NFE2L2 and adenocarcinoma: A549 cells are derived from an adenocarcinoma of human alveolar basal epithelium and exhibit aberrant activation of NRF2 owing to two mechanisms: one is a somatic mutation in Keap1 at G333C (Singh et al., 2006) and the other is the epigenetic silencing by methylation in the promoter of Keap1 (Wang et al., 2008).