Characterization of structural and functional properties of human 17 beta-hydroxysteroid dehydrogenase type 1 using recombinant enzymes and site-directed mutagenesis

Human 17 beta-hydroxysteroid dehydrogenase (17-HSD) type 1 catalyzes the conversion of the low activity estrogen, estrone, into highly active estradiol, both in the gonads and in target tissues. The present study was carried out to characterize the dimerization, microheterogeneity, and phosphorylation of human 17-HSD type 1 and to evaluate the current model of hydride transfer and substrate recognition of the enzyme, based on its x-ray structure. 17-HSD type 1 is a homodimer consisting of noncovalently bound subunits, and the data in the present study indicate an exceptionally strong association between the monomers [dissociation constant (Kd) < 5 pmol/monomers liter]. Furthermore, substitutions constructed at the hydrophobic dimer interface always resulted in inactive aggregates of the protein. The enzyme was shown to be phosphorylated by protein kinase A exclusively at Ser134 only in vitro. However, in contrast to previous suggestions, phosphorylation of Ser134 was shown to play no role in the activity or microheterogeneity of human 17-HSD type 1. The presence of microheterogeneity in the recombinant enzyme also indicates that it does not result from the frequent protein polymorphism previously found for the enzyme. In line with the x-ray structure and the proposed catalytic mechanism of the enzyme, our results indicate that Ser142, Tyr155, and Lys159 are all critical for hydride transfer in human 17-HSD type 1. In contrast, the proposed interaction between His221, Glu282, and the 3-OH group of the steroid at the substrate recognition helix could not be shown to exist. Neither of these residues plays a critical role in the catalytic action of the enzyme in cultured cells.

Aromatase and 17 beta-hydroxysteroid dehydrogenase type 1 in human breast carcinoma

The in situ formation of estradiol plays an important role in the development and biological behavior of human breast cancer Aromatase and 17 beta-hydroxysteroid dehydrogenase type 1 (17 beta-HSD type 1) are two principal enzymes involved in in situ estradiol production. We evaluated the expression of aromatase and 17 beta-HSD type 1 by immunohistochemistry in 41 cases of invasive breast carcinoma (19 lobular and 22 ductal). We then examined the correlation among the expression of these enzymes, estrogen (ER) and progesterone (PR) receptor status, Ki67 labeling index of carcinoma cells, age, and the clinical stage of the patients. Marked aromatase immunoreactivity was observed in stromal cells around carcinomatous glands in 32 of 41 cases (78%), and 17 beta-HSD type 1 immunoreactivity was detected in carcinoma cells in 23 of 41 cases (56%). There was a significant correlation observed between expression of 17 beta-HSD type 1 and aromatase in invasive lobular carcinoma (P = 0.0119), but not in invasive ductal carcinoma. There was an inverse correlation between aromatase and ER status in invasive ductal carcinoma (P = 0.0213), but not in invasive lobular carcinoma. No other correlations were observed among 17 beta-HSD type 1, aromatase, PR, ER, clinical stage, age, and Ki67 labeling indexes. Aromatase and 17 beta-HSD are not always expressed simultaneously in human breast carcinoma, but their simultaneous expression is more frequent in invasive lobular carcinoma than invasive ductal carcinoma. Consequently, different mechanisms may be involved in the regulation of expression of these two enzymes in human breast carcinoma.

Expression and regulation of 17 beta-hydroxysteroid dehydrogenase type 1

The current data indicate that during a woman's reproductive years, 17 beta-hydroxysteroid dehydrogenase type 1 is the major 17 beta-hydroxysteroid dehydrogenase (17HSD) involved in glandular oestradiol biosynthesis. The type 1 enzyme catalyses reduction from low-activity oestrone to high-activity oestradiol in ovarian granulosa cells and placental syncytiotrophoblasts, in which it is abundantly expressed. In addition to steroidogenic cells, 17HSD type 1 is present in certain peripheral tissues in which it reduces circulating oestrone, thus regulating the intracellular ligand supply for oestrogen receptors. Several factors and second messenger pathways are involved in the cell-specific expression of 17HSD type 1. In ovarian granulosa cells, 17HSD type 1 expression is strictly regulated by pituitary gonadotrophins, steroid hormones and growth factors, while in peripheral tissues progestins and retinoic acids, at least, affect 17HSD type 1 concentrations.

Cloning of rat 17 beta-hydroxysteroid dehydrogenase type 2 and characterization of tissue distribution and catalytic activity of rat type 1 and type 2 enzymes

17 beta-Hydroxysteroid dehydrogenases (17HSDs) are enzymes catalyzing the conversion between 17 beta-hydroxy- and 17-ketosteroids. Both estrogens and androgens possess their highest activity in the 17 beta-hydroxy form, and the enzymes, therefore, regulate the biological activity of sex hormones. In this study, we have characterized the complementary DNA (cDNA) for rat 17HSD type 2. The cDNA encodes a protein with a predicted mol wt of 42,010 Da. The protein has 77% similarity and 62% identity with the human 17HSD type 2 enzyme. Furthermore, the hydropathicity profiles of the enzymes are very similar. The two isozymes contain a putative transmembrane region close to the N-terminus. However, the rat isozyme lacks the two lysine-rich amino acid cluster present at the N- and C-terminals of human 17HSD type 2. The tissue distribution of the rat 17HSD type 1 and type 2 enzymes is very similar to that of the human enzymes. The highest expression of 17HSD type 2 was detected in the placenta. In addition, a 1.5-kilobase messenger RNA for the enzyme was detected in the small intestine, liver, and kidney of both sexes. The two messenger RNAs for rat 17HSD type 1 (1.4 and 1.7 kilobases) were highly expressed only in the ovary, and at very low concentrations in the kidney of both sexes. Transiently expressed rat 17HSD type 2 showed oxidative activity almost exclusively in cultured human embryonic kidney 293 cells, converting estradiol into estrone and testosterone into androstenedione, whereas the opposite was observed for the rat type 1 enzyme. The data suggest that similarly to the corresponding human isoforms, rat 17HSD type 2 is mostly involved in the oxidation of 17 beta-hydroxysteroids into their relatively inactive keto derivative in peripheral tissues, whereas rat 17HSD type 1 is mainly involved in the glandular biosynthesis of estradiol.

Characterization of 17beta-hydroxysteroid dehydrogenase isoenzyme expression in benign and malignant human prostate

In the present study, expressions of 17beta-hydroxysteroid dehydrogenase (17HSD) types 1, 2, and 3, 5alpha-reductase type 2 and human androgen receptor mRNAs were determined in 12 benign prostatic hyperplasia and 17 prostatic carcinoma specimens. 17HSD type 2 was found to be the principle isoenzyme expressed in the prostate. Significantly higher expressions of 17HSD type 2 and 5alpha-reductase type 2 were detected in benign prostatic hyperplasia compared with the carcinoma specimens. Expression of the androgen receptor in the 2 groups was not significantly different. 17HSD type 3 mRNA was not detected in any of the specimens investigated. Only low constructive expression of the 2.3 kb mRNA of 17HSD type 1 was seen. Immunohistochemical analysis indicated that this did not lead to significant enzyme expression, only faint staining for the enzyme protein being detected, mainly in uroepithelial cells. No significant correlation was found between any of the mRNAs analysed, but the data on 5alpha-reductase type 2 mRNA support the presence of an increased proportion of 5alpha-dihydrotesterone in the hyperplastic prostate. In cultured PC-3 prostatic cancer cells and in the transiently transfected human embryonic kidney 293 cells, 17HSD type 2 was found exclusively to convert 5alpha-dihydrotestosterone and testosterone into the less potent 17-keto compounds 5alpha-androstanedione and 4-androstenedione, respectively. We suggest that the 17HSD type 2 isoenzyme plays a part in the metabolic pathway, resulting in the inactivation of testosterone and 5alpha-dihydrotestosterone locally in the prostate. The enzyme expressed in the prostate could, therefore, protect cells from excessive androgen action.

Role of 17 beta-hydroxysteroid dehydrogenase type 1 in endocrine and intracrine estradiol biosynthesis

Enzymes with 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) activity catalyse reactions between the low-active female sex steroid, estrone, and the more potent estradiol, for example. 17 beta-HSD activity is essential for glandular (endocrine) sex hormone biosynthesis, but it is also present in several extra-gonadal tissues. Hence, 17 beta-HSD enzymes also take part in local (intracrine) estradiol production in the target tissues of estrogen action. Four distinct 17 beta-HSD isozymes have been characterized so far, and the data strongly suggests that different 17 beta-HSD isozymes have distinct roles in endocrine and intracrine metabolism of sex steroids. Current data suggest that 17 beta-HSD type 1 is the principal isoenzyme involved in glandular estradiol production both in humans and rodents. During ovarian follicular development and luteinization, rat 17 beta-HSD type 1 is regulated by gonadotropins, and the effects of gonadotropins are modulated by steroid hormones and paracrine growth factors. Human 17 beta-HSD type 1 favors the reduction reaction, thereby converting estrone to estradiol both in vitro and in cultured cells. Hence, the enzymatic properties of the enzyme are also in line with its suggested role in estradiol biosynthesis. Interestingly, 17 beta-HSD type 1 is also expressed in certain target tissues of estrogen action such as normal and malignant human breast and endometrium. Hence, 17 beta-HSD type 1 could be one of the factors leading to a relatively high tissue/plasma ratio of estradiol in breast cancer tissues of postmenopausal women. We conclude that 17 beta-HSD type 1 has a central role in regulating the circulating estradiol concentration as well as its local production in estrogen target cells.

Regulation of oestrogen action: role of 17 beta-hydroxysteroid dehydrogenases

The target cell responses to steroid hormones, such as oestrogens, are dependent on the expression of their receptors. Apart from receptor concentration, another key regulatory factor in steroid hormone action is the intracellular hormone concentration, which is affected by three main variables: the concentration of the steroid in plasma, local production and local conversion into metabolites. During the reproductive years the main source of oestrogens is the ovarian follicle, but in postmenopausal women most of the oestrogens are formed in peripheral tissues. The present overview deals with the formation of active oestrogens in steroidogenic tissues and in oestrogen target tissues, and the main focus is on 17 beta-hydroxysteroid dehydrogenases, which catalyse the interconversion between oestradiol and oestrone. It is evident that different 17 beta-hydroxysteroid dehydrogenase isoenzymes are responsible for the oxidation/reduction of oestradiol or oestrone in oestrogen target cells. Because these enzymes are involved in the biosynthesis and metabolism of oestrogens, they have an important physiological significance for the growth of oestrogen-dependent tissues and, hence, the growth and progression of hormone-dependent tumours.

Estrogen-specific 17 beta-hydroxysteroid oxidoreductase type 1 (E.C. 1.1.1.62) as a possible target for the action of phytoestrogens

Several plant estrogens, especially coumestrol and genistein, were found to reduce the conversion of [3H]estrone to [3H] 17 beta-estradiol catalyzed by estrogen-specific 17 beta-hydroxysteroid oxidoreductase Type 1 (E.C. 1.1.1.62) in vitro. Coumestrol, the most potent inhibitor in our experiments, is the best inhibitor of the enzyme known to date. All compounds with inhibitory effects were also estrogenic. However, structural demands for 17 beta-HSOR Type 1 inhibition and estrogenicity of tested compounds in breast cancer cells (judged by increased cell proliferation) were not identical. Zearalenone and diethylstilbestrol, both potent estrogens, did not inhibit 17 beta-HSOR Type 1. Thus, changes in the estrogen molecule may discriminate between active sites of 17 beta-HSOR Type 1 and estrogen binding sites of the ER. The effects of these compounds in vivo cannot be predicted on the basis of these results. Inhibition of 17 beta-HSOR Type 1 enzyme could lead to a decrease in the availability of the highly active endogenous estrogen. However, these compounds are estrogenic per se, and they may thus replace endogenous estrogens. Additional studies are needed to further understand the role of these plant estrogens in the etiology of hormone-dependent cancers. It is not easily conceivable how the chemopreventive action of Asian diets, possibly mediated by phytoestrogens in soya products, can be based on the inhibition of estrone reduction at the target cells by phytoestrogens or related compounds, unless they are "incomplete estrogens" (i.e., unable to induce all effects typical of endogenous estrogens).

Hormonal regulation of rat 17 beta-hydroxysteroid dehydrogenase type 1 in cultured rat granulosa cells: effects of recombinant follicle-stimulating hormone, estrogens, androgens, and epidermal growth factor

Ovarian estradiol (E2) production is regulated by complex interaction of different hormones, such as gonadotropins, steroids, and growth factors. Despite the key role of 17 beta-hydroxysteroid dehydrogenase (17HSD) in E2 biosynthesis, little is known about its regulation in the ovary. Recently, we have characterized the structure of rat 17HSD type 1 and demonstrated that its expression is regulated by gonadotropins and diethylstilbestrol (DES) in rat ovary in vivo. In the present study, the hormonal regulation of 17HSD type 1, and the expression of cytochrome P450 aromatase were examined in parallel in cultured granulosa cells obtained from DES-primed immature rats. Under these conditions, the cells show high expression of 17HSD type 1. Both the enzyme activity and 17HSD type 1 messenger RNA expression in these cells decreased over 2 days of culture in serum-free medium. However, recombinant FSH (recFSH) partially prevented the decreases in enzyme activity and messenger RNA expression in a dose-dependent manner. This effect appears to be mediated by a cAMP-dependent pathway. In contrast to recFSH, neither estrogens (DES or E2) nor androgens (testosterone or dihydrotestosterone) alone affected expression of the enzyme in the cultured cells. However, both estrogens and androgens clearly enhanced the effect of recFSH on 17HSD type 1 expression and 17HSD activity in a dose-dependent manner. Among the growth factors, epidermal growth factor (EGF) has previously been shown to decrease the expression of cytochrome P450 aromatase and E2 biosynthesis in granulosa cells. In the present study, we found that treatment with EGF caused a marked decrease in the effect of recFSH on 17HSD type 1 expression and 17HSD activity. The fact that 17HSD type 1 expression and 17HSD activity always behaved in parallel suggests that 17HSD type 1 is the major 17HSD enzyme involved in estradiol biosynthesis in rat granulosa cells. In conclusion, these data indicate that expression of 17HSD type 1 in rat granulosa cells is under multihormonal regulation. The enzyme is regulated by FSH, via cAMP, and the effect of FSH is modulated by estrogens, androgens, and EGF.

Rat 17 beta-hydroxysteroid dehydrogenase type 1: primary structure and regulation of enzyme expression in rat ovary by diethylstilbestrol and gonadotropins in vivo

17 beta-Hydroxysteroid dehydrogenase (17HSD) catalyzes the reversible conversion of estrone into estradiol. The complementary DNA (cDNA) coding for rat 17HSD type 1 was cloned from a commercial rat ovarian cDNA library, using human 17HSD type 1 cDNA as a probe. The nucleotide sequence extends for 1160 basepairs (bp), including 1035 bp of open reading frame, a stop codon, and 125 bp of 3'-untranslated sequence. The cDNA encodes a protein of 344 amino acids, with a calculated molecular mass of 36,967 daltons. The overall amino acid identity and similarity between rat and human 17HSD type 1 enzymes are 68% and 80%, respectively. Immunohistochemistry and in situ and Northern hybridizations were used to study regulation of the enzyme in rat ovary in vivo. Enzyme expression was detected in granulosa cells only, whereas no expression was observed in stromal or thecal cells. The enzyme was almost undetectable in ovaries from immature hypophysectomized rats. After 2-day treatment with recombinant FSH (recFSH), an induction of 17HSD type 1 expression was observed in granulosa cells of growing antral follicles. During 5 days of diethylstilbestrol (DES) treatment, a time-dependent increase in developing follicles was observed, showing strong expression of 17HSD type 1 in granulosa cells. Treatment with recFSH for 2 days in DES-primed animals resulted in down-regulation of ovarian enzyme expression. This reduction of enzyme expression was associated with luteinization of the follicles. hCG treatment of recFSH- or DES- plus recFSH-primed animals further induced luteinization, resulting in strong down-regulation of 17HSD type 1 expression. The enzyme was not detected in corpora lutea. The data show that 17HSD type 1 expression in rat ovary is regulated by gonadotropins and estrogens. The results suggest that expression of 17HSD type 1 and that of cytochrome P450 aromatase are regulated by distinct mechanisms, and 17HSD type 1 may be down-regulated earlier than P450 aromatase during luteinization, limiting estradiol biosynthesis in luteinizing granulosa cells in rat ovary.

A point mutation in the putative TATA box, detected in nondiseased individuals and patients with hereditary breast cancer, decreases promoter activity of the 17 beta-hydroxysteroid dehydrogenase type 1 gene 2 (EDH17B2) in vitro

EDH17B2, the gene encoding 17 beta-hydroxysteroid dehydrogenase type 1, has been suggested as a candidate for the familial breast cancer gene, BRCA1, located on 17q12-q21. We analyzed the promoter region of EDH17B2 in DNA from 20 control individuals and 40 patients with familial breast cancer. Two frequent (designated vI and vIII) and two rare (vII and vIV) nucleotide variations were present in both the breast cancer patients and the controls, except the alteration vII, which was found only in one patient. Although the data do not support the identification of EDH17B2 as the BRCA1 gene, it is of interest that point mutation vIV (A-->C) was located in the putative TATA box of the EDH17B2 gene. Reporter gene analyses showed that the mutation vIV decreases EDH17B2 promoter activity by an average of 45% in in vitro assays, suggesting that nucleotide A at position -27 is significant for efficient transcription.

Human familial and sporadic breast cancer: analysis of the coding regions of the 17 beta-hydroxysteroid dehydrogenase 2 gene (EDH17B2) using a single-strand conformation polymorphism assay

17 beta-Hydroxysteroid dehydrogenase (17HSD) is one of the key enzymes in estrogen metabolism, catalyzing the reversible reaction between estradiol and the less active estrogen, estrone. The gene encoding this enzyme, EDH17B2, has been mapped to chromosome 17, region q12-q21, in the vicinity of BRCA1, as as yet unidentified gene that appears to be involved in familial breast cancer and in familial ovarian cancer. The possibility that EDH17B2 gene is the same as BRCA1 was tested by screening for mutations in the coding regions of EDH17B2, using a polymerase chain reaction/single-strand conformation polymorphism method. An A-->G transition creating a new BstUI site at exon 6 was the only frequent sequence alteration found in the coding region of the gene. This mutation also led to an amino acid substitution of serine to glycine at position 312 (312S-->312G) in the 17HSD protein. Since the nucleotide change was detected both in specimens from patients with familial or sporadic cancer and in control samples, and at similar rates, this mutation appears to be of a polymorphic nature. In addition, a rare polymorphism located at intron 5 was detected. This C-->T substitution creates a BbvI site and is not thought to have any effect on 17HSD activity. The results indicate that there are no major alterations in the coding areas of EDH17B2 and thus studies testing the hypothesis that EDH17B2 may be the same as BRCA1 should be extended to the promoter and regulatory elements of EDH17B2.

Differential estrogen substrate specificities for transiently expressed human placental 17 beta-hydroxysteroid dehydrogenase and an endogenous enzyme expressed in cultured COS-m6 cells

The metabolism of estrogens catalyzed by human placental 17 beta-hydroxysteroid dehydrogenase (17HSD) transiently expressed in COS-m6 cells was studied, and the properties of the enzyme were compared with those of an endogenous hydroxysteroid dehydrogenase (HSD) expressed in the cells. In cultured cells, the endogenous HSD had almost exclusively oxidative activity, converting estradiol to estrone (oxidative and reductive activity, 0.84 +/- 0.164 and 0.034 +/- 0.01 nmol/mg protein.h, respectively). This was, nevertheless, opposed to the activity of the transiently expressed human placental 17HSD, as a high reductive activity (0.86 +/- 0.30 nmol/mg protein.h) appeared in the cells after transfection, whereas oxidative activity was not significantly induced. In the different transfections, the reductive activity was induced 13- to 34-fold, and the oxidative activity in the 17HSD-transfected cells was 65-162% of that in the mock-transfected cells. Thus, in cultured cells, these two enzymes preferentially catalyze opposite reactions. When the metabolism of the estrogens was followed up to 20 h, the two enzymes were found to regulate the proportion of estrone to estradiol in the culture medium. The different properties found for the enzymes show that the endogenous HSD expressed in the COS-m6 cells is an additional member of the family of 17HSD enzymes. It is suggested that different 17HSD enzymes exist, with differential estrogen substrate specificities in cultured cells. Thus, in addition to cofactor and substrate availability, the biological activity of estrogens in different cell types may be regulated by the expression of different forms of 17HSD enzymes, resulting in the dominance of either estradiol or estrone production.

Immunohistochemical detection of human estrogen receptor with region D-specific antipeptide antibodies

To study the possibility of using antipeptide antibodies for the immunohistochemical determination of human estrogen receptors (ER), three peptides corresponding to the putative major antigenic regions of the human ER (Met12-Leu26, or ERP1; Thr227-Gln267, or ERP2; Leu256-Gly275, or ERP3) were used to produce site-specific rabbit polyclonal antipeptide antisera. High titer antibodies were obtained against all the peptides used, as judged by time-resolved fluoroimmunoassay. The antibodies against region D (ERP3) specifically immunoprecipitated the ER proteins in vitro, as did the antiERP2 antibodies to a much smaller extent. With one of the region D-specific antibodies (antiERP3 Ab2) ER could also be immunohistochemically detected. When benign and malignant human breast and normal endometrial tissues were used, the immunohistochemical staining observed with these antipeptide antibodies correlated well with the staining obtained with an established method. Thus, the results reported here show that this part of region D in ER is a potential antigenic epitope for the production of site-specific antibodies against ER. Antipeptide antibodies produced against this region can be used to immunolocalize the ER in various normal and pathological human tissues.

Immunological analysis of 17 beta-hydroxysteroid dehydrogenase in benign and malignant human breast tissue

The expression of 17 beta-hydroxysteroid dehydrogenase (17-HSD) enzyme protein was studied in benign and malignant human breast tissue using the time-resolved immunofluorometric assay (IFMA), immunoblotting and immunohistochemistry. The presence and distribution of estrogen and progestin receptors was also analyzed immunohistochemically. Cytosolic 17-HSD concentrations in malignant breast specimens were highly variable (less than or equal to 0.2-311 ng/mg protein). As was previously found for the placental enzyme, the molecular weight of the 17-HSD expressed in malignant breast tissue was 35 kDa, estimated following polyacrylamide gel electrophoresis and immunoblotting. The cellular distribution of 17-HSD was further studied by immunohistochemistry. Immunostaining for 17-HSD was observed in 71% of the benign breast lesions (fibroadenomas and cases of mastopathia chronica) and in 47% of the cancer specimens (intra-ductal carcinomas, invasive ductal carcinomas). In benign lesions, the staining was exclusively localized in the cytoplasm of epithelial cells, with no immunoreactivity in the stromal cells. The staining in the cancer specimens was also detected only in the cytoplasm of malignant epithelial cells. A strong or moderate expression of 17-HSD was related to the presence of PR in the specimen (chi 2 = 4.657, p = 0.031). However, the expression of PR was not a prerequisite for expression of 17-HSD in all the cancer specimens. Our data suggest that, in addition to the reported regulation of 17-HSD by progestins, other factors are also involved in this process in breast tissue.

17 beta-hydroxysteroid dehydrogenase gene expression in human breast cancer cells: regulation of expression by a progestin

The expression of the 17 beta-hydroxysteroid dehydrogenase (17-HSD) gene in a series of human breast cancer cell lines was studied by Northern blot hybridization with a cDNA probe and by a time-resolved immunofluorometric assay using polyclonal antibodies against the enzyme protein. The 17-HSD enzyme protein concentration was measured in the 800 x g cell extract. A high concentration was measured in the BT-20 cell line, corresponding to one-fourth of the average concentration in placental tissue. Western blot analysis indicated that the antigen corresponded to a single Mr 35,000 band. In 2 other cell lines (MDA-MB-361 and T-47D), the 17-HSD protein concentration was much lower, but still measurable, whereas in the remaining 5 cell lines (HBL-100, MCF-7, MDA-MB-231, MDA-MB-468, and ZR-75-1) it was below the detection limit of the assay. Treatment of the cells for 5 days with the synthetic progestin, ORG2058, resulted in an increase of the 17-HSD protein concentration only in the T-47D cell line. By Northern blot analysis, a low level of 2.3-kilobase mRNA transcripts was detected in all 8 cell lines. In addition, a 1.3-kilobase 17-HSD mRNA was present in the samples from the 3 cell lines containing measurable amounts of 17-HSD protein in the cell extract, and the band intensities were proportional to the amount of protein measured with the immunofluorometric assay. Only in the T-47D cell line did progestin treatment correspond to an increased amount of the 17-HSD 1.3-kilobase mRNA. These results suggest that the 1.3-kilobase mRNA for 17-HSD is the form most closely associated with protein expression and is also the only form responding to the progestin induction of the 17-HSD gene.

Progestin induction of 17 beta-hydroxysteroid dehydrogenase enzyme protein in the T-47D human breast-cancer cell line

Steroid regulation of 17 beta-hydroxysteroid dehydrogenase (17-HSD) was studied in the T-47D human breast-cancer cell line, using a radioimmunoassay. In addition, 3 mRNA species (2.4, 1.4, and 0.9 kb) specific for the enzyme were shown to be present in these cells. All the synthetic progestins tested (ORG 2058, R5020, medroxyprogesterone acetate) significantly increased the immunoreactive enzyme protein concentration, while other types of steroids, such as testosterone, oestradiol and dexamethasone, were ineffective. The progestin-specific induction of 17-HSD was dose-related and was maximum in about 5 days. An antiprogestin, RU 486, when used in combination with synthetic progestins, blocked the progestin-induced increase of 17-HSD concentration very effectively. A good correlation was observed in the different experiments between the enzyme activity and the immunoreactive 17-HSD concentration. We conclude that progestins induce 17-HSD in T-47D cells and that the induction occurs via an increased accumulation of enzyme protein.