Centrosomal aberrations in primary invasive breast cancer are associated with nodal status and hormone receptor expression

CDK2 inhibition disorders centrosome stoichiometry and alters cellular outcomes in aneuploid cancer cells

Cyclin-dependent Kinase 2 (CDK2) inhibition prevents supernumerary centrosome clustering. This causes multipolarity, anaphase catastrophe and apoptotic death of aneuploid cancers. This study elucidated how CDK2 antagonism affected centrosome stoichiometry. Focused ion beam scanning electron microscopy (FIB-SEM) and immunofluorescent imaging were used. Studies interrogated multipolar mitosis after pharmacologic or genetic repression of CDK2. CDK2/9 antagonism with CYC065 (Fadraciclib)-treatment disordered centrosome stoichiometry in aneuploid cancer cells, preventing centrosome clustering. This caused ring-like chromosomes or multipolar cancer cells to form before onset of cell death. Intriguingly, CDK2 inhibition caused a statistically significant increase in single centrioles rather than intact centrosomes with two centrioles in cancer cells having chromosome rings or multipolarity. Statistically significant alterations in centrosome stoichiometry were undetected in other mitotic cancer cells. To confirm this pharmacodynamic effect, CDK2 but not CDK9 siRNA-mediated knockdown augmented cancer cells with chromosome ring or multipolarity formation. Notably, engineered gain of CDK2, but not CDK9 expression, reversed emergence of cancer cells with chromosome rings or multipolarity, despite CYC065-treatment. In marked contrast, CDK2 inhibition of primary human alveolar epithelial cells did not confer statistically significant increases of cells with ring-like chromosomes or multipolarity. Hence, CDK2 antagonism caused differential effects in malignant versus normal alveolar epithelial cells. Translational relevance was confirmed by CYC065-treatment of syngeneic lung cancers in mice. Mitotic figures in tumors exhibited chromosome rings or multipolarity. Thus, CDK2 inhibition preferentially disorders centrosome stoichiometry in cancer cells. Engaging this disruption is a strategy to explore against aneuploid cancers in future clinical trials.

Chromosomal Instability as Enabling Feature and Central Hallmark of Breast Cancer

Chromosomal instability (CIN) has become a topic of great interest in recent years, not only for its implications in cancer diagnosis and prognosis but also for its role as an enabling feature and central hallmark of cancer. CIN describes cell-to-cell variation in the number or structure of chromosomes in a tumor population. Although extensive research in recent decades has identified some associations between CIN with response to therapy, specific associations with other hallmarks of cancer have not been fully evidenced. Such associations place CIN as an enabling feature of the other hallmarks of cancer and highlight the importance of deepening its knowledge to improve the outcome in cancer. In addition, studies conducted to date have shown paradoxical findings about the implications of CIN for therapeutic response, with some studies showing associations between high CIN and better therapeutic response, and others showing the opposite: associations between high CIN and therapeutic resistance. This evidences the complex relationships between CIN with the prognosis and response to treatment in cancer. Considering the above, this review focuses on recent studies on the role of CIN in cancer, the cellular mechanisms leading to CIN, its relationship with other hallmarks of cancer, and the emerging therapeutic approaches that are being developed to target such instability, with a primary focus on breast cancer. Further understanding of the complexity of CIN and its association with other hallmarks of cancer could provide a better understanding of the cellular and molecular mechanisms involved in prognosis and response to treatment in cancer and potentially lead to new drug targets.

Centrosome Aberrations as Drivers of Chromosomal Instability in Breast Cancer

Chromosomal instability (CIN), or the dynamic change in chromosome number and composition, has been observed in cancer for decades. Recently, this phenomenon has been implicated as facilitating the acquisition of cancer hallmarks and enabling the formation of aggressive disease. Hence, CIN has the potential to serve as a therapeutic target for a wide range of cancers. CIN in cancer often occurs as a result of disrupting key regulators of mitotic fidelity and faithful chromosome segregation. As a consequence of their essential roles in mitosis, dysfunctional centrosomes can induce and maintain CIN. Centrosome defects are common in breast cancer, a heterogeneous disease characterized by high CIN. These defects include amplification, structural defects, and loss of primary cilium nucleation. Recent studies have begun to illuminate the ability of centrosome aberrations to instigate genomic flux in breast cancer cells and the tumor evolution associated with aggressive disease and poor patient outcomes. Here, we review the role of CIN in breast cancer, the processes by which centrosome defects contribute to CIN in this disease, and the emerging therapeutic approaches that are being developed to capitalize upon such aberrations.

Coding variants in the PCNT and CEP295 genes contribute to breast cancer risk in Chinese women

BACKGROUND

Centrioles play pivotal roles in the assembly of centrosomes, their dysfunction is associated with multiple inherited diseases or cancers. To date, few studies have focused on the associations between coding single nucleotide polymorphisms (SNPs) in the centriole duplication cycle genes and the risk of breast cancer in Chinese women.

METHODS

Twenty-one SNPs were selected from the coding regions of 10 critical centriole genes. The associations between the selected SNPs and breast cancer susceptibility were assessed in a case-control study of Chinese women, which included 1032 cases and 1063 controls. Potential biological functions in the influence of protein stability and the profile of expression quantitative trait loci (eQTL) of the identified SNPs were further evaluated using in silico databases.

RESULTS

Multivariate logistic regression analyses revealed that a missense SNP rs7279204 in PCNT was significantly associated with an increased risk of breast cancer (additive model: adjusted OR=1.19, 95% CI: 1.02-1.38), while a missense SNP rs77922978 in CEP295 was significantly associated with a decreased risk of breast cancer (additive model: adjusted OR=0.74, 95% CI: 0.56-0.97). Stratification analyses suggested that rs7279204 and rs77922978 exhibited different effects among later first live birth, ER-negative and PR-negative women (P<0.05). Moreover, rs77922978 showed significant differences for ER and PR status strata (heterogeneity test P=0.028, P=0.046). In addition, bioinformatic analyses indicated that the two variants may possess potential functions of reducing the protein stability of their host genes. Further eQTL analysis showed that the rs7279204 was not only correlated with the expression of its host gene PCNT, but also correlated with the expression of its nearby genes, implying its potential roles in regulation of some cancer susceptibility genes.

CONCLUSIONS

The SNPs rs7279204 and rs77922978 within the coding region of the PCNT and CEP295 genes may contribute to the susceptibility of breast cancer in Han Chinese population.

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 amplification: a quantifiable cancer cell trait with prognostic value in solid malignancies

Numerical and/or structural centrosome amplification (CA) is a hallmark of cancers that is often associated with the aberrant tumor karyotypes and poor clinical outcomes. Mechanistically, CA compromises mitotic fidelity and leads to chromosome instability (CIN), which underlies tumor initiation and progression. Recent technological advances in microscopy and image analysis platforms have enabled better-than-ever detection and quantification of centrosomal aberrancies in cancer. Numerous studies have thenceforth correlated the presence and the degree of CA with indicators of poor prognosis such as higher tumor grade and ability to recur and metastasize. We have pioneered a novel semi-automated pipeline that integrates immunofluorescence confocal microscopy with digital image analysis to yield a quantitative centrosome amplification score (CAS), which is a summation of the severity and frequency of structural and numerical centrosome aberrations in tumor samples. Recent studies in breast cancer show that CA increases across the disease progression continuum, while normal breast tissue exhibited the lowest CA, followed by cancer-adjacent apparently normal, ductal carcinoma in situ and invasive tumors, which showed the highest CA. This finding strengthens the notion that CA could be evolutionarily favored and can promote tumor progression and metastasis. In this review, we discuss the prevalence, extent, and severity of CA in various solid cancer types, the utility of quantifying amplified centrosomes as an independent prognostic marker. We also highlight the clinical feasibility of a CA-based risk score for predicting recurrence, metastasis, and overall prognosis in patients with solid cancers.

RACK1 regulates centriole duplication through promoting the activation of polo-like kinase 1 by Aurora A

Breast cancer gene 1 (BRCA1) contributes to the regulation of centrosome number. We previously identified receptor for activated C kinase 1 (RACK1) as a BRCA1-interacting partner. RACK1, a scaffold protein that interacts with multiple proteins through its seven WD40 domains, directly binds to BRCA1 and localizes to centrosomes. RACK1 knockdown suppresses centriole duplication, whereas RACK1 overexpression causes centriole overduplication in a subset of mammary gland-derived cells. In this study, we showed that RACK1 binds directly to polo-like kinase 1 (PLK1) and Aurora A, and promotes the Aurora A-PLK1 interaction. RACK1 knockdown decreased phosphorylated PLK1 (p-PLK1) levels and the centrosomal localization of Aurora A and p-PLK1 in S phase, whereas RACK1 overexpression increased p-PLK1 level and the centrosomal localization of Aurora A and p-PLK1 in interphase, resulting in an increase of cells with abnormal centriole disengagement. Overexpression of cancer-derived RACK1 variants failed to enhance the Aurora A-PLK1 interaction, PLK1 phosphorylation and the centrosomal localization of p-PLK1. These results suggest that RACK1 functions as a scaffold protein that promotes the activation of PLK1 by Aurora A in order to promote centriole duplication.This article has an associated First Person interview with the first author of the paper.

A semi-automated machine learning-aided approach to quantitative analysis of centrosomes and microtubule organization

Microtubules (MTs) promote important cellular functions including migration, intracellular trafficking, and chromosome segregation. The centrosome, comprised of two centrioles surrounded by the pericentriolar material (PCM), is the cell's central MT-organizing center. Centrosomes in cancer cells are commonly numerically amplified. However, the question of how the amplification of centrosomes alters MT organization capacity is not well studied. We developed a quantitative image-processing and machine learning-aided approach for the semi-automated analysis of MT organization. We designed a convolutional neural network-based approach for detecting centrosomes, and an automated pipeline for analyzing MT organization around centrosomes, encapsulated in a semi-automatic graphical tool. Using this tool, we find that breast cancer cells with supernumerary centrosomes not only have more PCM protein per centrosome, which gradually increases with increasing centriole numbers, but also exhibit expansion in PCM size. Furthermore, cells with amplified centrosomes have more growing MT ends, higher MT density and altered spatial distribution of MTs around amplified centrosomes. Thus, the semi-automated approach developed here enables rapid and quantitative analyses revealing important facets of centrosomal aberrations.

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.

CEP135 isoform dysregulation promotes centrosome amplification in breast cancer cells

The centrosome, composed of two centrioles surrounded by pericentriolar material, is the cell's central microtubule-organizing center. Centrosome duplication is coupled with the cell cycle such that centrosomes duplicate once in S phase. Loss of such coupling produces supernumerary centrosomes, a condition called centrosome amplification (CA). CA promotes cell invasion and chromosome instability, two hallmarks of cancer. We examined the contribution of centriole overduplication to CA and the consequences for genomic stability in breast cancer cells. CEP135, a centriole assembly protein, is dysregulated in some breast cancers. We previously identified a short isoform of CEP135, CEP135mini, that represses centriole duplication. Here, we show that the relative level of full-length CEP135 (CEP135full) to CEP135mini (the CEP135full:mini ratio) is increased in breast cancer cell lines with high CA. Inducing expression of CEP135full in breast cancer cells increases the frequency of CA, multipolar spindles, anaphase-lagging chromosomes, and micronuclei. Conversely, inducing expression of CEP135mini reduces centrosome number. The differential expression of the CEP135 isoforms in vivo is generated by alternative polyadenylation. Directed genetic mutations near the CEP135mini alternative polyadenylation signal reduces the CEP135full:mini ratio and decreases CA. We conclude that dysregulation of CEP135 isoforms promotes centriole overduplication and contributes to chromosome segregation errors in breast cancer cells.

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.

Centrosome amplification, chromosomal instability and cancer: mechanistic, clinical and therapeutic issues

Centrosomes, the main microtubule-organizing centers in most animal cells, are of crucial importance for the assembly of a bipolar mitotic spindle and subsequent faithful segregation of chromosomes into two daughter cells. Centrosome abnormalities can be found in virtually all cancer types and have been linked to chromosomal instability (CIN) and tumorigenesis. Although our knowledge on centrosome structure, replication, and amplification has greatly increased within recent years, still only very little is known on nature, causes, and consequences of centrosome aberrations in primary tumor tissues. In this review, we summarize our current insights into the mechanistic link between centrosome aberrations, aneuploidy, CIN and tumorigenesis. Mechanisms of induction and cellular consequences of aneuploidy, tetraploidization and CIN, as well as origin and effects of supernumerary centrosomes will be discussed. In addition, animal models for both CIN and centrosome amplification will be outlined. Finally, we describe approaches to exploit centrosome amplification, aneuploidy and CIN for novel and specific anticancer treatment strategies based on the modulation of chromosome missegregation rates.

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.

Using high-throughput sequencing transcriptome data for INDEL detection: challenges for cancer drug discovery

INTRODUCTION

A cancer cell is a mosaic of genomic and epigenomic alterations. Distinct cancer molecular signatures can be observed depending on tumor type or patient genetic background. One type of genomic alteration is the insertion and/or deletion (INDEL) of nucleotides in the DNA sequence, which may vary in length, and may change the encoded protein or modify protein domains. INDELs are associated to a large number of diseases and their detection is done based on low-throughput techniques. However, high-throughput sequencing has also started to be used for detection of novel disease-causing INDELs. This search may identify novel drug targets.

AREAS COVERED

This review presents examples of using high-throughput sequencing (DNA-Seq and RNA-Seq) to investigate the incidence of INDELs in coding regions of human genes. Some of these examples successfully utilized RNA-Seq to identify INDELs associated to diseases. In addition, other studies have described small INDELs related to chemo-resistance or poor outcome of patients, while structural variants were associated with a better clinical outcome.

EXPERT OPINION

On average, there is twice as much RNA-Seq data available at the most used repositories for such data compared to DNA-Seq. Therefore, using RNA-Seq data is a promising strategy for studying cancer samples with unknown mechanisms of drug resistance, aiming at the discovery of proteins with potential as novel drug targets.

Centrosome amplification induces high grade features and is prognostic of worse outcomes in breast cancer

Background

Centrosome amplification (CA) has been reported in nearly all types of human cancer and is associated with deleterious clinical factors such as higher grade and stage. However, previous reports have not shown how CA affects cellular differentiation and clinical outcomes in breast cancer.

Methods

We analyzed centrosomes by immunofluorescence and compared to ploidy and chromosomal instability (CIN) as assessed by 6-chromosome FISH in a cohort of 362 breast cancers with median clinical follow-up of 8.4 years. Centrosomes were recognized by immunofluorescence using antibodies for pericentriolar material (PCM; pericentrin) and centrioles (polyglutamylated tubulin). CA was experimentally induced in cell culture by overexpression of polo-like kinase 4 (PLK4).

Results

CA is associated with reduced all-cause and breast cancer-specific overall survival and recurrence-free survival. CA correlates strongly with high-risk subtypes (e.g. triple negative) and higher stage and grade, and the prognostic nature of CA can be explained largely by these factors. A strong correlation between CA and high tumor ploidy demonstrates that chromosome and centrosome doubling often occur in concert. CA is proposed to be a method of inducing CIN via aberrant mitotic cell divisions; consonant with this, we observed a strong correlation between CA and CIN in breast cancers. However, some CA tumors had low levels of CIN, indicating that protective mechanisms are at play, such as centrosome clustering during mitosis. Intriguingly, some high-risk tumors have more acentriolar centrosomes, suggesting PCM fragmentation as another mechanism of CA. In vitro induction of CA in two non-transformed human cell lines (MCF10A and RPE) demonstrated that CA induces a de-differentiated cellular state and features of high-grade malignancy, supporting the idea that CA intrinsically causes high-grade tumors.

Conclusions

CA is associated with deleterious clinical factors and outcomes in breast cancer. Cell doubling events are the most prevalent causes of CA in cancer, although PCM fragmentation may be a secondary cause. CA promotes high-risk breast cancer in part by inducing high-grade features. These findings highlight the importance of centrosome aberrations in the biology of human breast cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2083-x) contains supplementary material, which is available to authorized users.

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.

CDK11p58 inhibits ERα-positive breast cancer invasion by targeting integrin β3 via the repression of ERα signaling

Background

CDK11^p58, a Ser/Thr kinase that belongs to the cell division cycle 2-like 1 (CDC2L1) subfamily, is associated with cell cycle progression, tumorigenesis and apoptotic signaling. CDK11^p58 is also involved in the regulation of steroid receptors, such as androgen and estrogen receptors. We previously found that CDK11^p58 was abnormally expressed in prostate cancer. However, its role in breast cancer remains unclear.

Methods

CDK11^p58 expression was evaluated by immunohistochemical staining in a tissue array. A Transwell assay was used to detect invasion and metastasis in breast cancer cells. The TaqMan® Metastasis Gene Expression Assay was used to search for potential downstream factors in the CDK11^p58 signaling pathway. qRT-PCR was used to evaluate mRNA levels, and the dual luciferase array was used to analyze promoter activity. Western blotting was used to detect the protein level.

Results

CDK11^p58 expression was negatively correlated with node status (P = 0.012), relapse status (P = 0.002) and metastasis status (P = 0.023). Kaplan-Meier survival curves indicated that the disease-free survival (DFS) was significantly poor in breast cancer patients with low CDK11 expression. Interestingly, using the breast cancer cell lines ZR-75-30 and MDA-MB-231, we found that CDK11^p58 was capable of repressing the migration and invasion of ERα-positive breast cancer cells, but not ERα-negative breast cancer cells, in a kinase-dependent manner. Gene expression assays demonstrated that integrin β3 mRNA was dramatically repressed by CDK11^p58, and luciferase results confirmed that the integrin β3 promoter was inhibited by CDK11^p58 through ERα repression. The expression of integrin β3 was highly related to ERα signaling; ERα overexpression stimulated integrin β3 expression, whereas siRNA-mediated knockdown of ERα attenuated integrin β3 expression.

Conclusions

These data indicate that CDK11^p58 is an anti-metastatic gene in ERα-positive breast cancer and that the regulation of integrin β3 by CDK11^p58 via the repression of ERα signaling may constitute part of a signaling pathway underlying breast cancer invasion.

Nek2 and Plk4: prognostic markers, drivers of breast tumorigenesis and drug resistance

The Nek2 and Plk4 kinases serve as crucial regulators of mitotic processes such as the centrosome duplication cycle and spindle assembly. Deregulation of these processes can trigger chromosome instability and aneuploidy, which are hallmarks of many solid tumors, including breast cancer. Emerging data from the literature illustrated various functions of Nek2 in breast cancer models, with compelling evidence of its prognostic value in breast tumors. The two kinases control distinct steps in the centrosome-centriole cycle and their dysregulation lead to centrosome amplification, marked by the presence of more than two centrosomes within the cell. We found single or composite overexpression of these kinases in breast tumor samples, regardless of subtype, which strongly associated with poor prognosis. Interestingly, in a panel of established cell lines, both kinases are highly expressed in Her2-positive breast cancer cells exhibiting centrosome amplification and trastuzumab resistance. In summary, it appears that Nek2 and Plk4 might synergize to promote breast tumorigenesis and may also be involved in tamoxifen and trastuzumab resistance.

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.

Centrosome aberrations in bone marrow cells from patients with myelodysplastic syndromes correlate with chromosomal instability

Centrosomes play important roles in the maintenance of genetic stability and centrosomal aberrations are a hallmark of cancer. Deregulation of centriole duplication leads to supernumerary centrosomes, sister chromatid missegregation and could result in chromosomal instability (CIN) and aneuploidy. CIN is a common feature in at least 45% of patients with myelodysplastic syndromes (MDS). Therefore, we sought to investigate the centrosomal status and its role for development of CIN in bone marrow (BM) cells of MDS patients. BM cells of 34 MDS patients were examined cytogenetically. Furthermore, cells were immunostained with a centrosome-specific antibody to pericentrin to analyze the centrosomal status. Umbilical cord blood specimens and BM cells of healthy persons (n = 11 and n = 4) served as controls. In addition, the protein expression of the protease separase responsible for genetic stability was examined by western blot analysis. Centrosome abnormalities were detected in 10% (range, 4-17%) of cells of MDS samples, but in only 2% (range, 0-4%) of cells of healthy controls. Normal karyotypes were found in control cells and in BM cells of 16/34 MDS patients. The incidence of centrosomal alterations was higher in BM cells of patients with cytogenetic alterations (mean, 12%) compared to BM cells of patients without cytogenetic changes (mean, 7%). Our results indicate that centrosome alterations are a common and early detectable feature in MDS patients and may contribute to the acquisition of chromosomal aberrations. We assume that centrosome defects could be involved in disease progression and may serve as a future prognostic marker.

Centrosome amplification in bladder washing cytology specimens is a useful prognostic biomarker for non-muscle invasive bladder cancer

We investigated whether centrosome amplification (CA) obtained from bladder washing cytology (BWC) specimens may be a useful prognostic biomarker for patients with non-muscle invasive bladder cancer (NMIBC). The study cohort included 78 patients with pathologically confirmed NMIBC. BWC specimens were obtained from all patients during transurethral resection of bladder tumor (TURBT), and CA was evaluated by immunofluorescence staining using a pericentrin polyclonal antibody. A positive case of CA was defined as a specimen in which >5% of cells contained ≥3 centrosomes per cell. CA was detected in 26.9% (21 of 78) of BWC specimens obtained from NMIBC patients. Disease progression was observed in 11.5% (9 of 78) of patients, with a median follow-up of 32 months. In univariate analyses, CA obtained from BWC specimens, initial or recurrent, and washing cytology were significantly associated with progression-free survival (P = 0.009, 0.02, and 0.03, respectively). Multivariate Cox model analyses revealed that CA was the most significant prognostic factor for disease progression (hazard ratio: 2.22, 95% confidence interval: 1.13-4.90, P = 0.022). These data suggest that analysis of CA using bladder washing cytological specimens may provide crucial predictive information regarding disease progression in NMIBC.

Proteomic analysis of the effect of triterpenes from Patrinia heterophylla on leukemia K562 cells

For centuries, Patrinia heterophylla had been used in China to treat many diseases including tumor. Triterpenes has been identified as the major active constituents in Patrinia heterophylla. To elucidate the antitumor mechanism of triterpenes from Patrinia heterophylla1 (TPH), a proteomic analysis is carried out with TPH treatment in K562 cells. The total proteins extracted from TPH treated K562 cells are analyzed by two dimensional gel electrophoresis (2-DE) and compared with those untreated K562 cells. Mass spectrometry is applied to identify the differentially expressed proteins. Twenty-three differentially expressed significant proteins are discovered. Eight proteins are later identified by mass spectrometry (MALDI-TOF-MS) and Mascot software. Among them, four proteins are up-regulated (Aldolase A, Glyceraldehyde-3-phosphate dehydrogenase, Flavin reductase and Hemoglobin subunit) and four proteins were down-regulated (Heat-shock protein 90 〈Alpha〉 (HSP90-〈Alpha〉), Eukaryotic translation initiation factor 5A, Moesin, tublin) by TPH treatment in K562 cells. The identified proteins are associated with energy metabolism, oxidative stress, apoptosis, signal transduction, differential induction, and protein biosynthesis. These findings might provide valuable insights into the antitumor mechanism of TPH in K562 cells.

Genetic polymorphisms in centrobin and Nek2 are associated with breast cancer susceptibility in a Chinese Han population

Centrosome aberrations have been suggested to cause chromosomal instability and aneuploidy, and eventually promote cancer development. The Centrobin and Nek2 proteins interact with each other and both are involved in centrosome duplication and chromosome segregation. This study aimed to investigate whether genetic polymorphisms in these two genes may affect breast cancer susceptibility in Chinese Han population using a haplotype-based analysis. Five single nucleotide polymorphisms (SNPs) in centrobin and four SNPs in Nek2 were genotyped in 1,215 cases of infiltrating ductal breast cancer and 1,215 age-matched cancer-free controls from Chinese Han population. The results showed that CATCG haplotype of centrobin was strongly associated with decreased breast cancer risk (adjusted OR = 0.14, 95 % CI = 0.09-0.22), which was mainly driven by the C allele of SNP rs11650083 (A>C, located in exon 12, resulting in Pro578Gln). None of the individual SNPs in Nek2 was associated with breast cancer risk. However, haplotype GTAT of Nek2 was associated with increased risk of breast cancer (adjusted OR = 1.56, 95 % CI = 1.18-2.06) and its risk was significantly elevated among women with both family history of cancer and a longer menarche-first full-term pregnancy (FFTP) interval (>11 years) (adjusted OR = 5.31, 95 % CI = 1.97-14.32). Furthermore, women harboring both at-risk haplotype GTAT of Nek2 and protective haplotype CATCG of centrobin were linked with decreased breast cancer risk, suggesting that the association between genetic variants of Nek2 and increased breast cancer risk was modified by genetic variants of centrobin. Our results indicate that genetic polymorphisms of centrobin and Nek2 are related to breast cancer susceptibility in Chinese Han women.

A clinical overview of centrosome amplification in human cancers

The turn of the 21st century had witnessed a surge of interest in the centrosome and its causal relation to human cancer development - a postulate that has existed for almost a century. Centrosome amplification (CA) is frequently detected in a growing list of human cancers, both solid and haematological, and is a candidate "hallmark" of cancer cells. Several lines of evidence support the progressive involvement of CA in the transition from early to advanced stages of carcinogenesis, being also found in pre-neoplastic lesions and even in histopathologically-normal tissue. CA constitutes the major mechanism leading to chromosomal instability and aneuploidy, via the formation of multipolar spindles and chromosomal missegregation. Clinically, CA may translate to a greater risk for initiation of malignant transformation, tumour progression, chemoresistance and ultimately, poor patient prognosis. As mechanisms underlying CA are progressively being unravelled, the centrosome has emerged as a novel candidate target for cancer treatment. This Review summarizes mainly the clinical studies performed to date focusing on the mechanisms underlying CA in human neoplasia, and highlights the potential utility of centrosomes in the diagnosis, prognosis and treatment of human cancers.

Targeting chromosomal instability and tumour heterogeneity in HER2-positive breast cancer

Chromosomal instability (CIN) is a common cause of tumour heterogeneity and poor prognosis in solid tumours and describes cell-cell variation in chromosome structure or number across a tumour population. In this article we consider evidence suggesting that CIN may be targeted and may influence response to distinct chemotherapy regimens, using HER2-positive breast cancer as an example. Pre-clinical models have indicated a role for HER2 signalling in initiating CIN and defective cell-cycle control, and evidence suggests that HER2-targeting may attenuate this process. Anthracyclines and platinum agents may target tumours with distinct patterns of karyotypic complexity, whereas taxanes may have preferential activity in tumours with relative chromosomal stability. A greater understanding of karyotypic complexity and identification of methods to directly examine and target CIN may support novel strategies to improve outcome in cancer.

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

Because centrosome amplification generates aneuploidy and since centrosome amplification is ubiquitous in human tumors, a strong case is made for centrosome amplification being a major force in tumor biogenesis. Various evidence showing that oncogenes and altered tumor suppressors lead to centrosome amplification and aneuploidy suggests that oncogenes and altered tumor suppressors are a major source of genomic instability in tumors, and that they generate those abnormal processes to initiate and sustain tumorigenesis. We discuss how altered tumor suppressors and oncogenes utilize the cell cycle regulatory machinery to signal centrosome amplification and aneuploidy.

Urine from current smokers induces centrosome aberrations and spindle defects in vitro in nonmalignant human cell lines

Tobacco smoke containing numerous derived chemical carcinogens is the main risk factor for urothelial carcinoma. These carcinogens can induce DNA damage leading to chromosomal instability, which plays a fundamental role in urothelial carcinogenesis. Possible mechanisms could be centrosomal aberrations, which cause defective spindles and may be responsible for genetic instability. We evaluated the effect of urine from never smokers (NS) and current smokers (CS) in concentrations of 0 to 50% on cell proliferation, chromosomes, centrosomes, and the spindle status of normal human dermal fibroblasts and normal human urothelial cells (UROtsa). After 2 weeks of urine treatment, cell cultures were analyzed by centrosome and spindle immunostaining and conventional cytogenetics. Effects were compared to results of untreated controls. Analysis of normal human dermal fibroblasts and UROtsa cells revealed that urine from CS induced higher values of centrosome aberrations in a dose-dependent and cell line-independent manner when compared to cultures treated with urine from NS and untreated controls. Centrosomal alterations correlated with spindle defects and an increase of sporadic chromosomal aberrations. The observations suggest a causative role of chemical carcinogens in urine from CS in the origin of centrosome and spindle defects in vitro leading to chromosomal instability and may be involved in urothelial carcinogenesis.

The Ras oncogene signals centrosome amplification in mammary epithelial cells through cyclin D1/Cdk4 and Nek2

Centrosome amplification (CA) contributes to carcinogenesis by generating aneuploidy. Elevated frequencies of CA in most benign breast lesions and primary tumors suggest a causative role for CA in breast cancers. Clearly, identifying which and how altered signal transduction pathways contribute to CA is crucial to breast cancer control. Although a causative and cooperative role for c-Myc and Ras in mammary tumorigenesis is well documented, their ability to generate CA during mammary tumor initiation remains unexplored. To answer that question, K-Ras(G12D) and c-Myc were induced in mouse mammary glands. Although CA was observed in mammary tumors initiated by c-Myc or K-Ras(G12D), it was detected only in premalignant mammary lesions expressing K-Ras(G12D). CA, both in vivo and in vitro, was associated with increased expression of the centrosome-regulatory proteins, cyclin D1 and Nek2. Abolishing the expression of cyclin D1, Cdk4 or Nek2 in MCF10A human mammary epithelial cells expressing H-Ras(G12V) abrogated Ras-induced CA, whereas silencing cyclin E1 or B2 had no effect. Thus, we conclude that CA precedes mammary tumorigenesis, and interfering with centrosome-regulatory targets suppresses CA.

A novel role of the aryl hydrocarbon receptor (AhR) in centrosome amplification - implications for chemoprevention

BACKGROUND

Centrosome aberrations can cause genomic instability and correlate with malignant progression in common human malignancies such as breast and prostate cancer. Deregulation of cyclin/cyclin-dependent kinase 2 (CDK2) activity has previously been shown to be critically involved in centrosome overduplication. We therefore test here whether small molecule CDK inhibitors derived from the bis-indole indirubin can be used to suppress centrosome aberrations as a novel approach to chemoprevention of malignant progression.

RESULTS

As expected, we found that the CDK inhibitor indirubin-3'-oxime (IO) suppresses centrosome amplification in breast cancer cells. However, we made the unexpected discovery that indirubin-derived compounds that have been chemically modified to be inactive as kinase inhibitors such as 1-methyl-indirubin-3'-oxime (MeIO) still significantly reduced centrosome amplification. All indirubins used in the present study are potent agonists of the aryl hydrocarbon receptor (AhR), which is known for its important role in the cellular metabolism of xenobiotics. To corroborate our results, we first show that the coincidence of nuclear AhR overexpression, reflecting a constitutive activation, and numerical centrosome aberrations correlates significantly with malignancy in mammary tissue specimens. Remarkably, a considerable proportion (72.7%) of benign mammary tissue samples scored also positive for nuclear AhR overexpression. We furthermore provide evidence that continued expression of endogenous AhR is critical to promote centriole overduplication induced by cyclin E and that AhR and cyclin E may function in the same pathway. Overexpression of the AhR in the absence of exogenous ligands was found to rapidly disrupt centriole duplication control. Nonetheless, the AhR agonists IO and MeIO were still found to significantly reduce centriole overduplication stimulated by ectopic AhR expression.

CONCLUSIONS

Our results indicate that continued expression of endogenous AhR promotes centrosome amplification in breast cancer cells in a pathway that involves cyclin E. AhR agonists such as indirubins inhibit centrosome amplification even when stimulated by ectopic expression of the AhR suggesting that these compounds are potentially useful for the chemoprevention of centrosome-mediated cell division errors and malignant progression in neoplasms in which the AhR is overexpressed. Future studies are warranted to determine whether individuals in which nuclear AhR overexpression is detected in benign mammary tissue are at a higher risk for developing pre-cancerous or cancerous breast lesions.

Centrosome-related genes, genetic variation, and risk of breast cancer

Centrosome amplification has been detected in premalignant lesions and in situ tumors in the breast and in over 70% of invasive breast tumors, and has been associated with aneuploidy and tumor development. Based on these observations, the contribution of commonly inherited genetic variation in candidate genes related to centrosome structure and function to breast cancer risk was evaluated in an association study. Seven-hundred and 82 single nucleotide polymorphisms (SNPs) from 101 centrosomal genes were analyzed in 798 breast cancer cases and 843 controls from the Mayo Clinic Breast Cancer Study to assess the association between these SNPs (both individually and combined) and risk of breast cancer in this population. Eleven SNPs out of 782 from six genes displayed associations with breast cancer risk (P < 0.01). Haplotypes in five genes also displayed significant associations with risk. A two SNP combination of rs10145182 in NIN and rs2134808 in the TUBG1 locus (P-interaction = 0.00001), suggested SNPs in mediators of microtubule nucleation from the centrosome contribute to breast cancer. Evaluation of the simultaneous significance of all SNPs in the centrosome pathway suggested that the centrosome pathway is highly enriched (P = 4.76 × 10(-50)) for SNPs that are associated with breast cancer risk. Collections of weakly associated genetic variants in the centrosome pathway, rather than individual highly significantly associated SNPs, may account for a putative role for the centrosome pathway in predisposition to breast cancer.

Delocalization of gamma-tubulin due to increased solubility in human breast cancer cell lines

The centrosome is the major organelle responsible for the nucleation and organization of microtubules into arrays. Recent studies demonstrate that microtubules can nucleate outside the centrosome. The molecular mechanisms controlling acentrosomal microtubule nucleation are currently poorly defined, and the function of this type of microtubule regulation in tumor cell biology is particularly unclear. Since microtubule nucleation is initiated by the gamma-tubulin protein, we examined the regulation of gamma-tubulin in a panel of human breast tumor cell lines, ranging from non-tumorigenic to highly aggressive. We have identified a more dispersive subcellular localization of gamma-tubulin in aggressive breast cancer cell lines, while gamma-tubulin localization remains largely centrosomal in non-aggressive cell lines. Delocalization of gamma-tubulin occurs independently from changes in protein expression and is therefore regulated at the post-translational level. Subcellular fractionation revealed that tumor cell lines show an aberrantly increased release of gamma-tubulin into a soluble cytoplasmic fraction, with the most dramatic changes observed in tumor cell lines of greater aggressiveness. Extraction of soluble gamma-tubulin revealed acentrosomal incorporation of gamma-tubulin in cytoplasmic microtubules and along cell junctions. Moreover, acentrosomal delocalization of gamma-tubulin yielded resistance to colchicine-mediated microtubule collapse. These findings support a model where the solubility of gamma-tubulin can be altered through post-translational modification and provides a new mechanism for microtubule dysregulation in breast cancer. Gamma-tubulin that is delocalized from the centrosome can still clearly be incorporated into filaments, and defines a novel mechanism for tumor cells to develop resistance to microtubule-targeted chemotherapies.

Centrosomin: a complex mix of long and short isoforms is required for centrosome function during early development in Drosophila melanogaster

Centrosomin (Cnn) is a required core component in mitotic centrosomes during syncytial development and the presence of Cnn at centrosomes has become synonymous with fully functional centrosomes in Drosophila melanogaster. Previous studies of Cnn have attributed this embryonic function to a single isoform or splice variant. In this study, we present new evidence that significantly increases the complexity of cnn. Rather than a single isoform, Cnn function can be attributed to two unique classes of proteins that comprise a total of at least 10 encoded protein isoforms. We present the initial characterization of a new class of Cnn short isoforms required for centrosome function during gametogenesis and embryogenesis. We also introduce new evidence for a complex mix of Cnn isoforms present during early embryogenesis. Finally, we reexamine cnn mutations, in light of the short isoforms, and find previously overlooked differences attributable to allele-specific mutant phenotypes. This study addresses several questions surrounding Cnn function at the centrosome during embryogenesis and shows that cnn function cannot be ascribed to a single protein.

Increased expression of centrosomal alpha, gamma-tubulin in atypical ductal hyperplasia and carcinoma of the breast

Centrosomal abnormalities have been found in various cancer types. We sought to determine whether centrosomal dysfunctions occur in the atypical ductal hyperplasia (ADH)-carcinoma sequence of breast cancer. As alpha and gamma-tubulins are the structural components of centrosomes, we performed real time quantitative polymerase chain reaction (qPCR), in situ hybridization (ISH) and immunnohistochemistry (IHC) to determine the DNA copy levels, messenger RNA (mRNA) expression, and protein expression of alpha and gamma-tubulins respectively. Gamma-tubulin staining was used for the localization and quantification of centrosomes. We found that alpha-tubulin or gamma-tubulin mRNA was increasingly expressed from normal breast tissue (NBT) to ADH, ductal carcinoma in situ (DCIS), and infiltrative ductal carcinoma (IDC), respectively, with the highest expressions being found in DCIS. The expression profiles of alpha, gamma-tubulin proteins were concordant with that of mRNA, except that the highest expression was found in IDC. Similarly, DNA copies of alpha, gamma-tubulins showed a rising tendency, with the highest level for gamma-tubulin attained in IDC and that for alpha-tubulin was found in DCIS. However, there was no significant difference of alpha, gamma-tubulin DNA copy levels, mRNA expression, and protein expression between DCIS and IDC. Our results demonstrate that centrosomal aberrations may play key roles in the early stage of breast tumorogenesis. The malignant transformation sequence is probably attributable to the amplification of centrosomal DNA leading to mRNA and protein over-expression of these centrosomal proteins. Furthermore, determination of alpha, gamma-tubulins using combined qPCR with ISH may be useful in assisting the diagnosis of premalignant lesions of the breast.

Centrosomal PKCbetaII and pericentrin are critical for human prostate cancer growth and angiogenesis

Angiogenesis is critical in the progression of prostate cancer. However, the interplay between the proliferation kinetics of tumor endothelial cells (angiogenesis) and tumor cells has not been investigated. Also, protein kinase C (PKC) regulates various aspects of tumor cell growth, but its role in prostate cancer has not been investigated in detail. Here, we found that the proliferation rates of endothelial and tumor cells oscillate asynchronously during the growth of human prostate cancer xenografts. Furthermore, our analyses suggest that PKCbetaII was activated during increased angiogenesis and that PKCbetaII plays a key role in the proliferation of endothelial cells and tumor cells in human prostate cancer; treatment with a PKCbetaII-selective inhibitor, betaIIV5-3, reduced angiogenesis and tumor cell proliferation. We also find a unique effect of PKCbetaII inhibition on normalizing pericentrin (a protein regulating cytokinesis), especially in endothelial cells as well as in tumor cells. PKCbetaII inhibition reduced the level and mislocalization of pericentrin and normalized microtubule organization in the tumor endothelial cells. Although pericentrin has been known to be up-regulated in epithelial cells of prostate cancers, its level in tumor endothelium has not been studied in detail. We found that pericentrin is up-regulated in human tumor endothelium compared with endothelium adjacent to normal glands in tissues from prostate cancer patients. Our results suggest that a PKCbetaII inhibitor such as betaIIV5-3 may be used to reduce prostate cancer growth by targeting both angiogenesis and tumor cell growth.

Association of loss of BRCA1 expression with centrosome aberration in human breast cancer

PURPOSE

Centrosome aberration in number and/or size is reportedly often observed in human breast cancer. The aim of this study was to investigate the relationship between centrosome aberration and chromosomal instability as well as the expression of centrosome regulators such as BRCA1, Aurora-A, and p53.

METHODS

Centrosome aberration in number and size was determined immunohistochemically using the anti-gamma-tubulin antibody, and chromosomal instability was evaluated by fluorescence in situ hybridization analysis of chromosomes 1, 11, and 17 in paraffin sections from 50 human breast cancers. Immunohistochemical examination of BRCA1, Aurora-A, and p53 was also performed to examine the relationship of their expression with centrosome aberration.

RESULTS

Percentage of tumor cells with centrosome aberration in size varied from 0.9 to 30.4% (median 9.5%) and in number it varied from 0.5 to 86.5% (median 34.5%) in each tumor. No significant association in number or size, however, was observed between chromosomal instability and centrosome aberration. Numerical centrosome aberration was significantly associated with negative BRCA1 expression (P = 0.001). Breast tumors (n = 3) from patients with a proven BRCA1 germline mutation also showed a significant relationship with numerical centrosome aberration (P = 0.011). On the other hand, expression of Aurora-A or p53 was not significantly associated with centrosome aberration in either number or size.

CONCLUSIONS

Centrosome aberration is not associated with chromosomal instability, indicating the importance of other mechanisms in the induction of chromosomal instability in human breast cancer. BRCA1, but not Aurora-A and p53, is significantly involved in the pathogenesis of centrosome aberration.

Analysis of the cellular centrosome in fine-needle aspirations of the breast

Background

The purpose of the present investigation is to determine whether centrosome amplifications are present in breast tumor cells, whether there are differences of centrosome amplification between benign breast lesions and breast carcinomas, and whether centrosomal analysis can be of value in the diagnosis and prognosis of breast carcinoma.

Methods

Using immunofluorescence analysis with an antibody against γ-tubulin, we analyzed centrosome abnormalities in fine-needle aspirations of 100 breast lesions (25 cases with benign lesions and 75 cases with carcinomas).

Results

We found that centrosome amplifications, including numerical centrosome amplification and structural centrosome amplification, were present in most breast tumors. Cells with numerical centrosome amplification were found in 23 of 25 benign lesions, and in all 75 cases of breast carcinomas. Cells with structural centrosome amplification were found in three of 25 benign lesions, and in 69 of 75 breast carcinomas. The breast carcinomas showed a mean percentage of cells with numerical centrosome amplification of 4.86% and a mean percentage of cells with structural centrosome amplification of 3.98%. These percentages were significantly higher than those in benign lesions, with a numerical centrosome amplification of 2.77% and a structural centrosome amplification of 0.10%. Furthermore, the mean percentage of cells with structural centrosome amplification was significantly associated with HER2/neu overexpression (P < 0.05) and with negative estrogen receptor status (P < 0.05), and had a borderline association with negative progesterone receptor status (P = 0.056) in breast carcinomas.

Conclusion

Structural centrosome amplification may bear a close relationship with breast carcinoma and may be a potential biomarker for diagnosis and prognosis of breast carcinoma.

Human T-cell leukemia virus type 1 Tax and cellular transformation

Infection of T-cells by human T-cell leukemia virus type 1 (HTLV-1) causes a lymphoproliferative malignancy known as adult T-cell leukemia (ATL). ATL is characterized by abnormal lymphocytes, called flower cells, which have cleaved and convoluted nuclei. Tax, encoded by the HTLV-1 pX region, is a critical nonstructural protein that plays a central role in leukemogenesis; however, the mechanisms of HTLV-1 oncogenesis have not been clarified fully. In this review, we summarize current thinking on how Tax may affect ATL leukemogenesis.

Identification of griseofulvin as an inhibitor of centrosomal clustering in a phenotype-based screen

A major drawback of cancer chemotherapy is the lack of tumor-specific targets which would allow for the selective eradication of malignant cells without affecting healthy tissues. In contrast with normal cells, most tumor cells contain multiple centrosomes, associated with the formation of multipolar mitotic spindles and chromosome segregation defects. Many tumor cells regain mitotic stability after clonal selection by the coalescence of multiple centrosomes into two functional spindle poles. To overcome the limitations of current cancer treatments, we have developed a cell-based screening strategy to identify small molecules that inhibit centrosomal clustering and thus force tumor cells with supernumerary centrosomes to undergo multipolar mitoses, and subsequently, apoptosis. Using a chemotaxonomic selection of fungi from a large culture collection, a relatively small but diverse natural product extract library was generated. Screening of this compound library led to the identification of griseofulvin, which induced multipolar spindles by inhibition of centrosome coalescence, mitotic arrest, and subsequent cell death in tumor cell lines but not in diploid fibroblasts and keratinocytes with a normal centrosome content. The inhibition of centrosome clustering by griseofulvin was not restricted to mitotic cells but did occur during interphase as well. Whereas the formation of multipolar spindles was dynein-independent, depolymerization of interphase microtubules seemed to be mechanistically involved in centrosomal declustering. In summary, by taking advantage of the tumor-specific phenotype of centrosomal clustering, we have developed a screening strategy that might lead to the identification of drugs which selectively target tumor cells and spare healthy tissues.

Expression of the p210BCR-ABL oncoprotein drives centrosomal hypertrophy and clonal evolution in human U937 cells

Centrosomes play fundamental roles in mitotic spindle organization, chromosome segregation and maintenance of genetic stability. Recently, we have shown that centrosome aberrations occur early in chronic myeloid leukemia (CML) and are induced by imatinib in normal fibroblasts in vitro. To investigate the influence of BCR-ABL on centrosomes, we performed long-term in vitro experiments employing the conditionally p210BCR-ABL-expressing (tetracycline-inducible promoter) human monocytic cell line U937p210BCR-ABL/c6 as a model of CML chronic phase. Centrosome hypertrophy was detectable after 4 weeks of transgene expression onset, increasing up to a rate of 25.7% aberrant cells within 13 weeks of propagation. This concurred with clonal expansion of aneuploid cells displaying a hyperdiploid phenotype with 57 chromosomes. Partial reversibility of centrosome aberrations (26-8%) was achieved under prolonged propagation (14 weeks) after abortion of induction and bcr-abl silencing using small interfering RNA. Therapeutic doses of imatinib did not revert the aberrant phenotype, but counteracted the observed reverting effect of bcr-abl gene expression switch off. Suggesting a mechanistic model that features distinct abl-related tyrosine kinase activity levels as essential determinants of centrosomal integrity, this is the first report mechanistically linking p210BCR-ABL oncoprotein activity to centrosomal hypertrophy.

Human T-cell leukaemia virus type 1 (HTLV-1) infectivity and cellular transformation

It has been 30 years since a 'new' leukaemia termed adult T-cell leukaemia (ATL) was described in Japan, and more than 25 years since the isolation of the retrovirus, human T-cell leukaemia virus type 1 (HTLV-1), that causes this disease. We discuss HTLV-1 infectivity and how the HTLV-1 Tax oncoprotein initiates transformation by creating a cellular environment favouring aneuploidy and clastogenic DNA damage. We also explore the contribution of a newly discovered protein and RNA on the HTLV-1 minus strand, HTLV-1 basic leucine zipper factor (HBZ), to the maintenance of virus-induced leukaemia.

High rate of centrosome aberrations and correlation with proliferative activity in patients with untreated B-cell chronic lymphocytic leukemia

B-cell chronic lymphocytic leukemia (CLL) is characterized by a high rate of clonal genomic alterations and a low proliferative activity with cell cycle arrest in G(0)/G(1) phase. Recently, centrosome aberrations have been described as a possible cause of chromosomal instability and aneuploidy in many human malignancies. To investigate whether centrosome aberrations do occur in CLL and whether they correlate with common prognostic factors and disease activity, we examined peripheral blood mononuclear cells (PBMC) from 70 patients with previously untreated CLL using an antibody to gamma-tubulin. All 70 CLL samples displayed significantly more cells with centrosome aberrations (median: 26.0%, range 11.0-41.5%) as compared to peripheral blood B lymphocytes from 20 age-matched, healthy individuals (median: 2.0%, range 0-6%; p < 0.001). The extent of centrosome aberrations correlated with the proliferative activity of the CLL cases as measured by lymphocyte doubling time (p = 0.02) as well as with time to first treatment (p = 0.05). Accordingly, more centrosome aberrations were found in PHA-stimulated T lymphocytes from healthy individuals as well as in B cells from surgically removed tonsil tissue of patients with acute tonsillitis as compared to the peripheral blood B lymphocytes from the control group. In contrast, no correlation was observed between centrosome aberrations and immunoglobulin VH gene mutation status or cytogenetically defined risk groups. These findings suggest that, despite the common observation of most CLL cells remaining in G(0)/G(1) phase, their centrosome replication process is deregulated and correlates to the proliferative activity of CLL cells.

Abnormal centrosome amplification in cells through the targeting of Ran-binding protein-1 by the human T cell leukemia virus type-1 Tax oncoprotein

Human T cell leukemia virus type-1 (HTLV-1) is an oncogenic retrovirus etiologically causal of adult T cell leukemia. The virus encodes a Tax oncoprotein that functions in transcriptional regulation, cell cycle control, and transformation. Because adult T cell leukemia like many other human cancers is a disease of genomic instability with frequent gains and losses of chromosomes, to understand this disease it is important to comprehend how HTLV-1 engenders aneuploidy in host cells. In this regard, loss of cell cycle checkpoints permits tolerance of aneuploidy but does not explain how aneuploidy is created. We show here that HTLV-1 Tax causes abnormal centrosome fragmentation in the mitotic phase of the cell cycle. We report that Tax directly binds Ran and Ran-binding protein-1, locates to centrosomes/spindle poles, and causes supernumerary centrosomes.

Centrosome aberrations in chronic myeloid leukemia correlate with stage of disease and chromosomal instability

Centrosome abnormalities are hallmarks of various cancers and have been implicated in chromosome missegregation, chromosomal instability, and aneuploidy. Since genetic instability is a common feature in chronic myeloid leukemia (CML), we sought to investigate whether centrosome aberrations occur and correlate with disease stage and cytogenetic findings in CML. We examined 34 CML samples including CD 34+Ph+cells of 18 newly diagnosed patients (chronic phase (CP)) and 16 blast crisis (BC) specimens by using a centrosome-specific antibody to pericentrin. All CP and BC samples displayed centrosome alterations as compared with corresponding CD 34+control cells. Centrosome abnormalities were detected in 29.1+/-5.9% of CP blasts and in 54.3+/-4.8% of BC blasts, but in only 2.4+/-1.1% of controls (P<0.0001). Additional karyotypic alterations to the t(9;22) translocation were found in only 1/18 CML-CP patients. In contrast, 11/16 (73%) CML-BC patients displayed additional karyotype alterations in 48.7% of analyzed cells, correlating with an abnormal centrosome status (P=0.0005). Our results indicate that centrosome defects are a common and early detectable feature in CML that may contribute to acquisition of chromosomal aberrations and aneuploidy. They may be considered as the driving force of disease progression and could serve as future prognostic markers.

Centrosome aberrations as a possible mechanism for chromosomal instability in non-Hodgkin's lymphoma

Recently, centrosome aberrations have been described as a possible cause of aneuploidy in many solid tumors. To investigate whether centrosome aberrations occur in non-Hodgkin's lymphoma (NHL) and correlate with histologic subtype, karyotype, and other biological disease features, we examined 24 follicular lymphomas (FL), 18 diffuse large-B-cell lymphomas (DLCL), 33 mantle cell lymphomas (MCL), and 17 extranodal marginal zone B-cell lymphomas (MZBCL), using antibodies to centrosomal proteins. All 92 NHL displayed numerical and structural centrosome aberrations as compared to nonmalignant lymphoid tissue. Centrosome abnormalities were detectable in 32.3% of the cells in NHL, but in only 5.5% of lymphoid cells from 30 control individuals (P<0.0001). Indolent FL and MZBCL contained only 25.8 and 28.8% cells with abnormal centrosomes. In contrast, aggressive DLCL and MCL harbored centrosome aberrations in 41.8 and 35.0% of the cells, respectively (P<0.0001). Centrosomal aberrations correlated to lymphoma grade, mitotic, and proliferation indices, but not to the p53 labeling index. Importantly, diploid MCL contained 31.2% cells with abnormal centrosomes, while tetraploid samples harbored centrosome aberrations in 55.6% of the cells (P<0.0001). These results indicate that centrosome defects are common in NHL and suggest that they may contribute to the acquisition of chromosomal instability typically seen in NHL.