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  • 1
    Online Resource
    Online Resource
    Recycling pathways of glucosylceramide in BHK cells: distinct involvement of early and late endosomes
    The Company of Biologists ; 1992
    In:  Journal of Cell Science Vol. 103, No. 4 ( 1992-12-01), p. 1139-1152
    Details
    In: Journal of Cell Science, The Company of Biologists, Vol. 103, No. 4 ( 1992-12-01), p. 1139-1152
    Abstract: Recycling pathways of the sphingolipid glucosylceramide were studied by employing a fluorescent analog of glucosylceramide,6-[N-(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]hexanoylglucosylsphingosine (C6-NBD-glucosylceramide). Direct recycling of the glycolipid from early endosomes to the plasma membrane occurs, as could be shown after treating the cells with the microtubule-disrupting agent nocodazole, which causes inhibition of the glycolipid’s trafficking from peripheral early endosomes to centrally located late endosomes. When the microtubuli are intact, at least part of the glucosylceramide is transported from early to late endosomes together with ricin. Interestingly, also N-(lissamine rhodamine B sulfonyl)phosphatidylethanolamine (N-Rh-PE), a membrane marker of the fluid-phase endocytic pathway, is transported to this endosomal compartment. However, in contrast to both ricin and N-Rh-PE, the glucosylceramide can escape from this organelle and recycle to the plasma membrane. Monensin and brefeldin A have little effect on this recycling pathway, which would exclude extensive involvement of early Golgi compartments in recycling. Hence, the small fraction of the glycolipid that colocalizes with transferrin (Tf) in the Golgi area might directly recycle via the trans-Golgi network. When the intracellular pH was lowered to 5.5, recycling was drastically reduced, in accordance with the impeding effect of low intracellular pH on vesicular transport during endocytosis and in the biosynthetic pathway. Our results thus demonstrate the existence of at least two recycling pathways for glucosylceramide and indicate the relevance of early endosomes in recycling of both proteins and lipids.
    Type of Medium: Online Resource
    ISSN: 0021-9533 , 1477-9137
    URL: Article
    DOI: 10.1242/jcs.103.4.1139
    Language: English
    Publisher: The Company of Biologists
    Publication Date: 1992
    detail.hit.zdb_id: 219171-4
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  • 2
    Online Resource
    Online Resource
    Analysis of shared heritability in common disorders of the brain
    American Association for the Advancement of Science (AAAS) ; 2018
    In:  Science Vol. 360, No. 6395 ( 2018-06-22)
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 360, No. 6395 ( 2018-06-22)
    Abstract: Disorders of the brain can exhibit considerable epidemiological comorbidity and often share symptoms, provoking debate about their etiologic overlap. We quantified the genetic sharing of 25 brain disorders from genome-wide association studies of 265,218 patients and 784,643 control participants and assessed their relationship to 17 phenotypes from 1,191,588 individuals. Psychiatric disorders share common variant risk, whereas neurological disorders appear more distinct from one another and from the psychiatric disorders. We also identified significant sharing between disorders and a number of brain phenotypes, including cognitive measures. Further, we conducted simulations to explore how statistical power, diagnostic misclassification, and phenotypic heterogeneity affect genetic correlations. These results highlight the importance of common genetic variation as a risk factor for brain disorders and the value of heritability-based methods in understanding their etiology.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.aap8757
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2018
    detail.hit.zdb_id: 128410-1
    detail.hit.zdb_id: 2066996-3
    detail.hit.zdb_id: 2060783-0
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  • 3
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    Online Resource
    Aggregation reroutes molecules from a recycling to a vesicle-mediated secretion pathway during reticulocyte maturation
    The Company of Biologists ; 1997
    In:  Journal of Cell Science Vol. 110, No. 16 ( 1997-08-15), p. 1867-1877
    Details
    In: Journal of Cell Science, The Company of Biologists, Vol. 110, No. 16 ( 1997-08-15), p. 1867-1877
    Abstract: Endocytosis of the Tf/TfR complex is essentially the only pathway active in maturing reticulocytes, while exosomes, formed by invagination of the endosomal membrane, provide a mechanism to eliminate seemingly obsolescent proteins, including the TfR, when their function is completed. In this study, we examined molecular trafficking in the recycling and exosome-directed pathways during endocytosis in maturing reticulocytes. To this end, the flow of two exogenously inserted fluorescent lipid analogs, N-(N-[6-[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]caproyl] ) sphingomyelin (C6-NBD-SM) and N-(lissamine rhodamine B sulfonyl) phosphatidyl ethanolamine (N-Rh-PE) was monitored and compared to that of the transferrin (Tf)/Tf receptor (TfR) complex. Prior to elimination via exosomes, the TfR actively recycles with a half-time of approx. 2 minutes. The recycling kinetics of C6-NBD-SM, as bulk plasma membrane marker, are identical to those of the apoTf/TfR complex, as shown by fluorescence microscopy and biochemical analysis. By contrast, although efficiently internalized along the same pathway, N-Rh-PE does not return to the cell surface. More specifically, sucrose gradient analysis and immunoisolation experiments demonstrated that N-Rh-PE accumulates in exosomes, which are eventually released into the extracellular medium. Fluorometric measurements showed that exogenously inserted N-Rh-PE is present in the reticulocyte plasma membrane as small molecular clusters. Moreover, a close correlation was observed between the fate of crosslinked proteins, including the TfR and acetylcholinesterase (AChE), and the fate of the clustered lipid N-Rh-PE. Thus antibody-induced aggregation of specific proteins like the TfR and AChE, which are normally sorted into exosomes during reticulocyte maturation, enhances their shedding by the exosomal pathway. Taken together, the results support the hypothesis that aggregation of either proteins or lipids act as a general sorting signal for exosomal processing, thereby inhibiting reentry in a recycling pathway and providing an effective means for clearing molecules from the cell surface and their eventual elimination from the cells.
    Type of Medium: Online Resource
    ISSN: 0021-9533 , 1477-9137
    URL: Article
    DOI: 10.1242/jcs.110.16.1867
    Language: English
    Publisher: The Company of Biologists
    Publication Date: 1997
    detail.hit.zdb_id: 219171-4
    detail.hit.zdb_id: 1483099-1
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  • 4
    Online Resource
    Online Resource
    On the Mechanism of Intracellular Membrane Fusion: In Search of the Genuine Fusion Factor
    Portland Press Ltd. ; 2000
    In:  Bioscience Reports Vol. 20, No. 6 ( 2000-12-01), p. 613-631
    Details
    In: Bioscience Reports, Portland Press Ltd., Vol. 20, No. 6 ( 2000-12-01), p. 613-631
    Abstract: Intracellular membrane fusion events require a general protein machinery that functions in vesicular traffic and in assembly and maintenance of organelles. An array of cytosolic and integral membrane proteins are currently identified, and in conjunction with ongoing detailed structural studies, rapid progress is made in understanding basic features of the overall mechanism of the fusion machinery, but above all a proper appreciation of its enormous complexity. Thus a highly sophisticated level of regulation of the different steps involved in tethering, docking and merging itself is apparent. Apart from the relevance of protein–protein interactions, also a role of distinct lipids is gradually emerging, particularly in fusion. However, although various suggestions have been made recently, largely based upon in vitro studies, the identity of the actual fusion factor(s) remains to be determined.
    Type of Medium: Online Resource
    ISSN: 0144-8463 , 1573-4935
    URL: Article
    DOI: 10.1023/A:1010419223143
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 2000
    detail.hit.zdb_id: 2014993-1
    SSG: 12
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  • 5
    Online Resource
    Online Resource
    Fusion of enveloped viruses with cells and liposomes : Activity and inactivation
    Springer Science and Business Media LLC ; 1990
    In:  Cell Biophysics Vol. 17, No. 2 ( 1990-10), p. 181-201
    Details
    In: Cell Biophysics, Springer Science and Business Media LLC, Vol. 17, No. 2 ( 1990-10), p. 181-201
    Type of Medium: Online Resource
    ISSN: 0163-4992
    URL: Article
    DOI: 10.1007/BF02990496
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 1990
    detail.hit.zdb_id: 2072590-5
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  • 6
    Online Resource
    Online Resource
    Exosome Secretion: The Art of Reutilizing Nonrecycled Proteins?
    Wiley ; 2004
    In:  Traffic Vol. 5, No. 11 ( 2004-09), p. 896-903
    Details
    In: Traffic, Wiley, Vol. 5, No. 11 ( 2004-09), p. 896-903
    Abstract: Multivesicular bodies contain membrane vesicles which either undergo lysosomal digestion or are released in the extracellular environment as exosomes. Evidence is accumulating that supports a physiological role for exosomes in, for example, antigen presentation or removal of transferrin receptor during reticulocyte development. Here, inspired by observations on exosomal release from reticulocytes, we discuss the potential involvement of the so‐called ESCRT mechanism in the entrapment of both lysosomal and exosomal cargo within the intralumenal vesicles of multivesicular bodies. We propose that this mechanism operates at different sites in the endocytic itinerary in different cells, thereby providing a tool for directional sorting. We also explore the possibility that the efficiency of sorting of molecules into exosomes increases when the recycling kinetics of molecules decreases, exosomal sorting being favored by intermolecular interactions occurring within lipid domains, or with protein webs, that slow lateral mobility. These considerations are mirrored in the context of current knowledge on the mechanism of protein sorting for degradation in lysosomes, and the hijacking of such mechanisms by some retroviruses for particle budding.
    Type of Medium: Online Resource
    ISSN: 1398-9219 , 1600-0854
    URL: Issue
    URL: Article
    DOI: 10.1111/tra.2004.5.issue-11
    DOI: 10.1111/j.1600-0854.2004.00223.x
    Language: English
    Publisher: Wiley
    Publication Date: 2004
    detail.hit.zdb_id: 2020962-9
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  • 7
    Online Resource
    Online Resource
    Use of photoactivatable sphingolipid analogues to monitor lipid transport in mammalian cells
    Portland Press Ltd. ; 1997
    In:  Biochemical Journal Vol. 328, No. 2 ( 1997-12-01), p. 489-498
    Details
    In: Biochemical Journal, Portland Press Ltd., Vol. 328, No. 2 ( 1997-12-01), p. 489-498
    Abstract: Photoactivatable derivatives of ceramide, glucosylceramide (GlcCer) and sphingomyelin {3-(p-azido-m-[125I]iodophenyl)propionylceramide, 3-(p-azido-m-[125I] iodophenyl)propionyl-GlcCer and 3-(p-azido-m-[125I]iodophenyl)propionylsphingomyelin} were synthesized in an attempt to identify compartment-specific proteins involved in sphingolipid sorting or metabolism. In HT29 and BHK cells the ceramide analogue entered the cell by monomeric diffusion, as evidenced by the probe's efficient internalization at low temperature (4 °C). In contrast, the photoactivatable GlcCer was internalized only at elevated temperatures (37 °C), presumably reflecting an endocytic mechanism of uptake. The photoactivatable ceramide was mainly metabolized to the corresponding sphingomyelin analogue, but small amounts of GlcCer and galactosylceramide were also synthesized. The newly synthesized photoreactive sphingomyelin was subsequently transported to the cell surface, a process that was effectively inhibited by the presence of brefeldin A. The incubation of cells with photoactivatable analogues at 4 °C, followed by illumination, led to the association of sphingolipid with a specific subset of proteins. The protein labelling pattern of ceramide differed from that of glucosylceramide. A further shift in labelling pattern was apparent when the cells were incubated with the lipid analogues at 37 °C. Moreover, most of the proteins labelled by photoreactive sphingomyelin seemed to be detergent-insoluble, which is indicative of a location in sphingolipid-rich microdomains at the plasma membrane. The potential of applying photoactivatable sphingolipids to further define and identify the role of distinct proteins in sphingolipid biosynthesis, transport and sorting, is discussed.
    Type of Medium: Online Resource
    ISSN: 0264-6021 , 1470-8728
    URL: Article
    DOI: 10.1042/bj3280489
    RVK:
    WA 15000
    Language: English
    Publisher: Portland Press Ltd.
    Publication Date: 1997
    detail.hit.zdb_id: 1473095-9
    SSG: 12
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  • 8
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    Online Resource
    Actin Filaments and Microtubules are Involved in Different Membrane Traffic Pathways That Transport Sphingolipids to the Apical Surface of Polarized HepG2 Cells
    American Society for Cell Biology (ASCB) ; 1998
    In:  Molecular Biology of the Cell Vol. 9, No. 7 ( 1998-07), p. 1939-1949
    Details
    In: Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 9, No. 7 ( 1998-07), p. 1939-1949
    Abstract: In polarized HepG2 hepatoma cells, sphingolipids are transported to the apical, bile canalicular membrane by two different transport routes, as revealed with fluorescently tagged sphingolipid analogs. One route involves direct, transcytosis-independent transport of Golgi-derived glucosylceramide and sphingomyelin, whereas the other involves basolateral to apical transcytosis of both sphingolipids. We show that these distinct routes display a different sensitivity toward nocodazole and cytochalasin D, implying a specific transport dependence on either microtubules or actin filaments, respectively. Thus, nocodazole strongly inhibited the direct route, whereas sphingolipid transport by transcytosis was hardly affected. Moreover, nocodazole blocked “hyperpolarization,” i.e., the enlargement of the apical membrane surface, which is induced by treating cells with dibutyryl-cAMP. By contrast, the transcytotic route but not the direct route was inhibited by cytochalasin D. The actin-dependent step during transcytotic lipid transport probably occurs at an early endocytic event at the basolateral plasma membrane, because total lipid uptake and fluid phase endocytosis of horseradish peroxidase from this membrane were inhibited by cytochalasin D as well. In summary, the results show that the two sphingolipid transport pathways to the apical membrane must have a different requirement for cytoskeletal elements.
    Type of Medium: Online Resource
    ISSN: 1059-1524 , 1939-4586
    URL: Article
    DOI: 10.1091/mbc.9.7.1939
    Language: English
    Publisher: American Society for Cell Biology (ASCB)
    Publication Date: 1998
    detail.hit.zdb_id: 1474922-1
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  • 9
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    Rho Kinase, Myosin-II, and p42/44 MAPK Control Extracellular Matrix-mediated Apical Bile Canalicular Lumen Morphogenesis in HepG2 Cells
    American Society for Cell Biology (ASCB) ; 2006
    In:  Molecular Biology of the Cell Vol. 17, No. 7 ( 2006-07), p. 3291-3303
    Details
    In: Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 17, No. 7 ( 2006-07), p. 3291-3303
    Abstract: The molecular mechanisms that regulate multicellular architecture and the development of extended apical bile canalicular lumens in hepatocytes are poorly understood. Here, we show that hepatic HepG2 cells cultured on glass coverslips first develop intercellular apical lumens typically formed by a pair of cells. Prolonged cell culture results in extensive organizational changes, including cell clustering, multilayering, and apical lumen morphogenesis. The latter includes the development of large acinar structures and subsequent elongated canalicular lumens that span multiple cells. These morphological changes closely resemble the early organizational pattern during development, regeneration, and neoplasia of the liver and are rapidly induced when cells are cultured on predeposited extracellular matrix (ECM). Inhibition of Rho kinase or its target myosin-II ATPase in cells cultured on glass coverslips mimics the morphogenic response to ECM. Consistently, stimulation of Rho kinase and subsequent myosin-II ATPase activity by lipoxygenase-controlled eicosatetranoic acid metabolism inhibits ECM-mediated cell multilayering and apical lumen morphogenesis but not initial apical lumen formation. Furthermore, apical lumen remodeling but not cell multilayering requires basal p42/44 MAPK activity. Together, the data suggest a role for hepatocyte-derived ECM in the spatial organization of hepatocytes and apical lumen morphogenesis and identify Rho kinase, myosin-II, and MAPK as potentially important players in different aspects of bile canalicular lumen morphogenesis.
    Type of Medium: Online Resource
    ISSN: 1059-1524 , 1939-4586
    URL: Article
    DOI: 10.1091/mbc.e06-01-0067
    Language: English
    Publisher: American Society for Cell Biology (ASCB)
    Publication Date: 2006
    detail.hit.zdb_id: 1474922-1
    SSG: 12
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  • 10
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    Polarized Sphingolipid Transport from the Subapical Compartment Changes during Cell Polarity Development
    American Society for Cell Biology (ASCB) ; 2000
    In:  Molecular Biology of the Cell Vol. 11, No. 3 ( 2000-03), p. 1093-1101
    Details
    In: Molecular Biology of the Cell, American Society for Cell Biology (ASCB), Vol. 11, No. 3 ( 2000-03), p. 1093-1101
    Abstract: The subapical compartment (SAC) plays an important role in the polarized transport of proteins and lipids. In hepatoma-derived HepG2 cells, fluorescent analogues of sphingomyelin and glucosylceramide are sorted in the SAC. Here, evidence is provided that shows that polarity development is regulated by a transient activation of endogenous protein kinase A and involves a transient activation of a specific membrane transport pathway, marked by the trafficking of the labeled sphingomyelin, from the SAC to the apical membrane. This protein kinase A–regulated pathway differs from the apical recycling pathway, which also traverses SAC. After reaching optimal polarity, the direction of the apically activated pathway switches to one in the basolateral direction, without affecting the apical recycling pathway.
    Type of Medium: Online Resource
    ISSN: 1059-1524 , 1939-4586
    URL: Article
    DOI: 10.1091/mbc.11.3.1093
    Language: English
    Publisher: American Society for Cell Biology (ASCB)
    Publication Date: 2000
    detail.hit.zdb_id: 1474922-1
    SSG: 12
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