Mitotic entry: The interplay between Cdk1, Plk1 and Bora

Crosstalk Between Plk1 and PTEN in Mitosis Affects Chromosomal Stability

The mitotic phase involves the distribution and regulation of genetic material. Defects in gene regulation can lead to serious errors in genetic transmission, such as increased instability of chromosomes, thereby increasing susceptibility to cancer and promoting its development. The maintenance of chromosome stability depends on several mechanisms, such as efficient DNA repair, proper sister chromatid separation, and timely cytokinesis. The serine/threonine kinase Plk1 is a key molecule in maintaining chromosome stability, participating in multiple stages of precise regulation during mitosis, including promoting entry into mitosis, facilitating centrosome maturation and bipolar spindle formation, promoting sister chromatid separation, and facilitating cytokinesis. Several proteins can regulate the kinase activity of Plk1 through protein-protein interactions, coordinating the genetic stability of the cell, including the kinases Aurora A, c-Abl, and Chk1 as well as the phosphatase phosphatase and tension homolog (PTEN). PTEN has been described as an essential regulator of Plk1 for dephosphorylation and chromosomal stability during cell division, and Plk1 may directly interact with and phosphorylate PTEN at centromeres. Here, we review the bidirectional interplay between Plk1 and PTEN and how it contributes to genomic stability during mitosis.

Construction and high-throughput screening of gradient nanowire coatings on titanium surface towards ameliorated osseointegration

Surface nano-modification has emerged as an effective strategy to enhance osseointegration of titanium (Ti) implants. Despite its promise, rational optimization of surface nanomorphology for ameliorated osseointegration remains a significant challenge. Our research pioneering developed a one-step alkali etching technique to produce a gradient nanowire coating with continuously varied dimensions on Ti surfaces, which was subsequently served as a versatile platform for high-throughput screening of optimal dimensions to enhance osseointegration. The results showed that macrophages (MФs) that mainly governed the initial inflammatory reaction exhibited a polarization tendency towards pro-healing M2 phenotype with decreased nanowire dimension due to nanomorphology-mediated focal adhesion formation and activation of its downstream signaling pathways (typically PI3K-Akt). Simultaneously, small-sized nanowires with diameter of 5.63-14.25 nm and inter-spacing of 29.42-57.97 nm were conductive to angiogenesis of endothelial cells (ECs) and osteogenesis of bone marrow mesenchymal stem cells (BMSCs), which may share similar mechanisms of MФs. The in vivo results well corroborated these in vitro observations. The knowledge gained from the present work not only advance our understanding of the interaction between surface morphology and cells, but also potentially pave the way for efficient and cost-effective design of advanced biomaterial surfaces for better osseointegration.

Only Infant MLL-Rearranged Leukemia Is Susceptible to an Inhibition of Polo-like Kinase 1 (PLK-1) by Volasertib

MLL-rearranged (MLLr) leukemia is characterized by a poor prognosis. Depending on the cell of origin, it differs in the aggressiveness and therapy response. For instance, in adults, volasertib blocking Polo-like kinase 1 (PLK-1) exhibited limited success. Otherwise, PLK-1 characterizes an infant MLLr signature, indicating potential sensitivity. By using our CRISPR/Cas9 MLLr model in CD34+ cells from human cord blood (huCB) and bone marrow (huBM) mimicking the infant and adult patient diseases, we were able to shed light on this phenomenon. The PLK-1 mRNA level was significantly increased in our huCB compared to the huBM model, which was underpinned by analyzing infant and adult MLLr leukemia patients. Importantly, the expression levels correlated with a functional response. Volasertib induced a significant dose-dependent decrease in proliferation and cell cycle arrest, most pronounced in the infant model. Mechanistically, upon volasertib treatment, we uncovered negative feedback only in the huBM model by compensatory upregulation of PLK-1 and related genes like AURKA involved in mitosis. Importantly, the poor response could be overcome by a combinatorial strategy with alisertib, an Aurora kinase A inhibitor. Our study emphasizes the importance of considering the cell of origin in therapeutic decision-making and provides the rationale for evaluating volasertib and alisertib in MLLr leukemia.

Polo-Like Kinase 1 and DNA Damage Response

Polo-like kinase 1 (Plk1), an evolutionarily conserved serine/threonine protein kinase, is a key regulator involved in the mitotic process of the cell cycle. Mounting evidence suggests that Plk1 is also involved in a variety of nonmitotic events, including the DNA damage response, DNA replication, cytokinesis, embryonic development, apoptosis, and immune regulation. The DNA damage response (DDR) includes activation of the DNA checkpoint, DNA damage recovery, DNA repair, and apoptosis. Plk1 is not only an important target of the G2/M DNA damage checkpoint but also negatively regulates the G2/M checkpoint commander Ataxia telangiectasia-mutated (ATM), promotes G2/M phase checkpoint recovery, and regulates homologous recombination repair by interacting with Rad51 and BRCA1, the key factors of homologous recombination repair. This article briefly reviews the function of Plk1 in response to DNA damage.

CDC6 as a Key Inhibitory Regulator of CDK1 Activation Dynamics and the Timing of Mitotic Entry and Progression

Timely mitosis is critically important for early embryo development. It is regulated by the activity of the conserved protein kinase CDK1. The dynamics of CDK1 activation must be precisely controlled to assure physiologic and timely entry into mitosis. Recently, a known S-phase regulator CDC6 emerged as a key player in mitotic CDK1 activation cascade in early embryonic divisions, operating together with Xic1 as a CDK1 inhibitor upstream of the Aurora A and PLK1, both CDK1 activators. Herein, we review the molecular mechanisms that underlie the control of mitotic timing, with special emphasis on how CDC6/Xic1 function impacts CDK1 regulatory network in the Xenopus system. We focus on the presence of two independent mechanisms inhibiting the dynamics of CDK1 activation, namely Wee1/Myt1- and CDC6/Xic1-dependent, and how they cooperate with CDK1-activating mechanisms. As a result, we propose a comprehensive model integrating CDC6/Xic1-dependent inhibition into the CDK1-activation cascade. The physiological dynamics of CDK1 activation appear to be controlled by the system of multiple inhibitors and activators, and their integrated modulation ensures concomitantly both the robustness and certain flexibility of the control of this process. Identification of multiple activators and inhibitors of CDK1 upon M-phase entry allows for a better understanding of why cells divide at a specific time and how the pathways involved in the timely regulation of cell division are all integrated to precisely tune the control of mitotic events.

Functional Differentiation of Cyclins and Cyclin-Dependent Kinases in Giardia lamblia

Cyclin-dependent kinases (CDKs) are serine/threonine kinases that control the eukaryotic cell cycle. Limited information is available on Giardia lamblia CDKs (GlCDKs), GlCDK1 and GlCDK2. After treatment with the CDK inhibitor flavopiridol-HCl (FH), division of Giardia trophozoites was transiently arrested at the G1/S phase and finally at the G2/M phase. The percentage of cells arrested during prophase or cytokinesis increased, whereas DNA synthesis was not affected by FH treatment. Morpholino-mediated depletion of GlCDK1 caused arrest at the G2/M phase, while GlCDK2 depletion resulted in an increase in the number of cells arrested at the G1/S phase and cells defective in mitosis and cytokinesis. Coimmunoprecipitation experiments with GlCDKs and the nine putative G. lamblia cyclins (Glcyclins) identified Glcyclins 3977/14488/17505 and 22394/6584 as cognate partners of GlCDK1 and GlCDK2, respectively. Morpholino-based knockdown of Glcyclin 3977 or 22394/6584 arrested cells in the G2/M phase or G1/S phase, respectively. Interestingly, GlCDK1- and Glcyclin 3977-depleted Giardia showed significant flagellar extension. Altogether, our results suggest that GlCDK1/Glcyclin 3977 plays an important role in the later stages of cell cycle control and in flagellar biogenesis. In contrast, GlCDK2 along with Glcyclin 22394 and 6584 functions from the early stages of the Giardia cell cycle. IMPORTANCE Giardia lamblia CDKs (GlCDKs) and their cognate cyclins have not yet been studied. In this study, the functional roles of GlCDK1 and GlCDK2 were distinguished using morpholino-mediated knockdown and coimmunoprecipitation. GlCDK1 with Glcyclin 3977 plays a role in flagellum formation as well as cell cycle control of G. lamblia, whereas GlCDK2 with Glcyclin 22394/6584 is involved in cell cycle control.

Poison cassette exon splicing of SRSF6 regulates nuclear speckle dispersal and the response to hypoxia

Hypoxia induces massive changes in alternative splicing (AS) to adapt cells to the lack of oxygen. Here, we identify the splicing factor SRSF6 as a key factor in the AS response to hypoxia. The SRSF6 level is strongly reduced in acute hypoxia, which serves a dual purpose: it allows for exon skipping and triggers the dispersal of nuclear speckles. Our data suggest that cells use dispersal of nuclear speckles to reprogram their gene expression during hypoxic adaptation and that SRSF6 plays an important role in cohesion of nuclear speckles. Down-regulation of SRSF6 is achieved through inclusion of a poison cassette exon (PCE) promoted by SRSF4. Removing the PCE 3' splice site using CRISPR/Cas9 abolishes SRSF6 reduction in hypoxia. Aberrantly high SRSF6 levels in hypoxia attenuate hypoxia-mediated AS and impair dispersal of nuclear speckles. As a consequence, proliferation and genomic instability are increased, while the stress response is suppressed. The SRSF4-PCE-SRSF6 hypoxia axis is active in different cancer types, and high SRSF6 expression in hypoxic tumors correlates with a poor prognosis. We propose that the ultra-conserved PCE of SRSF6 acts as a tumor suppressor and that its inclusion in hypoxia is crucial to reduce SRSF6 levels. This may prevent tumor cells from entering the metastatic route of hypoxia adaptation.

Six Cell Cycle-related Genes Serve as Potential Prognostic Biomarkers and Correlated with Immune Infiltrates in Hepatocellular Carcinoma

Background: Cell cycle-related genes (CDK1, CDK5, CDC20, CCNA2, CCNB1, and CCNB2) play important roles in the regulation of mitotic cell cycle in eukaryotes. However, the correlation between cell cycle-related genes and tumor-infiltrating and prognosis of hepatocellular carcinoma (HCC) needs further investigation. Methods: Two public websites, Tumor Immune Estimate Resource (TIMER) and Oncomine, were used to assess the expression levels of cycle-related genes. We also analyzed the protein expression levels of six cell cycle-related genes using the HPA database. In addition, Kaplan-Meier plotter and Gene Expression Profiling Interactive Analysis (GEPIA) database were used to investigate the impact of cell cycle-related gene expression levels on the clinical prognosis of HCC. The correlation between cell cycle-related genes and cancer immune infiltrates was analyzed through TIMER site. Subsequently, GEPIA and TIMER database were used to assess the correlation between the expression of six cell cycle-related genes and polygenic markers in monocytes and macrophages, respectively. The cell cycle-related genes were also analyzed to find the associated genes with the highest alteration frequency, by the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) approaches of Metascape and String database, respectively. Results: The expression levels of cell cycle-related genes were up-regulated in tumor tissues compared with normal tissues. Subsequently, the expression of high cell cycle-related genes was positively correlated with poor overall survival (OS) and progression-free survival (PFS) in HCC, for CDK1 (OS: HR = 2.15, P = 1.1E-05 PFS: HR = 2.03, P = 2.3E-06), CDK5 (OS: HR = 1.85, P = 0.0035 PFS: HR = 1.26, P = 0.17), CDC20 (OS: HR = 2.49, P = 5.1E-07 PFS: HR = 1.77, P = 0.00012), CCNA2 (OS: HR = 1.92, P = 0.00018 PFS: HR = 1.96, P = 5.2E-06), CCNB1 (OS: HR = 2.34, P = 3.4E-05 PFS: HR = 1.97, P = 5.3E-06), and CCNB2 (OS: HR = 1.91, P = 0.0013 PFS: HR = 1.63, P = 0.0011), respectively. Furthermore, the transcription level of cell cycle-related genes was significantly correlated with immune infiltrating levels of CD4+ T and CD8+ T cells, neutrophils, macrophages, and dendritic cells (DCs) in HCC, respectively. Amongst them, the expression levels of CDK1, CDC20, CCNA2, CCNB1 and CCNB2 manifest strongly correlated with diverse immune marker sets in HCC. Conclusions: Our results demonstrated that cell cycle-related genes played key roles in the prognosis of HCC. Meanwhile, they were significantly correlated with immune infiltrating levels of CD4⁺ T cells, CD8⁺ T cells, neutrophils, macrophages and DCs in HCC, respectively. In addition, CDK1, CDC20, CCNA2, CCNB1 and CCNB2 expressions may be involved in the regulation of monocytes and tumor-associated macrophages (TAMs) in HCC, respectively. These findings strongly suggested that cell cycle-related genes could be used as novel biomarkers for exploring the prognosis and immune cells infiltration of HCC.

DNA damage checkpoint execution and the rules of its disengagement

Chromosomes are susceptible to damage during their duplication and segregation or when exposed to genotoxic stresses. Left uncorrected, these lesions can result in genomic instability, leading to cells' diminished fitness, unbridled proliferation or death. To prevent such fates, checkpoint controls transiently halt cell cycle progression to allow time for the implementation of corrective measures. Prominent among these is the DNA damage checkpoint which operates at G2/M transition to ensure that cells with damaged chromosomes do not enter the mitotic phase. The execution and maintenance of cell cycle arrest are essential aspects of G2/M checkpoint and have been studied in detail. Equally critical is cells' ability to switch-off the checkpoint controls after a successful completion of corrective actions and to recommence cell cycle progression. Interestingly, when corrective measures fail, cells can mount an unusual cellular response, termed adaptation, where they escape checkpoint arrest and resume cell cycle progression with damaged chromosomes at the cost of genome instability or even death. Here, we discuss the DNA damage checkpoint, the mitotic networks it inhibits to prevent segregation of damaged chromosomes and the strategies cells employ to quench the checkpoint controls to override the G2/M arrest.

Design of new disubstituted imidazo[1,2-b]pyridazine derivatives as selective Haspin inhibitors. Synthesis, binding mode and anticancer biological evaluation

Haspin is a mitotic protein kinase required for proper cell division by modulating Aurora B kinase localisation and activity as well as histone phosphorylation. Here a series of imidazopyridazines based on the CHR-6494 and Structure Activity Relationship was established. An assessment of the inhibitory activity of the lead structures on human Haspin and several other protein kinases is presented. The lead structure was rapidly optimised using a combination of crystal structures and effective docking models, with the best inhibitors exhibiting potent inhibitory activity on Haspin with IC₅₀ between 6 and 100 nM in vitro. The developed inhibitors displayed anti-proliferative properties against various human cancer cell lines in 2D and spheroid cultures and significantly inhibited the migration ability of osteosarcoma U-2 OS cells. Notably, we show that our lead compounds are powerful Haspin inhibitors in human cells, and did not block G2/M cell cycle transition due to improved selectivity against CDK1/CyclinB.

Bora phosphorylation substitutes in trans for T-loop phosphorylation in Aurora A to promote mitotic entry

Polo-like kinase 1 (Plk1) is instrumental for mitotic entry and progression. Plk1 is activated by phosphorylation on a conserved residue Thr210 in its activation segment by the Aurora A kinase (AURKA), a reaction that critically requires the co-factor Bora phosphorylated by a CyclinA/B-Cdk1 kinase. Here we show that phospho-Bora is a direct activator of AURKA kinase activity. We localize the key determinants of phospho-Bora function to a 100 amino acid region encompassing two short Tpx2-like motifs and a phosphoSerine-Proline motif at Serine 112, through which Bora binds AURKA. The latter substitutes in trans for the Thr288 phospho-regulatory site of AURKA, which is essential for an active conformation of the kinase domain. We demonstrate the importance of these determinants for Bora function in mitotic entry both in Xenopus egg extracts and in human cells. Our findings unveil the activation mechanism of AURKA that is critical for mitotic entry.

Cyclin A2 localises in the cytoplasm at the S/G2 transition to activate PLK1

Cyclin A2 is a key regulator of the cell cycle, implicated both in DNA replication and mitotic entry. Cyclin A2 participates in feedback loops that activate mitotic kinases in G2 phase, but why active Cyclin A2-CDK2 during the S phase does not trigger mitotic kinase activation remains unclear. Here, we describe a change in localisation of Cyclin A2 from being only nuclear to both nuclear and cytoplasmic at the S/G2 border. We find that Cyclin A2-CDK2 can activate the mitotic kinase PLK1 through phosphorylation of Bora, and that only cytoplasmic Cyclin A2 interacts with Bora and PLK1. Expression of predominately cytoplasmic Cyclin A2 or phospho-mimicking PLK1 T210D can partially rescue a G2 arrest caused by Cyclin A2 depletion. Cytoplasmic presence of Cyclin A2 is restricted by p21, in particular after DNA damage. Cyclin A2 chromatin association during DNA replication and additional mechanisms contribute to Cyclin A2 localisation change in the G2 phase. We find no evidence that such mechanisms involve G2 feedback loops and suggest that cytoplasmic appearance of Cyclin A2 at the S/G2 transition functions as a trigger for mitotic kinase activation.

Structure-activity relationships of Wee1 inhibitors: A review

Wee1 kinase plays an important role in regulating G2/M checkpoint and S phase, and the inhibition of it will lead to mitotic catastrophe in cancer cells with p53 mutation or deletion. Therefore, the mechanism of Wee1 kinase in cancer treatment and the development of its inhibitors have become a research hotspot. However, although a variety of Wee1 inhibitors with different scaffolds and considerable activity have been successfully identified, so far no one has systematically summarized the structure-activity relationships (SARs) of Wee1 inhibitors. Previous reviews mainly focused on its mechanism and clinical application. To facilitate the rational design and development of Wee1 inhibitors in the future, this paper systematically summarizes its structural types, SARs and binding modes according to the Wee1 inhibitors reported in scientific journals, and also summarizes the regulatory effect of Wee1 kinase on cell cycle and the progress of its inhibitors in clinical application.

Kv10.1 Regulates Microtubule Dynamics during Mitosis

Kv10.1 (potassium voltage-gated channel subfamily H member 1, known as EAG1 or Ether-à-go-go 1), is a voltage-gated potassium channel, prevailingly expressed in the central nervous system. The aberrant expression of Kv10.1 is detected in over 70% of all human tumor tissues and correlates with poorer prognosis. In peripheral tissues, Kv10.1 is expressed almost exclusively during the G2/M phase of the cell cycle and regulates its progression-downregulation of Kv10.1 extends the duration of the G2/M phase both in cancer and healthy cells. Here, using biochemical and imaging techniques, such as live-cell measurements of microtubule growth and of cytosolic calcium, we elucidate the mechanisms of Kv10.1-mediated regulation at the G2/M phase. We show that Kv10.1 has a dual effect on mitotic microtubule dynamics. Through the functional interaction with ORAI1 (calcium release-activated calcium channel protein 1), it modulates cytosolic calcium oscillations, thereby changing microtubule behavior. The inhibition of either Kv10.1 or ORAI1 stabilizes the microtubules. In contrast, the knockdown of Kv10.1 increases the dynamicity of mitotic microtubules, resulting in a stronger spindle assembly checkpoint, greater mitotic spindle angle, and a decrease in lagging chromosomes. Understanding of Kv10.1-mediated modulation of the microtubule architecture will help to comprehend how cancer tissue benefits from the presence of Kv10.1, and thereby increase the efficacy and safety of Kv10.1-directed therapeutic strategies.

BORA regulates cell proliferation and migration in bladder cancer

Background

Bladder cancer is having a gradually increasing incidence in China. Except for the traditional chemotherapy drugs, there are no emerging new drugs for almost 30 years in bladder cancer. New potential therapeutic targets and biomarkers are urgently needed.

Methods

BORA is the activator of kinase Aurora A and plays an important role in cell cycle progression. To investigate the function of BORA in BCa, we established BORA knockdown and overexpression cell models for in vitro studies, xenograft and pulmonary metastasis mouse models for in vivo studies.

Results

Our results indicated that BORA was upregulated in human bladder cancer (BCa) compared to the normal bladder and paracancerous tissues at transcriptional and translational levels. We found that BORA was positively related to BCa cell proliferation. Furthermore, BORA knockdown induced cell cycle arrest in G2/M phase while BORA overexpression decreased the proportion of cells in G2/M, associated with PLK1–CDC25C–CDK1 alteration. Interestingly, we observed that knockdown of BORA inhibited BCa cell migration and invasion, accompanied with alterations of epithelial–mesenchymal transition (EMT) pathway related proteins. In vivo studies confirmed the inhibition effect of BORA knockdown on BCa cell growth and migration.

Conclusions

Our study indicates that BORA regulates BCa cell cycle and growth, meanwhile influences cell motility by EMT, and could be a novel biomarker and potential therapeutic target in BCa.

CDK1-PLK1/SGOL2/ANLN pathway mediating abnormal cell division in cell cycle may be a critical process in hepatocellular carcinoma

This study aims to investigate the potential mechanisms and identify core biomarkers of Hepatocellular carcinoma (HCC). The profile GSE113850 was downloaded to analyze the differentially expressed genes. Gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and protein-protein interaction network analysis were used to reveal the main signal pathways of the differentially expressed genes (DEGs) and hub genes. The correlation between core gene expression and pathological stages, the disease-free survival analysis, the overall survival analysis were analyzed by Gene Expression Profiling Interactive Analysis. Furthermore, we reidentified the expression level of core genes of carcinoma tissues and para-carcinoma tissues from 14 HCC patients with real-time reverse transcription-polymerase chain reaction analysis (RT-PCR) and western blotting. After SK-Hep1 cell was treated with cyclin-dependent kinase 1 (CDK1) siRNA for 72 h, we detected the expression of the core genes and fluorescence-activated cell sorting analysis. A total of 378 DEGs were found. GO and KEGG analysis revealed that the DEGs were mainly enriched in the cell cycle. There were positive correlations among CDK1, polo-like kinase 1, shugoshin2 and anillin actin-binding protein. Moreover, the expression levels of four core genes were related to the HCC occurrence, pathological stages, and survivorship curve. The clinical HCC specimens verified the higher expression level of core genes by real-time RT-PCR. The transfection of siCDK1 in SK-Hep1 resulted in a disordered cell cycle. Furthermore, CDK1 knockdown suppressed the expression of PLK1, ANLN, and SGOL2. The CDK1-PLK1/SGOL2/ANLN pathway mediating abnormal cell division in the cell cycle might be a critical process in HCC.

Aurora Borealis (Bora), Which Promotes Plk1 Activation by Aurora A, Has an Oncogenic Role in Ovarian Cancer

Identifying novel actionable factors that critically contribute to tumorigenesis is essential in ovarian cancer, an aggressive and disseminative tumor, with limited therapeutic options available. Here we show that Aurora Borealis (BORA), a mitotic protein that plays a key role in activating the master mitotic kinase polo-like kinase 1 (PLK1), has an oncogenic role in ovarian cancer. Gain and loss of function assays on mouse models and ex vivo patient-derived ascites cultures revealed an oncogenic role of BORA in tumor development and a transcriptome-analysis in clinically representative models depicted BORA's role in survival, dissemination and inflammatory cancer related-pathways. Importantly, combinatory treatments of FDA-approved inhibitors against oncogenic downstream effectors of BORA displayed synergistic effect in ovarian cancer models, offering promising therapeutic value. Altogether, our findings uncovered for the first time a critical role of BORA in the viability of human cancer cells providing potential novel therapeutic opportunities for ovarian cancer management.

Exploratory study on application of MALDI‑TOF‑MS to detect serum and urine peptides related to small cell lung carcinoma

Matrix‑assisted laser desorption/ionization time‑of‑flight mass spectrometry (MALDI‑TOF‑MS) was employed to analyze differential serum and urine peptides in patients with small cell lung cancer (SCLC) and healthy individuals, and SCLC diagnostic classification models were constructed. Serum and urine samples from 72 patients with SCLC, age‑ and gender‑matched with 72 healthy individuals, were divided into training and testing sets in a 3:1 ratio. Serum and urine peptides were extracted using copper ion‑chelating nanomagnetic beads, and mass spectra were obtained using MALDI‑TOF‑MS. Peptide spectra for the training set were analyzed, and the classification model was constructed using ClinProTools (CPT). The testing set was used for blinded model validation. For training‑set sera, 122 differential peptide signal peaks with a mass of 0.8‑10 kDa were observed, and 19 peptides showed significantly different expression [P<0.0005; area under curve (AUC) ≥0.80]. CPT screened 5 peptide peaks (0.8114, 0.83425, 1.86655, 4.11133 and 5.81192 kDa) to construct the classification model. The testing set was used for the blinded validation, which had 95.0% sensitivity and 90.0% specificity. For the training‑set urine, 132 differential peptide signal peaks with m/z ratios of 0.8‑10 kDa were observed, and 8 peptides had significantly different expression (P<0.0005; AUC ≥0.80). Then, 5 peaks (1.0724, 2.37692, 2.7554, 4.75475 and 4.7949 kDa) were used for classification model construction. The testing set was used for 36 blinded validation, which had 85.0% sensitivity and 80.0% specificity. Among the differential peptides, 3 had the same significant peaks at 2.3764, 0.8778 and 0.8616 kDa, identified as fibrinogen α, glucose‑6‑phosphate isomerase and cyclin‑dependent kinase‑1, respectively. The present study highlighted the differences that exist in serum and urine peptides between patients with SCLC and healthy individuals. Serum and urine peptide diagnostic classification models could be constructed using MALDI‑TOF‑MS, and showed high sensitivity and specificity.

HPV-18 E2 protein downregulates antisense noncoding mitochondrial RNA-2, delaying replicative senescence of human keratinocytes

Human and mouse cells display a differential expression pattern of a family of mitochondrial noncoding RNAs (ncmtRNAs), according to proliferative status. Normal proliferating and cancer cells express a sense ncmtRNA (SncmtRNA), which seems to be required for cell proliferation, and two antisense transcripts referred to as ASncmtRNA-1 and -2. Remarkably however, the ASncmtRNAs are downregulated in human and mouse cancer cells, including HeLa and SiHa cells, transformed with HPV-18 and HPV-16, respectively. HPV E2 protein is considered a tumor suppressor in the context of high-risk HPV-induced transformation and therefore, to explore the mechanisms involved in the downregulation of ASncmtRNAs during tumorigenesis, we studied human foreskin keratinocytes (HFK) transduced with lentiviral-encoded HPV-18 E2. Transduced cells displayed a significantly extended replicative lifespan of up to 23 population doublings, compared to 8 in control cells, together with downregulation of the ASncmtRNAs. At 26 population doublings, cells transduced with E2 were arrested at G₂/M, together with downregulation of E2 and SncmtRNA and upregulation of ASncmtRNA-2. Our results suggest a role for high-risk HPV E2 protein in cellular immortalization. Additionally, we propose a new cellular phenotype according to the expression of the SncmtRNA and the ASncmtRNAs.

Integration of Bioinformatics Resources Reveals the Therapeutic Benefits of Gemcitabine and Cell Cycle Intervention in SMAD4-Deleted Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is the most common and aggressive type of pancreatic cancer. The five-year survival rate of PDAC is very low (less than 8%), which is associated with the late diagnosis, high metastatic potential, and resistance to therapeutic agents. The identification of better prognostic or therapeutic biomarker may have clinical benefits for PDAC treatment. SMAD4, a central mediator of transforming growth factor beta (TGFβ) signaling pathway, is considered a tumor suppressor gene. SMAD4 inactivation is frequently found in PDAC. However, its role in prognosis and therapeutics of PDAC is still unclear. In this study, we applied bioinformatics approaches, and integrated publicly available resources, to investigate the role of SMAD4 gene deletion in PDAC. We found that SMAD4 deletion was associated with poorer disease-free, but not overall, survival in PDAC patients. Cancer hallmark enrichment and pathway analysis suggested that the upregulation of cell cycle-related genes in SMAD4-deleted PDAC. Chemotherapy response profiling of PDAC cell lines and patient-derived organoids revealed that SMAD4-deleted PDAC was sensitive to gemcitabine, the first-line treatment for PDAC, and specific cell cycle-targeting drugs. Taken together, our study provides an insight into the prognostic and therapeutic roles of SMAD4 gene deletion in PDAC, and SMAD4 gene copy numbers may be used as a therapeutic biomarker for PDAC treatment.

LSD1 Inhibition Attenuates Tumor Growth by Disrupting PLK1 Mitotic Pathway

Lysine-specific demethylase 1 (LSD1) is a histone modifier that is highly overexpressed in lung adenocarcinoma, which results in aggressive tumor biology. Tumor cell proliferation and migration analysis after LSD1 inhibition in the lung adenocarcinoma cell line PC9, using the LSD1 inhibitor HCI-2509 and siRNA, demonstrated that LSD1 activity was essential for proliferation and migration capacities of tumor cells. Moreover, reduced proliferation rates after LSD1 inhibition were shown to be associated with a cell-cycle arrest of the tumor cells in the G2-M-phase. Expression profiling followed by functional classification and pathway analysis indicated prominent repression of the polo-like kinase 1 (PLK1) pathway upon LSD1 inhibition. In contrast, transient overexpression of exogenous PLK1 plasmid rescued the LSD1 inhibition-mediated downregulation of PLK1 pathway genes. Mechanistically, LSD1 directly regulates expression of PLK1 by binding to its promoter region that subsequently affects expression of its downstream target genes. Notably, using lung adenocarcinoma TCGA datasets a significant correlation between LSD1 and PLK1 along with its downstream targets was observed. Furthermore, the LSD1/PLK1 linkage was confirmed by IHC analysis in a clinical lung adenocarcinoma cohort (n = 43). Conclusively, this is the first study showing a direct transcriptional link between LSD1 and PLK1. IMPLICATIONS: These findings point to a role of LSD1 in regulating PLK1 and thus efficient G2-M-transition-mediating proliferation of tumor cells and suggest targeting the LSD1/PLK1 axis as a novel therapeutic approach for lung adenocarcinoma treatment.

Cep85 Relays Plk1 Activity to Phosphorylated Nek2A for Its Timely Activation in Centrosome Disjunction

Timely centrosome separation is critical for accurate chromosome separation. It is initiated by Nek2A at the onset of mitosis, but the mechanism for the strict requirement of phosphorylated Nek2A for its own activation remains unclear. In this study, we have found that Plk1 interacts with Cep85 and forms a ternary complex with Cep85-Nek2A. Nek2A binding, but not its kinase activity, is pre-required for Cep85 to be phosphorylated by Plk1. Nek2A-dependent Cep85 phosphorylation, in turn, leads to the dissociation of phosphorylated Cep85 exclusively from phospho-Nek2A, thereby increasing the freed phospho-Nek2A activity. Both kinases are also required for phosphorylating endogenous Cep85 in cells, and timely phosphorylation of Cep85 and Nek2A is crucial for initiating centrosome disjunction at G2/M. Overall, our study has uncovered a previously unrecognized role of Plk1 and Nek2A and identified Cep85 as a missing piece directly relaying Plk1 activity to Nek2A for its activation in centrosome disjunction.

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Cep85 prevents centrosome separation by binding to and inhibiting Nek2A in interphase

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Plk1 binds to Cep85 and forms a ternary Plk1-Cep85-Nek2A complex in late G2

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Nek2A-assisting Cep85 phosphorylation by Plk1 releases phospho-Nek2A from Cep85

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Freed phospho-Nek2A initiates centrosome separation in G2/M

Hepatitis B virus X protein promotes DNA damage propagation through disruption of liver polyploidization and enhances hepatocellular carcinoma initiation

Hepatitis B virus X protein (HBx) contributes to Hepatitis B virus (HBV)-related liver cancer. However, its impact on hepatocyte proliferation and genomic stability remains elusive. We studied the role of HBx expression on the progression of cell cycle and liver polyploidization during proliferation and liver carcinogenesis. Full-length HBx transgenic mice (FL-HBx) were developed to investigate liver ploidy as well as hepatocyte proliferation, along normal liver maturation and during cancer initiation (chemical carcinogen treatment). Investigation of postnatal liver development in FL-HBx showed an aberrant G1/S and G2/M transitions, triggered (1) a delay of the formation of hepatocytes binucleation, (2) the early synthesis of polyploidy nuclei (≥4n) and (3) DNA damage appearance. Moreover, HBV infection during hepatocytes proliferation in a humanized liver mouse model led, to modifications in polyploidy of hepatocytes. In initiation of hepatocellular carcinoma, FL-HBx protein decreased ChK1 phosphorylation, Mre11 and Rad51 expression, upregulated IL-6 expression and impaired apoptosis. This was related to DNA damage accumulation in FL-HBx mice. At day 75 after initiation of hepatocellular carcinoma, FL-HBx mice revealed significant cell cycle changes related to the increased amount of 4n nuclei and of markers of cancer progenitor cells. Finally, PLK1 upregulation and p38/ERK activation in FL-HBx mice were implicated in aberrant polyploidization favoring DNA damage propagation and hepatocyte transformation. In conclusion, our data indicate that FL-HBx protein increases DNA damage through the hijack of hepatocyte polyploidization. That leads to enhancement of hepatocellular carcinoma initiation in an inflammatory context.

CKAP2 expression is associated with glioma tumor growth and acts as a prognostic factor in high‑grade glioma

Cytoskeletal‑associated protein 2 (CKAP2), which is also known as tumor‑associated microtubule‑associated protein, has been reported to be dysregulated in various types of human cancer. However, the role of CKAP2 in glioma has not been fully elucidated. The present study evaluated the expression pattern of CKAP2 using the Chinese Glioma Genome Atlas microarray database, which included 301 patients, and validated the findings using The Cancer Genome Atlas RNA sequencing database. Kaplan‑Meier survival analysis, and univariate and multivariate Cox analyses, were used to estimate survival distributions. Furthermore, the biological implication of aberrant CKAP2 expression in high‑grade glioma (HGG) was investigated using Gene Ontology analysis, gene set enrichment analysis, gene set variation analysis and STRING. The results indicated that patients with HGG exhibited significantly higher CKAP2 expression levels compared with patients with low‑grade glioma in both databases. Higher expression levels of CKAP2 were significantly associated with shorter overall survival and progression‑free survival of patients with HGG. Furthermore, CKAP2 was also positively correlated with known malignant factors, including high Ki67 expression and phosphatase and tensin homolog mutations. The univariate and multivariate Cox regression analyses demonstrated that CKAP2 may be a novel independent prognostic biomarker for patients with HGG. Functional assays also indicated that CKAP2 was closely associated with the cell cycle, mitosis and cell proliferation. These results suggested that CKAP2 may be associated with tumor growth and could serve as an independent prognostic factor, particularly in patients with HGG.

A unified view of spatio-temporal control of mitotic entry: Polo kinase as the key

The Polo kinase is an essential regulator of cell division. Its ability to regulate multiple events at distinct subcellular locations and times during mitosis is remarkable. In the last few years, a much clearer mechanistic understanding of the functions and regulation of Polo in cell division has emerged. In this regard, the importance of coupling changes in activity with changes in localization is striking, both for Polo itself and for its upstream regulators. This review brings together several new pieces of the puzzle that are gradually revealing how Polo is regulated, in space and time, to enable its functions in the early stages of mitosis in animal cells. As a result, a unified view of how mitotic entry is spatio-temporally regulated is emerging.

Effects of Sepantronium Bromide (YM-155) on the Whole Transcriptome of MDA-MB-231 Cells: Highlight on Impaired ATR/ATM Fanconi Anemia DNA Damage Response

Sepantronium bromide (YM-155) is believed to elicit apoptosis and mitotic arrest in tumor cells by reducing (BIRC5, survivin) mRNA. In this study, we monitored changes in survivin mRNA and protein after treating MDA-MB-231 cells with YM-155 concurrent with evaluation of whole transcriptomic (WT) mRNA and long intergenic non-coding RNA at 2 time points: 8 h sub-lethal (83 ng/mL) and 20 h at the LC50 (14.6 ng/mL). The data show a tight association between cell death and the precipitating loss of survivin protein and mRNA (-2.67 fold-change (FC), p<0.001) at 20 h, questioning if the decline in survivin is attributed to cell death or drug impact. The meager loss of survivin mRNA was overshadowed by enormous differential change to the WT in both magnitude and significance for over 2000 differentially up/down-regulated transcripts: (+22 FC to -12 FC, p<0.001). The data show YM-155 to up-regulate transcripts in control of circadian rhythm (NOCT, PER, BHLHe40, NFIL3), tumor suppression (SIK1, FOSB), histone methylation (KDM6B) and negative feedback of NF-kappa B signaling (TNFAIP3). Down-regulated transcripts by YM-155 include glucuronidase (GUSBP3), numerous micro-RNAs, DNA damage repair elements (CENPI, POLQ, RAD54B) and the most affected system was the ataxia-telangiectasia mutated (ATM)/Fanconi anemia E3 monoubiquitin ligase core complexes (FANC transcripts - A/B/E/F/G/M), FANC2, FANCI, BRCA1, BRCA2, RAD51, PALB2 gene and ATR (ATM- and Rad3-Related) pathway. In conclusion, these findings suggest that a primary target of YM-155 is the loss of replicative DNA repair systems.

Fluorescence techniques in developmental biology

Advanced fluorescence techniques, commonly known as the F-techniques, measure the kinetics and the interactions of biomolecules with high sensitivity and spatiotemporal resolution. Applications of the F-techniques, which were initially limited to cells, were further extended to study in vivo protein organization and dynamics in whole organisms. The integration of F-techniques with multi-photon microscopy and light-sheet microscopy widened their applications in the field of developmental biology. It became possible to penetrate the thick tissues of living organisms and obtain good signal-to-noise ratio with reduced photo-induced toxicity. In this review, we discuss the principle and the applications of the three most commonly used F-techniques in developmental biology: Fluorescence Recovery After Photo-bleaching (FRAP), Fo¨ rster Resonance Energy Transfer (FRET), and Fluorescence Correlation and Cross-Correlation Spectroscopy (FCS and FCCS).

The therapeutic potential of cell cycle targeting in multiple myeloma

Proper cell cycle progression through the interphase and mitosis is regulated by coordinated activation of important cell cycle proteins (including cyclin-dependent kinases and mitotic kinases) and several checkpoint pathways. Aberrant activity of these cell cycle proteins and checkpoint pathways results in deregulation of cell cycle progression, which is one of the key hallmarks of cancer. Consequently, intensive research on targeting these cell cycle regulatory proteins identified several candidate small molecule inhibitors that are able to induce cell cycle arrest and even apoptosis in cancer cells. Importantly, several of these cell cycle regulatory proteins have also been proposed as therapeutic targets in the plasma cell malignancy multiple myeloma (MM). Despite the enormous progress in the treatment of MM the past 5 years, MM still remains most often incurable due to the development of drug resistance. Deregulated expression of the cyclins D is observed in virtually all myeloma patients, emphasizing the potential therapeutic interest of cyclin-dependent kinase inhibitors in MM. Furthermore, other targets have also been identified in MM, such as microtubules, kinesin motor proteins, aurora kinases, polo-like kinases and the anaphase promoting complex/cyclosome. This review will provide an overview of the cell cycle proteins and checkpoint pathways deregulated in MM and discuss the therapeutic potential of targeting proteins or protein complexes involved in cell cycle control in MM.