Role of CYP2E1 activity in endoplasmic reticulum ubiquitination, proteasome association, and the unfolded protein response

In an experimental model of liver cirrhosis, marked increases in ER proteasome content in rat livers were observed 5 h after acute i.p. injection of the hepatotoxicant CCl4. To confirm the role of CYP2E1 in mediating protein misfolding/damage in the ER via its metabolism of CCl4, 293T cells stably transfected with human CYP2El were exposed to CCl4 and cell ER fractions assessed for ubiquitination. Increases in ER ubiquitin conjugates were noted in CYP2EI/293T cells treated with CCl4 and not in controls, suggesting these effects are CYP2E I specific. Finally, the role of CYP2E I in ER homeostasis was investigated by examining the unfolded protein response (UPR). When exposed to CCl4, CYP2EI/293T cells but not 293T or CYPIA2/293T cells showed rapid induction of the UPR-inducible ER chaperone BiP. Collectively, the data presented suggest that CYP2El is capable of inducing significant ER protein damage and stress via its catalytic activation of pro-oxidants. (c) 2005 Elsevier Inc. All rights reserved.