Epigenetic silencing of NDRG2 promotes colorectal cancer proliferation and invasion

Biological and prognostic significance of NDRG2 downregulation in oral squamous cell carcinoma

OBJECTIVE

Downregulation of N-myc downstream-regulated gene 2 (NDRG2), a tumor suppressor gene, has been associated with poor clinical outcomes in various cancers. However, the prognostic significance of NDRG2 in oral squamous cell carcinoma (OSCC) remains unknown. This study aimed to evaluate the prognostic value of NDRG2 downregulation in OSCC and to elucidate the mechanism by which NDRG2 is downregulated and the biological role of NDRG2 in tumor progression.

METHODS

Immunohistochemical and in silico analyses of NDRG2 expression were performed, and the correlation between NDRG2 expression and clinicopathological data was analyzed. The effect of NDRG2 knockdown on the biological behavior of OSCC cells was investigated and the effect of 5-aza-2'-deoxycytidine (5-aza-dC) on NDRG2 expression was determined.

RESULTS

NDRG2 expression was significantly downregulated and DNA hypermethylation of NDRG2 was frequently found in head and neck SCC, including OSCC. Low NDRG2 expression was significantly correlated with adverse clinicopathological features and worse survival in OSCC. NDRG2 knockdown could enhance the oncogenic properties of OSCC cells. NDRG2 mRNA levels in OSCC cells could be restored by 5-aza-dC.

CONCLUSION

Downregulation of NDRG2 promotes tumor progression and predicts poor prognosis in OSCC. Therefore, restoration of NDRG2 expression may be a potential therapeutic strategy in OSCC.

The Function of N-Myc Downstream-Regulated Gene 2 (NDRG2) as a Negative Regulator in Tumor Cell Metastasis

N-myc downstream-regulated gene 2 (NDRG2) is a tumor-suppressor gene that suppresses tumorigenesis and metastasis of tumors and increases sensitivity to anti-cancer drugs. In this review, we summarize information on the clinicopathological characteristics of tumor patients according to NDRG2 expression in various tumor tissues and provide information on the metastasis inhibition-related cell signaling modulation by NDRG2. Loss of NDRG2 expression is a prognostic factor that correlates with TNM grade and tumor metastasis and has an inverse relationship with patient survival in various tumor patients. NDRG2 inhibits cell signaling, such as AKT-, NF-κB-, STAT3-, and TGF-β-mediated signaling, to induce tumor metastasis, and induces activation of GSK-3β which has anti-tumor effects. Although NDRG2 operates as an adaptor protein to mediate the interaction between kinases and phosphatases, which is essential in regulating cell signaling related to tumor metastasis, the molecular mechanism of NDRG2 as an adapter protein does not seem to be fully elucidated. This review aims to assist the research design regarding NDRG2 function as an adaptor protein and suggests NDRG2 as a molecular target to inhibit tumor metastasis and improve the prognosis in tumor patients.

The Crosstalk Between Signaling Pathways and Cancer Metabolism in Colorectal Cancer

Colorectal cancer (CRC) is one of the most frequently diagnosed cancers worldwide. Metabolic reprogramming represents an important cancer hallmark in CRC. Reprogramming core metabolic pathways in cancer cells, such as glycolysis, glutaminolysis, oxidative phosphorylation, and lipid metabolism, is essential to increase energy production and biosynthesis of precursors required to support tumor initiation and progression. Accumulating evidence demonstrates that activation of oncogenes and loss of tumor suppressor genes regulate metabolic reprogramming through the downstream signaling pathways. Protein kinases, such as AKT and c-MYC, are the integral components that facilitate the crosstalk between signaling pathways and metabolic pathways in CRC. This review provides an insight into the crosstalk between signaling pathways and metabolic reprogramming in CRC. Targeting CRC metabolism could open a new avenue for developing CRC therapy by discovering metabolic inhibitors and repurposing protein kinase inhibitors/monoclonal antibodies.

LncRNA RAD51-AS1/miR-29b/c-3p/NDRG2 crosstalk repressed proliferation, invasion and glycolysis of colorectal cancer

LncRNAs are recently increasingly emerging as molecules that take its part in human carcinogenesis. A large body of literature has identified the functional roles of lncRNAs in the pathophysiology of CRC. The current study was intended to provide new ideas and perspectives for the functional role of lncRNA RAD51-AS1 in regulating CRC progression. Herein, a survey of RAD51-AS1 expression profile in The Cancer Genome Atlas (TCGA)-colon adenocarcinoma (COAD) dataset revealed that RAD51-AS1 was downregulated in COAD specimens. Consistently, RAD51-AS1 expression was observed to be lower in CRC cell lines compared with normal cell line (NCM460). In the meanwhile, both the levels of miR-29b-3p and miR-29c-3p were prominently elevated in CRC cells. Functionally, administration of RAD51-AS1 refrained growth, invasion and migration of CRC cells. Additionally, accumulation of RAD51-AS1 hampered glucose consumption and lactate production, as well as the restraint of hexokinase 2 (HK2) and glucose transporter 1 (GLUT1) levels. More important, RAD51-AS1 functioned as a competing endogenous RNA (ceRNA) for sponging miR-29b-3p and miR-29c-3p, leading to enhancement of their common target N-myc downstream-regulated gene 2 (NDRG2). Mechanistically, the delivery of miR-29b/c-3p mimics or ablation of NDRG2 effectively blunted the salutary effects of RAD51-AS1 on CRC cell behaviors. Moreover, augmentation of RAD51-AS1 inhibited the tumorigenesis of CRC cells in vivo. Collectively, these findings provide comprehensive evidence that RAD51-AS1 repressed cell proliferation, migration, invasion and glycolysis process, ultimately contributing to the progression of CRC by repressing the miR-29b/c-3p/NDRG2 signaling axis, insinuating the putative potential of RAD51-AS1/miR-29b/c-3p/NDRG2 interaction network in unraveling CRC pathology and hopefully contributed to the treatment of CRC patients.

Roles of N-myc downstream-regulated gene 2 in the central nervous system: molecular basis and relevance to pathophysiology

N-myc downstream-regulated gene 2 (NDRG2) is a member of the NDRG family, whose members have multiple functions in cell proliferation, differentiation, and stress responses. NDRG2 is widely distributed in the central nervous system and is uniquely expressed by astrocytes; however, its role in brain function remains elusive. The clinical relevance of NDRG2 and the molecular mechanisms in which it participates have been reported by studies using cultured cells and specimens of patients with neurological disorders. In recent years, genetic tools, including several lines of Ndrg2-knockout mice and virus-mediated gene transfer, have improved understanding of the roles of NDRG2 in vivo. This review aims to provide an update of recent growing in vivo evidence that NDRG2 is involved in brain function, focusing on research of Ndrg2-knockout mice with neurological disorders such as brain tumors, chronic neurodegenerative diseases, and acute brain insults including brain injury and cerebral stroke. These studies demonstrate that NDRG2 plays diverse roles in the regulation of astrocyte reactivity, blood-brain barrier integrity, and glutamate excitotoxicity. Further elucidation of the roles of NDRG2 and their molecular basis may provide novel therapeutic approaches for various neurological disorders.

Structural and Biophysical Analyses of Human N-Myc Downstream-Regulated Gene 3 (NDRG3) Protein

The N-Myc downstream-regulated gene (NDRG) family belongs to the α/β-hydrolase fold and is known to exert various physiologic functions in cell proliferation, differentiation, and hypoxia-induced cancer metabolism. In particular, NDRG3 is closely related to proliferation and migration of prostate cancer cells, and recent studies reported its implication in lactate-triggered hypoxia responses or tumorigenesis. However, the underlying mechanism for the functions of NDRG3 remains unclear. Here, we report the crystal structure of human NDRG3 at 2.2 Å resolution, with six molecules in an asymmetric unit. While NDRG3 adopts the α/β-hydrolase fold, complete substitution of the canonical catalytic triad residues to non-reactive residues and steric hindrance around the pseudo-active site seem to disable the α/β-hydrolase activity. While NDRG3 shares a high similarity to NDRG2 in terms of amino acid sequence and structure, NDRG3 exhibited remarkable structural differences in a flexible loop corresponding to helix α6 of NDRG2 that is responsible for tumor suppression. Thus, this flexible loop region seems to play a distinct role in oncogenic progression induced by NDRG3. Collectively, our studies could provide structural and biophysical insights into the molecular characteristics of NDRG3.

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.

Clinical and Molecular Comparative Study of Colorectal Cancer Based on Age-of-onset and Tumor Location: Two Main Criteria for Subclassifying Colorectal Cancer

Our aim was to characterize and validate that the location and age of onset of the tumor are both important criteria to classify colorectal cancer (CRC). We analyzed clinical and molecular characteristics of early-onset CRC (EOCRC) and late-onset CRC (LOCRC), and we compared each tumor location between both ages-of-onset. In right-sided colon tumors, early-onset cases showed extensive Lynch syndrome (LS) features, with a relatively low frequency of chromosomal instability (CIN), but a high CpG island methylation phenotype. Nevertheless, late-onset cases showed predominantly sporadic features and microsatellite instability cases due to BRAF mutations. In left colon cancers, the most reliable clinical features were the tendency to develop polyps as well as multiple primary CRC associated with the late-onset subset. Apart from the higher degree of CIN in left-sided early-onset cancers, differential copy number alterations were also observed. Differences among rectal cancers showed that early-onset rectal cancers were diagnosed at later stages, had less association with polyps, and more than half of them were associated with a familial LS component. Stratifying CRC according to both location and age-of-onset criteria is meaningful, not only because it correlates the resulting categories with certain molecular bases, but with the confirmation across larger studies, new therapeutical algorithms could be defined according to this subclassification.

Association of HIF-1α and NDRG2 Expression with EMT in Gastric Cancer Tissues

OBJECTIVE

This study aims to investigate the differences in the expression of hypoxia-inducible factor-1α (HIF-1α), N-myc downstream-regulated gene 2 (NDRG2) and epithelial mesenchymal transition (EMT)-related proteins in normal gastric tissues, gastric cancer tissues and lymph node metastasis.

METHODS

Immunohistochemistry was used to detect the expression of HIF-1α, NDRG2, E-cadherin, Snail and Twist in normal gastric tissues, gastric cancer tissues and lymph node metastasis.

RESULTS

In normal gastric tissues, HIF-1α was not expressed, NDRG2 was highly expressed. There was a significant between the expression of NDRG2 and Snail, as well as of NDRG2 and Twist. In gastric cancer tissues, there was no statistically difference between the expression of HIF-1α and E-cadherin, NDRG2 and E-cadherin. However, there was a significant difference in expression between the expression of HIF-1α and Snail, HIF-1α and Twist, NDRG2 and Snail, and NDRG2 and Twist. In lymph node metastasis tissues, we show that HIF-1α was highly expressed, while NDRG2 was not, and the difference between the expression of HIF-1α and E-cadherin, HIF-1α and Snail, HIF-1α and Twist was not significant.

CONCLUSION

HIF-1α may promote EMT, possibly by inhibiting the expression of NDRG2.

N-myc downstream-regulated gene 2 (NDRG2) promoter methylation and expression in pituitary adenoma

BACKGROUND

Pituitary adenoma (PA) is a benign primary tumor that arises from the pituitary gland and is associated with ophthalmological, neurological and endocrinological abnormalities. However, causes that increase tumor progressing recurrence and invasiveness are still undetermined. Several studies have shown N-myc downstream regulated gene 2 (NDRG2) as a tumor suppressor gene, but the role of NDRG2 gene in pituitary adenoma pathogenesis has not been elucidated. The aim of our research has been to examine NDRG2 mRNA expression in PA and to determine the associations between the NDRG2 gene epigenetic changes and the development of recurrence or invasiveness of PA and patient clinical data.

METHODS

The MS-PCR was used for NDRG2 promoter methylation analysis and gene mRNA expression levels were evaluated by qRT-PCR in 68 non-functioning and 73 functioning adenomas. Invasiveness was evaluated using magnetic resonance imaging with Hardy's modified criteria. Statistical analysis was performed to find correlations between NDRG2 gene mRNA expression, promoter methylation and patient clinical characteristics and PA activity.

RESULTS

The NDRG2 mRNA expression was significantly lower in the case of acromegaly (GH and IGF-1 hypersecretion) than in other diagnoses of PAs (p < 0.05). Also, the NDRG2 expression was significantly higher in prolactinoma (PRL hypersecretion) than in in other diagnoses of PAs (p < 0.05). The promoter of NDRG2 was methylated in 22.69% (12/58 functioning and 15/61 non-functioning) of patients with PA. However, the NDRG2 gene mRNA expression was not significantly related to its methylation status. Clinical factors, such as: age, gender, relapse and diagnoses of Cushing syndrome were of no significance for NDRG2 promoter methylation and mRNA expression levels, as well as secreting or non-secreting PAs and the invasiveness of PAs.

CONCLUSION

The different NDRG2 promoter methylation and expression levels in PA samples showed tumor heterogeneity and indicates a potential role of this gene in pituitary adenoma pathogenesis, but the corresponding details require intensive research.

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.

Hypermethylation of the N-Myc Downstream-Regulated Gene 2 Promoter in Peripheral Blood Mononuclear Cells is Associated with Liver Fibrosis in Chronic Hepatitis B

DNA methylation is a fundamental epigenetic modification to regulate gene expression. N-Myc downstream-regulated gene (NDRG) 2 is a cytoplasmic protein and participates in the pathogenesis of liver fibrosis. In this study, the mRNA expression and methylation status of NDRG2 was evaluated in patients with chronic hepatitis B (CHB). The study included 143 CHB patients and 65 normal controls (NC). The mRNA expression of NDRG2 in peripheral blood mononuclear cells (PBMCs) was detected by quantitative real-time polymerase chain reaction. The methylation status of the NDRG2 promoter in PBMCs was detected by methylation-specific polymerase chain reaction. The NDRG2 mRNA level was lower in the CHB group than in the NC group (p < 0.001). Methylation frequency of the NDRG2 promoter was significantly higher in CHB patients than in the NC group (52.44% vs. 26.15%, p < 0.001). Importantly, the relative expression levels of NDRG2 mRNA were significantly lower in the methylated group than in the unmethylated group in both CHB patients and NC (p < 0.001). Furthermore, a lower mRNA level and hypermethylation of NDRG2 were associated with liver fibrosis and inflammation grade in CHB. The aspartate aminotransferase-to-platelet ratio index (APRI) score is widely used to predict liver fibrosis. The mRNA expression levels and methylation status of NDRG2 showed a better score compared to APRI for discriminating the severity of liver fibrosis. In conclusion, hypermethylation of NDRG2 in PBMCs was correlated with decreased mRNA expression and with liver fibrosis. The methylation status of the NDRG2 promoter in PBMCs is a potential noninvasive biomarker to predict the severity of liver fibrosis.

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.

Drug Discovery via Human-Derived Stem Cell Organoids

Patient-derived cell lines and animal models have proven invaluable for the understanding of human intestinal diseases and for drug development although both inherently comprise disadvantages and caveats. Many genetically determined intestinal diseases occur in specific tissue microenvironments that are not adequately modeled by monolayer cell culture. Likewise, animal models incompletely recapitulate the complex pathologies of intestinal diseases of humans and fall short in predicting the effects of candidate drugs. Patient-derived stem cell organoids are new and effective models for the development of novel targeted therapies. With the use of intestinal organoids from patients with inherited diseases, the potency and toxicity of drug candidates can be evaluated better. Moreover, owing to the novel clustered regularly interspaced short palindromic repeats/CRISPR-associated protein-9 genome-editing technologies, researchers can use organoids to precisely modulate human genetic status and identify pathogenesis-related genes of intestinal diseases. Therefore, here we discuss how patient-derived organoids should be grown and how advanced genome-editing tools may be applied to research on modeling of cancer and infectious diseases. We also highlight practical applications of organoids ranging from basic studies to drug screening and precision medicine.