Demonstration of a 1,25-dihydroxyvitamin D3-responsive protein in human lymphocytes: immunologic crossreactivity and inverse regulation with the vitamin D receptor

Risk factors for vitamin D deficiency in sickle cell disease

Vitamin D deficiency (VDD), 25-OHD levels <20 ng/ml, is prevalent among patients with sickle cell disease (SCD) and is linked to acute and chronic pain and bone fracture in this population. There is limited literature regarding VDD-associated risk factors for SCD. We examined potential clinical and genomic parameters associated with VDD in 335 adults with SCD in a cross-sectional study. VDD was present in 65% of adult SCD patients, and 25-OHD levels independently and positively correlated with older age (P < 0·001) and vitamin D supplementation (P < 0·001). 25-OHD levels were higher in SCD patients over 40 years of age compared to the general African-American population. Both lower 25-OHD levels and increased pain frequency were associated with increased expression of SLC6A5 encoding glycine transporter-2 (GlyT2), a protein involved in neuronal pain pathways. Lower 25-OHD levels were also associated with increased expression of CYP3A4, and with decreased expression of GC (also termed DBP) and VDR, three genes involved in vitamin D metabolism. We conclude that vitamin D supplementation should be an almost universal feature of the care of young adults with SCD, and that further research is warranted into genomic factors that regulate vitamin D metabolism in SCD.

Role of Vitamin D in Rheumatoid Arthritis

Vitamin D is a fat soluble hormone, with a well described role in bone health and calcium/phosphate metabolism. Recent evidences have related vitamin D to other physiological functions and pathological conditions. Specifically, vitamin D has widely proven activities on immune system and evidences suggest that it may be implicated in the pathogenesis of rheumatoid arthritis (RA). The relationship between vitamin D and RA is complex, also because a deficitary vitamin D status, which is very common in RA patients, can contribute to the increased risk of osteoporosis typical of RA. In this chapter, will be described and discussed the main aspects of the relationship between RA and vitamin D.

Vitamin D up-regulates the vitamin D receptor by protecting it from proteasomal degradation in human CD4+ T cells

The active form of vitamin D3, 1,25(OH)2D3, has significant immunomodulatory properties and is an important determinant in the differentiation of CD4+ effector T cells. The biological actions of 1,25(OH)2D3 are mediated by the vitamin D receptor (VDR) and are believed to correlate with the VDR protein expression level in a given cell. The aim of this study was to determine if and how 1,25(OH)2D3 by itself regulates VDR expression in human CD4+ T cells. We found that activated CD4+ T cells have the capacity to convert the inactive 25(OH)D3 to the active 1,25(OH)2D3 that subsequently up-regulates VDR protein expression approximately 2-fold. 1,25(OH)2D3 does not increase VDR mRNA expression but increases the half-life of the VDR protein in activated CD4+ T cells. Furthermore, 1,25(OH)2D3 induces a significant intracellular redistribution of the VDR. We show that 1,25(OH)2D3 stabilizes the VDR by protecting it from proteasomal degradation. Finally, we demonstrate that proteasome inhibition leads to up-regulation of VDR protein expression and increases 1,25(OH)2D3-induced gene activation. In conclusion, our study shows that activated CD4+ T cells can produce 1,25(OH)2D3, and that 1,25(OH)2D3 induces a 2-fold up-regulation of the VDR protein expression in activated CD4+ T cells by protecting the VDR against proteasomal degradation.

Astemizole synergizes calcitriol antiproliferative activity by inhibiting CYP24A1 and upregulating VDR: a novel approach for breast cancer therapy

Background

Calcitriol antiproliferative effects include inhibition of the oncogenic ether-à-go-go-1 potassium channel (Eag1) expression, which is necessary for cell cycle progression and tumorigenesis. Astemizole, a new promising antineoplastic drug, targets Eag1 by blocking ion currents. Herein, we characterized the interaction between calcitriol and astemizole as well as their conjoint antiproliferative action in SUM-229PE, T-47D and primary tumor-derived breast cancer cells.

Methodology/Principal Findings

Molecular markers were studied by immunocytochemistry, Western blot and real time PCR. Inhibitory concentrations were determined by dose-response curves and metabolic activity assays. At clinically achievable drug concentrations, synergistic antiproliferative interaction was observed between calcitriol and astemizole, as calculated by combination index analysis (CI <1). Astemizole significantly enhanced calcitriol’s growth-inhibitory effects (3–11 folds, P<0.01). Mean IC₂₀ values were 1.82±2.41 nM and 1.62±0.75 µM; for calcitriol (in estrogen receptor negative cells) and astemizole, respectively. Real time PCR showed that both drugs alone downregulated, while simultaneous treatment further reduced Ki-67 and Eag1 gene expression (P<0.05). Astemizole inhibited basal and calcitriol-induced CYP24A1 and CYP3A4 mRNA expression (cytochromes involved in calcitriol and astemizole degradation) in breast and hepatoma cancer cells, respectively, while upregulated vitamin D receptor (VDR) expression.

Conclusions/Significance

Astemizole synergized calcitriol antiproliferative effects by downregulating CYP24A1, upregulating VDR and targeting Eag1. This study provides insight into the molecular mechanisms involved in astemizole-calcitriol combined antineoplastic effect, offering scientific support to test both compounds in combination in further preclinical and clinical studies of neoplasms expressing VDR and Eag1. VDR-negative tumors might also be sensitized to calcitriol antineoplastic effects by the use of astemizole. Herein we suggest a novel combined adjuvant therapy for the management of VDR/Eag1-expressing breast cancer tumors. Since astemizole improves calcitriol bioavailability and activity, decreased calcitriol dosing is advised for conjoint administration.

Vitamin D3 receptor is highly expressed in Hodgkin's lymphoma

Background

Hodgkin lymphoma (HL) is one of the most frequent lymphoma in the western world. Despite a good overall prognosis, some patients suffer relapsing tumors which are difficult to cure. Over a long period Vitamin D has been shown to be a potential treatment for cancer. Vitamin D acts via the vitamin D receptor, a nuclear receptor, acting as an inducible transcription factor. We aimed to investigate the expression of vitamin D receptor as a possible diagnostic marker and potential therapeutic target in HL as well as in B-cell derived non-Hodgkin lymphoma (B-NHL).

Methods

We used a panel of 193 formalin fixed tissues of lymphoma cases consisting of 55 cases of HL and 138 cases on several B-NHL entities.

Results

Vitamin D receptor is strongly expressed in tumor cells of HL, regardless of the sub entity with an overall positivity of 80% of all HL cases. In contrast, only about 17% of the analyzed origin-NHL showed positivity for vitamin D receptor. The detection of nuclear localization of vitamin D receptor in the tumor cells of HL suggests activated status of the vitamin D receptor.

Conclusions

Our study suggests VDR as a specific marker for tumor cells of HL, but not of B-NHL subtypes. Further, the observed nuclear localization suggests an activated receptor status in tumor cells of HL. Further investigations of mutational status and functional studies may shed some light in functional relevance of vitamin D receptor signaling in HL.

Calcitriol stimulates prolactin expression in non-activated human peripheral blood mononuclear cells: breaking paradigms

Calcitriol, the hormonal form of vitamin D(3), exerts immunomodulatory effects through the vitamin D(3) receptor (VDR) and increases prolactin (PRL) expression in the pituitary and decidua. Nevertheless, the effects of calcitriol upon lymphocyte PRL have not been evaluated. Therefore, we investigated calcitriol effects upon PRL in resting and phytohemagglutinin-activated human peripheral blood mononuclear cells (PBMNC) and Jurkat T lymphoma cells. Immunoblots showed constitutive expression of the 50-kDa VDR species in activated PBMNC and Jurkat cells, while a 75-kDa species was recognized in both resting and activated-PBMNC. Only in resting PBMNC calcitriol significantly stimulated PRL expression in a dose-dependent manner. The positive control CYP24A1, a highly VDR-responsive gene, was stimulated by calcitriol, effect that was stronger in resting than in activated-PBMNC (P<0.05), and without effect in Jurkat cells. Calcitriol upregulation of PRL and CYP24A1 was significantly inhibited by the VDR antagonist TEI-9647. EMSA showed that resting PBMNC contain a protein that binds to DR3-type VDRE. Cell activation reduced basal CYP24A1 while induced CYP27B1, VDR and pregnane X receptor (PXR) expression. In summary, calcitriol stimulated PRL and CYP24A1 gene expression in quiescent lymphocytes through a VDR-mediated mechanism. Our results suggest that the 75-kDa VDR species could be participating in calcitriol-mediated effects, and that activation induces factors such as PXR that restrain VDR transcriptional processes. This study supports the presence of a functional VDR in quiescent lymphocytes, providing evidence to reevaluate the VDR paradigm that assumes that lymphocytes respond to calcitriol only after activation. Altogether, our results offer new insights into the mechanisms whereby PRL is regulated in immune cells.

New highly calcemic 1 alpha,25-dihydroxy-19-norvitamin D(3) compounds with modified side chain: 26,27-dihomo- and 26,27-dimethylene analogs in 20S-series

New highly potent 2-substituted (20S)-1 alpha,25-dihydroxy-19-norvitamin D(3) analogs with elongated side chain were prepared by Wittig-Horner coupling of A-ring phosphine oxide with the corresponding protected (20S)-25-hydroxy Grundmann's ketones. Biologic evaluation in vitro and in vivo of the synthesized compounds was accomplished. All the synthesized vitamins possessing a 25-hydroxylated saturated side chain were slightly less active (3-5X) than 1 alpha,25-dihydroxyvitamin D(3) in binding to the porcine intestinal vitamin D receptor and significantly more potent (12-150X) in causing differentiation of HL-60 cells. In vivo, 2-methylene-26,27-dihomo and 2 alpha-methyl-26,27-dimethylene analogs were at least 10 times more active, and 2 alpha-methyl-26,27-dihomo compound at least 5 times more active than the vitamin D hormone both in stimulating intestinal calcium transport and bone calcium mobilization (serum calcium increase). It was also established that a 260 pmol dose of the corresponding 2 beta-methyl analogs had a similar effect on intestinal calcium transport and a much more pronounced effect on bone calcium mobilization as the same dose of 1 alpha,25-dihydroxyvitamin D(3).

Association of primary biliary cirrhosis with vitamin D receptor BsmI genotype polymorphism in a Hungarian population

We sought to determine the distribution of vitamin D receptor genotypes defined by the BsmI polymorphism and to investigate their association with bone mineral density in patients with primary biliary cirrhosis. Vitamin D receptor genotype and bone mineral density at the lumbar spine was determined in 31 female Hungarian patients with primary biliary cirrhosis and 51 age-matched healthy female controls. The genotype frequency (BB: 45%, Bb: 32%, bb: 22%) of the patients was significantly different from the control group (P = 0.01) due to an overrepresentation of the BB genotype. There was an apparent trend, not reaching statistical significance, for a lower bone mineral density in both the patient and control groups carrying a B allele. In conclusion, we found a strikingly high frequency of the BB genotype in patients with primary biliary cirrhosis, which raises questions about hormonal influences on the development of primary biliary cirrhosis.

Expression of 1,25-dihydroxyvitamin D(3) receptor in the immune system

In addition to its role in calcium and skeletal homeostasis, there is increasing evidence that the hormonal form of vitamin D, 1, 25-dihydroxyvitamin D(3), appears to serve as a modulator of the immune system. We have determined the level of the 1, 25-dihydroxyvitamin D(3) receptor (VDR) in resting and activated lymphocytes by immuno- and ligand-binding assays. As expected from previous work, the total T lymphocyte population contains VDR whose levels are increased when activated and treated with 1, 25-dihydroxyvitamin D(3). Surprisingly, the highest concentrations of VDR are found in CD8 lymphocytes, although significant amounts are also present in CD4 lymphocytes. Furthermore, B lymphocytes do not contain detectable amounts of VDR. Cells of the monocyte/macrophage lineage possess small amounts of VDR that are not affected by activation but are increased by treatment with 1, 25-dihydroxyvitamin D(3). These results suggest that CD8 lymphocytes may be a major site of 1,25-dihydroxyvitamin D(3) action, while B lymphocytes are likely not directly regulated by 1, 25-dihydroxyvitamin D(3).

Uncoupling of cell cycle arrest from the expression of monocytic differentiation markers in HL60 cell variants

Differentiation generally leads to cell cycle arrest. Human leukemia HL60 cells respond to the presence of 1,25-dihydroxyvitamin D3 (1,25D3) by expressing a number of markers of the monocyte/macrophage phenotype and become arrested predominantly in the G1 phase of the cell cycle. We have recently reported a series (A) of 1,25D3-resistant variants of HL60 cells which proliferate in the presence of 1,25D3 and do not express differentiation markers (Exp. Cell Res. 224, 312, 1996). We now describe another series (B) of such variants, which differ from A series cells grown in similar concentrations of 1,25D3 in that they express the CD14 antigen and nonspecific esterase, characteristic of the monocyte, while continuing to proliferate and they develop hypotetraploid DNA (4C) content at higher concentrations of ambient 1,25D3 than the A series cells. Cells in the B series with 4C DNA content (100B and 200B) also differed from the A series 4C cells by the absence of DNA binding by the full-length Sp1 transcription factor. However, B series cells resembled the A series cells in exhibiting faster growth rates than the parental HL60 cells and showed high levels of vitamin D receptor and retinoid receptor X proteins. These results show that the initial steps in the 1,25D3 signaling pathway are intact in B series resistant cells and lead to the appearance of early markers of monocytic differentiation. However, the progression to subsequent events which comprise terminal differentiation and cell cycle arrest is halted during the adaptation to the presence of 1,25D3 in these cells. Thus, the availability of these variant cells should provide a system for studying the link between differentiation and cell cycle arrest.

Effects of 1 alpha,25-dihydroxy-vitamin D3 and calcipotriol on organotypic cultures of outer root sheath cells: a potential model to evaluate antipsoriatic drugs

In the human hair follicle, outer root sheath (ORS) cells constitutively express the hyperproliferation-associated keratins 6, 16 and 17 instead of keratins 1 and 10 found in interfollicular epidermis. In organotypic cultures. ORS cells form a stratified epithelium which in many respects resembles psoriatic skin: it has a hyperplastic tissue architecture and a poorly developed granular layer, and expresses hyperproliferation-associated keratins. Therefore, we studied the effects of the antipsoriatic compounds 1 alpha,25-dihydroxy-vitamin D3 (1 alpha,25-(OH)2-D3) and its synthetic derivative calcipotriol on cultured ORS cells. In monolayer cultures, 10(-6) M 1 alpha,25-(OH)2-D3 or calcipotriol completely blocked ORS cell proliferation. This inhibitory effect was substantially reduced at 10(-8) M. Incubation of organotypic ORS cultures with both vitamin D analogues resulted in a marked thinning of the living cell compartment concomitant with a thickening of the horny layer. A reduced expression of differentiation markers such as keratins 10, 16 and 17, involucrin and filaggrin paralleled the thinning of the stratum Malpighi. As determined by quantification of BrdU-positive cells, ORS cell proliferation was apparently not affected by the vitamin D analogues, indicating that these compounds mainly operate by accelerating the differentiation pathway within the suprabasal living cell compartment. No alteration in the expression of the alpha 6- and beta 1-integrin chains was found.

Increased intestinal vitamin D receptor in genetic hypercalciuric rats. A cause of intestinal calcium hyperabsorption

In humans, familial or idiopathic hypercalciuria (IH) is a common cause of hypercalciuria and predisposes to calcium oxalate nephrolithiasis. Intestinal calcium hyperabsorption is a constant feature of IH and may be due to either a vitamin D-independent process in the intestine, a primary overproduction of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], or a defect in renal tubular calcium reabsorption. Selective breeding of spontaneously hypercalciuric male and female Sprague-Dawley rats resulted in offspring with hypercalciuria, increased intestinal calcium absorption, and normal serum 1,25(OH)2D3 levels. The role of the vitamin D receptor (VDR) in the regulation of intestinal calcium absorption was explored in 10th generation male genetic IH rats and normocalciuric controls. Urine calcium excretion was greater in IH rats than controls (2.9 +/- 0.3 vs. 0.7 +/- 0.2 mg/24 h, P < 0.001). IH rat intestine contained twice the abundance of VDR compared with normocalciuric controls (536 +/- 73 vs. 243 +/- 42 nmol/mg protein, P < 0.001), with no difference in the affinity of the receptor for its ligand. Comparable migration of IH and normal intestinal VDR on Western blots and of intestinal VDR mRNA by Northern analysis suggests that the VDR in IH rat intestine is not due to large deletion or addition mutations of the wild-type VDR. IH rat intestine contained greater concentrations of vitamin D-dependent calbindin 9-kD protein. The present studies strongly suggest that increased intestinal VDR number and normal levels of circulating 1,25(OH)2D3 result in increased functional VDR-1,25(OH)2D3 complexes, which exert biological actions in enterocytes to increase intestinal calcium transport. Intestinal calcium hyperabsorption in the IH rat may be the first example of a genetic disorder resulting from a pathologic increase in VDR.

Signal-dependent pleiotropic regulation of lymphocyte proliferation and cytokine production by 1,25-dihydroxyvitamin D3: potent modulation of the hormonal effects by phorbol esters

The influence of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on the proliferation of lymphocytes and on the production of interleukin-6 (IL-6), interleukin-1 beta (IL-1 beta) and interferon-gamma (IFN-gamma) was examined in normal human peripheral blood mononuclear cells (PBMC) activated in vitro either by phytohaemagglutinin (PHA) or by the monoclonal antibody to the T-cell receptor OKT3, or by the combination of each of these two stimuli with phorbol myristate acetate (PMA). 1,25(OH)2D3 inhibited the proliferative response of PBMC to PHA; this effect, however, was abrogated by the addition of PMA (1.6 nM), and it was reversed from inhibition to stimulation by higher concentrations of the phorbol ester. In contrast to the PHA-activated cells, 1,25(OH)2D3 had no effect on the proliferative response of PBMC to OKT3. Further, 1,25(OH)2D3 inhibited the release of IL-6 in cultures of PHA-activated PBMC, whereas it stimulated IL-6 with the addition of PMA in these cultures. In contrast to the PHA-activated cells, 1,25(OH)2D3 increased IL-6 release in OKT3-activated cells. IL-1 beta production was not affected in either PHA- or OKT3-activated cells by the presence of the hormone, but it was stimulated by 1,25(OH)2D3 when PMA was used as a co-stimulus with either PHA or OKT3. Finally, 1,25(OH)2D3 inhibited IFN-gamma in both PHA- and OKT3-activated cells, but these effects were attenuated in the presence of PMA. These findings demonstrate that the in vitro effects of 1,25(OH)2D3 on lymphocyte proliferation and cytokine production by PBMC are pleiotropic, and that such pleiotropism depends upon the mode of PBMC activation and presumably the signals that are generated in response to the specific agents used to activate these cells.