Isolation of two syngeneic cell lines from a rat mammary carcinoma: growth factor production by neoplastic epithelial cells.

Two distinctly different clonal cell lines were isolated from a mammary tumor induced by ingestion of 7,12-dimethylbenz[a]anthracene (CAS: 57-97-6) in a SD rat. Cells of one of the clones, RMT-1 clone E4, showed typical epithelial characters; it was concluded that they were derived from neoplastic mammary epithelial cells. The other clone, M2, exhibited characters consistent with its derivation from the normal mammary myoepithelial component. The 2 cell lines had different proliferative responses to growth factors (GF) such as cholera toxin, dexamethasone, and epidermal GF. The epithelioid E4 cells were found to produce potent growth-promoting activity in culture medium that stimulated proliferation of myoepithelial M2 cells as well as that of stromal fibroblasts. The present work provides supporting evidence that the mechanism of "paracrine stimulation" is operative in the mammary tumorigenesis of the rat.