scholarly journals Solute Transport Controls Membrane Tension and Organellar Volume

2021 ◽  
Vol 55 (S1) ◽  
pp. 1-24
Keyword(s):  
Solute Transport ◽  
Endocytic Pathway ◽  
Coat Proteins ◽  
Lysosomal Storage ◽  
Transport Pathways ◽  
Osmotic Change ◽  
Solute Fluxes ◽  
Organic Solute ◽  
Membrane Bound ◽  
Sense And Respond

The regulation of cellular volume in response to osmotic change has largely been studied at the whole cell level. Such regulation occurs by the inhibition or activation of ionic and organic solute transport pathways at the cell surface and is coincident with remodelling of the plasma membrane. However, it is only in rare instances that osmotic insults are experienced by cells and tissues. By contrast, the relatively minute luminal volumes of membrane-bound organelles are constantly subject to shifts in their solute concentrations as exemplified in the endocytic pathway where these evolve alongside with maturation. In this review, we summarize recent evidence that suggests trafficking events are in fact orchestrated by the solute fluxes of organelles that briefly impose osmotic gradients. We first describe how hydrostatic pressure and the resultant tension on endomembranes can be readily dissipated by controlled solute efflux since water is obliged to exit. In such cases, the relief of tension on the limiting membrane of the organelle can promote its remodelling by coat proteins, ESCRT machinery, and motors. Second, and reciprocally, we propose that osmotic gradients between organellar lumens and the cytosol may persist or be created. Such gradients impose osmotic pressure and tension on the endomembrane that prevent its remodelling. The control of endomembrane tension is dysregulated in lysosomal storage disorders and can be usurped by pathogens in endolysosomes. Since trafficking and signaling pathways conceivably sense and respond to endomembrane tension, we anticipate that understanding how cells control organellar volumes and the movement of endocytic fluid in particular will be an exciting new area of research.

scholarly journals Endomembrane Tension and Trafficking

2021 ◽  
Vol 8 ◽  
Author(s):  
Amra Saric ◽  
Spencer A. Freeman
Keyword(s):  
Retrograde Transport ◽  
Building Blocks ◽  
Endocytic Pathway ◽  
Coat Proteins ◽  
Curvature Sensing ◽  
Late Endosomes ◽  
High Tension ◽  
Early Endosomes ◽  
Molecular Machinery ◽  
Membrane Bound

Eukaryotic cells employ diverse uptake mechanisms depending on their specialized functions. While such mechanisms vary widely in their defining criteria: scale, molecular machinery utilized, cargo selection, and cargo destination, to name a few, they all result in the internalization of extracellular solutes and fluid into membrane-bound endosomes. Upon scission from the plasma membrane, this compartment is immediately subjected to extensive remodeling which involves tubulation and vesiculation/budding of the limiting endomembrane. This is followed by a maturation process involving concomitant retrograde transport by microtubule-based motors and graded fusion with late endosomes and lysosomes, organelles that support the degradation of the internalized content. Here we review an important determinant for sorting and trafficking in early endosomes and in lysosomes; the control of tension on the endomembrane. Remodeling of endomembranes is opposed by high tension (caused by high hydrostatic pressure) and supported by the relief of tension. We describe how the timely and coordinated efflux of major solutes along the endocytic pathway affords the cell control over such tension. The channels and transporters that expel the smallest components of the ingested medium from the early endocytic fluid are described in detail as these systems are thought to enable endomembrane deformation by curvature-sensing/generating coat proteins. We also review similar considerations for the lysosome where resident hydrolases liberate building blocks from luminal macromolecules and transporters flux these organic solutes to orchestrate trafficking events. How the cell directs organellar trafficking based on the luminal contents of organelles of the endocytic pathway is not well-understood, however, we propose that the control over membrane tension by solute transport constitutes one means for this to ensue.

Claudin Tight Junction Proteins: Novel Aspects in Paracellular Transport

2008 ◽  
Vol 28 (6) ◽  
pp. 577-584 ◽  
Author(s):  
Constanze Will ◽  
Michael Fromm ◽  
Dominik Müller
Keyword(s):  
Tight Junction ◽  
Solute Transport ◽  
Molecular Mechanisms ◽  
Family Members ◽  
Transport Processes ◽  
Paracellular Transport ◽  
Solute Flux ◽  
Solute Fluxes ◽  
Essential Components ◽  
Renal Tubular

Claudins are essential components of the intercellular tight junction and major determinants of paracellular solute fluxes across epithelia and endothelia. Many members of this family display a distinct charge or size specificity, whereas others render the epithelium impermeable to transport. Due to intercellular localization, claudin-mediated transport processes are passive and driven by an electrochemical gradient. In epithelial tissues, claudins exhibit a temporal–spatial expression pattern corresponding with regional and local solute transport profiles. Whereas paracellular transport mechanisms in organs such as intestine and kidney have been extensively investigated, little is known about the molecular mechanisms determining solute transport in the peritoneum, and thus the determinants of peritoneal dialysis. Given the ubiquitous expression of claudins in endothelia and epithelia, it is predictable that claudins also contribute to pore formation and determination in the peritoneum, and that they are involved in solute flux. Therefore, we review the basic characteristics of claudin family members and their function as exemplified in renal tubular transport and give an outlook to what extent claudin family members might be of importance for solute reabsorption across the peritoneal membrane.

scholarly journals Chs1p and Chs3p, two proteins involved in chitin synthesis, populate a compartment of the Saccharomyces cerevisiae endocytic pathway.

1996 ◽  
Vol 7 (12) ◽  
pp. 1909-1919 ◽  
Author(s):  
M Ziman ◽  
J S Chuang ◽  
R W Schekman
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Cycle ◽  
Endocytic Pathway ◽  
Chitin Synthase ◽  
Cell Fractionation ◽  
Cell Wall Polysaccharide ◽  
Chitin Synthesis ◽  
A Cell ◽  
Steady State Levels ◽  
Membrane Bound

In Saccharomyces cerevisiae, the synthesis of chitin, a cell-wall polysaccharide, is temporally and spatially regulated with respect to the cell cycle and morphogenesis. Using immunological reagents, we found that steady-state levels of Chs1p and Chs3p, two chitin synthase enzymes, did not fluctuate during the cell cycle, indicating that they are not simply regulated by synthesis and degradation. Previous cell fractionation studies demonstrated that chitin synthase I activity (CSI) exists in a plasma membrane form and in intracellular membrane-bound particles called chitosomes. Chitosomes were proposed to act as a reservoir for regulated transport of chitin synthase enzymes to the division septum. We found that Chs1p and Chs3p resided partly in chitosomes and that this distribution was not cell cycle regulated. Pulse-chase cell fractionation experiments showed that chitosome production was blocked in an endocytosis mutant (end4-1), indicating that endocytosis is required for the formation or maintenance of chitosomes. Additionally, Ste2p, internalized by ligand-induced endocytosis, cofractionated with chitosomes, suggesting that these membrane proteins populate the same endosomal compartment. However, in contrast to Ste2p, Chs1p and Chs3p were not rapidly degraded, thus raising the possibility that the temporal and spatial regulation of chitin synthesis is mediated by the mobilization of an endosomal pool of chitin synthase enzymes.

scholarly journals Regulation of Clathrin-Mediated Endocytosis

2018 ◽  
Vol 87 (1) ◽  
pp. 871-896 ◽  
Author(s):  
Marcel Mettlen ◽  
Ping-Hung Chen ◽  
Saipraveen Srinivasan ◽  
Gaudenz Danuser ◽  
Sandra L. Schmid
Keyword(s):  
Conformational Changes ◽  
Posttranslational Modifications ◽  
Mammalian Cells ◽  
Environmental Changes ◽  
Protein Complexes ◽  
Adaptor Protein ◽  
Endocytic Pathway ◽  
Coat Proteins ◽  
Membrane Composition ◽  
Coated Pits

Clathrin-mediated endocytosis (CME) is the major endocytic pathway in mammalian cells. It is responsible for the uptake of transmembrane receptors and transporters, for remodeling plasma membrane composition in response to environmental changes, and for regulating cell surface signaling. CME occurs via the assembly and maturation of clathrin-coated pits that concentrate cargo as they invaginate and pinch off to form clathrin-coated vesicles. In addition to the major coat proteins, clathrin triskelia and adaptor protein complexes, CME requires a myriad of endocytic accessory proteins and phosphatidylinositol lipids. CME is regulated at multiple steps—initiation, cargo selection, maturation, and fission—and is monitored by an endocytic checkpoint that induces disassembly of defective pits. Regulation occurs via posttranslational modifications, allosteric conformational changes, and isoform and splice-variant differences among components of the CME machinery, including the GTPase dynamin. This review summarizes recent findings on the regulation of CME and the evolution of this complex process.

Lysosomal Storage Disorders

2021 ◽  
pp. 1106-1113
Author(s):  
Radhika Dhamija ◽  
Erin Conboy ◽  
Lily C. Wong-Kisiel
Keyword(s):  
Lysosomal Storage Diseases ◽  
Lysosomal Storage Disorders ◽  
Lysosomal Storage ◽  
Storage Diseases ◽  
Activator Proteins ◽  
Autophagic Vacuoles ◽  
Enzyme Substrate ◽  
Membrane Bound ◽  
Considerable Morbidity ◽  
Storage Disorders

Lysosomes are membrane-bound organelles that degrade various macromolecules. Lysosomal storage diseases are a clinically, enzymatically, and genetically heterogeneous group of disorders resulting from intracellular accumulation of substrates. Mechanisms of lysosomal storage disorders include 1) primary deficiency of specific hydrolases; 2) defects in activator proteins required for enzyme-substrate interactions in posttranslational modification of enzymes or in transport of the substrate from lysosomes; and 3) abnormalities of fusion between autophagic vacuoles and lysosomes. Substrate accumulation is slowly progressive, leading to considerable morbidity and mortality.

Oatp2 Mediates Bidirectional Organic Solute Transport: A Role for Intracellular Glutathione

2000 ◽  
Vol 58 (2) ◽  
pp. 335-340 ◽  
Author(s):  
Liqiong Li ◽  
Peter J. Meier ◽  
Nazzareno Ballatori
Keyword(s):  
Solute Transport ◽  
Intracellular Glutathione ◽  
Organic Solute

scholarly journals Preferential Pathways for Fluid and Solutes in Heterogeneous Groundwater Systems: Self-Organization, Entropy, Work

2021 ◽  
Author(s):  
Erwin Zehe ◽  
Ralf Loritz ◽  
Yaniv Edery ◽  
Brian Berkowitz
Keyword(s):  
Fluid Flow ◽  
Steady State ◽  
Hydraulic Conductivity ◽  
Solute Transport ◽  
Energy Input ◽  
Self Organization ◽  
Saturated Porous Media ◽  
Concentration Gradients ◽  
Transport Pathways ◽  
Preferential Pathways

Abstract. Patterns of distinct preferential pathways for fluid flow and solute transport are ubiquitous in heterogeneous, saturated and partially saturated porous media. Yet, the underlying reasons for their emergence, and their characterization and quantification, remain enigmatic. Here we analyze simulations of steady state fluid flow and solute transport in two-dimensional, heterogeneous saturated porous media with a relatively short correlation length. We demonstrate that the downstream concentration of solutes in preferential pathways implies a downstream declining entropy in the transverse distribution of solute transport pathways. This reflects the associated formation and downstream steepening of a concentration gradient transversal to the main flow direction. With an increasing variance of the hydraulic conductivity field, stronger transversal concentration gradients emerge, which is reflected in an even smaller entropy of the transversal distribution of transport pathways. By defining "self-organization" through a reduction in entropy (compared to its maximum), our findings suggest that a higher variance and thus randomness of the hydraulic conductivity coincides with stronger macroscale self-organization of transport pathways. While this finding appears at first sight striking, it can be explained by recognizing that emergence of spatial self-organization requires, in light of the second law of thermodynamics, that work be performed to establish transversal concentration gradients. The emergence of steeper concentration gradients requires that even more work be performed, with an even higher energy input into an open system. Consistently, we find that the energy input necessary to sustain steady-state fluid flow and tracer transport grows with the variance of the hydraulic conductivity field as well. Solute particles prefer to move through pathways of very high power, and these pathways pass through bottlenecks of low hydraulic conductivity. This is because power depends on the squared spatial head gradient, which is in these simulations largest in regions of low hydraulic conductivity.

Golgi processed foot-and-mouth disease virus proteins

1983 ◽  
Vol 41 ◽  
pp. 642-643
Author(s):  
S. H. Wool ◽  
J. Polatnick
Keyword(s):  
Guinea Pig ◽  
Rna Polymerase ◽  
Nonstructural Protein ◽  
Foot And Mouth Disease ◽  
Viral Rna ◽  
Coat Proteins ◽  
Mouth Disease Virus ◽  
Viral Coat ◽  
Membrane Bound

The Golgi apparatus was isolated from infected baby hamster kidney cells by centrifugation through discontinuous sucrose gradients. Tritium-labeled protein samples were analyzed by polyacrylamide gel electrophoretic autoradiograms. Pulse-chase studies showed that the viral-induced RNA polymerase passed through the Golgi as infection progressed. Some viral coat proteins were also associated with the Golgi as were other as yet unidentified viral proteins (Fig. 1). Immune labeling of isolated and in situ Golgi confirmed the presence of viral RNA polymerase. The isolated (Fig. 2) and in situ Golgi were labeled with guinea pig antipolymerase antibody and ferritin-labeled goat anti-guinea pig sera to show the presence of viral RNA polymerase.Earlier work in this laboratory established that the RNA polymerase was bound to membranes of newly formed smooth vacuoles during infection with FMDV. The smaller protein on the gel in Fig. 1 (arrow) corresponds in size to VPg (a nonstructural protein bound to the 5' end of viral RNA) has also been shown to be membrane bound.

scholarly journals The F-Box Protein Rcy1p Is Involved in Endocytic Membrane Traffic and Recycling Out of an Early Endosome in Saccharomyces cerevisiae

2000 ◽  
Vol 149 (2) ◽  
pp. 397-410 ◽  
Author(s):  
Andreas Wiederkehr ◽  
Sandrine Avaro ◽  
Cristina Prescianotto-Baschong ◽  
Rosine Haguenauer-Tsapis ◽  
Howard Riezman
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Membrane Trafficking ◽  
Fluorescent Dyes ◽  
Lucifer Yellow ◽  
Endocytic Pathway ◽  
Major Fraction ◽  
Membrane Bound ◽  
Recycling Pathway ◽  
F Box Protein ◽  
Vacuolar Protein

In Saccharomyces cerevisiae, endocytic material is transported through different membrane-bound compartments before it reaches the vacuole. In a screen for mutants that affect membrane trafficking along the endocytic pathway, we have identified a novel mutant disrupted for the gene YJL204c that we have renamed RCY1 (recycling 1). Deletion of RCY1 leads to an early block in the endocytic pathway before the intersection with the vacuolar protein sorting pathway. Mutation of RCY1 leads to the accumulation of an enlarged compartment that contains the t-SNARE Tlg1p and lies close to areas of cell expansion. In addition, endocytic markers such as Ste2p and the fluorescent dyes, Lucifer yellow and FM4-64, were found in a similar enlarged compartment after their internalization. To determine whether rcy1Δ is defective for recycling, we have developed an assay that measures the recycling of previously internalized FM4-64. This method enables us to follow the recycling pathway in yeast in real time. Using this assay, it could be demonstrated that recycling of membranes is rapid in S. cerevisiae and that a major fraction of internalized FM4-64 is secreted back into the medium within a few minutes. The rcy1Δ mutant is strongly defective in recycling.

scholarly journals A prelysosomal compartment sequesters membrane-impermeant fluorescent dyes from the cytoplasmic matrix of J774 macrophages.

1988 ◽  
Vol 107 (3) ◽  
pp. 887-896 ◽  
Author(s):  
T H Steinberg ◽  
J A Swanson ◽  
S C Silverstein
Keyword(s):  
Plasma Membrane ◽  
Lucifer Yellow ◽  
Organic Anion ◽  
Buoyant Density ◽  
Endocytic Pathway ◽  
Cytoplasmic Matrix ◽  
Cytoplasmic Vacuoles ◽  
J774 Cells ◽  
Membrane Bound ◽  
Texas Red

After the membrane impermeant dye Lucifer Yellow is introduced into the cytoplasmic matrix of J774 cells, the dye is sequestered within cytoplasmic vacuoles and secreted into the extracellular medium. In the present work we studied the intracellular transport of Lucifer Yellow in J774 macrophages and the nature of the cytoplasmic vacuoles into which this dye is sequestered. When the lysosomal system of J774 cells was prelabeled with a Texas red ovalbumin conjugate and Lucifer Yellow was then loaded into the cytoplasm of the cells by ATP-mediated permeabilization of the plasma membrane, the vacuoles that sequestered Lucifer Yellow 30 min later were distinct from the Texas red-stained lysosomes. After an additional 30 min Lucifer Yellow and Texas red colocalized in the same membrane bound compartments, indicating that the Lucifer Yellow had been delivered to lysosomes. We next prelabeled the plasma membrane of J774 cells with anti-macrophage antibody and Texas red protein A before Lucifer Yellow was loaded into the cells. The phase-lucent vacuoles that subsequently sequestered Lucifer Yellow also stained with Texas red, showing that they were part of the endocytic pathway. J774 cells were fractionated on percoll density gradients either 15 or 60 min after Lucifer Yellow was introduced into the cytoplasmic matrix of the cells. In cells fractionated after 15 min, Lucifer Yellow was contained within the fractions of light buoyant density that contain plasma membrane and endosomes; the dye later appeared in vesicles of higher density which contained lysosomes. Secretion of Lucifer Yellow from the cytoplasmic matrix of J774 cells is inhibited by the organic anion transport blocker probenecid. We found that probenecid also reversibly inhibited sequestration of dye, indicating that sequestration of dye within cytoplasmic vacuoles was also mediated by organic anion transporters. These studies show that the vacuoles that sequester Lucifer Yellow from the cytoplasmic matrix of J774 cells possess the attributes of endosomes. Thus, in addition to their role in sorting of membrane bound and soluble substances, macrophage endosomes may play a role in the accumulation and transport of molecules resident in the soluble cytoplasm.

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