Polo‑like kinase 4 promotes tumorigenesis and induces resistance to radiotherapy in glioblastoma

Spermatocytes have the capacity to segregate chromosomes despite centriole duplication failure

Centrosomes are the canonical microtubule organizing centers (MTOCs) of most mammalian cells, including spermatocytes. Centrosomes comprise a centriole pair within a structurally ordered and dynamic pericentriolar matrix (PCM). Unlike in mitosis, where centrioles duplicate once per cycle, centrioles undergo two rounds of duplication during spermatogenesis. The first duplication is during early meiotic prophase I, and the second is during interkinesis. Using mouse mutants and chemical inhibition, we have blocked centriole duplication during spermatogenesis and determined that non-centrosomal MTOCs (ncMTOCs) can mediate chromosome segregation. This mechanism is different from the acentriolar MTOCs that form bipolar spindles in oocytes, which require PCM components, including gamma-tubulin and CEP192. From an in-depth analysis, we identified six microtubule-associated proteins, TPX2, KIF11, NuMA, and CAMSAP1-3, that localized to the non-centrosomal MTOC. These factors contribute to a mechanism that ensures bipolar MTOC formation and chromosome segregation during spermatogenesis when centriole duplication fails. However, despite the successful completion of meiosis and round spermatid formation, centriole inheritance and PLK4 function are required for normal spermiogenesis and flagella assembly, which are critical to ensure fertility.

CRISPR screens reveal convergent targeting strategies against evolutionarily distinct chemoresistance in cancer

Resistance to chemotherapy has been a major hurdle that limits therapeutic benefits for many types of cancer. Here we systematically identify genetic drivers underlying chemoresistance by performing 30 genome-scale CRISPR knockout screens for seven chemotherapeutic agents in multiple cancer cells. Chemoresistance genes vary between conditions primarily due to distinct genetic background and mechanism of action of drugs, manifesting heterogeneous and multiplexed routes towards chemoresistance. By focusing on oxaliplatin and irinotecan resistance in colorectal cancer, we unravel that evolutionarily distinct chemoresistance can share consensus vulnerabilities identified by 26 second-round CRISPR screens with druggable gene library. We further pinpoint PLK4 as a therapeutic target to overcome oxaliplatin resistance in various models via genetic ablation or pharmacological inhibition, highlighting a single-agent strategy to antagonize evolutionarily distinct chemoresistance. Our study not only provides resources and insights into the molecular basis of chemoresistance, but also proposes potential biomarkers and therapeutic strategies against such resistance.

Role of non-coding RNAs in neuroblastoma

Neuroblastoma is known as the most prevalent extracranial malignancy in childhood with a neural crest origin. It has been widely accepted that non-coding RNAs (ncRNAs) play important roles in many types of cancer, including glioma and gastrointestinal cancers. They may regulate the cancer gene network. According to recent sequencing and profiling studies, ncRNAs genes are deregulated in human cancers via deletion, amplification, abnormal epigenetic, or transcriptional regulation. Disturbances in the expression of ncRNAs may act either as oncogenes or as anti-tumor suppressor genes, and can lead to the induction of cancer hallmarks. ncRNAs can be secreted from tumor cells inside exosomes, where they can be transferred to other cells to affect their function. However, these topics still need more study to clarify their exact roles, so the present review addresses different roles and functions of ncRNAs in neuroblastoma.

Tumor-Promoting ATAD2 and Its Preclinical Challenges

ATAD2 has received extensive attention in recent years as one prospective oncogene with tumor-promoting features in many malignancies. ATAD2 is a highly conserved bromodomain family protein that exerts its biological functions by mainly AAA ATPase and bromodomain. ATAD2 acts as an epigenetic decoder and transcription factor or co-activator, which is engaged in cellular activities, such as transcriptional regulation, DNA replication, and protein modification. ATAD2 has been reported to be highly expressed in a variety of human malignancies, including gastrointestinal malignancies, reproductive malignancies, urological malignancies, lung cancer, and other types of malignancies. ATAD2 is involved in the activation of multiple oncogenic signaling pathways and is closely associated with tumorigenesis, progression, chemoresistance, and poor prognosis, but the oncogenic mechanisms vary in different cancer types. Moreover, the direct targeting of ATAD2’s bromodomain may be a very challenging task. In this review, we summarized the role of ATAD2 in various types of malignancies and pointed out the pharmacological direction.

Polo-like kinases as potential targets and PLK2 as a novel biomarker for the prognosis of human glioblastoma

The most prevalent malignant central nervous system (CNS) cancer is glioblastoma multiforme (GBM). PLKs (polo-like kinases) are a kind of serine-threonine kinase that modulate DNA replication, mitosis, and stress responses. PLKs in GBM need to be better studied and examined in terms of their expression, function, along with prognostic significance. Using an existing publicly available data set, we evaluated the expression level and prognostic relevance of PLKs in GBM patients at the molecular level. The biological processes along with cascades of the screened gene were predicted using the functional enrichment of Gene Set Enrichment Analysis, Gene Ontology, and Kyoto Encyclopedia of Genes and Genomes pathways. The data illustrated that PLK1/3/4 contents were greater in GBM tissues than in non-tumorous tissues, but PLK2/5 expression levels were lower. PLK2 expression was also linked to patient outcome in GBM. Our findings imply that PLKs might be useful molecular indicators as well as prospective treatment targets for GBM. A PLK2 inhibitor has been studied for the first time in a glioma cell in this work. In glioma cells, ON1231320 has anticancer effects. Finally, a summary of PLK inhibitors is presented, along with projections for future progress.

Identification and assessment of PLK1/2/3/4 in lung adenocarcinoma and lung squamous cell carcinoma: Evidence from methylation profile

Lung cancer is a very aggressive cancer characterized with molecular heterogeneities in different subtypes, including lung adenocarcinoma and lung squamous cell carcinoma. However, few related molecular signatures have been established for the treatment of lung cancer subtypes. Polo-like kinase (PLK) family is a crucial regulator during cell division. Aberrant genetic and epigenetic alteration of PLK members plays a controversial role among different cancers. In this study, we performed an analysis of transcriptional and protein expression to identify overexpressed PLK1/4 and under-expressed PLK2/3 in lung cancer subtypes. We then analysed biological function of PLKs and related genes. Besides, we estimated a correlation of PLKs with patient's genders and TP53 mutation in lung cancer. Higher PLK1/4 expression was significantly associated with male patient and TP53 mutant status, separately. Moreover, we carried out a methylation profile analysis including methylation level, DNA methyltransferases correlation and survival analysis of global methylation. Global methylation survival analysis showed that prognostic value of PLK1/2/4 methylation remained the same significant trend between two lung cancer subtypes, whereas prognostic value of PLK3 methylation lacked consistency. Taken together, these results provided instructive insights into a comprehensive evaluation for advanced therapeutic strategy based on epigenetic evidences.

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.

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.

CircKIF2A contributes to cell proliferation, migration, invasion and glycolysis in human neuroblastoma by regulating miR-129-5p/PLK4 axis

Multiple circular RNAs (circRNAs) have been identified to act as essential mediators in diverse human cancers. However, the roles of circRNAs in neuroblastoma (NB) are largely unknown. In this study, we aimed to explore the function of circKIF2A in NB. Quantitative real-time polymerase chain reaction was executed to detect the levels of circKIF2A, KIF2A mRNA, miR-129-5p and polo-like kinase 4 (PLK4) mRNA. Actinomycin D assay and RNase R digestion assay were conducted to analyze the feature of circKIF2A. 3-(4, 5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay, transwell assay and specific kits were utilized to evaluate cell proliferation, metastasis and glycolysis, respectively. Western blot assay was performed to examine the protein levels of matrix metalloproteinase 2 (MMP2), MMP9 and PLK4. Bioinformatics analysis, RNA pull-down assay and dual-luciferase reporter assay were conducted to analyze the relationship between miR-129-5p and circKIF2A or PLK4. Murine xenograft model assay was done to investigate the role of circKIF2A in NB in vivo. CircKIF2A level was increased in NB tissue samples and cell lines. Silencing of circKIF2A impeded NB cell proliferation, migration, invasion and glycolysis. For mechanism analysis, circKIF2A could positively modulate PLK4 expression via sponging miR-129-5p. Moreover, miR-129-5p inhibition reversed the inhibitory effects of circKIF2A silencing on the behaviors of NB cells. MiR-129-5p overexpression weakened the malignant biological behaviors of NB cells by targeting PLK4. Additionally, circKIF2A knockdown hampered tumorigenesis in vivo. CircKIF2A knockdown suppressed cell proliferation, migration, invasion and glycolysis via downregulating PLK4 expression through miR-129-5p.

SNHG16 promotes tumorigenesis and cisplatin resistance by regulating miR-338-3p/PLK4 pathway in neuroblastoma cells

Background

Long noncoding RNA small nucleolar RNA host gene 16 (lncRNA SNHG16) has been revealed to be involved in the tumorigenesis of neuroblastoma. However, the role of SNHG16 in regulating cisplatin sensitivity in neuroblastoma remains largely unknown.

Methods

The expression of SNHG16, microRNA (miR)-338-3p and polo-like kinase 4 (PLK4) mRNA was measured using quantitative real-time polymerase chain reaction. The protein levels of PLK4, multidrug resistance protein 1 (MRP1), multidrug-resistance gene 1-type p-glycoprotein (P-gp) and phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) pathway-related proteins were detected by Western blot. The half maximal inhibitory concentration (IC50) value, cell proliferation, migration and invasion were analyzed using Cell Counting Kit-8 assays or Transwell assay. Apoptotic cells were measured by Flow cytometry. The interaction between miR-338-3p and SNHG16 or PLK4 was confirmed by dual-luciferase reporter and RNA immunoprecipitation assay. In vivo experiments were conducted through the murine xenograft model.

Results

SNHG16 was up-regulated, while miR-338-3p was down-regulated in cisplatin-resistant neuroblastoma tissues and cells. SNHG16 silencing weakened cisplatin resistance, reflected by the reduction of IC50 value, down-regulation of MRP-1 and P-gp protein expression, suppression of proliferation, migration and invasion, as well as enhancement of apoptosis in SNHG16 deletion cisplatin-resistant neuroblastoma cells. Besides that, SNHG16 could regulate PLK4 expression by sponging miR-338-3p and SNHG16/miR-338-3p/PLK4 axis could affect the activation of PI3K/AKT pathway in cisplatin-resistant neuroblastoma cells. MiR-338-3p inhibition attenuated SNHG16 deletion-mediated impairment on cisplatin resistance and PLK4 overexpression reversed the decrease of cisplatin-resistance induced by miR-338-3p re-expression. Furthermore, SNHG16 knockdown contributed to the anti-tumor effect of cisplatin in neuroblastoma in vivo.

Conclusion

SNHG16 contributed to the tumorigenesis and cisplatin resistance in neuroblastoma possibly through miR-338-3p/PLK4 pathway, indicating a novel insight for overcoming chemoresistance in neuroblastoma patients.

Targeting centrosome amplification, an Achilles' heel of cancer

Due to cell-cycle dysregulation, many cancer cells contain more than the normal compliment of centrosomes, a state referred to as centrosome amplification (CA). CA can drive oncogenic phenotypes and indeed can cause cancer in flies and mammals. However, cells have to actively manage CA, often by centrosome clustering, in order to divide. Thus, CA is also an Achilles' Heel of cancer cells. In recent years, there have been many important studies identifying proteins required for the management of CA and it has been demonstrated that disruption of some of these proteins can cause cancer-specific inhibition of cell growth. For certain targets therapeutically relevant interventions are being investigated, for example, small molecule inhibitors, although none are yet in clinical trials. As the field is now poised to move towards clinically relevant interventions, it is opportune to summarise the key work in targeting CA thus far, with particular emphasis on recent developments where small molecule or other strategies have been proposed. We also highlight the relatively unexplored paradigm of reversing CA, and thus its oncogenic effects, for therapeutic gain.

Polo-like kinase 4 correlates with greater tumor size, lymph node metastasis and confers poor survival in non-small cell lung cancer

BACKGROUND

Our study aimed to investigate the association of polo-like kinase 4 (PLK4) expression with tumor features as well as survival in non-small cell lung cancer (NSCLC) patients.

METHODS

Five hundred and sixty NSCLC patients who underwent pulmonary resection were recruited, and their tumor specimens were obtained. Immunohistochemistry (IHC) staining was performed to assess PLK4 expression in tumor specimen. Follow-up documents were reviewed, and the disease-free survival (DFS) and overall survival (OS) were evaluated.

RESULTS

According to IHC staining, there were 277 (49.5%) patients with PLK4 low expression and 283 (50.5%) patients with PLK4 high expression. PLK4 high expression was further classified into three different classes: high+, high++, high+++, and 122 (21.8%), 127 (22.7%), 34 (6.1%) patients were with PLK4 high+, high++, high+++ expression, respectively. Polo-like kinase 4 expression was correlated with larger tumor size, LYN metastasis, and higher TNM stage. As for survival, DFS and OS were lower in patients with PLK4 high expression compared with patients with PLK4 low expression. In addition, DFS and OS were the lowest in patients with PLK4 high+++ expression, followed by those with PLK4 high++ expression, PLK4 high+ expression, and then patients with PLK4 low expression. Univariate and multivariate Cox's proportional hazard regression model analyses further disclosed that PLK4 was an independent predictive factor for poor DFS and OS in NSCLC patients.

CONCLUSION

Our study preliminarily illuminates the clinical implication of PLK4 in NSCLC, while further studies are still needed to explicit the value of PLK4 in surveillance and treatment of NSCLC.

Precision Revisited: Targeting Microcephaly Kinases in Brain Tumors

Glioblastoma multiforme and medulloblastoma are the most frequent high-grade brain tumors in adults and children, respectively. Standard therapies for these cancers are mainly based on surgical resection, radiotherapy, and chemotherapy. However, intrinsic or acquired resistance to treatment occurs almost invariably in the first case, and side effects are unacceptable in the second. Therefore, the development of new, effective drugs is a very important unmet medical need. A critical requirement for developing such agents is to identify druggable targets required for the proliferation or survival of tumor cells, but not of other cell types. Under this perspective, genes mutated in congenital microcephaly represent interesting candidates. Congenital microcephaly comprises a heterogeneous group of disorders in which brain volume is reduced, in the absence or presence of variable syndromic features. Genetic studies have clarified that most microcephaly genes encode ubiquitous proteins involved in mitosis and in maintenance of genomic stability, but the effects of their inactivation are particularly strong in neural progenitors. It is therefore conceivable that the inhibition of the function of these genes may specifically affect the proliferation and survival of brain tumor cells. Microcephaly genes encode for a few kinases, including CITK, PLK4, AKT3, DYRK1A, and TRIO. In this review, we summarize the evidence indicating that the inhibition of these molecules could exert beneficial effects on different aspects of brain cancer treatment.