bluuebunny/crossref_metadata_2025 huggingface dataset:
Fibre-type specific modification of the activity and regulation of skeletal muscle pyruvate dehydrogenase kinase (PDK) by prolonged starvation and refeeding is associated with targeted regulation of PDK isoenzyme 4 expression
Authors: SUGDEN Mary C. , KRAUS Alexandra , HARRIS Robert A. , HOLNESS Mark J.
Published: August 2015

Using immunoblot analysis with antibodies raised against recombinant pyruvate dehydrogenase kinase (PDK) isoenzymes PDK2 and PDK4, we demonstrate selective changes in PDK isoenzyme expression in slow-twitch versus fast-twitch skeletal muscle types in response to prolonged (48 h) starvation and refeeding after starvation. Starvation increased PDK activity in both slow-twitch (soleus) and fast-twitch (anterior tibialis) skeletal muscle and was associated with loss of sensitivity of PDK to inhibition by pyruvate, with a greater effect in anterior tibialis. Starvation significantly increased PDK4 protein expression in both soleus and anterior tibialis, with a greater response in anterior tibialis. Starvation did not effect PDK2 protein expression in soleus, but modestly increased PDK2 expression in anterior tibialis. Refeeding for 4 h partially reversed the effect of 48-h starvation on PDK activity and PDK4 expression in both soleus and anterior tibialis, but the response was more marked in soleus than in anterior tibialis. Pyruvate sensitivity of PDK activity was also partially restored by refeeding, again with the greater response in soleus. It is concluded that targeted regulation of PDK4 isoenzyme expression in skeletal muscle in response to starvation and refeeding underlies the modulation of the regulatory characteristics of PDK in vivo. We propose that switching from a pyruvate-sensitive to a pyruvate-insensitive PDK isoenzyme in starvation (a) maintains a sufficiently high pyruvate concentration to ensure that the glucose → alanine → glucose cycle is not impaired, and (b) may ‘spare’ pyruvate for anaplerotic entry into the tricarboxylic acid cycle to support the entry of acetyl-CoA derived from fatty acid (FA) oxidation into the tricarboxylic acid cycle. We further speculate that FA oxidation by skeletal muscle is both forced and facilitated by upregulation of PDK4, which is perceived as an essential component of the operation of the glucose-FA cycle in starvation.
Kinetic analysis of the internalization and recycling of [3H]TRH and C-terminal truncations of the long isoform of the rat thyrotropin-releasing hormone receptor-1
Authors: DRMOTA Tomas , MILLIGAN Graeme
Published: August 2015

The C-terminal tail of the long splice variant of the rat thyrotropin-releasing hormone (TRH) receptor-1 (TRHR-1L) comprises around 93 amino acids. A series of C-terminal truncations was constructed and expressed transiently in HEK-293 cells. The extent of steady-state internalization of these in response to [3H]TRH was dependent upon the degree of truncation. Little effect was produced by deletion of the C-terminal to 50 amino acids, although there was a substantial decrease in the extent of internalization by deletion to 45-46 amino acids. The rate of internalization of TRHR-1L in response to ligand was substantially decreased by the acid-wash procedures often used in the analysis of cellular distribution of receptors with peptide ligands, and thus an alternative procedure using a Mes-containing buffer was employed in the present study. Apart from a truncation anticipated to eliminate post-translational acylation of the re-ceptor, which altered both the association and dissociation rates of [3H]TRH, the kinetics of ligand binding were unaffected by C-terminal truncation. Equally, the rate of recycling to the plasma membrane of internalized receptors was unaffected by C-terminal truncation. Although the extent of internalization of the full-length receptor was impaired by pre-exposure of cells to TRH, this was not true of C-terminal truncation mutants, which displayed limited steady-state internalization ratios. A mutant with a substantial C-terminal deletion also displayed decreased functional desensitization compared with the full-length receptor.
Different Ca2+-releasing abilities of sperm extracts compared with tissue extracts and phospholipase C isoforms in sea urchin egg homogenate and mouse eggs
Authors: JONES Keith T. , MATSUDA Miho , PARRINGTON John , KATAN Matilda , SWANN Karl
Published: August 2015

A soluble phospholipase C (PLC) from boar sperm generates InsP3 and hence causes Ca2+ release when added to sea urchin egg homogenate. This PLC activity is associated with the ability of sperm extracts to cause Ca2+ oscillations in mammalian eggs following fractionation. A sperm PLC may, therefore, be responsible for causing the observed Ca2+ oscillations at fertilization. In the present study we have further characterized this boar sperm PLC activity using sea urchin egg homogenate. Consistent with a sperm PLC acting on egg PtdIns(4,5)P2, the ability of sperm extracts to release Ca2+ was blocked by preincubation with the PLC inhibitor U73122 or by the addition of neomycin to the homogenate. The Ca2+-releasing activity was also detectable in sperm from other species and in whole testis extracts. However, activity was not observed in extracts from other tissues. Moreover recombinant PLCβ1, -γ1, -γ2, -∆1, all of which had higher specific activities than boar sperm extracts, were not able to release Ca2+ in the sea urchin egg homogenate. In addition these PLCs were not able to cause Ca2+ oscillations following microinjection into mouse eggs. These results imply that the sperm PLC possesses distinct properties that allow it to hydrolyse PtdIns(4,5)P2 in eggs.
Cyclolinteinone, a sesterterpene from sponge Cacospongia linteiformis, prevents inducible nitric oxide synthase and inducible cyclo-oxygenase protein expression by blocking nuclear factor-κB activation in J774 macrophages
Authors: D'ACQUISTO Fulvio , LANZOTTI Virginia , CARNUCCIO Rosa
Published: August 2015

We investigated the effect of cyclolinteinone, a sesterterpene from Caribbean sponge Cacospongia linteiformis, on inducible NO synthase (iNOS) and cyclo-oxygenase-2 (COX-2) protein expression in lipopolysaccharide (LPS)-stimulated J774 macrophages. Incubation of J774 cells with LPS (1 μg/ml) caused an increase of both iNOS and COX-2 protein expression, which was prevented in a concentration-dependent fashion by cyclolinteinone (12.5, 25 and 50 μM). Electrophoretic mobility-shift assay indicated that cyclolinteinone blocked the activation of nuclear factor-ĸB (NF-ĸB), a transcription factor necessary for either iNOS or COX-2 induction. Cyclolinteinone also blocked disappearance of IĸB-α from cytosolic fraction and nuclear translocation of NF-ĸB subunits p50 and p65. These results show that cyclolinteinone down-regulates iNOS and COX-2 protein expression by inhibiting NF-ĸB activation and suggest that it may represent a novel anti-inflammatory compound capable of controlling the excessive production of prostaglandins and nitric oxide occurring in several inflammatory diseases.
Functional CB1 cannabinoid receptors in human vascular endothelial cells
Authors: LIU Jie , GAO Bin , MIRSHAHI Faridoddin , SANYAL Arun J. , KHANOLKAR Atmaram D. , MAKRIYANNIS Alexandros , KUNOS George
Published: August 2015

Cannabinoid CB1 receptor mRNA was detected using reverse transcription-polymerase chain reaction (RT-PCR) in endothelial cells from human aorta and hepatic artery and in the ECV304 cell line derived from human umbilical vein endothelial cells. CB1 receptor-binding sites were detected by the high-affinity antagonist radioligand [125I]AM-251. In ECV304 cells, both the highly potent synthetic cannabinoid agonist HU-210 and the endogenous ligand anandamide induce activation of mitogen-activated protein (MAP) kinase, and the effect of HU-210 was completely blocked, whereas the effect of anandamide was partially inhibited by SR141716A, a selective CB1 receptor antagonist. Transfection of ECV304 cells with CB1 receptor antisense, but not sense, oligonucleotides caused the same pattern of inhibition as SR141716A. This provides more definitive evidence for the involvement of CB1 receptors in MAP kinase activation and suggests that anandamide may also activate MAP kinase via an additional, CB1 receptor-independent, SR141716A-resistant mechanism. The MAP kinase activation by anandamide in ECV304 cells requires genistein-sensitive tyrosine kinases and protein kinase C (PKC), and anandamide also activates p38 kinase and c-Jun kinase. These findings indicate that CB1 receptors located in human vascular endothelium are functionally coupled to the MAP kinase cascade. Activation of protein kinase cascades by anandamide may be involved in the modulation of endothelial cell growth and proliferation.
Internal-ribosome-entry-site functional activity of the 3′-untranslated region of the mRNA for the β subunit of mitochondrial H+-ATP synthase
Authors: IZQUIERDO José M. , CUEZVA José M.
Published: August 2015

Translation in vitro of the mammalian nucleus-encoded mRNA for the β subunit of mitochondrial H+-ATP synthase (β-mRNA) of oxidative phosphorylation is promoted by a 150 nt translational enhancer sequence in the 3ʹ-untranslated region (3ʹ UTR). Titration of the eukaryotic initiation factor eIF4E with cap analogue revealed that translation of capped β-mRNA was pseudo-cap independent. The 3ʹ UTR of β-mRNA stimulates the translation of heterologous uncapped mRNA species, both when the 3ʹ UTR is placed at the 3ʹ end and at the 5ʹ end of the transcripts. The 3ʹ UTRs of the α subunit of mitochondrial H+-ATP synthase (α-F1-ATPase) and subunit IV of cytochrome c oxidase (COX IV) mRNA species, other nucleus-encoded transcripts of oxidative phosphorylation, do not have the same activity in translation as the 3ʹ UTR of β-mRNA. On dicistronic RNA species, the 3ʹ UTR of β-mRNA, and to a smaller extent that of COX IV mRNA, is able to promote the translation of the second cistron to a level comparable to the activity of internal ribosome entry sites (IRESs) described in picornavirus mRNA species. These results indicate that the 3ʹ UTRs of certain mRNA species of oxidative phosphorylation have IRES-like functional activity. Riboprobes of the active 3ʹ UTRs on dicistronic assays formed specific RNA-protein complexes when cross-linked by UV to proteins of the lysate, suggesting that cytoplasmic translation of the mRNA species bearing an active 3ʹ UTR is assisted by specific RNA-protein interactions.
Physical characterization of the MUC5AC mucin: a highly oligomeric glycoprotein whether isolated from cell culture or in vivo from respiratory mucous secretions
Authors: SHEEHAN John K. , BRAZEAU Caroline , KUTAY Saduman , PIGEON Helena , KIRKHAM Sara , HOWARD Marj , THORNTON David J.
Published: August 2015

We have isolated the high-Mr mucins from growth medium of the early stage of an HT-29 cell culture by gel chromatography and isopycnic density gradient centrifugation. The mucins (buoyant density 1.34-1.44 g/ml) were reactive with an anti-peptide antiserum (MAN-5ACI) raised against a sequence from within the MUC5AC mucin. Similar antisera raised against the MUC2 and MUC5B mucins were not reactive. The MUC5AC reduced-mucin subunits exhibited a homogeneous charge distribution on anion-exchange chromatography, but appeared as two bands, one major and one more minor, after agarose gel electrophoresis. The unreduced mucins had an average Mr in excess of 40 MDa and were visualized in the electron microscope as large, fine filamentous threads (many microns in length) that after reduction were greatly reduced in size (number average length 570 nm). Agarose gel electrophoresis of unreduced MUC5AC mucins identified a major band just entering the gel with evidence of a ‘ladder’ of faster-migrating minor bands. Partial reduction of the mucins increased the proportion of the faster bands and at least 16 could be discriminated. Mr measurements showed that these bands differed by single monomer units. The mucins behaved as very stiff extended structures in solution and this characteristic might explain the poor separation of different-sized oligomers in sedimentation-rate experiments. The cell-culture mucin preparation had similar characteristics of charge and buoyant density to MUC5AC mucins from respiratory secretions in vivo. In addition the MUC5AC mucin from respiratory tract secretions exhibited similar behaviour, reduced and unreduced on agarose gel electrophoresis, indicating that the mucin has a similar molecular phenotype in vivo and in vitro.
Biosynthesis of heparin/heparan sulphate: mechanism of epimerization of glucuronyl C-5
Authors: HAGNER-MCWHIRTER Åsa , LINDAHL Ulf , LI Jin-ping
Published: August 2015

In the biosynthesis of heparin and heparan sulphate, D-glucuronic acid residues are converted into L-iduronic acid (IdoA) units by C-5 epimerization, at the polymer level. The reaction catalysed by the epimerase occurs by reversible abstraction and readdition of a proton at C-5 of target hexuronic acid residues, through a carbanion intermediate, with or without an inversion of configuration at C-5 [Prihar, Campbell, Feingold, Jacobsson, Jensen, Lindahl and Rodén (1980) Biochemistry 19, 495-500]. Incubation of chemically N-sulphated capsular polysaccharide from Escherichia coli K5 ([4GlcAβ1-4GlcNSO3α1-]n), or of O-desulphated heparin (predominantly [4IdoAα1-4GlcNSO3α1-]n) with purified C-5 epimerase from bovine liver, resulted in the interconversion of glucuronic acid and IdoA residues, which reached equilibrium (30-40% IdoA/total hexuronic acid) after approx. 1 h of incubation. Similar incubations performed in the presence of 3H2O resulted in progressive labelling at C-5 of the target hexuronic acid units of either substrate polysaccharide. Contrary to chemical D-gluco/L-ido equilibrium, established within 1 h of incubation, the accumulation of 3H label continued for at least 6 h. This isotope effect suggests that the second stage of the reaction, i.e. the re-addition of a proton to the carbanion intermediate, is the rate-limiting step of the overall process. Analysis of the 5-3H-labelled polysaccharide products showed that the 3H was approximately equally distributed between glucuronic acid and IdoA units, irrespective of incubation time (from 15 min to 72 h) and of the relative proportions of the two epimers in the substrate. This finding points to a catalytic mechanism in which the abstraction and re-addition of C-5 protons are effected by two polyprotic bases, presumably lysine residues. Previous experiments relating to the biosynthesis of dermatan sulphate were similarly interpreted in terms of a two-base epimerization mechanism but differed from the present findings by implicating one monoprotic and one polyprotic base function [Hannesson, Hagner-McWhirter, Tiedemann, Lindahl and Malmström (1996) Biochem. J. 313, 589-596].
The effect of inositol 1,3,4,5-tetrakisphosphate on inositol trisphosphate-induced Ca2+ mobilization in freshly isolated and cultured mouse lacrimal acinar cells
Authors: SMITH Peter M. , HARMER Alexander R. , LETCHER Andrew J. , IRVINE Robin F.
Published: August 2015

Earlier reports have shown a remarkable synergism between InsP4 and InsP3 [either Ins(1,4,5)P3 or Ins(2,4,5)P3] in activating Ca2+-dependent K+ and Cl- currents in mouse lacrimal cells [Changya, Gallacher, Irvine, Potter and Petersen (1989) J. Membr. Biol. 109, 85-93; Smith (1992) Biochem. J. 283, 27-30]. However, Bird, Rossier, Hughes, Shears, Armstrong and Putney [(1991) Nature (London) 352, 162-165] reported that they could see no such synergism in the same cell type. A major experimental difference between the two laboratories lies in whether or not the cells were maintained in primary culture before use. Here we have compared directly the responses to inositol polyphosphates in freshly isolated cells versus cells cultured for 6-72 h. In the cultured cells, Ins(2,4,5)P3 at 100 μM produced a robust stimulation of K+ and Cl- currents, as much as an order of magnitude greater than that observed in the freshly isolated cells. However, the freshly isolated cells could be restored to a sensitivity similar to cultured cells by the addition of InsP4 at a concentration two orders of magnitude lower than that of Ins(2,4,5)P3. We discuss the implications of this with respect to the actions of InsP4, including the possibility that disruption of the cellular structure during the isolation of the cells exposes an extreme manifestation of a possible physiological role for InsP4 in controlling calcium-store integrity.
Characterization of heterosubunit complexes formed by the R1 and R2 subunits of herpes simplex virus 1 and equine herpes virus 4 ribonucleotide reductase
Authors: SUN Yunming , CONNER Joe
Published: August 2015

We report on the separate PCR cloning and subsequent expression and purification of the large (R1) and small (R2) subunits from equine herpes virus type 4 (EHV-4) ribonucleotide reductase. The EHV-4 R1 and R2 subunits reconstituted an active enzyme and their abilities to complement the R1 and R2 subunits from the closely related herpes simplex virus 1 (HSV-1) ribonucleotide reductase, with the use of subunit interaction and enzyme activity assays, were analysed. Both EHV-4 R1/HSV-1 R2 and HSV-1 R1/EHV-4 R2 were able to assemble heterosubunit complexes but, surprisingly, neither of these complexes was fully active in enzyme activity assays; the EHV-4 R1/HSV-1 R2 and HSV-1 R1/EHV-4 R2 enzymes had 50% and 5% of their respective wild-type activities. Site-directed mutagenesis was used to alter two non-conserved residues located within the highly conserved and functionally important C-termini of the EHV-4 and HSV-1 R1 proteins. Mutation of Pro-737 to Lys and Lys-1084 to Pro in EHV-4 and HSV-1 R1 respectively had no effects on subunit assembly. Mutation of Pro-737 to Lys in EHV-4 R1 decreased enzyme activity by 50%; replacement of Lys-1084 by Pro in HSV-1 R1 had no effect on enzyme activity. Both alterations failed to restore full enzyme activities to the heterosubunit enzymes. Therefore probably neither of these amino acids has a direct role in catalysis. However, mutation of the highly conserved Tyr-1111 to Phe in HSV-1 R1 inactivated enzyme activity without affecting subunit interaction.
Human amiloride-sensitive epithelial Na+ channel γ subunit promoter: functional analysis and identification of a polypurine-polypyrimidine tract with the potential for triplex DNA formation
Authors: AUERBACH Scott D. , LOFTUS Randy W. , ITANI Omar A. , THOMAS Christie P.
Published: August 2015

The mRNA for the epithelial Na+ channel γ subunit (γENaC) is regulated developmentally in the lung, colon and distal nephron and in response to Na+ deprivation and systemic corticosteroids in the distal colon. Because such regulation is likely to be at the level of gene transcription, we examined the function of the promoter and other 5ʹ flanking elements of the human γENaC gene. The proximal 5ʹ flanking region contains two GC boxes but does not contain a TATA box. A 450 bp human γENaC fragment (-459 to +40) directed the expression of luciferase in H441 cells and primer extension analysis in transfected cells confirmed the correct initiation of human γENaC-luciferase chimaeric transcripts. By deletional analysis, GC boxes at -21 and -52 were found to be critical for this promoter activity. To begin to identify transcription factors that bind to the core promoter, a double-stranded oligonucleotide that corresponded to this region was synthesized and tested in a gel mobility-shift assay. Incubation of this radiolabelled oligonucleotide with nuclear extracts from H441 and FRTL5 cells resulted in the formation of four specific and distinct DNA-protein complexes. On the basis of antibody ‘supershift’ assays, one of these factors corresponds to Sp1, whereas the other three correspond to Sp3. Further upstream, an approx. 300 nt (-1143 to -839) polypurine-polypyrimidine tract (PPy tract) containing internal mirror repeats was identified. When contained in a supercoiled plasmid, the approx. 1200 nt 5ʹ flanking region was sensitive to S1 endonuclease, which was consistent with the formation of an intramolecular triplex DNA (‘H-DNA’) structure with an unpaired single strand. High-resolution mapping with S1 endonuclease and sequencing of S1-generated clones confirmed that all S1-sensitive sites were within the PPy tract. Finally, a negative regulatory element was identified between -1525 and -1296 that functioned in lung, colon and collecting duct cell lines.
Nucleotides of the tRNA D-stem that play an important role in nuclear-tRNA export in Saccharomyces cerevisiae
Authors: CLEARY John D. , MANGROO Dev
Published: August 2015

Nuclear export of tRNA in Saccharomyces cerevisiae involves Los1p and Arc1p. Los1p facilitates tRNA translocation across the nuclear pore complex whereas Arc1p plays a role in delivering some species of tRNA exiting the nucleus to their cognate aminoacyl-tRNA synthetases. Here, we show that mutations of C11 and G24 of the D-stem of the yeast tyrosine amber-suppressor tRNA have different effects on nuclear export of the tRNA. Changing G24 had no effect on export of the tRNA to the cytoplasm. In contrast, mutating C11 resulted in nuclear retention of the tRNA. Nuclear retention of the tRNA mutants was not due to lack of processing, since only the mature forms of the tRNA mutants were found. The fact that mutations of G24 did not affect export of the tRNA also indicates that the effect of mutating C11 is not due to gross alteration of the tertiary structure resulting from disruption of the C11/G24 base pair. Expression of Los1p and the mammalian tRNA export receptor exportin-t rescued nuclear export of the tRNA with changes at position 11. The export-defective mutations of the tRNA mutants were suppressed by introducing the complementary nucleotides at position 24. Taken together, these findings suggest that C11 is important for binding of the tRNA to the export receptor, and that this binding is influenced by the conformation of the base. Finally, the export-defective tRNA mutants described can be used as reporters to identify eukaryotic proteins involved in the nuclear-tRNA export process, and characterize the molecular interactions between known receptors and the tRNA substrate.
Intracellular maturation and localization of the tumour necrosis factor α convertase (TACE)
Authors: SCHLÖNDORFF Johannes , BECHERER J. David , BLOBEL Carl P.
Published: August 2015

Tumour necrosis factor α convertase (TACE) is a metalloprotease/disintegrin involved in the ectodomain shedding of several proteins, a process thought to be important in inflammation, rheumatoid arthritis and murine development. The characterization of the intracellular maturation and subcellular localization of endogenous TACE is decribed in the present study. Similarly to other proteolytically active metalloprotease/disintegrins, two forms of TACE are found in cells; a full-length precursor and a mature form lacking the prodomain. Prodomain removal occurs in a late Golgi compartment, consistent with the proposed role of a furin type proprotein convertase in this process. An additional form of TACE, lacking the pro and cytoplasmic domains, is detected when cell lysates are prepared in the presence of EDTA instead of a hydroxamate-based metalloprotease inhibitor or 1,10-phenanthroline. This form appears to be generated by mature TACE cleaving its own cytoplasmic tail and may explain why little mature TACE has been detected in previous studies. In cell-surface labelling experiments, mature TACE was detected on the cell surface but immunofluorescence data indicate that TACE is predominantly localized to a perinuclear compartment similar to that described for tumour necrosis factor (TNF)α. This raises the possibility that TACE-mediated ectodomain shedding may occur in an intracellular compartment in addition to the cell surface.
Involvement of the θ-type protein kinase C in translocation of myristoylated alanine-rich C kinase substrate (MARCKS) during myogenesis of chick embryonic myoblasts
Authors: KIM Sang Soo , KIM Jung Hwa , KIM Hye Sun , PARK Dong Eun , CHUNG Chin Ha
Published: August 2015

The phosphorylation pattern of numerous proteins in the soluble extracts of chick embryonic muscle cells changes dramatically during myogenesis. One of these proteins, the 63 kDa protein, whose phosphorylation state declines during the differentiation process, was identified as the myristoylated alanine-rich C kinase substrate (MARCKS), a major, specific substrate of protein kinase C (PKC). This decrease in the phosphorylation state of MARCKS was due to a decrease in the level of protein in the cytosol with a simultaneous increase in its level in the membrane fraction. Immunostaining of the cultured myoblasts also revealed that MARCKS translocated from the cytosol to the plasma membrane and to the peripheral region of nuclei as the mononucleated myoblasts fused to form multinucleated myotubes. Immunoprecipitation with an anti-PKC-θ antibody, but not with the antibodies against the other PKC isoforms, such as conventional PKC-α, novel PKC-∆, and novel PKC-ϵ, inhibited phosphorylation of MARCKS. Moreover, expression of PKC-θ was found to be down-regulated during the course of myogenic differentiation. In addition, treatment of the cells with PMA, which activates PKC-θ and hence increases the phosphorylation state of MARCKS, reversibly inhibited both MARCKS translocation and myoblast fusion. These results suggest that MARCKS is preferentially phosphorylated by PKC-θ in cultured myoblasts and that the down-regulation of PKC-θ is partly responsible for MARCKS translocation during myogenesis. These results also suggest that PKC-θ-controlled MARCKS translocation is associated with, or a requisite event for, myoblast fusion.
Function of the farnesyl moiety in visual signalling
Authors: MCCARTHY Nina E. M. , AKHTAR Muhammad
Published: August 2015

The aim of this work was to search for the biological function of protein isoprenylation. For this purpose, peptides were synthesized and, by using a convenient protocol, were farnesylated or geranylated at the thiol group of the C-terminal cysteine. The interaction of these peptides with photoactivated rhodopsin (Rho*, which is functionally equivalent to metarhodopsin II) was studied with the use of sheep rod outer segments. The sheep rod outer segments, although chosen because of the unavailability of bovine material in the U.K., had favourable optical properties for the direct determination of spectral changes in membrane suspensions. At 20 °C and pH 8.0, the t of the conversion of metarhodopsin II (Meta II) (λmax 389 nm) into Meta III (λmax 463 nm) was 3.2 min (less than 1.5 min at 37 °C). The t was unaltered in the presence of non-farnesyl peptides but increased by approx. 20% with farnesyl-N-acetylcysteine, by approx. 60% with farnesyl peptide containing residues 544-558 of rhodopsin kinase and by approx. 140% with farnesyl peptide corresponding to residues 60-71 of the γ-subunit of visual transducin. The effect of various peptides on the activities of bovine and sheep rhodopsin kinase was also studied. In this assay the non-farnesyl peptides and common detergents were found to be inactive; however, all the farnesyl peptides inhibited the activity to various extents. Cumulatively, the results show that, whereas the farnesyl peptides as well as a number of membrane-disrupting detergents affected the conversion from Meta II into Meta III, the inhibition of the activity of rhodopsin kinase was achieved only by the farnesyl peptides. The results are interpreted as showing that Meta II possesses a binding site for the recognition of the farnesyl group that can be used either by the farnesyl moiety of rhodopsin kinase or transducin to make the initial encounter, which can then develop into multivalent interactions characterized by the structure, and the desired function, of each protein.
Protein kinase C-β contributes to NADPH oxidase activation in neutrophils
Authors: DEKKER Lodewijk V. , LEITGES Michael , ALTSCHULER Gabriel , MISTRY Nishil , MCDERMOTT Aileen , ROES Jurgen , SEGAL Anthony W.
Published: August 2015

We have analysed the involvement of the β isotype of the protein kinase C (PKC) family in the activation of NADPH oxidase in primary neutrophils. Using immunofluorescence and cell fractionation, PKC-β is shown to be recruited to the plasma membrane upon stimulation with phorbol ester and to the phagosomal membrane upon phagocytosis of IgG-coated particles (Fcγ-receptor stimulus). The time course of recruitment is similar to that of NADPH oxidase activation by these stimuli. The PKC-β specific inhibitor 379196 inhibits the response to PMA as well as to IgG-coated bacteria. Partial inhibition occurs between 10 and 100 nM of inhibitor, the concentration at which PKC-β, but not other PKC isotypes, is targeted. Neutrophils isolated from a mouse that lacks PKC-β also showed an inhibition of NADPH oxidase activation by PMA and IgG-coated particles. The level of inhibition is comparable to that achieved with 379196 in human neutrophils. Thus the PKC-β isotype mediates activation of NADPH oxidase by PMA and by stimulation of Fcγ receptors in neutrophils.
Human cystathionine γ-lyase: developmental and in vitro expression of two isoforms
Authors: LEVONEN Anna-Liisa , LAPATTO Risto , SAKSELA Mika , RAIVIO Kari O.
Published: August 2015

Cystathionine γ-lyase (CGL) is the last enzyme of the trans-sulphuration pathway, which converts methionine into cysteine. To study the possible differences in enzymic activity of the two human cystathionine γ-lyase isoforms characterized earlier, these were separately expressed in human kidney embryonic 293T cells. Furthermore, developmental changes in the expression of the two mRNA forms as well as the enzymic activity in human liver were studied, as it has been postulated that a change in the relative expression of CGL isoforms causes the postnatal increase in CGL activity. Transfection with the longer isoform increased the CGL activity 1.5-fold, while the activity of the cells transfected with the shorter form did not differ from the basal activity. In human liver samples, CGL activity was only detected in adult tissue (68±9 nmol of cysteine/h per mg of protein), whereas activity in fetal, premature and full-term neonatal liver tissue was undetectable. In contrast, strong mRNA expression of both mRNA isoforms was detected from the 19th gestational week onwards and the longer form of CGL appeared to be predominant. The expression of the two mRNA forms varied in parallel. In conclusion, we have shown that only cells overexpressing the longer form of CGL have increased activity, and CGL appears to be regulated at the post-transcriptional level during development.
The CB1 cannabinoid receptor is coupled to the activation of protein kinase B/Akt
Authors: GÓMEZ DEL PULGAR Teresa , VELASCO Guillermo , GUZMÁN Manuel
Published: August 2015

Cannabinoids exert most of their effects in the central nervous system through the CB1 cannabinoid receptor. This G-protein-coupled receptor has been shown to be functionally coupled to inhibition of adenylate cyclase, modulation of ion channels and activation of extracellular-signal-regulated kinase. Using Chinese hamster ovary cells stably transfected with the CB1 receptor cDNA we show here that ∆9-tetrahydrocannabinol (THC), the major active component of marijuana, induces the activation of protein kinase B/Akt (PKB). This effect of THC was also exerted by the endogenous cannabinoid anandamide and the synthetic cannabinoids CP-55940 and HU-210, and was prevented by the selective CB1 antagonist SR141716. Pertussis toxin and wortmannin blocked the CB1 receptor-evoked activation of PKB, pointing to the sequential involvement of a Gi/Go protein and phosphoinositide 3ʹ-kinase. The functionality of the cannabinoid-induced stimulation of PKB was proved by the increased phosphorylation of glycogen synthase kinase-3 serine 21 observed in cannabinoid-treated cells and its prevention by SR141716 and wortmannin. Cannabinoids activated PKB in the human astrocytoma cell line U373 MG, which expresses the CB1 receptor, but not in the human promyelocytic cell line HL-60, which expresses the CB2 receptor. Data indicate that activation of PKB may be responsible for some of the effects of cannabinoids in cells expressing the CB1 receptor.
Involvement of activator protein 1 complexes in the epithelium-specific activation of the laminin γ2-chain gene promoter by hepatocyte growth factor (scatter factor)
Authors: OLSEN J⊘rgen , LEFEBVRE Olivier , FRITSCH Christine , TROELSEN Jesper T. , ORIAN-ROUSSEAU Veronique , KEDINGER Michèle , SIMON-ASSMANN Patricia
Published: August 2015

Laminin-5 is a trimer of laminin α3, β3 and γ2 chains that is found in the intestinal basement membrane. Deposition of the laminin γ2 chain at the basement membrane is of great interest because it undergoes a developmental shift in its cellular expression. Here we study the regulatory elements that control basal and cytokine-activated transcriptional expression of the LAMC2 gene, which encodes the laminin γ2 chain. By using transient transfection experiments we demonstrated the presence of constitutive and cytokine-responsive cis-elements. Comparison of the transcriptional activity of the LAMC2 promoter in the epithelial HT29mtx cells with that in small-intestinal fibroblastic cells (C20 cells) led us to conclude that two regions with constitutive epithelium-specific activity are present between positions -1.2 and -0.12 kb. This was further validated by transfections of primary foetal intestinal endoderm and mesenchyme. A 2.5 kb portion of the LAMC2 5ʹ flanking region was equally responsive to PMA and hepatocyte growth factor (HGF), whereas it was less responsive to transforming growth factor β1. A minimal promoter limited to the initial 120 bp upstream of the transcriptional start site maintained inducibility by PMA and HGF. This short promoter fragment contains two activator protein 1 (AP-1) elements and the 5ʹ-most of these is a composite AP-1/Sp1 element. The 5ʹAP-1 element is crucial to the HGF-mediated activity of the promoter; analysis of interacting nuclear proteins demonstrated that AP-1 proteins containing JunD mediate the response to HGF.
Protein-tyrosine-phosphatase-mediated epidermal growth factor (EGF) receptor transinactivation and EGF receptor-independent stimulation of mitogen-activated protein kinase by bradykinin in A431 cells
Authors: GRANESS Angela , HANKE Sabine , BOEHMER Frank D. , PRESEK Peter , LIEBMANN Claus
Published: August 2015

Transactivation of the epidermal growth factor (EGF) receptor (EGFR) has been proposed to represent an essential link between G-protein-coupled receptors and the mitogen-activated protein kinase (MAPK) pathway in various cell types. In the present work we report, in contrast, that in A431 cells bradykinin transinactivates the EGFR and stimulates MAPK activity independently of EGFR tyrosine phosphorylation. Both effects of bradykinin are mediated by a pertussis-toxin-insensitive G-protein. Three lines of evidence suggest the activation of a protein tyrosine phosphatase (PTP) by bradykinin: (i) treatment of A431 cells with bradykinin decreases both basal and EGF-induced EGFR tyrosine phosphorylation, (ii) this effect of bradykinin can be blocked by two different PTP inhibitors, and (iii) bradykinin significantly increased the PTP activity in total A431 cell lysates when measured in vitro. The transmembrane receptor PTP σ was identified as a putative mediator of bradykinin-induced downregulation of EGFR autophosphorylation. Activation of MAPK in response to bradykinin was insensitive towards AG 1478, a specific inhibitor of EGFR tyrosine kinase, but was blocked by wortmannin or bisindolylmaleimide, inhibitors of phosphatidylinositol 3-kinase (PI3-K) and protein kinase C (PKC) respectively. These results also suggest that the bradykinin-induced activation of MAPK is independent of EGFR and indicate a pathway involving PI3-K and PKC. In addition, bradykinin evokes a rapid and transient increase in Src kinase activity. Although Src does not participate in bradykinin-induced stimulation of PTP activity, inhibition of Src by 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo(3,4-d)pyrimidine leads to an increase in MAPK activation by bradykinin. Our results suggest that in A431 cells the Gq/11-protein-coupled bradykinin B2 receptor may stimulate PTP activity and thereby transinactivate the EGFR, and may simultaneously activate MAPK by an alternative signalling pathway which can bypass EGFR.
Nitric oxide-induced autoinhibition of neuronal nitric oxide synthase in the presence of the autoxidation-resistant pteridine 5-methyltetrahydrobiopterin
Authors: GORREN Antonius C. F. , SCHRAMMEL Astrid , RIETHMÜLLER Christoph , SCHMIDT Kurt , KOESLING Doris , WERNER Ernst R. , MAYER Bernd
Published: August 2015

Nitric oxide synthase (NOS) catalysis results in formation of NO or superoxide (O2-−) depending on the presence or absence of the cofactor tetrahydrobiopterin (BH4). In the absence of O2-− scavengers, net NO formation cannot be detected even at saturating BH4 concentrations, which is thought to be due to O2-− production by BH4 autoxidation. Because the N-5-methylated analogue of BH4 (5-Me-BH4) sustains NOS catalysis and is autoxidation-resistant, net NO formation by the neuronal isoform of NOS (nNOS) can be observed at saturating 5-Me-BH4 concentrations. Here we compare the effects of 5-Me-BH4 on L-citrulline formation, NADPH oxidation, H2O2 production and soluble guanylate cyclase (sGC) stimulation. All activities were stimulated biphasically (EC50 approx. 0.2 μM and more than 1 mM), with an intermediate inhibitory phase at the same pterin concentration as that required for net NO generation and sGC stimulation (4 μM). Concomitantly with inhibition, the NADP+/L-citrulline stoichiometry decreased from 2.0 to 1.6. Inhibition occurred only at high enzyme concentrations (IC50 approx. 10 nM nNOS) and was antagonized by oxyhaemoglobin and by BH4. We ascribe the first stimulatory phase to high-affinity binding of 5-Me-BH4. The inhibitory phase is due to low-affinity binding, resulting in fully coupled catalysis, complete inhibition of O2-− production and net NO formation. At high enzyme concentrations and thus high NO levels, this causes autoinhibition. NO scavenging by 5-Me-BH4 at concentrations above 1 mM, resulting in the antagonization of inhibition of NOS, explains the second stimulatory phase. In agreement with these assignments 5-Me-BH4 was found to stimulate formation of a haem-NO complex during NOS catalysis. The observation of inhibition with 5-Me-BH4 but not with BH4 implies that, unless O2-− scavengers are present, a physiological role for NO-induced autoinhibition is unlikely.
Conserved residue lysine165 is essential for the ability of O6-alkylguanine–DNA alkyltransferase to react with O6-benzylguanine
Authors: XU-WELLIVER Meng , KANUGULA Sreenivas , LOKTIONOVA Natalia A. , CRONE Tina M. , PEGG Anthony E.
Published: August 2015

The role of lysine165 in the activity of the DNA repair protein, O6-alkylguanine-DNA alkyltransferase (AGT), and the ability of AGT to react with the pseudosubstrate inhibitor, O6-benzylguanine (BG), was investigated by changing this lysine to all other 19 possibilities. All of these mutants (except for K165T, which could not be tested as it was too poorly active for assay in crude cell extracts) gave BG-resistant AGTs with increases in the amount of inhibitor needed to produce a 50% loss of activity in a 30 min incubation (ED50) from 100-fold (K165A) to 2400-fold (K165F). Lys165 is a completely conserved residue in AGTs from many species, and all of the mutations at this site also reduced the ability to repair methylated DNA. The least deleterious change was that to arginine, which reduced the rate constant for DNA repair by approx. 2.5-fold. Mutant K165R resembled all of the other mutants in being highly resistant to BG, with an ED50 value for inactivation by BG > 200-fold greater than wild-type. Detailed studies of purified K165A AGT showed that the rate constant for repair and the binding to methylated DNA substrates were reduced by 10-20-fold. Despite this, the K165A mutant AGT was able to protect cells from alkylating agents and this protection was not abolished by BG. These results show that, firstly, lysine at position 165 is needed for optimal activity of AGT towards methylated DNA substrates and is essential for efficient reaction with BG; and second, even if the AGT activity towards methylated DNA substrates is impaired by mutations at codon 165, such mutants can protect tumour cells from therapeutic alkylating agents. These results raise the possibility that the conservation of Lys165 is due to the need for AGT activity towards substrates containing more bulky adducts than O6-methylguanine. They also suggest that alterations at Lys165 may occur during chemotherapy with BG and alkylating agents and could limit the effectiveness of this therapy.
Inositol 1,4,5-trisphosphate-induced Ca2+ release is inhibited by mitochondrial depolarization
Authors: COLLINS Tony J. , LIPP Peter , BERRIDGE Michael J. , LI Wenhong , BOOTMAN Martin D.
Published: August 2015

We investigated the consequences of depolarizing the mitochondrial membrane potential (∆ψmit) on Ca2+ signals arising via inositol 1,4,5-trisphosphate receptors (InsP3R) in hormone-stimulated HeLa cells. Carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) or a mixture of antimycin A+oligomycin were found to rapidly depolarize ∆ψmit. Mitochondrial depolarization enhanced the number of cells responding to a brief application of a Ca2+-mobilizing hormone and prolonged the recovery of cytosolic Ca2+ after washout of the hormone; effects consistent with the removal of a passive Ca2+ buffer. However, with repeated application of the same hormone concentration both the number of responsive cells and peak Ca2+ changes were observed to progressively decline. The inhibition of Ca2+ signalling was observed using different Ca2+-mobilizing hormones and also with a membrane-permeant Ins(1,4,5)P3 ester. Upon washout of FCCP, the Ca2+ signals recovered with a time course similar to the re-establishment of ∆ψmit. Global measurements indicated that none of the obvious factors such as changes in pH, ATP concentration, cellular redox state, permeability transition pore activation or reduction in Ca2+-store loading appeared to underlie the inhibition of Ca2+ signalling. We therefore suggest that local changes in one or more of these factors, as a consequence of depolarizing ∆ψmit, prevents InsP3R activation.
The human vasoactive intestinal peptide/pituitary adenylate cyclase-activating peptide receptor 1 (VPAC1) promoter: characterization and role in receptor expression during enterocytic differentiation of the colon cancer cell line Caco-2Cl.20
Authors: COUVINEAU Alain , MAORET Jean-José , ROUYER-FESSARD Christiane , CARRERO Isabel , LABURTHE Marc
Published: August 2015

The basic organization of the human vasoactive intestinal peptide/pituitary adenylate cyclase-activating peptide receptor (VPAC) 1 promoter was investigated after cloning the 5ʹ-flanking region (1.4 kb) of the VPAC1 gene from a human genomic library. Subsequent functional analysis of various deletions of the 5ʹ-flanking sequence, subcloned upstream of a luciferase reporter gene, was carried out in HT-29 cells. The minimal promoter region identified encompasses the -205/+76 sequence and contains a crucial CCAAT box (-182/-178) and a GC-rich sequence. Moreover a region (-1348/-933) containing a silencer element was identified. We previously showed that the expression of the VPAC1 receptor binding site is strictly dependent upon the enterocytic differentiation of human colon cancer Caco-2 cells [Laburthe, Rousset, Rouyer-Fessard, Couvineau, Chantret, Chevalier and Zweibaum (1987) J. Biol. Chem. 262, 10180-10184]. In the present study we show that VPAC1 mRNA increases dramatically when Caco-2Cl.20 cells differentiate, as measured by RNase protection assays and reverse transcriptase-PCR. A single transcript species of 3 kb is detected in differentiated cells by Northern-blot analysis. Accumulation of VPAC1 receptor mRNA is due to a 5-fold increase of transcription rate (run-on assay) without a change in mRNA half-life (9 h). Stable transfections of various constructs in Caco-2Cl.20 cells and subsequent analysis of reporter gene expression, during the enterocytic differentiation process over 25 days of culture, further indicated that the -254/+76 5ʹ-flanking sequence is endowed with the regulatory element(s) necessary for transcriptional regulation of VPAC1 during differentiation. Altogether, these observations provide the first characterization of the basic organization of the human VPAC1 gene promoter and unravel the crucial role of a short promoter sequence in the strict transcriptional control of VPAC1 expression during differentiation of human colon cancer Caco-2 cells.
Persistent activation of Gsα through limited proteolysis by calpain
Authors: SATO-KUSUBATA Kaori , YAJIMA Yukiko , KAWASHIMA Seiichi
Published: August 2015

Treatment of rat pituitary GH4C1 cell membranes with calpain, a calcium-activated cysteine protease, increased adenylate cyclase activity, and this activity was inhibited by a calpain inhibitor, leupeptin. Calpain treatment potentiated the activity of guanosine 5ʹ-[γ-thio]triphosphate (GTP[S]), but did not attenuate MnCl2 action on adenylate cyclase, suggesting that calpain acted at the G-protein level, rather than directly on adenylate cyclase. This calpain stimulation of adenylate cyclase was inhibited by an antibody raised against the C-terminal portion of Gsα, but not by anti-Gi2α or anti-Gβ antibodies. Furthermore, it was shown that Gsα is more susceptible to calpain-mediated proteolysis than Gi2α or Gβ. Therefore the stimulatory effect of calpain on adenylate cyclase is due to the cleavage of Gsα in GH4C1 cell membranes. Proteolysis of Gsα by μ-calpain involved sequential cleavages at two sites, resulting in the generation of a 39 kDa fragment first, and then a 20 kDa fragment, from the C-terminus. Treatment of GH4C1 cell membranes with cholera toxin increased the rate of cleavage. Cholera toxin treatment of intact GH4C1 cells induced the translocation of calpain from the cytosol to the membranes, a hallmark of calpain activation. In addition, treatment of intact GH4C1 cells with a calpain-specific inhibitor, benzyloxycarbonyl-Leu-leucinal, blocked the increased cAMP production and the down-regulation of Gsα, which were produced by cholera toxin or pituitary adenylate cyclase-activating polypeptide. These results suggest that calpain sustains adenylate cyclase in an active form through the cleavage of Gsα to an active Gsα fragment. This is a novel calpain-dependent activation mechanism of Gsα and, thus, of adenylate cyclase in rat pituitary cells.