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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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Glutamine Synthetase(GS) catalyzes the conversion of ammonia and glutamate to glutamine. This reaction consumes a molecule of ATP:
Glutamate + NH4+ + ATP
 Glutamine + ADP + Pi
GS is found in astrocytes as an octamer of identical 45kDa subunits. Most well known function of GS is the detoxification of brain ammonia. It also has an important role in controlling metabolic regulations of neurotransmitter glutamate. Because of the multiple functions and importance of GS in cellular metabolism, both catalytic activities and synthesis are highly regulated. The activity of GS is controlled by adenylylation. Its activity is decreased in the cerebral cortex of brains affected by Alzheimer’s disease, particularly in the vicinity of senile plaques. It is also decreased under conditions of glucose deprivation. On the other hands, the level of expression of GS is increased during ischemia in vivo or hypoxia in culture.

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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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Glutathione reductase (GR) is a member of pyridine nucleotide-disulfide oxidoreductases, which includes the closely related enzymes thioredoxin reductase, lipoamide dehydrogenase, trypanothione reductase and mercuric ion reductase. GR is a cytoplasmic flavoenzyme widely distributed in aerobic organisms. The dimeric protein is composed of two identical subunits, each containing 1 FAD and 1 redox-active disulfide/dithiol as components of the catalytic apparatus. It plays a role in maintaining glutathione (GSH) in its reduced form by catalyzing the reduction of glutathione disulfide (GSSG) (1):
GSSG + NADPH + H+  2GSH + NADP+
In most eukaryotic cells, GR maintains the ratio of [GSH]/[GSSG] elevated, and participates in several vital functions such as the detoxification of reactive oxygen species as well as protein and DNA biosynthesis (2).

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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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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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Btk (Bruton's tyrosine kinase) is a member of the Tec family of protein tyrosine kinases (PTKs) and plays a modulatory role in many cellular processes, such as proliferation, development, differentiation, survival, and apoptosis. The Tec kinases are the second largest family of non-receptor tyrosine kinases and include Tec, Btk, Bmx, Itk, and TXK/Rlk. Mutations of Btk gene cause a primary immunodeficiency disease in humans, X-linked aγglobulinemia (XLA) which is characterized by a lack of circulating B lymphocytes and an absence of immunoglobulins as a result of defects in B cell maturation and function. Btk is found in all hematopoietic cells, with the exception of T lymphocytes and plasma cells. Btk contains amino-terminal PH (pleckstrin homology) domain which binds phosphatidylinositol (3,4,5)-trisphosphate (PIP3) helping membrane translocation upon PI3 kinase activation. The Tec kinases have similar structure of N-terminal PH domains followed by Tec homology (TH), Src homology 3 (SH3), Src homology 2 (SH2), and kinase domains. Autophosphorylation of Tyr223 in SH3 domain is necessary for full activation of Btk. Various binding proteins have been reported to interact with different domains of Btk.

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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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PRAK is a 471 amino acid protein with 20-30% sequence identity to the known MAP kinase-regulated protein kinases RSK1/2/3, MNK1/2 and MAPKAPK2/3.
The p38 mitogen-activated protein kinase (MAPK) pathway plays an important role in cellular responses to inflammatory stimuli and environmental stress. There are at least six protein kinases that can be regulated by p38α and/or p38β. These downstream kinases of p38s include MAPK-activated protein kinase 2 (MAPKAPK2 or MK2), MAPKAPK3, MAPK-interacting kinase 1 (MNK1), MNK2, p38-activated/regulated protein kinase (PRAK or MAPKAPK5), and mitogen- and stress-activated protein kinase (MSK). PRAK can be activated in response to cellular stress and proinflammatory cytokines. T182 within the activation loop of PRAK has been determined to be the regulatory phosphorylation site. PRAK has been reoprted to be essential for ras-induced senescence and tumor suppression. PRAK mediates senescence upon activation by p38 in response to oncogenic ras.

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The members of the Src-family kinases are Src, Lyn, Fyn, Yes, Hck, Lck, Fgr, Blk, and Yrk. Each of these have a common structure consisting of an unique domain at the N-terminal, followed by SH3, SH2 and tyrosine kinase domains.
In immume cells, the Src-family kinases play roles as critical regulators of a large number of intracellular signaling pathways, including integrin signaling pathway. Integrins are major cellular receptor that mediate cell to cell and cell to substratum interactions.
Src is expressed ubiquitously, however the expression level is higher in brain, osteoclasts, and platelets. Src plays a role in cell adhesion, cell morphology and motility, and bone resorption.
Src contains a 14-carbon myristoyl group attached to an SH4 domain, a unique domain, an SH3 domain, an SH2 domain, an SH2-kinase linker, a protein–tyrosine kinase domain (the SH1 domain), and a C-terminal regulatory segment.
One of the two most important regulatory phosphorylation sites in Src is Tyr527. Under basal conditions in vivo, 90–95% of Src is phosphorylated at Tyr527, and phosphotyrosine 527 binds intramolecularly with the Src SH2 domain. Tyrosine 416 is present in the activation loop and its phosphorylation promotes kinase activity.

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ζ-chain associated protein kinase, ZAP70, is a 70 kDa member of the Syk family kinase predominantly involved in T cell receptor (TCR) signaling. It is structurally homologous to Syk, a PTK that is involved in proximal BCR signaling. ZAP-70 is a key signaling molecule in T cell activation and also plays a role in apoptosis and cell migration.
SYK family tyrosine kinases contain a C-terminal kinase domain and tandem N-terminal SH2 domains that bind phosphorylated ITAMs (immunoreceptor tyrosine-based activation motif). Linker region that contains multiple tyrosines separates the SH2 domains from the kinase domain. Phosphorylated tyrosines act as docking sites for phospholipase Cγ1 (PLCγ1).
ZAP-70 and Syk are functionally homologous in antigen receptor signaling. Expression of ZAP-70 in Syk− B cells reconstitutes SCR function. Reconstitution requires the presence of functional Src homology 2 (SH2) and catalytic domains of ZAP-70.
Expression of ZAP-70 is an important negative prognostic factor in chronic lymphocytic leukemia (CLL) with more rapid disease progression and shorter survival.

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Creatine kinase (CK), also known as phosphocreatine kinase or creatine phosphokinase (CPK) is an enzyme expressed by various tissue types. It catalyzes the reversible transfer of the N-phosphoryl group from phosphocreatine (PCr) to ADP to regenerate ATP. Creatine kinase plays a key role in the energy homeostasis of cells with intermittently high, fluctuating energy requirements, such as skeletal and cardiac muscle cells, neurons, photoreceptors, spermatozoa and electrocytes.
Creatine kinase consists of two subunits, which can be either B (brain type) or M (muscle type). Therefore, three different cytosolic isoenzymes exist: CK-MM, CK-BB and CK-MB. Cytosolic CK isoenzymes are always co-expressed in a tissue-specific fashion together with a mitochondrial isoform. Skeletal muscle expresses CK-MM (98%) and low levels of CK-MB (1%). The heart muscle expresses CK-MM at 70% and CK-MB at 25-30%. CK-BB is expressed in all tissues at low levels.
Cytosolic CKs, in close conjunction with Ca2+-pumps, play a crucial role for the energetics of Ca2+-homeostasis. Octameric mitochondrial Mi-CK binds and crosslinks mitochondrial membranes. The CK system is
regulated by AMP-activated protein kinase via PCr/Cr and ATP/AMP ratios.
The cardiac-specific isoenzyme of creatine kinase, CK-MB, is a biomarker for myocardial infarction along with other markers such as cardiac Troponin I and myoglobin. The introduction of immunologic mass determination of CK-MB was a major breakthrough that replaced the traditional enzymatic assay.

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The complement system is a part of the larger immune system and three biochemical pathways are present: the classical complement pathway, the alternative pathway, and the mannose-binding lectin pathway.
Human complement factor C6 is one of five components (C5b, C6, C7, C8, and C9) that interact to form the cytolytic membrane attack complex (MAC) which is the cytolytic end product of the complement cascade. MAC is typically formed on the surface of intruding pathogenic bacterial as a result of the activation of the complement system, and it is one of the ultimate weapons of the immune system.
The sixth component of complement, C6, is a 913 amino acid single polypeptide chain serum glycoprotein. Homology study suggests that C6 could contain two domains, an amino-terminal region that is related to complement C8 and C9, and a carboxyl-terminal region that has partial homology to the complement regulatory proteins factor H and factor I.
Genetic deficiencies of terminal complement components lead to markedly increased susceptibility to only one particular Gram-negative genus, the Neisseria. The susceptibility is attributable to the major role played by complement-mediated killing in host defense against the pathogen.

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Fibronectin is a high molecular weight glycoprotein containing about 5% carbohydrate that binds to receptor proteins that span the cells membrane, called integrins. In addition to integrins, they also bind extracellular matrix components such as collagen, fibrin and heparin. Fibronectin can be found in the blood plasma in its soluble form which is composed of two 250 kDa subunits joined together by disulfide bonds. Plasma fibronectin is made in the liver by hepatocytes. The insoluble form that serves as a linker in the extracellular matrix is a large complex of cross-linked subunits. Fibronectin is involved in many cellular processes, including tissue repair, embryogenesis, blood clotting, and cell migration/ adhesion, so it can be used as a therapeutic agent for wound healing. It is also one of the few proteins for which production increases with age without any associated pathology.

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ERK1 and ERK2 are widely expressed and are involved in the regulation of meiosis, mitosis, and postmitotic functions in differentiated cells. Many different stimuli, including growth factors, cytokines, virus infection, ligands for heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors and transforming agents, activate the ERK1 and ERK2 pathways.
When growth factors bind to the receptor tyrosine kinase, Ras interacts with Raf, the serine/threonine protein kinase and activates it as well. Once actived, Raf phosphorylates serine residue in 2 further kinases, MEK1/2, which in turn phosphorylates tyrosine/threonine in extracellular-signal regulated kinase(ERK) 1/2. Upon activation, the ERKs either phosphorylate a number of cytoplasmic targets or migrate to the nucleus, where they phosphorylate and activate a number of transcription factors such as c-Fos and Elk-1.

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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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Prothrombin precursor is synthesized in liver as a precursor of prothrombin containing a signal sequence and a propeptide domain at the N-terminus. Before its secretion into plasma, this precursor undergoes several posttranslational modifications, including removal of signal sequence and propeptide domains, glycosylation, and γ-glutamyl-carboxylation reaction. Prothrombin, cleaved by the prothrombinase enzyme complex that consists of serine protease factor Xa, cofactor Va, phospholipids and calcium, is converted to thrombin which converts fibrinogen into fibrin which in turn strengthens a protective clot. Activation of prothrombin is crucial in physiological and pathological coagulation. Various rare diseases involving prothrombin(e.g. hypoprothrombinemia) have been described.

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Dual specificity phosphatase(DUSP) inactivate their target kinases by dephosphorylating both the phosphoserine/threonine and phosphotyrosine residues. DUSPs can be divided into six subgroups on the basis of sequence similarity(PRLs, Cdc14 phosphatases, PTENs, myotubularins, MKPs, atypical DUSPs). DUSP inhibitors might be used to manipulate MAPK and cellular responses in both positive and negative ways. The regulated expression and activity of DUSP family members in different cells and tissues controls MAPK intensity and duration to determine the type of physiological response.
DUSP12(YVH1, GKAP) contains the consensus DUSP catalytic domain as well as an extended C-terminal domain of unknown function, thought to be related to its potential role in glucokinase regulation. It is localized in the cytoplasm and nucleus.

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The complement system is a part of the larger immune system and three biochemical pathways are present: the classical complement pathway, the alternative pathway, and the mannose-binding lectin pathway.
The biological functions of complement are opsonization and phagocytosis, stimulation of inflammatory reactions and lysis of bacteria.
C1 complex (C1q, C1r and C1s) is the first component of the classical pathway of complement activation which occurs when C1q binds to IgM or IgG complexed with antigens, or when C1q binds directly to the surface of the pathogen. Binding of C1 to immunoglobulins in the form of immune complexes leads to activation of proteases C1r and C1s, and the cleavage of C2 and C4 producing C2a and C4b. C4b and C2a bind to form C3-convertase.
C1q is a hexamer composed of globular heads attached to collagen-like triple-helix tails. The globular heads of C1q specifically bind to the CH2 domain of IgG molecules or the CH3 domain of IgM.
In mammals, hepatocyte is the major source of most C proteins with the exception of C1q, factor D and C7. Interestingly, C1q mRNA is essentially
expressed in spleen, thymus and heart.
C1q knockout mice show a profound impairment in the clearance of apoptotic cells which then accumulate in the kidney leading to glomerulonephritis with immune deposits. Individuals with deficiency of C1q have the highest prevalence of systemic lupus erythematosus.

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Vimentin is a member of the intermediate filament family of proteins found in various non-epithelial cells, especially mesenchymal cells. Vimentin is responsible for maintaining cell shape, integrity of the cytoplasm, and stabilizing cytoskeletal interactions. Vimentin plays a significant role in supporting and anchoring the position of the organelles in the cytosol. Although most intermediate filaments are stable structures, vimentin also has a dynamic nature which is important when offering flexibility to the cell.
Two monomers which have central α-helical domains, capped on each end by non-helical domains twist around each other to form a coiled-coil dimer. Two dimers then form a tetramer, which, in turn, form a sheet by interacting with other tetramers.
There are some reports related to the biochemical function of intermediate filament network. The intracellular movement of LDL-derived cholesterol from the lysosome to the site of esterification is a vimentin-dependent process. A role for vimentin in mechanotransduction of shear stress has also been suggested. The mechanical stress of fluid shear on endothelial cells seems to trigger MAPK signaling pathways and stimulates proliferation.

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Bcl-2 (B-cell lymphoma 2) family govern mitochondrial outer membrane permeabilization (MOMP) and can be either pro-apoptotic (Bax, BAD, Bak and Bok) or anti-apoptotic (Bcl-2, Bcl-xL, and Bcl-w). The mitochondrial release of cytochrome c through anion channel is regulated by Bcl-2 and Bcl-xL. The Bcl-2 family of proteins are key regulators of many signals leading to caspase, which when activated cause cellular destruction by cleaving a range of vital cellular substrates.
The members of the Bcl-2 family share one or more of the four characteristic domains of homology entitled the Bcl-2 homology (BH) domains (named BH1, BH2, BH3 and BH4).
The Bcl-2 gene has been implicated in a number of cancers, including melanoma, breast, prostate, and lung carcinomas, as well as schizophrenia and autoimmunity. It is also thought to be involved in resistance to conventional cancer treatment.
Apoptosis is an important component of the sequence of events during which anticancer drugs induce an antitumor response. The molecular mechanism for drug-induced apoptosis is associated with a mitochondrial dysfunction that is characterized by an increase in MOMP and a release of cytochrome c from mitochondria, indicating that Bcl-2 plays a critical role in anticancer drug-induced apoptosis.

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Focal adhesion kinase subfamily consists of the non-receptor proline-rich protein tyrosine kinases (PTKs). Two members of the family are focal adhesion kinase (FAK) and proline-rich tyrosine kinase 2 (PYK2). These two kinases have molecular mass between 110-125 kDa and are closely related in their structure. The presence of two proline-rich motifs within the C-terminal domains is conserved.
FAK is a nonreceptor and nonmembrane associated PTK which does not contain Src homology 2 (SH2) or SH3 protein interaction domains. The centrally located kinase domain of FAK is flanked by large N- and C-terminal noncatalytic domains.
FAK links integrin receptors to intracellular signaling pathways that are important for cell growth, survival, and migration. Integrin receptor engagement with ligands such as fibronectin can stimulate FAK autophosphorylation which enables FAK to function within a network of integrin-stimulated signaling pathways leading to the activation of targets such as the ERK and JNK/mitogen-activated protein kinase pathways. Recent study reveals that FAK is essential for angiogenesis in the embryo, functions in heart development and modulates the response of cardiomyocytes to pressure overload in adult mice.

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The epidermal growth factor receptor (EGFR) is a transmembrane receptor tyrosine kinase of the ErbB (also known as HER) family in which four members have been identified: EGFR (ErbB1), HER2/Neu (ErbB2), HER3 (ErbB3), and HER4 (ErbB4). All four erbB receptors are composed of an extracellular ligand-binding region consisting of glycosylated domains, a transmembrane domain containing a single hydrophobic anchor sequence, an intracellular region containing the catalytic tyrosine kinase domain, and a carboxyl-terminal region containing several tyrosine residues that become phosphorylated after receptor activation.
The epidermal growth factor receptor (EGFR) signaling pathway is one of the most important pathways that regulate growth, survival, proliferation, and differentiation in mammalian cells. EGFR and other members of the erbB family form either homodimers or heterodimers upon ligand binding, resulting in conformational changes that allow activation of protein kinases and transphosphorylation of key tyrosine residues within the carboxyl-terminal domain. After the induction of tyrosine phosphorylation, some signaling pathways appear to start with the recognition of the C-terminal phosphotyrosines by appropriate adaptor or signaling molecules.
The aberrant activation of the EGFR leads to enhanced proliferation and other tumor-promoting activities. Several mechanisms lead to aberrant receptor activation, including receptor overexpression, gene amplification, activating mutations, overexpression of receptor ligands, and/or loss of their negative regulatory mechanisms.
The epidermal growth factor receptor (EGFR) has been extensively investigated as a target for anti-neoplastic therapy. Anti-EGFR antibodies that interfere with ligand-dependent receptor activation have shown clinical activity in a variety of solid tumors.

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Actin is an abundant cytoskeletal protein found in all mammalian cells. Six distinct actin isotypes have been identified in mammalian cells. Each is encoded by a separated gene and is expressed in a developmentally regulated and tissue-specific manner. α and β-cytoplasmic actins are expressed in a wide variety of cells. Whereas, expression of α-skeletal, α-cardiac, α-vascular and γ-enteric actins
are more restricted to specialized muscle cell type. Actin's filaments form part of the cytoskeleton and play essential roles in regulating cell shape and movement.

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SHP1 and SHP2 represent a subfamily of non-transmembrane protein-tyrosine phosphatases (PTPs) that contain two tandem SH2 (src homology 2) domains. SHPs have two N-terminal SH2 domains (N-SH2 and C-SH2), a classic PTP domain and a C-terminal tail harboring two tyrosyl phosphorylation sites which are phosphorylated differentially by receptor and non-receptor protein-tyrosine kinases (PTKs).
Whereas SHP2 is expressed ubiquitously, SHP1 is primarily expressed in hematopoietic cells and behaves as a key regulator controlling intracellular phosphotyrosine levels in lymphocytes.
SH2 domains (particularly the N-SH2) also regulate PTP activity. Basal SHP activity is low, but addition of a phosphotyrosyl peptide that binds the N-SH2 (Tyr–P peptide ligand) markedly stimulates catalysis.
SHP1 is implicated in signaling from receptor tyrosine kinases (RTKs), cytokine receptors, chemokine receptors and integrins. SHP1-deficient bone marrow macrophages are hyper-adherent to β1- and β2-integrin ligands.
Decreased SHP1 level causes abnormal T-lymphocyte proliferation and induces various types of leukemias. Introduction of the SHP1 gene back into a leukemia cell line and a prostate cancer cell line demonstrated the tumor suppressor function of SHP1.

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Glutathione peroxidases (Gpxs) are ubiquitously expressed proteins which catalyze the reduction of hydrogen peroxides and organic hydroperoxides by glutathione. There are several isoforms which differ in their primary structure and localization. The classical cytosolic /mitochondrial GPx1 (cGPx) is a selenium-dependent enzyme, first of the GPx family to be discovered. GPx2, also known as gastrointestinal GPx (GI-GPx), is an intracellular enzyme expressed only at the epithelium of the gastrointestinal tract (1). Extracellular plasma GPx (pGPx or GPx3) is mainly expressed by the kidney from where it is released into the blood circulation (2). Phospholipid hydroperoxide GPx4 (PH-GPx) expressed in most tissues, can reduce many hydroperoxides including hydroperoxides integrated in membranes, hydroperoxy lipids in low density lipoprotein or thymine (3). All mammalian GPx family members, except for the recently described Cys containing GPx3 and epididymis-specific secretory GPx (eGPx or GPx5) isoforms, possess selenocysteine at the active site (4-5).

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The mammalian thioredoxin reductases (TrxRs) are a family of selenocysteine-containing pyridine nucleotide-disulfide oxidoreductases. All the mammalian TrxRs are homologous to glutathione reductase with respect to primary structure including the conserved redox catalytic site (-Cys-Val-Asn-Val-Gly-Cys-) but distinctively with a C-terminal extension containing a catalytically active penultimate selenocysteine (SeCys) residue in the conserved sequence(-Gly-Cys-SeCys-Gly). TrxR is homodimeric protein in which each monomer includes an FAD prosthetic group, a NADPH binding site and a redox catalytic site. Electrons are transferred from NADPH via FAD and the active-site disulfide to C-terminal SeCys-containing redox center, which then reduces the substrate like thioredoxin. The members of TrxR family are 55 – 58 kilodalton in molecular size and composed of three isoforms including cytosolic TrxR1, mitochondrial TrxR2, and TrxR3, known as Trx and GSSG reductase (TGR). TrxR plays a key role in protection of cells against oxidative stress and redox-regulatory mechanism of transcription factors and various biological phenomena (1).

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Nitrotyrosine has been identified as an indicator of cell damage and inflammation, as well as the production of NO. Nitrotyrosine is a relatively stable product formed from various reaction pathways. One of them is the reaction of peroxynitrite with tyrosine. Peroxynitrite formed from superoxide and nitric oxide radicals mediates tyrosine nitration reactions on proteins resulting in inactivation of certain house-keeping enzymes as well as endogenous antioxidant enzymes such as catalase and superoxide dismutase.
Nitrotyrosine has been implicated in the pathogenesis of many inflammatory, infectious and degenerative human diseases such as Alzheimer’s disease, atherosclerosis, asthma and a variety of conditions mediated by endothelial injury. Oxidative stress has been indicated as a mechanism of secondary neuronal injury in traumatic brain injury. Nitrotyrosine in the cerebrospinal fluid may be an in vivo marker of oxidative nitric oxide damage. Several pathologies of the cardiovascular system are also associated with an augmented production of nitric oxide and/or superoxide-derived oxidants that lead to nitroxidative stress. The high contents of iron (heme) in certain tissues such as heart and vascular smooth muscle cells could serve as a biological base for iron toxicity on free radical-mediated tissue damage, including formation of nitrotyrosine.

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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, PDGF-AA, 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–domain-containing 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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Anti-ANO1 (TMEM16A) Rabbit Polyclonal Antibody