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Biomedical subjects

G Beck

Publications and source records attributed to G Beck.

At least 181 records · Page 10Linked to original sources
PubMed1983

[Demonstration and partial purification of a convulsant from Cnestis glabra (Connaracea): effect on cells in culture].

A dialysable and thermostable compound was partially purified from Cnestis glabra (Connaracea) seeds. It is insoluble in organic solvents. At a dose corresponding to 0.5 g of seeds it has a lethal effect on mice after convulsive attacks. Sodium dipropylacetate, an anticonvulsive agent prevents the convulsions but not the death of the animals. The toxic compound inhibits protein synthesis in a rabbit reticulocyte lysate and in hepatoma tissue culture; moreover in the cell culture, the incorporation of thymidine into DNA is inhibited.

Animals↗
PubMed1982

Hormonal deinduction of tyrosine aminotransferase.

The effects of several antagonists of glucocorticoid action on a line of hepatoma cells (HTC strain) have been studied in order to determine their mechanisms of action. The induction of tyrosine aminotransferase by dexamethasone can be partially or totally inhibited if an antagonist is added simultaneously with dexamethasone or some time later. Antagonists, even if they have as much affinity for the cytoplasmic receptor as dexamethasone, must be administered at a 100-fold excess as compared to dexamethasone. Their receptor binding kinetics are not identical to those of inducer steroids: moreover there is no correlation between relative binding affinities and anti-inducing capacities. A short contact between the cells and the antagonist is sufficient to obtain a full antagonistic effect, but the antagonist is inactive if administered and removed from the cells before induction. An interpretation if suggested, considering these results which do not find a satisfactory explanation in the classical theory of receptor action.

Animals↗
PubMed1982

Role of tumor cell membrane-bound serine proteases in tumor-induced target cytolysis.

The tumor-induced marrow and red blood cell cytolysis assays have been used to explore the mechanism of cancer cell destruction of normal cells. Previously, we suggested that tumor-induced cytolysis was caused by tumor cell membrane-bound serine proteases. In this study, we have shown that concentrations of the broad-spectrum serine protease inhibitor diisopropylfluorophosphate that did not inhibit tumor cell DNA and protein synthesis completely abrogated tumor-induced red blood cell cytolysis. In addition, tumor cell membranes isolated by differential and sucrose density gradient centrifugation and characterized by electron microscopy and enzyme marker analysis were cytolytic for rat 59Fe-labeled red blood cells. The specific activity expressed as release index (%) per microgram of protein was 1.620 for the tumor cell membrane preparations as compared to 0.002 for intact Walker 256 tumor cells. Tumor cell membranes solubilized in Triton X-100 had activity in the p-toluenesulfonyl-L-arginine methyl ester assay for trypsin-like enzymes and the N-benzoyl-L-tyrosine ethyl ester assay for chymotrypsin-like enzymes. The enzyme activities demonstrated in these assays could be inhibited by N-alpha-p-tosyl-L-lysine chloromethyl ketone HCl and L-1-tosylamide-alpha-phenyl-ethyl chloromethyl ketone, respectively. Using [3H]diisopropylfluorophosphate affinity labeling of the tumor cell membrane proteins followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, we have identified membrane-bound serine protease(s) that appear to be responsible for tumor-induced marrow and red blood cell cytolysis.

Animals↗
PubMed1981

Inhibition of tyrosine aminotransferase induction by UTP deficiency and its reversal by 5-fluorouridine in cultured hepatoma cells.

Hepatoma tissue culture cells, grown in the presence of D-galactosamine and 6-azauridine, demonstrate a strong reduction of the intracellular UTP pool that can be replenished by formation of UTP from uridine and FUTP from 5-fluorouridine within 2 h. Concomitantly with the UTP deficiency, a decrease of dexamethasone-induced tyrosine aminotransferase activity occurs. 5-Fluorouridine, as compared to uridine, is even more efficient in restoring the activity of tyrosine aminotransferase. Treatment of the cells with D-galactosamine alone results in a minor lowering of UTP that is not followed by the inhibition of the enzyme induction. However, the administration of D-galactosamine, simultaneously or at any time up to 5 h before or after dexamethasone, leads to a 1.5- to 2-fold higher induction (superinduction) which appears 24 h later.

Animals↗
PubMed1981

Relations between steroid-cell contact, steroid-binding and induction of tyrosine aminotransferase.

The induction of tyrosine aminotransferase by a variety of steroids was studied in cells from a hepatoma tissue culture (HTC). We have defined a class of steroids that induce TAT synthesis to a higher level than optimal inducers described earlier; these are called supra-inducers. When TAT induction is compared with the binding of the steroids to the cytoplasmic receptor or to their binding in the whole cell, a good correlation between binding in vivo of the hormone and its induction capacity can be established, whereas such a correlation was not systematically observed in vitro. A very short exposure of HTC cells to either dexamethasone or corticosterone is sufficient to induce TAT. When the inducer is removed from the culture medium a few minutes after its administration, the intracellular hormone concentration decreases very rapidly but TAT will be synthesized at its maximal rate. Thus the hormones behave as a starting signal for the optimal synthesis of the enzyme, and their presence in the culture medium is not necessary throughout the entire induction period.

Animals↗
PubMed1981

Selective inhibition by sodium butyrate of glucocorticoid-induced tyrosine aminotransferase synthesis in hepatoma tissue-cultured cells.

Sodium butyrate in a 5 mM concentration prevents the induction of tyrosine aminotransferase in hepatoma culture cells, without affecting the basal level of the enzyme. This effect is reversible immediately after the removal of butyrate, or after a lag, if butyrate was present for more than 2 h. Neither the amount of cellular RNA nor the rate of total RNA synthesis were affected by sodium butyrate. Furthermore, butyrate does not inhibit protein synthesis: [35S]methionine incorporation into proteins, measured in a reticulocyte lysate system, shows no significant difference between the translation capacity of the RNAs from butyrate-treated cells and from dexamethasone-induced or uninduced cells. Nevertheless, when tyrosine aminotransferase was isolated from the translation products by its specific antiserum and analyzed by gel electrophoresis, we observed that the amount of the enzyme synthetized in the presence of RNAs from dexamethasone/butyrate-treated cells was strongly diminished relative to that synthesized in the presence of RNA from dexamethasone-induced cells. These experiments indicate that the treatment of the cells with butyrate decreases the activity of the specific messenger RNA for tyrosine aminotransferase to a level close to the basal level.

Animals↗
PubMed1981

Rat plasma lipoprotein inhibitors of lymphocyte proliferation: specific membrane receptor for very low density lipoproteins.

We have compared the inhibitory effects of plasma lipoproteins on DNA synthesis by phytohemagglutinin-stimulated rat lymphocytes. The order of suppressor potency was: very low density lipoproteins (VLDL) greater than low density lipoproteins much greater than high density lipoproteins. We have further demonstrated the presence of specific receptor sites for VLDL on rat spleen lymphocytes. The number of VLDL receptors was estimated at 31,000 by a modified Scatchard analysis. Our results suggest that in the normal physiologic state, the proliferation of circulating lymphocytes may be suppressed by the combined effects of plasma lipoproteins. Furthermore, it would appear that the binding of plasma VLDL to specific receptors on rat lymphocytes would be the initial physiological event in this inhibitory process.

Animals↗
PubMed1981

[Use of the tyrosine aminotransferase induction system for the demonstration of the signal effect of glucocorticoid hormones].

The induction of tyrosine aminotransferase (TAT) in the HTC hepatoma cell line is observed after a single administration of an active steroid. A few minutes of contact between the cells and dexamethasone or corticosterone is sufficient to induce TAT synthesis to its maximal level. When radiolabeled hormones are used, no radioactivity is found in the cell one hour after removal of the hormone from the culture medium, whereas TAT activity remains optimal. Thus, the hormone behaves like a start signal for the optimal synthesis of the enzyme and its continuous presence in the medium is not necessary during the whole induction cycle.

Animals↗
PubMed1981

[Characterization of tyrosine aminotransferase by an immunoadsorption technic. Application to the measurement of the specific messenger RNA].

A specific antiserum was used in an enzyme-linked immunoadsorbent assay (ELISA) for tyrosine amino-transferase TAT. Protein A bound on Sepharose was allowed to react with antiserum preincubated with the enzyme. Inhibition curves in the presence of protein A were parallel to those obtained in the absence of protein A. In the case of cell-free synthesized TAT, the complex bound to the solid phase contains the (35S) labelled enzyme; the sensitivity of the test was greatly increased when the bulk of protein was discarded by pretreatment of the reaction mixture at 70 degree and chromatography on DEAE cellulose. The immunoadsorbed polypeptides were analyzed by dodecylsulfate/polyacrylamide gel electrophoresis. The pattern of polypeptides neosynthesized using RNA from different origins (rat liver, hepatoma cells) and after various treatments (glucocorticoid hormones, sodium butyrate) exhibited some different in the TAT region which can be related to the level of the specific mRNA for TAT. This method is very useful for further studies on TAT gene expression and might also shed light on the mechanism of hormonal action and drug processes.

Animals↗
PubMed1981

Membrane receptors for very low density lipoprotein (VLDL) inhibitor of lymphocyte proliferation.

Physiologic concentrations of human plasma very low density lipoproteins inhibit the DNA synthesis of lymphocytes stimulated by allogeneic cells or lectins. In this report we have compared the effects of isolated lipoproteins [very low density lipoproteins (VLDL), low density lipoproteins (LDL), and high density lipoproteins (HDL)] and lipoprotein-depleted plasma (LDP) on DNA synthesis by phytohemagglutinin-stimulated human lymphocytes. The relative potency for the inhibition of lymphocyte proliferation was VLDL greater than LDL greater than HDL greater than LDP. Fifty percent inhibition of DNA synthesis was observed at a VLDL protein concentration of 1.5--2.0 microgram/ml. We have further demonstrated the presence of specific receptors for VLDL on human lymphocytes. Native VLDL was more effective than LDL in competing for 125I-VLDL binding sites. Subsequent to binding to lymphocytes, 125I-VLDL was internalized and degraded to acid-soluble products. Based on a Scatchard analysis of VLDL binding at 4 degrees C, the number of VLDL receptors per lymphocyte was estimated at 28,000 +/- 1300. Based on an estimated mean binding affinity for the VLDL receptor complex at half saturation of approximately 8.8 X 10(7) liter/mole, it is estimated that 91% of lymphocyte VLDL receptors are occupied at physiologic VLDL concentrations in blood. Although the immune regulatory role of plasma lipoproteins is uncertain, we suggest tha VLDL and LDL-In may maintain circulating blood lymphocytes in a nonproliferative state via their respective cell receptor mechanisms.

Cholesterol↗