PubMed Health⌕ Search

Biomedical subjects

H O Voorma

Publications and source records attributed to H O Voorma.

At least 55 records · Page 3Linked to original sources
PubMed1987

Inhibition of measles virus-induced cell-cell fusion with a monoclonal antibody directed against the haemagglutinin.

A neutralizing monoclonal antibody (C26-15) against the haemagglutinin (H protein) of measles virus was generated which caused cell-cell fusion inhibition in cultures of measles virus-infected cells. It was shown that this phenomenon coincided with a down-regulation of the expression of both the H protein and the fusion (F) protein. We also showed cell-cell fusion inhibition with a polyclonal rabbit serum directed against Tween-ether inactivated measles virus, which did not contain biologically active antibodies against the F protein. Cell-cell fusion inhibition caused by anti-H antibodies is distinct from cell-cell fusion inhibition induced by a direct interaction of anti-F antibody with the F protein in the membrane of infected cells. Since both mechanisms may also be involved in the in vivo situation, the exclusive role for the generation of anti-F antibody to prevent virus spread by cell-cell fusion in vivo is questioned. It is speculated that the observed down-regulation of both glycoproteins may lead to a less efficient killing of infected cells by cytotoxic T-lymphocytes, which may constitute an alternative explanation for the insufficient protection after vaccination with an inactivated measles vaccine.

Amino Acid Oxidoreductases↗
PubMed1986

Additional methylation at the N(2)-position of the cap of 26S Semliki Forest virus late mRNA and initiation of translation.

Cap analysis of the late 26S Semliki Forest viral mRNA reveals that almost 30% of the caps possess both a methyl group at the N(7)-position and one at the N(2)-position. We have compared the degree of methylation of the caps of polysomal and non-polysomal 26S mRNA in order to check whether this feature is responsible for its translation late in infection. It was found that extra methyl groups on the caps cause a lower rate of initiation. Polysomal 26S mRNA contained less m2,7G- and m2,2,7G-caps than free 26S. The cap analog m2,2,7Gp was slightly less inhibitory than m7Gp in an in vitro translation system.

Methylation↗
PubMed1985

Regulation of protein synthesis in eukaryotes. Eukaryotic initiation factor eIF-2 and eukaryotic recycling factor eRF from neuroblastoma cells.

eIF-2 purified from neuroblastoma cells consists of three subunits, which appear to be of molecular weight identical to those of the subunits of rabbit reticulocyte eIF-2. A protein fraction has been isolated from neuroblastoma cells with characteristics similar to eRF from reticulocytes: stimulation of amino acid incorporation in a hemin-deprived reticulocyte lysate, the removal of GDP from eIF-2-GDP complexes, a 4-5-fold stimulatory effect in a two-step reaction measuring 40 S preinitiation complex formation and a 3-3.5-fold stimulation in the methionyl-puromycin synthesis. In the methionyl-puromycin-synthesizing system phosphorylated eIF-2 is not responsive to the addition of this fraction from neuroblastoma cells. The protein fraction contains eRF which seems to be similar to the eRF isolated from Ehrlich ascites tumor cells and somewhat distinct from the reticulocyte factor. Incubation of neuroblastoma cell lysate in the presence of [gamma-32P]ATP results in the phosphorylation of a protein of Mr 36 000, migrating on SDS-polyacrylamide gels to the position of eIF-2 alpha. This protein is also phosphorylated in vitro by HRI from reticulocytes. These results may reflect a common underlying principle for the quantitative regulation of protein synthesis in eukaryotic cells.

Animals↗
PubMed1985

The effect of serum deprivation on the initiation of protein synthesis in mouse neuroblastoma cells.

Growth of mouse neuroblastoma cells becomes stationary when cultured in serum-free medium. Within 60 h, the protein-synthesizing capacity of the cells declines to 25% as compared to that of exponentially growing cells. The transitional activity of the crude ribosomal salt washes from serum-deprived and control cells was compared in in vitro protein-synthesizing pH 5 systems. It appears that the ribosomal salt wash from serum-deprived cells has significantly (70%) lost its ability to support the translation of neuroblastoma poly(A)+ RNA. This activity of the ribosomal wash from serum-deprived cells can be restored to control level with rabbit reticulocyte initiation factor eIF-4B only. The ability of the ribosomal wash from serum-deprived cells to support the translation of encephalomyocarditis virus (EMC) and Semliki Forest virus (SFV) 42 S mRNA was tested. We found that EMC-mRNA is efficiently translated with the ribosomal salt wash from serum-deprived cells, whereas on the other hand the translation of SFV 42 S mRNA is severely impaired. Therefore, we conclude that in serum-deprived neuroblastoma cells protein synthesis is regulated in both a quantitative and a qualitative way. Modulation of the activity of initiation factor of protein synthesis eIF-4B is at least partly responsible for the observed (selective) blockade of protein synthesis in serum-deprived cells.

Animals↗
PubMed1984

Regulation of protein synthesis in eukaryotes. Mode of action of eRF, an eIF-2-recycling factor from rabbit reticulocytes involved in GDP/GTP exchange.

The rate of initiation of protein synthesis appears to be controlled at the level of recycling of eIF-2. In this process a new factor, designated eRF, plays an important role. The factor has been purified from the post-ribosomal supernatant and has been called formerly anti-HRI and anti-inhibitor [Amesz, H., Goumans, H., Haubrich-Morree, Th., Voorma, H.O., and Benne, R. (1979) Eur. J. Biochem. 98, 513-520]. Its effect on the initiation of protein synthesis has been studied in several assays: a small but distinct effect is found in the assay for the formation of a ternary complex between eIF-2, GTP and Met-tRNA; a 4-5-fold stimulation is obtained in assays for 40S preinitiation complex formation and in the methionyl-puromycin reaction. In the latter assay a catalytic use of eIF-2 occurs provided that eRF is present. eRF forms a complex with eIF-2 which results in a decrease of the affinity of eIF-2 for GDP, giving it the properties of a GDP/GTP exchange factor. The model stresses the catalytic use of eIF-2 in initiation provided that conditions are met for GDP/GTP exchange by a transient complex formation between eIF-2 and eRF. On the other hand, it is shown that phosphorylation of eIF-2 by the hemin-regulated inhibitor (HRI) abolishes the recycling of eIF-2, by the formation of another stable complex comprising eIF-2 alpha P, GDP and eRF.

Animals↗
PubMed1984

Ultraviolet-crosslinking reveals specific affinity of eukaryotic initiation factors for Semliki Forest virus mRNA.

Eukaryotic initiation factors (eIF) associate readily with 32P-labeled Semliki Forest virus (SFV) mRNA in vitro, forming complexes which can be crosslinked by 254 nm ultraviolet irradiation. After ribonuclease digestion, the initiation factors were released and analysed by gel electrophoresis. Autoradiography revealed proteins by virtue of crosslinked 32P-labeled mRNA fragments. eIF-4A, -4B and -4C as well as three subunits of eIF-3 could be crosslinked with SFV mRNA. None of these proteins bound to ribosomal RNAs.

Cross-Linking Reagents↗
PubMed1984

Infection of neuroblastoma cells by Semliki Forest virus. The interference of viral capsid protein with the binding of host messenger RNAs into initiation complexes is the cause of the shut-off of host protein synthesis.

From ribosomal washes of neuroblastoma cells infected with Semliki Forest virus (SFV) a protein of Mr 33000 was purified, which comigrated with the viral capsid protein on sodium dodecyl sulfate/polyacrylamide gels and was recognized by antibodies against the capsid protein of SFV. This protein selectively inhibits the translation of host and early viral 42S mRNA in vitro, but has no effect on late viral 26S and encephalomyocarditis virus mRNA translation. Eukaryotic initiation factor 4B and cap-binding protein restore the translation of host and 42S mRNA to control levels. The capsid protein specifically prevents the binding of host mRNA into 80S initiation complexes, but has no effect on that of late viral mRNA. We propose that the capsid protein is the component responsible for the shut-off of host protein synthesis in SFV-infected cells and for the decreased translational activity of the crude ribosomal washes from these cells.

Animals↗
PubMed1983

Relationship between synthesis and cleavage of poliovirus-specific proteins.

Poliovirus proteinase was studied in vitro in lysates from poliovirus-infected HeLa cells. Preincubation of these lysates caused (i) a reduction in poliovirus proteinase activity and (ii) a partial dependence on exogenous mRNA for optimal translation. Proteins translated from endogenous poliovirus RNA in preincubated extracts from virus-infected HeLa cells are poorly cleaved. This cleavage deficiency is alleviated by adding fresh poliovirus RNA to the translation system, thus, allowing re-initiation to occur. This suggests that the poliovirus proteinase is highly unstable.

Endopeptidases↗
PubMed1983

Regulatory steps in the initiation of protein synthesis.

Regulation of protein synthesis is being exerted at different levels with a different extent of attenuation. The major control module seems to work by the inactivation of the elF-2 recycling which enables the cell to shift down from a high rate of initiation to a low rate. Certain events in the cell cycle like mitosis do show such a drastic change in initiation rate. It is suggested that modifications of elF-2 by phosphorylation of the alpha-subunit by different protein-kinases is the basis for such a control mechanism. Already two protein kinases of this type have been described, the hemin-regulated inhibitor and the ds-RNA activated inhibitor from interferon-treated cells. On the other hand modifications of the beta-subunit by other metabolic events, for instance low NADH/NAD+ ratio, can as yet not be excluded. Other conditions like amino acid starvation, serum deprivation, heat-shock and virus-infection seem to evoke quite different strategies. In some cases it has been demonstrated that inactivation of mRNA binding factors as elF-4B and elF-4E, favour the translation of low-dependence, i.e. low secondary structure, messengers. It shall be worthwhile to establish whether the mRNA's with such low degree of secondary structure encoded proteins that are aimed at the survival of the cell under extreme metabolic or stress conditions. Much more work on the structure and nucleotide sequences of the leader sequence is needed to prove these hypothetical points.

Kinetics↗
PubMed1982

Positive and negative cAMP-mediated control of tyrosine aminotransferase synthesis in Reuber H35 hepatoma cells.

Induction of L-tyrosine:2-oxoglutarate aminotransferase (EC 2.6.1.5) by N6,O2'-dibutyryl-adenosine 3',5'-monophosphate (Bt2cAMP) in Reuber H35 hepatoma cells reaches a maximum value between 3-5 h after addition of Bt2cAMP and subsequently decreases in the continuous presence of Bt2cAMP. We have investigated the kinetics of the increase, i.e. induction, and the decrease, i.e. the repressed state, of the tyrosine-aminotransferase-synthesizing system under these conditions. Our experimental results are as follows. 1. The repressed state of the tyrosine-aminotransferase-synthesizing system is not caused by a decrease in the intracellular cAMP concentration. 2. The repressed state is inhibited by actinomycin D (while induction is not inhibited). 3. During the repressed state no effect of dexamethasone on tyrosine aminotransferase synthesis is found, while during induction Bt2cAMP and dexamethasone act synergistically. 4. Longer starvation of the cells in serum-free medium has no influence on the kinetics of the induction/repressed state curve. From these results we have concluded that the mechanism of the transition to the repressed state of the tyrosine-aminotransferase-synthesizing system is essentially different from the mechanism of deinduction which occurs after removal of the inducer. Moreover, the repressed state of the system is a phenomenon which is induced by Bt2cAMP separately from induction at a different level of protein synthesis.

Animals↗
PubMed1981

The protein synthetic activity in vitro of ribosomes differing in the extent of phosphorylation of their ribosomal proteins.

We describe a re-examination of the cell-free protein synthetic activity of eukaryotic ribosomes having proteins phosphorylated to different extents. Ribosomal 40 S subunits were isolated both from a variety of cells in which there is relatively little phosphorylation of ribosomal protein S6, and from cells subjected in vivo to different stimuli that promote the extensive phosphorylation of protein S6. The ability of these subunits to bind Met-tRNA as well as the second amino acyl-tRNA (Val-tRNA) was compared in the presence of highly purified initiation factors, elongation factor EF-1 at various concentrations of 60S subunits, 9 S globin mRNA and potassium ions. The ability of the subunits to synthesize polyphenylalanine was also studied using highly purified elongation factors. In no case was any significant difference in activity observed between ribosomes with protein S6 phosphorylated to different extents. Similar, though less extensive, studies were preformed comparing 60 S ribosomal subunits differing in the extent of phosphorylation of the acidic phosphoprotein, L gamma , and of L14. No difference in activity was observed between these ribosomes.

Animals↗
PubMed1981

Further evidence for translational regulation of tyrosine aminotransferase synthesis by dibutyryl cyclic AMP in Reuber H35 hepatoma cells.

Cyclic AMP derivatives increase the rate of synthesis of tyrosine aminotransferase in Reuber H35 hepatoma cells. Various studies lend support to the hypothesis that cyclic AMP increases the synthesis of tyrosine aminotransferase by acting at a posttranscriptional site. The presence of a limited non-translatable pool of tyrosine aminotransferase mRNA prior to the formation of the translatable tyrosine aminotransferase mRNA implicates a possible site of action of cyclic AMP. We compared the capacity of N6,O2'-dibutyryl cyclic AMP to induce tyrosine aminotransferase synthesis when untranslatable tyrosine aminotransferase mRNA sequences are present or absent. The transition of a condition in which non-translatable tyrosine aminotransferase mRNA sequences were present to a condition in which they were absent was established by preinduction of Reuber H35 cells with dexamethasone, followed by addition of actinomycin D. In the time period thereafter, the amount of non-translatable mRNA decreased and 1.5-2 h after addition of actinomycin D, only translatable tyrosine aminotransferase mRNA was present. It can be seen that the induction of tyrosine aminotransferase synthesis by dibutyryl cyclic AMP follows the normal decrease of tyrosine aminotransferase mRNA. We present evidence that dibutyryl cyclic AMP in Reuber H35 hepatoma cells regulates tyrosine aminotransferase synthesis at a posttranscriptional site independent of the pool of non-translatable tyrosine aminotransferase mRNA sequences, but influencing the efficiency of translation of active tyrosine aminotransferase mRNA.

Animals↗
PubMed1981

Studies on the posttranscriptional site of cAMP action in the regulation of the synthesis of tyrosine aminotransferase.

Synthesis of L-tyrosine:2-oxoglutarate aminotransferase (EC 2.6.1.5) can be induced by N6,O2'-dibutyryl-adenosine 3',5'-monophosphate (Bt2cAMP) in Reuber H35 cell cultures. Actinomycin D fails to block this induction which indicates a target for Bt2cAMP at a posttranscriptional level. We have determined the influence of Bt2cAMP on several translational events during the tyrosine aminotransferase synthesis with the following results. (1) The number of nascent tyrosine aminotransferase chains increased, whereas no effect was measured on the number of nascent total protein chains. (2) The rate of elongation along the tyrosine aminotransferase mRNA and total mRNA is not enhanced by Bt2cAMP. (3) The induced synthesis of tyrosine aminotransferase is more sensitive to the inhibition of elongation. We conclude from our results that Bt2cAMP induces the synthesis of tyrosine aminotransferase by an increase in the rate of initiation on the tyrosine aminotransferase mRNA.

Animals↗