Propagation of the Signal

Propagation of the Signal tài liệu, giáo án, bài giảng , luận văn, luận án, đồ án, bài tập lớn về tất cả các lĩnh vực ki...

A functional role of the membrane-proximal extracellular domains of the signal transducer gp130 in heterodimerization with the leukemia inhibitory factor receptor Andreas Timmermann, Andrea Ku¨ ster, Ingo Kurth, Peter C. Heinrich and Gerhard Mu¨ ller-Newen Institut fu ¨ r Biochemie, Rheinisch-Westfa ¨ lische Technische Hochschule Aachen, Germany gp130 is the common signal transducing receptor subunit of interleukin (IL)-6-type cytokines. gp130 either homodimer- izes in response to IL-6 and IL-11 or forms heterodimers with the leukemia inhibitory factor (LIF) receptor (LIFR) in response to LIF, oncostatin M (OSM), ciliary neurotrophic factor (CNTF), cardiotrophin-1 (CT-1) or cardiotrophin- like cytokine resulting in the onset of cytoplasmic tyrosine phosphorylation cascades. The extracellular parts of both gp130 and LIFR consist of several Ig-like and fibronectin type III-like domains. The role of the membrane-distal domains of gp130 (D1, D2, D3) and LIFR in ligand binding is well established. In this study we investigated the func- tional significance of the membrane-proximal domains of gp130 (D4, D5, D6) in respect to heterodimerization with LIFR. Deletion of each of the membrane-proximal domains of gp130 (D4, D5andD6) leads to LIF unresponsiveness. Replacement of the gp130 domains by the corresponding domains of the related GCSF receptor either restores weak LIF responsiveness (D4-GCSFR), leads to constitutive activation of gp130 (D5-GCSFR) or results in an inactive receptor (D6-GCSFR). Mutation of a specific cysteine in D5 of gp130 (C458A) leads to constitutive heterodimerization with the LIFR and increased sensitivity towards LIF stimulation. Based on these findings, a functional model of the gp130–LIFR heterodimer is proposed that includes contacts between D5 of gp130 and the corresponding domain D7 of the LIFR and highlights the requirement for both receptor dimerization and adequate receptor orienta- tion as a prerequisite for signal transduction. Keywords: cytokines; receptors; signal transduction; leuke- mia inhibitory factor; gp130. Secretion of mediators by cells that are recognized by specific receptors on target cells is a basic mechanism of intercellular communication. The molecular mechanism by which binding of the ligand to the receptor on the plasma membrane leads to the onset of cytoplasmic signal trans- duction cascades has gained considerable attention during recent years. In the case of receptors that span the membrane only once, ligand induced receptor dimerization has been accepted as the main mechanism for receptor activation [1]. Only recently, several reports suggested that some receptors may exist as preformed dimers or multimers that switch from an inactive to an active conformation upon ligand binding [2,3]. Hematopoietic cytokine receptors [4] consist of an extracellular part, a single transmembrane region, and a cytoplasmic part that is devoid of any intrinsic enzymatic activity but constitutively associates with tyrosine kinases of the Janus kinase (Jak) family. Upon ligand binding the associated Jaks become activated by transphosphorylation and phosphorylate tyrosine residues in the cytoplasmic part of the receptor. These phosphotyrosines serve as docking sites for Propagation of the Signal Propagation of the Signal Bởi: OpenStaxCollege Once a ligand binds to a receptor, the signal is transmitted through the membrane and into the cytoplasm Continuation of a signal in this manner is called signal transduction Signal transduction only occurs with cell-surface receptors because internal receptors are able to interact directly with DNA in the nucleus to initiate protein synthesis When a ligand binds to its receptor, conformational changes occur that affect the receptor’s intracellular domain Conformational changes of the extracellular domain upon ligand binding can propagate through the membrane region of the receptor and lead to activation of the intracellular domain or its associated proteins In some cases, binding of the ligand causes dimerization of the receptor, which means that two receptors bind to each other to form a stable complex called a dimer A dimer is a chemical compound formed when two molecules (often identical) join together The binding of the receptors in this manner enables their intracellular domains to come into close contact and activate each other Binding Initiates a Signaling Pathway After the ligand binds to the cell-surface receptor, the activation of the receptor’s intracellular components sets off a chain of events that is called a signaling pathway or a signaling cascade In a signaling pathway, second messengers, enzymes, and activated proteins interact with specific proteins, which are in turn activated in a chain reaction that eventually leads to a change in the cell’s environment ([link]) The events in the cascade occur in a series, much like a current flows in a river Interactions that occur before a certain point are defined as upstream events, and events after that point are called downstream events Art Connection 1/7 Propagation of the Signal The epidermal growth factor (EGF) receptor (EGFR) is a receptor tyrosine kinase involved in the regulation of cell growth, wound healing, and tissue repair When EGF binds to the EGFR, a cascade of downstream events causes the cell to grow and divide If EGFR is activated at inappropriate times, uncontrolled cell growth (cancer) may occur In certain cancers, the GTPase activity of the RAS G-protein is inhibited This means that the RAS protein can no longer hydrolyze GTP into GDP What effect would this have on downstream cellular events? Signaling pathways can get very complicated very quickly because most cellular proteins can affect different downstream events, depending on the conditions within the cell A single pathway can branch off toward different endpoints based on the interplay between two or more signaling pathways, and the same ligands are often used to initiate different signals in different cell types This variation in response is due to differences in protein expression in different cell types Another complicating element is signal integration of the pathways, in which signals from two or more different cell-surface 2/7 Propagation of the Signal receptors merge to activate the same response in the cell This process can ensure that multiple external requirements are met before a cell commits to a specific response The effects of extracellular signals can also be amplified by enzymatic cascades At the initiation of the signal, a single ligand binds to a single receptor However, activation of a receptor-linked enzyme can activate many copies of a component of the signaling cascade, which amplifies the signal Methods of Intracellular Signaling The induction of a signaling pathway depends on the modification of a cellular component by an enzyme There are numerous enzymatic modifications that can occur, and they are recognized in turn by the next component downstream The following are some of the more common events in intracellular signaling Link to Learning Observe an animation of cell signaling at this site Phosphorylation One of the most common chemical modifications that occurs in signaling pathways is the addition of a phosphate group (PO4–3) to a molecule such as a protein in a process called phosphorylation The phosphate can be added to a nucleotide such as GMP to form GDP or GTP Phosphates are also often added to serine, threonine, and tyrosine residues of proteins, where they replace the hydroxyl group of the amino acid ([link]) The transfer of the phosphate is catalyzed by an enzyme called a kinase Various kinases are named for the substrate they phosphorylate Phosphorylation of serine and threonine residues often activates enzymes Phosphorylation of tyrosine residues can either affect the activity of an enzyme or create a binding site that interacts with downstream components in the signaling cascade Phosphorylation may activate or inactivate enzymes, and the reversal of phosphorylation, dephosphorylation by a phosphatase, will reverse the effect 3/7 Propagation of the Signal In protein phosphorylation, a phosphate group (PO4-3 ) is added to residues of the amino acids serine, ...BioMed Central Page 1 of 13 (page number not for citation purposes) Journal of Ovarian Research Open Access Research Functional significance of the signal transduction pathways Akt and Erk in ovarian follicles: in vitro and in vivo studies in cattle and sheep Kate E Ryan 1 , Claire Glister 3 , Pat Lonergan 1 , Finian Martin 2 , Phil G Knight 3 and Alexander CO Evans* 1 Address: 1 School of Agriculture Food Science and Veterinary Medicine, Conway Institute, College of Life Science, University College Dublin, Belfield, Dublin 4, Ireland, 2 School of Biomolecular and Biomedical Science, Conway Institute, College of Life Science, University College Dublin, Belfield, Dublin 4, Ireland and 3 School of Biological Sciences, University of Reading, Whiteknights, Reading, RG6 6AJ, UK Email: Kate E Ryan - katie.ryan1@gmail.com; Claire Glister - c.glister@reading.ac.uk; Pat Lonergan - pat.lonergan@ucd.ie; Finian Martin - finian.martin@ucd.ie; Phil G Knight - p.g.knight@reading.ac.uk; Alexander CO Evans* - alex.evans@ucd.ie * Corresponding author Abstract Background: The intracellular signalling mechanisms that regulate ovarian follicle development are unclear; however, we have recently shown differences in the Akt and Erk signalling pathways in dominant compared to subordinate follicles. The aim of this study was to investigate the effects of inhibiting Akt and Erk phosphorylation on IGF- and gonadotropin- stimulated granulosa and theca cell function in vitro, and on follicle development in vivo. Methods: Bovine granulosa and theca cells were cultured for six days and stimulated with FSH and/or IGF, or LH in combination with PD98059 (Erk inhibitor) and/or LY294002 (Akt inhibitor) and their effect on cell number and hormone secretion (estradiol, activin-A, inhibin-A, follistatin, progesterone and androstenedione) determined. In addition, ovarian follicles were treated in vivo with PD98059 and/or LY294002 in ewes on Day 3 of the cycle and follicles were recovered 48 hours later. Results: We have shown that gonadotropin- and IGF-stimulated hormone production by granulosa and theca cells is reduced by treatment with PD98059 and LY294002 in vitro. Furthermore, treatment with PD98059 and LY294002 reduced follicle growth and oestradiol production in vivo. Conclusion: These results demonstrate an important functional role for the Akt and Erk signalling pathways in follicle function, growth and development. Introduction Folliculogenesis is a vigorously controlled process that involves both proliferation and differentiation of both granulosa and theca cells. These coordinated processes are controlled by local and systemic regulatory factors. The gonadotropins, FSH and LH, are essential for the develop- ment of follicles beyond the early antral stage. In both cat- tle and sheep, ovarian antral follicle growth occurs in a wave-like pattern with 2 to 3 waves per cycle in cattle and 3 to 4 waves in sheep [1]. Wave emergence is triggered by a transient rise in circulating FSH concentrations [2-4], which promotes significant growth of granulosa cells by Published: 1 October 2008 Journal of Ovarian Research 2008, 1:2 doi:10.1186/1757-2215-1-2 Received: 10 July 2008 Accepted: 1 October 2008 This article is available Hindawi Publishing Corporation EURASIP Journal on Wireless Communications and Networking Volume 2009, Article ID 679430, 10 pages doi:10.1155/2009/679430 Research Article A Multiuser MIMO Transmit Beamformer Based on the Statistics of the Signal-to-Leakage Ratio Batu K. Chalise and Luc Vandendorpe Communication and Remote Sensing Laboratory, Universit ´ e Catholique de Louvain, Place du Levant 2, 1348 Louvain-la-Neuve, Belgium Correspondence should be addressed to Batu K. Chalise, batu.chalise@uclouvain.be Received 23 February 2009; Accepted 3 June 2009 Recommended by Alex Gershman A multiuser multiple-input multiple-output (MIMO) downlink communication system is analyzed in a Rayleigh fading environment. The approximate closed-form expressions for the probability density function (PDF) of the signal-to-leakage ratio (SLR), its average, and the outage probability have been derived in terms of the transmit beamformer weight vector. With the help of some conservative derivations, it has been shown that the transmit beamformer which maximizes the average SLR also minimizes the outage probability of the SLR. Computer simulations are carried out to compare the theoretical and simulation results for the channels whose spatial correlations are modeled with different methods. Copyright © 2009 B. K. Chalise and L. Vandendorpe. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1. Introduction The capacity of a wireless cellular system is limited by the mutual interference among simultaneous users. Using multiple antenna systems, and in particular, the adaptive beamforming, this problem can be minimized, and the system capacity can be improved. In recent years, the optimum downlink beamforming problem (including power control) has been extensively studied in [1–3] where the signal-to-interference-plus-noise ratio (SINR) is used as a quality of service (QoS) criterion. After it has been found that the multiple-input multiple-output (MIMO) techniques significantly enhance the performance of wireless communication systems [4, 5], the joint optimization of the transmit and receive beamformers [6] has also been investigated for MIMO systems. Motivated by the fact that the optimum transmit beamformers [1–3] and the joint optimum transmit-receive beamformers [6]canbe obtained only iteratively due to the coupled nature of the corresponding optimization problems, recently, the concept of leakage and subsequently the signal-to-leakage- plus-noise ratio (SLNR) as a figure of merit have been introducedin[7, 8]. (Note that SLNR as a performance criterion has been considered in [9–11] for multiple- input-single-output (MISO) systems.) Although the latter approach only gives suboptimum solutions, it leads to a decoupled optimization problem and admits closed-form solutions for downlink beamforming in multiuser MIMO systems. While investigating multiuser systems from a system level perspective, in many cases, the outage probability has also been widely used as a QoS parameter. The closed- form expressions of the outage probability with equal gain and optimum combining have been derived in [12, 13], respectively, in a flat-fading Rayleigh environment with cochannel interference. The latter work has Original article Effect of genotype and cutting type on the vegetative propagation of the pine hybrid (Pinus brutia (Ten) x Pinus halepensis (Mill))* K Panetsos, A Scaltsoyiannes, P Alizoti Laboratory of Forest Genetics, Department of Forestry and Natural Environment, Aristotelian University of Thessaloniki, 54006 Thessaloniki, Greece (Received 16 February 1993; accepted 12 April 1994) Summary — Improved methods to propagate vegetatively selected individuals of the promising arti- ficial pine hybrid Pinus brutia (Ten) x P halepensis (Mill) are required. Repeated spraying with 200 mg·l -1 BA or one spraying with 1 000 mg·l -1 of the herbicide Arsenal on the stems of 4-year-old seedlings, resulted in the production of the largest possible number of fascicle shoots. The fascicle shoots produced were taken as cuttings and were tested for rooting. In the rooting experiments the effect of genotype, cutting type, cutting size and auxin treatment were investigated. Genotype and cutting type proved to be the most crucial factors for rooting and clones with high rootability. Pinus brutia (Ten) x P halepensis (Mill) I induced fascicle shoot / genotype effect I rooting / cutting / vegetative propagation Résumé— L’effet du génotype et du type de bouture sur la multiplication végétative de l’hybride de pin (Pinus brutia (Ten) x Pinus halepensis (Mill)). L’amélioration des méthodes de multiplica- tion végétative des individus sélectionnés de l’hybride artificiel de pin Pinus brutia (Ten) x Pinus hale- pensis (Mill) est nécessaire. Quatre différents régulateurs de croissance (TIBA, Alar, GA 3, BA) ont été appliqués avec différentes combinaisons et concentrations sur la tige de plants de 4 ans de cet hybride artificiel afin d’obtenir l’induction de pousses interfasciculaires (tableau I). L’effet du meilleur trai- tement (200 mg·l -1 BA) de l’expérience a été comparé avec celui de l’herbicide Arsenal. La pulvérisation répétée de 200 mg·l -1 BA ou une pulvérisation de 1000 mg·l -1 d’Arsenal sur la tige de plants de 4 ans, conduit à la production du plus grand nombre des pousses interfasciculaires (tableau II, fig 1A). Ces pousses ont été utilisées comme boutures et étudiées pour leur enracinement. Dans cette expérience d’enracinement, on a analysé l’effet du génotype, du type de bouture, de la taille de la bouture et du traitement par l’auxine. Parmi les 8 clones testés, on a observé une grande variabilité en ce qui * This work was financially supported by the EEC in the framework of the Mediterranean Integrated Programmes of the project "Application of biotechnological methods for the mass production of fast- growing Mediterranean pines". Abbreviations: benzyladenine (BA); gibberelic acid (GA 3 ); triiodobenzoic acid (TIBA); dimethylaminosuccinamide (Alar); indole-3-butyric acid, potassium salt (K-IBA). concerne l’enracinement (fig 2). Les boutures interfasciculaires se sont enracinées plus facilement et elles ont développé un meilleur système racinaire que celui des boutures de tige (fig 1B, 1 C). En ce qui conceme l’effet du génotype, on a trouvé que quelques clones s’enracinent facilement ou difficilement indépendamment de leur hauteur ou du traitement par l’auxine (tableau III). Les concentrations variées d’auxine (0, 4000, 8000 ppm K-IBA) influent différemment sur les 2 types de bouture (fig 3). Les plan- tules provenant des pousses interfasciculaires se caractérisent par leur vigueur et leur orthotropie (fig 1D). P brutia (Ten) x P halepensis 28 EMSA = electrophoretic mobility shift assays; ERK = extracellular regulated kinase; IFN = interferon; IκB = inhibitors of κB; JNK = jun N-terminal kinase; mAB = monoclonal antibody; MAPK = mitogen activated protein kinase; MFI = mean fluorescence intensity; NF = nuclear factor; PBMC = peripheral blood mononuclear cell; PE = phycoerythrin; PerCP = peridinin chlorophyll protein; pTyr = phosphorylation of tyrosine; SLE = systemic lupus erythematosus; STATs = signal transducers and activators of transcription. Arthritis Research & Therapy Vol 6 No 1 Grammer et al. Introduction Engagement of surface molecules on lymphocytes initi- ates signaling cascades that change the quantity and bio- chemical nature of transcription factors that interact with DNA, thus altering gene expression and cellular function. Numerous contributions from the scientific community have yielded insights into the complex nature of the initia- tion and control of these intracellular signaling pathways. The vast majority of these studies were performed with human cell lines or genetically manipulated mice, using biochemical techniques to follow cytoplasmic events with in vitro kinase assays or Western blotting experiments with phosphospecific antibodies and nuclear events with electrophoretic mobility shift assays (EMSA) or with trans- Review Flow cytometric assessment of the signaling status of human B lymphocytes from normal and autoimmune individuals Amrie C Grammer 1 , Randy Fischer 1 , Olivia Lee 1 , Xuan Zhang 1 and Peter E Lipsky 2 1 B Cell Biology Group in the 2 Autoimmunity Branch of the Intramural Research Program of the National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, USA Corresponding author: Amrie C Grammer (email: grammera@mail.nih.gov) Received: 28 Jan 2004 Accepted: 2 Feb 2004 Published: 5 Feb 2004 Arthritis Res Ther 2004, 6:28-38 (DOI 10.1186/ar1155) © 2004 BioMed Central Ltd (Print ISSN 1478-6354; Online ISSN 1478-6362) Abstract Abnormalities in lymphocyte signaling cascades are thought to play an important role in the development of autoimmune disease. However, the large amount of cellular material needed for standard biochemical assessment of signaling status has made it difficult to evaluate putative abnormalities completely using primary lymphocytes. The development of technology to employ intracellular staining and flow cytometry to assess the signaling status of individual cells has now made it possible to delineate the perturbations that are present in lymphocytes from patients with autoimmune disease. As an example, human B cells from the Ramos B cell line and the periphery of systemic lupus erythematosus (SLE) patients or normal nonautoimmune controls were assessed for activation of the NF-κB and mitogen activated protein kinase (MAPK) signaling cascades by intracellular multiparameter flow cytometric analysis and biochemical Western blotting. In combination with fluorochrome conjugated antibodies specific for surface proteins that define B cell subsets, antibodies that recognize activated, or phosphorylated inhibitors of κB (IκB) as well as the extracellular regulated kinase (ERK), jun N-terminal kinase (JNK) or p38 MAPKs were used to stain fixed and permeabilized human B cells and analyze them flow cytometrically. Examination of the known signaling pathways following engagement of CD40 on human B cells confirmed that intracellular flow cytometry and Western blotting equivalently assay CD154- induced phosphorylation and degradation of IκB proteins as well as phosphorylation of the MAPKs ERK, JNK and p38. In addition, B cells from the periphery of SLE patients had a more activated status immediately ex vivo as assessed by intracellular flow cytometric analysis of phosphorylated ERK, JNK and p38 when compared with B cells from the periphery of normal, nonautoimmune individuals. Together, these results indicate that ... many copies of a component of the signaling cascade, which amplifies the signal Methods of Intracellular Signaling The induction of a signaling pathway depends on the modification of a cellular... residues of its target proteins, activating them in the process Akinase is found in many different types of cells, and the target proteins in each kind 4/7 Propagation of the Signal of cell are... flow into the cytoplasm, which raises the concentration of cytoplasmic Ca2+ The response to the increase in Ca2+ varies, depending on the cell type involved For example, in the β-cells of the pancreas,