Some properties of cytosolic progesterone and estrogen receptors in human breast tumor

Abstract

The study on progesterone receptor (PgR) in 120 human breast tumor specimens from the patients subjected to mastectomy in 6 hospitals and the National Cancer Institute in Bangkok was performed by the dextran-coated charcoal method (DCC). It was found that 95 samples (79%) contained progesterone receptor (PgR+) at the average level of 335.2 ± 32.0 fmol/mg protein, and the dissociation constant (Kd) was 8.58 ± 0.58 nmol/l. The correlation of the distribution of progesterone and estrogen receptor in this group of patients was observed: within the 80 samples (66.7% of total) which were estrogen receptor positive (ER+), there were 64 samples (80% of ER+) that also contained progesterone receptor. There were only 9 samples (7.5% of total), in which neither estrogen receptor nor progesterone receptor was detected. It was concluded that the probability of breast tumor in this group of Thai women to be classified as “hormone dependent” type was about 50% of the total incidences. Comparative study for ER and PgR was done in 2 groups of patients; the malignant group (n = 84) in which infliltrating ductal carcinoma (IDC) was the highest incident, and benign group (n = 29). The content of the ER and PGR in the benign and the malignant group were not significantly difference. The dissociation constant of PgR in the benign and the malignant group showed significant lower affinity than the . ER (P < 0.005). The distribution of both receptors among various age group of patients were similar, i.e. the tendency to find receptor in eldery patients, age above 50 years was higher than the patients in the age group below 40 years. The study biochemical properties of the receptors, such as the sedimentation coefficient was performed by the sucrose gradient centrifugation (SGC), comparing with standard protein, to determine the molecular size of the receptors. ER exhibited the sedimentation coefficient approximately at 8 - 9S and 4S. PgR exhibited the sedimentation coefficient approximately at 4S only, and was found in smaller content and less specific comparing to ER. The specimens which had high level of estrogen receptor also showed high specificity for 17- β- estradiol binding. The estrogen receptor showed high specific binding with 17- β- estradiol beyond other steroids such as, testosterone, corticosterone, as determined by competitive binding with tritiated estradiol. When diethylstilboestrol (DES) and tamoxifen (TAM), which have part of their structure similar to estradiol, and are currently used in human breast cancer treatment, were used to compete with tritiated estradiol in 4 cytosol specimens, it was found that DES could effectively compete for estradiol binding, whereas TAM could not. The specificity of PgR was studied by the same method. The results showed that other steroid hormones, such as estradiol, testosterone, corticosterone, and antiestrogen substance (DES and TAM), could not compete for the binding of tritiated progesterone (3H – Pg), except ORG 2058, the synthetic progesterone could compete more effectively than the unlabelled progesterone itself. Besides, from the study of the per cent variation in the assay of PgR, when the cytosols were stored at 70℃ at various time intervals from 15 days to 3 months, it was found that storage of cytosols for as long as 2 months resulted in the per cent variation of Kd values approximately 15% but storage for 3 months resulted in increased percentage of variation to 17.6 – 32.9%. The results suggested that the cytosols should not be stored linger than 2 months.