Estrogenic gene regulation in RC-4B/C1 cells: effects of Cimicifuga racemosa

Extracts of the rhizoma of Cimicifuga racemosa (CR) are used for the treatment of menopausal symptoms, mainly for changes in mood and hot flashes. Although the mechanism of action remains unclear an involvement of the pituitary gland seems to be reasonable. It is well known that the pituitary gland is an estrogen-target in the feedback loop of the reproductive endocrine axis. Therefore we established the rat lactogonadotrope RC-4B/C1 cell line as a pituitary derived experimental system to investigate potential pituitary effects of estradiol (E2) and to assess the potential estrogen-like effects of CR extracts in the pituitary. Using realtime PCR we identified estrogen-responsive marker genes within this cell line: LH β subunit (LHB), Prolactin (PRL), Glycoprotein α-subunit (CGA) and Neuropeptide Y1 receptor (Y1R). Furthermore we examined the regulation of the aryl hydrocarbon receptor (AhR) and its downstream regulated genes CYP1A1 and AhR Repressor (AhRR) by E2 and CR, because in the literature an interaction of AhR and ER binding and signaling through SP1 element is reported, as well as CR extracts interference with this crosstalk mechanism. After 48 hours of treatment E2 up-regulated significantly PRL mRNA levels whereas the expression levels of all other examined genes, inclusive AhR, CYP1A1 and AhRR, were down-regulated significantly. The induced changes of mRNA expression levels by E2 could be inhibited by simultaneous treatment of cells with the pure antagonist ICI 182,780 (Faslodex). In contrast no significant regulation of the mRNA levels of the estrogen responsive genes could be shown for the isopropanolic CR extract (iCR). In conclusion it can be stated that iCR did neither have any effect on the expression of the AhR and the AhR regulated genes CYP1A1 and AhRR nor on estrogen responsive genes in this lactogonadotrope pituitary in vitro-system. This is another piece of evidence that the mechanism of action of CR is different from estrogen receptor signaling pathways and may include others like serotonin receptor signaling.