Reduced Vitamin D Receptor Expression Research Articles

Downregulation of the vitamin D receptor expression during acute gastrointestinal graft versus host disease is associated with poor outcome after allogeneic stem cell transplantation.

The vitamin D receptor (VDR) is critical in regulating intestinal homeostasis and emerging evidence demonstrates that VDR deficiency is a critical factor in inflammatory bowel disease pathology. However, no clinical data exist regarding the intestinal expression of VDR in patients after allogeneic haematopoietic stem cell transplantation (HSCT). Analyzing intestinal biopsies from 90 patients undergoing HSCT with mortality follow-up, we demonstrated that patients with severe acute gastrointestinal graft versus host disease (GI-GvHD) showed significant downregulation of VDR gene expression compared to mild or no acute GI-GvHD patients (p = 0.007). Reduced VDR expression was already detectable at acute GI-GvHD onset compared to GvHD-free patients (p = 0.01). These results were confirmed by immunohistochemistry (IHC) where patients with severe acute GI-GvHD showed fewer VDR+ cells (p = 0.03) and a reduced VDR staining score (p = 0.02) as compared to mild or no acute GI-GvHD patients. Accordingly, low VDR gene expression was associated with a higher cumulative incidence of treatment-related mortality (TRM) (p = 1.6x10-6) but not with relapse-related mortality (RRM). A multivariate Cox regression analysis identified low VDR as an independent risk factor for TRM (p = 0.001, hazard ratio 4.14, 95% CI 1.78-9.63). Furthermore, VDR gene expression significantly correlated with anti-microbial peptides (AMPs) gene expression (DEFA5: r = 0.637, p = 7x10-5, DEFA6: r 0 0.546, p = 0.001). In conclusion, our findings suggest an essential role of the VDR in the pathogenesis of gut GvHD and the prognosis of patients undergoing HSCT.

PTH, FGF-23, Klotho and Vitamin D as regulators of calcium and phosphorus: Genetics, epigenetics and beyond.

The actions of several bone-mineral ion regulators, namely PTH, FGF23, Klotho and 1,25(OH)2 vitamin D (1,25(OH)2D), control calcium and phosphate metabolism, and each of these molecules has additional biological effects related to cell signaling, metabolism and ultimately survival. Therefore, these factors are tightly regulated at various levels – genetic, epigenetic, protein secretion and cleavage. We review the main determinants of mineral homeostasis including well-established genetic and post-translational regulators and bring attention to the epigenetic mechanisms that affect the function of PTH, FGF23/Klotho and 1,25(OH)2D. Clinically relevant epigenetic mechanisms include methylation of cytosine at CpG-rich islands, histone deacetylation and micro-RNA interference. For example, sporadic pseudohypoparathyroidism type 1B (PHP1B), a disease characterized by resistance to PTH actions due to blunted intracellular cAMP signaling at the PTH/PTHrP receptor, is associated with abnormal methylation at the GNAS locus, thereby leading to reduced expression of the stimulatory G protein α-subunit (Gsα). Post-translational regulation is critical for the function of FGF-23 and such modifications include glycosylation and phosphorylation, which regulate the cleavage of FGF-23 and hence the proportion of available FGF-23 that is biologically active. While there is extensive data on how 1,25(OH)2D and the vitamin D receptor (VDR) regulate other genes, much more needs to be learned about their regulation. Reduced VDR expression or VDR mutations are the cause of rickets and are thought to contribute to different disorders. Epigenetic changes, such as increased methylation of the VDR resulting in decreased expression are associated with several cancers and infections. Genetic and epigenetic determinants play crucial roles in the function of mineral factors and their disorders lead to different diseases related to bone and beyond.

Effects of calcitriol on the cell cycle of rhabdomyosarcoma cells

Rhabdomyosarcoma (RMS) is a type of cancer of skeletal muscle. Calcitriol is the active form of vitamin D3, also recognised as a steroid hormone called 1α, 25-dihydroxy vitamin D3 (1,25D). We previously reported that 1,25D promoted cell proliferation and differentiation in non-cancerous skeletal muscle cells C2C12. The aim of this work is to evaluate some of the events triggered by 1,25D in RD cells, a human RMS cell line. In this work we reported that RD cells expressed vitamin D receptor (VDR) and treatment with 1,25D reduced VDR expression at 72 h. At the same time an acute decrease in viable cells as well as in cells in S-phase of cell cycle was also observed. Furthermore, up-regulation of p15INK4b was accompanied in a timely manner by down-regulation of cyclin D3, p21Waf1/Cip1 and myogenin protein levels. Simultaneously, 1,25D induced early apoptosis markers such as cyclin D1 and CDK4, and the disruption of the mitochondrial network together with a redistribution of mitochondria around the nucleus. Finally, 1,25D induced changes in the plasma membrane of RD cells associated with early and late apoptosis at 72 h, as determined by flow cytometry. Taken together, these results determine that treatment with 1,25D for 72 h triggers apoptosis in RD cells.

VDR\u2013SOX2 signaling promotes colorectal cancer stemness and malignancy in an acidic microenvironment

The acidic tumor microenvironment provides an energy source driving malignant tumor progression. Adaptation of cells to an acidic environment leads to the emergence of cancer stem cells. The expression of the vitamin D receptor (VDR) is closely related to the initiation and development of colorectal carcinoma (CRC), but its regulatory mechanism in CRC stem cells is still unclear. Our study revealed that acidosis reduced VDR expression by downregulating peroxisome proliferator-activated receptor delta (PPARD) expression. Overexpression of VDR effectively suppressed the stemness and oxaliplatin resistance of cells in acidosis. The nuclear export signal in VDR was sensitive to acidosis, and VDR was exported from the nucleus. Chromatin immunoprecipitation (ChIP) and assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) analyses showed that VDR transcriptionally repressed SRY-box 2 (SOX2) by binding to the vitamin D response elements in the promoter of SOX2, impairing tumor growth and drug resistance. We demonstrated that a change in the acidic microenvironment combined with overexpression of VDR substantially restricted the occurrence and development of CRC in vivo. These findings reveal a new mechanism by which acidosis could affect the stemness of CRC cells by regulating the expression of SOX2 and show that abnormal VDR expression leads to ineffective activation of vitamin D signaling, resulting in a lack of efficacy of vitamin D in antineoplastic process.

A negative feedback loop of H19/miR-675/EGR1 is involved in diabetic nephropathy by downregulating the expression of the vitamin D receptor.

We aimed to explore the regulatory relationship among the long noncoding RNA H19, micorRNA-675 (miR-675), the vitamin D (VD) receptor (VDR), and the early growth response protein 1 (EGR1)in the pathogenesis of diabetic nephropathy (DN) among patients with diabetes mellitus (DM). Expression levels of H19, miR-675, VDR, and EGR in patients or CIHP-1/HEK 293 cells were measured via quantitative reverse-transcription polymerase chain reaction and western blot analysis. Computational analysis and luciferase assays were performed to determine EGR1 as a target gene of miR-675. The relative expression of miR-675 was higher in the presence of H19, whereas the expression of both VDR and EGR1 messenger RNA was decreased in the presence of H19 or miR-675. However, relative expression of H19 and miR-675 was increased, whereas VDR expression was suppressed upon the treatment of 1,25-dihydroxyvitamin D3 or EGR1. VDR was identified as a target gene of miR-675. The H19 promoter and EGR1 increased the luciferase activity of cells transfected with wild-type VDR. Compared with DM patients free of DN, the levels of H19 and miR-675 were increased in the DN(+) group, whereas the levels of VDR and EGR1 were decreased. In summary, the above results indicate the presence of a negative feedback loop in the pathological mechanism of DN, where H19 downregulates the expression of VDR by upregulating the expression of miR-675, whereas reduced VDR expression subsequently reduced the expression of EGR1. Moreover, reduced EGR1 expression inhibits H19 expression, thus forming a negative feedback loop required to maintain the homeostasis of VDR and to reduce the incidence of DN.

Abstract A03: Determining the role of Vitamin D Receptor (VDR) and Retinoid X Receptor Alpha (RXRα) in colitis

Abstract A03: Determining the role of Vitamin D Receptor (VDR) and Retinoid X Receptor Alpha (RXRα) in colitis

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.

Genomic Determinants of Gene Regulation by 1,25-Dihydroxyvitamin D3 during Osteoblast-lineage Cell Differentiation

The biological effects of 1α,25-dihydroxyvitamin D3 (1,25 (OH)2D3) on osteoblast differentiation and function differ significantly depending upon the cellular state of maturation. To explore this phenomenon mechanistically, we examined the impact of 1,25(OH)2D3 on the transcriptomes of both pre-osteoblastic (POBs) and differentiated osteoblastic (OBs) MC3T3-E1 cells, and assessed localization of the vitamin D receptor (VDR) at sites of action on a genome-scale using ChIP sequence analysis. We observed that the 1,25(OH)2D3-induced transcriptomes of POBs and OBs were quantitatively and qualitatively different, supporting not only the altered biology observed but the potential for a change in VDR interaction at the genome as well. This idea was confirmed through discovery that VDR cistromes in POBs and OBs were also strikingly different. Depletion of VDR-binding sites in OBs, due in part to reduced VDR expression, was the likely cause of the loss of VDR-target gene interaction. Continued novel regulation by 1,25(OH)2D3, however, suggested that factors in addition to the VDR might also be involved. Accordingly, we show that transcriptomic modifications are also accompanied by changes in genome binding of the master osteoblast regulator RUNX2 and the chromatin remodeler CCAAT/enhancer-binding protein β. Importantly, genome occupancy was also highlighted by the presence of epigenetic enhancer signatures that were selectively changed in response to both differentiation and 1,25(OH)2D3. The impact of VDR, RUNX2, and C/EBPβ on osteoblast differentiation is exemplified by their actions at the Runx2 and Sp7 gene loci. We conclude that each of these mechanisms may contribute to the diverse actions of 1,25(OH)2D3 on differentiating osteoblasts.

Successful Treatment of Alopecia Areata with Topical Calcipotriol

Alopecia areata (AA) is an inflammatory hair loss of unknown etiology. AA is chronic and relapsing, and no effective cure or preventive treatment has been established. Vitamin D was recently reported to be important in cutaneous immune modulation as well as calcium regulation and bone metabolism. It is well known that areata is common clinical finding in patients with vitamin D deficiency, vitamin D-resistant rickets, or vitamin D receptor (VDR) mutation. The biological actions of vitamin D3 derivatives include regulation of epidermal cell proliferation and differentiation and modulation of cytokine production. These effects might explain the efficacy of vitamin D3 derivatives for treating AA. In this study, we report a 7-year-old boy with reduced VDR expression in AA, recovery of whom was observed by topical application of calcipotriol, a strong vitamin D analog.

Epigenetic repression of transcription by the Vitamin D 3 receptor in prostate cancer cells

Normal prostate epithelial cells are acutely sensitive to the antiproliferative action of 1α,25-dihydroxyvitamin D 3 (1α,25(OH) 2D 3), whilst prostate cancer cell lines and primary cultures display a range of sensitivities. We hypothesised that key antiproliferative target genes of the Vitamin D receptor (VDR) were repressed by an epigenetic mechanism in 1α,25(OH) 2D 3-insensitive cells. Supportively, we found elevated nuclear receptor co-repressor and reduced VDR expression correlated with reduced sensitivity to the antiproliferative action of 1α,25(OH) 2D 3. Furthermore, the growth suppressive actions of 1α,25(OH) 2D 3 can be restored by co-treatment with low doses of histone deacetylation inhibitors, such as trichostatin A (TSA) to induce apoptosis. Examination of the regulation of VDR target genes revealed that co-treatment of 1α,25(OH) 2D 3 plus TSA co-operatively upregulated GADD45α. Similarly in a primary cancer cell culture, the regulation of appeared GADD45α repressed. These data demonstrate that prostate cancer cells utilise a mechanism involving deacetylation to suppress the responsiveness of VDR target genes and thus ablate the antiproliferative action of 1α,25(OH) 2D 3.

Epigenetic repression of transcription by the Vitamin D3 receptor in prostate cancer cells*1, *2

Normal prostate epithelial cells are acutely sensitive to the antiproliferative action of 1α,25-dihydroxyvitamin D 3 (1α,25(OH) 2 D 3 ), whilst prostate cancer cell lines and primary cultures display a range of sensitivities. We hypothesised that key antiproliferative target genes of the Vitamin D receptor (VDR) were repressed by an epigenetic mechanism in 1α,25(OH) 2 D 3 -insensitive cells. Supportively, we found elevated nuclear receptor co-repressor and reduced VDR expression correlated with reduced sensitivity to the antiproliferative action of 1α,25(OH) 2 D 3 . Furthermore, the growth suppressive actions of 1α,25(OH) 2 D 3 can be restored by co-treatment with low doses of histone deacetylation inhibitors, such as trichostatin A (TSA) to induce apoptosis. Examination of the regulation of VDR target genes revealed that co-treatment of 1α,25(OH) 2 D 3 plus TSA co-operatively upregulated GADD45α. Similarly in a primary cancer cell culture, the regulation of appeared GADD45α repressed. These data demonstrate that prostate cancer cells utilise a mechanism involving deacetylation to suppress the responsiveness of VDR target genes and thus ablate the antiproliferative action of 1α,25(OH) 2 D 3 .