Schattenberg Jörn M, Wang Yongjun, Rigoli Raina M, Koop Dennis R, Czaja Mark J
Department of Medicine and Marion Bessin Liver Research Center, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
Hepatology. 2004 Feb;39(2):444-55. doi: 10.1002/hep.20067.
Chronic oxidative stress induced by overexpression of the cytochrome P450 isoform 2E1 (CYP2E1) has been implicated in hepatocyte injury and death. However, the mechanism by which CYP2E1 overexpression may promote cell death is unknown. Acute oxidative stress activates mitogen-activated protein kinases (MAPK), suggesting that chronic oxidant generation by CYP2E1 may regulate cellular responses through these signaling pathways. The effect of CYP2E1 overexpression on MAPK activation and their function in altering death responses of CYP2E1-overexpressing hepatocytes were investigated. Chronic CYP2E1 overexpression led to increased extracellular signal-regulated kinase 1/2 (ERK1/2) activation constitutively and in response to oxidant stress from the superoxide generator menadione. CYP2E1-overexpressing cells were resistant to menadione toxicity through an ERK1/2-dependent mechanism. Similar to menadione, the polyunsaturated fatty acid (PUFA) arachidonic acid (AA) induced an increased activation of ERK1/2 in hepatocytes that overexpressed CYP2E1. However, CYP2E1-overexpressing cells were sensitized to necrotic death from AA and the PUFA gamma-linolenic acid, but not from saturated or monounsaturated fatty acids. Death from PUFA resulted from oxidative stress and was blocked by inhibition of ERK1/2, but not p38 MAPK or activator protein-1 signaling. CYP2E1 expression induced ERK1/2 activation through increased epidermal growth factor receptor (EGFR)/c-Raf signaling. Inhibition of EGFR signaling reversed CYP2E1-induced resistance to menadione and sensitization to AA toxicity. In conclusion, chronic CYP2E1 overexpression leads to sustained ERK1/2 activation mediated by EGFR/c-Raf signaling. This adaptive response in hepatocytes exposed to chronic oxidative stress confers differential effects on cellular survival, protecting against menadione-induced apoptosis, but sensitizing to necrotic death from PUFA.
细胞色素P450同工酶2E1（CYP2E1）过表达所诱导的慢性氧化应激与肝细胞损伤和死亡有关。然而，CYP2E1过表达促进细胞死亡的机制尚不清楚。急性氧化应激可激活丝裂原活化蛋白激酶（MAPK），这表明CYP2E1产生的慢性氧化剂可能通过这些信号通路调节细胞反应。研究了CYP2E1过表达对MAPK激活的影响及其在改变CYP2E1过表达肝细胞死亡反应中的作用。慢性CYP2E1过表达导致细胞外信号调节激酶1/2（ERK1/2）持续激活，并对超氧化物生成剂甲萘醌产生的氧化应激作出反应。CYP2E1过表达细胞通过ERK1/2依赖性机制对甲萘醌毒性具有抗性。与甲萘醌类似，多不饱和脂肪酸（PUFA）花生四烯酸（AA）在过表达CYP2E1的肝细胞中诱导ERK1/2激活增加。然而，CYP2E1过表达细胞对AA和PUFAγ-亚麻酸的坏死性死亡敏感，但对饱和或单不饱和脂肪酸不敏感。PUFA诱导的死亡是由氧化应激引起的，并被ERK1/2抑制所阻断，但不受p38 MAPK或活化蛋白-1信号通路的影响。CYP2E1表达通过增加表皮生长因子受体（EGFR）/c-Raf信号传导诱导ERK1/2激活。抑制EGFR信号传导可逆转CYP2E1诱导的对甲萘醌的抗性和对AA毒性的敏感性。总之，慢性CYP2E1过表达导致由EGFR/c-Raf信号传导介导的ERK1/2持续激活。这种暴露于慢性氧化应激的肝细胞中的适应性反应对细胞存活具有不同影响，可保护细胞免受甲萘醌诱导的凋亡，但对PUFA诱导的坏死性死亡敏感。
