BubR1 as a prognostic marker for recurrence-free survival rates in epithelial ovarian cancers

The insulin receptor endocytosis

Insulin signaling controls multiple aspects of animal physiology. At the cell surface, insulin binds and activates the insulin receptor (IR), a receptor tyrosine kinase. Insulin promotes a large conformational change of IR and stabilizes the active conformation. The insulin-activated IR triggers signaling cascades, thus controlling metabolism, growth, and proliferation. The activated IR undergoes internalization by clathrin- or caveolae-mediated endocytosis. The IR endocytosis plays important roles in insulin clearance from blood, and distribution and termination of the insulin signaling. Despite decades of extensive studies, the mechanism and regulation of IR endocytosis and its contribution to pathophysiology remain incompletely understood. Here we discuss recent findings that provide insights into the molecular mechanisms and regulatory pathways that mediate the IR endocytosis.

Identification of key molecular markers in epithelial ovarian cancer by integrated bioinformatics analysis

OBJECTIVE

The current research was aimed to identify candidate genes associated with development and progression of epithelial ovarian carcinoma using bioinformatics analysis.

MATERIALS AND METHODS

We screened and validated candidate genes associated with carcinogenesis and development of epithelial ovarian carcinoma via bioinformatic analysis in three microarray datasets (GSE14407, GSE29450, and GSE54388) downloaded from the Gene Expression Omnibus (GEO) database.

RESULTS

Our bioinformatic analysis identified 514 differentially expressed genes (DEGs) and nine candidate hub genes (CCNB1, CDK1, BUB1, CDC20, CCNA2, BUB1B, AURKA, RRM2, and TTK). Survival analysis using the Kaplan-Meier plotter showed that high expression levels of seven candidate genes (CCNB1, RRM2, BUB1, CCNA2, AURKA, CDK1, and BUB1B) were associated with poor overall survival (OS). Gene Expression Profiling Interactive Analysis (GEPIA) revealed a higher expression level of these seven candidate genes in ovarian carcinoma samples than in normal ovarian samples. Immunostaining results from the Human Protein Atlas (HPA) database suggested that the protein expression levels of CCNB1, CCNA2, AURKA, and CDK1 were increased in ovarian cancer tissues. No difference was observed in RRM2 protein expression level between normal ovarian and ovarian cancer samples. Oncomine analysis revealed an association between the expression patterns of BUB1B, CCNA2, AURKA, CCNB1, CDK1, and BUB1 and patient clinicopathological information. Finally, six genes, namely CCNB1, CCNA2, AURKA, BUB1, BUB1B, and CDK1, were identified as hub genes and a transcription factor (TF)-gene regulatory network was constructed to identify TFs, including POLR2A, ZBTB11, KLF9, and ELF1, that were implicated in regulating these hub genes.

CONCLUSION

Six significant hub DEGs associated with a poor prognosis in epithelial ovarian cancer were identified. These could be potential biomarkers for ovarian cancer patients.

Aurora kinases in ovarian cancer

Aurora kinases (AURK) are key regulators of the mitotic spindle formation. AURK is frequently overexpressed in ovarian cancer and this overexpression has been frequently associated with prognosis in these tumours. Interestingly, AURK have been shown to interact with DNA repair mechanisms and other cell cycle regulators. These functions have brought light to Aurora family as a potential target for anticancer therapy. In the last years, two clinical trials with different AURK inhibitors have shown activity in epithelial and clear-cell ovarian cancer. Although there is a lack of predictive factors of AURK inhibition activity, recent trials have identified some candidates. This review will focus in the functions of the AURK family, its role as prognostic factor in epithelial ovarian cancer and potential clinical implications.

Loss of BubR1 acetylation provokes replication stress and leads to complex chromosomal rearrangements

Accurate chromosomal segregation during mitosis is regulated by the spindle assembly checkpoint (SAC). SAC failure results in aneuploidy, a hallmark of cancer. However, many studies have suggested that aneuploidy alone is not oncogenic. We have reported that BubR1 acetylation deficiency in mice (K243R/+) caused spontaneous tumorigenesis via weakened SAC signaling and unstable chromosome-spindle attachment, resulting in massive chromosomal mis-segregation. In addition to aneuploidy, cells derived from K243R/+ mice exhibited moderate genetic instability and chromosomal translocation. Here, we investigated how the loss of BubR1 acetylation led to genetic instability and chromosomal rearrangement. To rescue all chromosomal abnormalities generated by the loss of BubR1 acetylation during development, K243R/+ mice were crossed with p53-deficient mice. Genome-wide sequencing and spectral karyotyping of tumors derived from these double-mutant mice revealed that BubR1 acetylation deficiency was associated with complex chromosomal rearrangements, including Robertsonian-like whole-arm translocations. By analyzing the telomeres and centromeres in metaphase chromosome spreads, we found that BubR1 acetylation deficiency increased the collapse of stalled replication forks, commonly referred to as replication stress, and led to DNA damage and chromosomal rearrangements. BubR1 mutations that are critical in interacting with PCAF acetyltransferase and acetylating K250, L249F and A251P, were found from human cancers. Furthermore, a subset of human cancer cells exhibiting whole-arm translocation also displayed defects in BubR1 acetylation, supporting that defects in BubR1 acetylation in mitosis contributes to tumorigenesis. Collectively, loss of BubR1 acetylation provokes replication stress, particularly at the telomeres, leading to genetic instability and chromosomal rearrangement.

Integrated bioinformatics analysis for the screening of hub genes and therapeutic drugs in ovarian cancer

Background

Ovarian cancer (OC) ranks fifth as a cause of gynecological cancer-associated death globally. Until now, the molecular mechanisms underlying the tumorigenesis and prognosis of OC have not been fully understood. This study aims to identify hub genes and therapeutic drugs involved in OC.

Methods

Four gene expression profiles (GSE54388, GSE69428, GSE36668, and GSE40595) were downloaded from the Gene Expression Omnibus (GEO), and the differentially expressed genes (DEGs) in OC tissues and normal tissues with an adjusted P-value < 0.05 and a |log fold change (FC)| > 1.0 were first identified by GEO2R and FunRich software. Next, Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) analyses were performed for functional enrichment analysis of these DEGs. Then, the hub genes were identified by the cytoHubba plugin and the other bioinformatics approaches including protein-protein interaction (PPI) network analysis, module analysis, survival analysis, and miRNA-hub gene network construction was also performed. Finally, the GEPIA2 and DGIdb databases were utilized to verify the expression levels of hub genes and to select the candidate drugs for OC, respectively.

Results

A total of 171 DEGs were identified, including 114 upregulated and 57 downregulated DEGs. The results of the GO analysis indicated that the upregulated DEGs were mainly involved in cell division, nucleus, and protein binding, whereas the biological functions showing enrichment in the downregulated DEGs were mainly negative regulation of transcription from RNA polymerase II promoter, protein complex and apicolateral plasma membrane, and glycosaminoglycan binding. As for the KEGG-pathway, the upregulated DEGs were mainly associated with metabolic pathways, biosynthesis of antibiotics, biosynthesis of amino acids, cell cycle, and HTLV-I infection. Additionally, 10 hub genes (KIF4A, CDC20, CCNB2, TOP2A, RRM2, TYMS, KIF11, BIRC5, BUB1B, and FOXM1) were identified and survival analysis of these hub genes showed that OC patients with the high-expression of CCNB2, TYMS, KIF11, KIF4A, BIRC5, BUB1B, FOXM1, and CDC20 were statistically more likely to have poorer progression free survival. Meanwhile, the expression levels of the hub genes based on GEPIA2 were in accordance with those based on GEO. Finally, DGIdb database was used to identify 62 small molecules as the potentially targeted drugs for OC treatment.

Conclusions

In summary, the data may produce new insights regarding OC pathogenesis and treatment. Hub genes and candidate drugs may improve individualized diagnosis and therapy for OC in future.

Diagnostic and Prognostic Biomarkers of Adrenal Cortical Carcinoma

The diagnosis of low-grade adrenal cortical carcinoma (ACC) confined to the adrenal gland can be challenging. Although there are diagnostic and prognostic molecular tests for ACC, they remain largely unutilized. We examined the diagnostic and prognostic value of altered reticulin framework and the immunoprofile of biomarkers including IGF-2, proteins involved in cell proliferation and mitotic spindle regulation (Ki67, p53, BUB1B, HURP, NEK2), DNA damage repair (PBK, γ-H2AX), telomere regulation (DAX, ATRX), wnt-signaling pathway (beta-catenin) and PI3K signaling pathway (PTEN, phospho-mTOR) in a tissue microarray of 50 adenomas and 43 carcinomas that were characterized for angioinvasion as defined by strict criteria, Weiss score, and mitotic rate-based tumor grade. IGF-2 and proteins involved in cell proliferation and mitotic spindle regulation (Ki67, p53, BUB1B, HURP, NEK2), DNA damage proteins (PBK, γ-H2AX), regulators of telomeres (DAXX, ATRX), and beta-catenin revealed characteristic expression profiles enabling the distinction of carcinomas from adenomas. Not all biomarkers were informative in all carcinomas. IGF-2 was the most useful biomarker of malignancy irrespective of tumor grade and cytomorphologic features, as juxtanuclear Golgi-pattern IGF-2 reactivity optimized for high specificity was identified in up to 80% of carcinomas and in no adenomas. Loss rather than qualitative alterations of the reticulin framework yielded statistical difference between carcinoma and adenoma. Angioinvasion defined as tumor cells invading through a vessel wall and intravascular tumor cells admixed with thrombus proved to be the best prognostic parameter, predicting adverse outcome in the entire cohort as well as within low-grade ACCs. Low mitotic tumor grade, Weiss score, global loss of DAXX expression, and high phospho-mTOR expression correlated with disease-free survival, but Weiss score and biomarkers failed to predict adverse outcome in low-grade disease. Our results underscore the importance of careful morphologic assessment coupled with ancillary diagnostic and prognostic biomarkers of ACC.

The Anaphase Promoting Complex/Cyclosome (APC/C): A Versatile E3 Ubiquitin Ligase

In the present chapter we discuss the essential roles of the human E3 ubiquitin ligase Anaphase Promoting Complex/Cyclosome (APC/C) in mitosis as well as the emerging evidence of important APC/C roles in cellular processes beyond cell division control such as regulation of genomic integrity and cell differentiation of the nervous system. We consider the potential incipient role of APC/C dysregulation in the pathophysiology of the neurological disorder Alzheimer's disease (AD). We also discuss how certain Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA) viruses take control of the host's cell division regulatory system through harnessing APC/C ubiquitin ligase activity and hypothesise the plausible molecular mechanisms underpinning virus manipulation of the APC/C. We also examine how defects in the function of this multisubunit protein assembly drive abnormal cell proliferation and lastly argue the potential of APC/C as a promising therapeutic target for the development of innovative therapies for the treatment of chronic malignancies such as cancer.

Aneuploidy: Cancer strength or vulnerability?

Aneuploidy is a very rare and tissue‐specific event in normal conditions, occurring in a low number of brain and liver cells. Its frequency increases in age‐related disorders and is one of the hallmarks of cancer. Aneuploidy has been associated with defects in the spindle assembly checkpoint (SAC). However, the relationship between chromosome number alterations, SAC genes and tumor susceptibility remains unclear. Here, we provide a comprehensive review of SAC gene alterations at genomic and transcriptional level across human cancers and discuss the oncogenic and tumor suppressor functions of aneuploidy. SAC genes are rarely mutated but frequently overexpressed, with a negative prognostic impact on different tumor types. Both increased and decreased SAC gene expression show oncogenic potential in mice. SAC gene upregulation may drive aneuploidization and tumorigenesis through mitotic delay, coupled with additional oncogenic functions outside mitosis. The genomic background and environmental conditions influence the fate of aneuploid cells. Aneuploidy reduces cellular fitness. It induces growth and contact inhibition, mitotic and proteotoxic stress, cell senescence and production of reactive oxygen species. However, aneuploidy confers an evolutionary flexibility by favoring genome and chromosome instability (CIN), cellular adaptation, stem cell‐like properties and immune escape. These properties represent the driving force of aneuploid cancers, especially under conditions of stress and pharmacological pressure, and are currently under investigation as potential therapeutic targets. Indeed, promising results have been obtained from synthetic lethal combinations exploiting CIN, mitotic defects, and aneuploidy‐tolerating mechanisms as cancer vulnerability.

Immunohistochemical expression of budding uninhibited by benzimidazole related 1 in leukoplakia and oral squamous cell carcinoma

Background:

Budding uninhibited by benzimidazole related 1 (BUBR1) is an important protein in the mitotic spindle assembly checkpoint. Alterations in expression of BUBR1 have been reported in many premalignant and malignant lesions.

Aim:

To compare the expression of BUBR1 with respect to the normal mucosa and degree of dysplasia in oral leukoplakia (OL) and also with respect to different histopathological grades of oral squamous cell carcinoma (OSCC).

Materials and Methods:

Neutral buffered formalin-fixed and paraffin-embedded biopsy specimens 30 each of normal, OL and OSCC tissue were included in this study. The expression of BUBR1 was detected using immunohistochemistry (IHC). The scores obtained were subjected to ANOVA test.

Results:

Significant correlation was found in immunostaining between normal, dysplasia and OSCC groups with a P value of 0.00001. The expression of BUBR1 was significant when compared with different degrees of dysplasia and in different histopathological grades of OSCC with a P value of 0.00001.

Conclusion:

Higher IHC scores were obtained with increased histopathological grades of OL and OSCC suggesting its role as a prognostic indicator.

BUBR1 overexpression predicts disease-specific survival after nephroureterectomy in patients with upper tract urothelial carcinoma

OBJECTIVE

To date, there are few reliable markers to distinguish tumors with aggressive characteristics in upper tract urothelial carcinoma. The purpose of this study was to identify a biomarker related to genetic instability (chromosomal instability or microsatellite instability) with prognostic value, in patients with upper tract urothelial carcinoma.

METHODS

Expression of chromosomal instability-related markers (BUBR1, p53, polo-like kinase 1) and microsatellite instability-related markers (mismatch repair proteins, MLH1 and MSH2) were assessed by immunohistochemistry in 100 patients who had radical nephroureterectomy for upper tract urothelial carcinoma. Numerical aberrations of chromosomes 7, 9 and 17 were evaluated by fluorescence in situ hybridization, which allowed an estimation of the degree of chromosomal instability. BUB1B copy number was examined by array-based comparative genomic hybridization in 32 patients with upper tract urothelial carcinoma.

RESULTS

BUBR1 status was most significantly correlated with chromosomal instability-related and low mismatch repair parameters, according to the molecular biomarkers examined. Overexpression of BUBR1 is frequently detected in tumors with higher histological grade (P < 0.0001) and is significantly associated with chromosomal instability (P = 0.0071). Array-based comparative genomic hybridization revealed that no tumors (0%) showed BUB1B amplification and gain, indicating that overexpression of BUBR1 was independent of BUB1B copy number. For disease-specific survival, BUBR1 overexpression, lymphovascular invasion, pathological tumor stage, pathological lymph node involvement and low MSH2 expression were significant prognostic factors in univariate analyses. In multivariate analyses, BUBR1 overexpression was an independent prognostic factor for disease-specific survival (P = 0.0483, risk ratio 3.76, 95% confidence interval: 1.01-18.43).

CONCLUSIONS

BUBR1 may have significant potential as a biomarker for estimating disease-specific survival in patients with upper tract urothelial carcinoma treated by radical nephroureterectomy.

Mad2 and BubR1 modulates tumourigenesis and paclitaxel response in MKN45 gastric cancer cells

Aneuploidy and chromosomal instability (CIN) are common features of gastric cancer (GC), but their contribution to carcinogenesis and antitumour therapy response is still poorly understood. Failures in the mitotic checkpoint induced by changes in expression levels of the spindle assembly checkpoint (SAC) proteins cause the missegregation of chromosomes in mitosis as well as aneuploidy. To evaluate the possible contribution of SAC to GC, we analyzed the expression levels of proteins of the mitotic checkpoint complex in a cohort of GC cell lines. We found that the central SAC proteins, Mad2 and BubR1, were the more prominently expressed members in disseminated GC cell lines. Silencing of Mad2 and BubR1 in MKN45 and ST2957 cells decreased their cell proliferation, migration and invasion abilities, indicating that Mad2 and BubR1 could contribute to cellular transformation and tumor progression in GC. We next evaluated whether silencing of SAC proteins could affect the response to microtubule poisons. We discovered that paclitaxel treatment increased cell survival in MKN45 cells interfered for Mad2 or BubR1 expression. However, apoptosis (assessed by caspase-3 activation, PARP proteolysis and levels of antiapoptotic Bcl 2-family members), the DNA damage response (assessed by H2Ax phosphorylation) and exit from mitosis (assessed by Cyclin B degradation and Cdk1 regulation) were activated equally between cells, independently of Mad2 or BubR1-protein levels. In contrast, we observed that the silencing of Mad2 or BubR1 in MKN45 cells showed the induction of a senescence-like phenotype accompanied by cell enlargement, increased senescence-associated β-galactosidase activity and increased IL-6 and IL-8 expression. In addition, the senescent phenotype is highly increased after treatment with PTX, indicating that senescence could prevent tumorigenesis in GC. In conclusion, the results presented here suggest that Mad2 and BubR1 could be used as prognostic markers of tumor progression and new pharmacological targets in the treatment for GC.

BubR1 Acts as a Promoter in Cellular Motility of Human Oral Squamous Cancer Cells through Regulating MMP-2 and MMP-9

BubR1 is a critical component of spindle assembly checkpoint, ensuring proper chromatin segregation during mitosis. Recent studies showed that BubR1 was overexpressed in many cancer cells, including oral squamous cell carcinomas (OSCC). However, the effect of BubR1 on metastasis of OSCC remains unclear. This study aimed to unravel the role of BubR1 in the progression of OSCC and confirm the expression of BubR1 in a panel of malignant OSCC cell lines with different invasive abilities. The results of quantitative real-time PCR showed that the mRNA level of BubR1 was markedly increased in four OSCC cell lines, Ca9-22, HSC3, SCC9 and Cal-27 cells, compared to two normal cells, normal human oral keratinocytes (HOK) and human gingival fibroblasts (HGF). Moreover, the expression of BubR1 in these four OSCC cell lines was positively correlated with their motility. Immunofluorescence revealed that BubR1 was mostly localized in the cytosol of human gingival carcinoma Ca9-22 cells. BubR1 knockdown significantly decreased cellular invasion but slightly affect cellular proliferation on both Ca9-22 and Cal-27 cells. Consistently, the activities of metastasis-associated metalloproteinases MMP-2 and MMP-9 were attenuated in BubR1 knockdown Ca9-22 cells, suggesting the role of BubR1 in promotion of OSCC migration. Our present study defines an alternative pathway in promoting metastasis of OSCC cells, and the expression of BubR1 could be a prognostic index in OSCC patients.

Requirement for BUB1B/BUBR1 in tumor progression of lung adenocarcinoma

Lung adenocarcinoma is often discovered as metastatic disease with very poor prognosis. However, much remains unknown about the mechanisms of lung adenocarcinoma tumor progression. In this study we showed that knockdown of BUB1B/BUBR1, a critical mitotic checkpoint protein, significantly inhibited anchorage-independent growth of lung adenocarcinoma cell lines. In allograft and tail vein mouse model studies, BUB1B suppression inhibited primary tumor growth and reduced metastasis to the lung and lymph nodes, resulting in prolonged survival in both tumor prevention and tumor intervention settings. Mechanistic studies revealed that BUB1B knockdown sensitized cells to anoikis. The N-terminal region and GLEBS domain of BUB1B were required for its functions in both anchorage-independent growth and anoikis resistance, whereas the kinase domain was less critical. Overexpression of BUB1B is associated with disease progression and poor survival in human lung adenocarcinoma patients. Collectively, these data reveal a novel function for BUB1B in mediating anchorage-independent survival and growth, thereby facilitating lung adenocarcinoma dissemination during metastasis. Thus, targeting BUB1B could provide potential therapeutic benefit in suppressing metastasis and prolonging survival in lung adenocarcinoma patients.

Predictive and prognostic values of BubR1 and synuclein-gamma expression in breast cancer

The aim of this study is to determine the expression level of spindle assembly checkpoint (SAC) proteins-BubR1 and synuclein-gamma (SNCG) in human breast cancer tissues and to test whether there is a relationship between their expression levels and clinicopathologic parameters including respons to taxanes, tumor grade, estrogen receptor (ER) pozitivity, HER2 status, and overall survival (OS). We analyzed retrospectively paraffin-embedded tissue sections from 55 breast cancer patients whose clinical outcomes had been tracked after taxane treatment in neoadjuvan and metastatic setting. The expression status of BubR1 and SNCG was defined by immunohistochemistry (IHC) using the anti-BubR1 and anti-SNCG antibody. The BubR1 and SNCG was overexpressed in 38% and 62% of the study group, respectively. There was borderline significant correlation between low BubR1 expression and increased taxane sensitivity (P=0.05). In contrast, high SNCG expression was significantly associated with decreased taxane sensitivity (P=0.01). There was no association between the clinicopathologic parameters including histologic grade, ER positivity and HER2 status and the level of these proteins. However, triple negative tumors showed significantly more high BubR1 expression than those other molecular subtypes (P=0.04). Kaplan-Meier survival analysis failed to show a significant correlation between expression levels of BubR1 and SNCG and overall survival although patients with low levels of both proteins had a marginally longer survival time compared to those with high levels. In summary, our data suggest that both BubR1 and SNCG may be promising predictive marker rather than prognostic marker in patients with breast cancer.

Partial Hepatectomy in Acetylation-Deficient BubR1 Mice Corroborates that Chromosome Missegregation Initiates Tumorigenesis

BACKGROUND

Aneuploidy has been suggested as one of the major causes of cancer from the time of Boveri. In support of this notion, many studies have shown that cancer cells exhibit aneuploidy. However, there are evidences that do not support the aneuploidy hypothesis. We have previously reported that the spindle assembly checkpoint protein BubR1 is acetylated in mitosis and that the acetylation of BubR1 is crucial for checkpoint maintenance and chromosome-spindle attachment. Mice heterozygous for acetylation-deficient BubR1 (K243R/+) spontaneously develop cancer with chromosome instability. As K243R/+ mice develop hepatocellular carcinoma, we set out to test if chromosome mis-segregation was the cause of their liver cancer.

METHODS

Primary hepatocytes in the regenerating liver after partial hepatectomy (PH) were analyzed and compared for various mitotic parameters.

RESULTS

Primary hepatocytes isolated from K243R/+ mice after PH displayed a marked increase of chromosome misalignment, accompanied by an increase of micronuclei. In comparison, the number of nuclei per cell and the centrosome numbers were not different between wild-type and K243R/+ mice. Taken together, chromosome mis-segregation provokes tumorigenesis in mouse liver.

CONCLUSION

Our results corroborate that PH provides a reliable tool for assessing mitotic infidelity and cancer in mice.

BUB1 mRNA is significantly co-expressed with AURKA and AURKB mRNA in advanced-stage ovarian serous carcinoma

The objective of this study was to investigate the expression and clinical role of the spindle checkpoint kinase budding uninhibited by benzimidazole 1 (Bub1) in primary and metastatic advanced-stage ovarian serous carcinoma. BUB1 mRNA expression was analyzed in 178 tumors (88 effusions, 38 primary carcinomas, and 52 solid metastases) from 144 patients with advanced-stage disease using quantitative real-time polymerase chain reaction (PCR). Bub1 protein expression by Western blotting was studied in 63 carcinomas (30 effusions and 33 solid lesions). BUB1 mRNA expression at different anatomic sites was studied for association with clinicopathologic parameters, including chemotherapy resistance and survival. BUB1 mRNA was universally expressed in serous carcinomas, irrespective of anatomic site. BUB1 mRNA levels were uniformly low in six ovarian surface epithelium specimens analyzed for comparative purposes. Bub1 protein was expressed in 22/30 effusions and 28/33 solid lesions. BUB1 mRNA expression was significantly higher in chemo-naïve primary carcinomas and solid metastases compared to specimens obtained following neoadjuvant chemotherapy (p < 0.001) and was unrelated to chemotherapy exposure in effusions nor to chemoresponse or survival at any anatomic site. BUB1 mRNA levels in both effusions and solid lesions were strongly related to the mRNA levels of AURKA and AURKB previously studied in this cohort (p < 0.001 for both). Bub1 is widely expressed in primary and metastatic OC, suggesting a biological role in this cancer. BUB1 mRNA levels are lower following chemotherapy exposure in solid lesions, though its presence is unrelated to clinical behavior including response to chemotherapy and survival. BUB1 is co-expressed with AURKA and AURKB suggesting biological relationship between these spindle cell components.

Spindle assembly checkpoint protein expression correlates with cellular proliferation and shorter time to recurrence in ovarian cancer

Ovarian carcinoma (OC) is the most lethal of the gynecological malignancies, often presenting at an advanced stage. Treatment is hampered by high levels of drug resistance. The taxanes are microtubule stabilizing agents, used as first-line agents in the treatment of OC that exert their apoptotic effects through the spindle assembly checkpoint. BUB1-related protein kinase (BUBR1) and mitotic arrest deficient 2 (MAD2), essential spindle assembly checkpoint components, play a key role in response to taxanes. BUBR1, MAD2, and Ki-67 were assessed on an OC tissue microarray platform representing 72 OC tumors of varying histologic subtypes. Sixty-one of these patients received paclitaxel and platinum agents combined; 11 received platinum alone. Overall survival was available for all 72 patients, whereas recurrence-free survival (RFS) was available for 66 patients. Increased BUBR1 expression was seen in serous carcinomas, compared with other histologies (P = .03). Increased BUBR1 was significantly associated with tumors of advanced stage (P = .05). Increased MAD2 and BUBR1 expression also correlated with increased cellular proliferation (P < .0002 and P = .02, respectively). Reduced MAD2 nuclear intensity was associated with a shorter RFS (P = .03), in ovarian tumors of differing histologic subtype (n = 66). In this subgroup, for those women who received paclitaxel and platinum agents combined (n = 57), reduced MAD2 intensity also identified women with a shorter RFS (P < .007). For the entire cohort of patients, irrespective of histologic subtype or treatment, MAD2 nuclear intensity retained independent significance in a multivariate model, with tumors showing reduced nuclear MAD2 intensity identifying patients with a poorer RFS (P = .05).

Loss of BubR1 acetylation causes defects in spindle assembly checkpoint signaling and promotes tumor formation

Failure of chromosome–spindle attachment and a weakened spindle assembly checkpoint lead to genetic instability and cancer in mice expressing acetylation-deficient BubR1.

BubR1 acetylation is essential in mitosis. Mice heterozygous for the acetylation-deficient BubR1 allele (K243R/+) spontaneously developed tumors with massive chromosome missegregations. K243R/+ mouse embryonic fibroblasts (MEFs) exhibited a weakened spindle assembly checkpoint (SAC) with shortened mitotic timing. The generation of the SAC signal was intact, as Mad2 localization to the unattached kinetochore (KT) was unaltered; however, because of the premature degradation of K243R-BubR1, the mitotic checkpoint complex disassociated prematurely in the nocodazole-treated condition, suggesting that maintenance of the SAC is compromised. BubR1 acetylation was also required to counteract excessive Aurora B activity at the KT for stable chromosome–spindle attachments. The association of acetylation-deficient BubR1 with PP2A-B56α phosphatase was reduced, and the phosphorylated Ndc80 at the KT was elevated in K243R/+ MEFs. In relation, there was a marked increase of micronuclei and p53 mutation was frequently detected in primary tumors of K243R/+ mice. Collectively, the combined effects of failure in chromosome–spindle attachment and weakened SAC cause genetic instability and cancer in K243R/+ mice.

Expression profiling of 519 kinase genes in matched malignant peripheral nerve sheath tumor/plexiform neurofibroma samples is discriminatory and identifies mitotic regulators BUB1B, PBK and NEK2 as overexpressed with transformation

About 50% of all malignant peripheral nerve sheath tumors (MPNSTs) arise as neurofibromatosis type 1 associated lesions. In those patients malignant peripheral nerve sheath tumors are thought to arise through malignant transformation of a preexisting plexiform neurofibroma. The molecular changes associated with this transformation are still poorly understood. We sought to test the hypothesis that dysregulation of expression of kinases contributes to this malignant transformation. We analyzed expression of all 519 kinase genes in the human genome using the nanostring nCounter system. Twelve cases of malignant peripheral nerve sheath tumor arising in a background of preexisting plexiform neurofibroma were included. Both components were separately sampled. Statistical analysis compared global changes in expression levels as well as changes observed in the pairwise comparison of samples taken from the same surgical specimen. Immunohistochemical studies were performed on tissue array slides to confirm expression of selected proteins. The expression pattern of kinase genes can separate malignant peripheral nerve sheath tumors and preexisting plexiform neurofibromas. The majority of kinase genes is downregulated rather than overexpressed with malignant transformation. The patterns of expression changes are complex without simple recurring alteration. Pathway analysis demonstrates that differentially expressed kinases are enriched for kinases involved in the direct regulation of mitosis, and several of these show increased expression in malignant peripheral nerve sheath tumors. Immunohistochemical studies for the mitotic regulators BUB1B, PBK and NEK2 confirm higher expression levels at the protein level. These results suggest that the malignant transformation of plexiform neurofibroma is associated with distinct changes in the expression of kinase genes. The patterns of these changes are complex and heterogeneous. There is no single unifying alteration. Kinases involved in mitotic regulation are particularly enriched in the pool of differentially expressed kinases. Some of these are overexpressed and are therefore possible targets for kinase inhibitors.

Predictive and prognostic values of Tau and BubR1 protein in prostate cancer and their relationship to the Gleason score

The aim of this study is to detect the expression levels of spindle assembly checkpoint protein-BubR1 and microtubule-associated protein-Tau in human prostate cancer tissues of different Gleason score, and to test whether there is a relationship between their expression levels and clinicopathologic parameters including response to docetaxel treatment, Gleason score, and overall survival (OS). Moreover, to test whether Tau protein expressed in the cancerous prostate tissue is phosphorylated. Thirty patients who received at least three cycles docetaxel for metastatic castrate-resistant prostate cancer were included into the trial. The patients' formalin-fixed and paraffin-embedded prostate tissue specimens were retrospectively obtained from the pathology department archives of Ege University School of Medicine. The expression status of BubR1 protein was defined by immunohistochemical (IHC) using the anti-BubR1 antibody. The expression status of Tau protein was defined by IHC using the two types of Tau antibodies: anti-Tau-1 antibody (that recognizes Tau only in its dephosphorylated form) and anti-PHF-Tau antibody (that recognizes all isoforms of human Tau proteins independent of its phosphorylation status). The BubR1 and Tau were overexpressed in about 63 and 23 % of the study group, respectively. Tau overexpression was significantly associated with lower Gleason score. There was no significant association between the expression levels of BubR1 and Tau proteins, and docetaxel response. Reduced BubR1 expression was strongly associated with longer survival (P = 0.008), whereas Tau expression status did not effect survival. Moreover, the Tau expression of cancerous prostate tissue was highly dephosphorylated. In this clinicopathological study, our findings did not confirm the preclinical observations that low BubR1 and Tau expression confer selective sensitivity to microtubulisin drugs. Our data imply that reduced BubR1 expression was a predictor for longer OS, and the possibility that high Tau expression may be involved in better prognosis due to its relationship to the Gleason score. Furthermore, our data suggest that both Tau and BubR1 may be a promising prognostic marker rather than predictive marker in patients with prostate cancer.

Elevated BUBR1 expression is associated with poor survival in early breast cancer patients: 15-year follow-up analysis

BUBR1 (budding uninhibited by benzimidazole-related 1) represents the component of a controlling complex in mitosis. Defects in mitotic control complex result in chromosomal instability and, as a result, disturb the mitotic process. This study was aimed at examining the prognostic value linked to the expression of BUBR1 in a group of patients with breast cancer. We analyzed the expression of BUBR1 in 98 stage II breast cancer patients with a median follow-up of 15 years. Immunohistochemical reactions were performed using monoclonal antibodies against BUBR1. We also studied the prognostic value of BUBR1 mRNA expression using the Kaplan-Meier (KM) plotter, which assessed the effect of 22,277 genes on survival in 2422 breast cancer patients. A background database was established using gene expression data and survival information on 2422 patients downloaded from the Gene Expression Omnibus (GEO; Affymetrix HGU133A and HGU133+2 microarrays). The median relapse-free survival was 6.43 years. Univariate and multivariate analyses showed that higher expression of BUBR1 was typical for cases of shorter overall survival, disease-free time, and disease-specific survival. KM plotter analysis showed that elevated BUBR1 mRNA expression had a negative impact on patients' relapse-free, distant metastases-free, and overall survival. Elevated BUBR1 expression was associated with poor survival in early stage breast cancer patients.

New insights into the role of BubR1 in mitosis and beyond

BubR1 is a critical component of the spindle assembly checkpoint, the surveillance mechanism that helps maintain the high fidelity of mitotic chromosome segregation by preventing cells from initiating anaphase if one or more kinetochores are not attached to the spindle. BubR1 also helps promote the establishment of stable kinetochore-microtubule attachments during prometaphase. In this chapter, we review the structure, functions, and regulation of BubR1 in these "classical roles" at the kinetochore. We discuss its recruitment to kinetochores, its assembly into the inhibitor of anaphase progression, and the importance of its posttranslational modifications. We also consider the evidence for its participation in other roles beyond mitosis, such as the meiosis-specific processes of recombination and prophase arrest of the first meiotic division, the cellular response to DNA damage, and in the regulation of centrosome and basal body function. Finally, studies are presented linking BubR1 dysfunction or misregulation to aging and human disease, particularly cancer.

Abnormal expression of the mitotic checkpoint protein BubR1 contributes to the anti-microtubule drug resistance of esophageal squamous cell carcinoma cells

Esophageal cancer is a common malignancy with a high mortality rate. The lack of effective chemotherapy and a means to overcome drug resistance leads to the predictable failure of esophageal cancer treatment. Mitotic checkpoint proteins play a critical role in regulating the cell cycle and proliferation. Abnormal expression of the mitotic checkpoint protein BubR1 has been reported in several types of cancers. In this study, we investigated the role of BubR1 in conferring resistance of esophageal cancer cells to anti-microtubule drugs. Using quantitative real-time PCR analysis on 50 samples of paired esophageal squamous cell cancer (ESC) tissues and adjacent non-cancerous tissues, we found that 72% (36 of 50) of the analyzed ESC samples exhibited high expression levels of BubR1, which was also confirmed in ESC cell lines. ESC cells with high levels of BubR1 were less sensitive to the anti-microtubule drugs paclitaxel and nocodazole. Recombinant adenovirus-mediated enforced expression of BubR1 in relatively sensitive ESC cell lines resulted in increased resistance to paclitaxel. Conversely, RNAi-mediated knockdown of BubR1 restored ESC cell sensitivity to paclitaxel. Cell cycle analysis indicated that the sub-G1 population increased in the ESC cells with reduced BubR1 levels. Taken together, our results suggest that upregulation of BubR1 expression may be associated with ESC resistance to paclitaxel treatment. Thus, BubR1 may serve as a potential chemosensitizing target to overcome chemoresistance.

BRCA2 fine-tunes the spindle assembly checkpoint through reinforcement of BubR1 acetylation

Germline mutations that inactivate BRCA2 promote early-onset cancer with chromosome instability. Here, we report that BRCA2 regulates the spindle assembly checkpoint (SAC). Previously, we reported that BubR1 acetylation is essential for SAC activity. In this study we show that BRCA2 recruits the PCAF acetyltransferase and aids in BubR1 acetylation during mitosis. In the absence of BRCA2, BubR1 acetylation is abolished, and the level of BubR1 decreases during mitosis. Similarly, Brca2-deficient mouse embryonic fibroblasts exhibited weak SAC activity. Transgenic mice that were engineered to have interruptions in the BRCA2-BubR1 association exhibited marked decrease of BubR1 acetylation, weakened SAC activity, and aneuploidy. These transgenic mice developed spontaneous tumors at 40% penetrance. Moreover, immunohistochemical analyses of human breast cancer specimens suggested that BRCA2 mutation and BubR1 status is closely linked. Our results provide an explanation for how mutation of BRCA2 can lead to chromosome instability without apparent mutations in SAC components.

The accuracy of survival time prediction for patients with glioma is improved by measuring mitotic spindle checkpoint gene expression

Identification of gene expression changes that improve prediction of survival time across all glioma grades would be clinically useful. Four Affymetrix GeneChip datasets from the literature, containing data from 771 glioma samples representing all WHO grades and eight normal brain samples, were used in an ANOVA model to screen for transcript changes that correlated with grade. Observations were confirmed and extended using qPCR assays on RNA derived from 38 additional glioma samples and eight normal samples for which survival data were available. RNA levels of eight major mitotic spindle assembly checkpoint (SAC) genes (BUB1, BUB1B, BUB3, CENPE, MAD1L1, MAD2L1, CDC20, TTK) significantly correlated with glioma grade and six also significantly correlated with survival time. In particular, the level of BUB1B expression was highly correlated with survival time (p<0.0001), and significantly outperformed all other measured parameters, including two standards; WHO grade and MIB-1 (Ki-67) labeling index. Measurement of the expression levels of a small set of SAC genes may complement histological grade and other clinical parameters for predicting survival time.

ASPM and microcephalin expression in epithelial ovarian cancer correlates with tumour grade and survival

BACKGROUND

The clinico-pathological and molecular heterogeneity of epithelial ovarian cancer (EOC) complicates its early diagnosis and successful treatment. Highly aneuploid tumours and the presence of ascitic fluids are hallmarks of EOC. Two microcephaly-associated proteins, abnormal spindle-like microcephaly-associated protein (ASPM) and microcephalin, are involved in mitosis and DNA damage repair. Their expression is deregulated at the RNA level in EOC. Here, ASPM and microcephalin protein expression in primary cultures established from the ascites of patients with EOC was determined and correlated with clinical data to assess their suitability as biomarkers.

METHODS

Five established ovarian cancer cell lines, cells derived from two benign ovarian ascites samples and 40 primary cultures of EOC derived from ovarian ascites samples were analysed by protein slot blotting and/or immunofluorescence to determine ASPM and microcephalin protein levels and their cellular localisation. Results were correlated with clinico-pathological data.

RESULTS

A statistically significant correlation was identified for ASPM localisation and tumour grade, with high levels of cytoplasmic ASPM correlating with grade 1 tumours. Conversely, cytoplasmic microcephalin was only identified in high-grade tumours. Furthermore, low levels of nuclear microcephalin correlated with reduced patient survival.

CONCLUSION

Our results suggest that ASPM and microcephalin have the potential to be biomarkers in ovarian cancer.

Comparison of expression profiles in ovarian epithelium in vivo and ovarian cancer identifies novel candidate genes involved in disease pathogenesis

Molecular events leading to epithelial ovarian cancer are poorly understood but ovulatory hormones and a high number of life-time ovulations with concomitant proliferation, apoptosis, and inflammation, increases risk. We identified genes that are regulated during the estrous cycle in murine ovarian surface epithelium and analysed these profiles to identify genes dysregulated in human ovarian cancer, using publically available datasets. We identified 338 genes that are regulated in murine ovarian surface epithelium during the estrous cycle and dysregulated in ovarian cancer. Six of seven candidates selected for immunohistochemical validation were expressed in serous ovarian cancer, inclusion cysts, ovarian surface epithelium and in fallopian tube epithelium. Most were overexpressed in ovarian cancer compared with ovarian surface epithelium and/or inclusion cysts (EpCAM, EZH2, BIRC5) although BIRC5 and EZH2 were expressed as highly in fallopian tube epithelium as in ovarian cancer. We prioritised the 338 genes for those likely to be important for ovarian cancer development by in silico analyses of copy number aberration and mutation using publically available datasets and identified genes with established roles in ovarian cancer as well as novel genes for which we have evidence for involvement in ovarian cancer. Chromosome segregation emerged as an important process in which genes from our list of 338 were over-represented including two (BUB1, NCAPD2) for which there is evidence of amplification and mutation. NUAK2, upregulated in ovarian surface epithelium in proestrus and predicted to have a driver mutation in ovarian cancer, was examined in a larger cohort of serous ovarian cancer where patients with lower NUAK2 expression had shorter overall survival. In conclusion, defining genes that are activated in normal epithelium in the course of ovulation that are also dysregulated in cancer has identified a number of pathways and novel candidate genes that may contribute to the development of ovarian cancer.

Targeting aneuploid cancer cells

INTRODUCTION

Most cancers are characterized by some degree of aneuploidy, although its relevance for tumor initiation or progression and the nature of the initial trigger are still not well understood. It was Theodor Boveri who first suggested a link between aneuploidy and cancer at the beginning of the last century, but it is only recently that the molecular mechanisms involved have started to be uncovered.

AREAS COVERED

The molecular mechanisms that are at the origin of aneuploidy and their cellular consequences. Based on these new findings molecular targets have emerged which could lead to a specific treatment of at least some types of aneuploid tumors.

EXPERT OPINION

Therapeutic intervention specifically for aneuploid cells is a very promising approach, however, although new promising targets have been spotted they still need to be tested for proof of concept. Targeting the spindle checkpoint could be an interesting approach for cancer therapy, however, as for other mitotic targets, the open question of the therapeutic window and sensitivity of normal hemopoietic cells has to be considered carefully. Future challenges will not only include identifying and validating druggable targets related to the relevant pathways, but also finding predictive biomarkers to define the responding patient population(s).

Correlation between reduced expression of the spindle checkpoint protein BubR1 and bad prognosis in tonsillar carcinomas

BACKGROUND

Spindle checkpoint proteins such as Mad2 and BubR1 are important for chromosome segregation during mitosis. The aim of the present study was to examine their possible impact on prognosis in tonsillar carcinomas and their relation to clinical variables, the prevalence of human papillomavirus (HPV), p53 status, and Ki-67 positivity.

METHODS

We examined the expression of Mad2 and BubR1 by immunohistochemistry on tissue microarrays from 105 patients with tonsillar carcinomas.

RESULTS

BubR1 and Mad2 were both expressed in tonsillar carcinomas. Expression of BubR1 was a significant prognostic factor in univariate survival analysis. In multivariate analyses, BubR1 was a significant prognostic factor together with stage, age, and HPV status p < .01), whereas Mad2 did not show any significant correlations.

CONCLUSION

We have shown that BubR1 expression is a novel and strong prognostic factor in tonsillar carcinomas, giving additional information to the TNM stage and other known prognostic factors.

BUBR1 expression in oral squamous cell carcinoma and its relationship to tumor stage and survival

BACKGROUND

Defects in the mitotic spindle checkpoint have been proposed to contribute to the chromosomal instability observed in human cancers, including oral squamous cell carcinoma (OSCC). BUBR1 is a key component of the spindle checkpoint, whose role in oral carcinogenesis still needs to be clarified.

METHODS

We have analyzed the expression of BUBR1 in 49 cases of OSCC by immunohistochemistry and compared the findings with clinicopathologic parameters, proliferative activity, and DNA ploidy.

RESULTS

BUBR1 was overexpressed in 11 cases (22.4%). Tumors with overexpression of BUBR1 were associated with a less advanced pathologic stage (p = .05) and showed longer survival periods (p = .38) but shorter recurrence-free survival periods (p = .13) than those without it.

CONCLUSIONS

Our data imply the possibility that BUBR1 may be involved in the progression of OSCC, and suggest that BUBR1 may be a promising prognostic marker in patients with OSCC.