1.
2.
Ellfolk, Maria, et al.
(författare)
Isolation and properties of the CYP2D25 promoter : Transcriptional regulation by vitamin D3 metabolites
2006
Ingår i: Biochemical and Biophysical Research Communications - BBRC. - : Elsevier BV. - 0006-291X .- 1090-2104. ; 345:2, s. 568-572
Tidskriftsartikel (refereegranskat) abstract
Previous studies have suggested that hepatic production of 25-hydroxyvitamin D3 may be suppressed by 1α,25-dihydroxyvitamin D3. However, the molecular details of these observations have not been clarified. In the current study, the 5´-flanking DNA sequence of CYP2D25, a porcine microsomal vitamin D 25-hydroxylase, was isolated and analyzed. The CYP2D25 promoter contains a putative vitamin D response element (VDRE). The promoter activity was markedly suppressed by 1α,25-dihydroxyvitamin D3 and 25-hydroxyvitamin D3 in presence of vitamin D receptor (VDR). The data suggest that VDR-mediated inhibition of 25-hydroxylase(s) by vitamin D3 metabolites at the transcriptional level may play an important role in the regulation of 25-hydroxyvitamin D3 production in liver and other tissues.
3.
Ellfolk, Maria, et al.
(författare)
Regulation of human vitamin D(3) 25-hydroxylases in dermal fibroblasts and prostate cancer LNCaP cells
2009
Ingår i: Molecular Pharmacology. - : American Society for Pharmacology & Experimental Therapeutics (ASPET). - 0026-895X .- 1521-0111. ; 75:6, s. 1392-1399
Tidskriftsartikel (refereegranskat) abstract
In this study, we examined whether 1alpha,25-dihydroxyvitamin D(3) (calcitriol), phenobarbital, and the antiretroviral drug efavirenz, drugs used by patient groups with high incidence of low bone mineral density, could affect the 25-hydroxylase activity or expression of human 25-hydroxylases in dermal fibroblasts and prostate cancer LNCaP cells. Fibroblasts express the 25-hydroxylating enzymes CYP2R1 and CYP27A1. LNCaP cells were found to express two potential vitamin D 25-hydroxylases-CYP2R1 and CYP2J2. The presence in different cells of nuclear receptors vitamin D receptor (VDR), pregnane X receptor (PXR), and constitutive androstane receptor (CAR) was also determined. Phenobarbital suppressed the expression of CYP2R1 in fibroblasts and CYP2J2 in LNCaP cells. Efavirenz suppressed the expression of CYP2R1 in fibroblasts but not in LNCaP cells. CYP2J2 was slightly suppressed by efavirenz, whereas CYP27A1 was not affected by any of the two drugs. Calcitriol suppressed the expression of CYP2R1 in both fibroblasts and LNCaP cells but had no clear effect on the expression of either CYP2J2 or CYP27A1. The vitamin D(3) 25-hydroxylase activity in fibroblasts was suppressed by both calcitriol and efavirenz. In LNCaP cells, consumption of substrate (1alpha-hydroxyvitamin D(3)) was used as indicator of metabolism because no 1alpha,25-dihydroxyvitamin D(3) product could be determined. The amount of 1alpha-hydroxyvitamin D(3) remaining in cells treated with calcitriol was significantly increased. Taken together, 25-hydroxylation of vitamin D(3) was suppressed by calcitriol and drugs. The present study provides new information indicating that 25-hydroxylation of vitamin D(3) may be regulated. In addition, the current results may offer a possible explanation for the impaired bone health after treatment with certain drugs.
4.
Ellfolk, Maria, 1976-
(författare)
Regulation of Vitamin D 25-hydroxylases : Effects of Vitamin D Metabolites and Pharmaceutical Compounds on the Bioactivation of Vitamin D
2008
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
A 700bp portion of the promoter of CYP2D25, the porcine microsomal vitamin D 25-hydroxylase was isolated and sequenced. The computer analysis of the sequence revealed the existence of a putative VDRE at 220 bp upstream of the transcription start site. A CYP2D25 promoter-luciferase reporter plasmid was constructed in order to study the transcriptional regulation of the gene. Treatment with the vitamin D metabolites calcidiol and calcitriol suppressed the promoter, provided that the nuclear receptors VDR and RXR were overexpressed. Phenobarbital was also capable of suppressing the promoter if the nuclear receptors PXR or CAR were overexpressed.The 25-hydroxylases are not expressed solely in liver but in a wide array of other organs as well. It is therefore possible at least in theory to study the vitamin D 25-hydroxylation in human subjects using cells from extrahepatic organs, from which biopsy retrieval is easier than from the liver. Dermal fibroblasts are frequently used to study different pathological conditions in human subjects and they are easy to come by. Dermal fibroblasts were shown to express two vitamin D 25-hydroxylases: CYP27A1 and CYP2R1. The expression pattern of CYP2R1 displayed considerable interindividual variation. The fibroblasts were also capable of measurable vitamin D 25-hydroxylation, which makes dermal fibroblasts a possible tool in studying vitamin D 25-hydroxylation in human subjects.Little is known about the regulation of expression and activity of the human vitamin D 25-hydroxylases. Therefore dermal fibroblasts – expressing CYP2R1 and CYP27A1 – and human prostate cancer LNCaP cells, that express CYP2R1 and CYP2J2, were treated with calcitriol and phenobarbital and efavirenz, two drugs that give rise to vitamin D deficiency. Treatment decreased the mRNA levels of CYP2R1 and CYP2J2 provided that the treated cells also expressed the necessary nuclear receptors. CYP27A1 did not respond to any of the treatments. The treatments also managed to decrease the 25-hydroxylating activity of the cells.The results show that vitamin D 25-hydroxylases can be regulated by both endogenous and xenobiotic compounds.
5.
Hosseinpour, Fardin, et al.
(författare)
Phenobarbital suppresses vitamin D3 25-hydroxylase expression : A potential new mechanism for drug-induced osteomalacia
2007
Ingår i: Biochemical and Biophysical Research Communications - BBRC. - : Elsevier BV. - 0006-291X .- 1090-2104. ; 357:3, s. 603-607
Tidskriftsartikel (refereegranskat) abstract
Prolonged therapy with phenobarbital may cause vitamin D deficiency or osteomalacia. In the current study, we propose a novel mechanism for drug-induced osteomalacia involving impaired bioactivation of vitamin D3 due to decreased 25-hydroxylation of vitamin D3 in liver. The present data, using the pig as model, demonstrate direct effects by phenobarbital on the expression of CYP27A1 and CYP2D25, two important 25-hydroxylases. Treatment by phenobarbital markedly reduced the rate of 25-hydroxylation by primary hepatocytes and suppressed the cellular CYP27A1 mRNA levels. The rate of 25-hydroxylation by two different purified 25-hydroxylases, microsomal CYP2D25, and mitochondrial CYP27A1, respectively, was dose-dependently inhibited by phenobarbital. Reporter assay experiments in liver-derived HepG2 cells revealed a marked PXR-mediated transcriptional downregulation of the CYP2D25 promoter. In addition, the data indicate that phenobarbital might affect the mRNA stability of CYP2D25. Taken together, the data suggest that vitamin D3 25-hydroxylation may be suppressed by phenobarbital. A downregulation of 25-hydroxylation by phenobarbital may explain, at least in part, the increased risk of osteomalacia, bone loss, and fractures in long-term phenobarbital therapy.
6.
Lundqvist, Johan, et al.
(författare)
1α,25-Dihydroxyvitamin D3 exerts tissue-specific effects on estrogen and androgen metabolism
2011
Ingår i: Biochimica et Biophysica Acta - Molecular and Cell Biology of Lipids. - : Elsevier BV. - 1388-1981 .- 1879-2618. ; 1811:4, s. 263-270
Tidskriftsartikel (refereegranskat) abstract
It is well-known that 1α,25-dihydroxyvitamin D(3) and analogs exert anti-proliferative and pro-differentiating effects and these compounds have therefore been proposed to be of potential use as anti-cancer agents. Due to its effects on aromatase gene expression and enzyme activity, 1α,25-dihydroxyvitamin D(3) has been proposed as an interesting substance in breast cancer treatment and prevention. In the present study, we have examined the effects of 1α,25-dihydroxyvitamin D(3) on estrogen and androgen metabolism in adrenocortical NCI-H295R cells, breast cancer MCF-7 cells and prostate cancer LNCaP cells. The NCI-H295R cell line has been proposed as a screening tool to study endocrine disruptors. We therefore studied whether this cell line reacted to 1α,25-dihydroxyvitamin D(3) treatment in the same way as cells from important endocrine target tissues. 1α,25-Dihydroxyvitamin D(3) exerted cell line-specific effects on estrogen and androgen metabolism. In breast cancer MCF-7 cells, aromatase gene expression and estradiol production were decreased, while production of androgens was markedly increased. In NCI-H295R cells, 1α,25-dihydroxyvitamin D(3) stimulated aromatase expression and decreased dihydrotestosterone production. In prostate cancer LNCaP cells, aromatase expression increased after the same treatment, as did production of testosterone and dihydrotestosterone. In summary, our data show that 1α,25-dihydroxyvitamin D(3) exerts tissue-specific effects on estrogen and androgen production and metabolism. This is important knowledge about 1α,25-dihydroxyvitamin D(3) as an interesting substance for further research in the field of breast cancer prevention and treatment. Furthermore, the observed cell line-specific effects are of importance in the discussion about NCI-H295R cells as a model for effects on estrogen and androgen metabolism.
7.
Lundqvist, Johan, 1979-
(författare)
Enzymatic Regulation of Steroidogenesis and Nuclear Receptor Activation : Special Focus on Vitamin D and Sex Hormones
2011
Doktorsavhandling (övrigt vetenskapligt/konstnärligt) abstract
Enzyme-catalyzed reactions are important to regulate steroidogenesis and nuclear receptor activation. The present investigation examines the role of steroid metabolism catalyzed by CYP7B1 for regulation of hormone receptor activation and the effects of vitamin D on enzymatic regulation of steroidogenesis. The study reports data indicating that CYP7B1 can regulate estrogenic signaling by converting estrogens into inactive or less active metabolites. Similar results were obtained for CYP7B1-mediated metabolism of some androgen receptor ligands, indicating that CYP7B1 can be involved also in the regulation of androgenic signaling. CYP7B1 substrates and metabolites were found to exert androgenic effects in a cell line-specific manner. Furthermore, cell line differences were observed in the expression pattern for androgen receptor comodulators. This thesis reports that 1α,25-dihydroxyvitamin D3 alters the gene expression and enzyme activity of CYP21A2 and CYP17A1 leading to suppressed production of aldosterone, dehydroepiandrosterone and androstenedione in adrenocortical cells. These are novel findings on vitamin D action. A mechanism is reported for the vitamin D-mediated regulation of the CYP21A2 gene. Data indicate that vitamin D receptor interacting repressor (VDIR) and Williams syndrome transcription factor (WSTF) are key comodulators in this novel vitamin D receptor (VDR)-mediated mechanism. Furthermore, the results indicate that altered expression levels of VDIR and WSTF can shift the suppressing effect of vitamin D to a stimulatory effect. Also, epigenetic components were found to be involved in the effects of vitamin D on CYP21A2 transcriptional rate. In addition, a functional vitamin D response element was identified in the CYP21A2 promoter. This study also reports that 1α,25-dihydroxyvitamin D3 affects sex hormone production in a tissue-specific way. Gene expression and enzyme activity of aromatase were found to be downregulated in cells derived from breast, but not in cells derived from prostate and adrenal cortex. The production of estradiol and dihydrotestosterone was altered in a tissue-selective manner following vitamin D treatment. These findings are of importance for the discussion on vitamin D as a potential anti-breast cancer agent.
8.
Norlin, Maria, et al.
(författare)
24-Hydroxycholesterol is a substrate for hepatic cholesterol 7 alpha-hydroxylase (CYP7A)
2000
Ingår i: Journal of Lipid Research. - 0022-2275 .- 1539-7262. ; 41:10, s. 1629-1639
Tidskriftsartikel (refereegranskat) abstract
(24S)-Hydroxycholesterol is formed from cholesterol in the brain and is important for cholesterol homeostasis in this organ. Elimination of (24S)-hydroxycholesterol has been suggested to occur in the liver but little is known about the metabolism of this oxysterol. In the present investigation, we report formation of 7alpha, 24-dihydroxycholesterol in pig and human liver. 7alpha-hydroxylase activity toward both isomers of 24-hydroxycholesterol [(24S) and (24R)] was found in a partially purified and reconstituted cholesterol 7alpha-hydroxylase (CYP7A) enzyme fraction from pig liver microsomes. In contrast, a purified enzyme fraction of pig liver oxysterol 7alpha-hydroxylase with high activity toward 27-hydroxycholesterol did not show any detectable activity toward 24-hydroxycholesterol. 7alpha-Hydroxylation of 24-hydroxycholesterol was strongly inhibited by 7-oxocholesterol, a known inhibitor of CYP7A. Human CYP7A, recombinantly expressed in Escherichia coli and in simian COS cells, showed 7alpha-hydroxylase activity toward both cholesterol and the two isomers of 24-hydroxycholesterol, with a preference for the (24S)-isomer. Our results show that 24-hydroxycholesterol is metabolized by CYP7A, an enzyme previously considered to be specific for cholesterol and cholestanol and not active toward oxysterols. Because CYP7A is the rate-limiting enzyme in the major pathway of bile acid biosynthesis, the possibility is discussed that at least part of the 24-hydroxycholesterol is converted into 7alpha-hydroxylated bile acids by the enzymes involved in the normal biosynthesis of bile acids.
9.
Norlin, Maria, et al.
(författare)
Androgen receptor-mediated regulation of the anti-atherogenic enzyme CYP27A1 involves the JNK/c-jun pathway
2011
Ingår i: Archives of Biochemistry and Biophysics. - : Elsevier BV. - 0003-9861 .- 1096-0384. ; 506:2, s. 236-241
Tidskriftsartikel (refereegranskat) abstract
CYP27A1, an enzyme with several important roles in cholesterol homeostasis and vitamin D3 metabolism, has been ascribed anti-atherogenic properties. This study addresses an important problem regarding how this enzyme, involved in cholesterol metabolism in the liver and peripheral tissues, is regulated. Our results identify the human CYP27A1 gene as a new target for the JNK/c-jun pathway. Initial experiments showed that an inhibitor of c-Jun N-terminal kinase (JNK) downregulated basal CYP27A1 promoter activity whereas overexpression of JNK slightly enhanced promoter activity. Androgen receptor (AR)-mediated upregulation of mRNA levels and endogenous enzyme activity was recently reported. In the present study, the AR antagonist nilutamide blocked the androgen induction of CYP27A1. The present data revealed that inhibition of the JNK/c-jun pathway abolishes the AR-mediated effect on CYP27A1 transcription and enzyme activity, whereas overexpression of JNK markedly increased androgenic upregulation of CYP27A1. In conclusion, the current results indicate involvement of the JNK/c-jun pathway in AR-mediated upregulation of human CYP27A1. The link to JNK signaling is interesting since inflammatory processes may upregulate CYP27A1 to clear cholesterol from peripheral tissues.
10.
