Prolactin-mediated inhibition of 20alpha-hydroxysteroid dehydrogenase gene expression and the tyrosine kinase system

PGF2alpha Inhibits 20alpha-HSD Expression by Suppressing CK1alpha-induced ERK and SP1 Activation in the Corpus Luteum of Pregnant Mice

Prostaglandin F2α (PGF2α) is a luteolytic hormone that promotes parturition in mammals at the end of pregnancy by reducing progesterone secretion from the corpus luteum (CL). In rodents and primates, PGF2α rapidly converts progesterone to 20α-hydroxyprogesterone (20α-OHP) by promoting 20α-hydroxysteroid dehydrogenase (20α-HSD) expression. However, the specific mechanism of 20α-HSD regulation by PGF2α remains unclear. Casein Kinase 1α (CK1α) is a CK1 family member that regulates a variety of physiological functions, including reproductive development. Here, we investigated the effects of CK1α on pregnancy in female mice. Our experiments showed that CK1α is expressed in mouse CL, and its inhibition enhanced progesterone metabolism, decreased progesterone levels, and affected mouse embryo implantation. Further, CK1α mediated the effect of PGF2α on 20α-HSD in mouse luteal cells in vitro. Our results are the first to show that CK1α affects the 20α-HSD mRNA level by affecting the ERK signalling pathway to regulate the expression of the transcription factor SP1. These findings improve our understanding of PGF2α regulation of 20α-HSD.

A possible function of Nik-related kinase in the labyrinth layer of delayed delivery mouse placentas

In mice and humans, Nik-related protein kinase (Nrk) is an X-linked gene that encodes a serine/threonine kinase belonging to GCK group 4. Nrk knockout (Nrk KO) mice exhibit delayed delivery, possibly due to defective communication between the Nrk KO conceptus and its mother. However, the mechanism of delayed labor remains largely unknown. Here, we found that in pregnant mothers with the Nrk KO conceptus, the serum progesterone (P4) and placental lactogen (PL-2) concentrations in late pregnancy were higher than those in the wild type. Moreover, we demonstrated that Nrk is expressed in trophoblast giant cells (TGCs) and syncytiotrophoblast-2 (SynT-2) in the labyrinth layer of the mouse placenta. In the human placenta, NRK is also expressed in Syn-T in villi. Both human Syn-T and mouse TGCs of the labyrinth layer are present within fetal tissues that are in direct contact with the maternal blood. The labyrinth layer of the Nrk KO conceptus was gigantic, with enlarged cytoplasm and Golgi bodies in the TGCs. To investigate the function of Nrk in the labyrinth layer, a differentially expressed gene (DEG) analysis was performed. The DEG analysis revealed that labor-promoting factors, such as prostaglandins, were decreased, and pregnancy-maintaining factors, such as the prolactin family and P4 receptor, were increased. These findings suggest that the Nrk KO mice exhibit delayed delivery owing to high P4 concentrations caused by the hypersecretion of pregnancy-maintaining factors, such as PL-2, from the placenta.

Evolution of Placental Hormones: Implications for Animal Models

Human placenta secretes a variety of hormones, some of them in large amounts. Their effects on maternal physiology, including the immune system, are poorly understood. Not one of the protein hormones specific to human placenta occurs outside primates. Instead, laboratory and domesticated species have their own sets of placental hormones. There are nonetheless several examples of convergent evolution. Thus, horse and human have chorionic gonadotrophins with similar functions whilst pregnancy-specific glycoproteins have evolved in primates, rodents, horses, and some bats, perhaps to support invasive placentation. Placental lactogens occur in rodents and ruminants as well as primates though evolved through duplication of different genes and with functions that only partially overlap. There are also placental hormones, such as the pregnancy-associated glycoproteins of ruminants, that have no equivalent in human gestation. This review focusses on the evolution of placental hormones involved in recognition and maintenance of pregnancy, in maternal adaptations to pregnancy and lactation, and in facilitating immune tolerance of the fetal semiallograft. The contention is that knowledge gained from laboratory and domesticated mammals can translate to a better understanding of human placental endocrinology, but only if viewed in an evolutionary context.

Contribution of Prostaglandin Transporter OATP2A1/SLCO2A1 to Placenta-to-Maternal Hormone Signaling and Labor Induction

We evaluated the contribution of organic anion transporting polypeptide 2A1 (OATP2A1/SLCO2A1), a high-affinity carrier for prostaglandins (PGs), to the parturition process. At gestational day (GD) 15.5, OATP2A1 is co-localized with 15-hydroxy-PG dehydrogenase in the mouse placental junctional zone and facilitates PG degradation by delivering PGs to the cytoplasm. Slco2a1 (+/-) females mated with Slco2a1 (-/-) males frequently showed elevated circulating progesterone at GD18.5 and delayed parturition. Progesterone receptor inhibition by RU486 treatment at GD18.5 blocked the delay of parturition. In the junctional zone, PGE2 stimulated placental lactogen II (PL-II) production, resulting in higher expression of PL-II in Slco2a1 (-/-) placenta at GD18.5. Indomethacin treatment at GD15.5 suppressed the PL-II overproduction at GD18.5 in Slco2a1 (-/-) embryo-bearing dams, which promoted progesterone withdrawal and corrected the delayed parturition. These results suggest that extracellular PGE2 reduction by OATP2A1 at mid-pregnancy would be associated with progesterone withdrawal by suppressing PL-II production, triggering parturition onset.

Hormonal behavior correlates with follicular recruitment at mid-gestation in the South American plains vizcacha, Lagostomus maximus (Rodentia, Caviomorpha)

In mammals, hormonal regulation during gestation is crucial for embryo implantation and pregnancy success. This regulation is controlled through the level of progesterone (P4) that blocks the activity of the hypothalamic-hypophyseal-gonadal (HHG) axis. Previous studies in the pregnant South American plains vizcacha, Lagostomus maximus, have shown that the HHG axis activates around mid-gestation, promoting pre-ovulatory follicle formation. However, the characterization of the hormonal dynamics throughout gestation and its ovarian correlation has not been studied in depth. We studied the ovarian dynamics of L. maximus and its correlation with the hormonal profile during gestation, analyzing serum levels of P4, 17β-estradiol (E2), 4Δ-androstenedione (A4), luteinizing hormone (LH) and follicle stimulating hormone (FSH) as well as the ovarian distribution and expression of their receptors. Additionally, we have analyzed the folliculogenesis and accessory corpora lutea (ACL) formation. P4 showed two concentration peaks reaching its highest level at mid-gestation decreasing at 91-100days post-coitum. P4 decrease is followed by an increase of circulating levels of A4, E2, FSH and LH and with an elevated number of antral/pre-ovulatory follicles which express PGR, ESR1, ESR2, AR, LHR and FSHR. In addition, ACL with oocyte retention and cytoplasmic lipid droplets in luteal cells were detected at this time point. These results show that in L. maximus the decrease of P4 level from mid-gestation enables follicular recruitment until pre-ovulatory stage and the development of functional ACL.

Low Prolactin and High 20-α-Hydroxysteroid Dehydrogenase Levels Contribute to Lower Progesterone Levels in HIV-Infected Pregnant Women Exposed to Protease Inhibitor-Based Combination Antiretroviral Therapy

BACKGROUND

It has been reported that pregnant women receiving protease inhibitor (PI)-based combination antiretroviral therapy (cART) have lower levels of progesterone, which put them at risk of adverse birth outcomes, such as low birth weight. We sought to understand the mechanisms involved in this decline in progesterone level.

METHODS

We assessed plasma levels of progesterone, prolactin, and lipids and placental expression of genes involved in progesterone metabolism in 42 human immunodeficiency virus (HIV)-infected and 31 HIV-uninfected pregnant women. In vitro studies and a mouse pregnancy model were used to delineate the effect of HIV from that of PI-based cART on progesterone metabolism.

RESULTS

HIV-infected pregnant women receiving PI-based cART showed a reduction in plasma progesterone levels (P= .026) and an elevation in placental expression of the progesterone inactivating enzyme 20-α-hydroxysteroid dehydrogenase (20α-HSD; median, 2.5 arbitrary units [AU]; interquartile range [IQR], 1.00-4.10 AU), compared with controls (median, 0.89 AU; IQR, 0.66-1.26 AU;P= .002). Prolactin, a key regulator of 20α-HSD, was lower (P= .012) in HIV-infected pregnant women. We observed similar data in pregnant mice exposed to PI-based cART. In vitro inhibition of 20α-HSD activity in trophoblast cells reversed PI-based cART-induced decreases in progesterone levels.

CONCLUSIONS

Our data suggest that the decrease in progesterone levels observed in HIV-infected pregnant women exposed to PI-based cART is caused, at least in part, by an increase in placental expression of 20α-HSD, which may be due to lower prolactin levels observed in these women.

Sex-Specific Placental Responses in Fetal Development

The placenta is an ephemeral but critical organ for the survival of all eutherian mammals and marsupials. It is the primary messenger system between the mother and fetus, where communicational signals, nutrients, waste, gases, and extrinsic factors are exchanged. Although the placenta may buffer the fetus from various environmental insults, placental dysfunction might also contribute to detrimental developmental origins of adult health and disease effects. The placenta of one sex over the other might possess greater ability to respond and buffer against environmental insults. Given the potential role of the placenta in effecting the lifetime health of the offspring, it is not surprising that there has been a resurging interest in this organ, including the Human Placental Project launched by the National Institutes of Child Health and Human Development. In this review, we will compare embryological development of the laboratory mouse and human chorioallantoic placentae. Next, evidence that various species, including humans, exhibit normal sex-dependent structural and functional placental differences will be examined followed by how in utero environmental changes (nutritional state, stress, and exposure to environmental chemicals) might interact with fetal sex to affect this organ. Recent data also suggest that paternal state impacts placental function in a sex-dependent manner. The research to date linking placental maladaptive responses and later developmental origins of adult health and disease effects will be explored. Finally, we will focus on how sex chromosomes and epimutations may contribute to sex-dependent differences in placental function, the unanswered questions, and future directions that warrant further consideration.

Evolution of Placental Function in Mammals: The Molecular Basis of Gas and Nutrient Transfer, Hormone Secretion, and Immune Responses

Placenta has a wide range of functions. Some are supported by novel genes that have evolved following gene duplication events while others require acquisition of gene expression by the trophoblast. Although not expressed in the placenta, high-affinity fetal hemoglobins play a key role in placental gas exchange. They evolved following duplications within the beta-globin gene family with convergent evolution occurring in ruminants and primates. In primates there was also an interesting rearrangement of a cassette of genes in relation to an upstream locus control region. Substrate transfer from mother to fetus is maintained by expression of classic sugar and amino acid transporters at the trophoblast microvillous and basal membranes. In contrast, placental peptide hormones have arisen largely by gene duplication, yielding for example chorionic gonadotropins from the luteinizing hormone gene and placental lactogens from the growth hormone and prolactin genes. There has been a remarkable degree of convergent evolution with placental lactogens emerging separately in the ruminant, rodent, and primate lineages and chorionic gonadotropins evolving separately in equids and higher primates. Finally, coevolution in the primate lineage of killer immunoglobulin-like receptors and human leukocyte antigens can be linked to the deep invasion of the uterus by trophoblast that is a characteristic feature of human placentation.

Generation of mice expressing only the long form of the prolactin receptor reveals that both isoforms of the receptor are required for normal ovarian function

Prolactin (PRL), a pleiotropic hormone essential for maintenance of corpus luteum (CL) function and pregnancy, transduces its signal through two types of receptors, a short form (PRLR-S) and a long form (PRLR-L). Both types of receptors are expressed in the CL, yet their individual roles are not well defined. We have shown previously that female transgenic mice expressing only PRLR-S display total infertility characterized by defective follicular development and early degeneration of CL, suggesting that expression of PRLR-L is a prerequisite for normal follicular development and maintenance of CL. To determine whether PRLR-L alone is the sole receptor required to maintain normal CL formation, differentiation, and progesterone secretion, we generated two transgenic mice which express only PRLR-L, either ubiquitously (Tg-RL) or in a CL-specific manner (CL-RL). To generate CL-specific expression, we used the HSD17B7 promoter. We found both transgenic mice models cycled normally, displayed no apparent defect in follicular development, and had normal ovulation rates. The STAT5 signaling pathway, considered essential for luteinization and progesterone production, was activated by PRL in both transgenic mice models. However, soon after mating, Tg-RL and CL-RL mice showed early regression of CL, lack of progesterone production, and implantation failure that rendered them totally infertile. Embryo transfer studies demonstrated no embryo abnormalities, and supplementation with progesterone rescued implantation failure in these mice. Close observation revealed lack of luteinization and reduced expression of proteins involved in progesterone biosynthesis despite normal levels of LHCGR (LH-R), ESR1 (ER-alpha), CEBPB (C/EBP-beta) and CDKN1B (p27), proteins essential for luteinization. However, we found VEGFA, a key regulator of angiogenesis and vascularization, to be dramatically reduced in both Tg-RL and CL-RL mice. We also found collagen IV, a marker for the basal lamina of endothelial cells, aberrantly expressed and a discordant organization of endothelial cells in CL. Although luteinization did not occur in vivo, granulosa cells isolated from these mice luteinized in culture. Taken together, these results suggest that a vascularization defect in the CL may be responsible for lack of luteinization, progesterone production, and infertility in mice expressing only PRLR-L. This investigation therefore demonstrates that in contrast to earlier presumptions that PRLR-L alone is able to support normal CL formation and function, both isoforms of the PRL receptor are required in the CL for normal female fertility.

Polymorphism Thr160Thr in SRD5A1, involved in the progesterone metabolism, modifies postmenopausal breast cancer risk associated with menopausal hormone therapy

Menopausal hormone therapy (MHT) is associated with an increased breast cancer risk in postmenopausal women, with combined estrogen-progestagen therapy posing a greater risk than estrogen monotherapy. However, few studies focused on potential effect modification of MHT-associated breast cancer risk by genetic polymorphisms in the progesterone metabolism. We assessed effect modification of MHT use by five coding single nucleotide polymorphisms (SNPs) in the progesterone metabolizing enzymes AKR1C3 (rs7741), AKR1C4 (rs3829125, rs17134592), and SRD5A1 (rs248793, rs3736316) using a two-center population-based case-control study from Germany with 2,502 postmenopausal breast cancer patients and 4,833 matched controls. An empirical-Bayes procedure that tests for interaction using a weighted combination of the prospective and the retrospective case-control estimators as well as standard prospective logistic regression were applied to assess multiplicative statistical interaction between polymorphisms and duration of MHT use with regard to breast cancer risk assuming a log-additive mode of inheritance. No genetic marginal effects were observed. Breast cancer risk associated with duration of combined therapy was significantly modified by SRD5A1_rs3736316, showing a reduced risk elevation in carriers of the minor allele (p (interaction,empirical-Bayes) = 0.006 using the empirical-Bayes method, p (interaction,logistic regression) = 0.013 using logistic regression). The risk associated with duration of use of monotherapy was increased by AKR1C3_rs7741 in minor allele carriers (p (interaction,empirical-Bayes) = 0.083, p (interaction,logistic regression) = 0.029) and decreased in minor allele carriers of two SNPs in AKR1C4 (rs3829125: p (interaction,empirical-Bayes) = 0.07, p (interaction,logistic regression) = 0.021; rs17134592: p (interaction,empirical-Bayes) = 0.101, p (interaction,logistic regression) = 0.038). After Bonferroni correction for multiple testing only SRD5A1_rs3736316 assessed using the empirical-Bayes method remained significant. Postmenopausal breast cancer risk associated with combined therapy may be modified by genetic variation in SRD5A1. Further well-powered studies are, however, required to replicate our finding.

The orphan nuclear receptor Nur77 regulates decidual prolactin expression in human endometrial stromal cells

Prolactin (PRL) is synthesized and released by several extrapituitary tissues, including decidualized stromal cells. Despite the important role of decidual PRL during pregnancy, little is understood about the factors involved in the proper regulation of decidual PRL expression. Here we present evidence that the transcription factor Nur77 plays an active role in decidual prolactin expression in human endometrial stromal cells (hESCs). Nur77 mRNA expression in hESCs was significantly increased after decidualization stimulated by 8-Br-cAMP and medroxyprogesterone acetate (MPA). Adenovirus-mediated overexpression of Nur77 in hESCs markedly increased PRL mRNA expression and enhanced decidual PRL promoter (dPRL/-332Luc) activity in a concentration-dependent manner. Furthermore, knockdown of Nur77 in hESCs significantly decreased decidual PRL promoter activation and substantially attenuated PRL mRNA expression and PRL secretion (P < 0.01) induced by 8-Br-cAMP and MPA. These results demonstrate that Nur77 is a novel transcription factor that contributes significantly to the regulation of prolactin gene expression in human endometrial stromal cells.

HoxA-11 and FOXO1A cooperate to regulate decidual prolactin expression: towards inferring the core transcriptional regulators of decidual genes

During the menstrual cycle, the ovarian steroid hormones estrogen and progesterone control a dramatic transcriptional reprogramming of endometrial stromal cells (ESCs) leading to a receptive state for blastocyst implantation and the establishment of pregnancy. A key marker gene of this decidualization process is the prolactin gene. Several transcriptional regulators have been identified that are essential for decidualization of ESCs, including the Hox genes HoxA-10 and HoxA-11, and the forkhead box gene FOXO1A. While previous studies have identified downstream target genes for HoxA-10 and FOXO1A, the role of HoxA-11 in decidualization has not been investigated. Here, we show that HoxA-11 is required for prolactin expression in decidualized ESC. While HoxA-11 alone is a repressor on the decidual prolactin promoter, it turns into an activator when combined with FOXO1A. Conversely, HoxA-10, which has been previously shown to associate with FOXO1A to upregulate decidual IGFBP-1 expression, is unable to upregulate PRL expression when co-expressed with FOXO1A. By co-immunoprecipitation and chromatin immunoprecipitation, we demonstrate physical association of HoxA-11 and FOXO1A, and binding of both factors to an enhancer region (−395 to −148 relative to the PRL transcriptional start site) of the decidual prolactin promoter. Because FOXO1A is induced upon decidualization, it serves to assemble a decidual-specific transcriptional complex including HoxA-11. These data highlight cooperativity between numerous transcription factors to upregulate PRL in differentiating ESC, and suggest that this core set of transcription factors physically and functionally interact to drive the expression of a gene battery upregulated in differentiated ESC. In addition, the functional non-equivalence of HoxA-11 and HoxA-10 with respect to PRL regulation suggests that these transcription factors regulate distinct sets of target genes during decidualization.

Adaptive changes in the transcription factor HoxA-11 are essential for the evolution of pregnancy in mammals

Evolutionary change in gene regulation can result from changes in cis-regulatory elements, leading to differences in the temporal and spatial expression of genes or in the coding region of transcription factors leading to novel functions or both. Although there is a growing body of evidence supporting the importance of cis-regulatory evolution, examples of protein-mediated evolution of novel developmental pathways have not been demonstrated. Here, we investigate the evolution of prolactin (PRL) expression in endometrial cells, which is essential for placentation/pregnancy in eutherian mammals and is a direct regulatory target of the transcription factor HoxA-11. Here, we show that (i) endometrial PRL expression is a derived feature of placental mammals, (ii) the PRL regulatory gene HoxA-11 experienced a period of strong positive selection in the stem-lineage of eutherian mammals, and (iii) only HoxA-11 proteins from placental mammals, including the reconstructed ancestral eutherian gene, are able to up-regulate PRL from the promoter used in endometrial cells. In contrast, HoxA-11 from the reconstructed therian ancestor, opossum, platypus, and chicken are unable to up-regulate PRL expression. These results demonstrate that the evolution of novel gene expression domains is not only mediated by the evolution of cis-regulatory elements but can also require evolutionary changes of transcription factor proteins themselves.

Pleiotropy and Redundancy of STAT Proteins in Early Pregnancy

Signal transducers and activators of transcription (STATs) are a group of proteins involved in signal transduction from numerous bioactive substances. Hormones and cytokines such as leukaemia inhibitory factor, interferon-tau and prolactin, which play key roles during early pregnancy, activate the Janus kinase (JAK)/STAT signalling pathway. The STATs are thus involved in the regulation of implantation, establishing uterine receptivity and regulation of the maternal immune response. It seems that STATs can orchestrate signals from hormones and cytokines in different cell types and may therefore generate numerous biological effects, despite the relatively small number of receptors activating the JAK/STAT pathway. This review summarizes the participation of STATs in the main processes of early pregnancy, especially regarding their pleiotropy and redundancy.

Decidual prolactin silences the expression of genes detrimental to pregnancy

Although the main role of prolactin (PRL) in pregnant rodents is to sustain progesterone production by the corpus luteum, progesterone treatment of PRL or PRL receptor (PRL-R) null mice is unable to prevent fetal loss. We have previously shown that the rat decidua is a site of PRL production and action. In this report, we examined the hypothesis, using PRL null mice and rat decidual cell culture, that the absence of this hormone leads to the expression in the decidua of genes detrimental to pregnancy. The results show that decidual growth is normal in PRL null mice treated with PRL, progesterone, or their combination. However, the decidua of mice treated with progesterone starts expressing IL-6 and 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD), two proteins absent from the decidua of wild-type mice and involved, respectively, in inflammation and progesterone catabolism. The expression of both IL-6 and 20alpha-HSD is prevented by PRL treatment. Our results further suggest that PRL inhibition of 20alpha-HSD expression is at the level of transcription and that decidual PRL (dPRL) inhibits 20alpha-HSD promoter activity. Inhibitors of Janus kinase 2 (Jak2) but not other kinases prevent dPRL down-regulation of the 20alpha-HSD promoter. Furthermore, cotransfection of the 20alpha-HSD promoter with expression vectors of constitutively active PRL-R, Jak2, or signal transducer and activator of transcription 5b (Stat5b) leads to substantial inhibition of promoter activity. Taken together, our investigation provides an explanation for the inability of progesterone to sustain pregnancy in PRL null mice and suggests that dPRL plays an important role in pregnancy by repressing the expression of IL-6 and 20alpha-HSD in the decidua. The study also demonstrates that PRL signals through the Jak2/Stat5 pathway to down-regulate 20alpha-HSD expression in the decidua.

Mechanisms of reduced luteal sensitivity to prostaglandin F2alpha during maternal recognition of pregnancy in ewes

During maternal recognition of pregnancy, the conceptus stimulates endometrial secretion of PGF2alpha and PGE2. However, PGF2alpha is less effective in causing luteal regression in pregnant than in non-pregnant ewes. Experiments were conducted to elucidate mechanisms for reduced luteal sensitivity to PGF2alpha during maternal recognition of pregnancy. Corpora lutea (CL) were collected from pregnant and non-pregnant ewes 0, 4, or 12h following treatment with PGF2alpha on day 12 after estrus. Luteal PTGHS2 mRNA did not differ due to PGF2alpha or pregnancy status. Luteal PTGES mRNA was reduced in both pregnant and non-pregnant ewes after PGF2alpha treatment; while, luteal PTGFS mRNA was reduced 4h after PGF2alpha in pregnant, but not non-pregnant ewes. The result was a greater ratio of PTGES to PTGFS mRNA in pregnant ewes. Luteal mRNA for HPGD did not differ between pregnant and non-pregnant ewes on day 12. Luteal END1 mRNA was reduced in pregnant as compared to non-pregnant ewes prior to PGF2alpha challenge. Luteal END1 mRNA was increased after PGF2alpha in pregnant and non-pregnant ewes; however, ECE1 mRNA was reduced 4h after PGF2alpha in pregnant, but not non-pregnant ewes. The in vitro conversion of PGF2alpha to PGFM was greater in CL of pregnant than non-pregnant ewes at day 14. Luteal conversion of PGF2alpha to PGFM appears to be regulated post-transcriptionally. During maternal recognition of pregnancy, mechanisms of reduced luteal sensitivity to PGF2alpha may include a shift in prostaglandin production to the luteotropin PGE2, a reduction of ECE1 mRNA, and increased catabolism of PGF2alpha.

The molecular control of corpus luteum formation, function, and regression

The corpus luteum (CL) is one of the few endocrine glands that forms from the remains of another organ and whose function and survival are limited in scope and time. The CL is the site of rapid remodeling, growth, differentiation, and death of cells originating from granulosa, theca, capillaries, and fibroblasts. The apparent raison d'etre of the CL is the production of progesterone, and all the structural and functional features of this gland are geared toward this end. Because of its unique importance for successful pregnancies, the mammals have evolved a complex series of checks and balances that maintains progesterone at appropriate levels throughout gestation. The formation, maintenance, regression, and steroidogenesis of the CL are among the most significant and closely regulated events in mammalian reproduction. During pregnancy, the fate of the CL depends on the interplay of ovarian, pituitary, and placental regulators. At the end of its life span, the CL undergoes a process of regression leading to its disappearance from the ovary and allowing the initiation of a new cycle. The generation of transgenic, knockout and knockin mice and the development of innovative technologies have revealed a novel role of several molecules in the reprogramming of granulosa cells into luteal cells and in the hormonal and molecular control of the function and demise of the CL. The current review highlights our knowledge on these key molecular events in rodents.

Expression and regulation of progestin membrane receptors in the rat corpus luteum

Despite evidence strongly supporting progesterone's autocrine actions in the rat corpus luteum (CL), classical progesterone receptors (PR) have not been detected in this gland. Alternatively, in several other systems, progestins have been reported to activate nongenomic pathways via putative progestin membrane receptors (PMRs). The aim of this investigation was to determine whether rat CL membranes bind progestins and contain PMR homologs and whether these proteins are expressed during CL development in a manner that parallels luteal function. We found that luteal cell membranes specifically bind progesterone. Low levels of progesterone and 20alpha-dihydroprogesterone decreased binding of [(3)H]progesterone, whereas androstenedione, 17alpha-hydroxyprogesterone, and pregnenolone were less potent. Other steroids, including corticosterone, mifepristone, and estradiol, were ineffective. We found that the rat CL expresses five genes previously postulated to encode for putative PMRs: PMRalpha, PMRbeta, PMRgamma, PR membrane component 1 (PRMC1), and Rda288. Pmralpha, Pmrgamma, and Prmc1 transcripts rose steadily during pregnancy whereas Pmrbeta and Rda288 remained constant. Just before parturition, concomitant with falling progesterone levels, Pmralpha, Pmrbeta, and Prmc1 decreased. Luteal PMRalpha and PRMC1 protein levels were lower in samples taken at the end of pregnancy compared with midpregnancy samples. Ergocriptine, which inhibits the secretion of prolactin, the primary luteotrophic hormone in the rat CL, reduced Pmralpha, Pmrbeta, and Prmc1 expression significantly. Ergocriptine effects were prevented by coadministration of prolactin. These findings provide evidence for the expression and regulation of putative membrane-bound progestin-binding proteins in the rat CL, a tissue that does not express detectable levels of nuclear progesterone receptors.

Expression and Possible Role of 20.ALPHA.-Hydroxysteroid Dehydrogenase in the Placenta of the Goat

20Alpha-hydroxysteroid dehydrogenase (20alpha-HSD) catalyzes the conversion of progesterone to its inactive form 20alpha-dihydroprogesterone (20alpha-OHP). 20Alpha-HSD is expressed in the murine placenta, suggesting a role, yet unidentified, played by this enzyme during the course of pregnancy. To elucidate the possible roles of 20alpha-HSD during pregnancy, 20alpha-HSD gene expression in the placenta was examined by Northern blot analysis, and progestin (progesterone and 20alpha-OHP) concentrations in the maternal and fetal sera and the amniotic fluid were measured by radioimmunoassay in pregnant Shiba goats. The expression of 20alpha-HSD mRNA was observed in the placenta and the intercaruncular part of the uterus during mid to late pregnancy. Analysis by in situ hybridization revealed that 20alpha-HSD mRNA was mainly localized in the endometrial epithelium of the caruncle side of the placenta. Considerable enzyme activity of 20alpha-HSD was also detected in the cytosolic fraction of the placenta and intercaruncular part of the uterus. Although concentrations of progesterone and 20alpha-OHP in the maternal serum showed similar profiles, progesterone levels in the fetal serum stayed extremely low throughout the pregnancy. The 20alpha-OHP concentration in the fetal serum was always higher than that in the maternal serum. In the amniotic fluid, the concentrations of both progesterone and 20alpha-OHP remained at very low levels throughout the pregnancy. These results support the notion that 20alpha-HSD protects the fetus from the cytotoxic effects of progesterone, and thereby maintains the normal development of the fetus.

The prolactin and growth hormone families: pregnancy-specific hormones/cytokines at the maternal-fetal interface

The prolactin (PRL) and growth hormone (GH) gene families represent species-specific expansions of pregnancy-associated hormones/cytokines. In this review we examine the structure, expression patterns, and biological actions of the pregnancy-specific PRL and GH families.

17β-Estradiol induces nuclear translocation of CrkL at the window of embryo implantation

Crk family adaptors are widely expressed and mediate the timely formation of signal transduction protein complexes upon a variety of extracellular stimuli, including various growth and differentiation factors. The window of implantation is the favorable time period when the uterus develops a receptive approach to the invading embryo. Various signaling cascades are likely to become active at the window of implantation both in the uterus and the embryo. This helps create maternal embryo dialogue leading to successful embryo implantation. In this study we report for the first time the presence and nuclear translocation of the adaptor molecule CrkL both in the uterine and embryonic partners at the window of implantation. We also report that estrogen, which initiates and guides crucial changes in the uterus and the embryo at the window of receptivity, causes a massive surge in the expression and subsequent nuclear translocation of CrkL. We have also identified the existence of one LXXLL motif in the CrkL amino acid sequence and a single LXD is sufficient for activation by the estrogen receptor. This is suggestive that CrkL can bind to estrogen receptors and act as a coactivator.

Prostaglandin F(2alpha) (PGF(2alpha)) and prolactin signaling: PGF(2alpha)-mediated inhibition of prolactin receptor expression in the Corpus luteum

It is well established that prolactin (PRL) sustains, whereas prostaglandin F(2alpha) (PGF(2alpha)) curtails, progesterone production by the rodent corpus luteum (CL). We have previously shown that PGF(2alpha) inhibits the expression of several luteal genes stimulated by PRL, whereas it stimulates other genes inhibited by this hormone. We have also found that PGF(2alpha) stimulation of 20alpha-hydroxysteroid dehydrogenase (20alphaHSD), an enzyme that catabolizes progesterone, at the end of pregnancy is accompanied by a dramatic decrease in PRL receptor (PRL-R) expression. These findings, and the fact that the factors that inhibit PRL-R are not known, led us to examine in vivo whether the decline in PRL-R at the end of pregnancy is due to PGF(2alpha) and to also find out whether PGF(2alpha) opposes PRL action by inhibiting PRL-R expression. Using the PGF(2alpha) receptor (PGF(2alpha)-R) knockout, we examined whether the absence of the PGF(2alpha)-R prevents the decline in the expression of both the short and long forms of the PRL-R in the CL. We found that, in sharp contrast to the wild-type mice, in which both forms of the PRL-R decline to low levels between d 18-20 of pregnancy, expression of these receptors remained elevated in the PGF(2alpha)-R null mice. Furthermore, administration of PGF(2alpha) to pregnant rats inhibited PRL-R expression. Time-course analysis revealed that PGF(2alpha) treatment decreases both isoforms of PRL-R within 1 h of treatment in vivo, whereas its stimulatory effect on 20alphaHSD expression was further delayed. Similar results were obtained with luteinized granulosa cells in culture. To examine whether the decline in PRL-R is involved/necessary for PGF(2alpha) action, cells were transfected with a constitutively active PRL-R. The expression of this receptor did not prevent PGF(2alpha) effect on PRL-R or 20alphaHSD expression. Taken together, these results demonstrate that PGF(2alpha) inhibits the expression of the PRL-R and that the decline in both forms of the PRL-R that occurs at the end of pregnancy in the CL is due to PGF(2alpha). The results further suggest that PGF(2alpha)-mediated stimulation of 20alphaHSD is independent from PGF(2alpha) inhibition of PRL signaling in luteal cell.

Effects of deletion of the prolactin receptor on ovarian gene expression

Prolactin (PRL) exerts pleiotropic physiological effects in various cells and tissues, and is mainly considered as a regulator of reproduction and cell growth. Null mutation of the PRL receptor (R) gene leads to female sterility due to a complete failure of embryo implantation. Pre-implantatory egg development, implantation and decidualization in the mouse appear to be dependent on ovarian rather than uterine PRLR expression, since progesterone replacement permits the rescue of normal implantation and early pregnancy. To better understand PRL receptor deficiency, we analyzed in detail ovarian and corpora lutea development of PRLR-/- females. The present study demonstrates that the ovulation rate is not different between PRLR+/+ and PRLR-/- mice. The corpus luteum is formed but an elevated level of apoptosis and extensive inhibition of angiogenesis occur during the luteal transition in the absence of prolactin signaling. These modifications lead to the decrease of LH receptor expression and consequently to a loss of the enzymatic cascades necessary to produce adequate levels of progesterone which are required for the maintenance of pregnancy.

Expression of 20alpha-hydroxysteroid dehydrogenase mRNA in human endometrium and decidua

Progesterone secreted from ovarian corpus luteum plays pivotal roles in endometrial differentiation, and local progesterone metabolism to regulate its concentration in endometrial tissues is essential for the successful implantation and maintenance of pregnancy. In this study, we evaluated the expression of mRNA for 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD), a key enzyme which converts progesterone to a biologically inactive metabolite, in human endometrial tissues and cultured endometrial stromal cells as well as decidua and chorionic tissues of early pregnancy. The level of 20alpha-HSD mRNA expression in secretory phase endometrium was significantly higher than that in proliferative phase endometrium and chorionic tissues. The expression level in decidual tissue was also significantly higher than that in chorionic tissue. In cultured endometrial stromal cells, 20alpha-HSD mRNA expression was slightly enhanced at a lower progesterone concentration of 0.01 micromol/l, and an increase in its expression was significantly suppressed at higher concentrations of 1 micromol/l or greater. No effect on the gene expression was seen in cultured endometrial stromal cells with various concentrations of 17beta-estradiol. These results suggest that progesterone itself contributes to the regulation of local progesterone concentration through 20alpha-HSD levels in endometrial stromal cells at peri-implantation periods.

A prostaglandin f(2alpha) analog induces suppressors of cytokine signaling-3 expression in the corpus luteum of the pregnant rat: a potential new mechanism in luteolysis

PRL and placental lactogen (PL) play key roles in maintaining the rodent corpus luteum through pregnancy. Suppressors of cytokine signaling (SOCS) have been shown to decrease cell sensitivity to cytokines, including PRL, and so here we have addressed the issue of whether luteolysis induced by prostaglandin F(2alpha) (PGF(2alpha)) might up-regulate SOCS proteins to inhibit PRL signaling. In d 19 pregnant rats, cloprostenol, a PGF(2alpha) analog, rapidly induced transcripts for SOCS-3 and, to a lesser extent, SOCS-1. We also found increased SOCS-3 protein in the ovary by immunoblot and in the corpus luteum by immunohistochemistry. Increased SOCS-3 expression was preceded by an increase in STAT3 tyrosine phosphorylation 10 min after cloprostenol injection and was maintained for 4 h, as determined by gel shift and immunohistochemistry. Induction of SOCS-3 was accompanied by a sharp decrease in active STAT5, as determined by gel-shift assay and by loss of nuclear localized STAT5. Four hours after cloprostenol administration, the corpus luteum was refractory to stimulation of STAT5 by PRL administration, and this was not due to down-regulation of PRL receptor. Therefore, induction of SOCS-3 by PGF(2alpha) may be an important element in the initiation of luteolysis via rapid suppression of luteotropic support from PL.

PRL-induced ERalpha gene expression is mediated by Janus kinase 2 (Jak2) while signal transducer and activator of transcription 5b (Stat5b) phosphorylation involves Jak2 and a second tyrosine kinase

In the rat corpus luteum of pregnancy, PRL stimulation of ER expression is a prerequisite for E2 to have any luteotropic effect. Previous work from our laboratory has established that PRL stimulates ERalpha expression at the level of transcription and that the transcription factor Stat5 (signal transducer and activator of transcription 5) mediates this stimulation. Since it is well established that PRL activates Stat5 through the tyrosine kinase, Janus kinase 2 (Jak2), the role of Jak2 in PRL regulation of ERalpha expression was investigated. In primary luteinized granulosa cells, the general tyrosine kinase inhibitors, genistein and AG18, and the Jak2 inhibitor, AG490, prevented PRL stimulation of ERalpha mRNA levels, suggesting that PRL signaling to the ERalpha gene requires Jak2 activity. However, using an antibody that recognizes the tyrosine-phosphorylated forms of both Stat5a and Stat5b (Y694/Y699), it was found that AG490 could inhibit PRL-induced Stat5a phosphorylation only and had little or no effect on Stat5b phosphorylation. These effects of AG490 were confirmed in COS cells overexpressing Stat5b. Also in COS cells, a kinase-negative Jak2 prevented PRL stimulation of ERalpha promoter activity and Stat5b phosphorylation while a constitutively active Jak2 could stimulate both in the absence of PRL. Furthermore, kinase-negative-Jak2, but not AG490, could inhibit Stat5b nuclear translocation and DNA binding. Therefore, it seems that in the presence of AG490, Stat5b remains phosphorylated, is located in the nucleus and capable of binding DNA, but is apparently transcriptionally inactive. These findings suggest that PRL may activate a second tyrosine kinase, other than Jak2, that is capable of phosphorylating Stat5b without inducing transcriptional activity. To investigate whether another signaling pathway is involved, the src kinase inhibitor PP2 and the phosphoinositol-3 kinase inhibitor (PI3K), LY294002, were used. Neither inhibitor alone had any major effect on PRL regulation of ERalpha promoter activity or on PRL-induced Stat5b phosphorylation. However, the combination of AG490 and LY294002 largely prevented PRL-induced Stat5b phosphorylation. These findings indicate that PRL stimulation of ERalpha expression requires Jak2 and also that PRL can induce Stat5b phosphorylation through two tyrosine kinases, Jak2 and one downstream of PI3K. Furthermore, these results suggest that the role of Jak2 in activating Stat5b may be through a mechanism other than simply inducing Stat5b phosphorylation.

Dependence on prolactin of the luteolytic effect of prostaglandin F2alpha in rat luteal cell cultures

Luteal regression is a multistep, prolonged process, and long-term luteal cultures are required for studying it in vitro. Cell suspensions from ovaries of superovulated rats were enriched with steroidogenic cells, seeded on laminin or fibronectin, and maintained in defined medium for up to 10 days. Progesterone secretion was much lower than that of 20alpha-dihydroprogesterone, a product of 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD). Prolactin added throughout the incubation period gradually increased the percent progesterone out of total progestins to fourfold, while reducing 20alpha-HSD mRNA by 73%. Luteinizing hormone accelerated the establishment of higher percent progesterone by prolactin but by itself had no effect. Prolactin did not increase total progestin production or cytochrome P450 side-chain cleavage (P450(scc)) mRNA. Cell viability was unaffected by prolactin and/or LH. Prostaglandin F2alpha (PGF2alpha) was added 7-8 days after seeding. In prolactin-treated cells, PGF2alpha reduced steroidogenesis after 4-45 h, and at 45 h total progestins and P450(scc) mRNA were reduced by 45%. At 8-45 h PGF2alpha reduced the percent progesterone out of total progestins, and at 45 h 20alpha-HSD mRNA was doubled. In contrast, in prolactin-deprived cultures, PGF2alpha had little effect on total progestins or 20alpha-HSD mRNA but doubled P450(scc) mRNA. Phospholipase C activity was stimulated by PGF2alpha regardless of prolactin. Thus, when prolactin-treated, our cultures are a good model for mature corpora lutea challenged with PGF2alpha; the finding that without prolactin PGF2alpha has an alternative set of actions could help in identifying the signaling pathways of PGF2alpha responsible for its luteolytic effects.

Modulation of the promoter region of prepro-hypocretin by alpha-interferon

Hypocretins 1 and 2 (also called orexins A and B, respectively) are hypothalamic neuropeptides that have recently been shown to be involved in the sleep disorder narcolepsy and possibly in the normal regulation of sleep and wake functions. These two peptides are derived from a single precursor molecule called prepro-hypocretin, also known as prepro-orexin. We have cloned a 450 bp fragment from the 5'-flanking region of the human prepro-hypocretin gene and demonstrated that this fragment has promoter activity in vitro. Deletions at the 5' end from -450 to -188 reduced the promoter activity by approximately 50%. Further deletion from the 5'-end to -69 almost completely abolished promoter activity. The 450 bp fragment contains a number of potential transcription factor binding sites, including an interferon (IFN) response element. Our studies demonstrate that alpha-IFN strongly inhibits the promoter activity of both 450 and 188 bp fragments in a dose-dependent manner. The inhibitory effect of alpha-IFN is consistent with recent studies which suggest that hypocretin 1/orexin A may be involved in modulating arousal states and with the literature indicating involvement of immune-related molecules in sleep regulation.

Regulation of PKC delta expression by estrogen and rat placental lactogen-1 in luteinized rat ovarian granulosa cells

Protein kinase C (PKC) delta is dramatically upregulated in the corpus luteum in the second half of pregnancy in the rat. To gain insight into the hormonal regulation of PKC delta expression, studies were undertaken to analyze the regulation of PKC delta expression in a luteinized rat granulosa cell model. PKC delta protein expression was evaluated in luteinized granulosa cells, isolated from human (h)CG-treated immature female rats 7 h after the injection of an ovulatory dose of hCG and cultured up to 12 days. Cytochrome P450 cholesterol side chain cleavage enzyme expression was observed throughout the culture period, and a majority of the cells expressed steroidogenic acute regulatory protein and responded to rat placental lactogen (rPL)-1 by exhibiting hypertrophy, consistent with maintenance of the luteal phenotype. Both PKC delta protein and mRNA expression increased 3.5-4-fold with time of culture, and PKC delta mRNA expression could be eliminated by treatment of cells with the PKC inhibitor GF109203X. E(2) caused a specific dose- and time-dependent increase in expression of PKC delta protein of twofold, whereas PKC delta mRNA was unaffected by E(2) over a 12-day culture period. Treatment of cells with 500 ng/ml rPL-1 for the final 4 days of a 12-day culture in the absence of E(2) had no effect on PKC delta protein or mRNA expression, while treatment with 500 or 3000 ng/ml rPL-1 in the presence of E(2) significantly enhanced both PKC delta protein and mRNA expression (up to threefold). These results show that two of the major regulators of luteal function in the second half of pregnancy in the rat, E(2) and rPL-1, cooperate to regulate PKC delta expression in luteinized granulosa cells.

Mechanisms controlling the function and life span of the corpus luteum

The primary function of the corpus luteum is secretion of the hormone progesterone, which is required for maintenance of normal pregnancy in mammals. The corpus luteum develops from residual follicular granulosal and thecal cells after ovulation. Luteinizing hormone (LH) from the anterior pituitary is important for normal development and function of the corpus luteum in most mammals, although growth hormone, prolactin, and estradiol also play a role in several species. The mature corpus luteum is composed of at least two steroidogenic cell types based on morphological and biochemical criteria and on the follicular source of origin. Small luteal cells appear to be of thecal cell origin and respond to LH with increased secretion of progesterone. LH directly stimulates the secretion of progesterone from small luteal cells via activation of the protein kinase A second messenger pathway. Large luteal cells are of granulosal cell origin and contain receptors for PGF(2alpha) and appear to mediate the luteolytic actions of this hormone. If pregnancy does not occur, the corpus luteum must regress to allow follicular growth and ovulation and the reproductive cycle begins again. Luteal regression is initiated by PGF(2alpha) of uterine origin in most subprimate species. The role played by PGF(2alpha) in primates remains controversial. In primates, if PGF(2alpha) plays a role in luteolysis, it appears to be of ovarian origin. The antisteroidogenic effects of PGF(2alpha) appear to be mediated by the protein kinase C second messenger pathway, whereas loss of luteal cells appears to follow an influx of calcium, activation of endonucleases, and an apoptotic form of cell death. If the female becomes pregnant, continued secretion of progesterone from the corpus luteum is required to provide an appropriate uterine environment for maintenance of pregnancy. The mechanisms whereby the pregnant uterus signals the corpus luteum that a conceptus is present varies from secretion of a chorionic gonadotropin (primates and equids), to secretion of an antiluteolytic factor (domestic ruminants), and to a neuroendocrine reflex arc that modifies the secretory patterns of hormones from the anterior pituitary (most rodents).

Rat decidual prolactin. Identification, molecular cloning, and characterization

Establishment and maintenance of pregnancy require the activity of a highly specialized maternal tissue, the decidua. It is well established that the human decidua synthesizes and releases prolactin. However, in the rat, no study has been able to demonstrate the production of prolactin by the decidua. In this report, we established for the first time using Northern blot analysis and reverse transcription-polymerase chain reaction, Western blot analysis, immunocytochemistry, and enzyme-linked immunosorbent assay, that a defined cell population located in the rat antimesometrial decidua expresses prolactin mRNA, as well as synthesizes and secretes this hormone. By reverse transcription-polymerase chain reaction and rapid amplification of cDNA ends, we cloned a full-length cDNA for rat decidua prolactin, whose sequence was identical to that of pituitary prolactin. Our results also showed that pituitary prolactin appeared to down-regulate decidual prolactin levels. Under these circumstances, inhibition of pituitary prolactin secretion led to a rise in both decidual prolactin mRNA and protein expression. Moreover, addition of exogenous prolactin to primary decidual cells in culture also caused a marked decrease in decidual prolactin mRNA expression. Finally, treatment of primary decidual cells with steroid hormones or 8-bromo-cAMP revealed a differential regulation of decidual prolactin expression from that of pituitary suggesting a tissue-specific regulation of prolactin gene expression, possibly through the use of an alternative promoter in rat decidua.

Autoregulation of the rat prolactin gene in lactotrophs

The autoregulation of prolactin (PRL) secretion in the rat has been demonstrated at both the hypothalamus and the pituitary levels. Studies on the direct negative feedback effect of PRL in the lactotrophs have concentrated on the acute effect on PRL secretion which does not involve change in PRL synthesis. In this study, we have developed a cotransfection assay in somatolactotrophs where we examine the effect of PRL on the transcription of its own gene. We found that oPRL, at physiological concentrations, exerts a strong and specific inhibition of the rPRL gene transcription in PRL-deficient GC cells. This effect is mediated by both the intermediate and the long forms of PRL receptor. The inhibition was also reproduced in GH3 cells, which secretes PRL, by adding exogenous oPRL in the presence of anti-rat PRL antiserum to neutralize endogenous rPRL. Cellular specificity was demonstrated by testing this regulation in non-pituitary cell types where no modulation of the PRL promoter reporter gene could be elicited by PRL, even with cotransfection with the Pit-1 expression vector. Finally, deletions of the rPRL promoter indicate that the full inhibitory effect of PRL requires the same regulatory domains (proximal and distal) that have been described for the other PRL gene regulators. These results strongly suggest the existence of the extra-short loop regulation of the rat PRL at the transcriptional level.

Hormonal regulation of copper-zinc superoxide dismutase and manganese superoxide dismutase messenger ribonucleic acid in the rat corpus luteum: induction by prolactin and placental lactogens

The corpus luteum expresses two enzymes that scavenge superoxide radicals and protect the cells from their toxic activities: cytosolic copper, zinc-superoxide dismutase (Cu,Zn-SOD) and mitochondrial manganese-SOD (Mn-SOD). The present study was undertaken to investigate whether the mRNA expression of each of these enzymes is regulated by luteotropic hormones. Cu,Zn-SOD and Mn-SOD mRNA levels were determined by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). We first examined the effects of prolactin (PRL) on Cu,Zn-SOD and Mn-SOD mRNA expression in the corpus luteum. Hypophysectomy of Day 3 pregnant rats caused a sharp decline in both Cu,Zn-SOD and Mn-SOD mRNA levels, which was completely reversed by PRL administration. To further examine the effects of PRL and rat placental lactogen (rPL) on the expression of these enzymes, either primary luteinized granulosa cells or temperature-sensitive simian virus-40 transformed luteal cells (GG-CL) were cultured with different doses of PRL or rPL. These hormones induced a remarkable increase in Cu,Zn-SOD and Mn-SOD mRNA levels in both primary luteinized granulosa cells and GG-CL cells. Interestingly, whereas PRL up-regulated the expression of the SOD in luteal cells, other luteotropic hormones such as estradiol and dexamethasone inhibited both SOD mRNA expression while progesterone had no effect. In conclusion, PRL and PRL-like hormones induce a protective ability against toxic oxygen radicals by stimulating the expression of SODs, a phenomenon that may play an important role in maintaining luteal cell integrity and steroidogenic capacity.

Molecular cloning and characterization of the rat ovarian 20 alpha-hydroxysteroid dehydrogenase gene

The rat 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSD) is an enzyme responsible for the catabolism of progesterone to the inactive 20 alpha-hydroxprogesterone. We have previously shown that the expression of this enzyme is not regulated by post-translational modification, but at the level of transcription. In this study we have established that the 20 alpha-HSD gene contains nine exons and have isolated a 2.5 kb promoter region. The transcription start site was identified and a TATA box was found. 5' deletions of this promoter significantly decreased basal promoter activity. Treatment with forskolin led to a dose dependent inhibition of the 2.5kg-20 alpha-HSD-luciferase construct. Computer analysis identified one CRE, two Nur77 response elements, two putative AP1 sites and one progesterone response element half-site. In summary, we have identified and partially characterized the promoter region of the rat ovarian 20 alpha-HSD and demonstrated that the regulatory elements for 20 alpha-HSD are present within a 2.5 kb 5' flanking region of the gene.

Stat5a and Stat5b proteins have essential and nonessential, or redundant, roles in cytokine responses

A variety of cytokines mediate the activation of Janus protein tyrosine kinases (Jaks). The Jaks then phosphorylate cellular substrates, including members of the signal transducers and activators of transcription (Stat) family of transcription factors. Among the Stats, the two highly related proteins, Stat5a and Stat5b, are activated by a variety of cytokines. To assess the role of the Stat5 proteins, mutant mice were derived that have the genes deleted individually or together. The phenotypes of the mice demonstrate an essential, and often redundant, role for the two Stat5 proteins in a spectrum of physiological responses associated with growth hormone and prolactin. Conversely, the responses to a variety of cytokines that activate the Stat5 proteins, including erythropoietin, are largely unaffected.