NDRG2 positively regulates E-cadherin expression and prolongs overall survival in colon cancer patients

Inhibition of RNA Polymerase III Augments the Anti-Cancer Properties of TNFα

Tumour necrosis factor alpha (TNFα) is a multifunctional cytokine that plays a pivotal role in apoptosis, cell survival, as well as in inflammation and immunity. Although named for its antitumor properties, TNFα also has tumour-promoting properties. TNFα is often present in large quantities in tumours, and cancer cells frequently acquire resistance to this cytokine. Consequently, TNFα may increase the proliferation and metastatic potential of cancer cells. Furthermore, the TNFα-driven increase in metastasis is a result of the ability of this cytokine to induce the epithelial-to-mesenchymal transition (EMT). Overcoming the resistance of cancer cells to TNFα may have a potential therapeutic benefit. NF-κB is a crucial transcription factor mediating inflammatory signals and has a wide-ranging role in tumour progression. NF-κB is strongly activated in response to TNFα and contributes to cell survival and proliferation. The pro-inflammatory and pro-survival function of NF-κB can be disrupted by blocking macromolecule synthesis (transcription, translation). Consistently, inhibition of transcription or translation strongly sensitises cells to TNFα-induced cell death. RNA polymerase III (Pol III) synthesises several essential components of the protein biosynthetic machinery, such as tRNA, 5S rRNA, and 7SL RNA. No studies, however, directly explored the possibility that specific inhibition of Pol III activity sensitises cancer cells to TNFα. Here we show that in colorectal cancer cells, Pol III inhibition augments the cytotoxic and cytostatic effects of TNFα. Pol III inhibition enhances TNFα-induced apoptosis and also blocks TNFα-induced EMT. Concomitantly, we observe alterations in the levels of proteins related to proliferation, migration, and EMT. Finally, our data show that Pol III inhibition is associated with lower NF-κB activation upon TNFα treatment, thus potentially suggesting the mechanism of Pol III inhibition-driven sensitisation of cancer cells to this cytokine.

Colorectal Cancer Cell Differentiation Is Dependent on the Repression of Aerobic Glycolysis by NDRG2-TXNIP Axis

BACKGROUND

Poorly differentiated colorectal cancers are more aggressive. Metabolism reprogramming is a significant hallmark in cancer, and aerobic glycolysis is common. However, how cancer cells reprogramming glucose metabolism contributes to cell differentiation was largely unknown. Previous studies have reported that tumor suppressor NDRG2 could promote colorectal cancers differentiation.

AIMS

This study aims to demonstrate that NDRG2 promotes the differentiation of colorectal cancers, potentially through the inhibition of aerobic glycolysis via TXNIP induction.

METHODS

Western blotting, qRT-PCR and immunohistochemical staining were used to detect the expression of related molecules. MTT assay was used to reflect cell viability and proliferation. Immunofluorescent assay was performed to identify the expression and distribution of molecules. Luciferase analysis and CHIP assays were used to investigate the mechanism. Bioinformatic analysis was performed to predict the relevance.

RESULTS

In colorectal cancers, NDRG2 could inhibit cell proliferation, reduce glucose uptake and decrease expression of key glycolysis enzymes. Upregulated NDRG2 is associated with differentiated cancer. However, deletion of TXNIP, a classic glucose metabolism inhibitor, could obviously alter the function of NDRG2 in differentiation, glucose uptake, expression of key glycolysis enzymes and proliferation. Mechanistically, high glucose flux promotes the activity of TXNIP promoter. And NDRG2 promotes the occupancy of transcription factor Mondo A on TXNIP promoter, predominantly through the suppression of c-myc, which could complete with Mondo A binding to TXNIP promoter. In clinical samples, high expression of TXNIP indicates good prognosis and outcome.

CONCLUSIONS

NDRG2-dependent induction of TXNIP is critical for the aerobic glycolysis during colorectal cancers differentiation.

Regulation of tumor-associated macrophage (TAM) differentiation by NDRG2 expression in breast cancer cells

Macrophages are a major cellular component of innate immunity and are mainly known to have phagocytic activity. In the tumor microenvironment (TME), they can be differentiated into tumor-associated macrophages (TAMs). As the most abundant immune cells in the TME, TAMs promote tumor progression by enhancing angiogenesis, suppressing T cells and increasing immunosuppressive cytokine production. N-myc downstream-regulated gene 2 (NDRG2) is a tumor suppressor gene, whose expression is down-regulated in various cancers. However, the effect of NDRG2 on the differentiation of macrophages into TAMs in breast cancer remains elusive. In this study, we investigated the effect of NDRG2 expression in breast cancer cells on the differentiation of macrophages into TAMs. Compared to tumor cell-conditioned medium (TCCM) from 4T1-mock cells, TCCM from NDRG2-overexpressing 4T1 mouse breast cancer cells did not significantly change the morphology of RAW 264.7 cells. However, TCCM from 4T1-NDRG2 cells reduced the mRNA levels of TAM-related genes, including MR1, IL-10, ARG1 and iNOS, in RAW 264.7 cells. In addition, TCCM from 4T1-NDRG2 cells reduced the expression of TAM-related surface markers, such as CD206, in peritoneal macrophages (PEM). The mRNA expression of TAM-related genes, including IL-10, YM1, FIZZ1, MR1, ARG1 and iNOS, was also downregulated by TCCM from 4T1-NDRG2 cells. Remarkably, TCCM from 4T1-NDRG2 cells reduced the expression of PD-L1 and Fra-1 as well as the production of GM-CSF, IL-10 and ROS, leading to the attenuation of T cell-inhibitory activity of PEM. These data showed that compared with TCCM from 4T1-mock cells, TCCM from 4T1-NDRG2 cells suppressed the TAM differentiation and activation. Collectively, these results suggest that NDRG2 expression in breast cancer may reduce the differentiation of macrophages into TAMs in the TME.

NDRG2 Expression in Breast Cancer Cells Downregulates PD-L1 Expression and Restores T Cell Proliferation in Tumor-Coculture

Simple Summary

N-myc downstream-regulated gene 2 (NDRG2) is a candidate tumor suppressor in various cancers, including breast cancer. Increased expression of programmed death ligand 1 (PD-L1) is frequently observed in human cancers. Despite its role in cancer cells, the effects of NDRG2 on PD-L1 expression and PD-L1-PD-1 pathway disruption have not been investigated. We demonstrated that NDRG2 overexpression inhibits PD-L1 expression in human breast cancer cells. Blocking T cell proliferation by coculture with 4T1 mouse tumor cells that express high levels of PD-L1 could be significantly reversed by NDRG2 overexpression in the same tumor cells. NDRG2 knockdown in NDRG2-transfected cells elicited the upregulation of PD-L1 expression and accelerated the inhibition of T cell proliferation. These findings were confirmed from The Cancer Genome Atlas (TCGA) data that PD-L1 expression in basal and triple-negative breast cancer (TNBC) patients, but not in luminal A or B cancer patients, was negatively correlated with the NDRG2 expression.

Abstract

(1) Background: The aim of the present study was to evaluate the effect of NDRG2 expression in regulating PD-L1 or PD-L2 on malignant breast cancer cells. (2) Methods: Overexpression and knockdown of the NDRG2 gene in human and mouse cancer cells were applied and quantitative real-time PCR and Western blot analysis were performed. T cell proliferation and TCGA analysis were conducted to validate negative correlation of the PD-L1 expression with the NDRG2 expression. (3) Results: We found that NDRG2 overexpression inhibits PD-L1 expression in human breast cancer cells through NF-κB signaling. NDRG2 overexpression in 4T1 mouse breast cancer cells followed by PD-L1 downregulation could block the suppressive activity of cancer cells on T cell proliferation and knockdown of NDRG2 expression enhanced the expression of PD-L1, leading to the inhibition of T cell proliferation by tumor cell coculture. Finally, we confirmed from TCGA data that PD-L1 expression in basal and triple-negative breast cancer patients was negatively correlated with the expression of NDRG2. Intriguingly, linear regression analysis using TNBC cell lines showed that the PD-L1 level was negatively associated with the NDRG2 expression level. (4) Conclusions: Our findings demonstrate that NDRG2 expression is instrumental in suppressing PD-L1 expression and restoring PD-L1-inhibited T cell proliferation activity in TNBC cells.

NDRG2 regulates adherens junction integrity to restrict colitis and tumourigenesis

BACKGROUND

Paracellular barriers play an important role in the pathogenesis of Inflammatory bowel disease (IBD) and maintain gut homeostasis. N-myc downstream-regulated gene 2 (NDRG2) has been reported to be a tumour suppressor gene and to inhibit colorectal cancer metastasis. However, whether NDRG2 affects colitis initiation and colitis-associated colorectal cancer is unclear.

METHODS

Intestine-specific Ndrg2 deficiency mice (Ndrg2^ΔIEC) were subjected to DSS- or TNBS-induced colitis, and AOM-DSS-induced colitis-associated tumour. HT29 cells, Caco2 cells, primary intestinal epithelial cells (IECs) from Ndrg2^ΔIEC mice, mouse embryo fibroblasts (MEFs) from systemic Ndrg2 knockout mice, HEK293 cells and human UC and DC specimens were used to investigate NDRG2 function in colitis and colitis-associated tumour.

FINDINGS

Ndrg2 loss led to adherens junction (AJ) structure destruction via E-cadherin expression attenuation, resulting in diminished epithelial barrier function and increased intestinal epithelial permeability. Mechanistically, NDRG2 enhanced the interaction of E3 ligase FBXO11 with Snail, the repressor of E-cadherin, to promote Snail degradation by ubiquitination and maintained E-cadherin expression. In human ulcerative colitis patients, reduced NDRG2 expression is positively correlated with severe inflammation.

INTERPRETATION

These findings demonstrate that NDRG2 is an essential colonic epithelial barrier regulator and plays an important role in gut homeostasis maintenance and colitis-associated tumour development.

FUNDING

National Natural Science Foundation of China (No. 81770523, 31571437, 81672751), Creative Research Groups of China (No. 81421003), State Key Laboratory of Cancer Biology Project (CBSKL2019ZZ11, CBSKL201406, CBSKL2017Z08 and CBSKL2017Z11), Fund for Distinguished Young Scholars of ShaanXi province (2019JC-22).

Low NDRG2 expression predicts poor prognosis in solid tumors: A meta-analysis of cohort study

BACKGROUND

As a member of the N-myc down-regulated gene family, N-Myc downstream-regulated gene 2 (NDRG2) contributes to the tumorigenesis of various types of cancers. However, the correlation between NDRG2 expression and the prognosis of solid tumor remains to be elucidated because of small sample sizes and inconsistent results in previous studies. In the present study, we conducted a systematic review and meta-analysis to explore the prognostic significance of NDRG2 in human solid tumors.

METHODS

PubMed, Web of Science, Embase, Chinese National Knowledge Infrastructure, and WanFang databases (up to April 2020) were searched for relevant studies that evaluated the impact of NDRG2 on clinical outcomes, including overall survival (OS), and disease-free survival (DFS), in solid tumors. Hazard ratios (HRs) with 95% confidence intervals (CIs) were pooled to assess the association between NDRG2 expression and the survival of patients with solid tumors. Odds ratios (ORs) with 95% CIs were pooled to estimate the correlation between NDRG2 expression and clinicopathologic characteristics in the patients.

RESULTS

A total of 13 eligible studies with 1980 patients were included in this meta-analysis. Low NDRG2 expression was significantly associated with poor OS (HR = 1.96, 95% CI: 1.60-2.40, P < .001) and DFS (HR = 2.70, 95% CI: 1.42-5.13, P = .002) in solid tumor. Furthermore, low NDRG2 expression was related to some phenotypes of tumor aggressiveness, such as clinical stage (OR = 3.21, 95% CI: 1.96-5.26, P < .001), lymph node metastasis (OR = 2.14, 95% CI: 1.49-3.07, P < .001), and degree of differentiation (OR = 0.60, 95% CI: 0.45-0.81, P = .001).

CONCLUSIONS

NDRG2 may be a meaningful biomarker of poor prognosis and a potential therapeutic target for human solid tumors.

Astrocyte-specific NDRG2 gene: functions in the brain and neurological diseases

In recent years, the roles of astrocytes of the central nervous system in brain function and neurological disease have drawn increasing attention. As a member of the N-myc downstream-regulated gene (NDRG) family, NDRG2 is principally expressed in astrocytes of the central nervous system. NDRG2, which is involved in cell proliferation and differentiation, is commonly regarded as a tumor suppressor. In astrocytes, NDRG2 affects the regulation of apoptosis, astrogliosis, blood-brain barrier integrity, and glutamate clearance. Several preclinical studies have revealed that NDRG2 is implicated in the pathogenesis of many neurological diseases not limited to tumors (mostly glioma in the nervous system), such as stroke, neurodegeneration (Alzheimer's disease and Parkinson's disease), and psychiatric disorders (depression and attention deficit hyperactivity disorder). This review summarizes the biological functions of NDRG2 under physiological and pathological conditions, and further discusses the roles of NDRG2 during the occurrence and development of neurological diseases.

An in vitro hyaluronic acid hydrogel based platform to model dormancy in brain metastatic breast cancer cells

Breast cancer cells (BCCs) can remain dormant at the metastatic site, which when revoked leads to formation of metastasis several years after the treatment of primary tumor. Particularly, awakening of dormant BCCs in the brain results in breast cancer brain metastasis (BCBrM) which marks the most advanced stage of the disease with a median survival period of ~4-16 months. However, our understanding of dormancy associated with BCBrM remains obscure, in part, due to the lack of relevant in vitro platforms to model dormancy associated with BCBrM. To address this need, we developed an in vitro hyaluronic acid (HA) hydrogel platform to model dormancy in brain metastatic BCCs via exploiting the bio-physical cues provided by HA hydrogels while bracketing the normal brain and metastatic brain malignancy relevant stiffness range. In this system, we observed that MDA-MB-231Br and BT474Br3 brain metastatic BCCs exhibited a dormant phenotype when cultured on soft (0.4 kPa) HA hydrogel compared to stiff (4.5 kPa) HA hydrogel as characterized by significantly lower EdU and Ki67 positivity. Further, we demonstrated the nuclear localization of p21 and p27 (markers associated with dormancy) in dormant MDA-MB-231Br cells contrary to their cytoplasmic localization in the proliferative population. We also demonstrated that the stiffness-based dormancy in MDA-MB-231Br cells was reversible and was, in part, mediated by focal adhesion kinases and the initial cell seeding density. Finally, RNA sequencing confirmed the dormant phenotype in MDA-MB-231Br cells. This platform could further our understanding of dormancy in BCBrM and could be adapted for anti-metastatic drug screening. STATEMENT OF SIGNIFICANCE: Our understanding of dormancy associated with BCBrM remains obscure, in part, due to the lack of relevant in vitro platforms to model dormancy associated with BCBrM. Herein, we present a HA hydrogel-based platform to model dormancy in brain metastatic BCCs while recapitulating key aspects of brain microenvironment. We demonstrated that the biophysical cues provided the HA hydrogel mediates dormancy in brain metastatic BCCs by assessing both proliferation and cell cycle arrest markers. We also established the role of focal adhesion kinases and initial cell seeding density in the stiffness-mediated dormancy in brain metastatic BCCs. Further, RNA-seq. confirmed the dormant phenotype in brain metastatic BCCs. This platform could be utilized to further our understanding of microenvironmental regulation of dormancy in BCBrM.

HTR1D, TIMP1, SERPINE1, MMP3 and CNR2 affect the survival of patients with colon adenocarcinoma

Colorectal cancer (CRC) is a tumor that derives from the rectum or colon, and colon adenocarcinoma (COAD) is the most common type of CRC. The present study was performed to identify genes that serve critical roles in the survival of patients with COAD. RNA-sequencing data of COAD was extracted from The Cancer Genome Atlas database, which included 480 tumor samples and 41 normal samples. Using the limma package, differential expression analysis was performed to identify the differentially expressed genes (DEGs). In addition, the potential functions and pathways for the identified DEGs were analyzed using the clusterProfiler package. After the samples were divided into high and low expression groups, survival analysis for the two groups was performed using the Kaplan-Meier model. Using Cytoscape software, a protein-protein interaction network was generated for the survival-associated genes. A total of 1,519 DEGs, including 568 upregulated genes and 951 downregulated genes, were identified in the COAD samples. Enrichment analysis suggested that the DEGs were implicated in numerous functional terms and pathways. Furthermore, 109 DEGs were identified to be survival-associated genes in COAD. According to the degrees of the network nodes, 5-hydroxytryptamine receptor 1D (HTR1D), TIMP metallopeptidase inhibitor 1 (TIMP1), serpin family E member 1 (SERPINE1), matrix metallopeptidase 3 (MMP3) and cannabinoid receptor 2 (CNR2) were key nodes, and the expression levels of these genes were analyzed in clinical samples of CRC. Therefore, the results of the present study suggest HTR1D, TIMP1, SERPINE1, MMP3 and CNR2 may affect the prognosis of patients with COAD.

Expression of NDRG2 in Human Colorectal Cancer and its Association with Prognosis

Objective: As a member of the N-myc downregulated gene family, N-Myc downstream-regulated gene 2 (NDRG2) contributes to tumorigenesis of various types of cancer. The expression status of NDRG2 in colorectal cancer (CRC) and its prognostic value remain to be elucidated. The goal of this study was to determine the expression pattern of NDRG2 in human CRC and its association of NDRG2 expression with prognosis.

Methods: Immunohistochemistry was used to determine the level of NDRG2 expressions in 316 CRC tissues. The medical records of consecutive CRC patients undergoing primary tumor resection from September 2000 to February 2015 were retrospectively selected. Then, we compared to specific clinicopathological features in patients with different level of NDRG2 expressions. The correlation of NDRG2 expression with 3-year survival rate was assessed by Kaplan-Meier method and Cox regression modeling.

Results: NDRG2 was expressed in 94.6% (299/316) of CRC tissues. The median IHC score of NDRG2 expression was significantly lower in tumor tissues compared with that of tumor-adjacent normal tissues [4.50(range 0.00-12.00) vs. 10.00 (range 0.00-12.00), P < 0.001].Survival analysis indicated that patients with low NDRG2 expression had poorer 3-year OS than those with high NDRG2 expression (59.9% vs. 76.6%, P = 0.017). Low NDRG2 expression also presented a significantly poorer 3-year OS rate in patient with stage IV disease (29.4% vs. 56.5%, P = 0.002), liver metastasis(32.2% vs. 54.7%, P = 0.005) and those receiving liver resection(56.5% vs. 71.9% , P = 0.012). Multivariate analysis indicated that high NDRG2 expression was independently associated with poor OS (hazard ratio [HR]: 1.499; 95% confidence interval [CI]: 1.037-2.165; P = 0.031).

Conclusions: Low expression of NDRG2 was associated with unfavorable prognosis in CRC patients with primary tumor resection. Detection of NDRG2 expression might be useful for providing valuable information of individualized therapy for CRC patients.

NDRG2 Sensitizes Myeloid Leukemia to Arsenic Trioxide via GSK3β-NDRG2-PP2A Complex Formation

N-Myc downstream-regulated gene 2 (NDRG2) was characterized as a tumor suppressor, inducing anti-metastatic and anti-proliferative effects in several tumor cells. However, NDRG2 functions on anticancer drug sensitivity, and its molecular mechanisms are yet to be fully investigated. In this study, we investigated the mechanism of NDRG2-induced sensitization to As₂O₃ in the U937 cell line, which is one of the most frequently used cells in the field of resistance to As₂O₃. NDRG2-overexpressing U937 cells (U937-NDRG2) showed a higher sensitivity to As₂O₃ than mock control U937 cell (U937-Mock). The higher sensitivity to As₂O₃ in U937-NDRG2 was associated with Mcl-1 degradation through glycogen synthase kinase 3β (GSK3β) activation. Inhibitory phosphorylation of GSK3β was significantly reduced in U937-NDRG2, and the reduction was diminished by okadaic acid, a protein phosphatase inhibitor. NDRG2 mediated the interaction between GSK3β and protein phosphatase 2A (PP2A), inducing dephosphorylation of GSK3β at S9 by PP2A. Although the C-terminal deletion mutant of NDRG2 (ΔC NDRG2), which could not interact with PP2A, interacted with GSK3β, the mutant failed to dephosphorylate GSK3β at S9 and increased sensitivity to As₂O₃. Our findings suggest that NDRG2 is a kind of adaptor protein mediating the interaction between GSK3β and PP2A, inducing GSK3β activation through dephosphorylation at S9 by PP2A, which increases sensitivity to As₂O₃ in U937 cells.

NDRG2 Regulates the Expression of Genes Involved in Epithelial Mesenchymal Transition of Prostate Cancer Cells

BACKGROUND

Metastasis is the main cause of prostate cancer (PCa) death. The inhibitory effect of N-myc downstream-regulated gene 2 (NDRG2) on the invasiveness properties of PCa cells has been demonstrated previously. However, its underlying mechanisms have not yet been investigated. The present study aimed to investigate the effects of NDRG2 overexpression on the expression of genes involved in epithelial-mesenchymal transition (EMT) including E-cadherin (E-CAD), α- and β-catenins, Slug and Snail, transforming growth factor (TGF)-α and -β, and vascular endothelial growth factor (VEGF).

METHODS

In the present in vitro study, LNCaP cells were divided into three groups, namely NDRG2 group (transfected with PSES-pAdenoVator-PSA-NDRG2-IRES-GFP plasmid), mock group (transfected with mock plasmid), and control group (without transfection). The effect of NDRG2 overexpression on the migration and invasion of LNCaP cells were investigated using the transwell assay. Real-time PCR was used for the evaluation of gene expression. For the statistical analyses, one-way ANOVA, student t test or Mann-Whitney U test were applied using the SPSS software (version 15.0). P values <0.05 were considered statistically significant.

RESULTS

The results demonstrated that the overexpression of NDRG2 reduced the invasion and migration of LNCaP cells compared to the control and mock groups (P<0.001). A decreased expression of TGF-β (P=0.002), VEGF (P=0.014), Slug (P=0.005), and Snail (P=0.012); and an increased expression of E-CAD (P=0.009) were observed following NDRG2 overexpression in LNCaP cells.

CONCLUSION

The results of the present study suggest that NDRG2 inhibits the invasiveness properties of LNCaP cells probably through changes in the expression of genes involved in EMT.

NDRG2 suppresses proliferation, migration, invasion and epithelial-mesenchymal transition of esophageal cancer cells through regulating the AKT/XIAP signaling pathway

N-Myc downstream-regulated gene 2 (NDRG2) has recently revealed as a candidate tumor suppressor gene. To inhibit tumor growth and decrease morbidity of esophageal cancer (EC), this study aims to test the hypothesis that the upregulation of NDRG2 may suppress proliferation, invasion, migration and epithelial-mesenchymal transition (EMT) of EC cells by regulating the AKT/XIAP signaling pathway. Immunohistochemistry was conducted for the identification of NDRG2, protein kinase B (p-AKT), X-linked inhibitor of apoptosis protein (XIAP) in EC tissues. To identify the regulatory mechanism of NDRG2 on the AKT/XIAP signaling pathway and EMT in EC, over-expressed lentiviral vector and shRNA were applied for up-regulating and interfering NDRG2 expression, and a series of determinations on the biological behavior of EC cells were performed to validate this regulation action. The results of immunohistochemistry showed NDRG2 was lowly expressed in EC tissues while p-AKT and XIAP are highly expressed. Over-expression of NDRG2 suppresses the proteins related to AKT/XIAP signaling pathway and EMT. Besides, a series of determinations shows the proliferation, migration and invasion of TE-13 cells were suppressed by over-expressed NDRG2, while the cell cycle progression was blocked and cell apoptosis was promoted. And in vivo experiment also demonstrated NDRG2 could inhibit tumor growth. Our findings demonstrate over-expression of NDRG2 works as tumor suppressive role in EC through its effects on inhibition of cell migration, invasion, and EMT by inhibiting the AKT/XIAP signaling pathway.

NDRG2 facilitates colorectal cancer differentiation through the regulation of Skp2-p21/p27 axis

Poorly differentiated colorectal cancers (CRCs) are more aggressive and lack targeted therapies. We and others previously reported the predominant role of tumor-suppressor NDRG2 in promoting CRC differentiation, but the underlying mechanism is largely unknown. Herein, we demonstrate that NDRG2 induction of CRC cell differentiation is dependent on the repression of E3 ligase Skp2 activity. In patients and Ndrg2 knockout mice, NDRG2 and Skp2 are negatively correlated and associated with cell differentiation stage. Further, NDRG2 suppression of Skp2 contributes to the inductions and stabilizations of p21 and p27, which are Skp2 target proteins for degradation. The reduction of either p21 or p27 levels by shRNA can decrease NDRG2-induced AKP activity and resume cell growth inhibition, thus both p21 and p27 are required for NDRG2 effect on the promotion of cell differentiation in CRCs. The mechanistic study shows that NDRG2 suppresses β-catenin nuclear translocation and decreases the occupancy of β-catenin/TCF complex on Skp2 promoter, potentially through dephosphorylating GSK-3β. By subjecting a series of NDRG2 deletion mutants to Skp2 expression, the loss of NH₂-terminal domain can completely abolish NDRG2-dependent differentiation induction. Supporting the biological significance of the reciprocal relationship between NDRG2 and Skp2, an NDRG2_low/Skp2_high gene expression signature correlates with poor CRC patient outcome and could be considered as a diagnostic marker of CRCs.

Clinical and pathological significance of N-Myc downstream-regulated gene 2 (NDRG2) in diverse human cancers

Human N-Myc downstream-regulated gene 2 (NDRG2), located at chromosome 14q11.2, has been reported to be down-regulated and associated with the progression and prognosis of diverse cancers. Collectively, previous studies suggest that NDRG2 functions as a candidate tumor-suppressor gene; thus, up-regulation of NDRG2 protein might act as a promising therapeutic strategy for malignant tumors. The aim of this review was to comprehensively present the clinical and pathological significance of NDRG2 in human cancers.

Effects of NDRG2 Overexpression on Metastatic Behaviors of HCT116 Colorectal Cancer Cell Line

Purpose: N-myc downstream-regulated gene 2 (NDRG2) is frequently down-regulated in cancer, and plays an important role in the control of tumor growth and metastasis. Its manipulation has been suggested as a therapy in cancer. Here, we examined the outcome of NDRG2 overexpression on proliferation, invasion, migration and MMP activity of HCT116 colorectal cancer cell line.

Methods: The HCT116 cell line (human colorectal cancer) was transfected with pCMV6-AC-GFP-NDRG2. 2,5diphenyltetrazolium bromide (MTT) assay was used to detect cell proliferation. The invasion and migration of the transfected cells were examined through transwell chambers while the MMP-9 activity was detected by the ability of the cells to digest gelatin.

Results: Overexpression of NDRG2 by stable NDRG2 transfection decreased cell proliferation, migration and invasion ability, along with decreasing MMP-9 activity.

Conclusion: Our data indicate that NDRG2 overexpression can suppress several aspect of tumorigenesis. Further investigations are necessitated to verify if NDRG2 molecule can be a therapeutic target in colorectal cancer.

Inhibition of pressure-activated cancer cell adhesion by FAK-derived peptides

Forces within the surgical milieu or circulation activate cancer cell adhesion and potentiate metastasis through signaling requiring FAK-Akt1 interaction. Impeding FAK-Akt1 interaction might inhibit perioperative tumor dissemination, facilitating curative cancer surgery without global FAK or AKT inhibitor toxicity. Serial truncation and structurally designed mutants of FAK identified a seven amino acid, short helical structure within FAK that effectively competes with Akt1-FAK interaction. Adenoviral overexpression of this FAK-derived peptide inhibited pressure-induced FAK phosphorylation and AKT-FAK coimmunoprecipitation in human SW620 colon cancer cells briefly exposed to 15mmHg increased pressure, consistent with laparoscopic or post-surgical pressures. Adenoviral FAK-derived peptide expression prevented pressure-activation of SW620 adhesion not only to collagen-I-coated plates but also to murine surgical wounds. A scrambled peptide did not. Finally, we modeled operative shedding of tumor cells before irrigation and closure by transient cancer cell adhesion to murine surgical wounds before irrigation and closure. Thirty minute preincubation of SW620 cells at 15mmHg increased pressure impaired subsequent tumor free survival in mice exposed to cells expressing the scrambled peptide. The FAK-derived sequence prevented this. These results suggest that blocking FAK-Akt1 interaction may prevent perioperative tumor dissemination and that analogs or mimics of this 7 amino acid FAK-derived peptide could impair metastasis.

NDRG2 gene copy number is not altered in colorectal carcinoma

AIM

To investigate if the down-regulation of N-myc Downstream Regulated Gene 2 (NDRG2) expression in colorectal carcinoma (CRC) is due to loss of the NDRG2 allele(s).

METHODS

The following were investigated in the human colorectal cancer cell lines DLD-1, LoVo and SW-480: NDRG2 mRNA expression levels using quantitative reverse transcription-polymerase chain reaction (qRT-PCR); interaction of the MYC gene-regulatory protein with the NDRG2 promoter using chromatin immunoprecipitation; and NDRG2 promoter methylation using bisulfite sequencing. Furthermore, we performed qPCR to analyse the copy numbers of NDRG2 and MYC genes in the above three cell lines, 8 normal colorectal tissue samples and 40 CRC tissue samples.

RESULTS

As expected, NDRG2 mRNA levels were low in the three colorectal cancer cell lines, compared to normal colon. Endogenous MYC protein interacted with the NDRG2 core promoter in all three cell lines. In addition, the NDRG2 promoter was heavily methylated in these cell lines, suggesting an epigenetic regulatory mechanism. Unaltered gene copy numbers of NDRG2 were observed in the three cell lines. In the colorectal tissues, one normal and three CRC samples showed partial or complete loss of one NDRG2 allele. In contrast, the MYC gene was amplified in one cell line and in more than 40% of the CRC cases.

CONCLUSION

Our study suggests that the reduction in NDRG2 expression observed in CRC is due to transcriptional repression by MYC and promoter methylation, and is not due to allelic loss.

A 22q11.2 amplification in the region encoding microRNA-650 correlates with the epithelial to mesenchymal transition in breast cancer primary cultures of Mexican patients

Breast cancer ranks first in incidence and mortality in working age women. Cancer initiation and progression relies on accumulation of genetic and epigenetic aberrations that alter cellular processes, among them, epithelial to mesenchymal transition (EMT) denotes particularly aggressive neoplasias given its capacity to invade and metastasize. Several microRNAs (miRNA) have been found able to regulate gene expression at the core of EMT. In this study, the Affymetrix CytoScan HD array was used to analyze three different primary tumor cell isolates from Mexican breast cancer patients. We found an amplification in band 22q11.2 shared by the three samples, in the region that encodes miRNA-650. Overexpression of this miRNA has been associated with downregulation of tumor suppressors ING4 and NDRG2, which have been implicated in cancer progression. Using the Pathway Linker platform the ING4 and NDRG2 interaction networks showed a significant association with signaling pathways commonly deregulated in cancer. Also, several studies support their participation in the EMT. Supporting the latter, we found that the three primary isolates were E-cadherin negative, vimentin positive, presented a cancer stem cell-like phenotype CD44⁺CD24^−/low and were invasive in Transwell invasion assays. This evidence suggests that the gain of region 22q11.2 contributes to trigger EMT. This is the first evidence linking miR-650 and breast cancer.

Emerging role of N-myc downstream-regulated gene 2 (NDRG2) in cancer

N-myc downstream-regulated gene 2 (NDRG2) is a tumor suppressor and cell stress-related gene. NDRG2 is associated with tumor incidence, progression, and metastasis. NDRG2 regulates tumor-associated genes and is regulated by multiple conditions, treatments, and protein/RNA entities, including hyperthermia, trichostatin A and 5-aza-2'-deoxycytidine, which are promising potential cancer therapeutics. In this review, we discuss the expression as well as the clinical and pathological significance of NDRG2 in cancer. The pathological processes and molecular pathways regulated by NDRG2 are also summarized. Moreover, mechanisms for increasing NDRG2 expression in tumors and the potential directions of future NDRG2 research are discussed. The information reviewed here should assist in experimental design and increase the potential of NDRG2 as a therapeutic target for cancer.

Analysis of different components in the peritumoral tissue microenvironment of colorectal cancer: A potential prospect in tumorigenesis

The present study aimed to observe the varying expression of biomarkers in the microenvironment adjacent to colorectal cancer lesions to provide additional insight into the functions of microenvironment components in carcinogenesis and present a novel or improved indicator for early diagnosis of cancer. A total of 144 human samples from three different locations in 48 patients were collected, these locations were 10, 5 and 2 cm from the colorectal cancer lesion, respectively. The biomarkers analyzed included E‑cadherin, cytokeratin 18 (CK18), hyaluronidase‑1 (Hyal‑1), collagen type I (Col‑I), Crumbs3 (CRB3), vimentin, proteinase activated receptor 3 (PAR‑3), α‑smooth muscle actin (α‑SMA), cyclin D1 (CD1) and cluster of differentiation (CD)133. In addition, crypt architecture was observed. Related functional analysis of proteins was performed using hierarchical index cluster analysis. More severe destroyed crypt architecture closer to the cancer lesions was observed compared with the 10 cm sites, with certain crypts degraded entirely. Expression levels of E‑cadherin, CK18, CRB3 and PAR‑3 were lower in 2 cm sites compared with the 10 cm sites (all P<0.001), while the expression levels of the other biomarkers in the 2 cm sites were increased compared with 10 cm sites (all P<0.0001). Notably, the expression of CK18 in 2 cm sites was higher than in the 5 cm site (P<0.0001), which was different from the expression of E‑cadherin, CRB3 and PAR‑3. The expression levels of Hyal‑1 and Col‑I at the 2 cm sites were lower than that of the 5 cm sites (P>0.05 and P=0.0001, respectively), while the expression of vimentin, α‑SMA, CD1 and CD133 were not. Hyal‑1 and Col‑I may be independently important in cancer initiation in the tumor microenvironment. The results of the present study suggest that the biomarkers in the tissue microenvironment are associated with early tumorigenesis and may contribute to the development of carcinomas. These observations may be useful for early diagnosis of colorectal cancer.

The Effects of NDRG2 Overexpression on Cell Proliferation and Invasiveness of SW48 Colorectal Cancer Cell Line

BACKGROUND

Colorectal cancer (CRC) is one of the most common causes of cancer-related death in the world. The expression of N-myc downstream-regulated gene 2 (NDRG2) is down-regulated in CRC. The aim of this study was to investigate the effect of NDRG2 overexpression on cell proliferation and invasive potential of SW48 cells.

METHODS

SW48 cells were transfected with a plasmid overexpressing NDRG2. After stable transfection, the effect of NDRG2 overexpression on cell proliferation was evaluated by MTT assay. The effects of NDRG2 overexpression on cell migration, invasion and cell motility and matrix metalloproteinase 9 (MMP9) activities were also investigated using matrigel transwell assay, wound healing assay and gelatin zymography, respectively.

RESULTS

MTT assay showed that overexpression of NDRG2 caused attenuation of SW48 cell proliferation. Transwell and wound healing assay revealed that NDRG2 overexpression led to inhibition of migration, invasion, and motility of SW48 cells. The overexpression of NDRG2 also reduced the activity of secreted MMP-9.

CONCLUSIONS

The results of this study suggest that NDRG2 overexpression inhibits proliferation and invasive potential of SW48 cells, which likely occurs via suppression of MMP-9 activity.

N-myc downstream-regulated gene 2 (NDRG2) suppresses the epithelial-mesenchymal transition (EMT) in breast cancer cells via STAT3/Snail signaling

Although NDRG2 has recently been found to be a candidate tumor suppressor, its precise role in the epithelial-mesenchymal transition (EMT) is not well understood. In the present study, we demonstrated that NDRG2 overexpression in MDA-MB-231 cells down-regulated the expression of Snail, a transcriptional repressor of E-cadherin and a key regulator of EMT, as well as the phosphorylation of signal transducer and activator of transcription 3 (STAT3), an oncogenic transcription factor that is activated in many human malignancies including breast cancer. In addition, we confirmed that the expression of Snail and phospho-STAT3 was recovered when NDRG2 was knocked down by siRNA in MCF7 cells in which NDRG2 is endogenously expressed. Interestingly, MDA-MB-231-NDRG2 cells showed remarkably decreased Snail expression after treatment with JSI-124 (also known as cucurbitacin I) or Stattic, STAT3 inhibitors, compared to MDA-MB-231-mock cells. Moreover, STAT3 activation by EGF treatment induced higher Snail expression, and NDRG2 overexpression resulted in the inhibition of Snail expression in MDA-MB-231 cells stimulated by EGF in the absence or presence of STAT3 inhibitor. Treatment of MDA-MB-231 cells with STAT3 inhibitor led to a moderate decrease in wound healing and migration capacity, whereas STAT3 inhibitor treatment of MDA-MB-231-NDRG2 cells resulted in a significant attenuation of migration in both resting and EGF-stimulated cells. Collectively, our data demonstrate that the inhibition of STAT3 signaling by NDRG2 suppresses EMT progression of EMT via the down-regulation of Snail expression.

Tumor suppressor NDRG2 tips the balance of oncogenic TGF-β via EMT inhibition in colorectal cancer

Transforming growth factor-beta (TGF-β), a pluripotent cytokine expressed in the colon, has a crucial but paradoxical role in colorectal cancer (CRC). TGF-β is a potent proliferation inhibitor of normal colon epithelial cells and acts as a tumor suppressor. However, TGF-β also promotes invasion and metastasis during late-stage CRC, thereby acting as an oncogene. Thus, understanding the factors behind the paradoxical roles of TGF-β and elucidating the mechanisms by which TGF-β-induced proliferation inhibition is impaired in CRC are necessary. Here, we found that the N-Myc tumor suppressor gene downstream-regulated gene NDRG2 (N-Myc downstream-regulated gene 2), which is a TGF-β-responsive gene, abrogated TGF-β-induced epithelial–mesenchymal transition (EMT) and further inhibited the invasion and migration of CRC cells. TGF-β positively induced NDRG2 expression through direct transactivation mediated by Sp1 and by abrogation of the repressive c-Myc/Miz-1 complex on NDRG2 promoter in normal epithelial cells. Aberrant hypermethylation of NDRG2, which could respond to TGF-β growth inhibition signaling, abrogated the inhibitory effect of NDRG2 in TGF-β-induced EMT in CRCs. Reduced NDRG2 expression was highly correlated with the invasion stage and metastasis of CRC. Our study establishes that NDRG2 is a new tumor suppressor gene that responds to TGF-β anti-proliferative signaling and tips the balance of oncogenic TGF-β during late-stage CRC.