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Aurora Kinase A (AURKA) is an oncogenic kinase with major roles in mitosis, but also exerts cell cycle- and kinase-independent functions linked to cancer. Therefore, control of its expression, as well as its activity, is crucial. A short and a long 3'UTR isoform exist for AURKA mRNA, resulting from alternative polyadenylation (APA). We initially observed that in triple-negative breast cancer, where AURKA is typically overexpressed, the short isoform is predominant and this correlates with faster relapse times of patients. The short isoform is characterized by higher translational efficiency since translation and decay rate of the long isoform are targeted by hsa-let-7a tumor-suppressor miRNA. Additionally, hsa-let-7a regulates the cell cycle periodicity of translation of the long isoform, whereas the short isoform is translated highly and constantly throughout interphase. Finally, disrupted production of the long isoform led to an increase in proliferation and migration rates of cells. In summary, we uncovered a new mechanism dependent on the cooperation between APA and miRNA targeting likely to be a route of oncogenic activation of human AURKA., Competing Interests: RC, HA, TT, AE, CL No competing interests declared, (© 2023, Cacioppo et al.)

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 FZR1 ) 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. In living cells, the N-terminal intrinsically disordered region of AURKA containing the A-box is sufficient to confer FZR1-dependent mitotic degradation. Both in silico and in cellulo assays predict the QRVL short linear interacting motif of the A-box to be a phospho-regulated D-box. We propose that degradation of full-length AURKA also depends on an intact C-terminal domain because of critical conformational parameters permissive for both activity and mitotic degradation of AURKA., (© 2022 Abdelbaki et al.)

Aurora B kinase plays essential roles in mitosis. Its protein levels increase before the onset of mitosis and sharply decrease during mitosis exit. The latter decrease is due to a balance between the actions of the E3 ubiquitin ligase anaphase-promoting complex or cyclosome (activated by the Cdh1 adapter), and the deubiquitinating enzyme USP35. Aurora B also executes important functions in interphase. Abnormal modulation of Aurora B in interphase leads to cell cycle defects often linked to aberrant chromosomal condensation and segregation. Very little is however known about how Aurora B levels are regulated in interphase. Here we found that USP13-associates with and stabilizes Aurora B in cells, especially before their entry into mitosis. In order for USP13 to exert its stabilizing effect on Aurora B, their association is promoted by the Aurora B-mediated phosphorylation of USP13 at Serine 114. We also present evidence that USP13 instigates Aurora B deubiquitination and/or protect it from degradation in a non-catalytic manner. In addition, we report that genetic or chemical modulation of the cellular levels/activity of USP13 affects unperturbed cell-cycle progression. Overall our study unveils the molecular and cellular connections of the USP13-Aurora B axis, which potentially participates in the rewiring of the cell cycle happening in cancer cells.

Activity of AURKA is controlled through multiple mechanisms including phosphorylation, ubiquitin-mediated degradation and allosteric interaction with TPX2. Activity peaks at mitosis, before AURKA is degraded during and after mitotic exit in a process strictly dependent on the APC/C coactivator FZR1. We used FZR1 knockout cells (FZR1 KO ) and a novel FRET-based AURKA biosensor to investigate how AURKA activity is regulated in the absence of destruction. We found that AURKA activity in FZR1 KO cells dropped at mitotic exit as rapidly as in parental cells, despite absence of AURKA destruction. Unexpectedly, TPX2 was degraded normally in FZR1 KO cells. Overexpression of an N-terminal TPX2 fragment sufficient for AURKA binding, but that is not degraded at mitotic exit, caused delay in AURKA inactivation. We conclude that inactivation of AURKA at mitotic exit is determined not by AURKA degradation but by degradation of TPX2 and therefore is dependent on CDC20 rather than FZR1. The biosensor revealed that FZR1 instead suppresses AURKA activity in interphase and is critically required for assembly of the interphase mitochondrial network after mitosis.This article has an associated First Person interview with the first authors of the paper., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2020. Published by The Company of Biologists Ltd.)

Alternative polyadenylation (APA) plays a role in gene expression regulation generally by shortening of 3'UTRs (untranslated regions) upon proliferative signals and relieving microRNA-mediated repression. Owing to high proliferative indices of triple negative breast cancers (TNBCs), we hypothesized APA to cause 3'UTR length changes in this aggressive subgroup of breast cancers. Our probe-based meta-analysis approach identified 3'UTR length alterations where the significant majority was shortening events (∼70%, 113 of 165) of mostly proliferation-related transcripts in 520 TNBC patients compared with controls. Representative shortening events were further investigated for their microRNA binding potentials by computational predictions and dual-luciferase assay. In silico-predicted 3'UTR shortening events were experimentally confirmed in patient and cell line samples. To begin addressing the underlying mechanisms, we found CSTF2 (cleavage stimulation factor 2), a major regulator of 3'UTR shortening to be up-regulated in response to epidermal growth factor (EGF). EGF treatment also resulted with further shortening of the 3'UTRs. To investigate the contribution of CSTF2 and 3'UTR length alterations to the proliferative phenotype, we showed pharmacological inhibition of the EGF pathway to lead to a reduction in CSTF2 levels. Accordingly, RNAi-induced silencing of CSTF2 decreased the proliferative rate of cancer cells. Therefore, our computational and experimental approach revealed a pattern of 3'UTR length changes in TNBC patients and a potential link between APA and EGF signaling. Overall, detection of 3'UTR length alterations of various genes may help the discovery of new cancer-related genes, which may have been overlooked in conventional microarray gene expression analyses., (© The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

MicroRNA (miRNA) deregulation is associated with various cancers. Among an expanding list of cancer-related miRNAs, deregulation of miR-125b has been well documented in many cancers including breast. Based on current knowledge, miR-125b is considered to be a tumor suppressor in breast cancers. While important messenger RNA (mRNA) targets have been defined for miR-125b, here, we aimed to further investigate direct/indirect consequences of miR-125b expression in breast cancer cells by using a transcriptome approach. Upon miR-125b expression, a total of 138 cancer-related genes were found to be differentially expressed in breast cancer cells. While only a few of these were predicted to be direct mRNA targets, majority of the gene expression changes were potentially downstream and indirect effects of miR-125b expression. Among these, activated leukocyte antigen molecule (ALCAM) mRNA and protein levels were found to be highly significantly increased upon miR-125b expression. Given the tumor suppressor role of miR-125b in our model system, upon silencing of ALCAM expression, cell proliferation rate re-increased in miR-125b-expressing cells. While ALCAM's possible context-dependent roles are not clear in breast cancer, a diverse expression pattern of ALCAM mRNA was detected in a panel of breast cancer patient samples. Differentially expressed/regulated cancer-related genes upon miR-125b expression along with the significant increase of ALCAM are of future interest to understand how deregulated expression of miR-125b may have a tumor suppressor role in breast and other cancers.