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TNF α‐induced ras activation due to ethanol promotes hepatocyte proliferation independently of liver injury in the mouse
Author(s) -
Isayama Fuyumi,
Froh Matthias,
Yin Ming,
Conzelmann Lars O.,
Milton Richard J.,
McKim Stephen E.,
Wheeler Michael D.
Publication year - 2004
Publication title -
hepatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.488
H-Index - 361
eISSN - 1527-3350
pISSN - 0270-9139
DOI - 10.1002/hep.20137
Subject(s) - liver injury , hepatocyte , endocrinology , medicine , ethanol , tumor necrosis factor alpha , lipid peroxidation , oncogene , alcoholic liver disease , chemistry , superoxide dismutase , necrosis , biology , oxidative stress , apoptosis , biochemistry , in vitro , cirrhosis , cell cycle
Tumor necrosis factor α (TNFα) has been shown to be both proapoptotic and mitogenic for hepatocytes and necessary for alcohol‐induced liver injury. Ras, a known proto‐oncogene, is very important in the regulation of cellular responses to TNFα. Therefore, the purpose of this study was to investigate the role of Ras in alcohol‐induced pathogenesis. Male C57Bl/6 mice were fed ethanol or high‐fat control diet via intragastric cannulation for 4 weeks. Ras activity was increased significantly after 4 weeks of ethanol and correlated with an increase in pathologic features. However, in mice deficient in the receptor‐type 1 for TNFα (TNFR1 ‐/‐ ), ethanol‐induced liver injury and the increase in Ras activity were significantly blunted compared with wild‐type mice. Furthermore, it was demonstrated that H‐, K‐, and R‐Ras isoforms were increased after ethanol exposure in wild‐type mice. In TNFR1 ‐/‐ mice, R‐Ras activity remained elevated by ethanol, whereas H‐Ras and K‐Ras activity was blunted significantly under these conditions. Interestingly, hepatocellular proliferation, which was elevated approximately fivefold after 4 weeks of chronic ethanol in wild‐type mice, was also blunted in TNFR1 ‐/‐ mice given ethanol. Inhibition of Ras with adenovirus containing a dominant‐negative Ras had no effect on ethanol‐induced liver injury, but significantly blunted ethanol‐induced hepatocyte proliferation by more than 50%. Overexpression of mitochondrial superoxide dismutase using recombinant adenovirus blunted lipid peroxidation and attenuated hepatic injury resulting from ethanol, but had no effect on Ras activation and hepatocyte proliferation caused by ethanol. In conclusion, these data support the hypotheses that hepatocellular oxidative stress leads to cell death and that TNFα‐induced Ras activation is important in hepatic proliferation in response to ethanol‐induced liver injury. (H EPATOLOGY 2004;39:721–731.)