Expression of an 86-kilodalton glycoprotein in an idiopathic mammary adenocarcinoma of a BALB/c mouse.

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Abstract
An epithelial cell line (BALB/c-ST) was established from a mammary adenocarcinoma that developed spontaneously in a 20 mo. old BALB/c mouse. Like uninfected normal tissues, the cell line was found to contain 3 endogenous murine mammary tumor virus (MuMTV) proviruses, but MuMTV particles and antigens were not detected. The cultured cells, after being inoculated s.c., 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. Evidently, the expression of gp86 in the mammary cells of BALB/c mice is a consequence of neoplastic transformation and MuMTV infection modulates its expression.