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G Fourel

Publications and source records attributed to G Fourel.

25 records · Page 2Linked to original sources
PubMed1990

Frequent activation of N-myc genes by hepadnavirus insertion in woodchuck liver tumours.

The recent finding of c-myc activation by insertion of woodchuck hepatitis virus DNA in two independent hepatocellular carcinoma has given support to the hypothesis that integration of hepatitis B viruses into the host genome, observed in most human and woodchuck liver tumours, might contribute to oncogenesis. We report here high frequency of woodchuck hepatitis virus DNA integrations in two newly identified N-myc genes: N-myc1, the homologue of known mammalian N-myc genes, and N-myc2, an intronless 'complementary DNA gene' or 'retroposon' that has retained extensive coding and transforming homology with N-myc. N-myc2 is totally silent in normal liver, but is overexpressed without genetic rearrangements in most liver tumours. Moreover, viral integrations occur within either N-myc1 or N-myc2 in about 20% of the tumours, giving rise to chimaeric messenger RNAs in which the 3' untranslated region of N-myc was replaced by woodchuck hepatitis virus sequences encompassing the viral enhancer. Insertion sites were clustered in a short sequence of the third exon that coincides with a retroviral integration hotspot within the murine N-myc gene, recently described in T-cell lymphomas induced by murine leukaemia virus. Thus, comparable mechanisms, leading to deregulated expression of N-myc genes, may operate in the development of tumours induced either by hepatitis virus or by nonacute retroviruses in rodents. Activation of myc genes by insertion of hepadnavirus DNA now emerges as a common event in the genesis of woodchuck hepatocellular carcinoma.

Amino Acid Sequence↗
PubMed1990

Integration of hepatitis virus DNA near c-myc in woodchuck hepatocellular carcinoma.

A total of 33 hepatocellular carcinomas, induced in woodchucks by chronic infection with woodchuck hepatitis virus (WHV), a virus closely related to the human hepatitis B virus, were analyzed for the state of viral DNA, the expression of viral genes and of different cellular proto-oncogenes. Low levels of viral replication and presence of integrated viral forms including sequences of the enhancer element, appeared as a general rule in these tumors. Enhanced expression of one or more of the nuclear protooncogenes: c-myc, N-myc, c-fos, c-jun and jun-B was frequently observed. In two hepatomas, elevated expression and allelic alterations of c-myc were subsequent to integration of WHV DNA near the c-myc coding domain. The viral strategy for insertional activation of c-myc in these tumors appeared basically identical to that of mammalian retroviruses in T-cell lymphomas of mice and rats. Whether insertional mutagenesis of different oncogenes may be more generally linked to liver oncogenesis induced by WHV and hepatitis B viruses remains to be determined.

Animals↗
PubMed1989

Evidence for direct regulation of diphtheria toxin gene transcription by an Fe2+-dependent DNA-binding repressor, DtoxR, in Corynebacterium diphtheriae.

Previous studies provided indirect evidence that in Corynebacterium diphtheriae regulation of diphtheria toxin gene (tox) transcription by iron is mediated by a bacterial repressor. By performing in vitro protein-DNA binding experiments, we establish that a corynebacterial Fe2+-sensitive protein, named DtoxR, can bind to a palindromic motif present in the tox promoter region. Binding of this factor prevents the interaction of the transcription initiation machinery with presumptive critical promoter elements, providing evidence that DtoxR is responsible for the repression of toxinogenesis observed in iron-containing growth medium.

Binding, Competitive↗
PubMed1988

Sp1, a CAAT-binding factor, and the adenovirus major late promoter transcription factor interact with functional regions of the gamma-fibrinogen promoter.

To study the factors which influence the coordinately and developmentally regulated expression of the three adjacent fibrinogen genes, we have defined the functional regions of the gamma-fibrinogen promoter and the proteins which bind to them. Using a series of 5' and internal deletion mutations, we found that sequences between 88 and 43 base pairs (bp) upstream of the gamma-fibrinogen transcription initiation site functioned in cis to direct properly initiated mRNA accumulation in transfected hepatocytes. The efficient function of these sequences was highly distance dependent, since transcriptional activity decreased by 92% when they were moved 32 bp upstream of the TATA box. We demonstrated that two known and one putative transcriptional factors interacted with this 47-bp sequence. The transcription factor Sp1 interacted with sequences between -51 and -46 as demonstrated by protection from DNase I digestion with the purified protein. Directly adjacent to the Sp1 site, between nucleotides -66 and -53, there was a sequence which bound a CAAT-binding factor. Finally, sequences just 5' to the CAAT factor-binding site interacted with the adenovirus major late transcriptional factor as previously demonstrated. Internal deletion mutations which disrupt these interactions diminished the activity of the promoter in vivo. One consequence of the interaction of these proteins is that a bend is placed in the DNA at or near their sites of interaction.

Base Sequence↗
PubMed1987

Interaction of a liver-specific nuclear factor with the fibrinogen and alpha 1-antitrypsin promoters.

The orderly and sequential activation of genes during development is hypothesized to be related to the selective expression of groups of regulatory proteins acting primarily at the level of transcription. A nuclear protein was found in hepatocytes, but not other cell types, that binds to a sequence required for hepatocyte-specific transcription of the gene for the beta chain of fibrinogen. This protein, hepatocyte nuclear factor 1 (HNF1), also interacts with homologous sequences required for optimal promoter function of the genes for the alpha chain of fibrinogen and alpha 1-antitrypsin. The promoter or enhancer regions for several viral and cellular genes not expressed in the liver did not compete for this binding. The restricted expression of HNF1 and its selective interaction with the control regions of several liver-specific genes indicate that it is involved in developmentally regulated gene expression in the liver.

Albumins↗