Localization of estradiol 17beta dehydrogenase in human endometrium

Intracrine Regulation of Estrogen and Other Sex Steroid Levels in Endometrium and Non-gynecological Tissues; Pathology, Physiology, and Drug Discovery

Our understanding of the intracrine (or local) regulation of estrogen and other steroid synthesis and degradation expanded in the last decades, also thanks to recent technological advances in chromatography mass-spectrometry. Estrogen responsive tissues and organs are not passive receivers of the pool of steroids present in the blood but they can actively modify the intra-tissue steroid concentrations. This allows fine-tuning the exposure of responsive tissues and organs to estrogens and other steroids in order to best respond to the physiological needs of each specific organ. Deviations in such intracrine control can lead to unbalanced steroid hormone exposure and disturbances. Through a systematic bibliographic search on the expression of the intracrine enzymes in various tissues, this review gives an up-to-date view of the intracrine estrogen metabolisms, and to a lesser extent that of progestogens and androgens, in the lower female genital tract, including the physiological control of endometrial functions, receptivity, menopausal status and related pathological conditions. An overview of the intracrine regulation in extra gynecological tissues such as the lungs, gastrointestinal tract, brain, colon and bone is given. Current therapeutic approaches aimed at interfering with these metabolisms and future perspectives are discussed.

Stromal cells of endometriosis fail to produce paracrine factors that induce epithelial 17beta-hydroxysteroid dehydrogenase type 2 gene and its transcriptional regulator Sp1: a mechanism for defective estradiol metabolism

OBJECTIVE

In endometrium, stromal progesterone receptors mediate production of paracrine factors, which enhance binding of the transcription factor specific protein-1 to the promoter of the gene encoding the 17beta-hydroxysteroid dehydrogenase type 2 enzyme responsible for converting biologically active estradiol to estrone in epithelium. The objective of this study is to define the cellular defect responsible for the disruption of this stromal-epithelial interaction in endometriosis.

STUDY DESIGN

We determined the effects of conditioned media generated from primary human eutopic endometrial stromal cells vs endometriotic stromal cells on Ishikawa malignant endometrial epithelial cells.

RESULTS

Conditioned media from progestin-pretreated eutopic endometrial stromal cells but not endometriotic stromal cells significantly stimulated specific protein-1 protein levels, 17beta-hydroxysteroid dehydrogenase type 2 messenger RNA levels and promoter activity, and binding activity of specific protein-1 to the 17beta-hydroxysteroid dehydrogenase type 2 promoter region in Ishikawa cells.

CONCLUSION

A stromal cell defect in endometriosis blocks formation of progesterone-dependent production of factors leading to 17beta-hydroxysteroid dehydrogenase type 2 deficiency and defective conversion of estradiol to estrone in epithelium.

SP1 and SP3 mediate progesterone-dependent induction of the 17beta hydroxysteroid dehydrogenase type 2 gene in human endometrium

The opposing actions of estrogen and progesterone during the menstrual cycle regulate the cyclical and predictable endometrial proliferation and differentiation that is required for implantation. Progesterone indirectly stimulates the expression of 17beta hydroxysteroid dehydrogenase type 2 (HSD17B2), which catalyzes the conversion of biologically potent estradiol to weakly estrogenic estrone in the endometrial epithelium. We previously demonstrated upregulation of the HSD17B2 gene in human endometrial epithelial cells by factors secreted from endometrial stromal cells in response to progesterone. We investigated the underlying mechanism by which these stroma-derived, progesterone-induced paracrine factors stimulate HSD17B2 expression. Here, we show that transcription factors SP1 and SP3 interact with specific motifs in HSD17B2 promoter to upregulate enzyme expression in human endometrial epithelial cell lines. Conditioned medium (CM) from progestin-treated stromal cells increased levels of SP1 and SP3 in endometrial epithelial cells and induced HSD17B2 mRNA expression. Mithramycin A, an inhibitor of SP1-DNA interaction, reduced epithelial HSD17B2 promoter activity in a dose-dependent manner. Serial deletion and site-directed mutants of the HSD17B2 promoter demonstrated that two overlapping SP1 motifs (nt -82/-65) are essential for induction of promoter activity by CM or overexpression of SP1/SP3. CM markedly enhanced, whereas anti-SP1/SP3 antibodies inhibited, binding of nuclear proteins to this region of the HSD17B2 promoter. In vivo, we demonstrated a significant spatiotemporal association between epithelial SP1/SP3 and HSD17B2 levels in human endometrial biopsies. Taken together, these data suggest that HSD17B2 expression in endometrial epithelial cells, and, therefore, estrogen inactivation, is regulated by SP1 and SP3, which are downstream targets of progesterone-dependent paracrine signals originating from endometrial stromal cells.

Progestogenic effects of tibolone on human endometrial cancer cells

Tibolone, a synthetic steroid acting in a tissue-specific manner and used in hormone replacement therapy, is converted into three active metabolites: a Delta(4) isomer (exerting progestogenic and androgenic effects) and two hydroxy metabolites, 3 alpha-hydroxytibolone (3 alpha-OH-tibolone) and 3beta-OH-tibolone (exerting estrogenic effects). In the present study an endometrial carcinoma cell line (Ishikawa PRAB-36) was used to investigate the progestogenic properties of tibolone and its metabolites. This cell line contains progesterone receptors A and B, but lacks estrogen and androgen receptors. When tibolone was added to the cells, complete conversion into the progestogenic/androgenic Delta(4) isomer was observed within 6 d. Furthermore, when cells were cultured with tibolone or when the Delta(4) isomer or the established progestagen medroxyprogesterone acetate was added to the medium, marked inhibition of growth was observed. Interestingly, 3 beta-OH-tibolone also induces some inhibition of growth. These growth inhibitions were not observed in progesterone receptor-negative parental Ishikawa cells, and progestagen-induced growth inhibition of PRAB-36 cells could readily be reversed using the antiprogestagen Org-31489. Upon measuring the expression of two progesterone-regulated genes (fibronectin and IGF-binding protein-3), tibolone, the Delta(4) isomer and medroxyprogesterone acetate showed similar gene expression regulation. These results indicate that tibolone, the Delta(4) metabolite, and to some extent 3 beta-OH-tibolone exert progestogenic effects. Tibolone and most likely 3 beta-OH-tibolone are converted into the Delta(4) metabolite.

Mechanisms of estradiol inactivation in primate endometrium

In uterine endometrium, the level of estradiol is controlled by oxidative 17beta-hydroxysteroid dehydrogenase (17HSD) activity which converts the bioactive hormone to the less active compound estrone. At least three different types of 17HSD (types 2, 4 and 8) use estradiol as their preferred substrate and may contribute to the overall rate of estradiol-inactivation in the uterus. In this study the marmoset monkey (Callithrix jacchus) was used for the investigation of the particular contribution of each type of 17HSD. Northern Blots revealed essentially the same tissue distribution as in the human. Likewise, uterine 17HSD enzyme activity increases in the secretory phase of the reproductive cycle, in parallel to the rise in circulating progesterone levels. Northern analysis of uteri from defined time points of the reproductive cycle showed that only the level of 17HSD2 expression is strongly upregulated in the secretory phase, whereas 17HSD4 and 17HSD8 seem to be expressed constitutively.

17 beta-Hydroxysteroid dehydrogenase activity in endometrial cancer cells: different metabolic pathways of estradiol in hormone-responsive and non-responsive intact cells

In this paper we report that two human long-term endometrial cancer cell lines, Ishikawa and HEC-1A, exhibit quite different abilities in metabolizing estrogens. As a matter of fact, incubation of Ishikawa cells with close-to-physiological concentrations of estradiol (E2) as precursor resulted in: (1) elevated formation (up to 90%) of E2-sulphate (E2-S), using lower precursor concentrations; (2) very limited conversion to estrone (E1) (< 10% at 24 h incubation), as either free or sulphate; and (3) low but consistent production of other estrogen derivatives, such as 2-hydroxy-estrogens and estriol. Conversely, scant amounts (if any) of E2-S were found in HEC-1A cells, while no detectable formation of other estrogen metabolites could be observed after 24 h. On the other hand, E1 production was significantly greater (nearly 60% at 24 h) than in Ishikawa cells, a large proportion of E1 (over 50% of the total) being formed after only 6 h incubation using time-course experiments. The hypothesis that E2 metabolism could be minor in Ishikawa cells as a consequence of the high rate of E2-S formation encountered is contradicted by the evidence that conversion to E1 also remains limited in the presence of much lower E2-S amounts, seen using higher molar concentrations of precursor. Overall, we observe that 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) activity diverges significantly in intact Ishikawa and HEC-1A endometrial cancer cells. This difference could not merely be accounted for by the diverse amounts of substrate (E2) available to the cells, nor may it be imputed to different levels of endogenous estrogens. It should rather be sought in different mechanisms controlling 17 beta-HSD activity or, alternatively, in the presence of distinct isoenzymes in the two different cell types.

Immunohistochemical localization of estrogen-specific 17 beta-hydroxysteroid oxidoreductase in the human and mouse prostate

The estrogen-specific 17 beta-hydroxysteroid oxidoreductase (17 beta-HSOR) enzyme protein was stained immunohistochemically in the newborn and adult human prostate as well as in the mouse prostate. In the newborn human prostate, ductal and urethral epithelia were faintly stained, whereas in the adult human prostate, intense staining for 17 beta-HSOR enzyme antigen could be detected in the epithelium of the collecting ducts and urethral epithelium as well as in the epithelium of the intraprostatic vas deferens and seminal vesicle epithelium. Immunostaining was weak in the prostatic tissues of both newborn and adult prostate. No positive cells were found in stroma. The activity of NADPH-dependent 3H-estrone reductase was detectable in cell-free homogenates prepared from human prostatic tissues. The activities showed a good correlation with immunocytochemical findings. In the mouse, neonatal estrogenization resulted in intensively stained epithelium of the collecting ducts at the age of 14 days. Moreover, when adult control and neonatally estrogenized mice were implanted with 17 beta-estradiol, the metaplastic epithelium of the periurethral collecting ducts of neonatally estrogenized mice was intensively stained with 17 beta-HSOR. These findings suggest that metaplastic epithelium rises from 17 beta-HSOR-positive cells. The similar distributions of 17 beta-HSOR-positive cells confirm the concept of homology in the posterior estrogen-responsive periurethral region (containing the periurethral ducts and periurethral glands) of the mouse and humans. Our findings further suggest that the 17 beta-HSOR-positive cells may have the same origin and hormonal control in both species.

Alterations in the subcellular distribution of 17 beta-estradiol dehydrogenase in porcine endometrial cells over the course of the estrous cycle

The uteri of German landrace gilts slaughtered at different days of the cycle were processed for immunocytochemistry and biochemical analyses. Plasma was collected for hormone assays. The monoclonal antibody F1 against the structure-bound 17 beta-estradiol dehydrogenase of porcine endometrial epithelium was applied to rehydrated paraffin sections either as a direct, peroxidase-linked probe or in combination with a fluorescing secondary antibody. The oxidation of estradiol was measured in homogenates of tissue powdered in liquid nitrogen. Immunoreactivity was restricted to endometrial epithelium. In the glandular epithelium, faint dots of fluorescence became visible at day 4, which apparently coalesced to spherical structures of 2-4 microns diameter at the cell basis between days 11 through 17 before disappearing by day 18. A similar distribution was observed for the oxidation products of diaminobenzidine beginning with a faint uniform staining and followed by the appearance of intensely stained basal bodies persisting until day 17. Essentially the same time course was seen in the luminal epithelium but with a different distribution. Immunoreactive material amassed in the apical region of the cells, but the conspicuous aggregations were absent. Time course and intensities of the immunological responses are matched by the enzymatic activity measured in parallel. Both correlate with the plasma progesterone levels, suggesting an induction of the enzyme by the hormone. An involvement of the cytoskeleton in the sequence of subcellular distribution patterns is discussed.

17 beta-Hydroxysteroid dehydrogenase type 2: chromosomal assignment and progestin regulation of gene expression in human endometrium

The cDNAs for two separate human 17 beta-hydroxysteroid dehydrogenases (17 beta-HSD) have been isolated and sequenced. The well-studied human placental cytosolic 17 beta-HSD (also referred to as estradiol dehydrogenase) preferentially catalyzes the reduction of estrone to estradiol-17 beta and the reduction of the C-20-ketone of progesterone to 20 alpha-dihydroprogesterone. This isoform of the enzyme has been referred to as 17 beta-HSD type 1 and localized to chromosome 17. A second 17 beta-HSD isoform (referred to as type 2) is localized in the endoplasmic reticulum of human trophoblast and is characterized by the preferential oxidation of the C-17 beta-hydroxyl group of C18- and C19-steroids and the C-20 alpha-hydroxyl group of 20 alpha-dihydroprogesterone. In this study, we determined the chromosomal localization of human 17 beta-HSD type 2, the expression of this gene in human endometrium, and the tissue distribution of the mRNA. We found that the human 17 beta-HSD type 2 gene is localized on chromosome 16, 16q24. 17 beta-HSD type 2 mRNA (approximately 1.5 kb) was identified in human endometrial tissues by Northern analysis of total RNA (10 micrograms). The highest levels of 17 beta-HSD type 2 mRNA were found in endometrial tissues obtained during the mid- to late secretory phase of the ovarian cycle (i.e., during the time of high plasma levels of progesterone). 17 beta-HSD type 2 mRNA levels were much greater in glandular epithelium than in the stromal cells isolated from secretory phase endometrium. The levels of 17 beta-HSD type 2 mRNA in secretory phase endometrium were approximately one-tenth that in villous trophoblast tissue from human placenta. We did not detect 17 beta-HSD type 1 mRNA in endometrial tissue by Northern analysis of total (10 micrograms) RNA. These findings are consistent with the view that the progestin-regulated 17 beta-HSD of the glandular epithelium of the human endometrium is primarily, if not exclusively, the product of the 17 beta-HSD type 2 gene. 17 beta-HSD type 2 mRNA was present in human placenta, liver, and small intestine; much smaller amounts, barely detectable by Northern analysis of poly(A)+ RNA, were present in prostate, kidney, pancreas, and colon, but not in heart, brain, skeletal muscle, spleen, thymus, ovary, or testis.

The 17 beta-oestradiol dehydrogenase of pig endometrial cells is localized in specialized vesicles

Two monoclonal antibodies against the 17 beta-oestradiol dehydrogenase of pig endometrial cells have been used in localization studies with immunogold electron microscopy. The antibodies attach both to a fraction of dehydrogenase-rich cytoplasmic vesicles isolated from homogenates and to vesicles of similar appearance in cells. The vesicles are filled with electron-dense material. Their tagging intensity indicates a high degree of specialization. Endometrial cells from mature animals contain a host of dehydrogenase vesicles, and cells from prepubertal animals only a few. Functional aspects of the novel organelle are discussed.

Steroid biosynthetic enzymes: 17 beta-hydroxysteroid dehydrogenase

Polyclonal antibodies produced against human placental 17 beta-hydroxysteroid dehydrogenase (17HSD), purified to homogeneity, and the corresponding cDNA for the enzyme were used to study the expression of 17HSD in a number of human tissues using various immunological methods together with RNA hybridization techniques. In addition, two 17HSD genes and their putative regulatory elements were sequenced. Immunoblotting analysis showed that the placental-type enzyme is expressed in granulosa-luteal cells, breast cancer tissue and breast cancer cell lines. An immunologically identical antigen was also detected in normal and carcinomatous human endometrium. The same antiserum, following affinity purification, was used for immunohistochemical studies of the endometrium and breast tissue, whereupon staining of the cytoplasm of the epithelial cells alone was observed. Immunostaining was also present in cultured human granulosa cells and in about half of the endometrial and breast carcinoma specimens investigated. Progesterone induction of the 17HSD enzyme protein was demonstrated in the human endometrium during the secretory phase of the menstrual cycle and in one breast cancer cell line (T-47D) following progestin treatment. There are at least two mRNAs for placental 17HSD (1.3 kb, 2.3 kb). RNA hybridization analysis of various breast cancer cell lines showed that the 1.3 kb mRNA was most closely associated with enzyme protein expression and was also the only form responding to progesterone induction. We conclude that placental-type 17HSD is also expressed in some other human tissues, both steroid-synthesizing and steroid-responding, and that the mRNA and enzyme protein are induced by progesterone. The availability of the sequence of 17HSD genes and surrounding regions allows us to study the sequences responsible for the expression and regulation of 17HSD.

Distribution of estradiol-17 beta hydroxysteroid oxidoreductase in the urogenital tract of control and neonatally estrogenized male mice: immunohistochemical, enzymehistochemical, and biochemical study

The present study was conducted to investigate the regional distribution of the enzymes catalyzing the interconversion of the hydroxyl and carbonyl groups at C-17 of the estrogen molecule within the male urogenital tract of adult mouse and to test the hypothesis, whether regional differences in the distribution are critical for estrogen responses. The highest ratios of NADPH-dependent 3H-estrogen reduction to oxidation at C-17 of cell-free homogenates were obtained from coagulating gland and seminal vesicle as well as from the prostatic and lower intrapelvic urethra, which are considered the most estrogen-sensitive parts of the male urogenital tract. Both NADP- and NAD-dependent oxidation of 3H-17 beta-estradiol were low or nondetectable at these sites. The epithelium of the lower and prostatic urethra as well as the periurethral collecting ducts were stained with the antibody prepared against human placental 17 beta-hydroxysteroid oxidoreductase. The NAD-dependent 3H-estradiol-17 beta oxidase activity was highest in the bladder epithelium, and the activity declined sharply in the urinary tract from the bladder downward. The lowest detectable activities were found in vas deferens and prostate (combined ventral and dorsolateral lobes). The uneven distribution of estradiol-17 beta oxidase activity may provide additional explanation for the regional differences of estrogen responses. The NADPH-dependent 17 beta-reduction of estrone and the immunohistochemical staining of the human placental estradiol-17 beta oxidoreductase antigenicity were not significantly altered after neonatal estrogenization. These findings do not lend any support to the idea that the increased estrogen sensitivity observed after neonatal estrogenization is associated with changes in 17 beta-oxidoreduction. However, the possibility remains that there are specific sites (e.g., epithelium of prostatic urethra and collecting ducts) in which the changes in 17 beta-oxidoreduction of estrogen does play a role in the regulation of estrogen action.

Immunological measurement of human 17 beta-hydroxysteroid dehydrogenase

Human placental 17 beta-hydroxysteroid dehydrogenase (17-HSD) was purified to apparent homogeneity using ammonium sulfate precipitation and chromatography on Red-Agarose and DEAE-Sepharose columns. Electrophoresis on polyacrylamide gels under denaturing conditions and using silver staining showed a single protein with an apparent molecular weight of 37,800. Antibodies to the purified protein were raised in rabbits and were found by immunoblotting to be specific to 17-HSD. A sensitive radioimmunoassay was established using 125I-labeled 17-HSD as a tracer, an appropriate dilution of the antibody, and a kaolin-coupled double antibody for separating the antibody-bound and free fractions. The detection limit of the assay was approximately 150 pg/tube (1.5 micrograms/l). The cytosol fraction (105,000 g) of term placental tissue contained approximately 0.7 mg of 17-HSD per gram of protein, and the concentrations of 17-HSD measured by immunoassay and enzymatic activity proved to be strictly parallel in different partly purified placental preparations. The supernatants from centrifugations of human endometrial homogenates at 800 g and 105,000 g (after detergent treatment) displayed cross-reactivity with the antibody. The mean concentration of the cross-reacting substance in the radioimmunoassay was 14.1 micrograms/g protein (range 2-62.3) in specimens taken on different days in the cycle. These concentrations showed a significant correlation with the 17-HSD activities measured in the endometrial specimens (r = 0.722, P less than 0.001, n = 21). Mean concentrations of substance were 8.3 micrograms/g protein in endometrial specimens taken during the follicular phase (days 4-12, n = 8) and 22.9 micrograms/g protein during the luteal phase (days 16-22, n = 6) were obtained using the radioimmunoassay. There was excellent parallelism between the competition curves for [125I]iodo-17-HSD with purified 17-HSD standards and placental and endometrial homogenate dilutions. These data strongly suggest that the substance measured in the endometrial specimens was 17-HSD.

The histochemistry of isocitric and oestradiol-17 beta dehydrogenases in the endometrium of postmenopausal women treated with oestrogens and progestogens

Endometrium was obtained from postmenopausal women during treatment with either oestrogen alone or on the third, sixth, tenth or twelfth day of combined therapy with oestrogens and progestogens. The activities of oestradiol-17 beta and isocitric dehydrogenases were measured in homogenates of the whole tissue and the enzymes were also located histochemically. Oestradiol dehydrogenase was located exclusively within the epithelium, whilst isocitric dehydrogenase was found in both epithelium and stroma, and also in stromal arterioles. Histochemically, oestradiol dehydrogenase was found in all the specimens which exhibited biochemical activity but in none of those from which it was absent. Isocitric dehydrogenase however, was seen in all tissue sections despite widely varying levels of biochemical activity in the homogenate. The method for measuring isocitric dehydrogenase activity was therefore nonspecific, whilst that for oestradiol dehydrogenase was reliable and low levels of enzyme activity could be detected. The latter technique may therefore be useful to predict the sensitivity of endometrial carcinomata to progestogens.

The histochemistry of oestradiol-17 beta and isocitric dehydrogenases in endometrial carcinoma

Specimens of endometrial carcinoma were obtained from 8 women, four of whom had previously been treated with oral medroxyprogesterone acetate 200 mg daily for 7 days. The activities of oestradiol-17 beta and isocitric dehydrogenases and nuclear oestradiol receptor concentrations were measured in the homogenised tissue and both enzymes were located histochemically. Histochemical evidence of oestradiol dehydrogenase activity was found in all but one of the specimens with biochemical activity. This anomalous specimen was obtained from a woman who had not been treated with MPA and whose endometrium exhibited only low levels of enzyme activity. The histochemical staining caused by isocitric dehydrogenase was intense but bore no relation to the biochemical measurement of enzyme activity in the homogenate. The modified technique for the histochemical demonstration of oestradiol dehydrogenase activity although not quantitative gave results similar to the biochemical methodology. It may therefore be useful as a simple test of the prediction of the sensitivity of endometrial carcinoma to progestogens.

Apparent immunologic nonidentity of human placental and endometrial 17beta-estradiol dehydrogenase

Immunohistochemical techniques were used to search for the presence of 17beta-estradiol dehydrogenase activity in human endometrial and placental tissues, with the use of antibodies raised against highly purified human placental 17beta-estradiol dehydrogenase. Sensitivity and specificity of the antibodies were documented by radioimmunoassay and immunodiffusion on cellulose acetate. Although staining was consistently demonstrated in the syncytiotrophoblast layer of term placentas, in both cytoplasm and nuclei, no immunohistochemical reaction was observed in endometrial samples. These results support the contention that placental 17beta-estradiol dehydrogenase is immunologically dissimilar from the endometrial enzyme.

Estrogen metabolism in normal and neoplastic endometrium

Studies on normal endometrium at different phases of the menstrual cycle have shown that progesterone and synthetic progestins reduce the levels of estradiol receptors in the tissue and increase the activity of estradiol-17beta-dehydrogenase, an enzyme that converts estradiol to estrone. These effects may account for the antiestrogenic characteristics of the progestins. Similar effects were obtained in some postmenopausal patients with endometrial adenocarcinoma treated for two to 10 days with oral medroxyprogesterone acetate. These results point to the potential usefulness of a short-term, in vivo biochemical test which, combined with histologic observations, may identify patients who are likely to respond to treatment with progestins.