| 1. |
- Araya, Zufan, et al.
(author)
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Hormonal regulation of the human sterol 27-hydroxylase gene CYP27A1.
- 2003
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In: Biochemical Journal. - 0264-6021 .- 1470-8728. ; 372:2, s. 529-534
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Journal article (peer-reviewed)abstract
- The mitochondrial sterol 27-hydroxylase (CYP27A1) is a multifunctional cytochrome P450 enzyme that catalyses important hydroxylations in the biosynthesis of bile acids and bioactivation of vitamin D3. Previous results [Babiker, Andersson, Lund, Xiu, Deeb, Reshef, Leitersdorf, Diczfalusy and Bj¨orkhem (1997) J. Biol. Chem. 272, 26253–26261] suggest that CYP27A1 plays an important role in cholesterol homoeostasis and affects atherogenesis. In the present study, the regulation of the human CYP27A1 gene by growth hormone (GH), insulin-like growth factor-1 (IGF-1), dexamethasone, thyroid hormones and PMA was studied. HepG2 cells were transfected transiently with luciferase reporter gene constructs containing DNA fragments flanking the 5_-region of the human CYP27A1 gene. GH, IGF-1 and dexamethasone increased the promoter activity by 2–3-fold, whereas thyroxine (T4) and PMA repressed the activity significantly when measured with luciferase activity expressed in the cells. The endogenous CYP27A1 enzyme activity in the cells was stimulated by GH, IGF-1 and dexamethasone, whereas T4 and PMA inhibited the activity. Experiments with progressive deletion/luciferase reporter gene constructs indicated that the response elements for GH may be localized in a region upstream to position −1094 bp. The putative response elements for dexamethasone were mapped to positions between −792 and −1095 bp. The −451 bp fragment of the human CYP27A1 gene was found to confer the activation by IGF-1, and the inhibition by T4 and PMA. Results of the present study suggest that CYP27A1 is regulated in human cells by hormones and signal-transduction pathways.
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| 2. |
- Hosseinpour, Fardin, et al.
(author)
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25-Hydroxylation of vitamin D3 in primary cultures of pig hepatocytes:evidence for a role of both CYP2D25 and CYP27A1
- 2003
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In: Biochemical and Biophysical Research Communications - BBRC. - 0006-291X .- 1090-2104. ; 303:3, s. 877-883
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Journal article (peer-reviewed)abstract
- There has been some controversy over whether the 25-hydroxylation of vitamin D(3) is carried out by one enzyme or two and whether this cytochrome P450 enzyme is found in the mitochondrial or microsomal fractions of liver. The pig is currently the only species in which both the microsomal 25-hydroxylase (CYP2D25) and the mitochondrial 25-hydroxylase (CYP27A1) have been cloned and characterized. In this paper, the roles of the two enzymes in 25-hydroxylation of vitamin D(3) are examined in primary cultures of hepatocytes. Inhibition experiments indicated that tolterodine and 7 alpha-hydroxy-4-cholesten-3-one were selective inhibitors of the CYP2D25- and CYP27A-mediated 25-hydroxylation of vitamin D(3), respectively. Addition of each inhibitor to primary hepatocytes decreased the total 25-hydroxylation of vitamin D(3) to about the same extent. No inhibition of other hydroxylase activities tested was found. Phorbol 12-myristate 13-acetate down-regulated the expression of both CYP2D25 and CYP27A1 as well as the 25-hydroxylase activity of the hepatocytes. The results implicate that both CYP2D25 and CYP27A1 contribute to the 25-hydroxylation in hepatocytes and are important in the bioactivation of vitamin D(3).
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| 3. |
- Norlin, Maria, et al.
(author)
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Androgen receptor-mediated regulation of the anti-atherogenic enzyme CYP27A1 involves the JNK/c-jun pathway
- 2011
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In: Archives of Biochemistry and Biophysics. - : Elsevier BV. - 0003-9861 .- 1096-0384. ; 506:2, s. 236-241
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Journal article (peer-reviewed)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.
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| 4. |
- Tang, Wanjin, et al.
(author)
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Estrogen-mediated regulation of CYP7B1 : a possible role for controlling DHEA levels in human tissues
- 2006
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In: Journal of Steroid Biochemistry and Molecular Biology. - : Elsevier BV. - 0960-0760 .- 1879-1220. ; 100:1-3, s. 42-51
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Journal article (peer-reviewed)abstract
- The current study examines regulation of CYP7B1, a DHEA 7alpha-hydroxylase, by sex hormones. Transfection with estrogen receptor alpha and treatment with 17beta-estradiol in human embryonic kidney 293 cells significantly increased CYP7B1 catalytic activity and mRNA, and stimulated a human CYP7B1 reporter gene. Transfection with estrogen receptor beta showed similar but less significant effects. In the absence of receptors, 17beta-estradiol suppressed CYP7B1 activity, suggesting that estrogenic effects may be different in cells not expressing receptors. Quantitation of CYP7B1 mRNA in adult and fetal human tissues showed markedly higher CYP7B1 mRNA levels in fetal tissues compared with the corresponding adult ones, except in the liver. This indicates a tissue-specific, developmental regulation of CYP7B1 and suggests an important function for this enzyme in fetal life. DHEA secreted by fetal adrenals is an essential precursor for placental estrogen formation. Since CYP7B1 diverts DHEA from the sex hormone biosynthetic pathway, estrogen receptor-mediated up-regulation of CYP7B1 should lead to less DHEA available for sex hormone synthesis and may help to maintain normal levels of estrogens and androgens in human tissues, especially during fetal development. Regulation by estrogens may also be of importance in other processes where CYP7B1 is involved, including cholesterol homeostasis, cellular proliferation, and CNS function.
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| 5. |
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| 6. |
- Tang, Wanjin, et al.
(author)
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Glucocorticoid receptor-mediated upregulation of human CYP27A1, a potential anti-atherogenic enzyme
- 2008
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In: Biochimica et Biophysica Acta - Molecular and Cell Biology of Lipids. - : Elsevier BV. - 1388-1981 .- 1879-2618. ; 1781:11-12, s. 718-723
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Journal article (peer-reviewed)abstract
- Sterol 27-hydroxylase (CYP27A1) is required for the hepatic conversion of cholesterol into bile acids and for production of 27-hydroxycholesterol which affects cholesterol homeostasis in several ways. Dexamethasone increases hepatic bile acid biosynthesis and CYP27A1-mediated enzyme activity in HepG2 cells. This study examines the mechanism of the dexamethasone-induced effect on the human CYP27A1 promoter. Dexamethasone treatment of HepG2 cells overexpressed with glucocorticoid receptor alpha (GRalpha) increased the CYP27A1 promoter activity more than four-fold as compared with untreated cells. The GR-antagonist mifepristone almost completely abolished the dexamethasone-induced effect on the promoter activity. Progressive deletion analysis of the CYP27A1 promoter indicated that sequences involved in GR-mediated induction by dexamethasone are present in a region between -1094 and -792. Several putative GRE sites could be found in this region and EMSA experiments revealed that two of these could bind GR. Site-directed mutagenesis of GR-binding sequences in the CYP27A1 promoter identified a GRE at -824/-819 important for GR-mediated regulation of the transcriptional activity. Endogenous and pharmacological glucocorticoids may have a strong impact on several aspects of cholesterol homeostasis and other processes related to CYP27A1-mediated metabolism. The glucocorticoid-mediated induction of human CYP27A1 transcription is of particular interest due to the anti-atherogenic properties ascribed to this enzyme.
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| 7. |
- Tang, Wanjin, 1976-
(author)
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Hormonal Regulation of the Human CYP27A1 and CYP7B1 Genes
- 2007
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Doctoral thesis (other academic/artistic)abstract
- CYP27A1 and CYP7B1 are widely expressed in various human tissues and are two key enzymes involved in the pathways for conversion of cholesterol to bile acids. Also, CYP27A1 is involved in bioactivation of vitamin D3 and CYP7B1 plays a role in 7alpha-hydroxylation of dehydroepiandrosterone and other steroids. Both enzymes have been reported to be relevant to prostate cell proliferation. The current study examines the hormonal regulation of CYP27A1 and CYP7B1.CYP7B1 was shown to be regulated by estrogens and androgens in human embryonic kidney HEK293 and prostate cancer LNCaP cells. Quantitation of CYP7B1 mRNA in adult and fetal human tissues showed markedly higher CYP7B1 mRNA levels in fetal tissues compared with the corresponding adult ones, except in the liver. This indicates a tissue-specific, developmental regulation of CYP7B1 and suggests an important function for this enzyme in fetal life. CYP7B1 regulation by estrogens may be of importance in fetal development and in other processes where CYP7B1 is involved, including cholesterol homeostasis, cellular proliferation, and CNS function. The regulation of CYP7B1 by sex hormones also suggests an important role for CYP7B1 in balancing prostate hormone levels in human cells. Results show that CYP27A1 can be regulated by dexamethasone, growth hormone, IGF-1, PMA, estrogens and androgens in liver-derived HepG2 cells. Dexamethasone, growth hormone and IGF-1 stimulated the promoter and endogenous activity of CYP27A1, whereas thyroid hormones and PMA inhibited CYP27A1. The regulatory effects of estrogens and androgens are different depending on the cell types. Thus, the results imply that human CYP27A1 gene is a target for estrogens and androgens, and the expression of CYP27A1 may be affected by endogenous sex hormones and pharmacological compounds with estrogenic or androgenic effects. The mechanism for the dexamethasone-induced effect on the human CYP27A1 promoter was examined. A GRE was identified important for GR-mediated regulation of CYP27A1 transcriptional activity.
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| 8. |
- Tang, Wanjin, et al.
(author)
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Involvement of the PI3K/Akt pathway in estrogen-mediated regulation of human CYP7B1 : identification of CYP7B1 as a novel target for PI3K/Akt and MAPK signalling
- 2008
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In: Journal of Steroid Biochemistry and Molecular Biology. - : Elsevier BV. - 0960-0760 .- 1879-1220. ; 112:1-3, s. 63-73
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Journal article (peer-reviewed)abstract
- The steroid hydroxylase CYP7B1 metabolizes neurosteroids, cholesterol derivatives, and estrogen receptor (ER) ligands. Previous studies identified CYP7B1 as a target for regulation by estrogen. The present study examines the mechanism for estrogen-mediated regulation of the human CYP7B1 gene promoter. Treatment with LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (PI3K), abolished ER-mediated up-regulation of a CYP7B1 promoter-luciferase reporter in HepG2 cells, whereas overexpression of PI3K or Akt significantly increased estrogenic up-regulation of CYP7B1. Overexpression of dominant-negative mutant Akt abolished ER-mediated stimulation of CYP7B1 in HepG2 cells. Data indicated no binding of ER to CYP7B1 promoter sequences, suggesting that ER interacts with the PI3K/Akt pathway without binding to the gene. At low ER levels, overexpression of Akt suppressed CYP7B1 promoter activity, suggesting that its effect on CYP7B1 is different when estrogens are absent. In HEK293 cells, CYP7B1 transcription was much less affected by Akt, indicating that the mechanism for up-regulation of CYP7B1 is different in different cell types. Other experiments indicated that MAPK signalling may affect basal CYP7B1 levels. The current results, indicating that regulation of CYP7B1 by ER can be mediated via the PI3K/Akt signal pathway, a regulatory pathway important for cellular survival and growth, suggest an important role for CYP7B1 in cellular growth, particularly in connection with estrogenic signalling.
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| 9. |
- Tang, Wanjin, et al.
(author)
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Regulation of human CYP27A1 by estrogens and androgens in HepG2 and prostate cells
- 2007
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In: Archives of Biochemistry and Biophysics. - : Elsevier BV. - 0003-9861 .- 1096-0384. ; 462:1, s. 13-20
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Journal article (peer-reviewed)abstract
- The regulation of the human CYP27A1 gene by estrogens and androgens was studied in human liver-derived HepG2 and prostate cells. Our results show that the promoter activity, enzymatic activity and mRNA levels of CYP27A1 in HepG2 cells are downregulated by estrogen in presence of ERα or ERβ. Similar effects by estrogen were found in RWPE-1 prostate cells. In contrast, estrogen markedly upregulated the transcriptional activity of CYP27A1 in LNCaP prostate cancer cells. 5α-Dihydrotestosterone and androgen receptor upregulated the transcriptional activity of CYP27A1 in HepG2 cells. Progressive deletion experiments indicate that the ERβ-mediated effects in HepG2 and LNCaP cells are conferred to the same region (−451/+42) whereas ERα-mediated effects on this promoter are more complex. The results indicate that the stimulating effect of androgen in HepG2 cells is conferred to a region upstream from –792 in the CYP27A1 promoter. In summary, we have identified the human CYP27A1 gene as a target for estrogens and androgens. The results imply that expression of CYP27A1 may be affected by endogenous sex hormones and pharmacological compounds with estrogenic or androgenic effects.
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| 10. |
- Tang, Wanjin, et al.
(author)
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Regulation of steroid hydroxylase CYP7B1 by androgens and estrogens in prostate cancer LNCaP cells
- 2006
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In: Biochemical and Biophysical Research Communications - BBRC. - : Elsevier BV. - 0006-291X .- 1090-2104. ; 344:2, s. 540-546
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Journal article (peer-reviewed)abstract
- The present study reports effects of androgens and estrogens on human CYP7B1 transcription in prostate cancer LNCaP cells. Studies with rodents have suggested a role for the CYP7B1 enzyme in balancing cellular hormone levels important for prostate growth. Little is, however, known about the regulation of human CYP7B1. The current study showed strong suppression of a human CYP7B1 luciferase reporter gene by dihydrotestosterone (DHT) in prostate cancer LNCaP cells. Also, DHT and overexpression of androgen receptor (AR) suppressed CYP7B1 promoter activity and CYP7B1-mediated catalysis in kidney-derived HEK293 cells. Effects on CYP7B1 transcription were observed also by estrogen receptors (ER). The effects appeared different for different estrogens. CYP7B1 was stimulated by synthetic ER agonists but suppressed by 17beta-estradiol and 5alpha-androstane-3beta,17beta-diol in LNCaP cells. Our data indicate an important role for CYP7B1 in balancing prostate hormone levels in human cells. In particular, the data suggest that androgens may control intraprostatic levels of estrogen via regulation of CYP7B1-mediated metabolism.
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