The 3' untranslated region of the chicken c-src protooncogene modulates gene expression.

Tight regulation of the Src tyrosine kinase activity is essential for a variety of cellular processes, namely transitions of the cell cycle. The peaks of Src activity are dependent on its posttranslational modifications as well as on the regulation of gene expression. The 3'UTRs of mRNAs are often crucial for rapid changes of the protein level. The chicken c-src 3'UTR effects on gene expression have been explored. The c-src 3'UTR decreased the in vivo tumorigenic potential of the src-activated mutants in chickens. This corresponds with the finding that the c-src 3'UTR reduced the Src protein and src mRNA levels and luciferase activity in vitro. Our results suggest that the chicken c-src 3'UTR plays a role in the negative control of gene expression, either transcriptionally or posttranscriptionally.

DNA vaccination against v-src oncogene-induced tumours in congenic chickens.

DNA vaccination is particularly efficient for induction of cytotoxic T-lymphocyte (CTL) response. In our experiments, we used MHC(B) congenic chicken lines CB and CC (regressors and progressors of v-src-induced tumours, respectively) and a mutated, non-oncogenic v-src gene construct as the DNA vaccine. A high degree of vaccine protection against oncogenic v-src challenge was achieved in the CB line chickens. CTL response was demonstrated in vitro and by adoptive transfer of immune cells to the syngeneic host and to the CC line chickens rendered tolerant to CB cells. In the CC line chickens we observed tumour growth retardation after a low-dose DNA vaccination administered to immature recipients while higher amounts of DNA vaccine in immunocompetent chickens exerted an enhancing effect.

Proviral load and expression of avian leukosis viruses of subgroup C in long-term persistently infected heterologous hosts (ducks).

Proviral DNA load and expression of avian leukosis viruses of subgroup C (ALV-C) in ducks infected in mid embryogenesis were studied using quantitative PCR, RT-PCR, in situ hybridization employing ALV-specific riboprobe, and immunohistochemistry. A group of long-term surviving, non-reviremic ducks was selected for the study and compared to control reviremic animals in order to obtain information about persisting retroviruses in different duck tissues. A widespread distribution of proviruses in the tested tissues was found, but the proviral load was significantly lower in non-reviremic in comparison to reviremic animals. The only exception were brain and blood cells, in which no significant difference in the quantity of integrated proviruses was found between both categories of ducks, thus indicating an exceptional position of the brain and blood cells among all tested tissues. Contrary to reviremic, the proviruses were not transcribed in non-reviremic ducks, with the exception of brain and thymus. In the majority of non-reviremic ducks viral RNA was revealed in the brain, but no infectious virus could be recovered from this tissue. The opposite situation was observed in the thymus, where infectious virus was recovered but viral RNA remained below the detection limit of the assay. As revealed by in situ analysis, infected cells were either disseminated or focally distributed in tissues. From the long-term follow up of ALV-C in intraembryonally infected ducks we conclude that this model is suitable for the study of retrovirus persistence accompained both by the presence and absence of reviremias. The possible consequences of transmission and long-term persistence of retroviruses in the heterologous host for retroviral evolution are discussed.

Inhibition of the rous sarcoma virus long terminal repeat-driven transcription by in vitro methylation: different sensitivity in permissive chicken cells versus mammalian cells.

Rous sarcoma virus (RSV) enhancer sequences in the long terminal repeat (LTR) have previously been shown to be sensitive to CpG methylation. We report further that the high density methylation of the RSV LTR-driven chloramphenicol acetyltransferase reporter is needed for full transcriptional inhibition in chicken embryo fibroblasts and for suppression of tumorigenicity of the RSV proviral DNA in chickens. In nonpermissive mammalian cells, however, the low density methylation is sufficient for full inhibition. The time course of inhibition differs strikingly in avian and mammalian cells: although immediately inhibited in mammalian cells, the methylated RSV LTR-driven reporter is fully inhibited with a significant delay after transfection in avian cells. Moreover, transcriptional inhibition can be overridden by transfection with a high dose of the methylated reporter plasmid in chicken cells but not in hamster cells. The LTR, v-src, LTR proviral DNA is easily capable of inducing sarcomas in chickens but not in hamsters. In contrast, Moloney murine leukemia virus LTR-driven v-src induces sarcomas in hamsters with high incidence. Therefore, the repression of integrated RSV proviruses in rodent cells is directed against the LTR.

Frequent detection of reviraemia in ducks persistently infected with avian leukosis retroviruses.

Ducks intraembryonally infected with avian leukosis viruses of subgroup C (ALV-C) were followed for a long period (up to 6.8 years), and the viraemia and production of virus-neutralizing antibodies were measured. In three independent experiments comprising ducks inoculated with uncloned and/or molecularly cloned ALV-C, we found that after the elimination of primary post-hatching viraemia, reviraemia could be detected in 60-70% of infected animals. Based on the course of viraemia, the individual ducks were assigned to four different groups: Group I (no reviraemia), Group II (one transient reviraemic period), Group III (one persistent reviraemic period), Group IV (fluctuating reviraemia). In comparison to sera from ducks included in Group I and/or II, a significant decrease in neutralizing activity of sera from animals comprised in Group III and/or IV was observed. Two out of four reviraemic viruses were not neutralized by antiserum against ALV-C, instead their infectivity was enhanced. Long-term follow-up of the cell-associated virus revealed that its rescuability by cocultivation with chicken embryo fibroblasts fluctuated in about 50% of animals. In the reviraemic phase of infection, integrated proviruses could be detected by Southern blotting in a majority of tissues examined. Our data document that many features recognized in lentiviruses are valid also for oncoviruses transmitted to heterologous hosts and substantiate further the suitability of ALV-C-infected ducks as a model for studying persistent retroviral infection.

Persistence of O6-guanine DNA adducts in styrene-exposed lamination workers determined by 32P-postlabelling.

A modified 32P-postlabelling method was used for the detection of styrene-specific DNA adducts in lamination workers. The persistence of O6-styrene DNA adducts was studied in DNA from lymphocytes and granulocytes of an exposed and a control group. We compared O6-adduct levels obtained from a sampling prior to vacation, after 2 weeks of vacation and after an additional 1 month of work. In granulocytes, there was no significant difference in adduct levels between the control and the exposed groups in any individual samplings. In lymphocytes of laminators the detected adduct levels were significantly higher (5.4 adducts/10(8) nucleotides) than those in the controls (1.0 adduct/10(8) nucleotides). The 2 week interruption of exposure did not influence the total O6-adduct level (4.9 adducts/10(8) nucleotides in the first sampling versus 5.1 adducts/10(8) nucleotides in the second), indicating very slow removal of the specific O6-styrene adducts from DNA.