The Aurora B specificity switch is required to protect from non-disjunction at the metaphase/anaphase transition

Cell cycle responses to Topoisomerase II inhibition: Molecular mechanisms and clinical implications

DNA Topoisomerase IIA (Topo IIA) is an enzyme that alters the topological state of DNA and is essential for the separation of replicated sister chromatids and the integrity of cell division. Topo IIA dysfunction activates cell cycle checkpoints, resulting in arrest in either the G2-phase or metaphase of mitosis, ultimately triggering the abscission checkpoint if non-disjunction persists. These events, which directly or indirectly monitor the activity of Topo IIA, have become of major interest as many cancers have deficiencies in Topoisomerase checkpoints, leading to genome instability. Recent studies into how cells sense Topo IIA dysfunction and respond by regulating cell cycle progression demonstrate that the Topo IIA G2 checkpoint is distinct from the G2-DNA damage checkpoint. Likewise, in mitosis, the metaphase Topo IIA checkpoint is separate from the spindle assembly checkpoint. Here, we integrate mechanistic knowledge of Topo IIA checkpoints with the current understanding of how cells regulate progression through the cell cycle to accomplish faithful genome transmission and discuss the opportunities this offers for therapy.

Metabolic protein kinase signalling in neuroblastoma

BACKGROUND

Neuroblastoma is a paediatric malignancy of incredibly complex aetiology. Oncogenic protein kinase signalling in neuroblastoma has conventionally focussed on transduction through the well-characterised PI3K/Akt and MAPK pathways, in which the latter has been implicated in treatment resistance. The discovery of the receptor tyrosine kinase ALK as a target of genetic alterations in cases of familial and sporadic neuroblastoma, was a breakthrough in the understanding of the complex genetic heterogeneity of neuroblastoma. However, despite progress in the development of small-molecule inhibitors of ALK, treatment resistance frequently arises and appears to be a feature of the disease. Moreover, since the identification of ALK, several additional protein kinases, including the PIM and Aurora kinases, have emerged not only as drivers of the disease phenotype, but also as promising druggable targets. This is particularly the case for Aurora-A, given its intimate engagement with MYCN, a driver oncogene of aggressive neuroblastoma previously considered 'undruggable.'

SCOPE OF REVIEW

Aided by significant advances in structural biology and a broader understanding of the mechanisms of protein kinase function and regulation, we comprehensively outline the role of protein kinase signalling, emphasising ALK, PIM and Aurora in neuroblastoma, their respective metabolic outputs, and broader implications for targeted therapies.

MAJOR CONCLUSIONS

Despite massively divergent regulatory mechanisms, ALK, PIM and Aurora kinases all obtain significant roles in cellular glycolytic and mitochondrial metabolism and neuroblastoma progression, and in several instances are implicated in treatment resistance. While metabolism of neuroblastoma tends to display hallmarks of the glycolytic "Warburg effect," aggressive, in particular MYCN-amplified tumours, retain functional mitochondrial metabolism, allowing for survival and proliferation under nutrient stress. Future strategies employing specific kinase inhibitors as part of the treatment regimen should consider combinatorial attempts at interfering with tumour metabolism, either through metabolic pathway inhibitors, or by dietary means, with a view to abolish metabolic flexibility that endows cancerous cells with a survival advantage.

Is the AURKB Gene Involved in Aml Cell Proliferation Since It is Targeted by miR-34a-5p and let-7b-5p?

ABSTRACT Objective: The production of normal blood cells in the bone marrow is interrupted in AML, which is characterized by the proliferation and accumulation of leukemic blasts. Therefore, patients experience anemia and thrombocytopenia. When gene expression of Aurora kinases, which is reported to be highly expressed in AML, decreases, it may be possible to alleviate the clinical findings in AML. In this study, it was aimed to examine the relationship of AURKB with important miRNAs that have the potential to regulate gene expression. Method: HL60 and NB4 cells were transfected with important tumor suppressor miRNAs miR-34a-5p and let-7b-5p mimics. Then, its effects on proliferation were examined with WST-8 technique and its effects on AURKB gene expression were examined with qRT-PCR. Results: It was determined that these miRNAs negatively regulated proliferation in both AML cell lines and downregulated the expression level of the Aurora kinase B (AURKB) gene in the miRNA transfected group compared to the control group. Conclusion: In conclusion, it was determined that miR-34a-5p and let-7b-5p could regulate AURKB expression in AML cells. Therefore, it was thought that these miRNAs may have an important potential as a therapeutic biomarker in preventing excessive cell division and poor prognosis in AML.

Overarching roles of diacylglycerol signaling in cancer development and antitumor immunity

Diacylglycerol (DAG) is a lipid second messenger that is generated in response to extracellular stimuli and channels intracellular signals that affect mammalian cell proliferation, survival, and motility. DAG exerts a myriad of biological functions through protein kinase C (PKC) and other effectors, such as protein kinase D (PKD) isozymes and small GTPase-regulating proteins (such as RasGRPs). Imbalances in the fine-tuned homeostasis between DAG generation by phospholipase C (PLC) enzymes and termination by DAG kinases (DGKs), as well as dysregulation in the activity or abundance of DAG effectors, have been widely associated with tumor initiation, progression, and metastasis. DAG is also a key orchestrator of T cell function and thus plays a major role in tumor immunosurveillance. In addition, DAG pathways shape the tumor ecosystem by arbitrating the complex, dynamic interaction between cancer cells and the immune landscape, hence representing powerful modifiers of immune checkpoint and adoptive T cell-directed immunotherapy. Exploiting the wide spectrum of DAG signals from an integrated perspective could underscore meaningful advances in targeted cancer therapy.

Novel Aurora A and Protein Kinase C (α, β1, β2, and θ) Multitarget Inhibitors: Impact of Selenium Atoms on the Potency and Selectivity

Aurora kinases and protein kinase C (PKC) have been shown to be involved in different aspects of cancer progression. To date, no dual Aurora/PKC inhibitor with clinical efficacy and low toxicity is available. Here, we report the identification of compound 2e as a potent small molecule capable of selectively inhibiting Aurora A kinase and PKC isoforms α, β1, β2 and θ. Compound 2e demonstrated significant inhibition of the colony forming ability of metastatic breast cancer cells in vitro and metastasis development in vivo. In vitro kinase screening and molecular modeling studies revealed the critical role of the selenium-containing side chains within 2e, where selenium atoms were shown to significantly improve its selectivity and potency by forming additional interactions and modulating the protein dynamics. In comparison to other H-bonding heteroatoms such as sulfur, our studies suggested that these selenium atoms also confer more favorable PK properties.

A genetically-encoded crosslinker screen identifies SERBP1 as a PKCε substrate influencing translation and cell division

The PKCε-regulated genome protective pathway provides transformed cells a failsafe to successfully complete mitosis. Despite the necessary role for Aurora B in this programme, it is unclear whether its requirement is sufficient or if other PKCε cell cycle targets are involved. To address this, we developed a trapping strategy using UV-photocrosslinkable amino acids encoded in the PKCε kinase domain. The validation of the mRNA binding protein SERBP1 as a PKCε substrate revealed a series of mitotic events controlled by the catalytic form of PKCε. PKCε represses protein translation, altering SERBP1 binding to the 40 S ribosomal subunit and promoting the assembly of ribonucleoprotein granules containing SERBP1, termed M-bodies. Independent of Aurora B, SERBP1 is shown to be necessary for chromosome segregation and successful cell division, correlating with M-body formation. This requirement for SERBP1 demonstrates that Aurora B acts in concert with translational regulation in the PKCε-controlled pathway exerting genome protection.

LncRNA THRIL is involved in the proliferation, migration, and invasion of rheumatoid fibroblast-like synoviocytes

Background

Fibroblast-like synoviocytes (FLSs), which can migrate and directly invade the cartilage and the bone, are crucial players in joint damage in rheumatoid arthritis (RA). Nevertheless, the detailed mechanisms underlying the aberrant activation of RA FLSs remain unclear. Several studies have attempted to explore the relationship between long non-coding RNAs (lncRNAs) and RA pathology; however, the role of lncRNAs in RA is unknown. The present study aimed to determine the functions of tumor necrosis factor-α and heterogeneous nuclear ribonucleoprotein L-related immunoregulatory lincRNA (THRIL) in RA FLSs migration and invasion.

Methods

Small interfering RNA targeting THRIL or lentivirus overexpressing THRIL was used to knockdown or overexpress THRIL. Quantitative reverse transcription polymerase chain reaction (PCR) was employed for the detection of RNA expression. The proliferation rate of RA FLSs was measured using a 5-ethynyl-2'-deoxyuridine (EdU) incorporation assay. Migration and invasion were detected using a transwell chamber. Downstream targets were identified using a human cell cycle real-time PCR array and a human cell motility real-time PCR array.

Results

A significant decrease in THRIL expression was found in RA FLSs compared with cells from healthy control (HC)patients. THRIL is mainly localized in the nucleus. Knockdown of THRIL increased the proliferation, migration, and invasion of RA FLSs. In contrast, THRIL overexpression had the opposite effect. THRIL knockdown increased interleukin-1β (IL-1β)-triggered expression of matrix metalloproteinase (MMP)-1, MMP-3, and MMP-13. THRIL overexpression led to a significant decrease in MMP-13 expression in response to stimulation with IL-1β. Furthermore, we observed that the expression levels of cyclin-dependent kinase 1 (CDK1) and G2 and S phase-expressed-1 (GTSE1), both of which are associated with cellular mobility and proliferation, were downregulated with THRIL overexpression.

Conclusions

Reduced expression of lncRNA THRIL represses the proliferation, migration, and invasion of RA FLSs, suggesting that lncRNA THRIL might be a potential target for RA therapy.

Co-ordinated control of the Aurora B abscission checkpoint by PKCε complex assembly, midbody recruitment and retention

A requirement for PKCε in exiting from the Aurora B dependent abscission checkpoint is associated with events at the midbody, however, the recruitment, retention and action of PKCε in this compartment are poorly understood. Here, the prerequisite for 14-3-3 complex assembly in this pathway is directly linked to the phosphorylation of Aurora B S227 at the midbody. However, while essential for PKCε control of Aurora B, 14-3-3 association is shown to be unnecessary for the activity-dependent enrichment of PKCε at the midbody. This localisation is demonstrated to be an autonomous property of the inactive PKCε D532N mutant, consistent with activity-dependent dissociation. The C1A and C1B domains are necessary for this localisation, while the C2 domain and inter-C1 domain (IC1D) are necessary for retention at the midbody. Furthermore, it is shown that while the IC1D mutant retains 14-3-3 complex proficiency, it does not support Aurora B phosphorylation, nor rescues division failure observed with knockdown of endogenous PKCε. It is concluded that the concerted action of multiple independent events facilitates PKCε phosphorylation of Aurora B at the midbody to control exit from the abscission checkpoint.

Equivocal, explicit and emergent actions of PKC isoforms in cancer

The maturing mutational landscape of cancer genomes, the development and application of clinical interventions and evolving insights into tumour-associated functions reveal unexpected features of the protein kinase C (PKC) family of serine/threonine protein kinases. These advances include recent work showing gain or loss-of-function mutations relating to driver or bystander roles, how conformational constraints and plasticity impact this class of proteins and how emergent cancer-associated properties may offer opportunities for intervention. The profound impact of the tumour microenvironment, reflected in the efficacy of immune checkpoint interventions, further prompts to incorporate PKC family actions and interventions in this ecosystem, informed by insights into the control of stromal and immune cell functions. Drugging PKC isoforms has offered much promise, but when and how is not obvious.

Use of the Polo-like kinase 4 (PLK4) inhibitor centrinone to investigate intracellular signalling networks using SILAC-based phosphoproteomics

Polo-like kinase 4 (PLK4) is the master regulator of centriole duplication in metazoan organisms. Catalytic activity and protein turnover of PLK4 are tightly coupled in human cells, since changes in PLK4 concentration and catalysis have profound effects on centriole duplication and supernumerary centrosomes, which are associated with aneuploidy and cancer. Recently, PLK4 has been targeted with a variety of small molecule kinase inhibitors exemplified by centrinone, which rapidly induces inhibitory effects on PLK4 and leads to on-target centrosome depletion. Despite this, relatively few PLK4 substrates have been identified unequivocally in human cells, and PLK4 signalling outside centriolar networks remains poorly characterised. We report an unbiased mass spectrometry (MS)-based quantitative analysis of cellular protein phosphorylation in stable PLK4-expressing U2OS human cells exposed to centrinone. PLK4 phosphorylation was itself sensitive to brief exposure to the compound, resulting in PLK4 stabilisation. Analysing asynchronous cell populations, we report hundreds of centrinone-regulated cellular phosphoproteins, including centrosomal and cell cycle proteins and a variety of likely 'non-canonical' substrates. Surprisingly, sequence interrogation of ∼300 significantly down-regulated phosphoproteins reveals an extensive network of centrinone-sensitive [Ser/Thr]Pro phosphorylation sequence motifs, which based on our analysis might be either direct or indirect targets of PLK4. In addition, we confirm that NMYC and PTPN12 are PLK4 substrates, both in vitro and in human cells. Our findings suggest that PLK4 catalytic output directly controls the phosphorylation of a diverse set of cellular proteins, including Pro-directed targets that are likely to be important in PLK4-mediated cell signalling.

A cancer-associated, genome protective programme engaging PKCε

Associated with their roles as targets for tumour promoters, there has been a long-standing interest in how members of the protein kinase C (PKC) family act to modulate cell growth and division. This has generated a great deal of observational data, but has for the most part not afforded clear mechanistic insights into the control mechanisms at play. Here, we review the roles of PKCε in protecting transformed cells from non-disjunction. In this particular cell cycle context, there is a growing understanding of the pathways involved, affording biomarker and interventional insights and opportunities.