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)

ATP released from damaged cells or by controlled secretion could be an important factor in the formation or remodeling of bone. In a variety of other tissues ATP has been shown to control cellular processes by acting on P2-purinoceptors and activating the calcium signaling pathway. Here we demonstrate for the first time that extracellular ATP increases the intracellular free calcium [Ca2+]i concentration in normal human osteoblasts and in SaOS-2 cells, a human osteosarcoma-derived cell line, but not in ROS 17/2.8 cells. The ATP-induced increase in [Ca2+]i was dose dependent, and the concentrations of ATP required were similar to those reported to regulate cellular functions in other cell types. Although ATP is metabolized rapidly by bone cells, the effects on [Ca2+]i appeared to be mediated directly by ATP rather than one of its metabolites. Adenosine 3-thiotriphosphate, a nonhydrolyzable analog of ATP, induced similar changes in [Ca2+]i. This indicates that P2-purinoceptors are present on osteoblast-like cells and that extracellular ATP from various sources might be an important factor in the regulation of osteoblast functions.
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PMID:Evidence for P2-purinoceptors on human osteoblast-like cells. 161 57

PTH activates multiple second messengers in its target cells, but the level at which the hormonal signal splits into different pathways is still unknown. To achieve insights on this issue, we have studied the structure-function relationship of PTH by analyzing the effects of bovine PTH-(1-34) [bPTH-(1-34)] and PTH fragments truncated at the N-terminus on the intracellular calcium concentration [( Ca2+]i) and cAMP production in the rat osteogenic sarcoma cell line UMR 106-01. [Ca2+]i was measured in single cells using fura-2. When exposed to 10(-7) M bPTH-(1-34), 20% of the cells responded with a transient increase in [Ca2+]i of variable amplitude. Equimolar doses of bPTH-(2-34), propionyl bPTH-(2-34) [(pbPTH-(2-34)], and bPTH-(3-34) also transiently increased [Ca2+]i, whereas both [tyrosine34]bPTH-(7-34) amide [bPTH-(7-34)] and bPTH-(30-34) were ineffective. The amplitude of the [Ca2+] i transients was dose-dependent, with threshold concentrations of 10(-10) M for bPTH-(1-34) and bPTH-(2-34), and 10(-9) M for bPTH-(3-34). The response rate to the active peptides ranged between 10-30%, without a clear dose-relatedness. A second addition of 10(-7) M bPTH-(1-34) to cells prestimulated with equimolar doses of bPTH-(2-34), pbPTH-(2-34), or bPTH-(3-34) produced another transient, whereas after exposure to 10(-7) M bPTH-(1-34), the cells were completely desensitized to a second homologous stimulation, suggesting that the binding affinity of the truncated peptides for the PTH receptor is lower than that of the intact bPTH-(1-34) fragment. In addition, both bPTH-(1-34) and bPTH-(2-34) dose-dependently stimulated cAMP production, but the former was more potent (ED50 = 10(-9) vs. 10(-7) M, respectively). On the contrary, pbPTH-(2-34), bPTH-(3-34), and bPTH-(7-34) had no effect on cAMP. Pretreating the cells with pertussis toxin to enhance cAMP responses via inhibition of Gi potentiated the effect of bPTH-(1-34) and bPTH-(2-34) and disclosed weak but detectable agonist action of pbPTH-(2-34). These results indicate that specific domains of the PTH molecule are linked to activation of different second messenger pathways; while the first two amino acids are indispensable for activating the cAMP system, generation of the [Ca2+]i signal appears to involve a longer domain, including the amino acid residue in position 3.
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PMID:Dissociation of second messenger activation by parathyroid hormone fragments in osteosarcoma cells. 164 59

Effects of increase in intracellular calcium on PTH-induced homologous desensitization were investigated using calcium ionophores. Pretreatment of UMR-106 cells (rat osteoblast like osteosarcoma cell line) with calcium ionophores (A23187 or ionomycin) for 6h resulted in approximately 50% decrease of PTH-stimulated cAMP production. PTH receptor binding, assessed with 125I-[Nle8,Nle18,Tyr34]PTH-(1-34) as radioligand, was significantly decreased in 10(-6) M calcium ionophore-pretreated (for 6h) cells without affecting the dissociation constant (Kd) for PTH. Minimal effective treatment period was 2h and similar inhibitory effect was observed in 12h-treated cells. These data suggest that increase in intracellular calcium might also act on PTH receptor in the similar manner as protein kinase C activation to induce desensitization.
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PMID:Role of increase in intracellular calcium in PTH-induced homologous desensitization in UMR-106 cells. 164 35

Osteoblast-like osteosarcoma cells (ROS 17/2.8) display a rapid transmembrane influx of extracellular calcium after stimulation by 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] that is mediated largely by the opening of voltage-gated calcium channels. These cells also constitutively express high numbers (greater than 18,000/cell) of nuclear receptors for this seco-steroid hormone that are involved in the modulation of genomic activity in the osteoblast and in the up-regulation of transcript ion of osteoblast-specific genes such as osteocalcin. The objective of this study was to determine the structural hierarchy of vitamin D3 analogs with regard to their efficacy as molecular transducers of the genomic and nongenomic pathways that are activated upon treatment of osteoblasts with 1,25-(OH)2D3. To test the structural features of the agonist required for initiation of these distinct pathways, a series of ligand analogs and naturally occurring metabolites of 1,25-(OH)2D3 were used that contain A-ring, D-ring, and side-chain modifications. The abilities of these analogs/metabolites to 1) bind to nuclear receptors and 2) stimulate transmembrane calcium influx were measured. Several analogs (25-hydroxy-16-ene-23-yne-D3 and 25-hydroxy-23-yne D3) were found to stimulate Ca2+ channel opening, but bind only poorly to the 1,25-(OH)2D3 nuclear receptor. Conversely, other analogs (1,24-dihydroxy-22-ene-24-cyclopropyl D3 and 1,25-dihydroxy-16-ene-23-yne,26,27 F6-D3) were found to bind very well to the nuclear receptor, but displayed little or no activity in opening Ca2+ channels. Pertussis toxin, which interferes with coupling of certain ligand-gated receptors to ion channels, failed to block the activation of calcium channels by 1,25-(OH)2D3 or active agonist analogs. Our results indicate that there are likely to be distinct nuclear and plasma membrane-associated forms of the 1,25-(OH)2D3 receptor that are involved in genomic and nongenomic activation of osteoblast activity, respectively. The membrane-associated receptors do not appear to be coupled to pertussis toxin-sensitive G-proteins.
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PMID:Nongenomic actions of 1,25-dihydroxyvitamin D3 in rat osteosarcoma cells: structure-function studies using ligand analogs. 165 87

We present evidence that the regulation of osteocalcin secretion by PTH and PGE2 in normal human bone cells can be produced in the human osteoblast-like cell line MG-63. Both cell cultures showed time- and dose-dependent stimulation of osteocalcin secretion in response to 1,25(OH)2D3. Bovine parathyroid hormone (PTH) amino acid fragment 1-34 (40 nM) and prostaglandin E2 (PGE2, 5 nM) significantly inhibited 1,25(OH)2D3-induced osteocalcin secretion by these cells. The inhibition reached 20 and 36%, respectively. In contrast, PTH 3-34 had no effect on osteocalcin secretion. Both cell cultures produced cAMP in response to PTH. Dexamethasone (Dex) (100 nM) potentiated PTH-induced (40 nM) cAMP synthesis in subconfluent MG-63 cells (1.5-fold increase, P less than 0.05). This treatment with Dex resulted in a greater inhibition of 1,25(OH)2D3-induced osteocalcin secretion (-30%, P less than 0.005) by PTH in MG-63 cells as compared to cells exposed to PTH and 1,25(OH)2D3 alone. Pretreatment of subconfluent MG-63 cells with Dex (100 nM) for 48 h also increased 1,25(OH)2D3-induced osteocalcin secretion by 40% (P less than 0.025). In contrast, treatments of confluent MG-63 cells with Dex inhibited osteocalcin secretion regardless of the 1,25(OH)2D3 doses used. Forskolin (10(-7)-10(-5) M) and dibutyryl cAMP (10(-6)-(10(-3) M) both reproduced the effects observed with PTH and PGE2 in the two cell cultures. Forskolin's action was time-dependent: addition of forskolin (10(-6) M) 12 h after 1,25(OH)2D3 (50 nM) resulted in a progressively weaker inhibition of osteocalcin secretion. Increasing the extracellular calcium concentration of the incubation media resulted in a dose-dependent increase in osteocalcin secretion (P less than 0.01). These results indicate that PTH and PGE2 inhibit osteocalcin secretion by a mechanism involving cAMP production. In contrast, an increase in extracellular calcium stimulated osteocalcin release. Thus the human osteosarcoma cell line MG-63 is a useful osteoblast-like cell model to study the regulation of osteocalcin secretion. Furthermore, a factor (or factors) between hormone-receptor coupling and gene induction can regulate the expression of the osteocalcin gene or affect pre- or posttranslational mechanisms implicated in osteocalcin synthesis and secretion.
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PMID:Regulation of osteocalcin secretion by human primary bone cells and by the human osteosarcoma cell line MG-63. 165 56

Cell-attached patch clamp experiments revealed 13-20 pS Na(+)-conducting channels active at normal resting potentials (-28 +/- 1 mV; +/- SEM; 7 cells) in the rat osteosarcoma cell line, ROS 17/2.8. These channels were not blocked by tetrodotoxin, Cd2+, verapamil, or nifedipine. Replacing all cations in the patch pipette except Ca2+ with tetraethylammonium (TEA+) abolishes channel activity; but adding TEA+ to a pipette solution containing only Na+ does not. Depolarization was not necessary to activate these channels, and the open times were much longer than the millisecond open times characteristic of Na+ channels in excitable cells. Current-voltage curves reconstructed from mean single channel currents and mean channel open times resemble L-type Ca2+ current-voltage curves obtained from whole-cell experiments, with current peaks shifted to resting or more hyperpolarized potentials. The voltage sensitivity of these channels has implications on membrane potential stability and on the hyperpolarizing membrane potential spiking activity exhibited by ROS 17/2.8 cells.
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PMID:Continuously active sodium channels in osteoblastic ROS 17/2.8 cells. 166 Jul 43

1 alpha,25-Dihydroxyvitamin D3 [1 alpha,25-(OH)2D3] rapidly increases cytosolic calcium in a variety of cell types. Although these rapid effects do not appear to directly involve genome activation, the requirement for the classic vitamin D receptor is unclear. Clonal rat osteosarcoma cells, ROS 17/2.8, respond to 1 alpha,25-(OH)2D3 with an increase in osteocalcin message but ROS 24/1 cells do not. The lack of the receptor for vitamin D in the ROS 24/1 cells has been confirmed by the absence of any detectable vitamin D-receptor complex binding to the vitamin D-responsive element (VDRE) of the osteocalcin gene and the absence of vitamin D receptor mRNA in the cells. Quin-2-loaded ROS 17/2.8 and ROS 24/1 cells were treated with 1 alpha,25-(OH)2D3 in the presence and absence of extracellular calcium and with the inactive epimer, 1 beta,25-dihydroxyvitamin D3 [1 beta,25-(OH)2D3]. The 1 alpha,25-(OH)2D3 increased cytosolic calcium in the ROS 17/2.8 and 24/1 cells after 5 minutes in a dose-responsive manner and in the presence and absence of extracellular calcium. Pretreatment of both cell lines with 1 beta,25-(OH)2D3 for 30 s blocked the hormone-induced rise in cytosolic calcium. The rapid effects of 1 alpha,25-(OH)2D3 on ROS cells with and without the vitamin D receptor and the ability of the inactive epimer to inhibit these effects indicate that the signaling system mediating the hormone's rapid actions is not the classic vitamin D receptor.
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PMID:1 Alpha,25-dihydroxyvitamin D3 rapidly increases cytosolic calcium in clonal rat osteosarcoma cells lacking the vitamin D receptor. 166 80

Stanniocalcin (STC), a calcium-regulating glycoprotein hormone isolated from the corpuscles of Stannius of salmon, was tested for effects on bone and calcium metabolism in mammalian species (rats and mice). STC generally failed to alter serum calcium of parathyroidectomized rats at concentrations equimolar with effective concentrations of parathyroid hormone (PTH). STC did not increase cAMP in ROS 17/2.8 or UMR-108 osteosarcoma cells, OK kidney cells, fetal rat limb bones, or neonatal mouse calvariae, and similarly failed to increase urinary cAMP in rats. STC did not consistently stimulate resorption in any of the rodent bone culture systems, although variable resorptive responses were elicited in fetal mouse calvariae. The results indicate that this fish hormone has limited, if any, PTH-like activity on calcium metabolism in mammalian systems.
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PMID:Salmon stanniocalcin and bovine parathyroid hormone have dissimilar actions on mammalian bone. 166 5

Cytosolic calcium and its parathyroid hormone induced increase was evaluated in rat osteosarcoma cells by quin 2 fluorometry. Electron microscopic calcium detection in depot organelles (i.e. the recently defined calciosomes) is improved by a new precipitation method with hydroxylamine naphthoic acid and fluoride combined with X-ray microanalysis. As shown in submandibulary gland and pancreatic B cells, a new combination of GBHA staining with laser microprobe mass analysis (LAMMA) for the first time enables direct kinetical studies of calcium at the microscopical level using stable calcium isotopes (i.e. Ca44) as tracers.
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PMID:[Morphological demonstration of function-dependent cellular calcium redistributions in secretory cells by x-ray microanalysis, LAMMA and fluorescence cytometry]. 170 2

Uptake of 86Rb was used to follow the activity of Na-K-2Cl cotransport in the osteosarcoma cell line UMR-106-01. The ouabain-resistant fraction of 86Rb uptake was sensitive to bumetanide and furosemide. Furosemide-sensitive 86Rb uptake required the presence of Na+, K+, and Cl- in the incubation medium. These observations indicate the presence of a Na-K-2Cl cotransport system in osteoblasts. Cotransporter activity was stimulated by agonists which increase adenosine 3',5'-cyclic monophosphate (cAMP), cytosolic free Ca2+ ([Ca2+]i), and protein kinase C (PKC) activity such as parathyroid hormone (PTH) and prostaglandin E2 (PGE2). However, endothelin, which increases [Ca2+]i and PKC activity without affecting cellular levels of cAMP, was ineffective in stimulating the cotransporter. Accordingly, increasing cellular cAMP with forskolin was as effective as PTH and PGE2 in stimulating the cotransporter. Stimulation of PKC with TPA inhibited the cotransporter in a time- and concentration-dependent manner. No stimulation of cotransport could be demonstrated at any 12-O-tetradecanoyl-phorbol-13-acetate (TPA) concentration or incubation time. The Na-K-2Cl cotransporter was stimulated by cell shrinkage. Maximal stimulation was observed after swelling the cells in hypotonic medium and subsequent shrinkage in isotonic medium. Stimulation by cell shrinkage can be demonstrated in control, agonist-, cAMP-, and TPA-treated cells. These observations suggest that 1) the osteoblastic Na-K-2Cl cotransporter is activated by calciotropic hormones predominantly through an increase in cellular cAMP, and 2) in osteoblasts, the cotransporter is independently regulated by different biochemical pathways.
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PMID:Regulation of Na-K-2Cl cotransport in osteoblasts. 171 50


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