bluuebunny/crossref_metadata_2025 huggingface dataset:
Metal-dependent nucleotide binding to the Escherichia coli rotamase SlyD
Authors: MITTERAUER Thomas , NANOFF Christian , AHORN Horst , FREISSMUTH Michael , HOHENEGGER Martin
Published: August 2015

Upon expression and purification of the first catalytic domain of mammalian adenylate cyclase type 1 (IC1), a 27 kDa contaminant was observed, which was labelled by three radioactive ATP analogues (8-azido-ATP, 3′-O-(4-benzoyl)benzoyl-ATP and 2′,3′-dialdehyde-ATP); the protein was purified separately and identified as Escherichiacoli SlyD by N-terminal amino acid sequence determination. SlyD is the host protein required for lysis of E.coli upon infection with bacteriophage ΦX174 and has recently been shown to display rotamase (peptidylproline cis-trans-isomerase) activity. The covalent incorporation of ATP analogues into SlyD was promoted by bivalent transition metal ions (Zn2+ ⩾ Ni2+ > Co2+ > Cu2+) but not by Mg2+ or Ca2+; this is consistent with the known metal ion specificity of SlyD. ATP, ADP, GTP and UTP suppressed labelling of SlyD with comparable potencies. Similarly, SlyD bound 2′,3′-O-(-2,4,6-trinitrophenyl)-ATP with an affinity in the range of 10 μM, as determined by fluorescence enhancement. This interaction was further augmented in the presence of Zn2+ (Kd = ∼ 2 μM at saturating Zn2+) but not of Mg2+. Irrespective of the assay conditions, hydrolysis of nucleotides by SlyD was not detected. Upon gel filtration on a Superose HR12 column, SlyD (predicted molecular mass = 21 kDa) migrated with an apparent molecular mass of 44 kDa, indicating that the protein was a dimer. However, the migration of SlyD was not affected by the presence of Zn2+ or of Zn2+ and ATP. Thus we concluded that SlyD binds nucleotides in the presence of metal ions. These findings suggest that SlyD serves a physiological role that goes beyond that accounted for by its intrinsic rotamase activity, which is observed in the absence of metal ions.
Caspase-mediated cleavage of eukaryotic translation initiation factor subunit 2α
Authors: SATOH Shinya , HIJIKATA Makoto , HANDA Hiroshi , SHIMOTOHNO Kunitada
Published: August 2015

Eukaryotic translation initiation factor 2α (eIF-2α), a target molecule of the interferon-inducible double-stranded-RNA-dependent protein kinase (PKR), was cleaved in apoptotic Saos-2 cells on treatment with poly(I)˙poly(C) or tumour necrosis factor α. This cleavage occurred with a time course similar to that of poly(ADP-ribose) polymerase, a well-known caspase substrate. In addition, eIF-2α was cleaved by recombinant active caspase-3 in vitro. By site-directed mutagenesis, the cleavage site was mapped to an Ala-Glu-Val-Asp300 ↓ Gly301 sequence located in the C-terminal portion of eIF-2α. PKR phosphorylates eIF-2α on Ser51, resulting in the suppression of protein synthesis. PKR-mediated translational suppression was repressed when the C-terminally cleaved product of eIF-2α was overexpressed in Saos-2 cells, even though PKR can phosphorylate this cleaved product. These results suggest that caspase-3 or related protease(s) can modulate the efficiency of protein synthesis by cleaving the α subunit of eIF-2, a key component in the initiation of translation.
Differential G-protein activation by alkaloid and peptide opioid agonists in the human neuroblastoma cell line SK-N-BE
Authors: ALLOUCHE Stéphane , POLASTRON Jocelyne , HASBI Ahmed , HOMBURGER Vincent , JAUZAC Philippe
Published: August 2015

Differences in the specificity of coupling of δ-opioid receptor with G-protein have been reported in the literature. We have observed a differential desensitization of δ-opioid receptors, endogenously expressed in the neuroblastoma cell line SK-N-BE, induced by peptide and alkaloid agonists. By combining photoaffinity labelling of receptor-activated G-proteins with [α-32P]azidoanilide-GTP and an anti-sense oligodeoxynucleotide strategy, we examined whether the chemical nature of opioid agonists, alkaloid or peptide, has a critical role in determining a Giα/Goα-protein-selective activation by the human δ-opioid receptors. Etorphine, a non-selective alkaloid agonist, was shown to stimulate the incorporation of [α-32P]azidoanilide-GTP into Giα1, Giα2, Giα3 and pertussis-toxin-insensitive Gα subunits. In contrast, [D-Pen2,D-Pen5]enkephalin (DPDPE; Pen is penicillamine) and Tyr-D-Ala-Phe-Asp-Val-Val-Gly-NH2 (deltorphin I), selective peptide agonists, mainly activated Giα2 and Goα2 subunits. The ‘knock-down’ of Goα2 subunits by anti-sense oligodeoxynucleotides selectively decreased the inhibition of adenylate cyclase induced by DPDPE and deltorphin I, whereas anti-sense oligodeoxynucleotides directed against Giα2 subunits only decreased the potency of etorphine in inhibiting cAMP accumulation. These results suggest that the nature of the agonist, peptide or alkaloid is critical in determining the interaction between human δ-opioid receptors and Gα subunits.
cDNA cloning and characterization of guinea-pig leukotriene B4 receptor
Authors: MASUDA Kazuyuki , YOKOMIZO Takehiko , IZUMI Takashi , SHIMIZU Takao
Published: August 2015

The cDNA for leukotriene B4 (LTB4) receptor (BLT) was cloned from a guinea-pig leucocyte cDNA library. The cloned receptor cDNA encodes 348 amino acid residues and shares 73% identity with the amino acid sequence of human BLT. Northern blot analysis showed the highest expression of the receptor mRNA in leucocytes, followed by lung and spleen. The membrane fractions of HEK-293 and Cos-7 cells transfected with the cDNA showed specific LTB4-binding activities, with Kd values of 0.27 and 0.17 nM respectively. Xenopus laevis oocytes injected with the cRNA of guinea-pig BLT showed LTB4-induced Cl- currents, indicating that the cloned receptor is functional. LTB4 is metabolized to 20-hydroxy-LTB4 and then to 20-carboxy-LTB4, a transformation considered as a major inactivation pathway of the compound. Using the cloned receptor, we analysed the agonistic effects of LTB4 and these two metabolites. 20-Carboxy-LTB4 is a much weaker agonist, with a Kd value higher than that of LTB4 by three orders of magnitude, corresponding to a much weaker chemotactic activity. Although 20-hydroxy-LTB4 is as potent as LTB4 in inhibiting [3H]LTB4 binding and cAMP formation, it is less potent than LTB4 in the mobilization of intracellular Ca2+ and the chemotaxis of Chinese hamster ovary cells expressing the guinea-pig BLT. The present study demonstrated that although LTB4 and 20-hydroxy-LTB4 bind to the receptor with similar affinities, they do differ in activating intracellular signalling.
Endothelin-1 activates p38 mitogen-activated protein kinase and cytosolic phospholipase A2 in cat iris sphincter smooth muscle cells
Authors: HUSAIN Shahid , ABDEL-LATIF Ata A.
Published: August 2015

We have shown previously that cytosolic phospholipase A2 (cPLA2) is responsible for endothelin-1-induced release of arachidonic acid for prostaglandin synthesis in cat iris sphincter smooth muscle (CISM) cells [Husain and Abdel-Latif (1998) Biochim. Biophys. Acta 1392, 127-144]. Here we show that p38 mitogen-activated protein (MAP) kinase, but not p42/p44 MAP kinases, plays an important role in the phosphorylation and activation of cPLA2 in endothelin-1-stimulated CISM cells. This conclusion is supported by the following findings. Both p38 MAP kinase and p42/p44 MAP kinases were present in the CISM cells and both were activated by endothelin-1. SB203580, a potent specific inhibitor of p38 MAP kinase, but not the p42/p44 MAP kinases specific inhibitor, PD98059, markedly suppressed endothelin-1-enhanced cPLA2 phosphorylation, cPLA2 activity and arachidonic acid release. The addition of endothelin-1 resulted in the phosphorylation and activation of cPLA2. Endothelin-1 stimulated p38 MAP kinase activity in a time- and concentration-dependent manner, and these effects were mediated through the endothelin-A receptor subtype. The protein kinase C (PKC) inhibitor, RO 31-8220, had no inhibitory effect on endothelin-1-induced p38 MAP kinase activation, suggesting that endothelin-1 activation of p38 MAP kinase is independent of PKC. Pertussis toxin inhibited both endothelin-1 and mastoparan stimulation of p38 MAP kinase activity and arachidonic acid release. The inhibitory effects of pertussis toxin are not mediated through cAMP formation. Mastoparan-stimulated [3H]arachidonic acid release and cPLA2 activation was inhibited by SB203580, but not by RO 31-8220. These data suggest that endothelin-1 binds to the endothelin-A receptor to activate the Gi-protein which, through a series of kinases, leads to the activation of p38 MAP kinase and subsequently to phosphorylation and activation of cPLA2. Activation of cPLA2 leads to the liberation of arachidonic acid from membrane phospholipids. The ability of the activated endothelin-A receptor, which is coupled to both Gq- and Gi-proteins, to recruit and activate this complex signal transduction pathway remains to be elucidated. Further studies on the mechanism of these relationships could provide important information about the functions of p38 MAP kinase in smooth muscle.
Homologous xylanases from Clostridium thermocellum: evidence for bi-functional activity, synergism between xylanase catalytic modules and the presence of xylan-binding domains in enzyme complexes
Authors: FERNANDES Ana C. , FONTES Carlos M. G. A. , GILBERT Harry J. , HAZLEWOOD Geoffrey P. , FERNANDES Tito H. , FERREIRA Luis M. A.
Published: August 2015

Clostridium thermocellum produces a consortium of plant-cell-wall hydrolases that form a cell-bound multi-enzyme complex called the cellulosome. In the present study two similar xylanase genes, xynU and xynV, were cloned from C. thermocellum strain YS and sequenced. The deduced primary structures of both xylanases, xylanase U (XylU) and xylanase V (XylV), were homologous with the previously characterized xylanases from C. thermocellum strain F1. Truncated derivatives of XylV were produced and their biochemical properties were characterized. The xylanases were shown to be remarkably thermostable and resistant to proteolytic inactivation. The catalytic domains hydrolysed xylan by a typical endo-mode of action. The type VI cellulose-binding domain (CBD) homologue of XylV bound xylan and, to a smaller extent, Avicel and acid-swollen cellulose. Deletion of the CBD from XylV abolished the capacity of the enzymes to bind polysaccharides. The polysaccharide-binding domain was shown to have a key role in the hydrolysis of insoluble substrates by XylV. The C-terminal domain of XylV, which is absent from XylU, removed acetyl groups from acetylated xylan and acted in synergy with the glycosyl hydrolase catalytic domain of the enzyme to elicit the hydrolysis of acetylated xylan.
Novel method for evaluation of the oligomeric structure of membrane proteins
Authors: RAMJEESINGH Mohabir , HUAN Ling-Jun , GARAMI Elizabeth , BEAR Christine E.
Published: August 2015

Assessment of the quaternary structure of membrane proteins by PAGE has been problematic owing to their relatively poor solubility in non-dissociative detergents. Here we report that several membrane proteins can be readily solubilized in their native quaternary structure with the use of the detergent perfluoro-octanoic acid (PFO). Further, PFO can be used with PAGE, thereby providing a novel, accessible tool with which to assess the molecular mass of homo-multimeric protein complexes.
Methotrexate inhibits the first committed step of purine biosynthesis in mitogen-stimulated human T-lymphocytes: a metabolic basis for efficacy in rheumatoid arthritis?
Authors: FAIRBANKS Lynette D. , RüCKEMANN Katarzyna , QIU Ying , HAWRYLOWICZ Catherine M. , RICHARDS David F. , SWAMINATHAN Ramasamyiyer , KIRSCHBAUM Bernhard , SIMMONDS H. Anne
Published: August 2015

The immunosuppressive and anti-inflammatory effects of low-dose methotrexate (MTX) have been related directly to inhibition of folate-dependent enzymes by polyglutamated derivatives, or indirectly to adenosine release and/or apoptosis and clonal deletion of activated peripheral blood lymphocytes in S-phase. In this study of phytohaemagglutinin-stimulated primary human T-lymphocytes we show that MTX (20 nM to 20 μM) was cytostatic not cytotoxic, halting proliferation at G1. This stasis of blastogenesis was associated with an inhibition of purine ribonucleotide synthesis but a stimulation of pyrimidine biosynthesis, the normal mitogen-induced expansion of ATP and GTP pools over 72 h being restricted to concentrations of unstimulated T-cells, whereas the increment in UTP pools exceeded that of controls. Decreased incorporation of H14CO-3 or [14C]glycine into purine ribonucleotides, with no radiolabel accumulation in any denovo synthetic intermediate but enhanced H14CO-3 incorporation into UTP, supported these MTX-related effects. Exaggerated [14C]hypoxanthine salvage (which normalized the purine and UTP pools) confirmed the increased availability of 5-phosphoribosyl-1-pyrophosphate (PP-ribose-P) as the molecular mechanism underlying these disparate changes. These results provide the first substantive evidence that the immunosuppressive effects of low-dose MTX in primary blasting human T-lymphocytes relate not to the inhibition of the two folate-dependent enzymes of purine biosynthesis but to inhibition of the first enzyme, amidophosphoribosyltransferase, thereby elevating PP-ribose-P and stimulating UTP synthesis. Varying cell types or incubation conditions employed by other workers, especially malignant/activated cells with high basal metabolic rates, might mask the effects noted in primary human T-lymphocytes. The findings imply the involvement of low-dose MTX in the inhibition of T-lymphocyte proliferation and proliferation-dependent processes in rheumatoid arthritis.
Immunodetection and molecular cloning of a bile-salt-dependent lipase isoform in HepG2 cells
Authors: VÉRINE Alain , BRUNEAU Nadine , VALETTE Anne , PETIT-THEVENIN Josette LE , PASQUALINI Eric , LOMBARDO Dominique
Published: August 2015

In this article, we report the nucleotide sequence of the cDNA encoding an isoform of bile-salt-dependent lipase (BSDL) expressed by human hepatoma cells. The BSDL is a 100-kDa glycoprotein normally expressed by the human pancreas. Using a polyclonal antibody raised against an internal peptide located between Ile327 and Glu350 of the human pancreatic BSDL, we have immunodetected an isoform of human pancreatic BSDL, with an apparent molecular mass of about 62 kDa. This isoform of BSDL was mainly associated with the cytosol of a human hepatoma cell line (HepG2), the remaining protein being found in the microsome fraction. In addition, esterolytic activity on p-nitrophenyl hexanoate measured in microsomes and cytosol appeared very low and was weakly stimulated by bile salts, such as taurocholate. In contrast to human pancreatic BSDL, which is secreted as a component of pancreatic juice, this isoform appeared to be retained in the HepG2 cells. Reverse transcription, followed by PCR and amplification, performed on RNA extracted from HepG2 cells using specific primers hybridizing to the sequence coding for the entire normal human pancreatic BSDL, allowed us to amplify a 1.7-kb transcript that appeared to be 0.5 kb shorter than the transcript of the pancreatic enzyme (2.2 kb). From the sequence of the transcript thus obtained, a protein with a molecular mass of 62 kDa might be predicted, which is in good agreement with the size of the isoform of BSDL immunodetected in HepG2 cells. The N-terminal amino-acid sequence, deduced from the 1.7-kb transcript sequence, matched that of the pancreatic BSDL. However, the C-terminal domain appeared truncated, bearing only a single mucin-like sequence compared with sixteen for the human pancreatic BSDL. The actual intracellular function of this human BSDL hepatoma isoform remains to be elucidated.
Receptors linked to polyphosphoinositide hydrolysis stimulate Ca2+ extrusion by a phospholipase C-independent mechanism
Authors: BROAD Lisa M. , CANNON Toby R. , SHORT Alison D. , TAYLOR Colin W.
Published: August 2015

In A7r5 cells with empty intracellular Ca2+ stores in which the cytosolic free Ca2+ concentration ([Ca2+]i) had been increased by capacitative Ca2+ entry, stimulation of receptors linked to phospholipase C (PLC), including those for Arg8-vasopressin (AVP) and platelet-derived growth factor (PDGF), caused a decrease in [Ca2+]i. This effect was further examined in a stable variant of the A7r5 cell line in which the usual ability of hormones to stimulate non-capacitative Ca2+ entry is not expresssed. In thapsigargin-treated cells, neither AVP nor PDGF affected capacitative Mn2+ or Ba2+ entry, but both stimulated the rate of Ca2+ extrusion, and their abilities to decrease [Ca2+]i were only partially inhibited by removal of extracellular Na+. These results suggest that receptors linked to PLC also stimulate plasma membrane Ca2+ pumps. Activation of protein kinase C by phorbol 12,13-dibutyrate (PDBu, 1 μM) also caused a decrease in [Ca2+]i by accelerating Ca2+ removal from the cytosol; the effect was again only partially inhibited by removal of extracellular Na+. An inhibitor of PKC, Ro31-8220 (10 μM), abolished the ability of PDBu to decrease [Ca2+]i,without affecting the response to maximal or submaximal concentrations of AVP. Similar experiments with PDGF were impracticable because Ro31-8220, presumably by inhibiting the tyrosine kinase activity of the PDGF receptor, abolished all responses to PDGF. U73122 (10 μM), an inhibitor of PLC, completely inhibited PDGF- or AVP-evoked Ca2+ mobilization, without preventing either stimulus from causing a decrease in [Ca2+]i. We conclude that receptors coupled to PLC, whether via G-proteins or protein tyrosine kinase activity, also share an ability to stimulate the plasma membrane Ca2+ pump via a mechanism that does not require PLC activity.
Molecular determinants of the physicochemical properties of a critical prion protein region comprising residues 106–126
Authors: SALMONA Mario , MALESANI Paolo , GIOIA Luca DE , GORLA Stefano , BRUSCHI Maurizio , MOLINARI Antonio , VEDOVA Franco DELLA , PEDROTTI Barbara , MARRARI Maria Anna , AWAN Tazeen , BUGIANI Orso , FORLONI Gianluigi , TAGLIAVINI Fabrizio
Published: August 2015

Prion diseases are marked by the cerebral accumulation of conformationally modified forms of the cellular prion protein (PrPC), known as PrPres. The region comprising the residues 106-126 of human PrP seems to have a key role in this conformational conversion, because a synthetic peptide homologous with this sequence (PrP106-126) adopts different secondary structures in different environments. To investigate the molecular determinants of the physicochemical characteristics of PrP106-126, we synthesized a series of analogues including PrP106-126 HD, PrP106-126 A and PrP106-126 K, with L-His → D-His, His → Ala and His → Lys substitutions respectively at position 111, PrP106-126 NH2 with amidation of the C-terminus, PrP106-126 V with an Ala → Val substition at position 117, and PrP106-126 VNH2 with an Ala → Val substitution at position 117 and amidation of the C-terminus. The analysis of the secondary structure and aggregation properties of PrP106-126 and its analogues showed the following. (1) His111 is central to the conformational changes of PrP peptides. (2) Amidation of the C-terminal Gly126 yields a predominantly random coil structure, abolishes the molecular polymorphism and decreases the propensity of PrP106-126 to generate amyloid fibrils. (3) PrP106-126 V, carrying an Ala → Val substitution at position 117, does not demonstrate a fibrillogenic ability superior to that of PrP106-126. However, the presence of Val at position 117 increases the aggregation properties of the amidated peptide. (4) Amyloid fibrils are not required for neurotoxicity because the effects of PrP106-126 NH2 on primary neuronal cultures were similar to those of the wild-type sequence. Conversely, astroglial proliferation is related to the presence of amyloid fibrils, suggesting that astrogliosis in prion encephalopathies without amyloid deposits is a mediated effect rather than a direct effect of disease-specific PrP isoforms.
Role of the Janus kinase (JAK)/signal transducters and activators of transcription (STAT) cascade in advanced glycation end-product-induced cellular mitogenesis in NRK-49F cells
Authors: HUANG Jau-Shyang , GUH Jinn-Yuh , HUNG Wen-Chun , YANG Mei-Li , LAI Yung-Hsiung , CHEN Hung-Chun , CHUANG Lea-Yea
Published: August 2015

Advanced glycation end product (AGE) is important in the pathogenesis of diabetic nephropathy, which is characterized by cellular hypertrophy/hyperplasia leading to renal fibrosis. However, the signal transduction pathways of AGE remain poorly understood. The Janus kinase (JAK)/signal transducers and activators of transcription (STAT) pathway has been associated with cellular proliferation in some extra-renal cells. Because interstitial fibroblast proliferation might be important in renal fibrosis, we studied the role of the JAK/STAT pathway in NRK-49F (normal rat kidney fibroblast) cells cultured in AGE/BSA and non-glycated BSA. We showed that AGE dose-dependently (10-200 μg/ml) increased cellular mitogenesis in NRK-49F cells at 5 and 7 days. However, cellular mitogenesis was unaffected by the simultaneous presence of BSA. Regarding the JAK/STAT pathway, AGE (100 μg/ml) induced tyrosine phosphorylation of JAK2 (but not JAK1, JAK3 or TYK2) at 15-60 min; it also induced the tyrosine phosphorylation of STAT1 and STAT3 at 1-2 h and 0.5-4 h respectively. Being a transcription factor, AGE also increased the DNA-binding activities of STAT1 and STAT3 AG-490 (a specific JAK2 inhibitor) (5 μM) inhibited tyrosine phosphorylation of JAK2 and the DNA-binding activities of STAT1 and STAT3. The same results were obtained by using specific ‘decoy’ oligodeoxynucleotides (ODNs) that prevented STAT1 and STAT3 from binding to DNA. Meanwhile, the STAT1 or STAT3 decoy ODN and AG-490 were effective in reversing AGE-induced cellular mitogenesis. We concluded that the JAK2-STAT1/STAT3 signal transduction pathway is necessary for AGE-induced cellular mitogenesis in NRK-49F cells.
Effects of photoreleased cADP-ribose on calcium transients and calcium sparks in myocytes isolated from guinea-pig and rat ventricle
Authors: CUI Yi , GALIONE Antony , TERRAR Derek A.
Published: August 2015

Actions of photoreleased cADP-ribose (cADPR), a novel regulator of calcium-induced calcium release (CICR) from ryanodine-sensitive stores, were investigated in cardiac myocytes. Photoreleased cADPR caused an increase in the magnitude of whole-cell calcium transients studied in mammalian cardiac ventricular myocytes (both guinea-pig and rat) using confocal microscopy). Approx. 15 s was required following photorelease of cADPR for the development of its maximal effect. Photoreleased cADPR also increased the frequency of calcium ‘sparks’, which are thought to be elementary events which make up the whole-cell calcium transient, and were studied in rat myocytes, but had little or no effect on spark characteristics (amplitude, rise time, decay time and distance to half amplitude). The potentiating effects of photoreleased cADPR on both whole-cell transients and the frequency of calcium sparks were prevented by cytosolic application of the antagonist 8-amino-cADPR (5 μM). These experiments, therefore, provide the first evidence in any cell type for an effect of cADPR on calcium sparks, and are the first to show the actions of photoreleased cADPR on whole-cell calcium transients in mammalian cells. The observations are consistent with the effects of cADPR in enhancing the calcium sensitivity of CICR from the sarcoplasmic reticulum in cardiac ventricular myocytes, leading to an increase in the probability of occurrence of calcium sparks and to an increase in whole-cell calcium transients. The slow time-course for development of the full effect on whole-cell calcium transients might be taken to indicate that the influence of cADPR on CICR may involve complex molecular interactions rather than a simple direct action of cADPR on the ryanodine-receptor channels.
Activation of TrkA by nerve growth factor upregulates expression of the cholinergic gene locus but attenuates the response to ciliary neurotrophic growth factor
Authors: BERSE Brygida , LOPEZ-COVIELLA Ignacio , BLUSZTAJN J. Krzysztof
Published: August 2015

Nerve growth factor (NGF) stimulates the expression of the cholinergic gene locus, which encodes choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT), the proteins necessary for the synthesis and storage of the neurotransmitter acetylcholine (ACh). To determine whether this action of NGF is mediated by the p140TrkA NGF receptor (a member of the Trk tyrosine kinase family) we used a murine basal forebrain cholinergic cell line, SN56, stably transfected with rat trkA cDNA. Treatment of these transfectants with NGF activated mitogen-activated protein kinase and increased cytosolic free calcium concentrations, confirming the reconstitution of TrkA-mediated signalling pathways. The expression of ChAT and VAChT mRNA, as well as ACh content, were coordinately up-regulated by NGF in SN56-trkA transfectants. None of these responses occurred in the parental SN56 cells, which do not express endogenous TrkA, indicating that these actions of NGF required TrkA. We previously reported that ciliary neurotrophic factor (CNTF) upregulates the expression of ChAT and VAChT, as well as ACh production, in SN56 cells. The combined treatment of SN56-trkA cells with CNTF and NGF revealed a complex interaction of these factors in the regulation of cholinergic gene locus expression. At low concentrations of CNTF (< 1 ng/ml), the upregulation of ACh synthesis evoked by these factors was additive. However, at higher concentrations of CNTF (> 1 ng/ml), NGF attenuated the stimulatory effect of CNTF on ChAT and VAChT mRNA and ACh content. This attenuation was not due to interference with early steps of CNTF receptor signalling, as pre-treatment of SN56-trkA cells with NGF did not affect the nuclear translocation of the transcription factor, Stat3, evoked by CNTF.
Structural requirement of the calcium-channel subunit α2δ for gabapentin binding
Authors: WANG Minghan , OFFORD James , OXENDER Dale L. , SU Ti-Zhi
Published: August 2015

Gabapentin [Neurontin, 1-(aminomethyl)cyclohexaneacetic acid] is a novel anticonvulsant drug with a high binding affinity for the Ca2+-channel subunit α2δ. In this study, the gabapentin-binding properties of wild-type and mutated porcine brain α2δ proteins were investigated. Removal of the disulphide bonds between the α2 and the δ subunits did not result in a significant loss of gabapentin binding, suggesting that the disulphide linkage between the two subunits is not required for binding. Singly expressed α2 protein remained membrane associated. However, α2 alone was unable to bind gabapentin, unless the cells were concurrently transfected with the expression vector for δ, suggesting that both α2 and δ are required for gabapentin binding. Using internal deletion mutagenesis, we mapped two regions [amino acid residues 339-365 (δF) and 875-905 (δJ)] within the α2 subunit that are not required for gabapentin binding. Further, deletion of three other individual regions [amino acid residues 206-222 (δD), 516-537 (δH) and 583-603 (δI)] within the α2 subunit disrupted gabapentin binding, suggesting the structural importance of these regions. Using alanine to replace four to six amino acid residues in each of these regions abolished gabapentin binding. These results demonstrate that region D, between the N-terminal end and the first putative transmembrane domain of α2, and regions H and I, between the putative splicing acceptor sites (Gln511 and Ser601), may play important roles in maintaining the structural integrity for gabapentin binding. Further single amino acid replacement mutagenesis within these regions identified Arg217 as critical for gabapentin binding.
Inwardly rectifying K+ channel Kir7.1 is highly expressed in thyroid follicular cells, intestinal epithelial cells and choroid plexus epithelial cells: implication for a functional coupling with Na+,K+-ATPase
Authors: NAKAMURA Nobuhiro , SUZUKI Yoshiro , SAKUTA Hidenari , OOKATA Kayoko , KAWAHARA Katsumasa , HIROSE Shigehisa
Published: August 2015

A novel inwardly rectifying K+ channel, Kir7.1, with unique pore properties, was cloned recently. Working in the field of osmoregulation, we have also identified the same human and rat channel and found that the channel is unique not only in its pore sequence but also in its dense localization in the follicular cells of the thyroid gland. Northern blot analysis revealed that the channel message was abundantly expressed in the thyroid gland and small intestine, and moderately in the kidney, stomach, spinal cord and brain. Immunohistochemistry of the rat thyroid, intestine and choroid plexus demonstrated the expression of the channel protein in the follicular cells and epithelial cells, suggesting a role in the regulation of the ion-transporting functions of these specialized cells. The unique pore properties of Kir7.1 make it a strong candidate for the hypothetical low-conductance K+ channel that is functionally coupled with Na+,K+-ATPase by recycling K+. We therefore further examined the co-localization of Kir7.1 and Na+,K+-ATPase and found that both are localized in the basolateral membrane of the thyroid follicular cell; in the choroid plexus, which is known to be unique in having Na+,K+-ATPase in the apical side of the epithelial cells, Kir7.1 was found in the apical membrane, implying a close functional coupling between the channel and Na+,K+-ATPase.
Ethanol and acetaldehyde elevate intracellular [Ca2+] and stimulate microneme discharge in Toxoplasma gondii
Authors: CARRUTHERS Vern B. , MORENO Silvia N. J. , SIBLEY David L.
Published: August 2015

One of the first steps in host-cell invasion by the protozoan parasite Toxoplasma gondii occurs when the parasite attaches by its apical end to the target host cell. The contents of apical secretory organelles called micronemes have recently been implicated in parasite apical attachment to host cells. Micronemes are regulated secretory vesicles that discharge in response to elevated parasite intracellular Ca2+ levels ([Ca2+]i). In the present study we found that ethanol and related compounds produced a dose-dependent stimulation of microneme secretion. In addition, using fluorescence spectroscopy on tachyzoites loaded with the Ca2+-sensitive fluorescent dye fura-2, we demonstrated that ethanol stimulated microneme secretion by elevating parasite [Ca2+]i. Furthermore, sequential addition experiments with ethanol and other Ca2+-mobilizing drugs showed that ethanol probably elevated parasite [Ca2+]i by mobilizing Ca2+ from a thapsigargin-insensitive compartment of neutral pH. Earlier studies have shown that ethanol also elevates [Ca2+]i in mammalian cells. Thus, because it is genetically tractable, T. gondii might be a convenient model organism for studying the Ca2+-elevating effects of alcohol in higher eukaryotes.
Elucidation of carbon sources used for the biosynthesis of fatty acids and sterols in the trypanosomatid Leishmania mexicana
Authors: GINGER Michael L. , CHANCE Michael L. , GOAD L. John
Published: August 2015

Sterols are necessary for the growth of trypanosomatid protozoans; sterol biosynthesis is a potential target for the use and development of drugs to treat the diseases caused by these organisms. This study has used 14C-labelled substrates to investigate the carbon sources utilized by promastigotes and amastigotes of Leishmania mexicana for the production of sterol [mainly ergosta-5,7,24(241)-trien-3β-ol] and the fatty acid moieties of the triacylglycerol (TAG) and phospholipid (PL) of the organism. The isoprenoid precursor mevalonic acid (MVA) was incorporated into the sterols, and the sterol precursor squalene, by the promastigotes of L. mexicana. However, acetate (the precursor to MVA in most organisms) was a very poor substrate for sterol production but was readily incorporated into the fatty acids of TAG and PL. Other substrates (glucose, palmitic acid, alanine, serine and isoleucine), which are metabolized to acetyl-CoA, were also very poor precursors to sterol but were incorporated into TAG and PL and gave labelling patterns of the lipids similar to those of acetate. In contrast, the amino acid leucine was the only substrate to be incorporated efficiently into the squalene and sterol of L. mexicana promastigotes. Quantitative measurements revealed that at least 70-80% of the sterol synthesized by the promastigotes of L. mexicana is produced from carbon provided by leucine metabolism. Studies with the amastigote form of L. mexicana showed that in this case leucine was again the major sterol precursor, whereas acetate was utilized for fatty acid production.
Differential regulation of extracellular signal-regulated protein kinases (ERKs) 1 and 2 by cAMP and dissociation of ERK inhibition from anti-mitogenic effects in rabbit vascular smooth muscle cells
Authors: COSPEDAL Rosario , LOBO Melvin , ZACHARY Ian
Published: August 2015

The inhibition of extracellular signal-regulated protein kinases (ERKs) is implicated in the negative regulation of vascular smooth muscle cell (VSMC) mitogenesis by cAMP-elevating agents and transforming growth factor β1 (TGF-β1). These factors inhibited rabbit aortic VSMC mitogenesis induced by platelet-derived growth factor (PDGF)-BB by preventing the entry of cells into S-phase. cAMP-elevating agents partly inhibited the late phase (1-4 h) of activation of ERKs 1 and 2 induced by PDGF-BB without inhibiting the early phase of activity (5-15 min) and had no effect on activity induced by basic fibroblast growth factor (bFGF). In contrast, cAMP elevation caused a marked inhibition of early ERK activation induced by angiotensin II and thrombin. TGF-β1 had no inhibitory effect on ERK activation induced by PDGF-BB or bFGF. The inhibition of PDGF-BB-stimulated DNA synthesis by either forskolin/3-isobutyl-1-methylxanthine (IBMX) or TGF-β1 was not decreased when the agents were added up to 8 h after growth factor. In contrast, the selective ERK kinase inhibitor PD98059 was a weak inhibitor of DNA synthesis; a combination of PD98059 and forskolin/IBMX had an additive inhibitory effect on DNA synthesis. Forskolin/IBMX inhibited the growth factor-induced expression of c-myc mRNA and cyclin D1 protein, and enhanced the protein expression of p27kip1. TGF-β1 had no effect on the expression of c-myc or p27kip1 and weakly attenuated the expression of cyclin D1. These findings support the conclusion that the suppression of VSMC mitogenesis by cAMP and TGF-β1 is independent of ERK inhibition. Anti-mitogenic effects of cAMP might be primarily mediated by events in late G1.
Anionic phospholipids decrease the rate of slippage on the Ca2+-ATPase of sarcoplasmic reticulum
Authors: DALTON Kate A. , PILOT Jeffrey D. , MALL Sanjay , EAST J. Malcolm , LEE Anthony G.
Published: August 2015

Accumulation of Ca2+ by the Ca2+-ATPase of skeletal-muscle sarcoplasmic reticulum has been measured in reconstituted, sealed vesicles as a function of lipid composition. Measurements were performed in the presence of carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) to eliminate any effects of H+ transport; in the presence of FCCP, addition of valinomycin had no effect on the level or rate of accumulation of Ca2+ showing that, in the presence of FCCP, no electrical potential built up across the membrane. Levels of accumulation were low when the phospholipid was dioleoylphosphatidylcholine (DOPC), even though DOPC supports high ATPase activity. Inclusion of 10 mol% anionic phospholipid [dioleoylphosphatidic acid (DOPA) or dioleoylphosphatidylserine (DOPS)] led to higher levels of accumulation of Ca2+, 10 mol% being the optimum concentration. Cardiolipin or phosphatidylinositol 4-phosphate were more effective than DOPA or DOPS in increasing accumulation of Ca2+. Effects of anionic phospholipids were seen in the presence of an ATP-regenerating system to remove ADP, and in the presence of phosphate within the reconstituted vesicles to precipitate calcium phosphate. Rates of passive leak of Ca2+ from the reconstituted vesicles were slow. The Ca2+-accumulation process was simulated assuming either simple passive leak of Ca2+ from the vesicles or assuming slippage on the ATPase, a process in which the phosphorylated intermediate of the ATPase releases bound Ca2+ on the cytoplasmic rather than the lumenal side of the membrane. The experimental data fitted to a slippage model, with anionic phospholipids decreasing the rate of slippage.
Characterization of a flavocytochrome that is induced during the anaerobic respiration of Fe3+ by Shewanella frigidimarina NCIMB400
Authors: DOBBIN Paul S. , BUTT Julea N. , POWELL Anne K. , REID Graeme A. , RICHARDSON David J.
Published: August 2015

A 63.9 kDa periplasmic tetrahaem flavocytochrome c3, designated Ifc3, was found to be expressed in Shewanellafrigidimarina NCIMB400 grown anaerobically with ferric citrate or ferric pyrophosphate as the sole terminal electron acceptor, but not in anaerobic cultures of the bacterium with other respiratory substrates. Ifc3 was purified to homogeneity and revealed by biochemical, spectroscopic and primary structure analyses to contain four low-spin bis-His-ligated c3-haems, with midpoint reduction potentials of -73, -141, -174 and -259 mV. A low-potential flavin was present in the form of non-covalently bound FAD; the protein possessed a unidirectional fumarate reductase activity. Disruption of the chromosomal gene encoding Ifc3, ifcA, did not lead to a significant change in the rate of Fe3+ reduction in batch culture. However, during such growth the Ifc3-deficient mutant produced both a 35 kDa periplasmic c-type cytochrome and a 45 kDa membrane-associated c-type cytochrome at markedly higher levels than did the parent strain. Nucleotide sequencing data from directly upstream of ifcA indicated the presence of an open reading frame encoding a putative outer-membrane β-barrel protein of 324 amino acid residues.
The type II and X cellulose-binding domains of Pseudomonas xylanase A potentiate catalytic activity against complex substrates by a common mechanism
Authors: GILL Jaitinder , RIXON Jane E. , BOLAM David N. , MCQUEEN-MASON Simon , SIMPSON Peter J. , WILLIAMSON Michael P. , HAZLEWOOD Geoffrey P. , GILBERT Harry J.
Published: August 2015

Xylanase A (Pf Xyn10A), in common with several other Pseudomonas fluorescens subsp. cellulosa polysaccharidases, consists of a Type II cellulose-binding domain (CBD), a catalytic domain (Pf Xyn10ACD) and an internal domain that exhibits homology to Type X CBDs. The Type X CBD of Pf Xyn10A, expressed as a discrete entity (CBDX) or fused to the catalytic domain (Pf Xyn10A′), bound to amorphous and bacterial microcrystalline cellulose with a Ka of 2.5×105 M-1. CBDX exhibited no affinity for soluble forms of cellulose or cello-oligosaccharides, suggesting that the domain interacts with multiple cellulose chains in the insoluble forms of the polysaccharide. Pf Xyn10A′ was 2-3 times more active against cellulose-hemicellulose complexes than Pf Xyn10ACD; however, Pf Xyn10A′ and Pf Xyn10ACD exhibited the same activity against soluble substrates. CBDX did not disrupt the structure of plant-cell-wall material or bacterial microcrystalline cellulose, and did not potentiate Pf Xyn10ACD when not covalently linked to the enzyme. There was no substantial difference in the affinity of full-length Pf Xyn10A and the enzyme's Type II CBD for cellulose. The activity of Pf Xyn10A against cellulose-hemicellulose complexes was similar to that of Pf Xyn10A′, and a derivative of Pf Xyn10A in which the Type II CBD is linked to the Pf Xyn10ACD via a serine-rich linker sequence [Bolam, Cireula, McQueen-Mason, Simpson, Williamson, Rixon, Boraston, Hazlewood and Gilbert (1998) Biochem J. 331, 775-781]. These data indicate that CBDX is functional in Pf Xyn10A and that no synergy, either in ligand binding or in the potentiation of catalysis, is evident between the Type II and X CBDs of the xylanase.
Repression of gene expression by oxidative stress
Authors: MOREL Yannick , BAROUKI Robert
Published: August 2015

Gene expression is modulated by both physiological signals (hormones, cytokines, etc.) and environmental stimuli (physical parameters, xenobiotics, etc.). Oxidative stress appears to be a key pleiotropic modulator which may be involved in either pathway. Indeed, reactive oxygen species (ROS) have been described as second messengers for several growth factors and cytokines, but have also been shown to rise following cellular insults such as xenobiotic metabolism or enzymic deficiency. Extensive studies on the induction of stress-response genes by oxidative stress have been reported. In contrast, owing to the historical focus on gene induction, less attention has been paid to gene repression by ROS. However, a growing number of studies have shown that moderate (i.e. non-cytotoxic) oxidative stress specifically down-regulates the expression of various genes. In this review, we describe the alteration of several physiological functions resulting from oxidative-stress-mediated inhibition of gene transcription. We will then focus on the repressive oxidative modulation of various transcription factors elicited by ROS.
High-efficiency Semliki Forest virus-mediated transduction in bovine adrenal chromaffin cells
Authors: DUNCAN Rory R. , DON-WAUCHOPE Andrew C. , TAPECHUM Sompol , SHIPSTON Michael J. , CHOW Robert H. , ESTIBEIRO Peter
Published: August 2015

Adrenal chromaffin cells are commonly used in studies of exocytosis. Progress in characterizing the molecular mechanisms has been slow, because no simple, high-efficiency technique is available for introducing and expressing heterologous cDNA in chromaffin cells. Here we demonstrate that Semliki Forest virus (SFV) vectors allow high-efficiency expression of heterologous protein in chromaffin cells.
Ornithine and glutamate decarboxylases catalyse an oxidative deamination of their α-methyl substrates
Authors: BERTOLDI Mariarita , CARBONE Virginia , VOLTATTORNI Carla BORRI
Published: August 2015

Ornithine decarboxylase (ODC) from Lactobacillus 30a catalyses the cleavage of α-methylornithine into ammonia and 2-methyl-1-pyrroline; glutamate decarboxylase (GAD) from Escherichia coli catalyses the cleavage of α-methylglutamate into ammonia and laevulinic acid. In our analyses, 2-methyl-1-pyrroline and laevulinic acid were identified by HPLC and mass spectroscopic analysis, and ammonia was identified by means of glutamate dehydrogenase. Molecular oxygen was consumed during these reactions in a 1:2 molar ratio with respect to the products. The catalytic efficiencies (kcat/Km) of the reactions catalysed by ODC and GAD were determined as 12500 and 9163 M-1˙min-1 respectively. When the reactions were performed under anaerobic conditions, no ammonia, 2-methyl-1-pyrroline or laevulinic acid was produced to a significant extent. The formation of ammonia and O2 consumption (in a 1:2 molar ratio with respect to ammonia) were also detected during the reaction of ODC and GAD with putrescine and γ-aminobutyrate respectively. Taken together, these findings clearly indicate that ODC and GAD catalyse an oxidative deamination of their decarboxylation products, a reaction similar to that catalysed by dopa decarboxylase (DDC) with α-methyldopa [Bertoldi, Dominici, Moore, Maras and Borri Voltattorni (1998) Biochemistry 37, 6552-6561]. Furthermore, this reaction was accompanied by a decarboxylation-dependent transamination occurring for GAD, DDC and ODC with a frequency of approx. 0.24%, 1% and 9% respectively compared with that of oxidative deamination.
Characterization of prenylated protein methyltransferase in Leishmania
Authors: HASNE Marie-Pierre , LAWRENCE Françoise
Published: August 2015

Prenylated protein methyltransferase, an enzyme involved in the post-translational modification of many signalling proteins, has been characterized in a parasitic flagellated protozoan, Leishmania donovani. The activity of this enzyme was monitored by the methylation of an artificial substrate, an S-prenylated cysteine analogue, with S-adenosyl-L-[methyl-3H]methionine as methyl donor. More than 85% of the methyltransferase activity was associated with membranes. The enzyme methylates N-acetyl-S-trans,trans-farnesyl-L-cysteine and N-acetyl-S-all-trans-geranylgeranyl-L-cysteine, but N-acetyl-S-trans,trans-geranyl-L-cysteine only very weakly. In contrast with the enzyme from mammals, the leishmanial enzyme had a greater affinity for the farnesylated substrate than for the geranylgeranylated one. Activity in vitro was not modulated by cAMP, protein kinase C activator or guanosine 5′-[γ-thio]triphosphate. An analysis of the endogenous substrates showed that the carboxymethylated proteins were also isoprenylated. The main carboxymethylated proteins have molecular masses of 95, 68, 55, 46, 34-23, 18 and less than 14 kDa. Treatment of cells with N-acetyl-S-trans,trans-farnesyl-L-cysteine decreased the carboxymethylation level, whereas treatment with guanosine 5′-[γ-thio]triphosphate increased the carboxymethylation of various proteins, particularly those of molecular masses 30-20 kDa.
Cellular stress in Xenopus kidney cells enhances the phosphorylation of eukaryotic translation initiation factor (eIF)4E and the association of eIF4F with poly(A)-binding protein
Authors: FRASER Christopher S. , PAIN Virginia M. , MORLEY Simon J.
Published: August 2015

Eukaryotic initiation factor (eIF) 4E binds to the 5′-cap structure of eukaryotic mRNA and has a central role in the control of cell proliferation. We have shown previously that the stimulation of cultured Xenopus kidney cells with serum resulted in the activation of protein synthesis, enhanced phosphorylation of eIF4E and increased binding of the adapter protein, eIF4G, and poly(A)-binding protein (PABP) to eIF4E to form the functional initiation factor complex, eIF4F/PABP. We now show that cellular stresses such as arsenite, anisomycin and heat shock also result in increased phosphorylation of eIF4E, eIF4F complex formation and the association of PABP with eIF4G, in conditions under which the rate of protein synthesis is severely inhibited. In contrast with reported effects on mammalian cells, the stress-induced increase in eIF4F complex formation occurs in the absence of changes in the association of eIF4E with its binding proteins 4E-BP1 or 4E-BP2. The stress-induced changes in eIF4E phosphorylation were totally abrogated by the p38 mitogen-activated protein (MAP) kinase inhibitor SB203580, and were partly inhibited by the phosphoinositide 3-kinase inhibitor LY294002 and the mammalian target of rapamycin (mTOR) inhibitor rapamycin. However, eIF4E phosphorylation was unaffected by extracellular signal-regulated protein kinase (MAP kinase) inhibitor PD98059. These results indicate that cellular stresses activate multiple signalling pathways that converge at the level of eIF4F complex formation to influence the interactions between eIF4E, eIF4G and PABP.
Effects of disrupting the 21 kDa subunit of complex I from Neurospora crassa
Authors: FERREIRINHA Fátima , DUARTE Margarida , MELO Ana M. P. , VIDEIRA Arnaldo
Published: August 2015

We have cloned and inactivated in vivo, by repeat-induced point mutations, the nuclear gene encoding a 21 kDa subunit of complex I from Neurospora crassa. Mitochondria from the nuo21 mutant lack this specific protein but retain other subunits of complex I in approximately normal amounts. In addition, this mutant is able to assemble an almost intact enzyme. The electron transfer activities from NADH to artificial acceptors of mitochondrial membranes from nuo21 differ from those of the wild-type strain, suggesting that the absence of the 21 kDa polypeptide results in conformational changes in complex I. Nevertheless, complex I of nuo21 is able to perform NADH:ubiquinone reductase activity, as judged by the observation that the respiration of mutant mitochondria is sensitive to inhibition by rotenone. We discuss these findings in relation to the involvement of complex I in mitochondrial diseases.