Endocytosis receptor

Figure 8 Ubiquitin and endocytosis. Receptors on the plasma membrane undergo monoubiquitination as a result of ligand (e.g., neurotransmitter). Ubiquitinated receptors bind to proteins called epsins, which in turn interact with adaptor proteins (adaptin) bound to clathrin-coated pits. Ubiquitination also functions to sort the internalized membrane protein into early endosomes, which directs them to degradation by lysosome through the multivesicular body. If ubiquitin from the endocytosed receptors is removed by an UBP, the receptor recycles back to the membrane. Proteasome inhibitors block endocytotic degradation of some proteins such as glutamate receptor subunits indicating a possible role for the proteasome.

Gene delivery systems can distribute plasmids to the desired target cells, after which the plasmid is internalized into the cell by a number of mechanisms, such as adsorptive endocytosis, receptor-mediated endocytosis, micropinocytosis, caveolae-mediated endocytosis and phagocytosis (see Section 1.3.3.2). The intracellular fate of plasmids depends on the means by which they are internalized and translocated to the cytoplasms and then to the nucleus. In coated-pit endocytosis, DNA complexes first bind to the cell surface, then migrate to clathrin-coated pits about 150 ran in diameter and are internalized from the plasma membrane to form coated vesicles. 

Both IDL and LDL can be removed from the circulation by the liver, which contains receptors for ApoE (IDL) and ApoB-100 (IDL and LDL). After IDL or LDL interacts with these receptors, they are internalized by the process of receptor-mediated endocytosis. Receptors for ApoB-100 are also present in peripheral tissues, so that clearance of LDL occurs one-half by the liver and one-half by other tissues. In the liver or other cells, LDL is degraded to cholesterol esters and its other component parts. Cholesterol esters are hydrolyzed by an acid lipase and may be used for cellular needs, such as the building of plasma membranes or bile salt synthesis, or they may be stored as such. Esterification of intracellular cholesterol by fatty acids is carried out by acyl-CoA-cholesterol acyltransferase (ACAT). Free cholesterol derived from LDL inhibits the biosynthesis of endogenous cholesterol. B-100 receptors are regulated by endogenous cholesterol levels. The higher the latter, the fewer ApoB-100 receptors are on the cell surface, and the less LDL uptake by cells takes place. 

Lennartz MR, Cole FS, Shepherd VL, Wileman TE, Stahl PD. Isolation and characterization of a mannose-specific endocytosis receptor from human placenta. JBiol Chem 1987 262(21) 9942-4. 

Fig. 6 Schematic depiction of cellular uptake mechanisms fluid-phase endocytosis, receptor-mediated endocytosis, and transc5dosis. (Illustration by Leigh A. Rondano, Boehringer Ingelheim Pharmaceuticals, Inc.)...

Cl cotransporter), (5) ion antiports (Na /H exchange), (6) facilitated diffusion (glucose via CLUT-1), (7) active transport (P-gp), (8) active antiport transport (Na /K ATPase), and (9) endocytosis (receptor as insulin or transferrin or adsorption mediated). Adapted from Huber etal. [47]. 

S. Olsnes and K. Sandvig, in Receptor Mediated Endocytosis Receptors and Recognition,... 

Figure 1. Schematic representation of HIV-1 depicting oligosaccharides of the envelope glycoprotein gp 120 (A), and binding of high mannose type V-glycans to the macrophage endocytosis receptor (B). (Taken from [1] with permission.)...

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