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Signaling Mechanisms (signaling + mechanism)
Selected AbstractsSignaling Mechanisms in NeuronsJOURNAL OF NEUROCHEMISTRY, Issue 2003Article first published online: 26 NOV 200 First page of article [source] Insights into Serotonin Signaling Mechanisms Associated with Canine Degenerative Mitral Valve DiseaseJOURNAL OF VETERINARY INTERNAL MEDICINE, Issue 1 2010M.A. Oyama Little is known about the molecular abnormalities associated with canine degenerative mitral valve disease (DMVD). The pathology of DMVD involves the differentiation and activation of the normally quiescent mitral valvular interstitial cell (VIC) into a more active myofibroblast phenotype, which mediates many of the histological and molecular changes in affected the valve tissue. In both humans and experimental animal models, increased serotonin (5-hydroxytryptamine, 5HT) signaling can induce VIC differentiation and myxomatous valve damage. In canine DMVD, numerous lines of evidence suggest that 5HT and related molecules such as transforming growth factor-, play a critical role in the pathogenesis of this disease. A variety of investigative techniques, including gene expression, immunohistochemistry, protein blotting, and cell culture, shed light on the potential role of 5HT in the differentiation of VIC, elaboration of myxomatous extracellular matrix components, and activation of mitogen-activated protein kinase pathways. These studies help support a hypothesis that 5HT and its related pathways serve as an important stimulus in canine DMVD. This review describes the pathological characteristics of canine DMVD, the organization and role of the 5HT pathway in valve tissue, involvement of 5HT in human and experimental models of valve disease, avenues of evidence that suggest a role for 5HT in naturally occurring DMVD, and finally, a overarching hypothesis describing a potential role for 5HT in canine DMVD. [source] Apoptotic and Anti-Apoptotic Synaptic Signaling MechanismsBRAIN PATHOLOGY, Issue 2 2000Mark P. Mattson Although several prominent morphological features of apoptosis are evident in the cell body (e.g., cell shrinkage, membrane blebbing, and nuclear DNA condensation and fragmentation) the biochemical and molecular cascades that constitute the cell death machinery can be engaged in synaptic terminals and neurites. Initiating events such as oxyradical production and calcium influx, and effector processes such as Par-4 production, mitochondrial alterations and caspase activation, can be induced in synapses and neurites. Several prominent signal transduction pathways in synaptic terminals play important roles in either promoting or preventing neuronal death in physiological and pathological conditions. For example, activation of glutamate receptors in postsynaptic spines can induce neuronal apoptosis, whereas local activation of neurotrophic factor receptors in presynaptic terminals can prevent neuronal death. Factors capable of inducing nuclear chromatin condensation and fragmentation can be produced locally in synaptic terminals and neurites, and may propogate to the cell body. Recent findings suggest that, beyond their roles in inducing or preventing cell death, apoptotic and anti-apoptotic cascades play roles in synaptic plasticity (structural remodelling and long-term functional changes). For example, caspase activation results in proteolysis of glutamate receptor (AMPA) subunits, which results in altered neuronal responsivity to glutamate. Activation of neurotrophic factor receptors in synaptic terminals can result in local changes in energy metabolism and calcium homeostasis, and can induce long-term changes in synaptic transmission. The emerging data therefore suggest that synapses can be considered as autonomous compartments in which both pro- and anti-apoptotic signaling pathways are activated resulting in structural and functional changes in neuronal circuits. A better understanding of such synaptic signaling mechanisms may reveal novel approaches for preventing and treating an array of neurodegenerative conditions that are initiated by perturbed synaptic homeostasis. [source] Signaling mechanisms in skeletal muscle: Acute responses and chronic adaptations to exerciseIUBMB LIFE, Issue 3 2008Katja S.C. Röckl Abstract Physical activity elicits physiological responses in skeletal muscle that result in a number of health benefits, in particular in disease states, such as type 2 diabetes. An acute bout of exercise/muscle contraction improves glucose homeostasis by increasing skeletal muscle glucose uptake, while chronic exercise training induces alterations in the expression of metabolic genes, such as those involved in muscle fiber type, mitochondrial biogenesis, or glucose transporter 4 (GLUT4) protein levels. A primary goal of exercise research is to elucidate the mechanisms that regulate these important metabolic and transcriptional events in skeletal muscle. In this review, we briefly summarize the current literature describing the molecular signals underlying skeletal muscle responses to acute and chronic exercise. The search for possible exercise/contraction-stimulated signaling proteins involved in glucose transport, muscle fiber type, and mitochondrial biogenesis is ongoing. Further research is needed because full elucidation of exercise-mediated signaling pathways would represent a significant step toward the development of new pharmacological targets for the treatment of metabolic diseases such as type 2 diabetes. © 2008 IUBMB IUBMB Life, 60(3): 145,153, 2008 [source] Signaling mechanisms that regulate actin-based motility processes in the nervous systemJOURNAL OF NEUROCHEMISTRY, Issue 3 2002Gary Meyer Abstract Actin-based motility is critical for nervous system development. Both the migration of neurons and the extension of neurites require organized actin polymerization to push the cell membrane forward. Numerous extracellular stimulants of motility and axon guidance cues regulate actin-based motility through the rho GTPases (rho, rac, and cdc42). The rho GTPases reorganize the actin cytoskeleton, leading to stress fiber, filopodium, or lamellipodium formation. The activity of the rho GTPases is regulated by a variety of proteins that either stimulate GTP uptake (activation) or hydrolysis (inactivation). These proteins potentially link extracellular signals to the activation state of rho GTPases. Effectors downstream of the rho GTPases that directly influence actin polymerization have been identified and are involved in neurite development. The Arp2/3 complex nucleates the formation of new actin branches that extend the membrane forward. Ena/VASP proteins can cause the formation of longer actin filaments, characteristic of growth cone actin morphology, by preventing the capping of barbed ends. Actin-depolymerizing factor (ADF)/cofilin depolymerizes and severs actin branches in older parts of the actin meshwork, freeing monomers to be re-incorporated into actively growing filaments. The signaling mechanisms by which extracellular cues that guide axons to their targets lead to direct effects on actin filament dynamics are becoming better understood. [source] Signaling mechanisms of melatonin in antiproliferation of hormone-refractory 22Rv1 human prostate cancer cells: implications for prostate cancer chemopreventionJOURNAL OF PINEAL RESEARCH, Issue 2 2007Chun W. Tam Abstract:, There is an unmet clinical demand for safe and effective pharmaceuticals/nutraceuticals for prostate cancer prevention and hormone-refractory prostate cancer treatment. Previous laboratory and human studies of our laboratory demonstrated an association between the antiproliferative action of melatonin and melatonin MT1 receptor expression in prostate cancer. The aim of this study was to determine, using a pharmacological approach, the signaling mechanisms of melatonin in hormone-refractory 22Rv1 human prostate cancer cell antiproliferation. Both immunoreactive MT1 and MT2 subtypes of G protein-coupled melatonin receptor were expressed in 22Rv1 cells. Melatonin inhibited, concentration dependently, cell proliferation, upregulated p27Kip1 gene transcription and protein expression, and downregulated activated androgen signaling in 22Rv1 cells. While the effects of melatonin were mimicked by 2-iodomelatonin, a high-affinity nonselective MT1 and MT2 receptor agonist, melatonin effects were blocked by luzindole, a nonselective MT1 and MT2 receptor antagonist, but were unaffected by 4-phenyl-2-propionamidotetraline, a selective MT2 receptor antagonist. Importantly, we discovered that the antiproliferative effect of melatonin exerted via MT1 receptor on p27Kip1 gene and protein upregulation is mediated by a novel signaling mechanism involving co-activation of protein kinase C (PKC) and PKA in parallel. Moreover, we also showed that a melatonin/MT1/PKC mechanism is involved in melatonin-induced downregulation of activated androgen signal transduction in 22Rv1 cells. Taken together with the known molecular mechanisms of prostate cancer progression and transition to androgen independence, our data provide strong support for melatonin to be a promising small-molecule useful for prostate cancer primary prevention and secondary prevention of the development and progression of hormone refractoriness. [source] Angiopoietin Affects Neutrophil MigrationMICROCIRCULATION, Issue 5 2005DANIEL H. STURN ABSTRACT Objective: After an ischemic event vascular growth factors are involved in regulating leukocyte infiltration in inflammatory processes. This study focused on effects of 2 other angiogenic growth factors, angiopoietin-1 and angiopoietin-2, on human neutrophils and on the involvement of the angiopoietin receptor Tie-2. Methods: Neutrophils were from venous blood of healthy donors and cell migration was studied by micropore filter assays. Receptor expression was investigated by reverse transcriptase,polymerase chain reaction (PCR) for mRNA and fluorescence-activated cell-sorter scanner (FACS) analysis. Signaling mechanisms required for angiopoietin-dependent effects were tested functionally by using signaling enzyme blockers. Results: The angiopoietins were chemotactic for neutrophils. They showed antagonistic effects on each other and both inhibited VEGF-directed migration of neutrophils. The effects of both angiopoietins were Tie-2 dependent. Tie-2 receptor immunoreactivity was confirmed on neutrophils by FACS. De novo synthesis is suggested by Tie-2 receptor mRNA expression as demonstrated by reverse transcriptase PCR. Conclusions: Data suggest that a Tie-2 receptor is expressed by human neutrophils whose active site ligation with either angiopoietin-1 or angiopoietin-2 exerts migratory effects on the one hand and arrests VEGF-mediated chemotaxis on the other. These effects suggest a role of angiopoietins in modulating neutrophilic inflammation. [source] Derailed regulates development of the Drosophila neuromuscular junctionDEVELOPMENTAL NEUROBIOLOGY, Issue 2 2008Faith L.W. Liebl Abstract Neural function is dependent upon the proper formation and development of synapses. We show here that Wnt5 regulates the growth of the Drosophila neuromuscular junction (NMJ) by signaling through the Derailed receptor. Mutations in both wnt5 and drl result in a significant reduction in the number of synaptic boutons. Cell-type specific rescue experiments show that wnt5 functions in the presynaptic motor neuron while drl likely functions in the postsynaptic muscle cell. Epistatic analyses indicate that drl acts downstream of wnt5 to promote synaptic growth. Structure,function analyses of the Drl protein indicate that normal synaptic growth requires the extracellular Wnt inhibitory factor domain and the intracellular domain, which includes an atypical kinase. Our findings reveal a novel signaling mechanism that regulates morphology of the Drosophila NMJ. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2008 [source] Mini-review SAP: a molecular switch regulating the immune response through a unique signaling mechanismEUROPEAN JOURNAL OF IMMUNOLOGY, Issue 5 2003André Veillette Abstract No Abstracts [source] Unit initial public offerings: Staged equity or signaling mechanism?ACCOUNTING & FINANCE, Issue 1 2003Martin Lee We investigate the use of unit (i.e., package) initial public offerings by Australian industrial firms and conclude that their use reflects their role as a signaling mechanism (Chemmanur and Fulghieri, 1997), as distinct from the agency,cost explanation offered by Schultz (1993). From a sample of 394 IPOs between 1976 and 1994, the 66 firms making unit offerings are typically riskier, use less prestigious underwriters and have a lower level of retained ownership than other IPO firms. While these results are also consistent with Schultz's agency cost explanation, other results we report are not. We find no difference in underpricing etween unit IPOs and other IPO firms, nor are there any significant differences in the planned uses of proceeds reported in the prospectus, post,listing failure rates or secondary equity offerings of the type predicted by Schultz. We do however, report evidence consistent with a prediction unique to the signaling explanation. After controlling for the level of ownership retained by insiders, the proportion of firm value sold as warrants is increasing in IPO firms' riskiness. [source] Strength of signal: a fundamental mechanism for cell fate specificationIMMUNOLOGICAL REVIEWS, Issue 1 2006Sandra M. Hayes Summary:, How equipotent cells develop into complex tissues containing many diverse cell types is still a mystery. However, evidence is accumulating from different tissue systems in multiple organisms that many of the specific receptor families known to regulate cell fate decisions target conserved signaling pathways. A mechanism for preserving specificity in the cellular response that has emerged from these studies is one in which quantitative differences in receptor signaling regulate the cell fate decision. A signal strength model has recently gained support as a means to explain ,,/,, lineage commitment. In this review, we compare the ,,/,, fate decision with other cell fate decisions that occur outside of the lymphoid system to attain a better picture of the quantitative signaling mechanism for cell fate specification. [source] TGF-, inhibits prolactin-induced expression of ,-casein by a Smad3-dependent mechanism,JOURNAL OF CELLULAR BIOCHEMISTRY, Issue 5 2008Wen-Jun Wu Abstract Transforming growth factor-, (TGF-,) is a multifunctional growth factor, affecting cell proliferation, apoptosis, and extracellular matrix homeostasis. It also plays critical roles in mammary gland development, one of which involves inhibition of the expression of milk proteins, such as ,-casein, during pregnancy. Here we further explore the underlying signaling mechanism for it. Our results show that TGF-, suppresses prolactin-induced expression of ,-casein mRNA and protein in primary mouse mammary epithelial cells, but its effect on protein expression is more evident. We also find out that this inhibition is not due to the effect of TGF-, on cell apoptosis. Furthermore, inhibition of TGF-, type I receptor kinase activity by a pharmacological inhibitor SB431542 or overexpression of dominant negative Smad3 substantially restores ,-casein expression. By contrast, inhibition of p38 and Erk that are known to be activated by TGF-, does not alleviate the inhibitory effect of TGF-,. These results are consistent with our other observation that Smad but not MAPK pathway is activated by TGF-, in mammary epithelial cells. Lastly, we show that prolactin-induced tyrosine phosphorylation of Jak2 and Stat5 as well as serine/threonine phosphorylation of p70S6K and S6 ribosomal protein are downregulated by TGF-,, although the former event requires considerably long exposure to TGF-,. We speculate that these events might be involved in repressing transcription and translation of ,-casein gene, respectively. Taken together, our results demonstrate that TGF-, abrogates prolactin-stimulated ,-casein gene expression in mammary epithelial cells through, at least in part, a Smad3-dependent mechanism. J. Cell. Biochem. 104: 1647,1659, 2008. © 2008 Wiley-Liss, Inc. [source] Integrative nuclear FGFR1 signaling (INFS) as a part of a universal "feed-forward-and-gate" signaling module that controls cell growth and differentiationJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 4 2003Michal K. Stachowiak Abstract A novel signaling mechanism is described through which extracellular signals and intracellular signaling pathways regulate proliferation, growth, differentiation, and other functions of cells in the nervous system. Upon cell stimulation, fibroblast growth factor receptor-1 (FGFR1), a typically plasma membrane-associated protein, is released from ER membranes into the cytosol and translocates to the cell nucleus by an importin-,-mediated transport pathway along with its ligand, FGF-2. The nuclear accumulation of FGFR1 is activated by changes in cell contacts and by stimulation of cells with growth factors, neurotransmitters and hormones as well as by a variety of different second messengers and thus was named integrative nuclear FGFR1 signaling (INFS). In the nucleus, FGFR1 localizes specifically within nuclear matrix-attached speckle-domains, which are known to be sites for RNA Pol II-mediated transcription and co-transcriptional pre-mRNA processing. In these domains, nuclear FGFR1 colocalizes with RNA transcription sites, splicing factors, modified histones, phosphorylated RNA Pol II, and signaling kinases. Within the nucleus, FGFR1 serves as a general transcriptional regulator, as indicated by its association with the majority of active nuclear centers of RNA synthesis and processing, by the ability of nuclear FGFR1 to activate structurally distinct genes located on different chromosomes and by its stimulation of multi-gene programs for cell growth and differentiation. We propose that FGFR1 is part of a universal "feed-forward-and-gate" signaling module in which classical signaling cascades initiated by specific membrane receptors transmit signals to sequence specific transcription factors (ssTFs), while INFS elicited by the same stimuli feeds the signal forward to the common coactivator, CREB-binding protein (CBP). Activation of CBP by INFS, along with the activation of ssTFs by classical signaling cascades brings about coordinated responses from structurally different genes located at different genomic loci. © 2003 Wiley-Liss, Inc. [source] Cactus-independent nuclear translocation of Drosophila RELISHJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 1 2001William D. Cornwell Abstract Insects can effectively and rapidly clear microbial infections by a variety of innate immune responses including the production of antimicrobial peptides. Induction of these antimicrobial peptides in Drosophila has been well established to involve NF-,B elements. We present evidence here for a molecular mechanism of Lipopolysaccharide (LPS)-induced signaling involving Drosophila NF-,B, RELISH, in Drosophila S2 cells. We demonstrate that LPS induces a rapid processing event within the RELISH protein releasing the C-terminal ankyrin-repeats from the N-terminal Rel homology domain (RHD). Examination of the cellular localization of RELISH reveals that the timing of this processing coincides with the nuclear translocation of the RHD and the retention of the ankyrin-repeats within the cytoplasm. Both the processing and the nuclear translocation immediately precede the expression of antibacterial peptide genes cecropin A1, attacin, and diptericin. Over-expression of the RHD but not full-length RELISH results in an increase in the promoter activity of the cecropin A1 gene in the absence of LPS. Furthermore, the LPS-induced expression of these antibacterial peptides is greatly reduced when RELISH expression is depleted via RNA-mediated interference. In addition, loss of cactus expression via RNAi revealed that RELISH activation and nuclear translocation is not dependent on the presence of cactus. Taken together, these results suggest that this signaling mechanism involving the processing of RELISH followed by nuclear translocation of the RHD is central to the induction of at least part of the antimicrobial response in Drosophila, and is largely independent of cactus regulation. J. Cell. Biochem. 82: 22,37, 2001. © 2001 Wiley-Liss, Inc. [source] Ras-mediated intestinal epithelial cell transformation requires cyclooxygenase-2-induced prostaglandin E2 signalingMOLECULAR CARCINOGENESIS, Issue 12 2007Gretchen A. Repasky Abstract Ras-mediated transformation is associated with upregulation of cyclooxygenase-2 (COX-2), which in turn promotes prostaglandin E2 (PGE2) synthesis and secretion. Although recent studies have identified molecular mechanisms by which Ras mediates upregulation of COX-2, conflicting observations have been made. Furthermore, while COX-2 upregulation has been shown to be important for Ras transformation, the signaling pathways initiated by PGE2 -stimulation of EP family of heterotrimeric G protein-coupled receptors (GPCR) and contribution of PGE2 signaling to Ras-mediated transformation are issues that remain unresolved. In this study, we first determined that Raf effector pathway activation of the extracellular-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) cascade alone was sufficient and necessary for COX-2 and PGE2 upregulation. However, Raf-independent regulation of the c- jun N-terminal kinase (JNK) and p38 MAPK cascades is also involved in COX-2 and PGE2 upregulation, with the JNK and p38 pathways exhibiting opposing roles in COX-2 and PGE2 upregulation. Furthermore, in contrast to previous studies, we found that an epidermal growth factor (EGF) receptor autocrine growth mechanism, another Raf-independent signaling mechanism, was necessary for COX-2 and PGE2 upregulation. Second, we determined that inhibition of EP1/2 receptor function blocked growth transformation by Ras, demonstrating that PGE2 upregulation is a key transforming function of COX-2. Finally, we found that PGE2 stimulated the activation of Ras and ERK, but not Akt, and reduced matrix deprivation-induced apoptosis, in untransformed epithelial cells. In summary, our studies define additional, multiple signaling mechanisms that promote COX-2 and PGE2 expression and show that COX-2-stimulated PGE2 -EP receptor signaling is required for growth and survival transformation by Ras. © 2007 Wiley-Liss, Inc. [source] Thermodynamic characterization of two homologous protein complexes: Associations of the semaphorin receptor plexin-B1 RhoGTPase binding domain with Rnd1 and active Rac1PROTEIN SCIENCE, Issue 5 2009Prasanta K. Hota Abstract Plexin receptors function in response to semaphorin guidance cues in a variety of developmental processes involving cell motility. Interactions with Rho, as well as Ras family small GTPases are critical events in the cell signaling mechanism. We have recently determined the structure of a cytoplasmic domain (RBD) of plexin-B1 and mapped its binding interface with several Rho-GTPases, Rac1, Rnd1, and RhoD. All three GTPases associate with a similar region of this plexin domain, but show different functional behavior in cells. To understand whether thermodynamic properties of the GTPase,RBD interaction contribute to such different behavior, we have examined the interaction at different temperatures, buffer, and pH conditions. Although the binding affinity of both Rnd1 and Rac1 with the plexin-B1 RBD is similar, the detailed thermodynamic properties of the interactions are considerably different. These data suggest that on Rac1 binding to the plexin-B1 RBD, the proteins become more rigid in the complex. By contrast, Rnd1 binding is consistent with unchanged or slightly increased flexibility in one or both proteins. Both GTPases show an appreciable reduction in affinity for the dimeric plexin-B1 RBD indicating that GTPase binding is not cooperative with dimer formation, but that a partial steric hindrance destabilizes the dimer. However, a reduced affinity binding mode to a disulphide stabilized model for the dimeric RBD is also possible. Consistent with cellular studies, the interaction thermodynamics imply that further levels of regulation involving additional binding partners and/or regions outside of the RhoGTPase binding domain are required for receptor activation. [source] Cellular patterns in the inner retina of adult zebrafish: Quantitative analyses and a computational model of their formationTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 1 2004David A. Cameron Abstract The mechanisms that control cellular pattern formation in the growing vertebrate central nervous system are poorly understood. In an effort to reveal mechanistic rules of cellular pattern formation in the central nervous system, quantitative spatial analysis and computational modeling techniques were applied to cellular patterns in the inner retina of the adult zebrafish. All the analyzed cell types were arrayed in nonrandom patterns tending toward regularity; specifically, they were locally anticlustered. Over relatively large spatial scales, only one cell type exhibited consistent evidence for pattern regularity, suggesting that cellular pattern formation in the inner retina is dominated by local anticlustering mechanisms. Cross-correlation analyses revealed independence between the patterns of different cell types, suggesting that cellular pattern formation may involve multiple, independent, homotypic anticlustering mechanisms. A computational model of cellular pattern formation in the growing zebrafish retina was developed, which featured an inhibitory, homotypic signaling mechanism, arising from differentiated cells, that controlled the spatial profile of cell fate decisions. By adjusting the spatial profile of this decaying-exponential signal, the model provided good estimates of all the cellular patterns that were observed in vivo, as objectively judged by quantitative spatial pattern analyses. The results support the hypothesis that cellular pattern formation in the inner retina of zebrafish is dominated by a set of anticlustering mechanisms that may control events at, or near, the spatiotemporal point of cell fate decision. J. Comp. Neurol. 471:11,25, 2004. © 2004 Wiley-Liss, Inc. [source] 1.8 Ĺ structure of murine GITR ligand dimer expressed in Drosophila melanogaster S2 cellsACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2009Kausik Chattopadhyay Glucocorticoid-induced TNF receptor ligand (GITRL), a prominent member of the TNF superfamily, activates its receptor on both effector and regulatory T cells to generate critical costimulatory signals that have been implicated in a wide range of T-cell immune functions. The crystal structures of murine and human orthologs of GITRL recombinantly expressed in Escherichia coli have previously been determined. In contrast to all classical TNF structures, including the human GITRL structure, murine GITRL demonstrated a unique `strand-exchanged' dimeric organization. Such a novel assembly behavior indicated a dramatic impact on receptor activation as well as on the signaling mechanism associated with the murine GITRL costimulatory system. In this present work, the 1.8,Ĺ resolution crystal structure of murine GITRL expressed in Drosophila melanogaster S2 cells is reported. The eukaryotic protein-expression system allows transport of the recombinant protein into the extracellular culture medium, thus maximizing the possibility of obtaining correctly folded material devoid of any folding/assembly artifacts that are often suspected with E. coli -expressed proteins. The S2 cell-expressed murine GITRL adopts an identical `strand-exchanged' dimeric structure to that observed for the E. coli -expressed protein, thus conclusively demonstrating the novel quaternary structure assembly behavior of murine GITRL. [source] Sex steroids, ANGELS and osteoporosisBIOESSAYS, Issue 3 2003Jonathan G. Moggs Osteoporosis is characterized by reduced bone density and strength. Bone mass peaks between age 30 and 40 and then declines. This can be accelerated by factors including menopause and insufficient dietary calcium. Hormone replacement therapy (HRT) is currently the standard treatment for osteoporosis. However, growing concern over potential side effects of HRT has driven a search for alternative therapies. A recent report1 reveals a potential alternative to HRT: a gender-neutral synthetic steroid that increases bone mass and strength without affecting reproductive organs. This compound acts via a novel extranuclear sex steroid receptor signaling mechanism that has important implications for nuclear receptor biology and human health. BioEssays 25:195,199, 2003. © 2003 Wiley Periodicals, Inc. [source] ,-Dystroglycan is essential for the induction of Egr3, a transcription factor important in muscle spindle formationDEVELOPMENTAL NEUROBIOLOGY, Issue 7 2010Stacey Williams Abstract Muscle spindle fibers are specialized stretch receptors that allow the perception and coordination of limb movement. The differentiation of these specialized structures is initiated by signals derived from the in growing Ia sensory neurons during development. While the direct molecular signaling mechanisms between sensory neurons and developing muscle at nascent spindle fibers have been well documented in past studies the roles of muscle basal lamina components on this process have not previously been described. As such, our initial experiments addressed potential roles for agrin (AGRN) and laminin (LN) in the expression of the transcription factor Egr3. Levels of Egr3 were monitored using immunoblot analysis and both basal lamina molecules proved effective in inducing Erg3 expression. Previous work had established neuregulin (NRG) as a critical signaling component in spindle fiber development so blocking experiments with NRG and ErbB inhibitors were then used to determine if LN-induced Egr3 expression was occurring as a result of NRG-ErbB signaling and not via other, novel pathway. Inhibiting signaling through this pathway did indeed reduce the expression of Egr3. Finally, we looked at ,-dystrogylcan, a shared receptor for AGRN and LN at neuromuscular junctions. Using a ,-dystroglycan (,-DG) silenced muscle cell line and an anti-,-DG antibody we attempted to block basal lamina/,-DG interactions. Again, and in both instances, Egr3 expression was significantly decreased. Taken together, analysis of the results from these experiments revealed that indeed AGRN, LN, and ,-DG influence Egr3 levels and therefore may play an important role in spindle fiber differentiation. © 2010 Wiley Periodicals, Inc. Develop Neurobiol 70:498,507, 2010 [source] High-resolution imaging demonstrates dynein-based vesicular transport of activated trk receptorsDEVELOPMENTAL NEUROBIOLOGY, Issue 4 2002Anita Bhattacharyya Abstract Target-derived neurotrophins signal from nerve endings to the cell body to influence cellular and nuclear responses. The retrograde signal is conveyed by neurotrophin receptors (Trks) themselves. To accomplish this, activated Trks may physically relocalize from nerve endings to the cell bodies. However, alternative signaling mechanisms may also be used. To identify the vehicle wherein the activated Trks are located and transported, and to identify associated motor proteins that would facilitate transport, we use activation-state specific antibodies in concert with immunoelectron microscopy and deconvolution microscopy. We show that the activated Trks within rat sciatic nerve axons are preferentially localized to coated and uncoated vesicles. These vesicles are moving in a retrograde direction and so accumulate distal to a ligation site. The P-Trk containing vesicles, in turn, colocalize with dynein components, and not with kinesins. Collectively, these results indicate activated Trk within axons travel in vesicles and dynein is the motor that drives these vesicles towards the cell bodies. © 2002 Wiley Periodicals, Inc. J Neurobiol 51: 302,312, 2002 [source] Metabolic gene switching in the murine female heart parallels enhanced mitochondrial respiratory function in response to oxidative stressFEBS JOURNAL, Issue 20 2007M. Faadiel Essop The mechanisms underlying increased cardioprotection in younger female mice are unclear. We hypothesized that serine-threonine protein kinase (protein kinase B; Akt) triggers a metabolic gene switch (decreased fatty acids, increased glucose) in female hearts to enhance mitochondrial bioenergetic capacity, conferring protection against oxidative stress. Here, we employed male and female control (db/+) and obese (db/db) mice. We found diminished transcript levels of peroxisome proliferator-activated receptor-alpha, muscle-type carnitine palmitoyltransferase 1 and pyruvate dehydrogenase kinase 4 in female control hearts versus male hearts. Moreover, females displayed improved recovery of cardiac mitochondrial respiratory function and higher ATP levels versus males in response to acute oxygen deprivation. All these changes were reversed in female db/db hearts. However, we found no significant gender-based differences in levels of Akt, suggesting that Akt-independent signaling mechanisms are responsible for the resilient mitochondrial phenotype observed in female mouse hearts. As glucose is a more energetically efficient fuel substrate when oxygen is limiting, this gene program may be a crucial component that enhances tolerance to oxygen deprivation in female hearts. [source] Activation of p21-activated kinase 1 is required for lysophosphatidic acid-induced focal adhesion kinase phosphorylation and cell motility in human melanoma A2058 cellsFEBS JOURNAL, Issue 8 2004In Duk Jung Lysophosphatidic acid (LPA), one of the naturally occurring phospholipids, stimulates cell motility through the activation of Rho family members, but the signaling mechanisms remain to be elucidated. In the present study, we investigated the roles of p21-activated kinase 1 (PAK1) on LPA-induced focal adhesion kinase (FAK) phosphorylation and cell motility. Treatment of human melanoma cells A2058 with LPA increased phosphorylation and activation of PAK1, which was blocked by treatment with pertussis toxin and by inhibition of phosphoinositide 3-kinase (PI3K) with an inhibitor LY294002 or by overexpression of catalytically inactive mutant of PI3K,, indicating that LPA-induced PAK1 activation was mediated via a Gi protein and the PI3K, signaling pathway. In addition, we demonstrated that Rac1/Cdc42 signals acted as upstream effector molecules of LPA-induced PAK activation. However, Rho-associated kinase, MAP kinase kinase 1/2 or phospholipase C might not be involved in LPA-induced PAK1 activation or cell motility stimulation. Furthermore, PAK1 was necessary for FAK phosphorylation by LPA, which might cause cell migration, as transfection of the kinase deficient mutant of PAK1 or PAK auto-inhibitory domain significantly abrogated LPA-induced FAK phosphorylation. Taken together, these findings strongly indicated that PAK1 activation was necessary for LPA-induced cell motility and FAK phosphorylation that might be mediated by sequential activation of Gi protein, PI3K, and Rac1/Cdc42. [source] Characterization of a Novel Fiber Composite Material for Mechanotransduction Research of Fibrous Connective TissuesADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Hazel R. C. Screen Abstract Mechanotransduction is the fundamental process by which cells detect and respond to their mechanical environment, and is critical for tissue homeostasis. Understanding mechanotransduction mechanisms will provide insights into disease processes and injuries, and may support novel tissue engineering research. Although there has been extensive research in mechanotransduction, many pathways remain unclear, due to the complexity of the signaling mechanisms and loading environments involved. This study describes the development of a novel hydrogel-based fiber composite material for investigating mechanotransduction in fibrous tissues. By encapsulating poly(2-hydroxyethyl methacrylate) rods in a bulk poly(ethylene glycol) matrix, it aims to create a micromechanical environment more representative of that seen in vivo. Results demonstrated that collagen-coated rods enable localized cell attachment, and cells are successfully cultured for one week within the composite. Mechanical analysis of the composite indicates that gross mechanical properties and local strain environments could be manipulated by altering the fabrication process. Allowing diffusion between the rods and surrounding matrix creates an interpenetrating network whereby the relationships between shear and tension are altered. Increasing diffusion enhances the shear bond strength between rods and matrix and the levels of local tension along the rods. Preliminary investigation into fibroblast mechanotransduction illustrates that the fiber composite upregulates collagen I expression, the main protein in fibrous tissues, in response to cyclic tensile strains when compared to less complex 2D and 3D environments. In summary, the ability to create and manipulate a strain environment surrounding the fibers, where combined tensile and shear forces uniquely impact cell functions, is demonstrated. [source] Fibroblast growth factor 23 reduces expression of type IIa Na+/Pi co-transporter by signaling through a receptor functionally distinct from the known FGFRs in opossum kidney cellsGENES TO CELLS, Issue 5 2005Xiaomei Yan Fibroblast growth factor (FGF) 23 is an important phosphaturic factor that inhibits inorganic phosphate (Pi) reabsorption from the renal proximal tubule. Its overproduction and proteolysis-resistant mutation such as R179Q cause tumor-induced osteomalacia and autosomal dominant hypophosphatemic rickets, respectively. To clarify the signaling mechanisms of FGF23 that mediate the reduction of Pi reabsorption, we inhibited the function of the known FGFRs in opossum kidney (OK-E) cells by expressing a dominant-negative (DN) form of FGFR. OK-E cells, which represent the renal proximal tubular cells, expressed all four known FGFRs. FGF23(R179Q) bound to and activated FGFR2, a prominent FGFR expressed in OK-E cells. The activated receptor transmitted a signal to increase the expression of type IIa Na+/Pi co-transporter and the Pi uptake. Expression of FGFR2(DN), which suppresses the major FGFR-mediated signal through the FRS2,-ERK pathway, reversed the function of FGF23(R179Q). When FGF23(R179Q) was applied to the basolateral side of polarized OK-E cells, regardless of the FGFR2(DN) expression, the apical Pi uptake decreased significantly. The apical application of FGF23(R179Q) in the polarized cells did not show such decrease but increase. The exogenously expressed FGFR2 was detectable only at the apical membrane. These results suggest that an FGF23 receptor, which is functionally distinct from the known FGFRs, is expressed at the basolateral membrane of OK-E cells. [source] TLR3-mediated signal induces proinflammatory cytokine and chemokine gene expression in astrocytes: Differential signaling mechanisms of TLR3-induced IP-10 and IL-8 gene expressionGLIA, Issue 3 2006Chanhee Park Abstract Viral infection is one of the leading causes of brain encephalitis and meningitis. Recently, it was reported that Toll-like receptor-3 (TLR3) induces a double-stranded RNA (dsRNA)-mediated inflammatory signal in the cells of the innate immune system, and studies suggested that dsRNA may induce inflammation in the central nervous system (CNS) by activating the CNS-resident glial cells. To explore further the connection between dsRNA and inflammation in the CNS, we have studied the effects of dsRNA stimulation in astrocytes. Our results show that the injection of polyinosinic-polycytidylic acid (poly(I:C)), a synthetic dsRNA, into the striatum of the mouse brain induces the activation of astrocytes and the expression of TNF-,, IFN-,, and IP-10. Stimulation with poly(I:C) also induces the expression of these proinflammatory genes in primary astrocytes and in CRT-MG, a human astrocyte cell line. Furthermore, our studies on the intracellular signaling pathways reveal that poly(I:C) stimulation activates I,B kinase (IKK), extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK) in CRT-MG. Pharmacological inhibitors of nuclear factor-,B (NF-,B), JNK, ERK, glycogen synthase kinase-3, (GSK-3,), and dsRNA-activated protein kinase (PKR) inhibit the expression of IL-8 and IP-10 in astrocytes, indicating that the activation of these signaling molecules is required for the TLR3-mediated chemokine gene induction. Interestingly, the inhibition of PI3 kinase suppressed the expression of IP-10, but upregulated the expression of IL-8, suggesting differential roles for PI3 kinase, depending on the target genes. These data suggest that the TLR3 expressed on astrocytes may initiate an inflammatory response upon viral infection in the CNS. © 2005 Wiley-Liss, Inc. [source] Gangliosides activate microglia via protein kinase C and NADPH oxidaseGLIA, Issue 3 2004Kyoung-Jin Min Abstract Microglia, the major immune effector cells in the central nervous system, are activated when the brain suffers injury. A number of studies indicate that gangliosides activate microglia. However, the signaling mechanisms involved in microglial activation are not yet to be elucidated. Our results show that gangliosides induce the expression of interleukin (IL)-1,, tumor necrosis factor-, (TNF-,), and inducible nitric oxide synthase (iNOS) in rat brain microglia and BV2 murine microglia via protein kinase C (PKC) and NADPH oxidase. Expression of IL-1,, TNF-,, and iNOS in ganglioside-treated cells was significantly reduced in the presence of inhibitors of PKC (GF109203X, Gö6976, Ro31-8220, and rottlerin) and NADPH oxidase (diphenyleneiodonium chloride [DPI]). In response to gangliosides, PKC-,, ,II, and , and NADPH oxidase p67phox translocated from the cytosol to the membrane. ROS generation was also activated within 5 min of ganglioside treatment. Ganglioside-induced ROS generation was blocked by PKC inhibitors. Furthermore, ganglioside-induced activation of NF-,B, an essential transcription factor that mediates the expression of IL-1,, TNF-,, and iNOS, was reduced in the presence of GF109203X and DPI. Our results collectively suggest that gangliosides activate microglia via PKC and NADPH oxidase, which regulate activation of NF-,B. © 2004 Wiley-Liss, Inc. [source] Long-term modulation of glucose utilization by IL-1, and TNF-, in astrocytes: Na+ pump activity as a potential target via distinct signaling mechanismsGLIA, Issue 1 2002Céline Véga Abstract Interleukin-1, (IL-1,) and tumor necrosis factor-, (TNF-,) markedly stimulate glucose utilization in primary cultures of mouse cortical astrocytes. The mechanism that gives rise to this effect, which takes place several hours after application of cytokine, has remained unclear. Experiments were conducted to identify the major signaling cascades involved in the metabolic action of cytokine. First, the selective IL-1 receptor antagonist (IL-1ra) prevents the effect of IL-1, on glucose utilization in a concentration-dependent manner, whereas it has no effect on the action of TNF-,. Then, using inhibitors of three classical signaling cascades known to be activated by cytokines, it appears that the PI3 kinase is essential for the effect of both IL-1, and TNF-,, whereas the action of IL-1, also requires activation of the MAP kinase pathway. Participation of a phospholipase C-dependent pathway does not appear critical for both IL-1, and TNF-,. Inhibition of NO synthase by L-NAME did not prevent the metabolic response to both IL-1, and TNF-,, indicating that nitric oxide is probably not involved. In contrast, the Na+/K+ ATPase inhibitor ouabain prevents the IL-1,- and TNF-,-stimulated 2-deoxyglucose (2DG) uptake. When treatment of astrocytes with a cytokine was followed 24 h later by an acute application of glutamate, a synergistic enhancement in glucose utilization was observed. This effect was greatly reduced by ouabain. These data suggest that Na+ pump activity is a common target for both the long-term metabolic action of cytokines promoted by the activation of distinct signaling pathways and the enhanced metabolic response to glutamate. GLIA 39:10,18, 2002. © 2002 Wiley-Liss, Inc. [source] A novel mechanism for mitogenic signaling via pro,transforming growth factor , within hepatocyte nucleiHEPATOLOGY, Issue 6 2002Bettina Grasl-Kraupp Transforming growth factor (TGF) ,, an important mediator of growth stimulation, is known to act via epidermal growth factor receptor (EGF-R) binding in the cell membrane. Here we show by immunohistology, 2-dimensional immunoblotting, and mass spectrometry of nuclear fractions that the pro-protein of wild-type TGF-, occurs in hepatocyte nuclei of human, rat, and mouse liver. Several findings show a close association between nuclear pro-TGF-, and DNA synthesis. (1) The number of pro-TGF-,+ nuclei was low in resting liver and increased dramatically after partial hepatectomy and after application of hepatotoxic chemicals or the primary mitogen cyproterone acetate (CPA); in any case, S phase occurred almost exclusively in pro-TGF-,+ nuclei. The same was found in human cirrhotic liver. (2) In primary culture, 7% of hepatocytes synthesized pro-TGF-,, which then translocated to the nucleus; 70% of these nuclei subsequently entered DNA replication, whereas only 2% of pro-TGF-,, hepatocytes were in S phase. (3) The frequency of hepatocytes coexpressing pro-TGF-, and DNA synthesis was increased by the hepatomitogens CPA or prostaglandin E2 and was decreased by the growth inhibitor TGF-,1. (4) Treatment with mature TGF-, increased DNA synthesis exclusively in pro-TGF-,, hepatocytes, which was abrogated by the EGF-R tyrosine kinase inhibitor tyrphostin A25. In conclusion, TGF-, gene products may exert mitogenic effects in hepatocytes via 2 different signaling mechanisms: (1) the "classic" pathway of mature TGF-, via EGF-R in the membrane and (2) a novel pathway involving the presence of pro-TGF-, in the nucleus. [source] Activation of eNOS in rat portal hypertensive gastric mucosa is mediated by TNF-, via the PI 3-kinase,Akt signaling pathwayHEPATOLOGY, Issue 2 2002Hirofumi Kawanaka Activation of endothelial nitric oxide synthase (eNOS) in portal hypertensive (PHT) gastric mucosa leads to hyperdynamic circulation and increased susceptibility to injury. However, the signaling mechanisms for eNOS activation in PHT gastric mucosa and the role of TNF-, in this signaling remain unknown. In PHT gastric mucosa we studied (1) eNOS phosphorylation (at serine 1177) required for its activation; (2) association of the phosphatidylinositol 3-kinase (PI 3-kinase), and its downstream effector Akt, with eNOS; and, (3) whether TNF-, neutralization affects eNOS phosphorylation and PI 3-kinase,Akt activation. To determine human relevance, we used human microvascular endothelial cells to examine directly whether TNF-, stimulates eNOS phosphorylation via PI 3-kinase. PHT gastric mucosa has significantly increased (1) eNOS phosphorylation at serine 1177 by 90% (P < .01); (2) membrane translocation (P < .05) and phosphorylation (P < .05) of p85 (regulatory subunit of PI 3-kinase) by 61% and 85%, respectively; (3) phosphorylation (P < .01) and activity (P < .01) of Akt by 40% and 52%, respectively; and (4) binding of Akt to eNOS by as much as 410% (P < .001). Neutralizing anti,TNF-, antibody significantly reduced p85 phosphorylation, phosphorylation and activity of Akt, and eNOS phosphorylation in PHT gastric mucosa to normal levels. Furthermore, TNF-, stimulated eNOS phosphorylation in human microvascular endothelial cells. In conclusion, these findings show that in PHT gastric mucosa, TNF-, stimulates eNOS phosphorylation at serine 1177 (required for its activation) via the PI 3-kinase,Akt signal transduction pathway. [source] | |||||||||||||||||||||||||||||||