Discovery of an NRF1-specific inducer from a large-scale chemical library using a direct NRF1-protein monitoring system

The multifaceted functions of NFE2L1 in metabolism and associated disorders

Nuclear factor erythroid 2-related factor 1 (NFE2L1, also known as Nrf1) is a crucial member of the CNC-bZIP subfamily of transcription factors expressed ubiquitously throughout our body. Recent findings have revealed its association with various metabolic processes, encompassing glucose, lipid, and protein metabolism. In the realm of glucose metabolism, NFE2L1 exerts regulatory control by modulating pancreatic β cells and insulin production. It also influences glucose metabolism in liver and the insulin sensitivity of adipose tissue. Regarding lipid metabolism, NFE2L1 governs this process by influencing the expression of specific adipogenic and lipolysis genes in both liver and adipose tissue. Additionally, NFE2L1 regulates specific lipids, such as cholesterol. These involvements underlie various manifestations of NFE2L1 deficiency such as adipocyte hypertrophy, inflammation, and steatohepatitis. In the realm of protein metabolism, NFE2L1 serves as a major transcription factor regulating the 26S proteasome genes expression, which dysfunction has been related with multiple diseases including neurodegenerative diseases, cancers, autoimmune conditions, etc. In this comprehensive review, we summarize the diverse roles that NFE2L1 plays in glucose, lipid, and protein metabolism, as well as its impact on diseases related to these metabolic processes.

NFE2L1/Nrf1 serves as a potential therapeutical target for neurodegenerative diseases

The failure of the proper protein turnover in the nervous system is mainly linked to a variety of neurodegenerative disorders. Therefore, a better understanding of key protein degradation through the ubiquitin-proteasome system is critical for effective prevention and treatment of those disorders. The proteasome expression is tightly regulated by a CNC (cap'n'collar) family of transcription factors, amongst which the nuclear factor-erythroid 2-like bZIP factor 1 (NFE2L1, also known as Nrf1, with its long isoform TCF11 and short isoform LCR-F1) has been identified as an indispensable regulator of the transcriptional expression of the ubiquitin-proteasome system. However, much less is known about how the pivotal role of NFE2L1/Nrf1, as compared to its homologous NFE2L2 (also called Nrf2), is translated to its physiological and pathophysiological functions in the nervous system insomuch as to yield its proper cytoprotective effects against neurodegenerative diseases. The potential of NFE2L1 to fulfill its unique neuronal function to serve as a novel therapeutic target for neurodegenerative diseases is explored by evaluating the hitherto established preclinical and clinical studies of Alzheimer's and Parkinson's diseases. In this review, we have also showcased a group of currently available activators of NFE2L1, along with an additional putative requirement of this CNC-bZIP factor for healthy longevity based on the experimental evidence obtained from its orthologous SKN1-A in Caenorhabditis elegans.

Transcription Factor NFE2L1 Decreases in Glomerulonephropathies after Podocyte Damage

Podocyte cellular injury and detachment from glomerular capillaries constitute a critical factor contributing to kidney disease. Notably, transcription factors are instrumental in maintaining podocyte differentiation and homeostasis. This study explores the hitherto uninvestigated expression of Nuclear Factor Erythroid 2-related Factor 1 (NFE2L1) in podocytes. We evaluated the podocyte expression of NFE2L1, Nuclear Factor Erythroid 2-related Factor 2 (NFE2L2), and NAD(P)H:quinone Oxidoreductase (NQO1) in 127 human glomerular disease biopsies using multiplexed immunofluorescence and image analysis. We found that both NFE2L1 and NQO1 expressions were significantly diminished across all observed renal diseases. Furthermore, we exposed human immortalized podocytes and ex vivo kidney slices to Puromycin Aminonucleoside (PAN) and characterized the NFE2L1 protein isoform expression. PAN treatment led to a reduction in the nuclear expression of NFE2L1 in ex vivo kidney slices and podocytes.

ER-Resident Transcription Factor Nrf1 Regulates Proteasome Expression and Beyond

Protein folding is a substantively error prone process, especially when it occurs in the endoplasmic reticulum (ER). The highly exquisite machinery in the ER controls secretory protein folding, recognizes aberrant folding states, and retrotranslocates permanently misfolded proteins from the ER back to the cytosol; these misfolded proteins are then degraded by the ubiquitin–proteasome system termed as the ER-associated degradation (ERAD). The 26S proteasome is a multisubunit protease complex that recognizes and degrades ubiquitinated proteins in an ATP-dependent manner. The complex structure of the 26S proteasome requires exquisite regulation at the transcription, translation, and molecular assembly levels. Nuclear factor erythroid-derived 2-related factor 1 (Nrf1; NFE2L1), an ER-resident transcription factor, has recently been shown to be responsible for the coordinated expression of all the proteasome subunit genes upon proteasome impairment in mammalian cells. In this review, we summarize the current knowledge regarding the transcriptional regulation of the proteasome, as well as recent findings concerning the regulation of Nrf1 transcription activity in ER homeostasis and metabolic processes.

Triptolide enhances chemotherapeutic efficacy of antitumor drugs in non-small-cell lung cancer cells by inhibiting Nrf2-ARE activity

Non-small cell lung cancer (NSCLC) has a high mortality rate worldwide. Various treatments strategies have been used against NSCLC including individualized chemotherapies, but innate or acquired cancer cell drug resistance remains a major obstacle. Recent studies revealed that the Kelch-like ECH associated protein 1/Nuclear factor erythroid 2-related factor 2 (Keap1/Nrf2) pathway is intimately involved in cancer progression and chemoresistance. Thus, antagonizing Nrf2 would seem to be a viable strategy in cancer therapy. In the present study a traditional Chinese medicine, triptolide, was identified that markedly inhibited expression and transcriptional activity of Nrf2 in various cancer cells, including NSCLC and liver cancer cells. Consequently, triptolide made cancer cells more chemosensitivity toward antitumor drugs both in vitro and in a xenograft tumor model system using lung carcinoma cells. These results suggest that triptolide blocks chemoresistance in cancer cells by targeting the Nrf2 pathway. Triptolide should be further investigated in clinical cancer trials.

Brown adipose tissue thermogenic adaptation requires Nrf1-mediated proteasomal activity

Adipocytes possess remarkable adaptive capacity to respond to nutrient excess, fasting or cold exposure, and they are thus an important cell type for the maintenance of proper metabolic health. Although the endoplasmic reticulum (ER) is a critical organelle for cellular homeostasis, the mechanisms that mediate adaptation of the ER to metabolic challenges in adipocytes are unclear. Here we show that brown adipose tissue (BAT) thermogenic function requires an adaptive increase in proteasomal activity to secure cellular protein quality control, and we identify the ER-localized transcription factor nuclear factor erythroid 2-like 1 (Nfe2l1, also known as Nrf1) as a critical driver of this process. We show that cold adaptation induces Nrf1 in BAT to increase proteasomal activity and that this is crucial for maintaining ER homeostasis and cellular integrity, specifically when the cells are in a state of high thermogenic activity. In mice, under thermogenic conditions, brown-adipocyte-specific deletion of Nfe2l1 (Nrf1) resulted in ER stress, tissue inflammation, markedly diminished mitochondrial function and whitening of the BAT. In mouse models of both genetic and dietary obesity, stimulation of proteasomal activity by exogenously expressing Nrf1 or by treatment with the proteasome activator PA28α in BAT resulted in improved insulin sensitivity. In conclusion, Nrf1 emerges as a novel guardian of brown adipocyte function, providing increased proteometabolic quality control for adapting to cold or to obesity.

Camptothecin suppresses NRF2-ARE activity and sensitises hepatocellular carcinoma cells to anticancer drugs

Background:

Resistance to chemotherapy is a major obstacle in the treatment of human hepatocellular carcinoma (HCC). Despite playing an important role in chemoprevention, nuclear factor erythroid 2-related factor 2 (NRF2) also contributes to chemo- and radio-resistance. The current study focusses on camptothecin as a novel NRF2 inhibitor to sensitise HCC to chemotherapy.

Methods:

The expression and transcriptional activity of NRF2 in human HCC biopsies and camptothecin-treated culture cells were determined using immunostaining, western blot, reverse-transcription quantitative real-time PCR (RT–qPCR) and luciferase reporter assay. The effect of camptothecin on chemosensitivity of cancer cells was assessed in vitro and in xenografts.

Results:

The expression and transcriptional activity of NRF2 were substantially elevated in HCC biopsies compared with corresponding adjacent tissues, and positively correlated with serum α-fetoprotein, a clinical indicator of pathological progression. In searching chemicals targeting NRF2 for chemotherapy, we discovered that camptothecin is a potent NRF2 inhibitor. Camptothecin markedly suppressed NRF2 expression and transcriptional activity in different types of cancer cells including HepG2, SMMC-7721 and A549. As a result, camptothecin sensitised these cells to chemotherapeutic drugs in vitro and in xenografts.

Conclusions:

Camptothecin is a novel NRF2 inhibitor that may be repurposed in combination with other chemotherapeutics to enhance their efficacy in treating high NRF2-expressing cancers.

Nuclear Factor Erythroid-2 Like 1 (NFE2L1): Structure, function and regulation

Nrf1 (also referred to as NFE2L1) is a member of the CNC-bZIP family of transcription factors that are characterized by a highly conserved CNC-domain, and a basic-leucine zipper domain required for dimerization and DNA binding. Nrf1 is ubiquitously expressed across tissue and cell types as various isoforms, and is induced by stress signals from a broad spectrum of stimuli. Evidence indicates that Nrf1 plays an important role in regulating a range of cellular functions including oxidative stress response, differentiation, inflammatory response, metabolism, and maintaining proteostasis. Thus, Nrf1 has been implicated in the pathogenesis of various disease processes including cancer development, and degenerative and metabolic disorders. This review summarizes our current understanding of Nrf1 and the molecular mechanism underlying its regulation and action in different cellular functions.