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

Adenylate cyclase activity in particulate fractions from a transplantable rat osteogenic sarcoma was stimulated in a dose-dependent manner by prostaglandins E1 and E2 (PGE1 and PGE2) and parathyroid hormone (PTH). Prostaglandin F2alpha was active at a high concentration (3 x 10(-4) mol/l). Pretreatment of membranes with collagenase plus hyaluronidase reduced the magnitude of the PTH effect but did not affect the size of the PGE1 effect. Guanosine 5'-triphosphate and its synthetic analogue 5'-guanylylimidodiphosphate (Gpp(NH)p) activated adenylate cyclase in particulate preparations from the osteogenic sarcoma. The latter agent produced much larger effects, although the concentrations required for half-maximal enzyme activation were the same for both agonists (approximately 2 x 10(-6) mol/l). The effects of PTH and Gpp(NH)p were supra-additive at some concentrations of hormone. The effects of PGE1 and Gpp(NH)p were supra-additive at all hormone concentrations tested. Pre-incubation of membrane particles for 6 min with PTH produced an enzyme activation which was not reversed by dilution through washing; pre-incubation with PGE1 did not produce this effect. The response of membrane adenylate cyclase to Gpp(NH)p (10(-4) mol/l) was 75% greater in preparations pre-incubated with PTH than in membranes pre-incubated in buffer alone or in buffer containing PGE1. The basal rate of cyclic AMP production in the adenylate cyclase assay system decreased over a 35 min incubation period. This decrease was prevented by addition of PTH or PGE1. Addition of NaF or Gpp(NH)p produced a steady increase in the rate of production of cyclic AMP with time. Membrane preparations did not reduce the biological activity of PTH and did not degrade 125I-labelled PTH. The results demonstrate that the PTH- and PGE-responsive adenylate cyclases of the osteogenic sarcoma have distinctly different properties and that particulate preparations of the tumour do not metabolize PTH.
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PMID:Membranes from a transplantable osteogenic sarcoma responsive to parathyroid hormone and prostaglandins: regulation of adenylate cyclase and of hormone metabolism. 27 36

An osteogenic sarcoma was induced in an inbred strain of the Sprague Dawley rat using seven serial injections of 32P-orthophosphate. The tumor was maintained by transplantation over a 3-year period in the same inbred strain. During this time it retained its bone-like differentiation. Tumor membranes and freshly isolated tumor cells also retained responsiveness to parathyroid hormone and to prostaglandins of adenylate cyclase and cyclic nucleotide formation respectively. The potencies of these agents and their analogues and metabolites were found to be proportional to their efficacies as bone resorbing agents. Thus, the tumor was shown to be a model for the study of hormone-responsiveness for tumor growth and differentiation, and also of the effects of agonists which act on bone-like cells.
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PMID:Radiation induced osteogenic sarcoma in the rat as a model of hormone-responsive differentiated cancer. 33 78

Parathyroid hormone (PTH), a major regulator of mineral ion metabolism, and PTH-related peptide (PTHrP), which causes hypercalcemia in some cancer patients, stimulate multiple signals (cAMP, inositol phosphates, and calcium) probably by activating common receptors in bone and kidney. Using expression cloning, we have isolated a cDNA clone encoding rat bone PTH/PTHrP receptor from rat osteosarcoma (ROS 17/2.8) cells. The rat bone PTH/PTHrP receptor is 78% identical to the opossum kidney receptor; this identity indicates striking conservation of this receptor across distant mammalian species. Additionally, the rat bone PTH/PTHrP receptor has significant homology to the secretin and calcitonin receptors but not to any other G protein-linked receptor. When expressed in COS cells, a single cDNA clone, expressing either rat bone or opossum kidney PTH/PTHrP receptor, mediates PTH and PTHrP stimulation of both adenylate cyclase and phospholipase C. These properties could explain the diversity of PTH action without the need to postulate other receptor subtypes.
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PMID:Expression cloning of a common receptor for parathyroid hormone and parathyroid hormone-related peptide from rat osteoblast-like cells: a single receptor stimulates intracellular accumulation of both cAMP and inositol trisphosphates and increases intracellular free calcium. 131 66

Injections of parathyroid hormone (PTH) result in increased bone formation in several species. Work in our laboratory and others has shown a stimulation of bone cell proliferation and growth factor production by PTH. Our purpose was to study the effects of PTH on a human bone cell line using TE-85 human osteosarcoma cells as a model. After 24 h treatment, PTH caused an increase in cell proliferation as measured by cell counts and [3H]-thymidine incorporation. Proliferation was not inhibited by an anti-transforming growth factor beta (TGF beta) antibody which could abolish stimulation by exogenous TGF beta. PTH did not stimulate cAMP production, alkaline phosphatase activity or production of insulin-like growth factors I or II (IGF-I or IGF-II) in TE-85 cells. Although basal TE-85 proliferation was slowed by incubation with the calcium channel blocking agent verapamil, PTH still caused an increase in growth rate. We conclude that PTH directly stimulates TE-85 proliferation via a mechanism not involving increased adenylate cyclase activity or increased secretion of IGF-I, IGF-II or TGF beta and may stimulate bone formation in vivo by activating some other mitogenic signal to increase bone cell proliferation.
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PMID:PTH stimulates the proliferation of TE-85 human osteosarcoma cells by a mechanism not involving either increased cAMP or increased secretion of IGF-I, IGF-II or TGF beta. 131 2

The effects of the monokines tumor necrosis factor alpha (TNF) and interleukin 1 (IL 1) on parathyroid hormone (PTH)-responsive adenylate cyclase were examined in clonal rat osteosarcoma cells (UMR-106) with the osteoblast phenotype. Recombinant TNF and IL 1 incubated with UMR-106 cells for 48 hr each produced concentration-dependent inhibition of PTH-sensitive adenylate cyclase, with maximal inhibition of PTH response (40% for TNF, 24% for IL 1) occurring at 10(-8) M of either monokine. Both monokines also decreased adenylate cyclase stimulation by the tumor-derived PTH-related protein (PTHrP). In contrast, TNF and IL 1 had little or no inhibitory effect on receptor-mediated stimulation of adenylate cyclase by isoproterenol and nonreceptor-mediated enzyme activation by cholera toxin and forskolin; both monokines increased prostaglandin E2 stimulation of adenylate cyclase. Binding of the radioiodinated agonist mono-[125I]-[Nle8,18, Tyr34]bPTH-(1-34)NH2 to UMR-106 cells in the presence of increasing concentrations of unlabeled [Nle8,18, Tyr34]bPTH-(1-34)NH2 revealed a decline in PTH receptor density (Bmax) without change in receptor binding affinity (dissociation constant, Kd) after treatment with TNF or IL 1. Pertussis toxin increased PTH-sensitive adenylate cyclase activity but did not attenuate monokine-induced inhibition of PTH response. In time course studies, brief (1 hr) exposure of cells to TNF or IL 1 during early culture was sufficient to decrease PTH response but only after exposed cells were subsequently allowed to grow for prolonged periods. Inhibition of PTH response by monokines was blocked by cycloheximide. The results indicate that TNF and IL 1 impair responsiveness to PTH (and PTHrP) by a time- and protein synthesis-dependent down-regulation of PTH receptors linked to adenylate cyclase.
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PMID:Tumor necrosis factor and interleukin 1 inhibit parathyroid hormone-responsive adenylate cyclase in clonal osteoblast-like cells by down-regulating parathyroid hormone receptors. 132 78

The presence of gap junctions between osteoblastic cells has been previously reported. For this study we used the rat osteosarcoma cell line UMR 106, which expresses the osteoblastic phenotype, as a model to characterize further the nature, physiology, and regulation of gap junctions. Northern blot analysis identified a 3.0-kilobase RNA species corresponding to the gap junction protein connexin 43. The presence of two other connexin RNA species (26 and 32) could not be detected by this method in these cells. The identified connexin RNA was amplified by reverse transcription coupled to polymerase chain reaction; the sequence of the amplified product appears identical to the sequence of a cloned rat heart connexin 43 gene. After treatment with PTH, forskolin, and 8-Br-cAMP (a cAMP analog), the levels of connexin 43 RNA in UMR 106 cells increased. Further evidence for the role of PTH and cAMP in the physiology of gap junctions in these cells was obtained with Lucifer yellow dye transfer experiments. Gap-junctional intercellular communication increased in response to PTH and forskolin (an inducer of adenylate cyclase activity). Expression of connexin 43 RNA increased severalfold in response to PTH in a concentration- and time-dependent fashion. Connexin 43 RNA and its PTH-mediated stimulation were also observed in several other osteoblastic cell lines. The roles of PTH and forskolin in regulating the physiological state of gap junctions were confirmed in primary cultures of rat calvaria osteoblasts.
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PMID:Hormonal regulation of intercellular communication: parathyroid hormone increases connexin 43 gene expression and gap-junctional communication in osteoblastic cells. 133 76

In UMR-106 osteosarcoma cells we found that PTH activated both the cAMP/protein kinase A and the Ca(2+)-dependent phosphoinositide/protein kinase C (PKC) pathways, but prostaglandin E2 (PGE2) activated only the cAMP pathway. Activation of PKC by the phorbol ester PMA had no effect on cAMP production but enhanced PTH-stimulated cAMP production by 50% or more; the effect on PGE2-induced cAMP was negligible. Inhibition of the alpha-subunit of the inhibitory guanine nucleotide binding protein (Gi) by pertussis toxin pretreatment also enhanced PTH-mediated cAMP production but had no effect on PGE2-induced cAMP production. These results suggest that although PTH-mediated adenylate cyclase activity is regulated via both the stimulatory (Gs) and inhibitory (Gi) guanine nucleotide binding proteins, only Gs regulates PGE2-mediated adenylate cyclase activity in UMR-106 cells. Costimulation with pertussis toxin and PMA did not increase PTH-stimulated cAMP production above that obtained with PMA alone. This implies a similar target of action for pertussis toxin and PMA, that is, the alpha-subunit of Gi. The alpha-subunit of Gi was found to be a substrate for in vitro PKC phosphorylation of membrane fractions from UMR-106 cells, seen as a +/- 40 kD band on SDS-PAGE. Stimulation of in situ 32P-labeled cells with either PMA or PTH also enhanced incorporation of 32P into the 40 kD band. Using the peptide antisera AS/7 and EC/2, we showed that pertussis toxin-labeled subunits of both Gi1 alpha/Gi2 alpha and Gi3 alpha could be immunoprecipitated, respectively, but immunoprecipitation of membrane proteins after in situ phosphorylation and stimulation with PMA precipitated only Gi2 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Protein kinase C modulates parathyroid hormone- but not prostaglandin E2-mediated stimulation of cyclic AMP production via the inhibitory guanine nucleotide binding protein in UMR-106 osteosarcoma cells. 133

The beta-adrenergic blocking agent propranolol was shown in previous studies to increase orthotopic bone formation in rats. To understand the cellular mechanisms underlying this observation, propranolol was tested for its effects on osteoblastic cells, which possess adenylate cyclase-coupled beta-adrenergic receptors. The ability of propranolol to modulate parathyroid hormone (PTH) and isoproterenol effects on adenylate cyclase activity and on alkaline phosphatase expression was studied in the osteoblast-like rat osteosarcoma cell line ROS 17/2.8. At concentrations between 0.1 and 10 microM, DL-propranolol specifically inhibited adenylate cyclase stimulation by the beta-adrenergic agonist isoproterenol, but did not alter either basal or PTH-stimulated activity. At these concentrations, propranolol also blunted the inhibition of alkaline phosphatase activity by isoproterenol but not PTH. Propranolol alone had minimal effects on ROS alkaline phosphatase activity at low concentrations (0.1-1 microM), but became inhibitory at high concentrations (10-100 microM). Thus, the direct effects of physiologically relevant propranolol concentrations on osteoblastic cells can be attributed principally to beta-adrenergic blockade. These findings further suggest that propranolol may enhance bone formation by preserving osteoblastic activity in the face of inhibition by beta-adrenergic agonists.
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PMID:Effects of beta-adrenergic blockade in an osteoblast-like cell line. 134 41

Nearly all models of skeleton, cartilage, and dentin mineralization evoke a specific role for matrix vesicles (MV) and alkaline phosphatase (ALP). Nevertheless, the mechanism underlying MV production, mineralization, and the pivotal role of ALP is largely unknown. Previous studies in this laboratory demonstrated that ALP in a human osteosarcoma cell line (SAOS-2) is of the tissue nonspecific ('bone') isoenzyme and lipid-anchored to the plasma membrane in ecto-orientation [1], thus reminiscent of osteoblasts in vivo [2]. Herein, we show that these cells spontaneously release ALP-rich structures (MVs) with the capacity to mineralize. MVs from SAOS-2 cells are 100-200 nm in diameter with characteristic trilaminar membranes. ALP in these vesicles is hydrophobic and lipid-anchored in ecto-orientation in a manner similar to the ALP in the parent SAOS-2 cells. 5'-Nucleotidase, another plasma membrane enzyme, is also abundant in MVs; adenylate cyclase is relatively deficient. Analysis of plasma membrane and MV proteins by 2-D gel electrophoresis reveals many common constituents; nevertheless, MVs contain several unique (or greatly enriched) proteins indicating that SAOS-2 MVs originate from specialized regions of the plasma membrane and are released in the same orientation as the plasma membrane. MVs, unlike plasma membrane vesicles, can cause the formation of insoluble calcium and phosphate in a manner that i) requires ALP substrates; ii) is blocked by ALP inhibition or inactivation; and iii) is not dependent on intact MVs. SAOS-2 derived MVs contain at least 3 protein kinases and their substrates. ALP does not, however, have a major role in regulating the phosphorylation state of these phosphoproteins.
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PMID:Human osteosarcoma cells spontaneously release matrix-vesicle-like structures with the capacity to mineralize. 161

During continuous culture with serial passage, the human osteosarcoma cell line SaOS-2 showed a time-dependent decrease in skeletal alkaline phosphatase (ALP) activity. Because this was indicative of heterogeneity, subpopulations of SaOS-2 cells were isolated from replicate low-density cultures. The subpopulations were less heterogeneous and more stable (with respect to ALP) than the parent population. ALP specific activity in the subpopulations ranged from 0.05 to 2.3 U/mg protein, and cytochemical analyses indicated multiple steady-state levels of ALP activity per cell. The amount of ALP activity in SaOS-2 subpopulations was proportional to collagen production ([3H]proline incorporation into collagenase-digestible protein; r = .84, P less than .005), and to parathyroid hormone (PTH)-linked synthesis of cyclic adenosine monophosphate (cAMP) (r = .88, P less than .01). From these data, we inferred that ALP activity in SaOS-2 cells can provide a useful index of the osteoblastic phenotype, and that ALP activity, collagen production, and PTH-linked adenylate cyclase were coordinately regulated in these osteoblast-like osteosarcoma cells (ie, selection of subpopulations for ALP activity coselected for collagen synthesis and PTH-linked synthesis of cAMP). Further comparative studies showed that micromolar fluoride concentrations stimulated cell proliferation ([3H]thymidine incorporation into DNA) in low-ALP SaOS-2 subpopulations, but not in high-ALP cells (P less than .001), and that this differential sensitivity to fluoride was associated with an inverse correlation between fluoride-sensitive acid phosphatase and ALP activities (r = -.91, P less than .001).
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PMID:Skeletal alkaline phosphatase specific activity is an index of the osteoblastic phenotype in subpopulations of the human osteosarcoma cell line SaOS-2. 165 38


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