TRIP13 and APC15 drive mitotic exit by turnover of interphase- and unattached kinetochore-produced MCC

Multitasking Proteins: Exploring Noncanonical Functions of Proteins during Mitosis

This review provides a comprehensive overview of how mitotic cells drive the repurposing of proteins to fulfill mitosis-specific functions. To ensure the successful completion of cell division, the cell strategically reallocates its "workforce" by assigning additional functions to available proteins. Protein repurposing occurs at multiple levels of cellular organization and involves diverse mechanisms. At the protein level, proteins may gain mitosis-specific functions through post-translational modifications. At the structural level, proteins that typically maintain cellular architecture in interphase are co-opted to participate in mitotic spindle formation, chromosome condensation, and kinetochore assembly. Furthermore, the dynamic reorganization of the nuclear envelope and other organelles relies on the temporary reassignment of enzymes, structural proteins, and motor proteins to facilitate these changes. These adaptive mechanisms underscore the remarkable versatility of the cellular proteome in responding to the stringent requirements of mitosis. By leveraging the existing proteome for dual or multiple specialized roles, cells optimize resource usage while maintaining the precision needed to preserve genomic integrity and ensure the survival of the next generation of cells.

The spindle assembly checkpoint: Molecular mechanisms and kinase-targeted drug discovery

The spindle assembly checkpoint (SAC) is a surveillance mechanism required for the fidelity of chromosome segregation, ensuring that anaphase is not initiated until all chromosomes are properly attached to the mitotic spindle. In cancer cells, SAC inactivation leads to aneuploidy beyond the cell's adaptation, culminating in cell death. This review provides a concise overview of the SAC signaling process and properties. Recent drug discovery strategies to selectively target kinases, particularly Aurora B and monopolar spindle kinase (MPS1), aimed at developing innovative anticancer agents able to override SAC are also presented.

Localization and function of APC15 during mouse oocyte meiotic progression

The Anaphase-Promoting Complex/Cyclosome (APC/C) is a critical regulator of cell cycle progression, with APC15 serving as an essential subunit. While the role of APC15 in mitosis is well characterized, its function during meiosis remains poorly understood. In this study, we investigated the expression, subcellular localization, and potential role of APC15 during mouse oocyte meiotic progression. Using immunofluorescence and confocal microscopy, we observed dynamic changes in APC15 localization throughout meiotic progression. Knockdown of APC15 via siRNA did not affect spindle organization, but led to meiotic arrest at metaphase I (MI) and impaired the removal of BUB3 from kinetochores, suggesting a disruption in Spindle Assembly Checkpoint (SAC) inactivation. Our results highlight the involvement of APC15 in the regulation of SAC and the transition from metaphase to anaphase in oocytes. These findings contribute to our understanding of APC15's role in meiotic regulation and provide insights into its potential impact on maintaining chromosomal stability during oocyte maturation.

Functional validation to explore the protective role of miR-223 in Staphylococcus aureus-induced bovine mastitis

BACKGROUND

Mastitis caused by Staphylococcus aureus (S. aureus) is one of the most intractable problems for the dairy industry, causing significantly reduced milk yields and early slaughter of cows worldwide. MicroRNAs (miRNAs) can post-transcriptionally regulate gene expression and studies in recent years have shown the importance of miRNA-associated gene regulation in S. aureus-induced mastitis.

RESULTS

In this study, to investigate the role of miR-223 in mastitis, we performed experiments to overexpress and suppress miR-223 in an immortalized bovine mammary epithelial cell line (MAC-T) infected with S. aureus. Overexpression of miR-223 in MAC-T cells repressed cell apoptosis and necrosis induced by S. aureus infection, whereas suppression of miR-223 had the opposite effect. Transcriptome expression profiling with weighted gene co-expression network analysis (WGCNA) and gene set variation analysis (GSVA) showed that miR-223 affects apoptosis and inflammation-related pathways. Furthermore, differentially expressed (DE) genes were evaluated, and genes exhibiting contrasting expression trends in the miR-223 overexpressed and suppressed groups were assessed as potential target genes of miR-223. Potential target genes, including CDC25B, PTPRF, DCTN1, and DPP9, were observed to be associated with apoptosis and necroptosis. Finally, through integrative analysis of genome-wide association study (GWAS) data and the animal quantitative trait loci (QTL) database, we determined that target genes of miR-223 were significantly enriched in single-nucleotide polymorphisms (SNP) and QTLs related to somatic cell count (SCC) and mastitis.

CONCLUSION

In summary, miR-223 has an inhibitory effect on S. aureus-induced cell apoptosis and necrosis by regulating PTPRF, DCTN1, and DPP9. These genes were significantly enriched in QTL regions associated with bovine mastitis resistance, underscoring their relevance in genetic regulation of disease resilience. Our findings provide critical genetic markers for enhancing mastitis resistance, particularly S. aureus-induced mastitis, through selective breeding. This work offers valuable insights for developing cattle with improved resistance to mastitis via targeted genetic selection.

Arabidopsis KNL1 recruits type one protein phosphatase to kinetochores to silence the spindle assembly checkpoint

Proper chromosome segregation during cell division is essential for genomic integrity and organismal development. This process is monitored by the spindle assembly checkpoint (SAC), which delays anaphase onset until all chromosomes are properly attached to the mitotic spindle. The kinetochore protein KNL1 plays a critical role in recruiting SAC proteins. Here, we reveal that Arabidopsis KNL1 regulates SAC silencing through the direct recruitment of type one protein phosphatase (TOPP) to kinetochores. We show that KNL1 interacts with all nine TOPPs via a conserved RVSF motif in its N terminus, and this interaction is required for the proper localization of TOPPs to kinetochores during mitosis. Disrupting KNL1-TOPP interaction leads to persistent SAC activation, resulting in a severe metaphase arrest and defects in plant growth and development. Our findings highlight the evolutionary conservation of KNL1 in coordinating kinetochore-localized phosphatase to ensure timely SAC silencing and faithful chromosome segregation in Arabidopsis.

Non-autonomous insulin signaling delays mitotic progression in C. elegans germline stem and progenitor cells

Stem and progenitor cell mitosis is essential for tissue development and homeostasis. How these cells ensure proper chromosome segregation, and thereby maintain mitotic fidelity, in the complex physiological environment of a living animal is poorly understood. Here we use in situ live-cell imaging of C. elegans germline stem and progenitor cells (GSPCs) to ask how the signaling environment influences stem and progenitor cell mitosis in vivo. Through a candidate screen we identify a new role for the insulin/IGF receptor (IGFR), daf-2, during GSPC mitosis. Mitosis is delayed in daf-2/IGFR mutants, and these delays require canonical, DAF-2/IGFR to DAF-16/FoxO insulin signaling, here acting cell non-autonomously from the soma. Interestingly, mitotic delays in daf-2/IGFR mutants depend on the spindle assembly checkpoint but are not accompanied by a loss of mitotic fidelity. Correspondingly, we show that caloric restriction, which delays GSPC mitosis and compromises mitotic fidelity, does not act via the canonical insulin signaling pathway, and instead requires AMP-activated kinase (AMPK). Together this work demonstrates that GSPC mitosis is influenced by at least two genetically separable signaling pathways and highlights the importance of signaling networks for proper stem and progenitor cell mitosis in vivo.

CCDC68 Maintains Mitotic Checkpoint Activation by Promoting CDC20 Integration into the MCC

The spindle assembly checkpoint (SAC) ensures chromosome segregation fidelity by manipulating unattached kinetochore-dependent assembly of the mitotic checkpoint complex (MCC). The MCC binds to and inhibits the anaphase promoting complex/cyclosome (APC/C) to postpone mitotic exit. However, the mechanism by which unattached kinetochores mediate MCC formation is not yet fully understood. Here, it is shown that CCDC68 is an outer kinetochore protein that preferentially localizes to unattached kinetochores. Furthermore, CCDC68 interacts with the SAC factor CDC20 to inhibit its autoubiquitination and MCC disassembly. Therefore, CCDC68 restrains APC/C activation to ensure a robust SAC and allow sufficient time for chromosome alignment, thus ensuring chromosomal stability. Hence, the study reveals that CCDC68 is required for CDC20-dependent MCC stabilization to maintain mitotic checkpoint activation.

TRIP13 regulates progression of gastric cancer through stabilising the expression of DDX21

GC (Gastric cancer) is one of the most common malignant tumours, with over 95% of gastric cancer patients being adenocarcinoma and most gastric cancer patients having no apparent symptoms in the early stages. Finding biomarkers for early screening of gastric cancer and exploring new targets for gastric cancer treatment are urgent problems to be solved in the treatment of gastric cancer, with significant clinical outcomes for the survival rate of gastric cancer patients. The AAA+ family ATPase thyroid hormone receptor-interacting protein 13 (TRIP13) has been reported to play an essential role in developing various tumours. However, the biological function and molecular mechanism of TRIP13 in gastric cancer remain unclear. This study confirms that TRIP13 is highly expressed in gastric cancer tissue samples and that TRIP13 participates in the proliferation, migration, invasion in vitro, and tumourigenesis and metastasis in vivo of gastric cancer cells. Mechanistically, this study confirms that TRIP13 directly interacts with DDX21 and stabilises its expression by restraining its ubiquitination degradation, thereby promoting gastric cancer progression. Additionally, histone deacetylase 1 (HDAC1) is an upstream factor of TRIP13, which could target the TRIP13 promoter region to promote the proliferation, migration, and invasion of gastric cancer cells. These results indicate that TRIP13 serve is a promising biomarker for the treating of gastric cancer patients, and the HDAC1-TRIP13/DDX21 axis might provide a solid theoretical basis for clinical treatment of gastric cancer patients.

Control of cell proliferation by memories of mitosis

Mitotic duration is tightly constrained, and extended mitosis is characteristic of problematic cells prone to chromosome missegregation and genomic instability. We show here that mitotic extension leads to the formation of p53-binding protein 1 (53BP1)-ubiquitin-specific protease 28 (USP28)-p53 protein complexes that are transmitted to, and stably retained by, daughter cells. Complexes assembled through a Polo-like kinase 1-dependent mechanism during extended mitosis and elicited a p53 response in G1 that prevented the proliferation of the progeny of cells that experienced an approximately threefold extended mitosis or successive less extended mitoses. The ability to monitor mitotic extension was lost in p53-mutant cancers and some p53-wild-type (p53-WT) cancers, consistent with classification of TP53BP1 and USP28 as tumor suppressors. Cancers retaining the ability to monitor mitotic extension exhibited sensitivity to antimitotic agents.

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

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

CAMK2D serves as a molecular scaffold for RNF8-MAD2 complex to induce mitotic checkpoint in glioma

MAD2 is a spindle assembly checkpoint protein that participates in the formation of mitotic checkpoint complex, which blocks mitotic progression. RNF8, an established DNA damage response protein, has been implicated in mitotic checkpoint regulation but its exact role remains poorly understood. Here, RNF8 proximity proteomics uncovered a role of RNF8-MAD2 in generating the mitotic checkpoint signal. Specifically, RNF8 competes with a small pool of p31comet for binding to the closed conformer of MAD2 via its RING domain, while CAMK2D serves as a molecular scaffold to concentrate the RNF8-MAD2 complex via transient/weak interactions between its p-Thr287 and RNF8's FHA domain. Accordingly, RNF8 overexpression impairs glioma stem cell (GSC) mitotic progression in a FHA- and RING-dependent manner. Importantly, low RNF8 expression correlates with inferior glioma outcome and RNF8 overexpression impedes GSC tumorigenicity. Last, we identify PLK1 inhibitor that mimics RNF8 overexpression using a chemical biology approach, and demonstrate a PLK1/HSP90 inhibitor combination that synergistically reduces GSC proliferation and stemness. Thus, our study has unveiled a previously unrecognized CAMK2D-RNF8-MAD2 complex in regulating mitotic checkpoint with relevance to gliomas, which is therapeutically targetable.

Proline-rich acidic protein 1 upregulates mitotic arrest deficient 1 to promote cisplatin-resistance of colorectal carcinoma by restraining mitotic checkpoint complex assembly

Background: The mechanism underlying cisplatin resistance in colorectal carcinoma (CRC) has not yet been elucidated. This study is aimed to illustrate the indispensable role of proline-rich acidic protein 1 (PRAP1) in cisplatin-resistant CRC. Methods: Cell viability and apoptosis were monitored using cell counting kit-8 and flow cytometry. Immunofluorescence and morphological analysis were used to determine mitotic arrest in cells. In vivo drug resistance was evaluated using a tumor xenograft assay. Results: PRAP1 was highly expressed in cisplatin-resistant CRC. PRAP1-upregulation in HCT-116 cells increased chemoresistance to cisplatin, whereas RNAi-mediated knockdown of PRAP1 sensitized cisplatin-resistant HCT-116 cells (HCT-116/DDP) to cisplatin. PRAP1-upregulation in HCT-116 cells hindered mitotic arrest and the formation of mitotic checkpoint complexes (MCC), followed by an increase in multidrug-resistant proteins such as p-glycoprotein 1 and multidrug resistance-associated protein 1, while PRAP1-knockdown in HCT-116/DDP cells partly restored colcemid-induced mitotic arrest and MCC assembly, resulting in decreased multidrug-resistant protein levels. PRAP1 downregulation-mediated sensitization to cisplatin in HCT-116/DDP cells was abolished by the inhibition of mitotic kinase activity by limiting MCC assembly. Additionally, PRAP1-upregulation increased cisplatin-resistance in CRC in vivo. Mechanistically, PRAP1 increased the expression of mitotic arrest deficient 1 (MAD1), that competitively binds to mitotic arrest deficient 2 (MAD2) in cisplatin-resistant CRC cells, leading to failed assembly of MCC and subsequent chemotherapy resistance. Conclusion: PRAP1-overexpression caused cisplatin resistance in CRC. Possibly, PRAP1 induced an increase in MAD1, which competitively interacted with MAD2 and subsequently restrained the formation of MCC, resulting in CRC cells escape from the supervision of MCC and chemotherapy resistance.

Shieldin complex assembly kinetics and DNA binding by SHLD3

The Shieldin complex represses end resection at DNA double-strand breaks (DSBs) and thereby serves as a pro-non homologous end joining (NHEJ) factor. The molecular details of the assembly of Shieldin and its recruitment to DSBs are unclear. Shieldin contains two REV7 molecules, which have the rare ability to slowly switch between multiple distinct native states and thereby could dynamically control the assembly of Shieldin. Here, we report the identification of a promiscuous DNA binding domain in SHLD3. At the N-terminus, SHLD3 interacts with a dimer of REV7 molecules. We show that the interaction between SHLD3 and the first REV7 is remarkably slow, while in contrast the interaction between SHLD3 and SHLD2 with a second REV7 molecule is fast and does not require structural remodeling. Overall, these results provide insights into the rate-limiting step of the molecular assembly of the Shieldin complex and its recruitment at DNA DSBs.

Principles and dynamics of spindle assembly checkpoint signalling

The transmission of a complete set of chromosomes to daughter cells during cell division is vital for development and tissue homeostasis. The spindle assembly checkpoint (SAC) ensures correct segregation by informing the cell cycle machinery of potential errors in the interactions of chromosomes with spindle microtubules prior to anaphase. To do so, the SAC monitors microtubule engagement by specialized structures known as kinetochores and integrates local mechanical and chemical cues such that it can signal in a sensitive, responsive and robust manner. In this Review, we discuss how SAC proteins interact to allow production of the mitotic checkpoint complex (MCC) that halts anaphase progression by inhibiting the anaphase-promoting complex/cyclosome (APC/C). We highlight recent advances aimed at understanding the dynamic signalling properties of the SAC and how it interprets various naturally occurring intermediate attachment states. Further, we discuss SAC signalling in the context of the mammalian multisite kinetochore and address the impact of the fibrous corona. We also identify current challenges in understanding how the SAC ensures high-fidelity chromosome segregation.

TRIP13 Participates in Immediate-Early Sensing of DNA Strand Breaks and ATM Signaling Amplification through MRE11

Thyroid hormone receptor-interacting protein 13 (TRIP13) participates in various regulatory steps related to the cell cycle, such as the mitotic spindle assembly checkpoint and meiotic recombination, possibly by interacting with members of the HORMA domain protein family. Recently, it was reported that TRIP13 could regulate the choice of the DNA repair pathway, i.e., homologous recombination (HR) or nonhomologous end-joining (NHEJ). However, TRIP13 is recruited to DNA damage sites within a few seconds after damage and may therefore have another function in DNA repair other than regulation of the pathway choice. Furthermore, the depletion of TRIP13 inhibited both HR and NHEJ, suggesting that TRIP13 plays other roles besides regulation of choice between HR and NHEJ. To explore the unidentified functions of TRIP13 in the DNA damage response, we investigated its genome-wide interaction partners in the context of DNA damage using quantitative proteomics with proximity labeling. We identified MRE11 as a novel interacting partner of TRIP13. TRIP13 controlled the recruitment of MDC1 to DNA damage sites by regulating the interaction between MDC1 and the MRN complex. Consistently, TRIP13 was involved in ATM signaling amplification. Our study provides new insight into the function of TRIP13 in immediate-early DNA damage sensing and ATM signaling activation.

CENP-F-dependent DRP1 function regulates APC/C activity during oocyte meiosis I

Chromosome segregation is initiated by cohesin degradation, which is driven by anaphase-promoting complex/cyclosome (APC/C). Chromosome cohesin is removed by activated separase, with the degradation of securin and cyclinB1. Dynamin-related protein 1 (DRP1), a component of the mitochondrial fission machinery, is related to cyclin dynamics in mitosis progression. Here, we show that DRP1 is recruited to the kinetochore by centromeric Centromere protein F (CENP-F) after nuclear envelope breakdown in mouse oocytes. Loss of DRP1 during prometaphase leads to premature cohesin degradation and chromosome segregation. Importantly, acute DRP1 depletion activates separase by initiating cyclinB1 and securin degradation during the metaphase-to-anaphase transition. Finally, we demonstrate that DRP1 is bound to APC2 to restrain the E3 ligase activity of APC/C. In conclusion, DRP1 is a CENP-F-dependent atypical spindle assembly checkpoint (SAC) protein that modulates metaphase-to-anaphase transition by controlling APC/C activity during meiosis I in oocytes.

Checkpoint control in meiotic prophase: Idiosyncratic demands require unique characteristics

Chromosomal transactions such as replication, recombination and segregation are monitored by cell cycle checkpoint cascades. These checkpoints ensure the proper execution of processes that are needed for faithful genome inheritance from one cell to the next, and across generations. In meiotic prophase, a specialized checkpoint monitors defining events of meiosis: programmed DNA break formation, followed by dedicated repair through recombination based on interhomolog (IH) crossovers. This checkpoint shares molecular characteristics with canonical DNA damage checkpoints active during somatic cell cycles. However, idiosyncratic requirements of meiotic prophase have introduced unique features in this signaling cascade. In this review, we discuss the unique features of the meiotic prophase checkpoint. While being related to canonical DNA damage checkpoint cascades, the meiotic prophase checkpoint also shows similarities with the spindle assembly checkpoint (SAC) that guards chromosome segregation. We highlight these emerging similarities in the signaling logic of the checkpoints that govern meiotic prophase and chromosome segregation, and how thinking of these similarities can help us better understand meiotic prophase control. We also discuss work showing that, when aberrantly expressed, components of the meiotic prophase checkpoint might alter DNA repair fidelity and chromosome segregation in cancer cells. Considering checkpoint function in light of demands imposed by the special characteristics of meiotic prophase helps us understand checkpoint integration into the meiotic cell cycle machinery.

Evolutionary Dynamics and Molecular Mechanisms of HORMA Domain Protein Signaling

Controlled assembly and disassembly of multi-protein complexes is central to cellular signaling. Proteins of the widespread and functionally diverse HORMA family nucleate assembly of signaling complexes by binding short peptide motifs through a distinctive safety-belt mechanism. HORMA proteins are now understood as key signaling proteins across kingdoms, serving as infection sensors in a bacterial immune system and playing central roles in eukaryotic cell cycle, genome stability, sexual reproduction, and cellular homeostasis pathways. Here, we describe how HORMA proteins' unique ability to adopt multiple conformational states underlies their functions in these diverse contexts. We also outline how a dedicated AAA+ ATPase regulator, Pch2/TRIP13, manipulates HORMA proteins' conformational states to activate or inactivate signaling in different cellular contexts. The emergence of Pch2/TRIP13 as a lynchpin for HORMA protein action in multiple genome-maintenance pathways accounts for its frequent misregulation in human cancers and highlights TRIP13 as a novel therapeutic target. Expected final online publication date for the Annual Review of Biochemistry, Volume 91 is June 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

DNA damage is overcome by TRIP13 overexpression during cisplatin nephrotoxicity

Cisplatin is a commonly used chemotherapeutic agent to treat a wide array of cancers that is frequently associated with toxic injury to the kidney due to oxidative DNA damage and perturbations in cell cycle progression leading to cell death. In this study, we investigated whether thyroid receptor interacting protein 13 (TRIP13) plays a central role in the protection of the tubular epithelia following cisplatin treatment by circumventing DNA damage. Following cisplatin treatment, double-stranded DNA repair pathways were inhibited using selective blockers to proteins involved in either homologous recombination or non-homologous end joining. This led to increased blood markers of acute kidney injury (AKI) (creatinine and neutrophil gelatinase–associated lipocalin), tubular damage, activation of DNA damage marker (γ-H2AX), elevated appearance of G2/M blockade (phosphorylated histone H3 Ser10 and cyclin B1), and apoptosis (cleaved caspase-3). Conditional proximal tubule–expressing Trip13 mice were observed to be virtually protected from the cisplatin nephrotoxicity by restoring most of the pathological phenotypes back toward normal conditions. Our findings suggest that TRIP13 could circumvent DNA damage in the proximal tubules during cisplatin injury and that TRIP13 may constitute a new therapeutic target in protecting the kidney from nephrotoxicants and reduce outcomes leading to AKI.

Spindle assembly checkpoint activation and silencing at kinetochores

The spindle assembly checkpoint (SAC) is a surveillance mechanism that promotes accurate chromosome segregation in mitosis. The checkpoint senses the attachment state of kinetochores, the proteinaceous structures that assemble onto chromosomes in mitosis in order to mediate their interaction with spindle microtubules. When unattached, kinetochores generate a diffusible inhibitor that blocks the activity of the anaphase-promoting complex/cyclosome (APC/C), an E3 ubiquitin ligase required for sister chromatid separation and exit from mitosis. Work from the past decade has greatly illuminated our understanding of the mechanisms by which the diffusible inhibitor is assembled and how it inhibits the APC/C. However, less is understood about how SAC proteins are recruited to kinetochores in the absence of microtubule attachment, how the kinetochore catalyzes formation of the diffusible inhibitor, and how attachments silence the SAC at the kinetochore. Here, we summarize current understanding of the mechanisms that activate and silence the SAC at kinetochores and highlight open questions for future investigation.

Evolutionary Dynamics of the Spindle Assembly Checkpoint in Eukaryotes

The tremendous diversity in eukaryotic life forms can ultimately be traced back to evolutionary modifications at the level of molecular networks. Deep understanding of these modifications will not only explain cellular diversity, but will also uncover different ways to execute similar processes and expose the evolutionary 'rules' that shape the molecular networks. Here, we review the evolutionary dynamics of the spindle assembly checkpoint (SAC), a signaling network that guards fidelity of chromosome segregation. We illustrate how the interpretation of divergent SAC systems in eukaryotic species is facilitated by combining detailed molecular knowledge of the SAC and extensive comparative genome analyses. Ultimately, expanding this to other core cellular systems and experimentally interrogating such systems in organisms from all major lineages may start outlining the routes to and eventual manifestation of the cellular diversity of eukaryotic life.

Genome-wide profile in DNA methylation in goat ovaries of two different litter size populations

Although some studies have investigated the DNA methylation modification in goat ovaries, it is not understood DNA methylation related to goat litter size. This investigation was designed to explore the DNA methylation status in the ovaries of high litter size and low litter size groups using whole-genome bisulfite sequencing (WGBS). We found that there was global difference on DNA methylation in high litter size and low litter size goat ovaries. Many differentially methylated region-related genes (DMGs) were found in the ovaries of these two different goat populations. Moreover, enrichment analysis discovered that many DMGs were involved in gamete development, reproductive system development, wingless-type MMTV integration site family (WNT) signalling pathways and mitogen-activated protein kinase 1 (MAPK) signalling pathways. The data indicated that DNA methylation in goat ovaries may play important roles in the folliculogenesis, the oocyte ovulation rate and finally the litter size. This study provides a comprehensive analysis of genome-wide DNA methylation patterns in ovaries of high and low litter size goat which helps the understanding of ovarian DNA methylation in relation to goat fertility capability.

CDC20 assists its catalytic incorporation in the mitotic checkpoint complex

Open (O) and closed (C) topologies of HORMA-domain proteins are respectively associated with inactive and active states of fundamental cellular pathways. The HORMA protein O-MAD2 converts to C-MAD2 upon binding CDC20. This is rate limiting for assembly of the mitotic checkpoint complex (MCC), the effector of a checkpoint required for mitotic fidelity. A catalyst assembled at kinetochores accelerates MAD2:CDC20 association through a poorly understood mechanism. Using a reconstituted SAC system, we discovered that CDC20 is an impervious substrate for which access to MAD2 requires simultaneous docking on several sites of the catalytic complex. Our analysis indicates that the checkpoint catalyst is substrate assisted and promotes MCC assembly through spatially and temporally coordinated conformational changes in both MAD2 and CDC20. This may define a paradigm for other HORMA-controlled systems.

State changes of the HORMA protein ASY1 are mediated by an interplay between its closure motif and PCH2

HORMA domain-containing proteins (HORMADs) play an essential role in meiosis in many organisms. The meiotic HORMADs, including yeast Hop1, mouse HORMAD1 and HORMAD2, and Arabidopsis ASY1, assemble along chromosomes at early prophase and the closure motif at their C-termini has been hypothesized to be instrumental for this step by promoting HORMAD oligomerization. In late prophase, ASY1 and its homologs are progressively removed from synapsed chromosomes promoting chromosome synapsis and recombination. The conserved AAA+ ATPase PCH2/TRIP13 has been intensively studied for its role in removing HORMADs from synapsed chromosomes. In contrast, not much is known about how HORMADs are loaded onto chromosomes. Here, we reveal that the PCH2-mediated dissociation of the HORMA domain of ASY1 from its closure motif is important for the nuclear targeting and subsequent chromosomal loading of ASY1. This indicates that the promotion of ASY1 to an ‘unlocked’ state is a prerequisite for its nuclear localization and chromosomal assembly. Likewise, we find that the closure motif is also necessary for the removal of ASY1 by PCH2 later in prophase. Our work results in a unified new model for PCH2 and HORMADs function in meiosis and suggests a mechanism to contribute to unidirectionality in meiosis.

Nanoenabled Tumor Oxygenation Strategies for Overcoming Hypoxia-Associated Immunosuppression

Cancer immunotherapy, which initiates or strengthens innate immune responses to attack cancer cells, has shown great promise in cancer treatment. However, low immune response impacted by immunosuppressive tumor microenvironment (TME) remains a key challenge, which has been found related to tumor hypoxia. Recently, nanomaterial systems are proving to be excellent platforms for tumor oxygenation, which can reverse hypoxia-associated immunosuppression, strengthen the systemic antitumor immune responses, and thus afford a striking abscopal effect to clear metastatic cancer cells. In this review, we would like to survey recent progress in utilizing nanomaterials for tumor oxygenation through approaches such as in situ O₂ generation, O₂ delivery, tumor vasculature normalization, and mitochondrial-respiration inhibition. Their effects on tumor hypoxia-associated immunosuppression are highlighted. We also discuss the ongoing challenges and how to further improve the clinical prospect of cancer immunotherapy.

Mps1-mediated release of Mad1 from nuclear pores ensures the fidelity of chromosome segregation

The spindle assembly checkpoint (SAC) relies on the recruitment of Mad1-C-Mad2 to unattached kinetochores but also on its binding to Megator/Tpr at nuclear pore complexes (NPCs) during interphase. However, the molecular underpinnings controlling the spatiotemporal redistribution of Mad1-C-Mad2 as cells progress into mitosis remain elusive. Here, we show that activation of Mps1 during prophase triggers Mad1 release from NPCs and that this is required for kinetochore localization of Mad1-C-Mad2 and robust SAC signaling. We find that Mps1 phosphorylates Megator/Tpr to reduce its interaction with Mad1 in vitro and in Drosophila cells. Importantly, preventing Mad1 from binding to Megator/Tpr restores Mad1 accumulation at kinetochores, the fidelity of chromosome segregation, and genome stability in larval neuroblasts of mps1-null mutants. Our findings demonstrate that the subcellular localization of Mad1 is tightly coordinated with cell cycle progression by kinetochore-extrinsic activity of Mps1. This ensures that both NPCs in interphase and kinetochores in mitosis can generate anaphase inhibitors to efficiently preserve genomic stability.

p31comet promotes homologous recombination by inactivating REV7 through the TRIP13 ATPase

The repair of DNA double strand breaks (DSBs) that arise from external mutagenic agents and routine cellular processes is essential for life. DSBs are repaired by two major pathways, homologous recombination (HR) and classical nonhomologous end joining (C-NHEJ). DSB repair pathway choice is largely dictated at the step of 5'-3' DNA end resection, which is promoted during S phase, in part by BRCA1. Opposing end resection is the 53BP1 protein, which recruits the ssDNA-binding REV7-Shieldin complex to favor C-NHEJ repair. We recently identified TRIP13 as a proresection factor that remodels REV7, causing its dissociation from the Shieldin subunit SHLD3. Here, we identify p31^comet, a negative regulator of MAD2 and the spindle assembly checkpoint, as an important mediator of the TRIP13-REV7 interaction. p31^comet binds to the REV7-Shieldin complex in cells, promotes REV7 inactivation, and causes PARP inhibitor resistance. p31^comet also participates in the extraction of REV7 from the chromatin. Furthermore, p31^comet can counteract REV7 function in translesion synthesis (TLS) by releasing it from REV3 in the Pol ζ complex. Finally, p31^comet, like TRIP13, is overexpressed in many cancers and this correlates with poor prognosis. Thus, we reveal a key player in the regulation of HR and TLS with significant clinical implications.

The conserved AAA-ATPase PCH-2 TRIP13 regulates spindle checkpoint strength

Spindle checkpoint strength is dictated by the number of unattached kinetochores, cell volume, and cell fate. We show that the conserved AAA-ATPase PCH-2/TRIP13, which remodels the checkpoint effector Mad2 from an active conformation to an inactive one, controls checkpoint strength in Caenorhabditis elegans. Having previously established that this function is required for spindle checkpoint activation, we demonstrate that in cells genetically manipulated to decrease in cell volume, PCH-2 is no longer required for the spindle checkpoint or recruitment of Mad2 at unattached kinetochores. This role is not limited to large cells: the stronger checkpoint in germline precursor cells also depends on PCH-2. PCH-2 is enriched in germline precursor cells, and this enrichment relies on conserved factors that induce asymmetry in the early embryo. Finally, the stronger checkpoint in germline precursor cells is regulated by CMT-1, the ortholog of p31^comet, which is required for both PCH-2′s localization to unattached kinetochores and its enrichment in germline precursor cells. Thus, PCH-2, likely by regulating the availability of inactive Mad2 at and near unattached kinetochores, governs checkpoint strength. This requirement may be particularly relevant in oocytes and early embryos enlarged for developmental competence, cells that divide in syncytial tissues, and immortal germline cells.

Homeostatic Control of Meiotic Prophase Checkpoint Function by Pch2 and Hop1

Checkpoint cascades link cell cycle progression with essential chromosomal processes. During meiotic prophase, recombination and chromosome synapsis are monitored by what are considered distinct checkpoints. In budding yeast, cells that lack the AAA+ ATPase Pch2 show an impaired cell cycle arrest in response to synapsis defects. However, unperturbed pch2Δ cells are delayed in meiotic prophase, suggesting paradoxical roles for Pch2 in cell cycle progression. Here, we provide insight into the checkpoint roles of Pch2 and its connection to Hop1, a HORMA domain-containing client protein. Contrary to current understanding, we find that Pch2 (together with Hop1) is crucial for checkpoint function in response to both recombination and synapsis defects, thus revealing a shared meiotic checkpoint cascade. Meiotic checkpoint responses are transduced by DNA break-dependent phosphorylation of Hop1. Based on our data and on the described effect of Pch2 on HORMA topology, we propose that Pch2 promotes checkpoint proficiency by catalyzing the availability of signaling-competent Hop1. Conversely, we demonstrate that Pch2 can act as a checkpoint silencer, also in the face of persistent DNA repair defects. We establish a framework in which Pch2 and Hop1 form a homeostatic module that governs general meiotic checkpoint function. We show that this module can-depending on the cellular context-fuel or extinguish meiotic checkpoint function, which explains the contradictory roles of Pch2 in cell cycle control. Within the meiotic prophase checkpoint, the Pch2-Hop1 module thus operates analogous to the Pch2/TRIP13-Mad2 module in the spindle assembly checkpoint that monitors chromosome segregation.

From the Nuclear Pore to the Fibrous Corona: A MAD Journey to Preserve Genome Stability

The relationship between kinetochores and nuclear pore complexes (NPCs) is intimate but poorly understood. Several NPC components and associated proteins are relocated to mitotic kinetochores to assist in different activities that ensure faithful chromosome segregation. Such is the case of the Mad1-c-Mad2 complex, the catalytic core of the spindle assembly checkpoint (SAC), a surveillance pathway that delays anaphase until all kinetochores are attached to spindle microtubules. Mad1-c-Mad2 is recruited to discrete domains of unattached kinetochores from where it promotes the rate-limiting step in the assembly of anaphase-inhibitory complexes. SAC proficiency further requires Mad1-c-Mad2 to be anchored at NPCs during interphase. However, the mechanistic relevance of this arrangement for SAC function remains ill-defined. Recent studies uncover the molecular underpinnings that coordinate the release of Mad1-c-Mad2 from NPCs with its prompt recruitment to kinetochores. Here, current knowledge on Mad1-c-Mad2 function and spatiotemporal regulation is reviewed and the critical questions that remain unanswered are highlighted.

Thyroid receptor-interacting protein 13 and EGFR form a feedforward loop promoting glioblastoma growth

Epidermal growth factor receptor (EGFR) amplification and EGFRvIII mutation drive glioblastoma (GBM) pathogenesis, but their regulation remains elusive. Here we characterized the EGFR/EGFRvIII "interactome" in GBM and identified thyroid receptor-interacting protein 13 (TRIP13), an AAA + ATPase, as an EGFR/EGFRvIII-associated protein independent of its ATPase activity. Functionally, TRIP13 augmented EGFR pathway activation and contributed to EGFR/EGFRvIII-driven GBM growth in GBM spheroids and orthotopic GBM xenograft models. Mechanistically, TRIP13 enhanced EGFR protein abundance in part by preventing Cbl-mediated ubiquitination and proteasomal degradation. Reciprocally, TRIP13 was phosphorylated at tyrosine(Y) 56 by EGFRvIII and EGF-activated EGFR. Abrogating TRIP13 Y56 phosphorylation dramatically attenuated TRIP13 expression-enhanced EGFR signaling and GBM cell growth. Clinically, TRIP13 expression was upregulated in GBM specimens and associated with poor patient outcome. In GBM, TRIP13 localized to cell membrane and cytoplasma and exhibited oncogenic effects in vitro and in vivo, depending on EGFR signaling but not the TRIP13 ATPase activity. Collectively, our findings uncover that TRIP13 and EGFR form a feedforward loop to potentiate EGFR signaling in GBM growth and identify a previously unrecognized ATPase activity-independent mode of action of TRIP13 in GBM biology.

Structural interconversions of the anaphase-promoting complex/cyclosome (APC/C) regulate cell cycle transitions

The anaphase-promoting complex/cyclosome (APC/C) is a large multi-subunit complex that functions as a RING domain E3 ubiquitin ligase to regulate transitions through the cell cycle, achieved by controlling the defined ubiquitin-dependent degradation of specific cell cycle regulators. APC/C activity and substrate selection are controlled at various levels to ensure that specific cell cycle events occur in the correct order and time. Structural and mechanistic studies over the past two decades have complemented functional studies to provide comprehensive insights that explain APC/C molecular mechanisms. This review discusses how modifications of the core APC/C are responsible for the APC/C's interconversion between different structural and functional states that govern its capacity to control transitions between specific cell cycle phases. A unifying theme is that these structural interconversions involve competition between short linear sequence motifs (SLIMs), shared between substrates, coactivators, inhibitors and E2s, for their common binding sites on the APC/C.

HORMA Domain Proteins and a Trip13-like ATPase Regulate Bacterial cGAS-like Enzymes to Mediate Bacteriophage Immunity

Bacteria are continually challenged by foreign invaders, including bacteriophages, and have evolved a variety of defenses against these invaders. Here, we describe the structural and biochemical mechanisms of a bacteriophage immunity pathway found in a broad array of bacteria, including E. coli and Pseudomonas aeruginosa. This pathway uses eukaryotic-like HORMA domain proteins that recognize specific peptides, then bind and activate a cGAS/DncV-like nucleotidyltransferase (CD-NTase) to generate a cyclic triadenylate (cAAA) second messenger; cAAA in turn activates an endonuclease effector, NucC. Signaling is attenuated by a homolog of the AAA+ ATPase Pch2/TRIP13, which binds and disassembles the active HORMA-CD-NTase complex. When expressed in non-pathogenic E. coli, this pathway confers immunity against bacteriophage λ through an abortive infection mechanism. Our findings reveal the molecular mechanisms of a bacterial defense pathway integrating a cGAS-like nucleotidyltransferase with HORMA domain proteins for threat sensing through protein detection and negative regulation by a Trip13 ATPase.

Polyanions provide selective control of APC/C interactions with the activator subunit

Transient interactions between the anaphase-promoting complex/cyclosome (APC/C) and its activator subunit Cdc20 or Cdh1 generate oscillations in ubiquitylation activity necessary to maintain the order of cell cycle events. Activator binds the APC/C with high affinity and exhibits negligible dissociation kinetics in vitro, and it is not clear how the rapid turnover of APC/C-activator complexes is achieved in vivo. Here, we describe a mechanism that controls APC/C-activator interactions based on the availability of substrates. We find that APC/C-activator dissociation is stimulated by abundant cellular polyanions such as nucleic acids and polyphosphate. Polyanions also interfere with substrate ubiquitylation. However, engagement with high-affinity substrate blocks the inhibitory effects of polyanions on activator binding and APC/C activity. We propose that this mechanism amplifies the effects of substrate affinity on APC/C function, stimulating processive ubiquitylation of high-affinity substrates and suppressing ubiquitylation of low-affinity substrates.

The G2-to-M Transition Is Ensured by a Dual Mechanism that Protects Cyclin B from Degradation by Cdc20-Activated APC/C

In the eukaryotic cell cycle, a threshold level of cyclin B accumulation triggers the G2-to-M transition, and subsequent cyclin B destruction triggers mitotic exit. The anaphase-promoting complex/cyclosome (APC/C) is the E3 ubiquitin ligase that, together with its co-activator Cdc20, targets cyclin B for destruction during mitotic exit. Here, we show that two pathways act in concert to protect cyclin B from Cdc20-activated APC/C in G2, in order to enable cyclin B accumulation and the G2-to-M transition. The first pathway involves the Mad1-Mad2 spindle checkpoint complex, acting in a distinct manner from checkpoint signaling after mitotic entry but employing a common molecular mechanism-the promotion of Mad2-Cdc20 complex formation. The second pathway involves cyclin-dependent kinase phosphorylation of Cdc20, which is known to reduce Cdc20's affinity for the APC/C. Cooperation of these two mechanisms, which target distinct APC/C binding interfaces of Cdc20, enables cyclin B accumulation and the G2-to-M transition.

Elevated TRIP13 drives the AKT/mTOR pathway to induce the progression of hepatocellular carcinoma via interacting with ACTN4

BACKGROUND

ATPase associated with a variety of cellular activities (AAA ATPase) family members are closely linked to tumor formation and progression. However, their roles in hepatocellular carcinoma (HCC) largely remain unclear.

METHODS

Bioinformatic analyses of public databases were used to excavate the potential AAA ATPases that may contribute to HCC, and thyroid hormone receptor interactor 13 (TRIP13) was selected to following researches because of its most prominently differential expression. Western blot, qRT-PCR and immunohistochemistry were used to detect the expression of TRIP13 in HCC tissues, and then the relationship between TRIP13 expression and clinicopathological parameters were evaluated. Finally, its functions and potential mechanisms were investigated through a series gain- and loss-of-function strategies both in vitro and in vivo.

RESULTS

TRIP13 was significantly overexpressed in HCC tissues and high level of TRIP13 was closely correlated with a worse clinical outcome. Functionally, elevated TRIP13 facilitated cell proliferation, migration, invasion, and promoted cellular epithelial-mesenchymal transition (EMT) in vitro, while promote tumor growth and lung metastasis in vivo. Mechanistically, TRIP13 interacted with ACTN4 and positively regulated its expression, thus activating the AKT/mTOR pathway to drive tumor progression. Moreover, miR-192-5p served as an upstream regulator of TRIP13 by directly binding to TRIP13 mRNA 3' UTR, which may partially explain the high expression of TRIP13 in HCC.

CONCLUSION

Our findings identified TRIP13 as a promising candidate oncogene in HCC, and TRIP13 induced cell migration, invasion and metastasis of HCC through the AKT/mTOR signaling via interacting with ACTN4.

Orchestration of the spindle assembly checkpoint by CDK1-cyclin B1

In mitosis, the spindle assembly checkpoint (SAC) monitors the formation of microtubule-kinetochore attachments during capture of chromosomes by the mitotic spindle. Spindle assembly is complete once there are no longer any unattached kinetochores. Here, we will discuss the mechanism and key components of spindle checkpoint signalling. Unattached kinetochores bind the principal spindle checkpoint kinase monopolar spindle 1 (MPS1). MPS1 triggers the recruitment of other spindle checkpoint proteins and the formation of a soluble inhibitor of anaphase, thus preventing exit from mitosis. On microtubule attachment, kinetochores become checkpoint silent due to the actions of PP2A-B56 and PP1. This SAC responsive period has to be coordinated with mitotic spindle formation to ensure timely mitotic exit and accurate chromosome segregation. We focus on the molecular mechanisms by which the SAC permissive state is created, describing a central role for CDK1-cyclin B1 and its counteracting phosphatase PP2A-B55. Furthermore, we discuss how CDK1-cyclin B1, through its interaction with MAD1, acts as an integral component of the SAC, and actively orchestrates checkpoint signalling and thus contributes to the faithful execution of mitosis.

Insights into a Crucial Role of TRIP13 in Human Cancer

Thyroid Hormone Receptor Interacting Protein 13 (TRIP13) plays a key role in regulating mitotic processes, including spindle assembly checkpoint and DNA repair pathways, which may account for Chromosome instability (CIN). As CIN is a predominant hallmark of cancer, TRIP13 may act as a tumor susceptibility locus. Amplification of TRIP13 has been observed in various human cancers and implicated in several aspects of malignant transformation, including cancer cell proliferation, drug resistance and tumor progression. Here, we discussed the functional significance of TRIP13 in cell progression, highlighted the recent findings on the aberrant expression in human cancers and emphasized its significance for the therapeutic potential.

Combinational phototherapy and hypoxia-activated chemotherapy favoring antitumor immune responses

Background: Tumor metastasis is responsible for most cancer death worldwide, which lacks curative treatment.

Purpose: The objective of this study was to eliminate tumor and control the development of tumor metastasis.

Methods: Herein, we demonstrated a smart nano-enabled platform, in which 2-[2-[2-chloro-3-[(1,3-dihydro-3,3-dimethyl-1-propyl-2h-indol-2-ylidene)ethylidene]-1-cyclohexen-1-yl]ethenyl]-3,3-dimethyl-1-propylindolium iodide (IR780) and tirapazamine (TPZ) were co-loaded in poly(ε-caprolactone)-poly(ethylene glycol) (PEG-PCL) to form versatile nanoparticles (PEG-PCL-IR780-TPZ NPs).

Results: The intelligence of the system was reflected in the triggered and controlled engineering. Specially, PEG-PCL not only prolonged the circulation time of IR780 and TPZ but also promoted tumor accumulation of nanodrugs through enhanced permeability and retention (EPR) effect. Moreover, reactive oxygen species (ROS) generated by IR780 armed by an 808 nm laser irradiation evoked a cargo release. Meanwhile, IR780, as a mitochondria-targeting phototherapy agent exacerbated tumor hypoxic microenvironment and activated TPZ for accomplishing hypoxia-activated chemotherapy. Most significantly, IR780 was capable of triggering immunogenic cell death (ICD) during the synergic treatment. ICD biomarkers as a “danger signal” accelerated dendritic cells (DCs) maturation, and subsequently activated toxic T lymphocytes.

Conclusion: Eventually, antitumor immune responses stimulated by combinational phototherapy and hypoxia-activated chemotherapy revolutionized the current landscape of cancer treatment, strikingly inhibiting tumor metastasis and providing a promising prospect in the clinical application.