Multiple centrosomes: together they stand, divided they fall

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.

TACC3: a multi-functional protein promoting cancer cell survival and aggressiveness

TACC3 is the most oncogenic member of the transforming acidic coiled-coil domain-containing protein (TACC) family. It is one of the major recruitment factors of distinct multi-protein complexes. TACC3 is localized to spindles, centrosomes, and nucleus, and regulates key oncogenic processes, including cell proliferation, migration, invasion, and stemness. Recently, TACC3 inhibition has been identified as a vulnerability in highly aggressive cancers, such as cancers with centrosome amplification (CA). TACC3 has spatiotemporal functions throughout the cell cycle; therefore, targeting TACC3 causes cell death in mitosis and interphase in cancer cells with CA. In the clinics, TACC3 is highly expressed and associated with worse survival in multiple cancers. Furthermore, TACC3 is a part of one of the most common fusions of FGFR, FGFR3-TACC3 and is important for the oncogenicity of the fusion. A detailed understanding of the regulation of TACC3 expression, its key partners, and molecular functions in cancer cells is vital for uncovering the most vulnerable tumors and maximizing the therapeutic potential of targeting this highly oncogenic protein. In this review, we summarize the established and emerging interactors and spatiotemporal functions of TACC3 in cancer cells, discuss the potential of TACC3 as a biomarker in cancer, and therapeutic potential of its inhibition.

The TRIM69-MST2 signaling axis regulates centrosome dynamics and chromosome segregation

Stringent control of centrosome duplication and separation is important for preventing chromosome instability. Structural and numerical alterations in centrosomes are hallmarks of neoplastic cells and contribute to tumorigenesis. We show that a Centrosome Amplification 20 (CA20) gene signature is associated with high expression of the Tripartite Motif (TRIM) family member E3 ubiquitin ligase, TRIM69. TRIM69-ablation in cancer cells leads to centrosome scattering and chromosome segregation defects. We identify Serine/threonine-protein kinase 3 (MST2) as a new direct binding partner of TRIM69. TRIM69 redistributes MST2 to the perinuclear cytoskeleton, promotes its association with Polo-like kinase 1 (PLK1) and stimulates MST2 phosphorylation at S15 (a known PLK1 phosphorylation site that is critical for centrosome disjunction). TRIM69 also promotes microtubule bundling and centrosome segregation that requires PRC1 and DYNEIN. Taken together, we identify TRIM69 as a new proximal regulator of distinct signaling pathways that regulate centrosome dynamics and promote bipolar mitosis.

Centrosome linker diversity and its function in centrosome clustering and mitotic spindle formation

The centrosome linker joins the two interphase centrosomes of a cell into one microtubule organizing center. Despite increasing knowledge on linker components, linker diversity in different cell types and their role in cells with supernumerary centrosomes remained unexplored. Here, we identified Ninein as a C-Nap1-anchored centrosome linker component that provides linker function in RPE1 cells while in HCT116 and U2OS cells, Ninein and Rootletin link centrosomes together. In interphase, overamplified centrosomes use the linker for centrosome clustering, where Rootletin gains centrosome linker function in RPE1 cells. Surprisingly, in cells with centrosome overamplification, C-Nap1 loss prolongs metaphase through persistent activation of the spindle assembly checkpoint indicated by BUB1 and MAD1 accumulation at kinetochores. In cells lacking C-Nap1, the reduction of microtubule nucleation at centrosomes and the delay in nuclear envelop rupture in prophase probably cause mitotic defects like multipolar spindle formation and chromosome mis-segregation. These defects are enhanced when the kinesin HSET, which normally clusters multiple centrosomes in mitosis, is partially inhibited indicating a functional interplay between C-Nap1 and centrosome clustering in mitosis.

A fine balance among key biophysical factors is required for recovery of bipolar mitotic spindle from monopolar and multipolar abnormalities

During mitosis, equal partitioning of chromosomes into two daughter cells requires assembly of a bipolar mitotic spindle. Because the spindle poles are each organized by a centrosome in animal cells, centrosome defects can lead to monopolar or multipolar spindles. However, the cell can effectively recover the bipolar spindle by separating the centrosomes in monopolar spindles and clustering them in multipolar spindles. To interrogate how a cell can separate and cluster centrosomes as needed to form a bipolar spindle, we developed a biophysical model, based on experimental data, which uses effective potential energies to describe key mechanical forces driving centrosome movements during spindle assembly. Our model identified general biophysical factors crucial for robust bipolarization of spindles that start as monopolar or multipolar. These factors include appropriate force fluctuation between centrosomes, balance between repulsive and attractive forces between centrosomes, exclusion of the centrosomes from the cell center, proper cell size and geometry, and a limited centrosome number. Consistently, we found experimentally that bipolar centrosome clustering is promoted as mitotic cell aspect ratio and volume decrease in tetraploid cancer cells. Our model provides mechanistic explanations for many more experimental phenomena and a useful theoretical framework for future studies of spindle assembly.

Mechanics of microtubule organizing center clustering and spindle positioning in budding yeast Cryptococcus neoformans

The dynamic process of mitotic spindle assembly depends on multitudes of inter-dependent interactions involving kinetochores (KTs), microtubules (MTs), spindle pole bodies (SPBs), and molecular motors. Before forming the mitotic spindle, multiple visible microtubule organizing centers (MTOCs) coalesce into a single focus to serve as an SPB in the pathogenic budding yeast, Cryptococcus neoformans. To explain this unusual phenomenon in the fungal kingdom, we propose a "search and capture" model, in which cytoplasmic MTs (cMTs) nucleated by MTOCs grow and capture each other to promote MTOC clustering. Our quantitative modeling identifies multiple redundant mechanisms mediated by a combination of cMT-cell cortex interactions and inter-cMT coupling to facilitate MTOC clustering within the physiological time limit as determined by time-lapse live-cell microscopy. Besides, we screen various possible mechanisms by computational modeling and propose optimal conditions that favor proper spindle positioning-a critical determinant for timely chromosome segregation. These analyses also reveal that a combined effect of MT buckling, dynein pull, and cortical push maintains spatiotemporal spindle localization.

Microtubule motors in centrosome homeostasis: A target for cancer therapy?

Cancer is a grievous concern to human health, owing to a massive heterogeneity in its cause and impact. Dysregulation (numerical, positional and/or structural) of centrosomes is one of the notable factors among those that promote onset and progression of cancers. In a normal dividing cell, a pair of centrosomes forms two poles, thereby governing the formation of a bipolar spindle assembly. A large number of cancer cells, however, harbor supernumerary centrosomes, which mimic the bipolar arrangement in normal cells by centrosome clustering (CC) into two opposite poles, thus developing a pseudo-bipolar spindle assembly. Manipulation of centrosome homeostasis is the paramount pre-requisite for the evasive strategy of CC in cancers. Out of the varied factors that uphold centrosome integrity, microtubule motors (MiMos) play a critical role. Categorized as dyneins and kinesins, MiMos are involved in cohesion of centrosomes, and also facilitate the maintenance of the numerical, positional and structural integrity of centrosomes. Herein, we elucidate the decisive mechanisms undertaken by MiMos to mediate centrosome homeostasis, and how dysregulation of the same might lead to CC in cancer cells. Understanding the impact of MiMos on CC might open up avenues toward a credible therapeutic target against diverse cancers.

A Precision Medicine Drug Discovery Pipeline Identifies Combined CDK2 and 9 Inhibition as a Novel Therapeutic Strategy in Colorectal Cancer

Colorectal cancer is the third most common cancer in the United States and responsible for over 50,000 deaths each year. Therapeutic options for advanced colorectal cancer are limited, and there remains an unmet clinical need to identify new treatments for this deadly disease. To address this need, we developed a precision medicine pipeline that integrates high-throughput chemical screens with matched patient-derived cell lines and patient-derived xenografts (PDX) to identify new treatments for colorectal cancer. High-throughput screens of 2,100 compounds were performed across six low-passage, patient-derived colorectal cancer cell lines. These screens identified the CDK inhibitor drug class among the most effective cytotoxic compounds across six colorectal cancer lines. Among this class, combined targeting of CDK1, 2, and 9 was the most effective, with IC₅₀s ranging from 110 nmol/L to 1.2 μmol/L. Knockdown of CDK9 in the presence of a CDK2 inhibitor (CVT-313) showed that CDK9 knockdown acted synergistically with CDK2 inhibition. Mechanistically, dual CDK2/9 inhibition induced significant G₂-M arrest and anaphase catastrophe. Combined CDK2/9 inhibition in vivo synergistically reduced PDX tumor growth. Our precision medicine pipeline provides a robust screening and validation platform to identify promising new cancer therapies. Application of this platform to colorectal cancer pinpointed CDK2/9 dual inhibition as a novel combinatorial therapy to treat colorectal cancer.

Cdc6 disruption leads to centrosome abnormalities and chromosome instability in pancreatic cancer cells

Cell division cycle 6 (Cdc6) plays key roles in regulating DNA replication, and activation and maintenance of cell cycle check points. In addition, Cdc6 exerts oncogenic properties via genomic instability associated with incomplete DNA replication. This study aimed to examine the effects of Cdc6 on pancreatic cancer (PC) cells. Our results showed that Cdc6 expression was higher in clinical PC specimens (based on analysis of the GEPIA database) and cell lines, and the high Cdc6 expression was associated with poorer survival in The Cancer Genome Atlas-PC cohort. In addition, Cdc6-depleted PC cells significantly inhibited cell proliferation and colony formation, delayed G₂/M cell cycle progression, and increased expression of p-histone H3 and cyclin A2 levels. These observations could be explained by Cdc6 depletion leading to multipolar and split spindles via centrosome amplification and microtubule disorganization which eventually increases chromosome missegregation. Furthermore, Cdc6-depleted PC cells showed significantly increased apoptosis, which was consistent with increased caspase-9 and caspase-3 activation. Collectively, our results demonstrated that Cdc6-depleted PC cells are arrested in mitosis and eventually undergo cell death by induced multipolar spindles, centrosome aberrations, microtubule disorganization, and chromosome instability. In conclusion, Cdc6 may be a potential biomarker and therapeutic target for PC.

Inhibition of kinesin motor protein KIFC1 by AZ82 induces multipolar mitosis and apoptosis in prostate cancer cell

Kinesin 14 family member KIFC1 is a mitotic kinesin which contains a C-terminal motor domain and plays a vital role for clustering the amplified centrosomes. Overexpression of KIFC1 in prostate cancer (PCa) cells showed resistance to docetaxel (DTX). The present study revealed that small KIFC1 inhibitor AZ82 suppresed the transcription and translation of KIFC1 significantly in PCa cells. AZ82 inhibited the KIFC1 expression both in the cytoplasm and nucleus of PCa cells. Inhibition of KIFC1 by AZ82 caused multipolar mitosis in PCa cells via de-clustering the amplified centrosomes and decreased the rate of cancer cell growth and proliferation. Moreover, depletion of KIFC1 reduced cells entering the cell cycle and caused PCa cells death through apoptosis by increasing the expression of Bax and Cytochrome C. Thereby, KIFC1 silencing and inhibition decreased the PCa cells survival by inducing multipolar mitosis as well as apoptosis, suggesting inhibition of KIFC1 using AZ82 might be a strategy to treat PCa by controlling the cancer cell proliferation.

Perlingeiro R, Cisneros B. Loss of Dystroglycan Drives Cellular Senescence via Defective Mitosis-Mediated Genomic Instability

Nuclear β-dystroglycan (β-DG) is involved in the maintenance of nuclear architecture and function. Nonetheless, its relevance in defined nuclear processes remains to be determined. In this study we generated a C2C12 cell-based DG-null model using CRISPR-Cas9 technology to provide insights into the role of β-DG on nuclear processes. Since DG-null cells exhibited decreased levels of lamin B1, we aimed to elucidate the contribution of DG to senescence, owing to the central role of lamin B1 in this pathway. Remarkably, the lack of DG enables C2C12 cells to acquire senescent features, including cell-cycle arrest, increased senescence-associated-β-galactosidase activity, heterochromatin loss, aberrant nuclear morphology and nucleolar disruption. We demonstrated that genomic instability is one driving cause of the senescent phenotype in DG-null cells via the activation of a DNA-damage response associated with mitotic failure, as shown by the presence of multipolar mitotic spindles, which in turn induced the formation of micronuclei and γH2AX foci (DNA-damage marker), telomere shortening and p53/p21 upregulation. Altogether, these events might ultimately lead to premature senescence, impeding the replication of the damaged genome. In summary, we present evidence supporting a role for DG in protecting against senescence, through the maintenance of proper lamin B1 expression/localization and proper mitotic spindle organization.

CSAG1 maintains the integrity of the mitotic centrosome in cells with defective p53

Centrosomes focus microtubules to promote mitotic spindle bipolarity, a critical requirement for balanced chromosome segregation. Comprehensive understanding of centrosome function and regulation requires a complete inventory of components. While many centrosome components have been identified, others yet remain undiscovered. We have used a bioinformatics approach, based on 'guilt by association' expression to identify novel mitotic components among the large group of predicted human proteins that have yet to be functionally characterized. Here, we identify chondrosarcoma-associated gene 1 protein (CSAG1) in maintaining centrosome integrity during mitosis. Depletion of CSAG1 disrupts centrosomes and leads to multipolar spindles, particularly in cells with compromised p53 function. Thus, CSAG1 may reflect a class of 'mitotic addiction' genes, whose expression is more essential in transformed cells.

Centrosome Abnormalities and Polyploidy in Murine Mammary Carcinomas with Different Degrees of Hormone Responsiveness

Centrosome amplification leads to aberrant mitosis, giving rise to aneuploidy and it has been associated with poor prognosis in human cancers. This study aimed to evaluate the relationship between polyploidy, centrosome abnormalities, and response to endocrine treatment in progestin-induced mouse mammary carcinomas. We found cells with three or more centrosomes in the polyploid tumors. The endocrine unresponsive tumors showed a higher average number of centrosomes per cell than the responsive tumors. The results suggest an association between polyploidy and centrosome amplification with the resistance to endocrine therapy in this luminal breast cancer model.

TRIGGERING ANAPHASE CATASTROPHE TO COMBAT ANEUPLOID CANCERS

Cancer cells are genetically unstable and often have supernumerary centrosomes. When supernumerary centrosome clustering is inhibited at mitosis, multipolar cell division is forced, triggering apoptosis in daughter cells. This proapoptotic pathway is called anaphase catastrophe. Cyclin-dependent kinase 1 (CDK1) or CDK2 inhibitors can antagonize centrosome clustering and cause anaphase catastrophe to occur in lung cancer and other types of cancer. The centrosome protein CP110, a CDK1 and CDK2 phosphorylation substrate, engages anaphase catastrophe. Intriguingly, CP110 is downregulated by the KRAS oncoprotein, enhancing sensitivity of KRAS-driven cancers to CDK2 inhibitors. Anaphase catastrophe eradicates aneuploid cancer cells while relatively sparing normal diploid cells with two centrosomes. This therapeutic window discriminates between normal and neoplastic cells and can be exploited in the cancer clinic. The work reviewed here establishes that pharmacologically-induced anaphase catastrophe is useful to combat aneuploid cancers, especially when the KRAS oncoprotein is activated. This addresses an unmet medical need in oncology.

SKA1 overexpression is associated with poor prognosis in hepatocellular carcinoma

BACKGROUND

SKA1, an important mitosis protein, has been indicated in the initiation and progression of several malignancies. However, its clinical significance in hepatocellular carcinoma (HCC) remain to be elucidated.

METHODS

mRNA expression of SKA1 was examined in 126 HCC and paired non-neoplastic tissues using real-time PCR and validated in The Cancer Genome Atlas (TCGA) database. SKA1 protein expression was detected using immunohistochemistry in the 126 HCC tissues and its associations with clinicopathological parameters and prognosis were analyzed. Hierarchical cluster analysis and gene set enrichment analysis (GSEA) were performed in selected Gene Expression Omnibus data sets.

RESULTS

SKA1 mRNA expression was significantly elevated in HCC tissues from both local hospital and TCGA database. Immunohistochemistry revealed that increased SKA1 expression was present in 65 of the 126 cases and was significantly associated with higher serum alpha-fetoprotein concentration, larger tumor size and higher TNM stage. Patients with positive SKA1 expression showed significantly worse overall and relapse-free survival. Multivariate Cox regression analysis revealed that SKA1 was an independent predictor of patient prognosis. Gene expression profiling analysis of public data showed that high-SKA1 expression HCC tissues had similar gene expression profiles with fetal liver tissues. Moreover, GSEA showed that genes up-regulated in high SKA1 HCC subgroup were significantly enriched in cell cycle pathway, while genes down-regulated were significantly enriched in apoptosis pathway.

CONCLUSIONS

Our findings indicate that the oncofetal gene SKA1 might be involved in the progression of the HCC and could serve as a prognostic marker for HCC.

Inhibition of CPAP-tubulin interaction prevents proliferation of centrosome-amplified cancer cells

Centrosome amplification is a hallmark of human cancers that can trigger cancer cell invasion. To survive, cancer cells cluster amplified extra centrosomes and achieve pseudobipolar division. Here, we set out to prevent clustering of extra centrosomes. Tubulin, by interacting with the centrosomal protein CPAP, negatively regulates CPAP‐dependent peri‐centriolar material recruitment, and concurrently microtubule nucleation. Screening for compounds that perturb CPAP–tubulin interaction led to the identification of CCB02, which selectively binds at the CPAP binding site of tubulin. Genetic and chemical perturbation of CPAP–tubulin interaction activates extra centrosomes to nucleate enhanced numbers of microtubules prior to mitosis. This causes cells to undergo centrosome de‐clustering, prolonged multipolar mitosis, and cell death. 3D‐organotypic invasion assays reveal that CCB02 has broad anti‐invasive activity in various cancer models, including tyrosine kinase inhibitor (TKI)‐resistant EGFR‐mutant non‐small‐cell lung cancers. Thus, we have identified a vulnerability of cancer cells to activation of extra centrosomes, which may serve as a global approach to target various tumors, including drug‐resistant cancers exhibiting high incidence of centrosome amplification.

Engaging Anaphase Catastrophe Mechanisms to Eradicate Aneuploid Cancers

Cancer cells often have supernumerary centrosomes that promote genomic instability, a pathognomonic feature of cancer. During mitosis, cancer cells with supernumerary centrosomes undergo bipolar cell division by clustering centrosomes into two poles. When supernumerary centrosome clustering is antagonized, cancer cells are forced to undergo multipolar division leading to death of daughter cells. This proapoptotic pathway, called anaphase catastrophe, preferentially eliminates aneuploid cancer cells and malignant tumors in engineered mouse models. Anaphase catastrophe occurs through the loss or inhibition of the centrosomal protein CP110, a direct cyclin-dependent kinase 1 (CDK1) and CDK2 target. Intriguingly, CP110 is repressed by the KRAS oncoprotein. This sensitizes KRAS-driven lung cancers (an unmet medical need) to respond to CDK2 inhibitors. Anaphase catastrophe-inducing agents like CDK1 and CDK2 antagonists are lethal to cancer cells with supernumerary centrosomes, but can relatively spare normal cells with two centrosomes. This mechanism is proposed to provide a therapeutic window in the cancer clinic following treatment with a CDK1 or CDK2 inhibitor. Taken together, anaphase catastrophe is a clinically tractable mechanism that promotes death of neoplastic tumors with aneuploidy, a hallmark of cancer. Mol Cancer Ther; 17(4); 724-31. ©2018 AACR.

Exploring the binding sites and binding mechanism for hydrotrope encapsulated griseofulvin drug on γ-tubulin protein

The protein γ-tubulin plays an important role in centrosomal clustering and this makes it an attractive therapeutic target for treating cancers. Griseofulvin, an antifungal drug, has recently been used to inhibit proliferation of various types of cancer cells. It can also affect the microtubule dynamics by targeting the γ-tubulin protein. So far, the binding pockets of γ-tubulin protein are not properly identified and the exact mechanism by which the drug binds to it is an area of intense speculation and research. The aim of the present study is to investigate the binding mechanism and binding affinity of griseofulvin on γ-tubulin protein using classical molecular dynamics simulations. Since the drug griseofulvin is sparingly soluble in water, here we also present a promising approach for formulating and achieving delivery of hydrophobic griseofulvin drug via hydrotrope sodium cumene sulfonate (SCS) cluster. We observe that the binding pockets of γ-tubulin protein are mainly formed by the H8, H9 helices and S7, S8, S14 strands and the hydrophobic interactions between the drug and γ-tubulin protein drive the binding process. The release of the drug griseofulvin from the SCS cluster is confirmed by the coordination number analysis. We also find hydrotrope-induced alteration of the binding sites of γ-tubulin protein and the weakening of the drug-protein interactions.

Targeting DNA Repair

Genomic instability is a characteristic of most human cancers and plays critical roles in both cancer development and progression. There are various forms of genomic instability arising from many different pathways, such as DNA damage from endogenous and exogenous sources, centrosome amplification, telomere damage, and epigenetic modifications. DNA-repair pathways can enable tumor cells to survive DNA damage. The failure to respond to DNA damage is a characteristic associated with genomic instability. Understanding of genomic instability in cancer is still very limited, but the further understanding of the molecular mechanisms through which the DNA damage response (DDR) operates, in combination with the elucidation of the genetic interactions between DDR pathways and other cell pathways, will provide therapeutic opportunities for the personalized medicine of cancer.

CKAP2 phosphorylation by CDK1/cyclinB1 is crucial for maintaining centrosome integrity

Previously, we have reported that CKAP2 is involved in the maintenance of centrosome integrity, thus allowing for proper mitosis in primary hepatocytes. To understand this biological process, we identified the mitosis-specific phosphorylation sites in mouse CKAP2 and investigated CKAP’s possible role in cell cycle progression. Because we observed mouse CKAP2 depletion in amplified centrosomes and aberrant chromosomal segregation, which was rescued by ectopic expression of wild-type CKAP2, we focused on the centrosome duplication process among the various aspects of the cell cycle. Among the identified phosphorylation sites, T603 and possibly S608 were phosphorylated by CDK1–cyclin B1 during mitosis, and the ectopic expression of both T603A and S608A mutants was unable to restore the centrosomal abnormalities in CKAP2-depleted cells. These results indicated that the phosphorylation status of CKAP2 during mitosis is critical for controlling both centrosome biogenesis and bipolar spindle formation.

A Motor-Gradient and Clustering Model of the Centripetal Motility of MTOCs in Meiosis I of Mouse Oocytes

Asters nucleated by Microtubule (MT) organizing centers (MTOCs) converge on chromosomes during spindle assembly in mouse oocytes undergoing meiosis I. Time-lapse imaging suggests that this centripetal motion is driven by a biased 'search-and-capture' mechanism. Here, we develop a model of a random walk in a drift field to test the nature of the bias and the spatio-temporal dynamics of the search process. The model is used to optimize the spatial field of drift in simulations, by comparison to experimental motility statistics. In a second step, this optimized gradient is used to determine the location of immobilized dynein motors and MT polymerization parameters, since these are hypothesized to generate the gradient of forces needed to move MTOCs. We compare these scenarios to self-organized mechanisms by which asters have been hypothesized to find the cell-center- MT pushing at the cell-boundary and clustering motor complexes. By minimizing the error between simulation outputs and experiments, we find a model of "pulling" by a gradient of dynein motors alone can drive the centripetal motility. Interestingly, models of passive MT based "pushing" at the cortex, clustering by cross-linking motors and MT-dynamic instability gradients alone, by themselves do not result in the observed motility. The model predicts the sensitivity of the results to motor density and stall force, but not MTs per aster. A hybrid model combining a chromatin-centered immobilized dynein gradient, diffusible minus-end directed clustering motors and pushing at the cell cortex, is required to comprehensively explain the available data. The model makes experimentally testable predictions of a spatial bias and self-organized mechanisms by which MT asters can find the center of a large cell.

CKAP2 is necessary to ensure the faithful spindle bipolarity in a dividing diploid hepatocyte

Spindle bipolarity is crucial for segregating chromosome during somatic cell division. Previous studies have suggested that cytoskeleton associated protein 2 (CKAP2) is involved in spindle assembly and chromosome segregation. In this study, we show that CKAP2-depleted primary hepatocytes exhibit over-duplicated centrosomes with disjoined chromosomes from metaphase plate. These cells proceed to apoptosis or multipolar cell division and subsequent apoptotic cell death. In addition, a mouse liver regeneration experiment showed a marked decrease in efficiency of hepatic regeneration in CKAP2-depleted liver. These data suggest a physiological role of CKAP2 in the formation of spindle bipolarity, which is necessary for maintaining chromosomal stability.

Polymorphisms of the centrosomal gene (FGFR1OP) and lung cancer risk: a meta-analysis of 14,463 cases and 44,188 controls

Centrosome abnormalities are often observed in premalignant lesions and in situ tumors and have been associated with aneuploidy and tumor development. We investigated the associations of 9354 single-nucleotide polymorphisms (SNPs) in 106 centrosomal genes with lung cancer risk by first using the summary data from six published genome-wide association studies (GWASs) of the Transdisciplinary Research in Cancer of the Lung (TRICL) (12,160 cases and 16 838 controls) and then conducted in silico replication in two additional independent lung cancer GWASs of Harvard University (984 cases and 970 controls) and deCODE (1319 cases and 26,380 controls). A total of 44 significant SNPs with false discovery rate (FDR) ≤ 0.05 were mapped to one novel gene FGFR1OP and two previously reported genes (TUBB and BRCA2). After combined the results from TRICL with those from Harvard and deCODE, the most significant association (P combined = 8.032 × 10(-6)) was with rs151606 within FGFR1OP. The rs151606 T>G was associated with an increased risk of lung cancer [odds ratio (OR) = 1.10, 95% confidence interval (95% CI) = 1.05-1.14]. Another significant tagSNP rs12212247 T>C (P combined = 9.589 × 10(-6)) was associated with a decreased risk of lung cancer (OR = 0.93, 95% CI = 0.90-0.96). Further in silico functional analyzes revealed that rs151606 might affect transcriptional regulation and result in decreased FGFR1OP expression (P trend = 0.022). The findings shed some new light on the role of centrosome abnormalities in the susceptibility to lung carcinogenesis.

Discovery of a novel inhibitor of kinesin-like protein KIFC1

Historically, drugs used in the treatment of cancers also tend to cause damage to healthy cells while affecting cancer cells. Therefore, the identification of novel agents that act specifically against cancer cells remains a high priority in the search for new therapies. In contrast with normal cells, most cancer cells contain multiple centrosomes which are associated with genome instability and tumorigenesis. Cancer cells can avoid multipolar mitosis, which can cause cell death, by clustering the extra centrosomes into two spindle poles, thereby enabling bipolar division. Kinesin-like protein KIFC1 plays a critical role in centrosome clustering in cancer cells, but is not essential for normal cells. Therefore, targeting KIFC1 may provide novel insight into selective killing of cancer cells. In the present study, we identified a small-molecule KIFC1 inhibitor, SR31527, which inhibited microtubule (MT)-stimulated KIFC1 ATPase activity with an IC50 value of 6.6 μM. By using bio layer interferometry technology, we further demonstrated that SR31527 bound directly to KIFC1 with high affinity (Kd=25.4 nM). Our results from computational modelling and saturation-transfer difference (STD)-NMR experiments suggest that SR31527 bound to a novel allosteric site of KIFC1 that appears suitable for developing selective inhibitors of KIFC1. Importantly, SR31527 prevented bipolar clustering of extra centrosomes in triple negative breast cancer (TNBC) cells and significantly reduced TNBC cell colony formation and viability, but was less toxic to normal fibroblasts. Therefore, SR31527 provides a valuable tool for studying the biological function of KIFC1 and serves as a potential lead for the development of novel therapeutic agents for breast cancer treatment.

Genomic instability in human cancer: Molecular insights and opportunities for therapeutic attack and prevention through diet and nutrition

Genomic instability can initiate cancer, augment progression, and influence the overall prognosis of the affected patient. Genomic instability arises from many different pathways, such as telomere damage, centrosome amplification, epigenetic modifications, and DNA damage from endogenous and exogenous sources, and can be perpetuating, or limiting, through the induction of mutations or aneuploidy, both enabling and catastrophic. Many cancer treatments induce DNA damage to impair cell division on a global scale but it is accepted that personalized treatments, those that are tailored to the particular patient and type of cancer, must also be developed. In this review, we detail the mechanisms from which genomic instability arises and can lead to cancer, as well as treatments and measures that prevent genomic instability or take advantage of the cellular defects caused by genomic instability. In particular, we identify and discuss five priority targets against genomic instability: (1) prevention of DNA damage; (2) enhancement of DNA repair; (3) targeting deficient DNA repair; (4) impairing centrosome clustering; and, (5) inhibition of telomerase activity. Moreover, we highlight vitamin D and B, selenium, carotenoids, PARP inhibitors, resveratrol, and isothiocyanates as priority approaches against genomic instability. The prioritized target sites and approaches were cross validated to identify potential synergistic effects on a number of important areas of cancer biology.

Discovery of AZ0108, an orally bioavailable phthalazinone PARP inhibitor that blocks centrosome clustering

The propensity for cancer cells to accumulate additional centrosomes relative to normal cells could be exploited for therapeutic benefit in oncology. Following literature reports that suggested TNKS1 (tankyrase 1) and PARP16 may be involved with spindle structure and function and may play a role in suppressing multi-polar spindle formation in cells with supernumerary centrosomes, we initiated a phenotypic screen to look for small molecule poly (ADP-ribose) polymerase (PARP) enzyme family inhibitors that could produce a multi-polar spindle phenotype via declustering of centrosomes. Screening of AstraZeneca's collection of phthalazinone PARP inhibitors in HeLa cells using high-content screening techniques identified several compounds that produced a multi-polar spindle phenotype at low nanomolar concentrations. Characterization of these compounds across a broad panel of PARP family enzyme assays indicated that they had activity against several PARP family enzymes, including PARP1, 2, 3, 5a, 5b, and 6. Further optimization of these initial hits for improved declustering potency, solubility, permeability, and oral bioavailability resulted in AZ0108, a PARP1, 2, 6 inhibitor that potently inhibits centrosome clustering and is suitable for in vivo efficacy and tolerability studies.

The Aspergillus nidulans bimC4 mutation provides an excellent tool for identification of kinesin-14 inhibitors

Centrosome amplification is a hallmark of many types of cancer cells, and clustering of multiple centrosomes is critical for cancer cell survival and proliferation. Human kinesin-14 HSET/KFIC1 is essential for centrosome clustering, and its inhibition leads to the specific killing of cancer cells with extra centrosomes. Since kinesin-14 motor domains are conserved evolutionarily, we conceived a strategy of obtaining kinesin-14 inhibitors using Aspergillus nidulans, based on the previous result that loss of the kinesin-14 KlpA rescues the non-viability of the bimC4 kinesin-5 mutant at 42 °C. However, it was unclear whether alteration of BimC or any other non-KlpA protein would be a major factor reversing the lethality of the bimC4 mutant. Here we performed a genome-wide screen for bimC4 suppressors and obtained fifteen suppressor strains. None of the suppressor mutations maps to bimC. The vast majority of them contain mutations in the klpA gene, most of which are missense mutations affecting the C-terminal motor domain. Our study confirms that the bimC4 mutant is suitable for a cell-based screen for chemical inhibitors of kinesin-14. Since the selection is based on enhanced growth rather than diminished growth, cytotoxic compounds can be excluded.

Growth factor dependent regulation of centrosome function and genomic instability by HuR

The mRNA binding protein HuR is over expressed in cancer cells and contributes to disease progression through post-transcriptional regulation of mRNA. The regulation of HuR and how this relates to glioma is the focus of this report. SRC and c-Abl kinases regulate HuR sub-cellular trafficking and influence accumulation in the pericentriolar matrix (PCM) via a growth factor dependent signaling mechanism. Growth factor stimulation of glioma cell lines results in the associate of HuR with the PCM and amplification of centrosome number. This process is regulated by tyrosine phosphorylation of HuR and is abolished by mutating tyrosine residues. HuR is overexpressed in tumor samples from patients with glioblastoma and associated with a reduced survival. These findings suggest HuR plays a significant role in centrosome amplification and genomic instability, which contributes to a worse disease outcome.

Tripolar mitosis in human cells and embryos: occurrence, pathophysiology and medical implications

Tripolar mitosis is a specific case of cell division driven by typical molecular mechanisms of mitosis, but resulting in three daughter cells instead of the usual count of two. Other variants of multipolar mitosis show even more mitotic poles and are relatively rare. In nature, this phenomenon was frequently observed or suspected in multiple common cancers, infected cells, the placenta, and in early human embryos with impaired pregnancy-yielding potential. Artificial causes include radiation and various toxins. Here we combine several pieces of the most recent evidence for the existence of different types of multipolar mitosis in preimplantation embryos together with a detailed review of the literature. The related molecular and cellular mechanisms are discussed, including the regulation of centriole duplication, mitotic spindle biology, centromere functions, cell cycle checkpoints, mitotic autocorrection mechanisms, and the related complicating factors in healthy and affected cells, including post-mitotic cell-cell fusion often associated with multipolar cell division. Clinical relevance for oncology and embryo selection in assisted reproduction is also briefly discussed in this context.

Small organelle, big responsibility: the role of centrosomes in development and disease

The centrosome, a key microtubule organizing centre, is composed of centrioles, embedded in a protein-rich matrix. Centrosomes control the internal spatial organization of somatic cells, and as such contribute to cell division, cell polarity and migration. Upon exiting the cell cycle, most cell types in the human body convert their centrioles into basal bodies, which drive the assembly of primary cilia, involved in sensing and signal transduction at the cell surface. Centrosomal genes are targeted by mutations in numerous human developmental disorders, ranging from diseases exclusively affecting brain development, through global growth failure syndromes to diverse pathologies associated with ciliary malfunction. Despite our much-improved understanding of centrosome function in cellular processes, we know remarkably little of its role in the organismal context, especially in mammals. In this review, we examine how centrosome dysfunction impacts on complex physiological processes and speculate on the challenges we face when applying knowledge generated from in vitro and in vivo model systems to human development.

Identification of novel small molecule inhibitors of centrosome clustering in cancer cells

Most normal cells have two centrosomes that form bipolar spindles during mitosis, while cancer cells often contain more than two, or "supernumerary" centrosomes. Such cancer cells achieve bipolar division by clustering their centrosomes into two functional poles, and inhibiting this process then leads to cancer-specific cell death. A major problem with clinically used anti-mitotic drugs, such as paclitaxel, is their toxicity in normal cells. To discover new compounds with greater specificity for cancer cells, we established a high-content screen for agents that block centrosome clustering in BT-549 cells, a breast cancer cell line that harbors supernumerary centrosomes. Using this screen, we identified 14 compounds that inhibit centrosome clustering and induce mitotic arrest. Some of these compounds were structurally similar, suggesting a common structural motif important for preventing centrosome clustering. We next compared the effects of these compounds on the growth of several breast and other cancer cell lines, an immortalized normal human mammary epithelial cell line, and progenitor-enriched primary normal human mammary epithelial cells. From these comparisons, we found some compounds that kill breast cancer cells, but not their normal epithelial counterparts, suggesting their potential for targeted therapy. One of these compounds, N2-(3-pyridylmethyl)-5-nitro-2-furamide (Centrosome Clustering Chemical Inhibitor-01, CCCI-01), that showed the greatest differential response in this screen was confirmed to have selective effects on cancer as compared to normal breast progenitors using more precise apoptosis induction and clonogenic growth endpoints. The concentration of CCCI-01 that killed cancer cells in the clonogenic assay spared normal human bone marrow hematopoietic progenitors in the colony-forming cell assay, indicating a potential therapeutic window for CCCI-01, whose selectivity might be further improved by optimizing the compound. Immunofluorescence analysis showed that treatment with CCCI-01 lead to multipolar spindles in BT-549, while maintaining bipolar spindles in the normal primary human mammary epithelial cells. Since centrosome clustering is a complex process involving multiple pathways, the 14 compounds identified in this study provide a potentially novel means to developing non-cross-resistant anti-cancer drugs that block centrosome clustering.

Beta human papillomavirus E6 expression inhibits stabilization of p53 and increases tolerance of genomic instability

Infections with the beta genus of human papillomaviruses (β-HPVs) may contribute to the development of nonmelanoma skin cancers. However, β-HPV genomes are found at too low a copy number in tumors for the virus to be necessary for tumor maintenance. Instead, they are hypothesized to destabilize the host genome by allowing the persistence of mutations that can drive tumorigenesis independently of the viral genome. Supporting this premise is our previous finding that the expression of some β-HPV E6 proteins can attenuate p53 signaling in response to DNA damage. We show that β-HPV E6 proteins can prevent the stabilization of p53 in response to two types of genome-destabilizing events, aberrant mitosis and dysregulated centrosome duplication. The inability to stabilize p53 in response to these stimuli allows cells expressing HPV5, HPV8, or HPV38 E6 to remain proliferatively active, leading to further genome deterioration in a proportion of these cells. These phenotypes are lost by the introduction of a mutation into the p300 binding domain of HPV8 E6 or by the transfection of mutated p300 that is resistant to the degradation mediated by HPV5 or HPV8 E6. These findings expand the understanding of the role played by p300 in promoting the faithful resolution of mitotic figures as well as proper centrosome duplication. Finally, we describe a phenomenon by which binucleated cells are resolved via cytokinesis into two cells, each with one nucleus. These data support the hypothesis that β-HPV infections may promote tumorigenesis via genome destabilization.

IMPORTANCE

The work described in this report provides support for the hypothesis that β-HPV infections may contribute to nonmelanoma skin cancer by increasing the likelihood that tumorigenic mutations are introduced into the host cell's genome. We demonstrate that expression of the E6 proteins from some of these viruses increases the tolerance of two genome-destabilizing events, aberrant cell division and dysregulated centrosome duplication. Typically, these mutagenic occurrences elicit the stabilization of the tumor suppressor p53, which prevents further propagation of cells containing these errors. We show that the expression of β-HPV E6 restricts this stabilization of p53, leading not only to continued cellular proliferation but also to further accumulation of similar mutagenic events. Finally, in addition to supporting a role for β-HPV infections in certain skin cancers, we present studies with a mutated β-HPV E6 protein suggesting that the histone acetyltransferase p300 plays a role in promoting genome stability during replication.

Novel piperazine-based compounds inhibit microtubule dynamics and sensitize colon cancer cells to tumor necrosis factor-induced apoptosis

We recently identified a series of mitotically acting piperazine-based compounds that potently increase the sensitivity of colon cancer cells to apoptotic ligands. Here we describe a structure-activity relationship study on this compound class and identify a highly active derivative ((4-(3-chlorophenyl)piperazin-1-yl)(2-ethoxyphenyl)methanone), referred to as AK301, the activity of which is governed by the positioning of functional groups on the phenyl and benzoyl rings. AK301 induced mitotic arrest in HT29 human colon cancer cells with an ED50 of ≈115 nm. Although AK301 inhibited growth of normal lung fibroblast cells, mitotic arrest was more pronounced in the colon cancer cells (50% versus 10%). Cells arrested by AK301 showed the formation of multiple microtubule organizing centers with Aurora kinase A and γ-tubulin. Employing in vitro and in vivo assays, tubulin polymerization was found to be slowed (but not abolished) by AK301. In silico molecular docking suggests that AK301 binds to the colchicine-binding domain on β-tubulin, but in a novel orientation. Cells arrested by AK301 expressed elevated levels of TNFR1 on their surface and more readily activated caspases-8, -9, and -3 in the presence of TNF. Relative to other microtubule destabilizers, AK301 was the most active TNF-sensitizing agent and also stimulated Fas- and TRAIL-induced apoptosis. In summary, we report a new class of mitosis-targeting agents that effectively sensitizes cancer cells to apoptotic ligands. These compounds should help illuminate the role of microtubules in regulating apoptotic ligand sensitivity and may ultimately be useful for developing agents that augment the anti-cancer activities of the immune response.

Centrosomal abnormalities characterize human and rodent cystic cholangiocytes and are associated with Cdc25A overexpression

Hepatic cystogenesis in polycystic liver diseases is associated with abnormalities of cholangiocyte cilia. Given the crucial association between cilia and centrosomes, we tested the hypothesis that centrosomal defects occur in cystic cholangiocytes of rodents (Pkd2(WS25/-) mice and PCK rats) and of patients with polycystic liver diseases, contributing to disturbed ciliogenesis and cyst formation. We examined centrosomal cytoarchitecture in control and cystic cholangiocytes, the effects of centrosomal abnormalities on ciliogenesis, and the role of the cell-cycle regulator Cdc25A in centrosomal defects by depleting cholangiocytes of Cdc25A in vitro and in vivo and evaluating centrosome morphology, cell-cycle progression, proliferation, ciliogenesis, and cystogenesis. The cystic cholangiocytes had atypical centrosome positioning, supernumerary centrosomes, multipolar spindles, and extra cilia. Structurally aberrant cilia were present in cystic cholangiocytes during ciliogenesis. Depletion of Cdc25A resulted in i) a decreased number of centrosomes and multiciliated cholangiocytes, ii) an increased fraction of ciliated cholangiocytes with longer cilia, iii) a decreased proportion of cholangiocytes in G1/G0 and S phases of the cell cycle, iv) decreased cell proliferation, and v) reduced cyst growth in vitro and in vivo. Our data support the hypothesis that centrosomal abnormalities in cholangiocytes are associated with aberrant ciliogenesis and that accelerated cystogenesis is likely due to overexpression of Cdc25A, providing additional evidence that pharmacological targeting of Cdc25A has therapeutic potential in polycystic liver diseases.

CEP proteins: the knights of centrosome dynasty

Centrosome forms the backbone of cell cycle progression mechanism. Recent debates have occurred regarding the essentiality of centrosome in cell cycle regulation. CEP family protein is the active component of centrosome and plays a vital role in centriole biogenesis and cell cycle progression control. A total of 31 proteins have been categorized into CEP family protein category and many more are under candidate evaluation. Furthermore, by the recent advancements in genomics and proteomics researches, several new CEP proteins have also been characterized. Here we have summarized the importance of CEP family proteins and their regulation mechanism involved in proper cell cycle progression. Further, we have reviewed the detailed molecular mechanism behind the associated pathological phenotypes and the possible therapeutic approaches. Proteins such as CEP57, CEP63, CEP152, CEP164, and CEP215 have been extensively studied with a detailed description of their molecular mechanisms, which are among the primary targets for drug discovery. Moreover, CEP27, CEP55, CEP70, CEP110, CEP120, CEP135, CEP192, CEP250, CEP290, and CEP350 also seem promising for future drug discovery approaches. Since the overview implicates that the overall researches on CEP proteins are not yet able to present significant details required for effective therapeutics development, thus, it is timely to discuss the importance of future investigations in this field.

Cell death associated with abnormal mitosis observed by confocal imaging in live cancer cells

Phenanthrene derivatives acting as potent PARP1 inhibitors prevented the bi-focal clustering of supernumerary centrosomes in multi-centrosomal human cancer cells in mitosis. The phenanthridine PJ-34 was the most potent molecule. Declustering of extra-centrosomes causes mitotic failure and cell death in multi-centrosomal cells. Most solid human cancers have high occurrence of extra-centrosomes. The activity of PJ-34 was documented in real-time by confocal imaging of live human breast cancer MDA-MB-231 cells transfected with vectors encoding for fluorescent γ-tubulin, which is highly abundant in the centrosomes and for fluorescent histone H2b present in the chromosomes. Aberrant chromosomes arrangements and de-clustered γ-tubulin foci representing declustered centrosomes were detected in the transfected MDA-MB-231 cells after treatment with PJ-34. Un-clustered extra-centrosomes in the two spindle poles preceded their cell death. These results linked for the first time the recently detected exclusive cytotoxic activity of PJ-34 in human cancer cells with extra-centrosomes de-clustering in mitosis, and mitotic failure leading to cell death. According to previous findings observed by confocal imaging of fixed cells, PJ-34 exclusively eradicated cancer cells with multi-centrosomes without impairing normal cells undergoing mitosis with two centrosomes and bi-focal spindles. This cytotoxic activity of PJ-34 was not shared by other potent PARP1 inhibitors, and was observed in PARP1 deficient MEF harboring extracentrosomes, suggesting its independency of PARP1 inhibition. Live confocal imaging offered a useful tool for identifying new molecules eradicating cells during mitosis.

Centrosome amplification causes microcephaly

Centrosome amplification is a hallmark of human tumours. In flies, extra centrosomes cause spindle position defects that result in the expansion of the neural stem cell (NSC) pool and consequently in tumour formation. Here we investigated the consequences of centrosome amplification during mouse brain development and homeostasis. We show that centrosome amplification causes microcephaly due to inefficient clustering mechanisms, where NSCs divide in a multipolar fashion producing aneuploid cells that enter apoptosis. Importantly, we show that apoptosis inhibition causes the accumulation of highly aneuploid cells that lose their proliferative capacity and differentiate, thus depleting the pool of progenitors. Even if these conditions are not sufficient to halt brain development, they cause premature death due to tissue degeneration. Our results support an alternative concept to explain the etiology of microcephaly and show that centrosome amplification and aneuploidy can result in tissue degeneration rather than overproliferation and cancer.

Tumor environmental factors glucose deprivation and lactic acidosis induce mitotic chromosomal instability--an implication in aneuploid human tumors

Mitotic chromosomal instability (CIN) plays important roles in tumor progression, but what causes CIN is incompletely understood. In general, tumor CIN arises from abnormal mitosis, which is caused by either intrinsic or extrinsic factors. While intrinsic factors such as mitotic checkpoint genes have been intensively studied, the impact of tumor microenvironmental factors on tumor CIN is largely unknown. We investigate if glucose deprivation and lactic acidosis--two tumor microenvironmental factors--could induce cancer cell CIN. We show that glucose deprivation with lactic acidosis significantly increases CIN in 4T1, MCF-7 and HCT116 scored by micronuclei, or aneuploidy, or abnormal mitosis, potentially via damaging DNA, up-regulating mitotic checkpoint genes, and/or amplifying centrosome. Of note, the feature of CIN induced by glucose deprivation with lactic acidosis is similar to that of aneuploid human tumors. We conclude that tumor environmental factors glucose deprivation and lactic acidosis can induce tumor CIN and propose that they are potentially responsible for human tumor aneuploidy.

Disruption of mouse Cenpj, a regulator of centriole biogenesis, phenocopies Seckel syndrome

Disruption of the centromere protein J gene, CENPJ (CPAP, MCPH6, SCKL4), which is a highly conserved and ubiquitiously expressed centrosomal protein, has been associated with primary microcephaly and the microcephalic primordial dwarfism disorder Seckel syndrome. The mechanism by which disruption of CENPJ causes the proportionate, primordial growth failure that is characteristic of Seckel syndrome is unknown. By generating a hypomorphic allele of Cenpj, we have developed a mouse (Cenpj(tm/tm)) that recapitulates many of the clinical features of Seckel syndrome, including intrauterine dwarfism, microcephaly with memory impairment, ossification defects, and ocular and skeletal abnormalities, thus providing clear confirmation that specific mutations of CENPJ can cause Seckel syndrome. Immunohistochemistry revealed increased levels of DNA damage and apoptosis throughout Cenpj(tm/tm) embryos and adult mice showed an elevated frequency of micronucleus induction, suggesting that Cenpj-deficiency results in genomic instability. Notably, however, genomic instability was not the result of defective ATR-dependent DNA damage signaling, as is the case for the majority of genes associated with Seckel syndrome. Instead, Cenpj(tm/tm) embryonic fibroblasts exhibited irregular centriole and centrosome numbers and mono- and multipolar spindles, and many were near-tetraploid with numerical and structural chromosomal abnormalities when compared to passage-matched wild-type cells. Increased cell death due to mitotic failure during embryonic development is likely to contribute to the proportionate dwarfism that is associated with CENPJ-Seckel syndrome.

The biology and evolution of polyspermy: insights from cellular and functional studies of sperm and centrosomal behavior in the fertilized egg

Recent studies of centrosome biogenesis, microtubule dynamics, and their management point to their role in mediating conditions such as aging and cancer. Centrosome dysfunction is also a hallmark of pathological polyspermy. Polyspermy occurs when the oocyte is penetrated by more than one sperm and can be pathological because an excess of centrosomes compromises development. However, in some taxa, multiple sperm enter the egg with no apparent adverse effect on zygote viability. Thus, some taxa can manage excess centrosomes and represent cases of non-pathological polyspermy. While these two forms of polyspermy have long been known, we argue that there is limited understanding of the proximate and ultimate processes that underlie this taxonomic variation in the outcome of polyspermy and that studying this variation could help uncover the control and role(s) of centrosomes during fertilization in particular, but also mitosis in general. To encourage such studies we: 1) describe taxonomic differences in the outcome of polyspermy, 2) discuss mechanistic aspects of reproductive biology that may contribute to the different consequences of polyspermy, and 3) outline the potential selective events that could lead to the evolution of variation in polyspermy outcomes. We suggest that novel insights into centrosome biology may occur by cooperative studies between reproductive and evolutionary biologists focusing on the mechanisms generating variation in the fitness consequences of polyspermy, and in the taxonomic distribution of all these events. The consequent discoveries of these studies may lead to informative insights into cancer and aging along with other centrosome-related diseases and syndromes.

A phenanthrene derived PARP inhibitor is an extra-centrosomes de-clustering agent exclusively eradicating human cancer cells

Background

Cells of most human cancers have supernumerary centrosomes. To enable an accurate chromosome segregation and cell division, these cells developed a yet unresolved molecular mechanism, clustering their extra centrosomes at two poles, thereby mimicking mitosis in normal cells. Failure of this bipolar centrosome clustering causes multipolar spindle structures and aberrant chromosomes segregation that prevent normal cell division and lead to 'mitotic catastrophe cell death'.

Methods

We used cell biology and biochemical methods, including flow cytometry, immunocytochemistry and live confocal imaging.

Results

We identified a phenanthrene derived PARP inhibitor, known for its activity in neuroprotection under stress conditions, which exclusively eradicated multi-centrosomal human cancer cells (mammary, colon, lung, pancreas, ovarian) while acting as extra-centrosomes de-clustering agent in mitosis. Normal human proliferating cells (endothelial, epithelial and mesenchymal cells) were not impaired. Despite acting as PARP inhibitor, the cytotoxic activity of this molecule in cancer cells was not attributed to PARP inhibition alone.

Conclusion

We identified a water soluble phenanthridine that exclusively targets the unique dependence of most human cancer cells on their supernumerary centrosomes bi-polar clustering for their survival. This paves the way for a new selective cancer-targeting therapy, efficient in a wide range of human cancers.

The requirement of p53 for maintaining chromosomal stability during tetraploidization

Tetraploidization is believed to promote genome instability and tumorigenesis. Whether tetraploids per se are intrinsically unstable and transforming remain incompletely understood. In this report, tetraploidization was induced with cell fusion using mouse fibroblasts. Due to the unequal segregation of chromosomes during multipolar mitosis, the majority of cells were eliminated by p53-dependent mechanisms after tetraploidization. The rare tetraploid fibroblasts that were able to undergo bipolar mitosis remained chromosomally stable and nontransformed over many generations. Suppression of p53 functions during tetraploidization, either by RNA interference or by using p53-deficient mouse fibroblasts, produced cells that were chromosomally unstable. They were fast growing and displayed anchorage-independent growth in soft agar. In contrast, impairment of p53 functions after tetraploids were established was ineffective in triggering chromosomal instability and transformation. Collectively, these results are consistent with a model that during early stages of tetraploidization, the lack of p53 promotes the survival of chromosomally unstable sub-tetraploids, leading to transformation. Once tetraploids are established, however, p53 is not essential for maintaining chromosome stability.

The requirement of p53 for maintaining chromosomal stability during tetraploidization

Tetraploidization is believed to promote genome instability and tumorigenesis. Whether tetraploids per se are intrinsically unstable and transforming remain incompletely understood. In this report, tetraploidization was induced with cell fusion using mouse fibroblasts. Due to the unequal segregation of chromosomes during multipolar mitosis, the majority of cells were eliminated by p53-dependent mechanisms after tetraploidization. The rare tetraploid fibroblasts that were able to undergo bipolar mitosis remained chromosomally stable and nontransformed over many generations. Suppression of p53 functions during tetraploidization, either by RNA interference or by using p53-deficient mouse fibroblasts, produced cells that were chromosomally unstable. They were fast growing and displayed anchorage-independent growth in soft agar. In contrast, impairment of p53 functions after tetraploids were established was ineffective in triggering chromosomal instability and transformation. Collectively, these results are consistent with a model that during early stages of tetraploidization, the lack of p53 promotes the survival of chromosomally unstable sub-tetraploids, leading to transformation. Once tetraploids are established, however, p53 is not essential for maintaining chromosome stability.

MOS, aneuploidy and the ploidy cycle of cancer cells

After DNA or spindle damage, p53-defective tumor cells undergo a complex cycle of reversible polyploidy. How this process occurs and more importantly, why, has recently become the focus of several research groups, prompting this review in which we discuss two related phenomena that accompany the reversible polyploidy of tumor cells: the induction of meiosis genes such as MOS and the decrease in genomic instability observed during the reversion from polyploidy to para-diploidy. The reversible polyploidy likely provides the means through which the balance between increased chromosome instability (CIN), driving genetic variation and decreased CIN, necessary for perpetuating these malignant clones, is maintained. These concepts are integrated with recent findings that many meiotic and self-renewal genes become activated during reversible polyploidy and lead us to the hypothesis that tumor cell immortality may be achieved through germline-like transmission.

Centrosome clustering and cyclin D1 gene amplification in double minutes are common events in chromosomal unstable bladder tumors

Background

Aneuploidy, centrosome abnormalities and gene amplification are hallmarks of chromosome instability (CIN) in cancer. Yet there are no studies of the in vivo behavior of these phenomena within the same bladder tumor.

Methods

Twenty-one paraffin-embedded bladder tumors were analyzed by conventional comparative genome hybridization and fluorescence in situ hybridization (FISH) with a cyclin D1 gene (CCND1)/centromere 11 dual-color probe. Immunofluorescent staining of α, β and γ tubulin was also performed.

Results

Based on the CIN index, defined as the percentage of cells not displaying the modal number for chromosome 11, tumors were classified as CIN-negative and CIN-positive. Fourteen out of 21 tumors were considered CIN-positive. All T1G3 tumors were included in the CIN-positive group whereas the majority of Ta samples were classified as CIN-negative tumors. Centrosome clustering was observed in six out of 12 CIN-positive tumors analyzed. CCND1 amplification in homogeneously staining regions was present in six out of 14 CIN-positive tumors; three of them also showed amplification of this gene in double minutes.

Conclusions

Complex in vivo behavior of CCND1 amplicon in bladder tumor cells has been demonstrated by accurate FISH analysis on paraffin-embedded tumors. Positive correlation between high heterogeneity, centrosome abnormalities and CCND1 amplification was found in T1G3 bladder carcinomas. This is the first study to provide insights into the coexistence of CCND1 amplification in homogeneously staining regions and double minutes in primary bladder tumors. It is noteworthy that those patients whose tumors showed double minutes had a significantly shorter overall survival rate (p < 0.001).