bluuebunny/crossref_metadata_2025 huggingface dataset:
Recombinant aequorin and green fluorescent protein as valuable tools in the study of cell signalling
Authors: CHIESA Anna , RAPIZZI Elena , TOSELLO Valeria , PINTON Paolo , DE VIRGILIO Maddalena , FOGARTY Kevin E. , RIZZUTO Rosario
Published: August 2015

Luminous proteins include primary light producers, such as aequorin, and secondary photoproteins that in some organisms red-shift light emission for better penetration in space. When expressed in heterologous systems, both types of proteins may act as versatile reporters capable of monitoring phenomena as diverse as calcium homoeostasis, protein sorting, gene expression, and so on. The Ca2+-sensitive photoprotein aequorin was targeted to defined intracellular locations (organelles, such as mitochondria, endoplasmic reticulum, sarcoplasmic reticulum, Golgi apparatus and nucleus, and cytoplasmic regions, such as the bulk cytosol and the subplasmalemmal rim), and was used to analyse Ca2+ homoeostasis at the subcellular level. We will discuss this application, reviewing its advantages and disadvantages and the experimental procedure. The applications of green fluorescent protein (GFP) are even broader. Indeed, the ability to molecularly engineer and recombinantly express a strongly fluorescent probe has provided a powerful tool for investigating a wide variety of biological events in live cells (e.g. tracking of endogenous proteins, labelling of intracellular structures, analysing promoter activity etc.). More recently, the demonstration that, using appropriate mutants and/or fusion proteins, GFP fluorescence can become sensitive to physiological parameters or activities (ion concentration, protease activity, etc.) has further expanded its applications and made GFP the favourite probe of cell biologists. We will here present two applications in the field of cell signalling, i.e. the use of GFP chimaeras for studying the recruitment of protein kinase C isoforms and the activity of intracellular proteases.
Conserved C-terminal residues within the lectin-like domain of LOX-1 are essential for oxidized low-density-lipoprotein binding
Authors: CHEN Mingyi , NARUMIYA Shuh , MASAKI Tomoh , SAWAMURA Tatsuya
Published: August 2015

Lectin-like oxidized low-density-lipoprotein (oxLDL) receptor-1 (LOX-1) is a cell-surface endocytosis receptor for atherogenic oxLDL, which is highly expressed in endothelial cells. Recent studies suggest that it may play significant roles in atherogenesis. LOX-1 is a type-II membrane protein that structurally belongs to the C-type lectin family molecules. This study was designed to characterize the specific domain on LOX-1 that recognizes oxLDL. Truncation of the lectin domain of LOX-1 abrogated oxLDL-binding activity. Deletion of the utmost C-terminal ten amino acid residues (261-270) was enough to disrupt the oxLDL-binding activity. Substitutions of Lys-262 and/or Lys-263 with Ala additively attenuated the activity. Serial-deletion analysis showed that residues up to 265 are required for the expression of minimal binding activity, although deletion of the C-terminal three residues (268-270) still retained full binding activity. Consistently, these alterations in LOX-1 impaired the recognition by a functionally blocking monoclonal antibody for LOX-1. These data demonstrated the distinct role of the lectin domain as the functional domain recognizing LOX-1 ligand. The conserved C-terminal residues of lectin-like domain are essential for binding oxLDL. Particularly, the basic amino acid pair is important for the binding.
Heat-shock protein 90 augments neuronal nitric oxide synthase activity by enhancing Ca2+/calmodulin binding
Authors: SONG Yao , ZWEIER Jay L. , XIA Yong
Published: August 2015

Heat-shock protein 90 (hsp90) has been shown to facilitate neuronal NO synthase (nNOS, type 1) activity in vivo. But the direct effect of hsp90 on purified nNOS has not been determined yet. Moreover, the mechanism underlying the action of hsp90 is not known. nNOS activity is primarily initiated and regulated by the binding of Ca2+/calmodulin (CaM). Therefore, we explored whether hsp90 modulates nNOS activity by affecting CaM binding. Recombinant rat nNOS was purified from the stably transfected cells by affinity chromatography. hsp90 increased nNOS activity in a dose-dependent manner with an EC50 of 24.1±6.4nM. In the presence of hsp90, the CaM-nNOS dose-response curve was shifted markedly to the left and the maximal activity was also elevated. Further in vitro protein-binding experiments confirmed that hsp90 increased the binding of CaM to nNOS. Taken together, these data indicate that hsp90 directly augments nNOS catalytic function and that this effect is, at least partially, mediated by CaM-binding enhancement.
Expression of indoleamine 2,3-dioxygenase and tryptophan 2,3-dioxygenase in early concepti
Authors: SUZUKI Sachiko , TONÉ Shigenobu , TAKIKAWA Osamu , KUBO Toshikazu , KOHNO Ichiro , MINATOGAWA Yohsuke
Published: August 2015

Indoleamine 2,3-dioxygenase (IDO)-initiated tryptophan degradation in the placenta has been implicated in the prevention of the allogeneic fetus rejection [Munn, Zhou, Attwood, Bondarev, Conway, Marshall, Brown, and Mellor (1998) Science 281, 1191-1193]. To determine how IDO is associated with the development of the fetus and placenta, the time course of IDO expression (tryptophan-degrading activity, IDO protein and IDO mRNA) in the embryonic and extra-embryonic tissues as well as maternal tissues of mice was examined. A high tryptophan-degrading activity was detected in early concepti on days 6.5 and 7.5, whereas IDO protein and its mRNA were not expressed during early gestation, but appeared 2-3 days later, lasted for about 3 days and declined rapidly thereafter. The expression of IDO basically coincided with the formation of the placenta. On the contrary, the early tryptophan-degrading activity was due to gene expression of tryptophan 2,3-dioxygenase (TDO), as shown by Northern and Western analysis. These findings indicate that IDO is transiently expressed in the placenta but that the expression does not last until birth, and that the IDO expression is preceded by expression of another tryptophan-degrading enzyme, TDO, in the maternal and/or embryonic tissues in early concepti.
Identification and characterization of UDP-N-acetylenolpyruvylglucosamine reductase (MurB) from the Gram-positive pathogen Streptococcus pneumoniae
Authors: SYLVESTER Daniel R. , ALVAREZ Emilio , PATEL Arun , RATNAM Kapila , KALLENDER Howard , WALLIS Nicola G.
Published: August 2015

The UDP-N-acetylenolpyruvylglucosamine reductase (MurB) from a Gram-positive pathogen, Streptococcus pneumoniae, was identified and characterized. The enzyme from S. pneumoniae shows 31% identity with the MurB protein from Escherichia coli, and contains the catalytic residues, substrate-binding residues and FAD-binding motif identified previously in the E. coli protein. The gene was cloned into the pET28a+ expression vector, and the 34.5kDa protein that it encodes was overexpressed in E. coli strain BL21(DE3) to 30% of total cell protein. The majority of the protein was found to be insoluble. A variety of methods were used to increase the amount of soluble protein to 10%. This was then purified to near homogeneity in a two-step process. The absorption spectrum of the purified protein indicated it to be a flavoprotein, like its E. coli homologue, with a characteristic absorption at 463nm. The enzyme was shown to be active, reducing UDP-N-acetylglucosamine enolpyruvate with the concomitant oxidation of NADPH, and was characterized kinetically with respect to its two substrates. The enzyme showed properties similar to those of its E. coli counterpart, being activated by univalent cations and being subject to substrate inhibition. The characterization of an important cell wall biosynthesis enzyme from a Gram-positive pathogen provides a good starting point for the discovery of antibacterial agents against MurB.
Epidermal transformation leads to increased perlecan synthesis with heparin-binding-growth-factor affinity
Authors: TAPANADECHOPONE Pairath , TUMOVA Sarka , JIANG Xinnong , COUCHMAN John R.
Published: August 2015

Perlecan, a proteoglycan of basement membrane and extracellular matrices, has important roles in both normal biological and pathological processes. As a result of its ability to store and protect growth factors, perlecan may have crucial roles in tumour-cell growth and invasion. Since the biological functions of different types of glycosaminoglycan vary with cellular origin and structural modifications, we analysed the expression and biological functions of perlecan produced by a normal epidermal cell line (JB6) and its transformed counterpart (RT101). Expression of perlecan in tumorigenic cells was significantly increased in both mRNA and protein levels. JB6 perlecan was exclusively substituted with heparan sulphate, whereas that of RT101 contained some additional chondroitin sulphate. Detailed structural analysis of the heparan sulphate (HS) chains from perlecan of both cell types revealed that their overall sulphation and chain length were similar (≈ 60kDa), but the HS chains of tumour-cell-derived perlecan were less sulphated. This resulted from reduced 2-O- and 6-O-sulphation, but not N-sulphation, and an increase in the proportion of unsulphated disaccharides. Despite this, the heparan sulphate of RT101- and JB6-derived perlecan bound fibroblast growth factor-1, -2, -4 and -7 and heparin-binding epidermal growth factor with similar affinity. Therefore abundant tumour-derived perlecan may support the angiogenic responses seen in vivo and be a key player in tumorigenesis.
Electrospray and tandem mass spectrometry in biochemistry
Authors: GRIFFITHS William J. , JONSSON Andreas P. , LIU Suya , RAI Dilip K. , WANG Yuqin
Published: August 2015

Over the last 20 years, biological MS has changed out of all recognition. This is primarily due to the development in the 1980s of ‘soft ionization’ methods that permit the ionization and vaporization of large, polar, and thermally labile biomolecules. These developments in ionization mode have driven the design and manufacture of smaller and cheaper mass analysers, making the mass spectrometer a routine instrument in the biochemistry laboratory today. In the present review the revolutionary ‘soft ionization’ methods will be discussed with particular reference to electrospray. The mass analysis of ions will be described, and the concept of tandem MS introduced. Where appropriate, examples of the application of MS in biochemistry will be provided. Although the present review will concentrate on the MS of peptides/proteins and lipids, all classes of biomolecules can be analysed, and much excellent work has been done in the fields of carbohydrate and nucleic acid biochemistry.
Monocyte chemoattractant protein 1 causes differential signalling mediated by proline-rich tyrosine kinase 2 in THP-1 cells
Authors: YAMASAKI Masahide , ARAI Hidenori , ASHIDA Noboru , ISHII Kenji , KITA Toru
Published: August 2015

Monocyte chemoattractant protein 1 (MCP-1) has a crucial role in atherogenesis and inflammation. However, MCP-1-mediated signalling pathways in monocytes have not been fully elucidated. In the present study we investigated the role of tyrosine kinases such as proline-rich tyrosine kinase 2 (Pyk2) in MCP-1-mediated signal transduction in the monocytic cell line THP-1. Pyk2 was tyrosine phosphorylated very quickly after stimulation with MCP-1. We found that Lyn, Shc and paxillin were also tyrosine phosphorylated by MCP-1. We examined the association of these molecules by immunoprecipitation and immunoblot analysis. The association of Pyk2 with Lyn was dependent on stimulation with MCP-1 and on tyrosine phosphorylation of Pyk2. Phosphorylation of p38 was also dependent on tyrosine phosphorylation of Pyk2. However, the association of Pyk2 with paxillin and Grb2 was not affected by stimulation with MCP-1. Phosphorylation of ERK (extracellular-signal-regulated protein kinase) was not affected by overexpression of kinase-negative Pyk2. Our results indicate that Pyk2 forms a complex with paxillin, Grb2 and Lyn in THP-1 cells. However, Pyk2 is not always involved in MCP-1-mediated signalling pathways.
Mammalian inositol polyphosphate 5-phosphatase II can compensate for the absence of all three yeast Sac1-like-domain-containing 5-phosphatases
Authors: O'MALLEY Cindy J. , McCOLL Brad K. , KONG Anne M. , ELLIS Sarah L. , WIJAYARATNAM A. Primrose W. , SAMBROOK Joe , MITCHELL Christina A.
Published: August 2015

Phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] plays a complex role in generating intracellular signalling molecules, and also in regulating actin-binding proteins, vesicular trafficking and vacuolar fusion. Four inositol polyphosphate 5-phosphatases (hereafter called 5-phosphatases) have been identified in Saccharomyces cerevisiae: Inp51p, Inp52p, Inp53p and Inp54p. Each enzyme contains a 5-phosphatase domain which hydrolyses PtdIns(4,5)P2, forming PtdIns4P, while Inp52p and Inp53p also express a polyphosphoinositide phosphatase domain within the Sac1-like domain. Disruption of any two yeast 5-phosphatases containing a Sac1-like domain results in abnormalities in actin polymerization, plasma membrane, vacuolar morphology and bud-site selection. Triple null mutant 5-phosphatase strains are non-viable. To investigate the role of PtdIns(4,5)P2 in mediating the phenotype of double and triple 5-phosphatase null mutant yeast, we determined whether a mammalian PtdIns(4,5)P2 5-phosphatase, 5-phosphatase II, which lacks polyphosphoinositide phosphatase activity, could correct the phenotype of triple 5-phosphatase null mutant yeast and restore cellular PtdIns(4,5)P2 levels to near basal values. Mammalian 5-phosphatase II expressed under an inducible promoter corrected the growth, cell wall, vacuolar and actin polymerization defects of the triple 5-phosphatase null mutant yeast strains. Cellular PtdIns(4,5)P2 levels in various 5-phosphatase double null mutant strains demonstrated significant accumulation (4.5-, 3- and 2-fold for ∆inp51∆inp53, ∆inp51∆inp52 and ∆inp52∆inp53 double null mutants respectively), which was corrected significantly following 5-phosphatase II expression. Collectively, these studies demonstrate the functional and cellular consequences of PtdIns(4,5)P2 accumulation and the evolutionary conservation of function between mammalian and yeast PtdIns(4,5)P2 5-phosphatases.
In vitro studies of amyloid β-protein fibril assembly and toxicity provide clues to the aetiology of Flemish variant (Ala692→Gly) Alzheimer's disease
Authors: WALSH Dominic M. , HARTLEY Dean M. , CONDRON Margaret M. , SELKOE Dennis J. , TEPLOW David B.
Published: August 2015

In a Flemish kindred, an Ala692 → Gly amino acid substitution in the amyloid β-protein precursor (AβPP) causes a form of early-onset Alzheimer's disease (AD) which displays prominent amyloid angiopathy and unusually large senile plaque cores. The mechanistic basis of this Flemish form of AD is unknown. Previous in vitro studies of amyloid β-protein (Aβ) production in HEK-293 cells transfected with cDNA encoding Flemish AβPP have shown that full-length [Aβ(1–40)] and truncated [Aβ(5–40) and Aβ(11–40)] forms of Aβ are produced. In an effort to determine how these peptides might contribute to the pathogenesis of the Flemish disease, comparative biophysical and neurotoxicity studies were performed on wild-type and Flemish Aβ(1–40), Aβ(5–40) and Aβ(11–40). The results revealed that the Flemish amino acid substitution increased the solubility of each form of peptide, decreased the rate of formation of thioflavin-T-positive assemblies, and increased the SDS-stability of peptide oligomers. Although the kinetics of peptide assembly were altered by the Ala21 → Gly substitution, all three Flemish variants formed fibrils, as did the wild-type peptides. Importantly, toxicity studies using cultured primary rat cortical cells showed that the Flemish assemblies were as potent a neurotoxin as were the wild-type assemblies. Our results are consistent with a pathogenetic process in which conformational changes in Aβ induced by the Ala21 → Gly substitution would facilitate peptide adherence to the vascular endothelium, creating nidi for amyloid growth. Increased peptide solubility and assembly stability would favour formation of larger deposits and inhibit their elimination. In addition, increased concentrations of neurotoxic assemblies would accelerate neuronal injury and death.
Repression of the heavy ferritin chain increases the labile iron pool of human K562 cells
Authors: KAKHLON Or , GRUENBAUM Yosef , CABANTCHIK Z. Ioav
Published: August 2015

The role of ferritin in the modulation of the labile iron pool was examined by repressing the heavy subunit of ferritin in K562 cells transfected with an antisense construct. Repression of the heavy ferritin subunit evoked an increase in the chemical levels and pro-oxidant activity of the labile iron pool and, in turn, caused a reduced expression of transferrin receptors and increased expression of the light ferritin subunit
Thermostability of endo-1,4-β-xylanase II from Trichoderma reesei studied by electrospray ionization Fourier-transform ion cyclotron resonance MS, hydrogen/deuterium-exchange reactions and dynamic light scattering
Authors: JÄNIS Janne , ROUVINEN Juha , LEISOLA Matti , TURUNEN Ossi , VAINIOTALO Pirjo
Published: August 2015

Endo-1,4-β-xylanase II (XYNII) from Trichoderma reesei is a 21kDa enzyme that catalyses the hydrolysis of xylan, the major plant hemicellulose. It has various applications in the paper, food and feed industries. Previous thermostability studies have revealed a significant decrease in enzymic activity of the protein at elevated temperatures in citrate buffer [Tenkanen, Puls and Poutanen (1992) Enzyme Microb. Technol. 14, 566–574]. Here, thermostability of XYNII was investigated using both conventional and nanoelectrospray ionization Fourier-transform ion cyclotron resonance MS and hydrogen/deuterium (H/D)-exchange reactions. In addition, dynamic light scattering (DLS) was used as a comparative method to observe possible changes in both tertiary and quaternary structures of the protein. We observed a significant irreversible conformational change and dimerization when the protein was exposed to heat. H/D exchange revealed two distinct monomeric protein populations in a narrow transition temperature region. The conformational change in both the water and buffered solutions occurred in the same temperature region where enzymic-activity loss had previously been observed. Approx. 10–30% of the protein was specifically dimerized when exposed to the heat treatment. However, adding methanol to the solution markedly lowered the transition temperature of conformational change as well as increased the dimerization up to 90%. DLS studies in water confirmed the change in conformation observed by electrospray ionization MS. We propose that the conformational change is responsible for the loss of enzymic activity at temperatures over 50°C and that the functioning of the active site in the enzyme is unfeasible in a new, more labile solution conformation.
Intracellular ascorbic acid enhances the DNA single-strand breakage and toxicity induced by peroxynitrite in U937 cells
Authors: GUIDARELLI Andrea , de SANCTIS Roberta , CELLINI Barbara , FIORANI Mara , DACHÀ Marina , CANTONI Orazio
Published: August 2015

A well-established protocol to increase the intracellular content of ascorbic acid was used to investigate the effects of the vitamin on DNA single-strand breakage and toxicity mediated by authentic peroxynitrite (ONOO−) in U937 cells. This protocol involved exposure for 60min to 100μM dehydroascorbic acid, which was taken up by the cells and converted into ascorbic acid via a GSH-independent mechanism. At the time of exposure to ONOO−, which was performed in fresh saline immediately after loading with dehydroascorbic acid, the vitamin present in the cells was all in its reduced form. It was found that, in cells that are otherwise ascorbate-deficient, an increase in their ascorbic acid content does not prevent, but rather enhances, the DNA-damaging and lethal responses mediated by exogenous ONOO−. These results therefore suggest that acute supplementation of ascorbic acid can be detrimental for individuals with pathologies associated with a decrease in ascorbic acid and in which ONOO− is known to promote deleterious effects.
Distribution of protein disulphide isomerase in rat liver mitochondria
Authors: RIGOBELLO Maria Pia , DONELLA-DEANA Arianna , CESARO Luca , BINDOLI Alberto
Published: August 2015

Here we report the localization of protein disulphide isomerase (PDI) in the mitochondrial compartments, comparing it with that of thioredoxin reductase. The latter enzyme is present mostly in the matrix, whereas PDI is located at the level of the outer membrane. We characterize the different submitochondrial fractions with specific marker enzymes. PDI, whether isolated from whole mitochondria or from purified outer membranes, exhibits the same electrophoretic mobility, indicating identical molecular masses. Moreover, immunoblot analysis with monoclonal anti-PDI antibody shows immunoreactivity only with the microsomal PDI, indicating the specificity of the mitochondrial isoform. The significance of these findings is discussed with reference to the potential role of PDI and thioredoxin reductase in regulating the mitochondrial functions dependent on the thiol–disulphide transition.
Endosomal localization of phospholipase D 1a and 1b is defined by the C-termini of the proteins, and is independent of activity
Authors: HUGHES William E. , PARKER Peter J.
Published: August 2015

The factors regulating the activity of cellular phospholipase D (PLD) have been well characterized; however, the cellular distribution of specific PLD isoforms and the factors defining localization are less clear. Two specific PLD1 isoforms, PLD1a and PLD1b, are shown in the present study to be localized in endosomal compartments with early endosomal autoantigen 1, internalizing epidermal growth factor receptor (ErbB1) and lysobisphosphatidic acid. Novel C-terminal splice variants of PLD1, PLD1a2 and PLD1b2, do not exhibit this endosomal localization. Studies using catalytically inactive and C-terminal deletion mutants of the four PLD1 isoforms led to the conclusion that the C-terminus plays an important part in the catalytic activity of PLD1, but that the endosomal localization of PLD1a and PLD1b is defined by the C-terminus and not catalytic activity.
Identification of novel β-mannan- and β-glucan-binding modules: evidence for a superfamily of carbohydrate-binding modules
Authors: SUNNA Anwar , GIBBS Moreland D. , BERGQUIST Peter L.
Published: August 2015

Many glycoside hydrolases, which degrade long-chain carbohydrate polymers, possess distinct catalytic modules and non-catalytic carbohydrate-binding modules (CBMs). On the basis of conserved protein secondary structure, we describe here the identification and experimental characterization of novel type of mannanase-associated mannan-binding module and also characterization of two CBM family 4 laminarinase-associated β-glucan-binding modules. These modules are predicted to belong to a superfamily of CBMs which include families 4, 16, 17, 22 and a proposed new family, family 27.
Interaction of human thymidine kinase 1 with p21Waf1
Authors: HUANG Duen-Yi , CHANG Zee-Fen
Published: August 2015

The overexpression of the cyclin-dependent kinase (CDK) inhibitor p21Waf1 can inhibit cell proliferation, which is mediated by direct binding to CDK and proliferating-cell nuclear antigen. In this study, we demonstrated that human cytosolic thymidine kinase 1 (TK1) polypeptide can form a complex with p21Waf1. The C-terminal domain of p21Waf1 appeared to interact with the TK1 polypeptide, but, despite the inhibitory function of p21Waf1, their association did not alter TK1 functional activity. However, overexpression of TK1 overcame p21Waf1-mediated growth suppression and blocked the association of CDK2 with p21Waf1, suggesting that TK1 interferes with the inhibitory function of p21Waf1. Based on these results, we here propose that the molecular function of p21Waf1 in cells can be perturbed through its interaction with another cellular protein, TK1.
Proteasomes are a target of the anti-tumour drug vinblastine
Authors: PICCININI Marco , TAZARTES Ornella , MEZZATESTA Caterina , RICOTTI Emanuela , BEDINO Stefano , GROSSO Franca , DIANZANI Umberto , TOVO Pier-Angelo , MOSTERT Michael , MUSSO Alberto , RINAUDO Maria T.
Published: August 2015

Proteasomes, the proteolytic machinery of the ubiquitin/ATP-dependent pathway, have a relevant role in many processes crucial for cell physiology and cell cycle progression. Proteasome inhibitors are used to block cell cycle progression and to induce apoptosis in certain cell lines. Here we examine whether proteasomal function is affected by the anti-tumour drug vinblastine, whose cytostatic action relies mainly on the disruption of mitotic spindle dynamics. The effects of vinblastine on the peptidase activities of human 20S and 26S proteasomes and on the proteolytic activity of 26S proteasome were assessed in the presence of specific fluorogenic peptides and 125I-lysozyme–ubiquitin conjugates respectively. The assays of ubiquitin–protein conjugates and of inhibitory κBα (IκBα), which are characteristic intracellular proteasome substrates, by Western blotting on lysates from HL60 cells incubated with or without vinblastine, illustrated the effects of vinblastine on proteasomes in vivo. We also evaluated the effects of vinblastine on the signal-induced degradation of IκBα. Vinblastine at 3–110μM reversibly inhibited the chymotrypsin-like activity of the 20 S proteasome and the trypsin-like and peptidyl-glutamyl-peptide hydrolysing activities of both proteasomes, but only at 110μM vinblastine was the chymotrypsin-like activity of the 26S proteasome inhibited; furthermore, at 25–200μM the drug inhibited the degradation of ubiquitinated lysozyme. In HL60 cells exposed for 6h to 0.5–10μM vinblastine, the drug-dose-related accumulation of polyubiquitinated proteins, as well as that of a high-molecular-mass form of IκBα, occurred. Moreover, vinblastine impaired the signal-induced degradation of IκBα. Cell viability throughout the test was approx. 95%. Proteasomes can be considered to be a new and additional vinblastine target.
Cholesterol-dependent interaction of syncollin with the membrane of the pancreatic zymogen granule
Authors: HODEL Alois , AN Seong J. , HANSEN Neal J. , LAWRENCE Jared , WÄSLE Barbara , SCHRADER Michael , EDWARDSON J. Michael
Published: August 2015

Syncollin is a protein of the pancreatic zymogen granule that was isolated through its ability to bind to syntaxin. Despite this in vitro interaction, it is now clear that syncollin is present on the luminal side of the zymogen granule membrane. Here we show that there are two pools of syncollin within the zymogen granule: one free in the lumen and the other tightly associated with the granule membrane. When unheated or cross-linked samples of membrane-derived syncollin are analysed by SDS/PAGE, higher-order forms are seen in addition to the monomer, which has an apparent molecular mass of 16kDa. Extraction of cholesterol from the granule membrane by treatment with methyl-β-cyclodextrin causes the detachment of syncollin, and this effect is enhanced at a high salt concentration. Purified syncollin is able to bind to brain liposomes at pH5.0, but not at pH11.0, a condition that also causes its extraction from granule membranes. Syncollin binds only poorly to dioleoyl phosphatidylcholine liposomes, but binding is dramatically enhanced by the inclusion of cholesterol. Finally, cholesterol can be co-immunoprecipitated with syncollin. We conclude that syncollin is able to interact directly with membrane lipids, and to insert into the granule membrane in a cholesterol-dependent manner. Membrane-associated syncollin apparently exists as a homo-oligomer, possibly consisting of six subunits, and its association with the membrane may be stabilized by electrostatic interactions with either other proteins or phospholipids.
Effect of iron deficiency on placental transfer of iron and expression of iron transport proteins in vivo and in vitro
Authors: GAMBLING Lorraine , DANZEISEN Ruth , GAIR Susan , LEA Richard G. , CHARANIA Zehane , SOLANKY Nita , JOORY Kavita D. , SRAI S. Kaila S. , McARDLE Harry J.
Published: August 2015

Maternal iron deficiency during pregnancy induces anaemia in the developing fetus; however, the severity tends to be less than in the mother. The mechanism underlying this resistance has not been determined. We have measured placental expression of proteins involved in iron transfer in pregnant rats given diets with decreasing levels of iron and examined the effect of iron deficiency on iron transfer across BeWo cell layers, a model for placental iron transfer. Transferrin receptor expression was increased at both mRNA and protein levels. Similarly, expression of the iron-responsive element (IRE)-regulated form of the divalent metal transporter 1 (DMT1) was also increased. In contrast, the non-IRE regulated isoform showed no change in mRNA levels. Protein levels of DMT1 increased significantly. Iron efflux is thought to be mediated by the metal transporter protein, IREG1/ferroportin1/MTP1, and oxidation of Fe(II) to Fe(III) prior to incorporation into fetal transferrin is carried out by the placental copper oxidase. Expression of IREG1 was not altered by iron deficiency, whereas copper oxidase activity was increased. In BeWo cells made iron deficient by treatment with desferrioxamine (‘deferioxamine’), iron accumulation from iron-transferrin increased, in parallel with increased expression of the transferrin receptor. At the same time, iron efflux also increased, showing a higher flux of iron from the apical to the basolateral side. The data show that expression of placental proteins of iron transport are up-regulated in maternal iron deficiency, resulting in an increased efficiency of iron flux and a consequent minimization of the severity of fetal anaemia.
Transcriptional regulation of the human cystathionine β-synthase −1b basal promoter: synergistic transactivation by transcription factors NF-Y and Sp1/Sp3
Authors: GE Yubin , KONRAD Mark A. , MATHERLY Larry H. , TAUB Jeffrey W.
Published: August 2015

Cystathionine β-synthase (CBS) catalyses the condensation of serine and homocysteine to form cystathionine, an intermediate step in the synthesis of cysteine. Human CBS encodes five distinct 5′ non-coding exons, the most frequent termed CBS −1a and CBS −1b, each transcribed from its own unique GC-rich TATA-less promoter. The minimal transcriptional region (−3792 to −3667) of the CBS −1b promoter was defined by 5′- and 3′-deletions, and transient transfections of reporter gene constructs in HepG2 cells, characterized by CBS transcription exclusively from the −1b promoter. Included in this 125bp region are 3 GC-boxes (termed GC-a, GC-b and GC-c), an inverted CAAT-box and an E-box. By gel-shift and supershift assays, binding of specificity protein (Sp)1 and Sp3 to the GC-box elements, upstream stimulatory factor 1 (USF-1) to the E-box, and both nuclear factor (NF)-Y and an NF-1-like factor to the CAAT box could be demonstrated. By transient trans fections and reporter gene assays in HepG2 and Drosophila SL2 cells, a functional interplay was indicated between NF-Y binding to the CAAT-box, or between USF-1 binding to the E-box, and Sp1/Sp3 binding to the GC-box elements. In SL2 cells, NF-Y and Sp1/Sp3 were synergistic. Furthermore, both Sp1 and the long Sp3 isoform transactivated the CBS −1b minimal promoter; however, the short Sp3 isoforms were potent repressors. These results may explain the cell- or tissue-specific regulation of CBS transcription, and clarify the bases for alterations in CBS gene expression in human disease and Down's syndrome.
Characterization of the cyanobacterial ycf37: mutation decreases the photosystem I content
Authors: WILDE Annegret , LÜNSER Katja , OSSENBÜHL Friedrich , NICKELSEN Jörg , BÖRNER Thomas
Published: August 2015

We have constructed and analysed a cyanobacterial mutant that lacks the putative homologue of ycf37, the chloroplast open reading frame 37, which is conserved in different algae, but missing in the plastome of higher plants. In this report we show that Ycf37 of Synechocystis sp. PCC 6803 contains three tetratrico-peptide repeat (TPR) units resembling the structural organization of Ycf3, a protein that has been suggested to function as a chaperone during photosystem (PS) I complex formation. We demonstrate a light-activated transcript accumulation of this gene. Inactivation of ycf37 leads to a lower PSI/PSII ratio and a higher phycocyanin/chlorophyll ratio in Synechocystis cells. The observed alterations in the ycf37 mutants and the structural organization of the gene product suggest a functional role in PSI stability or assembly.
Homocysteine stimulates the expression of monocyte chemoattractant protein-1 receptor (CCR2) in human monocytes: possible involvement of oxygen free radicals
Authors: WANG Guoping , O Karmin
Published: August 2015

Homocysteinaemia is an independent risk factor for atherosclerosis. The development of atherosclerosis involves monocyte chemoattractant protein 1 (MCP-1)-mediated monocyte recruitment to the lesion site. The action of MCP-1 is mostly via its interaction with MCP-1 receptor (CCR2), which is the major receptor for MCP-1 on the surface of monocytes. The objective of the present study was to investigate the effect of homocysteine on CCR2 expression in human THP-1 monocytes. Cells were incubated with various concentrations of homocysteine for 6, 12, 24 and 48h. The expression of CCR2 mRNA was determined by nuclease protection assay and the CCR2 protein was measured by Western immunoblotting analysis. The binding of MCP-1 to CCR2 as a functional receptor on the monocyte surface was determined by flow cytometry. Homocysteine (0.05–0.2mM) significantly enhanced the expression of CCR2 mRNA (129–209% of the control) and CCR2 protein (up to 183% of control) in these cells after 24h of incubation. Stimulation of CCR2 expression was associated with a parallel increase in the binding activity of CCR2 (129–191% of control) as well as an enhanced chemotactic response of homocysteine-treated monocytes. Further investigation revealed that the levels of superoxide were significantly elevated in cells incubated with homocysteine for 12–48h. The addition of superoxide dismutase, a scavenger of superoxide, to the culture medium abolished the stimulatory effect of homocysteine on CCR2 expression as well as the binding activity of the receptor. The stimulatory effect of homocysteine on the expression of CCR2 mRNA and the levels of CCR2 protein was also observed in human peripheral blood monocytes. In conclusion, the present study has clearly demonstrated that homocysteine stimulates CCR2 expression in monocytes, leading to an enhanced binding activity and chemotatic response. Homocysteine-induced superoxide formation might serve as one of the underlying mechanisms for this effect.
Fatty acids inhibit growth-factor-induced diacylglycerol kinase α activation in vascular smooth-muscle cells
Authors: DU Xiangnan , JIANG Ying , QIAN Weijun , LU Xiaolan , WALSH James P.
Published: August 2015

We have previously shown that unsaturated fatty acids amplify platelet-derived-growth-factor (PDGF)-induced protein kinase C (PKC) activation in vascular smooth-muscle cells (VSMCs). Diacylglycerol-induced PKC activation is normally terminated by diacylglycerol kinases (DGKs). We thus hypothesized that fatty acids act by inhibiting a DGK. Fractionation of VSMC extracts demonstrated that the DGK α isoform was the major DGK activity present. PDGF markedly increased the DGK activity of cultured cells. An inhibitor selective for the DGK α isoform,R59949[3-{2-[4-(bis-(4-fluorophenyl)methylene]piperidin-1-yl)ethyl}-2,3-dihydro-2-thioxo-4(1H)-quinazolinone], abolished the growth-factor-induced increase in DGK activity, but had little effect on basal activity. PDGF thus selectively activates DGKα. Epidermal growth factor and α-thrombin stimulated total DGK activity similarly to PDGF. Activation by epidermal growth factor was sensitive to R59949, again suggesting involvement of DGKα. However, the α-thrombin-induced activity was unaffected by this agent. Unsaturated fatty acids inhibited growth-factor-induced DGKα activation, but had no effect on basal activity. Fatty acids also amplified the PDGF-induced increase in cell diacylglycerol content. These results indicate that inhibition of DGKα contributes to fatty-acid-induced amplification of PKC activation. Increased levels of fatty acids in diabetes may thus contribute to chronic PKC activation associated with this disorder.
Mitogen-activated protein kinases control p27/Kip1 expression and growth of human melanoma cells
Authors: KORTYLEWSKI Marcin , HEINRICH Peter C. , KAUFFMANN Maria-Elisabeth , BÖHM Markus , MACKIEWICZ Andrzej , BEHRMANN Iris
Published: August 2015

The mitogen-activated protein kinases (MAPKs) extracellular signal-regulated protein kinase (ERK)1 and ERK2, involved in regulating cell growth and differentiation, are constitutively active in A375 and WM239 human melanoma cells. Using PD098059, an inhibitor of MAPK kinase (MEK), we investigated the role of persistently activated ERK1/2 in cell growth. The inhibition of MAPK activity induced a dose-dependent growth arrest in G0/G1 phase. Correspondingly, we observed the up-regulation of the cyclin-dependent kinase (Cdk) inhibitor p27/Kip1 and hypophosphorylation of the retinoblastoma protein. Further studies showed that PD098059 treatment significantly decreased Cdk2 kinase activity, most probably owing to an augmented level of p27/Kip1 associated with cyclin E–Cdk2 complexes. The accumulation of p27/Kip1 protein in A375 cells was attributed to its increased stability. Our findings suggest that constitutively active ERK1/2 kinases contribute to the growth of melanoma cells by negative regulation of the p27/Kip1 inhibitor.
Identification and characterization of molecular interactions between glucose-regulated proteins (GRPs) mortalin/GRP75/peptide-binding protein 74 (PBP74) and GRP94
Authors: TAKANO Syuichi , WADHWA Renu , MITSUI Youji , KAUL Sunil C.
Published: August 2015

A heat-shock protein (hsp) 70 family member mortalin/glucose-regulated protein (GRP) 75/peptide-binding protein 74 (PBP74) has been localized to various cellular compartments including mitochondria, endoplasmic reticulum and cytoplasmic vesicles. Here we describe its interactions with an endoplasmic reticulum protein GRP94, a member of the hsp90 family of GRPs. Interactions were identified, confirmed and characterized by far-Western screening, in vivo reporter and co-immunoprecipitation assays. Interacting domains of the two proteins were also characterized by mutational analysis. Such interactions of these two GRPs may be important for function of either or both and therefore provide important information for further studies.
Platelet-activating factor acetylhydrolase and transacetylase activities in human plasma low-density lipoprotein
Authors: TSOUKATOS Demokritos C. , LIAPIKOS Theodoros A. , TSELEPIS Alexandros D. , CHAPMAN M. John , NINIO Ewa
Published: August 2015

In this study, we demonstrate the presence of a transacetylase activity in human plasma low-density lipoprotein (LDL) that transfers short-chain fatty acids from platelet-activating factor (PAF) and its close ether- and ester-linked analogues to ether/ester-linked lysophospholipids (lyso-PL). We show evidence that both PAF acetylhydrolase (PAF-AH) and transacetylase activities are inhibited to the same extent by serine esterase inhibitors, are resistant to heat treatment, and exhibit identical distributions in lipoprotein classes and in LDL subfractions. Additionally, the competitive inhibition of PAF-AH by lyso-PL, and the evidence that the recombinant PAF-AH also showed a similar transacetylase activity, suggest that PAF-AH is responsible for both activities. Using PAF as a donor molecule and lyso-PAF (1-O-alkyl-sn-glycero-3-phosphocholine) as an acceptor, the transacetylase activity showed typical allosteric kinetics, due to the positive co-operativity of the substrates, with apparent Vmax = 19.6±3.4nmol/min per mg of protein, apparent h = 2.0±0.3 and apparent [S]0.5 = 9.4±2.3μM at saturation for the concentration of lyso-PAF. The substrate specificity of the donor molecules was decreased by increasing the chain length of the acyl moiety in the sn-2 position of the glycerol. The ether linkage in the sn-1 position of the substrate was 30% more effective than the ester bond; cholesteryl acetate was inactive as an acetyl donor. The two acceptors tested, lyso-PAF and the ester-linked lyso-PC (1-acyl-sn-glycero-3-phosphocholine), showed similar specificity. Addition of exogenous lyso-PAF induced the transient formation of PAF-like aggregating activity predominately in small dense LDL subfractions upon oxidation. We conclude that PAF-AH possesses both transacetylase and acetylhydrolase activities which remove PAF and its ether-linked analogues from LDL particles upon LDL oxidation. However, in atherogenic small dense LDL-5 particles, the transacetylase activity may acetylate extracellular lyso-PAF into biologically active PAF.
Wortmannin-sensitive trafficking steps in the endocytic pathway in rat liver endothelial cells
Authors: KJEKEN Rune , MOUSAVI Seyed A. , BRECH Andreas , GRIFFITHS Gareth , BERG Trond
Published: August 2015

Liver endothelial cells (LECs) play an important homoeostatic role by removing potentially harmful macromolecules from blood. The extremely efficient endocytosis in LECs makes these cells an interesting model for the study of the involvement of phosphoinositides in the different steps of the endocytic process. In the present investigation we have studied the effect of wortmannin, an inhibitor of phosphatidylinositol kinases, on uptake, recycling and intracellular transport of 125I-labelled ovalbumin, which is taken up in LECs via mannose-receptor-mediated endocytosis. Wortmannin was found to inhibit both uptake and degradation of ovalbumin. Further studies indicated that the reduced uptake via the mannose receptor was due both to a reduction of the number of surface receptors and a reduction in the rate of receptor–ligand internalization. Transport of ligand from endosomes to lysosomes was prevented, leading to increased recycling of internalized ligand. Wortmannin treatment released the Rab5 effector EEA1 from the endosomes and caused reduced size of early endosomes.
Determination of the chemical structure of the capsular polysaccharide of strain B33, a fast-growing soya bean-nodulating bacterium isolated from an arid region of China
Authors: RODRÍGUEZ-CARVAJAL Miguel A. , TEJERO-MATEO Pilar , ESPARTERO José L. , RUIZ-SAINZ José. E. , BUENDÍA-CLAVERÍA Ana M. , OLLERO Francisco Javier , YANG Su S. , GIL-SERRANO Antonio M.
Published: August 2015

We have determined the structure of a polysaccharide from strain B33, a fast-growing bacterium that forms nitrogen-fixing nodules with Asiatic and American soya bean cultivars. On the basis of monosaccharide analysis, methylation analysis, one-dimensional 1H- and 13C-NMR and two-dimensional NMR experiments, the structure was shown to consist of a polymer having the repeating unit → 6)-4-O-methyl-α-d-Glcp-(1 → 4)-3-O-methyl-β-d-GlcpA-(1 → (where GlcpA is glucopyranuronic acid and Glcp is glucopyranose). Strain B33 produces a K-antigen polysaccharide repeating unit that does not have the structural motif sugar-Kdx [where Kdx is 3-deoxy-d-manno-2-octulosonic acid (Kdo) or a Kdo-related acid] proposed for different Sinorhizobium fredii strains, all of them being effective with Asiatic soya bean cultivars but unable to form nitrogen-fixing nodules with American soya bean cultivars. Instead, it resembles the K-antigen of S. fredii strain HH303 (rhamnose, galacturonic acid)n, which is also effective with both groups of soya bean cultivars. Only the capsular polysaccharide from strains B33 and HH303have monosaccharide components that are also present in the surface polysaccharide of Bradyrhizobium elkanii strains, which consists of a 4-O-methyl-d-glucurono-l-rhamnan.
Human cyritestin genes (CYRN1 and CYRN2) are non-functional
Authors: GRZMIL Pawel , KIM Youngmin , SHAMSADIN Rahman , NEESEN Jürgen , ADHAM Ibrahim M. , HEINLEIN Uwe A. O. , SCHWARZER Ullrich J. , ENGEL Wolfgang
Published: August 2015

The mouse cyritestin gene is a member of the ADAM (adisintegrin and metalloprotease) gene family and codes for a membrane-anchored sperm protein. Recently, it was shown that cyritestin is critical for male fertility in the mouse. Spermatozoa of cyritestin-deficient mice are not able to bind to the zona pellucida of the oocyte and therefore unable to fertilize the egg. However, zona-free oocytes can be fertilized and the resulting embryos show normal development. In contrast to the mouse, where only one gene for cyritestin (Cyrn) is reported, two cyritestin genes (CYRN1 and CYRN2) are known in humans. The human CYRN1 and CYRN2 genes are located on chromosomes 8 and 16, respectively. We report that 27% of fertile men are deficient for the CYRN1 gene but that all have a CYRN2 gene, suggesting that the CYRN2 gene is the orthologous mouse cyritestin gene in humans and might be involved in sperm–egg interactions. However, the characterization of CYRN2 transcripts from testicular RNA of CYRN1-deficient men demonstrated many termination codons in the synthesized cyritestin cDNA. Furthermore, Western-blot analysis with human testicular protein extracts using an anti-cyritestin antibody failed to detect any cyritestin protein. These results demonstrate clearly that both cyritestin genes are non-functional in humans.
Glucose 6-phosphate transport in fibroblast microsomes from glycogen storage disease type 1b patients: evidence for multiple glucose 6-phosphate transport systems
Authors: LEUZZI Rosanna , FULCERI Rosella , MARCOLONGO Paola , BÁNHEGYI Gábor , ZAMMARCHI Enrico , STAFFORD Kirsten , BURCHELL Ann , BENEDETTI Angelo
Published: August 2015

In liver endoplasmic reticulum the intralumenal glucose-6-phosphatase activity requires the operation of a glucose 6-phosphate transporter (G6PT1). Mutations in the gene encoding G6PT1 cause glycogen storage disease type 1b, which is characterized by a loss of glucose-6-phosphatase activity and impaired glucose homoeostasis. We describe a novel glucose 6-phosphate (G6P) transport activity in microsomes from human fibroblasts and HeLa cells. This transport activity is unrelated to G6PT1 since: (i) it was similar in microsomes of skin fibroblasts from glycogen storage disease type 1b patients homozygous for mutations of the G6PT1 gene, and in microsomes from human control subjects; (ii) it was insensitive to the G6PT1 inhibitor chlorogenic acid; and (iii) it was equally active towards G6P and glucose 1-phosphate, whereas G6PT1 is highly selective for G6P. Taken together, our results provide evidence for the presence of multiple transporters for G6P (and other hexose phosphoesters) in the endoplasmic reticulum.