The E3 Ubiquitin Ligase Itch Couples JNK Activation to TNFα-induced Cell Death by Inducing c-FLIPL Turnover

Abstract

The proinflammatory cytokine tumor necrosis factor (TNF) alpha signals both cell survival and death. The biological outcome of TNFalpha treatment is determined by the balance between NF-kappaB and Jun kinase (JNK) signaling; NF-kappaB promotes survival, whereas JNK enhances cell death. Critically, identity of a JNK substrate that promotes TNFalpha-induced apoptosis has been outstanding. Here we show that TNFalpha-mediated JNK activation accelerates turnover of the NF-kappaB-induced antiapoptotic protein c-FLIP, an inhibitor of caspase-8. This is not due to direct c-FLIP phosphorylation but depends on JNK-mediated phosphorylation and activation of the E3 ubiquitin ligase Itch, which specifically ubiquitinates c-FLIP and induces its proteasomal degradation. JNK1 or Itch deficiency or treatment with a JNK inhibitor renders mice resistant in three distinct models of TNFalpha-induced acute liver failure, and cells from these mice do not display inducible c-FLIP(L) ubiquitination and degradation. Thus, JNK antagonizes NF-kappaB during TNFalpha signaling by promoting the proteasomal elimination of c-FLIP(L).

Resveratrol sensitizes melanomas to TRAIL through modulation of antiapoptotic gene expression

“…The well known control of Bcl-xL, Survivin, TRAIL and Fas genes by STAT3 certainly demonstrated its integral role as a regulator of apoptosis in melanomas [9]. An additional important target of RSV in melanoma cells was the activation of the JNK-cJun pathway, which was involved in regulating the expression and turnover of cFLIP [11,13] and the upregulation of sensitivity to TRAIL. Interestingly, that strong activation of MAPK p38-ATF2 by RSV in melanoma cells was involved in the regulation of cell survival that was strongly decreased after specific inhibition of this pathway (Fig.…”

“…Activation of the JNK-cJun pathway is involved in downregulation of cFLIP expression [11,13], which has been described as one of the main negative regulators of the extrinsic apoptotic pathway. Since inhibition of JNK activity modulates numerous cell functions besides cFLIP regulation, we used direct cFLIP suppression by specific RNAi to determine a role of cFLIP in TRAIL+RSV induced apoptosis.…”

“…One of the key contributors to radio-and chemoresistance of human melanomas is upregulation of transcription factors STAT3 and NF-κB, which control expression of numerous antiapoptotic genes in cancer cells, including cFLIP, cIAP, XIAP, Bcl-xL, Survivin, as well as suppressing proapoptotic genes [7][8][9][10]. On the other hand, via activation of cJun, JNK is involved in the negative regulation of cFLIP (an inhibitor of caspase-8) expression [11,12] and, via activation of E3 ubiquitin-protein ligase Itch, in acceleration of proteasome-dependent cFLIP degradation [13]. Taken together, these data suggest that agents that simultaneously downregulate NF-κB and STAT3 activities, while upregulating JNK-cJun activity, might increase sensitivity to TRAIL-or Fas-mediated apoptosis.…”

MAPK signaling in inflammation-associated cancer development

“…JNK-induced apoptosis was found to be largely dependent on the phosphorylation and expression of the Bcl-2 protein family (Lei et al, 2002). Sustained, but not transient, JNK activation has also been shown to promote the E3 ubiquitin ligase Itch-mediated degradation of the caspase inhibitor c-FLIP upon TNFα stimulation (Chang et al, 2006). Interestingly, it was proposed that the duration of JNK activation appears to determine the pro-or anti-apoptotic functions.…”

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

“…Although the extent to which NF-kBmediated inhibition of the JNK pathway suppresses apoptosis as opposed to necrosis remains an open question (Ventura et al, 2004); reviewed in Papa et al, 2006), it is clear that efficient NF-kB-dependent synthesis of antiapoptotic factors and antioxidant molecules is necessary to block death signaling induced by the caspase and JNK cascades. An interesting new addition to the interplay between NF-kB and JNK is the recent finding that JNK-dependent phosphorylation and stabilization of the E3 ligase ITCH promotes TNF-induced killing via degradation of the antiapoptotic NF-kB target c-FLIP(L) (Chang et al, 2006). Clearly, cross-talk between the NF-kB, caspase and JNK signaling pathways is critical to dictate the outcome for a cell and explains why TNFa-induced PCD is only observed under conditions where NF-kB is inhibited (reviewed in Papa et al, 2004b;Luo et al, 2005;Papa et al, 2006;see below).…”