Selective ligands of membrane progesterone receptors as a key to studying their biological functions in vitro and in vivo.

Progesterone modulates many processes in the body, acting through nuclear receptors (nPR) in various organs and tissues. However, a number of effects are mediated by membrane progesterone receptors (mPRs), which are members of the progestin and adipoQ (PAQR) receptor family. These receptors are found in most tissues and immune cells. They are expressed in various cancer cells and appear to play an important role in the development of tumors. The role of mPRs in the development of insulin resistance and metabolic syndrome has also attracted attention. Since progesterone efficiently binds to both nPRs and mPRs, investigation of the functions of the mPRs both at the level of the whole body and at the cell level requires ligands that selectively interact with mPRs, but not with nPRs, with an affinity comparable with that of the natural hormone. The development of such ligands faces difficulties primarily due to the lack of data on the three-dimensional structure of the ligand-binding site of mPR. This review is the first attempt to summarize available data on the structures of compounds interacting with mPRs and analyze them in terms of the differences in binding to membrane and nuclear receptors. Based on the identified main structural fragments of molecules, which affect the efficiency of binding to mPRs and are responsible for the selectivity of interactions, we propose directions of modification of the steroid scaffold to create new selective mPRs ligands.

A direct comparison of the transcriptional activities of progestins used in contraception and menopausal hormone therapy via the mineralocorticoid receptor.

A variety of structurally and functionally distinct progestins is used in contraception and menopausal hormone therapy (MHT). Some progestins elicit off-target effects by binding to steroid receptors other than the progesterone receptor, which may impact their therapeutic and side-effect profiles. We directly compared the binding affinities, efficacies and potencies of selected progestins via the mineralocorticoid receptor (MR). We did not detect a significant difference in the affinities of medroxyprogesterone acetate (MPA), norethisterone acetate (NET-A), levonorgestrel (LNG), gestodene (GES), etonogestrel (ETG), nestorone (NES) and nomegestrel acetate (NoMAC) for the MR, while these were significantly lower compared to drospirenone (DRSP). While GES and NoMAC display affinities indistinguishable from progesterone (P4), the binding affinity of DRSP is significantly greater and all other progestins significantly lower than that of P4. Dose-response analyses showed that P4, GES and ETG display indistinguishable MR antagonist potencies for transactivation to the well-known MR antagonist spironolactone, while LNG, NoMAC and DRSP are significantly more potent than spironolactone and MPA, NET-A and NES are significantly less potent. Similar to our previous findings for NET-A, we show that LNG, GES, ETG and NES dissociate between transactivation and transrepression via the MR. Together our results provide strong evidence for progestin- and promoter-specific transcriptional effects via the MR, which are poorly predicted by relative binding affinities. A comparison of the binding affinities and potencies with reported free serum concentrations of progestins relative to the endogenous mineralocorticoid aldosterone, suggest that all progestins except MPA, NET-A and NES will likely compete with aldosterone for binding to the MR in vivo at doses used in hormonal therapy to elicit physiologically significant off-target effects.

Equine placentitis is associated with a downregulation in myometrial progestin signaling†.

The current study aimed to elucidate the mechanisms underlying myometrial activation during equine placentitis related to progestogens and the progesterone receptor signaling pathways. Placentitis was induced via intracervical inoculation with Streptococcus equi ssp zooepidemicus in mares at approximately 290 days of gestation (placentitis group; n = 6) with uninoculated gestationally matched mares as controls (n = 4). Mares in the placentitis and control groups were euthanized, and myometrial samples were collected from two regions: region 1-parallel to active placentitis lesion with placental separation in placentitis group (P1) or caudal pole of the placenta in control group (C1); and region 2-parallel to apparently normal placenta without separation in placentitis group (P2) or uterine body in control group (C2). In the current study, SRD5A1 and AKR1C23, which encode for the key P4 metabolizing enzymes, were downregulated in P1 in comparison to C1, C2, and P2, and this was associated with a decline (P < 0.05) in 5αDHP, allopregnanolone (3αDHP), and 20αDHP in P1 in comparison to C1. Further, myometrial expression of PR was downregulated (P < 0.05) in P1 in comparison to C1 and P2, and this was associated with activation of the inflammatory cascade as reflected by significant upregulation of IL-1ß and IL-8 in P1 in comparison to C1, C2, and P2, and supported by increased tissue leukocytes in P1 in comparison to C1. In conclusion, equine placentitis is associated with a localized withdrawal of progestins and a downregulation of the PR in the myometrium concomitant with upregulation of inflammatory cytokines and subsequent myometrial activation.

Nuclear and membrane progestin receptors in the European eel: Characterization and expression in vivo through spermatogenesis.

Characterization of all the progestin receptor genes (PRs) found in the European eel has been performed. There were five membrane PRs (mPRs): mPRα (alpha), mPRAL1 (alpha-like1), mPRAL2 (alpha-like2), mPRγ (gamma), mPRδ (delta) and two nuclear PRs (nPRs or PGRs): pgr1 and pgr2. In silico studies showed that the C and E(F) domains of Pgr are well conserved among vertebrates whereas the A/B domain is not. Phylogeny and synteny analyses suggest that eel duplicated pgr (pgr1 and pgr2) originated from the teleost-specific third whole genome duplication (3R). mPR phylogeny placed three eel mPRs together with the mPRα clade, being termed mPRα, mPRAL1 and mPRAL2, while the other two eel mPRs clustered with mPRγ and mPRδ clades, respectively. The in vivo study showed differential expression patterns along the brain-pituitary-gonad axis. An increase in nPR transcripts was observed in brain (in pgr1) and pituitary (in pgr1 and pgr2) through the spermatogenesis, from the spermatogonia B/spermatocyte stage to the spermiation stage. In the testis, mPRγ, mPRδ and pgr2 transcripts showed the highest levels in testis with A spermatogonia as dominant germ cell, while the highest mPRα, mPRAL1 and mPRAL2 transcripts were observed in testis from spermiating males, where the dominant germ cell were spermatozoa. Further studies should elucidate the role of both nuclear and membrane progestin receptors on eel spermatogenesis.

Endometrial prostaglandin synthases, ovarian steroids, and oxytocin receptors in mares with oxytocin-induced luteal maintenance.

Oxytocin (OXT) has been used to prolong the luteal phase in mares, but its mechanism of action is unknown. The aim of this study was to evaluate the effect of chronic exogenous OXT administration to mid-luteal phase mares on luteal maintenance. Also, endometrial expression of prostaglandin endoperoxide synthase 2 (PTGS2), prostaglandin F2α, E2 and I2 synthases (AKR1C3, PTGES, and PTGIS), oxytocin receptor (OXTR), progesterone receptor (PGR), and estrogen receptors 1 (ESR1) and 2 (ESR2) were assessed in mares experiencing luteal maintenance 2 weeks after chronic exogenous OXT administration. Control mares (n = 5; C group) received 6 mL of saline im, whereas OXT (60 units/mare) was administered im (n = 6; OXT group), every 12 hours, on days 7 to 14 postovulation. After endometrial biopsy in groups C (Day 10) and OXT (Day 24), luteolysis occurred within 3 or 6 days, respectively. Luteal maintenance took place in 4 of 6 (67%) of OXT-treated mares. Progesterone in C group was the highest on biopsy day (P < 0.05). In OXT mares, PTGS2, ESR1 (P < 0.05), PTGES, PTGIS, PGR, and ESR2 (P < 0.01) gene transcription decreased, whereas OXTR increased (P < 0.05) in comparison with the C group. In OXT-treated mares, endometrial ESR2 protein expression decreased (P < 0.05), but OXTR increased (P < 0.05) compared with control animals. In both experimental groups, PTGS2 was mainly immunolocalized in surface epithelium, whereas AKR1C3, PTGES, PTGIS, and PGR were in surface and glandular epithelia. ESR1 and ESR2 were found in glandular epithelium and OXTR in stromal cells. High immunolabeling for PTGES, PTGIS, PGR, and OXTR and low for ESR2 was detected in endometrium of OXT-group mares with extended diestrus. Prolonged luteal function associated with chronic OXT treatment may be related to different spatial expression of OXTR and PGR in the endometrium. The observed reduction of endometrial ESR2 may be responsible for the maintenance of PGR in luminal and glandular epithelium. Also, ESR2 may attenuate the transcriptional activity of ESR1 in mare endometrium. This study offers new knowledge on the endometrial expression of ovarian steroids and OXT receptors in OXT pharmacologically induced luteal maintenance in the mare.

The synthetic gestagen levonorgestrel directly affects gene expression in thyroid and pituitary glands of Xenopus laevis tadpoles.

The synthetic gestagen levonorgestrel (LNG) was previously shown to perturb thyroid hormone-dependent metamorphosis in Xenopus laevis. However, so far the mechanisms underlying the anti-metamorphic effects of LNG remained unknown. Therefore, a series of in vivo and ex vivo experiments was performed to identify potential target sites of LNG action along the pituitary-thyroid axis of X. laevis tadpoles. Prometamorphic tadpoles were treated in vivo with LNG (0.01-10nM) for 72h and brain-pituitary and thyroid tissue was analyzed for marker gene expression. While no treatment-related changes were observed in brain-pituitary tissue, LNG treatment readily affected thyroidal gene expression in tadpoles including decreased slc5a5 and iyd mRNA expression and a strong induction of dio2 and dio3 expression. When using an ex vivo organ explant culture approach, direct effects of LNG on both pituitary and thyroid gland gene expression were detecTable Specifically, treatment of pituitary explants with 10nM LNG strongly stimulated dio2 expression and concurrently suppressed tshb expression. In thyroid glands, ex vivo LNG treatment induced dio2 and dio3 mRNA expression in a thyrotropin-independent manner. When thyroid explants were cultured in thyrotropin-containing media, LNG caused similar gene expression changes as seen after 72h in vivo treatment including a very strong repression of thyrotropin-induced slc5a5 expression. Concerning the anti-thyroidal activity of LNG as seen under in vivo conditions, our ex vivo data provide clear evidence that LNG directly affects expression of genes important for thyroidal iodide handling as well as genes involved in negative feedback regulation of pituitary tshb expression.

Genetic engineering of Bacillus megaterium for high-yield production of the major teleost progestogens 17α,20ß-di- and 17α,20ß,21α-trihydroxy-4-pregnen-3-one.

17α,20ß-Dihydroxy-4-pregnen-3-one (17α,20ßDiOH-P) and 17α,20ß,21α-trihydroxy-4-pregnen-3-one (20ßOH-RSS) are the critical hormones required for oocyte maturation in fish. We utilized B. megaterium's endogenous 20ß-hydroxysteroid dehydrogenase (20ßHSD) for the efficient production of both progestogens after genetically modifying the microorganism to reduce side-product formation. First, the gene encoding the autologous cytochrome P450 CYP106A1 was deleted, resulting in a strain devoid of any steroid hydroxylation activity. Cultivation of this strain in the presence of 17α-hydroxyprogesterone (17αOH-P) led to the formation of 17α,20α-dihydroxy-4-pregnen-3-one (17α,20αDiOH-P) as a major and 17α,20ßDiOH-P as a minor product. Four enzymes were identified as 20αHSDs and their genes deleted to yield a strain with no 20αHSD activity. The 3-oxoacyl-(acyl-carrier-protein) reductase FabG was found to exhibit 20ßHSD-activity and overexpressed to create a biocatalyst yielding 0.22g/L 17α,20ßDiOH-P and 0.34g/L 20ßOH-RSS after 8h using shake-flask cultivation, thus obtaining products that are at least a thousand times more expensive than their substrates.

[Molecular basis and tissue specificity of the progestins action].

The review considers the effect of progestins on the function, proliferation, and apoptosis of cells of various organs in health and noncancerous disorders. Data are summarized to describe the mechanism of progestin action through various progesterone receptors and sensors and the regulation of their levels. The effects of progestins depend on the cell phenotype, including the composition and proportion of different receptors, activity of signaling pathways, and expression of transcription factor coregulators and steroid metabolism enzymes. The role paracrine regulation plays in the progestin effect is described. Particular attention is paid to the progestin effect on the tissues where progestins are thought or known to affect carcinogenesis or to stimulate or suppress the tumor growth, that is, to modulate cell proliferation, apoptosis, and the epithelial-mesenchymal transition.

[Effect of drug-paste separated moxibustion on expression of estrogen, progestogen and their endometrial receptor mRNA in rats with primary dysmenorrhea].

OBJECTIVE: To observe the effect of drug-paste separated moxibustion of "Mingmen" (GV 4) on the levels of serum estrogen (E2) and progesterone (P) and their endometrial receptor mRNA expression in rats with primary dysmenorrhea in order to investigate its mechanism underlying improvement of primary dysmenorrhea. METHODS: A total of 100 female SD rats were randomized into control, model, medication, acupuncture and moxibustion groups, with 20 rats in each group. Primary dysmenorrhea model was established by subcutaneous injection of Benzestrofol for 10 days and intraperitoneal injection of Oxytocin for 1 d. Rats of the medication group were fed with extractum leonuri inspissatum (8 g/100 g) and those of the moxibustion group treated with drug-paste separated moxibustion at "Mingmen" (GV 4). For rats of the acupuncture group, a filiform needle was inserted into GV 4, manipulated for a while and retained for 30 min. The treatment of the latter 3 groups was conducted once daily for 7 days. The rat's body-writhing latency and times during 30 min were recorded. The contents of serum E2 and P were detected by ELISA, and the expression of estrogen receptor (ER) mRNA and progesterone receptor (PR) mRNA in the endometrium was determined by quantitative real-time (RT)-PCR. RESULTS: (1) The body-writhing latency was shorter and the writhing times were more in the model group than in the control group (P < 0.01). Compared with the model group, the body-writhing latency was significantly increased and the writhing times were obviously decreased in the medication, acupuncture and moxibustion groups (P < 0.01). There were no significant differences among the medication, acupuncture and moxibustion groups in the body-writhing latency (P > 0.05), but the body-writhing numbers of the acupuncture and moxibustion groups were markedly lower than that of the medication group (P < 0.01). (2) Compared with the control group, serum E2 content and endometrial ER mRNA expression level were significantly increased, and serum P content and endometrial PR mRNA level evidently decreased in the model group (P < 0.01, P < 0.05). In comparison with the model group, serum E2 contents and endometrial ER mRNA expression levels were considerably down-regulated, and serum P contents and endometrial PR mRNA expression levels markedly up-regulated in the medication, acupuncture and moxibustion groups (P < 0.01, P < 0.05). The effects of the moxibustion group were significantly superior to those of the acupuncture and medication groups, and those of the acupuncture group were also significantly superior to those of the medication group in lowering E2 and endometrial ER mRNA levels, and raising serum P and endometrial PR mRNA expression levels (P < 0.01, P < 0.05). CONCLUSION: Drug-paste separated moxibustion of GV 4 is effective in relieving pain in primary dysmenorrheal rats, which is probably associated with its effects in down-regulating serum E2 content and endometrial ER mRNA expression, and up-regulating serum P and endometrial PR mRNA expression levels.

Transcriptional signature of progesterone in the fathead minnow ovary (Pimephales promelas).

A growing number of studies have examined transcriptional responses to sex steroids along the hypothalamic-pituitary-gonadal axis in teleost fishes. However, data are lacking on the molecular cascades that underlie progesterone signaling. The objective of this study was to characterize the transcriptional response in the ovary of fathead minnows (Pimephales promelas) in response to progesterone (P4). Fathead minnow ovaries were exposed in vitro to 500 ng P4/L. Germinal vesicle migration and breakdown (GVBD) was observed and microarrays were used to identify gene cascades affected by P4. Microarray analysis identified 1702 differentially expressed transcripts after P4 treatment. Functional enrichment analysis revealed that transcripts involved in the molecular functions of protein serine/threonine kinase activity, ATP binding, and activity of calcium channels were increased after P4 treatment. There was an overwhelming decrease in levels of transcripts of genes that are structural constituents of ribosomes with P4 treatment. There was also evidence for gene expression changes in steroid and maturation-related transcripts. Pathway analyses identified cell cycle regulation, insulin action, hedgehog, and B cell activation as pathways containing an over-representation of highly regulated transcripts. Significant regulatory sub-networks of P4-mediated transcripts included genes regulated by tumor protein p53 and E2F transcription factor 1. These data provide novel insight into the molecular signaling cascades that underlie P4-signaling in the ovary and identify genes and processes that may indicate premature GVBD due to environmental pollutants that mimic progestins.

Evolution of minimal specificity and promiscuity in steroid hormone receptors.

Most proteins are regulated by physical interactions with other molecules; some are highly specific, but others interact with many partners. Despite much speculation, we know little about how and why specificity/promiscuity evolves in natural proteins. It is widely assumed that specific proteins evolved from more promiscuous ancient forms and that most proteins' specificity has been tuned to an optimal state by selection. Here we use ancestral protein reconstruction to trace the evolutionary history of ligand recognition in the steroid hormone receptors (SRs), a family of hormone-regulated animal transcription factors. We resurrected the deepest ancestral proteins in the SR family and characterized the structure-activity relationships by which they distinguished among ligands. We found that that the most ancient split in SR evolution involved a discrete switch from an ancient receptor for aromatized estrogens--including xenobiotics--to a derived receptor that recognized non-aromatized progestagens and corticosteroids. The family's history, viewed in relation to the evolution of their ligands, suggests that SRs evolved according to a principle of minimal specificity: at each point in time, receptors evolved ligand recognition criteria that were just specific enough to parse the set of endogenous substances to which they were exposed. By studying the atomic structures of resurrected SR proteins, we found that their promiscuity evolved because the ancestral binding cavity was larger than the primary ligand and contained excess hydrogen bonding capacity, allowing adventitious recognition of larger molecules with additional functional groups. Our findings provide an historical explanation for the sensitivity of modern SRs to natural and synthetic ligands--including endocrine-disrupting drugs and pollutants--and show that knowledge of history can contribute to ligand prediction. They suggest that SR promiscuity may reflect the limited power of selection within real biological systems to discriminate between perfect and "good enough."

Non-overlapping progesterone receptor cistromes contribute to cell-specific transcriptional outcomes.

The transcriptional effects of the ovarian hormone progesterone are pleiotropic, and binding to DNA of the nuclear progesterone receptor (PR), a ligand-activated transcription factor, results in diverse outcomes in a range of target tissues. To determine whether distinct patterns of genomic interaction of PR contribute to the cell specificity of the PR transcriptome, we have compared the genomic binding sites for PR in breast cancer cells and immortalized normal breast cells. PR binding was correlated with transcriptional outcome in both cell lines, with 60% of progestin-regulated genes associated with one or more PR binding regions. There was a remarkably low overlap between the PR cistromes of the two cell lines, and a similarly low overlap in transcriptional targets. A conserved PR binding element was identified in PR binding regions from both cell lines, but there were distinct patterns of enrichment of known cofactor binding motifs, with FOXA1 sites over-represented in breast cancer cell binding regions and NF1 and AP-1 motifs uniquely enriched in the immortalized normal line. Downstream analyses suggested that differential cofactor availability may generate these distinct PR cistromes, indicating that cofactor levels may modulate PR specificity. Taken together these data suggest that cell-specificity of PR binding is determined by the coordinated effects of key binding cofactors.

Variations in sex hormone metabolism genes, postmenopausal hormone therapy and risk of endometrial cancer.

We investigated whether variants in sex steroid hormone metabolism genes modify the effect of hormone therapy (HT) on endometrial cancer risk in postmenopausal non-Hispanic white women. A nested case-control study was conducted within the California Teachers Study (CTS). We genotyped htSNPs in six genes involved in the hormone metabolism in 286 endometrial cancer cases and 488 controls. Odds ratio (OR) and 95% confidence interval (CI) were estimated for each haplotype using unconditional logistic regression, adjusting for age. The strongest interaction was observed between duration of estrogen therapy (ET) use and haplotype 1A in CYP11A1 (p(interaction) = 0.0027; p(interaction) = 0.010 after correcting for multiple testing within each gene). The OR for endometrial cancer per copy of haplotype 1A was 2.00 (95% CI: 1.05-3.96) for long-term ET users and 0.90 (95% CI: 0.69-1.18) for never users. The most significant interaction with estrogen-progestin therapy (EPT) was found for two haplotypes on CYP19A1 and EPT use (haplotype 4A, p(interaction) = 0.024 and haplotype 3B, p(interaction) = 0.043). However, neither this interaction, nor the ET or EPT interactions for any other genes, was statistically significant after correction for multiple testing. Variations in CYP11A1 may modify the effect of ET use on risk of postmenopausal endometrial cancer; however, larger studies are needed to explore these findings further.

Gene expression profiles of progestin-induced canine mammary hyperplasia and spontaneous mammary tumors.

Spontaneous mammary tumors are the most prevalent type of neoplasms in women as well as in female dogs. Although ovarian hormones estrogen and progesterone are known to play a key role in mammary tumorigenesis, conflicting reports have been obtained from in vivo and in vitro studies concerning the role of especially progesterone in mammary tumorigenesis. Prolonged exposure to high concentrations of progesterone during the unusually long luteal phase of the estrous cycle is suspected to be the key event in canine mammary tumorigenesis. Accordingly, previous studies have shown the development of mammary hyperplasia in dogs upon prolonged progestin administration. In this study, a dog-specific cDNA microarray was used to identify oncogenic determinants in progestin-induced canine hyperplasia (CMH) and spontaneous mammary tumors (CMC) by comparing expression profiles to those obtained from mammary glands of healthy dogs. The CMH profile showed elevated expression of genes involved in cell proliferation such as PCNA, NPY, RAN and also alterations in expression of transcription factors and cell adhesion molecules. Whereas in CMC, major alterations to the expression of genes involved in cell motility, cytoskeletal organization and extra cellular matrix production was evident besides differential expression of cell proliferation inducing genes. The overall gene expression profile of CMH was related to cell proliferation where as that of CMC was associated with both cell proliferation as well as neoplastic transformation. In conclusion, our findings support a strong cell proliferation inducing potential of progestins in the canine mammary gland. Moreover, deregulated genes identified in CMC are potentially involved in their malignant and may serve as prospective therapeutic targets.

Progesterone receptor A-regulated gene expression in mammary organoid cultures.

Progesterone, through the progesterone receptor (PR), promotes development of the normal mammary gland and is implicated in the etiology of breast cancer. We identified PRA-regulated genes by microarray analysis of cultured epithelial organoids derived from pubertal and adult mouse mammary glands, developmental stages with differing progesterone responsiveness. Microarray analysis showed significant progestin (R5020)-regulation of 162 genes in pubertal organoids and 104 genes in adult organoids, with 68 genes regulated at both developmental stages. Greater induction of receptor activator of NFkappaB ligand and calcitonin expression was observed in adult organoids, suggesting possible roles in the differential progesterone responsiveness of the adult and pubertal mammary glands. Analysis of the R5020-responsive transcriptome revealed several enriched biological processes including cell adhesion, immune response, and survival. R5020 both induced Agtr1 and potentiated angiotensin II-stimulated proliferation, highlighting the functional significance of the latter process. Striking up-regulation of genes involved in innate immunity processes included the leukocyte chemoattractants serum amyloid A1, 2 and 3 (Saa1, 2, 3). In vivo analysis revealed that progesterone treatment increased SAA1 protein expression and leukocyte density in mammary gland regions undergoing epithelial expansion. These studies reveal novel targets of PRA in mammary epithelial cells and novel linkages of progesterone action during mammary gland development.

Identification of microRNAs controlling human ovarian cell steroidogenesis via a genome-scale screen.

The aim of our studies was to identify miRNAs affecting the release of the major ovarian steroid hormones progestagen, androgen and estrogen by human ovarian cells. The effect of transfection of cultured primary ovarian granulosa cells with 80 different gene constructs encoding human pre-miRNAs on release of progesterone, testosterone and estradiol was evaluated by enzyme immunoassay. In addition, effect of two selected antisense constructs blocking corresponding miRNA on progesterone release was tested. Efficiency of transfection (incorporation transfection reagent) and silencing of marker substances (GAPDH mRNA, GAPDH and CREB-1) were validated by fluorescent microscopy, real-time reverse transcription-PCR analysis and immunocytochemical analysis. Thirty-six out of 80 tested miRNA constructs resulted in inhibition of progesterone release in granulosa cells, and 10 miRNAs promoted progesterone release. Transfected of cells with antisense constructs to two selected miRNAs blocking progesterone release induced increase in progesterone output. Fifty-seven miRNAs tested inhibited testosterone release, and only one miRNA enhanced testosterone output. Fifty-one miRNAs suppressed estradiol release, while none of the miRNAs tested stimulated it. This is the first demonstration that miRNAs can control reproductive functions resulting in enhanced or inhibited release of ovarian progestagen, androgen and estrogen. We hypothesize that such miRNA-mediated effects could be potentially used for regulation of reproductive processes, including fertility, and for treatment of reproductive and other steroid-dependent disorders.

Gene polymorphisms that may influence the biological effects of progestins.

Many of the biological actions of progestins depend on binding to intracellular receptors and through a long chain of events to subsequent stimulation of transcriptional activity and protein synthesis. This process requires at least a few hours in time and many different proteins called coregulators do play a role after binding to the receptor. Evidence for polymorphisms in the gene coding for the PR has been obtained and many studies have already attempted to show associations between particular polymorphisms and human diseases. However, at present no consistent and conclusive picture has emerged on clinically important associations. Studies on links between polymorphisms in genes coding for coregulators are just beginning. The second pathway, the so-called non-genomic actions, is related to rapid effects of progestins that occur within minutes. At this moment a number of different membrane bound receptors have been identified. No data are available yet on polymorphisms in genes coding for these proteins or to link any of these membrane receptors to specific human pathology.

Progestin is an essential factor for the initiation of the meiosis in spermatogenetic cells of the eel.

Meiosis is an indispensable process of sexual reproduction. However, detailed information on the regulatory mechanisms that initiate meiosis is not available. Progestins are important steroids regulating final maturation in male and female vertebrates. In male teleosts, it is known that progestin induces spermiation and sperm maturation. However, a role for progestin in early spermatogenesis or meiosis has not yet been described. In this study, we examined the functions of progestin on the initiation of meiosis in male Japanese eel. A natural progestin in teleost fish 17alpha,20beta-dihydroxy-4-pregnen-3-one (DHP) and its receptors were present in the testis at an early stage of spermatogenesis. By using an eel testicular culture system, DHP was shown to induce DNA replication in spermatogonia. Although 11-ketotestosterone, a known initiator of spermatogenesis, also stimulated DNA synthesis in spermatogonia, antibodies against DHP prevented DNA replication when added during the period in which meiosis was initiated. DHP treatment also induced the expression of meiosis-specific markers, such as DmcI and Spo11. Furthermore, Spo11 expression and synaptonemal complexes, specific features of the meiotic prophase, were detected in testicular fragments cultured with DHP in some germ cells that showed morphological characteristics of undifferentiated spermatogonia. We conclude that DHP, a progestin, is an essential factor for the initiation of meiosis.

Progestin regulation in tumor growth of female genital tract cancers.

The irregular response to progestins directly in tumor growth might be caused by dominant negative progesterone receptor (PR) mutants and the damage to PR-A expression. Progestin treatment as an anti-angiogenic therapy would be less effective in the PR-mutated tumors. Therefore, various anti-angiogenic inhibitors must be used in progestin-refractory and progestin-dependent tumors.