Effects of estrogen and progesterone on thymidine kinase activity in the immature rat uterus

Lasofoxifene enhances vaginal mucus formation without causing hypertrophy and increases estrogen receptor β and androgen receptor in rats

OBJECTIVE

Lasofoxifene, a new selective estrogen-receptor modulator (SERM), shows efficacy in vaginal and vulvar atrophy in postmenopausal women. Here, we sought to explore the possible mechanisms of action for this effect in comparison with other SERMs using an immature ovariectomized rat model.

DESIGN

SERMs (lasofoxifene, raloxifene, and tamoxifen) and 17alpha-ethinyl estradiol were administered orally to immature ovariectomized rats daily for 1 or 4 days. Vaginal and uterine tissues were weighed and processed for histomorphometric measurements, vaginal mucopolysaccharide staining, and immunohistochemistry of 5-bromo-2'-deoxyuridine and steroid receptors. Receptor quantification was determined by a novel ultrasensitive enzyme-linked immunosorbent assay method.

RESULTS

Lasofoxifene and raloxifene showed a minimal increase in vaginal and uterine weight, epithelial cell proliferation, and epithelial thickness in comparison with estradiol and tamoxifen. Lasofoxifene significantly enhanced vaginal mucus formation in a dose-dependent manner. Vaginal progesterone receptor protein was increased fivefold by estradiol and all three SERMs tested. 17alpha-Ethinyl estradiol caused a significant decrease in estrogen receptor alpha, but no change with other treatments. Only lasofoxifene significantly increased vaginal estrogen receptor beta and androgen receptor protein levels.

CONCLUSIONS

These results demonstrated that lasofoxifene stimulated vaginal mucus formation without causing cell proliferation in the rat reproductive tract. These effects may be due to the increased vaginal estrogen receptor beta and androgen receptor levels. This cellular and molecular profile of lasofoxifene in the vagina may account for its efficacy in the treatment of vaginal and vulvar atrophy in postmenopausal women.

Synthesis and biological activity of 5-methylidene 1,2-dihydrochromeno[3,4-f]quinoline derivatives as progesterone receptor modulators

A series of 5-methylidene 1,2-dihydrochromeno[3,4-f]quinoline derivatives were synthesized and tested in biological assays to evaluate scope and limitations of the nonsteroidal SPRM pharmacophore (3). A number of orally available highly potent nonsteroidal modulators were identified by modification of the substituents at 5-methylidene position.

Sialic acid binding protein of human endometrium: its regulation by steroids

In the present study, we have observed that sialic acid binding protein (SABP - a 54 kDa glycoprotein which was isolated from human endometrial scrapings taken at various stages of the menstrual cycle from normal cycling females and purified to apparent homogeneity and was earlier reported from this laboratory) was found in sufficiently detectable amount in the endometrium of normal cycling women whereas it was found in lesser amount in tissue from women who have recently entered the postmenopause stage. SABP was observed in both follicular and luteal phase of menstrual cycle which was found by western blot analysis. In the de-novo synthesis experiment, synthesis and secretion of SABP was found to be stimulated by estradiol (E2) whereas progesterone (P4) was found to have no significant stimulatory effect on it which was also confirmed by HEC cell culture. In the HEC cell culture, priming of cells with E2 was found to influence the effect of P4 on SABP when it was added 2 h after E2 administration. This was observed by doing immunoprecipitation followed by SDS-PAGE and autoradiography. Hence this report clearly indicates that E2 regulates the synthesis and secretion of 54 kDa SABP from human endometrium. How E2 priming of endometrium influences the effect of P4 on SABP has been discussed.

Effect of estradiol on estrogen receptor expression in rat uterine cell types

In rodent uterus, both up- and down-regulation of estrogen receptor alpha (ERalpha) messenger ribonucleic acid (mRNA) and protein levels by estradiol has been demonstrated; however, it is not known which of the uterine compartments (endometrial epithelium, stroma, myometrium) respond to estradiol with autoregulation of ERalpha. The purpose of the present study was to investigate and compare the kinetics and cell type-specific effects of estradiol on uterine ERalpha expression in immature and adult rats. Ovariectomized female rats were injected s.c. with sesame oil or estradiol-17beta. Uteri were collected and analyzed for changes in ERalpha mRNA using RNase protection assays (RPA) and in situ hybridization using radiolabeled probes specific for ERalpha. Immunohistochemical analysis was performed with a polyclonal antibody specific to ERalpha. Expression of ERalpha in the uterine epithelial cells decreased at 3 and 6 h after estradiol administration to immature and adult rats, respectively. At 24 h, ERalpha mRNA levels in the immature and mature rat uterus were higher than pretreatment levels but returned to baseline by 72 h. Pretreatment with cycloheximide did not block the 3-h repressive effect of estradiol, suggesting that the estradiol-induced decrease in ERalpha mRNA occurs independent of new protein synthesis. A decrease in ERalpha mRNA and protein was also observed in uterine epithelia at 3 and 6 h after an estradiol injection to immature and adult rats, and intensity of both the in situ hybridization signal and the immunostaining in the epithelium increased at 24 and 72 h. However, the periluminal stromal cells in the adult uterus and the majority of stromal cells of the immature uterus appeared to have increased ERalpha expression. The results indicate that down-regulation of ERalpha in the epithelia and up-regulation of stromal ERalpha play a role in early events associated with estradiol-induced cell proliferation of the uterine epithelia.

5-Alkyl 1,2-dihydrochromeno[3,4-f]quinolines: a novel class of nonsteroidal progesterone receptor modulators

A series of nonsteroidal human progesterone receptor (hPR) agonists, 5-alkyl 1,2-dihydrochromeno[3,4-f]quinolines, was synthesized and evaluated in cotransfection and competitive receptor binding assays. The 5-alkyl substitution was shown to be responsible for the agonist activity and substitution at C9 dramatically enhanced the potency. A number of analogues in this series showed activities similar to or better than progesterone in the cotransfection and binding assays and analogue 15 exhibited similar in vivo activity as medroxyprogesterone acetate (MPA) in murine uterine wet weight/mammary gland morphology assays.

5-Benzylidene 1,2-dihydrochromeno[3,4-f]quinolines, a novel class of nonsteroidal human progesterone receptor agonists

A novel series of nonsteroidal progestins, 5-benzylidene-1, 2-dihydrochromeno[3,4-f]quinolines (2), was discovered, and a preliminary structure-activity relationship study around the 5-benzylidene ring generated several potent human progesterone receptor agonists (compounds 8, 16). These new progestins showed biological activities (EC50 = 5.7 and 7.6 nM) similar to progesterone (EC50 = 2.9 nM) in the cotransfection assay with high efficacy (132% and 166%) and binding affinity (Ki = 0.66 and 0.83 nM) similar to medroxyprogesterone acetate (MPA) (Ki = 0.34 nM). A representative analogue, 8, demonstrated similar oral potency to MPA in the uterine wet weight/mammary gland morphology assay in ovariectomized rats.

5-Aryl-1,2-dihydrochromeno[3,4-f]quinolines: a novel class of nonsteroidal human progesterone receptor agonists

The development of a novel class of nonsteroidal human progesterone receptor (hPR) agonists, 5-aryl-1,2-dihydro-5H-chromeno[3,4-f]quinolines 2, is described. The introduction of a 5-aryl group into the 1,2-dihydrocoumarino[3,4-f]quinoline core 1 is the key for progestational activities. The structure-activity relationship (SAR) studies of the 5-aryl substituents generated a series of potent hPR agonists, which exhibited similar biological activity (EC50 = 8-30 nM) to the natural hormone progesterone (EC50 = 2.9 nM) in cell-based assays with efficacies ranging from 28% to 96%. Most of the analogues displayed similar or greater binding affinity (Ki = 0.41-3.6 nM) than progesterone (Ki = 3.5 nM). Three representative analogues (13, 15, and 24) demonstrated in vivo activities in mammary gland morphology/uterine wet weight assay in ovariectomized rats.

Gap junction regulation in the uterus and ovaries of immature rats by estrogen and progesterone

The effects of estrogen (E2) and progesterone (P) were examined on the expression levels of multiple gap junction (GJ) gene products (alpha 1 = Cx43, beta 1 = Cx32, beta 2 = Cx26) in the uterus and ovaries of immature rats by immunohistochemistry, electron microscopy and northern blot analysis. E2 induced the expression of alpha 1 connexin in the uterus (specifically in the myometrium and in endometrial stroma proximal to luminal epithelium) and ovaries. The E2-induced alpha 1 expression was completely suppressed by P in the uterus, but only partly in ovaries. Steroid hormones also modulated the quantity, size, and distribution of beta 1 and beta 2 containing junctional plaques along lateral cell borders in polarized luminal and glandular uterine epithelia. Small GJs were detected at basolateral regions in proliferative luminal epithelium following administration of E2. In contrast, large GJs were localized at subapical-lateral cell borders of the secretory epithelium following P-treatment. The co-administration of E2 + P had a synergistic effect on beta 1 and beta 2 expression in the luminal epithelium, but an inhibitory effect on beta 2 expression in glandular epithelium. Myometrial GJs were detected in freeze-fracture replicas as aggregates containing regularly arranged particles with particle free zones. In contrast, GJs in secretory epithelium contained particles which were arranged in a non-crystalline fashion. These GJs contained domains of mixed and segregated beta 1 and beta 2 antigens within a single plaque as revealed by laser scanning confocal microscopy analysis of immuno-double-labeled secretory epithelium. The demonstration of segregated antigens within a single GJ plaque indicates the possibility of multiple channel populations formed by homo-oligomeric connexons. These results suggest that different connexins can be differentially regulated by steroid hormones in different cell types, and that the same steroid hormone can have different effects on the same connexin in different cell types.

Relationship between cellular DNA synthesis, PCNA expression and sex steroid hormone receptor status in the developing mouse ovary, uterus and oviduct

The proliferative activities of the different cellular compartments of the developing mouse ovary, uterus, and oviduct were studied by radioautographic assessment of DNA synthesis with [3H]-thymidine labeling and by immunohistochemical staining of proliferating cell nuclear antigen (PCNA). The distributions of estrogen and progesterone receptors (ER and PR) were studied by immunohistochemical staining. The values of the PCNA positive staining indices were a little higher than that of the radioautographic labeling indices. However, linear relations were shown for the two indices. The proliferative activities were high from postnatal day 1-7 and decreased from day 14 in the different cellular compartments of the ovary. The proliferative activities were high on days 1, 3 and decreased from day 7 in the uterus and oviduct. Staining of ER and PR was very weak in the surface epithelium, stroma and large follicles of the ovary. Positive staining for ER occurred from day 14 in the uterine epithelium and from day 7 in oviductal epithelium. Positive staining for PR was observed from day 1 in both the uterine and oviductal epithelium. However, the positivity of both ER and PR occurred from postnatal day 1 in the stromal cells of the uterus and oviduct. These results suggest that the appearance of the steroid receptors differ between the different cellular compartment of the reproductive organs. The proliferative activities have an inverse relation with the expression of the steroid hormone receptors in the female reproductive organs during developmental stages.(ABSTRACT TRUNCATED AT 250 WORDS)

Hormonal regulation of sialic acid-binding (SAS) protein synthesis of rat uterus

Sialic acid binding proteins (SAS) of rat uteri have been found in all three stages of the estrous cycle. To study the control of synthesis of these proteins two different animal models were used I-immature female rats (25 d) where the hormones estradiol (E2) and progesterone (P4) were given separately and together, and II-adult female rats where hormone treatment commenced 14 days after ovariectomy. The data indicated that E2 initiated the synthesis of SAS proteins in the immature animals, while P4 could inhibit SAS synthesis, either given alone or together with E2. However, prior priming of the rat with E2 and subsequent administration of P4 stimulated SAS protein synthesis.

Effects of danazol on DNA synthesis in rat prostate

Effects of danazol, an isoxazol derivative of the synthetic steroid 17 alpha-ethinyltestosterone, on activities of thymidylate synthetase and thymidine kinase, which are the DNA-synthesizing enzymes included in de novo and salvage pathways of pyrimidine metabolism, respectively, were investigated in rat prostate. Danazol markedly reduced plasma levels of luteinizing hormone and testosterone, and organ weight, both enzyme activities and bromodeoxyuridine-immunoreactive cells which were regarded as the S-phase cells in prostate. These results indicate that danazol shows a property as a potent antigonadotropin.

Increased activities of thymidylate synthetase and thymidine kinase in human thyroid tumors

Thymidylate synthetase (TS) is known to catalyse the methylation of deoxyuridine monophosphate (dUMP) for the de novo synthesis of deoxythymidine monophosphate (dTMP). Thymidine kinase (TK) catalyzes the formation of dTMP by the phosphorylation of thymidine via the pyrimidine salvage pathway. High TS and TK activities have been observed in rapidly proliferating tissues. Both TS and TK activities in human thyroid adenocarcinoma increased to approximately 2-fold that in normal thyroid tissue. The thyroid TK isozymes can be separated into two types by DEAE-cellulose column chromatography. One of them is associated with the cytosol cell fraction of rapidly proliferating cells, such as fetal or neoplastic cells. Its activity is not affected by low concentration of deoxycytidine triphosphate (dCTP), and its molecular weight and Km value for thymidine are 120 kD and 0.5 x 10(-6) M, respectively. The average activity of this cytosol-associated isozyme in thyroid adenocarcinoma was increased slightly to 2.3-fold that of normal thyroid tissue. These results obtained from the activities of TK and its isozyme may be indicative of the slow-growing property of thyroid adenocarcinoma compared to mammary or colonic adenocarcinoma, which has high activities of TK and its isozyme.

Hormonal regulation of rat uterine secretory protein synthesis

Treatment of the rat uterus with estradiol results in many morphological and biochemical changes. In order to examine the biochemical mechanisms of these changes, we are interested in finding a protein which can be used as an end-point indicator or marker. Estradiol administration results in the increased synthesis and release of a 115,000 and 65,000 dalton protein into the incubation media. In this paper, we demonstrate that these proteins are actually subunits of a larger protein having a molecular weight of 180,000 daltons. This protein appears to be specific to the uterus and may be produced mainly or solely by the epithelial cells. In the normal estrous cycle, maximal production is seen at estrus with essentially no production at diestrus. In the immature rat, synthesis of the 180K dalton protein is blocked by the interaction of progesterone and estradiol. However, unlike some uterine responses, the 180K protein is increased by treatment with several antiestrogens. This protein is also present in sufficient quantities to allow for the production of monoclonal antibodies. Thus this protein has many attributes of an excellent "marker protein" and will be of value in future studies aimed at elucidating the molecular mechanism(s) of steroid hormone action in the uterus.

Increased activities of thymidine kinase isozymes in human mammary tumours

Thymidine kinase, the enzyme in the pyrimidine salvage pathway, and its isozymes were examined in 10 specimens of normal mammary gland, 10 fibroadenomas and 11 adenocarcinomas in human breasts. The average thymidine kinase activities in fibroadenomas and adenocarcinomas were about 3 and 8 times that in normal mammary gland. The mammary thymidine kinase isozymes were separated into two types by diethylaminoethyl (DEAE) cellulose column chromatography. The activity of the thymidine kinase isozyme eluted with 0.1 M sodium chloride in buffer was twofold higher in fibroadenomas and fourfold higher in adenocarcinomas than that in normal tissue. In adenocarcinomas, but not fibroadenomas, the activity of the other isozyme eluted with buffer alone was increased to 22-fold that in normal tissues. As the activity of the latter isozyme was not affected by deoxycytidine triphosphate, it may be involved closely in DNA replication.

Hormonal control of gap junctions in the myometrium

Myometrial tissues from immature, ovariectomized mature, and pregnant rats were examined by thin-section or freeze-fracture electron microscopy for the presence of gap junctions following treatment with steroid hormones and inhibitors of prostaglandin synthesis. Gap junctions were present in the myometrium of immature rats after repeated injections of estradiol or diethylstilbestrol (500 micrograms/day). The frequency of gap junctions in immature rats after estradiol treatment was similar to that found during delivery. Concomitant administration of indomethacin or meclofenamate with estradiol (50 and 500 micrograms/day) for 3 or 4 days enhanced the effect of estradiol on gap junctions. Progesterone depressed the response of 500 micrograms/day estradiol and both 50 and 500 micrograms/day doses of estradiol when administered together with the inhibitors of prostaglandin synthesis. Gap junctions were also present in the myometria of ovariectomized mature rats after treatment with estradiol by itself or together with indomethacin, and these effects were suppressed by concomitant progesterone administration. These results indicate that the steroid hormones and prostaglandins may interact to modulate the presence of gap junctions in the myometrium.