Hormone-responsive genes of the mouse mammary tumor virus.

By optimal hormonal treatment the production of exogenously transmitted MMTV can be stimulated in vitro to different degrees, depending on cultivation conditions and origin of tumor cells. Moreover, after appropriate hormonal treatment, endogenous MMTV-Y can be rescued from primary cell cultures derived from dimethyl benzanthracene- and hormone-induced C57BL/10 mouse mammary adenocarcinoma, as determined by reverse transcriptase assay, distribution of 3H-uridine-labelled viral particles, immunofluorescence, and electron microscopy. On the contrary, all attempts to rescue MMTV-Y from cultures derived from urethane-induced C57BL/10 tumors failed. These data indicate that upon syncarcinogenic action of non-viral carcinogenes, estrogen and prolactin, the MMTV-Y genome can be expressed in mammary gland parenchymatous cells, which in turn may result in cell transformation. The full MMTV-Y gene expression occur after appropriate hormonal stimulation of the C57BL/10 mammary cancer cells in vitro.