Identification of Genes Affecting Vacuole Membrane Fragmentation in Saccharomyces cerevisiae.

The equilibrium of membrane fusion and fission influences the volume and copy number of organelles. Fusion of yeast vacuoles has been well characterized but their fission and the mechanisms determining vacuole size and abundance remain poorly understood. We therefore attempted to systematically characterize factors necessary for vacuole fission. Here, we present results of an in vivo screening for deficiencies in vacuolar fragmentation activity of an ordered collection deletion mutants, representing 4881 non-essential genes of the yeast Saccharomyces cerevisiae. The screen identified 133 mutants with strong defects in vacuole fragmentation. These comprise numerous known fragmentation factors, such as the Fab1p complex, Tor1p, Sit4p and the V-ATPase, thus validating the approach. The screen identified many novel factors promoting vacuole fragmentation. Among those are 22 open reading frames of unknown function and three conspicuous clusters of proteins with known function. The clusters concern the ESCRT machinery, adaptins, and lipases, which influence the production of diacylglycerol and phosphatidic acid. A common feature of these factors of known function is their capacity to change membrane curvature, suggesting that they might promote vacuole fragmentation via this property.

Ultrastructural changes of the internal limiting membrane removed during indocyanine green assisted peeling versus conventional surgery for idiopathic macular epiretinal membrane

Résumé : Introduction : L'objectif de cette étude était d'une part d'évaluer les caractéristiques histologiques des fragments cellulaires rétiniens attachés à la limitante interne après vitrectomie et pelage d'une membrane epirétinienne, et d'autre part de mettre en évidence des différences histologiques entre les cas opérés avec ou sans l'aide d'ICG dilué dans du glucose 5%. Méthodes Nous avons examiné rétrospectivement l'histologie de 88 spécimens de membranes épimaculaires contenant la limitante interne de la rétine, qui ont été enlevés chirurgicalement entre 1995 et 2003. L'analyse histologique a centré principalement l'attention sur la présence et les caractéristiques des fragments cellulaires rétiniens attachés à la limitante interne. L'analyse statistique a comparé les résultats entre le groupe I (chirurgie conventionnelle sans l'aide de l'ICG) et le groupe II (chirurgie à l'aide de l'ICG). Résultats Soixante et onze patients ont eu une vitrectomie sans l'aide de l'ICG (groupe I) et 17 avec l'aide de l'ICG (groupe II). Le nombre de débris de cellules de Müller à la surface rétinienne de la limitante interne était plus important dans le groupe I (sans ICG) que dans le groupe II (avec ICG) (40.8% versus 11.8% ; p = 0.024). Des larges fragments cellulaires rétiniens attachés à la limitante interne ont été plus fréquemment observés dans le groupe I (sans ICG) que dans le groupe II (avec ICG) (63.4% versus 23.5%; p= 0.003). Dans cinq (7%) cas du groupe I, de gros éléments cellulaires rétiniens ont été mis en évidence (des axones neuraux ou des vaisseaux sanguins). De tels éléments n'ont pas été retrouvés dans les spécimens du groupe II (avec ICG). Conclusions L'utilisation de l'ICG dilué dans du glucose 5% pour faciliter le pelage d'une membrane épimaculaire et notamment l'ablation de la limitante interne de la rétine semble diminuer de manière significative le nombre et la taille des débris des cellules de Muller adhérents à la face rétinienne de la membrane limitante interne de la rétine. Cette observation suggère que l'utilisation per-opératoire d'ICG dilué dans du glucose 5% facilite l'ablation de la limitante interne pendant la chirurgie de la membrane epirétinienne en diminuant l'adhérence de la limitante interne à la rétine.

Proteomic analysis of membrane rafts of melanoma cells identifies protein patterns characteristic of the tumor progression stage.

The molecular mechanisms controlling the progression of melanoma from a localized tumor to an invasive and metastatic disease are poorly understood. In the attempt to start defining a functional protein profile of melanoma progression, we have analyzed by LC-MS/MS the proteins associated with detergent resistant membranes (DRMs), which are enriched in cholesterol/sphingolipids-containing membrane rafts, of melanoma cell lines derived from tumors at different stages of progression. Since membrane rafts are involved in several biological processes, including signal transduction and protein trafficking, we hypothesized that the association of proteins with rafts can be regulated during melanoma development and affect protein function and disease progression. We have identified a total of 177 proteins in the DRMs of the cell lines examined. Among these, we have found groups of proteins preferentially associated with DRMs of either less malignant radial growth phase/vertical growth phase (VGP) cells, or aggressive VGP and metastatic cells suggesting that melanoma cells with different degrees of malignancy have different DRM profiles. Moreover, some proteins were found in DRMs of only some cell lines despite being expressed at similar levels in all the cell lines examined, suggesting the existence of mechanisms controlling their association with DRMs. We expect that understanding the mechanisms regulating DRM targeting and the activity of the proteins differentially associated with DRMs in relation to cell malignancy will help identify new molecular determinants of melanoma progression.

Membrane-destabilizing activity of pH-responsive cationic lysine-based surfactants: role of charge position and alkyl chain length

Many strategies for treating diseases require the delivery of drugs into the cell cytoplasm following internalization within endosomal vesicles. Thus, compounds triggered by low pH to disrupt membranes and release endosomal contents into the cytosol are of particular interest. Here, we report novel cationic lysine-based surfactants (hydrochloride salts of N¿- and N¿-acyl lysine methyl ester) that differ in the position of the positive charge and the length of the alkyl chain. Amino acid-based surfactants could be promising novel biomaterials in drug delivery systems, given their biocompatible properties and low cytotoxic potential. We examined their ability to disrupt the cell membrane in a range of pH values, concentrations and incubation times, using a standard hemolysis assay as a model of endosomal membranes. Furthermore, we addressed the mechanism of surfactant-mediated membrane destabilization, including the effects of each surfactant on erythrocyte morphology as a function of pH. We found that only surfactants with the positive charge on the ¿-amino group of lysine showed pH-sensitive hemolytic activity and improved kinetics within the endosomal pH range, indicating that the positive charge position is critical for pH-responsive behavior. Moreover, our results showed that an increase in the alkyl chain length from 14 to 16 carbon atoms was associated with a lower ability to disrupt cell membranes. Knowledge on modulating surfactant-lipid bilayer interactions may help us to develop more efficient biocompatible amino acid-based drug delivery devices.

ORMDL proteins are a conserved new family of endoplasmic reticulum membrane proteins

Background: Annotations of completely sequenced genomes reveal that nearly half of the genes identified are of unknown function, and that some belong to uncharacterized gene families. To help resolve such issues, information can be obtained from the comparative analysis of homologous genes in model organisms. Results: While characterizing genes from the retinitis pigmentosa locus RP26 at 2q31-q33, we have identified a new gene, ORMDL1, that belongs to a novel gene family comprising three genes in humans (ORMDL1, ORMDL2 and ORMDL3), and homologs in yeast, microsporidia, plants, Drosophila, urochordates and vertebrates. The human genes are expressed ubiquitously in adult and fetal tissues. The Drosophila ORMDL homolog is also expressed throughout embryonic and larval stages, particularly in ectodermally derived tissues. The ORMDL genes encode transmembrane proteins anchored in the endoplasmic reticulum (ER). Double knockout of the two Saccharomyces cerevisiae homologs leads to decreased growth rate and greater sensitivity to tunicamycin and dithiothreitol. Yeast mutants can be rescued by human ORMDL homologs. Conclusions: From protein sequence comparisons we have defined a novel gene family, not previously recognized because of the absence of a characterized functional signature. The sequence conservation of this family from yeast to vertebrates, the maintenance of duplicate copies in different lineages, the ubiquitous pattern of expression in human and Drosophila, the partial functional redundancy of the yeast homologs and phenotypic rescue by the human homologs, strongly support functional conservation. Subcellular localization and the response of yeast mutants to specific agents point to the involvement of ORMDL in protein folding in the ER.

Chiroptical measurement of chiral aggregates at liquid-liquid interface in centrifugal liquid membrane cell by Mueller matrix and conventional circular dichroism methods

The centrifugal liquid membrane (CLM) cell has been utilized for chiroptical studies of liquid-liquid interfaces with a conventional circular dichroism (CD) spectropolarimeter. These studies required the characterization of optical properties of the rotating cylindrical CLM glass cell, which was used under the high speed rotation. In the present study, we have measured the circular and linear dichroism (CD and LD) spectra and the circular and linear birefringence (CB and LB) spectra of the CLM cell itself as well as those of porphyrine aggregates formed at the liquid-liquid interface in the CLM cell, applying Mueller matrix measurement method. From the results, it was confirmed that the CLM-CD spectra of the interfacial porphyrin aggregates observed by a conventional CD spectropolarimeter should be correct irrespective of LD and LB signals in the CLM cell.

The membrane-associated transient receptor potential vanilloid channel is the central heat shock receptor controlling the cellular heat shock response in epithelial cells.

The heat shock response (HSR) is a highly conserved molecular response to various types of stresses, including heat shock, during which heat-shock proteins (Hsps) are produced to prevent and repair damages in labile proteins and membranes. In cells, protein unfolding in the cytoplasm is thought to directly enable the activation of the heat shock factor 1 (HSF-1), however, recent work supports the activation of the HSR via an increase in the fluidity of specific membrane domains, leading to activation of heat-shock genes. Our findings support the existence of a plasma membrane-dependent mechanism of HSF-1 activation in animal cells, which is initiated by a membrane-associated transient receptor potential vanilloid receptor (TRPV). We found in various non-cancerous and cancerous mammalian epithelial cells that the TRPV1 agonists, capsaicin and resiniferatoxin (RTX), upregulated the accumulation of Hsp70, Hsp90 and Hsp27 and Hsp70 and Hsp90 respectively, while the TRPV1 antagonists, capsazepine and AMG-9810, attenuated the accumulation of Hsp70, Hsp90 and Hsp27 and Hsp70, Hsp90, respectively. Capsaicin was also shown to activate HSF-1. These findings suggest that heat-sensing and signaling in mammalian cells is dependent on TRPV channels in the plasma membrane. Thus, TRPV channels may be important drug targets to inhibit or restore the cellular stress response in diseases with defective cellular proteins, such as cancer, inflammation and aging.

The role of the vacuolar H+ - ATPase in membrane fusion

RésuméLa H+-ATPase vacuolaire (V-ATPase) est un complexe enzymatique composé de deux secteurs multimériques (VQ et Vi) dont l'association dans la cellule est réversible. Le secteur intramembranaire de la V-ATPase (V0) interagit physiquement avec des protéines SNARE et stimule la fusion homotypique des vacuoles de la levure (lysosomes), la sécrétion de neurotransmetteurs et d'insuline, la fusion entre phagosome et lysosome ainsi que la sécrétion des corps multivésiculaires par un mécanisme inconnu. Dans cette étude j'ai identifié des résidues d'acides amines situés dans des sous-unités de V0 impliqués dans le mécanisme de fusion des vacuoles mais non essentiels pour l'acidification vacuolaire par la V-ATPase. j'ai utilisé un protocole de mutagenèse aléatoire pour produire des libraries de mutants des sous unités de V0. Ces libraries ont été analysées in vivo afin d'identifier des alleles qui permettent la translocation des protons mais produisent une vacuole fragmentée, phénotype indiquant un défaut dans la fusion membranaire. Les vacuoles des mutants ont été isolées et caractéisées en utilisant une grande variété d'outils biochimiques pour déterminer précisément l'impact des différentes mutations sur l'accomplissement d'événements clés du processus de fusion.J'ai identifié des mutations associées à des défauts spécifiques de la fusion dans plusieurs sous-unités de V0. Dans les protéolipides c, c' et c" ces mutations se concentrent dans la partie cytosolique des domaines transmembranaires. Elles renforcent les associations entre les secteurs de la V-ATPase et entre V0 et les SNAREs. Dans la fusion vacuolaire ces mutations permettent la formation de complexes SNAREs en trans mais inhibent l'induction de la fusion. Par contre, la deletion de la sous- unité d influence les étapes de la fusion qui précèdent la formation des complexes trans-SNAREs. Mes résultats démontrent que V0 joue des rôles différents dans plusieurs étapes de la fusion et que ces fonctions sont liées au système des SNAREs. Ils différencient génétiquement les activités de V0 dans la translocation des protons et dans la fusion et identifient de nombreux résidus importants pour la fusion vacuolaire. De plus, compte tenu de la grande conservation de sequence des protéolipides chez les eukaryotes les mutations identifiées dans cette l'étude apportent de nouvelles informations pour analyser la fonction de V0 dans des organismes multicellulaires pour lesquels la function catalytique de la V-ATPase est essentielle à la survie.Résumé pour le large publicLe transport de protéines et de membranes est important pour maintenir la fonction des organelles dans la cellule. Il s'excerce au niveau des vesicules. La fusion membranaire est un processus élémentaire de ce transport. Pour fusionner deux membranes, il faut la coordination de deux activités: le rapprochement et la déstabiiization des deux membranes. La collaboration d'un ensemble de proteins conservés chez les eukaryotes, est nécessaire pour catalyser ces activités. Les proteins SNAREs sont les protagonistes principaux dans la fusion membranaire. Néanmoins, d'autres protéines, comme des Rab-GTPases et des chaperonnes, sont nécessaires pour permettre ce phénomène de fusion. Toutes ces protéines sont temporairement associées avec les SNAREs et leur fonction dans la fusion membranaire est souvent directement liée à leur activité dans cette association. Le secteur transmembranaire V0 de la V-ATPase rnteragit avec des SNAREs et est essentiel pour la fusion dans une variété de systèmes modèles comme la mouche, la souris et la levure. Le secteur V0 est composé de six protéines différentes. Avec te secteur Va, qui réside dans le cytosol, il forme la V-ATPase dont la fonction principale est l'acidification des organelles par translocation des protons à travers la membrane par un mécanisme ressemblant à celui d'une pompe. V0joue un role dans la fusion membranaire, indépendamment de son activité catalytique liée au pompage des protons, et ce rôle est encore largement méconnu à ce jour. Le but de ma thèse était de mieux comprendre l'implication de V0 dans ce contexte.Pour étudier des activités liées à la V-ATPase, la levure est un excellent modèle d'étude car elle survie à une inactivation de l'enzyme alors que le meme traitement serait léthal pour des organismes multicellulaires. Dans ma thèse j'ai utilisé la fusion homotypique de la vacuole de levure comme système modèle pour étudier le rôle de V0 dans la fusion. J'ai muté des gènes qui encodent des sous- unités de V0 et les ai introduit dans des souches privées des gènes respectifs. Dans les librairies de souches portant différentes versions de ces gènes j'ai cherché des clones exprimant une V-ATPase intacte et fonctionnelle mais qui possèdent une vacuole fragmentée. Le plus souvent, une vacuole fragmentée indique un défaut dans la fusion vacuolaire. Dans les trois types de protéolipides qui composent un cylindre dans le secteur V0, j'ai trouvé des clones avec une vacuole fragmentée. Après avoir isolé les mutations responsable de ce type de morphologie vacuolaire, j'ai isolé les vacuoles de ces clones pour étudier leur activités dans différentes étapes de la fusion vacuolaire. Les résultats de ces analyses mettent en évidence une implication de V0 dans plusieurs étapes de la fusion vacuolaire. Certaines mutations sélectionnées dans mon étude inhibent une étape précoce de la fusion qui inclue la dissociation des complexes SNARE, tandis que d'autres mutations inhibent une étape tardive du processus de fusion qui inclue la transmission d'une force disruptive dans la membrane.AbstractThe membrane-integral V0 sector of the vacuolar H+-ATPase (V-ATPase) interacts with SNARE proteins. V0 stimulates fusion between yeast vacuoles (lysosomes) (Peters et al., 2001b), secretion of neurotransmitters and insulin (Hiesinger et al., 2005a, Sun-Wada et al., 2006a), phagosome-lysosome fusion (Peri and Nusslein-Volhard, 2008) and secretion of multivesicular bodies (Liegeois et al., 2006b) by a yet unknown mechanism. In my thesis, I identified sites in V0 subunits that are involved in yeast vacuole fusion but dispensable for the proton pumping by the V-ATPase. I randomly mutagenized V0 subunits and screened in vivo for mutant alleles that support proton pumping but cause fragmented vacuoles, a phenotype indicative of a fusion defect. Mutant vacuoles were isolated and analyzed in a cell-free system, allowing assay of key events in fusion, such as trans-SNARE pairing, lipid transition and fusion pore opening (Reese et al., 2005b).Mutants with selective fusion defects were found in several V0 subunits. In the proteolipids c, c' and c", critical mutations are concentated in the cytosolic half of the transmembrane domains. These mutations rendered the V-ATPase holoenzyme more stable and modulated V0-SNARE associations. In vacuole fusion critical proteolipid mutations permitted trans-SNARE pairing but impeded the induction of lipid flow between the membranes. Deletion of subunit d, by contrast, influenced early stages of fusion that precede trans-SNARE pairing. My results show that V0 acts in several steps of the fusion process and that its function is intimately connected to the SNARE system. They genetically separate the proton pump and fusion activities of V0 and identify numerous critical residues. Given the high sequence conservation of proteolipids in eukaryotic life, the identified mutations may be helpful in analyzing the fusion function of V0 also in mammalian cells, where V- ATPase pump function is essential for survival.

Ultrastructural changes of the internal limiting membrane removed during indocyanine green assisted peeling versus conventional surgery for idiopathic macular epiretinal membrane.

PURPOSE: To evaluate the histologic features of cellular retinal fragments on the internal limiting membrane (ILM) removed during idiopathic macular epiretinal membrane (MEM) peeling surgery with and without the aid of indocyanine green (ICG) diluted in 5% glucose. METHODS: ILM specimens removed from 88 eyes during idiopathic MEM surgery between 1995 and 2003 were reviewed retrospectively. Histologic analysis focused on the presence and characteristics of retinal fragments on the retinal surface of the ILM. Statistical analysis compared the results between group I (conventional surgery) and group II (ICG-assisted peeling). RESULTS: Seventy-one eyes underwent MEM surgery without the aid of ICG (group I) and seventeen underwent MEM ICG-assisted surgery (group II). The amount of Müller cell debris on the retinal surface of the ILM was more significant in the group I than in the group II (40.8 vs. 11.8; P = 0.024). Large fragments of Müller cells were more frequently observed in the group I (no ICG) than in the group II (ICG) (63.4 vs. 23.5%; P = 0.003). CONCLUSIONS: The use of ICG diluted with 5% glucose in ILM removal during MEM surgery was associated with less retinal debris attached to the retinal face of the ILM compared with surgery in which ICG was not used.

Mutual control of membrane fission and fusion proteins.

Membrane fusion and fission are antagonistic reactions controlled by different proteins. Dynamins promote membrane fission by GTP-driven changes of conformation and polymerization state, while SNAREs fuse membranes by forming complexes between t- and v-SNAREs from apposed vesicles. Here, we describe a role of the dynamin-like GTPase Vps1p in fusion of yeast vacuoles. Vps1p forms polymers that couple several t-SNAREs together. At the onset of fusion, the SNARE-activating ATPase Sec18p/NSF and the t-SNARE depolymerize Vps1p and release it from the membrane. This activity is independent of the SNARE coactivator Sec17p/alpha-SNAP and of the v-SNARE. Vps1p release liberates the t-SNAREs for initiating fusion and at the same time disrupts fission activity. We propose that reciprocal control between fusion and fission components exists, which may prevent futile cycles of fission and fusion.

Dopamine receptors on dispersed bovine anterior pituitary cells

The dopamine antagonist [3H]-domperidone-[3H]-DOM-bound to a single class of high-affinity (Kd = 1.24 +/- 0.14 nM) and saturable receptors on dispersed bovine anterior pituitary (AP) cells. The binding of [3H]-DOM was stereoselective and reversible with agonists and antagonists. Dopamine competitions for [3H]-DOM binding modeled best for a single site consistent with an interaction with a homogeneous population of receptors. The mean number of specific binding sites labeled by [3H]-DOM was 53,000 per cell in dispersed AP cells consisting of 42% lactotrophs. Dispersed bovine AP cells attached to extracellular matrix within 3 h, and prolactin secretion from these cells was effectively inhibited by dopamine. Several observations suggested that [3H]-DOM-labeled receptors on dispersed bovine AP cells were restricted to the outer plasma membrane and not internalized. These included (1) the rapid and complete dissociation of specific [3H]-DOM binding; (2) the ability of treatment with acid or proteolytic enzymes to entirely remove specifically bound [3H]-DOM, and (3) the lack of effect of metabolic inhibitors on specific [3H]-DOM binding.

Bridge Deck Waterproofing Membrane Study, R-262, 1974

One of the main problems of bridge maintenance in Iowa is the spalling and scaling of the decks. This problem stems from the continued use of deicing salts during the winter months. Since bridges will frost or freeze more often than roadways, the use of deicing salts on bridges is more frequent. The salt which is spread onto the bridge dissolves in water and permeates into the concrete deck. When the salt reaches the depth of the reinforcing steel and the concentration at that depth reaches the threshold concentration for corrosion (1.5 lbs./yd. 3 ), the steel will begin to oxidize. The oxidizing steel must then expand within the concrete. This expansion eventually forces undersurface fractures and spalls in the concrete. The spalling increases maintenance problems on bridges and in some cases has forced resurfacing after only a few years of service. There are two possible solutions to this problem. One solution is discontinuing the use of salts as the deicing agent on bridges and the other is preventing the salt from reaching or attacking the reinforcing steel. This report deals with one method which stops the salt from reaching the reinforcing steel. The method utilizes a waterproof membrane on the surface of a bridge deck. The waterproof membrane stops the water-salt solution from entering the concrete so the salt cannot reach the reinforcing steel.

Surgical treatment of lamellar macular hole associated with epimacular membrane.

BACKGROUND:: Although the surgical treatment of full-thickness macular hole is well established, the utility of pars plana vitrectomy in the treatment of lamellar macular hole (LMH) remains less clear. The purpose of the study is to report functional results of surgical treatment of LMH associated with epiretinal membrane. METHODS:: Retrospective chart review of patients undergoing pars plana vitrectomy and peeling of epiretinal membrane and internal limiting membrane, with or without air or gas tamponade, for symptomatic LMH associated with epimacular membrane. RESULTS:: Forty-five eyes of 44 patients were operated for LMH associated with epimacular membrane between May 2000 and July 2009. Pars plana vitrectomy and membrane peeling were combined with air or gas tamponade in 43 of 45 cases. Mean logarithm of the minimum angle of resolution best-corrected visual acuity improved from 0.4 preoperatively to 0.13 postoperatively (P < 0.0001). Improvement in visual acuity ranged from 0 Early Treatment Diabetic Retinopathy Study (ETDRS) lines to 8.9 ETDRS lines (mean, 2.65 ETDRS lines). Visual acuity improved by ≥1 ETDRS line(s) in 40 of 45 eyes (89%) and by ≥2 ETDRS lines in 26 of 45 eyes (58%) after the surgical procedure. No patient lost vision. CONCLUSION:: This small retrospective study suggests that surgical treatment of LMH associated with epimacular membrane may improve visual acuity in symptomatic patients.