N-myc downstream regulated gene1/Cap43 overexpression suppresses tumor growth by hepatic cancer cells through cell cycle arrest at the G0/G1 phase

A Review of the Regulatory Mechanisms of N-Myc on Cell Cycle

Neuroblastoma has obvious heterogeneity. It is one of the few undifferentiated malignant tumors that can spontaneously degenerate into completely benign tumors. However, for its high-risk type, even with various intensive treatment options, the prognosis is still unsatisfactory. At the same time, a large number of research data show that the abnormal amplification and high-level expression of the MYCN gene are positively correlated with the malignant progression, poor prognosis, and mortality of neuroblastoma. In this context, this article explores the role of the N-Myc, MYCN gene expression product on its target genes related to the cell cycle and reveals its regulatory network in promoting tumor proliferation and malignant progression. We hope it can provide ideas and direction for the research and development of drugs targeting N-Myc and its downstream target genes.

A Tumor Suppressor Gene, N-myc Downstream-Regulated Gene 1 (NDRG1), in Gliomas and Glioblastomas

The development of potent and selective therapeutic approaches to glioblastoma (GBM) requires the identification of molecular pathways that critically regulate the survival and proliferation of GBM. Glioblastoma stem-like cells (GSCs) possess stem-cell-like properties, self-renewal, and differentiation into multiple neural cell lineages. From a clinical point of view, GSCs have been reported to resist radiation and chemotherapy. GSCs are influenced by the microenvironment, especially the hypoxic condition. N-myc downstream-regulated gene 1 (NDRG1) is a tumor suppressor with the potential to suppress the proliferation, invasion, and migration of cancer cells. Previous studies have reported that deregulated expression of NDRG1 affects tumor growth and clinical outcomes of patients with GBM. This literature review aimed to clarify the critical role of NDRG1 in tumorigenesis and acquirement of resistance for anti-GBM therapies, further to discussing the possibility and efficacy of NDRG1 as a novel target of treatment for GBM. The present review was conducted by searching the PubMed and Scopus databases. The search was conducted in February 2022. We review current knowledge on the regulation and signaling of NDRG1 in neuro-oncology. Finally, the role of NDRG1 in GBM and potential clinical applications are discussed.

Pharmacological targeting and the diverse functions of the metastasis suppressor, NDRG1, in cancer

N-myc downstream regulated gene-1 (NDRG1) is a potent metastasis suppressor that is regulated by hypoxia, metal ions including iron, the free radical nitric oxide (NO^.), and various stress stimuli. This intriguing molecule exhibits diverse functions in cancer, inhibiting epithelial-mesenchymal transition (EMT), cell migration and angiogenesis by modulation of a plethora of oncogenes via cellular signaling. Thus, pharmacological targeting of NDRG1 signaling in cancer is a promising therapeutic strategy. Of note, novel anti-tumor agents of the di-2-pyridylketone thiosemicarbazone series, which exert the "double punch" mechanism by binding metal ions to form redox-active complexes, have been demonstrated to markedly up-regulate NDRG1 expression in cancer cells. This review describes the mechanisms underlying NDRG1 modulation by the thiosemicarbazones and the diverse effects NDRG1 exerts in cancer. As a major induction mechanism, iron depletion appears critical, with NO^. also inducing NDRG1 through its ability to bind iron and generate dinitrosyl-dithiol iron complexes, which are then effluxed from cells. Apart from its potent anti-metastatic role, several studies have reported a pro-oncogenic role of NDRG1 in a number of cancer-types. Hence, it has been suggested that NDRG1 plays pleiotropic roles depending on the cancer-type. The molecular mechanism(s) underlying NDRG1 pleiotropy remain elusive, but are linked to differential regulation of WNT signaling and potentially differential interaction with the tumor suppressor, PTEN. This review discusses NDRG1 induction mechanisms by metal ions and NO^. and both the anti- and possible pro-oncogenic functions of NDRG1 in multiple cancer-types and compares the opposite effects this protein exerts on cancer progression.

N-myc downstream-regulated gene 1 inhibits the proliferation of colorectal cancer through emulative antagonizing NEDD4-mediated ubiquitylation of p21

BACKGROUND

N-myc downstream-regulated gene 1 (NDRG1) has been shown to play a key role in tumor metastasis. Recent studies demonstrate that NDRG1 can suppress tumor growth and is related to tumor proliferation; however, the mechanisms underlying these effects remain obscure.

METHODS

Immunohistochemistry (IHC) was used to detect NDRG1 and p21 protein expression in colorectal cancer tissue, and clinical significance of NDRG1 was also analyzed. CCK-8 assay, colony formation assay, flow cytometry, and xenograft model were used to assess the effect of NDRG1 on tumor proliferation in vivo and in vitro. The mechanisms underlying the effect of NDRG1 were investigated using western blotting, immunofluorescence, immunoprecipitation, and ubiquitylation assay.

RESULTS

NDRG1 was down-regulated in CRC tissues and correlated with tumor size and patient survival. NDRG1 inhibited tumor proliferation through increasing p21 expression via suppressing p21 ubiquitylation. NDRG1 and p21 had a positive correlation both in vivo and in vitro. Mechanistically, E3 ligase NEDD4 could directly interact with and target p21 for degradation. Moreover, NDRG1 could emulatively antagonize NEDD4-mediated ubiquitylation of p21, increasing p21 expression and inhibit tumor proliferation.

CONCLUSION

Our study could fulfill potential mechanisms of the NDRG1 during tumorigenesis and metastasis, which may serve as a tumor suppressor and potential target for new therapies in human colorectal cancer.

CDKN1C (P57): one of the determinants of human endometrial stromal cell decidualization

Decidualization is regulated by crosstalk of progesterone and the cAMP pathway. It involves extensive reprogramming of gene expression and includes a wide range of functions. To investigate how cell cycle regulatory genes drive the human endometrial stromal cell (ESC) exit cell cycle and enter differentiation, primary cultured ESC was treated with 8-Br-cAMP and MPA and cell cycle distribution was investigated by flow cytometry. High-throughput cell cycle regulatory gene expression was also studied by microarray. To validate the results of microarray chip, immunohistochemistry and semi-quantitative method of optical density were used to analyze the expression of cell cycle regulator proteins in proliferative phase of endometrium (n = 6) and early pregnancy decidua (n = 6). In addition, we selected cyclin-dependent kinase inhibitor 1c (CDKN1C, also known as P57) and cyclin-dependent kinase inhibitor 2b (CDKN2B, also known as P15) in order to study their role in the process of decidualization by the RNAi method. ESC was arrested at G0/G1 checkpoints during decidualization. Cell cycle regulatory genes P57 and P15 were upregulated, while cyclin D1 (CCND1), cyclin-dependent kinase 2 (CDK2), and cell division cycle protein 2 homolog (CDC2) were downregulated during ESC differentiation both in vitro and vivo. P57 siRNA impaired ESC decidualization and caused different morphological and ultrastructural changes as well as a relatively low secretion of prolactin, but P15 siRNA had no effects. We concluded that P15, CCND1, CDK2, and CDC2 may participate in ESC withdraw from the cell cycle and go into differentiation both in vitro and in vivo. P57 is one of the key determinants of ESC differentiation due to its effect on the cell cycle distribution, but its association with the decidua-specific transcription factor needs further investigation.

Metformin Promotes Neuronal Differentiation via Crosstalk between Cdk5 and Sox6 in Neuroblastoma Cells

Metformin has recently emerged as a key player in promotion of neuroblastoma differentiation and neurite outgrowth. However, molecular mechanisms of how metformin promotes cellular differentiation have not yet been fully elucidated. In this study, we investigated how metformin promotes cell differentiation, via an inhibition of cell proliferation, by culturing SH-SY5Y neuroblastoma cells with or without metformin. Pretreatment with reactive oxygen species (ROS) scavenger, NAC, revealed that ROS plays a crucial role in induction of cell differentiation. Cell differentiation was observed under various morphological criteria: extension of neuritic processes and neuronal differentiation markers. Treatment with metformin significantly increased neurite length, number of cells with neurite, and expression of neuronal differentiation markers, β-tubulin III and tyrosine hydroxylase (TH) compared with untreated control. Further investigation found that metformin significantly decreased Cdk5 but increased Sox6 during cell differentiation. Analysis of the mechanism underlying these changes using Cdk5 inhibitor, roscovitine, indicated that expressions of Cdk5 and Sox6 corresponded to metformin treatment. These results suggested that metformin produces neuronal differentiation via Cdk5 and Sox6. In addition, phosphorylated Erk1/2 was decreased while phosphorylated Akt was increased in metformin treatment. Taken together, these findings suggest that metformin promotes neuronal differentiation via ROS activation through Cdk5/Sox6 crosstalk, relating to Erk1/2 and Akt signaling.

Lipoxin A4 Ameliorates Lipopolysaccharide-Induced A549 Cell Injury through Upregulation of N-myc Downstream-Regulated Gene-1

Background:

Lipoxin A4 (LXA4) can alleviate lipopolysaccharide (LPS)-induced acute lung injury (ALI) and acute respiratory distress syndrome through promoting epithelial sodium channel (ENaC) expression in lung epithelial cells. However, how LXA4 promote ENaC expression is still largely elusive. The present study aimed to explore genes and signaling pathway involved in regulating ENaC expression induced by LXA4.

Methods:

A549 cells were incubated with LPS and LXA4, or in combination, and analyzed by quantitative real-time polymerase chain reaction (qRT-PCR) of ENaC-α/γ. Candidate genes affected by LXA4 were explored by transcriptome sequencing of A549 cells. The critical candidate gene was validated by qRT-PCR and Western blot analysis of A549 cells treated with LPS and LXA4 at different concentrations and time intervals. LXA4 receptor (ALX) inhibitor BOC-2 was used to test induction of candidate gene by LXA4. Candidate gene siRNA was adopted to analyze its influence on A549 viability and ENaC-α expression. Phosphoinositide 3-kinase (PI3K) inhibitor LY294002 was utilized to probe whether the PI3K signaling pathway was involved in LXA4 induction of candidate gene expression.

Results:

The A549 cell models of ALI were constructed and subjected to transcriptome sequencing. Among candidate genes, N-myc downstream-regulated gene-1 (NDRG1) was validated by real-time-PCR and Western blot. NDRG1 mRNA was elevated in a dose-dependent manner of LXA4, whereas BOC-2 antagonized NDRG1 expression induced by LXA4. NDRG1 siRNA suppressed viability of LPS-treated A549 cells (treatment vs. control, 0.605 ± 0.063 vs. 0.878 ± 0.083, P = 0.040) and ENaC-α expression (treatment vs. control, 0.458 ± 0.038 vs. 0.711 ± 0.035, P = 0.008). LY294002 inhibited NDRG1 (treatment vs. control, 0.459 ± 0.023 vs. 0.726 ± 0.020, P = 0.001) and ENaC-α (treatment vs. control, 0.236 ± 0.021 vs. 0.814 ± 0.025, P < 0.001) expressions and serum- and glucocorticoid-inducible kinase 1 phosphorylation (treatment vs. control, 0.442 ± 0.024 vs. 1.046 ± 0.082, P = 0.002), indicating the PI3K signaling pathway was involved in regulating NDRG1 expression induced by LXA4.

Conclusion:

Our research uncovered a critical role of NDRG1 in LXA4 alleviation of LPS-induced A549 cell injury through mediating PI3K signaling to restore ENaC expression.

Phosphorylation of mTOR Ser2481 is a key target limiting the efficacy of rapalogs for treating hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide. Although recent studies facilitate the identification of crucial genes and relevant regulatory pathways, therapeutic approaches against advanced HCC are insufficiently effective. Therefore, we aimed here to develop potent therapeutics to provide a reliable biomarker for the therapeutic efficacy in patients with HCC. To this end, we first compared the cytotoxic effects of various anti-cancer drugs between well differentiated (HAK-1A) and poorly differentiated (HAK-1B) cell lines established from a single HCC tumor. Of various drug screened, HAK-1B cells were more sensitive by a factor of 2,000 to the mTORC1 inhibitors (rapalogs), rapamycin and everolimus, than HAK-1A cells. Although rapalogs inhibited phosphorylation of mTOR Ser2448 in HAK-1A and HAK-1B cells, phosphorylation of mTOR Ser2481 was specifically inhibited only in HAK-1B cells. Silencing of Raptor induced apoptosis and inhibited the growth of only HAK-1B cells. Further, three other cell lines established independently from the tumors of three patients with HCC were also approximately 2,000-fold times more sensitive to rapamycin, which correlated closely with the inhibition of mTOR Ser2481 phosphorylation by rapamycin. Treatment with everolimus markedly inhibited the growth of tumors induced by poorly differentiated HAK-1B and KYN-2 cells and phosphorylation of mTOR Ser2481 in vivo. To our knowledge, this is the first study showing that the phosphorylation of mTOR Ser2481 is selectively inhibited by rapalogs in mTORC1-addicted HCC cells and may be a potential reliable biomarker for the therapeutic efficacy of rapalogs for treating HCC patients.

Global proteomic profiling in multistep hepatocarcinogenesis and identification of PARP1 as a novel molecular marker in hepatocellular carcinoma

The more accurate biomarkers have long been desired for hepatocellular carcinoma (HCC). Here, we characterized global large-scale proteomics of multistep hepatocarcinogenesis in an attempt to identify novel biomarkers for HCC. Quantitative data of 37874 sequences and 3017 proteins during hepatocarcinogenesis were obtained in cohort 1 of 75 samples (5 pooled groups: normal livers, hepatitis livers, cirrhotic livers, peritumoral livers, and HCC tissues) by iTRAQ 2D LC-MS/MS. The diagnostic performance of the top six most upregulated proteins in HCC group and HSP70 as reference were subsequently validated in cohort 2 of 114 samples (hepatocarcinogenesis from normal livers to HCC) using immunohistochemistry. Of seven candidate protein markers, PARP1, GS and NDRG1 showed the optimal diagnostic performance for HCC. PARP1, as a novel marker, showed comparable diagnostic performance to that of classic markers GS and NDRG1 in HCC (AUCs = 0.872, 0.856 and 0.792, respectively). A significant higher AUC of 0.945 was achieved when three markers combined. For diagnosis of HCC, the sensitivity and specificity were 88.2% and 81.0% when at least two of the markers were positive. Similar diagnostic values of PARP1, GS and NDRG1 were confirmed by immunohistochemistry in cohort 3 of 180 HCC patients. Further analysis indicated that PARP1 and NDRG1 were associated with some clinicopathological features, and the independent prognostic factors for HCC patients. Overall, global large-scale proteomics on spectrum of multistep hepatocarcinogenesis are obtained. PARP1 is a novel promising diagnostic/prognostic marker for HCC, and the three-marker panel (PARP1, GS and NDRG1) with excellent diagnostic performance for HCC was established.

N-myc downstream-regulated gene 1 inhibits the proliferation and invasion of hepatocellular carcinoma cells via the regulation of integrin β3

N-myc downstream-regulated gene 1 (NDRG1) is a multifunctional protein associated with carcinogenesis and tumor progression. The function of NDRG1 in hepatocellular carcinoma (HCC) cells remains controversial. The present study investigated the role of NDRG1 in HCC as well as its molecular mechanism using a range of techniques, including western blot analysis, cellular proliferation test, wound healing assay and Transwell assay. In HCC, the levels of NDRG1 expression were highest in the cytoplasm, followed by the membrane, and were lowest in the nucleus. NDRG1 was revealed to inhibit the proliferation and invasion of BEL7402 cells, which facilitated the hypothesis that NDRG1 expression levels may be lower in cell line with a high metastatic potential compared with those in cell lines with a low metastatic potential. However, the present study identified that NDRG1 expression was higher in detached BEL7402 cells and MHCC-97H cells compared with that in attached BEL7402 cells and MHCC-97L cells. Thus, this finding was contrary to what was expected, suggesting that NDRG1 overexpression in the HCC with a high metastatic potential may be the compensatory mechanism. The human HCC BEL7402 cell line demonstrated a significant increase in the capability of motility, invasion and cellular proliferation following NDRG1-short hairpin RNA transfection. Integrin β3 (ITGB3) protein expression was increased in NDRG1-downregulated BEL7402 cells and SMMC7721 cells compared with that in the control cells. The present study suggested that NDRG1 may be a potential anti-tumor target for the treatment of patients with HCC. A potential mechanism for these roles of NDRG1 is by regulating ITGB3 expression; however, this requires additional investigation.

NDRG1 Controls Gastric Cancer Migration and Invasion through Regulating MMP-9

The purpose of this study is to detect the clinical significance of NDRG1 and its relationship with MMP-9 in gastric cancer metastatic progression. 101 cases of gastric cancer specimens were utilized to identify the protein expression of NDRG1 and MMP-9 by immunohistochemistry, their clinical significance was also analyzed. The suppression by siRNA-NDRG1 was employed to detect the role of NDRG1 in gastric cancer progression and its relationship with MMP-9. NDRG1 expression was correlated inversely with the degree of tumor cell differentiation (p < 0.01), invasion depth (p < 0.05), lymph node metastasis (p < 0.05) and TNM stage (p < 0.05), whereas MMP-9 was positive correlated with the degree of tumor cell differentiation (p < 0.01), lymph node metastasis (p < 0.05) and TNM stage (p < 0.05), but not correlated with invasion depth (p>0.05). Furthermore, cell proliferation and invasion effect were remarkably enhanced when NDRG1 was silencing, but MMP-9 expression was increased. NDRG1 silencing enhances gastric cancer cells progression through upregulating MMP-9. It suggests that NDRG1 may inhibit the metastasis of gastric cancer via regulating MMP-9.

Fucoidan protects hepatocytes from apoptosis and inhibits invasion of hepatocellular carcinoma by up-regulating p42/44 MAPK-dependent NDRG-1/CAP43

Fucoidan is a traditional Chinese medicine suggested to possess anti-tumor effects. In this study the anti-metastatic effects of fucoidan were investigated in vitro in human hepatocellular carcinoma (HCC) cells (Huh-7 and SNU-761) under normoxic and hypoxic conditions and in vivo using a distant liver metastasis model involving injection of MH134 cells into spleen via the portal vein. Its ability to protect hepatocytes against bile acid (BA)-induced apoptosis was investigated in primary hepatocytes. Fucoidan was found to suppress the invasion of HCC cells through up-regulation of p42/44 MAPK-dependent NDRG-1/CAP43 and partly, under normoxic conditions, through up-regulation of p42/44 MAPK-dependent VMP-1 expression. It also significantly decreased liver metastasis in vivo. As regards its hepatoprotective effect, fucoidan decreased BA-induced hepatocyte apoptosis as shown by the attenuation of caspase-8, and -7 cleavages and suppression of the mobilization of caspase-8 and Fas associated death domain (FADD) into the death-inducing signaling complex. In summary, fucoidan displays inhibitory effects on proliferation of HCC cells and protective effects on hepatocytes. The results suggest fucoidan is a potent suppressor of tumor invasion with hepatoprotective effects.

NDRG1 attenuates epithelial-mesenchymal transition of nasopharyngeal cancer cells via blocking Smad2 signaling

N-myc downstream-regulated gene 1 (NDRG1) has been implicated in tumorigenesis and metastasis in different cancers. However, its role in nasopharyngeal carcinoma remains unknown. We found that NDRG1 expression level was high in nasopharyngeal cancer 5-8F cells but low in 5-8F-LN cells with lymphatic metastasis potential. Knockdown of NDRG1 by shRNA promoted 5-8F cell proliferation, migration, and invasion in vitro and its tumorigenesis in vivo. Moreover, NDRG1 deficiency induced an epithelial-mesenchymal transition (EMT) of 5-8F cells as shown by an attenuation of E-cadherin and an induction of N-cadherin and vimentin expression. NDRG1 knockdown also enhanced Smad2 expression and phosphorylation. Smad2 signaling was attenuated in 5-8F cells but was significantly activated in 5-8F-LN cells. Knockdown of Smad2 restored E-cadherin but attenuated N-cadherin expression in NDRG1-deficient 5-8F cells, suggesting a reduction of EMT. Consistently, blockade of Smad2 in 5-8F-LN cells increased E-cadherin while diminishing N-cadherin and vimentin expression. These data indicate that Smad2 mediates the NDRG1 deficiency-induced EMT of 5-8F cells. In tumors derived from NDRG1-deficient 5-8F cells, E-cadherin expression was inhibited while vimentin and Smad2 were increased in a large number of cancer cells. Most importantly, NDRG1 expression was attenuated in human nasopharyngeal carcinoma tissues, resulted in a lower survival rate in patients. The NDRG1 was further decreased in the detached nasopharyngeal cancer cells, which was associated with a further reduced survival rate in patients with lymphatic metastasis. Taken together, these results demonstrated that NDRG1 prevents nasopharyngeal tumorigenesis and metastasis via inhibiting Smad2-mediated EMT of nasopharyngeal cells.

SUMO modification regulates the protein stability of NDRG1

N-myc Downstream Regulated Gene 1 (NDRG1) is a metastasis suppressor protein which suppresses metastasis without affecting primary tumorigenesis. There have been many reports about the anti-metastatic function of NDRG1 in various cancers. However, the regulatory mechanism of NDRG1 at the protein level has not been studied widely. Here, we found that NDRG1 is posttranslationally modified by Small Ubiquitin-like Modifier (SUMO), preferentially by SUMO-2, and the major SUMO acceptor site of NDRG1 is Lys 14. Using various SUMO-2 modification status mimicking NDRG1 mutants, we characterized the role of SUMO-2 modification on NDRG1. SUMO-2 modification does not affect the subcellular distribution of NDRG1. However, the protein stability of NDRG1 is influenced by SUMO-2 modification. We found that both the wildtype and the SUMO modification site mutant form of the NDRG1 protein were very stable but the protein stability of SUMO-2 fused NDRG1 K14R had dramatically decreased. In addition, the expression of p21 is downregulated by overexpression of SUMO-2 fused NDRG1 K14R mutants. These results indicate that SUMO-2 modification is implicated in the modulation of NDRG1 protein level and function. This novel link between SUMO modification and regulation of NDRG1 could be a therapeutic target for treatment of various metastatic cancers.

N-myc downstream-regulated gene 1 downregulates cell proliferation, invasiveness, and tumorigenesis in human oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is the most common phenotype of oral cancer. N-myc downstream regulated gene 1 (NDRG1) is a modulator for cell proliferation, differentiation, and invasion. The role and function of NDRG1 in OSCC cells remain inconclusive. The (3)H-thymidine incorporation and in vitro matrigel invasion assays revealed NDRG1-knockdown significantly enhanced OSCC cell proliferation and invasion. Overexpressed NDRG1 arrested the cell cycle at the S-phase, thus attenuated cell proliferation in OECM-1 cells. The NDRG1-knockdown enhanced tumorigenesis of OECM-1 cells in the xenograft animal model. Western-blot and zymographic assays revealed that NDRG1 downregulated the gelatinase activities and protein levels of metalloproteinase-2 (MMP-2) and metalloproteinase-9 (MMP-9). NDRG1 modulated epithelial-mesenchymal transition (EMT) through upregulation of the E-cadherin expression, but downregulation of the N-cadherin, Vimentin, Snail-1, and Slug. Immunofluorescence staining indicated knockdown of NDRG1 enhanced F-actin expression and polymerization. Our results indicated NDRG1 attenuated OSCC cell growth in vitro and in vivo. The downregulation of EMT, MMP-2, and MMP-9 may explain the role of anti-invasion of NDRG1 in human OSCC cells. The experiments recognize that NDRG1 is an antitumor gene in OSCC cells.

NDRG1 expression is related to the progression and prognosis of gastric cancer patients through modulating proliferation, invasion and cell cycle of gastric cancer cells

N-myc downstream-regulated gene 1 (NDRG1) has been proposed as a tumor suppressor gene in many different types of tumors, but its potential function and corresponding mechanism are not yet fully elucidated. This study aims to detect the possible function of NDRG1 in gastric cancer progression. In this study, 112 paired gastric cancer tissues and corresponding nonmalignant gastric tissues were utilized to identify the differential protein expression of NDRG1 by immunohistochemistry and its clinical significance was analyzed. Furthermore, 49 of 112 paired gastric specimens were used to detect the differential mRNA expression by real-time PCR. The over expression of NDRG1 in human gastric cancer cell line AGS by PcDNA3.1-NDRG1 transfection was utilized to detect the role of NDRG1 in regulating the biological behavior of gastric cancer. NDRG1 expression was significantly decreased in primary gastric cancer tissues, compared with its corresponding nonmalignant gastric tissues (p < 0.05), and its decreased expression was significantly associated with lymph node metastasis (p < 0.01), invasion depth (p < 0.01) and differentiation (p < 0.05). Additionally, the overall survival rate of gastric cancer patients with high expression of NDRG1 was higher than those with low expression during the follow-up period. NDRG1 overexpression suppressed cells proliferation, invasion and induced a G1 cell cycle arrest in gastric cancer. Furthermore, the down-regulation of NDRG1 in gastric cancer metastatic progression was correlated to E-cadherin and MMP-9. Our results verify that NDRG1 acts as a tumor suppressor gene and may play an important role in the metastasis progression and prognosis of gastric cancer.

N-myc downstream regulated gene 1 acts as a tumor suppressor in ovarian cancer

Although implicated in a number of tumor types, the role of N-myc downstream regulated gene 1 (NDRG1) in ovarian cancer (OC) is unclear. In the present study, we used short hairpin RNA (shRNA) to silence NDRG1 in the OC cell line OVCAR3 and assessed the effect of its knockdown on cell morphology, proliferation, colony formation, migration and invasion. To complement these knockdown studies, we overexpressed NDRG1 in the same cell line. We found that NDRG1 knockdown significantly enhanced OVCAR3 proliferation, migration and invasion; however, there were no apparent changes in cell morphology. We also examined the effect in vivo and found that NDRG1 depletion promoted OVCAR3 xenograft growth in nude mice. In accordance with these data, we found that NDRG1 overexpression decreased proliferation, adhesion and apoptosis, and induced G0/G1 cell cycle arrest in OVCAR3 cells; expression of p21 and p53 was also increased. In conclusion, we demonstrated that NDRG1 acts as a tumor suppressor in ovarian carcinogenesis and may be a potential therapeutic target in this disease.

N-myc downstream-regulated gene 1: Diverse and complicated functions in human hepatocellular carcinoma (Review)

N-myc downstream-regulated gene 1 (NDRG1) has been reported to be a multifunctional protein associated with carcinogenesis and tumor progression. However, the cellular function of NDRG1 remains elusive in human hepatocellular carcinoma (HCC). No NDRG1 expression is observed in normal liver tissue. Overexpression of NDRG1 has been observed in human HCC, particularly with aggressive invasion, metastasis, poor differentiation and short patient survival. In addition, recent studies have shown that NDRG1 exhibits an inhibitory effect on HCC growth in vitro and in vivo, which contrasts with previous reports indicating that NDRG1 promotes the proliferation and invasion of HCC cell lines. Further studies have shown that the localization of NDRG1 is variable, translocating to the nucleus or membrane according to the cell state, which may relate to the diverse function of NDRG1. The present study reviews our current knowledge with regard to the functions of NDRG1 in HCC and other types of human cancer.

Proteomics identified nuclear N-myc downstream-regulated gene 1 as a prognostic tissue biomarker candidate in renal cell carcinoma

The aim of this study was to identify proteins with aberrant expression in clear cell renal cell carcinoma (ccRCC), and elucidate their clinical utilities. The protein expression profiles of primary ccRCC tumor tissues and neighboring non-tumor tissues were obtained from 9 patients by two-dimensional difference gel electrophoresis and mass spectrometry. Comparative analysis of 3771 protein spots led to the identification of 73 proteins that were expressed at aberrant levels in tumor tissues compared with non-tumor tissues. Among these 73 proteins, we further focused on N-myc downstream-regulated gene 1 protein (NDRG1). NDRG1 expression is regulated by members of myc family as well as by p53, HIF1A, and SGK1. The biological and clinical significance of NDRG1 is controversial for various malignancies and no detailed studies on NDRG1 have been reported in ccRCC until our study. For the 82 newly enrolled ccRCC patients, immunohistochemical analysis revealed a significant association between nuclear NDRG1 and favorable prognosis (p<0.05). Multivariate analysis demonstrated the role of NDRG1 as an independent factor of progression-free survival (p=0.01). Subsequent in vitro gene suppression assay demonstrated that NDRG1 silencing significantly enhanced cell proliferation and invasion of RCC cells. The cytotoxic effects of NDRG1 up-regulation induced by an iron chelator were also confirmed. These findings suggest that nuclear NDRG1 has tumor suppressive effects, and the NDRG1 expression may have clinical values in ccRCC. Nuclear NDRG1 may provide additional insights on molecular backgrounds of ccRCC progression, and contribute to the development of novel therapeutic strategy.

The role of NDRG1 in the pathology and potential treatment of human cancers

N-myc downstream regulated gene 1 (NDRG1) has been well characterised to act as a metastatic suppressor in a number of human cancers. It has also been implicated to have a significant function in a number of physiological processes such as cellular differentiation and cell cycle. In this review, we discuss the role of NDRG1 in cancer pathology. NDRG1 was observed to be downregulated in the majority of cancers. Moreover, the expression of NDRG1 was found to be significantly lower in neoplastic tissues as compared with normal tissues. The most important function of NDRG1 in inhibiting tumour progression is associated with its ability to suppress metastasis. However, it has also been shown to have important effects on other stages of cancer progression (primary tumour growth and angiogenesis). Recently, novel iron chelators with selective antitumour activity (ie, Dp44mT, DpC) were shown to upregulate NDRG1 in cancer cells. Moreover, Dp44mT showed its antimetastatic potential only in cells expressing NDRG1, making this protein an important therapeutic target for cancer chemotherapy. This observation has led to increased interest in the examination of these novel anticancer agents.

Prohibitin-2 promotes hepatocellular carcinoma malignancy progression in hypoxia based on a label-free quantitative proteomics strategy

The rapid growth of hepatocellular carcinoma (HCC) leading to tumor hypoxia is a common pathological phenomenon. Meanwhile, tumor hypoxia can promote a change in the biological properties of tumor cells. It may enhance the survival of tumor cells under stress conditions, resulting in resistance to apoptosis and angiogenesis. The moleculars that could modulate the malignant phenotypes of HCC cells remain largely unknown. Based on label-free quantitative proteomic data, we found a significant upregulation of prohibitin-2 (PHB2) in HCC tissues. Treatment of hepatoma cells with small interfering RNAs against PHB2 suppressed cell growth and colony formation, led to G1 phase arrest and sensitized HCC cells to apoptosis. Moreover, inhibition of PHB2 expression dramatically repressed the ability of HCC cells to adapt to hypoxic microenvironments and resist chemotherapy-induced apoptosis. Thus, PHB2 in HCC supports the development and progression of hepatocellular malignancy to hypoxia, and implicates the potential antagonist function of PHB2 in transarterial chemoembolization treatment.

Prognostic significance of NDRG1 expression in oral and oropharyngeal squamous cell carcinoma

Human N-myc downstream-regulated gene 1 (NDRG1) is a metastasis suppressor gene with several potential functions, including cell differentiation, cell cycle regulation and response to hormones, nickel and stress. The purpose of this study was to investigate the immunoexpression of NDRG1 in oral and oropharyngeal squamous cell carcinomas searching for its role in the clinical course of these tumors. We investigated immunohistochemical expression of NDRG1 protein in 412 tissue microarray cores of tumor samples from 103 patients with oral and oropharyngeal squamous cell carcinomas and in 110 paraffin-embedded surgical margin sections. The results showed NDRG1 up-regulation in 101/103 (98.1 %) tumor samples, but no expression in any normal tissue sample. Western blot assays confirmed the immunohistochemical findings, suggesting that lower levels of NDRG1 are associated with a high mortality rate. NDRG1 overexpression was related to long-term specific survival (HR = 0.38; p = 0.009), whereas the presence of lymph-node metastasis showed the opposite association with survival (HR = 2.45; p = 0.013). Our findings reinforce the idea that NDRG1 plays a metastasis suppressor role in oral and oropharyngeal squamous cell carcinomas and may be a useful marker for these tumors.