Nuclear [3H]4-hydroxytamoxifen (4-OHTAM)- and [3H]estradiol (E2)-estrogen receptor complexes in the MCF-7 breast cancer and GH3 pituitary tumor cell lines.

Nuclear [3H]4-OHTAM-ER complexes extracted by 0.6 M KCl from the MCF-7 human breast cancer and the GH3 rat pituitary tumor cell lines, sedimented as a 5S form on sucrose gradients after 1 to 24 h exposure to ligand (20 nM). The nuclear [3H]4-OHTAM-ER from MCF-7 cells increased from 2 +/- 0.2 pmoles/mg DNA at 1 h to approximately 4 +/- 0.1 pmoles/mg DNA at 6 and 24 h. In the GH3 cells the nuclear binding of [3H]4-OHTAM increased rapidly, and there was no significant difference in the receptor levels at 1 and 6 h (10 +/- 1.3 and 8.9 +/- 1.1 pmoles/mg DNA, respectively). At 24 h there was a decrease in [3H]4-OHTAM-ER levels (7.0 +/- 0.2 pmoles/mg DNA); however, this was due primarily to an increase in DNA synthesis, which occurred in these cells by 24 h. It appears that in both cell lines there is no processing of nuclear [3H]4-OHTAM-ER, and it is not associated with changes in sedimentation coefficient of the complex. When both cell lines were incubated with [3H]E2 (20 nM), processing of the nuclear [3H]E2-ER occurred over 6 h. In the MCF-7 cells there was a decrease in receptor content within 6 h from 3.2 +/- 0.2 to 0.9 +/- 0.2 pmoles/mg DNA. The nuclear [3H]E2-ER in the GH3 cells decreased from 7.3 +/- 0.5 to 2.8 +/- 0.3 pmoles/mg DNA. Although these cell lines appeared to process the [3H]E2-ER complex, the nuclear forms of [3H]E2-ER were different.(ABSTRACT TRUNCATED AT 250 WORDS)