Down-regulation of NF-kappa B protein levels in activated human lymphocytes by 1,25-dihydroxyvitamin D3

Increased NF-kappaB activity in fibroblasts lacking the vitamin D receptor

1,25-Dihydroxyvitamin D [1,25(OH)2D3] is known to have anti-inflammatory activity; however, the molecular mechanism remains poorly defined. Here we show that the nuclear vitamin D receptor (VDR) is directly involved in the regulation of NF-kappaB activation, a pathway essential for inflammatory response. In mouse embryonic fibroblasts (MEFs) derived from VDR-/- mice, the basal level of kappaB inhibitor (IkappaB) alpha protein was markedly decreased compared with VDR+/- MEFs; however, degradation of IkappaBalpha and its phosphorylation in response to TNF-alpha treatment or Salmonella infection were not altered in VDR-/- cells, neither were the levels of IkappaB kinase-alpha and IkappaB kinase-beta proteins. Consistent with IkappaBalpha reduction, p65 accumulation in the nucleus was markedly increased in unstimulated VDR-/- cells. In addition, the physical interaction between VDR and p65 was absent in VDR-/- MEFs, which may free p65 and increase its activity. Consequently, these alterations combined led to a marked increase in nuclear p65 DNA binding and NF-kappaB transcriptional activity; consistently, induction of IL-6 by TNF-alpha or IL-1beta was much more robust in VDR-/- than in VDR+/- cells, indicating that VDR-/- cells are more susceptible to inflammatory stimulation. Therefore, cells lacking VDR appear to be more proinflammatory due to the intrinsic high NF-kappaB activity. The reduction of IkappaBalpha in VDR-/- MEFs may be partially explained by the lack of VDR-mediated stabilization of IkappaBalpha by 1,25(OH)2D3. This is supported by the observation that IkappaBalpha degradation induced by TNF-alpha was inhibited by 1,25(OH)2D3 in VDR+/- cells, but not in VDR-/- cells. Taken together, these data suggest that VDR plays an inhibitory role in the regulation of NF-kappaB activation.

1,25-Dihydroxyvitamin D inhibits lipopolysaccharide-induced immune activation in human endothelial cells

In addition to its well-known role in mineral and skeletal homeostasis, 1,25-dihydroxyvitamin D3 [1,25-(OH)2, D3] regulates the differentiation, growth and function of a broad range of immune system cells, including monocytes, dendritic cells, T and B lymphocytes. Vascular endothelial cells play a major role in the innate immune activation during infections, sepsis and transplant rejection; however, currently there are no data on the effect of 1,25-(OH)2 D3 on microbial antigen-induced endothelial cell activation. Here we show that 1,25-(OH)2 D3 pretreatment of human microvessel endothelial cells (HMEC) inhibited the enteric gram-negative bacterial lipopolysaccharide (LPS) activation of transcription factor NF-kappaB and interleukin (IL)-6, IL-8 and regulated upon activation normal T cell exposed and secreted (RANTES) release. The effect of 1,25-(OH)2 D3 was not due to increased cell death or inhibition of endothelial cell proliferation. 1,25-(OH)2 D3 pretreatment of HMEC did not block MyD88-independent LPS-induced interferon (IFN)-beta promoter activation. 1,25-(OH)2 D3 pretreatment of HMEC did not modulate Toll-like receptor 4 (TLR4) or MD-2 expression. These data suggest that 1,25-(OH)2 D3 may play a role in LPS-induced immune activation of endothelial cells during gram-negative bacterial infections, and a suggest a potential role for 1,25-(OH)2 D3 and its analogues as an adjuvant in the treatment of gram-negative sepsis.

1,25-dihydroxyvitamin D inhibits renal interstitial myofibroblast activation by inducing hepatocyte growth factor expression

BACKGROUND

Vitamin D and its metabolites play an important role in calcium homeostasis, bone remodeling, hormone secretion, cell proliferation, and differentiation. Recent studies also suggest a beneficial role of vitamin D in slowing the progression of chronic renal glomerular diseases. This study investigated the effects and potential mechanism of 1,25-dihydroxyvitamin D(3)[1,25(OH)(2)D(3)] on the regulation of myofibroblast activation from interstitial fibroblast, a critical event in generating alpha-smooth muscle actin (alphaSMA)-positive, matrix-producing effector cells in renal interstitial fibrosis.

METHODS

Normal rat renal interstitial fibroblast cell line (NRK-49F) was used as a model system. Myofibroblast activation was initiated by incubation with transforming growth factor (TGF)-beta1. Expression of alpha-SMA, collagen I, thrombospondin-1, and hepatocyte growth factor (HGF) was assessed by reverse transcription-polymerase chain reaction (RT-PCR), Western blot, and immunostaining, respectively. HGF promoter activity was evaluated by using luciferase reporter assay.

RESULTS

Incubation of rat renal interstitial fibroblasts (NRK-49F) with 1,25(OH)(2)D(3) suppressed TGF-beta1-induced de novo alpha-SMA expression in a dose-dependent manner. 1,25(OH)(2)D(3) also suppressed type I collagen and thrombospondin-1 expression induced by TGF-beta1. Interestingly, 1,25(OH)(2)D(3) induced HGF mRNA expression and protein secretion in renal interstitial fibroblasts. Transfection studies revealed that 1,25(OH)(2)D(3) stimulated HGF gene promoter activity, which was dependent on the presence of vitamin D response element (VDRE). 1,25(OH)(2)D(3) induced the binding of vitamin D receptor to the VDRE in HGF promoter region. Furthermore, 1,25(OH)(2)D(3) was capable of stimulating HGF receptor phosphorylation in renal fibroblasts. Incubation with specific HGF neutralizing antibody largely abolished 1,25(OH)(2)D(3)-mediated suppression of myofibroblast activation.

CONCLUSION

These observations suggest that vitamin D analogue possesses renoprotective activity through suppression of the matrix-producing myofibroblast activation. This action of vitamin D is mediated, at least in part, by up-regulating antifibrotic HGF gene expression in renal interstitial fibroblasts.

Twisting the Th1/Th2 immune response via the retinoid X receptor: Lessons from a genetic approach

The immune system is influenced by environmental factors such as hormones and nutrients. Previous studies have suggested that vitamins A and D influence the process of naive T helper (Th) cell differentiation into Th1 or Th2 cells. Vitamins A and D signal through the retinoid X receptor (RXR), which partners with either the retinoic acid receptor or the vitamin D receptor. Most previous studies into the role of RXR in Th differentiation have been performed in vitro and it was necessary for these to be verified in a physiological environment. However, in vivo study has been hindered since RXRalpha deficient mice are embryonic lethal. Du et al. in this issue of the European Journal of Immunology, overcome this obstacle using "pinkie" mice that harbor a hypomorphic mutation in the Rxralpha gene. The authors report that the mutant mice have an exaggerated Th1 immune response which is attributed to the aberrant antigen-presenting cell and CD4 T cell function. This study confirms previous studies indicating that RXR signaling plays an important role in Th cell differentiation and also provides a valuable tool with which to study the mechanisms and the in vivo functions of this signaling pathway.

1alpha,25-dihydroxyvitamin D3 inhibits prostate cancer cell invasion via modulation of selective proteases

Inhibition of invasion and metastasis has become a new approach for treatment of advanced prostate cancer in which secondary hormone therapy has failed. Accumulating evidence indicates that 1alpha,25-dihydroxyvitamin D3 (1,25-VD) suppresses prostate cancer progression by inhibition of tumor growth and metastasis. However, the detailed mechanisms underlying these effects remain to be determined. Here, we used the in vitro cell invasion assay to demonstrate that 1,25-VD inhibits the invasive ability of human prostate cancer cell lines, LNCaP, PC-3 and DU 145. Three major groups of proteases, the matrix metalloproteinases (MMPs), the plasminogen activators (PAs) and the cathepsins (CPs), that are involved in tumor invasion were then examined for changes in activity and expression after 1,25-VD treatment. We found that 1,25-VD decreased MMP-9 and CPs, but not PAs activities, while it increased the activity of their counterparts, tissue inhibitors of metalloproteinase-1 (TIMP-1) and cathepsin inhibitors. Mechanistic studies showed that 1,25-VD did not suppress MMP-9 expression at the transcriptional level, but reduced its mRNA stability. In addition, 1,25-VD increased AP-1 complexes binding to TIMP-1 promoter, which contributed to the enhancement of TIMP-1 activity, and thus resulted in inhibition of MMP activity and tumor invasion. These findings support the idea that vitamin D-based therapies might be beneficial in the management of advanced prostate cancer, especially among patients who have higher MMP-9 and CPs activities.

Inverse Regulation of the Nuclear Factor-κB Binding to the p53 and Interleukin-8 κB Response Elements in Lesional Psoriatic Skin

Nuclear factor-kappaB (NF-kappaB) is an inducible nuclear transcription factor regulating a range of cellular processes. An imbalance of the DNA binding activity of NF-kappaB may, therefore, be part of the pathophysiological mechanisms in psoriasis. The purpose of this study was to determine the NF-kappaB DNA binding activity in psoriatic skin using three different kappaB sites and to determine how DNA binding activity was modulated by the anti-psoriatic drug calcipotriol. By electrophoretic mobility shift assay, we demonstrated that the NF-kappaB DNA binding to the p53 kappaB site was decreased, whereas the NF-kappaB DNA binding to the interleukin-8 (IL-8) kappaB site was increased in lesional psoriatic skin compared with non-lesional psoriatic skin. No regulation was seen on the NF-kappaB DNA binding to the major histocompatibility complex class I kappaB site. These changes were paralleled by a similar decrease in p53 expression and an increase in IL-8 expression in involved psoriatic skin compared with uninvolved skin as determined by quantitative RT-PCR. The alteration in NF-kappaB DNA binding activity was neither accompanied by any change in the expression of the inhibitor kappaB (IkappaB) kinases, IKKalpha, IKKbeta, and IKKgamma nor in the expression of the NF-kappaB inhibitor proteins, IkappaBalpha and IkappaBbeta. Immunofluorescence analysis revealed that p65 was sequestered in the cytoplasm of keratinocytes, whereas p50 exhibited a cytoplasmic as well as a nuclear localization. Interestingly, this distribution of p50 and p65 was similar in lesional and non-lesional psoriatic skin. Topical application of calcipotriol to lesional psoriatic skin for 4 d resulted in increased NF-kappaB binding to the p53 kappaB site and decreased NF-kappaB binding to the IL-8 kappaB site. Taken together, our data demonstrate that the NF-kappaB DNA binding activity is regulated in a specific manner in psoriatic skin depending on the kappaB sites investigated, and that topical treatment of psoriatic skin normalizes the abnormal NF-kappaB binding activity seen in lesional psoriatic skin.

Effects of 1α,25 dihydroxyvitamin D3 on the expression of HO-1 and GFAP in glial cells of the photothrombotically lesioned cerebral cortex

In ischemic cerebral injuries a cascade of degenerative mechanisms, all participating in the development of oxidative stress, influence the condition of the tissue. The survival of viable tissue affected by secondary injury largely depends on the balance between endogenous protective mechanisms and the ongoing degenerative processes. The inducible enzyme, heme oxygenase-1 metabolizes and thus detoxifies free heme to the powerful endogenous antioxidants biliverdin and bilirubin therefore enhancing neuroprotection. The secosteroid 1alpha,25-dihydroxyvitamin D3 (1,25-D3) is a modulator of the immune system and also exhibits a strong potential for neuroprotection as recently shown in the MCAO model of cerebral ischemia. We studied the effects of 1,25-D3 treatment on heme oxygenase-1 expression following focal cortical ischemia elicited by photothrombosis. Postlesional treatment with 1,25-D3 (4 microg/kg body weight) resulted in a transient, but significant upregulation of glial heme oxygenase-1 immunoreactivity concomitant with a reduction in glial fibrillary acidic protein immunoreactivity in remote cortical regions affected by a secondary spread of injury, whereas the size of the lesion's core remained unaffected. 1,25-D3 did not produce a temporal shift or extension of injury-related heme oxygenase-1 responses, indicating that 1,25-D3 did not prolong ischemia-related heme oxygenase-1 expression. In contrast to glial heme oxygenase-1 upregulation, glial fibrillary acidic protein, a sensitive marker for reactive gliosis, was significantly reduced. These findings support an additional protective action of 1,25-D3 at the cellular level in regions affected by secondary injury-related responses.

1,25-dihydroxycholecalciferol inhibits apoptosis in C3H10T1/2 murine fibroblast cells through activation of nuclear factor kappaB

1,25-dihydroxycholecalciferol [1,25(OH)(2)D(3)] is important in the regulation of cell growth, differentiation, and apoptosis. Previous results from our laboratory demonstrate that 1,25(OH)(2)D(3) inhibits vitamin E succinate (VES) mediated apoptosis in untransformed C3H10T1/2 mouse fibroblast cells. The current work investigated cell survival signaling pathways that may be activated by 1,25(OH)(2)D(3), leading to protection from apoptosis. Results showed that nuclear factor kappaB (NFkappaB) transcriptional activity was significantly increased 1.8-fold over vehicle controls by 1,25(OH)(2)D(3) after 4 h of treatment. Protein kinase B/AKT, a downstream effector of phosphoinositide 3-kinase (PI3K), was activated 4-fold and 8-fold at 2 and 4 h, respectively, after treatment with 1,25(OH)(2)D(3). Pretreatment with two PI3K inhibitors, LY294002 and wortmannin, abolished the activation of NFkappaB by 1,25(OH)(2)D(3), suggesting that this pathway is essential for NFkappaB transcriptional activation. Additionally, the use of a p-21 activated kinase (PAK1) inhibitory construct (PAK(R299)) demonstrated that PAK1 was also required for NFkappaB transcriptional activation by 1,25(OH)(2)D(3). Inhibition of NFkappaB activity with transfection of the NFkappaB inhibitory construct (IkappaB(Ala32)) abolished the protective effect of 1,25(OH)(2)D(3) on VES-mediated apoptosis. In summary, NFkappaB transcriptional activation was essential to 1,25(OH)(2)D(3) protection from VES-mediated apoptosis and 1,25(OH)(2)D(3) regulated NFkappaB activity through PI3K and PAK pathways.

A vitamin D analog down-regulates proinflammatory chemokine production by pancreatic islets inhibiting T cell recruitment and type 1 diabetes development

Type 1 diabetes (T1D) is an autoimmune disease characterized by leukocyte infiltration into the pancreatic islets, and we have previously shown that treatment of adult NOD mice with a vitamin D analog arrests the progression of insulitis, blocks Th1 cell infiltration into the pancreas, and markedly reduces T1D development, suggesting inhibition of chemokine production by islet cells. In this study, we show that all TLRs are expressed by mouse and human islet cells, and their engagement by pathogen-derived ligands markedly enhances proinflammatory chemokine production. The vitamin D analog significantly down-regulates in vitro and in vivo proinflammatory chemokine production by islet cells, inhibiting T cell recruitment into the pancreatic islets and T1D development. The inhibition of islet chemokine production in vivo persists after restimulation with TLR ligands and is associated with up-regulation of IkappaBalpha transcription, an inhibitor of NF-kappaB and with arrest of NF-kappaBp65 nuclear translocation, highlighting a novel mechanism of action exerted by vitamin D receptor ligands potentially relevant for the treatment of T1D and other autoimmune diseases.

Vitamin D and its analogs as regulators of immune activation and antigen presentation

It has been a little more than 20 years since the first appreciation that the biologically active hormonal form of the secosteroid vitamin D-classically categorized as a regulator of calcium/phosphorous metabolism and bone mineralization-can exert effects on cells of the immune system. Since then a substantial literature has accumulated to suggest that these effects are exerted on multiple immune cell types, are predominantly suppressive at pharmacologic levels, and are potent enough to have true therapeutic potential in the management or prevention of immune-mediated diseases. Less clear at present, however, are the physiological roles played by the vitamin D endocrine system in the regulation of normal and abnormal immune responses. In this review, an appraisal of the current understanding of vitamin D-mediated immune regulation is presented that emphasizes progress towards its clinical application as well as the manner in which emerging models of normal immune function may facilitate a more complete understanding of its physiologic significance.

Direct transcriptional regulation of RelB by 1alpha,25-dihydroxyvitamin D3 and its analogs: physiologic and therapeutic implications for dendritic cell function

The nuclear factor-kappaB (NF-kappaB) protein RelB plays a unique role in dendritic cell (DC) function and, as such, is an important regulator of antigen presentation and immune regulation. In this study, inhibition of RelB expression in DCs exposed to an analog of the active form of vitamin D3 (1alpha,25-dihydroxyvitamin D3 (1alpha,25-(OH)2D3)) was observed and shown to be mediated by the vitamin D receptor (VDR). Potential vitamin D response elements were identified within promoter regions of human and mouse relB genes. In gel shift experiments, these motifs specifically bound VDR.retinoid X receptor-alpha complexes. Reporter assays confirmed that transcriptional activity of human and mouse relB promoters was inhibited by 1alpha,25-(OH)2D3 agonists in a DC-derived cell line. The inhibition was abolished by mutagenesis of the putative vitamin D response elements and was enhanced by overexpression of VDR. Mutagenesis of NF-kappaB response elements within the relB promoter did not affect the magnitude of 1alpha,25-(OH)2D3 analog-mediated inhibition, ruling out an indirect effect on NF-kappaB signaling. Glucocorticoid caused additional inhibition of relB promoter activity when combined with the 1alpha,25-(OH)2D3 analog. This effect was dependent on the integrity of the NF-kappaB response elements, suggesting separate regulatory mechanisms for the two steroid pathways on this promoter. We conclude that relB is a direct target for 1alpha,25-(OH)2D3-mediated negative transcriptional regulation via binding of VDR.retinoid X receptor-alpha to discrete DNA motifs. This mechanism has important implications for the inhibitory effect of 1alpha,25-(OH)2D3 on DC maturation and for the potential immunotherapeutic use of 1alpha,25-(OH)2D3 analogs alone or combined with other agents.

Generation of antigen-specific, interleukin-10-producing T-cells using dendritic cell stimulation and steroid hormone conditioning

The mechanisms by which regulatory T-cell populations are generated in vivo are poorly understood. Nonetheless, the possibility of generating T-cells with regulatory capacity ex vivo using pharmacologic agents or modified antigen presenting cells has been raised by a number of recent studies. In this study, the effect of combined glucocorticoid and 1,25 dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) agonists on dendritic cell (DC)-stimulated, antigen-specific CD4(+ve) T-cells was investigated. Following multiple rounds of DC-mediated stimulation in the presence of dexamethasone and an analog of 1,25(OH)(2)D(3), the resulting T-cells were characterized by: (a) enhanced IL-10 secretion upon subsequent antigen exposure, (b) attenuated secretion of IL-2 and interferon gamma, (c) lack of induction of Th2 (IL-4-secreting) phenotype, (d) significant antigen-specific suppression of primary T-cell proliferation and (e) retention of the ability to survive and proliferate to antigen in vivo. These IL-10-secreting T-cells were termed 'steroid hormone-conditioned T-cells'. When a co-stimulation-deficient population of DCs was employed for the in vitro, steroid hormone-conditioned stimulations, two additional effects were observed: (a) a further skewing towards antigen-specific IL-10 production and (b) enhanced activation-induced up-regulation of the inhibitory receptor CTLA-4 (CD152). It was concluded that DC-mediated generation of antigen-specific T-cells in vitro can be modulated to promote an IL-10-secreting, regulatory T-cell population using glucocorticoid and 1,25(OH)(2)D(3) agonists. This T-cell phenotype can be further enhanced by the use of co-stimulation-deficient DCs.

Treatment of experimental autoimmune encephalomyelitis in rat by 1,25-dihydroxyvitamin D3 leads to early effects within the central nervous system

We report here that curative treatment of the multiple sclerosis paradigm, chronic relapsing experimental autoimmune encephalomyelitis (EAE) of the Lewis rat, by 1,25-dihydroxyvitamin D(3 )(1,25-D3) leads to a rapid clinical improvement accompanied by an inhibition of CD4, MHC class II and type II nitric oxide synthase (NOS II) expression in the posterior areas of the central nervous system (CNS). In contrast, the hormone has no effect on transforming growth factor-beta1 transcripts. Computer analysis of the NOS II promoter, expressed by microglia and astrocytes, reveals consensus sequence for vitamin D receptor binding, emphasizing the idea that 1,25-D3 may regulate some aspects of EAE by acting directly on CNS constituent cells. We also demonstrate that vitamin D deprivation leads to minimal effects on the kinetic profile of EAE accompanied by a moderate exacerbation of the clinical symptoms. Interestingly, curative treatment of vitamin D-deprived rats with a non-toxic-1,25-D3 analogue (MC1288) strongly inhibited EAE symptoms, thus promulgating the potential interest of such compounds in the management of multiple sclerosis.

Liver X receptor activators display anti-inflammatory activity in irritant and allergic contact dermatitis models: liver-X-receptor-specific inhibition of inflammation and primary cytokine production

Activators of liver X receptors (LXR) stimulate epidermal differentiation and development, but inhibit keratinocyte proliferation. In this study, the anti-inflammatory effects of two oxysterols, 22(R)-hydroxy-cholesterol (22ROH) and 25-hydroxycholesterol (25OH), and a nonsterol activator of LXR, GW3965, were examined utilizing models of irritant and allergic contact dermatitis. Irritant dermatitis was induced by applying phorbol 12-myristate-13-acetate (TPA) to the surface of the ears of CD1 mice, followed by treatment with 22ROH, 25OH, GW3965, or vehicle alone. Whereas TPA treatment alone induced an approximately 2-fold increase in ear weight and thickness, 22ROH, 25OH, or GW3965 markedly suppressed the increase (greater than 50% decrease), and to an extent comparable to that observed with 0.05% clobetasol treatment. Histology also revealed a marked decrease in TPA-induced cutaneous inflammation in oxysterol-treated animals. As topical treatment with cholesterol did not reduce the TPA-induced inflammation, and the nonsterol LXR activator (GW3965) inhibited inflammation, the anti-inflammatory effects of oxysterols cannot be ascribed to a nonspecific sterol effect. In addition, 22ROH did not reduce inflammation in LXRbeta-/- or LXRalphabeta-/- animals, indicating that LXRbeta is required for this anti-inflammatory effect. 22ROH also caused a partial reduction in ear thickness in LXRalpha-/- animals, however (approximately 50% of that observed in wild-type mice), suggesting that this receptor also mediates the anti-inflammatory effects of oxysterols. Both ear thickness and weight increased (approximately 1.5-fold) in the oxazolone-induced allergic dermatitis model, and 22ROH and GW3965 reduced inflammation by approximately 50% and approximately 30%, respectively. Finally, immunohistochemistry demonstrated an inhibition in the production of the pro-inflammatory cytokines interleukin-1alpha and tumor necrosis factor alpha in the oxysterol-treated sites from both TPA- and oxazolone-treated animals. These studies demonstrate that activators of LXR display potent anti-inflammatory activity in both irritant and allergic contact models of dermatitis, requiring the participation of both LXRalpha and LXRbeta. LXR activators could provide a new class of therapeutic agents for the treatment of cutaneous inflammatory disorders.

Distinctive dendritic cell modulation by vitamin D3 and glucocorticoid pathways

Dendritic cell (DC) maturation plays a central role in regulating immunity. We show that glucocorticoid and 1alpha,25(OH)(2)D(3) agonists modulate DCs via distinct and additive signaling pathways. Phenotypic and functional indices were examined in DCs treated with dexamethasone (DEX) and/or a 1alpha,25(OH)(2)D(3) analog (D(3) analog). DEX potently attenuated pro-inflammatory cytokines and chemokines but had modest, reversible effects on T-cell stimulatory capacity. D(3) analog produced significantly greater inhibition of T-cell stimulation in vitro and in vivo and, unlike DEX, increased expression of the chemokines MCP-1 and MIP-1alpha. Both DEX and D(3) analog were associated with reduced expression of the NF-kappaB proteins c-Rel and Rel B but not Rel A. Combined DEX and D(3) analog treatment of DCs resulted in significant additive inhibition of pro-inflammatory cytokines, T-cell stimulation, chemokines, chemokine receptors, and NF-kappaB components. Additive inhibition was most striking for RANTES, CCR5, CCR7, and Rel B. The combined effects of the two hormonal pathways on DCs have unique immunomodulatory potential.

In vitro generation of interleukin 10-producing regulatory CD4(+) T cells is induced by immunosuppressive drugs and inhibited by T helper type 1 (Th1)- and Th2-inducing cytokines

We show that a combination of the immunosuppressive drugs, vitamin D3 and Dexamethasone, induced human and mouse naive CD4(+) T cells to differentiate in vitro into regulatory T cells. In contrast to the previously described in vitro derived CD4(+) T cells, these cells produced only interleukin (IL)-10, but no IL-5 and interferon (IFN)-gamma, and furthermore retained strong proliferative capacity. The development of these IL-10-producing cells was enhanced by neutralization of the T helper type 1 (Th1)- and Th2-inducing cytokines IL-4, IL-12, and IFN-gamma. These immunosuppressive drugs also induced the development of IL-10-producing T cells in the absence of antigen-presenting cells, with IL-10 acting as a positive autocrine factor for these T cells. Furthermore, nuclear factor (NF)-kappaB and activator protein (AP)-1 activities were inhibited in the IL-10-producing cells described here as well as key transcription factors involved in Th1 and Th2 subset differentiation. The regulatory function of these in vitro generated IL-10-producing T cells was demonstrated by their ability to prevent central nervous system inflammation, when targeted to the site of inflammation, and this function was shown to be IL-10 dependent. Generating homogeneous populations of IL-10-producing T cells in vitro will thus facilitate the use of regulatory T cells in immunotherapy.

Negative regulation of CD95 ligand gene expression by vitamin D3 in T lymphocytes

Fas (APO-1/CD95) and its ligand (FasL/CD95L) are cell surface proteins whose interaction activates apoptosis of Fas-expressing targets. In T lymphocytes, the Fas/FasL system regulates activation-induced cell death, a fundamental mechanism for negative selection of immature T cells in the thymus and for maintenance of peripheral tolerance. Aberrant expression of Fas and FasL has also been implicated in diseases in which the lymphocyte homeostasis is compromised, and several studies have described the pathogenic functions of Fas and FasL in vivo, particularly in the induction/regulation of organ-specific autoimmune diseases. The 1,25(OH)(2)D(3) is a secosteroid hormone that activates the nuclear receptor vitamin D(3) receptor (VDR), whose immunosuppressive activities have been well studied in different models of autoimmune disease and in experimental organ transplantation. We and others have recently described the molecular mechanisms responsible for the negative regulation of the IFN-gamma and IL-12 genes by 1,25(OH)(2)D(3) in activated T lymphocytes and macrophages/dendritic cells. In this study, we describe the effect of 1,25(OH)(2)D(3) on the activation of the fasL gene in T lymphocytes. We show that 1,25(OH)(2)D(3) inhibits activation-induced cell death, fasL mRNA expression, and that 1,25(OH)(2)D(3)-activated VDR represses fasL promoter activity by a mechanism dependent on the presence of a functional VDR DNA-binding domain and ligand-dependent transcriptional activation domain (AF-2). Moreover, we identified a minimal region of the promoter containing the transcription start site and a noncanonical c-Myc-binding element, which mediates this repression. These results place FasL as a novel target for the immunoregulatory activities of 1,25(OH)(2)D(3), and confirm the interest for a possible pharmacological use of this molecule and its derivatives.

1alpha,25-Dihydroxyvitamin d3 has a direct effect on naive CD4(+) T cells to enhance the development of Th2 cells

1alpha,25-Dihydroxyvitamin D3 (vitD3) is an immunoregulatory hormone with beneficial effects on Th1 mediated autoimmune diseases. Although the inhibitory effects of vitD3 on macrophages and dendritic cells are well documented, any direct effects of vitD3 on Th cell development are not clearly defined. Using CD4(+)Mel14(+) T cells derived from mice on a BALB/c and a C57BL/6 genetic background we examined the effect of vitD3 on Th cell development. We demonstrated that vitD3 affects Th cell polarization by inhibiting Th1 (IFN-gamma production) and augmenting Th2 cell development (IL-4, IL-5, and IL-10 production). These effects were observed in cultures driven with splenic APC and Ag, as well as with anti-CD3 and anti-CD28 alone, indicating that CD4(+) cells can also be direct targets for vitD3. The enhanced Th2 development by vitD3 was found in both BALB/c and C57BL/6 mice. An increased expression of the Th2-specific transcription factors GATA-3 and c-maf correlated with the increased production of Th2 cytokines after vitD3 treatment. The vitD3-induced effects were largely mediated via IL-4, because neutralization of IL-4 almost completely abrogated the augmented Th2 cell development after vitD3 treatment. These findings suggest that vitD3 acts directly on Th cells and can, in the absence of APC, enhance the development of a Th2 phenotype and augment the expression of the transcription factors c-maf and GATA-3. Our findings suggest that the beneficial effects of vitD3 in autoimmune diseases and transplantation operate through prevention of strong Th1 responses via the action on the APC, while simultaneously directly acting on the T cell to enhance Th2 cell development.

Sensitization to TNF-induced apoptosis by 1,25-dihydroxy vitamin D(3) involves up-regulation of the TNF receptor 1 and cathepsin B

The active form of vitamin D(3), 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), induces caspase-independent apoptosis in MCF-7 and T47D breast cancer cells. Before the appearance of apoptotic cells at Day 4 after the addition of 1,25(OH)(2)D(3), the MCF-7 cells are sensitized to the caspase-mediated apoptosis induced by TNF. We studied the mechanism underlying the cross talk between these 2 distinct death pathways in MCF-7 and T47D cells. Whereas 1,25(OH)(2)D(3) pre-treatment enhanced TNF-induced apoptosis of TNF sensitive MCF-7 cells, it failed to render TNF resistant T47D cells sensitive to this cytokine. Opposing to an earlier report suggesting that cytosolic phospholipase A(2) (cPLA(2)) mediates the 1,25(OH)(2)D(3)-induced sensitization to TNF, we could not detect any cPLA(2) protein in MCF-7 cells and its overexpression had no effect on cellular sensitivity to 1,25(OH)(2)D(3) or the combination with TNF. The sensitization of MCF-7 cells to TNF-induced apoptosis by pre-treatment with 1,25(OH)(2)D(3) may instead be partially explained by an increased surface expression of the TNF receptor 1 (TNF-R1). In line with this, not only the TNF-induced activation of caspases and apoptosis but also that of NF-kappaB was enhanced by 1,25(OH)(2)D(3) pre-treatment. Furthermore, 1,25(OH)(2)D(3) enhanced TNF-induced NF-kappaB activation in T47D cells suggesting that it potentiates TNF signaling in general. Interestingly, the lysosomal protease cathepsin B, which expression is up-regulated by 1,25(OH)(2)D(3), was released from the lysosomes upon TNF treatment, and inhibition of its activity rescued 1,25(OH)(2)D(3) treated MCF-7 cells from TNF-induced apoptosis. In conclusion, 1,25(OH)(2)D(3) may enhance TNF-induced apoptosis by increasing the expression of both the TNF-R1 and cathepsin B.

Mildly oxidized low-density lipoproteins decrease early production of interleukin 2 and nuclear factor kappaB binding to DNA in activated T-lymphocytes

Activated T-lymphocytes are found early in atherosclerosis lesions, but little is known about their role. Oxidized low-density lipoproteins (oxLDLs) are considered to be involved in the pathogenesis of the lesions, and we have previously demonstrated that oxLDLs inhibit not only interleukin (IL)-2-receptor expression on the surface of in vitro-activated T-lymphocytes but also their proliferation. We have now investigated the effect of oxLDLs on blast differentiation, on IL-2 synthesis and on the activation of the nuclear factor kappaB (NF-kappaB) system in activated lymphocytes. Mildly oxLDLs (50 and 100 microgram/ml) decreased the number of lymphoblasts and the level of IL-2 concentration in the culture supernatants after activation of lymphocytes by phytohaemagglutinin and PMA+ionomycin. The inhibition of IL-2 production was observed in the CD3(+) T-lymphocyte cytoplasm as early as 4 h after activation by PMA+ionomycin. The study of NF-kappaB showed that oxLDLs led to a decrease of activation-induced p65/p50 NF-kappaB heterodimer binding to DNA, whereas the presence of the constitutive nuclear form of p50 dimer was unchanged. This was correlated with an unchanged level of the active form of the cytosolic inhibitor protein IkappaB-alpha. Taken together, these observations suggest that the immunosuppressive effect of oxLDLs might operate via a dysregulation of the T-lymphocyte activation mechanisms.

1Alpha,25-dihydroxyvitamin D3 decreases DNA binding of nuclear factor-kappaB in human fibroblasts

1Alpha,25-dihydroxyvitamin D3 (1,25-(OH)2-D3), the active metabolite of vitamin D, can inhibit NF-kappaB activity in human MRC-5 fibroblasts, targeting DNA binding of NF-kappaB but not translocation of its subunits p50 and p65. The partial inhibition of NF-kappaB DNA binding by 1,25-(OH)2-D3 is dependent on de novo protein synthesis, suggesting that 1,25-(OH)2-D3 may regulate expression of cellular factors which contribute to reduced DNA binding of NF-kappaB. Although NF-kappaB binding is decreased by 1,25-(OH)2-D3 in MRC-5 cells, IL-8 and IL-6 mRNA levels are only moderately downregulated, demonstrating that inhibition of NF-kappaB DNA binding alone is not sufficient for optimal downregulation of these genes.

1,25-Dihydroxyvitamin D3 upregulates functional CXCR4 human immunodeficiency virus type 1 coreceptors in U937 minus clones: NF-kappaB-independent enhancement of viral replication

U937 cell clones which sustain efficient or poor replication of human immunodeficiency virus type 1 (HIV-1) (referred to herein as plus clones and minus clones, respectively) have been previously described. 1,25-Dihydroxyvitamin D3 (vitamin D3) potently induced HIV-1 replication and proviral DNA accumulation in minus clones but not in plus clones. Vitamin D3 did not induce NF-kappaB activation but selectively upregulated CXCR4 expression in minus clones. The CXCR4 ligand stromal-cell derived factor-1 induced Ca2+ fluxes and inhibited both constitutive and vitamin D3-enhanced HIV replication in minus clones.

Vitamin D3: a transcriptional modulator of the interferon-gamma gene

1Alpha,25-dihydroxyvitamin D3 [1,25-(OH)2D3] exerts several effects on the immune system, by regulating lymphocyte proliferation, differentiation of monocytes and secretion of cytokines as IL-2, granulocyte-macrophage colony-stimulating factor and IFN-gamma in T cells. Here, we analyze the effect of 1,25-(OH)2D3 on IFN-gamma gene transcription. Transient transfection assays in Jurkat T cells indicate that activation of the IFN-gamma promoter is down-regulated by 1,25-(OH)2D3. This effect is enhanced by retinoid X receptor (RXR), and a functional vitamin D3 receptor (VDR) DNA-binding domain in necessary for repression. We delineated two important promoter regions mainly involved in this modulation. The first of these is situated at the level of a promoter-silencer previously characterized and binds the heterodimer VDR-RXR in electrophoretic mobility shift assay. Residual negative regulation was also detected at the level of the promoter fragment -108 to +64 bp from the transcription start site and, surprisingly, the activity of the IFN-gamma enhancer from -108 to -36 bp in the context of a heterologous promoter was not affected by 1,25-(OH)2D3. Moreover, binding activity for VDR-RXR has been detected in the IFN-gamma minimal promoter, suggesting a possible mechanism of interference with transcription initiation/progression. The overall data indicate that direct modulation of the IFN-gamma promoter activity is one of the possible mechanisms involved in the repressive effect of 1,25-(OH)2D3 on IFN-gamma gene expression.

Decreased IL-12 production and Th1 cell development by acetyl salicylic acid-mediated inhibition of NF-kappaB

IL-12 is a 75-kDa heterodimeric cytokine composed of two covalently linked p35 and p40 chains. This pro-inflammatory cytokine plays a prominent role in the development of Th1 cell-mediated immune responses. Th1 cell-mediated immune responses have been implicated in the pathogenesis of chronic inflammatory autoimmune diseases. Thus, IL-12 appears to be a critical factor in the generation and maintenance of chronic inflammatory conditions. In this study, we investigated the effects of a commonly prescribed anti-inflammatory drug, acetyl salicylic acid (ASA), on IL-12 production and Th1 cell development. ASA was found to inhibit secretion of the IL-12 heterodimer as well as p40 monomer by human monocytic cells. This was associated with the down-regulation of IL-12p40 mRNA expression. Analysis of the regulation of the p40 gene promoter revealed that ASA inhibited NF-kappaB activation and binding to the p40-kappaB site in the p40 promoter, leading to transcriptional repression of the p40 gene. Addition of ASA to an in vitro T helper cell differentiation system, at concentrations compatible with plasma levels reached during anti-inflammatory therapy, resulted in reduced development of Th1 cells. These results suggest that the inhibition of NF-kappaB activation by ASA leads to down-regulation of IL-12 production and inhibition of Th1 cell development.

Inhibition of IL-12 production by 1,25-dihydroxyvitamin D3. Involvement of NF-kappaB downregulation in transcriptional repression of the p40 gene

Interleukin 12 (IL-12), produced by myelomonocytic cells, plays a pivotal role in the development of T helper 1 (Th1) cells, which are involved in the pathogenesis of chronic inflammatory autoimmune disorders. 1,25-Dihydroxyvitamin D3 [1,25(OH)2D3] inhibits IL-12 production by activated macrophages and dendritic cells, thus providing a novel interpretation to its immunosuppressive properties. 1,25(OH)2D3 significantly inhibits mRNA expression for both IL-12 p35 and p40 subunits acting at the transcriptional level. The effect of 1,25(OH)2D3 on p40 promoter activation was analyzed by cotransfecting monocytic RAW264.7 cells with p40 promoter/reporter constructs and expression vectors for vitamin D3 receptor (VDR) and/or retinoid X receptor (RXRalpha). We observed transcriptional repression of the p40 gene by 1,25(OH)2D3, which required coexpression of VDR with RXR and an intact VDR DNA-binding domain. The repressive effect maps to a region in the p40 promoter containing a binding site for NF-kappaB (p40-kappaB). Deletion of the p40-kappaB site abrogates part of the inhibitory effect on the p40 promoter, confirming the functional relevance of this site. Activation of monocytic THP-1 cells in the presence of 1,25(OH)2D3 results in reduced binding to the p40-kappaB site. Thus, 1,25(OH)2D3 may negatively regulate IL-12 production by downregulation of NF-kappaB activation and binding to the p40-kappaB sequence.

Nuclear Factor of Activated T Cells (NFAT) as a Molecular Target for 1α,25-Dihydroxyvitamin D3-Mediated Effects

The molecular basis of the immunomodulatory properties of 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3) remains elusive. We demonstrate here that 1α,25(OH)2D3-mediated suppressive effects on the inducible expression of cytokine genes in human T cells may, in part, be due to diminished activity of the transcription factor NFAT. The vitamin D3 receptor (VDR) and its heterodimeric partner retinoid X receptor α (RXRα) specifically bound to the distal NFAT site in the human IL-2 promoter, and this binding was abolished by mutating unique regions in the NFAT oligonucleotide. In vitro inhibition of NFAT complex formation was noted when VDR-RXRα heterodimers were added to DNA binding reactions containing nuclear extracts from activated B or T cells, whereas in vitro NFκB complex formation was not significantly influenced. Furthermore, 1α,25(OH)2D3 treatment of activated T cells resulted in decreased formation of NFAT complexes detected upon incubation of nuclear extracts from these cells with 32P-labeled probe. Transient expression of both VDR and RXRα, but not of a single component, was capable of inhibiting expression of a NFAT-driven reporter gene in stimulated Jurkat cells in a ligand-dependent manner. These results suggest that NFAT plays a crucial role in 1α,25(OH)2D3-mediated immunosuppressive activity.

1alpha,25-dihydroxyvitamin D3 and a variety of its natural metabolites transcriptionally repress nuclear-factor-kappaB-mediated interleukin-8 gene expression

Regulation of interleukin-8 (IL-8) gene transcription occurs mainly through the sequences -94 to -71 of the 5'-flanking region of the IL-8 gene, involving the transcription factors nuclear factor for interleukin-6 (NF-IL-6) and nuclear factor kappaB (NF-kappaB). The human melanoma cell line A3 was derived from G-361 cells by stable transfection with an IL-8 promoter-luciferase construct containing these sequences. 1alpha,25-Dihydroxyvitamin D3 (calcitriol) repressed IL-8 promoter activity induced by tumor necrosis factor-alpha (TNF-alpha) by 50%, compared to 30% inhibition using dexamethasone, an effect consistent with its effect on TNF-alpha-induced IL-8 release and IL-8 mRNA levels. A variety of vitamin D metabolites caused the same repressive effect on IL-8 promoter activation as calcitriol. However, only those metabolites which were able to transactivate a classical vitamin D response element had the ability to repress IL-8 promoter activation, suggesting that this repression is mediated via vitamin D receptor (VDR). Furthermore, overexpression of VDR in the parental G-361 cell line enhanced the repressive effect of calcitriol on activation of the IL-8 promoter by either TNF-alpha stimulation or overexpression of the NF-kappaB subunit p65. Electrophoretic mobility shift assays using nuclear extracts from A3 cells showed that calcitriol decreased the abundance of nuclear factors bound to the NF-kappaB binding site of the IL-8 promoter and this reduced binding of NF-kappaB proteins presumably contributes to its inhibitory action.

Activation of the Janus kinase/STAT (signal transducer and activator of transcription) signal transduction pathway by interleukin-6-type cytokines promotes osteoblast differentiation

We have previously established that stromal/osteoblastic cells collectively express receptors for all members of the cytokine subfamily that share the gp130 signal transducer and that different receptor repertoires may be expressed at different stages of differentiation of this lineage. We have now used human (MG-63) and murine (MC3T3-E1) osteoblastic cell lines as well as primary murine calvaria cells to test the hypothesis that these receptors mediate effects of the cytokines on the biology of osteoblasts. We report that as in other cell types, all of the osteoblastic cell models responded to interleukin-6 (IL-6)-type cytokines with activation of both the JAK/STAT (Janus kinase/signal transducer and activator of transcription) and the mitogen-activated protein kinase (MAPK) pathways. In addition, IL-6-type cytokines stimulated alkaline phosphatase activity and osteocalcin expression and inhibited (MG-63), stimulated (MC3T3-E1), or had no effect (calvaria cells) on the rate of cell proliferation. The ability of a given cell type to respond to a particular member of this family of cytokines was strictly dependent on the presence of the corresponding ligand-binding subunit (alpha) of the cytokine receptor, and the magnitude of all the effects was closely correlated with the concentration of this subunit. The relative contribution of the JAK/STAT and MAPK pathways to the biological effects of the cytokines was evaluated using kinase inhibitors. Cytokine-mediated modulation of cell proliferation as well as stimulation of alkaline phosphatase activity were abrogated by tyrosine kinase inhibitors as well as a threonine/serine kinase inhibitor, but were only minimally affected by a specific inhibitor of MAPK phosphorylation. These results demonstrate that IL-6-type cytokines, besides their osteoclastogenic properties, promote differentiation of committed osteoblastic cells toward a more mature phenotype and that this action is mediated primarily via the activation of the JAK/STAT pathway.