NF-κB Inducers Upregulate cFLIP, a Cycloheximide-Sensitive Inhibitor of Death Receptor Signaling

Abstract

The caspase 8 homologue FLICE-inhibitory protein (cFLIP) is a potent negative regulator of death receptorinduced apoptosis. We found that cFLIP can be upregulated in some cell lines under critical involvement of the NF-B pathway, but NF-B activation was clearly not sufficient for cFLIP induction in all cell lines. Treatment of SV80 cells with the proteasome inhibitor N-benzoyloxycarbonyl (Z)-Leu-Leu-leucinal (MG-132) or geldanamycin, a drug interfering with tumor necrosis factor (TNF)-induced NF-B activation, inhibited TNF-induced upregulation of cFLIP. Overexpression of a nondegradable IB␣ mutant (IB␣-SR) or lack of IB kinase ␥ expression completely prevented phorbol myristate acetate-induced upregulation of cFLIP mRNA in Jurkat cells. These data point to an important role for NF-B in the regulation of the cFLIP gene. SV80 cells normally show resistance to TNF-related apoptosis-inducing ligand (TRAIL) and TNF, as apoptosis can be induced only in the presence of low concentrations of cycloheximide (CHX). However, overexpression of IB␣-SR rendered SV80 cells sensitive to TRAIL-induced apoptosis in the absence of CHX, and cFLIP expression was able to reverse the proapoptotic effect of NF-B inhibition. Western blot analysis further revealed that cFLIP, but not TRAF1, A20, and cIAP2, expression levels rapidly decrease upon CHX treatment. In conclusion, these data suggest a key role for cFLIP in the antiapoptotic response of NF-B activation.Several years ago, p65/RelA knockout mice, which show an embryonic lethal phenotype due to extensive apoptosis of hepatocytes, gave a first clue that NF-B may have an important role in the inhibition of apoptosis (3). Subsequent studies revealed that inhibition of NF-B activation enhances the apoptotic effects of a variety of death inducers, like tumor necrosis factor (TNF), ionizing radiation, and chemotherapeutic agents (4,25,36,39,43), whereas pretreatment of cells with NF-B inducers, like interleukin 1 (IL-1), can confer resistance against the induction of apoptosis (12,19). On the other hand, NF-B activation can be inhibited by caspase-generated cleavage products of components of the NF-B signaling pathway that act as dominant-negative variants of their full-length parental forms (1,16,22,24,31). Hence, activation of the NF-B pathway and induction of apoptosis inhibit each other. This leads to a rapid amplification of the particular signaling pathway that is initially dominant. This regulatory circuit facilitates a clear decision between life and death at the cellular level in cells that are exposed to a complex pattern of distinct and possibly counteracting stimuli.In line with its antiapoptotic properties, NF-B regulates several genes encoding proteins with antiapoptotic properties, such as A20 (33), cIAP2 (8), TRAF1 (35, 40), Bfl-1/A1 (20, 45), IEX-1L (44), and Bcl-x L (7). Although ectopic overexpression of one or a combination of these proteins may efficiently prevent apoptosis induced by TNF, ionizing radiation, or chemotherapeutic agents, it is still questionable wheth...

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.…”

Guggulsterone inhibits tumor cell proliferation, induces S-phase arrest, and promotes apoptosis through activation of c-Jun N-terminal kinase, suppression of Akt pathway, and downregulation of antiapoptotic gene products

“…Because the constitutive expression of the proteins Bfl-1, xIAP, cFLIP, BclXL, Bcl-2, and survivin has been implicated in cell survival and anti-apoptosis [25][26][27][28][29][30][31][32][33], we examined the effect of guggulsterone on the constitutive expression of these genes. Guggulsterone suppressed the expression of these genes in a time-dependent manner ( Fig.…”