Expression of the estradiol-synthesizing 17beta-hydroxysteroid dehydrogenases type 1 and type 7 in the nonhuman primate Callithrix jacchus

Intracrine Control of Estrogen Action in Human Gestational Tissues at Parturition

OBJECTIVE

We examined whether estrogen action in human parturition is regulated by an intracrine mechanism mediated by target tissue expression of specific 17beta-hydroxysteroid dehydrogenase (17betaHSD) isozymes that interconvert estrone (E1) and estradiol (E2), such that the onset of labor is associated with an increase in local E2 bioavailability.

METHODS

The extent of 17betaHSD-1, -2, -3, -4, -5, and -7 expression (measured by quantitative reverse transcriptase polymerase chain reaction) and the capacity to interconvert E1 and E2 were compared in amnion, chorion, placenta, decidua, and myometrium obtained from women at term before (n = 6) and after (n = 6) the onset of labor.

RESULTS

In chorion, abundance of 17betaHSD-1 (converts E1 to E2) mRNA decreased 2.7-fold (P <.05) in association with labor onset. In myometrium, 17betaHSD-1 and 17betaHSD-4 (converts E2 to E1) mRNAs increased two-fold and five-fold, respectively, with the onset of labor (P <.05 for each). No other statistically significant labor-associated change in 17betaHSD expression was observed. In chorion, 17betaHSD oxidative (E2 to E1) and reductive (E1 to E2) activities and the net E2 synthetic capacity increased with labor. In decidua, both activities decreased with the onset of labor, but there was no change in net E2 synthetic capacity. The capacity to interconvert E1 and E2 did not change in the other tissues.

CONCLUSION

The increase in E2 synthetic capacity in the chorion might contribute to an increase in local estrogen bioactivity in association with the onset of labor. However, it cannot be explained by changes in 17betaHSD isozyme expression and is unlikely to account for the increased estrogen action at parturition. These data show that intracrine mechanisms based on 17betaHSD isozyme expression play a minor role, if any, in controlling estrogen action in gestational tissues during human parturition.

Current knowledge of the multifunctional 17β-hydroxysteroid dehydrogenase type 1 (HSD17B1)

At the late 1940s, 17β-HSD1 was discovered as the first member of the 17β-HSD family with its gene cloned. The three-dimensional structure of human 17β-HSD1 is the first example of any human steroid converting enzyme. The human enzyme's structure and biological function have thus been studied extensively in the last two decades. In humans, the enzyme is expressed in placenta, ovary, endometrium and breast. The high activity of estrogen activation provides the basis of 17β-HSD1's implication in estrogen-dependent diseases, such as breast cancer, endometriosis and non-small cell lung carcinomas. Its dual function in estrogen activation and androgen inactivation has been revealed in molecular and breast cancer cell levels, significantly stimulating the proliferation of such cells. The enzyme's overexpression in breast cancer was demonstrated by clinical samples. Inhibition of human 17β-HSD1 led to xenograft tumor shrinkage. Unfortunately, through decades of studies, there is still no drug using the enzyme's inhibitors available. This is due to the difficulty to get rid of the estrogenic activity of its inhibitors, which are mostly estrogen analogues. New non-steroid inhibitors for the enzyme provide new hope for non-estrogenic inhibitors of the enzyme.

Cloning and characterization of a 5' regulatory region of the prolactin receptor-associated protein/17{beta} hydroxysteroid dehydrogenase 7 gene

Prolactin receptor-associated protein (PRAP) originally cloned in our laboratory was shown to be a novel, luteal isoform of 17beta hydroxysteroid dehydrogenase 7 (17betaHSD7). In this study, we cloned the promoter region of rat PRAP/17betaHSD7 and investigated the mechanisms regulating both basal activity and LH-induced repression of this promoter. Truncated and site-specific mutants of PRAP/17betaHSD7 promoter identified two enhancer regions that contained highly conserved Sp1 binding site and bound Sp1 from nuclear extracts of both corpora lutea and a rat luteal cell line. Repression of PRAP/17betaHSD7 expression and promoter activity by human chorionic gonadotropin/forskolin was localized to a -52-bp proximal segment of the promoter. This region contained a conserved CCAAT site and bound nuclear factor Y; binding of this transcription factor was inhibited by human chorionic gonadotropin in vivo. Furthermore, mutation of the nuclear factor Y site in the -52-bp promoter-reporter construct abolished forskolin-mediated inhibition of the promoter in a rat luteal cell line. In summary, we have identified the promoter elements involved in the basal expression of PRAP/17betaHSD7. We have also found that LH-mediated repression of this gene is at the level of transcription and involves inhibition of nuclear factor YA binding to the CCAAT site within the proximal promoter.

Cloning and characterization of human form 2 type 7 17beta-hydroxysteroid dehydrogenase, a primarily 3beta-keto reductase and estrogen activating and androgen inactivating enzyme

Type 7 17beta-HSD catalyzes the transformation of estrone (E1) into estradiol (E2) and dihydrotestosterone (DHT) into 5alpha -androstane-3beta,17beta-diol (3beta-diol) as well as zymosterone into zymosterol. This suggests that in addition to cholesterol metabolism, the enzyme could play a critical role in estrogen-sensitive cells, since it inactivates DHT that generally shows antagonistic effect in the cells, while producing active E2 for cell proliferation. In this report, we describe the cloning and characterization of a second form of type 7 17beta-HSD (17beta-HSD7_2) that shares 95.6% identity with 17beta-HSD7_1. Using a 7.5kb genomic DNA fragment of 17beta-HSD7_1 as probe, we have obtained 7 BAC clones: three clones containing the 17beta-HSD7_1 gene and four containing the 17beta-HSD7_2 gene. The corresponding 17beta-HSD7_2 cDNA fragments of the coding region were obtained by amplification using RT-PCR and subcloned into pCMV expression vector and stably transfected into human embryonic kidney (HEK-293) cells. The overexpressed 17beta-HSD7_2 catalyzes efficiently the transformation of E1 into E2 and of DHT into 3beta-diol. Ribonuclease protection assays (RPA) indicate that 17beta-HSD7_2 is expressed in the liver, prostate, uterus and placenta. FISH mapping using the 7.5kb genomic DNA fragment as well as 2 BAC clones of each form allowed us to map the 17beta-HSD7_1 gene on chromosome band 1q23, and 17beta-HSD7_2 on band 10p11.2. These results contrast with a previous report that the 17beta-HSD7_1 gene was mapped to chromosomal band 10p11.2. This newly identified form of 17beta-HSD7 could have a significant role by modulating active hormone levels in estrogen-sensitive cells or tissues.

The role of 17 beta-hydroxysteroid dehydrogenases

The biological activity of steroid hormones is regulated at the pre-receptor level by several enzymes including 17 beta-hydroxysteroid dehydrogenases (17 beta -HSD). The latter are present in many microorganisms, invertebrates and vertebrates. Dysfunctions in human 17 beta-hydroxysteroid dehydrogenases result in disorders of biology of reproduction and neuronal diseases, the enzymes are also involved in the pathogenesis of various cancers. 17 beta-hydroxysteroid dehydrogenases reveal a remarkable multifunctionality being able to modulate concentrations not only of steroids but as well of fatty and bile acids. Current knowledge on genetics, biochemistry and medical implications is presented in this review.

Characterization of 17beta-hydroxysteroid dehydrogenase type 7 in reproductive tissues of the marmoset monkey

In contrast to the known rodent enzymes, the physiological significance of 17beta-hydroxysteroid dehydrogenase type 7 (17HSD7) and its presumed function in reproductive biology is not well understood in primates. As a first step, we recently cloned the complete coding regions of human and marmoset monkey (Callithrix jacchus) 17HSD7 (cj17HSD7). In the present work the complete cDNA of marmoset 17HSD1 (cj17HSD1), including the proximal promoter region, and a partial sequence of marmoset aromatase (cjARO) were sequenced in order to compare the expression of these estradiol synthesizing enzymes with that of 17HSD7 in a primate model and to identify tissues where 17HSD7 might participate in the pathway of estradiol synthesis. The gene structures of cj17HSD1 and cj17HSD7 were determined and proved to be very similar to the human orthologues. Northern hybridization showed that cjARO mRNA seems to be coexpressed preferably with cj17HSD1 in placenta, whereas in other tissues it is expressed in parallel only with cj17HSD7. Especially in corpora lutea, the cj17HSD7 transcript is detectable throughout the luteal phase of the ovarian cycle and increases during pregnancy, in parallel with the transcript of aromatase. Results were confirmed by immunoblots and immunohistochemistry using new polyclonal antisera directed against cj17HSD7 and cjARO protein. The enzymatic conversion of estrone to estradiol was assessed in marmoset corpora lutea. The pattern of coexpression with aromatase supports the hypothesis that luteal 17HSD7 complements placental 17HSD1, ensuring continued estradiol synthesis throughout pregnancy in primates.

A guide to 17beta-hydroxysteroid dehydrogenases

17beta-Hydroxysteroid dehydrogenases (17beta-HSD) are pivotal in controlling the biological potency of steroid hormones by catalyzing oxidation or reduction at position 17. Several 17beta-HSDs may as well metabolize further substrates including alcohols, bile acids, fatty acids and retinols. This review summarizes recent progress in the field of 17beta-HSD research provides an update of nomenclature.