Nitric oxide suppresses tumor cell migration through N-Myc downstream-regulated gene-1 (NDRG1) expression: role of chelatable iron

The expression and localization of N-myc downstream-regulated gene 1 in human trophoblasts

The protein N-Myc downstream-regulated gene 1 (NDRG1) is implicated in the regulation of cell proliferation, differentiation, and cellular stress response. NDRG1 is expressed in primary human trophoblasts, where it promotes cell viability and resistance to hypoxic injury. The mechanism of action of NDRG1 remains unknown. To gain further insight into the intracellular action of NDRG1, we analyzed the expression pattern and cellular localization of endogenous NDRG1 and transfected Myc-tagged NDRG1 in human trophoblasts exposed to diverse injuries. In standard conditions, NDRG1 was diffusely expressed in the cytoplasm at a low level. Hypoxia or the hypoxia mimetic cobalt chloride, but not serum deprivation, ultraviolet (UV) light, or ionizing radiation, induced the expression of NDRG1 in human trophoblasts and the redistribution of NDRG1 into the nucleus and cytoplasmic membranes associated with the endoplasmic reticulum (ER) and microtubules. Mutation of the phosphopantetheine attachment site (PPAS) within NDRG1 abrogated this pattern of redistribution. Our results shed new light on the impact of cell injury on NDRG1 expression patterns, and suggest that the PPAS domain plays a key role in NDRG1’s subcellular distribution.

Long-term nitric oxide exposure enhances lung cancer cell migration

Nitric oxide (NO) found in the vicinity of lung cancer cells may play a role in the regulation of cancer cell behaviors. To explore the possible effects of NO on cell motility, human lung cancer cells were exposed to nontoxic concentrations of NO for 0–14 days, and the migratory characteristics of the cells were determined. The present study found that long-term treatment with NO significantly enhanced cell migration in a dose- and time-dependent manner. Furthermore, we found that the increased migratory action was associated with the increased expression of caveolin-1 (Cav-1), which in turn activated the focal adhesion kinase (FAK) and ATP-dependent tyrosine kinase (Akt) pathways. Notably, the NO-treated cells exhibited an increased number of filopodia per cell, as well as an increase in the levels of cell division cycle 42 (Cdc42) protein. Together, these results indicate that extended NO exposure has a novel effect on cell migration through a Cav-1-dependent mechanism, a finding that strengthens our understanding of cancer biology.

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.

Enhancement of head and neck squamous cell carcinoma proliferation, invasion, and metastasis by tumor-associated fibroblasts in preclinical models

BACKGROUND

Head and neck squamous cell carcinoma (HNSCC) has had little improvement in mortality rates in decades. A clearer understanding of the HNSCC tumor microenvironment will aid in finding more effective targeted therapies for this disease. Tumor-associated fibroblasts (TAFs) are the largest stromal cellular components of the tumor microenvironment in HNSCC.

METHODS

We isolated TAFs from clinical HNSCC cases and propagated in vitro. The effects of TAF-secreted paracrine factors on in vitro HNSCC migration, invasion, and proliferation was assessed. The effect of TAFs on HNSCC growth and metastases was determined in an orthotopic floor-of-the-mouth tumor model.

RESULTS

TAF-conditioned media increased HNSCC cell migration, invasion, and proliferation. TAFs increased HNSCC tumor growth and metastases in vivo.

CONCLUSION

TAFs play a major role in increasing tumor growth and metastasis in HNSCC. Targeting the tumor stroma may be important to reduce the rate of HNSCC metastasis.

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

The metastasis suppressor, N-myc downstream regulated gene 1 (NDRG1), is negatively correlated with tumor progression in multiple neoplasms, being a promising new target for cancer treatment. However, the precise molecular effects of NDRG1 remain unclear. Herein, we summarize recent advances in understanding the impact of NDRG1 on cancer metastasis with emphasis on its interactions with the key oncogenic nuclear factor-kappaB, phosphatidylinositol-3 kinase/phosphorylated AKT/mammalian target of rapamycin and Ras/Raf/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase signaling pathways. Recent studies demonstrating the inhibitory effects of NDRG1 on the epithelial-mesenchymal transition, a key initial step in metastasis, TGF-β pathway and the Wnt/β-catenin pathway are also described. Furthermore, NDRG1 was also demonstrated to regulate molecular motors in cancer cells, leading to inhibition of F-actin polymerization, stress fiber formation and subsequent reduction of cancer cell migration. Collectively, this review summarizes the underlying molecular mechanisms of the antimetastatic effects of NDRG1 in cancer cells.

Nitric oxide modifies global histone methylation by inhibiting Jumonji C domain-containing demethylases

Methylation of lysine residues on histone tails is an important epigenetic modification that is dynamically regulated through the combined effects of methyltransferases and demethylases. The Jumonji C domain Fe(II) α-ketoglutarate family of proteins performs the majority of histone demethylation. We demonstrate that nitric oxide ((•)NO) directly inhibits the activity of the demethylase KDM3A by forming a nitrosyliron complex in the catalytic pocket. Exposing cells to either chemical or cellular sources of (•)NO resulted in a significant increase in dimethyl Lys-9 on histone 3 (H3K9me2), the preferred substrate for KDM3A. G9a, the primary methyltransferase acting on H3K9me2, was down-regulated in response to (•)NO, and changes in methylation state could not be accounted for by methylation in general. Furthermore, cellular iron sequestration via dinitrosyliron complex formation correlated with increased methylation. The mRNA of several histone demethylases and methyltransferases was also differentially regulated in response to (•)NO. Taken together, these data reveal three novel and distinct mechanisms whereby (•)NO can affect histone methylation as follows: direct inhibition of Jumonji C demethylase activity, reduction in iron cofactor availability, and regulation of expression of methyl-modifying enzymes. This model of (•)NO as an epigenetic modulator provides a novel explanation for nonclassical gene regulation by (•)NO.

The yin and yang of nitric oxide in cancer progression

Nitric oxide (NO) is a short-lived, pleiotropic molecule that affects numerous critical functions in the body. Presently, there are markedly conflicting findings in the literature regarding NO and its role in carcinogenesis and tumor progression. NO has been shown to have dichotomous effects on cellular proliferation, apoptosis, migration, invasion, angiogenesis and many other important processes in cancer biology. It has been shown to be both pro- and antitumorigenic, depending on the concentration and the tumor microenvironment in question. NO is generated by three isoforms of NO synthase (NOS) that are widely expressed and sometimes upregulated in human tumors. Due to its vast array of physiological functions, it presents a huge challenge to researchers to discover its true potential in cancer biology and consequently, its use in anticancer therapies. In this study, we review the current knowledge in this area, with an emphasis placed on NO modulation as an anticancer therapy, focusing on NO-donating drugs and NOS inhibitors.

Targeting the metastasis suppressor, NDRG1, using novel iron chelators: regulation of stress fiber-mediated tumor cell migration via modulation of the ROCK1/pMLC2 signaling pathway

The iron-regulated metastasis suppressor, N-myc downstream-regulated gene 1 (NDRG1), is up-regulated by cellular iron depletion mediated by iron chelators and can inhibit cancer cell migration. However, the mechanism of how NDRG1 achieves this effect remains unclear. In this study, we implemented established and newly constructed NDRG1 overexpression and knockdown models using the DU145, HT29, and HCT116 cancer cell lines to investigate the molecular basis by which NDRG1 exerts its inhibitory effect on cell migration. Using these models, we demonstrated that NDRG1 overexpression inhibits cell migration by preventing actin-filament polymerization, stress fiber assembly and formation. In contrast, NDRG1 knockdown had the opposite effect. Moreover, we identified that NDRG1 inhibited an important regulatory pathway mediated by the Rho-associated, coiled-coil containing protein kinase 1 (ROCK1)/phosphorylated myosin light chain 2 (pMLC2) pathway that modulates stress fiber assembly. The phosphorylation of MLC2 is a key process in inducing stress fiber contraction, and this was shown to be markedly decreased or increased by NDRG1 overexpression or knockdown, respectively. The mechanism involved in the inhibition of MLC2 phosphorylation by NDRG1 was mediated by a significant (P < 0.001) decrease in ROCK1 expression that is a key kinase involved in MLC2 phosphorylation. Considering that NDRG1 is up-regulated after cellular iron depletion, novel thiosemicarbazone iron chelators (e.g., di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone) were demonstrated to inhibit ROCK1/pMLC2-modulated actin-filament polymerization, stress fiber assembly, and formation via a mechanism involving NDRG1. These results highlight the role of the ROCK1/pMLC2 pathway in the NDRG1-mediated antimetastatic signaling network and the therapeutic potential of iron chelators at inhibiting metastasis.

Is S-nitrosocysteine a true surrogate for nitric oxide?

S-Nitrosothiol (RSNO) formation is one manner by which nitric oxide (•NO) exerts its biological effects. There are several proposed mechanisms of formation of RSNO in vivo: auto-oxidation of •NO, transnitrosation, oxidative nitrosylation, and from dinitrosyliron complexes (DNIC). Both free •NO, generated by •NO donors, and S-nitrosocysteine (CysNO) are widely used to study •NO biology and signaling, including protein S-nitrosation. It is assumed that the cellular effects of both compounds are analogous and indicative of in vivo •NO biology. A quantitative comparison was made of formation of DNIC and RSNO, the major •NO-derived cellular products. In RAW 264.7 cells, both •NO and CysNO were metabolized, leading to rapid intracellular RSNO and DNIC formation. DNIC were the dominant products formed from physiologic •NO concentrations, however, and RSNO were the major product from CysNO treatment. Chelatable iron was necessary for DNIC assembly from either •NO or CysNO, but not for RSNO formation. These profound differences in RSNO and DNIC formation from •NO and CysNO question the use of CysNO as a surrogate for physiologic •NO. Researchers designing experiments intended to elucidate the biological signaling mechanisms of •NO should be aware of these differences and should consider the biological relevance of the use of exogenous CysNO.

Decreased levels of nitric oxide production and nitric oxide synthase-2 expression are associated with the development and metastasis of hepatocellular carcinoma

Many studies have demonstrated the function of nitric oxide (NO) or nitric oxide synthase-2 (NOS-2) in cancer as pro-neoplastic or anti-neoplastic effectors, but the role of NO and NOS-2 in hepatocellular carcinoma (HCC) remains unclear. The aim of this study was to investigate the levels of NO production and NOS-2 expression in HCC and adjacent non-tumor liver tissues and to clarify whether the levels of NO/NOS-2 are related to the clinicopathological features of HCC. The levels of NO production were examined in tumor and adjacent non-tumor liver tissues of 30 patients with HCC. The expression of NOS-2 was detected by real-time polymerase chain reaction (RT-PCR) and immunohistochemical analysis in HCC and/or adjacent non-tumor liver tissues. Mutant p53 and proliferating cell nuclear antigen (PCNA) were also immunohistochemically investigated in liver tissues. The levels of NO in HCC were significantly lower compared to adjacent non-tumor liver tissues (P<0.001). The relative mRNA and protein expression levels of NOS-2 in HCC were also significantly lower compared to adjacent non-tumor liver tissues (P<0.01 for both). We found that the levels of NO in patients suffering from HCC metastasis were lower compared to those without metastasis (P<0.05) and NOS-2 expression was correlated with tumor diameter (P<0.05) and metastasis (P<0.05). In addition, mutant p53 protein was expressed in the majority of HCC samples and the proliferation rate of HCC was significantly higher than that of adjacent non-tumor liver tissues. These data indicate that decreased levels of NO/NOS-2 may partially contribute to overexpression of the mutant p53 protein and excessive proliferation; this may be a potential mechanism in the development and progression of HCC.

Heparin inhibits Hepatocyte Growth Factor induced motility and invasion of hepatocellular carcinoma cells through early growth response protein 1

The Hepatocyte Growth Factor (HGF)/c-Met signaling pathway regulates hepatocyte proliferation, and pathway aberrations are implicated in the invasive and metastatic behaviors of hepatocellular carcinoma (HCC). In addition to c-Met, heparin acts as a co-receptor to modulate pathway activity. Recently, anti-metastatic and anti-cancer effects of heparin have been reported. However, the role of heparin in the regulation of HGF signaling remains controversial and the effects of heparin on HGF-induced biological responses during hepatocarcinogenesis is not yet defined. In this study we determined the effects of heparin on HGF-induced activities of HCC cells and the underlying molecular mechanisms. Here, we report for the first time that heparin inhibits HGF-induced adhesion, motility and invasion of HCC cells. In addition, heparin reduced HGF-induced activation of c-Met and MAPK in a dose-dependent manner, as well as decreased transcriptional activation and expression of Early growth response factor 1 (Egr1). HGF-induced MMP-2 and MMP-9 activation, and MT1-MMP expression, also were inhibited by heparin. Stable knockdown of Egr1 caused a significant decrease in HGF-induced invasion, as well as the activation and expression of MMPs. Parallel to these findings, the overexpression of Egr1 increased the invasiveness of HCC cells. Our results suggest that Egr1 activates HGF-induced cell invasion through the regulation of MMPs in HCC cells and heparin inhibits HGF-induced cellular invasion via the downregulation of Egr1. Therefore, heparin treatment might be a therapeutic approach to inhibit invasion and metastasis of HCC, especially for patients with active HGF/c-Met signaling.

Transcriptome and Coexpression Network Analysis of the Human Glioma Cell Line Hs683 Exposed to Candoxin

OBJECTIVE: Gliomas are the most common primary tumours of the central nervous system. Snake venom, such as candoxin (CDX) isolated from Bungarus candidus, inhibits glioma cell proliferation. This study explored the gene regulation profile of CDX-treated human glioma Hs683 cells. METHODS: Using microarray technology and bioinformatics analyses the underlying molecular mechanism of action of CDX was evaluated by constructing gene regulation and protein—protein interaction coexpression networks. RESULTS: CDX treatment induced a large number of related genes at the transcriptional level. The MYC gene (v-myc myelocytomatosis viral oncogene homologue [avian]) had a key role in the response of Hs683 cells to CDX treatment. Activation of MYC upregulated NDRG1 (N-myc downstream regulated 1), WNT10B (wingless-type mouse mammary tumour virus integration site family, member 10B), CASP9 (caspase 9, apoptosis-related cysteine peptidase) and CDKN2A (cyclin-dependent kinase inhibitor 2A), and downregulated ID3 (inhibitor of DNA binding 3, dominant negative helix—loop—helix protein) and SLC1A4 (solute carrier family 1 [glutamate/neutral amino acid transporter], member 4). In addition, a subnetwork was constructed among SPP1 (secreted phosphoprotein 1), SDC1 (syndecan 1) and CD44 based on protein—protein interactions, and these genes were predicted to be involved in glioma cell invasion. CONCLUSION: These findings might provide novel therapeutic targets for glioma chemotherapy.

Nitrogen monoxide (NO) storage and transport by dinitrosyl-dithiol-iron complexes: long-lived NO that is trafficked by interacting proteins

Nitrogen monoxide (NO) markedly affects intracellular iron metabolism, and recent studies have shown that molecules traditionally involved in drug resistance, namely GST and MRP1 (multidrug resistance-associated protein 1), are critical molecular players in this process. This is mediated by interaction of these proteins with dinitrosyl-dithiol-iron complexes (Watts, R. N., Hawkins, C., Ponka, P., and Richardson, D. R. (2006) Proc. Natl. Acad. Sci. U.S.A. 103, 7670-7675; Lok, H. C., Suryo Rahmanto, Y., Hawkins, C. L., Kalinowski, D. S., Morrow, C. S., Townsend, A. J., Ponka, P., and Richardson, D. R. (2012) J. Biol. Chem. 287, 607-618). These complexes are bioavailable, have a markedly longer half-life compared with free NO, and form in cells after an interaction between iron, NO, and glutathione. The generation of dinitrosyl-dithiol-iron complexes acts as a common currency for NO transport and storage by MRP1 and GST P1-1, respectively. Understanding the biological trafficking mechanisms involved in the metabolism of NO is vital for elucidating its many roles in cellular signaling and cytotoxicity and for development of new therapeutic targets.