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Marino Zerial - One of the best experts on this subject based on the ideXlab platform.
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mammalian corvet is required for fusion and conversion of distinct early Endosome subpopulations
Traffic, 2014Co-Authors: Enrico D Perini, Ramona Schaefer, Martin Stoter, Yannis Kalaidzidis, Marino ZerialAbstract:Early Endosomes are organized in a network of vesicles shaped by cycles of fusion, fission, and conversion to late Endosomes. In yeast, Endosome fusion and conversion are regulated, among others, by CORVET, a hexameric protein complex. In the mammalian endocytic system, distinct subpopulations of early Endosomes labelled by the Rab5 effectors APPL1 and EEA1 are present. Here, the function of mammalian CORVET with respect to these endosomal subpopulations was investigated. Tgfbrap1 as CORVET-specific subunit and functional ortholog of Vps3p was identified, demonstrating that it is differentially distributed between APPL1 and EEA1 Endosomes. Surprisingly, depletion of CORVET-specific subunits caused fragmentation of APPL1-positive Endosomes but not EEA1 Endosomes in vivo. These and in vitro data suggest that CORVET plays a role in Endosome fusion independently of EEA1. Depletion of CORVET subunits caused accumulation of large EEA1 Endosomes indicative of another role in the conversion of EEA1 Endosomes into late Endosomes. In addition, depletion of CORVET-specific subunits caused alterations in transport depending on both the type of cargo and the specific endosomal subpopulation. These results demonstrate that CORVET plays distinct roles at multiple stages in the mammalian endocytic pathway.
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rhod regulates Endosome dynamics through diaphanous related formin and src tyrosine kinase
Nature Cell Biology, 2003Co-Authors: Stephane Gasman, Yannis Kalaidzidis, Marino ZerialAbstract:Early Endosomes move bidirectionally between the cell periphery and the interior through a mechanism regulated by the low molecular weight GTPase RhoD. Here, we identify a novel splice variant of human Diaphanous, hDia2C, which specifically binds to RhoD and is recruited onto early Endosomes. Expression of RhoD and hDia2C induces a striking alignment of early Endosomes along actin filaments and reduces their motility. This activity depends on the membrane recruitment and activation of c-Src kinase, thus uncovering a new role in Endosome function. Our results define a novel signal transduction pathway, in which hDia2C and c-Src are sequentially activated by RhoD to regulate the motility of early Endosomes through interactions with the actin cytoskeleton.
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Rab5 regulates motility of early Endosomes on microtubules
Nature cell biology, 1999Co-Authors: Erik Nielsen, Fedor F. Severin, Jonathan M. Backer, Anthony A. Hyman, Marino ZerialAbstract:The small GTPase Rab5 regulates membrane docking and fusion in the early endocytic pathway. Here we reveal a new role for Rab5 in the regulation of Endosome interactions with the microtubule network. Using Rab5 fused to green fluorescent protein we show that Rab5-positive Endosomes move on microtubules in vivo. In vitro, Rab5 stimulates both association of early Endosomes with microtubules and early-Endosome motility towards the minus ends of microtubules. Moreover, similarly to Endosome membrane docking and fusion, Rab5-dependent Endosome movement depends on the phosphatidylinositol-3-OH kinase hVPS34. Thus, Rab5 functionally links regulation of membrane transport, motility and intracellular distribution of early Endosomes.
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eea1 links pi 3 k function to rab5 regulation of Endosome fusion
Nature, 1998Co-Authors: Anne Simonsen, Jean Michel Gaullier, Roger Lippe, Savvas Christoforidis, Andreas Brech, Judy M Callaghan, Banhock Toh, Carol Murphy, Marino ZerialAbstract:GTPases and lipid kinases regulate membrane traffic along the endocytic pathway by mechanisms that are not completely understood. Fusion between early Endosomes requires phosphatidylinositol-3-OH kinase (PI(3)K) activity as well as the small GTPase Rab5. Excess Rab5-GTP complex restores Endosome fusion when PI(3)K is inhibited. Here we identify the early-endosomal autoantigen EEA1 which binds the PI(3)K product phosphatidylinositol-3-phosphate, as a new Rab5 effector that is required for Endosome fusion. The association of EEA1 with the endosomal membrane requires Rab5-GTP and PI(3)K activity, and excess Rab5-GTP stabilizes the membrane association of EEA1 even when PI(3)K is inhibited. The identification of EEA1 as a direct Rab5 effector provides a molecular link between PI(3)K and Rab5, and its restricted distribution to early Endosomes indicates that EEA1 may confer directionality to Rab5-dependent endocytic transport.
Philip D. Stahl - One of the best experts on this subject based on the ideXlab platform.
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Evidence for a Symmetrical Requirement for Rab5-GTP in in Vitro Endosome-Endosome Fusion
The Journal of biological chemistry, 1998Co-Authors: M. Alejandro Barbieri, Amitabha Mukhopadhyay, Simon Hoffenberg, Richard Roberts, Andrea Pomrehn, Burton F. Dickey, Philip D. StahlAbstract:Abstract Early Endosome fusion, which has been extensively characterized using an in vitro reconstitution assay, is Rab5-dependent. To examine the requirement for Rab5 on both fusion partners, we prepared cytosol and Endosomes depleted of Rab5. Unlike control cytosol, Rab5-depleted cytosol was only marginally active in the in vitro Endosome fusion. However, fusion could be restored by the addition of wild-type Rab5 or Rab5 D136N, a mutant whose nucleotide specificity favors xanthine over guanine. The addition of Rab5 D136N restored fusion only in the presence of XTP. In the absence of XTP or in the presence of XDP, Rab5 D136N failed to restore fusion. When fusion was carried out with endosomal vesicles depleted of Rab GTPases (by preincubation of vesicles with GDP dissociation inhibitor), together with cytosol immunodepleted of Rab5, fusion was virtually absent. We then used immunodepleted cytosol and GDP dissociation inhibitor-treated vesicles to determine whether Rab5 is required by both fusion partners. Using separate sets of endosomal vesicles, we found that priming both sets of Rab5-depleted vesicles with Rab5 Q79L, a GTPase-defective mutant, substantially stimulated Endosome fusion. Priming one set of vesicles with Rab5 Q79L and a second set of vesicles with Rab5 S34N failed to activate fusion. When both sets of Rab5-depleted vesicles were primed with Rab5 D136N supplemented with XTP, Endosome fusion was stimulated, similar to that observed with Rab5 Q79L. However, when one set of vesicles was preincubated with Rab5 D136N plus XTP and the second set with Rab5 D136N and XDP, no stimulation of fusion was observed. We conclude that Rab5-GTP is required on both fusion partners for docking and fusion of early Endosomes. To confirm the fusion of Rab5-GTP-positive vesiclesin vivo, we expressed GFP-Rab5 Q79L in fibroblasts and observed fusion of Rab5-positive vesicles. We failed to record fusion of Rab5-positive vesicles with Rab5-negative vesicles. We conclude that Rab5-GTP is required on both sets of Endosomes for fusion in vitro and in living cells.
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Calmodulin Regulates Endosome Fusion
The Journal of biological chemistry, 1997Co-Authors: María Isabel Colombo, Walter Berón, Philip D. StahlAbstract:Abstract Calmodulin (CaM) has previously been implicated in regulated exocytosis, transcytosis, and receptor recycling. We have investigated the role of CaM in endocytic transport by examining the effects of several CaM antagonists in intact cells. We present evidence indicating that the mixing of sequentially internalized ligands is inhibited by CaM antagonists, indicating that CaM may play a general role in regulating endosomal membrane trafficking. To address the specific events that are affected by CaM we studied its role in an in vitro assay that reconstitutes fusion among Endosomes. CaM antagonists inhibited Endosome fusion, and the inhibition was reversed by the addition of CaM. Moreover, we found that Ca2+ stimulates fusion among Endosomes and that addition of CaM stimulates fusion beyond that produced by Ca2+ alone. Our data indicate that one of the possible targets for CaM in Endosome fusion is the CaM-dependent kinase II. We propose that CaM regulates endocytic transport by modulating an essential component(s) of the membrane traffic machinery.
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Characterization of Endosome-Endosome fusion in a cell-free system using Dictyostelium discoideum.
The Journal of biological chemistry, 1992Co-Authors: James M. Lenhard, Luis S. Mayorga, Philip D. StahlAbstract:An in vitro Endosome fusion assay using Dictyostelium discoideum is described. The method requires endocytosis of anti-dinitrophenol (DNP) IgG or DNP-derivitized beta-glucuronidase into two sets of cells. After homogenizing the cells, the vesicles were mixed, and fusion was measured by quantitating immune complex formation between DNP-beta-glucuronidase and anti-DNP IgG. Fusion was dependent upon ATP, temperature, pH, ionic strength, and cytosol and sensitive to detergent, dilution, trypsin, N-ethylmaleimide, and guanosine 5'-3-O-(thio)triphosphate. Although weak bases, ionophores, hadacidin, [ethylenebis(oxyethylenenitrilo)]tetraacetic acid, and caffeine inhibit endocytosis in vivo, these reagents had no affect on in vitro Endosome fusion. Comparison of Dictyostelium with mammalian cells showed differences in the temperature, pH, and salt requirements for fusion, possibly reflecting differences in the life-styles of various cell types. Like mammalian cells, Dictyostelium required GTP-binding protein(s) and an N-ethylmaleimide-sensitive factor for Endosome fusion. Thus, the mechanism driving Endosome fusion may have been conserved throughout evolution. Electron microscopic studies confirmed in vitro Endosome fusion and revealed Endosomes were being engulfed by other Endosomes, resulting in formation of multivesicular elements (i.e. autophagic vesicles). This system may be useful for characterizing mutations, evolution, and developmental regulation along the endocytic pathway.
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Characterization of trypsin-sensitive factor(s) required for Endosome-Endosome fusion.
The Journal of biological chemistry, 1991Co-Authors: María Isabel Colombo, Susana Gonzalo, P Weidman, Philip D. StahlAbstract:Abstract Fusion of Endosomes appears to be required at early steps of receptor-mediated endocytosis. These fusion events have been reconstituted using a cell-free assay and have been shown to require both cytosolic and membrane-associated proteins. We report here that trypsinization of Endosomes completely inhibited fusion. Addition of untreated cytosol cannot restore fusion of trypsinized Endosomes. However, fusion activity is restored by the addition of either untreated vesicles or a high salt extract containing peripheral membrane proteins (KE). KE contains both the membrane-associated factor(s) required for the reconstitution of fusion using trypsinized Endosomes and the factors that are normally provided by the cytosol. The restorative activity of KE was sensitive to trypsin treatment or incubation at 100 degrees C, but was largely N-ethylmaleimide (NEM)-resistant. This and other criteria demonstrated that the trypsin-sensitive factor is distinct from N-ethylmaleimide-sensitive factor (NSF), an NEM-sensitive protein involved in vesicular fusion, and from other known factors that may participate in membrane fusion events. Preliminary fractionation studies indicate that the restorative activity of KE is associated with one or more high molecular weight proteins. The present study indicates that a novel trypsin-sensitive protein(s) is involved in Endosome-Endosome fusion. This factor is membrane-associated and is not found in an active form in cytosol as prepared.
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Localization of cathepsin D in Endosomes: characterization and biological importance.
Advances in experimental medicine and biology, 1991Co-Authors: Janice S. Blum, Maria Luisa Fiani, Philip D. StahlAbstract:Proteases were initially identified in Endosomes through studies of receptor-ligand transport.1 During receptor-mediated endocytosis, cell surface receptors bind exogenous ligands (Figure 1). These receptor-ligand complexes are internalized by clathrin-coated vesicles, which give rise to Endosomes. Shortly after Endosome formation, the internal pH of these vesicles drops to between pH 5–6.2 Many internalized receptor-ligand complexes dissociate upon Endosome acidification, with the released receptors recycling back to the cell surface. Ligands delivered into Endosomes undergo a variety of fates including transport back to the cell surface3 or sorting to different intracellular compartments such as lysosomes and the Golgi.4,5 Susceptible protein ligands are cleaved in Endosomes indicating that these vesicles also serve as a processing compartment.1,6,8
Gia K Voeltz - One of the best experts on this subject based on the ideXlab platform.
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a novel class of er membrane proteins regulates er associated Endosome fission
Cell, 2018Co-Authors: Melissa J Hoyer, Patrick J Chitwood, Gia K Voeltz, Christopher C Ebmeier, Jonathan F Striepen, William M OldAbstract:Endoplasmic reticulum (ER) membrane contact sites (MCSs) mark positions where Endosomes undergo fission for cargo sorting. To define the role of ER at this unique MCS, we targeted a promiscuous biotin ligase to cargo-sorting domains on Endosome buds. This strategy identified the ER membrane protein TMCC1, a member of a conserved protein family. TMCC1 concentrates at the ER-Endosome MCSs that are spatially and temporally linked to Endosome fission. When TMCC1 is depleted, Endosome morphology is normal, buds still form, but ER-associated bud fission and subsequent cargo sorting to the Golgi are impaired. We find that the Endosome-localized actin regulator Coronin 1C is required for ER-associated fission of actin-dependent cargo-sorting domains. Coronin 1C is recruited to Endosome buds independently of TMCC1, while TMCC1/ER recruitment requires Coronin 1C. This link between TMCC1 and Coronin 1C suggests that the timing of TMCC1-dependent ER recruitment is tightly regulated to occur after cargo has been properly sequestered into the bud.
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er contact sites define the position and timing of Endosome fission
Cell, 2014Co-Authors: Ashley A Rowland, Patrick J Chitwood, Melissa J Phillips, Gia K VoeltzAbstract:Summary Endocytic cargo and Rab GTPases are segregated to distinct domains of an Endosome. These domains maintain their identity until they undergo fission to traffic cargo. It is not fully understood how segregation of cargo or Rab proteins is maintained along the continuous endosomal membrane or what machinery is required for fission. Endosomes form contact sites with the endoplasmic reticulum (ER) that are maintained during trafficking. Here, we show that stable contacts form between the ER and Endosome at constricted sorting domains, and free diffusion of cargo is limited at these positions. We demonstrate that the site of constriction and fission for early and late Endosomes is spatially and temporally linked to contact sites with the ER. Lastly, we show that altering ER structure and dynamics reduces the efficiency of Endosome fission. Together, these data reveal a surprising role for ER contact in defining the timing and position of Endosome fission. PaperFlick
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endoplasmic reticulum Endosome contact increases as Endosomes traffic and mature
Molecular Biology of the Cell, 2013Co-Authors: Jonathan R. Friedman, Ashley A Rowland, Jared R. Dibenedetto, Matthew West, Gia K VoeltzAbstract:The endosomal pathway is responsible for plasma membrane cargo uptake, sorting, and, in many cases, lysosome targeting. Endosome maturation is complex, requiring proper spatiotemporal recruitment of factors that regulate the size, maturity, and positioning of endosomal compartments. In animal cells, it also requires trafficking of Endosomes on microtubules. Recent work has revealed the presence of contact sites between some Endosomes and the endoplasmic reticulum (ER). Although these contact sites are believed to have multiple functions, the frequency, dynamics, and physical attributes of these contacts are poorly understood. Here we use high-resolution three-dimensional electron microscopy to reveal that ER tubules wrap around Endosomes and find that both organelles contact microtubules at or near membrane contact sites. As Endosomes traffic, they remain bound to the ER, which causes the tubular ER to rearrange its structure around dynamic Endosomes at contact sites. Finally, as Endosomes transition through steps of maturation, they become more tightly associated with the ER. The major implication of these results is that Endosomes mature and traffic while coupled to the ER membrane rather than in isolation.
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Endoplasmic reticulum–Endosome contact increases as Endosomes traffic and mature
Molecular biology of the cell, 2013Co-Authors: Jonathan R. Friedman, Ashley A Rowland, Jared R. Dibenedetto, Matthew West, Gia K VoeltzAbstract:The endosomal pathway is responsible for plasma membrane cargo uptake, sorting, and, in many cases, lysosome targeting. Endosome maturation is complex, requiring proper spatiotemporal recruitment of factors that regulate the size, maturity, and positioning of endosomal compartments. In animal cells, it also requires trafficking of Endosomes on microtubules. Recent work has revealed the presence of contact sites between some Endosomes and the endoplasmic reticulum (ER). Although these contact sites are believed to have multiple functions, the frequency, dynamics, and physical attributes of these contacts are poorly understood. Here we use high-resolution three-dimensional electron microscopy to reveal that ER tubules wrap around Endosomes and find that both organelles contact microtubules at or near membrane contact sites. As Endosomes traffic, they remain bound to the ER, which causes the tubular ER to rearrange its structure around dynamic Endosomes at contact sites. Finally, as Endosomes transition through steps of maturation, they become more tightly associated with the ER. The major implication of these results is that Endosomes mature and traffic while coupled to the ER membrane rather than in isolation.
Jean Gruenberg - One of the best experts on this subject based on the ideXlab platform.
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The Late Endosome
Encyclopedia of Cell Biology, 2016Co-Authors: Fabrizio Vacca, Cameron C. Scott, Jean GruenbergAbstract:Late Endosome and lysosomes form the second major membrane network along the endocytic pathway, after early/recycling Endosomes, and as such, late Endosomes function as the last portal before lysosomes. In mammalian cells, they also link the endosomal system to other cellular destinations, including the trans-Golgi complex and the plasma membrane. Finally it has become clear in recent years that late Endosomes operate as a major sensing and signaling organelle that informs the cell about its nutrient and supply situation.
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Endosome maturation, transport and functions.
Seminars in cell & developmental biology, 2014Co-Authors: Cameron C. Scott, Fabrizio Vacca, Jean GruenbergAbstract:Efficient sorting of the material internalized by endocytosis is essential for key cellular functions and represents a, if not the, major trafficking pathway in mammalian cells. Incoming material - solutes, receptors and cargos, lipids and even pathogenic agents - are routed to various destinations within mammalian cells at two major sorting stations: the early and late Endosome. The early Endosome receives all manner of incoming material from the plasma membrane, as well as from the Golgi, and serves as an initial sorting nexus routing molecules back to the cell surface through recycling Endosomes, to the trans-Golgi network by retrograde transport, or on to the late Endosome/lysosome. The early Endosome also regulates cell signaling, through the downregulation of internalized receptors, which are packaged into intralumenal vesicles that arise from inward invaginations of the limiting membrane. These multivesicular regions detach or mature from early Endosomes and become free endocytic carrier vesicle/multivesicular body, which transports cargoes to late Endosomes. The late Endosome provides a central hub for incoming traffic from the endocytic, biosynthetic and autophagic pathways and outgoing traffic to the lysosomes, the Golgi complex or the plasma membrane. They also function as a key sensing/signaling platform that inform the cell about the nutrient situation. Herein we summarize the current understanding of the organization and functions of the endocytic pathway, differences across species, and the process of Endosome maturation.
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ion flux and the function of Endosomes and lysosomes ph is just the start the flux of ions across endosomal membranes influences Endosome function not only through regulation of the luminal ph
BioEssays, 2011Co-Authors: Cameron C. Scott, Jean GruenbergAbstract:The ionic nature of Endosomes varies considerably in character along the endocytic pathway. Counter-ion flux across the limiting membrane of Endosomes has long been considered essential for full acidification and normal Endosome/lysosomal function. The proximal functions of luminal ions, however, have been difficult to assess. The recent development of transgenic mice carrying mutations in the intracellular chloride channels (ClCs) has provided a tool to uncouple Cl(-) influx from endosomal acidification. Intriguingly, many of the defects of the endo-lysomal system attributed to aberrant pH persist in the Cl(-)-deficient mice implying a direct regulatory role for Cl(-) influx in Endosome function. These observations may begin to explain the abundance of endosomal ion transporters, including ClCs, sodium-proton exchangers, two-pore channels and mucolipins, that have been localized to endo-lysosomes, and the extensive changes in luminal ion composition therein. In this review, we summarize what is known regarding the mediators of endosomal ion flux, and discuss the implications of changing ionic content on endo-lysosomal function.
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Annexin A2-dependent polymerization of actin mediates Endosome biogenesis
Developmental cell, 2009Co-Authors: Etienne Morel, Robert G. Parton, Jean GruenbergAbstract:Early Endosomes give rise to multivesicular intermediates during transport toward late Endosomes. Much progress has been made in understanding the sorting of receptors into these intermediates, but the mechanisms responsible for their biogenesis remain unclear. Here, we report that F-actin is necessary for transport beyond early Endosomes and Endosome formation. We found that Endosomes captured by actin cables were essentially stationary, but early Endosomes also exhibited patches of F-actin and facilitated selective F-actin nucleation and polymerization. Our data show that nucleation of actin patches by early Endosomes is strictly dependent on annexin A2, a protein involved in early-to-late Endosome transport. It also requires the actin nucleation factor Spire1 and involves Arp2/3, which is needed for filament branching. We conclude that actin patches are nucleated on early Endosomes via annexin A2 and Spire1, and that these patches control Endosome biogenesis, presumably by driving the membrane remodeling process.
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the recycling Endosome of madin darby canine kidney cells is a mildly acidic compartment rich in raft components
Molecular Biology of the Cell, 2000Co-Authors: Raluca Gagescu, Robert G. Parton, Nicolas Demaurex, Walter Hunziker, Lukas A Huber, Jean GruenbergAbstract:We present a biochemical and morphological characterization of recycling Endosomes containing the transferrin receptor in the epithelial Madin-Darby canine kidney cell line. We find that recycling Endosomes are enriched in molecules known to regulate transferrin recycling but lack proteins involved in early Endosome membrane dynamics, indicating that recycling Endosomes are distinct from conventional early Endosomes. We also find that recycling Endosomes are less acidic than early Endosomes because they lack a functional vacuolar ATPase. Furthermore, we show that recycling Endosomes can be reached by apically internalized tracers, confirming that the apical endocytic pathway intersects the transferrin pathway. Strikingly, recycling Endosomes are enriched in the raft lipids sphingomyelin and cholesterol as well as in the raft-associated proteins caveolin-1 and flotillin-1. These observations may suggest that a lipid-based sorting mechanism operates along the Madin-Darby canine kidney recycling pathway, contributing to the maintenance of cell polarity. Altogether, our data indicate that recycling Endosomes and early Endosomes differ functionally and biochemically and thus that different molecular mechanisms regulate protein sorting and membrane traffic at each step of the receptor recycling pathway.
Harald Alfred Stenmark - One of the best experts on this subject based on the ideXlab platform.
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Protrudin-mediated ER–Endosome contact sites promote MT1-MMP exocytosis and cell invasion
Journal of Cell Biology, 2020Co-Authors: Nina Marie Pedersen, Harald Alfred Stenmark, Eva Maria Wenzel, Ling Wang, Sandra Antoine, Philippe Chavrier, Camilla RaiborgAbstract:Cancer cells break tissue barriers by use of small actin-rich membrane protrusions called invadopodia. Complete invadopodia maturation depends on protrusion outgrowth and the targeted delivery of the matrix metalloproteinase MT1-MMP via endosomal transport by mechanisms that are not known. Here, we show that the ER protein Protrudin orchestrates invadopodia maturation and function. Protrudin formed contact sites with MT1-MMP-positive Endosomes that contained the RAB7-binding Kinesin-1 adaptor FYCO1, and depletion of RAB7, FYCO1, or Protrudin inhibited MT1-MMP-dependent extracellular matrix degradation and cancer cell invasion by preventing anterograde translocation and exocytosis of MT1-MMP. Moreover, when Endosome translocation or exocytosis was inhibited by depletion of Protrudin or Synaptotagmin VII, respectively, invadopodia were unable to expand and elongate. Conversely, when Protrudin was overexpressed, noncancerous cells developed prominent invadopodia-like protrusions and showed increased matrix degradation and invasion. Thus, Protrudin-mediated ER-Endosome contact sites promote cell invasion by facilitating translocation of MT1-MMP-laden Endosomes to the plasma membrane, enabling both invadopodia outgrowth and MT1-MMP exocytosis.
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ER–Endosome contact sites in Endosome positioning and protrusion outgrowth
Biochemical Society transactions, 2016Co-Authors: Camilla Raiborg, Eva Maria Wenzel, Nina Pedersen, Harald Alfred StenmarkAbstract:The endoplasmic reticulum (ER) makes abundant contacts with Endosomes, and the numbers of contact sites increase as Endosomes mature. It is already clear that such contact sites have diverse compositions and functions, but in this mini-review we will focus on two particular types of ER–Endosome contact sites that regulate Endosome positioning. Formation of ER–Endosome contact sites that contain the cholesterol-binding protein oxysterol-binding protein-related protein 1L (ORP1L) is coordinated with loss of the minus-end-directed microtubule motor Dynein from Endosomes. Conversely, formation of ER–Endosome contact sites that contain the Kinesin-1-binding protein Protrudin results in transfer of the plus-end-directed microtubule motor Kinesin-1 from ER to Endosomes. We discuss the possibility that formation of these two types of contact sites is coordinated as a ‘gear-shift’ mechanism for Endosome motility, and we review evidence that Kinesin-1-mediated motility of late Endosomes (LEs) to the cell periphery promotes outgrowth of neurites and other protrusions.
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ER–Endosome contact sites: molecular compositions and functions
The EMBO journal, 2015Co-Authors: Camilla Raiborg, Eva Maria Wenzel, Harald Alfred StenmarkAbstract:Recent studies have revealed the existence of numerous contact sites between the endoplasmic reticulum (ER) and Endosomes in mammalian cells. Such contacts increase during Endosome maturation and play key roles in cholesterol transfer, Endosome positioning, receptor dephosphorylation, and Endosome fission. At least 7 distinct contact sites between the ER and Endosomes have been identified to date, which have diverse molecular compositions. Common to these contact sites is that they impose a close apposition between the ER and Endosome membranes, which excludes membrane fusion while allowing the flow of molecular signals between the two membranes, in the form of enzymatic modifications, or ion, lipid, or protein transfer. Thus, ER–Endosome contact sites ensure coordination of molecular activities between the two compartments while keeping their general compositions intact. Here, we review the molecular architectures and cellular functions of known ER–Endosome contact sites and discuss their implications for human health.
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Class III phosphatidylinositol 3–kinase and its catalytic product PtdIns3P in regulation of endocytic membrane traffic
FEBS Journal, 2013Co-Authors: Camilla Raiborg, Kay Oliver Schink, Harald Alfred StenmarkAbstract:Endocytosis and subsequent membrane traffic through Endosomes are cellular processes that are integral to eukaryotic evolution, and numerous human diseases are associated with their dysfunction. Consequently, it is important to untangle the molecular machineries that regulate membrane dynamics and protein flow in the endocytic pathway. Central in this context is class III phosphatidylinositol 3–kinase, an evolutionarily conserved enzyme complex that phosphorylates phosphatidylinositol into phosphatidylinositol 3–phosphate. Phosphatidylinositol 3–phosphate recruits specific effector proteins, most of which contain FYVE or PX domains, to promote endocytosis, Endosome fusion, Endosome motility and Endosome maturation, as well as cargo sorting to lysosomes, the biosynthetic pathway or the plasma membrane. Here we review the functions of key phosphatidylinositol 3–phosphate effectors in regulation of endocytic membrane dynamics and protein sorting.
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Protein sorting into multivesicular Endosomes.
Current opinion in cell biology, 2003Co-Authors: Camilla Raiborg, Tor Erik Rusten, Harald Alfred StenmarkAbstract:Multivesicular Endosomes are important as compartments for receptor downregulation and as intermediates in the formation of secretory lysosomes. Work during the past year has shed light on the molecular mechanisms of protein sorting into multivesicular Endosomes and yielded information about the machinery involved in multivesicular Endosome formation. Monoubiquitination functions as a signal for sorting transmembrane proteins into intraluminal vesicles of multivesicular Endosomes and subsequent delivery to lysosomes. A molecular machinery that contains the ubiquitin-binding protein Hrs/Vps27 appears to be central in this sorting process. Three conserved multisubunit complexes, ESCRT-I, -II and -III, are essential for both sorting and multivesicular Endosomes formation. Enveloped RNA viruses such as HIV can redirect these complexes from multivesicular Endosomes to the plasma membrane to facilitate viral budding.