Overexpression of aurora kinase A in mouse mammary epithelium induces genetic instability preceding mammary tumor formation

Aurora A is differentially expressed in gliomas, is associated with patient survival in glioblastoma and is a potential chemotherapeutic target in gliomas

Aurora A is critical for mitosis and is overexpressed in several neoplasms. Its overexpression transforms cultured cells, and both its overexpression and knockdown cause genomic instability. In transgenic mice, Aurora A haploinsufficiency, not overexpression, leads to increased malignant tumor formation. Aurora A thus appears to have both tumor-promoting and tumor-suppressor functions. Here, we report that Aurora A protein, measured by quantitative protein gel blotting, is differentially expressed in major glioma types in lineage-specific patterns. Aurora A protein levels in WHO grade II oligodendrogliomas (n=16) and grade III anaplastic oligodendrogliomas (n=16) are generally low, similar to control epilepsy cerebral tissue (n=11). In contrast, pilocytic astrocytomas (n=6) and ependymomas (n=12) express high Aurora A levels. Among grade II to grade III astrocytomas (n=7, n=14, respectively) and grade IV glioblastomas (n=31), Aurora A protein increases with increasing tumor grade. We also found that Aurora A expression is induced by hypoxia in cultured glioblastoma cells and is overexpressed in hypoxic regions of glioblastoma tumors. Retrospective Kaplan-Meier analysis revealed that both lower Aurora A protein measured by quantitative protein gel blot (n=31) and Aurora A mRNA levels measured by real-time quantitative RT-PCR (n=58) are significantly associated with poorer patient survival in glioblastoma. Furthermore, we report that the selective Aurora A inhibitor MLN8237 is potently cytotoxic to glioblastoma cells, and that MLN8237 cytotoxicty is potentiated by ionizing radiation. MLN8237 also appeared to induce senescence and differentiation of glioblastoma cells. Thus, in addition to being significantly associated with survival in glioblastoma, Aurora A is a potential new drug target for the treatment of glioblastoma and possibly other glial neoplasms.

Tumorigenic polyploid cells contain elevated ROS and ARE selectively targeted by antioxidant treatment

Polyploidy has been linked to tumorigenicity mainly due to the chromosomal aberrations. Elevated reactive oxygen species (ROS) generation, on the other hand, has also been associated with oncogenic transformation in most cancer cells. However, a possible link between ploidy and ROS is largely unexplored. Here we have examined the role of ROS in the tumorigenicity of polyploid cells. We show that polyploid prostate and mammary epithelial cells contain higher levels of ROS due to their higher mitochondrial contents. ROS levels and mitochondrial mass are also higher in dihydrocytochalasin B (DCB)-induced polyploid cells, suggesting that higher levels of ROS observed in polyploid cell can occur due to cytokinesis failure. Interestingly, polyploid cells were more sensitive to the inhibitory effect of the antioxidant, N-Acetyl-L-cysteine (NAC), than control diploid cells. Treatment of polyploid/diploid cells with NAC led to the selective elimination of polyploid cells over time and abrogated the tumorigenicity of polyploid cells. This effect was partially mediated via the Akt signaling pathway. We next explored a possible role for ROS in promoting chromosomal instability by analyzing the effects of ROS on the mitotic stage of the cell cycle. Enhancing ROS levels by treating cells with hydrogen peroxide delayed not only entry into and but also exit from mitosis. Furthermore, increasing ROS levels significantly increased taxol resistance. Our results indicated that increased ROS in polyploid cells can contribute to tumorigenicity and highlight the therapeutic potential of antioxidants by selectively targeting the tumorigenic polyploid cells and by reversing taxol resistance.

Danusertib, an aurora kinase inhibitor

INTRODUCTION

Drugs that interfere with the normal progression of mitosis belong to the most successful cytotoxic agents currently used for anticancer treatment. Aurora kinases are serine/threonine kinases that function as key regulators of mitosis and are frequently overexpressed in human cancers. The use of several small molecule aurora kinase inhibitors as potential anticancer therapeutic is being investigated. Danusertib (formerly PHA-739358) is a small ATP competitive molecule that inhibits aurora A, B and C kinases. Interestingly, danusertib also inhibits several receptor tyrosine kinases such as Abl, Ret, FGFR-1 and TrkA. These tyrosine kinases are involved in the pathogenesis of a variety of malignancies and the observed multi-target inhibition may increase the antitumor activity resulting in extending the indication. Danusertib was one of the first aurora kinase inhibitors to enter the clinic and has been studied in Phase I and II trials.

AREAS COVERED

This review provides an updated summary of preclinical and clinical experience with danusertib up to July 2011.

EXPERT OPINION

Future studies with danusertib should focus on the possibility of combining this agent with other targeted anticancer agents, chemotherapy or radiotherapy. As a single agent, danusertib may show more promise in the treatment of leukemias than in solid tumors.

PHLDA1 is a crucial negative regulator and effector of Aurora A kinase in breast cancer

Aurora A kinase is overexpressed in the majority of breast carcinomas. A chemical genetic approach was used to identify the malignant targets of Aurora A, which revealed pleckstrin-homology-like domain protein PHLDA1 as an Aurora A substrate. PHLDA1 downregulation is a powerful prognostic predictor for breast carcinoma, which was confirmed in our study. We further show that downregulation of PHLDA1 is associated with estrogen receptor (ER) expression in breast carcinoma. Aurora A directly phosphorylates PHLDA1 leading to its degradation. PHLDA1 also negatively regulates Aurora A, thereby triggering a feedback loop. We demonstrate the underlying mechanisms by which PHLDA1 upregulation strongly antagonizes Aurora-A-mediated oncogenic pathways, thereby revealing PHLDA1 degradation as a key mechanism by which Aurora A promotes breast malignancy. Thus, not surprisingly, PHLDA1 upregulation acts synergistically with Aurora A inhibition in promoting cell death. PHLDA1 overexpression might therefore be an alternative method to modulate Aurora A deregulation in breast carcinoma. Finally, this study led to the discovery of a mutation in the Aurora A active site that renders it amenable to the chemical genetic approach. Similar mutations are required for Aurora B, suggesting that this modified approach can be extended to other kinases that have hitherto not been amenable to this methodology.

Overcoming CML acquired resistance by specific inhibition of Aurora A kinase in the KCL-22 cell model

Serine/threonine kinase Aurora A is essential for regulating mammalian cell division and is overexpressed in many types of human cancer. However, the role of Aurora A in chemoresistance of chronic myelogenous leukemia (CML) is not well understood. Using the KCL-22 cell culture model we have recently developed for studying mechanisms of CML acquired resistance, we found that Aurora A expression was partially reduced in these cells upon treatment with the tyrosine kinase inhibitor imatinib, which accompanied the acquisition of BCR-ABL mutation for imatinib resistance. Gene knockdown of BCR-ABL also reduced Aurora A expression, and conversely, Aurora A expression increased in hematopoietic progenitor cells after BCR-ABL expression. Inhibition of Aurora A induced apoptosis of CML cells with or without T315I BCR-ABL mutation and suppressed CML cell growth. Inhibition of Aurora A by gene knockdown or a highly specific small molecule inhibitor sensitized CML cells to imatinib treatment and effectively blocked acquisition of BCR-ABL mutations and KCL-22 cell relapse on imatinib, nilotinib or dasatinib. Our results show that Aurora A plays an important role for facilitating acquisition of BCR-ABL mutation and acquired resistance to tyrosine kinase inhibitors in the culture model and suggest that inhibition of Aurora A may provide an alternative strategy to improve CML treatment to overcome resistance.

[The serine/threonine kinases that control cell cycle progression as therapeutic targets]

Cell cycle progression corresponds to a series of events, which succeed one another to end in the division of a mother cell to give two daughter cells. The processes that allow the cell to divide are very precisely controlled by a multitude of enzymatic reactions among which protein phosphorylation, carried out by protein kinases, plays a key role. Serine/threonine kinases are enzymes that catalyse the transfer of a phosphate from ATP to a protein substrate, more precisely on a serine or threonine amino acid residue. Three important families of serine/threonine kinases are involved in the regulation of cell cycle progression, the cyclin dependent kinase (CDK) the polo-like kinase (PLK) and those of the Aurora family. The cancer is described as an uncontrolled cell division process. Cancer cells proliferate indeed in an anarchic way, and carry out cycles of cellular division by being unaware of the signals of alarm. A simple idea thus appeared soon: to stop or to slow down cell cycle progression would result in inhibiting cell proliferation and thus fighting against cancer. Cell cycle progression being controlled in particular by protein kinases of the CDK, PLK and Aurora families, it was rapidly decided to look for inhibitors of those protein kinases. We will first make a general recall on cell cycle progression and the mechanisms that control it. The functions of protein kinases of the CDK, PLK and Aurora families will then be described by concentrating on the sensitive phase of the cell cycle progression, i.e. mitosis. Finally, we will approach the consequences of the inhibition of these protein kinases within the framework of the fight against cancer.

The novel protein suppressed in lung cancer down-regulated in lung cancer tissues retards cell proliferation and inhibits the oncokinase Aurora-A

INTRODUCTION

In an attempt to search for genes with abnormal expression in cancers, Suppressed in Lung Cancer (SLAN, also known as KIAA0256) is found underexpressed in human lung cancer tissues by quantitative real-time PCR (Q-RT-PCR). The study set out to characterize SLAN protein and explore its cellular functions.

METHODS

SLAN or its specific short hairpin RNA, full length or various deletion mutants were overexpressed in 293T or lung cancer cell lines, and cell proliferation, cell cycle, mitosis progression, and spindle configuration were surveyed.

RESULTS

SLAN and its deletion mutants are localized to many subcellular locations such as endoplasmic reticulum (ER), nucleus, nucleolus, spindle pole and midbody, suggesting SLAN may function as a multifunctional protein. Overexpression of SLAN per se or its short hairpin RNAs (shRNAs) inhibits or accelerates cell proliferation through prolonging or shortening mitosis. Time-lapse microscopic recording reveals that cells overexpressing exogenous SLAN are arrested in mitosis or cannot undergo cytokinesis. SLAN 2-551 mutants drastically arrest cells in mitosis, where α- and γ-tubulin are disorganized. SLAN employs C-terminal to interact with Aurora-A, a key mitosis regulator and an oncogenic kinase associated with a wide range of human cancers. SLAN negatively regulates the activity of Aurora-A by directly inhibiting kinase activity in vitro or reducing the level of active Aurora-A in cells. SLAN is frequently reduced in lung cancer tissues overexpressing Aurora-A, arguing for the necessity to suppress SLAN during the Aurora-A-associated cancer formation.

CONCLUSIONS

Taken together, we have identified a novel protein SLAN downregulated in lung caner, having multiple subcellular localization including spindle matrix and midbody, inhibiting cell proliferation and Aurora-A.

Overexpression of active Aurora-C kinase results in cell transformation and tumour formation

Aurora kinases belong to a conserved family of serine/threonine kinases key regulators of cell cycle progression. Aurora-A and Aurora-B are expressed in somatic cells and involved mainly in mitosis while Aurora-C is expressed during spermatogenesis and oogenesis and is involved in meiosis. Aurora-C is hardly detectable in normal somatic cells. However all three kinases are overexpressed in many cancer lines. Aurora-A possesses an oncogenic activity while Aurora-B does not. Here we investigated whether Aurora-C possesses such an oncogenic activity. We report that overexpression of Aurora-C induces abnormal cell division resulting in centrosome amplification and multinucleation in both transiently transfected cells and in stable cell lines. Only stable NIH3T3 cell clones overexpressing active Aurora-C formed foci of colonies when grown on soft agar, indicating that a gain of Aurora-C activity is sufficient to transform cells. Furthermore, we reported that NIH-3T3 stable cell lines overexpressing Aurora-C induced tumour formation when injected into nude mice, demonstrating the oncogenic activity of enzymatically active Aurora kinase C. Interestingly enough tumor aggressiveness was positively correlated with the quantity of active kinase, making Aurora-C a potential anti-cancer therapeutic target.

SIRT2 maintains genome integrity and suppresses tumorigenesis through regulating APC/C activity

Members of sirtuin family regulate multiple critical biological processes, yet their role in carcinogenesis remains controversial. To investigate the physiological functions of SIRT2 in development and tumorigenesis, we disrupted Sirt2 in mice. We demonstrated that SIRT2 regulates the anaphase-promoting complex/cyclosome activity through deacetylation of its coactivators, APC(CDH1) and CDC20. SIRT2 deficiency caused increased levels of mitotic regulators, including Aurora-A and -B that direct centrosome amplification, aneuploidy, and mitotic cell death. Sirt2-deficient mice develop gender-specific tumorigenesis, with females primarily developing mammary tumors, and males developing more hepatocellular carcinoma (HCC). Human breast cancers and HCC samples exhibited reduced SIRT2 levels compared with normal tissues. These data demonstrate that SIRT2 is a tumor suppressor through its role in regulating mitosis and genome integrity.

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.

Centrosomes and cilia in human disease

Centrioles are microtubule-derived structures that are essential for the formation of centrosomes, cilia and flagella. The centrosome is the major microtubule organiser in animal cells, participating in a variety of processes, from cell polarisation to cell division, whereas cilia and flagella contribute to several mechanisms in eukaryotic cells, from motility to sensing. Although it was suggested more than a century ago that these microtubule-derived structures are involved in human disease, the molecular bases of this association have only recently been discovered. Surprisingly, there is very little overlap between the genes affected in the different diseases, suggesting that there are tissue-specific requirements for these microtubule-derived structures. Knowledge of these requirements and disease mechanisms has opened new avenues for therapeutical strategies. Here, we give an overview of recent developments in this field, focusing on cancer, diseases of brain development and ciliopathies.

p53: guardian of ploidy

Aneuploidy, often preceded by tetraploidy, is one of the hallmarks of solid tumors. Indeed, both aneuploidy and tetraploidy are oncogenic occurrences that are sufficient to drive neoplastic transformation and cancer progression. True to form, the tumor suppressor p53 obstructs propagation of these dangerous chromosomal events by either instigating irreversible cell cycle arrest or apoptosis. The tumor suppressor Lats2, along with other tumor inhibitory proteins such as BRCA1/2 and BubR1, are central to p53-dependent elimination of tetraploid cells. Not surprisingly, these proteins are frequently inactivated or downregulated in tumors, synergizing with p53 inactivation to establish an atmosphere of "tolerance" for a non-diploid state.

Suppression of Aurora-A oncogenic potential by c-Myc downregulation

The abnormality of serine/threonine kinase Aurora-A is seen in many types of cancers. Although in physiological context it has been shown to play a vital role in cellular mitosis, how this oncogene contributes to tumorigenesis remains unclear. Here we demonstrate that Aurora-A overexpression enhances both the expression level and transcriptional activity of c-Myc. The inhibition of c-Myc expression by RNA interference significantly impaired the oncogenic potential of Aurora-A, resulting in attenuated cellular proliferation and transformation rates as well as fewer centrosomal aberrations. Furthermore, downregulation of c-Myc effectively overcame Aurora-A-induced resistance to cisplatin in esophageal cancer cells. Taken together, our results suggest an important role for c-Myc in mediating the oncogenic activity of Aurora-A, which may in turn allow for future targeting of c-Myc as a potential therapeutic strategy for tumors with Aurora-A overexpression.

Control of centrin stability by Aurora A

Aurora A is an oncogenic serine/threonine kinase which can cause cell transformation and centrosome amplification when over-expressed. Human breast tumors show excess Aurora A and phospho-centrin in amplified centrosomes. Here, we show that Aurora A mediates the phosphorylation of and localizes with centrin at the centrosome, with both proteins reaching maximum abundance from prophase through metaphase, followed by their precipitous loss in late stages of mitosis. Over-expression of Aurora A results in excess phospho-centrin and centrosome amplification. In contrast, centrosome amplification is not seen in cells over-expressing Aurora A in the presence of a recombinant centrin mutant lacking the serine phosphorylation site at residue 170. Expression of a kinase dead Aurora A results in a decrease in mitotic index and abrogation of centrin phosphorylation. Finally, a recombinant centrin mutation that mimics centrin phosphorylation increases centrin's stability against APC/C-mediated proteasomal degradation. Taken together, these results suggest that the stability of centrin is regulated in part by Aurora A, and that excess phosphorylated centrin may promote centrosome amplification in cancer.

YB-1 evokes susceptibility to cancer through cytokinesis failure, mitotic dysfunction and HER2 amplification

Y-box binding protein-1 (YB-1) expression in the mammary gland promotes breast carcinoma that demonstrates a high degree of genomic instability. In the present study, we developed a model of premalignancy to characterize the role of this gene during breast cancer initiation and early progression. Antibody microarray technology was used to ascertain global changes in signal transduction following the conditional expression of YB-1 in human mammary epithelial cells (HMEC). Cell cycle associated proteins were frequently altered with the most dramatic being LIM Kinase 1/2 (LIMK1/2). Consequently, the misexpression of LIMK1/2 was associated with cytokinesis failure that acted as a precursor to centrosome amplification. Detailed investigation revealed that YB-1 localized to the centrosome in a phosphorylation-dependent manner where it complexed with pericentrin and γ-tubulin. This was found to be essential in maintaining the structural integrity and microtubule nucleation capacity of the organelle. Prolonged exposure to YB-1 led to rampant acceleration toward tumourigenesis with the majority of cells acquiring numerical and structural chromosomal abnormalities. Slippage through the G₁/S checkpoint due to overexpression of cyclin E promoted continued proliferation of these genomically compromised cells. As malignancy further progressed, we identified a subset of cells harbouring HER2 amplification. Our results recognize YB-1 as a cancer susceptibility gene with the capacity to prime cells for tumourigenesis.

CINister thoughts

Chromosome instability (CIN) is the process that leads to aneuploidy, a known hallmark of human tumours for over a century. Nowadays, it is believed that CIN promotes tumorigenesis by shuffling the genome into a malignant order through translocations, amplifications, deletions (structural CIN), and gains and losses of whole chromosomes (numerical CIN or nCIN). The present review focuses on the causes and consequences of nCIN. Several roads can lead to nCIN, including a compromised spindle assembly checkpoint, cohesion defects, p53 deficiency and flawed microtubule-kinetochore attachments. Whereas the link between nCIN and tumorigenesis is becoming more evident, indications have emerged recently that nCIN can suppress tumour formation as well. To understand these paradoxical findings, novel reagents and more sophisticated mouse models are needed. This will provide us with a better understanding of nCIN and eventually with therapies that exploit this characteristic of human tumours.

A non-genetic route to aneuploidy in human cancers

Aneuploidy is common in human tumours and is often indicative of aggressive disease. Aneuploidy can result from cytokinesis failure, which produces binucleate cells that generate aneuploid offspring with subsequent divisions. In cancers, disruption of cytokinesis is known to result from genetic perturbations to mitotic pathways or checkpoints. Here we describe a non-genetic mechanism of cytokinesis failure that occurs as a direct result of cell-in-cell formation by entosis. Live cells internalized by entosis, which can persist through the cell cycle of host cells, disrupt formation of the contractile ring during host cell division. As a result, cytokinesis frequently fails, generating binucleate cells that produce aneuploid cell lineages. In human breast tumours, multinucleation is associated with cell-in-cell structures. These data define a previously unknown mechanism of cytokinesis failure and aneuploid cell formation that operates in human cancers.

Targeting aneuploid cancer cells

INTRODUCTION

Most cancers are characterized by some degree of aneuploidy, although its relevance for tumor initiation or progression and the nature of the initial trigger are still not well understood. It was Theodor Boveri who first suggested a link between aneuploidy and cancer at the beginning of the last century, but it is only recently that the molecular mechanisms involved have started to be uncovered.

AREAS COVERED

The molecular mechanisms that are at the origin of aneuploidy and their cellular consequences. Based on these new findings molecular targets have emerged which could lead to a specific treatment of at least some types of aneuploid tumors.

EXPERT OPINION

Therapeutic intervention specifically for aneuploid cells is a very promising approach, however, although new promising targets have been spotted they still need to be tested for proof of concept. Targeting the spindle checkpoint could be an interesting approach for cancer therapy, however, as for other mitotic targets, the open question of the therapeutic window and sensitivity of normal hemopoietic cells has to be considered carefully. Future challenges will not only include identifying and validating druggable targets related to the relevant pathways, but also finding predictive biomarkers to define the responding patient population(s).

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.

Aurora-A expression, hormone receptor status and clinical outcome in hormone related cancers

AIMS

We investigated the correlation between protein expression of Aurora-A with hormone receptor expression and clinicopathological parameters in ovarian, breast and prostate cancer.

METHODS

Subcellular expression of Aurora-A, and androgen receptor (AR), oestrogen receptor (ER) and progesterone receptor (PR) expression, were examined by immunohistochemistry in human tissue microarrays of the three cancer types and by Western blot in cancer cell lines and selected patient tissues.

RESULTS

Subgroups of all three cancer types exhibited both nuclear and cytoplasmic expression of Aurora-A. Nuclear presence of Aurora-A was observed in ER positive and negative breast cancer cell lines and tissues. Eighteen of the 126 (14%) tumour tissues that showed nuclear expression of Aurora-A were strongly associated with ER and PR positive breast tumours (p = 0.001). Cytoplasmic expression of AR and Aurora-A was strongly associated in prostate cancer tissues (45% versus 0, p = 0.015). Ovarian tumours (n = 45) with Aurora-A nuclear expression had decreased patient survival (mean survival, 29.5 versus 106.7 months; p < 0.0005) and showed a significant association with recurrence-free survival (mean survival 19.7 versus 95.9 months; p = 0.002).

CONCLUSION

Association between nuclear Aurora-A with hormone receptors in breast cancer and with poor clinical outcome in ovarian cancer suggests the significance of active Aurora-A in disease initiation and progression.

Shared and separate functions of polo-like kinases and aurora kinases in cancer

Large numbers of inhibitors for polo-like kinases and aurora kinases are currently being evaluated as anticancer drugs. Interest in these drugs is fuelled by the idea that these kinases have unique functions in mitosis. Within the polo-like kinase family, the emphasis for targeted therapies has been on polo-like kinase 1 (PLK1), and in the aurora kinase family drugs have been developed to specifically target aurora kinase A (AURKA; also known as STK6) and/or aurora kinase B (AURKB; also known as STK12). Information on the selectivity of these compounds in vivo is limited, but it is likely that off-target effects within the same kinase families will affect efficacy and toxicity profiles. In addition, it is becoming clear that interplay between polo-like kinases and aurora kinases is much more extensive than initially anticipated, and that both kinase families are important factors in the response to classical chemotherapeutics that damage the genome or the mitotic spindle. In this Review we discuss the implications of these novel insights on the clinical applicability of polo-like kinase and aurora kinase inhibitors.

Illicit survival of cancer cells during polyploidization and depolyploidization

Tetraploidy and the depolyploidization of tetraploid cells may contribute to oncogenesis. Several mechanisms have evolved to avoid the generation, survival, proliferation and depolyploidization of tetraploids. Cells that illicitly survive these checkpoints are prone to chromosomal instability and aneuploidization. Along with their replication, tetraploids constantly undergo chromosomal rearrangements that eventually lead to pseudodiploidy by two non-exclusive mechanisms: (i) multipolar divisions and (ii) illicit bipolar divisions in the presence of improper microtubule-kinetochore attachments. Here, we describe the regulation and the molecular mechanisms that underlie such a 'polyploidization-depolyploidization' cascade, while focusing on the role of oncogenes and tumor suppressor genes in tetraploidy-driven tumorigenesis. We speculate that the identification of signaling/metabolic cascades that are required for the survival of tetraploid or aneuploid (but not diploid) cancer cells may pave the way for the development of novel broad-spectrum anticancer agents.

Synthetic lethal screen of an EGFR-centered network to improve targeted therapies

Intrinsic and acquired cellular resistance factors limit the efficacy of most targeted cancer therapeutics. Synthetic lethal screens in lower eukaryotes suggest that networks of genes closely linked to therapeutic targets would be enriched for determinants of drug resistance. We developed a protein network centered on the epidermal growth factor receptor (EGFR), which is a validated cancer therapeutic target, and used small interfering RNA screening to comparatively probe this network for proteins that regulate the effectiveness of both EGFR-targeted agents and nonspecific cytotoxic agents. We identified subnetworks of proteins influencing resistance, with putative resistance determinants enriched among proteins that interacted with proteins at the core of the network. We found that clinically relevant drugs targeting proteins connected in the EGFR network, such as protein kinase C or Aurora kinase A, or the transcriptional regulator signal transducer and activator of transcription 3 (STAT3), synergized with EGFR antagonists to reduce cell viability and tumor size, suggesting the potential for a direct path to clinical exploitation. Such a focused approach can potentially improve the coherent design of combination cancer therapies.

Phase 1 study of MLN8054, a selective inhibitor of Aurora A kinase in patients with advanced solid tumors

PURPOSE

Aurora A kinase is critical in assembly and function of the mitotic spindle. It is overexpressed in various tumor types and implicated in oncogenesis and tumor progression. This trial evaluated the dose-limiting toxicities (DLTs) and maximum tolerated dose (MTD) of MLN8054, a selective small-molecule inhibitor of Aurora A kinase.

METHODS

In this first-in-human, dose-escalation study, MLN8054 was given orally for 7, 14, or 21 days followed by a 14-day treatment-free period. Escalating cohorts of 3-6 patients with advanced solid tumors were treated until DLT was seen in ≥2 patients in a cohort. Serial blood samples were collected for pharmacokinetics and skin biopsies were collected for pharmacodynamics.

RESULTS

Sixty-one patients received 5, 10, 20, 30, or 40 mg once daily for 7 days; 25, 35, 45, or 55 mg/day in four divided doses (QID) for 7 days; or 55, 60, 70, or 80 mg/day plus methylphenidate or modafinil with daytime doses (QID/M) for 7-21 days. DLTs of reversible grade 3 benzodiazepine-like effects defined the estimated MTD of 60 mg QID/M for 14 days. MLN8054 was absorbed rapidly, exposure was dose proportional, and terminal half-life was 30-40 h. Three patients had stable disease for >6 cycles.

CONCLUSIONS

MLN8054 dosing for up to 14 days of a 28-day cycle was feasible. Reversible somnolence was dose limiting and prevented achievement of plasma concentrations predicted necessary for target modulation. A recommended dose for investigation in phase 2 trials was not established. A second-generation Aurora A kinase inhibitor is in development.

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.

Characterization of a novel mechanism of genomic instability involving the SEI1/SET/NM23H1 pathway in esophageal cancers

Amplification of 19q is a frequent genetic alteration in many solid tumors, and SEI1 is a candidate oncogene within the amplified region. Our previous study found that the oncogenic function of SEI1 was associated with chromosome instability. In this study, we report a novel mechanism of genomic instability involving the SEI1-SET-NM23H1 pathway. Overexpression of SEI1 was observed in 57 of 100 of esophageal squamous cell carcinoma cases. Functional study showed that SEI1 had strong tumorigenic ability, and overexpression of SEI1 could induce the genomic instability by increasing micronuclei formation and reducing the number of chromosomes. Further study found that SEI1 was able to upregulate SET expression and subsequently promote the translocation of a small amount of NM23H1 from the cytoplasm to the nucleus. Nuclear NM23H1 can induce DNA damage through its DNA nick activity. Unlike CTL attack, only a small amount of NM23H1 translocated into the nucleus (<10%) induced by the overexpression of SEI1. Further study found that the small amount of NM23H1 only induced minor DNA damage and subsequently increased genomic instability, rather than inducing irreparable DNA damage and initiating apoptosis by CTL attack. Sister chromatid exchange experiment found that the translocation of small amount of NM23H1 into the nucleus induced by the overexpressions of SEI1/SET could increase the frequency of sister chromatid exchange. In addition, overexpression of SEI1 was associated with poor prognosis of esophageal squamous cell carcinoma. Taken together, these findings define a novel mechanism of genomic instability and malignant progression in esophageal cancers, a deadly disease of increasing incidence in developed countries.

Genetic instability and mammary tumor formation in mice carrying mammary-specific disruption of Chk1 and p53

Checkpoint kinase 1 (Chk1) is a key element in the DNA-damage response pathway that is required for maintaining genomic stability. To study the potential role of Chk1 in mammary tumorigenesis, we disrupted it using a Cre/loxP system. We showed that although Chk1 heterozygosity caused abnormal development of the mammary gland, it was not sufficient to induce tumorigenesis. Simultaneous deletion of one copy of p53 failed to rescue the developmental defects; however, it synergistically induced mammary tumor formation in Chk1(+/-);MMTV-Cre animals with a median time to tumor latency of about 10 months. Chk1 deficiency caused a preponderance of abnormalities, including prolongation, multipolarity, misalignment, mitotic catastrophe and loss of spindle checkpoint, that are accompanied by reduced expression of several cell cycle regulators, including Mad2. On the other hand, we also showed that Chk1 deficiency inhibited mammary tumor formation in mice carrying a homozygous deletion of p53, uncovering a complex relationship between Chk1 and p53. Furthermore, inhibition of Chk1 with a specific inhibitor, SB-218078, or acute deletion of Chk1 using small hairpin RNA killed mammary tumor cells effectively. These data show that Chk1 is critical for maintaining genome integrity and serves as a double-edged sword for cancer: although its inhibition kills cancer cells, it also triggers tumorigenesis when favorable mutations are accumulated for cell growth.

Aurora-a is essential for the tumorigenic capacity and chemoresistance of colorectal cancer stem cells

Colorectal cancer stem cells (CR-CSC) are responsible for the generation and maintenance of intestinal tumors and are highly resistant to conventional chemotherapeutic agents. Aurora-A, a serine-threonine kinase involved in mitosis regulation, plays multiple key functions in tumor initiation and progression. We found that Aurora-A is overexpressed in primary colorectal tumor cells, in the CR-CSC fraction, and in stem cell-derived differentiated cells, compared with normal colon tissue. Aurora-A expression was functionally linked to centrosome amplification in CR-CSC, as indicated by the decrease in cells with multiple centrosomes that followed Aurora-A silencing. Knockdown of Aurora-A resulted in growth inhibition of CR-CSC, alteration of cell cycle kinetics, and downregulation of the expression levels of antiapoptotic Bcl-2 family members, strongly sensitizing to chemotherapy-induced cell death. Moreover, Aurora-A silencing compromised the ability to form tumor xenografts in immunocompromised mice and reduced the migratory capacity of CR-CSC. Altogether, these results indicate that Aurora-A is essential for CR-CSC regeneration and resistance to cytotoxic stimuli and suggest that therapies directed against Aurora-A may effectively target the stem cell population in colorectal cancer.

Aurora A selective inhibitor MLN8237 suppresses the growth and survival of HTLV-1-infected T-cells in vitro

Aurora A kinase plays an essential role in the proper assembly and function of the mitotic spindle. We have shown previously that Aurora A expression is increased aberrantly in human T-cell leukemia virus type 1 (HTLV-1)-infected T-cell lines and primary adult T-cell leukemia cells, and a pan-Aurora kinase inhibitor, which inhibits both Aurora A and Aurora B kinases, reduces viability and induces apoptosis in these cells. However, the specific effects of Aurora A inhibition on HTLV-1-infected T-cells are poorly understood. In this study, we addressed this question by comparing the effects of MLN8237, a selective inhibitor of Aurora A, on cell viability, cell cycle progression, and induction of apoptosis in HTLV-1-infected and -uninfected T-cell lines. MLN8237 reduced the viability of HTLV-1-infected T-cell lines within 24 h, but its effects on that of HTLV-1-uninfected T-cell lines were moderate. MLN8237 induced early apoptosis of HTLV-1-infected T-cell lines without induction of polyploidy. It induced p53 and p21 expression in HTLV-1-infected but not in -uninfected T-cell lines, suggesting that MLN8237-treated HTLV-1-infected T-cell lines exit from mitosis and activate a p53-dependent postmitotic G(1) checkpoint, leading to G(1) arrest followed by the induction of apoptosis. Our results suggest that specific inhibition of Aurora A kinase is a potentially useful therapeutic strategy in the treatment of adult T-cell leukemia and that further in vivo exploration is warranted.

Multipolar mitosis of tetraploid cells: inhibition by p53 and dependency on Mos

Tetraploidy can constitute a metastable intermediate between normal diploidy and oncogenic aneuploidy. Here, we show that the absence of p53 is not only permissive for the survival but also for multipolar asymmetric divisions of tetraploid cells, which lead to the generation of aneuploid cells with a near-to-diploid chromosome content. Multipolar mitoses (which reduce the tetraploid genome to a sub-tetraploid state) are more frequent when p53 is downregulated and the product of the Mos oncogene is upregulated. Mos inhibits the coalescence of supernumerary centrosomes that allow for normal bipolar mitoses of tetraploid cells. In the absence of p53, Mos knockdown prevents multipolar mitoses and exerts genome-stabilizing effects. These results elucidate the mechanisms through which asymmetric cell division drives chromosomal instability in tetraploid cells.

Mitotic chromosomal instability and cancer: mouse modelling of the human disease

The stepwise progression from an early dysplastic lesion to full-blown metastatic malignancy is associated with increases in genomic instability. Mitotic chromosomal instability - the inability to faithfully segregate equal chromosome complements to two daughter cells during mitosis - is a widespread phenomenon in solid tumours that is thought to serve as the fuel for tumorigenic progression. How chromosome instability (CIN) arises in tumours and what consequences it has are still, however, hotly debated issues. Here we review the recent literature with an emphasis on models that recapitulate observations from human disease.

Critical roles of T-LAK cell-originated protein kinase in cytokinesis

We previously reported up-regulation of T-LAK cell-originated protein kinase (TOPK), a novel mitotic kinase, in the great majority of breast cancers. Here we report its critical roles in mitosis, especially in cytokinesis. We found that protein phosphatase 1 alpha (PP1alpha) inactivation by cyclin-dependent kinase 1 (CDK1)/cyclin B1 caused enhancement of autophosphorylation of TOPK and resulted in its activation at an early stage of mitosis. Then TOPK interacted with and phosphorylated p97, a member of the AAA+ family of ATPase proteins, through an interaction with p47 protein as an adaptor protein. Interestingly, knockdown of TOPK or p97 in breast cancer cells caused the mitotic failures in the abscission process. This mitotic failure could be rescued by additional exogenous introduction of wild-type TOPK protein, but not by that of its kinase-dead form. Our findings suggest that TOPK is indispensable for cancer cell cytokinesis throughout phosphorylation on p97.

MK-5108, a highly selective Aurora-A kinase inhibitor, shows antitumor activity alone and in combination with docetaxel

Aurora-A kinase is a one of the key regulators during mitosis progression. Aurora-A kinase is a potential target for anticancer therapies because overexpression of Aurora-A, which is frequently observed in some human cancers, results in aberrant mitosis leading to chromosomal instability and possibly tumorigenesis. MK-5108 is a novel small molecule with potent inhibitory activity against Aurora-A kinase. Although most of the Aurora-kinase inhibitors target both Aurora-A and Aurora-B, MK-5108 specifically inhibited Aurora-A kinase in a panel of protein kinase assays. Inhibition of Aurora-A by MK-5108 in cultured cells induced cell cycle arrest at the G(2)-M phase in flow cytometry analysis. The effect was confirmed by the accumulation of cells with expression of phosphorylated Histone H3 and inhibition of Aurora-A autophosphorylation by immunostaining assays. MK-5108 also induced phosphorylated Histone H3 in skin and xenograft tumor tissues in a nude rat xenograft model. MK-5108 inhibited growth of human tumor cell lines in culture and in different xenograft models. Furthermore, the combination of MK-5108 and docetaxel showed enhanced antitumor activities compared with control and docetaxel alone-treated animals without exacerbating the adverse effects of docetaxel. MK-5108 is currently tested in clinical trials and offers a new therapeutic approach to combat human cancers as a single agent or in combination with existing taxane therapies.

Danusertib (formerly PHA-739358)--a novel combined pan-Aurora kinases and third generation Bcr-Abl tyrosine kinase inhibitor

The Aurora kinases belong to a family of highly conserved serine/threonine protein kinases. They play an essential role as key mitotic regulators, controlling entry into mitosis, centrosome function, chromosome assembly, and segregation. As many other regulators of mitosis, Aurora kinases are frequently found to be aberrantly overexpressed in cancer cells. Therefore, these proteins have become an attractive target for the development of new anticancer therapies. In fact, several small-molecule inhibitors of Aurora kinases have already been developed and some of them have shown promising clinical efficacy in a number of human tumors in Phase I and II clinical trials. Among those, one of the most advanced clinical compound currently is Danusertib (formerly PHA-739358), which exhibits inhibitory activity against all known Aurora kinases as well as other cancer-relevant kinases such as the Bcr-Abl tyrosine kinase, including its multidrug-resistant T315I mutant. This mutation is responsible for up to 25% of all clinically observed resistances in CML patients undergoing Imatinib therapy. However, this particular mutation is predicted to play an even more important clinical role in the future, since in addition to Imatinib, it also confers resistance to second-generation Bcr-Abl inhibitors such as Nilotinib, Dasatinib, and Bosutinib. Therefore, combined Aurora and Bcr-Abl inhibition (the latter including high-grade resistance conferring mutations) with compounds such as Danusertib represents a promising new strategy for treatment of Bcr-Abl positive leukemias, especially those in second and third line of treatment.

Physiological and oncogenic Aurora-A pathway

Aurora family of protein kinases have emerged as crucial factors of, not only mitosis and cytokinesis, but also human carcinogenesis. Among these family members is Aurora-A that is frequently overexpressed in varieties of human cancer. Both in vitro and in vivo studies demonstrated that Aurora-A induces tumorigenesis through genome instability. These studies have further shown that cell signaling cross-talk between Aurora-A and other cellular proteins are essential for fully-transformed phenotypes. This review summarizes recent progress of Aurora-A-associated carcinogenesis.

Aurora-A phosphorylates, activates, and relocalizes the small GTPase RalA

The small GTPase Ras, which transmits extracellular signals to the cell, and the kinase Aurora-A, which promotes proper mitosis, can both be inappropriately activated in human tumors. Here, we show that Aurora-A in conjunction with oncogenic Ras enhances transformed cell growth. Furthermore, such transformation and in some cases also tumorigenesis depend upon S194 of RalA, a known Aurora-A phosphorylation site. Aurora-A promotes not only RalA activation but also translocation from the plasma membrane and activation of the effector protein RalBP1. Taken together, these data suggest that Aurora-A may converge upon oncogenic Ras signaling through RalA.

Aurora A, centrosome structure, and the centrosome cycle

The centrosome, also known as the microtubule organizing center of the cell, is a membrane-less organelle composed of a pair of barrel-shaped centrioles surrounded by electron-dense pericentriolar material. The centrosome progresses through the centrosome cycle in step with the cell cycle such that centrosomes are duplicated in time to serve as the spindle poles during mitosis and that each resultant daughter cell contains a single centrosome. Regulation of the centrosome cycle with relation to the cell cycle is an essential process to maintain the ratio of one centrosome per new daughter cell. Numerous mitosis-specific kinases have been implicated in this regulation, and phosphorlyation plays an important role in coordinating the centrosome and cell cycles. Centrosome amplification can occur when the cycles are uncoupled, and this amplification is associated with cancer and with an increase in the levels of chromosomal instability. The aurora kinases A, B, and C are serine/threonine kinases that are active during mitosis. Aurora A is associated with centrosomes, being localized at the centrosome just prior to the onset of mitosis and for the duration of mitosis. Overexpression of aurora A leads to centrosome amplification and cellular transformation. The activity of aurora A is regulated by phosphorlyation and proteasomal degradation.

A genetic variant of Aurora kinase A promotes genomic instability leading to highly malignant skin tumors

Aurora kinase A (Aurora-A) belongs to a highly conserved family of mitotis-regulating serine/threonine kinases implicated in epithelial cancers. Initially we examined Aurora-A expression levels at different stages of human skin cancer. Nuclear Aurora-A was detected in benign lesions and became more diffused but broadly expressed in well and poorly differentiated squamous cell carcinomas (SCC), indicating that Aurora-A deregulation may contribute to SCC development. To mimic the overexpression of Aurora-A observed in human skin cancers, we established a gene-switch mouse model in which the human variant of Aurora-A (Phe31Ile) was expressed in the epidermis upon topical application of the inducer RU486 (Aurora-AGS). Overexpression of Aurora-A alone or in combination with the tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA), did not result in SCC formation in Aurora-AGS mice. Moreover, Aurora-A overexpression in naive keratinocytes resulted in spindle defects in vitro and marked cell death in vivo, suggesting that the failure of Aurora-A to initiate tumorigenesis was due to induction of catastrophic cell death. However, Aurora-A overexpression combined with exposure to TPA and the mutagen 7,12-dimethylbenz(a)anthracene accelerated SCC development with greater metastatic activity than control mice, indicating that Aurora-A cannot initiate skin carcinogenesis but rather promotes the malignant conversion of skin papillomas. Further characterization of SCCs revealed centrosome amplification and genomic alterations by array CGH analysis, indicating that Aurora-A overexpression induces a high level of genomic instability that favors the development of aggressive and metastatic tumors. Our findings strongly implicate Aurora-A overexpression in the malignant progression of skin tumors and suggest that Aurora-A may be an important therapeutic target.

Aurora-A expression is independently associated with chromosomal instability in colorectal cancer

AURKA (the official symbol for Aurora-A, STK15, or BTAK) regulates the function of centrosomes, spindles, and kinetochores for proper mitotic progression. AURKA overexpression is observed in various cancers including colon cancer, and a link between AURKA and chromosomal instability (CIN) has been proposed. However, no study has comprehensively examined AURKA expression in relation to CIN or prognosis using a large number of tumors. Using 517 colorectal cancers in two prospective cohort studies, we detected AURKA overexpression (by immunohistochemistry) in 98 tumors (19%). We assessed other molecular events including loss of heterozygosity (LOH) in 2p, 5q, 17q, and 18q, the CpG island methylation phenotype (CIMP), and microsatellite instability (MSI). Prognostic significance of AURKA was evaluated by Cox regression and Kaplan-Meier method. In both univariate and multivariate logistic regressions, AURKA overexpression was significantly associated with CIN (defined as the presence of LOH in any of the chromosomal segments; multivariate odds ratio, 2.97; 95% confidence interval, 1.40-6.29; P = .0045). In multivariate analysis, AURKA was associated with cyclin D1 expression (P = .010) and inversely with PIK3CA mutation (P=.014), fatty acid synthase expression (P=.028), and family history of colorectal cancer (P = .050), but not with sex, age, body mass index, tumor location, stage, CIMP, MSI, KRAS, BRAF, BMI, LINE-1 hypomethylation, p53, p21, beta-catenin, or cyclooxygenase 2. AURKA was not significantly associated with clinical outcome or survival. In conclusion, AURKA overexpression is independently associated with CIN in colorectal cancer, supporting a potential role of Aurora kinase-A in colorectal carcinogenesis through genomic instability (rather than epigenomic instability).

Aurora kinase inhibitors in preclinical and clinical testing

BACKGROUND

Mitosis is a key step in the cell cycle governing the distribution of genetic material to the daughter cells. Any aberration in this process could lead to genomic instability. Aurora A, B and C, are members of the serine/threonine kinase family. Aurora kinases are essential for spindle assembly, centrosome maturation, chromosomal segregation and cytokinesis during mitosis. Abnormalities in the mitotic process through overexpression/amplification of aurora kinase have been linked to genomic instability leading to tumorigenesis. Hence, use of aurora kinase small molecule inhibitors as potential molecular-targeted therapeutic intervention for cancer is being pursued by various researchers.

OBJECTIVE

To review the literature of aurora kinase inhibitors in clinical and preclinical testing.

METHOD

Pubmed, Scifinder and (www.clinicaltrials.gov) databases were used to search the literature for aurora kinase. CONCLUSION/RESULTS: Approximately 13 aurora kinase inhibitors are under Phase I/II evaluation at present for various cancers of different origins; and several others are in preclinical testing. Details of their preclinical/clinical results and important considerations for future aurora kinase inhibitor development are discussed. Considering the fact that aurora kinase plays an important role in the mitosis process and is involved in tumorigenesis, development of aurora kinase inhibitors for the treatment of cancer, either as a single agent or in combination with existing cancer treatment is warranted.

Boveri revisited: chromosomal instability, aneuploidy and tumorigenesis

The mitotic checkpoint is a major cell cycle control mechanism that guards against chromosome missegregation and the subsequent production of aneuploid daughter cells. Most cancer cells are aneuploid and frequently missegregate chromosomes during mitosis. Indeed, aneuploidy is a common characteristic of tumours, and, for over 100 years, it has been proposed to drive tumour progression. However, recent evidence has revealed that although aneuploidy can increase the potential for cellular transformation, it also acts to antagonize tumorigenesis in certain genetic contexts. A clearer understanding of the tumour suppressive function of aneuploidy might reveal new avenues for anticancer therapy.

Essential roles of mTOR/Akt pathway in Aurora-A cell transformation

We have recently demonstrated that Aurora-A kinase is a potential oncogene to develop mammary gland tumors in mice, when expressed under MMTV promoter. These tumors contain phosphorylated forms of Akt and mTOR, suggesting that Akt-mTOR pathway is involved in transformed phenotype induced by Aurora-A. In the present studies, we discovered that stable cell lines expressing Aurora-A contain phosphorylation of Akt Ser473 after prolonged passages of cell culture, not in cells of the early period of cell culture. Levels of PTEN tumor suppressor are significantly reduced in these late passage cells at least in part due to increased poly ubiquitination of the protein. Akt-activated Aurora-A cells formed larger colonies in soft agar and are resistant to UV-induced apoptosis. Aurora-A inhibitor, VX-680, can cause cell death of Aurora-A cells in which Akt is not activated. siRNA-mediated depletion of mTOR in those cells resulted in decreased phosphorylation of Akt Ser473, suggesting that TORC2 complex phosphorylates Akt in Aurora-A cells. Treatment of late-passage Aurora-A cells with mTOR inhibitor reduced colony formation in soft agar. These results strongly suggest that commitment of cell transformation by Aurora-A is determined by at least co-activation of Akt/mTOR pathway.

Genetic variation in the chromosome 17q23 amplicon and breast cancer risk

BACKGROUND

Gene amplification leading to overexpression is a common event in breast tumors that is linked to tumor development and progression. The 17q23 region is amplified in >40% of breast tumors and contains several candidate oncogenes. Because common genetic variation in several oncogenes has been associated with cancer risk, we assessed the relevance of common variants in the 17q23 candidate oncogenes to breast cancer.

METHODS

We investigated 60 polymorphisms in the TUBD1, SEPT4, PRKCA, TBX2, TBX4, TEX14, TLK2, YPEL2, and PPM1E genes from this amplicon for association with breast cancer risk among 798 Caucasian breast cancer cases and 843 unaffected Caucasian controls from the Mayo Clinic.

RESULTS

Eight polymorphisms in PRKCA, TBX4, TLK2, and YPEL2 displayed significant dose-response associations with breast cancer risk (P(trend) < 0.05). Of these, PRKCA rs7342847 and TLK2 rs2245092 and rs733025 were also associated with hormone receptor-positive breast cancer: PRKCA rs7342847 (odds ratio, 0.7; 95% confidence interval, 0.6-0.9; P(trend) = 0.002) and TLK2 rs733025 and rs2245092 (both: odds ratio, 0.8; 95% confidence interval, 0.7-1.0; P(trend) = 0.03). Interactions between SEPT4 rs758377 and TEX14 rs302864 (P(interaction) = 0.0003) and between TLK2 rs733025 and YPEL2 rs16943468 (P(interaction) = 0.05) for risk of breast cancer were also observed.

CONCLUSION

These findings suggest that single polymorphisms and combinations of polymorphisms within candidate oncogenes from the 17q23 amplicon may influence risk of breast cancer overall and possibly specific molecular subtypes of breast tumors. The findings are discussed within the context of the results from two independent data sets.

Aurora-A overexpression in mouse liver causes p53-dependent premitotic arrest during liver regeneration

Aurora-A, a serine-threonine kinase, is frequently overexpressed in human cancers, including hepatocellular carcinoma. To study the phenotypic effects of Aurora-A overexpression on liver regeneration and tumorigenesis, we generated transgenic mice overexpressing human Aurora-A in the liver. The overexpression of Aurora-A after hepatectomy caused an earlier entry into S phase, a sustaining of DNA synthesis, and premitotic arrest in the regenerating liver. These regenerating transgenic livers show a relative increase in binuclear hepatocytes compared with regenerating wild-type livers; in addition, multipolar segregation and trinucleation could be observed only in the transgenic hepatocytes after hepatectomy. These results together suggest that defects accumulated after first round of the hepatocyte cell cycle and that there was a failure to some degree of cytokinesis. Interestingly, the p53-dependent checkpoint was activated by these abnormalities, indicating that p53 plays a crucial role during liver regeneration. Indeed, the premitotic arrest and abnormal cell death, mainly necrosis, caused by Aurora-A overexpression were genetically rescued by p53 knockout. However, trinucleation of hepatocytes remained in the regenerating livers of the transgenic mice with a p53 knockout background, indicating that the abnormal mitotic segregation and cytokinesis failure were p53 independent. Moreover, overexpression of Aurora-A in transgenic liver led to a low incidence (3.8%) of hepatic tumor formation after a long latency period. This transgenic mouse model provides a useful system that allows the study of the physiologic effects of Aurora-A on liver regeneration and the genetic pathways of Aurora-A-mediated tumorigenesis in liver.

The cell cycle as a therapeutic target against Trypanosoma brucei: Hesperadin inhibits Aurora kinase-1 and blocks mitotic progression in bloodstream forms

Aurora kinase family members co-ordinate a range of events associated with mitosis and cytokinesis. Anti-cancer therapies are currently being developed against them. Here, we evaluate whether Aurora kinase-1 (TbAUK1) from pathogenic Trypanosoma brucei might be targeted in anti-parasitic therapies as well. Conditional knockdown of TbAUK1 within infected mice demonstrated its essential contribution to infection. An in vitro kinase assay was developed which used recombinant trypanosome histone H3 as a substrate. Tandem mass spectroscopy identified a novel phosphorylation site in the carboxyl-tail of recombinant trypanosome histone H3. Hesperadin, an inhibitor of human Aurora B, prevented the phosphorylation of substrate with IC(50) of 40 nM. Growth of cultured bloodstream forms was also sensitive to Hesperadin (IC(50) of 50 nM). Hesperadin blocked nuclear division and cytokinesis but not other aspects of the cell cycle. Consequently, growth arrested cells accumulated multiple kinetoplasts, flagella and nucleoli, similar to the effects of RNAi-dependent knockdown of TbAUK1 in cultured bloodstream forms cells. Molecular models predicted high-affinity binding of Hesperadin to both conserved and novel sites in TbAUK1. Collectively, these data demonstrate that cell cycle progression is essential for infections with T. brucei and that parasite Aurora kinases can be targeted with small-molecule inhibitors.

The consequences of tetraploidy and aneuploidy

Polyploidy, an increased number of chromosome sets, is a surprisingly common phenomenon in nature, particularly in plants and fungi. In humans, polyploidy often occurs in specific tissues as part of terminal differentiation. Changes in ploidy can also result from pathophysiological events that are caused by viral-induced cell fusion or erroneous cell division. Tetraploidization can initiate chromosomal instability (CIN), probably owing to supernumerary centrosomes and the doubled chromosome mass. CIN, in turn, might persist or soon give way to a stably propagating but aneuploid karyotype. Both CIN and stable aneuploidy are commonly observed in cancers. Recently, it has been proposed that an increased number of chromosome sets can promote cell transformation and give rise to an aneuploid tumor. Here, we review how tetraploidy can occur and describe the cellular responses to increased ploidy. Furthermore, we discuss how the specific physiological changes that are triggered by polyploidization might be used as novel targets for cancer therapy.

Expression of STK15 mRNA in hepatocellular carcinoma and its prognostic significance

OBJECTIVES

To investigate whether the STK15 mRNA expression correlates with clinicopathologic features and the prognosis of HCC patients.

DESIGN AND METHODS

Three hepatoma cell lines, two normal liver epithelial cell lines, hepatoma tissues, adjacent tumor tissues and normal liver tissues were obtained from 46 HCC patients. Semi-quantitative RT-PCR assays were performed to detect the expression of STK15 mRNA in above cell lines and tissues. Moreover, the expression of STK15 protein in hepatoma tissues, adjacent tumor tissues and normal liver tissues was also examined by immunohistochemical staining. Finally, correlations between STK15 mRNA expression and the clinicopathological features and prognosis of HCC patients were evaluated.

RESULTS

STK15 mRNA showed higher levels in hepatoma cell lines than in normal liver epithelial cell lines. Moreover, the mean levels of STK15 mRNA and protein expression showed statistical difference between tumor tissues, tumor adjacent tissues and normal liver tissues (P<0.01). By immunohistochemical analysis, we found that paraffin-embedded archival HCC tissues showed higher expression of STK15 than adjacent tumors and normal liver tissues. Furthermore, HCC patients with higher STK15 mRNA expression showed poorer prognosis than those with lower STK15 mRNA expression. The high level of STK15 mRNA expression was significantly correlated with tumor stage (P=0.0081), more frequent lymph node (P=0.0380) or hematogenous metastasis (P=0.0066), and a higher incidence of cancer-related death (P=0.0083). Furthermore, the disease-free survival (DFS) and overall survival (OS) rates of HCC patients with higher STK15 mRNA expression group (47.6% and 52.7%) were significantly lower than those of patients with low STK15 mRNA expression group (56.9% and 68.8%, P=0.0018 and 0.0047).

CONCLUSIONS

STK15 mRNA might be a good marker for predicting the prognosis of HCC patients.

Stabilization of N-Myc is a critical function of Aurora A in human neuroblastoma

In human neuroblastoma, amplification of the MYCN gene predicts poor prognosis and resistance to therapy. In a shRNA screen of genes that are highly expressed in MYCN-amplified tumors, we have identified AURKA as a gene that is required for the growth of MYCN-amplified neuroblastoma cells but largely dispensable for cells lacking amplified MYCN. Aurora A has a critical function in regulating turnover of the N-Myc protein. Degradation of N-Myc requires sequential phosphorylation by cyclin B/Cdk1 and Gsk3. N-Myc is therefore degraded during mitosis in response to low levels of PI3-kinase activity. Aurora A interacts with both N-Myc and the SCF(Fbxw7) ubiquitin ligase that ubiquitinates N-Myc and counteracts degradation of N-Myc, thereby uncoupling N-Myc stability from growth factor-dependent signals.