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)

We have previously shown that some transformed derivatives of the human osteosarcoma-derived cell line HOS are killed by treatment with 1 microM ouabain at pH 8.2, whereas their nontransformed counterparts are relatively unharmed by the same conditions. HOS cells transformed by v-Ki-ras and RAS, v-fms, or MET are susceptible to 1 microM ouabain while those transformed by v-fes are not. Here we describe the adaptation of this differentially cytotoxic effect as a method to enrich for cells which revert to a nontransformed phenotype. We have optimized parameters which increase the differential cytotoxicity, including pH and potassium concentration during and subsequent to ouabain treatment. The efficiency of this procedure was tested in mixed cell experiments where model populations were constructed consisting of HOS cells mixed with an excess of v-Ki-ras-transformed HOS cells. Two successive OAK treatments (ouabain/alkaline/K+-free) were sufficient to recover nontransformed cells free of ras-transformants as indicated by genetic markers and morphology. This HOS/ouabain system is currently being used to derive revertants of ras-transformed human cells and could facilitate the isolation of genes interacting in the pathways by which these cells are transformed.
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PMID:A system for deriving revertants of oncogene-transformed human cells. 319 49

A number of cellular functions have recently been associated with alterations of the membrane potential in non-excitable cells. To assess the electrophysiologic regulation of osteoblast function, a method for measuring the membrane potential (Em) of a rat osteogenic sarcoma cell line (UMR 106) by the voltage-sensitive oxonol dye di-BA-C4(3) was developed. The fluorescent signal of di-BA-C4(3) was calibrated through a null point method using the protonophore FCCP. At null point, Em is equivalent to H+ equilibrium potential, and may be calculated by the Nernst equation. Intracellular pH (pHi) changes induced by the protonophore were monitored using BCECF, a pH-sensitive fluorescent probe. In the presence of FCCP, intracellular pH was found to be linearly correlated to extracellular pH (pHo). Therefore, the value of pHi at null point was extrapolated as well. With this technique, we estimated the plasma membrane potential of the "putative" rat osteoblasts (UMR 106) as -28.3 +/- 4.0 mV (n = 10). This method corrected the 16% overestimation of Em derived from the assumption that pHi does not change during the calibration procedure, as described in previous studies employing pH null point techniques. With null point methods, using BCECF and the carboxylic ionophores nigericin and monensin, intracellular concentrations of potassium and sodium were also measured and found to be 125 +/- 0.7 mM (n = 3) and 24 +/- 5.3 mM (n = 3), respectively. Although the Em of UMR 106 cells was dependent on extracellular potassium concentration, these cells did not behave as a potassium electrode. The sodium/potassium permeability ratio, calculated by the Goldman equation, was estimated at 0.317. This high membrane permeability to sodium may contribute to the genesis of the low plasma membrane potential of UMR 106 cells.
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PMID:Membrane potential and cation content of osteoblast-like cells (UMR 106) assessed by fluorescent dyes. 347 36

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

In certain neurons, alternative RNA processing generates calcitonin gene-related peptide (CGRP) from the same gene that encodes the hormone calcitonin. As CGRP-containing nerve fibers are prominent in skeleton, we evaluated the effects of CGRP on osteoblasts. Because the vasodilatory effect of neural CGRP in smooth muscle probably involves inhibition of unstimulated Ca2+ uptake, we examined the acute effects of CGRP on this parameter in rat osteoblastic cells. CGRP inhibits 45Ca2+ uptake in both UMR 106 osteosarcoma and RCOB-3 osteoblastic cells. This inhibition is rapid (0.5 min), occurs with an EC50 of 1 nM, and cannot be demonstrated in the presence of 0.1 mM diltiazem, a blocker of voltage-dependent Ca2+ channels. Depolarization of bone cells with high extracellular potassium (K+) also blocks the effect of CGRP on 45Ca2+ uptake, suggesting a central role for K+ channels in mediating this action. In agreement with this hypothesis, the effect of CGRP is blocked by 1 microM glybenclamide, a specific inhibitor of ATP-sensitive potassium (K(ATP)) channels, or by pretreatment of cells with 1 mM iodoacetic acid to deplete intracellular ATP. Blocking Ca2+-activated potassium channels with 1 mM tetraethylammonium does not prevent CGRP's effect. Pinacidil, a specific activator of K(ATP) channels, mimics CGRP's effect. Both CGRP and pinacidil also produce a small significant stimulation of cellular Ca2+ efflux in UMR 106 cells. These data suggest that inhibition of diltiazem-sensitive Ca2+ channels occurs secondary to the hyperpolarization engendered by CGRP activation of K(ATP) channels in osteoblastic cells, an effect similar to that of CGRP on smooth muscle cells.
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PMID:Calcitonin gene-related peptide rapidly inhibits calcium uptake in osteoblastic cell lines via activation of adenosine triphosphate-sensitive potassium channels. 860 12

Previous reports have suggested the involvement of voltage-activated calcium (Ca2+) channels in bone metabolism and in particular on the secretion of osteocalcin by osteoblast-like cells. We now report that potassium (K+) channels can also modulate the secretion of osteocalcin by MG-63 cells, a human osteosarcoma cell line. When 1,25-dihydroxyvitamin D3(1,25(OH)2D3)-treated MG-63 cells were depolarized by step increases of the extracellular K+ concentration ([K+]out) from 5-30 mM, osteocalcin (OC) secretion increased from a control value of 218 +/- 13 to 369 +/- 18 ng/mg of protein/48 h (p < 0.005 by analysis of variance). In contrast, in the absence of 1,25(OH)2D3, there is no osteocalcin secretion nor any effect of cell depolarization on this activity. The depolarization-induced increase in 1,25(OH)2D3-dependent osteocalcin secretion was totally inhibited in the presence of 10 microM Nitrendipine (a Ca2+ channel blocker, p < 0.005) without affecting cellular alkaline phosphatase nor cell growth. Charybdotoxin, a selective blocker of Ca2+-dependent K+ channels (maxi-K) present in MG-63 cells, stimulated 1,25(OH)2D3-induced osteocalcin synthesis about 2-fold (p < 0.005) after either 30, 60, or 120 minutes of treatment. However, Charybdotoxin was without effect on basal release of osteocalcin in the absence of 1,25(OH)2D3 pretreatment. Using patch clamp technique, we occasionally observed the presence of a small conductance K+ channel, compatible with an ATP-dependent K+ channel (GK[ATP]) in nonstimulated cells, whereas multiple channel openings were observed when cells were treated with Diazoxide, a sulfonamide derivative which opens GK(ATP). Western blot analysis revealed the presence of the N-terminal peptide of GK(ATP) in MG-63 cells, and its expression was regulated with the proliferation rate of these cells, maximal detection by Western blots being observed during the logarithmic phase of the cycle. Glipizide and Glybenclamide, selective sulfonylureas which can block GK(ATP), dose-dependently enhanced 1,25(OH)2D3-induced OC secretion (p < 0.005). Reducing the extracellular calcium concentration with EGTA (microM range) totally inhibited the effect of Glipizide and Glybenclamide on osteocalcin secretion (p < 0.005), which remained at the same levels as controls. Diazoxide totally prevented the effect of these sulfonylureas. These results suggest that voltage-activated Ca2+ channels triggered via cell depolarization can enhance 1,25(OH)2D3-induced OC release by MG-63 cells. In addition, OC secretion is increased by blocking two types of K+ channels: maxi-K channels, which normally hyperpolarize cells and close Ca2+ channels, and GK(ATP) channels. The role of these channels is closely linked to the extracellular Ca2+ concentration.
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PMID:Pharmacological and biochemical evidence for the regulation of osteocalcin secretion by potassium channels in human osteoblast-like MG-63 cells. 942 Dec 31

The acute renal effects of chemotherapy are known, but long-term nephrotoxicity has rarely been investigated. The aim of the present study was to assess long-term renal function in children and adolescents who received at-risk chemotherapy, including cisplatin, ifosfamide, and methotrexate, to treat an osteosarcoma. Renal function tests [creatinine clearance, microalbuminuria, and renal excretion of sodium, potassium, chloride, calcium, magnesium (Mg), phosphorus (P), and uric acid] were prospectively performed 5.4+/-2.2 (+/-SD) years after chemotherapy (total cumulative dose: methotrexate 41+/-31 g/m2, ifosfamide 39+/-14 g/m2, cisplatin 674+/-188 mg/m2) in 18 children and adolescents. The results were compared with 13 normal volunteers matched for age and sex. Creatinine clearance, which was greater than 80 ml/min per 1.73 m2 in all patients, correlated with the total dose of ifosfamide (r=0.55, P<0.05) and cisplatin (r=0.48, P<0.05). Microalbuminuria was noted in 4 patients. Hypomagnesemia was present in 4 and hypercalciuria in 3 patients; renal excretion of P, Mg, and uric acid was higher in patients than in controls. Glomerular function was not significantly altered and only mild tubular dysfunction was present. Since renal excretion of P and Mg were increased in patients compared with normal volunteers and hypercalciuria was occasionally seen, divalent ion disorders are the most-likely potential complications.
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PMID:Long-term nephrotoxicity of cisplatin, ifosfamide, and methotrexate in osteosarcoma. 976 57

The effects of natural lipid-soluble antioxidant, alpha-tocopherol (alpha-TP), and the synthetic water-soluble antioxidant, phenosan potassium salt (Ph-K), in a broad range of concentrations down to ultralow doses (10(-4)-10(-20) M) on the activity of protein kinase C (PKC) have been studied. It was shown that alpha-TP is a potent inhibitor of the rabbit heart enzyme: the maximum extent of inhibition is 80%. The effects of alpha-TP on the main kinetic parameters of the PKC activity differ at the alpha-TP physiological (10(-4) M) and ultralow (10(-14) M) concentrations: at 10(-14) M, alpha-TP acts as an allosteric inhibitor with Hill's coefficient about 2 and doubles the PKC affinity to the substrate (histone H-1). It was concluded that alpha-TP is more efficient inhibitor at ultralow concentration. Ph-K added to normal (A7r5 rat vascular smooth muscle cells, VSMC) and tumor cells (Saos-2 human osteosarcoma) growing in a culture has been found to be a PKC superactivator. The maximum activation is 400-500%, which is more than two times as high as the effect of the best activator of this enzyme, phorbol ester (TPA). It was demonstrated that irrespective of the effector action (activation or inhibition), the dose-effect curves are of the bimodal type with two maxima at the high (or physiological) (10(-4)-10(-7) M) and ultralow (10(-14)-10(-19) M) concentrations of the antioxidants and the so-called "silence zones" between them, in which the effect of antioxidants is significantly reduced or absent (tumor cells). For the first time, these bimodal curves were observed at the enzyme level. The results obtained are discussed considering various hypotheses of the effect of ultralow doses of biologically active compounds and the PKC activity regulation in normal and tumor cells by the antioxidants.
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PMID:Natural (alpha-tocopherol) and synthetic (phenosan potassium salt) antioxidants regulate the protein kinase C activity in a broad concentration range (10(-4)-10(-20) M). 987 48

We report a girl who developed severe and fatal hyperkalemia following rapid and massive blood transfusion during surgery. She was 7-year-old, 20-kg in weight, and received wide resection of the femoral bone with custom prosthesis implant because of malignant femoral osteosarcoma. During the procedure, bleeding was active and profuse and amounted to about 3,000 mL in 4 h, eventuating in shock. Despite rapid transfusion with 15 units of packed red blood cells (RBC) still she remained hypotensive and hypovolemic. When we switched to give her whole blood, actually 100 mL having been given, widening of QRS complex followed immediately by cardiac arrest developed. Cardiopulmonary resuscitation although started at once was unsuccessful. At this juncture, arterial blood gas analysis showed acidosis and severe hyperkalemia (10.3 mmol/L), possibly resulting from transfusion of blood of older storage. The case reminded us once again the importance and necessity of the use of potassium-low blood component (fresh, saline-washed RBCs) in case of massive and rapid blood transfusion especially in pediatric patients with hypovolemia and low cardiac output.
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PMID:Fatal hyperkalemia during rapid and massive blood transfusion in a child undergoing hip surgery--a case report. 1060 52

Selective estrogen receptor modulators (SERMs), tamoxifen (Tam) and toremifene (Tor), are widely used in the treatment of breast cancer. In addition, they have been demonstrated to prevent estrogen deficiency-induced bone loss in postmenopausal women. These effects are thought to be caused by the interaction of the SERMs with the estrogen receptor, although SERMs have also been shown to conduct non-receptor-mediated effects such as rapid changes in membrane functions. We compared the effects of Tam, Tor, and 17beta-estradiol (E2) on the viability of rat osteoclasts and osteoblasts. Both Tam and Tor were found to cause osteoclast apoptosis in in vitro cultures, which was reversed by E2. In addition, at higher concentration (10 microM), both SERMs had an estrogen receptor-independent effect, which involved interaction with the plasma membrane as demonstrated with UMR-108 osteosarcoma cells by Tam and Tor, but not E2. A leak of protons leading to changes in intracellular pH was shown both in medullary bone derived membrane vesicles and in intact cells. These effects were followed by a rapid loss of cell viability and subsequent cell lysis. Our results show that both Tam and Tor have an ionophoric effect on the plasma membranes of bone cells and that these SERMs differed in this ability: Tor induced rapid membrane depolarization only in the presence of high concentration of potassium. These non-receptor-mediated effects may be involved in therapeutic responses and explain some clinical side effects associated with the treatment of patients with these SERMs.
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PMID:The effects of tamoxifen and toremifene on bone cells involve changes in plasma membrane ion conductance. 1261 32

The effects of estrogen on gene expression in mammary cells are mediated by interaction of the estrogen receptor (ER) with estrogen response elements in target DNA. Whereas the ER is the primary initiator of transcription, the recruitment of coregulatory proteins to the DNA-bound receptor influences estrogen responsiveness. To better understand how estrogen alters gene expression, we identified proteins associated with the DNA-bound ERalpha. Surprisingly, the antioxidant enzyme Cu/Zn superoxide dismutase (SOD1), which is known primarily as a scavenger of superoxide, was associated with the DNA-bound receptor. We have now demonstrated that SOD1 interacts with ERalpha from MCF-7 cell nuclear extracts and with purified ERalpha and that SOD1 enhances binding of ERalpha to estrogen response element-containing DNA. Although SOD1 decreases transcription of an estrogen-responsive reporter plasmid in transiently transfected U2 osteosarcoma cells, RNA interference assays demonstrate that SOD1 is required for effective estrogen responsiveness of the endogenous pS2, progesterone receptor, cyclin D1, and Cathepsin D genes in MCF-7 breast cancer cells. Furthermore, ERalpha and SOD1 are associated with regions of the pS2 and progesterone receptor genes involved in conferring estrogen-responsive gene expression. Interestingly, when MCF-7 cells are exposed to 17beta-estradiol and superoxide generated by addition of potassium superoxide (KO2) to the cell medium, SOD1 levels are increased and tyrosine nitration, which is an indicator of oxidative stress-induced protein damage, is significantly diminished. Our studies have identified a new role for SOD1 in regulating estrogen-responsive gene expression and suggest that the 17beta-estradiol- and KO2-induced increase in SOD1 may play a role in the survival of breast cancer cells and the progression of mammary tumors.
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PMID:Effects of Cu/Zn superoxide dismutase on estrogen responsiveness and oxidative stress in human breast cancer cells. 1825 88


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