Identification of a Single Nucleotide Polymorphism of Vitamin D Receptor (VDR) and Vitamin D Binding Protein (VDBP) Gene and Its Dysregulated Pathway Through VDR-VDBP Interaction Network Analysis in Vitamin D-Deficient Infertile Females

INTRODUCTION

The prevalence of female infertility in Pakistan is currently estimated at 22%, and emerging research suggests that vitamin D (VD) deficiency (VDD) may play a significant role in influencing female fertility. The focus of this study was to investigate the single nucleotide polymorphism (SNP) patterns within the VD binding protein (VDBP). The study aimed to explore dysregulated pathways and gene enrichment through an interaction network analysis, specifically focusing on the interplay between the VD receptor (VDR) and VDBP in females experiencing unexplained infertility (UI) coupled with VDD.

METHODS

A cross-sectional study was conducted on VD-deficient, fertile, and UI female subjects. VDBP and VDR were assessed by enzyme-linked immunoassay and genotyping performed. FunRich (version 3.1.3; http://funrich.org/index.html) was employed for analysis of the identified proteins: VDR and VDBP and with their mapped gene datasets, gene enrichment, and protein-protein interaction (PPI) network.

RESULTS

The mean VD and VDR values of infertile females were significantly lower than those of fertile females. VDBP in infertile females (median (IQR)): 296.05 (232.58-420.23)) was lower than that of fertile females (469.9 (269.57-875.55), (p=0.01)). On sequence analysis, a mutation rs 4588 SNP (Thr 436 Lys) was found in exon 11 of the VDBP gene of UI females, but no mutation in exons 8 and 9 of the VDR gene, with some insignificant intronic variants, was observed. The proteins such as plasma membrane estrogen receptor signaling pathway (p < 0.001), VDR, SMAD3, NCOR1, CREBBP, NCOA1, STAT1, GRB2, PPP2CA, TP53, and NCOA2 were enriched after biological pathway grouping when VDR was made the focused gene and directly interacting with VDBP.

CONCLUSION

The females with UI exhibited significantly low VD, VDBP, and VDR. The plasma membrane estrogen receptor signaling pathway was enriched in VDD infertile females.

MiR-222-3p Aggravates the Inflammatory Response by Targeting SOCS1 to Activate STAT3 Signaling in Ulcerative Colitis

BACKGROUND

Ulcerative colitis is characterized by relapsing inflammation in the gastrointestinal tract with limited treatment options. The aim of the present study was to assess the anti-inflammatory effect of Suppressor of cytokine signaling (SOCS1) on lipopolysac- charide-stimulated RAW264.7 cells and to investigate its potential mechanisms.

METHODS

The in vitro ulcerative colitis model was established by using lipopolysaccharide-stimulated RAW264.7 cells. Western blot- ting was used to detect the protein expression levels of SOCS1, JAK2, STAT3, and VDR. Reverse transcription-quantitative polymerase chain reaction was used to measure the mRNA expression of SOCS1, miR-222-3p, and VDR. An enzyme-linked immunosorbent assay was performed to measure the levels of inflammatory cytokines. A luciferase assay assessed the binding of SOCS1 to miR-222-3p. A total of 15 patients with ulcerative colitis and 18 healthy controls were recruited. The expression levels of SOCS1 and miR-222-3p in the colonic mucosa tissues of patients with ulcerative colitis and healthy controls were determined by reverse transcription-quantitative polymerase chain reaction.

RESULTS

SOCS1 upregulation inhibited the lipopolysaccharide-induced inflammation in RAW264.7 cells. SOCS1 was confirmed to be tar- geted by miR-222-3p. Silencing SOCS1 significantly abolished the inhibitory effects of miR-222-3p downregulation on inflammation. MiR-222-3p activated STAT3 signaling and reduced VDR expression by targeting SOCS1 in lipopolysaccharide-treated RAW264.7 cells. Additionally, miR-222-3p expression was upregulated in ulcerative colitis patients (P = 5.16E-10), while SOCS1 (P = 2.75E-10) and VDR (P = 52.5E-9) expression was downregulated in ulcerative colitis patients. Endoscopic scores (UCEIS) revealed significant positive cor- relation with miR-222-3p and negative correlation with SOCS1 and VDR.

CONCLUSION

MiR-222-3p targets SOCS1 to aggravate the inflammatory response by suppressing VDR and activating STAT3 signaling in ulcerative colitis.

Evaluation of association studies and a systematic review and meta-analysis of VDR polymorphisms in type 2 diabetes mellitus risk

Numerous original studies and 4 published meta-analyses have reported the association between the Vitamin D receptor (VDR) BsmI, FokI, ApaI, and TaqI polymorphisms and type 2 diabetes mellitus (T2DM) risk. However, the results were inconsistent. Therefore, an updated meta-analysis was performed to further explore these issues.To further explore the association between the VDR BsmI, FokI, ApaI, and TaqI polymorphisms and T2DM risk.PubMed, EMBASE, Scopus, and Wanfang databases were searched. The following search strategy were used: (VDR OR vitamin D receptor) AND (polymorphism OR variant OR mutation) AND (diabetes OR mellitus OR diabetes mellitus). Pooled crude odds ratios with 95% confidence intervals were applied to evaluate the strength of association in 5 genetic models. Statistical heterogeneity, the test of publication bias, and sensitivity analysis were carried out using the STATA software (Version 12.0). To evaluate the credibility of statistically significant associations, we applied the false-positive report probabilities (FPRP) and Bayesian false discovery probability (BFDP) test.Overall, the VDR BsmI polymorphism was associated with a significantly decreased T2DM risk in Asians; the VDR FokI polymorphism was associated with a significantly decreased T2DM risk in Asians, African countries, and Asian countries; the VDR ApaI polymorphism was associated with a significantly decreased T2DM risk in Caucasians and North American countries.On the VDR ApaI polymorphism, a significantly increased T2DM risk was found in a mixed population. However, when we further performed a sensitivity analysis, FPRP, and BFDP test, less-credible positive results were identified (all FPRP > 0.2 and BFDP > 0.8) in any significant association.In summary, this study strongly indicates that all significant associations were less credible positive results, rather than from true associations.

Vitamin D in Type 2 Diabetes: Genetic Susceptibility and the Response to Supplementation

Variants of vitamin D metabolism-genes may predispose to type 2 diabetes (T2D). This study investigated the impact of these variants on disease susceptibility, Vitamin D, parathyroid hormone, C-peptide and HbA1c levels before and after cholecalciferol supplementation in patients with T2D.Twelve polymorphisms within CYP2R1, CYP27B1, DBP, VDR and CYP24A1 were genotyped in 553 T2D patients and 916 controls. In addition 65 patients receiving either cholecalciferol or placebo were analyzed during 6 months intervention and 6 months follow-up.T2D risk alleles are VDR rs7975232 "G" (p_c=0.031), rs1544410 "G" (p_c=0.027) and CYP2R1 rs10741657 "A" (p_c=0.016). Patients with genotypes CYP27B1 rs10877012 "CC" (p_c=4x10^-5), DBP rs7041 "GG" (p_c=0.003), rs4588 "CC" (p_c = 3x10^-4), CYP24A1 rs2585426 "CG" (p_c=0.006) and rs2248137 "CG" (p_c=0.001) showed lower 25(OH)D3 and DBP rs4588 "CC" lower 1,25(OH)2D3 levels (p_c=0.005). Whereas DBP rs4588 "CC" (p_c=0.009), CYP27B1 rs10877012 "AC" (p_c=0.059), VDR rs7975323 "AG" (p_c=0.033) and rs1544410 "GG" (p_c=0.013) are associated with higher 25(OH)D3 levels at 6 months' follow-up. Significant PTH suppression was detected for CYP2R1 "AG" (p_c=0.002), DBP rs4588 "CC" (p_c<0.001), VDR rs110735810 "CT" (p_c<0.001) and CYP24A1 rs2248137 "GG" (p_c=0.021).Genetic variants of the vitamin D system predispose to type 2 diabetes and regulate - partially - vitamin D metabolism, concentrations and the vitamin D status. Vitamin D insufficiency is a T2D risk factor. The response to cholecalciferol supplementation can be measured as 25(OH)D3 increment and PTH suppression. This process is regulated by genes of the vitamin D system conferring modest T2D risk.

Prevalence and risk factors for efavirenz-based antiretroviral treatment-associated severe vitamin D deficiency: A prospective cohort study

Initiation of efavirenz-based combination antiretroviral therapy (cART) is associated with Vitamin D deficiency, but the risk factors including efavirenz pharmacokinetics for cART-induced severe vitamin D deficiency (SVDD) and the impact of anti-tuberculosis (TB) cotreatment are not explored. We investigated the prevalence of SVDD in HIV and TB-HIV coinfected patients and associated risk factors for treatment-induced SVDD.Treatment-naïve Ethiopian HIV patients with (n = 102) or without (n = 89) TB co-infection were enrolled prospectively and received efavirenz-based cART. In TB-HIV coinfected patients, rifampicin-based anti-TB treatment was initiated 4 or 8 weeks before starting cART. Plasma 25-hydroxyvitamin D (25 [OH]D), cholesterol and 4-beta hydroxycholesterol concentrations were measured at baseline, 4, 16, and 48 week of cART. Plasma efavirenz concentrations were determined at 4 and 16 weeks of cART.TB-HIV patients had significantly lower plasma 25 (OH)D3 levels than HIV-only patients at baseline. TB co-infection, low Karnofsky score, high viral load, and high CYP3A activity as measured by plasma 4β-hydroxycholesterol/cholesterol ratios were significant predictors of low 25 (OH)D3 levels at baseline. In HIV-only patients, initiation of efavirenz-based cART increased the prevalence of SVVD from 27% at baseline to 76%, 79%, and 43% at 4, 16, and 48 weeks of cART, respectively. The median 25 (OH)D3 levels declined from baseline by -40%, -50%, and -14% at 4, 16, and 48 weeks of cART, respectively.In TB-HIV patients, previous anti-TB therapy had no influence on 25 (OH)D3 levels, but the initiation of efavirenz-based cART increased the prevalence of SVDD from 57% at baseline to 70% and 72% at the 4 and 16 weeks of cART, respectively. Median plasma 25 (OH)D3 declined from baseline by -17% and -21% at week 4 and 16 of cART, respectively.Our results indicate low plasma cholesterol, high CYP3A activity, and high plasma efavirenz concentrations as significant predictors of early efavirenz-based cART-induced vitamin D deficiency. Low plasma 25 (OH)D3 level at baseline is associated with TB co-infection and HIV diseases progression. Initiation of efavirenz-based cART is associated with high incidence of SVDD, whereas rifampicin based anti-TB therapy co-treatment has no significant effect. Supplementary vitamin D during cART initiation may be beneficial for HIV patients regardless of TB coinfection.

Lack of association between FokI polymorphism in vitamin D receptor gene (VDR) & type 2 diabetes mellitus in the Tunisian population

BACKGROUND & OBJECTIVES

The impact of several environmental and genetic factors on diabetes is well documented. Though the association between the vitamin D receptor (VDR) gene polymorphisms and type 2 diabetes mellitus (T2DM) has been analyzed in different ethnic groups, the results have been inconsistent. The aim of this study was to evaluate the possible association between VDR FokI polymorphism and genetic susceptibility to T2DM in Tunisian population.

METHODS

A total of 439 unrelated patients with T2DM and 302 healthy controls were included in the study. Genomic DNA was extracted from blood and genotyped for the single nucleotide polymorphism (SNP) of FokI (T/C: (rs2228570) by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) analysis.

RESULTS

The genotype distribution and the relative allelic frequencies for the FokI polymorphism were not significantly different between T2DM and controls: in T2DM patients the frequencies of the CC, CT, and TT genotypes were 52.6, 41.0, and 6.1 per cent, respectively, and in controls the genotype frequencies were 55.6, 38.7, and 5.6 per cent, respectively. In our study, the TT genotype of the FokI polymorphism was not associated with T2DM (OR =1.19, 95% CI 0.63 - 2.25, P=0.577).

INTERPRETATION & CONCLUSIONS

Our study showed no significant association of the FokI polymorphism in the vitamin D receptor gene with type 2 diabetes mellitus in Tunisian population.

Integrative role of vitamin D related and Interleukin-28B genes polymorphism in predicting treatment outcomes of Chronic Hepatitis C

BACKGROUND

Improving prediction of treatment outcomes in chronic hepatitis C (CHC) genotype 4 (G4) is necessary to increase sustained viral response (SVR) rates. Vitamin D related and interferon stimulated genes are good candidates as they are recently crosstalk altering interferon response. Thus single nucleotide polymorphisms (SNPs) within some of these genes and multiple stepwise regression analysis including other independent predictors (IL28B(rs12979860), serum 25OH-vitamin D, serum alfa-fetoprotein (AFP)) were performed on a cohort of 200 Egyptian CHC patients treated with Pegylated interferon-alpha (Peg-IFN) plus ribavirin.

METHODS

SNPs in cytochrome P-450 (CYP2R1)(rs10741657AG), vitamin D receptor (VDR)(rs2228570AG, rs1544410CT), oligoadenylate synthetases-like (OASL)(rs1169279CT) and adenosine deaminases acting on RNA (ADAR)(rs1127309TC) genes were analyzed by real-time PCR.

RESULTS

The carrier state of A allele in VDR rs2228570 and CYP2R1 rs10741657 genes were independently associated with SVR [OR 6.453 & 3.536, p < 0.01 respectively]. Combining carriers of A allele in CYP2R1 and VDR genes with IL28B C/C genotype increased the probability of SVR from 80 % to reach 87.8 %, 93 % and 100 %. No relation was found between VDR rs1544410CT, ADAR rs1127309TC, OASL rs1169279CT polymorphisms and treatment outcome. Combining VDR rs2228570 A/A genotype with IL28B C/C genotype increased the probability of SVR from 82 % to reach 100 % and from 29 % to reach 80 % in C/T+ T/T IL28B genotype in none F4 liver disease patients.

CONCLUSION

Vitamin D related (VDR rs2228570 and CYP2R1 rs10741657) and IL28B rs12979860 genes polymorphisms accurately assure SVR in naïve CHC G4 patients treated with low cost standard therapy.

Pesticide exposure and inherited variants in vitamin d pathway genes in relation to prostate cancer

BACKGROUND

Vitamin D and its metabolites are believed to impede carcinogenesis by stimulating cell differentiation, inhibiting cell proliferation, and inducing apoptosis. Certain pesticides have been shown to deregulate vitamin D's anticarcinogenic properties. We hypothesize that certain pesticides may be linked to prostate cancer via an interaction with vitamin D genetic variants.

METHODS

We evaluated interactions between 41 pesticides and 152 single-nucleotide polymorphisms (SNP) in nine vitamin D pathway genes among 776 prostate cancer cases and 1,444 male controls in a nested case-control study of Caucasian pesticide applicators within the Agricultural Health Study. We assessed Pinteraction values using likelihood ratio tests from unconditional logistic regression and a false discovery rate (FDR) to account for multiple comparisons.

RESULTS

Five significant interactions (P < 0.01) displayed a monotonic increase in prostate cancer risk with individual pesticide use in one genotype and no association in the other. These interactions involved parathion and terbufos use and three vitamin D genes (VDR, RXRB, and GC). The exposure-response pattern among participants with increasing parathion use with the homozygous CC genotype for GC rs7041 compared with unexposed participants was noteworthy [low vs. no exposure: OR, 2.58, 95% confidence interval (CI), 1.07-6.25; high vs. no exposure: OR, 3.09, 95% CI, 1.10-8.68; Pinteraction = 3.8 × 10(-3)].

CONCLUSIONS

In this study, genetic variations in vitamin D pathway genes, particularly GC rs7041, an SNP previously linked to lower circulating vitamin D levels, modified pesticide associations with prostate cancer risk.

IMPACT

Because our study is the first to examine this relationship, additional studies are needed to rule out chance findings.

Epigenetic distortion to VDR transcriptional regulation in prostate cancer cells

The current study aimed to examine the gene specific mechanisms by which the actions of the vitamin D receptor (VDR) are distorted in prostate cancer. Transcriptional responses toward the VDR ligand, 1α,25(OH)2D3, were examined in non-malignant prostate epithelial cells (RWPE-1) and compared to the 1α,25(OH)2D3-recalcitrant prostate cancer cells (PC-3). Time resolved transcriptional studies for two VDR target genes revealed selective attenuation and repression of VDR transcriptional responses in PC-3 cells. For example, responses in PC-3 cells revealed suppressed responsiveness of IGFBP3 and G0S2. Furthermore, Chromatin Immunoprecipitation (ChIP) assays revealed that suppressed transcriptional responses in PC-3 cells of IGFBP3 and G0S2 were associated with selective VDR-induced NCOR1 enrichment at VDR-binding regions on target-gene promoter regions. We propose that VDR inappropriately recruits co-repressors in prostate cancer cells. Subsequent direct and indirect mechanisms may induce local DNA methylation and stable transcriptional silencing. Thus a transient epigenetic process mediated by co-repressor binding, namely, the control of H3K9 acetylation, is distorted to favor a more stable epigenetic event, namely DNA methylation. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Corepressors (NCoR and SMRT) as well as coactivators are recruited to positively regulated 1α,25-dihydroxyvitamin D3-responsive genes

Transcription factors require coactivators and corepressors to modulate transcription in mammalian cells. The vitamin D receptor (VDR) utilizes coactivators and corepressors to gain tight control over the activity of a diverse set of genes that can regulate calcium transport, slow proliferation and promote immune responses. We have recently established the VDR/RXR cistrome in human colon cancer cells and have linked these binding sites to the genes that are regulated by 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3). In additional studies described herein, we demonstrate that the coactivators SRC1, CBP and MED1 are recruited to upregulated genes to facilitate transcription as expected. SRC1 was the most highly correlated to VDR/RXR binding (50%). However, we also found that corepressor molecules such as NCoR and SMRT were present along with SRC1, CBP or MED1 at these 1,25(OH)2D3 activated gene enhancers. Interestingly, genome-wide NCoR binding mimicked VDR binding by increasing its association with VDR binding in response to 1,25(OH)2D3 treatment. Overall, these data indicate a complex role for corepressor and coactivator complexes in the activation or active repression of 1,25(OH)2D3 responsive genes. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

1,25(OH)(2)vitamin D(3) enhances myogenic differentiation by modulating the expression of key angiogenic growth factors and angiogenic inhibitors in C(2)C(12) skeletal muscle cells

Vitamin D is mostly recognized for its regulation of calcium homeostasis in relation to the intestine, kidney, and bone. Although clinical studies have linked vitamin D with increased muscle function and strength, little is known of its underlying molecular mechanism. We recently demonstrated that 1,25-D3 exerts a direct pro-myogenic effect on skeletal muscle cells; this has provoked our investigation of 1,25-D's effect on angiogenesis, a vital process for new capillary development and tissue repair. In this study, we examined the mechanism by which 1,25-D3 modulates key angiogenic growth factors and angiogenic inhibitors. C(2)C(12) myoblasts were incubated with 100 nM 1,25-D3 or placebo for 1, 4 and 10 days. At the end of the respective incubation time, total RNA was isolated for PCR arrays and for qRT-PCR. Total proteins were isolated for Western blots and proteome profiler arrays. The addition of 1,25-D3 to C(2)C(12) myoblasts increased VEGFa and FGF-1: two pro-angiogenic growth factors that promote neo-vascularization and tissue regeneration, and decreased FGF-2 and TIMP-3: two myogenic and/or angiogenic inhibitors. Our previous study demonstrated that 1,25-D3 altered IGF-I/II expression, consistent with the observed changes in VEGFa and FGF-2 expression. These results extend our previous findings and demonstrate the modulation of angiogenesis which may be an additional mechanism by which 1,25-D3 promotes myogenesis. This study supports the mechanistic rationale for assessing the administration of vitamin D and/or vitamin D analogs to treat select muscle disorders and may also provide an alternative solution for therapies that directly manipulate VEGF and FGF's to promote angiogenesis.

Dysregulated Krüppel-like factor 4 and vitamin D receptor signaling contribute to progression of hepatocellular carcinoma

BACKGROUND & AIMS

Krüppel-like factor 4 (KLF4) is a transcription factor and putative tumor suppressor. However, little is known about its effects in hepatocellular carcinogenesis. We investigated the clinical significance, biologic effects, and mechanisms of dysregulated KLF4 signaling.

METHODS

We performed microarray analysis of hepatocellular carcinoma (HCC) tissues. We used molecular biology analyses and animal models to evaluate activation and function of KLF4-vitamin D receptor (VDR) pathway.

RESULTS

Expression of KLF4 protein was decreased or lost in primary HCC samples, in particular, lymph node metastases, compared with normal liver tissues. Loss of KLF4 from primary tumors was significantly associated with reduced survival time and was identified as a prognostic marker. Most human HCC cell lines had losses or substantial decreases in levels of KLF4. Exogenous expression of KLF4 in HCC cells upregulated expression of mesenchymal-epithelial transition (MET) and inhibited their migration, invasion, and proliferation in vitro. When these cells were injected into mice, tumors grew more slowly and metastasis was inhibited, compared with HCC cells that did not express KLF4. VDR is a direct transcriptional target of KLF4; we identified 2 sites in the VDR promoter that bound specifically to KLF4. Increased expression of VDR sensitized tumor cells to the inhibitory effects of vitamin D.

CONCLUSIONS

KLF4 binds to the promoter of VDR to regulate its expression; levels of KLF4 are reduced and levels of VDR are increased in HCC cell lines and primary tumor samples. Expression of KLF4 in HCC cells sensitizes them to the anti-proliferative effects of VD3. This pathway might be manipulated to prevent or treat liver cancer.

Genome-wide principles of gene regulation by the vitamin D receptor and its activating ligand

The vitamin D receptor (VDR) mediates virtually all of the known biological actions of the hormonal ligand 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)). These actions are directed toward the nucleus, where the VDR binds to the regulatory regions of target genes and modulates their transcriptional output. Recent technological advances have enabled the study of transcription factor binding on a genome-wide scale in cells and tissues that are major targets of vitamin D action. In this review, the results of several of these studies are discussed wherein overarching principles of gene regulation by the vitamin D hormone are beginning to emerge. In addition, several specific genes that are regulated by 1,25(OH)(2)D(3) and which provide new insight into the increasingly complex mechanism whereby the receptor functions to modulate gene expression are considered. These studies suggest that while many of the principles that are now accepted regarding the regulation of gene expression by hormones and other regulatory factors are well grounded, others require extensive modification.

Vitamin D analogs in the treatment of psoriasis: Where are we standing and where will we be going?

Vitamin D and analogs exert in the skin and other tissues potent effects on cellular differentiation and proliferation. Moreover, these compounds regulate apoptosis and exert immunomodulatory effects. During the last decades, it has convincingly been shown that vitamin D compounds are effective and safe in the topical treatment of psoriasis, where they nowadays represent a standard therapy. This review summarizes laboratory and clinical investigations related to the treatment of psoriasis with calcitriol or analogs. Additionally, promising concepts for the development of new vitamin D analogs are discussed. As a matter of fact, the final goal to create strong antiproliferative or antiinflammatory acting vitamin D analogs that exert only minor calcemic activity has not been reached until today. New agents that may activate selective vitamin D signalling pathways but may exert only negligible calcemic activity would declare a new era in dermatologic therapy and may also be effective in the topical or systemic treatment of various inflammatory skin diseases including atopic dermatitis and in various cutaneous malignancies, including lymphomas, squamous cell carcinoma or basal cell carcinoma.

The Fok1 vitamin D receptor gene polymorphism is associated with plasma renin activity in Caucasians

OBJECTIVES

25-Hydroxyvitamin D (25(OH)D) deficiency and excess activity of the renin-angiotensin system (RAS) are both associated with cardiovascular disease. Vitamin D interacts with the vitamin D receptor (VDR) to negatively regulate renin expression in mice; however, human studies linking genetic variation in the VDR with renin are lacking. We evaluated (i) whether genetic variation in the VDR at the Fok1 polymorphism was associated with plasma renin activity (PRA) in a population of hypertensives and a separate population of normotensives and (ii) whether the association between Fok1 genotype and PRA was independent of 25(OH)D levels.

DESIGN/PATIENTS/MEASUREMENTS

Genetic association study, assuming an additive model of inheritance, of 375 hypertensive and 146 normotensive individuals from the HyperPATH cohort, who had PRA assessments after 1 week of high dietary sodium balance (HS) and l week of low dietary sodium balance (LS).

RESULTS

The minor allele (T) at the Fok1 polymorphism was significantly associated with lower PRA in hypertensives (LS: β = -0·22, P < 0·01; HS: β = -0·19, P < 0·01); when repeated in normotensives, a similar relationship was observed (LS: β = -0·17, P < 0·05; HS: β = -0·18, P = 0·14). In multivariable analyses, both higher 25(OH)D levels and the T allele at Fok1 were independently associated with lower PRA in hypertensives; however, 25(OH)D was not associated with PRA in normotensives.

CONCLUSIONS

Genetic variation at the Fok1 polymorphism of the VDR gene, in combination with 25(OH)D levels, was associated with PRA in hypertension. These findings support the vitamin D-VDR complex as a potential regulator of renin activity in humans.

Genome-wide analysis of the VDR/RXR cistrome in osteoblast cells provides new mechanistic insight into the actions of the vitamin D hormone

The vitamin D receptor (VDR) mediates the actions of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) in target cells and tissues by orchestrating the expression of gene networks responsible for vitamin D-induced phenotypes. The molecular mechanisms of these regulatory systems have been studied for decades under the principle that transcriptional regulation occurs near the transcriptional start site of the gene. However, this now appears to be an outdated view of transcriptional control. In this study, we examined the genome-wide chromatin immunoprecipitation on microarray (ChIP-chip) across pre-osteoblastic cells for VDR, retinoid X receptor (RXR), RNA polymerase II, and histone H4 acetylation (H4ac). We uncovered potential regulatory mechanisms for genes important to osteoblast biology as well as skeletal formation under the control of 1,25(OH)2D3. We found that VDR, along with RXR and H4ac, binds to distal regions 43% of the time; and within gene introns and exons 44%, leaving only 13% of activation at traditional promoter regions. Here, we briefly summarize our findings for all the VDR/RXR cis-acting transcriptional elements (VDR/RXR cistrome) in pre-osteoblastic cells, MC3T3-E1, provide a few examples of this dynamic control by VDR and 1,25(OH)2D3, and demonstrate that distal transcriptional control contributes to the majority of vitamin D3-mediated transcription.

Interaction between vitamin D receptor with caveolin-3 and regulation by 1,25-dihydroxyvitamin D3 in adult rat cardiomyocytes

We show that 1alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3) and a synthetic non-genotropic vitamin D analog agonist, 1a,25(OH)2-lumisterol (JN), exhibit similar rapid effects on sarcomere shortening (contraction) of isolated adult cardiomyocyte. We also report that the vitamin D receptor (VDR) specifically interacts with caveolin-3 in the t-tubules and sarcolemma of isolated adult rat cardiac myocytes. Confocal immunofluorescence microscopy analysis showed co-localization of VDR and caveolin-3 in the t-tubules and sarcolemma of cardiomyocytes. Co-immunoprecipitation studies using VDR antibodies revealed that caveolin-3 specifically co-precipitates with the VDR and similarly the VDR is co-precipitated with caveolin-3 antibody. VDR is also in association with Serca-2, the sarcoplasmic reticulum Ca2+-ATPase, as demonstrated by co-immunoprecipitation, suggesting a role of VDR in regulating cardiac contractility by direct interaction with Serca-2. Treatment of isolated adult rat cardiomyocytes with 10 nM 1,25(OH)2D3 for 1 h caused decreased association between VDR and caveolin-3. These discoveries of the association between VDR and caveolin-3 and the regulation of this interaction by 1,25(OH)2D3 are fundamentally important in understanding 1,25(OH)2D3 signal transduction in heart cells and suggest a novel mechanism for VDR in the regulation of heart structure and function.

Association between polymorphic variation in VDR and RXRA and circulating levels of vitamin D metabolites

The vitamin D metabolite 1,25(OH)2D is the bioactive ligand of the vitamin D receptor (VDR). VDR forms a heterodimer with the retinoid X receptors (RXRs) that when bound to ligand influences the transcriptional control of genes that regulate circulating levels of vitamin D metabolites. Whether genetic variation in VDR or RXRA affects circulating levels of 1,25(OH)2D or 25(OH)D has not been established. We used a single nucleotide polymorphism (SNP) tagging approach to evaluate the association between SNPs in VDR and RXRA and serum levels of 1,25(OH)2D and 25(OH)D. A total of 42 tagSNPs in VDR and 32 in RXRA were analyzed in a sample of 415 participants. Principal components analyses revealed a gene-level association between RXRA and serum 1,25(OH)2D concentrations (P=0.01), but not 25(OH)D. No gene-level association was found for VDR with either serum biomarker. At the single-SNP level, a significant positive trend was observed for increasing 1,25(OH)2D levels with each additional copy of the A allele for RXRA SNP rs9409929 (P-trend=0.003). After a multiple comparisons adjustment, no individual SNP in VDR or RXRA was significantly associated with either outcome. These results demonstrate an association between genetic variation in RXRA and 1,25(OH)2D serum concentrations.

A molecular description of ligand binding to the two overlapping binding pockets of the nuclear vitamin D receptor (VDR): structure-function implications

Molecular modeling results indicate that the VDR contains two overlapping ligand binding pockets (LBP). Differential ligand stability and fractional occupancy of the two LBP has been physiochemically linked to the regulation of VDR-dependent genomic and non-genomic cellular responses. The purpose of this report is to develop an unbiased molecular modeling protocol that serves as a good starting point in simulating the dynamic interaction between 1alpha,25(OH)2-vitamin D3 (1,25D3) and the VDR LBP. To accomplish this goal, the flexible docking protocol developed allowed for flexibility in the VDR ligand and the VDR atoms that form the surfaces of the VDR LBP. This approach blindly replicated the 1,25D3 conformation and side-chain dynamics observed in the VDR X-ray structure. The results are also consistent with the previously published tenants of the vitamin D sterol (VDS)-VDR conformational ensemble model. Furthermore, we used flexible docking in combination with whole-cell patch-clamp electrophysiology and steroid competition assays to demonstrate that (a) new non-vitamin D VDR ligands show a different pocket selectivity when compared to 1,25D3 that is qualitatively consistent with their ability to stimulate chloride channels and (b) a new route of ligand binding provides a novel hypothesis describing the structural nuances that underlie hypercalceamia.

1,25(OH)2vitamin D3 inhibits cell proliferation by promoting cell cycle arrest without inducing apoptosis and modifies cell morphology of mesenchymal multipotent cells

The vitamin D receptor (VDR) and its ligand 1,25D play an important role in regulating cell growth and cell fate. We examined the effect of 1,25D on cell morphology, cell proliferation, cell cycle progression and apoptosis on mesenchymal multipotent cells. Multipotent cells were treated with and without 1,25D in a time- and dose-dependent manner. Changes in cell morphology were evaluated by a green fluorescence fluorocrome. Cell proliferation was determined by the Formazan assay and PCNA antigen expression. The expression of genes related to the cell cycle was analyzed by DNA microarrays, RT(2)PCR arrays and western blots. Apoptosis was evaluated by TUNEL assay, and the expression of pro- and anti-apoptotic related genes by RT(2)PCR arrays and western blots. 1,25D inhibited cell proliferation, induced cell cycle arrest, and promoted accumulation of cells in G0/G1 phase without inducing apoptosis. An increase in cell size was associated with a decrease in the GTPase Rho and the atypical Rho family GTPase Rhou/Wrch-1 expression without inducing Wnt-1 expression. Survivin expression was also increased and may represent a novel 1,25D-mediated pathway regulating tissue injury and fibrosis. The data provide a mechanistic explanation for the anti-proliferative and anti-apoptotic properties of 1,25D in mesenchymal multipotent cells.

Vitamin D binding protein genotype and osteoporosis

Osteoporosis is a bone disease leading to an increased fracture risk. It is considered a complex multifactorial genetic disorder with interaction of environmental and genetic factors. As a candidate gene for osteoporosis, we studied vitamin D binding protein (DBP, or group-specific component, Gc), which binds to and transports vitamin D to target tissues to maintain calcium homeostasis through the vitamin D endocrine system. DBP can also be converted to DBP-macrophage activating factor (DBP-MAF), which mediates bone resorption by directly activating osteoclasts. We summarized the genetic linkage structure of the DBP gene. We genotyped two single-nucleotide polymorphisms (SNPs, rs7041 = Glu416Asp and rs4588 = Thr420Lys) in 6,181 elderly Caucasians and investigated interactions of the DBP genotype with vitamin D receptor (VDR) genotype and dietary calcium intake in relation to fracture risk. Haplotypes of the DBP SNPs correspond to protein variations referred to as Gc1s (haplotype 1), Gc2 (haplotype 2), and Gc1f (haplotype3). In a subgroup of 1,312 subjects, DBP genotype was found to be associated with increased and decreased serum 25-(OH)D(3) for haplotype 1 (P = 3 x 10(-4)) and haplotype 2 (P = 3 x 10(-6)), respectively. Similar associations were observed for 1,25-(OH)(2)D(3). The DBP genotype was not significantly associated with fracture risk in the entire study population. Yet, we observed interaction between DBP and VDR haplotypes in determining fracture risk. In the DBP haplotype 1-carrier group, subjects of homozygous VDR block 5-haplotype 1 had 33% increased fracture risk compared to noncarriers (P = 0.005). In a subgroup with dietary calcium intake <1.09 g/day, the hazard ratio (95% confidence interval) for fracture risk of DBP hap1-homozygote versus noncarrier was 1.47 (1.06-2.05). All associations were independent of age and gender. Our study demonstrated that the genetic effect of the DBP gene on fracture risk appears only in combination with other genetic and environmental risk factors for bone metabolism.

Chemopreventive efficacy of 25-hydroxyvitamin D3 in colon cancer

Recently, it has been reported that 25-hydroxyvitamin D3-1alpha-hydroxylase [1alpha(OH)ase, CYP27B1], required to convert non-toxic 25-hyxdroxyvitamin D3 [25(OH)D(3)] to its active metabolite [1alpha,25(OH)(2)D(3)], is present in the epithelial cells of the human colon. In the present study, the potential chemoprotective role of 25(OH)D(3) was evaluated for colon cancer using the HT-29, human colon cancer cell line. Colon cancer cells were treated with 25(OH)D(3) (500nM or 1muM), 1alpha,25(OH)(2)D(3) (500nM), cholecalciferol (D3, 1muM) or vehicle and cell number determined at days 2 and 5 post-treatment. Results showed that both 25(OH)D(3) and 1alpha,25(OH)(2)D(3) induced dose- and time-dependent anti-proliferative effects on the HT-29 cells, with maximum inhibition noted at day 5. Western blot analyses revealed an up-regulation of VDR and 1alpha(OH)ase expression following 24h of treatment with 25(OH)D(3), and 1alpha,25(OH)(2)D(3). These results are consistent with the expression of VDR and 1alpha(OH)ase in samples of normal colonic tissue, aberrant crypt foci (ACFs) and colon adenocarcinomas. The VDR expression was sequentially increased from normal to pre-cancerous lesions to well-differentiated tumors and then decreased in poorly differentiated tumors. Expression of 1alpha(OH)ase was equally expressed in normal, pre-cancerous lesions and malignant human colon tissues. The increased expression of 1alpha(OH)ase in colon cancer cells treated with the pro-hormone and its anti-proliferative effects, suggest that 25(OH)D(3) may offer possible therapeutic and chemopreventive option in colon cancer.

Identification of novel mediators of Vitamin D signaling and 1,25(OH)2D3 resistance in mammary cells

Since the discovery of the Vitamin D receptor (VDR) in mammary cells, the role of the Vitamin D signaling pathway in normal glandular function and in breast cancer has been extensively explored. In vitro studies have demonstrated that the VDR ligand, 1,25(OH)(2)D(3), modulates key proteins involved in signaling proliferation, differentiation and survival of normal mammary epithelial cells. Anti-proliferative and pro-differentiating effects of 1,25(OH)(2)D(3) have also been observed in VDR positive breast cancer cells, indicating that transformation per se does not abolish Vitamin D signaling. However, many breast cancer cell lines are less sensitive to 1,25(OH)(2)D(3) than normal mammary epithelial cells. Reduced sensitivity to 1,25(OH)(2)D(3) has been linked to alterations in Vitamin D metabolizing enzymes as well as down regulation of VDR expression or function. In this report, we describe results from a proteomics screening approach used to search for proteins involved in dictating sensitivity or resistance to Vitamin D mediated apoptosis in breast cancer cells. Several proteins not previously linked to 1,25(OH)(2)D(3) signaling were identified with this approach, and a distinct subset of proteins was linked to 1,25(OH)(2)D(3) resistance. Follow-up studies to determine the relevance of these proteins to Vitamin D signaling in general are in progress.

New insights into Vitamin D sterol-VDR proteolysis, allostery, structure-function from the perspective of a conformational ensemble model

Recently, we have developed a Vitamin D sterol (VDS)-VDR conformational ensemble model. This model can be broken down into three individual, yet interlinked parts: (a) the conformationally flexible VDS, (b) the apo/holo-VDR helix-12 (H12) conformational ensemble, and (c) the presence of two VDR ligand binding pockets (LBPs); one thermodynamically favored (the genomic pocket, G-pocket) and the other kinetically favored by VDSs (the alternative pocket, A-pocket). One focus of this study is to use directed VDR mutagenesis to (1) demonstrate H12 is stabilized in the transcriptionally active closed conformation (hVDR-c1) by three salt-bridges that span the length of H12 (cationic residues R154, K264 and R402), (2) to elucidate the VDR trypsin sites [R173 (hVDR-c1), K413 (hVDR-c2) and R402 (hVDR-c3)] and (3) demonstrate the apo-VDR H12 equilibrium can be shifted. The other focus of this study is to apply the model to generate a mechanistic understanding to discrepancies observed in structure-function data obtained with a variety of 1alpha,25(OH)(2)-Vitamin D(3) (1,25D) A-ring and side-chain analogs, and side-chain metabolites. We will demonstrate that these structure-function conundrums can be rationalized, for the most part by focusing on alterations in the VDS conformational flexibility and the elementary interaction between the VDS and the VDR A- and G-pockets, relative to the control, 1,25D.

The 1alpha,25-dihydroxy Vitamin D3 receptor preferentially recruits the coactivator SRC-1 during up-regulation of the osteocalcin gene

Binding of 1alpha,25-dihydroxy Vitamin D3 to the C-terminal domain (LBD) of its receptor (VDR), induces a conformational change that enables interaction of VDR with transcriptional coactivators such as the members of the p160/SRC family or the DRIP (Vitamin D interacting complex)/Mediator complex. These interactions are critical for VDR-mediated transcriptional enhancement of target genes. Recent reports indicate that nuclear receptors, including VDR, interact with p160/SRC members and the DRIP/Mediator complex in a sequential, cyclical, and mutually exclusive manner when bound to a target promoter, exhibiting also a high exchange rate. Here, we present an overview of how these coactivators are recruited to the bone-specific osteocalcin (OC) gene in response to short and long exposures to 1alpha,25-dihydroxy Vitamin D3. We find that in intact osteoblastic cells VDR and SRC-1 rapidly bind to the OC promoter in response to the ligand. This recruitment correlates with transcriptional enhancement of the OC gene and with increased histone acetylation at the OC promoter. In contrast, binding of the DRIP205 subunit, which anchors the DRIP/Mediator complex to the VDR, is detected at the OC promoter after several hours of incubation with 1alpha,25-dihydroxy Vitamin D3. Together, our results indicate that VDR preferentially recruits SRC-1 to enhance basal bone-specific OC gene transcription. We propose a model where specific protein-DNA and protein-protein interactions that occur within the context of the OC gene promoter in osteoblastic cells stabilize the preferential association of the VDR-SRC-1 complex.

Conservative mutageneic perturbations of amino acids connecting helix 12 in the 1alpha,25(OH)2-D3 receptor (VDR) to the ligand cause significant transactivational effects

The positioning of helix 12 activation domain of nuclear receptor proteins is critically important for gene regulation. Perturbations of the helix 12 by larger analogs may alter interactions with transcriptional machinery which might give rise to selectivity. To explore the topology of the ligand binding pocket and how the bound ligand conceivably gives rise to altered transcriptional efficiencies, we have targeted 4 hydrophobic residues which contact the 25-carbon of the ligand, 1alpha,25(OH)(2)-vitamin D(3), and made a series of 13 mutants. Substitution of a smaller hydrophobic residue was poorly tolerated compared to a larger one for transactivation. The larger amino acids are likely better tolerated by promoting stronger Van der Waals forces with the ligand. Valine-418 mutants demonstrated an extreme example of this observation with mutation to leucine being transactivationally unaffected with alanine being the most affected of all single mutants. V418L resulted in a 1.3-fold increase in EC(50) for 1,25-D mediated transactivation whereas V418A resulted in a 53-fold increase when compared to wildtype VDR. Importantly, this difference is not explained by ligand binding data but by differential VDR protease sensitivity implying that V418L-VDR mutation assumes a better conformational interaction surface for coactivator than V418A. Importantly, the V418 location may accommodate larger sidechains and may even enhance the interaction with specific nuclear coactivators.

SNAIL vs vitamin D receptor expression in colon cancer: therapeutics implications

Vitamin D analogues with reduced hypercalcemic activity are under clinical investigation for use against colon cancer and other neoplasias. However, only a subset of patients responds to this therapy, most probably due to loss of vitamin D receptor (VDR) expression during tumour progression. Recent data show that SNAIL transcription factor represses VDR expression, and thus abolishes the antiproliferative and prodifferentiation effects of VDR ligands in cultured cancer cells and their antitumour action in xenografted mice. Accordingly, upregulation of SNAIL in human colon tumours associates with downregulation of VDR. These findings suggest that SNAIL may be associated with loss of responsiveness to vitamin D analogues and may thus be used as an indicator of patients who are unlikely to respond to this therapy.

Crystal structures of the vitamin D receptor complexed to superagonist 20-epi ligands

The crystal structures of the ligand-binding domain (LBD) of the vitamin D receptor complexed to 1alpha,25(OH)(2)D(3) and the 20-epi analogs, MC1288 and KH1060, show that the protein conformation is identical, conferring a general character to the observation first made for retinoic acid receptor (RAR) that, for a given LBD, the agonist conformation is unique, the ligands adapting to the binding pocket. In all complexes, the A- to D-ring moieties of the ligands adopt the same conformation and form identical contacts with the protein. Differences are observed only for the 17beta-aliphatic chains that adapt their conformation to anchor the 25-hydroxyl group to His-305 and His-397. The inverted geometry of the C20 methyl group induces different paths of the aliphatic chains. The ligands exhibit a low-energy conformation for MC1288 and a more strained conformation for the two others. KH1060 compensates this energy cost by additional contacts. Based on the present data, the explanation of the superagonist effect is to be found in higher stability and longer half-life of the active complex, thereby excluding different conformations of the ligand binding domain.