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C H Reynolds

Publications and source records attributed to C H Reynolds.

At least 19 recordsLinked to original sources
PubMed2001

Conformational analysis of the eight-membered ring of the oxidized cysteinyl-cysteine unit implicated in nicotinic acetylcholine receptor ligand recognition.

Nicotinic acetylcholine receptors (nAChRs) are membrane-bound, pentameric ligand-gated ion channels associated with a variety of human disorders such as Alzheimer's disease, Parkinson's disease, schizophrenia, and pain. Most known nAChRs contain an unusual eight-membered disulfide-containing cysteinyl-cysteine ring, ox-[Cys-Cys], as does the soluble acetylcholine binding protein (AChBP) found in the snail Lymnaea stagnalis. The cysteinyl-cysteine ring is located in a region implicated in ligand binding, and conformational changes involving this ring may be important for modulation of nAChR function. We have studied the preferred conformations of Ac-ox-[Cys-Cys]-NH2 by NMR in water and computationally by Monte Carlo simulations using the OPLS-AA force field and GB/SA water model. ox-[Cys-Cys] adopts four distinct low-energy conformers at slightly above 0 degrees C in water. Two populations are dependent on the peptide omega2 dihedral angle, with the trans amide favored over the cis amide by a ratio of ca. 60:40. Two ox-[Cys-Cys] conformers with a cis amide bond (C+ and C-) differ from each other primarily by variation of the chi3 dihedral angle, which defines the orientation of the helicity about the S-S bond (+/- 90 degrees ). Two trans amide conformers have the same S-S helicity (chi3 approximately -90 degrees ), but are distinguished by a backbone rotation about phi2 and psi1 (T- and T'-). The ratio of T-/T'-/C+/C- is 47:15:29:9. The orientation of the pendant moieties from the eight-membered ring is more compact for the major trans conformer (T-) than for the extended conformations adopted by T'-, C+, and C-. These conformational preferences are also observed in tetrapeptide and undecapeptide fragments of the human alpha7 subtype of the nAChR that contains the ox-[Cys-Cys] unit. Conformer T- is nearly identical to the conformation seen in the X-ray structure of ox-[Cys(187)-Cys(188)] found in the unliganded AChBP, and is a Type VIII beta-turn.

Computer Simulation↗
PubMed2001

Sites of phosphorylation in tau and factors affecting their regulation.

The microtubule-associated protein, tau, is the principal component of paired helical filaments (PHFs) in Alzheimer's disease. PHF-tau is highly phosphorylated and a total of 25 sites of phosphorylation have so far been identified. Many of these sites are serine or threonine residues that are immediately followed in the sequence by proline residues, and hence are candidate phosphorylation sites for proline-directed kinases. In vitro, glycogen synthase kinase-3 (GSK-3), extracellular signal-related kinase-1 and -2, and mitogen-activated protein kinases, p38 kinase and c-jun N-terminal kinase, all phosphorylate many of these sites, although with different efficiencies for particular sites. Phosphorylation studies in transfected cells and neurons show that GSK-3 phosphorylates tau more extensively than do these other proline-directed kinases. Mutations in tau have been shown to affect in vitro phosphorylation of tau by GSK-3. The Arg406-->Trp (R406W) tau mutation also affects tau phosphorylation in cells.

Alzheimer Disease↗
PubMed2000

GB/SA water model for the Merck molecular force field (MMFF).

A revised generalized Born/surface area (GB/SA) continuum solvation model has been developed for water that is compatible with the Merck molecular force field (MMFF). This model gives free energies of aqueous solvation that are comparable in accuracy to the original water model when the OPLS* force field is employed. The average unsigned error in aqueous deltaGsol using the new water model and MMFF is 0.62 kcal/mol for a training set of 82 solutes compared to 1.24 kcal/mol for the original GB/SA water model and MMFF. The average unsigned errors for 47 neutral solutes outside the training set and 10 ions are 0.96 and 2.32 kcal/mol, respectively. By comparison, the average errors for the test set and ions using the original GB/SA water model are 1.76 and 5.32 kcal/mol. This revised parameter set provides a more accurate representation of aqueous solvation for use with MMFF.

Artificial Intelligence↗
PubMed2000

Phosphorylation sites on tau identified by nanoelectrospray mass spectrometry: differences in vitro between the mitogen-activated protein kinases ERK2, c-Jun N-terminal kinase and P38, and glycogen synthase kinase-3beta.

The stress-activated kinases c-Jun N-terminal kinase (JNK) and p38 are members of the mitogen-activated protein (MAP) kinase family and take part in signalling cascades initiated by various forms of stress. Their targets include the microtubule-associated protein tau, which becomes hyperphosphorylated in Alzheimer's disease. It is necessary, as a forerunner for in vivo studies, to identify the protein kinases and phosphatases that are responsible for phosphate turnover at individual sites. Using nanoelectrospray mass spectrometry, we have undertaken an extensive comparison of phosphorylation in vitro by several candidate tau kinases, namely, JNK, p38, ERK2, and glycogen synthase kinase 3beta (GSK3beta). Between 10 and 15 sites were identified for each kinase. The three MAP kinases phosphorylated Ser202 and Thr205 but not detectably Ser199, whereas conversely GSK3beta phosphorylated Ser199 but not detectably Ser202 or Thr205. Phosphorylated Ser404 was found with all of these kinases except JNK. The MAP kinases may not be strictly proline specific: p38 phosphorylated the nonproline sites Ser185, Thr245, Ser305, and Ser356, whereas ERK2 was the most strict. All of the sites detected except Thr245 and Ser305 are known or suspected phosphorylation sites in paired helical filament-tau extracted from Alzheimer brains. Thus, the three MAP kinases and GSK3beta are importantly all strong candidates as tau kinases that may be involved in the pathogenic hyperphosphorylation of tau in Alzheimer's disease.

Alzheimer Disease↗
PubMed2000

Clinical efficacy of rhIL-11.

Placebo-controlled clinical trials of recombinant human interleukin-11 (rhIL-11, also known as oprelvekin [Neumega]) in patients with nonmyeloid malignancies have demonstrated significant efficacy in preventing postchemotherapy platelet nadirs of < or = 20,000/microL, and reducing the need for platelet transfusions while continuing chemotherapy without dose reductions. The likelihood of requiring a platelet transfusion in rhIL-11-treated patients receiving chemotherapy is approximately 40% lower than the risk for untreated patients. Treatment with rhIL-11 appears to accelerate earlier recovery to platelet counts of 20,000/microL, 50,000/microL, and 100,000/microL, suggesting that patients treated with rhIL-11 are more likely to be able to receive their next chemotherapy cycle in a timely fashion. rhIL-11 shows sustained efficacy over multiple cycles of full-dose chemotherapy. Activity has also been demonstrated in pediatric patients with solid tumors. The use of rhIL-11 in combination with granulocyte colony-stimulating factor (G-CSF, filgrastim [Neupogen]) may also produce a synergistic hematopoietic effect, resulting in earlier neutrophil recovery. The recommended adult dose regimen for rhIL-11 is 50 micrograms/kg administered subcutaneously once daily beginning 6 to 24 hours after the administration of chemotherapy until a postnadir platelet count of > or = 50,000/microL is reached. The recommended pediatric dose of rhIL-11 is 75 micrograms/kg subcutaneously, once daily beginning 6 to 24 hours after the administration of chemotherapy until a postnadir platelet count of > or = 50,000/microL is reached. The administration of rhIL-11 for greater than 21 days has not been studied and therefore is not recommended.

Adult↗
PubMed1998

Effects of peripheral flicker masking on M- and P-pathway response.

PURPOSE: The effects of metahue and metacontrast masking on the responses of the M- and P-pathways of the human visual system were investigated using temporal analysis of the multifocal flash visually evoked potential (VEP) (VERIS system). METHODS: The experiments were carried out at three achromatic luminance contrasts, 24, 70 and 96%, with three peripheral masks: a steady 65% grey mask, a grey flicker mask and an isoluminant red/green flicker mask. The stimuli were viewed monocularly and the mask and VERIS stimuli superposed with a mirror-aperture system. RESULTS/CONCLUSIONS: The masks had no significant effect on the behaviour of the M-pathway as stimulus contrast increased. The amplitude of the P-pathway was found to be approximately level at all contrasts of the stimulus and with all three masks rather than showing the expected steady increase in activity with increasing stimulus contrast.

Adult↗
PubMed1997

Phosphorylation of tau by glycogen synthase kinase 3beta affects the ability of tau to promote microtubule self-assembly.

To study the effects of phosphorylation by glycogen synthase kinase-3beta (GSK-3beta) on the ability of the microtubule-associated protein tau to promote microtubule self-assembly, tau isoform 1 (foetal tau) and three mutant forms of this tau isoform were investigated. The three mutant forms of tau had the following serine residues, known to be phosphorylated by GSK-3, replaced with alanine residues so as to preclude their phosphorylation: (1) Ser-199 and Ser-202 (Ser-199/202-->Ala), (2) Ser-235 (Ser-235-->Ala) and (3) Ser-396 and Ser-404 (Ser-396/404-->Ala). Wild-type tau and the mutant forms of tau were phosphorylated with GSK-3beta, and their ability to promote microtubule self-assembly was compared with the corresponding non-phosphorylated tau species. In the non-phosphorylated form, wild-type tau and all of the mutants affected the mean microtubule length and number concentrations of assembled microtubules in a manner consistant with enhanced microtubule nucleation. Phosphorylation of these tau species with GSK-3beta consistently reduced the ability of a given tau species to promote microtubule self-assembly, although the affinity of the tau for the microtubules was not greatly affected by phosphorylation since the tau species remained largely associated with the microtubules. This suggests that the regulation of microtubule assembly can be controlled by phosphorylation of tau at sites accessible to GSK-3beta by a mechanism that does not necessarily involve the dissociation of tau from the microtubules.

Alzheimer Disease↗
PubMed1997

Oxidative stress induces dephosphorylation of tau in rat brain primary neuronal cultures.

Oxidative stress and free radical damage have been implicated in the neurodegenerative changes characteristic of several neurodegenerative diseases, including Alzheimer's disease. There is experimental evidence that the neurotoxicity of beta-amyloid is mediated via free radicals, and as the deposition of beta-amyloid apparently precedes the formation of paired helical filaments (PHF) in Alzheimer's disease, we have investigated whether subjecting primary neuronal cultures to oxidative stress induces changes in the phosphorylation state of the principal PHF protein tau that resemble those found in PHF-tau. Contrary to causing an increase in tau phosphorylation, treatment of neurones with hydrogen peroxide caused a dephosphorylation of tau and so we conclude that oxidative stress is not the direct cause of tau hyperphosphorylation and hence of PHF formation.

Animals↗
PubMed1997

Stress-activated protein kinase/c-jun N-terminal kinase phosphorylates tau protein.

A proportion of the neuronal microtubule-associated protein (MAP) tau is highly phosphorylated in foetal and adult brain, whereas the majority of tau in the neurofibrillary tangles of Alzheimer's patients is hyperphosphorylated; many of the phosphorylation sites are serines or threonines followed by prolines. Several kinases phosphorylate tau at such sites in vitro. We have now shown that purified recombinant stress-activated protein kinase/c-Jun N-terminal kinase, a proline-directed kinase of the MAP kinase extended family, phosphorylates recombinant tau in vitro on threonine and serine residues. Western blots using antibodies to phosphorylation-dependent tau epitopes demonstrated that phosphorylation occurs in both of the main phosphorylated regions of tau protein. Unlike glycogen synthase kinase-3, the c-Jun N-terminal kinase readily phosphorylates Thr205 and Ser422, which are more highly phosphorylated in Alzheimer tau than in foetal or adult tau. Glycogen synthase kinase-3 may preferentially phosphorylate the sites found physiologically, in foetal and to a smaller extent in adult tau, whereas stress-activated/c-Jun N-terminal kinase and/or other members of the extended MAP kinase family may be responsible for pathological proline-directed phosphorylations. Inflammatory processes in Alzheimer brain might therefore contribute directly to the pathological formation of the hyperphosphorylated tau found in neurofibrillary tangles.

Antibody Specificity↗
PubMed1997

Reactivating kinase/p38 phosphorylates tau protein in vitro.

Neurofibrillary tangles, one of the major pathological hallmarks of Alzheimer-diseased brains, consist primarily of aggregated paired helical filaments (PHFs) of hyperphosphorylated tau protein. Tau from normal brain and especially from foetal brain is also phosphorylated on some of the sites phosphorylated in PHFs, mainly at serines or threonines followed by prolines. A number of protein kinases can phosphorylate tau in vitro; those that require or accept prolines include GSK3 and members of the mitogen-activated protein (MAP) kinase family, ERK1, ERK2, and SAP kinase-beta/JNK. In this report, we show that another member of the MAP kinase family, the stress-activated kinase p38/RK, can phosphorylate tau in vitro. Western blots with phosphorylation-sensitive antibodies showed that p38, like ERK2 and SAP kinase-beta/JNK, phosphorylated tau at sites found phosphorylated physiologically (Thr181, Ser202, Thr205, and Ser396) and also at Ser422, which is phosphorylated in neurofibrillary tangles but not in normal adult or foetal brain. These findings support the possibility that cellular stress might contribute to tau hyperphosphorylation during the formation of PHFs, and hence, to the development of tau pathology.

Alzheimer Disease↗
PubMed1995

Stimulation of MAP kinase by v-raf transformation of fibroblasts fails to induce hyperphosphorylation of transfected tau.

A proportion of the microtubule-associated protein, tau, is in an elevated state of phosphorylation in foetal and adult brain whereas all of the tau in paired helical filaments, which are characteristic of Alzheimer's disease is hyperphosphorylated; it is important therefore to elucidate the mechanisms that regulate tau phosphorylation. Here we describe results that show that although MAP kinase can hyperphosphorylate tau in vitro, activation of MAP kinase in transformed fibroblasts does not result in hyperphosphorylation of transfected tau, whereas glycogen synthase kinase-3 beta (GSK-3 beta) when co-transfected with tau does result in tau hyperphosphorylation. The findings imply that GSK-3 beta may be a stronger candidate than MAP kinase for inducing tau hyperphosphorylation in vivo.

3T3 Cells↗
PubMed1994

Alzheimer's disease-like phosphorylation of the microtubule-associated protein tau by glycogen synthase kinase-3 in transfected mammalian cells.

BACKGROUND: Paired helical filaments (PHFs) are a characteristic pathological feature of Alzheimer's disease; their principal component is the microtubule-associated protein tau. The tau in PHFs (PHF-tau) is hyperphosphorylated, but the cellular mechanisms responsible for this hyperphosphorylation have yet to be elucidated. A number of kinases, including mitogen-activated protein (MAP) kinase, glycogen synthase kinase (GSK)-3 alpha, GSK-3 beta and cyclin-dependent kinase-5, phosphorylate recombinant tau in vitro so that it resembles PHF-tau as judged by its reactivity with a panel of antibodies capable of discriminating between normal tau and PHF-tau, and by a reduced electrophoretic mobility that is characteristic of PHF-tau. To determine whether MAP kinase, GSK-3 alpha and GSK-3 beta can also induce Alzheimer's disease-like phosphorylation of tau in mammalian cells, we studied the phosphorylation status of tau in primary neuronal cultures and transfected COS cells following changes in the activities of MAP kinase and GSK-3. RESULTS: Activating MAP kinase in cultures of primary neurons or transfected COS cells expressing tau isoforms did not increase the level of phosphorylation for any PHF-tau epitope investigated. But elevating GSK-3 activity in the COS cells by co-transfection with GSK-3 alpha or GSK-3 beta decreased the electrophoretic mobility of tau so that it resembled that of PHF-tau, and induced reactivity with eight PHF-tau-selective monoclonal antibodies. CONCLUSIONS: Our data indicate that GSK-3 alpha and/or GSK-3 beta, but not MAP kinase, are good candidates for generating PHF-type phosphorylation of tau in Alzheimer's disease. The involvement of other kinases in the generation of PHFs cannot, however, be eliminated. Our results suggest that aberrant regulation of GSK-3 may be a pathogenic mechanism in Alzheimer's disease.

Alzheimer Disease↗
PubMed1993

Comparison of baculovirus-expressed c-Abl and BCR/ABL protein tyrosine kinases.

Mouse c-Abl type IV and human BCR/ABL proteins have been expressed in insect cells using the baculovirus system. The proteins were expressed as full-length polypeptides as judged by electrophoresis in denaturing gels. They were identified by immunoprecipitation and immunoblotting with antibodies against ABL peptides and, for BCR/ABL, against a BCR peptide. In these immunoprecipitates both proteins gave autophosphorylation principally on tyrosine. Both proteins were active tyrosine kinases, phosphorylating a variety of tyrosine-containing substrates. In fresh extracts both proteins contained phosphotyrosine as shown by Western blots with antiphosphotyrosine antibodies. Partial purification could be achieved readily using ion exchange columns, and the BCR/ABL protein, p210BCR/ABL, could be further purified to near-homogeneity using an antiphosphotyrosine column. Both enzymes required a divalent metal ion for activity. At low concentrations of ATP (2 microM) and with angiotensin II as substrate both enzymes were activated by Mn2+ or by Mg2+. No major differences in catalytic properties were found between the two isolated enzymes in solution. The oncogenic properties of p210BCR/ABL may be due to its different subcellular location, or to the presence of an intracellular inhibitor of c-Abl that does not inhibit BCR/ABL, or to altered substrate-specificity such that it can phosphorylate a unique substrate which is not recognised by c-Abl.

Amino Acid Sequence↗
PubMed1993

Specific glycosaminoglycans support the inhibition of thrombin by plasminogen activator inhibitor 1.

In the absence of accessory components, plasminogen activator inhibitor 1 (PAI-1) rapidly forms equimolar, inactive complexes both with tissue-type (t-PA) and with urokinase-type (u-PA) plamsinogen activator. In the presence of either the glycoprotein vitronectin or the glycosaminoglycan heparin, PAI-1 is endowed with additional, efficient thrombin-inhibitory properties (Ehrlich et al., 1990, 1991a). Here, we have investigated the interaction between PAI-1, thrombin, and glycosaminoglycans in more detail. Inhibition of thrombin by PAI-1 was quantitatively analyzed in the presence of a wide range of concentrations of heparin, heparan sulfate, dermatan sulfate, chondroitin 4-sulfate, chondroitin 6-sulfate, keratan sulfate, and hyaluronic acid by measuring residual amidolytic activity. In addition, a qualitative analysis was performed by determining the formation of SDS-stable, equimolar complexes between thrombin and PAI-1 in the presence of various glycosaminoglycans. Heparin, at concentrations between 0.1 and 1 microgram/mL, significantly promoted thrombin inhibition by PAI-1 as well as SDS-stable complex formation. Suboptimal inhibition was observed with dermatan sulfate, chondroitin 4-sulfate, and heparan sulfate at concentrations that are at least 1 order of magnitude higher than that required for optimal inhibition in the presence of heparin. Virtually no inhibition of thrombin and SDS-stable complex formation was detected with any of the other glycosaminoglycans at concentrations between 0.1 and 1 microgram/mL.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophoresis, Polyacrylamide Gel↗
PubMed1992

Expression of the mouse c-abl type IV proto-oncogene product in the insect cell baculovirus system.

The cellular gene c-abl is the normal homologue of the transforming gene (v-abl) within the genome of the Abelson leukaemia virus. The cDNA sequence coding for the cellular form of the murine abl gene (c-abl type IV) has been inserted into the baculovirus transfer vector, pAc36C, so that the c-abl gene is under the control of the polyhedrin promoter of Autographa californica nuclear polyhedrosis virus (AcNPV). Spodoptera frugiperda cells infected with the recombinant transfer vector in the presence of wild type AcNPV DNA yielded recombinant, polyhedrin negative virus that expressed moderate levels of the c-Abl protein (representing approx. 0.5-1% of the stained cellular proteins as determined by densitometric scanning). The insect derived c-Abl protein was compared to the P210-BCR/ABL protein from K562 cells, a cell line derived from a patient with chronic myelogenous leukaemia. Antibodies raised against synthetic peptides based on c-abl encoded peptides react with the insect derived c-Abl. In addition, the baculovirus derived c-Abl protein has a tyrosine kinase activity as demonstrated by phosphorylation of a synthetic polypeptide and also by autophosphorylation. Phosphoamino acid analysis of immunoprecipitated, autophosphorylated baculovirus derived c-Abl protein indicates that the majority of label incorporated is on the tyrosine residues. Immunofluorescence microscopy has been used to show that the majority of the c-Abl protein expressed in cells infected with recombinant virus is located in the nuclear and plasma membranes.

Animals↗
PubMed1991

Activation of casein kinase II by sphingosine.

Sphingosine activates casein kinase II in the presence of endogenous substrates as well as a synthetic peptide substrate. The activation response occurred between 12 and 25 micrograms/ml sphingosine and exhibited positive cooperativity with a Hill coefficient of 3.0. Sphingosine not only increased the Vmax of casein kinase II but decreased the Km(app) for the peptide substrate from 0.5 to 0.08 mM. In contrast, the Km(app) for MgCl2 was increased from 0.12 to 0.7 mM. Consequently, sphingosine altered significantly several parameters which determine casein kinase II activity. The effect of sphingosine was relatively specific, inasmuch as related lipids were less potent activators or largely ineffective in stimulating casein kinase II. On the other hand, the effect of sphingosine itself could be potentiated or inhibited by other lipids. Ceramide and sphingosylphosphorylcholine augmented the sphingosine effect. Phospholipids alone did not alter the activity of casein kinase II significantly, but abolished enzyme activation by sphingosine with different potencies (phosphatidylserine greater than phosphatidylethanolamine greater than phosphatidylinositol greater than phosphatidylcholine). Moreover, the sphingosine effect could be abrogated by KCI and NaCl, which alone are known to induce enzyme activation and dissociation of aggregated casein kinase II protein; LiCl and NH4Cl also inhibited the sphingosine effect. Polyamines, known activators of casein kinase II, partially mimicked the effect of sphingosine on endogenous polypeptide phosphorylation but failed to do so with the peptide substrate. These observations demonstrate that sphingosine is a potent activator of casein kinase II. The potential pharmacological and physiological modulation of casein kinase II by sphingoid bases is discussed.

Animals↗
PubMed1989

Modeling the reactivity of acrylic acid and acrylate anion with biological nucleophiles.

Based on the results of prior in-vitro reactivity experiments, the pathway for the Michael addition of two representative nucleophiles (methylamine and imidazole) to acrylate anion (AA-) was explored with the semiempirical quantum model, AM1. The results of the calculations indicate that there is no viable reaction pathway for the addition of nucleophiles to AA-. An alternative route for the formation of the Michael products via the non-ionized form of acrylic acid (AA) was explored and found to be theoretically possible. The alternative route is plausible, but is considered to be insignificant in vivo based upon the rapid metabolism and excretion of AA (excretion half-life of 1-8 h after oral dosing).

Acrylates↗