PubMed Health⌕ Search

Biomedical subjects

N Darracq

Publications and source records attributed to N Darracq.

14 recordsLinked to original sources
PubMed2000

Repression of virus-induced interferon A promoters by homeodomain transcription factor Ptx1.

Interferon A (IFN-A) genes are differentially expressed after virus induction. The differential expression of individual IFN-A genes is modulated by substitutions in the proximal positive virus responsive element A (VRE-A) of their promoters and by the presence or absence of a distal negative regulatory element (DNRE). The functional feature of the DNRE is to specifically act by repression of VRE-A activity. With the use of the yeast one-hybrid system, we describe here the identification of a specific DNRE-binding protein, the pituitary homeobox 1 (Ptx1 or Pitx1). Ptx1 is detectable in different cell types that differentially express IFN-A genes, and the endogenous Ptx1 protein binds specifically to the DNRE. Upon virus induction, Ptx1 negatively regulates the transcription of DNRE-containing IFN-A promoters, and the C-terminal region, as well as the homeodomain of the Ptx1 protein, is required for this repression. After virus induction, the expression of the Ptx1 antisense RNA leads to a significant increase of endogenous IFN-A gene transcription and is able to modify the pattern of differential expression of individual IFN-A genes. These studies suggest that Ptx1 contributes to the differential transcriptional strength of the promoters of different IFN-A genes and that these genes may provide new targets for transcriptional regulation by a homeodomain transcription factor.

Animals↗
PubMed1997

Synergism between multiple virus-induced factor-binding elements involved in the differential expression of interferon A genes.

Comparative transfection analysis of murine interferon A4 and interferon A11 promoter constructs transiently transfected in mouse L929 and human HeLa S3 cells infected with Newcastle disease virus showed that the second positive regulatory domain I-like domain (D motif), located between nucleotides -57 and -46 upstream of the transcription start site, contributes to the activation of virus-induced transcription of the interferon (IFN)-A4 gene promoter by cooperating with the positive regulatory domain I-like and TG-like domains previously described. Electrophoretic mobility shift assay performed with the virus-inducible fragments containing these motifs indicated that the binding activity that we have denoted as virus-induced factor (Génin, P., Bragança, J., Darracq, N., Doly, J., and Civas, A. (1995) Nucleic Acids Res. 23, 5055-5063) is different from interferon-stimulated gene factor 3. It binds to the D motif but not to the virus-unresponsive form of the D motif disrupted by a G-57 --> C substitution. We show that the low levels of IFN-A11 gene expression are caused essentially by the lack of two inducible enhancer domains disrupted by the A-78 --> G and the G-57 --> C substitutions. These data suggest a model taking account of the differential regulation of IFN-A gene family members. They also suggest that virus-induced factor may correspond to the primary transcription factor directly activated by virus that is involved in the initiation of IFN-A gene transcription.

Animals↗
PubMed1995

A novel PRD I and TG binding activity involved in virus-induced transcription of IFN-A genes.

Comparative analysis of the inducible elements of the mouse interferon A4 and A11 gene promoters (IE-A4 and IE-A11) by transient transfection experiments, DNase 1 footprinting and electrophoretic mobility shift assays resulted in identification of a virus-induced binding activity suggested to be involved in NDV-induced activation of transcription of these genes. The virus-induced factor, termed VIF, is activated early by contact of virions with cells. It specifically recognizes the PRD I-like domain shared by both inducible elements, as well as the TG-like domain of IE-A4. This factor, distinct from the IRF-1, IRF-2 and the alpha F1 binding proteins and presenting a different affinity pattern from that of the TG protein, is proposed as a candidate for IFN-type I gene regulation.

Animals↗
PubMed1992

Membrane proteins from lymphoblastoid cells showing cross-affinity for alpha-fetoprotein and albumin. Isolation and characterization.

AFP or SA immobilized on nitrocellulose membranes (AFP-NC or SA-NC) were used as affinity matrices to purify cell membrane proteins with affinity for AFP (AFP-BP) and for SA (SA-BP) from membrane-enriched extracts of Raji cells (a B-lymphoma cell line), as well as for normal resting and activated peripheral blood lymphocytes (PBMC). SDS-PAGE and ligand blotting assays showed that AFP-BP and SA-BP isolated from Raji cells are probably identical molecules. They consisted of two sets of polypeptides of 31 kDa and 18 kDa. The glycoprotein nature of isolated 31 kDa and 18 kDa peptides was suggested by positive staining with Schiff's reagent, and amino-acid analysis revealed similar amino-acid composition for the two glycoproteins. In human PHA-activated PBMC, only the 18 kDa polypeptide was identified and isolated as AFP-BP or SA-BP. As in Raji cells, this 18 kDa polypeptide, isolated by affinity for AFP or for SA, appeared to be the same molecule. Contrary to Raji cells and activated PBMC, no proteins with an affinity for AFP or for SA were identified or isolated in resting PBMC. These observations strongly suggest that the isolated 31 kDa and 18 kDa glycoproteins are probably AFP receptors previously demonstrated in several neoplastic and normal cells undergoing growth and/or differentiation; indeed, they were identical to albumin-binding proteins described by others.

Amino Acids↗
PubMed1989

Expression of alpha-fetoprotein receptors by human T-lymphocytes during blastic transformation.

Alpha-fetoprotein (AFP) and transferrin (Tf) are actively internalized by many growing cells during ontogenic and neoplastic development, including human malignant T- and B-lymphoblastoid cells. Their internalization is, on the contrary, greatly diminished or absent in mature, non-proliferating elements. In the present work, peripheral blood mononuclear cells (PBMCs) and T-lymphocytes, harvested from normal human donors, were induced to blastic transformation with phytohemagglutinin (PHA) and their ability to uptake AFP and Tf was measured and compared with Tf uptake in the same conditions. The capacity of the cells to internalize both proteins was quantified by fluorescence activated cell sorter (FACS) using fluoresceinated derivatives of these proteins. The results obtained show a significant uptake of AFP by T-lymphocytes upon PHA stimulation. The values of AFP incorporation were similar for all the cells studied (PBMCs, T-cells and T4, T8 cell subsets). The time course of AFP uptake paralleled, under the same conditions, the uptake of Tf and the expression of IL2 receptors. AFP uptake increased rapidly from the zero time (resting T-cells) and reached a maximum around 72 hr after PHA activation. Scatchard analysis of kinetic data at 4 degrees C revealed for Hu-AFP one single group of specific binding sites in PHA activated T-lymphocytes with a dissociation constant of 3.03 x 10(-7) M and around 88,000 sites/cell. There results strongly suggest the transitory expression of AFP receptors in T-lymphocytes during blastic transformation.

Cells, Cultured↗
PubMed1984

Absence of DNA breaks during repair of DNA-protein cross-links induced by the mycotoxin botryodiplodin in mammalian cells.

Botryodiplodin induces DNA-protein cross-links (DPC) in mammalian cells in culture. Removal of the mycotoxin followed by incubation of cells in fresh medium leads to the gradual disappearance of DPC. The present experiments attempted to determine to what extent the repair mechanism acts through a system involving transient formation of single-strand breaks (SSB). The data reported here show that no SSB were detected in DNA of various strains of cells, even in the presence of inhibitors (hydroxyurea and 1-beta-D-arabinofuranosyl cytosine). These data demonstrate that neither the base excision, nor the excision repair process was involved in the repair of DPC or of any other lesions induced by botryodiplodin in mammalian cells.

Animals↗
PubMed1984

Repair of DNA-protein cross-links induced by the mycotoxin botryodiplodin in mammalian cells.

Repair of DNA--protein cross-links (DPC) induced by the mycotoxin botryodiplodin in three cell strains (LF, VA and XP) was studied after removal of the drug and postincubation in fresh medium. Immediately after botryodiplodin was removed, DPC progressively disappeared with an efficiency which depended upon the dose of mycotoxin applied and the cell strain considered. Experiments using [14C]botryodiplodin suggested that DPC repair involved at least one splitting step, located between the DNA and the drug. Botryodiplodin also inhibited the replication process. After incubation of cells in fresh medium, DPC repair was not associated with concomitant resumption of DNA replication ability. Immediately after botryodiplodin removal, inhibition of DNA synthesis was strengthened for a few hours before DNA replication recovered. Possible mechanisms involved in the DPC repair process are discussed.

Animals↗
PubMed1981

Effects of the mycotoxin botryodiplodin on mammalian cells in culture.

The effects of botryodiplodia, a mycotoxin synthesized by Botryodiplodia theobromae and by some strains of Penicillium roqueforti. The toxin inhibited cell multiplication in growing cultures at concentrations which were without toxic effect on cultures nearing or at confluence. In growing cultures the toxin affected DNA, RNA and protein synthesis, the effect on DNA synthesis being the greatest. The removal of mycotoxin from the culture medium brought about partial recovery of the synthetic activities of the cells. The implications of the results with respect of the recovery of DNA synthesis are discussed.

Animals↗
PubMed1977

Action of monovalent cations on the biological properties of PR toxin, a mycotoxin from Penicillium roqueforti.

PR toxin impairs liver cell metabolism by inhibiting RNA and protein synthesis. In vitro, the drug inhibits the transcription carried out by isolated rat liver nuclei and the translation promoted by polysomes. The action of monovalent cations on the biological activities of PR toxin has been studied. The increased ionic strength due to the presence of salt in the incubation medium, lowers the inhibitory action of PR toxin on in vitro transcription and translation activities; this action is reversible. Besides the overall effect of the ionic strength, ammonium salts possess a specific ability to suppress irreversibly the biological properties of PR toxin (in vivo toxicity and capacity of inhibiting RNA and protein synthesis). The mechanism of this action is discussed.

Ammonium Sulfate↗