Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0029463 (osteosarcoma)
 16,637 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have studied the role of retinoid X receptor alpha (RXR alpha) in vitamin D receptor (VDR) responsive interactions using nuclear extracts from human osteoblast-like MG-63 osteosarcoma cells and its specific response element from human osteocalcin gene (OC-VDRE). An RXR alpha-specific antibody was not capable of recognizing the two VDR responsive complexes formed with the OC-VDRE. Addition of in-vitro-produced RXR alpha to the binding reaction resulted in decreased binding of the two VDR-responsive interactions and, simultaneously, formation of a new complex, which was identified with RXR alpha- and VDR-specific antibodies. A similarly migrating RXR alpha- and VDR-responsive complex was also formed when baculovirus-expressed VDR was used with the in-vitro-produced RXR alpha in the absence of a nuclear extract or when VDRE from mouse osteopontin gene (OP-VDRE) was used as a binding site. Characterization of DNA binding properties for this VDR-RXR alpha complex revealed that both half sites of OC-VDRE are required for DNA binding. These results indicate that RXR alpha is probably not the physiological accessory factor in the MG-63 osteosarcoma cells needed for the VDR-VDRE interactions within the human osteocalcin gene promoter, although it is capable of dimerizing with recombinant VDR and the native VDR from these cells and although these dimers are capable of binding in vitro to the OC-VDRE.
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PMID:Retinoid-X-receptor-alpha-independent binding of vitamin D receptor to its response element from human osteocalcin gene. 770 32

Previous studies have shown that 1,25(OH)2D3 activates multiple signaling pathways in osteoblasts, including rapid nongenomic and long-term genomic pathways. Genomic pathways are mediated by the vitamin D receptor (VDR), a member of the steroid receptor superfamily, and involve transcriptional regulation of target genes. Nongenomic pathways involve lipid turnover, activation of Ca+2 channels and elevation of intracellular Ca+2, all of which occur within seconds after addition of seco-steroid. The interaction of other physiological metabolites of vitamin D, such as 24,25(OH)2D3, with target cells such as osteoblasts is much less clear. We have used a combination of electrophysiological, biochemical, molecular and ion tracer studies to dissect the physiological responses of osteoblast-like osteosarcoma cells (ROS 17/2.8) to 1,25(OH)2D3 and related metabolites. We conclude the following: 1) the structural requirements for activation of genomic vs. nongenomic pathways by seco-steroid are distinct and likely to involve separate receptors; 2) activation of rapid nongenomic pathways is independent of the long-term regulation of target genes; and 3) 1,25(OH)2D3 and 24,25(OH)2D3 interact at the level of the plasma membrane to regulate Ca+2 permeability. Present studies are aimed toward the understanding of the role of both genomic and nongenomic pathways in osteoblast physiology.
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PMID:Vitamin D metabolites modulate osteoblast activity by Ca+2 influx-independent genomic and Ca+2 influx-dependent nongenomic pathways. 778 30

The effects of steroid and thyroid hormones are mediated by intracellular hormone receptors. An important mechanism modulating target tissue responsiveness to hormones is homologous and heterologous regulation of the receptors. We have characterized the expression of steroid hormone receptors in human MG-63 osteosarcoma cells. The MG-63 cells express receptor mRNAs for glucocorticoids, estrogen, retinoic acid, and 1,25(OH)2D3. We found that only the vitamin D receptor (VDR) mRNA concentration was influenced by the hormones. The stability of the VDR message was identical in control, dexamethasone- and estradiol-treated cells. On the other hand, both 1,25(OH)2D3 and retinoic acid separately stabilized the VDR mRNA levels increasing the apparent half-life by 11 h and 6 h, respectively. The VDR protein levels, however, as measured by immunoprecipitation, increased only after the 1,25(OH)2D3 treatment.
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PMID:Steroid hormone modulation of vitamin D receptor levels in human MG-63 osteosarcoma cells. 780 48

The steroid hormone vitamin D is a principal mediator of skeletal homeostasis. 1,25-Dihydroxyvitamin D3 treatment of ROS 17/2.8 osteoblast-like cells results in a ligand-dependent increase in transcription of the bone-specific osteocalcin gene. This transcriptional upregulation requires the positive cis-acting vitamin D responsive element (VDRE). We have used the ligation-mediated polymerase chain reaction to demonstrate that protein occupancy of the VDRE within the intact cell correlates with increased synthesis of osteocalcin transcripts. These protein-DNA contacts were not present in the absence of vitamin D or in osteosarcoma cells (ROS 24.1) lacking the vitamin D receptor. Our results establish in intact cells the requirement for both ligand- and receptor-dependent occupancy of the VDRE for vitamin D responsive enhancement of osteocalcin gene transcription.
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PMID:In vivo occupancy of the vitamin D responsive element in the osteocalcin gene supports vitamin D-dependent transcriptional upregulation in intact cells. 780 44

Treatment of human MG-63 osteosarcoma cells with human recombinant transforming growth factor beta 1 (TGF-beta 1) was found to inhibit cell proliferation. In addition, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]-induced osteocalcin synthesis was greatly influenced by TGF-beta 1. Dose- and time-dependent inhibition was seen both in medium osteocalcin and the corresponding mRNA concentrations. Furthermore, TGF-beta 1 decreased osteocalcin synthesis modulated negatively by dexamethasone or positively by retinoic acid. The stability of osteocalcin mRNA was not decreased by the TGF-beta 1 treatment, but in vitro transcription assays demonstrated diminished osteocalcin gene transcription caused by the TGF-beta 1 treatment. Binding of vitamin D receptor (VDR) to an oligonucleotide probe containing the osteocalcin vitamin D response element (VDRE) was not influenced by TGF-beta 1, however. Incubation of the cells with the serine/threonine kinase inhibitor H-7 did not block the ability of TGF-beta 1 to decrease osteocalcin synthesis but caused a further inhibition. Also, the 1,25(OH)2D3-induced osteocalcin synthesis was decreased by H-7 treatment, suggesting that phosphorylation as such is involved in the transcriptional activation mechanism of VDR. These results demonstrate that TGF-beta 1 is a strong inhibitor of the synthesis of osteocalcin, a calcium binding protein participating in bone mineralization, by counteracting the stimulatory effects of other hormones on its synthesis. We further suggest that TGF-beta 1 affects the synthesis of osteocalcin at the level of transcription through mechanism(s) different from the serine/threonine kinase pathway.
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PMID:Effects of transforming growth factor beta 1 on the regulation of osteocalcin synthesis in human MG-63 osteosarcoma cells. 781 11

The regulation of vitamin D receptor (VDR) abundance in MC3T3-E1 mouse osteoblasts and UMR 106-01 rat osteosarcoma cells by rat PTH 1-34, human PTH-related protein 1-34, and agents that activate specific signal transduction pathways was studied. Treatment of these cells with forskolin (FSK) caused up-regulation of VDR, whereas treatment with phorbol esters suppressed VDR levels. PTH or PTH-related protein treatment induced a 2- to 3-fold increase in VDR, which was equivalent to that elicited by FSK in UMR 106-01 cells but less than the FSK-induced increase (approximately 8-fold) in MC3T3-E1 cells. PTH treatment of MC3T3-E1 cells resulted in an approximately 3-fold increase in VDR levels with maximum stimulation occurring at 10(-9) M PTH after 4 h of treatment. In UMR 4-7 cells, a subclone of UMR 106-01 cells that express cAMP resistance due to regulated expression of a mutant form of the type 1 regulatory subunit of the cAMP-dependent protein kinase A (PKA), the up-regulation of VDR abundance due to FSK and PTH treatment was mostly prevented. Pretreatment of MC3T3-E1 cells with staurosporine, an inhibitor of PKC, resulted in an approximately 3-fold increase in basal VDR levels but did not enhance the PTH-mediated up-regulation of VDR. Collectively, these data suggest that the increase in VDR abundance observed in these target cells is mainly due to the activation of the PKA signal transduction pathway. Treatment of UMR 106-01 cells with PTH for 4 h before exposure of the cells to 1,25-dihydroxyvitamin D3 resulted in a 2-fold increase in the induction of 25-hydroxyvitamin D3-24 hydroxylase messenger RNA. Thus, exposure of target cells to PTH augments their response to 1,25-dihydroxyvitamin D3 due to up-regulation of VDR abundance.
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PMID:Regulation of 1,25-dihydroxyvitamin D3 receptors by parathyroid hormone in osteoblastic cells: role of second messenger pathways. 783 3

1,25-(OH)2-Vitamin D3, the active metabolite of vitamin D, is a secosteroid hormone with known differentiating activity in leukemic cells. Studies have demonstrated the presence of vitamin D receptors (VDR) in a wide range of tissues and cell types. Antiproliferative activity of 1,25-(OH)2-vitamin D3 has been documented in osteosarcoma, melanoma, colon carcinoma, and breast carcinoma cells. This study was designed to analyze vitamin D receptor level in breast cancer cells as a marker of differentiation and as a predictor of growth inhibition by 1,25-(OH)2-vitamin D3. VDR messenger RNA was found to be present in relatively high levels in well-differentiated cells and in low levels in poorly differentiated cells. All cell lines had detectable VDR mRNA. Radiolabeled ligand binding assay showed a similar pattern. MCF-7 and T47D cells, which express VDR at moderate levels, showed significant growth inhibition by 10(-9) M1,25-(OH)2-vitamin D3 (p < 0.05). MDA-MB-231 cells, which have very low levels of VDR, demonstrated no growth inhibition by 1,25-(OH)2-vitamin D3 at concentrations up to 10(-6) M. Based on these results it can be stated that VDR expression is lost with de-differentiation and that receptor is essential for the antiproliferative response to 1,25-(OH)2-vitamin D3.
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PMID:Vitamin D receptors in breast cancer cells. 788 Oct 99

The subnuclear distribution of the vitamin D receptor was investigated to begin addressing the contribution of nuclear architecture to vitamin D-responsive control of gene expression in ROS 17/2.8 rat osteosarcoma cells. The nuclear matrix is an anastomosing network of filaments that is functionally associated with DNA replication, transcription, and RNA processing. The representation of vitamin D receptor in the nuclear matrix and nonmatrix nuclear fractions was determined by the combined application of 1) sequence-specific interactions with the vitamin D receptor binding element of the rat bone-specific osteocalcin gene promoter and 2) Western blot analysis. Both methods confirmed the presence of vitamin D receptor in the nonmatrix nuclear fraction and the absence of detectable vitamin D receptors associated with the nuclear matrix. In contrast, these same nuclear matrix proteins preparations exhibited association with the general transcription factor AP-1 and a bone tissue-specific promoter binding factor NMP2. NMP-2 exhibits recognition for a promoter domain contiguous to the vitamin D-responsive element of the osteocalcin gene, although the vitamin D receptor does not appear to be a component of the nuclear matrix proteins. Interrelationships between nuclear matrix proteins and nonmatrix nuclear proteins, in mediating steroid hormone responsiveness of a vitamin D-regulated promoter, are therefore suggested.
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PMID:Subnuclear distribution of the vitamin D receptor. 801 99

A peptide of 27 amino acids, VDR(102-76), representing residues 76-102 immediately C-terminal to the second Zn finger of human vitamin D receptor (hVDR) was conjugated to fluorescein-labelled IgG using a bifunctional coupling reagent, m-maleimidobenzoyl n-hydroxysuccinimide. Upon microinjection into the cytoplasm of human osteosarcoma MG-63 cells, the chimeras accumulated in the nuclei. This transport was arrested by chilling or energy depletion. Two other peptides, VDR(80-67), spanning the N-terminal part of VDR(102-76), and VDR(108-97), spanning the C-terminal part of VDR(102-76), were not able to target the linked proteins to the nuclei. SV40(135-112), a peptide containing a well-characterized nuclear localization sequence (amino acids 112-135) of simian virus 40 (SV40) large T-antigen, caused complete nuclear accumulation under the same conditions. Wheat germ agglutinin, which inhibits SV40(135-112) transport, also inhibited the nuclear accumulation of VDR(102-76) as did energy depletion.
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PMID:A peptide C-terminal to the second Zn finger of human vitamin D receptor is able to specify nuclear localization. 805 6

The binding of transcription factor AP-1 and vitamin D receptor (VDR) to the composite AP-1 plus vitamin-D-responsive promoter region (AP-1 + VDRE) of the human osteocalcin gene was characterized in osteocalcin-producing (MG-63) and non-producing (U2-Os, SaOs-2) human osteosarcoma cell lines. In mobility-shift assays with AP-1 + VDRE, AP-1, and VDRE probes and nuclear extracts from these cells, one AP-1-specific and two VDR-specific (fast and slow mobility) interactions were observed. Characterization of the complexes indicated that AP-1 and VDR do not bind simultaneously to the AP-1 + VDRE oligonucleotide. Intensity of the complexes was greatly influenced by cell density: in MG-63 and SaOs-2 cells, AP-1 binding was strong during the proliferative period disappearing at confluency whereas, in U2-Os cells, AP-1 binding was prominent also at the confluent stage. Furthermore, MG-63 cells possessed the faster migrating VDR complex at all stages of confluency whereas, in U2-Os and SaOs-2 cells, it was very weak or absent. There were no detectable differences in the levels of VDR protein between these cell lines. In U2-Os cells, the level of c-jun mRNA was higher than in the other two cell lines, whereas none of these cell lines exhibited detectable levels of c-fos mRNA at the confluent stage. Exogenous c-Jun protein effectively blocked the VDR-DNA interaction. Further, all these cell lines expressed mRNA for retinoid X receptor alpha (RXR alpha), the factor suggested to be required for the VDR-DNA interaction. The presence of an accessory factor in the VDR-DNA complexes was indirectly shown by treatment of the cells with 9-cis retinoic acid and by cycloheximide. Both treatments reduced VDR binding without affecting the VDR protein level. These results suggest that AP-1 interferes with VDR binding to the AP-1 + VDRE element and that the vitamin D responsiveness of the osteocalcin gene correlates with weak AP-1 binding and strong binding of the faster migrating VDR complex.
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PMID:Functional interference between AP-1 and the vitamin D receptor on osteocalcin gene expression in human osteosarcoma cells. 807 31


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