develop drugs that can induce declustering in cancer cells. Such chemotherapeutics would theoretically spare healthy cells, whose normal centrosome complement should preclude multipolar spindle formation. In search of the 'Holy Grail' of nontoxic, cancer cell-selective, and superiorly efficacious chemotherapy, research is underway to elucidate the underpinnings of centrosome clustering mechanisms. Here, we detail the progress made towards that end, highlighting seminal work and suggesting directions for future research, aimed at demystifying this riddling cellular tactic and exploiting it for chemotherapeutic purposes. We also propose a model to highlight the integral role of microtubule dynamicity and the delicate balance of forces on which cancer cells rely for effective centrosome clustering. Finally, we provide insights regarding how perturbation of this balance may pave an inroad for inducing lethal centrosome dispersal and death selectively in cancer cells.

Gene profiling of early and advanced liver disease in chronic hepatitis C patients

PURPOSE

Strong impact of hepatitis C virus (HCV) on normal regulation of cellular processes has been reported that could have significant implications for HCV pathogenesis. We aimed to determine the altered cellular processes during HCV infection with particular reference to advanced disease stages.

METHODS

Liver biopsy specimens of chronic hepatitis C patients classified on histological basis as early (fibrosis stage 1-2) or advanced (fibrosis stage 3-4) HCV disease were studied using microarray technology (Affymetrix GeneChip™ System). For comparison, liver specimens from patients with non-viral hepatitis (NV-hepatitis) were also analyzed by microarray. Expression data generated were analyzed using software Genespring GX and Ingenuity Pathway analysis to find the association with biological functions. We further validated the microarray results using quantitative reverse transcriptase-polymerase chain reaction.

RESULTS

Data analysis through Genespring software revealed that in advanced HCV (A-HCV) a total of 792 genes are differentially expressed when compared to early HCV (E-HCV) and 417 genes are differentially expressed when compared to NV-hepatitis. Most of these genes are involved in cancer, cellular growth and proliferation, and tissue morphology. Real time (RT) PCR analysis confirmed the differential expression of six of these genes.

CONCLUSION

The results of this study reflect the changes taking place during the transition from early to advanced liver fibrosis, when the liver function becomes impaired and extracellular matrix deposition increases. In addition, it showed altered expression of genes with functions in cancer development, cell growth, proliferation, and cell death that might indicate high risk of cell transformation and hepatocellular carcinoma (HCC) in A-HCV disease patients.

Mitotic chromosomal instability and cancer: mouse modelling of the human disease

The stepwise progression from an early dysplastic lesion to full-blown metastatic malignancy is associated with increases in genomic instability. Mitotic chromosomal instability - the inability to faithfully segregate equal chromosome complements to two daughter cells during mitosis - is a widespread phenomenon in solid tumours that is thought to serve as the fuel for tumorigenic progression. How chromosome instability (CIN) arises in tumours and what consequences it has are still, however, hotly debated issues. Here we review the recent literature with an emphasis on models that recapitulate observations from human disease.

BUB3 that dissociates from BUB1 activates caspase-independent mitotic death (CIMD)

The cell death mechanism that prevents aneuploidy caused by a failure of the spindle checkpoint has recently emerged as an important regulatory paradigm. We previously identified a new type of mitotic cell death, termed caspase-independent mitotic death (CIMD), which is induced during early mitosis by partial BUB1 (a spindle checkpoint protein) depletion and defects in kinetochore-microtubule attachment. In this study, we have shown that survived cells that escape CIMD have abnormal nuclei, and we have determined the molecular mechanism by which BUB1 depletion activates CIMD. The BUB3 protein (a BUB1 interactor and a spindle checkpoint protein) interacts with p73 (a homolog of p53), specifically in cells wherein CIMD occurs. The BUB3 protein that is freed from BUB1 associates with p73 on which Y99 is phosphorylated by c-Abl tyrosine kinase, resulting in the activation of CIMD. These results strongly support the hypothesis that CIMD is the cell death mechanism protecting cells from aneuploidy by inducing the death of cells prone to substantial chromosome missegregation.

Reduced expression of cenp-e in human hepatocellular carcinoma

Background

CENP-E, one of spindle checkpoint proteins, plays a crucial role in the function of spindle checkpoint. Once CENP-E expression was interrupted, the chromosomes can not separate procedurally, and may result in aneuploidy which is a hallmark of most solid cancers, such as hepatocellular carcinoma (HCC). We investigate the expression of CENP-E in human hepatocellular carcinoma,. and analyze the effect of low CENP-E expression on chromosome separation in normal liver cell line (LO2).

Methods

We determined its levels in HCC and para-cancerous tissues, human hepatocellular carcinoma-derived cell line (HepG2) and LO2 cell line using real time quantitative PCR (QPCR) and Western blot. Further to know whether reduction in CENP-E expression impairs chromosomes separation in LO2 cells. we knocked down CENP-E using shRNA expressing vector and then count the aneuploid in LO2 cells using chromosomal counts assay.

Results

We found that both CENP-E mRNA and protein levels were significantly reduced in HCC tissues and HepG2 cells compared with para-cancerous tissues and LO2 cells, respectively. A significantly-increased proportion of aneuploid in these down-knocked LO2 cells compared with those treated with control shRNA vector.

Conclusions

Together with other results, these results reveal that CENP-E expression was reduced in human HCC tissue, and low CENP-E expression result in aneuploidy in LO2 cells.

Role of a novel splice variant of mitotic arrest deficient 1 (MAD1), MAD1beta, in mitotic checkpoint control in liver cancer

Loss of mitotic checkpoint contributes to chromosomal instability, leading to carcinogenesis. In this study, we identified a novel splicing variant of mitotic arrest deficient 1 (MAD1), designated MAD1beta, and investigated its role in mitotic checkpoint control in hepatocellular carcinoma (HCC). The expression levels of human MAD1beta were examined in hepatoma cell lines and human HCC samples. The functional roles of MAD1beta in relation to the mitotic checkpoint control, chromosomal instability, and binding with MAD2 were assessed in hepatoma cell lines. On sequencing, MAD1beta was found to have deletion of exon 4. It was expressed at both mRNA and protein levels in the nine hepatoma cell lines tested and was overexpressed in 12 of 50 (24%) human HCCs. MAD1beta localized in the cytoplasm, whereas MAD1alpha was found in the nucleus. This cytoplasmic localization of MAD1beta was due to the absence of a nuclear localization signal in MAD1alpha. In addition, MAD1beta was found to physically interact with MAD2 and sequester it in the cytoplasm. Furthermore, expression of MAD1beta induced mitotic checkpoint impairment, chromosome bridge formation, and aberrant chromosome numbers via binding with MAD2. Our data suggest that the novel splicing variant MAD1beta may have functions different from those of MAD1alpha and may play opposing roles to MAD1alpha in mitotic checkpoint control in hepatocarcinogenesis.

Clinicopathologic significance of mitotic arrest defective protein 2 overexpression in hepatocellular carcinoma

Mitotic arrest defective protein 2 (MAD2) gene plays a central role in the mitotic checkpoint. Elevated MAD2 expression was observed in a number of human malignancies; its role in the development of hepatocellular carcinoma is still not understood and is controversial. The purpose of this study was to investigate the clinicopathologic significance of MAD2 expression in hepatocellular carcinoma. The MAD2 protein and its messenger RNA levels were measured in hepatocellular carcinomas, high-grade dysplastic nodules, and their paired nontumorous liver tissues by quantitative real-time polymerase chain reaction, Western blot, and immunohistochemistry. The results showed that MAD2 at both messenger RNA and protein levels was overexpressed in 8 of 9 high-grade dysplastic nodules and in 51 of 58 hepatocellular carcinomas, including 12 of 14 unifocal small hepatocellular carcinomas. There was a tendency for MAD2 expression to increase in the process of this multistep carcinogenesis. A significantly high tumor MAD2 immunostaining was associated with the progression of histologic grade and the overall low survival. In conclusion, MAD2 is overexpressed frequently in hepatocellular carcinoma, including high-grade dysplastic nodules and early-stage small hepatocellular carcinoma, indicating that overexpression of MAD2 plays a role in the development and progression of hepatocellular carcinoma. It may be an early event in hepatocarcinogenesis and could be used as a potential prognostic indicator.

Mitotic checkpoint gene MAD1 in hepatocellular carcinoma is associated with tumor recurrence after surgical resection

OBJECTIVE

Underlying mechanism of mitotic checkpoint gene mitosis arrest deficiency 1 (MAD1) in human hepatocellular carcinoma (HCC) is rarely known.

MATERIALS AND METHODS

We studied genetic change of the MAD1 gene as well as protein expression in 44 HCC and their associated non-cancerous surrounding liver tissues.

RESULTS

Genotype AG of MAD1 G-1849 A promoter was highly significant in microscopic vascular invasion than other genotypes (P = 0.006). Moreover, the mean tumor size of HCC with genotype AG (7.71 cm) was significantly larger than those of other genotypes (AA, 4.41 cm; GG, 4.59 cm; P = 0.033). After a median follow-up of 22 months, 18 (41%) of the 44 patients relapsed. Eleven (32.4%) of 34 with MAD1 protein expression and 7 (70%) of 10 with no expression of MAD1 protein showed tumor recurrence. The incidence of tumor recurrence in patients with the lost MAD1 expression was significantly higher than in those with the expressed MAD1 protein (P = 0.011).

CONCLUSION

These results suggest that MAD1 promoter genotype may be involved in tumor progression. Moreover, the loss of MAD1 protein expression may be related to the tumor recurrence after surgical resection of HCC.

Preventing aneuploidy: the contribution of mitotic checkpoint proteins

Aneuploidy, an abnormal number of chromosomes, is a trait shared by most solid tumors. Chromosomal instability (CIN) manifested as aneuploidy might promote tumorigenesis and cause increased resistance to anti-cancer therapies. The mitotic checkpoint or spindle assembly checkpoint is a major signaling pathway involved in the prevention of CIN. We review current knowledge on the contribution of misregulation of mitotic checkpoint proteins to tumor formation and will address to what extent this contribution is due to chromosome segregation errors directly. We propose that both checkpoint and non-checkpoint functions of these proteins contribute to the wide array of oncogenic phenotypes seen upon their misregulation.

Human T-cell leukemia virus type 1 Tax and cellular transformation

Infection of T-cells by human T-cell leukemia virus type 1 (HTLV-1) causes a lymphoproliferative malignancy known as adult T-cell leukemia (ATL). ATL is characterized by abnormal lymphocytes, called flower cells, which have cleaved and convoluted nuclei. Tax, encoded by the HTLV-1 pX region, is a critical nonstructural protein that plays a central role in leukemogenesis; however, the mechanisms of HTLV-1 oncogenesis have not been clarified fully. In this review, we summarize current thinking on how Tax may affect ATL leukemogenesis.

MAD2 expression and its significance in mitotic checkpoint control in testicular germ cell tumour

Chromosomal instability (CIN) is a common characteristic in testicular germ cell tumour (TGCT). A functional mitotic checkpoint control is important for accurate chromosome segregation during mitosis. Mitotic arrest deficient 2 (MAD2) is a key component of this checkpoint and inactivation of MAD2 is correlated with checkpoint impairment. The aim of this study was to investigate the function of mitotic checkpoint control in TGCT cells and to study its association with MAD2 expression using 8 TGCT cell lines as well as 23 TGCT tissue samples. We found that in response to microtubule disruption, 6 of 8 TGCT cell lines (75%) failed to arrest in mitosis demonstrated by the decreased mitotic index and aberrant expression of mitosis regulators, indicating that mitotic checkpoint defect is a common event in TGCT cells. This loss of mitotic checkpoint control was correlated with reduced MAD2 protein expression in TGCT cell lines implicating that downregulation of MAD2 may play a critical role in an impaired mitotic checkpoint control in these cells. In addition, immunohistochemistry studies on 23 seminomas and 12 normal testis tissues demonstrated that nuclear expression of MAD2 was much lower in seminomas (p<0.0001) but cytoplasmic MAD2 expression was higher in seminomas (p=0.06) than normal samples. Our results suggest that aberrant MAD2 expression may play an essential role in a defective mitotic checkpoint in TGCT cells, which may contribute to CIN commonly observed in TGCT tumours.

Heterozygous deletion of mitotic arrest-deficient protein 1 (MAD1) increases the incidence of tumors in mice

Mitotic arrest-deficient protein 1 (MAD1) is a component of the mitotic spindle assembly checkpoint. We have created a knockout mouse model to examine the physiologic consequence of reduced MAD1 function. Mad1(+/-) mice were successfully generated, but repeated paired mating of Mad1(+/-) with Mad1(+/-) mice failed to produce a single Mad1(-/-) animal, suggesting that the latter genotype is embryonic lethal. In aging studies conducted for >18 months, Mad1(+/-) mice compared with control wild-type (wt) littermates showed a 2-fold higher incidence of constitutive tumors. Moreover, 42% of Mad1(+/-) (P < 0.03), but 0% of wt, mice developed neoplasia after treatment with vincristine, a microtubule depolymerization agent. Mad1(+/-) mouse embryonic fibroblasts (MEF) were found to be more prone than wt cells to become aneuploid; Mad1(+/-), but not wt, MEFs produced fibrosarcomas when explanted into nude mice. Our results indicate an essential MAD1 function in mouse development and correlate Mad1 haploinsufficiency with increased constitutive tumors.

Does aneuploidy cause cancer?

Aneuploidy has been recognized as a common characteristic of cancer cells for >100 years. Aneuploidy frequently results from errors of the mitotic checkpoint, the major cell cycle control mechanism that acts to prevent chromosome missegregation. The mitotic checkpoint is often compromised in human tumors, although not as a result of germline mutations in genes encoding checkpoint proteins. Less obviously, aneuploidy of whole chromosomes rapidly results from mutations in genes encoding several tumor suppressors and DNA mismatch repair proteins, suggesting cooperation between mechanisms of tumorigenesis that were previously thought to act independently. Cumulatively, the current evidence suggests that aneuploidy promotes tumorigenesis, at least at low frequency, but a definitive test has not yet been reported.