The stability of rabbit reticulocyte polysomes at high hydrostatic pressure

High hydrostatic pressure inhibits the biosynthesis of eukaryotic elongation factor-2

High continuous hydrostatic pressure is known to inhibit the total cellular protein synthesis. In this study, our goal was to identify pressure-regulated proteins by using two dimensional gel electrophoresis and mass spectrometry. This analysis showed that under 30 MPa continuous hydrostatic pressure the biosynthesis of eukaryotic elongation factor-2 (eEF-2) was inhibited both in HeLa carcinoma and T/C28a4 chondrocytic cell lines. Western blot analysis of HeLa cells revealed that the cellular protein level of eEF-2 decreased by 40%-50% within 12 h of the pressure treatment. However, the steady-state mRNA level of eEF-2 was not affected by the pressure. Cycloheximide addition after 4 h-pressure treatment suggested that the half-life of eEF-2 protein was shorter in pressurized cells. eEF-2 is responsible for the translocation of ribosome along the specific mRNA during translation, and its phosphorylation prevents the ribosomal translocation. Therefore, increased phosphorylation of eEF-2 was considered as one mechanism that could explain the reduced level of protein synthesis in pressurized HeLa cell cultures. However, Western blot analysis with an antibody recognizing the Thr56-phosphorylated form of eEF-2 showed that phosphorylation of eEF-2 was not elevated in pressurized samples. In conclusion, the inhibition of protein synthesis under high pressure occurs independent of the phosphorylation of eEF-2. However, this inhibition may result from the decrease of cellular eEF-2 protein.

Effects of isolation and high helium pressure on the nucleolus of sympathetic neurons in the rat superior cervical ganglion

In prokaryotes, unicellular eukaryotes and cell-free systems, pressure is known to exert an inhibitory effect on protein synthesis and RNA metabolism, the mechanism(s) of which remain to be investigated in detail. The purpose of the present in vitro study was to compare ultrastructural and quantitative changes of the nucleolus, which is the site of ribosome biogenesis, in sympathetic neurons of rat superior cervical ganglia (SCG) maintained for 2, 3 and 5 h in NCTC 109 medium and subjected to pressure or not. In control SCG (left) the nucleolus greatly increased in volume (+ 33%) 2 h after excision, in comparison with SCG fixed immediately. This overall enlargement was found to reflect a marked increase in all nucleolar components (from 16 to 87%). After 5 h, volumes of nucleolus, fibrillar centers and vacuolar component returned to control values, whereas dense fibrillar and granular components remained affected. Such early and transient changes are regarded as reflecting basic metabolic changes associated with increased nucleolar RNA that should be of primary concern to experiments using SCG transplanted in culture media. Compression under helium up to 180 atmospheric pressure for 1 h of right SCG maintained for 2 h in culture medium, was shown to induce, on the contrary, a marked decrease in nucleolar volume (-39%) and in volumes of all nucleolar components (from -36 to -51%). When they were kept at constant high pressure for 1 and 3 h a progressive recovery of volumes of nucleoli and nucleolar components was observed. Consequently, compression was shown to exert opposite effects to those of isolation of SCG. Present data are interpreted as an inhibitory effect of pressure on ribosome biogenesis. Such observations on a vertebrate neuron might open a new field in the search for cellular mechanisms underlying the effects of pressure on living organisms and especially on the nervous system.