Evolution of broad host range in retroviruses leads to cell death mediated by highly cytopathic variants.
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The ability of many retroviruses to cause disease can be correlated to their cytopathic effect (CPE) in tissue culture characterized by an acute period of cell death and viral DNA accumulation. Here, we show that mutants of a subgroup B avian retrovirus (Alpharetrovirus) cause a very dramatic CPE in certain susceptible avian cells that is coincident with elevated levels of apoptosis, as measured by nuclear morphology, and persistent viral DNA accumulation. These mutants also have a broadly extended host range that includes rodent, cat, dog, monkey, and human cells (31). Previously, we have shown that the mutants exhibit diminished resistance to superinfection. The results presented here have important implications for the process of evolution of retroviruses to use distinct cellular receptors. (+info)
Susceptibility of thymocytes for infection by chicken anemia virus is related to pre- and posthatching development.
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To investigate the age-dependent mechanism of susceptibility for chicken anemia virus (CAV) infection, we inoculated embryos and chickens of ages between day 9 of embryonic development and day 28 after hatching with CAV. Chicken embryos inoculated at days 9 and 11 of development showed no CAV-infected cells in the thymus, nor in other lymphoid organs. Many CAV-infected cells were detected in the thymic cortex of all chicken embryos inoculated at days 13 and 16 of development and of all chickens inoculated 1, 3, and 7 days after hatching. All embryos and chickens that contained CAV-infected cells in the thymus also contained CAV-infected cells in the bone marrow, but not in the bursa of Fabricius or the spleen. In chickens inoculated at days 14 and 21, only few CAV-infected cells were detected in the thymus, whereas these cells were not detected in thymi of 28-day-old inoculated chickens. Depletion of the thymic cortex was only detected in chickens inoculated from day 16 of embryonic development till day 21 after hatching. Only hematocrit values of the chickens inoculated 1 and 3 days after hatching were below normal. The rationale for the simultaneous susceptibility of cells of the T-cell lineage and cells of the erythrocyte lineage is discussed. As far as the thymus is concerned, the absence of clinical and microscopical signs of CAV infection in older chickens and the inability of CAV to infect embryos at days 9 and 11 of embryonic development may be caused by a lack of susceptible thymocytes.(ABSTRACT TRUNCATED AT 250 WORDS) (+info)
Immune response and resistance to Rous sarcoma virus challenge of chickens immunized with cell-associated glycoproteins provided with a recombinant avian leukosis virus.
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The Rous-associated virus 1 env gene, which encodes the envelope gp85 and gp37 glycoproteins, was isolated and inserted in place of the v-erbB oncogene into an avian erythroblastosis virus-based vector, carrying the neo resistance gene substituted for the v-erbA oncogene, to generate the pNEA recombinant vector. A helper-free virus stock of the pNEA vector was produced on an avian transcomplementing cell line and used to infect primary chicken embryo fibroblasts (CEFs) or quail QT6 cells. These infected cells, selected with G418 (CEF/NEA and QT6/NEA, respectively) were found to be resistant to superinfections with subgroup A retroviruses. The CEF/NEA preparations were used as a cell-associated antigen to inoculate adult chickens by the intravenous route compared with direct inoculations of NEA recombinant helper-free virus used as a cell-free antigen. Chickens injected with the cell-associated antigen (CEF/NEA) exhibited an immune response demonstrated by induction of high titers of neutralizing antibodies and were found to be protected against tumor production after Rous sarcoma virus A challenge. Conversely, no immune response and no protection against Rous sarcoma virus A challenge were observed in chickens directly inoculated with cell-free NEA recombinant virus or in sham-inoculated chickens. (+info)
Replication of reticuloendotheliosis viruses in cell culture: chronic infection.
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After an initial acute infection with cell killing, chicken or duck embryo fibroblasts infected in culture with reticuloendotheliosis viruses set up a chronic infection with no cell killing or morphological transformation. Essentially all of the chronically infected cells produced virus. The virus production was not sensitive to cytosine arabinoside or mitomycin C as was virus production in an acute infection. The chronically infected cells had a strong group-specific resistancto the c.p.e. of superinfecting reticuloendotheliosis viruses. However, they were sensitive to vesicular stomatitis virus and avian leukosis-sarcoma viruses. After double infection, single cells produced reticuloendotheliosis virus and avian leukosis-sarcoma virus. (+info)
Thyroid hormone receptor/and v-erbA. A single amino acid difference in the C-terminal region influences dominant negative activity and receptor dimer formation.
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Thyroid hormone receptors are cellular homologues (c-erbAs) of the v-erbA oncoprotein of the avian erythroblastosis virus. Exclusive of the viral gag region, v-erbA differs from the chick c-erbA-alpha receptor by two amino acid changes N-terminal of the DNA binding domain, two amino acid changes in the DNA binding domain, nine amino acid changes in the C-terminal region corresponding to the ligand binding domain of c-erbA, and a nine-amino acid deletion near the C terminus. v-erbA does not bind thyroid hormone and when expressed in cells inhibits the activity of wild-type thyroid hormone receptors. We reported previously that mutants of chick c-erbA/thyroid hormone receptor which lack the DNA binding domain (DBD-) inhibit transcriptional activition by wild-type thyroid hormone and retinoic acid receptors (Forman, B. M., Yang, C.-R., Au, M., Casanova, J., Ghysdael, J., and Samuels, H. H. (1989) Mol. Endocrinol. 3, 1610-1626). This dominant negative activity mapped to a series of hydrophobic heptad motifs which are conserved in the C terminus of these receptors and have been suggested to play a role in receptor dimerization. In this study we show that unlike DBD- c-erbA, DBD- v-erbA does not block receptor activity, suggesting that v-erbA acts by competing for DNA response elements rather than by formation of nonfunctional v-erbA/c-erbA heterodimers. This difference in activity was localized to a single Pro to Ser change in v-erbA just N-terminal of the last heptad motif. Introduction of this Pro to Ser change into DBD- c-erbA resulted in a protein which was inactive both functionally and in blocking receptor dimer formation in vitro. (+info)
Induction of differentiation of avian erythroblastosis virus-transformed erythroblasts by the protein kinase inhibitor H7: analysis of the transcription factor EF1.
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The protein kinase inhibitor H7 [1-5(isoquinolinesulfonyl-2-methylpiperazine)] together with a temperature shift to 42 degrees C was found to reproducibly and efficiently induce differentiation of avian erythroblasts transformed with the avian erythroblastosis virus containing v-erbA and a temperature-sensitive v-erbB oncogene. Although a temperature shift to 42 degrees C without H7 results in some elevation of globin transcripts, much higher levels of transcripts accrue when cells are incubated at 42 degrees C with H7; under such conditions, 50-70% of the cells become benzidine positive. In order to investigate the mechanism by which the differentiation occurs, we have characterized and analyzed the levels of the erythroid transcription factor EF1, originally described as a factor binding to the beta H-globin promoter. Protein sequencing of EF1 shows that it is identical to the factor Eryf1. Using a peptide antibody and DNA-binding assays, we demonstrate that EF1 is present at high levels in the nucleus of undifferentiated HD3 cells, and, although there may be a small change when the cells are shifted to 42 degrees C, incubation of the cells with H7 at 42 degrees C does not result in a further elevation commensurate with the high levels of globin transcripts. It is concluded that v-erbA and v-erbB do not repress differentiation by limiting the levels of EF1. (+info)
Dissecting the activating mutations in v-erbB of avian erythroblastosis virus strain R.
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The v-erbB oncogene isolated from the R (or ES4) strain of avian erythroblastosis virus is capable of inducing erythroleukemia and fibrosarcomas. This oncogene differs from the proto-oncogene c-erbB, the avian homolog of the epidermal growth factor receptor, by its lack of an intact ligand-binding domain as well as additional alterations in its cytoplasmic coding sequences. By contrast, the insertionally activated c-erbB, a variant oncogene, which encodes a product that also lacks the ligand-binding domain but is otherwise unaltered in its cytoplasmic coding sequences, is capable of inducing leukemia but cannot induce sarcomas. In this report, we show that the critical changes for activating the sarcomagenic potential displayed by v-erbB R are two point mutations within the tyrosine kinase domain and an internal deletion of 21 amino acids in the carboxyl-terminal regulatory domain. The removal of the carboxyl-terminal autophosphorylation sites is not obligatory. These activating mutations (Arg-263 to His, Ile-384 to Ser, and the deletion of residues 494 to 514), when introduced singly into the insertionally activated c-erbB, all dramatically increase fibroblast-transforming potential. Arg-263 resides near the highly conserved HRD motif of the kinase domain, and its mutation to His increases the autophosphorylation activity. The other two mutations do not alter the intrinsic kinase activity and presumably affect other aspects of the receptor involved in growth signaling. Therefore, the high transforming potential of v-erbB R is a consequence of synergism among multiple activating mutations. (+info)
Genetic susceptibility of chicken times quail hybrid embryos to avian RNA tumour viruses.
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An attempt was made to hybridize the chicken (Gallus domesticus) male with Japanese quail (Coturnix coturnix japonica) female in order to study the genetic susceptibility of hybrid embryos to avian RNA tumour viruses of subgroups, A, B, D and E. In the hybrids the results supported the prevailing concept that susceptibility is dominant over resistance regardless of the dominant trait contributed by either parent. It was also observed that the Ie gene of the chicken was unable to suppress the 'quail-coded' susceptibility to subgroup E virus in the hybrid system, suggesting the lack of penetrance of the Ie gene. Despite the fact that some hybrids were resistant to viruses of subgroups B and D, they were susceptible to subgroup E virus, which was not expected on the basis of the concept that subgroup B-resistant cells cannot be E-susceptible. Also, the hybrids were susceptible to E virus regardless of gs antigen expression and presence of the Ie gene in the genome. This indicates that our earlier suggestion that the Ie gene is another expression of the gs antigen-determining gene is inconsistent. (+info)