241 human active and 13 inactive phosphatases in total;
194 phosphatases have substrate data;
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336 protein substrates;
83 non-protein substrates;
1215 dephosphorylation interactions;
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299 KEGG pathways;
876 Reactome pathways;
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last scientific update: 11 Mar, 2019
last maintenance update: 01 Sep, 2023
Most upstream protease of the activation cascade ofcaspases responsible for the TNFRSF6/FAS mediated and TNFRSF1Ainduced cell death Binding to the adapter molecule FADD recruitsit to either receptor The resulting aggregate called death-inducing signaling complex (DISC) performs CASP8 proteolyticactivation The active dimeric enzyme is then liberated from theDISC and free to activate downstream apoptotic proteasesProteolytic fragments of the N-terminal propeptide (termed CAP3,CAP5 and CAP6) are likely retained in the DISC Cleaves andactivates CASP3, CASP4, CASP6, CASP7, CASP9 and CASP10 Mayparticipate in the GZMB apoptotic pathways Cleaves ADPRTHydrolyzes the small-molecule substrate, Ac-Asp-Glu-Val-Asp-|-AMCLikely target for the cowpox virus CRMA death inhibitory proteinIsoform 5, isoform 6, isoform 7 and isoform 8 lack the catalyticsite and may interfere with the pro-apoptotic activity of thecomplex
Catalytic Activity (UniProt annotation)
Strict requirement for Asp at position P1 andhas a preferred cleavage sequence of (Leu/Asp/Val)-Glu-Thr-Asp-|-(Gly/Ser/Ala)
Platinum-based drugs cisplatin, carboplatin and oxaliplatin are widely used in the therapy of solid malignancies, including testicular, ovarian, head and neck, colorectal, bladder and lung cancers. The mechanism of action of Platinum-based drugs involves covalent binding to purine DNA bases, which primarily leads to cellular apoptosis. Their clinical success is, however, limited due to severe side effects and intrinsic or acquired resistance to the treatment. Platinum resistance could arise from decreased drug influx, increased drug efflux, intracellular detoxification by glutathione, etc., decreased binding (e.g., due to high intracellular pH), increased DNA repair, decreased mismatch repair, defective apoptosis, and altered oncogene expression.
p53 activation is induced by a number of stress signals, including DNA damage, oxidative stress and activated oncogenes. The p53 protein is employed as a transcriptional activator of p53-regulated genes. This results in three major outputs; cell cycle arrest, cellular senescence or apoptosis. Other p53-regulated gene functions communicate with adjacent cells, repair the damaged DNA or set up positive and negative feedback loops that enhance or attenuate the functions of the p53 protein and integrate these stress responses with other signal transduction pathways.
Apoptosis is a genetically programmed process for the elimination of damaged or redundant cells by activation of caspases (aspartate-specific cysteine proteases). The onset of apoptosis is controlled by numerous interrelating processes. The 'extrinsic' pathway involves stimulation of members of the tumor necrosis factor (TNF) receptor subfamily, such as TNFRI, CD95/Fas or TRAILR (death receptors), located at the cell surface, by their specific ligands, such as TNF-alpha, FasL or TRAIL, respectively. The 'intrinsic' pathway is activated mainly by non-receptor stimuli, such as DNA damage, ER stress, metabolic stress, UV radiation or growth-factor deprivation. The central event in the 'intrinsic' pathway is the mitochondrial outer membrane permeabilization (MOMP), which leads to the release of cytochrome c. These two pathways converge at the level of effector caspases, such as caspase-3 and caspase-7. The third major pathway is initiated by the constituents of cytotoxic granules (e.g. Perforin and Granzyme B) that are released by CTLs (cytotoxic T-cells) and NK (natural killer) cells. Granzyme B, similarly to the caspases, cleaves its substrates after aspartic acid residues, suggesting that this protease has the ability to activate members of the caspase family directly. It is the balance between the pro-apoptotic and anti-apoptotic signals that eventually determines whether cells will undergo apoptosis, survive or proliferate. TNF family of ligands activates anti-apoptotic or cell-survival signals as well as apoptotic signals. NGF and Interleukin-3 promotes the survival, proliferation and differentiation of neurons or hematopoietic cells, respectively. Withdrawal of these growth factors leads to cell death, as described above.
Apoptosis is an evolutionarily conserved process used by multicellular organisms to developmentally regulate cell number or to eliminate cells that are potentially detrimental to the organism. The major players are caspases, caspase inhibitors, members of the Bcl-2 family of pro- and anti-apoptotic proteins and adaptors of the Ced-4/APAF-1 type. Mammals, by comparison with Caenorhabditis and Drosophila, exhibit highly complex extrinsic and intrinsic pathways for apoptosis induction. However, recent analyses of whole genome sequences from cnidarians (e.g. Hydra) suggest that the caspase and Bcl-2 families were already highly complex in cnidarians and that Caenorhabditis and Drosophila lost many of the genes involved in apoptosis.
Necroptosis is a programmed form of necrosis. It can be initiated by different stimuli, such as tumor necrosis factor (TNF), TNF-related apoptosis-inducing ligand (TRAIL), Fas ligand (FasL), interferon (IFN), LPS, viral DNA or RNA, DNA-damage agent and requires the kinase activity of receptor-interacting protein 1 (RIPK1) and RIPK3. Its execution involves ROS generation, calcium overload, the opening of the mitochondrial permeability transition pore, mitochondrial fission, inflammatory response and chromatinolysis. Necroptosis participates in many pathogenesis of diseases, including neurological diseases, retinal disorders, acute kidney injury, inflammatory diseases and microbial infections.
Specific families of pattern recognition receptors are responsible for detecting microbial pathogens and generating innate immune responses. Toll-like receptors (TLRs) are membrane-bound receptors identified as homologs of Toll in Drosophila. Mammalian TLRs are expressed on innate immune cells, such as macrophages and dendritic cells, and respond to the membrane components of Gram-positive or Gram-negative bacteria. Pathogen recognition by TLRs provokes rapid activation of innate immunity by inducing production of proinflammatory cytokines and upregulation of costimulatory molecules. TLR signaling pathways are separated into two groups: a MyD88-dependent pathway that leads to the production of proinflammatory cytokines with quick activation of NF-{kappa}B and MAPK, and a MyD88-independent pathway associated with the induction of IFN-beta and IFN-inducible genes, and maturation of dendritic cells with slow activation of NF-{kappa}B and MAPK.
Specific families of pattern recognition receptors are responsible for detecting various pathogens and generating innate immune responses. The intracellular NOD-like receptor (NLR) family contains more than 20 members in mammals and plays a pivotal role in the recognition of intracellular ligands. NOD1 and NOD2, two prototypic NLRs, sense the cytosolic presence of the bacterial peptidoglycan fragments that escaped from endosomal compartments, driving the activation of NF-{kappa}B and MAPK, cytokine production and apoptosis. On the other hand, a different set of NLRs induces caspase-1 activation through the assembly of multiprotein complexes called inflammasomes. The activated of caspase-1 regulates maturation of the pro-inflammatory cytokines IL-1B, IL-18 and drives pyroptosis.
Specific families of pattern recognition receptors are responsible for detecting viral pathogens and generating innate immune responses. Non-self RNA appearing in a cell as a result of intracellular viral replication is recognized by a family of cytosolic RNA helicases termed RIG-I-like receptors (RLRs). The RLR proteins include RIG-I, MDA5, and LGP2 and are expressed in both immune and nonimmune cells. Upon recognition of viral nucleic acids, RLRs recruit specific intracellular adaptor proteins to initiate signaling pathways that lead to the synthesis of type I interferon and other inflammatory cytokines, which are important for eliminating viruses.
C-type lectin receptors (CLRs) are a large superfamily of proteins characterized by the presence of one or more C-type lectin-like domains (CTLDs). CLRs function as pattern-recognition receptors (PRRs) for pathogen-derived ligands in dendric cells, macrophages, neutrophils, etc., such as Dectin-1 and Dectin-2 for recognition of fungi-derived B-glucan and high mannose-type carbohydrates. Upon ligand binding, CLRs stimulate intracellular signaling cascades that induce the production of inflammatory cytokines and chemokines, consequently triggering innate and adaptive immunity to pathogens.
The interleukin 17 (IL-17) family, a subset of cytokines consisting of IL-17A-F, plays crucial roles in both acute and chronic inflammatory responses. IL-17A, the hallmark cytokine of the newly defined T helper 17 (TH17) cell subset, has important roles in protecting the host against extracellular pathogens, but also promotes inflammatory pathology in autoimmune disease, whereas IL-17F is mainly involved in mucosal host defense mechanisms. IL-17E (IL-25) is an amplifier of Th2 immune responses. IL-17C has biological functions similar to those of IL-17A. The functions of IL-17B and IL-17D remain largely elusive. The IL-17 family signals via their correspondent receptors and activates downstream pathways that include NF-kappaB, MAPKs and C/EBPs to induce the expression of antimicrobial peptides, cytokines and chemokines. The receptor proximal adaptor Act1 (an NF-kappaB activator 1) is considered as the master mediator in IL-17A signaling. It is likely that Act1 is a common signal adaptor also shared by other members mediated signalings in this family.
Tumor necrosis factor (TNF), as a critical cytokine, can induce a wide range of intracellular signal pathways including apoptosis and cell survival as well as inflammation and immunity. Activated TNF is assembled to a homotrimer and binds to its receptors (TNFR1, TNFR2) resulting in the trimerization of TNFR1 or TNFR2. TNFR1 is expressed by nearly all cells and is the major receptor for TNF (also called TNF-alpha). In contrast, TNFR2 is expressed in limited cells such as CD4 and CD8 T lymphocytes, endothelial cells, microglia, oligodendrocytes, neuron subtypes, cardiac myocytes, thymocytes and human mesenchymal stem cells. It is the receptor for both TNF and LTA (also called TNF-beta). Upon binding of the ligand, TNFR mediates the association of some adaptor proteins such as TRADD or TRAF2, which in turn initiate recruitment of signal transducers. TNFR1 signaling induces activation of many genes, primarily controlled by two distinct pathways, NF-kappa B pathway and the MAPK cascade, or apoptosis and necroptosis. TNFR2 signaling activates NF-kappa B pathway including PI3K-dependent NF-kappa B pathway and JNK pathway leading to survival.
Non-alcoholic fatty liver disease (NAFLD) represents a spectrum ranging from simple steatosis to more severe steatohepatitis with hepatic inflammation and fibrosis, known as nonalcoholic steatohepatitis (NASH). NASH may further lead to cirrhosis and hepatocellular carcinoma (HCC). This map shows a stage-dependent progression of NAFLD. In the first stage of NAFLD, excess lipid accumulation has been demonstrated. The main cause is the induction of insulin resistance, which leads to a defect in insulin suppression of free fatty acids (FAAs) disposal. In addition, two transcription factors, SREBP-1c and PPAR-alpha, activate key enzymes of lipogenesis and increase the synthesis of FAAs in liver. In the second stage, as a consequence of the progression to NASH, the production of reactive oxygen species (ROS) is enhanced due to oxidation stress through mitochondrial beta-oxidation of fatty acids and endoplamic reticulum (ER) stress, leading to lipid peroxidation. The lipid peroxidation can further cause the production of cytokines (Fas ligand, TNF-alpha, IL-8 and TGF), promoting cell death, inflammation and fibrosis. The activation of JNK, which is induced by ER stress, TNF-alpha and FAAs, is also associated with NAFLD progression. Increased JNK promotes cytokine production and initiation of HCC.
Alzheimer disease (AD) is a chronic disorder that slowly destroys neurons and causes serious cognitive disability. AD is associated with senile plaques and neurofibrillary tangles (NFTs). Amyloid-beta (Abeta), a major component of senile plaques, has various pathological effects on cell and organelle function. The extracellular Abeta oligomers may activate caspases through activation of cell surface death receptors. Alternatively, intracellular Abeta may contribute to pathology by facilitating tau hyper-phosphorylation, disrupting mitochondria function, and triggering calcium dysfunction. To date genetic studies have revealed four genes that may be linked to autosomal dominant or familial early onset AD (FAD). These four genes include: amyloid precursor protein (APP), presenilin 1 (PS1), presenilin 2 (PS2) and apolipoprotein E (ApoE). All mutations associated with APP and PS proteins can lead to an increase in the production of Abeta peptides, specfically the more amyloidogenic form, Abeta42. FAD-linked PS1 mutation downregulates the unfolded protein response and leads to vulnerability to ER stress.
Huntington disease (HD) is an autosomal-dominant neurodegenerative disorder that primarily affects medium spiny striatal neurons (MSN). The symptoms are choreiform, involuntary movements, personality changes and dementia. HD is caused by a CAG repeat expansion in the IT15gene, which results in a long stretch of polyglutamine close to the amino-terminus of the HD protein huntingtin (Htt). Mutant Htt (mHtt) has effects both in the cytoplasm and in the nucleus. In the cytoplasm, full-length mHtt can interfere with BDNF vesicular transport on microtubules. This mutant protein also may lead to abnormal endocytosis and secretion in neurons, because normal Htt form a complex with the proteins Hip1, clathrin and AP2 that are involved in endocytosis. In addition, mHtt affects Ca2+ signaling by sensitizing InsP3R1 to activation by InsP3, stimulating NMDAR activity, and destabilizing mitochondrial Ca2+ handling. The mHtt translocates to the nucleus, where it forms intranuclear inclusions. Nuclear toxicity is believed to be caused by interference with gene transcription, leading to loss of transcription of neuroprotective molecules such as BDNF. While mHtt binds to p53 and upregulates levels of nuclear p53 as well as p53 transcriptional activity. Augmented p53 mediates mitochondrial dysfunction.
Legionellosis is a potentially fatal infectious disease caused by the bacterium Legionella pneumophila and other legionella species. Two distinct clinical and epidemiological syndromes are associated with Legionella species: Legionnaires' disease is the more severe form of the infection, which may involve pneumonia, and Pontiac fever is a milder respiratory illness.The pathogenesis of L. pneumophila is derived from its growth within lung macrophages. One of the L. pneumophila's type IV secretion systems, the Dot/Icm secretion system, is of critical importance for its ability to replicate and to cause disease. The Dot/Icm substrates modulate multiple host cell processes and in particular, redirect trafficking of the L. pneumophila phagosome and mediate its conversion into an ER-derived organelle competent for intracellular bacterial replication. L. pneumophila also manipulates host cell death and survival pathways in a way that allows continued intracellular replication.
Trypanosoma cruzi is an intracellular protozoan parasite that causes Chagas disease. The parasite life cycle involves hematophagous reduviid bugs as vectors. Once parasites enter the host body, they invade diverse host cells including cardiomyocytes. Establishment of infection depends on various parasite molecules such as cruzipain, oligopeptidase B, and trans-sialidase that activate Ca2+ signaling. Internalized parasites escape from the parasitophorous vacuole using secreted pore-forming TcTOX molecule and replicate in the cytosol. Multiplied parasites eventually lyse infected host cells and are released in the circulation. During these events, the parasites manipulate host innate immunity and elicit cardiomyocyte hypertrophy. T lymphocyte responses are also disturbed.
Toxoplasma gondii is an obligate intracellular parasite that is prevalent worldwide. The tachyzoite form acquired by oral ingestion downmodulates proinflammatory signaling pathways via various mechanisms. During early infection, nuclear translocation of NFkB is temporally blocked and p38 MAPK phosphorylation is prevented, suppressing IL-12 production. Another pathway for IL-12 induction occurs through CCR5 dependent pathway, but parasitic induction of an eicosanoid LXA4 contributes to the downregulation of IL-12. Direct activation of STAT3 by the parasite enhance anti-inflammatory function of IL-10 and TGF beta. T. gondii can cause lifelong chronic infection by establishing an anti-apoptotic environment through induction of bcl-2 or IAPs and by redirecting LDL-mediated cholesterol transport to scavenge nutrients from the host.
Tuberculosis, or TB, is an infectious disease caused by Mycobacterium tuberculosis. One third of the world's population is thought to be infected with TB. About 90% of those infected result in latent infections, and about 10% of latent infections develop active diseases when their immune system is impaired due to the age, other diseases such as AIDS or exposure to immunosuppressive drugs. TB is transmitted through the air and primarily attacks the lungs, then it can spread by the circulatory system to other parts of body. Once TB bacilli have entered the host by the respiratory route and infected macrophages in the lungs, they interfere with phagosomal maturation, antigen presentation, apoptosis and host immune system to establish persistent or latent infection.
Hepatitis B virus (HBV) is an enveloped virus and contains a partially double-stranded relaxed circular DNA (RC-DNA) genome. After entry into hepatocytes, HBV RC-DNA is transported to the nucleus and converted into a covalently closed circular molecule cccDNA. The cccDNA is the template for transcription of all viral RNAs including the pregenomic RNA (pgRNA), encoding for 7 viral proteins: large, middle, and small envelope proteins (LHBs, MHBs, and SHBs) that form the surface antigen (HBsAg), the core antigen (HBcAg), the e antigen (HBeAg), the HBV polymerase, and the regulatory protein X (HBx). The pgRNA interacts with the viral polymerase protein to initiate the encapsidation into the core particles. Through endoplasmic reticulum, the core particles finish assembling with the envelope proteins and are released. HBV infection leads to a wide spectrum of liver diseases raging from chronic hepatitis, cirrhosis to hepatocellular carcinoma. The mechanism of liver injury is still not clear. However, HBV proteins target host proteins, involved in a variety of functions, thus regulating transcription, cellular signaling cascades, proliferation, differentiation, and apoptosis.
Human cytomegalovirus (HCMV) is an enveloped, double-stranded DNA virus that is a member of beta-herpesvirus family. HCMV is best known for causing significant morbidity and mortality in immunocompromised populations. As with other herpesviruses, HCMV gB and gH/gL envelope glycoproteins are essential for virus entry. HCMV gB could activate the PDGFRA, and induce activation of the oncogenic PI3-K/AKT pathway. Though it is unlikely that HCMV by itself can act as an oncogenic factor, HCMV may have an oncomodulatory role, to catalyze an oncogenic process that has already been initiated. US28, one of the four HCMV-encoded vGPCRs (US27, US28, UL33 and UL78), also has a specific role in the oncomodulatory properties. In addition, HCMV has developed numerous mechanisms for manipulating the host immune system. The virally encoded US2, US3, US6 and US11 gene products all interfere with major histocompatibility complex (MHC) class I antigen presentation. HCMV encodes several immediate early (IE) antiapoptotic proteins (IE1, IE2, vMIA and vICA). These proteins might avoid immune clearance of infected tumor cells by cytotoxic lymphocytes and NK cells.
Human papillomavirus (HPV) is a non-enveloped, double-stranded DNA virus. HPV infect mucoal and cutaneous epithelium resulting in several types of pathologies, most notably, cervical cancer. All types of HPV share a common genomic structure and encode eight proteins: E1, E2, E4, E5, E6, and E7 (early) and L1 and L2 (late). It has been demonstrated that E1 and E2 are involved in viral transcription and replication. The functions of the E4 protein is not yet fully understood. E5, E6, and E7 act as oncoproteins. E5 inhibits the V-ATPase, prolonging EGFR signaling and thereby promoting cell proliferation. The expression of E6 and E7 not only inhibits the tumor suppressors p53 and Rb, but also alters additional signalling pathways. Among these pathways, PI3K/Akt signalling cascade plays a very important role in HPV-induced carcinogenesis. The L1 and L2 proteins form icosahedral capsids for progeny virion generation.
Kaposi sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus 8 (HHV-8), is the most recently identified human tumor virus, and is associated with the pathogenesis of Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and Multicentric Castleman's disease (MCD). Like all other herpesviruses, KSHV displays two modes of life cycle, latency and lytic replication, which are characterized by the patterns of viral gene expression. Genes expressed in latency (LANA, v-cyclin, v-FLIP, Kaposins A, B and C and viral miRNAs) are mainly thought to facilitate the establishment of life long latency in its host and survival against the host innate, and adaptive immune surveillance mechanisms. Among the viral proteins shown to be expressed during lytic replication are potent signaling molecules such as vGPCR, vIL6, vIRFs, vCCLs, K1 and K15, which have been implicated experimentally in the angiogenic and inflammatory phenotype observed in KS lesions. Several of these latent viral and lytic proteins are known to transform host cells, linking KSHV with the development of severe human malignancies.
Herpes simplex virus (HSV) infections are very common worldwide, with the prevalence of HSV-1 reaching up to 80%-90%. Primary infection with HSV takes place in the mucosa, followed by the establishment of latent infection in neuronal ganglia. HSV is the main cause of herpes infections that lead to the formation of characteristic blistering lesion. HSV express multiple viral accessory proteins that interfere with host immune responses and are indispensable for viral replication. Among these proteins, the immediate early (IE) gene ICP0, ICP4, and ICP27 are essential for regulation of HSV gene expression in productive infection. On the other hand, ORF P and ORF O gene are transcribed during latency and blocks the expression of the IE genes, thus maintaining latent infection.
Epstein-Barr virus (EBV) is a gamma-herpes virus that widely infects human populations predominantly at an early age but remains mostly asymptomatic. EBV has been linked to a wide spectrum of human malignancies, including nasopharyngeal carcinoma and other hematologic cancers, like Hodgkin's lymphoma, Burkitt's lymphoma (BL), B-cell immunoblastic lymphoma in HIV patients, and posttransplant-associated lymphoproliferative diseases. EBV has the unique ability to establish life-long latent infection in primary human B lymphocytes. During latent infection, EBV expresses a small subset of genes, including 6 nuclear antigens (EBNA-1, -2, -3A, -3B, -3C, and -LP), 3 latent membrane proteins (LMP-1, -2A, and -2B), 2 small noncoding RNAs (EBER-1 and 2). On the basis of these latent gene expression, three different latency patterns associated with the types of cancers are recognized.
Human immunodeficiency virus type 1 (HIV-1) , the causative agent of AIDS (acquired immunodeficiency syndrome), is a lentivirus belonging to the Retroviridae family. The primary cell surface receptor for HIV-1, the CD4 protein, and the co-receptor for HIV-1, either CCR5 or CXCR4, are found on macrophages and T lymphocytes. At the earliest step, sequential binding of virus envelope (Env) glycoprotein gp120 to CD4 and the co-receptor CCR5 or CXCR4 facilitates HIV-1 entry and has the potential to trigger critical signaling that may favor viral replication. At advanced stages of the disease, HIV-1 infection results in dramatic induction of T-cell (CD4+ T and CD8+ T cell) apoptosis both in infected and uninfected bystander T cells, a hallmark of HIV-1 pathogenesis. On the contrary, macrophages are resistant to the cytopathic effect of HIV-1 and produce virus for longer periods of time.
There is a strong association between viruses and the development of human malignancies. We now know that at least six human viruses, Epstein-Barr virus (EBV), hepatitis B virus (HBV), hepatitis C virus (HCV), human papilloma virus (HPV), human T-cell lymphotropic virus (HTLV-1) and Kaposi's associated sarcoma virus (KSHV) contribute to 10-15% of the cancers worldwide. Via expression of many potent oncoproteins, these tumor viruses promote an aberrant cell-proliferation via modulating cellular cell-signaling pathways and escape from cellular defense system such as blocking apoptosis. Human tumor virus oncoproteins can also disrupt pathways that are necessary for the maintenance of the integrity of host cellular genome. Viruses that encode such activities can contribute to initiation as well as progression of human cancers.
Myocarditis is a cardiac disease associated with inflammation and injury of the myocardium. It results from various etiologies, both noninfectious and infectious, but coxsackievirus B3 (CVB3) is still considered the dominant etiological agent. Myocarditis may be caused by direct cytopathic effects of virus, a pathologic immune response to persistent virus, or autoimmunity triggered by the viral infection. The virus enters the myocyte through internalization of the coxsackie-adenoviral receptor (CAR) and its coreceptor, decay-accelerating factor (DAF). Viral proteases cleave various proteins in the host cell. One example is viral protease 2A, which cleaves eukaryote initiation factor 4G (eIF4G) and the dystrophin protein, resulting in a complete shutdown of cap-dependent RNA translation and cytoskeletal destruction in infected cardiomyocytes, respectively. CVB3 also cleaves the member of the Bcl-2 family Bid, leading to apoptosis. CVB3 infection also induces the cleavage of cyclin D protein through a proteasome-dependent pathway, leading to the host cell-growth arrest. Viral infection and necrosis of myocytes may lead to the release of intracellular antigens, resulting in activation of self-reactive T cells. CVB infection is a significant cause of dilated cardiomyopathy (DCM) as well as myocarditis. Epidemiologically, myocarditis underlies a significant portion of patients with DCM.
Apoptotic cell death is achieved by the caspase-mediated\rcleavage of various vital proteins. Among caspase targets are proteins such as E-cadherin, Beta-catenin, alpha fodrin, GAS2, FADK, alpha adducin, HIP-55, and desmoglein involved in cell adhesion and maintenance of the cytoskeletal architecture. Cleavage of proteins such as APC and CIAP1 can further stimulate apoptosis by produce proapoptotic proteins (reviewed in Fischer et al., 2003. See also Wee et al., 2006 and the CASVM Caspase Substrates Database: http://www.casbase.org/casvm/squery/index.html )
Caspase-8 is synthesized as zymogen (procaspase-8) and is formed from procaspase-8 as a cleavage product. However, the cleavage itself appears not to be sufficient for the formation of an active caspase-8. Only the coordinated dimerization and cleavage of the zymogen produce efficient activation in vitro and apoptosis in cellular systems [Boatright KM and Salvesen GS 2003; Keller N et al 2010; Oberst A et al 2010].
The caspase-8 zymogens are present in the cells as inactive monomers, which are recruited to the death-inducing signaling complex (DISC) by homophilic interactions with the DED domain of FADD. The monomeric zymogens undergo dimerization and the subsequent conformational changes at the receptor complex, which results in the formation of catalytically active form of procaspase-8.[Boatright KM et al 2003; Donepudi M et al 2003; Keller N et al 2010; Oberst A et al 2010]
NOD1 is ubiquitously expressed, while NOD2 expression is restricted to monocytes, macrophages, dendritic cells, and intestinal Paneth cells (Inohara et al. 2005). NOD1 and NOD2 activation induces transcription of immune response genes, predominantly mediated by the proinflammatory transcriptional factor NFkappaB but also by AP-1 and Elk-1 (Inohara et al. 2005). NFkappaB translocates to the nucleus following release from IkappaB proteins. NOD1 and NOD2 signaling involves an interaction between their caspase-recruitment domain (CARD) and the CARD of the kinase RIPK2 (RIP2/RICK). This leads to the activation of the NFkappaB pathway and MAPK pathways (Windheim et al. 2007).Activated NODs oligomerize via their NACHT domains, inducing physical proximity of RIP2 proteins that is believed to trigger their K63-linked polyubiquitination, facilitating recruitment of the TAK1 complex. RIP2 also recruits NEMO, bringing the TAK1 and IKK complexes into proximity, leading to NF-kappaB activation and activation of MAPK signaling. Recent studies have demonstrated that K63-linked regulatory ubiquitination of RIP2 is essential for the recruitment of TAK1 (Hasegawa et al. 2008, Hitosumatsu et al. 2008). As observed for toll-like receptor (TLR) signaling, ubiquitination can be removed by the deubiquitinating enzyme A20, thereby dampening NOD1/NOD2-induced NF-kappaB activation. NOD1 and NOD2 both induce K63-linked ubiquitination of RIP2, but NOD2-signaling appears to preferentially utilize the E3 ligase TRAF6, while TRAF2 and TRAF5 were shown to be important for NOD1-mediated signaling. In both cases, activation of NF-kappaB results in the upregulated transcription and production of inflammatory mediators
TLR3 and -4 trigger TRIF-dependent programmed cell death in various human and mouse cells (Kalai M et al. 2002; Han KJ et al. 2004; Kaiser WJ and Offermann MK 2005; Estornes Y et al. 2012; He S et al. 2011). Apoptosis is a prevalent form of programmed cell death and is mediated by the activation of a set of caspases. In addition to apoptosis, TLR3/TLR4 activation induces RIP3-dependent necroptosis. These two programmed cell-death pathways may suppress each other. When the caspase activity is impaired or inhibited, certain cell types switch the apoptotic death program to necroptosis in response to various stimuli (TNF, Fas, viral infection and other stress stimuli) (Kalai M et al. 2002; Weber A et al. 2010; Feoktistova M et al. 2011, Tenev et al 2011)
Caspase-mediated cleavage of a number of proteins in the cortical actin network ( ) microfilament system and others involved in maintenance of the cytoskeletal architecture (vimentin, or Gas2 and plectin) may directly contribute to apoptotic changes in cell shape
c-FLIP proteins (CASP8 and FADD-like apoptosis regulators or c-FLICE inhibitory proteins) are death effector domain (DED)-containing proteins that are recruited to the death-inducing signaling complex (DISC) to regulate activation of caspases-8. Three out of 13 distinct spliced variants of c-FLIP had been found to be expressed at the protein level, the 26 kDa short form FLIP(S), the 24 kDa form FLIP(R), and the 55 kDa long form FLIP(L) (Irmler M et al. 1997; Shu HB et al. 1997; Srinivasula SM et al. 1997; Scaffidi C et al. 1999; Golks A et al. 2005; Haag C et al. 2011)
All c-FLIP proteins carry two DEDs at their N termini, which can bind FADD and procaspase-8. In addition to two DEDs, FLIP(L) contains a large (p20) and a small (p12) caspase-like domain without catalytic activity. FLIP(S) and FLIP(R) consist of two DEDs and a small C terminus. Depending on its level of expression FLIP(L) may function as an anti-apoptotic or pro-apoptotic factor, while FLIP(S) and FLIP(R) protect cells from apoptosis by blocking the processing of caspase-8 at the receptor level (Scaffidi C et al. 1999; Golks A et al. 2005; Toivonen HT et al. 2011; Fricker N et al. 2010)
Receptor-interacting kinase protein 1 (RIPK1) and RIPK3-dependent necrosis is called necroptosis or programmed necrosis. The kinase activities of RIPK1 and RIPK3 are essential for the necroptotic cell death in human, mouse cell lines and genetic mice models (Cho YS et al. 2009; He S et al. 2009, 2011; Zhang DW et al. 2009; McQuade T et al. 2013; Newton et al. 2014). The initiation of necroptosis can be stimulated by the same death ligands that activate apoptosis, such as tumor necrosis factor (TNF) alpha, Fas ligand (FasL), and TRAIL (TNF-related apoptosis-inducing ligand) or toll like receptors 3 and 4 ligands (Holler N et al. 2000; He S et al. 2009; Feoktistova M et al. 2011; Voigt S et al. 2014). In contrast to apoptosis, necroptosis represents a form of cell death that is optimally induced when caspases are inhibited (Holler N et al. 2000; Hopkins?Donaldson S et al. 2000; Sawai H 2014). Specific inhibitors of caspase-independent necrosis, necrostatins, have recently been identified (Degterev A et al. 2005, 2008). Necrostatins have been shown to inhibit the kinase activity of RIPK1 (Degterev A et al. 2008). Importantly, cell death of apoptotic morphology can be shifted to a necrotic phenotype when caspase 8 activity is compromised, otherwise active caspase 8 blocks necroptosis by the proteolytic cleavage of RIPK1 and RIPK3 (Kalai M et al. 2002; Degterev A et al. 2008; Lin Y et al. 1999; Feng S et al. 2007). When caspase activity is inhibited under certain pathophysiological conditions or by pharmacological agents, deubiquitinated RIPK1 is engaged in physical and functional interactions with its homolog RIPK3 leading to formation of necrosome, a necroptosis-inducing complex consisting of RIPK1 and RIPK3 (Sawai H 2013; Moquin DM et al. 2013; Kalai M et al. 2002; Cho YS et al. 2009, He S et al. 2009, Zhang DW et al. 2009). Within the necrosome RIPK1 and RIPK3 bind to each other through their RIP homotypic interaction motif (RHIM) domains. The RHIMs can facilitate RIPK1:RIPK3 oligomerization, allowing them to form amyloid?like fibrillar structures (Li J et al. 2012). RIPK3 in turn interacts with mixed lineage kinase domain?like protein (MLKL) (Sun L et al. 2012; Zhao J et al. 2012). The complex of RIPK1:RIPK3:MLKL is crucial for an execution phase of necroptosis which is strictly dependent on RIPK3-mediated phosphorylation of MLKL followed by MLKL oligomerization and translocation to membrane surfaces (Sun L et al. 2012; Wang H et al. 2014). Immunoblot analysis of cell fractions obtained by differential centrifugation of human colorectal adenocarcinoma (HT29) whole cell extracts suggests that upon necroptosis RIPK1:RIPK3:MLKL complexes shift to the plasma membrane and membranous organelles such as mitochondria, lysosome, endosome and ER (Wang H et al. 2014). These findings are supported by immunofluorescent imaging of subcellular distribution of necrosome components expressed in human cells (Wang H et al. 2014; Cai Z et al. 2014). The mechanisms of necroptosis regulation and execution downstream of MLKL remain elusive. MLKL has been proposed to induce necrosis execution in human cells (shown for HeLA and HT29 cell lines) by binding and activating phosphoglycerate mutase 5 (PGAM5) resulting in the induction of mitochondrial fission (Wang Z et al 2012). However, other studies showed that PGAM5-mediated mitochondrial fragmentation was dispensable for RIP?mediated necrosis in mouse cells (Murphy et al. 2013, Remijsen Q et al. 2014; Moujalled DM et al. 2014). Moreover, mitochondria-depleted 3T3 mouse embryo fibroblast cells were found to undergo necroptosis, suggesting that mitochondria axis may not be required for this process (Tait SW et al. 2013). Finally, RIPK3-activated MLKL has been also reported to translocate to lipid rafts of the plasma membrane where it facilitate cell death through membrane permeabilization (Cai Z et al. 2014; Dondelinger Y et al. 2014).
The Reactome module describes MLKL-mediated necroptotic events on the plasma membrane
Cell death triggered by extrinsic stimuli via death receptors or toll-like receptors (e.g., TLR3, TLR4) may result in either apoptosis or regulated necrosis (necroptosis) (Holler N et al. 2000; Kalai M et al. 2002; Kaiser WJ and Offermann MK 2005; Yang P et al. 2007). Caspase-8 (CASP8) is a cysteine peptidase, which functions as a key mediator for determining which form of cell death will occur (Kalai M et al. 2002; ). The proteolytic activity of a fully processed, heterotetrameric form of CASP8 in human and rodent cells is required for proapoptotic signaling and also for a cleavage of kinases RIPK1 and RIPK3, while at the same time preventing RIPK1/RIPK3-dependent regulated necrosis (Juo P et al. 1998; Lin Y et al. 1999; Holler N et al. 2000; Hopkins-Donaldson S et al. 2000). A blockage of CASP8 activity in the presence of caspase inhibitors such as Z-VAD-FMK (pan-caspase inhibitor), endogenous FLIP(S) or viral FLIP-like protein was found to switch signaling to necrotic cell death (Thome M et al. 1997; Kalai M et al. 2002; Feoktistova M et al. 2011; Sawai H 2013)
Activation of tumor necrosis factor receptor 1 (TNFR1) can trigger multiple signal transduction pathways to induce cell survival or cell death (Ward C et al. 1999; Micheau O and Tschopp J 2003; Widera D et al. 2006). While pro-survival signaling is initiated and regulated via the activated TNFR1 receptor complex at the cell membrane, cell death signals are induced upon the release of TRADD:TRAF2:RIP1 complex from the membrane to the cytosol where it forms death-inducing signaling complex (DISC) (Micheau O and Tschopp J 2003; Schneider-Brachert W et al. 2004). Upon apoptotic stimulation procaspase-8 or 10 is recruited into the DISC, and close proximity promotes the dimerization, autocatalytic processing, and activation of the initiator caspase-8 (and/or caspase-10) (Wang J et al. 2001; Boatright KM and Salvesen GS 2003). The initiator caspases then process and activate the downstream effector caspases such as caspase-3 in a proteolytic cascade (Stennicke HR et al. 1998). The effector caspases in turn cleave many diverse substrates, ultimately inducing cell death
Tumor necrosis factor-alpha (TNFalpha) is an inflammatory cytokine, that activates either cell survival (e.g.,inflammation, proliferation) or cell death upon association with TNF receptor 1 (TNFR1). Stimuli and the cellular context dictate cell fate decisions between survival and death which rely on tightly regulated mechanisms with checkpoints on many levels. TNFR1-mediated NFkappaB activation leads to the pro-survival transcriptional program that is both anti-apoptotic and highly proinflammatory. The constitutive NFkappaB or AP1 activation may lead to excessive inflammation which has been associated with a variety of aggressive tumor types (Jackson-Bernitsas DG et al. 2007; Zhang JY et al. 2007). Thus, the tight regulation of TNFalpha:TNFR1 signaling is required to ensure the appropriate cell response to stimuli
Antifungal immunity through the induction of T-helper 17 cells (TH17) responses requires the production of mature, active interleukin-1beta (IL1B). CLEC7A (dectin-1) through the SYK route induces activation of NF-kB and transcription of the gene encoding pro-IL1B via the CARD9-BCL10-MALT1 complex as well as the formation and activation of a MALT1-caspase-8-ASC complex that mediated the processing of pro-IL1B. The inactive precursor pro-IL1B has to be processed into mature bioactive form of IL1B and is usually mediated by inflammatory cysteine protease caspase-1. Gringhuis et al. showed that CLEC7A mediated processing of IL1B occurs through two distinct mechanisms: CLEC7A triggering induced a primary noncanonical caspase-8 inflammasome for pro-IL1B processing that was independent of caspase-1 activity, whereas some fungi triggered a second additional mechanism that required activation of the NLRP3/caspase 1 inflammasome. Unlike the canonical caspase-1 inflammasome, CLEC7A mediated noncanonical caspase-8-dependent inflammasome is independent of pathogen internalization. CLEC7A/inflammasome pathway enables the host immune system to mount a protective TH17 response against fungi and bacterial infection (Gringhuis et al. 2012, Cheng et al. 2011)
A regulated balance between cell survival and cell death is essential for normal development and homeostasis of multicellular organisms. Defects in control of this balance may contribute to autoimmune disease, neurodegeneration and cancer
Procaspase-8 monomers undergo dimerization. The dimerization event occurs at death-inducing signaling complex (DISC) and results in a reposition of the procaspase-8 inter-subunit linker to become accessible for intermolecular processing by the associated procaspase-8 molecule [Keller N et al 2010; Oberst A et al 2010]
BID may promote cell death by activating BAX and BAK while inactivating anti-apoptotic proteins. The engagement of cell surface receptors activates the caspase-8, a heterodimer, that cleaves BID in its amino terminal region. This particular event may act as a link between Extrinsic (caspase 8/10 dependent) and Intrinsic (Bcl-2 inhibitable) pathways although some evidences from mouse genetic experiments suggest the contrary. It has been suggested that the death signals from the extrinsic or death receptor pathway may get amplified by the mechanisms of intrinsic pathway and that this functional loop may be enabled by the molecules like tBID (truncated BID). Cleavage of BID to tBID can also be achieved by Granzyme B. The truncated protein is myristoylated and translocates to mitochondria
In the execution phase of apoptosis, effector caspases cleave vital cellular proteins leading to the morphological changes that characterize apoptosis. These changes include destruction of the nucleus and other organelles, DNA fragmentation, chromatin condensation, cell shrinkage and cell detachment and membrane blebbing (reviewed in Fischer et al., 2003)
The Fas family of cell surface receptors initiate the apototic pathway through interaction with the external ligand, FasL. The cytoplasmic domain of Fas interacts with a number of molecules in the transduction of the external signal to the cytoplasmic side of the cell membrane. The most notable cytoplasmic domain is the Death Domain (DD) that is involved in recruiting the FAS-associating death domain-containing protein (FADD). This interaction drives downstream events
Tumor necrosis factor-related apoptosis-inducing ligand or Apo 2 ligand (TRAIL/Apo2L) is a member of the tumor necrosis factor (TNF) family. This group of apoptosis induction pathways all work through protein interactions mediated by the intracellular death domain (DD), encoded within the cytoplasmic domain of the receptor. TRAIL selectively induces apoptosis through its interaction with the Fas-associated death domain protein (FADD) and caspase-8/10 (Wang S & el-Deiry WS 2003; Sprick MR et al. 2002). TRAIL and its receptors, TRAIL-R1 and TRAIL-R2, were shown to be rapidly endocytosed via clathrin-dependent and -independent manner in human Burkitt's lymphoma B cells (BJAB) (Kohlhaas SL et al. 2007). However, FADD and caspase-8 were able to bind TRAIL-R1/R2 in TRAIL-stimulated BJAB cells at 4oC (at which membrane trafficking is inhibited), suggesting that the endocytosis was not required for an assembly of the functional TRAIL DISC complex. Moreover, blocking of clathrin-dependent endocytosis did not interfere with the capacity of TRAIL to promote apoptosis (Kohlhaas SL et al. 2007)
TLR3 and TLR4 trigger TRIF(TICAM1)-dependent programmed cell death in various human and mouse cells (Kalai M et al. 2002; Han KJ et al. 2004; Kaiser WJ and Offermann MK 2005; Estornes Y et al. 2012; He S et al. 2011). Apoptosis is a prevalent form of programmed cell death and is mediated by the activation of a set of caspases. In addition to apoptosis, TLR3/TLR4 activation induces RIP3-dependent necroptosis. These two programmed cell-death pathways may suppress each other. When the caspase activity is impaired or inhibited, certain cell types switch the apoptotic death program to necroptosis in response to various stimuli (TNF, Fas, viral infection and other stress stimuli) (Kalai M et al. 2002; Weber A et al. 2010; Feoktistova M et al. 2011, Tenev et al 2011)
Fas-AssociatedDeathDomain (FADD) and receptor interacting protein 1 (RIP1) are death domain containing molecules that interact with the C-terminal portion of IPS-1 and induce NF-kB through interaction and activation of initiator caspases (caspase-8 and -10). Caspases are usually involved in apoptosis and inflammation but they also exhibit nonapoptotic functions. These nonapoptotic caspase functions involve prodomain-mediated activation of NF-kB. Processed caspases (caspase-8/10) encoding the DED (death effector domain) strongly activate NF-kB. The exact mechanism by which caspases mediate NF-kB activation is unclear, but the prodomains of caspase-8/10 may act as a scaffolding and allow the recruitment of the IKK complex in association with other signaling molecules
Affinity Capture-Western, Biochemical Activity, Co-purification, anti bait coimmunoprecipitation, anti tag coimmunoprecipitation, fluorescent resonance energy transfer
association, direct interaction, physical, physical association
Affinity Capture-Western, Co-purification, Reconstituted Complex, Two-hybrid, anti bait coimmunoprecipitation, anti tag coimmunoprecipitation, cosedimentation through density gradient, fluorescent resonance energy transfer, pull down, two hybrid, two hybrid array
association, colocalization, direct interaction, physical, physical association
Affinity Capture-MS, Affinity Capture-Western, Co-purification, anti bait coimmunoprecipitation, coimmunoprecipitation, cosedimentation through density gradient, imaging technique
association, colocalization, physical, physical association
Affinity Capture-Western, Biochemical Activity, Co-purification, anti bait coimmunoprecipitation, anti tag coimmunoprecipitation, fluorescent resonance energy transfer
association, direct interaction, physical, physical association
Affinity Capture-Western, Co-purification, Reconstituted Complex, Two-hybrid, anti bait coimmunoprecipitation, anti tag coimmunoprecipitation, cosedimentation through density gradient, fluorescent resonance energy transfer, pull down, two hybrid, two hybrid array
association, colocalization, direct interaction, physical, physical association
Affinity Capture-MS, Affinity Capture-Western, Co-purification, anti bait coimmunoprecipitation, coimmunoprecipitation, cosedimentation through density gradient, imaging technique
association, colocalization, physical, physical association
Affinity Capture-Western, Biochemical Activity, Co-purification, anti bait coimmunoprecipitation, anti tag coimmunoprecipitation, fluorescent resonance energy transfer
association, direct interaction, physical, physical association
Affinity Capture-Western, Co-purification, Reconstituted Complex, Two-hybrid, anti bait coimmunoprecipitation, anti tag coimmunoprecipitation, cosedimentation through density gradient, fluorescent resonance energy transfer, pull down, two hybrid, two hybrid array
association, colocalization, direct interaction, physical, physical association
Affinity Capture-MS, Affinity Capture-Western, Co-purification, anti bait coimmunoprecipitation, coimmunoprecipitation, cosedimentation through density gradient, imaging technique
association, colocalization, physical, physical association
Affinity Capture-Western, Biochemical Activity, Co-purification, anti bait coimmunoprecipitation, anti tag coimmunoprecipitation, fluorescent resonance energy transfer
association, direct interaction, physical, physical association
Affinity Capture-Western, Co-purification, Reconstituted Complex, Two-hybrid, anti bait coimmunoprecipitation, anti tag coimmunoprecipitation, cosedimentation through density gradient, fluorescent resonance energy transfer, pull down, two hybrid, two hybrid array
association, colocalization, direct interaction, physical, physical association
Affinity Capture-MS, Affinity Capture-Western, Co-purification, anti bait coimmunoprecipitation, coimmunoprecipitation, cosedimentation through density gradient, imaging technique
association, colocalization, physical, physical association