Nrf-2 transcriptionally activates P21Cip/WAF1 and promotes A549 cell survival against oxidative stress induced by H2O2

Cancer cells possess elevated ROS coupled with increased levels of antioxidant enzymes which render them resistant against cytotoxic chemotherapies. Therefore, an understanding of the interaction between key molecules involved in stress adaptive mechanisms is important to innovate strategies against cancer cell chemoresistance. Here, the lung adenocarcinoma cell line A549 with constitutively expressed Nrf2 was found to be more tolerant to H2O2 (0.1, 0.2, 0.5 and 1 mM) than normal lung cell line L132 or p53 null lung cancer cell line H1299. Maximum cytoprotection was observed at 0.2mM H2O2 accompanied by a significant increase in p21, Nrf2 and antioxidant enzymes in A549 cells. The increased p21 expression was independent of p53 but dependent on Nrf2 as evident from qPCR, Western blotting and dual luciferase assays after silencing Nrf-2 and p53 genes. Highly conserved Nrf-2 binding sites were identified in p21 promoter by bioinformatics and homology modeling which was further confirmed by ChIP and reporter assay.