Note that TNF but not Fas-induced apoptosis leads to RIP1-mediated NFkB activation (Ting et al. EMBO J. 1996). pubmed: 12485619 Also, CD95 (= Fas, Apo-1) can trigger both survival and death. Wajant et al, Growth factor reviews 2003 When apoptosis in blocked, activation of NFkB pathway via Fas can be as strong as TNF induced NFkB activation. pubmed: 8947041 Kreuz et al. JCB 2004 "With the exception of necrosis induction, caspase-8 is necessary for all other Fas signaling events" For activation of NF-kB, the enzymatic activity of caspase-8 is not needed. pubmed: 15289496 Matsumara et al. JCB 2000 "the engagement of Fas usually causes apoptosis. However, when Fas is strongly activated for long periods of time without phagocytosis of the apoptotic cells, the cells may undergo necrotic cell death." pubmed: 11121439

PMID: 9529147 The death domain kinase RIP mediates the TNF-induced NF-kappaB signal TNF but not Fas-induced apoptosis leads to RIP1-mediated NFkB activation (Ting et al. EMBO J. 1996 15: 6189-6196). PMID: 16469705 The proinflammatory cytokine tumor necrosis factor (TNF) alpha signals both cell survival and death. 11121439 Matsumara et al. JCB 2000 Genotoxic agents that cause apoptosis also cause necrosis in several cell lines when the apoptotic process is inhibited by caspase inhibitors (Lemaire et al. 1998) PMID: 14668343 Vanden Berghe e al, JBC 2004 "TNFR1-induced necrosis can occur independently of FADD, whereas Fas-induced necrosis cannot" PMID: 17171720 Rangamani et al Low concentrations of TNFalpha usually do not lead to apoptosis but higher concentrations induce shock like symptoms (Wajant, 2003). PMID: 16200195 Luo JL, Kamata H, Karin M. 2005 TNF-deficient cells

TNFR1, TRADD and TRAF2 are implicitely included in the complex which, with RIP1, corresponds to complex I Rangamani et al. Biotechnol Bioeng. 2007 Formation of this complex within 30 min pubmed: 17171720

Rangamani et al. Biotechnol Bioeng. 2007 ComplexII is composed of TRADD, TRAF2, FADD and caspase-8 but not TNFR1 (Micheau and Tschopp, 2003) Formation of this complex within 60 min (follows complexI) pubmed: 17171720 Micheau O, Tschopp J. Cell 2003 When NF-B is activated by complex I, complex II harbors the caspase-8 inhibitor FLIPL and the cell survives pubmed: 12887920

procaspase8 is also called FLICE

Kreuz et al. JCB 2004 "With the exception of necrosis induction, caspase-8 is necessary for all other Fas signaling events" For activation of NF-kB, the enzymatic activity of caspase-8 is not needed. pubmed: 15289496 Denecker et al. Cell Mol Life Sci. 2001 "Enforced oligomerization of FADD in Jurkat cells, pre-treated with zVAD-fmk or deficient for procaspase-8, has been demonstrated to result in necrotic cell death, whereas the same FADD construct induced apoptosis in wild-type Jurkat cells" + "The bifurcation between apoptotic and necrotic signaling, at least during TNF-induced necrosis of L929sA cells, might be situated at the level of FADD. FADD-DED would propagate apoptosis, while FADD-DD would initiate necrotic signaling" pubmed: 11315185 Kawahara et al. JCB 1998 the sensitivity of the cells to necrosis may depend on the strength of the death signal evoked by Fas or FADD, the expression level of the downstream signal transducer for necrosis, and/or the balance between apoptotic and necrotic signals. In L929 cells, a downstream molecule(s) leading to necrosis is more abundant than in Jurkat cells, and the necrotic signal can be easily seen with the weak signal from the Fas receptor in the presence of caspase inhibitors, while its strong activation by direct oligomerization of FADD may be necessary to activate the necrotic pathway in Jurkat cells. pubmed: 9832562 Rangamani et al. Biotechnol Bioeng. 2007 ComplexII is composed of TRADD, TRAF2, FADD and caspase-8 but not TNFR1 (Micheau and Tschopp, 2003) Formation of this complex within 60 min (follows complexI) pubmed: 17171720 Micheau O, Tschopp J. Cell 2003 When NF-B is activated by complex I, complex II harbors the caspase-8 inhibitor FLIPL and the cell survives pubmed: 12887920 Micheau, O. Cell 114, 181-90(2003). Following TNFR1 engagement and internalization, complex II is formed by the recruitment of FADD and CASP8 Chinnaiyan, A.M. Cell 81, 505-12(1995). FADD directly binds the cytoplasmic death domain of Fas

In TNF stimulated cells, RIP1 translocates to mitochondria, suggesting a role in this DD kinase in the displacement of CypD from ANT. The direct consequence is enhanced production of ROS and diminished ATP production. Lamkanfi M et al. Cell death Differ 2007 cFLIP is cleaved by casp8 and recruits TRAF2 and RIP1 to induce NF-kB activation. pubmed: 17053807 Festjens N et al, Cell Death Differ 2007 RIP1, a kinase on the crossroads of a cell's decision to live or die. pubmed: 17301840 Kelliher, Immunity 1998 The death domain kinase RIP mediates the TNF-induced NF-kappaB signal pubmed: 9529147 Lin et al Genes Dev 1999 Cleavage of the death domain kinase RIP by caspase-8 prompts TNF-induced apoptosis. RIP1 is in the complex I. It associates with TRADD and TNF-R1 to form Complex I. It then initiates either NFkB activation or necrosis. pubmed: 10521396 Leist, Jaattela, Nat Rev Mol Cell Biol, 2001 "RIP1-mediated activation of necrosis is inhibited by Caspase-8". In the model: When RIP1 activates necrosis, we assume that its value is equal to 2. pubmed: 11483992 Karin et al, Nature Immunol. 2002 Casp8 cleaves RIP at Asp and RIP cannot activate NFkB anymore pubmed: 11875461 Festjens et al., Cell death Diff, 2007 "NFkB mediated antiapoptotic signaling is blocked through the caspase-8 mediated cleavage of RIP1" pubmed: 17301840 Holler et al. Nat Immunol. 2000 "Fas triggers an alternative, caspase-8-independent cell death pathway using the kinase RIP as effector molecule." "Unlike the role of RIP1 in recruitment of IKK-complex to the TNFR, which leads to the activation of NFkB, the kinase activity of RIP has death-promoting activity that is indispensable." pubmed: 11101870 Kreuz et al. JCB 2004 RIP1 necessary for IKK fas-mediated activation in the absence of caspase. pubmed: 15289496 PROBLEM (not in the model): Imamura, R. J Biol Chem 279, 46415-23(2004). It has been proposed that RIP1 is not necessary for Fas mediated NF-kB activation. However, in this work, if the use of a dominant negative RIP1-death domain highlighted a difference in the mechanism of activation of NF-kB by TNF or FasL, it did not completely rule out the requirement for RIP1 in Fas induced NF-kB activation. pubmed: 15337758 Festjens, N. Cell Death Differ 14, 400-410(2007). RIP1 polyubiquitinated within complex I recruits member of the IKK complex NEMO upstream of NF-kB activation Lee, T.H. J Biol Chem 279, 33185-91(2004). The kinase activity of Rip1 is not required for tumor necrosis factor-alpha-induced IKK activation Kreuz, S. J Cell Biol 166, 369-80(2004). activation of NF-kB downstream of engagement of Fas requires a functional DISC that contains FADD and RIP1, but not the kinase activity of the latter. Holler, N. Nat Immunol 1, 489-95(2000). non apoptotic cell death induced by Fas when caspases are inhibited requires RIP1

Festjens, N. Cell Death Differ 14, 400-410(2007). RIP1 polyubiquitinated within complex I recruits member of the IKK complex NEMO upstream of NF-kB activation Lee, T.H. J Biol Chem 279, 33185-91(2004). The kinase activity of Rip1 is not required for tumor necrosis factor-alpha-induced IKK activation

RIP1K corresponds to the kinase activity of RIP1 PMID: 11101870 Holler et al. "Fas triggers an alternative, caspase-8-independent cell death pathway using the kinase RIP as effector molecule." "Unlike the role of RIP1 in recruitment of IKK-complex to the TNFR, which leads to the activation of NFkB, the kinase activity of RIP has death-promoting activity that is indispensable." Festjens, N. Cell Death Differ 14, 400-410(2007). RIP1 polyubiquitinated within complex I recruits member of the IKK complex NEMO upstream of NF-kB activation Lee, T.H. J Biol Chem 279, 33185-91(2004). The kinase activity of Rip1 is not required for tumor necrosis factor-alpha-induced IKK activation

List of all target genes of NFkB at: http://people.bu.edu/gilmore/nf-kb/target/index.html#regu Kelliher et al. Immunity, 1998 The death domain kinase RIP mediates the TNF-induced NF-kappaB signal pubmed: 9529147 Ting et al. EMBO J. 1996 TNF but not Fas-induced apoptosis leads to RIP1-mediated NFkB activation Wajant, JCB 2000 "overexpression of cellular FLICE inhibitory protein (cFLIP) inhibited death receptor-induced NF-kappa B activation. Thus, a novel functional role of cFLIP as a negative regulator of gene induction by death receptors became apparent. " "Overexpression of FLIPL inhibits death receptor-mediated NF-kappa B activation" pubmed: 10823821 Kreuz et al, JCB 2004 cFLIP inhibits NFkB pathway (not included in this model for reasons linked to boolean modeling and details of the processes unclear) pubmed: 15289496

Luo JL, Kamata H, Karin M. 2005 NF-kB can also prevent programmed necrosis by inducing genes encoding antioxidant proteins pubmed: 16200195 Morgan et al. 2008 TNF induced NFkB activation can reduce ROS levels via increased expression of the antioxidant proteins FHC and MnSOD pubmed: 18301379

Activated by complex II Lamkanfi et al. Cell Death Differ, 2007 When casp8 is activated, it cleaves cFLIP (Not included in the graph) Caspase-8 is activated within the DISC pubmed: 17053807 Chen and Wang, Apoptosis 2002 Fas assembles the DISC, formed by FADD, Casp8 and 10. pubmed: 12101390 Medema, J.P. EMBO J 16, 2794-804(1997). Upon Fas engagement, CASP8 is recruited to the DISC through interaction with FADD, which leads to its activation by proteolytic cleavage

Bax and Bak oligomerize and are inserted into the OMM. Ow et al, Nature 2008 Truncated Bid (tBid) induces the oligomerization of Bax and Bak and the formation of pores that permits the release of proteins in the cytosol. (implied in the arrow CASP8 => Bax) pubmed: 18568041 Wei et al, Science 2001 "Proapoptotic BAX and BAK: a requisite gateway to mitochondrial dysfunction and death." pubmed: 11326099 Orrenius et al, Annual Review of pharmacology and toxicology, 2007 Bcl-2, Bcl_XL, Mcl-1 and Bcl-w prevent the oligomerization of Bax and Bak. pubmed: 17029566 Karin et al, Nature Immunol. 2002 Half-life of Bax is very long. pubmed: 11875461

Localized to the mitochondrial outer membrane Transcriptional regulation of bcl-2 by nuclear factor kappa B Also a transcription factor of Bcl_XL pubmed: 11704864

Morgan, Cell Res, 2008 "The mechanism of superoxide generation further establishes RIP1 as the central molecule in ROS production and cell death initiated by TNF and other death receptors." pubmed: 18301379 Leist, Nat. Rev. Mol. Cell Biol. 2001 "RIP1 initiates caspase-independent necrosis pathway mediated by the formation of ROS". pubmed: 11483992 Cai et Jones, J Biol Chem, 1998 ROS can be generated by: - inhibition of electron transfer - accumulation of reducing equivalents in the middle portion of the electron transport chain - direct one-electron transfer to 02 to produce superoxide pubmed: 9565547 Vanden Berghe et al. Mol. Cell 2007 Activation of external ROS through NADPH oxidases. TRADD and RIP1 recruits Rac1 and Nox1/NOXO1. Superoxide anions (02-) and hydrogen peroxides (H2O2) are generated. NOTE: the production of ROS via this route is less important than that of the mitochondria route. pubmed: 17588511 Gogvadze et al, Curr Protoc cell Biol, 2003 Mitochondria are a major source of ROS. pubmed: 18228423 Ow et al, Nature 2008 "The detachment of cytochrome c can cause the disruption of the electron transport chain, which in turn can lead to an immediate burst of ROS generation." pubmed: 18568041 Orrenius et al, Annual Review of pharmacology and toxicology, 2007 "The majority of ROS are products of mitochondrial respiration ... The one-electron reduction of molecular oxygen produces a relatively stable intermediate, the superoxide anion (O2-) which can be regarded as the precursor of most ROS" Through p66Shc protein, a redox enzyme. pubmed: 17029566 Karin et al. et al, Nature Immunol, 2002 pubmed: 11875461 Karin et al. Nature 2006 NFkB induces antioxidants (SOD2, FHC) that inhibit ROS (Figure 3). pubmed: 16724054

Gogvadze et al, Curr Protoc cell Biol, 2003 Cancer cells produce most of their ATP through glycolysis pubmed: 18228423 Matsumara et al, JBC 2000 loss of {Delta}{Psi}m would reduce the cellular ATP level, which may lead to necrotic cell death (Eguchi et al. 1997 Down; Leist et al. 1997

This corresponds to the permeabilization of apoptotic mitochondria. MPT=0 : normal and sane case MPT = 1: - Mitochondria responsive to death signals and leading to apoptotic situation - when signals are too high or cellular conditions not "proper" for apoptosis, then necrosis.