科研资料整理

J. Biol. Chem., Vol. 283, Issue 3, 1628-1636, January 18, 2008

Membrane phospholipids are susceptible to oxidation, which is involved in various pathological processes such as inflammation, atherogenesis, neurodegeneration, and aging. One enzyme that may help to remove oxidized phospholipids from cells is intracellular type II platelet-activating factor acetylhydrolase (PAF-AH (II)), which hydrolyzes oxidatively fragmented fatty acyl chains attached to phospholipids. Overexpression of PAF-AH (II) in cells or tissues was previously shown to suppress oxidative stress-induced cell death. In this study we investigated the functions of PAF-AH (II) by generating PAF-AH (II)-deficient (Pafah2-/-) mice. PAF-AH (II) was predominantly expressed in epithelial cells such as kidney proximal and distal tubules, intestinal column epithelium, and hepatocytes. Although PAF-AH activity was almost abolished in the liver and kidney of Pafah2-/- mice, Pafah2-/- mice developed normally and were phenotypically indistinguishable from wild-type mice. However, mouse embryonic fibroblasts derived from Pafah2-/- mice were more sensitive to tert-butylhydroperoxide treatment than those derived from wild-type mice. When carbon tetrachloride (CCl4) was injected into mice, Pafah2-/- mice showed a delay in hepatic injury recovery. Moreover, after CCl4 administration, liver levels of the esterified form of 8-iso-PGF2{alpha}, a known in vitro substrate of PAF-AH (II), were higher in Pafah2-/- mice than in wild-type mice. These results indicate that PAF-AH (II) is involved in the metabolism of esterified 8-isoprostaglandin F2{alpha} and protects tissue from oxidative stress-induced injury.

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Cell Research advance online publication 24 December 2007; doi: 10.1038/cr.2007.112

Intracellular redox homeostasis plays a critical role in determining
tumor cells’ sensitivity to drug-induced apoptosis. Here we
investigated the role of thioredoxin-1 (TRX1), a key component of redox
regulation, in arsenic trioxide (As₂O₃)-induced apoptosis. Over-expression of wild-type TRX1 in HepG₂ cells led to the inhibition of As₂O₃-induced
cytochrome c (cyto c) release, caspase activation and apoptosis, and
down-regulation of TRX1 expression by RNAi sensitized HepG₂ cells to As₂O₃-induced apoptosis. Interestingly, mutation of the active site of TRX1 from Cys^32/35 to Ser^32/35
converted this molecule from an apoptotic protector to an apoptotic
promoter. In an effort to understand the mechanisms of this conversion,
we used isolated mitochondria from mouse liver and found that
recombinant wild-type TRX1 could protect mitochondria from the
apoptotic changes. In contrast, the mutant form of TRX1 alone elicited
mitochondria-related apoptotic changes, including the mitochondrial
permeability transition pore (mPTP) opening, loss of mitochondrial
membrane potential, and cyto c release from mitochondria. These
apoptotic effects were inhibited by cyclosporine A (CsA), indicating
that mutant TRX1 targeted to mPTP. Alteration of TRX1 from its reduced
form to oxidized form in vivo by 2,4-dinitrochlorobenzene (DNCB), a specific inhibitor of TRX reductase, also sensitized HepG₂ cells to As₂O₃-induced
apoptosis. These data suggest that TRX1 plays a central role in
regulating apoptosis by blocking cyto c release, and inactivation of
TRX1 by either mutation or oxidization of the active site cysteines may
sensitize tumor cells to As₂O₃-induced apoptosis.

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