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Binding of progestagens to receptor proteins in MCF-7 cells
Abstract:
With the aim of finding an explanation for the biological properties of progestagens currently used for contraceptive purposes, we have assessed their specificity for progesterone, androgen and oestrogen receptors in MCF-7 cells. The specificity of progestagens for the progesterone receptors in the cytosol fraction of MCF-7 cells was similar to that for progesterone receptors in human and rabbit myometrial cytosol but different from that for the progesterone receptor in rat myometrial cytosol. At 37 degrees C the relative affinity of 3-keto-desogestrel, the major metabolite of desogestrel, for the progesterone receptor in intact MCF-7 cells was twice that of levonorgestrel and Org 2058, three times that of medroxy-progesterone acetate (MPA), 4.5 times that of norethisterone and 5 times that of progesterone and cyproterone acetate whereas at 4 degrees C in the cytosol fraction of MCF-7 cells exposed to molybdate (nontransformed receptor complexes) 3-keto-desogestrel and Org 2058 displayed similar affinity. The stronger binding of 3-keto-desogestrel in intact cells was due to the higher stability of its complex with the progesterone receptor. At 37 degrees C the relative affinity of 3-keto-desogestrel for the androgen receptor in intact MCF-7 cells was half that of levonorgestrel, similar to that of norethisterone and medroxyprogesterone acetate (MPA) and at least three times higher than that of progestagens with anti-androgenic activity whereas at 4 degrees C in the cytosol fraction exposed to molybdate there was no clear difference between the relative affinities of progestagens with androgenic and anti-androgenic properties. Of the progestagens tested in this study, only norethinodrel displayed measurable but very low relative affinity for the oestrogen receptor in MCF-7 cells. We conclude that the present results of binding studies with intact MCF-7 cells correlate better with the known hormonal properties of progestagens than those obtained with the cytosol fraction exposed to molybdate at 4 degrees C.
Insights
This study investigated progestagen receptor binding in MCF-7 cells, finding that 3-keto-desogestrel shows strong progesterone receptor affinity. These findings help explain the biological effects of contraceptive progestagens.
Area of Science:
- Endocrinology
- Molecular Pharmacology
Background:
- Progestagens are widely used for contraceptive purposes.
- Understanding their receptor binding specificities is crucial for explaining their biological effects.
Purpose of the Study:
- To assess the specificity of contraceptive progestagens for progesterone, androgen, and oestrogen receptors in MCF-7 cells.
- To correlate binding affinities with known hormonal properties of these progestagens.
Main Methods:
- Binding assays were performed on intact MCF-7 cells and cytosol fractions at different temperatures (37°C and 4°C).
- Relative affinities for progesterone, androgen, and oestrogen receptors were determined for various progestagens, including 3-keto-desogestrel, levonorgestrel, and medroxy-progesterone acetate (MPA).
Main Results:
- 3-keto-desogestrel exhibited significantly higher relative affinity for the progesterone receptor in intact MCF-7 cells compared to other progestagens.
- Binding affinities in intact cells correlated better with known hormonal properties than those observed in cytosol fractions at 4°C.
- Norethinodrel showed very low affinity for the oestrogen receptor; other progestagens had minimal or no affinity for this receptor.
Conclusions:
- The binding characteristics of progestagens in intact MCF-7 cells provide a better explanation for their biological activities than studies using cytosol fractions.
- The high affinity of 3-keto-desogestrel for the progesterone receptor contributes to its contraceptive efficacy.