UMLS:C0029463 - FACTA Search

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Query: UMLS:C0029463 (osteosarcoma)
16,637 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Prostaglandin E (PGE) stimulates resorption in bone. Since osteoblast-like osteosarcoma cells secrete PGE2, the possibility that osteoclasts were the major target for PGE was considered. To study this question, it was first established that in isolated bone cells enriched for either osteoclastic (OC) or osteoblastic (OB) characteristics, PGE1 can induce biochemical effects similar to those seen with bovine parathyroid hormone 1-84 (PTH), another potent stimulator of bone resorption. These changes include increased cAMP and hyaluronate synthesis in OC cells, and increased cAMP but decreased citrate decarboxylation in OB cells. By following these markers, it is demonstrated that PGE1 can activate OC cells at doses as low as 1 nM, whereas OB cells require 250 nM. Bone cell responses to various doses of PTH and PGE1 were also compared. In OC cells the lowest effective dose of PGE1 and PTH was similar (1 nM), but increasing response to PGE1 was seen up to 1000 nM in contrast to PTH response which peaked at 20 nM. In addition, the magnitude of PGE1-induced OC cell hyaluronate was two to four times greater than that of PTH at all doses tested. In OB cells, PTH induced significant decreases in citrate decarboxylation at 0.1 nM, compared to 250 nM for PGE1. Half-maximal inhibition of citrate decarboxylation (19% of control) by PTH occurred at 0.5 nM, whereas 500 nM of PGE1 was required for an equivalent effect. Thus, (i) OC cells responded to PGE1 doses that were approximately 200 times lower than the minimum required by OB cells, and (ii) OB cells responded to 100 times lower doses of PTH than PGE1.
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PMID:Differential sensitivity of osteoclasts and osteoblasts suggests that prostaglandin E1 effects on bone may be mediated primarily through the osteoclasts. 630 50

We have investigated the binding of biologically active radioiodinated bovine PTH-(1-84) to cloned osteoblast-like rat osteosarcoma cells (ROS 17/2.8) and correlated binding with biological response assessed as cAMP production. The hormone was labeled with 125I on tyrosine-43 using a constant current microelectrolytic method which allows full retention of biological activity. At confluency, cells were removed from culture, and assays were carried out on intact cells in suspension. At 22 C, saturable binding reached equilibrium by 90 min. At that time, the apparent dissociation rate constant was 8 X 10(-8) min-1. At an earlier time, 10 min of incubation, the dissociation rate was twice that observed at equilibrium. Nonsaturable binding was 30-35% of the total binding. The dissociation constant derived from kinetic analysis was 41 nM and correlated with the half-maximal cAMP production at 36 nM. The results obtained suggest that cleavage amino-terminal to residue 43 is not required for binding to these bone-derived cells. Binding to receptors on the osteosarcoma cells was specific and reversible, and appeared biologically relevant, since it correlated closely with the biological response, cAMP production. The competitive inhibitor [Nle8,Nle18,Tyr34]bPTH-(3-34)amide showed the same apparent affinity in inhibiting receptor binding as in inhibiting cAMP production.
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PMID:Binding of radioiodinated parathyroid hormone to cloned bone cells. 631 31

We have previously reported that vasoactive intestinal peptide (VIP) stimulates bone resorption in organ culture via a cAMP-dependent mechanism. Here we describe functional receptors for VIP on a clonal line of human osteosarcoma cells, SaOs-2. SaOs-2 cells respond to VIP with an increase in cAMP. The effect was rapid (2 min) and dose dependent from 0.15-15 nM VIP, with half-maximal stimulation at 1.4 nM. SaOs-2 cells produce prostaglandin E2 (PGE2) and respond to exogenous PGE2 with increases in cAMP approximately one third as great as those induced by VIP. However, the VIP-stimulated increases in cAMP occurred without detectable increases in PGE2 production, and increases in cAMP were unaffected by the cyclooxygenase inhibitor indomethacin. SaOs-2 cells pretreated with VIP for 24 h were significantly less responsive to a second acute challenge with VIP, but retained their ability to respond to PGE2. Similarly, pretreatment with PGE2 induced homologous desensitization to PGE2, but had no effect on the VIP-stimulated increase in cAMP. These patterns of response paralleled those previously described in whole bone in organ culture. Binding studies with [125I]VIP demonstrated specific, saturable, high affinity receptors for VIP on SaOs-2 cells. Scatchard analysis of [125I]VIP binding at 37 C resulted in a curvilinear plot. Analysis based upon the assumption of two independent binding sites gave Kd values of 0.44 and 17 nM for high and low affinity binding sites, respectively. The numbers of high and low affinity sites per cell were determined to be 8,500 and 57,000, respectively. Binding of [125I]VIP was partially inhibited by two related peptides, secretin and PHI-27, but not by PTH, calcitonin or a variety of unrelated peptides. We conclude that the action of VIP on human SaOs-2 cells is similar to that observed in intact mouse calvaria, and that these cells provide a good model for the study of the initial steps of VIP action in bone.
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PMID:Functional receptors for vasoactive intestinal peptide on human osteosarcoma cells. 632 42

Formycin 5'-triphosphate (FoTP), a fluorescent analog of ATP, is shown to be a substrate for the membrane-bound adenylate cyclase activity [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] from rat osteosarcoma cells. The formation of the adenylate cyclase reaction product, 3',5'-cyclic formycin monophosphate (cFoMP), was followed by the conventional radioimmunoassay (RIA) procedure used to detect cAMP and by an assay procedure in which the reaction product was separated from the substrate by reverse-phase high-pressure liquid chromatography (HPLC) and the reaction product was detected by fluorometry. Because the HPLC--fluorometric procedure can determine the amount of cFoMP present in the reaction mixture within 6 min, the enzymatic conversion of FoTP to cFoMP can be followed directly during the course of a typical 15-min incubation. The amount of cFoMP detected by this procedure was found to be within 2% of the values obtained by the RIA. The rate of product formation with FoTP was similar to that observed with ATP and the activity of the enzyme was enhanced about 5-fold with guanyl-5'-yl imidodiphosphate when either ATP or FoTP was used as the substrate. Kinetic studies revealed values for the Vmax of 120 pmol/min per mg of protein and apparent Km values of 220 microM with both substrates. In addition to suggesting that the recognition of the substrate by the adenylate cyclase may not require a specific chemical structure of the 5-membered ring of the base or a unique configuration about either the glycosyl or the C(5')-C(4') bond, the results of this study are consistent with the idea that the cytotoxicity observed with the adenosine analog formycin may be the result of its metabolism to cFoMP. Furthermore, these studies indicate that the fluorescent analog FoTP can be used, in combination with HPLC, to provide an alternative, nonradioactive direct method for the assay of adenylate cyclase catalytic activity.
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PMID:Formycin 5'-triphosphate, a fluorescent analog of ATP, as a substrate for adenylate cyclase. 694 Dec 84

Osteoblasts express calcium channels that are thought to be involved in the transduction of extracellular signals regulating bone metabolism. The molecular identity of the pore-forming subunit (alpha 1) of L-type calcium channel(s) was determined in rat osteosarcoma UMR-106 cells, which express an osteoblast phenotype. A homology-based reverse transcriptase-polymerase chain reaction cloning strategy was employed that used primers spanning the fourth domain. Three types of cDNAs were isolated, corresponding to the alpha 1S (skeletal), alpha 1C (cardiac), and alpha 1D (neuroendocrine) isoforms. In the transmembrane segment IVS3 and the extracellular loop formed by the IVS3-S4 linker, a single pattern of mRNA splicing was found that occurs in all three types of calcium channel transcripts. Northern blot analysis revealed an 8.6-kb mRNA that hybridized to the alpha 1C probe and 4.8- and 11.7-kb mRNAs that hybridized to the alpha 1S and alpha 1D probes. Antisense oligonucleotides directed to the calcium channel alpha 1D transcript, but not those directed to alpha 1S or alpha 1C transcripts, inhibited the rise of intracellular calcium induced by parathyroid hormone. However, alpha 1D antisense oligonucleotides had no effect on the accumulation of cAMP induced by parathyroid hormone. When L-type calcium channels were activated with Bay K 8644, antisense oligonucleotides to each of the three isoforms partially inhibited the rise of intracellular calcium. The present results provide evidence for the expression of three distinct calcium channel alpha 1-subunit isoforms in an osteoblast-like cell line. We conclude that the alpha 1D isoform is selectively activated by parathyroid hormone.
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PMID:Multiple calcium channel transcripts in rat osteosarcoma cells: selective activation of alpha 1D isoform by parathyroid hormone. 747 9

In studies of the regulation of parathyroid hormone (PTH) signal transduction, we observed that the peptide endothelin-1 (ET) added prior to PTH greatly increased the calcium transients elicited by PTH in UMR-106 osteosarcoma cells and mouse primary osteoblastic cells. Enhancement by ET also occurred in the presence of EGTA. The ETB receptor-specific agonist sarafotoxin 6c (S6c) likewise enhanced PTH-induced Ca2+ transients. Blocking the ETA receptor-mediated component of the ET signal with BQ123 failed to abolish enhancement of PTH responses by ET. The nonselective ETA/ETB receptor antagonist PD 142893 blocked both ET and S6c-induced enhancement of the PTH responses. Prostaglandin F1 alpha (PGF1 alpha) pretreatment also maximally potentiated PTH responses, whereas alpha-thrombin, epidermal growth factor (EGF), or prostaglandin E1 (PGE1) did not affect the PTH responses. Neither active phorbol ester nor forskolin mimicked the ET effect. The ET effect was not prevented by indomethacin, NG-mono-methylarginine, genistein, pertussis toxin, 4-aminopyridine, tetraethylammonium chloride, okadaic acid, or long-term treatment with phorbol-12,13-dibutyrate. ET pretreatment did not abolish the inhibition of PTH signals by PTH(3-34), although in ET-pretreated cells the suppression of the PTH signal by PTH(3-34) was not as great. ET pretreatment did not enhance the cAMP response to PTH; rather, there was a significant inhibition of the cAMP response. Thus, the calcium signal elicited by PTH is selectively modulated by activation of the ETB receptor.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:EndothelinB receptor activation enhances parathyroid hormone-induced calcium signals in UMR-106 cells. 750 6

We report here that osteoblasts and osteoblast-like osteosarcoma cells express PMCA1b, an alternatively spliced transcript of plasma membrane Ca(2+)-ATPase. Synthetic oligonucleotide pairs were designed based upon unique regions of the cDNA encoding known PMCA isoforms (PMCA1-3) and used as primers in PCR-mediated amplification of cDNA synthesized from ROS 17/2.8 osteosarcoma cell RNA. A product was observed only when PMCA1-specific primers were present; no products were seen with PMCA2 or PMCA3 primers unless cDNA synthesized from rat brain RNA was present. Examination of the cDNA encoding the C terminus of PMCA1 from ROS 17/2.8 cells revealed that the mRNA is spliced to yield the PMCA1b isoform, a Ca(2+)-ATPase containing a consensus phosphorylation site for cAMP-dependent protein kinase A and a modified calmodulin binding domain. PMCA1b was also detected in UMR-106-01 osteosarcoma cells and unpassaged primary rat calvarial osteoblasts. These results suggest that the regulation of osteoblast function by agents that act via cAMP-mediated pathways may involve alterations in the activity of the plasma membrane Ca(2+)-ATPase.
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PMID:Osteoblasts express the PMCA1b isoform of the plasma membrane Ca(2+)-ATPase. 750 68

It is known that osteopenia is frequently associated with diabetes mellitus. Although its mechanism is not well understood, impaired bone formation due to an osteoblast deficit seems to be a major factor as reflected by a fall in serum levels of osteocalcin and by the findings of low bone formation with bone histomorphometry. In the present study, we studied the effect of high glucose conditions on osteoblast by examining the responsiveness of human osteosarcoma (MG-63) cells to human parathyroid hormone 1-34 [hPTH-(1-34)]. MG-63 cells were cultured either with 5.5 mM glucose (normal glucose), 55.0 mM glucose (high glucose) or 5.5 mM glucose plus 49.5 mM mannitol (high mannitol) condition for 7 days. Both an increase in cAMP levels and an immediate increase in [Ca2+]i, induced by hPTH(1-34), were significantly lower in high glucose-treated cells than in those treated with normal glucose or high mannitol. Basal cAMP levels in the cells after a 7-day culture in high glucose conditions were significantly higher than in those in the other two groups. We concluded that high glucose specifically impaired the response to hPTH(1-34). This impairment seemed to arise from an increase in intracellular cAMP levels, which is reported to induce downregulation of PTH receptors.
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PMID:Impaired response of human osteosarcoma (MG-63) cells to human parathyroid hormone induced by sustained exposure to high glucose. 756 50

We have characterized the distribution, expression, and hormonal regulation of gap junctions in primary cultures of rat osteoblast-like cells (ROBs), and three osteosarcoma cell lines, ROS 17/2.8, UMR-106, and SAOS-2, and a continuous osteoblastic cell line, MC3T3-E1. All cell lines we examined were functionally coupled. ROS 17/2.8 were the more strongly coupled, while ROB and MC3T3-E1 were moderately coupled and UMR-106 and SAOS-2 were weakly coupled. Exposure to parathyroid hormone (PTH) for 1 h increased functional coupling in ROB cells in a concentration-dependent manner. Furthermore, PTH(3-34), an analog of PTH with binds to the PTH receptor and thus attenuates PTH-stimulated cAMP accumulation, also attenuated PTH-stimulated functional coupling in ROB. This suggests that PTH increases functional coupling partly through a cAMP-dependent mechanism. A 1 h exposure to PTH did not affect coupling in ROS 17/2.8, UMR-106, MC3T3-E1, or SAOS-2. To examine whether connexin43 (Cx43), a specific gap junction protein, is present in functionally coupled osteoblastic cells, we characterized Cx43 distribution and expression. Indirect immunofluorescence with antibodies to Cx43 revealed that ROS 17/2.8, ROB, and to a lesser extent MC3T3-E1 and UMR-106, expressed Cx43 immunoreactivity. SAOS-2 showed little if any Cx43 immunoreactivity. Cx43 mRNA and Cx43 protein were detected by Northern blot analysis and immunoblot analysis, respectively, in all cell lines examined, including SAOS-2. Our findings suggest that acute exposure to PTH regulates gap junction coupling, in a cell-line dependent manner, in osteoblastic cells.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Cell-to-cell communication in osteoblastic networks: cell line-dependent hormonal regulation of gap junction function. 757 12

There is increasing evidence that parathyroid hormone (PTH) and PTH-related peptides (PTHrP) are involved in normal skin cell growth; therefore, we investigated whether the PTH/PTHrP receptor was expressed in cultured human keratinocytes and dermal fibroblasts. Northern analyses of poly (A)+ RNA isolated from cultured fibroblasts revealed two PTH/PTHrP receptor transcripts with one major band at 2.5 kb and one minor band at 2.3 kb. These transcripts were consistent with those found in human osteosarcoma cells, which are known to express PTH/PTHrP-R mRNAs. In contrast, after repeated Northern analyses no PTH/PTHrP receptor transcripts were found in poly (A)+ RNA isolated from cultured keratinocytes. Reverse-transcriptase/nested polymerase chain reaction analyses of total RNA isolated from cultured keratinocytes and fibroblasts confirmed the Northern analyses data that the PTH/PTHrP receptor was expressed in cultured fibroblasts but not in cultured keratinocytes. When cultured fibroblasts and keratinocytes were exposed to 10(-7) M PTH (1-34) there was a twofold increase in cAMP levels in the fibroblasts and no demonstrable increase was noted in keratinocytes. These results suggest that skin fibroblasts possess the classical PTH/PTHrP receptor and are target cells for PTH and PTHrP whereas keratinocytes do not have the receptor and are unresponsive to its N-terminal agonist in the stimulation of cAMP formation.
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PMID:Cultured human fibroblasts and not cultured human keratinocytes express a PTH/PTHrP receptor mRNA. 761 67

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