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PubMedDate not supplied

Differential effects of phorbol ester on tumor cells induced by avian sarcoma virus.

Avian sarcoma virus-induced tumors usually grow progressively for several weeks and then regress. We have injected phorbol myristate acetate (PMA) directly into tumors in an effort to stimulate neoplastic growth. The results show instead that PMA exerted an inhibitory effect in this regard and, in fact, caused an acceleration of tumor regression. At the same time, treatment of cultured avian sarcoma cells with PMA resulted in greatly diminished levels of the kinase activity associated with the src gene product, pp60src. PMA-treated tumor cells from regressing sarcomas were, however, stimulated to express viral antigens at their surface and produced more progeny virus than did untreated tumor cells.

Animals↗
PubMed1984

Characterization of two strains of avian sarcoma virus isolated from avian lymphatic leukosis virus-induced sarcomas.

Two replication-defective avian sarcoma viruses, S1 and S2, which were independently isolated from tumors of chickens inoculated with avian lymphatic leukosis virus (LLV) were characterized. The genomes of S1 and S2 contain src-related sequences and are, respectively, about 3.9 and 4.5 kilobases long. pp60src-related proteins with molecular weights of 62,000 (p62) were detected in cells infected with these viruses, and protein kinase activity was found to be associated with these proteins. No other viral proteins, such as gag, pol, and env gene products, were detected. These results suggested that the c-src sequence in normal chicken cells was incorporated into LLV genomes by recombination at the expense of most of the viral genes to generate highly defective new sarcoma viruses.

Alpharetrovirus↗
PubMed1984

Molecular cloning and characterization of avian sarcoma virus UR2 and comparison of its transforming sequence with those of other avian sarcoma viruses.

Avian sarcoma virus UR2 and its associated helper virus, UR2AV , were molecularly cloned into lambda gtWES X lambda B by using unintegrated viral DNAs. One UR2 and several UR2AV clones were obtained. The UR2 DNA was subsequently cloned into pBR322. Both UR2 and UR2AV DNAs were tested for their biological activity by transfection onto chicken embryo fibroblasts. When cotransfected with UR2AV DNA, UR2 DNA was able to induce transformation of chicken embryo fibroblasts with a morphology similar to that of parental UR2 . UR2 -specific protein with kinase activity and UR2 -specific RNA were detected in the transfected cells. Transforming virus, UR2 ( UR2AV ), was produced from the doubly transfected cells. Five of the six UR2AV clones tested were also shown to be biologically active. The insert of the UR2 DNA clone is 3.4 kilobases in length and contains two copies of the long terminal repeat. Detailed restriction mapping showed that UR2 DNA shared with UR2AV DNA 0.8 kilobases of 5' sequence, including a portion of 5' gag, and 1.4 kilobases of 3' sequence, including a portion of 3' env. The UR2 transforming sequence, ros, is ca. 1.2 kilobases. No significant homology was found between v-ros and the conserved regions of v-src, v-yes, or v- abl . By contrast, a significant homology was found between v-ros and v-fps. The v-fps-related sequence was mapped within a 300-base-pair sequence in the middle of ros.

Animals↗
PubMed1992

Wounding acts as a tumor promoter in chickens inoculated with avian sarcoma virus 17.

Avian sarcoma virus 17 (ASV17) is an acutely transforming retrovirus which carries the oncogene v-jun. The virus induces fibrosarcomas in chickens at the site of inoculation. Here we describe wound-related tumor formation in 77% of chickens inoculated with ASV17 in one wing and wounded by metal clip insertion in the opposite wing. Tumors from both wound-related and inoculation-related sites were histologically diagnosed as fibrosarcomas. Tissues cultured from both tumor sites produced infectious virus in culture and expressed high levels of the v-Jun oncoprotein detectable by immunofluorescent staining. By varying the time of wounding relative to virus inoculation we defined the early stages of wound healing (2-7 days postinoculation) as favoring wound-related tumor formation. Three other acutely transforming retroviruses containing oncogenes coding for nonreceptor protein tyrosine kinases (v-src, v-yes, and v-fps), inoculated in the same manner, induced wound-related tumors in all cases. We conclude that in chickens, ASV17 collaborates with wound healing to promote tumorigenesis by a process which may relate either to a biochemical function of Jun or to a more general, shared characteristic of transforming retroviruses.

Animals↗
PubMed1996

Influence of the transduced 3'UTR of the c-src oncogene on tumour growth induced by the v-src gene of avian sarcoma virus PR2257.

Avian sarcoma virus PR2257 contains 952 bp transduced from the left part of the 3'UTR of the chicken c-src oncogene. Deletion mutants were constructed to determine the effect of the 3'UTR on tumorigenicity in vivo and in vitro. In the presence of the 3'UTR, tumours were 3.4 times larger in vivo, and tumorigenicity was increased 2.5-fold in vitro. Several regulatory submotifs were also found within the 3'UTR. Parts of the 3'UTR were cloned into the LTR CAT plasmid and analysed for CAT expression. A 170 bp element was found to be responsible for the enhanced expression of the CAT gene. These results demonstrate the effect of the transduced 3'UTR sequence during long-term interaction between PR2257 virus and the chicken genome, and suggest a novel regulatory mechanism of the src oncogene.

Animals↗
PubMed1994

Origin and evolution of the c-src-transducing avian sarcoma virus PR2257.

Avian sarcoma virus PR2257 transduced de novo the c-src gene and about 900 bp of 3' non-coding sequences belonging to the src locus. This virus contains only one mutation in the c-src coding sequence causing a reading frame shift after Pro-525. The molecular clone studied was derived from a cell line of transformed quail fibroblasts, C7. It contains endogenous virus (ev) derived sequences in the U5 and 3' non-coding regions, indicating that multiple recombination occurred with endogenous virus. Here we investigated the possible evolution of PR2257 when the original tumour was repeatedly passaged in vivo. After 16 passages a new virus, designated PR2257/16, appeared with a tenfold higher titre. The sequence of PR2257/16 was determined and showed that PR2257/16 resulted from recombination of PR2257 with the env gene of the helper virus (td daPR-C). This recombination expanded the env gene content in PR2257/16 and, in addition, five point mutations occurred in its genome. Because we thought that an endogenous virus might be involved in the mechanism of c-src transduction, we also reinvestigated the presence of ev sequences in PR2257 proviruses from several early passages of the original tumour. We found that in contrast with the first isolate from the C7 cell line, the provirus in these tumours did not contain such sequences. These results do not support the hypothesis that endogenous sequences were involved in the transduction process.

Animals↗
PubMed1980

Effect of glucosamine on phenotype mixing of vesicular stomatitis virus with avian sarcoma virus.

The effect of glucosamine on phenotypic mixing between vesicular stomatitis virus (VSV) and avian sarcoma virus (ASV) was studied. Phenotypic mixing decreased with increase in glucosamine concentration, and, in the presence of 20 mM glucosamine, was no longer detectable. In the presence of 20 mM glucosamine, cells still produced 10(2)--10(3) focus forming units (FFU) of ASV and 10(6) plaque forming units (PFU) of VSV per milliliter. These results suggest that cells producing a relatively large amount of ASV (more than 10(3) FFU/ml) are essential for phenotypic mixing of VSV with ASV.

Animals↗
PubMed1980

Towards a molecular description of cell transformation by avian sarcoma virus.

The avian sarcoma virus transforming gene product has been identified and partially purified from extracts of transformed cells. It is a phosphoprotein with a relative molecular mass of 60 000 (pp60src) with two major sites of phosphorylation. pp60src appears to be a cyclic-AMP-independent protein kinase as judged by protein phosphorylation with partly purified fractions. The specificity of the phosphorylation observed was judged by inhibition with anti-pp60src IgG but not by normal IgG and by the fact that the protein kinase activity isolated from ts transformation-mutant infected cells was more thermolabile than that from wild-type transformed cells, thus showing more directly the origin of the enzymic activity. A cellular protein substrate of pp60src has been identified as a 34 000 molecular mass protein. These data together suggest that protein phosphorylation by pp60src may be a function of the molecule that plays a major role in transformation.

Alpharetrovirus↗
PubMed1983

Antigenic and structural studies on the transforming proteins of Rous sarcoma virus and Yamaguchi 73 avian sarcoma virus.

A widely cross reactive antiserum raised against denatured pp60v-src, the transforming protein encoded by Rous sarcoma virus, was used to test antigenic relationships with the transforming gene products encoded by other avian sarcoma viruses. The results showed that P90gag-yes, the transforming protein of a representative of Class III avian sarcoma viruses, is antigenically related to pp60v-src. Tryptic phosphopeptide analysis of P90gag-yes revealed two phosphotyrosine-containing peptides and one phosphoserine-containing peptide. One of the phosphotyrosine-containing peptides comigrated with the phosphotyrosine-containing tryptic peptide from pp60v-src.

Antigens, Viral↗
PubMed1980

Double transformation of Indian muntjac cells by avian and murine sarcoma viruses.

Avian sarcoma virus-transformed Indian muntjac cells, SR-Mm-1, formed foci by murine sarcoma-xenotropic murine leukemia virus complex [MSV(X-MuLV)] superinfection. The response of SR-Mm-1 and parental normal Indian muntjac Mm-2K cells to MSV(X-MuLV) infection was compared. Focus formation by MSV(X-MuLV) followed two-hit kinetics in Mm-2K, but one-hit kinetics in SR-Mm-1 cells. MSV(X-MuLV)-infected SR-Mm-1 cells formed larger colonies than uninfected SR-Mm-1 cells in soft agar, while no colony was formed in the MSV(X-MuLV)-infected Mm-2K cells. After infection with MSV(X-MuLV), cell clones doubly transformed by avian and murine sarcoma viruses could be established in SR-Mm-1 cells, whereas no cell clone could be established in Mm-2K cells. The doubly transformed cells were more round and refractile than SR-Mm-1 cells. No specific chromosomal change could be detected among Mm-2K, SR-Mm-1, and the doubly transformed cells. By two-dimensional polyacrylamide gel electrophoresis of cellular proteins, several changes were seen between Mm-2K and SR-Mm-1 cells. In MSV(X-MuLV)-infected Mm-2K and SR-Mm-1 cells, several similar changes in polypeptide patterns were seen as compared with uninfected cells. These results indicate that Mm-2K cells were doubly transformed by avian and murine sarcoma viruses, and MSV transformation in SR-Mm-1 cells was different from that in Mm-2K cells.

Animals↗
PubMed1984

Identification of the viral sequence required for the generation of recovered avian sarcoma viruses and characterization of a series of replication-defective recovered avian sarcoma viruses.

The ability of transformation-defective deletion mutants of Schmidt-Ruppin Rous sarcoma virus to induce tumors and generate recovered sarcoma viruses (rASVs) was correlated with the partial src sequences retained in the transformation-defective viral genomes. Since all the transformation-defective viruses that were capable of generating rASVs retained a portion of the 3' src sequence, regardless of the extent of the 5' src deletion, and those lacking the 3' src were unable to generate rASVs, it appears that the 3', but most likely not the 5', src sequence retained in the transformation-defective viral genome is essential for rASV formation. However, rASVs derived from a particular mutant, td109, which retained a portion of the 3' src sequence, but lacked most (if not all) of the 5' src sequence, were all found to be defective in replication. Analyses of the genomic sequences of 13 isolates of td109-derived rASVs revealed that they contained various deletions in viral envelope (env), polymerase (pol), and structural protein (gag) genes. Ten isolates of rASVs contained env deletions. One isolate (rASV3812) contained a deletion of env and the 3' half of pol, and one isolate (rASV398) contained a deletion of env and pol. The one with the most extensive deletion (rASV374) had a deletion from the p12-coding sequence through pol and env. In addition, the 5' src region of td109-derived rASVs were heterogeneous. Among the 7 isolates analyzed in detail, one isolate of rASV had a small deletion of the 5' src sequence, whereas three other isolates contained extra new sequences upstream from src. Both env- and env- pol- rASVs were capable of directing the synthesis of precursor and mature gag proteins in the infected nonproducer cells. We attribute the deletions in the replication-defective rASVs to the possibility that the 5' recombination site between the td109 and c-src sequence, involved regions of only partial homology due to lack of sufficient 5' src sequence in the td109 genome for homologous recombination. A model of recombination between the viral genome and the c-src sequence is proposed to account for the requirement of the 3' src sequence and the basis for the generation of deletions in td109-derived rASVs.

Animals↗
PubMed1980

Reverse transcriptase as the major determinant for selective packaging of tRNA's into Avian sarcoma virus particles.

Mutants of avian sarcoma virus which lack a functional DNA polymerase were found to be nonselective in the incorporation of host cell tRNA's into virus particles. In contrast, mutants which possess a functional DNA polymerase but lack the viral genome RNA contained a specific subset of the host cell tRNA population, indistinguishable from that of the wild-type virus. Thus the reverse transcriptase, and not the viral RNA, is probably the major factor determining which tRNA's are incorporated into avian sarcoma virus particles. Supporting evidence was obtained in an in vitro binding assay between purified reverse transcriptase and unfractionated cellular tRNA's. However, the subset of tRNA's which associated with the genome in the 70S complex was determined primarily by the viral RNA. In the absence of DNA polymerase, the 70S RNA complex in mature virus particles contained the normal complement of associated tRNA's with the exception of tRNATrp, the primer for RNA-directed DNA synthesis.

Alpharetrovirus↗
PubMed1975

Ethidium bromide inhibits appearance of closed circular viral DNA and integration of virus-specific DNA in duck cells infected by avian sarcoma virus.

The DNA of avian sarcoma virus assumes a closed circular configuration before integration into the host cell chromosomal DNA. Ethidium bromide reduces the formation of superhelical viral DNA and concurrently blocks integration of the viral genome. Inhibition of integration of viral DNA results in the inhibition of virus replication.

Alpharetrovirus↗
PubMed1981

Comparison between the viral transforming gene (src) of recovered avian sarcoma virus and its cellular homolog.

Recovered avian sarcoma viruses are recombinants between transformation-defective mutants of Rous sarcoma virus and the chicken cellular gene homologous to the src gene of Rous sarcoma virus. We have constructed and analyzed molecular clones of viral deoxyribonucleic acid from recovered avian sarcoma virus and its transformation-competent progenitor, the Schmidt-Ruppin A strain of Rous sarcoma virus. A 2.0-megadalton EcoRI fragment containing the entire src gene from each of these clones was subcloned and characterized. These fragments were also used as probes to isolate recombinant phage clones containing the cellular counterpart of the viral src gene, termed cellular src, from a lambda library of chicken deoxyribonucleic acid. The structure of cellular src was analyzed by restriction endonuclease mapping and electron microscopy. Restriction endonuclease mapping revealed extensive similarity between the src regions of Rous sarcoma virus and recovered avian sarcoma virus, but striking differences between the viral src's and cellular src. Electron microscopic analysis of heteroduplexes between recovered virus src and cellular src revealed a 1.8-kilobase region of homology. In the cellular gene, the homologous region was interrupted by seven nonhomologous regions which we interpret to be intervening sequences. We estimate the minimum length of cellular src to be about 7.2 kilobases. These findings have implications concerning the mechanism of formation of recovered virus src and possibly other cell-derived retrovirus transforming genes.

Alpharetrovirus↗
PubMed1981

Viral and cellular src genes contribute to the structure of recovered avian sarcoma virus transforming protein.

Recovered avian sarcoma viruses (rASVs) were obtained from tumors induced by certain transformation-defective (td) mutants of Schmidt-Ruppin strain Rous sarcoma virus of subgroup A (SR-A). The genomes of these td SR-A mutants lack most but not all of the src gene. rASV genomes, however, possess intact src genes, which are largely derived from cellular genetic information, presumably an endogenous cellular gene called c-src, which shares considerable homology with the viral src. To further define the genetic origin of rASV src, we examined by tryptic peptide analysis the product of this gene, pp60src, from rASV and SR-A, as well as the normal cellular homolog pp60c-src. We found peptides unique to each putative "parental" protein present together in maps of rASV p60src, demonstrating that the endogenous cellular c-src gene itself contributes to the structure of rASV pp60src. Certain isolates of rASV encode pp60srcS of altered apparent molecular weight. In these cases, the variation in structure was located in the amino-terminal portion of the protein. That such polymorphism can be tolerated suggests that this region of the protein is less critical to the ability of these agents to transform cells.

Amino Acids↗
PubMed1985

Variation in susceptibility to avian sarcoma viruses and expression of endogenous avian leukosis virus antigens in specific pathogen-free chicken lines.

Five lines of chickens maintained as specific pathogen-free flocks in Australia were characterized in relation to endogenous antigens and endogenous avian leukosis virus expression. Embryos of line N were predominantly of C/E phenotype, uniformly positive for group-specific antigen and chick helper factor (gs+chf+) and 38% expressed endogenous virus at a very low titre. Embryos of line M4 were uniformly of C/ABE phenotype and were either gs+chf+ or gs-chf+. Line W19 embryos segregated for susceptibility to viruses of subgroup A, B and D and were either of C/E or C/ABE phenotype. The majority of W19 embryos were gs+chf+ with a small proportion being gs+chf-. Line I13 embryos were either of C/0 or C/ABE phenotype, uniformly gs-chf- and 44% of embryos expressed endogenous virus at a low titre. Line S segregated for susceptibility to subgroup E virus and embryos were either of C/E or C/0 phenotype, while the majority of embryos from line S were gs-chf- with some embryos being gs+chf+ or gs-chf+. The degree of interference of gs+chf+ and gs-chf+ phenotypes with subgroup E virus infection was identical with the interference patterns of classical gs+chf+ and gs-chf+ phenotypes. The resistance to infection with avian sarcoma viruses of subgroups E in lines N and M4, and to a degree in line W19, was highly associated with the presence of chf. Resistance to subgroup E virus was independent of chf in lines S and I13, probably being under the control of an independent locus. Cellular restriction of endogenous virus replication existed in all subgroup E virus-susceptible cells of line I13 in contrast to cells of line S which supported replication of endogenous virus. The phenotype of chicken cells for the expression of endogenous gs antigen and chf could accurately be predicted from the test performed on whole blood cells.

Animals↗