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Oestradiol-17β hydroxysteroid dehydrogenase (EC 1.1.1.62) is involved in the glandular synthesis of oestradiol. Oestradiol dehydrogenase also has a pivotal role in regulating tissue concentrations of this biologically active oestrogen, mediating the conversion of oestrone to oestradiol or metabolism of oestradiol to oestrone. In addition to the ovary and testis, oestradiol dehydrogenase activity is detectable in many human tissues including the placenta, endometrium, lung, prostate and breast. Recent advances in molecular endocrinology have provided some intriguing insights into the possible ancestry of this enzyme but important questions about the control of its activity still remain unanswered.
The steroid dehydrogenase family
Two human placental oestradiol dehydrogenase cDNA clones have now been isolated and a unique primary structure of 327 amino acids has been deduced from the nucleotide sequence (Peltoketo, Isomaa, Mäenausta & Vihko, 1988; Luu-The, Labrie, Zhao et al. 1989). Based upon measurements of enzyme activity, multiple forms of oestradiol dehydrogenase have
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ABSTRACT
Oestradiol-17β hydroxysteroid dehydrogenase (E2DH) is present in normal and malignant breast tissues and also in cultured breast cancer cells. It can act in a reductive direction to convert oestrone to the biologically active oestrogen, oestradiol, or in an oxidative direction to metabolize oestradiol to oestrone and may therefore have a crucial role in regulating breast tissue concentrations of oestradiol. Insulin-like growth factor-type I (IGF-I) and IGF-II are both mitogens for breast cancer cells. In this study we have examined the effect of these growth factors on the reductive and oxidative activities of E2DH in MCF-7 (receptor positive) and MDA-MB-231 (receptor negative) breast cancer cells. Both IGF-I (80 ng/ml) and IGF-II (80 ng/ml) significantly stimulated E2DH reductive activity (up to 138%) in MCF-7 cells but had no effect on oxidative activity. Addition of IGF-II (100 ng/ml) to MDA-MB-231 cells resulted in a small but statistically significant (p<0.05) increase in E2DH reductive activity (18%) but in these cells reductive activity is 25-70 times lower than oxidative activity. If IGF-I and IGF-II act to stimulate E2DH reductive activity in breast tumours then such a mechanism could account for the increased concentrations of oestradiol detected in breast tumours.
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SUMMARY
[4-14C]Ethynyloestradiol was administered to women at varying times before hysterectomy. At operation, samples of blood, adipose tissue and tissue from the reproductive tract were obtained. All tissues examined took up radioactivity, the concentration at 1 h varying from 0·22 to 0·4% of the dose per 100 g of tissue except for stroma and endometrium which showed high levels (0·68% and 0·60%, respectively). By 24 h the amount of radioactivity in the tissues had decreased markedly. Mean values for the amount of radioactivity present in total tissues at 1 h were: uterus, 0·9%; adipose tissue, 28·2%; blood, 8·8%. By 24 h these values had declined to 0·2%, 6·8% and 1·6%, respectively. In adipose tissue almost all the radioactivity was present in a freely extractable state whereas in myometrium and cervix about 20% of the radioactivity was in a conjugated form. In plasma, more than 80% of the metabolites were conjugated, mainly as sulphates. The major metabolite detected in the uterus was ethynyloestradiol itself and most of the radioactivity in the myometrium was associated with the nuclear fraction. In one pregnant subject studied, radioactivity crossed the placenta and small amounts of the dose were found in the foetus.
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SUMMARY
The metabolism of 17α-ethynyloestradiol was studied in one man and 16 women. After intravenous or oral administration, 22·6–46·9% of the dose was excreted in the urine over a 5-day period. Up to 36% of the urinary radioactivity may be present in the unconjugated form with a further 64% being extractable after enzymic hydrolysis. Sulphate conjugates formed only 11·4% of the urinary radioactivity. Semi-quantitation of these extracts showed ethynyloestradiol itself to be the major metabolite, accounting for 3·2–8·4% of the administered dose in the unconjugated fraction with a further 2·4–16·5% in the enzyme hydrolysed fraction. Up to 16·5% of the dose was therefore excreted unchanged, and metabolites less and more polar than ethynyloestradiol were also found. Excretion via the faeces accounted for up to 30% of the administered dose, with most of the extractable radioactivity being in the unconjugated form. Ethynyloestradiol accounted for up to 29·6% of faecal radioactivity. No significant amounts of radioactivity were detected in sweat collected from one subject 2 or 24 h after administration of the dose. Plasma levels of 3·32% and 1·72% of the administered dose per litre were found 1 and 24 h after administration. Metabolites in plasma were present mainly as sulphate conjugates.
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SUMMARY
[3H]Norethisterone was administered to women 1, 3 and 24 h before hysterectomy, when samples of blood, adipose tissue and tissues from the reproductive tract were obtained. At 1 h the highest concentrations of radioactivity were found in endometrium and stroma (0·77 and 0·78% respectively of the dose per 100 g tissue), the values in other tissues varying from 0·13 to 0·39%. By 3 h there was a decrease in the concentration in all tissues except adipose tissue and plasma and at this time the range of concentrations in all tissues, apart from plasma (0·40%), were similar (0·08 to 0·19%). There was a further decrease by 24 h. Mean values for the amount of radioactivity present in the tissues at 1 h were: uterus, 0·55%; adipose tissue, 21·6%; blood, 10·1%. By 24 h these values had decreased to 0·1, 7·0 and 6·6% respectively. In adipose tissue most of the radioactivity was present in the freely extractable state at all times studied, whereas in myometrium and cervix the amount of radioactivity freely extractable at 1 h (77%) had decreased by 24 h (39·0%). In plasma the amount of conjugated radioactivity increased from 54% at 1 h to 88% by 24 h. Whereas at 1 h most metabolites in plasma were conjugated as sulphates, by 24 h glucuronide conjugates were also important. In myometrial tissue 17·5 to 47·8% of the radioactivity was associated with the nuclear fraction.
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Abstract
In situ oestrogen synthesis makes an important contribution to the high oestrogen concentration found in breast tumours. Cytokines, including interleukin-6 (IL-6) and tumour necrosis factor α (TNFα), have been shown to regulate aromatase activity in fibroblasts derived from normal and malignant breast tissues. In the present study, the ability of other cytokines in the IL-6 superfamily (IL-11 and oncostatin M) to stimulate aromatase activity has been confirmed. Formation of oestrone via the oestrone sulphatase pathway may be the major route of tumour oestrogen synthesis and in the present study TNFα was found to stimulate sulphatase activity in a dose-dependent manner. Human serum albumin was also found to be a potent stimulator of oestrone sulphatase activity. Its stimulatory effect was blocked by basic fibroblast growth factor, but not by several other growth factors tested. Insight into the regulation of oestrogen synthesis in breast tumours should enable the development of novel compounds to inhibit oestrogen synthesis in women with breast cancer.
Journal of Endocrinology (1996) 150, S65–S71
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ABSTRACT
Concentrations of 5-androstene-3β, 17β-diol (androstenediol), dehydroepiandrosterone (DHA) and DHA sulphate (DHAS) were measured in endometrium and plasma from normal premenopausal and perimenopausal women (average ages 37 and 48 years respectively) at different stages of the menstrual cycle. Plasma levels did not vary with the stage of the cycle for any of the three steroids. Mean plasma levels of androstenediol ranged between 2·03 and 2·92 nmol/l for premenopausal women and 1·38 and 1·58 nmol/l for perimenopausal women while mean concentrations of DHA were 20·80–36·41 nmol/l (premenopausal women) and 13·87–19·07 nmol/l (perimenopausal women). The values for DHAS were more variable and ranged between 3·20 and 4·56 and 2·94 and 4·25 μmol/l for pre- and perimenopausal women respectively.
In premenopausal women endometrial tissue concentrations of androstenediol and DHA increased three to fourfold in the secretory phase while no increase was observed in DHAS. There was a similar increase in androstenediol but not DHA or DHAS during the secretory phase for perimenopausal women. A significant positive correlation was found for tissue androstenediol and DHA in both groups of women but the relationship between DHAS and the other androgens was significant only for perimenopausal women.
We suggest that the increase in androstenediol and DHA concentrations could be due to an increase in a receptor or binding protein, possibly progesterone dependent, present in secretory phase endometrium.
J. Endocr. (1984) 101, 181–188
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ABSTRACT
The interleukin-6 soluble receptor (IL-6sR) may regulate the ability of IL-6 to stimulate oestrogen synthesis in breast cancer cells and breast tumours. Significant aromatase activity was detectable in IL-6 stimulated fibroblasts derived from subcutaneous adipose tissue, but the combination of IL-6sR plus IL-6 resulted in a marked 21-fold stimulation of aromatase activity. To examine the control of IL-6sR release, the effects of oestradiol, 4-hydroxytamoxifen (4-OHT), dexamethasone, TPA, TNFα or IL-6 on this process was examined using MCF-7 breast cancer cells. Oestradiol, TNFα and dexamethasone all markedly increased IL-6sR release. While 4-OHT had a small stimulatory effect on IL-6sR release, it blocked the ability of oestradiol to increase IL-6sR release. Significant concentrations of IL-6sR were also detected in conditioned medium collected from lymphocytes and macrophages and in cytosols prepared from normal and malignant breast tissues. These results indicate that IL-6sR may have an important role in potentiating the effect of IL-6 on oestrogen synthesis in breast cancer cells. The abilities of oestradiol or tamoxifen to potentiate or inhibit the IL-6 stimulation of oestrogen synthesis in breast cancer cells may result from their effects on IL-6sR release.
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ABSTRACT
Dietary factors are known to modulate concentrations of sex hormone-binding globulin (SHBG). In the present study we have investigated the possibility that insulin like growth factor-type I (IGF-I) may be an additional regulator of SHBG using cultured human hepatoma cells which secrete SHBG. The inhibitory effect of insulin on SHBG secretion by these cells was confirmed but, in addition, IGF-I was shown to inhibit SHBG secretion by about 40% at a concentration of 100 nmol/l. A similar degree of inhibition was achieved using insulin at a concentration of 10 umol/l. Insulin, but not IGF-I, was also found to inhibit the secretion of a low molecular weight IGF-binding protein (IBP-I), which is also secreted by hepatoma cells. It is concluded that IGF-I is an additional regulator of SHBG secretion by these cells and that it may be involved in regulating SHBG secretion in vivo in response to dietary factors.
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ABSTRACT
Gross cystic breast disease is a common benign disease which may be associated with an increased risk for breast cancer. Breast cyst fluid (BCF) contains many steroids, peptide growth factors and proteins. We have now identified interleukin-1 (IL-1) and IL-6 in BCF by specific radioimmunoassays. Concentrations of IL-1 were similar in BCF with low or high Na+/K+ ratios (ratio <3 vs >3; 357 ± 72 pg/ml vs 308 ± 126 pg/ml). In contrast, IL-6 concentrations were significantly higher (P<0.01) in BCF with a Na+/K+ ratio >3 (2.75 ± 2.34 ng/ml) compared with BCF with a low electrolyte ratio (0.21 ± 0.09 ng/ ml). BCF (10%, v/v) stimulated aromatase activity when added to dexamethasone stimulated breast tumour-derived fibroblasts and there was a significant correlation between the stimulation of aromatase activity and BCF Na+/K+ ratio (r = 0.95, P<0.001). A significant correlation was also found between stimulation of aromatase activity and concentration of IL-6 in BCF (r = 0.80, P<0.01) but not IL-1 concentration (r = −0.39, not significant). Addition of IL-1 or IL-6 (50 ng/ml) to fibroblasts stimulated aromatase activity but was associated with a small (20%) decrease in cell growth. It is concluded that IL-6 may have an important role in regulating aromatase activity in breast cancer cells.
