Characterization of rat NDRG2 (N-Myc downstream regulated gene 2), a novel early mineralocorticoid-specific induced gene

Sexual Dimorphism of Corticosteroid Signaling during Kidney Development

Sexual dimorphism involves differences between biological sexes that go beyond sexual characteristics. In mammals, differences between sexes have been demonstrated regarding various biological processes, including blood pressure and predisposition to develop hypertension early in adulthood, which may rely on early events during development and in the neonatal period. Recent studies suggest that corticosteroid signaling pathways (comprising glucocorticoid and mineralocorticoid signaling pathways) have distinct tissue-specific expression and regulation during this specific temporal window in a sex-dependent manner, most notably in the kidney. This review outlines the evidence for a gender differential expression and activation of renal corticosteroid signaling pathways in the mammalian fetus and neonate, from mouse to human, that may favor mineralocorticoid signaling in females and glucocorticoid signaling in males. Determining the effects of such differences may shed light on short term and long term pathophysiological consequences, markedly for males.

TGF-β1 can be regulated by NDRG2 via the NF-κB pathway in hypoxia-induced liver fibrosis

Background

The identification of the important elements that control hepatic stellate cell (HSC) activation will expand our understanding of the mechanism of liver fibrosis induced by hypoxia and affect the outcome of clinical treatment. A previous research demonstrated that N-Myc downstream-regulated gene 2 (NDRG2) is a potential regulator of fibrosis and a downstream target gene of hypoxia-inducible factor 1 (HIF-1). In this research, we studied the expression and function of NDRG2 in liver fibrosis induced by hypoxia.

Methods

LX-2 cells/NF-κB-silenced LX-2 cells were exposed to hypoxic conditions (1% O₂) to activate HSCs in vitro. The protein and mRNA expression levels of NDRG2, α-SMA and transforming growth factor beta 1 (TGF-β1) were evaluated by western blotting and real-time polymerase chain reaction (RT-PCR), respectively. Functional studies were performed using adenovirus-mediated gene upregulation.

Results

The NDRG2 mRNA and protein levels were reduced under hypoxic conditions in LX-2 cells and overexpression of NDRG2 resulted in a decrease in the expression of TGF-β1 and α-SMA. Interestingly, no relationship was observed between NDRG2 and TGF-β1 when the NF-κB pathway was blocked, which indicates that NDRG2 can regulate the expression of TGF-β1 in LX-2 cells via the NF-κB pathway under hypoxic conditions.

Conclusions

NDRG2 may regulate the expression of TGF-β1 via the NF-κB pathway and may be a novel therapeutic target for liver fibrosis induced by hypoxia.

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.

MiR-130a/Ndrg2 Axis Inhibits the Proliferation of Fibroblast-Like Synoviocytes in Rheumatoid Arthritis

Studies have found that N-myc downstream-regulated gene 2 (Ndrg2) is involved in the progression of rheumatoid arthritis (RA); however, the specific mechanism still remains unclear. Gene expression profiles in the tibial joints of the collagen-induced rheumatoid arthritis model were obtained using Gene Expression Omnibus database. Western blot and real-time PCR were respectively performed to determine the expression of Ndrg2 and gene messenger RNA. Cell viability was measured by Cell Counting Kit-8 (CCK-8) method, and cell cycle was detected by flow cytometry. Cell scratch assays were carried out to detect migration. The binding ability of miR-130a to Ndrg2-3'-UTR was predicted by TargetScan website and confirmed by dual luciferase assay. A collagen-induced arthritis rat model was constructed to observe the effects of miR-130a on arthritis index, hind limb swelling, volume of rat hind paw, and inflammation. Ndrg2 was found downregulated in RA tissues, and knockdown of Ndrg2 promoted fibroblast-like synoviocytes (FLS) proliferation and inflammation, while overexpressed Ndrg2 produced opposite results. Ndrg2 was predicted as a target gene for miR-130a, and miR-130a mimic promoted FLS proliferation, while miR-130a inhibitor suppressed FLS proliferation. Moreover, we found that miR-130a antagomir could significantly reduce the arthritis index, swelling degree, foot volume, and inflammatory factor levels; inhibit the expression of miR-130a; and promote the expression of Ndrg2. The miR-130a/Ndrg2 axis signaling pathway is involved in the progression of RA. Our findings provide a theoretical basis for the clinical treatment of RA.

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.

The regulation of NDRG2 expression during ATLL development after HTLV-1 infection

N-myc downstream-regulated gene 2 (NDRG2) is a candidate tumor suppressor that is frequently downregulated in adult T-cell leukemia/lymphoma (ATLL) and functions to negatively regulate several cellular signaling pathways as PP2A recruiter. To clarify the molecular mechanisms of suppression of NDRG2 expression, we initially determined the expression pattern of NDRG2 in various types of T-cells and ATLL cells. NDRG2 expression was significantly upregulated in HTLV-1/Tax-immortalized T-cells, which was mediated by NF-κB activation through Tax expression. On the other hand, NDRG2 expression was suppressed in HTLV-1-infected cell lines and various types of ATLL cells, which was dependent on the DNA methylation of the NDRG2 promoter. We found that the expression of enhancer of zeste homolog 2 (EZH2), a member of the polycomb family, is increased in ATLL, and that EZH2 directly binds to the NDRG2 promoter and induces DNA methylation of the NDRG2 promoter. Since the expression of EZH2 were anti-parallelly regulated with the NDRG2 expression, EZH2 might be one of the most important regulators of the downregulation of NDRG2, contributing to enhanced activation of signaling pathways during ATLL development.

Anti-fibrotic Effects and Mechanism of Shengmai Injection () on Human Hepatic Stellate Cells LX-2

OBJECTIVE

To investigate the effects of Shengmai Injection (, SMI) on the proliferation, apoptosis and N-myc downstream-regulated gene 2 (NDRG2, a tumour suppressor gene) expression in varying densities of human hepatic stellate cells LX-2.

METHODS

LX-2 cells were cultured in vitro. Then, cells were plated in 96-well plates at an approximate density of 2.5×10⁴ cells/mL and cultured for 48, 72, 96 or 120 h followed by the application of different concentrations of SMI (0.6, 1.2, 2.4, 4.8 or 6 μL/mL). Cell proliferation was measured after an additional 24 or 48 h using the 3(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The effects of SMI on different cell growth states (cultured for 48, 72, 96, or 120 h) were observed by light microscopy at 24 h after treatment. When the cells reached 80% conflfluence, apoptosis was detected by flflow cytometry after 24 h. Lastly, LX-2 cells were treated with different concentrations of SMI and extracted with protein lysis buffer. The levels of NDRG2 were measured by Western blot.

RESULTS

When the LX-2 cells grew for 48, 72, 96 and 120 h, 4.8 and 6 μL/mL of SMI significantly inhibited cell proliferation at 24 and 48 h after treatment (P<0.05). And 2.4 μL/mL of SMI also inhibited cell proliferation at 24 h after treatment when cell growth for 48 h (P<0.05) and at 48 h after treatment when cell growth for 72, 96 and 120 h (P<0.05). The NDRG2 expression level in the LX-2 cell was significantly increased when treated with SMI at concentrations of 1.2, 2.4, 4.8 or 6 μL/mL (P<0.05).

CONCLUSION

The inhibitory effects of SMI on the proliferation of LX-2 cells were related to not only concentration dependent but also cell density. In addition, SMI (2.4, 4.8 and 6 μL/mL) could accelerate apoptosis in LX-2 cells, and the mechanism might be associated with NDRG2 over-expression.

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.

N-Myc downstream-regulated gene 2 restrains glycolysis and glutaminolysis in clear cell renal cell carcinoma

Glycolysis and glutaminolysis are heavily involved in the metabolic reprogramming of cancer cells. The activation of oncogenes and inactivation of tumor suppressor genes has a marked effect on the cellular metabolic processes glycolysis and glutaminolysis. N-Myc downstream-regulated gene 2 (NDRG2) is a tumor suppressor gene that previous studies have demonstrated can inhibit the growth, proliferation and metastasis of clear cell renal cell carcinoma (ccRCC) cells. However, the function of NDRG2 in ccRCC metabolism remains unknown. In the present study, NDRG2 significantly inhibited the consumption of glucose and glutamine, as well as the production of lactate and glutamate in ccRCC. NDRG2 significantly suppressed the expression of glucose transporter 1, hexokinase 2, pyruvate kinase M2, lactate dehydrogenase A, glutamine transporter ASC amino acid transporter 2 and glutaminase 1 at the mRNA (by quantitative polymerase chain reaction) and protein level (by western blot analysis), all of which are key regulators and enzymes in glycolysis and glutaminolysis. Data from the present study also revealed that overexpression of NDRG2 suppressed cell proliferation in ccRCC in vitro and in vivo, demonstrated by colony formation assays, wound healing assay and nude mouse transplantation tumor experiment. The present findings demonstrate for the first time that NDRG2 acts as a key inhibitor of glycolysis and glutaminolysis in ccRCC and could be a promising target for the metabolic treatment of ccRCC.

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.

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.

Abundant NDRG2 Expression Is Associated with Aggressiveness and Unfavorable Patients' Outcome in Basal-Like Breast Cancer

NDRG2, a member of the N-myc downstream-regulated gene family, is thought to be a putative tumor suppressor gene with promising clinical impact in breast cancer. Since breast cancer comprises heterogeneous intrinsic subtypes with distinct clinical outcomes we investigated the pivotal role of NDRG2 in basal-type breast cancers. Based on subtype classified tumor (n = 45) and adjacent normal tissues (n = 17) we examined NDRG2 mRNA expression and CpG-hypermethylation, whose significance was further validated by independent data sets from The Cancer Genome Atlas (TCGA). In addition, NDRG2 protein expression was evaluated immunohistochemically using a tissue micro array (TMA, n = 211). In vitro, we investigated phenotypic effects caused by NDRG2 silencing in the basal A-like HCC1806 as well as NDRG2 over-expression in basal A-like BT20 compared to luminal-type MCF7 breast cancer cells. Our tissue collections demonstrated an overall low NDRG2 mRNA expression in breast cancer subtypes compared to normal breast tissue in line with an increased CpG-hypermethylation in breast cancer tissue. Independent TCGA data sets verified a significant (P<0.001) expression loss of NDRG2 in breast tumors. Of interest, basal-like tumors more frequently retained abundant NDRG2 expression concordant with a lower CpG-hypermethylation. Unexpectedly, basal-like breast cancer revealed an association of NDRG2 expression with unfavorable patients’ outcome. In line with this observation, in vitro experiments demonstrated reduced proliferation and migration rates (~20%) in HCC1806 cells following NDRG2 silencing. In contrast, NDRG2 over-expressing luminal-type MCF7 cells demonstrated a 26% decreased proliferation rate. Until now, this is the first study investigating the putative role of NDRG2 in depth in basal-type breast cancer. Our data indicate that the described putative tumor suppressive function of NDRG2 may be confined to luminal- and basal B-type breast cancers.

Histone Deacetylase 6-Controlled Hsp90 Acetylation Significantly Alters Mineralocorticoid Receptor Subcellular Dynamics But Not its Transcriptional Activity

The mineralocorticoid receptor (MR) is a member of the nuclear receptor superfamily that transduces the biological effects of corticosteroids. Its best-characterized role is to enhance transepithelial sodium reabsorption in response to increased aldosterone levels. In addition, MR participates in other aldosterone- or glucocorticoid-controlled processes such as cardiovascular homeostasis, adipocyte differentiation or neurogenesis, and regulation of neuronal activity in the hippocampus. Like other steroid receptors, MR forms cytosolic heterocomplexes with heat shock protein (Hsp) 90), Hsp70, and other proteins such as immunophilins. Interaction with Hsp90 is thought to maintain MR in a ligand-binding competent conformation and to regulate ligand-dependent and -independent nucleocytoplasmatic shuttling. It has previously been shown that acetylation of residue K295 in Hsp90 regulates its interaction with the androgen receptor and glucocorticoid receptor (GR). In this work we hypothesized that Hsp90 acetylation provides a regulatory step to modulate MR cellular dynamics and activity. We used Hsp90 acetylation mimic mutant K295Q or nonacetylatable mutant K295R to examine whether MR nucleocytoplasmatic shuttling and gene transactivation are affected. Furthermore, we manipulated endogenous Hsp90 acetylation levels by controlling expression or activity of histone deacetylase 6 (HDAC6), the enzyme responsible for deacetylation of Hsp90-K295. Our data demonstrates that HDAC6-mediated Hsp90 acetylation regulates MR cellular dynamics but it does not alter its function. This stands in contrast with the down-regulation of GR by HDAC6, suggesting that Hsp90 acetylation may play a role in balancing relative MR and GR activity when both factors are co-expressed in the same cell.

N-Myc Downstream-Regulated Gene 2 (Ndrg2) Is Involved in Ischemia-Hypoxia-Induced Astrocyte Apoptosis: a Novel Target for Stroke Therapy

Nearly all clinical trials that have attempted to develop effective strategies against ischemic stroke have failed, excluding those for thrombolysis, and most of these trials focused only on preventing neuronal loss. However, astrocytes have gradually become a target for neuroprotection in stroke. In previous studies, we showed that the newly identified molecular N-myc downstream-regulated gene 2 (Ndrg2) is specifically expressed in astrocytes in the brain and involved in some neurodegenerative diseases. However, the role of NDRG2 in ischemic stroke remained unclear. In this study, we investigated the role of NDRG2 in middle cerebral artery occlusion (MCAO)-induced focal cerebral ischemia and in oxygen-glucose deprivation (OGD)-induced cellular apoptosis in the M1800 astrocyte cell line. NDRG2 mRNA and protein expression began to increase at 6 and 2 h after reperfusion and peaked at 24 h in the ischemic penumbra and in M1800 cells, as detected by RT-PCR and Western blotting. Double immunofluorescence staining showed that the number of apoptotic cells increased as the NDRG2-positive signal increased and that the NDRG2 signal was sometimes co-localized with TUNEL-positive cells and translocated from the cytoplasm to the nucleus in both the ischemic penumbra and the M1800 cells. Using a lentivirus, we successfully constructed two stable astrocytic cell lines in which NDRG2 expression was significantly up- or down-regulated. NDRG2 silencing had a proliferative effect and reduced the percentage of apoptotic cells, reactive oxygen species (ROS) production, and cleaved Caspase-3 protein expression following OGD, whereas NDRG2 over-expression had the opposite effects. In conclusion, NDRG2 is involved in astrocyte apoptosis following ischemic-hypoxic injury, and inhibiting NDRG2 expression significantly reduces ROS production and astrocyte apoptosis. These findings provide insight into the role of NDRG2 in ischemic-hypoxic injury and provide potential targets for future clinical therapies for stroke.

2-Arachidonylglycerol Protects Primary Astrocytes Exposed to Oxygen-Glucose Deprivation Through a Blockade of NDRG2 Signaling and STAT3 Phosphorylation

The human N-Myc downstream-regulated gene 2 (NDRG2) is expressed in astrocytes, and may be involved in the modulation of gliacyte function in the central nervous system. Our previous study found suppression of NDRG2 up-regulation in reactive astrocytes in cerebral ischemic tolerance. 2-Arachidonylglycerol (2-AG) can induce cerebral ischemic tolerance. However, the underlying mechanism of NDRG2 in cytoprotection induced by 2-AG in primary astrocytesis still unknown. In this study, we investigated the role of NDRG2 in cerebral ischemic tolerance induced by 2-AG after oxygen-glucose deprivation (OGD) in primary astrocytes. The results showed that primary astrocytes exposed to OGD resulted in marked increase of lactate dehydrogenase (LDH) release and decrease of methyl thiazolyl tetrazolium (MTT) reduction activity in comparison to control cultures. The levels of NDRG2 and phospho-signal transducer and activator of transcription 3 (pSTAT3) in the OGD group were comparably higher than those in the control group, and the up-regulation of NDRG2 and pSTAT3 was suppressed in NDRG2 siRNA group. The cell viability in the 2-AG group was higher than that in the OGD group, and transfecting the NDRG2 pSRL-CDH1-GFP vector reversed the protective effects of 2-AG. The levels of NDRG2 and pSTAT3 in the 2-AG group were lower than those in the OGD group. 2-AG suppressed STAT3 phosphorylation by decreased expression of NDRG2. In conclusion, 2-AG protects primary astrocytes exposed to oxygen-glucose deprivation through a blockade of NDRG2 signaling and STAT3 phosphorylation. These findings bring insight to the roles of NDRG2 in ischemic-hypoxic injury and provide novel potential targets for future potent clinical therapies on cerebral ischemia injury.

N-myc downstream-regulated gene 2 in the nervous system: from expression pattern to function

Human N-myc downstream-regulated gene 2 (NDRG2) has been shown to be a multifunctional protein associated with cell proliferation, differentiation, transmembrane transport, and stress responses. In most mammalian brains, NDRG2 is principally expressed in astrocytic cells throughout different regions. NDRG2 has been increasingly implicated in the regulation of neurogenesis and in the development of nervous system diseases, including neurodegeneration, ischemia, and glioblastoma. This review summarizes the distribution and subcellular localization of NDRG2 in brain tissues, highlights the physiological actions of NDRG2 in the nervous system, and further discusses the roles of NDRG2 during the occurrence and development of several nervous system diseases.

N‑Myc downstream‑regulated gene 2 suppresses the proliferation of T24 human bladder cancer cells via induction of oncosis

Previous studies have reported the antitumor activity of N-Myc downstream-regulated gene 2 (NDRG2), a novel p53-inducible gene, in several types of cancer. The present study aimed to investigate the effects of NDRG2 expression on the proliferation of a human bladder cancer cell line. NDRG2 and control green fluorescent protein (GFP) recombinant adenovirus plasmids were constructed and transfected into a bladder cancer cell line with mutant p53 (T24 cells). NDRG2 expression was analyzed using western blot analysis and immunofluorescence assay (IFA); in addition, the subcellular localization of NDRG2 was detected using a confocal microscope. The proliferation rate of cells was measured using colony formation and MTT assays. Furthermore, the cell cycle of transfected T24 cells was detected by flow cytometry. The results indicated that T24 cells expressed low levels of NDRG2 prior to infection with GFP-NDRG2 recombinant adenovirus; by contrast, following infection, NDRG2 was primarily over-expressed in mitochondria. The proliferation rate of T24 cells was significantly reduced by NDRG2 expression (P<0.01). In addition, 82.1% of NDRG2-expressing cells were in S-phase, compared to 74.4% in the control virus-infected cells (P<0.05). Furthermore, upregulation of NDRG2 induced an increase in oncosis, rather than apoptosis, in T24 cell. In conclusion, the results of the present study indicated that NDRG2 expression in mitochondria may arrest bladder cancer cells in S-phase as well as decrease cell proliferation through inducing oncosis. It was therefore proposed that NDRG2 was not only a biomarker, but also a tumor suppressor for bladder cancer.

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.

Epithelial sodium transport and its control by aldosterone: the story of our internal environment revisited

Transcription and translation require a high concentration of potassium across the entire tree of life. The conservation of a high intracellular potassium was an absolute requirement for the evolution of life on Earth. This was achieved by the interplay of P- and V-ATPases that can set up electrochemical gradients across the cell membrane, an energetically costly process requiring the synthesis of ATP by F-ATPases. In animals, the control of an extracellular compartment was achieved by the emergence of multicellular organisms able to produce tight epithelial barriers creating a stable extracellular milieu. Finally, the adaptation to a terrestrian environment was achieved by the evolution of distinct regulatory pathways allowing salt and water conservation. In this review we emphasize the critical and dual role of Na(+)-K(+)-ATPase in the control of the ionic composition of the extracellular fluid and the renin-angiotensin-aldosterone system (RAAS) in salt and water conservation in vertebrates. The action of aldosterone on transepithelial sodium transport by activation of the epithelial sodium channel (ENaC) at the apical membrane and that of Na(+)-K(+)-ATPase at the basolateral membrane may have evolved in lungfish before the emergence of tetrapods. Finally, we discuss the implication of RAAS in the origin of the present pandemia of hypertension and its associated cardiovascular diseases.

Adenovirus-mediated NDRG2 inhibits the proliferation of human renal cell carcinoma cell line OS-RC-2 in vitro

OBJECTIVE

To investigate the inhibitory effects of adenovirus-mediated NDRG2 on the proliferation of human renal cell carcinoma cell line OS-RC-2 in vitro.

METHOD

NDRG2 was harvested by RT-PCR, confirmed by DNA sequencing, and then cloned into the eukaryotic expression vector pIRES2-EGFP, which encodes green fluorescent protein (GFP), to construct pIRES2-EGFP-NDRG2 plasmid. OS-RC-2 cells with NDRG2 negative expression were transfected with pIRES2-EGFP-NDRG2 plasmid. The growth of transfected OS-RC-2 cells was observed under light and fluorescence microscopes. After colony-forming cell assays, cell proliferation detection and MTT assays, the growth curves of cells in each group were plotted to investigate the inhibitory effects of adenovirus-mediated NDRG2 on the proliferation of OS-RC-2 cells. Cell cycle was determined by flow cytometry. Confocal laser scanning microscopy showed that NDRG2 protein was specifically located on subcellular organelle.

RESULTS

A eukaryotic expression vector pIRES2-EGFP-NDRG2 was successfully constructed. After NDRG2 transfection, the growth of OS-RC-2 cells was inhibited. Flow cytometry showed that cells were arrested in S phase but the peak of cell apoptosis was not present, and confocal laser scanning microscopy showed that NDRG2 protein was located in mitochondrion.

CONCLUSIONS

NDRG2 can significantly inhibit the proliferation of OS-RC-2 cells in vitro and its protein is specifically expressed in the mitochondrion.

Estrogen regulates the expression of Ndrg2 in astrocytes

N-myc downstream-regulated gene 2 (Ndrg2) is a newly identified molecule that is mainly expressed in astrocytes within the central nervous system (CNS) and is involved in the proliferation and activation of astrocytes. 17β-estradiol (E2) is one of the most important circulating hormones, and in the CNS, astrocytes are a target and potential mediator of the action of E2. Our most recent study found that DPN, an estrogen receptor (ER) β-specific agonist, activated the Ndrg2 promoter and elevated endogenous NDRG2 protein expression in MCF7, HSG and T-47D cells. However, whether E2 regulates Ndrg2 expression in astrocytes remains unknown. Here, we conducted both in vivo and in vitro experiments and found that ERβ co-localized with NDRG2 in astrocytes. Furthermore, in primary cultured astrocytes, we demonstrated that E2 up-regulated Ndrg2 mRNA and protein expression in a dose- and time-dependent manner and that the ERβ agonist DPN but not the ERα agonist PPT up-regulated Ndrg2 expression. In vivo, we found that in the hippocampus of adult ovariectomized (OVX) female mice, Ndrg2 mRNA and protein expression were significantly decreased compared with those in normal adult female mice. After the OVX mice received continuous subcutaneous injections of 50μg/kg E2, 100μg/kg E2 or the ERβ agonist DPN for 10 days, the Ndrg2 expression significantly increased compared with that of the OVX mice. Our results indicate that E2 may affect astrocytes by regulating Ndrg2 expression.

Deletion of N-myc downstream-regulated gene 2 attenuates reactive astrogliosis and inflammatory response in a mouse model of cortical stab injury

N-myc downstream-regulated gene 2 (Ndrg2) is a differentiation- and stress-associated molecule predominantly expressed in astrocytes in the CNS. In this study, we examined the expression and the role of Ndrg2 after cortical stab injury. We observed that Ndrg2 expression was elevated in astrocytes surrounding the wounded area as early as day 1 after injury in wild-type mice. Deletion of Ndrg2 resulted in lower induction of reactive astroglial and microglial markers in the injured cortex. Histological analysis showed reduced levels of hypertrophic changes in astrocytes, accumulation of microglia, and neuronal death in Ndrg2(-/-) mice after injury. Furthermore, activation of the IL-6/signal transducer and activator of transcription 3 (STAT3) pathway, including the expression of IL-6 family cytokines and phosphorylation of STAT3, was markedly reduced in Ndrg2(-/-) mice after injury. In a culture system, both of Il6 and Gfap were up-regulated in wild-type astrocytes treated with forskolin. Deletion of Ndrg2 attenuated induction of these genes, but did not alter proliferation or migration of astrocytes. Adenovirus-mediated reexpression of Ndrg2 rescued the reduction of IL-6 expression after forskolin stimulation. These findings suggest that Ndrg2 plays a key role in reactive astrogliosis after cortical stab injury through a mechanism involving the positive regulation of IL-6/STAT3 signaling.

N-myc downstream-regulated gene 2 expression is associated with glucose transport and correlated with prognosis in breast carcinoma

Introduction

N-myc downstream-regulated gene 2 (NDRG2), a novel tumour suppressor and cell stress-related gene, is involved in many cell metabolic processes, such as hormone, ion and fluid metabolism. We investigated whether NDRG2 is involved in any glucose-dependent energy metabolism, as well as the nature of its correlation with breast carcinoma.

Methods

The correlations between NDRG2 expression and glucose transporter 1 (GLUT1) expression in clinical breast carcinoma tissues were analysed. The effects of NDRG2 on glucose uptake were assessed in breast cancer cells and xenograft tumours. The consequences of NDRG2-induced regulation of GLUT1 at the transcription and translation levels and the interaction between NDRG2 and GLUT1 were examined.

Results

Data derived from clinical breast carcinoma specimens revealed that (1) patients with high NDRG2 expression had better disease-free survival and overall survival than those with low NDRG2 expression and (2) NDRG2 expression was negatively correlated with GLUT1 expression in these breast carcinoma tissues. NDRG2 inhibited glucose uptake by promoting GLUT1 protein degradation without affecting GLUT1 transcription in both breast cancer cells and xenograft tumours. In addition, NDRG2 protein interacted and partly colocalised with GLUT1 protein in cell cytoplasm areas.

Conclusions

The results of our study support the notion that NDRG2 plays an important role in tumour glucose metabolism, in which GLUT1 is a likely candidate contributor to glucose uptake suppression and tumour growth. Targeting the actions of NDRG2 in cell glucose-dependent energy delivery may provide an attractive strategy for therapeutic intervention in human breast carcinoma.

Ndrg2 is a PGC-1α/ERRα target gene that controls protein synthesis and expression of contractile-type genes in C2C12 myotubes

The stress-responsive, tumor suppressor N-myc downstream-regulated gene 2 (Ndrg2) is highly expressed in striated muscle. In response to anabolic and catabolic signals, Ndrg2 is suppressed and induced, respectively, in mouse C2C12 myotubes. However, little is known about the mechanisms regulating Ndrg2 expression in muscle, as well as the biological role for Ndrg2 in differentiated myotubes. Here, we show that Ndrg2 is a target of a peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α) and estrogen-related receptor alpha (ERRα) transcriptional program and is induced in response to endurance exercise, a physiological stress known also to increase PGC-1α/ERRα activity. Analyses of global gene and protein expression profiles in C2C12 myotubes with reduced levels of NDRG2, suggest that NDRG2 affects muscle growth, contractile properties, MAPK signaling, ion and vesicle transport and oxidative phosphorylation. Indeed, suppression of NDRG2 in myotubes increased protein synthesis and the expression of fast glycolytic myosin heavy chain isoforms, while reducing the expression of embryonic myosin Myh3, other contractile-associated genes and the MAPK p90 RSK1. Conversely, enhanced expression of NDRG2 reduced protein synthesis, and furthermore, partially blocked the increased protein synthesis rates elicited by a constitutively active form of ERRα. In contrast, suppressing or increasing levels of NDRG2 did not affect mRNA expression of genes involved in mitochondrial biogenesis that are regulated by PGC-1α or ERRα. This study shows that in C2C12 myotubes Ndrg2 is a novel PGC-1α/ERRα transcriptional target, which influences protein turnover and the regulation of genes involved in muscle contraction and function.

Suppressed expression of NDRG2 correlates with poor prognosis in pancreatic cancer

Pancreatic cancer is a highly lethal disease with a poor prognosis; the molecular mechanisms of the development of this disease have not yet been fully elucidated. N-myc downstream regulated gene 2 (NDRG2), one of the candidate tumor suppressor genes, is frequently downregulated in pancreatic cancer, but there has been little information regarding its expression in surgically resected pancreatic cancer specimens. We investigated an association between NDRG2 expression and prognosis in 69 primary resected pancreatic cancer specimens by immunohistochemistry and observed a significant association between poor prognosis and NDRG2-negative staining (P=0.038). Treatment with trichostatin A, a histone deacetylase inhibitor, predominantly up-regulated NDRG2 expression in the NDRG2 low-expressing cell lines (PANC-1, PCI-35, PK-45P, and AsPC-1). In contrast, no increased NDRG2 expression was observed after treatment with 5-aza-2' deoxycytidine, a DNA demethylating agent, and no hypermethylation was detected in either pancreatic cancer cell lines or surgically resected specimens by methylation specific PCR. Our present results suggest that (1) NDRG2 is functioning as one of the candidate tumor-suppressor genes in pancreatic carcinogenesis, (2) epigenetic mechanisms such as histone modifications play an essential role in NDRG2 silencing, and (3) the expression of NDRG2 is an independent prognostic factor in pancreatic cancer.

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.

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.

Two populations of glucocorticoid receptor-binding sites in the male rat hippocampal genome

In the present study, genomic binding sites of glucocorticoid receptors (GR) were identified in vivo in the rat hippocampus applying chromatin immunoprecipitation followed by next-generation sequencing. We identified 2470 significant GR-binding sites (GBS) and were able to confirm GR binding to a random selection of these GBS covering a wide range of P values. Analysis of the genomic distribution of the significant GBS revealed a high prevalence of intragenic GBS. Gene ontology clusters involved in neuronal plasticity and other essential neuronal processes were overrepresented among the genes harboring a GBS or located in the vicinity of a GBS. Male adrenalectomized rats were challenged with increasing doses of the GR agonist corticosterone (CORT) ranging from 3 to 3000 μg/kg, resulting in clear differences in the GR-binding profile to individual GBS. Two groups of GBS could be distinguished: a low-CORT group that displayed GR binding across the full range of CORT concentrations, and a second high-CORT group that displayed significant GR binding only after administering the highest concentration of CORT. All validated GBS, in both the low-CORT and high-CORT groups, displayed mineralocorticoid receptor binding, which remained relatively constant from 30 μg/kg CORT upward. Motif analysis revealed that almost all GBS contained a glucocorticoid response element resembling the consensus motif in literature. In addition, motifs corresponding with new potential GR-interacting proteins were identified, such as zinc finger and BTB domain containing 3 (Zbtb3) and CUP (CG11181 gene product from transcript CG11181-RB), which may be involved in GR-dependent transactivation and transrepression, respectively. In conclusion, our results highlight the existence of 2 populations of GBS in the rat hippocampal genome.

Heterogeneous nuclear ribonucleoprotein A2/B1 is a tissue-specific aldosterone target gene with prominent induction in the rat distal colon

The steroid hormone aldosterone enhances transepithelial Na(+) reabsorption in tight epithelia and is crucial to achieve extracellular volume homeostasis and control of blood pressure. One of the main transport pathways regulated by aldosterone involves the epithelial Na(+) channel (ENaC), which constitutes the rate-limiting step of Na(+) reabsorption in parts of the distal nephron and the collecting duct, the distal colon, and sweat and salivary glands. Although these epithelial tissues share the same receptor for aldosterone (mineralocorticoid receptor, MR), and the same transport system (ENaC), it has become clear that the molecular mechanisms involved in the modulation of channel activity are tissue-specific. Recent evidence suggests that aldosterone controls transcription and also translation of ENaC subunits in some cell types. A possible pathway for translational regulation is binding of regulatory proteins to ENaC subunit mRNAs, such as the heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNP A2/B1). In this study, we examined whether hnRNP A2/B1 is an aldosterone-target gene in vivo. Our data show that physiological levels of aldosterone markedly induce hnRNP A2/B1 expression in an early and sustained manner in the late distal colon epithelium but not in other aldosterone-target tissues. The effect depends on MR but not on glucocorticoid receptor activity. We also demonstrate that the genomic region upstream of hnRNP A2/B1 contains aldosterone-responsive elements involved in the control of gene expression. We hypothesize that hnRNP A2/B1 is involved in the tissue-specific regulation of ENaC biosynthesis and may coordinate the response of other genes relevant for transepithelial Na(+) reabsorption by aldosterone.

Acid stress increases gene expression of proinflammatory cytokines in Madin-Darby canine kidney cells

Metabolic acidosis is thought to exacerbate chronic kidney disease in part by stimulating the release of potentially injurious substances. To define the genes whose expression is affected by exposure to an acidic milieus, we examined the effect of exposure of MDCK cells to pH 7.4 and pH 7.0 for 24 h on gene expression using a canine derived microarray. Exposure to this pH stress for 24 h led to increased expression of 278 genes (2.2% of the transcriptome) by at least 2-fold and 60 of these (21%) were upregulated by >3-fold. On the other hand, 186 genes (1.5% of the transcriptome) were downregulated by at least 2-fold and 16 of these (9%) were downregulated by 3-fold or more. Ten percent of the genes upregulated by at least threefold encode proinflammatory cytokine proteins, including colony stimulating factor 2, chemokine ligand 7, chemokine ligand 20, chemokine ligand 8, and interleukin-1α. Two others encode metallopeptidases. The most highly upregulated gene encodes a protein, lubricin, shown to be important in preventing cartilage damage and in tissue injury or repair. Upregulation of four genes was confirmed by quantitative PCR. Housekeeping genes were not increased. To examine the effect of decreasing medium pH, we measured intracellular pH (pHi) using 2,7-bis (2-carboxyethyl)5-carboxyfluorescein. With extracellular pH (pHo) of 7.0, pHi fell and remained depressed. These findings suggest that a pH stress alone can increase renal expression of proinflammatory and other genes that contribute to renal injury.

Deep RNA sequencing reveals novel cardiac transcriptomic signatures for physiological and pathological hypertrophy

Although both physiological hypertrophy (PHH) and pathological hypertrophy (PAH) of the heart have similar morphological appearances, only PAH leads to fatal heart failure. In the present study, we used RNA sequencing (RNA-Seq) to determine the transcriptomic signatures for both PHH and PAH. Approximately 13-20 million reads were obtained for both models, among which PAH showed more differentially expressed genes (DEGs) (2,041) than PHH (245). The expression of 417 genes was barely detectable in the normal heart but was suddenly activated in PAH. Among them, Foxm1 and Plk1 are of particular interest, since Ingenuity Pathway Analysis (IPA) using DEGs and upstream motif analysis showed that they are essential hub proteins that regulate the expression of downstream proteins associated with PAH. Meanwhile, 52 genes related to collagen, chemokines, and actin showed opposite expression patterns between PHH and PAH. MAZ-binding motifs were enriched in the upstream region of the participating genes. Alternative splicing (AS) of exon variants was also examined using RNA-Seq data for PAH and PHH. We found 317 and 196 exon inclusions and exon exclusions, respectively, for PAH, and 242 and 172 exon inclusions and exclusions, respectively for PHH. The AS pattern was mostly related to gains or losses of domains, changes in activity, and localization of the encoded proteins. The splicing variants of 8 genes (i.e., Fhl1, Rcan1, Ndrg2, Synpo, Ttll1, Cxxc5, Egfl7, and Tmpo) were experimentally confirmed. Multilateral pathway analysis showed that the patterns of quantitative (DEG) and qualitative (AS) changes differ depending on the type of pathway in PAH and PHH. One of the most significant changes in PHH is the severe downregulation of autoimmune pathways accompanied by significant AS. These findings revealed the unique transcriptomic signatures of PAH and PHH and also provided a more comprehensive understanding at both the quantitative and qualitative levels.

Genomic profiling of microRNAs and proteomics reveals an early molecular alteration associated with tumorigenesis induced by MC-LR in mice

Studies have demonstrated that microcystins (MCs) can act as potential carcinogens and have caused serious risk to public environmental health. The molecular mechanisms of MC-induced susceptibility to carcinogenesis are largely unknown. In this study, we performed for the first time a comprehensive analysis of changes in microRNAs (miRNAs) and proteins expression in livers of mice treated with MC-LR. Utilizing microarray and two-dimensional gel electrophoresis (2-DE) analysis, we identified 37 miRNAs and 42 proteins significantly altered. Many aberrantly expressed miRNAs were related to various cancers (e.g., miR-125b, hepatocellular carcinoma; miR-21, leukemia; miR-16, chronic lymphocytic leukemia; miR-192, pituitary adenomas; miR-199a-3p, ovarian cancer; miR-34a, pancreatic cancer). Several miRNAs (e.g., miR-34a, miR-21) and proteins (e.g., TGM2, NDRG2) that play crucial roles in liver tumorigenesis were first found to be affected by MC-LR in mouse liver. MC-LR also altered the expression of a number of miRNAs and proteins involved in several pathways related to tumorigenesis, such as glutathione metabolism, VEGF signaling, and MAPK signaling pathway. Integration of post-transcriptomics, proteomics, and transcriptomics reveals that the networks miRNAs and their potential target genes and proteins involved in had a close association with carcinogenesis. These results provide an early molecular mechanism for liver tumorigenesis induced by MCs.

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.

N-myc downstream-regulated gene 2, a novel estrogen-targeted gene, is involved in the regulation of Na+/K+-ATPase

Na(+)/K(+)-ATPase, a plasma membrane protein abundantly expressed in epithelial tissues, has been identified and linked to numerous biological events, including ion transport and reabsorption. In Na(+)/K(+)-ATPase, the β-subunit plays a fundamental role in the structural integrity and functional maturation of holoenzyme. Estrogens are important circulating hormones that can regulate Na(+)/K(+)-ATPase abundance and activity; however, the specific molecules participating in this process are largely unknown. Here, we characterize that N-myc downstream-regulated gene 2 (NDRG2) is an estrogen up-regulated gene. 17β-Estradiol binds with estrogen receptor β but not estrogen receptor α to up-regulate NDRG2 expression via transcriptional activation. We also find that NDRG2 interacts with the β1-subunit of Na(+)/K(+)-ATPase and stabilizes the β1-subunit by inhibiting its ubiquitination and degradation. NDRG2-induced prolongation of the β1-subunit protein half-life is accompanied by a similar increase in Na(+)/K(+)-ATPase-mediated Na(+) transport and Na(+) current in epithelial cells. In addition, NDRG2 silencing largely attenuates the accumulation of β1-subunit regulated by 17β-estradiol. Our results demonstrate that estrogen/NDRG2/Na(+)/K(+)-ATPase β1 pathway is important in promoting Na(+)/K(+)-ATPase activity and suggest this novel pathway might have substantial roles in ion transport, fluid balance, and homeostasis.

Role of the Renin-Angiotensin system and aldosterone on cardiometabolic syndrome

Aldosterone facilitates cardiovascular damage by increasing blood pressure and through different mechanisms that are independent of its effects on blood pressure. In this respect, recent evidence involves aldosterone in the pathogenesis of metabolic syndrome. Although this relationship is complex, there is some evidence suggesting that different factors may play an important role, such as insulin resistance, renin-angiotensin-aldosterone system, oxidative stress, sodium retention, increased sympathetic activity, levels of free fatty acids, or inflammatory cytokines and adipokines. In addition to the classical pathway by which aldosterone acts through the mineralocorticoid receptors leading to sodium retention, aldosterone also has other mechanisms that influence cardiovascular tissue remodelling. Finally, overweight and obesity promote the adrenal secretion of aldosterone, increasing the predisposition to type 2 diabetes mellitus. Further studies are needed to better establish therapeutic strategies that act on the blockade of mineralocorticoid receptor in the treatment and prevention of cardiovascular diseases related to the excess of aldosterone and the metabolic syndrome.

NDRG2 inhibits hepatocellular carcinoma adhesion, migration and invasion by regulating CD24 expression

BACKGROUND

The prognosis of most hepatocellular carcinoma (HCC) patients is poor due to the high metastatic rate of the disease. Understanding the molecular mechanisms underlying HCC metastasis is extremely urgent. The role of CD24 and NDRG2 (N-myc downstream-regulated gene 2), a candidate tumor suppressor gene, has not yet been explored in HCC.

METHODS

The mRNA and protein expression of CD24 and NDRG2 was analyzed in MHCC97H, Huh7 and L-02 cells. Changes in cell adhesion, migration and invasion were detected by up- or down-regulating NDRG2 by adenovirus or siRNA. The expression pattern of NDRG2 and CD24 in HCC tissues and the relationship between NDRG2 and HCC clinical features was analyzed by immunohistochemical and western blotting analysis.

RESULTS

NDRG2 expression was negatively correlated with malignancy in HCC. NDRG2 exerted anti-tumor activity by regulating CD24, a molecule that mediates cell-cell interaction, tumor proliferation and adhesion. NDRG2 up-regulation decreased CD24 expression and cell adhesion, migration and invasion. By contrast, NDRG2 down-regulation enhanced CD24 expression and cell adhesion, migration and invasion. Immunohistochemical analysis of 50 human HCC clinical specimens showed a strong correlation between NDRG2 down-regulation and CD24 overexpression (P = 0.04). In addition, increased frequency of NDRG2 down-regulation was observed in patients with elevated AFP serum level (P = 0.006), late TNM stage (P = 0.009), poor differentiation grade (P = 0.002), tumor invasion (P = 0.004) and recurrence (P = 0.024).

CONCLUSIONS

Our findings indicate that NDRG2 and CD24 regulate HCC adhesion, migration and invasion. The expression level of NDRG2 is closely related to the clinical features of HCC. Thus, NDRG2 plays an important physiological role in HCC metastasis.

NDRG2 inhibits hepatocellular carcinoma adhesion, migration and invasion by regulating CD24 expression

BACKGROUND

The prognosis of most hepatocellular carcinoma (HCC) patients is poor due to the high metastatic rate of the disease. Understanding the molecular mechanisms underlying HCC metastasis is extremely urgent. The role of CD24 and NDRG2 (N-myc downstream-regulated gene 2), a candidate tumor suppressor gene, has not yet been explored in HCC.

METHODS

The mRNA and protein expression of CD24 and NDRG2 was analyzed in MHCC97H, Huh7 and L-02 cells. Changes in cell adhesion, migration and invasion were detected by up- or down-regulating NDRG2 by adenovirus or siRNA. The expression pattern of NDRG2 and CD24 in HCC tissues and the relationship between NDRG2 and HCC clinical features was analyzed by immunohistochemical and western blotting analysis.

RESULTS

NDRG2 expression was negatively correlated with malignancy in HCC. NDRG2 exerted anti-tumor activity by regulating CD24, a molecule that mediates cell-cell interaction, tumor proliferation and adhesion. NDRG2 up-regulation decreased CD24 expression and cell adhesion, migration and invasion. By contrast, NDRG2 down-regulation enhanced CD24 expression and cell adhesion, migration and invasion. Immunohistochemical analysis of 50 human HCC clinical specimens showed a strong correlation between NDRG2 down-regulation and CD24 overexpression (P = 0.04). In addition, increased frequency of NDRG2 down-regulation was observed in patients with elevated AFP serum level (P = 0.006), late TNM stage (P = 0.009), poor differentiation grade (P = 0.002), tumor invasion (P = 0.004) and recurrence (P = 0.024).

CONCLUSIONS

Our findings indicate that NDRG2 and CD24 regulate HCC adhesion, migration and invasion. The expression level of NDRG2 is closely related to the clinical features of HCC. Thus, NDRG2 plays an important physiological role in HCC metastasis.

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.

The effect of Ndrg2 expression on astroglial activation

N-myc downstream-regulated gene 2 (Ndrg2) is a differentiation- and stress-associated molecule predominantly expressed in astrocytes in the central nervous system (CNS). To study the expression and possible role of Ndrg2 in quiescent and activated astrocytes, mice were administrated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropypridine (MPTP), a Parkinson disease (PD)-related neurotoxin which causes both neurodegeneration and glial activation. Immunohistological analysis revealed that Ndrg2 was highly expressed in both types of astrocytes, but less so in astrocytes during the early process of activation. Ndrg2 was also expressed in astrocyte-like cells, but not in neurons, in human brains from PD and Cortico-basal degeneration (CBD) patients. In cultured astrocytes, gene silencing of Ndrg2 significantly enhanced the numbers of 5-bromo-2'-deoxy-uridine (BrdU)-incorporated and proliferating cell nuclear antigen (PCNA)-positive cells, and reduced the length of cell processes and the amount of F-actin. In contrast, adenovirus-mediated overexpression of Ndrg2 significantly reduced the numbers of BrdU-incorporated and PCNA-positive cells, and enhanced the amount of F-actin. Fractionation and immunocytochemical analysis further revealed that Ndrg2 was located in different cellular fractions including the cytosol and cell surface membranes. These results suggest that Ndrg2 may regulate astroglial activation through the suppression of cell proliferation and stabilization of cell morphology.

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.

NDRG2 in rat liver regeneration: role in proliferation and apoptosis

Liver regeneration is a complex process that is orchestrated by the precise interplay of cell proliferation, differentiation control, and molecular pathways, but this complicated molecular signaling network is not fully understood. In this study, we showed that N-Myc downstream-regulated gene 2 (NDRG2) is involved in this process. The mRNA and protein levels of NDRG2 were strongly reduced when liver regeneration reached a peak of activity. In addition, we found that rat NDRG2 expression and C-Myc expression were inversely correlated during this process. A low level of NDRG2 was observed as the C-Myc expression increased during regeneration. Moreover, a dramatic cell cycle arrest was found in normal rat liver-derived BRL cells 48 hours after being infected by adenoviral vectors expressing rat NDRG2. Meanwhile, the apoptotic rates were increased from 9.4% in control group to 64.7% in adenoviral vectors expressing rat NDRG2 group. These phenomena could also be observed in BRL 3A and L-02 cells. Further analysis revealed that NDRG2 overexpression may mediate the antiproliferative effect by inducing p53 and p21 regulated Bax/Bcl-2 increase and cyclin E-Cdk2 inhibition. In conclusion, our findings point to physiological roles for NDRG2 in liver regeneration.

Mineralocorticoid receptor mutations differentially affect individual gene expression profiles in pseudohypoaldosteronism type 1

CONTEXT

Type 1 pseudohypoaldosteronism (PHA1), a primary form of mineralocorticoid resistance, is due to inactivating mutations of the NR3C2 gene, coding for the mineralocorticoid receptor (MR).

OBJECTIVE

The objective of the study was to assess whether different NR3C2 mutations have distinct effects on the pattern of MR-dependent transcriptional regulation of aldosterone-regulated genes.

DESIGN AND METHODS

Four MR mutations affecting residues in the ligand binding domain, identified in families with PHA1, were tested. MR proteins generated by site-directed mutagenesis were analyzed for their binding to aldosterone and were transiently transfected into renal cells to explore the functional effects on the transcriptional activity of the receptors by cis-trans-cotransactivation assays and by measuring the induction of endogenous gene transcription.

RESULTS

Binding assays showed very low or absent aldosterone binding for mutants MR(877Pro), MR(848Pro), and MR(947stop) and decreased affinity for aldosterone of MR(843Pro). Compared with wild-type MR, the mutations p.Leu843Pro and p.Leu877Pro displayed half-maximal aldosterone-dependent transactivation of reporter genes driven by mouse mammary tumor virus or glucocorticoid response element-2 dependent promoters, whereas MR(848Pro) and MR(947stop) nearly or completely lost transcriptional activity. Although MR(848Pro) and MR(947stop) were also incapable of inducing aldosterone-dependent gene expression of endogenous sgk1, GILZ, NDRG2, and SCNN1A, MR(843Pro) retained complete transcriptional activity on sgk1 and GILZ gene expression, and MR(877Pro) negatively affected the expression of sgk1, NDRG2, and SCNN1A.

CONCLUSIONS

Our data demonstrate that MR mutations differentially affect individual gene expression in a promoter-dependent manner. Investigation of differential gene expression profiles in PHA1 may allow a better understanding of the molecular substrate of phenotypic variability and to elucidate pathogenic mechanisms underlying the disease.

Variation of NDRG2 and c-Myc expression in rat heart during the acute stage of ischemia/reperfusion injury

N-Myc downstream regulated gene 2 (NDRG2), a Myc-repressed gene, is highly expressed in heart tissue. NDRG2 increases in response to hypoxia-induced stress and is involved in hypoxia-induced radioresistance. However, little is known about the expression changes and possible roles of NDRG2 in the heart under hypoxia condition. Here, the authors show that NDRG2, mainly localized in cardiomyocyte cytoplasm, was significantly reduced in myocardial tissue after acute ischemia/reperfusion (I/R) injury. Meanwhile, c-Myc was up-regulated following acute I/R injury, and the expression of c-Myc was significantly inversely correlated with that of NDRG2. In addition, overexpression of c-Myc in primary cultured cardiomyocyte repressed NDRG2 expression. Furthermore, the increase of cardiomyocyte apoptosis was correlated with the decrease of NDRG2 protein during the acute phase of reperfusion. These data suggested for the first time that I/R injury-induced up-regulation of pro-apoptotic c-Myc expression may contribute to the down-regulation of anti-apoptotic NDRG2. This stress response might be involved in the novel mechanism of myocardial apoptosis induced by I/R injury in rat.