Cytokinesis Failure Research Articles

Critical Role for Cold Shock Protein YB-1 in Cytokinesis.

Simple SummaryY-box-binding protein-1, YB-1, plays an important role in regulating the cell cycle, although precisely how it does the is unknown. Using live cell imaging, we show that YB-1 is essential for initiating the last step of cell division (cytokinesis), required for creation of two daughter cells. Using confocal microscopy we showed that YB-1 regulates the spatial distribution of key proteins essential for cytokinesis to occur and that this required YB-1 to be phosphorylated on several residues. In-silico modeling demonstrated that modifications at these residues resulted in conformational changes in YB-1 protein allowing it to interact with proteins essential for cytokinesis. As many cancers have high levels YB-1 and these are associated with poor prognosis, our data suggest developing small molecule inhibitors to block YB-1 phosphorylation could be a novel approach to cancer therapy.High levels of the cold shock protein Y-box-binding protein-1, YB-1, are tightly correlated with increased cell proliferation and progression. However, the precise mechanism by which YB-1 regulates proliferation is unknown. Here, we found that YB-1 depletion in several cancer cell lines and in immortalized fibroblasts resulted in cytokinesis failure and consequent multinucleation. Rescue experiments indicated that YB-1 was required for completion of cytokinesis. Using confocal imaging we found that YB-1 was essential for orchestrating the spatio-temporal distribution of the microtubules, β-actin and the chromosome passenger complex (CPC) to define the cleavage plane. We show that phosphorylation at six serine residues was essential for cytokinesis, of which novel sites were identified using mass spectrometry. Using atomistic modelling we show how phosphorylation at multiple sites alters YB-1 conformation, allowing it to interact with protein partners. Our results establish phosphorylated YB-1 as a critical regulator of cytokinesis, defining precisely how YB-1 regulates cell division.

Divergent Impact of Actin Isoforms on Division of Epithelial Cells

We investigated distribution and functions of beta- and gamma-cytoplasmic actins (CYAs) at different stages of non-neoplastic epithelial cell division using laser scanning microscopy (LSM). Here, we demonstrated that beta- and gamma-CYAs are spatially segregated in the early prophase, anaphase, telophase, and cytokinesis. Small interfering RNA (siRNA) experiments revealed that in both beta-CYA- and gamma-CYA-depleted cells, the number of cells was significantly reduced compared with the siRNA controls. Beta-CYA depletion resulted in an enlargement of the cell area in metaphase and high percentage of polynuclear cells compared with the siRNA control, indicating a potential failure of cytokinesis. Gamma-CYA depletion resulted in a reduced percentage of mitotic cells. We also observed the interdependence between the actin isoforms and the microtubule system in mitosis: (i) a decrease in the gamma-CYA led to impaired mitotic spindle organization; (ii) suppression of tubulin polymerization caused impaired beta-CYA reorganization, as incubation with colcemid blocked the transfer of short beta-actin polymers from the basal to the cortical compartment. We conclude that both actin isoforms are essential for proper cell division, but each isoform has its own specific functional role in this process.

Abstract 3530: Investigating aneuploidy, CIN and mechanisms of DNA content reduction in cancer

Abstract Chromosomal instability (CIN) is a form of genomic instability that refers to a dynamic state in which the cells are constantly changing the number and/or the structure of their chromosomes. CIN leads to aneuploidy, a state in which a cell's set of chromosomes deviates from the euploid set. Causes of aneuploidy include errors during DNA replication, mitosis and cell fusion events. Furthermore, aneuploidy has been shown to promote tumorigenesis and tumor progression, but also to reduce cell fitness or induce cell death, especially when high levels of aneuploidy are present. Nevertheless, antimitotic drugs that induce high levels of aneuploidy, such as Paclitaxel, are not always effective in the clinic. In this study, we aim to investigate the mechanisms by which cancer cells tolerate aneuploidy, to elucidate the mechanisms by which cell fusion can lead to aneuploidy and resistance to paclitaxel and to identify new targets in aneuploidy and CIN. Towards this direction, aneuploid clones of pseudo-diploid cancer cells were generated after treatment with anti-mitotic drugs and single cell sorting and were characterized by cell cycle profile, metaphase spreads and CGH or SNP profile. Furthermore, CIN was induced by inhibition of CENP-E or ATM or impairment of the SWI/ SNF complex and quantified by induction of chromosome missegregation and micronuclei formation. Interestingly, several near tetraploid clones that were isolated after anti-mitotic drug treatment, reduced their DNA content to near diploid during propagation in culture. Thus, we hypothesize that cancer cells may utilize specific mechanisms to change their DNA content and maintain tolerable levels of aneuploidy. By time-lapse microscopy, we observed that cells treated with Paclitaxel, can increase their DNA content by abortive mitosis, cytokinesis failure or by undergoing cell fusion. Interestingly, these multinucleated cells could reduce their DNA content by undergoing independent mitosis, independent nucleus catastrophe or independent nucleus separation (cell exodus). We identify cell exodus, as a potential mechanism by which cells can recover after treatment with Paclitaxel. Inhibition of ROCK pathway, that stabilizes actin filaments and prevents cellular contractility, reduced cell fusion and exodus events and delayed cell recovery after paclitaxel treatment. Finally, in order to identify new targets in CIN and aneuploidy, we setup sgRNA loss of function screening conditions in the generated CIN and aneuploid cell models and we aim to identify genes that are essential for the survival of aneuploid and/or CIN cancer cells. Citation Format: Mara Mandelia, Kostas Drosopoulos, Spiros Linardopoulos. Investigating aneuploidy, CIN and mechanisms of DNA content reduction in cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3530.

β-HPV 8E6 combined with TERT expression promotes long-term proliferation and genome instability after cytokinesis failure

Human papillomavirus (HPV) is a family of viruses divided into five genera: alpha, beta, gamma, mu, and nu. There is an ongoing discussion about whether beta genus HPVs (β-HPVs) contribute to cutaneous squamous cell carcinoma (cSCC). The data presented here add to this conversation by determining how a β-HPV E6 protein (β-HPV 8E6) alters the cellular response to cytokinesis failure. Specifically, cells were observed after cytokinesis failure was induced by dihydrocytochalasin B (H2CB). β-HPV 8E6 attenuated the immediate toxicity associated with H2CB but did not promote long-term proliferation after H2CB. Immortalization by telomerase reverse transcriptase (TERT) activation also rarely allowed cells to sustain proliferation after H2CB exposure. In contrast, TERT expression combined with β-HPV 8E6 expression allowed cells to proliferate for months following cytokinesis failure. However, this continued proliferation comes with genome destabilizing consequences. Cells that survived H2CB-induced cytokinesis failure suffered from changes in ploidy.

Abstract 516: Homotypic Fusion Can Generate Bi- and Multi-nucleated Cardiomyocytes in the Postnatal Murine Heart

Multinucleation is an important and prominent phenotype of postnatal mammalian cardiomyocytes, and its occurrence in early life correlates with the loss of regenerative potential in mice. This phenomenon is believed to be the result of mitosis followed by cytokinesis failure, although direct proof of this mechanism has not been provided for every single adult cardiomyocyte. Moreover, many multi-nucleated cells in other organs are formed after homotypic cell fusion. Although heterotypic cell fusion between cardiomyocytes and circulating cells has been described as a rare event, it is not known whether homotypic myocyte fusion occurs and if it can lead to bi- and multi-nucleation. We developed a novel mouse model wherein multi-color fluorescent protein reporter expression occurs stochastically only in cardiomyocytes (Myh6-MerCreMer;Rosa26-Confetti). Using pulse-chase experiments during development and at birth, we show that a small fraction of cardiomyocytes fuses with other myocytes to generate binucleated and multinucleated cells; we calculate a fusion rate of at least 2%, although this reflects the lower limit of the phenomenon due to technical limitations of our model. We reveal that this process occurs in the first week of life and is stable at one month of age. Our findings suggest a revision of the dogma in postnatal cardiac development by providing another mechanism for multinucleation of cardiomyocytes. Future experiments will address whether fusion is a reversible process and whether fused myocytes can undergo abscission in response to physiological or pathological cues.

Early genotoxic damage through micronucleus test in exfoliated buccal cells and occupational dust exposure in construction workers: a cross-sectional study in L'Aquila, Italy

AimThe city of L'Aquila (central Italy) was hit by a strong earthquake in 2009 that caused the collapse of several buildings, deaths and injured people. In the following years, a great number of building sites were activated, building workers resulted intensely exposed and represent a relevant target for research on environmental mutagenesis and epidemiological surveillance. Cells of buccal mucosa are considered an appropriate site for early detecting of cytogenetic damage, since it represents the first barrier in inhalation or ingestion and can metabolize carcinogenic agents into reactive chemicals. Our study is aimed 1) at comparing the early genotoxic damage as measured by the buccal mucosa micronucleus test in two subgroups of workers defined by different occupational exposure and 2) at evaluating possible confounding variables such as lifestyle factors. Methods and resultsA cross-sectional study was conducted in L'Aquila, on 24 outdoor workers (OWs) highly exposed on the construction sites and 26 indoor workers (IWs), all subjected to the compulsory occupational surveillance system, in the period 2017–2018. Buccal cells samples were collected and, based on the Micronucleus test, the exfoliated cells were classified in respect of nuclear changes observed. Moreover, a self-report questionnaire composed of 84 items, was administered to the workers. ResultsSignificant differences were observed between Exp+ (OWs) and Exp− (IWs) in the number of the analyzed cells (expressed as mean value out of 1000 cells): respectively 954.46 vs 990.06 normal cells, (p < 0.001); 19.79 vs 4.95 micronucleated cells, as marker of chromosomal damage (p < 0.001); 13.93 vs 8.96 binucleated cells, as marker of failed cytokinesis (p < 0.001); 2.09 vs 1.18 karyolytic cells, as marker of cell death and damaged DNA (p < 0.05). According with a multivariate regression analysis, in addition to the job exposure (OW vs IW, beta = 12.221, p < 0.001), the only variable independently associated with an increase in Micronuclei (MNs) is the smoking habit (OWs vs IWs, beta = 6.683, p < 0.001) which, even if not associated with dust exposure, worsens cell integrity. Moreover, this worsening effect is weaker in workers not exposed to the site dust (moderation effect). Within social demographic factors, the high educational level only apparently seems to affect MNs number: even if unbalanced in favor of IWs vs OWs, this variable resulted a confounder, since its effect disappears when the interaction between these two factors is considered, because it is a covariate of smoking habit as well as of the job condition. ConclusionDespite some limitation, our findings clearly confirm the role of occupational exposure as a marker of cytogenetic damage associated with MNs number in construction workers. Moreover, smoking status appears as the only other investigated factor independently associated to the outcome. The statistical model, in addition, highlights possible moderation and confounding effects, such as interaction between smoking and occupational exposure and the unbalanced school education level in workers. Micronucleus test in exfoliated buccal cells would be considered a suitable method for studying the early genotoxic damage in the construction occupational setting as well as in evaluating the efficacy of preventive practices.

Giant multinucleated plasma cells in relapsed plasma cell myeloma.

A 47-year-old woman was diagnosed with plasma cell myeloma in 2018, received first-line induction chemotherapy, and made a partial response. She then received two cycles of DT-PACE chemotherapy. Her paraprotein levels remained static and a repeat bone marrow test in February 2019 revealed persistent bone marrow involvement by plasma cell myeloma showing usual (mononuclear) morphology with no multinucleated giant cells. She was treated with daratumumab as a bridge to an autologous stem cell transplant in June 2019. Her day 100 post autograft bone marrow trephine biopsy contained a plasma cell population making up 10% of all nucleated cells. More than 95% of the atypical plasma cells showed multinucleated giant cell morphology containing up to 40 nuclei. On immunohistochemistry, these multinucleated giant cells showed positive staining for CD138, CD38, and CD56 and were lambda restricted. CD45 was negative. Bone marrow trephine sections stained (clockwise from top left) with H&E, and for CD138, lambda light chains, and CD38. Multinucleated tumor giant cells are thought to form by two mechanisms: by cell-cell fusion via syncytins or as a result of a failure of cytokinesis at the end of the anaphase stage of mitosis. Occasional case reports of giant multinucleated plasma cells have been published since the 1970s. However, the presence of giant plasma cells with more than 10 nuclei is extremely rare. One previous case had also been treated with daratumumab, an IgG1k monoclonal antibody directed against cell surface CD38 (Guijarro F, Rozman M, Matutes E. Multinucleated giant myeloma cells after failure of daratumumab therapy. Br J Haematol 2018;181:432). Plasma cell membrane alterations promoting cell-cell fusion may be a side effect of immunotherapies targeting cell surface molecules. Giant multinucleated plasma cells may be observed more frequently as such immunotherapies become increasingly used.

Profiling cytotoxic microRNAs in pediatric and adult glioblastoma cells by high-content screening, identification, and validation of miR-1300

MicroRNAs play an important role in the regulation of mRNA translation and have therapeutic potential in cancer and other diseases. To profile the landscape of microRNAs with significant cytotoxicity in the context of glioblastoma (GBM), we performed a high-throughput screen in adult and pediatric GBM cells using a synthetic oligonucleotide library representing all known human microRNAs. Bioinformatics analysis was used to refine this list and the top seven microRNAs were validated in a larger panel of GBM cells using state-of-the-art in vitro assays. The cytotoxic effect of our most relevant candidate was assessed in a preclinical model. Our screen identified ~100 significantly cytotoxic microRNAs with 70% concordance between cell lines. MicroRNA-1300 (miR-1300) was the most potent and robust candidate. We observed a striking binucleated phenotype in miR-1300 transfected cells due to cytokinesis failure followed by apoptosis. This was also observed in two stem-like patient-derived cultures. We identified the physiological role of miR-1300 as a regulator of endomitosis in megakaryocyte differentiation where blockade of cytokinesis is an essential step. In GBM cells, where miR-1300 is normally not expressed, the oncogene Epithelial Cell Transforming 2 (ECT2) was validated as a direct key target. ECT2 siRNA phenocopied the effects of miR-1300, and ECT2 overexpression led to rescue of miR-1300 induced binucleation. We showed that ectopic expression of miR-1300 led to decreased tumor growth in an orthotopic GBM model. Our screen provides a resource for the neuro-oncology community and identified miR-1300 as a novel regulator of endomitosis with translatable potential for therapeutic application.

Beta Human Papillomavirus 8E6 Attenuates LATS Phosphorylation after Failed Cytokinesis.

Beta genus human papillomaviruses (β-HPVs) cause cutaneous squamous cell carcinomas (cSCCs) in a subset of immunocompromised patients. However, β-HPVs are not necessary for tumor maintenance in the general population. Instead, they may destabilize the genome in the early stages of cancer development. Supporting this idea, β-HPV's 8E6 protein attenuates p53 accumulation after failed cytokinesis. This paper offers mechanistic insight into how β-HPV E6 causes this change in cell signaling. An in silico screen and characterization of HCT 116 cells lacking p300 suggested that the histone acetyltransferase is a negative regulator of Hippo pathway (HP) gene expression. HP activation restricts growth in response to stimuli, including failed cytokinesis. Loss of p300 resulted in increased HP gene expression, including proproliferative genes associated with HP inactivation. β-HPV 8E6 expression recapitulates some of these phenotypes. We used a chemical inhibitor of cytokinesis (dihydrocytochalasin B [H2CB]) to induce failed cytokinesis. This system allowed us to show that β-HPV 8E6 reduced activation of large tumor suppressor kinase (LATS), an HP kinase. LATS is required for p53 accumulation following failed cytokinesis. These phenotypes were dependent on β-HPV 8E6 destabilizing p300 and did not completely attenuate the HP. It did not alter H2CB-induced nuclear exclusion of the transcription factor YAP. β-HPV 8E6 also did not decrease HP activation in cells grown to a high density. Although our group and others have previously described inhibition of DNA repair, to the best of our knowledge, this marks the first time that a β-HPV E6 protein has been shown to hinder HP signaling.IMPORTANCE β-HPVs contribute to cSCC development in immunocompromised populations. However, it is unclear if these common cutaneous viruses are tumorigenic in the general population. Thus, a more thorough investigation of β-HPV biology is warranted. If β-HPV infections do promote cSCCs, they are hypothesized to destabilize the cellular genome. In vitro data support this idea by demonstrating the ability of the β-HPV E6 protein to disrupt DNA repair signaling events following UV exposure. We show that β-HPV E6 more broadly impairs cellular signaling, indicating that the viral protein dysregulates the HP. The HP protects genome fidelity by regulating cell growth and apoptosis in response to a myriad of deleterious stimuli, including failed cytokinesis. After failed cytokinesis, β-HPV 8E6 attenuates phosphorylation of the HP kinase (LATS). This decreases some, but not all, HP signaling events. Notably, β-HPV 8E6 does not limit senescence associated with failed cytokinesis.

Targeting Actomyosin Contractility Suppresses Malignant Phenotypes of Acute Myeloid Leukemia Cells.

Actomyosin-mediated contractility is required for the majority of force-driven cellular events such as cell division, adhesion, and migration. Under pathological conditions, the role of actomyosin contractility in malignant phenotypes of various solid tumors has been extensively discussed, but the pathophysiological relevance in hematopoietic malignancies has yet to be elucidated. In this study, we found enhanced actomyosin contractility in diverse acute myeloid leukemia (AML) cell lines represented by highly expressed non-muscle myosin heavy chain A (NMIIA) and increased phosphorylation of the myosin regulatory light chain. Genetic and pharmacological inhibition of actomyosin contractility induced multivalent malignancy- suppressive effects in AML cells. In this context, perturbed actomyosin contractility enhances AML cell apoptosis through cytokinesis failure and aryl hydrocarbon receptor activation. Moreover, leukemic oncogenes were downregulated by the YAP/TAZ-mediated mechanotransduction pathway. Our results provide a theoretical background for targeting actomyosin contractility to suppress the malignancy of AML cells.

Heavy metals analysis and toxicity evaluation of some textile and dyeing effluents in Kano, Nigeria using &lt;I&gt;Allium cepa&lt;/I&gt; bioassay

Insufficiencies in dyeing and textile processing coupled with incomplete sewage treatment system lead to indiscriminate discharge of large amount of dyestuff into water bodies mostly used for irrigation and fishing. These wastes are potentially mutagenic and some are even carcinogenic. In this research, cytotoxicity of three industrial effluents viz; African Textile Manufacturer (ATM), Kofar Naisa and Kofar Mata dyeing centres were evaluated using Allium cepa bioassay. The concentrations of some heavy metals (Cr, Cd, Zn, Fe, Cu, Co, Pb, Mn and Ni) were also determined. Three sets of small onion bulbs were cultivated in 25%, 50% 75% and 100% effluent concentrations (v/v) and a control for each site. Root tips from each bulb were harvested and processed for cytological studies using squashing technique. After 48hrs of exposure, cytotoxic effects of the effluents on root tips (compared to control) showed root growth retardation which was more apparent at higher concentrations. This indicated that, the root growth inhibition was concentration dependent. Number of dividing cells observed and the Mitotic Index (MI) were also concentration dependent. There were decrease in number of dividing cells and MI with increase in concentration of the treatment. The effective concentrations that caused 50% effect (EC50) was 95% for ATM and K/Naisa dyeing points while it was 100% in K/mata dyeing point. Diverse structural aberrations and abnormalities were observed ranging from chromosomal bridge, which was apparent even at low concentrations of the treatment to cytokinesis failure, Micronucleus (MN) and nuclear buds or vacuolated nuclei. Analysis of Variance (ANOVA) showed no significant difference (P&gt;0.05) in mean concentrations of Cr, Fe, Cu and Mn for K/Naisa and K/Mata dyeing centres, but there was statistical difference (P&lt;0.05) for these parameters in ATM. Likewise, there was significant difference (P&lt;0.05) in the root growth of A. cepa exposed to different concentrations of the effluent in ATM and K/Naisa sites but no statistical difference existed in root growth of A. cepa exposed to K/Mata effluents.&#x0D; Keywords: Allium cepa, Bioassay, Effluents, Cytotoxicity, Mitotic Index

CITK Loss Inhibits Growth of Group 3 and Group 4 Medulloblastoma Cells and Sensitizes Them to DNA-Damaging Agents.

Medulloblastoma (MB) is the most common malignant brain tumor in children, and it is classified into four biological subgroups: WNT, Sonic Hedgehog (SHH), Group 3 and Group 4. The current treatment is surgery, followed by irradiation and chemotherapy. Unfortunately, these therapies are only partially effective. Citron kinase protein (CITK) has been proposed as a promising target for SHH MB, whose inactivation leads to DNA damage and apoptosis. D283 and D341 cell lines (Group 3/Group 4 MB) were silenced with established siRNA sequences against CITK, to assess the direct effects of its loss. Next, D283, D341, ONS-76 and DAOY cells were treated with ionizing radiation (IR) or cisplatin in combination with CITK knockdown. CITK depletion impaired proliferation and induced cytokinesis failure and apoptosis of G3/G4 MB cell lines. Furthermore, CITK knockdown produced an accumulation of DNA damage, with reduced RAD51 nuclear levels. Association of IR or cisplatin with CITK depletion strongly impaired the growth potential of all tested MB cells. These results indicate that CITK inactivation could prevent the expansion of G3/G4 MB and increase their sensitivity to DNA-damaging agents, by impairing homologous recombination. We suggest that CITK inhibition could be broadly associated with IR and adjuvant therapy in MB treatment.

Misaponin B Induces G2/M Arrest, Cytokinesis Failure and Impairs Autophagy.

Saponins are a group of naturally occurring plant glycosides with the features of their strong foam-forming properties and multibiological effects such as antitumor activity. Though Misaponin B, one of the triterpenoid saponins from Madhuca longifolia, is known to have spermicidal and antioxidant activity, the other biological activities have been never reported so far. Thus, in the present study, the antitumor mechanism of Misaponin B was investigated in A549 and AsPC-1 cancer cells. Misaponin B exerted significant cytotoxicity in A549, H460, SKOV3, and AsPC-1 cancer cells. Among them, A549 and AsPC-1 cells were more susceptible to Misaponin B. Misaponin B induced G2/M arrest and cytokinesis failure and increased the expression of LC3B and p62 with autophagic vacuoles and GFP-LC3 punctae in A549 and AsPC-1 cells. Furthermore, Misaponin B suppressed autophagy flux in A549 cells transfected by GFP-mRFP-LC3 constructs by showing merged yellow color by autophagy flux assay. Overall, our findings provide evidences that Misaponin B induces G2M arrest and impairs autophagy in A549 and AsPC-1 cells.

RIPK3 upregulation confers robust proliferation and collateral cystine-dependence on breast cancer recurrence.

The molecular and genetic basis of tumor recurrence is complex and poorly understood. RIPK3 is a key effector in programmed necrotic cell death and, therefore, its expression is frequently suppressed in primary tumors. In a transcriptome profiling between primary and recurrent breast tumor cells from a murine model of breast cancer recurrence, we found that RIPK3, while absent in primary tumor cells, is dramatically reexpressed in recurrent breast tumor cells by an epigenetic mechanism. Unexpectedly, we found that RIPK3 knockdown in recurrent tumor cells reduced clonogenic growth, causing cytokinesis failure, p53 stabilization, and repressed the activities of YAP/TAZ. These data uncover a surprising role of the pro-necroptotic RIPK3 kinase in enabling productive cell cycle during tumor recurrence. Remarkably, high RIPK3 expression also rendered recurrent tumor cells exquisitely dependent on extracellular cystine and undergo necroptosis upon cystine deprivation. The induction of RIPK3 in recurrent tumors unravels an unexpected mechanism that paradoxically confers on tumors both growth advantage and necrotic vulnerability, providing potential strategies to eradicate recurrent tumors.

Aqueous extract of bulbus Fritillaria cirrhosa induces cytokinesis failure by blocking furrow ingression in human colon epithelial NCM460 cells

Bulbus Fritillariacirrhosa D. Don (BFC) has been widely used as an herbal medicament for respiratory diseases in China for over 2000 years. The ethnomedicinal effects of BFC have been scientifically verified, nevertheless its toxicity has not been completely studied. Previously, we have reported that the aqueous extract of BFC induces mitotic aberrations and chromosomal instability (CIN) in human colon epithelial NCM460 cells via dysfunctioning the mitotic checkpoint. Here, we extend this study and specifically focus on the influence of BFC on cytokinesis, the final step of cell division. One remarkable change in NCM460 cells following BFC treatment is the high incidence of binucleated cells (BNCs). More detailed investigation of the ana-telophases reveals that furrow ingression, the first stage of cytokinesis, is inhibited by BFC. Asynchronous cultures treatment demonstrates that furrow ingression defects induced by BFCs are highly associated with the formation of BNCs in ensuing interphase, indicating the BNCs phenotype after BFC treatment was resulted from cytokinesis failure. In line with this, the expression of genes involved in the regulation of furrow ingression is significantly de-regulated by BFC (e.g., LATS-1/2 and Aurora-B are upregulated, and YB-1 is downregulated). Furthermore, long-term treatment of BFC elucidates that the BNCs phenotype is transient and the loss of BNCs is associated with increased frequency of micronuclei and nuclear buds, two biomarkers of CIN. In supporting of these findings, the Nin Jiom Pei Pa Koa and Chuanbei Pipa Gao, two commercially available Chinese traditional medicines containing BFC, are able to induce multinucleation and CIN in NCM460 cells. Altogether, these data provide the first in vitro experimental evidence linking BFC to cytokinesis failure and suggest the resultant BNCs may be intermediates to produce CIN progenies.

URH49 exports mRNA by remodeling complex formation and mediating the NXF1-dependent pathway

The TREX complex integrates information from nuclear mRNA processing events to ensure the timely export of mRNA to the cytoplasm. In humans, UAP56 and its paralog URH49 form distinct complexes, the TREX complex and the AREX complex, respectively, which cooperatively regulate the expression of a specific set of mRNA species on a genome wide scale. The difference in the complex formation between UAP56 and URH49 are thought to play a critical role in the regulation of target mRNAs. To date, the underlying mechanism remains poorly understood. Here we characterize the formation of the TREX complex and the AREX complex. In the ATP depleted condition, UAP56 formed an Apo-TREX complex containing the THO subcomplex but not ALYREF and CIP29. URH49 formed an Apo-AREX complex containing CIP29 but not ALYREF and the THO subcomplex. However, with the addition of ATP, both the Apo-TREX complex and the Apo-AREX complex were remodeled to highly similar ATP-TREX complex containing the THO subcomplex, ALYREF and CIP29. The knockdown of URH49 caused a reduction in its target mRNAs and a cytokinesis failure. Similarly, cytokinesis abnormality was observed in CIP29 knockdown cells, suggesting that CIP29 belongs to the URH49 regulated mRNA export pathway. Lastly, we confirmed that the export of mRNA in URH49-dependent pathway is achieved by NXF1, which is also observed in UAP56-dependent pathway. Our studies propose an mRNA export model that the mRNA selectivity depends on the Apo-form TREX/AREX complex, which is remodeled to the highly similar ATP-form complex upon ATP loading, and integrated to NXF1.

Myocardial Protection with Beta Blocker Treatment in Infants with Heart Failure Due to Congenital Heart Defects and Duchenne Muscular Dystrophy

Our first intention to treat infants’ heart failure with beta blockers was to improve the clinical condition as shown in our prospective randomized trial. We only use non-selective beta blockers in these infants, carvedilol in those with left ventricular dysfunction and propranolol in those with congenital heart disease without ventricular dysfunction. Despite a significant improvement of Ross’s heart failure score, we could not convince most colleagues within the last 25 years if the concept of neurohumoral activation in heart failure is not well-established pediatric cardiology. Recently, Honghai Liu et al. published that cardiomyocyte cytokinesis failure was increased in congenital heart disease. Inactivation of the beta adreno receptors genes and administration of the beta-blocker propranolol increased cardiomyocyte division in neonatal mice, which increased the number of cardiomyocytes (endowment) and conferred benefit after myocardial infarction in adults. We currently realize that propranolol in infants with congenital heart disease not only decrease highly elevated NT-Pro-BNP values but also decrease cardiac troponin T values that may indicate myocardial injury due to neurohumoral activation. We reproduce this observation, primarily seen in infants with congenital heart disease, in an infant with Duchenne muscular dystrophy. These observations were in good accordance with current data from H. Liu et al., who showed that treatment with non-selective beta blockers early after birth might rescue cytokinesis defects and prevent heart dysfunction in adulthood in a mouse model.

Aurora A-Selective Inhibitor LY3295668 Leads to Dominant Mitotic Arrest, Apoptosis in Cancer Cells, and Shows Potent Preclinical Antitumor Efficacy.

Although Aurora A, B, and C kinases share high sequence similarity, especially within the kinase domain, they function distinctly in cell-cycle progression. Aurora A depletion primarily leads to mitotic spindle formation defects and consequently prometaphase arrest, whereas Aurora B/C inactivation primarily induces polyploidy from cytokinesis failure. Aurora B/C inactivation phenotypes are also epistatic to those of Aurora A, such that the concomitant inactivation of Aurora A and B, or all Aurora isoforms by nonisoform-selective Aurora inhibitors, demonstrates the Aurora B/C-dominant cytokinesis failure and polyploidy phenotypes. Several Aurora inhibitors are in clinical trials for T/B-cell lymphoma, multiple myeloma, leukemia, lung, and breast cancers. Here, we describe an Aurora A-selective inhibitor, LY3295668, which potently inhibits Aurora autophosphorylation and its kinase activity in vitro and in vivo, persistently arrests cancer cells in mitosis, and induces more profound apoptosis than Aurora B or Aurora A/B dual inhibitors without Aurora B inhibition-associated cytokinesis failure and aneuploidy. LY3295668 inhibits the growth of a broad panel of cancer cell lines, including small-cell lung and breast cancer cells. It demonstrates significant efficacy in small-cell lung cancer xenograft and patient-derived tumor preclinical models as a single agent and in combination with standard-of-care agents. LY3295668, as a highly Aurora A-selective inhibitor, may represent a preferred approach to the current pan-Aurora inhibitors as a cancer therapeutic agent.

Formin Links Erythroid Cytoskeleton to Organelle Clearance through Escrt-III Complex during Reticulocyte Maturation

The final stages of mammalian terminal erythropoiesis involve cell cycle exit of orthochromatic erythroblast, enucleation of the condensed nucleus, and organelle clearance of the nascent reticulocytes. Although many critical factors in these processes have been discovered over the past years, several key questions remain unanswered. For example, what are the factors that regulate the exit of the last mitosis of erythroblast for enucleation? How does the nascent reticulocyte separate from the extruded nucleus? What are the signals involved in regulating the clearance of organelles in reticulocyte? Answers to these questions with mechanistic insights are important not only for our understanding of the basic biology of terminal erythropoiesis and pathophysiology of many red cell-related diseases, but also to provide clues for efficient strategies for in vitro or ex vivo generation of red blood cells in transfusion medicine. Our work on formin family proteins, enzymes involved in linear actin filament polymerization, in erythropoiesis may shed light on the clues to these questions. We show in our published work that mDia2, one of the diaphanous-related formins, plays critical roles in enucleation and cytokinesis of erythroblasts. However, the mechanism of how mDia2 regulates these processes is unclear. In this study, we used mDia2 hematopoietic-specific knockout mouse model and revealed that mDia2 controls the motility of the nascent reticulocyte that is required for the detachment of the pyknotic nucleus. Reticulocytes in mDia2 deficient mice are rigid with extended spectrin chains, possibly due to disrupted actin protofilaments. Indeed, a stochastic optical reconstruction (STORM) high resolution microscopy analysis revealed that actin protofilaments were completely disrupted with loss of mDia2 in the reticulocytes. Using immuno-gold stain and electron microscopy, we further found that mDia2 localized at the junctional complex, confirming its critical role in the polymerization of actin protofilaments and maintenance of erythroid cytoskeleton. In addition to the cytoskeleton defects, reticulocytes from mDia2 deficient mice also showed enlarged volume with many organelles failed to be eliminated. Flow cytometry analyses showed that several membrane proteins destined to be downregulated, as well as mitochondria and lysosome markers, remained high in mDia2 deficient reticulocytes. We also performed a tandem mass tagging (TMT) mass spectrometry, which revealed numerous chromatin-associated proteins that failed to be downregulated. Together, these results demonstrated an important role of mDia2 in the reticulocyte maturation. The erythroid phenotypes in mDia2 deficient mice, including failure of cytokinesis and organelle clearance, prompted us to investigate whether there are any defects in ESCRT complexes that are cellular components essential for these processes. Indeed, several ESCRT III complex and associated proteins, including Chmp5, Vta1, and Usp8, were significantly downregulated. mDia2 is known to function though actin polymerization to influence the transcriptional activity of SRF. We found that Chmp5 was a novel target of SRF through ChIP assay. Transplantation of mDia2 knockout c-kit positive progenitors transduced with Chmp5 into the lethally irradiated WT recipient mice dramatically reduced the percentages of bi-nuclear erythroblasts and reverted anemia. Consistent with phenotypes of Chmp5 knockout cells where increased late endosome and lysosome are commonly found, markers for late stage endosome and lysosome were significantly increased in mDia2 deficient erythroblasts and reticulocytes. These data support that mDia2 regulates endosome/MVB and lysosome discharge through Chmp5 during reticulocyte maturation. More importantly, overexpression of Chmp5 largely rescued the defects in lysosome and mitochondria clearance in mDia2 deficient reticulocytes. Our study reveals mDia2 formin as a master regulator of the late stage terminal erythropoiesis in the maintenance of erythroid cytoskeleton and organelle clearance. The novel mDia2-SRF-ESCRT III complex pathway provides the first signaling axis that connects erythroid cytoskeleton to reticulocyte maturation, which may open a new field in signaling networks that modulate enucleation to reticulocyte formation. Disclosures Ji: Longbiopharma: Consultancy.

The Dual Cell Cycle Kinase Inhibitor JNJ-7706621 Reverses Resistance to CD37 Targeted Radioimmunotherapy in Activated B Cell like Diffuse Large B Cell Lymphoma Cell Lines

The CD37 targeting radioimmunoconjugate 177Lu-lilotomab satetraxetan (Betalutin®) is currently being evaluated as monotherapy in a clinical phase 2b trial for patients with follicular lymphoma (FL) and in a phase 1 trial for patients with diffuse large B-cell lymphoma (DLBCL), as well as in a phase 1b trial in combination with rituximab for patients with relapsed/refractory FL. Herein we have investigated the effect of 177Lu-lilotomab satetraxetan in seven activated B-cell like (ABC) DLBCL cell lines. Although the radioimmunoconjugate showed anti-tumor activity, primary resistance was observed in a subset of cell lines: U-2932 and RIVA. Both cell lines are representative for TP53 deficient Double Expressor (DE) DLBCL. Importantly, resistance was not a consequence of reduced binding of the radioimmunoconjugate to cell surface expressed CD37. Thus, we set out to identify drugs able to overcome the resistance to 177Lu-lilotomab satetraxetan in both resistant ABC-DLBCL cell lines. We performed a viability-based screen combining 177Lu-lilotomab satetraxetan with the 384-compound Cambridge Cancer Compound Library. Drug combinations were scored using Bliss and Chou-Talalay algorithms. We identified and characterized the dual-specific CDK1/2 and AURA/B kinase inhibitor JNJ-7706621 as compound able to revert the resistance to radioimmunotherapy (RIT), alongside topoisomerase and histone deacetylases (HDAC) inhibitors. Kinetic studies of the effect of mono- and combination therapy of U-2932 and RIVA cells with JNJ-7706621 and 177Lu-lilotomab satetraxetan are suggestive of a model in which radiation damage induced G2-arrested lymphoma cells eventually enter mitosis (repair or escape) and mitotic entry, progression and exit are impaired by JNJ-7706621 mediated inhibition of CDK1/2 and AURKA/B. Extended residence-time of cells in mitosis due to chromosome condensation and congression defects as well as spindle and mid-spindle assembly failure is likely pivotal for the increased sensitivity to persistent 177Lu-lilotomab satetraxetan deposited DNA damage, ultimately promoting cytokinesis failure (multinucleation, aneuploidy, increased cell size) and cell death. In conclusion, CD37-targeting 177Lu-lilotomab satetraxetan RIT showed activity in several ABC-DLBCL lymphoma cell lines. CD37-independent RIT-resistance was identified in two cell lines representative of aggressive DE ABC-DLBCLs with inactive TP53, and reversed by subsequent inhibition of CDK1/2 and AURKA/B by JNJ-7706621. These findings may be of potential relevance for ongoing clinical trials of 177Lu-lilotomab satetraxetan in relapsed, ASCT-non-eligible DLBCL, and may also be more generally applicable to other 177Lu-based RITs and alternative radionuclide utilizing targeted therapies. Future pre-clinical investigations are required to elucidate the potential application of CDK1/2 and AURKA/B inhibitors as a strategy to revert RIT resistance in TP53 deficient cancers. Disclosures Rødland: Nordic Nanovector ASA: Patents &amp; Royalties, Research Funding. Melhus:Nordic Nanovector ASA: Employment, Equity Ownership, Patents &amp; Royalties. Generalov:Nordic Nanovector ASA: Employment, Equity Ownership, Patents &amp; Royalties. Bertoni:Nordic Nanovector ASA: Research Funding; Oncology Therapeutic Development: Research Funding; PIQUR Therapeutics AG: Other: travel grant, Research Funding; HTG: Other: Expert Statements ; Amgen: Other: travel grants; Astra Zeneca: Other: travel grants; Jazz Pharmaceuticals: Other: travel grants; NEOMED Therapeutics 1: Research Funding; Acerta: Research Funding; ADC Therapeutics: Research Funding; Bayer AG: Research Funding; Cellestia: Research Funding; CTI Life Sciences: Research Funding; EMD Serono: Research Funding; Helsinn: Consultancy, Research Funding; ImmunoGen: Research Funding; Menarini Ricerche: Consultancy, Research Funding. Dahle:Nordic Nanovector ASA: Employment, Equity Ownership, Patents &amp; Royalties. Syljuåsen:Nordic Nanovector ASA: Patents &amp; Royalties, Research Funding. Patzke:Nordic Nanovector ASA: Employment, Patents &amp; Royalties.