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)

A RNA-dependent DNA polymerase (RTase) was purified from human osteosarcoma tissue by successive column chromatography of the microsomal fraction on DEAE-cellulose (DE-23 and DE-52) and phosphocellulose. The purified enzyme has a molecular weight of about 68,000, a pH optimum of 8.1, a Mg2+ optimum of 0.8 mM, Mn2+ optimum of 1.0 mM and a KCl optimum of 60 mM. The enzyme transcribes (rA)n . (dT)12, (rC)n . (dG)12-18 and (2-O-methyl C)n . (dG)18, but is unable to transcribe (dA)n . (dT)10. The enzyme has no catalytic activity in the presence of oligodeoxynucleotide initiators alone, indicating the absence of terminal deoxynucleotidyl transferase. The purified enzyme is able to transcribe the heteropolymeric regions of a 70S RNA from R(Mu)LV. The presented data support the presence of a RNA-dependent DNA polymerase in human osteosarcoma tissue with biochemical properties, resembling those of C-type RNA tumor viruses.
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PMID:Purification and biochemical characterization of a virus-specific reverse transcriptase from human osteosarcoma tissue. 9 60

Measurements of free cystolic Ca2+ ([Ca2+]i) and Ba2+ ([Ba2+]i) concentrations with Fura 2 were used to identify and characterize the properties of a depolarization-activated Ca2+ and Ba2+ entry in the plasma membrane of osteoblast-like cells. The presence of this pathway was demonstrated in two osteoblastic cell lines, UMR-106 and MC3T3-E1 and osteoblasts isolated from rat long bone and rat neonatal calvariae. Subsequent characterization of the pathway was performed in the osteosarcoma cell line UMR-106. Depolarization of the cells with high medium K+ was followed by an increase in [Ca2+]i which was dependent on medium Ca2+. Ba2+ ions depolarized the cells and were transported by this pathway. Mg2+ ions interfered with Ca2+ and Ba2+ entry. At 140 mM KCl and 1 mM MgCl2, the pathway could be saturated with Ca2+ or Ba2+. The apparent affinity for Ca2+ was 0.78 mM and for Ba2+ 1.82 mM. Ca2+ or Ba2+ entry into the cells was blocked by low concentrations of nicardipine, diltiazem, verapamil, and La3+. In the absence of an increase in [Ca2+]i or [Ba2+]i, the pathway inactivated within about 5 min after depolarization. When [Ca2+]i or [Ba2+]i was allowed to increase, the pathway inactivated within about 20 s. These properties suggest that Ca2+ and Ba2+ entry are mediated by an L-type, depolarization-activated Ca2+ channel in osteoblasts. The activity of these channels changes little with an increase or decrease in cell volume. Thus, it is concluded that these pathways do not provide the Ca2+ entry pathway required for initiation of volume decrease by osteoblasts.
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PMID:Properties of the depolarization-activated calcium and barium entry in osteoblast-like cells. 249 47

Recent evidence suggests that guanyl nucleotide binding (G) proteins are involved in receptor-mediated bone resorption and in osteoblastic function, but the nature of the G protein coupled to effectors that are involved in these skeletal effects is unknown. The purposes of this study were to determine (1) whether a G protein mediates activation of phosphoinositide-specific phospholipase C in UMR-106 rat osteosarcoma cells, and (2) whether parathyroid hormone (PTH) and a PTH-like protein (PLP) associated with humoral hypercalcemia of malignancy promote GTP-dependent PIP2 hydrolysis. Addition of GTP (10(-4) M) or guanosine 5'-0-(3-thiotriphosphate, GTP gamma S, 10(-5) M) to membranes prepared from UMR-106 cells labeled with [3H]myo-inositol increased both [3H]inositol trisphosphate (IP3) and [3H]inositol bisphosphate (IP2) formation. The increases in [3H]IP2 and [3H]IP3 produced by GTP were 8.6- and 4.3-fold, respectively. GTP gamma S produced a 17.6- and 11.9-fold increase in [3H]IP2 and [3H]IP3, respectively. The stimulatory effects of GTP and GTP gamma S were dose dependent (GTP ED50 = 3.9 x 10(-6) M; GTP gamma S ED50 = 2.5 x 10(-7) M) and progressive over 10 minutes and required the presence of Mg2+.GTP (10(-4) M) and GTP gamma S (10(-5) M) decreased membrane [3H]phosphoinositides concomitantly with increased [3H]IP2 and [3H]IP3. The GDP analog guanosine 5'-O-(2-thiodiphosphate, GDP beta S) alone did not alter [3H]IP2 or [3H]IP3 production but at 10(-4) M blocks the stimulatory effects of GTP and GTP gamma S. NaF (3 x 10(-2)M) produced a 2.8- and 2.0-fold stimulation of [3H]IP2 and [3H]IP3, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:G protein-dependent activation of a phosphoinositide-specific phospholipase C in UMR-106 osteosarcoma cell membranes. 255 86

To study regulation of the parathyroid hormone (PTH)-responsive adenylate cyclase of osteoblast-like cells by 1,25-dihydroxyvitamin D (1,25(OH)2D), cAMP levels and adenylate cyclase activity were assayed in the hormone-responsive ROS 17/2.8 rat osteosarcoma cell line. Treatment of cells with 1,25(OH)2D3: alone markedly attenuated the cAMP response to subsequent PTH; decreased adenylate cyclase stimulated by PTH; and completely antagonized the positive regulatory effects of cell treatment with glucocorticosteroid (GC) on these responses to PTH. Sterol receptor mediation was indicated by specificity for the 1,25(OH)2D metabolite and high sensitivity (half-maximal attenuation at 7 X 10(-11) M). The effects of 1,25(OH)2D and GC were primarily on the maximal activity of adenylate cyclase and not on sensitivity to Mg2+, guanine nucleotide, or PTH. GC augmentation of ROS 17/2.8 cell cAMP accumulation was also seen with another receptor agonist (beta-adrenergic), cholera toxin or forskolin; 1,25(OH)2D antagonized all these GC effects. Opposing effects of GC and 1,25(OH)2D were seen as well on activation of the guanine nucleotide-binding regulatory protein (Ns) by guanyl-5'-yl imidodiphosphate and F- and on activation of the catalyst (C) by Mn2+. In contrast, with the activators other than PTH, cell treatment with 1,25(OH)2D in the absence of GC produced only minor attenuation of cAMP accumulation and no effect on adenylate cyclase activities. The data suggest that GC acts strongly on or near the PTH receptor-Ns complex in ROS 17/2.8 and to a lesser degree on the Ns-C interaction. Direct GC enhancement of C could not be concluded because of the influence of Ns on forskolin action and present data that Mn2+ does not uncouple Ns from C in this system. A GC effect on membrane structure or composition, as seen in other cell types, could explain these changes in adenylate cyclase function without the need to postulate multiple mechanisms. The data dissociate two 1,25(OH)2D effects, direct attenuation of activation of Ns via the PTH receptor and interference with the as yet undefined mechanism(s) of GC augmentation. These may represent dissimilar pathways of 1,25(OH)2D action on osteoblasts.
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PMID:1,25-Dihydroxycholecalciferol and glucocorticosteroid regulation of adenylate cyclase in an osteoblast-like cell line. 257 54

A high affinity, calmodulin-sensitive (Ca2 + Mg2+)-ATPase was demonstrated in the plasma membrane preparation of three different osteosarcoma cell lines previously demonstrated to respond to parathyroid hormone with an increase in cytosolic calcium and a decrease in pH. The maximal velocity of the enzyme activity in the membrane preparations ranged from 0.83 to 2.42 nmol Pi released per min per mg protein with half-saturation constants of 26 nM of free Ca. The enzyme activity was not affected by Na+, K+, ouabain and azide, and exhibited an absolute requirement for Mg2+ ions. These results suggest a possible role for a membrane Ca2 + Mg2+-ATPase in initiating and perpetuating the ionic control of osteoblastic function.
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PMID:Characterization of a (Ca2+ + Mg2+)-ATPase system in the osteoblast plasma membrane. 297 93

Previously, human diploid fibroblasts from some donors infected in vitro by avian sarcoma virus (ASV) were transformed and found, by electron microscopy, to produce small numbers of virus particles that were infectious by bioassay; also, a line of human osteosarcoma cells infected with ASV developed additional characteristics of transformation and released a small number of infectious virus particles. In this study the complete proviral sequence was shown to be integrated in the genome of these cells. The env-related proteins gp85 and gp37 and the gag-related proteins pr76, pr60, and p19 can be detected in cytoplasmic extracts of ASV-infected human cells. Comparable amounts of pp60v-src were found in human and avian cells infected with ASV. The associated kinase activity in infected human cells was dramatically increased as compared to that of uninfected controls; the enzyme had the same cation and substrate requirements as those from ASV-transformed avian cells. Replicating particles from infected human cells were purified and were significantly modified compared to those from avian hosts as shown by a) higher specific gravity, b) the presence of RSV gag-related but not env-related antigens, and c) the fact that the virus-associated reverse transcriptase preferred the divalent cations Mn2+ and Fe2+ over Mg2+.
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PMID:Integration and expression of provirus in human cells transformed by avian sarcoma virus. 303 82

Although acute alterations in Ca2+ fluxes may mediate the skeletal responses to certain humoral agents, the processes subserving those fluxes are not well understood. We have sought evidence for Ca2+-dependent ATPase activity in isolated osteoblast-like cells maintained in primary culture. Two Ca2+-dependent ATPase components were found in a plasma membrane fraction: a high affinity component (half-saturation constant for Ca2+ of 280 nM, Vmax of 13.5 nmol/mg per min) and a low affinity component, which was in reality a divalent cation ATPase, since Mg2+ could replace Ca2+ without loss of activity. The high affinity component exhibited a pH optimum of 7.2 and required Mg2+ for full activity. It was unaffected by potassium or sodium chloride, ouabain or sodium azide, but was inhibited by lanthanum and by the calmodulin antagonist trifluoperazine. This component was prevalent in a subcellular fraction which was also enriched in 5'-nucleotidase and adenylate cyclase activities, suggesting the plasma membrane as its principal location. Osteosarcoma cells, known to resemble osteoblasts in their biological characteristics and responses to bone-seeking hormones, contained similar ATPase activities. Inclusion of purified calmodulin in the assay system caused small non-reproducible increases in the Ca2+-dependent ATPase activity of EGTA-washed membranes. Marked, consistent calmodulin stimulation was demonstrated in membranes exposed previously to trifluoperazine and then washed in trifluoperazine-free buffer. These results indicate the presence of a high affinity, calmodulin-sensitive Ca2+-dependent ATPase in osteoblast-like bone cells. As one determinant of Ca2+ fluxes in bone cells, this enzyme may participate in the hormonal regulation of bone cell function.
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PMID:A high affinity, calmodulin-responsive (Ca2+ + Mg2+)-ATPase in isolated bone cells. 613 20

The adenylate cyclase (ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1)-stimulating factor from rat osteosarcoma cytosol was purified 600-fold by ion-exchange chromatography. The factor has an apparent Mr of 20000, is cold-labile, but retains activity at -20 degrees C in 10% glycerol. The factor enhanced parathyroid hormone stimulation of adenylate cyclase and restored hormone responsiveness to membranes washed with 0.5 M NaCl. These 'GTP-like' effects were not inhibited by 100 microM GDP-beta-S, which completely abolished the GTP enhancement of both basal and hormone-stimulated adenylate cyclase. Adenylate cyclase activity in the presence of the stimulating factor was linear with time, and showed hyperbolic dependence on factor concentration. The factor also linearized (in double reciprocal plots) the downward-concave Mg2+-dependence of adenylate cyclase, increasing the apparent affinity of the enzyme for Mg2+. The presence of the factor in two clonal osteosarcoma cell lines correlated with parathyroid hormone-stimulatable adenylate cyclase. Factor stimulation was absent while GTP stimulation was retained in the hormone-nonresponsive clone. Factor and hormone sensitivity were restored by in vivo passage. This factor thus may represent a guanyl nucleotide-independent path for cellular regulation of hormone response.
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PMID:Osteosarcoma cytosol factor promotes parathyroid hormone stimulation of adenylate cyclase independent of GTP. 693 11

1. Mg2+ concentration dependence of adenylate cyclase activity, in a rat osteosarcoma cell line (ROS 2/3), exhibits two apparent affinities with Km values of approx. 2 mM and 10 mM. 2. Only one Mg2+ affinity with a Km value of around 1 mM was apparent at saturating concentrations of: (i) guanosine-5'-(beta, gamma-imido)triphosphate; (ii) parathyroid hormone and GTP; and (iii) (-)-isoproterenol and GTP. 3. Conversely, at saturating concentrations of Mg2+ (40 mM) only high hormone concentrations, acting on low affinity sites, stimulated adenylate cyclase. 4. At saturating concentrations of guanosine-5'-(beta, gamma-imido)triphosphate, hormone stimulation decreased with increasing Mg2+ concentrations and none was seen at 40 mM Mg2+. The findings suggest that hormone stimulation of adenylate cyclase is associated with Mg2+ activation of a 'high hormone affinity' responsive state dependent on triphosphoguanine nucleotide. The hormone effect on Mg2+ affinity fully accounts for hormone stimulation of adenylate cyclase at physiologically relevant concentrations.
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PMID:The role of Mg2+ in hormone stimulation of rat osteosarcoma adenylate cyclase. 693 17

Extracellular divalent cations are important regulators of integrin ligand binding activity. In this study we evaluated how divalent cations affect the organization of integrins into focal adhesion sites. Integrins alpha v beta 3 and alpha v beta 5 were compared because they share a high degree of structural homology and because both integrins mediate cell adhesion to vitronectin. On MG-63 osteosarcoma cells, we found that both the extent and pattern of integrin organization was regulated by the type of extracellular divalent ion. Integrin alpha v beta 3 organized in focal contacts when Mn2+ or Mg2+ was present, but not in Ca2+. In contrast, alpha v beta 5 organized in focal contacts only when Ca2+ or Mg2+ was present. Integrin alpha v beta 5 clustered in a centrally located punctate field on the ventral surface of the cell in the presence of Mn2+. These observations reveal a previously unappreciated role for divalent ions in regulating the organization of integrins into focal adhesion sites.
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PMID:Divalent cations regulate the organization of integrins alpha v beta 3 and alpha v beta 5 on the cell surface. 881 6


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