Translation initiation factor modifications and the regulation of protein synthesis in apoptotic cells.

The rate of protein synthesis is rapidly down-regulated in mammalian cells following the induction of apoptosis. Inhibition occurs at the level of polypeptide chain initiation and is accompanied by the phosphorylation of the alpha subunit of initiation factor eIF2 and the caspase-dependent cleavage of initiation factors eIF4G, eIF4B, eIF2alpha and the p35 subunit of eIF3. Proteolytic cleavage of these proteins yields characteristic products which may exert regulatory effects on the translational machinery. Inhibition of caspase activity protects protein synthesis from long-term inhibition in cells treated with some, but not all, inducers of apoptosis. This review describes the initiation factor modifications and the possible signalling pathways by which translation may be regulated during apoptosis. We discuss the significance of the initiation factor cleavages and other changes for protein synthesis, and the implications of these events for our understanding of the cellular changes associated with apoptosis.

Inhibition of the double-stranded RNA-dependent protein kinase PKR by mammalian ribosomes.

Previous evidence has shown that the majority of the interferon-inducible, double-stranded RNA-dependent protein kinase PKR is associated with ribosomes in vivo. Here we show that ribosomes are inhibitory for PKR activity since they compete with dsRNA for binding to PKR, inhibit the activation of the protein kinase by dsRNA, and prevent the phosphorylation of the PKR substrate eIF2alpha. We suggest that ribosomes constitute a reservoir of inactive PKR and that the protein kinase must be displaced from the ribosome by dsRNA in order to become activated.

Insulin processing and action in adipocytes: evidence for generation of insulin-containing vesicles by leupeptin and monensin.

Incubation of adipocytes with 125I-insulin plus leupeptin or monensin, but not chloroquine, resulted in the appearance of a novel peak of 125I-insulin (modal density about 1.20 g/ml) on density gradient centrifugation; the appearance of the peak depended on the presence of specific insulin receptors on the cell surface. The fractions comprising this peak contained vesicles, probably originating from the Golgi apparatus, and dit not appear to be contaminated with lysosomes, mitochondria or plasma membrane. Entrapment of insulin in these vesicles per se did not prevent the activation of glucose transport, acetyl-CoA carboxylase or pyruvate dehydrogenase by insulin.

Stimulation by insulin of protein synthesis in cultured chick embryo fibroblasts.

Insulin stimulates protein synthesis in skeletal muscle of young animals and has been reported to exert similar effects on a variety of mammalian cell types in culture. However, with chick embryo fibroblasts we found that the extent of this effect was very sensitive to the culture conditions of the cells prior to the insulin treatment. The most reproducible results were obtained with cells that had been sub-cultured into medium in which fetal calf serum was replaced with 2% horse serum. Insulin only stimulated protein synthesis when added at supra-physiological concentrations. Insulin-like growth factor 1 was effective at much lower concentrations. Since chick embryo fibroblasts can be obtained in good yield, they offer, if treated under appropriate conditions, a suitable system for study of the mechanisms by which insulin and IGF-1 promote the initiation of protein synthesis in eukaryotic cells.

Effect of starvation and diabetes on the activity of the eukaryotic initiation factor eIF-2 in rat skeletal muscle.

The ability of the initiation factor eIF-2 in skeletal muscle extracts to form ternary initiation complexes ([Met-tRNA(f).eIF-2.GDP]) is decreased by either starvation or diabetes. These conditions also impair the ability of muscle extracts to dissociate [eIF-2.GDP], suggesting inhibition of the guanine nucleotide exchange reaction essential for eIF-2 recycling. We could not, however, detect any change in the phosphorylation state of the alpha subunit of eIF-2. This suggests that eIF-2 activity may be regulated in this system by a mechanism not involving its phosphorylation.

Regulation of the interferon-inducible eIF-2 alpha protein kinase by small RNAs.

This review describes the structure and function of the double-stranded RNA-dependent protein kinase (PKR) and its interaction with RNA activators and inhibitors. The abilities of small virally-encoded RNAs such as VAI RNA of adenovirus, the Epstein-Barr virus encoded (EBER) RNAs and the Tat-responsive region RNA of HIV-1 to bind to and regulate PKR are reviewed, and the physiological implications of such regulation for the control of viral replication and cell growth are discussed. The potential effects on the activity of PKR of other proteins that bind double-stranded RNA and/or small viral and cellular RNAs are also considered.

Finishing of amalgam restorations: to what degree is it necessary?

This paper attempts to elicit from the literature evidence to guide the clinician in deciding what degree of finishing and polishing is appropriate for amalgam restorations. Much of the justification for the polishing of amalgams has, in the past, been empirically based. Comprehensive scientific investigation into the validity of this practice does, however, present a number of methodological problems which have yet to be successfully overcome. An attempt is made to define what is meant by the term 'polished' (in a clinical context) while the benefits of polishing, as far as they are known, are discussed. The roles that cavity preparation, carving and burnishing play in the finishing of a restoration are reviewed, as is the conflicting evidence regarding their respective advantages and disadvantages. The importance of marginal adaptation, the relationship of polishing to secondary caries, and the dilemma in choosing (in appropriate cases) between the replacement of a restoration or its improvement by polishing are also considered.

Dentinal temperature transients caused by exposure to CO2 laser irradiation and possible pulpal damage.

An investigation is described that attempts to establish, in vitro, the characteristics of heat transference following laser irradiation of bovine dentinal tissue and the relationship with the periodicity of radiation. The results of this study appear to indicate that at depths of overlying dentine of up to 3 mm, laser-induced thermal injury to the pulp is a definite possibility. Fail-safe facilities to prevent build up of heat must be incorporated into the design of dental lasers to allow their beneficial effects to be utilized without the risk of iatrogenic damage.

CO2 laser application to the mineralized dental tissues--the possibility of iatrogenic sequelae.

From the many types of laser that are available commercially, the CO2 laser is presently thought to have the greatest potential for use in dentistry. An outline of the generation of emitted radiation from such a laser is given together with a review of work previously carried out and reported in the literature regarding application to the teeth. The main points of interest are the effects of radiation on the enamel and dentine, but concern is felt towards the possible iatrogenic damage of thermal origin that may occur within the pulp following irradiation of the dental tissues.

The integration of restorations with existent partial dentures.

The relationship between an occlusal rest or clasp arm of a partial denture and the respective supporting tooth is critical and should be exact. Because of the necessity on occasion to remove the natural supportive enamel due to underlying caries, it becomes important that any restoration replacing the enamel should have the same configuration as before if the function of the rest or clasp is to be restored. This intricacy is often casually dealt with in practice. A simple but more exact technique to overcome this problem is described.

Time involvement in journal reading and a suggested facilitation.

In the field of continuing postgraduate education, the reading of professional journals is an accepted method of keeping informed in regard to new developments and contemporary thought on different philosophies of treatment. Not only is such reading realized as being an efficient educational vehicle, but there is now a growing awareness of the actual necessity for any clinician to set aside specific time to the exercise. It is not always readily apparent, however, how great the time commitment can be, even when the reading is limited to selected articles. This paper sets out to indicate in quantitative terms the time that could be expected to be utilized by both general dental practitioners and academic teachers if a thorough and conscientious perusal of the journals were to be undertaken. A practical strategy for facilitating at least part of the problem is put forward in the hope of reaching a helpful compromise.