Bioinformatics analysis and experimental validation reveal that CDC20 overexpression promotes bladder cancer progression and potential underlying mechanisms

BACKGROUND

Bladder cancer is a prevalent malignancy. CDC20, a pivotal cell cycle regulator gene, plays a significant role in tumour cell proliferation, but its role in bladder cancer remains unclear.

OBJECTIVE

This study aimed to analyse CDC20 expression in bladder cancer and explore its roles in tumour progression, treatment response, patient prognosis, and cellular proliferation mechanisms.

METHODS

We systematically analysed CDC20 expression in bladder cancer using bioinformatics. Our study investigated the impact of CDC20 on chemotherapy and radiotherapy sensitivity, patient prognosis, and changes in CDC20 methylation levels. We also explored the role and potential underlying mechanisms of CDC20 in bladder cancer cell growth. We used lentiviral transfection to downregulate CDC20 expression in 5637 and T24 cells, followed by CCK-8, colony formation, scratch, invasion, apoptosis, and cell cycle analyses.

RESULTS

CDC20 is highly expressed in bladder cancer and is significantly correlated with poor prognosis. Moreover, CDC20 demonstrated high diagnostic potential for bladder cancer (AUC > 0.9). The tumour methylation levels of CDC20 in tumour tissues markedly decreased compared with those in normal tissues, and lower methylation levels were associated with a worse prognosis. Elevated CDC20 expression is linked to increased mutation burden. Our findings suggested a potential association between high CDC20 expression and resistance to chemotherapy and radiotherapy, as CDC20 expression may impact immune cell infiltration levels. Mechanistic analysis revealed the influence of CDC20 on bladder cancer cell proliferation through cell cycle-related pathways. According to the cell experiments, CDC20 downregulation significantly impedes bladder cancer cell proliferation and invasion, leading to G1 phase arrest.

CONCLUSION

Aberrantly high CDC20 expression promotes tumour progression in bladder cancer, resulting in a poor prognosis, and may also constitute a promising therapeutic target.

MAPK-dependent control of mitotic progression in S. pombe

BACKGROUND

Mitogen-activated protein kinases (MAPKs) preserve cell homeostasis by transducing physicochemical fluctuations of the environment into multiple adaptive responses. These responses involve transcriptional rewiring and the regulation of cell cycle transitions, among others. However, how stress conditions impinge mitotic progression is largely unknown. The mitotic checkpoint is a surveillance mechanism that inhibits mitotic exit in situations of defective chromosome capture, thus preventing the generation of aneuploidies. In this study, we investigate the role of MAPK Pmk1 in the regulation of mitotic exit upon stress.

RESULTS

We show that Schizosaccharomyces pombe cells lacking Pmk1, the MAP kinase effector of the cell integrity pathway (CIP), are hypersensitive to microtubule damage and defective in maintaining a metaphase arrest. Epistasis analysis suggests that Pmk1 is involved in maintaining spindle assembly checkpoint (SAC) signaling, and its deletion is additive to the lack of core SAC components such as Mad2 and Mad3. Strikingly, pmk1Δ cells show up to twofold increased levels of the anaphase-promoting complex (APC/C) activator Cdc20Slp1 during unperturbed growth. We demonstrate that Pmk1 physically interacts with Cdc20Slp1 N-terminus through a canonical MAPK docking site. Most important, the Cdc20Slp1 pool is rapidly degraded in stressed cells undergoing mitosis through a mechanism that requires MAPK activity, Mad3, and the proteasome, thus resulting in a delayed mitotic exit.

CONCLUSIONS

Our data reveal a novel function of MAPK in preventing mitotic exit and activation of cytokinesis in response to stress. The regulation of Cdc20Slp1 turnover by MAPK Pmk1 provides a key mechanism by which the timing of mitotic exit can be adjusted relative to environmental conditions.

SETDB2 interacts with BUBR1 to induce accurate chromosome segregation independently of its histone methyltransferase activity

SETDB2 is a H3K9 histone methyltransferase required for accurate chromosome segregation. Its H3K9 histone methyltransferase activity was reported to be associated with chromosomes during metaphase. Here, we confirm that SETDB2 is required for mitosis and accurate chromosome segregation. However, these functions are independent of its histone methyltransferase activity. Further analysis showed that SETDB2 can interact with BUBR1, and is required for CDC20 binding to BUBR1 and APC/C complex and CYCLIN B1 degradation. The ability of SETDB2 to regulate the binding of CDC20 to BUBR1 or APC/C complex, and stabilization of CYCLIN B1 are also independent of its histone methyltransferase activity. These results suggest that SETDB2 interacts with BUBR1 to promote binding of CDC20 to BUBR1 and APC3, then degrades CYCLIN B1 to ensure accurate chromosome segregation and mitosis, independently of its histone methyltransferase activity.

Functional analysis of Cdc20 reveals a critical role of CRY box in mitotic checkpoint signaling

Accurate mitosis is coordinated by the spindle assembly checkpoint (SAC) through the mitotic checkpoint complex (MCC), which inhibits the anaphase-promoting complex or cyclosome (APC/C). As an essential regulator, Cdc20 promotes mitotic exit through activating APC/C and monitors kinetochore-microtubule attachment through activating SAC. Cdc20 requires multiple interactions with APC/C and MCC subunits to elicit these functions. Functionally assessing these interactions within cells requires efficient depletion of endogenous Cdc20, which is highly difficult to achieve by RNA interference (RNAi). Here we generated Cdc20 RNAi-sensitive cell lines which display a penetrant metaphase arrest by a single RNAi treatment. In this null background, we accurately measured the contribution of each known motif of Cdc20 on APC/C and SAC activation. The CRY box, a previously identified degron, was found critical for SAC by promoting MCC formation and its interaction with APC/C. These data reveal additional regulation within the SAC and establish a novel method to interrogate Cdc20.

The oscillation of mitotic kinase governs cell cycle latches in mammalian cells

The mammalian cell cycle alternates between two phases - S-G2-M with high levels of A- and B-type cyclins (CycA and CycB, respectively) bound to cyclin-dependent kinases (CDKs), and G1 with persistent degradation of CycA and CycB by an activated anaphase promoting complex/cyclosome (APC/C) bound to Cdh1 (also known as FZR1 in mammals; denoted APC/C:Cdh1). Because CDKs phosphorylate and inactivate Cdh1, these two phases are mutually exclusive. This 'toggle switch' is flipped from G1 to S by cyclin-E bound to a CDK (CycE:CDK), which is not degraded by APC/C:Cdh1, and from M to G1 by Cdc20-bound APC/C (APC/C:Cdc20), which is not inactivated by CycA:CDK or CycB:CDK. After flipping the switch, cyclin E is degraded and APC/C:Cdc20 is inactivated. Combining mathematical modelling with single-cell timelapse imaging, we show that dysregulation of CycB:CDK disrupts strict alternation of the G1-S and M-G1 switches. Inhibition of CycB:CDK results in Cdc20-independent Cdh1 'endocycles', and sustained activity of CycB:CDK drives Cdh1-independent Cdc20 endocycles. Our model provides a mechanistic explanation for how whole-genome doubling can arise, a common event in tumorigenesis that can drive tumour evolution.

CDC20 promotes radioresistance of prostate cancer by activating Twist1 expression

Currently, radiotherapy is one of the most attractive treatments for prostate cancer (PCa) patients. However, radioresistance remains a challenging issue and the underlying mechanism is unknown. Growing evidence has demonstrated that CDC20 (Cell division cycle protein 20) plays a pivotal role in a variety of tumors, including PCa. Here, GEPIA database mining and western blot analysis showed that higher expression of CDC20 was observed in PCa tissues and cells. We demonstrated that the expression of CDC20 was increased in PCa cells by irradiation, and knockdown of CDC20 resulted in inhibition of cell proliferation, migration, tumor formation, induced cell apoptosis and increased radiosensitivity in PCa in vitro and in vivo. Furthermore, we observed that CDC20 regulated Twist1 pathway, influencing cell proliferation and migration. These results suggest that targeting CDC20 and Twist1 may be an effective way to improve the radiosensitivity of PCa.

Functional analysis of recurrent CDC20 promoter variants in human melanoma

Small nucleotide variants in non-coding regions of the genome can alter transcriptional regulation, leading to changes in gene expression which can activate oncogenic gene regulatory networks. Melanoma is heavily burdened by non-coding variants, representing over 99% of total genetic variation, including the well-characterized TERT promoter mutation. However, the compendium of regulatory non-coding variants is likely still functionally under-characterized. We developed a pipeline to identify hotspots, i.e. recurrently mutated regions, in melanoma containing putatively functional non-coding somatic variants that are located within predicted melanoma-specific regulatory regions. We identified hundreds of statistically significant hotspots, including the hotspot containing the TERT promoter variants, and focused on a hotspot in the promoter of CDC20. We found that variants in the promoter of CDC20, which putatively disrupt an ETS motif, lead to lower transcriptional activity in reporter assays. Using CRISPR/Cas9, we generated an indel in the CDC20 promoter in human A375 melanoma cell lines and observed decreased expression of CDC20, changes in migration capabilities, increased growth of xenografts, and an altered transcriptional state previously associated with a more proliferative and less migratory state. Overall, our analysis prioritized several recurrent functional non-coding variants that, through downregulation of CDC20, led to perturbation of key melanoma phenotypes.

Spo13/MEIKIN ensures a Two-Division meiosis by preventing the activation of APC/CAma1 at meiosis I

Genome haploidization at meiosis depends on two consecutive nuclear divisions, which are controlled by an oscillatory system consisting of Cdk1-cyclin B and the APC/C bound to the Cdc20 activator. How the oscillator generates exactly two divisions has been unclear. We have studied this question in yeast where exit from meiosis involves accumulation of the APC/C activator Ama1 at meiosis II. We show that inactivation of the meiosis I-specific protein Spo13/MEIKIN results in a single-division meiosis due to premature activation of APC/CAma1 . In the wild type, Spo13 bound to the polo-like kinase Cdc5 prevents Ama1 synthesis at meiosis I by stabilizing the translational repressor Rim4. In addition, Cdc5-Spo13 inhibits the activity of Ama1 by converting the B-type cyclin Clb1 from a substrate to an inhibitor of Ama1. Cdc20-dependent degradation of Spo13 at anaphase I unleashes a feedback loop that increases Ama1's synthesis and activity, leading to irreversible exit from meiosis at the second division. Thus, by repressing the exit machinery at meiosis I, Cdc5-Spo13 ensures that cells undergo two divisions to produce haploid gametes.

BUB-1-bound PLK-1 directs CDC-20 kinetochore recruitment to ensure timely embryonic mitoses

During mitosis, chromosomes assemble kinetochores to dynamically couple with spindle microtubules.1,2 Kinetochores also function as signaling hubs directing mitotic progression by recruiting and controlling the fate of the anaphase promoting complex/cyclosome (APC/C) activator CDC-20.3,4,5 Kinetochores either incorporate CDC-20 into checkpoint complexes that inhibit the APC/C or dephosphorylate CDC-20, which allows it to interact with and activate the APC/C.4,6 The importance of these two CDC-20 fates likely depends on the biological context. In human somatic cells, the major mechanism controlling mitotic progression is the spindle checkpoint. By contrast, progression through mitosis during the cell cycles of early embryos is largely checkpoint independent.7,8,9,10 Here, we first show that CDC-20 phosphoregulation controls mitotic duration in the C. elegans embryo and defines a checkpoint-independent temporal mitotic optimum for robust embryogenesis. CDC-20 phosphoregulation occurs at kinetochores and in the cytosol. At kinetochores, the flux of CDC-20 for local dephosphorylation requires an ABBA motif on BUB-1 that directly interfaces with the structured WD40 domain of CDC-20.6,11,12,13 We next show that a conserved "STP" motif in BUB-1 that docks the mitotic kinase PLK-114 is necessary for CDC-20 kinetochore recruitment and timely mitotic progression. The kinase activity of PLK-1 is required for CDC-20 to localize to kinetochores and phosphorylates the CDC-20-binding ABBA motif of BUB-1 to promote BUB-1-CDC-20 interaction and mitotic progression. Thus, the BUB-1-bound pool of PLK-1 ensures timely mitosis during embryonic cell cycles by promoting CDC-20 recruitment to the vicinity of kinetochore-localized phosphatase activity.

Alternative CDC20 translational isoforms tune mitotic arrest duration

Mitotic defects activate the spindle-assembly checkpoint, which inhibits the anaphase-promoting complex co-activator CDC20 to induce a prolonged cell cycle arrest1,2. Once errors are corrected, the spindle-assembly checkpoint is silenced, allowing anaphase onset to occur. However, in the presence of persistent unresolvable errors, cells can undergo 'mitotic slippage', exiting mitosis into a tetraploid G1 state and escaping the cell death that results from a prolonged arrest. The molecular logic that enables cells to balance these duelling mitotic arrest and slippage behaviours remains unclear. Here we demonstrate that human cells modulate the duration of their mitotic arrest through the presence of conserved, alternative CDC20 translational isoforms. Downstream translation initiation results in a truncated CDC20 isoform that is resistant to spindle-assembly-checkpoint-mediated inhibition and promotes mitotic exit even in the presence of mitotic perturbations. Our study supports a model in which the relative levels of CDC20 translational isoforms control the duration of mitotic arrest. During a prolonged mitotic arrest, new protein synthesis and differential CDC20 isoform turnover create a timer, with mitotic exit occurring once the truncated Met43 isoform achieves sufficient levels. Targeted molecular changes or naturally occurring cancer mutations that alter CDC20 isoform ratios or its translational control modulate mitotic arrest duration and anti-mitotic drug sensitivity, with potential implications for the diagnosis and treatment of human cancers.

The structural flexibility of MAD1 facilitates the assembly of the Mitotic Checkpoint Complex

The spindle assembly checkpoint (SAC) safeguards the genome during cell division by generating an effector molecule known as the Mitotic Checkpoint Complex (MCC). The MCC comprises two subcomplexes: BUBR1:BUB3 and CDC20:MAD2, and the formation of CDC20:MAD2 is the rate-limiting step during MCC assembly. Recent studies show that the rate of CDC20:MAD2 formation is significantly accelerated by the cooperative binding of CDC20 to the SAC proteins MAD1 and BUB1. However, the molecular basis for this acceleration is not fully understood. Here, we demonstrate that the structural flexibility of MAD1 at a conserved hinge near the C-terminus is essential for catalytic MCC assembly. This MAD1 hinge enables the MAD1:MAD2 complex to assume a folded conformation in vivo. Importantly, truncating the hinge reduces the rate of MCC assembly in vitro and SAC signaling in vivo. Conversely, mutations that preserve hinge flexibility retain SAC signaling, indicating that the structural flexibility of the hinge, rather than a specific amino acid sequence, is important for SAC signaling. We summarize these observations as the 'knitting model' that explains how the folded conformation of MAD1:MAD2 promotes CDC20:MAD2 assembly.

APC/CCDC20 targets SCFFBL17 to activate replication stress responses in Arabidopsis

DNA replication stress threatens genome stability and affects plant growth and development. How plants resolve replication stress is poorly understood. The protein kinase WEE1-mediated cell cycle arrest is required for replication stress responses. The E3 ubiquitin ligases anaphase-promoting complex/cyclosome (APC/C) and Skp1/Cullin 1/F-box (SCF) are essential regulators of the cell cycle. Here, we show that APC/CCDC20 mediates the degradation of SCFFBL17 during replication stress responses in Arabidopsis thaliana. Biochemically, WEE1 interacts with and phosphorylates the APC/C co-activator APC10, which enhances the interaction between F-BOX-LIKE17 (FBL17) and CELL DIVISION CYCLE 20 (CDC20), an activator of APC/C. Both APC10 and CDC20 are required for the polyubiquitination and degradation of FBL17. Genetically, silencing CDC20 or APC10 confers plant hypersensitivity to replication stress, which is suppressed by loss of FBL17. Collectively, our study suggests that WEE1 activates APC/C to inhibit FBL17, providing insight into replication stress responses in plants.

Current Progress and Perspectives of CDC20 in Female Reproductive Cancers

The cancers of the cervix, endometrium, ovary, and breast are great threats to women's health. Cancer is characterized by the uncontrolled proliferation of cells and deregulated cell cycle progression is one of the main causes of malignancy. Agents targeting cell cycle regulators may have potential anti-tumor effects. CDC20 (cell division cycle 20 homologue) is a co-activator of the anaphase-promoting complex/cyclosome (APC/C) and thus acts as a mitotic regulator. In addition, CDC20 serves as a subunit of the mitotic checkpoint complex (MCC) whose function is to inhibit APC/C. Recently, higher expression of CDC20 has been reported in these cancers and was closely associated with their clinicopathological parameters, indicating CDC20 a potential target for cancer treatment that is worth further study. In the present review, we summarized current progress and put forward perspectives of CDC20 in female reproductive cancers.

Juxtaposition of Bub1 and Cdc20 on phosphorylated Mad1 during catalytic mitotic checkpoint complex assembly

In response to improper kinetochore-microtubule attachments in mitosis, the spindle assembly checkpoint (SAC) assembles the mitotic checkpoint complex (MCC) to inhibit the anaphase-promoting complex/cyclosome, thereby delaying entry into anaphase. The MCC comprises Mad2:Cdc20:BubR1:Bub3. Its assembly is catalysed by unattached kinetochores on a Mad1:Mad2 platform. Mad1-bound closed-Mad2 (C-Mad2) recruits open-Mad2 (O-Mad2) through self-dimerization. This interaction, combined with Mps1 kinase-mediated phosphorylation of Bub1 and Mad1, accelerates MCC assembly, in a process that requires O-Mad2 to C-Mad2 conversion and concomitant binding of Cdc20. How Mad1 phosphorylation catalyses MCC assembly is poorly understood. Here, we characterized Mps1 phosphorylation of Mad1 and obtained structural insights into a phosphorylation-specific Mad1:Cdc20 interaction. This interaction, together with the Mps1-phosphorylation dependent association of Bub1 and Mad1, generates a tripartite assembly of Bub1 and Cdc20 onto the C-terminal domain of Mad1 (Mad1CTD). We additionally identify flexibility of Mad1:Mad2 that suggests how the Cdc20:Mad1CTD interaction brings the Mad2-interacting motif (MIM) of Cdc20 near O-Mad2. Thus, Mps1-dependent formation of the MCC-assembly scaffold functions to position and orient Cdc20 MIM near O-Mad2, thereby catalysing formation of C-Mad2:Cdc20.

Germline Missense Variants in CDC20 Result in Aberrant Mitotic Progression and Familial Cancer

CDC20 is a coactivator of the anaphase promoting complex/cyclosome (APC/C) and is essential for mitotic progression. APC/CCDC20 is inhibited by the spindle assembly checkpoint (SAC), which prevents premature separation of sister chromatids and aneuploidy in daughter cells. Although overexpression of CDC20 is common in many cancers, oncogenic mutations have never been identified in humans. Using whole-exome sequencing, we identified heterozygous missense CDC20 variants (L151R and N331K) that segregate with ovarian germ cell tumors in two families. Functional characterization showed these mutants retain APC/C activation activity but have impaired binding to BUBR1, a component of the SAC. Expression of L151R and N331K variants promoted mitotic slippage in HeLa cells and primary skin fibroblasts derived from carriers. Generation of mice carrying the N331K variant using CRISPR-Cas9 showed that, although homozygous N331K mice were nonviable, heterozygotes displayed accelerated oncogenicity of Myc-driven cancers. These findings highlight an unappreciated role for CDC20 variants as tumor-promoting genes.

SIGNIFICANCE

Two germline CDC20 missense variants that segregate with cancer in two families compromise the spindle assembly checkpoint and lead to aberrant mitotic progression, which could predispose cells to transformation. See related commentary by Villarroya-Beltri and Malumbres, p. 3432.

CDC20 May Serve as a Potential Biomarker-Based Risk Score System in Predicting the Prognosis of Patients with Hepatocellular Carcinoma

Background

The specificity and sensitivity of hepatocellular carcinoma (HCC) diagnostic markers are limited, hindering the early diagnosis and treatment of HCC patients. Therefore, improving prognostic biomarkers for patients with HCC is urgently needed.

Methods

HCC-related datasets were downloaded from the public databases. Differentially expressed genes (DEGs) between HCC and adjacent nontumor liver tissues were then identified. Moreover, the intersection of DEGs in four datasets (GSE138178, GSE77509, GSE84006, and TCGA) was used in the functional enrichment, and module genes were obtained by a coexpression network. Cox and Kaplan-Meier analyses were used to identify overall survival- (OS-) related genes from module genes. Area under the curve (AUC) > 0.9 of OS-related genes was then carried out in order to perform the protein-protein interaction network. The feature genes were identified by least absolute shrinkage and selection operator (LASSO). Furthermore, the hub gene was identified through the univariate Cox model, after which the correlation analysis between the hub gene and pathways was explored. Finally, infiltration in immune cell types in HCC was analyzed.

Results

A total of 2,227 upregulated genes and 1,501 downregulated DEGs were obtained in all four datasets, which were mainly found to be involved in the cell cycle and retinol metabolism. Accordingly, 998 OS-related genes were screened to construct the LASSO model. Finally, 8 feature genes (BUB1, CCNB1, CCNB2, CCNA2, AURKB, CDC20, OIP5, and TTK) were obtained. CDC20 was shown to serve as a poor prognostic gene in HCC and was mainly involved in the cell cycle. Moreover, a positive correlation was noted between the high degree of infiltration with Th2 and CDC20.

Conclusion

High expression of CDC20 predicted poor survival, as potential target in the treatment for HCC.

Proximity Labeling Reveals Spatial Regulation of the Anaphase-Promoting Complex/Cyclosome by a Microtubule Adaptor

The anaphase-promoting complex/cyclosome (APC/C) coordinates advancement through mitosis via temporally controlled polyubiquitination events. Despite the long-appreciated spatial organization of key events in mitosis mediated largely by cytoskeletal networks, the spatial regulation of APC/C, the major mitotic E3 ligase, is poorly understood. We describe a microtubule-resident protein, PLEKHA5, as an interactor of APC/C and spatial regulator of its activity in mitosis. Microtubule-localized proximity biotinylation tools revealed that PLEKHA5 depletion decreased APC/C association with the microtubule cytoskeleton, which prevented efficient loading of APC/C with its coactivator CDC20 and led to reduced APC/C E3 ligase activity. PLEKHA5 knockdown delayed mitotic progression, causing accumulation of APC/C substrates dependent upon the PLEKHA5-APC/C interaction in microtubules. We propose that PLEKHA5 functions as an adaptor of APC/C that promotes its subcellular localization to microtubules and facilitates its activation by CDC20, thus ensuring the timely turnover of key mitotic APC/C substrates and proper progression through mitosis.

Recovery from spindle checkpoint-mediated arrest requires a novel Dnt1-dependent APC/C activation mechanism

The activated spindle assembly checkpoint (SAC) potently inhibits the anaphase-promoting complex/cyclosome (APC/C) to ensure accurate chromosome segregation at anaphase. Early studies have recognized that the SAC should be silenced within minutes to enable rapid APC/C activation and synchronous segregation of chromosomes once all kinetochores are properly attached, but the underlying silencers are still being elucidated. Here, we report that the timely silencing of SAC in fission yeast requires dnt1+, which causes severe thiabendazole (TBZ) sensitivity and increased rate of lagging chromosomes when deleted. The absence of Dnt1 results in prolonged inhibitory binding of mitotic checkpoint complex (MCC) to APC/C and attenuated protein levels of Slp1Cdc20, consequently slows the degradation of cyclin B and securin, and eventually delays anaphase entry in cells released from SAC activation. Interestingly, Dnt1 physically associates with APC/C upon SAC activation. We propose that this association may fend off excessive and prolonged MCC binding to APC/C and help to maintain Slp1Cdc20 stability. This may allow a subset of APC/C to retain activity, which ensures rapid anaphase onset and mitotic exit once SAC is inactivated. Therefore, our study uncovered a new player in dictating the timing and efficacy of APC/C activation, which is actively required for maintaining cell viability upon recovery from the inhibition of APC/C by spindle checkpoint.

CDC20 regulates sensitivity to chemotherapy and radiation in glioblastoma stem cells

Glioblastoma stem cells (GSCs) are an important subpopulation in glioblastoma, implicated in tumor growth, tumor recurrence, and radiation resistance. Understanding the cellular mechanisms for chemo- and radiation resistance could lead to the development of new therapeutic strategies. Here, we demonstrate that CDC20 promotes resistance to chemotherapy and radiation therapy. CDC20 knockdown does not increase TMZ- and radiation-induced DNA damage, or alter DNA damage repair, but rather promotes cell death through accumulation of the pro-apoptotic protein, Bim. Our results identify a CDC20 signaling pathway that regulates chemo- and radiosensitivity in GSCs, with the potential for CDC20-targeted therapeutic strategies in the treatment of glioblastoma.

CDC20 regulates the cell proliferation and radiosensitivity of P53 mutant HCC cells through the Bcl-2/Bax pathway

Purpose: The incidence of hepatocellular carcinoma (HCC) is extremely high, and China accounts for approximately 50% of global liver cancer cases. Previous studies reported that CDC20 is involved in the occurrence and progression of a variety of malignant tumors. So, whether CDC20 will affect the development of HCC, we have conducted in-depth research on this. Methods: We selected Hep3B and HepG2 for cell culture, and performed siRNA transfection, lentiviral infection, western blot, MTS determination, cell cycle determination, apoptosis test, immunodeficiency test, clone survival test and subcutaneous parthenogenesis in nude mice. Results: Knockdown of CDC20 greatly enhanced the radiation efficacy on the growth retardation in HepG2, and protein level of CDC20 was decreased for the activation of P53 by radiation. Downregulation of CDC20 combined with radiation can inhibit proliferation, aggravate DNA damage, increase G2/M arrest, and promote apoptosis of HCC cells to a greater extent, and the relative survival fraction of HCC cells was gradually reduced with radiation dose increased in P53 mutated Hep3B cells. After knocking down CDC20 in HCC, Bcl-2 was down-regulated and Bax expression increased. Down-regulation of CDC20 can inhibit further invasion by promoting the radiosensitivity of HCC. Conclusion: In this study, we found that that CDC20 was highly expressed in HCC and participated in radio resistance of HCC cells with P53 mutation Bcl-2/Bax via signaling pathway. This study is the first to present evidence that CDC20 may play a role in improving the efficacy of radiotherapy in HCC.

CDC20 and PTTG1 are Important Biomarkers and Potential Therapeutic Targets for Metastatic Prostate Cancer

INTRODUCTION

Metastatic prostate cancer (mPCa) is responsible for most prostate cancer (PCa) deaths worldwide. The present study aims to explore the molecular differences between mPCa and PCa.

METHODS

The authors downloaded GSE6752, GSE6919, and GSE32269 from the Gene Expression Omnibus and employed integrated analysis to identify differentially expressed genes (DEGs) between mPCa and PCa. Functional and pathway-enrichment analyses were performed, and a protein-protein interaction (PPI) network and modules were constructed. Clinical mPCa specimens were collected to verify the results by performing RT-qPCR. The Cancer Genome Atlas database was used to conduct a survival analysis, and an immunohistochemical assay was performed. The invasion ability of PCa cells was verified by Transwell assay.

RESULTS

One-hundred six consistently DEGs were found in mPCa compared with PCa. DEGs significantly enriched the positive regulation of cell proliferation, cell division, and cell adhesion in small cell lung cancer and PCa. Cell division, nucleoplasm, and cell cycle were selected from the PPI network, and the top 10 hub genes were selected. CDC20 and PTTG1 with genetic alterations were significantly associated with poorer disease-free survival. Immunohistochemical assay results showed that the expression levels of CDC20 and PTTG1 in mPCa were higher than those in PCa. The results of the migration assay indicated that CDC20 and PTTG1 could enhance the migration ability of PCa cells.

CONCLUSION

The present study revealed that CDC20 and PTTG1 contribute more to migration, progression, and poorer prognoses in mPCa compared with PCa. CDC20 and PTTG1 could represent therapeutic targets in mPCa medical research and clinical studies.

PP1 promotes cyclin B destruction and the metaphase-anaphase transition by dephosphorylating CDC20

Ubiquitin-dependent proteolysis of cyclin B and securin initiates sister chromatid segregation and anaphase. The anaphase-promoting complex/cyclosome and its coactivator CDC20 (APC/CCDC20) form the main ubiquitin E3 ligase for these two proteins. APC/CCDC20 is regulated by CDK1-cyclin B and counteracting PP1 and PP2A family phosphatases through modulation of both activating and inhibitory phosphorylation. Here, we report that PP1 promotes cyclin B destruction at the onset of anaphase by removing specific inhibitory phosphorylation in the N-terminus of CDC20. Depletion or chemical inhibition of PP1 stabilizes cyclin B and results in a pronounced delay at the metaphase-to-anaphase transition after chromosome alignment. This requirement for PP1 is lost in cells expressing CDK1 phosphorylation-defective CDC206A mutants. These CDC206A cells show a normal spindle checkpoint response and rapidly destroy cyclin B once all chromosomes have aligned and enter into anaphase in the absence of PP1 activity. PP1 therefore facilitates the metaphase-to-anaphase transition by promoting APC/CCDC20-dependent destruction of cyclin B in human cells.

Squamous differentiation requires G2/mitosis slippage to avoid apoptosis

The cellular mechanisms controlling cell fate in self-renewal tissues remain unclear. Cell cycle failure often leads to an apoptosis anti-oncogenic response. We have inactivated Cdk1 or Polo-like-1 kinases, essential targets of the mitotic checkpoints, in the epithelia of skin and oral mucosa. Here, we show that inactivation of the mitotic kinases leading to polyploidy in vivo, produces a fully differentiated epithelium. Cells within the basal layer aberrantly differentiate and contain large or various nuclei. Freshly isolated KO cells were also differentiated and polyploid. However, sustained metaphase arrest downstream of the spindle anaphase checkpoint (SAC) due to abrogation of CDC20 (essential cofactor of anaphase-promoting complex), impaired squamous differentiation and resulted in apoptosis. Therefore, upon prolonged arrest keratinocytes need to slip beyond G2 or mitosis in order to initiate differentiation. The results altogether demonstrate that mitotic checkpoints drive squamous cell fate towards differentiation or apoptosis in response to genetic damage.

A unique binding mode of Nek2A to the APC/C allows its ubiquitination during prometaphase

The anaphase-promoting complex (APC/C) is the key E3 ubiquitin ligase which directs mitotic progression and exit by catalysing the sequential ubiquitination of specific substrates. The activity of the APC/C in mitosis is restrained by the spindle assembly checkpoint (SAC), which coordinates chromosome segregation with the assembly of the mitotic spindle. The SAC effector is the mitotic checkpoint complex (MCC), which binds and inhibits the APC/C. It is incompletely understood how the APC/C switches substrate specificity in a cell cycle-specific manner. For instance, it is unclear how in prometaphase, when APC/C activity towards cyclin B and securin is repressed by the MCC, the kinase Nek2A is ubiquitinated. Here, we combine biochemical and structural analysis with functional studies in cells to show that Nek2A is a conformational-specific binder of the APC/C-MCC complex (APC/CMCC ) and that, in contrast to cyclin A, Nek2A can be ubiquitinated efficiently by the APC/C in conjunction with both the E2 enzymes UbcH10 and UbcH5. We propose that these special features of Nek2A allow its prometaphase-specific ubiquitination.

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.

Network mechanisms and dysfunction within an integrated computational model of progression through mitosis in the human cell cycle

The cellular protein-protein interaction network that governs cellular proliferation (cell cycle) is highly complex. Here, we have developed a novel computational model of human mitotic cell cycle, integrating diverse cellular mechanisms, for the purpose of generating new hypotheses and predicting new experiments designed to help understand complex diseases. The pathogenic state investigated is infection by a human herpesvirus. The model starts at mitotic entry initiated by the activities of Cyclin-dependent kinase 1 (CDK1) and Polo-like kinase 1 (PLK1), transitions through Anaphase-promoting complex (APC/C) bound to Cell division cycle protein 20 (CDC20), and ends upon mitotic exit mediated by APC/C bound to CDC20 homolog 1 (CDH1). It includes syntheses and multiple mechanisms of degradations of the mitotic proteins. Prior to this work, no such comprehensive model of the human mitotic cell cycle existed. The new model is based on a hybrid framework combining Michaelis-Menten and mass action kinetics for the mitotic interacting reactions. It simulates temporal changes in 12 different mitotic proteins and associated protein complexes in multiple states using 15 interacting reactions and 26 ordinary differential equations. We have defined model parameter values using both quantitative and qualitative data and using parameter values from relevant published models, and we have tested the model to reproduce the cardinal features of human mitosis determined experimentally by numerous laboratories. Like cancer, viruses create dysfunction to support infection. By simulating infection of the human herpesvirus, cytomegalovirus, we hypothesize that virus-mediated disruption of APC/C is necessary to establish a unique mitotic collapse with sustained CDK1 activity, consistent with known mechanisms of virus egress. With the rapid discovery of cellular protein-protein interaction networks and regulatory mechanisms, we anticipate that this model will be highly valuable in helping us to understand the network dynamics and identify potential points of therapeutic interventions.

Securin-independent regulation of separase by checkpoint-induced shugoshin-MAD2

Separation of eukaryotic sister chromatids during the cell cycle is timed by the spindle assembly checkpoint (SAC) and ultimately triggered when separase cleaves cohesion-mediating cohesin1-3. Silencing of the SAC during metaphase activates the ubiquitin ligase APC/C (anaphase-promoting complex, also known as the cyclosome) and results in the proteasomal destruction of the separase inhibitor securin1. In the absence of securin, mammalian chromosomes still segregate on schedule, but it is unclear how separase is regulated under these conditions4,5. Here we show that human shugoshin 2 (SGO2), an essential protector of meiotic cohesin with unknown functions in the soma6,7, is turned into a separase inhibitor upon association with SAC-activated MAD2. SGO2-MAD2 can functionally replace securin and sequesters most separase in securin-knockout cells. Acute loss of securin and SGO2, but not of either protein individually, resulted in separase deregulation associated with premature cohesin cleavage and cytotoxicity. Similar to securin8,9, SGO2 is a competitive inhibitor that uses a pseudo-substrate sequence to block the active site of separase. APC/C-dependent ubiquitylation and action of the AAA-ATPase TRIP13 in conjunction with the MAD2-specific adaptor p31comet liberate separase from SGO2-MAD2 in vitro. The latter mechanism facilitates a considerable degree of sister chromatid separation in securin-knockout cells that lack APC/C activity. Thus, our results identify an unexpected function of SGO2 in mitotically dividing cells and a mechanism of separase regulation that is independent of securin but still supervised by the SAC.

Getting out of mitosis: spatial and temporal control of mitotic exit and cytokinesis by PP1 and PP2A

Here, we will review the evidence showing that mitotic exit is initiated by regulated proteolysis and then driven by the PPP family of phosphoserine/threonine phosphatases. Rapid APC/CCDC20 and ubiquitin-dependent proteolysis of cyclin B and securin initiates sister chromatid separation, the first step of mitotic exit. Because proteolysis of Aurora and Polo family kinases dependent on APC/CCDH1 is relatively slow, this creates a new regulatory state, anaphase, different to G2 and M-phase. We will discuss how the CDK1-counteracting phosphatases PP1 and PP2A-B55, together with Aurora and Polo kinases, contribute to the temporal regulation and order of events in the different stages of mitotic exit from anaphase to cytokinesis. For PP2A-B55, these timing properties are created by the ENSA-dependent inhibitory pathway and differential recognition of phosphoserine and phosphothreonine. Finally, we will discuss how Aurora B and PP2A-B56 are needed for the spatial regulation of anaphase spindle formation and how APC/C-dependent destruction of PLK1 acts as a timer for abscission, the final event of cytokinesis.

Cyclin A2 degradation during the spindle assembly checkpoint requires multiple binding modes to the APC/C

The anaphase-promoting complex/cyclosome (APC/C) orchestrates cell cycle progression by controlling the temporal degradation of specific cell cycle regulators. Although cyclin A2 and cyclin B1 are both targeted for degradation by the APC/C, during the spindle assembly checkpoint (SAC), the mitotic checkpoint complex (MCC) represses APC/C's activity towards cyclin B1, but not cyclin A2. Through structural, biochemical and in vivo analysis, we identify a non-canonical D box (D2) that is critical for cyclin A2 ubiquitination in vitro and degradation in vivo. During the SAC, cyclin A2 is ubiquitinated by the repressed APC/C-MCC, mediated by the cooperative engagement of its KEN and D2 boxes, ABBA motif, and the cofactor Cks. Once the SAC is satisfied, cyclin A2 binds APC/C-Cdc20 through two mutually exclusive binding modes, resulting in differential ubiquitination efficiency. Our findings reveal that a single substrate can engage an E3 ligase through multiple binding modes, affecting its degradation timing and efficiency.

Targeting cell cycle protein in gastric cancer with CDC20siRNA and anticancer drugs (doxorubicin and quercetin) co-loaded cationic PEGylated nanoniosomes

BACKGROUND AND PURPOSE

In a past study, we developed and optimized a novel cationic PEGylated niosome containing anticancer drugs (doxorubicin or quercetin) and siRNA. This study intended to evaluate the anti-tumor effects of the combination therapy to target both the proteins and genes responsible for the development of gastric cancer. CDC20, known as an oncogene, is a good potential therapeutic candidate for gastric cancer.

METHODS

In order to increase the loading capacity of siRNA and achieve appropriate physical properties, we optimized the cationic PEGylated niosome in terms of the amount of the cationic lipids. Drugs (doxorubicin and quercetin) and CDC20siRNA were loaded into the co-delivery system, and physical characteristics, thermosensitive controlled-release, gene silencing efficiency, and apoptosis rate were determined.

RESULTS

The results showed that the designed co-delivery system for the drugs and gene silencer had an appropriate size and a high positive charge for loading siRNA, and also showed a thermosensitive drug release behavior, which successfully silenced the CDC20 expression when compared with the single delivery of siRNA or the drug. Moreover, the co-delivery of drugs and CDC20siRNA exhibited a highly inhibitory property for the cell growth of gastric cancer cells.

CONCLUSION

It seems that the novel cationic PEGylated niosomes co-loaded with anticancer drug and CDC20siRNA has a promising application for the treatment of gastric cancer.

ESRP1 Induces Cervical Cancer Cell G1-Phase Arrest Via Regulating Cyclin A2 mRNA Stability

Accumulating evidence indicates that epithelial splicing regulatory protein 1 (ESRP1) can inhibit the epithelial-to-mesenchymal transition (EMT), thus playing a central role in regulating the metastatic progression of tumors. However, it is still not clear whether ESRP1 directly influences the cell cycle, or what the possible underlying molecular mechanisms are. In this study, we showed that ESRP1 protein levels were significantly correlated with the Ki-67 proliferative index (r = −0.521; p < 0.01), and that ESRP1 overexpression can significantly inhibit cervical carcinoma cell proliferation and induced G1-phase arrest by downregulating cyclin A2 expression. Importantly, ESRP1 can bind to GGUGGU sequence in the 3′UTR of the cyclin A2 mRNA, and ESRP1 overexpression significantly decreases the stability of the cyclin A2 mRNA. In addition, our experimental results confirm that ESRP1 overexpression results in enhanced CDC20 expression, which is known to be responsible for cyclin A2 degradation. This study provides the first evidence that ESRP1 overexpression induces G1-phase cell cycle arrest via reducing the stability of the cyclin A2 mRNA, and inhibits cervical carcinoma cell proliferation. The findings suggest that the ESRP1/cyclin A2 regulatory axis may be essential as a regulator of cell proliferation, and may thus represent an attractive target for cervical cancer prevention and treatment.

Camptothecin induces mitotic arrest through Mad2-Cdc20 complex by activating the JNK-mediated Sp1 pathway

Camptothecin (CPT) is a popular therapeutic agent that targets topoisomerase I. Our findings demonstrated that CPT-induced microtubule polymerization results in markedly increased histone H3 phosphorylation. CPT also enhanced interactions between the mitotic checkpoint proteins, Mad2 and Cdc20, and thereby increased mitotic arrest. Transient knockdown of Mad2 completely restored cell cycle progression from CPT-induced mitotic arrest, while simultaneously reduced cyclin B1 and Cdk1 expression. Moreover, we found that c-Jun N-terminal kinase (JNK) acts upstream of Sp1, which upregulates p21-mediated mitotic arrest in response to CPT; furthermore, knockdown of p21 restored cell cycle progression, while inhibition of Cdks completely restored cell cycle progression from CPT-induced mitotic arrest. We hypothesized that, during mitotic arrest in response to CPT, cell survival signaling blocks apoptosis, thereby enhancing mitotic arrest. As expected, a caspase-9 inhibitor, z-LEHD-FMK, and an autophagy inhibitor, 3-methyladenine (3 MA), significantly diminished CPT-induced mitotic arrest. On the other hand, when Mad2 was depleted, z-LEHD-FMK and 3 MA markedly increased apoptosis, and restored cell cycle progression. Taken together, these results suggest that CPT decodes the action of topoisomerase I-mediated tubulin targeting drugs, leading to mitotic arrest by upregulating Mad2 through the JNK-mediated Sp1 pathway and autophagy formation from tubulin polymerization.

CDC20 overexpression leads to poor prognosis in solid tumors: A system review and meta-analysis

BACKGROUND

A plenty of previous researches have reported the prognostic value of CDC20 (Cell Division Cycle Protein 20) in solid tumors. Nevertheless, these researches were restricted by the small sample databases and the results were not strongly consistent among them.

METHODS

We comprehensively searched these relevant studies by PubMed, Web of Science, and EMBASE, in which publications before March 2017 were included. Pooled HR values for OS were cumulatively pooled and quantitatively analyzed in the meta-analysis.

RESULTS

Hence we composed a meta-analysis based on 8 studies with 1856 patients in order to assess the potential relationship between CDC20 overexpression and OS (overall survival) in human solid tumors. There were a total of 8 studies (n = 1856) assessed in the meta-analysis. What suggested in both univariate and multivariate analysis for survival is that high level of CDC20 expression apparently pointed to poor prognosis. In the univariate analysis, the combined hazard ratio (HR) for OS was 1.75 (95% confidence interval [CI]: 1.07-2.86, P = .03). The pooled HR of multivariate analysis for OS was 2.48 (95% confidence interval [CI]: 2.10-2.94, P < .001).

CONCLUSIONS

The meta-analysis indicated that high level of CDC20 expression is significantly correlated with decreased survival in most case of human solid tumors. In addition, CDC20 shows promise as a meaningful prognostic biomarker and original therapeutic target, on the basis of its expression level in solid tumors.

Predicting position along a looping immune response trajectory

When we get sick, we want to be resilient and recover our original health. To measure resilience, we need to quantify a host's position along its disease trajectory. Here we present Looper, a computational method to analyze longitudinally gathered datasets and identify gene pairs that form looping trajectories when plotted in the space described by these phases. These loops enable us to track where patients lie on a typical trajectory back to health. We analyzed two publicly available, longitudinal human microarray datasets that describe self-resolving immune responses. Looper identified looping gene pairs expressed by human donor monocytes stimulated by immune elicitors, and in YF17D-vaccinated individuals. Using loops derived from training data, we found that we could predict the time of perturbation in withheld test samples with accuracies of 94% in the human monocyte data, and 65-83% within the same cohort and in two independent cohorts of YF17D vaccinated individuals. We suggest that Looper will be useful in building maps of resilient immune processes across organisms.

Implications of alternative routes to APC/C inhibition by the mitotic checkpoint complex

The mitotic checkpoint (also called spindle assembly checkpoint) is a signaling pathway that ensures faithful chromosome segregation. Mitotic checkpoint proteins inhibit the anaphase-promoting complex (APC/C) and its activator Cdc20 to prevent precocious anaphase. Checkpoint signaling leads to a complex of APC/C, Cdc20, and checkpoint proteins, in which the APC/C is inactive. In principle, this final product of the mitotic checkpoint can be obtained via different pathways, whose relevance still needs to be fully ascertained experimentally. Here, we use mathematical models to compare the implications on checkpoint response of the possible pathways leading to APC/C inhibition. We identify a previously unrecognized funneling effect for Cdc20, which favors Cdc20 incorporation into the inhibitory complex and therefore promotes checkpoint activity. Furthermore, we find that the presence or absence of one specific assembly reaction determines whether the checkpoint remains functional at elevated levels of Cdc20, which can occur in cancer cells. Our results reveal the inhibitory logics behind checkpoint activity, predict checkpoint efficiency in perturbed situations, and could inform molecular strategies to treat malignancies that exhibit Cdc20 overexpression.

Cell division is a fundamental event in the life of cells. It requires that a mother cell gives rise to two daughters which carry the same genetic material of their mother. Thus, during each cell cycle the genetic material needs to be replicated, compacted into chromosomes and redistributed to the two daughter cells. Any mistake in chromosome segregation would attribute the wrong number of chromosomes to the progeny. Hence, the process of chromosome segregation is closely watched by a surveillance mechanism known as the mitotic checkpoint. The molecular players of the checkpoint pathway are well known: we know both the input (ie, the species to be inhibited and their inhibitors), and the output (ie, the inhibited species). However, we do not exactly know the path that leads from the former to the latter. In this manuscript, we use a mathematical approach to explore the properties of plausible mitotic checkpoint networks. We find that seemingly similar circuits show very different behaviors for high levels of the protein targeted by the mitotic checkpoint, Cdc20. Interestingly, this protein is often overexpressed in cancer cells. For physiological levels of Cdc20, instead, all the models we have analyzed are capable to mount an efficient response. We find that this is due to a series of consecutive protein-protein binding reactions that funnel Cdc20 towards its inhibited state. We call this the funneling effect. Our analysis helps understanding the inhibitory logics underlying the checkpoint, and proposes new concepts that could be applied to other inhibitory pathways.

Atypical APC/C-dependent degradation of Mcl-1 provides an apoptotic timer during mitotic arrest

The initiation of apoptosis in response to the disruption of mitosis provides surveillance against chromosome instability. Here, we show that proteolytic destruction of the key regulator Mcl-1 during an extended mitosis requires the anaphase-promoting complex or cyclosome (APC/C) and is independent of another ubiquitin E3 ligase, SCFFbw7 Using live-cell imaging, we show that the loss of Mcl-1 during mitosis is dependent on a D box motif found in other APC/C substrates, while an isoleucine-arginine (IR) C-terminal tail regulates the manner in which Mcl-1 engages with the APC/C, converting Mcl-1 from a Cdc20-dependent and checkpoint-controlled substrate to one that is degraded independently of checkpoint strength. This mechanism ensures a relatively slow but steady rate of Mcl-1 degradation during mitosis and avoids its catastrophic destruction when the mitotic checkpoint is satisfied, providing an apoptotic timer that can distinguish a prolonged mitotic delay from normal mitosis. Importantly, we also show that inhibition of Cdc20 promotes mitotic cell death more effectively than loss of APC/C activity through differential effects on Mcl-1 degradation, providing an improved strategy to kill cancer cells.

Mechanism for remodelling of the cell cycle checkpoint protein MAD2 by the ATPase TRIP13

The maintenance of genome stability during mitosis is coordinated by the spindle assembly checkpoint (SAC) through its effector the mitotic checkpoint complex (MCC), an inhibitor of the anaphase-promoting complex (APC/C, also known as the cyclosome)1,2. Unattached kinetochores control MCC assembly by catalysing a change in the topology of the β-sheet of MAD2 (an MCC subunit), thereby generating the active closed MAD2 (C-MAD2) conformer3-5. Disassembly of free MCC, which is required for SAC inactivation and chromosome segregation, is an ATP-dependent process driven by the AAA+ ATPase TRIP13. In combination with p31comet, an SAC antagonist6, TRIP13 remodels C-MAD2 into inactive open MAD2 (O-MAD2)7-10. Here, we present a mechanism that explains how TRIP13-p31comet disassembles the MCC. Cryo-electron microscopy structures of the TRIP13-p31comet-C-MAD2-CDC20 complex reveal that p31comet recruits C-MAD2 to a defined site on the TRIP13 hexameric ring, positioning the N terminus of C-MAD2 (MAD2NT) to insert into the axial pore of TRIP13 and distorting the TRIP13 ring to initiate remodelling. Molecular modelling suggests that by gripping MAD2NT within its axial pore, TRIP13 couples sequential ATP-driven translocation of its hexameric ring along MAD2NT to push upwards on, and simultaneously rotate, the globular domains of the p31comet-C-MAD2 complex. This unwinds a region of the αA helix of C-MAD2 that is required to stabilize the C-MAD2 β-sheet, thus destabilizing C-MAD2 in favour of O-MAD2 and dissociating MAD2 from p31comet. Our study provides insights into how specific substrates are recruited to AAA+ ATPases through adaptor proteins and suggests a model of how translocation through the axial pore of AAA+ ATPases is coupled to protein remodelling.

Peptide inhibitors of the anaphase promoting-complex that cause sensitivity to microtubule poison

There is an interest in identifying Anaphase Promoting-Complex/Cyclosome (APC/C) inhibitors that lead to sensitivity to microtubule poisons as a strategy for targeting cancer cells. Using budding yeast Saccharomyces cerevisiae, peptides derived from the Mitotic Arrest Deficient 2 (Mad2)-binding motif of Cell Division Cycle 20 (Cdc20) were observed to inhibit both Cdc20- and CDC20 Homology 1 (Cdh1)-dependent APC/C activity. Over expression of peptides in vivo led to sensitivity to a microtubule poison and, in a recovery from a microtubule poison arrest, delayed degradation of yeast Securin protein Precocious Dissociation of Sisters 1 (Pds1). Peptides with mutations in the Cdc20 activating KILR-motif still bound APC/C, but lost the ability to inhibit APC/C in vitro and lost the ability to induce sensitivity to a microtubule poison in vivo. Thus, an APC/C binding and activation motif that promotes mitotic progression, namely the Cdc20 KILR-motif, can also function as an APC/C inhibitor when present in excess. Another activator for mitotic progression after recovery from microtubule poison is p31^comet, where a yeast predicted open-reading frame YBR296C-A encoding a 39 amino acid predicted protein was identified by homology to p31^comet, and named Tiny Yeast Comet 1 (TYC1). Tyc1 over expression resulted in sensitivity to microtubule poison. Tyc1 inhibited both APC/C^Cdc20 and APC/C^Cdh1 activities in vitro and bound to APC/C. A homologous peptide derived from human p31^comet bound to and inhibited yeast APC/C demonstrating evolutionary retention of these biochemical activities. Cdc20 Mad2-binding motif peptides and Tyc1 disrupted the ability of the co-factors Cdc20 and Cdh1 to bind to APC/C, and co-over expression of both together in vivo resulted in an increased sensitivity to microtubule poison. We hypothesize that Cdc20 Mad2-binding motif peptides, Tyc1 and human hp31 peptide can serve as novel molecular tools for investigating APC/C inhibition that leads to sensitivity to microtubule poison in vivo.

Dynamics and control of sister kinetochore behavior during the meiotic divisions in Drosophila spermatocytes

Sister kinetochores are connected to the same spindle pole during meiosis I and to opposite poles during meiosis II. The molecular mechanisms controlling the distinct behavior of sister kinetochores during the two meiotic divisions are poorly understood. To study kinetochore behavior during meiosis, we have optimized time lapse imaging with Drosophila spermatocytes, enabling kinetochore tracking with high temporal and spatial resolution through both meiotic divisions. The correct bipolar orientation of chromosomes within the spindle proceeds rapidly during both divisions. Stable bi-orientation of the last chromosome is achieved within ten minutes after the onset of kinetochore-microtubule interactions. Our analyses of mnm and tef mutants, where univalents instead of bivalents are present during meiosis I, indicate that the high efficiency of normal bi-orientation depends on pronounced stabilization of kinetochore attachments to spindle microtubules by the mechanical tension generated by spindle forces upon bi-orientation. Except for occasional brief separation episodes, sister kinetochores are so closely associated that they cannot be resolved individually by light microscopy during meiosis I, interkinesis and at the start of meiosis II. Permanent evident separation of sister kinetochores during M II depends on spindle forces resulting from bi-orientation. In mnm and tef mutants, sister kinetochore separation can be observed already during meiosis I in bi-oriented univalents. Interestingly, however, this sister kinetochore separation is delayed until the metaphase to anaphase transition and depends on the Fzy/Cdc20 activator of the anaphase-promoting complex/cyclosome. We propose that univalent bi-orientation in mnm and tef mutants exposes a release of sister kinetochore conjunction that occurs also during normal meiosis I in preparation for bi-orientation of dyads during meiosis II.

For production of oocytes and sperm, cells have to complete meiosis which includes two successive divisions. These divisions convert diploid cells with a maternal and a paternal copy of each chromosome into haploid cells with only one copy of each chromosome. Chromosome copy reduction requires regulation of sister kinetochore behavior during the meiotic divisions. Kinetochores are protein networks assembled at the start of divisions within the centromeric region of chromosomes. They provide attachment sites for spindle microtubules which in turn exert poleward pulling forces. During pre-meiotic S phase, each chromosome is duplicated into two closely associated sister chromatids. At the start of the first meiotic division, both sister chromatids together assemble only one functional kinetochore, permitting subsequent separation of paired homologous chromosomes to opposite spindle poles. In contrast, at the onset of the second meiotic division, each sister chromatid organizes its own kinetochore followed by separation of sister chromatids to opposite spindle poles. To analyze when and how sister kinetochores are individualized, we have improved time lapse imaging with Drosophila spermatocytes. Our analyses in normal and genetically altered spermatocytes suggest that the release of sister kinetochore conjunction occurs during the first meiotic division after activation of the anaphase promoting complex/cyclosome.

USP9X Limits Mitotic Checkpoint Complex Turnover to Strengthen the Spindle Assembly Checkpoint and Guard against Chromosomal Instability

Faithful chromosome segregation during mitosis depends on the spindle assembly checkpoint (SAC), which delays progression through mitosis until every chromosome has stably attached to spindle microtubules via the kinetochore. We show here that the deubiquitinase USP9X strengthens the SAC by antagonizing the turnover of the mitotic checkpoint complex produced at unattached kinetochores. USP9X thereby opposes activation of anaphase-promoting complex/cyclosome (APC/C) and specifically inhibits the mitotic degradation of SAC-controlled APC/C substrates. We demonstrate that depletion or loss of USP9X reduces the effectiveness of the SAC, elevates chromosome segregation defects, and enhances chromosomal instability (CIN). These findings provide a rationale to explain why loss of USP9X could be either pro- or anti-tumorigenic depending on the existing level of CIN.

Identification of genes related to consecutive trauma-induced sepsis via gene expression profiling analysis

We aimed to identify crucial genes relevant to the development of consecutive trauma-induced sepsis.A microarray dataset was used to identify genes differentially expressed between peripheral blood samples from consecutive traumatized patients complicated with sepsis and not complicated with sepsis. The dataset GSE12624 was obtained from Gene Expression Omnibus, containing 34 peripheral blood samples from consecutive traumatized patients complicated by sepsis and 36 consecutive traumatized controls. The differentially expressed genes (DEGs) were identified using Linear Models for Microarray Data package. Then, gene ontology (GO) enrichment analysis for DEGs was performed by Onto-Express. Subsequently, the protein-protein interaction (PPI) network was constructed and pathway enrichment analysis was performed by Search Tool for the Retrieval of Interacting Genes (STRING). Furthermore, protein complexes in the PPI network were predicted by ClusterONE and validated through GO and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses, and protein domain analysis.Totally, 446 upregulated and 447 downregulated DEGs were identified. Some DEGs were related to acyl-CoA binding (eg, ACBD6), chromosome, and centromeric region (eg, CENPN). In the PPI network, some DEGs were enriched in renin-angiotensin system (RAS, eg, AGTR1 and AGTR2). Three predicted protein complexes were validated in the PPI network. Some genes composing protein complex A were associated with cell proliferation (eg, CDC20, CCNB1, MCM4, RPA2, and PRIM2), and several genes composing protein complex F were implicated in regulation of actin cytoskeleton (eg, PFN2, ARPC2, and WASL).The results suggest that those DEGs may be crucial in the etiology of consecutive trauma-induced sepsis, and they are expected to be therapeutic targets.

Plk1 phosphorylation of CAP-H2 triggers chromosome condensation by condensin II at the early phase of mitosis

Condensin complexes play crucial roles in chromosome condensation that is a fundamental process to establish the "rod-like" shape of chromosome structure in mitosis. Failure of the chromosome assembly causes chromosome segregation errors and subsequent genomic instability. However, a molecular mechanism that controls condensin function for the chromosomal organization has not been fully understood. Here, we show that the abundance of CAP-H2, one of the condensin II subunits, is fluctuated during the cell cycle in accordance with Plk1 kinase activity. Inhibition of Plk1 leads to Cdc20-mediated degradation of CAP-H2 in mitosis. Plk1 phosphorylation of CAP-H2 at Ser288 is required for the accumulation of CAP-H2 and accurate chromosomal condensation during prophase. These findings suggest that Plk1 phosphorylation regulates condensin II function by modulating CAP-H2 expression levels to facilitate proper mitotic chromosome organization.

CDC20 with malignant progression and poor prognosis of astrocytoma revealed by analysis on gene expression

The malignant transformation of astrocytoma may result from the accumulation of multiple genetic alterations. Current research shows that diffuse astrocytoma (AIIs, WHO grade II) is inherently predisposed to recur locally, and to spontaneously progress to anaplastic astrocytoma (AAIIIs, WHO grade III) and eventually secondary glioblastoma (sGBMIVs, WHO grade IV). The aim of the study was to identify and validate the important gene(s) associated with malignant progression and poor prognosis of astrocytoma. Average expression levels of 82 samples (35 AIIs, 13 AAIIIs and 34 sGBMIVs) were compared to each other through no-paired student test. Candidate genes were screened by DAVID and Kaplan-Meier survival analysis. Further, the significant candidate genes were validated through real-time PCR(qPCR), western blot and immunohistochemistry (IHC) in different grades of glioma. Finally, the association of target gene and clinical molecular characterization was analyzed by Chi-squared analysis. The cell-division cycle protein 20(CDC20, p = 0.0129) and the polo-like kinase 1(PLK1, p = 0.0046) were screened by statistical and Kaplan-Meier survival analysis. The expression levels of CDC20 and PLK1 rose significantly through real-time PCR(qPCR), western blot and IHC. A chi-squared analysis showed that patients with CDC20 high-expression differ from patients with CDC20 low-expression in terms of WHO classification (p < 0.0001), karnofsky performance score (KPS, p < 0.0001), isocitrate dehydrogenase mutation (IDH1, p < 0.0001), phosphatase and tensin homolog mutation (PTEN, p = 0.027) and epidermal growth factor receptor protein amplification (EGFR, p = 0.048). Moreover, the biological processes analyses indicate CDC20 might have an essential role in astrocyte cell proliferation. We demonstrated that the expression level of CDC20 increases significantly along with malignant progression and poor prognosis of astrocytoma.

The Mitotic Checkpoint Complex Requires an Evolutionary Conserved Cassette to Bind and Inhibit Active APC/C

The Spindle Assembly Checkpoint (SAC) ensures genomic stability by preventing sister chromatid separation until all chromosomes are attached to the spindle. It catalyzes the production of the Mitotic Checkpoint Complex (MCC), which inhibits Cdc20 to inactivate the Anaphase Promoting Complex/Cyclosome (APC/C). Here we show that two Cdc20-binding motifs in BubR1 of the recently identified ABBA motif class are crucial for the MCC to recognize active APC/C-Cdc20. Mutating these motifs eliminates MCC binding to the APC/C, thereby abolishing the SAC and preventing cells from arresting in response to microtubule poisons. These ABBA motifs flank a KEN box to form a cassette that is highly conserved through evolution, both in the arrangement and spacing of the ABBA-KEN-ABBA motifs, and association with the amino-terminal KEN box required to form the MCC. We propose that the ABBA-KEN-ABBA cassette holds the MCC onto the APC/C by binding the two Cdc20 molecules in the MCC-APC/C complex.

Prostate cancer-associated mutation in SPOP impairs its ability to target Cdc20 for poly-ubiquitination and degradation

Recent studies revealed that mutations in SPOP (Speckle-type POZ protein) occur in up to 15% of patients with prostate cancer. However, the physiological role of SPOP in regulating prostate tumorigenesis remains elusive. Here, we identified the Cdc20 oncoprotein as a novel ubiquitin substrate of SPOP. As such, pharmacological inhibition of Cullin-based E3 ligases by MLN4924 could stabilize endogenous Cdc20 in cells. Furthermore, we found that Cullin 3, and, to a less extent, Cullin 1, specifically interacted with Cdc20. Depletion of Cullin 3, but not Cullin 1, could upregulate the abudance of Cdc20 largely via prolonging Cdc20 half-life. Moreover, SPOP, the adaptor protein of Cullin 3 family E3 ligase, specifically interacted with Cdc20, and promoted the poly-ubiquitination and subsequent degradation of Cdc20 in a degron-dependent manner. Importantly, prostate cancer-derived SPOP mutants failed to interact with Cdc20 to promote its degradation. As a result, SPOP-deficient prostate cancer cells with elevated Cdc20 expression became resistant to a pharmacological Cdc20 inhibitor. Therefore, our results revealed a novel role of SPOP in tumorigenesis in part by promoting the degradation of the Cdc20 oncoprotein.

Molecular basis of APC/C regulation by the spindle assembly checkpoint

In the dividing eukaryotic cell, the spindle assembly checkpoint (SAC) ensures that each daughter cell inherits an identical set of chromosomes. The SAC coordinates the correct attachment of sister chromatid kinetochores to the mitotic spindle with activation of the anaphase-promoting complex (APC/C), the E3 ubiquitin ligase responsible for initiating chromosome separation. In response to unattached kinetochores, the SAC generates the mitotic checkpoint complex (MCC), which inhibits the APC/C and delays chromosome segregation. By cryo-electron microscopy, here we determine the near-atomic resolution structure of a human APC/C–MCC complex (APC/C(MCC)). Degron-like sequences of the MCC subunit BubR1 block degron recognition sites on Cdc20, the APC/C coactivator subunit responsible for substrate interactions. BubR1 also obstructs binding of the initiating E2 enzyme UbcH10 to repress APC/C ubiquitination activity. Conformational variability of the complex enables UbcH10 association, and structural analysis shows how the Cdc20 subunit intrinsic to the MCC (Cdc20(MCC)) is ubiquitinated, a process that results in APC/C reactivation when the SAC is silenced.

Molecular mechanism of APC/C activation by mitotic phosphorylation

In eukaryotes, the anaphase-promoting complex (APC/C, also known as the cyclosome) regulates the ubiquitin-dependent proteolysis of specific cell-cycle proteins to coordinate chromosome segregation in mitosis and entry into the G1 phase. The catalytic activity of the APC/C and its ability to specify the destruction of particular proteins at different phases of the cell cycle are controlled by its interaction with two structurally related coactivator subunits, Cdc20 and Cdh1. Coactivators recognize substrate degrons, and enhance the affinity of the APC/C for its cognate E2 (refs 4-6). During mitosis, cyclin-dependent kinase (Cdk) and polo-like kinase (Plk) control Cdc20- and Cdh1-mediated activation of the APC/C. Hyperphosphorylation of APC/C subunits, notably Apc1 and Apc3, is required for Cdc20 to activate the APC/C, whereas phosphorylation of Cdh1 prevents its association with the APC/C. Since both coactivators associate with the APC/C through their common C-box and Ile-Arg tail motifs, the mechanism underlying this differential regulation is unclear, as is the role of specific APC/C phosphorylation sites. Here, using cryo-electron microscopy and biochemical analysis, we define the molecular basis of how phosphorylation of human APC/C allows for its control by Cdc20. An auto-inhibitory segment of Apc1 acts as a molecular switch that in apo unphosphorylated APC/C interacts with the C-box binding site and obstructs engagement of Cdc20. Phosphorylation of the auto-inhibitory segment displaces it from the C-box-binding site. Efficient phosphorylation of the auto-inhibitory segment, and thus relief of auto-inhibition, requires the recruitment of Cdk-cyclin in complex with a Cdk regulatory subunit (Cks) to a hyperphosphorylated loop of Apc3. We also find that the small-molecule inhibitor, tosyl-l-arginine methyl ester, preferentially suppresses APC/C(Cdc20) rather than APC/C(Cdh1), and interacts with the binding sites of both the C-box and Ile-Arg tail motifs. Our results reveal the mechanism for the regulation of mitotic APC/C by phosphorylation and provide a rationale for the development of selective inhibitors of this state.

The Bub1-Plk1 kinase complex promotes spindle checkpoint signalling through Cdc20 phosphorylation

The spindle checkpoint senses unattached kinetochores and inhibits the Cdc20-bound anaphase-promoting complex or cyclosome (APC/C), to delay anaphase, thereby preventing aneuploidy. A critical checkpoint inhibitor of APC/C(Cdc20) is the mitotic checkpoint complex (MCC). It is unclear whether MCC suffices to inhibit all cellular APC/C. Here we show that human checkpoint kinase Bub1 not only directly phosphorylates Cdc20, but also scaffolds Plk1-mediated phosphorylation of Cdc20. Phosphorylation of Cdc20 by Bub1-Plk1 inhibits APC/C(Cdc20) in vitro and is required for checkpoint signalling in human cells. Bub1-Plk1-dependent Cdc20 phosphorylation is regulated by upstream checkpoint signals and is dispensable for MCC assembly. A phospho-mimicking Cdc20 mutant restores nocodazole-induced mitotic arrest in cells depleted of Mad2 or BubR1. Thus, Bub1-Plk1-mediated phosphorylation of Cdc20 constitutes an APC/C-inhibitory mechanism that is parallel, but not redundant, to MCC formation. Both mechanisms are required to sustain mitotic arrest in response to spindle defects.

Mps1Mph1 Kinase Phosphorylates Mad3 to Inhibit Cdc20Slp1-APC/C and Maintain Spindle Checkpoint Arrests

The spindle checkpoint is a mitotic surveillance system which ensures equal segregation of sister chromatids. It delays anaphase onset by inhibiting the action of the E3 ubiquitin ligase known as the anaphase promoting complex or cyclosome (APC/C). Mad3/BubR1 is a key component of the mitotic checkpoint complex (MCC) which binds and inhibits the APC/C early in mitosis. Mps1^Mph1 kinase is critical for checkpoint signalling and MCC-APC/C inhibition, yet few substrates have been identified. Here we identify Mad3 as a substrate of fission yeast Mps1^Mph1 kinase. We map and mutate phosphorylation sites in Mad3, producing mutants that are targeted to kinetochores and assembled into MCC, yet display reduced APC/C binding and are unable to maintain checkpoint arrests. We show biochemically that Mad3 phospho-mimics are potent APC/C inhibitors in vitro, demonstrating that Mad3p modification can directly influence Cdc20^Slp1-APC/C activity. This genetic dissection of APC/C inhibition demonstrates that Mps1^Mph1 kinase-dependent modifications of Mad3 and Mad2 act in a concerted manner to maintain spindle checkpoint arrests.

When cells divide they need to ensure that a complete copy of their genetic material is transmitted to both daughter cells. Cells have evolved many controls to ensure that every division is carried out with very high fidelity. The spindle checkpoint is one such control, which acts as a surveillance system during mitosis. Defects in this checkpoint control lead to unequal segregation of DNA/chromosomes, termed aneuploidy, which is responsible for human birth defects and is very common in tumour cells.

The molecular components of the spindle checkpoint, identified initially through yeast genetics, include several protein kinases. Surprisingly few of their substrates have been identified. Here we identify the checkpoint protein Mad3 as an important substrate of the Mps1^Mph1 kinase. We show that Mps1^Mph1-dependent modification of Mad3 and Mad2 acts to delay cell division in situations where the genetic material would not be equally inherited by daughter cells. This delay enables the cell to correct any problems within the division machinery and thus avoid aneuploidy.

Cotargeting Polo-Like Kinase 1 and the Wnt/β-Catenin Signaling Pathway in Castration-Resistant Prostate Cancer

The Wnt/β-catenin signaling pathway has been identified as one of the predominantly upregulated pathways in castration-resistant prostate cancer (CRPC). However, whether targeting the β-catenin pathway will prove effective as a CRPC treatment remains unknown. Polo-like kinase 1 (Plk1) is a critical regulator in many cell cycle events, and its level is significantly elevated upon castration of mice carrying xenograft prostate tumors. Indeed, inhibition of Plk1 has been shown to inhibit tumor growth in several in vivo studies. Here, we show that Plk1 is a negative regulator of Wnt/β-catenin signaling. Plk1 inhibition or depletion enhances the level of cytosolic and nuclear β-catenin in human prostate cancer cells. Furthermore, inhibition of Wnt/β-catenin signaling significantly potentiates the antineoplastic activity of the Plk1 inhibitor BI2536 in both cultured prostate cancer cells and CRPC xenograft tumors. Mechanistically, axin2, a negative regulator of the β-catenin pathway, serves as a substrate of Plk1, and Plk1 phosphorylation of axin2 facilitates the degradation of β-catenin by enhancing binding between glycogen synthase kinase 3β (GSK3β) and β-catenin. Plk1-phosphorylated axin2 also exhibits resistance to Cdc20-mediated degradation. Overall, this study identifies a novel Plk1-Wnt signaling axis in prostate cancer, offering a promising new therapeutic option to treat CRPC.