Modulation of Glucose-6-phosphate Dehydrogenase Activity and Expression Is Associated with Aryl Hydrocarbon Resistance in Vitro

Abstract

The mutagenic effect of environmental carcinogens has been well documented in animal models and in human studies but the mechanisms involved in preventing carcinogen insult have not been fully elucidated. In this study we examined the molecular and biochemical changes associated with carcinogen resistance in a series of aryl hydrocarbon-resistant MCF-7 cell lines developed by exposure to benzo[a]pyrene (BP). The cell lines were designated as AH R40, AH R100, and AH R200 to denote their increasing fold resistance to BP compared with wild type cells. These cell lines were also resistant to another aryl hydrocarbon (AH), dimethylbenz[a]anthracene, but not to pleiotropic drugs (doxorubicin, vinblastine, and taxol). The resistant cell lines showed an increase in the level of the primary intracellular antioxidant, reduced glutathione, corresponding to increasing AH resistance. However, there was no change in glutathione reductase activity. The generation of reduced glutathione requires NADPH, and we therefore examined the activity and expression of the rate-limiting enzyme in NADPH production, glucose-6-phosphate dehydrogenase (G6PD). An increase in G6PD specific activity was associated with increasing aryl hydrocarbon resistance. This was due to an increased expression of G6PD in resistant cells, which was demonstrated by increases in both protein and mRNA levels. However, there was no increase in the transcription rate of G6PD in the resistant cell lines, indicating that the increase G6PD expression is due to a post-transcriptional modulation, which was confirmed by actinomycin D chase experiments. These results demonstrate that modulation of G6PD expression and activity is an important mechanism in AH resistance.

Sulindac and its metabolites induce carcinogen metabolizing enzymes in human colon cancer cells

“…In addition, the colonic epithelium possesses members of the ATP-binding cassette superfamily of transport proteins, which mediate the efflux of metabolized xenobiotics such as BP. 37,52,53 Thus, one mechanism to prevent the development of colon cancer is to increase the metabolic capacity of the colonic epithelium. Oxidation of PAHs by CYP enzymes results in the metabolic activation of PAHs to reactive intermediates that either bind covalently to DNA to form adducts or are detoxified by Phase 2 enzymes.…”

Multiple transcripts encode glucose 6-phosphate dehydrogenase in the southern cattle tick, Rhipicephalus (Boophilus) microplus

“…NADPH is important in fatty acid synthesis and in detoxification reactions, acting as a cofactor for the regeneration of reduced glutathione and enabling activity of NADPHdependent enzymes necessary for the protection of cells from oxidative damage (Stryer 1995). The G6PDH enzyme has been reported as playing a role in resistance to carcinogens (Yeh et al 2001) and pyrethroids (Kumar et al 1991), and deficiencies of the enzyme manifest as neonatal jaundice and hemolytic anemia in humans (Luzzatto 2006).…”

The Effect of Antioxidant Caffeic Acid Phenethyl Ester (Cape) on Some Enzyme Activities in Cisplatin-Induced Neurotoxicity in Rats

“…NADPH is also generated by the next step in the PPP, the conversion of 6-phosphogluconate to ribulose 5-phosphate by 6-phosphogluconate dehydrogenase (21). NADPH plays an important role in antioxidant reactions together with glutathion (GSH), glutathion-peroxidase (GS-Px) and catalase (CAT).…”