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PubMed2005

Immunosteroid as a regulator for Th1/Th2 balance: its possible role in autoimmune diseases.

Immune balance controlled by Th1 and Th2 cells is critical for the protection of host from pathogenic invasion while its imbalance becomes the cause of various immune disorders including autoimmune diseases. Cytokines, such as IL-12 and IL-4, are critical factor to drive the differentiation of naïve CD4(+) T cells to Th1 or Th2 cells. In addition to cytokines, steroid hormones have been demonstrated to affect on the control of Th1/Th2 balance and the onset of autoimmune diseases. Here, we will propose a new concept that immunosteroid, which is designated as a steroid produced by immunoregulatory cells, also play a critical role for regulation of Th1/Th2 balance. First example of immunosteroid is Th2-dependently produced progesterone. Th2 cells, but not Th1 cells expressed P450scc and 20alpha-HSD and produced progesterone from 22R-hydroxycholesterol in cooperation with 3beta-HSD-expressing mouse fibroblasts. Th2-dependently produced progesterone induced apoptotic cell death of Th1 cells and inhibited the differentiation of Th1 cells. While Th2 cells were escaped from toxic effect of progesterone by metabolizing it to non-toxic 20alpha-hydroxyprogesterone with 20alpha-HSD. Second example of immunosteroid is dendritic cell (DC)-dependently produced 1alpha,25-dihydroxyvitamin D3 [1,25(OH)(2)D] secosteroid hormone, which has been demonstrated to inhibit autoimmune diseases. We found that 25-hydroxyvitamin D3 1alpha-hydroxylase, which metabolize 25-hydroxyvitamin D3 (inactive form) to 1,25(OH)(2)D was expressed in Th2-cytokine induced bone marrow-derived DC2 but not Th1-cytokine induced DC1. Moreover, 1,25(OH)(2)D was significantly inhibited DC1-induced type1 immunity. Thus, we initially demonstrated the critical role of immunosteroids in the control of Th1/Th2 balance influencing on the onset of autoimmune diseases. Therefore, it will be an important issue to investigate the possible role of immunosteroids for the regulation of autoimmune diseases.

Animals↗
PubMed2002

Vitamin D as immunomodulatory therapy for kidney transplantation.

Vitamin D (1alpha,25-dihydroxyvitamin D(3) [1alpha,25-(OH)(2)D(3)]) has been studied in the past for its immunosuppressive properties, and, in that context, it may also have potential utility as an immunomodulatory agent for transplantation. A number of studies have demonstrated that 1alpha,25-(OH)(2)D(3) or its analogs regulate immune cell proliferation, differentiation, and responsiveness. A burgeoning number of studies have also explored using 1alpha,25-(OH)(2)D(3) and its analogs directly as therapy in animal models of kidney transplantation with success in prolonging allograft function and preventing acute rejection. Some of these in vivo effects may well be caused by alterations in immune cell function, but it is also possible that exogenous 1alpha,25-(OH)(2)D(3) and its analogs are altering the intragraft milieu as well, specifically through changes in the TGF-beta signaling cascade. Such provocative data and the availability of newer 1alpha,25-(OH)(2)D(3) analogs that may limit side effects (e.g. hypercalcemia) have created interest in examining this secosteroid clinically in kidney transplantation.

Adjuvants, Immunologic↗
PubMed1988

Human melanocytes as a target tissue for hormones: in vitro studies with 1 alpha-25, dihydroxyvitamin D3, alpha-melanocyte stimulating hormone, and beta-estradiol.

Clinical evidence exists which suggests that normal pigment cell (melanocyte) function is subject to hormonal influences, but the nature of these interactions at a cellular level is poorly understood. We have investigated the effects of the vitamin D-derived secosteroid hormone 1 alpha-25, dihydroxyvitamin D3 (1,25(OH)2D3), the pituitary-derived peptide alpha-melanocyte stimulating hormone (alpha-MSH), and the sex steroid beta-estradiol on melanocytes cultured from normal human foreskin. Human melanocytes specifically internalized 1,25(OH)2D3 with high affinity (Kd 0.5-0.8 nM). Incubation with 1,25(OH)2D3 (10(-9) M) for 48 h resulted in a 100% increase in 25-hydroxyvitamin D3-24-hydroxylase activity and a 50% increase in tyrosinase activity. There was no significant effect of 1,25(OH)2D3 on intracellular cyclic adenosine monophosphate (cAMP). In contrast to 1,25(OH)2D3, alpha-MSH at a concentration of 5 X 10(-7) M caused a sevenfold increase in intracellular cAMP after 12 min but only a modest increase (less than 20%) in melanocyte tyrosinase activity after 48 h. Incubation with beta-estradiol for 24 h caused a dose-dependent increase in tyrosinase activity. The maximal response varied from 145%-213% of basal activity depending on the donor source. These results indicate that melanocytes from normal human foreskin in culture have the capacity to respond directly to several hormones. They also suggest that these cells form a useful model to study the effect of various hormones on pigment cell function.

Calcitriol↗
PubMed2003

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.

Animals↗
PubMed2000

Immunochemical studies on the putative plasmalemmal receptor for 1, 25(OH)(2)D(3). I. Chick intestine.

Antisera were raised against the NH(2)-terminus of the putative basal lateral membrane (BLM) receptor for 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3); BLM-VDR]. In Western analyses of BLM proteins, antibody (Ab) 099 was monospecific for a 64.5-kDa band. A protein of 64.5 kDa was also labeled by the affinity ligand [(14)C]1, 25(OH)(2)D(3)-bromoacetate; label was diminished in the presence of excess unlabeled secosteroid. The monoclonal antibody against the nuclear VDR (9A7) failed to detect an appropriate band in BLM fractions. Preincubation of isolated intestinal cells with Ab 099, but not 9A7, affected the following two 1,25(OH)(2)D(3)-mediated signal transduction events: augmented intracellular calcium and protein kinase C activity. Subcellular distribution of Ab 099 reactivity by Western analyses and fluorescence microscopy revealed the highest concentrations in BLM followed by the endoplasmic reticulum. Exposure of isolated intestinal cells to 1,25(OH)(2)D(3) for 10 s or vascular perfusion of duodena for 5 min resulted in a time-dependent increase in nuclear localization of the BLM-VDR antigen, as judged by electron microscopy, whereas 24, 25-dihydroxyvitamin D(3) failed to increase antigenic labeling in nuclei. Densitometric quantitation of Western blots of subcellular fractions prepared from isolated intestinal cells treated with vehicle or 1,25(OH)(2)D(3) confirmed a hormone-induced increase of putative BLM-VDR in the nucleus. It is concluded that a novel cell surface binding protein for 1,25(OH)(2)D(3) has been identified.

Affinity Labels↗
PubMed1985

Intestinal absorption of 1,25-dihydroxyvitamin D3 in the rat.

Intestinal absorption of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] from in vivo jejunal sacs was studied in rats with thoracic duct and bile duct cannulas. In 6 h 86.5% of the administered 1,25(OH)2D3 was absorbed, but only 7.3% was recovered in thoracic duct lymph. Appearance in plasma of [3H]-1,25(OH)2D3 after intrajejunal administration was identical in rats with and without diverting lymph cannulas, indicating that the 1,25(OH)2D3 is absorbed almost entirely via portal blood. When 1,25(OH)2D3 was instilled into the jejunum in a fat suspension without bile salts rather than a mixed micellar solution, less was recovered in lymph, but total intestinal absorption was unchanged. High-pressure liquid chromatography of a lymph extract demonstrated that 1,25(OH)2D3 was present only as the unchanged secosteroid. In lymph, only 4.1% of the 1,25(OH)2D3 was in the chylomicrons, with the remainder bound to the plasma protein fraction of lymph. Treatment of rats with cycloheximide to block chylomicron synthesis did not decrease absorption of 1,25(OH)2D3. These results indicate that intestinal absorption of 1,25(OH)2D3 is effective and not very dependent on luminal bile salts. Almost all 1,25(OH)2D3 is released from the intestine directly into portal blood and does not require packaging in chylomicrons for transport into intestine lymph.

Animals↗
PubMed1993

Effect of 1,25(OH)2D3 and its analogues on membrane phosphoinositide turnover and [Ca2+]i in Caco-2 cells.

Our laboratory has recently reported that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] rapidly stimulates membrane polyphosphoinositide turnover and increases intracellular calcium concentration ([Ca2+]i) in Caco-2 cells. The role of binding to the vitamin D receptor (VDR) in the regulation of these rapid biochemical events, however, remains unclear. The present studies were, therefore, conducted using analogues of 1,25(OH)2D3, which differ markedly in their affinities for the VDR, to assess and compare their effects on [Ca2+]i and on inositol 1,4,5-trisphosphate (IP3) formation. Competitive binding studies performed with both intact cells and high-salt cytosolic extracts from Caco-2 cells demonstrated that 1,25(OH)2D3 and 1,24-(OH)2-22-ene-24-cyclopropyl-D3 (BT) have high affinities for the VDR; 25(OH)-16-ene,23-yne-D3 (AT), however, has a much lower affinity (approximately 1,000-fold less) for the VDR. Despite these large differences in binding affinities for the VDR, AT and BT produced similar concentration-dependent increases in [Ca2+]i and in IP3 formation while 1,25(OH)2D3 was approximately 10-fold less active. These results indicate that the structural requirements for the rapid action of these secosteroids on signal transduction in Caco-2 cells are different from those for receptor binding and transcriptional regulation.

Binding, Competitive↗
PubMed1999

1,25-dihydroxyvitamin D3 stimulates transforming growth factor-beta1 synthesis by mouse renal proximal tubular cells.

1,25-dihydroxyvitamin D3 [1,25-(OH)2 D3] is a secosteroid hormone with effects on cell growth, differentiation and immunoregulatory functions in a number of tissues not primarily involved in mineral metabolism. We recently demonstrated growth-regulating effects of 1, 25-(OH)2 D3 on human mesangial cells and proximal tubular cells. To investigate whether 1,25-(OH)2 D3 might also affect the synthesis of cytokines and growth factors in proximal tubular cells, we assessed in the present study the expression and secretion of transforming growth factor-beta1 (TGF-beta1) in a mouse proximal tubular cell line (MCT) in vitro. TGF-beta1 synthesis was measured by a monospecific ELISA in culture supernatant. The secreted TGF-beta1 was proven to be biologically active by means of a bioassay system (CCL-64 mink lung epithelial cell proliferation assay). TGF-beta1 gene expression was assessed by RT-PCR. To analyze whether TGF-beta1 expression mediates the 1,25-(OH)2 D3-induced antiproliferative actions in MCT, proliferation studies in the absence or presence of a blocking monoclonal anti TGF-beta1-3 antibody were performed. 1, 25-(OH)2 D3 (10(-11) to 10(-7) M) specifically increased the TGF-beta1 protein secretion in MCT with a maximum at 10(-8) M. No detectable effect was found with 25 D3 at 10 times higher concentrations. A synthetic 20-epi analogue, MC 1288, increased TGF-beta1 secretion up to similar amounts at equimolar concentrations as the natural hormone 1,25-(OH)2 D3. Steady-state TGF-beta1 mRNA concentration in MCT was transiently increased by 1, 25-(OH)2 D3 between 12 and 24 h, returning to control values at 48 h. Blocking TGF-beta1 did not reduce or abrogate the antiproliferative effect of 1,25-(OH)2 D3. In conclusion, 1,25-(OH)2 D3 stimulates TGF-beta1 expression in renal proximal tubular cells, a growth factor with anti-inflammatory and profibrotic actions which plays an important role in the development and progression of nephrosclerosis.

Animals↗
PubMed1995

1,25-Dihydroxyvitamin D3 and 12-O-tetradecanoyl phorbol 13-acetate cause differential activation of Ca(2+)-dependent and Ca(2+)-independent isoforms of protein kinase C in rat colonocytes.

Considerable evidence that alterations in protein kinase C (PKC) are intimately involved in important physiologic and pathologic processes in many cells, including colonic epithelial cells, has accumulated. In this regard, phorbol esters, a class of potent PKC activators, have been found to induce a number of cellular events in normal or transformed colonocytes. In addition, our laboratory has demonstrated that the major active metabolite of vitamin D3, 1,25(OH)2D3, also rapidly (seconds-minutes) activated PKC and increased intracellular calcium in isolated rat colonocytes. These acute responses, however, were lost in vitamin D deficiency and partially restored with the in vivo repletion of 1,25(OH)2D3. The Ca(2+)-independent or novel isoforms of PKC expressed in the rat colon and the isoform-specific responses of PKC to acute treatment with phorbol esters or 1,25(OH)2D3 have not been previously characterized. Moreover, the effects of vitamin D status on PKC isoform expression, distribution, and response to agonists are also unknown. In the present experiments, in addition to PKC-alpha, rat colonocytes were found to express the novel isoforms delta, epsilon, and zeta by Western blotting using isoform-specific PKC antibodies. The tumor-promoting phorbol ester, 12-O-tetradecanoyl phorbol 13-acetate, caused time- and concentration-dependent translocations of all these isoforms except PKC-zeta. In vitamin D deficiency, there were no alterations in colonic PKC isoform expression but significant changes in the subcellular distribution of PKC-alpha, -delta, and -zeta. Acute treatment of colonocytes from D-sufficient, but not D-deficient, rats with 1,25(OH)2D3 caused a rapid transient redistribution of only PKC-alpha from the soluble to the particulate fraction. The alterations in PKC isoform distribution and PKC-alpha responsiveness to 1,25(OH)2D3 in vitamin D deficiency were partially, but significantly, restored with 5-7 d in vivo repletion of this secosteroid. Both 12-O-tetradecanoyl phorbol 13-acetate and 1,25(OH)2D3 activated endogenous PKC, as assessed by inhibition of myristoylated alanine-rich C kinase substrate back-phosphorylation by exogenous PKC. These studies indicate that PKC-alpha, -delta, and/or -epsilon likely mediate important phorbol ester-stimulated events described in the rat colon. In contrast, PKC-alpha is implicated in the rapid (s-min) PKC-dependent events initiated by 1,25(OH)2D3 in rat colonocytes.

Animals↗
PubMed2005

Expression of the inhibitory receptor ILT3 on dendritic cells is dispensable for induction of CD4+Foxp3+ regulatory T cells by 1,25-dihydroxyvitamin D3.

1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) is a secosteroid hormone that renders dendritic cells (DCs) tolerogenic, favoring the induction of regulatory T cells. Induction of DCs with tolerogenic properties by 1,25(OH)(2)D(3) is associated with increased selective expression of immunoglobulin-like transcript 3 (ILT3), suggesting its involvement in the immunoregulatory properties of this hormone. Here we show an in vivo correlate of the increased ILT3 expression on DCs in healing psoriatic lesions following topical treatment with the 1,25(OH)(2)D(3) analog calcipotriol. Analysis of DC subsets reveals a differential regulation of ILT3 expression by 1,25(OH)(2)D(3), with a marked up-regulation in myeloid DCs but no effect on its expression by plasmacytoid DCs. A regulatory role for ILT3 expressed on DCs is indicated by the increased interferon-gamma (IFN-gamma) secretion promoted by anti-ILT3 addition to cultures of DCs and T cells, but this effect is blunted in 1,25(OH)(2)D(3)-treated DCs, suggesting ILT3-independent mechanisms able to regulate T-cell activation. Although ILT3 expression by DCs is required for induction of regulatory T cells, DC pretreatment with 1,25(OH)(2)D(3) leads to induction of CD4(+)Foxp3(+) cells with suppressive activity irrespective of the presence of neutralizing anti-ILT3 monoclonal antibody (mAb), indicating that ILT3 expression is dispensable for the capacity of 1,25(OH)(2)D(3)-treated DCs to induce regulatory T cells.

Antibodies↗
PubMed2006

Common angiotensin receptor blockers may directly modulate the immune system via VDR, PPAR and CCR2b.

BACKGROUND: There have been indications that common Angiotensin Receptor Blockers (ARBs) may be exerting anti-inflammatory actions by directly modulating the immune system. We decided to use molecular modelling to rapidly assess which of the potential targets might justify the expense of detailed laboratory validation. We first studied the VDR nuclear receptor, which is activated by the secosteroid hormone 1,25-dihydroxyvitamin-D. This receptor mediates the expression of regulators as ubiquitous as GnRH (Gonadatrophin hormone releasing hormone) and the Parathyroid Hormone (PTH). Additionally we examined Peroxisome Proliferator-Activated Receptor Gamma (PPARgamma), which affects the function of phagocytic cells, and the C-CChemokine Receptor, type 2b, (CCR2b), which recruits monocytes to the site of inflammatory immune challenge. RESULTS: Telmisartan was predicted to strongly antagonize (Ki asymptotically equal to 0.04 nmol) the VDR. The ARBs Olmesartan, Irbesartan and Valsartan (Ki asymptotically equal to10 nmol) are likely to be useful VDR antagonists at typical in-vivo concentrations. Candesartan (Ki asymptotically equal to 30 nmol) and Losartan (Ki asymptotically equal to 70 nmol) may also usefully inhibit the VDR. Telmisartan is a strong modulator of PPARgamma (Ki asymptotically equal to 0.3 nmol), while Losartan (Ki asymptotically equal to 3 nmol), Irbesartan (Ki asymptotically equal to 6 nmol), Olmesartan and Valsartan (Ki asymptotically equal to 12 nmol) also seem likely to have significant PPAR modulatory activity. Olmesartan and Irbesartan (Ki asymptotically equal to 9 nmol) additionally act as antagonists of a theoretical model of CCR2b. Initial validation of this CCR2b model was performed, and a proposed model for the Angiotensin II Type1 receptor (AT2R1) has been presented. CONCLUSION: Molecular modeling has proven valuable to generate testable hypotheses concerning receptor/ligand binding and is an important tool in drug design. ARBs were designed to act as antagonists for AT2R1, and it was not surprising to discover their affinity for the structurally similar CCR2b. However, this study also found evidence that ARBs modulate the activation of two key nuclear receptors-VDR and PPARgamma. If our simulations are confirmed by experiment, it is possible that ARBs may become useful as potent anti-inflammatory agents, in addition to their current indication as cardiovascular drugs.

Amino Acid Sequence↗
PubMed2006

VDR-dependent regulation of mast cell maturation mediated by 1,25-dihydroxyvitamin D3.

1,25-Dihydroxyvitamin D3 [1,25(OH)2D3] is a secosteroid hormone that regulates bone metabolism, controls calcium homeostasis, and possesses immunomodulatory properties. We show here that 1,25(OH)2D3 contributes to the regulation of development and function of mast cells, which play a critical role in several inflammatory disorders. 1,25(OH)2D3 promotes apoptosis and inhibits maturation of mouse bone marrow-derived mast cell precursors. Dose-dependent inhibition of mast cell differentiation by 1,25(OH)2D3 is observed at discrete, intermediate stages of mast cell development, identified by expression of c-kit, FcepsilonRI, and IL-3 receptor-alpha chain, and depends on the expression of the vitamin D receptor (VDR). It is important that mast cell progenitors obtained from VDR-ablated mice undergo an accelerated maturation in vitro and give rise to more responsive mast cells than wild-type. Furthermore, histological analysis of mast cell density in peripheral tissues reveals a moderate increase in the number of mast cells in the skin of VDR-deficient mice compared with wild-type animals. These data support the hypothesis of a physiological role of 1,25(OH)2D3 in mast cell development and suggest novel, therapeutic uses of 1,25(OH)2D3 analogs.

Animals↗
PubMed1984

Calcium transport in perfused duodena from normal chicks: enhancement within fourteen minutes of exposure to 1,25-dihydroxyvitamin D3.

The effect of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3) on calcium transport was studied in vascularly perfused duodena of normal, vitamin D-replete chicks. Addition of 130 pM 1,25(OH)2D3 to the perfusate resulted in a significant increase in 45Ca transport from the lumen to the vascular effluent within 14 min; the transport rate rose to 140% of levels in comparable preparations exposed for 40 min to vehicle. No effects of 1,25(OH)2D3 were noted on the back flux or transfer of 45Ca from the vascular effluent to the lumen. Vascular perfusion with 100 microM colchicine, an antimicrotubular agent, abolished the rapid lumen-to-vascular effluent effect of 1,25(OH)2D3 on 45Ca transport, relative to preparations exposed to the secosteroid and 100 microM lumicolchicine, (a light inactivated analog of colchicine). Colchicine did not, however, alter basal 45Ca transport rates. Addition of 130 pM 1,25(OH)2D3 to the lumenal compartment of normal chicks or vascular perfusion of duodena from vitamin D-deficient birds failed to increase 45Ca transport above control levels. Perfusion of duodena from normal chicks with 650 pM 1,25(OH)2D3 further increased calcium transport to 170% of levels observed in preparations treated with 130 pM steroid, and 210% of levels in controls. Although 15 nM vitamin D3 had no effect, in one series of experiments 125 nM 25-hydroxyvitamin D3 elicited vascular calcium levels that were 185% of controls at 40 min. These results suggest that 1,25(OH)2D3 can act in vitamin D-replete animals to produce rapid unidirectional calcium transport responses (through unknown mechanisms), as well as by interaction with intestinal nuclear receptors in D-deficient animals to promote induction of protein(s) that support long acting calcium transport responses.

Animals↗
PubMed1985

Time course study of insulin secretion after 1,25-dihydroxyvitamin D3 administration.

Vitamin D3 is known to be involved in pancreatic endocrine function. The rapidity of action of the biologically active form of vitamin D3, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], was studied over time (from 0-72 h) on pancreatic insulin secretion by the subsequently isolated perfused pancreas of vitamin D-deficient rats pair-fed with vitamin D-deficient control rats treated with vehicle alone. At 8 h after 1,25(OH)2D3 administration (1.3 nmol), augmentation of the insulin secretion in response to 16.6 mM glucose had already significantly appeared and reached a maximum at 14 h, and then markedly decreased to pretreatment baseline values by 36 h. In a separate experiment using 20 mM arginine as a stimulus, insulin secretion from the isolated perfused pancreas also showed a significant increase at 8 h and demonstrated a maximum response at 14 h after 1,25(OH)2D3 administration, followed by gradual decrease to 72 h. The prevailing levels of serum parameters, including calcium, phosphorus, and glucose, seemed not to be involved in this mechanism, since these were not correlated to the amount of insulin secretion by the subsequently isolated perfused pancreas. Also the observed rapid effects of 1,25(OH)2D3 on insulin secretion appear not to be related to a rapid effect of the secosteroid on increased dietary/caloric intake. These results clearly establish both the dependence of and rapid dynamics response of the perfused pancreas to the potentiating effects of in vivo administered 1,25(OH)2D3 on either glucose- or arginine-mediated insulin secretion from the perfused pancreas.

Animals↗
PubMed1988

1,25-Dihydroxycholecalciferol-dependent calcium uptake by mouse mammary gland in culture.

Mammary explants from pregnant mice cultured in the presence of lactogenic hormones express their differentiated function by producing milk components in vitro. In the present paper radioactive calcium uptake was studied in the mammary gland during terminal differentiation, when lactogenesis was initiated. Under these conditions a relevant accumulation of calcium in the tissue was clearly demonstrable. We have characterized the calcium uptake by the tissue as a saturable and energy dependent process. When 1,25-dihydroxycholecalciferol [1,25-(OH)2D3], the major calcium regulator hormone, was added to the incubation medium the secosteroid strongly stimulated this process by increasing the maximal velocity without significantly altering the Michaelis Menten constant (Km). Detectable increases in calcium uptake could be measured after the explants were cultured with 1,25-(OH)2D3 for 30 min, with the response continuing to increase sharply over time and reaching a plateau at 3 h. The increase was not affected by the presence of actinomycin D or cycloheximide suggesting that the 1,25-(OH)2D3 stimulation of calcium uptake may be independent of de novo protein synthesis. These results provide evidence for early and direct action of the hormonal form of vitamin D in affecting calcium transport across membranes of functionally differentiated epithelial cells of the mammary gland.

Animals↗
PubMed1994

Inhibition of 1,25-dihydroxyvitamin D3 stimulated osteocalcin gene transcription by tumor necrosis factor-alpha: structural determinants within the vitamin D response element.

Control of osteoblast function requires the coordinate activity of systemic and local regulatory factors. We have investigated the mechanism of interaction between the secosteroid 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] and the cytokine tumor necrosis factor-alpha (TNF-alpha) by measuring their effects on two 1,25-(OH)2D3 responsive matrix protein genes, osteocalcin (OC) and osteopontin (OP). Our previous studies revealed that an inhibitory effect of TNF-alpha on 1,25-(OH)2D3-stimulated OC gene transcription is conferred by the same 25 base pair region of 5'-flanking DNA that confers a response to vitamin D (VDRE). Gel mobility shift studies of [32P]VDRE binding to ROS 17/2.8 cell nuclear extract revealed that TNF-alpha inhibits 1,25-(OH)2D3 stimulated formation of specific retinoid X receptor/vitamin D receptor (RXR/VDR)-DNA complexes in vitro. To determine if TNF-alpha was inhibiting nuclear protein-VDRE binding by modulation of VDR availability, we measured intranuclear VDR in cells treated with 1,25-(OH)2D3 (10(-8) M), TNF-alpha (100 ng/ml), or both, by western blot. 1,25-(OH)2D3 caused upregulation of the nuclear VDR. Treatment with TNF-alpha inhibited the 1,25-(OH)2D3-stimulated up-regulation of VDR nuclear protein content. However, down-regulation of VDR was unlikely to be the mechanism of TNF-alpha action because TNF-alpha had no effect on 1,25-(OH)2D3 stimulation of steady state OP messenger RNA or transcription of an OP-VDRE-chloramphenicol acetyl transferase reporter construct. These results suggest that decreased VDR alone does not explain the mechanism of TNF-alpha action. VDRE structural requirements for TNF-alpha action were characterized by comparing binding of mutant and hybrid forms of mouse (m)OP-, rat (r)OC-, and human (h)OC-VDRE probes to nuclear protein from cells treated with 1,25-(OH)2D3 and/or TNF-alpha. These homologous vitamin D response elements differ in that an AP-1 sequence is included in the rOC-VDRE and hOC-VDRE but not in the OP-VDRE. Gel mobility shift analysis revealed that TNF-alpha inhibited 1,25-(OH)2D3 stimulation of nuclear protein binding to rOC-VDRE and hOC-VDRE to 59% and 69% of control, respectively, but had no effect on 1,25-(OH)2D3 stimulation of nuclear protein binding to OP-VDRE. The effect of TNF-alpha could not be conferred in a mutant OP-VDRE in which the rOC-VDRE AP-1 sequence was inserted.(ABSTRACT TRUNCATED AT 400 WORDS)

Base Sequence↗
PubMed1994

The role of protein kinase-C alpha in the activation of particulate guanylate cyclase by 1 alpha,25-dihydroxyvitamin D3 in CaCo-2 cells.

Recent studies have implicated protein kinase-C (PKC) in the regulation of guanylate cyclase in several cell types. In view of prior experiments by our laboratory which have demonstrated that 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25-(OH)2D3] can activate PKC in CaCo-2 cells, it was of interest to determine whether this secosteroid influenced particulate guanylate cyclase and, if so, to determine which isoforms of PKC were involved. To address these issues, CaCo-2 cells were treated with 1 alpha,25-(OH)2D3 or other agents (see below), and crude membranes prepared from these cells were assayed for guanylate cyclase activity. In several experiments, agents were added directly to isolated membranes, and guanylate cyclase activity was then assayed. These studies demonstrated that 1) the addition of 1 alpha,25-(OH)2D3 or 12-O-tetradecanoyl phorbol 13-acetate (TPA), a known activator of PKC, to intact CaCo-2 cells stimulated particulate guanylate cyclase activity in a time- and concentration-dependent manner; 2) these agents induced the translocation of PKC alpha, but not PKC zeta, from the cytosolic to the membrane fraction of these cells; 3) preincubation of cells with staurosporine (50 nM), a PKC inhibitor, or U73122 (10 microM), an inhibitor of phospholipase-C-dependent processes, significantly reduced (P < 0.05) the stimulatory effect of 1 alpha,25-(OH)2D3 (3 nM) on guanylate cyclase; 4) preincubation of isolated membranes with TPA, calcium, and Mg(2+)-ATP increased guanylate cyclase activity, an affect that was augmented by purified rat brain PKC and inhibited by the PKC inhibitor peptide, PKC-(19-36); and 5) selective down-regulation of PKC alpha by treatment of cells with TPA (200 nM) for 24 h concomitantly abolished the activation of guanylate cyclase by 1 alpha,25-(OH)2D3. Taken together, these studies demonstrate that 1 alpha,25-(OH)2D3 activates particulate guanylate cyclase at least in part via a PKC alpha-dependent mechanism.

Bacterial Toxins↗
PubMed1996

Stable expression of the nuclear vitamin D receptor in the human prostatic carcinoma cell line JCA-1: evidence that the antiproliferative effects of 1 alpha, 25-dihydroxyvitamin D3 are mediated exclusively through the genomic signaling pathway.

The secosteroid hormone 1 alpha, 25-dihydroxyvitamin D3 [1,25-(OH)2D3] has been found to regulate the growth and differentiation of human prostate cancer cells, although the precise mechanisms mediating these effects have not been defined. 1,25-(OH)2D3 is capable of acting through both nongenomic signaling pathways involving a membrane-associated receptor and genomic pathways involving the nuclear vitamin D receptor (VDR). The primary purpose of this study was to directly evaluate the role of the nuclear VDR in mediating the growth inhibitory effects of 1,25-(OH)2D3 on human prostate cancer cells. The cell line JCA-1 was used because it fails to express detectable number of VDRs and is not measurable affected by 1,25-(OH)2D3 in growth studies. These cells were stably transfected with a wild-type VDR complementary DNA construct producing the following results: 1) the expression of high affinity nuclear VDRs, 2) the dose-dependent inhibition of growth by 1,25-(OH)2D3, and 3) a significant increase in 24-hydroxylase up-regulation by 1,25-(OH)2D3 compared to that in controls. These data indicate that nuclear VDR expression is sufficient to mediate the antiproliferative effects of 1,25-(OH)2D3 on prostate cancer cells. In addition, because the stereoisomer 1 beta, 25-dihydroxyvitamin D3 failed to block these antiproliferative effects, we conclude that nongenomic mechanisms of action are not requisite for growth inhibition by 1,25-(OH)2D3.

Base Sequence↗