The role of glutathione in the regulation of nucleotide excision repair during oxidative stress

Nucleotide excision repair (NER) mainly repairs bulky DNA adducts and helix distorting lesions, but is additionally considered to be a back-up system for base excision repair to remove oxidative stress induced DNA damage. Therefore, it can be speculated that NER is up-regulated or primed by oxidative stress. Exposure of human pulmonary epithelial cells (A549) to non-toxic doses of 100 μM H2O2 indeed showed a 2 to 4.5-fold increase in expression of XPA, XPC, ERCC4, and ERCC5, whereas the expression of ERCC1 was 5-fold decreased. Phenotypical assessment of NER capacity (i.e. recognition and incision of benzo[a]pyrene-DNA adducts) showed a significant decrease to less than 50% after H2O2 exposure, which paralleled the effects of H2O2 on ERCC1 expression. To study the possible involvement of glutathione (GSH) in the regulation of NER, cells were pre-incubated with 0.5 mM BSO, resulting in total GSH depletion and increased intracellular oxidative stress. In GSH-depleted cells, the down-regulation of ERCC1 expression by H2O2 was completely abolished and the up-regulation of ERCC4 expression was potentiated from 2.5-fold to >10-fold. Similarly, the H2O2-induced decrease in NER capacity was absent in GSH-depleted cells. Overall, our data suggest that NER capacity as well as the expression of NER related genes can be modulated by oxidative stress. ERCC1 expression and NER capacity correlated strongly (R2 = 0.85, P < 0.01) after oxidant exposure, indicating ERCC1 as a specific target for oxidative stress induced modification of NER.