Biological activities of 24-fluoro-1 alpha,25-dihydroxyvitamin D-2 and its 24-epimer.

Biological activities of two epimeric 24-fluorinated vitamin D-2 analogs, 24-fluoro-1 alpha,25-dihydroxyvitamin D-2 [24-F-1,25-(OH)2D2] and its 24-epimer [24-epi-24-F-1,25-(OH)2D2], were studied and compared with 1 alpha,25-dihydroxyvitamin D-3 [1,25-(OH)2D3] and 1 alpha,25-dihydroxyvitamin D-2 [1,25-(OH)2D2]. 24-F-1,25-(OH)2D2 was nearly as active as 1,25-(OH)2D3 and 1,25-(OH)2D2 both in regulating calcium metabolism in vivo including bone mineral mobilization and intestinal calcium transport and in inducing differentiation of HL-60 cells. While 24-epi-24-F-1,25-(OH)2D2 showed distinct properties in these two types of the actions. Though the 24-epimer was nearly as potent as 1,25-(OH)2D3 in inducing differentiation of HL-60 cells, it showed little activity in regulating calcium metabolism in vivo. The fluorine atom introduced at the 24-position of either 1,25-(OH)2D2 or its 24-epimer had no potentiating effect. This is in sharp contrast with the cases of 24- and 26,27-multifluorinated analogs of active vitamin D-3.

Polyamines are involved in the 1-alpha,25-dihydroxyvitamin D3-induced fusion of mouse alveolar macrophages.

We have reported that 1-alpha,25-dihydroxyvitamin D3 [1-alpha,25-(OH)2D3] directly induces fusion of mouse alveolar macrophages at a very high rate (circa 70-80%) by a mechanism involving protein synthesis (Proc. Natl. Acad. Sci. USA 80:5583, 1983; FEBS Letters 174:61, 1984). While examining further the mechanism of the 1-alpha,25-(OH)2D3-induced fusion of macrophages, we found that polyamines are involved in this mechanism. Mouse alveolar macrophages incubated with 12 nM 1-alpha,25-(OH)2D3 began to fuse at 36 h and the fusion rate increased linearly up to 60 h. Addition of as much as 0.05-5 mM alpha-difluoromethylornithine (alpha-DFMO), a specific inhibitor of ornithine decarboxylase, did not inhibit fusion appreciably, but addition of 0.05-5 microM methylglyoxal bis(guanylhydrazone) (MGBG), an inhibitor of S-adenosylmethionine decarboxylase, strikingly inhibited fusion. When macrophages were treated with both 12 nM 1-alpha,25-(OH)2D3 and 5 microM MGBG for the first 12 h and incubated further for 60 h in fresh medium containing 1-alpha,25-(OH)2D3, fusion was significantly inhibited, suggesting that the 1-alpha,25-(OH)2D3-induced synthesis of polyamines precedes fusion. The inhibition by MGBG of the 1-alpha,25-(OH)2D3-induced fusion was restored completely by adding 1 microM spermidine or spermine or 100 microM putrescine. None of the polyamines alone induced fusion. MGBG suppressed the 1-alpha,25-(OH)2D3-induced incorporation of [3H]-leucine into the trichloroacetic acid-insoluble fraction in macrophages, but its inhibitory effect was restored completely by adding 1 microM spermidine.(ABSTRACT TRUNCATED AT 250 WORDS)

Importance of membrane- or matrix-associated forms of M-CSF and RANKL/ODF in osteoclastogenesis supported by SaOS-4/3 cells expressing recombinant PTH/PTHrP receptors.

SaOS-4/3, a subclone of the human osteosarcoma cell line SaOS-2, established by transfecting the human parathyroid hormone/parathyroid hormone-related protein (PTH/PTHrP) receptor complementary DNA (cDNA), supported osteoclast formation in response to PTH in coculture with mouse bone marrow cells. Osteoclast formation supported by SaOS-4/3 cells was completely inhibited by adding either osteoprotegerin (OPG) or antibodies against human macrophage colony-stimulating factor (M-CSF). Expression of messenger RNAs (mRNAs) for receptor activator of NF-kappaB ligand/osteoclast differentiation factor (RANKL/ODF) and both membrane-associated and secreted forms of M-CSF by SaOS-4/3 cells was up-regulated in response to PTH. SaOS-4/3 cells constitutively expressed OPG mRNA, expression of which was down-regulated by PTH. To elucidate the mechanism of PTH-induced osteoclastogenesis, SaOS-4/3 cells were spot-cultured for 2 h in the center of a culture well and then mouse bone marrow cells were uniformly plated over the well. When the spot coculture was treated for 6 days with both PTH and M-CSF, osteoclasts were induced exclusively inside the colony of SaOS-4/3 cells. Osteoclasts were formed both inside and outside the colony of SaOS-4/3 cells in coculture treated with a soluble form of RANKL/ODF (sRANKL/sODF) in the presence of M-CSF. When the spot coculture was treated with sRANKL/sODF, osteoclasts were formed only inside the colony of SaOS-4/3 cells. Adding M-CSF alone failed to support osteoclast formation in the spot coculture. PTH-induced osteoclast formation occurring inside the colony of SaOS-4/3 cells was not affected by the concentration of M-CSF in the culture medium. Mouse primary osteoblasts supported osteoclast formation in a similar fashion to SaOS-4/3 cells. These findings suggest that the up-regulation of RANKL/ODF expression is an essential step for PTH-induced osteoclastogenesis, and membrane- or matrix-associated forms of both M-CSF and RANKL/ ODF are essentially involved in osteoclast formation supported by osteoblasts/stromal cells.

The possible role of calcium-binding protein induced by 1 alpha,25-dihydroxyvitamin D3 in the intestinal calcium transport mechanism.

The relationship between the appearance of vitamin D-dependent calcium-binding protein (CaBP) and calcium absorption was studied in sequentially isolated duodenal mucosal preparations from vitamin D-deficient chicks and those supplemented with vitamin D3 or 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25-(OH)2D3]. The duodenal calcium absorption activity was significantly increased 6 h after a single iv injection of 0.625 microgram of 1 alpha,25-(OH)2D3, attained a maximum at 12 h, and declined gradually thereafter. On the other hand, only small amounts of CaBP appeared in the crypt and lower villus regions 6 h after 1 alpha,25-(OH)2D3 administration. At 12 h, the CaBP was found in the entire villus, but its content was still much higher in the crypt and lower villus. At 24 h and 48 h, the distribution of CaBP showed the opposite gradient, higher in the villus and lower in the crypt. At 72 h, CaBP was found only in the upper villus. The life time of duodenal mucosal cells was calculated to be 108 h as indicated by the cells labeled with [3H]thymidine. Thus, the movement of CaBP from the crypt to the villus tip was considered to be much faster than the cell migration, suggesting that both crypt and villus cells are capable of producing CaBP. Daily administration of vitamin D3 or 1 alpha,25-(OH)2D3 for 2 weeks resulted in a marked increase in CaBP levels mainly in the mid- and upper villus regions. The higher the intestinal calcium transport activity was, the higher the duodenal CaBP content. These results suggest that CaBP is not necessary in initiating intestinal calcium transport, but it plays an important role in maintaining the enhanced transport mechanism.

Regulation of messenger ribonucleic acid expression of 1 alpha,25-dihydroxyvitamin D3-24-hydroxylase in rat osteoblasts.

We have reported that PTH inhibits 25-hydroxyvitamin D3-24-hydroxylase messenger RNA (mRNA) expression induced by 1 alpha,25-dihydroxyvitamin D3 [1 alpha, 25-(OH)2D3] in rat kidney but not intestine. In the present study, we examined whether the suppression of 24-hydroxylase mRNA expression by PTH occurs commonly in tissues and cells which have PTH receptors. Administration of 1 alpha, 25-(OH)2D3 into rats fed a synthetic vitamin D-repleted diet containing adequate calcium greatly increased serum levels of calcium and 1 alpha, 25-(OH)2D3. Also, there was a 4-fold increase in bone 24-hydroxylase activity in response to 1 alpha, 25-(OH)2D3 administration. In rats fed a low calcium diet, renal 24-hydroxylase activity was suppressed probably due to secondary hyperparathyroidism. In contrast, the low calcium feeding did not suppress bone 24-hydroxylase activity. The expression of 24-hydroxylase mRNA in rat osteoblastic C-26 and C-11 cells was similar and attained maximal levels 24 h after cells were incubated with 10(-8) M 1 alpha, 25-(OH)2D3. Induction of 24-hydroxylase mRNA expression by 1 alpha, 25-(OH)2D3 was much greater and earlier in immature C-26 cells than mature C-11 cells. Simultaneous addition of PTH, prostaglandin E2, or cAMP together with 1 alpha, 25-(OH)2D3 did not down-regulate mRNA expression of 24-hydroxylase induced by the vitamin in both C-26 and C-11 cells. Of the three osteoblastic cells (C-26, C-20, and C-11) examined, C-26 cells showed the least mRNA expression of vitamin D receptors, in spite of the highest expression of 24-hydroxylase mRNA. These results suggest that unlike in the kidney, bone 24-hydroxylase mRNA expression is not down-regulated by PTH despite of the presence of PTH receptors. They also suggest that the degree of the induction of 24-hydroxylase mRNA by 1 alpha, 25-(OH)2D3 is not explained simply by the vitamin D receptors content.

Distribution of ornithine decarboxylase activity induced by 1 alpha,25-dihydroxyvitamin D3 in chick duodenal villus mucosa.

The distribution of enzymes involved in polyamine synthesis and that of the polyamine levels were investigated in the duodenal mucosa of vitamin D-deficient chicks and those supplemented with 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25-(OH)2D3]. Duodenal epithelial cells were isolated sequentially from the villus tip to the crypt region using a nonenzymatic method. In vitamin D-deficient chicks, the activities of ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase were markedly higher in the crypt cells than in the villus cells. Similar gradients were observed in the distribution of putrescine and spermidine. Six hours after iv administration of 625 ng 1 alpha,25-(OH)2D3, ODC activity and putrescine levels markedly increased both in the villus and crypt region. The rate of the increase in ODC activity and putrescine levels, however, was much higher in the villus than in the crypt region. Neither S-adenosylmethionine decarboxylase activity nor spermidine levels were affected by the treatment with 1 alpha,25-(OH)2D3. To investigate differential uptake of 1 alpha,25-(OH)2D3 in the duodenal mucosa, 0.1 nmol 1 alpha,25-(OH)2[3H]D3 with or without a 200-fold excess of unlabeled 1 alpha,25-(OH)2D3 was injected into rachitic chicks, and epithelial cells were sequentially isolated 2 h later. The radioactivity specifically incorporated in the nuclear fraction was distributed uniformly from the villus tip to crypt cells. The cytoplasmic receptor for 1 alpha,25-(OH)2D3 was similarly distributed in the crypt and villus cells. These results suggest that 1 alpha,25-(OH)2D3 plays a physiological role in cellular activities not only in the villus but also in the crypt region through polyamine biosynthesis.

1 alpha,25-dihydroxyvitamin D3 regulates in vivo production of the third component of complement (C3) in bone.

We previously reported that 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25-(OH)2D3] specifically stimulates production of the third component of complement (C3) by murine osteoblastic cells and marrow-derived stromal cells (ST2) in vitro. In the present study we examined tissue-specific production of C3 in vivo in vitamin D-deficient mice, some of which received supplemental 1 alpha,25-(OH)2D3. Western blot analysis indicated that the C3 protein band in bone was undetectable in vitamin D-deficient mice, but became distinct 48 h after 1 alpha,25-(OH)2D3 administration. The mRNA expression of C3 in bone was also undetectable in vitamin D-deficient mice and appeared as early as 24 h after 1 alpha,25-(OH)2D3 administration. mRNA expression apparently preceded the appearance of C3 protein. In contrast, there was no significant difference in the expression of hepatic C3 mRNA among normal mice fed laboratory chow and vitamin D-deficient mice with and without 1 alpha,25-(OH)2D3 administration. The serum concentration of C3 in vitamin D-deficient mice was almost identical to that in normal mice and was unchanged after 1 alpha,25-(OH)2D3 administration. 1 alpha,25-(OH)2D3 receptor (VDR) mRNAs were detected in the kidney and intestine, whereas no appreciable mRNA expression of VDR occurred in the liver. Osteopontin mRNA was expressed in response to 1 alpha,25-(OH)2D3 in the kidney, but not in the intestine. Immunohistochemical studies showed that in normal mice, the C3 protein was located mainly in the periosteal regions of calvaria and on the surfaces of bone trabeculae in the tibial metaphyses. These results demonstrate that 1 alpha,25-(OH)2D3 tissue-specifically regulates in vivo production of C3 in bone. The production of bone C3 cannot be attributed to the presence of VDR alone, and we speculate that other tissue-specific factors are required.

Osteoprotegerin produced by osteoblasts is an important regulator in osteoclast development and function.

Osteoprotegerin (OPG), a soluble decoy receptor for receptor activator of nuclear factor-kappaB ligand (RANKL)/osteoclast differentiation factor, inhibits both differentiation and function of osteoclasts. We previously reported that OPG-deficient mice exhibited severe osteoporosis caused by enhanced osteoclastic bone resorption. In the present study, potential roles of OPG in osteoclast differentiation were examined using a mouse coculture system of calvarial osteoblasts and bone marrow cells prepared from OPG-deficient mice. In the absence of bone-resorbing factors, no osteoclasts were formed in cocultures of wild-type (+/+) or heterozygous (+/-) mouse-derived osteoblasts with bone marrow cells prepared from homozygous (-/-) mice. In contrast, homozygous (-/-) mouse-derived osteoblasts strongly supported osteoclast formation in the cocultures with homozygous (-/-) bone marrow cells, even in the absence of bone-resorbing factors. Addition of OPG to the cocultures with osteoblasts and bone marrow cells derived from homozygous (-/-) mice completely inhibited spontaneously occurring osteoclast formation. Adding 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] to these cocultures significantly enhanced osteoclast differentiation. In addition, bone-resorbing activity in organ cultures of fetal long bones derived from homozygous (-/-) mice was markedly increased, irrespective of the presence and absence of bone-resorbing factors, in comparison with that from wild-type (+/+) mice. Osteoblasts prepared from homozygous (-/-), heterozygous (+/-), and wild-type (+/+) mice constitutively expressed similar levels of RANKL messenger RNA, which were equally increased by the treatment with 1alpha,25(OH)2D3. When homozygous (-/-) mouse-derived osteoblasts and hemopoietic cells were cocultured, but direct contact between them was prevented, no osteoclasts were formed, even in the presence of 1alpha,25(OH)2D3 and macrophage colony-stimulating factor. These findings suggest that OPG produced by osteoblasts/stromal cells is a physiologically important regulator in osteoclast differentiation and function and that RANKL expressed by osteoblasts functions as a membrane-associated form.

The specific production of the third component of complement by osteoblastic cells treated with 1 alpha,25-dihydroxyvitamin D3.

A 190 kDa protein was purified from conditioned media of mouse marrow-derived stromal cell (ST2) cultures treated with 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25(OH)2D3) and identified as the third component of mouse complement (C3). Northern and Western blot analysis revealed that the production of C3 by ST2 and primary osteoblastic cells was strictly dependent on 1 alpha,25(OH)2D3, but the production by hepatocytes was not. Adding 1 alpha,25(OH)2D3 together with mouse C3 antibody to bone marrow cultures greatly inhibited the formation of tartrate-resistant acid phosphatase (TRAP)-positive osteoclast-like multinucleated cells. Adding C3 alone induced no TRAP-positive cell formation. These results suggest that, in bone tissues, C3 is specifically produced by osteoblasts in response to 1 alpha,25(OH)2D3 and somehow involved in inducing differentiation of bone marrow cells into osteoclasts in concert with other factors produced by osteoblasts in response to 1 alpha,25(OH)2D3.

The role of gravity in chick embryogenesis.

Thirty fertilized chick eggs preincubated for 0, 7 and 10 days on earth (10 eggs each) were flown in the space shuttle 'Endeavour' and further incubated for 7 days under microgravity. Twenty out of thirty eggs (9/10 ten-day-old; 10/10 seven-day-old; 1/10 zero-day-old) were recovered alive after landing. The only living embryo of the zero-day-old group died 24 days after launch, and was comparable to a 16-day-old embryo. The high mortality of the 0-day-old eggs appeared to be related to the specific inner structure of the egg. Simulation experiments performed on earth indicated that when yolk stayed in the albumen for more than 2 days, most of the embryos died. The subtle difference in specific gravity between the yolk (1.029) and albumen (1.040) plays a critical role in early chick embryogenesis.

Mouse primary osteoblasts express vitamin D3 25-hydroxylase mRNA and convert 1 alpha-hydroxyvitamin D3 into 1 alpha,25-dihydroxyvitamin D3.

We examined whether 1 alpha-hydroxyvitamin D3 (1 alpha(OH)D3) is metabolized into 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25(OH)2D3) in bone. Northern blot analysis indicated that the expression of vitamin D3 25-hydroxylase mRNA was highest in the liver, followed by the duodenum, calvaria, lung, kidney, skin and long bone, and lowest in the spleen. Of the bone cell fractions isolated from fetal mouse calvaria by a sequential enzymatic digestion, fraction 3, which consisted of mostly osteoblastic cells, showed the highest expression of vitamin D3 25-hydroxylase mRNA. When either cultured bone cells of fraction 3 or mouse calvaria were incubated with [3H]-1 alpha (OH)D3, a radioactive peak which comigrated at the same position as authentic 1 alpha,25(OH)2D3 was found on an HPLC chromatogram. The radioactive fraction obtained from the conditioned media of fetal mouse calvaria was tentatively identified as 1 alpha,25(OH)2D3 by cochromatography with authentic 1 alpha,25(OH)2D3 on three different HPLC systems and a thermal isomerization analysis. These results indicate that 1 alpha(OH)D3 is hydroxylated at the 25-position in bones, resulting in the local synthesis of 1 alpha,25(OH)2D3 from 1 alpha(OH)D3 in the skeletal tissues.

Regulation of vitamin D-responsive gene expression by fluorinated analogs of calcitriol in rat osteoblastic ROB-C26 cells.

We compared the activation of vitamin D-responsive genes by 24,24-difluorocalcitriol [F2-1 alpha,25(OH)2D3] and 26,26,26,27,27,27-hexafluorocalcitriol [F6-1 alpha,25(OH)2D3] with that by calcitriol [1 alpha,25(OH)2D3] in rat osteoblastic ROB-C26 cells. F2-1 alpha,25(OH)2D3 and F6-1 alpha, 25(OH)2D3 were ten times more potent than 1 alpha,25(OH)2D3 in inducing the expression of 1 alpha, 25(OH)2D3-24-hydroxylase (24-OHase) mRNA 6 h after adding vitamin D compounds. The lower affinity of these two fluorinated analogs compared with that of 1 alpha,25(OH)2D3 for vitamin D binding protein in serum (serum DBP) seemed to be partly involved in their increased ability to activate the 24-OHase gene. A time course study revealed that the expression of the 24-OHase and osteopontin mRNAs in the cells incubated with 1 alpha, 25(OH)2D3 and F2-1 alpha,25(OH)2D3 attained maximal levels at 6 h for 24-OHase mRNA and 18 h for osteopontin mRNA, the both decreased thereafter. On the contrary, F6-1 alpha,25(OH)2D3 increased the expression of 24-OHase and osteopontin exponentially until 72 h. While F2-1 alpha,25(OH)2[1 beta-3H]D3 was catabolized quickly by ROB-C26 cells, F6-1 alpha,25(OH)2[1 beta-3H]D3 was slowly and quantitatively converted into putative 26,26,26,27,27,27-hexafluoro-23S-hydroxy[1 beta-3H]calcitriol (F6-1 alpha,23S,25(OH)3[1 beta-3H]D3). This may explain why the time-course profiles of the accumulation of mRNAs for 24-OHase and osteopontin differed in the cells exposed to the fluorinated analogs. In addition to the longer retention, unknown up-regulating mechanisms appeared to be involved in the exponential activation of the 24-OHase and osteopontin genes induced by F6-1 alpha,25(OH)2D3.

Mg2+ binding and catalytic function of sphingomyelinase from Bacillus cereus.

The modes of Mg2+ binding to SMase from Bacillus cereus were studied on the basis of the changes in the tryptophyl fluorescence intensity. This enzyme was shown to possess at least two binding sites for Mg2+ with low and high affinities. The effects of Mg2+ binding on the enzymatic activity and structural stability of the enzyme molecule were also studied. The results indicated that the binding of Mg2+ to the low-affinity site was essential for the catalysis, but was independent of the substrate binding to the enzyme. It was also indicated that the alkaline denaturation of the enzyme was partly prevented by the Mg2+ binding, whereas no significant protective effect was observed against the denaturation by urea. The pH dependence of the kinetic parameters for the hydrolysis of micellar HNP and mixed micellar SM with Triton X-100 (1:10), catalyzed by SMase from B. cereus, was studied in the presence of a large amount of Mg2+ to saturate both the low- and high-affinity sites. The pH dependence curves of the logarithm of 1/Km for these two kinds of substrates were similar in shape to each other, and showed a single transition. On the other hand, the shapes of the pH dependence curves of the logarithm of kcat for these two kinds of substrates were different from each other. The pH dependence curve for micellar HNP showed three transitions and, counting from the acidic end of the pH region, the first and third transitions having tangent lines with slopes of +1 and -1, respectively. On the other hand, the curve for mixed micellar SM with Triton X-100 showed one large transition with a slope of +1 (the first transition) and a very small transition (the third transition). On the basis of the present results and the three-dimensional structure of bovine pancreatic DNase I, which has a primary structure similar to that of B. cereus SMase, we proposed a catalytic mechanism for B. cereus SMase based on general-base catalysis.

Tissue-specific production of the third component of complement(C3) by vitamin D in bone.

The third component of complement (C3) is a protein produced by osteoblastic cells in response to 1 alpha,25(OH)2D3. The bone C3 appears to be involved in differentiation of bone marrow cells into osteoclasts in concert with other vitamin D-dependent factors. Further studies are needed to understand the precise role of C3 in bone.

Microgravity generated by space flight has little effect on the growth and development of chick embryonic bone.

Seven days' space flight of fertilized chicken eggs pre- incubated for 7 and 10 days on earth caused no differences in the morphology of osteoblasts, osteoclasts, and osteocytes of humerus and tibia from those of control embryos. Bone-resorbing and -forming activities of the femur were not different between control and flight groups. As a consequence, calcium and phosphorus contents of the femora between control and flight groups were not changed. Alkaline phosphatase activity of 3 different regions (resting cartilage, growth cartilage, and cortical bone) of tibia showed no significant difference between control and flight groups. No significant difference of gene expressions of hepatocyte growth factor and receptors of fibroblast growth factor was observed in perichondrium, trabecula, and skeletal muscles and tendons of hind limbs between control and flight groups. Unlike the results of previous space flight experiments in which young growing mammals were used, these morphological and biochemical results indicate that microgravity has little effect on bone metabolism of the chick embryo.

[The mechanism which calcitonin activates vitamin D].

Calcitropic hormones, such as calcitonin and vitamin D, are one of the most common drugs used in the treatment of osteoporosis. Recently, three enzymes involved in vitamin D metabolism (25-hydroxylase, 24-hydroxylase, 1alpha-hydroxylase) were cloned and enabled us to analyze the vitamin D metabolism at a molecular level. We summarize the mechanism which CT activates vitamin D.

[The regulation of vitamin D metabolism and PTH secretion by phosphorus].

Vitamin D and PTH are major hormones that regulate calcium metabolism. Also, the serum level of phosphorus is known to change according to the level of calcium and to regulate the vitamin D and PTH. Recently, cloning of 1alpha- hydroxylase cDNA which is the key enzyme in vitamin D metabolism, enabled us to examine the effects of phosphorus in vitamin D metabolism at a molecular level. Furthermore, the direct effect of phosphorus in PTH synthesis is being elucidated in recent reports. In this paper, we summarized the regulation of vitamin D and PTH by phosphorus.

[Cloning and expression of 25-hydroxyvitamin D3-1 alpha-hydroxylase gene].

A full-length cDNA for the rat kidney mitochondrial cytochrome P450 mixed function oxidase, 25-hydroxyvitamin D3-1 alpha-hyroxylase, was cloned from a vitamin D-deficient rat kidney cDNA library and subcloned into the mammalian expression vector pcDNA 3.1(+). When 1 alpha-hydroxylase cDNA was transfected into COS-7 cells, they expressed 25-hydroxyvitamin D3-1 alpha-hydroxylase activity. The sequence analysis showed that 1 alpha-hydroxylase cDNA consisted of 2469 bp in length and contained an open reading frame encoding 501 amino acids. The expression of 1 alpha-hydroxylase mRNA was greatly increased in the kidney of vitamin D-deficient rats. In rats with the enhanced renal production of 1 alpha, 25-dihydroxyvitamin D3 (rats fed a low Ca diet), expression of 1 alpha-hydroxylase mRNA was greatly enhanced in the renal proximal convoluted tubules. These results clearly demonstrate that the expression of 1 alpha-hydroxylase is regulated at a transcriptional level. The DNA flanking the 5'-sequence of the mouse 1 alpha-hydroxylase gene has been cloned and sequenced. The promoter has 3 potential CRE sites, 2 perfect and 1 imperfect AP-1 sites, while no DR-3 was detected. Parathyroid hormone stimulates this promoter-directed synthesis of luciferase by 17-fold, while forskolin stimulates it by 3-fold. These results indicate that parathyroid hormone stimulates 25-hydroxyvitamin D3-1 alpha-hydroxylase by acting on the promoter of the 1 alpha-hydroxylase gene.

Mitogen-activated protein kinases mediate interleukin-1beta-induced receptor activator of nuclear factor-kappaB ligand expression in human periodontal ligament cells.

BACKGROUND AND OBJECTIVE: Interleukin-1beta-stimulated receptor activator of nuclear factor-kappaB ligand (RANKL) expression in human periodontal ligament cells is partially mediated by endogenous prostaglandin E2, whereas mitogen-activated protein kinases (MAPKs) are implicated in regulating various interleukin-1-responsive genes. We investigated herein the involvement of MAPKs in interleukin-1beta-stimulated RANKL expression in human periodontal ligament cells. MATERIAL AND METHODS: Human periodontal ligament cells were pretreated separately with specific inhibitors of MAPKs, including extracellular signal-regulated kinase, p38 MAPK and c-Jun N-terminal kinase, and subsequently treated with interleukin-1beta. Following each treatment, the phosphorylation of each MAPK, the expression of RANKL, and the production of prostaglandin E2 were determined. RANKL activity was evaluated using an assay to determine the survival of prefusion osteoclasts. RESULTS: Interleukin-1beta induced RANKL expression at the mRNA and protein levels, as well as RANKL activity in human periodontal ligament cells. Interleukin-1beta also activated extracellular signal-regulated kinase, p38 MAPK, and c-Jun N-terminal kinase. Pretreatment with each MAPK inhibitor partially, but significantly, suppressed interleukin-1beta-induced RANKL expression and its activity, as well as prostaglandin E2 production. CONCLUSION: In human periodontal ligament cells, three types of MAPK inhibitor may abrogate RANKL expression and activity induced by interleukin-1beta, directly or indirectly through partial suppression of prostaglandin E2 synthesis. In addition, extracellular signal-regulated kinase, p38 MAPK, and c-Jun N-terminal kinase signals may co-operatively mediate interleukin-1beta-stimulated RANKL expression and its activity in those cells.