The immunopathology of SV40-induced transformation

Induction of simian virus 40 transplantation immunity in hamsters by gel-purified SV40 large T antigen

Simian virus 40 (SV40) large T antigen and p53 cellular protein were isolated from an SV40-transformed hamster cell line by immunoprecipitation with anti-T sera and purified by sodium dodecyl sulfate-gel electrophoresis. These two protein were tested in hamsters for the presence of SV40 transplantation rejection antigenic sites by in vivo transplantation rejection assay. The large T antigen immunized the hamsters against a challenge of SV40 tumor cells and the protected animals generated cytotoxic spleen cells. Hamsters immunized with the p53 cellular protein were not protected against SV40-induced tumor but there was some delay in the appearance of tumor.

The transformation-related protein p53 is not bound to the SV40 T antigen in BALB 3T12 cells expressing T antigen

In most murine cells transformed by the SV40 virus, virtually all of the cellular phosphoprotein p53 is in a complex with the SV40 T antigen. Here, we report that, in SV40-infected T-antigen-positive Balb 3T12 mouse cells, most (approximately 80%) of the p53 is not in complex. Complex formation was determined by measuring the amounts of [35S]methionine-labeled p53 which coprecipitated with T antigen when using monoclonal antibody to T antigen. The amount of complex formation was expressed as a percentage of total p53 present, measured by the amount of p53 precipitated with the monoclonal antibody to the p53. The values were confirmed by Western blotting procedure, in which the steady-state levels of the proteins were measured. In these measurements after complete precipitation with antibody to T antigen, the residual p53 in the supernatant was precipitated by antibody to p53, and this amount was denoted as free p53. There was no significant difference seen between the [35S]methionine-labeled tryptic peptides of complexed and the free p53 (or between complexed and free T antigens) as determined by two-dimensional gel electrophoresis and chromatography. Virus rescue experiments and retransformation by the rescued virus showed that there was no mutation in the SV40 DNA coding for the T antigen which could account for the lack of complex formation. Both p53 and T antigen were underphosphorylated in cells which exhibited reduced complex formation. Tumorigenicity in syngeneic mice and anchorage-independent cell growth in culture of various cloned mouse cells with or without T antigen expression was compared. The changes in the biologic properties were explainable solely on the basis of known or expected effects of expression of the T antigen and were independent of complex formation or of absence of complex formation between p53 and T antigen.

Cell lines derived from tumors induced in syngeneic rats by FR 3T3 SV40 transformants no longer synthesize the early viral proteins

Several SV40-transformed FR 3T3 rat cell lines formed tumors upon inoculation to syngeneic immunocompetent Fisher rats. These tumors, which appeared only after a long latency period, showed a fast rate of growth. Tumor-derived (TD) cell lines were established in culture from several tumors induced by independent transformants, and their properties were analyzed. Though TD cells were highly tumorigenic, their level of transformation in culture was similar to that of the original transformants. They did not synthesize detectable amounts of the two early viral gene products, the large-T and small-T polypeptides. However, the transformation-associated cellular p53 protein was detected in all of them by [35S]methionine labeling and immune precipitation with monoclonal antibodies directed against the mouse p53. Growth in the animal apparently counterselected the cells expressing the early viral proteins, and hence, possibly, the tumor-specific transplantation antigen. This selection was mediated at least in part by the T-cell immune response, as the tumors induced by the same transformants in nu/nu mice still expressed the nuclear T-antigen. Absence of expression of the early viral region was frequently correlated with the loss of the integrated SV40 DNA. Some tumors, however, still contained early viral DNA sequences, which were, in even fewer cases, transcribed into RNA. These results altogether suggest that tumor formation by the FR 3T3-SV40 transformed cells in immunocompetent rats requires two events, the selection for the acquisition of a high tumorigenic potential, and against the expression of the early viral genes. Only the first of these two events was observed upon tumor formation in nude mice.