Effect of estriol, estriol-3-sulfate and estriol-17-sulfate on progesterone and estrogen receptors of MCF-7 human breast cancer cells.

The levels of progesterone receptors (PR [cytosol (Cy) and nuclear (N)] and estrogen receptors (ER) [cytosol and nuclear; occupied and unoccupied specific binding sites] were evaluated in the MCF-7 cancer cell line incubated with estriol (E3), estriol-3-sulfate (E3-3-S) or estriol-17-sulfate (E3-17-S) for 7 days in culture. Cells were grown in MEM medium containing 2 mM glutamine, 10% v/v dialysed calf serum and penicillin-streptomycin (100 U/ml) in the absence (control) or in the presence of 5 X 10(-8) M E3, E3-3-S or E3-17-S. The total PR (Cy + N) concentration which was 0.47 +/- 0.10 (SE) pmol/mg DNA in the non-treated cells, increased to 1.95 +/- 0.48 in the E3 and to 1.55 +/- 0.26 in the E3-3-S treated cells. No effect (PR: 0.47 +/- 0.15 pmol/mg DNA) was observed with the E3-17-S treatment. Total ER (Cy + N, occupied + unoccupied binding sites) in pmol/mg DNA +/- SE, were as follows: control 0.79 +/- 0.17; + E3: 0.33 +/- 0.09; +E3-3-S: 0.90 +/- 0.18 and +E3-17-S: 1.82 +/- 0.58. The measurement by radioimmunoassay of unconjugated estriol in the culture medium indicated that after incubation with E3-3-S, a fraction (0.5-1%) of the sulfate was hydrolyzed but no hydrolysis was observed in the incubations with E3-17-S. It is concluded that in the MCF-7 human mammary cancer cell line E3 and E3-3-S stimulate PR very significantly, but it is suggested that E3-3-S acts through the hydrolyzed E3. On the other hand, E3-17-S is inactive because it is not hydrolyzed. Consequently, E3-3-S can play an important role in the biological responses of this mammary cancer cell line.