Endocytic coated vesicle

Damke, H., Baba, T., Wamock, D. E., and Schmid, S. L. (1994). Induction of mutant dynamin specifically blocks endocytic coated vesicle formation. J. Cell Biol 127,915-934. 

Clathrin-coated vesicles mediate transport within the late secretory and the endocytic pathways. Their major coat constituents are clathrin and various adaptor complexes. 

Shortly after formation of coated vesicles, the clathrin coat is removed and the vesicles are referred to as endosomes. Endosomes are roughly 300 400 nm in diameter when fully mature. Antibodies to earlier and late endosomes are available from antibodies-online GmbH, Aachen, Germany (http //www.antikoerper-online. de/). Early endosomal antigen 1 (EEA1) is a 162 kDa membrane-bound protein component specific to the early endosomes and is essential for their fusion with early endocytic vesicles for subsequent redistribution of extracellular compounds to... 

Le Borgne, R., and Hoflack, B. (1998a). Mechanisms of protein sorting and coat assembly insights from the clathrin-coated vesicle pathway. Curr. Opin. Cell Biol. 10, 499-503. Le Borgne, R., and Hoflack, B. (1998b). Protein transport from the secretory to the endocytic pathway in mammalian cells. Biochim. Biophys. Acta 1404, 195-209. 

The clathrin-coated vesicles bud continuously from the plasma membrane and transport both the plasma membrane and the fluid content of the vesicle into the cell. After entering the cytoplasm, the endocytic vesicle loses its clathrin coat and fuses quickly with other vesicles to form early endosomes. 

Portion of an endocytic vacuole forming in the plasma membrane of a cultured fibroblast. The view is from the inside of the cell and shows a large clathrin cage assembling to form a coated vesicle. The overall diameter of the vacuole is 0.2 pm. Clathrin cages vary in size and in the number of faces but are typically 0.1 pm in diameter (see Fig. 8-27 and associated references). Courtesy of Barbara Pearse. 

Specifically, the data reviewed in Chapters 12 and 13 indicate that LCM are rapidly removed from the circulation by the tumor the maximum accumulation of LCM in the tumor area occurs within the first 30 min after administration (ref. 531). These rapid kinetics for LCM uptake are quite consistent with the well-documented kinetics long-known for the LDL receptor-mediated endocytic pathway (ref. 616). For example, Goldstein et al. (ref. 643) reported that LDL-ferritin bound to coated pits at 4°C is rapidly internalized when fibroblasts in tissue culture are warmed to 37°C. In this uptake process, the coated pits invaginate to form coated endocytic vesicles. After 5 to 10 min at 37°C, LDL-ferritin is observed in lysosomes as the result of their fusion with the incoming coated vesicles (ref. 643). The rapid sequence of events visualized in electron micrographs precisely parallels biochemically-derived data on the rapid uptake and degradation of radiolabeled LDL (ref. 644,645). 

The internalization of Tf occurs via an endocytotic clathrin-coated process, and the internalization signal YTRF is also recognized by clathrin lattices in the trans-Golgi (127). In vitro studies have indicated that there are two different endocytic pathways of clathrin-coated vesicles in cells a short-term (10-20 min) recycling... 

Figure 4 Transcellular transport in the proximal and distal intestine of the suckling rat. (A) In the proximal intestine, macromolecules may be selectively absorbed in coated pits along luminal membranes (M) and transported via coated vesicles to the basolateral surface (arrows). Alternatively, selection may occur in tubular compartments (T) or from endosomal vesicles (V). (B) In the distal intestine selective absorption may occur in coated pits at the luminal membrane (M) or from the numerous tubules (T) of the elaborate endocytic complex. (From Ref. 18.)...

Pearse and Bretscher (1981) have discussed the role of coated vesicles in membrane synthesis and function. Eukaryotic cells are able to specifically take up macromolecules by absorptive endocytosis. The macromolecules are usually transferred to lyso-somes where they may be degraded. The first stage of the process involves the binding of macromolecules to receptors which are localized in coated pits. The latter are indented sites on the plasma membrane and the coated pit buds into the cytoplasm to form a coated vesicle in which lie the endocytosed macromolecules. The coated vesicle sheds its coat rapidly and the endocytic vesicles fuse with each other. This allows receptors to be returned to the plasma membrane while the contents are transferred to the lyso-somes. In order to explain how lysosomal and plasma membranes remain different, it was suggested that the coated pits are able to accept certain macromolecules while excluding others. The accepted proteins enter the coated pit and were presumed to bind directly or indirectly to clathrin. Clathrin, a 180000-dalton protein on the cytoplasmic face of coated pits, provides the polyhedron skeleton for the coated vesicles. Examples of the use of coated vesicles for mediated endocytosis are in the uptake of low-density lipoprotein from the blood and in humans for the transport of immunoglobulins from the mother to the child. For other mammals such as the rat the antibodies are selectively absorbed from the mother s milk by the intestinal epithelium. Coated vesicles also provide a mechanism for virus transport into cells. 

More recently, however, CI-976 has also been used to implicate LPAATs in coated vesicle formation. For example, following redistribution to the ER, Golgi membrane proteins remain in the ER as long as CI-976 is kept in the media, suggesting that CI-976 may also inhibit export via COPII vesicles. Indeed, we have recently found that CI-976 potently inhibits a very late step, possibly the fission step, in the formation of COPII vesicles at ER exit sites (ERESs) (Brown et al, submitted). In addition, CI-976 also inhibits the recycling of transferrin and transferrin receptors from endocytic recycling compartment to the cell surface (Chambers et al., 2005). 

Endocytic clathrin-coated vesicle (CCV) formation is a complex process involving a large number of proteins and lipids. The minimum machinery and the hierarchy of the events involved in CCV formation have yet to be dehned. Here we describe an in vitro assay for CCV formation from highly purified rat liver plasma membranes. This rapid and easy assay can be used to quantitatively evaluate the different protein requirements for different endocytic receptors. 

Caveolae are invaginations of the plasma membrane. They contain the protein caveolin and are rich in certain phospholipids. Similar to coated pits, they bud off internally forming endocytic vesicles. Caveolae play an important role in the internalization of certain cell surface receptors. 

Specialized regions of internalization from the plasma membrane, coated with a polyhedral lattice of the protein clathrin. It is in these regions that the first step of the process of endocytosis takes place, with the formation of clathrin-coated endocytic vesicles. 

Figure 13.9 represents the TEM image of LDH particles and their cellular internalization. As expected, LDH particles are internalized by endocytosis. Figure 13.9(A) shows the cellular uptake process of LDHs after 3h of treatment, and demonstrates a successive entry of LDH by endocytosis first the LDH particles were located around the cell membrane due to their positive charge ( ), then they migrate to the membrane ruffles which are considered as endocytic bodies ( ), finally the coated intracellular vesicles were formed as early endosomes ( ). Figure 13.9(B)...

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