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

PLK3 is linked with higher tumor stage and unfavorable prognosis in patients with colorectal cancer

Objective: This study intended to explore the relationship of PLK3 with prognosis in patients with colorectal cancer (CRC). Methods: PLK3 positivity was detected by immunohistochemistry in 160 patients with CRC receiving surgical resection. Results: The median tumor PLK3-positive rate was 26.5%. Tumor PLK3-positive rate was related to increased lymph node stage (p = 0.002) and tumor-node-metastasis stage (p < 0.001) of CRC. Tumor PLK3-positive rate ≥30% was related to shortened disease-free survival (p = 0.009) and overall survival (p = 0.003); tumor PLK3-positive rate ≥50% showed a stronger correlation with them (both p = 0.001), which was validated by multivariate Cox regression analyses (both p < 0.05). Conclusion: Tumor PLK3-positive rate ≥50% relates to increased tumor stage and unfavorable survival in patients with CRC.

Plk3 Enhances Cisplatin Sensitivity of Nonsmall-Cell Lung Cancer Cells through Inhibition of the PI3K/AKT Pathway via Stabilizing PTEN

Polo-like kinase 3 (Plk3) is involved in tumor development with a tumor suppressive function. However, the effect of Plk3 on the chemoresistance remains unclear. It has been documented that activation of the PI3K/AKT signaling pathway by PTEN loss significantly enhances chemoresistance in nonsmall-cell lung cancer (NSCLC). This study aims to evaluate the PTEN regulation by Plk3 and identify targets and underlying mechanisms that could be used to relieve chemoresistance. Our results showed that silencing Plk3 reduced PTEN expression and activated PI3K/AKT signaling by dephosphorylating and destabilizing PTEN in NSCLC cells. Reducing Plk3 expression promoted drug resistance to cisplatin (DDP), while overexpressing Plk3 promoted DDP sensitivity. However, these effects were attenuated when MK2206, a PI3K/AKT inhibitor, was applied. In conclusion, upregulation of Plk3 sensitized NSCLC cells toward DDP, which provides a potential target to restore DDP chemoresponse. We provided novel evidence that the PTEN/PI3K/AKT signaling pathway could be regulated by Plk3 through phosphorylation of PTEN and highlighted the critical role of Plk3 in the DDP resistance of NSCLC.

PLK1 and PARP positively correlate in Middle Eastern breast cancer and their combined inhibition overcomes PARP inhibitor resistance in triple negative breast cancer

Background

Despite advancements in treatment approaches, patients diagnosed with aggressive breast cancer (BC) subtypes typically face an unfavorable prognosis. Globally, these cancers continue to pose a significant threat to women's health, leading to substantial morbidity and mortality. Consequently, there has been a significant struggle to identify viable molecular targets for therapeutic intervention in these patients. Polo-like Kinase-1 (PLK1) represents one of these molecular targets currently undergoing rigorous scrutiny for the treatment of such tumors. Yet, its role in the pathogenesis of BC in Middle Eastern ethnicity remains unexplored.

Methods

We investigated the expression of PLK1 protein in a cohort of more than 1500 Middle Eastern ethnicity BC cases by immunohistochemistry. Association with clinicopathological parameters and prognosis were performed. In vitro studies were conducted using the PLK1 inhibitor volasertib and the PARP inhibitor olaparib, either alone or in combination, in PTC cell lines.

Results

Overexpression of PLK1 was detected in 27.4% of all BC cases, and this was notably correlated with aggressive clinicopathological markers. PLK1 was enriched in the triple-negative breast cancer (TNBC) subtype and exhibited poor overall survival (p = 0.0347). Notably, there was a positive correlation between PLK1 and PARP overexpression, with co-expression of PLK1 and PARP observed in 15.7% of cases and was associated with significantly poorer overall survival (OS) compared to the overexpression of either protein alone (p = 0.0050). In vitro, we studied the effect of PLK1 and PARP inhibitors either single or combined treatments in two BRCA mutated, and one BRCA proficient TNBC cell lines. We showed that combined inhibition significantly reduced cell survival and persuaded apoptosis in TNBC cell lines. Moreover, our findings indicate that inhibition of PLK1 can reinstate sensitivity in PARP inhibitor (PARPi) resistant TNBC cell lines.

Conclusion

Our results shed light on the role of PLK1 in the pathogenesis and prognosis of Middle Eastern BC and support the potential clinical development of combined inhibition of PLK1 and PARP, a strategy that could potentially broaden the use of PLK1 and PARP inhibitors beyond BC cases lacking BRCA.

Inhibition of PLK4 remodels histone methylation and activates the immune response via the cGAS-STING pathway in TP53-mutated AML

Acute myeloid leukemia (AML) with TP53 mutation is one of the most lethal cancers and portends an extremely poor prognosis. Based on in silico analyses of druggable genes and differential gene expression in TP53-mutated AML, we identified pololike kinase 4 (PLK4) as a novel therapeutic target and examined its expression, regulation, pathogenetic mechanisms, and therapeutic potential in TP53-mutated AML. PLK4 expression was suppressed by activated p53 signaling in TP53 wild-type AML and was increased in TP53-mutated AML cell lines and primary samples. Short-term PLK4 inhibition induced DNA damage and apoptosis in TP53 wild-type AML. Prolonged PLK4 inhibition suppressed the growth of TP53-mutated AML and was associated with DNA damage, apoptosis, senescence, polyploidy, and defective cytokinesis. A hitherto undescribed PLK4/PRMT5/EZH2/H3K27me3 axis was demonstrated in both TP53 wild-type and mutated AML, resulting in histone modification through PLK4-induced PRMT5 phosphorylation. In TP53-mutated AML, combined effects of histone modification and polyploidy activated the cGAS-STING pathway, leading to secretion of cytokines and chemokines and activation of macrophages and T cells upon coculture with AML cells. In vivo, PLK4 inhibition also induced cytokine and chemokine expression in mouse recipients, and its combination with anti-CD47 antibody, which inhibited the "don't-eat-me" signal in macrophages, synergistically reduced leukemic burden and prolonged animal survival. The study shed important light on the pathogenetic role of PLK4 and might lead to novel therapeutic strategies in TP53-mutated AML.

Characteristics and prognostic significance of polo-like kinase-1 (PLK1) expression in breast cancer

AIM

Polo-like kinase-1 (PLK1) plays a crucial role in cell cycle progression, and it is considered a potential therapeutic target in many cancers. Although the role of PLK1 is well established in triple-negative breast cancer (TNBC) as an oncogene, its role in luminal BC is still controversial. In this study, we aimed to evaluate the prognostic and predictive role of PLK1 in BC and its molecular subtypes.

METHODS

A large BC cohort (n = 1208) were immunohistochemically stained for PLK1. The association with clinicopathological, molecular subtypes, and survival data was analysed. PLK1 mRNA was evaluated in the publicly available datasets (n = 6774), including The Cancer Genome Atlas and the Kaplan-Meier Plotter tool.

RESULTS

20% of the study cohort showed high cytoplasmic PLK1 expression. High PLK1 expression was significantly associated with a better outcome in the whole cohort, luminal BC. In contrast, high PLK1 expression was associated with a poor outcome in TNBC. Multivariate analyses indicated that high PLK1 expression is independently associated with longer survival in luminal BC, and in poorer prognosis in TNBC. At the mRNA levels, PLK1 expression was associated with short survival in TNBC consistent with the protein expression. However, in luminal BC, its prognostic value significantly varies between cohorts.

CONCLUSION

The prognostic role of PLK1 in BC is molecular subtype-dependent. As PLK1 inhibitors are introduced to clinical trials for several cancer types, our study supports evaluation of the pharmacological inhibition of PLK1 as an attractive therapeutic target in TNBC. However, in luminal BC, PLK1 prognostic role remains controversial.

Comprehensive analysis of PLKs expression and prognosis in breast cancer

OBJECTIVE

A thorough examination of PLKs in breast cancer, including their expression and prognosis.

METHODS

With the help of the Oncomine database, the transcript levels of PLKs in breast cancer were examined. The changes in PLKs expression with tumor stage and indeed the relationship between PLKs expression and stage of cancer in women with breast cancer were scrutinized by using the GEPIA database. Based on Kaplan-Meier plots, breast cancer patients were assessed for their prognosis. Breast cancer gene expression and mutations were analyzed within the cBioPortal database.

RESULTS

According to Oncomine data, PLK1 and PLK4 mRNA expression levels were dramatically elevated in breast cancer patients while PLK2 and PLK5P levels were significantly downregulated. PLK1 and PLK4 expression were discovered to be greater in breast cancer tissues than in healthy tissues following analysis of the GEPIA database (P < 0.05). High levels of PLK1 and PLK4 transcripts have been linked to poor relapse-free survival rates across all patients with breast cancer according to the Kaplan-Meier Plotter database. The high levels of PLK2, PLK3, and PLK5 were associated with a higher recurrence-free survival rate. In the cBioPortal database, PLK was altered in 9.6% of breast cancer samples. Genetic alterations occurred in 15.07% of clinically counted invasive breast cancers, with mutations in 4.11%, gene amplifications in 9.59%, and gene deletion mutations in 1.37%. Additionally, the KEGG database demonstrates that PLKs are crucial for the cell cycle. The findings imply that elevated PLK1 and PLK4 expression in tissues of breast cancer might contribute significantly to the carcinogenesis of breast cancer. Moreover, PLK1 and PLK4 are highly expressed in breast cancer, and their use as molecular markers to identify high-risk subsets from patients with breast cancer is potentially possible.

CONCLUSIONS

For the precise therapy of breast cancers, PLK1 and PLK4 are potential targets, while PLK2, PLK3, and PLK5 are brand-new biomarkers for predicting the prognosis of breast cancer.

Polo-Like Kinase 2: From Principle to Practice

Polo-like kinase (PLK) 2 is an evolutionarily conserved serine/threonine kinase that shares the n-terminal kinase catalytic domain and the C-terminal Polo Box Domain (PBD) with other members of the PLKs family. In the last two decades, mounting studies have focused on this and tried to clarify its role in many aspects. PLK2 is essential for mitotic centriole replication and meiotic chromatin pairing, synapsis, and crossing-over in the cell cycle; Loss of PLK2 function results in cell cycle disorders and developmental retardation. PLK2 is also involved in regulating cell differentiation and maintaining neural homeostasis. In the process of various stimuli-induced stress, including oxidative and endoplasmic reticulum, PLK2 may promote survival or apoptosis depending on the intensity of stimulation and the degree of cell damage. However, the role of PLK2 in immunity to viral infection has been studied far less than that of other family members. Because PLK2 is extensively and deeply involved in normal physiological functions and pathophysiological mechanisms of cells, its role in diseases is increasingly being paid attention to. The effect of PLK2 in inhibiting hematological tumors and fibrotic diseases, as well as participating in neurodegenerative diseases, has been gradually recognized. However, the research results in solid organ tumors show contradictory results. In addition, preliminary studies using PLK2 as a disease predictor and therapeutic target have yielded some exciting and promising results. More research will help people better understand PLK2 from principle to practice.

Balancing the scales: fine-tuning Polo-like kinase 4 to ensure proper centriole duplication

Polo-like kinase 4 (Plk4) is the master regulator of centriole assembly. Several evolutionarily conserved mechanisms strictly regulate Plk4 abundance and activity to ensure cells maintain a proper number of centrioles. In this issue of Genes & Development, Phan et al. (pp. 718-736) add to this growing list by describing a new mechanism of control that restricts Plk4 translation through competitive ribosome binding at upstream open reading frames (uORFs) in the mature Plk4 mRNA. Fascinatingly, this mechanism is especially critical in the development of primordial germ cells in mice that are transcriptionally hyperactive and thus exquisitely sensitive to Plk4 mRNA regulation.

Inhibition of Polo-like Kinase 1 by HMN-214 Blocks Cell Cycle Progression and Inhibits Neuroblastoma Growth

Polo-like kinase 1 (PLK1) is an essential cell cycle mitotic kinase component that plays an important role in cell cycle progression and has been reported to be involved in various cancers, including neuroblastoma (NB). PLK1 also regulates G2/M transition, chromosomal segregation, spindle assembly maturation, and mitotic exit. NB is an early embryonic-stage heterogeneous solid tumor and accounts for 15% of all pediatric cancer-related deaths. Therefore, we aimed to develop a targeting strategy for PLK1 by repurposing HMN-214 in NB. HMN-214 is a prodrug of HMN-176 and is known to selectively interfere with PLK1 function. In the present study, we performed the transcriptomic analysis of a large cohort of primary NB patient samples and revealed that PLK1 expression is inversely correlated with the overall survival of NB patients. Additionally, we found that PLK1 strongly correlates with NB disease and stage progression. HMN-214 significantly inhibited NB proliferation and colony formation in both MYCN-amplified and -nonamplified cell lines in a dose-dependent manner. Furthermore, HMN-214 induces apoptosis and significantly obstructs the cell cycle at the G2/M phase in NB cells by inhibiting multiple cell-cycle-related genes, such as PLK1, WEE1, CDK1, CDK2, Cyclin B1, CHK1, and CHK2. HMN-214 significantly inhibits cell cycle regulator CDK1 and the phosphorylation and activation of PLK1 in NB. In the NB 3D spheroid tumor model, HMN-214 significantly and in a dose-dependent manner inhibits spheroid tumor mass and growth. Overall, our study highlights that targeting PLK1 using HMN-214 is a novel therapeutic approach for NB.

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.