Intracellular compartmentation

A problem with employment of ASON in a larger clinical setting is their poor uptake and inappropriate intracellular compartmentalization, e.g., sequestration in endosomal or lysosomal complexes. In addition, there is a need for a very careful selection of the ASON-mRNA pair sequences that would most efficiently hybridize. To date, several computer programs are used to predict the secondary and tertiary structures of the target mRNA and, in turn, which of the mRNA sequences are most accessible to the ASON. However, even with this sophisticated techniques, the choice of base-pairing partners still usually includes a component of empiricism. Despite these principal limitations, it has become clear that ASON can penetrate into cells and mediate their specific inhibitory effect of the protein synthesis in various circumstances. 

Wallimann, T., Wyss. M., Brdicza, D., Nicolay, K.. Eppenberger, H.M. (1992). Intracellular compartmentation. structure and function of creatine kinase isoenzymes in tissues with high and fluctuating energy demands The phosphocreatine circuit for cellular energy homeostasis. Biochem. J. 281,21-40. 

Jeschke, W.D. (1984). K -Na exchange at cellular membranes, intracellular compartmentation of cations, and salt tolerance. In Salinity Tolerance in Plants, ed. R.C. Staples and G. Toenniessen, pp. 37-66. New York John Wiley. 

Pohnert G, Jung V (2003) Intracellular compartmentation in the biosynthesis of caulerpenyne study on intact macroalgae using stable-isotope-labeled precursors. Org Lett 5 5091-5093 Potin P, Bouarab K, Salaun JP, Pohnert G, Kloareg B (2002) Biotic interactions of marine algae. Curr Opin Plant Biol 5 308-317... 

Ovadi J, Saks V. 2004. On the origin of intracellular compartmentation and organized metabolic systems. Molec Cel Biochem 256/257 5-12. 

Edwards, G.E., Foster, J.G. Winter, K. (1982). Activity and intracellular compartmentation of enzymes of carbon metabolism in CAM... 

Peters-Golden M and Brock TG (2001) Intracellular compartmentalization of leukotriene synthesis unexpected nuclear secrets. FEBS Lett 487, 323-326. 

Gendraud, M. and Lafleuriel, J., Intracellular compartmentation of ATP in dormant and non-dormant tubers of Jerusalem artichoke (Helianthus tuberosus L.) grown in vitro, J. Plant Physiol., 118, 251-258, 1985. 

AMANN, M., WANNER, G., ZENK, M.H., Intracellular compartmentation of two enzymes of berberine biosynthesis in plant cell cultures. Planta, 1986, 167, 310-320. 

How could these data be useful in investigating intracellular compartmentation ... 

It is well known that occupied VDR is predominantly in the nucleus, but how the VDR localizes to the nucleus has long been a controversial issue and is still poorly understood. Cell fractionation studies show the VDR to be exclusively nuclear [228]. The presence of VDR in both nuclear and cytosolic fractions, however, has been reported with the use of physiological ionic strength buffers or by gentle fractionation methods [261, 262]. The work of Barsony et al. [263] has used immunocytochemical detection to study the intracellular compartmentalization of VDR. They report the transcellular movement of VDR from the cytoplasm to the nucleus in microwave-fixed cells. In the presence of l,25-(OH)2D3, VDR becomes organized on cytoplasmic fibres that resemble or are microtubules [264] and are oriented in... 

Huls M, Brown CD, Windass AS, Sayer R, van den Heuvel JJ, Heemskerk S, Russel FG, Masereeuw R.The breast cancer resistance protein transporter ABCG2 is expressed in the human kidney proximal tubule apical membrane. Kidney int 2007 73 220-225. Miller DS, Stewart DE, Pritchard JB. Intracellular compartmentation of organic anions within renal cells. Am J Physiol 1993 264 ... 

Intracellular compartmentation of the newly synthesized proteins is a complex process, and disorders in this process lead to severe abnormalities (see below). 

Miller DS, Stewart DE, Pritchard JB. Intracellular compartmentation of organic anions within renal cells. Am J Physiol 1993 264 R882-R890. 

The pulse mechanism for intracellular Zn(II) mobilization in eukaryotes presents some significant questions. For example, how does the released Zn(II) from the vacuoles find its way to the newly-made Zn(II)-metalloproteins and how does the unused and non-specifically bound Zn(II) get returned to the transporters in the vacuolar membrane In prokaryotes, the lack of intracellular compartmentalization presents the additional problem of many more nonspecific Zn(II)-binding sites in the cytoplasm of these cells. It is possible that when the cell needs Zn(II), the non-specifically bound Zn(II) could be mobilized (by shifts in pH, for example) to provide the cell with the needed Zn(II). This latter scenario is not likely since the pH required to release Zn(II) from nucleic acids, for example, would be so low that the cell would not survive. Moreover, previous studies have shown that there are no significant concentrations of free or aquated transition metal ions present in the cytoplasm of a cell at equilibrium. 

Conceivably, the target of the chemically reactive metabolite could be an intracellular enzyme or its substrates required for the function of cells. It could be a phospholipid in cellular membranes, which control the intracellular compartmentalization of intracellular components. It could be part of the protein synthesis machinery required for the normal replacement of intracellular enzymes. It could also be DNA required for cellular replication. We also envisioned the possibility that the manifestation of the toxicity might not occur unless several of these targets were impaired simultaneously. 

To evade the interferences due to metabolism or intracellular compartmentalization and sequestration, isolated membrane preparations in the form of vesicles have proved useful, and can be obtained either directly from isolated natural membranes [32,36] or, going one step further, by extracting transport-related proteins and reconstituting them into artificial phospholipid vesicles (liposomes) [34,98]. The preparation of the natural membrane vesicles is aided by the natural tendency of membrane fragments to form closed vesicles spontaneously under suitable conditions. Reconstituted vesicles are more difficult to obtain, for even rather pure preparations of transport components show little tendency to spontaneously integrate themselves in an artificial lipid membrane. Nonetheless, some successful attempts have been described in the literature of such an incorporation. 

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