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Characteristics of normal rat mammary epithelial cells and N-ethyl-N-nitrosourea-induced mammary adenocarcinoma cells grown in culture.

The characteristics of normal mammary epithelial cells derived from Lewis and Sprague-Dawley rats and N-Ethyl-N-Nitrosourea (ENU)-induced mammary gland adenocarcinoma cells derived from Sprague-Dawley (CD) and Fisher (CDF) rats and grown in culture were compared. After collagenase treatment, the rat mammary epithelial cell aggregates were placed in a hormone-supplemented medium. The normal mammary epithelial cells (NE) attached to the surface of the dish within 50 hours, whereas the mammary adenocarcinoma cells (MA) attached within 24 hours and grew as cell multilayers. After the colonies of NE and MA cells became confluent, the culture system entered a steady state in which the cells from the upper layer were shed into the medium. The rate of proliferation and squame detachment in confluent cultures was increased by the presence of epidermal growth factor (EGF). Rhodanile blue staining and transmission electron microscopy showed that the shed cells were partially keratinized. In addition, cultured MA (but not normal) cells were able to grow in soft agar and form tumors when inoculated into appropriate hosts. The opposite was true in each case for the mammary adenocarcinoma cells. Karyotypes of normal and neoplastic rat epithelial cells revealed a hypodiploid modal number of chromosomes.