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M N Thang

Publications and source records attributed to M N Thang.

At least 19 recordsLinked to original sources
PubMed1992

Post-transcriptional regulation of transferrin receptor mRNA by IFN gamma.

IFN gamma inhibits the rise in transferrin receptor mRNA level which is normally observed when stationary WISH cells are stimulated to proliferate. This effect is not attributable to a change in the transcription rate of the transferrin receptor gene or in the cytoplasmic stability of the mRNA. The IFN gamma-induced reduction of the transferrin receptor mRNA content is already present at the nuclear level to an extent comparable to that observed in whole cells. Thus, IFN gamma does not impair the passage of this mRNA from the nuclear to the cytoplasmic compartment but probably interferes with a nuclear post-transcriptional event during the processing of the immature transferrin receptor mRNA. Two different levels of regulation of transferrin receptor mRNA have been previously reported. Iron modulates the cytoplasmic stability of this mRNA through the binding of a specific cytoplasmic factor, whereas cell growth variation influences the transcription of this gene. Our results suggest the existence of another mechanism of regulation for transferrin receptor gene expression not so far considered. Furthermore, the distinction between the mechanism of regulation exerted by IFN gamma and that exerted by cell proliferation on transferrin receptor gene expression suggests that, in WISH cells, the IFN-induced transferrin receptor decay is not a consequence of cell growth arrest but rather one of the causes of the antiproliferative effect of IFN through iron deprivation.

Blotting, Northern↗
PubMed1992

Non-neutralizing monoclonal antibodies against Ras GTPase-activating protein: production, characterization and use in an enzyme immunometric assay.

We studied several monoclonal antibodies (mAbs) raised against the 100 kD Ras GTPase activating protein (p100-GAP), which was purified from human placenta. These antibodies recognized p120-GAP and p100-GAP in native and in denatured forms. The most reactive, GP15 and GP200, both recognized distinct epitopes and did not neutralize GTPase stimulatory activity. These two mAbs were selected for a two-site enzyme immunoassay, using covalent conjugates of the antibodies coupled to the tetrameric form of acetylcholinesterase as tracer. This assay was used to quantify Ras-GAP in both normal and tumor tissues and cell extracts.

Animals↗
PubMed1992

The effects of poly(I).poly(C12U) and interferon on the multiplication of a mammalian type C retrovirus in human cells.

Poly(I).poly(C12U) or interferon treatment inhibited multiplication of the xenotropic baboon type C endogenous retrovirus M7 in chronically infected human AV3-M7 cells, as determined by a reverse transcriptase (RT) assay and electron microscopy. Furthermore, this polynucleotide induced 2'5' oligoadenylate (2'5'A) synthetase activity. In contrast to interferon (IFN), poly(I).poly(C12U) did not give rise to the appearance of a trapping phenomenon observable by electron microscopy. When AV3-M7 cells were treated simultaneously with poly(I).poly(C12U) and anti-IFN-beta/alpha antibodies, the induction of 2'5'A synthetase was abolished without any alteration of the inhibitory effect of RT activity. Taken together, these results suggest that different mechanisms are used by poly(I).poly(C12U) and IFN in blocking type C retrovirus multiplication.

2',5'-Oligoadenylate Synthetase↗
PubMed1992

[Biological actions and therapeutic perspectives of double stranded polyribonucleotides: a reappraisal].

Double-stranded polynucleotides, which are composed of two complementary homopolyribonucleotides containing no genetic information, are synthetic molecules capable of mimicking the action of natural double-stranded RNA or viral RNA on cells. Double-stranded polyribonucleotides act as an alarm system alerting the cell to the presence of an external aggression, e.g. a viral attack. In addition, polyribonucleotides have a more active function in that they trigger cell defense processes through activation of a family of genes, of which some encode cytokines, activation of cytoplasmic enzymes involved in antiviral mechanisms or signal transduction, and activation of nonspecific immune responses. Double-stranded polyribonucleotides containing one mismatched base pair per helix have been found to be especially interesting. The best known example is poly(I).poly(C12U), also called ampligen. Poly(I).poly(C12U) is capable, in experimental models, of limiting the development of viruses (including HIV), reducing tumor growth, eliminating metastases, and, according to one report, preventing steady declines in T-cell counts in HIV-positive patients. Therapeutic doses used in the USA as an experimental drug induced little toxicity. In vitro, poly(I).poly(C12U) acts synergistically with interferon, interleukin 2 or AZT, suggesting that these latter drugs may be effective in lower, less toxic doses when used in combination with poly(I).poly(C12U). The therapeutic activity of poly(I).poly(C12U) holds promise. More extensive prospective studies of this agent are warranted.

Cytomegalovirus Infections↗
PubMed1991

Direct induction of interferon-gamma- and interferon-alpha/beta-inducible genes by double-stranded RNA.

Using Northern analysis, we here show that the inducibility by double-stranded (ds) RNA of interferon-alpha/beta-inducible genes is not restricted to a few genes but extends to all the genes known to be stimulated by IFN type I in fibroblasts. Moreover, we show that some genes, preferentially regulated by IFN-gamma, are also activated by dsRNA. We present a series of arguments demonstrating that the induction by dsRNA is not mediated by IFN. In addition to the fact that this induction occurs in the presence of cycloheximide and/or anti-IFN-alpha/beta antibodies in fibroblasts, we observed that, in IFN-resistant Daudi cells, ISG15 and IP-10 genes which are not induced by IFN-beta, are still inducible by dsRNA. dsRNA is also still active on 2-5 AS and ISG15 genes in cells carrying homozygous deletions of IFN alpha/beta genes. Actinomycin D experiments and nuclear in vitro elongation assays reveal that the induction by dsRNA involves, as its early step, a transcriptional event. This induction was found not to require protein synthesis, suggesting that activation of preexisting cellular factors is involved. The opposite inducibility by dsRNA of IFN-beta and 2',5'-oligoadenylate (2-5A) synthetase genes in serum-deprived fibroblasts indicates that pathways of induction by dsRNA of these two genes are not identical. Inhibition by 2-aminopurine of the induction of IFN-inducible mRNAs by IFN-beta or dsRNA suggests the participation of a protein kinase in their mechanism of action.

2-Aminopurine↗
PubMed1990

A murine model of NK cell mediated resorption.

There is increasing evidence that some models of immunologically mediated murine embryo demise involve nonspecific lytic effector cells. In this paper, we use two double stranded synthetic RNAs, known as potent interferon inducers and NK cell activators, the Poly (I). Poly (C) and the less toxic Poly (I). Poly (C12U). These polynucleotides enhance fetal resorption rates in both resorption prone and none-resorption prone strains of mice. We have studied the kinetics of the phenomenon, and observed an anti-implantation-like effect of early injection during early pregnancy. The abortifacient effects can be adoptively transferred to naive recipients by spleen cells from Ds RNA injected donors. Such effects are abrogated if the cells are pretreated with anti-NK cell antiserum. The relevance of these findings to the survival of the conceptus is suggested.

Animals↗
PubMed1990

[Vasoactive intestinal peptide induces 2',5'-oligoadenylate synthetase and antiviral state in cells of HT-29 colonic cancer].

Vasoactive Intestinal Peptide (VIP) is able at the concentration 10 to 100 nM to induce in HT-29 cells 2'5' oligoadenylate (2'5' A) synthetase activity. The kinetics of this induction show that the maximal effect is attained after 24 hrs. VIP induces 2'5' A synthetase parallel to inhibition of vesicular stomatitis virus growth. The levels of these two induced activities after VIP treatment are comparable to those induced by the poly (I).poly (C), an inducer of IFN beta/alpha in mammalian cells. Moreover the anti-IFN beta/alpha antibodies abolish the VIP-induced 2'5' A synthetase whereas anti-IFN gamma antibodies are ineffective. The fact that VIP establishes an antiviral state in HT-29 cells potentiates new pharmaceutical applications for this neuropeptide.

2',5'-Oligoadenylate Synthetase↗
PubMed1989

[Demonstration of an interferon alpha receptor in human colonic cancer cells in culture].

The IFN-alpha 2 receptor present in human cancerous colonic cells in culture has a capacity of 1,800 sites per cell with a kd of 0.5 nM. The molecular mass of the interferon alpha 2 (IFN-alpha 2) receptor complex is 134 kd. The IFN-alpha 2 induces the activity of the 2'5' oligoadenylate (2'5' A) synthetase activity in these cells and partly inhibits their growth.

2',5'-Oligoadenylate Synthetase↗
PubMed1988

Reduction of transferrin receptor expression by interferon gamma in a human cell line sensitive to its antiproliferative effect.

Interferon gamma (IFN gamma) reduced 125I-transferrin binding to WISH cells which are sensitive to its antiproliferative effect. IFN gamma did not affect transferrin binding to Daudi cells or phytohemagglutinin-stimulated human lymphocytes, neither of which respond to its antigrowth action. Scatchard analyses of the equilibrium binding of 125I-transferrin to WISH cells exposed to IFN gamma revealed a decrease in the number of cell surface receptors but no change in the apparent association constant compared with control cells. When 125I-transferrin binding was measured using detergent-extracted cells, the IFN-induced reduction of binding was smaller than with intact cells. This suggests that in WISH cells, IFN gamma not only reduced the total number of transferrin receptors, but also modified the process of receptor internalization and recycling. Labeling of newly synthesized receptors with [35S]-methionine indicated that a reduction in the biosynthesis might account for the decrease in the total number of transferrin receptors in IFN gamma-treated cells. Our results suggest that the antigrowth effect of IFN gamma is at least partly due to its inhibitory action on transferrin receptor expression leading to iron starvation.

Cell Division↗
PubMed1988

Effect of endogenous and exogenous interferons on the differentiation of human monocyte cell line U937.

The effect of interferons (IFNs) on the differentiation of hematopoietic cells was examined with the human monocyte cell line U937. The differentiation of U937 was induced by hydroxyvitamin D3 and was evaluated through the study of specific markers. The induction of the U937 differentiation was associated with a production of IFN and with a marked increase in (2'5') oligoadenylate synthetase. Addition of anti-IFN-alpha/beta antibodies inhibited the enhancement of (2'5') oligoadenylate synthetase and reduced the inhibitory effect of hydroxyvitamin D3 on cell growth. Nevertheless, neutralization of endogenous IFN excreted during U937 cell maturation did not modify the expression of the differentiation markers examined. Exogenous natural IFN-alpha, IFN-beta, or recombinant (r) IFN-gamma, when added to the culture medium, did not promote a "global" U937 differentiation. Most of the differentiation markers, except for reduction of nitroblue-tetrazolium, were not induced by IFN-alpha or -beta. However, rIFN-gamma was able to induce the appearance of several monocytic membrane markers at an extent comparable or slightly inferior to that elicited by hydroxyvitamin D3. Different effects on the expression of HLA antigens were obtained with these IFNs: IFN-alpha or -beta enhanced mainly class I HLA antigen expression, whereas rIFN-gamma increased selectively the expression of class II HLA DC1 but not HLA DR antigens. In contrast, phytohemagglutinin-leukocyte conditioned medium elicited a marked and selective enhancement of the expression of HLA-DR antigens. This induction of HLA DC1 antigens by rIFN-gamma was not observed in two other leukemic cell lines (HL60 and HEL). The present study shows that IFN-alpha or -beta may participate in the antiproliferative effect occurring during cellular differentiation, while IFN-gamma may be involved in the induction of the expression of specific monocytic markers involved in cellular immunoregulation.

2',5'-Oligoadenylate Synthetase↗
PubMed1988

Stimulation of natural killer cytotoxicity by long-term treatment with double-stranded polynucleotides without induction of hyporesponsiveness.

Treatment of Wistar/AG rats with a single i.p. injection of 1 mg/kg of synthetic double-stranded polynucleotides, either polyadenylic-polyuridylic acid (rAn.rUn), or a mismatched analogue of polyinosinic-polycytidylic acid (rIn.r(C12U)n), enhanced the cytotoxicity of natural killer (NK) cells among peripheral blood leukocytes and lung intracapillary leukocytes (LICL). The enhancement reached a peak 24 h after treatment and returned to control values after 4 days. In rats given repeated injections of double-stranded polynucleotides (2 per week), the NK cytotoxicity expressed by LICL reached more than ten times (in lytic units) the control levels between day 8, after 3 injections, and day 360, after 100 injections. No hyporesponsiveness was observed. Moreover, NK activity was frequently and significantly higher in rats given multiple injections than in those given a single injection. In rats with experimentally induced P77 lung fibrohistiocytoma colonies, repeated injections of rIn.r(C12U)n stimulated NK activity and reduced the number of metastatic nodules from 172 to 19. The same significant reduction (from 172 to 27) was also observed in animals given repeated injections of rAn.rUn. However, with two models of spontaneous metastases, significant reduction in lung metastases (M37 bronchioloalveolar carcinoma) or lack of effect (S4T19 rhabdomyosarcoma) were observed.

Animals↗
PubMed1987

Cloned human interferons alpha: differential affinities for polyinosinic acid and relationship between molecular structure and species specificity.

The HuIFN-alpha A and HuIFN-alpha D interferons, produced by two independent recombinant bacterial clones, have different affinities for polyinosinic acid (poly I). The monomeric form HuIFN-alpha A (FMM), but not the HuIFN-alpha D, binds to poly (I)-agarose and is protected by poly (I) from thermal inactivation. Other subtypes of HuIFN-alpha A including the monomer SMM and oligomers have no affinity for this polynucleotide. In addition, these interferons show different target cell preferences in agreement with our previous suggestion (23) that the polynucleotide binding domain may be responsible for species specificity. Two significant observations are 1) the fractions of HuIFN-alpha D and HuIFN-alpha A unbound on poly (I)-agarose show higher antiviral inducing activity on heterologous (MDBK) than on homologous (WISH) cells, whereas they induce about the same activity of 2'5' oligoadenylate synthetase in these two cell lines. These fractions are also active on L929 cells. 2) The bound fraction of HuIFN-alpha A induces almost the same antiviral and 2'5' oligoadenylate synthetase activities in MDBK and in WISH cells but neither activity in L929 cells.

2',5'-Oligoadenylate Synthetase↗
PubMed1987

2',5'-Oligoadenylate synthetase expression is induced in response to heat shock.

Hyperthermia (45 degrees C) induced the synthesis of a characteristic heat-shock protein of 70,000 daltons (70 hsp) in Madin-Darby bovine kidney (MDBK) cells. In addition, subsequent to heat shock, there was a substantial increase in the 2',5'-oligoadenylate synthetase (2',5'-A synthetase) activity in both MDBK and human WISH cells. However, in contrast to 70 hsp synthesis, which reached its maximum 3 h after cell transfer from 45 to 37 degrees C, increase in 2',5'-A synthetase expression, conspicuous after 6 h, attained its maximum only 18 h after transfer. Another interesting observation is that, during recovery at 37 degrees C, the cells released into the medium heat-shock-induced factor(s) (HSIF) capable of inducing an increase in 2',5'-A synthetase activity in fresh MDBK cells. HSIF behaves as a polypeptide with a molecular weight of more than 5,000; it is relatively heat stable and sensitive to acidic treatment. HISF seems different from interferon (IFN) since: 1) no detectable antiviral state developed after infection in cells treated with HSIF; 2) antibovine IFN antibodies did not abolish the inducing capacity of HSIF; 3) IFN had an additive effect on the inducing capacity of HSIF, and 4) HSIF released from bovine cells induced a net enhancement of 2',5'-A synthetase activity in human WISH cells. The first three of these observations applied also to heat-shocked MDBK cells.

2',5'-Oligoadenylate Synthetase↗
PubMed1987

Relationship between inhibition of cell growth and of transferrin receptor expression by interferon (IFN) alpha: studies in IFN-sensitive and IFN-resistant Daudi cells.

We previously showed that treatment of different cell lines with interferon-alpha (IFN-alpha) concurrently inhibited both cell growth and the rise observed in 125I-labelled transferrin binding when cells are exposed to culture conditions that stimulate proliferation. To gain insight into the relationship between these two IFN-induced inhibitory processes, we investigated the effect of IFN-alpha on the binding of 125I-labelled transferrin to Daudi cells sensitive or resistant to its antiproliferative action. We found a close correlation between the ability of IFN-alpha to inhibit cell growth and to inhibit transferrin receptor expression. Since growth inhibition induced by other agents is not always accompanied by an inhibition of transferrin receptor expression, the previous and present observations suggest that the inhibitory effect of IFN on this expression is at least one of the mechanisms by which IFN inhibits cell proliferation. We also observed that IFN-alpha did not modify transferrin receptor biosynthesis in IFN-sensitive Daudi cells, suggesting that IFN-alpha may change the processing of the transferrin receptor molecules, making them unable to bind transferrin.

Cell Cycle↗
PubMed1986

Multiple molecular forms of interferon display different specific activities in the induction of the antiviral state and 2'5' oligoadenylate synthetase.

Both Hu IFN-alpha A and Hu IFN-alpha D, produced by two independent recombinant bacterial clones, are mixtures of monomers, dimers and trimers. These forms, when assayed individually in heterologous MDBK cells, induced different degree of antiviral and 2'5' oligoadenylate synthetase (2'5' A synthetase) activities: the antiviral activity of the monomer is greater than that of the dimer and the trimer, whereas the activity of 2'5' A synthetase induction is lower with the monomer than with the dimer or the trimer. Similar differences are also observed on human cells. Compared to the mononeric form, the dimeric and the trimeric forms of Hu IFN-alpha A show higher antiviral inducing activity on heterologous MDBK cells than on homologous WISH cells, whereas the 2'5' A synthetase inducing activity in these two cell lines is about the same. Thus for the same antiviral activity, the trimer or the dimer compared to the monomer are much better inducers of the 2'5' A synthetase on human than on MDBK cells.

2',5'-Oligoadenylate Synthetase↗
PubMed1985

Chloroquine impairs the interferon-induced antiviral state without affecting the 2',5'-oligoadenylate synthetase.

Chloroquine, a weak base which raises the pH in acidic cellular compartments such as lysosomes and endosomes, counteracts the induction by interferon of the antiviral state but not that of the 2',5'-oligoadenylate synthetase in three different types of cell lines (MDBK, WISH, and L929). Active interferon is recovered in crude extracts of cells which have been treated with interferon and chloroquine together, but not in extracts of cells treated with interferon alone, indicating that chloroquine has inhibited the intralysosomal proteolysis of interferon. A low pH-dependent event in the intracellular fate of interferon (perhaps its intralysosomal degradation) is, therefore, necessary for the establishment of the antiviral state but not for the induction of the 2',5'-oligoadenylate synthetase.

2',5'-Oligoadenylate Synthetase↗
PubMed1985

Induction of (2'-5') oligoadenylate synthetase activity during granulocyte and monocyte differentiation.

Variations in the (2'-5') oligoadenylate synthetase (2-5 A synthetase) level were examined prior to and during the differentiation in culture of the human monocyte cell line U937 and the promyelocytic cell line HL60 in an attempt to reveal whether the enzyme is actively involved in hematopoietic cell maturation. The basal level of this enzyme was much higher in U937 than in HL60 cells. The activity of 2-5 A synthetase was enhanced in both cell lines in response to alpha, beta interferons. During cell differentiation, ten markers were measured. The level of the enzyme rose during the process of cellular maturation in both cell lines. The 2-5 A synthetase activity observed in differentiated HL60 and U937 cells was comparable to that observed in mature normal granulocytes and monocytes respectively. Induction of U937 differentiation by chemicals was associated with detectable production of IFN. The increase in enzyme activity observed was mostly dependent on endogenous production of interferon, since it was inhibited by interferon antibodies. Kinetic studies showed that in U937 cells 2-5 A synthetase was expressed prior to several of the differentiation markers. The rise in the enzyme's level observed during the differentiation of HL60 cells was independent of endogenous production of interferon, since it was not inhibited by the addition of anti-interferon antibodies. These results suggest that different biochemical and molecular mechanisms are responsible for the induction of 2-5 A synthetase observed during the differentiation of hematopoietic cells. In any case, 2-5 A synthetase can be considered as a biochemical marker of cell status and differentiation in hematopoietic cells.

2',5'-Oligoadenylate Synthetase↗