Interaction between Raf and Myc oncogenes in transformation in vivo and in vitro

3611 MSV, a raf-oncogene-transducing murine retrovirus, induces fibrosarcomas and erythroid hyperplasia in newborn mice after a latency of 4-8 wk. In contrast, new recombinant murine retroviruses carrying the myc oncogene (J-3, J-5 construct viruses) do not induce tumors before greater than 9 wk. A combination of both oncogenes in an infectious murine retrovirus (J-2) induces hematopoietic neoplasms in addition to less prominent fibrosarcomas and pancreatic adenocarcinoma 1-3 wk after inoculation. The hematologic neoplasms consist of immunoblastic lymphomas of T and B cell lineage and erythroblastosis. If animals were inoculated with a variant of the J-3 virus, which induces altered foci in cultures of NIH 3T3 cells, carcinoma developed in the pancreas with a 2-6 mo latency. In parallel to the synergistic action of both oncogenes on hematopoietic cells in vivo, we find that raf-oncogene-induced transformation of bone marrow cells in culture is enhanced by the addition of myc, which by itself does not transform these cells when grown in standard media. We conclude that concomitant expression of raf and myc oncogenes in hematopoietic and epithelial cells alters their respective transforming activities. The contribution of v-myc in this synergism was examined by use of a series of recombinant murine retroviruses capable of expressing the avian v-myc to study the effect of altered myc expression on hematopoietic/lymphoid cells. With either interleukin 3- or interleukin 2-dependent cell lines, introduction of the recombinant viruses abrogated the requirement for IL 3 or IL 2 for growth, and associated with this was the suppression of c-myc expression. The findings suggest that myc is a component in the signal transduction pathway for IL 3 and IL 2 and support an autoregulatory mechanism of c-myc expression. In contrast to v-myc, expression of v-raf in primary lymphoid/hematopoietic cells has an immortalizing function without abrogating the requirement for IL 3 for growth. This suggests that v-raf and v-myc affect different components of growth regulation, as, for example, commitment (v-myc) and cell cycle progression (v-raf).

Isolation of three new avian sarcoma viruses: ASV 9, ASV 17, and ASV 25

The newly isolated avian sarcoma viruses, ASV 9, 17, and 25, cause fibrosarcomas in young chickens and induce foci of transformed cells in chick embryo fibroblast cultures. They are defective in replication and belong to envelope subgroup A. The sizes of their genomes are 6 kb (ASV 9), 5 kb (ASV 17), and 6 kb (ASV 25), respectively. All three contain long terminal repeat (LTR) and gag sequences but lack pol. env is absent from ASV 9 and ASV 25, but some env sequences are detectable in ASV 17. None of the defective viral genomes hybridized to selected onc probes representing src, fps, yes, myc, myb, and erb A. erb B appears absent from ASV 9 and ASV 17, but some hybridization between the erb B probe and the RNA of ASV 25 was detected. ASV 9 codes for a transformation-specific gag-linked protein of 130kDa. Multiple gag-linked transformation-specific proteins are seen in ASV 17 and 25; they require further study.

Avian leukosis virus-induced osteopetrosis is associated with the persistent synthesis of viral DNA

DNAs from 19 cases of avian leukosis virus-induced osteopetrosis have been analyzed for viral sequences. Among these were instances of rapid, intermediate, and slow onset osteopetrosis. The DNAs from osteopetrotic bone contained no evidence for osteopetrosis being caused by proviral insertions into or viral transductions of a host protooncogene. Instead, DNAs from osteopetrotic bone displayed evidence for osteopetrosis being associated with the persistent synthesis of viral DNA. Each of the 19 DNAs contained unintegrated as well as integrated viral DNA. Rapid onset osteopetrosis contained about 3X more viral and proviral DNA than intermediate or late onset osteopetrosis. Unintegrated viral DNA could not be detected in DNAs extracted from the bursa bone marrow of osteopetrotic chickens or in DNA extracted from the normal bones of an avian leukosis virus-infected chicken. Thus, the persistent synthesis of unintegrated viral DNA was observed in osteopetrotic but not normal tissues of avian leukosis virus-infected chickens.

The oncogene and its potential role in carcinogenesis

Cellular onc genes are a group of evolutionarily conserved sequences which are homologous to the transforming genes (v-onc) of oncogenic retroviruses. Although their functions in normal cells are largely not known, the sequence homology between viral and cellular onc genes is consistent with the idea that neoplastic transformation may, in some cases, be due to abnormal levels of cellular onc gene expression. Several models can be proposed for such a mechanism, including the insertion nearby of a viral promoter, alteration of the physiological promoter by a mutagenic agent, gene amplification, relocation in a transcriptionally active region of the genome as a consequence of chromosomal rearrangements and point mutations induced by external factors. Examples of these different mechanisms of onc gene activation can be found in animal and human tumors. Finally, the detail description of one cellular onc gene (c-sis), its relation to the viral gene and to a known cellular growth factor and its possible mode of activation in neoplastic transformation is presented.

Selection and rejection of retrovirus-expressing tumor cells from a heterogeneous murine leukemia virus-infected cell population

We studied the basis of tumor recurrence at sites of rejection of retrovirus-infected guinea pig fibrosarcoma cells. Tumor recurrences, in contrast to the parent tumor, lacked retroviral antigens and did not release infectious virus. When reinjected into syngeneic animals, cell lines derived from tumor recurrences grew progressively. Tumor recurrences could be infected with the homologous retrovirus. Tumor rejection and recurrence were modulated by host immunity. In guinea pigs immunized to virus-infected cells, tumor recurrences occurred earlier and in a higher proportion of animals than in nonimmune guinea pigs. In some immunosuppressed guinea pigs, retrovirus-infected tumor cells grew progressively. Progressively growing tumors of immunosuppressed guinea pigs contained large amounts of infectious virus and expressed viral antigens. To identify the source of tumor recurrences, the parent virus-infected tumor was cloned. Clones were heterogeneous in virus expression; some clones released large quantities of infectious virus; others did not. Two clones formed tumors in syngeneic animals. Injection of a virus producer clone into virus-immune animals was not followed by tumor recurrence. The data suggest that the reappearance of tumors at sites of injection of retrovirus-infected fibrosarcoma cells represents immune selection and rejection of retrovirus-expressing cells. Cells with the potential to form tumor recurrences existed in the parent virus-infected tumor population.

Two strains of avian sarcoma virus newly isolated from chick fibrosarcomas induced by lymphatic leukemia virus subgroup A in two lines of chickens

Two strains of avian sarcoma virus, designated S1 and S2, have been newly isolated from avian lymphatic leukemia virus (LLV) subgroup A [LLV(A)]-induced fibrosarcomas in 2 chickens from 2 White Leghorn flocks of lines 151 and BK. Each stock of S1 and S2 contained 2-3 X 10(3) focus-forming units of virus/ml and 10(6) tissue culture infective dose of LLV(A)/ml. The focus-forming titer of S1 and S2 estimated in chick embryo fibroblast cultures was almost consistent with that estimated by tumor (fibrosarcoma) formation in the chicks. All of the chicks bearing wingweb tumors (fibrosarcomas at the site of inoculation) had macroscopically neoplastic lesions (fibrosarcomas) in a number of visceral organs, such as the lung, liver, and spleen. Each stock of S1 and S2 was cloned by picking a single focus, and each focus was examined for the production of focus-forming virus and LLV. The results suggest that S1 and S2 are heterogenous stocks of sarcoma viruses that are replication-defective to various degrees. The low titer of focus-forming virus in the stocks of S1 and S2 was considered to be due to the small amounts of avian sarcoma virus that could be complemented by LLV.

European elk papillomavirus: characterization of the genome, induction of tumors in animals, and transformation in vitro

The European elk papillomavirus (EEPV) genome was cloned in the BamHI cleavage site of the pBR322 vector. The cloned genome was used for construction of a physical map, employing restriction endonucleases BamHI, BglII, HindIII, PvuII, SacI, and XhoI. The sequence homology between the EEPV and bovine papillomavirus type 1 genomes was elucidated by performing hybridizations in different concentrations of formamide. Sequence homology could only be revealed under less stringent conditions, i.e., Tm - 43 degrees C. Nucleotide sequence information was also collected from the regions which lie adjacent to the three HindIII sites that are present in the EEPV genome. The results made it possible to align the EEPV and bovine papillomavirus type 1 genomes. Transformation by EEPV was demonstrated with the C127 mouse cell line, and fibrosarcomas were induced in young hamsters after subcutaneous injection. The transformed cells and the tumors contain multiple, nonintegrated copies of the EEPV genome. Virus particles could not be detected either in tumors or in transformed cells.

[Scanning microscopy of hamster cells transformed by herpes simplex virus type 2]

Scanning microscopy was used to examine the features of morphology and attachment to a solid substrate of a transformed and tumor lines of hamster cells. These cell lines differed from normal hamster fibroblasts by changes in the mode of attachment and the degree of flattening on the solid substrate, relief of the cell surface and pattern of intercellular interactions. The observed morphological changes correlated with the degree of cell transformation.

Studies on the structure and organization of avian sarcoma proviruses in the rat XC cell line

The structure and arrangement of the multiple provirus copies of avian sarcoma virus in a rat XC cell line were studied by restriction endonucleases. The following observations were made: (i) the majority of the proviruses integrated randomly with respect to cell DNA; (ii) no gross deletions or rearrangements in the proviruses were observed; (iii) two types of proviruses (type I and type II) could be distinguished on the basis of restriction endonuclease cleavage sites; (iv) the virus rescued from these cells was derived from type II provirus, which has a novel EcoRI site between the env and pol genes; (v) most of the provirus units contained the src gene.

Inhibition of artificial and spontaneous lung metastases by preirradiation of abdomen--II. Target organ and mechanism

We have previously reported that irradiation of the abdomen of mice before i.v. injection of both immunogenic and nonimmunogenic tumour cells is capable of suppressing their ability to form metastatic lung nodules in a time and dose-dependent fashion. Experiments with segmental exposure indicated the target organ to be located in the ventral half of the abdomen. The effect has now been shown positively to depend upon irradiation of the caecum, and can be abolished either by shielding the caecum from irradiation or by surgically removing it prior to irradiation. Further experiments have shown that the effect cannot be elicited in germ-free mice and that its magnitude is markedly reduced in animals given gut-sterilizing antibiotics. Split-dose irradiation only slightly reduced the magnitude of suppression, provided both doses were given within the time window of effectiveness of single doses. Tumour-growth retardation was observed and spontaneous lung metastases were also suppressed when tumour-bearing mice received abdominal irradiation 7 days after tumour cell transplantation into the leg. However, abdominal irradiation did not significantly reduce subsequent tumour transplantability by the s.c. or i.p. routes. The experimental data are consistent with a mechanism by which transmigration of enteric bacteria across the radiation-damaged mucous membrane of the caecum effectively results in an endogenous infusion of endotoxin.

Modification of herpes 2-transformed cell-induced tumors in mice fed different sources of protein, fat and carbohydrate

The effects of different sources of protein (milk, soy, wheat, fish and beef), fat (corn oil and butter), and carbohydrate (dextrin and sucrose) on tumor development and on spleen characteristics were investigated in BALB/c mice injected subcutaneously with 5 X 10(5) herpes simplex virus Type 2-transformed cells (H238 cells). Low or high levels of protein and fat were used. Several weeks post-injection results indicated that a high level of fat significantly enhanced tumor incidence. A high fat level was also associated with a lower spleen weight and a smaller proportion of mature granulocytes in the spleen. Butter, compared to corn oil, significantly restricted tumor volume. Among the most highly significant findings was the low tumor incidence in mice fed protein from either a milk or a fish source.

Unintegrated viral DNA sequences in a hamster tumor induced by bovine papilloma virus

A fibrosarcoma was induced in a hamster by bovine papilloma virus type 2 (BPV2). The content of BPV2 DNA sequences was measured by DNA-DNA and cRNA-DNA hybridizations. The tumor contained approximately 300 BPV2 genome equivalents per cell. Southern blot hybridization indicated that the viral DNA was in free form, the entire genome most likely being present. In situ hybridization with BPV2 cRNA showed that multiple genome copies were present in each cell. Neither virus particles nor virus coat antigens could be detected in the tumor. A cell line was established from the fibrosarcoma, and the cells contained multiple copies of the BPV2 genome. The latter was in free form, and all of the DNA sequences appeared to be present in multiple copies and in all cells. An extensive search failed to reveal the presence of virus or viral antigens.

In vitro curing of persistent infection of HVJ (sendai virus) carrier tumor cells by spleen cells

The viral antigens of hamster tumor cells persistently infected with HVJ (Sendai virus) disappeared upon transplantation, showing that HVJ persistent infection can be cured in vivo. In order to analyze these phenomena, an attempt to achieve a similar cure in vitro was made. When HVJ carrier tumor cells (GM2-HVJpi) were cultured in the presence of sera from GM2-HVJpi- tumor-bearing hamsters or rabbit antiserum against glycoproteins (GP) of HVJ, the cells showed only weak stainability with fluorescent antibody (FA). Lymphokines produced by spleen cells from GM2-HVJpi-tumor bearers could not cause GM2-HVJpi cells to lose their viral antigens. However, the viral antigens of GM2-HVJpi cells became undetectable upon cocultivation with spleen cells from either normal of GM2-HVJpi tumor-bearing hamsters. These cells from which HVJ antigens had been lost were reconfirmed to be cured in vitro through single colony isolation and subsequent establishment of a new HVJ infection after superinfection of the isolated cells with HVJ. The above results indicate that the curing of virus persistent infections in HVJ carrier tumor cells by transplantation was due to the in vivo action of spleen cells against transplanted HVJ carrier tumor cells.

Curing of virus persistent infection in HVJ (sendai virus) carrier hamster tumor cells by transplantation

Transplantability of hamster tumor cells in the syngeneic system was considerably reduced by HVJ (Sendai virus) persistent infection of the cells, but these HVJ carrier cells still showed tumorigenicity, especially at high transplantation doses. Therefore, the existence of HVJ antigens or infectious HVJ in the tumors formed in vivo by transplanted HVJpi (temperature-sensitive HVJ) or HVJo (non-temperature-sensitive HVJ) carrier tumor cells was examined in relation to the reduced transplantability of the cells. In stamp preparations of tumors cells, no HVJ antigens were detected from 14 days after transplantation, though they were positive if observed within 7 days. Infections HVJ particles could also be recovered from tumor tissues which were cocultivated with LLCMK2 cells within 7 days after transplantation. However, tumor cells recultured in vitro after more than 3 weeks post transplantation did not show HVJ antigens, even after various attempts at HVJ induction such as culture at low temperature, serial passages in vitro, treatment with 5-iododeoxyuridine, etc. The cytopathic effects and fluorescent antibody staining of these cells became positive when they were superinfected with wild-type HVJ, indicating a new establishment of HVJ infection after the curing of the HVJ genome initially carried. In contrast, the original HVJ carrier tumor cells were demonstrated to be completely resistant to this superinfection (one of the characteristics of persistent infection). These results seem to show that HVJ persistence in its carrier tumor cells was ultimately cured by transplantation and may provide at least a partial explanation of why the xenogenization of tumor cell by HVJ persistent infection was relatively weak.

In vivo antigenic modification of tumor cells. I. Introduction of murine leukemia virus antigens on non-virus-producing murine sarcomas

Murine oncovirus antigens represent excellent targets for immune recognition, and virus-associated tumors are generally susceptible to various immunotherapy protocols. Virus-negative tumors, however, are nonimmunogenic and refractory to immunologic control. Therefore, the feasibility of the introduction of antigens onto non-virus-expressing tumors in situ in inbred C57BL/6J mice by systemic administration of nononcogenic murine retroviruses was investigated. Two classes of murine fibrosarcomas were studied: a 3-methylcholanthrene-induced fibrosarcoma syngeneic to C57BL/6 mice (MCA-FS) and a Harvey murine sarcoma virus-transformed, nonproducer fibrosarcoma syngeneic to C57BL/6 mice (H-NP). Both were found to be devoid of infectious ecotropic murine leukemia virus (MuLV) or MuLV antigens. A single dose of Friend murine leukemia virus (F-MuLV) was used to superinfect MCA-FS- and H-NP-induced tumors in vivo and converted these tumors to a highly productive, virus-positive state. In vivo superinfected tumors were indistinguishable from their preinfected counterparts by competition radioimmunoassays for the virion's major envelope glycoprotein, gp71, and its group-specific antigen, p30, and by assays for infectious virus. Analysis of virus from tumor extracts proved that the antigenic specificity of the superinfected tumor was provided by F-MuLV administered systemically to the animals. Finally, an immunoperoxidase technique, applied to tumor cross sections, demonstrated the uniform appearance of viral antigens in the superinfected tumors.

In vivo antigenic modification of tumor cells. II. Distribution of virus in sarcoma-bearing mice

Murine leukemia viruses were previously demonstrated to be able to infect efficiently non-virus-expressing tumors in vivo. In the present study the infectivity and tissue distribution of Friend murine leukemia virus (F-MuLV) in normal and tumor-bearing C57BL/6J (B6) mice were examined. Two syngeneic fibrosarcoma-inducing cell lines were used: Cells from a 3-methylcholanthrene-induced fibrosarcoma syngeneic to B6 mice (MCA-FS) and cells from a Harvey murine sarcoma virus-transformed, nonproducer sarcoma syngeneic to B6 mice (H-NP) were described in the preceding study. Both cell lines lacked ecotropic viral expression. F-MuLV produced in vitro was rarely able to infect normal adult B6 tissue in vivo and lacked pathogenic potential. Adult animals receiving F-MuLV remained clinically normal during 20 months of follow-up and had no detectable viremia, although some had persistently infected thymuses and long bones. In animals receiving a single dose of F-MuLV given to superinfect either the MCA-FS or the H-NP induced tumors, virion antigens were found only in tumor tissue and not in the normal host organs studied. Infectious virus was abundant in tumors; occasionally, it was found in thymuses and long bones of animals bearing superinfected H-NP tumors but rarely in other organs. Localization of F-MuLV in MCA-FS tumors appeared to be more selective with rare contamination of host organs. The presence of a rescuable sarcoma genome in H-NP may explain the discrepancy between MCA-FS and H-NP tumors. The possibility of increasing the efficiency and selectivity of infection as well as the therapeutic application of this technique are discussed.

Morphological study of virus-like particles in two transplantable tumours from BDX rats

Virus-like particles were found in two transplantable tumours, Sp56 and Sp6, from BDX rats. Sp56, a neurogenic sarcoma, contains abundant C-type particles in all stadia nof morphogeneis. This tumour reacts with anti-Friend leukaemia virus gp70 and anti-Rauscher leukaemia virus p30 sera. Sp6, a fibrosarcoma, has abundant virus-like particles in the cytoplasm, very often associated with centrioles or basal bodies of a cilium. These particles consist of two concentric shells with a diam. of 60 to 65 nm. Released particles were found outside the cell with a diam. of 85 to 100 nm characterized by an envelope and an eccentrically located electron-dense nucleoid, surrounded by an intermediate layer. These virus-like particles show no cross-reaction with antisera against murine C- or B-type particles, but show ultrastructural similarity with virus particles recently described in Chinese hamster cells and in mouse cell lines infected with two retrovirus isolates from South-East Asian mice.

Xenotropic virus expression and susceptibility to 3-methylcholanthrene-induced cancer

This paper reports the lack of genetic linkage between spontaneous production of substantial amounts of infectious xenotropic (X-tropic) virus and the susceptibility to chemically induced cancers in two inbred strains of mice, NZB/BLNJ and 129/J, and their genetic crosses. The parental strains and F1, backcross, and F2 progeny between these two strains were partially splenectomized to ascertain X-tropic viral status and were subsequently treated s.c. with 500 microgram of 3-methylcholanthrene in trioctanoin. Progeny from second backcrosses [(F1 X 129) X 129] were also tested for their X-tropic viral status and susceptibility to 3-methylcholanthrene carcinogenesis. Mice were observed for evidence of fibrosarcomas at the site of inoculation over a 10-month period. In this genetic system, spontaneous production of high titers of X-tropic virus segregated as a single autosomal dominant gene. Susceptibility to 3-methylcholanthrene-induced fibrosarcomas did not segregate in these crosses, and susceptibility did not correlate with the degree of X-tropic virus expression.