Metastasis suppressor, NDRG1, mediates its activity through signaling pathways and molecular motors

Overexpression of NDRG1 leads to poor prognosis in hepatocellular carcinoma through mediating immune infiltration and EMT

BACKGROUND

NDRG1, the first member of the NDRG family, is a multifunctional protein associated with carcinogenesis. Its function in human cancer is currently poorly understood. The aim of this study was to explore the importance of NDRG1 in tumor immune cell infiltration and epithelial-mesenchymal transition (EMT) in hepatocellular carcinoma.

METHODS

NDRG1 expression in various cancers was analyzed using TIMER 2.0, the Human Protein Atlas (HPA), UALCAN and PrognoScan. Wound healing, Transwell, MTT and colony formation assays were performed to confirm the effects of NDRG1 on the metastasis and proliferation of HCC cells. Western blotting was used to study the effect of NDRG1 on the expression of EMT-related proteins. Signaling networks were constructed using LinkedOmics and Metascape. TIMER2.0 and TISIDB were used for comprehensive analysis of tumor-infiltrating immune cells and tumor-infiltrating lymphocytes (TILs).

RESULT

NDRG1 expression was higher in HCC tissue than in normal liver tissue at both the mRNA and protein levels. Overexpression of NDRG1 is associated with poor prognosis in HCC patients. Genomic analysis suggests that NDRG1 promoter hypermethylation leads to enhanced transcription, which may be one mechanism for NDRG1 upregulation in HCC. The overexpression of NDRG1 promotes the invasion, migration, and proliferation of HCC cells and induces the expression of EMT-related proteins. Immunoinfiltration analysis suggests that NDRG1 is involved in the recruitment of immune cells.

CONCLUSIONS

The present study showed that NDRG1 may induce metastasis and invasion through EMT and immune cell infiltration. NDRG1 could be used as a biomarker for the diagnosis and prognosis of HCC and could be a potential therapeutic target in HCC.

Multi-modal mechanisms of the metastasis suppressor, NDRG1: Inhibition of WNT/β-catenin signaling by stabilization of protein kinase Cα

The metastasis suppressor, N-myc downstream regulated gene-1 (NDRG1), inhibits pro-oncogenic signaling in pancreatic cancer (PC). This investigation dissected a novel mechanism induced by NDRG1 on WNT/β-catenin signaling in multiple PC cell types. NDRG1 overexpression decreased β-catenin and downregulated glycogen synthase kinase-3β (GSK-3β) protein levels and its activation. However, β-catenin phosphorylation at Ser33, Ser37, and Thr41 are classically induced by GSK-3β was significantly increased after NDRG1 overexpression, suggesting a GSK-3β-independent mechanism. Intriguingly, NDRG1 overexpression upregulated protein kinase Cα (PKCα), with PKCα silencing preventing β-catenin phosphorylation at Ser33, Ser37, and Thr41, and decreasing β-catenin expression. Further, NDRG1 and PKCα were demonstrated to associate, with PKCα stabilization occurring after NDRG1 overexpression. PKCα half-life increased from 1.5 ± 0.8 h (3) in control cells to 11.0 ± 2.5 h (3) after NDRG1 overexpression. Thus, NDRG1 overexpression leads to the association of NDRG1 with PKCα and PKCα stabilization, resulting in β-catenin phosphorylation at Ser33, Ser37, and Thr41. The association between PKCα, NDRG1, and β-catenin was identified, with the formation of a potential metabolon that promotes the latter β-catenin phosphorylation. This anti-oncogenic activity of NDRG1 was multi-modal, with the above mechanism accompanied by the downregulation of the nucleo-cytoplasmic shuttling protein, p21-activated kinase 4 (PAK4), which is involved in β-catenin nuclear translocation, inhibition of AKT phosphorylation (Ser473), and decreased β-catenin phosphorylation at Ser552 that suppresses its transcriptional activity. These mechanisms of NDRG1 activity are important to dissect to understand the marked anti-cancer efficacy of NDRG1-inducing thiosemicarbazones that upregulate PKCα and inhibit WNT signaling.

Metastasis suppressor genes in clinical practice: are they druggable?

Since the identification of NM23 (now called NME1) as the first metastasis suppressor gene (MSG), a small number of other gene products and non-coding RNAs have been identified that suppress specific parameters of the metastatic cascade, yet which have little or no ability to regulate primary tumor initiation or maintenance. MSG can regulate various pathways or cell biological functions such as those controlling mitogen-activated protein kinase pathway mediators, cell-cell and cell-extracellular matrix protein adhesion, cytoskeletal architecture, G-protein-coupled receptors, apoptosis, and transcriptional complexes. One defining facet of this gene class is that their expression is typically downregulated, not mutated, in metastasis, such that any effective therapeutic intervention would involve their re-expression. This review will address the therapeutic targeting of MSG, once thought to be a daunting task only facilitated by ectopically re-expressing MSG in metastatic cells in vivo. Examples will be cited of attempts to identify actionable oncogenic pathways that might suppress the formation or progression of metastases through the re-expression of specific metastasis suppressors.

LADON, a Natural Antisense Transcript of NODAL, Promotes Tumour Progression and Metastasis in Melanoma

The TGFβ family member NODAL, repeatedly required during embryonic development, has also been associated with tumour progression. Our aim was to clarify the controversy surrounding its involvement in melanoma tumour progression. We found that the deletion of the NODAL exon 2 in a metastatic melanoma cell line impairs its ability to form tumours and colonize distant tissues. However, we show that this phenotype does not result from the absence of NODAL, but from a defect in the expression of a natural antisense transcript of NODAL, here called LADON. We show that LADON expression is specifically activated in metastatic melanoma cell lines, that its transcript is packaged in exosomes secreted by melanoma cells, and that, via its differential impact on the expression of oncogenes and tumour suppressors, it promotes the mesenchymal to amoeboid transition that is critical for melanoma cell invasiveness. LADON is, therefore, a new player in the regulatory network governing tumour progression in melanoma and possibly in other types of cancer.

Early-life ozone exposure modulates region-specific gene expression in the developing rat lung

Early-life ozone exposure disrupts normal patterns of lung development, but the molecular determinants underlying these changes are not well understood. This study aimed to elucidate changes in gene expression following episodic ozone exposure to identify potential mechanisms of ozone-mediated impairments in lung development. Rat pups were exposed to either filtered air or ozone (0.5 ppm, 6 hr./day, 5 days/week) from postnatal day (PND) 7-28 (16 dams total with 8 pups each, 4 M & 4 F) and sacrificed at either PND 30-31 or PND 80-84. Lung microdissection isolated major regions for RNA-Seq analysis. Ozone modified inherent differences in gene expression between lung regions in both male and female rat pups, whereas statistically significant changes in gene expression directly attributed to ozone were only identified in females. The greatest number of differentially expressed genes was observed between the distal airways and the parenchyma of ozone-exposed juvenile female rats, with 355 genes being differentially expressed. Genes modulating epithelial-to-mesenchymal transition, cell growth, and adhesion were differentially expressed in the parenchyma of ozone exposed juvenile females, suggesting that episodic ozone exposure may affect branching morphogenesis and lung cell growth. Importantly, our study provides novel targets for future experiments investigating the impact of ozone on lung development.

Hydrostatic pressure under hypoxia facilitates fabrication of tissue-engineered vascular grafts derived from human vascular smooth muscle cells in vitro

Biologically compatible vascular grafts are urgently required. The scaffoldless multi-layered vascular wall is considered to offer theoretical advantages, such as facilitating cells to form cell-cell and cell-matrix junctions and natural extracellular matrix networks. Simple methods are desired for fabricating physiological scaffoldless tissue-engineered vascular grafts. Here, we showed that periodic hydrostatic pressurization under hypoxia (HP/HYP) facilitated the fabrication of multi-layered tunica media entirely from human vascular smooth muscle cells. Compared with normoxic atmospheric pressure, HP/HYP increased expression of N-myc downstream-regulated 1 (NDRG1) and the collagen-cross-linking enzyme lysyl oxidase in human umbilical artery smooth muscle cells. HP/HYP increased N-cadherin-mediated cell-cell adhesion via NDRG1, cell-matrix interaction (i.e., clustering of integrin α5β1 and fibronectin), and collagen fibrils. We then fabricated vascular grafts using HP/HYP during repeated cell seeding and obtained 10-layered smooth muscle grafts with tensile rupture strength of 0.218-0.396 MPa within 5 weeks. Implanted grafts into the rat aorta were endothelialized after 1 week and patent after 5 months, at which time most implanted cells had been replaced by recipient-derived cells. These results suggest that HP/HYP enables fabrication of scaffoldless human vascular mimetics that have a spatial arrangement of cells and matrices, providing potential clinical applications for cardiovascular diseases. STATEMENT OF SIGNIFICANCE: Tissue-engineered vascular grafts (TEVGs) are theoretically more biocompatible than prosthetic materials in terms of mechanical properties and recipient cell-mediated tissue reconstruction. Although some promising results have been shown, TEVG fabrication processes are complex, and the ideal method is still desired. We focused on the environment in which the vessels develop in utero and found that mechanical loading combined with hypoxia facilitated formation of cell-cell and cell-matrix junctions and natural extracellular matrix networks in vitro, which resulted in the fabrication of multi-layered tunica media entirely from human umbilical artery smooth muscle cells. These scaffoldless TEVGs, produced using a simple process, were implantable and have potential clinical applications for cardiovascular diseases.

Molecular interaction of metastasis suppressor genes and tumor microenvironment in breast cancer

Breast cancer (BC) is a leading cause of cancer-related deaths in women worldwide where the process of metastasis is a major contributor to the mortality associated with this disease. Metastasis suppressor genes are a group of genes that play a crucial role in preventing or inhibiting the spread of cancer cells. They suppress the metastasis process by inhibiting colonization and by inducing dormancy. These genes function by regulating various cellular processes in the tumor microenvironment (TME), such as cell adhesion, invasion, migration, and angiogenesis. Dysregulation of metastasis suppressor genes can lead to the acquisition of an invasive and metastatic phenotype and lead to poor prognostic outcomes. The components of the TME generally play a necessary in the metastasis progression of tumor cells. This review has identified and elaborated on the role of a few metastatic suppressors associated with the TME that have been shown to inhibit metastasis in BC by different mechanisms, such as blocking certain cell signaling molecules involved in cancer cell migration, invasion, enhancing immune surveillance of cancer cells, and promoting the formation of a protective extracellular matrix (ECM). Understanding the interaction of metastatic suppressor genes and the components of TME has important implications for the development of novel therapeutic strategies to target the metastatic cascade. Targeting these genes or their downstream signaling pathways offers a promising approach to inhibiting the spread of cancer cells and improves patient outcomes.

A review on the role of NDRG1 in different cancers

NDRG1 is a member of the α/β hydrolase superfamily that resides in the cytoplasm and participates in the stress responses, hormone response, cell growth, and differentiation. Several studies have pointed to the importance of NDRG1 in the carcinogenesis. This gene has been found to be up-regulated in an array of cancer types such as bladder, esophageal squamous cell carcinoma, endometrial, lung and liver cancers, but being down-regulated in other types of cancers such as colorectal, gastric and ovarian cancers. The current study summarizes the evidence on the role of NDRG1 in the carcinogenic processes in different types of tissues.

Disulfiram suppresses epithelial-mesenchymal transition (EMT), migration and invasion in cervical cancer through the HSP90A/NDRG1 pathway

Disulfiram (DSF) has proven to be a promising anti-tumor drug in preclinical studies. However, its anti-cancer mechanism has not yet been elucidated. As an activator in tumor metastasis, N-myc downstream regulated gene-1 (NDRG1) is involved in multiple oncogenic signaling pathways and is upregulated by cell differentiation signals in various cancer cell lines. DSF treatment results in a significant reduction in NDRG1, while down-regulated NDRG1 has a pronounced effect on invading cancer cells, as shown in our previous work. Here, in vitro and in vivo experiments confirm that DSF contributes to regulating tumor growth, EMT, and the migration and invasion of cervical cancer. Furthermore, our results show DSF binds to the ATP-binding pocket in the N-terminal domain of HSP90A, thereby affecting the expression of its client protein NDRG1. To our knowledge, this is the first report of DSF binding to HSP90A. In conclusion, this study sheds light on the molecular mechanism by which DSF inhibits tumor growth and metastasis through the HSP90A/NDRG1/β-catenin pathway in cervical cancer cells. These findings provide novel insights into the mechanism underlying DSF function in cancer cells.

Re-Shaping the Pancreatic Cancer Tumor Microenvironment: A New Role for the Metastasis Suppressor NDRG1

Pancreatic cancer (PaC) is a highly aggressive disease, with poor response to current treatments and 5-year survival rates of 10-15%. PaC progression is facilitated by its interaction with the complex and multifaceted tumor microenvironment (TME). In the TME, cancer cells and surrounding stromal cells constantly communicate with each other via the secretion and uptake of factors including cytokines, chemokines, growth factors, metabolites, and extracellular vesicles (EVs), reshaping the landscape of PaC. Recent studies demonstrated that the metastasis suppressor N-myc downstream regulated 1 (NDRG1) not only inhibits oncogenic signaling pathways in PaC cells but also alters the communication between PaC cells and the surrounding stroma. In fact, NDRG1 was found to influence the secretome of PaC cells, alter cancer cell metabolism, and interfere with intracellular trafficking and intercellular communication between PaC cells and surrounding fibroblasts. This review will present recent advancements in understanding the role of NDRG1 in PaC progression, with a focus on how this molecule influences PaC-stroma communication and its potential for re-shaping the PaC TME.

KISS1 metastasis suppressor in tumor dormancy: a potential therapeutic target for metastatic cancers?

Present therapeutic approaches do not effectively target metastatic cancers, often limited by their inability to eliminate already-seeded non-proliferative, growth-arrested, or therapy-resistant tumor cells. Devising effective approaches targeting dormant tumor cells has been a focus of cancer clinicians for decades. However, progress has been limited due to limited understanding of the tumor dormancy process. Studies on tumor dormancy have picked up pace and have resulted in the identification of several regulators. This review focuses on KISS1, a metastasis suppressor gene that suppresses metastasis by keeping tumor cells in a state of dormancy at ectopic sites. The review explores mechanistic insights of KISS1 and discusses its potential application as a therapeutic against metastatic cancers by eliminating quiescent cells or inducing long-term dormancy in tumor cells.

The role of the NDRG1 in the pathogenesis and treatment of breast cancer

Breast cancer (BC) is the leading cause of cancer death in women. This disease is heterogeneous, with clinical subtypes being estrogen receptor-α (ER-α) positive, having human epidermal growth factor receptor 2 (HER2) overexpression, or being triple-negative for ER-α, progesterone receptor, and HER2 (TNBC). The ER-α positive and HER2 overexpressing tumors can be treated with agents targeting these proteins, including tamoxifen and pertuzumab, respectively. Despite these treatments, resistance and metastasis are problematic, while TNBC is challenging to treat due to the lack of suitable targets. Many studies examining BC and other tumors indicate a role for N-myc downstream-regulated gene-1 (NDRG1) as a metastasis suppressor. The ability of NDRG1 to inhibit metastasis is due, in part, to the inhibition of the initial step in metastasis, namely the epithelial-to-mesenchymal transition. Paradoxically, there are also reports of NDRG1 playing a pro-oncogenic role in BC pathogenesis. The oncogenic effects of NDRG1 in BC have been reported to relate to lipid metabolism or the mTOR signaling pathway. The molecular mechanism(s) of how NDRG1 regulates the activity of multiple signaling pathways remains unclear. Therapeutic strategies that up-regulate NDRG1 have been developed and include agents of the di-2-pyridylketone thiosemicarbazone class. These compounds target oncogenic drivers in BC cells, suppressing the expression of multiple key hormone receptors including ER-α, progesterone receptor, androgen receptor, and prolactin receptor, and can also overcome tamoxifen resistance. Considering the varying role of NDRG1 in BC pathogenesis, further studies are required to examine what subset of BC patients would benefit from pharmacopeia that up-regulate NDRG1.

NDRG1 Signaling Is Essential for Endothelial Inflammation and Vascular Remodeling

BACKGROUND

NDRG-1 (N-myc downstream-regulated gene 1) is a member of NDRG family that plays essential roles in cell differentiation, proliferation, and stress responses. Although the expression of NDRG1 is regulated by fluid shear stress, its roles in vascular biology remain poorly understood. The purpose of the study is to determine the functional significance of NDRG1 in vascular inflammation and remodeling.

METHODS AND RESULTS

By using quantitative polymerase chain reaction, western blot, and immunohistochemistry, we demonstrate that the expression of NDRG1 is markedly increased in cytokine-stimulated endothelial cells and in human and mouse atherosclerotic lesions. To determine the role of NDRG1 in endothelial activation, we performed loss-of-function studies using NDRG1 short hairpin RNA. Our results demonstrate that NDRG1 knockdown by lentivirus bearing NDRG1 short hairpin RNA substantially attenuates both IL-1β (interleukin-1β) and TNF-α (tumor necrosis factor-α)-induced expression of cytokines/chemokines and adhesion molecules. Intriguingly, inhibition of NDRG1 also significantly attenuates the expression of procoagulant molecules, such as PAI-1 (plasminogen activator inhibitor type 1) and TF (tissue factor), and increases the expression of TM (thrombomodulin) and t-PA (tissue-type plasminogen activator), thus exerting potent antithrombotic effects in endothelial cells. Mechanistically, we showed that NDRG1 interacts with orphan Nur77 (nuclear receptor) and functionally inhibits the transcriptional activity of Nur77 and NF-κB (nuclear factor Kappa B) in endothelial cells. Moreover, in NDRG1 knockdown cells, both cytokine-induced mitogen-activated protein kinase activation, c-Jun phosphorylation, and AP-1 (activator protein 1) transcriptional activity are substantially inhibited. Neointima and atherosclerosis formation induced by carotid artery ligation and arterial thrombosis were markedly attenuated in endothelial cell-specific NDRG1 knockout mice compared with their wild-type littermates.

CONCLUSIONS

Our results for the first time identify NDRG1 as a critical mediator implicated in regulating endothelial inflammation, thrombotic responses, and vascular remodeling, and suggest that inhibition of NDRG1 may represent a novel therapeutic strategy for inflammatory vascular diseases, such as atherothrombosis and restenosis.

NDRG1 is induced by antigen-receptor signaling but dispensable for B and T cell self-tolerance

Peripheral tolerance prevents the initiation of damaging immune responses by autoreactive lymphocytes. While tolerogenic mechanisms are tightly regulated by antigen-dependent and independent signals, downstream pathways are incompletely understood. N-myc downstream-regulated gene 1 (NDRG1), an anti-cancer therapeutic target, has previously been implicated as a CD4⁺ T cell clonal anergy factor. By RNA-sequencing, we identified Ndrg1 as the third most upregulated gene in anergic, compared to naïve follicular, B cells. Ndrg1 is upregulated by B cell receptor activation (signal one) and suppressed by co-stimulation (signal two), suggesting that NDRG1 may be important in B cell tolerance. However, though Ndrg1^-/- mice have a neurological defect mimicking NDRG1-associated Charcot-Marie-Tooth (CMT4d) disease, primary and secondary immune responses were normal. We find that B cell tolerance is maintained, and NDRG1 does not play a role in downstream responses during re-stimulation of in vivo antigen-experienced CD4⁺ T cells, demonstrating that NDGR1 is functionally redundant for lymphocyte anergy.

The miR-182-5p/NDRG1 Axis Controls Endometrial Receptivity through the NF-κB/ZEB1/E-Cadherin Pathway

Endometrial receptivity is essential for successful pregnancy, and its impairment is a major cause of embryo-implantation failure. MicroRNAs (miRNAs) that regulate epigenetic modifications have been associated with endometrial receptivity. However, the molecular mechanisms whereby miRNAs regulate endometrial receptivity remain unclear. Therefore, we investigated whether miR-182 and its potential targets influence trophoblast cell attachment. miR-182 was expressed at lower levels in the secretory phase than in the proliferative phase of endometrium tissues from fertile donors. However, miR-182 expression was upregulated during the secretory phase in infertile women. Transfecting a synthetic miR-182-5p mimic decreased spheroid attachment of human JAr choriocarcinoma cells and E-cadherin expression (which is important for endometrial receptivity). miR-182-5p also downregulated N-Myc downstream regulated 1 (NDRG1), which was studied further. NDRG1 was upregulated in the secretory phase of the endometrium tissues and induced E-cadherin expression through the nuclear factor-κΒ (NF-κΒ)/zinc finger E-box binding homeobox 1 (ZEB1) signaling pathway. NDRG1-overexpressing or -depleted cells showed altered attachment rates of JAr spheroids. Collectively, our findings indicate that miR-182-5p-mediated NDRG1 downregulation impaired embryo implantation by upregulating the NF-κΒ/ZEB1/E-cadherin pathway. Hence, miR-182-5p is a potential biomarker for negative selection in endometrial receptivity and a therapeutic target for successful embryo implantation.

Anti-proliferative effect and underlying mechanism of ethoxy-substituted phylloquinone (vitamin K1 derivative) from Spinacia oleracea leaf and enhancement of its extractability using radiation technology

In our previous studies, a novel antimutagenic compound, 2-ethoxy-3-(3,7,11,15-tetramethylhexadec-2-ethyl) naphthaquinone-1,4-dione (ethoxy-substituted phylloquinone; ESP) from spinach was characterized and mechanism contributing to its antimutagenicity was deduced. In the current study, anti-proliferative activity of ESP was assessed in lung cancer (A549) cells using MTT [3-(4,5-dimethylthiazole-2yl)-2,5-diphenyl tetrazolium bromide], clonogenic assays and cell cycle analysis. ESP treatment showed selective cytotoxicity against lung cancer cells and no cytotoxicity in normal lung (WI38) cells. Cell cycle analysis revealed that ESP treatment arrests A549 cell population in G2-M phase. In-silico analysis indicated positive drug-likeness features of ESP. Molecular docking showed H-bonding and hydrophobic interactions between ESP and B-DNA dodecamer residues at minor groove. SWATH-MS (Sequential Window Acquisition of All Theoretical Mass Spectra) based proteomic analysis indicated down-regulation of proteins involved in EGFR signaling, NEDDylation and other metabolic pathways and up-regulation of tumor suppressor (STAT1 and NDRG1) proteins. Treatment of spinach powder with gamma radiation (5-20 kGy) from cobalt (Co-60) enhanced the extractability of ESP up to 4.4-fold at the highest dose of 20 kGy. Scanning electron microscopy of spinach powder displayed decrease in smoothness and compactness with increase in radiation dose attributing to its enhanced extractability. Increase in the extractability of ESP with increasing radiation doses as measured by fluorescence intensity and dry weight basis was strongly correlated. Nonetheless, radiation treatment did not affect the functionality of ESP in terms of anti-proliferative and antimutagenic activities. Current findings thus highlight broad spectrum bioactivity of ESP from spinach, its underlying mechanism and applicability of radiation technology in enhancing extractability.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03264-6.

The Ni(II)-Binding Activity of the Intrinsically Disordered Region of Human NDRG1, a Protein Involved in Cancer Development

Nickel exposure is associated with tumors of the respiratory tract such as lung and nasal cancers, acting through still-uncharacterized mechanisms. Understanding the molecular basis of nickel-induced carcinogenesis requires unraveling the mode and the effects of Ni(II) binding to its intracellular targets. A possible Ni(II)-binding protein and a potential focus for cancer treatment is hNDRG1, a protein induced by Ni(II) through the hypoxia response pathway, whose expression correlates with higher cancer aggressiveness and resistance to chemotherapy in lung tissue. The protein sequence contains a unique C-terminal sequence of 83 residues (hNDRG1*C), featuring a three-times-repeated decapeptide, involved in metal binding, lipid interaction and post-translational phosphorylation. In the present work, the biochemical and biophysical characterization of unmodified hNDRG1*C was performed. Bioinformatic analysis assigned it to the family of the intrinsically disordered regions and the absence of secondary and tertiary structure was experimentally proven by circular dichroism and NMR. Isothermal titration calorimetry revealed the occurrence of a Ni(II)-binding event with micromolar affinity. Detailed information on the Ni(II)-binding site and on the residues involved was obtained in an extensive NMR study, revealing an octahedral paramagnetic metal coordination that does not cause any major change of the protein backbone, which is coherent with CD analysis. hNDRG1*C was found in a monomeric form by light-scattering experiments, while the full-length hNDRG1 monomer was found in equilibrium between the dimer and tetramer, both in solution and in human cell lines. The results are the first essential step for understanding the cellular function of hNDRG1*C at the molecular level, with potential future applications to clarify its role and the role of Ni(II) in cancer development.

Clinical Diagnostic and Prognostic Potential of NDRG1 and NDRG2 in Hepatocellular Carcinoma Patients

Background

Primary liver cancer is still the most common lethal malignancy. The N-myc downstream-regulated gene family (NDRG1–4) is a group of multifunctional proteins associated with carcinogenesis. However, systematic evaluation of the diagnostic and prognostic values of NDRG1 or NDRG2 expression in liver cancer is poorly investigated.

Method

The gene expression matrix of liver hepatocellular carcinoma (LIHC) was comprehensively analyzed by the “limma” and “Dseq2” R packages. The Gene Ontology (GO) and Gene Set Enrichment Analysis (GSEA) were used to identify the biological functional differences. A single-sample GSEA (ssGSEA) was conducted to quantify the extent of immune cell infiltration. Finally, the clinical and prognostic information of LIHC patients was systematically investigated using Kaplan–Meier analysis and logistic and Cox regression analysis.

Results

Compared with normal tissues, NDRG1 expression was higher, whereas NDRG2 expression was lower in tumor tissues (P <0.001). The area under the receiver operator characteristic curve (AUROC) of NDRG1 and NDRG2 for LIHC was 0.715 and 0.799, respectively. Kaplan–Meier analysis revealed that NDRG1 and NDRG2 were independent clinical prognostic biomarkers for the overall survival (OS, P = 0.001 and 2.9e−06), progression-free interval (PFI, P = 0.028 and 0.005) and disease-specific survival (DSS, P = 0.027 and P <0.001). The C-indexes and calibration plots of the nomogram suggest that NDRG1 and NDRG2 have an effective predictive performance for OS (C-index: 0.676), DSS (C-index: 0.741) and PFI (C-index: 0.630) of liver cancer patients. The mutation rate of NDRG1 in liver cancer reached up to 14%, and DNA methylation levels of NDRG1 and NDRG2 promoters correlated significantly with clinical prognosis.

Conclusions

The mRNA expression and DNA methylation of NDRG superfamily members have the potential for LIHC diagnosis and prognosis via integrative analysis from multiple cohorts.

Targeting Wnt/tenascin C-mediated cross talk between pancreatic cancer cells and stellate cells via activation of the metastasis suppressor NDRG1

A major barrier to successful pancreatic cancer (PC) treatment is the surrounding stroma, which secretes growth factors/cytokines that promote PC progression. Wnt and tenascin C (TnC) are key ligands secreted by stromal pancreatic stellate cells (PSCs) that then act on PC cells in a paracrine manner to activate the oncogenic β-catenin and YAP/TAZ signaling pathways. Therefore, therapies targeting oncogenic Wnt/TnC cross talk between PC cells and PSCs constitute a promising new therapeutic approach for PC treatment. The metastasis suppressor N-myc downstream-regulated gene-1 (NDRG1) inhibits tumor progression and metastasis in numerous cancers, including PC. We demonstrate herein that targeting NDRG1 using the clinically trialed anticancer agent di-2-pyridylketone-4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC) inhibited Wnt/TnC-mediated interactions between PC cells and the surrounding PSCs. Mechanistically, NDRG1 and DpC markedly inhibit secretion of Wnt3a and TnC by PSCs, while also attenuating Wnt/β-catenin and YAP/TAZ activation and downstream signaling in PC cells. This antioncogenic activity was mediated by direct inhibition of β-catenin and YAP/TAZ nuclear localization and by increasing the Wnt inhibitor, DKK1. Expression of NDRG1 also inhibited transforming growth factor (TGF)-β secretion by PC cells, a key mechanism by which PC cells activate PSCs. Using an in vivo orthotopic PC mouse model, we show DpC downregulated β-catenin, TnC, and YAP/TAZ, while potently increasing NDRG1 expression in PC tumors. We conclude that NDRG1 and DpC inhibit Wnt/TnC-mediated interactions between PC cells and PSCs. These results further illuminate the antioncogenic mechanism of NDRG1 and the potential of targeting this metastasis suppressor to overcome the oncogenic effects of the PC-PSC interaction.

N-myc downstream regulated family member 1 (NDRG1) is enriched in myelinating oligodendrocytes and impacts myelin degradation in response to demyelination

The N-myc downstream regulated gene family member 1 (NDRG1) is a gene whose mutation results in peripheral neuropathy with central manifestations. While most of previous studies characterized NDRG1 role in Schwann cells, the detection of central nervous system symptoms and the identification of NDRG1 as a gene silenced in the white matter of multiple sclerosis brains raise the question regarding its role in oligodendrocytes. Here, we show that NDRG1 is enriched in oligodendrocytes and myelin preparations, and we characterize its expression using a novel reporter mouse (TgNdrg1-EGFP). We report NDRG1 expression during developmental myelination and during remyelination after cuprizone-induced demyelination of the adult corpus callosum. The transcriptome of Ndrg1-EGFP+ cells further supports the identification of late myelinating oligodendrocytes, characterized by expression of genes regulating lipid metabolism and bioenergetics. We also generate a lineage specific conditional knockout (Olig1^cre/+ ;Ndrg1^fl/fl ) line to study its function. Null mice develop normally, and despite similar numbers of progenitor cells as wild type, they have fewer mature oligodendrocytes and lower levels of myelin proteins than controls, thereby suggesting NDRG1 as important for the maintenance of late myelinating oligodendrocytes. In addition, when control and Ndrg1 null mice are subject to cuprizone-induced demyelination, we observe a higher degree of demyelination in the mutants. Together these data identify NDRG1 as an important molecule for adult myelinating oligodendrocytes, whose decreased levels in the normal appearing white matter of human MS brains may result in greater susceptibility of myelin to damage.

Lack of CFTR alters the ferret pancreatic ductal epithelial secretome and cellular proteome: Implications for exocrine/endocrine signaling

BACKGROUND

Cystic fibrosis (CF) related diabetes is the most common comorbidity for CF patients and associated with islet dysfunction. Exocrine pancreas remodeling in CF alters the microenvironment in which islets reside. Since CFTR is mainly expressed in pancreatic ductal epithelium, we hypothesized altered CF ductal secretions could impact islet function through paracrine signals.

METHOD

We evaluated the secretome and cellular proteome of polarized WT and CF ferret ductal epithelia using quantitative ratiometric mass spectrometry. Differentially secreted proteins (DSPs) or expressed cellular proteins were used to mine pathways, upstream regulators and the CFTR interactome to map candidate CF-associated alterations in ductal signaling and phenotype. Candidate DSPs were evaluated for their in vivo pancreatic expression patterns and their functional impact on islet hormone secretion.

RESULTS

The secretome and cellular proteome of CF ductal epithelia was significantly altered relative to WT and implicated dysregulated TGFβ, WNT, and BMP signaling pathways. Cognate receptors of DSPs from CF epithelia were equally distributed among endocrine, exocrine, and stromal pancreatic cell types. IGFBP7 was a downregulated DSP in CF ductal epithelia in vitro and exhibited reduced CF ductal expression in vivo. IGFBP7 also altered WT islet insulin secretion in response to glucose. Many CFTR-associated proteins, including SLC9A3R1, were differentially expressed in the CF cellular proteome. Upstream regulators of the differential CF ductal proteome included TGFβ, PDX1, AKT/PTEN, and INSR signaling. Data is available via ProteomeXchange with identifier PXD025126.

CONCLUSION

These findings provide a proteomic roadmap for elucidating disturbances in autocrine and paracrine signals from CF pancreatic ducts and how they may alter islet function and maintenance.

Microrchidia family CW‑type zinc finger 2 promotes the proliferation, invasion, migration and epithelial‑mesenchymal transition of glioma by regulating PTEN/PI3K/AKT signaling via binding to N‑myc downstream regulated gene 1 promoter

Glioma is a common malignant tumor of the central nervous system with high incidence and mortality. The present study aimed to investigate the role of Microrchidia family CW‑type zinc finger 2 (MORC2) in the development of glioma. Firstly, MORC2 expression was detected in several glioma cell lines (U251, SHG44, LN229 and T98G). Following MORC2 silencing, cell proliferation was evaluated using the Cell Counting Kit‑8 assay and the expression of proliferation‑related proteins was assessed via immunofluorescence staining or western blotting. Cell invasion and migration were assessed using transwell and wound healing assays, respectively. Western blotting and immunofluorescence staining were employed to determine the expression of epithelial‑mesenchymal transition (EMT)‑associated proteins. The protein expression of N‑myc downstream regulated gene 1 (NDRG1) and PTEN/PI3K/AKT signaling was determined with western blot analysis. Then, the luciferase reporter assay and chromatin immunoprecipitation (ChIP) assay were employed to evaluate the binding between MORC2 and NDRG1 promoter. Subsequently, cellular functional experiments were performed to assess the effects of NDRG1 on the progression of glioma after NDRG1 and MORC2 overexpression. In addition, tumor‑bearing experiments were conducted using a U251 tumor‑bearing nude mice model to detect tumor growth. The expression of proliferation (proliferating cell nuclear antigen, cyclin‑dependent kinase 2 and cyclin E1), migration [matrix metalloproteinase (MMP)2 and MMP9], EMT (E‑cadherin, N‑cadherin and Vimentin) and PTEN/PI3K/AKT signaling proteins in tumor tissues was examined with immunohistochemistry assay or western blotting. Results revealed that MORC2 was notably unregulated in glioma cells compared with the normal human astrocyte. Loss‑function of MORC2 inhibited the proliferation, invasion, migration and EMT of glioma cells. Importantly, MORC2 silencing upregulated NDRG1 expression and inactivated PTEN/PI3K/AKT signaling. Additionally, the luciferase reporter‑ and ChIP assays confirmed that MORC2 could bind to the NDRG1 promoter. NDRG1 upregulation suppressed the progression of glioma and these effects were partially reversed by MORC2 overexpression. Results of tumor‑bearing experiments suggested that gain‑function of NDRG1 inhibited tumor growth and downregulated the expression of proliferation, migration and EMT‑related proteins in tumorous tissue in U251 tumor‑bearing mice, which was partially counteracted after MORC2 overexpression. In addition, MORC2 overexpression abrogated the inhibitory effect of NDRG1 on PTEN/PI3K/AKT signaling. In summary, MORC2 promoted the progression of glioma by inactivation of PTEN/PI3K/AKT signaling via binding to NDRG1 promoter, providing a novel and potent target for the treatment of glioma.

Claudin-2 promotes colorectal cancer growth and metastasis by suppressing NDRG1 transcription

Colorectal cancer (CRC) is one of the most common malignant tumours, with multiple driving factors and biological transitions involved in its development. Claudin-2 (CLDN2), a well-defined component of cellular tight junction, has been indicated to associate with CRC progression. However, the function of CLDN2 and the underlying mechanism whereby the downstream signalling transduction is regulated in CRC remains largely unclear. In this study, we demonstrated that CLDN2 is upregulated in CRC samples and associated with poor survival. And CLDN2 depletion significantly promotes N-myc downstream-regulated gene 1 (NDRG1) transcription, leading to termination of the CRC growth and metastasis in vitro and in vivo. Mechanistically, this process promotes CLDN2/ZO1/ZONAB complex dissociation and ZONAB shuttle into nucleus to enrich in the promoter of NDRG1. Thus, this study reveals a novel CLDN2/ZO1/ZONAB-NDRG1 axis in CRC by regulating the expression of EMT-related genes and CDKIs, suggesting CLDN2 may serve as a promising target for CRC treatment.

Differential expression and hypoxia-mediated regulation of the N-myc downstream regulated gene family

Many organisms rely on oxygen to generate cellular energy (adenosine triphosphate or ATP). During severe hypoxia, the production of ATP decreases, leading to cell damage or death. Conversely, excessive oxygen causes oxidative stress that is equally damaging to cells. To mitigate pathological outcomes, organisms have evolved mechanisms to adapt to fluctuations in oxygen levels. Zebrafish embryos are remarkably hypoxia-tolerant, surviving anoxia (zero oxygen) for hours in a hypometabolic, energy-conserving state. To begin to unravel underlying mechanisms, we analyze here the distribution of the N-myc Downstream Regulated Gene (ndrg) family, ndrg1-4, and their transcriptional response to hypoxia. These genes have been primarily studied in cancer cells and hence little is understood about their normal function and regulation. We show here using in situ hybridization that ndrgs are expressed in metabolically demanding organs of the zebrafish embryo, such as the brain, kidney, and heart. To investigate whether ndrgs are hypoxia-responsive, we exposed embryos to different durations and severity of hypoxia and analyzed transcript levels. We observed that ndrgs are differentially regulated by hypoxia and that ndrg1a has the most robust response, with a ninefold increase following prolonged anoxia. We further show that this treatment resulted in de novo expression of ndrg1a in tissues where the transcript is not observed under normoxic conditions and changes in Ndrg1a protein expression post-reoxygenation. These findings provide an entry point into understanding the role of this conserved gene family in the adaptation of normal cells to hypoxia and reoxygenation.

Innovative therapies for neuroblastoma: The surprisingly potent role of iron chelation in up-regulating metastasis and tumor suppressors and down-regulating the key oncogene, N-myc

Iron is an indispensable requirement for essential biological processes in cancer cells. Due to the greater proliferation of neoplastic cells, their demand for iron is considerably higher relative to normal cells, making them highly susceptible to iron depletion. Understanding this sensitive relationship led to research exploring the effect of iron chelation therapy for cancer treatment. The classical iron-binding ligand, desferrioxamine (DFO), has demonstrated effective anti-proliferative activity against many cancer-types, particularly neuroblastoma tumors, and has the surprising activity of down-regulating the potent oncogene, N-myc, which is a major oncogenic driver in neuroblastoma. Even more significant is the ability of DFO to simultaneously up-regulate the potent metastasis suppressor, N-myc downstream-regulated gene-1 (NDRG1), which plays a plethora of roles in suppressing a variety of oncogenic signaling pathways. However, DFO suffers the disadvantage of demonstrating poor membrane permeability and short plasma half-life, requiring administration by prolonged subcutaneous or intravenous infusions. Considering this, the specifically designed di-2-pyridylketone thiosemicarbazone (DpT) series of metal-binding ligands was developed in our laboratory. The lead agent from the first generation DpT series, di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone (Dp44mT), showed exceptional anti-cancer properties compared to DFO. However, it exhibited cardiotoxicity in mouse models at higher dosages. Therefore, a second generation of agents was developed with the lead compound being di-2-pyridylketone-4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC) that progressed to Phase I clinical trials. Importantly, DpC showed better anti-proliferative activity than Dp44mT and no cardiotoxicity, demonstrating effective anti-cancer activity against neuroblastoma tumors in vivo.

The role of N-cadherin/c-Jun/NDRG1 axis in the progression of prostate cancer

The dysregulation of androgen receptor (AR) signaling is a critical event in the progression of prostate cancer (PCa) and hormone therapy consisting of androgen deprivation (ADT) or AR inhibition is therefore used to treat advanced cases. It is known that N-cadherin becomes upregulated following ADT and can directly induce PCa transformation to the castration-resistant stage (CRPC). However, the relationship between AR and N-cadherin is unclear and may promote better understanding of CRPC pathogenesis and progression. Here, we demonstrate a new axis of N-cadherin/c-Jun/N-myc downstream regulated gene 1 (NDRG1) that N-cadherin promotes c-Jun expression and suppresses NDRG1 to promote invasion and migration of PCa cells through epithelial to mesenchymal transition (EMT). Targeting N-cadherin in combination with enzalutamide (ENZ) treatment synergistically suppressed PC3 cell proliferation in vivo and in vitro. Further studies showed that compared to lower Gleason score (GS) (GS < 7) cases, high GS (GS > 7) cases exhibited elevated N-cadherin expression and reduced NDRG1 expression, corroborating our in vitro observations. We further demonstrate that c-Jun, AR, and DNA methyltransferase-1 (DNMT1) form a complex in the 12-O-tetradecanoyl phorbol-13-acetate (TPA) response elements (TREs) region of the NDRG1 promoter, which suppresses NDRG1 transcription through DNA hypermethylation. In conclusion, we demonstrate an underlying mechanism for how N-cadherin collaborates with AR and NDRG1 to promote CRPC progression. Controlling N-cadherin/c-Jun/NDRG1 axis may help to overcome resistance to commonly used hormone therapy to improve long-term patient outcomes.

The Oncogenic Signaling Disruptor, NDRG1: Molecular and Cellular Mechanisms of Activity

NDRG1 is an oncogenic signaling disruptor that plays a key role in multiple cancers, including aggressive pancreatic tumors. Recent studies have indicated a role for NDRG1 in the inhibition of multiple tyrosine kinases, including EGFR, c-Met, HER2 and HER3, etc. The mechanism of activity of NDRG1 remains unclear, but to impart some of its functions, NDRG1 binds directly to key effector molecules that play roles in tumor suppression, e.g., MIG6. More recent studies indicate that NDRG1s-inducing drugs, such as novel di-2-pyridylketone thiosemicarbazones, not only inhibit tumor growth and metastasis but also fibrous desmoplasia, which leads to chemotherapeutic resistance. The Casitas B-lineage lymphoma (c-Cbl) protein may be regulated by NDRG1, and is a crucial E3 ligase that regulates various protein tyrosine and receptor tyrosine kinases, primarily via ubiquitination. The c-Cbl protein can act as a tumor suppressor by promoting the degradation of receptor tyrosine kinases. In contrast, c-Cbl can also promote tumor development by acting as a docking protein to mediate the oncogenic c-Met/Crk/JNK and PI3K/AKT pathways. This review hypothesizes that NDRG1 could inhibit the oncogenic function of c-Cbl, which may be another mechanism of its tumor-suppressive effects.

PI3K-AKT, JAK2-STAT3 pathways and cell-cell contact regulate maspin subcellular localization

Background

Maspin (SERPINB5) is a potential tumor suppressor gene with pleiotropic biological activities, including regulation of cell proliferation, death, adhesion, migration and gene expression. Several studies indicate that nuclear localization is essential for maspin tumor suppression activity. We have previously shown that the EGFR activation leads to maspin nuclear localization in MCF-10A cells. The present study investigated which EGFR downstream signaling molecules are involved in maspin nuclear localization and explored a possible role of cell–cell contact in this process.

Methods

MCF-10A cells were treated with pharmacological inhibitors against EGFR downstream pathways followed by EGF treatment. Maspin subcellular localization was determined by immunofluorescence. Proteomic and interactome analyses were conducted to identify maspin-binding proteins in EGF-treated cells only. To investigate the role of cell–cell contact these cells were either treated with chelating agents or plated on different cell densities. Maspin and E-cadherin subcellular localization was determined by immunofluorescence.

Results

We found that PI3K-Akt and JAK2-STAT3, but not MAP kinase pathway, regulate EGF-induced maspin nuclear accumulation in MCF-10A cells. We observed that maspin is predominantly nuclear in sparse cell culture, but it is redistributed to the cytoplasm in confluent cells even in the presence of EGF. Proteomic and interactome results suggest a role of maspin on post-transcriptional and translation regulation, protein folding and cell–cell adhesion.

Conclusions

Maspin nuclear accumulation is determined by an interplay between EGFR (via PI3K-Akt and JAK2-STAT3 pathways) and cell–cell contact.

Metastasis Suppressor Genes in Pancreatic Cancer: An Update

ABSTRACT

Pancreatic cancer, especially pancreatic ductal adenocarcinoma (PDAC), has for long remained a deadly form of cancer characterized by high mortality rates resulting from metastasis to multiple organs. Several factors, including the late manifestation of the disease, partly amplified by lack of efficient screening methods, have hampered the drive to design an effective therapeutic strategy to treat this deadly cancer. Understanding the biology of PDAC progression and identifying critical genes regulating these processes are essential to overcome the barriers toward effective treatment. Metastasis suppressor genes have been shown to inhibit multiple steps in the metastatic cascade without affecting primary tumor formation and are considered to hold promise for treating metastatic cancers. In this review, we catalog the bona fide metastasis suppressor genes reported in PDAC and discuss their known mechanism of action.

Comparison of Osteosarcoma Aggregated Tumour Models with Human Tissue by Multimodal Mass Spectrometry Imaging

Osteosarcoma (OS) is the most common primary bone malignancy and largely effects adolescents and young adults, with 60% of patients under the age of 25. There are multiple cell models of OS described in vitro that express the specific genetic alterations of the sarcoma. In the work reported here, multiple mass spectrometry imaging (MSI) modalities were employed to characterise two aggregated cellular models of OS models formed using the MG63 and SAOS-2 cell lines. Phenotyping of the metabolite activity within the two OS aggregoid models was achieved and a comparison of the metabolite data with OS human tissue samples revealed relevant fatty acid and phospholipid markers. Although, annotations of these species require MS/MS analysis for confident identification of the metabolites. From the putative assignments however, it was suggested that the MG63 aggregoids are an aggressive tumour model that exhibited metastatic-like potential. Alternatively, the SAOS-2 aggregoids are more mature osteoblast-like phenotype that expressed characteristics of cellular differentiation and bone development. It was determined the two OS aggregoid models shared similarities of metabolic behaviour with different regions of OS human tissues, specifically of the higher metastatic grade.

Breaking the cycle: Targeting of NDRG1 to inhibit bi-directional oncogenic cross-talk between pancreatic cancer and stroma

Pancreatic cancer (PaCa) is characterized by dense stroma that hinders treatment efficacy, with pancreatic stellate cells (PSCs) being a major contributor to this stromal barrier and PaCa progression. Activated PSCs release hepatocyte growth factor (HGF) and insulin-like growth factor (IGF-1) that induce PaCa proliferation, metastasis and resistance to chemotherapy. We demonstrate for the first time that the metastasis suppressor, N-myc downstream regulated gene 1 (NDRG1), is a potent inhibitor of the PaCa-PSC cross-talk, leading to inhibition of HGF and IGF-1 signaling. NDRG1 also potently reduced the key driver of PaCa metastasis, namely GLI1, leading to reduced PSC-mediated cell migration. The novel clinically trialed anticancer agent, di-2-pyridylketone 4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC), which upregulates NDRG1, potently de-sensitized PaCa cells to ligands secreted by activated PSCs. DpC and NDRG1 also inhibited the PaCa-mediated activation of PSCs via inhibition of sonic hedgehog (SHH) signaling. In vivo, DpC markedly reduced PaCa tumor growth and metastasis more avidly than the standard chemotherapy for this disease, gemcitabine. Uniquely, DpC was selectively cytotoxic against PaCa cells, while "re-programming" PSCs to an inactive state, decreasing collagen deposition and desmoplasia. Thus, targeting NDRG1 can effectively break the oncogenic cycle of PaCa-PSC bi-directional cross-talk to overcome PaCa desmoplasia and improve therapeutic outcomes.

Potentiating Therapeutic Effects of Epidermal Growth Factor Receptor Inhibition in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a subset of breast cancer with aggressive characteristics and few therapeutic options. The lack of an appropriate therapeutic target is a challenging issue in treating TNBC. Although a high level expression of epidermal growth factor receptor (EGFR) has been associated with a poor prognosis among patients with TNBC, targeted anti-EGFR therapies have demonstrated limited efficacy for TNBC treatment in both clinical and preclinical settings. However, with the advantage of a number of clinically approved EGFR inhibitors (EGFRis), combination strategies have been explored as a promising approach to overcome the intrinsic resistance of TNBC to EGFRis. In this review, we analyzed the literature on the combination of EGFRis with other molecularly targeted therapeutics or conventional chemotherapeutics to understand the current knowledge and to provide potential therapeutic options for TNBC treatment.

Overview of Evidence-Based Chemotherapy for Oral Cancer: Focus on Drug Resistance Related to the Epithelial-Mesenchymal Transition

The increasing incidence of resistance to chemotherapeutic agents has become a major issue in the treatment of oral cancer (OC). Epithelial-mesenchymal transition (EMT) has attracted a great deal of attention in recent years with regard to its relation to the mechanism of chemotherapy drug resistance. EMT-activating transcription factors (EMT-ATFs), such as Snail, TWIST, and ZEB, can activate several different molecular pathways, e.g., PI3K/AKT, NF-κB, and TGF-β. In contrast, the activated oncological signal pathways provide reciprocal feedback that affects the expression of EMT-ATFs, resulting in a peritumoral extracellular environment conducive to cancer cell survival and evasion of the immune system, leading to resistance to multiple chemotherapeutic agents. We present an overview of evidence-based chemotherapy for OC treatment based on the National Comprehensive Cancer Network (NCCN) Chemotherapy Order Templates. We focus on the molecular pathways involved in drug resistance related to the EMT and highlight the signal pathways and transcription factors that may be important for EMT-regulated drug resistance. Rapid progress in antitumor regimens, together with the application of powerful techniques such as high-throughput screening and microRNA technology, will facilitate the development of therapeutic strategies to augment chemotherapy.

NDRG1 regulates osteosarcoma cells via mediating the mitochondrial function and CSCs differentiation

BACKGROUND

Cancer stem cells (CSCs) are mainly contributed to malignancy metastatic potential and resistant therapy of osteosarcoma (OS). The mitochondria-related apoptosis was generally accepted as the target of tumor therapy. However, the effect of N-myc downstream-regulated gene 1 (NDRG1) on CSCs and mitochondrial health in OS is still unknown.

METHODS

In OS cells, MG63 and U2OS, the siRNA of NDRG1 were conducted. Transwell, western blot, RT-qPCR, and mitochondria isolation were used to identify the effect of NDRG on OS cells and mitochondria. Moreover, the differentiation-related factors of CSCs were determined.

RESULTS

After downregulation of NDRG1, the cell viability, invasion ability decreased whereas cell apoptosis increased. The expressions profiles of fibronectin, vimentin, vascular endothelial growth factor (VEGF), matrix metalloproteinase (MMP) 2, MMP9, and MMP13 were downregulated, but E-cadherin expression level was upregulated by NDRG1 siRNA. At the same time, cytochrome (Cyt) C levels were increased in cytosol with the decreasing in mitochondria after siRNA treatment. The mitochondrial membrane potential (MMPs) was declined, and the function of mitochondria was impeded. The expressions of uncoupling proteins (UCP) 2, voltage dependent anion channel (VDAC), peroxisome proliferator-activated receptor gamma coactivator (PGC)-1α, and cyclooxygenase (COX) 2 were downregulated by NDRG1 silencing. Moreover, NDRG performed its function primarily through the Wnt pathway and could regulate the differentiation of osteosarcoma stem cells.

CONCLUSION

Silencing of NDRG1 could damage the function of mitochondria, promote the CSCs differentiation, alleviating OS progression.

NDRG1 facilitates lytic replication of Kaposi's sarcoma-associated herpesvirus by maintaining the stability of the KSHV helicase

The presumed DNA helicase encoded by ORF44 of Kaposi's sarcoma-associated herpesvirus (KSHV) plays a crucial role in unwinding viral double-stranded DNA and initiating DNA replication during lytic reactivation. However, the regulatory mechanism of KSHV ORF44 has not been fully elucidated. In a previous study, we identified that N-Myc downstream regulated gene 1 (NDRG1), a host scaffold protein, facilitates viral genome replication by interacting with proliferating cell nuclear antigen (PCNA) and the latent viral protein latency-associated nuclear antigen (LANA) during viral latency. In the present study, we further demonstrated that NDRG1 can interact with KSHV ORF44 during viral lytic replication. We also found that the mRNA and protein levels of NDRG1 were significantly increased by KSHV ORF50-encoded replication and transcription activator (RTA). Remarkably, knockdown of NDRG1 greatly decreased the protein level of ORF44 and impaired viral lytic replication. Interestingly, NDRG1 enhanced the stability of ORF44 and inhibited its ubiquitin-proteasome-mediated degradation by reducing the polyubiquitination of the lysine residues at positions 79 and 368 in ORF44. In summary, NDRG1 is a novel binding partner of ORF44 and facilitates viral lytic replication by maintaining the stability of ORF44. This study provides new insight into the mechanisms underlying KSHV lytic replication.

MicroRNA-27b inhibits the development of melanoma by targeting MYC

Cutaneous malignant melanoma is a malignancy with one of the fastest increasing incidence rates worldwide; however, the mechanism underlying the occurrence and development of melanoma remains unclear. The aim of the present study was to identify novel biomarkers for the occurrence and development of melanoma. The results of the present study demonstrated that the expression levels of microRNA (miR)-27b were decreased in melanoma tissue samples compared with those in adjacent noncancerous tissue samples and cells according to online and experimental data. By contrast, MYC expression levels were upregulated in melanoma compared with those in adjacent noncancerous tissue samples. miR-27b overexpression significantly inhibited A375 and A2085 melanoma cell DNA synthesis, viability and invasive ability. Dual-luciferase reporter assay results demonstrated that miR-27b inhibited MYC expression through binding to the 3′-untranslated region of MYC mRNA. MYC knockdown in melanoma cells exerted similar effects to those of miR-27b overexpression on DNA synthesis, cell viability and invasive ability; the effects of miR-27b inhibition were significantly reversed by MYC knockdown. In conclusion, the miR-27b/MYC axis may modulate malignant melanoma cell biological behaviors and may be a potential target for melanoma treatment.

Cystic proliferation of germline stem cells is necessary to reproductive success and normal mating behavior in medaka

The production of an adequate number of gametes is necessary for normal reproduction, for which the regulation of proliferation from early gonadal development to adulthood is key in both sexes. Cystic proliferation of germline stem cells is an especially important step prior to the beginning of meiosis; however, the molecular regulators of this proliferation remain elusive in vertebrates. Here, we report that ndrg1b is an important regulator of cystic proliferation in medaka. We generated mutants of ndrg1b that led to a disruption of cystic proliferation of germ cells. This loss of cystic proliferation was observed from embryogenic to adult stages, impacting the success of gamete production and reproductive parameters such as spawning and fertilization. Interestingly, the depletion of cystic proliferation also impacted male sexual behavior, with a decrease of mating vigor. These data illustrate why it is also necessary to consider gamete production capacity in order to analyze reproductive behavior.

An Integrated Bioinformatics Study of a Novel Niclosamide Derivative, NSC765689, a Potential GSK3β/β-Catenin/STAT3/CD44 Suppressor with Anti-Glioblastoma Properties

Despite management efforts with standard surgery, radiation, and chemotherapy, glioblastoma multiform (GBM) remains resistant to treatment, which leads to tumor recurrence due to glioma stem cells (GSCs) and therapy resistance. In this study, we used random computer-based prediction and target identification to assess activities of our newly synthesized niclosamide-derived compound, NSC765689, to target GBM oncogenic signaling. Using target prediction analyses, we identified glycogen synthase kinase 3β (GSK3β), β-Catenin, signal transducer and activator of transcription 3 (STAT3), and cluster of differentiation 44 (CD44) as potential druggable candidates of NSC765689. The above-mentioned signaling pathways were also predicted to be overexpressed in GBM tumor samples compared to adjacent normal samples. In addition, using bioinformatics tools, we also identified microRNA (miR)-135b as one of the most suppressed microRNAs in GBM samples, which was reported to be upregulated through inhibition of GSK3β, and subsequently suppresses GBM tumorigenic properties and stemness. We further performed in silico molecular docking of NSC765689 with GBM oncogenes; GSK3β, β-Catenin, and STAT3, and the stem cell marker, CD44, to predict protein-ligand interactions. The results indicated that NSC765689 exhibited stronger binding affinities compared to its predecessor, LCC09, which was recently published by our laboratory, and was proven to inhibit GBM stemness and resistance. Moreover, we used available US National Cancer Institute (NCI) 60 human tumor cell lines to screen in vitro anticancer effects, including the anti-proliferative and cytotoxic activities of NSC765689 against GBM cells, and 50% cell growth inhibition (GI₅₀) values ranged 0.23~5.13 μM. In summary, using computer-based predictions and target identification revealed that NSC765689 may be a potential pharmacological lead compound which can regulate GBM oncogene (GSK3β/β-Catenin/STAT3/CD44) signaling and upregulate the miR-135b tumor suppressor. Therefore, further in vitro and in vivo investigations will be performed to validate the efficacy of NSC765689 as a novel potential GBM therapeutic.

Crystal and solution structure of NDRG1, a membrane-binding protein linked to myelination and tumour suppression

N-myc downstream-regulated gene 1 (NDRG1) is a tumour suppressor involved in vesicular trafficking and stress response. NDRG1 participates in peripheral nerve myelination, and mutations in the NDRG1 gene lead to Charcot-Marie-Tooth neuropathy. The 43-kDa NDRG1 is considered as an inactive member of the α/β hydrolase superfamily. In addition to a central α/β hydrolase fold domain, NDRG1 consists of a short N terminus and a C-terminal region with three 10-residue repeats. We determined the crystal structure of the α/β hydrolase domain of human NDRG1 and characterised the structure and dynamics of full-length NDRG1. The structure of the α/β hydrolase domain resembles the canonical α/β hydrolase fold with a central β sheet surrounded by α helices. Small-angle X-ray scattering and CD spectroscopy indicated a variable conformation for the N- and C-terminal regions. NDRG1 binds to various types of lipid vesicles, and the conformation of the C-terminal region is modulated upon lipid interaction. Intriguingly, NDRG1 interacts with metal ions, such as nickel, but is prone to aggregation in their presence. Our results uncover the structural and dynamic features of NDRG1, as well as elucidate its interactions with metals and lipids, and encourage studies to identify a putative hydrolase activity of NDRG1. DATABASES: The coordinates and structure factors for the crystal structure of human NDRG1 were deposited to PDB (PDB ID: 6ZMM).

Identification of PIM1 substrates reveals a role for NDRG1 phosphorylation in prostate cancer cellular migration and invasion

PIM1 is a serine/threonine kinase that promotes and maintains prostate tumorigenesis. While PIM1 protein levels are elevated in prostate cancer relative to local disease, the mechanisms by which PIM1 contributes to oncogenesis have not been fully elucidated. Here, we performed a direct, unbiased chemical genetic screen to identify PIM1 substrates in prostate cancer cells. The PIM1 substrates we identified were involved in a variety of oncogenic processes, and included N-Myc Downstream-Regulated Gene 1 (NDRG1), which has reported roles in suppressing cancer cell invasion and metastasis. NDRG1 is phosphorylated by PIM1 at serine 330 (pS330), and the level of NDRG1 pS330 is associated higher grade prostate tumors. We have shown that PIM1 phosphorylation of NDRG1 at S330 reduced its stability, nuclear localization, and interaction with AR, resulting in enhanced cell migration and invasion.

NDRG1 enhances the sensitivity of cetuximab by modulating EGFR trafficking in colorectal cancer

N-myc downstream-regulated gene 1 (NDRG1) is a key regulator that interacts with many classic tumor signaling pathways, including some molecules downstream of the epidermal growth factor receptor (EGFR). However, whether NDRG1 is involved in the mechanism of resistance to cetuximab (CTX), the first monoclonal antibody targeting the EGFR has not been reported. Here, we found that NDRG1 enhanced the sensitivity of CTX in colorectal cancer (CRC) cell lines. Afterwards, we determined the underlying mechanism of this phenomenon. We demonstrated that NDRG1 inhibited the expression of EGFR; blocked EGFR phosphorylation and reduced the EGFR distribution in the cell membrane, cytoplasm and nucleus. And then, NDRG1 suppressed the EGFR downstream signaling: RAS/RAF/ERK and PI3k/AKT/mTOR pathways. Moreover, we discovered that NDRG1 attenuated the endocytosis and degradation of EGFR induced by caveolin-1 (Cav1). Additionally, our findings were further observed in an animal model and human tissues. Our results represent a potentially significant discovery that explains the mechanisms of NDRG1 in CTX resistance. NDRG1 could be a promising biomarker to predict optimum responses to CTX, and a key target to enhance CTX activity in the treatment of metastatic CRC (mCRC).

Pharmacological Inhibition of mTORC2 Reduces Migration and Metastasis in Melanoma

Despite recent advances in therapy, liver metastasis from melanoma is still associated with poor prognosis. Although targeting the mTOR signaling pathway exerts potent anti-tumor activity, little is known about specific mTORC2 inhibition regarding liver metastasis. Using the novel mTORC2 specific inhibitor JR-AB2-011, we show significantly reduced migration and invasion capacity by impaired activation of MMP2 in melanoma cells. In addition, blockade of mTORC2 induces cell death by non-apoptotic pathways and reduces tumor cell proliferation rate dose-dependently. Furthermore, a significant reduction of liver metastasis was detected in a syngeneic murine metastasis model upon therapy with JR-AB2-011 as determined by in vivo imaging and necropsy. Hence, our study for the first time highlights the impact of the pharmacological blockade of mTORC2 as a potent novel anti-cancer approach for liver metastasis from melanoma.

Novel Thiosemicarbazones Sensitize Pediatric Solid Tumor Cell-Types to Conventional Chemotherapeutics through Multiple Molecular Mechanisms

Simple Summary

Combination of chemotherapeutics for the treatment of childhood cancer can lead to the use of lower cytotoxic drug doses and better therapeutic tolerability (i.e., lower side effects) for patients. We discovered novel molecular targets of two lead thiosemicarbazone agents of the di-2-pyridylketone thiosemicarbazone class. These molecular targets include: cyclooxygenase, the DNA repair protein, O6-methylguanine DNA methyltransferase, mismatch repair proteins, and topoisomerase 2α. This research also identifies promising synergistic interactions of these thiosemicarbazones particularly with the standard chemotherapeutic, celecoxib.

Abstract

Combining low-dose chemotherapies is a strategy for designing less toxic and more potent childhood cancer treatments. We examined the effects of combining the novel thiosemicarbazones, di-2-pyridylketone 4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC), or its analog, di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone (Dp44mT), with the standard chemotherapies, celecoxib (CX), etoposide (ETO), or temozolomide (TMZ). These combinations were analyzed for synergism to inhibit proliferation of three pediatric tumor cell-types, namely osteosarcoma (Saos-2), medulloblastoma (Daoy) and neuroblastoma (SH-SY5Y). In terms of mechanistic dissection, this study discovered novel thiosemicarbazone targets not previously identified and which are important for considering possible drug combinations. In this case, DpC and Dp44mT caused: (1) up-regulation of a major protein target of CX, namely cyclooxygenase-2 (COX-2); (2) down-regulation of the DNA repair protein, O⁶-methylguanine DNA methyltransferase (MGMT), which is known to affect TMZ resistance; (3) down-regulation of mismatch repair (MMR) proteins, MSH2 and MSH6, in Daoy and SH-SY5Y cells; and (4) down-regulation in all three cell-types of the MMR repair protein, MLH1, and also topoisomerase 2α (Topo2α), the latter of which is an ETO target. While thiosemicarbazones up-regulate the metastasis suppressor, NDRG1, in adult cancers, it is demonstrated herein for the first time that they induce NDRG1 in all three pediatric tumor cell-types, validating its role as a potential target. In fact, siRNA studies indicated that NDRG1 was responsible for MGMT down-regulation that may prevent TMZ resistance. Examining the effects of combining thiosemicarbazones with CX, ETO, or TMZ, the most promising synergism was obtained using CX. Of interest, a positive relationship was observed between NDRG1 expression of the cell-type and the synergistic activity observed in the combination of thiosemicarbazones and CX. These studies identify novel thiosemicarbazone targets relevant to childhood cancer combination chemotherapy.

NDRG1 deficiency is associated with regional metastasis in oral cancer by inducing epithelial-mesenchymal transition

Regional metastasis is the single most important prognostic factor in oral squamous cell carcinoma (OSCC). Abnormal expression of N-myc downstream-regulated genes (NDRGs) has been identified to occur in several tumor types and to predict poor prognosis. In OSCC, the clinical significance of deregulated NDRG expression has not been fully established. In this study, NDRG1 relevance was assessed at gene and protein levels in 100 OSCC patients followed up by at least 10 years. Survival outcome was analyzed using a multivariable analysis. Tumor progression and metastasis was investigated in preclinical model using oral cancer cell lines (HSC3 and SCC25) treated with epidermal growth factor (EGF) and orthotopic mouse model of metastatic murine OSCC (AT84). We identified NDRG1 expression levels to be significantly lower in patients with metastatic tumors compared with patients with local disease only (P = 0.001). NDRG1 expression was associated with MMP-2, -9, -10 (P = 0.022, P = 0.002, P = 0.042, respectively) and BCL2 (P = 0.035). NDRG1 lower expression was able to predict recurrence and metastasis (log-rank test, P = 0.001). In multivariable analysis, the expression of NDRG1 was an independent prognostic factor (Cox regression, P = 0.013). In invasive OSCC cells, NDRG1 expression is diminished in response to EGF and this was associated with a potent induction of epithelial-mesenchymal transition phenotype. This result was further confirmed in an orthotopic OSCC mouse model. Together, this data support that NDRG1 downregulation is a potential predictor of metastasis and approaches aimed at NDRG1 signaling rescue can serve as potential therapeutic strategy to prevent oral cancer progression to metastasis.

The Role of Extracellular Proteases in Tumor Progression and the Development of Innovative Metal Ion Chelators that Inhibit their Activity

The crucial role of extracellular proteases in cancer progression is well-known, especially in relation to the promotion of cell invasion through extracellular matrix remodeling. This also occurs by the ability of extracellular proteases to induce the shedding of transmembrane proteins at the plasma membrane surface or within extracellular vesicles. This process results in the regulation of key signaling pathways by the modulation of kinases, e.g., the epidermal growth factor receptor (EGFR). Considering their regulatory roles in cancer, therapeutics targeting various extracellular proteases have been discovered. These include the metal-binding agents di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT) and di-2-pyridylketone-4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC), which increase c-MET degradation by multiple mechanisms. Both the direct and indirect inhibition of protease expression and activity can be achieved through metal ion depletion. Considering direct mechanisms, chelators can bind zinc(II) that plays a catalytic role in enzyme activity. In terms of indirect mechanisms, Dp44mT and DpC potently suppress the expression of the kallikrein-related peptidase-a prostate-specific antigen-in prostate cancer cells. The mechanism of this activity involves promotion of the degradation of the androgen receptor. Additional suppressive mechanisms of Dp44mT and DpC on matrix metalloproteases (MMPs) relate to their ability to up-regulate the metastasis suppressors N-myc downstream regulated gene-1 (NDRG1) and NDRG2, which down-regulate MMPs that are crucial for cancer cell invasion.

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.

Thiosemicarbazones as Potent Anticancer Agents and their Modes of Action

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Thiosemicarbazones (TSCs) are a class of Schiff bases usually obtained by the condensation of thiosemicarbazide with a suitable aldehyde or ketone. TSCs have been the focus of chemists and biologists due to their wide range of pharmacological effects. One of the promising areas in which these excellent metal chelators are being developed is their use against cancer. TSCs have a wide clinical antitumor spectrum with efficacy in various tumor types such as leukemia, pancreatic cancer, breast cancer, non-small cell lung cancer, cervical cancer, prostate cancer and bladder cancer. To obtain better activity, different series of TSCs have been developed by modifying the heteroaromatic system in their molecules. These compounds possessed significant antineoplastic activity when the carbonyl attachment of the side chain was located at a position α to the ring nitrogen atom, whereas attachment of the side chain β or γ to the heterocyclic N atom resulted in inactive antitumor agents. In addition, replacement of the heterocyclic ring N with C also resulted in a biologically inactive compound suggesting that a conjugated N,N,S-tridentate donor set is essential for the biological activities of thiosemicarbazones. Several possible mechanisms have been implemented for the anticancer activity of thiosemicarbazones.

NDRG1 suppresses basal and hypoxia-induced autophagy at both the initiation and degradation stages and sensitizes pancreatic cancer cells to lysosomal membrane permeabilization

BACKGROUND

N-myc downstream regulated gene 1 (NDRG1) is an established stress-response protein. This study investigated the effects of NDRG1 on autophagic degradation and how this can be therapeutically exploited.

METHODS

Cell culture, western analysis, confocal microscopy, acridine orange staining, cholesterol determination, cellular proliferation assessment and combination index (CI) estimation.

RESULTS

NDRG1 expression suppressed autophagic degradation and autolysosome formation, measured by increased p62 expression and reduced co-localization between the well-characterized, autophagosomal and lysosomal markers, LC3 and LAMP2, respectively. NDRG1 elicited autophagic suppression at the initiation stage of autophagy. The NDRG1-inducer and anti-cancer agent, di-2-pyridylketone 4,4,-dimethyl-3-thiosemicarbazone (Dp44mT), was able to induce lysosomal membrane permeabilization (LMP). Over-expression of NDRG1 further sensitized cells to LMP mediated by both Dp44mT, or the redox active Dp44mT‑copper complex. This sensitization may be mediated via a decrease in cholesterol levels upon NDRG1 expression, as cholesterol stabilizes lysosomal membranes. However, the effect of NDRG1 on cholesterol appeared independent of the key energy homeostasis sensor, 5' AMP-activated protein kinase (AMPK), whose activation was significantly (p < 0.001) reduced by NDRG1. Finally, Dp44mT synergistically potentiated the anti-proliferative activity of Gemcitabine that activates autophagy. In fact, Dp44mT and Gemcitabine (Combination Index (CI): 0.38 ± 0.07) demonstrated higher synergism versus the autophagy inhibitor, Bafilomycin A1 and Gemcitabine (CI: 0.64 ± 0.19).

CONCLUSIONS AND GENERAL SIGNIFICANCE

Collectively, this study demonstrated a dual-inhibitory mechanism of NDRG1 on autophagic activity, and that NDRG1 expression sensitized cells to Dp44mT-induced LMP. Considering the ability of Dp44mT to inhibit autophagy, studies demonstrated the potential of combination therapy for cancer treatment of Dp44mT with Gemcitabine.

Transcriptomic analysis reveals the oncogenic role of S6K1 in hepatocellular carcinoma

The p70 ribosomal protein S6 kinase 1 (S6K1), a serine/threonine kinase, is commonly overexpressed in a variety of cancers. However, its expression level and functional roles in hepatocellular carcinoma (HCC), which ranks as the third leading cause of cancer-related death worldwide, is still largely unknown. In the current report, we show the in vivo and in vitro overexpression of S6K1 in HCC. In the functional analysis, we demonstrate that S6K1 is required for the proliferation and colony formation abilities in HCC. By using comparative transcriptomic analysis followed by gene ontology enrichment analysis and Ingenuity Pathway Analysis, we find that the depletion of S6K1 can elevate the expression of a cluster of apoptotic genes, tumor suppressor genes and immune responsive genes. Moreover, the knockdown of S6K1 is predicted to reduce the tumorigenicity of HCC through the regulation of hubs of genes including STAT1, HDAC4, CEBPA and ONECUT1. In conclusion, we demonstrate the oncogenic role of S6K1 in HCC, suggesting the possible use of S6K1 as a therapeutic target for HCC treatment.

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.