Isolated Plasma Membranes Research Articles

Plasma membrane vesicles decorated with glycolipid-anchored antigens and adjuvants via protein transfer as an antigen delivery platform for inhibition of tumor growth

Antigen delivered within particulate materials leads to enhanced antigen-specific immunity compared to soluble administration of antigen. However, current delivery approaches for antigen encapsulated in synthetic particulate materials are limited by the complexity of particle production that affects stability and immunogenicity of the antigen. Herein, we describe a protein delivery system that utilizes plasma membrane vesicles (PMVs) derived from biological materials such as cultured cells or isolated tissues and a simple protein transfer technology. We show that these particulate PMVs can be easily modified within 4 h by a protein transfer process to stably incorporate a glycosylphosphatidylinositol (GPI)-anchored form of the breast cancer antigen HER-2 onto the PMV surface. Immunization of mice with GPI-HER-2-modified-PMVs induced strong HER-2-specific antibody responses and protection from tumor challenge in two different breast cancer models. Further incorporation of the immunostimulatory molecules IL-12 and B7-1 onto the PMVs by protein transfer enhanced tumor protection and induced beneficial Th1 and Th2-type HER-2-specific immune responses. Since protein antigens can be easily converted to GPI-anchored forms, these results demonstrate that isolated plasma membrane vesicles can be modified with desired antigens along with immunostimulatory molecules by protein transfer and used as a vaccine delivery vehicle to elicit potent antigen-specific immunity.

High Efficacy but Low Potency of δ-Opioid Receptor-G Protein Coupling in Brij-58-Treated, Low-Density Plasma Membrane Fragments.

Principal FindingsHEK293 cells stably expressing PTX-insensitive δ-opioid receptor-Gi1α (C351I) fusion protein were homogenized, treated with low concentrations of non-ionic detergent Brij-58 at 0°C and fractionated by flotation in sucrose density gradient. In optimum range of detergent concentrations (0.025–0.05% w/v), Brij-58-treated, low-density membranes exhibited 2-3-fold higher efficacy of DADLE-stimulated, high-affinity [32P]GTPase and [35S]GTPγS binding than membranes of the same density prepared in the absence of detergent. The potency of agonist DADLE response was significantly decreased. At high detergent concentrations (>0.1%), the functional coupling between δ-opioid receptors and G proteins was completely diminished. The same detergent effects were measured in plasma membranes isolated from PTX-treated cells. Therefore, the effect of Brij-58 on δ-opioid receptor-G protein coupling was not restricted to the covalently bound Gi1α within δ-opioid receptor-Gi1α fusion protein, but it was also valid for PTX-sensitive G proteins of Gi/Go family endogenously expressed in HEK293 cells. Characterization of the direct effect of Brij-58 on the hydrophobic interior of isolated plasma membranes by steady-state anisotropy of diphenylhexatriene (DPH) fluorescence indicated a marked increase of membrane fluidity. The time-resolved analysis of decay of DPH fluorescence by the “wobble in cone” model of DPH motion in the membrane indicated that the exposure to the increasing concentrations of Brij-58 led to a decreased order and higher motional freedom of the dye.SummaryLimited perturbation of plasma membrane integrity by low concentrations of non-ionic detergent Brij-58 results in alteration of δ-OR-G protein coupling. Maximum G protein-response to agonist stimulation (efficacy) is increased; affinity of response (potency) is decreased. The total degradation plasma membrane structure at high detergent concentrations results in diminution of functional coupling between δ-opioid receptors and G proteins.

Proteomic Analysis of Isolated Plasma Membrane Fractions from the Mammary Gland in Lactating Cows.

The mammary gland of dairy cows is a formidable lipid-synthesizing machine for lactation. This unique function depends on the activities of plasma membrane (PM) proteins in mammary cells. Little information is known about the expression profiles of PM proteins and their functions during the lactating process. This study investigated the proteome map of PM fractions of mammary gland in lactating cows using 1D-Gel-LC-MS/MS and identified 872 nonredundant proteins with 141 unknown proteins, wherein 215 were PM-associated proteins. Most of the PM-associated proteins were binding, transport, and catalytic proteins such as annexin proteins, heat shock proteins, integrins, RAS oncogene family members, and S100 calcium binding proteins. The PM-associated pathways such as caveolae-mediated endocytosis, leukocyte extravasation, aldosterone signaling in epithelial cells, and remodeling of epithelial adherens junctions were also significantly over-represented. Proteomic analysis revealed the characteristics and predicted functions of PM proteins isolated from the lactating bovine mammary gland. These results further provide experimental evidence for the presence of many proteins predicted in the annotated bovine genome. The data generated here also provide a reference for the PM-related functional research in the mammary gland of lactating cows.

Cell adhesion and spreading at a charged interface: Insight into the mechanism using surface techniques and mathematical modelling

We study the kinetics of adhesion and spreading of an algal cell and its plasma membrane vesicle at the charged interface. A simple system of an isolated plasma membrane vesicle without internal content has been developed and characterized by atomic force microscopy (AFM). We extend the methodology based on the reaction kinetics model and empirical fitting for the analysis of amperometric signals, and demonstrate its validity and pertinence in a wide range of surface charge densities. Adhesion kinetics of the algal cell is slower than that of its plasma membrane vesicle. Isolated plasma membrane contributes about one quarter to the cell contact area. The model reconstructs and quantifies individual states of the three-step adhesion process of the algal cell and makes it possible to associate them with various features of amperometric signal. At the time of current amplitude, the ruptured state predominates and the cell spread contact area is larger than its initial area as well as the contact area of the plasma membrane vesicle. These results suggest that a major structural disruption of the cell membrane, collapse of cytoskeleton and leakage of intracellular material could appear close to the time of current amplitude. Further, slow kinetics of the organic film spreading at the interface to its maximal extent is considered as the rate determining step, which could be a consequence of the attenuated effect of potential at the modified interface, stronger intermolecular interactions and reorganization of molecules in the film. Our findings offer an insight into the mechanism of algal cell adhesion and spreading at charged interfaces, relevant for electroporation based studies.

Lectin-Magnetic Beads for Plasma Membrane Isolation

Plasma membrane proteins mainly function to transmit external signals into the cell. Many plasma membrane receptor tyrosine kinases (e.g., HER2 and EGFR) are known to mediate oncogenic progression, making them prime targets for cancer therapy. Recently, it has become important to identify plasma membrane proteins that are differentially expressed in normal versus cancer cells, in drug-sensitive versus drug-resistant cells, or among tumor cells that metastasize to different organ sites because these differentially expressed membrane proteins may lead to the identification of therapeutic targets or diagnostic markers. In addition, there is an increased interest in identifying cell-surface proteins that could serve as markers for stem cells, progenitor cells, or cells of different lineages. Traditionally, membrane isolation requires multiple centrifugation steps to isolate different organelles based on their density. With the advent of affinity matrix technology, it is possible to separate organelles based on their molecular differences. A defining characteristic of the plasma membrane is that plasma membrane proteins are more extensively glycosylated than are intracellular membrane proteins. As a result, affinity chromatography employing lectin, a carbohydrate-binding protein, is commonly used to isolate plasma membrane proteins. We have extended this concept for plasma membrane isolation by using concanavalin A (ConA), a lectin with mannose specificity. Here we describe a protocol that uses immobilized ConA bound to magnetic beads to isolate plasma membranes from homogenized cell lysates. The captured plasma membrane proteins are then solubilized from the ConA-magnetic beads by detergents in the presence of a competing sugar, methyl α-mannopyranoside.

Does PtdIns(4,5)P2 concentrate so it can multitask?

PtdIns(4,5)P2 drives many plasma membrane (PM) functions which can be summarized as the delivery of materials and information into, out of and across the membrane, as well as the assembly of structural components. How does the lipid execute so many disparate functions involving a vast array of different protein complexes? A leading hypothesis is that the PM organizes into nanoscopic PtdIns(4,5)P2‐rich platforms that associate with specific molecular complexes. Here, we have employed single molecule, super‐resolution techniques to test this hypothesis. Imaging fixed cells expressing PtdIns(4,5)P2 biosensors (< 40 nm resolution) reveals no evidence for discrete domains. Experiments where the dynamics of biosensor molecules are tracked in living cells reveals rapid diffusion of biosensor/PtdIns(4,5)P2 in the PM, indicating that biosensor:lipid complexes may be released from pre‐existing PtdIns(4,5)P2‐rich platforms. On the other hand, diffusion of biosensor/lipid complexes shows clear signs of anomalous diffusion. To circumvent potential occlusion of PtdIns(4,5)P2‐rich platforms by an expressed biosensor, we have interrogated isolated plasma membrane sheets with exogenous PtdIns(4,5)P2 probes. Again, these results reveal no evidence for PtdIns(4,5)P2‐rich platforms at a resolution levels of < 40 nm. Given the rapid diffusion of the free lipid molecules across such small distances as this, our results are inconsistent with pre‐existing PtdIns(4,5)P2‐rich platforms that recruit protein complexes. Rather, it seems more likely that protein complexes recruit the lipid into functionally dedicated complexes in the PM.

Resin-Embedded Multicycle Imaging of Cells and Isolated Plasma Membranes

Studies of the plasma membrane protein organization have undergone numerous advances; however, the large number of protein species involved complicates their examination. One approach which has the ability to resolve this complication is that of resin-embedded multicycle imaging (REMI), which stabilizes protein structure and antigenicity while labels are removed and replaced, allowing an arbitrarily large number of proteins of interest to be imaged in the same area. The implementation spearheading this technique is array tomography, which is ideal for many applications, but certain organelles or spatially restricted volumes of interest, such as the plasma membrane, present considerable difficulty. We have developed a method by which cells or isolated plasma membranes unroofed by osmotic shock can be embedded in thin films of acrylic resin (LR White, Lowicryl), making their spatially dependent proteomic information amenable to repeated immunostaining and other methods of analysis. Here we present our latest work in the development of this method.

Proteomic approaches and their application to plant gravitropism.

Proteomics is a powerful technique that allows researchers a window into how an organism responds to a mutation, a specific environment, or at a distinct point during development by quantifying relative protein abundance and posttranslational modifications. Here, we describe methods for the proteomic analysis of Arabidopsis thaliana tissue. Extraction protocols are provided for isolation of soluble, plasma membrane, and tonoplast proteins. In addition, basic analysis and quality metrics for MS/MS data are discussed. The protocols outlined have the potential to unlock new avenues of research that are not possible through basic genetics or transcriptomic approaches. By combining proteomic information with known gene regulatory patterns, researchers can gain a complete picture of how molecular pathways, such as those required for gravitropism, are initiated, regulated, and terminated.

Short-term effects of ultrahigh concentration cationic silica nanoparticles on cell internalization, cytotoxicity, and cell integrity with human breast cancer cell line (MCF-7)

High concentrations of cationic colloidal silica nanoparticles (CCS-NPs) have been widely used for the enrichment of plasma membrane proteins. However, the interaction between the CCS-NPs and cells under the required concentration for the isolation of plasma membrane are rarely investigated. We evaluated the internalization and toxicity of the 15 nm CCS-NPs which were exposed at high concentrations with short time in human breast cancer cells (MCF-7) with transmission electron microscopy, energy dispersive X-ray spectroscopy, inductively coupled plasma atomic emission spectroscopy, and colorimetric assays. The NPs were observed throughout the cells, particularly in the cytoplasm and the nucleus, after short incubation periods. Additionally, the NPs significantly influenced the membrane integrity of the MCF-7 cells.

Hexadecanol Reverses Ethanol Induced Tadpole Anesthesia and Raises Critical Temperatures in Isolated Plasma Membrane Vesicles

Many small molecules induce general anesthesia in animals ranging from insects to mammals. Although their mechanism of action remains controversial, it is known that a compound's efficacy as an anesthetic is strongly predicted by both its hydrophobicity and its potency in inhibiting certain ligand gated ion channels. We recently published experiments showing that n-alcohol anesthetics (n≤10) take plasma membrane derived vesicles away from a biologically tuned, two dimensional (2D) liquid-liquid critical point [1]. Here, we present one line of investigation into our working hypothesis that anesthetics exert at least some of their effects by interfering with native regulation by the nearly critical plasma membrane. While most compounds, including the n≤10-alcohol anesthetics, lower critical temperatures in membranes, certain compounds raise critical temperatures counteracting the effects of anesthetics on membrane criticality. These compounds should specifically reverse effects mediated through membrane criticality. We demonstrate that hexadecanol (n=16) is such a compound, raising critical temperatures in cell-derived vesicles in a dose-dependent manner. We also present evidence that hexadecanol reverses ethanol's anesthetic effects on the tadpole righting response, in a manner quantitatively predicted by its effects on membrane criticality.1. Gray, E.; Karslake, J.; Machta, B.B.; Veatch, S.L.; Biophys. J. 105(12): 2751-9 (2013).

Isolation of giant plasma membrane vesicles for evaluation of plasma membrane structure and protein partitioning.

Although investigation into the structure of eukaryotic cell membranes has been an intense focus of cell biology for the past two decades, definitive insights have been limited by the lack of coherent methods for the isolation of specific organelle membranes and the identification of membrane subdomains. Here we describe a method for the isolation of mammalian cell plasma membranes as Giant Plasma Membrane Vesicles (GPMVs) and strategies for imaging membrane lateral structure and quantification of protein partitioning between coexisting domains by fluorescence microscopy.

Electron microscopy methods for studying plasma membranes.

Electron microscopy allows direct visualization of the underlying organization of cell surface components on a nano-scale. Immuno-gold labelling of isolated plasma membranes generates point patterns that enable mapping of protein and lipid distributions. 2D spatial statistics reveals the extent to which these distributions are clustered or dispersed and allows the extent of co-localization between different cell surface components to be precisely determined. This approach has been successfully applied to the study of signalling network organization and the consequences of physiological changes in modulating cell surface function.

Spatiotemporal lipid profiling during early embryo development of Xenopus laevis using dynamic ToF-SIMS imaging

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging has been used for the direct analysis of single intact Xenopus laevis embryo surfaces, locating multiple lipids during fertilization and the early embryo development stages with subcellular lateral resolution (∼4 μm). The method avoids the complicated sample preparation for lipid analysis of the embryos, which requires selective chemical extraction of a pool of samples and chromatographic separation, while preserving the spatial distribution of biological species. The results show ToF-SIMS is capable of profiling multiple components (e.g., glycerophosphocholine, SM, cholesterol, vitamin E, diacylglycerol, and triacylglycerol) in a single X. laevis embryo. We observe lipid remodeling during fertilization and early embryo development via time course sampling. The study also reveals the lipid distribution on the gamete fusion site. The methodology used in the study opens the possibility of studying developmental biology using high resolution imaging MS and of understanding the functional role of the biological molecules.

Isolation of cellular membranes from lignin-producing tissues of Norway spruce and analysis of redox enzymes.

There are no earlier reports with successful isolation of plasma membranes from lignin-forming tissues of conifers. A method to isolate cellular membranes from extracellular lignin-producing tissue-cultured cells and developing xylem of Norway spruce was optimized. Modifications to the homogenization buffer were needed to obtain membranes from these phenolics-rich tissues. Membranes were separated by aqueous polymer two-phase partitioning. Chlorophyll a determination, marker enzyme assays and western blot analyses using antibodies for each membrane type showed that mitochondrial, chloroplastic and to a certain extent also ER and Golgi membranes were efficiently diminished from the upper phase, but tonoplast and plasma membranes distributed evenly between the upper and lower phases. Redox enzymes present in the partially purified membrane fractions were assayed in order to reveal the origin of H(2)O(2) needed for lignification. The membranes of spruce contained enzymes able to generate superoxide in the presence of NAD(P)H. Besides members of the flavodoxin and flavodoxin-like family proteins, cytochrome b5, cytochrome P450 and several stress responsive proteins were identified by nitroblue tetrazolium staining of isoelectric focusing gels and by mass spectrometry. Naphthoquinones juglone and menadione increased superoxide production in activity-stained gels. Some juglone-activated enzymes were preferentially using NADH. With NADH, menadione activated only some of the enzymes that juglone did, whereas with NADPH the activation patterns were identical. Duroquinone, a benzoquinone, did not affect superoxide production. Superoxide dismutase, ascorbate peroxidase, catalase and an acidic class III peroxidase isoenzyme were detected in partially purified spruce membranes. The possible locations and functions of these enzymes are discussed.

Polyamines cause plasma membrane depolarization, activate Ca2+-, and modulate H+-ATPase pump activity in pea roots.

Polyamines regulate a variety of cation and K(+) channels, but their potential effects on cation-transporting ATPases are underexplored. In this work, noninvasive microelectrode ion flux estimation and conventional microelectrode techniques were applied to study the effects of polyamines on Ca(2+) and H(+) transport and membrane potential in pea roots. Externally applied spermine or putrescine (1mM) equally activated eosin yellow (EY)-sensitive Ca(2+) pumping across the root epidermis and caused net H(+) influx or efflux. Proton influx induced by spermine was suppressed by EY, supporting the mechanism in which Ca(2+) pump imports 2 H(+) per each exported Ca(2+). Suppression of the Ca(2+) pump by EY diminished putrescine-induced net H(+) efflux instead of increasing it. Thus, activities of Ca(2+) and H(+) pumps were coupled, likely due to the H(+)-pump inhibition by intracellular Ca(2+). Additionally, spermine but not putrescine caused a direct inhibition of H(+) pumping in isolated plasma membrane vesicles. Spermine, spermidine, and putrescine (1mM) induced membrane depolarization by 70, 50, and 35 mV, respectively. Spermine-induced depolarization was abolished by cation transport blocker Gd(3+), was insensitive to anion channels' blocker niflumate, and was dependent on external Ca(2+). Further analysis showed that uptake of polyamines but not polyamine-induced cationic (K(+)+Ca(2+)+H(+)) fluxes were a main cause of membrane depolarization. Polyamine increase is a common component of plant stress responses. Activation of Ca(2+) efflux by polyamines and contrasting effects of polyamines on net H(+) fluxes and membrane potential can contribute to Ca(2+) signalling and modulate a variety of transport processes across the plasma membrane under stress.

Lysophosphatidic acid signaling is required for NADPH oxidase activation during agonist stimulation in pulmonary microvascular endothelial cells (1153.8)

The phospholipase A2 (PLA2) activity of peroxiredoxin 6 (Prdx6) is required for NADPH oxidase 2 (Nox2) activation in pulmonary microvascular endothelial cells (PMVEC; JBC 286:1196, 2011). Lysophosphatidylcholine is a major product of the PLA2 activity of Prdx6 that is readily metabolized to lysophosphatidic acid (LPA). LPA is a bioactive lipid that signals through distinct G protein‐coupled receptors (LPA receptors 1‐5). LPA receptor activation results in the stimulation of signaling pathways regulated by small GTPases, such as the Nox2 cytosolic activator Rac1. We propose that LPA receptor signaling activates Nox2 by stimulating Rac1 in PMVEC. Treatment with Ki16425, a selective antagonist of the LPA receptors 1/3, decreased Rac1 translocation to the plasma membrane during phorbol 12‐myristate 13‐acetate (PMA) stimulation in PMVEC; as demonstrated by in situ proximity ligation assays (Duolink®) and western blotting of isolated plasma membrane proteins. In the same way, LPA receptor blockade decreased superoxide and hydrogen peroxide production in response to PMA stimulation. These results suggest that LPA signaling is required for Nox2 activation during agonist stimulation in PMVEC and that Rac1 is a main target of LPA receptor signaling during this process.Grant Funding Source: Supported by HL105509

Isolation and characterization of the plasma membrane from the yeast Pichia pastoris

Despite similarities of cellular membranes in all eukaryotes, every compartment displays characteristic and often unique features which are important for the functions of the specific organelles. In the present study, we biochemically characterized the plasma membrane of the methylotrophic yeast Pichia pastoris with emphasis on the lipids which form the matrix of this compartment. Prerequisite for this effort was the design of a standardized and reliable isolation protocol of the plasma membrane at high purity. Analysis of isolated plasma membrane samples from P. pastoris revealed an increase of phosphatidylserine and a decrease of phosphatidylcholine compared to bulk membranes. The amount of saturated fatty acids in the plasma membrane was higher than in total cell extracts. Ergosterol, the final product of the yeast sterol biosynthetic pathway, was found to be enriched in plasma membrane fractions, although markedly lower than in Saccharomyces cerevisiae. A further characteristic feature of the plasma membrane from P. pastoris was the enrichment of inositol phosphorylceramides over neutral sphingolipids, which accumulated in internal membranes. The detailed analysis of the P. pastoris plasma membrane is discussed in the light of cell biological features of this microorganism especially as a microbial cell factory for heterologous protein production.

Long-term exposure to muscarinic agonists decreases expression of contractile proteins and responsiveness of rabbit tracheal smooth muscle cells

BackgroundChronic airway diseases, like asthma or COPD, are characterized by excessive acetylcholine release and airway remodeling. The aim of this study was to investigate the long-term effect of muscarinic agonists on the phenotype and proliferation of rabbit tracheal airway smooth muscle cells (ASMCs).MethodsASMCs were serum starved before treatment with muscarinic agonists. Cell phenotype was studied by optical microscopy and indirect immunofluorescence, using smooth muscle α-actin, desmin and SM-Myosin Heavy Chain (SM-MHC) antibodies. [N-methyl-3H]scopolamine binding studies were performed in order to assess M3 muscarinic receptor expression on isolated cell membranes. Contractility studies were performed on isolated ASMCs treated with muscarinic agonists. Proliferation was estimated using methyl-[3H]thymidine incorporation, MTT or cell counting methods. Involvement of PI3K and MAPK signalling pathways was studied by cell incubation with the pathway inhibitors LY294002 and PD98059 respectively.ResultsProlonged culture of ASMCs with acetylcholine, carbachol or FBS, reduced the expression of α-actin, desmin and SM-MHC compared to cells cultured in serum free medium. Treatment of ASMCs with muscarinic agonists for 3-15 days decreased muscarinic receptor expression and their responsiveness to muscarinic stimulation. Acetylcholine and carbachol induced DNA synthesis and increased cell number, of ASMCs that had acquired a contractile phenotype by 7 day serum starvation. This effect was mediated via a PI3K and MAPK dependent mechanism.ConclusionsProlonged exposure of rabbit ASMCs to muscarinic agonists decreases the expression of smooth muscle specific marker proteins, down-regulates muscarinic receptors and decreases ASMC contractile responsiveness. Muscarinic agonists are mitogenic, via the PI3K and MAPK signalling pathways.

Isolation of plasma membrane–associated membranes from rat liver

Dynamic interplay between intracellular organelles requires a particular functional apposition of membrane structures. The organelles involved come into close contact, but do not fuse, thereby giving rise to notable microdomains; these microdomains allow rapid communication between the organelles. Plasma membrane-associated membranes (PAMs), which are microdomains of the plasma membrane (PM) interacting with the endoplasmic reticulum (ER) and mitochondria, are dynamic structures that mediate transport of proteins, lipids, ions and metabolites. These structures have gained much interest lately owing to their roles in many crucial cellular processes. Here we provide an optimized protocol for the isolation of PAM, PM and ER fractions from rat liver that is based on a series of differential centrifugations, followed by the fractionation of crude PM on a discontinuous sucrose gradient. The procedure requires ∼8-10 h, and it can be easily modified and adapted to other tissues and cell types.

Basolateral expression of GRP94 in parietal cells of gastric mucosa

GRP94 is a member of the heat shock protein family normally confined to the endoplasmic reticulum that sometimes escapes the KDEL-mediated retention system. It is overexpressed in some gastric and other gastrointestinal carcinomas, but little is known about the physiological role of GRP94 in gastric mucosa. We investigated the membrane presence of GRP94 in parietal cells, which secrete acid into the gastric lumen, using subcellular fractionation, selective solubilization of membrane proteins, Western blotting, and radio-ligand binding and provided evidence of functional GRP94 expression at the surface of gastric mucosa parietal cells anchored to the basolateral domain. Our results show that GRP94 is not an integral membrane protein since 50 mM Na2CO3 treatment dissociates part of it from the membrane. However, 100 mM Na2CO3 treatment did not extract all GRP94 from the membrane, which indicates that it is strongly associated with it. The presence of GRP94 in isolated plasma membrane was demonstrated by Western blotting and its functionality by radio-ligand binding experiments. Both the K(D) value obtained in saturation experiments with N-ethylcarboxamido-[3H]adenosine at 4°C, at the nanomolar range, and the inhibition constant of its binding by radicicol, the most specific GRP94 inhibitor, indicate that active receptor regions are exposed at the membrane surface. Western blotting of plasma membrane subfractions showed that GRP94 is mainly expressed in the basolateral membrane of gastric parietal cells, while its presence in the apical domain is negligible, thereby inferring a role for GRP94 in processes operating in this membrane domain.