Suppression of the STK15 oncogenic activity requires a transactivation-independent p53 function

Deubiquitinase-Targeting Chimeras (DUBTACs) as a Potential Paradigm-Shifting Drug Discovery Approach

Developing proteolysis-targeting chimeras (PROTACs) is well recognized through target protein degradation (TPD) toward promising therapeutics. While a variety of diseases are driven by aberrant ubiquitination and degradation of critical proteins with protective functions, target protein stabilization (TPS) rather than TPD is emerging as a unique therapeutic modality. Deubiquitinase-targeting chimeras (DUBTACs), a class of heterobifunctional protein stabilizers consisting of deubiquitinase (DUB) and protein-of-interest (POI) targeting ligands conjugated with a linker, can rescue such proteins from aberrant elimination. DUBTACs stabilize the levels of POIs in a DUB-dependent manner, removing ubiquitin from polyubiquitylated and degraded proteins. DUBTACs can induce a new interaction between POI and DUB by forming a POI-DUBTAC-DUB ternary complex. Herein, therapeutic benefits of TPS approaches for human diseases are introduced, and recent advances in developing DUBTACs are summarized. Relevant challenges, opportunities, and future perspectives are also discussed.

TF-DUBTACs Stabilize Tumor Suppressor Transcription Factors

Targeted protein degradation approaches have been widely used for degrading oncogenic proteins, providing a potentially promising therapeutic strategy for cancer treatment. However, approaches to targeting tumor suppressor proteins are very limited, and only a few agonists have been developed to date. Here, we report the development of a platform termed TF-DUBTAC, which links a DNA oligonucleotide to a covalent ligand of the deubiquitinase OTUB1 via a click reaction, to selectively stabilize tumor suppressor transcription factors. We developed three series of TF-DUBTACs, namely, FOXO-DUBTAC, p53-DUBTAC, and IRF-DUBTAC, which stabilize FOXO3A, p53, and IRF3 in cells, respectively, in an OTUB1-dependent manner. These results suggest that TF-DUBTAC is a generalizable platform to achieve selective stabilization of tumor suppressor transcription factors as a therapeutic means to suppress tumorigenesis.

CF-PPiD technology based on cell-free protein array and proximity biotinylation enzyme for in vitro direct interactome analysis

Protein–protein interaction (PPI) analysis is a key process to understand protein functions. Recently, we constructed a human protein array (20 K human protein beads array) consisting of 19,712 recombinant human proteins produced by a wheat cell-free protein production system. Here, we developed a cell-free protein array technology for proximity biotinylation-based PPI identification (CF-PPiD). The proximity biotinylation enzyme AirID-fused TP53 and -IκBα proteins each biotinylated specific interacting proteins on a 1536-well magnetic plate. In addition, AirID-fused cereblon was shown to have drug-inducible PPIs using CF-PPiD. Using the human protein beads array with AirID-IκBα, 132 proteins were biotinylated, and then selected clones showed these biological interactions in cells. Although ZBTB9 was not immunoprecipitated, it was highly biotinylated by AirID-IκBα, suggesting that this system detected weak interactions. These results indicated that CF-PPiD is useful for the biochemical identification of directly interacting proteins.

Targeting DNA damage response kinases in cancer therapy

Cancer cells die when their decimated DNA damage response (DDR) unsuccessfully handles DNA damage. This notion has been successfully exploited when targeting PARP (poly ADP-ribose polymerase) in homologous recombination-deficient cells. With the greater understanding of DDR achieved in the last decade, new cancer therapy targets within the DDR network have been identified. Intriguingly, many of the molecules that have advanced into clinical trials are inhibitors of DDR kinases. This special issue is devoted to discussing the mechanism of cell killing and the level of success that such inhibitors have reached in pre-clinical and clinical settings.

AURKA Increase the Chemosensitivity of Colon Cancer Cells to Oxaliplatin by Inhibiting the TP53-Mediated DNA Damage Response Genes

AURKA, a cell cycle-regulated kinase, is associated with malignant transformation and progression in many cancer types. We analyzed the expression change of AURKA in pan-cancer and its effect on the prognosis of cancer patients using the TCGA dataset. We revealed that AURKA was extensively elevated and predicted a poor prognosis in most of the detected cancer types, with an exception in colon cancer. AURKA was elevated in colon cancer, but the upregulation of AURKA indicated better outcomes of colon cancer patients. Then we revealed that undermethylation of the AURKA gene and several transcription factors contributed to the upregulation of AURKA in colon cancer. Moreover, we demonstrated that AURKA overexpression promoted the death of colon cancer cells induced by Oxaliplatin, whereas knockdown of AURKA significantly weakened the chemosensitivity of colon cancer cells to Oxaliplatin. Mechanistically, AURKA inhibited DNA damage response by suppressing the expression of various DNA damage repair genes in a TP53-dependent manner, which can partly explain that ARUKA is associated with a beneficial outcome of colon cancer. This study provided a possibility to use AURKA as a biomarker to predict the chemosensitivity of colon cancer to platinum in the clinic.

Aurora kinases and DNA damage response

It is well established that Aurora kinases perform critical functions during mitosis. It has become increasingly clear that the Aurora kinases also perform a myriad of non-mitotic functions including DNA damage response. The available evidence indicates that inhibition Aurora kinase A (AURKA) may contribute to the G₂ DNA damage checkpoint through AURKA's functions in PLK1 and CDC25B activation. Both AURKA and Aurora kinase B (AURKB) are also essential in mitotic DNA damage response that guard against DNA damage-induced chromosome segregation errors, including the control of abscission checkpoint and prevention of micronuclei formation. Dysregulation of Aurora kinases can trigger DNA damage in mitosis that is sensed in the subsequent G₁ by a p53-dependent postmitotic checkpoint. Aurora kinases are themselves linked to the G₁ DNA damage checkpoint through p53 and p73 pathways. Finally, several lines of evidence provide a connection between Aurora kinases and DNA repair and apoptotic pathways. Although more studies are required to provide a comprehensive picture of how cells respond to DNA damage, these findings indicate that both AURKA and AURKB are inextricably linked to pathways guarding against DNA damage. They also provide a rationale to support more detailed studies on the synergism between small-molecule inhibitors against Aurora kinases and DNA-damaging agents in cancer therapies.

Targeted therapies for non-HPV-related head and neck cancer: challenges and opportunities in the context of predictive, preventive, and personalized medicine

Head and neck squamous cell carcinoma (HNSCC) develops in the mucosal lining of the upper aerodigestive tract, principally as a result of exposure to carcinogens present in tobacco products and alcohol, with oncogenic papillomaviruses also being recognized as etiological agents in a limited proportion of cases. As such, there is considerable scope for prevention of disease development and progression. However, despite multimodal approaches to treatment, tumor recurrence and metastatic disease are common problems, and clinical outcome is unsatisfactory. As our understanding of the genetics and biochemical aberrations in HNSCC has improved, so the development and use of molecularly targeted drugs to combat the disease have come to the fore. In this article, we review molecular mechanisms that alter signal transduction downstream of the epidermal growth factor receptor (EGFR) as well as those that perturb orderly cell cycle progression, such as p53 mutation, cyclin overexpression, and loss of cyclin-dependent kinase inhibitor function. We outline some of the tactics that have been employed to combat the altered biochemistry. These include blockade of the EGFR using humanized monoclonal antibodies such as cetuximab and small molecule tyrosine kinase inhibitors (TKIs) such as erlotinib/gefitinib and subsequent generations of TKIs, restoration of p53 function using MIRA compounds, and inhibition of cyclin-dependent kinase and aurora kinase activity using drugs such as palbociclib and alisertib. Knowledge of the underlying molecular mechanisms may be utilizable in order to predict disease behavior and tailor therapeutic interventions in a more personalized approach to improve clinical response. Use of liquid biopsy, omics platforms, and salivary diagnostics hold promise in this regard.

A Network-guided Association Mapping Approach from DNA Methylation to Disease

Aberrant DNA methylation may contribute to development of cancer. However, understanding the associations between DNA methylation and cancer remains a challenge because of the complex mechanisms involved in the associations and insufficient sample sizes. The unprecedented wealth of DNA methylation, gene expression and disease status data give us a new opportunity to design machine learning methods to investigate the underlying associated mechanisms. In this paper, we propose a network-guided association mapping approach from DNA methylation to disease (NAMDD). Compared with existing methods, NAMDD finds methylation-disease path associations by integrating analysis of multiple data combined with a stability selection strategy, thereby mining more information in the datasets and improving the quality of resultant methylation sites. The experimental results on both synthetic and real ovarian cancer data show that NAMDD substantially outperforms former disease-related methylation site research methods (including NsRRR and PCLOGIT) under false positive control. Furthermore, we applied NAMDD to ovarian cancer data, identified significant path associations and provided hypothetical biological path associations to explain our findings.

Identification of key candidate genes and pathways in hepatocellular carcinoma by integrated bioinformatical analysis

Hepatocellular carcinoma (HCC) is one of the most common malignant neoplasms worldwide, however the underlying mechanisms and gene signatures of HCC are unknown. In the present study the profile datasets of four cohorts were integrated to elucidate the pathways and candidate genes of HCC. The expression profiles GSE25097, GSE45267, GSE57957 and GSE62232 were downloaded from the Gene Expression Omnibus database, including 436 HCC and 94 normal liver tissues. A total of 185 differentially expressed genes (DEGs) were identified in HCC, including 92 upregulated genes and 92 downregulated genes. Gene ontology (GO) was performed, which revealed that the upregulated DEGs were primarily enriched in cell division, mitotic nuclear division, mitotic cytokinesis and G1/S transition of the mitotic cell cycle. Pathway enrichment was analyzed based on the Kyoto Encyclopedia of Genes and Genomes database to assess the functional relevance of DEGs. The most significant module was selected from protein-protein interactions and 15 important hub genes were identified. The sub-networks of hub genes were involved in cell division, p53 signaling, and T lymphotropic virus type I infection signaling pathways. In conclusion, the present study revealed that the identified DEG candidate genes may promote the understanding of the cause and molecular mechanisms underlying the development of HCC and that these candidates and signal pathways may be potential targets of clinical therapy for HCC.

Antitumor activity of the aurora a selective kinase inhibitor, alisertib, against preclinical models of colorectal cancer

Background

The Aurora kinases are a family of serine/threonine kinases comprised of Aurora A, B, and C which execute critical steps in mitotic and meiotic progression. Alisertib (MLN8237) is an investigational Aurora A selective inhibitor that has demonstrated activity against a wide variety of tumor types in vitro and in vivo, including CRC.

Results

CRC cell lines demonstrated varying sensitivity to alisertib with IC₅₀ values ranging from 0.06 to > 5 umol/L. Following exposure to alisertib we observed a decrease in pAurora A, B and C in four CRC cell lines. We also observed an increase in p53 and p21 in a sensitive p53 wildtype cell line in contrast to the p53 mutant cell line or the resistant cell lines. The addition of alisertib to standard CRC treatments demonstrated improvement over single agent arms; however, the benefit was largely less than additive, but not antagonistic.

Methods

Forty-seven CRC cell lines were exposed to alisertib and IC₅₀s were calculated. Twenty-one PDX models were treated with alisertib and the Tumor Growth Inhibition Index was assessed. Additionally, 5 KRAS wildtype and mutant PDX models were treated with alisertib as single agent or in combination with cetuximab or irinotecan, respectively.

Conclusion

Alisertib demonstrated anti-proliferative effects against CRC cell lines and PDX models. Our data suggest that the addition of alisertib to standard therapies in colorectal cancer if pursued clinically, will require further investigation of patient selection strategies and these combinations may facilitate future clinical studies.

Functional Significance of Aurora Kinases-p53 Protein Family Interactions in Cancer

Aurora kinases play critical roles in regulating spindle assembly, chromosome segregation, and cytokinesis to ensure faithful segregation of chromosomes during mitotic cell division cycle. Molecular and cell biological studies have revealed that Aurora kinases, at physiological levels, orchestrate complex sequential cellular processes at distinct subcellular locations through functional interactions with its various substrates. Aberrant expression of Aurora kinases, on the other hand, cause defects in mitotic spindle assembly, checkpoint response activation, and chromosome segregation leading to chromosomal instability. Elevated expression of Aurora kinases correlating with chromosomal instability is frequently detected in human cancers. Recent genomic profiling of about 3000 human cancer tissue specimens to identify various oncogenic signatures in The Cancer Genome Atlas project has reported that recurrent amplification and overexpression of Aurora kinase-A characterize distinct subsets of human tumors across multiple cancer types. Besides the well-characterized canonical pathway interactions of Aurora kinases in regulating assembly of the mitotic apparatus and chromosome segregation, growing evidence also supports the notion that deregulated expression of Aurora kinases in non-canonical pathways drive transformation and genomic instability by antagonizing tumor suppressor and exacerbating oncogenic signaling through direct interactions with critical proteins. Aberrant expression of the Aurora kinases–p53 protein family signaling axes appears to be critical in the abrogation of p53 protein family mediated tumor suppressor pathways frequently deregulated during oncogenic transformation process. Recent findings reveal the existence of feedback regulatory loops in mRNA expression and protein stability of these protein families and their consequences on downstream effectors involved in diverse physiological functions, such as mitotic progression, checkpoint response pathways, as well as self-renewal and pluripotency in embryonic stem cells. While these investigations have focused on the functional consequences of Aurora kinase protein family interactions with wild-type p53 family proteins, those involving Aurora kinases and mutant p53 remain to be elucidated. This article presents a comprehensive review of studies on Aurora kinases–p53 protein family interactions along with a prospective view on the possible functional consequences of Aurora kinase–mutant p53 signaling pathways in tumor cells. Additionally, we also discuss therapeutic implications of these findings in Aurora kinases overexpressing subsets of human tumors.

Aurora-A Kinase: A Potent Oncogene and Target for Cancer Therapy

The Aurora kinase family is comprised of three serine/threonine kinases, Aurora-A, Aurora-B, and Aurora-C. Among these, Aurora-A and Aurora-B play central roles in mitosis, whereas Aurora-C executes unique roles in meiosis. Overexpression or gene amplification of Aurora kinases has been reported in a broad range of human malignancies, pointing to their role as potent oncogenes in tumorigenesis. Aurora kinases therefore represent promising targets for anticancer therapeutics. A number of Aurora kinase inhibitors (AKIs) have been generated; some of which are currently undergoing clinical evaluation. Recent studies have unveiled novel unexpected functions of Aurora kinases during cancer development and the mechanisms underlying the anticancer actions of AKIs. In this review, we discuss the most recent advances in Aurora-A kinase research and targeted cancer therapy, focusing on the oncogenic roles and signaling pathways of Aurora-A kinases in promoting tumorigenesis, the recent preclinical and clinical AKI data, and potential alternative routes for Aurora-A kinase inhibition.

Aurora Kinase A expression predicts platinum-resistance and adverse outcome in high-grade serous ovarian carcinoma patients

High-Grade Serous Ovarian Carcinoma (HGSOC) is the predominant histotype of epithelial ovarian cancer (EOC), characterized by advanced stage at diagnosis, frequent TP53 mutation, rapid progression, and high responsiveness to platinum-based-chemotherapy. To date, standard first-line-chemotherapy in advanced EOC includes platinum salts and paclitaxel with or without bevacizumab. The major prognostic factor is the response duration from the end of the platinum-based treatment (platinum-free interval) and about 10–0 % of EOC patients bear a platinum-refractory disease or develop early resistance (platinum-free interval shorter than 6 months). On these bases, a careful selection of patients who could benefit from chemotherapy is recommended to avoid unnecessary side effects and for a better disease outcome. In this retrospective study, an immunohistochemical evaluation of Aurora Kinase A (AURKA) was performed on 41 cases of HGSOC according to platinum-status. Taking into account the number and intensity of AURKA positive cells we built a predictive score able to discriminate with high accuracy platinum-sensitive patients from platinum-resistant patients (p < 0.001). Furthermore, we observed that AURKA overexpression correlates to worse overall survival (p = 0.001; HR 0.14). We here suggest AURKA as new effective tool to predict the biological behavior of HGSOC. Particularly, our results indicate that AURKA has a role both as predictor of platinum-resistance and as prognostic factor, that deserves further investigation in prospective clinical trials. Indeed, in the era of personalized medicine, AURKA could assist the clinicians in selecting the best treatment and represent, at the same time, a promising new therapeutic target in EOC treatment.

Alisertib Induces Cell Cycle Arrest, Apoptosis, Autophagy and Suppresses EMT in HT29 and Caco-2 Cells

Colorectal cancer (CRC) is one of the most common malignancies worldwide with substantial mortality and morbidity. Alisertib (ALS) is a selective Aurora kinase A (AURKA) inhibitor with unclear effect and molecular interactome on CRC. This study aimed to evaluate the molecular interactome and anticancer effect of ALS and explore the underlying mechanisms in HT29 and Caco-2 cells. ALS markedly arrested cells in G₂/M phase in both cell lines, accompanied by remarkable alterations in the expression level of key cell cycle regulators. ALS induced apoptosis in HT29 and Caco-2 cells through mitochondrial and death receptor pathways. ALS also induced autophagy in HT29 and Caco-2 cells, with the suppression of phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR), but activation of 5′ AMP-activated protein kinase (AMPK) signaling pathways. There was a differential modulating effect of ALS on p38 MAPK signaling pathway in both cell lines. Moreover, induction or inhibition of autophagy modulated basal and ALS-induced apoptosis in both cell lines. ALS potently suppressed epithelial to mesenchymal transition (EMT) in HT29 and Caco-2 cells. Collectively, it suggests that induction of cell cycle arrest, promotion of apoptosis and autophagy, and suppression of EMT involving mitochondrial, death receptor, PI3K/Akt/mTOR, p38 MAPK, and AMPK signaling pathways contribute to the cancer cell killing effect of ALS on CRC cells.

Aurora kinase A has a significant role as a therapeutic target and clinical biomarker in endometrial cancer

Aurora kinase A (AURKA) regulates the cell cycle checkpoint and maintains genomic integrity. AURKA is overexpressed in various malignant tumors and its upregulation induces chromosomal instability, which leads to aneuploidy and cell transformation. To investigate the role of AURKA in endometrial cancer, we evaluated the association of immunohistochemical expression of AURKA with clinicopathological factors. Furthermore, we examined the effects of AURKA inhibition by transfected siRNA in HEC-1B cells on colony-forming ability, invasion and migration capacity, and chemosensitivity. Immunohistochemical staining showed that overexpression of AURKA was significantly associated with tumor grade (P<0.05) and poor histologic differentiation (P<0.05). The recurrence rate also tended to be high in cases with overexpression of AURKA (P<0.1) and these cases also had a tendency for shorter disease-free survival (DFS) (P<0.1). AURKA inhibition in endometrial cancer cell lines significantly decreased cell growth, invasion and migration (P<0.05), and increased chemosensitivity to paclitaxel. We also evaluated the efficacy of a combination of AURKA siRNA and paclitaxel against subcutaneous tumors formed in a nude mouse. After treatment, the tumor volume shrank significantly compared to treatment with paclitaxel only (P<0.05). To our knowledge, this is the first study in endometrial carcinoma to show a correlation between overexpression of AURKA and tumor grade, histological type and sensitivity to paclitaxel. AURKA is a promising therapeutic target in endometrial cancer and the combination therapy with AURKA inhibitors and paclitaxel could be effective for endometrial cancer that is resistant to conventional treatment and has a poor prognosis.

Issues in interpreting the in vivo activity of Aurora-A

INTRODUCTION

Based on its role as a mitotic regulatory kinase, overexpressed and associated with aneuploidy in cancer, small-molecule inhibitors have been developed for Aurora-A (AURKA) kinase. In preclinical and clinical assessments, these agents have shown efficacy in inducing stable disease or therapeutic response. In optimizing the use of Aurora-A inhibitors, it is critical to have robust capacity to measure the kinase activity of Aurora-A in tumors.

AREAS COVERED

We provide an overview of molecular mechanisms of mitotic and non-mitotic activation of Aurora-A kinase, and interaction of Aurora-A with its regulatory partners. Typically, Aurora-A activity is measured by use of phospho-antibodies targeting an autophosphorylated T288 epitope. However, recent studies have identified alternative means of Aurora-A activation control, including allosteric regulation by partners, phosphorylation on alternative activating residues (S51, S98), dephosphorylation on inhibitory sites (S342) and T288 phosphorylation by alternative kinases such as Pak enzymes. Additional work has shown that the relative abundance of Aurora-A partners can affect the activity of Aurora-A inhibitors, and that Aurora-A activation also occurs in interphase cells.

EXPERT OPINION

Taken together, this work suggests the need for comprehensive analysis of Aurora-A activity and expression of Aurora-A partners in order to stratify patients for likely therapeutic response.

Update on anaplastic thyroid carcinoma: morphological, molecular, and genetic features of the most aggressive thyroid cancer

Anaplastic thyroid carcinoma (ATC) is the most aggressive form of thyroid cancer. It shows a wide spectrum of morphological presentations and the diagnosis could be challenging due to its high degree of dedifferentiation. Molecular and genetic features of ATC are widely heterogeneous as well and many efforts have been made to find a common profile in order to clarify its cancerogenetic process. A comprehensive review of the current literature is here performed, focusing on histopathological and genetic features.

SMAD4 suppresses AURKA-induced metastatic phenotypes via degradation of AURKA in a TGFβ-independent manner

SMAD4 has been suggested to inhibit the activity of the WNT/β-catenin signaling pathway in cancer. However, the mechanism by which SMAD4 antagonizes WNT/β-catenin signaling in cancer remains largely unknown. Aurora A kinase (AURKA), which is frequently overexpressed in cancer, increases the transcriptional activity of β-catenin/T-cell factor (TCF) complex by stabilizing β-catenin through the inhibition of GSK-3β. Here, SMAD4 modulated AURKA in a TGFβ-independent manner. Overexpression of SMAD4 significantly suppressed AURKA function, including colony formation, migration, and invasion of cell lines. In addition, SMAD4 bound to AURKA induced degradation of AURKA by the proteasome. A luciferase activity assay revealed that the transcriptional activity of the β-catenin/TCF complex was elevated by AURKA, but decreased by SMAD4 overexpression. Moreover, target gene analysis showed that SMAD4 abrogated the AURKA-mediated increase of β-catenin target genes. However, this inhibitory effect of SMAD4 was abolished by overexpression of AURKA or silencing of AURKA in SMAD4-overexpressed cells. Meanwhile, the SMAD4-mediated repression of AURKA and β-catenin was independent of TGFβ signaling because blockage of TGFβR1 or restoration of TGFβ signaling did not prevent suppression of AURKA and β-catenin signaling by SMAD4. These results indicate that the tumor-suppressive function of SMAD4 is mediated by downregulation of β-catenin transcriptional activity via AURKA degradation in a TGFβ-independent manner.

IMPLICATIONS

SMAD4 interacts with AURKA and antagonizes its tumor-promoting potential, thus demonstrating a novel mechanism of tumor suppression.

Role of Human papilloma virus infection and altered methylation of specific genes in esophageal cancer

BACKGROUND

Evaluation of Human papilloma virus (HPV) and its association with promoter methylation of candidate genes, p53 and Aurora A in esophageal cancer.

MATERIALS AND METHODS

One hundred forty-one esophageal tissue samples from different pathologies were evaluated for HPV infection by PCR, while the promoter methylation status of p53 and Aurora A was assessed by methylation-specific restriction based PCR assay. Statistical analyses were performed with MedCalc and MDR software.

RESULTS

Based on endoscopy and histopathology, samples were categorized: cancers (n=56), precancers (n=7), esophagitis (n=19) and normals (n=59). HPV infection was found to be less common in cancers (19.6%), whereas its prevalence was relatively high in precancers (71.4%), esophagitis (57.8%) and normals (45.7%). p53 promoter methylation did not show any significant difference between cancer and normal tissues, whereas Aurora A promoter methylation demonstrated significant association with disease (p=0.00016, OR:5.6452, 95%CI:2.18 to 14.6) when compared to normals. Aurora A methylation and HPV infection was found in a higher percentages of precancer (66.6%), esophagitis (54.5%) and normal (45.2%) when compared to cancers (14.2%).

CONCLUSIONS

Aurora A promoter methylation is significantly associated with esophageal cancer, but the effect of HPV infection on this epigenetic alteration is not significant. However MDR analysis showed that the hypostatic effect of HPV was nullified when the cases had Aurora methylation and tobacco exposure. Further HPV sub-typing may give an insight into its reduced prevalence in esophageal cancer verses normal tissue. However, with the present data it is difficult to assign any significant role to HPV in the etiopathology of esophageal cancer.

Aurora-A: a potential DNA repair modulator

It is well-known that overexpression of Aurora-A promotes tumorigenesis, but the role of Aurora-A in the development of cancer has not been fully investigated. Recent studies indicate that Aurora-A may confer cancer cell chemo- and radioresistance through dysregulation of cell cycle progression and DNA damage response. Direct evidences from literatures suggest that Aurora-A inhibits pRb, p53, p21(waf1/cip1), and p27(cip/kip) but enhances Plk1, CDC25, CDK1, and cyclin B1 to repeal cell cycle checkpoints and to promote cell cycle progression. Other studies indicate that Aurora-A suppresses BRCA1, BRCA2, RAD51, poly(ADP ribose) polymerase (PARP), and gamma-H2AX to dysregulate DNA damage response. Aurora-A may also interact with RAS and Myc to control DNA repair indirectly. In this review, we summarized the potential role of Aurora-A in DNA repair from the current literatures and concluded that Aurora-A may function as a DNA repair modulator to control cancer cell radio- and chemosensitivity, and that Aurora-A-associated DNA repair molecules may be considered for targeted cancer therapy.

Aurora kinases in head and neck cancer

In healthy cells, controlled activation of aurora kinases regulates mitosis. Overexpression and hyperactivation of aurora kinases A and B have major roles in tumorigenesis, and can induce aneuploidy and genomic instability. In squamous-cell carcinomas of the head and neck, overexpression of aurora kinase A is associated with decreased survival, and a reduction in aurora kinase A and aurora kinase B expression inhibits cell growth and increases apoptosis. In this Review, we provide an overview of the biological functions of aurora kinases in healthy cells and in cancer cells, and we review small studies and high-throughput datasets that particularly implicate aurora kinase A in the pathogenesis of squamous-cell carcinomas of the head and neck. Early phase trials are beginning to assess the activity of small-molecule inhibitors of aurora kinases. We summarise trials of aurora kinase inhibitors in squamous-cell carcinomas of the head and neck, and discuss directions for future drug combination trials and biomarkers to use with drugs that inhibit aurora kinases.

Telmisartan exerts pleiotropic effects in endothelial cells and promotes endothelial cell quiescence and survival

OBJECTIVE

Telmisartan, an angiotensin II type 1 receptor blocker, and amlodipine, a calcium channel blocker, are antihypertensive agents clinically used as monotherapy or in combination. They exert beneficial cardiovascular effects independently of blood pressure lowering and classic mechanisms of action. In this study, we investigate molecular mechanisms responsible for the off-target effects of telmisartan and telmisartan-amlodipine in endothelial cells (ECs), using an unbiased genomic approach.

APPROACH AND RESULTS

In human umbilical vein ECs, microarray analysis of gene expression followed by pathway enrichment analysis and quantitative polymerase chain reaction validation revealed that telmisartan modulates the expression of key genes responsible for cell cycle progression and apoptosis. Amlodipine's effect was similar to control. ECs exposed to telmisartan, but not amlodipine, losartan, or valsartan, exhibited a dose-dependent impairment of cell growth and failed to enter the S-phase of the cell cycle. Similarly, telmisartan inhibited proliferation in COS-7 cells lacking the angiotensin II type 1 receptor. In telmisartan-treated ECs, phosphorylation and activation of Akt, as well as MDM2, were reduced, leading to accumulation of p53 in the nucleus, where it represses the transcription of cell cycle-promoting genes. Phosphorylation of glycogen synthase kinase-3β was also reduced, resulting in rapid proteolytic turnover of CyclinD1. Telmisartan induced downregulation of proapoptotic genes and protected ECs from serum starvation-induced and 7-ketocholesterol-induced apoptosis.

CONCLUSIONS

Telmisartan exerts antiproliferative and antiapoptotic effects in ECs. This may account for the improved endothelial dysfunction observed in the clinical setting.

Aurora A kinase (AURKA) in normal and pathological cell division

Temporally and spatially controlled activation of the Aurora A kinase (AURKA) regulates centrosome maturation, entry into mitosis, formation and function of the bipolar spindle, and cytokinesis. Genetic amplification and mRNA and protein overexpression of Aurora A are common in many types of solid tumor, and associated with aneuploidy, supernumerary centrosomes, defective mitotic spindles, and resistance to apoptosis. These properties have led Aurora A to be considered a high-value target for development of cancer therapeutics, with multiple agents currently in early-phase clinical trials. More recently, identification of additional, non-mitotic functions and means of activation of Aurora A during interphase neurite elongation and ciliary resorption have significantly expanded our understanding of its function, and may offer insights into the clinical performance of Aurora A inhibitors. Here we review the mitotic and non-mitotic functions of Aurora A, discuss Aurora A regulation in the context of protein structural information, and evaluate progress in understanding and inhibiting Aurora A in cancer.

Cancer cell resistance to aurora kinase inhibitors: identification of novel targets for cancer therapy

Drug resistance is the major obstacle to successful cancer therapy. Our study focuses on resistance to Aurora kinase inhibitors tested as anti-cancer drugs in clinical trials. We have used 2D electrophoresis in the pH ranges of 4-7 and 6-11 followed by protein identification using MALDI-TOF/TOF to compare the protein composition of HCT116 colon cancer cells either sensitive to CYC116 and ZM447439 inhibitors or resistant toward these drugs. The analysis also included p53(+/+) and p53(-/-) phenotypes of HCT116 cells. Our findings demonstrate that platelet-activating factor acetylhydrolase and GTP-binding nuclear protein Ran contribute to the development of resistance to ZM447439 only where resistance is related to p53. On the other hand, serine hydroxymethyltransferase was found to promote the tumor growth in cells resistant to CYC116 without the influence of p53. Computer modeling of interaction networks highlighted a direct link of the p53-independent mechanism of resistance to CYC116 with autophagy. Importantly, serine hydroxymethyltransferase, serpin B5, and calretinin represent the target proteins that may help overcome resistance in combination therapies. In addition, serpin B5 and calretinin appear to be candidate biomarkers that may be accessible in patients for monitoring of cancer therapy with ease.

A novel Aurora-A-mediated phosphorylation of p53 inhibits its interaction with MDM2

PURPOSE

Crosstalk between Aurora-A kinase and p53 has been proposed. While the genetic amplification of Aurora-A has been observed in many human cancers, how p53 is regulated by Aurora-A remains ambiguous. In this study, Aurora-A-mediated phosphorylation of p53 was analyzed by mass spectrometry in order to identify a new phosphorylation site. Subsequently, the functional consequences of such phosphorylation were examined.

EXPERIMENTAL DESIGN

In vitro phosphorylation of p53 by Aurora-A was performed and the phosphorylated protein was then digested with trypsin and enriched for phosphopeptides by immobilized metal affinity chromatography. Subsequently, a combination of β-elimination and Michael addition was applied to the phosphopeptides in order to facilitate the identification of phosphorylation sites by MS. The functional consequences of the novel phosphorylation of p53 on the protein-protein interactions, protein stability and transactivation activity were then examined using co-immunoprecipitation, Western blotting and reporter assays.

RESULTS

Ser-106 of p53 was identified as a novel site phosphorylated by Aurora-A. A serine-to-alanine mutation at this site was found to attenuate Aurora-A-mediated phosphorylation in vitro. In addition, phosphate-sensitive Phos-tag SDS-PAGE was used to confirm that the Ser-106 of p53 is in vivo phosphorylated by Aurora-A. Finally, co-immunoprecipitation studies suggested that Ser-106 phosphorylation of p53 decreases its interaction with MDM2 and prolongs the half-life of p53.

CONCLUSIONS

The inhibition of the interaction between p53 and MDM2 by a novel Aurora-A-mediated p53 phosphorylation was identified in this study and this provides important information for further investigations into the interaction between p53 and Aurora-A in terms of cancer biology.

Ribavirin enhances the action of interferon-α against hepatitis C virus by promoting the p53 activity through the ERK1/2 pathway

Background/Aims

Ribavirin significantly enhances the antiviral response of interferon-α (IFN-α) against Hepatitis C virus (HCV), but the underlying mechanisms remain poorly understood. Recently, p53 has been identified as an important factor involving the suppression of HCV replication in hepatocytes. We, therefore, decided to investigate whether and how ribavirin inhibits the replication of HCV by promoting the activity of p53.

Methods

HepG2 and HCV replicons (JFH1/HepG2) were utilized to study the relationship between ribavirin and p53. The effect of ribavirin on cell cycles was analyzed by flow cytometry. The activation of p53 and the signaling pathways were determined using immunoblotting. By knocking down ERK1/ERK2 and p53 utilizing RNA interference strategy, we further assessed the role of ERK1/2 and p53 in the suppression of HCV replication by ribavirin in a HCV replicon system.

Results

Using HepG2 and HCV replicons, we demonstrated that ribavirin caused the cell cycle arrest at G1 phase and stabilized and activated p53, which was associated with the antiviral activity of ribavirin. Compared to either ribavirin or IFN-α alone, ribavirin plus IFN-α resulted in greater p53 activation and HCV suppression. We further identified ERK1/2 that linked ribavirin signals to p53 activation. More importantly, knockdown of ERK1/2 and p53 partially mitigated the inhibitory effects of ribavirin on the HCV replication, indicating that ERK1/2-p53 pathway was involved in the anti-HCV effects of ribavirin.

Conclusion

Ribavirin stimulates ERK1/2 and subsequently promotes p53 activity which at least partly contributes to the enhanced antiviral response of IFN-α plus ribavirin against HCV.

Association of Aurora-A (STK15) kinase polymorphisms with clinical outcome of esophageal cancer treated with preoperative chemoradiation

BACKGROUND

Aurora-A/STK15 is a serine/threonine kinase critical for regulated chromosome segregation and cytokinesis. We investigated the association between 2 nonsynonymous single nucleotide polymorphisms in the coding region of STK15, T91A (Phe31Ile) and G169A (Val57Ile), and clinical outcome of esophageal cancer treated with preoperative chemoradiation.

METHODS

Genotypes at Phe31Ile and Val57Ile were assessed from peripheral blood lymphocytes of 190 esophageal cancer patients and were correlated to response to treatment, recurrence rate, risk of death, disease-free survival (DFS) and median survival time (MTS).

RESULTS

All patients had resectable esophageal or gastroesophageal junction cancer and received preoperative chemoradiation followed by esophagectomy. The heterozygous variant Phe31/Ile variant was significantly associated with tumor recurrence (odds ratio [OR] = 4.39; 95% confidence interval [CI], 2.12-8.94; P < .001), shorter DFS (P = .0001), and shorter MTS (P = .012). For patients receiving cisplatin-based therapy, only the variant Phe31/Ile had an adverse effect on response (OR = 2.8; 95% CI, 1.01-5.17; P = .048) and MTS (P = .026). The variant 91A-169G haplotype carried a significant risk for lack of complete response (OR = 2.54; 95% CI, 1.15-5.54) and higher rate of recurrence (OR = 2.73; 95%CI, 1.00-7.29). The presence of at least 1 variant allele at each locus further increased the risk of recurrence (adjusted OR = 6.21; 95% CI, 2.28-17.11; P = <.001), and was associated significantly shorter DFS (P = .003).

CONCLUSIONS

Our study shows that functional SNPs in the STK15 gene are associated with higher rate of recurrence, higher likelihood of chemoratiotherapy-resistance, shorter DFS, and shorter MTS. Confirmation of our data and understanding the mechanisms through which STK15 functional SNPs mediate resistance to chemoradiotherapy are warranted.

Aurora A mediates cross-talk between N- and C-terminal post-translational modifications of p53

The serine/threonine protein kinase Aurora A is known to interact with and phosphorylate tumor suppressor p53 at Serine 215 (S215), inhibiting the transcriptional activity of p53. We show that Aurora A positively regulates human p53 protein levels and, using isogenic p53 wild-type and p53-null colorectal carcinoma cells, further show that p53 regulates human Aurora A protein expression. S215 is located in the DNA-binding core of p53 and at the center of the cryptic epitope for PAb240 antibody, which is used to detect mutant and denatured p53. Following denaturing SDS PAGE, the PAb240 epitope was detectable by immunoblotting in only two out of eight cell lines. The efficacy of novel p53-targeted anticancer therapies may be influenced by the conformational state of p53, therefore, the initial determination of p53 status may be relevant. We found no correlation between phosphorylation of p53 at S215 and PAb240 antibody recognition. However, phosphorylation at S37 was positively associated with PAb240 reactivity. More importantly, we provide the first evidence of Aurora A-mediated cross-talk between N- and C-terminal p53 post-translational modifications. As p53 and Aurora A are targets for anticancer therapy the impact of their reciprocal relationship and Aurora A-induced post-translational modification of p53 should be considered.

Chromosome aberrations associated with centrosome defects: a study of comparative genomic hybridization in breast cancer

Centrosome abnormalities occur frequently in various tumors and can cause chromosomal instability and eventually promote cancer development. We investigated the chromosome aberrations associated with centrosome abnormalities in 30 cases of breast cancer, combining immunohistochemical staining and comparative genomic hybridization. Except for some common chromosome alterations (including gains of 1q, 8q, 17q, 20q, and Xq and losses of 8p, 11q, 13q, 14q, 16q, 17p, 22q, and Xp) that have also been seen more frequently in other studies, we discovered some new changes that have rarely been reported, including gains at 2p, 5p, 10p, 15q, 16p, 18q, 21q, and 22q and losses at 6p, 8p23, 11p13-pter, 13q34, and 14q32-qter. We also identified some changes (such as gains of 17q, 20q, and Xq and losses of 17p, 13q, and 14q) harboring candidate genes. We also explored the expression of centrosome protein in different molecular subtypes of breast cancer. Our findings provide a new way to explore the molecular mechanisms of breast tumorigenesis and accordingly potential new targets for therapy for this disease.

Aurora-A overexpression and aneuploidy predict poor outcome in serous ovarian carcinoma

OBJECTIVE

Aurora-A is a potential oncogene and therapeutic target in ovarian carcinoma. It is involved in mitotic events and overexpression leads to centrosome amplification and chromosomal instability. The objective of this study was to evaluate the clinical significance of Aurora-A and DNA ploidy in serous ovarian carcinoma.

METHODS

Serous ovarian carcinomas were analysed for Aurora-A protein by immunohistochemistry (n=592), Aurora-A copy number by CISH (n=169), Aurora-A mRNA by real-time PCR (n=158) and DNA ploidy by flowcytometry (n=440).

RESULTS

Overexpression of Aurora-A was found in 27% of the tumors, cytoplasmic overexpression in 11% and nuclear in 17%. The cytoplasmic and nuclear overexpression were nearly mutually exclusive. Both cytoplasmic and nuclear overexpression were associated with shorter survival, high grade, high proliferation index and aberrant p53. Interestingly, only cytoplasmic expression was associated with aneuploidy and expression of phosphorylated Aurora-A. DNA ploidy was associated with poor patient outcome as well as aggressive clinicopathological parameters. In multivariate analysis, Aurora-A overexpression appeared as an independent prognostic factor for disease-free survival, together with grade, stage and ploidy.

CONCLUSIONS

Aurora-A protein expression is strongly linked with poor patient outcome and aggressive disease characteristics, which makes Aurora-A a promising biomarker and a potential therapeutic target in ovarian carcinoma. Cytoplasmic and nuclear Aurora-A protein may have different functions. DNA aneuploidy is a strong predictor of poor prognosis in serous ovarian carcinoma.

Genetic variants of NPAT-ATM and AURKA are associated with an early adverse reaction in the gastrointestinal tract of patients with cervical cancer treated with pelvic radiation therapy

PURPOSE

This study sought to associate polymorphisms in genes related to cell cycle regulation or genome maintenance with radiotherapy (RT)-induced an early adverse reaction (EAR) in patients with cervical cancer.

METHODS AND MATERIALS

This study enrolled 243 cervical cancer patients who were treated with pelvic RT. An early gastrointestinal reaction was graded using the National Cancer Institute Common Toxicity Criteria, version 2. Clinical factors of the enrolled patients were analyzed, and 208 patients were grouped for genetic analysis according to their EAR (Grade ≤1, n = 150; Grade ≥2, n = 58). Genomic DNA was genotyped, and association with the risk of EAR for 44 functional single-nucleotide polymorphisms (SNPs) of 19 candidate genes was assessed by single-locus, haplotype, and multilocus analyses.

RESULTS

Our analysis revealed two haplotypes to be associated with an increased risk of EAR. The first, comprising rs625120C, rs189037T, rs228589A, and rs183460G, is located between the 5' ends of NPAT and ATM (OR = 1.86; 95% CI, 1.21-2.87), whereas the second is located in the AURKA gene and comprises rs2273535A and rs1047972G (OR = 1.75; 95% CI, 1.10-2.78). A third haplotype, rs2273535T and rs1047972A in AURKA, was associated with a reduced EAR risk (OR = 0.42; 95% CI, 0.20-0.89). The risk of EAR was significantly higher among patients with both risk diplotypes than in those possessing the other diplotypes (OR = 3.24; 95% CI, 1.52-6.92).

CONCLUSIONS

Individual radiosensitivity of intestine may be determined by haplotypes in the NPAT-ATM and AURKA genes. These variants should be explored in larger association studies in cervical cancer patients.

Deregulation of Aurora kinase gene expression in human testicular germ cell tumours

The Aurora kinases regulate chromosome segregation and cytokinesis, and alterations in their expression associate with cell malignant transformation. In this study, we demonstrated by qRT-PCR analysis of 14 seminomas that Aurora-A mRNA was, with respect to control tissues, augmented in five of 14 tumour tissues by 2.17 +/- 0.30 fold (P < 0.05) and reduced in 9 to 0.38 +/- 0.10 (P < 0.01). Aurora-B mRNA was increased in 11 tumour tissues by 4.33 +/- 0.82 fold (P < 0.01) and reduced in 3 to 0.41 +/- 0.11 fold. Aurora-C mRNA was reduced to 0.20 +/- 0.32 fold (P < 0.01) in 13 seminomas and up-regulated in one case. Western blot experiments, performed on protein extracts of nine seminomas and six normal testes, showed an up-regulation of Aurora-B protein by 10.14 +/- 3.51 fold (P < 0.05), while Aurora-A protein was found increased in four seminomas by 2.16 +/- 0.43 (P < 0.05), unchanged in three and reduced in two tumour tissues. Aurora-C protein was increased by 9.2 +/- 2.90 fold (P < 0.05), suggesting that post-transcriptional mechanisms modulate its expression. In conclusion, we demonstrated that expression of Aurora kinases is deregulated in seminomas, suggesting that they may play a role in the progression of testicular cancers.

Human papillomavirus 16 E6 increases the radiosensitivity of p53-mutated cervical cancer cells, associated with up-regulation of aurora A

PURPOSE

To examine the effect of the human papillomavirus (HPV) type 16-E6 (HPV 'early' gene) oncoprotein on in vitro radiosensitivity of HPV-negative/p53 mutant C33a cervical cancer cells.

METHODS AND MATERIALS

The human cervical cancer cell line C33a was stably transfected with either the HPV16 E6 cDNA cloned into the vector pcDNA3.0 (C33aE6) or the empty-vector control (C33aV). Radiosensitivity, DNA damage, and cell cycle measurements were made using standard clonogenic assays, immunofluorescent assessment of nuclear histone H2AX phosphorylated on serine-139 (gamma-H2AX) foci, and flow cytometry. Western immunoblotting and fluorescence confocal microscopy were used to analyse the changes in cellular proteins. Real-time polymerase chain reaction (PCR) was used to compare levels of aurora A mRNA.

RESULTS

Compared to C33aV cells, C33aE6 cells showed enhanced radiation cell killing. This was associated with a large amount of polyploidy which was followed by late cell death in C33aE6 cells. Aurora A was highly expressed in C33aE6 cells at pre- and post-irradiation times compared to C33aV cells. Silencing aurora A resulted in a reduced amount of residual gamma-H2AX foci in C33aE6 cells, and diminished the difference in radiosensitivity between the C33aE6 and C33aV cells.

CONCLUSION

Our in vitro results indicate that genetic instability could be augmented in the HPV-infected cancer cells by up-regulation of aurora A, especially against a background of dysfunctional p53. Further studies are needed to examine whether aurora A could be a viable therapeutic target in HPV-related tumours.

Biology of Aurora A kinase: implications in cancer manifestation and therapy

The Aurora A kinase belongs to serine/threonine group of kinases, well known for its role in cell cycle, especially in the regulation of mitosis. Numerous substrates of Aurora A kinase have been identified, which are predominantly related to cell cycle progression while some of them are transcription factors. Aurora A-mediated phosphorylation can either directly or indirectly regulate the function of its substrates. There are overwhelming evidences which report overexpression and gene amplification of Aurora A in several human cancers, and suggest that Aurora A could be a bona fide oncogene involved in tumorigenesis. Hence, Aurora A plays wide-ranging roles in both mitosis and its deregulation manifests in cancer progression. These observations have favored the choice of Aurora kinases as a target for cancer therapy. Recently, numerous small molecules have been discovered against Aurora kinases and many have entered clinical trials. Most of these small-molecule modulators designed are specific against either Aurora A or Aurora B, but some are dual inhibitors targeting the ATP-binding site which is highly conserved among the three human homologues of Aurora kinase. In this review, we discuss the physiological functions of Aurora A, interactions between Aurora A kinase and its cellular substrates, tumorigenesis mediated by Aurora A kinase upon overexpression, and small-molecule modulators of Aurora kinase as targets for cancer therapy.

TRF1 mediates mitotic abnormalities induced by Aurora-A overexpression

Aurora-A, a conserved serine-threonine kinase, plays essential roles in mitosis. Aberrant upregulation of Aurora-A perturbs proper mitotic progression and results in a generation of multinucleated cells with centrosome amplification. The molecular mechanisms for these mitotic defects remain elusive. Here, we show that the overexpressed Aurora-A-induced mitotic defects depend on the telomeric protein TRF1. Live and fixed cell analyses revealed that Aurora-A overexpression in HeLa cells compromises chromosome biorientation, which leads to cytokinetic failure and tetraploidization with increased centrosome numbers. TRF1 depletion by small interfering RNAs or by tankyrase-1 overexpression suppresses Aurora-A-induced occurrence of unaligned chromosomes in metaphase, thus preventing the subsequent abnormalities. We found that Aurora-A binds and phosphorylates TRF1. When TRF1 knockdown cells are complemented with wild-type TRF1, Aurora-A-induced mitotic defects recur. By contrast, a TRF1 mutant that is not phosphorylatable by Aurora-A does not restore such Aurora-A-induced phenotype. We propose that TRF1 phosphorylation by excessive Aurora-A may provoke abnormal mitosis and chromosomal instability.

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.

MAD2B, a novel TCF4-binding protein, modulates TCF4-mediated epithelial-mesenchymal transdifferentiation

T cell factor 4 (TCF4) interacts with beta-catenin in the WNT signaling pathway and transactivates downstream target genes involved in cancer progression. To identify proteins that regulate TCF4-mediated biological responses, we performed a yeast two-hybrid screen to search for a TCF4-binding protein(s) and found that MAD2B interacts with TCF4. We confirmed that MAD2B is a TCF4-binding protein by co-immunoprecipitation. Using the TOPFLASH reporter assay, we found that MAD2B blocks TCF4-mediated transactivation. The MAD2B binding regions of TCF4 were identified by TCF4 deletion mapping and electrophoretic mobility shift assay analysis. TCF4 and MAD2B interactions abolished the DNA binding ability of TCF4. Knockdown of MAD2B in SW480 colorectal cancer cells led to the conversion of epithelial cells to a mesenchymal fibroblastoid phenotype (epithelial-mesenchymal transdifferentiation). An E-cadherin promoter reporter analysis showed that MAD2B modulates TCF4-mediated E-cadherin expression. MAD2B knockdown blocked E-cadherin expression and significantly induced mesenchymal markers, such as N-cadherin and vimentin. Mesenchymal induction was accompanied by F-actin redistribution and the appearance of a fibroblastoid phenotype. MAD2B knockdown also increased both mRNA and protein levels of Slug, a known TCF4-induced E-cadherin transcriptional repressor. A chromatin immunoprecipitation assay showed that MAD2B silencing enhances the ability of TCF4 to bind the Slug promoter. Thus, MAD2B is a novel TCF4-interacting protein. This study provides the first evidence for the involvement of MAD2B in TCF4-mediated epithelial-mesenchymal transdifferentiation.

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.

Aurora kinases as prognostic biomarkers in ovarian carcinoma

We investigated the expression of Aurora kinases A and B by immunohistochemistry in 68 ovarian carcinomas to analyze their prognostic value. The amplification of AURKA gene by fluorescence in situ hybridization was also assessed. Overall, 58.8% and 85.3% of ovarian carcinomas showed expression of Aurora A and B, respectively. Amplification of AURKA was found in 27.6% of cases examined. Tumors with Aurora A expression showed a lower rate of recurrence than those tumors without Aurora A expression (65% versus 91.7%, P = .019). In the univariate analysis, patients with Aurora A and B expression showed an increased progression-free survival (P = .023 and .06, respectively, log-rank test) and overall survival (P = .03 and .02, respectively, log-rank test). The multivariate analysis adjusted to optimal surgery by Cox proportional hazards regression showed Aurora A expression as an independent prognostic factor for progression-free survival (P = .03) and overall survival (P = .02). In conclusion, Aurora A expression seems to have a prognostic value in ovarian carcinoma.

Phosphorylation of p53 is regulated by TPX2-Aurora A in xenopus oocytes

p53 is an important tumor suppressor regulating the cell cycle at multiple stages in higher vertebrates. The p53 gene is frequently deleted or mutated in human cancers, resulting in loss of p53 activity. This leads to centrosome amplification, aneuploidy, and tumorigenesis, three phenotypes also observed after overexpression of the oncogenic kinase Aurora A. Accordingly, recent studies have focused on the relationship between these two proteins. p53 and Aurora A have been reported to interact in mammalian cells, but the function of this interaction remains unclear. We recently reported that Xenopus p53 can inhibit Aurora A activity in vitro but only in the absence of TPX2. Here we investigate the interplay between Xenopus Aurora A, TPX2, and p53 and show that newly synthesized TPX2 is required for nearly all Aurora A activation and for full p53 synthesis and phosphorylation in vivo during oocyte maturation. In vitro, phosphorylation mediated by Aurora A targets serines 129 and 190 within the DNA binding domain of p53. Glutathione S-transferase pull-down studies indicate that the interaction occurs via the p53 transactivation domain and the Aurora A catalytic domain around the T-loop. Our studies suggest that targeting of TPX2 might be an effective strategy for specifically inhibiting the phosphorylation of Aurora A substrates, including p53.

Analysis of p53 dependent damage response in sperm-irradiated mouse embryos

Ionizing radiation activates a series of DNA damage response, cell cycle checkpoints to arrest cells at G1/S, S and G2/M, DNA repair, and apoptosis. The DNA damage response is thought to be the major determinant of cellular radiosensitivity and thought to operate in all higher eukaryotic cells. However, the radiosensitivity is known to differ considerably during ontogeny of mammals and early embryos of mouse for example are much more sensitive to radiation than adults. We have focused on the radiation-induced damage response during pre-implantation stage of mouse embryo. Our study demonstrates a hierarchy of damage responses to assure the genomic integrity in early embryonic development. In the sperm-irradiated zygotes, p53 dependent S-phase checkpoint functions to suppress erroneous replication of damaged DNA. The transcription-dependent function is not required and the DNA-binging domain of the protein is essential for this p53 dependent S-phase checkpoint. p21 mediated cleavage arrest comes next during early embryogenesis to prevent delayed chromosome damage at morula/ blastocyst stages. Apoptosis operates even later only in the cells of ICM at the blastocyst stage to eliminate deleterious cells. Thus, early development of sperm-irradiated embryos is protected at least by three mechanisms regulated by p53 and by p21.

Pdx-1-driven overexpression of aurora a kinase induces mild ductal dysplasia of pancreatic ducts near islets in transgenic mice

OBJECTIVES

To further explore the oncogenic activity of Aurora A kinase while attempting to develop a useful mouse model for pancreatic cancer, Aurora A kinase was targeted to pancreatic duodenal homeobox gene-1 (Pdx-1)-positive cells.

METHODS

Aurora A kinase overexpression was targeted to mouse pancreas tissues using the Pdx-1 promoter in a transgenic model. The pancreas tissues of 7- to 11-month-old transgenic animals were evaluated for metastatic adenocarcinomas, preinvasive ductal neoplasia, or other histological anomalies.

RESULTS

Examination of pancreatic tissue from Pdx-1-Aurora A transgenic mice revealed abnormalities, such as mild islet cell hyperplasia, lymphocytic infiltration, and general dysplasia between ductal/islet cell interfaces. However, most tissues from these transgenic mice were normal.

CONCLUSIONS

The overexpression of Aurora A can potentially initiate the development of mild abnormalities in pancreatic tissue; however, neither preinvasive ductal neoplasia nor fully metastatic adenocarcinomas were observed. Combining the Pdx-1-Aurora A transgenic model with other genetic alterations may provide additional insight.

Plk1 regulates mitotic Aurora A function through betaTrCP-dependent degradation of hBora

Polo-like kinase 1 (Plk1) and Aurora A play key roles in centrosome maturation, spindle assembly, and chromosome segregation during cell division. Here we show that the functions of these kinases during early mitosis are coordinated through Bora, a partner of Aurora A first identified in Drosophila. Depletion of human Bora (hBora) results in spindle defects, accompanied by increased spindle recruitment of Aurora A and its partner TPX2. Conversely, hBora overexpression induces mislocalization of Aurora A and monopolar spindle formation, reminiscent of the phenotype seen in Plk1-depleted cells. Indeed, Plk1 regulates hBora. Following Cdk1-dependent recruitment, Plk1 triggers hBora destruction by phosphorylating a recognition site for SCF(Beta-TrCP). Plk1 depletion or inhibition results in a massive accumulation of hBora, concomitant with displacement of Aurora A from spindle poles and impaired centrosome maturation, but remarkably, co-depletion of hBora partially restores Aurora A localization and bipolar spindle formation. This suggests that Plk1 controls Aurora A localization and function by regulating cellular levels of hBora.

Pituitary tumor transforming gene 1 regulates Aurora kinase A activity

Pituitary tumor transforming gene 1 (PTTG1), a transforming gene highly expressed in several cancers, is a mammalian securin protein regulating both G1/S and G2/M phases. Using protein array screening, we showed PTTG1 interacting with Aurora kinase A (Aurora-A), and confirmed the interaction using co-immunoprecipitation, His-tagged pull-down assays and intracellular immunofluorescence colocalization. PTTG1 transfection into HCT116 cells prevented Aurora-A T288 autophosphorylation, inhibited phosphorylation of the histone H3 Aurora-A substrate and resulted in abnormally condensed chromatin. PTTG1-null cell proliferation was more sensitive to Aurora-A knock down and to Aurora kinase Inhibitor III treatment. The results indicate that PTTG1 and Aurora-A interact to regulate cellular responses to anti-neoplastic drugs. PTTG1 knockdown is therefore a potential approach to improve the efficacy of tumor Aurora kinase inhibitors.

The Aurora kinase family in cell division and cancer

The Aurora protein kinase family (consisting of Aurora-A, -B and -C) is an important group of enzymes that controls several aspects of cell division in mammalian cells. Dysfunction of these kinases has been associated with a failure to maintain a stable chromosome content, a state that can contribute to tumourigenesis. Additionally, Aurora-A is frequently found amplified in a variety of tumour types and displays oncogenic activity. On the other hand, therapeutic inhibition of these kinases has shown great promise as potential anti-cancer treatment, most likely because of their essential roles during cell division. This review will focus on our present understanding of the different roles played by these kinases, their regulation throughout cell division, their deregulation in human cancers and on the progress that is made in targeting these important regulators in the treatment of cancer.

Aurora kinase inhibitors: identification and preclinical validation of their biomarkers

Aurora kinases are key regulators of mitosis and inhibitors being developed by a wide range of pharmaceutical and biotechnology companies for the treatment of cancer. Tumor cells respond differentially on inhibition of different Aurora kinase family members and these differences have to be considered in the clinical development of small-molecule inhibitors with respect to the chosen indications, the schedules or the selection of appropriate end points and they should also guide the development of biomarkers. Preclinical validation of potential biomarkers for Aurora kinase inhibitors led to a first application in clinical trials, as exemplified for the phosphorylation of histone H3 to follow Aurora-B inhibition. This review discusses the criteria for translation into the clinic and the value of pharmacodynamic biomarkers and their potential, but also their limitations to be used as surrogate markers for clinical end points.

Fbw7 regulates the activity of endoreduplication mediators and the p53 pathway to prevent drug-induced polyploidy

Fbw7 is a tumor suppressor that is mutated in numerous cancers. It encodes an E3 ubiquitin ligase, whose ability to decrease the levels of pivotal regulators of cell growth and proliferation underlies its tumor suppressor function. Here, we explore the consequences of Fbw7 inactivation on the outcome of chemotherapeutic treatments. When exposed to spindle toxins such as vinblastine and taxol, Fbw7-deficient cells undergo extensive mitotic slippage and endoreduplication, rendering them polyploid. A combined deregulation of several Fbw7 target proteins is required for this phenotype. Specifically, elevated expression of cyclin E and Aurora A in Fbw7-deficient cells is required for drug-induced polyploidy. However, overexpression of either cyclin E or Aurora A alone is not sufficient for drug-induced polyploidy. In addition, we demonstrate that Fbw7 deficiency limits the ability of p53 to respond to mitotic toxins but not to DNA damage. Furthermore, Fbw7 expression regulates the p53-dependent induction of genes such as Lats2 and p21 in response to vinblastine. Hence, we suggest that Fbw7 serves as a master regulator of the mitotic and tetraploidy checkpoints.