Active cyclin B1-Cdk1 first appears on centrosomes in prophase

Spatial control of the APC/C ensures the rapid degradation of cyclin B1

The proper control of mitosis depends on the ubiquitin-mediated degradation of the right mitotic regulator at the right time. This is effected by the Anaphase Promoting Complex/Cyclosome (APC/C) ubiquitin ligase that is regulated by the Spindle Assembly Checkpoint (SAC). The SAC prevents the APC/C from recognising Cyclin B1, the essential anaphase and cytokinesis inhibitor, until all chromosomes are attached to the spindle. Once chromosomes are attached, Cyclin B1 is rapidly degraded to enable chromosome segregation and cytokinesis. We have a good understanding of how the SAC inhibits the APC/C, but relatively little is known about how the APC/C recognises Cyclin B1 as soon as the SAC is turned off. Here, by combining live-cell imaging, in vitro reconstitution biochemistry, and structural analysis by cryo-electron microscopy, we provide evidence that the rapid recognition of Cyclin B1 in metaphase requires spatial regulation of the APC/C. Using fluorescence cross-correlation spectroscopy, we find that Cyclin B1 and the APC/C primarily interact at the mitotic apparatus. We show that this is because Cyclin B1, like the APC/C, binds to nucleosomes, and identify an 'arginine-anchor' in the N-terminus as necessary and sufficient for binding to the nucleosome. Mutating the arginine anchor on Cyclin B1 reduces its interaction with the APC/C and delays its degradation: cells with the mutant, non-nucleosome-binding Cyclin B1 become aneuploid, demonstrating the physiological relevance of our findings. Together, our data demonstrate that mitotic chromosomes promote the efficient interaction between Cyclin B1 and the APC/C to ensure the timely degradation of Cyclin B1 and genomic stability.

Cryo-EM structure of the CDK2-cyclin A-CDC25A complex

The cell division cycle 25 phosphatases CDC25A, B and C regulate cell cycle transitions by dephosphorylating residues in the conserved glycine-rich loop of CDKs to activate their activity. Here, we present the cryo-EM structure of CDK2-cyclin A in complex with CDC25A at 2.7 Å resolution, providing a detailed structural analysis of the overall complex architecture and key protein-protein interactions that underpin this 86 kDa complex. We further identify a CDC25A C-terminal helix that is critical for complex formation. Sequence conservation analysis suggests CDK1/2-cyclin A, CDK1-cyclin B and CDK2/3-cyclin E are suitable binding partners for CDC25A, whilst CDK4/6-cyclin D complexes appear unlikely substrates. A comparative structural analysis of CDK-containing complexes also confirms the functional importance of the conserved CDK1/2 GDSEID motif. This structure improves our understanding of the roles of CDC25 phosphatases in CDK regulation and may inform the development of CDC25-targeting anticancer strategies.

Cyclin A/B RxL Macrocyclic Inhibitors to Treat Cancers with High E2F Activity

Cancer cell proliferation requires precise control of E2F1 activity; excess activity promotes apoptosis. Here, we developed cell-permeable and bioavailable macrocycles that selectively kill small cell lung cancer (SCLC) cells with inherent high E2F1 activity by blocking RxL-mediated interactions of cyclin A and cyclin B with select substrates. Genome-wide CRISPR/Cas9 knockout and random mutagenesis screens found that cyclin A/B RxL macrocyclic inhibitors (cyclin A/Bi) induced apoptosis paradoxically by cyclin B- and Cdk2-dependent spindle assembly checkpoint activation (SAC). Mechanistically, cyclin A/Bi hyperactivate E2F1 and cyclin B by blocking their RxL-interactions with cyclin A and Myt1, respectively, ultimately leading to SAC activation and mitotic cell death. Base editor screens identified cyclin B variants that confer cyclin A/Bi resistance including several variants that disrupted cyclin B:Cdk interactions. Unexpectedly but consistent with our base editor and knockout screens, cyclin A/Bi induced the formation of neo-morphic Cdk2-cyclin B complexes that promote SAC activation and apoptosis. Finally, orally-bioavailable cyclin A/Bi robustly inhibited tumor growth in chemotherapy-resistant patient-derived xenograft models of SCLC. This work uncovers gain-of-function mechanisms by which cyclin A/Bi induce apoptosis in cancers with high E2F activity, and suggests cyclin A/Bi as a therapeutic strategy for SCLC and other cancers driven by high E2F activity.

The centrosome: a critical hub for cell cycle regulation

Cyclins and cyclin-dependent kinases (CDKs) localize to the centrosome, but their significance in the cell cycle is unclear. Recently, Roberts et al. revealed that centrosomal cyclin B-CDK is required for mitotic entry and phosphorylation of substrates. This suggests that the centrosome acts as a signaling hub controlling the cell cycle.

Spatiotemporal regulation of plant cell division

Plant morphogenesis largely depends on the orientation and rate of cell division and elongation, and their coordination at all levels of organization. Despite recent progresses in the comprehension of pathways controlling division plane determination in plant cells, many pieces are missing to the puzzle. For example, we have a partial comprehension of formation, function and evolutionary significance of the preprophase band, a plant-specific cytoskeletal array involved in premitotic setup of the division plane, as well as the role of the nucleus and its connection to the preprophase band of microtubules. Likewise, several modeling studies point to a strong relationship between cell shape and division geometry, but the emergence of such geometric rules from the molecular and cellular pathways at play are still obscure. Yet, recent imaging technologies and genetic tools hold a lot of promise to tackle these challenges and to revisit old questions with unprecedented resolution in space and time.

CDK activity at the centrosome regulates the cell cycle

In human cells and yeast, an intact "hydrophobic patch" substrate docking site is needed for mitotic cyclin centrosomal localization. A hydrophobic patch mutant (HPM) of the fission yeast mitotic cyclin Cdc13 cannot enter mitosis, but whether this is due to defective centrosomal localization or defective cyclin-substrate docking more widely is unknown. Here, we show that artificially restoring Cdc13-HPM centrosomal localization promotes mitotic entry and increases CDK (cyclin-dependent kinase) substrate phosphorylation at the centrosome and in the cytoplasm. We also show that the S-phase B-cyclin hydrophobic patch is required for centrosomal localization but not for S phase. We propose that the hydrophobic patch is essential for mitosis due to its requirement for the local concentration of cyclin-CDK with CDK substrates and regulators at the centrosome. Our findings emphasize the central importance of the centrosome as a hub coordinating cell-cycle control and explain why the cyclin hydrophobic patch is essential for mitosis.

Interplay between paclitaxel, gap junctions, and kinases: unraveling mechanisms of action and resistance in cancer therapy

This comprehensive review elucidates the multifaceted roles of paclitaxel, a key chemotherapeutic agent, in cancer therapy, with a focus on its interactions with gap junctions and related kinases. Paclitaxel, with its complex diterpene structure, mediates its anticancer effects predominantly through specific interactions with β-tubulin, instigating cell cycle arrest and triggering various cell death pathways, including apoptosis, pyroptosis, ferroptosis, and necroptosis. The paper systematically delineates the chemical attributes and action mechanisms of paclitaxel and its analogs, underscoring their capacity to disrupt microtubule dynamics, thereby leading to mitotic arrest and subsequent cell death induction. It also scrutinizes the pivotal role of gap junctions, composed of connexin proteins, in the modulation of cancer cell behavior and chemoresistance, especially in the milieu of paclitaxel administration. The review articulates how gap junctions can either suppress tumors or contribute to cancer progression, thereby influencing chemotherapy outcomes. Furthermore, the paper provides an in-depth analysis of how paclitaxel modulates gap junction-associated kinases via phosphorylation, influencing the drug's therapeutic efficacy and resistance profiles. By integrating insights from numerous key studies, the review offers a comprehensive understanding of the interplay between paclitaxel, gap junctions, and kinases, shedding light on potential approaches to augment paclitaxel's anti-tumor effectiveness and counteract chemoresistance in cancer treatment.

Transcriptome analysis of meiotic and post-meiotic spermatogenic cells reveals the potential hub genes of aging on the decline of male fertility

Genetic and epigenetic changes in sperm caused by male aging may be essential factors affecting semen parameters, but the effects and specific molecular mechanisms of aging on male reproduction have not been fully clarified. In this study, to explore the effect of aging on male fertility and seek the potential molecular etiology, we performed high-throughput RNA-sequencing in isolated spermatogenic cells, including pachytene spermatocytes (marked by the completion of chromosome synapsis) and round spermatids (produced by the separation of sister chromatids) from the elderly and the young men. Functional enrichment analysis of differentially expressed genes (DEGs) in round spermatids between the elderly and young showed that they were significantly enriched in gamete generation, spindle assembly, and cilium movement involved in cell motility. In addition, the expression levels of DEGs in round spermatids (post-meiotic cells) were found to be more susceptible to age. Furthermore, ten genes (AURKA, CCNB1, CDC20, CCNB2, KIF2C, KIAA0101, NR5A1, PLK1, PTTG1, RAD51AP1) were identified to be the hub genes involved in the regulation of sperm quality in the elderly through Protein-Protein Interaction (PPI) network construction and measuring semantic among GO terms and gene products. Our data provide aging-related molecular alterations in meiotic and post-meiotic spermatogenic cells, and the information gained from this study may explain the abnormal aging-related male fertility decline.

CSTB accelerates the progression of hepatocellular carcinoma via the ERK/AKT/mTOR signaling pathway

Hepatocellular carcinoma (HCC) is a significant contributor to global cancer-related deaths, leading to high mortality rates. However, the pathogenesis of HCC remains unclear. In this research, by the bioinformatics data analysis, we found that elevated CSTB expression correlated with advanced disease and predicted diminished overall survival (OS) in HCC patients. We subsequently verified the oncogenic role of CSTB as well as the potential underlying mechanisms in HCC through a series of in vitro experiments, such as CCK-8 assays, cloning assays, flow cytometry, Transwell assays, and western blotting. Our findings illustrated that the silencing of CSTB effectively suppressed cellular proliferation by inducing cell cycle arrest in the G2 phase and impaired HCC cell invasion and migration by stimulating epithelial-mesenchymal transition (EMT). Additionally, we analyzed the pathways enriched in HCC using RNA sequencing and found that the ERK/AKT/mTOR signaling pathway was related to increased CSTB expression in HCC. Finally, we confirmed the tumorigenic role of CSTB via in vivo experiments. Thus, our findings revealed that silencing CSTB inhibited the HCC progression via the ERK/AKT/mTOR signaling pathway, highlighting new perspectives for investigating the mechanisms of HCC.

BubR1 and cyclin B1 immunoexpression in pleomorphic adenoma and polymorphous adenocarcinoma of minor salivary glands

The immunoexpression of BubR1 and cyclin B1 in pleomorphic adenoma (PA) and polymorphic adenocarcinoma (PAC) in minor salivary glands is poorly studied. Thus, a retrospective and observational study was performed to provide a better understanding of the role and immunopositivity patterns of these proteins in these lesions. Sixteen cases of PA and 16 cases of PAC were selected. Parenchyma cells were submitted to quantitative immunohistochemical analysis through the labeling index. Cytoplasmic immunoexpression of BubR1 was observed in neoplastic cells from all analyzed PA and PAC cases. All PA cases and 93.7% of PAC exhibited nuclear immunoexpression of BubR1. Higher cytoplasmic and nuclear immunoexpression of BubR1 was observed in PAC (p = 0.001 and p = 0.122, respectively). Cytoplasmic immunoexpression of cyclin B1 was observed in all cases of PA and PAC, with a higher labeling index in the latter (p < 0.001). There was a significant positive correlation between nuclear and cytoplasmic BubR1 immunoexpressions (p < 0.001) in PA and a significant negative correlation between BubR1 and cyclin B1 cytoplasmic immunoexpressions (p = 0.014) in PAC. The higher cytoplasmic and nuclear immunoexpression of BubR1 in PACs suggests the continuous maintenance of neoplastic cells in the cell cycle and migration. Higher immunoexpression of cyclin B1 supports this lesion's enhanced proliferative and migration ability.

The Impact of Centrosome Pathologies on Ovarian Cancer Development and Progression with a Focus on Centrosomes as Therapeutic Target

The impact of centrosome abnormalities on cancer cell proliferation has been recognized as early as 1914 (Boveri, Zur Frage der Entstehung maligner Tumoren. Jena: G. Fisher, 1914), but vigorous research on molecular levels has only recently started when it became fully apparent that centrosomes can be targeted for new cancer therapies. While best known for their microtubule-organizing capabilities as MTOC (microtubule organizing center) in interphase and mitosis, centrosomes are now further well known for a variety of different functions, some of which are related to microtubule organization and consequential activities such as cell division, migration, maintenance of cell shape, and vesicle transport powered by motor proteins, while other functions include essential roles in cell cycle regulation, metabolic activities, signal transduction, proteolytic activity, and several others that are now heavily being investigated for their role in diseases and disorders (reviewed in Schatten and Sun, Histochem Cell Biol 150:303-325, 2018; Schatten, Adv Anat Embryol Cell Biol 235:43-50, 2022a; Schatten, Adv Anat Embryol Cell Biol 235:17-35, 2022b).Cancer cell centrosomes differ from centrosomes in noncancer cells in displaying specific abnormalities that include phosphorylation abnormalities, overexpression of specific centrosomal proteins, abnormalities in centriole and centrosome duplication, formation of multipolar spindles that play a role in aneuploidy and genomic instability, and several others that are highlighted in the present review on ovarian cancer. Ovarian cancer cell centrosomes, like those in other cancers, display complex abnormalities that in part are based on the heterogeneity of cells in the cancer tissues resulting from different etiologies of individual cancer cells that will be discussed in more detail in this chapter.Because of the critical role of centrosomes in cancer cell proliferation, several lines of research are being pursued to target centrosomes for therapeutic intervention to inhibit abnormal cancer cell proliferation and control tumor progression. Specific centrosome abnormalities observed in ovarian cancer will be addressed in this chapter with a focus on targeting such aberrations for ovarian cancer-specific therapies.

Vinculin is required for interkinetic nuclear migration (INM) and cell cycle progression

Vinculin is an actin-binding protein (ABP) that strengthens the connection between the actin cytoskeleton and adhesion complexes. It binds to β-catenin/N-cadherin complexes in apical adherens junctions (AJs), which maintain cell-to-cell adhesions, and to talin/integrins in the focal adhesions (FAs) that attach cells to the basal membrane. Here, we demonstrate that β-catenin targets vinculin to the apical AJs and the centrosome in the embryonic neural tube (NT). Suppression of vinculin slows down the basal-to-apical part of interkinetic nuclear migration (BAINM), arrests neural stem cells (NSCs) in the G2 phase of the cell cycle, and ultimately dismantles the apical actin cytoskeleton. In the NSCs, mitosis initiates when an internalized centrosome gathers with the nucleus during BAINM. Notably, our results show that the first centrosome to be internalized is the daughter centrosome, where β-catenin and vinculin accumulate, and that vinculin suppression prevents centrosome internalization. Thus, we propose that vinculin links AJs, the centrosome, and the actin cytoskeleton where actomyosin contraction forces are required.

Cytoplasmic SIRT1 promotes paclitaxel resistance in ovarian carcinoma through increased formation and survival of polyploid giant cancer cells

Therapeutic resistance is a notable cause of death in patients with ovarian carcinoma. Polyploid giant cancer cells (PGCCs), commonly arising in tumor tissues following chemotherapy, have recently been considered to contribute to drug resistance. As a type III deacetylase, Sirtuin1 (SIRT1) plays essential roles in the cell cycle, cellular senescence, and drug resistance. Accumulating evidence has suggested that alteration in its subcellular localization via nucleocytoplasmic shuttling is a critical process influencing the functions of SIRT1. However, the roles of SIRT1 subcellular localization in PGCC formation and subsequent senescence escape remain unclear. In this study, we compared the differences in the polyploid cell population and senescence state of PGCCs following paclitaxel treatment between tumor cells overexpressing wild-type SIRT1 (WT SIRT1) and those expressing nuclear localization sequence (NLS)-mutated SIRT1 (SIRT1NLSmt ). We investigated the involvement of cytoplasmic SIRT1 in biological processes and signaling pathways, including the cell cycle and cellular senescence, in ovarian carcinoma cells' response to paclitaxel treatment. We found that the SIRT1NLSmt tumor cell population contained more polyploid cells and fewer senescent PGCCs than the SIRT1-overexpressing tumor cell population. Comparative proteomic analyses using co-immunoprecipitation (Co-IP) combined with liquid chromatography-mass spectrometry (LC-MS)/MS showed the differences in the differentially expressed proteins related to PGCC formation, cell growth, and death, including CDK1 and CDK2, between SIRT1NLSmt and SIRT1 cells or PGCCs. Our results suggested that ovarian carcinoma cells utilize polyploidy formation as a survival mechanism during exposure to paclitaxel-based treatment via the effect of cytoplasmic SIRT1 on PGCC formation and survival, thereby boosting paclitaxel resistance. © 2023 The Pathological Society of Great Britain and Ireland.

In Silico Mixed Ligand/Structure-Based Design of New CDK-1/PARP-1 Dual Inhibitors as Anti-Breast Cancer Agents

CDK-1 and PARP-1 play crucial roles in breast cancer progression. Compounds acting as CDK-1 and/or PARP-1 inhibitors can induct cell death in breast cancer with a selective synthetic lethality mechanism. A mixed treatment by means of CDK-1 and PARP-1 inhibitors resulted in radical breast cancer cell growth reduction. Inhibitors with a dual target mechanism of action could arrest cancer progression by simultaneously blocking the DNA repair mechanism and cell cycle, resulting in advantageous monotherapy. To this aim, in the present work, we identified compound 645656 with a significant affinity for both CDK-1 and PARP-1 by a mixed ligand- and structure-based virtual screening protocol. The Biotarget Predictor Tool was used at first in a Multitarget mode to filter the large National Cancer Institute (NCI) database. Then, hierarchical docking studies were performed to further screen the compounds and evaluate the ligands binding mode, whose putative dual-target mechanism of action was investigated through the correlation between the antiproliferative activity data and the target proteins' (CDK-1 and PARP-1) expression pattern. Finally, a Molecular Dynamics Simulation confirmed the high stability of the most effective selected compound 645656 in complex with both PARP-1 and CDK-1.

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.

MYO10 regulates genome stability and cancer inflammation through mediating mitosis

Genomic instability can promote inflammation and tumor development. Previous research revealed an unexpected layer of regulation of genomic instability by a cytoplasmic protein MYO10; however, the underlying mechanism remained unclear. Here, we report a protein stability-mediated mitotic regulation of MYO10 in controlling genome stability. We characterized a degron motif and phosphorylation residues in the degron that mediate β-TrCP1-dependent MYO10 degradation. The level of phosphorylated MYO10 protein transiently increases during mitosis, which is accompanied by a spatiotemporal cellular localization change first accumulating at the centrosome then at the midbody. Depletion of MYO10 or expression of MYO10 degron mutants, including those found in cancer patients, disrupts mitosis, increases genomic instability and inflammation, and promotes tumor growth; however, they also increase the sensitivity of cancer cells to Taxol. Our studies demonstrate a critical role of MYO10 in mitosis progression, through which it regulates genome stability, cancer growth, and cellular response to mitotic toxins.

Cyclins and cyclin-dependent kinases: from biology to tumorigenesis and therapeutic opportunities

The discussion on cell proliferation cannot be continued without taking a look at the cell cycle regulatory machinery. Cyclin-dependent kinases (CDKs), cyclins, and CDK inhibitors (CKIs) are valuable members of this system and their equilibrium guarantees the proper progression of the cell cycle. As expected, any dysregulation in the expression or function of these components can provide a platform for excessive cell proliferation leading to tumorigenesis. The high frequency of CDK abnormalities in human cancers, together with their druggable structure has raised the possibility that perhaps designing a series of inhibitors targeting CDKs might be advantageous for restricting the survival of tumor cells; however, their application has faced a serious concern, since these groups of serine-threonine kinases possess non-canonical functions as well. In the present review, we aimed to take a look at the biology of CDKs and then magnify their contribution to tumorigenesis. Then, by arguing the bright and dark aspects of CDK inhibition in the treatment of human cancers, we intend to reach a consensus on the application of these inhibitors in clinical settings.

On the assembly of the mitotic spindle, bistability and hysteresis

During cell division, the transition from interphase to mitosis is dictated by activation of the cyclin B-cdk1 (Cdk1) complex, master mitotic kinase. During interphase, Cdk1 accumulates in an inactive state (pre-Cdk1). When Cdk1 overcomes a certain threshold of activity upon initial activation of pre-Cdk1, then the stockpiled pre-Cdk1 is rapidly converted into overshooting active Cdk1, and mitosis is established irreversibly in a switch-like fashion. This is granted by positive Cdk1 activation loops and the concomitant inactivation of Cdk1 counteracting phosphatases, empowering Cdk1 activity and favoring the Cdk1-dependent phosphorylations that are required to establish mitosis. These circuitries prevent backtracking and ensure unidirectionality so that interphase and mitosis are considered bistable states. Mitosis also shows hysteresis, meaning that the levels of Cdk1 activity needed to establish mitosis are higher than those required to maintain it; therefore, once in mitosis cells can tolerate moderate drops in Cdk1 activity without exiting mitosis. Whether these features have other functional implications in addition to the general action of preventing backtracking is unknown. Here, we contextualize these concepts in the view of recent evidence indicating that loss of activity of small and compartmentalized amounts of Cdk1 within mitosis is necessary to assemble the mitotic spindle, the structure required to segregate replicated chromosomes. We further propose that, in addition to prevent backtracking, the stability and hysteresis properties of mitosis are also essential to move forward in mitosis by allowing cells to bear small, localized, drops in Cdk1 activity that are necessary to build the mitotic spindle.

Anti-Leukaemic Activity of Rilpivirine Is Mediated by Aurora A Kinase Inhibition

Acute myeloid leukaemia (AML) affects predominantly elderly people and has an incidence of 1% of all cancers and 2% of all cancer deaths. Despite using intensive chemotherapy and allogeneic stem cell transplantation, the treatment options for AML remain open for innovation. Thus, there is a need to explore alternative therapies such as less toxic targeted therapies in AML. Aurora A kinase is a well-established target for the treatment of various cancers, including AML. This kinase plays a pivotal role in the cell-division cycle, particularly in different stages of mitosis, and is also involved in many other cellular regulatory processes. In a previous study, we demonstrated that the anti-viral drug rilpivirine is an Aurora A kinase inhibitor. In the current study, we have further explored the selectivity of rilpivirine for Aurora A kinase inhibition by testing this drug against a panel of 429 kinases. Concurrently, we demonstrated that rilpivirine significantly inhibited the proliferation of AML cells in a time- and concentration-dependent manner that was preceded by G₂/M cell-cycle arrest leading to the induction of apoptosis. Consistent with its kinase inhibitory role, rilpivirine modulated the expression of critical proteins in the Aurora A kinase-signalling pathway. Importantly, orally administered rilpivirine significantly inhibited tumour growth in an HL-60 xenograft model without showing body weight changes or other clinical signs of toxicity. Furthermore, rilpivirine enhanced the anti-proliferative efficacy of the conventional anti-leukaemic chemotherapeutic agent cytarabine. Collectively, these findings provide the stimulus to explore further the anti-leukaemic activity of the anti-viral drug rilpivirine.

Piperine-Chlorogenic Acid Hybrid Inhibits the Proliferation of the SK-MEL-147 Melanoma Cells by Modulating Mitotic Kinases

Melanoma is considered the most aggressive form of skin cancer, showing high metastatic potential and persistent high mortality rates despite the introduction of immunotherapy and targeted therapies. Thus, it is important to identify new drug candidates for melanoma. The design of hybrid molecules, with different pharmacophore fragments combined in the same scaffold, is an interesting strategy for obtaining new multi-target and more effective anticancer drugs. We designed nine hybrid compounds bearing piperine and chlorogenic acid pharmacophoric groups and evaluated their antitumoral potential on melanoma cells with distinct mutational profiles SK-MEL-147, CHL-1 and WM1366. We identified the compound named PQM-277 (3a) to be the most cytotoxic one, inhibiting mitosis progression and promoting an accumulation of cells in pro-metaphase and metaphase by altering the expression of genes that govern G2/M transition and mitosis onset. Compound 3a downregulated FOXM1, CCNB1, CDK1, AURKA, AURKB, and PLK1, and upregulated CDKN1A. Molecular docking showed that 3a could interact with the CUL1-RBX1 complex, which activity is necessary to trigger molecular events essential for FOXM1 transactivation and, in turn, G2/M gene expression. In addition, compound 3a effectively induced apoptosis by increasing BAX/BCL2 ratio. Our findings demonstrate that 3a is an important antitumor candidate prototype and support further investigations to evaluate its potential for melanoma treatment, especially for refractory cases to BRAF/MEK inhibitors.

Biodegradable Carbon Dioxide-Derived Non-Viral Gene Vectors for Osteosarcoma Gene Therapy

Osteosarcoma often occurs in children and adolescents with high invasiveness and high mortality. Polo-like kinase 1 (PLK1) overexpressed in most tumors promotes cancer cell proliferation and transformation. PLK1 is considered as a therapeutic target for osteosarcoma. RNA interference-based therapies are employed to combat osteosarcoma through silencing PLK1 gene expression. However, the treatment results remain unsatisfactory due to the lack of a safe and efficient nonviral gene vector. To tackle this hurdle, biodegradable and CO₂ -derivative cationic poly(vinylcyclohexene carbonates) (CPCHCs) are used as gene vectors to perform a siPLK1 therapeutic strategy for osteosarcoma treatment. Of those CPCHCs, CPCHC60 demonstrates the most excellent performance in gene transfection efficiency, endo-lysosome escaping, biodegradability, and biosafety. With the treatment of CPCHCs/siRNA nanoparticles, the expression level of PLK1 gene in osteosarcoma cells is significantly down-regulated. Subsequently, cells are arrested in the G₂ /M phase and subsequently dead in the form of apoptosis, resulting in significant tumor regression both in vitro and in vivo. This study brings a new insight into the development of superior nonviral gene vectors for practical cancer treatment. Based on the results, the resulting nanoparticle-based gene drug formation is considered to have a highly successful chance in further translational nanomedicine applications.

G2/M checkpoint regulation and apoptosis facilitate the nuclear egress of parvoviral capsids

The nuclear export factor CRM1-mediated pathway is known to be important for the nuclear egress of progeny parvovirus capsids in the host cells with virus-mediated cell cycle arrest at G2/M. However, it is still unclear whether this is the only pathway by which capsids exit the nucleus. Our studies show that the nuclear egress of DNA-containing full canine parvovirus. capsids was reduced but not fully inhibited when CRM1-mediated nuclear export was prevented by leptomycin B. This suggests that canine parvovirus capsids might use additional routes for nuclear escape. This hypothesis was further supported by our findings that nuclear envelope (NE) permeability was increased at the late stages of infection. Inhibitors of cell cycle regulatory protein cyclin-dependent kinase 1 (Cdk1) and pro-apoptotic caspase 3 prevented the NE leakage. The change in NE permeability could be explained by the regulation of the G2/M checkpoint which is accompanied by early mitotic and apoptotic events. The model of G2/M checkpoint activation was supported by infection-induced nuclear accumulation of cyclin B1 and Cdk1. Both NE permeability and nuclear egress of capsids were reduced by the inhibition of Cdk1. Additional proof of checkpoint function regulation and promotion of apoptotic events was the nucleocytoplasmic redistribution of nuclear transport factors, importins, and Ran, in late infection. Consistent with our findings, post-translational histone acetylation that promotes the regulation of several genes related to cell cycle transition and arrest was detected. In conclusion, the model we propose implies that parvoviral capsid egress partially depends on infection-induced G2/M checkpoint regulation involving early mitotic and apoptotic events.

In silico analysis of a Skp1 protein homolog from the human pathogen E. histolytica

SCF complex consisting of Skp1, Cullins, F-box proteins, is the largest family of E3 ubiquitin ligases that promotes ubiquitination of many substrate proteins and controls numerous cellular processes. Skp1 is an adapter protein that binds directly to the F-box proteins. In this study, we have presented the first comprehensive analysis of the presence of peptides or proteins in the human pathogen Entamoeba histolytica having homology to Skp1protein. The occurrence of other protein components of the SCF complex has been identified from protein-protein interaction network of EhSkp1A. Studying the role of Skp1protein in this pathogen would help to understand its unique chromosome segregation and cell division which are different from higher eukaryotes. Further, owing to the development of resistance over several drugs that are currently available, there is a growing need for a novel drug against E. histolytica. Proteins from ubiquitin-proteasome pathway have received attention as potential drug targets in other parasites. We have identified four homologs of Skp1 protein in E. histolytica strain HM-1: IMSS. Molecular docking study between EhSkp1A and an F-box/WD domain-containing protein (EhFBXW) shows that the F-box domain in the N-terminal region of EhFBXW interacts with EhSkp1A. Therefore, the results of the present study shall provide a stable foundation for further research on the cell cycle regulation of E. histolytica and this will help researchers to develop new drugs against this parasite.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12639-022-01523-0.

A quantitative and spatial analysis of cell cycle regulators during the fission yeast cycle

We have carried out a systems-level analysis of the spatial and temporal dynamics of cell cycle regulators in the fission yeast Schizosaccharomyces pombe. In a comprehensive single-cell analysis, we have precisely quantified the levels of 38 proteins previously identified as regulators of the G2 to mitosis transition and of 7 proteins acting at the G1- to S-phase transition. Only 2 of the 38 mitotic regulators exhibit changes in concentration at the whole-cell level: the mitotic B-type cyclin Cdc13, which accumulates continually throughout the cell cycle, and the regulatory phosphatase Cdc25, which exhibits a complex cell cycle pattern. Both proteins show similar patterns of change within the nucleus as in the whole cell but at higher concentrations. In addition, the concentrations of the major fission yeast cyclin-dependent kinase (CDK) Cdc2, the CDK regulator Suc1, and the inhibitory kinase Wee1 also increase in the nucleus, peaking at mitotic onset, but are constant in the whole cell. The significant increase in concentration with size for Cdc13 supports the view that mitotic B-type cyclin accumulation could act as a cell size sensor. We propose a two-step process for the control of mitosis. First, Cdc13 accumulates in a size-dependent manner, which drives increasing CDK activity. Second, from mid-G2, the increasing nuclear accumulation of Cdc25 and the counteracting Wee1 introduce a bistability switch that results in a rapid rise of CDK activity at the end of G2 and thus, brings about an orderly progression into mitosis.

Mad2 promotes Cyclin B2 recruitment to the kinetochore for guiding accurate mitotic checkpoint

Accurate mitotic progression relies on the dynamic phosphorylation of multiple substrates by key mitotic kinases. Cyclin-dependent kinase 1 is a master kinase that coordinates mitotic progression and requires its regulatory subunit Cyclin B to ensure full kinase activity and substrate specificity. The function of Cyclin B2, which is a closely related family member of Cyclin B1, remains largely elusive. Here, we show that Mad2 promotes the kinetochore localization of Cyclin B2 and that their interaction at the kinetochores guides accurate chromosome segregation. Our biochemical analyses have characterized the Mad2-Cyclin B2 interaction and delineated a novel Mad2-interacting motif (MIM) on Cyclin B2. The functional importance of the Cyclin B2-Mad2 interaction was demonstrated by real-time imaging in which MIM-deficient mutant Cyclin B2 failed to rescue the chromosomal segregation defects. Taken together, we have delineated a previously undefined function of Cyclin B2 at the kinetochore and have established, in human cells, a mechanism of action by which Mad2 contributes to the spindle checkpoint.

Cell cycle-dependent binding between Cyclin B1 and Cdk1 revealed by time-resolved fluorescence correlation spectroscopy

Measuring the dynamics with which the regulatory complexes assemble and disassemble is a crucial barrier to our understanding of how the cell cycle is controlled that until now has been difficult to address. This considerable gap in our understanding is due to the difficulty of reconciling biochemical assays with single cell-based techniques, but recent advances in microscopy and gene editing techniques now enable the measurement of the kinetics of protein-protein interaction in living cells. Here, we apply fluorescence correlation spectroscopy and fluorescence cross-correlation spectroscopy to study the dynamics of the cell cycle machinery, beginning with Cyclin B1 and its binding to its partner kinase Cdk1 that together form the major mitotic kinase. Although Cyclin B1 and Cdk1 are known to bind with high affinity, our results reveal that in living cells there is a pool of Cyclin B1 that is not bound to Cdk1. Furthermore, we provide evidence that the affinity of Cyclin B1 for Cdk1 increases during the cell cycle, indicating that the assembly of the complex is a regulated step. Our work lays the groundwork for studying the kinetics of protein complex assembly and disassembly during the cell cycle in living cells.

CDK5RAP3, an essential regulator of checkpoint, interacts with RPL26 and maintains the stability of cell growth

PURPOSE AND MATERIALS

CDK5RAP3 (CDK5 regulatory subunit associated protein 3) was originally identified as a binding protein of CDK5. It is a crucial gene controlling biological functions, such as cell proliferation, apoptosis, invasion, and metastasis. Although previous studies have also shown that CDK5RAP3 is involved in a variety of signalling pathways, however, the mechanism of CDK5RAP3 remains largely undefined. This study utilized MEFs from conditional knockout mice to inhibit CDK5RAP3 and knockdown CDK5RAP3 in MCF7 to explore the role of CDK5RAP3 in cell growth, mitosis, and cell death.

RESULTS

CDK5RAP3 was found to be widely distributed throughout the centrosome, spindle, and endoplasmic reticulum, indicating that it is involved in regulating a variety of cellular activities. CDK5RAP3 deficiency resulted in instability of cell growth. CDK5RAP3 deficiency partly blocks the cell cycle in G₂ /M by downregulating CDK1 (Cyclin-dependent kinase 1) and CCNB1 (Cyclin B1) expression levels. The cell proliferation rate was decreased, thereby slowing down the cell growth rate. Furthermore, the results showed that CDK5RAP3 interacts with RPL26 (ribosome protein L26) to regulate the mTOR pathway. CDK5RAP3 and RPL26 deficiency inhibited mTOR/p-mTOR protein and induce autophagy, resulting in an upregulation of the percentage of apoptosis, and the upregulated percentage of apoptosis also slowed cell growth.

CONCLUSIONS

Our experiments show that CDK5RAP3 interacts with RPL26 and maintains the stability of cell growth. It shows that CDK5RAP3 plays an important role in cell growth and can be used as the target of gene medicine.

CCNE1 amplification is synthetic lethal with PKMYT1 kinase inhibition

Amplification of the CCNE1 locus on chromosome 19q12 is prevalent in multiple tumour types, particularly in high-grade serous ovarian cancer, uterine tumours and gastro-oesophageal cancers, where high cyclin E levels are associated with genome instability, whole-genome doubling and resistance to cytotoxic and targeted therapies1-4. To uncover therapeutic targets for tumours with CCNE1 amplification, we undertook genome-scale CRISPR-Cas9-based synthetic lethality screens in cellular models of CCNE1 amplification. Here we report that increasing CCNE1 dosage engenders a vulnerability to the inhibition of the PKMYT1 kinase, a negative regulator of CDK1. To inhibit PKMYT1, we developed RP-6306, an orally bioavailable and selective inhibitor that shows single-agent activity and durable tumour regressions when combined with gemcitabine in models of CCNE1 amplification. RP-6306 treatment causes unscheduled activation of CDK1 selectively in CCNE1-overexpressing cells, promoting early mitosis in cells undergoing DNA synthesis. CCNE1 overexpression disrupts CDK1 homeostasis at least in part through an early activation of the MMB-FOXM1 mitotic transcriptional program. We conclude that PKMYT1 inhibition is a promising therapeutic strategy for CCNE1-amplified cancers.

An updated view on the centrosome as a cell cycle regulator

The centrosome is a multifunctional organelle that is known primarily for its microtubule organising function. Centrosomal defects caused by changes in centrosomal structure or number have been associated with human diseases ranging from congenital defects to cancer. We are only beginning to appreciate how the non-microtubule organising roles of the centrosome are related to these clinical conditions. In this review, we will discuss the historical evidence that led to the proposal that the centrosome participates in cell cycle regulation. We then summarize the body of work that describes the involvement of the mammalian centrosome in triggering cell cycle progression and checkpoint signalling. Then we will highlight work from the fission yeast model organism, revealing the molecular details that explain how the spindle pole body (SPB, the yeast functional equivalent of the centrosome), participates in these cell cycle transitions. Importantly, we will discuss some of the emerging questions from recent discoveries related to the role of the centrosome as a cell cycle regulator.

Mapping the invisible chromatin transactions of prophase chromosome remodeling

We have used a combination of chemical genetics, chromatin proteomics, and imaging to map the earliest chromatin transactions during vertebrate cell entry into mitosis. Chicken DT40 CDK1as cells undergo synchronous mitotic entry within 15 min following release from a 1NM-PP1-induced arrest in late G2. In addition to changes in chromatin association with nuclear pores and the nuclear envelope, earliest prophase is dominated by changes in the association of ribonucleoproteins with chromatin, particularly in the nucleolus, where pre-rRNA processing factors leave chromatin significantly before RNA polymerase I. Nuclear envelope barrier function is lost early in prophase, and cytoplasmic proteins begin to accumulate on the chromatin. As a result, outer kinetochore assembly appears complete by nuclear envelope breakdown (NEBD). Most interphase chromatin proteins remain associated with chromatin until NEBD, after which their levels drop sharply. An interactive proteomic map of chromatin transactions during mitotic entry is available as a resource at https://mitoChEP.bio.ed.ac.uk.

Beyond Protein Synthesis; The Multifaceted Roles of Tuberin in Cell Cycle Regulation

The ability of cells to sense diverse environmental signals, including nutrient availability and conditions of stress, is critical for both prokaryotes and eukaryotes to mount an appropriate physiological response. While there is a great deal known about the different biochemical pathways that can detect and relay information from the environment, how these signals are integrated to control progression through the cell cycle is still an expanding area of research. Over the past three decades the proteins Tuberin, Hamartin and TBC1D7 have emerged as a large protein complex called the Tuberous Sclerosis Complex. This complex can integrate a wide variety of environmental signals to control a host of cell biology events including protein synthesis, cell cycle, protein transport, cell adhesion, autophagy, and cell growth. Worldwide efforts have revealed many molecular pathways which alter Tuberin post-translationally to convey messages to these important pathways, with most of the focus being on the regulation over protein synthesis. Herein we review the literature supporting that the Tuberous Sclerosis Complex plays a critical role in integrating environmental signals with the core cell cycle machinery.

Identification of polo-like kinase 1 as a therapeutic target in murine lupus

Introduction

The signalling cascades that contribute to lupus pathogenesis are incompletely understood. We address this by using an unbiased activity‐based kinome screen of murine lupus.

Methods

An unbiased activity‐based kinome screen (ABKS) of 196 kinases was applied to two genetically different murine lupus strains. Systemic and renal lupus were evaluated following in vivo PLK1blockade. The upstream regulators and downstream targets of PLK1 were also interrogated.

Results

Multiple signalling cascades were noted to be more active in murine lupus spleens, including PLK1. In vivo administration of a PLK1‐specific inhibitor ameliorated splenomegaly, anti‐dsDNA antibody production, proteinuria, BUN and renal pathology in MRL.lpr mice (P < 0.05). Serum IL‐6, IL‐17 and kidney injury molecule 1 (KIM‐1) were significantly decreased after PLK1 inhibition. PLK1 inhibition reduced germinal centre and marginal zone B cells in the spleen, but changes in T cells were not significant. In vitro, splenocytes were treated with anti‐mouse CD40 Ab or F(ab’)2 fragment anti‐mouse IgM. After 24‐h stimulation, IL‐6 secretion was significantly reduced upon PLK1 blockade, whereas IL‐10 production was significantly increased. The phosphorylation of mTOR was assessed in splenocyte subsets, which revealed a significant change in myeloid cells. PLK1 blockade reduced phosphorylation associated with mTOR signalling, while Aurora‐A emerged as a potential upstream regulator of PLK1.

Conclusion

The Aurora‐A → PLK1 → mTOR signalling axis may be central in lupus pathogenesis, and emerges as a potential therapeutic target.

Identification of novel non-toxic and anti-angiogenic α-fluorinated chalcones as potent colchicine binding site inhibitors

α-Fluorinated chalcones were prepared and evaluated for their cell growth inhibitory properties against six human cancer cell lines. The most potent chalcone 4c demonstrated excellent selective toxicity against cancer cells versus normal human cells, with IC₅₀ values at nanomolar concentration ranges against 5 cancer cell lines. A further study revealed that 4c could bind to the colchicine site of tubulin, disrupt the cell microtubule networks, and effectively inhibit tubulin polymerisation. Cellular-based mechanism studies elucidated that 4c arrested MGC-803 cell cycle at G2/M phase. In addition, 4c dose-dependently caused Caspase-induced apoptosis of MGC-803 cells through mitochondrial dysfunction. Notably, compound 4c was found to inhibit the HUVECs tube formation, migration, and invasion in vitro. Furthermore, our data suggested that treatment with 4c significantly reduced MGC-803 cells metastasis and proliferation in vitro. Overall, this work showed that chalcone hybrid 4c is a potent inhibitor of tubulin assembly with prominent anti-angiogenesis and anti-cancer properties.

Disruption of desmosome function leads to increased centrosome clustering in 14-3-3γ-knockout cells with supernumerary centrosomes

14-3-3 proteins are conserved, dimeric, acidic proteins that regulate multiple cellular pathways. Loss of either 14-3-3ε or 14-3-3γ leads to centrosome amplification. However, we find that while the knockout of 14-3-3ε leads to multipolar mitoses, the knockout of 14-3-3γ results in centrosome clustering and pseudo-bipolar mitoses. 14-3-3γ knockouts demonstrate compromised desmosome function and a decrease in keratin levels, leading to decreased cell stiffness and an increase in centrosome clustering. Restoration of desmosome function increased multipolar mitoses, whereas knockdown of either plakoglobin or keratin 5 led to decreased cell stiffness and increased pseudo-bipolar mitoses. These results suggest that the ability of the desmosome to anchor keratin filaments maintains cell stiffness, thus inhibiting centrosome clustering, and that phenotypes observed upon 14-3-3 loss reflect the dysregulation of multiple pathways.

NF2 Gene Participates in Regulation of the Cell Cycle of Meningiomas by Restoring Spindle Assembly Checkpoint Function and Inhibiting the Binding of Cdc20 Protein to Anaphase Promoting Complex/Cyclosome

BACKGROUND

The neurofibromatosis type 2 (NF2) gene mutation is the leading genetic event in meningiomas, usually accompanied by malignant features. Dysfunction of the spindle assembly checkpoint (SAC) induces tumorigenesis. However, the crosstalk between NF2 and SAC in meningiomas remains unclear.

METHODS

Cell proliferation, invasion, apoptosis, and cell cycle of meningiomas were determined by cell counting kit-8 assay, transwell assay, and flow cytometry, respectively. The expression of SAC in meningioma cells was detected by quantitative real-time polymerase chain reaction and Western blot. The interaction between anaphase promoting complex/cyclosome (APC/C) and cell division cycle 20 (Cdc20) protein in meningioma cells was further explored by co-immunoprecipitation.

RESULTS

We found that the expression of NF2/merlin was low or absent in malignant meningiomas. Overexpression of NF2 suppressed the proliferation and invasion of meningioma cells, prolonged the G₂/M phase, and elevated the expression of SAC proteins at posttranscription. Furthermore, the interaction between APC/C and Cdc20 was inhibited by NF2.

CONCLUSIONS

Our findings suggested that NF2 might restore SAC function by impairing the binding of APC/C and Cdc20, thereby limiting the mitotic rate and inhibiting proliferation of meningiomas.

The multifaceted PDCD10/CCM3 gene

The programmed cell death 10 (PDCD10) gene was originally identified as an apoptosis-related gene, although it is now usually known as CCM3, as the third causative gene of cerebral cavernous malformation (CCM). CCM is a neurovascular disease that is characterized by vascular malformations and is associated with headaches, seizures, focal neurological deficits, and cerebral hemorrhage. The PDCD10/CCM3 protein has multiple subcellular localizations and interacts with several multi-protein complexes and signaling pathways. Thus PDCD10/CCM3 governs many cellular functions, which include cell-to-cell junctions and cytoskeleton organization, cell proliferation and apoptosis, and exocytosis and angiogenesis. Given its central role in the maintenance of homeostasis of the cell, dysregulation of PDCD10/CCM3 can result in a wide range of altered cell functions. This can lead to severe diseases, including CCM, cognitive disability, and several types of cancers. Here, we review the multifaceted roles of PDCD10/CCM3 in physiology and pathology, with a focus on its functions beyond CCM.

Interaction mechanism of endogenous PP2A inhibitor protein ENSA with PP2A

The vast diversity of protein phosphatase 2A (PP2A) holoenzyme composition ensures its multifaceted role in the regulation of cellular growth and signal transduction. In several pathological conditions, such as cancer, PP2A is inhibited by endogenous inhibitor proteins. Several PP2A inhibitor proteins have been identified, one of which is α-endosulfine (ENSA). ENSA inhibits PP2A activity when it is phosphorylated at Ser67 by Greatwall (Gwl) kinase. The role of ENSA in PP2A inhibition is rather well characterized, but knowledge of the mechanism of inhibition is scarce. In this study, we have performed comprehensive structural characterization of ENSA, and its interaction with PP2A A- and various B56-subunit isoforms by combining NMR spectroscopy, small-angle X-ray scattering (SAXS) and interaction assays. The results clearly indicate that ENSA is an intrinsically disordered protein containing three transient α-helical structures. ENSA was observed to interact PP2A mainly via A-subunit, as the affinity with the A-subunit is significantly stronger than with any of the B56 subunits. Based on our results, it seems that ENSA follows the dock-and-coalesce mechanism in associating with PP2A A-subunit. Taken together, our results provide an essential structural and molecular framework to understanding molecular bases of ENSA-mediated PP2A inhibition, which is crucial for the development of new therapies for diseases linked to PP2A inhibition.

Label-Free and Quantitative Dry Mass Monitoring for Single Cells during In Situ Culture

Quantitative measurement of single cells can provide in-depth information about cell morphology and metabolism. However, current live-cell imaging techniques have a lack of quantitative detection ability. Herein, we proposed a label-free and quantitative multichannel wide-field interferometric imaging (MWII) technique with femtogram dry mass sensitivity to monitor single-cell metabolism long-term in situ culture. We demonstrated that MWII could reveal the intrinsic status of cells despite fluctuating culture conditions with 3.48 nm optical path difference sensitivity, 0.97 fg dry mass sensitivity and 2.4% average maximum relative change (maximum change/average) in dry mass. Utilizing the MWII system, different intrinsic cell growth characteristics of dry mass between HeLa cells and Human Cervical Epithelial Cells (HCerEpiC) were studied. The dry mass of HeLa cells consistently increased before the M phase, whereas that of HCerEpiC increased and then decreased. The maximum growth rate of HeLa cells was 11.7% higher than that of HCerEpiC. Furthermore, HeLa cells were treated with Gemcitabine to reveal the relationship between single-cell heterogeneity and chemotherapeutic efficacy. The results show that cells with higher nuclear dry mass and nuclear density standard deviations were more likely to survive the chemotherapy. In conclusion, MWII was presented as a technique for single-cell dry mass quantitative measurement, which had significant potential applications for cell growth dynamics research, cell subtype analysis, cell health characterization, medication guidance and adjuvant drug development.

The Anticancer Effects of FDI-6, a FOXM1 Inhibitor, on Triple Negative Breast Cancer

Triple-negative breast cancer (TNBC) presents an important clinical challenge, as it does not respond to endocrine therapies or other available targeting agents. FOXM1, an oncogenic transcriptional factor, has reported to be upregulated and associated with poor clinical outcomes in TNBC patients. In this study, we investigated the anti-cancer effects of FDI-6, a FOXM1 inhibitor, as well as its molecular mechanisms, in TNBC cells. Two TNBC cell lines, MDA-MB-231 and HS578T, were used in this study. The anti-cancer activities of FDI-6 were evaluated using various 2D cell culture assays, including Sulforhodamine B (SRB), wound healing, and transwell invasion assays together with 3D spheroid assays, mimicking real tumour structural properties. After treatment with FDI-6, the TNBC cells displayed a significant inhibition in cell proliferation, migration, and invasion. Increased apoptosis was also observed in the treated cells. In addition, we found that FDI-6 lead to the downregulation of FOXM1 and its key oncogenic targets, including CyclinB1, Snail, and Slug. Interestingly, we also found that the FDI-6/Doxorubicin combination significantly enhanced the cytotoxicity and apoptotic properties, suggesting that FDI-6 might improve chemotherapy treatment efficacy and reduce unwanted side effects. Altogether, FDI-6 exhibited promising anti-tumour activities and could be developed as a newly effective treatment for TNBC.

Nuclear lamin phosphorylation: an emerging role in gene regulation and pathogenesis of laminopathies

Decades of studies have established that nuclear lamin polymers form the nuclear lamina, a protein meshwork that supports the nuclear envelope structure and tethers heterochromatin to the nuclear periphery. Much less is known about unpolymerized nuclear lamins in the nuclear interior, some of which are now known to undergo specific phosphorylation. A recent finding that phosphorylated lamins bind gene enhancer regions offers a new hypothesis that lamin phosphorylation may influence transcriptional regulation in the nuclear interior. In this review, we discuss the regulation, localization, and functions of phosphorylated lamins. We summarize kinases that phosphorylate lamins in a variety of biological contexts. Our discussion extends to laminopathies, a spectrum of degenerative disorders caused by lamin gene mutations, such as cardiomyopathies and progeria. We compare the prevailing hypothesis for laminopathy pathogenesis based on lamins’ function at the nuclear lamina with an emerging hypothesis based on phosphorylated lamins’ function in the nuclear interior.

Protein regulator of cytokinesis 1 regulates chromosome dynamics and cytoplasmic division during mouse oocyte meiotic maturation and early embryonic development

In contrast to the homeokinesis of mitosis, asymmetric division of cytoplasm is the conspicuous feature of meiosis in mammalian oocytes. Protein regulator of cytokinesis 1 (PRC1) is an important regulator during mitotic spindle assembly and cytoplasmic division, but its functions in oocyte meiosis and early embryo development have not been fully elucidated. In this study, we detected PRC1 expression and localization and revealed a nuclear, spindle midzone-related dynamic pattern throughout meiotic and mitotic progressions. Treatment of oocytes with the reagents taxol or nocodazole disturbed the distribution of PRC1 in metaphase II oocytes. Further, PRC1 depletion led to failure of first polar body (PB1) extrusion and spindle migration, aneuploidy and defective kinetochore-microtubule attachment and spindle assembly. Overexpression of PRC1 resulted in PB1 extrusion failure, aneuploidy and serious defects of spindle assembly. To investigate PRC1 function in early embryos, we injected Prc1 morpholino into zygotes and 2-cell stage embryos. Depletion of PRC1 in zygotes impaired 4-cell, morula and blastocyst formation. Loss of PRC1 in single or double blastomeres in 2-cell stage embryos significantly impaired cell division, indicating its indispensable role in early embryo development. Co-immunoprecipitation showed that PRC1 interacts with polo-like kinase 1 (PLK1), and functional knockdown and rescue experiments demonstrated that PRC1 recruits PLK1 to the spindle midzone to regulate cytoplasmic division during meiosis. Finally, kinesin family member 4 knockdown downregulates PRC1 expression and leads to PRC1 localization failure. Taken together, our data suggest PRC1 plays an important role during oocyte maturation and early embryonic development by regulating chromosome dynamics and cytoplasmic division.

ESRRA promotes gastric cancer development by regulating the CDC25C/CDK1/CyclinB1 pathway via DSN1

Background: Estrogen-related receptor-α (ESRRA) is an orphan nuclear receptor, expressing at high level in exuberant metabolism organs and acting as transcription factor. High expression was found in many malignances but no research was done in gastric cancer (GC), where lipid metabolism disorder is common. Methods: Kaplan-Meier plot was utilized to find the relationship between ESRRA expression and patients' prognoses. The expression level of ESRRA was measured by real-time PCR. The protein expression levels were tested with western-blot and immunohistochemistry. Cell cycle and apoptosis was identified with flow cytometry. RNA-seq, bioinformatics analysis, dual-luciferase assay and ChIP assay were used to predict and validate ESRRA's target gene and binding motif. Animal models were also introduced in our study. Results: ESRRA expression is notably higher in GC cell lines and high ESRRA levels are correlated to poor prognoses. ESRRA silencing decreased GC cell viability, migration, and invasion capacities. Its downstream gene DSN1 was spotted by RNA-seq and confirmed by later bioinformatics analyses, dual-luciferase, and ChIP assays. Western-blot showed G2M arrest caused by ESRRA silencing was via CDC25C-CDK1-Cyclin B1 pathway. Conclusion: ESRRA/DSN1/CDC25C-CDK1-Cyclin B1 is of great importance in GC development. ESRRA could be a potential target as well as prognostic marker in GC.

Identification of a novel Bax-Cdk1 signalling complex that links activation of the mitotic checkpoint to apoptosis

In eukaryotes, entry into and exit from mitosis is regulated, respectively, by the transient activation and inactivation of Cdk1. Taxol, an anti-microtubule anti-cancer drug, prevents microtubule-kinetochore attachments to induce spindle assembly checkpoint (SAC; also known as the mitotic checkpoint)-activated mitotic arrest. SAC activation causes mitotic arrest by chronically activating Cdk1. One consequence of prolonged Cdk1 activation is cell death. However, the cytoplasmic signal(s) that link SAC activation to the initiation of cell death remain unknown. We show here that activated Cdk1 forms a complex with the pro-apoptotic proteins Bax and Bak (also known as BAK1) during SAC-induced apoptosis. Bax- and Bak-mediated delivery of activated Cdk1 to the mitochondrion is essential for the phosphorylation of the anti-apoptotic proteins Bcl-2 and Bcl-xL (encoded by BCL2L1) and the induction of cell death. The interactions between a key cell cycle control protein and key pro-apoptotic proteins identify the Cdk1-Bax and Cdk1-Bak complexes as the long-sought-after cytoplasmic signal that couples SAC activation to the induction of apoptotic cell death.

Pyrrolizidine alkaloids cause cell cycle and DNA damage repair defects as analyzed by transcriptomics in cytochrome P450 3A4-overexpressing HepG2 clone 9 cells

Pyrrolizidine alkaloids (PAs) are a large group of highly toxic chemical compounds, which are found as cross-contaminants in numerous food products (e.g., honey), dietary supplements, herbal teas, and pharmaceutical herbal medicines. PA contaminations are responsible for serious hepatotoxicity and hepatocarcinogenesis. Health authorities have to set legal limit values to guarantee the safe consumption of plant-based nutritional and medical products without harmful health. Toxicological and chemical analytical methods are conventionally applied to determine legally permitted limit values for PAs. In the present investigation, we applied a highly sensitive transcriptomic approach to investigate the effect of low concentrations of five PAs (lasiocarpine, riddelliine, lycopsamine, echimidine, and monocrotaline) on human cytochrome P450 3A4-overexpressing HepG2 clone 9 hepatocytes. The transcriptomic profiling of deregulated gene expression indicated that the PAs disrupted important signaling pathways related to cell cycle regulation and DNA damage repair in the transfected hepatocytes, which may explain the carcinogenic PA effects. As PAs affected the expression of genes that involved in cell cycle regulation, we applied flow cytometric cell cycle analyses to verify the transcriptomic data. Interestingly, PA treatment led to an arrest in the S phase of the cell cycle, and this effect was more pronounced with more toxic PAs (i.e., lasiocarpine and riddelliine) than with the less toxic monocrotaline. Using immunofluorescence, high fractions of cells were detected with chromosome congression defects upon PA treatment, indicating mitotic failure. In conclusion, the tested PAs revealed threshold concentrations, above which crucial signaling pathways were deregulated resulting in cell damage and carcinogenesis. Cell cycle arrest and DNA damage repair point to the mutagenicity of PAs. The disturbance of chromosome congression is a novel mechanism of Pas, which may also contribute to PA-mediated carcinogenesis. Transcriptomic, cell cycle, and immunofluorescence analyses should supplement the standard techniques in toxicology to unravel the biological effects of PA exposure in liver cells as the primary target during metabolization of PAs.

14-3-3γ prevents centrosome duplication by inhibiting NPM1 function

14-3-3 proteins bind to ligands via phospho-serine containing consensus motifs. However, the molecular mechanisms underlying complex formation and dissociation between 14-3-3 proteins and their ligands remain unclear. We identified two conserved acidic residues in the 14-3-3 peptide-binding pocket (D129 and E136) that potentially regulate complex formation and dissociation. Altering these residues to alanine led to opposing effects on centrosome duplication. D129A inhibited centrosome duplication, whereas E136A stimulated centrosome amplification. These results were due to the differing abilities of these mutant proteins to form a complex with NPM1. Inhibiting complex formation between NPM1 and 14-3-3γ led to an increase in centrosome duplication and over-rode the ability of D129A to inhibit centrosome duplication. We identify a novel role of 14-3-3γ in regulating centrosome licensing and a novel mechanism underlying the formation and dissociation of 14-3-3 ligand complexes dictated by conserved residues in the 14-3-3 family.

Long non-coding RNA LIFR-AS1 regulates the proliferation, migration and invasion of human thyroid cancer cells

The long non-coding RNA (lncRNA) LIFR-AS1 has been shown to be involved in the development of several human cancers. This study was designed to determine the expression profile and role of lncRNA-LIFR-AS1 in human thyroid cancer. The results showed significant (p < 0.05) upregulation of LncRNA-LIFR-AS1 in thyroid cancer tissues and cells. However, silencing of LncRNA-LIFR-AS1 inhibited the viability and proliferation of human thyroid cancer cells inducing G2/M cell cycle arrest. The G2/M phase cells increased from 8.56% in negative control (NC) to around 35.03% in si-LIFR-AS1. This was also found to be concomitant with the downregulation of cyclin B1 and CDK1 expressions. The thyroid cancer cells exhibited remarkably lower invasion and migration under transcriptional knockdown of lncRNA-LIFR-AS1 which was also associated with downregulation of MMP-2 and MMP-9 expression. Importantly, transcriptional silencing of lncRNA-LIFR-AS1 inhibited thyroid cancer tumorigenesis, in vivo. Collectively, the results suggest the tumor-promoting role of lncRNA-LIFR-AS1 in thyroid cancer and highlight its potential as therapeutic target.

AMPKα2 activation by an energy-independent signal ensures chromosomal stability during mitosis

AMP-activated protein kinase (AMPK) senses energy status and impacts energy-consuming events by initiating metabolism regulatory signals in cells. Accumulating evidences suggest a role of AMPK in mitosis regulation, but the mechanism of mitotic AMPK activation and function remains elusive. Here we report that AMPKα2, but not AMPKα1, is sequentially phosphorylated and activated by CDK1 and PLK1, which enables AMPKα2 to accurately guide chromosome segregation in mitosis. Phosphorylation at Thr485 by activated CDK1-Cyclin B1 brings the ST-stretch of AMPKα2 to the Polo box domain of PLK1 for subsequent Thr172 phosphorylation by PLK1. Inserting of the AMPKα2 ST-stretch into AMPKα1, which lacks the ST-stretch, can correct mitotic chromosome segregation defects in AMPKα2-depleted cells. These findings uncovered a specific signaling cascade integrating sequential phosphorylation by CDK1 and PLK1 of AMPKα2 with mitosis to maintain genomic stability, thus defining an isoform-specific AMPKα2 function, which will facilitate future research on energy sensing in mitosis.

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AMPKα2 is selectively activated during mitosis by CDK1 and PLK1

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A conserved motif in AMPKα2 determines its interaction with and activation by PLK1

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Mitotic AMPK activation contributes to maintain genomic stability in normal mitosis

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.

From the cytoskeleton to the nucleus: An integrated view on early spindle assembly

Accurate chromosome segregation requires a complete restructuring of cellular organization. Microtubules remodel to assemble a mitotic spindle and the actin cytoskeleton rearranges to form a stiff actomyosin cortex. These cytoplasmic events must be spatially and temporally coordinated with mitotic chromosome condensation and nuclear envelope permeabilization, in order to ensure mitotic timing and fidelity. Here, we discuss the main cytoskeletal and nuclear events that occur during mitotic entry in proliferating animal cells, focusing on their coordinated contribution for early mitotic spindle assembly. We will also explore recent progress in understanding their regulatory biochemical and mechanical pathways.

Homoharringtonine inhibits melanoma cells proliferation in vitro and vivo by inducing DNA damage, apoptosis, and G2/M cell cycle arrest

Homoharringtonine (HHT), an approved anti-leukemic alkaloid, has been reported effectively in many types of tumor cells. However, its effect on melanoma cells has not been investigated. And the anti-melanoma mechanism of HHT is still unknown. In this study, we detected the effects of HHT on two melanoma cell lines (A375 and B16F10) and on the A375 xenograft mouse model. HHT significantly inhibited the proliferation of melanoma cells as investigated by the CCK8 method, cell cloning assay, and EdU experiment. HHT induced A375 and B16F10 cells DNA damage, apoptosis, and G2/M cell cycle arrest as proved by TdT-mediated dUTP Nick-End Labeling (TUNEL) and flow cytometry assay. Additionally, the loss of mitochondrial membrane potential in HHT-treated cells were visualized by JC-1 fluorescent staining. For the molecule mechanism study, western blotting results indicated the protein expression levels of ATM, P53, p-P53, p-CHK2, γ-H2AX, PARP, cleaved-PARP, cleaved caspase-3, cleaved caspase-9, Bcl-2, Bax, Aurka, p-Aurka, Plk1, p-Plk1, Cdc25c, CDK1, cyclin B1, and Myt1 were regulated by HHT. And the relative mRNA expression level of Aurka, Plk1, Cdc25c, CDK1, cyclin B1, and Myt1 were ascertained by q-PCR assay. The results in vivo experiment showed that HHT can slow down the growth rate of tumors. At the same time, the protein expression levels in vivo were consistent with that in vitro. Collectively, our study provided evidence that HHT could be considered an effective anti-melanoma agent by inducing DNA damage, apoptosis, and cell cycle arrest.