Endocytosis consequences

In addition to binding to sialic acid residues of the carbohydrate side chains of cellular proteins that the virus exploits as receptors, hemagglutinin has a second function in the infection of host cells. Viruses, bound to the plasma membrane via their membrane receptors, are taken into the cells by endocytosis. Proton pumps in the membrane of endocytic vesicles that now contain the bound viruses cause an accumulation of protons and a consequent lowering of the pH inside the vesicles. The acidic pH (below pH 6) allows hemagglutinin to fulfill its second role, namely, to act as a membrane fusogen by inducing the fusion of the viral envelope membrane with the membrane of the endosome. This expels the viral RNA into the cytoplasm, where it can begin to replicate. 

Ubiquitin/Proteasome. Figure 2 Functional consequences of ubiquitin linkage. Substrates (blue bars) are linked via lysine residues (K) to ubiquitin or ubiquitin chains, (a) Attachment of chains connected via Lysines in position 48 of ubiquitin (K48) targets substrates for proteasomal degradation. In contrast modification of one (b) or multiple (c) lysines by a single ubiquitin molecule mediates novel protein interactions or initiates endocytosis. Conjugation of K63-linked polyubiquitin (d) alters protein function and can also serve as a signal for endocytosis. 

A study investigating the consequences of diesel exhaust particles in human airway epithelial cells also concluded that any effects of these particles occurred after their endocytosis. However, organic components rather than the metals on the surface of the particles were considered to be responsible for subsequent events. Thus, treatment with the iron chelator desferrioxamine had no inhibitory effect on the secretion of the inflammatory cytokines interleukin-8,... 

Haptoglobin binds hemoglobin in a 1 1 molar complex (two ap dimers per haptoglobin) (42). This complex is quickly removed from the circulation via a suicidal receptor-mediated endocytosis (43,44), which consequently depletes haptoglobin. Even a short bout of exercise can deplete haptoglobin (45), whose total plasma amount is equivalent to the hemoglobin in about 4.5 cm of red cells. 

Fig. I. Endocytic pathways used by cells to internalize soluble macromolecules [25] fluid-phase pinocytosis (1), adsorptive pinocytosis (2), and receptor-mediated endocytosis (pinocytosis) (6). Each of these processes involves a formation of a sealed vesicle formed from the plasma membrane which encloses part of the extracellular medium. The internalization of a polymer-drug conjugate (P-D), and targeted polymer-drug conjugate ( => —P-D) is shown. Other abbreviations — = cell surface receptor/antigen 1 = clathrin molecule X = lysosomal enzyme. Fluid-phase pinocytosis (1) and adsorptive pinocytosis (2) are nonspecific processes which direct the macromolecule into the lysosomal compartment of the cell. Once P-D is internalized, whether by (1) or (2), the resulting endosome (3) is ultimately fused with a primary lysosome (4) forming a secondary lysosome (5). In the latter compartment P-D is in contact with several types of lysosomal enzymes. The membrane of (5) is impermeable to macromolecules. Consequently, the structure of P-D may be designed in such...

After binding, the LDL-receptor complex is internalized by endocytosis. [Note A deficiency of functional LDL receptors causes a significant elevation in plasma LDL and, therefore, of plasma cholesterol. Patients with such deficiencies have type II hyperlipidemia (familial hypercholesterolemia) and premature atherosclerosis. The thyroid hormone, T3, has a positive effect on the binding of LDL to its receptor. Consequently, hypothyroidism is a common cause of hypercholesterolemia.]... 

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