Nfe2l3 (Nrf3) deficiency predisposes mice to T-cell lymphoblastic lymphoma. Blood. 2011;117:2005-2008. [PMID: 21148084 DOI: 10.1182/blood-2010-02-271460]

New insight into the CNC-bZIP member, NFE2L3, in human diseases

Nuclear factor erythroid 2 (NF-E2)-related factor 3 (NFE2L3), a member of the CNC-bZIP subfamily and widely found in a variety of tissues, is an endoplasmic reticulum (ER) membrane-anchored transcription factor that can be released from the ER and moved into the nucleus to bind the promoter region to regulate a series of target genes involved in antioxidant, inflammatory responses, and cell cycle regulation in response to extracellular or intracellular stress. Recent research, particularly in the past 5 years, has shed light on NFE2L3's participation in diverse biological processes, including cell differentiation, inflammatory responses, lipid homeostasis, immune responses, and tumor growth. Notably, NFE2L3 has been identified as a key player in the development and prognosis of multiple cancers including colorectal cancer, thyroid cancer, breast cancer, hepatocellular carcinoma, gastric cancer, renal cancer, bladder cancer, esophageal squamous cell carcinoma, T cell lymphoblastic lymphoma, pancreatic cancer, and squamous cell carcinoma. Furthermore, research has linked NFE2L3 to other cancers such as lung adenocarcinoma, malignant pleural mesothelioma, ovarian cancer, glioblastoma multiforme, and laryngeal carcinoma, indicating its potential as a target for innovative cancer treatment approaches. Therefore, to gain a better understanding of the role of NFE2L3 in disease, this review offers insights into the discovery, structure, function, and recent advancements in the study of NFE2L3 to lay the groundwork for the development of NFE2L3-targeted cancer therapies.

Nfe2l3 promotes neuroprotection and long-distance axon regeneration after injury in vivo

Nuclear factor erythroid 2 like (Nfe2l) gene family members 1-3 mediate cellular response to oxidative stress, including in the central nervous system (CNS). However, neuronal functions of Nfe2l3 are unknown. Here, we comparatively evaluated expression of Nfe2l1, Nfe2l2, and Nfe2l3 in singe cell RNA-seq (scRNA-seq)-profiled cortical and retinal ganglion cell (RGC) CNS projection neurons, investigated whether Nfe2l3 regulates neuroprotection and axon regeneration after CNS injury in vivo, and characterized a gene network associated with Nfe2l3 in neurons. We showed that, Nfe2l3 expression transiently peaks in developing immature cortical and RGC projection neurons, but is nearly abolished in adult neurons and is not upregulated after injury. Furthermore, within the retina, Nfe2l3 is enriched in RGCs, primarily neonatally, and not upregulated in injured RGCs, whereas Nfe2l1 and Nfe2l2 are expressed robustly in other retinal cell types as well and are upregulated in injured RGCs. We also found that, expressing Nfe2l3 in injured RGCs through localized intralocular viral vector delivery promotes neuroprotection and long-distance axon regeneration after optic nerve injury in vivo. Moreover, Nfe2l3 provided a similar extent of neuroprotection and axon regeneration as viral vector-targeting of Pten and Klf9, which are prominent regulators of neuroprotection and long-distance axon regeneration. Finally, we bioinformatically characterized a gene network associated with Nfe2l3 in neurons, which predicted the association of Nfe2l3 with established mechanisms of neuroprotection and axon regeneration. Thus, Nfe2l3 is a novel neuroprotection and axon regeneration-promoting factor with a therapeutic potential for treating CNS injury and disease.

Hypomethylation-Mediated Upregulation of NFE2L3 Promotes Malignant Phenotypes of Clear Cell Renal Cell Carcinoma Cells

This work aimed to study the effect of NFE2 like bZIP transcription factor 3 (NFE2L3) on clear cell renal cell carcinoma (ccRCC) cells and whether NFE2L3 expression was mediated by DNA methylation. Twenty-one ccRCC patients were collected. The gene methylation and expression data of TCGA-KIRC were accessed from TCGA. Candidate methylation driver genes were identified by "MethylMix" package, and finally, NFE2L3 was selected as the target gene. The methylation of NFE2L3 was assayed by Ms PCR and QMSP. mRNA level of NFE2L3 was analyzed by qRT-PCR. Protein level of NFE2L3 was measured by Western blot. Demethylation was performed with methylation inhibitor 5-Aza-2'-deoxycytidine (5-Aza-CdR). Proliferative, migratory, and invasive abilities of ccRCC cells were assayed via cell colony formation assay, scratch healing assay, and transwell assay, respectively. Analysis of TCGA database presented that DNA hypomethylation occurred in the NFE2L3 promoter region in ccRCC tissues. NFE2L3 was significantly upregulated in ccRCC tissues and cells. Its expression in cells treated with 5-Aza-CdR was proportional to the concentration of methylation inhibitor. In cell function experiments, overexpressing NFE2L3 or demethylation could stimulate proliferation, migration, and invasion abilities of ccRCC and normal cells. 5-Aza-CdR treatment rescued repressive impact of knockdown NFE2L3 on malignant phenotypes of ccRCC and normal cells. DNA hypomethylation could induce high expression of NFE2L3 and facilitate malignant phenotypes of ccRCC cells. These results may generate insights into ccRCC therapy.

NRF3 suppresses squamous carcinogenesis, involving the unfolded protein response regulator HSPA5

Epithelial skin cancers are extremely common, but the mechanisms underlying their malignant progression are still poorly defined. Here, we identify the NRF3 transcription factor as a tumor suppressor in the skin. NRF3 protein expression is strongly downregulated or even absent in invasively growing cancer cells of patients with basal and squamous cell carcinomas (BCC and SCC). NRF3 deficiency promoted malignant conversion of chemically induced skin tumors in immunocompetent mice, clonogenic growth and migration of human SCC cells, their invasiveness in 3D cultures, and xenograft tumor formation. Mechanistically, the tumor-suppressive effect of NRF3 involves HSPA5, a key regulator of the unfolded protein response, which we identified as a potential NRF3 interactor. HSPA5 levels increased in the absence of NRF3, thereby promoting cancer cell survival and migration. Pharmacological inhibition or knock-down of HSPA5 rescued the malignant features of NRF3-deficient SCC cells in vitro and in preclinical mouse models. Together with the strong expression of HSPA5 in NRF3-deficient cancer cells of SCC patients, these results suggest HSPA5 inhibition as a treatment strategy for these malignancies in stratified cancer patients.

Nrf3 promotes the proliferation and migration of triple‑negative breast cancer by activating PI3K/AKT/mTOR and epithelial‑mesenchymal transition

Nuclear factor erythroid 2-related factor 3 (Nrf3) is increasingly implicated in multiple types of cancer; however, its function in triple-negative breast cancer (TNBC) remains unclear. This study aimed to examine the role of Nrf3 in TNBC. Compared with adjacent normal tissues, TNBC tissues expressed higher levels of Nrf3, and its expression was negatively correlated with survival time. Additionally, Nrf3 knockdown reduced the proliferation and migration of TNBC cells, whereas overexpression of Nrf3 had the opposite effects in vitro and in vivo. Moreover, functional enrichment of TNBC cells overexpressing Nrf3 allowed for the identification of numerous genes and pathways that were altered following Nrf3 overexpression. Further study showed that overexpression of Nrf3 activated the PI3K/AKT/mTOR signaling pathway and regulated the expression of proteins associated with epithelial-mesenchymal transition. Nrf3 was found to directly bind to p110α promoter regions, as evidenced by luciferase reporter and chromatin immunoprecipitation assays. Furthermore, PI3K inhibitors partially decreased the proliferation and migration of the Nrf3 overexpressing TNBC cells. In conclusion, Nrf3 enhances cellular proliferation and migration by activating PI3K/AKT/mTOR signaling pathways, highlighting a novel therapeutic target for TNBC.

NFE2L3 as a Potential Functional Gene Regulating Immune Microenvironment in Human Kidney Cancer

With the increasing incidence and mortality of renal cancer, it is pressing to find new biomarkers and drug targets for diagnosis and treatment. However, as one negative upstream regulator of p53, the prognostic and immunological role of NFE2L3 in renal cancer is still barely known. We investigated the expression, prognostic value, and relevant pathways of NFE2L3 using the datasets from public databases, including The Cancer Genome Atlas Program (TCGA), Genotype-Tissue Expression (GTEx), Cancer Cell Line Encyclopedia (CCLE), and UALCAN. Furthermore, we analyzed the relationship between NFE2L3 expression and the immune microenvironment using distinct methods. We found that NFE2L3 was higher expressed in kidney renal clear cell carcinoma (KIRC) and kidney renal papillary cell carcinoma (KIRP) tissues than adjacent normal tissues. Additionally, we identified NFE2L3 as one survival-related factor for KIRC and KIRP. The enrichment analyses revealed that NFE2L3 was associated with a variety of immune-relevant pathways in KIRC and related to the infiltration ratios of 17 types of immune cells in KIRC patients. Ultimately, we demonstrated nine significantly enriched mutations, such as TP53 and MET, in NFE2L3-expression-changing groups. The elevated expression of NFE2L3 in renal cancerous tissues versus normal tissues is associated with poor outcomes in patients. Besides, NFE2L3 has a role in the regulation of the immune microenvironment in renal cancer patients. The findings of our study provide a potential prognostic biomarker and a new drug target for renal cancer.

Loss of NFE2L3 protects against inflammation-induced colorectal cancer through modulation of the tumor microenvironment

We investigated the role of the NFE2L3 transcription factor in inflammation-induced colorectal cancer. Our studies revealed that Nfe2l3^−/− mice exhibit significantly less inflammation in the colon, reduced tumor size and numbers, and skewed localization of tumors with a more pronounced decrease of tumors in the distal colon. CIBERSORT analysis of RNA-seq data from normal and tumor tissue predicted a reduction in mast cells in Nfe2l3^−/− animals, which was confirmed by toluidine blue staining. Concomitantly, the transcript levels of Il33 and Rab27a, both important regulators of mast cells, were reduced and increased, respectively, in the colorectal tumors of Nfe2l3^−/− mice. Furthermore, we validated NFE2L3 binding to the regulatory sequences of the IL33 and RAB27A loci in human colorectal carcinoma cells. Using digital spatial profiling, we found that Nfe2l3^−/− mice presented elevated FOXP3 and immune checkpoint markers CTLA4, TIM3, and LAG3, suggesting an increase in Treg counts. Staining for CD3 and FOXP3 confirmed a significant increase in immunosuppressive Tregs in the colon of Nfe2l3^−/− animals. Also, Human Microbiome Project (HMP2) data showed that NFE2L3 transcript levels are higher in the rectum of ulcerative colitis patients. The observed changes in the tumor microenvironment provide new insights into the molecular differences regarding colon cancer sidedness. This may be exploited for the treatment of early-onset colorectal cancer as this emerging subtype primarily displays distal/left-sided tumors.

MicroRNA-1246 Mediates Drug Resistance and Metastasis in Breast Cancer by Targeting NFE2L3

MicroRNA (miR)-1246 is abnormally expressed and has pro-oncogenic functions in multiple types of cancer. In the present study, its functions in breast cancer and the underlying mechanisms were further elucidated. The clinical relevance of miR-1246 was analyzed and its expression in clinical specimens and cell lines was examined by reverse transcription-quantitat000000ive PCR analysis. FACS was used to detect cell apoptosis and mitochondrial transmembrane potential. A Transwell system was used to detect cell migration and invasion. Luciferase assay was used to confirm the target gene of miR-1246. Xenograft and metastasis mouse models were constructed to determine the function of miR-1246 in vivo. miR-1246 was found to be negatively associated with overall survival in breast cancer. miR-1246 inhibitor could effectively increase the cytotoxicity of docetaxel (Doc) by inducing apoptosis, and impair cell migration and invasion by suppressing epithelial-to-mesenchymal transition. Nuclear factor (erythroid 2)-like factor 3 (NFE2L3) was confirmed as a new target gene of miR-1246, and its overexpression was shown to reduce drug resistance and migration of MDA-MB-231 cells. More importantly, NFE2L3-silencing attenuated the effect of miR-1246 inhibitor. Finally, the inhibition of miR-1246 effectively enhanced the cytotoxicity of Doc in xenografts and impaired breast cancer metastasis. Therefore, miR-1246 may promote drug resistance and metastasis in breast cancer by targeting NFE2L3.

Elevated expression of NFE2L3 promotes the development of gastric cancer through epithelial-mesenchymal transformation

Gastric cancer (GC) is a malignant tumor with high mortality, but research on its molecular mechanisms remain limited. This study is the first to explore the biological role of nuclear factor NFE2L3 (nuclear factor, erythroid 2 like 3) in GC. We used Western blot and RT–qPCR to detect gene expression at the protein or mRNA level. Short hairpin RNA (shRNA) transfection was used to inhibit NFE2L3 expression. CCK-8 and colony formation assays were used to detect cell proliferation. Cell migration, invasion, cell cycle and apoptosis were detected by Transwell assays and flow cytometry. The results showed that NFE2L3 was highly expressed in gastric cancer tissues and promoted gastric cancer cell proliferation and metastasis. Inhibiting NFE2L3 expression blocks the cell cycle and increases the proportion of apoptotic cells, whereas NFE2L3 expression promotes the epithelial-mesenchymal transformation (EMT) process. In summary, NFE2L3 is highly expressed in gastric cancer and promotes gastric cancer cell proliferation and metastasis and the EMT process.

NFE2L3 Controls Colon Cancer Cell Growth through Regulation of DUX4, a CDK1 Inhibitor

Constitutive nuclear factor κB (NF-κB) activation is a hallmark of colon tumor growth. Cyclin-dependent kinases (CDKs) are critical cell-cycle regulators, and inhibition of CDK activity has been used successfully as anticancer therapy. Here, we show that the NFE2L3 transcription factor functions as a key regulator in a pathway that links NF-κB signaling to the control of CDK1 activity, thereby driving colon cancer cell proliferation. We found that NFE2L3 expression is regulated by the RELA subunit of NF-κB and that NFE2L3 levels are elevated in patients with colon adenocarcinoma when compared with normal adjacent tissue. Silencing of NFE2L3 significantly decreases colon cancer cell proliferation in vitro and tumor growth in vivo. NFE2L3 knockdown results in increased levels of double homeobox factor 4 (DUX4), which functions as a direct inhibitor of CDK1. The discovered oncogenic pathway governing cell-cycle progression may open up unique avenues for precision cancer therapy.

Roles of NRF3 in the Hallmarks of Cancer: Proteasomal Inactivation of Tumor Suppressors

Simple Summary

This review summarizes recent advances in our understanding of the physiological roles of the NFE2-related factor 2 (NRF2)-related transcription factor NRF3 in cancer. NRF3 confers cells with six so-called “hallmarks of cancer” through upregulating gene expression of specific target genes, leading to tumorigenesis and cancer malignancy. These driver gene-like functions of NRF3 in cancer are distinct from those of NRF2.

Abstract

The physiological roles of the NRF2-related transcription factor NRF3 (NFE2L3) have remained unknown for decades. The remarkable development of human cancer genome databases has led to strong suggestions that NRF3 has functional significance in cancer; specifically, high NRF3 mRNA levels are induced in many cancer types, such as colorectal cancer and pancreatic adenocarcinoma, and are associated with poor prognosis. On the basis of this information, the involvement of NRF3 in tumorigenesis and cancer malignancy has been recently proposed. NRF3 confers cancer cells with selective growth advantages by enhancing 20S proteasome assembly through induction of the chaperone gene proteasome maturation protein (POMP) and consequently promoting degradation of the tumor suppressors p53 and retinoblastoma (Rb) in a ubiquitin-independent manner. This new finding offers insight into the proteasomal but not the genetic inactivation mechanism of tumor suppressors. Moreover, NRF3 promotes cancer malignancy-related processes, including metastasis and angiogenesis. Finally, the molecular mechanisms underlying NRF3 activation have been elucidated, and this knowledge is expected to provide many insights that are useful for the development of anticancer drugs that attenuate NRF3 transcriptional activity. Collectively, the evidence indicates that NRF3 confers cells with six so-called “hallmarks of cancer”, implying that it exhibits cancer driver gene-like function. This review describes recent research advances regarding the newly discovered addiction of cancer cells to NRF3 compared to NRF2.

Molecular Mechanisms Underlying Hepatocellular Carcinoma Induction by Aberrant NRF2 Activation-Mediated Transcription Networks: Interaction of NRF2-KEAP1 Controls the Fate of Hepatocarcinogenesis

NF-E2-related factor 2 (NRF2) is a basic leucine zipper transcription factor, a master regulator of redox homeostasis regulating a variety of genes for antioxidant and detoxification enzymes. NRF2 was, therefore, initially thought to protect the liver from oxidative stress. Recent studies, however, have revealed that mutations in NRF2 cause aberrant accumulation of NRF2 in the nucleus and exert the upregulation of NRF2 target genes. Moreover, among all molecular changes in hepatocellular carcinoma (HCC), NRF2 activation has been revealed as a more prominent pathway contributing to the progression of precancerous lesions to malignancy. Nevertheless, how its activation leads to poor prognosis in HCC patients remains unclear. In this review, we provide an overview of how aberrant activation of NRF2 triggers HCC development. We also summarize the emerging roles of other NRF family members in liver cancer development.

Identification and Comprehensive Validation of a DNA Methylation-Driven Gene-Based Prognostic Model for Clear Cell Renal Cell Carcinoma

Clear cell renal cell carcinoma (ccRCC) is the most prevalent renal malignancy in adults with generally poor prognosis. This study aimed to establish a DNA methylation-driven gene-based prognostic model for ccRCC. We collected DNA methylation and gene expression profiles of over 1500 ccRCC samples from The Cancer Genome Atlas (TCGA) dataset, four Gene Expression Omnibus (GEO) datasets, the Genotype-Tissue Expression (GTEx) dataset, and cancer cell lines from Cancer Cell Line Encyclopedia database and performed comprehensive bioinformatics analysis. As a result, a total of 31 differentially expressed methylation-driven genes (DEMDGs) were identified. After univariate Cox regression, least absolute shrinkage and selection operator, and multivariate Cox regression analyses, four (NFE2L3, HHLA2, IFI16, and ZNF582) were finally selected to construct a risk score prognostic model. The high-risk group demonstrated significantly poor prognosis than the low-risk group did in TCGA training (hazard ratio [HR] = 3.533, p < 0.001), TCGA internal, and GEO external validation datasets. Furthermore, the nomogram, including the prognostic model and clinical factors, showed promising prognostic value (HR = 5.756, p < 0.001, and area under the curve at 1 year = 0.856). In addition, the model was found to be significantly associated with drug sensitivity of eight targeted agents. These findings provided a novel and reliable four DEMDG-based prognostic model for ccRCC.

Comparative toxicity analysis of corannulene and benzo[a]pyrene in mice

Increasing production of corannulene (COR), a non-planar polycyclic aromatic hydrocarbon (PAH) with promising applications in many fields, has raised a concern about its potential toxic effects. However, no study has been undertaken to evaluate its metabolism and toxicity in mammals. In this study, the acute toxicities of COR in mice were compared with benzo[apyrene (BaP), a typical planar PAH with almost the same molecular weight. After 3-day exposures, the concentrations of COR in both plasma and tissues of mice were higher than that of BaP. However, blood chemistry and tissue weight monitoring showed no observable toxicities in COR-exposed mice. Compared to BaP, exposure to COR resulted in less activation of the aryl hydrocarbon receptor (AhR) and thus less induction of hepatic cytochrome P450 1A(CYP1A) enzymes, which play a critical role in metabolism of both COR and BaP. Additionally, COR also elicited less oxidative stress and microbiota alteration in the intestine than did BaP. RNA-seq analysis revealed that liver transcriptomes are responsive to COR and BaP, with less alterations observed in COR-exposed mice. Unlike BaP, exposure to COR had no effects on hepatic lipid and xenobiotic metabolism pathways. Nonetheless, COR appeared to alter the mRNA expressions of genes involved in carcinogenicity, oxidative stress, and immune-suppression. To conclude, this study for the first time unveils a comparative understanding of the acute toxic effects of COR to BaP in mice, and provides crucial insights into the future safety assessment of COR.

NFE2L3 promotes malignant behavior and EMT of human hepatocellular carcinoma (HepG2) cells via Wnt/β‑catenin pathway

Objective: NFE2L3 is a member of the cap 'n' collar basic-region leucine zipper family. NFE2L3 has turned out to be associated with oxidative stress, but the relevance of NFE2L3 in hepatocellular carcinoma (HCC) has remained elusive. This study aimed to investigate the role of NFE2L3 in HCC and explore underlying mechanisms. Methods: Quantitative real-time PCR, western blot and immunohistochemistry were used to detect the mRNA and protein expression of NFE2L3, the expression of epithelial-mesenchymal transition (EMT) markers and Wnt/β-catenin signaling pathway-related proteins. In loss-function experiments, HepG2 cells were transfected with lentiviral vector containing NFE2L3 short hairpin RNA or scramble control. Cell proliferation and migration were measured by Cell Counting Kit-8, Colony formation, EdU incorporation and Transwell assays respectively. Flow cytometry was used to analyze cell cycle and apoptosis. HepG2 cells were subcutaneously injected into nude mice and tumor size was measured once every other day. Results: The results revealed that high expression of NFE2L3 was positively associated with malignant behavior and EMT in HCC. Knockdown of NFE2L3 inhibited cell proliferation and migration, led to cell cycle G0/G1 arrest and induction of cell apoptosis, increased expression of E-cadherin and decreased expression of N‑cadherin, Vimentin, MMP2, CDK2 and PCNA. In addition, tumor growth was inhibited by silencing of NFE2L3 in vivo. Expression of β-catenin and Wnt target genes cyclin D1 and TCF4 was reduced in HepG2-shNFE2L3 cells. Conclusions: NFE2L3 promotes cell proliferation, metastasis, and induces EMT of hepatocellular carcinoma (HepG2) cells via activation of Wnt/β-catenin pathway.

New addiction to the NRF2-related factor NRF3 in cancer cells: Ubiquitin-independent proteolysis through the 20S proteasome

Accumulating evidence has revealed that human cancers develop by sequentially mutating pivotal genes, including driver genes, and acquiring cancer hallmarks. For instance, cancer cells are addicted to the transcription factor NRF2 (NFE2L2), which is a driver gene that utilizes the cellular cytoprotection system against oxidative stress and metabolic pathway reprogramming for sustaining high growth. Our group has recently discovered a new addiction to the NRF2-related factor NRF3 (NFE2L3) in cancer. For many years, the physiological function of NRF3 remained obscure, in part because Nrf3-deficient mice do not show apparent abnormalities. Nevertheless, human cancer genome databases suggest critical roles of NRF3 in cancer because of high NRF3 mRNA induction in several cancer types, such as colorectal cancer and pancreatic adenocarcinoma, with a poor prognosis. We found that NRF3 promotes tumor growth and malignancy by activating ubiquitin-independent 20S proteasome assembly through inducing the expression of the proteasome maturation protein (POMP) chaperone and thereby degrading the tumor suppressors p53 and Rb. The NRF3-POMP-20S proteasome axis has an entirely different effect on cancer than NRF2. In this review, we describe recent research advances regarding the new cancer effector NRF3, including unclarified ubiquitin-independent proteolysis by the NRF3-POMP-20S proteasome axis. The expected development of cancer therapeutic interventions for this axis is also discussed.

Differential and overlapping targets of the transcriptional regulators NRF1, NRF2, and NRF3 in human cells

The nuclear factor (erythroid 2)-like (NRF) transcription factors are a subset of cap'n'collar transcriptional regulators. They consist of three members, NRF1, NRF2, and NRF3, that regulate the expression of genes containing antioxidant-response elements (AREs) in their promoter regions. Although all NRF members regulate ARE-containing genes, each is associated with distinct roles. A comprehensive study of differential and overlapping DNA-binding and transcriptional activities of the NRFs has not yet been conducted. Here, we performed chromatin immunoprecipitation (ChIP)-exo sequencing, an approach that combines ChIP with exonuclease treatment to pinpoint regulatory elements in DNA with high precision, in conjunction with RNA-sequencing to define the transcriptional targets of each NRF member. Our approach, done in three U2OS cell lines, identified 31 genes that were regulated by all three NRF members, 27 that were regulated similarly by all three, and four genes that were differentially regulated by at least one NRF member. We also found genes that were up- or down-regulated by only one NRF member, with 84, 84, and 22 genes that were regulated by NRF1, NRF2, and NRF3, respectively. Analysis of the ARE motifs identified in ChIP peaks revealed that NRF2 prefers binding to AREs flanked by GC-rich regions and that NRF1 prefers AT-rich flanking regions. Thus, sequence preference, likely in combination with upstream signaling events, determines NRF member activation under specific cellular contexts. Our analysis provides a comprehensive description of differential and overlapping gene regulation by the transcriptional regulators NRF1, NRF2, and NRF3.

Binding partners of NRF2: Functions and regulatory mechanisms

NRF2 is a redox-sensitive transcription factor that plays an important role in protecting organisms against diverse types of electrophiles or oxidants. The level of NRF2 is maintained low in normal cells, but highly elevated in cancer provoking chemoresistance or radioresistance. It is now recognized that NRF2 does not merely maintain the redox balance, but also plays significant roles in autophagy, apoptosis, cell cycle progression, and stem cell differentiation, all of which could be possibly attributable to the existence of multiple binding proteins. In the present manuscript, we summarize direct binding partners of NRF2 and illustrate how they bind to NRF2 and regulate its stability or activity.

β-Catenin/TCF4 Complex-Mediated Induction of the NRF3 (NFE2L3) Gene in Cancer Cells

Remarkable upregulation of the NRF2 (NFE2L2)-related transcription factor NRF3 (NFE2L3) in several cancer tissues and its correlation with poor prognosis strongly suggest the physiological function of NRF3 in tumors. Indeed, we had recently uncovered the function of NRF3, which promotes cancer cell proliferation by p53 degradation via the 20S proteasome. Nevertheless, the molecular mechanism underlying the induction of NRF3 gene expression in cancer cells is highly elusive. We herein describe that NRF3 upregulation is induced by the β-catenin/TCF4 complex in colon cancer cells. We first confirmed high NRF3 mRNA expression in human colon cancer specimens. The genome database indicated that the human NRF3 gene possesses a species-conserved WRE sequence (TCF/LEF consensus element), implying that the β-catenin/TCF complex activates NRF3 expression in colon cancer. Consistently, we observed that the β-catenin/TCF4 complex mediates NRF3 expression by binding directly to the WRE site. Furthermore, inducing NRF3 activates cell proliferation and the expression of the glucose transporter GLUT1. The existence of the β-catenin/TCF4-NRF3 axis was also validated in the intestine and organoids of Apc-deficient mice. Finally, the positive correlation between NRF3 and β-catenin target gene expression strongly supports our conclusion. Our findings clearly demonstrate that NRF3 induction in cancer cells is controlled by the Wnt/β-catenin pathway.

NFE2L3 Inhibition Induces Cell Cycle Arrest at the G0/G1 Phase in Colorectal Cancer Cells through Downregulating CCND1 and pRb1-ser807/811

The molecular mechanism for colorectal cancer to develop remains unelucidated. To find biomarkers related to colorectal cancer development, we analyzed the gene expression profile of 380 colorectal cancer patients and 51 healthy controls by R software. Finally, 1579 upregulated differential expression genes (DEGs) and 3218 downregulated DEGs were identified. Then, the top 20 upregulated DEGs were compared with 181 upregulated DEGs that we reported previously, and 11 overlapped DEGs were found. NFE2L3 (nuclear factor, erythroid 2-like 3) was among those overlapped DEGs and was rarely reported in colorectal cancer. Real-time polymerase chain reaction (PCR) results showed that higher NFE2L3 expression levels were identified in paired tumor samples than in paratumor samples (48 paired samples). Flow cytometry analysis revealed that the cell cycle was arrested at the G0/G1 phase after inhibition of NFE2L3 in both HCT116 and SW480 cell lines. Western blot detection showed that CCND1 and phosphorylated Rb transcriptional corepressor 1 at ser-807/811 (pRb1-ser807/811) expression levels were downregulated when NFE2L3 was inhibited in those two cell lines. A significant positive correlation was observed between NFE2L3 and CCND1 expression levels in colorectal tissue samples. These evidences indicate that downregulation of NFE2L3 induces cell cycle arrest at the G0/G1 phase through downregulation of CCND1 and pRb1-ser807/811.

NRF3 suppresses breast cancer cell metastasis and cell proliferation and is a favorable predictor of survival in breast cancer

Background: Cancer metastasis is the leading cause of cancer-related death in breast cancer. However, our understanding of its mechanisms is still limited. At this study, the biological roles and clinical significance of NRF3 (NFE2L3, nuclear factor, Erythroid 2 Like 3) in breast cancer are evaluated for the first time.

Methods: NRF3 expression in breast cancer cell lines and clinical specimens was determined by western blot and immunohistochemistry, respectively. Cell proliferation, cell cycle distribution, cell migration, and invasion were detected by MTT, colony formation, flow cytometry, and transwell assays, respectively. All other proteins were measured by western blot. The clinical significance of NRF3 was analyzed using the data from tissue microarray.

Results: We found that NRF3 expression was obviously suppressed in breast cancer tissues, and negatively associated with the Lymph node metastasis status and tumor stages. Our data also indicated NRF3 expression was much higher in MCF-7 cells than that in MDA-MB-231 and SKBR3 cells which were more malignant. Silence of NRF3 in MCF-7 cells could significantly promote cell proliferation by reducing the cell number in the G0/G1 phase. Exogenous expression of NRF3 in SKBR3 and MDA-MB-231 cells effectively inhibited both cell growth and metastasis with epithelial–mesenchymal transition and MMPs expression suppressed. NRF3 overexpression also impaired the ID3 expression by inactivating the AKT signaling pathway. Exogenous expression of ID3 could not only effectively promote breast cancer cell invasion by inhibiting E-cadherin expression and upregulating MMP-2 expression, but also attenuated the inhibitory function of NRF3 on the breast cancer cell invasion.

Conclusion: Our findings suggested that NRF3 inhibited breast cancer cell proliferation and metastasis via inhibiting AKT/ID3 axis at least partially, and potentially to be a valuable clinic marker in breast cancer prognosis.

Low tumour PPM1H indicates poor prognosis in colorectal cancer via activation of cancer-associated fibroblasts

BACKGROUND

Vimentin (VIM) is considered a prognostic marker in colorectal cancer (CRC). Our aim is to identify genes that fulfil a "X-low implies VIM-high" Boolean relationship and to evaluate their prognostic value and potential mechanism.

METHODS

Potential biomarkers related to VIM expression were searched using a bioinformatics approach across gene-expression arrays. Based on subgroup analysis of 2 CRC cohorts, the selected gene was tested for its association with patient's survival outcomes. The regulatory link between the selected gene and VIM was further examined with in vitro models.

RESULTS

PPM1H was identified as the top candidate in our search. Patients with PPM1H-low tumours have a lower 5-year disease-free survival rate than patients with PPM1H-high tumours in 2 independent cohorts. In multivariate Cox analysis, patients with PPM1H-low tumours were independently associated with relapse in both the discovery cohort (hazard ratio [HR], 1.362; 95% confidence interval [CI], 1.015-1.826; P = 0.039) and the validation cohort (HR for DFS, 4.052; 95% CI, 2.634-6.234; P < 0.001). PPM1H knockdown in CRC cells and growth in the corresponding conditional medium increased VIM expression and colon fibroblast proliferation, indicating a transformation of cancer-association fibroblasts (CAFs). Conversely, educated CAFs also facilitated the growth of CRC cells with low PPM1H expression.

CONCLUSIONS

Lack of tumour PPM1H expression identifies a patient subgroup with a high relapse risk, and CRC cells with low expression of PPM1H activate CAFs and inversely get promoted by CAFs.

Short hairpin RNA-mediated knockdown of nuclear factor erythroid 2-like 3 exhibits tumor-suppressing effects in hepatocellular carcinoma cells

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors with high mortality-to-incidence ratios. Nuclear factor erythroid 2-like 3 (NFE2L3), also known as NRF3, is a member of the cap ‘n’ collar basic-region leucine zipper family of transcription factors. NFE2L3 is involved in the regulation of various biological processes, whereas its role in HCC has not been elucidated.

AIM

To explore the expression and biological function of NFE2L3 in HCC.

METHODS

We analyzed the expression of NFE2L3 in HCC tissues and its correlation with clinicopathological parameters based on The Cancer Genome Atlas (TCGA) data portal. Short hairpin RNA (shRNA) interference technology was utilized to knock down NFE2L3 in vitro. Cell apoptosis, clone formation, proliferation, migration, and invasion assays were used to identify the biological effects of NFE2L3 in BEL-7404 and SMMC-7721 cells. The expression of epithelial-mesenchymal transition (EMT) markers was examined by Western blot analysis.

RESULTS

TCGA analysis showed that NFE2L3 expression was significantly positively correlated with tumor grade, T stage, and pathologic stage. The qPCR and Western blot results showed that both the mRNA and protein levels of NFE2L3 were significantly decreased after shRNA-mediated knockdown in BEL-7404 and SMMC-7721 cells. The shRNA-mediated knockdown of NFE2L3 could induce apoptosis and inhibit the clone formation and cell proliferation of SMMC-7721 and BEL-7404 cells. NFE2L3 knockdown also significantly suppressed the migration, invasion, and EMT of the two cell lines.

CONCLUSION

Our study showed that shRNA-mediated knockdown of NFE2L3 exhibited tumor-suppressing effects in HCC cells.

Elevated expression of NFE2L3 predicts the poor prognosis of pancreatic cancer patients

The highly malignant feature and difficulties for early diagnosis are the key reasons contributing to the poor prognosis of pancreatic cancer (PC) patients. NFE2L3 is a nuclear transcription factor, which has been reported an important biomarker of several tumors. But the role of NFE2L3 in PC remained undefined. Herein, through qPCR and immunohistochemistry, we found a significantly increased NFE2L3 in PC tissues as compared with adjacent non-tumor tissues. While reducing NFE2L3 expression suppressed the invasion abilities of PC cells, elevated NFE2L3 was found associated with lymph node metastasis (P = 0.001; HR = 3.95; 95% CI: 1.70 - 9.17) and advanced TNM stages (P < 0.001; HR = 4.06; 95% CI: 1.74 - 9.46). Consistently, data from both our two cohorts and the TCGA database revealed that higher NFE2L3 PC carriers had worse outcomes than those lower NFE2L3 expressers. Lastly, we confirmed the regulatory role of NFE2L3 on VEGFA, an important player involved in tumor angiogenesis. Collectively, our investigations suggested the oncogenic role of NFE2L3 in PC development and provided the rational for future adding NFE2L3 for the risk assessment of PC patients.

ABBREVIATIONS

NFE2L3: NF-E2-related factor 3; UHMK1: U2AF homology motif kinase 1; VEGFA: vascular endothelial growth factor A; GEO: gene expression omnibus; TCGA: The Cancer Genome Atlas; HPDE: human pancreas duct cells; OS: overall survival; IHC: immunohistochemistry; FFPE: formalin-fixed and paraffin-embedded; SEM: standard error of mean.

Nrf3 promotes UV-induced keratinocyte apoptosis through suppression of cell adhesion

The transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) is a key regulator of the cellular stress response, but the biological functions of the related Nrf3 protein are largely unknown. Here we demonstrate a novel pro-apoptotic function of Nrf3 in mouse and human keratinocytes. In response to UV irradiation, Nrf3-deficient keratinocytes were protected from apoptosis in vitro and in vivo. The protective function was also seen under oxidative or hyperosmotic stress conditions, but not when apoptosis was induced by disruption of cell–matrix interactions. Mechanistically, we show that Nrf3-deficient keratinocytes exhibit stronger cell–cell and cell-matrix adhesion, which correlates with higher cell surface integrin levels and enhanced activation of focal adhesion kinase. Nrf3-deficient cells also formed more and larger focal adhesions and exhibited a higher motility. These results suggest that the strong expression of Nrf3 in basal keratinocytes promotes their elimination in response to DNA damage-inducing agents, thereby preventing accumulation of mutated stem and transit amplifying cells in the epidermis.

Multiple regulatory mechanisms of the biological function of NRF3 (NFE2L3) control cancer cell proliferation

Accumulated evidence suggests a physiological relationship between the transcription factor NRF3 (NFE2L3) and cancers. Under physiological conditions, NRF3 is repressed by its endoplasmic reticulum (ER) sequestration. In response to unidentified signals, NRF3 enters the nucleus and modulates gene expression. However, molecular mechanisms underlying the nuclear translocation of NRF3 and its target gene in cancer cells remain poorly understood. We herein report that multiple regulation of NRF3 activities controls cell proliferation. Our analyses reveal that under physiological conditions, NRF3 is rapidly degraded by the ER-associated degradation (ERAD) ubiquitin ligase HRD1 and valosin-containing protein (VCP) in the cytoplasm. Furthermore, NRF3 is also degraded by β-TRCP, an adaptor for the Skp1-Cul1-F-box protein (SCF) ubiquitin ligase in the nucleus. The nuclear translocation of NRF3 from the ER requires the aspartic protease DNA-damage inducible 1 homolog 2 (DDI2) but does not require inhibition of its HRD1-VCP-mediated degradation. Finally, NRF3 mediates gene expression of the cell cycle regulator U2AF homology motif kinase 1 (UHMK1) for cell proliferation. Collectively, our study provides us many insights into the molecular regulation and biological function of NRF3 in cancer cells.

Arsenic trioxide and all-trans-retinoic acid selectively exert synergistic cytotoxicity against FLT3-ITD AML cells via co-inhibition of FLT3 signaling pathways

FLT3-ITD mutations occur in approximately 30% of acute myeloid leukemia (AML) and are associated with a poor outcome. Currently available FLT3 inhibitors have in vitro but limited clinical activity in FLT3-ITD AML. Reports have shown that an arsenic trioxide (ATO)/all-trans-retinoic acid (ATRA) combination improves prognosis in acute promyelocytic leukemia, especially with FLT3-ITD, and ATO or ATRA alone enhances apoptosis in FLT3-ITD AML cells treated with FLT3 inhibitors, providing a rationale to investigate the role of ATO/ATRA in FLT3-ITD AML. Here, we demonstrate that an ATO/ATRA combination selectively exerts synergistic cytotoxicity against FLT3-ITD AML cell lines (MV4;11/MOLM-13). The signaling pathways affected by ATO/ATRA include FLT3/STAT5/MYC, FLT3/STAT5/E2F1, FLT3/ERK/ATF5 and FLT3/AKT/ATF5.ATF5 may function as an oncogene in FLT3-ITD AML. Our findings provide experimental evidence that supports further exploration of ATO/ATRA in FLT3-ITD AML in vivo and warrants a clinical evaluation of regimens comprising an ATO/ATRA combination.

Nrf2 and Nrf2-related proteins in development and developmental toxicity: Insights from studies in zebrafish (Danio rerio)

Oxidative stress is an important mechanism of chemical toxicity, contributing to developmental toxicity and teratogenesis as well as to cardiovascular and neurodegenerative diseases and diabetic embryopathy. Developing animals are especially sensitive to effects of chemicals that disrupt the balance of processes generating reactive species and oxidative stress, and those anti-oxidant defenses that protect against oxidative stress. The expression and inducibility of anti-oxidant defenses through activation of NFE2-related factor 2 (Nrf2) and related proteins is an essential process affecting the susceptibility to oxidants, but the complex interactions of Nrf2 in determining embryonic response to oxidants and oxidative stress are only beginning to be understood. The zebrafish (Danio rerio) is an established model in developmental biology and now also in developmental toxicology and redox signaling. Here we review the regulation of genes involved in protection against oxidative stress in developing vertebrates, with a focus on Nrf2 and related cap'n'collar (CNC)-basic-leucine zipper (bZIP) transcription factors. Vertebrate animals including zebrafish share Nfe2, Nrf1, Nrf2, and Nrf3 as well as a core set of genes that respond to oxidative stress, contributing to the value of zebrafish as a model system with which to investigate the mechanisms involved in regulation of redox signaling and the response to oxidative stress during embryolarval development. Moreover, studies in zebrafish have revealed nrf and keap1 gene duplications that provide an opportunity to dissect multiple functions of vertebrate NRF genes, including multiple sensing mechanisms involved in chemical-specific effects.

Developmental expression of the Nfe2-related factor (Nrf) transcription factor family in the zebrafish, Danio rerio

Transcription factors in the CNC-bZIP family (NFE2, NRF1, NRF2 and NRF3) regulate genes with a wide range of functions in response to both physiological and exogenous signals, including those indicating changes in cellular redox status. Given their role in helping to maintain cellular homeostasis, it is imperative to understand the expression, regulation, and function of CNC-bZIP genes during embryonic development. We explored the expression and function of six nrf genes (nfe2, nrf1a, nrf1b, nrf2a, nrf2b, and nrf3) using zebrafish embryos as a model system. Analysis by microarray and quantitative RT-PCR showed that genes in the nrf family were expressed throughout development from oocytes to larvae. The spatial expression of nrf3 suggested a role in regulating the development of the brain, brachia and pectoral fins. Knock-down by morpholino anti-sense oligonucleotides suggested that none of the genes were necessary for embryonic viability, but nfe2 was required for proper cellular organization in the pneumatic duct and subsequent swim bladder function, as well as for proper formation of the otic vesicles. nrf genes were induced by the oxidant tert-butylhydroperoxide, and some of this response was regulated through family members Nrf2a and Nrf2b. Our results provide a foundation for understanding the role of nrf genes in normal development and in regulating the response to oxidative stress in vertebrate embryos.

Role of nrf2 in oxidative stress and toxicity

Organismal life encounters reactive oxidants from internal metabolism and environmental toxicant exposure. Reactive oxygen and nitrogen species cause oxidative stress and are traditionally viewed as being harmful. On the other hand, controlled production of oxidants in normal cells serves useful purposes to regulate signaling pathways. Reactive oxidants are counterbalanced by complex antioxidant defense systems regulated by a web of pathways to ensure that the response to oxidants is adequate for the body's needs. A recurrent theme in oxidant signaling and antioxidant defense is reactive cysteine thiol-based redox signaling. The nuclear factor erythroid 2-related factor 2 (Nrf2) is an emerging regulator of cellular resistance to oxidants. Nrf2 controls the basal and induced expression of an array of antioxidant response element-dependent genes to regulate the physiological and pathophysiological outcomes of oxidant exposure. This review discusses the impact of Nrf2 on oxidative stress and toxicity and how Nrf2 senses oxidants and regulates antioxidant defense.

Detection of collagen triple helix repeat containing-1 and nuclear factor (erythroid-derived 2)-like 3 in colorectal cancer

BACKGROUND

Collagen Triple Helix Repeat Containing-1 (CTHRC1) and Nuclear factor (erythroid-derived 2)-like 3 (NFE2L3) may be useful biomarker candidates for the diagnosis of colorectal cancer (CRC) since they have shown an increase messenger RNA transcripts (mRNA) expression level in adenomas and colorectal tumours when compared to normal tissues.

METHODS

To evaluate CTHRC1 and NFE2L3 as cancer biomarkers, it was generated and characterised several novel specific polyclonal antibodies (PAb), monoclonal antibodies (MAbs) and soluble Fab fragments (sFabs) against recombinant CTHRC1 and NFE2L3 proteins, which were obtained from different sources, including a human antibody library and immunised animals. The antibodies and Fab fragments were tested for recognition of native CTHRC1 and NFE2L3 proteins by immunoblotting analysis and enzyme-linked immunosorbent assay (ELISA) in colorectal cell lines derived from tumour and cancer tissues.

RESULTS

Both, antibodies and a Fab fragment showed high specificity since they recognised only their corresponding recombinant antigens, but not a panel of different unrelated- and related proteins.In Western blot analysis of CTHRC1, a monoclonal antibody designated CH21D7 was able to detect a band of the apparent molecular weight of a full-length CTHRC1 in the human colon adenocarcinoma cell line HT29. This result was confirmed by a double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) with the monoclonal antibodies CH21D7 and CH24G2, detecting CTHRC1 in HT29 and in the colon adenocarcinoma cell line SW620.Similar experiments were performed with PAb, MAbs, and sFab against NFE2L3. The immunoblot analysis showed that the monoclonal antibody 41HF8 recognised NFE2L3 in HT29, and leukocytes. These results were verified by DAS-ELISA assay using the pairs PAb/sFab E5 and MAb 41HF8/sFab E5.Furthermore, an immunoassay for simultaneous detection of the two cancer biomarkers was developed using a Dissociation-Enhanced Lanthanide Fluorescent Immunoassay technology (DELFIA).

CONCLUSIONS

In conclusion, the antibodies obtained in this study are specific for CTHRC1 and NFE2L3 since they do not cross-react with unrelated- and related proteins and are useful for specific measurement of native CTHRC1 and NFE2L3 proteins. The antibodies and immunoassays may be useful for the analysis of CTHRC1 and NFE2L3 in clinical samples and for screening of therapeutic compounds in CRC.

NFE2L3 (NRF3): the Cinderella of the Cap'n'Collar transcription factors

NFE2L3 [Nuclear factor (erythroid-derived 2)-like 3] or NRF3, a member of the Cap'n'Collar (CNC) family, is a basic-region leucine zipper (bZIP) transcription factor that was first identified over 10 years ago. Contrary to its extensively studied homolog NFE2L2 (NRF2), the regulation and function of the NFE2L3 protein have not yet attracted as much attention. Nevertheless, several recent reports have now shed light on the possible roles of NFE2L3. Structural and biochemical studies revealed a series of domains and modifications that are critical for its cellular regulation. The control of the subcellular localization of NFE2L3 appears to be essential for understanding its role in various cellular processes. Importantly, newer studies provide fascinating insights linking NFE2L3 to differentiation, inflammation, and carcinogenesis. Here, we present an overview of the current level of knowledge of NFE2L3 transcription factor biology in humans and mice. From being the Cinderella of the CNC transcription factors for many years, NFE2L3 may now rapidly come into its own.

mRNA expression profiles of primary high-grade central osteosarcoma are preserved in cell lines and xenografts

Background

Conventional high-grade osteosarcoma is a primary malignant bone tumor, which is most prevalent in adolescence. Survival rates of osteosarcoma patients have not improved significantly in the last 25 years. Aiming to increase this survival rate, a variety of model systems are used to study osteosarcomagenesis and to test new therapeutic agents. Such model systems are typically generated from an osteosarcoma primary tumor, but undergo many changes due to culturing or interactions with a different host species, which may result in differences in gene expression between primary tumor cells, and tumor cells from the model system. We aimed to investigate whether gene expression profiles of osteosarcoma cell lines and xenografts are still comparable to those of the primary tumor.

Methods

We performed genome-wide mRNA expression profiling on osteosarcoma biopsies (n = 76), cell lines (n = 13), and xenografts (n = 18). Osteosarcoma can be subdivided into several histological subtypes, of which osteoblastic, chondroblastic, and fibroblastic osteosarcoma are the most frequent ones. Using nearest shrunken centroids classification, we generated an expression signature that can predict the histological subtype of osteosarcoma biopsies.

Results

The expression signature, which consisted of 24 probes encoding for 22 genes, predicted the histological subtype of osteosarcoma biopsies with a misclassification error of 15%. Histological subtypes of the two osteosarcoma model systems, i.e. osteosarcoma cell lines and xenografts, were predicted with similar misclassification error rates (15% and 11%, respectively).

Conclusions

Based on the preservation of mRNA expression profiles that are characteristic for the histological subtype we propose that these model systems are representative for the primary tumor from which they are derived.

Clustered genomic alterations in chromosome 7p dictate outcomes and targeted treatment responses of lung adenocarcinoma with EGFR-activating mutations

PURPOSE

Although epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) have been proven more effective for patients with lung adenocarcinoma with EGFR-activating mutation rather than wild type, the former group still includes approximately 30% nonresponders. The molecular basis of this substantial response heterogeneity is unknown. Our purpose was to seek molecular aberrations contributing to disease progression at the genome-wide level and identify the prognostic signature unique to patients with EGFR-activating mutation.

PATIENTS AND METHODS

We first investigated the molecular differences between tumors with EGFR-activating mutation and wild-type tumors by conducting high-density array comparative genomic hybridization on a collection of 138 adenocarcinoma tissues. We then used an independent group of 114 patients to validate the clinical relevance of copy-number alterations (CNAs) in predicting overall and disease-free survival. Finally, focusing on 23 patients with EGFR mutation receiving EGFR-TKI treatment, we investigated the association between CNAs and response to EGFR-TKIs.

RESULTS

We identified chromosome regions with differential CNAs between tumors with EGFR-activating mutation and wild-type tumors and found the aberration sites to cluster highly on chromosome 7p. A cluster of six representative chromosome 7p genes predicted overall and disease-free survival for patients with EGFR-activating mutation but not for those with wild type. Importantly, simultaneous presence of more genes with increased CNAs in this cluster correlated with less favorable response to EGFR-TKIs in patients with EGFR-activating mutation.

CONCLUSION

Our results shed light on why responses to EGFR-TKIs are heterogeneous among patients with EGFR-activating mutation. They may lead to better patient management in this population.