bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasma convection in Saturn's outer magnetosphere determined from ions detected by the Cassini INCA experiment
Authors: Kane M. , Mitchell D. G. , Carbary J. F. , Krimigis S. M. , Crary F. J.
Published: February 2008

The Ion and Neutral Camera (INCA), one of three sensors comprising the Magnetospheric Imaging Instrument (MIMI) on the Cassini spacecraft, measures intensities of hydrogen and oxygen ions and neutral atoms in the Saturnian magnetosphere. The measured intensity spectrum and anisotropy of hot hydrogen and oxygen ions may be used to deduce the spectral parameters and the velocity of the ion population. The anisotropies are frequently convective in nature, allowing for the determination of a bulk velocity. Under the “frozen in” assumption, this is also the velocity of the cold plasma of magnetospheric ions. Initial analysis of selected measurements of nightside ion populations with strong anisotropies indicates nearly rigid corotation of magnetospheric plasma interior to Titan's orbit. Beyond this distance, these measurements infer that the plasma maintains at best a constant rotation velocity, falling farther behind the rigid corotation rate at increasing distance.
Storm enhanced densities (SED) as possible sources for Cleft Ion Fountain dayside ionospheric outflows
Authors: Zeng W. , Horwitz J. L.
Published: February 2008

Foster et al. (2002) and others have reported on elevated ionospheric density regions being convected from the subauroral plasmaspheric region toward noon, in association with convection of plasmaspheric tails in the dayside magnetosphere. It has been suggested that these so‐called Storm Enhanced Density (SED) regions could serve as ionospheric plasma source populations for cleft ion fountain outflows. To investigate this scenario, the University of Texas at Arlington Dynamic Fluid Kinetic (DyFK) model is employed to simulate the entry of a high‐density plasmasphere‐like flux tube entering the cleft region and subjected to an episode of wave‐driven transverse ion heating. In these transport simulations, the O+ ion density at higher altitudes is found to increase while the densities at lower altitudes decrease, following this heating episode. Substantial O+ outfluxes are found indicating that the SED‐associated O+ ions acquire sufficient energy to reach higher altitudes after the effects of transverse wave heating. O+ outfluxes of 2–3.5 × 108 cm−2 s−1 persist for more than 90 minutes during the simulation episode considered. The simulation results indicate that SED can be a significant source for the cleft ion fountain, and thus in turn, O+ ions to the magnetosphere.
CO2 sensitivity of Southern Ocean phytoplankton
Authors: Tortell Philippe D. , Payne Christopher D. , Li Yingyu , Trimborn Scarlett , Rost Björn , Smith Walker O. , Riesselman Christina , Dunbar Robert B. , Sedwick Pete , DiTullio Giacomo R.
Published: February 2008

The Southern Ocean exerts a strong impact on marine biogeochemical cycles and global air‐sea CO2 fluxes. Over the coming century, large increases in surface ocean CO2 levels, combined with increased upper water column temperatures and stratification, are expected to diminish Southern Ocean CO2 uptake. These effects could be significantly modulated by concomitant CO2‐dependent changes in the region's biological carbon pump. Here we show that CO2 concentrations affect the physiology, growth and species composition of phytoplankton assemblages in the Ross Sea, Antarctica. Field results from in situ sampling and ship‐board incubation experiments demonstrate that inorganic carbon uptake, steady‐state productivity and diatom species composition are sensitive to CO2 concentrations ranging from 100 to 800 ppm. Elevated CO2 led to a measurable increase in phytoplankton productivity, promoting the growth of larger chain‐forming diatoms. Our results suggest that CO2 concentrations can influence biological carbon cycling in the Southern Ocean, thereby creating potential climate feedbacks.
Signature of Hale and Gleissberg solar cycles in the geomagnetic activity
Authors: Demetrescu Crisan , Dobrica Venera
Published: February 2008

The aa index, designed to describe the geomagnetic activity at global scale, has been shown to have increased in the twentieth century by about 65%. The increase in the case of a corrected aa is about 38%, similar to the ones of the recently introduced interhour variability (IHV) and interdiurnal variability (IDV) indices of geomagnetic activity. In terms of 11‐year running averages, there is a long‐term similarity between aa, R (the sunspot number), x, y, z, and r (geomagnetic indices designed to characterize the solar quiet daily variation, controlled by the solar UV radiation), and S (the solar irradiance). We show that the variation depicted by 11‐year running averages of aa and R (and by consequence also of the other parameters mentioned) results from the superposition of Hale and Gleissberg cycle signatures in the corresponding time series. The IHV and IDV indices are included in the analysis. The two signals have a substantial contribution in R (10–30% and 20–34%, respectively, of the amplitude of the solar cycle 22) and aa (<12–27% and ∼30%, respectively, of the corresponding cycle 22 in aa). Characteristics of the two signals in the solar and geomagnetic activity and several implications of the geomagnetic activity and the solar quiet daily variation relationship with various solar outputs at the Hale and Gleissberg timescales are discussed.
Wind work on the geostrophic ocean circulation: An observational study of the effect of small scales in the wind stress
Authors: Hughes Chris W. , Wilson Chris
Published: February 2008

We use QuikSCAT scatterometer data, together with geostrophic surface currents calculated from a combination of satellite altimetry, gravity and drifter data, to investigate the rate of work done on the geostrophic circulation by wind stress. In particular, we test the suggestion that accounting for ocean currents in the calculation of stress from 10 m winds can result in a reduction of 20–35% in the wind work, compared with an approximate calculation in which currents are not accounted for. We calculate the predicted effect of accounting for ocean currents to be a reduction in power of about 0.19 TW, and find a total power input from observations which include this effect to be 0.76 TW, smaller than earlier estimates by about the right amount. By recalculating the power input using smoothed wind stresses or currents, we demonstrate that the effect of ocean currents is visible in the midlatitude data, and close to the predicted value. Proof that the data are adequate to resolve the effect in the tropics, however, is lacking, suggesting that additional processes may also be important in this region.
Partitioning the solar radiant fluxes in forest canopies in the presence of snow
Authors: Pinty B. , Lavergne T. , Kaminski T. , Aussedat O. , Giering R. , Gobron N. , Taberner M. , Verstraete M. M. , Voßbeck M. , Widlowski J.‐L.
Published: February 2008

The main goal of this study is to help bridge the gap between available remote sensing products and large‐scale global climate models. We present results from the application of an inversion method conducted using both MODerate resolution Imaging Spectroradiometer (MODIS) and Multiangle Imaging SpectroRadiometer (MISR) derived broadband visible and near‐infrared surface albedo products. This contribution is an extension of earlier efforts to optimally retrieve land surface fluxes and associated two‐stream model parameters (Pinty et al., 2007). It addresses complex geophysical scenarios involving snow occurrence in mid and high‐latitude evergreen and deciduous forest canopy systems. The detection of snow during the winter and spring seasons is based on the MODIS snow product. This information is used by our package to adapt the prior values, specifically the maximum likelihood and width of the 2‐D probability density functions (PDF) characterizing the background conditions of the forest floor. Our results (delivered as a Gaussian approximation of the PDFs of the retrieved model parameter values and radiant fluxes) illustrate the capability of the inversion package to retrieve meaningful land vegetation fluxes and associated model parameters during the year, despite the rather high temporal variability in the input products, in large part due to the occurrence of snow events. As a matter of fact, most of this temporal variability, as well as the small differences between the MODIS and MISR broadband albedos, appear to be largely captured by the albedo of the forest canopy background.
An analysis of drag force and moment for upright porous wind fences
Authors: Dong Zhibao , Mu Qingsong , Luo Wanyin , Qinan Guangqiang , Lu Ping , Wang Hongtao
Published: February 2008

Upright porous wind fences have been studied extensively because of their wide use. This paper analyzes the drag force and moment of fences to provide corroborating evidence for design of the optimal porosity that has been suggested in previous studies. The analysis of drag force and moment was based on the velocity measurements from scaled simulation tests in a wind tunnel. Particle image velocimetry was employed to provide detailed measurements of the instantaneous velocity fields around fences with different levels of porosity at different free‐stream wind velocities. The data enabled us to calculate drag force and moment of fences using the integral form of momentum equation and the integral form of angular momentum equation. The drag force and moment were converted to dimensionless drag coefficient and moment coefficient. Drag force, moment, drag coefficient and moment coefficient revealed a critical fence porosity of around 0.3, which was consistent with the optimal porosity suggested in previous studies. At this critical porosity, the vertical drag force was zero, and the means of drag coefficients and moment coefficients for different wind velocities attained their maximum. The vertical drag force changed direction when the fence porosity became greater or less than the critical porosity. When the porosity was increased beyond the critical value the drag coefficient and moment coefficient decreased rapidly. Empirical equations were developed to relate drag force and moment to wind velocity, fence porosity and height.
Wnt4 inhibits β‐catenin/TCF signalling by redirecting β‐catenin to the cell membrane
Authors: Bernard Pascal , Fleming Alice , Lacombe Arnaud , Harley Vincent R. , Vilain Eric
Published: February 2008

Background information. During embryonic development, β‐catenin is central both to the transcriptional activation of Wnt [wingless‐type MMTV (murine‐mammary‐tumour virus) integration site family] target genes and as a mediator of cell—cell adhesion. Signals that regulate its levels and subcellular localization are critical. One mechanism of Wnt signalling results in stabilization of β‐catenin protein, which leads to its translocation into the nucleus, where it interacts with TCF (T‐cell factor, HMG box) and activates transcription of target genes. Less well understood are mechanisms of Wnt signalling that do not involve β‐catenin stabilization and result in inhibition of β‐catenin‐mediated transcription.

Results. Here, we show that a member of the Wnt protein family, Wnt4 (Wnt, member 4), regulates the subcellular localization of β‐catenin, redirecting it to the cell membrane. Unique among Wnts, this action does not affect the stability of β‐catenin but does prohibit its involvement in TCF gene transactivation.

Conclusions. This novel mechanism suggests that Wnt4 acts as a switch between the two modes of β‐catenin function, transcriptional activation and cell—cell adhesion.
Replicative aging down‐regulates the myogenic regulatory factors in human myoblasts
Authors: Bigot Anne , Jacquemin Virginie , Debacq‐Chainiaux Florence , Butler‐Browne Gillian S. , Toussaint Olivier , Furling Denis , Mouly Vincent
Published: February 2008

Background information. Aging of human skeletal muscle results in a decline in muscle mass and force, and excessive turnover of muscle fibres, such as in muscular dystrophies, further increases this decline. Although it has been shown in rodents, by cross‐age transplantation of whole muscles, that the environment plays an important role in this process, the implication of proliferating aging of the muscle progenitors has been poorly investigated, particularly in humans, since the regulation of cell proliferation differs between rodents and humans. The myogenic differentiation of human myoblasts is regulated by the muscle‐specific regulatory factors. Cross‐talk between the muscle‐specific regulatory factors and the cell cycle regulators is essential for differentiation. The aim of the present study was to determine the effects of replicative senescence on the myogenic programme of human myoblasts.

Results. We showed that senescent myoblasts, which could not re‐enter the cell cycle, are still able to differentiate and form multinucleated myotubes. However, these myotubes are significantly smaller. The expression of muscle‐specific regulatory factors and cell cycle regulators was analysed in proliferating myoblasts and compared with senescent cells. We have observed a delay and a decrease in the muscle‐specific regulatory factors and the cyclin‐dependent kinase inhibitor p57 during the early step of differentiation in senescent myoblasts, as well as an increase in the fibroblastic markers.

Conclusions. Our results demonstrate that replicative senescence alters the expression of the factors triggering muscle differentiation in human myoblasts and could play a role in the regenerative defects observed in muscular diseases and during normal skeletal‐muscle aging.
Non‐coding RNAs in imprinted gene clusters
Authors: Royo Hélène , Cavaillé Jérôme
Published: February 2008

Imprinted ncRNA (non‐coding RNA) genes represent a family of untranslated transcripts that are mono‐allelically expressed in a parent‐of‐origin manner (their expression is restricted to either the maternal or the paternal allele). Although the expression of a few long imprinted ncRNAs act as cis‐acting silencers in the epigenetic regulation of chromatin at imprinted gene clusters, many of them fall into the growing class of small regulatory RNAs, namely C/D small nucleolar RNAs, microRNAs and also likely piRNAs (Piwi‐interacting RNAs), which are known to act as antisense trans‐acting regulators of gene expression (for example, site‐specific RNA modifications and RNA‐mediated gene silencing). Although their biological functions remain elusive, recent studies have pointed to their functional importance in development, in brain plasticity and also perhaps in some pathological situations, such as cancers or Prader—Willi syndrome. In this review, we summarize our current understanding of the molecular and biological roles of these ncRNAs, both in terms of their contribution to genomic imprinting control, as well as in terms of cellular RNA targets they might interact with.
Dominant-negative effect of Southeast Asian ovalocytosis anion exchanger 1 in compound heterozygous distal renal tubular acidosis
Authors: Kittanakom Saranya , Cordat Emmanuelle , Reithmeier Reinhart A. F.
Published: February 2008

The human chloride/bicarbonate AE1 (anion exchanger) is a dimeric glycoprotein expressed in the red blood cell membrane, and expressed as an N-terminal (Δ1–65) truncated form, kAE1 (kidney AE1), in the basolateral membrane of α-intercalated cells in the distal nephron. Mutations in AE1 can cause SAO (Southeast Asian ovalocytosis) or dRTA (distal renal tubular acidosis), an inherited kidney disease resulting in impaired acid secretion. The dominant SAO mutation (Δ400–408) that results in an inactive transporter and altered eythrocyte shape occurs in many dRTA families, but does not itself result in dRTA. Compound heterozygotes of four dRTA mutations (R602H, G701D, ΔV850 and A858D) with SAO exhibit dRTA and abnormal red blood cell properties. Co-expression of kAE1 and kAE1 SAO with the dRTA mutants was studied in polarized epithelial MDCK (Madin–Darby canine kidney) cells. Like SAO, the G701D and ΔV850 mutants were predominantly retained intracellularly, whereas the R602H and A858D mutants could traffic to the basolateral membrane. When co-expressed in transfected cells, kAE1 WT (wild-type) and kAE1 SAO could interact with the dRTA mutants. MDCK cells co-expressing kAE1 SAO with kAE1 WT, kAE1 R602H or kAE1 A858D showed a decrease in cell-surface expression of the co-expressed proteins. When co-expressed, kAE1 WT co-localized with the kAE1 R602H, kAE1 G701D, kAE1 ΔV850 and kAE1 A858D mutants at the basolateral membrane, whereas kAE1 SAO co-localized with kAE1 WT, kAE1 R602H, kAE1 G701D, kAE1 ΔV850 and kAE1 A858D in MDCK cells. The decrease in cell-surface expression of the dRTA mutants as a result of the interaction with kAE1 SAO would account for the impaired expression of functional kAE1 at the basolateral membrane of α-intercalated cells, resulting in dRTA in compound heterozygous patients.
Mucolipin 1 channel activity is regulated by protein kinase A-mediated phosphorylation
Authors: Vergarajauregui Silvia , Oberdick Ross , Kiselyov Kirill , Puertollano Rosa
Published: February 2008

Mucolipins constitute a family of cation channels with homology with the transient receptor potential family. Mutations in MCOLN1 (mucolipin 1) have been linked to mucolipidosis type IV, a recessive lysosomal storage disease characterized by severe neurological and ophthalmologic abnormalities. At present, little is known about the mechanisms that regulate MCOLN1 activity. In the present paper, we addressed whether MCOLN1 activity is regulated by phosphorylation. We identified two PKA (protein kinase A) consensus motifs in the C-terminal tail of MCOLN1, containing Ser557 and Ser559. Ser557 was the principal phosphorylation site, as mutation of this residue to alanine caused a greater than 75% reduction in the total levels of phosphorylated MCOLN1 C-terminal tail. Activation of PKA with forskolin promoted MCOLN1 phosphorylation, both in vitro and in vivo. In contrast, addition of the PKA inhibitor H89 abolished MCOLN1 phosphorylation. We also found that PKA-mediated phosphorylation regulates MCOLN1 channel activity. Forskolin treatment decreased MCOLN1 channel activity, whereas treatment with H89 increased MCOLN1 channel activity. The stimulatory effect of H89 on MCOLN1 function was not observed when Ser557 and Ser559 were mutated to alanine residues, indicating that these two residues are essential for PKA-mediated negative regulation of MCOLN1. This paper presents the first example of regulation of a member of the mucolipin family by phosphorylation.
Phosphatidylcholine/sphingomyelin metabolism crosstalk inside the nucleus
Authors: Albi Elisabetta , Lazzarini Remo , Viola Magni Mariapia
Published: February 2008

It is known that phospholipids represent a minor component of chromatin. It has been highlighted recently that these lipids are metabolized directly inside the nucleus, thanks to the presence of enzymes related to their metabolism, such as neutral sphingomyelinase, sphingomyelin synthase, reverse sphingomyelin synthase and phosphatidylcholine-specific phospholipase C. The chromatin enzymatic activities change during cell proliferation, differentiation and/or apoptosis, independently from the enzyme activities present in nuclear membrane, microsomes or cell membranes. This present study aimed to investigate crosstalk in lipid metabolism in nuclear membrane and chromatin isolated from rat liver in vitro and in vivo. The effect of neutral sphingomyelinase activity on phosphatidylcholine-specific phospholipase C and sphingomyelin synthase, which enrich the intranuclear diacylglycerol pool, and the effect of phosphatidylcholine-specific phospholipase C activity on neutral sphingomyelinase and reverse sphingomyelin synthase, which enrich the intranuclear ceramide pool, was investigated. The results show that in chromatin, there exists a phosphatidylcholine/sphingomyelin metabolism crosstalk which regulates the intranuclear ceramide/diacylglycerol pool. The enzyme activities were inhibited by D609, which demonstrated the specificity of this crosstalk. Chromatin lipid metabolism is activated in vivo during cell proliferation, indicating that it could play a role in cell function. The possible mechanism of crosstalk is discussed here, with consideration to recent advances in the field.
Insulin-triggered repositioning of munc18c on syntaxin-4 in GLUT4 signalling
Authors: Smithers Natalie P. , Hodgkinson Conrad P. , Cuttle Matt , Sale Graham J.
Published: February 2008

One of the most important actions of insulin is the stimulation of the uptake of glucose into fat and muscle cells. Crucial to this response is the translocation of GLUT4 (glucose transporter-4) to the plasma membrane. The insulin-stimulated GLUT4 vesicle docking at the plasma membrane requires an interaction between VAMP-2 (vesicle-associated membrane protein-2) on the GLUT4 vesicle and syntaxin-4 in the plasma membrane. In the basal state, munc18c is thought to preclude GLUT4 vesicle docking by inhibiting this interaction. Here, we have used FCS (fluorescence correlation spectroscopy) in single living cells to show that munc18c binds to syntaxin-4 in both the basal and insulin-stimulated states. We show that munc18c contains two binding sites for syntaxin-4, one of which is disrupted by insulin, while the other is activated by insulin. Insulin-triggered repositioning of munc18c on syntaxin-4 in this way in turn allows syntaxin-4 to adopt its ‘open’ conformation and bind VAMP-2, resulting in the docking of the GLUT4 vesicle at the cell surface. The results also demonstrate the utility of using FCS in intact single living cells to elucidate cell signalling events.
RXR heterodimerization allosterically activates LXR binding to the second NR box of activating signal co-integrator-2
Authors: Son You Lee , Park Ok Gu , Kim Gwang Sik , Lee Jae Woon , Lee Young Chul
Published: February 2008

ASC-2 (activating signal co-integrator-2) is a transcriptional co-activator that mediates the transactivation of NRs (nuclear receptors) via direct interactions with these receptors. ASC-2 contains two separate NR-interaction domains harbouring a core signature motif, LXXLL (where X is any amino acid), named the NR box. Although the first NR box (NR box-1) of ASC-2 interacts with many different NRs, the second NR box (NR box-2) specifically interacts with only LXR (liver X receptor), whose transactivation in vivo requires heterodimerization with RXR (retinoid X receptor). Interestingly, RXR has been shown to enhance the LXR transactivation, even in the absence of LXR ligand via a unique mechanism of allosteric regulation. In the present study we demonstrate that LXR binding to an ASC-2 fragment containing NR box-2 (Co4aN) is enhanced by RXR and even further by liganded RXR. We also identified specific residues in Co4aN involved in its interaction with LXR that were also required for the ASC-2-mediated transactivation of LXR in mammalian cells. Using these mutants, we found that the Co4aN–LXR interaction surface is not altered by the presence of RXR and RXR ligand and that the Ser1490 residue is the critical determinant for the LXR-specific interaction of Co4aN. Notably the NR box-2, but not the NR box-1, is essential for ASC-2-mediated transactivation of LXR in vivo and for the interaction between LXR–RXR and ASC-2 in vitro. These results indicate that RXR does not interact directly with NR box-1 of ASC-2, but functions as an allosteric activator of LXR binding to NR box-2 of ASC-2.
Interactions of cubilin with megalin and the product of the amnionless gene (AMN): effect on its stability
Authors: Ahuja Rajiv , Yammani Raghunatha , Bauer Joseph A. , Kalra Seema , Seetharam Shakuntla , Seetharam Bellur
Published: February 2008

Cubilin, a 456 kDa multipurpose receptor lacking in both transmembrane and cytoplasmic domains is expressed in the apical BBMs (brush border membranes) of polarized epithelia. Cubilin interacts with two transmembrane proteins, AMN, a 45–50 kDa protein product of the amnionless gene, and megalin, a 600 kDa giant endocytic receptor. In vitro, three fragments of cubilin, the 113-residue N-terminus and CUB domains 12–17 and 22–27, demonstrated Ca2+-dependent binding to megalin. Immunoprecipitation and immunoblotting studies using detergent extracts of rat kidney BBMs revealed that cubilin interacts with both megalin and AMN. Ligand (intrinsic factor–cobalamin)-affinity chromatography showed that in renal BBMs, functional cubilin exists as a complex with both AMN and megalin. Cubilin and AMN levels were reduced by 80% and 55–60% respectively in total membranes and BBMs obtained from kidney of megalin antibody-producing rabbits. Immunohistochemical analysis and turnover studies for cubilin in megalin or AMN gene-silenced opossum kidney cells showed a significant reduction (85–90%) in cubilin staining and a 2-fold decrease in its half-life. Taken together, these results indicate that three distinct regions of cubilin bind to megalin and its interactions with both megalin and AMN are essential for its intracellular stability.
Targeting of PKCζ and PKB to caveolin-enriched microdomains represents a crucial step underpinning the disruption in PKB-directed signalling by ceramide
Authors: Hajduch Eric , Turban Sophie , Le Liepvre Xavier , Le Lay Soazig , Lipina Christopher , Dimopoulos Nikolaos , Dugail Isabelle , Hundal Harinder S.
Published: February 2008

Elevated ceramide concentrations in adipocytes and skeletal muscle impair PKB (protein kinase B; also known as Akt)-directed insulin signalling to key hormonal end points. An important feature of this inhibition involves the ceramide-induced activation of atypical PKCζ (protein kinase C-ζ), which associates with and negatively regulates PKB. In the present study, we demonstrate that this inhibition is critically dependent on the targeting and subsequent retention of PKCζ–PKB within CEM (caveolin-enriched microdomains), which is facilitated by kinase interactions with caveolin. Ceramide also recruits PTEN (phosphatase and tensin homologue detected on chromosome 10), a 3′-phosphoinositide phosphatase, thereby creating a repressive membrane microenvironment from which PKB cannot signal. Disrupting the structural integrity of caveolae by cholesterol depletion prevented caveolar targeting of PKCζ and PKB and suppressed kinase–caveolin association, but, importantly, also ameliorated ceramide-induced inhibition of PKB. Consistent with this, adipocytes from caveolin-1−/− mice, which lack functional caveolae, exhibit greater resistance to ceramide compared with caveolin-1+/+ adipocytes. We conclude that the recruitment and retention of PKB within CEM contribute significantly to ceramide-induced inhibition of PKB-directed signalling.
Sphingosylphosphorylcholine as a novel calmodulin inhibitor
Authors: Kovacs Erika , Liliom Karoly
Published: February 2008

S1P (sphingosine 1-phosphate) and SPC (sphingosylphosphorylcholine) have been recently recognized as important mediators of cell signalling, regulating basic cellular processes such as growth, differentiation, apoptosis, motility and Ca2+ homoeostasis. Interestingly, they can also act as first and second messengers. Although their activation of cell-surface G-protein-coupled receptors has been studied extensively, not much is known about their intracellular mechanism of action, and their target proteins are yet to be identified. We hypothesized that these sphingolipids might bind to CaM (calmodulin), the ubiquitous intracellular Ca2+ sensor. Binding assays utilizing intrinsic tyrosine fluorescence of the protein, dansyl-labelled CaM and surface plasmon resonance revealed that SPC binds to both apo- and Ca2+-saturated CaM selectively, when compared with the related lysophospholipid mediators S1P, LPA (lysophosphatidic acid) and LPC (lysophosphatidylcholine). Experiments carried out with the model CaM-binding domain melittin showed that SPC dissociates the CaM–target peptide complex, suggesting an inhibitory role. The functional effect of the interaction was examined on two target enzymes, phosphodiesterase and calcineurin, and SPC inhibited the Ca2+/CaM-dependent activity of both. Thus we propose that CaM might be an intracellular receptor for SPC, and raise the possibility of a novel endogenous regulation of CaM.
3-Keto-5α-steroid Δ1-dehydrogenase from Rhodococcus erythropolis SQ1 and its orthologue in Mycobacterium tuberculosis H37Rv are highly specific enzymes that function in cholesterol catabolism
Authors: Knol Jan , Bodewits Karin , Hessels Gerda I. , Dijkhuizen Lubbert , van der Geize Robert
Published: February 2008

The Rhodococcus erythropolis SQ1 kstD3 gene was cloned, heterologously expressed and biochemically characterized as a KSTD3 (3-keto-5α-steroid Δ1-dehydrogenase). Upstream of kstD3, an ORF (open reading frame) with similarity to Δ4 KSTD (3-keto-5α-steroid Δ4-dehydrogenase) was found, tentatively designated kst4D. Biochemical analysis revealed that the Δ1 KSTD3 has a clear preference for 3-ketosteroids with a saturated A-ring, displaying highest activity on 5α-AD (5α-androstane-3,17-dione) and 5α-T (5α-testosterone; also known as 17β-hydroxy-5α-androstane-3-one). The KSTD1 and KSTD2 enzymes, on the other hand, clearly prefer (9α-hydroxy-)4-androstene-3,17-dione as substrates. Phylogenetic analysis of known and putative KSTD amino acid sequences showed that the R. erythropolis KSTD proteins cluster into four distinct groups. Interestingly, Δ1 KSTD3 from R. erythropolis SQ1 clustered with Rv3537, the only Δ1 KSTD present in Mycobacterium tuberculosis H37Rv, a protein involved in cholesterol catabolism and pathogenicity. The substrate range of heterologously expressed Rv3537 enzyme was nearly identical with that of Δ1 KSTD3, indicating that these are orthologous enzymes. The results imply that 5α-AD and 5α-T are newly identified intermediates in the cholesterol catabolic pathway, and important steroids with respect to pathogenicity.
Activators of the farnesoid X receptor negatively regulate androgen glucuronidation in human prostate cancer LNCAP cells
Authors: Kaeding Jenny , Bouchaert Emmanuel , Bélanger Julie , Caron Patrick , Chouinard Sarah , Verreault Mélanie , Larouche Olivier , Pelletier Georges , Staels Bart , Bélanger Alain , Barbier Olivier
Published: February 2008

Androgens are major regulators of prostate cell growth and physiology. In the human prostate, androgens are inactivated in the form of hydrophilic glucuronide conjugates. These metabolites are formed by the two human UGT2B15 [UGT (UDP-glucuronosyltransferase) 2B15] and UGT2B17 enzymes. The FXR (farnesoid X receptor) is a bile acid sensor controlling hepatic and/or intestinal cholesterol, lipid and glucose metabolism. In the present study, we report the expression of FXR in normal and cancer prostate epithelial cells, and we demonstrate that its activation by chenodeoxycholic acid or GW4064 negatively interferes with the levels of UGT2B15 and UGT2B17 mRNA and protein in prostate cancer LNCaP cells. FXR activation also causes a drastic reduction of androgen glucuronidation in these cells. These results point out activators of FXR as negative regulators of androgen-conjugating UGT expression in the prostate. Finally, the androgen metabolite androsterone, which is also an activator of FXR, dose-dependently reduces the glucuronidation of androgens catalysed by UGT2B15 and UGT2B17 in an FXR-dependent manner in LNCaP cells. In conclusion, the present study identifies for the first time the activators of FXR as important regulators of androgen metabolism in human prostate cancer cells.
Peroxiredoxins play a major role in protectingTrypanosoma cruziagainst macrophage- and endogenously-derived peroxynitrite
Authors: Piacenza Lucía , Peluffo Gonzalo , Alvarez María Noel , Kelly John M. , Wilkinson Shane R. , Radi Rafael
Published: February 2008

There is increasing evidence that Trypanosoma cruzi antioxidant enzymes play a key immune evasion role by protecting the parasite against macrophage-derived reactive oxygen and nitrogen species. Using T. cruzi transformed to overexpress the peroxiredoxins TcCPX (T. cruzi cytosolic tryparedoxin peroxidase) and TcMPX (T. cruzi mitochondrial tryparedoxin peroxidase), we found that both cell lines readily detoxify cytotoxic and diffusible reactive oxygen and nitrogen species generated in vitro or released by activated macrophages. Parasites transformed to overexpress TcAPX (T. cruzi ascorbate-dependent haemoperoxidase) were also more resistant to H2O2 challenge, but unlike TcMPX and TcCPX overexpressing lines, the TcAPX overexpressing parasites were not resistant to peroxynitrite. Whereas isolated tryparedoxin peroxidases react rapidly (k=7.2×105 M−1·s−1) and reduce peroxynitrite to nitrite, our results demonstrate that both TcMPX and TcCPX peroxiredoxins also efficiently decompose exogenous- and endogenously-generated peroxynitrite in intact cells. The degree of protection provided by TcCPX against peroxynitrite challenge results in higher parasite proliferation rates, and is demonstrated by inhibition of intracellular redox-sensitive fluorescence probe oxidation, protein 3-nitrotyrosine and protein–DMPO (5,5-dimethylpyrroline-N-oxide) adduct formation. Additionally, peroxynitrite-mediated over-oxidation of the peroxidatic cysteine residue of peroxiredoxins was greatly decreased in TcCPX overexpressing cells. The protective effects generated by TcCPX and TcMPX after oxidant challenge were lost by mutation of the peroxidatic cysteine residue in both enzymes. We also observed that there is less peroxynitrite-dependent 3-nitrotyrosine formation in infective metacyclic trypomastigotes than in non-infective epimastigotes. Together with recent reports of up-regulation of antioxidant enzymes during metacyclogenesis, our results identify components of the antioxidant enzyme network of T. cruzi as virulence factors of emerging importance.
Structural elements of the ubiquitin-independent proteasome degron of ornithine decarboxylase
Authors: Takeuchi Junko , Chen Hui , Hoyt Martin A. , Coffino Philip
Published: February 2008

Mouse ODC (ornithine decarboxylase) is quickly degraded by the 26S proteasome in mammalian and fungal cells. Its degradation is independent of ubiquitin but requires a degradation signal composed of residues 425–461 at the ODC C-terminus, cODC (the last 37 amino acids of the ODC C-terminus). Mutational analysis of cODC revealed the presence of two essential elements in the degradation signal. The first consists of cysteine and alanine at residues 441 and 442 respectively. The second element is the C-terminus distal to residue 442; it has little or no sequence specificity, but is intolerant of insertions or deletions that alter its span. Reducing conditions, which preclude all well-characterized chemical reactions of the Cys441 thiol, are essential for in vitro degradation. These experiments imply that the degradative function of Cys441 does not involve its participation in chemical reaction; it, instead, functions within a structural element for recognition by the 26S proteasome.
A lipoxygenase with linoleate diol synthase activity from Nostoc sp. PCC 7120
Authors: Lang Imke , Göbel Cornelia , Porzel Andrea , Heilmann Ingo , Feussner Ivo
Published: February 2008

The dioxygenation of PUFAs (polyunsaturated fatty acids) in plants is mainly catalysed by members of the LOX (lipoxygenase) enzyme family. LOX products may be further metabolized, and are known as signalling substances in plant development and in responses to wounding and pathogen attack. In contrast with the situation in eukaryotes, information on the relevance of lipid peroxide metabolism in prokaryotic organisms is scarce. Therefore, we aimed to analyse LOXs and oxylipin patterns of cyanobacterial origin. A search of the genomic sequence of the cyanobacterium Nostoc sp. PCC 7120 suggested an open reading frame encoding a putative LOX named NspLOX that harboured an N-terminal extension. Individual analysis of recombinant C-terminal domain revealed enzymatic activity as a linoleate (9R)-LOX. Analysis of the full-length NspLOX protein, however, revealed linoleate diol synthase activity, generating (10E,12E)-9,14-dihydroxy-10,12-octadecadienoic acid as the main product from LA (linoleic acid) and (10E,12E,14E)-9,16-dihydroxy-10,12,14-octadecatrienoic acid as the main product from ALA (α-LA) substrates respectively, with ALA as preferred substrate. The enzyme exhibited a broad pH optimum between pH 7 and pH 10. Soluble extracts of Nostoc sp. contain more 9-LOX-derived hydroperoxides in sonified than in non-sonified cells, but products of full-length NspLOX were not detectable under the conditions used. As no other LOX-like sequence was identified in the genome of Nostoc sp. PCC 7120, the results presented suggest that (9R)-LOX-derived oxylipins may represent the endogenous products of NspLOX. Based on the biochemical results of NspLOX, we suggest that this bifunctional enzyme may represent a more ancient way to control the intracellular amount of oxylipins in this cyanobacterium.
A transplanted NPVY sequence in the cytosolic domain of the erythropoietin receptor enhances maturation
Authors: Nahari Tal , Barzilay Eran , Hirschberg Koret , Neumann Drorit
Published: February 2008

Activation of the EPO-R [EPO (erythropoietin) receptor] by its ligand EPO promotes erythropoiesis. Low cell surface EPO-R levels are traditionally attributed to inefficient folding mediated by the receptor extracellular domain. In the present study, we addressed the role of the EPO-R intracellular domain in exit from the ER (endoplasmic reticulum) and surface expression. A fusion protein between the thermo-reversible folding mutant of VSVG (vesicular-stomatitis-virus glycoprotein) (VSVGtsO45) and the EPO-R cytosolic domain [VSVG-WT (wild-type)] displayed delayed intracellular trafficking as compared with the parental VSVGtsO45, suggesting that the EPO-R cytosolic domain can hamper ER exit. Although NPXY-based motifs were originally associated with clathrin binding and endocytosis, they may also function in other contexts of the secretory pathway. A fusion protein between VSVGtsO45 and the cytosolic portion of EPO-R containing an NPVY insert (VSVG-NPVY) displayed enhanced glycan maturation and surface expression as compared with VSVG-WT. Notably, the NPVY insert also conferred improved maturation and augmented cell surface EPO-R. Our findings highlight three major concepts: (i) the EPO-R cytosolic domain is involved in ER exit of the receptor. (ii) Sequence motifs that participate in endocytosis can also modulate transport along the secretory pathway. (iii) VSVG-fusion proteins may be employed to screen for intracellular sequences that regulate transport.
Electrostatic and potential cation-π forces may guide the interaction of extracellular loop III with Na+ and bile acids for human apical Na+-dependent bile acid transporter
Authors: Banerjee Antara , Hussainzada Naissan , Khandelwal Akash , Swaan Peter W.
Published: February 2008

The hASBT (human apical Na+-dependent bile acid transporter) constitutes a key target of anti-hypercholesterolaemic therapies and pro-drug approaches; physiologically, hASBT actively reclaims bile acids along the terminal ileum via Na+ co-transport. Previously, TM (transmembrane segment) 7 was identified as part of the putative substrate permeation pathway using SCAM (substitute cysteine accessibility mutagenesis). In the present study, SCAM was extended through EL3 (extracellular loop 3; residues Arg254–Val286) that leads into TM7 from the exofacial matrix. Activity of most EL3 mutants was significantly hampered upon cysteine substitution, whereas ten (out of 31) were functionally inactive (<10% activity). Since only E282C lacked plasma membrane expression, EL3 amino acids predominantly fulfill critical functional roles during transport. Oppositely charged membrane-impermeant MTS (methanethiosulfonate) reagents {MTSET [(2-trimethylammonium) ethyl MTS] and MTSES [(2-sulfonatoethyl) MTS]} produced mostly similar inhibition profiles wherein only middle and descending loop segments (residues Thr267–Val286) displayed significant MTS sensitivity. The presence of bile acid substrate significantly reduced the rates of MTS modification for all MTS-sensitive mutants, suggesting a functional association between EL3 residues and bile acids. Activity assessments at equilibrative [Na+] revealed numerous Na+-sensitive residues, possibly performing auxiliary functions during transport such as transduction of protein conformational changes during translocation. Integration of these data suggests ligand interaction points along EL3 via electrostatic interactions with Arg256, Glu261 and probably Glu282 and a potential cation-π interaction with Phe278. We conclude that EL3 amino acids are essential for hASBT activity, probably as primary substrate interaction points using long-range electrostatic attractive forces.
Genetic aspects of inflammation and cancer
Authors: Hold Georgina L. , El-Omar M. Emad
Published: February 2008

Chronic inflammation is involved in the pathogenesis of most common cancers. The aetiology of the inflammation is varied and includes microbial, chemical and physical agents. The chronically inflamed milieu is awash with pro-inflammatory cytokines and is characterized by the activation of signalling pathways that cross-talk between inflammation and carcinogenesis. Many of the factors involved in chronic inflammation play a dual role in the process, promoting neoplastic progression but also facilitating cancer prevention. A comprehensive understanding of the molecular and cellular inflammatory mechanisms involved is vital for developing preventive and therapeutic strategies against cancer. The purpose of the present review is to evaluate the mechanistic pathways that underlie chronic inflammation and cancer with particular emphasis on the role of host genetic factors that increase the risk of carcinogenesis.
The chemistry of copper binding to PrP: is there sufficient evidence to elucidate a role for copper in protein function?
Authors: Davies Paul , Brown David R.
Published: February 2008

There has been an enormous body of literature published in the last 10 years concerning copper and PrP (prion protein). Despite this, there is still no generally accepted role for copper in the function of PrP or any real consensus as to how and to what affinity copper associates with the protein. The present review attempts to look at all the evidence for the chemistry, co-ordination and affinity of copper binding to PrP, and then looks at what effect this has on the protein. We then connect this evidence with possible roles for PrP when bound to copper. No clear conclusions can be made from the available data, but it is clear from the present review what aspects of copper association with PrP need to be re-investigated.
The LEA proteins and trehalose loving couple: a step forward in anhydrobiotic engineering
Authors: Iturriaga Gabriel
Published: February 2008

Adaptation to desiccation tolerance or anhydrobiosis has puzzled scientists for more than 300 years. Over the last few decades, considerable emphasis has been placed on understanding the role of two key molecules involved in anhydrobiosis: a peculiar disaccharide named trehalose and the hydrophilic LEA (Late Embryogenesis Abundant) proteins. In an article published in the Biochemical Journal in 2005, Alan Tunnacliffe and colleagues found that LEA proteins (alone, or more so in combination with trehalose) can protect stress-sensitive enzymes, such as citrate synthase and lactate dehydrogenase, from aggregation due to desiccation and freezing. Upon heat-stress, however, LEA proteins alone cannot prevent these enzymes from aggregating unless trehalose is present. This is the first report that LEA proteins can act as ‘molecular shields’ to prevent aggregation-induced cell damage due to water loss.
Unpacking User Relations in an Emerging Ubiquitous Computing Environment: Introducing the Bystander
Authors: Ferneley Elaine , Light Ben
Published: February 2008

The move towards technological ubiquity is allowing a more idiosyncratic and dynamic working environment to emerge that may result in the restructuring of information communication technologies, and changes in their use through different user groups’ actions. Taking a ‘practice’ lens to human agency, we explore the evolving roles of, and relationships between these user groups and their appropriation of emergent technologies by drawing upon Lamb and Kling's social actor framework. To illustrate our argument, we draw upon a study of a UK Fire Brigade that has introduced a variety of technologies in an attempt to move towards embracing mobile and ubiquitous computing. Our analysis of the enactment of such technologies reveals that Bystanders, a group yet to be taken as the central unit of analysis in information systems research, or considered in practice, are emerging as important actors. The research implications of our work relate to the need to further consider Bystanders in deployments other than those that are mobile and ubiquitous. For practice, we suggest that Bystanders require consideration in the systems development life cycle, particularly in terms of design and education in processes of use.
Fourth generation electron cyclotron resonance ion sources (invited)
Authors: Lyneis Claude M. , Leitner D. , Todd D. S. , Sabbi G. , Prestemon S. , Caspi S. , Ferracin P.
Published: February 2008

The concepts and technical challenges related to developing a fourth generation electron cyclotron resonance (ECR) ion source with a rf frequency greater than 40GHz and magnetic confinement fields greater than twice BECR will be explored in this article. Based on the semiempirical frequency scaling of ECR plasma density with the square of operating frequency, there should be significant gains in performance over current third generation ECR ion sources, which operate at rf frequencies between 20 and 30GHz. While the third generation ECR ion sources use NbTi superconducting solenoid and sextupole coils, the new sources will need to use different superconducting materials, such as Nb3Sn, to reach the required magnetic confinement, which scales linearly with rf frequency. Additional technical challenges include increased bremsstrahlung production, which may increase faster than the plasma density, bremsstrahlung heating of the cold mass, and the availability of high power continuous wave microwave sources at these frequencies. With each generation of ECR ion sources, there are new challenges to be mastered, but the potential for higher performance and reduced cost of the associated accelerator continues to make this a promising avenue for development.
Negative ion production in cesium seeded high electron temperature plasmas
Authors: Inoue T. , Tobari H. , Takado N. , Hanada M. , Kashiwagi M. , Hatayama A. , Wada M. , Sakamoto K.
Published: February 2008

In experiments on uniformity improvement in a large negative ion source, steep gradients have been observed in the profiles of electron temperature and H− ion beam intensity. It has been observed that the gradient in the H− ion beam intensity is altered by seeding cesium, though the electron temperature distribution is not affected by Cs. Thus in the Cs seeded condition, the H− ion beam intensity is enhanced in local area illuminated by high electron temperature plasmas. A brief analysis suggests possible advantages of high electron temperature plasmas for the negative ion surface production, by enhancement of dissociation to yield proton or atoms as parent particles of the negative ions.