Human Zw10 and ROD are mitotic checkpoint proteins that bind to kinetochores

KNTC1 knockdown inhibits the proliferation and migration of osteosarcoma cells by MCM2

Osteosarcoma (OS) is a common primary malignant bone tumor, and it is necessary to further investigate the molecular mechanism of OS progression. The expression of kinetochore associated protein 1 (KNTC1) and minichromosome maintenance 2 (MCM2) was detected by immunohistochemistry, quantitative PCR (qPCR) and Western blot. Gene knockdown or overexpression cell models were constructed and the proliferation, apoptosis, cell cycle and migration were detected in vitro, besides, xenograft models were established to explore the effects of KNTC1 downregulation in vivo. Public databased and bioinformatics analysis were performed to screen the downstream molecules and determine the expression of MCM2 in cancers. KNTC1 was overexpressed in OS tissues and positively correlated with overall survival of OS patients. KNTC1 knockdown inhibited the proliferation and migration, and arrested G2 phase, and induced apoptosis. Besides, KNTC1 downregulation restricted the xenograft tumor formation. MCM2, one of the coexpressed genes, was highly expressed in sarcoma and downregulated after KNTC1 knockdown. MCM2 overexpression heightened the proliferation and migration ability of OS cells, which was reversed the inhibiting effects of KNTC1 knockdown. KNTC1 was overexpressed in OS and promoted the progression of OS by upregulating MCM2.

The dynamic role of nucleoprotein SHCBP1 in the cancer cell cycle and its potential as a synergistic target for DNA-damaging agents in cancer therapy

BACKGROUND

Malignant tumours seriously threaten human life and health, and effective treatments for cancer are still being explored. The ability of SHC SH2 domain-binding protein 1 (SHCBP1) to induce cell cycle disturbance and inhibit tumour growth has been increasingly studied, but its dynamic role in the tumour cell cycle and corresponding effects leading to mitotic catastrophe and DNA damage have rarely been studied.

RESULTS

In this paper, we found that the nucleoprotein SHCBP1 exhibits dynamic spatiotemporal expression during the tumour cell cycle, and SHCBP1 knockdown slowed cell cycle progression by inducing spindle disorder, as reflected by premature mitotic entry and multipolar spindle formation. This dysfunction was caused by G2/M checkpoint impairment mediated by downregulated WEE1 kinase and NEK7 (a member of the mammalian NIMA-related kinase family) expression and upregulated centromere/kinetochore protein Zeste White 10 (ZW10) expression. Moreover, both in vivo and in vitro experiments confirmed the significant inhibitory effects of SHCBP1 knockdown on tumour growth. Based on these findings, SHCBP1 knockdown in combination with low-dose DNA-damaging agents had synergistic tumouricidal effects on tumour cells. In response to this treatment, tumour cells were forced into the mitotic phase with considerable unrepaired DNA lesions, inducing mitotic catastrophe. These synergistic effects were attributed not only to the abrogation of the G2/M checkpoint and disrupted spindle function but also to the impairment of the DNA damage repair system, as demonstrated by mass spectrometry-based proteomic and western blotting analyses. Consistently, patients with low SHCBP1 expression in tumour tissue were more sensitive to radiotherapy. However, SHCBP1 knockdown combined with tubulin-toxic drugs weakened the killing effect of the drugs on tumour cells, which may guide the choice of chemotherapeutic agents in clinical practice.

CONCLUSION

In summary, we elucidated the role of the nucleoprotein SHCBP1 in tumour cell cycle progression and described a novel mechanism by which SHCBP1 regulates tumour progression and through which targeting SHCBP1 increases sensitivity to DNA-damaging agent therapy, indicating its potential as a cancer treatment.

KNTC1 and MCM2 are the molecular targets of gallbladder cancer

BACKGROUND

Gallbladder carcinoma is a malignant epithelial tumor of gallbladder with a high degree of malignancy. However, relationship between KNTC1 and MCM2 and gallbladder cancer is unclear.

METHODS

GSE139682 and GSE202479 were downloaded from gene expression omnibus (GEO). Differentially expressed genes (DEGs) were screened. Functional enrichment analysis and gene set enrichment analysis (GSEA) were performed. Protein-protein interaction (PPI) Network was constructed and analyzed. Gene expression heat map was drawn. Comparative toxicogenomics database (CTD) analysis was performed to find diseases most related to core genes. TargetScan was performed for screening miRNAs that regulated central DEGs.

RESULTS

230 DEGs were identified. According to GObp analysis, they were mainly concentrated in regulation of ossification, regulation of spindle microtubule and centromere attachment, cytoskeleton tissue of cortical actin. According to GOcc analysis, they are mainly concentrated in plasma membrane part, cell junction, plasma membrane region and anterior membrane. According to GOmf analysis, they are mainly enriched in protein homodimerization activity, proximal promoter sequence-specific DNA binding and sulfur compound binding. KEGG showed that target genes were mainly enriched in Hippo signal pathway, p53 signal pathway and cancer pathway. KIFC2, TUBG1, RACGAP1, CHMP4C, SFN and MYH11 were identified as core genes. Gene expression heat map showed that KNTC1, MCM2, CKAP2, RACGAP1, CCNB1 were highly expressed in gallbladder carcinoma samples. CTD analysis showed that KNTC1, MCM2, CKAP2, RACGAP1, CCNB1 were associated with head and neck squamous cell carcinoma, necrosis, inflammation and hepatomegaly.

CONCLUSIONS

KNTC1 and MCM2 are highly expressed in gallbladder cancer. Higher expression level correlates with worse prognosis.

The role of kinetochore dynein in checkpoint silencing is restricted to disassembly of the corona

During mitosis, kinetochore-microtubule attachments are monitored by a molecular surveillance system known as the spindle assembly checkpoint. The prevailing model posits that dynein evicts checkpoint proteins (e.g., Mad1, Mad2) from stably attached kinetochores by transporting them away from kinetochores, thus contributing to checkpoint silencing. However, the mechanism by which dynein performs this function, and its precise role in checkpoint silencing remain unresolved. Here, we find that dynein's role in checkpoint silencing is restricted to evicting checkpoint effectors from the fibrous corona, and not the outer kinetochore. Dynein evicts these molecules from the corona in a manner that does not require stable, end-on microtubule attachments. Thus, by disassembling the corona through indiscriminate microtubule encounters, dynein primes the checkpoint signaling apparatus so it can respond to stable end-on microtubule attachments and permit cells to progress through mitosis. Accordingly, we find that dynein function in checkpoint silencing becomes largely dispensable in cells in which checkpoint effectors are excluded from the corona.

The role of KNTC1 in the regulation of proliferation, migration and tumorigenesis in colorectal cancer

BACKGROUND

Current findings have revealed that kinetochore-associated protein 1 (KNTC1) plays a pivotal role in the carcinogenesis of numerous types of cancer. This study was undertaken to inspect the role and probable underlying mechanisms of KNTC1 during the genesis and progression of colorectal cancer.

METHODS

Immunohistochemistry was implemented to determine KNTC1 expression levels in colorectal cancer tissues and para-carcinoma tissues. The association between KNTC1 expression profiles and several clinicopathological traits of colorectal cancer cases was examined employing Mann-Whitney U, Spearman, and Kaplan-Meier analyses. To track the proliferation, apoptosis, cell cycle, migration and in vivo carcinogenesis of colorectal cancer cells, KNTC1 was knocked down in colorectal cell line via RNA interference. To investigate the potential mechanism, the expression profile alterations of associated proteins were detected using human apoptosis antibody arrays, and verified by Western blot analysis.

RESULTS

In colorectal cancer tissues, KNTC1 was substantially expressed, and it was associated with the pathological grade as well as overall survival rate of the disease. The knockdown of KNTC1 was able to inhibit proliferation, cell cycle, migration and in vivo tumorigenesis of colorectal cancer cells, but promote apoptosis.

CONCLUSIONS

KNTC1 is a key player in the emergence of colorectal cancer and may serve as an early diagnostic indicator of precancerous lesions.

Identification of the cell cycle characteristics of non-small cell lung cancer and its relationship with tumor immune microenvironment, cell death pathways, and metabolic reprogramming

Background

The genes related to the cell cycle progression could be considered the key factors in human cancers. However, the genes involved in cell cycle regulation in non-small cell lung cancer (NSCLC) have not yet been reported. Therefore, it is necessary to evaluate the genes related to the cell cycle in all types of cancers, especially NSCLC.

Methods

This study constituted the first pan-cancer landscape of cell cycle signaling. Cluster analysis based on cell cycle signaling was conducted to identify the potential molecular heterogeneity of NSCLC. Further, the discrepancies in the tumor immune microenvironment, metabolic remodeling, and cell death among the three clusters were investigated. Immunohistochemistry was performed to validate the protein levels of the ZWINT gene and examine its relationship with the clinical characteristics. Bioinformatics analyses and experimental validation of the ZWINT gene were also conducted.

Results

First, pan-cancer analysis provided an overview of cell cycle signaling and highlighted its crucial role in cancer. A majority of cell cycle regulators play risk roles in lung adenocarcinoma (LUAD); however, some cell cycle genes play protective roles in lung squamous cell carcinoma (LUSC). Cluster analysis revealed three potential subtypes for patients with NSCLC. LUAD patients with high cell cycle activities were associated with worse prognosis; while, LUSC patients with high cell cycle activities were associated with a longer survival time. Moreover, the above three subtypes of NSCLC exhibited distinct immune microenvironments, metabolic remodeling, and cell death pathways. ZWINT, a member of the cell signaling pathway, was observed to be significantly associated with the prognosis of LUAD patients. A series of experiments verified the higher expression levels of ZWINT in NSCLC compared to those in paracancerous tissues. The activation of epithelial-mesenchymal transition (EMT) induced by ZWINT might be responsible for tumor progression.

Conclusion

This study revealed the regulatory function of the cell cycle genes in NSCLC, and the molecular classification based on cell cycle-associated genes could evaluate the different prognoses of patients with NSCLC. ZWINT expression was found to be significantly upregulated in NSCLC tissues, which might promote tumor progression via activation of the EMT pathway.

Loss of RanGAP1 drives chromosome instability and rapid tumorigenesis of osteosarcoma

Chromothripsis is a catastrophic event of chromosomal instability that involves intensive fragmentation and rearrangements within localized chromosomal regions. However, its cause remains unclear. Here, we show that reduction and inactivation of Ran GTPase-activating protein 1 (RanGAP1) commonly occur in human osteosarcoma, which is associated with a high rate of chromothripsis. In rapidly expanding mouse osteoprogenitors, RanGAP1 deficiency causes chromothripsis in chr1q, instant inactivation of Rb1 and degradation of p53, consequent failure in DNA damage repair, and ultrafast osteosarcoma tumorigenesis. During mitosis, RanGAP1 anchors to the kinetochore, where it recruits PP1-γ to counteract the activity of the spindle-assembly checkpoint (SAC) and prevents TOP2A degradation, thus safeguarding chromatid decatenation. Loss of RanGAP1 causes SAC hyperactivation and chromatid decatenation failure. These findings demonstrate that RanGAP1 maintains mitotic chromosome integrity and that RanGAP1 loss drives tumorigenesis through its direct effects on SAC and decatenation and secondary effects on DNA damage surveillance.

KNTC1, regulated by HPV E7, inhibits cervical carcinogenesis partially through Smad2

Cervical cancer is the second most common malignancy of the female reproductive tract worldwide. Although cervical cancer is caused by human papillomavirus (HPV) infection, its underlying pathogenesis requires further investigation. The present study investigated the role of kinetochore associated protein 1 (KNTC1) in cervical cancer and its association with the key virus oncoprotein, HPV E7. A series of bioinformatic analyses revealed that KNTC1 might be involved in the tumorigenesis of multiple human malignancies, including cervical cancer. Tissue microarray analysis showed that in vivo KNTC1 expression was higher in high-grade squamous intraepithelial lesions (HSILs) than in normal cervix and even higher in cervical cancer. In vitro silencing of KNTC1 increased the proliferation, invasion and migration of cervical cancer cell lines. Although not affecting apoptosis, KNTC1 silencing significantly promoted G1/S phase transition of the cell cycle. High-throughput analysis of mRNA expression showed that KNTC1 could regulate its downstream target protein Smad2 at the transcriptional level. Moreover, as the key oncoprotein of the virus, HPV E7 could inhibit the expression of KNTC1 protein, and decrease Smad2 protein expression with or without the aid of KNTC1. These results indicated that KNTC1 is a novel tumor suppressor that can impede the initiation and progression of cervical carcinoma, providing insight into the molecular mechanism by which HPV induces cervical cancer.

Silencing of KNTC1 inhibits hepatocellular carcinoma cells progression via suppressing PI3K/Akt pathway

Kinetochore associated 1 (KNTC1) encodes a kinetochore component in Rod-Zwilch-ZW10 (RZZ) complex which is essential for the segregation of sister chromatids during mitosis and participates in the spindle checkpoint. Recent research demonstrated that kinetochore proteins may be potential biomarkers and may contribute to the development of human malignancies. Our immunohistochemistry experiment showed that KNTC1 was highly expressed in hepatocellular carcinoma (HCC) tissues and correlated with terrible prognosis, indicating that KNTC1 acts a pivotal role in HCC development. Furthermore, lentivirus delivered short hairpin RNA (shRNA) KNTC1 (Lv-shKNTC1) was applied to infect BEL-7404 and SK-HEP-1 to identify roles of KNTC1 on HCC. Lv-shKNTC1 cells showed reduced proliferation ability, increased apoptosis and decreased migration ability. In vivo experiments suggested that xenografts grow significantly slower upon the silencing of KNTC1. Mechanistically, the protein levels of PIK3CA, p-Akt, CCND1, CDK6 are all down-regulated in Lv-KNTC1 cells and the Lv-shKNTC1 tumor tissues of nude mice. Therefore, KNTC1 may affect the biological activity of HCC cells through PI3K/Akt signaling pathway. Further studies revealed that ZW10 is a pivotal protein that participates in KNTC1-induced regulation of PI3K/Akt signaling pathway. In summary, the key finding of this report highlighted the significance of KNTC1 in tumor regression of HCC, demonstrating KNTC1 as an innovative target for adjuvant treatment of HCC.

Expression of kinesin family member C1 in pancreatic ductal adenocarcinoma affects tumor progression and stemness

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer and the third leading cause of cancer-related deaths. Therefore, there is an urgent need for a novel molecular target for the treatment of PDAC. Kinesin family member C1 (KIFC1) belongs to the kinesin superfamily proteins and has been reported to be involved in the pathogenesis of a wide variety of carcinomas. However, the role of KIFC1 in PDAC remains unknown. This study aimed to analyze the expression and biological function of KIFC1 in PDAC. Immunohistochemically, KIFC1 was found in 37 of 81 PDAC cases (46%). A high expression of KIFC1 was significantly related to tumor size (p = 0.023) and poor overall survival (p = 0.011). Univariate and multivariate analysis indicated that KIFC1 expression was a prognostic factor in PDAC cases. As for cancer stem cell markers, KIFC1 expression tended to co-express significantly with CD44 (p < 0.01). The growth and spheroid colony formation of KIFC1 small interfering RNA (siRNA)-transfected PDAC cells were significantly lower than those of negative control siRNA-transfected cells. Therefore, our findings suggest that KIFC1 is an independent prognostic factor in PDAC and may represent a new promising therapeutic target in PDAC.

Identification of Candidate Genes in Breast Cancer Induced by Estrogen Plus Progestogens Using Bioinformatic Analysis

Menopausal hormone therapy (MHT) was widely used to treat menopause-related symptoms in menopausal women. However, MHT therapies were controversial with the increased risk of breast cancer because of different estrogen and progestogen combinations, and the molecular basis behind this phenomenon is currently not understood. To address this issue, we identified differentially expressed genes (DEGs) between the estrogen plus progestogens treatment (EPT) and estrogen treatment (ET) using the Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) data. As a result, a total of 96 upregulated DEGs were first identified. Seven DEGs related to the cell cycle (CCNE2, CDCA5, RAD51, TCF19, KNTC1, MCM10, and NEIL3) were validated by RT-qPCR. Specifically, these seven DEGs were increased in EPT compared to ET (p < 0.05) and had higher expression levels in breast cancer than adjacent normal tissues (p < 0.05). Next, we found that estrogen receptor (ER)-positive breast cancer patients with a higher CNNE2 expression have a shorter overall survival time (p < 0.05), while this effect was not observed in the other six DEGs (p > 0.05). Interestingly, the molecular docking results showed that CCNE2 might bind to 17β-estradiol (−6.791 kcal/mol), progesterone (−6.847 kcal/mol), and medroxyprogesterone acetate (−6.314 kcal/mol) with a relatively strong binding affinity, respectively. Importantly, CNNE2 protein level could be upregulated with EPT and attenuated by estrogen receptor antagonist, acolbifene and had interactions with cancer driver genes (AKT1 and KRAS) and high mutation frequency gene (TP53 and PTEN) in breast cancer patients. In conclusion, the current study showed that CCNE2, CDCA5, RAD51, TCF19, KNTC1, MCM10, and NEIL3 might contribute to EPT-related tumorigenesis in breast cancer, with CCNE2 might be a sensitive risk indicator of breast cancer risk in women using MHT.

shRNA‑mediated knockdown of KNTC1 inhibits non-small-cell lung cancer through regulating PSMB8

In view of the important roles played by Kinetochore proteins in mitosis, we believed that they may contribute to the development and progression of human cancers, which has been reported recently elsewhere. Kinetochore-associated 1 (KNTC1) participates in the segregation of sister chromatids during mitosis, the effects of which on non-small-cell lung cancer (NSCLC) remain unclear. Here, we sought to identify the biological significance of KNTC1 in NSCLC. KNTC1 protein expression in NSCLC tissues was investigated by immunohistochemistry. Lentivirus delivered short hairpin RNA (shRNA) was utilized to establish KNTC1 silence NSCLC cell lines. The effects of KNTC1 depletion on NSCLC cell proliferation, migration, apoptosis, and tumor formation were analyzed by MTT assay, wound-healing assay, transwell assay, flow cytometry assay, and in nude mouse models in vivo. After KNTC1 reduction, NSCLC cell viability, proliferation, migration, and invasion were restrained. A xenograft tumor model was also provided to demonstrate the inhibited tumorigenesis in NSCLC. In addition, the downstream mechanism analysis indicated that KNTC1 depletion was positively associated with PSMB8. The findings of the present study suggested that KNTC1 may have a pivotal role in mediating NSCLC progression and may act as a novel therapeutic target for NSCLC.

Zombies Never Die: The Double Life Bub1 Lives in Mitosis

When eukaryotic cells enter mitosis, dispersed chromosomes move to the cell center along microtubules to form a metaphase plate which facilitates the accurate chromosome segregation. Meanwhile, kinetochores not stably attached by microtubules activate the spindle assembly checkpoint and generate a wait signal to delay the initiation of anaphase. These events are highly coordinated. Disruption of the coordination will cause severe problems like chromosome gain or loss. Bub1, a conserved serine/threonine kinase, plays important roles in mitosis. After extensive studies in the last three decades, the role of Bub1 on checkpoint has achieved a comprehensive understanding; its role on chromosome alignment also starts to emerge. In this review, we summarize the latest development of Bub1 on supporting the two mitotic events. The essentiality of Bub1 in higher eukaryotic cells is also discussed. At the end, some undissolved questions are raised for future study.

Kinetochore-associated protein 1 promotes the invasion and tumorigenicity of cervical cancer cells via matrix metalloproteinase-2 and matrix metalloproteinase-9

Cervical cancer, a common cancer in women, has become a serious social burden. Kinetochore-associated protein 1 (KNTC1) that regulates the cell cycle by regulating mitosis is related to the malignant behavior of different types of tumors. However, its role in the development of cervical cancer remains unclear. In this study, we initially explored the role of KNTC1 in cervical cancer. KNTC1 expression and relevant information were downloaded from The Cancer Genome Atlas (TCGA) and dataset GSE63514 in the Gene Expression Omnibus (GEO) database for bioinformatics analyses. Cell proliferation was detected by cell counting kit-8 (CCK8) and colony formation assays. Wound healing and Transwell assays were used to evaluate cell migration and invasion abilities. Protein expression levels of matrix metallopeptidase 2 (MMP2) and matrix metallopeptidase 9 (MMP9) were measured by western blotting. Nude mouse models of subcutaneous xenograft tumor were constructed to analyze tumor growth in vivo. CCK8 and colony formation assay results demonstrated that the proliferation rate of SiHa and C-33A cells decreased when KNTC1 was silenced. Western blot and Transwell assays indicated that KNTC1 knockdown weakened the invasion and migration abilities of SiHa and C-33A cells and decreased the expression of MMP-2 and MMP-9. In-vivo experiments suggested that the inhibition of KNTC1 reduced tumor growth. Taken together, our study showed that KNTC1 plays an important role in cervical cancer. Further, we verified the promotional effect of KNTC1 on cervical cancer through in-vivo and in-vitro experiments and speculated that KNTC1 might mediate tumor invasion via MMP9 and MMP2.

The origins and genetic interactions of KRAS mutations are allele- and tissue-specific

Mutational activation of KRAS promotes the initiation and progression of cancers, especially in the colorectum, pancreas, lung, and blood plasma, with varying prevalence of specific activating missense mutations. Although epidemiological studies connect specific alleles to clinical outcomes, the mechanisms underlying the distinct clinical characteristics of mutant KRAS alleles are unclear. Here, we analyze 13,492 samples from these four tumor types to examine allele- and tissue-specific genetic properties associated with oncogenic KRAS mutations. The prevalence of known mutagenic mechanisms partially explains the observed spectrum of KRAS activating mutations. However, there are substantial differences between the observed and predicted frequencies for many alleles, suggesting that biological selection underlies the tissue-specific frequencies of mutant alleles. Consistent with experimental studies that have identified distinct signaling properties associated with each mutant form of KRAS, our genetic analysis reveals that each KRAS allele is associated with a distinct tissue-specific comutation network. Moreover, we identify tissue-specific genetic dependencies associated with specific mutant KRAS alleles. Overall, this analysis demonstrates that the genetic interactions of oncogenic KRAS mutations are allele- and tissue-specific, underscoring the complexity that drives their clinical consequences.

Five candidate biomarkers associated with the diagnosis and prognosis of cervical cancer

Purpose: Cervical cancer (CC) is one of the most general gynecological malignancies and is associated with high morbidity and mortality. We aimed to select candidate genes related to the diagnosis and prognosis of CC.

Methods: The mRNA expression profile datasets were downloaded. We also downloaded RNA-sequencing gene expression data and related clinical materials from TCGA, which included 307 CC samples and 3 normal samples. Differentially expressed genes (DEGs) were obtained by R software. GO function analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of DEGs were performed in the DAVID dataset. Using machine learning, the optimal diagnostic mRNA biomarkers for CC were identified. We used qRT-PCR and Human Protein Atlas (HPA) database to exhibit the differences in gene and protein levels of candidate genes.

Results: A total of 313 DEGs were screened from the microarray expression profile datasets. DNA methyltransferase 1 (DNMT1), Chromatin Assembly Factor 1, subunit B (CHAF1B), Chromatin Assembly Factor 1, subunit A (CHAF1A), MCM2, CDKN2A were identified as optimal diagnostic mRNA biomarkers for CC. Additionally, the GEPIA database showed that the DNMT1, CHAF1B, CHAF1A, MCM2 and CDKN2A were associated with the poor survival of CC patients. HPA database and qRT-PCR confirmed that these genes were highly expressed in CC tissues.

Conclusion: The present study identified five DEmRNAs, including DNMT1, CHAF1B, CHAF1A, MCM2 and Kinetochore-related protein 1 (KNTC1), as potential diagnostic and prognostic biomarkers of CC.

Bioinformatics Analysis of Key Genes and Pathways of Cervical Cancer

Background and Objective

Globally, cervical cancer (CC) is the fourth most common cancer affecting women. Although effective screening reduces its incidence, it remains one of the most serious cancers threatening the health of women. Therefore, the purpose of this study is to find new genes that can be used as potential biomarkers for the prognosis of CC.

Methods and Results

After downloading three datasets such as GSE6791, GSE63678, and GSE63514 from the Gene Expression Omnibus (GEO), we combined the expression matrixes and analyzed them to obtain the differential expressed genes (DEGs). Next, using the STRING website, we performed the protein interaction network analysis. Subsequently, hub genes were screened using the R and Cytoscape software. Then, the expression difference and survival analyses of the hub genes were confirmed using GIPIA. Here, we established that the KNTC1 gene was correlated to the overall survival prognosis of CC. Besides, the expression of the KNTC1 gene in the GSE63514 dataset was significantly different from that of the normal cervix, cervical pre-cancerous lesions, and CC. Consequently, immunohistochemistry analysis showed that the results have a definite diagnostic value.

Conclusion

The KNTC1 gene could be linked with the pathophysiology of CC and maybe one of the early diagnostic markers for the diagnosis of cervical pre-cancerous lesions.

The N-terminus region of Drp1, a Rint1 family protein is essential for cell survival and its interaction with Rad50 protein in fission yeast S.pombe

BACKGROUND

Defects in DNA repair pathway can lead to double-strand breaks leading to genomic instability. Earlier we have shown that S.pombe Drp1, a Rint1/Tip1 family protein is required for the recovery from DNA damage.

METHODS

Various truncations of Drp1 protein were constructed and their role in DNA damage response and interaction with Rad50 protein has been studied by co-immunoprecipitation and pull-down assays.

RESULTS

The structural and functional analysis of Drp1 protein revealed that the N-terminus region of Drp1 is indispensable for the survival. The C-terminus truncation mutants, drp1C1Δ and drp1C2Δ exhibit temperature sensitive phenotype and are hypersensitive against DNA damaging agents with elevated level of Rad52-YFP foci at non-permissive temperature indicating the impairment for DNA damage repair pathway. The essential N-terminus region of Drp1 interacts with the C-terminus region of Rad50 and might be involved in influencing the MRN/X function. Small-angle X-ray (SAXS) analysis revealed three-domain like shapes in Drp1 protein while the C-terminus region of Rad50 exhibit unusual bulges. Computational docking studies revealed the amino acid residues at the C-terminus region of Rad50 that are involved in the interaction with the residues present at the N-terminal region of Drp1 indicating the importance of the N-terminal region of Drp1 protein.

CONCLUSIONS

We have identified the region of Drp1 and Rad50 proteins that are involved in the interaction and their role in the DNA damage response pathway has been analyzed.

GENERAL SIGNIFICANCE

The functional and structural aspects of fission yeast Drp1 protein and its interaction with Rad50 have been elucidated.

Dynamics of kinetochore structure and its regulations during mitotic progression

Faithful chromosome segregation during mitosis in eukaryotes requires attachment of the kinetochore, a large protein complex assembled on the centromere of each chromosome, to the spindle microtubules. The kinetochore is a structural interface for the microtubule attachment and provides molecular surveillance mechanisms that monitor and ensure the precise microtubule attachment as well, including error correction and spindle assembly checkpoint. During mitotic progression, the kinetochore undergoes dynamic morphological changes that are observable through electron microscopy as well as through fluorescence microscopy. These structural changes might be associated with the kinetochore function. In this review, we summarize how the dynamics of kinetochore morphology are associated with its functions and discuss recent findings on the switching of protein interaction networks in the kinetochore during cell cycle progression.

Anaphase-promoting complex/cyclosome-Cdc-20 promotes Zwint-1 degradation

ZW10 interactor (Zwint-1) is an important component of the centromere and can recruit the dynamic protein kinase and dynein to promote chromosome movement and regulate the spindle assembly checkpoint (SAC). Zwint-1 activity is tightly regulated during the cell cycle. However, how the stability of Zwint-1 is regulated has not been clarified. Here, we show that the relative levels of Zwint-1 expression gradually decreased with the progression of cell cycling and decline sharply during mitotic exit. Treatment with cycloheximide reduced the levels of Zwint-1 while treatment with MG132 to inhibit endogenous ubiquitin-proteasome elevated the levels of Zwint-1 in HEK293T cells or Hela cells. Such data suggest that Zwint-1 may be degraded by endogenous ubiquitin-proteasome. Furthermore, induction of cell-division cycle protein 20 (Cdc20) overexpression decreased the levels of Zwint-1, which was abrogated by MG132 treatment. In contrast, Cdc20 silencing promoted the accumulation of Zwint-1. in vivo ubiquitination assay revealed that Cdc20 promoted the formation of Zwint-1 and ubiquitin-proteasome conjugates. Cotransfection with Cdc20 and wild-type Zwint-1, but not Zwint-1^ΔD-box , reduced the levels of Zwint-1. Immunoprecipitation and western blot analyses showed that Cdc20 interacted with wild-type Zwint-1, but not Zwint-1^ΔD-box although both Zwint-1 and Zwint-1^ΔD-box overexpression did not induce mitotic arrest. Collectively, our data indicated that Zwint-1 was ubiquitinated by anaphase-promoting complex/cyclosome (APC/C)-Cdc20 in a D-box-dependent manner. Therefore, the APC/C-Cdc20 controls the stability of Zwint-1, ensuring accurate regulation of the spindle assembly during the cell cycling in HEK293T cells.

Crowning the Kinetochore: The Fibrous Corona in Chromosome Segregation

The kinetochore is at the heart of chromosome segregation in mitosis and meiosis. Rather than a static linker complex for chromatin and spindle microtubules, it is highly dynamic in composition, size, and shape. While known for decades that it can expand and grow a fibrous meshwork known as the corona, it was until recently unclear what constitutes this 'crown' and what its relevance is for kinetochore function. Here, we highlight recent discoveries in fibrous corona biology, and place them in the context of the processes that orchestrate high-fidelity chromosome segregation.

Chromosome Instability; Implications in Cancer Development, Progression, and Clinical Outcomes

Chromosome instability (CIN) refers to an ongoing rate of chromosomal changes and is a driver of genetic, cell-to-cell heterogeneity. It is an aberrant phenotype that is intimately associated with cancer development and progression. The presence, extent, and level of CIN has tremendous implications for the clinical management and outcomes of those living with cancer. Despite its relevance in cancer, there is still extensive misuse of the term CIN, and this has adversely impacted our ability to identify and characterize the molecular determinants of CIN. Though several decades of genetic research have provided insight into CIN, the molecular determinants remain largely unknown, which severely limits its clinical potential. In this review, we provide a definition of CIN, describe the two main types, and discuss how it differs from aneuploidy. We subsequently detail its impact on cancer development and progression, and describe how it influences metastatic potential with reference to cancer prognosis and outcomes. Finally, we end with a discussion of how CIN induces genetic heterogeneity to influence the use and efficacy of several precision medicine strategies, including patient and risk stratification, as well as its impact on the acquisition of drug resistance and disease recurrence.

Screening and Discovery of New Potential Biomarkers and Small Molecule Drugs for Cervical Cancer: A Bioinformatics Analysis

BACKGROUND

Cervical cancer (CC) is the second most common type of malignant tumor survival rate is low in advanced stage, metastatic, and recurrent CC patients. This study aimed at identifying potential genes and drugs for CC diagnosis and targeting therapies.

METHODS

Three GEO mRNA microarray datasets of CC tissues and non-cancerous tissues were analyzed for differentially expressed genes (DEGs) by limma package. GO (Gene Ontologies) and KEGG (Kyoto Encyclopedia of Genes and Genomes) were used to explore the relationships between the DEGs. Protein-protein interaction (PPI) of these genes was established by the STRING database. MCODE was used for screening significant modules in the PPI networks to select hub genes. Biochemical mechanisms of the hub genes were investigated with Metascape. GEPIA database was used for validating the core genes. According to these DEGs, molecular candidates for CC were recognized from the CMAP database.

RESULTS

We identified 309 overlapping DEGs in the 2 tissue-types. Pathway analysis revealed that the DEGs were involved in cell cycle, DNA replication, and p53 signaling. PPI networks between overlapping DEGs showed 68 high-connectivity DEGs that were chosen as hub genes. The GEPIA database showed that the expression levels of RRM2, CDC45, GINS2, HELLS, KNTC1, MCM2, MYBL2, PCNA, RAD54 L, RFC4, RFC5, TK1, TOP2A, and TYMS in CC tissues were significantly different from those in the healthy tissues and were significantly relevant to the OS of CC. We found 10 small molecules from the CMAP database that could change the trend of gene expression in CC tissues, including piperlongumine and chrysin.

CONCLUSIONS

The 14 DEGs identified in this study could serve as novel prognosis biomarkers for the detection and forecasting of CC. Small molecule drugs like piperlongumine and chrysin could be potential therapeutic drugs for CC treatment.

Epistatic Analysis of the Contribution of Rabs and Kifs to CATCHR Family Dependent Golgi Organization

Multisubunit members of the CATCHR family: COG and NRZ complexes, mediate intra-Golgi and Golgi to ER vesicle tethering, respectively. We systematically addressed the genetic and functional interrelationships between Rabs, Kifs, and the retrograde CATCHR family proteins: COG3 and ZW10, which are necessary to maintain the organization of the Golgi complex. We scored the ability of siRNAs targeting 19 Golgi-associated Rab proteins and all 44 human Kifs, microtubule-dependent motor proteins, to suppress CATCHR-dependent Golgi fragmentation in an epistatic fluorescent microscopy-based assay. We found that co-depletion of Rab6A, Rab6A’, Rab27A, Rab39A and two minus-end Kifs, namely KIFC3 and KIF25, suppressed both COG3- and ZW10-depletion-induced Golgi fragmentation. ZW10-dependent Golgi fragmentation was suppressed selectively by a separate set of Rabs: Rab11A, Rab33B and the little characterized Rab29. 10 Kifs were identified as hits in ZW10-depletion-induced Golgi fragmentation, and, in contrast to the double suppressive Kifs, these were predominantly plus-end motors. No Rabs or Kifs selectively suppressed COG3-depletion-induced Golgi fragmentation. Protein-protein interaction network analysis indicated putative direct and indirect links between suppressive Rabs and tether function. Validation of the suppressive hits by EM confirmed a restored organization of the Golgi cisternal stack. Based on these outcomes, we propose a three-way competitive model of Golgi organization in which Rabs, Kifs and tethers modulate sequentially the balance between Golgi-derived vesicle formation, consumption, and off-Golgi transport.

BUB1 Is Essential for the Viability of Human Cells in which the Spindle Assembly Checkpoint Is Compromised

The spindle assembly checkpoint (SAC) ensures faithful segregation of chromosomes. Although most mammalian cell types depend on the SAC for viability, we found that human HAP1 cells can grow SAC independently. We generated MAD1- and MAD2-deficient cells and mutagenized them to identify synthetic lethal interactions, revealing that chromosome congression factors become essential upon SAC deficiency. Besides expected hits, we also found that BUB1 becomes essential in SAC-deficient cells. We found that the BUB1 C terminus regulates alignment as well as recruitment of CENPF. Second, we found that BUBR1 was not essential in SAC-deficient HAP1 cells. We confirmed that BUBR1 does not regulate chromosome alignment in HAP1 cells and that BUB1 does not regulate chromosome alignment through BUBR1. Taken together, our data resolve some long-standing questions about the interplay between BUB1 and BUBR1 and their respective roles in the SAC and chromosome alignment.

Recent Progress on the Localization of the Spindle Assembly Checkpoint Machinery to Kinetochores

Faithful chromosome segregation during mitosis is crucial for maintaining genome stability. The spindle assembly checkpoint (SAC) is a surveillance mechanism that ensures accurate mitotic progression. Defective SAC signaling leads to premature sister chromatid separation and aneuploid daughter cells. Mechanistically, the SAC couples the kinetochore microtubule attachment status to the cell cycle progression machinery. In the presence of abnormal kinetochore microtubule attachments, the SAC prevents the metaphase-to-anaphase transition through a complex kinase-phosphatase signaling cascade which results in the correct balance of SAC components recruited to the kinetochore. The correct kinetochore localization of SAC proteins is a prerequisite for robust SAC signaling and, hence, accurate chromosome segregation. Here, we review recent progresses on the kinetochore recruitment of core SAC factors.

Efficient mitotic checkpoint signaling depends on integrated activities of Bub1 and the RZZ complex

Kinetochore localized Mad1 is essential for generating a "wait anaphase" signal during mitosis, hereby ensuring accurate chromosome segregation. Inconsistent models for the function and quantitative contribution of the two mammalian Mad1 kinetochore receptors: Bub1 and the Rod-Zw10-Zwilch (RZZ) complex exist. By combining genome editing and RNAi, we achieve penetrant removal of Bub1 and Rod in human cells, which reveals that efficient checkpoint signaling depends on the integrated activities of these proteins. Rod removal reduces the proximity of Bub1 and Mad1, and we can bypass the requirement for Rod by tethering Mad1 to kinetochores or increasing the strength of the Bub1-Mad1 interaction. We find that Bub1 has checkpoint functions independent of Mad1 localization that are supported by low levels of Bub1 suggesting a catalytic function. In conclusion, our results support an integrated model for the Mad1 receptors in which the primary role of RZZ is to localize Mad1 at kinetochores to generate the Mad1-Bub1 complex.

shRNA‑mediated knockdown of KNTC1 suppresses cell viability and induces apoptosis in esophageal squamous cell carcinoma

Kinetochore‑associated proteins are critical components of mitotic checkpoints, which are essential for faithful chromosomal segregation and spindle assembly during cell division. Recent advances have demonstrated that kinetochore‑associated proteins are upregulated and serve significant roles in the carcinogenesis of numerous types of cancer. However, the effects of kinetochore‑associated protein 1 (KNTC1) on human cancer, particularly on esophageal squamous cell carcinoma (ESCC), remain unclear. The present study revealed that KNTC1 was highly expressed in ESCC cell lines. Subsequently, lentivirus‑mediated short hairpin RNAs were used to knockdown KNTC1 expression in human ESCC cell lines. Cell growth and viability were measured using multiparametric high‑content screening and the MTT assay, respectively. Cell apoptosis was assessed by staining cells with Annexin V‑allophycocyanin and was detected using FACScan flow cytometry. The results demonstrated that knockdown of KNTC1 effectively inhibited cell viability and increased apoptosis. In addition, a gene set enrichment analysis of online ESCC datasets indicated that KNTC1 overexpression was associated with increases in the mitotic spindle and hypoxia pathways, and decreases in the DNA repair and mismatch repair pathways. The findings of the present study suggested that KNTC1 may have an essential role in mediating cell viability and apoptosis in human ESCC cells and may serve as a novel therapeutic target for ESCC.

Importance of gene expression signatures in pancreatic cancer prognosis and the establishment of a prediction model

Background and aim

Pancreatic cancer (PC) is one of the most common tumors with a poor prognosis. The current American Joint Committee on Cancer (AJCC) staging system, based on the anatomical features of tumors, is insufficient to predict PC outcomes. The current study is endeavored to identify important prognosis-related genes and build an effective predictive model.

Methods

Multiple public datasets were used to identify differentially expressed genes (DEGs) and survival-related genes (SRGs). Bioinformatics analysis of DEGs was used to identify the main biological processes and pathways involved in PC. A risk score based on SRGs was computed through a univariate Cox regression analysis. The performance of the risk score in predicting PC prognosis was evaluated with survival analysis, Harrell's concordance index (C-index), area under the curve (AUC), and calibration plots. A predictive nomogram was built through integrating the risk score with clinicopathological information.

Results

A total of 945 DEGs were identified in five Gene Expression Omnibus datasets, and four SRGs (LYRM1, KNTC1, IGF2BP2, and CDC6) were significantly associated with PC progression and prognosis in four datasets. The risk score showed relatively good performance in predicting prognosis in multiple datasets. The predictive nomogram had greater C-index and AUC values, compared with those of the AJCC stage and risk score.

Conclusion

This study identified four new biomarkers that are significantly associated with the carcinogenesis, progression, and prognosis of PC, which may be helpful in studying the underlying mechanism of PC carcinogenesis. The predictive nomogram showed robust performance in predicting PC prognosis. Therefore, the current model may provide an effective and reliable guide for prognosis assessment and treatment decision-making in the clinic.

MAD1: Kinetochore Receptors and Catalytic Mechanisms

The mitotic checkpoint monitors kinetochore-microtubule attachment, delays anaphase onset and prevents aneuploidy when unattached or tensionless kinetochores are present in cells. Mitotic arrest deficiency 1 (MAD1) is one of the evolutionarily conserved core mitotic checkpoint proteins. MAD1 forms a cell cycle independent complex with MAD2 through its MAD2 interaction motif (MIM) in the middle region. Such a complex is enriched at unattached kinetochores and functions as an unusual catalyst to promote conformational change of additional MAD2 molecules, constituting a crucial signal amplifying mechanism for the mitotic checkpoint. Only MAD2 in its active conformation can be assembled with BUBR1 and CDC20 to form the Mitotic Checkpoint Complex (MCC), which is a potent inhibitor of anaphase onset. Recent research has shed light on how MAD1 is recruited to unattached kinetochores, and how it carries out its catalytic activity. Here we review these advances and discuss their implications for future research.

The ESCRT protein Chmp4c regulates mitotic spindle checkpoint signaling

The mitotic spindle checkpoint delays anaphase onset in the presence of unattached kinetochores, and efficient checkpoint signaling requires kinetochore localization of the Rod-ZW10-Zwilch (RZZ) complex. In the present study, we show that human Chmp4c, a protein involved in membrane remodeling, localizes to kinetochores in prometaphase but is reduced in chromosomes aligned at the metaphase plate. Chmp4c promotes stable kinetochore-microtubule attachments and is required for proper mitotic progression, faithful chromosome alignment, and segregation. Depletion of Chmp4c diminishes localization of RZZ and Mad1-Mad2 checkpoint proteins to prometaphase kinetochores and impairs mitotic arrest when microtubules are depolymerized by nocodazole. Furthermore, Chmp4c binds to ZW10 through a small C-terminal region, and constitutive Chmp4c kinetochore targeting causes a ZW10-dependent checkpoint metaphase arrest. In addition, Chmp4c spindle functions do not require endosomal sorting complex required for transport-dependent membrane remodeling. These results show that Chmp4c regulates the mitotic spindle checkpoint by promoting localization of the RZZ complex to unattached kinetochores.

Rs2459976 in ZW10 gene associated with congenital heart diseases in Chinese Han population

Congenital heart diseases (CHD) are a large group of prevalent and complex anatomic malformations of the heart, with the genetic basis remaining largely unknown. Since genes or factors associated with the differentiation of human embryonic stem (HES) cells would affect the development of all embryonic tissues, including cardiac progenitor cells, we postulated their potential roles in CHD. In this study, we focused on ZW10, a kinetochore protein involved in the process of proper chromosome segregation, and conducted comparative studies between CHD patients and normal controls matched in gender and age in Chinese Han populations. We identified three variations in the ZW10 gene, including rs2885987, rs2271261 and rs2459976, which all had high genetic heterozygosity. Association analysis of these genetic variations with CHD showed correlation between rs2459976 and the risk of CHD. We conclude that rs2459976 in the ZW10 gene is associated with CHD in Chinese Han populations.

STAT5BN642H is a driver mutation for T cell neoplasia

STAT5B is often mutated in hematopoietic malignancies. The most frequent STAT5B mutation, Asp642His (N642H), has been found in over 90 leukemia and lymphoma patients. Here, we used the Vav1 promoter to generate transgenic mouse models that expressed either human STAT5B or STAT5B^N642H in the hematopoietic compartment. While STAT5B-expressing mice lacked a hematopoietic phenotype, the STAT5B^N642H-expressing mice rapidly developed T cell neoplasms. Neoplasia manifested as transplantable CD8⁺ lymphoma or leukemia, indicating that the STAT5B^N642H mutation drives cancer development. Persistent and enhanced levels of STAT5B^N642H tyrosine phosphorylation in transformed CD8⁺ T cells led to profound changes in gene expression that were accompanied by alterations in DNA methylation at potential histone methyltransferase EZH2-binding sites. Aurora kinase genes were enriched in STAT5B^N642H-expressing CD8⁺ T cells, which were exquisitely sensitive to JAK and Aurora kinase inhibitors. Together, our data suggest that JAK and Aurora kinase inhibitors should be further explored as potential therapeutics for lymphoma and leukemia patients with the STAT5B^N642H mutation who respond poorly to conventional chemotherapy.

Prolonged mitotic arrest induced by Wee1 inhibition sensitizes breast cancer cells to paclitaxel

Wee1 kinase is a crucial negative regulator of Cdk1/cyclin B1 activity and is required for normal entry into and exit from mitosis. Wee1 activity can be chemically inhibited by the small molecule MK-1775, which is currently being tested in phase I/II clinical trials in combination with other anti-cancer drugs. MK-1775 promotes cancer cells to bypass the cell-cycle checkpoints and prematurely enter mitosis. In our study, we show premature mitotic cells that arise from MK-1775 treatment exhibited centromere fragmentation, a morphological feature of mitotic catastrophe that is characterized by centromeres and kinetochore proteins that co-cluster away from the condensed chromosomes. In addition to stimulating early mitotic entry, MK-1775 treatment also delayed mitotic exit. Specifically, cells treated with MK-1775 following release from G1/S or prometaphase arrested in mitosis. MK-1775 induced arrest occurred at metaphase and thus, cells required 12 times longer to transition into anaphase compared to controls. Consistent with an arrest in mitosis, MK-1775 treated prometaphase cells maintained high cyclin B1 and low phospho-tyrosine 15 Cdk1. Importantly, MK-1775 induced mitotic arrest resulted in cell death regardless the of cell-cycle phase prior to treatment suggesting that Wee1 inhibitors are also anti-mitotic agents. We found that paclitaxel enhances MK-1775 mediated cell killing. HeLa and different breast cancer cell lines (T-47D, MCF7, MDA-MB-468 and MDA-MB-231) treated with different concentrations of MK-1775 and low dose paclitaxel exhibited reduced cell survival compared to mono-treatments. Our data highlight a new potential strategy for enhancing MK-1775 mediated cell killing in breast cancer cells.

Molecular mechanism of dynein recruitment to kinetochores by the Rod-Zw10-Zwilch complex and Spindly

The dynein motor is recruited to the kinetochore to capture spindle microtubules and control the spindle assembly checkpoint. Gama et al. reveal the molecular mechanism of how the Rod–Zw10–Zwilch complex and Spindly mediate dynein recruitment in Caenorhabditis elegans and human cells.

The molecular motor dynein concentrates at the kinetochore region of mitotic chromosomes in animals to accelerate spindle microtubule capture and to control spindle checkpoint signaling. In this study, we describe the molecular mechanism used by the Rod–Zw10–Zwilch complex and the adaptor Spindly to recruit dynein to kinetochores in Caenorhabditis elegans embryos and human cells. We show that Rod’s N-terminal β-propeller and the associated Zwilch subunit bind Spindly’s C-terminal domain, and we identify a specific Zwilch mutant that abrogates Spindly and dynein recruitment in vivo and Spindly binding to a Rod β-propeller–Zwilch complex in vitro. Spindly’s N-terminal coiled-coil uses distinct motifs to bind dynein light intermediate chain and the pointed-end complex of dynactin. Mutations in these motifs inhibit assembly of a dynein–dynactin–Spindly complex, and a null mutant of the dynactin pointed-end subunit p27 prevents kinetochore recruitment of dynein–dynactin without affecting other mitotic functions of the motor. Conservation of Spindly-like motifs in adaptors involved in intracellular transport suggests a common mechanism for linking dynein to cargo.

Association of Human Papillomavirus 16 E2 with Rad50-Interacting Protein 1 Enhances Viral DNA Replication

Rad50-interacting protein 1 (Rint1) associates with the DNA damage response protein Rad50 during the transition from the S phase to the G₂/M phase and functions in radiation-induced G₂ checkpoint control. It has also been demonstrated that Rint1 is essential in vesicle trafficking from the Golgi apparatus to the endoplasmic reticulum (ER) through an interaction with Zeste-White 10 (ZW10). We have isolated a novel interaction between Rint1 and the human papillomavirus 16 (HPV16) transcription and replication factor E2. E2 binds to Rint1 within its ZW10 interaction domain, and we show that in the absence of E2, Rint1 is localized to the ER and associates with ZW10. E2 expression results in a disruption of the Rint1-ZW10 interaction and an accumulation of nuclear Rint1, coincident with a significant reduction in vesicle movement from the ER to the Golgi apparatus. Interestingly, nuclear Rint1 and members of the Mre11/Rad50/Nbs1 (MRN) complex were found in distinct E2 nuclear foci, which peaked during mid-S phase, indicating that the recruitment of Rint1 to E2 foci within the nucleus may also result in the recruitment of this DNA damage-sensing protein complex. We show that exogenous Rint1 expression enhances E2-dependent virus replication. Conversely, the overexpression of a truncated Rint1 protein that retains the E2 binding domain but not the Rad50 binding domain acts as a dominant negative inhibitor of E2-dependent HPV replication. Put together, these experiments demonstrate that the interaction between Rint1 and E2 has an important function in HPV replication.

IMPORTANCE HPV infections are an important driver of many epithelial cancers, including those within the anogenital and oropharyngeal tracts. The HPV life cycle is tightly regulated and intimately linked to the differentiation of the epithelial cells that it infects. HPV replication factories formed in the nucleus are locations where viral DNA is copied to support virus persistence and amplification of infection. The recruitment of specific cellular protein complexes to these factories aids efficient and controlled viral replication. We have identified a novel HPV-host interaction that functions in the cellular response to DNA damage and cell cycle control. We show that the HPV E2 protein targets Rad50-interacting protein 1 (Rint1) to facilitate virus genome replication. These findings add to our understanding of how HPV replicates and the host cell pathways that are targeted by HPV to support virus replication. Understanding these pathways will allow further research into novel inhibitors of HPV genome replication.

The mitotic checkpoint complex (MCC): looking back and forth after 15 years

The mitotic checkpoint is a specialized signal transduction pathway that contributes to the fidelity of chromosome segregation. The signaling of the checkpoint originates from defective kinetochore-microtubule interactions and leads to formation of the mitotic checkpoint complex (MCC), a highly potent inhibitor of the Anaphase Promoting Complex/Cyclosome (APC/C)—the E3 ubiquitin ligase essential for anaphase onset. Many important questions concerning the MCC and its interaction with APC/C have been intensively investigated and debated in the past 15 years, such as the exact composition of the MCC, how it is assembled during a cell cycle, how it inhibits APC/C, and how the MCC is disassembled to allow APC/C activation. These efforts have culminated in recently reported structure models for human MCC:APC/C supra-complexes at near-atomic resolution that shed light on multiple aspects of the mitotic checkpoint mechanisms. However, confusing statements regarding the MCC are still scattered in the literature, making it difficult for students and scientists alike to obtain a clear picture of MCC composition, structure, function and dynamics. This review will comb through some of the most popular concepts or misconceptions about the MCC, discuss our current understandings, present a synthesized model on regulation of CDC20 ubiquitination, and suggest a few future endeavors and cautions for next phase of MCC research.

A network medicine approach to build a comprehensive atlas for the prognosis of human cancer

The Cancer Genome Atlas project has generated multi-dimensional and highly integrated genomic data from a large number of patient samples with detailed clinical records across many cancer types, but it remains unclear how to best integrate the massive amount of genomic data into clinical practice. We report here our methodology to build a multi-dimensional subnetwork atlas for cancer prognosis to better investigate the potential impact of multiple genetic and epigenetic (gene expression, copy number variation, microRNA expression and DNA methylation) changes on the molecular states of networks that in turn affects complex cancer survivorship. We uncover an average of 38 novel subnetworks in the protein-protein interaction network that correlate with prognosis across four prominent cancer types. The clinical utility of these subnetwork biomarkers was further evaluated by prognostic impact evaluation, functional enrichment analysis, drug target annotation, tumor stratification and independent validation. Some pathways including the dynactin, cohesion and pyruvate dehydrogenase-related subnetworks are identified as promising new targets for therapy in specific cancer types. In conclusion, this integrative analysis of existing protein interactome and cancer genomics data allows us to systematically dissect the molecular mechanisms that underlie unexpected outcomes for cancer, which could be used to better understand and predict clinical outcomes, optimize treatment and to provide new opportunities for developing therapeutics related to the subnetworks identified.

Cep57 is a Mis12-interacting kinetochore protein involved in kinetochore targeting of Mad1-Mad2

The spindle assembly checkpoint (SAC) arrests cells in mitosis by sensing unattached kinetochores, until all chromosomes are bi-oriented by spindle microtubules. Kinetochore accumulation of the SAC component Mad1–Mad2 is crucial for SAC activation. However, the mechanism by which Mad1–Mad2 accumulation at kinetochores is regulated is not clear. Here we find that Cep57 is localized to kinetochores in human cells, and binds to Mis12, a KMN (KNL1/Mis12 complex/Ndc80 complex) network component. Cep57 also interacts with Mad1, and depletion of Cep57 results in decreased kinetochore localization of Mad1–Mad2, reduced SAC signalling and increased chromosome segregation errors. We also show that the microtubule-binding activity of Cep57 is involved in the timely removal of Mad1 from kinetochores. Thus, these findings reveal that the KMN network-binding protein Cep57 is a mitotic kinetochore component, and demonstrate the functional connection between the KMN network and the SAC.

The spindle assembly checkpoint relies on the accumulation of Mad1-Mad2 at kinetochores, but the mechanism of regulation is not known. Here Zhou et al. show that the centrosomal protein Cep57 interacts with the kinetochore proteins Mis12 and Mad1, and regulates the recruitment of Mad1/Mad2 to kinetochores.

A novel role of farnesylation in targeting a mitotic checkpoint protein, human Spindly, to kinetochores

The mitotic checkpoint protein Spindly is farnesylated in vivo and this modification is required for its interaction with the RZZ complex and its localization to kinetochores.

Kinetochore (KT) localization of mitotic checkpoint proteins is essential for their function during mitosis. hSpindly KT localization is dependent on the RZZ complex and hSpindly recruits the dynein–dynactin complex to KTs during mitosis, but the mechanism of hSpindly KT recruitment is unknown. Through domain-mapping studies we characterized the KT localization domain of hSpindly and discovered it undergoes farnesylation at the C-terminal cysteine residue. The N-terminal 293 residues of hSpindly are dispensable for its KT localization. Inhibition of farnesylation using a farnesyl transferase inhibitor (FTI) abrogated hSpindly KT localization without affecting RZZ complex, CENP-E, and CENP-F KT localization. We showed that hSpindly is farnesylated in vivo and farnesylation is essential for its interaction with the RZZ complex and hence KT localization. FTI treatment and hSpindly knockdown displayed the same mitotic phenotypes, indicating that hSpindly is a key FTI target in mitosis. Our data show a novel role of lipidation in targeting a checkpoint protein to KTs through protein–protein interaction.

Connecting the microtubule attachment status of each kinetochore to cell cycle arrest through the spindle assembly checkpoint

Kinetochores generate a signal that inhibits anaphase progression until every kinetochore makes proper attachments to spindle microtubules. This spindle assembly checkpoint (SAC) increases the fidelity of chromosome segregation. We will review the molecular mechanisms by which kinetochores generate the SAC and extinguish the signal after making proper attachments, with the goal of identifying unanswered questions and new research directions. We will emphasize recent breakthroughs in how phosphorylation changes drive the activation and inhibition of the signal. We will also emphasize the dramatic changes in kinetochore structure that occur after attaching to microtubules and how these coordinate SAC function with microtubule attachment status. Finally, we will review the emerging cross talk between the DNA damage response and the SAC.

Complex assembly, crystallization and preliminary X-ray crystallographic analysis of the human Rod-Zwilch-ZW10 (RZZ) complex

The spindle-assembly checkpoint (SAC) monitors kinetochore-microtubule attachment during mitosis. In metazoans, the three-subunit Rod-Zwilch-ZW10 (RZZ) complex is a crucial SAC component that interacts with additional SAC-activating and SAC-silencing components, including the Mad1-Mad2 complex and cytoplasmic dynein. The RZZ complex contains two copies of each subunit and has a predicted molecular mass of ∼800 kDa. Given the low abundance of the RZZ complex in natural sources, its recombinant reconstitution was attempted by co-expression of its subunits in insect cells. The RZZ complex was purified to homogeneity and subjected to systematic crystallization attempts. Initial crystals containing the entire RZZ complex were obtained using the sitting-drop method and were subjected to optimization to improve the diffraction resolution limit. The crystals belonged to space group P3₁ (No. 144) or P3₂ (No. 145), with unit-cell parameters a = b = 215.45, c = 458.7 Å, α = β = 90.0, γ = 120.0°.

Mitotic catenation is monitored and resolved by a PKCε-regulated pathway

Exit from mitosis is controlled by silencing of the spindle assembly checkpoint (SAC). It is important that preceding exit, all sister chromatid pairs are correctly bioriented, and that residual catenation is resolved, permitting complete sister chromatid separation in the ensuing anaphase. Here we determine that the metaphase response to catenation in mammalian cells operates through PKCε. The PKCε-controlled pathway regulates exit from the SAC only when mitotic cells are challenged by retained catenation and this delayed exit is characterized by BubR1-high and Mad2-low kinetochores. In addition, we show that this pathway is necessary to facilitate resolution of retained catenanes in mitosis. When delayed by catenation in mitosis, inhibition of PKCε results in premature entry into anaphase with PICH-positive strands and chromosome bridging. These findings demonstrate the importance of PKCε-mediated regulation in protection from loss of chromosome integrity in cells failing to resolve catenation in G2.

CENP-I and Aurora B act as a molecular switch that ties RZZ/Mad1 recruitment to kinetochore attachment status

The integrated activities of Aurora B and CENP-I generate a molecular switch that maintains a robust spindle checkpoint signal at prometaphase kinetochores until they attain mature attachments to microtubules.

The RZZ (Rod, ZW10, and Zwilch) complex and Mad1 proteins tightly associate with kinetochores to generate the spindle checkpoint signal, but they are released when a kinetochore forms mature microtubule attachments. Here we demonstrate that the centromere protein CENP-I is required to generate a stable association of RZZ and Mad1 with kinetochores. CENP-I also inhibits their removal by dynein stripping. This regulation of Mad1 and RZZ dissociation functions independently of Aurora B, which regulates their association. We show that the microtubule status of each kinetochore independently dictates the recruitment of Aurora B kinase, kinase activity on a kinetochore substrate, and loading of spindle checkpoint proteins. This dynamic regulation of Mad1 association by Aurora B is only uncovered when CENP-I is depleted, consistent with our finding that CENP-I inhibits the dissociation of Mad1. We conclude that the dual activities of Aurora B and CENP-I generate a molecular switch that maintains a robust spindle checkpoint signal at prometaphase kinetochores until they attain mature attachments to microtubules.

COX-2 inhibitors arrest prostate cancer cell cycle progression by down-regulation of kinetochore/centromere proteins

BACKGROUND

Previous studies have shown that COX-2 inhibitors inhibit cancer cell proliferation. However, the molecular mechanism remains elusive.

METHODS

Prostate cancer LNCaP, 22Rv1, and PC3 cells were cultured and treated with the COX-2 inhibitors celecoxib and CAY10404. Knockdown of COX-2 in LNCaP cells was carried out using lentiviral vector-loaded COX-2 shRNA. Cell cycle progression and cell proliferation were analyzed by flow cytometry, microscopy, cell counting, and the MTT assay. The antagonists of EP1, EP2, EP3, and EP4 were used to examine the effects of the PGE2 signaling. The effect of COX-2 inhibitors and COX-2 knockdown on expression of the kinetochore/centromere genes and proteins was determined by RT-PCR and immunoblotting.

RESULTS

Treatment with the COX-2 inhibitors celecoxib and CAY10404 or knockdown of COX-2 significantly inhibited prostate cancer cell proliferation. Flow-cytometric analysis and immunofluorescent staining confirmed the cell cycle arrested at the G2/M phase. Biochemical analysis showed that inhibition of COX-2 or suppression of COX-2 expression induced a dramatic down-regulation of key proteins in the kinetochore/centromere assembly, such as ZWINT, Cdc20, Ndc80, CENP-A, Bub1, and Plk1. Furthermore, the EP1 receptor antagonist SC51322, but not the EP2, EP3, and EP4 receptor antagonists, produced similar effects to the COX-2 inhibitors on cell proliferation and down-regulation of kinetochore/centromere proteins, suggesting that the effect of the COX-2 inhibition is through inactivation of the EP1 receptor signaling.

CONCLUSIONS

Our studies indicate that inhibition of COX-2 can arrest prostate cancer cell cycle progression through inactivation of the EP1 receptor signaling and down-regulation of kinetochore/centromere proteins.

Moonlighting functions of the NRZ (mammalian Dsl1) complex

The yeast Dsl1 complex, which comprises Dsl1, Tip20, and Sec39/Dsl3, has been shown to participate, as a vesicle-tethering complex, in retrograde trafficking from the Golgi apparatus to the endoplasmic reticulum. Its metazoan counterpart NRZ complex, which comprises NAG, RINT1, and ZW10, is also involved in Golgi-to-ER retrograde transport, but each component of the complex has diverse cellular functions including endosome-to-Golgi transport, cytokinesis, cell cycle checkpoint, autophagy, and mRNA decay. In this review, we summarize the current knowledge of the metazoan NRZ complex and discuss the "moonlighting" functions and intercorrelation of their subunits.

Conditional targeting of MAD1 to kinetochores is sufficient to reactivate the spindle assembly checkpoint in metaphase

Fidelity of chromosome segregation is monitored by the spindle assembly checkpoint (SAC). Key components of the SAC include MAD1, MAD2, BUB1, BUB3, BUBR1, and MPS1. These proteins accumulate on kinetochores in early prometaphase but are displaced when chromosomes attach to microtubules and/or biorient on the mitotic spindle. As a result, stable attachment of the final chromosome satisfies the SAC, permitting activation of the anaphase promoting complex/cyclosome (APC/C) and subsequent anaphase onset. SAC satisfaction is reversible, however, as addition of taxol during metaphase stops cyclin B1 degradation by the APC/C. We now show that targeting MAD1 to kinetochores during metaphase is sufficient to reestablish SAC activity after initial silencing. Using rapamycin-induced heterodimerization of FKBP-MAD1 to FRB-MIS12 and live monitoring of cyclin B1 degradation, we show that timed relocalization of MAD1 during metaphase can stop cyclin B1 degradation without affecting chromosome-spindle attachments. APC/C inhibition represented true SAC reactivation, as FKBP-MAD1 required an intact MAD2-interaction motif and MPS1 activity to accomplish this. Our data show that MAD1 kinetochore localization dictates SAC activity and imply that SAC regulatory mechanisms downstream of MAD1 remain functional in metaphase.

Plzf as a candidate gene predisposing the spontaneously hypertensive rat to hypertension, left ventricular hypertrophy, and interstitial fibrosis

BACKGROUND

The spontaneously hypertensive rat (SHR) is the most widely used model of essential hypertension and is susceptible to left ventricular hypertrophy (LVH) and myocardial fibrosis. Recently, a quantitative trait locus (QTL) that influences heart interstitial fibrosis was mapped to chromosome 8. Our aim was to dissect the genetic basis of this QTL(s) predisposing SHR to hypertension, LVH, and interstitial fibrosis.

METHODS

Hemodynamic and histomorphometric analyses were performed in genetically defined SHR.PD-chr.8 minimal congenic strain (PD5 subline) rats.

RESULTS

The differential segment, genetically isolated within the PD5 subline, spans 788kb and contains 7 genes, including the promyelocytic leukemia zinc finger (Plzf) gene that has been implicated in hypertrophy and cardiac fibrosis. Mutant Plzf allele contains a 2,964-bp deletion in intron 2. The PD5 congenic strain, when compared with the SHR, showed significantly reduced systolic blood pressure by approximately 15mm Hg (P = 0.002), amelioration of LVH (0.23±0.02 vs. 0.39±0.02g/100g body weight; P < 0.00001), and reduced interstitial fibrosis (17,478±1,035 vs. 41,530±3,499 μm(2); P < 0.0001). The extent of amelioration of LVH and interstitial fibrosis was disproportionate to blood pressure decrease in congenic rats, suggesting an important role for genetic factors. Cardiac expression of Plzf was significantly reduced in prehypertensive (8 and 21 days) congenic animals compared with controls.

CONCLUSIONS

These results provide compelling evidence of a significant role for genetic factors in regulating blood pressure, LVH, and cardiac fibrosis and identify mutant Plzf as a prominent candidate gene.