bluuebunny/crossref_metadata_2025 huggingface dataset:
Metallothionein modulates lipopolysaccharide-stimulated tumour necrosis factor expression in mouse peritoneal macrophages
Authors: KANEKIYO Masako , ITOH Norio , KAWASAKI Atsuko , MATSUYAMA Akiko , MATSUDA Kimihiro , NAKANISHI Tsuyoshi , TANAKA Keiichi
Published: August 2015

Metallothionein (MT) is a low-molecular-mass, cysteine-rich metal binding protein thought to be involved in the detoxification of heavy metals and scavenging of free radicals. MT is directly induced not only by heavy metals, but also by hormones and cytokines. The present study, which uses mice with genetic deletions of the MT proteins (MT−/- mice), was designed to evaluate the effects of MT on the expression of pro-inflammatory cytokines in macrophages. We found that the production of tumour necrosis factor (TNF) induced by lipopolysaccharide (LPS) in peritoneal macrophages is up-regulated by MT via the modulation of nuclear factor κB (NF-κB) activity. This conclusion is supported by the following observations: (1) LPS stimulated the secretion of less TNF activity from MT−/- peritoneal exudate macrophages (PEMs) than from wild-type controls (MT+/+ mice) without a difference in the pattern of kinetics; (2) LPS-stimulated expression of TNF-α mRNA was decreased in MT−/- PEMs; (3) LPS-stimulated activation of NF-κB was decreased in MT−/- PEMs; and (4) production of TNF in PEMs of MT−/- mice after LPS treatment in vivo was decreased (compared with MT+/+ PEMs). Expression of other inflammatory cytokines, interleukin (IL)-1α and IL-6 mRNA, which were modulated by NF-κB, were also down-regulated in MT−/- PEMs. Thus MT plays a key role in the LPS-induced activation of PEMs via the modulation of NF-κB activity.
A novel cycling assay for cellular cADP-ribose with nanomolar sensitivity
Authors: GRAEFF Richard , LEE Hon Cheung
Published: August 2015

cADP-ribose (cADPR) is a novel cyclic nucleotide derived from NAD+ that has now been established as a general Ca2+ messenger in a wide variety of cells. Despite the obvious importance of monitoring its cellular levels under various physiological conditions, its measurement has been technically difficult and requires specialized reagents. In this study a widely applicable high-sensitivity assay for cADPR is described. ADP-ribosyl cyclase normally catalyses the synthesis of cADPR from NAD+, but the reaction can be reversed in the presence of high concentrations of nicotinamide, producing NAD+ from cADPR stoichiometrically. The resultant NAD+ can then be coupled to a cycling assay involving alcohol dehydrogenase and diaphorase. Each time NAD+ cycles through these coupled reactions, a molecule of highly fluorescent resorufin is generated. The reaction can be conducted for hours, resulting in more than a thousand-fold amplification of cADPR. Concentrations of cADPR in the nanomolar range can be measured routinely. The unique ability of ADP-ribosyl cyclase to catalyse the reverse reaction provides the required specificity. Using this assay, it is demonstrated that cADPR is present in all tissues tested and that the levels measured are directly comparable with those obtained using a radioimmunoassay. All the necessary reagents are widely available and the assay can be performed using a multiwell fluorescence plate reader, providing a high-throughput method for monitoring cADPR levels. This assay should be valuable in elucidating the messenger role of cADPR in cells.
Carnitine biosynthesis in mammals
Authors: VAZ Frédéric M. , WANDERS Ronald J. A.
Published: August 2015

Carnitine is indispensable for energy metabolism, since it enables activated fatty acids to enter the mitochondria, where they are broken down via β-oxidation. Carnitine is probably present in all animal species, and in numerous micro-organisms and plants. In mammals, carnitine homoeostasis is maintained by endogenous synthesis, absorption from dietary sources and efficient tubular reabsorption by the kidney. This review aims to cover the current knowledge of the enzymological, molecular, metabolic and regulatory aspects of mammalian carnitine biosynthesis, with an emphasis on the human and rat.
Tankyrase-2 oligomerizes with tankyrase-1 and binds to both TRF1 (telomere-repeat-binding factor 1) and IRAP (insulin-responsive aminopeptidase)
Authors: SBODIO Juan I. , LODISH Harvey F. , CHI Nai-Wen
Published: August 2015

The poly(ADP-ribose) polymerase (PARP) tankyrase-1 contains an ankyrin-repeat domain that binds to various partners, including the telomeric protein TRF1 (telomere-repeat-binding factor 1) and the vesicular protein IRAP (insulin-responsive aminopeptidase). TRF1 binding recruits tankyrase-1 to telomeres and allows its PARP activity to regulate telomere homoeostasis. By contrast, IRAP binding and the Golgi co-localization of tankyrase-1 with IRAP might allow tankyrase-1 to affect the targeting of IRAP-containing vesicles. A closely related protein, tankyrase-2, has also been implicated in vesicular targeting. Unlike tankyrase-1, tankyrase-2 has not been shown to have PARP activity. In addition, it has not been implicated in telomere homoeostasis, because it did not interact with TRF1 in previous studies. Here we show that tankyrase-2 contains intrinsic PARP activity and, like tankryase-1, binds to both TRF1 and IRAP. Our analysis suggests that the ankyrin (ANK) domain of tankyrase-2 comprises five subdomains that provide redundant binding sites for IRAP. Moreover, tankyrase-2 associates and co-localizes with tankyrase-1, suggesting that both tankyrases might function as a complex. Taken together, our findings indicate that tankyrase-1 and tankyrase-2 interact with the same set of proteins and probably mediate overlapping functions, both at telomeres and in vesicular compartments.
Oxysterol-binding-protein (OSBP)-related protein 4 binds25-hydroxycholesterol and interacts with vimentin intermediate filaments
Authors: WANG Cheng , JeBAILEY Lellean , RIDGWAY Neale D.
Published: August 2015

Oxysterol-binding protein (OSBP) is the prototypical member of a class of phospholipid and oxysterol-binding proteins that interacts with the Golgi apparatus and regulates lipid and cholesterol metabolism. As a result of recent sequencing efforts, eleven other OSBP-related proteins (ORPs) have been identified in humans. We have investigated the structure, oxysterol-binding activity, cellular localization and function of ORP4 (also designated OSBP2 or HLM), a homologue that shares the highest degree of similarity with OSBP. Two ORP4 cDNAs were identified: a full-length ORP4 containing a pleckstrin homology (PH) domain and an oxysterol-binding region (designated ORP4-L), and a splice variant in which the PH domain and part of the oxysterol-binding domain were deleted (designated ORP4-S). ORP4 mRNA and protein expression overlapped partially with OSBP and were restricted to brain, heart, muscle and kidney. Like OSBP, ORP4-L bound [3H]25-hydroxycholesterol with high affinity and specificity. In contrast, ORP4-S did not bind [3H]25-hydroxycholesterol or [3H]7-ketocholesterol. Immunofluorescence localization in stably transfected Chinese hamster ovary cells showed that ORP4-S co-localized with vimentin and caused the intermediate filament network to bundle or aggregate. ORP4-L displayed a diffuse staining pattern that did not overlap with vimentin except when the microtubule network was disrupted with nocodazole. Oxysterols had no effect on the localization of either ORP4. Cells overexpressing ORP4-S had a 40% reduction in the esterification of low-density-lipoprotein-derived cholesterol, demonstrating that ORP4 interaction with intermediate filaments inhibits an intracellular cholesterol-transport pathway mediated by vimentin. These studies elucidate a hitherto unknown relationship between OSBPs and the intermediate filament network that influences cholesterol transport.
Chimaeric gonadotropin-releasing hormone (GnRH) peptides with improved affinity for the catfish (Clarias gariepinus) GnRH receptor
Authors: BLOMENRÖHR Marion , TER LAAK Ton , KÜHNE Ronald , BEYERMANN Michael , HUND Eveline , BOGERD Jan , LEURS Rob
Published: August 2015

The gonadotropin-releasing hormone (GnRH) receptor in catfish differs from its mammalian counterparts in showing a very low affinity for the hypothalamic GnRH form [i.e. catfish GnRH (cfGnRH)] and a very high affinity for the highly conserved mesencephalic GnRH, chicken GnRH-II (cGnRH-II). In the present study we investigated the molecular interactions between ligand and receptor involved in determining the ligand selectivity of the catfish GnRH receptor. Studies on the binding characteristics of the catfish GnRH receptor for cfGnRH and cGnRH-II as well as for mammalian GnRH (mGnRH) and synthetic chimaeric GnRHs, differing at positions 5, 7 and 8, revealed that the low affinity of the catfish receptor for cfGnRH can be improved by replacing Leu7 by a tryptophan residue and/or Asn8 by either a tyrosine or an arginine residue. Testing cfGnRH and cGnRH-II as well as mGnRH and the chimaeric GnRHs on Asp304 → Ala, Asp304 → Glu and Asp304 → Asn mutant catfish GnRH receptors revealed that Asp304 of the catfish receptor mediates the recognition of Arg8 in mGnRH, as well as in the chimaeric peptides [Arg8]cfGnRH and [Arg8]cGnRH-II, but seems to be less important for the recognition of Tyr8 in cGnRH-II. On the basis of these results, a three-dimensional model for the binding of [Arg8]cGnRH-II to the catfish GnRH receptor is proposed.
Evidence that the tandem-pleckstrin-homology-domain-containing protein TAPP1 interacts with Ptd(3,4)P2 and the multi-PDZ-domain-containing protein MUPP1 in vivo
Authors: KIMBER Wendy A. , TRINKLE-MULCAHY Laura , CHEUNG Peter C. F. , DEAK Maria , MARSDEN Louisa J. , KIELOCH Agnieszka , WATT Stephen , JAVIER Ronald T. , GRAY Alex , DOWNES C. Peter , LUCOCQ John M. , ALESSI Dario R.
Published: August 2015

PtdIns(3,4,5)P3 is an established second messenger of growth-factor and insulin-induced signalling pathways. There is increasing evidence that one of the immediate breakdown products of PtdIns(3,4,5)P3, namely PtdIns(3,4)P2, whose levels are elevated by numerous extracellular agonists, might also function as a signalling molecule. Recently, we identified two related pleckstrin-homology (PH)-domain-containing proteins, termed ‘tandem-PH-domain-containing protein-1’ (TAPP1) and TAPP2, which interacted in vitro with high affinity with PtdIns(3,4)P2, but did not bind PtdIns(3,4,5)P3 or other phosphoinositides. In the present study we demonstrate that stimulation of Swiss 3T3 or 293 cells with agonists that stimulate PtdIns(3,4)P2 production results in the marked translocation of TAPP1 to the plasma membrane. This recruitment is dependent on a functional PtdIns(3,4)P2-binding PH domain and is inhibited by wortmannin, a phosphoinositide 3-kinase inhibitor that prevents PtdIns(3,4)P2 generation. A search for proteins that interact with TAPP1 identified the multi-PDZ-containing protein termed ‘MUPP1’, a protein possessing 13 PDZ domains and no other known modular or catalytic domains [PDZ is postsynaptic density protein (PSD-95)/Drosophila disc large tumour suppressor (dlg)/tight junction protein (ZO1)]. We demonstrate that immunoprecipitation of endogenously expressed TAPP1 from 293-cell lysates results in the co-immunoprecipitation of endogenous MUPP1, indicating that these proteins are likely to interact with each other physiologically. We show that TAPP1 and TAPP2 interact with the 10th and 13th PDZ domain of MUPP1 through their C-terminal amino acids. The results of the present study suggest that TAPP1 and TAPP2 could function in cells as adapter proteins to recruit MUPP1, or other proteins that they may interact with, to the plasma membrane in response to signals that elevate PtdIns(3,4)P2.
Heterogeneity of airways mucus: variations in the amounts and glycoforms of the major oligomeric mucins MUC5AC and MUC5B
Authors: KIRKHAM Sara , SHEEHAN John K. , KNIGHT David , RICHARDSON Paul S. , THORNTON David J.
Published: August 2015

Respiratory mucus contains a mixture of gel-forming mucins but the functional significance of these different mucin species is unknown. To help gain a better understanding of mucus in airways we therefore need to ascertain the concentration of each of the gel-forming mucins within respiratory secretions. Thus the aim of this study was to determine the amounts of specific gel-forming mucins directly from solubilized secretions of the airways and purified mucin preparations. We investigated the feasibility of using direct-binding ELISA employing mucin-specific antisera but were unable to obtain reliable data owing to interference with the immobilization of the mucins on the assay surface by 6M urea and high levels of non-mucin proteins. We therefore developed an alternative approach based on quantitative Western blotting after agarose-gel electrophoresis, which was not subject to these problems. Here we demonstrate that this procedure provides reliable and reproducible data and have employed it to determine the amounts of the MUC2, MUC5AC and MUC5B mucins in saline-induced sputa from healthy airways and spontaneous sputa from asthmatic airways. Additionally we have used this procedure to analyse these glycoproteins in mucin preparations purified from cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) mucus. Our findings indicate that MUC5AC and MUC5B are the major oligomeric mucins and that airways mucus contains variable amounts of these glycoproteins. By contrast, the MUC2 mucin comprised, at most, only 2.5% of the weight of the gel-forming mucins, indicating that MUC2 is a minor component in sputum. Finally, we show that the amounts and glycosylated variants of the MUC5AC and MUC5B mucins can be altered significantly in diseased airways with, for instance, an increase in the low-charge form of the MUC5B mucin in CF and COPD mucus.
Retinoic acid activation of the ERK pathway is required for embryonic stem cell commitment into the adipocyte lineage
Authors: BOST Frédéric , CARON Leslie , MARCHETTI Irène , DANI Christian , MARCHAND-BRUSTEL Yannick LE , BINÉTRUY Bernard
Published: August 2015

Mouse embryonic stem (ES) cells are pluripotent cells that differentiate into multiple cell lineages. The commitment of ES cells into the adipocyte lineage is dependent on an early 3-day treatment with all-trans retinoic acid (RA). To characterize the molecular mechanisms underlying this process, we examined the contribution of the extracellular-signal-regulated kinase (ERK) pathway. Treatment of ES cell-derived embryoid bodies with RA resulted in a prolonged activation of the ERK pathway, but not the c-Jun N-terminal kinase, p38 mitogen-activated protein kinase or phosphoinositide 3-kinase pathways. To investigate the role of ERK activation, co-treatment of RA with PD98059, a specific inhibitor of the ERK signalling pathway, prevented both adipocyte formation and expression of the adipogenic markers, adipocyte lipid-binding protein and peroxisome-proliferator-activated receptor γ. Furthermore, we show that ERK activation is required only during RA treatment. PD98059 does not interfere with the commitment of ES cells into other lineages, such as neurogenesis, myogenesis and cardiomyogenesis. As opposed to the controversial role of the ERK pathway in terminal differentiation, our results clearly demonstrate that this pathway is specifically required at an early stage of adipogenesis, corresponding to the RA-dependent commitment of ES cells.
Induction of Bach1 and ARA70 gene expression at an early stage of adipocyte differentiation of mouse 3T3-L1 cells
Authors: NISHIZUKA Makoto , TSUCHIYA Tomoko , NISHIHARA Tsutomu , IMAGAWA Masayoshi
Published: August 2015

Using a subtraction method, we have isolated genes that are induced early in the differentiation of mouse 3T3-L1 preadipocyte cells into adipocytes. These include the genes encoding transcription factors and signalling proteins, as well as unknown genes. Bach1, a transcription factor, and ARA70, a cofactor, were rapidly induced during differentiation. The induction of these two genes was observed only in growth-arrested 3T3-L1 cells, and not in proliferating cells. In NIH-3T3 cells, no induction was observed under either set of conditions. These results strongly indicate that Bach1 and ARA70 have valuable roles at the onset of adipocyte differentiation.
Human Hand1 basic helix-loop-helix (bHLH) protein: extra-embryonic expression pattern, interaction partners and identification of its transcriptional repressor domains
Authors: KNÖFLER Martin , MEINHARDT Gudrun , BAUER Sandra , LOREGGER Thomas , VASICEK Richard , BLOOR Debra J. , KIMBER Susan J. , HUSSLEIN Peter
Published: August 2015

The basic helix-loop-helix (bHLH) transcription factor, Hand1, plays an important role in the development of the murine extra-embryonic trophoblast cell lineage. In the present study, we have analysed the expression of Hand1 in human extra-embryonic cell types and determined its binding specificity and transcriptional activity upon interaction with different class A bHLH factors. Northern blotting and in situ hybridization showed that Hand1 mRNA is specifically expressed in amnion cells at different stages of gestation. Accordingly, we demonstrate that the protein is exclusively produced in the amniotic epithelium in vivo and in purified amnion cells in vitro using a novel polyclonal Hand1 antiserum. Reverse transcriptase-PCR and immunohistochemical staining of blastocysts revealed the production of Hand1 mRNA and polypeptide in the trophectodermal cell layer. In the presence of E12/E47, Hand1 stimulated the transcription of luciferase reporters harbouring degenerate E-boxes, suggesting that E-proteins are potential dimerization partners in trophoblastic tumour and amnion cells. In contrast, Hand1 diminished E12/E47-dependent transcription of reporters containing perfect E-boxes by inhibiting the interaction of Hand1/E-protein heterodimers with the palindromic cognate sequence. Furthermore, we show that Hand1 down-regulated GAL—E12-dependent reporter expression, indicating that the protein can also act directly as a transcriptional repressor. Mutational analyses of GAL-Hand1 suggested that two protein regions located within its N-terminal portion mainly confer the repressing activity. In conclusion, human Hand1 may play an important role in the differentiation of the amniotic membrane and the pre-implanting trophoblast. Furthermore, the data suggest that Hand1 can act as a repressor by two independent mechanisms; sequestration of class A bHLH factors from E-boxes and inhibition of their transcriptional activity.
Structural requirements for palmitoylation of surfactant protein C precursor
Authors: ten BRINKE Anja , VAANDRAGER Arie B. , HAAGSMAN Henk P. , RIDDER Anja N. J. A. , van GOLDE Lambert M. G. , BATENBURG Joseph J.
Published: August 2015

Pulmonary surfactant protein C (SP-C) propeptide (proSP-C) is a type II transmembrane protein that is palmitoylated on two cysteines adjacent to its transmembrane domain. To study the structural requirements for palmitoylation of proSP-C, His-tagged human proSP-C and mutant forms were expressed in Chinese hamster ovary cells and analysed by metabolic labelling with [3H]palmitate. Mutations were made in the amino acid sequence representing mature SP-C, as deletion of the N- and C-terminal propeptide parts showed that this sequence by itself could already be palmitoylated. Substitution of the transmembrane domain by an artificial transmembrane domain had no effect on palmitoylation. However, an inverse correlation was found between palmitoylation of proSP-C and the number of amino acids present between the cysteines and the transmembrane domain. Moreover, substitution by alanines of amino acids localized on the N-terminal side of the cysteines had drastic effects on palmitoylation, probably as a result of the removal of hydrophobic amino acids. These data, together with the observation that substitution by alanines of the amino acids localized between the cysteines and the transmembrane domain had no effect on palmitoylation, suggest that the palmitoylation of proSP-C depends not on specific sequence motifs, but more on the probability that the cysteine is in the vicinity of the membrane surface. This is probably determined not only by the number of amino acids between the cysteines and the transmembrane domain, but also by the hydrophobic interaction of the N-terminus with the membrane. This may also be the case for the palmitoylation of other transmembrane proteins.
myo-Inositol 1,4,5-trisphosphate and Ca2+/calmodulin-dependent factors mediate transduction of compression-induced signals in bovine articular chondrocytes
Authors: VALHMU Wilmot B. , RAIA Frank J.
Published: August 2015

Although the effects of mechanical loading on chondrocyte metabolic activities have been extensively characterized, the sequence of events through which extracellular mechanical signals are transduced into chondrocytes and ultimately modulate cell activities is not well understood. Here, studies were performed to map out the sequential intracellular signalling pathways through which compression-induced signals modulate aggrecan mRNA levels in bovine articular chondrocytes. Bovine articular cartilage explants were subjected to a compressive stress of 0.1MPa for 1h in the presence or absence of inhibitors or antagonists of the phosphoinositol and Ca2+/calmodulin signalling pathways in order to determine the roles of second messengers and effector molecules of these pathways in transducing the compression-induced signals. In the absence of the inhibitors, aggrecan mRNA levels were stimulated by compression 2–4-fold relative to levels in tare-loaded (see below) explants. Treatment of the explants with graded levels of the protein kinase C inhibitor chelerythrine or bisindolylmaleimide I, followed by 1h compressive loading, did not significantly alter the load-induced elevation of aggrecan mRNA levels. In contrast, thapsigargin, which depletes the Ins(1,4,5)P3-sensitive intracellular Ca2+ stores, completely blocked the load response without significantly altering aggrecan mRNA levels in tare-loaded explants. Similarly, antagonists of the Ca2+/calmodulin signalling pathway dose-dependently or completely blocked the load-response. The results obtained demonstrate that transduction of the compression-induced aggrecan mRNA-regulating signals requires Ins(1,4,5)P3- and Ca2+/calmodulin-dependent signalling processes in bovine articular chondrocytes.
Reciprocal regulation of capacitative and non-capacitative Ca2+ entry in A7r5 vascular smooth muscle cells: only the latter operates during receptor activation
Authors: MONEER Zahid , TAYLOR Colin W.
Published: August 2015

In A7r5 vascular smooth muscle cells, Arg8-vasopressin (AVP) stimulates phospholipase C leading to activation of two distinct Ca2+ entry pathways. The capacitative Ca2+ entry (CCE) pathway is activated by depletion of Ca2+ stores, is permeable to Mn2+, Ba2+ and Ca2+, and is selectively blocked by Gd3+ (1μM). A7r5 cells also express a non-capacitative Ca2+ entry (NCCE) pathway, which is activated by arachidonic acid that is released by the sequential activities of phospholipase C and diacylglycerol lipase. This pathway is permeable to Sr2+, Ba2+ and Ca2+ and selectively blocked by (R,S)-(3,4-dihydro-6,7-dimethoxy-isochinolin-1-yl)-2-phenyl-N,N-di[2-(2,3,4-trimethoxyphenyl)ethyl]acetamid mesylate ('LOE-908'). We use these selective tools to show that AVP, via the same signalling pathway that leads to activation of NCCE, also inhibits CCE and that the inhibition is not due to depolarization of the plasma membrane. Using the selective inhibitors to resolve the contributions of each Ca2+ entry pathway during stimulation with AVP, we establish that reciprocal regulation of CCE and NCCE by arachidonic acid ensures that only NCCE is active in the presence of AVP, whereas CCE is active only after its removal. NCCE and CCE are therefore activated in a strict temporal sequence: NCCE first and then CCE. Because Ca2+ passing through different Ca2+ entry pathways can selectively regulate different responses, reciprocal regulation of CCE and NCCE may allow a stimulus to first evoke a response and then recruit actively a different response when the stimulus is removed.
Inhibition of mitochondrial calcium-independent phospholipase A2 (iPLA2) attenuates mitochondrial phospholipid loss and is cardioprotective
Authors: WILLIAMS Scott D. , GOTTLIEB Roberta A.
Published: August 2015

Calcium-independent phospholipase A2 (iPLA2) is the predominant phospholipase A2 present in myocardium, and its pathophysiological role in acute myocardial infarction has been suggested by the rapid increase in membrane-associated iPLA2 activity during myocardial ischaemia and reperfusion (I/R). We therefore examined iPLA2 in mitochondrial fractions prepared from Langendorff-perfused adult rabbit hearts. Our studies indicate that iPLA2β is present in rabbit heart mitochondrial inner membranes with no apparent translocation during ischaemia, I/R or preconditioning. Mitochondrion-associated iPLA2 was catalytically competent and exhibited 2-, 3- and 2.5-fold increases in measured iPLA2 activity following ischaemia, I/R and preconditioning, respectively, when compared with the activity of iPLA2 measured in mitochondria from control hearts. Mitochondrial phospholipids are essential for maintaining the ordered structure and function of the organelle. I/R resulted in a rapid overall decrease in phosphatidylcholine and phosphatidylethanolamine glycerophospholipid species, as determined by electrospray ionization MS, that was partially alleviated by pretreatment of hearts with the iPLA2-specific inhibitor, bromoenol lactone (BEL). Pretreatment of I/R hearts with 10μM BEL significantly reduced the infarct size almost to that of continuously perfused hearts and was cardioprotective only when administered prior to ischaemia. Cardioprotection by BEL was reversed by the simultaneous perfusion of 100μM 5-hydroxydecanoate, implicating the mitochondrial KATP channel in BEL-mediated protection from I/R. Preconditioning also significantly reduced the infarct size in response to I/R but protection was lost by concurrent perfusion of 10μM arachidonic acid. Taken together, these data strongly implicate mitochondria-associated iPLA2 in the signal transduction of myocardial I/R injury.
Role of Rac and Cdc42 in lysophosphatidic acid-mediated cyclo-oxygenase-2 gene expression
Authors: HAHN Angelika , BARTH Holger , KRESS Michaela , MERTENS Peter R. , GOPPELT-STRUEBE Margarete
Published: August 2015

The role of Rho proteins in lysophosphatidic acid (LPA)-mediated induction of cyclo-oxygenase-2 (Cox-2) was investigated in renal mesangial cells. Previous studies had shown that toxin B, an inhibitor of Rho, Rac and Cdc42, suppressed Cox-2 induction. A role for RhoA in pertussis toxin-sensitive LPA signalling was excluded with C3 transferase from Clostridium limosum, used as the fusion toxin C2IN—C3 (where C2IN is part of the C2I toxin of C. botulinum). Incubation of the cells with C2IN—C3 disrupted cytosolic actin stress fibres, but had no effect on Cox-2 induction. Similarly, activation of p42/44 mitogen-activated protein kinase (MAP kinase), an upstream step in Cox-2 induction, was inhibited by toxin B, but not affected by C2IN—C3. Upon treatment with toxin B, focal adhesion kinase and paxillin were dephosphorylated at tyrosine residues and the actin cytoskeleton was completely destroyed. An intact cytoskeleton, however, was not required for p42/44 MAP-kinase activation or Cox-2 induction, as shown by the actin-depolymerizing agent cytochalasin D. Toxin B did not influence functionality of LPA receptors, because Gi-mediated Ca2+ release from intracellular stores remained unchanged. Within 1h, toxin B inactivated and translocated RhoA and Cdc42 to the cellular membranes. Within the same time frame, monoglucosylated Rac1 was degraded. Direct stimulation of Rho proteins by cytotoxic necrotizing factor type 1 (CNF1) induced Cox-2 expression, which was sensitive to inhibition of the MAP-kinase pathway by PD98059, but not to an inhibitor of RhoA kinase. By exclusion of RhoA and non-specific cytoskeletal effects, the results in the present study indicate an important role for Rac and/or Cdc42 in pertussis toxin-sensitive LPA-mediated Cox-2 induction.
Lipid deprivation increases surfactant phosphatidylcholine synthesis via a sterol-sensitive regulatory element within the CTP:phosphocholine cytidylyltransferase promoter
Authors: MALLAMPALLI Rama K. , RYAN Alan J. , CARROLL James L. , OSBORNE Timothy F. , THOMAS Christie P.
Published: August 2015

Lipid-deprived mice increase alveolar surfactant disaturated phosphatidylcholine (DSPtdCho) synthesis compared with mice fed a standard diet by increasing expression of CTP:phosphocholine cytidylyltransferase (CCT), the rate-limiting enzyme for DSPtdCho synthesis. We previously observed that lipid deprivation increases mRNA synthesis for CCT [Ryan, McCoy, Mathur, Field and Mallampalli (2000) J. Lipid Res. 41, 1268–1277]. To evaluate regulatory mechanisms for this gene, we cloned the proximal ∼ 1900bp of the 5′ flanking sequence of the murine CCT gene, coupled this to a luciferase reporter, and examined transcriptional regulation in a murine alveolar epithelial type II cell line (MLE-12). The core promoter was localized to a region between −169 and +71bp, which exhibited strong basal activity comparable with the simian virus 40 promoter. The full-length construct, from −1867 to +71, was induced 2–3-fold when cells were cultured in lipoprotein-deficient serum (LPDS), similar to the level of induction of the endogenous CCT gene. By deletional analysis the sterol regulatory element (SRE) was localized within a 240bp region. LPDS activation of the CCT promoter was abolished by mutation of this SRE, and gel mobility-shift assays demonstrated specific binding of recombinant SRE-binding protein to this element within the CCT promoter. These observations indicate that sterol-regulated expression of CCT is mediated by an SRE within its 5′ flanking region.
Less hydrophobic phosphatidylcholine species simplify biliary vesicle morphology, but induce bile metastability with a broad spectrum of crystal forms
Authors: SAKOMOTO Minoru , TAZUMA Susumu , CHAYAMA Kazuaki
Published: August 2015

Cholesterol crystallization in bile is affected by phosphatidylcholine (PtdCho) hydrophobicity. The aim of the present study was to determine whether PtdCho species modulate the metastable—labile limit and equilibrium solubility of cholesterol in the micellar phase of bile, thereby altering the distribution of cholesterol to biliary lipid carriers and thus influencing cholesterol crystallization. Supersaturated model bile (with a cholesterol saturation index of 2.0 and a total lipid concentration of 10g/dl) was prepared with various PtdCho/(bile salt+PtdCho) ratios (0.1–0.5) using egg yolk or soya bean PtdCho. Subsequently, the following features were determined: metastable—labile limit, equilibrium solubility of cholesterol, metastable zone, and cholesterol crystallization process. Less hydrophobic PtdCho species destabilized bile cholesterol to induce rapid crystallization, because of a broad integrated metastable zone, whereas more hydrophobic species stabilized bile cholesterol with a less integrated metastable zone and thus retarded cholesterol crystallization. Cholesterol crystallization was accelerated by a decrease in the PtdCho/(bile salt+PtdCho) ratio, whereas the final nucleated crystal mass was increased by an increase in this ratio. With decreasing hydrophobicity of the PtdCho species, the intermixed micellar/vesicular concentration of bile salts decreased in association with less formation of vesicles and increased formation of micelles, and a variety of crystal forms were detected. In conclusion, PtdCho species directly influenced the cholesterol crystallization process in model bile by remodelling the bile mesophase, and also had an indirect influence by altering the balance between bile salt micelles and vesicles.
CD38 is the major enzyme responsible for synthesis of nicotinic acid–adenine dinucleotide phosphate in mammalian tissues
Authors: CHINI Eduardo N. , CHINI Claudia C. S. , KATO Ichiro , TAKASAWA Shin , OKAMOTO Hiroshi
Published: August 2015

In the present study, we have determined the role of the enzyme CD38 upon the synthesis of the Ca2+-releasing nucleotide nicotinic acid—adenine dinucleotide phosphate (NAADP). In rat tissues, we observed that the capacity for NAADP synthesis could be co-immunoprecipitated with CD38 using an anti-CD38 antibody. Furthermore, we observed that several tissues from CD38 knockout mice had no capacity for the synthesis of this nucleotide. In addition, CD38 was also identified as the major enzyme responsible for the synthesis of the second messenger cyclic ADP-ribose. These observations lead to the conclusion that CD38 is the major enzyme responsible for the synthesis of NAADP and cyclic ADP-ribose, and raises the possibility of a new signalling pathway where two different Ca2+-releasing nucleotides are synthesized by the same enzyme.
Purification, characterization, gene cloning and preliminary X-ray data of the exo-inulinase from Aspergillus awamori
Authors: ARAND Michael , GOLUBEV Alexander M. , NETO J. R. Brandao , POLIKARPOV Igor , WATTIEZ R. , KORNEEVA Olga S. , ENEYSKAYA Elena V. , KULMINSKAYA Anna A. , SHABALIN Konstantin A. , SHISHLIANNIKOV Sergei M. , CHEPURNAYA Olga V. , NEUSTROEV Kirill N.
Published: August 2015

Extracellular exo-inulinase has been isolated from a solid-phase culture of the filamentous fungus Aspergillus awamori var. 2250. The apparent molecular mass of the monomer enzyme was 69±1kDa, with a pI of 4.4 and a pH optimum of 4.5. The enzyme hydrolysed the β-(2 → 1)-fructan (inulin) and β-(2 → 6)-fructan (levan) via exo-cleavage, releasing fructose. The values for the Michaelis constants Km and Vmax in the hydrolysis of inulin were 0.003±0.0001mM and 175±5μmol·min−1·mg−1. The same parameters in the hydrolysis of levan were 2.08±0.04mg/ml and 1.2±0.02μmol/min per mg, respectively. The gene and cDNA encoding the A. awamori exo-inulinase were cloned and sequenced. The amino acid sequence indicated that the protein belongs to glycoside hydrolase family 32. A surprisingly high similarity was found to fructosyltransferase from Aspergillus foetidus (90.7% on the level of the amino acid sequence), despite the fact that the latter enzyme is unable to hydrolyse inulin and levan. Crystals of the native exo-inulinase were obtained and found to belong to the orthorhombic space group P212121 with cell parameters a = 64.726 Å (1Å = 0.1 nm), b = 82.041 Å and c = 136.075 Å. Crystals diffracted beyond 1.54 Å, and useful X-ray data were collected to a resolution of 1.73 Å.
The C-terminal domain, but not the interchain disulphide, is required for the activity and intracellular trafficking of aminopeptidase A
Authors: OFNER Lisa D. , HOOPER Nigel M.
Published: August 2015

Mammalian aminopeptidase A (APA; glutamyl aminopeptidase; EC 3.4.11.7) is a type II membrane-spanning protein consisting of a short N-terminal cytosolic domain, a single transmembrane domain and a large extracellular C-terminal domain containing the active site. The extracellular domain consists of a 107kDa domain, containing the zinc-binding motif and all the residues involved in catalysis, separated by a protease-susceptible hinge region from the 45kDa C-terminal domain of unknown function. To investigate the role of the 45kDa domain, a construct of murine APA (G594Δ) lacking this C-terminal domain was expressed in COS-1 cells. This truncated form of APA, although expressed, lacked enzymic activity and failed to reach the cell surface. Confocal immunofluorescence microscopy revealed that G594Δ co-localized with the lectin concanavalin A and had a similar staining pattern as protein disulphide-isomerase, indicating that it was retained in the endoplasmic reticulum. Thus the C-terminal 45kDa domain appears to be acting like a pro-domain and seems to be required for the correct folding and trafficking of APA. In contrast, mutation of cysteine-43 to serine, which is involved in the disulphide-linkage of the APA homodimer, did not affect the enzymic activity, cellular location or rate of trafficking through the secretory pathway of APA.
Complete sequence, recombinant analysis and binding to laminins and sulphated ligands of the N-terminal domains of laminin α3B and α5 chains
Authors: GARBE Jörg H. O. , GÖHRING Walter , MANN Karlheinz , TIMPL Rupert , SASAKI Takako
Published: August 2015

The N-terminal sequences of mouse laminin α3B and α5 chains have been completed and demonstrate the presence of a signal peptide followed by a complete laminin N-terminal (LN) module (domain VI). These signal peptides were released after recombinant production of larger fragments comprising domains VI/V (45–65kDa) from this region yielding properly folded proteins, which were secreted from HEK-293—EBNA cells. Pepsin digestion of these fragments yielded products of 25–35kDa, which consisted only of domain V. The αVI/V fragments were able to inhibit self-assembly of laminin-1, with those from the α3B and α5 chains being more active than those from α1 and α2 chains. Domain V fragments, however, showed a reduced activity, indicating the major contribution of the LN module in inhibition. These interactions were confirmed by surface-plasmon-resonance assays demonstrating moderate affinities (Kd = 0.02 to > 6μM) for the binding to laminin-1. This indicated that laminins containing α3B or α5 chains should also be able to form non-covalent networks by polymerization. The LN modules also showed heparin binding in affinity chromatography, which was strongest for α1/α2, moderate for α3B, whereas no binding was observed for α5. They all bound to heparan sulphate chains of perlecan and to sulphatides, with a lower variability in binding activity. Specific antibodies were raised against α3BVI/V and α5VI/V and were shown to stain basement membrane zones in various mouse tissues. These antibodies also allowed the identification of a new laminin assembly form 5B consisting of α3B, β3 and γ2 chains.
Interactions of Porphyromonas gingivalis with oxyhaemoglobin and deoxyhaemoglobin
Authors: SMALLEY John W. , BIRSS Andrew J. , WITHNALL Robert , SILVER Jack
Published: August 2015

When grown on blood-containing solid media, the anaerobic periodontal pathogen Porphyromonas gingivalis produces a haem pigment, the major component of which is the μ-oxo bishaem of iron protoporphyrin IX [Smalley, Silver, Marsh and Birss (1998) Biochem. J. 331, 681–685]. In this study, μ-oxo bishaem generation by P. gingivalis from oxy- and deoxyhaemoglobin was examined. Bacterial cells were shown to convert oxyhaemoglobin into methaemoglobin, which was degraded progressively, generating a mixture of both monomeric and μ-oxo dimeric iron protoporphyrin IX. The rate of methaemoglobin formation was accelerated in the presence of bacterial cells, but was inhibited by N-ethylmaleimide and tosyl-lysylchloromethylketone. Interaction of cells with deoxyhaemoglobin resulted in formation of an iron(III) haem species (Soret λmax, 393nm), identified as pure μ-oxo bishaem.
Ceramide and sphingosine have an antagonistic effect on the plasma-membrane Ca2+-ATPase from human erythrocytes
Authors: COLINA Claudia , CERVINO Vincenza , BENAIM Gustavo
Published: August 2015

The plasma-membrane Ca2+-ATPase is a key enzyme in the regulation of the intracellular Ca2+ concentration. On the other hand, sphingolipids have been recognized recently as important second messengers, acting in many systems in combination with Ca2+. In view of the fact that the Ca2+-ATPase is stimulated by ethanol, and since sphingolipids possess free hydroxy groups, we decided to study the possible effect of ceramide and sphingosine on this calcium pump. Here we show that ceramide stimulates the Ca2+-ATPase in a dose-dependent manner and additively to the activation observed in the presence of calmodulin or ethanol, when compared with any of these effectors added alone. Ceramide affects both the affinity for Ca2+ and the Vmax of the enzyme. Furthermore, this second messenger also stimulates Ca2+ transport in inside—out plasma-membrane vesicles from erythro cytes. Conversely, sphingosine, which is reported to act in many systems antagonistically with ceramide, showed an inhibitory effect on Ca2+-ATPase activity. This inhibition was also observed on the calmodulin-stimulated enzyme. These results, taken together, suggest that ceramide and sphingosine act antagonistically on the plasma-membrane Ca2+-ATPase. This is in accordance with the frequently reported opposite effect of these sphingolipids on intracellular Ca2+ concentration.
Effect of C-domain N-glycosylation and deletion on rat pancreaticα-amylase secretion and activity
Authors: DOYON Yannick , HOME William , DAULL Philippe , LeBEL Denis
Published: August 2015

Even though all animal α-amylases include glycosylation sequons (Asn-Xaa-Thr/Ser) in their sequences, amylases purified from natural sources are not quantitatively glycosylated. When wild-type rat pancreatic α-amylase, which contains two glycosylation sequons, was expressed in animal cell lines the protein displayed a very low rate of glycosylation (approx. 2%), even after Brefeldin A treatment to increase the contact with the glycosylation machinery. Site-directed mutagenesis of the first glycosylation sequon (Asn410 → Gln) resulted in 90% of the protein being glycosylated at the second glycosylation sequon (Asn459). Mutation of the second sequon completely inhibited glycosylation. In order to ascertain if the interference in the glycosylation of Asn459 that was eliminated by the Asn410 →Gln mutation could be due to the position of the asparagine residue in the Cys448-Cys460 disulphide bridge, these cysteine residues were mutated to serine residues. The resulting mutant was found to be 100% glycosylated. All mutants with mutations in the C-domain had specific activities identical to that of the wild-type enzyme, indicating that enzymic activity is independent of the structure and modification of the C-terminal domain. To further test the independence of the C-domain with respect to the two N-terminal domains of the protein, which harbour the catalytic site, the last seven of the ten β-strands that make up the β-sandwich configuration of the domain were deleted. The truncated protein was not secreted from cells and all enzyme activity was destroyed. These observations show that Asn459 is the only site that can be glycosylated in wild-type amylase, and confirm the relative independence of the C-terminal domain of α-amylase with respect to enzyme activity. In addition, they also establish that the C-terminal domain is absolutely essential for the correct post-translational folding of the enzyme that is responsible for its activity and allows for its secretion.
The transfer of transthyretin and receptor-binding properties from the plasma retinol-binding protein to the epididymal retinoic acid-binding protein
Authors: SUNDARAM Manickavasagam , van AALTEN Daan M. F. , FINDLAY John B. C. , SIVAPRASADARAO Asipu
Published: August 2015

Members of the lipocalin superfamily share a common structural fold, but differ from each other with respect to the molecules with which they interact. They all contain eight β-strands (A—H) that fold to form a well-defined β-barrel, which harbours a binding pocket for hydrophobic ligands. These strands are connected by loops that vary in size and structure and make up the closed and open ends of the pocket. In addition to binding ligands, some members of the family interact with other macromolecules, the specificity of which is thought to be associated with the variable loop regions. Here, we have investigated whether the macromolecular-recognition properties can be transferred from one member of the family to another. For this, we chose the prototypical lipocalin, the plasma retinol-binding protein (RBP) and its close structural homologue the epididymal retinoic acid-binding protein (ERABP). RBP exhibits three molecular-recognition properties: it binds to retinol, to transthyretin (TTR) and to a cell-surface receptor. ERABP binds retinoic acid, but whether it interacts with other macromolecules is not known. Here, we show that ERABP does not bind to TTR and the RBP receptor, but when the loops of RBP near the open end of the pocket (L-1, L-2 and L-3, connecting β-strands A—B, C—D and E—F, respectively) were substituted into the corresponding regions of ERABP, the resulting chimaera acquired the ability to bind TTR and the receptor. L-2 and L-3 were found to be the major determinants of the receptor- and TTR-binding specificities respectively. Thus we demonstrate that lipocalins serve as excellent scaffolds for engineering novel biological functions.
Concentrated solutions of salivary MUC5B mucin do not replicate the gel-forming properties of saliva
Authors: RAYNAL Bertrand D. E. , HARDINGHAM Timothy E. , THORNTON David J. , SHEEHAN John K.
Published: August 2015

We have developed a new approach to study the molecular organization of salivary mucus and salivary mucins using confocal fluorescence recovery after photobleaching (confocal-FRAP). MUC5B mucin, its reduced subunit and T-domains were prepared from saliva and fluorescently labelled. The translational self-diffusion coefficients were determined up to 3.6mg/ml by confocal-FRAP. The results suggest that, in solutions of purified MUC5B mucin, at concentrations at which the hydrodynamic domains overlap, the intermolecular interactions are predominantly due to dynamic entanglements, and there was no evidence of specific self-association of MUC5B mucin, or of its subunits, or T-domains. The analysis of the salivary mucus gel also showed no specific interactions with the purified MUC5B components, but it was much less permeable than expected from its MUC5B content. The saliva was completely permeable to microspheres of 207nm diameter, but showed size-dependent effects on the diffusion of larger microspheres (499nm and 711nm diameter). From these analyses the salivary mucus was shown to be both permeable and dynamic, and with the characteristics of a semi-dilute transient network at physiological concentration. Comparison of the results from saliva and purified MUC5B mucin solutions showed that the network properties of saliva were equivalent to a solution of purified MUC5B mucin of 10–20 times higher concentration. This showed that saliva has additional structure and organization not present in the purified MUC5B mucin and suggests there are other interactions and/or components within saliva that combine with MUC5B to produce its complete properties.