The intrinsic (Bcl-2 inhibitable or mitochondrial) pathway of apoptosis functions in response to various types of intracellular stress including growth factor withdrawal, DNA damage, unfolding stresses in the endoplasmic reticulum and death receptor stimulation. Following the reception of stress signals, proapoptotic BCL-2 family proteins are activated and subsequently interact with and inactivate antiapoptotic BCL-2 proteins. This interaction leads to the destabilization of the mitochondrial membrane and release of apoptotic factors. These factors induce the caspase proteolytic cascade, chromatin condensation, and DNA fragmentation, ultimately leading to cell death. The key players in the Intrinsic pathway are the Bcl-2 family of proteins that are critical death regulators residing immediately upstream of mitochondria. The Bcl-2 family consists of both anti- and proapoptotic members that possess conserved alpha-helices with sequence conservation clustered in BCL-2 Homology (BH) domains. Proapoptotic members are organized as follows:
1. "Multidomain" BAX family proteins such as BAX, BAK etc. that display sequence conservation in their BH1-3 regions. These proteins act downstream in mitochondrial disruption. <p> 2. "BH3-only" proteins such as BID,BAD, NOXA, PUMA,BIM, and BMF have only the short BH3 motif. These act upstream in the pathway, detecting developmental death cues or intracellular damage. Anti-apoptotic members like Bcl-2, Bcl-XL and their relatives exhibit homology in all segments BH1-4. One of the critical functions of BCL-2/BCL-XL proteins is to maintain the integrity of the mitochondrial outer membrane.
View original pathway at:Reactome.</div>
Chen XQ, Fung YW, Yu AC.; ''Association of 14-3-3gamma and phosphorylated bad attenuates injury in ischemic astrocytes.''; PubMedEurope PMCScholia
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Du C, Fang M, Li Y, Li L, Wang X.; ''Smac, a mitochondrial protein that promotes cytochrome c-dependent caspase activation by eliminating IAP inhibition.''; PubMedEurope PMCScholia
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Li CQ, Robles AI, Hanigan CL, Hofseth LJ, Trudel LJ, Harris CC, Wogan GN.; ''Apoptotic signaling pathways induced by nitric oxide in human lymphoblastoid cells expressing wild-type or mutant p53.''; PubMedEurope PMCScholia
Bhattacharya S, Ray RM, Johnson LR.; ''STAT3-mediated transcription of Bcl-2, Mcl-1 and c-IAP2 prevents apoptosis in polyamine-depleted cells.''; PubMedEurope PMCScholia
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Itahana K, Zhang Y.; ''Mitochondrial p32 is a critical mediator of ARF-induced apoptosis.''; PubMedEurope PMCScholia
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Chau BN, Cheng EH, Kerr DA, Hardwick JM.; ''Aven, a novel inhibitor of caspase activation, binds Bcl-xL and Apaf-1.''; PubMedEurope PMCScholia
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Ruffolo SC, Shore GC.; ''BCL-2 selectively interacts with the BID-induced open conformer of BAK, inhibiting BAK auto-oligomerization.''; PubMedEurope PMCScholia
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Yang E, Zha J, Jockel J, Boise LH, Thompson CB, Korsmeyer SJ.; ''Bad, a heterodimeric partner for Bcl-XL and Bcl-2, displaces Bax and promotes cell death.''; PubMedEurope PMCScholia
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Bratton SB, Walker G, Srinivasula SM, Sun XM, Butterworth M, Alnemri ES, Cohen GM.; ''Recruitment, activation and retention of caspases-9 and -3 by Apaf-1 apoptosome and associated XIAP complexes.''; PubMedEurope PMCScholia
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Datta SR, Dudek H, Tao X, Masters S, Fu H, Gotoh Y, Greenberg ME.; ''Akt phosphorylation of BAD couples survival signals to the cell-intrinsic death machinery.''; PubMedEurope PMCScholia
Khor TO, Gul YA, Ithnin H, Seow HF.; ''Positive correlation between overexpression of phospho-BAD with phosphorylated Akt at serine 473 but not threonine 308 in colorectal carcinoma.''; PubMedEurope PMCScholia
Martin MC, Allan LA, Mancini EJ, Clarke PR.; ''The docking interaction of caspase-9 with ERK2 provides a mechanism for the selective inhibitory phosphorylation of caspase-9 at threonine 125.''; PubMedEurope PMCScholia
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Renatus M, Stennicke HR, Scott FL, Liddington RC, Salvesen GS.; ''Dimer formation drives the activation of the cell death protease caspase 9.''; PubMedEurope PMCScholia
Saelens X, Festjens N, Vande Walle L, van Gurp M, van Loo G, Vandenabeele P.; ''Toxic proteins released from mitochondria in cell death.''; PubMedEurope PMCScholia
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Kashkar H, Haefs C, Shin H, Hamilton-Dutoit SJ, Salvesen GS, Kronke M, Jurgensmeier JM.; ''XIAP-mediated caspase inhibition in Hodgkin's lymphoma-derived B cells.''; PubMedEurope PMCScholia
del Peso L, González-García M, Page C, Herrera R, Nuñez G.; ''Interleukin-3-induced phosphorylation of BAD through the protein kinase Akt.''; PubMedEurope PMCScholia
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Antonsson B, Montessuit S, Sanchez B, Martinou JC.; ''Bax is present as a high molecular weight oligomer/complex in the mitochondrial membrane of apoptotic cells.''; PubMedEurope PMCScholia
Kang W, Hong SH, Lee HM, Kim NY, Lim YC, Le le TM, Lim B, Kim HC, Kim TY, Ashida H, Yokota A, Hah SS, Chun KH, Jung YK, Yang JK.; ''Structural and biochemical basis for the inhibition of cell death by APIP, a methionine salvage enzyme.''; PubMedEurope PMCScholia
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Song Z, Yao X, Wu M.; ''Direct interaction between survivin and Smac/DIABLO is essential for the anti-apoptotic activity of survivin during taxol-induced apoptosis.''; PubMedEurope PMCScholia
Shakeri R, Kheirollahi A, Davoodi J.; ''Apaf-1: Regulation and function in cell death.''; PubMedEurope PMCScholia
Yang QH, Du C.; ''Smac/DIABLO selectively reduces the levels of c-IAP1 and c-IAP2 but not that of XIAP and livin in HeLa cells.''; PubMedEurope PMCScholia
Wilson AM, Morquette B, Abdouh M, Unsain N, Barker PA, Feinstein E, Bernier G, Di Polo A.; ''ASPP1/2 regulate p53-dependent death of retinal ganglion cells through PUMA and Fas/CD95 activation in vivo.''; PubMedEurope PMCScholia
Datta SR, Katsov A, Hu L, Petros A, Fesik SW, Yaffe MB, Greenberg ME.; ''14-3-3 proteins and survival kinases cooperate to inactivate BAD by BH3 domain phosphorylation.''; PubMedEurope PMCScholia
Bergamaschi D, Samuels Y, Jin B, Duraisingham S, Crook T, Lu X.; ''ASPP1 and ASPP2: common activators of p53 family members.''; PubMedEurope PMCScholia
Sakai T, Liu L, Teng X, Mukai-Sakai R, Shimada H, Kaji R, Mitani T, Matsumoto M, Toida K, Ishimura K, Shishido Y, Mak TW, Fukui K.; ''Nucling recruits Apaf-1/pro-caspase-9 complex for the induction of stress-induced apoptosis.''; PubMedEurope PMCScholia
Yi X, Yin XM, Dong Z.; ''Inhibition of Bid-induced apoptosis by Bcl-2. tBid insertion, Bax translocation, and Bax/Bak oligomerization suppressed.''; PubMedEurope PMCScholia
Kim HE, Du F, Fang M, Wang X.; ''Formation of apoptosome is initiated by cytochrome c-induced dATP hydrolysis and subsequent nucleotide exchange on Apaf-1.''; PubMedEurope PMCScholia
Wei MC, Lindsten T, Mootha VK, Weiler S, Gross A, Ashiya M, Thompson CB, Korsmeyer SJ.; ''tBID, a membrane-targeted death ligand, oligomerizes BAK to release cytochrome c.''; PubMedEurope PMCScholia
Gao Z, Tian Y, Wang J, Yin Q, Wu H, Li YM, Jiang X.; ''A dimeric Smac/diablo peptide directly relieves caspase-3 inhibition by XIAP. Dynamic and cooperative regulation of XIAP by Smac/Diablo.''; PubMedEurope PMCScholia
Signaling by AKT is one of the key outcomes of receptor tyrosine kinase (RTK) activation. AKT is activated by the cellular second messenger PIP3, a phospholipid that is generated by PI3K. In ustimulated cells, PI3K class IA enzymes reside in the cytosol as inactive heterodimers composed of p85 regulatory subunit and p110 catalytic subunit. In this complex, p85 stabilizes p110 while inhibiting its catalytic activity. Upon binding of extracellular ligands to RTKs, receptors dimerize and undergo autophosphorylation. The regulatory subunit of PI3K, p85, is recruited to phosphorylated cytosolic RTK domains either directly or indirectly, through adaptor proteins, leading to a conformational change in the PI3K IA heterodimer that relieves inhibition of the p110 catalytic subunit. Activated PI3K IA phosphorylates PIP2, converting it to PIP3; this reaction is negatively regulated by PTEN phosphatase. PIP3 recruits AKT to the plasma membrane, allowing TORC2 to phosphorylate a conserved serine residue of AKT. Phosphorylation of this serine induces a conformation change in AKT, exposing a conserved threonine residue that is then phosphorylated by PDPK1 (PDK1). Phosphorylation of both the threonine and the serine residue is required to fully activate AKT. The active AKT then dissociates from PIP3 and phosphorylates a number of cytosolic and nuclear proteins that play important roles in cell survival and metabolism. For a recent review of AKT signaling, please refer to Manning and Cantley, 2007.
Once activated BAK insterts in the outer mitochondrial membrane, it oligomerizes and these oligomeric BAK complexes are important for the cytochrome C efflux (Ruffolo and Shore 2003).
Once integrated in the outer mitochondrial membrane, BAX forms oligomeric complexes which play an important role in cytochrome C release (Antonsson et al. 2001)
Permeabilization of the outer mitochondrial membrane by pro-apoptotic BCL2 family proteins, such as BAK and BAX, allows cytochrome c eflux from the mitochondrial intermembrane space into the cytosol (Arnoult et al. 2003).
At the beginning of this reaction, 1 molecule of 'SMAC', and 1 molecule of 'XIAP:Caspase-3' are present. At the end of this reaction, 1 molecule of 'SMAC:XIAP:Caspase-3' is present.
Permeabilization of the outer mitochondrial membrane by pro-apoptotic BCL2 family members BAK and BAX allows release of DIABLO (SMAC) from the mitochondrial intermembrane space into the cytosol (Arnoult et al. 2003). Binding of DIABLO (SMAC) to survivin leads to the inhibition of apoptosis (Song et al. 2003).
At the beginning of this reaction, 1 molecule of 'XIAP:Caspase-7', and 1 molecule of 'SMAC' are present. At the end of this reaction, 1 molecule of 'SMAC:XIAP:Caspase-7' is present.
At the beginning of this reaction, 1 molecule of 'SMAC', and 1 molecule of 'XIAP:Caspase-9' are present. At the end of this reaction, 1 molecule of 'SMAC:XIAP:Caspase-9' is present.
Binding of DIABLO (SMAC) to the BIR2 domain of XIAP competes with binding of caspase-7 to the same domain of BIR2. As DIABLO has a higher affinity for the BIR2 domain than caspase-7, DIABLO (SMAC) binding to XIAP results in the liberation of caspase-7 (Huang et al. 2001).
tBID binds to its mitochondrial partner BAK to release cytochrome c. It has been observed in mouse systems that the activated tBID results in an allosteric activation of BAK. Activated BAK induces intramembranous oligomerization leading to a pore for cytochrome c efflux (Wei et al. 2000).
The caspase 8 -mediated cleavage of cytosolic, inactive p22 BID at internal Asp sites yields a major p15 and minor p13 and p11 fragments. After myristoylation, tBID translocates to mitochondria as an integral membrane protein.
14-3-3 proteins bind BAD phosphorylated by activated AKT on serine residue S99 (corresponds to mouse Bad serine residue S136). Binding of 14-3-3 proteins to p-S99-BAD facilitates subsequent phosphorylation of BAD on serine residue S118 (corresponds to mouse serine S155), which disrupts binding of BAD to BCL2 proteins and promotes cell survival (Datta et al. 2000). Caspase-3 mediated cleavage of 14-3-3 proteins releases BAD and promotes apoptosis (Won et al. 2003). All known 14-3-3 protein isoforms (beta/alpha i.e. YWHAB, gamma i.e. YWHAG, zeta/delta i.e. YWHAZ, epsilon i.e. YWHAE, eta i.e. YWHAH, sigma i.e. SFN and theta i.e. YWHAQ) can interact with BAD and inhibit it (Subramanian et al. 2001, Chen et al. 2005).
Calcineurin, the Ca2+ activated protein phosphatase, dephosphorylates BAD, promoting dissociation of BAD from 14-3-3 proteins and the translocation of BAD to the outer mitochondrial membrane (Wang et al. 1999).
MAPK8 (JNK) phosphorylates BMF on a DLC binding motif DKATQTLSP involved in interaction with dynein DYNLL2 (DLC2), which sequesters BMF to the cytoskeleton. Phosphorylated BMF dissociates from dynein. Two JNK consensus sites exist in BMF: S74 and S77 (Lei and Davis 2003).
TP53 (p53) stimulates the transcription of BBC3 (PUMA) (p53 upregulated modulator of apoptosis) (Nakano and Vousden 2001). The transcription of BBC3 is also stimulated by p53 family members TP63 (p63) and TP73 (p73) (Bergamaschi et al. 2004, Patel et al. 2008). ASPP proteins PPP1R13B (ASPP1) and TP53BP2 (ASPP2) form a complex with p53 family members and enhance transcriptional activation of BBC3 (Bergamaschi et al. 2004, Patel et al. 2008, Wilson et al. 2013).
It is thought that due to its p53 dependence for expression, PUMA could function as a mediator of p53-induced apoptosis. Newly synthesized PUMA protein translocates to mitochondria and binds to BCL-2 and Bcl-X(L) through a BH3 domain.
During certain types of apoptosis, activated tBID (p15) induces a change in conformation of Bax which leads to the unmasking of its NH2-terminal domain. This change in confirmation usually results in the release of cytochrome c from mitochondria.
MAPK8 (JNK) phosphorylates BCL2L11 (BIM) on a DLC-binding motif (DKSTQTP), involved in dynein (DYNLL2 i.e. DLC1) binding and sequestration of BCL2L11 (BIM) to the cytoskeleton. Phosphorylated BCL2L11 dissociates from dynein. Three sites in BCL2L11 match the JNK consensus: S44, T56 and S58 in BCL2L11 isoform BimL (these residues correspond to S104, T116 and S118 in BCL2L11 isoform BimEL), and all sites appear to be phosphorylated by MAPK8 (JNK) both in vitro and in vivo (Lei and Davis 2003).
Once BCL2L11 (BIM) dissociates from the cytoskeleton, it translocates to the outer mitochondrial membrane where it associates with BCL2 (Puthalakath et al. 1999).
TP53 (p53) stimulates transcription of PMAIP1 (NOXA) (Oda et al. 2000, Li et al. 2004). The complex of TP53 with ASPP proteins PPP1R13B (ASPP1) or TP53BP2 (ASPP2) is likely involved in the transcriptional activation of PMAIP1 (Wang et al. 2012, Wilson et al. 2013).
It was observed that cytosolic Noxa underwent BH3 motif-dependent localization to mitochondria and interacted with anti-apoptotic Bcl-2 family members, resulting in the activation of caspase-9.
After proteolytic activation, tBID is myristoylated by NMT-1 at an exposed glycine. N-myristoylation may enable the activated tBID to associate with the lipid components of the mitochondrial membrane.
tBID binds to its mitochondrial partner BAK to release cytochrome c. It has been observed in mouse systems that the activated tBID results in an allosteric activation of BAK. Activated BAK induces intramembranous oligomerization leading to a pore for cytochrome c efflux (Wei et al. 2000).
Activated AKT phosphorylates the BCL-2 family member BAD at serine 99 (corresponds to serine residue S136 of mouse Bad), blocking the BAD-induced cell death (Datta et al. 1997, del Peso et al. 1997, Khor et al. 2004).
TP53 (p53) binds the promoter of the PMAIP1 (NOXA) gene to induce PMAIP1 transcription (Oda et al. 2000, Li et al. 2004). TP53 likely associates with the PMAIP1 promoter as part of the complex with ASPP proteins PPP1R13B (ASPP1) or TP53BP2 (ASPP2) (Wang et al. 2012, Wilson et al. 2013).
TP53 (p53) binding sites are found in the promoter (Han et al. 2001) and intron 1 (Nakano and Vousden 2001) of the BBC3 (PUMA) gene, and are necessary for TP53-mediated induction of BBC3 transcription. TP53 family members TP63 (p63) and TP73 (p73) can also bind p53 response elements within the BBC3 gene locus (Bergamaschi et al. 2004, Patel et al. 2008). Formation of the complex between TP53 family members and ASPP proteins PPP1R13B (ASPP1) or TP53BP2 (ASPP2) enhances binding of the p53 family members to the BBC3 gene locus (Bergamaschi et al. 2004, Patel et al. 2008, Wilson et al. 2013).
BH3-only proteins (tBid, BIM, PUMA, BAD, NOXA) associate with and inactivate anti-apoptotic protein Bcl-XL( Yi et al., 2003; Puthalakath et al., 1999; Nakano and Vousden, 2001; Wang et al., 1999; Oda et al., 2000). The interactions of NOXA with Bcl-XL are inferred from experiments performed in mice (Oda et al., 2000).
Bcl-2 interacts with tBid (Yi et al. 2003), BIM (Puthalakath et al. 1999), PUMA (Nakano and Vousden 2001), NOXA (Oda et al. 2000), BAD (Yang et al. 2005), BMF (Puthalakath et al. 2001), resulting in inactivation of BCL2.
Signal transducer and activator of transcription 3 (STAT3) is a key regulator of gene expression in response to signaling of many cytokines including interleukin-6 (IL6), Oncostatin M, and leukemia inhibitory factor. Using microarray techniques, hundreds of genes have been reported as potential STAT3 target genes (Dauer et al. 2005, Hsieh et al. 2005). Some of these genes have been proven to be direct STAT3 targets using genome-wide chromatin immunoprecipitation screening (Snyder et al. 2008, Carpenter & Lo 2014), including the mitochondrial outer membrane protein genes Apoptosis regulator BCL2 (Bhattacharya et al. 2005) and Bcl-2-like protein 1 (BCL2L1, Bcl-XL) (Catlett-Falcone et al. 1999).
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proteins:p-S99-BAD
complexTetramer:PMAIP1
GeneAnnotated Interactions
proteins:p-S99-BAD
complexproteins:p-S99-BAD
complexThis reaction takes place in the 'cytosol'.
This reaction takes place in the 'cytosol'.
This reaction takes place in the 'cytosol'.
Tetramer:PMAIP1
GeneTetramer:PMAIP1
Gene