RESUMO
An epithelial cell line (BALB/c-ST) was established from a mammary adenocarcinoma that developed spontaneously in a 20-month-old BALB/c mouse. Like uninfected normal tissues, the cell line was found to contain three endogeneous murine mammary tumor virus (MuMTV) proviruses, but MuMTV particles and antigens were not detected. The cultured cells, after being inoculated subcutaneously, produced tumors in syngeneic mice, and sera from a high percentage of the tumor-bearing mice specifically immunoprecipitated an 86-kilodalton antigen from the extracts of BALB/c-ST cells. This antigen was found to be glycosylated, but whether or not it was exposed to the cell surface could not be demonstrated by cell-surface iodination and immunoprecipitation studies. The 86-kilodalton antigen, a glycoprotein designated gp86, was not detected in immunoprecipitates from extracts of normal mammary cells or from the extracts of GR, C3H, and BALB/cfC3H mammary tumor cells. After being infected in vitro with RIII-derived MuMTV but not with C3H-derived MuMTV, the BALB/c-ST cells appeared to undergo a phenotypic change in that they did not produce tumors in syngeneic mice, and the expression of gp86 was inhibited. Our results indicate that the expression of gp86 in the mammary cells of BALB/c mice is a consequence of neoplastic transformation and that MuMTV infection modulates its expression.