241 human active and 13 inactive phosphatases in total;
194 phosphatases have substrate data;
336 protein substrates;
83 non-protein substrates;
1215 dephosphorylation interactions;
299 KEGG pathways;
876 Reactome pathways;
last scientific update: 11 Mar, 2019
last maintenance update: 01 Sep, 2023
Involved in the activation cascade of caspasesresponsible for apoptosis execution At the onset of apoptosis itproteolytically cleaves poly(ADP-ribose) polymerase (PARP) at a'216-Asp-|-Gly-217' bond Cleaves and activates sterol regulatoryelement binding proteins (SREBPs) between the basic helix-loop-helix leucine zipper domain and the membrane attachment domainCleaves and activates caspase-6, -7 and -9 Involved in thecleavage of huntingtin Triggers cell adhesion in sympatheticneurons through RET cleavage
Catalytic Activity (UniProt annotation)
Strict requirement for an Asp residue atpositions P1 and P4 It has a preferred cleavage sequence of Asp-Xaa-Xaa-Asp-|- with a hydrophobic amino-acid residue at P2 and ahydrophilic amino-acid residue at P3, although Val or Ala are alsoaccepted at this position
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.
The mitogen-activated protein kinase (MAPK) cascade is a highly conserved module that is involved in various cellular functions, including cell proliferation, differentiation and migration. Mammals express at least four distinctly regulated groups of MAPKs, extracellular signal-related kinases (ERK)-1/2, Jun amino-terminal kinases (JNK1/2/3), p38 proteins (p38alpha/beta/gamma/delta) and ERK5, that are activated by specific MAPKKs: MEK1/2 for ERK1/2, MKK3/6 for the p38, MKK4/7 (JNKK1/2) for the JNKs, and MEK5 for ERK5. Each MAPKK, however, can be activated by more than one MAPKKK, increasing the complexity and diversity of MAPK signalling. Presumably each MAPKKK confers responsiveness to distinct stimuli. For example, activation of ERK1/2 by growth factors depends on the MAPKKK c-Raf, but other MAPKKKs may activate ERK1/2 in response to pro-inflammatory stimuli.
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.
Natural killer (NK) cells are lymphocytes of the innate immune system that are involved in early defenses against both allogeneic (nonself) cells and autologous cells undergoing various forms of stress, such as infection with viruses, bacteria, or parasites or malignant transformation. Although NK cells do not express classical antigen receptors of the immunoglobulin gene family, such as the antibodies produced by B cells or the T cell receptor expressed by T cells, they are equipped with various receptors whose engagement allows them to discriminate between target and nontarget cells. Activating receptors bind ligands on the target cell surface and trigger NK cell activation and target cell lysis. However Inhibitory receptors recognize MHC class I molecules (HLA) and inhibit killing by NK cells by overruling the actions of the activating receptors. This inhibitory signal is lost when the target cells do not express MHC class I and perhaps also in cells infected with virus, which might inhibit MHC class I exprssion or alter its conformation. The mechanism of NK cell killing is the same as that used by the cytotoxic T cells generated in an adaptive immune response; cytotoxic granules are released onto the surface of the bound target cell, and the effector proteins they contain penetrate the cell membrane and induce programmed cell death.
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.
Serotonin (5-Hydroxytryptamine, 5-HT) is a monoamine neurotransmitter that plays important roles in physiological functions such as learning and memory, emotion, sleep, pain, motor function and endocrine secretion, as well as in pathological states including abnormal mood and cognition. Once released from presynaptic axonal terminals, 5-HT binds to receptors, which have been divided into 7 subfamilies on the basis of conserved structures and signaling mechanisms. These families include the ionotropic 5-HT3 receptors and G-protein-coupled 5-HT receptors, the 5-HT1 (Gi /Go -coupled), 5-HT2(Gq-coupled), 5-HT4/6/7 (Gs-coupled) and 5-HT5 receptors. Presynaptically localized 5-HT1B receptors are thought to be the autoreceptors that suppress excess 5-HT release. 5-HT's actions are terminated by transporter- mediated reuptake into neurons, leading to catabolism by monoamine oxidase.
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.
Advanced glycation end products (AGEs) are a complex group of compounds produced through the non-enzymatic glycation and oxidation of proteins, lipids and nucleic acids, primarily due to aging and under certain pathologic condition such as huperglycemia. Some of the best chemically characterized AGEs include N-epsilon-carboxy-methyl-lysine (CML), N-epsilon-carboxy-ethyl-lysine (CEL), and Imidazolone. The major receptor for AGEs, known as receptor for advanced glycation end products (RAGE or AGER), belongs to the immunoglobulin superfamily and has been described as a pattern recognition receptor. AGE/RAGE signaling elicits activation of multiple intracellular signal pathways involving NADPH oxidase, protein kinase C, and MAPKs, then resulting in NF-kappaB activity. NF-kappa B promotes the expression of pro-inflammatory cytokines such as IL-1, IL-6 and TNF-alpha and a variety of atherosclerosis-related genes, including VCAM-1, tissue factor, VEGF, and RAGE. In addition, JAK-STAT-mediated and PI3K-Akt-dependent pathways are induced via RAGE, which in turn participate in cell proliferation and apoptosis respectively. Hypoxia-mediated induction of Egr-1 was also shown to require the AGE-RAGE interaction. The results of these signal transductions have been reported to be the possible mechanism that initates diabetic complications.
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.
Parkinson disease (PD) is a progressive neurodegenerative movement disorder that results primarily from the death of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNc). Mutations in alpha-synuclein, UCHL1 (a ubiquitin carboxy-terminal hydrolase L1), parkin, DJ1 (a parkin-associated protein involved with oxidative stress), and PINK1 (a putative serine threonine kinase) are known to cause early-onset PD. Mutations or altered expression of these proteins contributes to the damage and subsequent loss of DA neurons through common mechanisms that result in proteasome dysfunction, mitochondrial impairment, and oxidative stress. The demise of DA neurons located in the SNc leads to a drop in the dopaminergic input to the striatum. This results in a reduced activation of the direct pathway and in a disinhibition of the indirect pathway, which is associated with the elevation of adenosine A2A receptor transmission. Such unbalanced activity of the striatal output pathway is at the basis of the motor impairment observed in PD.
Amyotrophic lateral sclerosis (ALS) is a progressive, lethal, degenerative disorder of motor neurons. The hallmark of this disease is the selective death of motor neurons in the brain and spinal cord, leading to paralysis of voluntary muscles. Mutant superoxide dismutase 1 (SOD1), as seen in some familial ALS (FALS) cases, is unstable, forming aggregates in the motor neuron cytoplasm, axoplasm and mitochondria. Within mitochondria, mutant SOD1 may interfere with the anti-apoptotic function of Bcl-2, affect mitochondrial import by interfering with the translocation machinery (TOM/TIM), and generate toxic free radicals (ROS). Reactive oxygen species (ROS), produced within mitochondria, inhibit the function of EAAT2, the main glial glutamate transporter protein, responsible for most of the reuptake of synaptically released glutamate. Glutamate excess increases intracellular calcium, which enhances oxidative stress and mitochondrial damage. Mutant SOD1 can also trigger oxidative reactions , which can then cause damage through the formation of hydroxyl radicals or via nitration of tyrosine residues on proteins. Nitration may target neurofilament proteins, affecting axonal transport. Collectively, these mechanisms are predicted to disturb cellular homeostasis, ultimately triggering motor neuron death.
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.
Two major virulence factors of H. pylori are the vacuolating cytotoxin (VacA) and the cag type-IV secretion system (T4SS) and its translocated effector protein, cytotoxin-associated antigen A (CagA).VacA binds to lipid rafts and glycosylphosphatidylinositol-anchored proteins (GPI-APs) of the target cell membrane. After insertion into the plasma membrane, VacA channels are endocytosed and eventually reach late endosomal compartments, increasing their permeability to anions with enhancement of the electrogenic vacuolar ATPase (v-ATPase) proton pump. In the presence of weak bases, osmotically active acidotropic ions will accumulate in the endosomes. This leads to water influx and vesicle swelling, an essential step in vacuole formation. In addition, it is reported that the VacA cleavage product binds to the tyrosine phosphatase receptor zeta (Ptprz) on epithelial cells and the induced signaling leads to the phosphorylation of the G protein-coupled receptor kinase-interactor 1 (Git1) and induces ulcerogenesis in mice.The other virulence factor cag T4SS mediates the translocation of the effector protein CagA, which is subsequently phosphorylated by a Src kinase. Phosphorylated CagA interacts with the protein tyrosine phosphatase SHP-2, thus stimulating its phosphatase activity. Activated SHP-2 is able to induce MAPK signalling through Ras/Raf-dependent and -independent mechanisms. Deregulation of this pathway by CagA may lead to abnormal proliferation and movement of gastric epithelial cells.
Pertussis, also known as whooping cough, is an acute respiratory infectious disease caused by a bacteria called Bordetella Pertussis. The characteristic symptoms are paroxysmal cough, inspiratory wheezing and post-tussive vomiting.Following the inhalation of respiratory secretions from an infected individual, bacteria enter the upper respiratory tract and adhere to epithelial cells. Several adhesion factors have been implicated: the filamentous hemagglutinin (FHA), fimbriae, and pertactin (Prn).Pertussis toxin (Ptx) and adenylate cyclase toxin (ACT) have been identified so far as major protein toxins of B. pertussis. PTX is a hexameric AB5-type exotoxin. Catalytic A subunit catalyzes the ADP-ribosylation of the Gi subunits of the heterotrimeric G protein, then inhibits multiple downstream pathways. ACT is able to penetrate the cytoplasmic membrane of host cells and becomes activated through the cleavage and the binding of calmodulin (CaM). Activated ACT converts ATP to cyclic AMP and subverts cellular signaling pathways.
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.
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.
Entamoeba histolytica, an extracellular protozoan parasite is a human pathogen that invades the intestinal epithelium. Infection occurs on ingestion of contaminated water and food. The pathogenesis of amoebiasis begins with parasite attachment and disruption of the intestinal mucus layer, followed by apoptosis of host epithelial cells. Intestinal tissue destruction causes severe dysentery and ulcerations in amoebic colitis. Several amoebic proteins such as lectins, cysteine proteineases, and amoebapores are associated with the invasion process. The parasite can cause extraintestinal infection like amoebic liver abscess by evading immune response.
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.
Many proteoglycans (PGs) in the tumor microenvironment have been shown to be key macromolecules that contribute to biology of various types of cancer including proliferation, adhesion, angiogenesis and metastasis, affecting tumor progress. The four main types of proteoglycans include hyaluronan (HA), which does not occur as a PG but in free form, heparan sulfate proteoglycans (HSPGs), chondroitin sulfate proteoglycans (CSPGs), dematan sulfate proteoglycans (DSPG) and keratan sulfate proteoglycans (KSPGs) [BR:00535]. Among these proteoglycans such as HA, acting with CD44, promotes tumor cell growth and migration, whereas other proteoglycans such as syndecans (-1~-4), glypican (-1, -3) and perlecan may interact with growth factors, cytokines, morphogens and enzymes through HS chains [BR: 00536], also leading to tumor growth and invasion. In contrast, some of the small leucine-rich proteolgycans, such as decorin and lumican, can function as tumor repressors, and modulate the signaling pathways by the interaction of their core proteins and multiple receptors.
MicroRNA (miRNA) is a cluster of small non-encoding RNA molecules of 21 - 23 nucleotides in length, which controls gene expression post-transcriptionally either via the degradation of target mRNAs or the inhibition of protein translation. Using high-throughput profiling, dysregulation of miRNAs has been widely observed in different stages of cancer. The upregulation (overexpression) of specific miRNAs could lead to the repression of tumor suppressor gene expression, and conversely the downregulation of specific miRNAs could result in an increase of oncogene expression; both these situations induce subsequent malignant effects on cell proliferation, differentiation, and apoptosis that lead to tumor growth and progress. The miRNA signatures of cancer observed in various studies differ significantly. These inconsistencies occur due to the differences in the study populations and methodologies used. This pathway map shows the summarized results from various studies in 9 cancers, each of which is presented in a review article.
Colorectal cancer (CRC) is the second largest cause of cancer-related deaths in Western countries. CRC arises from the colorectal epithelium as a result of the accumulation of genetic alterations in defined oncogenes and tumour suppressor genes (TSG). Two major mechanisms of genomic instability have been identified in sporadic CRC progression. The first, known as chromosomal instability (CIN), results from a series of genetic changes that involve the activation of oncogenes such as K-ras and inactivation of TSG such as p53, DCC/Smad4, and APC. The second, known as microsatellite instability (MSI), results from inactivation of the DNA mismatch repair genes MLH1 and/or MSH2 by hypermethylation of their promoter, and secondary mutation of genes with coding microsatellites, such as transforming growth factor receptor II (TGF-RII) and BAX. Hereditary syndromes have germline mutations in specific genes (mutation in the tumour suppressor gene APC on chromosome 5q in FAP, mutated DNA mismatch repair genes in HNPCC).
Lung cancer is a leading cause of cancer death among men and women in industrialized countries. Small cell lung carcinoma (SCLC) is a highly aggressive neoplasm, which accounts for approximately 25% of all lung cancer cases. Molecular mechanisms altered in SCLC include induced expression of oncogene, MYC, and loss of tumorsuppressor genes, such as p53, PTEN, RB, and FHIT. The overexpression of MYC proteins in SCLC is largely a result of gene amplification. Such overexpression leads to more rapid proliferation and loss of terminal differentiation. Mutation or deletion of p53 or PTEN can lead to more rapid proliferation and reduced apoptosis. The retinoblastoma gene RB1 encodes a nuclear phosphoprotein that helps to regulate cell-cycle progression. The fragile histidine triad gene FHIT encodes the enzyme diadenosine triphosphate hydrolase, which is thought to have an indirect role in proapoptosis and cell-cycle control.
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.
Smac/DIABLO regulates IAP function. Residues 56-59 of Smac/DIABLO are homologous to the amino-terminal motif that is used by caspase-9 to bind to the BIR3 domain of XIAP. Binding of Smac/DIABLO to XIAP thus displaces caspase-9 from the XIAP:Caspase complex (reviewed in Salvesen et al., 2002)
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 )
Matrix metalloproteinases (MMPs), previously referred to as matrixins because of their role in degradation of the extracellular matrix (ECM), are zinc and calcium dependent proteases belonging to the metzincin family. They contain a characteristic zinc-binding motif HEXXHXXGXXH (Stocker & Bode 1995) and a conserved Methionine which forms a Met-turn. Humans have 24 MMP genes giving rise to 23 MMP proteins, as MMP23 is encoded by two identical genes. All MMPs contain an N-terminal secretory signal peptide and a prodomain with a conserved PRCGXPD motif that in the inactive enzyme is localized with the catalytic site, the cysteine acting as a fourth unpaired ligand for the catalytic zinc atom. Activation involves delocalization of the domain containing this cysteine by a conformational change or proteolytic cleavage, a mechanism referred to as the cysteine-switch (Van Wart & Birkedal-Hansen 1990). Most MMPs are secreted but the membrane type MT-MMPs are membrane anchored and some MMPs may act on intracellular proteins. Various domains determine substrate specificity, cell localization and activation (Hadler-Olsen et al. 2011). MMPs are regulated by transcription, cellular location (most are not activated until secreted), activating proteinases that can be other MMPs, and by metalloproteinase inhibitors such as the tissue inhibitors of metalloproteinases (TIMPs). MMPs are best known for their role in the degradation and removal of ECM molecules. In addition, cleavage of the ECM and other cell surface molecules can release ECM-bound growth factors, and a number of non-ECM proteins are substrates of MMPs (Nagase et al. 2006). MMPs can be divided into subgroups based on domain structure and substrate specificity but it is clear that these are somewhat artificial, many MMPs belong to more than one functional group (Vise & Nagase 2003, Somerville et al. 2003)
Human Hippo signaling is a network of reactions that regulates cell proliferation and apoptosis, centered on a three-step kinase cascade. The cascade was discovered by analysis of Drosophila mutations that lead to tissue overgrowth, and human homologues of its components have since been identified and characterized at a molecular level. Data from studies of mice carrying knockout mutant alleles of the genes as well as from studies of somatic mutations in these genes in human tumors are consistent with the conclusion that in mammals, as in flies, the Hippo cascade is required for normal regulation of cell proliferation and defects in the pathway are associated with cell overgrowth and tumorigenesis (Oh and Irvine 2010; Pan 2010; Zhao et al. 2010). This group of reactions is also notable for its abundance of protein:protein interactions mediated by WW domains and PPxY sequence motifs (Sudol and Harvey 2010).
There are two human homologues of each of the three Drosophila kinases, whose functions are well conserved: expression of human proteins rescues fly mutants. The two members of each pair of human homologues have biochemically indistinguishable functions. Autophosphorylated STK3 (MST2) and STK4 (MST1) (homologues of Drosophila Hippo) catalyze the phosphorylation and activation of LATS1 and LATS2 (homologues of Drosophila Warts) and of the accessory proteins MOB1A and MOB1B (homologues of Drosophila Mats). LATS1 and LATS2 in turn catalyze the phosphorylation of the transcriptional co-activators YAP1 and WWTR1 (TAZ) (homologues of Drosophila Yorkie).
In their unphosphorylated states, YAP1 and WWTR1 freely enter the nucleus and function as transcriptional co-activators. In their phosphorylated states, however, YAP1 and WWTR1 are instead bound by 14-3-3 proteins, YWHAB and YWHAE respectively, and sequestered in the cytosol.
Several accessory proteins are required for the three-step kinase cascade to function. STK3 (MST2) and STK4 (MST1) each form a complex with SAV1 (homologue of Drosophila Salvador), and LATS1 and LATS2 form complexes with MOB1A and MOB1B (homologues of Drosophila Mats).
In Drosophila a complex of three proteins, Kibra, Expanded, and Merlin, can trigger the Hippo cascade. A human homologue of Kibra, WWC1, has been identified and indirect evidence suggests that it can regulate the human Hippo pathway (Xiao et al. 2011). A molecular mechanism for this interaction has not yet been worked out and the molecular steps that trigger the Hippo kinase cascade in humans are unknown.
Four additional processes related to human Hippo signaling, although incompletely characterized, have been described in sufficient detail to allow their annotation. All are of physiological interest as they are likely to be parts of mechanisms by which Hippo signaling is modulated or functionally linked to other signaling processes. First, the caspase 3 protease cleaves STK3 (MST2) and STK4 (MST1), releasing inhibitory carboxyterminal domains in each case, leading to increased kinase activity and YAP1 / TAZ phosphorylation (Lee et al. 2001). Second, cytosolic AMOT (angiomotin) proteins can bind YAP1 and WWTR1 (TAZ) in their unphosphorylated states, a process that may provide a Hippo-independent mechanism to down-regulate the activities of these proteins (Chan et al. 2011). Third, WWTR1 (TAZ) and YAP1 bind ZO-1 and 2 proteins (Remue et al. 2010; Oka et al. 2010). Fourth, phosphorylated WWTR1 (TAZ) binds and sequesters DVL2, providing a molecular link between Hippo and Wnt signaling (Varelas et al. 2010)
NADE protein (p75NTR-associated cell death executor) may induce cell death upon NGF binding, but not BDNF, NT3, or NT4/5 binding, to p75NTR. The NADE-dependent apoptosis is modulated by the 14-3-3-epsilon protein (Kimura MT et al, 2001)
DNA fragmentation in response to apoptotic signals is achieved, in part, through the activity of apoptotic nucleases, termed DNA fragmentation factor (DFF) or caspase-activated DNase (CAD) (reviewed in Widlak and Garrard, 2005). In non-apoptotic cells, DFF is a nuclear heterodimer consisting of a 45 kD chaperone and inhibitor subunit (DFF45)/inhibitor of CAD (ICAD-L)] and a 40 kD nuclease subunit (DFF40/CAD)( Liu et al. 1997, 1998; Enari et al. 1998). During apoptosis, activated caspase-3 or -7 cleave DFF45/ICAD releasing active DFF40/CAD nuclease. The activity of DFF is tightly controlled at multiple stages. During translation, DFF45/ICAD, Hsp70, and Hsp40 proteins play a role in insuring the appropriate folding of DFF40 during translation(Sakahira and Nagata, 2002). The nuclease activity of DFF40 is enhanced by the chromosomal proteins histone H1, Topoisomerase II and HMGB1/2(Widlak et al., 2000). In addition, the inhibitors (DFF45/35; ICAD-S/L) are produced in stoichiometric excess (Widlak et al., 2003)
In response to stress signals, the p21-activated protein kinase PAK-2 stimulates a cell death response characterized by increased cell rounding and apoptotic chromatin condensation (see Jakobi et al., 2003). PAK-2 is proteolytically cleaved by caspase-3 producing a constitutively active fragment, PAK-2p34. Following cleavage, PAK-2p34 is autophosphorylated at Thr 402 and transported to the nucleus where it accumulates due to the loss of its nuclear export signal motif (Jakobi et al., 2003). The activity of PAK-2p34 appears to be regulated both by proteosomal degradation (Jakobi et al., 2003) and by association with the GTPase-activating protein PS-GAP/\nRHG-10. This interaction inhibits the kinase activity of PAK-2p34 and changes the localization of PAK-2p34 from the nucleus to the perinuclear region (Koeppel et al., 2004). PAK-2p34 may function in the down-regulation of translation initiation in apoptosis through phosphorylation of Mnk1 (Orton et al.,2004)
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
Apoptotic cells show dramatic rearrangements of tight junctions, adherens junctions, and desmosomes (Abreu et al., 2000). Desmosome-specific members of the cadherin superfamily of cell adhesion molecules including desmoglein-3, plakophilin-1 and desmoplakin are cleaved by caspases after onset of apoptosis (Weiske et al., 2001). Cleavage results in the disruption of the desmosome structure and thus contributes to cell rounding and disintegration of the intermediate filament system (Weiske et al., 2001)
In the presence of Netrin1, DCC and UNC5 generate attractive and repulsive signals to growing axons. In the absence of Netrin-1, DCC induces cell death signaling initiated via caspase cleavage of DCC and the interaction of caspase-9. Recent reports have shown that UNC5 receptors similarly induce apoptosis in the absence of Netrin-1. These reactions proceed without a requirement for cytochrome c release from mitochondria or interaction with apoptotic protease activating factor 1 (APAF1). DCC thus regulates an apoptosome-independent pathway for caspase activation. DCC and UNC-5 are hence defined as dependence receptors. Dependence receptors exhibit dual functions depending on the availability of ligand. They create cellular states of dependence on their respective ligands by either inducing apoptosis when unoccupied by the ligand, or inhibiting apoptosis in the presence of the ligand
Interleukins are low molecular weight proteins that bind to cell surface receptors and act in an autocrine and/or paracrine fashion. They were first identified as factors produced by leukocytes but are now known to be produced by many other cells throughout the body. They have pleiotropic effects on cells which bind them, impacting processes such as tissue growth and repair, hematopoietic homeostasis, and multiple levels of the host defense against pathogens where they are an essential part of the immune system