NRF2 and the Ambiguous Consequences of Its Activation during Initiation and the Subsequent Stages of Tumourigenesis

NF-E2 p45-related factor 2 (NRF2, encoded in the human by NFE2L2) mediates short-term adaptation to thiol-reactive stressors. In normal cells, activation of NRF2 by a thiol-reactive stressor helps prevent, for a limited period of time, the initiation of cancer by chemical carcinogens through induction of genes encoding drug-metabolising enzymes. However, in many tumour types, NRF2 is permanently upregulated. In such cases, its overexpressed target genes support the promotion and progression of cancer by suppressing oxidative stress, because they constitutively increase the capacity to scavenge reactive oxygen species (ROS), and they support cell proliferation by increasing ribonucleotide synthesis, serine biosynthesis and autophagy. Herein, we describe cancer chemoprevention and the discovery of the essential role played by NRF2 in orchestrating protection against chemical carcinogenesis. We similarly describe the discoveries of somatic mutations in NFE2L2 and the gene encoding the principal NRF2 repressor, Kelch-like ECH-associated protein 1 (KEAP1) along with that encoding a component of the E3 ubiquitin-ligase complex Cullin 3 (CUL3), which result in permanent activation of NRF2, and the recognition that such mutations occur frequently in many types of cancer. Notably, mutations in NFE2L2, KEAP1 and CUL3 that cause persistent upregulation of NRF2 often co-exist with mutations that activate KRAS and the PI3K-PKB/Akt pathway, suggesting NRF2 supports growth of tumours in which KRAS or PKB/Akt are hyperactive. Besides somatic mutations, NRF2 activation in human tumours can occur by other means, such as alternative splicing that results in a NRF2 protein which lacks the KEAP1-binding domain or overexpression of other KEAP1-binding partners that compete with NRF2. Lastly, as NRF2 upregulation is associated with resistance to cancer chemotherapy and radiotherapy, we describe strategies that might be employed to suppress growth and overcome drug resistance in tumours with overactive NRF2

Nrf2-mediated neuroprotection response to recurrent hypoglycemia is insufficient to prevent cognitive impairment in a rodent model of type 1 diabetes

It remains uncertain whether recurrent nonsevere hypoglycemia (Hypo) results in long-term cognitive impairment in type 1 diabetes (T1D). This study tested the hypothesis that specifically in the T1D state, Hypo leads to cognitive impairment via a pathological response to oxidative stress. Wild-type (Control) and nuclear factor–erythroid 2 p45–related factor 2 (Nrf2) null mice were studied. Eight groups of mice (Control and Nrf2−/− ± T1D and ± Hypo) were subject to recurrent, twice-weekly, insulin or saline injections over 4 weeks, after which cognitive function was assessed and brain tissue analyzed. Recurrent moderate hypoglycemia in T1D, but not Control, mice significantly impaired cognitive performance, and this was associated with hippocampal oxidative damage and inflammation despite an enhanced expression of Nrf2 and its target genes Hmox1 and Nqo1. In Nrf2−/− mice, both T1D and Hypo independently resulted in impaired cognitive performance, and this was associated with oxidative cell damage and marked inflammation. Together, these data suggest that Hypo induces an Nrf2-dependent antioxidant response in the hippocampus, which counteracts oxidative damage. However, in T1D, this neuroprotective mechanism is insufficient to prevent neuronal oxidative damage, resulting in chronic deficits in working and long-term memory.</jats:p

Biopreservation of chocolate mousse with Lactobacillus helveticus 2/20: Microbial Challenge Test

Probiotic bacteria are used for food biopreservation because their metabolic products might contribute to ensuring food microbiological safety and/or increase its shelf life without the addition of chemical preservatives. Moreover, biopreserved foods are excellent vehicles for the delivery of probiotic bacteria. The aim of the study was to investigate the potential of chocolate mousse food matrix for the delivery of the probiotic strain Lactobacillus helveticus 2/20 (Lb. helveticus 2/20) and to investigate its capacity to inhibit the growth of two foodborne pathogenic bacteria (Staphylococcus aureus and Escherichia coli). Therefore, the populations of free or encapsulated in calcium alginate Lb. helveticus 2/20 cells and/or of each pathogen (used to voluntarily contaminate each sample) were monitored both in complex nutrient medium (MRS broth) and in chocolate mousse under refrigeration conditions and at room temperature. Lb. helveticus 2/20 alone in free or encapsulated state effectively inhibited the growth of Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923 in chocolate mousse when stored at 20 ± 2 °C. Practically no viable unwanted bacteria were identified on the 7th day from the beginning of the process. High viable Lb. helveticus 2/20 cell populations were maintained during storage under refrigerated conditions (4 ± 2 °C) and at room temperature. Chocolate mousse is thus a promising food matrix to deliver probiotic Lb. helveticus 2/20 cells, which could also protect it from contamination by unwanted bacteria

Inhibition of glycogen synthase kinase-3 enhances NRF2 protein stability, nuclear localisation and target gene transcription in pancreatic beta cells

Accumulation of reactive oxygen species (i.e., oxidative stress) is a leading cause of beta cell dysfunction and apoptosis in diabetes. NRF2 (NF-E2 p45-related factor-2) regulates the adaptation to oxidative stress, and its activity is negatively regulated by the redox-sensitive CUL3 (cullin-3) ubiquitin ligase substrate adaptor KEAP1 (Kelch-like ECH-associated protein-1). Additionally, NRF2 is repressed by the insulin-regulated Glycogen Synthase Kinase-3 (GSK3). We have demonstrated that phosphorylation of NRF2 by GSK3 enhances β-TrCP (beta-transducin repeat-containing protein) binding and ubiquitylation by CUL1 (cullin-1), resulting in increased proteasomal degradation of NRF2. Thus, we hypothesise that inhibition of GSK3 activity or β-TrCP binding upregulates NRF2 and so protects beta cells against oxidative stress. We have found that treating the pancreatic beta cell line INS-1832/13 with the KEAP1 inhibitor TBE31 significantly enhanced NRF2 protein levels. The presence of the GSK3 inhibitor CT99021 or the β-TrCP-NRF2 protein-protein interaction inhibitor PHAR, along with TBE31, resulted in prolonged NRF2 stability and enhanced nuclear localisation (p

Loss of Nrf2 abrogates the protective effect of Keap1 down regulation in a preclinical model of cutaneous squamous cell carcinoma

Cutaneous squamous cell carcinomas (cSCC) are the most common and highly mutated human malignancies, challenging identification of driver mutations and targeted therapies. Transcription factor NF-E2 p45-related factor 2 (Nrf2) orchestrates a cytoprotective inducible program, which counteracts the damaging effects of solar UV radiation, the main etiological factor in cSCC development. Downregulation of Kelch-like ECH-associated protein 1 (Keap1), a Cullin-3/Rbx1 ubiquitin ligase substrate adaptor protein, which mediates the ubiquitination and proteasomal degradation of Nrf2, has a strong protective effect in a preclinical model of cSCC. However, in addition to Nrf2, Keap1 affects ubiquitination of other proteins in the carcinogenesis process, including proteins involved in inflammation and DNA damage repair. Here, we generated Keap1(flox/flox) SKH-1 hairless mice in which Nrf2 is disrupted (Keap1(flox/flox)/Nrf2(−/−)) and subjected them chronically to solar-simulated UV radiation. We found that the incidence, multiplicity and burden of cSCC that form in Keap1(flox/flox)/Nrf2(−/−) mice are much greater than in their Keap1(flox/flox)/Nrf2(+/+) counterparts, establishing Nrf2 activation as the protection mediator. Our findings further imply that inhibition of Nrf2 globally, a strategy proposed for cancer treatment, is unlikely to be beneficial