Borealin dimerization mediates optimal CPC checkpoint function by enhancing localization to centromeres and kinetochores

Organization of the chromosomal passenger complex clusters at inner centromeres in mitosis

Stable transmission of the genome during cell division is crucial for all life forms and is universally achieved by Aurora B-mediated error correction of the kinetochore-microtubule attachments. Aurora B is the enzymatic subunit of the tetrameric protein complex called the chromosomal passenger complex (CPC), and its centromeric enrichment is required for Aurora B to ensure accurate chromosome segregation. How cells enrich the CPC at centromeres is therefore an outstanding question to be elucidated. We review our recent understanding of how CPCs are assembled at inner centromeres in mitosis, the mechanism depending on mitotic histone phosphorylations and beyond.

The landscape in telomere related gene prognostic signature for survival and medication treatment effectiveness prediction in hepatocellular carcinoma

OBJECTIVE

Telomeres, made of repetitive DNA sequences and shelterin complexes, which were found at the ends of chromosomes and had been extensively studied in cancer research. However, in hepatocellular carcinoma (HCC) was still relatively scarce. In this study, we investigated the correlation between telomerase-related genes (TRGs) and the prognosis and immunotherapy of HCC patients to enhance clinical outcomes.

METHODS

In this work, TRGs were gathered using TelNet, while clinical information and gene expression data for HCC patients were retrieved from the Cancer Genome Atlas (TCGA) database. A risk prediction model based on TRGs was created using COX and Lasso regression analyses, with ROC curves used to assess prognostic efficacy. Univariate and multifactorial COX regression analyses were used to determine if the risk model had an independent impact on prognosis. Nomograms were created to enhance clinical usability, and calibration curves were used to assess predictive ability at various time points. The Tumor Immune Dysfunction and Exclusion (TIDE) score was used to analyze differences in immune infiltrating cells between risk groups. The study analyzed the relationship between risk ratings and drug treatment effectiveness using data from the CellMiner database. The hub gene was identified and its relationship to prognostic markers of HCC patients was examined. The expression of hub genes in immune cell subpopulations was also investigated by single-cell data.

RESULTS

2093 TRGs were identified, with 949 showing significant differences in expression between HCC and paracancerous tissues. Seven risk genes were overexpressed in tumor tissues, leading to lower survival rates in high-risk patients. Risk model could independently predict the prognosis of HCC patients. Analysis of tumor immune infiltrating cells revealed significant differences in cell abundance between risk groups, with notable variations in immune subset enrichment between subgroups. Higher risk scores correlated with increased sensitivity to sorafenib, mitoxantrone, oxaliplatin, gemcitabine, and entinostat, while sensitivity decreased for vincristine, etc. CDCA8 was identified as a key gene in the Protein Interaction Network, while high expression associated with poorer overall survival, tumor proliferation and metastasis. The results of single-cell data analysis suggest that CDCA8 may promote the development of HCC by affecting T lymphocytes.

CONCLUSION

The TRG-based risk model could predict HCC patient prognosis and closely linked to tumor immune environment, which could offer new possibilities for clinical treatment.

Cyclin A/Cdk1 promotes chromosome alignment and timely mitotic progression

To ensure genomic fidelity, a series of spatially and temporally coordinated events is executed during prometaphase of mitosis, including bipolar spindle formation, chromosome attachment to spindle microtubules at kinetochores, the correction of erroneous kinetochore-microtubule (k-MT) attachments, and chromosome congression to the spindle equator. Cyclin A/Cdk1 kinase plays a key role in destabilizing k-MT attachments during prometaphase to promote correction of erroneous k-MT attachments. However, it is unknown whether Cyclin A/Cdk1 kinase regulates other events during prometaphase. Here, we investigate additional roles of Cyclin A/Cdk1 in prometaphase by using an siRNA knockdown strategy to deplete endogenous Cyclin A from human cells. We find that depleting Cyclin A significantly extends mitotic duration, specifically prometaphase, because chromosome alignment is delayed. Unaligned chromosomes display erroneous monotelic, syntelic, or lateral k-MT attachments suggesting that bioriented k-MT attachment formation is delayed in the absence of Cyclin A. Mechanistically, chromosome alignment is likely impaired because the localization of the kinetochore proteins BUB1 kinase, KNL1, and MPS1 kinase are reduced in Cyclin A-depleted cells. Moreover, we find that Cyclin A promotes BUB1 kinetochore localization independently of its role in destabilizing k-MT attachments. Thus, Cyclin A/Cdk1 facilitates chromosome alignment during prometaphase to support timely mitotic progression.

Role of cell division cycle-associated proteins in regulating cell cycle and promoting tumor progression

The cell division cycle-associated protein (CDCA) family is important in regulating cell division. High CDCA expression is significantly linked to tumor development. This review summarizes clinical and basic studies on CDCAs conducted in recent decades. Furthermore, it systematically introduces the molecular expression and function, key mechanisms, cell cycle regulation, and roles of CDCAs in tumor development, cell proliferation, drug resistance, invasion, and metastasis. Additionally, it presents the latest research on tumor diagnosis, prognosis, and treatment targeting CDCAs. These findings are pivotal for further in-depth studies on the role of CDCAs in promoting tumor development and provide theoretical support for their application as new anti-tumor targets.

Advancing Cancer Therapy: The Role of KIF20A as a Target for Inhibitor Development and Immunotherapy

The analysis begins with a detailed examination of the gene expression and protein structure of KIF20A, highlighting its interaction with critical cellular components that influence key processes such as Golgi membrane transport and mitotic spindle assembly. The primary focus is on the development of specific KIF20A inhibitors, detailing their roles and the challenges encountered in enhancing their efficacy, such as achieving specificity, overcoming tumor resistance, and optimizing delivery systems. Additionally, it delves into the prognostic value of KIF20A across multiple cancer types, emphasizing its role as a novel tumor-associated antigen, which lays the groundwork for the development of targeted peptide vaccines. The therapeutic efficacy of these vaccines as demonstrated in recent clinical trials is discussed. Future directions are proposed, including the integration of precision medicine strategies to personalize treatments and the use of combination therapies to improve outcomes. By concentrating on the significant potential of KIF20A as both a direct target for inhibitors and an antigen in cancer vaccines, this review sets a foundation for future research aimed at harnessing KIF20A for effective cancer treatment.

A validation strategy to assess the role of phase separation as a determinant of macromolecular localization

Liquid-liquid phase separation (LLPS) of putative assembly scaffolds has been proposed to drive the biogenesis of membraneless compartments. LLPS scaffolds are usually identified through in vitro LLPS assays with single macromolecules (homotypic), but the predictive value of these assays remains poorly characterized. Here, we apply a strategy to evaluate the robustness of homotypic LLPS assays. When applied to the chromosomal passenger complex (CPC), which undergoes LLPS in vitro and localizes to centromeres to promote chromosome biorientation, LLPS propensity in vitro emerged as an unreliable predictor of subcellular localization. In vitro CPC LLPS in aqueous buffers was enhanced by commonly used crowding agents. Conversely, diluted cytomimetic media dissolved condensates of the CPC and of several other proteins. We also show that centromeres do not seem to nucleate LLPS, nor do they promote local, spatially restrained LLPS of the CPC. Our strategy can be adapted to purported LLPS scaffolds of other membraneless compartments.

Cyclin A/Cdk1 promotes chromosome alignment and timely mitotic progression

To ensure genomic fidelity a series of spatially and temporally coordinated events are executed during prometaphase of mitosis, including bipolar spindle formation, chromosome attachment to spindle microtubules at kinetochores, the correction of erroneous kinetochore-microtubule (k-MT) attachments, and chromosome congression to the spindle equator. Cyclin A/Cdk1 kinase plays a key role in destabilizing k-MT attachments during prometaphase to promote correction of erroneous k-MT attachments. However, it is unknown if Cyclin A/Cdk1 kinase regulates other events during prometaphase. Here, we investigate additional roles of Cyclin A/Cdk1 in prometaphase by using an siRNA knockdown strategy to deplete endogenous Cyclin A from human cells. We find that depleting Cyclin A significantly extends mitotic duration, specifically prometaphase, because chromosome alignment is delayed. Unaligned chromosomes display erroneous monotelic, syntelic, or lateral k-MT attachments suggesting that bioriented k-MT attachment formation is delayed in the absence of Cyclin A. Mechanistically, chromosome alignment is likely impaired because the localization of the kinetochore proteins BUB1 kinase, KNL1, and MPS1 kinase are reduced in Cyclin A-depleted cells. Moreover, we find that Cyclin A promotes BUB1 kinetochore localization independently of its role in destabilizing k-MT attachments. Thus, Cyclin A/Cdk1 facilitates chromosome alignment during prometaphase to support timely mitotic progression.

Chromosome biorientation requires Aurora B's spatial separation from its outer kinetochore substrates, but not its turnover at kinetochores

For correct chromosome segregation in mitosis, sister kinetochores must interact with microtubules from opposite spindle poles (biorientation). For this, aberrant kinetochore-microtubule interaction must be resolved (error correction) by Aurora B kinase. Once biorientation is formed, tension is applied on kinetochore-microtubule interaction, stabilizing this interaction. The mechanism for this tension-dependent process has been debated. Here, we study how Aurora B localizations at different kinetochore sites affect the biorientation establishment and maintenance in budding yeast. Without the physiological Aurora B-INCENP recruitment mechanisms, engineered recruitment of Aurora B-INCENP to the inner kinetochore, but not to the outer kinetochore, prior to biorientation supports the subsequent biorientation establishment. Moreover, when the physiological Aurora B-INCENP recruitment mechanisms are present, an engineered Aurora B-INCENP recruitment to the outer kinetochore, but not to the inner kinetochore, during metaphase (after biorientation establishment) disrupts biorientation, which is dependent on the Aurora B kinase activity. These results suggest that the spatial separation of Aurora B from its outer kinetochore substrates is required to stabilize kinetochore-microtubule interaction when biorientation is formed and tension is applied on this interaction. Meanwhile, Aurora B exhibits dynamic turnover on the centromere/kinetochore during early mitosis, a process thought to be crucial for error correction and biorientation. However, using the engineered Aurora B-INCENP recruitment to the inner kinetochore, we demonstrate that, even without such a turnover, Aurora B-INCENP can efficiently support biorientation. Our study provides important insights into how Aurora B promotes error correction for biorientation in a tension-dependent manner.

Non-canonical MLL1 activity regulates centromeric phase separation and genome stability

Epigenetic dysregulation is a prominent feature in cancer, as exemplified by frequent mutations in chromatin regulators, including the MLL/KMT2 family of histone methyltransferases. Although MLL1/KMT2A activity on H3K4 methylation is well documented, their non-canonical activities remain mostly unexplored. Here we show that MLL1/KMT2A methylates Borealin K143 in the intrinsically disordered region essential for liquid-liquid phase separation of the chromosome passenger complex (CPC). The co-crystal structure highlights the distinct binding mode of the MLL1 SET domain with Borealin K143. Inhibiting MLL1 activity or mutating Borealin K143 to arginine perturbs CPC phase separation, reduces Aurora kinase B activity, and impairs the resolution of erroneous kinetochore-microtubule attachments and sister-chromatid cohesion. They significantly increase chromosome instability and aneuploidy in a subset of hepatocellular carcinoma, resulting in growth inhibition. These results demonstrate a non-redundant function of MLL1 in regulating inner centromere liquid condensates and genome stability via a non-canonical enzymatic activity.

CDCA8 promotes bladder cancer survival by stabilizing HIF1α expression under hypoxia

Hypoxia is an essential hallmark of solid tumors and HIF1α is a central regulator of tumor cell adaptation and survival in the hypoxic environment. In this study, we explored the biological functions of cell cycle division-related gene 8 (CDCA8) in bladder cancer (BCa) cells in the hypoxic settings. Specifically, we found that CDCA8 was significantly upregulated in BCa cell lines and clinical samples and its expression was positively correlated with advanced BCa stage, grade, and poor overall survival (OS). The expression of CDCA8 proteins was required for BCa cells to survive in the hypoxic condition. Mechanistically, CDCA8 stabilizes HIF1α by competing with PTEN for AKT binding, consequently leading to PTEN displacement and activation of the AKT/GSK3β signaling cascade that stimulates HIF1α protein stability. Significantly, HIF1α proteins bind to CDCA8 promoter for transcriptional activation, forming a positive-feedback loop to sustain BCa tumor cells under oxygen-deficient environment. Together, we defined CDCA8 as a key regulator for BCa cells to sense and prevail oxygen deprivation and as a novel BCa therapeutic target.

Mechanistic basis for Sgo1-mediated centromere localization and function of the CPC

Centromere association of the chromosomal passenger complex (CPC; Borealin-Survivin-INCENP-Aurora B) and Sgo1 is crucial for chromosome biorientation, a process essential for error-free chromosome segregation. Phosphorylated histone H3 Thr3 (H3T3ph; directly recognized by Survivin) and histone H2A Thr120 (H2AT120ph; indirectly recognized via Sgo1), together with CPC’s intrinsic nucleosome-binding ability, facilitate CPC centromere recruitment. However, the molecular basis for CPC–Sgo1 binding and how their physical interaction influences CPC centromere localization are lacking. Here, using an integrative structure-function approach, we show that the “histone H3-like” Sgo1 N-terminal tail-Survivin BIR domain interaction acts as a hotspot essential for CPC–Sgo1 assembly, while downstream Sgo1 residues and Borealin contribute for high-affinity binding. Disrupting Sgo1–Survivin interaction abolished CPC–Sgo1 assembly and perturbed CPC centromere localization and function. Our findings reveal that Sgo1 and H3T3ph use the same surface on Survivin to bind CPC. Hence, it is likely that these interactions take place in a spatiotemporally restricted manner, providing a rationale for the Sgo1-mediated “kinetochore-proximal” CPC centromere pool.

Synthetic Antibodies Detect Distinct Cellular States of Chromosome Passenger Complex Proteins

High performance affinity reagents are essential tools to enable biologists to profile the cellular location and composition of macromolecular complexes undergoing dynamic reorganization. To support further development of such tools, we have assembled a high-throughput phage display pipeline to generate Fab-based affinity reagents that target different dynamic forms of a large macromolecular complex, using the Chromosomal Passenger Complex (CPC), as an example. The CPC is critical for the maintenance of chromosomal and cytoskeleton processes during cell division. The complex contains 4 protein components: Aurora B kinase, survivin, borealin and INCENP. The CPC acts as a node to dynamically organize other partnering subcomplexes to build multiple functional structures during mitotic progression. Using phage display mutagenesis, a cohort of synthetic antibodies (sABs) were generated against different domains of survivin, borealin and INCENP. Immunofluorescence established that a set of these sABs can discriminate between the form of the CPC complex in the midbody versus the spindle. Others localize to targets, which appear to be less organized, in the nucleus or cytoplasm. This differentiation suggests that different CPC epitopes have dynamic accessibility depending upon the mitotic state of the cell. An Immunoprecipitation/Mass Spectrometry analysis was performed using sABs that bound specifically to the CPC in either the midbody or MT spindle macromolecular assemblies. Thus, sABs can be exploited as high performance reagents to profile the accessibility of different components of the CPC within macromolecular assemblies during different stages of mitosis suggesting this high throughput approach will be applicable to other complex macromolecular systems.

Genetic analysis of C. elegans Haspin-like genes shows that hasp-1 plays multiple roles in the germline

Haspin is a histone kinase that promotes error-free chromosome segregation by recruiting the Chromosomal Passenger Complex (CPC) to mitotic and meiotic chromosomes. Haspin remains less well studied than other M-phase kinases and the models explaining Haspin function have been developed primarily in mitotic cells. Here, we generate strains containing new conditional or nonsense mutations in the C. elegans Haspin homologs hasp-1 and hasp-2 and characterize their phenotypes. We show that hasp-1 is responsible for all predicted functions of Haspin and that loss of function of hasp-1 using classical and conditional alleles produces defects in germline stem cell proliferation, spermatogenesis, and confirms its role in oocyte meiosis. Genetic analysis suggests hasp-1 acts downstream of the Polo-like kinase plk-2 and shows synthetic interactions between hasp-1 and two genes expected to promote recruitment of the CPC by a parallel pathway that depends on the kinase Bub1. This work adds to the growing understanding of Haspin function by characterizing a variety of roles in an intact animal.

The phospho-docking protein 14-3-3 regulates microtubule-associated proteins in oocytes including the chromosomal passenger Borealin

Global regulation of spindle-associated proteins is crucial in oocytes due to the absence of centrosomes and their very large cytoplasmic volume, but little is known about how this is achieved beyond involvement of the Ran-importin pathway. We previously uncovered a novel regulatory mechanism in Drosophila oocytes, in which the phospho-docking protein 14-3-3 suppresses microtubule binding of Kinesin-14/Ncd away from chromosomes. Here we report systematic identification of microtubule-associated proteins regulated by 14-3-3 from Drosophila oocytes. Proteins from ovary extract were co-sedimented with microtubules in the presence or absence of a 14-3-3 inhibitor. Through quantitative mass-spectrometry, we identified proteins or complexes whose ability to bind microtubules is suppressed by 14-3-3, including the chromosomal passenger complex (CPC), the centralspindlin complex and Kinesin-14/Ncd. We showed that 14-3-3 binds to the disordered region of Borealin, and this binding is regulated differentially by two phosphorylations on Borealin. Mutations at these two phospho-sites compromised normal Borealin localisation and centromere bi-orientation in oocytes, showing that phospho-regulation of 14-3-3 binding is important for Borealin localisation and function.

Expression profiles of cdca9 related to ovarian development in loach (Misgurnus anguillicaudatus)

The function of borealin proteins has been widely reported in the cell division of animals. Nonetheless, there is little research about their only known paralogue (cell division cycle associated 9, cdca9). In this study, cdca9 was investigated in loach (Misgurnus anguillicaudatus) for the first time. cdca9 was highly expressed in the embryo before the gastrula stage, and it was predominantly expressed in the ovary, especially in the oocytes of stage II. In conclusion, this study reveals a potential function of cdca9 in the early embryogenesis and ovarian development of fish.

C9ORF78 partially localizes to centromeres and plays a role in chromosome segregation

C9ORF78 is a poorly characterized protein found in diverse eukaryotes. Previous work indicated overexpression of C9ORF78 in malignant tissues indicating a possible involvement in growth regulatory pathways. Additional studies in fission yeast and humans uncover a potential function in regulating the spliceosome. In studies of GFP-tagged C9ORF78 we observed a dramatic reduction in protein abundance in cells grown to confluence and/or deprived of serum growth factors. Serum stimulation induced synchronous re-expression of the protein in HeLa cells. This effect was also observed with the endogenous protein. Overexpressing either E2F1 or N-Myc resulted in elevated C9ORF78 expression potentially explaining the serum-dependent upregulation of the protein. Immunofluorescence analysis indicates that C9ORF78 localizes to nuclei in interphase but does not appear to concentrate in speckles as would be expected for a splicing protein. Surprisingly, a subpopulation of C9ORF78 co-localizes with ACA, Mad1 and Ndc80 in mitotic cells suggesting that this protein associates with kinetochores or centromeres. Levels of C9ORF78 at the centromere/kinetochore also increased upon activation of the mitotic checkpoint. Furthermore, knocking-down C9ORF78 caused mitotic defects. These studies uncover novel mitotic function and subcellular localization of C9ORF78.

The mutation screening in candidate genes related to thyroid dysgenesis by targeted next-generation sequencing panel in the Chinese congenital hypothyroidism

OBJECTIVE

Congenital hypothyroidism (CH) is known to be due to thyroid dyshormonogenesis (DH), which is mostly inherited in an autosomal recessive inheritance pattern or thyroid dysgenesis (TD), whose inheritance pattern is controversial and whose molecular etiology remains poorly understood.

DESIGN AND METHODS

The variants in 37 candidate genes of CH, including 25 genes related to TD, were screened by targeted exon sequencing in 205 Chinese patients whose CH cannot be explained by biallelic variants in genes related to DH. The inheritance pattern of the genes was analyzed in family trios or quartets.

RESULTS

Of the 205 patients, 83 patients carried at least one variant in 19 genes related to TD, and 59 of those 83 patients harbored more than two variants in distinct candidate genes for CH. Biallelic or de novo variants in the genes related to TD in Chinese patients are rare. We also found nine probands carried only one heterozygous variant in the genes related to TD that were inherited from a euthyroid either paternal or maternal parent. These findings did not support the monogenic inheritance pattern of the genes related to TD in CH patients. Notably, in family trio or quartet analysis, of 36 patients carrying more than two variants in distinct genes, 24 patients carried these variants inherited from both their parents, which indicated that the oligogenic inheritance pattern of the genes related to TD should be considered in CH.

CONCLUSIONS

Our study expanded the variant spectrum of the genes related to TD in Chinese CH patients. It is rare that CH in Chinese patients could be explained by monogenic germline variants in genes related to TD. The hypothesis of an oligogenic origin of the CH should be considered.

Borealin Promotes Tumor Growth and Metastasis by Activating the Wnt/β-Catenin Signaling Pathway in Hepatocellular Carcinoma

Background and Aims

Hepatocellular carcinoma (HCC) is a common malignant disease with high morbidity and mortality throughout the world. While Borealin is a putative oncogene that is dysregulated in multiple tumors, its exact role in HCC remains less investigated.

Methods

Quantitative reverse transcription polymerase chain reaction (qRT-PCR) and immunohistochemistry (IHC) assays were employed to examine the relative amount of Borealin. Gene set enrichment analysis (GSEA) and other bioinformatic analyses were implemented to probe into the potential functions of Borealin. The biological roles and mechanisms of Borealin in the tumorigenesis and development of HCC were further evaluated using a battery of functional assays in vivo and in vitro.

Results

Borealin was enhanced in the HCC tissue samples and hepatoma cells when compared with the nontumor tissues and normal liver cells. Higher Borealin expression was positively linked with advanced pathological phenotypes and inferior overall survival. The overexpression of Borealin promoted the cells' abilities on proliferation, invasion and epithelial-mesenchymal transition (EMT) in vitro, facilitated tumor growth and lung metastasis in vivo, whereas the silencing of Borealin inhibited these capabilities in vitro. Furthermore, Borealin interacted with β-catenin and further activated the Wnt/β-catenin signaling pathway, which endowed HCC cells with highly aggressive and metastatic capabilities.

Conclusion

Borealin was identified as an oncogene that could promote HCC growth and metastasis by activating the WNT/β-catenin signaling pathway. These findings extended the understanding of Borealin in HCC tumorigenesis and development and highlighted the significance of Borealin in HCC diagnosis and treatment.

Distinct roles of haspin in stem cell division and male gametogenesis

The kinase haspin phosphorylates histone H3 at threonine-3 (H3T3ph) during mitosis. H3T3ph provides a docking site for the Chromosomal Passenger Complex at the centromere, enabling correction of erratic microtubule-chromosome contacts. Although this mechanism is operational in all dividing cells, haspin-null mice do not exhibit developmental anomalies, apart from aberrant testis architecture. Investigating this problem, we show here that mouse embryonic stem cells that lack or overexpress haspin, albeit prone to chromosome misalignment during metaphase, can still divide, expand and differentiate. RNA sequencing reveals that haspin dosage affects severely the expression levels of several genes that are involved in male gametogenesis. Consistent with a role in testis-specific expression, H3T3ph is detected not only in mitotic spermatogonia and meiotic spermatocytes, but also in non-dividing cells, such as haploid spermatids. Similarly to somatic cells, the mark is erased in the end of meiotic divisions, but re-installed during spermatid maturation, subsequent to methylation of histone H3 at lysine-4 (H3K4me₃) and arginine-8 (H3R8me₂). These serial modifications are particularly enriched in chromatin domains containing histone H3 trimethylated at lysine-27 (H3K27me₃), but devoid of histone H3 trimethylated at lysine-9 (H3K9me₃). The unique spatio-temporal pattern of histone H3 modifications implicates haspin in the epigenetic control of spermiogenesis.

A degron-based strategy reveals new insights into Aurora B function in C. elegans

The widely conserved kinase Aurora B regulates important events during cell division. Surprisingly, recent work has uncovered a few functions of Aurora-family kinases that do not require kinase activity. Thus, understanding this important class of cell cycle regulators will require strategies to distinguish kinase-dependent from independent functions. Here, we address this need in C. elegans by combining germline-specific, auxin-induced Aurora B (AIR-2) degradation with the transgenic expression of kinase-inactive AIR-2. Through this approach, we find that kinase activity is essential for AIR-2’s major meiotic functions and also for mitotic chromosome segregation. Moreover, our analysis revealed insight into the assembly of the ring complex (RC), a structure that is essential for chromosome congression in C. elegans oocytes. AIR-2 localizes to chromosomes and recruits other components to form the RC. However, we found that while kinase-dead AIR-2 could load onto chromosomes, other components were not recruited. This failure in RC assembly appeared to be due to a loss of RC SUMOylation, suggesting that there is crosstalk between SUMOylation and phosphorylation in building the RC and implicating AIR-2 in regulating the SUMO pathway in oocytes. Similar conditional depletion approaches may reveal new insights into other cell cycle regulators.

During cell division, chromosomes must be accurately partitioned to ensure the proper distribution of genetic material. In mitosis, chromosomes are duplicated once and then divided once, generating daughter cells with the same amount of genetic material as the original cell. Conversely, during meiosis chromosomes are duplicated once and divided twice, to cut the chromosome number in half to generate eggs and sperm. One important protein that is required for both mitotic and meiotic chromosome segregation is the kinase Aurora B, which phosphorylates a variety of other cell division proteins. However, previous research has shown that some kinases have functions that are independent of their ability to phosphorylate other proteins. Thus, fully understanding how Aurora B regulates cell division requires methods to test whether its various functions require kinase activity. We designed and implemented such a strategy in the model organism C. elegans, by depleting Aurora B from meiotically and mitotically-dividing cells, leaving in place a kinase-inactive version. This work has lent insight into how Aurora B regulates cell division in C. elegans, and also serves as a proof of principle for our approach, which can now be applied to study other essential cell division kinases.

The right place at the right time: Aurora B kinase localization to centromeres and kinetochores

The fidelity of chromosome segregation during mitosis is intimately linked to the function of kinetochores, which are large protein complexes assembled at sites of centromeric heterochromatin on mitotic chromosomes. These key "orchestrators" of mitosis physically connect chromosomes to spindle microtubules and transduce forces through these connections to congress chromosomes and silence the spindle assembly checkpoint. Kinetochore-microtubule attachments are highly regulated to ensure that incorrect attachments are not prematurely stabilized, but instead released and corrected. The kinase activity of the centromeric protein Aurora B is required for kinetochore-microtubule destabilization during mitosis, but how the kinase acts on outer kinetochore substrates to selectively destabilize immature and erroneous attachments remains debated. Here, we review recent literature that sheds light on how Aurora B kinase is recruited to both centromeres and kinetochores and discuss possible mechanisms for how kinase interactions with substrates at distinct regions of mitotic chromosomes are regulated.

A novel carbon-11 radiolabeled maternal embryonic leucine zipper kinase inhibitor for PET imaging of triple-negative breast cancer

Maternal embryonic leucine zipper kinase (MELK) plays an important role in the regulation of tumor cell growth. It is abundant in triple-negative breast cancers (TNBC), making it a promising target for molecular imaging and therapy. Based on the structure of a potent MELK inhibitor (OTSSP167) with high affinity, we developed a novel carbon-11 radiolabeled molecular probe ¹¹C-methoxy-OTSSP167, and evaluated its application in positron emission tomography (PET) imaging of TNBC. ¹¹C-methoxy-OTSSP167 was successfully synthesized and was identical to its non-radiolabeled compound methoxy-OTSSP167 in high-pressure liquid chromatography (HPLC) chromatogram. The obtained tracer had 10 ± 2% radiolabeling yield with a total synthesis time of 40 min. The radiochemical purity of the tracer was more than 95%. The maximum uptake (9.97 ± 0.70%) of ¹¹C-methoxy-OTSSP167 in MELK-overexpressing MDA-MB-231 cells was at 60 min in vitro. On PET, MDA-MB-231 tumors were clearly visible at 30, 60, and 90 min after injection of ¹¹C-methoxy-OTSSP167, while no obvious radioactivity accumulation was found in the low-MELK MCF-7 tumors. In vivo biodistribution data were consistent with the findings of the PET images. However, the radioactive tracer showed high uptake in normal organs such as liver and intestine, which may limit the application of the tracer. In addition, a markedly different MELK expression level in MDA-MBA-231 and MCF-7 tumors was verified via IHC staining. In conclusion, ¹¹C-methoxy-OTSSP167 was successfully developed and exhibited elevated uptake in MELK overexpressed tumor, indicating its potential for noninvasively imaging of MELK overexpressed TNBC.

Untangling the contribution of Haspin and Bub1 to Aurora B function during mitosis

Aurora B kinase is essential for faithful chromosome segregation during mitosis. During (pro)metaphase, Aurora B is concentrated at the inner centromere by the kinases Haspin and Bub1. However, how Haspin and Bub1 collaborate to control Aurora B activity at centromeres remains unclear. Here, we show that either Haspin or Bub1 activity is sufficient to recruit Aurora B to a distinct chromosomal locus. Moreover, we identified a small, Bub1 kinase–dependent Aurora B pool that supported faithful chromosome segregation in otherwise unchallenged cells. Joined inhibition of Haspin and Bub1 activities fully abolished Aurora B accumulation at centromeres. While this impaired the correction of erroneous KT–MT attachments, it did not compromise the mitotic checkpoint, nor the phosphorylation of the Aurora B kinetochore substrates Hec1, Dsn1, and Knl1. This suggests that Aurora B substrates at the kinetochore are not phosphorylated by centromere-localized pools of Aurora B, and calls for a reevaluation of the current spatial models for how tension affects Aurora B–dependent kinetochore phosphorylation.

Aurora B kinase is recruited to multiple discrete kinetochore and centromere regions in human cells

Aurora B kinase has a critical role in regulating attachments between kinetochores and spindle microtubules during mitosis. Early in mitosis, kinase activity at kinetochores is high to promote attachment turnover, and in later mitosis, activity decreases to ensure attachment stabilization. Aurora B localizes prominently to inner centromeres, and a population of the kinase is also detected at kinetochores. How Aurora B is recruited to and evicted from these regions to regulate kinetochore-microtubule attachments remains unclear. Here, we identified and investigated discrete populations of Aurora B at the centromere/kinetochore region. An inner centromere pool is recruited by Haspin phosphorylation of histone H3, and a kinetochore-proximal outer centromere pool is recruited by Bub1 phosphorylation of histone H2A. Finally, a third pool resides ~20 nm outside of the inner kinetochore protein CENP-C in early mitosis and does not require either the Bub1/pH2A/Sgo1 or Haspin/pH3 pathway for localization or activity. Our results suggest that distinct molecular pathways are responsible for Aurora B recruitment to centromeres and kinetochores.

APC/CCdh1 is required for the termination of chromosomal passenger complex activity upon mitotic exit

During mitosis, the chromosomal passenger complex (CPC) ensures the faithful transmission of the genome. The CPC is composed of the enzymatic component Aurora B (AURKB) and the three regulatory and targeting components borealin, INCENP, and survivin (also known as BIRC5). Although the CPC is known to be involved in diverse mitotic events, it is still unclear how CPC function terminates after mitosis. Here we show that borealin is ubiquitylated by the anaphase promoting complex/cyclosome (APC/C) and its cofactor Cdh1 (also known as FZR1) and is subsequently degraded in G1 phase. Cdh1 binds to regions within the N terminus of borealin that act as a non-canonical degron. Aurora B has also been shown previously to be degraded by the APC/C^Cdh1 from late mitosis to G1. Indeed, Cdh1 depletion sustains an Aurora B activity with stable levels of borealin and Aurora B throughout the cell cycle, and causes reduced efficiency of DNA replication after release from serum starvation. Notably, inhibition of Aurora B kinase activity improves the efficiency of DNA replication in Cdh1-depleted cells. We thus propose that APC/C^Cdh1 terminates CPC activity upon mitotic exit and thereby contributes to proper control of DNA replication.

Summary: APC/C^Cdh1 ubiquitylates both borealin, via a non-canonical degron motif, and Aurora B to terminate activity of the CPC in G1 phase. Disruption of this ubiquitylation reduces the efficiency of DNA replication.

Centromere-localized Aurora B kinase is required for the fidelity of chromosome segregation

Aurora B kinase plays an essential role in chromosome bi-orientation, which is a prerequisite for equal segregation of chromosomes during mitosis. However, it remains largely unclear whether centromere-localized Aurora B is required for faithful chromosome segregation. Here we show that histone H3 Thr-3 phosphorylation (H3pT3) and H2A Thr-120 phosphorylation (H2ApT120) can independently recruit Aurora B. Disrupting H3pT3-mediated localization of Aurora B at the inner centromere impedes the decline in H2ApT120 during metaphase and causes H2ApT120-dependent accumulation of Aurora B at the kinetochore-proximal centromere. Consequently, silencing of the spindle assembly checkpoint (SAC) is delayed, whereas the fidelity of chromosome segregation is negligibly affected. Further eliminating an H2ApT120-dependent pool of Aurora B restores proper timing for SAC silencing but increases chromosome missegregation. Our data indicate that H2ApT120-mediated localization of Aurora B compensates for the loss of an H3pT3-dependent pool of Aurora B to correct improper kinetochore-microtubule attachments. This study provides important insights into how centromeric Aurora B regulates SAC and kinetochore attachment to microtubules to ensure error-free chromosome segregation.

Establishing correct kinetochore-microtubule attachments in mitosis and meiosis

Faithful chromosome segregation in mitosis and meiosis requires that chromosomes properly attach to spindle microtubules. Initial kinetochore-microtubule attachments are often incorrect and rely on error correction mechanisms to release improper attachments, allowing the formation of new attachments. Aurora B kinase and, in mammalian germ cells, Aurora C kinase function as the enzymatic component of the Chromosomal Passenger Complex (CPC), which localizes to the inner centromere/kinetochore and phosphorylates kinetochore proteins for microtubule release during error correction. In this review, we discuss recent findings of the molecular pathways that regulate the chromosomal localization of Aurora B and C kinases in human cell lines, mice, fission yeast, and budding yeast. We also discuss differences in the importance of localization pathways between mitosis and meiosis.

Functional Analysis of the Plant Chromosomal Passenger Complex

The Aurora B kinase, encoded by the AURORA 3 (AUR3) gene in Arabidopsis (Arabidopsis thaliana), is a key regulator of cell division in all eukaryotes. Aurora B has at least two central functions during cell division; it is essential for the correct, i.e. balanced, segregation of chromosomes in mitosis and meiosis by controlling kinetochore function, and it acts at the division plane, where it is necessary to complete cytokinesis. To accomplish these two spatially distinct functions, Aurora B in animals is guided to its sites of action by Borealin, inner centromere protein (INCENP), and Survivin, which, together with Aurora B, form the chromosome passenger complex (CPC). However, besides Aurora homologs, only a candidate gene with restricted homology to INCENP has been described in Arabidopsis, raising the question of whether a full complement of the CPC exists in plants and how Aurora homologs are targeted subcellularly. Here, we have identified and functionally characterized a Borealin homolog, BOREALIN RELATED (BORR), in Arabidopsis. Together with detailed localization studies including the putative Arabidopsis INCENP homolog, these results support the existence of a CPC in plants.

Topoisomerase II SUMOylation activates a metaphase checkpoint via Haspin and Aurora B kinases

To prevent chromosome missegregation, a metaphase checkpoint is activated when topoisomerase II is catalytically inhibited and DNA catenations persist. Pandey et al. dissect the key molecular events triggering this regulatory system.

Topoisomerase II (Topo II) is essential for mitosis since it resolves sister chromatid catenations. Topo II dysfunction promotes aneuploidy and drives cancer. To protect from aneuploidy, cells possess mechanisms to delay anaphase onset when Topo II is perturbed, providing additional time for decatenation. Molecular insight into this checkpoint is lacking. Here we present evidence that catalytic inhibition of Topo II, which activates the checkpoint, leads to SUMOylation of the Topo II C-terminal domain (CTD). This modification triggers mobilization of Aurora B kinase from inner centromeres to kinetochore proximal centromeres and the core of chromosome arms. Aurora B recruitment accompanies histone H3 threonine-3 phosphorylation and requires Haspin kinase. Strikingly, activation of the checkpoint depends both on Haspin and Aurora B. Moreover, mutation of the conserved CTD SUMOylation sites perturbs Aurora B recruitment and checkpoint activation. The data indicate that SUMOylated Topo II recruits Aurora B to ectopic sites, constituting the molecular trigger of the metaphase checkpoint when Topo II is catalytically inhibited.

The Borealin dimerization domain interacts with Sgo1 to drive Aurora B-mediated spindle assembly

The chromosomal passenger complex (CPC), which includes the kinase Aurora B, is a master regulator of meiotic and mitotic processes that ensure the equal segregation of chromosomes. Sgo1 is thought to play a major role in the recruitment of the CPC to chromosomes, but the molecular mechanism and contribution of Sgo1-dependent CPC recruitment is currently unclear. Using Xenopus egg extracts and biochemical reconstitution, we found that Sgo1 interacts directly with the dimerization domain of the CPC subunit Borealin. Borealin and the PP2A phosphatase complex can bind simultaneously to the coiled-coil domain of Sgo1, suggesting that Sgo1 can integrate Aurora B and PP2A activities to modulate Aurora B substrate phosphorylation. A Borealin mutant that specifically disrupts the Sgo1–Borealin interaction results in defects in CPC chromosomal recruitment and Aurora B–dependent spindle assembly, but not in spindle assembly checkpoint signaling at unattached kinetochores. These findings establish a direct molecular connection between Sgo1 and the CPC and have major implications for the different functions of Aurora B, which promote the proper interaction between spindle microtubules and chromosomes.

Molecular basis of MKLP2-dependent Aurora B transport from chromatin to the anaphase central spindle

The Aurora B chromosomal passenger complex (CPC) is a conserved regulator of mitosis. Its functions require localization first to the chromosome arms and then centromeres in mitosis and subsequently the central spindle in anaphase. Here, we analyze the requirements for core CPC subunits, survivin and INCENP, and the mitotic kinesin-like protein 2 (MKLP2) in targeting to these distinct localizations. Centromere recruitment of the CPC requires interaction of survivin with histone H3 phosphorylated at threonine 3, and we provide a complete structure of this assembly. Furthermore, we show that the INCENP RRKKRR-motif is required for both centromeric localization of the CPC in metaphase and MKLP2-dependent transport in anaphase. MKLP2 and DNA bind competitively to this motif, and INCENP T59 phosphorylation acts as a switch preventing MKLP2 binding in metaphase. In anaphase, CPC binding promotes the microtubule-dependent ATPase activity of MKLP2. These results explain how centromere targeting of the CPC in mitosis is coupled to its movement to the central spindle in anaphase.

Haspin-dependent and independent effects of the kinase inhibitor 5-Iodotubercidin on self-renewal and differentiation

The kinase Haspin phosphorylates histone H3 at threonine-3 (H3T3ph), creating a docking site for the Chromosomal Passenger Complex (CPC). CPC plays a pivotal role in preventing chromosome misalignment. Here, we have examined the effects of 5-Iodotubercidin (5-ITu), a commonly used Haspin inhibitor, on self-renewal and differentiation of mouse embryonic stem cells (ESCs). Treatment with low concentrations of 5-ITu eliminates the H3T3ph mark during mitosis, but does not affect the mode or the outcome of self-renewal divisions. Interestingly, 5-ITu causes sustained accumulation of p53, increases markedly the expression of histone genes and results in reversible upregulation of the pluripotency factor Klf4. However, the properties of 5-ITu treated cells are distinct from those observed in Haspin-knockout cells generated by CRISPR/Cas9 genome editing, suggesting “off-target” effects. Continuous exposure to 5-ITu allows modest expansion of the ESC population and growth of embryoid bodies, but release from the drug after an initial treatment aborts embryoid body or teratoma formation. The data reveal an unusual robustness of ESCs against mitotic perturbants and suggest that the lack of H3T3ph and the “off-target” effects of 5-ITu can be partially compensated by changes in expression program or accumulation of suppressor mutations.

Enrichment of Aurora B kinase at the inner kinetochore controls outer kinetochore assembly

Outer kinetochore assembly enables chromosome attachment to microtubules and spindle assembly checkpoint (SAC) signaling in mitosis. Aurora B kinase controls kinetochore assembly by phosphorylating the Mis12 complex (Mis12C) subunit Dsn1. Current models propose Dsn1 phosphorylation relieves autoinhibition, allowing Mis12C binding to inner kinetochore component CENP-C. Using Xenopus laevis egg extracts and biochemical reconstitution, we found that autoinhibition of the Mis12C by Dsn1 impedes its phosphorylation by Aurora B. Our data indicate that the INCENP central region increases Dsn1 phosphorylation by enriching Aurora B at inner kinetochores, close to CENP-C. Furthermore, centromere-bound CENP-C does not exchange in mitosis, and CENP-C binding to the Mis12C dramatically increases Dsn1 phosphorylation by Aurora B. We propose that the coincidence of Aurora B and CENP-C at inner kinetochores ensures the fidelity of kinetochore assembly. We also found that the central region is required for the SAC beyond its role in kinetochore assembly, suggesting that kinetochore enrichment of Aurora B promotes the phosphorylation of other kinetochore substrates.

A Kinase-Phosphatase Network that Regulates Kinetochore-Microtubule Attachments and the SAC

The KMN network (for KNL1, MIS12 and NDC80 complexes) is a hub for signalling at the outer kinetochore. It integrates the activities of two kinases (MPS1 and Aurora B) and two phosphatases (PP1 and PP2A-B56) to regulate kinetochore-microtubule attachments and the spindle assembly checkpoint (SAC). We will first discuss each of these enzymes separately, to describe how they are regulated at kinetochores and why this is important for their primary function in controlling either microtubule attachments or the SAC. We will then discuss why inhibiting any one of them individually produces secondary effects on all the others. This cross-talk may help to explain why all enzymes have been linked to both processes, even though the direct evidence suggests they each control only one. This chapter therefore describes how a network of kinases and phosphatases work together to regulate two key mitotic processes.

The COMA complex interacts with Cse4 and positions Sli15/Ipl1 at the budding yeast inner kinetochore

Kinetochores are macromolecular protein complexes at centromeres that ensure accurate chromosome segregation by attaching chromosomes to spindle microtubules and integrating safeguard mechanisms. The inner kinetochore is assembled on CENP-A nucleosomes and has been implicated in establishing a kinetochore-associated pool of Aurora B kinase, a chromosomal passenger complex (CPC) subunit, which is essential for chromosome biorientation. By performing crosslink-guided in vitro reconstitution of budding yeast kinetochore complexes we showed that the Ame1/Okp1^CENP-U/Q heterodimer, which forms the COMA complex with Ctf19/Mcm21^CENP-P/O, selectively bound Cse4^CENP-A nucleosomes through the Cse4 N-terminus. The Sli15/Ipl1^{INCENP/Aurora-B} core-CPC interacted with COMA in vitro through the Ctf19 C-terminus whose deletion affected chromosome segregation fidelity in Sli15 wild-type cells. Tethering Sli15 to Ame1/Okp1 rescued synthetic lethality upon Ctf19 depletion in a Sli15 centromere-targeting deficient mutant. This study shows molecular characteristics of the point-centromere kinetochore architecture and suggests a role for the Ctf19 C-terminus in mediating CPC-binding and accurate chromosome segregation.

Small-Molecule Ferroptotic Agents with Potential to Selectively Target Cancer Stem Cells

Effective management of advanced cancer requires systemic treatment including small molecules that target unique features of aggressive tumor cells. At the same time, tumors are heterogeneous and current evidence suggests that a subpopulation of tumor cells, called tumor initiating or cancer stem cells, are responsible for metastatic dissemination, tumor relapse and possibly drug resistance. Classical apoptotic drugs are less effective against this critical subpopulation. In the course of generating a library of open-chain epothilones, we discovered a new class of small molecule anticancer agents that has no effect on tubulin but instead kills selected cancer cell lines by harnessing reactive oxygen species to induce ferroptosis. Interestingly, we find that drug sensitivity is highest in tumor cells with a mesenchymal phenotype. Furthermore, these compounds showed enhanced toxicity towards mesenchymal breast cancer populations with cancer stem cell properties in vitro. In summary, we have identified a new class of small molecule ferroptotic agents that warrant further investigation.

The binding of Borealin to microtubules underlies a tension independent kinetochore-microtubule error correction pathway

Proper chromosome segregation depends upon kinetochore phosphorylation by the Chromosome Passenger Complex (CPC). Current models suggest the activity of the CPC decreases in response to the inter-kinetochore stretch that accompanies the formation of bi-oriented microtubule attachments, however little is known about tension-independent CPC phosphoregulation. Microtubule bundles initially lie in close proximity to inner centromeres and become depleted by metaphase. Here we find these microtubules control kinetochore phosphorylation by the CPC in a tension independent manner via a microtubule-binding site on the Borealin subunit. Disruption of Borealin-microtubule interactions generates reduced phosphorylation of prometaphase kinetochores, improper kinetochore-microtubule attachments and weakened spindle checkpoint signals. Experimental and modeling evidence suggests that kinetochore phosphorylation is greatly stimulated when the CPC binds microtubules that lie near the inner centromere, even if kinetochores have high inter-kinetochore stretch. We propose the CPC senses its local environment through microtubule structures to control phosphorylation of kinetochores.

How the chromosome passenger complex (CPC) phosphorylates the kinetochores that can be a micron away to control mitotic events is unknown. Here the authors find that the CPC directly binds microtubules near inner centromeres, which controls its ability to phosphorylate kinetochores independently of tension generated by kinetochore microtubule attachments.

RecQL4-Aurora B kinase axis is essential for cellular proliferation, cell cycle progression, and mitotic integrity

Human RecQL4 helicase plays critical roles in the maintenance of genomic stability. Mutations in RecQL4 helicase results in three clinically related autosomal recessive disorders: Rothmund–Thomson syndrome (RTS), RAPADILINO, and Baller–Gerold syndrome. In addition to several premature aging features, RTS patients are characterized by aneuploidy involving either loss or gain of a single chromosome. Chromosome mosaicism and isochromosomes involving chromosomes 2, 7, and 8 have been reported in RecQL4-deficient RTS patients, but the precise role of RecQL4 in chromosome segregation/stability remains to be elucidated. Here, we demonstrate that RecQL4 physically and functionally interacts with Aurora B kinase (AURKB) and stabilizes its expression by inhibiting its ubiquitination process. Our study indicates that the N-terminus of RecQL4 interacts with the catalytic domain of AURKB. Strikingly, RecQL4 suppression reduces the expression of AURKB leading to mitotic irregularities and apoptotic cell death. RecQL4 suppression increases the proportion of cells at the G2/M phase followed by an extensive cell death, presumably owing to the accumulation of mitotic irregularities. Both these defects (accumulation of cells at G2/M phase and an improper mitotic exit to sub-G1) are complemented by the ectopic expression of AURKB. Finally, evidence is provided for the requirement of both human telomerase reverse transcriptase and RecQL4 for stable immortalization and longevity of RTS fibroblasts. Collectively, our study suggests that the RecQL4–AURKB axis is essential for cellular proliferation, cell cycle progression, and mitotic stability in human cells.

Aurora-PLK1 cascades as key signaling modules in the regulation of mitosis

Mitosis is controlled by reversible protein phosphorylation involving specific kinases and phosphatases. A handful of major mitotic protein kinases, such as the cyclin B-CDK1 complex, the Aurora kinases, and Polo-like kinase 1 (PLK1), cooperatively regulate distinct mitotic processes. Research has identified proteins and mechanisms that integrate these kinases into signaling cascades that guide essential mitotic events. These findings have important implications for our understanding of the mechanisms of mitotic regulation and may advance the development of novel antimitotic drugs. We review collected evidence that in vertebrates, the Aurora kinases serve as catalytic subunits of distinct complexes formed with the four scaffold proteins Bora, CEP192, INCENP, and TPX2, which we deem "core" Aurora cofactors. These complexes and the Aurora-PLK1 cascades organized by Bora, CEP192, and INCENP control crucial aspects of mitosis and all pathways of spindle assembly. We compare the mechanisms of Aurora activation in relation to the different spindle assembly pathways and draw a functional analogy between the CEP192 complex and the chromosomal passenger complex that may reflect the coevolution of centrosomes, kinetochores, and the actomyosin cleavage apparatus. We also analyze the roles and mechanisms of Aurora-PLK1 signaling in the cell and centrosome cycles and in the DNA damage response.

CDCA8 expression and its clinical relevance in patients with bladder cancer

Cell division cycle associated 8 (CDCA8) overexpression is detected in various malignant tumors and closely associated with tumor growth. However, the correlations of CDCA8 expression with clinicopathological factors and prognosis of bladder cancer (BC) remain unclear. The purpose of this study was to identify the expression of CDCA8 and its clinical relevance in BC patients.GEO datasets were employed to obtain CDCA8 expression data and its clinical information in BC samples. Real-time PCR (RT-PCR) was performed to detect the expression of CDCA8 in BC and the adjacent normal tissues. Nonpaired t test was used to statistically analyze the difference between the 2 groups. Cox univariable and multivariable analyses of overall survival (OS) and cancer specific survival (CSS) among BC patients were performed. Biological processes or signaling pathways that might mediate the activity of CDCA8 in BC were analyzed.CDCA8 levels were significantly higher in BC (8.870 ± 0.08281 vs 7.472 ± 0.07035, P < .0001). CDCA8 expression was significantly associated with tumor progression (P = .001), T stage (P < .0001), N stage (P = .013), and grade (P < .0001). Higher expression of CDCA8 predicted poor cancer-specific survival (P < .0001, HR = 0.2752, 95% CI:0.1364-0.5554) and overall survival (P < .0001, HR = 0.4270, 95% CI: 0.2630-0.6930) in patients with BC. Cox univariable and multivariable analyses showed that intravesical therapy, N stage and progression were the independent influence factors of overall survival among bladder cancer patients, CDCA8 expression, tumor grade and progression were the independent influence factors of cancer specific survival among bladder cancer patients. The results of GSEA indicated that CDCA8-regulated gene sets associated with spermatogenesis, G2M checkpoint, E2F targets, Myc targets, mTORC1 signaling, mitotic spindle angiogenesis, PI3K/AKT/mTOR signaling, cholesterol homeostasis and glycolysis. Finally, RT-PCR results confirmed that CDCA8 expression was upregulated in BC (P = .0039).CDCA8 is overexpressed in BC and its high levels are correlated with poor clinicopathological features of BC patients. Therefore, CDCA8 may act as a novel prognostic marker and therapeutical target in the diagnosis and treatment of patients with BC.

Kinase and Phosphatase Cross-Talk at the Kinetochore

Multiple kinases and phosphatases act on the kinetochore to control chromosome segregation: Aurora B, Mps1, Bub1, Plk1, Cdk1, PP1, and PP2A-B56, have all been shown to regulate both kinetochore-microtubule attachments and the spindle assembly checkpoint. Given that so many kinases and phosphatases converge onto two key mitotic processes, it is perhaps not surprising to learn that they are, quite literally, entangled in cross-talk. Inhibition of any one of these enzymes produces secondary effects on all the others, which results in a complicated picture that is very difficult to interpret. This review aims to clarify this picture by first collating the direct effects of each enzyme into one overarching schematic of regulation at the Knl1/Mis12/Ndc80 (KMN) network (a major signaling hub at the outer kinetochore). This schematic will then be used to discuss the implications of the cross-talk that connects these enzymes; both in terms of why it may be needed to produce the right type of kinetochore signals and why it nevertheless complicates our interpretations about which enzymes control what processes. Finally, some general experimental approaches will be discussed that could help to characterize kinetochore signaling by dissociating the direct from indirect effect of kinase or phosphatase inhibition in vivo. Together, this review should provide a framework to help understand how a network of kinases and phosphatases cooperate to regulate two key mitotic processes.

The Ins and Outs of Aurora B Inner Centromere Localization

Error-free chromosome segregation is essential for the maintenance of genomic integrity during cell division. Aurora B, the enzymatic subunit of the Chromosomal Passenger Complex (CPC), plays a crucial role in this process. In early mitosis Aurora B localizes predominantly to the inner centromere, a specialized region of chromatin that lies at the crossroads between the inter-kinetochore and inter-sister chromatid axes. Two evolutionarily conserved histone kinases, Haspin and Bub1, control the positioning of the CPC at the inner centromere and this location is thought to be crucial for the CPC to function. However, recent studies sketch a subtler picture, in which not all functions of the CPC require strict confinement to the inner centromere. In this review we discuss the molecular pathways that direct Aurora B to the inner centromere and deliberate if and why this specific localization is important for Aurora B function.

Haspin: a promising target for the design of inhibitors as potent anticancer drugs

Protein kinases constitute a large group of enzymes in eukaryotes and have an important role in many cellular processes. Several of these proteins are active kinases, such as haploid germ cell-specific nuclear protein kinase (Haspin), an atypical eukaryotic protein kinase that lacks sequence similarity with other eukaryotic protein kinases. Haspin is a serine/threonine kinase that associates with chromosome and phosphorylates threonine 3 of histone 3 during mitosis. Haspin overexpression or deletion results in defective mitosis. It has been shown that Haspin inhibitors have potent anti-tumoral effects. Given that the only Haspin substrate is threonine 3 of histone 3, inhibition of Haspin might have fewer adverse effects compared with other anticancer agents. Here, we highlight the chemical structures and actions of currently known Haspin inhibitors.

Mutations in BOREALIN cause thyroid dysgenesis

Congenital hypothyroidism is the most common neonatal endocrine disorder and is primarily caused by developmental abnormalities otherwise known as thyroid dysgenesis (TD). We performed whole exome sequencing (WES) in a consanguineous family with TD and subsequently sequenced a cohort of 134 probands with TD to identify genetic factors predisposing to the disease. We identified the novel missense mutations p.S148F, p.R114Q and p.L177W in the BOREALIN gene in TD-affected families. Borealin is a major component of the Chromosomal Passenger Complex (CPC) with well-known functions in mitosis. Further analysis of the missense mutations showed no apparent effects on mitosis. In contrast, expression of the mutants in human thyrocytes resulted in defects in adhesion and migration with corresponding changes in gene expression suggesting others functions for this mitotic protein. These results were well correlated with the same gene expression pattern analysed in the thyroid tissue of the patient with BOREALIN-p.R114W. These studies open new avenues in the genetics of TD in humans.

An engineered minimal chromosomal passenger complex reveals a role for INCENP/Sli15 spindle association in chromosome biorientation

The four-subunit chromosomal passenger complex (CPC), whose enzymatic subunit is Aurora B kinase, promotes chromosome biorientation by detaching incorrect kinetochore-microtubule attachments. In this study, we use a combination of truncations and artificial dimerization in budding yeast to define the minimal CPC elements essential for its biorientation function. We engineered a minimal CPC comprised of the dimerized last third of the kinase-activating Sli15/INCENP scaffold and the catalytic subunit Ipl1/Aurora B. Although native Sli15 is not oligomeric, artificial dimerization suppressed the biorientation defect and lethality associated with deletion of a majority of its microtubule-binding domain. Dimerization did not act through a physical clustering-based kinase activation mechanism but instead promoted spindle association, likely via a putative helical domain in Sli15 that is essential even when dimerized and is required to target kinetochore substrates. Based on the engineering and characterization of a minimal CPC, we suggest that spindle association is important for active Ipl1/Aurora B complexes to preferentially destabilize misattached kinetochores.

Specialize and Divide (Twice): Functions of Three Aurora Kinase Homologs in Mammalian Oocyte Meiotic Maturation

The aurora kinases (AURKs) comprise an evolutionarily conserved family of serine/threonine kinases involved in mitosis and meiosis. While most mitotic cells express two AURK isoforms (AURKA and AURKB), mammalian germ cells also express a third, AURKC. Although much is known about the functions of the kinases in mitosis, less is known about how the three isoforms function to coordinate meiosis. This review is aimed at describing what is known about the three isoforms in female meiosis, the similarities and differences between kinase functions, and speculates as to why mammalian germ cells require expression of three AURKs instead of two.

Dual recognition of chromatin and microtubules by INCENP is important for mitotic progression

The chromosomal passenger complex (CPC), composed of inner centromere protein (INCENP), Survivin, Borealin, and the kinase Aurora B, contributes to the activation of the mitotic checkpoint. The regulation of CPC function remains unclear. Here, we reveal that in addition to Survivin and Borealin, the single α-helix (SAH) domain of INCENP supports CPC localization to chromatin and the mitotic checkpoint. The INCENP SAH domain also mediates INCENP's microtubule binding, which is negatively regulated by Cyclin-dependent kinase-mediated phosphorylation of segments flanking the SAH domain. The microtubule-binding capacity of the SAH domain is important for mitotic arrest in conditions of suppressed microtubule dynamics, and the duration of mitotic arrest dictates the probability, but not the timing, of cell death. Although independent targeting of INCENP to microtubules or the kinetochore/centromere promotes the mitotic checkpoint, it is insufficient for a robust mitotic arrest. Altogether, our results demonstrate that dual recognition of chromatin and microtubules by CPC is important for checkpoint maintenance and determination of cell fate in mitosis.

The Ska complex promotes Aurora B activity to ensure chromosome biorientation

Chromosome biorientation and accurate segregation rely on the plasticity of kinetochore-microtubule (KT-MT) attachments. Aurora B facilitates KT-MT dynamics by phosphorylating kinetochore proteins that are critical for KT-MT interactions. Among the substrates whose microtubule and kinetochore binding is curtailed by Aurora B is the spindle and kinetochore-associated (Ska) complex, a key factor for KT-MT stability. Here, we show that Ska is not only a substrate of Aurora B, but is also required for Aurora B activity. Ska-deficient cells fail to biorient and display chromosome segregation errors underlying suppressed KT-MT turnover. These defects coincide with KNL1-Mis12-Ndc80 network hypophosphorylation, reduced mitotic centromere-associated kinesin localization, and Aurora B T-loop phosphorylation at kinetochores. We further show that Ska requires its microtubule-binding capability to promote Aurora B activity in cells and stimulates Aurora B catalytic activity in vitro. Finally, we show that protein phosphatase 1 counteracts Aurora B activity to enable Ska kinetochore accumulation once biorientation is achieved. We propose that Ska promotes Aurora B activity to limit its own microtubule and kinetochore association and to ensure that KT-MT dynamics and stability fall within an optimal balance for biorientation.