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)

Exposure of osteosarcoma cell lines to chronic intermittent strain increases the activity of mechano-sensitive cation (SA-cat) channels. The impact of mechano-transduction on osteoblast function has not been well studied. We analyzed the expression and production of bone matrix proteins in human osteoblast-like osteosarcoma cells, OHS-4, in response to chronic intermittent mechanical strain. The OHS-4 cells exhibit type I collagen production, 1,25-Dihydroxyvitamin D-inducible osteocalcin, and mineralization of the extracellular matrix. The matrix protein message level was determined from total RNA isolated from cells exposed to 1-4 days of chronic intermittent strain. Northern analysis for type I collagen indicated that strain increased collagen message after 48 h. Immunofluorescent labeling of type I collagen demonstrated that secretion was also enhanced with mechanical strain. Osteopontin message levels were increased several-fold by the application of mechanical load in the absence of vitamin D, and the two stimuli together produced an additive effect. Osteocalcin secretion was also increased with cyclic strain. Osteocalcin levels were not detectable in vitamin D-untreated control cells. However, after 4 days of induced load, significant levels of osteocalcin were observed in the medium. With vitamin D present, osteocalcin levels were 4 times higher in the medium of strained cells compared to nonstrained controls. We conclude that mechanical strain of osteoblast-like cells is sufficient to increase the transcription and secretion of matrix proteins via mechano-transduction without hormonal induction.
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PMID:Human osteoblast-like cells respond to mechanical strain with increased bone matrix protein production independent of hormonal regulation. 753 Jun 47

The 1,25-dihydroxyvitamin D3 (vitamin D) receptor (VDR) is a key trans-activating protein that mediates calcium regulation as well as cellular proliferation and differentiation. Phosphorylation of the VDR contributes significantly to its functional activity, but the specific mechanisms that mediate this regulation are not well understood. Phosphorylation may influence DNA binding, ligand binding, and protein-protein interactions, including heterodimerization and/or transactivation functions. We used a protein kinase C inhibitor, staurosporine (ST), and an inhibitor of serine-threonine phosphatases, okadaic acid (OA), to elucidate the contribution of VDR phosphorylation to vitamin D-mediated transcription of the osteocalcin (OC) gene. Vitamin D-induced transcription was assayed in transfected ROS 17/2.8 osteosarcoma cells using chloraminphenicol acetyltransferase constructs containing the vitamin D-responsive element (VDRE) at its native locus in the rat OC promoter as well as fused to a heterologous promoter. Both ST and OA inhibit VDRE-mediated and vitamin D-dependent enhancement of OC gene transcription as well as OC biosynthesis, as assessed by RIAs. Results from gel mobility shift and Western blot analyses using nuclear proteins from ROS 17/2.8 cells show that binding of the VDR-retinoid-X receptor heterodimer complex to the OC VDRE is not inhibited in the presence of ST. In contrast, OA does inhibit the formation of complexes interacting with both the OC and osteopontin VDREs; immunoprecipitation studies using 32P-labeled ROS 17/2.8 cells reveal that OA treatment result in ligand-independent hyperphosphorylation of the VDR. Our results suggest that two distinct phosphorylation events modulate rat VDR function. One event is related to transactivation, and the other is also critical to the VDRE-binding activity of VDR-retinoid X receptor-DNA complexes with consequential effects on transactivation.
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PMID:Control of 1,25-dihydroxyvitamin D3 receptor-mediated enhancement of osteocalcin gene transcription: effects of perturbing phosphorylation pathways by okadaic acid and staurosporine. 758 24

The effects of two vitamin D analogs, 1,25-dihydroxyvitamin D-2 and 24-epi-1,25-dihydroxyvitamin D-2, were examined on osteocalcin gene expression in the rat osteosarcoma cell line ROS 17/28. Our results indicate that these analogs are more transcriptionally active than 1,25-dihydroxyvitamin D-3, particularly the 24-epimer. Assessment of reporter gene chloramphenicol acetyltransferase (CAT) activity, using the vitamin D responsive element (VDRE) derived from the human osteocalcin gene promoter. revealed that both analogs stimulated CAT activity 5- to 10-fold. 1,25-Dihydroxyvitamin D-2 was slightly more active than 1,25-dihydroxyvitamin D-3, while the 24-epimer was twice as effective. 1,25-Dihydroxyvitamin D-3 also stimulated osteocalcin mRNA accumulation by 2-fold over vehicle-treated cells, 1,25-dihydroxyvitamin D-2 by 2.5-fold, and 24-epi-1,25-dihydroxyvitamin D-2 by 4-fold. Electrophoretic mobility shift assays using the osteocalcin vitamin D responsive element revealed no increase in DNA binding with either analog when compared to 1,25-(OH)2D3. Examination of CAT activity using the rat 24-hydroxylase VDRE indicated no significant difference in transcription with these compounds, suggesting that the vitamin D-2 analogs preferentially activate osteocalcin gene expression.
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PMID:Transcriptional control of the osteocalcin gene by 1,25-dihydroxyvitamin D-2 and its 24-epimer in rat osteosarcoma cells. 764 Mar 5

24-Oxa-vitamin D3 (24-oxa-D3) and 24-oxa-1 alpha-hydroxyvitamin D3 were designed as possible inhibitors of the vitamin D metabolic activation pathway. Their affinity for the vitamin D receptor (from pig intestine) and human vitamin binding protein were reduced, and their potency to induce cell differentiation of human leukemia cells (HL 60) or osteosarcoma cells (MG 63) was markedly reduced (19% and 3%, respectively), in comparison with calcitriol. A single or chronic injection of 24-oxa-D3 had no biological activity, whereas chronic administration of 24-oxa-1 alpha-hydroxy-D3 showed weak agonist activity in rachitic chicks. When the 24-oxa-D3 was given prior to a single injection of vitamin D3, lower values of serum calcium (64% of the value obtained in vitamin D-treated animals), osteocalcin (52%), 25-(OH)D3 (45%) and duodenal calbindin-D 28K (9.4%) were found. When given chronically in a 100-fold more excess no clear antagonistic effects were observed. 24-Oxa-D3 is thus a new metabolic weak antagonist of vitamin D3, but adding a hydroxyl group at C-1 creates a weak agonist.
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PMID:Antagonistic activity of 24-oxa-analogs of vitamin D. 767 83

The 9-cis retinoic acid receptor (RXR) alpha, a co-regulator of the thyroid hormone and vitamin D receptors, has previously been shown to be expressed predominantly in metabolic organs such as the liver and the kidney. In this study we have used a reverse transcription polymerase chain reaction (RT-PCR) to examine the expression of retinoic acid (RA) nuclear receptors in primary human osteoblasts and in SaOS-2, a human osteosarcoma-derived cell line with osteoblastic characteristics. Our results demonstrate that human osteoblasts express RXR alpha, as well as the all-trans RA receptors (RAR) alpha, beta, and gamma. These data further establish bone as a major target for retinoids and suggest that RA can regulate vitamin D and thyroid hormone actions in osteoblasts.
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PMID:Reverse transcription-polymerase chain reaction assay demonstrates that the 9-cis retinoic acid receptor alpha is expressed in human osteoblasts. 768 68

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 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

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 osteocalcin (OC) silencer is a unique example of exonic sequences contributing to negative transcriptional control of mammalian gene expression. In this paper we demonstrate, using a reporter transfection assay, that multiple elements reside within the OC +24/+151 domain. Thirty-fold repression is mediated by the +49/+104 fragment, experimentally relocated 3' of the poly(A) signal. Deletion of either the +49/+54 protein-coding sequence or the +98/+104 intronic part of this fragment results in loss of repression activity, suggesting a bipartite organization of the +49/+104 silencer. Of particular interest, we have mapped an antisilencer activity to the ACCCTCTCT motif (+40/+48), found in silencers associated with several other genes. Extension of the +49/+104 silencer to include the +24/+48 and/or the +105/+151 sequences results in increased silencer activity up to 170-fold, suggesting the presence of additional silencer elements within these sequences. The activity of the silencer contained within the +24/+151 OC sequence is directed to the basal promoter and is not dependent on 5' distal enhancer elements, including those that mediate responsiveness of OC transcription to vitamin D. The OC silencer represses the heterologous thymidine kinase promoter and is operative in osseous (normal diploid osteoblasts, ROS 17/2.8 osteosarcoma) as well as HeLa cells. Our results, which suggest the presence of at least five regulatory elements downstream of the OC transcription start site, indicate the complexity of sequences that mediate repression of OC promoter activity.
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PMID:A composite intragenic silencer domain exhibits negative and positive transcriptional control of the bone-specific osteocalcin gene: promoter and cell type requirements. 797 85


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