bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of a H+-ATPase in the regulation of cytoplasmic pH in Trypanosoma cruzi epimastigotes
Authors: VANDERHEYDEN Nicole , BENAIM Gustavo , DOCAMPO Roberto
Published: August 2015

Cytoplasmic pH (pHi) regulation was studied in Trypanosoma cruzi epimastigotes using fluorescent probes. Steady-state pHi was maintained even in the absence of extracellular Na+ or K+, but was significantly decreased in the absence of Cl-. Acid-loaded epimastigotes regained normal pHi by a process that was ATP-dependent and sensitive to N-ethylmaleimide, dicyclohexylcarbodi-imide and diethylstilboestrol, suggesting involvement of a H+-pumping ATPase. Recovery from an acid load was independent of extracellular Na+ or K+ and insensitive to omeprazole, vanadate and low concentrations of bafilomycin A1. Using the fluorescent probe bisoxonol to measure the membrane potential of intact cells, acid loading of epimastigotes was shown to result in a dicyclohexylcarbodi-imide-sensitive hyperpolarization, which suggests electrogenic pumping of protons across the plasma membrane. Addition of glucose, but not of 6-deoxyglucose, produced a transient cellular acidification of possible metabolic origin, and increased the rate of recovery from an acid load. Taken together, these results are consistent with an important role of a H+-ATPase in the regulation of pHi homoeostasis in T. cruzi.
Towards a classification of glycosyltransferases based on amino acid sequence similarities: prokaryotic α-mannosyltransferases
Authors: GEREMIA Roberto A , PETRONI E Alejandro , IELPI Luis , HENRISSAT Bernard
Published: August 2015

A number of genes encoding bacterial glycosyltransferases have been sequenced during the last few years, but their low sequence similarity has prevented a straightforward grouping of these enzymes into families. The sequences of several bacterial α-mannosyltransferases have been compared using current alignment algorithms as well as hydrophobic cluster analysis (HCA). These sequences show a similarity which is significant but too low to be reliably aligned using automatic alignment methods. However, a region spanning approx. 270 residues in these proteins could be aligned by HCA, and several invariant amino acid residues were identified. These features were also found in several other glycosyltransferases, as well as in proteins of unknown function present in sequence databases. This similarity most probably reflects the existence of a family of proteins with conserved structural and mechanistic features. It is argued that the present IUBMB classification of glycosyltransferases could be complemented by a classification of these enzymes based on sequence similarities analogous to that which we proposed for glycosyl hydrolases [Henrissat, B. (1991) Biochem. J. 280, 309–316].
Functional domains on elastin and microfibril-associated glycoprotein involved in elastic fibre assembly
Authors: BROWN-AUGSBURGER Patricia , BROEKELMANN Thomas , ROSENBLOOM Joel , MECHAM Robert P.
Published: August 2015

Studies in vitro suggest that the C-terminus of tropoelastin mediates elastin polymerization through an interaction with microfibril-associated proteins. In this study we have used cultured auricular chondrocytes as a model system to examine whether this interaction is critical for elastic fibre formation in vivo. Auricular chondrocytes, which deposit an abundant elastic fibre matrix, were cultured in the presence of Fab fragments of antibodies directed against the C-terminus (CTe) or an N-terminal domain (ATe) of tropoelastin. Immunofluorescent staining of the extracellular matrix deposited by the cells showed that the CTe antibody inhibited the deposition of elastin without affecting microfibril structure. Cells grown under identical conditions in the presence of ATe, however, formed fibres that stained normally for both elastin and microfibril proteins. Chondrocytes cultured in the presence of microfibril-associated glycoprotein (MAGP):21–35, an antibody directed against a domain near the N-terminus of MAGP, did not organize tropoelastin into fibres. However, immunostaining for MAGP and fibrillin revealed normal microfibrils. In agreement with the immunofluorescence staining patterns, fewer elastin-specific cross-links, indicative of insoluble elastin, were detected in the extracellular matrix of cells cultured in the presence of CTe. The medium from these cultures, however, contained more soluble elastin, consistent with an antibody-induced alteration of elastin assembly but not its synthesis. Northern analysis of antibody-treated and control cultures substantiated equivalent levels of tropoelastin mRNA. These results confirm that the C-terminus of tropoelastin interacts with microfibrils during the assembly of elastic fibres. Further, the results suggest that the interaction between tropoelastin and microfibrils might be mediated by a domain involving the N-terminal half of MAGP.
Large-scale chromatographic purification of F1F0-ATPase and complex I from bovine heart mitochondria
Authors: BUCHANAN Susan K , WALKER John E.
Published: August 2015

A new chromatographic procedure has been developed for the isolation of F1Fo-ATPase and NADH:ubiquinone oxidoreductase (complex I) from a single batch of bovine heart mitochondria. The method employed dodecyl β-Δ-maltoside, a monodisperse, homogeneous detergent in which many respiratory complexes exhibit high activity, for solubilization and subsequent purification by ammonium sulphate fractionation and column chromatography. A combination of anion-exchange, gel-filtration, and dye-ligand affinity chromatography was used to purify both complexes to homogeneity. The F1Fo-ATPase preparation contains only the 16 known subunits of the enzyme. It has oligomycin-sensitive ATP hydrolysis activity and, as demonstrated elsewhere, when reconstituted into lipid vesicles it is capable of ATP-dependent proton pumping and of ATP synthesis driven by a proton gradient [Groth and Walker (1996) Biochem. J. 318, 351–357]. The complex I preparation contains all of the subunits identified in other preparations of the enzyme, and has rotenone-sensitive NADH:ubiquinone oxidoreductase and NADH:ferricyanide oxidoreductase activities. The procedure is rapid and reproducible, yielding 50–80 mg of purified F1Fo-ATPase and 20–40 mg of purified complex I from 1 g of mitochondrial membranes. Both preparations are devoid of phospholipids, and gel filtration and dynamic light scattering experiments indicate that they are monodisperse. Therefore, the preparations fulfil important prerequisites for structural analysis.
Isothiazolones interfere with normal matrix metalloproteinase activation and inhibit cartilage proteoglycan degradation
Authors: ARNER Elizabeth C , PRATTA Michael A , FREIMARK Bruce , LISCHWE Michael , TRZASKOS James M , MAGOLDA Ronald L , WRIGHT Stephen W
Published: August 2015

A series of isothiazolones that inhibit pro-(matrix metalloproteinase) (proMMP) activation but do not inhibit the active enzyme are effective as cartilage protectants in bovine nasal cartilage organ culture, preventing interleukin-1 (IL-1)-induced proteoglycan (aggrecan) degradation without affecting its synthesis. These compounds were found to bind to prostromelysin (proMMP-3) in a non-dialysable and stoichiometric manner. Preincubation with cartilage-protectant isothiazolones prevented the binding of [14C]iodoacetamide to Cys75 of the MMP-3 propeptide, suggesting that the activity of these compounds involves their binding to the Cys75 of the MMP zymogen. Studies following chymotrypsin activation of proMMP-3 by SDS/PAGE indicated that altered processing of the 57 kDa zymogen to the active form occurred in the presence of compound. The 53 kDa intermediate seen on normal activation was not formed; instead a different intermediate appeared with a molecular mass of approx. 46 kDa. N-terminal sequence analysis indicated that this intermediate was formed by cleavage at the putative 4-aminophenylmercuric acid cleavage site. Importantly the 45 kDa active MMP-3 species formed in the presence of compound was one amino acid residue shorter than the native MMP-3. These results suggest that the inhibition of cartilage proteoglycan degradation by isothiazolones might be due to their ability to bind to the Cys75 in the propeptide region of the MMP zymogen and interfere with its normal activation process.
Cross-link analysis of the C-telopeptide domain from type III collagen
Authors: HENKEL W.
Published: August 2015

Several peptides were isolated from tryptic digests of insoluble calf aorta matrix by chromatography. Reductive pyridylethylation of a tryptic 15 kDa pool released fragments deriving from the C-terminus of type III collagen. A 50-residue peptide TC(III) was shown by sequence analysis to be the C-terminal peptide from the α1(III)-chain, containing a helical and non-helical region of equal sizes. The peptide was further digested with collagenase to give ColC(III), comprising the complete C-terminal non-helical region of α1(III) including a hydroxylysine in position 16C. The peptide TC(III)×TN(III) was isolated, demonstrating covalent cross-linking between the C-terminal non-helical region of one type III molecule and the N-terminal helical cross-linking region of another. Its digestion with cyanogen bromide yielded the small fragments α1(III)CB3B* and α1(III)CB3C, confirming TN(III) as an N-terminal helical cross-link site. Sequence analysis of both TC(III)×TN(III) and its collagenase-derived cross-linked peptide ColC(III)×TN(III) established the 4D-staggered alignment of adjacent collagen III molecules. The cross-link structure of both peptides was mainly dihydroxylysinonorleucine with a small amount of hydroxylysinonorleucine, indicating that the lysine residues involved in formation of the cross-links are both hydroxylated. No pyridinoline or histidinohydroxylysinonorleucine cross-links were found within the non-reduced C-telopeptide region of type III collagen.
The co-mitogenic combination of transforming growth factor β1 and bombesin protects protein kinase C-δ from late-phase down-regulation, despite synergy in diacylglycerol accumulation
Authors: OLIVIER Andrée R. , HANSRA Gurdip , PETTITT Trevor R. , WAKELAM Michael J. O. , PARKER Peter J.
Published: August 2015

Bombesin induces the down-regulation of protein kinase C-Δ (PKC-Δ) and PKC-ϵ in Swiss 3T3 cells. Simultaneous addition of transforming growth factor β1 (TGFβ1) selectively blocks PKC-Δ down-regulation at mid-S-phase, whereas PKC-ϵ levels continue to decline. Northern blot analysis shows that PKC-ϵ levels could be controlled in part at the level of transcription; PKC-Δ mRNA levels remained constant at these later times. Bombesin induces a sustained elevation of some species of diacylglycerol (DAG), consistent with the observed loss of PKC-Δ and PKC-ϵ. Interestingly, the combination of bombesin and TGF-β1 produces an even greater DAG response. Flow cytometric analysis demonstrates that bombesin induces only 15% of the cells to enter the cell cycle, in contrast to the combination of TGFβ1 plus bombesin which induces 75–80% of the cells to progress through the cycle. The protection of PKC-Δ from down-regulation under conditions of sustained DAG elevation correlates with the mitogenic response and implies that the down-regulation process itself is regulated. Consistent with this, it is demonstrated that bombesin plus TGFβ1 protects PKC-Δ from phorbol ester-induced down-regulation.
Localization of a high-affinity inositol 1,4,5-trisphosphate/inositol 1,4,5,6-tetrakisphosphate binding domain to the pleckstrin homology module of a new 130 kDa protein: characterization of the determinants of structural specificity
Authors: TAKEUCHI Hiroshi , KANEMATSU Takashi , MISUMI Yoshio , YAAKOB Hassan Bin , YAGISAWA Hitoshi , IKEHARA Yukio , WATANABE Yutaka , TAN Zheng , SHEARS Stephen B. , HIRATA Masato
Published: August 2015

We have previously identified a novel 130 kDa protein (p130) which binds Ins(1,4,5)P3 and shares 38% sequence identity with phospholipase C-Δ1 [Kanematsu, Misumi, Watanabe, Ozaki, Koga, Iwanaga, Ikehara and Hirata (1996) Biochem. J. 313, 319–325]. We have now transfected COS-1 cells with genes encoding the entire length of the molecule or one of several truncated mutants, in order to locate the region for binding of Ins(1,4,5)P3. Deletion of N-terminal residues 116–232, the region which corresponds to the pleckstrin homology (PH) domain of the molecule, completely abolished binding activity. This result was confirmed when the PH domain itself (residues 95–232), isolated from a bacterial expression system, was found to bind [3H]Ins(1,4,5)P3. We also found that Ins(1,4,5,6)P4 was as efficacious as Ins(1,4,5)P3 in displacing [3H]Ins(1,4,5)P3, suggesting that these two polyphosphates bind to p130 with similar affinity. This conclusion was confirmed by direct binding studies using [3H]Ins(1,4,5,6)P4 with high specific radioactivity which we prepared ourselves. Binding specificity was also examined with a variety of inositol phosphate derivatives. As is the case with other PH domains characterized to date, we found that the 4,5-vicinal phosphate pair was an essential determinant of ligand specificity. However, the PH domain of p130 exhibited some novel features. For example, the 3- and/or 6-phosphates could also contribute to overall binding; this contrasts with some other PH domains where these phosphate groups decrease ligand affinity by imposing a steric constraint. Secondly, a free monoester 1-phosphate substantially increased binding affinity, which is a situation so far unique to the PH domain of p130.
Intracellular single-chain antibody inhibits integrin VLA-4 maturation and function
Authors: YUAN Qian , STRAUCH Kathryn L. , LOBB Roy R. , HEMLER Martin E.
Published: August 2015

A single-chain antibody construct was prepared containing the VH and VL regions of anti-(integrin α4) antibody HP1/2, an interchain linker and a KDEL endoplasmic reticulum retention sequence. Intracellular expression of this single-chain antibody caused cell-surface expression of α4β1 integrin to be decreased by 80% on selected RD cells and by 65–100% on selected Jurkat cells, relative to mock transfectants. Immunoprecipitation from single-chain-antibody-transfected cells showed that the single-chain antibody was complexed with the integrin α4 and β1 subunits, and the diminished sizes of α4 and β1 were consistent with impaired maturation. Furthermore, cell adhesion to α4β1 ligands [VCAM-1 (vascular cell adhesion molecule-1), FN40 (40 kDa chymotryptic fragment of fibronectin) and CS1] was greatly impaired in both RD and Jurkat cells, and cell spreading on immobilized FN40 protein was almost completely eliminated. Thus we conclude that intracellular single-chain antibodies may be used to reduce or eliminate cell-surface expression of a specific integrin, with specific functional consequences. This approach should be generally applicable to other integrin subunits.
Induction of cell surface blebbing by increased cellular Pi concentration
Authors: MARCUSSEN Mads
Published: August 2015

Cell surface blebbing is an early, reversible characteristic of anoxia described in several different cell types. Blebbing may lead to the formation of large terminal blebs, and ultimately cell death upon rupture of the membrane. In the present work, evidence is presented indicating that Pi may be the immediate mediator of cell surface blebbing: (1) cell surface blebbing can be induced in normoxic Ehrlich ascites tumour cells by a high extracellular concentration of Pi, leading to an increase in the cellular Pi concentration; (2) anoxia induces sustained elevation of the cellular Pi concentration and (3) cell surface blebbing during anoxia is reversed upon reoxygenation, and the disappearence of blebbing depends on the decrease in cellular Pi concentration. The rate of disappearence of blebs may be enhanced by the simultaneous addition of adenine and inosine to the growth medium. This leads to a decrease in cellular Pi concentration and to an almost complete restoration of the cellular ATP concentration. It is suggested that Pi is an important mediator of anoxia induced cell damage.
Identification of a novel proteinase (ameloprotease-I) responsible for the complete degradation of amelogenin during enamel maturation
Authors: MORADIAN-OLDAK Janet , LEUNG Wendy , SIMMER James P. , ZEICHNER-DAVID Margarita , FINCHAM Alan G
Published: August 2015

During enamel formation the proteins of the extracellular matrix, particularly amelogenins, are removed prior to maturation. In order to investigate this process and to improve our understanding of the function of proteinases during enamel maturation, proteinase fractions were isolated from developing pig enamel and assayed for proteolytic activity in vitro. A recombinant murine amelogenin, M179, was used as a substrate. Two major groups of enamel proteinases were defined as high-molecular-mass [‘high-molecular-weight’ in Moradian-Oldak, Simmer, Sarte, Zeichner-David and Fincham (1994) Arch. Oral Biol. 39, 647–656] and low-molecular-mass proteinases. Here we report the characterization of one of the proteinases present in the low-molecular-mass group. We demonstrate that this proteinase is a serine proteinase capable of degradation of M179 following cleavage of the tyrosine-rich amelogenin polypeptide from the N-terminal region. A partial N-terminal sequence of the proteinase was obtained (LPHVPHRIPPGYGRPXTXNEEGXNPYFXFFXXHG). An anti-peptide antibody directed against a synthetic peptide corresponding to the first 14 amino acids of the above sequence was produced. The presence of the proteinase in the acetic acid extract was confirmed by Western blotting. Searching using the amino acid sequence determined in this study showed it to be also present in the 32 kDa and 89 kDa enamelin proteins reported by Fukae, Tanabe, Murakami and Tohi [(1996) Adv. Dent. Res., in the press]. We therefore identify the 32 kDa enamelin as an enamel proteinase (‘ameloprotease-I’) which is responsible for amelogenin degradation in maturing enamel. We propose that the 89 kDa enamelin is a precursor of ameloprotease-I, the first enamel protein for which a function has been defined.
Purification and biochemical characterization of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate-sensitive l-glutamate receptors of pig brain
Authors: CHANG Yen-Chung , WU Tzong-Yuan , LI Bee-Fen , GAO Ling-Hao , LIU Chun-I , WU Chia-Lin
Published: August 2015

Two preparations of glutamate receptors were purified from the synaptic junctions of pig brain by a combination of detergent solubilization, anion-exchange chromatography, wheat-germ agglutinin affinity chromatography and sedimentation through sucrose gradients. These preparations were enriched in specific L-[3H]glutamate binding activity (> 5000 pmol of glutamate binding sites/mg of protein), and the rank order of ligand affinity for binding to these preparations was: quisqualate > 6-cyano-7-nitroquinoxaline-2,3-dione > α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) > L-glutamate > kainate ≫ N-methyl-D-aspartate≈ L-2-amino-4-phosphonobutyrate. SDS/PAGE analysis revealed that more than 80% of the protein in either of these preparations appeared as a single protein band of 106 kDa. Two-dimensional gel electrophoresis further revealed that these 106 kDa proteins consisted of a series of acidic proteins which were recognized by antibodies against rat AMPA receptor subunits. These 106 kDa proteins were also recognized by wheat-germ agglutinin and concanavalin A; in addition, peptide N-glycosidase F treatment of these preparations decreased their size to 99 kDa. Our results suggest that the putative glutamate receptors isolated here are likely to belong to the AMPA subtype of glutamate receptors in pig brain. Using the purification procedure reported here, 5 µg of AMPA receptor proteins can be isolated from 250 g of pig brain tissue.
Post-transcriptional regulation of H-ferritin gene expression in human monocytic THP-1 cells by protein kinase C
Authors: PANG Jong-Hwei S. , WU Chia-Jung , CHAU Lee-Young
Published: August 2015

The mRNA coding for H-ferritin was highly induced in human monocytic THP-1 cells following treatment with phorbol 12-myristate 13-acetate (PMA). The induction was detected at 3 h, reached maximal levels at 12 h, and was sustained for up to 48 h subsequent to PMA exposure. PMA-induced up-regulation of H-ferritin gene expression was also observed in other leukaemic cell lines, HL60 and U937, but not in non-leukaemic cell types, including human fibroblasts, endothelial cells and smooth muscle cells. The effect of PMA could be completely blocked by the protein kinase C inhibitor, H-7. Furthermore, treatment of THP-1 cells with bacterial phospholipase C also produced a marked increase in expression of H-ferritin mRNA, suggesting the activation of protein kinase C was responsible for the accumulation of mRNA. Nuclear run-off experiments demonstrated that PMA did not increase the transcriptional rate of the H-ferritin gene. In contrast, the half-life of the H-ferritin mRNA measured in the presence of actinomycin D was greatly prolonged in PMA-treated cells. The induction of H-ferritin mRNA by PMA required no protein synthesis. Conversely, treatment of THP-1 cells with protein synthesis inhibitor, cycloheximide, resulted in a 4–5-fold increase in H-ferritin mRNA. The increase in the stability of the H-ferritin mRNA was also observed in cells treated with cycloheximide. Taken together, these results suggest that the stability of H-ferritin mRNA in THP-1 is subjected to regulation via a protein kinase C-mediated phosphorylation on existing putative protein factor(s).
Nitric oxide-dependent NAD linkage to glyceraldehyde-3-phosphate dehydrogenase: possible involvement of a cysteine thiyl radical intermediate
Authors: MINETTI Maurizio , PIETRAFORTE Donatella , Michela DI STASI A. M. , MALLOZZI Cinzia
Published: August 2015

Previous studies have demonstrated that glyceraldehyde-3-phosphate dehydrogenase (GAPDH) undergoes NAD(H) linkage to an active site thiol when it comes into contact with •NO-related oxidants. We found that a free-radical generator 2,2´-azobis-(2-amidinopropane) hydrochloride (AAPH), which does not release either •NO or •NO-related species, was indeed able to induce the NAD(H) linkage to GAPDH. We performed spin-trapping studies with purified apo-GAPDH to identify a putative thiol intermediate produced by AAPH as well as by •NO-related oxidants. As •NO sources we used •NO gas and two •NO-donors, S-nitroso-N-acetyl-D,L-penicillamine and 3-morpholinosydnonimine hydrochloride (SIN-1). Because SIN-1 produces •NO and a superoxide radical simultaneously, we also tested the effects of peroxynitrite. All the •NO-related oxidants were able to induce the linkage of NAD(H) to GAPDH and the formation of a protein free-radical identified as a thiyl radical (inhibited by N-ethylmaleimide). •NO gas and the •NO-donors required molecular oxygen to induce the formation of the GAPDH thiyl radical, suggesting the possible involvement of higher nitrogen oxides. Thiyl radical formation was decreased by the reconstitution of GAPDH with NAD+. Apo-GAPDH was a strong scavenger of AAPH radicals, but its scavenging ability was decreased when its cysteine residues were alkylated or when it was reconstituted with NAD+. In addition, after treatment with AAPH, a thiyl radical of GAPDH was trapped at high enzyme concentrations. We suggest that the NAD(H) linkage to GAPDH is mediated by a thiyl radical intermediate not specific to •NO or •NO-related oxidants. The cysteine residue located at the active site of GAPDH (Cys-149) is oxidized by free radicals to a thiyl radical, which reacts with the neighbouring coenzyme to form Cys-NAD(H) linkages. Studies with the NAD+ molecule radiolabelled in the nicotinamide or adenine portion revealed that both portions of the NAD+ molecule are linked to GAPDH.
Nicotinamide inhibits cyclic ADP-ribose-mediated calcium signalling in sea urchin eggs
Authors: SETHI Jaswinder K , EMPSON Ruth M , GALIONE Antony
Published: August 2015

Cyclic ADP ribose (cADPR) is a potent Ca2+-releasing agent, and putative second messenger, the endogenous levels of which are tightly regulated by synthetic (ADP-ribosyl cyclases) and degradative (cADPR hydrolase) enzymes. These enzymes have been characterized in a number of mammalian and invertebrate tissues and their activities are often found on a single polypeptide. β-NAD+, cGMP and nitric oxide (NO) have been reported to mobilize Ca2+ in the sea urchin egg via the cADPR-mediated pathway. We now report that in sea urchin egg homogenates, nicotinamide inhibits the Ca2+-mobilizing action of β-NAD+, cGMP and NO, but has no effect on cADPR-induced Ca2+ release. Moreover, nicotinamide inhibits cGMP-induced regenerative Ca2+ waves in the intact sea urchin egg. By successfully separating the cADPR-metabolizing machinery from that which releases Ca2+, we have shown that nicotinamide inhibits cADPR-mediated Ca2+ signalling at the level of cADPR generation. Importantly, nicotinamide had no effect upon the hydrolysis of cADPR, and its selective action on cyclase activity was supported by its inhibition of purified Aplysia ADP-ribosyl cyclase, which does not exhibit detectable hydrolytic activity. The action of nicotinamide in blocking Ca2+ release by β-NAD+, cGMP and NO strongly suggests that these agents act as modulators of cADPR synthesis rather than to sensitize calcium release channels to cADPR.
Phorbol 12-myristate 13-acetate inhibits epidermal growth factor signalling in human keratinocytes, leading to decreased ornithine decarboxylase activity
Authors: XUE Guo Z , ZHENG Zai S , CHEN Rong Z , LLOYD Mary B. , PRYSTOWSKY Janet H.
Published: August 2015

Several studies have suggested that murine and human keratinocytes respond differently to phorbol 12-myristate 13-acetate (PMA). Using an in vitro assay, we found that in contrast to its effect on murine skin, PMA did not induce ornithine decarboxylase (ODC) activity in human skin biopsies. To explore the signalling induced by PMA and to determine whether an in vitro culture system could be used to predict biological activity of retinoids in human keratinocytes, we studied a simian virus 40 (SV40)-transformed human keratinocyte cell line. Epidermal growth factor (EGF) stimulates ODC activity and increases the steady-state level of ODC mRNA in a dose- and time-dependent manner in these cells [Prystowsky, Clevenger and Zheng (1993) Exp. Dermatol. 2, 125–132]. In this report, 10-10 M–10-7 M PMA induced ODC mRNA and enzyme synthesis at 7 h, but did not significantly induce ODC activity and inhibited the EGF induction of ODC activity. To explore the mechanism whereby PMA interferred with EGF signalling, the effect of PMA on EGF binding to its cell-surface receptor was studied; acute treatment with PMA (within 7 h) decreased EGF binding to 41–57% of the baseline level. In contrast, chronic treatment with PMA (24 h) increased EGF binding to 156% of the baseline level and was associated with an increase in quantity of EGF receptor protein. Protein kinase C (PKC) activation correlated with the acute decrease in EGF binding following PMA treatment. In summary, PMA induced ODC mRNA and ODC enzyme synthesis, while steady-state levels of immunoprecipitable ODC enzyme protein and ODC activity were not increased, demonstrating possible increased turnover of ODC enzyme protein. Additionally, PMA inhibited the induction of ODC by EGF through decreased EGF binding, possibly mediated by PKC activation. Finally treatment of the keratinocytes with retinoids including etretinate, Ro13-7410, etarotene, Ro40-8757, 13-cis-retinoic acid, and acitretin blocked the PMA induction of ODC mRNA, suggesting this in vitro model could be a valuable screening assay for predicting biological activity in humans.
An amino acid channel activated by hypotonically induced swelling of Leishmania major promastigotes
Authors: VIEIRA Lita L , LAFUENTE Esther , GAMARRO Francisco , CABANTCHIK Z. Ioav
Published: August 2015

Leishmania promastigotes accumulate amino acids (AAs) by an uphill transport mechanism that is dependent on membrane potential. The accumulated AAs provide the cell with an osmotic reservoir that can be utilized for osmoregulation. Exposure of Leishmania promastigotes to hypotonic media induced a rapid release of AAs that was proportional to the imposed osmotic gradients and independent of the ionic strength or the presence of Cl-, K+, Na+ or Ca2+ in the medium. The hypotonically activated AA release pathway was of relatively low chemical specificity. The solutes released included most of the zwitterionic and anionic AAs, predominantly alanine, hydroxyproline, glycine and glutamic acid, whereas cationic AAs were virtually excluded. AA release was markedly blocked by classical anion transport inhibitors such as the disulphonic stilbene 4,4´-di-isothiocyanostilbene-2,2´-disulphonate (DIDS) and its dihydro derivative H2DIDS and others, by restoration of isotonicity or by lowering the temperature (4 °C). The temperature profile of AA release showed a low energy of activation (Ea 46±1.3 (S.E.M.) kJ/mol) in the range 15-30 °C and a very high Ea (147±8 kJ/mol) in the range 4–15 °C. Parasites exposed to hypotonic media containing AAs also showed a hypotonically stimulated AA uptake under favourable solute concentration gradients. This uptake was analogous for L- and D-isomers of threonine. After hypotonic exposure, cells underwent a depolarization that was largely prevented by anion transport blockers. On the basis of all these results we propose that after hypotonic stress Leishmania promastigotes restore their internal volume by a regulated release of AAs, which involves activation of channels that allow the passage of both neutral and anionic AAs and possibly other anionic substances.
Glutathione S-transferase class Kappa: characterization by the cloning of rat mitochondrial GST and identification of a human homologue
Authors: PEMBLE Sally E , WARDLE Anthony F , TAYLOR John B
Published: August 2015

We have isolated a cDNA clone that encodes rat glutathione S-transferase (GST) subunit 13, a GST originally isolated from rat liver mitochondrial matrix by Harris, Meyer, Coles and Ketterer [(1991) Biochem. J. 278, 137–141]. The 896 bp cDNA contains an open reading frame of 678 bp encoding a deduced protein sequence of which the first 33 residues (excluding the initiation methionine residue) correspond to the N-terminal sequence reported by Harris et al. Hence like many other nuclear-encoded, mitochondrially located proteins, there is no cleavable mitochondrial presequence at the N-terminus. GST subunit 13 was originally placed into the Theta class of GSTs on the basis of sequence identity at the N-terminus; however, this is the only identity with the Theta class and in fact GST subunit 13 shows little sequence similarity to any of the known GST classes. Most importantly it lacks the SNAIL/TRAIL motif that has so far been a characteristic of soluble GSTs, although it does possess a second motif (FGXXXXVXXVDGXXXXXF) reported for GST-related proteins (Koonin, Mushegian, Tatusov, Altschul, Bryant, Bork and Valencia [(1994) Protein Sci. 3, 2045–2054]. Southern and Northern blot analyses of rat DNA and mRNA are consistent with GST subunit 13's being the product of a single hybridizing gene locus. Searches of EST databases identified numerous similar human DNA sequences and a single pig sequence. We have derived a human cDNA sequence from these EST sequences which shows a high nucleotide similarity (77%) to rat GST subunit 13. The largest open reading frame is identical in length with subunit 13 and yields a deduced protein sequence identity of 70%. Most unusually the 3´ non-coding nucleotide sequence identity is also 77%. We conclude that these cDNAs belong to a novel GST class hereby designated Kappa, with the rat GST subunit 13 gene designated rGSTK1 and the human gene being called hGSTK1.
Induction of the membrane alanyl aminopeptidase gene and surface expression in human T-cells by mitogenic activation
Authors: LENDECKEL Uwe , WEX Th. , REINHOLD D. , KÄHNE Th. , FRANK K. , FAUST J. , NEUBERT K. , ANSORGE S.
Published: August 2015

The metal-dependent membrane alanyl aminopeptidase (aminopeptidase N, APN, CD13; EC 3.4.11.2) is a well-established marker of normal and malignant cells of the myelo-monocytic lineage. It is also expressed by leukaemic blasts of a small group of patients suffering from acute or chronic lymphoid leukaemia. CD13-specific monoclonal antibodies do not bind to the surface of normal B lymphocytes, and APN mRNA was not detectable by Northern analysis in normal lymphocytes or in T-cell lines. Recently the expression of the APN gene in T-cell lines as well as the ability of these cells to cleave chromogenic substrates preferred by APN have been demonstrated [Lendeckel, Wex, Kähne, Frank, Reinhold and Ansorge (1994) Cell. Immunol. 153, 214–226]. Here, by means of dot-blot hybridization and RNase protection assay, evidence is provided that human peripheral T-cells as well as derived cell lines contain significant amounts of APN mRNA, comparable to that in the promyeloic cell line U937, and that mitogenic activation of peripheral human T-cells leads to a more than 4-fold increase in their APN mRNA content. In the course of activation, T-cells increase their total alanine p-nitroanilide-hydrolysing activity to approx. 7-fold that of resting cells. Furthermore these cells become immunoreactive towards CD13 to a significant extent (up to 51%) as shown by surface staining and confirmed by activity staining and immunostaining after isoelectric focusing (pI of T-cell APN = 4.6). In addition it is demonstrated by fluorescence microscopy that viable, activated T-cells effectively cleave the fluorogenic aminopeptidase substrate bis-glycyl-rhodamine 110 and that the corresponding aminopeptidase activity is associated with the cell surface. We show that specific inhibitors of APN, probestin and actinonin, strongly decrease DNA synthesis in phytohaemagglutinin (PHA)-stimulated T-cells. In summary, evidence is presented that in the course of mitogenic activation human peripheral T-cells increase the expression of APN both at the transcriptional level and at the cell surface. This has been demonstrated both at the APN mRNA level and at the protein level with respect to aminopeptidase enzymic activity and CD13 immunoreactivity.
Primary structure of the cytosolic β-glucosidase of guinea pig liver
Authors: HAYS William S , JENISON Steven A. , YAMADA Takashi , PASTUSZYN Andrzej , GLEW Robert H.
Published: August 2015

The cytosolic β-glucosidase (EC 3.2.1.21) present in the livers of mammalian species is distinguished by its broad specificity for sugars and its preference for hydrophobic aglycones. We purified the cytosolic β-glucosidase from guinea pig liver and sequenced 142 amino acid residues contained within 12 trypsin digest fragments. Using degenerate oligonucleotide primers deduced from the peptide sequences, a 622 bp cytosolic β-glucosidase cDNA was amplified by reverse-transcriptase PCR, using total guinea pig liver RNA as template. The ‘rapid amplification of cDNA ends (RACE)’ method [Frohman (1993) Methods Enzymol. 218, 340–356] was used to synthesize the remaining segments of the full-length cDNA. The complete cDNA contained 1671 nucleotides with an open reading frame coding for 469 amino acid residues. The amino acid sequence deduced from the cDNA sequence included the amino acid sequences of all 12 trypsin digest fragments derived from the purified enzyme. Amino acid sequence analysis indicates that the guinea pig liver cytosolic β-glucosidase is a Family 1 β-glycosidase and that it is most closely related to mammalian lactase-phlorizin hydrolase. These results suggest that the cytosolic β-glucosidase and lactase-phlorizin hydrolase diverged from a common evolutionary precursor.
Divergent effects of α1-antitrypsin on the regulation of iron metabolism in human erythroleukaemic (K562) and myelomonocytic (THP-1) cells
Authors: WEISS Günter , GRAZIADEI Ivo , URBANEK Martina , GRÜNEWALD Kurt , VOGEL Wolfgang
Published: August 2015

The acute-phase protein α1-antitrypsin (α1-AT) has been shown to inhibit the binding of transferrin to its cell-surface receptor. Here we demonstrate that in human erythroleukaemic cells (K562) α1-AT enhances the binding affinity of iron-regulatory protein (IRP), the central regulator of cellular iron metabolism, to iron-responsive elements. Activation of IRP by α1-AT is associated with a marked increase in transferrin receptor (trf-rec) mRNA levels in K562 and enhanced cell-surface expression of transferrin-binding sites, whereas ferritin production is decreased, although ferritin mRNA levels remain unchanged. In agreement with the well-established mechanism of cellular iron regulation, α1-AT seems to modulate trf-rec and ferritin expression primarily post-transcriptionally/translationally by influencing IRP activity. In contrast, α1-AT produces only minor changes in IRP activity, and subsequently in trf-rec expression and ferritin synthesis in THP-1 cells. Moreover the effects of α1-AT on iron homeostasis in K562 cannot be overcome by the addition of iron salts, whereas concomitant treatment of THP-1 with iron and α1-AT results in the same metabolic changes as the addition of iron alone. Because α1-AT blocks transferrin binding on K562 as well as on THP-1 cells, it is suggested, on the basis of the results presented here, (1) that erythroid and monocytic cells might differ in their dependence on transferrin-mediated iron supply and (2) that THP-1 might be able to acquire iron by a transferrin-independent iron uptake system. α1-AT might therefore be involved in the diversion of iron traffic between various cellular compartments under inflammatory conditions.
Hypusine modification in eukaryotic initiation factor 5A in rodent cells selected for resistance to growth inhibition by ornithine decarboxylase-inhibiting drugs
Authors: TOME Margaret E , GERNER Eugene W
Published: August 2015

Selection of HTC cells in drugs that inhibit ornithine decarboxylase (ODC) has produced two cell lines, HMOA and DH23A/b, that contain increased amounts of more stable ODC. In addition to alterations in ODC, these cells appear to produce modified eukaryotic initiation factor 5A (eIF-5A) at different rates, a reaction that both requires spermidine and is essential for proliferation. Alterations to the modification of eIF-5A by spermidine cannot be accounted for by changes in eIF-5A protein or modified eIF-5A turnover. Deoxyhypusine synthetase activity is similar in the parental and variant cell lines and is unaltered by growth into plateau phase or by spermidine depletion. The increased rate of eIF-5A modification in DH23A/b cells is due to an increased accumulation of the unmodified eIF-5A precursor. Increased precursor accumulation is not due to increased eIF-5A transcription, but rather it can be attributed to a metabolic accumulation caused by growth under conditions of chronically limiting spermidine. Selection using drugs that inhibit ODC apparently does not cause alterations in the eIF-5A modification pathway. These data support the hypothesis that one of the main effects of spermidine depletion is depletion of the modified eIF-5A pool, and that this is a critical factor in the cytostasis often observed after depletion of cellular polyamines.
Bombesin and thrombin affect discrete pools of intracellular calcium through different G-proteins
Authors: WANG Jin-Lin , KALYANARAMAN Somasundaram , DE VIVO Michael , GAUTAM Narasimhan
Published: August 2015

In mouse NIH 3T3 cells, the mitogens bombesin and thrombin induced Ca2+ release from intracellular stores. Ca2+ release induced by bombesin was inhibited by the Ca2+-ATPase inhibitor thapsigargin, while Ca2+ release induced by thrombin was unaffected by this agent. The Ca2+-release response to bombesin was not affected by pertussis toxin, but the response to thrombin was abolished by the toxin. Stable transfectants overexpressing the G-protein subunit type αq showed an accentuated response to bombesin, indicating that the bombesin receptor was coupled to a Gq-like G-protein. Together, these results show that the two mitogenic receptors are coupled to distinct G-proteins that affect functionally different pools of Ca2+. Organization of signalling pathways in this manner may allow cells to differentially encode information from different signals.
Production of the R2 subunit of ribonucleotide reductase from herpes simplex virus with prokaryotic and eukaryotic expression systems: higher activity of R2 produced by eukaryotic cells related to higher iron-binding capacity
Authors: LAMARCHE Nathalie , MATTON Gilles , MASSIE Bernard , FONTECAVE Marc , ATTA Mohamed , DUMAS France , GAUDREAU Pierrette , LANGELIER Yves
Published: August 2015

The R2 subunit of ribonucleotide reductase from herpes simplex virus type 2 was overproduced with prokaryotic and eukaryotic expression systems. The recombinant R2 purified by a two-step procedure exhibited a 3-fold higher activity when produced in eukaryotic cells. Precise quantification of the R2 concentration at each step of the purification indicated that the activity was not altered during the purification procedure. Moreover, we have observed that the level of R2 expression, in eukaryotic cells as well as in prokaryotic cells, did not influence R2 activity. Extensive characterization of the recombinant R2 purified from eukaryotic and prokaryotic expression systems has shown that both types of pure R2 preparations were similar in their 76 kDa dimer contents (more than 95%) and in their ability to bind the R1 subunit. However, we have found that the higher activity of R2 produced in eukaryotic cells is more probably related to a higher capability of binding the iron cofactor as well as a 3-fold greater ability to generate the tyrosyl free radical.
Purification and properties of cystathionine β-lyase from Arabidopsis thaliana overexpressed in Escherichia coli
Authors: RAVANEL Stéphane , JOB Dominique , DOUCE Roland
Published: August 2015

Cystathionine β-lyase is a key enzyme in sulphur metabolism that catalyses the second reaction specific for methionine biosynthesis, the pyridoxal 5´-phosphate-dependent β-cleavage of cystathionine to produce homocysteine. To obtain insight into the biochemical properties of the plant enzyme, the cDNA encoding cystathionine β-lyase from Arabidopsis thaliana was used to construct an overproducing Escherichia coli strain. The recombinant enzyme was isolated at high yield (29 mg of pure protein/litre of cell culture) using an efficient two-step purification procedure. Physicochemical properties of the Arabidopsis cystathionine β-lyase were similar to those previously reported for the bacterial enzymes. In particular, the native recombinant protein is a tetramer composed of four identical subunits of 46 kDa, each being associated with one molecule of pyridoxal 5´-phosphate. Interaction between the apoenzyme and pyridoxal 5´-phosphate is extremely tight, being characterized by a Kd value of 0.5 µM. Purification and sequencing of the phosphopyridoxyl peptide established that Schiff base formation between the cofactor and the holoenzyme occurs at lysine-278. The substrate specificity of the recombinant cystathionine β-lyase resembles that of the enzyme isolated from other sources, cystathionine and djenkolate being the most effective substrates. The cystathionine analogue aminoethoxyvinylglycine irreversibly inactivates the recombinant cystathionine β-lyase. The inactivation is accompanied by dramatic modification of the spectral properties of the enzyme that can be attributed to the attack of the azomethine linkage between pyridoxal 5´-phosphate and lysine-278 of the polypeptide by aminoethoxyvinylglycine.
Protein kinase C in cultured human placental trophoblasts: identification of isoforms and role in cAMP signalling
Authors: KARL Peter I. , DIVALD Andras
Published: August 2015

The protein kinase C (PKC) superfamily is a family of serine/threonine kinases involved in the regulation of many cell functions. The objective of the present work was to identify the PKC isoenzymes present in human placental trophoblasts and to compare their relative responses to acute and chronic phorbol 12-myristate 13-acetate (PMA) treatment. In addition, the effect of PMA treatment on ligand-stimulated cAMP production was determined. In total extracts prepared from cultured or freshly purified trophoblasts, PKC isoforms α, ε and ζ were detected. Following acute treatment with PMA, PKCα and PKCε were translocated from the cytosol to the particulate fraction. Prolonged treatment (up to 36 h) with PMA resulted in the temporal down-regulation of PKCα and PKCε. PKCζ did not respond to either acute or chronic treatment with PMA. An acute 10 min treatment of the cells with PMA (10-10–10-6 M) enhanced isoprenaline- and adrenaline-stimulated cAMP production. An enhanced response was observed at all concentrations of isoprenaline tested (10-9–10-4 M), suggesting an increased capacity to respond. The acute PMA effect was evident within 2 min and near maximal by 5 min. The acute response to PMA was lost in cells where PKC was down-regulated by prior PMA treatment. Epidermal growth factor, a potential ligand for the activation of PKC in trophoblasts, enhanced isoprenaline-stimulated cAMP production. In summary, activation of PMA-responsive PKCs (PKCα or PKCε) appears to enhance ligand-stimulated cAMP production in trophoblasts. This may be a physiologically important example of ‘cross-talk’ between various signalling pathways in human placental trophoblasts.
High-affinity binding of laurate to naturally occurring mutants of human serum albumin and proalbumin
Authors: KRAGH-HANSEN Ulrich , PEDERSEN Anders Overgaard , GALLIANO Monica , MINCHIOTTI Lorenzo , BRENNAN Stephen O. , TÁRNOKY András L. , FRANCO Maria H. L. P. , SALZANO Francisco M.
Published: August 2015

Binding of laurate (n-dodecanoate) to genetic variants of albumin or its proprotein and to normal albumin isolated from the same heterozygous carriers was studied by a kinetic dialysis technique at physiological pH. The first stoichiometric association constant for binding to proalbumin Lille (Arg-2 → His) and albumin (Alb) Roma (Glu321 → Lys) was increased to 126% and 136% respectively compared with that for binding to normal albumin, whereas the constant for Alb Maku (Lys541 → Glu) was decreased to 80%. In contrast, normal laurate-binding properties were found for as many as nine other albumin variants with single amino acid substitutions. Because the net charges of all these mutants were different from that of normal albumin, the results suggest that the examples of modified laurate binding are not caused by long-range electrostatic effects. Rather, the three positions mentioned are located close to different binding sites for the fatty acid anion. The most pronounced effect was observed for the glycosylated Alb Casebrook, the binding constant of which was decreased to 20%. Binding to the glycosylated Alb Redhill was also decreased, but to a smaller extent (68%). These decreases in binding are caused by partial or total blocking of the high-affinity site by the oligosaccharides, by the negative charges of the oligosaccharides, and/or by conformational changes induced by these bulky moieties. Laurate binding to two chain-termination mutants (Alb Catania and Alb Venezia) was normal, indicating that the C-terminus of albumin is not important for binding. By using different preparations of normal albumin as controls in the binding experiments, it was also possible to compare the effect of various methods for isolation and defatting on laurate binding.