Anti-oxidative stress regulator NF-E2-related factor 2 mediates the adaptive induction of antioxidant and detoxifying enzymes by lipid peroxidation metabolite 4-hydroxynonenal

When HeLa cells were treated with 4-HNE, NRF2 rapidly transloated into the nucleus, as determined by the distribution of NRF2 tagged with the enhanced green fluorescent protein (EGFP) and increased NRF2 protein in the nuclear fraction. Transcriptional activity of ARE-luciferase was significantly induced by 0.01-10 μM of 4-HNE in a dose-dependent manner, and the induction could be blocked by pretreatment with glutathione (GSH). 4-HNE induced transcriptional expression of glutathione S-transferase (GST) A4, aldoketone reductase (AKR) 1C1 and heme oxygenase-1 (HO-1), and the induction was attenuated by knocking down NRF2 using small interfering RNA.NRF2 is critical in mediating 4-HNE induced expression of antioxidant and detoxifying genes. This may account for one of the major cellular defense mechanisms against reactive metabolites of lipids peroxidation induced by oxidative stress and protect cells from cytotoxicity.Polyunsaturated fatty acids (PUFA), essential components of cell membrane, are susceptible to oxidation initiated by free radicals [1]. 4-hydroxylnonenal (4-HNE) is an end product from lipid peroxidation of omega-6 (n-6) PUFA [2]. The physiological concentration of 4-HNE is generally at the low micromolar level, but is remarkably increased under continuous oxidative stress [3]. As an α,β-unsaturated aldehyde, 4-HNE is highly reactive to a variety of nucleophilic sites in DNA and proteins [4]. Exposure to excessive 4-HNE can cause cytotoxicity, inactivation of enzymes, redox imbalance and activation of multiple signaling events, and 4-HNE is implied in the detrimental pathogenesis of a number of degenerative diseases including cancer [5,6]. Several metabolic pathways are involved in the detoxification of 4-HNE, including conjugation with glutathione (GSH) catalyzed by glutathione S-transferases (GST) and reduction of the aldehyde group to corresponding alcohol by aldoketone reductases (AKR) [5].Eukaryotic cells have developed highly efficient machineries t