Characterization of a 7,12-dimethylbenz(α)anthracene-induced BALB/c mouse mammary tumor epithelial cell line

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Abstract
Characterization of numerous independently derived cell lines is necessary in order to establish reliable biological criteria applicable to transformed mammary epithelial cells. A mammary tumor cell line (DMBA-2/BALB) and clonal derivatives have been established from an adenocarcinoma induced in vivo in a BALB/c mouse by the administration of the chemical, 7,12-dimethylbenz(α)anthracene. The parental and clonal lines in vitro, as well as tumors derived from them in vivo, maintained an epithelial morphology at the light microscope level. Electron microscopic observations demonstrated the presence of desmosomes and numerous microtubules and microfilaments, but low levels of rough endoplasmic reticulum and Golgi apparatus. Growth characteristics were examined, including saturation density levels and colony-forming ability on plastic and in suspension. None of the in vitro growth parameters was found to correlate with the tumorigenicity of the lines in syngeneic mice or with their ability to produce C- or B-type virions by reverse transcriptase assay. Peroxidase/antiperoxidase (PAP) immunological staining failed to detect virus-specified antigens, MuMTV gp52, Rauscher MuLV gp69/71, or BALB virus-2 gp70, in the cells. Although epithelial in appearance, the parental cell line did not appear to be functionally differentiated in culture as evidenced by a very low level of casein messenger RNA. Passage of the parental cell line in vivo in a lactating mouse failed to activate virus expression, but a few cells in scattered focal areas in the tumor did synthesize casein detect-able by PAP staining.