Induction of estrogen receptor-α and -β activities by synthetic progestins

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Abstract
The cellular action of steroid hormones is mediated by specific receptors. Recently, two different estrogen receptors (ER), α and β, have been cloned with a specific tissue distribution. Active estrogen as well as active progestin are compounds of oral hormonal contraceptives and hormone replacement therapy. To examinate the regulation of ER-α and -β activities after treatment with synthetic progestins and synthetic and natural estrogens, COS 7 cells were transfected with the vector expressing ER-α and -β in combination with a luciferase reporter vector. ER-α activity was upregulated in the presence of synthetic progestins in a dose-dependent manner. Norethisterone, norethynodrel and desogestrel proved to be the most potent stimulatory agents of ER-α expression. On the other hand, not all progestins exhibited a stimulatory action on ER-β activity. Only norgestrel, levonorgestrel, norethynodrel and norethisterone induced ER-β-activating functions in a dose-dependent manner. Luciferase activity due to estrogen stimulation served as a positive control. Our results indicate that progestins have different effects on the activities of ER-α and -β.

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