China
Africa
Explore chapters and articles related to this topic
Introduction to virus structure, classification, replication, and hosts
Published in Avindra Nath, Joseph R. Berger, Clinical Neurovirology, 2020
Philippe Simon, Kevin M. Coombs
Receptor-mediated endocytosis: Both enveloped and nonenveloped viruses may be engulfed by the cell in clathrin-coated vesicles to form endosomes. Once the virus is enclosed in this endosome, acid-dependent events are believed in some cases to trigger either the fusion of the membranes, in the case of enveloped viruses, or the lysis of the endosome, in the case of nonenveloped viruses. The endosomal decrease in pH appears to trigger a conformational change in specific viral proteins that mediate the subsequent release of the nucleocapsid. For example, acidification of influenza virus causes a conformational change in the hemagglutinin protein, which may cause internal fusion of the membranes. Sometimes (e.g., adenoviruses), the low pH-induced conformational change in a protein serves to disrupt and in turn lyse the endosomal membrane at key membrane–viral protein contacts.
Cytotoxicology Studies of 2-D Nanomaterials
Published in Suresh C. Pillai, Yvonne Lang, Toxicity of Nanomaterials, 2019
Priyanka Ganguly, Ailish Breen, Suresh C. Pillai
Clathrin-coated vesicles are utilised to internalise NMs of size usually <100 nm. It is a receptor-mediated endocytosis pathway, where the plasma membrane undergoes inward budding and forms vesicles. The vesicles are layered with various protein receptors permitted to internalise the specific molecule (Sorkin and Puthenveedu, 2013). In this energy-dependent process the clathrin does not interact with the membrane or the ingested particles. It completely depends on the protein receptors and the accessory proteins present on the walls of the vesicles. The accessory proteins are the cytoplasmic proteins which are later subjected to reuse for another endocytosis cycle. The internalised NMs experience organization in the endosomes and are later sent to the surface or delivered to other mature endosomes like lysosomes (McMahon and Boucrot, 2011). The uptake of nutrients, activation of signalling pathways, regulation of surface expression of proteins, and retrieval of proteins deposited after vesicle fusion are some of the functions associated with clathrin-mediated endocytosis (Chen et al., 1998; Liu et al., 2001; McMahon and Boucrot, 2011; Motley et al., 2003; Sikora et al., 2017).
Growth Factor Receptors
Published in Enrique Pimentel, Handbook of Growth Factors, 2017
Receptor-mediated endocytosis has been classified into four categories, based on the final destination of both receptor and ligand.55 In the class I category, receptor and ligand dissociate from one another and the receptor is recycled to the cell surface whereas the ligand is degraded in lysosomes. In the class II category, receptor and ligand both recycle to plasma membrane. In the class III category, both receptor and ligand are transported to lysosomes. Finally, in the class IV category the ligand-receptor complexes are delivered to the opposite sides of polarized cells in a process referred to as transcytosis, the ligand is released intact on the opposite side of the membrane, and the receptor is either degraded or recycled. Despite the heterogeneity of receptors, the initial step of endocytosis for all four classes of cell surface receptors is the same: the ligand-receptor complex is internalized via clathrin-coated pits. When clathrin-coated pits are saturated with receptors, they invaginate, forming a clathrin-coated vesicle. These vesicles lose their clathrin and undergo an acidic shift in pHi resulting in an endosome.
Human ovarian granulosa cells use clathrin-mediated endocytosis for LDL uptake: immunocytochemical and electron microscopic study
Published in Ultrastructural Pathology, 2023
Aynur Abdulova, Merjem Purelku, Hakan Sahin, Gamze Tanrıverdi
Regarding the clathrin-mediated endocytic pathway, an important component is the clathrin protein. Clathrin-coated vesicles have a three-layered structure consisting of an outer region formed by clathrin proteins in the form of a cage, an intermediate region consisting of a lipid membrane, as well as internal adaptor proteins (APs).8 Along with clathrin, more than 60 other cytosolic proteins are involved in the formation of clathrin-coated endocytic vesicles.9 All these proteins assemble from the cytosol to the endocytic region in a highly ordered manner. The collected vesicles are transported to the target site by SNARE (N-ethylmaleimide-sensitive factor binding protein receptor) proteins. SNAREs manage the transfer of material to be transported during vesicular transport. In an animal cell, there are at least 20 different organelle-associated SNARE proteins, each attached to a specific membrane involved in the biosynthetic-secretion or endocytic pathway. These proteins function as transmembrane proteins and are referred to as vesicular SNAREs (v-SNAREs) with characteristic spiral domains.10
Surface charge, glycocalyx, and blood-brain barrier function
Published in Tissue Barriers, 2021
Fruzsina R. Walter, Ana R. Santa-Maria, Mária Mészáros, Szilvia Veszelka, András Dér, Mária A. Deli
Charge can affect the permeability of a molecule across the BBB via different mechanisms, including affinity for transporters, protein binding, and adsorptive-mediated transcytosis.28 During adsorptive-mediated transcytosis at the BBB the first step is the binding of the biomolecules with net positive charge to the negatively charged endothelial surface followed by internalization.34 In this very first step, the ionic interactions drive membrane invagination and mediate adsorptive transcytosis. Both clathrin coated vesicles and caveolae participate in this energy-dependent process, which can be divided into three major steps, endocytosis, transcytosis and exocytosis.34 It has been recently discovered, that there are differences between vesicular trafficking in brain endothelial cells and in epithelial cells,35 although how adsorptive-mediated transcytosis at the BBB may differ from that of other endothelium is not known.
Delivery of pDNA to lung epithelial cells using PLGA nanoparticles formulated with a cell-penetrating peptide: understanding the intracellular fate
Published in Drug Development and Industrial Pharmacy, 2020
Larissa Gomes dos Reis, Wing-Hin Lee, Maree Svolos, Lyn M. Moir, Rima Jaber, Andrea Engel, Norbert Windhab, Paul M. Young, Daniela Traini
Chlorpromazine, an inhibitor that disrupts the formation of clathrin-coated pits, hence inhibiting clathrin-mediated endocytosis, led to the most significant decrease in NP–DNA–CPP uptake in both cell lines, with only 22% of positive cells in A549 and 67% in Beas-2B, respectively. To a lesser extent, the disruption of microtubules formation via the microtubule depolymerizing agent nocodazole also significantly decreases internalization to ∼63% in both cell lines. The inhibition of GTPase activity dynamin was also able to significantly decrease NP–DNA–CPP uptake in both cell lines. Dynamin is essential for membrane fission of clathrin-coated vesicles [18] and also plays a role on caveola-mediated and lipid-raft endocytosis [16]. Wortmannin, a pharmacological inhibitor that affects the formation of the double-shell of the endosomes, hence inhibiting clathrin-mediated endocytosis, led to a significant decrease by 20 and 25% of NP–DNA–CPP uptake in A549 and Beas-2B respectively. When colchicine was used to bind tubulin, thereby inhibiting cytoskeleton function, a significant decrease in A549 internalization was observed. Similarly, incubation with cytochalasin D decreased internalization to 61% of NP–DNA–CPP in A549. While the depletion of cholesterol in the cellular membrane caused by MβCD and the inhibition of scavenger receptors by Polyisinosinic acid did not affect internalization in A549, a decrease by 16 and 14%, respectively, was observed in Beas-2B.