Enhanced glutathione levels confer resistance to apoptotic and ferroptotic programmed cell death in NEIL DNA glycosylase deficient HAP1 cells
The NTHL1 and NEIL1-3 DNA glycosylases are major enzymes in the removal of oxidative DNA base lesions, via the base excision repair (BER) pathway. To investigate their interplay in human cells, we engineered single, double, triple, and quadruple DNA glycosylase deficient HAP1 cells using the Crisp-cas 9 technology. We found that these DNA glycosylase deficient cells are more resistant to oxidative stress caused by genotoxic agents than wild type cells, and a further augment in resistance was observed upon inhibition of glutathione synthesis. Gene expression analysis revealed that GSH depletion activates the NRF2/KEAP1 pathway and ER stress induced apoptosis. Furthermore, glutathione depleted NEIL triple KO cells are also more resistant to cell death induced via ferroptosis than wild type cells. Finally, we observed higher basal level of glutathione and differential expression of NRF2-regulated genes associated with glutathione homeostasis in these cells. We propose that NEIL deficiency leads to aberrant transcription and subsequent errors in protein synthesis, which cause ER- and proteotoxic stress. This triggers the unfolded protein response, which consequently upregulates intracellular antioxidant defence mechanisms. Altogether, our data suggest that NEIL deficient cells developed an oxidative stress defence mechanism termed hormesis mediated by elevated GSH levels in response to the increased intracellular stress inflicted by loss of NEIL123 activities. Overall design: A panel of HAP1 cells deficient for the DNA glycosylases NEIL11, NEIL2, and NEIL3 were treated after 4h with 200µM BSO or media alone for 48 h. The total RNA was isolated for transcriptome profiling.