Search PubMed⌕ Search

Biomedical subjects

L Carrasco

Publications and source records attributed to L Carrasco.

At least 271 records · Page 15Linked to original sources
PubMed1981

Reversion by hypotonic medium of the shutoff of protein synthesis induced by encephalomyocarditis virus.

Infection of human HeLa cells by picornaviruses produces a drastic inhibition of host protein synthesis. Treatment of encephalomyocarditis virus-infected HeLa cells with hypotonic medium reversed this inhibition; no viral protein synthesis was detected. The blockade of viral translation by hypotonic conditions was observed for a wide range of multiplicities of infection. However, only with low virus-to-cell ratios did cellular protein synthesis resume. The ratio of cellular to viral mRNA translation was strongly influenced by the concentration of monovalent ions present in the culture medium: a high concentration of NaCl or KCl favored the translation of viral mRNA and strongly inhibited cellular protein synthesis, whereas the opposite was true when NaCl was omitted from the culture medium. Once viral protein synthesis had been blocked by hypotonic medium treatment, it resumed when the infected cells were placed in a normal or hypertonic medium, indicating that the viral components synthesized in the infected cells were not destroyed by this treatment. These observations reinforced the idea that ions play a role in discriminating between viral and cellular mRNA translation in virus-infected animal cells.

Culture Media↗
PubMed1981

Reversal by hypotonic medium of the antiviral state induced by lymphoblastoid interferon in human HeLa cells.

The induction kinetics of the antiviral state in HeLa cells treated with human lymphoblastoid interferon (IFN) was studied. In cells treated with 4-200 U/ml IFN, the antiviral state was fully established in 7-9 h. Inhibition of virus multiplication was more rapid if the concentration of IFN was increased to 1,000 U/ml. This antiviral state gradually disappeared during the 48 h after IFN removal. Several compounds known to act on the cell membrane or on the cytoskeleton were tested for their influence on the establishment and reversal of the antiviral state. None of them were found to influence these two parameters to a significant extent. In contrast, placing HeLa cells in medium lacking NaCl partially reversed the blockade to virus multiplication induced by IFN treatment. Cells treated with IFN and later placed in hypotonic medium synthesized virus proteins after encephalomyocarditis virus infection, although at a reduced level compared to cells that had not been treated with IFN.

Alkaloids↗
PubMed1980

Antibiotics that specifically block translation in virus-infected cells.

Several antibiotics including anthelmycin, blasticidin S, destomycin A, gougerotin, hygromycin B and edeine complex, known to powerfully block translation in cell-free systems, did neither inhibit protein synthesis in intact mouse L and 3T6 cells, nor in hamster BHK 21 cells, due to failure to cross the cell plasma membrane. However, after viral infection, these antibiotics exhibited a marked blockade of translation, that is related to the permeability changes induced by viral infection. The inhibition of protein synthesis by hygromycin B in virus-infected cells was studied over the time course of infection, both in encephalomyocarditis virus-infected mouse L cells and in Semliki forest virus-infected hamster BHK cells. We have observed that the entry of hygromycin B into virus-infected cells parallels the inhibition of cellular protein synthesis, i.e., the cells became permeable to this antibiotic at the time the shut-off of host translation occurred. A marked inhibition of picornavirus RNA synthesis by hygromycin B was also noticed, likely as a consequence of the inhibition of the viral replicase synthesis. Finally, a reduction in the virus yield by treatment of virus-infected cells with several antibiotics is also described. All these observations are considered in the context of the interference of viral infection with cellular functions and the potential use of inhibitors non-permeable to normal cells as antiviral agents.

Aminoglycosides↗
PubMed1979

Compounds affecting membranes that inhibit protein synthesis in yeast.

The regulation of translation has been investigated in yeast cells by means of ionophores and other compounds affecting the ionic concentration inside the cell. Treatment of a variety of cells with these compounds produces a drastic inhibition in the protein-synthesizing activity of the cell. Protein synthesis in yeast is strongly inhibited by amphotericin B and nystatin. Mammalian cells are blocked in their translation capacity by gramicidin D, nigericin, monensin, nystatin, A23187, and bromolasalocid. The effects of these compounds on protein synthesis in Escherichia coli and Staphylococcus aureus were also investigated. Amphotericin B is a powerful inhibitor of both protein and ribonucleic acid syntheses in yeast cells at concentrations that do not affect the transport of the labeled amino acid or nucleoside precursor. The analysis of the polysomal profiles in yeast spheroplasts could indicate that initiation is the target of amphotericin B action on translation. Studies on the reversion of the protein synthesis blockade by amphotericin B by increasing the potassium concentration in the medium suggest that changes in the potassium concentration in cellular cytoplasm might be responsible, at least in part, for the inhibition of protein synthesis.

Amphotericin B↗
PubMed1979

Selective inhibition of protein synthesis in virus-infected mammalian cells.

A number of translation inhibitors were tested for their effects on both control and encephalomyocarditis virus-infected mouse 3T6 cells. The virus-infected cells were specifically inhibited by gougerotin, edeine, and blasticidin S, whereas these drugs failed to penetrate into uninfected cells. Inhibition of infected cells by gougerotin became apparent when the synthesis of viral proteins commenced, suggesting that the latter process is accompanied by a permeability change in the cells that allows uptake of the drug. This permeability change was not observed in cells treated with cycloheximide soon after viral infection, although treatment with actinomycin D did not prevent inhibition of gougerotin. It is possible, therefore, that a specific viral protein is involved in the permeability change of the plasma membrane. Moreover, gougerotin was unable to inhibit protein synthesis in the presence of zinc ions, thus preventing gougerotin from entering into the infected cell. Membrane leakiness was not restricted to the encephalomyocarditis virus-3T6 system; it was also observed in mengovirus-infected 3T6 cells, Semliki Forest virus-infected BHK cells, and simian virus 40-infected CVI1 cells at the time in which the synthesis of late proteins is maximal.

Anti-Bacterial Agents↗
PubMed1978

Inhibition, by selected antibiotics, of protein synthesis in cells growing in tissue cultures.

A large number of compounds including actinobolin, adrenochrome, amicetin, anisomycin, aurintricarboxylic acid, blasticidin S, chartreusin, chlortetracycline, cycloheximide, doxycycline, edeine A1, edeine complex, emetine, fusidic acid, gougerotin, GppCH2p, oxytetracycline, pactamycin, polydextran sulphate, puromycin, pyrocatechol violet, sparsomycin and tubulosine have been tested for inhibitory effects on protein synthesis in cultured cells from both mouse fibroblasts (3T6 cells) and chick embryo fibroblasts (CEF). Essentially, similar results were obtained with both cell types with the most effective inhibitors being pactamycin, emetine, tubulosine, anisomycin and cycloheximide and with no significant inhibitory activity being detected with edeine complex, edeine A1, GppCH2p, polydextran sulphate, aurintricarboxylic acid, pyrocatechol violet and adrenochrome. The concentration of pactamycin required to produce 50% inhibition of protein synthesis approximated 5 X 10(-9) M, but for most of the inhibitors it ranged from 5 X 10(-6) M to 5 X 10(4) M. The molecular basis underlying these differences may be related, in addition to their intrinsic inhibitory power, to differences in permeability of the cells towards the various drugs tested. Alternatively, active accumulation of the drugs by the cells may be the variable parameter.

Animals↗
PubMed1976

Site of action of ricin on the ribosome.

The extent of the inhibitory effect of ricin in polyphenylalanine synthesis by eukaryotic ribosomes is strongly dependent upon the concentration of ribosomes and the elongation factors EF 1 and EF2. Maximal inhibition by ricin, in this assay is observed when either ribosomes or the two elongation factors are added under limiting conditions, whereas ricin-treated ribosomes support protein synthesis at saturating concentrations of elongation factors and ribosomes. Similarly, the enzymatic binding of Phe-tRNA to ribosomes is drastically blocked in ricin-treated ribosomes when low EF 1 concentrations are added to the reaction mixture, but there is no inhibition when EF 1 is at saturating concentrations. Furthermore, formation of the complex EF 2-guanosine triphosphate-ribosome, using free ribosomes pretreated with ricin, is strongly inhibited at limiting concentrations of EF2, but is not affected at saturating concentrations of this factor. However, ricin does not inhibit the EF 2-dependent translocation of peptidyl-tRNA by polysomes, although the toxin is very active in preventing amino acid incorporation by polysomes. Our results suggest that the damaging effect of ricin on the ribosome causes a decreased affinity for both elongation factors EF 1 and EF 2. Thus, the toxin inhibits the enzymatic binding of aminoacyl-tRNA to ribosomes. The lack of inhibition of translocation by ricin suggests that the toxin cannot interact with ribosomes with substrate bound to the acceptor site. Essentially similar results are observed with ricin, abrin, ricin A chain, abrin A chain, and ricinus agglutinin A chain. A possible effect of the toxins on initiation and/or termination is further discussed.

Abrin↗
PubMed1976

Initiation of the polypeptide chain by reticulocyte cell-free systems. Survey of different inhibitors of translation.

In order to elucidate the mechanism of action of inhibitors that block the initiation of protein synthesis in mammalian systems, we have studied the following steps: (a) formation of the ternary complex Met-tRNAr-IF-E2-GTP, (b) binding of the initiator Met-tRNAf to the 40-S ribosomal subunit in the presence of initiation factors and dependent or not on the addition of mRNA, (c) formation of the initiation complex with 80-S ribosomes and (d) formation of the first peptide bond. Adrenochrome, aurintricarboxylic acid, polydextran sulphate, pyrochatechol violet and showdomycin block the formation of the ternary complex Met-tRNAf-IF-E2-GTP. Edeine A1, aurintricarboxylic acid and polydextran sulphate block the binding of the mRNA to the 40-S ribosomal subunit. Pactamycin induces the formation of stable smaller initiation complexes which are unable to go through the subsequent steps of initiation. Stimulation of the binding of the initiator Met-tRNAf to the 80-S ribosome in the presence of initiation factors is observed with sparsomycin and antibiotics of the sesquiterpene family (verrucarin A, trichodermin and trichothecin). However, these antibiotics block the reaction of the bound Met-tRNAf with puromycin. Narciclasine has no effect on the binding of the initiator to the ribosome but strongly blocks its reaction with puromycin. We have developed a simple technique to detect the Met-tRNAf-40-S-subunit-poly(A, G, U) initiation complexes by chromatography on Sepharose 6B columns. The requirements for the formation of such complexes measured by this technique and its comparison with the sucrose gradient centrifugation method are described.

Animals↗