AurkA/TPX2 co-overexpression in nontransformed cells promotes genome instability through induction of chromosome mis-segregation and attenuation of the p53 signalling pathway.

The Aurora-A kinase (AurkA) and its major regulator TPX2 (Targeting Protein for Xklp2) are key mitotic players frequently co-overexpressed in human cancers, and the link between deregulation of the AurkA/TPX2 complex and tumourigenesis is actively investigated. Chromosomal instability, one of the hallmarks of cancer related to the development of intra-tumour heterogeneity, metastasis and chemo-resistance, has been frequently associated with TPX2-overexpressing tumours. In this study we aimed to investigate the actual contribution to chromosomal instability of deregulating the AurkA/TPX2 complex, by overexpressing it in nontransformed hTERT RPE-1 cells.

ALFI: Cell cycle phenotype annotations of label-free time-lapse imaging data from cultured human cells.

Detecting and tracking multiple moving objects in a video is a challenging task. For living cells, the task becomes even more arduous as cells change their morphology over time, can partially overlap, and mitosis leads to new cells. Differently from fluorescence microscopy, label-free techniques can be easily applied to almost all cell lines, reducing sample preparation complexity and phototoxicity.

AurkA nuclear localization is promoted by TPX2 and counteracted by protein degradation.

The AurkA kinase is a well-known mitotic regulator, frequently overexpressed in tumors. The microtubule-binding protein TPX2 controls AurkA activity, localization, and stability in mitosis. Non-mitotic roles of AurkA are emerging, and increased nuclear localization in interphase has been correlated with AurkA oncogenic potential.

Revisiting degron motifs in human AURKA required for its targeting by APC/C.

Mitotic kinase Aurora A (AURKA) diverges from other kinases in its multiple active conformations that may explain its interphase roles and the limited efficacy of drugs targeting the kinase pocket. Regulation of AURKA activity by the cell is critically dependent on destruction mediated by the anaphase-promoting complex (APC/C) during mitotic exit and G1 phase and requires an atypical N-terminal degron in AURKA called the "A-box" in addition to a reported canonical D-box degron in the C-terminus. Here, we find that the reported C-terminal D-box of AURKA does not act as a degron and instead mediates essential structural features of the protein.

M2 Muscarinic Receptor Activation Impairs Mitotic Progression and Bipolar Mitotic Spindle Formation in Human Glioblastoma Cell Lines.

Background: Glioblastoma multiforme (GBM) is characterized by several genetic abnormalities, leading to cell cycle deregulation and abnormal mitosis caused by a defective checkpoint. We previously demonstrated that arecaidine propargyl ester (APE), an orthosteric agonist of M2 muscarinic acetylcholine receptors (mAChRs), arrests the cell cycle of glioblastoma (GB) cells, reducing their survival. The aim of this work was to better characterize the molecular mechanisms responsible for this cell cycle arrest.

The Aurora-A/TPX2 Axis Directs Spindle Orientation in Adherent Human Cells by Regulating NuMA and Microtubule Stability.

Mitotic spindle orientation is a crucial process that defines the axis of cell division, contributing to daughter cell positioning and fate, and hence to tissue morphogenesis and homeostasis. The trimeric NuMA/LGN/Gαi complex, the major determinant of spindle orientation, exerts pulling forces on the spindle poles by anchoring astral microtubules (MTs) and dynein motors to the cell cortex. Mitotic kinases contribute to correct spindle orientation by regulating nuclear mitotic apparatus protein (NuMA) localization, among which the Aurora-A centrosomal kinase regulates NuMA targeting to the cell cortex in metaphase.

Excess TPX2 Interferes with Microtubule Disassembly and Nuclei Reformation at Mitotic Exit.

The microtubule-associated protein TPX2 is a key mitotic regulator that contributes through distinct pathways to spindle assembly. A well-characterised function of TPX2 is the activation, stabilisation and spindle localisation of the Aurora-A kinase. High levels of TPX2 are reported in tumours and the effects of its overexpression have been investigated in cancer cell lines, while little is known in non-transformed cells.

Visualization of human karyopherin beta-1/importin beta-1 interactions with protein partners in mitotic cells by co-immunoprecipitation and proximity ligation assays.

Karyopherin beta-1/Importin beta-1 is a conserved nuclear transport receptor, acting in protein nuclear import in interphase and as a global regulator of mitosis. These pleiotropic functions reflect its ability to interact with, and regulate, different pathways during the cell cycle, operating as a major effector of the GTPase RAN. Importin beta-1 is overexpressed in cancers characterized by high genetic instability, an observation that highlights the importance of identifying its partners in mitosis.

Subcellular localization of the five members of the human steroid 5α-reductase family.

In humans the steroid 5alpha-reductase (SRD5A) family comprises five integral membrane enzymes that carry out reduction of a double bond in lipidic substrates: Δ-3-keto steroids, polyprenol and trans-enoyl CoA. The best-characterized reaction is the conversion of testosterone into the more potent dihydrotestosterone carried out by SRD5A1-2. Some controversy exists on their possible nuclear or endoplasmic reticulum localization.

Identification of small molecule inhibitors of the Aurora-A/TPX2 complex.

Aurora kinases are a family of cell division regulators that govern the correct assembly of a bipolar mitotic spindle and the fidelity of chromosome segregation. Their overexpression is associated with genomic instability and aneuploidy, and is frequently observed in cancer. Accordingly, competitive inhibitors targeting Aurora kinase activity at the ATP-binding site are being investigated for therapeutic purposes.

NuMA Phosphorylation by Aurora-A Orchestrates Spindle Orientation.

Spindle positioning is essential for tissue morphogenesis and homeostasis. The signaling network synchronizing spindle placement with mitotic progression relies on timely recruitment at the cell cortex of NuMA:LGN:Gαi complexes, in which NuMA acts as a receptor for the microtubule motor Dynein. To study the implication of Aurora-A in spindle orientation, we developed protocols for the partial inhibition of its activity.

Cross-Talk between AURKA and Plk1 in Mitotic Entry and Spindle Assembly.

The Aurora kinase A (AURKA) is involved in different aspects of mitotic control, from mitotic entry to cytokinesis. Consistent with its pleiotropic roles, several AURKA interactors are able to modulate its activity, the best characterized being the microtubule-binding protein TPX2, the centrosomal protein Cep192, and Bora. Bora has been described as an essential cofactor of AURKA for phosphorylation-mediated activation of the mitotic kinase polo-like kinase 1 (Plk1) at the G2/M transition.

The Aurora-A inhibitor MLN8237 affects multiple mitotic processes and induces dose-dependent mitotic abnormalities and aneuploidy.

Inhibition of Aurora kinase activity by small molecules is being actively investigated as a potential anti-cancer strategy. A successful therapeutic use of Aurora inhibitors relies on a comprehensive understanding of the effects of inactivating Aurora kinases on cell division, a challenging aim given the pleiotropic roles of those kinases during mitosis. Here we have used the Aurora-A inhibitor MLN8237, currently under phase-I/III clinical trials, in dose-response assays in U2OS human cancer cells synchronously proceeding towards mitosis.

Aurora-A inactivation causes mitotic spindle pole fragmentation by unbalancing microtubule-generated forces.

Background: Aurora-A is an oncogenic kinase playing well-documented roles in mitotic spindle organisation. We previously found that Aurora-A inactivation yields the formation of spindles with fragmented poles that can drive chromosome mis-segregation. Here we have addressed the mechanism through which Aurora-A activity regulates the structure and cohesion of spindle poles.

Control of Aurora-A stability through interaction with TPX2.

The Aurora-A kinase has well-established roles in spindle assembly and function and is frequently overexpressed in tumours. Its abundance is cell cycle regulated, with a peak in G2 and M phases, followed by regulated proteolysis at the end of mitosis. The microtubule-binding protein TPX2 plays a major role in regulating the activity and localisation of Aurora-A in mitotic cells.

The Aurora-A/TPX2 complex: a novel oncogenic holoenzyme?

The Aurora-A kinase regulates cell division by phosphorylating multiple downstream targets in the mitotic apparatus. Aurora-A is frequently overexpressed in tumor cells and it is therefore regarded as a novel candidate target in anti-cancer therapy. Its actual contribution to cell transformation, however, is not entirely clarified; furthermore, its transforming ability has been found to vary broadly depending on the systems and experimental conditions in which it was assayed.