Structure/Function Analysis of p55 Tumor Necrosis Factor Receptor and Fas-associated Death Domain

Abstract

Tumor necrosis factor (TNF)1 can induce cell death by necrosis or apoptosis, depending on the cell line (1-4) and/or the intracellular ATP concentration (5). Apoptosis is morphologically characterized by membrane blebbing, shrinking of the cell and its organelles, and internucleosomal degradation of DNA (6). Finally, the cell disintegrates and apoptotic bodies are cleared by phagocytosis, in most cases without any detrimental effects on the surrounding tissue (7,8). In contrast, cell death by necrosis is often accompanied by inflammation due to massive release of the cytoplasmic cell content. Necrosis is characterized by swelling of the cell and its organelles and an immediate loss of the plasma membrane integrity (1). A key step in the pathway to apoptosis is activation of procaspases. Activation of these cysteinyl aspartate-specific proteases is initiated by formation of a death-inducing signaling complex (DISC) after oligomerization of the p55 TNF receptor (TNF-R55) or the Fas receptor by the respective ligands (9, 10). Both death receptors contain a homologous C-terminal cytoplasmic death domain (DD) involved in apoptosis (11,12). After binding of TNF to TNF-R55, the clustered DDs recruit the TNF-R55-associated DD-containing protein TRADD (13-15). TRADD in turn recruits Fas-associated DD protein (FADD) by DD-DD interaction (13). In contrast, the DD of Fas does not require the TRADD adaptor protein but serves as a direct docking surface for FADD (16 -18). Besides its C-terminal DD, FADD contains a death effector domain (DED) implicated in the recruitment of procaspase-8 (19, 20). Oligomerization of procaspase-8 leads to proximity-induced autocatalytic activation followed by direct or indirect downstream activation of executionary caspases, which cleave substrates involved in apoptotic morphology (21,22).The initial intracellular molecular events responsible for necrosis are less well understood. Leist and co-workers (5) proposed a model in which low cellular ATP concentrations give rise to a necrotic cell death process, whereas in the presence of high ATP concentrations the apoptotic, caspase-dependent pathway becomes apparent. On the other hand, it was shown that mitochondria are crucial in the necrotic process (reviewed in Ref. 4). Depletion of mitochondria protects L929sA cells from necrotic cell death (23), and TNF induces the production of mitochondrial reactive oxygen intermediates (ROI) (24). This oxidative phosphorylation-linked ROI production is required for TNF-induced necrotic cell death, since addition of butylated hydroxyanisole (BHA), an oxygen radical scavenger and inhibitor of oxidative phosphorylation (25), blocks TNF cytotoxicity (24). Recently, we demonstrated that inhibition of caspase ac-* This work was supported in part by the Interuniversitaire Attractiepolen. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.‡ T...

Death receptor-induced apoptotic and necrotic cell death: differential role of caspases and mitochondria

“…In cell lines that die apoptotically after TNF exposure the DD of FADD is not cytotoxic; moreover it acts as a dominant negative inhibitor of apoptotic cell death induced by TNF. 33 These results suggest that the common initiator between TNF-RI-and Fas-induced necrosis is the DD of FADD. In Jurkat cells necrotic signaling by death domain receptor has been pinpointed on the kinase activity of RIP 31 and the death effector domain of FADD.…”

“…32 In L929sA cells we have found that the DD of FADD has strong cytotoxic activity, while in apoptotically dying cells it functions as a dominant negative molecule. 33 Less is known about the executioner program of necrotic cell death, although mitochondrial ROS 30 and a variety of proteases have been implicated. 34,35 In order to study possible differences in TNF-and antiFas-induced downstream cytotoxic necrotic and apoptotic pathways we compared a number of cell death parameters in L929sAhFas cells, viz.…”

Inflammatory Response and Glutathione Peroxidase in a Model of Stroke

“…Despite several reports of beneficial effects of this cytokine from in vitro studies and knockout mice, endogenous production of TNF-␣ in I/R brain models is deleterious (38). TNF-␣ is a potent activator of necrosis and/or apoptosis through TNF Rp55 receptor depending on the cell type and/or the intracellular ATP concentration (15).…”

“…These mechanisms may involve levels of other mediators, differences in intrinsic cell sensitivity from those brain regions, or significantly deeper oxygen deprivation and ATP depletion in a core region of the infarct compared with the penumbral zone. It was recently reported that both TNF-␣-and FasL-induced pathways could lead to apoptosis as well as necrosis (15,16), and in at least one model system (17) it has been reported that cellular ATP concentration is a critical parameter in the decision between the two cell death pathways.…”

RIP1, a kinase on the crossroads of a cell's decision to live or die

“…Whereas the DED of FADD is able to propagate apoptotic cell death, its DD seems to be crucial to initiate necrotic signalling. 36,37 In the case of Fas and TRAIL-R-induced signalling, FADD is recruited to the receptor and can directly initiate downstream signalling cascades among which is necrosis. The role of FADD in TNF-R1-induced necrosis is still unclear.…”