Cellular mechanisms of redox cell signalling: role of cysteine modification in controlling antioxidant defences in response to electrophilic lipid oxidation products

Abstract

The molecular mechanisms through which oxidized lipids and their electrophilic decomposition products mediate redox cell signalling is not well understood and may involve direct modification of signal-transduction proteins or the secondary production of reactive oxygen or nitrogen species in the cell. Critical in the adaptation of cells to oxidative stress, including exposure to subtoxic concentrations of oxidized lipids, is the transcriptional regulation of antioxidant enzymes, many of which are controlled by antioxidant-responsive elements (AREs), also known as electrophile-responsive elements. The central regulator of the ARE response is the transcription factor Nrf2 (NF-E2-related factor 2), which on stimulation dissociates from its cytoplasmic inhibitor Keap1, translocates to the nucleus and transactivates ARE-dependent genes. We hypothesized that electrophilic lipids are capable of activating ARE through thiol modification of Keap1 and we have tested this concept in an intact cell system using induction of glutathione synthesis by the cyclopentenone prostaglandin, 15-deoxy-Delta12,14-prostaglandin J2. On exposure to 15-deoxy-Delta12,14-prostaglandin J2, the dissociation of Nrf2 from Keap1 occurred and this was dependent on the modification of thiols in Keap1. This mechanism appears to encompass other electrophilic lipids, since 15-A(2t)-isoprostane and the lipid aldehyde 4-hydroxynonenal were also shown to modify Keap1 and activate ARE. We propose that activation of ARE through this mechanism will have a major impact on inflammatory situations such as atherosclerosis, in which both enzymic as well as non-enzymic formation of electrophilic lipid oxidation products are increased.

γ-Glutamyl transpeptidase is induced by 4-hydroxynonenal via EpRE/Nrf2 signaling in rat epithelial type II cells

“…An alternative hypothesis of Nrf2 liberation, modification of Keap1, proposes that some reactive -SH groups on Keap1 act as oxidative stress sensors and that modification of them by ROS or electrophiles disrupts the Nrf2-Keap1 complex leading to Nrf2 dissociation. This hypothesis is supported by evidence of continuous Nrf2 activation by mutation of the active cysteine residues of Keap1 [67,70,71] and by the finding of conjugate formation between the electrophiles and the thiol group in Keap1 [72]. It seems that in the case of Nrf2 activation by HNE, Keap1 modification may be involved.…”

“…It seems that in the case of Nrf2 activation by HNE, Keap1 modification may be involved. Levonen et al found that HNE could conjugate with Keap1 in vivo, and the author proposed that this might be the underlying mechanism of HNE-mediated Nrf2 nuclear translocation [72]. Nonetheless, since HNE has been found to activate various signaling pathways including PKC [73][74][75][76][77][78][79], the possibility of Nrf2 phosphorylation by HNE-mediated signaling pathways cannot be excluded.…”

Oxidative stress-inducible lentiviral vectors for gene therapy

“…10,27,28 AREregulated gene transcription has been shown to be a central mechanism providing protection against oxidative stress in the cardiovascular system. [29][30][31] Oxidized low density lipoprotein and 15d-PGJ 2 , agents that are important in vascular inflammatory processes such as atherogenesis and are present in atherosclerotic lesions, 22,32 are also potent instigators of ARE activation, 17,33 suggesting that vascular inflammatory processes could be targets for ARE-regulated gene therapy. In addition, in I/R injury, activation of Nrf2 during reperfusion mediates cytoprotective gene expression, 34 implying that ARE-regulated vectors could also be used for attenuation of reperfusion injury.…”

“…23,24 It is also a potent inducer of Nrf2. 17,19 In HUVECs, the reporter gene expression of all constructs was increased by 15d-PGJ 2 ( Figure 2c). Similar to 293T cells, the basal luciferase activity was higher when the number of inserts was increased.…”

“…15 Agents which activate ARE include heavy metals, heme, ultraviolet irradiation and oxidized lipids. 12,16,17 A number of ARE target-genes encoding antioxidant or phase II detoxification genes have been characterized. These include glutamate-cysteine ligase, the rate-limiting enzyme of glutathione synthesis, which consists of catalytic and modifier (GCLM) subunits, HO-1 and NAD(P)H:quinone oxidoreductase-1 (NQO1).…”