Direct interaction between CEP85 and STIL mediates PLK4-driven directed cell migration

circRNA-SMO upregulates CEP85 to promote proliferation and migration of glioblastoma via sponging miR-326

Circular RNAs (circRNAs) play an important role in cancer development by sponging microRNAs (miRNAs) to regulate the signaling axis. However, more comprehensive mechanisms of circRNAs in glioblastoma need to be elucidated. RT-qPCR was used to detect the expression levels of circRNA-SMO and miR-326. Dual-luciferase reporter assays were conducted to verify the interaction among circRNA-SMO, miR-326, and CEP85. Flow cytometric analysis was performed to detect apoptosis. Western blotting was used to determine the protein levels of the different molecules. Animal xenograft experiments were performed to evaluate the role of circRNA-SMO in vivo. CircRNA-SMO was upregulated in glioblastoma tissues and glioblastoma cells. CircRNA-SMO downregulation inhibited the viability and colony-forming ability of the glioblastoma cells. In addition, miR-326 was downregulated in glioblastoma cells, which was verified to sponge circRNA-SMO and interact with CEP85. Moreover, circRNA-SMO inhibition induced the elevation of miR-326 and apoptosis, accompanied by a decrease in CEP85. CircRNA-SMO knockdown-mediated tumor inhibition was prevented by an miR-326 inhibitor. Furthermore, circRNA-SMO inhibition inhibited tumor growth in vivo, accompanied by an increase in miR-326 and a decline in CEP85 in tumor tissues. Conclusions. CircRNA-SMO sponges miR-326 to promote glioblastoma proliferation and migration by upregulating CEP85 expression. This study clarified the role of circRNA-SMO in the development of glioblastoma, providing novel insights for its treatment.

Modelling the Functions of Polo-Like Kinases in Mice and Their Applications as Cancer Targets with a Special Focus on Ovarian Cancer

Polo-like kinases (PLKs) belong to a five-membered family of highly conserved serine/threonine kinases (PLK1-5) that play differentiated and essential roles as key mitotic kinases and cell cycle regulators and with this in proliferation and cellular growth. Besides, evidence is accumulating for complex and vital non-mitotic functions of PLKs. Dysregulation of PLKs is widely associated with tumorigenesis and by this, PLKs have gained increasing significance as attractive targets in cancer with diagnostic, prognostic and therapeutic potential. PLK1 has proved to have strong clinical relevance as it was found to be over-expressed in different cancer types and linked to poor patient prognosis. Targeting the diverse functions of PLKs (tumor suppressor, oncogenic) are currently at the center of numerous investigations in particular with the inhibition of PLK1 and PLK4, respectively in multiple cancer trials. Functions of PLKs and the effects of their inhibition have been extensively studied in cancer cell culture models but information is rare on how these drugs affect benign tissues and organs. As a step further towards clinical application as cancer targets, mouse models therefore play a central role. Modelling PLK function in animal models, e.g., by gene disruption or by treatment with small molecule PLK inhibitors offers promising possibilities to unveil the biological significance of PLKs in cancer maintenance and progression and give important information on PLKs' applicability as cancer targets. In this review we aim at summarizing the approaches of modelling PLK function in mice so far with a special glimpse on the significance of PLKs in ovarian cancer and of orthotopic cancer models used in this fatal malignancy.

Recent progress in agents targeting polo-like kinases: Promising therapeutic strategies

Polo-like kinases (PLKs) play important roles in regulating multiple aspects of cell cycle and cell proliferation. In many cancer types, PLK family members are often dysregulated, which can lead to uncontrolled cell proliferation and aberrant cell division and has been shown to associate with poor prognosis of cancers. The key roles of PLK kinases in cancers lead to an enhanced interest in them as promising targets for anticancer drug development. In consideration of PLK inhibitors and some other anticancer agents, such as BRD4, EEF2K and Aurora inhibitors, exert synergy effects in cancer cells, dual-targeting of PLK and other cancer-related targets is regarded as an rational and potent strategy to enhance the effectiveness of single-targeting therapy for cancer treatment. This review introduces the PLK family members at first and then focuses on the recent advances of single-target PLK inhibitors and summarizes the corresponding SARs of them. Moreover, we discuss the synergisms between PLK and other anti-tumor targets, and sum up the current dual-target agents based on them.

Role of Polo-Like Kinase 4 (PLK4) in Epithelial Cancers and Recent Progress in its Small Molecule Targeting for Cancer Management

The polo-like kinases (PLKs) are a family of serine/threonine kinases traditionally linked to cell-cycle regulation. A structurally unique member of this family, PLK4, has been shown to regulate centriole duplication during the cell cycle via interactions with a variety of centrosomal proteins. Recent findings suggest that PLK4 is overexpressed in various human cancers and associated with poor cancer prognosis. Although several studies have shown that PLK4 inhibition may lead to cancer cell death, the underlying mechanisms are largely unknown. In this review, we discuss the structure, localization, and function of PLK4, along with the functional significance of PLK4 in epithelial cancers and some preliminary work suggesting a role for PLK4 in the key cancer progression process epithelial-mesenchymal transition. We also discuss the potential of PLK4 as a druggable target for anticancer drug development based on critical analysis of the available data of PLK4 inhibitors in preclinical development and clinical trials. Overall, the emerging data suggest that PLK4 plays an essential role in epithelial cancers and should be further explored as a potential biomarker and/or therapeutic target. Continued detailed exploration of available and next-generation PLK4 inhibitors may provide a new dimension for novel cancer therapeutics following successful clinical trials.

Polo-Like Kinase 4's Critical Role in Cancer Development and Strategies for Plk4-Targeted Therapy

Polo-like kinases (Plks) are critical regulatory molecules during the cell cycle process. This family has five members: Plk1, 2, 3, 4, and 5. Plk4 has been identified as a master regulator of centriole replication, and its aberrant expression is closely associated with cancer development. In this review, we depict the DNA, mRNA, and protein structure of Plk4, and the regulation of Plk4 at a molecular level. Then we list the downstream targets of Plk4 and the hallmarks of cancer associated with these targets. The role of Plk4 in different cancers is also summarized. Finally, we review the inhibitors that target Plk4 in the hope of discovering effective anticancer drugs. From authors' perspective, Plk4 might represent a valuable tumor biomarker and critical target for cancer diagnosis and therapy.

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.

First person – Yi Liu

First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Yi Liu is first author on ‘Direct interaction between CEP85 and STIL mediates PLK4-driven directed cell migration’, published in JCS. Yi conducted the research described in this article while a PhD student in Dr Laurence Pelletier's lab at Lunenfeld-Tanenbaum Research Institute, University of Toronto, Canada. He is now a Postdoc in the lab of Dr Rudolf Jaenisch at Whitehead Institute for Biomedical Research, MIT, USA, where he uses stem cells to study complex human brain disorders.