Mode of interaction of TRIP13 AAA-ATPase with the Mad2-binding protein p31comet and with mitotic checkpoint complexes

TRIP13 - a potential drug target in cancer pharmacotherapy

ATPases Associated with Diverse Cellular Activity (AAA+ATPases) are important enzymatic functional proteins in human cells. Thyroid Hormone Receptor Interacting Protein-13 (TRIP13) is a member of this protein superfamily, that partly regulates DNA repair pathways and spindle assembly checkpoints during mitosis. TRIP13 is reported as an oncogene involving multiple pathways in many human malignancies, including multiple myeloma, brain tumors, etc. The structure of TRIP13 reveals the mechanisms for ATP binding and how TRIP13 recognizes the Mitotic Arrest Deficiency-2 (MAD2) protein, with p31comet acting as an adapter protein. DCZ0415, TI17, DCZ5417, and DCZ5418 are the reported small-molecule inhibitors of TRIP13, which have been demonstrated to inhibit TRIP13's biological functions significantly and effective in suppressing various types of malignant cells, indicating that TRIP13 is a significant anticancer drug target. Currently, no systematic reviews are cutting across the functions, structure, and novel inhibitors of TRIP13. This review provides a comprehensive overview of TRIP13's biological functions, its roles in eighteen different cancers, four small molecule inhibitors, different underlying molecular mechanisms, and its functionality as a potential anticancer drug target.

In silico analysis unveiling potential biomarkers in gallbladder carcinogenesis

Gallbladder cancer (GBC) is a rare but very aggressive most common digestive tract cancer with a high mortality rate due to delayed diagnosis at the advanced stage. Moreover, GBC progression shows asymptomatic characteristics making it impossible to detect at an early stage. In these circumstances, conventional therapy like surgery, chemotherapy, and radiotherapy becomes refractive. However, few studies reported some molecular markers like KRAS (Kirsten Rat Sarcoma) mutation, upregulation of HER2/neu, EGFR (Epidermal Growth Factor Receptor), and microRNAs in GBC. However, the absence of some specific early diagnostic and prognostic markers is the biggest hurdle for the therapy of GBC to date. The present study has been designed to identify some specific molecular markers for precise diagnosis, and prognosis, for successful treatment of the GBC. By In Silico a network-centric analysis of two microarray datasets; (GSE202479) and (GSE13222) from the Gene Expression Omnibus (GEO) database, shows 50 differentially expressed genes (DEGs) associated with GBC. Further network analysis revealed that 12 genes are highly interconnected based on the highest MCODE (Molecular Complex Detection) value, among all three genes; TRIP13 (Thyroid Receptor Interacting Protein), NEK2 (Never in Mitosis gene-A related Kinase 2), and TPX2 (Targeting Protein for Xklp2) having highest network interaction with transcription factors and miRNA suggesting critically associated with GBC. Further survival analysis data corroborate the association of these genes; TRIP13, NEK2, and TPX2 with GBC. Thus, TRIP13, NEK2, and TPX2 genes are significantly correlated with a greater risk of mortality, transforming them from mere biomarkers of the GBC for early detections and may emerge as prognostic markers for treatment.

MicroRNA-495: a therapeutic and diagnostic tumor marker

Therapeutic and diagnostic progresses have significantly reduced the mortality rate among cancer patients during the last decade. However, there is still a high rate of mortality among cancer patients. One of the important reasons involved in the high mortality rate is the late diagnosis in advanced tumor stages that causes the failure of therapeutic strategies in these patients. Therefore, investigating the molecular mechanisms involved in tumor progression has an important role in introducing the efficient early detection markers. MicroRNAs (miRNAs) as stable factors in body fluids are always considered as non-invasive diagnostic and prognostic markers. In the present review, we investigated the role of miR-495 in tumor progression. It has been reported that miR-495 has mainly a tumor suppressor function through the regulation of transcription factors and tyrosine kinases as well as cellular processes such as multidrug resistance, chromatin remodeling, and signaling pathways. This review can be an effective step towards introducing the miR-495 as a non-invasive diagnostic/prognostic marker as well as a suitable target in tumor therapy.

The novel norcantharidin derivative DCZ5417 suppresses multiple myeloma progression by targeting the TRIP13-MAPK-YWHAE signaling pathway

BACKGROUND

Multiple myeloma (MM), an incurable disease owing to drug resistance, requires safe and effective therapies. Norcantharidin (NCTD), an active ingredient in traditional Chinese medicines, possesses activity against different cancers. However, its toxicity and narrow treatment window limit its clinical application. In this study, we synthesized a series of derivatives of NCTD to address this. Among these compounds, DCZ5417 demonstrated the greatest anti-MM effect and fewest side effects. Its anti-myeloma effects and  the mechanism were further tested.

METHODS

Molecular docking, pull-down, surface plasmon resonance-binding, cellular thermal shift, and ATPase assays were used to study the targets of DCZ5417. Bioinformatic, genetic, and pharmacological approaches were used to elucidate the mechanisms associated with DCZ5417 activity.

RESULTS

We confirmed a highly potent interaction between DCZ5417 and TRIP13. DCZ5417 inhibited the ATPase activity of TRIP13, and its anti-MM activity was found to depend on TRIP13. A mechanistic study verified that DCZ5417 suppressed cell proliferation by targeting TRIP13, disturbing the TRIP13/YWHAE complex and inhibiting the ERK/MAPK signaling axis. DCZ5417 also showed a combined lethal effect with traditional anti-MM drugs. Furthermore, the tumor growth-inhibitory effect of DCZ5417 was demonstrated using in vivo tumor xenograft models.

CONCLUSIONS

DCZ5417 suppresses MM progression in vitro, in vivo, and in primary cells from drug-resistant patients, affecting cell proliferation by targeting TRIP13, destroying the TRIP13/YWHAE complex, and inhibiting ERK/MAPK signaling. These results imply a new and effective therapeutic strategy for MM treatment.

CHAMP1 binds to REV7/FANCV and promotes homologous recombination repair

A critical determinant of DNA repair pathway choice is REV7, an adaptor that binds to various DNA repair proteins through its C-terminal seatbelt domain. The REV7 seatbelt binds to either REV3, activating translesion synthesis, or to SHLD3, activating non-homologous end joining (NHEJ) repair. Recent studies have identified another REV7 seatbelt-binding protein, CHAMP1 (chromosome alignment-maintaining phosphoprotein 1), though its possible role in DNA repair is unknown. Here, we show that binding of CHAMP1 to REV7 activates homologous recombination (HR) repair. Mechanistically, CHAMP1 binds directly to REV7 and reduces the level of the Shieldin complex, causing an increase in double-strand break end resection. CHAMP1 also interacts with POGZ in a heterochromatin complex further promoting HR repair. Importantly, in human tumors, CHAMP1 overexpression promotes HR, confers poly (ADP-ribose) polymerase inhibitor resistance, and correlates with poor prognosis. Thus, by binding to either SHLD3 or CHAMP1 through its seatbelt, the REV7 protein can promote either NHEJ or HR repair, respectively.

Feng et al. demonstrate that CHAMP1 promotes homologous recombination by binding to REV7 and reducing the level of the Shieldin complex, causing an increase in double-strand break end resection. CHAMP1 and POGZ form a complex to further promote HR. Upregulation of CHAMP1 expression is a mechanism of acquired PARP inhibitor resistance.

Evaluation of the TRIP13 level in breast cancer and insights into potential molecular pathways

TRIP13 is a member of the large superfamily of the AAA + ATPase proteins and is associated with a variety of activities. Emerging evidence has shown that TRIP13 may serve as an oncogene. However, the function of TRIP13 in breast cancer (BC) has not yet been elucidated. Here, a variety of bioinformatic tools and laboratory experiments were combined to analyse the expression patterns, prognostic value and functional network of TRIP13 in BC. Multiple databases and immunohistochemistry (IHC) indicated a higher TRIP13 expression in BC tissue compared with normal tissue. TRIP13 was highly expressed in lung metastatic lesions compared with primary tumours in a 4T1 cell implantation BALB/c mouse model of BC. Kaplan–Meier plots also revealed that high TRIP13 expression correlated with poor survival in patients with BC. Furthermore, gene set enrichment analysis revealed that TRIP13 was primarily enriched in the signalling pathway of PI3K‐AKT‐mTOR. Suppressing TRIP13 could inhibit the expression of related genes, as well as the proliferation and migration of BC cell. Finally, 10 hub genes with a high score of connectivity were filtered from the protein–protein interaction (PPI) network, including MAD2L1, CDC20, CDC5L, CDK1, CCNA2, BUB1B, RAD51, SPO11, KIF11 and AURKB. Thus, TRIP13 may be a promising prognostic biomarker and an effective therapeutic target for BC.

KIF18B promotes breast cancer cell proliferation, migration and invasion by targeting TRIP13 and activating the Wnt/β‑catenin signaling pathway

Kinesin superfamily member 18B (KIF18B) has previously been reported to be upregulated in breast cancer (BC) and is involved in BC tumorigenesis. Therefore, the present study aimed to investigate the effects and underlying mechanisms of KIF18B in BC. Comprehensive bioinformatics analysis was performed, using data from The Cancer Genome Atlas. KIF18B knockdown and thyroid hormone receptor-interacting protein 13 (TRIP13) overexpression in BC cells were induced via transfection, by using the short hairpin RNA-KIF18B and overexpression-TRIP13 vectors, respectively. Cellular processes, including proliferation, migration and invasion were assessed using colony formation, wound healing and Transwell assays, respectively. mRNA and protein expression levels were determined using reverse transcription-quantitative PCR and western blot analysis, respectively. Protein-protein interactions were determined using co-immunoprecipitation. The results demonstrated that the KIF18B expression levels were upregulated in BC, particularly in triple-negative BC (TNBC) tissues and cell lines. KIF18B knockdown inhibited the proliferation, migration and invasion of HCC-1937 TNBC cells. Furthermore, MMP12 and MMP9 protein expression levels were decreased by KIF18B knockdown. TRIP13 expression was also demonstrated to be upregulated in BC, particularly in TNBC tissues and cell lines. TRIP13 expression levels positively correlated with those of KIF18B in BC tissues and cells, and further analysis verified that TRIP13 and KIF14B were able to directly bind to each other. However, TRIP13 overexpression abolished the effects of KIF18B knockdown on HCC-1937 cells. Furthermore, KIF18B knockdown decreased β-catenin, c-Myc and cyclin D1 protein expression levels; however, TRIP13 overexpression resulted in the recovery of all respective protein expression levels. On the whole, the present study demonstrates that KIF18B promotes BC malignant events, including the proliferation, migration and invasion of TNBC cells. These results indicate that KIF18B may play an oncogenic role in BC by upregulating TRIP13 expression, thereby activating the Wnt/β-catenin signaling pathway.

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.

MAD2L2 dimerization and TRIP13 control shieldin activity in DNA repair

MAD2L2 (REV7) plays an important role in DNA double-strand break repair. As a member of the shieldin complex, consisting of MAD2L2, SHLD1, SHLD2 and SHLD3, it controls DNA repair pathway choice by counteracting DNA end-resection. Here we investigated the requirements for shieldin complex assembly and activity. Besides a dimerization-surface, HORMA-domain protein MAD2L2 has the extraordinary ability to wrap its C-terminus around SHLD3, likely creating a very stable complex. We show that appropriate function of MAD2L2 within shieldin requires its dimerization, mediated by SHLD2 and accelerating MAD2L2-SHLD3 interaction. Dimerization-defective MAD2L2 impairs shieldin assembly and fails to promote NHEJ. Moreover, MAD2L2 dimerization, along with the presence of SHLD3, allows shieldin to interact with the TRIP13 ATPase, known to drive topological switches in HORMA-domain proteins. We find that appropriate levels of TRIP13 are important for proper shieldin (dis)assembly and activity in DNA repair. Together our data provide important insights in the dependencies for shieldin activity.

TRIP13 exerts a cancer-promoting role in cervical cancer by enhancing Wnt/β-catenin signaling via ACTN4

Increasing evidence has indicated that thyroid hormone receptor interacting protein 13 (TRIP13) exerts a cancer-promoting role in a broad spectrum of cancers. However, the detailed relevance and function of TRIP13 in cervical cancer remain undefined. The goal of this work was to evaluate the functional significance and mechanism of TRIP13 in cervical cancer. Our data demonstrated that TRIP13 expression was markedly increased in cervical cancer tissue, and high expression of TRIP13 predicted a low survival rate in cervical cancer patients. Knockdown of TRIP13 caused a significant reduction in the proliferation and invasion of cervical cancer cells. By contrast, over-expression of TRIP13 accelerated the proliferation and invasion of cervical cancer cells. Further data revealed that TRIP13 enhanced the activation of Wnt/β-catenin signaling associated with modulation of α-Actinin-4 (ACTN4). Knockdown of ACTN4 markedly reversed TRIP13-mediated activation of Wnt/β-catenin signaling. In addition, inhibition of Wnt/β-catenin signaling reversed TRIP13-induced cancer-promoting effects in cervical cancer cells. Knockdown of TRIP13 markedly retarded the tumor formation and growth of cervical cells in vivo in nude mice. Taken together, the data of this work indicate that TRIP13 accelerates the proliferation and invasion of cervical cancer by enhancing Wnt/β-catenin signaling via regulation of ACTN4. These findings underscore a relevance of the TRIP13/ACTN4/Wnt/β-catenin signaling axis in the progression of cervical cancer and suggest TRIP13 as a potential target for treatment of cervical cancer.

Dynein intermediate chain 2c (DNCI2c) complex is essential for exiting Mad2-dependent spindle assembly checkpoint

The Mad2 protein plays a key role in the spindle assembly checkpoint (SAC) function. The SAC pathway delays mitotic progression into anaphase until all kinetochores attach to the spindle during mitosis. The formation of the Mad2-p31^comet complex correlates with the completion of spindle attachment and the entry into anaphase during mitosis. Herein, we showed that dynein intermediate chain 2c (DNCI2c)-a subunit of dynein motor protein-forms an immunocomplex with p31^comet during mitosis. DNCI2c-knockdown resulted in prolonged mitotic arrest in a Mad2-dependent manner. Furthermore, DNCI2c-knockdown-induced mitotic arrest was not rescued by p31^comet overexpression. However, the combination of p31^comet overexpression with the mitotic drug treatment reversed the mitotic arrest in DNCI2c-knockdown. Together, these results indicate that the DNCI2c-p31^comet complex plays an important role in exiting Mad2-dependent SAC.

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.

Cryo-EM reveals conformational flexibility in apo DNA polymerase ζ

The translesion synthesis (TLS) DNA polymerases Rev1 and Polζ function together in DNA lesion bypass during DNA replication, acting as nucleotide inserter and extender polymerases, respectively. While the structural characterization of the Saccharomyces cerevisiae Polζ in its DNA-bound state has illuminated how this enzyme synthesizes DNA, a mechanistic understanding of TLS also requires probing conformational changes associated with DNA- and Rev1 binding. Here, we used single-particle cryo-electron microscopy to determine the structure of the apo Polζ holoenzyme. We show that compared with its DNA-bound state, apo Polζ displays enhanced flexibility that correlates with concerted motions associated with expansion of the Polζ DNA-binding channel upon DNA binding. We also identified a lysine residue that obstructs the DNA-binding channel in apo Polζ, suggesting a gating mechanism. The Polζ subunit Rev7 is a hub protein that directly binds Rev1 and is a component of several other protein complexes such as the shieldin DNA double-strand break repair complex. We analyzed the molecular interactions of budding yeast Rev7 in the context of Polζ and those of human Rev7 in the context of shieldin using a crystal structure of Rev7 bound to a fragment of the shieldin-3 protein. Overall, our study provides new insights into Polζ mechanism of action and the manner in which Rev7 recognizes partner proteins.

Intricate Regulatory Mechanisms of the Anaphase-Promoting Complex/Cyclosome and Its Role in Chromatin Regulation

The ubiquitin (Ub)-proteasome system is vital to nearly every biological process in eukaryotes. Specifically, the conjugation of Ub to target proteins by Ub ligases, such as the Anaphase-Promoting Complex/Cyclosome (APC/C), is paramount for cell cycle transitions as it leads to the irreversible destruction of cell cycle regulators by the proteasome. Through this activity, the RING Ub ligase APC/C governs mitosis, G1, and numerous aspects of neurobiology. Pioneering cryo-EM, biochemical reconstitution, and cell-based studies have illuminated many aspects of the conformational dynamics of this large, multi-subunit complex and the sophisticated regulation of APC/C function. More recent studies have revealed new mechanisms that selectively dictate APC/C activity and explore additional pathways that are controlled by APC/C-mediated ubiquitination, including an intimate relationship with chromatin regulation. These tasks go beyond the traditional cell cycle role historically ascribed to the APC/C. Here, we review these novel findings, examine the mechanistic implications of APC/C regulation, and discuss the role of the APC/C in previously unappreciated signaling pathways.

Getting there: understanding the chromosomal recruitment of the AAA+ ATPase Pch2/TRIP13 during meiosis

The generally conserved AAA+ ATPase Pch2/TRIP13 is involved in diverse aspects of meiosis, such as prophase checkpoint function, DNA break regulation, and meiotic recombination. The controlled recruitment of Pch2 to meiotic chromosomes allows it to use its ATPase activity to influence HORMA protein-dependent signaling. Because of the connection between Pch2 chromosomal recruitment and its functional roles in meiosis, it is important to reveal the molecular details that govern Pch2 localization. Here, we review the current understanding of the different factors that control the recruitment of Pch2 to meiotic chromosomes, with a focus on research performed in budding yeast. During meiosis in this organism, Pch2 is enriched within the nucleolus, where it likely associates with the specialized chromatin of the ribosomal (r)DNA. Pch2 is also found on non-rDNA euchromatin, where its recruitment is contingent on Zip1, a component of the synaptonemal complex (SC) that assembles between homologous chromosomes. We discuss recent findings connecting the recruitment of Pch2 with its association with the Origin Recognition Complex (ORC) and reliance on RNA Polymerase II-dependent transcription. In total, we provide a comprehensive overview of the pathways that control the chromosomal association of an important meiotic regulator.

TRIP13 promotes lung cancer cell growth and metastasis through AKT/mTORC1/c-Myc signaling

BACKGROUND

Lung adenocarcinoma (LUAD) is a primary cause of cancer-patient mortality throughout the world. Thyroid hormone receptor interactor 13 (TRIP13) is a gene that expresses a protein involved in cell division, including tumorigenesis. Its expression is high in various human tumors; however, its role in LUAD cells remains undetermined.

OBJECTIVE

To investigate the TRIP13's role in the development of LUAD.

METHODS

Bioinformation analysis was used to analyze the expression of TRIP13 in LUAD tissues and the impact on the prognosis of LUAD; CRISPR/Cas9 was used to construct the cell lines; CCK-8 was used to explore the cell proliferation; Transwell assays was applied to exam the cell migration and cell invasion abilities; Western blot and immunoprecipitation was used to explore the relation between TRIP13 and AKT/mTORC1/c-Myc signaling pathway.

RESULTS

By analyzing LUAD data from The Cancer Genome Atlas and the Gene Expression Omnibus databases, we determined that TRIP13 is highly expressed in LUAD tissues and that this expression level has a negative impact on the patient mortality. TRIP13 has also proved to promote LUAD cell proliferation, migration, and invasion. In this study, we demonstrated that TRIP13 activates AKT/mTORC1/c-Myc signaling in these cells.

CONCLUSION

Our results have identified the role and potential mechanism by which TRIP13 affects LUAD cells, which may provide a useful marker for helping to diagnose this disease and create new therapies against it.

The Mad2-Binding Protein p31comet as a Potential Target for Human Cancer Therapy

The spindle assembly checkpoint (SAC) is a surveillance mechanism that prevents mitotic exit at the metaphase-to-anaphase transition until all chromosomes have established correct bipolar attachment to spindle microtubules. Activation of SAC relies on the assembly of the mitotic checkpoint complex (MCC), which requires conformational change from inactive open Mad2 (OMad2) to the active closed Mad2 (C-Mad2) at unattached kinetochores. The Mad2-binding protein p31^comet plays a key role in controlling timely mitotic exit by promoting SAC silencing, through preventing Mad2 activation and promoting MCC disassembly. Besides, increasing evidences highlight the p31^comet potential as target for cancer therapy. Here, we provide an updated overview of the functional significance of p31^comet in mitotic progression, and discuss the potential of deregulated expression of p31^comet in cancer and in therapeutic strategies.

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.

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.

PCH-2 collaborates with CMT-1 to proofread meiotic homolog interactions

The conserved ATPase, PCH-2/TRIP13, is required during both the spindle checkpoint and meiotic prophase. However, its specific role in regulating meiotic homolog pairing, synapsis and recombination has been enigmatic. Here, we report that this enzyme is required to proofread meiotic homolog interactions. We generated a mutant version of PCH-2 in C. elegans that binds ATP but cannot hydrolyze it: pch-2E253Q. In vitro, this mutant can bind a known substrate but is unable to remodel it. This mutation results in some non-homologous synapsis and impaired crossover assurance. Surprisingly, worms with a null mutation in PCH-2's adapter protein, CMT-1, the ortholog of p31comet, localize PCH-2 to meiotic chromosomes, exhibit non-homologous synapsis and lose crossover assurance. The similarity in phenotypes between cmt-1 and pch-2E253Q mutants suggest that PCH-2 can bind its meiotic substrates in the absence of CMT-1, in contrast to its role during the spindle checkpoint, but requires its adapter to hydrolyze ATP and remodel them.

Long non-coding RNA NORAD exhaustion represses prostate cancer progression through inhibiting TRIP13 expression via competitively binding to miR-495-3p

Background

Prostate cancer (PCa) is a malignant heterogeneous tumor that threatens men's health. Long non-coding RNA activated by DNA damage (NORAD) and microRNA-495-3p (miR-495-3p) have been revealed to be concerned with the tumorigenesis and progression of diverse cancers. Nevertheless, the regulatory mechanism between NORAD and miR-495-3p in PCa is unclear.

Methods

The expression of NORAD, miR-495-3p, and thyroid hormone receptor interactor 13 (TRIP13) mRNA was detected with quantitative real-time polymerase chain reaction (qRT-PCR). The levels of Bcl-2, Bax, Cleaved-casp-3, TRIP13, cyclin D1, and PCNA were detected through western blot analysis. The proliferation, apoptosis, migration, and invasion of PCa cells were assessed through 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT), flow cytometry, or transwell assays. The relationship between NORAD or TRIP13 and miR-495-3p was confirmed via dual-luciferase reporter, RIP, or RNA pull-down assays.

Results

NORAD and TRIP13 were upregulated while miR-495-3p was downregulated in PCa tissues and cells. Both NORAD silencing and miR-495-3p upregulation accelerated cell apoptosis and curbed cell proliferation, migration, and invasion in PCa cells. Also, NORAD silencing repressed tumor growth in vivo. Notably, NORAD modulated TRIP13 expression by competitively binding to miR-495-3p. Furthermore, miR-495-3p repression reversed NORAD knockdown-mediated effects on the malignant behaviors of PCa cells. Moreover, TRIP13 enhancement overturned the effects of miR-495-3p overexpression on the proliferation, apoptosis, migration, and invasion of PCa cells.

Conclusion

NORAD depletion inhibited PCa advancement via the miR-495-3p/ TRIP13 axis, which provided a potential tactic for PCa treatment.

Bi-allelic Missense Pathogenic Variants in TRIP13 Cause Female Infertility Characterized by Oocyte Maturation Arrest

Normal oocyte meiosis is a prerequisite for successful human reproduction, and abnormalities in the process will result in infertility. In 2016, we identified mutations in TUBB8 as responsible for human oocyte meiotic arrest. However, the underlying genetic factors for most affected individuals remain unknown. TRIP13, encoding an AAA-ATPase, is a key component of the spindle assembly checkpoint, and recurrent homozygous nonsense variants and a splicing variant in TRIP13 are reported to cause Wilms tumors in children. In this study, we identified homozygous and compound heterozygous missense pathogenic variants in TRIP13 responsible for female infertility mainly characterized by oocyte meiotic arrest in five individuals from four independent families. Individuals from three families suffered from oocyte maturation arrest, whereas the individual from the fourth family had abnormal zygote cleavage. All displayed only the infertility phenotype without Wilms tumors or any other abnormalities. In vitro and in vivo studies showed that the identified variants reduced the protein abundance of TRIP13 and caused its downstream molecule, HORMAD2, to accumulate in HeLa cells and in proband-derived lymphoblastoid cells. The chromosome mis-segregation assay showed that variants did not have any effects on mitosis. Injecting TRIP13 cRNA into oocytes from one affected individual was able to rescue the phenotype, which has implications for future therapeutic treatments. This study reports pathogenic variants in TRIP13 responsible for oocyte meiotic arrest, and it highlights the pivotal but different roles of TRIP13 in meiosis and mitosis. These findings also indicate that different dosage effects of mutant TRIP13 might result in two distinct human diseases.

Elevated TRIP13 drives cell proliferation and drug resistance in bladder cancer

Dysregulation of mitotic processes can induce chromosome instability, which results in aneuploidy, tumorigenesis, and chemo-resistance. Thyroid hormone receptor interactor 13 (TRIP13) is a critical mitosis regulator, and recent studies suggest that it functions as an oncogene in multiple cancers. However, the role of TRIP13 in bladder cancer (BC) is still unknown. In this study, our analysis of RNA-sequencing data from the Cancer Genome Atlas and Gene expression profiling databases showed that TRIP13 expression was upregulated in BC tissues, and overexpression of TRIP13 was significantly associated with poor prognosis of BC patients. In addition, we found a remarkable elevation of TRIP13 in BC samples compared to normal controls by immunohistochemistry. Furthermore, our in vitro functional assays showed that overexpression of TRIP13 promoted the growth/viability, colony formation ability by inducing cell cycle arrest in G2/M phase, as well as enhancing drug resistance of BC cells to cisplatin and doxorubicin. Conversely, knockdown of TRIP13 inhibited cell growth and induced apoptosis of BC cells. Furthermore, TRIP13 acted as an oncogene in BC by inhibiting spindle assembly checkpoint signaling by targeting mitotic arrest deficient 2 (MAD2) protein. TRIP13 overexpression also alleviated cisplatin- and doxorubicin-induced DNA damage and enhanced DNA repair as evidenced by the reduced expression of γH2AX and enhanced expression of RAD50 in drug-treated BC cells. In conclusion, TRIP13 may be a novel target for the treatment of BC.

Conformational dynamics of the Hop1 HORMA domain reveal a common mechanism with the spindle checkpoint protein Mad2

The HORMA domain is a highly conserved protein–protein interaction module found in eukaryotic signaling proteins including the spindle assembly checkpoint protein Mad2 and the meiotic HORMAD proteins. HORMA domain proteins interact with short ‘closure motifs’ in partner proteins by wrapping their C-terminal ‘safety belt’ region entirely around these motifs, forming topologically-closed complexes. Closure motif binding and release requires large-scale conformational changes in the HORMA domain, but such changes have only been observed in Mad2. Here, we show that Saccharomyces cerevisiae Hop1, a master regulator of meiotic recombination, possesses conformational dynamics similar to Mad2. We identify closure motifs in the Hop1 binding partner Red1 and in Hop1 itself, revealing that HORMA domain–closure motif interactions underlie both Hop1’s initial recruitment to the chromosome axis and its self-assembly on the axis. We further show that Hop1 adopts two distinct folded states in solution, one corresponding to the previously-observed ‘closed’ conformation, and a second more extended state in which the safety belt region has disengaged from the HORMA domain core. These data reveal strong mechanistic similarities between meiotic HORMADs and Mad2, and provide a mechanistic basis for understanding both meiotic chromosome axis assembly and its remodeling by the AAA+ ATPase Pch2/TRIP13.

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.

Role of Polo-like kinase 1 in the regulation of the action of p31comet in the disassembly of mitotic checkpoint complexes

The Mad2-binding protein p31comet has important roles in the inactivation of the mitotic checkpoint system, which delays anaphase until chromosomes attach correctly to the mitotic spindle. The activation of the checkpoint promotes the assembly of a Mitotic Checkpoint Complex (MCC), which inhibits the action of the ubiquitin ligase APC/C (Anaphase-Promoting Complex/Cyclosome) to degrade inhibitors of anaphase initiation. The inactivation of the mitotic checkpoint requires the disassembly of MCC. p31comet promotes the disassembly of mitotic checkpoint complexes by liberating their Mad2 component in a joint action with the ATPase TRIP13. Here, we investigated the regulation of p31comet action. The release of Mad2 from checkpoint complexes in extracts from nocodazole-arrested HeLa cells was inhibited by Polo-like kinase 1 (Plk1), as suggested by the effects of selective inhibitors of Plk1. Purified Plk1 bound to p31comet and phosphorylated it, resulting in the suppression of its activity (with TRIP13) to disassemble checkpoint complexes. Plk1 phosphorylated p31comet on S102, as suggested by the prevention of the phosphorylation of this residue in checkpoint extracts by the selective Plk1 inhibitor BI-2536 and by the phosphorylation of S102 with purified Plk1. An S102A mutant of p31comet had a greatly decreased sensitivity to inhibition by Plk1 of its action to disassemble mitotic checkpoint complexes. We propose that the phosphorylation of p31comet by Plk1 prevents a futile cycle of MCC assembly and disassembly during the active mitotic checkpoint.

Mapping Mitotic Death: Functional Integration of Mitochondria, Spindle Assembly Checkpoint and Apoptosis

Targeting the mitotic pathways of rapidly proliferating tumor cells has been an effective strategy in traditional cancer therapy. Chemotherapeutics such as taxanes and vinca alkaloids, which disrupt microtubule function, have enjoyed clinical success; however, the accompanying side effects, toxicity and multi drug resistance remain as serious concerns. The emerging classes of inhibitors targeting mitotic kinases and proteasome face their own set of challenges. It is hoped that elucidation of the regulatory interface between mitotic checkpoints, mitochondria and mitotic death will aid the development of more efficacious anti-mitotic agents and improved treatment protocols. The links between the spindle assembly checkpoint (SAC) and mitochondrial dynamics that control the progression of anti-mitotic agent-induced apoptosis have been under investigation for several years and the functional integration of these various signaling networks is now beginning to emerge. In this review, we highlight current research on the regulation of SAC, the death pathway and mitochondria with particular focus on their regulatory interconnections.

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

The mitotic checkpoint ensures accurate chromosome segregation through assembly of the mitotic checkpoint complex (MCC), a soluble inhibitor of the anaphase-promoting complex/cyclosome (APC/C) produced by unattached kinetochores. MCC is also assembled during interphase by Mad1/Mad2 bound at nuclear pores, thereby preventing premature mitotic exit prior to kinetochore maturation and checkpoint activation. Using degron tagging to rapidly deplete the AAA+ ATPase TRIP13, we show that its catalytic activity is required to maintain a pool of open-state Mad2 for MCC assembly, thereby supporting mitotic checkpoint activation, but is also required for timely mitotic exit through catalytic disassembly of MCC. Strikingly, combining TRIP13 depletion with elimination of APC15-dependent Cdc20 ubiquitination/degradation results in a complete inability to exit mitosis, even when MCC assembly at unattached kinetochores is prevented. Thus, mitotic exit requires MCC produced either in interphase or mitosis to be disassembled by TRIP13-catalyzed removal of Mad2 or APC15-driven ubiquitination/degradation of its Cdc20 subunit.

Rev7 dimerization is important for assembly and function of the Rev1/Polζ translesion synthesis complex

The translesion synthesis (TLS) polymerases Polζ and Rev1 form a complex that enables replication of damaged DNA. The Rev7 subunit of Polζ, which is a multifaceted HORMA (Hop1, Rev7, Mad2) protein with roles in TLS, DNA repair, and cell-cycle control, facilitates assembly of this complex by binding Rev1 and the catalytic subunit of Polζ, Rev3. Rev7 interacts with Rev3 by a mechanism conserved among HORMA proteins, whereby an open-to-closed transition locks the ligand underneath the "safety belt" loop. Dimerization of HORMA proteins promotes binding and release of this ligand, as exemplified by the Rev7 homolog, Mad2. Here, we investigate the dimerization of Rev7 when bound to the two Rev7-binding motifs (RBMs) in Rev3 by combining in vitro analyses of Rev7 structure and interactions with a functional assay in a Rev7^-/- cell line. We demonstrate that Rev7 uses the conventional HORMA dimerization interface both to form a homodimer when tethered by the two RBMs in Rev3 and to heterodimerize with other HORMA domains, Mad2 and p31^comet Structurally, the Rev7 dimer can bind only one copy of Rev1, revealing an unexpected Rev1/Polζ architecture. In cells, mutation of the Rev7 dimer interface increases sensitivity to DNA damage. These results provide insights into the structure of the Rev1/Polζ TLS assembly and highlight the function of Rev7 homo- and heterodimerization.

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.

TRIP13 impairs mitotic checkpoint surveillance and is associated with poor prognosis in multiple myeloma

AAA-ATPase TRIP13 is one of the chromosome instability gene recently established in multiple myeloma (MM), the second most common and incurable hematological malignancy. However, the specific function of TRIP13 in MM is largely unknown. Using sequential gene expression profiling, we demonstrated that high TRIP13 expression levels were positively correlated with progression, disease relapse, and poor prognosis in MM patients. Overexpressing human TRIP13 in myeloma cells prompted cell growth and drug resistance, and overexpressing murine TRIP13, which shares 93% sequence identity with human TRIP13, led to colony formation of NIH/3T3 fibroblasts in vitro and tumor formation in vivo. Meanwhile, the knockdown of TRIP13 inhibited myeloma cell growth, induced cell apoptosis, and reduced tumor burden in xenograft MM mice. Mechanistically, we observed that the overexpression of TRIP13 abrogated the spindle checkpoint and induced proteasome-mediated degradation of MAD2 primarily through the Akt pathway. Thus, our results demonstrate that TRIP13 may serve as a biomarker for MM disease development and prognosis, making it a potential target for future therapies.

Mechanistic insight into TRIP13-catalyzed Mad2 structural transition and spindle checkpoint silencing

The spindle checkpoint maintains genomic stability and prevents aneuploidy. Unattached kinetochores convert the latent open conformer of the checkpoint protein Mad2 (O-Mad2) to the active closed conformer (C-Mad2), bound to Cdc20. C-Mad2–Cdc20 is incorporated into the mitotic checkpoint complex (MCC), which inhibits the anaphase-promoting complex/cyclosome (APC/C). The C-Mad2-binding protein p31^comet and the ATPase TRIP13 promote MCC disassembly and checkpoint silencing. Here, using nuclear magnetic resonance (NMR) spectroscopy, we show that TRIP13 and p31^comet catalyze the conversion of C-Mad2 to O-Mad2, without disrupting its stably folded core. We determine the crystal structure of human TRIP13, and identify functional TRIP13 residues that mediate p31^comet–Mad2 binding and couple ATP hydrolysis to local unfolding of Mad2. TRIP13 and p31^comet prevent APC/C inhibition by MCC components, but cannot reactivate APC/C already bound to MCC. Therefore, TRIP13–p31^comet intercepts and disassembles free MCC not bound to APC/C through mediating the local unfolding of the Mad2 C-terminal region.

The spindle checkpoint ensures the fidelity of chromosome segregation during mitosis and meiosis. Here the authors use a combination of biochemical and structural biology approaches to show how the TRIP13 ATPase and its adaptor, p31^comet, catalyze the conversion of the checkpoint protein Mad2 between latent and active forms

Dynamic ubiquitin signaling in cell cycle regulation

Gilberto and Peter discuss the role of ubiquitylation in the regulation of DNA replication and mitosis.

The cell division cycle is driven by a collection of enzymes that coordinate DNA duplication and separation, ensuring that genomic information is faithfully and perpetually maintained. The activity of the effector proteins that perform and coordinate these biological processes oscillates by regulated expression and/or posttranslational modifications. Ubiquitylation is a cardinal cellular modification and is long known for driving cell cycle transitions. In this review, we emphasize emerging concepts of how ubiquitylation brings the necessary dynamicity and plasticity that underlie the processes of DNA replication and mitosis. New studies, often focusing on the regulation of chromosomal proteins like DNA polymerases or kinetochore kinases, are demonstrating that ubiquitylation is a versatile modification that can be used to fine-tune these cell cycle events, frequently through processes that do not involve proteasomal degradation. Understanding how the increasing variety of identified ubiquitin signals are transduced will allow us to develop a deeper mechanistic perception of how the multiple factors come together to faithfully propagate genomic information. Here, we discuss these and additional conceptual challenges that are currently under study toward understanding how ubiquitin governs cell cycle regulation.

The AAA+ ATPase TRIP13 remodels HORMA domains through N-terminal engagement and unfolding

Proteins of the conserved HORMA domain family, including the spindle assembly checkpoint protein MAD2 and the meiotic HORMADs, assemble into signaling complexes by binding short peptides termed "closure motifs". The AAA+ ATPase TRIP13 regulates both MAD2 and meiotic HORMADs by disassembling these HORMA domain-closure motif complexes, but its mechanisms of substrate recognition and remodeling are unknown. Here, we combine X-ray crystallography and crosslinking mass spectrometry to outline how TRIP13 recognizes MAD2 with the help of the adapter protein p31^comet We show that p31^comet binding to the TRIP13 N-terminal domain positions the disordered MAD2 N-terminus for engagement by the TRIP13 "pore loops", which then unfold MAD2 in the presence of ATP N-terminal truncation of MAD2 renders it refractory to TRIP13 action in vitro, and in cells causes spindle assembly checkpoint defects consistent with loss of TRIP13 function. Similar truncation of HORMAD1 in mouse spermatocytes compromises its TRIP13-mediated removal from meiotic chromosomes, highlighting a conserved mechanism for recognition and disassembly of HORMA domain-closure motif complexes by TRIP13.

Ubiquitin in Cell-Cycle Regulation and Dysregulation in Cancer

Uncontrolled cell proliferation and genomic instability are common features of cancer and can arise from, respectively, the loss of cell-cycle control and defective checkpoints. Ubiquitin-mediated proteolysis, ultimately executed by ubiquitin-ligating enzymes (E3s), plays a key part in cell-cycle regulation and is dominated by two multisubunit E3s, the anaphase-promoting complex (or cyclosome) (APC/C) and SKP1–cullin-1–F-box (SCF) complex. We highlight the role of APC/C and the SCF bound to F-box proteins, FBXW7, SKP2, and β-TrCP, in regulating the abundance of select fundamental proteins, primarily during the cell cycle, that are associated with human cancer. The clinical success of the first proteasome inhibitor, bortezomib, in treating multiple myeloma and mantle-cell lymphoma set the precedent for viewing the ubiquitin–proteasome system as a druggable target for cancer. Given that there are more E3s than kinases, selective, small-molecule E3 inhibitors have the potential of opening up another dimension in the therapeutic armamentarium for the treatment of cancer.

TRIP13-deficient tubular epithelial cells are susceptible to apoptosis following acute kidney injury

Damage to renal tubular epithelial cells by genetic, environmental, or biological insults can initiate complex signaling mechanisms that promote kidney repair and functional recovery. In this study, we demonstrated that thyroid receptor interacting protein 13 (TRIP13) is a critical modulator of tubular epithelial cell repair following ischemia‐reperfusion injury (IRI), a common type of renal stressor. In Trip13^Gt/Gthypomorph mice treated with unilateral renal IRI, persistent tubular epithelial cell damage was determined in the IRI-treated kidney throughout the 168 hours of experimental period compared to the contralateral kidneys. The damaged epithelial cells were associated with increased levels of DNA damage (ɣH2AX) and apoptotic markers (p53, cleaved caspase-7, and TUNEL-positive cells). Correspondingly, TRIP13 was found to directly interact with Tetratricopeptide Repeat Domain 5 (TTC5), a p53 co‐factor, and genetic knockdown of TRIP13 in murine inner medullary collecting duct cells in the presence of hydrogen peroxide showed increased activity of p53 at Serine 15. In all, these studies suggest that insufficient TRIP13 increased the susceptibility of damaged tubular epithelial cells to progress towards apoptotic cell death.

Role of CCT chaperonin in the disassembly of mitotic checkpoint complexes

The mitotic checkpoint system prevents premature separation of sister chromatids in mitosis and thus ensures the fidelity of chromosome segregation. When this checkpoint is active, a mitotic checkpoint complex (MCC), composed of the checkpoint proteins Mad2, BubR1, Bub3, and Cdc20, is assembled. MCC inhibits the ubiquitin ligase anaphase promoting complex/cyclosome (APC/C), whose action is necessary for anaphase initiation. When the checkpoint signal is turned off, MCC is disassembled, a process required for exit from checkpoint-arrested state. Different moieties of MCC are disassembled by different ATP-requiring processes. Previous work showed that Mad2 is released from MCC by the joint action of the TRIP13 AAA-ATPase and the Mad2-binding protein p31^comet Now we have isolated from extracts of HeLa cells an ATP-dependent factor that releases Cdc20 from MCC and identified it as chaperonin containing TCP1 or TCP1-Ring complex (CCT/TRiC chaperonin), a complex known to function in protein folding. Bacterially expressed CCT5 chaperonin subunits, which form biologically active homooligomers [Sergeeva, et al. (2013) J Biol Chem 288(24):17734-17744], also promote the disassembly of MCC. CCT chaperonin further binds and disassembles subcomplexes of MCC that lack Mad2. Thus, the combined action of CCT chaperonin with that of TRIP13 ATPase promotes the complete disassembly of MCC, necessary for the inactivation of the mitotic checkpoint.

Molecular Mechanisms of Spindle Assembly Checkpoint Activation and Silencing

In eukaryotic cell division, the Spindle Assembly Checkpoint (SAC) plays a key regulatory role by monitoring the status of chromosome-microtubule attachments and allowing chromosome segregation only after all chromosomes are properly attached to spindle microtubules. While the identities of SAC components have been known, in some cases, for over two decades, the molecular mechanisms of the SAC have remained mostly mysterious until very recently. In the past few years, advances in biochemical reconstitution, structural biology, and bioinformatics have fueled an explosion in the molecular understanding of the SAC. This chapter seeks to synthesize these recent advances and place them in a biological context, in order to explain the mechanisms of SAC activation and silencing at a molecular level.

DNA repair in ischemic acute kidney injury

Ischemia-reperfusion injury (IRI) is a common cause of acute kidney injury leading to an induction of oxidative stress, cellular dysfunction, and loss of renal function. DNA damage, including oxidative base modifications and physical DNA strand breaks, is a consequence of renal IRI. Like many other organs in the body, a redundant and highly conserved set of endogenous repair pathways have evolved to selectively recognize the various types of cellular DNA damage and combat its negative effects on cell viability. Severe damage to the DNA, however, can trigger cell death and elimination of the injured tubular epithelial cells. In this minireview, we summarize the state of the current field of DNA damage and repair in the kidney and provide some expected and, in some cases, unexpected effects of IRI on DNA damage and repair in the kidney. These findings may be applicable to other forms of acute kidney injury and could provide new opportunities for renal research.

A Cell Biological Perspective on Past, Present and Future Investigations of the Spindle Assembly Checkpoint

The spindle assembly checkpoint (SAC) is a quality control mechanism that ensures accurate chromosome segregation during cell division. It consists of a mechanochemical signal transduction mechanism that senses the attachment of chromosomes to the spindle, and a signaling cascade that inhibits cell division if one or more chromosomes are not attached. Extensive investigations of both these component systems of the SAC have synthesized a comprehensive understanding of the underlying molecular mechanisms. This review recounts the milestone results that elucidated the SAC, compiles a simple model of the complex molecular machinery underlying the SAC, and highlights poorly understood facets of the biochemical design and cell biological operation of the SAC that will drive research forward in the near future.

Synergistic inhibition of the APC/C by the removal of APC15 in HCT116 cells lacking UBE2C

The spindle assembly checkpoint (SAC) inhibits the anaphase-promoting complex/cyclosome (APC/C) in response to unattached kinetochores by generating a diffusible inhibitor termed the mitotic checkpoint complex (MCC). At metaphase, rapid activation of the APC/C requires removal of the MCC, a process that has been shown to depend on the APC/C E2 enzymes, UBE2C and UBE2S. Here we investigate the in vivo role of the APC/C E2 enzymes in SAC silencing using CRISPR/Cas9 genetically engineered HCT116 UBE2C or UBE2S null cell lines. Using live cell assays, we show that UBE2C and UBE2S make a minor contribution to SAC silencing in HCT116 cells. Strikingly, in cells specifically lacking UBE2C, we observe a strong synergistic inhibition of mitotic progression when we stabilize the MCC on the APC/C by depleting APC15, potentially reflecting increased competition between the MCC and the remaining initiating E2 enzyme UBE2D. In conclusion, we provide in vivo insight into the APC/C E2 module and its interplay with SAC silencing components.

P31comet, a member of the synaptonemal complex, participates in meiotic DSB formation in rice

The human mitotic arrest-deficient 2 (Mad2) binding protein p31(comet) participates in the spindle checkpoint and coordinates cell cycle events in mitosis although its function in meiosis remains unknown in all organisms. Here, we reveal P31(comet) as a synaptonemal complex (SC) protein in rice (Oryza sativa L.). In p31(comet), homologous pairing and synapsis are eliminated, leading to the homologous nondisjunction and complete sterility. The failure in loading of histone H2AX phosphorylation (γH2AX) in p31(comet), together with the suppressed chromosome fragmentation in rice completion of meiotic recombination 1 (com1) p31(comet) and radiation sensitive 51c (rad51c) p31(comet) double mutants, indicates that P31(comet) plays an essential role in double-strand break (DSB) formation. Interestingly, the dynamic colocalization pattern between P31(comet) and ZEP1 (a transverse filament protein of SC) by immunostaining, as well as the interaction between P31(comet) and CENTRAL REGION COMPONENT 1 (CRC1) in yeast two-hybrid assays, suggests possible involvement of P31(comet) in SC installation. Together, these data indicate that P31(comet) plays a key role in DSB formation and SC installation, mainly through its cooperation with CRC1.

Intermediates in the assembly of mitotic checkpoint complexes and their role in the regulation of the anaphase-promoting complex

The mitotic (or spindle assembly) checkpoint system prevents premature separation of sister chromatids in mitosis and thus ensures the fidelity of chromosome segregation. Kinetochores that are not attached properly to the mitotic spindle produce an inhibitory signal that prevents progression into anaphase. The checkpoint system acts on the Anaphase-Promoting Complex/Cyclosome (APC/C) ubiquitin ligase, which targets for degradation inhibitors of anaphase initiation. APC/C is inhibited by the Mitotic Checkpoint Complex (MCC), which assembles when the checkpoint is activated. MCC is composed of the checkpoint proteins BubR1, Bub3, and Mad2, associated with the APC/C coactivator Cdc20. The intermediary processes in the assembly of MCC are not sufficiently understood. It is also not clear whether or not some subcomplexes of MCC inhibit the APC/C and whether Mad2 is required only for MCC assembly and not for its action on the APC/C. We used purified subcomplexes of mitotic checkpoint proteins to examine these problems. Our results do not support a model in which Mad2 catalytically generates a Mad2-free APC/C inhibitor. We also found that the release of Mad2 from MCC caused a marked (although not complete) decrease in inhibitory action, suggesting a role of Mad2 in MCC for APC/C inhibition. A previously unknown species of MCC, which consists of Mad2, BubR1, and two molecules of Cdc20, contributes to the inhibition of APC/C by the mitotic checkpoint system.

The spindle assembly checkpoint: More than just keeping track of the spindle

Genome stability is essential for cell proliferation and survival. Consequently, genome integrity is monitored by two major checkpoints, the DNA damage response (DDR) and the spindle assembly checkpoint (SAC). The DDR monitors DNA lesions in G1, S, and G2 stages of the cell cycle and the SAC ensures proper chromosome segregation in M phase. There have been extensive studies characterizing the roles of these checkpoints in response to the processes for which they are named; however, emerging evidence suggests significant crosstalk between the checkpoints. Here we review recent findings demonstrating overlapping roles for the SAC and DDR in metaphase, and in response to DNA damage throughout the cell cycle.