Cytosolic transport

Intracellular pathways after escape from the endolysosomal system into the cytosol are less clear. Obvious bottlenecks include, in the case of gene transfer (pDNA delivery), cytosolic transport to the perinuclear area, nuclear uptake, and nuclear presentation of the pDNA to the transcriptional machinery in bioactive form. In the case of siRNA (or mRNA and some other nucleic acids such as oligonucleotides), cytosolic accessibility for the required function is essential. Besides cytosolic transport [176, 177] and the nuclear import of large nucleic acid molecules [178-180], incorporation of functional nuclear import peptide domains has been evaluated [181-186]. Another bottleneck, nucleic acid unpackaging [187], i.e., partial or complete dissociation from the polymeric carrier, which is required for biological accessibility of the delivered nucleic acid, will be discussed in Sect. 3.3. 

The exact mechanism by which Rev interferes with the transport and splicing process is largely unknown. One possible scenario is that Rev interacts with components of the spliceosome, which leads to the release of splice factors that allow cytosolic transport without actual splicing. 

Cytosolic Transport in Epithelium, Mesothelium, and Other Tissues... 

It has been proposed that a low molecular weight phosphoprotein of phosvitin nature (47) which binds iron with high affinity may be involved in the cytosolic transport of iron in liver cells (48, 49), but no energized uptake of iron has been demonstrated such as in isolated rat liver mitochondria using a Fe(III)-phosvitin from avian egg yolk (mol wt 40,000) as the substrate (50). The biochemical significance of the cytosolic iron binding phosphoprotein is therefore still uncertain. 

Le BI, Luyet PP, Pons V, et al. (2005) Endosome-to-cytosol transport of viral nucleocapsids. Nat Cell Biol 7 653-664... 

SUMOylation is a post-translational modification involved in various cellular processes, such as nuclear-cytosolic transport, transcriptional regulation, apoptosis, protein stability, response to stress and progression through the cell cycle. Small ubiquitin-like modifier or SUMO proteins are a family of small proteins that are covalently attached to and detached from other proteins in cells to modify their function. 

An unresolved issue is the question whether the transporters at their target membranes such as the tonoplast or the plasmalemma use substrates that diffuse freely in the cytosol transporter model Fig. 1). As an alternative to diffusion, a protected delivery or binding protein model suggests that flavonoids such as anthocyanins... 

The transfer of C20-C24 fatty acids (and probably of shorter fatty acyl chains) involves, at least in part, a transit through the (3olgi apparatus. To what extent, and associated with which polar heads remains to be elucidated. However, one has to keep in mind that, even if the forthcoming work definitely establishes this point, this will not imply that all lipids must use this pathway and that a cytosolic transport via LTPs is not also operative. It is thus extremely important that an in vivo approach able to study this pathway be developed, and that a visualization of the intracellular journey of the lipids destined to the plasmalemma be obtained in situ. 

---