Induction of resistance to TNF cytotoxicity and mitochondrial superoxide dismutase on U-937 cells by 1,25-dihydroxyvitamin D3

1,25-dihydroxyvitamin D3 (1,25(OH)2D3) dose-dependently inhibited the cytotoxicity of tumor necrosis factor (TNF) in a human monoblastic leukemic cell line, U-937. Combination of TNF and 1,25(OH)2D3 remarkably increased mitochondrial superoxide dismutase (mSOD) of U-937 cells, TNF alone increased it only slightly and 1,25(OH)2D3 alone did not. The cytosolic SOD (cSOD) activity was not changed by TNF or/and 1,25(OH)2D3. The mSOD activity was not inhibited by 2 mM KCN, suggesting that mSOD should be a manganese SOD (MnSOD). These results suggest that 1,25(OH)2D3 may reduce the susceptibility to TNF cytotoxicity of U-937 cells by enhancing the ability of inducing MnSOD by TNF.     

Reduced expression of manganese superoxide dismutase in cells resistant to cytolysis by tumor necrosis factor.

Tumor necrosis factor (TNF) induces synthesis of manganese superoxide dismutase (MnSOD). It was previously shown that overexpression of MnSOD protected some mammalian cells from TNF cytotoxicity. The purpose of this study was to establish whether MnSOD was increased in cells selected for resistance to cytolysis by TNF in combination with cycloheximide. Melanoma SK-MEL-109 and HeLa cell-resistant variants were selected by repeated treatments with TNF and cycloheximide. The SK-MEL-109 variants had relatively low levels of MnSOD that were inducible by TNF. Surprisingly, the HeLa variants had very low levels of MnSOD that were poorly inducible by either TNF or interleukin-1 alpha. Therefore, an elevated level of MnSOD was not required to protect these cells from TNF-mediated cytolysis. The HeLa variants were more sensitive than parental cells to superoxide radical (O2-) generating compounds, such as paraquat or xanthine/xanthine oxidase. Pretreatment of these variants with TNF did not provide protection against damage by superoxide radicals.     

Increase of MnSOD expression and decrease of JNK activity determine the TNF sensitivity in bcl2-transfected L929 cells.

To investigate the protection mechanism of Bcl-2 against tumour necrosis factor (TNF)-mediated cell death, the bcl2 gene was transfected into the L929 cells and stably expressed. Two clones having different sensitivity among bcl2-transfected L929 clones had been isolated, and termed clone R1 and R2. It was observed that activation of manganese superoxide dismutase (MnSOD) and suppression of Jun kinase of clone R1 and R2 were correlated with protection from TNF cytotoxicity. Upon treatment with TNF, clone R1 and R2 were more resistant than control L929 cells against TNF cytotoxicity and the protective effect of clone R1 was stronger than clone R2. However, in case of TNF plus actinomycin D treatment, clone R1 was still resistant against TNF cytotoxicity, whereas clone R2 became more sensitive than control L929 cells. The JNK activities of clone R1 and R2 were suppressed upon TNF treatment and in case of TNF plus actinomycin D treatment, clone R2 showed a marked increase in JNK activities and had higher activity than control L929 cells. The specific activities of MnSOD of clone R1 and R2 upon TNF treatment were 70 U/ml and 33 U/ml, respectively, while the MnSOD activity was not detectable in control L929 cells. When TNF and actinomycin D were treated simultaneously, MnSOD activity was not detectable in control L929 cells and bcl2 -transfected L929 cells (clone R1, R2). Consistent with these results, both clone R1 and R2 showed higher levels of MnSOD mRNA expression than control L929 cells after TNF treatment. These data suggest that suppression of Jun kinase and increase of MnSOD may be involved in inhibitory action of Bcl-2 against TNF, and the balance between MnSOD and JNK signalling pathway may be an important factor for the protection of bcl2-transfected L929 cells from TNF cytotoxicity.     

Manganous superoxide dismutase is essential for cellular resistance to cytotoxicity of tumor necrosis factor

Tumor necrosis factor (TNF) induces the synthesis of protein(s) that can protect cells against subsequent killing by TNF in the presence of cycloheximide. Here we demonstrate that manganous superoxide dismutase (MnSOD), a mitochondrial enzyme involved in the scavenging of superoxide radicals (O2-), is such a protein. Overexpression of MnSOD confers increased resistance to TNF plus cycloheximide on the 293 human embryonic kidney cell line. Conversely, expression of antisense MnSOD RNA renders these cells sensitive to TNF even in the absence of cycloheximide. The TNF sensitivity of the ME-180 human cervical carcinoma cell line can also be modulated through expression of sense and antisense MnSOD RNAs. These data identify MnSOD as an important determinant of cellular resistance to TNF and implicate mitochondrially generated O2- as a key component of TNF-mediated tumor cell killing.     

Tumor-suppressive activity of 1,25-dihydroxyvitamin D3 against kidney cancer cells via up-regulation of FOXO3

1,25-Dihydroxyvitamin D3 has been known to have the tumor-suppressive activity in various kinds of tumors. However, the exact effect and working mechanism of 1,25-dihydroxyvitamin D3 on the tumor-suppressive activity in human kidney cancer cells remains poorly understood. 1,25-Dihydroxyvitamin D3 has cytotoxicity to ACHN cells and inhibited ACHN cell proliferation compared to the vehicle control. 1,25-Dihydroxyvitamin D3 increased the expression of the cleaved PARP1, active Caspase3, Bax, and Bim but decreased the expression of Bcl2 in ACHN cells. Moreover, 1,25-dihydroxyvitamin D3 down-regulated the phosphorylated Akt and Erk which might lead to apoptosis through activation of FOXO3 in ACHN cells. Transfection of siRNA against FOXO3 attenuated the pro-apoptotic BimEL expression in ACHN cells treated with 1,25-dihydroxyvitamin D3. These results suggest that FOXO3 is involved in the apoptosis induced by 1,25-dihydroxyvitamin D3.     

1,25-Dihydroxyvitamin D3 inhibits the clonogenic growth of transformed cells via its receptor

Anchorage-independent growth in soft agar is a unique property of transformed cells which is known to be correlated with tumorigenicity. We report here that 1,25-dihydroxyvitamin D3 suppresses colony formation by a number of cultured cancer cell lines in soft agar in a dose dependent manner with an ID50 of 5-7 X 10(-10) M. This effect is also achieved with analogues of 1,25-dihydroxyvitamin D3 in accordance with their binding affinity for the hormone's receptor. Only cells with 1,25-dihydroxyvitamin D3 receptor protein are inhibited in their colony formation by vitamin D analogs indicating that the hormone receptor complex may be integrally involved in the in vitro suppression of the anchorage-independent phenotype.     

Antioxidant defenses in the TNF-treated MCF-7 cells: selective increase in MnSOD

Oxidative stress has been implicated in the mechanism of tumor necrosis factor-alpha (TNF)-induced apoptosis, raising a question about the status of antioxidant defenses in TNF-sensitive cells. Antioxidant defenses were examined in MCF-7 cells after treatment with TNF. Cell morphology and DNA fragmentation assays were used to confirm increased apoptosis as a result of TNF treatment. The expression and activity of antioxidant defenses were assessed using Northern blot hybridization analyses and biochemical assays, respectively. Five- and ten-fold increases in manganese superoxide dismutase (MnSOD) mRNA were measured after one and five days of TNF treatment, respectively. The expression of copper,zinc superoxide dismutase, catalase or thioredoxin was not altered. An approximate five-fold increase in MnSOD activity followed the change in gene expression, but no difference in the activity of catalase or glutathione peroxidase was seen. Thus, increased MnSOD activity was not accompanied by an increase in other antioxidant defenses and in particular, H2O2-scavenging enzymes. MnSOD has previously been shown to afford protection against TNF-mediated cytotoxicity. The observed lack of increased peroxidase activity is consistent with mitochondrially-generated superoxide anion radical contributing to the mechanism of TNF-induced apoptosis.     

A synthetic analogue of vitamin D3, 22-oxa-1,25-dihydroxy-vitamin D3, stimulates the production of prostacyclin by vascular tissues.

We investigated the effect of 22-oxa-1,25-dihydroxyvitamin D3, a synthetic analogue of vitamin D3, on the production of prostacyclin by vascular tissues using rat aortic rings and A7r5 cells derived from fetal rat aortic smooth muscle. Prostacyclin synthesis by aortic rings of rats treated with 22-oxa-1,25-dihydroxyvitamin D3 was much higher than that of non-treated controls, but did not cause any significant hypercalcemia. Treatment with 22-oxa-1,25-dihydroxyvitamin D3 significantly increased the production of prostacyclin by A7r5 cells for 48 hours in a dose-dependent manner. In time-course studies, cells incubated with 22-oxa-1,25-dihydroxyvitamin D3 or 1,25-dihydroxyvitamin D3 produced prostacyclin progressively over a period of 48 hours. The shortest period of incubation that produced a significant amount of prostacyclin compared with control cultures was 24 hours. We observed that treatment with 22-oxa-1,25-dihydroxyvitamin D3 induced cyclooxygenase mRNA in A7r5 cells. Our data suggest that 22-oxa-1,25-dihydroxyvitamin D3 may possibly be a protective substance against the development of atherosclerosis by modulating prostaglandin metabolism.     

Interleukin-2 is one of the targets of 1,25-dihydroxyvitamin D3 in the immune system

Interleukin (IL)-2 knockout (KO) mice, which spontaneously develop symptoms of inflammatory bowel disease similar to ulcerative colitis in humans, were made vitamin D deficient (D-) or vitamin D sufficient (D+) or were supplemented with 1,25-dihydroxyvitamin D(3) (1,25D3). 1,25-Dihydroxyvitamin D3 supplementation, but not vitamin D supplementation, reduced the early mortality of IL-2 KO mice. However, colitis severity was not different in D-, D+, or 1,25D3 IL-2 KO mice. Cells from D- IL-2 KO mice produced more interferon (IFN)-gamma than cells from all other mice. Con A-induced proliferation was upregulated in IL-2 KO mice and downregulated in wildtype (WT) mice fed 1,25D3. All other measured immune responses in cells from IL-2 KO mice were unchanged by vitamin D status. In vitro addition of 1,25-dihydroxyvitamin D3 significantly reduced the production of IL-10 and IFN-gamma in cells from D- and D+ WT mice. Conversely, IFN-gamma and IL-10 production in cells from IL-2 KO mice were refractory to in vitro 1,25-dihydroxyvitamin D3 treatments. In the absence of IL-2, vitamin D was ineffective for suppressing colitis and ineffective for the in vitro downregulation of IL-10 or IFN-gamma production. One target of 1,25-dihydroxyvitamin D3 in the immune system is the IL-2 gene.     

1,25-Dihydroxyvitamin D3 increases citrate secretion from osteosarcoma cells

Rat osteosarcoma cells respond to 1,25-dihydroxyvitamin D3 with a 6- to 10-fold increase in the secretion of citric acid. The time required to attain a half-maximal response is 12 h, a time course which is consistent with the postulated steroidal hormone action of this vitamin D metabolite. The citrate response is achieved by physiological concentrations of 1,25-dihydroxyvitamin D3, with half of the maximal response at a vitamin concentration of 0.03 ng/ml. Both the time course and the dose dependence of the citrate response closely parallel the previously reported stimulation of bone Gla protein synthesis by 1,25-dihydroxyvitamin D3 in these cells. Citrate and bone Gla protein bind avidly to bone mineral and are numerically the most abundant organic acid and protein in bone. The parallel secretion of both in 1,25-dihydroxyvitamin D3-treated osteoblastic cells suggests that they may act in tandem to mediate an action of this vitamin D metabolite on the mineral phase of bone.     

Differential effects of Vitamin D analogs on calcium transport

It is well known that the efficiency of intestinal active calcium transport is regulated by the Vitamin D receptor pathway and Vitamin D analogs seem to exhibit differential effects on intestinal active calcium transport. To investigate the molecular basis for the difference among Vitamin D analogs, we tested three Vitamin D analogs: 1,25-dihydroxyvitamin D(3), 19-nor-1,25-dihydroxyvitamin D(2), and 1alpha-hydroxyvitamin D(2) ex vivo and in vitro. In 5/6 nephrectomized rat intestinal active calcium transport, 19-nor-1,25-dihydroxyvitamin D(2) did not show a significant effects on intestinal active calcium transport at all the concentrations tested, while 1alpha-hydroxyvitamin D(2) at 0.33 and 0.67 microg/kg and 1,25-dihydroxyvitamin D(3) at 1microg/kg significantly stimulated calcium transport. In Caco-2 cells, 19-nor-1,25-dihydroxyvitamin D(2) did not show a significant effect on calcium transport, while 1,25-dihydroxyvitamin D(3) and 1,25-dihydroxyvitamin D(2) (the active form of 1alpha-hydroxyvitamin D(2)) stimulated calcium transport by 934 and 501% at 0.1microM, respectively. 1,25-Dihydroxyvitamin D(2) potently induced the expression of CALB3 and TRPV6 mRNA with an EC(50) of 0.3 and 1.0nM, whereas 19-nor-1,25-dihydroxyvitamin D(2) was 10-fold less potent than 1,25-dihydroxyvitamin D(2) in inducing CALB3 and TRPV6 mRNA. The three Vitamin D analogs had no significant effect on the expression of PMCA1 mRNA. These Vitamin D analogs did not change the expression of Vitamin D receptor (VDR) up to 10nM, but stimulated CYP24A1 expression in a dose-dependent manner with the potency in the order of 1,25-dihydroxyvitamin D(3)>1,25-dihydroxyvitamin D(2)=19-nor-1,25-dihydroxyvitamin D(2). These results suggest that the differential effect of Vitamin D analogs on stimulating intestinal and Caco-2 calcium transport may be in part due to its different effect on stimulating CALB3 and TRPV6 mRNA expression.     

Stimulation of rat intestinal protein synthesis by 1,25-dihydroxyvitamin D3

To study general stimulatory effects of 1,25-dihydroxyvitamin D3 on intestinal protein synthesis, slices of duodenal villi from 1,25-dihydroxyvitamin D3-treated and vitamin D-deficient rats were incubated in vitro for 90 min at the surface of medium containing [3H]leucine. Incorporation of the [3H]leucine into TCA-precipitated protein, which was shown to be linear for 12 h and 90% inhibited by cycloheximide, was increased by 50-60% at 26 h after a single injection of 125 ng of 1,25-dihydroxyvitamin D3 (three experiments, P less than 0.001). The increase, which was not due to circadian rhythm fluctuations of the intestine, was in synchrony with the second Ca2+ transport response observed by Halloran and DeLuca (Arch. Biochem. Biophys. 208, 477-486, 1981). However, no significant difference in [3H]leucine incorporation was observed before or during the initial Ca2+ transport response observed by Halloran and DeLuca, i.e., at 1.0, 3.0, and 6.5 h following an injection of 1,25-dihydroxyvitamin D3. The late onset of the 1,25-dihydroxyvitamin D3-induced increase in total protein synthesis implies that it is an indirect rather than a direct effect of the hormone.     

Characterization of a specific, high affinity binding macromolecule for 1 alpha, 25-dihydroxyvitamin D3 in cultured chick kidney cells

Cytosol prepared from vitamin D3-deficient kidney cells in culture contains a 3.7 S protein that specifically binds 1,25-dihydroxyvitamin D3 with high affinity and low capacity. Whole kidney homogenate cytosol preparations are shown to possess two 1,25-dihydroxyvitamin D3 binding macromolecules. One of the binding proteins sediments at 3.5 to 3.7 S while the second sediments at 6.0 S. The 6.0 S component has a greater affinity for 25-dihydroxyvitamin D3 than for 1,25-dihydroxyvitamin D3. Cultured cell cytosol was found to have little 6.0 S 25-hydroxyvitamin D3 binding protein. Scatchard analysis of the cultured cell cytosol reveals an equilibrium binding constant (KD) of 5.6 x 10 (-11) with 57 fmol of sites/mg of protein. The receptor-like protein has a Mr = 72,000 and as with other steroid receptors it aggregates in the presence of low potassium concentrations. Analog competition for receptor binding reveals the following potency order: 1,25-dihydroxyvitamin D3 > 25-hydroxyvitamin D3 > 1 alpha-hydroxyvitamin D3 > 24(R),25-dihydroxyvitamin D3; the receptor had no detectable affinity for vitamin D3. The kidney cells respond to 1,25-dihydroxyvitamin D3 by diminishing 25-hydroxyvitamin D3 1 alpha-hydroxylation and increasing 24R-hydroxylation. Cultured cells provide a preparation of cytosol which has allowed extensive characterization of the renal 1,25-dihydroxyvitamin D3 receptor and should facilitate investigations into the role this receptor plays in renal control of vitamin D3 metabolism.     

Effect of 1,25-dihydroxyvitamin D3 on cyclic AMP responses to hormones in clonal osteogenic sarcoma cells.

The effect of 1,25-dihydroxyvitamin D3 on adenylate cyclase responsiveness was studied in the clonal osteogenic sarcoma cell line, UMR 106-06, which responds to several bone active hormones. 1,25-dihydroxyvitamin D3 treatment had no consistent effect on basal formation of cyclic AMP in intact cells, but the responses to parathyroid hormone, isoproterenol, prostaglandin E2, salmon calcitonin and the plant diterpene, forskolin, were all attenuated, by up to 90%. The effect of 1,25-dihydroxyvitamin D3 was dose-dependent, with half-maximal effectiveness at 0.1 nM, and required 48 h treatment of cells before it became apparent. The relative potencies of other vitamin D3 compounds correlated closely with their relative affinities for the 1,25-dihydroxyvitamin D3 receptor and their biological activities in other systems. 1,25-dihydroxyvitamin D3 treatment had no effect on the kinetics of labelled calcitonin binding to UMR 106-06 cells. Furthermore, the fact that such a range of hormones was affected made a receptor mediated mechanism unlikely. Nucleotide stimulatory (Ns) unit activity was assayed after 1,25-dihydroxyvitamin D3 treatment and found to be unchanged. Islet activating protein, an inhibitor of nucleotide inhibitory unit (Ni) activity, failed to modify the 1,25-dihydroxyvitamin D3 effect. Thus the effect of 1,25-dihydroxyvitamin D3 appeared to be exerted beyond hormone receptor and nucleotide regulatory components of the adenylate cyclase complex. It is concluded that 1,25-dihydroxyvitamin D3 attenuates adenylate cyclase response to hormones by a direct or indirect action on the catalytic component of adenylate cyclase.     

Intestinal synthesis of 24-keto-1,25-dihydroxyvitamin D3. A metabolite formed in vivo with high affinity for the vitamin D cytosolic receptor

24-Keto-1,25-dihydroxyvitamin D3 has been identified as an intestinal metabolite of 1,25-dihydroxyvitamin D3 by ultraviolet absorbance, mass spectroscopy, and chemical reactivity. The metabolite was produced from 1,25-dihydroxyvitamin D3 and 1,24R,25-trihydroxyvitamin D3 in rat intestinal mucosa homogenates. 24-Keto-1,25-dihydroxyvitamin D3 is present in vivo in the plasma and small intestinal mucosa of rats fed a stock diet, receiving no exogenous 1,25-dihydroxyvitamin D3, and in the plasma and small intestinal mucosa of rats dosed chronically with 1,25-dihydroxyvitamin D3. 24-Keto-1,25-dihydroxyvitamin D3 has affinity equivalent to 1,24R,25-trihydroxyvitamin D3 for the 3.7 S cytosolic receptor specific for 1,25-dihydroxyvitamin D3 in the intestine and thymus. In cytosolic preparations contaminated with the 5 S vitamin D-binding protein, both metabolites are about 7-fold less potent than 1,25-dihydroxyvitamin D3. In contrast, in cytosolic preparations largely free of the 5 S binding protein, both metabolites are equipotent with the parent compound. No evidence was obtained supporting a substantial presence of 23-keto-1,25-dihydroxyvitamin D3 in vivo; nor was the latter compound generated in detectable amounts from 1,25-dihydroxyvitamin D3 by intestinal homogenates. Thus, C-24 oxidation is a significant pathway of intestinal 1,25-dihydroxyvitamin D3 metabolism that produces metabolites with high affinity for the cytosolic receptor which mediates vitamin D action.     

The synthesis and biological activity of 25-hydroxy-26,27-dimethylvitamin D3 and 1,25-dihydroxy-26,27-dimethylvitamin D3: highly potent novel analogs of vitamin D3

We synthesized 25-hydroxy-26,27-dimethylvitamin D3, 9, and 1,25-dihydroxy-26,27-dimethylvitamin D3, 14, from chol-5-enic acid-3 beta-ol and tested their biological activity in vivo and in vitro. 9 was found to be highly potent vitamin D analog with bioactivity similar to that of 25-hydroxyvitamin D3. 9 bound to rat plasma vitamin D binding protein with approximately one-third the affinity of 25-hydroxyvitamin D3. In a duodenal organ culture system and in a competitive binding assay with chick intestinal 1,25-dihydroxyvitamin D receptor, 9 was significantly more potent than 25-hydroxyvitamin D3. 1,25-Dihydroxy-26,27-dimethylvitamin D3, 14 was also highly active in vivo. At doses of 1000-5000 pmol/rat, its action was more sustained than that of 1,25-dihydroxyvitamin D3. 14 bound to vitamin D binding protein about 18 times less effectively than 1,25-dihydroxyvitamin D3. 14 bound to the chick intestinal cytosol receptor with an affinity one-half that of 1,25-dihydroxyvitamin D3. In a duodenal organ culture system, 14 was about half as active as 1,25-dihydroxyvitamin D3. Extension of the sterol side chain, at C-26 and C-27, by methylene groups, prolongs the bioactivity of a vitamin D sterol hydroxylated at C-1 and C-25; the corresponding sterol, hydroxylated only at C-25, does not show any alteration of its bioactivity in vivo. These newly synthesized analogs may potentially be of therapeutic use in various mineral disorders.