Structure, regulation and role of 3 beta-hydroxysteroid dehydrogenase, 17 beta-hydroxysteroid dehydrogenase and aromatase enzymes in the formation of sex steroids in classical and peripheral intracrine tissues

Purification and characterization of 17beta-hydroxysteroid dehydrogenase from the filamentous fungus Cochliobolus lunatus

17beta-Hydroxysteroid dehydrogenase (17beta-HSD) from the filamentous fungus Cochliobolus lunatus was purified in three steps, yielding a protein of an apparent molecular mass of 28 kDa. According to the obtained experimental data, the native form of the enzyme could be a dimer (60 kDa) and/or a tetramer (120 kDa). The enzyme was found to catalyse preferentially the reduction of steroid substrates using NADPH as an electron donor. Both androgens and estrogens are substrates for 17beta-HSD. Kinetic studies revealed the equilibrium ordered kinetic mechanism with NADPH as the first ligand to be bound to the enzyme followed by the addition of the substrate androstenedione. The purification and characterization of 17beta-HSD from Cochliobolus lunatus represents a step towards the elucidation of the role of this enzyme in fungal metabolism.

Transcriptional regulation of the lutropin/human choriogonadotropin receptor and three enzymes of steroidogenesis by growth factors in cultured pig Leydig cells

Recent data have shown that Leydig-cell-specific functions, and therefore steroidogenic capacity, can be regulated by lutropin/human choriogonadotropin collectively termed gonadotropin and by several growth factors that are produced by and act within the testis. However, the molecular mechanisms by which these factors regulate Leydig cells are not understood. In the present study, we have investigated the effects of basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), insulin-like growth factor I (IGF-I) and transforming growth factor beta (TGF-beta) on mRNA for the gonadotropin receptor and three steroidogenic enzymes: cytochrome P-450scc, cytochrome P-450 17 alpha-hydroxylase/C17-20 lyase (17 alpha-hydroxylase), and 3 beta-hydroxysteroid dehydrogenase. IGF-1, which can enhance testosterone production, increased gonadotropin-receptor density after an increase in receptor mRNA levels, and it increased the level of mRNA for cytochrome P-450scc and 17 alpha-hydrolyase. Micromolar concentrations of insulin had similar effects to those of IGF-I. Moreover, the three factors that decreased testosterone production (EGF, bFGF and TGF beta 1) decreased gonadotropin receptor density, receptor mRNA levels and the mRNA levels for 17 alpha-hydroxylase. The potential effects of these growth factors on the transcription on the gonadotropin genes for the receptor and these three steroidogenic enzymes were measured by means of nuclear run-on assays. We demonstrated that the long-term inhibitory (EGF, bFGF, TGF beta 1) or stimulatory (IGF-I) effects of these growth factors are primarily due to a variation in the transcription rates of genes for the gonadotropin receptor, cytochrome P-450scc and 17 alpha-hydroxylase. Moreover, since previous studies have shown than some of these growth factors are expressed within the testis, they may play a physiological role in the regulation of differentiated testicular functions.

Steroid hormone signalling system and fungi

Three components of the steroid hormone signalling system, 17 beta-hydroxysteroid dehydrogenase, androgen binding proteins and steroid hormone signalling molecule testosterone were determined in the filamentous fungus Cochliobolus lunatus for the first time in a fungus. Their possible role in C. lunatus is discussed in comparison with their role in mammalian steroid hormone signalling system. The results are in accordance with the hypothesis, that the elements of primordial signal transduction system should exist in present day eukaryotic microorganisms.

Expression and regulation of aromatase and 17 beta-hydroxysteroid dehydrogenase type 4 in human THP 1 leukemia cells

Estradiol is active in proliferation and differentiation of sex-related tissues like ovary and breast. Glandular steroid metabolism was for a long time believed to dominate the estrogenic milieu around any cell of the organism. Recent reports verified the expression of estrogen receptors in "non-target" tissues as well as the extraglandular expression of steroid metabolizing enzymes. Extraglandular steroid metabolism proved to be important in the brain, skin and in stromal cells of hormone responsive tumors. Aromatase converts testosterone into estradiol and androstenedione into estrone, thereby activating estrogen precursors. The group of 17 beta-hydroxysteroid dehydrogenases catalyzes the oxidation and/or reduction of the forementioned compounds, e.g. estradiol/estrone, thereby either activating or inactivating estradiol. Aromatase is expressed and regulated in the human THP 1 myeloid leukemia cell line after vitamin D/GMCSF-propagated differentiation. Aromatase expression is stimulated by dexamethasone, phorbolesters and granulocyte/macrophage stimulating factor (GMCSF). Exons I.2 and I.4 are expressed in PMA-stimulated cells only, exon I.3 in both PMA- and dexamethasone-stimulated cells. Vitamin D-differentiated THP 1 cells produce a net excess of estradiol in culture supernatants, if testosterone is given as aromatase substrate. In contrast, the 17 beta-hydroxysteroid dehydrogenase type 4 (17 beta-HSD 4) is abundantly expressed in unstimulated THP 1 cells and is further stimulated by glucocorticoids (2-fold). The expression is unchanged after vitamin D/GMCSF-propagated differentiation. 17 beta-HSD 4 expression is not altered by phorbolester treatment in undifferentiated cells but is abolished after vitamin D-propagated differentiation along with downregulation of beta-actin. Protein kinase C activation therefore appears to dissociate the expression of aromatase and 17 beta-HSD 4 in this differentiation stage along the monocyte/phagocyte pathway of THP 1 myeloid cells. The expression of steroid metabolizing enzymes in myeloid cells is able to create a microenvironment which is uncoupled from dominating systemic estrogens. These findings may be relevant in the autocrine, paracrine or iuxtacrine cellular crosstalk of myeloid cells in their respective states of terminal differentiation, e.g. in bone metabolism and inflammation.