The G1 phase Cdks regulate the centrosome cycle and mediate oncogene-dependent centrosome amplification

Mitotic kinases are emerging therapeutic targets against metastatic breast cancer

This review aims to outline mitotic kinase inhibitors' roles as potential therapeutic targets and assess their suitability as a stand-alone clinical therapy or in combination with standard treatments for advanced-stage solid tumors, including triple-negative breast cancer (TNBC). Breast cancer poses a significant global health risk, with TNBC standing out as the most aggressive subtype. Comprehending the role of mitosis is crucial for understanding how TNBC advances from a solid tumor to metastasis. Chemotherapy is the primary treatment used to treat TNBC. Some types of chemotherapeutic agents target cells in mitosis, thus highlighting the need to comprehend the molecular mechanisms governing mitosis in cancer. This understanding is essential for devising targeted therapies to disrupt these mitotic processes, prevent or treat metastasis, and improve patient outcomes. Mitotic kinases like Aurora kinase A, Aurora Kinase B, never in mitosis gene A-related kinase 2, Threonine-Tyrosine kinase, and Polo-kinase 1 significantly impact cell cycle progression by contributing to chromosome separation and centrosome homeostasis. When these kinases go awry, they can trigger chromosome instability, increase cell proliferation, and activate different molecular pathways that culminate in a transition from epithelial to mesenchymal cells. Ongoing clinical trials investigate various mitotic kinase inhibitors as potential biological treatments against advanced solid tumors. While clinical trials against mitotic kinases have shown some promise in the clinic, more investigation is necessary, since they induce severe adverse effects, particularly affecting the hematopoietic system.

Epigenetic alterations impede epithelial-mesenchymal transition by modulating centrosome amplification and Myc/RAS axis in triple negative breast cancer cells

Alterations in centrosome proteins may result in centrosome abnormalities such as disorganized spindles and centrosome amplification, leading to aneuploidy and genomic instability. Centrosomes exhibit unique epigenetic properties in which structural or positional information is propagated through somatic lineage by non-genetic pathways. Excessive centrosome amplification in breast cancer is accompanied by efficient clustering and loss of E-cadherin, indicating an important adaptive mechanism of cancer. This study sought to elucidate the effect of epigenetic alterations on centrosome amplification, epithelial-mesenchymal transition (EMT) and apoptosis in triple negative human breast adenocarcinoma derived MDA-MB-231 cell line. The results obtained here show that siRNA mediated silencing of DNMT1 and specific inhibition of HDAC1 & HDAC2 by Tricostatin A (TSA) synergistically inhibit cell proliferation through modulation of centrosome proteins γ-tubulin, TUBGCP2 and pericentrin. In addition, induction of apoptosis was observed by downregulation of Bcl2, upregulation of Bax and activation of PARP cleavage. Inhibition of EMT was confirmed through upregulation of E-cadherin and downregulation of N-cadherin and vimentin. Similarly, downregulation of Myc, RAS and CDK2, which plays important roles in proliferation and survival, was observed. Nuclear protein analysis revealed downregulation in the nuclear translocation of E2F1, which regulates centrosome amplification and metastasis in breast cancer. In conclusion, this study confirmed the role of epigenetic regulators in centrosome amplification and suggests that inhibition of DNA methylation and histone deacetylation-mediated chromatin remodelling synergistically disrupt EMT through modulation of centrosome amplification and Myc/RAS axis to potentiate apoptosis and attenuate cell proliferation in triple negative breast cancer cells.

The Nek2 centrosome-mitotic kinase contributes to the mesenchymal state, cell invasion, and migration of triple-negative breast cancer cells

Nek2 (NIMA-related kinase 2) is a serine/threonine-protein kinase that localizes to centrosomes and kinetochores, controlling centrosome separation, chromosome attachments to kinetochores, and the spindle assembly checkpoint. These processes prevent centrosome amplification (CA), mitotic dysfunction, and chromosome instability (CIN). Our group and others have suggested that Nek2 maintains high levels of CA/CIN, tumor growth, and drug resistance. We identified that Nek2 overexpression correlates with poor survival of breast cancer. However, the mechanisms driving these phenotypes are unknown. We now report that overexpression of Nek2 in MCF10A cells drives CA/CIN and aneuploidy. Besides, enhanced levels of Nek2 results in larger 3D acinar structures, but could not initiate tumors in a p53+/+ or a p53-/- xenograft model. Nek2 overexpression induced the epithelial-to-mesenchymal transition (EMT) while its downregulation reduced the expression of the mesenchymal marker vimentin. Furthermore, either siRNA-mediated downregulation or INH6's chemical inhibition of Nek2 in MDA-MB-231 and Hs578t cells showed important EMT changes and decreased invasion and migration. We also showed that Slug and Zeb1 are involved in Nek2 mediated EMT, invasion, and migration. Besides its role in CA/CIN, Nek2 contributes to breast cancer progression through a novel EMT mediated mechanism.

Centrosome aberrations and chromosome instability contribute to tumorigenesis and intra-tumor heterogeneity

Centrosomes serve as the major microtubule organizing centers in cells and thereby contribute to cell shape, polarity, and motility. Also, centrosomes ensure equal chromosome segregation during mitosis. Centrosome aberrations arise when the centrosome cycle is deregulated, or as a result of cytokinesis failure. A long-standing postulate is that centrosome aberrations are involved in the initiation and progression of cancer. However, this notion has been a subject of controversy because until recently the relationship has been correlative. Recently, it was shown that numerical or structural centrosome aberrations can initiate tumors in certain tissues in mice, as well as invasion. Particularly, we will focus on centrosome amplification and chromosome instability as drivers of intra-tumor heterogeneity and their consequences in cancer. We will also discuss briefly the controversies surrounding this theory to highlight the fact that the role of both centrosome amplification and chromosome instability in cancer is highly context-dependent. Further, we will discuss single-cell sequencing as a novel technique to understand intra-tumor heterogeneity and some therapeutic approaches to target chromosome instability.

A minimal "push-pull" bistability model explains oscillations between quiescent and proliferative cell states

A minimal model for oscillating between quiescent and growth/proliferation states, dependent on the availability of a central metabolic resource, is presented. From the yeast metabolic cycles, metabolic oscillations in oxygen consumption are represented as transitions between quiescent and growth states. We consider metabolic resource availability, growth rates, and switching rates (between states) to model a relaxation oscillator explaining transitions between these states. This frustrated bistability model reveals a required communication between the metabolic resource that determines oscillations and the quiescent and growth state cells. Cells in each state reflect memory, or hysteresis of their current state, and “push–pull” cells from the other state. Finally, a parsimonious argument is made for a specific central metabolite as the controller of switching between quiescence and growth states. We discuss how an oscillator built around the availability of such a metabolic resource is sufficient to generally regulate oscillations between growth and quiescence through committed transitions.

Noncanonical Biogenesis of Centrioles and Basal Bodies

Centrioles and basal bodies (CBBs) organize centrosomes and cilia within eukaryotic cells. These organelles are composed of microtubules and hundreds of proteins performing multiple functions such as signaling, cytoskeleton remodeling, and cell motility. The CBB is present in all branches of the eukaryotic tree of life and, despite its ultrastructural and protein conservation, there is diversity in its function, occurrence (i.e., presence/absence), and modes of biogenesis across species. In this review, we provide an overview of the multiple pathways through which CBBs are formed in nature, with a special focus on the less studied, noncanonical ways. Despite the differences among each mechanism herein presented, we highlighted some of their common principles. These principles, governing different steps of biogenesis, ensure that CBBs may perform a multitude of functions in a huge diversity of organisms but yet retained their robustness in structure throughout evolution.

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.

Cytokinesis arrest and multiple centrosomes in B cell chronic lymphocytic leukaemia

Cytokinesis failure leads to the emergence of tetraploid cells and multiple centrosomes. Chronic lymphocytic leukaemia (CLL) is the most common haematological malignancy in adults and is characterized by clonal B cell expansion. Here, we show that a significant number of peripheral blood CLL cells are arrested in cytokinesis and that this event occurred after nuclear envelope reformation and before cytoplasmic abscission. mRNA expression data showed that several genes known to be crucial for cell cycle regulation, checkpoint and centromere function, such as ING4, ING5, CDKN1A and CDK4, were significantly dysregulated in CLL samples. Our results demonstrate that CLL cells exhibit difficulties in completing mitosis, which is different from but may, at least in part, explain the previously reported accumulation of CLL cells in G0/1.

The E2F activators control multiple mitotic regulators and maintain genomic integrity through Sgo1 and BubR1

The E2F1, E2F2, and E2F3a transcriptional activators control proliferation. However, how the E2F activators regulate mitosis to maintain genomic integrity is unclear. Centrosome amplification (CA) and unregulated spindle assembly checkpoint (SAC) are major generators of aneuploidy and chromosome instability (CIN) in cancer. Previously, we showed that overexpression of single E2F activators induced CA and CIN in mammary epithelial cells, and here we show that combined overexpression of E2F activators did not enhance CA. Instead, the E2F activators elevated expression of multiple mitotic regulators, including Sgo1, Nek2, Hec1, BubR1, and Mps1/TTK. cBioPortal analyses of the TCGA database showed that E2F overexpression in lobular invasive breast tumors correlates with overexpression of multiple regulators of chromosome segregation, centrosome homeostasis, and the SAC. Kaplan-Meier plots identified correlations between individual or combined overexpression of E2F1, E2F3a, Mps1/TTK, Nek2, BubR1, or Hec1 and poor overall and relapse-free survival of breast cancer patients. In MCF10A normal mammary epithelial cells co-overexpressing E2Fs, transient Sgo1 knockdown induced CA, high percentages of premature sister chromatid separation, chromosome losses, increased apoptosis, and decreased cell clonogenicity. BubR1 silencing resulted in chromosome losses without CA, demonstrating that Sgo1 and BubR1 maintain genomic integrity through two distinct mechanisms. Our results suggest that deregulated activation of the E2Fs in mammary epithelial cells is counteracted by activation of a Sgo1-dependent mitotic checkpoint.

NEK7 is required for G1 progression and procentriole formation

As cells exit mitosis, the decision to commit to the next cell cycle is made during G1. Not only DNA replication, but also centriole duplication is initiated as cells enter the S-phase. The kinase NEK7 is required for the timely regulation of G1 progression, S-phase entry, and procentriole formation.

The decision to commit to the cell cycle is made during G1 through the concerted action of various cyclin–CDK complexes. Not only DNA replication, but also centriole duplication is initiated as cells enter the S-phase. The NIMA-related kinase NEK7 is one of many factors required for proper centriole duplication, as well as for timely cell cycle progression. However, its specific roles in these events are poorly understood. In this study, we find that depletion of NEK7 inhibits progression through the G1 phase in human U2OS cells via down-regulation of various cyclins and CDKs and also inhibits the earliest stages of procentriole formation. Depletion of NEK7 also induces formation of primary cilia in human RPE1 cells, suggesting that NEK7 acts at least before the restriction point during G1. G1-arrested cells in the absence of NEK7 exhibit abnormal accumulation of the APC/C cofactor Cdh1 at the vicinity of centrioles. Furthermore, the ubiquitin ligase APC/C^Cdh1 continuously degrades the centriolar protein STIL in these cells, thus inhibiting centriole assembly. Collectively our results demonstrate that NEK7 is involved in the timely regulation of G1 progression, S-phase entry, and procentriole formation.

Centrosome - a promising anti-cancer target

The centrosome, an organelle discovered >100 years ago, is the main microtubule-organizing center in mammalian organisms. The centrosome is composed of a pair of centrioles surrounded by the pericentriolar material (PMC) and plays a major role in the regulation of cell cycle transitions (G1-S, G2-M, and metaphase-anaphase), ensuring the normality of cell division. Hundreds of proteins found in the centrosome exert a variety of roles, including microtubule dynamics, nucleation, and kinetochore–microtubule attachments that allow correct chromosome alignment and segregation. Errors in these processes lead to structural (shape, size, number, position, and composition), functional (abnormal microtubule nucleation and disorganized spindles), and numerical (centrosome amplification [CA]) centrosome aberrations causing aneuploidy and genomic instability. Compelling data demonstrate that centrosomes are implicated in cancer, because there are important oncogenic and tumor suppressor proteins that are localized in this organelle and drive centrosome aberrations. Centrosome defects have been found in pre-neoplasias and tumors from breast, ovaries, prostate, head and neck, lung, liver, and bladder among many others. Several drugs/compounds against centrosomal proteins have shown promising results. Other drugs have higher toxicity with modest or no benefits, and there are more recently developed agents being tested in clinical trials. All of this emerging evidence suggests that targeting centrosome aberrations may be a future avenue for therapeutic intervention in cancer research.

Silencing of E2F3 suppresses tumor growth of Her2+ breast cancer cells by restricting mitosis

The E2F transcriptional activators E2F1, E2F2 and E2F3a regulate many important cellular processes, including DNA replication, apoptosis and centrosome duplication. Previously, we demonstrated that silencing E2F1 or E2F3 suppresses centrosome amplification (CA) and chromosome instability (CIN) in Her2+ breast cancer cells without markedly altering proliferation. However, it is unknown whether and how silencing a single E2F activator, E2F3, affects malignancy of human breast cancer cells. Thus, we injected HCC1954 Her2+ breast cancer cells silenced for E2F3 into mammary fat pads of immunodeficient mice and demonstrated that loss of E2F3 retards tumor growth. Surprisingly, silencing of E2F3 led to significant reductions in mitotic indices relative to vector controls, while the percentage of cells undergoing S phase were not affected. Nek2 is a mitotic kinase commonly upregulated in breast cancers and a critical regulator of Cdk4- or E2F-mediated CA. In this report, we found that Nek2 overexpression rescued back the CA caused by silencing of shE2F3. However, the effects of Nek2 overexpression in affecting tumor growth rates of shE2F3 and shE2F3; GFP cells were inconclusive. Taken together, our results indicate that E2F3 silencing decreases mammary tumor growth by reducing percentage of cells undergoing mitosis.

Centrosome aberrations in human mammary epithelial cells driven by cooperative interactions between p16INK4a deficiency and telomere-dependent genotoxic stress

Virtually all human cancers display chromosome instability (CIN), a condition in which chromosomes are gained or lost at a high rate. CIN occurs early in cancer development where it may undermine the advance of the neoplastic disease. With the aim of establishing the mechanisms underlying CIN in cancer, we investigated possible links between telomere-dysfunction and centrosome defects, which were seen to coincide in early in breast carcinogenesis using human mammary epithelial cells (HMECs). In this study, we show that TP53 proficient vHMECs cells develop centrosome aberrations when telomere-dysfunction genotoxic stress is produced in the presence of a defective p16^INK4a setting and in parallel with an activation of the DNA damage checkpoint response. These aberrations consist of the accumulation of centrosomes in polyploid vHMECs, plus centriole overduplication in both diploid and polyploid cells, thus reflecting that distinct mechanisms underlie the generation of centrosome aberrations in vHMECs. Transduction of vHMEC with hTERT, which rescued the telomere dysfunction phenotype and consequently reduced DNA damage checkpoint activation, led to a progressive reduction of centrosome aberrations with cell culture, both in diploid and in polyploid vHMECs. Radiation-induced DNA damage also raised centrosome aberrations in vHMEC-hTERT. Collectively, our results, using vHMECs define a model where p16^INK4a deficiency along with short dysfunctional telomeres cooperatively engenders centrosome abnormalities before p53 function is compromised.

Depletion of the LINC complex disrupts cytoskeleton dynamics and meiotic resumption in mouse oocytes

The SUN (Sad-1/UNC-84) and KASH (Klarsicht/ANC-1/Syne/homology) proteins constitute the linker of nucleoskeleton and cytoskeleton (LINC) complex on the nuclear envelope. To date, the SUN1/KASH5 complex is known to function as meiotic-specific factors. In this study, gene-silencing methods were used to explore the roles of SUN1 and KASH5 in mouse oocytes after prophase. SUN1 was detected throughout the nucleus; however, KASH5 was dispersed through the cell. After germinal vesicle breakdown (GVBD), SUN1 and KASH5 migrated during spindle formation and localized to the spindle poles at the MII stage. Most oocytes were arrested at the germinal vesicle (GV) stage after depletion of either SUN1 or KASH5. The DNA damage response was triggered in SUN1-depleted oocytes and thus gave rise to the G2/M checkpoint protein, p-CHK1. Oocytes that underwent GVBD had relatively small and abnormal spindles and lower levels of cytoplasm F-actin mesh. Immunofluorescence results also indicated the dislocation of pericentrin and P150^Glued after SUN1 or KASH5 depletion. Furthermore, KASH5 localized exclusively near the oocyte cortex after SUN1 depletion, but SUN1 localization was unaffected in KASH5-depleted oocytes. Taken together, the results suggest that SUN1 and KASH5 are essential factors in the regulation of meiotic resumption and spindle formation.

Turning the headlights on novel cancer biomarkers: Inspection of mechanics underlying intratumor heterogeneity

Although the existence of intratumoral heterogeneity (ITH) in the expression of common biomarkers has been described by pathologists since the late 1890s, we have only recently begun to fathom the staggering extent and near ubiquity of this phenomenon. From the tumor's perspective, ITH provides a stabilizing diversity that allows for the evolution of aggressive cancer phenotypes. As the weight of the evidence correlating ITH to poor prognosis burgeons, it has become increasingly important to determine the mechanisms by which a tumor acquires ITH, find clinically-adaptable means to quantify ITH and design strategies to deal with the numerous profound clinical ramifications that ITH forces upon us. Elucidation of the drivers of ITH could enable development of novel biomarkers whose interrogation might permit quantitative evaluation of the ITH inherent in a tumor in order to predict the poor prognosis risk associated with that tumor. This review proposes centrosome amplification (CA), aided and abetted by centrosome clustering mechanisms, as a critical driver of chromosomal instability (CIN) that makes a key contribution to ITH generation. Herein we also evaluate how a tumor's inherent mitotic propensity, which reflects the cell cycling kinetics within the tumor's proliferative cells, functions as the indispensable engine underpinning CIN, and determines the rate of CIN. We thus expound how the forces of centrosome amplification and mitotic propensity collaborate to sculpt the genetic landscape of a tumor and spawn extensive subclonal diversity. As such, centrosome amplification and mitotic propensity profiles could serve as clinically facile and powerful prognostic biomarkers that would enable more accurate risk segmentation of patients and design of individualized therapies.

CDK2 Inhibition Causes Anaphase Catastrophe in Lung Cancer through the Centrosomal Protein CP110

Aneuploidy is frequently detected in human cancers and is implicated in carcinogenesis. Pharmacologic targeting of aneuploidy is an attractive therapeutic strategy, as this would preferentially eliminate malignant over normal cells. We previously discovered that CDK2 inhibition causes lung cancer cells with more than two centrosomes to undergo multipolar cell division leading to apoptosis, defined as anaphase catastrophe. Cells with activating KRAS mutations were especially sensitive to CDK2 inhibition. Mechanisms of CDK2-mediated anaphase catastrophe and how activated KRAS enhances this effect were investigated. Live-cell imaging provided direct evidence that following CDK2 inhibition, lung cancer cells develop multipolar anaphase and undergo multipolar cell division with the resulting progeny apoptotic. The siRNA-mediated repression of the CDK2 target and centrosome protein CP110 induced anaphase catastrophe of lung cancer cells. In contrast, CP110 overexpression antagonized CDK2 inhibitor-mediated anaphase catastrophe. Furthermore, activated KRAS mutations sensitized lung cancer cells to CDK2 inhibition by deregulating CP110 expression. Thus, CP110 is a critical mediator of CDK2 inhibition-driven anaphase catastrophe. Independent examination of murine and human paired normal-malignant lung tissues revealed marked upregulation of CP110 in malignant versus normal lung. Human lung cancers with KRAS mutations had significantly lower CP110 expression as compared with KRAS wild-type cancers. Thus, a direct link was found between CP110 and CDK2 inhibitor antineoplastic response. CP110 plays a mechanistic role in response of lung cancer cells to CDK2 inhibition, especially in the presence of activated KRAS mutations.

E2F activators signal and maintain centrosome amplification in breast cancer cells

Centrosomes ensure accurate chromosome segregation by directing spindle bipolarity. Loss of centrosome regulation results in centrosome amplification, multipolar mitosis and aneuploidy. Since centrosome amplification is common in premalignant lesions and breast tumors, it is proposed to play a central role in breast tumorigenesis, a hypothesis that remains to be tested. The coordination between the cell and centrosome cycles is of paramount importance to maintain normal centrosome numbers, and the E2Fs may be responsible for regulating these cycles. However, the role of E2F activators in centrosome amplification is unclear. Because E2Fs are deregulated in Her2(+) cells displaying centrosome amplification, we addressed whether they signal this abnormal process. Knockdown of E2F1 or E2F3 in Her2(+) cells decreased centrosome amplification without significantly affecting cell cycle progression, whereas the overexpression of E2F1, E2F2, or E2F3 increased centrosome amplification in MCF10A mammary epithelial cells. Our results revealed that E2Fs affect the expression of proteins, including Nek2 and Plk4, known to influence the cell/centrosome cycles and mitosis. Downregulation of E2F3 resulted in cell death and delays/blocks in cytokinesis, which was reversed by Nek2 overexpression. Nek2 overexpression enhanced centrosome amplification in Her2(+) breast cancer cells silenced for E2F3, revealing a role for the E2F activators in maintaining centrosome amplification in part through Nek2.

Differential expression of centrosome regulators in Her2+ breast cancer cells versus non-tumorigenic MCF10A cells

Centrosome amplification (CA) amongst particular breast cancer subtypes (Her2+ subtype) is associated with genomic instability and aggressive tumor phenotypes. However, changes in signaling pathways associated with centrosome biology have not been fully explored in subtype specific models. Novel centrosome regulatory genes that are selectively altered in Her2+ breast cancer cells are of interest in discerning why CA is more prevalent in this subtype. To determine centrosome/cell cycle genes that are altered in Her2+ cells that display CA (HCC1954) versus non-tumorigenic cells (MCF10A), we carried out a gene microarray. Expression differences were validated by real-time PCR and Western blotting. After the microarray validation, we pursued a panel of upregulated and downregulated genes based on novelty/relevance to centrosome duplication. Functional experiments measuring CA and BrdU incorporation were completed after genetic manipulation of targets (TTK, SGOL1, MDM2 and SFRP1). Amongst genes that were downregulated in HCC1954 cells, knockdown of MDM2 and SFRP1 in MCF10A cells did not consistently induce CA or impaired BrdU incorporation. Conversely, amongst upregulated genes in HCC1954 cells, knockdown of SGOL1 and TTK decreased CA in breast cancer cells, while BrdU incorporation was only altered by SGOL1 knockdown. We also explored the Kaplan Meier Plot resource and noted that MDM2 and SFRP1 are positively associated with relapse free survival in all breast cancer subtypes, while TTK is negatively correlated with overall survival of Luminal A patients. Based on this functional screen, we conclude that SGOL1 and TTK are important modulators of centrosome function in a breast cancer specific model.

The expression of Nek7, FoxM1, and Plk1 in gallbladder cancer and their relationships to clinicopathologic features and survival

PURPOSE

Gallbladder carcinoma (GC) is generally considered as a relatively rare malignancy with poor prognosis. In order to guide clinicians in selecting suitable treatment for GC patients, reliable markers predictive of poor clinical outcome are desirable. This study analyzed the expression of Polo-like kinase 1 (Plk1), Nima related kinases 7 (Nek7) and Forkhead box M1 (FoxM1) in GC tissues and their relationship to clinicopathologic features and survival.

METHODS

We immunohistochemically investigated the 76 specimens of gallbladder carcinoma, pericarcinoma and normal tissues using Nek7, FoxM1 and Plk1 antibodies and analyzed the overall survival time of these 76 patients.

RESULTS

There were significant correlations between the high level expression of Nek7, FoxM1 and Plk1 and the tumor differentiation, Nevin staging and metastasis. The high level expression of Nek7, FoxM1 and Plk1 was significantly associated with shorter overall survival time in univariate analysis (log-rank test), also identified as an independent prognostic factor in multivariate analysis.

CONCLUSION

Nek7, FoxM1 and Plk1 were significantly associated with certain clinicopathologic indices in GC. Evaluation of Nek7, FoxM1 and Plk1 expression may be an important factor in identifying a group of poor GC prognosis.

Silencing CDK4 radiosensitizes breast cancer cells by promoting apoptosis

Background

The discovery of molecular markers associated with various breast cancer subtypes has greatly improved the treatment and outcome of breast cancer patients. Unfortunately, breast cancer cells acquire resistance to various therapies. Mounting evidence suggests that resistance is rooted in the deregulation of the G1 phase regulatory machinery.

Methods

To address whether deregulation of the G1 phase regulatory machinery contributes to radiotherapy resistance, the MCF10A immortalized human mammary epithelial cell line, ER-PR-Her2+ and ER-PR-Her2- breast cancer cell lines were irradiated. Colony formation assays measured radioresistance, while immunocytochemistry, Western blots, and flow cytometry measured the cell cycle, DNA replication, mitosis, apoptosis, and DNA breaks.

Results

Molecular markers common to all cell lines were overexpressed, including cyclin A1 and cyclin D1, which impinge on CDK2 and CDK4 activities, respectively. We addressed their potential role in radioresistance by generating cell lines stably expressing small hairpin RNAs (shRNA) against CDK2 and CDK4. None of the cell lines knocked down for CDK2 displayed radiosensitization. In contrast, all cell lines knocked down for CDK4 were significantly radiosensitized, and a CDK4/CDK6 inhibitor sensitized MDA-MB-468 to radiation induced apoptosis. Our data showed that silencing CDK4 significantly increases radiation induced cell apoptosis in cell lines without significantly altering cell cycle progression, or DNA repair after irradiation. Our results indicate lower levels of phospho-Bad at ser136 upon CDK4 silencing and ionizing radiation, which has been shown to signal apoptosis.

Conclusion

Based on our data we conclude that knockdown of CDK4 activity sensitizes breast cancer cells to radiation by activating apoptosis pathways.

Cdk4 and nek2 signal binucleation and centrosome amplification in a her2+ breast cancer model

Centrosome amplification (CA) is a contributor to carcinogenesis, generating aneuploidy, and chromosome instability. Previous work shows that breast adenocarcinomas have a higher frequency of centrosome defects compared to normal breast tissues. Abnormal centrosome phenotypes are found in pre-malignant lesions, suggesting an early role in breast carcinogenesis. However, the role of CA in breast cancers remains elusive. Identification of pathways and regulatory molecules involved in the generation of CA is essential to understanding its role in breast tumorigenesis. We established a breast cancer model of CA using Her2-positive cells. Our goal was to identify centrosome cycle molecules that are deregulated by aberrant Her2 signaling and the mechanisms driving CA. Our results show some Her2+ breast cancer cell lines harbor both CA and binucleation. Abolishing the expression of Cdk4 abrogated both CA and binucleation in these cells. We also found the source of binucleation in these cells to be defective cytokinesis that is normalized by downregulation of Cdk4. Protein levels of Nek2 diminish upon Cdk4 knockdown and vice versa, suggesting a molecular connection between Cdk4 and Nek2. Knockdown of Nek2 reduces CA and binucleation in this model while its overexpression further enhances centrosome amplification. We conclude that CA is modulated through Cdk4 and Nek2 signaling and that binucleation is a likely source of CA in Her2+ breast cancer cells.

CAND1 promotes PLK4-mediated centriole overduplication and is frequently disrupted in prostate cancer

Centrosomes play a crucial role in the maintenance of genome stability by orchestrating bipolar mitotic spindle formation. The centrosome normally duplicates precisely once before mitosis in a process that is extensively regulated by protein degradation including SKP1-Cullin 1 (CUL1)-F-box (SCF) E3 ubiquitin ligase activity. The core SCF component CUL1 has recently been found to be required to suppress the formation of supernumerary centrosomes and centrioles, the core-forming units of centrosomes. Here, we identify the CUL1-interacting protein cullin-associated and neddylation-dissociated 1 (CAND1) as a novel centrosomal protein with a role in centriole duplication control. CAND1 was found to synergize with Polo-like kinase 4 (PLK4), a master regulator of centriole biogenesis, in the induction of centriole overduplication. We provide evidence that CAND1 functions in this process by increasing PLK4 protein stability. Furthermore, mutants of CUL1 that lack the ability to interact with CAND1 and are unable to assemble functional E3 ubiquitin ligase complexes were impaired in their ability to restrain aberrant daughter centriole synthesis. To corroborate a role of CAND1 in human carcinogenesis, we analyzed a series of prostate adenocarcinomas and found altered expression of CAND1 on the mRNA or protein level in 52.9% and 40.8%, respectively, of the tumor samples analyzed. These results highlight the role of altered SCF components in cancer in general and encourage further studies to explore the SCF-CAND1 axis for the development of novel predictive biomarkers and therapeutic approaches in prostate cancer.

Regulation of the g1/s transition in hepatocytes: involvement of the cyclin-dependent kinase cdk1 in the DNA replication

A singular feature of adult differentiated hepatocytes is their capacity to proliferate allowing liver regeneration. This review emphasizes the literature published over the last 20 years that established the most important pathways regulating the hepatocyte cell cycle. Our article also aimed at illustrating that many discoveries in this field benefited from the combined use of in vivo models of liver regeneration and in vitro models of primary cultures of human and rodent hepatocytes. Using these models, our laboratory has contributed to decipher the different steps of the progression into the G1 phase and the commitment to S phase of proliferating hepatocytes. We identified the mitogen dependent restriction point located at the two-thirds of the G1 phase and the concomitant expression and activation of both Cdk1 and Cdk2 at the G1/S transition. Furthermore, we demonstrated that these two Cdks contribute to the DNA replication. Finally, we provided strong evidences that Cdk1 expression and activation is correlated to extracellular matrix degradation upon stimulation by the pro-inflammatory cytokine TNFα leading to the identification of a new signaling pathway regulating Cdk1 expression at the G1/S transition. It also further confirms the well-orchestrated regulation of liver regeneration via multiple extracellular signals and pathways.