NDRG1 promotes growth of hepatocellular carcinoma cells by directly interacting with GSK-3β and Nur77 to prevent β-catenin degradation

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.

Nur77 inhibition of β-catenin expression mediates Hepatoblastoma progression and enhances cisplatin's therapeutic effect

Hepatoblastoma (HB) is the most common malignant tumor in children under 5 years old, but its pathogenesis remains unclear. Nur77 has been reported to be an important regulator for cancer progression in various cancer types. This study found that Nur77 was downregulated in HB tumors, compared with paracancer tissue. Knockout or overexpression of Nur77 in HB tumor cell line HepG2 and HuH6 could significantly enhance or inhibit the proliferation, migration and invasion of tumor cells both in vitro and in vivo. Further studies illustrated that Nur77 regulated the proliferation of tumor cells by affecting the expression of β-catenin. Nur77 agonist Csn-B effectively enhanced the therapeutic effect of cisplatin on HB tumors both in vitro and in vivo. This study confirms that Nur77 may act as an oncogene in HB tumors and mediate the progression of HB by inhibiting the expression of β-catenin, which provides a new targeted therapy for the clinical treatment of HB patients; meanwhile, the combination of Nur77 agonist and cisplatin treatment may improve the chemotherapeutic efficacy of HB patients, which provides a new idea for the improvement of the clinical prognosis of HB patients.

CircSSBP2 acts as a MiR-2400 sponge to promote intramuscular preadipocyte proliferation by regulating NDRG1

Intramuscular fat (IMF) is a critical factor in beef quality. IMF is mainly distributed between muscle fibres and its accumulation can affect the marbling and meat quality of beef. IMF formation and deposition is a complex process and in recent years a group of non-coding RNAs (ncRNAs), known as circRNAs, have been discovered to play an important role in regulating intramuscular fat deposition. CircRNAs form a covalent loop structure after reverse splicing of precursor mRNAs. They can act by adsorbing miRNAs, thereby reducing their repressive effects on downstream target genes. Based on high-throughput sequencing of circRNAs in intramuscular fat of Qinchuan and Japanese black cattle, we identified a novel circSSBP2 that is differentially expressed between the two species and associated with adipogenesis. We show that circSSBP2 knockdown promotes bovine intramuscular preadipocyte proliferation, whereas overexpression inhibits bovine intramuscular preadipocyte proliferation. We also show that circSSBP2 can act as a molecular sponge for miR-2400 and that miR-2400 overexpression promotes bovine intramuscular preadipocyte proliferation. Furthermore, N-myc downstream-regulated gene 1 (NDRG1) was identified as a direct target gene of miR-2400, and NDRG1 interference promoted the proliferation of bovine intramuscular preadipocytes. In conclusion, our results suggest that circSSBP2 inhibits the proliferation of bovine intramuscular preadipocytes by regulating the miR-2400/NDRG1 axis.

Nur77 alleviates cardiac fibrosis by upregulating GSK-3β transcription during aging

Cardiac fibrosis is associated with aging, for which no targeted therapies are available. With aging, the levels of nerve growth factor-induced gene B (Nur77) are reduced during cardiac remodelling; however, its role in cardiac fibrosis in aging remains unclear. Here, we found that Nur77 knockout increased cardiac structure abnormalities, systolic and diastolic dysfunction, cardiac hypertrophy, and fibrotic marker expression in 15-month-old mice. Furthermore, Nur77 deficiency induced collagen type I (Col-1) and α-smooth muscle actin overproduction in transforming growth factor beta (TGF-β) treated H9c2 cells, whereas Nur77 overexpression attenuated this effect. Nur77 deficiency in vivo and in vitro downregulated glycogen synthase kinase (GSK)-3β expression and increased β-catenin activity, while its overexpression increased GSK-3β expression. GSK-3β knockdown counteracted the anti-fibrotic effect of Nur77 on TGF-β-treated H9c2 cells. Chromatin immunoprecipitation and luciferase reporter assay results suggested GSK-3β as the direct target of Nur77. Our findings suggest that Nur77 directly initiates GSK-3β transcription and age-related cardiac fibrosis partly through the GSK-3β/β-catenin pathway. This study proposes a novel mechanism for Nur77 regulating cardiac fibrosis and suggests Nur77 as a target for the prevention and treatment of aging-associated cardiac fibrosis and heart failure.

The Myc Family and the Metastasis Suppressor NDRG1: Targeting Key Molecular Interactions with Innovative Therapeutics

Cancer is a leading cause of death worldwide, resulting in ∼10 million deaths in 2020. Major oncogenic effectors are the Myc proto-oncogene family, which consists of three members including c-Myc, N-Myc, and L-Myc. As a pertinent example of the role of the Myc family in tumorigenesis, amplification of MYCN in childhood neuroblastoma strongly correlates with poor patient prognosis. Complexes between Myc oncoproteins and their partners such as hypoxia-inducible factor-1α and Myc-associated protein X (MAX) result in proliferation arrest and pro-proliferative effects, respectively. Interactions with other proteins are also important for N-Myc activity. For instance, the enhancer of zest homolog 2 (EZH2) binds directly to N-Myc to stabilize it by acting as a competitor against the ubiquitin ligase, SCFFBXW7, which prevents proteasomal degradation. Heat shock protein 90 may also be involved in N-Myc stabilization since it binds to EZH2 and prevents its degradation. N-Myc downstream-regulated gene 1 (NDRG1) is downregulated by N-Myc and participates in the regulation of cellular proliferation via associating with other proteins, such as glycogen synthase kinase-3β and low-density lipoprotein receptor-related protein 6. These molecular interactions provide a better understanding of the biologic roles of N-Myc and NDRG1, which can be potentially used as therapeutic targets. In addition to directly targeting these proteins, disrupting their key interactions may also be a promising strategy for anti-cancer drug development. This review examines the interactions between the Myc proteins and other molecules, with a special focus on the relationship between N-Myc and NDRG1 and possible therapeutic interventions. SIGNIFICANCE STATEMENT: Neuroblastoma is one of the most common childhood solid tumors, with a dismal five-year survival rate. This problem makes it imperative to discover new and more effective therapeutics. The molecular interactions between major oncogenic drivers of the Myc family and other key proteins; for example, the metastasis suppressor, NDRG1, may potentially be used as targets for anti-neuroblastoma drug development. In addition to directly targeting these proteins, disrupting their key molecular interactions may also be promising for drug discovery.

Construction and validation of 3-genes hypoxia-related prognostic signature to predict the prognosis and therapeutic response of hepatocellular carcinoma patients

BACKGROUND

Previous studies have shown that the hypoxia microenvironment significantly impacted tumor progression. However, the clinical prognostic value of hypoxia-related risk signatures and their effects on the tumor microenvironment (TME) in hepatocellular carcinoma (HCC) remains hazy. This study aimed to conduct novel hypoxia-related prognostic signatures and improve HCC prognosis and treatment.

METHODS

Differentially expressed hypoxia-related genes (HGs) were identified with the gene set enrichment analysis (GSEA). Univariate Cox regression was utilized to generate the tumor hypoxia-related prognostic signature, which consists of 3 HGs, based on the least absolute shrinkage and selection operator (LASSO) algorithm. Then the risk score for each patient was performed. The prognostic signature's independent prognostic usefulness was confirmed, and systematic analyses were done on the relationships between the prognostic signature and immune cell infiltration, somatic cell mutation, medication sensitivity, and putative immunological checkpoints.

RESULTS

A prognostic risk model of four HGs (FDPS, SRM, and NDRG1) was constructed and validated in the training, testing, and validation datasets. To determine the model's performance in patients with HCC, Kaplan-Meier curves and time-dependent receiver operating characteristic (ROC) curves analysis was implemented. According to immune infiltration analysis, the high-risk group had a significant infiltration of CD4+ T cells, M0 macrophages, and dendritic cells (DCs) than those of the low-risk subtype. In addition, the presence of TP53 mutations in the high-risk group was higher, in which LY317615, PF-562271, Pyrimethamine, and Sunitinib were more sensitive. The CD86, LAIR1, and LGALS9 expression were upregulated in the high-risk subtype.

CONCLUSIONS

The hypoxia-related risk signature is a reliable predictive model for better clinical management of HCC patients and offers clinicians a holistic viewpoint when determining the diagnosis and course of HCC treatment.

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.

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.

TGFβ Governs the Pleiotropic Activity of NDRG1 in Triple-Negative Breast Cancer Progression

In triple-negative breast cancer (TNBC), the pleiotropic NDRG1 (N-Myc downstream regulated gene 1) promotes progression and worse survival, yet contradictory results were documented, and the mechanisms remain unknown. Phosphorylation and localization could drive NDRG1 pleiotropy, nonetheless, their role in TNBC progression and clinical outcome was not investigated. We found enhanced p-NDRG1 (Thr346) by TGFβ1 and explored whether it drives NDRG1 pleiotropy and TNBC progression. In tissue microarrays of 81 TNBC patients, we identified that staining and localization of NDRG1 and p-NDRG1 (Thr346) are biomarkers and risk factors associated with shorter overall survival. We found that TGFβ1 leads NDRG1, downstream of GSK3β, and upstream of NF-κB, to differentially regulate migration, invasion, epithelial-mesenchymal transition, tumor initiation, and maintenance of different populations of cancer stem cells (CSCs), depending on the progression stage of tumor cells, and the combination of TGFβ and GSK3β inhibitors impaired CSCs. The present study revealed the striking importance to assess both total NDRG1 and p-NDRG1 (Thr346) positiveness and subcellular localization to evaluate patient prognosis and their stratification. NDRG1 pleiotropy is driven by TGFβ to differentially promote metastasis and/or maintenance of CSCs at different stages of tumor progression, which could be abrogated by the inhibition of TGFβ and GSK3β.

Therapeutic potential of NR4A1 in cancer: Focus on metabolism

Metabolic reprogramming is a vital hallmark of cancer, and it provides the necessary energy and biological materials to support the continuous proliferation and survival of tumor cells. NR4A1 is belonging to nuclear subfamily 4 (NR4A) receptors. NR4A1 plays diverse roles in many tumors, including melanoma, colorectal cancer, breast cancer, and hepatocellular cancer, to regulate cell growth, apoptosis, metastasis. Recent reports shown that NR4A1 exhibits unique metabolic regulating effects in cancers. This receptor was first found to mediate glycolysis via key enzymes glucose transporters (GLUTs), hexokinase 2 (HK2), fructose phosphate kinase (PFK), and pyruvate kinase (PK). Then its functions extended to fatty acid synthesis by modulating CD36, fatty acid-binding proteins (FABPs), sterol regulatory element-binding protein 1 (SREBP1), glutamine by Myc, mammalian target of rapamycin (mTOR), and hypoxia-inducible factors alpha (HIF-1α), respectively. In addition, NR4A1 is involving in amino acid metabolism and tumor immunity by metabolic processes. More and more NR4A1 ligands are found to participate in tumor metabolic reprogramming, suggesting that regulating NR4A1 by novel ligands is a promising approach to alter metabolism signaling pathways in cancer therapy. Basic on this, this review highlighted the diverse metabolic roles of NR4A1 in cancers, which provides vital references for the clinical application.

Multifaceted and Intricate Oncogenic Mechanisms of NDRG1 in Head and Neck Cancer Depend on Its C-Terminal 3R-Motif

N-Myc downstream-regulated 1 (NDRG1) has inconsistent oncogenic functions in various cancers. We surveyed and characterized the role of NDRG1 in head and neck cancer (HNC). Cellular methods included spheroid cell formation, clonogenic survival, cell viability, and Matrigel invasion assays. Molecular techniques included transcriptomic profiling, RT-qPCR, immunoblotting, in vitro phosphorylation, immunofluorescent staining, and confocal microscopy. Prognostic significance was assessed by Kaplan–Meier analysis. NDRG1 participated in diverse oncogenic functions in HNC cells, mainly stress response and cell motility. Notably, NDRG1 contributed to spheroid cell growth, radio-chemoresistance, and upregulation of stemness-related markers (CD44 and Twist1). NDRG1 facilitated cell migration and invasion, and was associated with modulation of the extracellular matrix molecules (fibronectin, vimentin). Characterizing the 3R-motif in NDRG1 revealed its mechanism in the differential regulation of the phenotypes. The 3R-motif displayed minimal effect on cancer stemness but was crucial for cell motility. Phosphorylating the motif by GSK3b at serine residues led to its nuclear translocation to promote motility. Clinical analyses supported the oncogenic function of NDRG1, which was overexpressed in HNC and associated with poor prognosis. The data elucidate the multifaceted and intricate mechanisms of NDRG1 in HNC. NDRG1 may be a prognostic indicator or therapeutic target for refractory HNC.

Identification of an immune-related RNA-binding protein signature to predict survival and targeted therapy responses in liver cancer

RNA-binding proteins (RBPs) play crucial roles in multiple cancers. However, very few RBPs and their association with immune genes have been systematically studied in liver cancer (LC). We aimed to identify an immune-related RBP signature to predict the survival of LC patients. Bioinformatics methods were used to identify differentially expressed, immune-related, and prognostic RBPs and to develop an immune-related RBP signature based on data from the Cancer Genome Atlas (TCGA) cohort. We obtained eight differentially expressed, immune-related, and prognostic RBPs to construct a risk signature. The signature could effectively distinguish between high- and low-risk patients, and its predictive capacity was validated in the International Cancer Genomics Consortium (ICGC) cohort. We speculated that the high-risk group was more sensitive to targeted therapy. The immune-related RBP signature is an independent prognostic biomarker for LC patients and can expand the application of targeted therapy through patient stratification.

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.

GSK-3 in liver diseases: Friend or foe?

Liver diseases, including hepatitis due to hepatitis B or C virus infection, non-alcoholic fatty liver disease, and hepatocellular carcinoma pose major challenges for overall health due to limited curative treatment options. Thus, there is an urgent need to develop new therapeutic strategies for the treatment of these diseases. A better understanding of the signaling pathways involved in the pathogenesis of liver diseases can help to improve the efficacy of emerging therapies, mainly based on pharmacological approaches, which influence one or more specific molecules involved in key signal transduction pathways. These emerging therapies are very promising for the prevention and treatment of liver diseases. One promising druggable molecular target is the multifunctional serine/threonine kinase, glycogen synthase kinase 3 (GSK-3). In this review, we discuss conditions in which GSK-3 is implicated in liver diseases. In addition, we explore newly emerging drugs that target GSK-3β, as well as their potential use in and impact on the management of liver diseases.

Hypoxia-induced elevated NDRG1 mediates apoptosis through reprograming mitochondrial fission in HCC

Hypoxia, as a form of stress, plays a critical role in oncogenesis, including metabolic reprogramming. Mitochondrial, the centers of energy production, re-balance mitochondria dynamic to maintain cell survival during high levels of environmental stresses. NDRG1 is a hypoxia-inducible protein that is involved in various human cancers, including HCC. However, little is known about whether NDRG1 participants in the quality control of mitochondrial in times of stress. Here, we firstly showed that how NDRG1 exerted its role through mediating mitochondrial dynamic in HCC cells under hypoxia. Initially, we identified that NDRG1 expression varies with oxygen content. NDRG1 silencing notably induced cell apoptosis under hypoxia, while no obviously change of wildtype cells in hypoxia compared with that in normoxia. Further analysis revealed that NDRG1 silencing in HCC cells led to increase of pro apoptotic protein BAX and decrease in anti-apoptotic proteins Bcl-2 and Bclx, which meant mitochondrial damage were induced. In the analysis of mitochondria, we found that more released cytochrome c located in cytosolic with NDRG1 knockdown in hypoxia, which may be due to mitochondria division. And the following experiment proved that more fragmented mitochondria were presented in NDRG1 silencing cells, as well as destroyed mitochondrial membrane potential with evidence by JC-1 was verified. Moreover, these trends could be reversed by Mdivi1. Further research showed that NDRG1 silencing disrupt hypoxia-enhanced aerobic glycolysis through effectively decreased glucose uptake, lactate output and ECAR value. In sum, we provide the first direct evidence that NDRG1-driven change in mitochondrial dynamics and aerobic glycolysis maintain cells survival in HCC during hypoxia.

High NDRG3 expression facilitates HCC metastasis by promoting nuclear translocation of β-catenin

NDRG1 has been reported to exert pivotal roles in tumor progression and metastasis via Wnt/β-catenin signaling pathway. However, little is known about the role of NDRG3 in hepatocarcinogenesis despite its classification in the same subfamily of NDRG1. The present study was aimed to characterize the expression pattern and understand the biological roles of NDRG3 in hepatocarcinogenesis, as a means to exploit its therapeutic potential. It was observed that NDRG3 was up-regulated in HCC tissues and higher NDRG3 expression was associated with significantly shorter overall survival. Furthermore, a lower level of NDRG3 exhibited marked positive correlation with metastasis-free survival. In vitro and in vivo experiments revealed that knock-down of NDRG3 inhibits HCC metastasis and angiogenesis. We further demonstrated that activation of WNT/β-catenin signaling and enhanced CSC-like properties were responsible for NDRG3- mediated promoting effect on HCC. In conclusion, the principal findings demonstrated that high NDRG3 expression facilitates HCC metastasis via regulating the turnover of β-catenin, as well as provides a potential therapeutic target for future therapeutic interventions.

Merkel Cell Polyomavirus Downregulates N-myc Downstream-Regulated Gene 1, Leading to Cellular Proliferation and Migration

Merkel cell polyomavirus (MCPyV) is the first human polyomavirus etiologically associated with Merkel cell carcinoma (MCC), a rare and aggressive form of skin cancer. Similar to other polyomaviruses, MCPyV encodes early T antigen genes, viral oncogenes required for MCC tumor growth. To identify the unique oncogenic properties of MCPyV, we analyzed the gene expression profiles in human spontaneously immortalized keratinocytes (NIKs) expressing the early genes from six distinct human polyomaviruses (PyVs), including MCPyV. A comparison of the gene expression profiles revealed 28 genes specifically deregulated by MCPyV. In particular, the MCPyV early gene downregulated the expression of the tumor suppressor gene N-myc downstream-regulated gene 1 (NDRG1) in MCPyV gene-expressing NIKs and hTERT-MCPyV gene-expressing human keratinocytes (HK) compared to their expression in the controls. In MCPyV-positive MCC cells, the expression of NDRG1 was downregulated by the MCPyV early gene, as T antigen knockdown rescued the level of NDRG1. In addition, NDRG1 overexpression in hTERT-MCPyV gene-expressing HK or MCC cells resulted in a decrease in the number of cells in S phase and cell proliferation inhibition. Moreover, a decrease in wound healing capacity in hTERT-MCPyV gene-expressing HK was observed. Further analysis revealed that NDRG1 exerts its biological effect in Merkel cell lines by regulating the expression of the cyclin-dependent kinase 2 (CDK2) and cyclin D1 proteins. Overall, NDRG1 plays an important role in MCPyV-induced cellular proliferation.IMPORTANCE Merkel cell carcinoma was first described in 1972 as a neuroendocrine tumor of skin, most cases of which were reported in 2008 to be caused by a PyV named Merkel cell polyomavirus (MCPyV), the first PyV linked to human cancer. Thereafter, numerous studies have been conducted to understand the etiology of this virus-induced carcinogenesis. However, it is still a new field, and much work is needed to understand the molecular pathogenesis of MCC. In the current work, we sought to identify the host genes specifically deregulated by MCPyV, as opposed to other PyVs, in order to better understand the relevance of the genes analyzed on the biological impact and progression of the disease. These findings open newer avenues for targeted drug therapies, thereby providing hope for the management of patients suffering from this highly aggressive cancer.

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.

Linc00173 promotes chemoresistance and progression of small cell lung cancer by sponging miR-218 to regulate Etk expression

The functional effects of long noncoding RNAs (lncRNAs) in cancer have been widely recognized. However, there is little research on SCLC-related lncRNAs. Here, long intergenic nonprotein coding RNA 173 (Linc00173) was first shown to be involved in chemoresistance and progression of small-cell lung cancer (SCLC). We found that Linc00173 was highly expressed in SCLC chemoresistant cell lines, and promoted SCLC cells chemoresistance, proliferation, and migration-invasion. Animal studies validated that Linc00173 induced tumor chemoresistance and growth of SCLC in vivo. Moreover, Linc00173 upregulated Etk through functioning as a competitive endogenous RNA (ceRNA) by "sponging" miRNA-218 and led to the upregulation of GSKIP and NDRG1, resulting in the translocation of β-catenin. Importantly, expression analysis revealed that both Linc00173 and Etk were upregulated in SCLC patient samples and exhibiting positive Linc00173/Etk correlation. High expression of Linc00173 closely correlated with chemoresistance, extensive stage, and shorter survival in SCLC patients. Collectively, our study illustrated a Linc00173-mediated process that facilitated chemoresistance and progression in SCLC, which might provide treatment strategy against SCLC.

Targeting DNAJB9, a novel ER luminal co-chaperone, to rescue ΔF508-CFTR

The molecular mechanism of Endoplasmic Reticulum-associated degradation (ERAD) of Cystic fibrosis transmembrane-conductance regulator (CFTR) is largely unknown. Particularly, it is unknown what ER luminal factor(s) are involved in ERAD. Herein, we used ProtoArray to identify an ER luminal co-chaperone, DNAJB9, which can directly interact with CFTR. For both WT- and ΔF508 (deletion of phenylalanine at position 508, the most common CF-causing mutant)-CFTR, knockdown of DNAJB9 by siRNA increased their expression levels on the cell surface and, consequently, upregulated their function. Furthermore, genetic ablation of DNAJB9 in WT mice increased CFTR expression and enhanced CFTR-dependent fluid secretion in enteroids. Importantly, DNAJB9 deficiency upregulated enteroids' fluid secretion in CF mice (homozygous for ΔF508), and silencing one allele of DNAJB9 is sufficient to rescue ΔF508-CFTR in vitro and in vivo, suggesting that DNAJB9 may be a rate-limiting factor in CFTR ERAD pathway. Our studies identified the first ER luminal co-chaperone involved in CFTR ERAD, and DNAJB9 could be a novel therapeutic target for CF.

Upregulation of NDRG1 predicts poor outcome and facilitates disease progression by influencing the EMT process in bladder cancer

N-myc downstream regulated gene 1 (NDRG1) is an intracellular protein involved in cell differentiation and was recently reported to exert various effects in several cancers. However, its expression and role in bladder cancer remain unclear. Our study enrolled 100 bladder cancer patients to detect NDRG1 expression in tumour tissues by immunohistochemistry. Correlations between NDRG1 expression and clinical factors were analysed. An NDRG1 overexpression plasmid and NDRG1 siRNAs were transfected into bladder cancer cell lines. Cell biological behaviours were assessed by CCK-8, flow cytometry, wound healing and Transwell assays. Additionally, the influence of NDRG1 on epithelial-mesenchymal transition (EMT) was investigated by western blotting and real-time PCR. NDRG1 expression in urine from bladder cancer patients was examined by ELISA. NDRG1 protein levels were significantly increased in bladder cancer patients and correlated with tumour stage (p = 0.025), lymph node metastasis (p = 0.034) and overall survival (p = 0.016). Patients with high NDRG1 expression had poorer outcomes than those with low NDRG1 expression. NDRG1 overexpression was associated with increased cell proliferation, migration, and invasion and decreased apoptotic cell numbers; NDRG1 knockdown resulted in the inverse effects. Moreover, upregulated NDRG1 expression was associated with downregulated Cytokeratin 7 and Claudin-1 expression and upregulated N-cad, β-catenin and slug expression. Downregulated NDRG1 expression was associated with the inverse effects. Urine protein levels could distinguish bladder cancer patients from healthy controls, with an area under the curve of 0.909. NDRG1 promoted EMT in bladder cancer and could be an effective diagnostic and prognostic biomarker in bladder cancer patients.

The prognostic value of decreased NDRG1 expression in patients with digestive system cancers: A meta-analysis

BACKGROUND

Digestive system cancers are recognized as associated with high morbidity and mortality. It is generally accepted that N-myc downstream-regulated gene 1 (NDRG1) is aberrantly overexpressed or downregulated in digestive system cancers, and its prognostic value remains controversial. Accordingly, we herein conducted a meta-analysis to explore whether NDRG1 expression is correlated with overall survival (OS) and clinicopathological characteristics of patients with digestive system cancers.

METHODS

We systematically searched PubMed, EMBASE, and Web of Science for eligible studies up to June 6, 2017. In all, 19 publications with 21 studies, were included.

RESULTS

The pooled results showed that low NDRG1 expression was significantly associated with worse OS in colorectal cancer (pooled HR = 1.67, 95% CI: 1.22-2.28, P < .001) and pancreatic cancer (pooled HR = 1.87, 95% CI: 1-3.5, P < .0001). Moreover, the relationships between low NDRG1 expression and higher OS ratio of patients with liver cancer (pooled HR = 0.44, 95% CI: 0.32-0.62, P = .009) and gallbladder cancer (pooled HR = 0.56, 95% CI: 0.23-1.38, P = .01) were observed. Nevertheless, no significant association was observed between low NDRG1 expression and OS in gastric cancer (pooled HR = 0.81, 95% CI: 0.45-1.43, P = .46) or esophageal cancer (pooled HR = 0.76, 95% CI: 0.26-2.24, P = .62).

CONCLUSION

The prognostic significance of NDRG1 expression varies according to cancer type in patients with DSCs. Considering that several limitations existed in this meta-analysis, more studies are required to further assess the prognostic value of NDRG1 expression in patients with DSCs and relevant mechanisms.

The novel dithiocarbamate, DpdtC suppresses HER2-overexpressed cancer cells by up-regulating NDRG1 via inactivation of HER2-ERK 1/2 signaling

Dithiocarbamate has been tested for its effective anti-tumor activity, but the underlying mechanism remains unclear. We previously prepared a novel diththiocarbamate derivative, DpdtC with an ability of catalase inhibition. Here, we for the first time investigated the growth inhibition effects of DpdtC on HER2-amplified cancer cells and elucidated its mechanism of action. Results showed that DpdtC exerted the potent anti-tumor effects against HER2-overexpressed SK-OV-3 and SK-BR-3 cells, especially on SK-OV-3 cells with a higher NDRG1 level, which was also confirmed in the SK-OV-3 xenograft model. Interestingly, we observed that NDRG1 was up-regulated, while membrane expression of HER2 was regressed in SK-OV-3 cells upon DpdtC treatment. In agreement, silencing endogenous NDRG1 also increased the expression of HER2 in SK-OV-3 cells, while overexpressing NDRG1 decreased HER2 expression in SK-BR-3 cells. Furthermore, our results showed the formation of the EGFR/HER2 heterodimer was attenuated and phosphorylation of ERK1/2 was inhibited in SK-OV-3 cells when treated with DpdtC. Collectively, these observations demonstrated that NDRG1 plays an important role in mediating the inhibition effects of DpdtC in HER2-overexpressed cancer cells via selective targeting of the HER2-ERK1/2 pathway. Hence, our investigation suggests that up-regulation of NDRG1 by DpdtC is a promising therapeutic approach in HER2-overexpressed cancers.

Glycogen synthase kinase-3β inhibition promotes lysosome-dependent degradation of c-FLIPL in hepatocellular carcinoma

Glycogen synthase kinase-3β (GSK-3β) is a ubiquitously expressed serine/threonine kinase involved in a variety of functions ranging from the control of glycogen metabolism to transcriptional regulation. We recently demonstrated that GSK-3β inhibition triggered ASK1-JNK-dependent apoptosis in human hepatocellular carcinoma (HCC) cells. However, the comprehensive picture of downstream GSK-3β-regulated pathways/functions remains elusive. In this study, we showed that GSK-3β was aberrantly activated in HCC. Pharmacological inhibition and genetic depletion of GSK-3β suppressed the growth and induced caspase-dependent apoptosis in HCC cells. In addition, GSK-3β inhibition-induced apoptosis through downregulation of c-FLIP_L in HCC, which was caused by biogenesis of functional lysosomes and subsequently c-FLIP_L translocated to lysosome for degradation. This induction of the lysosome-dependent c-FLIP_L degradation was associated with nuclear translocation of transcription factor EB (TFEB), a master regulator of lysosomal biogenesis. Moreover, GSK-3β inhibition-induced TFEB translocation acts through activation of AMPK and subsequently suppression of mTOR activity. Thus our findings reveal a novel mechanism by which inhibition of GSK-3β promotes lysosome-dependent degradation of c-FLIP_L. Our study shows that GSK-3β may become a promising therapeutic target for HCC.

NDRG1 Downregulates ATF3 and Inhibits Cisplatin-Induced Cytotoxicity in Lung Cancer A549 Cells

N-myc downstream regulated gene 1 (NDRG1) plays a variety of roles in human cancers. Our previous studies showed that NDRG1 expression is elevated in non-small cell lung cancer and contributes to cancer growth. However, its function in apoptosis and chemoresistance in malignant tumors, including lung cancer, is not yet fully understood. In this study, we investigated the roles of NDRG1 in chemoresistance to cisplatin in lung cancer cells. We found that overexpression of NDRG1 significantly reduced cisplatin-induced cytotoxicity in lung cancer A549 cells, while overexpression of activating transcription factor 3 (ATF3), a stress-inducible gene found to be associated with apoptosis in some human cancers, significantly promoted cytotoxicity (P < 0.05). Further investigation showed that overexpression of NDRG1 significantly downregulated ATF3 and P53 expression in A549 cells, while overexpression of ATF3 significantly upregulated P53 expression (P < 0.05). In addition, cisplatin significantly upregulated ATF3, phospho-P53(ser46), and cleaved caspase 3 expression in lung cancer cells, but overexpression of NDRG1 in the presence of cisplatin reduced the level of these proteins elevated by cisplatin (P < 0.05). While, overexpression of ATF3 significantly promoted the cytoxicity induced by cisplatin in 1299 cells (p<0.05) (Figure 4), but overexpression of NDRG1 didn't regulate the cytoxicity induced by cisplatin (p>0.05). These results indicate that NDRG1 may contribute to cisplatin-resistance in lung cancer, possibly due to its function in the regulation of ATF3 expression.

Transforming Growth Factor β/NR4A1-Inducible Breast Cancer Cell Migration and Epithelial-to-Mesenchymal Transition Is p38α (Mitogen-Activated Protein Kinase 14) Dependent

Transforming growth factor β (TGF-β)-induced migration of triple-negative breast cancer (TNBC) cells is dependent on nuclear export of the orphan receptor NR4A1, which plays a role in proteasome-dependent degradation of SMAD7. In this study, we show that TGF-β induces p38α (mitogen-activated protein kinase 14 [MAPK14]), which in turn phosphorylates NR4A1, resulting in nuclear export of the receptor. TGF-β/p38α and NR4A1 also play essential roles in the induction of epithelial-to-mesenchymal transition (EMT) and induction of β-catenin in TNBC cells, and these TGF-β-induced responses and nuclear export of NR4A1 are blocked by NR4A1 antagonists, the p38 inhibitor SB202190, and kinase-dead [p38(KD)] and dominant-negative [p38(DN)] forms of p38α. Inhibition of NR4A1 nuclear export results in nuclear export of TGF-β-induced β-catenin, which then undergoes proteasome-dependent degradation. TGF-β-induced β-catenin also regulates NR4A1 expression through formation of the β-catenin-TCF-3/TCF-4/LEF-1 complex on the NR4A1 promoter. Thus, TGF-β-induced nuclear export of NR4A1 in TNBC cells plays an essential role in cell migration, SMAD7 degradation, EMT, and induction of β-catenin, and all of these pathways are inhibited by bis-indole-derived NR4A1 antagonists that inhibit nuclear export of the receptor and thereby block TGF-β-induced migration and EMT.

GSK-3β phosphorylation-dependent degradation of ZNF281 by β-TrCP2 suppresses colorectal cancer progression

Zinc finger protein 281 (ZNF281) has been recently shown to be critical for CRC progression. However, the immediate upstream regulators of ZNF281 remain unclear. Here we reported that the E3 ligase the β-transducin repeat-containing protein 2 (β-TrCP2) governs the ubiquitination and degradation of ZNF281. In human CRC specimens, endogenous β-TrCP2 were inversely correlated with ZNF281. Beta-TrCP2 reversed the phenotype of CRC cell with overexpressed ZNF281. Moreover, we found that glycogen synthase kinase 3β (GSK-3β), not GSK-α, could bind to and phosphorylate ZNF281 at one consensus motif (TSGEHS; phosphorylation site is shown in italics), which promotes the interaction of ZNF281 with β-TrCP2, not β-TrCP1, and leads to the subsequent ubiquitination and degradation of phosphorylated ZNF281. A mutant of ZNF281 (ZNF281-S638A) is much more stable than wild-type ZNF281 because ZNF281-S638A mutant abolishes the phosphorylation by GSK-3β and can not be ubiquitinated and degraded by β-TrCP2. Conversely, ZNF281 transcriptionally repressed the expression of β-TrCP2, indicating a negative feedback loop between ZNF281 and β-TrCP2 in CRC cells. These findings suggest that the turnover of ZNF281 by β-TrCP2 might provide a potentially novel treatment for patients with CRC.

Ndrg1 promotes adipocyte differentiation and sustains their function

Adipocytes play a central role in maintaining metabolic homeostasis in the body. Differentiation of adipocyte precursor cells requires the transcriptional activity of peroxisome proliferator-activated receptor-γ (Pparγ) and CCAAT/enhancer binding proteins (C/Ebps). Transcriptional activity is regulated by signaling modules activated by a plethora of hormones and nutrients. Mechanistic target of rapamacin complexes (mTORC) 1 and 2 are central for the coordination of hormonal and nutritional inputs in cells and are essential for adipogenesis. Serum glucocorticoid kinase 1 (Sgk1)-dependent phosphorylation of N-Myc downstream-regulated gene 1 (Ndrg1) is a hallmark of mTORC2 activation in cells. Moreover, Pparγ activation promotes Ndrg1 expression. However, the impact of Ndrg1 on adipocyte differentiation and function has not yet been defined. Here, we show that Ndrg1 expression and its Sgk1-dependent phosphorylation are induced during adipogenesis. Consistently, we demonstrate that Ndrg1 promotes adipocyte differentiation and function by inducing Pparγ expression. Additionally, our results indicate that Ndrg1 is required for C/Ebpα phosphorylation. Moreover, we found that Ndrg1 phosphorylation by Sgk1 promotes adipocyte formation. Taken together, we show that induction of Ndrg1 expression by Pparγ and its phosphorylation by Sgk1 kinase are required for the acquisition of adipocyte characteristics by precursor cells.

Pivotal roles of glycogen synthase-3 in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common cancers in the world, and represents the second most frequently cancer and third most common cause of death from cancer worldwide. At advanced stage, HCC is a highly aggressive tumor with a poor prognosis and with very limited response to common therapies. Therefore, there is still the need for new effective and well-tolerated therapeutic strategies. Molecular-targeted therapies hold promise for HCC treatment. One promising molecular target is the multifunctional serine/threonine kinase glycogen synthase kinase 3 (GSK-3). The roles of GSK-3β in HCC remain controversial, several studies suggested a possible role of GSK-3β as a tumor suppressor gene in HCC, whereas, other studies indicate that GSK-3β is a potential therapeutic target for this neoplasia. In this review, we will focus on the different roles that GSK-3 plays in HCC and its interaction with signaling pathways implicated in the pathogenesis of HCC, such as Insulin-like Growth Factor (IGF), Notch, Wnt/β-catenin, Hedgehog (HH), and TGF-β pathways. In addition, the pivotal roles of GSK3 in epithelial-mesenchymal transition (EMT), invasion and metastasis will be also discussed.

Quantitative proteomics reveal the anti-tumour mechanism of the carbohydrate recognition domain of Galectin-3 in Hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a serious threat to human health. The carbohydrate recognition domain of Galectin-3 (Gal3C) has been reported to be an anti-tumour molecule. In this study, we aim to explore effects of Gal3C in HCC and its possible molecular mechanism with quantitative proteomics approach. We found that rGal3C stimulation could inhibit cell viability, migration and invasion of HepG2. After rGal3C stimulating, 190 proteins were differentially expressed. Eighty up-regulated proteins located mainly in extracellular exosome and involved in cell adhesion and metabolism, and 110 down-regulated proteins located in mitochondria and extracellular exosome, and related to processes of metabolism and oxidation-reduction. Of the differentially expressed proteins, CLU, NDRG1, CD166, S100A11 and Galectin-1 were carcinoma-related proteins affected by rGal3C. Potential receptors of rGal3C were explored by an UV cross-linking capture strategy. We showed that rGal3C could induce dephosphorylating of FAK/SRC. Blocking of the FAK/SRC pathway resulted in down-regulation of NDRG1. Immunofluorescence suggested that rGal3C could disrupt integrin clustering. Our study provides valuable insight into the anti-tumour mechanism of rGal3C in HCC on a proteomics level and is the first to reveal the possible mechanism involving integrin/FAK/SRC pathway and NDRG1. These results provide useful guidance of developing new therapies for HCC.

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

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

Downregulation of the N-myc downstream regulated gene 1 is related to enhanced proliferation, invasion and migration of pancreatic cancer

The N-myc downstream regulated gene 1 (NDRG1) is differently expressed in human malignancies according to the tumor type. We investigated the expression of NDRG1 in pancreatic cancer tissues and cell lines as well as how it affects tumor growth, invasion and migration in pancreatic cancer cells. Experimental groups included NDRG1 overexpression and knockdown pancreatic cancer cell lines. Lentivirus-based empty vector transfected cells (NC group) were considered control groups. Proliferation, invasion and migration related proteins such as STAT3, MMPs, PTEN, PI3K/AKT were assessed by CCK-8, Transwell assay and western blotting. Efficient NDRG1 overexpression results in reduced cell proliferation, invasion and migration. Inversely, downregulation of NDRG1 promoted proliferation, invasion and migration. We also found NDRG1 could deactivate p-STAT3, PI3K, p-AKT, MMP2, MMP9 and activate PTEN. NDRG1 is a potential anti-oncogene. Its upregulation significantly decreases pancreatic cancer tumorigenesis, likely by inhibiting STAT3 and the PI3K/AKT signaling pathway.

Redox cycling metals: Pedaling their roles in metabolism and their use in the development of novel therapeutics

Essential metals, such as iron and copper, play a critical role in a plethora of cellular processes including cell growth and proliferation. However, concomitantly, excess of these metal ions in the body can have deleterious effects due to their ability to generate cytotoxic reactive oxygen species (ROS). Thus, the human body has evolved a very well-orchestrated metabolic system that keeps tight control on the levels of these metal ions. Considering their very high proliferation rate, cancer cells require a high abundance of these metals compared to their normal counterparts. Interestingly, new anti-cancer agents that take advantage of the sensitivity of cancer cells to metal sequestration and their susceptibility to ROS have been developed. These ligands can avidly bind metal ions to form redox active metal complexes, which lead to generation of cytotoxic ROS. Furthermore, these agents also act as potent metastasis suppressors due to their ability to up-regulate the metastasis suppressor gene, N-myc downstream regulated gene 1. This review discusses the importance of iron and copper in the metabolism and progression of cancer, how they can be exploited to target tumors and the clinical translation of novel anti-cancer chemotherapeutics.