Heat shock protein 72 modulates pathways of stress-induced apoptosis
ABSTRACT The resistance to stress-induced apoptosis conferred by the thermotolerant state or by exogenous expression of HSP72 was measured in mouse embryo fibroblasts. The induction of thermotolerance protects cells from heat, tumor necrosis factor alpha (TNFalpha), and ceramide-induced apoptosis but not from ionizing radiation. Because the development of thermotolerance is associated with increased levels of heat shock proteins, we determined whether constitutive expression of one of the major inducible heat shock proteins, HSP72, could also protect cells from stress-induced apoptosis. Cells expressing constitutive HSP72 were shown to have significantly reduced levels of apoptosis after heat, TNFalpha, and ceramide but not after ionizing radiation. Activation of stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) was found to be strongly inhibited in thermotolerant cells after heat shock but not after other stresses. Cells that constitutively express HSP72 did not demonstrate decreased SAPK/JNK activation after any of these stresses. Thus, factors other than HSP72 that are induced in the thermotolerant state are able to reduce activation of SAPK/JNK after heat stress. Notably, the level of activation of SAPK/JNK did not correlate with the amount of apoptosis detected after different stresses. Constitutive HSP72 expression inhibited poly(ADP-ribose) polymerase cleavage in cells after heat shock and TNFalpha but not after ceramide or ionizing radiation. The results suggest either that SAPK/JNK activation is not required for apoptosis in mouse embryo fibroblasts or that HSP72 acts downstream of SAPK/JNK. Furthermore, the data support the concept that caspase activity, which can be down-regulated by HSP72, is a crucial step in stress-induced apoptosis. Based on data presented here and elsewhere, we propose that the heat shock protein family can be classified as a class of anti-apoptotic genes, in addition to the Bcl-2 and inhibitor of apoptosis protein families of genes.
Toxicological Sciences 01/2002; 68(1):82-92. DOI:10.1093/toxsci/68.1.82 · 4.48 Impact Factor
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ABSTRACT: During sepsis, hepatic apoptosis occurred, which is associated with inactivation of PKCα and elevation of tumor necrosis factor-alpha (TNFα), an apoptosis trigger. Heat shock, accompanied by the increase of heat-shock protein (Hsp72), has been shown to exhibit a protective role on cell survival. However, Hsp72 was unable to express during sepsis when the apoptosis was markedly increased. We hypothesized that hepatic apoptosis during sepsis may be due to the failure to induce expression of Hsp72, which is activated by PKC-phosphorylated HSF. This study was designed to examine the role of PKCα in Hsp72 expression and the anti-apoptotic effect of Hsp72 on hepatic epithelial cells by analyzing a TNFα-induced apoptosis system. The following results were observed: (1) Hsp72 was highly expressed at 8 h after heat-shock treatment in a clone 9 hepatic epithelial cell line; (2) the protein expression of PKCα in membrane-associated fraction was decreased by TNFα treatment; (3) the TNFα-induced cell death, especially apoptosis, was diminished by heat-shock pretreatment; (4) in the presence of PKCα antisense, which blocks the PKCα resynthesis, no protective effect of heat-shock pretreatment was observed, and the protein expression of Hsp72 was significantly suppressed. These results suggest that PKCα plays a critical role in the expression of Hsp72, which subsequently protects against TNFα-induced hepatic apoptosis.Experimental Cell Research 06/2004; 296(2):276-284. DOI:10.1016/S0014-4827(04)00052-7 · 3.37 Impact Factor
Arteriosclerosis Thrombosis and Vascular Biology 01/2002; 22(10):1547-1559. DOI:10.1161/01.ATV.0000029720.59649.50 · 5.53 Impact Factor