ABCC1 and malignant colon neoplasm: Representative flow cytometry histograms of MRP1 protein in human chemoresistant colon cancer HT29/MDR cells and ER stress-resistant clones (HT29/Tg, HT29/Tun, HT29/Bfa), stably and inducibly transduced with a silencing vector for PERK, or treated with PD98059 (10 μM, 72 h), which blocks Nrf2 nuclear translocation.