科研之友
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摘要
Tumor necrosis factor-alpha(TNF alpha) stimulation of hepatocytes induces either cell survival or apoptosis, which seems to be regulated by the ubiquitin-proteasome system. Here we investigated the role of TNF alpha-induced down-modulation of the deubiquitinating enzyme USP2 for hepatocyte survival. Inhibition of hepatocyte apoptosis by pre-treatment with TNF alpha (TNF alpha tolerance) was analyzed in the mouse model of galactosamine/TNF alpha-induced liver injury and in actinomycin D/TNF alpha-treated primary mouse hepatocytes. The role of USP2 for TNF alpha-induced hepatocyte survival was studied using small interference RNA or an expression clone. Injection of mice or preincubation of hepatocytes with TNF alpha caused a rapid down-regulation of hepatic USP2-41kD, the predominant USP2 isoform in the liver. In vitro an artificial knockdown of USP2 inhibited actinomycin D/TNF alpha-induced hepatocyte apoptosis, which was associated with elevated levels of the anti-apoptotic protein c-Flip(L/S) and a concomitant decrease of cellular levels of the ubiquitin-ligase Itch, a negative regulator of c-Flip. USP2-41kD overexpression abrogated TNF alpha tolerance in vitro, prevented accumulation of c-Flip(L/S) and resulted in elevated levels of Itch. Accordingly, c-Flip(L/S) protein levels were elevated in livers of TNF alpha-tolerant mice, which correlated to a switch from JNK and ERK to p38 signaling after galactosamine/TNF re-challenge. Our results indicate that TNF alpha-induced USP2 down-regulation is an effective cytoprotective mechanism in hepatocytes. Hence, USP2 could be a novel pharmacological target, and specific USP2 inhibitors might be potential candidates for the treatment of inflammation-related apoptotic liver damage.
- 出版日期2009-1-2
