Steroid biosynthesis

About: Steroid biosynthesis is a research topic. Over the lifetime, 1721 publications have been published within this topic receiving 58977 citations.

Steroid Effects on Secretion from Subsets of Lactotrophs: Role of Folliculo-Stellate Cells and Annexin 1

Abstract: Prolactin secretion is controlled by the hypothalamus, and by circulating steroids; oestrogens stimulate, but glucocorticoids inhibit prolactin release. Lactotrophs express intracellular receptors for oestrogens, but apparently not glucocorticoids. Therefore, a genomic effect of oestrogens could be direct, but that of glucocorticoids appears to be indirect. Lactotrophs are not a homogeneous cell population: some have large irregular dense-cored vesicles, others have small round vesicles, but the functional significance of this inhomogeneity is far from clear. Oestradiol and testosterone can stimulate rapid release of prolactin selectively from type II lactotrophs characterised by small round vesicles. Progesterone and other steroids do not exert this effect, which results from a non-genomic action of oestradiol and testosterone. Glucocorticoid inhibition of secretagogue-induced prolactin secretion is mimicked by annexin 1 (lipocortin 1), a protein induced by glucocorticoids in the pituitary and many other tissues, and can be blocked by annexin 1 immunoneutralisation and antisense. Glucocorticoid inhibition of ACTH and growth hormone secretion also involves annexin 1. Pituitary annexin 1 is located in folliculo-stellate cells; these express glucocorticoid receptors, and glucocorticoids induce annexin-1 synthesis. Annexin 1 is externalised from folliculo-stellate cells in response to glucocorticoids, despite the fact that it lacks a secretory signal sequence and is not packaged in vesicles. Inhibition of annexin 1 externalisation by glyburide suggests involvement of an ABC (ATP-binding cassette) transporter in externalisation. Both oestradiol and glucocorticoids therefore influence the secretion of prolactin by novel direct and indirect mechanisms, in addition to their much better understood effects on transcription via classical intracellular steroid receptors.

Effects of anticonvulsants on human p450c17 (17alpha-hydroxylase/17,20 lyase) and 3beta-hydroxysteroid dehydrogenase type 2.

Abstract: Summary: Purpose: Women with epilepsy apparently have a higher incidence of polycystic ovary syndrome (PCOS) than do women without epilepsy. Whether the underlying disease or the antiepileptic drug (AED) treatment is responsible for this increased risk is unknown, although clinical reports implicate valproic acid (VPA) as a potential cause. The steroidogenic enzymes 3βHSDII (3β-hydroxysteroid dehydrogenase) and P450c17 (17α-hydroxylase/17,20 lyase) are essential for C19 steroid biosynthesis, which is enhanced during adrenarche and in PCOS. Methods: To determine whether the AEDs VPA, carbamazepine (CBZ), topiramate (TPM), or lamotrigine (LYG) directly affect the activities of human 3βHSDII and P450c17, we added them to yeast expressing human P450c17 or 3βHSDII and assayed enzymatic activities in the microsomal fraction. Results: Concentrations of VPA ≤10 mM had no effect on activities of P450c17; however, VPA inhibited 3βHSDII activity starting at 0.3 mM (reference serum unbound concentration, 0.035–0.1 mM) with an IC50 of 10.1 mM. CBZ, TPM, and LTG did not influence 3βHSDII or P450c17 activities at typical reference serum unbound concentrations, but did inhibit 3βHSDII and P450c17 at concentrations >10-fold higher. Conclusions: None of the tested AEDs influenced 3βHSDII or P450c17 activities at concentrations normally used in AED therapy. However, VPA started to inhibit 3βHSDII activity at concentrations 3 times above the typical reference serum unbound concentration. Because inhibition of 3βHSDII activity will shift steroidogenesis toward C19 steroid production when P450c17 activities are unchanged, very high doses of VPA may promote C19 steroid biosynthesis, thus resembling PCOS. CBZ, TPM, and LTG influenced 3βHSDII and P450c17 only at toxic concentrations.

A novel compound heterozygous mutation in the CYP17 (P450 17α-hydroxylase) gene leading to 17α-hydroxylase/17,20-lyase deficiency

Abstract: Mutations in the CYP17 gene impair steroid biosynthesis in the adrenals and gonads and often cause 17α-hydroxylase/17,20-lyase deficiency, leading to amenorrhea, sexual infantilism, and hypokalemic low aldosterone hypertension. Several CYP17 mutations resulting in 17α-hydroxylase/17,20-lyase deficiency have been reported previously. In the present study, we found a novel CYP17 mutation from the molecular analysis of a Korean patient with primary amenorrhea with a 46,XX karyotype, and hypokalemic hypertension. We sequenced all 8 exons of the CYP17 gene that were amplified from patient's genomic DNA using polymerase chain reaction (PCR) and found a compound heterozygous mutation in the CYP17 structural gene; a 1-base deletion and a 1-base transversion (TAC→AA) at codon 329, leading to the production of a truncated protein (1-417 amino acids), and a 3-base deletion (TCC, either 350-351 or 351-352 codon) in the other allele. Restriction enzyme digestion analysis of patient's and parental DNA showed that the 1-base deletion and the 3-base deletion are inherited from mother and father, respectively. Here we conclude that these novel compound heterozygous mutations might account for the patient's clinical manifestations of 17α-hydroxylase/17,20-lyase deficiency. Copyright 2003 Elsevier, Inc. All rights reserved.