Progesterone receptor contains a proline-rich motif that directly interacts with SH3 domains and activates c-Src family tyrosine kinases

Steroid hormones have rapid nongenomic effects on cell-signaling pathways, but the receptor mechanisms responsible for this are not understood. We have identified a specific polyproline motif in the amino-terminal domain of conventional progesterone receptor (PR) that mediates direct progestin-dependent interaction of PR with SH3 domains of various cytoplasmic signaling molecules, including c-Src tyrosine kinases. Through this interaction, PR is a potent activator of Src kinases working by an SH3 domain displacement mechanism. By mutagenesis, we also show that rapid progestin-induced activation of Src and downstream MAP kinase in mammalian cells is dependent on PR-SH3 domain interaction, but not on the transcriptional activity of PR. Preliminary evidence for the biological significance of this PR signaling pathway through regulatory SH3 domains was shown with respect to an influence on progestin-induced growth arrest of breast epithelial cells and induction of Xenopus oocyte maturation.

Effects of hormone replacement therapy on endometrial histology in postmenopausal women. The Postmenopausal Estrogen/Progestin Interventions (PEPI) Trial. The Writing Group for the PEPI Trial

OBJECTIVE

To report the histological findings of the endometrium of postmenopausal women who were randomized to receive placebo, estrogen only, or one of three estrogen plus progestin (E+P) regimens in the Postmenopausal Estrogen/Progestin Interventions (PEPI) Trial.

DESIGN

A 3-year multicenter, randomized, double-masked, placebo-controlled trial.

PARTICIPANTS

A total of 596 postmenopausal women aged 45 through 64 years without contraindication to hormone therapy.

INTERVENTION

Participants were randomized and stratified in equal numbers to one of the following treatments in 28-day cycles: placebo, 0.625 mg/d of conjugated equine estrogens (CEE), 0.625 mg/d of CEE plus 10 mg/d of medroxyprogesterone acetate (MPA) for the first 12 days, 0.625 mg/d of CEE plus 2.5 mg/d of MPA, or 0.625 mg/d of CEE plus 200 mg/d of micronized progesterone (MP) for the first 12 days.

OUTCOME MEASURE

Histology of endometrium collected at baseline, annual, or unscheduled visits by biopsy, curettage, or hysterectomy.

ANALYSIS

Intention to treat.

RESULTS

During follow-up women assigned to estrogen alone were more likely to develop simple (cystic), complex (adenomatous), or atypical hyperplasia than those given placebo (27.7% vs 0.8%, 22.7% vs 0.8%, and 11.8% vs 0%, respectively) for the same types of hyperplasia (P < .001). Participants administered one of the three E+P regimens had similar rates of hyperplasia as those given placebo (P = .16). The occurrence of hyperplasia was distributed evenly across the 3 years of the trial. Women taking estrogens alone also had more unscheduled biopsies (66.4% vs 8.4%; P < .001) and curettages (17.6% vs 0.8%; P < .001) than women receiving placebo. The number of surgical procedures was similar for women receiving placebo and women receiving the E+P regimens (P = .38). Of the 45 women with complex (adenomatous) or atypical hyperplasia, study medications were discontinued in all, and the biopsy results of 34 (94%) of 36 women with hyperplasia reverted to normal with progestin therapy. The remainder had dilatation and curettage (n = 2) or hysterectomy with (n = 2) or without (n = 6) prior medical therapy, or refused further biopsies (n = 1). One woman developed adenocarcinoma of the endometrium while receiving placebo.

CONCLUSIONS

At a dosage of 0.625 mg, the daily administration of CEE enhanced the development of endometrial hyperplasia. Combining CEE with cyclic or continuous MPA or cyclic MP protected the endometrium from hyperplastic changes associated with estrogen-only therapy.

Serum high-density-lipoprotein cholesterol in women using oral contraceptives, estrogens and progestins

To determine the associations between high-density-lipoprotein cholesterol levels and use of oral contraceptives or of noncontraceptive estrogens and progestins we analyzed the serum levels of this lipid in 4978 women, 21 to 62 years of age. In estrogen users, the mean level was 6.7 to 15.1 mg per deciliter above the nonuser level (P less than 0.001), whereas in a group of progestin users it was 15.8 mg per deciliter below (P less than 0.001). In women using combination oral contraceptives, the level varied with the type and dose of the component steroids, in general increasing with increasing dose of estrogen and decreasing with increasing dose or potency of progestin. Thus, the net effect of use of a combination oral contraceptive on high-density-lipoprotein cholesterol depends on its formulation.

Prevention of bone loss with alendronate in postmenopausal women under 60 years of age. Early Postmenopausal Intervention Cohort Study Group

BACKGROUND

Estrogen-replacement therapy prevents osteoporosis in postmenopausal women by inhibiting bone resorption, but the balance between its long-term risks and benefits remains unclear. Whether other antiresorptive therapies can prevent osteoporosis in these women is also not clear.

METHODS

We studied the effect of 2.5 mg or 5 mg of alendronate per day or placebo on bone mineral density in 1174 postmenopausal women under 60 years of age. An additional 435 women who were prepared to receive a combination of estrogen and progestin were randomly assigned to one of the above treatments or open-label estrogen-progestin. The main outcome measure was the change in bone mineral density of the lumbar spine, hip, distal forearm, and total body measured annually for two years by dual-energy x-ray absorptiometry.

RESULTS

The women who received placebo lost bone mineral density at all measured sites, whereas the women treated with 5 mg of alendronate daily had a mean (+/-SE) increase in bone mineral density of 3.5+/-0.2 percent at the lumbar spine, 1.9+/-0.1 percent at the hip, and 0.7+/-0.1 percent for the total body (all P<0.001). Women treated with 2.5 mg of alendronate daily had smaller increases in bone mineral density. Alendronate did not increase bone mineral density of the forearm, but it slowed the loss. The responses to estrogen-progestin were 1 to 2 percentage points greater than those to the 5-mg dose of alendronate. Alendronate was well tolerated, with a safety profile similar to that of placebo or estrogen-progestin.

CONCLUSIONS

Alendronate prevents bone loss in postmenopausal women under 60 years of age to nearly the same extent as estrogen-progestin.

The effects of different formulations of oral contraceptive agents on lipid and carbohydrate metabolism

BACKGROUND

Oral contraceptives can induce changes in lipid and carbohydrate metabolism similar to those associated with an increased risk of coronary heart disease, including increased serum triglyceride, low-density lipoprotein (LDL) cholesterol, and insulin levels and decreased high-density lipoprotein (HDL) cholesterol levels. In this study, we examined whether modification of the type or dose of progestin in oral-contraceptive preparations diminishes these changes.

METHODS

We measured plasma lipoprotein levels and performed oral glucose-tolerance tests in a cross section of 1060 women who took one of nine types of oral contraceptives for at least three months and 418 women who took none. Seven of the contraceptive formulations contained various doses and types of progestin: levonorgestrel in low (150 micrograms), high (250 micrograms), and triphasic (50 to 125 micrograms) doses; norethindrone in low (500 micrograms), high (1000 micrograms), and triphasic (500 to 1000 micrograms) doses; and a new progestin, desogestrel, in one dose (150 micrograms). All seven contained 30 to 40 micrograms of ethinyl estradiol. Two additional formulations contained progestin alone.

RESULTS

As compared with controls, women taking combination drugs did not have increased serum total cholesterol levels but did have increases of 13 to 75 percent in fasting triglyceride levels. Levels of LDL cholesterol were reduced by 14 percent in women taking the combination containing desogestrel and by 12 percent in those taking low-dose norethindrone. Levels of HDL cholesterol were lowered by 5 percent and 16 percent by the combinations containing low-dose and high-dose levonorgestrel, respectively; these decreases were due to reductions of 29 percent and 43 percent, respectively, in the levels of HDL subclass 2. The combination pill containing high-dose norethindrone did not affect HDL cholesterol levels, whereas that containing low-dose norethindrone increased HDL cholesterol levels by 10 percent. The desogestrel combination increased HDL cholesterol levels by 12 percent. Levels of apolipoproteins A-I, A-II, and B were generally increased by combination drugs. Depending on the dose and type of progestin, combination drugs were associated with plasma glucose levels on the glucose-tolerance test that were 43 to 61 percent higher than in controls, insulin responses 12 to 40 percent higher, and C-peptide responses 18 to 45 percent higher. Progestin-only formulations had only minor metabolic effects.

CONCLUSIONS

The appropriate dose and type of progestin may reduce the adverse effects of oral contraceptives on many metabolic markers of risk for coronary heart disease. Progestin-only formulations or combinations containing desogestrel or low-dose norethindrone were associated wtih the most favorable profiles.

Effects of different progestogens on lipoproteins during postmenopausal replacement therapy

To study the effects of different types of progestogens on lipoprotein metabolism, we treated three groups of postmenopausal women (six subjects each) for three weeks with estradiol valerate, 2 mg per day, and continued the treatment with different sequential estradiol-progestogen regimens as follows: Group A received norethindrone acetate, 10 mg per day, from Day 15 to Day 24 of the cycle; Group B, medroxyprogesterone acetate, 10 mg per day; and Group C, norgestrel, 0.5 mg per day. These regimens were followed by two consecutive cycles. Total cholesterol decreased in all groups by 10 to 18 per cent from the base-line values (P < 0.05). High-density-lipoprotein (HDL) cholesterol decreased by 20 per cent from the base-line level during treatment with both the estradiol-norethindrone acetate (P < 0.05) and estradiol-norgestrel (P < 0.01) regimens, whereas estradiol with medroxyprogesterone acetate was not associated with a significant change in HDL cholesterol. Our results suggest that the androgenic progestogens of the 19-nortestosterone series reverse the beneficial effect of postmenopausal estrogen treatment on HDL cholesterol, whereas the hydroxyprogesterone derivative medroxyprogesterone acetate has no such effect.

The opposing transcriptional activities of the two isoforms of the human progesterone receptor are due to differential cofactor binding

The human progesterone receptor (PR) exists as two functionally distinct isoforms, hPRA and hPRB. hPRB functions as a transcriptional activator in most cell and promoter contexts, while hPRA is transcriptionally inactive and functions as a strong ligand-dependent transdominant repressor of steroid hormone receptor transcriptional activity. Although the precise mechanism of hPRA-mediated transrepression is not fully understood, an inhibitory domain (ID) within human PR, which is necessary for transrepression by hPRA, has been identified. Interestingly, although ID is present within both hPR isoforms, it is functionally active only in the context of hPRA, suggesting that the two receptors adopt distinct conformations within the cell which allow hPRA to interact with a set of cofactors that are different from those recognized by hPRB. In support of this hypothesis, we identified, using phage display technology, hPRA-selective peptides which differentially modulate hPRA and hPRB transcriptional activity. Furthermore, using a combination of in vitro and in vivo methodologies, we demonstrate that the two receptors exhibit different cofactor interactions. Specifically, it was determined that hPRA has a higher affinity for the corepressor SMRT than hPRB and that this interaction is facilitated by ID. Interestingly, inhibition of SMRT activity, by either a dominant negative mutant (C'SMRT) or histone deacetylase inhibitors, reverses hPRA-mediated transrepression but does not convert hPRA to a transcriptional activator. Together, these data indicate that the ability of hPRA to transrepress steroid hormone receptor transcriptional activity and its inability to activate progesterone-responsive promoters occur by distinct mechanisms. To this effect, we observed that hPRA, unlike hPRB, was unable to efficiently recruit the transcriptional coactivators GRIP1 and SRC-1 upon agonist binding. Thus, although both receptors contain sequences within their ligand-binding domains known to be required for coactivator binding, the ability of PR to interact with cofactors in a productive manner is regulated by sequences contained within the amino terminus of the receptors. We propose, therefore, that hPRA is transcriptionally inactive due to its inability to efficiently recruit coactivators. Furthermore, our experiments indicate that hPRA interacts efficiently with the corepressor SMRT and that this activity permits it to function as a transdominant repressor.

Drospirenone: pharmacology and pharmacokinetics of a unique progestogen

The pharmacology and pharmacokinetics of drospirenone, a unique progestogen, are reviewed in this paper. Unlike other progestogens, drospirenone, an analogue of spironolactone, has biochemical and pharmacologic profiles similar to endogenous progesterone, especially regarding antimineralocorticoid and antiandrogenic activities. Drospirenone counteracts the estrogen-induced stimulation of the renin-angiotensin-aldosterone system and blocks testosterone from binding to androgen receptors. Because of these characteristics, it has the potential to reduce body weight, blood pressure, and low-density lipoprotein levels and to enhance high-density lipoprotein levels. As a combination oral contraceptive, drospirenone with ethinyl estradiol is effective and has positive effects on weight and lipid levels. Additionally, it relieves menstrually related symptoms (e.g., negative affect and water retention) that are commonly observed with other combination oral contraceptives. Based on the biochemical and pharmacodynamic data, drospirenone appears to be a viable alternative to the currently available progestogens.

Effect of lower doses of conjugated equine estrogens with and without medroxyprogesterone acetate on bone in early postmenopausal women

CONTEXT

Lower-than-commonly-prescribed doses of conjugated equine estrogens (CEEs) with medroxyprogesterone acetate (MPA) improve vasomotor symptoms and vaginal atrophy, provide acceptable bleeding and lipid profiles, and afford endometrial protection. This lower-dose therapy's protection against loss of bone mineral density (BMD) associated with menopause has not been thoroughly investigated.

OBJECTIVE

To determine the effects of lower doses of CEEs only or CEEs-MPA on spine and hip BMD, total body bone mineral content (BMC), and biochemical markers of bone turnover in postmenopausal women.

DESIGN AND SETTING

Two-year randomized, double-blind, placebo-controlled substudy of the Women's Health, Osteoporosis, Progestin, Estrogen trial, conducted at 19 US centers between August 1995 and October 2000.

PARTICIPANTS

Eight hundred twenty-two healthy postmenopausal women aged 40 to 65 years who were within 4 years of their last menstrual period.

INTERVENTIONS

Patients were randomly assigned to receive CEEs, 0.625; CEEs, 0.625 and MPA, 2.5; CEEs, 0.45; CEEs, 0.45 and MPA, 2.5; CEEs, 0.45 and MPA, 1.5; CEEs, 0.3; CEEs 0.3 and MPA, 1.5 (all doses in mg/d); or placebo for 2 years. All participants also received elemental calcium at 600 mg/d.

MAIN OUTCOME MEASURES

Changes from baseline in spine and total hip BMD, total body BMC, and biochemical markers of bone turnover (serum osteocalcin and urinary cross-linked N-telopeptides of type I collagen), assessed at 6-month intervals and compared among treatment groups with a modified intention-to-treat approach.

RESULTS

At 24 months, women assigned to all of the active treatment groups had significant gains from baseline (P<.001) in spine and hip BMD and total body BMC (except total body BMC in the group receiving CEEs, 0.3 mg/d). These changes were significantly different from those in the placebo group, in which losses of bone mass in spine and total body were evident over the course of the study (P<.001). The loss in hip BMD from baseline in the placebo group was significant at 18 (P =.02) but not at 24 months (P =.06). Osteocalcin and N-telopeptides of type I collagen were significantly reduced from baseline (P<.001) for all active treatment groups at all time points; no changes were found for the placebo group. For women treated with CEEs alone, the gains in spine BMD for the group taking CEEs, 0.625 mg/d, were significantly higher than those of the group taking CEEs, 0.3 mg/d (P =.02), but not the group treated with CEEs, 0.45 mg/d (P =.48).

CONCLUSIONS

Doses of CEEs or CEEs-MPA lower than 0.625 mg/d effectively increase BMD and BMC in early postmenopausal women.

Impact of progestins on estrogen-induced neuroprotection: synergy by progesterone and 19-norprogesterone and antagonism by medroxyprogesterone acetate

Estrogen replacement therapy is associated with improvement of cognitive deficits and reduced incidence of Alzheimer's disease. To compare the impact of therapeutically relevant progestins on estrogen-induced neuroprotection, we treated primary hippocampal neuron cultures with 17beta-E2 and progestin, alone and in combination, 48 h before glutamate insult. Estrogen, progesterone, and 19-norprogesterone, alone or in combination, protected against glutamate toxicity. In contrast, medroxyprogesterone acetate (MPA) failed to protect against glutamate toxicity. Not only was MPA an ineffective neuroprotectant but it attenuated the estrogen- induced neuroprotection when coadministered. We addressed the role of MAPK activation in neuroprotection by ovarian steroids. Estrogen and all three progestins tested, alone or in combination, activated MAPK, indicating another mechanism of protection. Bcl-2 expression has been shown to prevent cell death and is up-regulated by 17beta-E2. Progesterone and 19-norprogesterone, alone or in combination with estrogen, increased Bcl-2 expression. In contrast, MPA blocked estrogen-induced Bcl-2 expression when coadministered. These results may have important implications for the effective use of hormone replacement therapy in the maintenance of neuronal function during menopause and aging and for protection against neurodegenerative diseases such as Alzheimer's disease.

Reproductive factors, hormonal contraception, and risk of uterine leiomyomata in African-American women: a prospective study

The authors assessed the risk of uterine leiomyomata in relation to reproductive factors and hormonal contraception in a prospective cohort study of US Black women. From March 1997 through March 2001, the authors followed 22,895 premenopausal women with intact uteri and no prior self-reported diagnosis of uterine leiomyomata. The authors used age- and time-stratified Cox regression models to estimate incidence rate ratios for self-reported uterine leiomyomata, confirmed by ultrasound or hysterectomy, in association with selected reproductive and hormonal factors. During 76,711 person-years of follow-up, 2,279 new cases of ultrasound- or hysterectomy-confirmed uterine leiomyomata were self-reported. After adjustment for age, body mass index, smoking, alcohol intake, and other reproductive covariates, the risk of ultrasound- or hysterectomy-confirmed leiomyomata was inversely associated with age at menarche, parity, and age at first birth and positively associated with years since last birth. Overweight or obesity appeared to attenuate the inverse association between parity and uterine leiomyomata. Current use of progestin-only injectables was inversely associated with risk. No consistent patterns were observed for other forms of hormonal contraception. Reproductive history is an important determinant of leiomyomata risk in premenopausal US Black women. Progestin-only injectables may reduce risk.

Association between the duration of dominance of the ovulatory follicle and pregnancy rate in beef heifers

After luteolysis, subluteal concentrations of progesterone or treatment with a synthetic progestagen result in an extended period of dominance (persistence) of the dominant follicle in cattle. Two experiments studied (1) the relationship between the duration of dominance of the ovulatory follicle and pregnancy rate and (2) the ability of a persistent dominant follicle to ovulate and form a normal functioning corpus luteum. In Expt 1, beef heifers were either untreated (n = 30) or given a synthetic progestagen implant (3 mg norgestomet) for 12 days starting on day 16 of their cycle (n = 32). The mean duration of dominance of the ovulatory follicle differed (P < 0.05) between treated and control heifers (10.8 +/- 1.2 and 3.3 +/- 0.8 days, respectively) and 20 of 26 control and 7 of 30 treated heifers were diagnosed pregnant 28 days after artificial insemination (P < 0.01). In Expt 2, on the first day of dominance of the second dominant follicle, heifers received either a PGF2 alpha analogue alone (controls; n = 18), or prostaglandin and a norgestomet implant for 6 (T6; n = 19) or 10 days (T10; n = 20). Increases in the duration of dominance of the second dominant follicle (controls, 4.1 +/- 0.2 days; T6, 8.6 +/- 0.2 days; T10, 12.1 +/- 0.2 days; P < 0.05) resulted in a decrease in pregnancy rate (controls, 14 of 16; T6, 11 of 19; T10, 0 of 13; P < or = 0.05). Progesterone concentrations on days 7 and 12 and the area of luteal tissue on day 12 after artificial insemination were not different (P > 0.05) between treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular mechanisms of steroid receptor-mediated actions by synthetic progestins used in HRT and contraception

Synthetic progestins are used by millions of women as contraceptives and in hormone replacement therapy (HRT), although their molecular mechanisms of action are not well understood. The importance of investigating these mechanisms, as compared to those of progesterone, has been highlighted by clinical evidence showing that medroxyprogesterone acetate (MPA), a first generation progestin, increases the risk of breast cancer and coronary heart disease in HRT users. A diverse range of later generation progestins with varying structures and pharmacological properties is available for therapeutic use and it is becoming clear that different progestins elicit beneficial and adverse effects to different extents. These differences in biological activity are likely to be due to many factors including variations in dose, metabolism, pharmacokinetics, bioavailability, and regulation of, and/or binding, to serum-binding proteins and steroidogenic enzymes. Since the intracellular effects on gene expression and cell signaling of steroids are mediated via intracellular steroid receptors, differential actions via the progesterone and other steroid receptors and their isoforms, are likely to be the major cause of differential intracellular actions of progestins. Since many progestins bind not only to the progesterone receptor, but also to the glucocorticoid, androgen, mineralocorticoid, and possibly the estrogen receptors, it is plausible that synthetic progestins exert therapeutic actions as well as side-effects via some of these receptors. Here we review the molecular mechanisms of intracellular actions of old (MPA, norethisterone, levonorgestrel, gestodene) vs. new (drospirenone, dienogest, trimegestone) generation progestins, via steroid receptors.

Quality-of-life and depressive symptoms in postmenopausal women after receiving hormone therapy: results from the Heart and Estrogen/Progestin Replacement Study (HERS) trial

CONTEXT

Postmenopausal hormone therapy is commonly used by women for disease prevention, but its effects on quality of life have not been well documented.

OBJECTIVE

To determine the effect on quality of life of estrogen plus progestin therapy used as secondary prevention in women with coronary artery disease.

DESIGN, SETTING, AND PARTICIPANTS

A total of 2763 postmenopausal women with documented coronary artery disease (mean age, 67 years) in the Heart and Estrogen/Progestin Replacement Study, a randomized, placebo-controlled, double-blind trial conducted from January 1993 to July 1998 at outpatient and community settings at 20 US clinical centers.

INTERVENTION

Participants were randomly assigned to receive either 0.625 mg/d of conjugated equine estrogen plus 2.5 mg/d of medroxyprogesterone acetate (n = 1380) or placebo (n = 1383) for 36 months.

MAIN OUTCOME MEASURES

Physical activity, measured by the Duke Activity Status Index; energy/fatigue and mental health, measured by RAND scales; and depressive symptoms, measured on the Burnam screening scale, at 3 years of follow-up.

RESULTS

In all patients, scores declined significantly over 3 years for physical function (-3.8; P<.001), mental health (-0.6; P =.05), and energy/fatigue (-3.8; P<.001), but depressive symptoms were not significantly changed (P =.20). The effect of hormone therapy on these measures depended on the presence (n = 434) or absence (n = 2325) of flushing at study entry. Women with flushing who were assigned to hormone therapy had improved mental health (+2.6 vs - 0.5; P =.04) and fewer depressive symptoms (-0.5 vs + 0.007; P =.01) over follow-up compared with those assigned to placebo. Women without flushing who were assigned to hormone therapy had greater declines in physical function (-4.2 vs -3.3; P =.04) and energy/fatigue (-4.6 vs -3.1; P =.03) over follow-up. Quality-of-life scores were significantly lower among patients with older age, diabetes, hypertension, chest pain, or heart failure. These differences in quality of life among women classified by clinical characteristics were much greater than the effects of hormone therapy.

CONCLUSION

Hormone therapy has mixed effects on quality of life among older women. The effects of hormone therapy depend on the presence of menopausal symptoms; women without flushing had greater declines in physical measures, while women with flushing had improvements in emotional measures of quality of life.

Regulation of dominant follicle turnover during the oestrous cycle in cows

The effect of progestin and luteinizing hormone (LH) pulse frequency on dynamics of dominant follicle growth during the first follicular wave after oestrus was examined in non-lactating Holstein cows by ultrasonography. On day 8 of the cycle, cows (n = 8) received a luteolytic dose of prostaglandin F2 alpha (PGF2 alpha; 25 mg) and an ear implant of Norgestomet (6 mg). On day 18, cows were assigned to a crossover design in which the implants were retained (T1) or replaced with a new implant (T2). All implants were removed on day 23. After oestrus, cows underwent a normal intervening oestrus cycle. On day 8 of the third cycle, T1 and T2 were reversed among cows. Ultrasonography and blood sampling were performed on alternate days throughout the experiment. On days 10 and 19 of the third cycle, blood was sampled every 15 min for 8 h in concert with an additional control group (n = 3) sampled on day 10 of the cycle. Progesterone concentration on day 8 before PGF2 alpha was 6.5 +/- 0.5 ng ml-1. Dominance of the first wave dominant follicle was extended beyond day 18 in 15 of 16 cows for T1 and T2 periods. The original dominant follicle ovulated in five of eight T1 and none of eight T2 periods (P < 0.01). New dominant follicles were detected on day 24 +/- 1 in T1 (n = 3) and on day 20.6 +/- 1 in T2 (n = 8; P < 0.01) cows.(ABSTRACT TRUNCATED AT 250 WORDS)

The Role of Extranuclear Signaling Actions of Progesterone Receptor in Mediating Progesterone Regulation of Gene Expression and the Cell Cycle

Human progesterone receptor (PR) contains a motif that interacts with the SH3 domain of Src and mediates rapid activation of Src and downstream MAPK (Erk-1/-2) without relying on the transcriptional activity of the receptor. Here we investigated the role and intracellular location of this nontranscriptional activity of PR. Progestin activation of Src/MAPK occurred outside the nucleus with the B isoform of PR that was distributed between the cytoplasm and nucleus, but not with PR-A that was predominantly nuclear. Breast cancer cells stably expressing wild-type PR-B or PR-B with disrupting point mutations in the SH3 domain binding motif (PR-BDeltaSH3) that do not affect the transcriptional activity of PR, were compared for effects of progestin on endogenous target gene expression and cell proliferation. Progestin induction of the cyclin D1 gene, which lacks a progesterone response element, was dependent on PR activation of the Src/MAPK pathway, whereas induction of the Sgk (serum and glucocorticoid regulated kinase) gene that contains a functional progesterone response element was unaffected by mutations that interfere with PR activation of Src. Progestin induction of cell cycle progression was also abrogated in cells expressing PR-BDeltaSH3, and no effect of progestin on cyclin D1 expression and cell cycle was observed in the presence of PR-A. These results highlight the importance of PR activation of the Src/MAPK signaling pathway for progesterone-induced transcription of select target genes and cell cycle progression.

The novel progestin drospirenone and its natural counterpart progesterone: biochemical profile and antiandrogenic potential

Drospirenone is a novel progestin under clinical development that is similar to the natural hormone progesterone, combining potent progestogenic with antimineralocorticoid and antiandrogenic activities. This specific pharmacological profile of drospirenone is defined by its pattern of binding affinities to a variety of steroid hormone receptors. In the present study the affinity of drospirenone to the progesterone receptor (PR), the androgen receptor (AR), the glucocorticoid receptor (GR), the mineralocorticoid receptor (MR), and the estrogen receptor (ER) was re-evaluated by steroid binding assays and compared to those obtained for the natural hormone progesterone. Drospirenone displayed high affinity to PR and MR and low binding to AR, similar to progesterone. Unlike progesterone, which showed considerable binding to GR, drospirenone exhibited only low binding to this receptor. Neither drospirenone nor progesterone did bind to the ER. In addition to receptor binding studies, transactivation assays were carried out to investigate the effects of drospirenone and progesterone on AR-, GR-, and MR-mediated induction of transcription. Both progestins showed no androgenic but antiandrogenic activity by inhibiting AR-mediated transcription in a dose-dependent manner. This observation could be confirmed by in vivo experiments carried out with orchiectomized male rats, where the antiandrogenic potency of drospirenone was found to be about five- to ten-fold higher than that of progesterone. In contrast to progesterone, drospirenone was devoid of glucocorticoid activity. Both progestins did not show any antiglucocorticoid action. Furthermore, drospirenone and progesterone both showed considerable antimineralocorticoid activity and weak mineralocorticoid activity.

Nestorone: a progestin with a unique pharmacological profile

Nestorone(R) (Nestorone 16-methylene-17alpha-acetoxy-19-norpregn-4-ene-3,20-dione), formerly referred to as ST 1435, is a potent progestin when given parenterally via sustained release formulations. The pharmacological profile of Nestorone was compared with that of levonorgestrel and 3-keto-desogestrel by steroid receptor binding studies and by in vivo bioassays in rats and rabbits. 3-Keto-desogestrel showed the highest binding affinity to progesterone receptors (PR) followed by Nestorone, levonorgestrel, and progesterone. The binding affinity of Nestorone to androgen receptors (AR) was 500- to 600-fold less than that of testosterone. However, both levonorgestrel and 3-keto-desogestrel showed significant binding (40 to 70% of testosterone) to AR. None of the progestins bound to estrogen receptors (ER). The progestational activity of Nestorone, levonorgestrel, and progesterone was compared using McPhail index in immature rabbits and pregnancy maintenance and ovulation inhibition tests in rats after subcutaneous (s.c.) administration. In all three tests, Nestorone was the most potent progestin. The progestational activity of Nestorone was also compared after oral and s.c. administration in rabbits. The potency of Nestorone was over 100-fold higher upon s.c. administration than via the oral route. The androgenic activity of progestins, based on the stimulation of ventral prostate (androgenic target) and levator ani (anabolic target) growth in castrated immature rats, showed good correlation with their binding affinity to AR. Nestorone showed no androgenic or anabolic activity. Nestorone did not bind to sex hormone binding globulin (SHBG), whereas both levonorgestrel and 3-keto-desogestrel showed significant binding to SHBG. The estrogenic/antiestrogenic activity of Nestorone was investigated in immature ovariectomized rats. In contrast to estradiol and levonorgestrel, Nestorone showed no uterotropic activity in ovariectomized rats. Despite significant binding to glucocorticoid receptors (GR), Nestorone showed no glucocorticoid activity in vivo. It is concluded that a strong progestational activity, combined with lack of androgenic, estrogenic, and glucocorticoid-like activities, confer special advantages to Nestorone for use in contraception and hormone replacement therapy.

Progesterone and neuroprotection

Numerous studies aimed at identifying the role of estrogen on the brain have used the ovariectomized rodent as the experimental model. And while estrogen intervention in these animals has, at least partially, restored cholinergic, neurotrophin and cognitive deficits seen in the ovariectomized animal, it is worth considering that the removal of the ovaries results in the loss of not only circulating estrogen but of circulating progesterone as well. As such, the various deficits associated with ovariectomy may be attributed to the loss of progesterone as well. Similarly, one must also consider the fact that the human menopause results in the precipitous decline of not just circulating estrogens, but in circulating progesterone as well and as such, the increased risk for diseases such as Alzheimer's disease during the postmenopausal period could also be contributed by this loss of progesterone. In fact, progesterone has been shown to exert neuroprotective effects, both in cell models, animal models and in humans. Here, we review the evidence that supports the neuroprotective effects of progesterone and discuss the various mechanisms that are thought to mediate these protective effects. We also discuss the receptor pharmacology of progesterone's neuroprotective effects and present a conceptual model of progesterone action that supports the complementary effects of membrane-associated and classical intracellular progesterone receptors. In addition, we discuss fundamental differences in the neurobiology of progesterone and the clinically used, synthetic progestin, medroxyprogesterone acetate that may offer an explanation for the negative findings of the combined estrogen/progestin arm of the Women's Health Initiative-Memory Study (WHIMS) and suggest that the type of progestin used may dictate the outcome of either pre-clinical or clinical studies that addresses brain function.

Pharmacokinetics of oestrogens and progestogens

There are large inter- and intra-individual variations in the serum concentrations of natural and synthetic sex steroids irrespective of the route of administration. Oral ingestion of steroids has a stronger effect on hepatic metabolism than parenteral administration, as the local concentration in liver sinusoids are 4-5 times higher during the first liver passage. Oestradiol and oestrone are interconvertible, dependent on the local concentrations in liver and target organs, and oestrone sulphate serves as a large reservoir. The oestrone/oestradiol ratio has no physiological significance, as oestrone is only a weak oestrogen. Oestrone is both a precursor and a metabolite of oestradiol. Oestriol is extensively conjugated after oral administration. Therefore, the oestriol serum levels are similar after oral intake of 10 mg and after vaginal application of 0.5 mg oestriol resulting in similar systemic effectiveness. Conjugated oestrogens can easily enter the hepatocytes but are hormonally active only after hydrolyzation into the parent steroids. Ethinylestradiol which exerts strong effects on hepatic metabolism and inhibits metabolizing enzymes, should not be used for hormone replacement therapy. Among the progestogens, the progesterone derivatives have less effects on liver metabolism than the norethisterone derivatives (13-methyl-gonanes and 13-ethyl-gonanes). The highly potent 13-ethyl-gonanes are effective at very low doses, because of a slow inactivation and elimination rate due to the ethinyl group.

Novel perspectives for progesterone in hormone replacement therapy, with special reference to the nervous system

The utility and safety of postmenopausal hormone replacement therapy has recently been put into question by large clinical trials. Their outcome has been extensively commented upon, but discussions have mainly been limited to the effects of estrogens. In fact, progestagens are generally only considered with respect to their usefulness in preventing estrogen stimulation of uterine hyperplasia and malignancy. In addition, various risks have been attributed to progestagens and their omission from hormone replacement therapy has been considered, but this may underestimate their potential benefits and therapeutic promises. A major reason for the controversial reputation of progestagens is that they are generally considered as a single class. Moreover, the term progesterone is often used as a generic one for the different types of both natural and synthetic progestagens. This is not appropriate because natural progesterone has properties very distinct from the synthetic progestins. Within the nervous system, the neuroprotective and promyelinating effects of progesterone are promising, not only for preventing but also for reversing age-dependent changes and dysfunctions. There is indeed strong evidence that the aging nervous system remains at least to some extent sensitive to these beneficial effects of progesterone. The actions of progesterone in peripheral target tissues including breast, blood vessels, and bones are less well understood, but there is evidence for the beneficial effects of progesterone. The variety of signaling mechanisms of progesterone offers exciting possibilities for the development of more selective, efficient, and safe progestagens. The recognition that progesterone is synthesized by neurons and glial cells requires a reevaluation of hormonal aging.

Distinguishing androgen receptor agonists and antagonists: distinct mechanisms of activation by medroxyprogesterone acetate and dihydrotestosterone

Natural and pharmacological androgen receptor (AR) ligands were tested for their ability to induce the AR NH2-terminal and carboxyl-terminal (N/C) interaction in a two-hybrid protein assay to determine whether N/C complex formation distinguishes in vivo AR agonists from antagonists. High-affinity agonists such as dihydrotestosterone, mibolerone, testosterone, and methyltrienolone at concentrations between 0.1 and 1 nM induce the N/C interaction more than 40-fold. The lower affinity anabolic steroids, oxandrolone and fluoxymesterone, require concentrations of 10-100 nM for up to 23-fold induction of the N/C interaction. However no N/C interaction was detected in the presence of the antagonists, hydroxyflutamide, cyproterone acetate, or RU56187, at concentrations up to 1 microM, or with 1 microM estradiol, progesterone, or medroxyprogesterone acetate; each of these steroids at 1-500 nM inhibited the dihydrotestosterone-induced N/C interaction, with medroxyprogesterone acetate being the most effective. In transient and stable cotransfection assays using the mouse mammary tumor virus reporter vector, all ligands displayed concentration-dependent AR agonist activity that paralleled induction of the N/C interaction, with antagonists and weaker agonists failing to induce the N/C interaction. AR dimerization and DNA binding in mobility shift assays and AR stabilization reflected, but were not dependent on, the N/C interaction. The results indicate that the N/C interaction facilitates agonist potency at low physiological ligand concentrations as detected in transcription, dimerization/DNA binding, and stabilization assays. However the N/C interaction is not required for agonist activity at sufficiently high ligand concentrations, nor does its inhibition imply antagonist activity.

The FK506-binding immunophilin FKBP51 is transcriptionally regulated by progestin and attenuates progestin responsiveness

FKBP51 and FKBP52 are large molecular weight FK506-binding immunophilins that have diverse biochemical functions. Best studied is the role that they play as components of steroid hormone receptors. Differential display and gene array screens have identified FKBP51 as a progestin-inducible gene. Here we demonstrate progestin enhancement of FKBP51 mRNA and protein in T-47D cells. FKBP51 mRNA and protein levels were increased 3-fold by 20 nM R5020. Induction of FKBP51 mRNA was unaffected by 1 micro g/ml cycloheximide but was blocked by the progestin receptor (PR) antagonist RU486 (1 micro M). Reporter plasmids containing 3.4 kb and 427 bp of 5'-flanking sequences of the human FKBP51 protein gene (FKBP5) exhibited regulation by progestin in T-47D cells. A construct containing 19 bp of upstream sequence demonstrated diminished basal activity and no stimulation by R5020. To test whether elevated FKBP51 affects progestin responsiveness, HepG2 cells were transfected with human FKBP51, PR, and mouse mammary tumor virus-luciferase plasmids, and treated with R5020 (0.03-10 nM). Expression of FKBP51 increased the EC(50) for PR transactivation by 3.2-fold. Expression of FKBP51 from squirrel monkey, a New World primate with naturally occurring progestin resistance, increased the EC(50) more dramatically (11.7-fold vs. control). Expression of FKBP51 bearing a double-point mutation in the tetratricopeptide repeat domain had no effect on PR transactivation. These results suggest that increased expression of FKBP51 by progestin may attenuate progestin responsiveness in hormone-conditioned cells. Furthermore, overexpression of FKBP51 in the squirrel monkey may be a contributing cause of progesterone resistance in this species.

RETRACTED: The pharmacodynamics and efficacy of Implanon. An overview of the data

Implanon is a long-acting reversible contraceptive method, consisting of a single rod that is applied subdermally. Ovulation inhibition was determined by serum progesterone (P) levels and ultrasound scanning (USS) of the ovaries. Ovarian function was further assessed by serum estradiol (E2) levels. The effects of Implanon on serum gonadotropin levels (follicle-stimulating hormone [FSH] and luteinizing hormone [LH]) and on cervical mucus were also investigated, by means of Insler scores and sperm penetration tests. The effect of the endometrium was assessed by endometrial biopsies and USS. The Pearl index was calculated over 13 studies performed according to Good Clinical Practice (GCP), including 1716 women using Implanon. Return of ovulation after implant removal was determined by P levels and USS of the ovaries. The contraceptive efficacy of Implanon was high, with zero pregnancies during 53,530 cycles (4103 woman-years), resulting in a Pearl index of 0.0 (95% confidence interval, 0.00-0.09). This was achieved by inhibition of ovulation, which was reflected by suppressed P levels, as the primary mode of action. Ovulation was inhibited, but otherwise ovarian activity was still present (follicle growth, E2 synthesis). The FSH serum concentrations were only slightly lower than preinsertion levels and LH surges were prevented. The viscosity of the cervical mucus was increased. The endometrium was thin but not atrophic; it showed primarily inactive or weak proliferation. Return of ovulation after removal of Implanon was rapid.

Synthetic progestins used in HRT have different glucocorticoid agonist properties

The synthetic progestins, medroxyprogesterone acetate (MPA) and norethisterone acetate (NET-EN or NET-A), are widely used as female contraceptive agents and in hormone replacement therapy (HRT). Competitive binding revealed that MPA displays a higher relative binding affinity than NET-A and progesterone (prog) for the human GR (Kd of 4.2 nM for dexamethasone (dex) and Ki's of 10.8, 270 and 215 nM for MPA, NET-A and prog, respectively). Furthermore, MPA displays much greater glucocorticoid (GC) transactivation agonist potency than NET-A or prog (EC50s of 1.1, 7.2, >1000 and 280 nM for dex, MPA, NET-A and prog, respectively) and much greater GC agonist potency for transrepression than NET-A or prog (EC50s of 0.21, 2.7, >100 and 26 nM for dex, MPA, NET-A and prog, respectively). In addition, MPA induces phosphorylation of the GR at Ser 211 to a much greater extent than NET-A or prog and protects the GR from partial trypsin digestion in vitro to a much greater extent than NET-A or prog at saturating concentrations. Together these results suggest that the differences in biological activity of the progestins are not merely due to differences in their affinity for the GR but also due to the induction of different conformational changes in the liganded-GR. MPA and NET-A therefore display very different GC-like properties compared to each other and to prog, and are likely to exhibit different side effects via the GR.