Intracellular trafficking pathway

Several intracellular trafficking pathways converge at lysosomes 150 Both constitutive and regulated neuroendocrine secretion pathways exist in cells of the nervous system 151... 

All in all, uptake studies with targeted systems carrying a pH-dependent fluorescent label in conjunction with monensin treatment at the end of the incubation period offer the possibility to discriminate between different intracellular trafficking pathways. At 37°C, an increasing fluorescence emission upon addition of monensin points toward accumulation of the targeted drug delivery system within acidic compartments of the cell, such as lysosomes. 

Watson, P., Jones, A.T., Stephens, D.J., Intracellular trafficking pathways and drug delivery Fluorescence imaging of living and fixed cells. Adv Drug Deliv Rev 57, 43-61 (2005). 

Figure 11.1 The intracellular trafficking pathway of plasmid DNA complexed by poly cationic lipid (lipoplex). Critical steps are indicated by numbers (1) endocytosis, sorting and recycling via vesicular compartments comprising the early (EE) and sorting endosomes (2) entrapment and degradation in the late-endosomes (LE) and lysosomes (3) destabilization of the endo-lysosomal membrane and release into the cytosol, (the precise location of this step is not known) (4) diffusion toward the nuclear pore complex (NPC) and degradation in the cytoplasm, and (5) nuclear translocation across the NPC.

The intracellular trafficking pathway of plasmid DNA complexed by polycationic lipid 192... 

Presently, it cannot be excluded that despite the apparently highly specific function of certain Rabs in intracellular trafficking pathways there is redundancy with respect to vesicle docking in the synapse. The surprising diversity of Rabs on highly purified synaptic vesicles (more than 30 different Rabs) supports the view that multiple Rabs are required for synaptic vesicle recycling, which may have overlapping functions. 

Insulin-dependent diabetes mellitus is an autoimmune disease and high titers of auto-antibodies against both insulin and sulfatide were found in patients with insulin-dependent diabetes (Andersson et ah, 2002 Buschard et al., 2005). Sulfatide and insulin are present in the same cellular compartments and share the same intracellular trafficking pathways (Buschard et ah, 2005 Fredman et ah, 2000). The inhibition of sulfatide synthesis with chloroquine and fumo-nisine B1 leads to inhibition of insulin granule formation in vivo (Fredman et al.,... 

Lao BJ, Kamei DT (2008) Improving therapeutic properties of protein drugs through alteration of intracellular trafficking pathways. Biotechnol Prog 24 2-7... 

In this section, we provide an overview of the physical characteristics of nanomaterials that enable them to interact with animal cells and cellular compartments. Because they are chemically stable and relatively inert, 1-D nanostructures (1-D NS) have relatively low cell cytotoxicity (as outlined above), while their chemical modification also provides a means for linkage with specific biomolecules. Thus, 1-D NS may interact directly with cellular substructures. In addition, a typical cellular targeted delivery strategy is also discussed that can support the cellular uptake of these nanoshuctures. Notably, 1-D NS with dimensions of 2 to lOOnm are particularly suited to the adoption of intrinsic cellular transport mechanisms, and can be used for the targeted delivery of specific biomolecules to specific cells and tissues. Moreover, 1-D NS may also provide nanoplatform constructs for the delivery of specific biomolecules through interactions in well-characterized intracellular trafficking pathways. 

Since the SUMO pathway affects multiple pathways ranging from transcription, DNA repair, and intracellular trafficking over cell signaling and cell cycle control to basic metabolism, it is not suiprising that links to diseases and viral assaults are emerging. However, the field is not yet at a stage sufficiently developed for pharmacological intervention. Below we will describe selected examples for links of the SUMO pathway to diseases and viral functions. 

Blanpain C, Wittamer V, Vanderwinden JM, et al. Palmitoylation of CCR5 is critical for receptor trafficking and efficient activation of intracellular signaling pathways. J Biol Chem 2001 276(26) 23795-23804. 

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 ). 

Several aspects of intracellular trafficking should be kept in mind in the intracellular trafficking section. The first is the dependence of acidification of endosomes on the uptake of liposomes. This aspect is sometimes discussed when analyzing clathrin uptake. However, several other pathways are also in need of acidic compartments as a destination of uptake so, we list this factor as an individual aspect. Other aspects of intracellular trafficking that are of interest are the transport from early endosomes to late endosomes, the dependence of actin filaments and dynamin, and/or microtubules. Furthermore, the energy dependence of liposome uptake is discussed. 

The use of the term marker is often misleading because it can be interpreted to imply an absolute specificity that does not reflect the dynamic nature of intracellular compartments. It is important to remember that the predominant location of these markers reflects a balance of trafficking pathways into and out of each compartment. Marker can be internalized not only by one but by different mechanisms. Even SV40, which is known to be a specific marker for caveolae uptake, is now also described as entering the cells via a different mechanism (121). Therefore, not just one but several inhibitors or markers for each mechanism should be applied and all results should be taken into account before reaching a conclusion. 

Jones TJ, Gumbleton M, Duncan R. Understanding endocytic pathways and intracellular trafficking a prerequisite for effective design of advanced drug delivery systems. Adv Drug Deliv Rev 2003 55(11) 1359-1383. 

This is in contrast to viruses, where the virus particles also show active transport when present in the cytosol after fusion with the plasma membrane or endosomal membrane [60-62], This is due to the ability of specific proteins of the virus particle to bind motor proteins. Single-particle tracking reveals that the quantitative intracellular transport properties of internalized non-viral gene vectors (e.g., polyplexes) are similar to that of viral vectors (e.g., adenovirus) [63]. Suk et al. showed that over 80% of polyplexes and adenoviruses in neurons are subdiffusive and 11-13% are actively transported. However, their trafficking pathways are substantially different. Polyplexes colocalized with endosomal compartments whereas adenovirus particles quickly escaped endosomes after endocytosis. Nevertheless, both exploit the intracellular transport machinery to be actively transported. 

Khalil IA, Kogure K, Akita H, Harashima H (2006) Uptake pathways and subsequent intracellular trafficking in nonviral gene delivery. Pharmacol Rev 58 32-45... 

Liu, G., Thomas, L., Warren, R. A., et al. (1997) Cytoskeletal protein ABP-280 directs the intracellular trafficking of furin and modulates proprotein processing in the endocytic pathway. J. Cell Biol. 139, 1719-1733. 

All identified TLRs are type I transmembrane proteins, whose intracellular domains contain regions homologous to the intracellular domains of IL-1R and are referred to as TIR domains (Takeda et ah, 2003). These intracellular domains are able to trigger signalling pathways known to activate the nuclear factor kappa B (NF-kB) (Medzhitov et ah, 1998 O Neill, 2000), which in turn leads to the secretion of pro-inflammatory cytokines such as TNF-a, IL-6 and IL-8. The membrane distribution of TLRs as well as their intracellular trafficking has only now beginning... 

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