Dexamethasone indirectly induces Ndrg2 expression in rat astrocytes

Pathophysiological significance of N-myc downstream-regulated gene 2 in cancer development through protein phosphatase 2A phosphorylation regulation

N-myc downstream-regulated gene 2 (NDRG2) is a candidate tumor suppressor in various cancers, including adult T-cell leukemia/lymphoma (ATLL). NDRG2, as a stress-responsive protein, is induced by several stress-related signaling pathways and NDRG2 negatively regulates various signal transduction pathways. Although it has not been found to function alone, NDRG2 binds serine/threonine protein phosphatase 2A (PP2A), generating a complex that is involved in the regulation of various target proteins. The main function of NDRG2 is to maintain cell homeostasis by suppressing stress-induced signal transduction; however, in cancer, genomic deletions and/or promoter methylation may inhibit the expression of NDRG2, resulting in enhanced tumor development through overactivated signal transduction pathways. A wide variety of tumors develop in Ndrg2-deficient mice, including T-cell lymphoma, liver, lung and other tumors, the characteristics of which are similar to those in Pten-deficient mice. In particular, PTEN is a target molecule of the NDRG2/PP2A complex, which enhances PTEN phosphatase activity by dephosphorylating residues in the PTEN C-terminal region. In ATLL cells, loss of NDRG2 expression leads to the failed recruitment of PP2A to PTEN, resulting in the inactivation of PTEN phosphatase with phosphorylation, ultimately leading to the activation of PI3K/AKT. Thus, NDRG2, as a PP2A adaptor, regulates the global phosphorylation of important signaling molecules. Moreover, the downregulation of NDRG2 expression by long-term stress-induced methylation is directly correlated with the development of ATLL and other cancers. Thus, NDRG2 might be important for the development of stress-induced leukemia and other cancers and has become an important target for novel molecular therapies.

17β-Oestradiol Attenuates the Photoreceptor Apoptosis in Mice with Retinitis Pigmentosa by Regulating N-myc Downstream Regulated Gene 2 Expression

Retinitis pigmentosa (RP) is a heterogeneous group of retinal degenerative diseases in which the final pathological feature is photoreceptor cell apoptosis. Currently, the pathogenesis of RP remains poorly understood and therapeutics are ineffective. 17β-Oestradiol (βE2) is universally acknowledged as a neuroprotective factor in neurodegenerative diseases and has manifested neuroprotective effects in a light-induced retinal degeneration model. Recently, we identified N-myc downstream regulated gene 2 (NDRG2) suppression as a molecular marker of mouse retinal photoreceptor-specific cell death. βE2 has also been reported to regulate NDRG2 in salivary acinar cells. Therefore, in this study, we investigated whether βE2 plays a protective role in RP and regulates NDRG2 in photoreceptor cells. To this end, we generated RP models and observed that βE2 not only reduced the apoptosis of photoreceptor cells, but also restored the level of NDRG2 expression in RP models. Then, we showed that siNDRG2 inhibits the anti-apoptotic effect of βE2 on photoreceptor cells in a cellular RP model. Subsequently, we used a classic oestrogen receptor (ER) antagonist to attenuate the effects of βE2, suggesting that βE2 exerted its effects on RP models via the classic ERs. In addition, we performed a bioinformatics analysis, and the results indicated that the reported oestrogen response element (ERE) sequence is present in the promoter region of the mouse NDRG2 gene. Overall, our results suggest that βE2 attenuated the apoptosis of photoreceptor cells in RP models by maintaining NDRG2 expression via a classic ER-mediated mechanism.

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.

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.

MicroRNA suppression of stress-responsive NDRG2 during dexamethasone treatment in skeletal muscle cells

Background

MicroRNAs (miRNAs) are increasingly being identified as modulatory molecules for physiological and pathological processes in muscle. Here, we investigated whether miRNAs influenced the expression of the stress-responsive gene N-myc downstream-regulated gene 2 (Ndrg2) in skeletal muscle cells through the targeted degradation or translation inhibition of NDRG2 mRNA transcripts during basal or catabolic stress conditions.

Results

Three miRNAs, mmu-miR-23a-3p (miR-23a), mmu-miR-23b-3p (miR-23b) and mmu-miR-28-5p (miR-28), were identified using an in silico approach and confirmed to target the 3′ untranslated region of the mouse Ndrg2 gene through luciferase reporter assays. However, miR-23a, -23b or -28 overexpression had no influence on NDRG2 mRNA or protein levels up to 48 h post treatment in mouse C2C12 myotubes under basal conditions. Interestingly, a compensatory decrease in the endogenous levels of the miRNAs in response to each other’s overexpression was measured. Furthermore, dexamethasone, a catabolic stress agent that induces NDRG2 expression, decreased miR-23a and miR-23b endogenous levels at 24 h post treatment suggesting an interplay between these miRNAs and NDRG2 regulation under similar stress conditions. Accordingly, when overexpressed simultaneously, miR-23a, -23b and -28 attenuated the dexamethasone-induced increase of NDRG2 protein translation but did not affect Ndrg2 gene expression.

Conclusion

These findings highlight modulatory and co-regulatory roles for miR-23a, -23b and -28 and their novel regulation of NDRG2 during stress conditions in muscle.

Electronic supplementary material

The online version of this article (10.1186/s12860-019-0194-3) contains supplementary material, which is available to authorized users.

NDRG2 suppression as a molecular hallmark of photoreceptor-specific cell death in the mouse retina

Photoreceptor cell death is recognized as the key pathogenesis of retinal degeneration, but the molecular basis underlying photoreceptor-specific cell loss in retinal damaging conditions is virtually unknown. The N-myc downstream regulated gene (NDRG) family has recently been reported to regulate cell viability, in particular NDRG1 has been uncovered expression in photoreceptor cells. Accordingly, we herein examined the potential roles of NDRGs in mediating photoreceptor-specific cell loss in retinal damages. By using mouse models of retinal degeneration and the 661 W photoreceptor cell line, we showed that photoreceptor cells are indeed highly sensitive to light exposure and the related oxidative stress, and that photoreceptor cells are even selectively diminished by phototoxins of the alkylating agent N-Methyl-N-nitrosourea (MNU). Unexpectedly, we discovered that of all the NDRG family members, NDRG2, but not the originally hypothesized NDRG1 or other NDRG subtypes, was selectively expressed and specifically responded to retinal damaging conditions in photoreceptor cells. Furthermore, functional experiments proved that NDRG2 was essential for photoreceptor cell viability, which could be attributed to NDRG2 control of the photo-oxidative stress, and that it was the suppression of NDRG2 which led to photoreceptor cell loss in damaging conditions. More importantly, NDRG2 preservation contributed to photoreceptor-specific cell maintenance and retinal protection both in vitro and in vivo. Our findings revealed a previously unrecognized role of NDRG2 in mediating photoreceptor cell homeostasis and established for the first time the molecular hallmark of photoreceptor-specific cell death as NDRG2 suppression, shedding light on improved understanding and therapy of retinal degeneration.

Glucocorticoids, genes and brain function

The identification of key genes in transcriptomic data constitutes a huge challenge. Our review of microarray reports revealed 88 genes whose transcription is consistently regulated by glucocorticoids (GCs), such as cortisol, corticosterone and dexamethasone, in the brain. Replicable transcriptomic data were combined with biochemical and physiological data to create an integrated view of the effects induced by GCs. The most frequently reported genes were Errfi1 and Ddit4. Their up-regulation was associated with the altered transcription of genes regulating growth factor and mTORC1 signaling (Gab1, Tsc22d3, Dusp1, Ndrg2, Ppp5c and Sesn1) and progression of the cell cycle (Ccnd1, Cdkn1a and Cables1). The GC-induced reprogramming of cell function involves changes in the mRNA level of genes responsible for the regulation of transcription (Klf9, Bcl6, Klf15, Tle3, Cxxc5, Litaf, Tle4, Jun, Sox4, Sox2, Sox9, Irf1, Sall2, Nfkbia and Id1) and the selective degradation of mRNA (Tob2). Other genes are involved in the regulation of metabolism (Gpd1, Aldoc and Pdk4), actin cytoskeleton (Myh2, Nedd9, Mical2, Rhou, Arl4d, Osbpl3, Arhgef3, Sdc4, Rdx, Wipf3, Chst1 and Hepacam), autophagy (Eva1a and Plekhf1), vesicular transport (Rhob, Ehd3, Vps37b and Scamp2), gap junctions (Gjb6), immune response (Tiparp, Mertk, Lyve1 and Il6r), signaling mediated by thyroid hormones (Thra and Sult1a1), calcium (Calm2), adrenaline/noradrenaline (Adcy9 and Adra1d), neuropeptide Y (Npy1r) and histamine (Hdc). GCs also affected genes involved in the synthesis of polyamines (Azin1) and taurine (Cdo1). The actions of GCs are restrained by feedback mechanisms depending on the transcription of Sgk1, Fkbp5 and Nr3c1. A side effect induced by GCs is increased production of reactive oxygen species. Available data show that the brain's response to GCs is part of an emergency mode characterized by inactivation of non-core activities, restrained inflammation, restriction of investments (growth), improved efficiency of energy production and the removal of unnecessary or malfunctioning cellular components to conserve energy and maintain nutrient supply during the stress response.

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.

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

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

NDRG2 phosphorylation provides negative feedback for SGK1-dependent regulation of a kainate receptor in astrocytes

Glutamate receptors play an important role in the function of astrocytes. Among their tasks is the regulation of gliotransmission, gene expression and exocytosis of the tissue-type plasminogen activator (tPA), which has an enhancing effect on N-methyl-D-aspartate (NMDA) receptors and thus prevent over-excitation of neighboring neurons. The kainate receptor GluK2, which is expressed in neurons and astrocytes, is under tight regulation of the PI3-kinase SGK pathway as shown in neurons. SGK1 targets include N-myc downstream-regulated genes (NDRGs) 1 and 2 (NDRG1, NDRG2), proteins with elusive function. In the present study, we analyzed the effects of SGK1, NDRG1, and NDRG2 on GluK2 current amplitude and plasma membrane localization in astrocytes and heterologous expression. We demonstrate that NDRG1 and NDRG2 themselves have no effect on GluK2 current amplitudes in heterologous expressed ion channels. However, when NDRG2 is coexpressed with GluK2 and SGK1, the stimulating effect of SGK1 on GluK2 is suppressed both in heterologous expression and in astrocytes. Here, we reveal a new negative feedback mechanism, whereby GluK2 stimulation by SGK1 is regulated by parallel phosphorylation of NDRG2. This regulation of GluK2 by SGK1 and NDRG2 in astrocytes may play an important role in gliotransmission, modulation of gene expression and regulation of exocytosis of tPA.

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.

Loss of NDRG2 enhanced activation of the NF-κB pathway by PTEN and NIK phosphorylation for ATL and other cancer development

The activation of nuclear factor kappa B (NF-κB) signaling has a central role in the development of adult T-cell leukemia/lymphoma (ATL) and many other cancers. However, the activation mechanism of the NF-κB pathways remains poorly understood. Recently, we reported that N-myc downstream-regulated gene 2 (NDRG2) is a negative regulator of the phosphoinositide 3-kinase (PI3K)/AKT pathway by promoting the active dephosphorylated form of PTEN at its C-terminus via the recruitment of PP2A. Additionally, the down-regulation of NDRG2 expression promotes the inactive phosphorylated form of PTEN, which results in constitutively active PI3K/AKT signaling in various cancer cell types. Here, we investigated the involvement of NDRG2 in modulating NF-κB signaling. The forced expression of NDRG2 in ATL cells down-regulates not only the canonical pathway by inhibiting AKT signaling but also the non-canonical pathway by inducing NF-κB-inducing kinase (NIK) dephosphorylation via the recruitment of PP2A. Therefore, NDRG2 works as a PP2A recruiter to suppress not only PI3K/AKT signaling but also NF-κB signaling, which is particularly important in host defenses or immune responses to Human T-cell leukemia virus type 1 (HTLV-1) infection. Furthermore, the loss of NDRG2 expression might play an important role in the progression of tumor development after HTLV-1 infection.

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.

Inhibition of N-myc Downstream–regulated Gene-2 Is Involved in an Astrocyte-specific Neuroprotection Induced by Sevoflurane Preconditioning

Background:

Mechanism of sevoflurane preconditioning–induced cerebral ischemic tolerance is unclear. This study investigates the role of N-myc downstream–regulated gene-2 (NDRG2) in the neuroprotection of sevoflurane preconditioning in ischemic model both in vivo and in vitro.

Methods:

At 2 h after sevoflurane (2%) preconditioning for 1 h, rats were subjected to middle cerebral artery occlusion for 120 min. Neurobehavioral scores (n = 10), infarct volumes (n = 10), cellular apoptosis (n = 6), and NDRG2 expression (n = 6) were determined at 24 h after reperfusion. In vitro, cultural astrocytes were exposed to oxygen–glucose deprivation for 4 h. Cellular viability, cytotoxicity, apoptosis, and NDRG2 expression (n = 6) were evaluated in the presence or absence of NDRG2-specific small interfering RNA or NDRG2 overexpression plasmid.

Results:

Sevoflurane preconditioning decreased apoptosis (terminal deoxynucleotidyl transferase–mediated 2’-deoxyuridine 5’-triphosphate nick-end labeling–positive cells reduced to 31.2 ± 5.3% and cleaved Caspase-3 reduced to 1.42 ± 0.21 fold) and inhibited NDRG2 expression (1.28 ± 0.15 fold) and nuclear translocation (2.21 ± 0.29 fold) in ischemic penumbra. Similar effects were observed in cultural astrocytes exposed to oxygen–glucose deprivation. NDRG2 knockdown by small interfering RNA attenuated oxygen–glucose deprivation–induced injury (cell viability increased to 80.5 ± 4.1%; lactate dehydrogenase release reduced to 30.5 ± 4.0%) and cellular apoptosis (cleaved Caspase-3 reduced to 1.55 ± 0.21 fold; terminal deoxynucleotidyl transferase–mediated 2’-deoxyuridine 5’-triphosphate nick-end labeling–positive cells reduced to 18.2 ± 4.3%), whereas NDRG2 overexpression reversed the protective effects of sevoflurane preconditioning. All the data are presented as mean ± SD.

Conclusion:

Sevoflurane preconditioning inhibits NDRG2 up-regulation and nuclear translocation in astrocytes to induce cerebral ischemic tolerance via antiapoptosis, which represents one new mechanism of sevoflurane preconditioning and provides a novel target for neuroprotection.

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.

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.

Chronic psychosocial stress and citalopram modulate the expression of the glial proteins GFAP and NDRG2 in the hippocampus

RATIONALE

It has been suggested that there are causal relationships between alterations in brain glia and major depression.

OBJECTIVES

To investigate whether a depressive-like state induces changes in brain astrocytes, we used chronic social stress in male rats, an established preclinical model of depression. Expression of two astrocytic proteins, the intermediate filament component glial fibrillary acidic protein (GFAP) and the cytoplasmic protein N-myc downregulated gene 2 (NDRG2), was analyzed in the hippocampus. For comparison, expression of the neuronal protein syntaxin-1A was also determined.

METHODS

Adult male rats were subjected to daily social defeat for 5 weeks and were concomitantly treated with citalopram (30 mg/kg/day, via the drinking water) for 4 weeks.

RESULTS

Western blot analysis showed that the chronic stress downregulated GFAP but upregulated NDRG2 protein. Citalopram did not prevent these stress effects, but the antidepressant per se downregulated GFAP and upregulated NDRG2 in nonstressed rats. In contrast, citalopram prevented the stress-induced upregulation of the neuronal protein syntaxin-1A.

CONCLUSIONS

These data suggest that chronic stress and citalopram differentially affect expression of astrocytic genes while the antidepressant drug does not prevent the stress effects. The inverse regulation of the cytoskeletal protein GFAP and the cytoplasmic protein NDRG2 indicates that the cells undergo profound metabolic changes during stress and citalopram treatment. Furthermore, the present findings indicate that a 4-week treatment with citalopram does not restore normal glial function in the hippocampus, although the behavior of the animals was normalized within this treatment period, as reported previously.

Glucocorticoid treatment of astrocytes results in temporally dynamic transcriptome regulation and astrocyte-enriched mRNA changes in vitro

While general effects of glucocorticoids are well established, the specific cellular mechanisms by which these hormones exert tissue-dependent effects continue to be elaborated. Diseases that demonstrate altered glucocorticoid signaling have been associated with alterations in astrocytes, yet relatively little is known about the effects of glucocorticoids upon this cell type. We have analyzed mRNA expression patterns following glucocorticoid treatment of mouse primary astrocyte cultures. Microarray analysis of cortical astrocyte cultures treated with dexamethasone over an eight-point, 24 h time course identified 854 unique genes with ≥twofold change in mRNA expression at one or more time points. Clustering analysis associated subsets of these mRNA expression changes with gene ontology categories known to be impacted by glucocorticoids. Numerous mRNAs regulated by dexamethasone were also regulated by the natural ligand corticosterone; all of the mRNAs regulated ≥twofold by corticosterone were substantially attenuated by cotreatment with the glucocorticoid receptor antagonist RU486. Of the mRNAs demonstrating ≥twofold expression change in response to both glucocorticoids, 33 mRNAs were previously associated with glucocorticoid regulation, and 36 mRNAs were novel glucocorticoid targets. All genes tested by qPCR for glucocorticoid regulation in cortical astrocyte cultures were also regulated by glucocorticoids in hippocampal astrocyte cultures (18/18). Interestingly, a portion of glucocorticoid-regulated genes were astrocyte enriched; the percentage of astrocyte-enriched genes per total number of regulated genes was highest for the early time points and steadily decreased over the time course. These findings suggest that astrocytes in vitro may initially deploy cell type-specific patterns of mRNA regulatory responses to glucocorticoids and subsequently activate additional cell type-independent responses.