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      Heat Stress Causes Spatially-Distinct Membrane Re-Modelling in K562 Leukemia Cells

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          Abstract

          Cellular membranes respond rapidly to various environmental perturbations. Previously we showed that modulations in membrane fluidity achieved by heat stress (HS) resulted in pronounced membrane organization alterations which could be intimately linked to the expression and cellular distribution of heat shock proteins. Here we examine heat-induced membrane changes using several visualisation methods. With Laurdan two-photon microscopy we demonstrate that, in contrast to the enhanced formation of ordered domains in surface membranes, the molecular disorder is significantly elevated within the internal membranes of cells preexposed to mild HS. These results were compared with those obtained by anisotropy, fluorescence lifetime and electron paramagnetic resonance measurements. All probes detected membrane changes upon HS. However, the structurally different probes revealed substantially distinct alterations in membrane heterogeneity. These data call attention to the careful interpretation of results obtained with only a single label. Subtle changes in membrane microstructure in the decision-making of thermal cell killing could have potential application in cancer therapy.

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          Quantitation of lipid phases in phospholipid vesicles by the generalized polarization of Laurdan fluorescence.

          T Parasassi, G. de Stasio, G Ravagnan … (1991)
          The sensitivity of Laurdan (6-dodecanoyl-2-dimethylaminonaphthalene) excitation and emission spectra to the physical state of the membrane arises from dipolar relaxation processes in the membrane region surrounding the Laurdan molecule. Experiments performed using phospholipid vesicles composed of phospholipids with different polar head groups show that this part of the molecule is not responsible for the observed effects. Also, pH titration in the range from pH 4 to 10 shows that the spectral variations are independent of the charge of the polar head. A two-state model of dipolar relaxation is used to qualitatively explain the behavior of Laurdan. It is concluded that the presence of water molecules in the phospholipid matrix are responsible for the spectral properties of Laurdan in the gel phase. In the liquid crystalline phase there is a relaxation process that we attribute to water molecules that can reorientate during the few nanoseconds of the excited state lifetime. The quantitation of lipid phases is obtained using generalized polarization which, after proper choice of excitation and emission wavelengths, satisfies a simple addition rule.
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            Order of lipid phases in model and plasma membranes.

            Lucie Kalvodova, Hermann-Josef Kaiser, Kai Simons … (2009)
            Lipid rafts are nanoscopic assemblies of sphingolipids, cholesterol, and specific membrane proteins that contribute to lateral heterogeneity in eukaryotic membranes. Separation of artificial membranes into liquid-ordered (Lo) and liquid-disordered phases is regarded as a common model for this compartmentalization. However, tight lipid packing in Lo phases seems to conflict with efficient partitioning of raft-associated transmembrane (TM) proteins. To assess membrane order as a component of raft organization, we performed fluorescence spectroscopy and microscopy with the membrane probes Laurdan and C-laurdan. First, we assessed lipid packing in model membranes of various compositions and found cholesterol and acyl chain dependence of membrane order. Then we probed cell membranes by using two novel systems that exhibit inducible phase separation: giant plasma membrane vesicles [Baumgart et al. (2007) Proc Natl Acad Sci USA 104:3165-3170] and plasma membrane spheres. Notably, only the latter support selective inclusion of raft TM proteins with the ganglioside GM1 into one phase. We measured comparable small differences in order between the separated phases of both biomembranes. Lateral packing in the ordered phase of giant plasma membrane vesicles resembled the Lo domain of model membranes, whereas the GM1 phase in plasma membrane spheres exhibited considerably lower order, consistent with different partitioning of lipid and TM protein markers. Thus, lipid-mediated coalescence of the GM1 raft domain seems to be distinct from the formation of a Lo phase, suggesting additional interactions between proteins and lipids to be effective.
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              Visualizing lipid structure and raft domains in living cells with two-photon microscopy.

              Wendy Jessup, Enrico Gratton, Stephanie Jones … (2003)
              The lateral organization of cellular membranes is formed by the clustering of specific lipids, such as cholesterol and sphingolipids, into highly condensed domains (termed lipid rafts). Hence such domains are distinct from the remaining membrane by their lipid structure (liquid-ordered vs. -disordered domains). Here, we directly visualize membrane lipid structure of living cells by using two-photon microscopy. In macrophages, liquid-ordered domains are particularly enriched on membrane protrusions (filopodia), adhesion points and cell-cell contacts and cover 10-15% of the cell surface at 37 degrees C. By deconvoluting the images, we demonstrate the existence of phase separation in vivo. We compare the properties of microscopically visible domains (<1 microm2), with those of isolated detergent-resistant membranes and provide evidence that membrane coverage by lipid rafts and their fluidity are principally governed by cholesterol content, thereby providing strong support for the lipid raft hypothesis.
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                Author and article information

                Contributors
                : Role: Editor
                Journal
                Journal ID (nlm-ta): PLoS One
                Journal ID (publisher-id): plos
                Journal ID (pmc): plosone
                Title: PLoS ONE
                Publisher: Public Library of Science (San Francisco, USA )
                ISSN (Electronic): 1932-6203
                Publication date Collection: 2011
                Publication date (Electronic): 16 June 2011
                Volume: 6
                Issue: 6
                Electronic Location Identifier: e21182
                Affiliations
                [1 ]Institute of Biochemistry, Biological Research Centre, Hungarian Academy of Sciences, Szeged, Hungary
                [2 ]Institute of Biophysics, Biological Research Centre, Hungarian Academy of Sciences, Szeged, Hungary
                [3 ]First Department of Internal Medicine, Albert Szent-Györgyi Clinical Center, University of Szeged, Szeged, Hungary
                [4 ]Institute of Translational Pharmacology, CNR, Rome, Italy
                [5 ]Istituto di Fisica, Universitá Cattolica Sacro Cuore, Rome, Italy
                [6 ]School of Biosciences, Cardiff University, Cardiff, Wales, United Kingdom
                Semmelweis University, Hungary
                Author notes

                Conceived and designed the experiments: GB LV ZT EF IG MDS T. Par. Performed the experiments: GB GM IG MD EF T. Par SB. Analyzed the data: GB GM IG EF T. Páli T. Par. Wrote the paper: GB IH MP EF T. Páli JLH LV. Critically reviewed the paper: IH T. Par JLH.

                Article
                Publisher ID: PONE-D-11-07819
                DOI: 10.1371/journal.pone.0021182
                PMC ID: 3116874
                PubMed ID: 21698159
                SO-VID: 61df646b-0668-4c14-83cd-83a8b84213e0
                Copyright © Balogh et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
                History
                Date received : 1 May 2011
                Date accepted : 22 May 2011
                Page count
                Pages: 12
                Categories
                Subject: Research Article
                Subject: Biology
                Subject: Biochemistry
                Subject: Cytochemistry
                Subject: Cell Membrane
                Subject: Membrane Characteristics
                Subject: Membrane Composition
                Subject: Membrane Metabolism
                Subject: Membrane Proteins
                Subject: Membrane Structures
                Subject: Lipids
                Subject: Lipid Metabolism
                Subject: Lipid Structure
                Subject: Metabolism
                Subject: Lipid Metabolism
                Subject: Macromolecular Assemblies
                Subject: Biophysics
                Subject: Biomechanics
                Subject: Biophysics Theory
                Subject: Molecular Cell Biology
                Subject: Signal Transduction
                Subject: Signaling Cascades
                Subject: Stress Signaling Cascade
                Subject: Signaling in Cellular Processes
                Subject: Transmembrane Signaling
                Subject: Membrane Receptor Signaling
                Subject: Cellular Stress Responses
                Subject: Membranes and Sorting
                Subject: Medicine
                Subject: Oncology
                Subject: Basic Cancer Research

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                ScienceOpen disciplines: Uncategorized

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