Induction of Reactive Oxygen Species-mediated Autophagy by a Novel Microtubule-modulating Agent

Autophagy is being increasingly implicated in both cell survival and death. However, the intricate relationships between drug-induced autophagy and apoptosis remain elusive. Here we demonstrate that a tubulin-binding noscapine analog, (R)-9-bromo-5-((S)-4,5-dimethoxy-1,3-dihydroisobenzofuran-1-yl)-4-methoxy-6-methyl-5,6,7,8-tetrahydro-[1,3]-di-oxolo[4,5-g]isoquinoline (Red-Br-nos), exerts a novel autophagic response followed by apoptotic cell death in human prostate cancer PC-3 cells. Red-Br-nos-induced autophagy was an early event detectable within 12 h that displayed a wide array of characteristic features including double membranous vacuoles with entrapped organelles, acidic vesicular organelles, and increased expression of LC3-II and beclin-1. Red-Br-nos-triggered release of reactive oxygen species (ROS) and attenuation of ROS by tiron, a ROS scavenger, reduced the sub-G₁ population suggesting ROS-dependent apoptosis. Abrogation of ROS also reduced autophagy indicating that ROS triggers autophagy. Pharmacological and genetic approaches to inhibit autophagy uncovered the protective role of Red-Br-nos-induced autophagy in PC-3 cells. Direct effects of the drug on mitochondria viz. disruption of normal cristae architecture and dissipation of mitochondrial transmembrane potential revealed a functional link between ROS generation, autophagy, and apoptosis induction. This is the first report to demonstrate the protective role of ROS-mediated autophagy and induction of caspase-independent ROS-dependent apoptosis in PC-3 cells by Red-Br-nos, a member of the noscapinoid family of microtubule-modulating anticancer agents.     

DNA polymorphism in recombining and non-recombining mating-type-specific loci of the smut fungus Microbotryum

The population-genetic processes leading to the genetic degeneration of non-recombining regions have mainly been studied in animal and plant sex chromosomes. Here, we report population genetic analysis of the processes in the non-recombining mating-type-specific regions of the smut fungus Microbotryum violaceum. M. violaceum has A1 and A2 mating types, determined by mating-type-specific ‘sex chromosomes'' that contain 1–2 Mb long non-recombining regions. If genetic degeneration were occurring, then one would expect reduced DNA polymorphism in the non-recombining regions of this fungus. The analysis of DNA diversity among 19 M. violaceum strains, collected across Europe from Silene latifolia flowers, revealed that (i) DNA polymorphism is relatively low in all 20 studied loci (π∼0.15%), (ii) it is not significantly different between the two mating-type-specific chromosomes nor between the non-recombining and recombining regions, (iii) there is substantial population structure in M. violaceum populations, which resembles that of its host species, S. latifolia, and (iv) there is significant linkage disequilibrium, suggesting that widespread selfing in this species results in a reduction of the effective recombination rate across the genome. We hypothesise that selfing-related reduction of recombination across the M. violaceum genome negates the difference in the level of DNA polymorphism between the recombining and non-recombining regions, and may possibly lead to similar levels of genetic degeneration in the mating-type-specific regions of the non-recombining ‘sex chromosomes'' and elsewhere in the genome.     

A novel microtubule-modulating noscapinoid triggers apoptosis by inducing spindle multipolarity via centrosome amplification and declustering

We have previously shown that a non-toxic noscapinoid, EM011 binds tubulin without altering its monomer/polymer ratio. EM011 is more active than the parent molecule, noscapine, in inducing G2/M arrest, inhibiting cellular proliferation and tumor growth in various human xenograft models. However, the mechanisms of mitotic-block and subsequent cell death have remained elusive. Here, we show that EM011-induced attenuation of microtubule dynamics was associated with impaired association of microtubule plus-end tracking proteins, such as EB1 and CLIP-170. EM011 treatment then led to the formation of multipolar spindles containing 'real' centrioles indicating drug-induced centrosome amplification and persistent centrosome declustering. Centrosome amplification was accompanied by an upregulation of Aurora A and Plk4 protein levels, as well as a surge in the kinase activity of Aurora A, suggesting a deregulation of the centrosome duplication cycle. Cell-cycle phase-specific experiments showed that the 'cytotoxicity-window' of the drug encompasses the late S-G2 period. Drug-treatment, excluding S-phase, not only resulted in lower sub-G1 population but also attenuated centrosome amplification and spindle multipolarity, suggesting that drug-induced centrosome amplification is essential for maximal cell death. Subsequent to a robust mitotic arrest, EM011-treated cells displayed diverse cellular fates suggesting a high degree of intraline variation. Some 'apoptosis-evasive' cells underwent aberrant cytokinesis to generate rampant aneuploidy that perhaps contributed to drug-induced cell death. These data indicate that spindle multipolarity induction by means of centrosome amplification has an exciting chemotherapeutic potential that merits further investigation.     

Integrin-linked kinase regulates senescence in an Rb-dependent manner in cancer cell lines

Anti-integrin-linked kinase (ILK) therapies result in aberrant mitosis including altered mitotic spindle organization, centrosome declustering and mitotic arrest. In contrast to cells that expressed the retinoblastoma tumor suppressor protein Rb, we have shown that in retinoblastoma cell lines that do not express Rb, anti-ILK therapies induced aberrant mitosis that led to the accumulation of temporarily viable multinucleated cells. The present work was undertaken to: 1) determine the ultimate fate of cells that had survived anti-ILK therapies and 2) determine whether or not Rb expression altered the outcome of these cells. Our data indicate that ILK, a chemotherapy drug target is expressed in both well-differentiated, Rb-negative and relatively undifferentiated, Rb-positive retinoblastoma tissue. We show that small molecule targeting of ILK in Rb-positive and Rb-deficient cancer cells results in increased centrosomal declustering, aberrant mitotic spindle formation and multinucleation. However, anti-ILK therapies in vitro have different outcomes in retinoblastoma and glioblastoma cell lines that depend on Rb expression. TUNEL labeling and propidium iodide FACS analysis indicate that Rb-positive cells exposed to anti-ILK therapies are more susceptible to apoptosis and senescence than their Rb-deficient counterparts wherein aberrant mitosis induced by anti-ILK therapies exhibit mitotic arrest instead. These studies are the first to show a role for ILK in chemotherapy-induced senescence in Rb-positive cancer lines. Taken together these results indicate that the oncosuppressive outcomes for anti-ILK therapies in vitro, depend on the expression of the tumor suppressor Rb, a known G₁ checkpoint and senescence regulator.     

Structural alterations of the mitotic apparatus induced by the heat shock response in Drosophila cells

The general architecture of the mitotic apparatus was studied at the ultrastructural level in Drosophila cultured cells. Its two main characteristics are a very polarized spindle and a strong compartmentalization, ensured by large remnants of the nuclear envelope. Such compartmentalization has previously been reported for the rapid syncytial divisions of the early embryo; a similar finding in these cells with a long cycle strongly suggests that this organization constitutes a general mechanism for mitosis in Drosophila. We followed the modifications of these structures after a heat shock of 20, 50 or 120 min at 37°C. Contrary to interphase cells, mitotic cells appear very sensitive to hyperthermia. This stress treatment induced a disruption of the mitotic spindle, a reappearance and an extension of the Golgi apparatus, an inactivation of microtubule nucleation and a disorganization of the centrosome. This organelle seems the first to be affected by the heat shock response. The centrosome is not only inactivated, but also is structurally affected. During the recovery phase after heat stress, the mitotic cells presented a remarkable ring-shaped accumulation of electrondense material around the centrioles. We conclude that in Drosophila cells the mitotic phase, and more specifically the centrosome, are targets of the stress response.     

Functional role of centrosomes in spindle assembly and organization

The centrosome is the main MT organizing center in animal cells, and has traditionally been regarded as essential for organization of the bipolar spindle that facilitates chromosome segregation during mitosis. Centrosomes are associated with the poles of the mitotic spindle, and several cell types require these organelles for spindle formation. However, most plant cells and some female meiotic systems get along without this organelle, and centrosome‐independent spindle assembly has now been identified within some centrosome containing cells. How can such observations, which point to mutually incompatible conclusions regarding the requirement of centrosomes in spindle formation, be interpreted? With emphasis on the functional role of centrosomes, this article summarizes the current models of spindle formation, and outlines how observations obtained from spindle assembly assays in vitro may reconcile conflicting opinions about the mechanism of spindle assembly. It is further described how Drosophila mutants are used to address the functional interrelationships between individual centrosomal proteins and spindle formation in vivo. © 2004 Wiley‐Liss, Inc.     

Centrosome amplification induced by DNA damage occurs during a prolonged G2 phase and involves ATM

Centrosomes are the principal microtubule organising centres in somatic cells. Abnormal centrosome number is common in tumours and occurs after gamma-irradiation and in cells with mutations in DNA repair genes. To investigate how DNA damage causes centrosome amplification, we examined cells that conditionally lack the Rad51 recombinase and thereby incur high levels of spontaneous DNA damage. Rad51-deficient cells arrested in G2 phase and formed supernumerary functional centrosomes, as assessed by light and serial section electron microscopy. This centrosome amplification occurred without an additional DNA replication round and was not the result of cytokinesis failure. G2-to-M checkpoint over-ride by caffeine or wortmannin treatment strongly reduced DNA damage-induced centrosome amplification. Radiation-induced centrosome amplification was potentiated by Rad54 disruption. Gene targeting of ATM reduced, but did not abrogate, centrosome amplification induced by DNA damage in both the Rad51 and Rad54 knockout models, demonstrating ATM-dependent and -independent components of DNA damage-inducible G2-phase centrosome amplification. Our data suggest DNA damage-induced centrosome amplification as a mechanism for ensuring death of cells that evade the DNA damage or spindle assembly checkpoints.     

Centrosomes enhance the fidelity of cytokinesis in vertebrates and are required for cell cycle progression

When centrosomes are destroyed during prophase by laser microsurgery, vertebrate somatic cells form bipolar acentrosomal mitotic spindles (Khodjakov, A., R.W. Cole, B.R. Oakley, and C.L. Rieder. 2000. Curr. Biol. 10:59-67), but the fate of these cells is unknown. Here, we show that, although these cells lack the radial arrays of astral microtubules normally associated with each spindle pole, they undergo a normal anaphase and usually produce two acentrosomal daughter cells. Relative to controls, however, these cells exhibit a significantly higher (30-50%) failure rate in cytokinesis. This failure correlates with the inability of the spindle to properly reposition itself as the cell changes shape. Also, we destroyed just one centrosome during metaphase and followed the fate of the resultant acentrosomal and centrosomal daughter cells. Within 72 h, 100% of the centrosome-containing cells had either entered DNA synthesis or divided. By contrast, during this period, none of the acentrosomal cells had entered S phase. These data reveal that the primary role of the centrosome in somatic cells is not to form the spindle but instead to ensure cytokinesis and subsequent cell cycle progression.     

Caspase-independent apoptosis is activated by diazepam-induced mitotic failure in HeLa cells,but not in human primary fibroblasts

DZ, a benzodiazepine known to affect centrosome separation at prophase, leads to a higher degree of mitotic arrest in HeLa cells than in primary human fibroblasts. In fact, differently from fibroblasts, which undergo a transient block in prophase-to-prometaphase transition, a high proportion of tumor cells attempt to escape from the DZ-imposed mitotic block, fail to undergo complete mitosis and die by mitotic failure. DZ-treated samples showed certain biochemical hallmarks of apoptosis, such as induction of the proapototic Bax protein, mitochondrial alterations assessed by JC-1 staining and TEM analysis, PARP cleavage, and DNA fragmentation. However, in DZ-treated cells, we observed a very low or absent caspase activation as shown by immunofluorescence and immunoblot experiments with antibodies directed to activated caspases and by staining with the pancaspase inhibitor FITC-VAD-FMK. Experiments on mitochondrial depolymerization and apoptosis induction carried out in the presence of specific inhibitors of caspase-2 and caspase-3/7 indicated a caspase-independent apoptotic process induced by DZ. Accordingly, TEM analysis of treated cells revealed ultrastructural features resembling those reported for caspase-independent apoptosis. In conclusion, we hypothesize that HeLa cells override the prophase block imposed by DZ, producing a high rate of aberrant pro-metaphases, which, in turn, activates caspase-independent, apoptosis-like mitotic catastrophe.     

Community genomic analysis of an extremely acidophilic sulfur-oxidizing biofilm

Highly acidic (pH 0–1) biofilms, known as ‘snottites'', form on the walls and ceilings of hydrogen sulfide-rich caves. We investigated the population structure, physiology and biogeochemistry of these biofilms using metagenomics, rRNA methods and lipid geochemistry. Snottites from the Frasassi cave system (Italy) are dominated (>70% of cells) by Acidithiobacillus thiooxidans, with smaller populations including an archaeon in the uncultivated ‘G-plasma'' clade of Thermoplasmatales (>15%) and a bacterium in the Acidimicrobiaceae family (>5%). Based on metagenomic evidence, the Acidithiobacillus population is autotrophic (ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), carboxysomes) and oxidizes sulfur by the sulfide–quinone reductase and sox pathways. No reads matching nitrogen fixation genes were detected in the metagenome, whereas multiple matches to nitrogen assimilation functions are present, consistent with geochemical evidence, that fixed nitrogen is available in the snottite environment to support autotrophic growth. Evidence for adaptations to extreme acidity include Acidithiobacillus sequences for cation transporters and hopanoid synthesis, and direct measurements of hopanoid membrane lipids. Based on combined metagenomic, molecular and geochemical evidence, we suggest that Acidithiobacillus is the snottite architect and main primary producer, and that snottite morphology and distributions in the cave environment are directly related to the supply of C, N and energy substrates from the cave atmosphere.     

Mitochondrial genome regulates mitotic fidelity by maintaining centrosomal homeostasis

Centrosomes direct spindle morphogenesis to assemble a bipolar mitotic apparatus to enable error-free chromosome segregation and preclude chromosomal instability (CIN). Amplified centrosomes, a hallmark of cancer cells, set the stage for CIN, which underlies malignant transformation and evolution of aggressive phenotypes. Several studies report CIN and a tumorigenic and/or aggressive transformation in mitochondrial DNA (mtDNA)-depleted cells. Although several nuclear-encoded proteins are implicated in centrosome duplication and spindle organization, the involvement of mtDNA encoded proteins in centrosome amplification (CA) remains elusive. Here we show that disruption of mitochondrial function by depletion of mtDNA induces robust CA and mitotic aberrations in osteosarcoma cells. We found that overexpression of Aurora A, Polo-like kinase 4 (PLK4), and Cyclin E was associated with emergence of amplified centrosomes. Supernumerary centrosomes in rho0 (mtDNA-depleted) cells resulted in multipolar mitoses bearing “real” centrosomes with paired centrioles at the multiple poles. This abnormal phenotype was recapitulated by inhibition of respiratory complex I in parental cells, suggesting a role for electron transport chain (ETC) in maintaining numeral centrosomal homeostasis. Furthermore, rho0 cells displayed a decreased proliferative capacity owing to a G₂/M arrest. Downregulation of nuclear-encoded p53 in rho0 cells underscores the importance of mitochondrial and nuclear genome crosstalk and may perhaps underlie the observed mitotic aberrations. By contrast, repletion of wild-type mtDNA in rho0 cells (cybrid) demonstrated a much lesser extent of CA and spindle multipolarity, suggesting partial restoration of centrosomal homeostasis. Our study provides compelling evidence to implicate the role of mitochondria in regulation of centrosome duplication, spindle architecture, and spindle pole integrity.     

Gamma-actin is involved in regulating centrosome function and mitotic progression in cancer cells

Reorganization of the actin cytoskeleton during mitosis is crucial for regulating cell division. A functional role for γ-actin in mitotic arrest induced by the microtubule-targeted agent, paclitaxel, has recently been demonstrated. We hypothesized that γ-actin plays a role in mitosis. Herein, we investigated the effect of γ-actin in mitosis and demonstrated that γ-actin is important in the distribution of β-actin and formation of actin-rich retraction fibers during mitosis. The reduced ability of paclitaxel to induce mitotic arrest as a result of γ-actin depletion was replicated with a range of mitotic inhibitors, suggesting that γ-actin loss reduces the ability of broad classes of anti-mitotic agents to induce mitotic arrest. In addition, partial depletion of γ-actin enhanced centrosome amplification in cancer cells and caused a significant delay in prometaphase/metaphase. This prolonged prometaphase/metaphase arrest was due to mitotic defects such as uncongressed and missegregated chromosomes, and correlated with an increased presence of mitotic spindle abnormalities in the γ-actin depleted cells. Collectively, these results demonstrate a previously unknown role for γ-actin in regulating centrosome function, chromosome alignment and maintenance of mitotic spindle integrity.     

Life in an unusual intracellular niche: a bacterial symbiont infecting the nucleus of amoebae

Amoebae serve as hosts for various intracellular bacteria, including human pathogens. These microbes are able to overcome amoebal defense mechanisms and successfully establish a niche for replication, which is usually the cytoplasm. Here, we report on the discovery of a bacterial symbiont that is located inside the nucleus of its Hartmannella sp. host. This symbiont, tentatively named ‘Candidatus Nucleicultrix amoebiphila'', is only moderately related to known bacteria (∼90% 16S and 23S rRNA sequence similarity) and member of a novel clade of protist symbionts affiliated with the Rickettsiales and Rhodospirillales. Screening of 16S rRNA amplicon data sets revealed a broad distribution of these bacteria in freshwater and soil habitats. ‘Candidatus Nucleicultrix amoebiphila'' traffics within 6 h post infection to the host nucleus. Maximum infection levels are reached after 96–120 h, at which time point the nucleus is pronouncedly enlarged and filled with bacteria. Transmission of the symbionts occurs vertically upon host cell division but may also occur horizontally through host cell lysis. Although we observed no impact on the fitness of the original Hartmannella sp. host, the bacteria are rather lytic for Acanthamoeba castellanii. Intranuclear symbiosis is an exceptional phenomenon, and amoebae represent an ideal model system to further investigate evolution and underlying molecular mechanisms of these unique microbial associations.     

Celastrus paniculatus Willd. mitigates t-BHP induced oxidative and apoptotic damage in C2C12 murine muscle cells

Identification, exploration and scientific validation of antioxidant rich herbal extracts to mitigate the radical induced cell damage provide new insights in the field of ayurvedic research/therapies. In the present study, we evaluated the anti-oxidant and anti-apoptotic potential of Celastrus paniculatus seed extract (CPSE) against tertiary butyl hydroperoxide (t-BHP) induced mice muscle cell damage. The extract at a dose of 50 µg/ml protected the cells up to 70 % as evidenced by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell survival assay and also prevented LDH leakage against t-BHP induced cytotoxicity. CPSE showed potential antioxidant activity by restoring mitochondrial membrane potential and inhibited reactive oxygen species generation and lipid peroxidation. CPSE pretreatment also regulated the antioxidant markers such as superoxide dismutase and catalase enzymes content and proteins expression. Further CPSE showed anti-apoptotic effects by regulating cytochrome-C and heat shock protein-70 expression and also showed 43 % muscle cell DNA damage inhibitory activity against t-BHP challenge as observed by single cell gel electrophoresis assay. Overall the extract inhibits the muscle cell damage, thus explaining the possible anti-oxidant/anti-apoptotic defense status of the C. paniculatus seed extract.     

Loss of PIDD limits NF-κB activation and cytokine production but not cell survival or transformation after DNA damage

Activation of NF-κB (nuclear factor of kappa light chain gene enhancer in B cells) in response to DNA damage is considered to contribute to repair of genetic lesions, increased cell survival and cytokine release. The molecular mechanisms orchestrating this cytoplasmic event involve core components of the nuclear DNA damage response machinery, including ATM-kinase (ataxia telangiectasia mutated kinase) and PARP-1 (poly (ADP-ribose) polymerase 1). The physiological consequences of defective NF-κB activation in this context, however, remain poorly investigated. Here we report on the role of the ‘p53-induced protein with a death domain'', PIDD, which appears rate limiting in this process, as is PARP-1. Despite impaired NF-κB activation, DNA damage did not increase cell death or reduce clonal survival of various cell types lacking PIDD, such as mouse embryonic fibroblasts or stem and progenitor cells of the hematopoietic system. Furthermore, lymphomagenesis induced by γ-irradiation (IR) was unaffected by deficiency for PIDD or PARP-1, indicating that loss of DNA damage-triggered NF-κB signalling does not affect IR-driven tumorigenesis. However, loss of either gene compromised cytokine release after acute IR injury. Hence, we propose that NF-κB''s most notable function after DNA damage in primary cells is related to the release of cytokines, thereby contributing to sterile inflammation.     

Nucleophosmin is required for chromosome congression, proper mitotic spindle formation, and kinetochore-microtubule attachment in HeLa cells

Nucleophosmin (NPM) is an abundantly expressed multifunctional nucleolar phosphoprotein. Here we show that depletion of NPM by RNA interference causes defects in cell division, followed by an arrest of DNA synthesis due to activation of a p53-dependent checkpoint response in HeLa cells. Depletion of NPM leads to mitotic arrest due to spindle checkpoint activation. The mitotic cells arrested by NPM depletion have defects in chromosome congression, proper mitotic spindle and centrosome formation, as well as defects in kinetochore-microtubule attachments. Loss of NPM thus causes severe mitotic defects and delayed mitotic progression. These findings indicate that NPM is essential for mitotic progression and cell proliferation.     

Centrosome-declustering drugs mediate a two-pronged attack on interphase and mitosis in supercentrosomal cancer cells

Classical anti-mitotic drugs have failed to translate their preclinical efficacy into clinical response in human trials. Their clinical failure has challenged the notion that tumor cells divide frequently at rates comparable to those of cancer cells in vitro and in xenograft models. Given the preponderance of interphase cells in clinical tumors, we asked whether targeting amplified centrosomes, which cancer cells carefully preserve in a tightly clustered conformation throughout interphase, presents a superior chemotherapeutic strategy that sabotages interphase-specific cellular activities, such as migration. Herein we have utilized supercentrosomal N1E-115 murine neuroblastoma cells as a test-bed to study interphase centrosome declustering induced by putative declustering agents, such as Reduced-9-bromonoscapine (RedBr-Nos), Griseofulvin and PJ-34. We found tight ‘supercentrosomal'' clusters in the interphase and mitosis of ~80% of patients'' tumor cells with excess centrosomes. RedBr-Nos was the strongest declustering agent with a declustering index of 0.36 and completely dispersed interphase centrosome clusters in N1E-115 cells. Interphase centrosome declustering caused inhibition of neurite formation, impairment of cell polarization and Golgi organization, disrupted cellular protrusions and focal adhesion contacts—factors that are crucial prerequisites for directional migration. Thus our data illustrate an interphase-specific potential anti-migratory role of centrosome-declustering agents in addition to their previously acknowledged ability to induce spindle multipolarity and mitotic catastrophe. Centrosome-declustering agents counter centrosome clustering to inhibit directional cell migration in interphase cells and set up multipolar mitotic catastrophe, suggesting that disbanding the nuclear–centrosome–Golgi axis is a potential anti-metastasis strategy.Unlike in vitro cell cultures, cancer cells in patients'' tumor tissues have low mitotic indices and proliferation rates.¹ Consequently, drugs targeting mitosis demonstrate limited clinical efficacy, which exposes a fundamental weakness in the rationale underlying their clinical development. By contrast, classical microtubule-targeting agents (MTAs), largely believed to act by perturbing mitosis, remain the mainstay of chemotherapy in the clinic. Given the miniscule population of mitotic cells in patient tumors,^{2, 3} it stands to reason that MTAs must target interphase.⁴ This paradigm shift has spurred an intense search for novel interphase targets that combine the ‘ideal'' attributes of cancer-cell selectivity and the ability to confer vulnerability on a large proportion of tumor cells.Centrosomes, the major microtubule-organizing centers (MTOCs) of cells, are required for accurate cell division, cell motility and cilia formation.⁵ The number of centrosomes within a cell is strictly controlled, and their duplication occurs only once per cell cycle. Nearly all types of cancer cells have abnormal numbers of centrosomes,^{6, 7, 8} which correlates with chromosomal instability during tumorigenesis.^{9, 10, 11} Supernumerary centrosomes in cancer cells can cause spindle multipolarity and thus non-viable progeny. Cancer cells avoid this outcome by clustering centrosomes to assemble a pseudo-bipolar mitotic spindle, which yields viable daughter cells.¹² Thus disrupting centrosome clustering may selectively drive cancer cells with amplified centrosomes to mitotic catastrophe and apoptosis without affecting normal cells.The fate and interphase role of the supercentrosomal cluster inherited by each daughter cell at the end of a pseudobipolar mitosis is unknown. This is an important research question, because a majority of cells within tumors are in interphase and the centrosomes'' command over microtubule nucleation is crucial for the cellular organization and motility in interphase. If cancer cells cluster centrosomes in interphase, then disrupting the cluster could impact interphase-specific processes, opening up a vital therapeutic avenue. We envision that centrosome declustering would (a) derail interphase-specific polarization and migration processes and (b) precipitate multipolar mitosis culminating in apoptosis. This two-pronged strategy would impact a significantly larger proportion of tumor cells and consign them to death. Our study herein establishes that centrosome-declustering drugs (RedBr-Nos, Griseofulvin and PJ-34) achieve this two-pronged attack as a unique class of agents that exhibit multiple cellular activities.     

Nucleoporin Nup62 maintains centrosome homeostasis

Centrosomes are comprised of 2 orthogonally arranged centrioles surrounded by the pericentriolar material (PCM), which serves as the main microtubule organizing center of the animal cell. More importantly, centrosomes also control spindle polarity and orientation during mitosis. Recently, we and other investigators discovered that several nucleoporins play critical roles during cell division. Here, we show that nucleoporin Nup62 plays a novel role in centrosome integrity. Knockdown of Nup62 induced mitotic arrest in G₂/M phases and mitotic cell death. Depletion of Nup62 using RNA interference results in defective centrosome segregation and centriole maturation during the G₂ phase. Moreover, Nup62 depletion in human cells leads to the appearance of multinucleated cells and induces the formation of multipolar centrosomes, centriole synthesis defects, dramatic spindle orientation defects, and centrosome component rearrangements that impair cell bi-polarity. Our results also point to a potential role of Nup62 in targeting gamma-tubulin and SAS-6 to the centrioles.