The tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate elevates serum progesterone levels

Down regulation of c-myc, c-fos and erb-B during estrogen induced proliferation of the chick oviduct

Oncogenes c-myc, H-ras, c-fos and erb-B were constitutively expressed in immature chick oviduct withdrawn from estrogen administration for 2.5 weeks after 10 d of primary estrogen stimulation. Following secondary estrogen stimulation of the withdrawn chicks, synthesis of egg white proteins is rapidly induced and remaining non-functioning tubular gland cells are stimulated to proliferate with a doubling time of 24 h. During first 12 h of secondary estrogen stimulation, H-ras mRNA levels doubled and did not increase further at 24 h and 48 h. The steady state levels of c-myc, erb-B and c-fos mRNA decreased 24 h following secondary estrogen stimulation. The levels of these oncogene RNAs in oviduct were similar at 48 h following secondary estrogen stimulation to those from immature chicks administered 10 d of primary estrogen stimulation. Thus elevated expression of c-myc and c-fos mRNA does not appear to be necessary components for sustained estrogen induced cell proliferation in the chick oviduct.

Failure of tumor promoter 12-O-tetradecanoylphorbol-13-acetate to displace estradiol from its specific receptor

A permanent cell line derived from rat endometrium which contains a specific, low capacity, high affinity estrogen binding protein in cytosol and nuclear fractions (estrogen receptor) is available. Extracts of cells from this line did not appreciably bind the tumor promoter, 12-0-tetradecanoylphorbol-13-acetate. The result suggests that the action of the promoter does not involve translocation to the cell nucleus via binding to the specific estrogen receptor.