Suppression of Viral RNA Binding and the Assembly of Infectious Hepatitis C Virus Particles In Vitro by Cyclophilin Inhibitors

Nonstructural protein 5A (NS5A) of hepatitis C virus (HCV) is an indispensable component of the HCV replication and assembly machineries. Although its precise mechanism of action is not yet clear, current evidence indicates that its structure and function are regulated by the cellular peptidylprolyl isomerase cyclophilin A (CyPA). CyPA binds to proline residues in the C-terminal half of NS5A, in a distributed fashion, and modulates the structure of the disordered domains II and III. Cyclophilin inhibitors (CPIs), including cyclosporine (CsA) and its nonimmunosuppressive derivatives, inhibit HCV infection of diverse genotypes, both in vitro and in vivo. Here we report a mechanism by which CPIs inhibit HCV infection and demonstrate that CPIs can suppress HCV assembly in addition to their well-documented inhibitory effect on RNA replication. Although the interaction between NS5A and other viral proteins is not affected by CPIs, RNA binding by NS5A in cell culture-based HCV (HCVcc)-infected cells is significantly inhibited by CPI treatment, and sensitivity of RNA binding is correlated with previously characterized CyPA dependence or CsA sensitivity of HCV mutants. Furthermore, the difference in CyPA dependence between a subgenomic and a full-length replicon of JFH-1 was due, at least in part, to an additional role that CyPA plays in HCV assembly, a conclusion that is supported by experiments with the clinical CPI alisporivir. The host-directed nature and the ability to interfere with more than one step in the HCV life cycle may result in a higher genetic barrier to resistance for this class of HCV inhibitors.     

The discrimination between Rb+ and K+ by Escherichia coli is changed after bacteriophage T7 infection

Rb+ and K+ have similar chemical properties. They share the uptake systems in Escherichia coli and can replace each other inside the cell. These common features led to experiments in which the radioactive isotope 86Rb was used to trace intracellular K+ fluxes. However, the E. coli pumps discriminate between these two ions and one should thus be cautious using 86Rb+ as a tracer for K+. We now report that T7 infection alters the degree of discrimination in such a way that changes of intracellular Rb+ do not reflect changes of K+. It has been observed that shortly after infection the 86Rb+ level was strongly reduced (Ponta, H., Altendorf, K.-H. and Schweiger, M. (1976) Mol. Gen. Genet. 149, 145-150). In contrast, determination of the K+ content showed no change directly after infection (Kuhn, A., Jütte, H. and Kellenberger, E. (1983) J. Virol. 47, 540-552). The efflux of 86Rb was only evident when Rb+ was used in trace amounts. In media conditions under which intracellular K+ was mainly replaced by Rb+, 86Rb+ efflux was not observed.     

The Enucleation of Cells on Plastic Leighton Coverslips

A simple enucleation technique that facilitates autoradiographic and electron microscopic examination of cytoplasms is described. Cells were grown on commercially available plastic Leighton coverslips and these were centrifuged in the presence of cytochalasin B. The centrifugation requires no special holders and only a high speed centrifuge. Enucleation frequencies of greater than 90% were obtained for Chinese hamster fibroblasts and mouse B-82 cells.     

Nitrogenase activity,hydrogen evolution and biomass production in different Casuarina symbioses

Nitrogenase activity, hydrogen evolution, biomass production and nodulation were studied in threeCasuarina species,C. equisetifolia Forst.,C. glauca Sieber ex Spreng andC. obesa Miq., either inoculated with a crushed nodule inoculum prepared fromC. glauca nodules or inoculated with the pure cultureHFP CcI3. Nodulation was also studied inC. cristata Miq. inoculated with the above mentionedFrankia sources. C. equisetifolia, C. glauca andC. obesa were nodulated when inoculated with both of theFrankia inoculum, whileC. cristata was very poorly nodulated. Nitrogenase activity per plant and on a nodule dry weight basis was significantly highest inC. glauca inoculated withC. glauca inoculum after 150 days from planting. This difference decreased and at 217 days from planting there was no significant difference between the symbioses, except forC. obesa inoculated withC. glauca inoculum which showed the significantly lowest nitrogenase activity. After 150 days from planting relative efficiency of nitrogenase was lowest inC. equisetifolia inoculated withHFP CcI3 and inC. equisetifolia inoculated withC. glauca inoculum. Biomass production was similar inC. glauca inoculated withC. glauca inoculum, inC. equisetifolia inoculated withHFP CcI3 and inC. obesa inoculated withHFP CcI3 at the final harvest. The data presented here show that there is a strong interrelationship between host plant and endobiont. This interrelationship is of considerable importance when introducing Casuarina symbioses for production of fuel wood.     

Angiotensin III and IV activation of the brain AT1 receptor subtype in cardiovascular function

The present investigation determined that native angiotensins II and III (ANG II and III) were equipotent as pressor agents when ICV infused in alert rats, whereas native angiotensin IV (ANG IV) was less potent. An analogue of each of these angiotensins was prepared with a hydroxyethylamine (HEA) amide bond replacement at the N-terminus, yielding additional resistance to degradation. These three angiotensin analogues, HEA-ANG II, HEA-ANG III, and HEA-ANG IV, were equivalent with respect to maximum elevation in pressor responses when ICV infused; and each evidenced significantly extended durations of effect compared with their respective native angiotensin. Comparing analogues, HEA-ANG II had a significantly longer effect compared with HEA-ANG III, and HEA-ANG IV, whereas the latter were equivalent. Pretreatment with the AT₁ receptor subtype antagonist, Losartan (DuP753), blocked subsequent pressor responses to each of these analogues, suggesting that these responses were mediated by the AT₁ receptor subtype. Pretreatment with the specific AT₄ receptor subtype antagonist, Divalinal (HED 1291), failed to influence pressor responses induced by the subsequent infusion of these analogues. These results suggest an important role for Ang III, and perhaps ANG IV, in brain angiotensin pressor responses mediated by the AT₁ receptor subtype.     

Mammalian Fbh1 is important to restore normal mitotic progression following decatenation stress

We have addressed the role of the F-box helicase 1 (Fbh1) protein during genome maintenance in mammalian cells. For this, we generated two mouse embryonic stem cell lines deficient for Fbh1: one with a homozygous deletion of the N-terminal F-box domain (Fbh1^f/f), and the other with a homozygous disruption (Fbh1^?/?). Consistent with previous reports of Fbh1-deficiency in vertebrate cells, we found that Fbh1^?/? cells show a moderate increase in Rad51 localization to DNA damage, but no clear defect in chromosome break repair. In contrast, we found that Fbh1^f/f cells show a decrease in Rad51 localization to DNA damage and increased cytoplasmic localization of Rad51. However, these Fbh1^f/f cells show no clear defects in chromosome break repair. Since some Rad51 partners and F-box-associated proteins (Skp1-Cul1) have been implicated in progression through mitosis, we considered whether Fbh1 might play a role in this process. To test this hypothesis, we disrupted mitosis using catalytic topoisomerase II inhibitors (bisdioxopiperazines), which inhibit chromosome decatenation. We found that both Fbh1^f/f and Fbh1^?/? cells show hypersensitivity to topoisomerase II catalytic inhibitors, even though the degree of decatenation stress was not affected. Furthermore, following topoisomerase II catalytic inhibition, both Fbh1-deficient cell lines show substantial defects in anaphase separation of chromosomes. These results indicate that Fbh1 is important for restoration of normal mitotic progression following decatenation stress.     

Subcellular localization of acetyl-CoA synthetase in leaf protoplasts of Spinacia oleracea

The localization of acetyl-CoA synthetase in the spinach leaf cell was examined. When the different compartments of lysed spinach protoplasts were assayed for marker enzymes and acetyl-CoA synthetase, it was determined that the synthetase was totally localized in the chloroplast compartment. Analysis of spinach leaf for free acetate revealed that this acid was present at a 1 mm level in the leaf cell. It is suggested that free acetate probably derived from a number of sources in the cell diffuses into the chloroplast stroma compartment where it is converted to acetyl-CoA and thence employed for biosynthetic reactions. Thus, free acetate is metabolically inert in the leaf cell until it is transported to the only compartment that contains acetyl-CoA synthetase, namely the chloroplast.