Multiple promoters direct the tissue-specific expression of novel N-terminal variant human vitamin D receptor gene transcripts

Modulation of the vitamin D receptor by traditional Chinese medicines and bioactive compounds: potential therapeutic applications in VDR-dependent diseases

The Vitamin D receptor (VDR) is a crucial nuclear receptor that plays a vital role in various physiological functions. To a larger extent, the genomic effects of VDR maintain general wellbeing, and its modulation holds implications for multiple diseases. Current evidence regarding using vitamin D or its synthetic analogs to treat non-communicable diseases is insufficient, though observational studies suggest potential benefits. Traditional Chinese medicines (TCMs) and bioactive compounds derived from natural sources have garnered increasing attention. Interestingly, TCM formulae and TCM-derived bioactive compounds have shown promise in modulating VDR activities. This review explores the intriguing potential of TCM and bioactive compounds in modulating VDR activity. We first emphasize the latest information on the genetic expression, function, and structure of VDR, providing a comprehensive understanding of this crucial receptor. Following this, we review several TCM formulae and herbs known to influence VDR alongside the mechanisms underpinning their action. Similarly, we also discuss TCM-based bioactive compounds that target VDR, offering insights into their roles and modes of action.

Vitamin D receptor induces oxidative stress to promote esophageal squamous cell carcinoma proliferation via the p53 signaling pathway

Background

Esophageal squamous cell carcinoma (ESCC) is a common pathological esophageal cancer with poor prognosis. Vitamin D deficiency reportedly occurs in ESCC patients, and this is related to single nucleotide polymorphism of vitamin D receptor (VDR).

Objective

We investigated the effect of VDR on ESCC proliferation, invasion, and metastasis and its potential mechanism.

Methods

ESCC and normal tissues were collected from 20 ESCC patients. The ESCC tissue microarray contained 116 pairs of ESCC and normal tissues and 73 single ESCC tissues. VDR expression and its clinicopathological role were determined by real-time quantitative polymerase chain reaction, Western blot, and immunohistochemistry staining. sh-VDR and VDR overexpression were used to validate the effect of VDR on ESCC cell phenotype, and tandem mass tag-based quantitative proteomics and bioinformatics methods identified differential VDR-related proteins. The downstream pathway and regulatory effect were analyzed using ingenuity pathway analysis (IPA). Differentially expressed proteins were verified through parallel reaction monitoring and Western blot. In vivo imaging visualized subcutaneous tumor growth following tail vein injection of VDR-deficient ESCC cells.

Results

High VDR expression was observed in ESCC tissues and cells. Gender, T stage, and TNM stage were related to VDR expression, which was the independent prognostic factor related to ESCC. VDR downregulation repressed ESCC cell proliferation, invasion, and migration in vitro and subcutaneous tumor growth and lung metastases in vivo. The cell phenotype changes were reversed upon VDR upregulation, and differential proteins were mainly enriched in the p53 signaling pathway. TP53 cooperated with ABCG2, APOE, FTH1, GCLM, GPX1, HMOX1, JUN, PRDX5, and SOD2 and may activate apoptosis and inhibit oxidative stress, cell metastasis, and proliferation. TP53 was upregulated after VDR knockdown, and TP53 downregulation reversed VDR knockdown-induced cell phenotype changes.

Conclusions

VDR may inhibit p53 signaling pathway activation and induce ESCC proliferation, invasion, and metastasis by activating oxidative stress.

Detecting the vitamin D receptor (VDR) protein in mouse and human skeletal muscle: Strain-specific, species-specific and inter-individual variation

Vitamin D, and its receptor (VDR), play roles in muscle development/function, however, VDR detection in muscle has been controversial. Using different sample preparation methods and antibodies, we examined differences in muscle VDR protein abundance between two mouse strains and between mice and humans. The mouse D-6 VDR antibody was not reliable for detecting VDR in mouse muscle, but was suitable for human muscle, while the rabbit D2K6W antibody was valid for mouse and human muscle. VDR protein was generally lower in muscles from C57 B l/6 than FVB/N mice and was higher in human than mouse muscle. Two putative VDR bands were detected in human muscle, possibly representing VDR isoforms/splice variants, with marked inter-individual differences. This study provides new information on detecting VDR in muscle and on inter-mouse strain and inter-human individual differences in VDR expression. These findings may have implications for future pre-clinical and clinical studies and prompt further investigation to confirm possible VDR isoforms in human muscle.

Association Between Vitamin D Receptor Polymorphism and the Response to Helicobacter Pylori Treatment

Background & Aims

This research aimed to determine how variations in the vitamin D receptor gene affected the response of H. pylori infections to eradication therapy.

Patients and Methods

On 105 adult H. Pylori-positive patients, a prospective cohort study was carried out. PCR was used to genotype all patients' VDR gene polymorphisms. The patients in the study received standard triple eradication medication (clarithromycin 500 mg, amoxicillin 1000 mg, and omeprazole 20 mg) twice daily for 14 days. A stool test for H. pylori Ag was conducted 4 weeks following the end of treatment.

Results

In our study, the usual triple therapy's H. pylori eradication rate was 75.2%. The successful eradication of H. pylori and VDR rs 2228570 gene polymorphisms was more prevalent in CT gene polymorphism (64.6%) compared to non-responders (19.2%), while treatment failure was more prevalent in CC gene polymorphism (73.1% in non-responders compared to responders 24.1%), which is statistically significant. In regards to the eradication of H. pylori and VDR rs7975232 gene polymorphisms, the success of eradication was more prevalent in AC gene polymorphism (54.4%) vs non-responders (30.4%), while all patients (14) with gene AA (17.7%) are responders to standard treatment, while the failure of treatment was more prevalent in CC gene polymorphism (69.2% in non-responder vs 27.8% in responders) which is statistically significant. Our findings demonstrated a strong correlation between patients' responses to H. pylori treatment and polymorphisms in the VDR gene (ApaI and TaqI) (P 0.05).

Conclusion

As far as we are aware, this is the first study to identify a potential link between the FokI and Apal VDR polymorphism and treatment response in H pylori-positive patients. To evaluate the findings, more research with larger number of patients and different population is required.

Valproate and Short-Chain Fatty Acids Activate Transcription of the Human Vitamin D Receptor Gene through a Proximal GC-Rich DNA Region Containing Two Putative Sp1 Binding Sites

The vitamin D receptor (VDR) mediates 1,25-dihydroxyvitamin D3 pleiotropic biological actions through transcription regulation of target genes. The expression levels of this ligand-activated nuclear receptor are regulated by multiple mechanisms both at transcriptional and post-transcriptional levels. Vitamin D3 is the natural VDR activator, but other molecules and signaling pathways have also been reported to regulate VDR expression and activity. In this study, we identify valproic acid (VPA) and natural short-chain fatty acids (SCFAs) as novel transcriptional activators of the human VDR (hVDR) gene. We further report a comprehensive characterization of VPA/SCFA-responsive elements in the 5' regulatory region of the hVDR gene. Two alternative promoter DNA regions (of 2.4 and 3.8 kb), as well as subsequent deletion fragments, were cloned in pGL4-LUC reporter vector. Transfection of these constructs in HepG2 and human Upcyte hepatocytes followed by reporter assays demonstrated that a region of 107 bp (from -107 to -1) upstream of the transcription start site in exon 1a is responsible for most of the increase in transcriptional activity in response to VPA/SCFAs. This short DNA region is GC-rich, does not contain an apparent TATA box, and includes two bona fide binding sites for the transcription factor Sp1. Our results substantiate the hypothesis that VPA and SCFAs facilitate the activity of Sp1 on novel Sp1 responsive elements in the hVDR gene, thus promoting VDR upregulation and signaling. Elevated hepatic VDR levels have been associated with liver steatosis and, therefore, our results may have clinical relevance in epileptic pediatric patients on VPA therapy. Our results could also be suggestive of VDR upregulation by SCFAs produced by gut microbiota.

Role of Neural Stem Cells and Vitamin D Receptor (VDR)-Mediated Cellular Signaling in the Mitigation of Neurological Diseases

Specific stem cell-based therapies for treating Alzheimer's disease, Parkinson's disease, and schizophrenia are gaining importance in recent years. Accumulating data is providing further support by demonstrating the efficacy of neural stem cells in enhancing the neurogenesis in the aging brain. In addition to stem cells, recent studies have shown the efficacy of supplementing vitamin D in promoting neurogenesis and neuronal survival. Studies have also demonstrated the presence of mutational variants and single-nucleotide polymorphisms of the vitamin D receptor (VDR) in neurological disorders; however, implications of these mutations in the pathophysiology and response to drug treatment are yet to be explored. Hence, in this article, we have reviewed recent reports pertaining to the role of neural stem cells and VDR-mediated cellular signaling cascades that are involved in enhancing the neurogenesis through Wnt/β-catenin and Sonic Hedgehog pathways. This review benefits neurobiologists and pharmaceutical industry experts to develop stem cell-based and vitamin D-based therapies to better treat the patients suffering from neurological diseases.

Integrative profiling of Epstein-Barr virus transcriptome using a multiplatform approach

BACKGROUND

Epstein-Barr virus (EBV) is an important human pathogenic gammaherpesvirus with carcinogenic potential. The EBV transcriptome has previously been analyzed using both Illumina-based short read-sequencing and Pacific Biosciences RS II-based long-read sequencing technologies. Since the various sequencing methods have distinct strengths and limitations, the use of multiplatform approaches have proven to be valuable. The aim of this study is to provide a more complete picture on the transcriptomic architecture of EBV.

METHODS

In this work, we apply the Oxford Nanopore Technologies MinION (long-read sequencing) platform for the generation of novel transcriptomic data, and integrate these with other's data generated by another LRS approach, Pacific BioSciences RSII sequencing and Illumina CAGE-Seq and Poly(A)-Seq approaches. Both amplified and non-amplified cDNA sequencings were applied for the generation of sequencing reads, including both oligo-d(T) and random oligonucleotide-primed reverse transcription. EBV transcripts are identified and annotated using the LoRTIA software suite developed in our laboratory.

RESULTS

This study detected novel genes embedded into longer host genes containing 5'-truncated in-frame open reading frames, which potentially encode N-terminally truncated proteins. We also detected a number of novel non-coding RNAs and transcript length isoforms encoded by the same genes but differing in their start and/or end sites. This study also reports the discovery of novel splice isoforms, many of which may represent altered coding potential, and of novel replication-origin-associated transcripts. Additionally, novel mono- and multigenic transcripts were identified. An intricate meshwork of transcriptional overlaps was revealed.

CONCLUSIONS

An integrative approach applying multi-technique sequencing technologies is suitable for reliable identification of complex transcriptomes because each techniques has different advantages and limitations, and the they can be used for the validation of the results obtained by a particular approach.

Time course profiling of host cell response to herpesvirus infection using nanopore and synthetic long-read transcriptome sequencing

Third-generation sequencing is able to read full-length transcripts and thus to efficiently identify RNA molecules and transcript isoforms, including transcript length and splice isoforms. In this study, we report the time-course profiling of the effect of bovine alphaherpesvirus type 1 on the gene expression of bovine epithelial cells using direct cDNA sequencing carried out on MinION device of Oxford Nanopore Technologies. These investigations revealed a substantial up- and down-regulatory effect of the virus on several gene networks of the host cells, including those that are associated with antiviral response, as well as with viral transcription and translation. Additionally, we report a large number of novel bovine transcript isoforms identified by nanopore and synthetic long-read sequencing. This study demonstrates that viral infection causes differential expression of host transcript isoforms. We could not detect an increased rate of transcriptional readthroughs as described in another alphaherpesvirus. According to our knowledge, this is the first report on the use of LoopSeq for the analysis of eukaryotic transcriptomes. This is also the first report on the application of nanopore sequencing for the kinetic characterization of cellular transcriptomes. This study also demonstrates the utility of nanopore sequencing for the characterization of dynamic transcriptomes in any organisms.

Immunogenetic Prediction of VDR Gene SNPs: Lack of Association with Susceptibility to Type 1 Diabetes in Jordanian Patients

PURPOSE

The interaction of Vitamin D and its receptor plays a crucial role in immune modulation. Therefore, the relationship between the pathogenesis of type 1 diabetes and the genetic variants of Vitamin D receptor, which is involved in the activity of Vitamin D, was studied extensively in different populations. The association of Vitamin D receptor gene polymorphisms with predisposition to type 1 diabetes revealed controversial and inconclusive results. The aim of this study was to examine the association of four Vitamin D receptor polymorphisms with type 1 diabetes in Jordanian patients.

PATIENTS AND METHODS

Analysis of the single nucleotide polymorphisms FokI (rs2228570), ApaI (rs7975232), TaqI (rs731236) and BsmI (rs1544410) in 100 Jordanian volunteers (50 control and 50 Type 1 diabetes patients) was performed using the highly specific New Generation Sequencing technology.

RESULTS

The distribution of allele, genotype as well as haplotype frequencies exhibited no significant (P > 0.05) differences between type 1 diabetes patients and controls. Furthermore, no differences (P > 0.05) in the frequency of the genotypes of the Vitamin D receptor genetic variants were found in relation to the age of disease onset.

CONCLUSION

These findings suggest these four single nucleotide polymorphisms of the Vitamin D receptor gene seem not to be associated with type 1 diabetes predisposition in Jordanian patients. Further wide genome studies are recommended to detect other genetic variant associations with type 1 diabetes among Jordanians.

Investigating the Role of Methylation in Silencing of VDR Gene Expression in Normal Cells during Hematopoiesis and in Their Leukemic Counterparts

(1) Background: Vitamin D receptor (VDR) is present in multiple types of blood cells, and its ligand, 1,25-dihydroxyvitamin D (1,25D), is important for the proper functioning of the immune system. Activity of VDR is higher in hematopoietic stem and progenitor cells than in fully differentiated blood cells of mice and humans. In some human acute myeloid leukemia (AML) blasts, the expression of the VDR gene is also high. The mechanism of silencing the VDR gene expression during differentiation of blood cells has been addressed in this work. (2) Methods: The cells have been obtained using fluorescence activated sorting from murine tissues and from human umbilical cord blood (UCB). Then, the expression of the VDR gene and transcriptional activity of the VDR protein has been tested in real-time polymerase chain reaction (PCR). Eventually, the methylation of VDR promoter regions was tested using bisulfite sequencing. (3) Results: The CpG islands in VDR promoters were not methylated in the cells studied both in mice and in humans. The use of hypomethylating agents had no effect toward expression of human VDR transcripts, but it increased expression of the VDR-target gene, CYP24A1. (4) Conclusions: The expression of the VDR gene and transcriptional activity of the VDR protein varies at successive stages of hematopoietic differentiation in humans and mice, and in blasts from AML patients. The experiments presented in this case indicate that methylation of the promoter region of the VDR gene is not the major mechanism responsible for these differences.

Association Between Vitamin D Receptor Gene Polymorphisms and Helicobacter Pylori Infection

Background & Aims:

Human genetic polymorphism has been reported in the susceptibility and clinical development of infection. In this regard, this study aimed to investigate the link between Vitamin D Receptor (VDR) gene polymorphism and H. pylori infection.

Materials and Methods:

This cross-sectional study was conducted on 224 adult patients with upper gastrointestinal symptoms who underwent an upper gastrointestinal endoscopy between July 2017 and May 2019 in two major university hospitals. All patients were evaluated for helicobacter pylori infection. Two gastric antral biopsy specimens were taken from each patient. One of those Biopsy specimens was evaluated for histopathology examination and the other one was immersed in a saline solution ready for genomic DNA extraction.

Results:

There were statistically significant differences between different genotypes of VDR rs7975232 polymorphism between H. pylori infected and non-infected groups (CC was higher in H. pylori negative and AC and AA were the most common in H. pylori positive group). There were statistical differences between different genotypes of VDR rs2228570 between H. pylori infected and non-infected groups (TT was higher in H. pylori negative and CT and CC were the most common in H. pylori positive group). Regarding VDR rs 7975232 gene polymorphisms; the (A) allele was significantly higher H. pylori infected, while (C) allele was significantly higher in uninfected patients. Regarding VDR rs 2228570 gene polymorphisms; the (C) allele was significantly higher H. pylori infected, while (T) allele was significantly higher in uninfected patients.

Conclusion:

There is a possible association between the FokI and Apal VDR polymorphism and H. pylori infection.

The Vitamin D System in Humans and Mice: Similar but Not the Same

Vitamin D is synthesized in the skin from 7-dehydrocholesterol subsequently to exposure to UVB radiation or is absorbed from the diet. Vitamin D undergoes enzymatic conversion to its active form, 1,25-dihydroxyvitamin D (1,25D), a ligand to the nuclear vitamin D receptor (VDR), which activates target gene expression. The best-known role of 1,25D is to maintain healthy bones by increasing the intestinal absorption and renal reuptake of calcium. Besides bone maintenance, 1,25D has many other functions, such as the inhibition of cell proliferation, induction of cell differentiation, augmentation of innate immune functions, and reduction of inflammation. Significant amounts of data regarding the role of vitamin D, its metabolism and VDR have been provided by research performed using mice. Despite the fact that humans and mice share many similarities in their genomes, anatomy and physiology, there are also differences between these species. In particular, there are differences in composition and regulation of the VDR gene and its expression, which is discussed in this article.

Vitamin D Receptor Gene Polymorphisms Are Associated With Leprosy in Southern Brazil

Vitamin D, together with its nuclear receptor (VDR), plays an important role in modulating the immune response, decreasing the inflammatory process. Some polymorphisms of the VDR gene, such as BsmI (G>A rs1544410), ApaI (G>T rs7975232), and TaqI (T>C rs731236) could affect its stability and mRNA transcription activity, while FokI T>C (rs2228570) gives a truncated protein with three fewer amino acids and more efficiency in binding vitamin D. This study evaluated these four polymorphisms in the immunopathogenesis of leprosy in 404 patients and 432 control individuals without chronic or infectious disease in southern Brazil. When analyzing differences in the allele and genotype frequency of polymorphisms between patients (leprosy per se, multibacillary, and paucibacillary clinical forms) and controls, we found no statistically significant association. Regarding haplotype analysis, the bAt haplotype was associated with protection from leprosy per se (P = 0.004, OR = 0.34, CI = 0.16–0.71) and from the multibacillary clinical form (P = 0.005, OR = 0.30, CI = 0.13–0.70). In individuals aged 40 or more years, this haplotype has also showed protection against leprosy per se and multibacillary (OR = 0.26, CI = 0.09–0.76; OR = 0.26, CI = 0.07–0.78, respectively), while the BAt haplotype was a risk factor for leprosy per se in the same age group (OR = 1.34, CI = 1.04–1.73). In conclusion, despite having found no associations between the VDR gene polymorphisms with the development of leprosy, the haplotypes formed by the BsmI, ApaI, and TaqI polymorphisms were associated with leprosy per se and the multibacillary clinical form.

Vitamin D and Gastrointestinal Cancers: A Narrative Review

Calcitriol (1,25(OH)₂D₃) performs various activities throughout the body. Although low serum 25-hydroxyvitamin D [25(OH)D] levels are associated with several disease processes such as risk of fractures and falls, hypertension, cardiovascular disease, and diabetes mellitus, recent evidence attests that this important hormone also regulates several cellular pathways involved in cancer development and progression. Calcitriol modulates several genes controlling gut physiology and calcium homeostasis and also maintains the integrity of epithelial barriers, regulates the absorption of phosphate and calcium, and modulates host defense against pathogens and inflammatory response by interplaying with several types of secretory and immune cells. Vitamin D deficiency is significantly related to increased risk of developing certain types of cancer. This deficiency can be prevented by vitamin D supplementation which is both economical and safe. This can lower the risk of developing cancer and also improve the prognosis of patients with gastrointestinal malignancy, but epidemiological data remain inconsistent. Several retrospective observational studies have demonstrated the benefits of vitamin D supplementation, but a few randomized controlled trials have not seemingly supported the beneficial role of vitamin D supplementation in gastrointestinal cancers. Therefore, in this literature review, we aimed to examine the possible role of vitamin D in gastrointestinal malignancies, including gastric, esophageal, pancreatic, hepatic, and colorectal cancers.

Relationship of four vitamin D receptor gene polymorphisms with type 1 diabetes mellitus susceptibility in Kuwaiti children

Background

The incidence of type 1 diabetes mellitus (T1DM) in Kuwait is amongst the highest in the world. Vitamin D is considered to be involved in immune modulation and its deficiency contribute to autoimmune destruction of insulin producing beta cells in T1DM patients. Vitamin D has been shown to exert its effects via a nuclear vitamin D receptor (VDR) and therefore, VDR gene may be considered a candidate for T1DM susceptibility.

Methods

The genotypes of four VDR gene polymorphisms were determined in 253 Kuwaiti Arab T1DM patients and 214 healthy controls by PCR-RFLP analysis. Serum concentrations of three autoantibodies i.e. ICA (Islet cell autoantibody), GADA (Glutamic acid decarboxylase) and INS (Insulin autoantibody) were determined by radio-immunoassays.

Results

Statistically significant differences were detected between the genotypes of two VDR gene polymorphisms (FokI, C > T, rs10735810 and TaqI, C > T, rs731236) between T1DM patients and controls (P < 0.0001). In both, the frequency of variant alleles was considerably high in T1DM than in the controls. In contrast, the VDR gene ApaI (G > T, rs7975232) and BsmI (A > G, rs1544410) polymorphisms did not show association with T1DM. The homozygous variant genotypes of FokI, ApaI and TaqI polymorphisms show significant differences between various age-of-onset subgroups while no such association was detected in the case of BsmI polymorphism. Significant differences were also noted between heterozygous genotypes of all four polymorphisms especially between 4-6y and > 6y age-of-onset subgroups of T1DM patients. Three autoantibodies, ICA (Islet cell), GADA (glutamate decarboxylase) and INS (insulin) were positively associated to, varying degrees, with T1DM in Kuwaiti Arabs harboring different VDR gene polymorphism genotypes.

Conclusions

Our results demonstrate a significant effect of two VDR gene polymorphisms (FokI and TaqI) and three autoantibodies on genetic susceptibility of T1DM in Kuwaiti Arabs along with other factors.

Relationship between vitamin D receptor gene polymorphisms and anemia in postmenopausal Vietnamese women

Background: Both in vitro and in vivo studies have shown that calcitriol, the active form of vitamin D, is involved in hematopoiesis. Vitamin D receptor (VDR) gene has been suggested as one of the candidate genes for anemia. Objective: Investigate relationship between anemia and the commonly studied polymorphisms of VDR gene (FokI, BsmI, ApaI and TaqI) in terms of genotype and haplotype in Vietnamese. Methods: A case-control study including 132 postmenopausal women without chronic kidney diseases was designed to investigate the relationship between VDR polymorphism and anemia. Four single nucleotide polymorphisms (SNPs) FokI (rs2228570), BsmI (rs1544410), ApaI (rs7975232), and TaqI (rs731236) were typed by polymerase chain reaction and restriction fragment length polymorphism method. Results: Genotype distributions of four SNPs were in Hardy-Weinberg equilibrium in both anemia and control groups. The SNPs at the 3’end of the VDR gene (BsmI, ApaI and TaqI) exhibited a strong linkage disequilibrium. There was no significant association between anemia and VDR polymorphism in terms of allele, genotype, and haplotype in the analyses unadjusted or adjusted for the covariates (age, body mass index, educational level, serum ferritin, iron and albumin). Conclusion: VDR gene did not influence anemia in postmenopausal women without chronic kidney disease. For further study on the association between VDR gene and anemia, the use of larger sample size, a prospective study design, and additional markers would enhance the reliability and validity of findings.

Association of vitamin D receptor gene polymorphism (TaqI and Apa1) with bone mineral density in North Indian postmenopausal women

Vitamin D receptor (VDR) gene has an important role as a candidate gene for the regulation of bone mass in osteoporosis. However, its association with bone mineral density (BMD) is controversial and has not been established in different ethnic populations. To enhance the understanding of VDR gene polymorphism in the context of BMD, we investigated the plausible genetic association of TaqI and ApaI polymorphism with BMD in North Indian postmenopausal women with osteoporosis.254 osteoporotic women (Age 55.82 ± 6.91) and 254 postmenopausal non osteoporotic women (Age 54.76 ± 6.26) were included in the study. VDR TaqI and ApaI polymorphism were determined by PCR (polymerase chain reaction) and RFLP (restriction fragment length polymorphism). BMD was assessed by dual energy X-ray absorptiometry (DXA) at the lumbar spine (L₁-L₄), hip, forearm and femoral neck. The average BMD with TT genotype was significantly lower at lumbar spine, hip and forearm. The Frequency of TT genotype and t allele was significantly high in osteoporotic women when compared with controls. The average BMD with Aa genotype was higher in ApaI. Furthermore, comparison of frequency distribution of genotype and allele for VDR ApaI between osteoporotic patients and controls did not show any significant difference. Our findings revealed that TaqI gene TT genotype was associated with low BMD in North Indian osteoporotic women. Moreover, TT genotype and t allele associated significantly with osteoporosis in postmenopausal women. Therefore, VDR TaqI gene is an important determinant of risk factor for osteoporosis.

Fine tuning of vitamin D receptor (VDR) activity by post-transcriptional and post-translational modifications

Vitamin D receptor (VDR) is a member of the nuclear receptor (NR) superfamily of ligand-activated transcription factors. Activated VDR is responsible for maintaining calcium and phosphate homeostasis, and is required for proper cellular growth, cell differentiation and apoptosis. The expression of both phases I and II drug-metabolizing enzymes is also regulated by VDR, therefore it is clinically important.

Post-translational modifications of NRs have been known as an important mechanism modulating the activity of NRs and their ability to drive the expression of target genes. The aim of this mini review is to summarize the current knowledge about post-transcriptional and post-translational modifications of VDR.

Stop codon readthrough generates a C-terminally extended variant of the human vitamin D receptor with reduced calcitriol response

Although stop codon readthrough is used extensively by viruses to expand their gene expression, verified instances of mammalian readthrough have only recently been uncovered by systems biology and comparative genomics approaches. Previously, our analysis of conserved protein coding signatures that extend beyond annotated stop codons predicted stop codon readthrough of several mammalian genes, all of which have been validated experimentally. Four mRNAs display highly efficient stop codon readthrough, and these mRNAs have a UGA stop codon immediately followed by CUAG (UGA_CUAG) that is conserved throughout vertebrates. Extending on the identification of this readthrough motif, we here investigated stop codon readthrough, using tissue culture reporter assays, for all previously untested human genes containing UGA_CUAG. The readthrough efficiency of the annotated stop codon for the sequence encoding vitamin D receptor (VDR) was 6.7%. It was the highest of those tested but all showed notable levels of readthrough. The VDR is a member of the nuclear receptor superfamily of ligand-inducible transcription factors, and it binds its major ligand, calcitriol, via its C-terminal ligand-binding domain. Readthrough of the annotated VDR mRNA results in a 67 amino acid-long C-terminal extension that generates a VDR proteoform named VDRx. VDRx may form homodimers and heterodimers with VDR but, compared with VDR, VDRx displayed a reduced transcriptional response to calcitriol even in the presence of its partner retinoid X receptor.

Relationship of vitamin D receptor gene polymorphisms in Helicobacter pylori gastric patients

Purpose

The present study aimed to investigate the association between the human VDR gene and Helicobacter pylori infection.

Patients and methods

A cross-sectional study was conducted on 208 adult patients with upper gastrointestinal symptoms. Gastric biopsy specimens were obtained from each patient for molecular DNA and histological examination. Patients were genotyped for VDR gene polymorphisms using polymerase chain reaction and restriction fragment length polymorphism analysis.

Results

The allelic and genotypic distribution analyses of the FokI, ApaI and TaqI polymorphisms of the VDR gene did not show distribution differences between H. pylori-positive and -negative groups. The genotype distribution observed for polymorphism BsmI deviated significantly from what was expected in a Hardy–Weinberg equilibrium test in the H. pylori-positive group (χ²=29.048, p<0.001). The distribution of BsmI genotypes differed significantly between the H. pylori-negative and H. pylori-positive groups (p=0.0034), where the frequency of the bb genotype increased among H. pylori-positive individuals compared with those without infection (63.25% versus 50.55%, respectively). Conversely, the H. pylori-negative group showed a Bb frequency that was 20.27% higher than in the infected group.

Conclusion

We identified a possible association between the BsmI polymorphism and infection by H. pylori. However, further research is required to clarify this relationship.

Vitamin D Receptor Gene Polymorphisms Influence T1D Susceptibility among Pakistanis

BACKGROUND

The vitamin D receptor (VDR) gene regulates insulin secretion from the pancreas and acts as a mediator of the immune response through vitamin D. Polymorphism in VDR causes alterations in the functioning of vitamin D, leading to type 1 diabetes (T1D) predisposition. The aim of the present study was to determine VDR gene polymorphism in association with T1D in Pakistanis.

METHODS

The association was evaluated by selecting rs2228570 (FokΙ), rs7975232 (ApaΙ), and rs731236 (TaqΙ) polymorphic sites in 102 patients and 100 controls. Genotypes were identified by DNA sequencing and PCR-RFLP.

RESULTS

The allelic and genotypic frequencies of FokΙ and ApaI were significantly associated with T1D (p < 0.001) development. At the FokΙ site, tryptophan was replaced with arginine due to polymorphism. A novel SNP (GeneBank acc number KT280406) was identified through the sequencing of intron 8, 62 bp downstream from the ApaI polymorphic site, and significantly associated with T1D development. The TaqΙ did not depict any association with T1D at the allelic or genotypic level (p > 0.05). CCGC, CCGG, CCTC, and CCTG haplotypes were significantly associated with disease development (p < 0.05). However, CTGG haplotype was protective towards T1D (p < 0.01).

CONCLUSION

VDR polymorphisms were identified as susceptible regions for T1D development in the Pakistani population.

Role of CYP24A1, VDR and GC gene polymorphisms on deferasirox pharmacokinetics and clinical outcomes

β-Thalassemia patients develop deficiency in vitamin D absorption and liver hydroxylation, resulting in extremely low calcitriol levels. We explored the role of single-nucleotide polymorphisms (SNPs) involved in vitamin D metabolism, transport and activity on deferasirox pharmacokinetics and outcomes (effectiveness trough levels (C_trough) and the area under the curve (AUC) cutoffs of 20 μg ml^-1 and 360 μg ml^-1 h^-1, respectively; nonresponse AUC limit of 250 μg ml^-1 h^-1). Ninety-nine β-thalassemic patients were enrolled. Drug plasma C_trough and AUC were measured by the high-performance liquid chromatography system coupled with an ultraviolet determination method. Allelic discrimination for VDR, CYP24A1, CYP27B1 and GC gene SNPs was performed by real-time PCR. CYP24A1 22776 TT significantly influenced C_min and negatively predicted it in regression analysis. CYP24A1 3999 CC was associated with C_trough and C_min and was a negative predictor of T_max, whereas CYP24A1 8620 GG seemed to have a role in C_trough, AUC, t_1/2 and C_min, and was an AUC negative predictor factor. Considering treatment outcome, Cdx2 and GC 1296 were retained in regression analysis as AUC efficacy cutoff negative predictors.

Decreased sensitivity to 1,25-dihydroxyvitamin D3 in T cells from the rheumatoid joint

1,25-dihydroxyvitaminD₃ (1,25(OH)₂D₃), has potent anti-inflammatory effects, including suppression of IL-17 + and IFNγ+ T cells implicated in rheumatoid arthritis (RA), but efficacy at the site of active disease is unclear. To investigate this, T cells from synovial fluid (SF) and paired blood of patients with active RA were studied. 1,25(OH)₂D₃ had significantly less suppressive effect on Th17 cells (IL-17+IFNγ-) and Th17.1 cells (IL-17+IFNγ+) from SF compared to those from blood, and had no effect on SF CD4⁺ or CD8⁺ IFNγ+ T cell frequencies. Memory T cells (CD45RO+) predominate in SF, and 1,25(OH)₂D₃ had less effect on memory T cells relative to naïve (CD45RA+) T cells. RT-PCR and flow cytometry showed that this was not due to decreased expression of the vitamin D receptor or its transcription partners in memory T cells. Further studies using stimulated CD4⁺ T cells sorted according to IL-17 and IFNγ expression confirmed the ability of 1,25(OH)₂D₃ to suppress pre-existing cytokines. However, 1,25(OH)₂D₃ was most effective at suppressing de novo IL-17 and IFNγ induction. Correspondingly, T cell responses to 1,25(OH)₂D₃ correlated directly with capacity for phenotype change, which was lower in cells from SF compared to blood. These findings indicate that anti-inflammatory effects of 1,25(OH)₂D₃ in active RA are impaired because of reduced effects on phenotype-committed, inflammatory memory T cells that are enriched in SF. Restoration of 1,25(OH)₂D₃ responses in memory T cells may provide a new strategy for treatment of inflammatory diseases such as RA.

Study of Vitamin D Receptor Gene Polymorphism (FokI, TaqI and ApaI) Among Prostate Cancer Patients in North India

INTRODUCTION

Incidence of prostate cancer is rising worldwide. Multiple factors have been suggested for the aetiology of prostate cancer including ethnic, genetic and diet. Vitamin D (calcitriol) has been shown to have role in cell growth and differentiation and its deficiency is implicated as one of the aetiological factors in prostate cancer. Prostatic epithelial cells express Vitamin D Receptor (VDR) as well as 1α- hydroxylase enzyme that are required for the synthesis of calcitriol and its action. Polymorphism in VDR gene has been associated with prostate cancer in some epidemiological studies; but, there is paucity of information in the Indian context.

AIM

The present study was aimed to explore the association of VDR gene polymorphism with the development of prostate cancer.

MATERIALS AND METHODS

Three Single Nucleotide Polymorphisms (SNP) sites viz., FokI, TaqI and ApaI were analysed in 120 cases of prostate cancer which were compared with their 120 healthy first degree relatives and 120 non-related controls in the Department of Biochemistry in collaboration with the Department of Urology.

RESULTS

Analysis showed significantly decreased incidence of Tt and Aa genotype in prostate cancer patients as compared to healthy non-relative controls (p=0.016 and 0.043 respectively). As compared to first degree relatives, incidence of Tt genotype is significantly lower in cases (p=0.005). No significant association was found with FokI polymorphism.

CONCLUSION

This study suggests the protective role of heterozygous genotypes of TaqI and ApaI polymorphism against the development of prostate cancer.

Diverse Regulation of Vitamin D Receptor Gene Expression by 1,25-Dihydroxyvitamin D and ATRA in Murine and Human Blood Cells at Early Stages of Their Differentiation

Vitamin D receptor (VDR) is present in multiple blood cells, and the hormonal form of vitamin D, 1,25-dihydroxyvitamin D (1,25D) is essential for the proper functioning of the immune system. The role of retinoic acid receptor α (RARα) in hematopoiesis is very important, as the fusion of RARα gene with PML gene initiates acute promyelocytic leukemia where differentiation of the myeloid lineage is blocked, followed by an uncontrolled proliferation of leukemic blasts. RARα takes part in regulation of VDR transcription, and unliganded RARα acts as a transcriptional repressor to VDR gene in acute myeloid leukemia (AML) cells. This is why we decided to examine the effects of the combination of 1,25D and all-trans-retinoic acid (ATRA) on VDR gene expression in normal human and murine blood cells at various steps of their development. We tested the expression of VDR and regulation of this gene in response to 1,25D or ATRA, as well as transcriptional activities of nuclear receptors VDR and RARs in human and murine blood cells. We discovered that regulation of VDR expression in humans is different from in mice. In human blood cells at early stages of their differentiation ATRA, but not 1,25D, upregulates the expression of VDR. In contrast, in murine blood cells 1,25D, but not ATRA, upregulates the expression of VDR. VDR and RAR receptors are present and transcriptionally active in blood cells of both species, especially at early steps of blood development.

Role of vitamin D pathway gene polymorphisms on rifampicin plasma and intracellular pharmacokinetics

AIM

We retrospectively evaluate the pharmacogenetic role of single nucleotide polymorphisms involved in rifampicin transport (SLCO1B1, MDR1 and PXR genes) and vitamin D (VDR, CYP24A1 and CYP27B1 genes) metabolism and activity on drug plasma and intracellular concentrations.

PATIENTS & METHODS

Rifampicin C_max and C_trough were measured at weeks 2 and 4 using Ultra-Performance Liquid Chromatography-tandem mass spectroscopy methods. Allelic discrimination was performed by real-time polymerase chain reaction.

RESULTS

Twenty-four patients were enrolled. At week 2, OATP1B1 521TT and CYP27B1 +2838CC/CT considering plasma and BsmIAA for intraperipheral blood mononuclear cells C_max, remained in regression analysis. Concerning week 4, TaqITC/CC and CYP24A1 22776CT/TT were retained in plasma C_max regression model.

CONCLUSION

This study confirms the role of SLCO1B1 and it suggests the involvement of vitamin D pathway gene polymorphisms in rifampicin pharmacokinetics.

Association between Serum 25-hydroxy Vitamin D Concentration and TaqI Vitamin D Receptor Gene Polymorphism among Jordanian Females with Breast Cancer

BACKGROUND

Breast cancer is the most common type of cancer among females. Genetic polymorphisms might have a role in carcinogenesis. The aim of this study was to determine whether C to T base substitution within TaqI Vitamin D receptor (VDR) gene (rs731236) in exon 9 was a risk factor among patients with breast cancer.

METHODS

Peripheral blood was drawn from 122 Jordanian breast cancer patients and 100 healthy Jordanian volunteers in Al-Basheer Hospital during the summer months (from June to November of 2013, 2014, and 2015). DNA was amplified using polymerase chain reaction (PCR), followed by TaqI restriction enzyme digestion. Quantification of serum 25-hydroxy Vitamin D (25[OH]D) level was determined by competitive immunoassay Elecsys.

RESULTS

Genotypic frequencies for TaqI TT, Tt, and tt genotypes were 41%, 46%, and 13% for breast cancer compared to 42%, 50%, and 8% for control, respectively. Vitamin D serum level was significantly lower in the breast cancer patients (8.1 ± 0.3 ng/ml) compared to the control group (21.2 ± 0.6 ng/ml; P= 0.001). This study showed an inverse association between 25(OH)D serum level and breast cancer risk (odds ratio [OR], 22.72, 95% confidence interval [CI], 10.06-51.29).

CONCLUSIONS

An inverse association was found between 25(OH)D serum level and breast cancer risk. Statistical difference was also found between different VDR TaqI genotypes and circulating levels of 25(OH)D among Jordanian females with breast cancer.

Identification of Genotypes and Allelic Frequencies of Vitamin D Receptor Gene Polymorphism (TaqI) in Egyptian Melasma Patients

Background:

Melasma is a characteristic pattern of facial hyperpigmentation, occurring primarily on the forehead, cheeks, and chin, in a mask-like distribution. The pathogenesis of melasma is not fully understood. Vitamin D plays a role in skin pigmentation. It exerts its effect through vitamin D receptor (VDR), which is expressed in variable cells including normal melanocytes.

Aim and Objective:

The aim of the current work was to investigate if VDR gene polymorphism (TaqI) confers susceptibility to melasma in Egyptian patients.

Materials and Methods:

A total of 45 female patients with melasma were recruited and 50 healthy subjects that were matched on age, sex, body mass index, and skin phototype, were included as a control group. TaqI polymorphism was investigated using restriction fragment length polymorphism polymerase chain reaction (RFLP PCR).

Results:

Presence of (t) allele and (tt) genotype was significantly associated with melasma cases compared with control group (P < 0.001 for both). No significant association was found between (tt) genotype or (t) allele and clinical data of the studied cases.

Conclusion:

TaqI polymorphism is associated with melasma. Further, large-scale studies are recommended to underscore and validate the current findings. It is also necessary for future studies to extend the research to other populations and ethnicities. Investigating other VDR gene polymorphisms in melasma is also warranted. Since melasma is a multifactorial disease, gene–gene and gene–environment interactions should be considered in future genetic-epidemiologic researches to apply more comprehensive insight into the role of VDR gene in its pathogenesis.

Meta-analysis on vitamin D receptor and cancer risk: focus on the role of TaqI, ApaI, and Cdx2 polymorphisms

Vitamin D plays a significant role in our health, including cancer incidence and mortality. Vitamin D receptor (VDR) single-nucleotide polymorphisms (SNPs) may affect its activity, influencing the risk of cancer. Several studies have investigated VDR SNPs, but the association with the risk of cancer is controversial. Here, we present a meta-analysis to assess the association of TaqI, ApaI, and Cdx2 SNPs with the risk of cancer. A systematic literature search was performed following a predefined protocol and using validated search strategies. This meta-analysis shows the summary odd ratio (SOR) overall, by cancer sites and by ethnicity. Up to January 2014, we identified 73 independent studies with 35 525 cases and 38 675 controls. The meta-analysis of Cdx2 gg versus GG showed a significant 12% increased risk for all cancers [SOR=1.12; 95% confidence interval (CI): 1.00–1.25]. The other SNPs analyzed did not show an overall significant association with the risk of cancer: SOR=0.98 (95% CI: 0.90–1.07) and 1.06 (95% CI: 0.95–1.19) for TaqI tt versus TT and ApaI aa versus AA, respectively. TaqI shows a significant 43% increased risk for colorectal cancer (SOR=1.43; 95% CI: 1.30–1.58 for tt vs. TT). Strong frequency variations are present among different ethnic groups. This meta-analysis showed an overall increased risk of cancer associated with Cdx2 SNP and a specific higher risk of colorectal cancer associated with the TaqI polymorphism. The VDR genotype might become more relevant when clustered in a specific haplotype, associated with other SNPs of genes involved in vitamin D metabolism, or for specific tumors and/or patient characteristics.

Role of vitamin D receptor gene Cdx2 and Apa1 polymorphisms in prostate cancer susceptibility: a meta-analysis

BACKGROUND

Vitamin D receptor (VDR) gene polymorphisms affect the risk of prostate cancer. However, studies investigating the relationship between VDR gene polymorphisms (Cdx2 and ApaI) and prostate cancer risk are equivocal. Therefore, we conducted a meta-analysis of all the studies to review the evidence available.

METHODS

A comprehensive search of PubMed, EMBASE, and ISI Web of Science for studies published until September 2015 was conducted. Odds ratios (ORs) and 95 % confidence intervals (CIs) were analyzed to determine the association between VDR Cdx2 and ApaI polymorphisms, and prostate cancer risk.

RESULTS

The meta-analysis included 10 studies involving 4979 cases and 4380 controls to analyze the VDR Cdx2 polymorphism. An additional 11 studies involving 2837 cases and 2884 controls were analyzed for the VDR ApaI polymorphism. Evidence failed to support the role of VDR Cdx2 and ApaI polymorphisms in prostate cancer. For Cdx2, the pooled OR was 1.11 (95 % CI = 0.93-1.33) for AA vs. GG genotypes, 0.97 (95 % CI = 0.88-1.06) for GA vs. AA genotypes, 0.99 (95 % CI = 0.91-1.08) for AA + GA vs. GG, and 1.12 (95 % CI = 0.95-1.31) for AA vs. GA + GG. No significant relationship was observed in any subgroup analysis based on ethnicity, controls, and Hardy-Weinberg equilibrium (HWE). ORs for the ApaI polymorphism were similar.

CONCLUSIONS

VDR Cdx2 and ApaI polymorphisms are not associated with prostate cancer. Additional evidence is required to confirm this conclusion.

Regulation of vitamin D receptor expression by retinoic acid receptor alpha in acute myeloid leukemia cells

Acute myeloid leukemia (AML) is the predominant acute leukemia among adults, characterized by an accumulation of malignant immature myeloid precursors. A very promising way to treat AML is differentiation therapy using either all-trans-retinoic acid (ATRA) or 1,25-dihydroxyvitamin D3 (1,25D), or the use of both these differentiation-inducing agents. However, the effect of combination treatment varies in different AML cell lines, and this is due to ATRA either down- or up-regulating transcription of vitamin D receptor (VDR) in the cells examined. The mechanism of transcriptional regulation of VDR in response to ATRA has not been fully elucidated. Here, we show that the retinoic acid receptor α (RARα) is responsible for regulating VDR transcription in AML cells. We have shown that a VDR transcriptional variant, originating in exon 1a, is regulated by RARα agonists in AML cells. Moreover, in cells with a high basal level of RARα protein, the VDR gene is transcriptionally repressed as long as RARα agonist is absent. In these cells down-regulation of the level of RARα leads to increased expression of VDR. We consider that our findings provide a mechanistic background to explain the different outcomes from treating AML cell lines with a combination of ATRA and 1,25D.

Role of vitamin D receptor gene polymorphisms in aplastic anemia: a case-control study from China

INTRODUCTION

Vitamin D receptor (VDR) gene and its polymorphisms are highlighted as candidate components for susceptibility to various autoimmune diseases. The aim of this study was to investigate the role of VDR polymorphisms (rs2228570, rs1544410, rs7975232, and rs731236) in aplastic anemia (AA).

METHODS

In this case-control study, the genotyping of VDR rs1544410 (c.1024 + 283G>A), rs7975232 (c.1025-49G>T), and rs731236 (c.1056T>C) polymorphisms was conducted using polymerase chain reaction (PCR)-ligase detection reaction, while the genotyping of rs2228570 (c.2T>C) was detected by PCR-restriction fragment length polymorphism.

RESULTS

The frequencies of GG genotype and G allele of rs1544410 were significantly higher in patients with AA than in controls. Further analysis indicated that rs1544410 and rs7975232 polymorphisms were correlated with the risk to nonsevere AA, while rs2228570 was relevant to severe AA. Moreover, TT carriers of rs2228570 were closely associated with a poor response to treatment and a higher risk of myelodysplastic syndrome/acute leukemia transformation, while CT carriers more easily evolved to overt paroxysmal nocturnal hemoglobinuria.

CONCLUSIONS

VDR polymorphisms may contribute to susceptibility to AA and influence the severity and prognosis of AA in a Chinese population.

Polymorphisms of vitamin D receptor gene TaqI susceptibility of prostate cancer: a meta-analysis

Objective

Many studies have investigated the association of the vitamin D receptor gene TaqI polymorphism with prostate cancer (PCa) risk. However, the evidence is inadequate to draw robust conclusions. To shed light on these inconclusive findings, we conducted a meta-analysis.

Materials and methods

We searched PubMed for eligible articles. The relevant data were abstracted by two independent reviewers with the Stata 11.0 software.

Results

A total of 27 studies were included. The pooled outcomes indicated that the TaqI genetic polymorphisms were significantly associated with the risk of PCa (T vs t allele: odds ratio [OR] =1.11, 95% confidence interval [CI] =1.03–1.21, P=0.008; TT vs tt: OR =1.19, 95% CI =1.01–1.42, P=0.040; TT + Tt vs tt: OR =1.18, 95% CI =1.02–1.38, P=0.031), especially in the Asian population (T vs t allele: OR =1.11, 95% CI =1.03–1.21, P=0.008; TT/Tt vs tt: OR =1.93, 95% CI =1.02–3.66, P=0.043). In the tumor stage stratified analyses, the pooled results showed no significant difference in genetic polymorphisms between the local tumor group and the control group or between the local tumor group and the advanced tumor group. However, the genotypes TT and TT/Tt were significantly higher in the advanced PCa group compared to the control group (T vs t allele: OR =1.20, 95% CI =1.01–1.42, P=0.040; TT vs tt: OR =1.34, 95% CI =1.08–1.67, P=0.009; TT/Tt vs tt: OR =1.28, 95% CI =1.05–1.56, P=0.015).

Conclusion

The vitamin D receptor gene TaqI allele polymorphism might be associated with a PCa risk, especially in Asians, which might provide new clues for the pathogenesis research and clinical diagnosis of PCa in the future.

The Fok1 vitamin D receptor gene polymorphism and 25(OH) D serum levels and prostate cancer among Jordanian men

BACKGROUND

Prostate cancer (PCa) is one of the most commonly diagnosed neoplasms and the second leading cause of cancer death in men in the Western world. Vitamin D (1,25dihydroxy vitamin D) is linked to many biological processes that influence oncogenesis but data on relations between its genetic variants and cancer risk have been inconsistent. The aim of this study was to determine associations between a vitamin D genetic polymorphism and 25-hydroxyvitamin D [25(OH)D] levels and prostate cancer.

MATERIALS AND METHODS

Genomic DNA was extracted from 124 Jordanian prostate cancer patients and 100 healthy volunteers. Ethical approval was granted from the ethical committee at Hashemite University and written consent was given by all patients. PCR was used to amplify the vitamin D receptor Fok1 polymorphism fragment. 25(OH)D serum levels were measured by competitive immunoassay.

RESULTS

All genotypes were in Hardy-Weinberg equilibrium. Genotype frequency for Fok1 genotypes FF, Ff and ff was 30.7%, 61.3% and 8.06%, for prostate cancer patients, while frequencies for the control group was 28.0%, 66.0% and 6.0%, respectively, with no significant differences. Vitamin D serum level was significantly lower in prostate cancer patients (mean 7.7 ng/ml) compared to the control group (21.8 ng/ml). No significant association was noted between 25(OH)D and VDR Fok1 gene polymorphism among Jordanians overall, but significant associations were evident among prostate cancer patients (FF, Ff and ff : 25(OH)D levels of 6.2, 8.2 and 9.9) and controls (19.0, 22.5 and 26.3, respectively). An inverse association was noted between 25(OH)D serum level less than 10 ng/ml and prostate cancer risk (OR 35.5 and 95% CI 14.3- 88.0).

CONCLUSIONS

There is strong inverse association between 25(OH)D serum level less than 10 ng/ml level and prostate cancer risk.

Vitamin D: Metabolism, Molecular Mechanism of Action, and Pleiotropic Effects

1,25-Dihydroxvitamin D3 [1,25(OH)2D3] is the hormonally active form of vitamin D. The genomic mechanism of 1,25(OH)2D3 action involves the direct binding of the 1,25(OH)2D3 activated vitamin D receptor/retinoic X receptor (VDR/RXR) heterodimeric complex to specific DNA sequences. Numerous VDR co-regulatory proteins have been identified, and genome-wide studies have shown that the actions of 1,25(OH)2D3 involve regulation of gene activity at a range of locations many kilobases from the transcription start site. The structure of the liganded VDR/RXR complex was recently characterized using cryoelectron microscopy, X-ray scattering, and hydrogen deuterium exchange. These recent technological advances will result in a more complete understanding of VDR coactivator interactions, thus facilitating cell and gene specific clinical applications. Although the identification of mechanisms mediating VDR-regulated transcription has been one focus of recent research in the field, other topics of fundamental importance include the identification and functional significance of proteins involved in the metabolism of vitamin D. CYP2R1 has been identified as the most important 25-hydroxylase, and a critical role for CYP24A1 in humans was noted in studies showing that inactivating mutations in CYP24A1 are a probable cause of idiopathic infantile hypercalcemia. In addition, studies using knockout and transgenic mice have provided new insight on the physiological role of vitamin D in classical target tissues as well as evidence of extraskeletal effects of 1,25(OH)2D3 including inhibition of cancer progression, effects on the cardiovascular system, and immunomodulatory effects in certain autoimmune diseases. Some of the mechanistic findings in mouse models have also been observed in humans. The identification of similar pathways in humans could lead to the development of new therapies to prevent and treat disease.

Mechanisms of Enhancer-mediated Hormonal Control of Vitamin D Receptor Gene Expression in Target Cells

The biological actions of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) are mediated by the vitamin D receptor (VDR), whose expression in bone cells is regulated positively by 1,25(OH)2D3, retinoic acid, and parathyroid hormone through both intergenic and intronic enhancers. In this report, we used ChIP-sequencing analysis to confirm the presence of these Vdr gene enhancers in mesenchyme-derived bone cells and to describe the epigenetic histone landscape that spans the Vdr locus. Using bacterial artificial chromosome-minigene stable cell lines, CRISPR/Cas9 enhancer-deleted daughter cell lines, transient transfection/mutagenesis analyses, and transgenic mice, we confirmed the functionality of these bone cell enhancers in vivo as well as in vitro. We also identified VDR-binding sites across the Vdr gene locus in kidney and intestine using ChIP-sequencing analysis, revealing that only one of the bone cell-type enhancers bound VDR in kidney tissue, and none were occupied by the VDR in the intestine, consistent with weak or absent regulation by the 1,25(OH)2D3 hormone in these tissues, respectively. However, a number of additional sites of VDR binding unique to either kidney or intestine were present further upstream of the Vdr gene, suggesting the potential for alternative regulatory loci. Importantly, virtually all of these regions retained histone signatures consistent with those of enhancers and exhibited unique DNase I hypersensitivity profiles that reflected the potential for chromatin access. These studies define mechanisms associated with hormonal regulation of the Vdr and hint at the differential nature of VDR binding activity at the Vdr gene in different primary target tissues in vivo.

VDR gene polymorphisms impact on anemia at 2 weeks of anti-HCV therapy: a possible mechanism for early RBV-induced anemia

OBJECTIVES

Vitamin D receptors (VDR) bind calcitriol and modulate several physiological systems through genomic and nongenomic pathways. Calcitriol stimulates store-operated channels Ca²⁺ influx by translocation of the caveolar VDR to the plasma membrane. Intracellular Ca²⁺ levels in erythrocytes control biophysical properties and an increase in its concentration can deregulate membrane composition, cell volume, glycolytic enzymes regulation, redox state, and cell clearance.We evaluated the role of single nucleotide polymorphisms in ITPA, CYP27B1, CYP24A1, and VDR genes in the prediction of ribavirin-induced anemia in HCV-1/2/3/4 patients at 2 and 4 weeks of treatment.

PATIENTS AND METHODS

Two hundred and twenty-five patients treated with ribavirin and pegylated interferon-α were genotyped by real-time PCR.

RESULTS

BMI at baseline more than 30 kg/m² [P=0.013, odds ratio (OR): 10.95, 95% confidence interval (CI): 1.66-74.21], alanine aminotransferase at baseline more than 37 IU/l (P=0.020, OR: 0.26, 95% CI: 0.09-0.81), and the VDR BsmI AA profile (P=0.003, OR: 5.09, 95% CI: 1.72-15.05) were anemia-predictive factors at 2 weeks of therapy. At week 4, the ITPA rs6051702 AC/CC profile (P=0.001, OR: 0.19, 95% CI: 0.07-0.51) was the only factor that could predict this side effect.

CONCLUSION

The BsmI AA genotype is a predictive factor of 2-week anemia and it could be related to a VDR-enhanced activity, and thus an increased calcium influx, resulting in the deregulation of the Ca²⁺-dependent signaling, which can lead to erythrocytes hemolysis. This rapid mechanism could be responsible for the development of early anemia.These results indicate for the first time the strong, significant, and independent role of VDR in the early development of ribavirin-induced anemia and confirm the ITPA function in the prediction of anemia at week 4.

Vitamin D Receptor Polymorphisms Are Associated with Reduced Esophageal Vitamin D Receptor Expression and Reduced Esophageal Adenocarcinoma Risk

Epidemiological studies indicate that vitamin D exerts a protective effect on the development of various solid cancers. However, concerns have been raised regarding the potential deleterious role of high vitamin D levels in the development of esophageal adenocarcinoma (EAC). This study investigated genetic variation in the vitamin D receptor (VDR) in relation to its expression and risk of Barrett esophagus (BE) and EAC. VDR gene regulation was investigated by immunohistochemistry, reverse transcriptase-polymerase chain reaction (RT-PCR) and gel shift assays. Fifteen haplotype tagging single-nucleotide polymorphisms (SNPs) of the VDR gene were analyzed in 858 patients with reflux esophagitis (RE), BE or EAC and 202 healthy controls. VDR mRNA expression was higher in BE compared with squamous epithelium. VDR protein was located in the nucleus in BE. An rs1989969T/rs2238135G haplotype was identified in the 5' regulatory region of the VDR gene. It was associated with an approximately two-fold reduced risk of RE, BE and EAC. Analysis of a replication cohort was done for BE that confirmed this. The rs1989969T allele causes a GATA-1 transcription factor binding site to appear. The signaling of GATA-1, which is regarded as a negative transcriptional regulator, could explain the findings for rs1989969. The rs2238135G allele was associated with a significantly reduced VDR expression in BE; for the rs1989969T allele, a trend in reduced VDR expression was observed. We identified a VDR haplotype associated with reduced esophageal VDR expression and a reduced incidence of RE, BE and EAC. This VDR haplotype could be useful in identifying individuals who benefit most from vitamin D chemoprevention.

Expression of vitamin D receptor as a potential prognostic factor and therapeutic target in pancreatic cancer

AIMS

Vitamin D insufficiency and deficiency are common among patients with pancreatic carcinoma, but epidemiological studies have shown inconsistent results for vitamin D intake/circulation level and pancreatic cancer risk. The study aims were to investigate the effects of vitamin D on patient survival, and the proliferation or survival of pancreatic cancer cell lines.

METHODS AND RESULTS

The present study examined the local expression of vitamin D receptor (VDR) in pancreatic normal and tumour tissues from a cohort of 61 patients, and analysed the potential correlation between VDR and pathological characteristics, including disease prognosis. Among 61 pairs of normal and tumour specimens, VDR was detected in all normal tissues, and was abundantly expressed in 62.5% (15/24) of tumour tissues with high differentiation, but had a significantly lower or undetectable expression level in 75.7% (28/37) of tissues with moderate or low differentiation (P = 0.004). Moreover, high VDR expression was detected in 63.6% (14/22) of small tumours (≤25 mm) and in only 25.6% (10/39) of large tumours (>25 mm) (P = 0.06). Kaplan-Meier analysis showed that a low level of VDR expression in tumour tissues was associated with a poor prognosis (P = 0.037).

CONCLUSIONS

VDR expression could be a potential prognostic factor for patients with pancreatic adenocarcinoma, and its effects should be examined in a prospective study. Vitamin D analogues may provide a therapeutic choice for patients with high VDR expression in tumours but a low vitamin D level in the circulation.

Vitamin D receptor genetic polymorphisms are associated with PSA level, Gleason score and prostate cancer risk in African-American men

BACKGROUND/AIM

Several studies have revealed an association between single nucleotide polymorphisms (SNPs) in the VDR gene and prostate cancer (PCa) risk in European and Asian populations. To investigate whether VDR SNPs are associated with PCa risk in African-American (AA) men, nine VDR SNPs were analyzed in a case-control study.

MATERIALS AND METHODS

Multiple and binary logistic regression models were applied to analyze the clinical and genotypic data.

RESULTS

rs731236 and rs7975232 were significantly associated with PCa risk (p<0.05). In the analysis of clinical phenotypes, rs731236, rs1544410 and rs3782905 were strongly associated with high PSA level (p<0.05), whereas rs1544410 and rs2239185 showed a statistically significant association with high Gleason score (p<0.05). Haplotype analysis revealed several VDR haplotypes associated with PCa risk. Additionally, a trend existed, where as the number of risk alleles increased in the haplotype, the greater was the association with risk (p-trend=0.01).

CONCLUSION

These results suggest that the VDR SNPs may be associated with PCa risk and other clinical phenotypes of PCa in AA men.

Regulation of the vitamin D receptor gene by environment, genetics and epigenetics

The vitamin D receptor (VDR) plays a pivotal role as a mediator of 1α,25(OH)2D signalling. Besides its role in calcium homeostasis, ligand- bound VDR supports immunity and cell cycle control. While VDR regulates numerous genes across the genome, much remains to be learned about the regulation of the VDR gene itself. Hindered VDR expression and function have a broad impact, contributing to diverse diseases, including cancer, multiple sclerosis, type 1 diabetes and tuberculosis. A better understanding of the three main factors regulating the VDR, namely environment, genetics and epigenetics, may facilitate the development of improved strategies for treatment and prevention of diseases associated with impaired VDR function. This review aims to illuminate the complex interaction and contributions of the three levels of VDR gene regulation to endorse consideration of all three regulatory factors when studying gene regulation.

Insights into genetic and epigenetic determinants with impact on vitamin d signaling and cancer association studies: the case of thyroid cancer

Vitamin D is a key regulator of calcium metabolism and has been implicated as a cancer preventive agent. However, clinical studies have revealed conflicting results on its cancer preventive properties, attributed in part to multiple metabolic and regulatory factors susceptible to affect individual responses to exogenous vitamin D. Vitamin D is obtained from dietary sources and sun exposure, which depends on numerous parameters such as skin type, latitude, and lifestyle factors. Focusing on thyroid cancer (TC), we document that genetic and epigenetic determinants can greatly impact individual response to vitamin D and may outweigh the classical clinical correlative studies that focus on sun exposure/dietary intake factors. In particular, genetic determinants innate to host intrinsic metabolic pathways such as highly polymorphic cytochromes P450s responsible for the metabolic activation of vitamin D are expressed in many organs, including the thyroid gland and can impact vitamin D interaction with its nuclear receptor (VDR) in thyroid tissue. Moreover, downstream regulatory pathways in vitamin D signaling as well as VDR are also subject to wide genetic variability among human populations as shown by genome-wide studies. These genetic variations in multiple components of vitamin D pathways are critical determinants for the revaluation of the potential preventive and anticancer properties of vitamin D in TC.

Mouse and human BAC transgenes recapitulate tissue-specific expression of the vitamin D receptor in mice and rescue the VDR-null phenotype

The biological actions of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) are mediated by the vitamin D receptor (VDR), which is expressed in numerous target tissues in a cell type-selective manner. Recent studies using genomic analyses and recombineered bacterial artificial chromosomes (BACs) have defined the specific features of mouse and human VDR gene loci in vitro. In the current study, we introduced recombineered mouse and human VDR BACs as transgenes into mice and explored their expression capabilities in vivo. Individual transgenic mouse strains selectively expressed BAC-derived mouse or human VDR proteins in appropriate vitamin D target tissues, thereby recapitulating the tissue-specific expression of endogenous mouse VDR. The mouse VDR transgene was also regulated by 1,25(OH)2D3 and dibutyryl-cAMP. When crossed into a VDR-null mouse background, both transgenes restored wild-type basal as well as 1,25(OH)2D3-inducible gene expression patterns in the appropriate tissues. This maneuver resulted in the complete rescue of the aberrant phenotype noted in the VDR-null mouse, including systemic features associated with altered calcium and phosphorus homeostasis and disrupted production of parathyroid hormone and fibroblast growth factor 23, and abnormalities associated with the skeleton, kidney, parathyroid gland, and the skin. This study suggests that both mouse and human VDR transgenes are capable of recapitulating basal and regulated expression of the VDR in the appropriate mouse tissues and restore 1,25(OH)2D3 function. These results provide a baseline for further dissection of mechanisms integral to mouse and human VDR gene expression and offer the potential to explore the consequence of selective mutations in VDR proteins in vivo.

Perspectives of differentiation therapies of acute myeloid leukemia: the search for the molecular basis of patients' variable responses to 1,25-dihydroxyvitamin d and vitamin d analogs

The concept of differentiation therapy of cancer is ~40 years old. Despite many encouraging results obtained in laboratories, both in vitro and in vivo studies, the only really successful clinical application of differentiation therapy was all-trans-retinoic acid (ATRA)-based therapy of acute promyelocytic leukemia (APL). ATRA, which induces granulocytic differentiation of APL leukemic blasts, has revolutionized the therapy of this disease by converting it from a fatal to a curable one. However, ATRA does not work for other acute myeloid leukemias (AMLs). Since 1,25-dihydroxyvitamin D₃ (1,25D) is capable of inducing monocytic differentiation of leukemic cells, the idea of treating other AMLs with vitamin D analogs (VDAs) was widely accepted. Also, some types of solid cancers responded to in vitro applied VDAs, and hence it was postulated that VDAs can be used in many clinical applications. However, early clinical trials in which cancer patients were treated either with 1,25D or with VDAs, did not lead to conclusive results. In order to search for a molecular basis of such unpredictable responses of AML patients toward VDAs, we performed ex vivo experiments using patient’s blast cells. Experiments were also performed using 1,25D-responsive and 1,25D-non-responsive cell lines, to study their mechanisms of resistance toward 1,25D-induced differentiation. We found that one of the possible reasons might be due to a very low expression level of vitamin D receptor (VDR) mRNA in resistant cells, which can be increased by exposing the cells to ATRA. Our considerations concerning the molecular mechanism behind the low VDR expression and its regulation by ATRA are reported in this paper.