Characterization of rat mammary tumor cell populations.

Nodules of tumor cells have been isolated from 7, 12-dimethylbenz (alpha)anthracene-induced rat mammary tumors. These nodules consist of at least two cell populations which can be subfractionated by selective attachment in calcium-free medium. One cell population which attaches in the absence of calcium (basal cells) stains intensively with antibodies against type IV collagen and also with antibodies against keratin. The nonattaching population, the epithelial cells, stains much more weakly with either antibody. Biochemical analyses indicate that 27% of the protein labeled in basal cell culture is type IV collagen, while 8% is keratin. With epithelial cells, only 0.35% of the protein made is collagen, and only 2.4% is keratin. Basal cells contain about 2 times as much calmodulin as epithelial cells but only about one-tenth as many estrogen receptors. In culture, the basal cells stimulate the attachment and/or division of the epithelial cell population. The epithelial cells have little effect on the division or attachment of the basal cells. Interaction between the two cell populations may be important for tumor growth in vivo.