Aurora kinases

Aurora B kinase expression in ependymal neoplasms

Overexpression of Aurora B kinase, which regulates cell progression through mitosis and cytokinesis, has been shown to be associated with higher-grade tumors and shortened survival in astrocytomas. Aurora B expression was evaluated by immunohistochemistry in 32 ependymomas, 10 anaplastic ependymomas, 16 myxopapillary ependymomas, and 9 subependymomas. Aurora B expression was identified in 20 (62.5%) ependymomas, 5 (50%) anaplastic ependymomas, 1 (6.3%) myxopapillary ependymoma, and no subependymomas. The association between Aurora B expression and World Health Organization grade II/III tumors was statistically significant (P<0.0001). There was no difference in the level of Aurora B expression between ependymomas and anaplastic ependymomas. Aurora B expression was not associated with patient age, sex, tumor location, tumor recurrence, or death from tumor. In contrast to astrocytomas, elevated Aurora B expression in higher-grade ependymomas does not seem to correlate with clinical course, although it may be a potential target of Aurora kinase inhibitors.

[Inhibitors of aurora kinases]

Aurora kinases (A, B and C) are proteins expressed only in cells which divide actively and their increase is a factor of bad prognosis in cancer. They regulate the maturation of centrosomes, the separation and the condensation of chromosomes, mitotic checkpoint and cytokinesis. The inhibition of aurora kinases, by powerful and selective inhibitors, is due to the formation of abnormal cells which are eliminated by apoptosis. The purpose of this article is to present the role, the antitumor activity and the tolerability of these inhibitors. They can be administered orally or intravenously, on weekly or monthly schedules. In our knowledge, twelve molecules are evaluated at the present time and will be discussed only the most advanced namely: VX-680, ZM 447439, MLN 8054, AZD 1152, PHA 739358, SU 6668 and AT 9283. The main indications are breast, colon, lung, pancreas and bladder cancers as well as hematologic tumors such as leukemia (ALL, AML, CML) and lymphoma. These inhibitors can be associated with other chemotherapies. They seem well tolerated; the reported side effects are digestive disorders (diarrhea), fever, asthenia, alopecia, slumber, neutropenia, myelosuppression and disturbance of the biological markers.

Aurora kinases: structure, functions and their association with cancer

BACKGROUND

Aurora kinases are a recently discovered family of kinases (A, B & C) consisting of highly conserved serine\threonine protein kinases found to be involved in multiple mitotic events: regulation of spindle assembly checkpoint pathway, function of centrosomes and cytoskeleton, and cytokinesis. Aberrant expression of Aurora kinases may lead to cancer. For this reason the Aurora kinases are potential targets in the treatment of cancer. In this review we discuss the biology of these kinases: structure, function, regulation and association with cancer.

METHODS AND RESULTS

A literature search.

CONCLUSION

Many of the multiple functions of mitosis are mediated by the Aurora kinases. Their aberrant expression can lead to the deregulation of cell division and cancer. For this reason, the Aurora kinases are currently one of the most interesting targets for cancer therapy. Some Aurora kinase inhibitors in the clinic have proven effectively on a wide range of tumor types. The clinical data are very encouraging and promising for development of novel class of structurally different Aurora kinase inhibitors. Hopefully the Aurora kinases will be potentially useful in drug targeted cancer treatment.

Hypoxia-inducible enhancer/alpha-fetoprotein promoter-driven RNA interference targeting STK15 suppresses proliferation and induces apoptosis in human hepatocellular carcinoma cells

STK15 (Aurora A/BTAK) is an oncogenic serine/threonine kinase that plays a role in centrosome separation and in the formation of the mitotic bipolar spindle. It is highly expressed and constitutively activated in various human tumors including hepatocellular carcinoma (HCC). To investigate its possibility as a molecular target for future therapies directed against hepatocellular carcinoma, we constructed a tissue-specific RNA interference (RNAi) system mediated by hypoxia-inducible (HI) enhancer/alpha-fetoprotein (AFP) promoter and employed it to downregulate exogenous reporters (LUC and EGFP) and endogenous STK15 gene expression and analyzed the phenotypical changes in HCC cells. Results showed that the expression of exogenous reporters (LUC and EGFP) was specifically downregulated in hepatoma cells but not in non-hepatoma cells. Moreover, the specific downregulation of STK15 expression in hepatocellular carcinoma cells (HepG2) significantly inhibited in vitro cellular proliferation and in vivo tumorigenicity. Furthermore, we also found that the downregulation of STK15 expression led to cell arrest in the G(2)/M phase and finally apoptosis induction of HepG2 cells. Thus, the HI enhancer/AFP promoter-mediated RNAi targeting STK15 may be a potential therapeutic strategy for the treatment of hepatocellular carcinoma with tumor specificity and high efficacy.

Aurora-A kinase: a novel target of cellular immunotherapy for leukemia

Aurora-A kinase (Aur-A) is a member of the serine/threonine kinase family that regulates the cell division process, and has recently been implicated in tumorigenesis. In this study, we identified an antigenic 9-amino-acid epitope (Aur-A(207-215): YLILEYAPL) derived from Aur-A capable of generating leukemia-reactive cytotoxic T lymphocytes (CTLs) in the context of HLA-A*0201. The synthetic peptide of this epitope appeared to be capable of binding to HLA-A*2402 as well as HLA-A*0201 molecules. Leukemia cell lines and freshly isolated leukemia cells, particularly chronic myelogenous leukemia (CML) cells, appeared to express Aur-A abundantly. Aur-A-specific CTLs were able to lyse human leukemia cell lines and freshly isolated leukemia cells, but not normal cells, in an HLA-A*0201-restricted manner. Importantly, Aur-A-specific CTLs were able to lyse CD34+ CML progenitor cells but did not show any cytotoxicity against normal CD34+ hematopoietic stem cells. The tetramer assay revealed that the Aur-A(207-215) epitope-specific CTL precursors are present in peripheral blood of HLA-A*0201-positive and HLA-A*2402-positive patients with leukemia, but not in healthy individuals. Our results indicate that cellular immunotherapy targeting Aur-A is a promising strategy for treatment of leukemia.

Perimembrane Aurora-A expression is a significant prognostic factor in correlation with proliferative activity in non-small-cell lung cancer (NSCLC)

Purpose

Aurora-A, also known as STK15/BTAK, is a member of the protein serine/threonine kinase family, and experimental studies have revealed that Aurora-A plays critical roles in cell mitosis and in carcinogenesis. However, no clinical studies on Aurora-A expression in non-small-cell lung cancer (NSCLC) have been reported. Thus, the present study was conducted to assess the clinical significance of Aurora-A status.

Experimental Design

A total of 189 consecutive patients with resected pathologic (p-)stage I-IIIA, NSCLC were retrospectively reviewed, and immunohistochemical staining was used to detect Aurora-A expression.

Results

Aurora-A expression was negative in 31 patients (16.4%); among Aurora-A positive patients, 124 patients showed pure diffuse cytoplasmic Aurora-A expression and the other 34 patients showed perimembrane Aurora-A expression. Perimembrane Aurora-A tumors showed the highest proliferative index (PI) (mean PIs for negative, diffuse cytoplasmic, and perimembrane tumors: 49.2, 41.7, and 63.5, respectively; P < .001). Five-year survival rates of Aurora-A negative, diffuse cytoplasmic, and perimembrane patients were 67.8%, 66.7%, and 47.6%, respectively, showing the poorest postoperative survival in perimembrane patients (P = .033). Subset analyses revealed that perimembrane Aurora-A expression was a significant factor to predict a poor prognosis in squamous cell carcinoma patients, not in adenocarcinoma patients. A multivariate analysis confirmed that perimembrane Aurora-A expression was an independent and significant factor to predict a poor prognosis.

Conclusions

Perimembrane Aurora-A status was a significant factor to predict a poor prognosis in correlation with enhanced proliferative activity in NSCLC.

An Integrated Computational Approach to the Phenomenon of Potent and Selective Inhibition of Aurora Kinases B and C by a Series of 7-Substituted Indirubins

A variation of the bromine substitution from 6- to 7-position converts the glycogen synthase kinase-3alpha/beta-(GSK-3-alpha/beta) selective inhibitor 6-bromoindirubin-3'-oxime (6BIO) to a potent inhibitor of Aurora B and C kinases. The novel indirubin analogue 7-bromoindirubin-3'-oxime (7BIO) demonstrated unexpected selectivity against these two kinases since the homologous kinase Aurora A was poorly inhibited. A hypothesis regarding the 7BIO selectivity profile was stated and validated by docking, molecular dynamics, and free energy perturbation calculations. The residue (Thr217AurA, Glu161AurB, Glu127AurC) located in the active site was identified as a major contributor to the enhanced affinity of 7BIO for Aurora B and C versus Aurora A. Furthermore, the docking events of 7BIO and several of its analogues were approached by quantitative models based on semiempirical scoring functions. In the course of model construction and optimization, a number of important factors influencing the quality of each model like the application of force constraints or the sampling method were determined. Among these factors, the presence and treatment of structurally important water molecules had a pronounced impact on the quality of each model. The final model was validated by use of free energy perturbation calculations.

Multiple protein phosphatases are required for mitosis in Drosophila

BACKGROUND

Approximately one-third of the Drosophila kinome has been ascribed some cell-cycle function. However, little is known about which of its 117 protein phosphatases (PPs) or subunits have counteracting roles.

RESULTS

We investigated mitotic roles of PPs through systematic RNAi. We found that G(2)-M progression requires Puckered, the JNK MAP-kinase inhibitory phosphatase and PP2C in addition to string (Cdc25). Strong mitotic arrest and chromosome congression failure occurred after Pp1-87B downregulation. Chromosome alignment and segregation defects also occurred after knockdown of PP1-Flapwing, not previously thought to have a mitotic role. Reduction of several nonreceptor tyrosine phosphatases produced spindle and chromosome behavior defects, and for corkscrew, premature chromatid separation. RNAi of the dual-specificity phosphatase, Myotubularin, or the related Sbf "antiphosphatase" resulted in aberrant mitotic chromosome behavior. Finally, for PP2A, knockdown of the catalytic or A subunits led to bipolar monoastral spindles, knockdown of the Twins B subunit led to bridged and lagging chromosomes, and knockdown of the B' Widerborst subunit led to scattering of all mitotic chromosomes. Widerborst was associated with MEI-S332 (Shugoshin) and required for its kinetochore localization.

CONCLUSIONS

We identify cell-cycle roles for 22 of 117 Drosophila PPs. Involvement of several PPs in G(2) suggests multiple points for its regulation. Major mitotic roles are played by PP1 with tyrosine PPs and Myotubularin-related PPs having significant roles in regulating chromosome behavior. Finally, depending upon its regulatory subunits, PP2A regulates spindle bipolarity, kinetochore function, and progression into anaphase. Discovery of several novel cell-cycle PPs identifies a need for further studies of protein dephosphorylation.

Mouse Aurora A: expression in Escherichia coli and purification

Aurora kinases have recently become some of the most intensely pursued oncology targets for the design of small-molecule inhibitors. Most of the active Aurora-A protein variants are currently being expressed from baculoviruses in insect cells, while catalytically impaired proteins can also be generated in and purified from Escherichia coli. In this study we present a method of expressing large quantities of active mouse Aurora-A kinase domain as an N-terminal glutathione-S-transferase fusion protein in bacteria and outline a simple purification method that produces greater than 99% pure protein samples suitable for enzymatic assays and X-ray crystallography. The methods described in this report simplify mouse Aurora-A expression and purification, and may aid in the production of other difficult kinases in prokaryotes.

Mitotic kinases: the key to duplication, segregation, and cytokinesis errors, chromosomal instability, and oncogenesis

Chromosomal instability (CIN) and aneuploidy are commonly observed in the vast majority of human solid tumors and in many hematological malignancies. These features are considered defining characteristics of human breast, bladder and kidney cancers since they markedly exceed a 50% aneuploidy frequency. The detection of persistent mitotic kinase over-expression, particularly the Aurora family, and centrosome amplification in precursor/pre-malignant stages, strongly implicate these molecular changes in precipitating the aneuploidy seen in many human neoplasms. Mitotic spindle checkpoint defects may also lead to aneuploid tumors. However, the sustained over-expression and activity of various members of the mitotic kinase families, including Aurora (Aur) (A, B, C), Polo-like (Plk1-4), and Nek (NIMA1-11) in diverse human tumors strongly indicate that these entities are intimately involved in the development of errors in centrosome duplication, chromosome segregation, and cytokinesis. Mitotic kinases have also been implicated in regulating the centrosome cycle, spindle checkpoint and microtubule-kinetochore attachment, spindle assembly, and chromosome condensation. These mitotic kinases are modulated by de-novo synthesis, stability factors, phosphorylation, and ubiquitin-dependent proteolysis. They, in turn, phosphorylate a myriad of centrosomal/mitotic protein substrates, and have the ability to behave as oncogenes (i.e. Aur-A, Plk-1), providing a compelling link between errors in mitosis and oncogenic processes. The recent development of selective small molecule inhibitors of Aurora kinases, in particular, will provide useful tools to ascertain more precisely their role in cancer development. Potent inhibitors of mitotic kinases, when fully developed, have the promise to be effective agents against tumor growth, and possibly, tumor prevention as well.

Dynamic localization of the human papillomavirus type 11 origin binding protein E2 through mitosis while in association with the spindle apparatus

Papillomaviral DNA replicates as extrachromosomal plasmids in squamous epithelium. Viral DNA must segregate equitably into daughter cells to persist in dividing basal/parabasal cells. We have previously reported that the viral origin binding protein E2 of human papillomavirus types 11 (HPV-11), 16, and 18 colocalized with the mitotic spindles. In this study, we show the localization of the HPV-11 E2 protein to be dynamic. It colocalized with the mitotic spindles during prophase and metaphase. At anaphase, it began to migrate to the central spindle microtubules, where it remained through telophase and cytokinesis. It was additionally observed in the midbody at cytokinesis. A peptide spanning residues 285 to 308 in the carboxyl-terminal domain of HPV-11 E2 (E2C) is necessary and sufficient to confer localization on the mitotic spindles. This region is conserved in HPV-11, -16, and -18 and bovine papillomavirus type 4 (BPV-4) E2 and is also required for the respective E2C to colocalize with the mitotic spindles. The E2 protein of bovine papillomavirus type 1 is tethered to the mitotic chromosomes via the cellular protein Brd4. However, the HPV-11 E2 protein did not associate with Brd4 during mitosis. Lastly, a chimeric BPV-1 E2C containing the spindle localization domain from HPV-11 E2C gained the ability to localize to the mitotic spindles, whereas the reciprocal chimera lost the ability. We conclude that this region of HPV E2C is critical for localization with the mitotic apparatus, enabling the HPV DNA to sustain persistent infections.

MET meet adaptors: functional and structural implications in downstream signalling mediated by the Met receptor

The tyrosin kinase Met receptor regulates multiple cellular events, ranging from cell motility and angiogenesis to morphological differentiation and tissue regeneration. To conduce these activities, the cytoplasmic C-terminal region of this receptor acts as a docking site for multiple protein substrates, including Grb 2, Gab 1, STAT 3, Shc, SHIP-1 and Src. These substrates are characterised by the presence of multiple domains, including the PH, PTB, SH 2 and SH 3 domains, which directly interact with the multisubstrate C-terminal region of Met. How this receptor recognises and binds a specific substrate in a space-temporal mode is a central question in cell signalling. The recently solved crystal structure of the tyrosine kinase domain of the Met receptor and that of domains of diverse Met substrates provides the molecular framework to understand Met substrate specificity. This structural information also gives new insights on the plasticity of Met signalling and the implications of Met deregulation in tumorigenic processes. In the light of these advances, the present work discusses the molecular basis of Met-substrate recognition and its functional implications in signalling events mediated by this pleiotropic receptor.