bluuebunny/crossref_metadata_2025 huggingface dataset:
Importance of lactate dehydrogenase for the regulation of glycolytic flux and insulin secretion in insulin-producing cells
Authors: ALCAZAR Oscar , TIEDGE Markus , LENZEN Sigurd
Published: August 2015

The role of lactate dehydrogenase (LDH) in the generation of the metabolic signal for insulin secretion was studied after stable overexpression in INS-1 and RINm5F insulin-producing cells. INS-1 cells with a 25-fold overexpression of LDH-A, the highest level achieved, showed a 20–30% decrease in the glucose oxidation rate at glucose concentrations above 5mM when compared with control cells, whereas values were unchanged at lower glucose concentrations. Lactate release increased in parallel with a decrease in the glucose oxidation rate. However, the INS-1 cell glucose-induced insulin secretory response, together with the rate of glucose utilization, were not significantly affected by LDH-A overexpression. Despite 3-fold overexpression of LDH-A in glucose-unresponsive RINm5F cells, there was no change in insulin secretion, glucose metabolism or lactate production in these cells. Exogenously added pyruvate and lactate potentiated glucose-stimulated insulin secretion in INS-1 cells, an effect that was abolished after LDH-A overexpression. Both compounds significantly decreased glucose oxidation rates in control cells. After overexpression of LDH-A in INS-1 cells, the effects of pyruvate and lactate on glucose oxidation were diminished. On the other hand, after LDH-A overexpression, both glycolytic metabolites decreased the glucose utilization rate at 5mM glucose. The present data suggest that the level of LDH expression in insulin-secreting cells is critical for correct channelling of pyruvate towards mitochondrial metabolism. Interestingly, glucokinase-mediated glycolytic flux was decreased after LDH-A overexpression. Thus preferential channelling of glucose towards aerobic metabolism by glucokinase may be determined, at least in part, by the low level of constitutive expression of LDH-A in pancreatic β-cells. In conclusion, the level of LDH expression in insulin-secreting cells is an important determinant of the physiological insulin-secretory capacity, and also determines how pyruvate and lactate affect insulin secretion.
Contrasting effects of alloxan on islets and single mouse pancreatic β-cells
Authors: DREWS Gisela , KRÄMER Claudia , DÜFER Martina , KRIPPEIT-DREWS Peter
Published: August 2015

Alloxan is used to induce diabetes in animals; however, the underlying mechanisms are still a matter of debate. Alloxan evoked a rapid hyperpolarization of the plasma membrane potential and suppressed electrical activity elicited by 15mM glucose, thus terminating voltage-dependent Ca2+ influx. Accordingly, glucose-induced oscillations in intracellular free Ca2+ concentration were abolished. The effect of alloxan on membrane potential could not be reversed by glucose but was reversed by tolbutamide. However, the sensitivity to tolbutamide was decreased after treatment of the cells with alloxan. These effects closely resemble those described earlier for H2O2. H2O2 and alloxan decreased the mitochondrial membrane potential, indicating a decrease in ATP production and thus interference with cell metabolism. A decrease in ATP synthesis would explain the plasma membrane hyperpolarization observed in intact islets, reflecting the activation of ATP-dependent K+ channels. Surprisingly, alloxan inhibited the whole-cell K+ATP current measured in single cells and the single-channel K+ATP current registered in excised patches. This inhibitory effect of alloxan is not mediated by changes in cell metabolism but seems to be due to direct interactions with the K+ATP channels via thiol-group oxidation. We have monitored the appearance of reactive oxygen species in single cells and islets treated with alloxan and H2O2 for comparison. In contrast to H2O2, alloxan induced the appearance of measurable reactive oxygen species only in islets but not in single cells. The results show that alloxan evokes different effects in islets and single cells, giving a possible explanation for inconsistent results reported in the past. It is concluded that alloxan exerts its diabetogenic effect by the production of H2O2 in intact islets.
Mouse pseudouridine synthase 1: gene structure and alternative splicing of pre-mRNA
Authors: CHEN Jianguang , PATTON Jeffrey R.
Published: August 2015

Evidence for the alternative splicing of the message for mouse pseudouridine synthase 1 (mPus1p) was found when several expressed sequence tag clones were completely sequenced. The genomic DNA for the MPUS1 gene (6.9kb) was cloned from a mouse genomic library; the gene contains seven exons, of which three are alternatively spliced. In addition, one of the internal exons (exon VI) is unusually large. RNase protection analysis confirmed that several alternatively spliced messages were present in mouse tissues and cells in culture. A Western blot of total cellular protein from mouse tissues and cultured cells was reacted with an antibody specific for mPus1p; at least three proteins were detected. One protein corresponds to the predicted molecular mass of mPus1p (44kDa) and is the most abundant. The two other isoforms, one 2kDa larger and one 7kDa smaller than mPus1p, were differentially expressed. The cDNA species for the three isoforms were cloned into expression plasmids; the proteins were synthesized in vitro and tested for pseudouridine synthase activity. The two isoforms, one containing an insert of 18 amino acids in a region of the enzyme assumed to be critical for activity, and the other, which has a deletion of the protein coding potential of two exons, were both inactive on tRNA substrates that mPus1p modifies.
Inhibition of growth-factor-induced phosphorylation and activation of protein kinase B/Akt by atypical protein kinase C in breast cancer cells
Authors: MAO Muling , FANG Xianjun , LU Yiling , LAPUSHIN Ruth , BAST Robert C. , MILLS Gordon B.
Published: August 2015

The protein kinase B/Akt serine/threonine kinase, located downstream of phosphoinositide 3-kinase (PI-3K), is a major regulator of cellular survival and proliferation. Atypical protein kinase C (aPKC) family members are activated by PI-3K and also contribute to cell proliferation, suggesting that Akt and aPKC might interact to activate signalling through the PI-3K cascade. Here we demonstrate that blocking PKC activity in MDA-MB-468 breast cancer cells increased the phosphorylation and activity of Akt. Functional PI-3K was required for the PKC inhibitors to increase Akt phosphorylation and activation, potentially owing to the activation of specific PKC isoforms by PI-3K. The concentration dependence of the action of the PKC inhibitors implicates aPKC in the inhibition of Akt phosphorylation and activity. In support of a role for aPKC in the regulation of Akt, Akt and PKCζ or PKCλ/ℓ were readily co-precipitated from the BT-549 breast cancer cell line. Furthermore, the overexpression of PKCζ inhibited growth-factor-induced increases in Akt phosphorylation and activity. Thus PKCζ associates physically with Akt and decreases Akt phosphorylation and enzyme activity. The effects of PKC on Akt were transmitted through the PI-3K cascade as indicated by changes in p70 s6 kinase (p70s6k) phosphorylation. Thus PKCζ, and potentially other PKC isoenzymes, regulate growth-factor-mediated Akt phosphorylation and activation, which is consistent with a generalized role for PKCζ in limiting growth factor signalling through the PI-3K/Akt pathway.
PrPSc-like prion protein peptide inhibits the function of cellular prion protein
Authors: BROWN David R.
Published: August 2015

Mice lacking expression of the prion protein are protected against infection with prion disease. Neurodegeneration in prion disease requires the formation of the abnormal isoform of the prion protein (PrPSc) from host prion protein. Therefore expression of normal host prion protein is necessary for prion disease. In the present investigation, it was demonstrated that PrPSc and a peptide resembling PrPSc, PrP106–126, both bind to cellular prion protein at amino acid residues 112–119. Interaction between PrP106–126 and the prion protein strips the prion protein from cells. Direct interaction of PrP106–126 with the prion protein was found to make cells more susceptible to copper toxicity, inhibited copper uptake into cells and inhibited the superoxide dismutase-like activity of the prion protein. Direct inhibition of prion protein function by PrPSc may be necessary for neurodegeneration in prion disease.
In vivo mapping of the human adenine nucleotide translocator-2 (ANT2) promoter provides support for regulation by a pair of proximal Sp1-activating sites and an upstream silencer element
Authors: LUCIAKOVA Katarina , HODNY Zdenek , BARATH Peter , NELSON B. Dean
Published: August 2015

Regulatory factors bound to the human adenine nucleotide translocator-2 (ANT2) promoter have been mapped in HeLa cells by in vivo DNase I protection and ligation-mediated PCR amplification. Protein binding was detected at only three sites within the extended promoter region (to nt -703). One, starting at nt -61 and covering the TATA box and transcription start, most probably represents occupation by the transcription-initiation machinery. A repeated Sp1 element determined by in vitro studies to be the major activation element for the promoter was also protected in vivo on nucleotides responsible for strong binding to the zinc fingers. Occupation of two additional upstream Sp1 elements was not observed. The third site occupied in vivo was identified previously by in vitro studies as a unique silencer element. Treatment of cells with trichostatin A to induce hyperacetylation released the silencer-binding protein after 1h, but had no effect on the Sp1-activating elements. Prolonged treatment (24h) displaced Sp1 from the activating elements. These findings confirm and extend in vitro studies indicating that regulation of the ANT2 promoter is most probably exerted through a single pair of proximal Sp1-activating elements and an upstream silencer, and that chromatin organization plays a role in the interaction between the two.
Interaction of sigma factor σN with Escherichia coli RNA polymerase core enzyme
Authors: SCOTT David J. , FERGUSON Anna L. , GALLEGOS María-Trinidad , PITT Melinda , BUCK Martin , HOGGETT James G.
Published: August 2015

The equilibrium binding and kinetics of assembly of the DNA-dependent RNA polymerase (RNAP) σN-holoenzyme has been investigated using biosynthetically labelled 7-azatryptophyl- (7AW)σN. The spectroscopic properties of such 7AW proteins allows their absorbance and fluorescence to be monitored selectively, even in the presence of high concentrations of other tryptophan-containing proteins. The 7AWσN retained its biological activity in stimulating transcription from σN-specific promoters, and in in vitro gel electrophoresis assays of binding to core RNAP from Escherichia coli. Furthermore, five Trp → Ala single mutants of σN were shown to support growth under conditions of nitrogen limitation, and showed comparable efficiency in activating the σN-dependent nifH promoter in vivo, indicating that none of the tryptophan residues were essential for activity. The equilibrium binding of 7AWσN to core RNAP was examined by analytical ultracentrifugation. In sedimentation equilibrium experiments, absorbance data at 315nm (which reports selectively on the distribution of free and bound 7AWσN) established that a 1:1 complex was formed, with a dissociation constant lower than 2µM. The kinetics of the interaction between 7AWσN and core RNAP was investigated using stopped-flow spectrofluorimetry. A biphasic decrease in fluorescence intensity was observed when samples were excited at 280nm, whereas only the slower of the two phases was observed at 315nm. The kinetic data were analysed in terms of a mechanism in which a fast bimolecular association of σN with core RNAP is followed by a relatively slow isomerization step. The consequences of these findings on the competition between σN and the major sigma factor, σ70, in Escherichia coli are discussed.
Prosaposin: promoter analysis and central-nervous-system-preferential elements for expression in vivo
Authors: SUN Ying , JIN Peng , WITTE David P. , GRABOWSKI Gregory A.
Published: August 2015

The expression of prosaposin is temporally and spatially regulated at the transcriptional and post-translational levels. In vitro, the mouse prosaposin promoter contains functional RORE [retinoic acid-receptor-related orphan receptor α subunit (RORα)-binding element], Sp1 and U (unknown) sites within 310bp directly 5′ to the transcription start site and additional elements within 2400bp 5′ to the transcription start site. To elucidate promoter regions important to tissue-preferential expression in vivo, transgenic mice were created with 5′-flanking deletions of the prosaposin gene fused to a luciferase reporter. Nearly exclusive expression was observed in cerebrum, cerebellum and eyes of adult transgenic mice containing constructs with 234–310bp of 5ƀ-flanking DNA. This central nervous system (CNS) expression was due to the presence of RORE and overlapping Sp1 sites in this region. Internal deletion of RORE and the Sp1 cluster from the longer constructs with 2400bp of 5ƀ-flanking DNA significantly diminished expression in the CNS. The appearance of substantial visceral tissue (e.g. liver, spleen, lung, kidney, thymus and heart) expression was obtained with transgenic mice bearing constructs with 742–2400bp of 5ƀ-flanking DNA. The cellular localization of luciferase reporter-gene expression from these constructs corresponded closely with that for prosaposin. These results define important CNS and visceral regulatory regions in the promoter in vivo and may be sufficient to account for the majority of prosaposin's tissue-preferential expression.
Elevated levels of protein-bound p-hydroxyphenylacetaldehyde, an amino-acid-derived aldehyde generated by myeloperoxidase, are present in human fatty streaks, intermediate lesions and advanced atherosclerotic lesions
Authors: HAZEN Stanley L. , GAUT Joseph P. , CROWLEY Jan R. , HSU Fong F. , HEINECKE Jay W.
Published: August 2015

Reactive aldehydes might have a pivotal role in the pathogenesis of atherosclerosis by covalently modifying low-density lipoprotein (LDL). However, the identities of the aldehyde adducts that form on LDL in vivo are not yet clearly established. We previously demonstrated that the haem protein myeloperoxidase oxidizes proteins in the human artery wall. We also have shown that p-hydroxyphenylacetaldehyde (pHA), the aldehyde that forms when myeloperoxidase oxidizes L-tyrosine, covalently modifies the Nε-lysine residues of proteins. The resulting Schiff base can be quantified as Nε-[2-(p-hydroxyphenyl)ethyl]lysine (pHA-lysine) after reduction with NaCNBH3. Here we demonstrate that pHA-lysine is a marker for LDL that has been modified by myeloperoxidase, and that water-soluble, but not lipid-soluble, antioxidants inhibit the modification of LDL protein. To determine whether myeloperoxidase-generated aldehydes might modify LDL in vivo, we used a combination of isotope-dilution GC-MS to quantify pHA-lysine in aortic tissues at various stages of lesion evolution. We also analysed LDL isolated from atherosclerotic aortic tissue. Comparison of normal and atherosclerotic aortic tissue demonstrated a significant elevation (more than 10-fold) of the reduced Schiff base adduct in fatty streaks, intermediate lesions and advanced lesions compared with normal aortic tissue. Moreover, the level of pHA-lysine in LDL recovered from atherosclerotic aortic intima was 200-fold that in plasma LDL of healthy donors. These results indicate that pHA-lysine, a specific covalent modification of LDL, is generated in human atherosclerotic vascular tissue. They also raise the possibility that reactive aldehydes generated by myeloperoxidase have a role in converting LDL into an atherogenic lipoprotein.
Chloride channel activity of ClC-2 is modified by the actin cytoskeleton
Authors: AHMED Najma , RAMJEESINGH Mohabir , WONG Simeon , VARGA Alison , GARAMI Elizabeth , BEAR Christine E.
Published: August 2015

The chloride channel ClC-2has been implicated in essential physiological functions, including cell-volume regulation and fluid secretion by specific epithelial tissues. Although ClC-2 is known to be activated by hyperpolarization and hypo-osmotic shock, the molecular basis for the regulation of this channel remains unclear. Here we show in the Xenopus oocyte expression system that the chloride-channel activity of ClC-2 is enhanced after treatment with the actin-disrupting agents cytochalasin and latrunkulin. These findings suggest that the actin cytoskeleton normally exerts an inhibitory effect on ClC-2 activity. An inhibitory domain was previously defined in the N-terminus of ClC-2, so we sought to determine whether this domain might interact directly with actin in binding assays in vitro. We found that a glutathione S-transferase fusion protein containing the inhibitory domain was capable of binding actin in overlay and co-sedimentation assays. Further, the binding of actin to this relatively basic peptide (pI 8.4) might be mediated through electrostatic interactions because binding was inhibited at high concentrations of NaCl with a half-maximal decrease in signal at 180mM NaCl. This work suggests that electrostatic interactions between the N-terminus of ClC-2 and the actin cytoskeleton might have a role in the regulation of this channel.
Interaction between DNA-damage protein GADD34 and a new member of the Hsp40 family of heat shock proteins that is induced by a DNA-damaging reagent
Authors: HASEGAWA Tadao , XIAO Hengyi , HAMAJIMA Fumiyasu , ISOBE Ken-ichi
Published: August 2015

GADD34 is one of a subset of proteins induced after DNA damage or cell growth arrest. To examine the function of GADD34, we used the yeast two-hybrid system to clone the protein that interacts with murine GADD34. As bait we used the product of the partial GADD34 cDNA, including the regions rich in proline, glutamic acid, serine and threonine (PEST) and γ134.5 regions. A cDNA clone, named GAHSP40, which is a mouse DnaJ family protein with a high similarity to human HLJ1 was cloned. The interaction between GADD34 and GAHSP40 in cultured cells was confirmed by a co-immunoprecipitation experiment and in NIH 3T3 cells by two-hybrid analysis in vivo. For binding of the two proteins, the γ134.5-similar region of GADD34 was necessary; however, the PEST region was also involved and the C-terminus of GAHSP40, but not the J-domain, was important. GAHSP40 was detected in all mouse tissues examined, but a different transcript was found in the testis. Both GADD34 mRNA and GAHSP40 mRNA were significantly elevated by treatment with methyl methanesulphonate, although the time courses were different. In addition, both GAHSP40 and GADD34 mRNA were induced by heat shock.
A carbon-source-responsive element is required for regulation of the hypoxic ADP/ATP carrier (AAC3) isoform in Saccharomyces cerevisiae
Authors: SOKOLÍKOVÁ Barbora , ŠABOVÁ L'udmila , KIŠŠOVÁ Ingrid , KOLAROV Jordan
Published: August 2015

The mitochondrial ADP/ATP carrier in Saccharomyces cerevisiae is encoded by three genes that are differentially expressed under different physiological conditions. We investigated the transcriptional control of AAC3, an oxygen-repressed isoform. By deletion analysis, DNA electrophoretic mobility-shift assays, DNase I footprinting and site-directed mutagenesis, we have identified a promoter region (upstream repressing sequence 1, URS1) involved in a carbon-source-dependent repression of AAC3. It is different from the previously characterized oxygen-dependent ROX1 (regulation by oxygen 1) repressor-binding region (URS2). The complex character of URS1 includes the presence of two different cis-acting sequences: (i) a RAP1 (repressor activator protein 1)-binding site that is capable of binding the RAP1 protein in vitro and (ii) two putative ethanol-repression sequences, the modification of which derepresses the AAC3 gene. These findings demonstrate that the hypoxic AAC3 gene is regulated by two upstream repressor sites; one controlled by oxygen and haem, the other by the carbon source. Both sites function to completely switch off the expression of the AAC3 isoform when ATP is made by oxidative phosphorylation, and they modulate AAC3 expression when import of glycolytic ATP into mitochondria is required.
Identification of a novel isoform of the cyclic-nucleotide phosphodiesterase PDE3A expressed in vascular smooth-muscle myocytes
Authors: CHOI Young-Hun , EKHOLM Dag , KRALL Judith , AHMAD Faiyaz , DEGERMAN Eva , MANGANIELLO Vincent C. , MOVSESIAN Matthew A.
Published: August 2015

We have identified a new cyclic-nucleotide phosphodiesterase isoform, PDE3A, and cloned its cDNA from cultured aortic myocytes. The nucleotide sequence of its coding region is similar to that of the previously cloned myocardial isoform except for the absence of the initial 300–400nt that are present in the latter, as confirmed by reverse-transcriptase-mediated PCR, 5′ rapid amplification of cDNA ends and a ribonuclease protection assay. Expression in Spodoptera frugiperda (Sf9) cells yields a protein with catalytic activity and inhibitor sensitivity typical of the PDE3 family. The recombinant protein's molecular mass of approx. 131kDa is compatible with translation from an ATG sequence corresponding to nt 436–438 of the myocardial PDE3A coding region. Antibodies against residues 424–460 (nt 1270–1380) and 1125–1141 (nt 3373–3423) of the myocardial isoform react with an approx. 118kDa band in Western blots of homogenates of human aortic myocytes, whereas antibodies against residues 29–42 (nt 85–126) do not react with any bands in these homogenates. Our results suggest that a vascular smooth-muscle isoform (‘PDE3A2’) is a product of the same gene as the longer myocardial (‘PDE3A1’) and the shorter placental (‘PDE3A3’) isoforms and is generated pre-translationally in a manner that results in the absence of the 145 N-terminal amino acids of PDE3A1.
Evidence for the presence of phospholipid hydroperoxide glutathione peroxidase in human platelets: implications for its involvement in the regulatory network of the 12-lipoxygenase pathway of arachidonic acid metabolism
Authors: SUTHERLAND Mark , SHANKARANARAYANAN Pattabhiraman , SCHEWE Tankred , NIGAM Santosh
Published: August 2015

The 12-lipoxygenase pathway of arachidonic acid metabolism in platelets and other cells is bifurcated into a reduction route yielding 12-hydroxyeicosatetraenoic acid (12-HETE) and an isomerization route forming hepoxilins. Here we show for the first time the presence of phospholipid hydroperoxide glutathione peroxidase (PHGPx) protein and its activity in platelets. The ratio of the activity of PHGPx to that of cytosolic glutathione peroxidase (GPx-1) was consistently found to be approx. 1:60 in platelets and UT7 megakaryoblasts. Moreover, short-lived PHGPx mRNA was detected in megakaryocytes but not in platelets. Carboxymethylation of selenium-containing glutathione peroxidases by iodoacetate, which results in the inactivation of PHGPx and GPx-1 without inhibition of 12-lipoxygenase, markedly altered the pattern of arachidonic acid metabolism in human platelets. Whereas the formation of 12-HETE was inhibited by 80%, a concomitant accumulation of 12-hydroperoxyeicosatetraenoic acid (12-HpETE) by two orders of magnitude as well as the formation of hepoxilins A3 and B3 were observed. The formation of hepoxilins also occurred when 12-HpETE was added to untreated platelets. In selenium-deficient UT7 cells, which were devoid of GPx-1 but not of PHGPx, the reduction of 12-HPETE was retained, albeit with a lower rate than in control cells containing GPx-1. We therefore believe that both GPx-1 and PHGPx are involved in the regulatory network of the 12-lipoxygenase pathway in platelets and other mammalian cells. Moreover, the diminution of hydroperoxide tone in platelets incubated with arachidonic acid leads primarily to the formation of 12-HETE, whereas the increase in hydroperoxide tone (a situation found under oxidative stress or selenium deficiency or on incubation with 12-HPETE) partly diverts the 12-lipoxygenase pathway from the reduction route to the isomerization route, thus resulting in the formation of hepoxilins.
Interleukin 9 induces expression of three cytokine signal inhibitors: cytokine-inducible SH2-containing protein, suppressor of cytokine signalling (SOCS)-2 and SOCS-3, but only SOCS-3 overexpression suppresses interleukin 9 signalling
Authors: LEJEUNE Diane , DEMOULIN Jean-Baptiste , RENAULD Jean-Christophe
Published: August 2015

Interleukin 9 (IL-9) is a cytokine preferentially produced by T helper type 2 lymphocytes and active on various cell types such as T- and B-lymphocytes, mast cells and haemopoietic progenitors. The IL-9 receptor (IL-9R) belongs to the haemopoietic receptor superfamily and its signal transduction involves mainly the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway. Here we studied the implication of a novel family of suppressors of cytokine signalling (called CIS, for cytokine-inducible SH2-containing protein, and SOCS, for suppressor of cytokine signalling) in IL-9 signal attenuation. In BW5147 T-cell lymphoma, IL-9 induced the rapid expression of CIS, SOCS-2 and SOCS-3 with a peak after 2h of stimulation. Using IL-9R mutants, we showed that STAT activation is required for CIS/SOCS induction: CIS and SOCS-2 expression was induced either via STAT1 and/or STAT3 or via STAT5 but only STAT1 and/or STAT3 were involved in SOCS-3 expression. The effect of these three proteins on IL-9 signal transduction was assessed by transient transfection in HEK-293 cells expressing the components of the IL-9 signalling pathway and a STAT-responsive reporter construct. These experiments showed that only SOCS-3 is able to inhibit IL-9-induced signal transduction; neither CIS nor SOCS-2 exerted any effect. Stable transfection of CIS and SOCS-3 in BW5147 lymphoma cells showed that only overexpression of SOCS-3 had an inhibitory activity on STAT activation, gene induction and the anti-apoptotic activity of IL-9. By contrast, CIS failed to affect the IL-9 response.
Diacylglycerol kinase θ is translocated and phosphoinositide 3-kinase-dependently activated by noradrenaline but not angiotensin II in intact small arteries
Authors: WALKER Anthony J. , DRAEGER Annette , HOUSSA Brahim , VAN BLITTERSWIJK Wim J. , OHANIAN Vasken , OHANIAN Jacqueline
Published: August 2015

Diacylglycerol (DG) kinase (DGK) phosphorylates the lipid second messenger DG to phosphatidic acid. We reported previously that noradrenaline (NA), but not angiotensin II (AII), increases membrane-associated DGK activity in rat small arteries [Ohanian and Heagerty (1994) Biochem. J. 300, 51–56]. Here, we have identified this DGK activity as DGKθ, present in both smooth muscle and endothelial cells of these small vessels. Subcellular fractionation of artery homogenates revealed that DGKθ was present in nuclear, plasma membrane (and/or Golgi) and cytosolic fractions. Upon NA stimulation, DGKθ translocated towards the membrane and cytosol (155 and 153% increases relative to the control, respectively) at 30s, followed by a return to near-basal levels at 5min; AII was without effect. Translocation to the membrane was to both Triton-soluble and -insoluble fractions. NA, but not AII, transiently increased DGKθ activity in immunoprecipitates (126% at 60s). Membrane translocation and DGKθ activation were regulated differently: NA-induced DGKθ activation, but not translocation, was dependent on transient activation of phosphoinositide 3-kinase (PI 3-K). In addition, DGK activity co-immunoprecipitated with protein kinase B, a downstream effector of PI 3-K, and was increased greatly by NA stimulation. The rapid and agonist-specific activation of DGKθ suggests that this pathway may have a physiological role in vascular smooth-muscle responses.
Activation of blood coagulation factor IX by gingipains R, arginine-specific cysteine proteinases from Porphyromonas gingivalis
Authors: IMAMURA Takahisa , TANASE Sumio , HAMAMOTO Takayoshi , POTEMPA Jan , TRAVIS James
Published: August 2015

The effect of two arginine-specific cysteine proteinases (gingipains R) from Porphyromonas gingivalis, an aetiological factor of adult periodontitis, on the activation of human factor IX was investigated in the presence of ethylene glycol, an activity enhancer of activated factor IX (factor IXa), with the use of a fluorogenic oligopeptide substrate. Each gingipain R rapidly activated factor IX but the 95kDa proteinase complex (HRgpA) that contains both haemagglutinin/adhesion and catalytic domains was 2.4-fold more efficient than the single-chain 50kDa gingipain R (RgpB), which has only a catalytic domain. SDS/PAGE and N-terminal sequence analysis of factor IX digestion fragments indicated that, like all endogenous activators, gingipains R also produce factor IXaβ via an IXa intermediate. Significantly, phospholipids augmented the activation of factor IX by HRgpA but not by RgpB in a Ca2+-dependent manner. In the presence of both cofactors the kinetic efficiency of HRgpA to activate factor IX (kcat/Km = 1.9×106 M-1·s-1) was 8.5-fold higher than that of RgpB (kcat/Km = 2.3×105 M-1·s-1) and double that of the factor VIIaŐtissue factor complex, but 8-fold lower than that for factor XIa. A comparison of the relative activation rates of factor IX, factor X and prothrombin directly in plasma by HRgpA suggests a significant contribution for factor IX conversion in blood coagulation induced by gingipains R. Taken together, gingipains R are the first-reported activators of factor IX of bacterial origin. By this effect they could be involved in the production of thrombin as well as the subsequent generation of prostaglandins and interleukin 1, all of which have been found to be associated with the development and progression of periodontitis.
Identification of Cys140 in helix 4 as an exofacial cysteine residue within the substrate-translocation channel of rat equilibrative nitrobenzylthioinosine (NBMPR)-insensitive nucleoside transporter rENT2
Authors: YAO Sylvia Y. M. , SUNDARAM Manickavasagam , CHOMEY Eugene G. , CASS Carol E. , BALDWIN Stephen A. , YOUNG James D.
Published: August 2015

The human and rat equilibrative nucleoside transporter proteins hENT1, rENT1, hENT2 and rENT2 belong to a family of integral membrane proteins with 11 potential transmembrane segments (TMs), and are distinguished functionally by differences in transport of nucleobases and sensitivity to inhibition by nitrobenzylthioinosine (NBMPR) and vasoactive drugs. In the present study, we have produced recombinant hENT1, rENT1, hENT2 and rENT2 in Xenopus oocytes and investigated uridine transport following exposure to the impermeant thiol-reactive reagent p-chloromercuriphenyl sulphonate (PCMBS). PCMBS caused reversible inhibition of uridine influx by rENT2, but had no effect on hENT1, hENT2 or rENT1. This difference correlated with the presence in rENT2 of a unique Cys residue (Cys140) in the outer half of TM4 that was absent from the other ENTs. Mutation of Cys140 to Ser produced a functional protein (rENT2/C140S) that was insensitive to inhibition by PCMBS, identifying Cys140 as the exofacial Cys residue in rENT2 responsible for PCMBS inhibition. Uridine protected wild-type rENT2 against PCMBS inhibition, suggesting that Cys140 in TM4 lies within or is closely adjacent to the substrate-translocation channel of the transporter. TM4has been shown previously to be within a structural domain (TMs 3Ő6) responsible for interactions with NBMPR, vasoactive drugs and nucleobases.
Characterization of the mouse metal-regulatory-element-binding proteins, metal element protein-1 and metal regulatory transcription factor-1
Authors: LAROCHELLE Olivier , STEWART Gale , MOFFATT Pierre , TREMBLAY Véronique , SÉGUIN Carl
Published: August 2015

Metal activation of metallothionein gene transcription depends mainly on the presence of regulatory DNA sequences termed metal-regulatory elements (MREs) and involves MRE-binding transcription factor-1 (MTF-1) interacting with the MREs in a Zn2+-dependent manner. We previously identified and characterized a nuclear protein, termed metal element protein-1 (MEP-1), specifically binding with high affinity to MRE elements. The precise relationship between MTF-1 and MEP-1 was unclear, and to determine whether MEP-1 and MTF-1 were distinct protein species, we performed DNA binding analyses to characterize the binding properties of both proteins. Electrophoretic mobility-shift assays showed that MTF-1, produced in COS cells, produces a slower-migrating band compared with that obtained with purified MEP-1. Using an anti-MTF-1 antibody, we showed that both the MTF-1–MRE and the MEP-1–MRE complexes are supershifted by an anti-MTF-1 antibody, thus demonstrating that MEP-1 is antigenically related to MTF-1. RNase protection analyses carried out with RNA prepared from different tissues and cell lines failed to reveal the presence of MTF-1 splicing variants. This indicates that MEP-1 may be a proteolytic fragment of MTF-1. MTF-1 DNA-binding activity was rapidly activated in vivo by Zn2+ ions but not by Cd2+, UV irradiation or PMA, and occurred on ice as well as at 21°C. In control and Zn2+-treated cell extracts, DNA-binding activity was not enhanced in vitro following the addition of exogenous Zn2+ or a preincubation at 37°C. However, recombinant MTF-1 produced in vitro required Zn2+ activation for DNA binding. Interestingly, treatment of nuclear extracts with calf intestine phosphatase completely abrogated MTF-1 DNA-binding activity, thus suggesting that phosphorylation is involved in the regulation of MTF-1 activity.
5-Hydroxytryptamine 4(a) receptor expressed in Sf9 cells is palmitoylated in an agonist-dependent manner
Authors: PONIMASKIN Evgeni G. , SCHMIDT Michael F. G. , HEINE Martin , BICKMEYER Ulf , RICHTER Diethelm W.
Published: August 2015

The mouse 5-hydroxytryptamine 4(a) receptor [5-HT4(a)] was expressed with a baculovirus system in insect cells and analysed for acylation. [3H]Palmitic acid was effectively incorporated into 5-HT4(a) and label was sensitive to the treatment with reducing agents indicating a thioester-type bond. Analysis of protein-bound fatty acids revealed that 5-HT4(a) contains predominantly palmitic acid. Treatment of infected Sf9 (Spodoptera frugiperda) cells with BIMU8 {(endo-N-8-methyl-8-azabicyclo[3.2.1]oct-3-yl)-2,3-dehydro-2-oxo-3-(prop-2-yl)-1H-benzimid-azole-1-carboxamide}, a 5-HT4 receptor-selective agonist, generated a dose-dependent increase in [3H]palmitate incorporation into 5-HT4(a) with an EC50 of approx. 10nM. The change in receptor labelling after stimulation with agonist was receptor-specific and did not result from general metabolic effects. We also used both pulse labelling and pulse–chase labelling to address the dynamics of 5-HT4(a) palmitoylation. Incorporation studies revealed that the rate of palmitate incorporation was increased approx. 3-fold after stimulation with agonist. Results of pulse–chase experiments show that activation with BIMU8 promoted the release of radiolabel from 5-HT4(a), thereby reducing the levels of receptor-bound palmitate to approximately one-half. Taken together, our results demonstrate that palmitoylation of 5-HT4(a) is a reversible process and that stimulation of 5-HT4(a) with agonist increases the turnover rate for receptor-bound palmitate. This provides evidence for a regulated cycling of receptor-bound palmitate and suggests a functional role for palmitoylation/depalmitoylation in 5-hydroxytryptamine-mediated signalling.
Identification of synapsin I peptides that insert into lipid membranes
Authors: CHEETHAM James J. , HILFIKER Sabine , BENFENATI Fabio , WEBER Thomas , GREENGARD Paul , CZERNIK Andrew J.
Published: August 2015

The synapsins constitute a family of synaptic vesicle-associated phosphoproteins essential for regulating neurotransmitter release and synaptogenesis. The molecular mechanisms underlying the selective targeting of synapsin I to synaptic vesicles are thought to involve specific protein–protein interactions, while the high-affinity binding to the synaptic vesicle membrane may involve both protein–protein and protein–lipid interactions. The highly hydrophobic N-terminal region of the protein has been shown to bind with high affinity to the acidic phospholipids phosphatidylserine and phosphatidylinositol and to penetrate the hydrophobic core of the lipid bilayer. To precisely identify the domains of synapsin I which mediate the interaction with lipids, synapsin I was bound to liposomes containing the membrane-directed carbene-generating reagent 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine and subjected to photolysis. Isolation and N-terminal amino acid sequencing of 125I-labelled synapsin I peptides derived from CNBr cleavage indicated that three distinct regions in the highly conserved domain C of synapsin I insert into the hydrophobic core of the phospholipid bilayer. The boundaries of the regions encompass residues 166–192, 233–258 and 278–327 of bovine synapsin I. These regions are surface-exposed in the crystal structure of domain C of bovine synapsin I and are evolutionarily conserved among isoforms across species. The present data offer a molecular explanation for the high-affinity binding of synapsin I to phospholipid bilayers and synaptic vesicles.
Combined strong anion-exchange HPLC and PAGE approach for the purification of heparan sulphate oligosaccharides
Authors: VIVÈS Romain R. , GOODGER Sarah , PYE David A.
Published: August 2015

Heparan sulphates are highly sulphated linear polysaccharides involved in many cellular functions. Their biological properties stem from their ability to interact with a wide range of proteins. An increasing number of studies, using heparan sulphate-derived oligosaccharides, suggest that specific structural features within the polysaccharide are responsible for ligand recognition and regulation. In the present study, we show that strong anion-exchange HPLC alone, a commonly used technique for purification of heparan sulphate-derived oligosaccharides, may not permit the isolation of highly pure heparan sulphate oligosaccharide species. This was determined by PAGE analysis of hexa-, octa- and decasaccharide samples deemed to be pure by strong anion-exchange HPLC. In addition, subtle differences in the positioning of sulphate groups within heparan sulphate hexasaccharides were impossible to detect by strong anion-exchange HPLC. PAGE analysis on the other hand afforded excellent resolution of these structural isomers. The precise positioning of specific sulphate groups has been implicated in determining the specificity of heparan sulphate interactions and biological activities; hence, the purification of oligosaccharide species that differ in this way becomes an important issue. In this study, we have used strong anion-exchange HPLC and PAGE techniques to allow production of the homogeneous heparan sulphate oligosaccharide species that will be required for the detailed study of structure/activity relationships.
Long-chain fatty acids regulate liver carnitine palmitoyltransferase I gene (L-CPT I) expression through a peroxisome-proliferator-activated receptor α (PPARα)-independent pathway
Authors: LOUET Jean-Francç;ois , CHATELAIN Florence , DECAUX Jean-Francç;ois , PARK Edwards A. , KOHL Claude , PINEAU Thierry , GIRARD Jean , PEGORIER Jean-Paul
Published: August 2015

Liver carnitine palmitoyltransferase I (L-CPT I) catalyses the transfer of long-chain fatty acid (LCFA) for translocation across the mitochondrial membrane. Expression of the L-CPT I gene is induced by LCFAs as well as by lipid-lowering compounds such as clofibrate. Previous studies have suggested that the peroxisome-proliferator-activated receptor α (PPARα) is a common mediator of the transcriptional effects of LCFA and clofibrate. We found that free LCFAs rather than acyl-CoA esters are the signal metabolites responsible for the stimulation of L-CPT I gene expression. Using primary culture of hepatocytes we found that LCFAs failed to stimulate L-CPT I gene expression both in wild-type and PPARα-null mice. These results suggest that the PPARα-knockout mouse does not represent a suitable model for the regulation of L-CPT I gene expression by LCFAs in the liver. Finally, we determined that clofibrate stimulates L-CPT I through a classical direct repeat 1 (DR1) motif in the promoter of the L-CPT I gene while LCFAs induce L-CPT I via elements in the first intron of the gene. Our results demonstrate that LCFAs can regulate gene expression through PPARα-independent pathways and suggest that the regulation of gene expression by dietary lipids is more complex than previously proposed.
Src homology 3 domain-dependent interaction of Nck-2 with insulin receptor substrate-1
Authors: TU Yizeng , LIANG Liang , FRANK Stuart J. , WU Chuanyue
Published: August 2015

Insulin receptor substrate-1 (IRS-1) is a multi-domain protein that mediates signal transduction from receptors for insulin and other growth factors to a variety of downstream molecules through both tyrosine-phosphorylation-dependent and -independent interactions. While the tyrosine-phosphorylation-dependent interactions mediated by IRS-1 have been well characterized, the molecular basis underlying the tyrosine-phosphorylation-independent IRS-1 interactions is largely unknown. We previously detected, in an in vitro binding assay, interactions of Nck-2 Src homology (SH) 3 domains with IRS-1. We show here that IRS-1 associates with Nck-2 in vivo. Additionally, we have investigated the molecular basis underlying the IRS-1–Nck-2 complex formation. We have found that (i) mutations at the highly conserved tryptophan within the Nck-2 SH3 domains markedly reduced the association with IRS-1, (ii) interactions mediated by multiple SH3 domains enhance the complex formation of Nck-2 with IRS-1, (iii) deletion of either the phosphotyrosine-binding/Shc and IRS-1 NPXY-binding (PTB/SAIN) domains or the Pre-C-terminal domain of IRS-1, but not the pleckstrin homology (PH) domain, reduced the Nck-2 binding, (iv) PTB/SAIN domains or the Pre-C-terminal domain alone is capable of interacting with Nck-2, and (v) the IRS-1–Nck-2 interaction occurs in the absence of other proteins and therefore is direct. These results establish that IRS-1 is a bona fide target of the Nck-2 SH3 domains and reveal that IRS-1 forms a complex with Nck-2 via direct interactions mediated by multiple domains from both binding partners.
Ceramide dissociates 3′-phosphoinositide production from pleckstrin homology domain translocation
Authors: STRATFORD Suzanne , DEWALD Daryll B. , SUMMERS Scott A.
Published: August 2015

Numerous hormones, cytokines and transforming oncogenes activate phosphoinositide 3-kinase (PI-3K), a lipid kinase that initiates signal transduction cascades regulating cellular proliferation, survival, protein synthesis and glucose metabolism. PI-3K catalyses the production of the 3′-phosphoinositides PtdIns(3,4)P2 and PtdIns(3,4,5)P3, which recruit downstream effector enzymes to the membrane via their pleckstrin homology (PH) domains. Recent studies have indicated that another signalling lipid, the sphingolipid ceramide, inhibits several PI-3K-dependent events, including insulin-stimulated glucose uptake and growth-factor-stimulated cell survival. Here we show that ceramide analogues specifically prevent the recruitment of the PtdIns(3,4,5)P3-binding proteins Akt/protein kinase B (PKB) or the general receptor for phosphoinositides-1 (GRP1). Specifically, the short-chain ceramide derivative C2-ceramide inhibited the platelet-derived growth factor (PDGF)-stimulated translocation of full-length Akt/PKB, as well as truncated proteins encoding only the PH domains of Akt/PKB or GRP1. C2-ceramide did not alter the membrane localization of the PH domain for phospholipase Cδ, which preferentially binds PtdIns(4,5)P2, nor did it affect the PDGF-stimulated production of PtdIns(3,4)P2 or PtdIns(3,4,5)P3. Interestingly, a glucosylceramide synthase inhibitor, 1-phenyl-2-decanoylamino-3-morpholinopropan-1-ol (PDMP), shown previously to increase intracellular ceramide concentrations without affecting PI-3K [Rani, Abe, Chang, Rosenzweig, Saltiel, Radin and Shayman (1995) J. Biol. Chem. 270, 2859–2867], recapitulated the inhibitory effects of C2-ceramide on PDGF-stimulated Akt/PKB phosphorylation. These studies indicate that ceramide prevents the translocation of certain PtdIns(3,4,5)P3-binding proteins, despite the presence of a full complement of PtdIns(3,4)P2 or PtdIns(3,4,5)P3. Furthermore, these findings suggest a mechanism by which stimuli that induce ceramide synthesis could negate the fundamental signalling pathways initiated by PI-3K.
Aggregation-independent modulation of proteoglycan binding by neutralization of C-terminal acidic residues in the chemokine macrophage inflammatory protein 1α
Authors: OTTERSBACH Katrin , GRAHAM Gerard J.
Published: August 2015

Members of the chemokine family of proteins mediate their biological effects through interaction with a family of seven-transmembrane G-protein-coupled receptors. This interaction is complicated by the biochemical properties of chemokines, such as their ability to form self aggregates and their ability to bind to proteoglycans. With some chemokines there is a clear interrelationship between these interactions; the chemokine platelet factor 4 binds preferentially to proteoglycans in its aggregated form. Little is known about the role of aggregation in the proteoglycan binding of other chemokines. Here we demonstrate that the aggregation status of the chemokine macrophage inflammatory protein 1α (MIP-1α) has no detectable effect on its affinity for proteoglycans. Furthermore, we demonstrate that the alteration of acidic amino acid residues in MIP-1α influences the affinity of its interactions with heparin as these residues are progressively neutralized, leading to an enhanced binding affinity for heparin. Thus, with MIP-1α, aggregation is not a determinant of proteoglycan binding; however, overall charge does seem to have a major role in the interaction. These results therefore add to our understanding of the nature of the interaction between MIP-1α and proteoglycans and suggests that the basic amino acids might not be the sole regulators of proteoglycan binding.
Active-site characterization of Candida boidinii formate dehydrogenase
Authors: LABROU Nikolaos E. , RIGDEN Daniel J.
Published: August 2015

NAD+-dependent formate dehydrogenase (FDH) from Candida boidinii was cloned and expressed to a high level in Escherichia coli (20% of soluble E. coli protein). Molecular modelling studies were used to create a three-dimensional model of C. boidinii FDH, based on a known structure of the Pseudomonas sp. 101 enzyme. This model was used for investigating the catalytic mechanism by site-directed mutagenesis. Eleven forms of C. boidinii FDH were characterized by steady-state kinetic analysis: the wild type as well as 10 mutants involving single (Phe-69–Ala, Asn-119–His, Ile-175–Ala, Gln-197–Leu, Arg-258–Ala, Gln-287–Glu and His-311–Gln) and double amino acid substitutions (Asn-119–His/His-311–Gln, Gln-287–Glu/His-311–Gln and Gln-287–Glu/Pro-288–Thr). The kinetic results of the mutant enzymes provide the first experimental support that hydrophobic patches, formed by Phe-69 and Ile-175, destabilize substrates and stabilize products. Also, the key role of Arg-258 in stabilization of the negative charge on the migrating hydride was established. Asn-119, besides being an anchor group for formate, also may comprise one of the hinge regions around which the two domains shift on binding of NAD+. The more unexpected results, obtained for the His-311–Gln and Gln-287–Glu/His-311–Gln mutants, combined with molecular modelling, suggest that steric as well as electrostatic properties of His-311 are important for enzyme function. An important structural role has also been attributed to cis-Pro-288. This residue may provide the key residues Gln-287 and His-311 with the proper orientation for productive binding of formate.

The FDH nucleotide sequence has been submitted to the EMBL Nucleotide Sequence Database under the accession no. AJ011046.