bluuebunny/crossref_metadata_2025 huggingface dataset:
Cytological evidence that the C-terminus of carnitine palmitoyltransferase I is on the cytosolic face of the mitochondrial outer membrane
Authors: LEIJ Feike R. VAN DER , KRAM Anita M. , BARTELDS Beatrijs , ROELOFSEN Han , SMID Gioia B. , TAKENS Janny , ZAMMIT Victor A. , KUIPERS Jaap R. G.
Published: August 2015

Carnitine palmitoyltransferase I (CPT I) is a key enzyme in the regulation of β-oxidation. The topology of this enzyme has been difficult to elucidate by biochemical methods. We studied the topology of a fusion protein of muscle-type CPT I (M-CPT I) and green fluorescent protein (GFP) by microscopical means. To validate the use of the fusion protein, designated CPT I-GFP, we checked whether the main characteristics of native CPT I were retained. CPT I-GFP was expressed in HeLa cells after stable transfection. Confocal laser scanning microscopy in living cells revealed an extranuclear punctate distribution of CPT I-GFP, which coincided with a mitochondrial fluorescent marker. Immunogold electron microscopy localized CPT I-GFP almost exclusively to the mitochondrial periphery and showed that the C-terminus of CPT I must be on the cytosolic face of the mitochondrial outer membrane. Western analysis showed a protein that was 6 kDa smaller than predicted, which is consistent with previous results for the native M-CPT I. Mitochondria from CPT I-GFP-expressing cells showed an increased CPT activity that was inhibited by malonyl-CoA and was lost on solubilization with Triton X-100. We conclude that CPT I-GFP adopts the same topology as native CPT I and that its C-terminus is located on the cytosolic face of the mitochondrial outer membrane. The evidence supports a recently proposed model for the domain structure of CPT I based on biochemical evidence.
Co-expression of metabotropic glutamate receptor type 1α with Homer-1a/Vesl-1S increases the cell surface expression of the receptor
Authors: CIRUELA Francisco , SOLOVIEV Mikhail M. , Jeffrey McILHINNEY R. A.
Published: August 2015

Homer-1a is a 30 kDa protein that forms part of a family of conserved Homer-related proteins that interact with the C-termini of the metabotropic glutamate receptors mGluR1α and mGluR5a. Analysis of HEK-293 cells by PCR showed that they contained mRNA coding for members of the Homer family with the predominant form being Homer-1b, which is consistent with the immunochemical analysis of these cells. Homer-1a could not be detected by immunochemical analysis. To examine the function of Homer-1a, HEK-293 cells were transfected with cDNA encoding mGluR1α or Homer-1a or co-transfected with both cDNAs. When cells were co-transfected with the cDNAs for both proteins, immunofluorescent staining and biotinylation of cell surface molecules revealed a significant increase in the amount of receptor present at the cell surface in contrast to cells transfected with mGluR1α cDNA alone. This finding was consistent with a concomitant increase in the production of inositol phosphates after treatment of the doubly transfected cells with agonist. Intracellular immunostaining for both proteins revealed that they were co-localized and underwent a redistribution into a large vesicular compartment when they were co-expressed.
Characterization of homogeneous recombinant rat ovarian 20α-hydroxysteroid dehydrogenase: fluorescent properties and inhibition profile
Authors: MA Haiching , PENNING Trevor M.
Published: August 2015

In rat ovary, 20α-hydroxysteroid dehydrogenase (20α-HSD), a member of the aldo-keto reductase (AKR) superfamily, converts progesterone into the inactive progestin 20α-hydroxyprogesterone and has been implicated in the termination of pregnancy. Here we report a convenient overexpression system that permits the purification of milligram quantities of homogeneous recombinant 20α-HSD with wild-type enzyme activity. The availability of this enzyme has permitted detailed kinetic, inhibition and fluorescence analyses. The enzyme exhibited narrow steroid specificity, catalysing reactions only at C-20; it reduced progesterone and 17α-hydroxyprogesterone and oxidized 20α-hydroxypregnanes. It also turned over common AKR substrates, such as 9,10-phenanthrenequinone and 4-nitrobenzaldehyde. The intrinsic fluorescence spectrum of 20α-HSD was characterized and was quenched on the binding of NADP(H), yielding a KdNADP of 0.36 μM and a KdNADP of 0.64 μM. NADP(H) binding generated an energy transfer band that could not be quenched by steroids. Inhibition studies conducted with non-steroidal and steroidal anti-inflammatory drugs and synthetic oestrogens indicated that even though rat ovarian 20α-HSD and rat liver 3α-hydroxysteroid dehydrogenase (3α-HSD) share more than 67% amino acid identity, their inhibition profiles are markedly different. Unlike 3α-HSD, most of these compounds did not inhibit 20α-HSD. Only meclofenamic acid and hexoestrol were potent competitive inhibitors for 20α-HSD, yielding Ki values of 18.9 and 14.3 μM respectively. These studies suggest that selective non-steroidal AKR inhibitors could be developed for 20α-HSD that might be useful in maintaining pregnancy and that specific inhibitors might be developed from either N-phenylanthranilates or biphenols.
Efflux of hepatic ascorbate: a potential contributor to the maintenance of plasma vitamin C
Authors: UPSTON Joanne M. , KARJALAINEN Ari , BYGRAVE Fyfe L. , STOCKER Roland
Published: August 2015

Ascorbate (AH, the reduced form of vitamin C) is an important radical scavenger and antioxidant in human plasma; the resulting ascorbyl radical can disproportionate to AH and dehydroascorbic acid (DHA). Here we address potential maintenance mechanism(s) for extracellular AH by examining the ability of cells to convert extracellularly presented DHA to AH. DHA was rapidly transported into human liver (HepG2), endothelial and whole blood cells invitro by plasma membrane glucose transporters and reduced intracellularly. Liver cells displayed the highest capacity to release the intracellularly accumulated AH. The proteins responsible for DHA uptake and AH release could be distinguished by inhibitor studies. Thus, unlike DHA uptake, AH efflux was largely insensitive to cytochalasin B and thiol-reactive agents but was inhibited by phloretin, 4,4′-di-isothiocyanostilbene-2,2′-disulphonate and isoascorbate. Efflux of AH from cells was temperature-sensitive and saturable with a low affinity (millimolar, intracellular) for AH. In addition to isolated liver cells, perfusion of intact rat and guinea-pig liver with DHA resulted in AH in the circulating perfusate. Our results show that hepatocytes take up and reduce DHA and subsequently release part of the AH formed, probably via a membrane transporter. By converting extracellular DHA to extracellular AH, the liver might contribute to the maintenance of plasma AH, a process that could be important under conditions of oxidative stress.
Solution structure and dynamics of the A-T tract DNA decamer duplex d(GGTAATTACC)2: implications for recognition by minor groove binding drugs
Authors: BOSTOCK-SMITH Clare E. , LAUGHTON Charles A. , SEARLE Mark S.
Published: August 2015

The structure of the DNA decamer duplex d(GGTAATTACC)2 has been determined using NMR distance restraints and molecular dynamics simulations of 500 ps to 1 ns in aqueous solution at 300 K. Using both canonical A and canonical B starting structures [root-mean-square deviation (RMSD) 4.6 Å; 1 Å = 10-10 m], with and without experimental restraints, we show that all four simulations converge to a similar envelope of final conformations with B-like helical parameters (pairwise RMSD 1.27-2.03 Å between time-averaged structures). While the two restrained simulations reach a stable trajectory after 300-400 ps, the unrestrained trajectories take longer to equilibrate. We have analysed the dynamic aspects of these structures (sugar pucker, helical twist, roll, propeller twist and groove width) and show that the minor groove width in the AATT core of the duplex fluctuates significantly, sampling both wide and narrow conformations. The structure does not have the highly pre-organized narrow minor groove generally regarded as essential for recognition and binding by small molecules, suggesting that ligand binding carries with it a significant component of ‘induced-fit’. Our simulations show that there are significant differences in structure between the TpA step (where p = phosphate) and the ApA and ApT steps, where a large roll into the major groove at the TpA step appears to be an important factor in widening the minor groove at this position.
Poly(ADP-ribosyl)ation reactions in the regulation of nuclear functions
Authors: d'AMOURS Damien , DESNOYERS Serge , d'SILVA Icy , POIRIER Guy G.
Published: August 2015

Poly(ADP-ribosyl)ation is a post-translational modification of proteins. During this process, molecules of ADP-ribose are added successively on to acceptor proteins to form branched polymers. This modification is transient but very extensive in vivo, as polymer chains can reach more than 200 units on protein acceptors. The existence of the poly(ADP-ribose) polymer was first reported nearly 40 years ago. Since then, the importance of poly(ADP-ribose) synthesis has been established in many cellular processes. However, a clear and unified picture of the physiological role of poly(ADP-ribosyl)ation still remains to be established. The total dependence of poly(ADP-ribose) synthesis on DNA strand breaks strongly suggests that this post-translational modification is involved in the metabolism of nucleic acids. This view is also supported by the identification of direct protein-protein interactions involving poly(ADP-ribose) polymerase (113 kDa PARP), an enzyme catalysing the formation of poly(ADP-ribose), and key effectors of DNA repair, replication and transcription reactions. The presence of PARP in these multiprotein complexes, in addition to the actual poly(ADP-ribosyl)ation of some components of these complexes, clearly supports an important role for poly(ADP-ribosyl)ation reactions in DNA transactions. Accordingly, inhibition of poly(ADP-ribose) synthesis by any of several approaches and the analysis of PARP-deficient cells has revealed that the absence of poly(ADP-ribosyl)ation strongly affects DNA metabolism, most notably DNA repair. The recent identification of new poly(ADP-ribosyl)ating enzymes with distinct (non-standard) structures in eukaryotes and archaea has revealed a novel level of complexity in the regulation of poly(ADP-ribose) metabolism.
Protective role for proteoglycans against cationic lipid cytotoxicity allowing optimal transfection efficiency in vitro
Authors: BELTING Mattias , PETERSSON Per
Published: August 2015

A dependence on proteoglycans for cationic lipid-mediated gene transfer has been suggested in previous studies [Mislick and Baldeschwieler (1996) Proc. Natl. Acad. Sci. U.S.A. 93, 12349-12354; Mounkes, Zhong, Cipres-Palacin, Heath and Debs (1998) J. Biol. Chem. 273, 26164-26170]. We have evaluated the mechanism of proteoglycan involvement in cationic lipid-mediated gene transfer. DNA plasmid uptake and gene expression were studied in wild-type Chinese hamster ovary (CHO) cells (CHO-K1), heparan sulphate-deficient CHO cells (pgsD-677) and proteoglycan-deficient CHO cells (pgsB-618). At an optimal ratio of cationic lipid to DNA, a substantial decrease in reporter gene expression was observed in proteoglycan-deficient cells compared with that in heparan sulphate-deficient and wild-type cells. However, there were no differences in reporter gene expression between the cell lines when transfected by electroporation. Moreover, all cell lines exhibited equal cationic-lipid-DNA complex uptake activities, as assessed by the measurement of intracellular 32P-labelled and rhodamine-labelled DNA plasmid. An analysis of reflected-light images of wild-type and proteoglycan-deficient cells suggested that cationic lipids were preferentially toxic to proteoglycan-deficient cells. Cell-growth assays confirmed this, showing that cationic lipids exhibited a greater anti-proliferative activity in proteoglycan-deficient cells and in chlorate-treated wild-type cells than in the other cell lines. The growth-inhibitory effect of cationic lipids was abrogated by the addition of exogenous sulphated glycosaminoglycans. We conclude that the glycosaminoglycan part of proteoglycans serves a protective role against cationic lipid cytotoxicity, allowing optimal transfection efficiency in vitro.
In vitro analysis of the glucose-transport system in GLUT4-null skeletal muscle
Authors: RYDER Jeffrey W. , KAWANO Yuichi , CHIBALIN Alexander V. , RINCÓN Jorge , TSAO Tsu-Shuen , STENBIT Antine E. , COMBATSIARIS Terry , YANG Jing , HOLMAN Geoffrey D. , CHARRON Maureen J. , ZIERATH Juleen R.
Published: August 2015

We have characterized the glucose-transport system in soleus muscle from female GLUT4-null mice to determine whether GLUT1, 3 or 5 account for insulin-stimulated glucose-transport activity. Insulin increased 2-deoxyglucose uptake 2.8- and 2.1-fold in soleus muscle from wild-type and GLUT4-null mice, respectively. Cytochalasin B, an inhibitor of GLUT1- and GLUT4-mediated glucose transport, inhibited insulin-stimulated 2-deoxyglucose uptake by > 95% in wild-type and GLUT4-null soleus muscle. Addition of 35 mM fructose to the incubation media was without effect on insulin-stimulated 3-O-methylglucose transport activity in soleus muscle from either genotype, whereas 35 mM glucose inhibited insulin-stimulated (20 nM) 3-O-methylglucose transport by 65% in wild-type and 99% in GLUT4-null mice. We utilized the 2-N-4-1-(1-azi-2,2,2-t r i f l u o r o e t h y l ) b e n z o y l - 1, 3 - b i s (D - m a n n o s e - 4 - y l o x y ) - 2 - p ro p y lamine (ATB-BMPA) exofacial photolabel to determine if increased cell-surface GLUT1 or GLUT4 content accounted for insulin-stimulated glucose transport in GLUT4-null muscle. In wild-type soleus muscle, cell-surface GLUT4 content was increased by 2.8-fold under insulin-stimulated conditions and this increase corresponded to the increase in 2-deoxyglucose uptake. No detectable cell-surface GLUT4 was observed in soleus muscle from female GLUT4-null mice under either basal or insulin-stimulated conditions. Basal cell-surface GLUT1 content was similar between wild-type and GLUT4-null mice, with no further increase noted in either genotype with insulin exposure. Neither GLUT3 nor GLUT5 appeared to account for insulin-stimulated glucose-transport activity in wild-type or GLUT4-null muscle. In conclusion, insulin-stimulated glucose-transport activity in female GLUT4-null soleus muscle is mediated by a facilitative transport process that is glucose- and cytochalasin B-inhibitable, but which is not labelled strongly by ATB-BMPA.
cAMP induces co-translational modification of proteins in IPC-81 cells
Authors: HOVLAND Randi , DØSKELAND Anne P. , EIKHOM Thor S. , ROBAYE Bernard , DØSKELAND Stein O.
Published: August 2015

An elevated cAMP concentration results in growth arrest and protein synthesis-dependent apoptosis in the promyelocytic leukaemia cell line IPC-81. A comparison of two-dimensional gels of extracts from these cells labelled with [35S]methionine revealed that five distinct protein spots were induced by cAMP in a protein-synthesis-dependent manner. The spots seemed to result from the acidic shift of a precursor protein. The most abundant spot was phospho-actin. The spots induced by cAMP in intact cells were induced by cAMP-dependent protein kinase (cAPK) during the translation in vitro of mRNA from the leukaemia cells. The effect of cAPK was strictly co-translational, none of the spots being induced when cAPK was added after translation. This suggested that the protein spots arose by co-translational phosphorylation catalysed by cAPK. Two of the protein spots, phospho-actin and a protein with a molecular mass of 30 kDa and an isoelectric point of 4.5, were studied further with respect to expression. They were produced during the whole pre-apoptotic period, had cellular half-lives of several hours and were induced by the same concentrations of cAMP analogue that induced apoptosis. It is suggested that the accumulation of co-translationally modified proteins could be important for long-term cAMP signalling.
Inhibition of glycogenolysis in primary rat hepatocytes by 1,4-dideoxy-1,4-imino-D-arabinitol
Authors: ANDERSEN Birgitte , RASSOV Andreas , WESTERGAARD Niels , LUNDGREN Karsten
Published: August 2015

1,4-Dideoxy-1,4-imino-D-arabinitol (DAB) was identified previously as a potent inhibitor of both the phosphorylated and non-phosphorylated forms of glycogen phosphorylase (EC 2.4.1.1). In the present study, the effects of DAB were investigated in primary cultured rat hepatocytes. The transport of DAB into hepatocytes was dependent on time and DAB concentration. The rate of DAB transport was 192 pmol/min per mg of protein per mM DABmedium-concentration. In hepatocytes, DAB inhibited basal and glucagon-stimulated glycogenolysis with IC50 values of 1.0±0.3 and 1.1±0.2 μM, respectively. The primary inhibitory effect of DAB on glycogenolysis was shown to be due to inhibition of glycogen phosphorylase but, at higher concentrations of DAB, inhibition of the debranching enzyme (4-α-glucanotransferase, EC 2.4.1.25) may have an effect. No effects on glycogen synthesis were observed, demonstrating that glycogen recycling does not occur in cultured hepatocytes under the conditions tested. Furthermore, DAB had no effects on phosphorylase kinase, the enzyme responsible for phosphorylation and thereby activation of glycogen phosphorylase, or on protein phosphatase 1, the enzyme responsible for inactivation of glycogen phosphorylase through dephosphorylation.
Model of 2,3-bisphosphoglycerate metabolism in the human erythrocyte based on detailed enzyme kinetic equations1: in vivo kinetic characterization of 2,3-bisphosphoglycerate synthase/phosphatase using 13C and 31P NMR
Authors: MULQUINEY Peter J. , BUBB William A. , KUCHEL Philip W.
Published: August 2015

This is the first in a series of three papers [see also Mulquiney and Kuchel (1999) Biochem. J. 342, 579-594; Mulquiney and Kuchel (1999) Biochem. J. 342, 595-602] that present a detailed mathematical model of erythrocyte metabolism which explains the regulation and control of 2,3-bisphosphoglycerate (2,3-BPG) metabolism. 2,3-BPG is a modulator of haemoglobin oxygen affinity and hence plays an important role in blood oxygen transport and delivery. This paper presents an in vivo kinetic characterization of 2,3-BPG synthase/phosphatase (BPGS/P), the enzyme that catalyses both the synthesis and degradation of 2,3-BPG. Much previous work had indicated that the behaviour of this enzyme in vitro is markedly different from that in vivo. 13C and 31P NMR were used to monitor the time courses of selected metabolites when erythrocytes were incubated with or without [U-13C]glucose. Simulations of the experimental time courses were then made. By iteratively changing the parameters of the BPGS/P part of the model until a good match between the NMR-derived data and simulations were achieved, it was possible to characterize BPGS/P kineticallyin vivo. This work revealed that: (1) the pH-dependence of the synthase activity results largely from a strong co-operative inhibition of the synthase activity by protons; (2) 3-phosphoglycerate and 2-phosphoglycerate are much weaker inhibitors of 2,3-BPG phosphatase in vivo than in vitro; (3) the Km of BPGS/P for 2,3-BPG is significantly higher than that measured in vitro; (4) the maximal activity of the phosphatase in vivo is approximately twice that in vitro, when Pi is the sole activator (second substrate); and (5) 2-phosphoglycollate appears to play no role in the activation of the phosphatase in vivo. Using the newly determined kinetic parameters, the percentage of glycolytic carbon flux that passes through the 2,3-BPG shunt in the normal in vivo steady state was estimated to be 19%.
Localization of a carboxylic residue possibly involved in the inhibition of vacuolar H+-pyrophosphatase by N,N′-dicyclohexylcarbodi-imide
Authors: YANG Su J. , JIANG Shih S. , KUO Soong Y. , HUNG Shu H. , TAM Ming F. , PAN Rong L.
Published: August 2015

A vacuolar H+-pyrophosphatase (EC 3.6.1.1) that catalyses PPi hydrolysis and the electrogenic translocation of protons from the cytosol to the vacuole lumen, was purified from etiolated hypocotyls of mung bean seedlings (Vigna radiata L.). Group-specific modification was used to identify a carboxylic residue involved in the inhibition of vacuolar H+-pyrophosphatase. Carbodi-imides, such as N,N′-dicyclohexylcarbodi-imide (DCCD) and 1-ethyl-3-(3-dimethylamino-propyl)carbodi-imide, and Woodward's reagent K caused a progressive decline in the enzymic activity of vacuolar H+-pyrophosphatase in a time- and concentration-dependent manner. The stoichiometry of labelling of the vacuolar H+-pyrophosphatase by [14C]DCCD determined that DCCD modifies one carboxylic residue per subunit of the enzyme. Protection studies suggest that the DCCD-reactive carboxylic residue resides at or near the substrate-binding site. Furthermore, peptide mapping analysis reveals that Asp283, located in the putative loop V of a tentative topological model of vacuolar H+-pyrophosphatase on the cytosolic side, was labelled by radioactive [14C]DCCD. Cytosolic loop V contains both DCCD-sensitive Asp283 and a conserved motif sequence, rendering it a candidate for the catalytic site of vacuolar H+-pyrophosphatase. A topological picture of the active domain of vacuolar H+-pyrophosphatase is tentatively proposed.
The N-terminal LIM domain negatively regulates the kinase activity ofLIM-kinase 1
Authors: NAGATA Kyoko , OHASHI Kazumasa , YANG Neng , MIZUNO Kensaku
Published: August 2015

LIM-kinase 1 (LIMK1, where LIM is an acronym of the three gene products Lin-11, Isl-1 and Mec-3) is a serine/threonine kinase that phosphorylates cofilin and regulates actin cytoskeletal reorganization. LIMK1 contains two LIM domains and a PDZ (an acronym of the three proteins PSD-95, Dlg and ZO-1) domain in the N-terminal half and a kinase domain in the C-terminal half. In this study we examined the role of the extra-catalytic region in the regulation of kinase activity of LIMK1. Limited proteolysis of LIMK1 resulted in the production of the 35-40-kDa kinase core fragments with 3.5-5.5-fold increased kinase activity. The LIMK1 mutants with deleted LIM domains (δLIM) or conserved cysteines in the two LIM domains replaced with glycines (dmLIMK1) had 3-7-fold higher kinase activitiesin vitro, compared with the wild-type LIMK1. The C-terminal kinase fragment of LIMK1 bound to the LIM domain but not to the PDZ domain. Furthermore, the LIM fragment dose-dependently inhibited the kinase catalytic activity of the kinase core fragment of LIMK1. Taken together, these results suggest that the N-terminal LIM domain negatively regulates the kinase activity of LIMK1 by direct interaction with the C-terminal kinase domain. In addition, expression of the δLIM mutant in cultured cells induced punctate accumulation of actin filaments, an event distinct from the pattern of actin organization induced by expression of the wild-type LIMK1, suggesting that the LIM domain plays a role in the function of LIMK1in vivo.
An antibody present in normal human serum inhibits the binding of cytokines to their receptors in an in vitro system
Authors: MOSEDALE David E. , GRAINGER David J.
Published: August 2015

The presence of active transforming growth factor-β (TGF-β) in serum has not been widely accepted. In particular, although at least five studies have concluded that active TGF-β is present in normal human plasma and serum, assays that use the extracellular domain of the TGF-β type II receptor as a capture agent have given contradictory results. We show that there is an antagonist present in normal human serum which inhibits the binding of active TGF-β to the extracellular domain of the TGF-β type II receptor when it is coated on the well of an ELISA plate. This antagonist activity is due to a pool of immunoglobulins of the G2, D and M classes. Moreover, we show that this same pool of immunoglobulins also recognizes the extracellular domain of the platelet-derived growth factor α-receptor, insulin-like growth factor-1 receptor and interleukin-3 receptor, by serial transfer of serum over the different receptors. In addition, the same immunoglobulin pool inhibits the binding of platelet-derived growth factor-AA to its receptor, in an analogous way to the inhibition of binding of TGF-β to its type II receptor. Circumstantial evidence suggests that the pool of immunoglobulins is recognizing a carbohydrate residue that is attached to the protein when it is synthesized by the mouse myeloma cell line, NSO, in which it is made. If the cytokine receptors are similarly glycosylated in vivo, then the presence of these antibodies in normal human serum may modulate physiological cytokine signalling.
α3β3γ complex of F1-ATPase from thermophilic Bacillus PS3 can maintain steady-state ATP hydrolysis activity depending on the number of non-catalytic sites
Authors: AMANO Toyoki , MATSUI Tadashi , MUNEYUKI Eiro , NOJI Hiroyuki , HARA Kiyotaka , YOSHIDA Masasuke , HISABORI Toru
Published: August 2015

Homogeneous preparations of α3β3γ complexes with one, two or three non-competent non-catalytic site(s) were performed as described [Amano, Hisabori, Muneyuki, and Yoshida (1996) J. Biol. Chem. 271, 18128-18133] and their properties were compared with those of the wild-type complex. The ATPase activity of the complex with three non-competent non-catalytic sites decayed rapidly to an inactivated state, as reported previously [Matsui, Muneyuki, Honda, Allison, Dou, and Yoshida (1997) J. Biol. Chem. 272, 8215-8221]. In contrast, the complex with one or two non-competent non-catalytic sites displayed a substantial steady-state phase activity depending on the number of non-competent non-catalytic sites in the complex. This result indicates that one competent non-catalytic site can maintain the continuous catalytic turnover of the enzyme and can potentially relieve all three catalytic sites from inhibition by MgADP-. Furthermore, the results suggest that the interaction between three non-catalytic sites might not be as strong as that between catalytic sites, which are all strictly required for a continuous catalytic turnover.
Interactions between the thiol-group reagent N-ethylmaleimide and neutral and basic amino acid transporter-related amino acid transport
Authors: PETER George J. , DAVIES Anthony , WATT Peter W. , BIRRELL Jacqueline , TAYLOR Peter M.
Published: August 2015

The neutral and basic amino acid transport protein (NBAT) expressed in renal and jejunal brush-border membranes is involved in amino acid and cystine absorption. NBAT mutations result in Type 1 cystinuria. A C-terminal myc-tagged NBAT (NBATmyc) retains the amino acid transport and protein-protein interaction properties of NBAT when expressed in Xenopusoocytes. Neutral amino acid (Ala, Phe)-cationic amino acid (Arg) heteroexchanges related to NBATmyc expression in oocytes are inactivated by treatment with the thiol-group reagent N-ethylmaleimide (NEM), although significant Arg-Arg and Ala-Ala homoexchanges persist. Inactivation of heteroexchange activity by NEM is accompanied by loss of > 85% of alanine and cystine uptake, with smaller (< 50%) inhibition of arginine and phenylalanine uptake. NEM-sensitive cystine uptake and arginine-alanine heteroexchange (system b0,+ activity) are not expressed by an NBAT truncation mutant (NBATmyc-Sph1) lacking the 13 C-terminal amino acid residues, but the mutant expresses NEM-resistant transport activity (system y+L-like) equivalent to that of full-length NBATmyc. The deleted region of NBATmyc-Sph1 contains two cysteine residues (671/683) which may be the targets of NEM action. The synthetic amino acid 2-trifluoromethylhistidine (TFMH) stimulated alanine efflux at pH 7.5 and arginine at pH 5.5, but not vice versa, establishing the existence of distinct pathways for cationic and neutral amino acid homoexchange (TFMH is zwitterionic at pH 7.5 and cationic at pH 5.5). We suggest that NBAT expresses a combination of system b0,+ and y+L-like activities, possibly by interacting with different light-chain subunits endogenous to oocytes (as does the homologous 4F2hc protein). The C-terminus of NBAT may also have an additional, direct role in the mechanism of System b0,+ transport (the major transport activity that is defective in Type 1 cystinuria).
In contrast with docosahexaenoic acid, eicosapentaenoic acid and hypolipidaemic derivatives decrease hepatic synthesis and secretion of triacylglycerol by decreased diacylglycerol acyltransferase activity and stimulation of fatty acid oxidation
Authors: BERGE Rolf K. , MADSEN Lise , VAAGENES Hege , TRONSTAD Karl Johan , GÖTTLICHER Martin , RUSTAN Arild C.
Published: August 2015

Hypolipidaemic fatty acid derivatives and polyunsaturated fatty acids decrease concentrations of plasma triacylglycerol by mechanisms that are not fully understood. Because poor susceptibility to β- and/or ω-oxidation is apparently a determinant of the peroxisome proliferating and hypolipidaemic capacity of fatty acids and derivatives, the relative importance of activation of the peroxisome-proliferator-activated receptor α (PPARα), fatty acid oxidation and triacylglycerol synthesis were examined. We have compared the effects of differentially β-oxidizable fatty acids on these parameters in primary cultures of rat hepatocytes. Tetradecylthioacetic acid (TTA), 2-methyleicosapentaenoic acid and 3-thia-octadecatetraenoic acid, which are non-β-oxidizable fatty acid derivatives, were potent activators of a glucocorticoid receptor (GR)-PPARα chimaera. This activation was paradoxically reflected in an substantially increased oxidation of [1-14C]palmitic acid and/or oleic acid. The incorporation of [1-14C]palmitic acid and/or oleic acid into cell-associated and secreted triacylglycerol was decreased by 15-20% and 30% respectively with these non-β-oxidizable fatty acid derivatives. The CoA ester of TTA inhibited the esterification of 1,2-diacylglycerol in rat liver microsomes. Both eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) activated GR-PPARα. EPA increased the oxidation of [1-14C]palmitic acid but DHA had no effect. The CoA ester of EPA inhibited the esterification of 1,2-diacylglycerol, whereas DHA-CoA had no effect. The ratio between synthesized triacylglycerol and diacylglycerol was lower in hepatocytes cultured with EPA in the medium compared with DHA or oleic acid, indicating a decreased conversion of diacylglycerol to triacylglycerol. Indeed, the incorporation of [1-14C]oleic acid into secreted triacylglycerol was decreased by 20% in the presence of EPA. In conclusion, a decreased availability of fatty acids for triacylglycerol synthesis by increased mitochondrial β-oxidation and decreased triacylglycerol formation caused by inhibition of diacylglycerol acyltransferase might explain the hypolipidaemic effect of TTA and EPA.
A prespore-cell-inducing factor in Dictyostelium discoideum: its purification and characterization
Authors: NAKAGAWA Manabu , OOHATA Akiko A. , TOJO Hiromasa , FUJII Shigeru
Published: August 2015

Under starvation conditions, amoebae of Dictyostelium discoideum aggregate to form multicellular masses; the aggregates are then initiated to differentiate. We have reported previously that a signal substance exists in conditioned medium of D. discoideum, and we named it prespore-cell-inducing factor (psi, Ψ factor) [Oohata, Nakagawa, Tasaka, and Fujii (1997) Development 124, 2781-2787]. The factor can induce isolated amoebae to differentiate into prespore cells. Moreover, we suggested that it caused not only cell differentiation but also cell division. In the present study, we have purified Ψ factor from the conditioned medium and characterized it. The purified Ψ factor induced both prespore cell differentiation and cell division of prespore cells. Its apparent molecular mass was 180 kDa by gel filtration and 106 kDa by SDS/PAGE. Based on these results, Ψ factor exists as a dimer in normal conditions. Periodic acid/Schiff staining showed that Ψ factor was a glycoprotein. It was ascertained by Edman degradation that Ψ factor is blocked at the N-terminal. Treatment with pyroglutamate aminopeptidase removed the N-terminal block and allowed determination of the amino-acid sequence of Ψ factor. Moreover, three internal amino-acid sequences were determined in limited proteolysis experiments using trypsin and endoproteinase Lys-C. The homology search for these sequences supports the fact that Ψ factor is a novel differentiation factor.
Molecular characterization and expression of mandibular organ-inhibiting hormone, a recently discovered neuropeptide involved in the regulation of growth and reproduction in the crab Cancer pagurus
Authors: TANG Chenhui , LU Weiqun , WAINWRIGHT Geoffrey , WEBSTER Simon G. , REES Huw H. , TURNER Philip C.
Published: August 2015

Methyl farnesoate, the crustacean juvenoid, is synthesized and secreted from the mandibular organs of crustaceans under the negative control of the sinus gland-derived mandibular organ-inhibiting hormone (MO-IH). Previously we isolated and sequenced two isoforms, MO-IH-1 and MO-IH-2, differing by just one amino acid, from sinus glands of the edible crab, Cancer pagurus. We now report the isolation of cDNAs encoding MO-IH-1 and MO-IH-2 by a combination of reverse-transcriptase-mediated PCR in conjunction with 5′ and 3′ rapid amplification of cDNA ends (‘RACE’). Full-length clones of MO-IH-1 and MO-IH-2 encoded a 34-residue putative signal peptide and the mature 78-residue MO-IH sequences. Northern blot analysis of various tissues showed that MO-IH expression is confined to the X-organ (a cluster of perikarya within the eye). Southern blot analysis indicated that there are approx. 10 copies of the gene for MO-IH in C. pagurus. Additional Southern blotting experiments detected MO-IH-hybridizing bands in another Cancer species, C. antennarius. In support of this, an HPLC-radioimmunoassay analysis of sinus gland extracts of C. antennarius and C. magister also revealed MO-IH-like immunoreactivity.
Fibroblast growth factor-1 interacts with the glucose-regulated protein GRP75/mortalin
Authors: MIZUKOSHI Eiichi , SUZUKI Masashi , LOUPATOV Alexei , URUNO Takehito , HAYASHI Hisaki , MISONO Tomoko , KAUL Sunil C. , WADHWA Renu , IMAMURA Toru
Published: August 2015

Fibroblast growth factor-1 (FGF-1), which lacks a signal peptide and is intracellularly localized as a result of endogenous expression or endocytosis, is thought to be involved in regulating cell growth and differentiation. In the study reported here, we purified proteins that bind intracellular FGF-1. Affinity adsorption was used to purify FGF-1-binding proteins from rat L6 cells expressing FGF-1. One of the isolated proteins was identified as the glucose-regulated protein GRP75/mortalin/PBP-74/mthsp70, a member of the hsp70 family of heat-shock proteins known to be involved in regulating glucose responses, antigen processing and cell mortality. The interaction of FGF-1 and GRP75/mortalin in vivo was confirmed by co-immunoprecipitation, immunohistochemical co-localization in Rat-1 fibroblasts and by using the yeast two-hybrid system. Moreover, a binding assay in vitro with the use of recombinant FGF-1 and mortalin demonstrated a direct physical interaction between the two proteins. These results reveal that GRP75/mortalin is an intracellular FGF-1-binding protein in cells and suggest that GRP75/mortalin is involved in the trafficking of and/or signalling by FGF-1.
Molecular cloning and cell-cycle-dependent expression of the acetyl-CoA synthetase gene in Tetrahymena cells
Authors: WANG Shulin , NAKASHIMA Shigeru , NUMATA Osamu , FUJIU Kenta , NOZAWA Yoshinori
Published: August 2015

To identify transcriptionally regulated mediators associated with the cell cycle, we adopted the differential mRNA display technique for cell cultures of Tetrahymenapyriformis synchronized by cyclic heat treatment. One cDNA fragment that was expressed differently during synchronous cell division had a greatly decreased expression at 30 min after the end of heat treatment (EHT). Using this fragment as a probe, we isolated the full-length cDNA for T. pyriformis acetyl-CoA synthetase (TpAcs) which encodes a 651 amino acid polypeptide with a predicted molecular mass of 72.8 kDa. The deduced amino acid sequence of T. pyriformis ACS shows 42% sequence identity compared with that ofLysobacter sp. acetyl-CoA synthetase (ACS), an enzyme which catalyses the formation of acetyl-CoA from acetate via an acetyl-adenylate intermediate. The deduced sequence is also 41% and 40% identical compared with those of Pseudomonas putida and Coprinus cinereus ACS, respectively. The deduced sequence of T. pyriformis ACS also shares similar characteristics of the conserved motifs I and II in the ACS family. To further investigate the actions of the gene encoding this enzyme, mRNA expression was determined during the course of synchronized cell division in T. pyriformis. Northern blot results show that the mRNA level was dramatically decreased at 30 min after EHT prior to entering synchronous cell division (which occurs 75 min after EHT), suggesting that mRNA expression of the TpAcs was associated with the cell cycle and that the down-regulated expression of TpAcs at 30 min after EHT would be required for the initiation of the oncoming synchronous cell division in T. pyriformis.
Oligomerization properties of fragile-X mental-retardation protein (FMRP) and the fragile-X-related proteins FXR1P and FXR2P
Authors: TAMANINI Filippo , UNEN Leontine VAN , BAKKER Cathy , SACCHI Nicoletta , GALJAARD Hans , OOSTRA Ben A. , HOOGEVEEN André T.
Published: August 2015

The absence of fragile-X mental-retardation protein (FMRP) results in fragile-X syndrome. Two other fragile-X-related (FXR) proteins have been described, FXR1P and FXR2P, which are both very similar in amino acid sequence to FMRP. Interaction between the three proteins as well as with themselves has been demonstrated. The FXR proteins are believed to play a role in RNA metabolism. To characterize a possible functional role of the interacting proteins the complex formation of the FXR proteins was studied in mammalian cells. Double immunofluorescence analysis in COS cells over-expressing either FMRP ISO12/FXR1P or FMRP ISO12/FXR2P confirmed heterotypic interactions. However, Western-blotting studies on cellular homogenates containing physiological amounts of the three proteins gave different indications. Gel-filtration experiments under physiological as well as EDTA conditions showed that the FXR proteins were in complexes of > 600 kDa, as parts of messenger ribonuclear protein (mRNP) particles associated with polyribosomes. Salt treatment shifted FMRP, FXR1P and FXR2P into distinct intermediate complexes, with molecular masses between 200 and 300 kDa. Immunoprecipitations of FMRP as well as FXR1P from the dissociated complexes revealed that the vast majority of the FXR proteins do not form heteromeric complexes. Further analysis by [35S]methionine labelling in vivo followed by immunoprecipitation indicated that no proteins other than the FXR proteins were present in these complexes. These results suggest that the FXR proteins form homo-multimers preferentially under physiological conditions in mammalian cells, and might participate in mRNP particles with separate functions.
Novel bimodal effects of the G-protein tissue transglutaminase on adrenoreceptor signalling
Authors: ZHANG Jianwen , TUCHOLSKI Janusz , LESORT Mathieu , JOPE Richard S. , JOHNSON Gail V. W.
Published: August 2015

Tissue transglutaminase (tTG) is a novel G-protein that previous studies showed can couple ligand-bound activated α1B adrenoreceptors to phospholipase C-δ, resulting in phosphoinositide (PI) hydrolysis. In human neuroblastoma SH-SY5Y cells we found that although endogenous tTG can facilitate α1B adrenoreceptor-stimulated PI hydrolysis, its contribution is minor compared with the classical heterotrimeric G-protein Gq/11. Further, we show that the α1B adrenoreceptor recruits tTG to the membrane and that this recruitment is enhanced by agonist occupancy of the receptor. In addition, the effects of tTG on signalling are bimodal. At low expression levels, tTG enhanced α1B adrenoreceptor-stimulated PI hydrolysis, whereas at higher expression levels tTG attenuated significantly this response. These findings are the first to demonstrate that a protein can both facilitate and attenuate receptor-stimulated PI hydrolysis.
Identification of protein kinase C phosphorylation sites in the angiotensin II (AT1A) receptor
Authors: QIAN Hongwei , PIPOLO Luisa , THOMAS Walter G.
Published: August 2015

Protein kinase C (PKC) phosphorylates the C-terminus of the type 1 angiotensin II receptor (AT1), although the exact site(s) of phosphorylation are unidentified. In the present study, we examined the phosphorylation of epitope-tagged wild-type AT1A receptors, transiently expressed in Chinese hamster ovary K1 cells, in response to angiotensin II (AngII) and following selective activation and inhibition of PKC. This phosphorylation was compared with mutant receptors where C-terminal serine residues (Ser331, Ser338 and Ser348) within three putative PKC consensus sites were replaced with alanine, either individually or in combination. Stimulation by AngII or the phorbol ester PMA to activate PKC induced an increase in phosphorylation of the wild-type AT1A receptor, which was prevented by truncation of the receptor C-terminus to remove the last 34 amino acids, including Ser331, Ser338 and Ser348. Whereas single alanine mutation (Ser331Ala, Ser338Ala and Ser348Ala) resulted in decreased receptor phosphorylation, no single mutant completely inhibited either AngII- or PMA-induced phosphorylation. Combined mutation of the three PKC consensus sites caused an ≈ 70% reduction in PMA-mediated phosphorylation. The ≈ 60% reduction in AngII (1 μM)-induced phosphorylation of this triple mutant and the partial inhibition of wild-type receptor phosphorylation by bisindolylmaleimide, a specific PKC inhibitor, suggest a significant contribution of PKC to agonist-stimulated regulation. The ratio of PKC to total receptor phosphorylation was greatest at low doses of AngII (1 nM), consistent with the idea that PKC phosphorylates and regulates receptor function at low levels of stimulation, whereas phosphorylation by other kinases is more prevalent at high levels of agonist stimulation. To determine if a single PKC site is favoured when the contribution of PKC varies, the phosphorylation of wild-type and mutant receptors was examined over a range of AngII concentrations (0, 1, 10 and 100 nM). At all AngII concentrations, single mutation of Ser331, Ser338 or Ser348 was incapable of completely preventing receptor phosphorylation, suggesting no clear preference for PKC consensus-site utilization. Together, these results indicate a redundancy in PKC phosphorylation of the AT1A receptor, whereby all three consensus sites are utilized to some degree following homologous (AngII) and heterologous (PMA) stimulation. The contribution of PKC phosphorylation to receptor regulation is unclear, but multiple PKC phosphorylation of the AT1A receptor may allow independent and/or complementary events to occur at the three separate sites of the C-terminus.
Regulation of intestinal Na+-dependent phosphate co-transporters by a low-phosphate diet and 1,25-dihydroxyvitamin D3
Authors: KATAI Kanako , MIYAMOTO Ken-ichi , KISHIDA Satie , SEGAWA Hiroko , NII Tomoko , TANAKA Hiroko , TANI Yoshiko , ARAI Hidekazu , TATSUMI Sawako , MORITA Kyoko , TAKETANI Yutaka , TAKEDA Eiji
Published: August 2015

In a study of the rat intestinal Pi transport system, an activator protein for rat Na/Pi co-transport system (PiUS) was isolated and characterized. We also investigated the effects of restriction of vitamin D and Pi (two of the most important physiological and pathophysiological regulators of Pi absorption in the small intestine) on intestinal Pi transport activity and the expression of Na/Pi co-transporters that are expressed in rat small intestine. Rat PiUS encodes a 424-residue protein with a calculated molecular mass of 51463 Da. The microinjection of rat PiUS into Xenopus oocytes markedly stimulated Na+-dependent Pi co-transport activity. In rats fed with a low-Pi diet, Na+-dependent Pi co-transport activity was increased approx. 2-fold compared with that of rats fed a normal Pi diet. Kinetic studies demonstrated that this increased activity was due to an elevation of Vmax but not Km. The PiUS mRNA levels showed an approximate doubling in the rats fed with the low-Pi diet compared with those fed with the normal Pi diet. In addition, after the administration of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] to vitamin D-deficient animals, the Pi uptake was significantly increased in the Na+-dependent component in the brush border membrane vesicle (BBMV) at 24 and 48 h. In addition, we found a further high-affinity Na/Pi co-transport system in the BBMV isolated from the vitamin D-replete animals. The levels of type III Na/Pi co-transporter PiT-2 mRNA were increased 24 and 48 h after 1,25-(OH)2D3 administration to vitamin D-deficent animals, whereas PiUS and the type IIb Na/Pi co-transporter mRNA levels were unchanged. In conclusion, we first cloned a rat activator protein, PiUS, and then studied its role along with that of other type III Na/Pi co-transporters. PiUS and PiT-2 might be important components in the regulation of the intestinal Pi transport system by Pi restriction and 1,25-(OH)2D3.
Apolipoprotein serum amyloid A down-regulates smooth-muscle cell lipid biosynthesis
Authors: SCHREIBER Barbara M. , VEVERBRANTS Mara , FINE Richard E. , BLUSZTAJN Jan K. , SALMONA Mario , PATEL Apurva , SIPE Jean D.
Published: August 2015

The addition of acute-phase apolipoprotein serum amyloid A (SAA) to cultured aortic smooth-muscle cells caused a decrease in the incorporation of [14C]acetate into lipids. Optimal inhibition of lipid biosynthesis was achieved with 2 μM SAA, and the effect was maintained for up to 1 week when SAA was included in the culture medium. Lipid extracts were subjected to TLC and it was determined that the SAA-induced decrease in [14C]acetate incorporation into lipids was attributable to decreases in cholesterol, phospholipid and triglyceride levels. The accumulated mass of cholesterol and phospholipid in SAA-treated cultures was significantly less than that of controls, with no change in the accumulated protein. Moreover, SAA had no effect on either protein synthesis or DNA synthesis, suggesting that SAA specifically alters lipid synthesis. By using a peptide corresponding to the cholesterol-binding domain of acute-phase SAA (amino acids 1-18), it was shown that this region of the molecule was as effective as the full-length protein in decreasing lipid synthesis and the accumulation of cholesterol and phospholipid. The implications of these findings for atherosclerosis and Alzheimer's disease are discussed.