Dynamin endocytosis

CaMKI and CaMKII) Dynamin-1 GTPase required for endocytosis that is phosphorylated by protein kinase C and dephosphorylated by calcineurin upon membrane depolarization and binds to AP2. Important for budding and fusion pore closure. 

Some inhibitors for this pathway, often described in the literature, do not directly affect the clathrin pathway but rather affect features involved with other pathways. For example, the acidification of endosomes is employed by the other types of endocytosis as well—therefore, these inhibitors are less specific and are described in the section Intracellular Trafficking The same occurs with dynamin dependence or metabolic activity (section Metabolic Activity ). 

Chanez AL, Hehl AB, Engstler M, Schneider A (2006) Ablation of the single dynamin of T brucei blocks mitochondrial fission and endocytosis and leads to a precise cytokinesis arrest. J Cell Sci 119 2968-2974... 

Fig. 5 Synaptic vesicle recycling in the synapse. For synaptic vesicle recycling, several endocytic mechanisms appear to co-exist in synaptic nerve terminals. In the case of fast kiss-and-ran exo-cytosis/endocytosis, the fused vesicle does not collapse into the membrane but is retrieved directly by a fast process. The molecular machinery underlying this pathway is unknown. Vesicles that have fully collapsed into the membrane are recycled by clathrin-mediated endocytosis. Clathrin, along with other proteins, is involved in membrane invagination (see figure and text) and leads finally to the formation of a constricted pit. The GTPase dynamin (black ring) mediates membrane scission of the constricted pit. After removal of the clathrin coat, two pathways are possible (direct recycling and recycling via the early endosome). In all cases, before fusion the recycled vesicles have to be loaded with neurotransmitters (NT).

In the kiss-and-run mode exocytosis and endocytosis are directly coupled to each other, while in the case of classical complete vesicle fusion, exocytosis and slow clathrin-mediated endocytosis are timely and spatially separated. However, it appears that also in the latter case exocytosis and endocytosis occur coordinated, as both are stimulated by an increase of the cytoplasmic calcium concentration. It has been shown that after calcium entry the enzyme phospho-inositol-5 kinase Iy, which is enriched in the synapse, catalyzes the synthesis of phosphatidylinos-itol (4,5)-bisphosphate and that this mechanism is important for synaptic vesicle trafficking (Di Paolo et al. 2004). As many proteins involved in clathrin-mediated endocytosis are recruited to the plasma membrane by binding to phosphatidylinosi-tol (4,5)-bisphosphate (e.g., amphiphysin, dynamin, epsin, AP-180, and AP-2) it is attractive to speculate that elevated levels of calcium mediate the recruitment of en-docytic proteins to the plasma membrane by this mechanism. The increased level of phosphatidylinositol (4,5)-bisphosphate could be in part degraded by synaptojanin that thereby initiates the disassembly of the clathrin coat. Hence, calcium-induced transient increases in the level of phosphatidylinositol (4,5)-bisphosphate appear to play a central role for coupling exocytosis to clathrin-mediated endocytosis. In addition, it has been demonstrated that calcium also leads to the dephosphorylation of endocytic proteins as amphiphysin, dynamin, and synaptojanin, which in vitro is important for efficient coat assembly (Cousin and Robinson 2001). 

Artalejo CR, Elhamdani A, Palfrey HC (2002) Sustained stimulation shifts the mechanism of endocytosis from dynamin-1-dependent rapid endocytosis to clathrin- and dynamin-2-mediated slow endocytosis in chromaffin cells. Proc Natl Acad Sci USA 99 6358-63 Becher A, Drenckhahn A, Pahner I, Margittai M, Jahn R, Ahnert-Hilger G (1999) The synaptophysin-synaptobrevin complex a hallmark of synaptic vesicle maturation. J Neurosd 19 1922-31... 

Bhatnagar A, Willins DL, Gray JA, Woods J, Benovic JL, Roth BL. The dynamin-dependent, arrestin-independent internalization of 5-hydroxytryptamine 2A (5-HT2A) serotonin receptors reveals differential sorting of arrestins and 5-HT2A receptors during endocytosis. J Biol Chem 2001 276 8269-8277. 

Wittrup and Belting have in several studies on CPP-mediated DNA delivery established protocols for fluorescence assisted cell sorting (FACS) analysis to obtain reliable, quantitative data on CPP-DNA complex uptake in cultured cancer cells (9). Also, procedures for co-localization studies with known markers of various endocytotic pathways using confocal microscopy are described as well as the expression of dominant negative dynamin (GTPase deficient dynamin-2) to evaluate the dynamin dependence of the uptake mechanism. The use of various drugs commonly used to disrupt endocytosis is discussed, especially with regard to their limited specificity (9). 

Disruption of Dynamin-Dependent Endocytosis Using Dominant-Negative Dynamin... 

Clathrin-mediated endocytosis is a major vesicular transport mechanism in the neuron, which enables the internalization of plasma membrane-bound proteins, nutrients, hormones and other molecules associated with the plasma membrane into intracellular compartments. Clathrin and various adaptor and accessory proteins work in concert at different stages of clathrin coated vesicle formation and disassembly, and many of these proteins (such as clathrin light chain, AP-2, dynamin 1, synaptojanin 1, and the amphiphysins) are substrates for protein kinases (Korolchuk et al. 2003). In addition, it has been suggested that directing synaptotagmin 1 to the synaptic vesicle is dependent on the N-terminal glycosylation of this protein (Han et al. 2004). 

Early electron microscopic studies showed that adenovirus enters cells via receptor-mediated endocytosis (Patterson and Russell, 1983). Consistent with these early morphologic studies, adenovirus uptake into cells was shown to involve dynamin (Wang et al, 1998), a 100-kDa GTPase that regulates endosome formation (Sever et al, 1999 Marks et al, 2001). Adenovirus was one of the first viruses shown to use multiple receptors for cell entry (Nemerow et al, 1993 Wickham et al, 1993). The adenovirus... 

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