TNF-alpha signaling (WP231)

Homo sapiens

Tumor necrosis factor alpha (TNFα) is a proinflammatory cytokine involved in various biological processes including regulation of cell proliferation, differentiation, apoptosis and immune response. TNFα is mainly produced by macrophages, also by other tissues including lymphoid cells, mast cells, endothelial cells, fibroblasts and neuronal tissues. TNF was identified as a soluble cytokine produced upon the activation by the immune system and able to exert cytotoxicity on tumor cell lines and cause tumor necrosis in animal models. TNF is primarily produced as a type II transmembrane protein arranged as stable homotrimers. The members of TNFα family exert their cellular effect through two distinct surface receptors of the TNF receptor family, TNFRSF1A (TNF-R1) and TNFRSF1B (TNF-R2). TNF-R1 is ubiquitously expressed, whereas TNF-R2 is found typically on cells of the immune system and is highly regulated. TNF-R1 and TNF-R2 binds membrane-integrated TNF (memTNF) as well as soluble TNF (sTNF) TNF-R1 contains a protein-protein interaction domain, called death domain (DD). This domain interacts with other DD-containing proteins and couples the death receptors to caspase activation and apoptosis. TNF-R2 induces gene expression by a TRAF-2 dependent signaling mechanism and also crosstalk's with TNF-R1. The pleiotropic biological effects of TNF can be attributed to its ability to simultaneously activate multiple signaling pathways in cells. Binding of TNFα to TNF-R1 on the cell surface triggers trimerization of the receptor and exposes intracellular domain of TNF-R1 following the release of an inhibitory protein. This intracellular domain recruits a death-domain containing adaptor protein, TRADD by homophilic interactions. TRADD, which acts as a scaffold protein, recruits TRAF2 and RIPK1 to form a complex , referred to as complex 1. Complex 1 is believed to be important in NF-κB activation and JNK activation. Complex 1 eventually dissociates from the receptor and integrates FADD and procaspase8 to form a complex referred to as the complex 2. In some cases, FADD/CASP8 association depends on high molecular weight complexes containing unubiquitinated RIPK1 as scaffold. Activated CASP8 induces CASP3 activity and execution of apoptosis. CASP8 activates apoptotic signal through another mechanism involving BID cleavage to truncated BID (tBID). tBID translocates to the mitochondria, increasing its outer membrane permeability. This results in cytochrome C release and activation of other caspases ultimately leading to apoptosis. Reactive oxygen species (ROS) have been found to increase during or after complex 1 and 2 formation to mediate or potentiate apoptosis upon TNF stimulation. TRAF-2 in complex 1 also activates the MAP kinase cascade, that leads to the activation of JNK, which on prolonged activation is believed to mediate both apoptosis and necrotic cell death. On complex 1 formation, NF-κB regulated anti-apoptotic gene products efficiently block initiation of apoptosis by complex 2. There is evidence of an early attempt to signal for apoptosis, which precedes the activation of NF-κB. The intracellular part of TNF-R1 binds to NSMAF which in turn mediates SMPD2-dependant ceramide production from cell membrane. Ceramide induces membrane permeabilization and apoptosis. This is observed before TNF-R1 internalization and NF-κB activation. This process is repressed on TNF-R1 internalization. This signal however is enough to initiate apoptosis in some cells. Another form of cell death, necrosis, is also mediated through TNF stimulation. On TNF stimulation, deubiquitinated RIPK1 dissociates from complex 1 and recruits RIPK3, FADD and CASP8. RIPK3 is autophosphorylated and phosphorylates RIPK1. Taken together, it has been speculated that RIP1 and RIP3 increase carbohydrate and glutamine metabolism of the cell, leading to increased ROS production and eventual necrosis. Recruitment of CASP8, activation of FADD/RIP1 and apoptosis induction, is blunted when RIPK1 becomes ubiquitinated. IKBKG binds to ubiquitinated RIPK1 to induce the activation of NF-κB, which exerts antiapoptotic effects. Cellular inhibitor of apoptosis, BIRC2 and BIRC3 has E3-ubiquitin ligase activity and functionally interact with TRAF2 and RIPK1 to induce polyubiquitination of RIPK1 upon TNF stimulation. Loss of these inhibitors attenuates TNF-induced NF-κB activation. The adaptor proteins TAB2 and TAB3 bind preferentially to Lys-63 polyubiquitinated RIPK1. This facilitates dimerization of MAP3K7, promoting its phosphorylation and activation. The IKK complex, consisting of CHUK, IKBKB and IKBKG, is recruited to RIP1 through binding of IKBKG to the ubiquitin chain of RIP1. Activated TAK1 directly phosphorylates IKBKB within the activation loop, leading to activation of the IKK complex and NF-κB. Certain regulatory proteins have been known to intercept NF-κB activation at the level of ubiquitinated RIP1. TNFAIP3, an NF-κB inhibitory protein, removes Lys-63 polyubiquitin chain and promotes Lys-48 linked ubiquitination of RIPK1 leading to its degradation and NF-κB signal termination. IKBKG stabilizes the bound polyubiquitinated RIPK1 by inhibiting its degradation, most probably by impairing its interaction with TNFAIP3. OTUD7B is recruited to the activated TNF-R1 and promotes RIP1 deubiquitination, thereby attenuating NF-κB activation. At internalized TNF-receptosomes, RIPK1 is ubiquitinated by endocytic vesicle associated RFFL, inducing RIPK1 degradation, which terminates NF-κB activation. When successful, TNF-induced NF-κB activation induces transcription and expression of genes encoding proinflammatory IL-6, anti-apoptotic factors BIRC2, BIRC3 and BCL-2 homologue BCL2L1. This causes the cell to remain inert to apoptotic stimuli. Please access this pathway at [ NetSlim] database. Proteins on this pathway have targeted assays available via the [ CPTAC Assay Portal].


Akhilesh Pandey , Burak , Alex Pico , Chris Evelo , Nathan Salomonis , Kristina Hanspers , NetPath , Daniela Digles , Martina Summer-Kutmon , Zahra Roudbari , Egon Willighagen , Lauren J. Dupuis , and Eric Weitz


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Homo sapiens



Pathway Ontology

tumor necrosis factor mediated signaling pathway


Label Type Compact URI Comment
Ceramide Metabolite chebi:17761
ROS Metabolite chebi:26523
Hydroperoxides Metabolite chebi:35923
Arachidonic acid Metabolite chebi:15843
KRAS GeneProduct ncbigene:3845
HRAS GeneProduct ncbigene:3265
NRAS GeneProduct ncbigene:4893
MAP2K6 Protein ncbigene:5608
MAP3K5 Protein ncbigene:4217
NFKB2 Protein ncbigene:4791
REL Protein ncbigene:5966
NFKBIB Protein ncbigene:4793
CASP9 Protein ncbigene:842
MAP2K7 Protein ncbigene:5609
BAX Protein ncbigene:581
PYGL Protein ncbigene:5836
CREBBP Protein ncbigene:1387
CDC37 Protein ncbigene:11140
RFFL Protein ncbigene:117584
NFKBIA Protein ncbigene:4792
CYBA Protein ncbigene:1535
TAB1 Protein ncbigene:10454
GLUL Protein ncbigene:2752
MAP3K8 Protein ncbigene:1326
TRADD Protein ncbigene:8717
APAF1 Protein ncbigene:317
NOXO1 Protein ncbigene:124056 SH3 domain of NOXO1 interacts with TRADD in mouse embryonic fibroblasts and 293 cells.
GRB2 Protein ncbigene:2885
MAPK9 Protein ncbigene:5601
TAB2 Protein ncbigene:23118
SMPD2 Protein ncbigene:6610
DIABLO Protein ncbigene:56616
NOX1 Protein ncbigene:27035
CASP8 Protein ncbigene:841
RAF1 Protein ncbigene:5894
IKBKG Protein ncbigene:8517
RIPK3 Protein ncbigene:11035
TBK1 Protein ncbigene:29110
CUL1 Protein ncbigene:8454
HSP90AA1 Protein ncbigene:3320
MADD Protein ncbigene:8567
CFLAR Protein ncbigene:8837
FBXW11 Protein ncbigene:23291
RELA Protein ncbigene:5790
NFKBIE Protein ncbigene:4794
AKT1 Protein ncbigene:207
TNFRSF1A Protein ncbigene:7132
BID Protein ncbigene:637
CSNK2A1 Protein ncbigene:1457
TANK Protein ncbigene:10010
KSR2 Protein ncbigene:283455
PRKCZ Protein ncbigene:5590
TNFRSF1B Protein ncbigene:7133
RELA Protein ncbigene:5966
PLK1 Protein ncbigene:5347
MAP3K14 Protein ncbigene:9020
TNF Protein ncbigene:7124
TXN Protein ncbigene:7295
NFKB2 Protein ncbigene:4791
MAPK1 Protein ncbigene:5594
MAP4K2 Protein ncbigene:5871
CHUK Protein ncbigene:1147
TNFRSF1A Protein ncbigene:7132
KSR1 Protein ncbigene:8844
TNF Protein ncbigene:7124
TNFRSF1B Protein ncbigene:7133
MAP2K4 Protein ncbigene:6416
RAC1 Protein ncbigene:5879
RIPK1 Protein ncbigene:8737
OTUD7B Protein ncbigene:56957
DIABLO Protein ncbigene:56616
MAPK8 Protein ncbigene:5599
TAB3 Protein ncbigene:257397
BTRC Protein ncbigene:8945
TRADD Protein ncbigene:8717
TNFRSF1A Protein ncbigene:7132
MAP2K3 Protein ncbigene:5606
MAPK8 Protein ncbigene:5599
TNFAIP3 Protein ncbigene:7128
SOS1 Protein ncbigene:6654
Pro-CASP8 Protein ncbigene:541
TRAF1 Protein ncbigene:7185
FADD Protein ncbigene:8772
BIRC3 Protein ncbigene:330
TRAF2 Protein ncbigene:7186
REL Protein ncbigene:5966
CASP7 Protein ncbigene:840
CASP3 Protein ncbigene:836
BIRC2 Protein ncbigene:329
RIPK1 Protein ncbigene:8737
TNF Protein ncbigene:7124
BCL2L1 Protein ncbigene:598
TNF Protein ncbigene:7124
TNF Protein ncbigene:7124
PSMD2 Protein ncbigene:5708
IKBKB Protein ncbigene:3551
JUN Protein ncbigene:3725
MAP3K3 Protein ncbigene:4215
PPP2CA Protein ncbigene:5515
TNF Protein ncbigene:7124
TRAF2 Protein ncbigene:7186
MAPK3 Protein ncbigene:5595
MAPK9 Protein ncbigene:5601
RFK Protein ncbigene:55312
NFKB1 Protein ncbigene:4790
BAD Protein ncbigene:572
MAP3K7 Protein ncbigene:6885
TRAP1 Protein ncbigene:10131
NSMAF Protein ncbigene:8439
MAP3K1 Protein ncbigene:4214
TNFRSF1B Protein ncbigene:7133
SKP1 Protein ncbigene:6500
NFKB1 Protein ncbigene:4790