bluuebunny/crossref_metadata_2025 huggingface dataset:
Partial purification and characterization of a wortmannin-sensitive and insulin-stimulated protein kinase that activates heart 6-phosphofructo-2-kinase
Authors: DEPREZ Johan , BERTRAND Luc , ALESSI Dario R. , KRAUSE Ulrike , HUE Louis , RIDER Mark H.
Published: August 2015

A wortmannin-sensitive and insulin-stimulated protein kinase (WISK), which phosphorylates and activates cardiac 6-phosphofructo-2-kinase (PFK-2), was partially purified from perfused rat hearts. Immunoblotting showed that WISK was devoid of protein kinase B (PKB), serum- and glucocorticoid-regulated protein kinase and protein kinase Cζ (PKCζ). Comparison of the inhibition of WISK, PKCα and PKCζ by different protein kinase inhibitors suggested that WISK was not a member of the PKC family. In addition, WISK contained no detectable phosphoinositide-dependent protein kinase-1 (PDK1) activity. WISK phosphorylated recombinant heart PFK-2 in a time-dependent manner to the extent of 0.4 mol of phosphate incorporated/mol of enzyme subunit, and increased the Vmax of PFK-2 twofold, without affecting the Km for fructose 6-phosphate. WISK phosphorylated Ser-466 to a greater extent than Ser-483 in recombinant heart PFK-2, and both sites were demonstrated to be phosphorylated to the same extent by PKB. Gel filtration and in-gel kinase analysis indicated that WISK was a monomer with a Mr of 56500. Treatment of WISK with protein phosphatase 2A (PP2A) catalytic subunits reversed the effect of insulin, suggesting the involvement of an upstream activating kinase. Indeed, PDK1 was able to partially reactivate the PP2A-treated WISK and this reactivation was not enhanced by PtdIns(3,4,5)P3-containing vesicles. Moreover, a single 57000-Mr band was labelled on incubation of the dephosphorylated WISK preparation with PDK1 and [γ-32P]ATP. These findings provide evidence for the existence of a new protein kinase in the insulin signalling pathway, probably downstream of PDK1.
Regulation of cytochrome P450 (CYP) genes by nuclear receptors
Authors: HONKAKOSKI Paavo , NEGISHI Masahiko
Published: August 2015

Members of the nuclear-receptor superfamily mediate crucial physiological functions by regulating the synthesis of their target genes. Nuclear receptors are usually activated by ligand binding. Cytochrome P450 (CYP) isoforms often catalyse both formation and degradation of these ligands. CYPs also metabolize many exogenous compounds, some of which may act as activators of nuclear receptors and disruptors of endocrine and cellular homoeostasis. This review summarizes recent findings that indicate that major classes of CYP genes are selectively regulated by certain ligand-activated nuclear receptors, thus creating tightly controlled networks.
27-Oxygenation of C27-sterols and 25-hydroxylation of vitamin D3 in kidney: cloning, structure and expression of pig kidney CYP27A
Authors: POSTLIND Hans , HOSSEINPOUR Fardin , NORLIN Maria , WIKVALL Kjell
Published: August 2015

This paper describes the molecular cloning of a cytochrome P450 enzyme in pig kidney that catalyses the hydroxylations of vitamin D3 (cholecalciferol) and C27-sterols. DNA sequence analysis of the cDNA revealed that the enzyme belongs to the CYP27 family. The first 36 amino acids have many hallmarks of a mitochondrial signal sequence. The mature pig kidney CYP27 protein contains 498 amino acids. The Mr of the mature protein was calculated to be 56607. The structure of pig kidney CYP27, as deduced by DNA sequence analysis, shows 77-83% identity with CYP27A in rat, rabbit and human liver. Transfection of the renal CYP27A cDNA into simian COS cells resulted in the synthesis of an enzyme that catalysed the 25-hydroxylation of vitamin D3 and the 27-hydroxylation of 5β-cholestane-3α,7α,12α-triol, and the further oxidation of the product into the corresponding C27-acid 3α,7α,12α-trihydroxy-5β-cholestanoic acid. As part of these studies, the enzymic activities of cultured human embryonic kidney cells were examined using vitamin D3 and C27-sterols as substrates. The cells were found to express CYP27A mRNA and to convert the respective substrates into the same products as recombinantly expressed CYP27A, i.e. 25-hydroxyvitamin D3 and 27-oxygenated C27-sterols. The results of the present study describing the structure and expression of CYP27A in kidney suggest that this enzyme is involved in the renal metabolism of vitamin D3 and that the kidney plays a role in the metabolism of cholesterol and other C27-sterols.
Glucose and amino acids modulate translation factor activation by growth factors in PC12 cells
Authors: KLEIJN Miranda , PROUD Christopher G.
Published: August 2015

In PC12 phaeochromocytoma cells, protein synthesis is activated by epidermal and nerve growth factors (EGF and NGF). EGF and NGF also regulate a number of components of the translational machinery in these cells. Here we show that the ability of EGF and NGF to induce the phosphorylation of the 70 kDa ribosomal protein, S6 kinase, and the eukaryotic initiation factor (eIF), 4E-binding protein 1, is dependent upon the presence of amino acids (but not glucose) in the medium. This resembles the regulation of these proteins by insulin, which also requires amino acids. Glucose, but not amino acids, is required for the activation of eIF2B by EGF and NGF. In contrast, EGF and NGF can still activate protein synthesis in the absence of nutrients, suggesting that other regulatory events are important in this. In nutrient-deprived cells, an increase in the phosphorylation of eIF4E, and the assembly of the eIF4F complex by EGF and NGF, coincided with the activation of protein synthesis. In serum-starved cells, activation of protein synthesis, phosphorylation of eIF4E, and formation of the eIF4F complex, were blocked by inhibition of MEK, a component of the extracellular regulated kinase (ERK) signalling pathway. Thus the ERK pathway plays a key role in the regulation of protein synthesis in PC12 cells.
Lignin peroxidase initiates O2-dependent self-propagating chemical reactions which accelerate the consumption of 1-(3′,4′-dimethoxyphenyl)propene
Authors: TEN HAVE Rimko , FRANSSEN Maurice C. R. , FIELD Jim A.
Published: August 2015

Lignin peroxidase (LiP) has been used to study the Cα-Cβ cleavage of the propylene side chain in 1-(3ʹ,4ʹ-dimethoxyphenyl)propene (DMPP) to 3,4-dimethoxybenzaldehyde (veratraldehyde, VAD). Under an air atmosphere, LiP oxidized DMPP to VAD (27.8%) and 1-(3ʹ,4ʹ-dimethoxyphenyl)propan-2-one (DMPA, 8.7%), after 10 min of incubation. Dissolved O2 was rapidly consumed during DMPP conversion, of which one-third was converted into superoxide. The remaining two-thirds of the consumed O2 was involved in Cα-Cβ cleavage of DMPP to VAD and in self-propagating chemical reactions stimulating the consumption of DMPP. The involvement of peroxyl radicals, in the chemical consumption of DMPP, was confirmed by using the well-known peroxyl radical reductant Mn2+. This metal ion severely inhibited the DMPP consumption rate under air, but did not affect the lower enzymic DMPP consumption rate under N2. The substoichiometric requirement of LiP for H2O2 during DMPP oxidation could be explained in part by dismutation of superoxide, but more importantly by direct chemical reactions of DMPP-derived peroxyl radicals with fresh DMPP. Another VAD-producing route was found by incubating the DMPP oxidation product, DMPA, with LiP. Under air the molar yield of VAD was 29.7%. In the absence of O2, the Cα-Cβ cleavage of DMPA to VAD was strongly inhibited and side-chain coupling products (dimers) were formed instead. As a whole, the results suggest two new roles of O2 in LiP-mediated oxidation of aromatic substrates. First, O2 is responsible for the formation of reactive peroxyl intermediates, which can directly react with other substrate molecules and thereby accelerate consumption rates. Secondly, O2 can prevent coupling reactions by lowering the pool of carbon-centred radicals accumulating during LiP catalysis.
Role of lipids in the translocation of proteins across membranes
Authors: VAN VOORST Frank , DE KRUIJFF Ben
Published: August 2015

The architecture of cells, with various membrane-bound compartments and with the protein synthesizing machinery confined to one location, dictates that many proteins have to be transported through one or more membranes during their biogenesis. A lot of progress has been made on the identification of protein translocation machineries and their sorting signals in various organelles and organisms. Biochemical characterization has revealed the functions of several individual protein components. Interestingly, lipid components were also found to be essential for the correct functioning of these translocases. This led to the idea that there is a very intimate relationship between the lipid and protein components that enables them to fulfil their intriguing task of transporting large biopolymers through a lipid bilayer without leaking their contents. In this review we focus on the Sec translocases in the endoplasmic reticulum and the bacterial inner membrane. We also highlight the interactions of lipids and proteins during the process of translocation and integrate this into a model that enables us to understand the role of membrane lipid composition in translocase function.
Oxidative phosphorylation in cardiolipin-lacking yeast mitochondria
Authors: KOSHKIN Vasilij , GREENBERG Miriam L.
Published: August 2015

The role of cardiolipin in mitochondrial energy transformation was studied by comparing oxidative phosphorylation in the Saccharomyces cerevisiae cardiolipin synthase null mutant crd1∆, and in isogenic wild type. Oxygen consumption experiments and membrane potential kinetics during the phosphorylation cycle in isolated mitochondria indicated that the absence of cardiolipin causes only a moderate deficiency of mitochondrial energy-transforming machinery at 25 °C. However, at 40 °C, respiration was completely uncoupled from phosphorylation for the mutant mitochondria, in contrast with that for the wild-type. Membranepotential kinetics demonstrated an increased susceptibility of the mutant mitochondria to gradual deterioration during in vitro incubation. These results suggest that cardiolipin, although normally associated with several of the major enzymes of oxidative phosphorylation and required in vitro for their maximal activity, is not absolutely necessary for mitochondrial energy transformation under optimal conditions. The role of cardiolipin is, rather, to improve efficiency of oxidative phosphorylation and its resistance to unfavourable conditions, such as increased temperature.
Identification of abundant mRNAs from the third stage larvae of the parasitic nematode, Ostertagia ostertagi
Authors: MOORE Joyce , TETLEY Laurence , DEVANEY Eileen
Published: August 2015

Reverse transcriptase-PCR (RT-PCR) was carried out on total RNA prepared from the third-stage larvae (L3) of Ostertagia ostertagi in order to clone and characterize the major transcripts expressed in this larval stage, as an initial investigation of arrested larval development in the parasite. Distinct bands were visible on an agarose gel and four of these were cloned and sequenced. Three of the bands represented multiple transcripts, while the fourth band encoded the enzyme GTP cyclohydrolase I (GTP-CH), which catalyses the first and rate-limiting step in pteridine biosynthesis. Northern blot analysis and RT-PCR demonstrated that GTP-CH is highly up-regulated in the L3 stage and undetectable in either the L2 or adult stages. Using immunogold electron microscopy, GTP-CH was shown to be predominantly localized to the cell body of the body wall muscles and the cells of the intestine in the L3.
Endonuclease activity in lipocalins
Authors: YUSIFOV Taleh N. , ABDURAGIMOV Adil R. , GASYMOV Oktay K. , GLASGOW Ben J.
Published: August 2015

Several lipocalins contain conserved amino acid sequences similar to the phosphodiester bond cleavage domain of sugar non-specific magnesium-dependent nucleases of the Serratia marcescens type. His-89 and Glu-127 of the S. marcescens endonuclease are believed to have a role in the active catalytic site by the attack of a water molecule at the phosphorus atom of the bridging phosphate. Tear lipocalin contains both amino acids in analogous regions, and is active as a nuclease. Two forms of β-lactoglobulin contain only Glu-134 (analogous to Glu-127 of the Serratia nuclease) yet retain nuclease activity equal to or greater than that of tear lipocalin. However, retinol-binding protein lacks both of these motifs and shows no detectable activity. DNA-nicking activity is decreased by 80% in the mutant of tear lipocalin that replaces Glu-128 but is unchanged by mutations of His-84. The endonuclease activity of tear lipocalin is dependent on the bivalent cations Mg2+ or Mn2+ but is decreased at high concentrations of NaCl. These findings indicate that some lipocalins have non-specific endonuclease activity similar in characteristics to the Mg2+-dependent nucleases and related to the conserved sequence LEDFXR (where ‘X’ denotes ‘any other residue’), in which the glutamic residue seems to be important for activity.
Conserved Ca2+-antagonist-binding properties and putative folding structure of a recombinant high-affinity dihydropyridine-binding domain
Authors: HUBER Irene , WAPPL Edwin , HERZOG Alexander , MITTERDORFER Jörg , GLOSSMANN Hartmut , LANGER Thierry , STRIESSNIG Jörg
Published: August 2015

Sensitivity to 1,4-dihydropyridines (DHPs) can be transferred from L-type (α1C) to non-L-type (α1A) Ca2+ channel α1 subunits by the mutation of nine pore-associated non-conserved amino acid residues, yielding mutant α1ADHP. To determine whether the hallmarks of reversible DHP binding to L-type Ca2+ channels (nanomolar dissociation constants, stereoselectivity and modulation by other chemical classes of Ca2+ antagonist drugs) were maintained in α1ADHP, we analysed the pharmacological properties of (+)-[3H]isradipine-labelled α1ADHP Ca2+ channels after heterologous expression. Binding of (+)-isradipine (Ki 7.4 nM) and the non-benzoxadiazole DHPs nifedipine (Ki 86 nM), (±)-nitrendipine (Ki 33 nM) and (±)-nimodipine (Ki 67 nM) to α1ADHP occurred at low nanomolar Ki values. DHP binding was highly stereoselective [25-fold higher affinity for (+)-isradipine]. As with native channels it was stimulated by (+)-cis-diltiazem, (+)-tetrandrine and mibefradil. This suggested that the three-dimensional architecture of the channel pore was maintained within the non-L-type α1A subunit. To predict the three-dimensional arrangement of the DHP-binding residues we exploited the X-ray structure of a recently crystallized bacterial K+ channel (KcsA) as a template. Our model is based on the assumption that the Ca2+ channel S5 and S6 segments closely resemble the KcsA transmembrane folding architecture. In the absence of three-dimensional structural data for the α1 subunit this is currently the most reasonable approach for modelling this drug-interaction domain. Our model predicts that the previously identified DHP-binding residues form a binding pocket large enough to co-ordinate a single DHP molecule. It also implies that the four homologous Ca2+ channel repeats are arranged in a clockwise manner.
Purification and cloning of phosphatidylinositol transfer proteins from Dictyostelium discoideum: homologues of both mammalian PITPs and Saccharomyces cerevisiae Sec14p are found in the same cell
Authors: SWIGART Philip , INSALL Robert , WILKINS Andrew , COCKCROFT Shamshad
Published: August 2015

Soluble phosphatidylinositol transfer proteins (PITPs) have important roles in lipid-mediated signalling as well as in membrane traffic. Two PITPs (α and β) have been cloned from mammalian cells, which are unrelated in sequence to yeast PITP (the product of the SEC14 gene). However, all three PITPs can perform interchangeably to reconstitute function in mammalian cells. We have now purified the major PITP from the cytoplasm of Dictyostelium discoideum and cloned the gene. This protein, DdPITP1, is homologous with mammalian PITPα and PITPβ. We have also cloned a second gene (DdPITP2) related in sequence to DdPITP1. In addition, an independently cloned cDNA encodes a relative of the SEC14 family of yeast PITPs. DdPITP1, DdPITP2 and DdSec14 proteins were all able to mediate the transfer of PtdIns from one membrane compartment to another; they thus exhibited the hallmark of PITPs. Secondly, all three PITPs were able to rescue phospholipase C-mediated phosphoinositide hydrolysis in PITP-depleted HL60 cells, indicating that all three PITPs were capable of stimulating phosphoinositide synthesis. The identification of PITPs related to both mammalian PITPs and yeast Sec14p in a single organism will provide a unique opportunity to examine the functions of this class of protein with genetic approaches.
A novel 50 kDa protein forms complexes with protein phosphatase 4 and is located at centrosomal microtubule organizing centres
Authors: HASTIE C. James , CARNEGIE Graeme K. , MORRICE Nick , COHEN Patricia T. W.
Published: August 2015

Protein phosphatase 4 (PPP4) is a protein serine/threonine phosphatase that has been implicated in microtubule organization at centrosomes. Complexes of PPP4 with high apparent molecular masses (450 and 600 kDa) were purified from mammalian skeletal muscle and testis to near homogeneity. Amino acid sequences derived from a protein component present in both complexes were utilized to identify a human cDNA. The encoded putative PPP4 regulatory subunit (termed PPP4R2), comprising 453 amino acids, had a molecular mass of 50.4 kDa. The interaction of PPP4R2 with PPP4 catalytic subunit (PPP4c) was confirmed by co-sedimentation of PPP4c with PPP4R2 expressed in bacteria and human cells. PPP4c formed a complex of 450 kDa with baculovirus expressed His6-tagged PPP4R2. Immunocytological detection of PPP4R2 at centrosomes suggests that it may target PPP4c to this location. Native 450 kDa and 600 kDa PPP4 complexes are inactive, but can be activated by basic proteins, suggesting that PPP4R2 may also regulate the activity of PPP4c at centrosomal microtubule organising centres.
Role of N-oligosaccharide endoplasmic reticulum processing reactions in glycoprotein folding and degradation
Authors: PARODI Armando J.
Published: August 2015

The endoplasmic reticulum (ER) is the subcellular site where proteins following the secretory pathway acquire their proper tertiary and, in certain cases, quaternary structures. Species that are not yet properly folded are prevented from exit to the Golgi apparatus and, if permanently misfolded, are transported to the cytosol, where they are degraded in the proteasomes. This review deals with a mechanism, applicable to proteins that are N-glycosylated in the ER, by which the quality control of folding is performed. Protein-linked monoglucosylated glycans, formed by glucosidase I- and glucosidase II-dependent partial deglucosylation of the oligosaccharides transferred from dolichol diphosphate derivatives in N-glycosylation (Glc3Man9GlcNAc2), mediate glycoprotein recognition by two ER-resident lectins, membrane-bound calnexin (CNX) and its soluble homologue, calreticulin (CRT). A still not yet fully confirmed interaction between the lectins and the protein moieties of folding glycoproteins may occur after lectin recognition of monoglucosylated structures. Further deglucosylation of glycans by glucosidase II, and perhaps also by a change in CNX/CRT and/or in the substrate glycoprotein conformation, liberates the glycoproteins from their CNX/CRT anchors. Glycans may be then reglucosylated by the UDP-Glc:glycoprotein glucosyltransferase (GT), and thus be recognized again by CNX/CRT, but only when linked to not yet properly folded protein moieties, as this enzyme behaves as a sensor of glycoprotein conformation. Deglucosylation/reglucosylation cycles catalysed by the opposing activities of glucosidase II and GT only stop when proper folding is achieved. The interaction between CNX/CRT and a monoglucosylated glycan is one of the alternative mechanisms by which cells retain not yet properly folded glycoproteins in the ER; in addition, it enhances folding efficiency by preventing protein aggregation and thus allowing intervention of classical chaperones and other folding-assisting proteins. There is evidence suggesting that both glycoprotein glucosylation and mannose removal, respectively mediated by GT and ER mannosidase I, might be involved in cell recognition of permanently misfolded glycoproteins bound for proteasome degradation.
Cloning and characterization of ADAM28: evidence for autocatalytic pro-domain removal and for cell surface localization of mature ADAM28
Authors: HOWARD Linda , MACIEWICZ Rose A. , BLOBEL Carl P.
Published: August 2015

The metalloprotease disintegrins are a family of membrane-anchored glycoproteins with diverse functions in fertilization, myoblast fusion, neurogenesis and protein ectodomain shedding. Here we report a cDNA sequence, encoding a metalloprotease disintegrin, termed ADAM28 (‘a disintegrin and metalloprotease 28’), which was cloned from mouse lung. From protein sequence comparisons, ADAM28 is more closely related to snake venom metalloproteases (SVMPs) than to other ADAMs, and hence may cleave similar substrates to SVMPs, perhaps including components of the extracellular matrix. Northern blot analysis of selected mouse tissues revealed that ADAM28 is expressed highly and in alternatively spliced forms in the epididymis, suggesting a possible role in sperm maturation, and at lower levels in lung. The intracellular maturation of ADAM28 expressed in COS-7 cells resembles that of other ADAMs, in that ADAM28 is made as a precursor and processed to a mature form in a late Golgi compartment of the secretory pathway. Most or all of the mature, and thus presumably catalytically active, form of ADAM28 in COS-7 cells is accessible to cell surface trypsinization, suggesting that ADAM28 functions mainly on the cell surface. A mutation converting the catalytic-site glutamate residue into alanine abolishes pro-domain removal, even though this mutant form of ADAM28 can be transported to the cell surface in a manner similar to the wild-type protein. This suggests that pro-domain removal and maturation of ADAM28 may be, at least in part, autocatalytic. This is in contrast with several other ADAMs, for which furin-like proprotein convertases are involved in pro-domain removal, and in which a glutamate-to-alanine mutation in the catalytic site does not alter pro-domain removal.
Identification and expression analysis of leptin-regulated immediate early response and late target genes
Authors: WAELPUT Wim , VERHEE Annick , BROEKAERT Daniël , EYCKERMAN Sven , VANDEKERCKHOVE Joël , BEATTIE John H. , TAVERNIER Jan
Published: August 2015

Using PC12 cells as an in vitro model system, we have identified a series of transcripts induced through activation of the leptin receptor. On the basis of kinetic studies, two distinct gene sets could be discerned: signal transducer and activator of transciption-3 (STAT-3), suppressor of cytokine signalling-3 (SOCS-3), MT-II (metallothionein-II), the serine/threonine kinase fibroblast-growth-factor-inducible kinase (Fnk) and modulator recognition factor (MRF-1), which are immediate early response genes, and pancreatitis-associated protein I (PAP I), squalene epoxidase, uridine diphosphate glucuronosyltransferase and annexin VIII, which are late induced target genes. At late time points a strong co-stimulation with β-nerve growth factor or with the adenylate cyclase activator forskolin was observed. To assess the validity of the PC12-cell model system, we examined the effect of leptin administration on the gene transcription of STAT-3, MT-II, Fnk and PAP I in vivo. Leptin treatment of leptin-deficient ob/ob mice increased the STAT-3, SOCS-3, MT-II and Fnk mRNA, and MT-I protein levels in liver, whereas, in jejunum, expression of PAP I mRNA was down-regulated. Furthermore, administration of leptin to starved wild-type mice enhanced the expression of MT-II and Fnk mRNA in liver, but decreased MT-II and PAP I mRNA expression in jejunum. These findings may help to explain the obese phenotype observed in some colonies of MT-I- and MT-II-null mice and/or the observation that leptin protects against tumour-necrosis-factor toxicity in vivo.
Exon-skipping in BCR/ABL is induced by ABL exon 2
Authors: LICHTY Brian D. , KAMEL-REID Suzanne
Published: August 2015

The BCR/ABL fusion gene is pathognomonic for chronic myelogenous leukaemia (CML). We have previously reported alternative splicing of BCR/ABL, as indicated by the detection of both p190- and p210-encoding transcripts, in about 60% of CML patient samples. These exon-skipping events involved the joining of ABL exon 2 to variable upstream BCR exons. Similarly, ABL exon 2 is alternatively spliced to either of two upstream ABL exons (1a or 1b) in c-ABL. We have constructed BCR and BCR/ABL minigenes to study this phenomenon in more detail. These constructs were transfected into various cell types and splicing was assessed by reverse transcriptase PCR. Whereas the basic BCR minigene expressed exon-inclusive transcripts only, insertion of genomic DNA spanning ABL exon 2 induced exon-skipping but only when expressed in the CML cell lines K562 and EM3. In this study we localized the required sequence element to ABL exon 2 itself. These results mimic the splicing phenotype displayed by most CML patients. We propose a model where a trans-factor present in some CML cells interacts with ABL exon 2 pre-mRNA to promote skipping of upstream BCR exons.
Net release of individual fatty acids from white adipose tissue during lipolysis in vitro: evidence for selective fatty acid re-uptake
Authors: RACLOT Thierry , OUDART Hugues
Published: August 2015

During lipolysis, adipose tissue triacylglycerols (TAG) undergo concurrent breakdown and synthesis because some of the newly hydrolysed and released non-esterified (‘free’) fatty acids (NEFA) can subsequently be taken up and re-esterified. The present study examines whether and how the release of individual fatty acids is affected by the re-uptake of some of the newly hydrolysed fatty acids in vitro during lipolysis. To alter fatty acid release and re-uptake, adipose tissue fragments and isolated adipocytes from rats were incubated under various conditions, i.e. several cell concentrations or adipose fragment quantities, with or without glucose. In the various conditions tested, the NEFA/glycerol molar ratio ranged from 1.5 to 2.9. Whatever the incubation conditions, including those resulting in very low, medium or high fatty acid re-uptake (as assessed by the NEFA/glycerol ratio), the percentage weight of fatty acids in NEFA was significantly different from that in TAG for 20-24 of the 35 fatty acids that were considered. Thus the greater the fatty acid re-uptake, the higher the proportion of polyunsaturated fatty acids and the lower the proportion of long-chain saturated and monounsaturated fatty acids in NEFA. Moreover, the relative mobilization (%NEFA/%TAG) of the least readily mobilized fatty acid (C22:1,n-11) was 6.2-fold lower than that of the most readily mobilized fatty acid (C20:5,n-3) under conditions of very low fatty acid re-uptake, and 14.8-fold lower under conditions of high fatty acid re-uptake, indicating a widening of the range of relative mobilizations. We conclude that the composition of the NEFA pool is affected by the rate of fatty acid re-uptake. This provides strong evidence for the selective re-uptake of adipose tissue fatty acids during lipolysis.
Cloning of human Ca2+ homoeostasis endoplasmic reticulum protein (CHERP): regulated expression of antisense cDNA depletes CHERP, inhibits intracellular Ca2+ mobilization and decreases cell proliferation
Authors: LAPLANTE Janice M. , O'ROURKE Flavia , LU Xinghua , FEIN Alan , OLSEN Anne , FEINSTEIN Maurice B.
Published: August 2015

A monoclonal antibody which blocks InsP3-induced Ca2+ release from isolated endoplasmic reticulum was used to isolate a novel 4.0 kb cDNA from a human erythroleukaemia (HEL) cell cDNA expression library. A corresponding mRNA transcript of approx. 4.2 kb was present in all human cell lines and tissues examined, but cardiac and skeletal muscle had an additional transcript of 6.4 kb. The identification in GenBank® of homologous expressed sequence tags from many tissues and organisms suggests that the gene is ubiquitously expressed in higher eukaryotes. The gene was mapped to human chromosome 19p13.1. The cDNA predicts a 100 kDa protein, designated Ca2+ homoeostasis endoplasmic reticulum protein (CHERP), with two putative transmembrane domains, multiple consensus phosphorylation sites, a polyglutamine tract of 12 repeats and regions of imperfect tryptophan and histadine octa- and nona-peptide repeats. In vitro translation of the full-length cDNA produced proteins of Mr 128000 and 100000, corresponding to protein bands detected by Western blotting of many cell types. CHERP was co-localized in HEL cells with the InsP3 receptor by two-colour immunofluorescence. Transfection of HEL cells with antisense cDNA led to an 80% decline in CHERP within 5 days of antisense induction, with markedly decreased intracellular Ca2+ mobilization by thrombin, decreased DNA synthesis and growth arrest, indicating that the protein has an important function in Ca2+ homoeostasis, growth and proliferation.
Saccharomyces cerevisiae Yak1p protein kinase autophosphorylates on tyrosine residues and phosphorylates myelin basic protein on a C-terminal serine residue
Authors: KASSIS Shouki , MELHUISH Tiffany , ANNAN Roland S. , CHEN Susan L. , LEE John C. , LIVI George P. , CREASY Caretha L.
Published: August 2015

The serine/threonine protein kinase, Yak1p, functions as a negative regulator of the cell cycle in Saccharomyces cerevisiae, acting downstream of the cAMP-dependent protein kinase. In the present work we report that overexpression of haemagglutinin-tagged full-lengthYak1p and an N-terminally truncated form (residues 148-807) lead to growth arrest in PKA compromised yak1 null yeast cells. Both forms of recombinant Yak1p kinase were catalytically active and preferred myelin basic protein (MBP) as a substrate over several other proteins. Phosphopeptide analysis of bovine MBP by tandem MS revealed two major Yak1p phosphorylation sites, Thr-97 and Ser-164. Peptides containing each site were obtained and tested as Yak1p substrates. Both forms of Yak1p phosphorylated a peptide containing the Ser-164 residue with far more efficient kinetics than MBP. The maximal velocity (Vmax) values of the full-length Yak1p reaction were 110±21 (Ser-164) and 8.7±1.7 (MBP), and those of N-terminally truncated Yak1p were 560.7±74.8 (Ser-164) and 34.4±2.2 (MBP) pmol/min per mg of protein. Although neither form of Yak1p was able to phosphorylate two generic protein tyrosine kinase substrates, both were phosphorylated on tyrosine residues in vivo and underwent tyrosine autophosphorylation when reacted with ATP in vitro. Tandem MS showed that Tyr-530 was phosphorylated both in vivo and in vitro after reaction with ATP. Pre-treatment with protein tyrosine phosphatase 1B removed all of Yak1p phosphotyrosine content and drastically reduced Yak1p activity against exogenous substrates, suggesting that the phosphotyrosine content of the enzyme is essential for its catalytic activity. Although the N-terminally truncated Yak1p was expressed at a lower level than the full-length protein, its catalytic activity and phosphotyrosine content were significantly higher than those of the full-length enzyme. Taken together, our results suggest that Yak1p is a dual specificity protein kinase which autophosphorylates on Tyr-530 and phosphorylates exogenous substrates on Ser/Thr residues.
Chicken Y-box proteins chk-YB-1b and chk-YB-2 repress translation by sequence-specific interaction with single-stranded RNA
Authors: SWAMYNATHAN Shivalingappa K. , NAMBIAR Ashok , GUNTAKA Ramareddy V.
Published: August 2015

Y-Box proteins comprise a large family of multifunctional proteins with a wide spectrum of activities in both transcription and translational regulation of gene expression. Earlier, we have reported on the involvement of chk-YB-2 in transcriptional regulation of Rous sarcoma virus long terminal repeats and the involvement of chk-YB-1b in transcriptional regulation of alpha1(I) collagen genes. Here, we have investigated the potential role of chk-YB-2 and chk-YB-1b in RNA metabolism. We report that chk-YB-2 and chk-YB-1b are localized predominantly in the cytoplasm and that they both can bind single-stranded RNA in a sequence-specific and reversible manner. Well-conserved cold-shock domain, N-terminal proline-rich domain and the alternating clusters of acidic and basic amino acids located in the C-terminal ends of these two proteins were all found to be necessary for their RNA-binding ability. Further, we demonstrate that these two proteins inhibit translation in vitro and that binding to RNA is required for this inhibition. The significance of these results is discussed.
Expression of an active form of recombinant Ty1 reverse transcriptase in Escherichia coli: a fusion protein containing the C-terminal region of the Ty1 integrase linked to the reverse transcriptase–RNase H domain exhibits polymerase and RNase H activities
Authors: WILHELM Marcelle , BOUTABOUT Mansour , WILHELM François-Xavier
Published: August 2015

Replication of the Saccharomyces cerevisiae Ty1 retrotransposon requires a reverse transcriptase capable of synthesizing Ty1 DNA. The first description of an active form of a recombinant Ty1 enzyme with polymerase and RNase H activities is reported here. The Ty1 enzyme was expressed as a hexahistidine-tagged fusion protein in Escherichia coli to facilitate purification of the recombinant protein by metal-chelate chromatography. Catalytic activity of the recombinant protein was detected only when amino acid residues encoded by the integrase gene were added to the N-terminus of the reverse transcriptase-RNase H domain. This suggests that the integrase domain could play a role in proper folding of reverse transcriptase. Several biochemical properties of the Ty1 enzyme were analysed, including the effect of MgCl2, NaCl, temperature and of the chain terminator dideoxy GTP on its polymerase activity. RNase H activity was examined by monitoring the cleavage of a RNA-DNA template-primer. Our results suggest that the distance between the RNase H and polymerase active sites corresponds to the length of a 14-nucleotide RNA-DNA heteroduplex. The recombinant protein produced in E. coli should be useful for further biochemical and structural analyses and for a better understanding of the role of integrase in the activation of reverse transcriptase.
Increased translation efficiency and antizyme-dependent stabilization of ornithine decarboxylase in amino acid-supplemented human colon adenocarcinoma cells, Caco-2
Authors: CHABANON Hervé , PERSSON Lo , WALLACE Heather M. , FERRARA Marc , BRACHET Patrick
Published: August 2015

The mechanisms of the response of ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine biosynthesis, to amino acid supplementation were studied in the human colon adenocarcinoma cell line, Caco-2. Supplementation of serum-deprived, subconfluent Caco-2 cells with any one of a series of amino acids (10 mM) resulted in increased ODC activity, reaching a maximum of approx. 12.5-fold after approx. 4 h, over control cells either not supplemented or supplemented with iso-osmolar D-mannitol. Glycine, L-asparagine and L-serine, as well as their D-enantiomers, were the strongest effectors and acted in a concentration-dependent manner; millimolar concentrations of most of these amino acids being sufficient to significantly increase ODC activity. In contrast, supplementation with D-methionine, L-lysine, L-aspartate or L-glutamate had little or no effect on ODC activity, whereas supplemental L-methionine, L-arginine, L-ornithine or L-cysteine was inhibitory. Polyamine assays showed that the putrescine content of cells varied in accordance with the changes in ODC activity. Western-blot and Northern-blot analyses revealed specifically increased levels of ODC protein but not mRNA, respectively, in response to supplementation with an ODC-inducing amino acid. Suppression of the increase in cycloheximide-treated cells confirmed a requirement for protein synthesis. Pulse-labelling of cells with [35S]methionine showed a 3-fold increase in the synthesis of ODC protein after 4 h of supplementation with glycine or L-serine. Supplemental glycine also augmented, reversibly, the half-life of ODC by almost 4-fold and simultaneously decreased the activity of putrescine-induced free antizyme. These results suggest that translational, but not transcriptional, regulation of ODC takes part in ODC induction by amino acids in Caco-2 cells. However, it also appears to occur in concert with decreased enzyme inactivation and/or degradation.
Perivenous localization of insulin receptor protein in rat liver, and regulation of its expression by glucose and oxygen in hepatocyte cultures
Authors: KRONES Anja , KIETZMANN Thomas , JUNGERMANN Kurt
Published: August 2015

Insulin stimulates glucose utilization in the liver, which occurs mainly in the less aerobic, perivenous, zone. Accordingly, the insulin receptor protein was predominantly expressed in this area, although the insulin receptor mRNA was homogeneously distributed. In hepatocyte cultures venous O2 partial pressure (pO2) induced insulin receptor protein expression. High glucose concentrations enhanced insulin receptor protein under arterial and venous pO2. The induction of insulin receptor protein by venous pO2 would explain its zonated expression.
Action pattern and substrate specificity of the hyaluronan lyase from group B streptococci
Authors: BAKER John R. , PRITCHARD David G.
Published: August 2015

The hyaluronan lyase of group B streptococci rapidly cleaves hyaluronan by an elimination mechanism to yield the unsaturated disaccharide 2-acetamido-2-deoxy-3-O-(β-D-gluco-4-enepyranosyluronic acid)-D-glucose. Additionally, it has been shown that the enzyme has limited specificity for a chondroitin sulphate and cleaves the chain at unsulphated sites [Baker, Yu, Morrison, Averett and Pritchard (1997) Biochem. J. 327, 65-71]. In the present extension of that study it was found that 6-sulphated regions of chondroitin sulphate are also susceptible to cleavage by this hyaluronan lyase. Of the four 6- and/or 4-sulphated tetrasaccharides which can be isolated from testicular hyaluronidase digests of chondroitin sulphate, only those two tetrasaccharides with a 6-sulphated disaccharide at the reducing end were cleaved. From this and other data, a model is proposed for the cleavage specificity of hyaluronan lyase on a chondroitin sulphate. Evidence is presented in support of an action pattern for hyaluronan lyase which involves an initial random endolytic cleavage followed by rapid exolytic and processive release of unsaturated disaccharide. Since the only oligosaccharides which tend to accumulate in near-complete digests of hyaluronan are unsaturated, it is argued that the processive cleavage occurs from the non-reducing to the reducing end of a hyaluronan chain. This detailed knowledge of substrate specificity contributes to our understanding of the enzyme's role in Group B streptococcal pathogenesis. In addition, the hyaluronan lyase may find application in sequence studies of chondroitin sulphates.
Glycosylation-site-selective synthesis of N-acetyl-lactosamine repeats in bis-glycosylated human lysozyme
Authors: MELCHER Ralph , HILLEBRAND Alexandra , BAHR Ute , SCHRÖDER Bernd , KARAS Michael , HASILIK Andrej
Published: August 2015

We have studied the elongation of oligosaccharides containing N-acetyl-lactosamine repeats using glycosylated human lysozyme mutants as a model. We reported previously that a combination of glycosylation sites at the 49th (site IV) and 68th (site II) amino acid residues of the protein particularly stimulates the synthesis of N-acetyl-lactosamine repeats [Melcher, Grosch, Grosse and Hasilik (1998) Glycoconjugate J. 15, 987-993]. In the present study we show that it is the carbohydrate attached to site IV that is selectively affected. It contains more N-acetyl-lactosamine repeats when site II is glycosylated in the same molecule. As a corollary of the glycosylation at site II, the synthesis of a third antenna at site IV is increased. The triantennary oligosaccharides at site IV contain more N-acetyl-lactosamine repeats than the biantennary ones. Thus placing a carbohydrate at site II stimulates the branching and the elongation of the carbohydrate at the other site.
Ligand binding directly stimulates ubiquitination of the inositol 1,4,5-trisphosphate receptor
Authors: ZHU Chang-Cheng , WOJCIKIEWICZ Richard J. H.
Published: August 2015

Down-regulation of the Ins(1,4,5)P3 receptor is an adaptive response to the activation of certain phosphoinositidase C-linked cell-surface receptors. It is manifested as a profound decline in cellular Ins(1,4,5)P3 receptor content, occurs with a half-time of 0.5-2 h and is due to accelerated proteolysis. It has been shown that this process is mediated by the ubiquitin/proteasome pathway and is therefore initiated by Ins(1,4,5)P3 receptor ubiquitination. To investigate the role of ligand binding in Ins(1,4,5)P3 receptor ubiquitination, we expressed ‘exogenous’ wild-type and ligand-binding-defective mutant type I Ins(1,4,5)P3 receptors in human neuroblastoma SH-SY5Y cells, in which muscarinic receptor activation elicits Ins(1,4,5)P3 receptor down-regulation. We found (1) that exogenous wild-type Ins(1,4,5)P3 receptors are efficiently ubiquitinated in response to muscarinic receptor stimulation, (2) that exogenous ligand binding-defective mutant Ins(1,4,5)P3 receptors are resistant to ubiquitination, (3) that this resistance is not caused by the removal of potential ubiquitin-conjugating sites in the mutated region, and (4) that in heterotetramers of exogenous mutant receptors and ‘endogenous’ receptors, only the latter are targeted for ubiquitination. These results indicate that the binding of Ins(1,4,5)P3 directly stimulates ubiquitination of the Ins(1,4,5)P3 receptor and that the targeting of Ins(1,4,5)P3 receptors for ubiquitination is a highly specific process. We therefore propose that an Ins(1,4,5)P3-binding-induced conformational change in the receptor exposes a degradation signal that leads to ubiquitination.
Repression of transforming-growth-factor-β-mediated transcription by nuclear factor κB
Authors: NAGARAJAN Raman P. , CHEN Feifei , LI Wei , VIG Eva , HARRINGTON Maureen A. , NAKSHATRI Harikrishna , CHEN Yan
Published: August 2015

Activation of transforming growth factor-β (TGF-β) and activin receptors leads to phosphorylation of Sma- and Mad-related protein 2 (Smad2) and Smad3, which function as transcription factors to regulate gene expression. Smad7 is a regulatory protein which is able to inhibit TGF-β and activin signalling in a negative-feedback loop, mediated by a direct regulation by Smad3 and Smad4 via a Smad-binding element (SBE) in the Smad7 promoter. Interestingly, we found that the Smad7 promoter was also regulated by nuclear factor ĸB (NF-ĸB), a transcription factor which plays an important role in inflammation and the immune response. Expression of NF-ĸB p65 subunit was able to inhibit the Smad7 promoter activity, and this inhibition could be reversed by co-expression of IĸB, an inhibitor of NF-ĸB. In addition, the inhibitory activity of p65 was observed in a minimal promoter that contained only the Smad7 SBE and a TATA box, without any consensus NF-ĸB binding site. This inhibitory effect appeared to be common to other TGF-β- and activin-responsive promoters, since p65 also inhibited the forkhead-activin-signal-transducer-2-mediated activation of a Xenopus Mix.2 promoter, as well as the Smad3-mediated activation of 3TP-lux which contains PMA-responsive elements and a plasminogen-activator-inhibitor-1 promoter. Activation of endogenous NF-ĸB by tumour necrosis factor-α (TNF-α) was also able to inhibit the Smad7 promoter in human embryonic kidney 293 cells. In human hepatoma HepG2 cells, TNF-α was able to inhibit TGF-β- and activin-mediated transcriptional activation. Furthermore, overexpression of the transcription co-activator p300 could abrogate the inhibitory effect of NF-ĸB on the Smad7 promoter. Taken together, these data have indicated a novel mode of crosstalk between the Smad and the NF-ĸB signalling cascades at the transcriptional level by competing for a limiting pool of transcription co-activators.
Evidence that metformin exerts its anti-diabetic effects through inhibition of complex 1 of the mitochondrial respiratory chain
Authors: OWEN Mark R. , DORAN Elena , HALESTRAP Andrew P.
Published: August 2015

Although metformin is widely used for the treatment of non-insulin-dependent diabetes, its mode of action remains unclear. Here we provide evidence that its primary site of action is through a direct inhibition of complex 1 of the respiratory chain. Metformin (50 μM) inhibited mitochondrial oxidation of glutamate+malate in hepatoma cells by 13 and 30% after 24 and 60 h exposure respectively, but succinate oxidation was unaffected. Metformin also caused time-dependent inhibition of complex 1 in isolated mitochondria, whereas in sub-mitochondrial particles inhibition was immediate but required very high metformin concentrations (K0.5, 79 mM). These data are compatible with the slow membrane-potential-driven accumulation of the positively charged drug within the mitochondrial matrix leading to inhibition of complex 1. Metformin inhibition of gluconeogenesis from L-lactate in isolated rat hepatocytes was also time- and concentration-dependent, and accompanied by changes in metabolite levels similar to those induced by other inhibitors of gluconeogenesis acting on complex 1. Freeze-clamped livers from metformin-treated rats exhibited similar changes in metabolite concentrations. We conclude that the drug's pharmacological effects are mediated, at least in part, through a time-dependent, self-limiting inhibition of the respiratory chain that restrains hepatic gluconeogenesis while increasing glucose utilization in peripheral tissues. Lactic acidosis, an occasional side effect, can also be explained in this way.
Dynamics of haem oxygenase-1 expression and bilirubin production in cellular protection against oxidative stress
Authors: CLARK James E. , FORESTI Roberta , GREEN Colin J. , MOTTERLINI Roberto
Published: August 2015

The inducible isoform of haem oxygenase (HO-1) has been proposed as an effective system to counteract oxidant-induced cell injury. In several circumstances, this cytoprotective effect has been attributed to increased generation of the antioxidant bilirubin during haem degradation by HO-1. However, a direct implication for HO-1-derived bilirubin in protection against oxidative stress remains to be established. In the present study, we examined the dynamics of HO-1 expression and bilirubin production after stimulation of vascular smooth-muscle cells with hemin, a potent inducer of the HO-1 gene. We found that hemin-mediated increase in HO-1 protein expression and haem oxygenase activity is associated with augmented bilirubin levels. The majority of bilirubin production occurred early after exposure of cells to hemin. Hemin pre-treatment also resulted in high resistance to cell injury caused by an oxidant-generating system. Interestingly, this protective effect was manifest only when cells were actively producing bilirubin as a consequence of increased haem availability and utilization by HO-1. Tin protoporphyrin IX, an inhibitor of haem oxygenase activity, significantly reduced bilirubin generation and reversed cellular protection afforded by hemin treatment. Furthermore, addition of bilirubin to the culture medium markedly reduced the cytotoxicity produced by oxidants. Our findings provide direct evidence that bilirubin generated after up-regulation of the HO-1 pathway is cytoprotective against oxidative stress.