scholarly journals Spatiotemporal Analysis of Differential Akt Regulation in Plasma Membrane Microdomains

2008 ◽  
Vol 19 (10) ◽  
pp. 4366-4373 ◽  
Author(s):  
Xinxin Gao ◽  
Jin Zhang
Keyword(s):  
Plasma Membrane ◽  
Growth Factor ◽  
Lipid Rafts ◽  
Fluorescent Proteins ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Spatiotemporal Analysis ◽  
Membrane Microdomains ◽  
Cholesterol Depletion ◽  
Growth Factor Signaling

As a central kinase in the phosphatidylinositol 3-kinase pathway, Akt has been the subject of extensive research; yet, spatiotemporal regulation of Akt in different membrane microdomains remains largely unknown. To examine dynamic Akt activity in membrane microdomains in living cells, we developed a specific and sensitive fluorescence resonance energy transfer-based Akt activity reporter, AktAR, through systematic testing of different substrates and fluorescent proteins. Targeted AktAR reported higher Akt activity with faster activation kinetics within lipid rafts compared with nonraft regions of plasma membrane. Disruption of rafts attenuated platelet-derived growth factor (PDGF)-stimulated Akt activity in rafts without affecting that in nonraft regions. However, in insulin-like growth factor-1 (IGF)-1 stimulation, Akt signaling in nonraft regions is dependent on that in raft regions. As a result, cholesterol depletion diminishes Akt activity in both regions. Thus, Akt activities are differentially regulated in different membrane microdomains, and the overall activity of this oncogenic pathway is dependent on raft function. Given the increased abundance of lipid rafts in some cancer cells, the distinct Akt-activating characteristics of PDGF and IGF-1, in terms of both effectiveness and raft dependence, demonstrate the capabilities of different growth factor signaling pathways to transduce differential oncogenic signals across plasma membrane.

scholarly journals Distribution of a Glycosylphosphatidylinositol-anchored Protein at the Apical Surface of MDCK Cells Examined at a Resolution of <100 Å Using Imaging Fluorescence Resonance Energy Transfer

1998 ◽  
Vol 142 (1) ◽  
pp. 69-84 ◽  
Author(s):  
A.K. Kenworthy ◽  
M. Edidin
Keyword(s):  
Energy Transfer ◽  
Lipid Rafts ◽  
Fluorescence Resonance Energy Transfer ◽  
Mdck Cells ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Membrane Microdomains ◽  
Apical Surface ◽  
Donor And Acceptor ◽  
Fluorescence Resonance

Membrane microdomains (“lipid rafts”) enriched in glycosylphosphatidylinositol (GPI)-anchored proteins, glycosphingolipids, and cholesterol have been implicated in events ranging from membrane trafficking to signal transduction. Although there is biochemical evidence for such membrane microdomains, they have not been visualized by light or electron microscopy. To probe for microdomains enriched in GPI- anchored proteins in intact cell membranes, we used a novel form of digital microscopy, imaging fluorescence resonance energy transfer (FRET), which extends the resolution of fluorescence microscopy to the molecular level (&lt;100 Å). We detected significant energy transfer between donor- and acceptor-labeled antibodies against the GPI-anchored protein 5′ nucleotidase (5′ NT) at the apical membrane of MDCK cells. The efficiency of energy transfer correlated strongly with the surface density of the acceptor-labeled antibody. The FRET data conformed to theoretical predictions for two-dimensional FRET between randomly distributed molecules and were inconsistent with a model in which 5′ NT is constitutively clustered. Though we cannot completely exclude the possibility that some 5′ NT is in clusters, the data imply that most 5′ NT molecules are randomly distributed across the apical surface of MDCK cells. These findings constrain current models for lipid rafts and the membrane organization of GPI-anchored proteins.

scholarly journals Quantitative FRET Microscopy Reveals a Crucial Role of Cytoskeleton in Promoting PI(4,5)P2 Confinement

2021 ◽  
Vol 22 (21) ◽  
pp. 11727
Author(s):  
Maria J. Sarmento ◽  
Luís Borges-Araújo ◽  
Sandra N. Pinto ◽  
Nuno Bernardes ◽  
Joana C. Ricardo ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Hela Cells ◽  
Membrane Trafficking ◽  
Actin Polymerization ◽  
Fluorescent Proteins ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Cellular Functions ◽  
Cytoskeleton Organization

Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) is an essential plasma membrane component involved in several cellular functions, including membrane trafficking and cytoskeleton organization. This function multiplicity is partially achieved through a dynamic spatiotemporal organization of PI(4,5)P2 within the membrane. Here, we use a Förster resonance energy transfer (FRET) approach to quantitatively assess the extent of PI(4,5)P2 confinement within the plasma membrane. This methodology relies on the rigorous evaluation of the dependence of absolute FRET efficiencies between pleckstrin homology domains (PHPLCδ) fused with fluorescent proteins and their average fluorescence intensity at the membrane. PI(4,5)P2 is found to be significantly compartmentalized at the plasma membrane of HeLa cells, and these clusters are not cholesterol-dependent, suggesting that membrane rafts are not involved in the formation of these nanodomains. On the other hand, upon inhibition of actin polymerization, compartmentalization of PI(4,5)P2 is almost entirely eliminated, showing that the cytoskeleton network is the critical component responsible for the formation of nanoscale PI(4,5)P2 domains in HeLa cells.

Role of lipid rafts in Shiga toxin 1 interaction with the apical surface of Caco-2 cells

2001 ◽  
Vol 114 (22) ◽  
pp. 4025-4031
Author(s):  
Olga Kovbasnjuk ◽  
Michael Edidin ◽  
Mark Donowitz
Keyword(s):  
Lipid Rafts ◽  
Foodborne Pathogens ◽  
Shiga Toxin ◽  
Specific Binding ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Enterohemorrhagic Escherichia Coli ◽  
Cholesterol Depletion ◽  
Apical Surface ◽  
B Subunit

Enterohemorrhagic Escherichia coli producing Shiga toxins 1 and/or 2 have become major foodborne pathogens. The specific binding of Shiga toxin 1 B-subunit to its receptor, a neutral glycolipid globotriaosylceramide Gb3, on the apical surface of colonic epithelium followed by toxin entry into cells are the initial steps of the process, which can result in toxin transcytosis and systemic effects of infection including hemolytic uremic syndrome. Understanding the complex mechanisms of Shiga toxin 1 binding and internalization may help to develop new strategies directed at preventing toxin internalization. Fluorescence resonance energy transfer microscopy revealed the clustering of Shiga toxin receptors Gb3 in lipid rafts with another glycosphingolipid GM1 on the apical surface of highly polarized intestinal epithelial Caco-2 cells. Lipid rafts disruption significantly decreased internalization of Shiga toxin 1 B-subunit. Although disruption of lipid rafts by cholesterol depletion did not affect the amount of bound Shiga toxin 1 B-subunit, lipid rafts are necessary for toxin uptake across the apical membrane of Caco-2 cells.

scholarly journals Cholesterol-Enriched Membrane Microdomains Are Required for Inducing Host Cell Cytoskeleton Rearrangements in Response to Attaching-Effacing Escherichia coli

2005 ◽  
Vol 73 (11) ◽  
pp. 7113-7125 ◽  
Author(s):  
Jason D. Riff ◽  
John W. Callahan ◽  
Philip M. Sherman
Keyword(s):  
Escherichia Coli ◽  
Plasma Membrane ◽  
Lipid Rafts ◽  
Skin Fibroblasts ◽  
Membrane Microdomains ◽  
Membrane Cholesterol ◽  
Cholesterol Depletion ◽  
Host Membrane ◽  
Niemann Pick ◽  
Cytoskeletal Rearrangements

ABSTRACT The diarrheal pathogens enterohemorrhagic Escherichia coli (EHEC) O157:H7 strain CL56 and enteropathogenic Escherichia coli (EPEC) O127:H6 strain E2348/69 adhere intimately to epithelial cells through attaching-effacing lesions, which are characterized by rearrangements of the host cytoskeleton, intimate adherence, and destruction of microvilli. These cytoskeletal responses require activation of host signal transduction pathways. Lipid rafts are signaling microdomains enriched in sphingolipid and cholesterol in the plasma membrane. The effect of perturbing plasma membrane cholesterol on bacterial intimate adherence was assessed. Infection of both HEp-2 cells and primary skin fibroblasts with strains CL56 and E2348/69 caused characteristic rearrangements of the cytoskeleton at sites of bacterial adhesion. CL56- and E2348/69-induced cytoskeletal rearrangements were inhibited following cholesterol depletion. Addition of exogenous cholesterol to depleted HEp-2 cells restored cholesterol levels and rescued bacterially induced α-actinin mobilization. Quantitative bacterial adherence assays showed that EPEC adherence to HEp-2 cells was dramatically reduced following cholesterol depletion, whereas the adherence of EHEC remained high. Cytoskeletal rearrangements on skin fibroblasts obtained from children with Niemann-Pick type C disease were markedly reduced. These findings indicate that host membrane cholesterol contained in lipid rafts is necessary for the cytoskeletal rearrangements following infection with attaching-effacing Escherichia coli. Differences in initial adherence indicate divergent roles for host membrane cholesterol in the pathogenesis of EHEC and EPEC infections.

scholarly journals A FRET sensor of C-terminal movement reveals VRAC activation by plasma membrane DAG signaling rather than ionic strength

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Benjamin König ◽  
Yuchen Hao ◽  
Sophia Schwartz ◽  
Andrew JR Plested ◽  
Tobias Stauber
Keyword(s):  
Plasma Membrane ◽  
Ionic Strength ◽  
Patch Clamp ◽  
Fluorescent Proteins ◽  
Cell Volume Regulation ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Activation Mechanism ◽  
Live Cells ◽  
Whole Cell Patch Clamp

Volume-regulated anion channels (VRACs) are central to cell volume regulation. Recently identified as hetero-hexamers formed by LRRC8 proteins, their activation mechanism remains elusive. Here, we measured Förster resonance energy transfer (FRET) between fluorescent proteins fused to the C-termini of LRRC8 subunits. Inter-subunit FRET from LRRC8 complexes tracked VRAC activation. With patch-clamp fluorometry, we confirmed that the cytoplasmic domains rearrange during VRAC opening. With these FRET reporters, we determined VRAC activation, non-invasively, in live cells and their subcompartments. Reduced intracellular ionic strength did not directly activate VRACs, and VRACs were not activated on endomembranes. Instead, pharmacological manipulation of diacylglycerol (DAG), and protein kinase D (PKD) activity, activated or inhibited plasma membrane-localized VRACs. Finally, we resolved previous contradictory reports concerning VRAC activation, using FRET to detect robust activation by PMA that was absent during whole-cell patch clamp. Overall, non-invasive VRAC measurement by FRET is an essential tool for unraveling its activation mechanism.

scholarly journals Intramolecular Fluorescence Resonance Energy Transfer between Fused Autofluorescent Proteins Reveals Rearrangements of the N- and C-terminal Segments of the Plasma Membrane Ca2+ Pump Involved in the Activation

2007 ◽  
Vol 282 (49) ◽  
pp. 35440-35448 ◽  
Author(s):  
Gerardo R. Corradi ◽  
Hugo P. Adamo
Keyword(s):  
Plasma Membrane ◽  
Energy Transfer ◽  
Fluorescence Resonance Energy Transfer ◽  
Fluorescent Proteins ◽  
Average Distance ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Green Fluorescent Proteins ◽  
Fluorescence Resonance ◽  
Green Fluorescent

The blue and green fluorescent proteins (BFP and GFP) have been fused at the N- and C-terminal ends, respectively, of the plasma membrane Ca2+ pump (PMCA) isoform 4xb (hPMCA4xb). The fusion protein was successfully expressed in yeast and purified by calmodulin affinity chromatography. Despite the presence of the fused autofluorescent proteins BFP-PMCA-GFP performed similarly to the wild-type enzyme with respect to Ca2+-ATPase activity and sensitivity to calmodulin activation. In the autoinhibited state BFP-PMCA-GFP exhibited a significant intramolecular fluorescence resonance energy transfer (FRET) consistent with the location of the fluorophores at an average distance of 45Å. The FRET intensity in BFP-PMCA-GFP decreased when the enzyme was activated either by Ca2+-calmodulin, partial proteolysis, or acidic lipids. Moreover, FRET decreased and became insensitive to calmodulin when hPMCA4xb was activated by mutation D170N in BFP-PMCA(D170N)-GFP. The results suggest that the ends of the PMCA are in close proximity in the autoinhibited conformation, and they separate or reorient when the PMCA achieves its final activated conformation.

Nicotinic acetylcholine receptor α7 regulates cAMP signal within lipid rafts

2003 ◽  
Vol 285 (3) ◽  
pp. C567-C574 ◽  
Author(s):  
Jin Oshikawa ◽  
Yoshiyuki Toya ◽  
Takayuki Fujita ◽  
Masato Egawa ◽  
Junichi Kawabe ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Lipid Rafts ◽  
Nicotinic Acetylcholine Receptors ◽  
Acetylcholine Receptors ◽  
Plasma Membranes ◽  
Gradient Centrifugation ◽  
Membrane Microdomains ◽  
Cholesterol Depletion ◽  
Nicotinic Acetylcholine ◽  
Density Fractions

Neuronal nicotinic acetylcholine receptors (nAChRs) are made of multiple subunits with diversified functions. The nAChR α7-subunit has a property of high Ca2+ permeability and may have specific functions and localization within the plasma membrane as a signal transduction molecule. In PC-12 cells, fractionation by sucrose gradient centrifugation revealed that nAChRα7 existed in low-density, cholesterol-enriched plasma membrane microdomains known as lipid rafts where flotillin also exists. In contrast, nAChR α5- and β2-subunits were located in high-density fractions, out of the lipid rafts. Type 6 adenylyl cyclase (AC6), a calcium-inhibitable isoform, was also found in lipid rafts and was coimmunoprecipitated with nAChRα7. Cholesterol depletion from plasma membranes with methyl-β-cyclodextrin redistributed nAChRα7 and AC6 diffusely within plasma membranes. Nicotine stimulation reduced forskolin-stimulated AC activity by 35%, and this inhibition was negated by either treatment with α-bungarotoxin, a specific antagonist of nAChRα7, or cholesterol depletion from plasma membranes. The effect of cholesterol depletion was negated by the addition of cholesterol. These data suggest that nAChRα7 has a specific membrane localization relative to other nAChR subunits and that lipid rafts are necessary to localize nAChRα7 with AC within plasma membranes. In addition, nAChRα7 may regulate the AC activity via Ca2+ within lipid rafts.

scholarly journals Distinct calcium regulation of TRPM7 mechanosensitive channels at plasma membrane microdomains visualized by FRET-based single cell imaging

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Irina Starostina ◽  
Yoon-Kwan Jang ◽  
Heon-Su Kim ◽  
Jung-Soo Suh ◽  
Sang-Hyun Ahn ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Transient Receptor Potential ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Receptor Potential ◽  
Membrane Microdomains ◽  
Mechanosensitive Channels ◽  
Intracellular Ca ◽  
Transient Receptor ◽  
Plasma Membrane Microdomains

AbstractTransient receptor potential subfamily M member 7 (TRPM7), a mechanosensitive Ca2+ channel, plays a crucial role in intracellular Ca2+ homeostasis. However, it is currently unclear how cell mechanical cues control TRPM7 activity and its associated Ca2+ influx at plasma membrane microdomains. Using two different types of Ca2+ biosensors (Lyn-D3cpv and Kras-D3cpv) based on fluorescence resonance energy transfer, we investigate how Ca2+ influx generated by the TRPM7-specific agonist naltriben is mediated at the detergent-resistant membrane (DRM) and non-DRM regions. This study reveals that TRPM7-induced Ca2+ influx mainly occurs at the DRM, and chemically induced mechanical perturbations in the cell mechanosensitive apparatus substantially reduce Ca2+ influx through TRPM7, preferably located at the DRM. Such perturbations include the disintegration of lipid rafts, microtubules, or actomyosin filaments; the alteration of actomyosin contractility; and the inhibition of focal adhesion and Src kinases. These results suggest that the mechanical membrane environment contributes to the TRPM7 function and activity. Thus, this study provides a fundamental understanding of how the mechanical aspects of the cell membrane regulate the function of mechanosensitive channels.

scholarly journals Soluble klotho binds monosialoganglioside to regulate membrane microdomains and growth factor signaling

2017 ◽  
Vol 114 (4) ◽  
pp. 752-757 ◽  
Author(s):  
George Dalton ◽  
Sung-Wan An ◽  
Saif I. Al-Juboori ◽  
Nicole Nischan ◽  
Joonho Yoon ◽  
...  
Keyword(s):  
Growth Factor ◽  
Lipid Rafts ◽  
Membrane Lipid ◽  
General Mechanism ◽  
Membrane Microdomains ◽  
Pi3k Signaling ◽  
Growth Factor Signaling ◽  
Paracrine Factor ◽  
Common Motif

Soluble klotho, the shed ectodomain of the antiaging membrane protein α-klotho, is a pleiotropic endocrine/paracrine factor with no known receptors and poorly understood mechanism of action. Soluble klotho down-regulates growth factor-driven PI3K signaling, contributing to extension of lifespan, cardioprotection, and tumor inhibition. Here we show that soluble klotho binds membrane lipid rafts. Klotho binding to rafts alters lipid organization, decreases membrane’s propensity to form large ordered domains for endocytosis, and down-regulates raft-dependent PI3K/Akt signaling. We identify α2-3-sialyllactose present in the glycan of monosialogangliosides as targets of soluble klotho. α2-3-Sialyllactose is a common motif of glycans. To explain why klotho preferentially targets lipid rafts we show that clustering of gangliosides in lipid rafts is important. In vivo, raft-dependent PI3K signaling is up-regulated in klotho-deficient mouse hearts vs. wild-type hearts. Our results identify ganglioside-enriched lipid rafts to be receptors that mediate soluble klotho regulation of PI3K signaling. Targeting sialic acids may be a general mechanism for pleiotropic actions of soluble klotho.

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