Epigenetic regulation of NRF2-NQO1 axis in human head and neck-originating cancer cell lines and untransformed fibroblasts exposed to nutritional stress

Depletion of glucose/glutamine is associated with a reduced level of Nicotinamide Adenine Dinucleotide Phosphate (NADPH), which is an important cofactor for replenishing cellular glutathione. Accordingly, starvation leads to increased levels of reactive oxygen species (ROS). For decreasing the ROS, cells activate detoxifying machinery based on the action of transcription factor Nuclear Factor Erythroid 2 Like 2 (NRF2). One of the NRF2 targets is an antioxidative enzyme, NAD(P)H: Quinone Dehydrogenase 1 (NQO1), which has a binding site for NRF2 in its promoter. The NRF2-NQO1 axis was explored in three head and neck-originating cancer cell lines: Cal 27, Detroit 562 and FaDu and in immortalized fetal lung fibroblasts: IMR-90 Four nutritional conditions were applied for 48 hours:a)NC1: high glucose (4, 5 g/L) + glutamine (0, 584 g/L) ; b)NC2: low glucose (1 g/L) + glutamine (0, 584 g/L) ; c)NC3: traces of glucose and glutamine provided by fetal bovine serum (FBS ; 0.69 mM glucose ; 0.05 mM glutamine) ; d)NC4: traces of glucose + glutamine (0, 584 g/L). Cellular viability, proliferation and ROS were measured. Quantification of NRF2 and NQO1 transcripts was combined with chromatin immunoprecipitation (ChIP) for discovering H3K27me3 enrichment and the amount of NRF2 bound to NQO1 promoter. Among the three cancer cell lines, FaDu was the most dependent on glucose for maintaining proliferation and glutamine had a minimal effect on restoring FaDu replicative potential. IMR-90 cells were entirely dependent on glucose. NRF2- NQO1 axis response to nutritional stress was cell type specific. Cal 27, Detroit 562 and IMR-90 upregulated NQO1 transcription under the NC3 condition.e There was no significant change in the NQO1 transcription rate in FaDu. ChIP analyses revealed that NC3 influences the amount of H3K27me3 ( a 3.50 and 1.25-fold increase in Cal 27 and FaDu, respectively) and NRF2 a(3-fold increase in Cal 27, 33-fold decrease in FaDu), bound to the NQO1 promoter.