Expression and regulation of NDRG2 (N-myc downstream regulated gene 2) during the differentiation of dendritic cells

Cabergoline targets multiple pathways to inhibit PRL secretion and increases stromal fibrosis

OBJECTIVE

Unravel the potential mechanism(s) of the on- and off-target actions of dopamine agonist therapy in both human prolactinoma tumors and neighboring stromal and immune cells.

DESIGN AND METHODS

Five surgically resected prolactinomas (PRLomas) from 3 cabergoline (CBG)-treated patients and 2 treatment-naive patients were analyzed by using single-cell RNA sequencing (scRNA-seq) to compare the cellular composition and transcriptional landscape.

RESULTS

Six major cell populations, namely tumor (88.2%), immune (5.6%), stromal (4.9%), progenitor cells (0.6%), proliferating cells (0.4%), and erythrocytes (0.2%), were observed. Tumor cells from CBG-treated patients expressed lower levels of genes that regulated hormone secretion, such as SCG2, VGF, TIMP1, NNAT, and CALD1, consistent with the inhibitory effects of CBG on hormone processing and secretion. Interestingly, we also observed an increased number of CD8+ T cells in the CBG-treated tissues. These cytotoxic CD8+ T cells expressed killing granule components such as perforin and the granzymes GZMB, GNLY, and KLRD1 as well as the inflammatory cytokine CCL5. Immune cell activation of these CD8+ T cells was further analyzed in a compartment-specific manner, and increased CD25 (IL2R) expression was noted in the CD8+ T cells from the CBG-treated samples. Additionally, and confirming prior reports, we noted a higher stromal cell population in the CBG-treated samples.

CONCLUSIONS

Our scRNA-seq studies revealed key differences in the transcriptomic features of CBG-treated and CBG-untreated PRLomas in both tumor and microenvironment cellular constituents, and for the first time, describe the previously unknown activation of CD8+ T cells following CBG treatment, which may play a role in the tumoricidal actions of CBG.

Cas9-mediated knockout of Ndrg2 enhances the regenerative potential of dendritic cells for wound healing

Chronic wounds impose a significant healthcare burden to a broad patient population. Cell-based therapies, while having shown benefits for the treatment of chronic wounds, have not yet achieved widespread adoption into clinical practice. We developed a CRISPR/Cas9 approach to precisely edit murine dendritic cells to enhance their therapeutic potential for healing chronic wounds. Using single-cell RNA sequencing of tolerogenic dendritic cells, we identified N-myc downregulated gene 2 (Ndrg2), which marks a specific population of dendritic cell progenitors, as a promising target for CRISPR knockout. Ndrg2-knockout alters the transcriptomic profile of dendritic cells and preserves an immature cell state with a strong pro-angiogenic and regenerative capacity. We then incorporated our CRISPR-based cell engineering within a therapeutic hydrogel for in vivo cell delivery and developed an effective translational approach for dendritic cell-based immunotherapy that accelerated healing of full-thickness wounds in both non-diabetic and diabetic mouse models. These findings could open the door to future clinical trials using safe gene editing in dendritic cells for treating various types of chronic wounds.

The ndrg2 Gene Regulates Hair Cell Morphogenesis and Auditory Function during Zebrafish Development

Damages of sensory hair cells (HCs) are mainly responsible for sensorineural hearing loss, however, its pathological mechanism is not yet fully understood due to the fact that many potential deafness genes remain unidentified. N-myc downstream-regulated gene 2 (ndrg2) is commonly regarded as a tumor suppressor and a cell stress-responsive gene extensively involved in cell proliferation, differentiation, apoptosis and invasion, while its roles in zebrafish HC morphogenesis and hearing remains unclear. Results of this study suggested that ndrg2 was highly expressed in the HCs of the otic vesicle and neuromasts via in situ hybridization and single-cell RNA sequencing. Ndrg2 loss-of-function larvae showed decreased crista HCs, shortened cilia, and reduced neuromasts and functional HCs, which could be rescued by the microinjection of ndrg2 mRNA. Moreover, ndrg2 deficiency induced attenuated startle response behaviors to sound vibration stimuli. Mechanistically, there were no detectable HC apoptosis and supporting cell changes in the ndrg2 mutants, and HCs were capable of recovering by blocking the Notch signaling pathway, suggesting that ndrg2 was implicated in HC differentiation mediated by Notch. Overall, our study demonstrates that ndrg2 plays crucial roles in HC development and auditory sensory function utilizing the zebrafish model, which provides new insights into the identification of potential deafness genes and regulation mechanism of HC development.

Loss of ndrg2 Function Is Involved in Notch Activation in Neuromast Hair Cell Regeneration in Zebrafish

The regeneration of hair cells in zebrafish is a complex process involving the precise regulation of multiple signaling pathways, but this complicated regulatory network is not fully understood. Current research has primarily focused on finding molecules and pathways that can regulate hair cell regeneration and restore hair cell functions. Here, we show the role of N-Myc downstream regulated gene 2 (ndrg2) in zebrafish hair cell regeneration. We first found that ndrg2 was dynamically expressed in neuromasts of the developing zebrafish, and this expression was increased after neomycin-induced hair cell damage. Then, ndrg2 loss-of-function larvae showed reduced numbers of regenerated hair cells but increased numbers of supporting cells after neomycin exposure. By in situ hybridization, we further observed that ndrg2 loss of function resulted in the activation of Notch signaling and downregulation of atoh1a during hair cell regeneration in vivo. Additionally, blocking Notch signaling rescued the number of regenerated hair cells in ndrg2-deficient larvae. Together, this study provides evidence for the role of ndrg2 in regulating hair cell regeneration in zebrafish neuromasts.

Anti-inflammatory and immunoregulatory effects of pinolenic acid in rheumatoid arthritis

Objectives

In pre-clinical studies, pinolenic acid (PNLA), an omega-6-polyunsaturated fatty acid from pine nuts, has shown anti-inflammatory effects. We aimed to investigate the effect of PNLA in human cell lines and peripheral blood mononuclear cells (PBMCs) from RA patients and healthy controls (HCs).

Methods

A modified Boyden chamber was used to assess chemokine-induced migration of THP-1 monocytes. Macropinocytosis was assessed using Lucifer yellow and oxidized low-density lipoprotein (oxLDL) uptake using DiI-labelled oxLDL in THP-1 macrophages and human monocyte-derived macrophages (HMDMs). IL-6, TNF-α and prostaglandin E₂ (PGE2) release by lipopolysaccharide (LPS)-stimulated PBMCs from RA patients and HCs was measured by ELISA. The transcriptomic profile of PNLA-treated, LPS-activated PBMCs was investigated by RNA-sequencing.

Results

PNLA reduced THP-1 cell migration by 55% (P < 0.001). Macropinocytosis and DiI-oxLDL uptake were reduced by 50% (P < 0.001) and 40% (P < 0.01), respectively, in THP-1 macrophages and 40% (P < 0.01) and 25% (P < 0.05), respectively, in HMDMs. PNLA reduced IL-6 and TNF-α release from LPS-stimulated PBMCs from RA patients by 60% (P < 0.001) and from HCs by 50% and 35%, respectively (P < 0.01). PNLA also reduced PGE2 levels in such PBMCs from RA patients and HCs (P < 0.0001). Differentially expressed genes whose expression was upregulated included pyruvate dehydrogenase kinase-4, plasminogen activator inhibitor-1, fructose bisphosphatase1 and N-Myc downstream-regulated gene-2, which have potential roles in regulating immune and metabolic pathways. Pathway analysis predicted upstream activation of the nuclear receptors peroxisome proliferator-activated receptors involved in anti-inflammatory processes, and inhibition of nuclear factor-κB and signal transducer and activator of transcription 1.

Conclusions

PNLA has immune-metabolic effects on monocytes and PBMCs that are pathogenic in RA and atherosclerosis. Dietary PNLA supplementation may be beneficial in RA.

Expression Profile of Osteoclasts Following the Stimulation With Interleukin-23 in Mice

Objectives

This study aims to analyze the expression profile of osteoclasts (OCs) following the stimulation with interleukin 23 (IL-23) in mice, which would imply the underlying effects of IL-23 on the function of OCs in inflammatory arthritis.

Materials and methods

Mature OCs were induced from bone marrow mononuclear cells of 5 male mice (age 6 weeks; weighing 18-20 g) in the presence of macrophage-colony stimulating factor (50 ng/mL) and receptor activator of nuclear factor kappa B ligand (30 ng/mL) in vitro. The Agilent SurePrint G3 Mouse GE V2.0 Microarray was used to analyze the gene expression profile of OCs stimulated with IL-23 (30 ng/mL) or vehicle. The four major IL-23-modulated genes were validated by quantitative real-time polymerase chain reaction (qPCR) analysis.

Results

The expression levels of 23 genes were up-regulated and 32 genes were down-regulated by IL-23 stimulation (fold change ≥1.5 and p value <0.05). Among them, there were 37 genes with assigned gene symbols. Gene ontology analysis showed that the IL-23-regulated messenger ribonucleic acids (mRNAs) were related to positive regulation of leukocyte chemotaxis, chemokine-mediated signaling pathway and C-X-C chemokine receptors binding. The pathway analysis showed that the IL-23-regulated mRNAs were related to chemokine signaling pathway and cytokine-cytokine receptor interaction. The significant up-regulation of chemokine (C-X-C motif) ligand 1 and chemokine (C-X-C motif) ligand 2 induced by IL-23 was confirmed by qPCR. In addition, there were 18 long non-coding RNAs that were regulated by IL-23, while their function needs to be confirmed in the future.

Conclusion

Expression levels of genes related to chemotaxis in OCs were up-regulated by IL-23 in mice, which imply that IL-23 may facilitate chemotaxis of OCs in inflammatory arthritis.

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.

cDC2 and plasmacytoid dendritic cells diminish from tissues of patients with non-Hodgkin orbital lymphoma and idiopathic orbital inflammation

Non-Hodgkin orbital lymphoma (NHOL) and idiopathic orbital inflammation (IOI) are common orbital conditions with largely unknown pathophysiology. To investigate the immune cell composition of these diseases, we performed standardized 29 parameter flow cytometry phenotyping in peripheral blood mononuclear cells of 18 NHOL patients, 21 IOI patients, and 41 unaffected controls. Automatic gating by FlowSOM revealed decreased abundance of meta-clusters containing dendritic cells in patients, which we confirmed by manual gating. A decreased percentage of (HLA-DR⁺ CD303⁺ CD123⁺ ) plasmacytoid dendritic cells (pDC) in the circulation of IOI patients and decreased (HLA-DR⁺ CD11c⁺ CD1c⁺ ) conventional dendritic cells (cDC) type-2 for IOI patients were replicated in an independent cohort of patients and controls. Meta-analysis of both cohorts demonstrated that pDCs are also decreased in blood of NHOL patients and highlighted that the decrease in blood cDC type-2 was specific for IOI patients compared to NHOL or controls. Deconvolution-based estimation of immune cells in transcriptomic data of 48 orbital biopsies revealed a decrease in the abundance of pDC and cDC populations within the orbital microenvironment of IOI patients. Collectively, these data suggest a previously underappreciated role for dendritic cells in orbital disorders.

Characterization of the prognostic values of the NDRG family in gastric cancer

BACKGROUND

The N-myc downstream-regulated gene (NDRG) family, NDRG1-4, has been involved in a wide spectrum of biological functions in multiple cancers. However, their prognostic values remain sparse in gastric cancer (GC). Therefore, it is crucial to systematically investigate the prognostic values of the NDRG family in GC.

METHODS

The prognostic values of the NDRG family were evaluated by Kaplan-Meier Plotter and SurvExpress. The mRNA of the NDRG family was investigated in The Cancer Genome Atlas (TCGA). Transcription factors (TFs) and miRNAs associated with the NDRG family were predicted by NetworkAnalysis. The prognostic values of DNA methylation levels were analyzed by MethSurv. The correlation between immune cells and the NDRG family was evaluated by the Tumor Immune Estimation Resource (TIMER) database.

RESULTS

High levels of mRNA expression of NDRG2 and NDRG3 were associated with a favorable prognosis in all GCs. In HER2 ^- GC, NDRG1 was significantly associated with a poor prognosis of GC [hazard ratio (HR) = 1.65, 95% confidence interval (CI) = 1.16-2.33, p = 0.0046]. In HER2 ⁺ GC, NDRG4 showed a poor prognosis (HR = 1.4, 95% CI: 1.06-1.85, p = 0.017). NDRG4 was an independent prognostic factor in recurrence-free survival by TCGA cohort. The low-risk NDRG-signature group displayed a significantly favorable survival outcome than the high-risk group (HR = 1.76, 95% CI: 1.2-2.59, p = 0.00385). The phosphorylated protein NDRG1 (NDRG1_pT346) displayed a favorable overall survival and was significantly associated with HER2 and phosphorylated HER2. Epidermis development was the top biological process (BP) for coexpressed genes associated with NDRG1 and NDRG4, while mitotic nuclear division and mitotic cell processes were the top BPs for NDRG2 and NDRG3, respectively. Overall, 6 CpGs of NDRG1, 4 CpGs of NDRG2, 3 CpGs of NDRG3 and 24 CpGs of NDRG4 were associated with significant prognosis. CD4⁺ T-cells showed the highest correlation with NDRG4 (correlation = 0.341, p = 2.14e^-11). Furthermore, BCL6 in follicular helper T-cells (Tfh) cells showed the highest association with NDRG4 (correlation = 0.438, p = 00e⁺00).

CONCLUSIONS

This study analyzed the multilevel prognostic values and biological roles of the NDRG family in GC.

Spatiotemporal expression of NDRG2 in the human fetal brain

N-myc downstream-regulated gene 2 (NDRG2) has been implicated in the development of central nervous system and brain diseases such as brain tumors, ischemic stroke and neurodegenerative disorders. However, it remains unclear that the spatiotemporal distribution of NDRG2 in the human fetal brain. In this study, we examined the expression pattern of NDRG2 in different regions of human fetal brain at 16-28 gestational weeks (GWs) by using RT-PCR, western blot and immunohistochemistry. Firstly, RT-PCR revealed that mRNA of NDRG2 was detected in the human brain regions of fetuses at 16-28 GWs such as medulla oblongata (MdO), mesencephalon (MeE), cerebellum (Cbl), frontal lobe (Fr), ventricular (VZ)/subventricular zone (SVZ) and hippocampus (hip), and the expressions of NDRG2 mRNA in these human fetal brain regions were increased with gestational maturation. Furthermore, western blot and immunohistochemistry results revealed that at 28 GWs, the expression of NDRG2 protein was restricted to the MdO's olivary nucleus, MeE's aqueduct, cerebellar internal granular layers, cerebral cortex of the Fr, VZ/SVZ of lateral ventricle, and hippocampal dentate gyrus, and highest expression in the VZ/SVZ, and lowest in the MeE. Finally, double immunohistochemistry results showed that NDRG2 in the MdO, Cbl and VZ/SV at 28 GWS was mainly expressed in neurons (NeuN positive cells), and in some astrocytes (GFAP positive cells). Taken together, these results suggest that NDRG2 is mainly expressed in human fetal neurons of various brain regions during development, which may be involved in neuronal growth and maturation.

Identification of the Differential Expression Profiles of Serum and Tissue Proteins During Rat Hepatocarcinogenesis

The pathogenesis of hepatocellular carcinoma is complex and not fully known yet. This study aims to screen and identify the differentially expressed proteins in peripheral blood and liver tissue samples from rat hepatocellular carcinoma and to further clarify the pathogenesis and discover the specific tumor markers and molecular targets of hepatocellular carcinoma. The hepatocellular carcinoma model of Wistar rats were induced by chemical carcinogen. The serum and liver tissue samples were obtained after induction for 2, 4, 8, 14, 18, and 21 weeks. The results showed that the clusterin (IPI00198667), heat shock protein a8 (IPI00208205), and N-myc downstream-regulated gene-2 (IPI00382069) being closely related to hepatocarcinogenesis were eventually identified from the 30 different proteins. As the time progressed, the serum levels of clusterin and heat shock protein a8 increased gradually during induced liver cancer in rats. However, the serum N-myc downstream-regulated gene 2 level in induced liver cancer in rats underwent biphasic changes, and the serum N-myc downstream-regulated gene 2 level decreased at the 8th week, increased at the 14th week, and then decreased significantly. Statistical difference occurred in protein expression of clusterin and heat shock protein a8 in liver tissues at the different time points. In the liver tissues, the N-myc downstream-regulated gene 2 level decreased gradually at the 8th week, increased gradually at the 14th week, and then decreased significantly after 14 weeks. The study demonstrated that heat shock protein a8, clusterin, and N-myc downstream-regulated gene 2 participated in the process of abnormal cell division, proliferation, and carcinogenesis of liver cells during hepatocarcinogenesis.

Expression of N-Myc Downstream-Regulated Gene 2 in Bladder Cancer and Its Potential Utility as a Urinary Diagnostic Biomarker

BACKGROUND Initial diagnosis of carcinoma of the urinary bladder remains challenging. N-Myc downstream-regulated gene 2 (NDRG2) has been reported to be closely correlated with cell differentiation and proliferation in various cancers. However, its clinical significance in diagnosis of bladder cancer remains unclear. The purpose of this study was to detect the expression of NDRG2 and investigate its diagnostic value in bladder cancer. MATERIAL AND METHODS We recruited 127 patients with bladder cancer and 97 healthy controls. Quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) and Western blotting analysis were conducted to measure the NDRG2 expression levels in urine of patients with bladder cancer, bladder cancer cell lines, and healthy controls. The correlations between NDRG2 expression and clinicopathological characteristics were analyzed by chi-square test, and the diagnostic value of NDRG2 was estimated by establishing a receiver operating characteristic (ROC) curve. RESULTS The relative NDRG2 expression were significantly downregulated both at mRNA and protein levels in urine of patients with bladder cancer and in cell lines, and its low expression was distinctively correlated with tumor grade and stage. The ROC curve showed NDRG2 could be a good diagnostic marker, with an AUC of 0.888, indicating high sensitivity and specificity. CONCLUSIONS NDRG2 was decreased in patients with bladder cancer and might be involved in the progression of this malignancy. Moreover, NDRG2 could be a potential independent diagnostic biomarker for bladder cancer.

Overexpression of NDRG2 Increases Iodine Uptake and Inhibits Thyroid Carcinoma Cell Growth In Situ and In Vivo

Medullary thyroid carcinoma (MTC) is an uncommon and highly aggressive tumor of the neuroendocrine system, which derives from the neuroendocrine C cells of the thyroid gland. Except for surgical resection, there are not very many effective systemic treatment options for MTC. N-Myc downstream-regulated gene 2 (NDRG2) had a significantly lower expression in MTC compared with normal thyroid tissue. However, the function of NDRG2 in MTC oncogenesis is largely unknown. In this study, we found that overexpression of NDRG2 inhibited the proliferation of TT cells (human medullary thyroid carcinoma cells) in vitro and suppressed the development of MTC in a nude mouse xenograft model. Further analysis revealed that NDRG2 arrested the cell cycle G₀/G₁ phase progression and induced TT cell apoptosis. Moreover, NDRG2 overexpression may mediate the antiproliferative effect by reducing cyclin D1 and cyclin E protein levels. We also found aberrant NDRG2-mitigated TT cell migration and invasion in vitro. Sodium/iodide symporter (NIS) mediates active I⁻ transport into the thyroid follicular cells, and radionuclide treatment is a promising therapy for MTC. Our current data revealed that NDRG2 overexpression enhanced NIS level in TT cells and increased their iodine uptake in vitro. Furthermore, ^99mTcO₄⁻ radionuclide imaging of the xenograft tumors indicated that NDRG2 could promote NIS-mediated radionuclide transport. In conclusion, the present study suggested that NDRG2 is a critical molecule in the regulation of MTC biological behavior and a potential promoter in radioactive iodine therapy.

NDRG4 is a novel oncogenic protein and p53 associated regulator of apoptosis in malignant meningioma cells

Aggressive meningiomas exhibit high levels of recurrence, morbidity and mortality. When surgical and radiation options are exhausted, there is need for novel molecularly-targeted therapies. We have recently identified NDRG4 overexpression in aggressive meningiomas. NDRG4 is a member of the N-Myc Downstream Regulated Gene (NDRG) family of the alpha/beta hydrolase superfamily. We have demonstrated that NDRG4 downregulation results in decreased cell proliferation, migration and invasion. In follow up to our prior studies; here we demonstrate that the predominant form of cell death following NDRG4 silencing is apoptosis, utilizing Annexin-V flow cytometry assay. We show that apoptosis caused by p53 upregulation, phosphorylation at Ser15, BAX activation, Bcl-2 and BcL-xL downregulation, mitochondrial cytochrome c release and execution of caspases following NDRG4 depletion. Sub-cellular distribution of BAX and cytochrome c indicated mitochondrial-mediated apoptosis. In addition, we carried out the fluorescence cytochemical analysis to confirm mitochondrial-mediated apoptosis by changes in mitochondrial membrane potential (Ψm), using JC-1 dye. Immunoprecipitation and immunofluorescence confirmed binding of NDRG4 to p53. In addition, we demonstrate that apoptosis is mitochondrial and p53 dependent. The proapoptotic effect of p53 was verified by the results in which a small molecule compound PFT-α, an inhibitor of p53 phosphorylation, is greatly protected against targeting NDRG4 induced apoptosis. These findings bring novel insight to the roles of NDRG4 in meningioma progression. A better understanding of this pathway and its role in meningioma carcinogenesis and cell biology is promising for the development of novel therapeutic targets for the management of aggressive meningiomas.

Inhibition of osteoclast differentiation by overexpression of NDRG2 in monocytes

N-Myc downstream-regulated gene 2 (NDRG2), a member of the NDRG family of differentiation-related genes, has been characterized as a regulator of dendritic cell differentiation from monocytes, CD34(+) progenitor cells, and myelomonocytic leukemic cells. In this study, we show that NDRG2 overexpression inhibits the differentiation of U937 cells into osteoclasts in response to stimulation with a combination of macrophage colony-stimulating factor (M-CSF) and soluble receptor activator of NF-κB ligand (RANKL). U937 cells stably expressing NDRG2 are unable to differentiate into multinucleated osteoclast-like cells and display reduced tartrate-resistant acid phosphatase (TRAP) activity and resorption pit formation. Furthermore, NDRG2 expression significantly suppresses the expression of genes that are crucial for the proliferation, survival, differentiation, and function of osteoclasts, including c-Fos, Atp6v0d2, RANK, and OSCAR. The activation of ERK1/2 and p38 is also inhibited by NDRG2 expression during osteoclastogenesis, and the inhibition of osteoclastogenesis by NDRG2 correlates with the down-regulation of the expression of the transcription factor PU.1. Taken together, our results suggest that the expression of NDRG2 potentially inhibits osteoclast differentiation and plays a role in modulating the signal transduction pathway responsible for osteoclastogenesis.

Astrocytic NDRG2 is involved in glucocorticoid-mediated diabetic mechanical allodynia

AIMS

The present study aims to test whether astrocytes contribute to glucocorticoid-mediated diabetic mechanical allodynia.

METHODS

Streptozotocin (STZ)-induced diabetic rats were used in our study. The intrathecal operation was performed 21 days after the onset of diabetes. Diabetic mechanical allodynia was present 28 d after the onset of diabetes, and the mechanical threshold was tested using von Frey filaments. Immunohistochemistry, including immunofluorescent histochemical staining, was performed to observe the morphology of the spinal dorsal horn (SDH). Western blot analysis was employed as a semi-quantitative assay of the expression levels of GFAP and NDRG2 associated with diabetic mechanical allodynia.

RESULTS

Diabetic rats displayed mechanical allodynia and activated astrocytes in the SDH 28 days after the onset of diabetes. This allodynia was attenuated by intrathecal administration of the astrocyte-specific inhibitor l-α-aminoadipate. In parallel, intrathecal injection of RU486, a glucocorticoid receptor antagonist, inhibited the activation of astrocytes in the SDH, alleviating the diabetes-induced mechanical allodynia. Furthermore, we found that dorsal horn astrocytes express abundant N-myc downstream-regulated gene 2 (NDRG2), which contributes to astrocyte reactivity. NDRG2 was over-expressed in activated astrocytes in diabetic rats with mechanical allodynia. Intrathecal injection of RU486 prevented the over-expression of NDRG2, which reversed the astrocyte reactivity and diabetic tactile allodynia.

CONCLUSIONS

These results suggest that glucocorticoid-mediated over-expression of NDRG2 may contribute to the activation of dorsal horn astrocytes, which play a crucial role in diabetic mechanical allodynia. Thus, inhibiting glucocorticoid receptors and/or astrocyte reactivity in the SDH may be a therapeutic strategy for treating diabetic tactile allodynia.

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.

NDRG2 overexpression enhances glucose deprivation-mediated apoptosis in breast cancer cells via inhibition of the LKB1-AMPK pathway

The newly identified tumor suppressor, N-myc downstream-regulated gene 2 (NDRG2), has been studied in various cancers because of its anticancer and antimetastasis effects. In this study, we examined the effect of NDRG2 expression on cell viability in MDA-MB-231 human breast cancer cells under conditions that are similar to the microenvironment of solid tumors, which include glucose deprivation. NDRG2 overexpression enhanced the pro-apoptotic effects of glucose deprivation. Glucose deprivation also induced the activation of AMP-activated protein kinase (AMPK), which plays a role in protecting tumor cells from metabolic stresses. NDRG2 overexpression strongly reduced glucose deprivation-induced AMPK phosphorylation and increased the cleavage of poly (ADP-ribose) polymerase (PARP), which indicated the induction of apoptosis. The expression of a constitutively active form of AMPK effectively blocked glucose deprivation-induced apoptosis in NDRG2-overexpressing MDA-MB-231 cells. Moreover, NDRG2 overexpression also enhanced the pro-apoptotic effects of 2-deoxyglucose (2-DG) or hypoxia, an inducer of metabolic stresses. Finally, we showed that LKB1 is an upstream kinase of AMPK that is involved in the inhibition of glucose deprivation-induced AMPK activity in NDRG2-overexpressing cells. Our findings collectively suggest that NDRG2 is a negative regulator of AMPK activity and functions as a sensitizer of glucose deprivation.

The effect of adenovirus-conjugated NDRG2 on p53-mediated apoptosis of hepatocarcinoma cells through attenuation of nucleotide excision repair capacity

NDRG2 mRNA and protein levels can be upregulated in a p53-dependent manner. NDRG2 enhances p53-mediated apoptosis, whereas overexpression of NDRG2 suppresses tumor cell growth, regardless of whether p53 is mutated. However, the complicated mechanism by which NDRG2 suppresses tumor cell growth and enhances apoptosis mediated by p53 is not fully understood. Here, we demonstrated that Ad-NDRG2 enhanced the apoptosis of HepG2 cells (wild-type p53). Additionally, Ad-NDRG2 combined with rAd-p53 enhanced the apoptosis of Huh7 cells (mutant p53) after chemotherapy, and the expression of the ERCC6 gene (Cockayne syndrome group B protein gene) was suppressed in this process. Ad-NDRG2 combined with rAd-p53 induced the apoptosis of tumor cells (HepG2 and Huh7 cells); however, apoptosis was attenuated after transfection with ERCC6. Our results indicate that Ad-NDRG2 enhances the p53-mediated apoptosis of hepatocarcinoma cells (HepG2 and Huh7) by attenuating the nucleotide excision repair capacity (i.e., by downregulating ERCC6), and ERCC6 is a NDRG2-inducible target gene that is involved in the p53-mediated apoptosis pathway.

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.

NDRG2 is involved in anti-apoptosis induced by electroacupuncture pretreatment after focal cerebral ischemia in rats

OBJECTIVE

We first reported that electroacupuncture (EA) pretreatment at the Baihui acupoint (GV20) induces ischemic tolerance. Our recent study demonstrated that N-Myc downstream-regulated gene 2 (NDRG2) expression was up-regulated following transient focal cerebral ischemia. Therefore, we investigated whether NDRG2 was involved in the ischemic tolerance induced by EA pretreatment in rats.

METHODS

Twenty-four hours after the end of the last EA pretreatment, focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO) for 120 minutes in male Sprague-Dawley rats. The neurobehavioral score, infarction volume, and extent of neuronal apoptosis were evaluated at 24 hours after reperfusion. The expression of NDRG2 in the brain was evaluated by reverse transcriptase-polymerase chain reaction (RT-PCR), western blotting, and immunofluorescent staining.

RESULTS

Electroacupuncture pretreatment decreased infarction volume and improved neurologic scores at 24 hours after reperfusion. Double immunofluorescence revealed that NDRG2 expression in astrocytes was suppressed in the EA group at 24 hours after reperfusion, and that NDRG2 protein expression was weak in the nucleus and strong in the cytoplasm of the EA group, but strong in the nucleus of the MCAO group. Triple immunofluorescent staining for terminal deoxynucleotidyl transferase nick-end labeling (TUNEL), NDRG2, and 4',6-diamidino-2-phenylindole (DAPI) showed that NDRG2 co-localised with apoptotic cells. Moreover, the number of apoptotic cells decreased with the attenuation of NDRG2 expression in the EA group compared to the MCAO group.

CONCLUSION

Our results indicated that NDRG2 is involved in anti-apoptosis induced by EA pretreatment after focal cerebral ischemia in rats. N-Myc downstream-regulated gene 2 was involved in EA pretreatment-induced cerebral ischemic tolerance. These findings may be important for our understanding of the cellular signaling pathways induced by EA pretreatment.

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

To discover the molecular mechanism of N-Myc downstream-regulated gene 2 (NDRG2), a newly found differentiation-related tumor suppressor, the relationships between NDRG2 and E-cadherin were investigated in tumor cells and tissues. Positive correlations between the expression of E-cadherin and NDRG2 were shown in several colon cancer cell lines as well as in colon cancer tissues. According to the transcription assays using a reporter plasmid containing E-cadherin promoter region (-368~+51), NDRG2 introduction into colon cancer cell lines induced upregulation of E-cadherin promoter activity and its transcription. On the contrary, inhibition of NDRG2 expression by siRNA treatment caused the decrease of E-cadherin transcription. Snail, a zinc-finger transcriptional repressor, was shown to be a mediator of NDRG2-regulated E-cadherin expression. The enhancement of glycogen synthase kinase 3β (GSK-3β) activity by NDRG2 overexpression caused proteasomal degradation of Snail transcription factor followed by transcriptional de-repression of E-cadherin. We also found that NDRG2 could mediate cell density-regulated E-cadherin expression. The increase of NDRG2 expression with cell density preceded E-cadherin expression, and the regulation of Snail activity by GSK-3β was also related to this process.

Low expression of N-myc downstream-regulated gene 2 in oesophageal squamous cell carcinoma correlates with a poor prognosis

BACKGROUND

It is currently unclear whether a correlation exists between N-myc downstream-regulated gene 2 (NDRG2) expression and oesophageal squamous cell carcinoma (ESCC). The aim of this study was to examine the underlying clinical significance of NDRG2 expression in ESCC patients and to investigate the effects of NDRG2 up-regulation on ESCC cell growth in vitro and in vivo.

METHODS

Immunohistochemistry was used to determine the level of NDRG2 expressions in ESCC tissue, which was then compared to specific clinicopathological features in the patient and tissue specimens. Factors associated with patient survival were analysed. Moreover, the effects of up-regulating NDRG2 expression on the growth of an ESCC cell line were examined by MTT, colony formation, DNA replication activity and nude mouse model assays.

RESULTS

Notably low expression of NDRG2 in ESCC patients was inversely associated with clinical stage, NM classification, histological differentiation and patients' vital status (all P < 0.05). ESCC patients expressing high levels of NDRG2 exhibited a substantially higher 5-year overall survival rate than NDRG2-negative patients. Furthermore, NDRG2 over-expression reduced the proliferation, colony formation and DNA replication activity in ESCC cells, as well as inhibiting the growth of ESCC cells in vivo.

CONCLUSION

The present experiments demonstrated that NDRG2 may be a diagnostic and prognostic marker in patients with ESCC, and up-regulation of NDRG2 might act as a promising therapeutic strategy for aggressive ESCC.

Taurine prevented cell cycle arrest and restored neurotrophic gene expression in arsenite-treated SH-SY5Y cells

The study investigated the effect of taurine on cell viability and neurotrophic gene expression in arsenite-treated human neuroblastoma SH-SY5Y cells. Arsenite-induced intracellular reactive oxygen species (ROS) and interrupted cell cycle in SH-SY5Y cells. In addition, arsenite reduced mitochondria membrane potential (MMP) and decreased neurotrophic gene expressions such as n-myc downstream-regulated gene 4 (NDRG-4), brain-derived neurotrophic factor (BDNF) and sirtuin-1 (SIRT-1) in SH-SY5Y cells. In parallel, taurine prevented cell cycle, restored MMP and reduced the intracellular ROS level, and taurine recovered NDRG-4, BDNF and SIRT-1 gene expressions in arsenite-treated SH-SY5Y cells while taurine alone has no effect on these parameters.

Expression of NDRG2 in human lung cancer and its correlation with prognosis

We had reported that N-myc downstream–regulated gene (NDRG2) regulates colorectal cancer, breast cancer, clear cell renal cell carcinoma, pancreatic cancer, thyroid cancer and esophageal squamous cell proliferation, development, and apoptosis. The goal of this study was to determine the expression pattern of NDRG2 in human lung cancer and its correlation with prognosis. Immunohistochemistry, RT-PCR and western blot were used to explore the expression of NDRG2 in 185 human lung cancer patients. The correlation of NDRG2 expression with patients’ survival rate was assessed by Kaplan–Meier and Cox regression. Results showed that the expression level of NDRG2 was decreased in human lung cancer tissues, and NDRG2 was positively correlated with depth of invasion (P = 0.038), vascular invasion (P = 0.036), tumor grade (P = 0.039), and tumor size (P = 0.026). Both RT-PCR and Western blots demonstrated that NDRG2 mRNA and protein levels were lower in lung cancer compared to the adjacent normal tissue from the same individual, and NDRG2 level was negatively correlated with UICC stage. Additionally, survival time of lung cancer patients with high expression of NDRG2 was longer than those with low expression during the 5-year follow-up period (P = 0.001). Meanwhile, COX regression analysis indicated that low expression of NDRG2, ≥pT₃, pM₁, ≥pN₁ and vascular invasion were independent, poor prognostic factors of lung cancer patients. These data showed that NDRG2 may play an important role in human lung cancer tumourigenesis, and NDRG2 might serve as a novel prognostic marker in human lung cancer.

NDRG2 and PRA1 interact and synergistically inhibit T-cell factor/β-catenin signaling

NDRG2 is a member of the N-myc downstream regulated gene (NDRG) family, implicated in cell growth and differentiation. Investigation of NDRG2 molecular interactions by yeast two-hybrid screening identified prenylated Rab acceptor-1 (PRA1), involved in vesicle trafficking and protein transport, as binding partner. Binding of NDRG2 (and NDRG1-4) with PRA1 in vitro was confirmed by GST pull-down assay and immunoprecipitation, and colocalization was verified by confocal microscopy in HCT116 cells. Intracellular coexpression showed that NDRG2 and PRA1 synergistically downregulate T-cell factor (TCF) promoter activity and GSK3β phosphorylation. Results suggest that NDRG2 and PRA1 might act synergistically to prevent signaling of TCF/β-catenin.

NDRG2 correlated with favorable recurrence-free survival inhibits metastasis of mouse breast cancer cells via attenuation of active TGF-β production

N-myc downstream-regulated gene 2 (NDRG2) has been studied for its inhibitory effects against growth and metastasis of many tumor cell types. In this study, we showed NDRG2 expression was correlated with favorable recurrence-free survival of patients with breast cancer and inhibited metastasis of breast cancer cells (4T1). NDRG2 expression was examined in 189 breast carcinoma tissues and paired normal breast tissues using immunohistochemistry. Histological and clinicopathological data were correlated using Pearson's chi-square test of independence. NDRG2 expression in human breast cancer tissues was inversely associated with lymph node metastasis and pTNM stage. Furthermore, patients with breast cancer with a high level of NDRG2 expression showed favorable recurrence-free survival (P = 0.038). To study the effect of NDRG2 on metastasis in vivo, we established an NDRG2-overexpressing mouse breast cancer cell line (4T1-NDRG2) and measured the metastasis and survival of 4T1-NDRG2 tumor-bearing mice. To test whether transforming growth factor β (TGF-β)- mediated metastasis of 4T1 was inhibited by NDRG2 expression, TGF-Smad-binding element (SBE)-luciferase activity and/or measurement of active TGF-β were performed in cell or tumor tissue level. 4T1-NDRG2 cells grew gradually and showed less metastatic activity in vivo and low invasiveness in vitro. 4T1-NDRG2 cells showed lower SBE-luciferase activity and lower level of active autocrine TGF-β than 4T1-Mock did. Correctly, our data show that NDRG2 significantly suppress tumor metastasis by attenuating active autocrine TGF-β production, and the attenuation might be typically associated with the favorable recurrence-free survival of patients clinically.

Microarray profiling of HepG2 cells ectopically expressing NDRG2

Previous studies have demonstrated that N-Myc downstream-regulated gene 2 (NDRG2) is a tumor suppressor that is downregulated in many human cancers and when overexpressed, can inhibit tumor growth and metastasis. However, its molecular function, its modulatory targets, and signaling pathways associated with it remain unclear. Here, in an effort to identify the genes modulated by NDRG2 expression, a microarray study was conducted to detect the expression profile of HepG2 cells overexpressing NDRG2 or LacZ. Gene Ontology (GO) biological process analysis revealed that genes related to G protein signaling pathway were upregulated. Five of them were selected and verified by real-time PCR. Gene sets related to M phase of cell cycle were downregulated. This was in agreement with cell cycle analysis. Signaling pathway analysis demonstrated apparent augmented hematopoietic cell lineage pathway and cell adhesion, but reduced glycosylphosphatidylinositol (GPI)-anchor biosynthesis, protein degradation and SNARE interactions. Furthermore, through motif analysis and experimental validation, we found that the p38 phosphorylation can be increased by NDRG2. Our research provides the molecular basis for understanding the role of NDRG2 in tumor cells and raises interesting questions about its mechanisms and potential use in cancer therapy.

NDRG2 Promotes GATA-1 Expression through Regulation of the JAK2/STAT Pathway in PMA-stimulated U937 Cells

BACKGROUND

N-myc downstream-regulated gene 2 (NDRG2), a member of a newly described family of differentiation-related genes, has been characterized as a regulator of dendritic cells. However, the role of NDRG2 on the expression and activation of transcription factors in blood cells remains poorly understood. In this study, we investigated the effects of NDRG2 overexpression on GATA-1 expression in PMA-stimulated U937 cells.

METHODS

We generated NDRG2-overexpressing U937 cell line (U937-NDRG2) and treated the cells with PMA to investigate the role of NDRG2 on GATA-1 expression.

RESULTS

NDRG2 overexpression in U937 cells significantly induced GATA-1 expression in response to PMA stimulation. Interestingly, JAK2/STAT and BMP-4/Smad pathways associated with the induction of GATA-1 were activated in PMA-stimulated U937-NDRG2 cells. We found that the inhibition of JAK2 activation, but not of BMP-4/Smad signaling, can elicit a decrease of PMA-induced GATA-1 expression in U937-NDRG2 cells.

CONCLUSION

The results reveal that NDRG2 promotes the expression of GATA-1 through activation of the JAK2/STAT pathway, but not through the regulation of the BMP-4/Smad pathway in U937 cells. Our findings further suggest that NDRG2 may play a role as a regulator of erythrocyte and megakaryocyte differentiation during hematopoiesis.

NDRG2 ameliorates hepatic fibrosis by inhibiting the TGF-β1/Smad pathway and altering the MMP2/TIMP2 ratio in rats

Liver fibrosis is a worldwide clinical issue. It has been well established that activated hepatic stellate cells (HSCs) are responsible for excessive extracellular matrix (ECM) deposition in chronically damaged livers. The identification of key elements that control HSCs activation will help to further our understanding of liver fibrosis and improve the outcome of clinical treatment. This study demonstrates that N-Myc downstream-regulated gene 2 (NDRG2) is a potential regulator of liver fibrosis as NDRG2 mRNA and protein levels were reduced during HSCs activation. In addition, enhanced NDRG2 expression reduced Smad3 transcription and phosphorylation, which inhibited HSCs activation by blocking the TGF-β1 signal. Moreover, NDRG2 contributed to an increase in the ratio of matrix metalloproteinase 2 (MMP2) to tissue inhibitor of matrix metalloproteinase 2 (TIMP2), which may facilitate the degradation of the ECM. In dimethylnitrosamine (DMN)-induced fibrotic rat livers, adenovirus-mediated NDRG2 overexpression resulted in decreased ECM deposition and improved liver function compared with controls. In conclusion, the present findings indicate that the modulation of NDRG2 is a promising strategy for the treatment of liver fibrosis.

NDRG2 ameliorates hepatic fibrosis by inhibiting the TGF-β1/Smad pathway and altering the MMP2/TIMP2 ratio in rats

Liver fibrosis is a worldwide clinical issue. It has been well established that activated hepatic stellate cells (HSCs) are responsible for excessive extracellular matrix (ECM) deposition in chronically damaged livers. The identification of key elements that control HSCs activation will help to further our understanding of liver fibrosis and improve the outcome of clinical treatment. This study demonstrates that N-Myc downstream-regulated gene 2 (NDRG2) is a potential regulator of liver fibrosis as NDRG2 mRNA and protein levels were reduced during HSCs activation. In addition, enhanced NDRG2 expression reduced Smad3 transcription and phosphorylation, which inhibited HSCs activation by blocking the TGF-β1 signal. Moreover, NDRG2 contributed to an increase in the ratio of matrix metalloproteinase 2 (MMP2) to tissue inhibitor of matrix metalloproteinase 2 (TIMP2), which may facilitate the degradation of the ECM. In dimethylnitrosamine (DMN)-induced fibrotic rat livers, adenovirus-mediated NDRG2 overexpression resulted in decreased ECM deposition and improved liver function compared with controls. In conclusion, the present findings indicate that the modulation of NDRG2 is a promising strategy for the treatment of liver fibrosis.

Up-regulation of NDRG2 in senescent lens epithelial cells contributes to age-related cataract in human

Background

Human N-Myc downstream regulated gene2 (NDRG2), a novel gene has been cloned and shown to be related to a number of cellular processes, including proliferation, differentiation, stress, and apoptosis. NDRG2 has also been linked to age-related Alzheimer's disease. Since the role of this gene in senescence is limited, we have investigated the potential role of NDRG2 in human lens epithelial cells (HLECs), a paradigm implicated in age-related cataract.

Methodology/Principal Findings

Cultured HLECs (SRA01/04) were subjected to prolonged exposure to low dose of H₂O₂ to simulate senescence. After being exposed to 50 µM H₂O₂ for 2 weeks, HLECs senescent-morphological changes appeared, cell viability decreased dramatically, cell proliferation reduced from 37.4% to 16.1%, and senescence-associated β-galactosidase activity increased from 0 to 90.3%. Ndrg2 protein expression was also significantly increased in these senescent cells. To induce overexpression of NDRG2, SRA01/04 cells were infected with the adenoviral vector of NDRG2. In these cells, overexpression of NDRG2 resulted in a fibroblast-like appearance and the cell viability decreased about 20%. In addition, the NDRG2-overexpression cells demonstrated 20% lower viability when exposed to 50–200 µM H₂O₂ for acute oxidative stress. Furthermore, the expression of NDRG2 from age-related cataracts was up-regulated 2-fold at both mRNA and protein levels compared with the clear lenses.

Conclusions/Significance

NDRG2 is up regulated not only in the ageing process of HLECs in vitro but also in the cells from human age-related cortical cataract in vivo. Up-regulation of NDRG2 induces cell morphological changes, reduces cell viability, and especially lowers cellular resistance to oxidative stress. NDRG2-mediated affects in HLECs may associate with age-related cataract formation.

Dexamethasone indirectly induces Ndrg2 expression in rat astrocytes

N-myc downstream-regulated gene 2 (Ndrg2) has been associated with cell proliferation, differentiation, and apoptosis. Ndrg2 expression in the brain is induced by glucocorticoid treatment or chronic stress in vivo. It has been postulated that glucocorticoid-induced Ndrg2 expression in astrocytes is regulated by the glucocorticoid response element half-site (GRE1/2) upstream of the Ndrg2 transcription site. Here we examined the mechanisms of dexamethasone-induced Ndrg2 expression in rat astrocytes. Ndrg2 mRNA expression in primary astrocytes was significantly increased after 24 hr of exposure to dexamethasone in a concentration-dependent manner. Dexamethasone-induced Ndrg2 mRNA and protein expression was blocked by pretreatment with RU486, a glucocorticoid receptor antagonist. Moreover, dexamethasone-induced Ndrg2 mRNA expression was reduced by pretreatment with the protein synthesis inhibitor cycloheximide. The Ndrg2 reporter assay showed that deletion of a putative GRE1/2, located upstream of Ndrg2, did not affect induction by dexamethasone. A region between -755 and -701 bp from the transcription start site was shown to regulate induction by dexamethasone using promoter constructs progressively deleted from the 5' to 3' ends. This region contained the predicted transcription factor binding sites for early B-cell factor 1 (Ebf1), nuclear factor-κB (NFκB), and paired box gene 5 (Pax5). Mutation at the NFκB- or Pax5-binding site, but not the Ebf1 binding site, abolished dexamethasone-induced promoter activation. These results indicate that Ndrg2 expression was indirectly induced by dexamethasone at the DNA level, potentially by the binding of NFκB or Pax5 to the transcription factor binding sites, and GRE1/2 was not involved in this induction.

Regulation of histone acetylation by NDRG2 in glioma cells

NDRG2, a member of the N-Myc downstream-regulated gene family, was shown to be a putative tumor suppressor gene in glioblastoma and other cancers. Through a bioinformatic analysis, we found that NDRG2 protein contains an acyl carrier domain. In the current study, we therefore hypothesized that NDRG2 may play an important role in the regulation of histone acetylation. Treatment of U251 and U87 glioma cells with trichostatin A, an inhibitor of histone deacetylase, upregulated the expression of NDRG2 and acetylated forms of histones H3 and H4, reduced tumor cell viability and arrested the cell cycle at the G1/G0 phase. Overexpression of NDRG2 by transfecting glioma cells with adenovirus containing the NDRG2 gene upregulated the levels of acetylated forms of H3 and H4 whereas inhibition of NDRG2 expression by siRNA-mediated knockdown downregulated the level of histone acetylation. Furthermore, NDRG2 siRNA significantly reduced the level of histone acetylation induced by trichostatin A. Taken together, these data demonstrate that NDRG2 can regulate the level of histone acetylation to control glioma cell growth.

RU486 (mifepristone) ameliorates cognitive dysfunction and reverses the down-regulation of astrocytic N-myc downstream-regulated gene 2 in streptozotocin-induced type-1 diabetic rats

Diabetic cognitive dysfunction (DCD), usually accompanied with chronically elevated glucocorticoids and hippocampal astrocytic alterations, is one of the most serious complications in patients with type-1 diabetes. However, the role for chronically elevated glucocorticoids and hippocampal astrocytic activations in DCD remains to be elucidated, and it is not clear whether astrocytic N-myc downstream-regulated gene 2 (NDRG2, involved in cell differentiation and development) participated in DCD. In the present study, three months after streptozotocin (STZ)-induced type-1 diabetes onset, rats showed cognitive impairments in Morris water maze test as well as elevated corticosterone level. Diabetic rats also presented down-regulation of glial fibrillary acidic protein (GFAP, a key indicator of astrocytic reactivity) and NDRG2 in hippocampus revealed by immunohistochemistry staining, real-time PCR and Western blot. Moreover, the diabetic cognitive impairments were ameliorated by 9-day glucocorticoids receptor (GR) blockade with RU486, and the down-regulation of hippocampal NDRG2 and GFAP in diabetic animals was also attenuated by 9-day GR blockade. These results suggest that glucocorticoids-GR system is crucial for DCD, and that astrocytic reactivity and NDRG2 are involved in these processes. Thus, inhibiting GR activation in the hippocampus may be a novel therapeutic strategy for treating DCD.

NDRG4 protein-deficient mice exhibit spatial learning deficits and vulnerabilities to cerebral ischemia

The N-myc downstream-regulated gene (NDRG) family consists of four related proteins, NDRG1-NDRG4, in mammals. We previously generated NDRG1-deficient mice that were unable to maintain myelin sheaths in peripheral nerves. This condition was consistent with human hereditary motor and sensory neuropathy, Charcot-Marie-Tooth disease type 4D, caused by a nonsense mutation of NDRG1. In contrast, the effects of genetic defects of the other NDRG members remain unknown. In this study, we focused on NDRG4, which is specifically expressed in the brain and heart. In situ mRNA hybridization on the brain revealed that NDRG4 was expressed in neurons of various areas. We generated NDRG4-deficient mice that were born normally with the expected Mendelian frequency. Immunochemical analysis demonstrated that the cortex of the NDRG4-deficient mice contained decreased levels of brain-derived neurotrophic factor (BDNF) and normal levels of glial cell line-derived neurotrophic factor, NGF, neurotrophin-3, and TGF-β1. Consistent with BDNF reduction, NDRG4-deficient mice had impaired spatial learning and memory but normal motor function in the Morris water maze test. When temporary focal ischemia of the brain was induced, the sizes of the infarct lesions were larger, and the neurological deficits were more severe in NDRG4-deficient mice compared with the control mice. These findings indicate that NDRG4 contributes to the maintenance of intracerebral BDNF levels within the normal range, which is necessary for the preservation of spatial learning and the resistance to neuronal cell death caused by ischemic stress.

Down-regulation of NDRG2 gene expression in human colorectal cancer involves promoter methylation and microRNA-650

The expression of N-myc downstream-regulated gene 2 (NDRG2) is present in normal tissues but low or undetectable in various cancers and thus poses a potential tumor suppressor gene. However, the expression of NDRG2 in colorectal tissues remains unknown. Here, our results showed that NDRG2 was down-regulated in colorectal cancer compared to benign colorectal tissues by using immunohistochemical staining and semi-quantitative RT-PCR analyses. Bisulfite sequencing analysis showed that the reduced NDRG2 expression was accompanied by de novo DNA methylation at the NDRG2 promoter. We also found that microRNA-650 (miR-650) targets a homologous DNA region in the promoter region of the NDRG2 gene and represses its expression at the transcriptional level. Reporter assay with 3'untranslated region of NDRG2 cloned downstream of the luciferase gene showed reduced luciferase activity in the presence of miR-650, providing strong evidence that miR-650 is a direct regulator of NDRG2. In conclusion, these results suggest that NDRG2 expression is regulated by promoter methylation and miR-650 in human colorectal cancer cells, and endogenous small noncoding RNA induced control of transcription may be a potential system for expressional regulation in human colorectal cancer cells.

NDRG2-mediated Modulation of SOCS3 and STAT3 Activity Inhibits IL-10 Production

Background

N-myc downstream regulated gene 2 (NDRG2) is a member of the NDRG gene family. Our previous report indicated a possible role for NDRG2 in regulating the cytokine, interleukin-10 (IL-10), which is an important immunosuppressive cytokine. Several pathways, including p38-MAPK, NF-κB, and JAK/STAT, are used for IL-10 production, and the JAK/STAT pathway can be inhibited in a negative feedback loop by the inducible protein, SOCS3. In the present study, we investigated the effect of NDRG2 gene expression on IL-10 signaling pathway that is modulated via SOCS3 and STAT3.

Methods

We generated NDRG2-overexpressing U937 cell line (U937-NDRG2) and treated the cells with PMA to investigate the role of NDRG2 in IL-10 production. U937 cells were also transfected with SOCS3- or NDRG2-specific siRNAs to examine whether the knockdown of SOCS3 or NDRG2 influenced IL-10 expression. Lastly, STAT3 and SOCS3 induction was measured to identify the signaling pathway that was associated with IL-10 production.

Results

RT-PCR and ELISA assays showed that IL-10 was increased in U937-mock cells upon stimulation with PMA, but IL-10 was inhibited by overexpression NDRG2. After PMA treatment, STAT3 phosphorylation was decreased in a time-dependent manner in U937-mock cells, whereas it was maintained in U937-NDRG2 cells. SOCS3 was markedly reduced in U937-NDRG2 cells compared with U937-mock cells. IL-10 production after PMA stimulation was reduced in U937 cells when SOCS3 was inhibited, but this effect was less severe when NDRG2 was inhibited.

Conclusion

NDRG2 expression modulates SOCS3 and STAT3 activity, eventually leading to the inhibition of IL-10 production.

Phosphoproteomic analysis reveals site-specific changes in GFAP and NDRG2 phosphorylation in frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is a progressive neurodegenerative disease characterized by behavioral abnormalities, personality changes, language dysfunction, and can co-occur with the development of motor neuron disease. One major pathological form of FTLD is characterized by intracellular deposition of ubiquitinated and phosphorylated TAR DNA binding protein-43 (TDP-43), suggesting that dysregulation in phosphorylation events may contribute to disease progression. However, to date systematic analysis of the phosphoproteome in FTLD brains has not been reported. In this study, we employed immobilized metal affinity chromatography (IMAC) followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) to identify phosphopeptides from FTLD and age-matched control post-mortem human brain tissue. Using this approach, we identified 786 phosphopeptides in frontal cortex (control and FTLD), in which the population of phosphopeptides represented approximately 50% of the total peptides analyzed. Label-free quantification using spectral counts revealed six proteins with significant changes in the FTLD phosphoproteome. N-myc-Downstream regulated gene 2 (NDRG2) and glial fibrillary acidic protein (GFAP) had an increased number of phosphospectra in FTLD, whereas microtubule associated protein 1A (MAP1A), reticulon 4 (RTN4; also referred to as neurite outgrowth inhibitor (Nogo)), protein kinase C gamma (PRKCG), and heat shock protein 90 kDa alpha, class A member 1(HSP90AA1) had significantly fewer phosphospectra compared to control brain. To validate these differences, we examined NDRG2 phosphorylation in FTLD brain by immunoblot analyses, and using a phosphoserine-13 (pSer13) GFAP monoclonal antibody we show an increase in pSer13 GFAP levels by immunoblot concomitant with increased overall GFAP levels in FTLD cases. These data highlight the utility of combining proteomic and phosphoproteomic strategies to characterize post-mortem human brain tissue.

NDRG2 suppresses the proliferation of clear cell renal cell carcinoma cell A-498

Background

Recently, the anti-tumor activity of N-myc downstream-regulated gene 2 (NDRG2) was shown decreased expression in clear cell renal cell carcinoma (CCRCC), but the role of the down-expression of NDRG2 has not been described.

Methods

The NDRG2 recombinant adenovirus plasmid was constructed. The proliferation rate and NDRG2 expression of cell infected with recombinant plasmid were mesured by MTT, Flow cytometry analysis and western blot.

Results

The CCRCC cell A-498 re-expressed NDRG2 when infected by NDRG2 recombinant adenovirus and significantly decreased the proliferation rate. Fluorescence activated cell sorter analysis showed that 25.00% of cells expressed NDRG2 were in S-phase compared to 40.67% of control cells, whereas 62.08% of cells expressed NDRG2 were in G1-phase compared to 54.39% of control cells (P < 0.05). In addition, there were much more apoptotic cells in NDRG2-expressing cells than in the controls (P < 0.05). Moreover, upregulation of NDRG2 protein was associated with a reduction in cyclin D1, cyclin E, whereas cyclinD2, cyclinD3 and cdk2 were not affected examined by western blot. Furthermore, we found that p53 could upregulate NDRG2 expression in A-498 cell.

Conclusions

We found that NDRG2 can inhibit the proliferation of the renal carcinoma cells and induce arrest at G1 phase. p53 can up-regulate the expression of NDRG2. Our results showed that NDRG2 may function as a tumor suppressor in CCRCC.

The N-myc downstream regulated gene (NDRG) family: diverse functions, multiple applications

The N-myc downstream regulated gene (NDRG) family of proteins consists of 4 members, NDRG1-4, which are well conserved through evolution. The first member to be discovered and responsible for the family name was NDRG1, because its expression is repressed by the proto-oncogenes MYCN and MYC. All family members are characterized by an α/β hydrolase-fold motif; however, the precise molecular and cellular function of these family members has not been fully elucidated. Although the exact function of NDRG family members has not been clearly elucidated, emerging evidence suggests that mutations in these genes are associated with diverse neurological and electrophysiological syndromes. In addition, aberrant expression as well as tumor suppressor and oncogenic functions affecting key hallmarks of carcinogenesis such as cell proliferation, differentiation, migration, invasion, and stress response have been reported for several of the NDRG proteins. In this review, we summarize the current literature on the NDRG family members concerning their structure, origin, and tissue distribution. In addition, we review the current knowledge regarding the regulation and signaling of the NDRG family members in development and normal physiology. Finally, their role in disease and potential clinical applications (their role as detection or prognostic markers) are discussed.

NDRG2 is one of novel intrinsic factors for regulation of IL-10 production in human myeloid cell

N-myc downstream-regulated gene 2 (NDRG2) implicated in cellular growth and differentiation was previously reported as it is specifically expressed in primary and in vitro-differentiated dendritic cells (DCs) from monocytes and CD34(+) progenitor cells. However, its function has yet to be investigated in DCs. Here, the novel NDRG2 function about modulation of cytokines in DC was observed in this study. The secretion of IL-10 was not found in the monocyte-derived DC cells with high level of NDRG2 expression, but IL-10 was abundantly secreted up to 1ng/ml in the monocyte-derived macrophages with low level of NDRG2 expression, and further confirmed that the expression of IL-10 was dramatically increased in NDRG2-silenced DCs under presence of LPS, and significantly reduced in the NDRG2-overexpressed U937 cells under stimulation of PMA. The secretion of IL-12p70 was significantly reduced in the siNDRG2 introduced DC cells. The intracellular signaling of IL-10 secretion was markedly inhibited by SB203580, inhibitor of p38 MAPK, in the LPS-activated DCs and phosphorylation of p38 MAPK was decreased in the NDRG2 introduced U937 cells under PMA-stimulation. Taken together, NDRG2 might have a pivotal role as one of intrinsic factors for the modulation of p38 MAPK phosphorylation, and subsequently involve in controlling of IL-10 production.

Downregulation of MSP58 inhibits growth of human colorectal cancer cells via regulation of the cyclin D1-cyclin-dependent kinase 4-p21 pathway

We have investigated the expression and role of the 58-kDa microspherule protein (MSP58) in colorectal carcinoma (CRC). By immuhistochemistry and immunofluorescence, we observed MSP58 in the nucleus and cytoplasm of CRC cells, and found MSP58 to be present in CRC specimens more often than in adjacent non-tumor tissues (92.5 vs 36.3%, P < 0.01). The average staining score in adjacent non-tumor tissues was significantly lower than in CRC tissues (2.05 +/- 1.13 vs 5.23 +/- 1.38, P < 0.01). Moreover, MSP58 mRNA and protein appeared to be upregulated in six fresh CRC samples compared to their adjacent non-cancerous tissues. MSP58 expression was also detected in the human CRC-derived cell lines LoVo, CoLo205, HCT116, HT-29, SW620, and SW480. Downregulation of MSP58 inhibited in vitro growth and attenuated tumor growth in animal models by induction of cell cycle arrest, and was associated with reduced levels of cyclin D1, cyclin-dependent kinase 4, phosphorylation-Rb (p-Rb), p21, and Retino blastoma (Rb) proteins. These results indicated that MSP58 might play an important role in the carcinogenesis of CRC via regulation of the cyclin D1-cyclin-dependent kinase 4-p21 pathway.