Purification and Characterization of New Mammary Cell Growth Factor from Rat Pituitary Tumors : Preliminary Report.

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Normal rat mammary epithelial cell line was established from continuous cultures of rat mammary cells in chemically defined medium. These cells were shown to be mammary epithelial origin by in vivo transplantation assay, electron microscopic examination and immunocytochemical analysis. Using these mammary cells as target cells, in vitro bioassay system for the detection of the mitogenic activity on mammary cells was developed.Four rat pituitary cell lines, derived from mammotropic pituitary tumors (MtT-F4, MtT-F84), and radiation induced somatomammotropic pituitary tumors (PT1,PT3), were also established in chemically defined medium. As the results of in vitro analysis of mitogenic activity of conditioned medium from established pituitary cell cultures, conditioned medium from PT3 was shown to have strong growth-promoting effects on mammary cells. cc152 cells, isolated from PT3, were found to have unique growth characteristics that cc152 cells could proliferate in the chemically defined medium supplemented with insslin and hydrocortisone without any other growth-promoting factors. Furthermore, cc152-c3 cells derived from cc152 were able to proliferate in the chemically defined medium supplemented with hydrocortisone alone. Conditioned medium from cc152-c3 cells stimulated the growth of their own cells. The growth-stimulating effects of hydrocortisone on cc152 and cc152-c3 cells was inhibited by the addition of a glucocorticoid receptor antagonist, RV486. RV486 also blocked hydrocortisone-induced growth-stimulating effects of conditioned medium. These results indicated that stimulation of cc152-c3 cells with hydrocortisone resulted in secretion of an autocrine growth factor (s).A preliminary characterization of the growth factor (s) in the conditioned medium suggested that growth factor (s) was a polypeptide. Experiments are being carried out to purify and further characterize the glucocorticoid-induced growth factor (s).