943 Risultati per: "AbFrontier"

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Peroxiredoxin (Prx) is a growing peroxidase family, whose mammalian members have been known to connect with cell proliferation, differentiation, and apoptosis. Many isoforms (about 50 proteins), collected in accordance to the amino acid sequence homology, particularly amino-terminal region containing active site cysteine residue, and the thiol-specific antioxidant activity, distribute throughout all the kingdoms. Among them, mammalian Prx consists of 6 different members grouped into typical 2-Cys, atypical 2-Cys Prx, and 1-Cys Prx. Except Prx VI belonging to 1-Cys Prx subgroup, the other five 2-Cys Prx isotypes have the thioredoxin-dependent peroxidase (TPx) activity utilizing thioredoxin, thioredoxin reductase, and NADPH as a reducing system. Mammalian Prxs are 20 - 30 kilodalton in molecular size and vary in subcellular localization: Prx I, II, and VI in cytosol, Prx III in mitochondria, Prx IV in ER and secretion, Prx V showing complicated distribution including peroxisome, mitochondria and cytosol.

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Coilin is a component of the nuclear Cajar(coiled) bodies (CBs) which are involved in the function or assembly/disassembly of nucleoplasmic snRNPs.
Human coilin is a 576-amino acid protein found enriched in CBs, but is also found in large amounts in the nucleoplasm.
Coilin is a constitutive phosphoprotein that is hyperphosphorylated during mitosis and it is thought that hyperphosphorylation triggers CB disassembly during cell replication. Self-interaction and localization have been shown to depend on the phosphorylation state of coilin

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The p90 ribosomal S6 kinases (RSKs) comprise a family of serine/threonine kinases that lie at the terminus of the ERK pathway. In humans, the RSK family consists of four isoforms (RSK1 to -4). RSK family members are unusual among serine/threonine kinases in that they contain two distinct kinase domains, both of which are catalytically functional. Theses kinase dimains are activated in a sequential manner by a series of phosphorylations. RSK regulates gene expression via association and phosphorylation of transcriptional regulators including c-Fos, estrogen receptor, NFkappaB/IkappaB α, cAMP-response element-binding protein (CREB).
ERK activates the C-terminal kinase of RSK, leading to activation of the N-terminal kinase. Members of the RSK family are present in the cytoplasm as well as the nucleus. Addition of growth factor to the cells results in the activation of both cytosolic and nuclear RSK and the translocation of the cytosolic RSK into the nucleus upon activation. The activation and nuclear translocation of RSK result in phosphorylation and activation of transcription factors.

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β-Catenin was a cytosolic protein originally identified through its association with the cadherin class of cell-adhesion proteins. β-Catenin has two key cellular functions; one plays direct role in cell adhesion/migration, bridging between cadherins and tactin cytoskeleton. The other plays as a transcription cofactor with T cell factor/lymphoid enhancer factor (TCF/LEF) in the Wnt pathway. Wnt are powerful regulators of cell proliferation and differentiation, and their signaling pathway involves proteins that directly participate in both gene transcription and cell adhesion. Activation of Wnt signaling leads to inhibition of Glycogen synthase-3β (GSK-3β) activity, resulting in accumulation of cytoplasmic (signaling) β-Catenin, which becomes available to bind the TCF/LEF family of transcription factors and to induce target gene expression. In the absence of Wnt signaling, A complex of axin and casein kinase-I(CK-I) induces β-Catenin phospho- rylation at a single site: serine 45(Ser45). This likely serves as a priming site for subsequent phosphorylation by GSK3b. And then β-Catenin is phosphorylated by GSK-3β at Ser33/37 and Thr41. These serine/threonine phosphylation is required for the phosph rylation-dependant degradation of β catenin via ubiquitin-proteosome pathway. Mutation of these phosphorylation sites in β-Catenin has been found in many tumor cell lines.

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Cyclin-dependent kinases (cdk) belong to a group of protein kinases originally discovered as being involved in the regulation of the cell cycle. Cdks are also involved in the regulation of transcription and mRNA processing. A Cdk is activated by association with a cyclin, forming a cyclin-dependent kinase complex.
Cdk1, also known as cell division control protein 2 (cdc2), is one of the components of the maturation promoting factor (MPF) which is essential for G1/S and G2/M phase transitions of eukaryotic cell cycle. Cdk1, when bound to cyclin B, allows a dividing cell to enter into mitosis from G2 and permits the transition from G1 through S in conjunction with cyclin A and cyclin E. The Cdk1 protein is constantly present throughout the cell division cycle, but its activity is finely tuned by means of protein-protein interactions and reversible phosphorylation.
Cdk1 can also enhance cell migration. Increased levels of Cdk1 promote cell migration together with cyclin B2 and the actin-stabilizing protein caldesmon. Phosphorylation of caldesmon bound to actin results in the displacement of caldesmon from actin followed by the altered interaction of actin with myosin. These events contribute to increased cell migration.

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14-3-3, a family of acidic and soluble proteins, highly conserved in amino acid sequences from yeast to mammals, is expressed in all eukaryotic cells. Seven isoforms(beta, gamma, epsilon, eta, zeta, sigma and tau/phi) encoded by seven distinct genes are identified in mammals and forms homo- and hetero- dimeric cup-shaped structures. As 14-3-3 is interacted with more than 100 binding partners, it regulates key proteins involved in various biological processes such as signal trans-duction, cell cycle, transcriptional control, cell proliferation, apoptosis, and ion channel physiology. Most  14-3-3 requires phosphorylation of serine or threonine residues in the target sequence. This protein is abundantly expressed in the brain and has been detected in the cerebrospinal fluid of patients with different neurological disorders.

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Lactoferrin(Lf), one of transferrin family, is found in external fluids, including milk and mucosal secretions, and prominent components of the secondary granules of neutrophils. Lf consists of a single polypeptide chain (approximately 80 kDa) folded into two structurally homologous lobes, each of which can reversibly bind one ferric ion (Fe3+). Lf plays a central role in iron metabolism and host defense system against microbial infection.

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α1-antitrypsin, 52kDa, is the prototypic member of the serine protease inhibitor (serpin) superfamily, which have a major role in inactivating neutrophil elastase and other proteases to maintain protease-antiprotease balance. The protein is synthesized mainly in the liver, but exerts its main function in the lung where it inhibits a variety of serine proteases, but primarily neutrophil elastase. It provides more than 90% of the antiproteolytic shield of the lower respiratory tract protecting the elastic tissue from degradation. Disorders of the enzyme include α 1-antitrypsin deficiency, a hereditary disorder in which lack of α 1-antitrypsin leads to uninhibited tissue breakdown during inflammation. This causes pulmonary emphysema and leads to liver cirrhosis in severe cases.

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Thioredoxins (Trx) are small, multi-functional proteins with oxidoreductase activity and are ubiquitous in essentially all living cells. Trx contains a
redox-active disulfide/dithiol group within the conserved Cys-Gly-Pro-Cys active site. The two cystein residues in the conserved active centers can be oxidized to form intramolecular disulfide bonds (1). Reduction of the active site disulfide in oxidized Trx is catalyzed by Trx reductase with NADPH as the electron donor. The reduced Trx is a hydrogen donor for ribonucleotide reductase, the essential enzyme for DNA synthesis, and a potent general protein disulfide reductase with numerous functions in growth and redox regulations (2). Specific protein disulfide targets for reduction by Trx include protein disulfide –isomerase (PDI) (3) and a number of transcription factors such as p53 (4), NFkB (5) and AP-1 (T1-151). Trx is also capable of removing H2O2, particularly when it is coupled with either methionine sulfoxide reductase or several isoforms of peroxiredoxins (6-7).

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There are ten mitogen-activated protein kinase (MAPK) phosphatases
(MKPs) that act as negative regulators of MAPK activity in mammalian
cells.
MKP4(DUSP9) is a dual specificity phosphatase, which acts as a negative
regulator of insulin-stimulated pathways. MKP4 is expressed in kidney,
placenta and adipose tissue. MKP4, a cytosolic MKP with specificity to not
only Erk, but also, to a lesser extent, JNK and p38. MKP4 also reversed
the effect of TNF-a to inhibit insulin Signaling. MKP4 has a protective
effect against the development of insulin resistance through its ability to
dephosphorylate and inactivate crucial mediators of stress-induced insulin
resistance.

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α-fetoprotein (AFP) is a glycoprotein of 590 amino acids containing 3.4% carbohydrate content with a molecular weight of 61,000 – 75,000 Da. AFP is normally produced in the developing embryo and fetus by the fetal yolk sac, the fetal gastrointestinal tract, and eventually by the fetal liver. In humans, AFP levels decrease gradually after birth, reaching adult levels by 8 to 12 months. Normal adult AFP levels are low and AFP has no known function in normal adults.
The biologic role of AFP has not been defined yet. Because of its biochemical similarity to albumin, it has been postulated that AFP could be a carrier protein. It may have an immunoregulatory function during pregnancy.
Increased serum levels are found in some tumors, such as hepatocellular carcinoma (HCC), hepatoblastoma, and germ cell tumors. Although total AFP is a useful serological marker for diagnosis of HCC, the false-negative or positive rate with AFP level is very high. AFP-L3, an isoform of AFP which binds Lens culinaris agglutinin, can be particularly useful in early identification of aggressive tumors associated with HCC. AFP mRNA, the circulating genetic markers, also has been used in monitoring distal metastasis or postoperative recurrence of HCC.

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PTEN acts as a phosphatase to dephosphorylate phosphatidylinositol (3,4,5)-trisphosphate (PtdIns (3,4,5)P3). The product of this enzymatic reaction is PtdIns(4,5)P2. This dephosphorylation is important because it results in inhibition of the AKT signaling pathway.
PTEN is a 403 amino acid protein, and a member of the large PTP (protein tyrosine phosphatase) family. PTEN crystal structure revealed that the N-terminal phosphatase domain is followed by a tightly associated C-terminal C2 domain. These two domains together form a minimal catalytic unit. The phosphatase domain contains the active site which carries out the enzymatic function of the protein, whilst the C2 domain allows PTEN to bind to the phospholipid membrane.
PTEN is one of the most commonly lost tumour suppressors in human cancer, and its deregulation is also implicated in several other diseases. Hereditary mutation of PTEN causes tumor-susceptibility diseases such as Cowden disease.

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Anti-DISC1 (FRAG2) Rabbit Polyclonal Antibody

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Transferrin (Tf) is a blood plasma protein for iron delivery. Transferrin functions to deliver iron to cells via a receptor-mediated endocytotic process as well as to remove toxic free iron from the blood and to provide an antibacterial, low-iron environment.
Tf protein contains 679 amino acid residues and has a molecular weight of ~79 kD, having 2 specific high affinity Fe(III) binding sites. The molecule is stabilized by 19 intra-chain disulfide bonds and is protected by three carbohydrate side chains. Although iron bound to transferrin is less than 0.1% (4 mg) of the total body iron, it is the most important iron pool, with the highest rate of turnover (25 mg/24 h).
When a Tf protein loaded with iron encounters a transferrin receptor (TfR) on the surface of a cell it binds to it and is consequently transported into the cell by endosomes. ATP-dependent proton pumps then force H+ ions into the endosomes reducing the pH to 5.5, thus promoting iron release and conformational change of the receptor enabling apo-transferrin to remain bound. The binding characteristics of the apo-Tf–TfR complex are such that the apo-Tf is released only once the complex reaches the cell surface.
Cells expressing large amounts of TfR are correspondingly competent in securing iron from Tf. Rapidly proliferating cells, as in malignancy, generally express TfR1 abundantly.
Several studies have shown a link between Tf polymorphism and susceptibility to disease. These include the rare autosomal recessive disorder atransferrinemia, cardiovascular disease (CVD) and Alzheimer’s disease.

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Calcium binding proteins (CBPs) regulate intracellular levels of calcium Ca2+) ions. CBPs are involved in numerous functions, such as cell signaling, calcium uptake and transport, and cell motility. Calretinin (CR), calbindin D-28k (CB) and parvalbumin (PV) belong to the large family of Efhand calcium-binding proteins. The EF-hand is an amino acid sequence with a haracteristic threedimensional helix-loop-helix structure with high affinity for Ca2+. Calbindin D28k (calbindin) is a hexa EF-hand protein of 261 residues with 59% sequence identity to calretinin. It is a single-domain protein and the six EF hands interact extensively with one another so that they form one large globular domain. Calbindin is found in the brain and central nervous system with a distinct distribution over certain neuronal subtypes. Neuroprotective effects of calbindin has been reported in ischemic and glutamate toxicity models, primarily due to its ability to chelate calcium. Mice lacking calbindin have been shown to suffer from impaired motor coordination due to altered neuronal Ca2+-homeostasis. Notably, calbindin is found in high concentration in the kidney and in pancreatic b-cells, where it has been shown to protect against apoptosis. In osteoblasts, anti-apoptic activity of calbindin through the binding to caspase-3 has also been reported. Calbindin protects against apoptotic and necrotic cell death, suggesting its ability to buffer calcium.
Calbindin has been reported to binds Zn2+, revealing negative allosteric effect between the Zn2+- and Ca2+-binding events.

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Peroxiredoxin (Prx) is a growing peroxidase family, whose mammalian members have been known to connect with cell proliferation, differentiation, and apoptosis. Many isoforms (about 50 proteins), collected in accordance to the amino acid sequence homology, particularly amino-terminal region containing active site cysteine residue, and the thiol-specific antioxidant activity, distribute throughout all the kingdoms. Among them, mammalian Prx consists of 6 different members grouped into typical 2-Cys, atypical 2-Cys Prx, and 1-Cys Prx. Except Prx 6 belonging to 1-Cys Prx subgroup, the other five 2-Cys Prx isotypes have the thioredoxin-dependent peroxidase (TPx) activity utilizing thioredoxin, thioredoxin reductase, and NADPH as a reducing system. Mammalian Prxs are 20 - 30 kilodalton in molecular size and vary in subcellular localization: Prx 1, 2, and 6 in cytosol, Prx 3 in mitochondria, Prx 4 in ER and secretion, Prx 5 showing complicated distribution including peroxisome, mitochondria and cytosol (1).

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p21, also known as cyclin-dependent kinase inhibitor 1A or CDKN1A, directly inhibits the activity of cyclin-cdk2 and cyclin-cdk4 complexes. It mainly inhibits the activity of cyclin/cdk2 complexes and negatively modulates cell cycle progression. p21 also plays other fundamental roles including transcriptional regulation and the modulation of apoptosis.
p21 forms part of a family of structurally related proteins comprising p21, p27 and p57 that all share the ability to inhibit a wide range of cyclin -dependent kinase holoenzymes.
Besides its cdk inhibitor function, p21 is recognized to play a wide variety of physiological roles, many of which rely on its nuclear localization. p21 can bind to proliferating cell nuclear antigen (PCNA) thereby blocking DNA synthesis. p21 functions as a regulator of cell cycle progression at S phase. The expression of p21 is controlled by the tumor suppressor protein p53. Each of these functions of p21 is achieved through direct p21/protein interactions and the subcellular localization of p21 plays an important part in dictating the binding partners to which p21 is exposed.

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Cathepsin D(CatD) is a ubiquitously expressed lysosomal aspartyl
protease involved in the normal degradation of proteins apoptosis and
autophagy. Human CatD is synthesized on the endoplasmic reticulum as
a pre-pro-enzyme. Preprocathepsin D(412aa) is cleaved and glycosylated
to form an inactive procathepsin D (392aa) and then further cleaved to
generate an active intermediate (348aa) single-chain molecule. The active
intermediate is further processed into mature two chain form of cathepsin
D, this processing step is carried out by cathepsin B or L. The two-chain
form consists of an amino terminal light chain (14 kDa) and a
carboxyl-terminal heavy chain (34 kDa). Additionally, several more amino
acids are removed from the carboxyl terminus of the 34 kDa heavy chain.
Procathepsin D (pCD), secreted from cancer cells, acts as a mitogen on
both cancer and stromal cells and stimulates their proinvasive and
pro-metastatic properties.

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Integrin-linked kinase (ILK) is an adaptor and signaling protein that couples integrins to the actin cytoskeleton and coordinates signal transduction from extracellular matrix and growth factors.
By interacting with the focal adhesion proteins PINCH, paxillin, and parvin, ILK regulates integrin- mediated cell adhesion and cytoskeletal dynamics within focal adhesions to regulate cell adhesion, spreading, and migration.
ILK is involved in the suppression of apoptosis and promotion of cell survival through the phosphorylation of AKT(Ser473), GSK-3(Ser9), myosin light chain(Ser18/19), and affixin.
ILK activity is stimulated by PI3 kinase and negatively regulated by the tumor suppressor PTEN.

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GPI-PLD (glycosylphosphati- dylinositol-specific phospholipase D), a 815-amino acid protein, is expressed in numerous tissues and cells and specifically cleaves GPI-anchored proteins. Liver has the highest level of GPI-PLD expression and is the primary organ contributing to GPI-PLD in the serum. GPI-PLD is abundant in serum in which it associates with apolipoproteins AI and AIV. Increased serum GPI-PLD is associated with insulin resistance and elevated serum triglycerides. Many surface proteins are attached to eukaryotic cell membranes via glycosylphosphatidylinositol (GPI) anchors that are covalently bound to the C-terminus of the protein and cleavage of the GPI moiety by GPI-PLD, only enzyme known that cleavage GPI anchor, may represent a means of regulating attachment of these proteins to the cell surface, or alternatively, their release into the extracellular environment.

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Cytochrome c is a small heme protein consisting electron-transport chain in mitochondria and transfers electrons between complex III and IV. It is highly conserved through diverse species from unicellular microorganisms to animals and plants.
Cytochrome c is also an intermediate in apoptosis. Currently, it is widely accepted that mitochondria play a key role in the regulation of apoptosis. In mammalian cells, a major caspase activation pathway is the cytochrome c-initiated pathway. In this pathway, a variety of apoptotic stimuli cause cytochrome c release from mitochondria. In the cytosol, cytochrome c interacts with its adaptor molecule, Apaf-1, resulting in the recruitment, processing and activation of pro-caspase-9 in the presence of dATP or ATP. Caspase-9, in turn, cleaves and activates pro-caspase-3 and -7; these effector caspases are responsible for the cleavage of various proteins leading to biochemical and morphological features characteristic of apoptosis.

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The mammalian Phospholipase C(PLC) family has two closely related proteins, PLC1 and PLC2. The PLC isozymes have the core structure domains and a unique array of domains containing an additional PH domain, two SH2 domains and one SH3 domain. In response to extracellular stimuli, such as hormones and growth factors, receptor tyrosine kinases (RTKs) phosphorylate and activate PLC. Activated PLC catalyzes hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) to produce the metabolic second messenger molecules inositol 1,4,5-triphosphate (IP3) and diacylglycerol (DAG).

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Catalase is a homotetrameric heme-containing enzyme present within the matrix of all peroxisomes. It carries out a dismutation reaction in which hydrogen peroxide is converted to water and oxygen. Human catalase has the last four amino acids (-KANL) at the extreme C-terminus for peroxisome targeting. The monomer of human catalase is 61.3 kDa in molecular size. Catalase has been implicated as an important factor in inflammation, mutagenesis, preven-tion of apoptosis, and stimulation of a wide spectrum of tumors. Loss of catalase leads to the human genetic disease, acatalasemia, or Takahara’s disease (1).

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Ubiquitin+1 (Ub+1) is a novel mutant form of ubiquitin that can be produced through a process known as molecular frameshift. Ub+1 can be polyubiquitinated to produce aberrant polyubiquitin chains that inhibit the 26S proteasome. Especially ub+1 is accumulated in aggregates containing amyloid-β and phosphorylated-tau. Elevated expression of Ub+1 mRNA and protein has been observed in the brains of patients with Alzheimer's disease. Also ub +1 acts as an aggravating factor in polyglutamine-induced neuro-degeneration.

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Thioredoxins (Trx) are small, multi-functional proteins with oxidoreductase activity and are ubiquitous in essentially all living cells. Trx contains a redox-active disulfide/ dithiol group within the conserved Cys-Gly-Pro-Cys active site. The two cysteine residues in the conserved active centers can be oxidized to form intramolecular disulfide bonds (1). Reduction of the active site disulfide in oxidized Trx is catalyzed by Trx reductase with NADPH as the electron donor. The reduced Trx is a hydrogen donor for ribonucleotide reductase, the essential enzyme for DNA synthesis, and a potent general protein disulfide reductase with numerous functions in growth and redox regulations (2). Specific protein disulfide targets for reduction by Trx include protein disulfide–isomerase (PDI) (3) and a number of transcription factors such as p53 (4), NF-kB (5) and AP-1 (T1-151). Trx is also capable of removing H2O2, particularly when it is coupled with either methionine sulfoxide reductase or several isoforms of peroxiredoxins (6-7).

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Platelet-derived growth factors (PDGFs) have been implicated in the control of cell proliferation, survival and migration. The PDGF family of growth factors consists of five different disulphide-linked dimers built up of four different polypeptide chains encoded by four different genes. Theses isoforms, PDGFAA, PDGF-AB, PDGF-BB, PDGF-CC and PDGF-DD, act via two receptor tyrosine kinases, PDGF receptors α and β. Thus far, gene-targeting experiments have been attempted to create knockout mice deficient for PDGFR-α or PDGFR-β. Those mice, however, died either at the embryonic stage or several days after birth. Platelet-derived growth factor receptors, PDGFR-α and PDGFR-β, have five extracellular immunoglobulin-like domains and an intracellular tyrosine kinase domain. Upon binding a PDGF, the receptors form homo- and heterodimers. Dimerization of the receptors juxtaposes the intracellular part of the receptors, which allow phosphorylation in trans between the two receptors in the complex. These autophosphorylation provide docking sites for downstream signal transduction molecules. More than 10 different SH2– domaincontaining molecules have been shown to bind to different autophosphorylation sites in the PDGF α- and β-receptors. There are signal transduction molecules with enzymatic activity, such as PI3-kinase, PLC-γ, Src, SHP-2, GAP, as well as adaptor molecules such as Grb2, Shc, Nck, Grb7 and Crk, and Stats. Each of the different partners recruited by the activated receptor initiates different signaling pathways, making possible a great variety of cellular response.

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Peroxiredoxin VI (Prx VI, 1-Cys Prx) is a member of Peroxiredoxin Family, an antioxidant enzyme that detoxifies reactive oxygen species and has a cysteine at their active site. Six isoforms (Prx I to VI) of Prx exist in all eukaryotic cells. These isoforms are classified into three subgroups (2-Cys, atypical 2-Cys, and 1-Cys). Prx VI modulates various receptor-signaling pathways and protects cells from cell death induced by oxidative stress. The active site cysteine(Cys47) is oxidized to cysteine sulfenic acid(Cys47-SOH) by H2O2. However, the resulting Cys47-SOH does not form a disulfide bond because of unavailability of another Cys-SH nearby. It can be reduced by nonphysiological thiols such as DDT but is not transformed by Thioredoxin/Thioredoxin Reductase or GSH. Occasionally, the sulfenic intermediate is hyperoxidized to sulfinic or sulfonic acid, resulting in inactivation of peroxidase activity.

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Signal transducer and activator of transcription (STAT), named after their dual role, are latent cytoplasmic transcription factors that mediate various biological responses. The activation of STAT proteins is largely mediated by phosphorylation of C-terminal transactivation domain through Janus kinases (JAKs) and mitogen-activated protein kinases (MAPKs), which allows the activated STATs to dimerize and to translocate into the nucleus. By modulating target gene expression, STAT proteins play an important role in mediating a broad range of biological processes such as cell proliferation, survival, apoptosis, and differentiation. Seven mammalian members of the STAT family are known (STAT1, 2, 3, 4, 5a, 5b, and 6) and they all share common features and structure. STAT3 is activated by growth factors and oncogenic kinases where it mediates transcriptional activation of genes encoding apoptosis inhibitors, cell-cycle regulators and inducers of angiogenesis.

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Peroxiredoxin (Prx) is a growing peroxidase family, whose mammalian members have been known to connect with cell proliferation, differentiation, and apoptosis. Many isoforms (about 50 proteins), collected in accordance to the amino acid sequence homology, particularly amino-terminal region containing active site cysteine residue, and the thiol-specific antioxidant activity, distribute throughout all the kingdoms. Among them, mammalian Prx consists of 6 different members grouped into typical 2-Cys, atypical 2-Cys Prx, and 1-Cys Prx. Except Prx VI belonging to 1-Cys Prx subgroup, the other five 2-Cys Prx isotypes have the thioredoxin-dependent peroxidase (TPx) activity utilizing thioredoxin, thioredoxin reductase, and NADPH as a reducing system. Mammalian Prxs are 20 – 30 kilodalton in molecular size and vary in subcellular localization: Prx I, II, and VI in cytosol, Prx III in mitochondria, Prx IV in ER and secretion, Prx V showing complicated distribution including peroxisome, mitochondria and cytosol (1).

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Check point kinase 1 (Chk1) is a serine / threonine protein kinase and a key mediator in the DNA damage-induced checkpoint network. Chk1 is an evolutionarily conserved protein kinase that functions to ensure genomic integrity upon genotoxic stress. When the G2 or S checkpoint is abrogated by the inhibition of Chk1, p53-deficient cancer cells undergo mitotic catastrophe and eventually apoptosis, whereas normal cells are still arrested in the G1 phase. Thus, Chk1 inhibitors can preferentially potentiate the efficacy of DNA damaging agents in cancer cells, and Chk1 is an attractive therapeutic target for cancer treatment, especially since approximately 50% of all human cancers are p53-deficient.