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Carcinoembryonic antigen (CEA) was first described in 1965 by Gold and Freedman when they identified an antigen that was present in both fetal colon and colon adenocarcinoma but that appeared to be absent from
healthy adult colon. CEA is a glycoprotein containing approximately 50% carbohydrate with a molecular weight of 180 kDa.
CEA and related genes make up the CEA family belonging to the immunoglobulin superfamily. In humans, the carcinoembryonic antigen family consists of 29 genes, 18 of which are normally expressed.
CEA has proven to be a suitable target antigen for the detection of primary and metastatic colorectal and some other carcinomas. Although sera from healthy individuals and from patients with other diseases generally had low levels of CEA, CEA is one of the most widely used tumor markers worldwide. Its main application is mostly in gastrointestinal cancers, especially in colorectal malignancy. CEA assays are now generally accepted clinically as a useful and cost-efficient tool in monitoring of colon cancer following surgery.

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Green fluorescent protein (GFP) isolated from jellyfish Aequorea aequorea is a 238 amino acid protein with an apparent molecular weight of about 27-30 kDa on SDS-PAGE. Its chromophore is formed by cyclisation and oxidation of the three amino acids Ser65, Tyr66, and Gly67.
The numerous applications include : using GFP as a reporter for gene expression, as a marker to study cell lineage during development and as a tag to localize proteins in living cells. Other applications of GFP include assessment of protein protein interactions through the yeast two hybrid system and measurement of distance between proteins through fluorescence energy transfer (FRET) protocols. GFP technology has considerably contributed to a greater understanding of cellular physiology.

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Superoxide dismutase (SOD) is an antioxidant enzyme involved in the defense system against reactive oxygen species (ROS). SOD catalyzes the dismutation reaction of superoxide radical anion (O2-) to hydrogen peroxide, which is then catalyzed to innocuous O2 and H2O by glutathione peroxidase and catalase. Several classes of SOD have been identified. These include intracellular copper, zinc SOD (Cu, Zn-SOD/SOD-1), mitochondrial manganese SOD (Mn-SOD/SOD-2) and extracellular Cu, Zn-SOD (EC-SOD/SOD-3) (1). SOD1 is found in all eukaryotic species as a homodimeric 32 kDa enzyme containing one each of Cu and Zn ion per subunit (2). The manganese containing 80 kDa tetrameric enzyme SOD2, is located in the mitochondrial matrix in close proximity to a primary endogenous source of superoxide, the mitochondrial respiratory chain (3). SOD3 is a heparin-binding multimer of disulfide-linked dimers, primarily expressed in human lungs, vessel walls and airways (4). SOD4 is a copper chaperone for superoxide dismutase (CCS), which specifically delivers Cu to copper/zinc superoxide dismutase. CCS may activate copper/zinc superoxide dismutase through direct insertion of the Cu cofactor.

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Superoxide dismutase (SOD) is an antioxidant enzyme involved in the defense system against reactive oxygen species (ROS). SOD catalyzes the dismutation reaction of superoxide radical anion (O2-) to hydrogen peroxide, which is then catalyzed to innocuous O2 and H2O by glutathione peroxidase and catalase. Several classes of SOD have been identified. These include intracellular copper, zinc SOD (Cu, Zn-SOD/SOD-1), mitochondrial manganese SOD (Mn-SOD/SOD-2) and extracellular Cu, Zn-SOD (EC-SOD/SOD-3) (1). SOD1 is found in all eukaryotic species as a homodimeric 32 kDa enzyme containing one each of Cu and Zn ion per subunit (2). The manganese containing 80 kDa tetrameric enzyme SOD2, is located in the mitochondrial matrix in close proximity to a primary endogenous source of superoxide, the mitochondrial respiratory chain (3). SOD3 is a heparin-binding multimer of disulfide-linked dimers, primarily expressed in human lungs, vessel walls and airways (4). SOD4 is a copper chaperone for superoxide dismutase (CCS), which specifically delivers Cu to copper/zinc superoxide dismutase. CCS may activate copper/zinc superoxide dismutase through direct insertion of the Cu cofactor.

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Polo-like kinases (Plks) are important regulators of the cell cycle. Plk1, the most studied Plk, has been implicated in regulating centrosome maturation, mitotic entry, sister chromatid cohesion, the anaphase-promoting complex/cyclosome (APC/C), and cytokinesis. Sister chromatid separation and the subsequent formation of two genetically identical daughter cells depend on the symmetrical attachment of all chromosomes to the mitotic spindle, a process called chromosome biorientation. Several mitosis-specific protein kinases have been implicated in bipolar spindle assembly and chromosome biorientation. For example, Cdk1 (cyclin-dependent kinase 1) is known to phosphorylate Eg5, a kinesin that is required for the migration of centrosomes and is thus needed for the formation of bipolar spindles.
At the onset of mitosis, Plks contribute to the activation of Cdk1-cyclinB, and they are also required for the inactivation of Cdk1 and exit from mitosis. Plks are important regulators of the APC/C, a key component of the ubiquitin-dependent proteolytic degradation pathway.

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Complement factor C9, 71kDa, is the last of the human complement components creating the membrane attack complex (MAC). Activation of the complement system leads to the formation of the MAC, which in turn causes lysis, and death of target cells. C9 plays an important role in inflammatory reactions since it is essential for lytic action of the MAC. Such lytic action could be the basis for complement autotoxicity. Like most of the complement components, C9 belongs to the acute-phase proteins which are generally of hepatic origin, and their plasma concentrations increase (or decrease) following tissue injury and inflammation. Also, because C9 is required for the MAC of complement to become functional, interfering with signaling pathways that stimulate its production could offer new therapeutic strategies for treating various neurodegenerative disorders.

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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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Ceruloplasmin, 132kDa, is a serum ferroxidase that contains greater than 95% of the copper found in plasma. This protein is a member of the multicopper oxidase family, an evolutionarily conserved group of proteins that utilize copper to couple substrate oxidation with the four-electron reduction of oxygen to water. Despite the need for copper in ceruloplasmin function, this protein plays no essential role in the transport or metabolism of this metal. Serum ceruloplasmin level is reduced in Wilson's disease, malnutrition nephrotic syndrome and increased in pregnancy, oestrogen containing contraceptives, acute infection, some types of chronic liver disease, malignancy, rheumatoid arthritis.

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Human serum albumin (HSA) is the most abundant protein in mammalian plasma and is generally considered to be a multifunctional transport protein. HSA is a signle-chain protein synthesized in and secreted from liver cells. HSA has significant antioxidant activity and may represent the major and predominant circulating antioxidant in plasma, which is known to be exposed to continuous oxidative stress. HSA protects human low density lipoproteins against copper-mediated oxidation and blood against hemolysis by free radicals. HSA which are exposed to glucose and have a relatively slow turnover rate are particularly susceptible to nonenzymatic glycosylation. Structural changes in glycosylated albumin lead to a reduction in affinity for fatty acid.

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Cyclin-dependent kinase-5(CDK5) is a member of the cyclin-dependent kinase family of serine/threonine kinases. Its mRNA and protein are expressed in the kidneys, testes, and ovaries. And Its activity has been detected almost exclusively in brain extracts.
Similar to other Cdks, monomeric Cdk5 displays no enzymatic activity; however, Cdk5 is not activated by cyclins. Instead, Cdk5 activity requires association with one of two brain-specific regulatory subunits, called p35 and p39. These two activators regulate the spatial and temporal expression of active Cdk5, restricting its activity primarily to post-mitotic neurons.

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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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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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STAT2 (Signal transducer and activator of transcription 2), 113kDa, is a member of the STAT family of cytoplasmic transcription factors. STAT members generally mediate cytokine, growth factor and hormone receptor signal transduction. STAT2 is a transcription factor critical to the signal transduction pathway of type I interferons (e.g. IFNα). STAT2 resides primarily in the cytoplasm and is tyrosine-phosphorylated after IFNα binds to cell surface receptors. In response to tyrosine phosphorylation STAT2 rapidly localizes to the nucleus and acquires the ability to bind specific DNA targets in association with two other proteins, STAT1 and IFN regulatory factor-9 (IRF-9). STAT2 is phosphorylated at Y689 by receptor-associated Janus kinasses (JAKs) leading to STAT2 dimerization and subsequent translocation to the nucleus to activate gene transcription.

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The RIP(receptor-interacting protein) family of serine/Threonine kinases(RIP-1,2,3,4,5,6,7) are crucial regulators of cell survival and cell death that can trigger pro-survival, inflammatory and immune responses via the activation of transcription factors(NF-kB and AP-1) and death-inducing programs.
RIP2(also known as RICK, CARDIAK, CCK and Ripk2) transduces signals from receptors of both immune responses. RIP2 carries a CARD at its C-terminal, which is essential for NF-kB activation. RIP2 is a critical downstream mediator of Nod1 and Nod2 signaling. Overexpression of RIP2 results in the activation of, in addition to NF-kB, the MAPKs JNK and ERK2, requiring its kinase activity to activate ERK2, but not JNK.

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Heat shock proteins are ubiquitous proteins and have been characterized as cytoprotective molecular chaperones. The typical function of a chaperone is to assist a protein to attain its functional conformation to prevent non-functional aggregation of misfolded proteins. The principal HSP families are HSP90, HSP70, HSP60 and the small HSPs including HSP27, ubiquitin, α-crystallin, Hsp20 and others. The common functions of small Hsps are chaperone activity, thermotolerance, inhibition of apoptosis, regulation of cell development, and cell differentiation.
Hsp27 has a molecular weight of approximately 27 kDa, although it has been shown to form large aggregates of up to 800 kDa in the cytosol. Hsp27 is found in several types of human cells, including tumour cells. Hsp27 interferes with apoptosis through its ability to interact with and inhibit key components of the apoptotic signaling pathway, including the caspase activation complex. Overexpression of heat shock proteins can increase the tumorigenic potential of tumour cells. HSP27 also has been reported to be involved in development and progression of hormone-refractory prostate cancer.

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IA-2 (insulinoma-associated protein 2, ICA512, PTPRN) is a member of the transmembrane protein tyrosine phosphatase (PTP) family located in secretory granules of neuroendocrine cells. The IA-2 protein is 979 amino acids in length and consists of a luminal domain, transmembrane domain, and cytoplasmic domain. Although a member of the PTP family, IA-2 lacks phosphatase activity with known substrates due to amino acid substitutions at critical sites in its PTP domain. Two paralog RPTPs, IA-2 and IA-2β were identified as major autoantigens in type-1 diabetes mellitus. On granule exocytosis, the IA-2 cytoplasmic domain is cleaved and the resulting cytosolic fragment moves into the nucleus where it enhances the levels of phosphorylated STAT5 and STAT3, thereby inducing insulin gene transcription and granule biogenesis. IA-2 signaling enhances pancreatic β–cell proliferation by regulating cyclins D through STATs.

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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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Mitogen- and stress-activated protein kinases (MSK2) is nuclear kinase that act downstream of mitogen-activated protein/extracellular signal-regulated kinase pathways. It contains two kinase domains in the N-terminal and C-terminal region, respectively. MSK2 is activated in response to mitogenic stimuli via Erk1/2MAPK pathway and also by stress stimuli via p38MAPK pathway. Signals from mitogens and cellular stresses are involved in many functions including cell proliferation, differentiation, and survival through the phosphorylation of cyclic AMP response element-binding protein (CREB) at Ser133 which is catalyzed by MSK2. Recently, MSK2 has been shown to be required for stress-induced phosphorylation of histone H3-Ser and transcriptional activation of several immediate early genes.

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Anti-ACTB Rabbit Polyclonal Antibody

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Cyclin-dependent kinase-5 (CDK5) is a member of the cyclin-dependent kinase family of serine/threonine kinases. Its mRNA and protein are expressed in kidney, testes, and ovary. And Its activity is detected almost exclusively in brain extracts.
Similar to other Cdks, monomeric Cdk5 displays no enzymatic activity, but Cdk5 is not activated by cyclins. Instead, Cdk5 activity requires association with one of two brain-specific regulatory subunits called p35 and p39. The two activators regulate the spatial and temporal expression of active Cdk5 to restrict its activity primarily to post-mitotic neurons.

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The human Catecholamine-Sulfating Phenol Sulfotransferase (CSPS) is the only sulfotransferase that catalyses the sulfation of catecholamins, in particular the neurotransmitter dopamine, with high activity. CSPS is required for stimulation by Mn2+ of the sulfating activity and expressed in the human intestine, brain, platelet and other tissues. In the brain it may play a role in regulating the levels of dopamine. It also serves as a detoxifying function in the intestine, where it may detoxify potentially lethal dietary monoamines.

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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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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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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(β, γ, ε, η, ζ, σ and τ/θ) 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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Attractin is a serum glycoprotein of 175 kDa and found in both membrane-bound and secreted forms as a result of alternative splicing. Both the secreted and membrane-bound forms of attractin may be involved in the development and maintenance of the central nervous system. Membrane-bound attractin is a co-receptor for Agouti, antagonist of melanocortin-1 receptor. Secreted attractin, expressed by activated T lymphocytes and modulates interactions between T cells and monocytes/macrophages, was examined as a potential marker of immune activity. Attractin may be a component of a pathway for regulated protein turnover that also involves mahogunin, a wide-expressed E3 ubiquitin ligase found at particularly high levels in the brain. Attractin was considered as an extracellular target amenable for the development of obesity-regulating drugs, also.

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Insulin receptor substrate (IRS) proteins play a central role in maintaining basic cellular functions such as growth and metabolism through insulin/insulin like growth factor (IGF) signaling. Four members (IRS-1, IRS-2, IRS-3, IRS-4) of this family have been identified which differ in their subcellular distribution and interaction with SH2 domain proteins. After phosphorylation by activated receptors, these intracellular signaling molecules recruit various downstream effector pathways including phosphatidylinositol 3-kinase, tyrosine protein phosphatase SHPTP-2, and several smaller adapter molecules such as the growth factor receptor-binding protein Grb-2.
IRS-1, the best characterized IRS protein, has eighteen potential tyrosine phosphorylation sites which directly bind to SH2 domains in downstrem proteins. IRS-1 consists of amino terminal containing pleckstrin homology (PH) domain followed by a phosphotyrosine-binding (PTB) domain which binds to IR and IGFR, and carboxy terminal containing multiple tyrosine and serine residues which become docking sites for proteins that have PTB domain such as SH2 domain.
IRS-4 is the last identified member of the IRS family. Cloning of human IRS-4 revealed a predicted protein of similar length to both IRS-1 and IRS-2and showed only 27% and 29% identity with IRS-1 and IRS-2, respectively. In contrast, IRS-4 exhibits higher degree of homology in the PH domain (43 to 50 %) and the PTB domain (43 to 66%) with the corresponding domains in IRS-1, IRS-2 and IRS-3.
IRSs are also thought to be able to induce malignant transformation. IRS-1 has been shown to be constitutively active in breast cancer.

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Mammalian target of rapamycin (mTOR), a serine/threonine kinase involved in diverse cellular processes, including protein translation, mRNA turnover, and protein stability, mediates, at least in part, some of the biological actions of Akt. As a Kinase subunit of both mTORC1(complex1) and mTORC2(complex2), mTOR regulates cell growth and survival in response to nutrient and hormonal signals. mTORC1 is activated in response to growth factors or amino-acids. Activated mTORC1 up-regulates protein synthesis by phosphorylating key regulators of mRNA translation and ribosome synthesis. mTORC1 phosphorylates EIF4EBP1 and releases it from inhibiting the elongation initiation factor 4E (eiF4E). mTORC2 seems to function upstream of Rho GTPases to regulate the actin cytoskeleton, probably by activating one or more Rho-type guanine nucleotide exchange factors. mTORC2 promotes the serum-induced formation of stress-fibers or F-actin. mTORC2 plays a critical role in AKT1 'Ser-473' phosphorylation.

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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.
Complement component C4 is an essential component of humoral immune response. In its activated form, C4b becomes a subunit of the C3 convertase, which is an enzymatic complex that activates C3 of the classical and lectin complement activation pathways. The classical pathway is initiated by the activation of the C1-complex (C1q, C1r and C1s) by C1q's binding to antibody-antigen. The C1-complex now binds to and splits C2 and C4 producing C2a and C4b. C4b and C2a bind to form C3-convertase. Production of C3-convertase leads to cleavage of C3 into C3a and C3b and C3b joins with the C3 convertase to make C5 convertase.
Human C4 is the most polymorphic protein of the complement system. Complement C4 exists as two isotypes, C4A (acidic) and C4B (basic). Although the sequence identity is very high, they have different hemolytic activities, covalent affinities to antigens and immune complexes, and serological reactivities. Each C4 contains β chain, α chain, C4a anaphyltoxin, C4b, and γ chain.
C4-deficient mice shows incomplete clearance of microbial attack and C4-deficiency in human shows increased autoimmune diseases.

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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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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).