Downregulation of PLK1 by RNAi attenuates the tumorigenicity of esophageal squamous cell carcinoma cells via promoting apoptosis and inhibiting angiogenesis

Clinicopathological and prognostic implications of polo-like kinase 1 expression in colorectal cancer: A systematic review and meta-analysis

BACKGROUND

Polo-like kinase 1 (PLK1) is a potential prognostic marker in colorectal cancer (CRC). Nevertheless, the clinicopathological and prognostic roles of PLK1 in CRC are still undefined. Therefore, we performed a meta-analysis to investigate the clinicopathological and prognostic relevance of PLK1 expression in CRC patients.

METHODS

Studies published between 2003 and 2016 were selected for the meta-analysis based on an electronic literature search (PubMed, EMBASE and Chinese databases). Studies that investigated the clinicopathological and prognostic impacts of PLK1 expression in CRC patients were included for this analysis.

RESULTS

Eleven studies that enrolled 1147 CRC patients were included in our meta-analysis. The effect of PLK1 level on overall survival (OS) was reported in five studies, which included 702 patients. Ten studies investigated the clinicopathological role of PLK1 expression in CRC patients. Consequently, PLK1 overexpression was associated with poorer OS in CRC patients. Furthermore, the results revealed that higher PLK1 levels were also observed in CRC tissues compared with that of normal colorectal tissues. In addition, this meta-analysis also revealed positive correlations between PLK1 upregulation and lymph node metastasis or invasion. PLK1 overexpression was significantly correlated with advanced TNM stages and higher Dukes stages.

CONCLUSION

This meta-analysis strongly supports the hypothesis that PLK1 might serve as an important factor in evaluating the biological behavior and prognosis of CRC.

MicroRNA-1181 supports the growth of hepatocellular carcinoma by repressing AXIN1

Micro-RNAs regulate multiple biological behaviors of cancers, making them potential targets of new cancer therapies. MiR-1181 has been demonstrated to perform oncogenic or tumor-suppressing function in a tissue-dependent way, but its role in hepatocellular carcinoma (HCC) was unclear. Here, we showed that miR-1181 was significantly overexpressed in HCC tissues when compared with tumor-adjacent normal ones or normal liver tissues from donated organ, and that inhibition of miR-1181 could repress the growth of HCC cells. Through bioinformatics analysis and luciferase reporter assays, we found that axis inhibition protein 1 (AXIN1) was a direct target of miR-1181, and the expression of AXIN1 showed a negative correlation with that of miR-1181 in HCC. Therefore, these data indicated an oncogenic function of miRNA-1181 in the development of HCC and a potential target for the clinical treatment of HCC.

Systematic characterization of BAF mutations provides insights into intracomplex synthetic lethalities in human cancers

Aberrations in genes coding for subunits of the BAF chromatin remodeling complexes are highly abundant in human cancers. Currently, it is not understood how these loss-of-function mutations contribute to cancer development and how they can be targeted therapeutically. The cancer-type-specific occurrence patterns of certain subunit mutations suggest subunit-specific effects on BAF complex function, possibly by the formation of aberrant residual complexes. Here, we systematically characterize the effects of individual subunit loss on complex composition, chromatin accessibility and gene expression in a panel of knock-out cell lines deficient for 22 BAF subunits. We observe strong, specific and sometimes discordant alterations dependent on the targeted subunit and show that these explain intra-complex co-dependencies, including the synthetic lethal interactions SMARCA4-ARID2, SMARCA4-ACTB and SMARCC1-SMARCC2. These data provide insights into the role of different BAF subcomplexes in genome-wide chromatin organization and suggest approaches to therapeutically target BAF mutant cancers.

Bioinformatic analysis of differentially expressed genes and identification of key genes in EBV-transformed lymphoblasts

Although the Epstein-Barr virus (EBV) is a well-known human oncogenic virus, its molecular mechanisms involved in the transformation of healthy human cells remain poorly understood. In this study, human lymphocytes were isolated from the peripheral blood of healthy adults, and lymphocytes were transformed in vitro by EBV. Agilent human whole genome microarrays were used to detect the differential gene expression profiles of EBV-transformed lymphoblasts and healthy peripheral blood lymphocytes (PBLs). By constructing the gene functional network of EBV-induced lymphocyte transformation, we screened out candidate key genes in this process and verified their expression levels by real-time quantitative polymerase chain reaction (RT-qPCR) and Western blot. In the EBV-transformed lymphoblasts, 2335 differentially expressed genes, including 1328 up-regulated and 1007 down-regulated, were screened out. Five candidate key genes, namely, PLK1, E2F1, PTPN11, BIRC5 and FYN were mainly screened out according to the results of LIMMA, String, Cytoscape software analysis. RT-qPCR and Western blot showed that PLK1, E2F1, PTPN11, BIRC5 genes had increased expression levels, and FYN gene was down-regulated in EBV-transformed lymphoblasts. Silencing of PLK1 gene in Raji cells could inhibit cell proliferation and invasion, and induce cell cycle arrest and apoptosis. In conclusion, PLK1, E2F1, PTPN11, BIRC5 and FYN are the candidate key molecules of EBV-transformed lymphocytes.

Helicobacter pylori promotes gastric epithelial cell survival through the PLK1/PI3K/Akt pathway

Purpose

Helicobacter pylori (H. pylori) infection plays a critical role in the process of gastric carcinogenesis. However, the complicated pathogenic mechanism is still unclear. Polo-like kinase 1 (PLK1) is involved in the development of multiple human malignancies, including gastric cancer. Therefore, this study aimed to elucidate the role of PLK1 in H. pylori-induced gastric carcinogenesis and the underlying signaling mechanism.

Materials and methods

We detected the expression of PLK1 in 166 patients in different stages of gastric carcinogenesis as well as the established Mongolian gerbil model with H. pylori infection by immunohistochemistry. Cell Counting Kit-8 was used to estimate the survival of gastric cancer cells.

Results

We found that PLK1 expression in gastric cancer tissues was significantly higher than that of paired adjacent mucosa. PLK1 expression was increased in intestinal metaplasia, dysplasia, and gastric cancer tissues compared to chronic non-atrophic gastritis tissues. Notably, PLK1 expression was much lower in H. pylori-negative tissues than in H. pylori-positive tissues at intestinal metaplasia stage. In addition, H. pylori infection increased PLK1 expression in the gastric epithelial cells of the Mongolian gerbil model, which was positively related to the duration of H. pylori infection. Inhibition of PLK1 significantly reduced H. pylori-induced cell proliferation. Furthermore, incubation of MKN-28 cells with H. pylori resulted in a significant increase in PLK1, p-PTEN, and the downstream PI3K/Akt pathway, and pretreatment with a PLK1 inhibitor reversed these molecular changes.

Conclusion

PLK1 is involved in H. pylori-induced gastric carcinogenesis at the early stage by activating the PI3K/Akt signaling pathway. These results may contribute to the development of new control strategies for H. pylori infection-related gastric cancer.

Enhancing Gene-Knockdown Efficiency of Poly(N-isopropylacrylamide) Nanogels

Polo-like-kinase 1 (PLK1), which is a serine-threonine protein kinase overexpressed in cancer cells, is known to regulate tumor growth and have recently gathered attention as a target gene for RNA interference because of the poor bioavailability and nonspecificity of the available inhibitors. However, the lower transfection efficiency of siRNA and its poor stability in biological mileu necessitate the need of efficient siRNA delivery systems. Here, we report efficacious polymeric nanoparticles for the delivery of PLK1 siRNA in mammalian cancer cells. N-Isopropylacrylamide (NIPAm) and N-isopropylmethacrylamide-co-NIPAm nanogels were synthesized and modified using poly-ε-lysine. Furthermore, their ability to induce gene silencing was investigated by flow cytometry and real-time polymerase chain reaction, and the silencing efficiency observed was related to the polymer composition and its effect on the gene loading and protection ability and the endosomal escape capability. This study attempts to leverage the understanding of the cell-material interaction, thus, addressing the bottlenecks of siRNA delivery for enhancing the efficacy of the poly(N-isopropylacrylamide)-based delivery vehicle.

GE11 peptide conjugated selenium nanoparticles for EGFR targeted oridonin delivery to achieve enhanced anticancer efficacy by inhibiting EGFR-mediated PI3K/AKT and Ras/Raf/MEK/ERK pathways

Selenium nanoparticles (Se NPs) have attracted increasing interest in recent decades because of their anticancer, immunoregulation, and drug carrier functions. In this study, GE11 peptide-conjugated Se NPs (GE11-Se NPs), a nanosystem targeting EGFR over-expressed cancer cells, were synthesized for oridonin delivery to achieve enhanced anticancer efficacy. Oridonin loaded and GE11 peptide conjugated Se NPs (GE11-Ori-Se NPs) were found to show enhanced cellular uptake in cancer cells, which resulted in enhanced cancer inhibition against cancer cells and reduced toxicity against normal cells. After accumulation into the lysosomes of cancer cells and increase of oridonin release under acid condition, GE11-Ori-Se NPs were further transported into cytoplasm after the damage of lysosomal membrane integrity. GE11-Ori-Se NPs were found to induce cancer cell apoptosis by inducting reactive oxygen species (ROS) production, activating mitochondria-dependent pathway, inhibiting EGFR-mediated PI3K/AKT and inhibiting Ras/Raf/MEK/ERK pathways. GE11-Se NPs were also found to show active targeting effects against the tumor tissue in esophageal cancer bearing mice. And in nude mice xenograft model, GE11-Ori-Se NPs significantly inhibited the tumor growth via inhibition of tumor angiogenesis by reducing the angiogenesis-marker CD31 and activation of the immune system by enhancing IL-2 and TNF-α production. The selenium contents in mice were found to accumulate into liver, tumor, and kidney, but showed no significant toxicity against liver and kidney. This cancer-targeted design of Se NPs provides a new strategy for synergistic treating of cancer with higher efficacy and reduced side effects, introducing GE11-Ori-Se NPs as a candidate for further evaluation as a chemotherapeutic agent for EGFR over-expressed esophageal cancers.

PLK1, A Potential Target for Cancer Therapy

Polo-like kinase 1 (PLK1) plays an important role in the initiation, maintenance, and completion of mitosis. Dysfunction of PLK1 may promote cancerous transformation and drive its progression. PLK1 overexpression has been found in a variety of human cancers and was associated with poor prognoses in cancers. Many studies have showed that inhibition of PLK1 could lead to death of cancer cells by interfering with multiple stages of mitosis. Thus, PLK1 is expected to be a potential target for cancer therapy. In this article, we examined PLK1’s structural characteristics, its regulatory roles in cell mitosis, PLK1 expression, and its association with survival prognoses of cancer patients in a wide variety of cancer types, PLK1 interaction networks, and PLK1 inhibitors under investigation. Finally, we discussed the key issues in the development of PLK1-targeted cancer therapy.