Ian F. Pryme

The compartmentalization of protein synthesis: importance of cytoskeleton and role in mRNA targeting.

Following the synthesis of mRNA molecules in eukaryotic cells, the transcripts are processed in the nucleus and subsequently transported through the nuclear membrane into the cytoplasm before being sequestered into polysomes where the information contained in the RNA molecule is translated into an amino acid sequence. Recent evidence suggests that an association of mRNAs with the cytoskeleton might be important in targeting mechanisms and, furthermore, in the transport of mRNA from the nucleus to its correct location in the cytoplasm. Until recently, polysomes have been considered to exist in two classes, namely free or membrane-bound. There is now compelling evidence, however, that ribosomes, in addition to being associated with endoplasmic reticulum membranes, also are associated with components of the cytoskeleton. Thus, a large number of morphological and biochemical studies have shown that mRNA, polysomes and translational factors are associated with cytoskeletal structures. Although the actual nature and significance of the interaction between components of the translational apparatus and the cytoskeleton is not yet understood in detail, it would seem evident that such interactions are important in both the spatial organization and control of protein synthesis. Recent work has shown that a subcellular fraction, enriched in cytoskeletal components, contains polysomes and these (cytoskeletal-bound) polysomes have been shown to contain specific mRNA species. Thus, a population of cytoskeletal-bound polysomes may provide a specialized mechanism for the sorting, targeting and topographical segregation of mRNAs. In this review, current knowledge of the subcellular compartmentalization of mRNAs is discussed.

Lithium: A review of pharmacology, clinical uses, and toxicity

A radical drug treatment for bipolar affective disorder (BD) is currently unavailable. This is attributed to the fact that the precise pathophysiology of this ailment is unclear though a genetic factor is an essential element in etiology. Dissimilar to other serious psychiatric categories such as psychoses and major depression the forecast of this disease is unpredictable. There is a high suicidal risk among BD affected individuals. In this review we will consider lithium, the drug of choice in treatment of this disorder with special emphasis on pharmacology and toxicity. We have also elucidated the alternatives to lithium, since it has a wide spectrum of side-effects. Lithium is known to interact with many types of drugs used to treat different ailments in humans. This could cause either augmentation or minimization of the therapeutic action, causing secondary undesired effects of the agent. This necessitates a search for other alternatives and/or different combinations to lithium in order to decrease the range of unwanted effects for which it has received discredit. These alternatives should be potent mood stabilizers as monotherapy so as to avoid polypharmacy. If not, one should find the best combination of drugs (synergistic agents) such that the lithium dose can be minimized, thereby securing a more potent drug therapy. This study also focuses on the provision of instruction to psychiatric care givers, such as junior doctors in residency, nurses in psychiatric units, psychiatric emergency personnel and, additionally, medical and pharmacy students.

The characterization of free, cytoskeletal and membrane-bound polysomes in Krebs II ascites and 3T3 cells.

SummaryPolysomes from Krebs II ascites and 3T3 cells were separated into three populations by using a sequential extraction method. Free polysomes were released by using a combination of low salt (25 mM KCl) and NP-40 detergent in the lysis buffer. The cytoskeletal bound polysomes were subsequently released by raising the salt concentration to 130 mM and finally, polysomes bound to the membranes of the endoplasmic reticulum were extracted by the combined treatment with Triton X-100 and deoxycholate. The results presented here illustrate that the three polysome-containing fractions differ in many parameters such as polysome profiles, cytoskeletal components and phospholipid content. When polyA-containing mRNA was isolated from the three polysome fractions and translated in an in vitro system, some differences were observed in the patterns of proteins being synthesized.

In vivo studies on possible health consequences of genetically modified food and feed--with particular regard to ingredients consisting of genetically modified plant materials.

This synopsis reviews published in vivo studies on possible health consequences of genetically modified food and feed where the ingredients in question have consisted of genetically modified plant materials. The following, however, have not been taken into consideration: ingredients consisting of genetically modified microorganisms or parts of animals/fish ingredients produced by/from genetically modified organisms but without any DNA present studies on consequences for the environment or biodiversity in vitro studies or computer simulations According to a Norwegian report “Gen-mat” (NOU 2000:29), and a more recent search in Medline and Citations Index, to our knowledge a total of ten studies have been published on the health effects of GM-foods and feeds. In this minireview the data made available in these published studies is discussed.

Evidence that insulin increases the proportion of polysomes that are bound to the cytoskeleton in 3T3 fibroblasts

The association of polysome redistribution with changes in protein synthesis was investigated in insulin‐stimulated fibroblasts. Free polysomes were released by Nonidet‐P40 and 25 mM KCl, cytoskeletal‐bound polysomes were retained at 25 mM KCl but released at 130 mM, while membrane‐bound polysomes were released by deoxycholate. Insulin increased the proportion of polysomes which were retained at 25 mM KCl but had no effect when extraction was carried out at 130 mM KCl, suggesting that more polysomes were associated with the cytoskeleton. Insulin also reduced the amount of actin released from the detergent‐insoluble cytoskeleton indicating that the hormone affects microfilament organization.

The growth of an established murine non-Hodgkin lymphoma tumour is limited by switching to a phytohaemagglutinin-containing diet

The growth of a non-Hodgkin lymphoma, developing subcutaneously as a solid tumour in NMRI mice, is markedly diminished by including phytohaemagglutinin (PHA), a lectin present in raw kidney bean (Phaseolus vulgaris), in the diet. In the experiment described in this communication the effect of first allowing tumours to develop for 5 days before switching the mice to a diet containing PHA at different concentrations was tested to establish whether or not feeding the lectin at late times also resulted in reducing tumour growth. This switch of diet indeed proved to be effective in slowing down growth of the lymphoma tumour. The reduced rate of growth occurs in a dose-dependent manner. We have suggested that a competition between the gut epithelium undergoing PHA-stimulated hyperplasia and the developing tumour may occur for polyamines and other nutrients from a common body pool and this could be an important contributory factor with regard to the observed low level of tumour growth following the feeding of PHA-containing diet. Recent data which showed that the level of hyperplasia of the small bowel in response to feeding the PHA diets was higher in non-injected mice compared to those which had been injected with tumour cells substantiated the concept of competition between gut and tumour for nutrients and other requirements for growth.

Insulin and step-up conditions cause a redistribution of polysomes among free, cytoskeletal-bound and membrane-bound fractions in krebs II ascites cells

From 30 min to 1h of step-up conditions there was a redistribution of polysomes between free, cytoskeletal-bound and membrane-bound fractions such that more polysomes were recovered bound to the cytoskeleton and less in the free fraction. After 1h incubation with insulin there was a higher proportion of polysomes in the cytoskeletal fraction with a decrease occurring in the membrane-bound fraction. At 2h little change was observed in the presence of insulin while a large increase occurred in the cytoskeletal-bound fraction and a decrease in membrane-bound polysomes was seen in cells incubated in the absence of insulin. The results indicate that the proportions of polysomes in the three different fractions can be modulated by physiological stimuli, such as media replenishment and insulin.

A diet containing the lectin phytohaemagglutinin (PHA) slows down the proliferation of Krebs II cell tumours in mice

Mice injected intraperitoneally with Krebs II cells and then fed on a diet containing the lectin phytohaemagglutinin (PHA) developed ascites tumours more slowly than mice fed on a control diet. After an 8-day period following injection the number of cells recovered from mice maintained on the PHA diet was half that from those fed the control diet. A switch of diet from control to PHA on day 4 after injection resulted in a large decrease in number of tumour cells recovered. Mice injected s.c. also developed tumours at later times when fed on the PHA diet. A quantitative of ribosomes in polysome-containing fractions showed no major differences in protein synthesis in control mice and those fed the PHA diet.

The Sequestration of mRNA in the Cytoskeleton and Other Subcellular Structures

Publisher Summary This chapter reviews the subcellular compartmentalization of mRNAs. Before release from the nucleus, mRNA molecules are subjected to posttranscriptional processing: capping, polyadenylation, and splicing. Transport of mRNA from the nucleus to the cytoplasm is a heterogenous mechanism that involves several proteins and factors that influence these proteins. After their transport into the cytoplasm, mRNA molecules were sequestered into two compartments of polysomes: cytosolic or free polysomes and those associated with the rough endoplasmic reticulum (ER)—that is, membrane-bound polysomes. Several studies from different and specialized biological systems have indicated that mRNA and ribosomes are orientated with cellular components in a specific manner. The presence of specific mRNAs in cytoskeletal-bound polysomes requires a mechanism that directs the RNA species to the cytoskeletal compartment rather than to the ER or the cytoplasmic (“free”) compartment. The translational system in eukaryotic mitochondria has many unique characteristics that clearly distinguish it from the protein synthetic apparatus present in the cytoplasm of both prokaryotic and eukaryotic cells.

Anti-cancer therapy: diversion of polyamines in the gut.

The growth of a murine non-Hodgkin lymphoma (NHL) tumour, either as an intraperitoneal ascites tumour or as a solid subcutaneous tumour, has been shown to be greatly reduced by including phytohaemagglutinin (PHA), a lectin present in raw kidney bean (Phaseolus vulgaris) in the diet. The reduced rate of growth occurred in a dose-dependent manner. Based on the experimental observations it has been suggested that a competition occurs between the gut tissue undergoing hyperplasia and the developing tumour for nutrients (including polyamines) from a common body pool. This may be an important factor with regard to the observed initial low level of tumour growth following the feeding of a PHA-containing diet. Results showing that the level of hyperplasia of the small intestine in response to feeding the PHA diets was higher in non-injected mice compared to those which had been injected with tumour cells substantiated the concept of competition between gut and tumour for nutrients etc. required for growth. The observations suggest that lectins, which exhibit growth-promoting effects on the gut, may have interesting applications in the formulation of new approaches with respect to cancer treatment.