Transactivation of progestin- and estrogen-responsive promoters by 19-nor progestins in African Green Monkey Kidney CV1 cells

Concurrent estrogen action was essential for maximal progestin effect in oral contraceptives

OBJECTIVE

To investigate the impact of estrogen contained in oral contraceptives (OCs) on the action of progestin on ovarian endometrioma epithelial cells.

DESIGN

Experimental in vitro study and immunohistochemical analysis.

SETTING

University hospital.

PATIENT(S)

Patients who underwent surgery due to ovarian endometrioma.

INTERVENTION(S)

Not applicable.

MAIN OUTCOME MEASURE(S)

Telomerase-immortalized epithelial cells derived from ovarian endometrioma were treated with norethindorone (NET; 80 nmol/L) or levonorgestrel (LNG; 20 nmol/L) with or without 17β-ethynylestradiol (EE; 0.6 nmol/L) for 96 hours, and the cell growth was monitored. Estrogen receptor (ER) α, progesterone receptor (PR) A, and PRB expressions in clinical samples of ovarian endometrioma epithelial cells were analyzed with the use of immunohistochemistry.

RESULT(S)

NET or LNG effectively suppressed cell growth, and addition of EE significantly enhanced the growth suppression. This EE-mediated enhancement of cell growth suppression was observed only in cells that expressed ERα and therefore was ERα dependent. Western blot analysis revealed that expression of PRB was significantly induced by the addition of EE. Immunohistochemical analysis confirmed that ERα expression and PRB expression are significantly correlated, indicating that progestin-sensitive cells with PRB expression are predisposed to react with estrogen stimulation.

CONCLUSION(S)

These findings suggest that EE contained in OCs plays a supportive role in progestin-induced growth inhibition of ovarian endometrioma epithelial cells. In the absence of estrogen priming, concurrent estrogen action was essential for rapid induction of PR to achieve maximal progestin effect.

3- and 19-oximes of 16alpha,17alpha-cyclohexanoprogesterone derivatives: synthesis and interactions with progesterone receptor and other proteins

Series of 3- and 19-oximes of 16alpha,17alpha-cyclohexanoprogesterone derivatives (pregna-d'-pentaranes) have been synthesized with the aim of probing the surfaces of progesterone receptor's and two other protein ligand binding pockets neighboring to 3- and 19-positions of steroid core. The same derivatives were also studied as possible intermediates for attachment to matrixes. The data on affinity constants suggest the presence of hydrophobic cavities with hydrophilic necks in the progesterone receptor and serum pentaranophylin near C19 of bound ligand and the lack of such a cavity in uterine pentaranophylin. Any of 3-oxime substitutions were found to significantly diminish the ligand affinity for the progesterone receptor. It was also found that some of these modifications, in the Z-configuration particularly, might increase the affinity for serum and uterine pentaranophylins. The latter finding suggests the presence of large cavities near C3 of bound ligand in these proteins and interchangeability between 3-keto and 3-oxime groups in ligand-protein interactions.

Effects of FSH and 17beta-estradiol on the transactivation of estrogen-regulated promoters and cell proliferation in L cells

In the present study, we analyzed human follicle-stimulating hormone (FSH)-induced cell proliferation and transactivation of estrogen-sensitive reporter genes-in L cells stably expressing the human FSH receptor [L-(hFSHR(+)) cells]. In order to dissect the signaling pathways involved in this process, L-(hFSHR(+)) cells were transiently transfected with either the 3X-ERE-TAT-Luc or the ERE-VitA2-TK-CAT reporter genes and treated with FSH or PKA activators (cholera toxin, forskolin and 8-Br-cAMP) in the presence or absence of various kinase inhibitors. We found that FSH and all PKA activators, specifically induced transactivation of both reporter genes. Transactivation of estrogen-sensitive genes by FSH or PKA activators were blocked (approximately 90%) by H89 (PKA inhibitor) and LY294002 but not by Wortmannin (PI3-K inhibitors), 4-OH-tamoxifen, ICI182,780 or SB203580 (p38 MAPK inhibitor); PD98059 (ERK1/2 inhibitor) partially (approximately 30%) blocked the FSH-mediated effect. The combination of FSH and estradiol resulted in a synergistic effect on transactivation as well as on cell proliferation, and this enhancement was attenuated by antiestrogens. We additionally analyzed the participation of the coactivators SRC-1 and cAMP response element binding protein (CREB)-binding protein (CBP) in FSH-evoked estrogen receptor (ER)-dependent transactivation; we found that CBP but not SRC-1 potentiated FSH-induced transcriptional activation of both ER-sensitive reporters, being this effect stronger on the ERE-VitA2-TK-CAT than on the 3X-ERE-TAT-Luc reporter. Thus, in L-(hFSHR(+)) cells FSH induces transcriptional activation of estrogen-sensitive genes through an A-kinase-triggered signaling pathway, using also to a lesser extent the ERK1/2 and p38 pathways. PI3-K is not apparently involved in this FSH-mediated process since LY294002, but not Wortmannin, specifically binds ERs and completely blocks estrogen action. Presumably, CBP cooperates with the ER on genes that contain estrogen responsive elements through mechanisms involving the participation of other proteins and/or basal transcription factors (e.g. CREB), which in turn mediate the transcriptional response of estrogen-sensitive reporter genes to FSH stimulation.

The phosphatidylinositol 3-kinase inhibitor LY294002 binds the estrogen receptor and inhibits 17beta-estradiol-induced transcriptional activity of an estrogen sensitive reporter gene

Estrogen receptors (ERs) are members of the superfamily of ligand-activated transcription factors. In addition to the classical, hormone-mediated activation, ERs may alternatively be activated in a ligand-independent manner by a variety of agents including growth factors, neurotransmitters and cAMP. It has been demonstrated that the phosphatidylinositol 3 (PI3)-dependent kinase/Akt pathway may activate the ER alpha by increasing the activity of both estrogen independent activation function-1 and estrogen-dependent activation function-2 domains. The Akt phosphorylation site in the ER is Ser167. Phosphorylation of this residue is inhibited by LY294002, which blocks the PI3-kinase/Akt pathway. In the course of studies examining the effects of LY294002 on ligand-independent activation of ERs in L cells, we found that LY294002 exhibits antiestrogenic effects in a dose-dependent manner. By competition binding assays, we found that LY294002 specifically displaced radiolabelled estradiol from ERs with an IC(50) of 11+/-0.06 nM, being an estradiol competitor as effective as the antiestrogens ICI182,780 (IC(50), 21+/-0.13) and 4-OH-tamoxifen (IC(50), 15+/-0.09). Further, LY294002 irreversibly blocked estrogen-induced transactivation of an estradiol-sensitive reporter gene. These findings are of particular importance in the interpretation of studies demonstrating ERs inactivation by the PI3-kinase inhibitor. Our studies show that an apparent block of ER activation cannot be dissociated from inhibition of ligand-mediated events. Thus, this effect can be the result of the ability of LY294002 to bind the ERs and inhibit transactivation of estrogen-regulated genes.

Norethisterone is bioconverted to oestrogenic compounds that activate both the oestrogen receptor alpha and oestrogen receptor beta in vitro

In the present study, we used [3H]norethisterone to explore the bioconversion of this compound to A-ring reduced metabolites in African Green Monkey Kidney CV-1 cells and breast cancer T-47D cells. Additionally, we analyzed the capability of each norethisterone tetrahydro-reduced compound to bind the human oestrogen receptors alpha and beta and transactivate an oestrogen-sensitive reporter gene. The results showed that norethisterone is mainly metabolized to 3 alpha,5 alpha-norethisterone (>85% of total [3H]norethisterone added) by CV-1 and T-47D cells, and that both A-ring tetrahydro-reduced metabolites exhibit different capabilities to displace [3H]17beta-oestradiol from the oestrogen receptor alpha and beta, being 3 alpha,5 alpha-norethisterone the weakest competitor. We also found that 3 alpha,5 alpha-norethisterone and 3beta,5 alpha-norethisterone activate both oestrogen receptors at nanomolar concentrations and that the transactivation induced by the oestrogen receptor alpha was generally higher (1.7- to 4.0-fold) than that provoked by the beta receptor isoform. In oestrogen receptor alpha-transfected CV-1 and T-47 D cells, the oestrogenic-like potency of the 3beta,5 alpha-tetrahydro-reduced form was similar to that exhibited by 17beta-oestradiol and 2.5- to 4.0-fold higher than that shown by the 3 alpha,5 alpha-reduced compound; conversely, in the oestrogen receptor beta system the potency of the natural ligand was higher than that presented by the 3beta,5 alpha-tetrahydro-reduced metabolite. In CV-1 cells expressing the oestrogen receptor beta, the transactivation potency of 3beta,5 alpha-norethisterone was approximately 2-fold higher than that exhibited by its 3 alpha,5 alpha-tetrahydro-reduced isomer, whereas in T-47D cells the potency of the 3 alpha,5 alpha-tetrahydro-reduced compound was slightly higher than that shown by the 3beta,5 alpha A-ring reduced norethisterone metabolite. These results demonstrate that CV-1 and T-47D cells possess the enzymatic machinery to bioconvert norethisterone into the 5 alpha-reduced, 3 alpha-hydroxylated form and that neither 3 alpha,5 alpha- or 3beta,5 alpha-norethisterone exhibit preference or selectivity towards a particular oestrogen receptor isoform to induce a particular oestrogenic effect in these cell lines.