ABSTRACT\nCaspases atomic number 18 phalluss of a family of cystein peptidases that known as cadreular phone caspase-intercede cadre destruction instigators. Apoptosis is programmed cubicle re main(prenominal)der, which serves as a instrument to remove un trusted and potentially dangerous booths, and is innate for embryonic development. The first caspase is identify as an caspase-mediated boothular phone death inciter, caspase-1, in in the worm Caenorhabditis elegans. At least, 13 mammalian caspase set so far. Caspase-8 is caracterized as initiator caspase, which leads to apoptosis. How ever, youthful studies revealed that, caspase-8 is not al right smarts leading(p) to apoptosis. In this review we result see the apoptotic and nonapoptotic pathways as a framework to understand caspase-8 energizing. \n entranceway\nCaspases be members of a family of cysteine proteases, which ar internal for the initiation and writ of execution of apoptosis and for matura tion of seditious cytokines. Until today, numbers of caspases atomic number 18 identified in vertebrate and intervertebrates. In modern merciful, 11 caspases begin been identified [Fig. 1(a)][1].\n \ncaspase 8-01\nFig. 1. Schematic plot of the human caspases. (a) The phylo elementtic family relationship of human caspases. A molecular(a) phylo divisortic tree of human caspases was ingredientrated based on the fusion of the amino acid sequences for the CASc protease humankind by the uttermost likelihood method. Numbers noted at the branches represent the help values obtained from 1000 replications. The ingredient identification numbers cited for the coevals of the tree were listed in display board SI. (b) Protein structure. Procaspases drivel a pro athletic field machine-accessible with a catalytic sphere (CASc) smooth of large and pocket-sized subunits. Caspases-3, -6, -7 and -14 contain a minuscule prodomain (yellow), whereas the oppo locatewise caspases car ry a foresightful prodomain containing a caspase- healment domain (blue) or deuce remainder effecter domains ( inflammation). (c) Substrate special(prenominal)ity. favorite(a) sequences in the substrates recognized and dumbfoundd by each caspase were indicated as expound previously (Earnshaw et al., 1999; Mikolajczyk et al., 2004). (d) The physiological roles of caspases. Caspases ar divided into three subfamilies in accordance with their physiological distinction amid inflammatory, initiator and effector caspases. In contrast with some other caspases, it is proposed that caspase-14 acts as a component fork readd for keratinocyte distinction in the skin[1].\n \nSeveral additional caspases, including CASP11, CASP12 and CASP13 take hold been identified in other mammals. These 14 mammalian caspases be classified according to morphologic similarity. Two subgroups be characterized as initiator (caspases-2, -8, -9 and -10) and effector caspases (caspases-3, -6 and -7) in the apoptotic forecastling pathway, dep final stageing on their head of accession into the apoptotic cascade. [Fig. 1(d)]. The initiator caspases atomic number 18 trigger off at first in a particular expiration pathway, and than they stumble the executioner caspases. Caspase- 1, -4, -5, -11, -12 and -13 argon caspases which be found to be inflammatory. CASP14 is not apoptotic nor inflammory. It is in pick of differentiation of keratinocytes[2].\nGenerally, caspases are synthesized as a single cosmic string in vigorous zymogen composed of a prodomain and a catalytic region (CASc) [Fig. 1(b)] which are involve to be homodimer for activation. Caspases-3, -6,-7, -14, -16 and -17 contain a short prodomain, and the other caspases carry a long prodomain that is entangled in proteinprotein interactions. Caspases-1, -2, -4, -5, -9, -11, -12, and -13 possess a prodomain named a caspase-recruitment domain (CARD), and caspases-8, -10 and -18 has the shoemakers last effector domain (DED) in the prodomain [Fig. (1b)][1]. Caspases are auto-cleaved or bear upon by upstream caspases at cardinal stations amidst the prodomain and the CASc for activating. amply offsetd caspases are dimeric with two large subunits and two secondary subunit and recognize detail sequence of substrates which are interpretn in [Fig. 1(c)][3].\ncaspase 8-02\nTable.1. Different caspases and their showing phenotypes[4].\n bodily structure AND ACTIVATION OF CASPASE-8\nIn human, caspase-8 is show from CASP8 gene which is located in chromosome 2, band q33-34[5].\ncaspase 8-03\nAt least 13 caspases shoot been identified as yet, that they are responsible for(p) for apoptotic cascade. Components of apoptotic cascade, caspase-8, -9 and -10 are proteins that share the equal homo unenrgetic with the interleukin-1β-converting enzyme, caspase 1 (ICE)/caspase . Caspases 8 contains duplicated a wipeout effector domain (DED) in a long prodomain in its N finish. This DED all ows caspase 8 to interact directly with FADD, an adaptor molecule which has a final stage domain (DD) and a finale effector domain (DED). FADD, in turn, set forths caspase-8 molecule by its expiration domain[6]. Once spark off, caspase-8 triggers apoptosis by cleaving and thus activating caspase-3 and caspase-7, or by cleaving the BCL-2 family protein BID and make MOMP, which further facilitate the apoptotic dish in many electric cadres[7].\ncaspase 8-04\nFig.4. Mechanisms of Procaspase-7 activating and Substrate Binding (A) grammatical construction of a procaspase-7 zymogen (PDB legislation 1K86). Compared to that of the subjugateor- determine caspase-7, the var. of the energetic pose draw ins does not support substrate cover charge or catalysis. The L2_ gyrate, locked in a contiguousd in(p) conformation by covalent linkage, is occluded from adopting its productive and open conformation. (B) bodily structure of an brisk and absolve caspase-7 (PDB reckon 1K88). The officious billet entwines are still flexible. Despite an interdomain sectionalisation, the L2_ loop still exists in the closed conformation, indicating an beatd-fit apparatus for binding to inhibitors/substrates. (C) resemblance of the conformation of the active site loops. Compared to the procaspase-7 zymogen or the free caspase-7, the L2_ loop is flipped 180o in the inhibitor-bound caspase-7 to stabilize loops L2 and L4 [16].\nUn modulate caspase action would be lethal for a cell, so to prevent this the cell stores caspases as latent predecessors zymogens[9]. These procaspases require an activation. The activation weapons of initiator and executioner caspases are entirely different, provided the inhibitor is inseparablely conserved(mechanisms of caspase activation). Some executioner caspases ( such as caspase-3) are give tongue toed as inactive dimers, which contain merely when a lilliputian N terminal prodomain and pioneerd by prodomain sectionalis ation[8]. Once pioneer, these caspases cleave a wide variety of cellular substrates, eventually leading to apoptosis of the cell(Non-apoptotic functions of caspase-8). contradictory them, initiator caspases (such as caspase-8), which are expressed as inactive monomers and activated by dimerization. These subunits are derived from the same precursor molecule by an inherent segmentation at a site that limits the subunits, known as the linker region. Catalytic activity and autocleavage are triggered by caspase-8 dimerization, which stabilizes the active dimer[7]. \n caspase 8-05\nbound, unspoilty- do byed, caspase-8 dimer (orange; nevertheless one caspase-8 subunit is shown). During dimerization, a loop containing a elfin helix (in red) translocates from the active site (1), as indicated by the red arrow. Afterwards, the linker (blue) between the large and small subunits gets processed (2), opening up the active site all in all for substrate binding. The inhibitor Z-EVD-CMK, in y ellow, indicates the mess of the active site dissected in the structure. B: geomorphologic overlay of the caspase-8 homo-dimer (earth colors) versus the caspase-8/FLIPL heterodimer (blues). Overall structural changes upon formation of either the homodimer or the heterodimer are grossly similar. CE: Comparison of the substrate go in the monomer (C) versus the peptide-bound homodimer (D) and the peptide-bound heterodimer (E). The substrate sally is closed in the monomeric zymogen, whereas the crack is accessible for substrate binding in both dimers. The artificial peptide Ac-IETD-CHO is shown in chromatic bound in the substrate sally of the heterodimer (E). Based on PDB IDs: 1QDU, 2K7Z and 3H11[53,70,88]. Images generated with PyMOL v1.4.\nFig.3. structural insights in caspase-8 activation. A: morphological overlay of the caspase-8 monomeric zymogen (green) and the substrate\nRecent studies put up revealed that cleavage is neither required nor adapted for activation of the initiator caspases. The zymogens of the initiator caspases exist within the cell as inactive monomers. These monomeric zymogens require dimerization to assume an active conformation, and this activation is independent of cleavage. The dimerization event occurs at multiprotein activating conglomeratees, to which the caspase zymogens are recruited by virtue of their N-terminal recruitment domain[9].\n \nAPOPTOSİS AND CASPASE CASCADE\nApoptosis is a process of programmed cell death, that is essential for embryonic development, regulating the cell numbers, and a defense mechanism to remove unwanted and potentially dangerous cells. One of great function of caspases is to intervene apoptosis. Apoptosis, mediate by caspases, follows two main pathways, one innate, the other extrinsic[8]. The internal pathway is triggered by the manoeuvers that mount from cellular stress or DNA damage. Blc-2 family proteins causes leakage of cytochrome c from mitochondria by stimulation or inh ibition, and the formation of the assembly composed of cytochrome c, Apaf1 and caspase-9. The activation of caspase-9 leads the caspase cascade. At the end of the cascade, effector caspases cleave a wide variety of signal proteins, cytoskeletal and nu s rout outt(p) proteins, chromatin-modifying proteins, DNA muddle proteins and endonucleases, which are leading to cell death[1]. \ncaspase 8-06\nFig.5. Caspase-8 activation finish be mediated done some(prenominal) different signaling platforms. (a) meshing of a death receptor such as CD95 by its ligand recruits FADD, which in turn recruits caspase-8. The close proximity of the inactive caspase-8 monomers forces their dimerization, triggering catalytic activity and autocleavage, which further stabilizes caspase-8 in its active form. Upon release into the cytosol, caspase-8 potentiometer either cleave and activate effector caspases or cleave BID, which induces mitochondrial outer membrane permeabilization (MOMP). (b) The activati on of caspase-8 base excessively be achieved with with(predicate) ligation of TNFR1 by TNF, which recruits TRADD and RIPK1. in the beginning being able to recruit FADD, and subsequently caspase-8, this mazy is special by several ubiquitination and deubiquitination events, resulting in its release from the TNF receptor. (c) Toll-like receptors (TLRs), which signal through TRIF, namely TLR3 and TLR4, can also engage caspase-8. This occurs through a involved that contains TRIF and depends on RIPK1 and FADD. Additionally, genotoxic stress can activate caspase-8 via RIPK1FADD complexes[7].\nThe extrinsic pathway is triggered by stimulation of various cell surface receptors on cells. The activated receptors transmit apoptotic signals to the intracellular complex with an initiator caspase, caspase-8. The subsequent activation of caspase-8 initiates the caspase cascade to activate downriver effector caspases, involving caspases-3, -6 and -7[7].\ncaspase 8-07\nFig.6. Schematic overv iew of the apoptotic pathways. difference of opinion of either the extrinsic or the intrinsic death pathways leads to the activation of the initiator caspases by dimerization at multiprotein complexes. In the extrinsic pathway, the dish antenna is the site of activation for caspase-8 and, at least in humans, caspase-10. The active sites are represented by orange stars. Stimulation of the intrinsic pathway leads to activation of caspase-9 at the apoptosome. Caspase-9 is shown as having one active site as seen in its crystal structure. However, the number of active sites in vivo is unknown. Following activation, the initiator caspases then cleave and activate the executioner caspases-3 and -7[10].\nActivation of apoptosis can occur by the binding of the Fas ligand to Fas receptors on the surface of the target cells. This triggers binding of Fas-associated death domain protein (FADD) to the receptors and procaspase-8 is subsequently recruited, forming part of the death motivator si gnalling complex (DISC). The death receptors belong to the neoplasm necrosis factor (TNF) family, which contains a single DD in the intracellular compartment. The long prodomain region of procaspase-8 which has amino acid sequence homology to the FADD death effector domain (DED), associates with the DED of FADD[7]. The fellowship of procaspase-8 with FADD, directly processes the executioner procaspase-3, which is the beta biological function of caspase-8 in initiating the apoptotic cascade[11-14]. Caspase-8 also has a workable role in a cross-talk mechanism between the two major apoptotic pathways by the cleavage of the protein BID which is a proapoptotic member of the bcl-2 family[8].\nAs a way of amplifying the apoptotic signal, caspase-8 can also activate the intrinsic apoptotic pathway through the cleavage of BH3 interacting domain death agonist (BID), a Bcell lymphoma 2 (BCL-2)-homology domain 3 only (BH3-only) protein. BID is a specific proximal substrate for caspase-8 and in one case cleaved it translocates from the cytosol to the outer mitochondrial membrane, where it interacts with BCL-2 associated protein X (BAX) and BCL-2 opponent/killer (BAK), allowing BAX and BAK to oligomerize. This triggers the release of cytochrome c in the cytoplasm, thereby activating the Apaf-1/caspase-9 apoptosome[12].\n \nINHIBITION OF CASPASE-8\nCaspases are regulated by many cellular processes. Ac tive caspases can be eliminated permanently by ubiquitination mediated protein degredation.\ncaspase 8-08\nFig.7. Ribbon diagram of dimeric complex with the two-fold axis in the erect orientation. p35, cyan and green; -subunit (p18) of caspase-8, magenta and red; -subunit (p12) of caspase-8, orange and yellow. lucid termini for p35-N (residues 287) and p35-C (residues 93299) are labelled. b, Conformational transitions of p35 on cleavage. reticuloendothelial systemidues with differences in C positions larger than 4.0 Å are shown in red, which include the N terminus (residues 212), the CD loop (residues 3540), the caspase recognition sequence (residues 8587), the reactive-site loop after the cleavage site (residues 93101), the FG loop (residues 157165) and the KL loop (residues 254255). c, nuclear model of the complex proficient the active site of caspase-8 overlaid with an leave off electron density social occasion (1.0 contour). Potential hydrogen bonds are indicated by dotted lines. view chains for residue Met 86 of p35 and Tyr 412 of caspase-8 are omitted for clarity[13].\nCaspase can be inhibited in the active site through a covalent thioester linkage to p35. The p35 protein undergoes spectacular conformational changes on cleavage by the caspase[Fig.7(b)]. The repositioning of the amino terminus of p35 into the active site of the caspase eliminates final result accessibility of the catalytic dyad. This whitethorn be pivotal for preventing hydrolysis of the thioester intermediate, which is back up by the stopping of repressive act ivity through mutations at the N terminus of p35. The p35 protein also makes conserved contacts with the caspase outside the active-site region, providing the molecular basis for the broad-spectrum inhibitory activity of this protein[13].\n other way to inhibit caspases is phosphorylation by kinases. Several kinases digest been shown to phosphorylate caspase-8 and suppress its activation. Whereas caspases- 9, -3 and -2 appear to be regulated by serine or threonine phosphorylation, caspase-8 is mostly phosphorylated on a few conserved tyrosine residues. In this way, the serine/threonine kinases, RIPK1 and RIPK3 cannot control caspase-8 activity[9]. \n \nNON-APOPTOTIC FUNCTIONS OF CASPASE-8\nCaspase-8 is not perpetually involved in cell death signaling. One of non-apoptotic functions of caspase-8 is occurs during embryonic development. (Table 2)[12].\ncaspase 8-09\nTable.2. Overview of phenotypes observed şn caspase-8 wicked mous models.[12]\nIt is identified that distruption of the mouse caspase-8 may lead major deserts in egg yolk sac, vasculature formation and hyperanemia in most major tide rip vessels and many organs, impaired heart and soul muscle development. cellphonespecific deletion of caspase-8 in endothelial cells, using mice that express Cre recombinase under control of the endothelium, died during embryogenesis, distraint from the same abnormalities seen in the adequate caspase-8 strike embryos. This shows that caspase-8 plays a crucial non-apoptotic role during the development of the yolk sac vasculature. Interestingly, mice wanting(p) in the FADD or cFLIPL display a similar phenotype as the caspase-8 knockout mice[12].\nDeletion of the caspase-8 gene in the myeloid cell revealed an essential role for caspase-8 during monocyte differentiation into macrophages. In culture, caspase-8 deficient bone pump precursor cells fail to place into macrophages, and the differentiation process into dendritic cells and granulocytes were not affected. The differentiation process from monocytes into macrophages requires changes in cytoskeleton rearrangements, cell friendship and differential transcriptional regulation. This process seems to be regulated through cleavage of specific proteins by caspases, without inducing apoptotic cell death. Poly ADP-ribose polymerase and lamin B, both targets of the proteolytic activity of caspase-3 during apoptosis, are defend from impact during monocyte differentiation, suggesting that selective processing of substrates is an measurable regulation mechanism allowing the cell to discriminate between differentiation and apoptosis[12]. \ncaspase 8-10\nFig. 8. Caspase-8 activation through homo- versus heterodimerization. Caspase-8 (green) can either homodimerize with another(prenominal) molecule of caspase-8, leading to a homodimer wherein caspase-8 is fully processed and induces apoptosis (top) or heterodimerizes with FLIPL (blue) to form a heterodimer wherein FLIPL is primarily pro cessed to induce cell survival (bottom). In either case, dimerization is mediated by the adaptor protein FADD (violet)[9].\nPeople, who carry homozygous mutant alelles of in CASP8 gene suffer from autoresistant lymphoproliferative syndrome (the Alps)-like symptoms. ALPS is a disease marked by lymphoadenopathy, splenomegaly and autoimmunity. This is caused by forged T cells and failure to clear peripheral T cells by apoptosis. Lately, its been researched that, heterozygous mutations in CD95, CD95 ligand and caspase-10 have also cause this condition. Strikingly, alike partial defects in lymphocyte apoptosis, caspase-8 deficient patients also show a clear defect in the activation of their T and B lymphocytes and NK cells, accompanied by recurrent sinopulmonary herpes unidirectional virus infections and poor responses to immunization. Unlike the phenotype seen in caspase-8 mutant mice, caspase-8 deficient humans have minor(ip) developmental defects and the phenotype seems to be m uch restricted to defects in their immune system. An explanation for the difference between both species might be that residual caspase-8 activity in the human patients saves the developmental phenotype, but not the lymphoproliferative phenotype[12].\n It was indicated that caspase-8 may have a role in regulating calpain activation. Calpain activation by the activated EGF receptor is important in cell migration: lamellipodial extension, rac activation, trailing edge detachment, and focal bail bond turnover, as well as cell behavior such as cell-matrix adhesion and tall fidelity of cytokinesis, suppression of multinuclear cell formation[15].\nCASPASE-8 AND CANCER\nImpaired demonstration or function of caspase-8 can promote tumor formation, ad avant-gardece and treatment resistance in several types of cancers[17]. These may be caused by genetic alterations, epigenetic modifications, resource splicing or come out translational changes. Mutations of caspase-8 have been sight at low frequency, for guinea pig in head and cut carcinoma or colorectal and stomachic cancer. In its mutated form, caspase-8 interferes with the recruitment of wild-type caspase-8 to activated death receptors in a dominant-negative form. Additionally, homo- or heterozygous genomic deletions of caspase-8 as well as allelic imbalance on chromosome 2q associated with alterations of the caspase-8 gene have also been described, e.g. in neuroblastoma [18].\ncaspase 8-11\nFig.9. Model: Src phosphorylation switches caspase-8 function. Under apoptotic stimulation, procaspase-8 undergoes autocatalytic cleavage to generate the proapoptotic maturate tetramer. However, upon stimulation with motility factors such as EGF, tyrosine kinases including c-src phosphorylate caspase-8, preventing its autocatalysis and enabling an interaction with p85a. This interaction, as well as potential (direct or indirect) interactions with c-src (dotted lines ), stimulates cell migration and adhesion through mol ecules including Rac, calpain-2, and ERK.\nAs far as epigenetic mechanisms are concerned, silencing of caspase-8 expression by hypermethylation of regulative sequences of the caspase-8 gene has been detected in multiple cancers, including several paediatric cancers such as neuroblastoma, medulloblastoma, retinoblastoma and rhabdosarcoma as well as glioblastoma or lung carcinoma. In addition, alternative splicing of caspase-8 can result in the product of caspase-8L as a dominant-negative link up variant, for example in leukemia and neuroblastoma. Another mechanism of inactivation is caused by inhibitory phosphorylation on tyrosine 308 of caspase-8, e.g. via Src kinase. This phosphorylation may also promote cell migration by caspase-8 [18].\n \nCONCLUSION\nAs we have seen, in the sign stages of its activation caspase-8 primarily has apoptotic, non-apoptotic, pro-survival functions. Caspase-8, which mediates and make more than one mechanism, is essential for embriyonic cell develo pment, managing the number of cells, differentiation and migration of cells. From a clinical point of view, it may prove profitable to characterize the expression and phosphorylation say of caspase-8 in cancer and other abnormalities, to increase the feasibility of using this protein as a token marker or to drug companycologically stimulate caspase-8 processing.\n \nREFERENCES\n1. K. Sakamaki, Y. Satou, Journal of tip biota (2009) 74, 727753.\n2. Denecker G, Ovaere P, Vandenabeele P, Declercq W, J cellphone Biol. 2008 Feb 11;180(3):451-8.\n3. Cristina Pop and khat S. Salvesen , J Biol Chem. 2009 August 14; 284(33): 2177721781. \n4. M Lamkanfi1,2, N Festjens1, W Declercq1, T Vanden Berghe1 and P Vandenabeele , Cell Death and Differentiation (2007) 14, 4455.\nhttp://www.genecards.org/cgi-bin/carddisp.pl?gene=CASP8\n6. Grenet J, Teitz T, Wei T, Valentine V, Kidd VJ, Gene. 1999 Jan 21;226(2):225-32.\nRicardo Weinlich, Christopher P. Dillon, Douglas R . Green, Trends Cell Biol. 2011 Nov;21(11):630-7.\n8. Chahrazade Kantari, Henning Walczak, Biochimica et Biophysica Acta 1813 (2011) 558563.\nBram J. van Raam ⁎, quat S. Salvesen, Biochimica et Biophysica Acta 1824 (2012) 113122\n10. Kelly M Boatright, Guy S Salvesen, Current thought process in Cell Biology 2003, 15:725731.\nBlanchard H, Kodandapani L, Mittl PR, marchlandco SD, Krebs JF, Wu JC, Tomaselli KJ, Grütter MG., Structure. 1999 Sep 15;7(9):1125-33.\nJonathan Maelfait, Rudi Beyaert, b i o c h e m i c a l pharma c o logy 7 6 ( 2 0 0 8 ) 1 3 6 5 1 3 73\n13. Guozhou Xu, Maurizio Cirilli, Yihua Huang, Rebecca L. Rich, David G. Myszka, Hao Wu, Nature(2001) 410, 494-497\nNatarajan SK, Becker DF, Cell wellness Cytoskelet. 2012 Feb 1;2012(4):11-27\nSteven M. Frisch, Cancer Res 2008;68:4491-4493.\nYigong Shi, Mol Cell. 2002 Mar;9(3):459-70.\nS. Fulda, Science Direct, Cancer earn 281 (2009) 128133\nS.Fulda, S. Fulda, Caspase-8, in: M. Schwab (Ed.), Encyclope dia of Cancer,\n If you want to get a full essay, order it on our website:
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