The 3beta-hydroxysteroid dehydrogenase/Delta(5)-Delta(4) isomerase (3beta-HSD) isoenzymes are responsible for the oxidation and isomerization of Delta(5)-3beta-hydroxysteroid precursors into Delta(4)-ketosteroids, thus catalyzing an essential step in the formation of all classes of active steroid hormones. In humans, expression of the type I isoenzyme accounts for the 3beta-HSD activity found in placenta and peripheral tissues, whereas the type II 3beta-HSD isoenzyme is predominantly expressed in the adrenal gland, ovary, and testis, and its deficiency is responsible for a rare form of congenital adrenal hyperplasia. Phylogeny analyses of the 3beta-HSD gene family strongly suggest that the need for different 3beta-HSD genes occurred very late in mammals, with subsequent evolution in a similar manner in other lineages. Therefore, to a large extent, the 3beta-HSD gene family should have evolved to facilitate differential patterns of tissue- and cell-specific expression and regulation involving multiple signal transduction pathways, which are activated by several growth factors, steroids, and cytokines. Recent studies indicate that HSD3B2 gene regulation involves the orphan nuclear receptors steroidogenic factor-1 and dosage-sensitive sex reversal adrenal hypoplasia congenita critical region on the X chromosome gene 1 (DAX-1). Other findings suggest a potential regulatory role for STAT5 and STAT6 in transcriptional activation of HSD3B2 promoter. It was shown that epidermal growth factor (EGF) requires intact STAT5; on the other hand IL-4 induces HSD3B1 gene expression, along with IL-13, through STAT 6 activation. However, evidence suggests that multiple signal transduction pathways are involved in IL-4 mediated HSD3B1 gene expression. Indeed, a better understanding of the transcriptional factors responsible for the fine control of 3beta-HSD gene expression may provide insight into mechanisms involved in the functional cooperation between STATs and nuclear receptors as well as their potential interaction with other signaling transduction pathways such as GATA proteins. Finally, the elucidation of the molecular basis of 3beta-HSD deficiency has highlighted the fact that mutations in the HSD3B2 gene can result in a wide spectrum of molecular repercussions, which are associated with the different phenotypic manifestations of classical 3beta-HSD deficiency and also provide valuable information concerning the structure-function relationships of the 3beta-HSD superfamily. Furthermore, several recent studies using type I and type II purified enzymes have elegantly further characterized structure-function relationships responsible for kinetic differences and coenzyme specificity.

Molecular Biology of the 3β-Hydroxysteroid Dehydrogenase/Δ5-Δ4 Isomerase Gene Family

Characterization of the canine 3β-hydroxysteroid dehydrogenase and its expression in the corpus luteum during diestrus

Altered differentiation and clustering of Sertoli cells in transgenic mice showing a Sertoli cell specific knockout of the connexin 43 gene

The Sertoli cell (SC)-specific knockout (KO) of connexin43 (Cx43) results in spermatogenic arrest at the level of spermatogonia and/or SC-only syndrome. Histology of the interstitial compartment suggests Leydig cell (LC) hyperplasia. Our aim has been to investigate possible effects of the SC-specific KO of Cx43 (SCCx43KO) on interstitial LC. We therefore counted LC via the optical dissector method (per microliter of testicular tissue and per testis) and found LC to be significantly increased in SCCx43KO(-/-) compared with wild-type mice. Semiquantitative western blot together with Cx43 and 3β-hydroxysteroid dehydrogenase immunohistochemistry showed that Cx43 protein was significantly reduced and barely detectable in LC in adult SCCx43KO(-/-) mice. This reduction of Cx43 protein was accompanied by a reduction of Cx43 mRNA as analyzed by laser-assisted microdissection of interstitial cells and subsequent quantitative real-time polymerase chain reaction (PCR). Interestingly, Cx45, another recently detected connexin in LC, was also downregulated. Preliminary qualitative data of LC differentiation markers (Thb2, Hsd3b6) and a steroidogenic marker (Hsd17b3) obtained by reverse transcription plus PCR revealed no obvious differences. Thus, the loss of Cx43 in SC also provokes the downregulation of connexins in interstitial LC at the transcriptional and translational levels. Moreover, SCCx43KO leads to alterations in LC numbers. Despite these alterations, steroidogenesis seems not to be impaired. Further studies, including ultrastructural analysis of the tissue as well as quantitative examination of additional LC markers and testosterone, and functional in vitro experiments, should provide more information about LC differentiation and function in SCCx43KO(-/-) mice.

A Sertoli cell-specific connexin43 knockout leads to altered interstitial connexin expression and increased Leydig cell numbers.

Hydroxysteroid dehydrogenases (HSDs) belong to the NADPH/NAD+-dependent oxidoreductases, which interconvert ketones and the corresponding secondary alcohols. As their names imply, they catalyze the oxidoreduction in different positions of steroidal substrates (3α-, 3β-, 11β-, 17β-, 20αand 20β-position). The steroid-converting HSDs play central roles in the biosynthesis and inactivation of steroid hormones, but some of them are also involved in the metabolism of diverse non-steroidal compounds [1]. The HSDs are integral parts of systemic (endocrine) and local (intracrine) mechanisms. In target tissues they convert inactive steroid hormones to their corresponding active forms and viceversa, thus modulating the transactivation of steroid hormone receptors or other elements of the non-genomic signal transduction pathways. Therefore, HSDs act as molecular switches allowing pre-receptor modulation of steroid hormone action [2].

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Hydrohysteroid Dehydrogenases – Biological Role and Clinical Importance – Review

3β–Hydroxysteroid dehydrogenase (3β‐HSD) activity is essential for the synthesis of all classes of steroid hormones, converting various Δ5–3β–hydroxysteroids into hormonally active Δ4–3–ketosteroids in NAD+–dependent reactions. Certain 3β–HSD isoforms have been reported to exhibit additional dehydrogenase character (e.g., 17–hydroxysteroid dehydrogenase/reductase). We have investigated whether mouse type I (adrenal/gonadal) and type VI 3β–HSDs (uterine/embryonic) display significant 17β–HSD–like activity. Nonsteroidogenic HEK 293T cells were transiently transfected with pCMV–based expression vectors containing mouse type I and type VI 3β–HSDs. Transfected cells expressing either mouse type I or type VI 3β–HSD converted testosterone to androstenedione, albeit at rates one‐tenth of those of pregnenolone to progesterone in similarly transfected 293T cells. Our findings demonstrate that the mouse 3β–HSD I and VI isoforms can inactivate testosterone within an intact cell milieu. These findings are important no...

Promiscuous 3β–Hydroxysteroid Dehydrogenases: Testosterone 17β–Hydroxysteroid Dehydrogenase Activities of mouse Type I and VI 3β–Hydroxysteroid Dehydrogenases

B. E.C. Howe

Papers

Promiscuous 3β–Hydroxysteroid Dehydrogenases: Testosterone 17β–Hydroxysteroid Dehydrogenase Activities of mouse Type I and VI 3β–Hydroxysteroid Dehydrogenases