Transcriptional activation of the c-myc oncogene in the T-47D mammary cancer cells by conditioned media from embryonic mouse fibroblasts (BALB/c-3T3). Effect of the antiestrogen ICI 164,384.

The effects of the conditioned medium (CM) of embryonic mouse fibroblast (BALB/c-3T3) cells (clone A31) on the mRNA of the c-myc oncogene of the hormone-dependent T-47D mammary cancer cells were explored. After 6h incubation a significant stimulation of c-myc expression was observed with a 10% v/v concentration of CM, and the effect was even higher using a CM concentration of 30% v/v. It is suggested that this action of CM could be related to the stimulatory effect on proliferation and DNA synthesis induced by the CM, as was recently demonstrated for the T-47D cells. It was also observed that the antiestrogen ICI 164,384 (5 x 10(-6) M) can inhibit the stimulatory action of CM on c-myc expression. It is concluded that the fibroblast mouse embryonic cells contain and secrete factor(s) involved in the mechanism of proliferation of human hormone-dependent mammary cancer cells.