22,325 research outputs found
Distinct roles for Tsg101 and Hrs in multivesicular body formation and inward vesiculation
No full textin mammalian cells, epidermal growth factor (EGF) stimulation promotes multivesicular body (MVB) formation and inward vesiculation within MVB. Annexin 1 is required for EGF-stimulated inward vesiculation but not MVB formation, demonstrating that MVB formation (the number of MVBs/unit cytoplasm) and inward vesiculation (the number of internal vesicles/MVB) are regulated by different mechanisms. Here, we show that EGF-stimulated MVB formation requires the tumor susceptibility gene, Tsg101, a component of the ESCRT (endosomal sorting complex required for transport) machinery. Depletion of Tsg101 potently inhibits EGF degradation and MVB formation and causes the vacuolar domains of the early endosome to tubulate. Although Tsg101 depletion inhibits MVB formation and alters the morphology of the early endosome in unstimulated cells, these effects are much greater after EGF stimulation. In contrast, depletion of hepatocyte growth factor receptor substrate (Hrs) only modestly inhibits EGF degradation, does not induce tubulation of the early endosome, and causes the generation of enlarged MVBs that retain the ability to fuse with the lysosome. Together, these results indicate that Tsg101 is required for the formation of stable vacuolar domains within the early endosome that develop into MVBs and Hrs is required for the accumulation of internal vesicles within MVBs and that both these processes are up-regulated by EGF stimulation
The relationship between stress-induced endocytosis of epidermal growth factor receptor and cell survival
No full textThe epidermal growth factor receptor (EGFR) is best known for its role in triggering a variety of intracellular signalling pathways that promote cell growth, proliferation, differentiation and migration following the binding of its ligand (EGF). As a result of this, over-activation of EGFR can contribute to carcinogenesis. In parallel with receptor activation, ligand binding initiates receptor internalisation, which provides an important mechanism for negatively regulating the duration and potency of signalling by kick-starting EGFR traffic to the lysosome where it is degraded. However, a small proportion of EGFR can be recycled back to the plasma membrane, prolonging signalling. Another controversial fate has been suggested for the EGFR: traffic to the nucleus where it is believed to promote cell cycle progression, proliferation and DNA repair. In addition to ligand-dependent activation and internalisation of EGFR, these processes can also occur in a ligand-independent manner, following various stresses, including chemotherapy, radiotherapy and ultraviolet light C (UVC). The fate of EGFR following ligand-independent stimulation has not been fully characterised, but in some instances it has been reported to traffic to the nucleus. This would have therapeutic implications, as DNA damage following chemotherapy or radiotherapy could be repaired, resulting in the development of resistance to therapy. In this thesis I aimed to establish tools that inhibited stress-induced EGFR endocytosis in order to test the hypothesis that the fate of stress-induced EGFR regulates EGFR signalling, DNA repair and cell survival. I focused on UVC-induced internalisation, as this occurs rapidly and synchronously and shares a mechanism of internalisation with the chemotherapeutic drug cisplatin. I have shown that following UVC irradiation or cisplatin treatment of HeLa cells, EGFR is internalised and retained in a peri-nuclear compartment without being degraded or translocated to the nucleus. This internalisation depends on the activity of both p38 and Src but not the EGFR tyrosine kinase. Electron microscopy revealed EGFR to be sequestered in multivesicular endosomes/bodies (MVBs). Although these MVBs were morphologically indistinguishable from those that traffic ligand-stimulated EGFR to the lysosome, stress exposed EGFR showed little degradation despite apparent near normal lysosomal function. Stress-induced EGFR endocytosis was not directly linked to DNA damage as ionizing radiation and UVA treatment, which induced extensive DNA damage but did not activate p38, did not induce detectable EGFR internalisation in HeLa cells. EGFR internalisation also correlated with subsequent cell death, as only doses of UVC that induced cell death also induced EGFR endocytosis. Stress-induced EGFR internalisation was abrogated upon depletion of the clathrin adaptor complex AP-2, or mutation of the two AP-2 interaction motifs in the cytoplasmic domain of the EGFR, indicating that this endocytosis occurs via clathrin-coated pits. Inhibition of stress-induced EGFR endocytosis demonstrated that endocytosis of EGFR was necessary to maintain EGFR tyrosine kinase activity, downstream signalling and delay entry into apoptosis. In conclusion we have uncovered a potential role for EGFR in the development of therapeutic resistance. By understanding the molecular mechanisms affecting the endocytic fate of EGFR following stress exposure, it may be possible to design strategies that divert patients from such resistance in the future
The role of multivesicular bodies in the trafficking of the amyloid precursor protein
No full textIn Alzheimer’s disease, the beta-amyloid (Aβ) protein accumulates within neurons prior to amyloid plaque development. Recent evidence suggests that intracellular Aβ accumulation, rather than extracellular plaques, correlates best with disease progression. Aβ is generated by proteolytic processing of the amyloid precursor protein (APP) but the intracellular site of Aβ production is unclear. Aβ has been localised to multivesicular endosomes/bodies (MVBs), which have many cellular functions, including delivery of contents to the lysosome and release of intralumenal vesicles (ILVs) into the extracellular space. Several MVB and ILV populations exist that are formed by distinct mechanisms and have different fates. This study aimed to determine to which MVB population APP traffics, the role of MVBs in Aβ production and the functional consequences of Aβ production and accumulation within MVBs. Immunofluorescence and immuno-EM showed that APP trafficks to the ILVs of an EGF receptor-containing subpopulation of MVBs in a neuroglioma cell line overexpressing APP. To determine the mechanism of APP ILV targeting, we first characterized the effects of inhibition of ESCRT-dependent and ESCRT-independent mechanisms of ILV formation in HeLa cells. We found that EGF stimulation, which promotes ESCRT-dependent ILV formation, causes the generation of enlarged ILVs, whilst depletion of the ESCRT-0 component, Hrs, leads to the reduction of ILV number and size. In neuroblastoma cells overexpressing APP, APP is ubiquitinated and depletion of Hrs inhibits sorting of APP onto ILVs and Aβ secretion, implicating the ESCRT machinery in traffic of APP and Aβ generation. To analyse the effects of Aβ accumulation in the endocytic pathway, we determined the effects of exogenous Aβ endocytosed by HeLa cells and primary neurons, and demonstrated that Aβ can cause disruption of endosome-lysosome morphology and membrane impermeability. These results indicate that APP traffic to MVBs and generation of Aβ within them could contribute to early AD pathology
CE Challenges: Work to Do
No full textCE has been used for more than two decades now. Despite many successes and advantages, there are still many challenges to be addressed. These challenges are both technical and organisational. In the paper we will address the current challenges of CE. Many challenges are related to the exchange of data and knowledge and to the systems that make data and knowledge exchange possible. Although much progress has been made in enabling extensive data and knowledge exchange and use, much remains to be wished. For example, there are still barriers to data exchange. Technically, these barriers may consist of different formats, differences in infrastructures and systems, and different semantics. There are also organisational and political barriers. For example, investment in information system may heavily impact upstream suppliers, while revenues of better information exchange may predominantly be gained by downstream actors. Without sharing costs and revenues, chain-wide information exchange will not be easily realised. Another barrier is the possible lack of willingness to share information, because of potential misuse of knowledge and loss of power. The paper is organised as follows. First we will describe the current manifestation of CE as described in a recent book. Second, we will list current trends in CE. Third, we will present some Critical Success Factors (CSFs) that are considered relevant for implementing and adapting CE practices. Last, we indicate some research and practical questions to be addressed, especially for areas that have a high potential and actual impact. </p
An investigation into nonbronchoscopic bronchoalveolar lavage and endotracheal suctioning in critically ill infants and children
No full textIncludes bibliographical references.This thesis investigated the effects on critically ill, mechanically ventilated paediatric patients of two related, frequently performed physiotherapy procedures: nonbronchoscopic bronchoalveolar lavage (NB-BAL) and endotracheal (ET) suctioning. General aims: To investigate un- or poody-documented complications of paediatric NBBAL and ET suctioning, and to test a method for each procedure of reducing the incidence and/or severity of these complications
Synthesis optimization and charge carrier transfer mechanism in LiLuSiO<sub>4</sub>:Ce, Tm storage phosphor
No full textLiLuSiO4:Ce and LiLuSiO4:Ce, Tm show very efficient charge carrier storage properties upon beta irradiation after samples have received treatment in vacuum. They outperform the commercial storage phosphor BaFBr(I):Eu2+ in many aspects. The influence of the synthesis conditions, Ce and Tm concentration, nonstoichiometry and codoping with Ca, Hf, Al and Ge are reported. Based on the results of the synthesis optimization, thermoluminescence (TL) emission and TL excitation spectra a mechanism of charge carrier transfer, storage, and recombination during irradiation and thermal or optical readout is proposed.Accepted Author ManuscriptRST/Fundamental Aspects of Materials and EnergyRST/Luminescence Material
The impact of P(NDI2OD-T2) crystalline domains on the open-circuit voltage of bilayer all-polymer solar cells with an inverted configuration
Get PDFWe fabricated P(NDI2OD-T2)/PTB7 bilayer all-polymer solar cells with an inverted configuration, where the annealing temperature was systematically varied. The current density-voltage behavior was investigated and the structural properties of the P(NDI2OD-T2) layers were characterized. Absorption spectroscopy, surface morphology, and crystallite analysis showed that increasing phase segregation of P(NDI2OD-T2) films occurred as the annealing temperature increased. We found that, as the P(NDI2OD-T2) stacking improved, with larger domains, the open-circuit voltage decreased and the saturation dark current density increased. This work provides a guide for the processing of P(NDI2OD-T2) layers to maximize the power conversion efficiency of all-polymer solar cells. (C) 2015 Author(s).open1186sciescopu
Data and code for: Variational Graph Author Topic Modeling
No full textThis is the tensorflow implementation of KDD-2022 paper "Variational Graph Author Topic Modeling" by Delvin Ce Zhang and Hady W. Lauw.
VGATM is a Graph Neural Network model that extracts interpretable topics for documents with authors and venues. Topics of documents then fulfill document classification, citation prediction, etc.
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Updated analytical solutions of continuity equation for electron beams precipitation – I. Pure collisional and pure ohmic energy losses
Get PDFWe present updated analytical solutions of continuity equations for power-law beam electrons precipitating in (a) purely collisional losses and (b) purely ohmic losses. The solutions of continuity equation (CE) normalized on electron density presented in Dobranskis & Zharkova are found by method of characteristics eliminating a mistake in the density characteristic pointed out by Emslie et al. The corrected electron beam differential densities (DD) for collisions are shown to have energy spectra with the index of −(γ + 1)/2, coinciding with the one derived from the inverse problem solution by Brown, while being lower by 1/2 than the index of −γ/2 obtained from CE for electron flux. This leads to a decrease of the index of mean electron spectra from −(γ − 2.5) (CE for flux) to −(γ − 2.0) (CE for electron density). The similar method is applied to CE for electrons precipitating in electric field induced by the beam itself. For the first time, the electron energy spectra are calculated for both constant and variable electric fields by using CE for electron density. We derive electron DD for precipitating electrons (moving towards the photosphere, μ = +1) and ‘returning’ electrons (moving towards the corona, μ = −1). The indices of DD energy spectra are reduced from −γ − 1 (CE for flux) to −γ (CE for electron density). While the index of mean electron spectra is increased by 0.5, from −γ + 0.5 (CE for flux) to −γ + 1(CE for electron density). Hard X-ray intensities are also calculated for relativistic cross-section for the updated differential spectra revealing closer resemblance to numerical Fokker–Planck (FP) solutions
The role of Rab27a in the regulation of melanosome distribution within retinal pigment epithelial cells
No full textMelanosomes within the retinal pigment epithelium (RPE) of mammals have long been thought to exhibit no movement in response to light, unlike fish and amphibian RPE. Here we show that the distribution of melanosomes within the mouse RPE undergoes modest but significant changes with the light cycle. Two hours after light onset, there is a threefold increase in the number of melanosomes in the apical processes that surround adjacent photoreceptors. In skin melanocytes, melanosomes are motile and evenly distributed throughout the cell periphery. This distribution is due to the interaction with the cortical actin cytoskeleton mediated by a tripartite complex of Rab27a, melanophilin, and myosin Va. In ashen (Rab27a null) mice RPE, melanosomes are unable to move beyond the adherens junction axis and do not enter apical processes, suggesting that Rab27a regulates melanosome distribution in the RPE. Unlike skin melanocytes, the effects of Rab27a are mediated through myosin VIIa in the RPE, as evidenced by the similar melanosome distribution phenotype observed in shaker-1 mice, defective in myosin VIIa. Rab27a and myosin VIIa are likely to be required for association with and movement through the apical actin cytoskeleton, which is a prerequisite for entry into the apical processes
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