Inflammation is responsible for the development of wound-induced tumors in chickens infected with Rous sarcoma virus

When newly hatched chicks are given injections of Rous sarcoma virus, a tumor develops at the site of injection. In spite of the presence of the virus in the blood, no other tumors are found distant from the site of inoculation during the life span of the animal (4-6 weeks). However, if a wound is made away from the primary tumor, a tumor develops at the site of wounding. Work in our laboratory showed previously that these wound tumors do not develop as a result of metastasis, therefore, factors released upon wounding must contribute to the development of the wound tumors. In particular, we showed that transforming growth factor (TGF) beta, a growth factor implicated in wound healing, can replace wounding in tumor development. However, we also showed that epidermal growth factor and TGF-alpha, growth factors that also have roles in wound healing, do not induce tumors. To identify the critical event(s) and to determine the mechanism involved in wound tumor development, we have continued these studies. Here we show that: (a) wound tumor development correlates with the presence of circulating virus and inflammation; (b) the virus is present in serum and in heterophils of the peripheral blood; (c) cell division at the site of wounding precedes the expression of viral proteins; (d) in addition to TGF-beta, acidic and basic fibroblast growth factors can also replace wounding in tumor development; (e) these three factors (TGF-beta, acidic fibroblast growth factor, basic fibroblast growth factor) which promote tumors also induce inflammation, whereas epidermal growth factor and TGF-alpha do not; and (f) during the inflammatory response, blood vessel leakage occurs as tested by the release of fibrinogen into the tissues. To test the possibility that inflammation is the key element in the development of these wound tumors, we used beta-methylprednisolone, an antiinflammatory drug that inhibits inflammation (including blood vessel leakage), to determine if wound tumor development could be prevented. We found that when inflammation was inhibited, tumors were also inhibited; when inflammation could not be stopped, tumors developed as before. These results indicate that the effect of wounding on the development of wound tumors in Rous sarcoma virus-infected chicks is accomplished through the cytokines released by the inflammatory cells at the site of wounding. These inflammatory mediators play a critical role in providing the conducive environment for oncogene integration and activation, and subsequent development of tumors.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Restricted clonality of visceral sarcomas in avian sarcoma virus-infected chickens

Experiments were undertaken to analyze proviral DNA in primary (wing web) and visceral sarcomas arising in FP chickens infected with BH-RSV(RAV-2). Using the degree of heterogeneity of BH-RSV proviral integration sites as a measure of the degree of polyclonality of sarcoma tissue, we observed that a high proportion of the visceral sarcomas examined comprised dominant clones, independently of whether these sarcomas were isolated from immune-suppressed or nonsuppressed infected chickens; by contrast, a marked heterogeneity of BH-RSV proviral integration sites was noted with primary sarcoma tissue. Several visceral sarcomas containing dominant clones were characterized by the integration of a deleted form of the BH-RSV provirus. In addition, all of the primary and visceral sarcomas exhibited sequences specific for the RAV-2 provirus, and both types of sarcoma tissue were competent for infectious sarcoma virus production.

Wounding and its role in RSV-mediated tumor formation

Tumors induced in chickens by Rous sarcoma virus remain localized at the site of injection even though the animals become viremic. Tumors have now been shown to be inducible at other sites if a wound is inflicted or if the tissue is injured by administration of tumor promoters. These findings indicate that local wounding plays a role in the spread of tumorigenicity of Rous sarcoma virus.

Ablation of humoral immunity in 15I5 x 72 chickens is not predisposing to the formation of subgroup G virus-induced distal sarcomas

Clone (cl.) 85 infection of 15I5 x 72 chickens at 4 weeks posthatch results in a lower frequency of distal sarcomas than does Prague (Pr)-B infection. As higher titers of virus-neutralizing antibody are generated in the cl.85-infected chickens, the possibility was addressed in the present study that the low frequency of cl.85-induced distal sarcomas is a direct consequence of the strong neutralizing response. Our observations indicate that ablation of humoral immunity by embryonic bursectomy does not serve to increase this frequency, implying that the antiviral humoral response is not required to limit formation of cl.85-induced distal sarcomas.

[Generation of highly oncogenic retroviruses]

Modifications of cellular oncogenes during the steps of the generation of acutely oncogenic viruses were discussed.

Induction of murine tumors in adult mice by a combination of either avian sarcoma virus or human adenovirus and syngeneic mouse embryo cells

Primary murine Rous sarcoma was produced in adult mice of seven strains, C57BL/6, DBA/2, BALB/c, C3H/He, CBAJ, AKR, and DDD, by s.c. inoculation of a mixture of 5 X 10(6) chicken tumor cells containing Schmidt-Ruppin Rous sarcoma virus and 9- to 12-day-old mouse embryo cells (MEC) (2 X 10(6) ) of the syngeneic strain. The sarcoma developed at the site of injection in almost all mice tested, but there were some differences in the latent period and the survival time among mouse strains. When the number of cells inoculated was reduced to 5 X 10(4) for chicken tumor cells induced by the Schmidt-Ruppin strain of Rous sarcoma virus (SR-CTC) and 2 X 10(4) for MEC, no tumor was produced in C3H/He mice. These tumors had strain specificity and the Schmidt-Ruppin strain of Rous sarcoma virus genome in masked form. The tumor at the site of injection originated in the embryo cells injected along with SR-CTC. This was confirmed by CBAT6/T6 marker chromosome analysis of the tumor cells of CBA mice induced with SR-CTC plus CBAT6/T6 MEC and also confirmed by transplantation of a C57BL/6 X C3H/He F1 tumor which had been induced with SR-CTC plus C3H/He or C57BL/6 MEC. Tumor induction in adult mouse by a mixture of virus and syngeneic 9- to 14-day-old embryo cells was tested for human adenovirus serotype 12 (Ad12) and simian virus 40. Primary Ad12 tumor was also induced in adult CBA, C3H/He, and DDD mice by 4 X 10(5 to 6) 50% tissue culture infective dose of Ad12 with 5 X 10(6) syngeneic embryo cells. This tumor contained Ad12 T-antigen-positive particles in cells. But in the case of simian virus 40, the tumor did not appear for about 300 days of observation.

Role of 3'-end of viral genome in tumor heteroinduction by the avian sarcoma virus

Transformation defective virus was derived by restriction endonuclease cleavage from a clone of the avian sarcoma virus Schmidt-Ruppin strain, strongly oncogenic for rats. The transfection experiments of chicken cells by digested proviral DNA gave rise to transformation defective virus. The td virus was possible to recover in vivo in chickens. The tumors obtained after a long latent period contained the sarcoma virus which was able to transform chicken cells in vitro and to induce tumors in chickens. All viruses, parental, td- and recovered were of D subgroup specificity. The tumor induction experiments in rats have shown that the recovery of viral genome deletion in td mutant by cellular sequences was not enough to regain the oncogenicity for rats. The results stressed the importance of 3-end sequences of the virus genome, probably the sequences in C region for heteroinduction ability of the avian sarcoma virus.

[Schmidt Ruppin-D-ASV-induced primary rat brain tumor model for therapeutic screening]

It is important to evaluate the therapeutic and side effects of new therapy for malignant brain tumors in an adequate animal model prior to its initial clinical investigation. For decades, neurooncologists have argued for the use of primary, autochthonous tumors rather than transplanted tumors such as C 6 glioma cells and 9 L gliosarcoma cells. But unfortunately, no spontaneous animal astrocytomas are currently available as usable models. So we tried to establish the model of primary, autochthonous avian sarcoma virus-induced rat gliomas for experimental chemotherapy and immunotherapy. The present study was undertaken to determine the incidence and histologic pattern of tumors and the mean survival time of the animal model used. It was found that the intracerebral inoculation of 2 X 10(6) FFU/5 microliter of infectious cell free homogeneous subgroup D Schmidt-Ruppin avian sarcoma virus (SR-D-ASV) into 3-day-old inbred Fischer 344 rats induced small sized tumors in all rats 20 days later. The mean survival time of inoculated rats were 58.7 +/- 12 days. As to the classification of SR-D-ASV induced brain tumors in Fischer rats, astrocytoma was 70.6% (protoplasmic astrocytoma 23.5%, fibrillary astrocytoma 47.1%), sarcoma 17.6%, and mixed astrocytoma and sarcoma 11.8%. In conclusion, this SR-D-ASV induced tumor in the rat fulfilled the following criteria for the desirable animal model: (1) Spontaneously arising. (2) Glial origin. (3) Intraparenchymal growth. (4) Uniformly fatal within reasonable time period. Statistic evaluation of the effects of chemotherapy and immunotherapy was considered to be possible.

Changes in amino-terminal sequences of pp60src lead to decreased membrane association and decreased in vivo tumorigenicity

We have suggested previously that the amino-terminal 8 kilodaltons of pp60src may serve as a structural hydrophobic domain through which pp60src attaches to plasma membranes. Two isolates of recovered avian sarcoma viruses (rASVs), 1702 and 157, encode pp60src proteins that have alterations in this amino-terminal region. The rASV 1702 src protein (56 kilodaltons) and the 157 src protein (62.5 kilodaltons) show altered membrane association, and fractionate largely as soluble, cytoplasmic proteins in aqueous buffers, ion contrast with the membrane association of more than 80% of the src protein of standard avian sarcoma virus under the identical fractionation procedure. Plasma membranes purified from cells transformed by these rASVs contain less than 10% of the amount of pp60src found in membranes purified from cells transformed by Rous sarcoma virus or control rASVs. The altered membrane association of these src proteins had little or no effect on the properties of chick embryo fibroblasts transformed in monolayer culture. In contrast, rASV 1702 showed reduced in vivo tumorigenicity compared with Rous sarcoma virus or with other rASVs that encode membrane-associated src proteins. Rous sarcoma virus-induced tumors are malignant, poorly differentiated sarcomas that are lethal to their hosts. rASV 1702 induces a benign, differentiated sarcoma that regresses and is not lethal to its hosts. These data support the role of amino-terminal sequences in the membrane association of pp60src, and suggest that the amino terminus of pp60src may have a critical role in the promotion of in vivo tumorigenicity.

Increased growth of Rous sarcomas in chickens pretreated with formalinized syngeneic tumor cells

The effect of inoculating formalinized syngeneic or allogeneic Rous sarcoma cells on the growth of Rous sarcoma virus (RSV)-induced tumors in two related inbred strains of chickens was studied. Chickens from both strains that received three weakly inoculations of syngeneic tumor cells had a significant increase in tumor growth and mortality after subsequent challenge with RSV. Development of RSV-induced tumors in chickens pretreated with formalinized allogeneic tumor cells (i.e. incompatible for major histocompatibility complex (MHC) antigens) was similar to what we observed in nonpretreated control chickens. The finding that the tumor-host relationship is altered only in chickens pretreated with formalinized syngeneic RSV-transformed cells, suggests that tumor-associated antigens of Rous sarcomas are modified MHC antigens analogous to "altered self" antigens thought to be present on certain virus-infected cells. If this hypothesis is correct, the results we obtained with formalin-killed syngeneic tumor cells can be explained on the basis of three possible mechanisms: immunological enhancement, immune tolerance or induction of antibody to anti-tumor idiotype. The merits of each mechanism in accounting for the results are discussed.

The infectivity of fluid from regressing Rous sarcomas

Fluid was withdrawn from the site of regressing Rous sarcomas in chickens and inoculated into the wing-webs of untreated chickens from three strains of chickens with divergent degrees of resistance to Rous sarcomas. The transfer of fluid initiated progressive tumors in all three strains of chickens. The infectivity of the fluid was apparently due to tumor cells and not to virus.

Variation in susceptibility of chick embryo tissues to infection with Rous sarcoma virus in vitro

Second-generation whole chick embryo cultures were compared with second-generation limb bud, somite, and kidney cultures of various ages in their ability to support Rous Sarcoma virus infection. Limb bud cells yielded the highest proportion of infected cells and kidney cells the lowest 48 hours after infection in vitro. Cultures prepared from 9-day embryos were more susceptible to infection than those from younger or older embryos. When tissues from 9-day embryos were used for the in vitro assay of three strains of Rous Sarcoma virus, limb bud cells yielded slightly higher focus counts in each case than whole embryo, approximately 0.5 log higher than somite and approximately 2.0 logs higher than kidney cells. Limb bud cultures also showed less tendency to clump and foci were more easily counted than in cultures from the other tissues.

The induction of the Rous sarcoma in heterologous transplants of virus-infected adult chicken tissue

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