Raft-based sphingomyelin interactions revealed by new fluorescent sphingomyelin analogs

Sphingomyelin (SM) has been proposed to form cholesterol-dependent raft domains and sphingolipid domains in the plasma membrane (PM). How SM contributes to the formation and function of these domains remains unknown, primarily because of the scarcity of suitable fluorescent SM analogs. We developed new fluorescent SM analogs by conjugating a hydrophilic fluorophore to the SM choline headgroup without eliminating its positive charge, via a hydrophilic nonaethylene glycol linker. The new analogs behaved similarly to the native SM in terms of their partitioning behaviors in artificial liquid order-disorder phase-separated membranes and detergent-resistant PM preparations. Single fluorescent molecule tracking in the live-cell PM revealed that they indirectly interact with each other in cholesterol- and sphingosine backbone–dependent manners, and that, for ∼10–50 ms, they undergo transient colocalization-codiffusion with a glycosylphosphatidylinositol (GPI)-anchored protein, CD59 (in monomers, transient-dimer rafts, and clusters), in CD59-oligomer size–, cholesterol-, and GPI anchoring–dependent manners. These results suggest that SM continually and rapidly exchanges between CD59-associated raft domains and the bulk PM.

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Aberrant cytoplasmic sequestration of eNOS in endothelial cells after monocrotaline, hypoxia, and senescence: live-cell caveolar and cytoplasmic NO imaging

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00990.2006 ◽

2007 ◽

Vol 292 (3) ◽

pp. H1373-H1389 ◽

Cited By ~ 36

Author(s):

Somshuvra Mukhopadhyay ◽

Fang Xu ◽

Pravin B. Sehgal

Keyword(s):

Endothelial Cells ◽

Pulmonary Hypertension ◽

Plasma Membrane ◽

Live Cell ◽

Caveolin 1 ◽

Protein Levels ◽

Pulmonary Arterial ◽

And Function ◽

Endothelial Nitric Oxide ◽

Arterial Endothelial Cells

We previously reported the disruption of caveolae/rafts, dysfunction of Golgi tethers, N-ethylmaleimide-sensitive factor-attachment protein (SNAP) receptor proteins (SNAREs), and SNAPs, and inhibition of anterograde trafficking in endothelial cells in culture and rat lung exposed to monocrotaline pyrrole (MCTP) as a prelude to the development of pulmonary hypertension. We have now investigated 1) whether this trafficking block affects subcellular localization and function of endothelial nitric oxide (NO) synthase (eNOS) and 2) whether Golgi blockade and eNOS sequestration are observed after hypoxia and senescence. Immunofluorescence data revealed that MCTP-induced “megalocytosis” of pulmonary arterial endothelial cells (PAEC) was accompanied by a loss of eNOS from the plasma membrane, with increased accumulation in the cytoplasm. This cytoplasmic eNOS was sequestered in heterogeneous compartments and partially colocalized with Golgi and endoplasmic reticulum (ER) markers, caveolin-1, NOSTRIN, and ER Tracker, but not Lyso Tracker. Hypoxia and senescence also produced enlarged PAEC, with dysfunctional Golgi and loss of eNOS from the plasma membrane, with sequestration in the cytoplasm. Live-cell imaging of caveolar and cytoplasmic NO with 4,5-diaminofluorescein diacetate (DAF-2DA) as probe showed a marked loss of caveolar NO after MCTP, hypoxia, and senescence. Although ionomycin stimulated DAF-2DA fluorescence in control PAEC, this ionophore decreased DAF-2DA fluorescence in MCTP-treated and senescent PAEC, suggesting localization of eNOS in an aberrant cytoplasmic compartment that was readily discharged by Ca2+-induced exocytosis. Thus monocrotaline, hypoxia, and senescence produce a Golgi blockade in PAEC, leading to sequestration of eNOS away from its functional caveolar location and providing a mechanism for the often-reported reduction in pulmonary arterial NO levels in experimental pulmonary hypertension, despite sustained eNOS protein levels.

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Structure and cholesterol domain dynamics of an enriched caveolae/raft isolate

Biochemical Journal ◽

10.1042/bj20031562 ◽

2004 ◽

Vol 382 (2) ◽

pp. 451-461 ◽

Cited By ~ 22

Author(s):

Adalberto M. GALLEGOS ◽

Avery L. McINTOSH ◽

Barbara P. ATSHAVES ◽

Friedhelm SCHROEDER

Keyword(s):

Plasma Membrane ◽

Plasma Membranes ◽

Initial Rate ◽

Probe Molecules ◽

Factors Affecting ◽

Raft Domains ◽

And Function ◽

Sterol Carrier Protein 2 ◽

Multiple Probe ◽

Domain Dynamics

Despite the importance of cholesterol in the formation and function of caveolar microdomains in plasma membranes, almost nothing is known regarding the structural properties, cholesterol dynamics or intracellular factors affecting caveolar cholesterol dynamics. A non-detergent method was employed to isolate caveolae/raft domains from purified plasma membranes of murine fibroblasts. A series of fluorescent lipid probe molecules or a fluorescent cholesterol analogue, dehydroergosterol, were then incorporated into the caveolae/raft domains to show that: (i) fluorescence polarization of the multiple probe molecules {diphenylhexatriene analogues, DiI18 (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate), parinaric acids and NBD-stearic acid {12-(N-methyl)-N-[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-octadecanoic acid} indicated that acyl chains in caveolae/raft domains were significantly less ‘fluid’ (i.e. more rigid) and the transbilayer ‘fluidity gradient’ was 4.4-fold greater than in plasma membranes; (ii) although sterol was more ordered in caveolae/raft domains than plasma membranes, spontaneous sterol transfer from caveolae/raft domains was faster (initial rate, 32%; half-time, t1/2, 57%) than from the plasma membrane; (iii) although kinetic analysis showed similar proportions of exchangeable and non-exchangeable sterol pools in caveolae/raft domains and plasma membranes, addition of SCP-2 (sterol carrier protein-2) 1.3-fold more selectively increased sterol transfer from caveolae/raft domains by decreasing the t1/2 (50%) and increasing the initial rate (5-fold); (iv) SCP-2 was also 2-fold more selective in decreasing the amount of non-exchangeable sterol in caveolae/raft domains compared with plasma membranes, such that nearly 80% of caveolar/raft sterol became exchangeable. In summary, although caveolae/raft lipids were less fluid than those of plasma membranes, sterol domains in caveolae/rafts were more spontaneously exchangeable and more affected by SCP-2 than those of the bulk plasma membranes. Thus caveolae/raft domains isolated without the use of detergents display unique structure, cholesterol domain kinetics and responsiveness to SCP-2 as compared with the parent plasma membrane.

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Caveolin-1, galectin-3 and lipid raft domains in cancer cell signalling

Essays in Biochemistry ◽

10.1042/bse0570189 ◽

2015 ◽

Vol 57 ◽

pp. 189-201 ◽

Cited By ~ 13

Author(s):

Jay Shankar ◽

Cecile Boscher ◽

Ivan R. Nabi

Keyword(s):

Plasma Membrane ◽

Lipid Rafts ◽

Cancer Cell ◽

Cellular Response ◽

Spatial Organization ◽

Essential Feature ◽

Cell Signalling ◽

Coated Pits ◽

Signalling Molecules ◽

Raft Domains

Spatial organization of the plasma membrane is an essential feature of the cellular response to external stimuli. Receptor organization at the cell surface mediates transmission of extracellular stimuli to intracellular signalling molecules and effectors that impact various cellular processes including cell differentiation, metabolism, growth, migration and apoptosis. Membrane domains include morphologically distinct plasma membrane invaginations such as clathrin-coated pits and caveolae, but also less well-defined domains such as lipid rafts and the galectin lattice. In the present chapter, we will discuss interaction between caveolae, lipid rafts and the galectin lattice in the control of cancer cell signalling.

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Actin-membrane interaction in fibroblasts: what proteins are involved in this association?

The Journal of Cell Biology ◽

10.1083/jcb.99.1.95s ◽

1984 ◽

Vol 99 (1) ◽

pp. 95s-103s ◽

Cited By ~ 57

Author(s):

P Mangeat ◽

K Burridge

Keyword(s):

Plasma Membrane ◽

Actin Filaments ◽

Stress Fiber ◽

Membrane Interaction ◽

Microfilament Bundles ◽

The Family ◽

Form Part ◽

Membrane Attachment ◽

A Chain ◽

And Function

In this review we discuss some of the proteins for which a role in linking actin to the fibroblast plasma membrane has been suggested. We focus on the family of proteins related to erythrocyte spectrin, proteins that have generally been viewed as having an organization and a function in actin-membrane attachment similar to those of erythrocyte spectrin. Experiments in which we precipitated the nonerythrocyte spectrin within living fibroblasts have led us to question this supposed similarity of organization and function of the nonerythrocyte and erythrocyte spectrins. Intracellular precipitation of fibroblast spectrin does not affect the integrity of the major actin-containing structures, the stress fiber microfilament bundles. Unexpectedly, however, we found that the precipitation of spectrin results in a condensation and altered distribution of the vimentin class of intermediate filaments in most cells examined. Although fibroblast spectrin may have a role in the attachment of some of the cortical, submembranous actin, it is surprising how little the intracellular immunoprecipitation of the spectrin affects the cells. Several proteins have been found concentrated at the ends of stress fibers, where the actin filaments terminate at focal contacts. Two of these proteins, alpha-actinin and fimbrin, have properties that suggest that they are not involved in the attachment of the ends of the bundles to the membrane but are more probably involved in the organization and cross-linking of the filaments within the bundles. On the other hand, vinculin and talin are two proteins that interact with each other and may form part of a chain of attachments between the ends of the microfilament bundles and the focal contact membrane. Their role in this attachment, however, has not been established and further work is needed to examine their interaction with actin and to identify any other components with which they may interact, particularly in the plasma membrane.

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Impact of Membrane Lipids on UapA and AzgA Transporter Subcellular Localization and Activity in Aspergillus nidulans

Journal of Fungi ◽

10.3390/jof7070514 ◽

2021 ◽

Vol 7 (7) ◽

pp. 514

Author(s):

Mariangela Dionysopoulou ◽

George Diallinas

Keyword(s):

Plasma Membrane ◽

Subcellular Localization ◽

Aspergillus Nidulans ◽

Membrane Lipids ◽

Membrane Lipid ◽

Lipid Biosynthesis ◽

Transport Kinetics ◽

Negative Effect ◽

And Function

Recent biochemical and biophysical evidence have established that membrane lipids, namely phospholipids, sphingolipids and sterols, are critical for the function of eukaryotic plasma membrane transporters. Here, we study the effect of selected membrane lipid biosynthesis mutations and of the ergosterol-related antifungal itraconazole on the subcellular localization, stability and transport kinetics of two well-studied purine transporters, UapA and AzgA, in Aspergillus nidulans. We show that genetic reduction in biosynthesis of ergosterol, sphingolipids or phosphoinositides arrest A. nidulans growth after germling formation, but solely blocks in early steps of ergosterol (Erg11) or sphingolipid (BasA) synthesis have a negative effect on plasma membrane (PM) localization and stability of transporters before growth arrest. Surprisingly, the fraction of UapA or AzgA that reaches the PM in lipid biosynthesis mutants is shown to conserve normal apparent transport kinetics. We further show that turnover of UapA, which is the transporter mostly sensitive to membrane lipid content modification, occurs during its trafficking and by enhanced endocytosis, and is partly dependent on autophagy and Hect-type HulARsp5 ubiquitination. Our results point out that the role of specific membrane lipids on transporter biogenesis and function in vivo is complex, combinatorial and transporter-dependent.

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Plasma membrane integrity in health and disease: significance and therapeutic potential

Cell Discovery ◽

10.1038/s41421-020-00233-2 ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

Catarina Dias ◽

Jesper Nylandsted

Keyword(s):

Plasma Membrane ◽

Therapeutic Potential ◽

Calcium Influx ◽

Membrane Integrity ◽

Cell Types ◽

Physical Parameters ◽

Membrane Repair ◽

Plasma Membrane Integrity ◽

Repair Mechanisms ◽

And Function

AbstractMaintenance of plasma membrane integrity is essential for normal cell viability and function. Thus, robust membrane repair mechanisms have evolved to counteract the eminent threat of a torn plasma membrane. Different repair mechanisms and the bio-physical parameters required for efficient repair are now emerging from different research groups. However, less is known about when these mechanisms come into play. This review focuses on the existence of membrane disruptions and repair mechanisms in both physiological and pathological conditions, and across multiple cell types, albeit to different degrees. Fundamentally, irrespective of the source of membrane disruption, aberrant calcium influx is the common stimulus that activates the membrane repair response. Inadequate repair responses can tip the balance between physiology and pathology, highlighting the significance of plasma membrane integrity. For example, an over-activated repair response can promote cancer invasion, while the inability to efficiently repair membrane can drive neurodegeneration and muscular dystrophies. The interdisciplinary view explored here emphasises the widespread potential of targeting plasma membrane repair mechanisms for therapeutic purposes.

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Visualizing Association of the Retroviral Gag Protein with Unspliced Viral RNA in the Nucleus

mBio ◽

10.1128/mbio.00524-20 ◽

2020 ◽

Vol 11 (2) ◽

Cited By ~ 3

Author(s):

Rebecca J. Kaddis Maldonado ◽

Breanna Rice ◽

Eunice C. Chen ◽

Kevin M. Tuffy ◽

Estelle F. Chiari ◽

...

Keyword(s):

Plasma Membrane ◽

Nuclear Envelope ◽

Rous Sarcoma Virus ◽

Nuclear Export ◽

Live Cell ◽

Viral Rna ◽

Wild Type ◽

Gag Protein ◽

Rous Sarcoma ◽

Sarcoma Virus

ABSTRACT Packaging of genomic RNA (gRNA) by retroviruses is essential for infectivity, yet the subcellular site of the initial interaction between the Gag polyprotein and gRNA remains poorly defined. Because retroviral particles are released from the plasma membrane, it was previously thought that Gag proteins initially bound to gRNA in the cytoplasm or at the plasma membrane. However, the Gag protein of the avian retrovirus Rous sarcoma virus (RSV) undergoes active nuclear trafficking, which is required for efficient gRNA encapsidation (L. Z. Scheifele, R. A. Garbitt, J. D. Rhoads, and L. J. Parent, Proc Natl Acad Sci U S A 99:3944–3949, 2002, https://doi.org/10.1073/pnas.062652199; R. Garbitt-Hirst, S. P. Kenney, and L. J. Parent, J Virol 83:6790–6797, 2009, https://doi.org/10.1128/JVI.00101-09). These results raise the intriguing possibility that the primary contact between Gag and gRNA might occur in the nucleus. To examine this possibility, we created a RSV proviral construct that includes 24 tandem repeats of MS2 RNA stem-loops, making it possible to track RSV viral RNA (vRNA) in live cells in which a fluorophore-conjugated MS2 coat protein is coexpressed. Using confocal microscopy, we observed that both wild-type Gag and a nuclear export mutant (Gag.L219A) colocalized with vRNA in the nucleus. In live-cell time-lapse images, the wild-type Gag protein trafficked together with vRNA as a single ribonucleoprotein (RNP) complex in the nucleoplasm near the nuclear periphery, appearing to traverse the nuclear envelope into the cytoplasm. Furthermore, biophysical imaging methods suggest that Gag and the unspliced vRNA physically interact in the nucleus. Taken together, these data suggest that RSV Gag binds unspliced vRNA to export it from the nucleus, possibly for packaging into virions as the viral genome. IMPORTANCE Retroviruses cause severe diseases in animals and humans, including cancer and acquired immunodeficiency syndromes. To propagate infection, retroviruses assemble new virus particles that contain viral proteins and unspliced vRNA to use as gRNA. Despite the critical requirement for gRNA packaging, the molecular mechanisms governing the identification and selection of gRNA by the Gag protein remain poorly understood. In this report, we demonstrate that the Rous sarcoma virus (RSV) Gag protein colocalizes with unspliced vRNA in the nucleus in the interchromatin space. Using live-cell confocal imaging, RSV Gag and unspliced vRNA were observed to move together from inside the nucleus across the nuclear envelope, suggesting that the Gag-gRNA complex initially forms in the nucleus and undergoes nuclear export into the cytoplasm as a viral ribonucleoprotein (vRNP) complex.

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Positive charge modifications alter the ability of XIP to inhibit the plasma membrane calcium pump

AJP Cell Physiology ◽

10.1152/ajpcell.1996.271.3.c736 ◽

1996 ◽

Vol 271 (3) ◽

pp. C736-C741 ◽

Cited By ~ 22

Author(s):

W. Xu ◽

C. Gatto ◽

M. A. Milanick

Keyword(s):

Plasma Membrane ◽

Positive Charge ◽

Calcium Pump ◽

Inhibitory Peptide ◽

Ca Pump ◽

Contact Points ◽

Plasma Membrane Calcium Pump ◽

Peptide Analogues ◽

Positively Charged

Exchange inhibitory peptide (XIP; RRLLFYKYVYKRYRAGKQRG) is the shortest peptide that inhibits the plasma membrane Ca pump at high Ca (A. Enyedi, T. Vorherr, P. James, D. J. McCormick, A. G. Filoteo, E. Carafoli, and J. T. Penniston, J. Biol. Chem. 264: 12313-12321, 1989). Sulfosuccinimidyl acetate (SNA)-modified XIP does not inhibit the Ca pump; SNA neutralizes the positive charge on Lys at positions 7, 11, and 17. Peptide 2CK-XIP (RRLLFYRYVYRCYCAGRQKG) inhibits the pump, but the iodoacetamido-modified peptide does not inhibit. Three peptide analogues, in which 7, 11, and 17 were Ala, Cys, or Lys, inhibited about as well as XIP. SNA modification of these analogues (each with 1 Lys) did not inhibit. SNA modification of 2CK-XIP results in a peptide that does not inhibit; thus position 19 is important. Our results suggest that it is critical that position 19 be positively charged, that positions 7, 11, and 17 are important contact points between XIP and the Ca pump (with at least one positively charged), and that, whereas it is not essential that residues 12 and 14 be positive, they cannot be negative.

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