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1.
The effect of selenium-containing compounds on RNA synthesis in rat liver cells was studied in vivo. All the selenium derivatives under study inhibited the rRNA synthesis in liver cells. The most potent inhibiting effect was exerted by sodium selenite. It was shown that in a cell-free system of RNA biosynthesis sodium selenite selectively inhibited the activity of RNA-polymerase I in isolated nuclei and purified enzyme preparations of normal and tumour cells. A feasible mechanism of inhibition of the RNA-polymerase I activity by selenium and a hypothesis on the anticarcinogenic effect of selenium are postulated.  相似文献   

2.
Selenosis in animals is characterized by a variety of neurological abnormalities, but the chemical species of selenium and the molecular targets that mediate this neurotoxicity are unknown. We have previously shown that selenite is a potent inhibitor of squalene monooxygenase, the second enzyme in the committed pathway for cholesterol biosynthesis; inhibition of this enzyme by dimethyltellurium leads to a peripheral demyelinating neuropathy similar to that seen in selenosis. To evaluate the role methylation plays in selenium toxicity, we examined the ability of three methylselenium compounds, methylselenol, dimethylselenide, and trimethylselenonium iodide, to inhibit purified recombinant human squalene monooxygenase. IC(50) values for methylselenol (95 microM) and dimethylselenide (680 microM) were greater than that previously obtained for selenite (37 microM), and inhibition by trimethylselenonium iodide was evident only at concentrations above 3 mM. Inhibition by methylselenol as well as by selenite was slow and irreversible, suggestive of covalent binding to the enzyme, and thiol-containing compounds could prevent and reverse this inhibition, indicating that these compounds were reacting with sulfhydryl groups on the protein. Monothiols such as glutathione and beta-mercaptoethanol provided better protection than did dithiols, suggesting that these selenium compounds bind to only one of the two proposed vicinal cysteines on squalene monooxygenase. Unexpectedly, the inhibition by selenite was significantly enhanced by dithiols, indicating that a more toxic species, possibly selenide, was formed in the presence of these dithiol reductants.  相似文献   

3.
The effect of cell density on the sensitivity of tumor celles to selenite has been examined. The inhibitory effect of selenite on cellular DNA and RNA synthesis was significantly greater in higher density cultures of HeLa cells and A2780 ovarian tumor cells. High-density cells were also more sensitive to the inhibitory effect of selenite on cell attachment. This difference could not be accounted for by a higher intracellular level of glutathione, since there was no significant difference between the cells at high or low density. The high-density cells were found to take up more selenium per cell during the exposure period; the resulting higher level of intracellular Se could explain their greater sensitivity to selenite. This hypothesis is supported by the observation that DNA synthesis in nuclei isolated from high-density cells did not exhibit higher sensitivity to inhibition by selenite than synthesis in nuclei isolated from low-density cells.  相似文献   

4.
5.
6.
DNA methylase from rat liver was partially purified through a DEAE sephacel column and characterized in an in vitro assay with respect to time, protein, DNA and S-adenosylmethionine curves. The Km for S-adenosylmethionine was 2.5 microM. Sodium selenium inhibited the methylation of DNA in a dose dependent fashion when added to the assay. It was also demonstrated that selenite non-competitively inhibits rat-liver DNA methylase with a Ki of 6.7 microM. Dithiothreitol had no effect on selenite inhibition and increasing amounts of DNA did not alter the inhibition. However, increasing amounts of protein overcame the inhibition, suggesting that selenite is reacting with the DNA methylase protein. DNA methylase isolated from selenite treated animals had only 43% of the activity as enzyme from control rats. It appears that selenite is a good inhibitor of DNA methylase.  相似文献   

7.
ABSTRACT. [35S]methionine incorporation into proteins of either T. cruzi epimastigotes or trypomastigotes was drastically inhibited by low concentrations of crystal violet in a dose-dependent manner. This inhibition was not due to ATP depletion since cellular ATP levels did not change significantly after incubation of epimastigotes with 50 μM crystal violet for similar periods of time, and was unaffected by changes in the extracellular free calcium concentration. Although crystal violet was able to inhibit protein synthesis in a cell-free system from T. cruzi epimastigotes, half maximal inhibition was at 1 mM, a concentration three orders of magnitude higher than those that inhibited protein synthesis in intact cells. On the other hand, crystal violet was able to inhibit total [35S]methionine uptake at similar concentrations to those that inhibited protein synthesis while addition of increasing concentrations of cold methionine to the incubation medium protected the cells against crystal violet inhibition. Crystal violet also inhibited total [3H]proline uptake thus indicating that it has a general inhibitory effect upon the transport of amino acids, and not specifically upon methionine. These results indicate that inhibition of protein synthesis by crystal violet is probably due to inhibition of amino acid uptake.  相似文献   

8.
Previously it was reported that the herbicide propachlor (alpha-chloro-N-isopropyl-acetanilide) has a strong inhibitory effect on the proliferation of L1210 mouse leukemia cells. It is now demonstrated that propachlor treatment causes L1210 cells to accumulate in the G1 phase as determined by flow cytometric analysis. This effect of propachlor is dose-dependent with more than 90% of G1 cells accumulating at 10 microM. Kinetic experiments demonstrated that the accumulation of cells in G1 starts in about 10 hours, and increased for up to about 44 hours of incubation with 10 microM propachlor. Treated cells can be revised to a normal DNA distribution by removing propachlor.  相似文献   

9.
Several recent publications indicate that Ca2+ is required for protein synthesis in mammalian cells, including the Ehrlich ascites tumor cell. The present communication examines whether the effects of Ca2+ might be mediated through calmodulin or a related protein. Four calmodulin antagonists belonging to different chemical categories were used to provide evidence of calmodulin involvement. Three of the antagonists inhibited protein synthesis in intact cells; 50% inhibitory concentrations were 10 microM calmidazolium, 12 microM N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W7) and 17.5 microM trifluoperazine (TFP). Initiation was preferentially inhibited as indicated by an increase in the 80S monomers accompanied by a significant disaggregation of polyribosomes. All the antagonists also inhibited protein synthesis initiation in the cell-free protein-synthesizing system; 50% inhibitory concentrations for compound 48/80, calmidazolium, TFP, and W7 were 10 microM, 125 microM, 300 microM and 500 microM, respectively. A weak analogue of W7 inhibited only 20% at 1000 microM. Inhibition in the cell-free system was reversed by the addition of exogenous calmodulin in all four cases. The levels of 43S complexes were significantly elevated with all four antagonists, indicating a block in the utilization of 43S complexes. The similarity of the effects of four distinct classes of antagonists and their ready reversal by exogenous calmodulin leads us to suggest that there may be a role for calmodulin or a very similar calcium-binding protein in protein synthesis.  相似文献   

10.
Previous studies have demonstrated that copper (15.7 micromol/L) can inhibit selenite (12.6 micromol/L)-induced cytotoxicity and apoptosis in HT-29 cells. However, the exact nature of the interactions between selenium and copper is not fully understood. In this study, the effect of copper on the cell cycle arrest induced by selenite or selenocystine was examined. Both selenite and selenocystine were effective in inhibition of cell growth and cell cycle progression. Cell cycle analysis revealed that selenite (3-5 micromol/L) caused a decrease in G1 phase cells that corresponded with an increase in S and G2 phase cells, and that 0.625 or 1.25 micromol/L copper sufficiently inhibited selenite-induced cell cycle arrest. In contrast, selenocystine caused an increase in G1 phase cells that corresponded with a decrease in S and G2 phase cells. Interestingly, 0.625 or 1.25 micromol/L copper did not inhibit selenocystine-induced cell cycle arrest. In addition, cell free gel shift assay demonstrated that selenite suppressed the inhibitory effect of copper on SP-1 DNA binding. Furthermore, although 5 micromol/L selenite in culture media significantly increased the intracellular selenium content, 1.25 micromol/L copper sulfate blocked this increase of the intracellular selenium content. Collectively, these data demonstrate that selenite and selenocystine cause cell cycle arrest via distinct mechanisms, and suggest that copper may interact with selenite extracellularly, which represents the basis of antagonism between copper sulfate and selenite.  相似文献   

11.
5,10-Dideazatetrahydrofolate (DDATHF) is a new antimetabolite designed as an inhibitor of folate metabolism at sites other than dihydrofolate reductase. DDATHF was found to inhibit the growth of L1210 and CCRF-CEM cells in culture at concentrations in the range of 10-30 nM. The inhibitory effect of DDATHF on the growth of L1210 and CCRF-CEM cells was reversed by either hypoxanthine or aminoimidazole carboxamide. Growth inhibition by DDATHF was prevented by addition of both thymidine and hypoxanthine, but not by thymidine alone. 5-Formyltetrahydrofolate reversed the effects of DDATHF in a dose-dependent manner. DDATHF had no appreciable inhibitory activity against either dihydrofolate reductase or thymidylate synthase in vitro, but was found to be an excellent substrate for folylpolyglutamate synthetase. DDATHF had little or no effect on incorporation of either deoxyuridine or thymidine into DNA, in distinct contrast to the effects of the classical dihydrofolate reductase inhibitor, methotrexate. DDATHF was found to deplete cellular ATP and GTP over the same concentrations as those inhibitory to leukemic cell growth, suggesting that the locus of DDATHF action was in the de novo purine biosynthesis pathway. The synthesis of formylglycinamide ribonucleotide in intact L1210 cells was inhibited by DDATHF with the same concentration dependence as inhibition of growth. This suggested that DDATHF inhibited glycinamide ribonucleotide transformylase, the first folate-dependent enzyme of de novo purine synthesis. DDATHF is a potent folate analog which suppresses purine synthesis through direct or indirect inhibition of glycinamide ribonucleotide transformylase.  相似文献   

12.
We have studied the interaction of Na2SeO3 with microtubule proteins and tubulin. This selenium compound inhibits the polymerization of MTP (half-inhibition occurred for Na2SeO3 10 microM), and to a lesser that of tubulin. This effect of selenite is related to the formation of disulfide bridges between tubulin sulfhydryl groups, inducing a conformational change of the protein. This is corroborated by the modified binding of colchicine and vinblastine in presence of selenium. The selenite inhibitory concentrations are similar to the toxic blood levels of selenium (40 microM).  相似文献   

13.
Encephalomyocarditis (EMC) virus ribonucleic acid (RNA) stimulated the incorporation of (14)C-amino acids into polypeptides in cell-free systems using preincubated S10 extracts from L cells. Incorporation was linear for over 2 hr. Analysis of the tryptic peptides derived from the polypeptide products formed in response to EMC RNA showed them to be virus specific. The major product, a polypeptide of 140,000 in molecular weight, migrated on sodium dodecyl sulfate-polyacrylamide gels with one of the virus-specific polypeptides present in EMC-infected cells. A minor component of molecular weight about 230,000 may correspond to the product of complete translation of the EMC virus genome. Little or no effect of interferon or vaccinia virus infection was observed in the preincubated, cell-free system. The EMC RNA-stimulated incorporation of (14)C-amino acids into polypeptides was not inhibited in extracts derived from L cells early in virus infection, from interferon-treated cells, or from cells subjected to both treatments. Interferon treatment did appear to have a slight inhibitory effect on chain elongation in this system. However, treatment of cells with highly purified interferon before virus infection caused a decrease of about 80% in the capacity of non-preincubated cell extracts to translate added EMC RNA. This effect did not extend to the translation of polyuridylic acid and could be reversed by preincubation of the extracts at 37 C for 20 min. The inhibition of translation was manifest at interferon concentrations as low as 5IU/ml, and in this respect closely paralleled the inhibition of virus growth. Inactivation of the antiviral activity of the interferon by heating or digestion with trypsin also abolished the effect on cell-free protein synthesis. The EMC-specific polypeptides formed in reduced amounts in extracts of interferon-treated vaccinia-infected cells were smaller than those formed in extracts of untreated, vaccinia-infected cells. Thus, inhibition of initiation or elongation of polypeptides, or both, can be demonstrated in cell-free systems employing non-preincubated extracts from interferon-treated, virus-infected cells. These results indicate that antiviral activity of interferon is directed against the translation of viral messenger RNA.  相似文献   

14.
Polypeptide synthesis has been studied in cell-free systems prepared from vaccinia virus-infected and uninfected HeLa cells. Cytoplasmic extracts containing endogenous messenger ribonucleic acid were used. Amino acid incorporation into hot trichloroacetic acid-precipitable material was linear for 15 to 20 min at 37 C. The initial rate of protein synthesis was approximately 15% of the rate in intact cells. Optimal conditions for polypeptide synthesis were similar in cell-free systems prepared from infected or uninfected cells. Requirements for an energy source and Mg(++) were demonstrated. The optimal Mg(++) concentration was 4 to 5 mm. Ribonuclease, puromycin, and cycloheximide were inhibitory. The molecular weights of the polypeptides labeled in the cell-free systems, as determined by gel filtration in 5 m guanidine hydrochloride, ranged from 16,000 to above 68,000. Polyacrylamide gel electrophoresis indicated that the polypeptides labeled in cell-free extracts of uninfected and infected cells were different. The latter closely corresponded in electrophoretic mobility with the viral polypeptides made in intact, infected cells.  相似文献   

15.
Amino acid incorporation in a cell-free system derived from rat liver has previously been found to be inhibited by GSSeSG (selenodiglutathione). In the present experiments the effect of GSSeSG on protein synthesis in 3T3-f cells, on growth and protein synthesis in Escherichia coli, and on amino acid incorporation in a cell-free system derived from E. coli, was studied. GSSeSG inhibits the incorporation of [3H]leucine into protein by 3T3-f cells. This inhibition cannot be reversed by removing GSSeSG and is correlated with the uptake of GSSeSG. Sodium selenite (Na2SeO3) and oxidized glutathione had no inhibitory effect in this system. [3H]Uridine or [3H]thymidine incorporation into RNA or DNA was not inhibited, indicating that the primary action of GSSeSG was on protein synthesis. GSSeSG did not influence the growth of E. coli in a synthetic medium, although enhanced amino acid incorporation was observed. In the cell-free system derived from E. coli, amino acid incorporation was not changed by GSSeSG, indicating that elongation factor G, in contrast to elongation factor 2 of mammalian cell systems, is not blocked by GSSeSG.  相似文献   

16.
Incubation of L1210 murine leukemia cells in vitro with 10 microM of the bifunctional alkylating agent bis(2-chloroethyl)methylamine (nitrogen mustard, HN2) for 10 min brought about a fall of more than 99.9% in their ability to form colonies when the cells were suspended in 0.5% nutrient agar. Incubation with HN2 also inhibited the influx of the potassium congener 86Rb+ to exponentially proliferating L1210 cells in a concentration-dependent manner. This inhibition was specific and was accounted for by a reduction of a diuretic-sensitive component of 86Rb+ influx, identified in the preceding paper (Wilcock, C. and Hickman, J.A. (1988) Biochim. Biophys. Acta 946, 359-367) as being mediated by a Na+/K+/Cl- cotransporter. Inhibition by 10 microM HN2 was complete after a 3-h incubation. There was no inhibition at this time of the ouabain-sensitive component of 86Rb+ influx, mediated by Na+/K+-ATPase. After 3 h of incubation with 10 microM HN2 there was also no change in the membrane potential of the treated cells as measured by the distribution of the [3H]TPMP+, no decrease in cellular ATP concentration and no change in intracellular pH, and the ability of the cells to exclude the vital dye Trypan blue was not significantly different from control values. These effects of HN2, therefore, appeared to follow lethal damage, but precede cell death. In the stationary phase of L1210 cell growth, the component of HN2 and diuretic-sensitive K+ influx to L1210 cells was reduced, whilst the component constituting the HN2-insensitive ouabain-sensitive sodium pump was increased. The monofunctional alkylating agent MeHN1 (2-chloroethyldimethylamine) which cannot cross-link cellular targets and has no antitumor activity, did not inhibit 86Rb+ influx to L1210 cells when incubated at equimolar or equitoxic concentrations to HN2. Intracellular potassium concentration was maintained close to control values of 138 +/- 10 mM in HN2-treated cells because of an approx. 35% fall in cell volume. The results suggest that the Na+/K+/Cl- cotransporter is a selectively inhibitable target for HN2, and the lesion is discussed with reference to the cytotoxic effects of this agent.  相似文献   

17.
The incorporation of radioactive selenium into cellular proteins and the effect of selenite on proliferation were examined in human (HeLa, HT-29, and IMR-90) and mouse (3T3 and CMT-93) cell lines. Proteins incorporating selenium were detected by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Major polypeptide subunits at 60, 23, 21, 19, and 16 kD were detected in the two tumorigenic and one normal human cell lines. The 23 kD polypeptide migrated to the same position on the gel as the major subunit of human erythrocyte glutathione peroxidase. In the mouse cells, the 60 kD polypeptide was almost entirely absent; four other major selenoproteins were detected, with molecular weights similar to those in the human cells. In both mouse and human cells, the same pattern of selenoproteins was observed irrespective of whether the cells were grown in medium containing 10% fetal bovine serum or in defined medium supplemented with 0.1 or 1 microM selenite, or with 1% serum. The effect of selenite on proliferation of HeLa, HT-29, and CMT-93 cells in medium supplemented with 10% fetal bovine serum and in serum-free medium was examined. At concentrations up to about 1 microM, selenite stimulated proliferation of the human cells slightly in serum-free medium but not in serum-supplemented medium. At concentrations of about 5 microM and higher selenite significantly inhibited proliferation of all cells in both types of media. In CMT-93 cells, this inhibition was greater in serum-free medium, but there were no significant differences in this regard in the human cells. These results demonstrate that selenium is stably incorporated into several polypeptides in human and mouse cells, that there are no significant differences in this regard among several cell lines, and slight differences between human and mouse cells. They further confirm that selenium can have a slight stimulatory effect on cell growth, and a much larger inhibitory effect, depending on its concentration.  相似文献   

18.
We previously showed in intact L cells that interferon treatment did not modify the shut-off of cellular RNA and protein synthesis induced by infection with Mengo virus although viral replication is inhibited (1,2). We have also demonstrated that inhibition of host protein synthesis was not due to degradation of messengers since cellular mRNA could be extracted from interferon-treated infected cells and efficiently translated in a reticulocyte lysate(2). Cellular mRNA was not degraded although 2–5A was present as reported here. We prepared cell-free systems from such cells at a time when cellular shut-off was fully established. The undegraded messengers remained untranslated under cell-free protein synthesis conditions and almost no polysomes were detected. The decreased amount of [35S]Met-tRNA-40S complex observed in these lysates might account for the inhibition of protein synthesis at the level of initiation.  相似文献   

19.
Polypeptides removed from the HeLa cell surface by mild pronase treatment rapidly inhibit protein synthesis when added to HeLa cells or cell-free translation system derived from HeLa cells. The inhibitory activity is heat stable. Protein and carbohydrate components of these polypeptides are required for inhibition of protein synthesis in vivo and in vitro. Two peaks of activity can be recovered from polyacrylamide gels, corresponding to polypeptides with molecular weights of approximately 29 000 and 41 000. Inhibition of protein synthesis in cell-free translation systems appears to be primarily an effect on elongation of polypeptide chains, whereas in the intact cell the primary target may be polypeptide chain initiation.  相似文献   

20.
Selenium and mercuric chloride (MC) interactions regarding cellular uptake and selenium protection on MC toxicity have been studied. Human K-562 cells were pretreated or simultaneously treated with either selenite (5 or 50 microM) or selenomethionine (10 or 50 microM) together with MC (35 or 50 microM). Both treatments with selenite showed an increase of mercury uptake with increased selenium dose. In the pretreated or simultaneously treated selenite and 35 microM MC combinations, no inhibition of growth was seen, whereas all 50-microM MC combinations were toxic to the cells. A selenite-dependent protection was obtained for both exposure protocols when considering the cellular uptake of mercury. The cells died when the accumulation on d 4 reached more than about 0.8 x 10(-15) mol/cell of mercury, whereas they survived up to twofold more mercury uptake when exposed to selenite. Selenomethionine gave, with a few exceptions, similar effects as selenite on MC uptake and toxicity.  相似文献   

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