Overexpression of Plk1 promotes malignant progress in human esophageal squamous cell carcinoma

Therapeutic implications of signaling pathways and tumor microenvironment interactions in esophageal cancer

Esophageal cancer (EC) is significantly influenced by the tumor microenvironment (TME) and altered signaling pathways. Downregulating these pathways in EC is essential for suppressing tumor development, preventing metastasis, and enhancing therapeutic outcomes. This approach can increase tumor sensitivity to treatments, enhance patient outcomes, and inhibit cancer cell proliferation and spread. The TME, comprising cellular and non-cellular elements surrounding the tumor, significantly influences EC's development, course, and treatment responsiveness. Understanding the complex relationships within the TME is crucial for developing successful EC treatments. Immunotherapy is a vital TME treatment for EC. However, the heterogeneity within the TME limits the application of anticancer drugs outside clinical settings. Therefore, identifying reliable microenvironmental biomarkers that can detect therapeutic responses before initiating therapy is crucial. Combining approaches focusing on EC signaling pathways with TME can enhance treatment outcomes. This integrated strategy aims to interfere with essential signaling pathways promoting cancer spread while disrupting factors encouraging tumor development. Unraveling aberrant signaling pathways and TME components can lead to more focused and efficient treatment approaches, identifying specific cellular targets for treatments. Targeting the TME and signaling pathways may reduce metastasis risk by interfering with mechanisms facilitating cancer cell invasion and dissemination. In conclusion, this integrative strategy has significant potential for improving patient outcomes and advancing EC research and therapy. This review discusses the altered signaling pathways and TME in EC, focusing on potential future therapeutics.

Integrative ontology and pathway-based approach identifies distinct molecular signatures in transcriptomes of esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) remains a serious concern globally due to many factors that including late diagnosis, lack of an ideal biomarker for diagnosis and prognosis, and high rate of mortality. In this study, we aimed to identify the essential dysregulated genes and molecular signatures associated with the progression and development of ESCC. The dataset with 15 ESCCs and the 15 adjacent normal tissue samples from the surrounding histopathologically tumor-free mucosa was selected. We applied bioinformatics pipelines including various topological parameters from MCODE, CytoNCA, and cytoHubba to prioritize the most significantly associated DEGs with ESCC. We performed functional enrichment annotation for the identified DEGs using DAVID and MetaCore™ GeneGo platforms. Furthermore, we validated the essential core genes in TCGA and GTEx datasets between the normal mucosa and ESCC for their expression levels. These DEGs were primarily enriched in positive regulation of transferase activity, negative regulation of organelle organization, cell cycle mitosis/S-phase transition, spindle organization/assembly, development, and regulation of angiogenesis. Subsequently, the DEGs were associated with the pathways such as oocyte meiosis, cell cycle, and DNA replication. Our study identified the eight-core genes (AURKA, AURKB, MCM2, CDC20, TPX2, PLK1, FOXM1, and MCM7) that are highly expressed among the ESCC, and TCGA dataset. The multigene comparison and principal component analysis resulted in elevated signals for the AURKA, MCM2, CDC20, TPX2, PLK1, and FOXM1. Overall, our study reported GO profiles and molecular signatures that might help researchers to grasp the pathological mechanisms underlying ESCC development and eventually provide novel therapeutic and diagnostic strategies.

Dehydrocostus Lactone Induces Apoptosis and Cell Cycle Arrest through Regulation of JAK2/STAT3/PLK1 Signaling Pathway in Human Esophageal Squamous Cell Carcinoma Cells

BACKGROUND

Dehydrocostus lactone (DEH), one of the sesquiterpene lactones, has shown extensive pharmaceutical activities, including anti-cancer activity. However, its effects on human esophageal squamous cell carcinoma (ESCC) cells still unknown.

OBJECTIVE

To investigate the effect of DEH on ESCC cells and the underling molecular mechanisms.

METHOD

The cell proliferation was tested using CCK-8 and colony formation assay. Apoptosis was analyzed by flow cytometry, hoechst staining and caspase-3 activity assay. Cell cycle was analyzed by flow cytometry. IL-6 (STAT3 activator) was used to activate JAK2/STAT3 pathway. Immunofluorescence assay was performed to detect intracellular location of STAT3. SiRNA transfection was performed to knock down the expression of PLK1. The protein expression was analyzed by western blotting assay.

RESULT

DHE treatment significantly reduced the viability of ESCC cells through apoptosis induction and cell cycle arrest. Furthermore, DHE treatment significantly inhibited the phosphorylation of JAK2 and STAT3. IF assay showed that distribution of STAT3 in nucleus was decreased by DHE treatment. In addition, coculture with IL-6 significantly prevented the inhibition of phosphorylation of JAK2 and STAT3 by DHE treatment, and partly reversed the effect of DHE on ESCC cells. Moreover, DHE treatment significantly down-regulated the expression of PLK1, which was partly reversed by IL-6 coculture. Finally, knock down of PLK1 using siRNA reduced the viability of ESCC cells and induced apoptosis and cell cycle arrest.

CONCLUSION

our study demonstrated that DHE have potent anti-cancer effect on ESCC cells through apoptosis induction and cell cycle arrest via JAK2/STAT3/PLK signaling pathway.

CDC2 Is an Important Driver of Vascular Smooth Muscle Cell Proliferation via FOXM1 and PLK1 in Pulmonary Arterial Hypertension

A key feature of pulmonary arterial hypertension (PAH) is the hyperplastic proliferation exhibited by the vascular smooth muscle cells from patients (HPASMC). The growth inducers FOXM1 and PLK1 are highly upregulated in these cells. The mechanism by which these two proteins direct aberrant growth in these cells is not clear. Herein, we identify cyclin-dependent kinase 1 (CDK1), also termed cell division cycle protein 2 (CDC2), as having a primary role in promoting progress of the cell cycle leading to proliferation in HPASMC. HPASMC obtained from PAH patients and pulmonary arteries from Sugen/hypoxia rats were investigated for their expression of CDC2. Protein levels of CDC2 were much higher in PAH than in cells from normal donors. Knocking down FOXM1 or PLK1 protein expression with siRNA or pharmacological inhibitors lowered the cellular expression of CDC2 considerably. However, knockdown of CDC2 with siRNA or inhibiting its activity with RO-3306 did not reduce the protein expression of FOXM1 or PLK1. Expression of CDC2 and FOXM1 reached its maximum at G1/S, while PLK1 reached its maximum at G2/M phase of the cell cycle. The expression of other CDKs such as CDK2, CDK4, CDK6, CDK7, and CDK9 did not change in PAH HPASMC. Moreover, inhibition via Wee1 inhibitor adavosertib or siRNAs targeting Wee1, Myt1, CDC25A, CDC25B, or CDC25C led to dramatic decreases in CDC2 protein expression. Lastly, we found CDC2 expression at the RNA and protein level to be upregulated in pulmonary arteries during disease progression Sugen/hypoxia rats. In sum, our present results illustrate that the increased expression of FOXM1 and PLK1 in PAH leads directly to increased expression of CDC2 resulting in potentiated growth hyperactivity of PASMC from patients with pulmonary hypertension. Our results further suggest that the regulation of CDC2, or associated regulatory proteins, will prove beneficial in the treatment of this disease.

Polo-like Kinase 1 as an emerging drug target: structure, function and therapeutic implications

Polo-like kinase 1 (PLK1) is a conserved mitotic serine-threonine protein kinase, functions as a regulatory protein, and is involved in the progression of the mitotic cycle. It plays important roles in the regulation of cell division, maintenance of genome stability, in spindle assembly, mitosis, and DNA-damage response. PLK1 is consist of a N-terminal serine-threonine kinase domain, and a C-terminal Polo-box domain (regulatory site). The expression of PLK1 is controlled by transcription repressor in the G1 stage and transcription activators in the G2 stage of the cell cycle. Overexpression of PLK1 results in undermining of checkpoints causes excessive cellular division resulting in abnormal cell growth, leading to the development of cancer. Blocking the expression of PLK1 by an antibody, RNA interference, or kinase inhibitors, causes a subsequent reduction in the proliferation of tumour cells and induction of apoptosis in tumour cells without affecting the healthy cells, suggesting an attractive target for drug development. In this review, we discuss detailed information on expression, gene and protein structures, role in different diseases, and progress in the design and development of PLK1 inhibitors. We have performed an in-depth analysis of the PLK1 inhibitors and their therapeutic implications with special focus to the cancer therapeutics.

The CINs of Polo-Like Kinase 1 in Cancer

Simple Summary

Many alterations specific to cancer cells have been investigated as targets for targeted therapies. Chromosomal instability is a characteristic of nearly all cancers that can limit response to targeted therapies by ensuring the tumor population is not genetically homogenous. Polo-like Kinase 1 (PLK1) is often up regulated in cancers and it regulates chromosomal instability extensively. PLK1 has been the subject of much pre-clinical and clinical studies, but thus far, PLK1 inhibitors have not shown significant improvement in cancer patients. We discuss the numerous roles and interactions of PLK1 in regulating chromosomal instability, and how these may provide an avenue for identifying targets for targeted therapies. As selective inhibitors of PLK1 showed limited clinical success, we also highlight how genetic interactions of PLK1 may be exploited to tackle these challenges.

Abstract

Polo-like kinase 1 (PLK1) is overexpressed near ubiquitously across all cancer types and dysregulation of this enzyme is closely tied to increased chromosomal instability and tumor heterogeneity. PLK1 is a mitotic kinase with a critical role in maintaining chromosomal integrity through its function in processes ranging from the mitotic checkpoint, centrosome biogenesis, bipolar spindle formation, chromosome segregation, DNA replication licensing, DNA damage repair, and cytokinesis. The relation between dysregulated PLK1 and chromosomal instability (CIN) makes it an attractive target for cancer therapy. However, clinical trials with PLK1 inhibitors as cancer drugs have generally displayed poor responses or adverse side-effects. This is in part because targeting CIN regulators, including PLK1, can elevate CIN to lethal levels in normal cells, affecting normal physiology. Nevertheless, aiming at related genetic interactions, such as synthetic dosage lethal (SDL) interactions of PLK1 instead of PLK1 itself, can help to avoid the detrimental side effects associated with increased levels of CIN. Since PLK1 overexpression contributes to tumor heterogeneity, targeting SDL interactions may also provide an effective strategy to suppressing this malignant phenotype in a personalized fashion.

Molecular Weight-Dependent Activity of Aminated Poly(α)glutamates as siRNA Nanocarriers

RNA interference (RNAi) can contribute immensely to the area of personalized medicine by its ability to target any gene of interest. Nevertheless, its clinical use is limited by lack of efficient delivery systems. Polymer therapeutics can address many of the challenges encountered by the systemic delivery of RNAi, but suffer from inherent drawbacks such as polydispersity and batch to batch heterogeneity. These characteristics may have far-reaching consequences when dealing with therapeutic applications, as both the activity and the toxicity may be dependent on the length of the polymer chain. To investigate the consequences of polymers' heterogeneity, we have synthesized two batches of aminated poly(α)glutamate polymers (PGAamine), differing in their degree of polymerization, but not in the monomer units or their conjugation. Isothermal titration calorimetry study was conducted to define the binding affinity of these polymers with siRNA. Molecular dynamics simulation revealed that Short PGAamine:siRNA polyplexes exposed a higher amount of amine moieties to the surroundings compared to Long PGAamine. This resulted in a higher zeta potential, leading to faster degradation and diminished gene silencing. Altogether, our study highlights the importance of an adequate physico-chemical characterization to elucidate the structure⁻function-activity relationship, for further development of tailor-designed RNAi delivery vehicles.

Novel compounds with potent CDK9 inhibitory activity for the treatment of myeloma

Cyclin-dependent kinases (CDKs) and Polo-like kinases (PLKs) play key role in the regulation of the cell cycle. The aim of our study was originally the further development of our recently discovered polo-like kinase 1 (PLK1) inhibitors. A series of new 2,4-disubstituted pyrimidine derivatives were synthesized around the original hit, but their PLK1 inhibitory activity was very poor. However the novel compounds showed nanomolar CDK9 inhibitory activity and very good antiproliferative effect on multiple myeloma cell lines (RPMI-8226).

Cross Talk between Wnt/β-Catenin and CIP2A/Plk1 Signaling in Prostate Cancer: Promising Therapeutic Implications

Aberrant activation of the Wnt/β-catenin pathway and polo-like kinase 1 (Plk1) overexpression represent two common events in prostate cancer with relevant functional implications. This minireview analyzes their potential therapeutic significance in prostate cancer based on their role as androgen receptor (AR) signaling regulators and the pivotal role of the tumor suppressor protein phosphatase 2A (PP2A) modulating these pathways.

Unconventional Functions of Mitotic Kinases in Kidney Tumorigenesis

Human tumors exhibit a variety of genetic alterations, including point mutations, translocations, gene amplifications and deletions, as well as aneuploid chromosome numbers. For carcinomas, aneuploidy is associated with poor patient outcome for a large variety of tumor types, including breast, colon, and renal cell carcinoma. The Renal cell carcinoma (RCC) is a heterogeneous carcinoma consisting of different histologic types. The clear renal cell carcinoma (ccRCC) is the most common subtype and represents 85% of the RCC. Central to the biology of the ccRCC is the loss of function of the Von Hippel–Lindau gene, but is also associated with genetic instability that could be caused by abrogation of the cell cycle mitotic spindle checkpoint and may involve the Aurora kinases, which regulate centrosome maturation. Aneuploidy can also result from the loss of cell–cell adhesion and apical–basal cell polarity that also may be regulated by the mitotic kinases (polo-like kinase 1, casein kinase 2, doublecortin-like kinase 1, and Aurora kinases). In this review, we describe the “non-mitotic” unconventional functions of these kinases in renal tumorigenesis.

FOXM1 and polo-like kinase 1 are co-ordinately overexpressed in patients with gastric adenocarcinomas

BACKGROUND

Gastric cancers present late in life with advanced disease and carry a poor prognosis. Polo-like Kinase 1 (PLK1) is a mitotic kinase with regulatory functions during G2/M and mitosis in the cell cycle. In mammalian cells, there is an intricate co-regulatory relationship between PLK1 and the forkhead transcription factor FOXM1. It has been demonstrated that individually either PLK1 or FOXM1 expression predicts poorer survival. However, the co-expression of both of these markers in gastric adenocarcinomas has not been reported previously.

METHODS

We aimed to assess the expression of PLK1 and FOXM1 in Gastric adenocarcinomas in a Western Population, to examine whether there is a relationship of PLK1 to FOXM1 in cancer samples. We assess both the protein and mRNA expression in this patient population by Tissue Microarray immunohistochemistry and RT-PCR.

RESULTS

Immunohistochemistry was performed on biopsy samples from 79 patients with gastric cancer. Paired normal controls were available in 47 patients. FOXM1 expression was significantly associated with gastric adenocarcinoma (p = 0.001). PLK1 and FOXM1 co-expression was demonstrated in 6/8 (75 %) tumours when analysed by RT-PCR. FOXM1 is overexpressed in a large proportion of gastric carcinomas at the protein level and FOXM1 and PLK1 are concomitantly overexpressed at the mRNA level in this cancer type.

CONCLUSIONS

This study has demonstrated that FOXM1 and its target gene PLK1 are coordinately overexpressed in a proportion of gastric adenocarcinomas. This suggests that chemotherapeutic treatments that target this pathway may be of clinical utility.

SCF(FBXW7α) modulates the intra-S-phase DNA-damage checkpoint by regulating Polo like kinase-1 stability

The intra-S-checkpoint is essential to control cell progression through S phase under normal conditions and in response to replication stress. When DNA lesions are detected, replication fork progression is blocked allowing time for repair to avoid genomic instability and the risk of cancer. DNA replication initiates at many origins of replication in eukaryotic cells, where a series of proteins form pre-replicative complexes (pre-RCs) that are activated to become pre-initiation complexes and ensure a single round of replication in each cell cycle. PLK1 plays an important role in the regulation of DNA replication, contributing to the regulation of pre-RCs formation by phosphorylating several proteins, under both normal and stress conditions. Here we report that PLK1 is ubiquitinated and degraded by SCFFBXW7α/proteasome. Moreover, we identified a new Cdc4 phosphodegron in PLK1, conserved from yeast to humans, whose mutation prevents PLK1 destruction. We established that endogenous SCFFBXW7α degrades PLK1 in the G1 and S phases of an unperturbed cell cycle and in S phase following UV irradiation. Furthermore, we showed that FBXW7α overexpression or UV irradiation prevented the loading of proteins onto chromatin to form pre-RCs and, accordingly, reduced cell proliferation. We conclude that PLK1 degradation mediated by SCFFBXW7α modulates the intra-S-phase checkpoint.

DNA-PKcs associates with PLK1 and is involved in proper chromosome segregation and cytokinesis

Accurate mitotic regulation is as important as intrinsic DNA repair for maintaining genomic stability. It is believed that these two cellular mechanisms are interconnected with DNA damage. DNA-PKcs is a critical component of the non-homologous end-joining pathway of DNA double-stranded break repair, and it was recently discovered to be involved in mitotic processing. However, the underlying mechanism of DNA-PKcs action in mitotic control is unknown. Here, we demonstrated that depletion of DNA-PKcs led to the dysregulation of mitotic progression in response to DNA damage, which eventually resulted in multiple failures, including failure to segregate sister chromatids and failure to complete cytokinesis, with daughter cells becoming fused again. The depletion of DNA-PKcs resulted in a notable failure of cytokinesis, with a high incidence of multinucleated cells. There were also cytoplasmic bridges containing DNA that continuously connected the daughter cells after DNA damage was induced. Phosphorylated DNA-PKcs (T2609) colocalizes with PLK1 throughout mitosis, including at the centrosomes from prophase to anaphase and at the kinetochores from prometaphase to metaphase, with accumulation at the midbody during cytokinesis. Importantly, DNA-PKcs was found to associate with PLK1 in the mitotic phase, and the depletion of DNA-PKcs resulted in the overexpression of PLK1 due to increased protein stability. However, deficiency in DNA-PKcs attenuated the recruitment of phosphorylated PLK1 to the midbody but not to the kinetochores and centrosomes. Our results demonstrate the functional association of DNA-PKcs with PLK1, especially in chromosomal segregation and cytokinesis control.

The FOXM1-PLK1 axis is commonly upregulated in oesophageal adenocarcinoma

BACKGROUND

The transcription factor FOXM1 is an important regulator of the cell cycle through controlling periodic gene expression during the G2 and M phases. One key target for FOXM1 is the gene encoding the protein kinase PLK1 and PLK1 itself acts in a positive feedback loop to phosphorylate and activate FOXM1. Both FOXM1 and PLK1 have been shown to be overexpressed in a variety of different tumour types.

METHODS

We have used a combination of RT-PCR, western blotting, tissue microarrays and metadata analysis of microarray data to study whether the FOXM1-PLK1 regulatory axis is upregulated and operational in oesophageal adenocarcinoma.

RESULTS

FOXM1 and PLK1 are expressed in oesophageal adenocarcinoma-derived cell lines and demonstrate cross-regulatory interactions. Importantly, we also demonstrate the concomitant overexpression of FOXM1 and PLK1 in a large proportion of oesophageal adenocarcinoma samples. This co-association was extended to the additional FOXM1 target genes CCNB1, AURKB and CKS1. In a cohort of patients who subsequently underwent surgery, the expression of several FOXM1 target genes was prognostic for overall survival.

CONCLUSIONS

FOXM1 and its target gene PLK1 are commonly overexpressed in oesophageal adenocarcinomas and this association can be extended to other FOXM1 target genes, providing potentially important biomarkers for predicting post-surgery disease survival.

Phosphorylation of Tara by Plk1 is essential for faithful chromosome segregation in mitosis

Trio-associated repeat on actin (Tara) is an F-actin binding protein and regulates actin cytoskeletal organization. In our previous study, we have found that Tara associates with telomeric repeat binding factor 1 (TRF1) and mediates the function of TRF1 in mitotic regulation. We also found that overexpression HECTD3, a member of HECT E3 ubiquitin ligases, enhances the ubiquitination of Tara in vivo and promotes the degradation of Tara, and such degradation of Tara facilitates cell cycle progression. However, less is known about the post-translational modification of Tara in mitosis. Here we show that Tara is a novel Polo-like kinase 1 (Plk1) target protein. Plk1 interacts with and phosphorylates Tara in vivo and in vitro. Actually, the Thr-457 in Tara was a bona fide in vivo phosphorylation site for Plk1. Interestingly, we found that the centrosomal localization of Tara depended on the Thr-457 phosphorylation and the kinase activity of Plk1. Furthermore, overexpression of non-phosphorylatable mutant of Tara caused aberrant mitosis delay in HeLa cells. Our study demonstrated that Plk1-mediated phospho-dependent centrosomal localization of Tara is important for faithful chromosome segregation, and provided novel insights into understanding on the role of Plk1 in cooperation with Tara in mitotic progression.

PLK1 gene suppresses cell invasion of undifferentiated thyroid carcinoma through the inhibition of CD44v6, MMP-2 and MMP-9

The aim of this study was to observe the regulatory action of the polo-like kinase 1 (PLK1) gene in the invasion of anaplastic thyroid carcinoma cells and investigate its mechanisms. The expression of the PLK1 protein in 36 patients with anaplastic thyroid carcinoma was detected by immunohistochemical staining. siRNA against PLK1 was designed, synthesized and transfected into ARO cells. The effects of PLK1 siRNA on cell invasion were detected by a soft agar colony formation assay and a Transwell chamber assay. The corresponding protein was detected using western blot analysis. The expression of PLK1 in anaplastic thyroid carcinoma samples (67.5±10.6%) was significantly higher compared to that in cancer-adjacent samples (0.65%±0.12%; P<0.01). The expression of PLK1 correlated with clinical stage, lymph node metastasis and prognosis of anaplastic thyroid. The number of cell clones was reduced in a dose-dependent manner with increasing levels of siRNA and the number of cells permeating through the filter membrane decreased following transfection with siRNA. The inhibition of PLK1 caused a significant decrease in CD44v6, matrix metalloproteinase (MMP)-2 and MMP-9 (0.36±0.08, 0.12±0.03, 0.25±0.06, respectively) compared to the non-transfected group (1.15±0.18, 1.21±0.20, 1.25±0.21, respectively; P<0.01). In conclusion, the expression of PLK1 was found to be increased in anaplastic thyroid carcinoma and was correlated with clinical stage, lymph node metastasis and prognosis. Additionaly, PLK1 siRNA was found to inhibit the invasion of anaplastic thyroid carcinoma cells. Therefore, CD44v6, MMP-2 and MMP-9 are likely to be involved in the regulation of cell invasion induced by PLK1.

Overexpression of polo-like kinase 1 and its clinical significance in human non-small cell lung cancer

Polo-like kinase 1 is a serine/threonine kinase which plays an essential role in mitosis and malignant transformation. The aim of this study was to investigate the prognostic significance of polo-like kinase 1 expression and determine its possibility as a therapeutic target in non-small cell lung cancer. Semi-quantitative RT-PCR assay was performed to detect polo-like kinase 1 mRNA expression in non-small cell lung cancer cells or tissues. Immunohistochemistry was performed to detect polo-like kinase 1 protein expression in 100 non-small cell lung cancer tissue samples, and the associations of polo-like kinase 1 expression with clinicopathological factors or prognosis of non-small cell lung cancer patients were evaluated. RNA interference was employed to inhibit endogenous polo-like kinase 1 expression and analyzed the effects of polo-like kinase 1 inhibition on the malignant phenotypes of non-small cell lung cancer cells including growth, apoptosis, radio- or chemoresistance. Also, the possible molecular mechanisms were also investigated. The levels of polo-like kinase 1 mRNA expression in non-small cell lung cancer cell lines or tissues were significantly higher than those in normal human bronchial epithelial cell line or corresponding non-tumor tissues. High polo-like kinase 1 expression was significantly correlated with advanced clinical stage, higher tumor classification and lymph node metastasis of non-small cell lung cancer patients (P=0.001, 0.004 and 0.001, respectively). Meanwhile, high polo-like kinase 1 protein expression was also an independent prognostic molecular marker for non-small cell lung cancer patients (hazard ratio: 2.113; 95% confidence interval: 1.326-3.557; P=0.017). Polo-like kinase 1 inhibition could significantly inhibit in vitro and in vivo proliferation, induce cell arrest of G(2)/M phase and apoptosis enhancement in non-small cell lung cancer cells, which might be activation of the p53 pathway and the Cdc25C/cdc2/cyclin B1 feedback loop. Further, inhibition of polo-like kinase 1 could enhance the sensitivity of non-small cell lung cancer cells to taxanes or irradiation. Thus, polo-like kinase 1 might be a prognostic marker and a chemo- or radiotherapeutic target for non-small cell lung cancer.

Efficient inhibition of human colorectal carcinoma growth by RNA interference targeting polo-like kinase 1 in vitro and in vivo

Polo-like kinase 1 (PLK1) showing a high expression in various kinds of tumors is considered a candidate target for cancer therapy. The aim of our study was to explore the effects of silencing PLK1 gene on human colorectal carcinoma cell line HCT-116 in vitro and in vivo. In vitro, the plasmids generating short hairpin RNA (shRNA)-targeting PLK1 were transfected into HCT-116 by using FugeneHD reagent, and the silencing potency was measured by RT-PCR, western blot, flow cytometry, and Caspase-Glo 3/7 assay, respectively. In vivo, the growth inhibition capacity of PLK1-shRNA on HCT-116 xenograft was measured in nude mice. Then, the silencing effect of PLK1 was analyzed by RT-PCR, western blot, and immunohistochemistry, respectively. Apoptosis, angiogenesis, and proliferation in tumor tissues were measured by TUNEL, CD31, and PCNA stain, respectively. The RNA interference targeting PLK1 significantly decreased the expression of PLK1 in vitro. More importantly, anti-PLK1 treatment in HCT-116 xenograft decreased tumor weight by 81.58% compared with the control group (p<0.001), accompanied with decreased PLK1 mRNA and protein expression, increased cell apoptosis, and reduced angiogenesis and proliferation (p<0.001). Our study showed that knockdown of PLK1 by shRNA might be the potential therapeutic approach against human colorectal carcinoma.

Quantitative proteome analysis of pluripotent cells by iTRAQ mass tagging reveals post-transcriptional regulation of proteins required for ES cell self-renewal

Embryonic stem cells and embryonal carcinoma cells share two key characteristics: pluripotency (the ability to differentiate into endoderm, ectoderm, and mesoderm) and self-renewal (the ability to grow without change in an untransformed, euploid state). Much has been done to identify and characterize transcription factors that are necessary or sufficient to maintain these characteristics. Oct-4 and Nanog are necessary to maintain pluripotency; they are down-regulated at the mRNA level by differentiation. There may be additional regulatory genes whose mRNA levels are unchanged but whose proteins are destabilized during differentiation. We generated proteome-wide, quantitative profiles of ES and embryonal carcinoma cells during differentiation, replicating a microarray-based study by Aiba et al. (Aiba, K., Sharov, A. A., Carter, M. G., Foroni, C., Vescovi, A. L., and Ko, M. S. (2006) Defining a developmental path to neural fate by global expression profiling of mouse embryonic stem cells and adult neural stem/progenitor cells. Stem Cells 24, 889-895) who triggered differentiation by treatment with 1 μM all-trans-retinoic acid. We identified several proteins whose levels decreased during differentiation in both cell types but whose mRNA levels were unchanged. We confirmed several of these cases by RT-PCR and Western blot. Racgap1 (also known as mgcRacgap) was particularly interesting because it is required for viability of preimplantation embryos and hematopoietic stem cells, and it is also required for differentiation. To confirm our observation that RACGAP-1 declines during retinoic acid-mediated differentiation, we used multiple reaction monitoring, a targeted mass spectrometry-based quantitation method, and determined that RACGAP-1 levels decline by half during retinoic acid-mediated differentiation. We knocked down Racgap-1 mRNA levels using a panel of five shRNAs. This resulted in a loss of self-renewal that correlated with the level of knockdown. We conclude that RACGAP-1 is post-transcriptionally regulated during blastocyst development to enable differentiation by inhibiting ES cell self-renewal.