MAPK1 and colonic neoplasm: We next generated HT29/MDR, HT29/Tg, HT29/Tun, HT29/Bfa clones transduced with a doxycycline-inducible shRNA for PERK. In parallel, we treated these clones with the MEK/ERK inhibitor PD98059, which prevents the phosphorylation and transcriptional activity of Nrf2 in colon cancer [23].