A549 cells were treated with NLE for 6 or 12 h. a The mRNA levels of NRF2, p21, STAT3, and ATF4 were determined by qPCR assay. b The protein levels of NRF2, p21, STAT3, and ATF4 were detected by Western blot analysis. *P < 0.05, **P < 0.01, compared with the control group.