bluuebunny/crossref_metadata_2025 huggingface dataset:
Interleukin-1β enhances bradykinin-induced phosphoinositide hydrolysis and Ca2+ mobilization in canine tracheal smooth-muscle cells: involvement of the Ras/Raf/mitogen-activated protein kinase (MAPK) kinase (MEK)/MAPK pathway
Authors: YANG Chuen-Mao , CHIEN Chin-Sung , WANG Chuan-Chwan , HSU Yan-Mei , CHIU Chi-Tso , LIN Chih-Chung , LUO Shue-Fen , HSIAO Li-Der
Published: August 2015

Elevated levels of several cytokines including interleukin-1β (IL-1β) have been detected in airway fluid of asthmatic patients. Inhalation of IL-1β induced a bronchial hyper-reactivity to contractile agonists. However, the implication of IL-1β in the pathogenesis of bronchial hyper-reactivity is not completely understood. Therefore, we investigated the effect of IL-1β on bradykinin (BK)-induced inositol phosphate [Ins(X)P] accumulation and Ca2+ mobilization, and up-regulation of BK receptor density in canine cultured tracheal smooth-muscle cells (TSMCs). Treatment of TSMCs with IL-1β potentiated BK-induced Ins(X)P accumulation and Ca2+ mobilization. However, there was no effect on the Ins(X)P response induced by endothelin-1, 5-hydroxytryptamine or carbachol. Treatment with platelet-derived growth factor B-chain homodimer (PDGF-BB) also enhanced the BK-induced Ins(X)P response. These enhancements by IL-1β and PDGF-BB might be due to an up-regulation of BK B2 receptor density (Bmax), since [3H]BK binding to TSMCs was inhibited by the B2-selective agonist and antagonist, BK and Hoe 140, but not by B1-selective reagents. The enhancing effects of IL-1β and PDGF-BB on Ins(X)P accumulation, Ca2+ mobilization and Bmax were attenuated by PD98059 [an inhibitor of activation of mitogen-activated protein kinase (MAPK) kinase, MEK] and cycloheximide (an inhibitor of protein synthesis), suggesting that IL-1β may share a common signalling pathway with PDGF-BB via protein synthesis. Furthermore, overexpression of dominant negative mutants, H-Ras-15A and Raf-N4, significantly suppressed the up-regulation of BK receptors induced by IL-1β, indicating that Ras and Raf may be required for activation of these kinases. These results suggest that the augmentation of BK-induced responses produced by IL-1β might be, at least in part, mediated through activation of the Ras/Raf/MEK/MAPK pathway in TSMCs.
Identification of an extracellular segment of the oxytocin receptor providing agonist-specific binding epitopes
Authors: HAWTIN Stuart R. , HOWARD Helen C. , WHEATLEY Mark
Published: August 2015

The effects of the peptide hormone oxytocin are mediated by oxytocin receptors (OTRs) expressed by the target tissue. The OTR is a member of the large family of G-protein-coupled receptors. Defining differences between the interaction of agonists and antagonists with the OTR at the molecular level is of fundamental importance, and is addressed in this study. Using truncated and chimaeric receptor constructs, we establish that a small 12-residue segment in the distal portion of the N-terminus of the human OTR provides important epitopes which are required for agonist binding. In contrast, this segment does not contribute to the binding site for antagonists, whether peptide or non-peptide. It does, however, have a role in agonist-induced OTR signalling. Oxytocin is also an agonist at the vasopressin V1a receptor (V1aR). A chimaeric receptor (V1aRN-OTR) was engineered in which the N-terminus of the OTR was substituted by the corresponding, but unrelated, sequence from the N-terminus of the V1aR. We show that the V1aR N-terminus present in V1aRN-OTR fully restored both agonist binding and intracellular signalling to a dysfunctional truncated OTR construct. The N-terminal segment does not, however, contribute to receptor-selective agonism between the OTR and the V1aR. Our data establish a key role for the distal N-terminus of the OTR in providing agonist-specific binding epitopes.
Stopped-flow kinetics of locked nucleic acid (LNA)–oligonucleotide duplex formation: studies of LNA–DNA and DNA–DNA interactions
Authors: CHRISTENSEN Ulla , JACOBSEN Nana , RAJWANSHI Vivek K. , WENGEL Jesper , KOCH Troels
Published: August 2015

The locked nucleic acid (LNA) monomer is a conformationally restricted nucleotide analogue with an extra 2′-O,4′-C-methylene bridge added to the ribose ring. Oligonucleotides that contain LNA monomers have shown greatly enhanced thermal stability when hybridized to complementary DNA and RNA and are considered most promising candidates for efficient recognition of a given mixed sequence in a nucleic acid duplex and as an antisense molecule. Here the kinetics and thermodynamics of a series of oligonucleotide duplex formations of DNA–DNA and DNA–LNA octamers were studied using stopped-flow absorption measurements at 25°C and melting curves. The reactions of the DNA octamer 5′-CAGGAGCA-3′ with its complementary DNA octamer 5′-TGCTCCTG-3′, and with the LNA octamers 5′-TLGCTCCTG-3′ (LNA-1), 5′-TLGCTLCCTG-3′ (LNA-2) and 5′-TLGCTLCCTLG-3′(LNA-3), containing respectively one, two or three thymidine 2′-O,4′-C-methylene-(D-ribofuranosyl) nucleotide monomers, designated TL, were studied. In all cases were seen fast second-order association reactions with kobs = 2×107M-1˙s-1. At 25°C the dissociation constants of the duplexes obtained from melting curves were: DNA–DNA, 10nM; DNA–LNA-1, 20nM; DNA–LNA-2, 2nM; and DNA–LNA-3, 0.3nM; thus the greatly enhanced duplex stability induced by LNA is confirmed. Since the association rates were all equal this increase in stability is due to slower rates of dissociation of the complexes.
Expression pattern and localization of β,β-carotene 15,15′-dioxygenase in different tissues
Authors: WYSS Adrian , WIRTZ Gabriele M. , WOGGON Wolf-D. , BRUGGER Roland , WYSS Markus , FRIEDLEIN Arno , RISS Georges , BACHMANN Heinrich , HUNZIKER Willi
Published: August 2015

β,β-Carotene 15,15′-dioxygenase cleaves β,β-carotene into two molecules of retinal, and is the key enzyme in the metabolism of β,β-carotene to vitamin A. The enzyme has been known for more than 40 years, yet all attempts to purify the protein to homogeneity have failed. Recently, the successful cloning and sequencing of an enzyme with β,β-carotene 15,15′-dioxygenase activity from chicken, as well as from Drosophila, has been reported. Here, we describe in detail our attempt to enrich the chicken β,β-carotene 15,15′-dioxygenase to such an extent as to allow determination of partial amino acid sequences, which were then used to design degenerate oligonucleotides. Screening of a chicken duodenal expression library yielded a full-length clone containing a coding sequence of 1578bp. Functional expression in Escherichia coli and in eukaryotic cell lines confirmed that we had cloned the first vertebrate dioxygenase that cleaves β,β-carotene at the central 15,15′-double bond. By performing a sequence homology search, the cDNA sequence of the mouse homologue was found as an expressed sequence tag (EST) in the gene bank. At the amino-acid level, the degree of homology between the chicken and mouse sequences is 81%. Thus β,β-carotene 15,15′-dioxygenase can be considered as being an enzyme that is evolutionarily rather well conserved. We established the expression pattern of β,β-carotene 15,15′-dioxygenase in chicken and mouse tissues with a combination of Northern blots and in situ hybridization. The mRNA for β,β-carotene 15,15′-dioxygenase was localized primarily in duodenal villi, as well as in liver and in tubular structures of lung and kidney. These new findings demonstrate that β,β-carotene 15,15′-dioxygenase is also expressed in epithelial structures, where it serves to provide the tissue-specific vitamin A supply.
Perivenous expression of the mRNA of the three hypoxia-inducible factor α-subunits, HIF1α, HIF2α and HIF3α, in rat liver
Authors: KIETZMANN Thomas , CORNESSE Yvonne , BRECHTEL Katja , MODARESSI Said , JUNGERMANN Kurt
Published: August 2015

The cDNAs of three hypoxia-inducible factor (HIF) α-subunits were cloned from RNA of primary rat hepatocytes by reverse transcriptase PCR. All three cDNAs encoded functionally active proteins, of 825, 874 and 662 amino acids. After transfection they were able to activate luciferase activity of a luciferase gene construct containing three HIF-responsive elements. The mRNAs of the rat HIF α-subunits were expressed predominantly in the perivenous zone of rat liver tissue; the nuclear HIFα proteins, however, did not appear to be zonated.

The sequence data reported here have been deposited in the EMBL Nucleotide Sequence Database under the following accession numbers: rHIF1α, Y09507; rHIF2α, AJ277828; rHIF3α, AJ277827.
Roles of the forkhead in rhabdomyosarcoma (FKHR) phosphorylation sites in regulating 14-3-3 binding, transactivation and nuclear targetting
Authors: RENA Graham , PRESCOTT Alan R. , GUO Shaodong , COHEN Philip , UNTERMAN Terry G.
Published: August 2015

The transcription factor, forkhead in rhabdomyosarcoma (FKHR), is phosphorylated at three amino acid residues (Thr-24, Ser-256 and Ser-319) by protein kinase B (PKB)α. In the present study, mutagenesis has been used to study the roles of these phosphorylation events in regulating FKHR function in transfected HEK-293 cells. We find that the overexpression of FKHR[S256A] (where Ser-256 → Ala) blocks PKB activity in cells, preventing phosphorylation of the endogenous substrates FKHRL1 and glycogen synthase kinase-3. Thus some reported effects of overexpression of this and other mutants may be indirect, and result from suppression of the phosphorylation of other sites on FKHR and/or other PKB substrates. For example, we have shown that Thr-24 phosphorylation alone is critical for interaction with 14-3-3 proteins, and that the substitution of Ser-256 with an alanine residue indirectly blocks 14-3-3 protein binding by preventing the phosphorylation of Thr-24. We also found that insulin-like growth factor (IGF)-1 and serum-induced nuclear exclusion of FKHR[S256A] depends on the degree of overexpression of this mutant. Our results indicated that the interaction of FKHR with 14-3-3 proteins was not required for IGF-1-stimulated exclusion of FKHR from the nucleus. We present evidence in support of another mechanism, which depends on the phosphorylation of Ser-256 and may involve the masking of a nuclear localization signal. Finally, we have demonstrated that the failure of IGF-1 to suppress transactivation by FKHR[S256A] is not explained entirely by its failure to bind 14-3-3 proteins or to undergo nuclear exclusion. This result suggests that Ser-256 phosphorylation may also suppress transactivation by FKHR by yet another mechanism, perhaps by disrupting the interaction of FKHR with target DNA binding sites and/or the function of the transactivation domain.
Substrate-binding characteristics of proteins in the 90kDa heat shock protein family
Authors: NEMOTO Takayuki K. , ONO Toshio , TANAKA Ki-ichiro
Published: August 2015

In the present study we investigated the substrate-binding characteristics of three members of the 90kDa heat shock protein (HSP90) family, namely the α isoform of human HSP90 (HSP90α), human GRP94 (94kDa glucose-regulated protein, a form of HSP90 from endoplasmic reticulum), and HtpG (the Escherichia coli homologue of HSP90) and the domain responsible for these characteristics. The recombinant forms of HSP90α, GRP94 and HtpG existed as dimers and became oligomerized at higher temperatures. Among the three family members, HtpG required the highest temperature (65°C) for its transition to oligomeric forms. The precipitation of the substrate protein, glutathione S-transferase, which occurred at 55°C, was efficiently prevented by the simultaneous presence of a sufficient amount of HSP90α or GRP94, but not by HtpG, which was still present as a dimer at that temperature. However, precipitation was stopped completely at 65–70°C, at which temperature HtpG was oligomerized. Thus the transition of HSP90-family proteins to a state with self-oligomerization ability is essential for preventing the precipitation of substrate proteins. We then investigated the domain responsible for the substrate binding of HtpG on the basis of the three domain structures. The self-oligomerizing and substrate-binding activities towards glutathione S-transferase and citrate synthase were both located in a single domain, the N-terminal domain (residues 1–336) of HtpG. We therefore propose that the primary peptide-binding site is located in the N-terminal domain of HSP90-family proteins.
Phosphatidic acid–phosphatidylethanolamine interaction and apocytochrome c translocation across model membranes
Authors: MIAO Qi , HAN Xuehai , YANG Fuyu
Published: August 2015

The translocation of apocytochrome c (apocyt.c) across large unilamellar vesicles (LUVs) constructed from mixtures of anionic and zwitterionic phospholipids, phosphatidylethanolamine (PE) and phosphatidylcholine (PC), has been studied. It was shown that the import ratio of horse heart apocyt.c in LUVs composed of phosphatidic acid (PA) combined with PE and PC (62±10%) was much higher than that in LUVs made of PE and PC plus any other acidic phospholipid species (20±5%). This feature was shared by tuna heart and chicken heart apocyt.c. In addition, the greater efficiency of the PA/PE/PC system versus others in facilitating apocyt.c translocation was maintained using synthetic anionic phospholipids with the same acyl chains. Besides, apocyt.c induces more leakage of entrapped fluorescein sulphonate (FS) from the interior of PA/PC/PE vesicles compared with phosphatidylglycerol (PG)/PC/PE ones. By measuring the intrinsic fluorescence emission spectrum and the accessibility of the preprotein to the fluorescence quencher, acrylamide, differences could be detected in the conformational changes of apocyt.c as a consequence of its interaction with PA/PE/PC and PG/PE/PC vesicles, respectively. Particularly notable is that PE is indispensable for the PA/PE/PC system to most efficiently facilitate apocyt.c translocation across the model membranes. With the fraction of PE increasing from 0 to 30 mol%, the translocation efficiency of apocyt.c as well as its ability to induce FS efflux was significantly enhanced in PA-containing LUVs, whereas this was not observed in the case of replacement of PA by PG or phosphatidylserine. It is also interesting to note that in LUVs containing PA, dioleoyl-PE, but not dielaidoyl-PE, can exert such influences, indicative of the role of non-bilayer formation propensity. On the basis of these results it is postulated that PA might increase the bilayer-destabilizing effects of PE, and hence increase the translocation efficiency of apocyt.c and its leakage-induction ability.
α-Melanocyte-related tripeptide, Lys-d-Pro-Val, ameliorates endotoxin-induced nuclear factor κB translocation and activation: evidence for involvement of an interleukin-1β193–195 receptor antagonism in the alveolar epithelium
Authors: HADDAD John J. E. , LAUTERBACH Ryszard , SAADÉ Nayef E. , SAFIEH-GARABEDIAN Bared , LAND Stephen C.
Published: August 2015

The potential anti-inflammatory role of α-melanocyte-stimulating hormone (α-MSH)-related tripeptide, lysine11-D-proline-valine13 (KDPV), an analogue of interleukin (IL)-1β193–195 and an antagonist of IL-1β/prostaglandin E2, is not well characterized in the alveolar epithelium. In a model of foetal alveolar type II epithelial cells in vitro, we showed that lipopolysaccharide endotoxin (LPS) differentially, but selectively, induced the nuclear subunit composition of nuclear factor κB1 (NF-κB1) (p50), RelA (p65) and c-Rel (p75), in parallel to up-regulating the DNA-binding activity (supershift indicating the presence of the p50–p65 complex). LPS accelerated the degradation of inhibitory κB-α (IκB-α), accompanied by enhancing its phosphorylation in the cytosolic compartment but not in the nucleus. KDPV suppressed, in a dose-dependent manner, the nuclear localization of p50, p65 and p75, an effect that led to the subsequent inhibition of NF-κB activation. Interleukin-1 receptor antagonist (IL-1ra) decreased the nuclear abundance of p50, p65 and p75, and subsequently depressed the DNA-binding activity induced by LPS. Analysis of the mechanism involved in the KDPV- and IL-1ra-mediated inhibition of NF-κB nuclear localization revealed a reversal in IκB-α phosphorylation and degradation, followed by cytosolic accumulation. LPS induced endogenous IL-1β biosynthesis in a time-dependent manner; the administration of exogenous recombinant human interleukin 1 (rhIL-1) resulted in a dose-dependent activation of NF-κB. KDPV and IL-1ra abrogated the effect of rhIL-1. Pretreatment with the non-steroidal anti-inflammatory drug (NSAID) indomethacin, an inhibitor of cyclo-oxygenase, blocked the LPS-induced activation of NF-κB. These results indicate the involvement of prostanoid-dependent (NSAID-sensitive) and IL-1-dependent (IL-1ra-sensitive) mechanisms mediating LPS-induced NF-κB translocation and activation, a pathway that is regulated, in part, by a negative feedback mechanism transduced through IκB-α, the major cytosolic inhibitor of NF-κB.
Long-lived glycosyl-enzyme intermediate mimic produced by formate re-activation of a mutant endoglucanase lacking its catalytic nucleophile
Authors: VILADOT Josep-Lluís , CANALS Francesc , BATLLORI Xavier , PLANAS Antoni
Published: August 2015

The mutant E134A 1,3-1,4-β-glucanase from Bacilluslicheniformis, in which the catalytic nucleophilic residue has been removed by mutation to alanine, has its hydrolytic activity rescued by exogenous formate in a concentration-dependent manner. A long-lived α-glycosyl formate is detected and identified by 1H-NMR and matrix-assisted laser desorption ionization–time-of-flight-MS. The intermediate is kinetically competent, since it is, at least partially, enzymically hydrolysed, and able to act as a glycosyl donor in transglycosylation reactions. This transient compound represents a true covalent glycosyl-enzyme intermediate mimic of the proposed covalent intermediate in the reaction mechanism of retaining glycosidases.
Proinsulin C-peptide rapidly stimulates mitogen-activated protein kinases in Swiss 3T3 fibroblasts: requirement of protein kinase C, phosphoinositide 3-kinase and pertussis toxin-sensitive G-protein
Authors: KITAMURA Takanori , KIMURA Kazuhiro , JUNG Bae Dong , MAKONDO Kennedy , OKAMOTO Shiki , CAÑAS Xavier , SAKANE Naoki , YOSHIDA Toshihide , SAITO Masayuki
Published: August 2015

It has been demonstrated that proinsulin C-peptide possesses several biological activities and that its specific binding sites are present on the surface of cell membranes. However, the molecular and cellular mechanisms of C-peptide actions are poorly known. In the present study we examined the possible involvement of the mitogen-activated protein kinase (MAPK) pathway in C-peptide effects. C-peptide induced the phosphorylation of MAPK [p44 extracellular signal-regulated kinase 1 (ERK1) and p42 ERK2] in Swiss 3T3 and 3T3-F442A fibroblasts but not in 3T3-L1 fibroblasts and some other cell lines such as L6E9 muscle cells. In Swiss 3T3 cells, C-peptide-induced phosphorylation of MAPK was dependent on time and concentration, being maximal at 1min and at 1nM C-peptide and was accompanied by an increase in MAPK activity and MAPK kinase (MEK) phosphorylation. The MAPK phosphorylation by C-peptide was abolished by treatment with pertussis toxin (PTX) and also with a MEK inhibitor, PD 98059. In addition, MAPK phosphorylation was attenuated by treatment with a phosphoinositide 3-kinase (PI-3K) inhibitor, wortmannin, and with a protein kinase C (PKC) inhibitor, GF109203X, and by down-regulation of PKC by prolonged treatment with PMA. Similar effects of the inhibitors and PTX were found on the MAPK phosphorylation induced by neuropeptide Y. These results suggest that C-peptide activates MAPK through a putative Gi/Go-linked receptor for C-peptide and through PI-3K-dependent and PKC-dependent pathways.
Control of Ca2+ influx in human neutrophils by inositol 1,4,5-trisphosphate (IP3) binding: differential effects of micro-injected IP3 receptor antagonists
Authors: DAVIES-COX Eryl V. , LAFFAFIAN Iraj , HALLETT Maurice B.
Published: August 2015

Neutrophils signal Ca2+ changes in response to occupancy of G-protein-linked receptors such as the formylated peptide receptor. This Ca2+ signal is composed of two parts, inositol 1,4,5-trisphosphate (IP3)-triggered release of Ca2+ from an intracellular store and Ca2+ influx. In order to probe the relationship between these events, cytosolic free Ca2+ changes in neutrophils were monitored after micro-injection of agents which inhibit IP3 binding. Micro-injection of heparin into neutrophils totally inhibited both formylmethionyl-leucylphenylalanine-induced Ca2+ release and the subsequent Ca2+ influx. This effect was not due to prior depletion of Ca2+ stores. Furthermore, micro-injection with anti-IP3-receptor antibody also inhibited Ca2+ release. However, anti-IP3-receptor antibody and another high-molecular-mass IP3-binding antagonist, heparin–albumin conjugate, failed to inhibit the accompanying Ca2+ influx. It was concluded that two IP3-binding sites exist in neutrophils: one accessible by both heparin and the high-molecular-mass inhibitors of IP3 binding and responsible for Ca2+ release, and another inaccessible to high-molecular-mass molecules and responsible for Ca2+ influx.
Oxidative modification of H-ras: S-thiolation and S-nitrosylation of reactive cysteines
Authors: MALLIS Robert J. , BUSS Janice E. , THOMAS James A.
Published: August 2015

The reactive cysteines in H-ras are subject to oxidative modifications that potentially alter the cellular function of this protein. In this study, purified H-ras was modified by thiol oxidants such as hydrogen peroxide (H2O2), S-nitrosoglutathione, diamide, glutathione disulphide (GSSG) and cystamine, producing as many as four charge-isomeric forms of the protein. These results suggest that all four reactive cysteines of H-ras are potential sites of regulatory modification reactions. S-nitrosylated and S-glutathiolated forms of H-ras were identified by protocols that depend on separation of alkylated proteins on electrofocusing gels. S-nitrosoglutathione could S-nitrosylate H-ras on four cysteine residues, while reduced glutathione (GSH) and H2O2 mediate S-glutathiolation on at least one cysteine of H-ras. Either GSSG or diamide S-glutathiolated at least two cysteine residues of purified H-ras. Iodoacetic acid reacts with three cysteine residues. In intact NIH-3T3 cells, wild-type H-ras was S-glutathiolated by diamide. Similarly, cells expressing a C118S mutant or a C181S/C184S double mutant of H-ras were S-glutathiolated by diamide. These results suggest that H-ras can be S-glutathiolated on multiple thiols in vivo and that at least one of these thiols is normally lipid-modified. In cells treated with S-nitrosocysteine, evidence for both S-nitrosylated and S-glutathiolated H-ras was obtained and S-nitrosylation was the predominant modification. These results show that oxidative modification of H-ras can be extensive in vivo, that both S-nitrosylated and S-glutathiolated forms may be important, and that oxidation may occur on reactive cysteines that are normally targeted for lipid-modification reactions.
The mitochondrial consequences of uncoupling intact cells depend on the nature of the exogenous substrate
Authors: SIBILLE Brigitte , FILIPPI Céline , PIQUET Marie-Astrid , LECLERCQ Pascale , FONTAINE Eric , RONOT Xavier , RIGOULET Michel , LEVERVE Xavier
Published: August 2015

In isolated mitochondria the consequences of oxidative phosphorylation uncoupling are well defined, whereas in intact cells various effects have been described. Uncoupling liver cells with 2,4-dinitrophenol (DNP) in the presence of dihydroxyacetone (DHA) and ethanol results in a marked decrease in mitochondrial transmembrane electrical potential (∆ψ), ATP/ADP ratios and gluconeogenesis (as an ATP-utilizing process), whereas the increased oxidation rate is limited and transient. Conversely, when DHA is associated with octanoate or proline, DNP addition results in a very large and sustained increase in oxidation rate, whereas the decreases in ∆ψ, ATP/ADP ratios and gluconeogenesis are significantly less when compared with DHA and ethanol. Hence significant energy wastage (high oxidation rate) by uncoupling is achieved only with substrates that are directly oxidized in the mitochondrial matrix. Conversely in the presence of substrates that are first oxidized in the cytosol, uncoupling results in a profound decrease in mitochondrial ∆ψ and ATP synthesis, whereas energy wastage is very limited.
The molecular basis of oculocutaneous albinism type 1 (OCA1): sorting failure and degradation of mutant tyrosinases results in a lack of pigmentation
Authors: TOYOFUKU Kazutomo , WADA Ikuo , SPRITZ Richard A. , HEARING Vincent J.
Published: August 2015

Oculocutaneous albinism type 1 (OCA1) is an autosomal recessive disease resulting from mutations of the tyrosinase gene (TYR). To elucidate the molecular basis of OCA1 phenotypes, we analysed the early processing and maturation of several different types of mutant tyrosinase with various degrees of structural abnormalities (i.e. two large deletion mutants, two missense mutants that completely destroy catalytic function and three missense mutants that have a temperature-sensitive phenotype). When expressed in COS7 cells, all mutant tyrosinases were sensitive to endoglycosidase H digestion, and immunostaining showed their localization in the endoplasmic reticulum (ER) and their failure to be sorted further to their target organelles. Pulse-chase experiments showed that all mutant tyrosinases were retained by calnexin in the ER and that they were degraded at similarly rapid rates, which coincided with their dissociation from calnexin. Temperature-sensitive mutant enzymes were sorted more efficiently at 31°C than at 37°C, and their degradation was accelerated at 37°C compared with 31°C. Thus in contrast to the current concept that mutant tyrosinases are transported to melanosomes but are functionally inactive there, our results suggest that mutant tyrosinases may not be transported to melanosomes in the first place. We conclude that a significant component of mutant tyrosinase malfunction in OCA1 results from their retention and degradation in the ER compartment. This quality-control process is highly sensitive to minimal changes in protein folding, and so even relatively minor mutations in peripheral sequences of the enzyme not involved with catalytic activity may result in a significant reduction of functional enzyme in melanosomes.
Genomic organization and characterization of splice variants of the human histamine H3 receptor
Authors: COGÉ Francis , GUÉNIN Sophie-Pénélope , AUDINOT Valérie , RENOUARD-TRY Anne , BEAUVERGER Philippe , MACIA Christelle , OUVRY Christine , NAGEL Nadine , RIQUE Hervé , BOUTIN Jean A. , GALIZZI Jean-Pierre
Published: August 2015

In the present paper we report the genomic organization of the human histamine H3-receptor gene, which consists of four exons spanning 5.5kb on chromosome 20. Using PCR, six alternative splice variants of the H3 receptor were cloned from human thalamus. These variants were found to be coexpressed in human brain, but their relative distribution varied in a region-specific manner. These isoforms displayed either a deletion in the putative second transmembrane domain (TM), H3(∆TM2, 431aa) or a variable deletion in the third intracellular loop (i3), H3(∆i3, 415aa), H3(∆i3, 365aa), H3(∆i3, 329aa) and H3(∆TM5+∆i3, 326aa). In order to determine the biological role of the H3 receptor variants compared with the ‘original’ H3(445aa) receptor, three isoforms, namely H3(445aa), H3(∆TM2, 431aa) and H3(∆i3, 365aa), were expressed in CHO cells and their pharmacological properties were investigated. Binding studies showed that H3(∆TM2,431aa) transiently expressed in CHO cells was unable to bind [125I]iodoproxyfan, whereas both the H3(445aa) and H3(∆i3, 365aa) receptors displayed a high affinity for [125I]iodoproxyfan [Kd = 28±5pM (n = 4) and 8±1pM (n = 5) respectively]. In addition, H3(∆i3, 365aa) possessed the same pharmacological profile as the H3(445aa) receptor. However, in CHO cells expressing H3(∆i3, 365aa), H3 agonists did not inhibit forskolin-induced cAMP production, stimulate [35S]guanosine 5′-[γ-thio]triphosphate ([35S]GTP[S]) binding or stimulate intracellular Ca2+ mobilization. Therefore the 80-amino-acid sequence located at the C-terminal portion of i3 plays an essential role in H3 agonist-mediated signal transduction. The existence of multiple H3 isoforms with different signal transduction capabilities suggests that H3-mediated biological functions might be tightly regulated through alternative splicing mechanisms.
Differential effects of oncostatin M and leukaemia inhibitory factor expression in astrocytoma cells
Authors: KASZA Aneta , ROGOWSKI Krzysztof , KILARSKI Witold , SOBOTA Radoslaw , BERNAS Tytus , DOBRUCKI Jurek , TRAVIS James , KOJ Aleksander , BUGNO Marcin , KORDULA Tomasz
Published: August 2015

The effects of the production of two closely related cytokines, oncostatin M (OSM) and leukaemia inhibitory factor (LIF), by astrocytoma cells were investigated using the stable cell line human U373-MG, which expressed and secreted both biologically active polypeptides. The expression of LIF by these cells caused resistance to this cytokine due to loss of the LIF receptor (LIFR), from the cell surface, suggesting its retention. In contrast, cells expressing OSM were stimulated by this cytokine, utilizing an autocrine mechanism, and possessed receptors for OSM, but not LIF, on the cell surface. In these cells the continuous up-regulation of OSM-induced gene expression was found even though the Janus kinase-signal transducer and activator of transcription (‘JAK/STAT’) pathway was almost exhausted due to long-term autocrine stimulation of the cells by OSM. The amount of LIFR was down-regulated in both LIF- and OSM-producing cells and this effect was not found in wild-type U373-MG cells treated with externally added cytokines. To investigate the mechanism of autocrine stimulation by OSM we constructed a stable cell line expressing a form of OSM that is retained in the endoplasmic reticulum (ER). This biologically active cytokine was not secreted, but was localized in the ER. In addition, it did not stimulate the astrocytoma cells in an autocrine manner. We conclude that expression of LIF causes resistance of astrocytoma cells to this cytokine, whereas expression of OSM leads to autocrine stimulation.
Purification and characterization of thiol-reagent-sensitive glycerol-3-phosphate acyltransferase from the membrane fraction of an oleaginous fungus
Authors: MISHRA Sanjay , KAMISAKA Yasushi
Published: August 2015

Glycerol-3-phosphate acyltransferase (GPAT), responsible for the first committed, rate-limiting, step of glycerolipid synthesis, was purified to homogeneity from the membrane fraction of an oleaginous fungus, Mortierella ramanniana var. angulispora. The enzyme was solubilized from the membrane fraction by pretreatment with 0.05% Triton X-100 and treatment of the resulting pellet with 0.3% Triton X-100. The enzyme was subsequently purified by column chromatography on heparin-Sepharose, Yellow 86 agarose, a second heparin-Sepharose column, Superdex-200 and hydroxylapatite Bio-Gel. Enzyme activity was finally enriched 1308-fold over that of the starting membrane fraction. SDS/PAGE of the purified fraction revealed a single band with a molecular mass of 45kDa. Native PAGE showed a major band that corresponded to GPAT activity. Enzyme activity was inhibited by thiol reagents, suggesting that it originated from microsomes rather than mitochondria. Purified GPAT depended on exogenous oleoyl-CoA and sn-glycerol-3-phosphate, with the highest activity at approx. 50 and 250µM, respectively, and preferred oleoyl-CoA 5.4-fold over palmitoyl-CoA as an acyl donor. Anionic phospholipids, such as phosphatidic acid and phosphatidylserine, were absolutely required for activity of the purified enzyme, and their ability to activate GPAT was influenced by the purity of the GPAT preparation. Bivalent cations, such as Mg2+ and Ca2+, inhibited purified GPAT activity, whereas 5mM Mn2+ elevated activity approx. 2-fold. These results provide new insights into the molecular characterization of microsomal GPAT, which has not been well characterized compared with mitochondrial and plastidic GPAT.
cyp7b1 catalyses the 7α-hydroxylation of dehydroepiandrosterone and25-hydroxycholesterol in rat prostate
Authors: MARTIN Cécile , BEAN Rhona , ROSE Ken , HABIB Fouad , SECKL Jonathan
Published: August 2015

Dehydroepiandrosterone (DHEA) is the most prominent circulating steroid in humans, and it is a precursor for sex-steroid synthesis in peripheral tissues, including the prostate. Recently, enzyme-mediated pre-receptor metabolism has been recognized as a key step in determining steroid action in vivo. Hydroxylation of 3β-steroids at the 7α-position has been reported in rat and human prostate to be a major inhibitory pathway to sex-steroid synthesis/action. However, the molecular identity of the enzyme responsible is so far unknown. We recently described a novel cytochrome P450 enzyme, cyp7b1, strongly expressed in the hippocampus of rodent brain, which catalyses the metabolism of DHEA, pregnenolone and 25-hydroxycholesterol to 7α-hydroxy products. In the light of this new enzyme, we have examined its possible role in 7α-hydroxylation conversion in rat prostate. NADPH-dependent 7α-hydroxylation was confirmed for 3β-hydroxysteroids including DHEA and androstenediol, as well as 25-hydroxycholesterol. Kinetic analysis yielded an apparent Km of 14±1µM for 7α-hydroxylation of DHEA in the prostate gland, a value similar to that recorded for recombinant cyp7b1 enzyme [13.6µM; Rose, Stapleton, Dott, Kieny, Best, Schwarz, Russell, Bjoorkheim, Seckl and Lathe (1997) Proc. Natl. Acad. Sci. U.S.A. 94, 4925-4930]. The Vmax value of the prostate was 46±2pmol/min per mg, and this activity was inhibited by clotrimazole, a P450-enzyme blocker. Moreover, RNA analysis (reverse-transcription PCR, Northern blotting and in situ hybridization) revealed a high expression of cyp7b1 mRNA in the rat prostate, restricted to the epithelium, suggesting that cyp7b1 catalyses oxysterol 7α-hydroxylation in the prostate gland.
Co-operative regulation of the transcription of human dihydrodiol dehydrogenase (DD)4/aldo–keto reductase (AKR)1C4 gene by hepatocyte nuclear factor (HNF)-4α/γ and HNF-1α
Authors: OZEKI Takeshi , TAKAHASHI Yoshiki , KUME Toshiyuki , NAKAYAMA Kazuo , YOKOI Tsuyoshi , NUNOYA Ken-Ichi , HARA Akira , KAMATAKI Tetsuya
Published: August 2015

Human dihydrodiol dehydrogenase (DD) 4/aldo-keto reductase (AKR) 1C4 is a major isoform of hepatic DD that oxidizes trans-dihydrodiols of polycyclic aromatic hydrocarbons to reactive and redox-active o-quinones and that reduces several ketone-containing drugs. To investigate the mechanism of transcriptional regulation of the human DD4 gene, the 5′-flanking region of the gene was fused to the luciferase gene. The results of luciferase assays using HepG2 cells and of 1,10-phenanthroline-copper footprinting indicated that two positive regulatory regions were located in regions from -701 to -684 and from -682 to -666. The former region contained a putative hepatocyte nuclear factor (HNF)-4 binding motif, and the latter region contained an HNF-1 consensus binding sequence. DNA fragments of the HNF-4 or HNF-1 motif gave a shifted band in a gel-shift assay with nuclear extracts from HepG2 cells. The formation of the DNA-protein complex was inhibited by the HNF-4 or HNF-1 motif of the α1-antitrypsin gene. A supershift assay using antibodies to human HNF-4α, HNF-4γ and HNF-1α showed that HNF-4α and HNF-4γ bound to the HNF-4 motif, and that HNF-1α interacted with the HNF-1 motif. Introduction of mutations into the HNF-4 or HNF-1 motif lowered the luciferase activity to 10 or 8% respectively of that seen with the intact human DD4 gene. These results indicate that HNF-4α, HNF-4γ and HNF-1α regulate co-operatively the transcription of the human DD4 gene in HepG2 cells.
Controlled protonation of iron–molybdenum cofactor by nitrogenase: a structural and theoretical analysis
Authors: DURRANT Marcus C.
Published: August 2015

Qualitative molecular modelling has been used to identify possible routes for transfer of protons from the surface of the nitrogenase protein to the iron–molybdenum cofactor (FeMoco) and to substrates during catalysis. Three proton-transfer routes have been identified; a water-filled channel running from the protein exterior to the homocitrate ligand of FeMoco, and two hydrogen-bonded chains to specific FeMoco sulphur atoms. It is suggested that the water channel is used for multiple proton deliveries to the substrate, as well as in diffusion of products and substrates between FeMoco and the bulk solvent, whereas the two hydrogen-bonded chains each allow a single proton to be added to, and subsequently depart from, FeMoco during the catalytic cycle. Possible functional differences in the proton-transfer channels are discussed in terms of assessment of the protein environment and specific hydrogen-bonding effects. The implications of these observations are discussed in terms of the suppression of wasteful production of dihydrogen by nitrogenase and the Lowe–Thorneley scheme for dinitrogen reduction.
Ten isoenzymes of xyloglucan endotransglycosylase from plant cell walls select and cleave the donor substrate stochastically
Authors: STEELE Nancy M. , SULOVÁ Zdena , CAMPBELL Paul , BRAAM Janet , FARKAŠ Vladimír , FRY Stephen C.
Published: August 2015

To map the preferred cleavage sites of xyloglucan endotransglycosylases (XETs; EC 2.4.1.207) along the donor substrate chain, we incubated the enzymes with tamarind (Tamarindus indica) xyloglucan (donor substrate; ≈ 205kDa; 21µM) plus the nonasaccharide [3H]XLLGol (Gal2·Xyl3·Glc3· [3H]glucitol; acceptor substrate; 0.6µM). After short incubation times, to minimize multiple cleavages, the size of the 3H-labelled transglycosylation products (determined by gel-permeation chromatography) indicated the positions of the cleavage sites relative to the non-reducing terminus of the donor. There was very little difference between the size profiles of the products formed by any of ten XETs tested [one native XET purified from cauliflower (Brassica oleracea) florets, four native XET isoenzymes purified from etiolated mung-bean (Phaseolus aureus) shoots, native XETs purified from lentil (Lens culinaris) and nasturtium (Tropaeolum majus) seeds, and three insect-cell-produced thale-cress (Arabidopsis thaliana) XETs (EXGT, TCH4 and MERI-5)]. All such product profiles showed a good fit to a model in which the enzyme chooses its donor substrate independently of size and attacks it, once only, at a randomly selected cleavage site. The results therefore do not support the hypothesis that different XET isoenzymes are adapted to produce longer or shorter products such as might favour either the efficient integration of new xyloglucan into the cell wall or the re-structuring of old xyloglucan within an expanding wall.
Oxidative stress impairs insulin but not platelet-derived growth factor signalling in 3T3-L1 adipocytes
Authors: TIROSH Amir , RUDICH Assaf , POTASHNIK Ruth , BASHAN Nava
Published: August 2015

Activation of phosphatidylinositol 3-kinase (PI 3-kinase) is a common event in both insulin and platelet-derived growth factor (PDGF) signalling, but only insulin activates this enzyme in the high-speed pellet (HSP), and induces GLUT4 translocation. Recently, we have demonstrated that exposure of 3T3-L1 adipocytes to oxidative stress impairs insulin-stimulated GLUT4 translocation and glucose transport, associated with impaired PI 3-kinase translocation and activation in the HSP [Tirosh, Potashnik, Bashan and Rudich (1999) J. Biol. Chem. 274, 10595–10602]. In this study the effect of a 2h exposure to ≈ 30µM H2O2 on insulin versus PDGF-BB signalling and metabolic effects was compared. PDGF-stimulated p85-associated PI 3-kinase activity in total cell lysates, as well as co-precipitation of the PDGF receptor, were unaffected by oxidative stress. Additionally, the increase in p85 association with the plasma-membrane lawns by PDGF remained intact following oxidation, whereas the insulin effect was decreased. PDGF significantly increased protein kinase B (PKB) activity in early differentiated cells, and that of p70 S6-kinase in both early and fully differentiated 3T3-L1 adipocytes. Following oxidation the effect of PDGF on PKB and p70 S6-kinase activation remained intact, whereas significant inhibition of insulin-stimulated activation of those enzymes was observed. In accordance, in both early and fully differentiated cells, oxidative stress completely blunted insulin- but not PDGF-stimulated protein synthesis. In conclusion, oxidative stress impairs insulin, but not PDGF, signalling and metabolic actions in both early and fully differentiated 3T3-L1 adipocytes. This emphasizes compartment-specific activation of PI 3-kinase as an oxidation-sensitive step specifically leading to insulin resistance.
Involvement of mitogen-activated protein kinase activation in the signal-transduction pathways of the soya bean oxidative burst
Authors: TAYLOR Ann T.S. , KIM Jitae , LOW Philip S.
Published: August 2015

The oxidative burst constitutes one of the most rapid defence responses characterized in the Plant Kingdom. We have observed that four distinct elicitors of the soya bean oxidative burst activate kinases of masses ≈44kDa and ≈47kDa. Evidence that these kinases regulate production of reactive oxygen species include: (i) their rapid activation by oxidative burst elicitors, (ii) their tight temporal correlation between activation/deactivation of the kinases and activation/deactivation of the oxidative burst, (iii) the identical pharmacological profile of kinase activation and oxidant production for 13 commonly used inhibitors, and (iv) the autologous activation of both kinases and oxidant production by calyculin A and cantharidin, two phosphatase inhibitors. Immunological and biochemical studies reveal that the activated 44kDa and 47kDa kinases are mitogen-activated protein (MAP) kinase family members. The kinases prefer myelin basic protein as a substrate, and they phosphorylate primarily on threonine residues. The kinases are themselves phosphorylated on tyrosine residues, and this phosphorylation is required for activity. Finally, both kinases are recognized by an antibody against activated MAP kinase immediately after (but not before) cell stimulation by elicitors. Based on these and other observations, a preliminary sequence of signalling steps linking elicitor stimulation, kinase activation and Ca2+ entry, to initiation of oxidant production, is proposed.
Rat peptide methionine sulphoxide reductase: cloning of the cDNA, and down-regulation of gene expression and enzyme activity during aging
Authors: PETROPOULOS Isabelle , MARY Jean , PERICHON Martine , FRIGUET Bertrand
Published: August 2015

Peptide methionine sulphoxide reductase (PMSR, EC 1.8.4.6), the msrA or pmsR gene product, is a ubiquitous enzyme catalysing the reduction of methionine sulphoxide to methionine in proteins. Decreased expression and/or activity of the PMSR with age could explain, at least in part, the accumulation of oxidized protein observed upon aging. To test this hypothesis, the rat pmsR cDNA was cloned and sequenced. The recombinant protein was expressed, its catalytic activity checked with a synthetic substrate and polyclonal antibodies were raised against recombinant PMSR. The expression of the pmsR gene and protein as well as its catalytic activity were then analysed as a function of age in the rat brain and in two organs that express the most PMSR, liver and kidney. It appears that pmsR gene expression decreases with age in liver and kidney as early as 18 months, whereas protein level and protein activity are reduced in the three organs at the very end of the life of the rat (26 months). These results suggest that the down-regulation of PMSR can contribute to the accumulation of oxidized protein that has been associated with the aging process.

The rat peptide methionine sulphoxide reductase sequence reported in this paper has been deposited in the GenBank Nucleotide Sequence Database under accession number AY005464.
Catalytic mechanism of a family 3 β-glucosidase and mutagenesis study on residue Asp-247
Authors: LI Yaw-Kuen , CHIR Jiunly , CHEN Fong-Yi
Published: August 2015

A family 3 β-glucosidase (EC 3.2.1.21) from Flavobacterium meningosepticum has been cloned and overexpressed. The mechanistic action of the enzyme was probed by NMR spectroscopy and kinetic investigations, including substrate reactivity, secondary kinetic isotope effects and inhibition studies. The stereochemistry of enzymic hydrolysis was identified as occurring with the retention of an anomeric configuration, indicating a double-displacement reaction. Based on the kcat values with a series of aryl glucosides, a Bronsted plot with a concave-downward shape was constructed. This biphasic behaviour is consistent with a two-step mechanism involving the formation and breakdown of a glucosyl–enzyme intermediate. The large Bronsted constant (β =-0.85) for the leaving-group-dependent portion (pKa of leaving phenols > 7) indicates substantial bond cleavage at the transition state. Secondary deuterium kinetic isotope effects with 2,4-dinitrophenyl β-D-glucopyanoside, o-nitrophenyl β-D-glucopyanoside and p-cyanophenyl β-D-glucopyanoside as substrates were 1.17±0.02, 1.19±0.02 and 1.04±0.02 respectively. These results support an SN1-like mechanism for the deglucosylation step and an SN2-like mechanism for the glucosylation step. Site-directed mutagenesis was also performed to study essential amino acid residues. The activities (kcat/Km) of the D247G and D247N mutants were 30000- and 200000-fold lower respectively than that of the wild-type enzyme, whereas the D247E mutant retained 20% of wild-type activity. These results indicate that Asp-247 is an essential amino acid. It is likely that this residue functions as a nucleophile in the reaction. This conclusion is supported by the kinetics of the irreversible inactivation of the wild-type enzyme by conduritol-B-epoxide, compared with the much slower inhibition of the D247E mutant and the lack of irreversible inhibition of the D247G mutant.
A neutral sphingomyelinase resides in sphingolipid-enriched microdomains and is inhibited by the caveolin-scaffolding domain: potential implications in tumour necrosis factor signalling
Authors: VELDMAN Robert J. , MAESTRE Nicolas , ADUIB Osama M. , MEDIN Jeffrey A. , SALVAYRE Robert , LEVADE Thierry
Published: August 2015

Sphingomyelinases hydrolyse sphingomyelin to ceramide, a process involved in signal-transduction routes leading to apoptosis and various other cellular responses. In the present study, we investigated the sphingomyelinase content of caveolae, invaginated plasma-membrane microdomains that contain a variety of signalling molecules. These structures are highly enriched in sphingomyelin as well as in ceramide, which suggests that metabolism of these lipids might, to some extent, occur locally. By cell fractionation, we demonstrate that, in addition to a previously reported minute amount of acidic sphingomyelinase activity, a substantial amount of neutral sphingomyelinase activity resides in caveolae of human skin fibroblasts. This caveolar neutral sphingomyelinase activity was also detected in Niemann–Pick disease type A fibroblasts, which are completely devoid of functional acidic sphingomyelinase. Neutral (but not acidic) sphingomyelinase activity was specifically inhibited by a peptide that corresponds to the scaffolding domain of caveolin, which suggests a direct molecular interaction between the two proteins. In addition, this finding implies a cytosolic orientation of the caveolar neutral sphingomyelinase. Interestingly, stimulation of fibroblasts with tumour necrosis factor α (TNFα) resulted in a partial shift of its p55 receptor to caveolin-enriched membrane fractions and the appearance of caveolin-sensitive neutral sphingomyelinase activity in the non-caveolar fractions. These results suggest that (part of) the presently identified caveolar neutral sphingomyelinase activity is involved in TNFα signalling.