NF-κB Signals Induce the Expression of c-FLIP

Abstract

Members of the tumor necrosis factor (TNF) receptor family and their corresponding ligands are critical regulators of apoptosis and various other cellular processes. Some of the receptors (Fas, TNF-R1, TRAIL-R1, TRAIL-R2, TRAMP/ DR3, DR6, and EDA-R) contain a cytoplasmic region, called the death domain (DD), which is essential for cell death signaling (18,22). Signals emanating from Fas and TNF-R1 have been intensively studied (14). Upon receptor activation, the DD of Fas undergoes direct homotypic interaction with a DD in the adapter protein FADD, while FADD recruitment is indirect (via TRADD) in the case of TNF-R1 (4). The death effector domain (DED) at the amino terminus of FADD then recruits pro-caspase 8 via homotypic interaction with its two DEDs. The high local concentration of caspase 8 zymogens facilitates self-processing and assembly of the mature enzyme. Activated caspase 8 initiates apoptosis by subsequent cleavage of downstream caspases (caspase-3, -6, and -7).Death induced by death receptors is tightly regulated by genes that are activated by the transcription factor NF-B (25). Modulation of the response in favor of NF-B protects cells from apoptosis; failure to do so results in increased cell death. At least six NF-B-responsive genes are involved in this survival amplification loop (26), i.e., those that encode IAP-1 and IAP-2, which block caspase activity (7); that which encodes the Bcl-2 family member A1 (25); and those that encode TRAF-1, TRAF-2 (1), and A20 (21), which are themselves implicated in the NF-B signaling pathway. However, overexpression of all of these genes affords, at best, partial protection, in particular from death triggered by TNF (25). The only known potent inhibitor of death receptor signals is c-FLIP. Two c-FLIPs have been characterized (23, 24). The full-length 55-kDa-long form of FLIP (FLIP L ) exhibits overall structural homology to caspase 8, containing two DEDs that interact with FADD and an inactive caspase-like domain. An alternatively spliced short form of FLIP (FLIP S ) contains only the two DEDs and displays reduced antiapoptotic capacity.We undertook a series of experiments to investigate whether c-FLIP is implicated in the antiapoptotic NF-B response. Here we provide evidence that FLIP expression is upregulated upon the stimulation of several signaling pathways that are known to trigger activation of the transcription factor NF-B. Moreover, we found that cells that were rendered highly sensitive to death ligand-induced apoptosis by blocking NF-B activation could be rescued by expressing FLIP. FLIP may therefore play a key role in the NF-B-mediated control of death signals. MATERIALS AND METHODSAntibodies and materials. Rabbit anti-TRAF2 polyclonal antibody C20, rabbit anti-cIAP1 polyclonal antibody H-85, and mouse anti-TRAF1 monoclonal antibody H3 were purchased from Santa Cruz Biotechnology (Santa Cruz, Calif.). Rat anti-cFLIP monoclonal antibody Dave II was from Alexis, Lausen Switzerland, and anti-Phospho-IBa antibody was from Biolab. Anti-tubulin and antiFl...

In vitro generated human memory‐like T cells are CD95 type II cells and resistant towards CD95‐mediated apoptosis

“…Interestingly, whereas LTC are in most respects similar to freshly activated T cells -both are CD95 type II in terms of DISC formation, show similar DISC activity and similar expression levels of anti-apoptotic Bcl-2 family members, they differ markedly with respect to c-FLIP expression. Freshly activated T cells express elevated levels of c-FLIP, especially its short splice variant c-FLIP S [38], possibly a direct effect of TCR signaling and activation of the NF-jB pathway [42,43]. In contrast, we did not detect elevated levels of c-FLIP in LTC consistent with the absence of recent TCR stimulation.…”

Necrostatin Decreases Oxidative Damage, Inflammation, and Injury after Neonatal HI

“…In this model, consistent with previous reports, there is no effect of necrostatin on caspase activity (Degterev et al, 2005), and in necrostatin-treated mice, there is an increase in the number of cells with an apoptotic profile. The decrease in FLIP gene and protein expression in necrostatin-treated mice may also support increased apoptosis (Kreuz et al, 2001) because FLIP normally acts as a dominant negative for caspase 8 (Micheau et al, 2001). The shift to a greater incidence of apoptosis in necrostatin-treated mice after HI is consistent with these findings.…”

Current insights into the regulation of programmed cell death by NF-κB

“…Recent work has uncovered that A20 promotes the elimination of RIP1 in the TNF-R1 complex by replacing K63 ubiquitin chains with K48 polyubiquitin, thereby acting as both a deubiquitinating enzyme and as an E3 ligase to downregulate NF-kB signaling to suppress chronic inflammation and cell death . cFLIP potently suppresses death receptor-induced apoptosis, as it blunts activation of pro-caspase-8 and -10 (Micheau et al, 2001;Kreuz et al, 2004). It has recently been shown that cFLIP also participates along with caspase-8 in promoting NF-kB activation via BCL-10, mucosa-associated-lymphoidtissue lymphoma-translocation gene 1 (MALT1) and RIP1 and thus plays a key role in T-cell survival and proliferation following T-cell-receptor stimulation (Abraham and Shaham, 2004;Zhou et al, 2004;Launay et al, 2005, reviewed in Budd et al, 2006.…”