Systematic characterisation of the rat and human CYP24A1 promoter

Effects of glucocorticoids on vitamin D3-metabolizing 24-hydroxylase (CYP24A1) in Saos-2 cells and primary human osteoblasts

Vitamin D is essential for bone function and deficiency in active vitamin D hormone can lead to bone disorders. Long-term treatment with glucocorticoids results in osteoporosis and increased risk of fractures. Much remains unclear regarding the effects of these compounds in bone cells. In the current study, human osteosarcoma Saos-2 cells and primary human osteoblasts were found to express mRNA for the vitamin D receptor as well as activating and deactivating enzymes in vitamin D₃ metabolism. These bone cells exhibited CYP24A1-mediated 24-hydroxylation which is essential for deactivation of the active vitamin form. However, bioactivating vitamin D₃ hydroxylase activities could not be detected in either of these cells. Several glucocorticoids, including prednisolone, down regulated CYP24A1 mRNA and CYP24A1-mediated 24-hydroxylase activity in both Saos-2 and primary human osteoblasts. Also, prednisolone significantly suppressed a human CYP24A1 promoter-luciferase reporter gene in Saos-2 cells co-transfected with the glucocorticoid receptor. Thus, the results of the present study show suppression by glucocorticoids on CYP24A1 mRNA, CYP24A1-mediated metabolism and CYP24A1 promoter activity in human osteoblast-like cells. As part of this study we examined if glucocorticoids are formed locally in Saos-2 cells. The experiments indicate formation of 11-deoxycortisol, a steroid with glucocorticoid activity, which can bind the glucocorticoid receptor. Our data showing suppression by glucocorticoids on CYP24A1 expression in human osteoblasts suggest a previously unknown mechanism for effects of glucocorticoids in human bone, where these compounds may interfere with regulation of active vitamin D levels.

Vitamin D3 transactivates the zinc and manganese transporter SLC30A10 via the Vitamin D receptor

Vitamin D3 regulates genes critical for human health and its deficiency is associated with an increased risk for osteoporosis, cancer, diabetes, multiple sclerosis, hypertension, inflammatory and immunological diseases. To study the impact of vitamin D3 on genes relevant for the transport and metabolism of nutrients and drugs, we employed next-generation sequencing (NGS) and analyzed global gene expression of the human-derived Caco-2 cell line treated with 500nM vitamin D3. Genes involved in neuropeptide signaling, inflammation, cell adhesion and morphogenesis were differentially expressed. Notably, genes implicated in zinc, manganese and iron homeostasis were largely increased by vitamin D3 treatment. An ∼10-fold increase in ceruloplasmin and ∼4-fold increase in haptoglobin gene expression suggested a possible association between vitamin D and iron homeostasis. SLC30A10, the gene encoding the zinc and manganese transporter ZnT10, was the chiefly affected transporter, with ∼15-fold increase in expression. SLC30A10 is critical for zinc and manganese homeostasis and mutations in this gene, resulting in impaired ZnT10 function or expression, cause manganese intoxication, with Parkinson-like symptoms. Our NGS results were validated by real-time PCR in Caco-2 cells, as well as in duodenal biopsies taken from healthy human subjects treated with 0.5μg vitamin D3 daily for 10 days. In addition to increasing gene expression of SLC30A10 and the positive control TRPV6, vitamin D3 also increased ZnT10 protein expression, as indicated by Western blot and cytofluorescence. In silico identification of potential vitamin D responsive elements (VDREs) in the 5'-flanking region of the SLC30A10 promoter and dual-luciferase reporter assay showed enhanced promoter activity in the presence of vitamin D receptor (VDR) and retinoid X receptor (RXR) constructs, as well as vitamin D3, but not when one of these factors was absent. Electrophoretic mobility shift assay (EMSA) and competition EMSA revealed binding of select sequences, namely, nt -1623/-1588 and nt -1758/-1723 relative to the transcription start site, to VDR-containing nuclear extracts. In conclusion, we have shown that vitamin D3 transactivates the SLC30A10 gene in a VDR-dependent manner, resulting in increased ZnT10 protein expression. Because SLC30A10 is highly expressed in the small intestine, it is possible that the control of zinc and manganese systemic levels is regulated by vitamin D3 in the intestine. Zinc, manganese and vitamin D are important for bone metabolism and brain health. Future examination of a possible role for supplementation or chelation of zinc and manganese, alongside vitamin D3 administration, will further our understanding of its potential benefit in the treatment of specific illnesses, such as osteoporosis and Parkinson's disease.

Vitamin D status and metabolism in an ovine pregnancy model: effect of long-term, high-altitude hypoxia

Vitamin D status increases during healthy mammalian pregnancy, but the molecular determinants remain uncharacterized. The first objective of this study was to determine the effects of pregnancy, and the second objective was to examine the role of chronic hypoxia on vitamin D status and metabolism in an ovine model. We analyzed the plasma levels of cholecalciferol, 25-OH-D, and 1α,25-(OH)2D in nonpregnant ewes, near-term pregnant ewes, and their fetuses exposed to normoxia (low altitude) or hypoxia (high-altitude) for 100 days. Hypoxic sheep had increased circulating levels of 25-OH-D and 1α,25-(OH)2D compared with normoxic sheep. Hypoxia increases in 25-OH-D were associated with increased expression of renal 25-hydroxylases CYP2R1 and CYP2J. Pregnancy did not increase further the plasma levels of 25-OH-D, but it significantly increased those of the active metabolite, 1α,25-(OH)2D, in both normoxic and hypoxic ewes. Increased bioactivation of vitamin D correlated with increased expression of the vitamin D-activating enzyme CYP27b1 and decreased expression of the inactivating enzyme CYP24a1 in maternal kidneys and placentas. Hypoxia increased parathyroid hormone levels and further increased renal CYP27b1. Pregnancy and hypoxia decreased the expression of vitamin D receptor (VDR) in maternal kidney and lung, with opposite effects on placental VDR. We conclude that ovine pregnancy is a model of increased vitamin D status, and long-term hypoxia further improves vitamin D status due to pregnancy- and hypoxia-specific regulation of VDR and metabolic enzymes.

Vitamin D Activation and Function in Human Corneal Epithelial Cells During TLR-Induced Inflammation

PURPOSE

Vitamin D is recognized to be an important modulator of the immune system. In the eye, studies have shown that deficiencies and genetic differences in vitamin D-related genes have a significant impact on the development of various ocular diseases. Our current study examines the ability of human corneal epithelial cells (HCEC) to activate vitamin D and the effect of vitamin D treatment on antimicrobial peptide production and cytokine modulation during inflammation, with the ultimate goal of using vitamin D therapeutically for corneal inflammation.

METHODS

Human corneal epithelial cells were treated with 10-7M vitamin D3 (D3) or 25-hydroxyvitamin D3 (25D3) for 24 hours and 1,25-dihydroxyvitamin D3 (1,25D3) detected by immunoassay. Human cathelicidin (LL-37) expression was examined by RT-PCR, immunoblot, and immunostaining following 1,25D3 treatment and antimicrobial activity of 1,25D3-treated cells was determined. Cells were stimulated with TLR3 agonist polyinosinic-polycytidylic acid (Poly[I:C]) for 24 hours and cytokine levels measured by RT-PCR, ELISA, and Luminex. Immunostaining determined expression of vitamin D receptor (VDR) and retinoic acid inducible gene-1 receptor (RIG-1) as well as NF-κB nuclear translocation.

RESULTS

When treated with inactive vitamin D metabolites, HCEC produced active 1,25D3, leading to enhanced expression of the antimicrobial peptide, LL-37, dependent on VDR. 1,25-D3 decreased the expression of proinflammatory cytokines (IL-1β, IL-6, TNFα, and CCL20) and MMP-9 induced by Poly(I:C) as well as pattern recognition receptor expression (TLR3, RIG-1, MDA5). However, early activation of NF-κB was not affected.

CONCLUSIONS

These studies demonstrate the protective ability of vitamin D to attenuate proinflammatory mediators while increasing antimicrobial peptides and antipseudomonas activity in corneal cells, and further our knowledge on the immunomodulatory functions of the hormone.

Impact of CYP24A1 overexpression on growth of colorectal tumour xenografts in mice fed with vitamin D and soy

Our previous studies showed that the 1,25-dihydroxyvitamin D (1,25-D3) catabolizing enzyme, 1,25-dihydoxyvitamin D 24 hydroxylase (CYP24A1) was overexpressed in colorectal tumours and its level correlated with increased proliferation. We hypothesised that cells overexpressing CYP24A1 have growth advantage and a diet rich in vitamin D and soy would restore sensitivity to the anti-tumourigenic effects of vitamin D. Soy contains genistein, a natural CYP24A1 inhibitor. To determine causality between CYP24A1 and tumour growth, we established xenografts in male SCID mice with HT29 cells stably overexpressing either GFP-tagged CYP24A1 or GFP. Mice were fed with either high (2500 IU D3/kg) or low vitamin D (100 IU D3/kg) diet in the presence or absence of soy (20% diet). In vitro, cells overexpressing CYP24A1 grew faster than controls. 1,25-D3, the active vitamin D metabolite, reduced cell number only in the presence of the CYP24A1 inhibitor VID400. Regardless of the amount of vitamin D in the diet, xenografts overexpressing CYP24A1 grew faster, were heavier and more aggressive. Soy reduced tumour volume only in the control xenografts, while the tumours overexpressing CYP24A1 were larger in the presence of dietary soy. In conclusion, we demonstrate that CYP24A1 overexpression results in increased aggressiveness and proliferative potential of colorectal tumours. Irrespective of the dietary vitamin D3, dietary soy is able to increase tumour volume when tumours overexpress CYP24A1, suggesting that combination of vitamin D3 and soy could have an anti-tumourigenic effect only if CYP24A1 levels are normal.

Differential expression and regulation of vitamin D hydroxylases and inflammatory genes in prostate stroma and epithelium by 1,25-dihydroxyvitamin D in men with prostate cancer and an in vitro model

Previous work on vitamin D in the prostate has focused on the prostatic epithelium, from which prostate cancer arises. Prostatic epithelial cells are surrounded by stroma, which has well-established regulatory control over epithelial proliferation, differentiation, and the inflammatory response. Here we examined the regulation of vitamin D-related genes and inflammatory genes by 1α,25-dihydroxyvitamin D3 (1,25(OH)2D) in laser-capture microdissected prostate tissue from a vitamin D3 clinical trial and in an in vitro model that facilitates stromal-epithelial crosstalk. Analysis of the trial tissues showed that VDR was present in both cell types, whereas expression of the hydroxylases was the highest in the epithelium. Examination of gene expression by prostatic (1,25(OH)2D) concentrations showed that VDR was significantly lower in prostate tissues with the highest concentration of 1,25(OH)2D, and down-regulation of VDR by 1,25(OH) 2D was confirmed in the primary cell cultures. Analysis of inflammatory genes in the patient tissues revealed that IL-6 expression was the highest in the prostate stroma while PTGS2 (COX2) levels were lowest in the prostate cancer tissues from men in the highest tertile of prostatic 1,25(OH)2D. In vitro, TNF-α, IL-6 and IL-8 were suppressed by 1,25 (OH)2D in the primary epithelial cells, whereas TNF-α and PTGS2 were suppressed by 1,25(OH) 2D in the stromal cells. Importantly, the ability of 1,25(OH)2D to alter pro-inflammatory-induced changes in epithelial cell growth were dependent on the presence of the stromal cells. In summary, whereas both stromal and epithelial cells of the prostate express VDR and can presumably respond to 1,25(OH)2D, the prostatic epithelium appears to be the main producer of 1,25(OH)2D. Further, while the prostate epithelium was more responsive to the anti-inflammatory activity of 1,25 (OH)2D than stromal cells, stroma-epithelial crosstalk enhanced the phenotypic effects of 1,25(OH)2D and the inflammatory process in the prostate gland.

VDR activity is differentially affected by Hic-5 in prostate cancer and stromal cells

Patients with prostate cancer treated with androgen deprivation therapy (ADT) eventually develop castrate-resistant prostate cancer (CRPC). 1,25-Dihydroxyvitamin D3 (1,25D3/calcitriol) is a potential adjuvant therapy that confers antiproliferative and pro-differentiation effects in vitro, but has had mixed results in clinical trials. The impact of the tumor microenvironment on 1,25D3 therapy in patients with CRPC has not been assessed. Transforming growth factor β (TGFβ), which is associated with the development of tumorigenic "reactive stroma" in prostate cancer, induced vitamin D3 receptor (VDR) expression in the human WPMY-1 prostate stromal cell line. Similarly, TGFβ enhanced 1,25D3-induced upregulation of CYP24A1, which metabolizes 1,25D3 and thereby limits VDR activity. Ablation of Hic-5, a TGFβ-inducible nuclear receptor coregulator, inhibited basal VDR expression, 1,25D3-induced CYP24A1 expression and metabolism of 1,25D3 and TGFβ-enhanced CYP24A1 expression. A Hic-5-responsive sequence was identified upstream (392-451 bp) of the CYP24A1 transcription start site that is occupied by VDR only in the presence of Hic-5. Ectopic expression of Hic-5 sensitized LNCaP prostate tumor cells to growth-inhibitory effects of 1,25D3 independent of CYP24A1. The sensitivity of Hic-5-expressing LNCaP cells to 1,25D3-induced growth inhibition was accentuated in coculture with Hic-5-ablated WPMY-1 cells. Therefore, these findings indicate that the search for mechanisms to sensitize prostate cancer cells to the antiproliferative effects of VDR ligands needs to account for the impact of VDR activity in the tumor microenvironment.

IMPLICATIONS

Hic-5 acts as a coregulator with distinct effects on VDR transactivation, in prostate cancer and stromal cells, and may exert diverse effects on adjuvant therapy designed to exploit VDR activity in prostate cancer.

Characterization of an animal model of pregnancy-induced vitamin D deficiency due to metabolic gene dysregulation

Vitamin D deficiency has been associated with pregnancy complications such as preeclampsia, gestational diabetes, and recurrent miscarriage. Therefore, we hypothesized differences in vitamin D status between healthy [Sprague-Dawley (SD) and Lewis (LW)] and complicated [Brown Norway (BN)] rat pregnancies. In SD, LW, and BN rats, we analyzed the maternal plasma levels of the vitamin D metabolites 25-OH-D and 1,25-(OH)2-D at prepregnancy, pregnancy, and postpartum. Analysis of the active metabolite 1,25-(OH)2-D showed a twofold increase in pregnant SD and LW rats but a nearly 10-fold decrease in pregnant BN rats compared with nonpregnant controls. BN rats had a pregnancy-dependent upregulation of CYP24a1 expression, a key enzyme that inactivates vitamin D metabolites. In contrast, the maternal renal expression of CYP24a1 in SD and LW rats remained constant throughout pregnancy. Analysis of the vitamin D receptor (VDR) indicated that LW and SD but not BN rats experience a pregnancy-induced 10-fold decrease in maternal renal VDR protein levels. Further analysis of bisulfite-converted and genomic DNA indicated that the observed differences in maternal renal regulation of CYP24a1 during pregnancy and lactation are not due to differences in CYP24a1 promoter methylation or single-nucleotide polymorphisms. Finally, supplementation with 1,25-(OH)2-D significantly improved the reproductive phenotype of BN rats by increasing litter size and maternal-fetal weight outcomes. We conclude that BN rats represent a novel animal model of pregnancy-specific vitamin D deficiency that is linked to pregnancy complications. Vitamin D deficiency in BN rats correlates with maternal renal CYP24a1 upregulation followed by CYP27b1 upregulation.

Effect of phorbol 12-myristate 13-acetate activated signaling pathways on 1α, 25 dihydroxyvitamin D3 regulated human 25-hydroxyvitamin D3 24-hydroxylase gene expression in differentiated Caco-2 cells

Phorbol-12-myristate-13-acetate (PMA), a protein kinase C(PKC) activator, can modulate 1α, 25 dihydroxyvitamin D(3) (1,25(OH)(2)D(3))-induced expression of the 24-hydroxylase (CYP24A1) gene but this has not been studied in differentiated enterocytes, a primary 1,25(OH)(2) D(3) target cell. We found that in differentiated Caco-2 cells, an established model of the mature absorptive epithelial cell, PMA significantly enhanced 1,25(OH)(2)D(3)-induced human CYP24A1 (hCYP24A1) mRNA accumulation and hCYP24A1 promoter-luciferase reporter gene activation by 150%. Reporter gene studies further identified the region between -298 and +74 bp in the hCYP24A1 promoter as critical for the PMA enhancing effect and chromatin immunoprecipitation (ChIP) analysis showed that PMA enhanced 1,25(OH)(2)D(3)-induced binding of vitamin D receptor to this region. PMA can activate PKC, ERK1/2, and p38 MAP kinases and inhibition of these signaling pathways reduced both 1,25(OH)(2)D(3)-induced hCYP24A1 gene transcription and the enhancing effect of PMA. The PMA enhancing effect on 1,25(OH)(2)D(3) action was evident in a minimal promoter with three osteocalcin VDREs and was reduced after mutation of a putative vitamin D stimulatory site in the hCYP24A1 promoter. In contrast, mutation of a Ets binding site (EBS) in the hCYP24A1 promoter had no impact on 1,25(OH)(2)D(3) action or the PMA enhancing effect. These data suggest that in the differentiated enterocyte PMA-induced activation of several signaling pathways contribute to 1,25(OH)(2)D(3)-induced hCYP24A1 gene expression through multiple regulatory motifs within the proximal hCYP24A1 promoter.

Vitamin D and the kidney

The kidney is essential for the maintenance of normal calcium and phosphorus homeostasis. Calcium and inorganic phosphorus are filtered at the glomerulus, and are reabsorbed from tubular segments by transporters and channels which are regulated by 1α,25-dihydroxyvitamin (1α,25(OH)(2)D) and parathyroid hormone (PTH). The kidney is the major site of the synthesis of 1α,25(OH)(2)D under physiologic conditions, and is one of the sites of 24,25-dihydroxyvitamin D (24,25(OH)(2)D) synthesis. The activity of the 25(OH)D-1α-hydroxylase, the mixed function oxidase responsible for the synthesis of 1α,25(OH)(2)D, is regulated by PTH, 1α,25(OH)(2)D, fibroblast growth factor 23 (FGF23), inorganic phosphorus and other growth factors. Additionally, the vitamin D receptor which binds to, and mediates the activity of 1α,25(OH)(2)D, is widely distributed in the kidney. Thus, the kidney, by regulating multiple transport and synthetic processes is indispensible in the maintenance of mineral homeostasis in physiological states.

Vitamin D actions to regulate calcium and skeletal homeostasis

The endocrine action of plasma 1,25-dihydroxyvitamin D plays a key role in the regulation of plasma calcium and phosphate homeostasis with activities on the intestine, kidney and bone. A current, controversial question is whether vitamin D exerts direct actions on bone cells to regulate bone mineral homeostasis. Results from clinical, rodent model and in vitro studies on human bone cells provide an impressive body of data to support this proposal particularly at the level of serum 25-hydroxyvitamin D status. Each of the major bone cell types is capable of metabolising vitamin D to the active metabolite, 1,25-dihydroxyvitamin D. Thus under conditions when bone tissue synthesis of 1,25-dihydroxyvitamin D is optimal, vitamin D activity enhances bone mineral status. Dietary calcium and phosphate intakes are the critical environmental cues together with vitamin D status to determine whether 1,25-dihydroxyvitamin D exerts an anabolic or catabolic action on bone mineral status.