26-cholesterol hydroxylase in rat corpora lutea: A negative regulator of progesterone secretion. (1/46)

From a subtracted cDNA library of rat luteal tissue, where cDNA fragments in functional luteal tissue were subtracted from those in regressing luteal tissue, a cDNA clone corresponding to 26-cholesterol hydroxylase (P450(C26)) was obtained. It is known that P450(C26) catalyzes the conversion of cholesterol to 26-hydroxycholesterol, which blocks cholesterol utilization in the cell, and that 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) catalyzes the conversion of progesterone to an inactive steroid, 20alpha-dihydroprogesterone (20alpha-OHP). Thus, using pseudopregnant rats as a model, physiological cooperation of P450(C26) and 20alpha-HSD in the reduction of progesterone release toward the end of the luteal phase was evaluated. Levels of P450(C26) and 20alpha-HSD mRNA were examined in corpora lutea from pseudopregnant rats by Northern blot or reverse transcription-polymerase chain reaction or both. P450(C26) mRNA was ubiquitously expressed in corpora lutea, and its expression increased toward the end of pseudopregnancy, while 20alpha-HSD was expressed in all corpora lutea on Day 16 (Day 0 = the day of after cervical stimulation) but not detected before Day 10. An inhibitor of 20alpha-HSD, STZ26 (D-homo-16-oxa-4-androstene-3,16alpha-dione), was administered at various doses to rats from Day 12 to 20, effectively suppressing the elevation of 20alpha-OHP in a dose-dependent manner but not the depletion of progesterone completely. The expression of P450(C26) mRNA was increased as STZ26 dose increased, which negatively correlated with the progesterone levels. These results strongly suggest that P450(C26) cooperated with 20alpha-HSD in the reduction of progesterone release from the rat luteal tissue at the end of the functional luteal phase.  (+info)

Conversion of mammalian 3alpha-hydroxysteroid dehydrogenase to 20alpha-hydroxysteroid dehydrogenase using loop chimeras: changing specificity from androgens to progestins. (2/46)

Hydroxysteroid dehydrogenases (HSDs) regulate the occupancy and activation of steroid hormone receptors by converting potent steroid hormones into their cognate inactive metabolites. 3alpha-HSD catalyzes the inactivation of androgens in the prostate by converting 5alpha-dihydrotestosterone to 3alpha-androstanediol, where excess 5alpha-dihydrotestosterone is implicated in prostate disease. By contrast, 20alpha-HSD catalyzes the inactivation of progestins in the ovary and placenta by converting progesterone to 20alpha-hydroxyprogesterone, where progesterone is essential for maintaining pregnancy. Mammalian 3alpha-HSDs and 20alpha-HSDs belong to the aldo-keto reductase superfamily and share 67% amino acid sequence identity yet show positional and stereospecificity for the formation of secondary alcohols on opposite ends of steroid hormone substrates. The crystal structure of 3alpha-HSD indicates that the mature steroid binding pocket consists of 10 residues located on five loops, including loop A and the mobile loops B and C. 3alpha-HSD was converted to 20alpha-HSD by replacing these loops with those found in 20alpha-HSD. However, when pocket residues in 3alpha-HSD were mutated to those found in 20alpha-HSD altered specificity was not achieved. Replacement of loop A created a 17beta-HSD activity that was absent in either 3alpha- or 20alpha-HSD. Once loops A and C were replaced, the chimera had both 3alpha- and 20alpha-HSD activity. When loops A, B, and C were substituted, 3alpha-HSD was converted to a stereospecific 20alpha-HSD with a resultant shift in k(cat)/K(m) for the desired reaction of 2 x 10(11). This study represents an example where sex hormone specificity can be changed at the enzyme level.  (+info)

Prostaglandin F2alpha-induced expression of 20alpha-hydroxysteroid dehydrogenase involves the transcription factor NUR77. (3/46)

Prostaglandin F(2)alpha (PGF(2)alpha) binding to its receptor on the rat corpus luteum triggers various signal transduction pathways that lead to the activation of a steroidogenic enzyme, 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD), which in turn catabolizes progesterone. The molecular mechanism underlying PGF(2)alpha-induced 20alpha-HSD enzyme activity has not yet been explored. In this report we show, using mice lacking PGF(2)alpha receptor and pregnant rats, that PGF(2)alpha is responsible for the rapid and massive expression of the 20alpha-HSD gene at the end of pregnancy leading to a decrease in progesterone secretion. We also present evidence that PGF(2)alpha enhances 20alpha-HSD promoter activity. We have determined a region upstream of the -1590 position in the 20alpha-HSD promoter that confers regulation by PGF(2)alpha in ovarian primary cells. This region encompasses a unique transcription factor-binding site with a sequence of a NUR77 response element. Deletion of this motif or overexpression of a NUR77 dominant negative protein caused a complete loss of 20alpha-HSD promoter activation by PGF(2)alpha. NUR77 also transactivated the 20alpha-HSD promoter in transient transfection experiments in corpus luteum-derived cells (GG-CL). This induction required the NUR77-transactivating domain. We also show that PGF(2)alpha induces a very rapid expression of NUR77 that binds to a distal response element located at -1599/-1606 but does not interact with another proximal putative NUR77 response element located downstream in the promoter. A rapid increase in NUR77 mRNA was observed in mice corpora lutea just before parturition at a time when 20alpha-HSD becomes expressed. This increase in the expression of both genes was not seen in PGF(2)alpha receptor knockout mice. By using cyclosporin A and PGF(2)alpha treatment, we established that inhibition of NUR77 DNA binding in vivo prevents PGF(2)alpha induction of the 20alpha-HSD gene in the corpus luteum. Taken together, our results demonstrate, for the first time, that PGF(2)alpha induces in the corpus luteum the expression of the nuclear orphan receptor and transcription factor, NUR77, which in turn leads to the transcriptional stimulation of 20alpha-HSD, triggering the decrease in serum progesterone essential for parturition.  (+info)

Characterization of a human 20alpha-hydroxysteroid dehydrogenase. (4/46)

It has been suggested that 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) is a T-cell differentiation marker in mice. In the human, this enzyme has generally been associated with types 1 and 2 17beta-HSDs, which belong to the short-chain alcohol dehydrogenase family, whereas the rat, rabbit, pig and bovine 20alpha-HSDs are members of the aldoketo reductase superfamily, which also includes the 3alpha-HSD family. In this study, we report the cloning, from a human skin cDNA library, of a cDNA that shows, after transfection into human embryonic kidney (HEK-293) cells, high 20alpha-HSD activity but negligible 3alpha- and 17beta-hydroxysteroid dehydrogenase activities. A comparison of the amino acid sequence of the human 20alpha-HSD with those of other related 20alpha- and 3alpha-HSDs indicates that the human 20alpha-HSD shares 79.9, 68.7 and 52.3% identity with rabbit, rat and bovine 20alpha-HSDs, whereas it shows 97, 84 and 65% identity with human type 3, type 1 and rat 3alpha-HSDs. In contrast, the enzyme shares only 15.2 and 15.0% identity with type 1 and type 2 human 17beta-HSDs. DNA analysis predicts a protein of 323 amino acids, with a calculated molecular weight of 36 767 Da. In intact transfected cells, the human 20alpha-HSD preferentially catalyzes the reduction of progesterone to 20alpha-hydroxyprogesterone with a K(m) value of 0.6 microM, the reverse reaction (oxidation) being negligible. In a cell cytosolic preparation, the enzyme could use both NADPH and NADH as cofactors, but NADPH, which gave 4-fold lower K(m) values, was preferred. We detected the expression of 20alpha-HSD mRNA in liver, prostate, testis, adrenal, brain, uterus and mammary-gland tissues and in human keratinocyte (HaCaT) cells. The present study clearly indicates that the genuine human 20alpha-HSD belongs to the aldoketo reductase family, like the 20alpha-HSDs from other species.  (+info)

Dependence on prolactin of the luteolytic effect of prostaglandin F2alpha in rat luteal cell cultures. (5/46)

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.  (+info)

Luteal expression of cytochrome P450 side-chain cleavage, steroidogenic acute regulatory protein, 3beta-hydroxysteroid dehydrogenase, and 20alpha-hydroxysteroid dehydrogenase genes in late pregnant rats: effect of luteinizing hormone and RU486. (6/46)

A decrease in serum progesterone at the end of pregnancy is essential for the induction of parturition in rats. We have previously demonstrated that LH participates in this process through: 1) inhibiting 3beta-hydroxysteroid dehydrogenase (3beta-HSD) activity and 2) stimulating progesterone catabolism by inducing 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) activity. The objective of this investigation was to determine the effect of LH and progesterone on the luteal expression of the steroidogenic acute regulatory protein (StAR), cytochrome P450 side-chain cleavage (P450(scc)), 3beta-HSD, and 20alpha-HSD genes. Gene expression was analyzed by Northern blot analysis 24 and 48 h after administration of LH or vehicle on Day 19 of pregnancy. StAR and 3beta-HSD mRNA levels were lower in LH-treated rats than in rats administered with vehicle at both time points studied. P450(scc) mRNA levels were unaffected by LH. The 20alpha-HSD mRNA levels were not different between LH and control rats 24 h after treatment; however, greater expression of 20alpha-HSD, with respect to controls, was observed in LH-treated rats 48 h after treatment. Luteal progesterone content dropped in LH-treated rats at both time points studied, whereas serum progesterone decreased after 48 h only. In a second set of experiments, the anti-progesterone RU486 was injected intrabursally on Day 20 of pregnancy. RU486 had no effect on 3beta-HSD or P450(scc) expression but increased 20alpha-HSD mRNA levels after 8 h treatment. In conclusion, the luteolytic effect of LH is mediated by a drop in StAR and 3beta-HSD expression without effect on P450(scc) expression. We also provide the first in vivo evidence indicating that a decrease in luteal progesterone content may be an essential step toward the induction of 20alpha-HSD expression at the end of pregnancy in rats.  (+info)

Progesterone metabolism in human leukemic monoblast U937 cells. (7/46)

Progesterone markedly inhibits the functions of human macrophages and T lymphocytes, and acts as an immunosuppressant during pregnancy. It is important to examine progesterone metabolites to understand the overall bioactive properties of this sex steroid. However, progesterone metabolism has not been examined in human immune cells. The human leukemic monoblast U937 cell line exhibits monocytic lineage and provides a valuable model to analyze monocyte-macrophage differentiation. Therefore, in this study, we analyzed progesterone metabolism in U937 cells by thin-layer chromatography. Progesterone was metabolized to 5alpha-pregnan-3beta,6alpha-diol-20-one via 5alpha-dihydroprogesterone and 5alpha-pregnan-3beta-ol-20-one, and 5alpha-pregnan-3beta,20alpha-diol was also detected as a final metabolic product via 20alpha-dihydroprogesterone and 5alpha-pregnan-20alpha-ol-3-one. 5alpha-reduction (5alpha-reductase type 1) and 20alpha-reduction were involved in the first step of metabolism. To identify the enzyme responsible for the 20alpha-reduction, we screened an U937 cDNA library, and obtained a clone (1.2 kb), which was identical to the human hepatic bile acid-binding protein or 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD). 293 cells transfected with this cDNA demonstrated marked 20alpha-reduction of progesterone to 20alphaDHP, but 20alpha-oxidative, 3alpha-HSD or 17beta-HSD activity was found to be negligible. In experimental animals, the importance of 20alpha-HSD has been reported to be involved in the protection of immune cells from the toxic effects of progesterone. Therefore, our present data suggest that 20alpha-HSD plays an important role in the regulation of progesterone actions in human immune cells.  (+info)

Effects of deletion of the prolactin receptor on ovarian gene expression. (8/46)

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.  (+info)

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