Endoplasmic Reticulum Stress Increases Multidrug-resistance Protein 2 Expression and Mitigates Acute Liver Injury

Background: Multidrug-resistance protein (MRP) 2 is a key membrane transporter that is expressed on hepatocytes and regulated by nuclear factor kappa B (NF-ΚB). Interestingly, endoplasmic reticulum (ER) stress is closely associated with liver injury and the activation of NF-ΚB signaling. Objective: Here, we investigated the impact of ER stress on MRP2 expression and the functional involvement of MRP2 in acute liver injury. Methods: ER stress, MRP2 expression, and hepatocyte injury were analyzed in a carbon tetrachloride (CCl4)-induced mouse model of acute liver injury and in a thapsigargin (TG)-induced model of ER stress. Results: CCl4 and TG induced significant ER stress, MRP2 protein expression and NF- ΚB activation in mice and LO2 cells (P < 0.05). Pretreatment with ER stress inhibitor 4- phenyl butyric acid (PBA) significantly mitigated CCl4 and TG-induced ER stress and MRP2 protein expression (P < 0.05). Moreover, pretreatment with pyrrolidine dithiocarbamic acid (PDTC; NF-ΚB inhibitor) significantly inhibited CCl4-induced NF-ΚB activation and reduced MRP2 protein expression (1±0.097 vs. 0.623±0.054; P < 0.05). Furthermore, hepatic downregulation of MRP2 expression significantly increased CCl4- induced ER stress, apoptosis, and liver injury. Conclusion: ER stress enhances intrahepatic MRP2 protein expression by activating NF-ΚB. This increase in MRP2 expression mitigates ER stress and acute liver injury.