Characterization of CYP11A1 and its potential role in sex asynchronous gonadal development of viviparous black rockfish Sebastes schlegelii (Sebastidae)

Mitochondrial cytochrome P450 side-chain cleavage (P450scc), encoded by the cyp11a1 gene, initiates the first step of steroid biosynthesis. In this study, a 1554-bp open reading frame (ORF) of black rockfish (Sebastes schlegelii) cyp11a1 was cloned. The cyp11a1 gene is located on chromosome 5 and has 9 exons. The ORF encodes a putative precursor protein of 517 amino acids, and the predicted cleavable mitochondrial targeting peptide is located at amino acids 1-39. P450scc shares homology with other teleosts and tetrapods, which have relatively conserved binding regions with heme, cholesterol and adrenodoxin. Tissue distribution analysis revealed that the highest expression levels of cyp11a1 were detected in mature gonads and head kidney but that low levels were detected in gestational/regressed ovaries, regressed testes and other tissues. Immunostaining of P450scc was observed in testicular Leydig cells, ovarian theca cells, interrenal glands of head kidney, pituitary and multiple regions of brain. Particularly, two kinds of fish-specific P450scc-positive cells, including coronet cells of brain saccus vasculosus and hypophyseal somatolactin cells, were identified in black rockfish. Our results provide novel evidence for the potential role played by P450scc in reproduction behavior by mediating steroidogenesis in viviparous teleost.

The DNA methylation status alteration of two steroidogenic genes in gonads of rare minnow after bisphenol A exposure

Both cytochrome P450c17 (CYP17A1) and P-450 side chain cleavage (CYP11A1) play important roles in steroid biosynthesis. According to our previous studies, bisphenol A (BPA) could regulate the mRNA expression of cyp17a1 and cyp11a1 in rare minnow Gobiocypris rarus. However, the potential mechanism of the regulation is barely understood. In the present study, aiming to explore how BPA affects the mRNA expression of cyp17a1 and cyp11a1 in testes and ovaries of G. rarus, we firstly cloned 340-bp fragment of 5' flanking region of cyp11a1 and then detected the methylation level of CpG loci involved in 5' flanking of cyp11a1 and cyp17a1 and their mRNA expression levels. Results showed that exposure to BPA significantly increased serum estradiol (E2) and 11-ketotesterone (11-KT) concentrations. Ovarian mRNA expression of cyp17a1 and cyp11a1 were significantly decreased after BPA exposure 7- for and 14-days. However, transcriptions of testicular cyp17a1 and cyp11a1 were significantly increased and decreased respectively after BPA treatment for 14days. The DNA methylation levels of cyp17a1 were decreased in ovaries on day 7 and increased in ovaries and decreased in testes respectively on day 14. The methylation levels of cyp11a1 were increased in ovaries on day 7 and both ovaries and testes on day 14. There were a significant correlation between DNA methylation at specific CpG loci and cyp17a1 and cyp11a1 genes transcription levels. In conclusion, the CpG loci methylation in 5' flanking region appears to involve in the regulation of mRNA expression of cyp17a1 and cyp11a1 mediated by BPA.

Testosterone implants modify the steroid hormone balance and the gonadal physiology of gilthead seabream (Sparus aurata L.) males

Androgens can induce complete spermatogenesis in immature or prepubertal teleost fish; however, many aspects of the role of androgens in adult teleost spermatogenesis remain elusive. We used the in situ forming microparticle (ISM) system containing 1mg of testosterone (T)/kg body weight (T-ISM) in a homogenous population of gilthead seabream at testicular involution stage to study in vivo the effects of T on the sex steroid hormone balance and on the physiology of the gilthead seabream gonad. The levels of T, 11-ketotestosterone (11KT) and 17β-estradiol (E2) in plasma, gonad and liver were determined in T-ISM implanted specimens after 7, 14, 21 and 28 days. The effect of T-ISM was evaluated on (i) de novo synthesis and metabolism of T in the gonad and liver by measuring the gene expression levels of the main steroidogenic proteins involved, (ii) the progress of spermatogenesis, (iii) the presence of different leukocyte cell types in the gonad, and (iv) the mRNA expression of some genes involved in the leukocyte migratory influx into the gonad and of some immune-relevant molecules. T-ISM implants promote an increase of T up to supra-physiological levels which induce a depletion of E2 levels and maintain the 11KT levels at physiological concentrations. The gene expression profile of some steroidogenic enzymes in gonad and liver ruled out the transformation of T into estrogenic compounds following T-ISM implantation. Moreover, androgens may also be involved in the leukocyte migratory influx, which occurred even when cytokine, chemokine and cell adhesion molecule gene expressions were down-regulated. Moreover, T-ISM implants block germ cell proliferation, although increased dmrt1 gene expression may prevent the complete depletion of germ cells in the gonad. Furthermore, T down-regulated the expression of several tlr genes, which may result in the inhibition of the immune response in the gonad through the impaired ability to recognize and respond to pathogens.

Inhibition and stimulation of activity of purified recombinant CYP11A1 by therapeutic agents

In vertebrates, the biosynthesis of steroid hormones is initiated by cytochrome P450 CYP11A1 which converts cholesterol to pregnenolone. We investigated whether some of the experimental and FDA-approved therapeutic agents alter the activity of CYP11A1 in the reconstituted system in vitro. We found that under the experimental conditions used and when phospholipids are included, ketoconazole, posaconazole, carbenoxolone, and selegiline inhibit CYP11A1-mediated production of pregnenolone by at least 67%. Conversely, pemirolast, clobenpropit, desogestrel, dexmedetomidine, and tizanidine stimulate the enzyme activity by up to 70%. We then evaluated the identified inhibitors and activators for spectral binding to CYP11A1 and their effect on enzyme activity in the absence of phospholipids. The data obtained provide insight into how different drugs interact with CYP11A1 and demonstrate that P450 association with the lipid bilayer determines, in many cases, a drug's effect on enzyme activity.

Metabolism of 1alpha-hydroxyvitamin D3 by cytochrome P450scc to biologically active 1alpha,20-dihydroxyvitamin D3

Cytochrome P450scc (CYP11A1) metabolizes vitamin D3 to 20-hydroxyvitamin D3 as the major product, with subsequent production of dihydroxy and trihydroxy derivatives. The aim of this study was to determine whether cytochrome P450scc could metabolize 1alpha-hydroxyvitamin D3 and whether products were biologically active. The major product of 1alpha-hydroxyvitamin D3 metabolism by P450scc was identified by mass spectrometry and NMR as 1alpha,20-dihydroxyvitamin D3. Mass spectrometry of minor metabolites revealed the production of another dihydroxyvitamin D3 derivative, two trihydroxy-metabolites made via 1alpha,20-dihydroxyvitamin D3 and a tetrahydroxyvitamin D3 derivative. The Km for 1alpha-hydroxyvitamin D3 determined for P450scc incorporated into phospholipid vesicles was 1.4 mol substrate/mol phospholipid, half that observed for vitamin D3. The kcat was 3.0 mol/min/mol P450scc, 6-fold lower than that for vitamin D3. 1alpha,20-Dihydroxyvitamin D3 inhibited DNA synthesis by human epidermal HaCaT keratinocytes propagated in culture, in a time- and dose-dependent fashion, with a potency similar to that of 1alpha,25-dihydroxyvitamin D3. 1alpha,20-Dihydroxyvitamin D3 (10 microM) enhanced CYP24 mRNA levels in HaCaT keratinocytes but the potency was much lower than that reported for 1alpha,25-dihydroxyvitamin D3. We conclude that the presence of the 1-hydroxyl group in vitamin D3 does not alter the major site of hydroxylation by P450scc which, as for vitamin D3, is at C20. The major product, 1alpha,20-dihydroxyvitamin D3, displays biological activity on keratinocytes and therefore might be useful pharmacologically.