Biomedical subjects

N Panayotatos

Publications and source records attributed to N Panayotatos.

At least 19 recordsLinked to original sources

PubMed1998

Protective effect of ciliary neurotrophic factor (CNTF) in a model of endotoxic shock: action mechanisms and role of CNTF receptor alpha.

Ciliary neurotrophic factor (CNTF) inhibits the production of tumor necrosis factor (TNF) in lipopolysaccharide (LPS)-treated mice and protects against LPS lethality when coadministered with its soluble receptor (sCNTFR alpha). Both of these activities are abolished in adrenalectomized (ADX) mice. LPS-induced pulmonary polymorphonuclear neutrophil (PMN) infiltration and nitric oxide (NO) production were also inhibited by CNTF + sCNTFR alpha but not by CNTF alone. sCNTFR alpha did not alter the clearance or tissue distribution of CNTF. Furthermore, CNTF variants coadministered with sCNTFR alpha protected against LPS toxicity in a manner related to their affinity for the beta components of CNTFR. Thus, inhibition of TNF production and protection against LPS lethality by CNTF/sCNTFR alpha require an intact hypothalamus-pituitary-adrenal axis (HPAA) and may be mediated by endogenous glucocorticoids. This protective effect is, at least in part, due to the inhibition of PMN infiltration and NO production, and appears to be mediated by cells displaying only beta-receptor subtypes.

Adrenalectomy↗

PubMed1996

A shared, non-canonical DNA conformation detected at DNA/protein contact sites and bent DNA in the absence of supercoiling or cognate protein binding.

A hybrid protein (H144), consisting of Lac repressor and T7 endonuclease I, binds at the lac operator and cleaves relaxed double-stranded DNA at distal but distinct sites. These sites are shown here to coincide with a bacterial promoter, a phage T7 promoter, a site for gyrase and intrinsically bent DNA. The targets do not seem to share a particular DNA sequence, and in bent DNA, cleavage occurs at the physical center rather than at the common A-tracts. These results indicate that protein contact sites and intrinsic bends assume a non-canonical conformation in the absence of supercoiling or cognate protein binding. This feature may serve as a recognition signal or facilitate protein binding to initiate transcription and recombination.

Base Sequence↗

PubMed1996

Ciliary neurotrophic factor protects striatal output neurons in an animal model of Huntington disease.

Huntington disease is a dominantly inherited, untreatable neurological disorder featuring a progressive loss of striatal output neurons that results in dyskinesia, cognitive decline, and, ultimately, death. Neurotrophic factors have recently been shown to be protective in several animal models of neurodegenerative disease, raising the possibility that such substances might also sustain the survival of compromised striatal output neurons. We determined whether intracerebral administration of brain-derived neurotrophic factor, nerve growth factor, neurotrophin-3, or ciliary neurotrophic factor could protect striatal output neurons in a rodent model of Huntington disease. Whereas treatment with brain-derived neurotrophic factor, nerve growth factor, or neurotrophin-3 provided no protection of striatal output neurons from death induced by intrastriatal injection of quinolinic acid, an N-methyl-D-aspartate glutamate receptor agonist, treatment with ciliary neurotrophic factor afforded marked protection against this neurodegenerative insult.

Animals↗

PubMed1996

Six different cytokines that share GP130 as a receptor subunit, induce serum amyloid A and potentiate the induction of interleukin-6 and the activation of the hypothalamus-pituitary-adrenal axis by interleukin-1.

Ciliary neurotrophic factor (CNTF) and interleukin-6 (IL-6) potentiate the elevation of serum corticosterone induced by suboptimal doses of interleukin-1 (IL-1). CNTF also potentiates IL-1-induced serum IL-6. Here, we report that four other cytokines (leukemia inhibitory factor [LIF], oncostatin M [OSM], interleukin-11 and cardiotrophin-1) also potentiated the elevation of serum corticosterone and IL-6 levels induced by IL-1. Furthermore, all the six cytokines studied induced the acute-phase protein serum amyloid A when administered alone. Because these cytokines differ both in structure and in function, but share gp130 as a subunit of their receptors, these results indicate that signaling through gp130 mediates potentiation of IL-1 activities. The potentiation of IL-1-induced serum corticosterone levels is not a consequence of the increased serum IL-6 observed after IL-1 administration. In fact, in IL-6 deficient mice, IL-1 increased serum corticosterone to a level comparable to that observed in wild-type mice. Thus, either endogenous IL-6 does not mediate IL-1-induced corticosterone increase, or its role may be fulfilled by other cytokines. To the extent that gp130-dependent cytokines may serve this role, they may be important feedback regulators of inflammation through the activation of the hypothalamus-pituitary-adrenal axis and the potentiation of acute-phase protein synthesis.

Acute-Phase Reaction↗

PubMed1995

Crystal structure of dimeric human ciliary neurotrophic factor determined by MAD phasing.

Ciliary neurotrophic factor (CNTF) promotes the survival and differentiation of developing motor neurons and is a potential therapeutic for treating neurodegeneration and nerve injury. The crystal structure of human CNTF has been determined at 2.4 A resolution using multi-wavelength anomalous diffraction (MAD) phasing from a single Yb3+ ions. The structure reveals that CNTF is dimeric, with a novel anti-parallel arrangement of the subunits, not previously observed for other cytokines. Each subunit adopts a double crossover four-helix bundle fold, in which two helices contribute to the dimer interface, whilst two different helices show pronounced kinks. Analysis of the electrostatic surface of CNTF identified residues within these kinked helices that may contact the CNTF receptor-alpha. Solution experiments show that CNTF dimerizes at concentrations > 40 microM. Such dimers are likely to be relevant to the storage of CNTF in the peripheral nerve given the high concentrations present in this tissue. However, it is unlikely that they play a role in engaging the three distinct receptor subunits that comprise the CNTF receptor, given the low concentration of extracellular CNTF and its high potency.

Amino Acid Sequence↗

PubMed1995

Localization of functional receptor epitopes on the structure of ciliary neurotrophic factor indicates a conserved, function-related epitope topography among helical cytokines.

By rational mutagenesis, receptor-specific functional analysis, and visualization of complex formation in solution, we identified individual amino acid side chains involved specifically in the interaction of ciliary neurotrophic factor (CNTF) with CNTFR alpha and not with the beta-components, gp130 and LIFR. In the crystal structure, the side chains of these residues, which are located in helix A, the AB loop, helix B, and helix D, are surface accessible and are clustered in space, thus constituting an epitope for CNTFR alpha. By the same analysis, a partial epitope for gp130 was also identified on the surface of helix A that faces away from the alpha-epitope. Superposition of the CNTF and growth hormone structures showed that the location of these epitopes on CNTF is analogous to the location of the first and second receptor epitopes on the surface of growth hormone. Further comparison with proposed binding sites for alpha- and beta-receptors on interleukin-6 and leukemia inhibitory factor indicated that this epitope topology is conserved among helical cytokines. In each case, epitope I is utilized by the specificity-conferring component, whereas epitopes II and III are used by accessory components. Thus, in addition to a common fold, helical cytokines share a conserved order of receptor epitopes that is function related.

Animals↗

PubMed1995

Ciliary neurotrophic factor inhibits brain and peripheral tumor necrosis factor production and, when coadministered with its soluble receptor, protects mice from lipopolysaccharide toxicity.

BACKGROUND: The receptor of ciliary neurotrophic factor (CNTF) contains the signal transduction protein gp130, which is also a component of the receptors of cytokines such as interleukin (IL)-6, leukemia-inhibitory factor (LIF), IL-11, and oncostatin M. This suggests that these cytokines might share common signaling pathways. We previously reported that CNTF augments the levels of corticosterone (CS) and of IL-6 induced by IL-1 and induces the production of the acute-phase protein serum amyloid A (SAA). Since the elevation of serum CS is an important feedback mechanism to limit the synthesis of proinflammatory cytokines, particularly tumor necrosis factor (TNF), we have investigated the effect of CNTF on both TNF production and lipopolysaccharide (LPS) toxicity. MATERIALS AND METHODS: To induce serum TNF levels, LPS was administered to mice at 30 mg/kg i.p. and CNTF was administered as a single dose of 10 micrograms/mouse i.v., either alone or in combination with its soluble receptor sCNTFR alpha at 20 micrograms/mouse. Serum TNF levels were the measured by cytotoxicity on L929 cells. In order to measure the effects of CNTF on LPS-induced TNF production in the brain, mice were injected intracerebroventricularly (i.c.v.) with 2.5 micrograms/kg LPS. Mouse spleen cells cultured for 4 hr with 1 microgram LPS/ml, with or without 10 micrograms CNTF/ml, were also analyzed for TNF production. RESULTS: CNTF, administered either alone or in combination with its soluble receptor, inhibited the induction of serum TNF levels by LPS. This inhibition was also observed in the brain when CNTF and LPS were administered centrally. In vitro, CNTF only marginally affected TNF production by LPS-stimulated mouse splenocytes, but it acted synergistically with dexamethasone (DEX) in inhibiting TNF production. Most importantly, CNTF administered together with sCNTFR alpha protected mice against LPS-induced mortality. CONCLUSIONS: These data suggest that CNTF might act as a protective cytokine against TNF-mediated pathologies both in the brain and in the periphery.

Animals↗

PubMed1994

Recombinant human CNTF receptor alpha: production, binding stoichiometry, and characterization of its activity as a diffusible factor.

The primary ligand-binding protein (CNTFR alpha) of the multicomponent receptor for ciliary neurotrophic factor was produced in Escherichia coli. Using novel applications of size-exclusion chromatography and a protein gel-shift assay, we obtained quantitative separation of correctly refolded protein, as well as analytical monitoring of the refolding process and ligand binding. By these and other methods, we determined a 1:1 stoichiometry for the receptor-ligand complex. To investigate the proposed activity and mechanism of soluble CNTFR alpha as a diffusible factor, we studied the response of TF-1 cells which lack CNTFR alpha to various CNTF ligands and the stimulation of this response by sCNTFR alpha. The results show that sCNTFR alpha combines with CNTF and mediates cell survival with the same relative ligand specificity and relative affinity as the cell-surface form. Thus, soluble receptor can reconstitute on a cell surface active complexes that are analogous to the native complexes. Moreover, both the relative ligand potency in the absence of CNTFR alpha and the kinetics of the response to sCNTFR alpha indicate that the other components of the receptor complex contribute little, but measurably, to the specific potency of CNTF.

Animals↗

PubMed1994

Characterization and crystallization of recombinant human neurotrophin-4.

Neurotrophin-4 (NT-4) is the most recently discovered member of the neurotrophin family. We have expressed, refolded, and purified recombinant human NT-4 from Escherichia coli and compared it with recombinant human NT-4 secreted into the culture medium of baculovirus-infected insect cells. Both preparations were characterized and determined to be indistinguishable according to several biochemical criteria. Recombinant NT-4 from E. coli was crystallized in a form suitable for x-ray analysis, and characterization of these crystals indicated that NT-4 was present as a dimer within the asymmetric unit. NT-4 was active in promoting the survival of rat TrkB receptor-expressing fibroblasts, but was inactive on embryonic chicken sensory neurons, unlike the other members of the neurotrophin family and in contrast to the reported activities of partially purified NT-4.

Animals↗

PubMed1994

Ciliary neurotrophic factor combined with soluble receptor inhibits synthesis of proinflammatory cytokines and prostaglandin-E2 in vitro.

In human peripheral blood mononuclear cells, ciliary neurotrophic factor (CNTF) weakly suppressed endotoxin-induced interleukin (IL)-1 and prostaglandin E2(PGE2). Suppression of PGE2 and IL-8 synthesis was significantly greater (up to 42.6%, P < 0.05) by adding a 10-fold molar excess of soluble CNTF receptor (sCNTFR alpha). In cultured human fibroblasts, CNTF at 12 micrograms/ml did not suppress IL-1 alpha-induced IL-8. However, in the presence of a 10-fold excess of sCNTFR alpha, 300 ng/ml of CNTF suppressed IL-1 alpha-induced IL-8 by 44%. Therefore, sCNTFR alpha can confer to CNTF anti-inflammatory properties in vitro. IL-6 which, like CNTF, utilizes the gp130 signal transducer, possesses similar inhibitory effects. That CNTF and IL-6 share gp130 as a receptor component suggests that gp130 mediates these anti-inflammatory responses.

Cells, Cultured↗

PubMed1993

Exchange of a single amino acid interconverts the specific activity and gel mobility of human and rat ciliary neurotrophic factors.

Human and rat ciliary neurotrophic factors (CNTF), which share 85% sequence identity, promote the survival of chicken embryo ciliary ganglia neurons in vitro, but display a 4-5-fold difference in specific activity. To explore the origin of this difference and gain insight into the structural organization of CNTF, we created chimeric proteins of these two species. Surprisingly, we found that the differences in two apparently unrelated properties, gel mobility and specific activity, resided in a single amino acid. Substituting arginine residue 63 of rat CNTF into the human sequence created a protein with the properties of rat CNTF. Conversely, substituting the human CNTF glutamine residue 63 into rat CNTF generated a protein with the properties of human CNTF. Binding experiments confirmed that the distinct specific activities of human and rat CNTF and their chimeras reside in structural differences among these ligands rather than species differences in their receptors. Alanine substitution (Q63A) had no effect on the properties of human CNTF, whereas the R63A substitution reduced both the gel mobility and the specific activity of rat CNTF. Finally, a Q95R substitution at a different position of human CNTF had no effect on its properties. These results demonstrate that Arg-63 is both specific and critical in determining the structural differences of human and rat CNTF.

Amino Acid Sequence↗

PubMed1993

Released form of CNTF receptor alpha component as a soluble mediator of CNTF responses.

The alpha component of the receptor for ciliary neurotrophic factor (CNTF) differs from other known growth factor receptors in that it is anchored to cell membranes by a glycosylphosphatidylinositol linkage. One possible function of this type of linkage is to allow for the regulated release of this receptor component. Cell lines not normally responsive to CNTF responded to treatment with a combination of CNTF and a soluble form of the CNTF alpha receptor component. These findings not only demonstrate that the CNTF receptor alpha chain is a required component of the functional CNTF receptor complex but also reveal that it can function in soluble form as part of a heterodimeric ligand. Potential physiological roles for the soluble CNTF receptor are suggested by its presence in cerebrospinal fluid and by its release from skeletal muscle in response to peripheral nerve injury.

Animals↗

PubMed1991

Microtubule-associated protein 2 kinases, ERK1 and ERK2, undergo autophosphorylation on both tyrosine and threonine residues: implications for their mechanism of activation.

Microtubule-associated protein 2 kinase (MAP kinase), which exists in several forms, is a protein serine/threonine kinase that participates in a growth factor-activated protein kinase cascade in which it activates a ribosomal protein S6 kinase (pp90rsk) while being regulated itself by a cytoplasmic factor (MAP kinase activator). Experiments with recombinant MAP kinase, ERK2, purified from Escherichia coli in a nonactivated form revealed a self-catalyzed phosphate incorporation into both tyrosine and threonine residues. Another MAP kinase, ERK1, purified from insulin-stimulated cells also autophosphorylated on tyrosine and threonine residues. Autophosphorylation of ERK2 correlated with its autoactivation, although both autophosphorylation and autoactivation were slow compared to that occurring in the presence of MAP kinase activator. Therefore, we propose that autophosphorylation is probably involved in the MAP kinase activation process in vitro, but it may not be sufficient for full activation. The specificity toward tyrosine and threonine residues indicates that the MAP kinases ERK1 and ERK2 are members of a group of kinases with specificity for tyrosine as well as serine and threonine residues.

Amino Acid Sequence↗

PubMed1991

Recombinant human and rat ciliary neurotrophic factors.

The human ciliary neurotrophic factor (CNTF) gene was identified and cloned, based on homology with the recently cloned rat cDNA. The gene encodes a protein of 200 amino acids, which shares about 80% sequence identity with rat and rabbit CNTF and, like these homologues, lacks an apparent secretion signal sequence. The human CNTF gene, like the rat gene, appears to contain a single intron separating two protein coding exons. An intronless human CNTF gene was constructed by the use of polymerase chain reactions and introduced into vectors designed for expression of foreign proteins in E. coli. The rat CNTF gene was also introduced into similar vectors. Both the human and rat proteins were expressed at exceptionally high levels, at 20-40% and 60-70% of total protein, respectively. Extraction of the recombinant proteins from inclusion bodies by guanidinium chloride, followed by two column chromatography steps, produced high yields of pure CNTF that supported survival and neurite outgrowth from embryonic chick ciliary neurons in culture. The biological activity of both recombinant proteins was comparable to that of native rat CNTF.

Amino Acid Sequence↗

PubMed1991

The neurotrophins and CNTF: specificity of action towards PNS and CNS neurons.

The availability of relatively large amounts of nerve growth factor (NGF) has allowed extensive in vitro and in vivo characterization of the neuronal specificity of this neurotrophic factor. The restricted neuronal specificity of NGF (sympathetic neurons, neural crest-derived sensory neurons, basal forebrain cholinergic neurons) has long predicted the existence of other neurotrophic factors possessing different neuronal specificities. Whereas there have been many reports of "activities" distinct from NGF, full characterization of such molecules has been hampered by their extremely low abundance. The recent molecular cloning of brain-derived neurotrophic factor (BDNF) revealed that this protein is closely related to NGF and suggested that these two factors might be members of an even larger gene family. A PCR cloning strategy based on homologies between NGF and BDNF has allowed us to identify and clone a third member of the NGF family which we have termed neurotrophin-3 (NT-3). The establishment of suitable expression systems has now made available sufficient quantities of these proteins to allow us to begin to establish the neuronal specificity of each member of the neurotrophin family, and the role of each in development, maintenance and repair of the PNS and CNS. Using primary cultures of various PNS and CNS regions of the developing chick and rat, and Northern blot analysis, we describe novel neuronal specificities of BDNF, NT-3 and an unrelated neurotrophic factor-ciliary neurotrophic factor (CNTF).

Animals↗

PubMed1991

Ciliary neurotrophic factor enhances neuronal survival in embryonic rat hippocampal cultures.

First described as a survival factor for chick ciliary ganglion neurons, ciliary neurotrophic factor (CNTF) has recently been shown to promote survival of chick embryo motor neurons. We now report neurotrophic effects of CNTF toward three populations of rat hippocampal neurons, the first demonstration of effects of CNTF upon rodent CNS neurons in culture. CNTF elicited an increase in the neurofilament content of hippocampal cultures prepared from embryonic day 18 (E18) rat brain. This was accompanied by increases of 2-, 28-, and 3-fold in the number of GABAergic, cholinergic, and calbindin-immunopositive cells, respectively. CNTF totally prevented the 67% loss of GABAergic neurons that occurred in control cultures over 8 d. CNTF also increased high-affinity GABA uptake and glutamic acid decarboxylase activity. Effects of CNTF were in all cases dose dependent, with maximal stimulation at approximately 100 pg/ml. When addition was delayed for 3 d, CNTF failed to elicit increases either in the number of cholinergic neurons or in GABA uptake.

Acetylcholinesterase↗

PubMed1989

Biosynthesis of a repressor/nuclease hybrid protein.

The phage T7 endonuclease gene was fused to the 3' end of the lac repressor gene. The hybrid protein exhibits repressor and nuclease functions in a manner dependent on the conformation of the DNA. With supercoiled DNA, nuclease activity is directed to the major cruciform, whereas with linear DNA, the enzyme cleaves preferentially restriction fragments carrying the operator. These properties render the hybrid protein a unique probe of DNA conformation in vitro and in vivo.

DNA, Superhelical↗

PubMed1989

A site-targeted recombinant nuclease probe of DNA structure.

A genetically engineered lac repressor/T7 endonuclease hybrid protein shows repressor-like binding toward restriction fragments carrying the lac operator. In addition, fragments carrying the operator near a particular pBR322 sequence are cleaved into specific products. Cleavage occurs at precise positions within that sequence, is independent of the orientation of the operator, is inhibited by isopropyl-1-thio-beta-D-galactopyranoside, and is observed when the target is separated from the operator by at least as few as 150 and as many as 240 base pairs. This evidence indicates that the hybrid protein is a site-directed nuclease that requires the following two structural elements for activity: the lac operator and a target. Repressor-like binding directs the enzyme to the operator and nearby single-stranded DNA targets. The discovery of an unusual target in a well-studied DNA sequence is evidence of the power of this approach for probing unusual structures in non-supercoiled duplex DNA.

Binding, Competitive↗