Modulation of Gene Expression by Cancer Chemopreventive Dithiolethiones through the Keap1-Nrf2 Pathway

Abstract

Enzyme inducers such as 3H-1,2-dithiole-3-thione (D3T) enhance the detoxication of environmental carcinogens and protect against neoplasia. The putative molecular sensor for inducers is Keap1, a sulfhydrylrich protein that sequesters the transcription factor Nrf2 in the cytoplasm. Expression of these detoxication enzymes is blunted in nrf2-deficient mice; moreover, these mice are more sensitive to carcinogenesis, and the protective actions of dithiolethiones are lost with nrf2 disruption. Hepatic gene expression profiles were examined by oligonucleotide microarray analysis in vehicleor D3T-treated wild-type mice as well as in nrf2 single and keap1-nrf2 double knockout mice to identify those genes regulated by the Keap1-Nrf2 pathway. Transcript levels of 292 genes were elevated in wild-type mice 24 h after treatment with D3T; 79% of these genes were induced in wild-type, but not nrf2-deficient mice. These nrf2-dependent, D3T-inducible genes included known detoxication and antioxidative enzymes. Unexpected clusters included genes for chaperones, protein trafficking, ubiquitin/26 S proteasome subunits, and signaling molecules. Gene expression patterns in keap1-nrf2 double knockout mice were similar to those in nrf2-single knockout mice. D3T also led to nrf2-dependent repression of 31 genes at 24 h; principally genes related to cholesterol/lipid biosynthesis. Collectively, D3T increases the expression of genes through the Keap1-Nrf2 signaling pathway that directly detoxify toxins and generate essential cofactors such as glutathione and reducing equivalents. Induction of nrf2-dependent genes involved in the recognition and repair/removal of damaged proteins expands the role of this pathway beyond primary control of electrophilic and oxidative stresses into secondary protective actions that enhance cell survival.

Transcriptional expression analysis of ABC efflux transporters and xenobiotic-metabolizing enzymes in the Chinese rare minnow

“…In line with this, the role of Nrf2 in mediating the co-regulation of the phase II enzymes and ABC transporters was further confirmed by the discovery of AREs (antioxidant response elements) in many of these genes. For example, the AREs have been detected in many genes of the phase II enzymes including the GST (Wasserman and Fahl, 1997;Kwak et al, 2003), GCLC (Kwak et al, 2003), and UGT1A1 genes (Yueh and Tukey, 2007); ARE-like sequences were also identified in the mouse ABCCs (Vollrath et al, 2006). These finding suggest that a common regulatory mechanism is possible for the GST, GCLC and ABCC genes (Meijerman et al, 2008).…”

Deficiency of the Nrf1 and Nrf2 Transcription Factors Results in Early Embryonic Lethality and Severe Oxidative Stress

“…Since p53 transcript levels were not elevated in compound mutant cells, the accumulation of p53 protein levels may be due to a decrease in protein turnover and may be a major mechanism by which p53 is regulated by its degradation through the ubiquitin-proteosome pathway (37). It is interesting in this regard that a recent gene profiling experiment showed that cancer chemopreventive agent-mediated induction of ubiquitin-proteosome genes was compromised in livers of Nrf2 mutant mice (53). It is therefore possible that down-regulation of the ubiquitin-proteosome pathway plays a part in p53 activation in compound mutant cells.…”

Modulation of multiple pathways involved in the maintenance of neuronal function during aging by fisetin

“…Although it is not clear at this time how fisetin increases proteasome activity in nerve cells, the time-and substrate-dependence of its effects suggest that fisetin may have both direct and indirect actions on proteasome activity. Many of the protein components of the proteasome are transcriptionally regulated by Nrf2 [47] and Nrf2 inducers can increase proteasome activity in several different cell types [44][45][46]. However, preliminary data suggest that the regulation of proteasome activity by fisetin is likely to be more complex.…”