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A20 inhibits oxidized low‐density lipoprotein‐induced apoptosis through negative Fas/Fas ligand‐dependent activation of caspase‐8 and mitochondrial pathways in murine RAW264.7 macrophages
Author(s) -
Li HongLiang,
Wang AiBing,
Zhang Ran,
Wei YuSheng,
Chen HouZao,
She ZhiGang,
Huang Yue,
Liu DePei,
Liang ChihChuan
Publication year - 2006
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.20665
Subject(s) - fadd , fas ligand , apoptosis , fas receptor , cytochrome c , caspase 8 , microbiology and biotechnology , chemistry , mitochondrion , caspase 3 , tumor necrosis factor alpha , caspase , biology , programmed cell death , immunology , biochemistry
A20 was originally characterized as a TNF‐inducible gene in human umbilical vein endothelial cells. As an NF‐κB target gene, A20 is also induced in many other cell types by a wide range of stimuli. Expression of A20 has been shown to protect from TNF‐induced apoptosis and also functions via a negative‐feedback loop to block NF‐κB activation induced by TNF and other stimuli. To date, there are no reports on whether A20 can protect OxLDL‐induced apoptosis in macrophages. For the first time we report that A20 expression blocks OxLDL‐mediated cell toxicity and apoptosis. OxLDL induced the expression of Fas and FasL, and the subsequent caspase‐8 cleavage and treatment with a neutralizing ZB4 anti‐Fas antibody blocked apoptosis induced by OxLDL. Expression of dominant negative FADD efficiently prevented OxLDL‐induced apoptosis and caspase‐8 activation. A20 expression significantly attenuated the increased expression of Fas and FasL, and Fas‐mediated apoptosis. These findings suggest that A20‐mediated protection from OxLDL may occur at the level of Fas/FADD‐caspase‐8 and be FasL dependent. Treatment of RAW264.7 cells with OxLDL induces a series of time‐dependent events, including the release of cytochrome c, Smac and Omi from the mitochondria to the cytosol, activation of caspase‐9, ‐6, ‐2, and ‐3, which are blocked by A20 expression. No cleaved form of Bid was detected, even treatment with OxLDL for 48 h. Expression of dominant negative FADD also efficiently prevented OxLDL‐induced the above apoptotic events. The release of cyto c , Smac and Omi from mitochondria to cytosol, activated by OxLDL treatment, and the activation of caspase‐9 may not be a downstream event of caspase‐8‐mediated Bid cleavage. Therefore, the protective effect of A20 on mitochondrial apoptotic pathway activated by OxLDL may be dependent on FADD. A20 expression reversed OxLDL‐mediated G 0 /G 1 stage arrest by maintaining the expression of cyclin B1, cyclin D1, and cyclin E, and p21 and p73. Thus, A20 expression blocks OxLDL‐mediated apoptosis in murine RAW264.7 macrophages through disrupting Fas/FasL‐dependent activation of caspase‐8 and the mitochondria pathway. J. Cell. Physiol. 208: 307–318, 2006. © 2006 Wiley‐Liss, Inc.