Distribution of progesterone receptors between the cytosol and nuclear fraction in normal and neoplastic human endometrium.

The progesterone receptor (PR) content was determined in the cytosol and in the nuclear fraction in 28 cases of endometrial adenocarcinoma after in vitro incubation of tissue slices in the presence of progesterone. In 17 instances besides the malignant, nontransformed tissue from the same uterus was taken for analysis. The level of PR was estimated by Scatchard plot analysis or by one-point assay, whenever not enough tissue was available. The distribution of PR between the cytosol and the nuclear fraction was studied. Positive correlation between the concentrations of total and of nuclear progesterone binding sites was found in all samples of nontransformed tissue whereas in cancerous tissue this was true only in about 40% of cases. In about 60% of neoplastic tissue samples the PR were namely found predominantly in the cytosol. Since we observe that in many malignant endometria the PR are poorly transferred from the cytoplasm to the nucleus even under optimal conditions for in vitro activation/translocation, we conclude that in these cases the action of progesterone is for some reason altered either at the level of receptor activation or at the level of translocation of the hormone-receptor complex from the cytoplasm to the nucleus.