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)

PTH-related peptide (PTHrP) may be a major cause of the humoral hypercalcemia of malignancy. The circulating form of PTHrP is unknown, but mRNA analysis of tumor tissue suggests that multiple forms of PTHrP may exist. Therefore, we examined the ability of the full 141-amino acid protein as well as 2 amino-terminal fragments, PTHrP-(1-34) and PTHrP-(1-74), to increase cytosolic calcium ion concentrations ([Ca2+]i; assessed by aequorin luminescence) and stimulate cAMP accumulation in osteoblast-like rat osteosarcoma cells (ROS 17/2.8). PTH and all PTH-related peptides examined increased [Ca2+]i and cAMP in a concentration-dependent manner. The [Ca2+]i response to PTHrP-(1-34) closely resembled that to rat PTH-(1-34); both peptides produced biphasic responses. However, the responses to the longer PTHrP fragments generally were not biphasic. There were no significant differences among the three PTHrP forms in increasing [Ca2+]i or stimulating cAMP accumulation, although PTHrP-(1-74) was consistently weaker than the other two PTHrP peptides. PTHrP-(1-34) was more potent than rPTH-(1-34), which, in turn, was more potent than human PTH-(1-34) in increasing [Ca2+]i. However, PTHrP-(1-34) was not consistently more potent than either human PTH-(1-34) or rat PTH-(1-34) in stimulating cAMP accumulation. The inhibitory PTH analog bovine PTH-(3-34) attenuated both cAMP and [Ca2+]i responses to PTHrP-(1-34), but bovine PTH-(7-34) only reduced the [Ca2+]i response. Our data are generally consistent with PTHrP's acting through the PTH receptor, but differences in the effects of inhibitory PTH analogs on PTH and PTHrP action suggest as yet unexplained complexities, such as the existence of a PTH/PTHrP receptor family.
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PMID:Structure-function relationships for full-length recombinant parathyroid hormone-related peptide and its amino-terminal fragments: effects on cytosolic calcium ion mobilization and adenylate cyclase activation in rat osteoblast-like cells. 230 14

Studies on humoral hypercalcemia of malignancy have shown that tumors produce a protein that acts through the parathyroid hormone (PTH) receptor but is immunologically distinct from PTH. We have recently purified and cloned a parathyroid hormone-related protein (PTHrP) from a human lung cancer cell line. Full length cDNA clones were isolated and found to encode a prepropeptide of 36 amino acids and a mature protein of 141 amino acids. Eight of the first 13 amino terminal residues are identical with human PTH, although antisera directed at the amino terminus of PTHrP do not recognize PTH. A 34-amino acid synthetic peptide, PTHrP(1-34), was several times more potent than bovine or human PTH(1-34) in bioassays promoting the formation of cAMP and plasminogen activity in osteogenic sarcoma cells and activation of adenylate cyclase in chick kidney membranes. PTHrP(1-34) was also more potent than PTH(1-34) in stimulating cAMP and phosphate excretion and reducing calcium excretion in the isolated perfused rat kidney. PTHrP has been consistently demonstrated by immunohistochemistry in squamous cell carcinomas and in keratinocytes present in normal skin, but not in normal or hyperplastic parathyroid tissues or other tumors. PTHrP-like activity has been extracted from ovine placenta and fetal parathyroid tissue, suggesting that PTHrP may play a role in fetal calcium homeostasis.
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PMID:Humoral hypercalcemia of malignancy. 233 5

A variety of tumors stimulate platelet activation. Because platelet activation may, in part, require calcium channel mobilization, we evaluated whether calcium channel blocking agents inhibit osteogenic sarcoma induced platelet aggregation. Platelet rich plasma (PRP) from normal subjects was incubated with one of four calcium channel-blocking agents: nifedipine, diltiazem, verapamil, or amlodopine, all 0-25 micrograms/ml, or diluent. Osteogenic sarcoma cells (2 or 4 x 10(6)/ml) were then added. Platelet aggregation was monitored by light transmission through PRP, and residual PRP was processed for electron microscopy. MG63 cells caused aggregation of PRP in most subjects (mean, 36 +/- 3%). Calcium channel-blocking agents (nifedipine greater than diltiazem greater than amlodopine greater than verapamil) caused partial inhibition of osteogenic sarcoma-induced platelet aggregation, at high concentrations only. Electron microscopy showed platelets aggregating to each other and to tumor cell membranes within 1-5 minutes. Changes in pattern of platelet clumping around tumor cells occurred when PRP was incubated with high concentration of diltiazem (50 micrograms). This study shows that calcium channel-blocking agents inhibit osteogenic sarcoma-induced platelet aggregation when used in high doses.
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PMID:Effects of calcium channel-blocking agents on platelet-osteogenic sarcoma interaction: platelet aggregation and electron microscopic findings. 238 1

Using microelectrode techniques, we have observed that the application of serum or alpha 2-macroglobulin (alpha 2M) induces transient hyperpolarizations in the membrane potential of a rat osteosarcoma clone (ROS 17/2). Hyperpolarizations arose from activation of Ca2+-dependent K+ channels by transient increases in the concentration of intracellular free Ca2+. Hyperpolarizing spikes were observed for several h following the addition of fetal bovine serum (FBS) to cell cultures. Application of small volumes of FBS or alpha 2M rapidly induced synchronized bursts of hyperpolarizing spikes. No response was elicited by serum-free medium, latex beads, or bovine serum albumin (BSA). Immunofluorescence labeling patterns were consistent with the receptor-mediated endocytosis of alpha 2M but not BSA. The ligand specificity and kinetics of these hyperpolarizations suggest that they are associated with a receptor-mediated event, possibly an early stage of receptor-mediated endocytosis.
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PMID:Serum and alpha 2-macroglobulin induce transient hyperpolarizations in the membrane potential of an osteoblastlike clone. 244 77

The amino acid sequence of the vitronectin receptor alpha subunit deduced from cDNA is presented. The sequence defines a 1047-amino-acid polypeptide precursor with a putative signal sequence, a large extracellular domain with several sites homologous to calcium binding sites in other proteins, a transmembrane domain, and a 32-amino-acid cytoplasmic domain. The 7-kilobase vitronectin receptor alpha subunit mRNA was found to be expressed in all cell lines examined, including endothelial cells, K562 and HEL leukemia cells, and osteosarcoma cells. In the two leukemia cell lines, the expression of the vitronectin receptor mRNA, as well as that of the fibronectin receptor, was enhanced in the presence of phorbol ester, a treatment known to increase the adhesiveness of these cells. The HEL cells were the only ones among the cell lines tested that also contained the mRNA of the platelet adhesion receptor alpha subunit, glycoprotein IIb. The expression of glycoprotein IIb was slightly enhanced by treatment of the cells with phorbol ester. These results complete the partial cDNA sequence of the vitronectin receptor alpha subunit published previously (Suzuki, S., Argraves, W. S., Pytela, R., Arai, H., Krusius, T., Pierschbacher, M. D., and Ruoslahti, E. (1986) Proc. Natl. Acad. Sci. U.S.A., 83, 8614-8618), confirm that the vitronectin receptor, and not IIb, is expressed in endothelial cells, and show that changes in the level of its expression correlate with changes in cell adhesiveness.
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PMID:Amino acid sequence of the vitronectin receptor alpha subunit and comparative expression of adhesion receptor mRNAs. 244

We have reported previously that serum and alpha 2-macroglobulin (alpha 2M) induce Ca2+-activated hyperpolarizations in the membrane potential of a clonal rat osteosarcoma cell line (ROS 17/2) (Dixon and Aubin, J. Cell, Physiol., 132:215-225, 1987). In this report, we describe morphological changes that accompany these hyperpolarizations. Both cell surface blebbing (zeiosis) and transient hyperpolarizations were induced by application of 10% fetal bovine serum (FBS) or alpha 2M; neither was induced by serum-free medium, a suspension of latex beads, or purified bovine serum albumin. Following a brief application of FBS or alpha 2M at time 0, electrical activity typically occurred between 7-40 s and was always followed by blebbing activity that began at 30 s and persisted for 3-5 min. In contrast, continuous exposure to FBS resulted in the persistence of both blebbing activity and transient hyperpolarizations for periods of at least several hours. Scanning electron microscopy (SEM) revealed that the blebs appeared concomitantly with the disappearance of microvilli and the appearance of surface pits that measured 100-300 nm in diameter. Coated pits and vesicles, similar in size to the pits observed by SEM, were observed using transmission electron microscopy (TEM). By TEM, blebs were found to contain few organelles other than centrally located free ribosomes. Fluorescence microscopy of nitrobenzooxadizole-phallacidin-labeled cells indicated that blebs contained filamentous actin and that microfilament bundles remained primarily on the substratum side of blebbed cells. We propose that blebbing results from a dynamic local reorganization of microfilaments initiated by ligand-induced transient increases in intracellular Ca2+.
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PMID:Membrane blebbing is associated with Ca2+-activated hyperpolarizations induced by serum and alpha 2-macroglobulin. 244 13

Rat osteogenic sarcoma cells have been used widely as a model system to study actions of 1,25(OH)2D3 and other hormones in osteoblastlike cells. However, some of the pleiotypic manifestations of hormones in these cells vary greatly dependent upon the cell population density and other conditions of culture. Therefore, we have studied the effect of cell density on the relationship between 1,25(OH)2D3 and the initial 45Ca accumulation in ROS 17/2 cells in order to establish conditions suitable for studying the effect of 1,25(OH)2D3 on calcium fluxes in these cells. Cells were grown in the presence and absence of 1,25(OH)2D3 for 48 hours and then incubated for 4 min in the culture medium containing 0.5 microCi/ml of 45CaCl2. In high population density cultures, 0.25-1.0 pg/ml of 1,25(OH)2D3 stimulated the intracellular accumulation of 45Ca (cpm/mg protein), whereas 80 pg/ml or higher concentrations inhibited accumulation of 45Ca. In low density cultures, concentrations less than 80 pg/ml had no effect, 80-120 pg/ml increased the intracellular accumulation, and as much as 200 pg/ml failed to show the inhibitory effect. These results indicate that the ROS 17/2 cell responses to 1,25(OH)2D3 are biphasic--low concentrations stimulating and high concentrations inhibiting 45Ca accumulation. The sensitivity of the cells to 1,25(OH)2D3 increases as the cell population density increases. These observations suggest that the culture density and dose-response relationship must be carefully defined in in vitro studies utilizing osteogenic cell culture systems.
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PMID:Cell density-dependent vitamin D effects on calcium accumulation in rat osteogenic sarcoma cells (ROS 17/2). 244 55

Platelet-derived growth factor (PDGF) is generally considered to stimulate phosphoinositide turnover resulting in activation of protein kinase C and increased cytoplasmic [Ca2+]. We have examined the role of these secondary effects in regulation of c-myc mRNA accumulation in the MG-63 human osteogenic sarcoma line. Treatment of quiescent cells with 12-O-tetradecanoyl phorbol-13-acetate (TPA) to down-regulate protein kinase C inhibited TPA-stimulated c-myc expression but did not affect the PDGF-modulated process. When cytoplasmic [Ca2+] was increased by addition of a Ca2+ ionophore (A23187 or ionomycin), no stimulation of c-myc RNA was seen; furthermore, these agents did not enhance the PDGF-modulated c-myc expression. Addition of EGTA to cultures treated with both PDGF and a Ca2+ ionophore did not inhibit c-myc induction but rather caused a superinduction of c-myc RNA accumulation. Superinduction occurred only if the [EGTA] was greater than [Ca2+] in the medium. This superinduction was distinct from the increased induction caused by inhibition of protein synthesis. Because PDGF-induced c-myc expression is independent of protein kinase C and increased cytoplasmic [Ca2+], the evidence suggests that PDGF modulates c-myc RNA accumulation in MG-63 cells via a novel pathway, seemingly uncoupled from the classic action of increased phosphoinositide metabolism.
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PMID:Platelet-derived growth factor-induced c-myc RNA expression. Analysis of an inducible pathway independent of protein kinase C. 244 30

Conditioned medium from cultured normal human foreskin keratinocytes enhanced the release of calcium from neonatal mouse calvaria in organ culture. Unfractionated keratinocyte-conditioned medium (KCM) stimulated bone resorption in a dose-dependent manner, but it did not increase the concentration of prostaglandin E2 (PGE2) in the bone culture medium until a maximal dose of KCM for resorption was used. Furthermore, inhibitors of PGE2 synthesis, indomethacin, ibuprofen, and piroxicam, did not inhibit KCM-induced calcium release. High concentrations of KCM increased cAMP production by calvaria in the presence of isobutylmethylxanthine, but the increase was small compared with that produced by a dose of bovine PTH that caused a similar level of bone resorption. The bone resorption-stimulating activity of KCM was not lost after incubation at 56 C for 60 min, but it was lost after heating at 100 C for 10 min. Fractionation of KCM by gel filtration chromatography revealed two distinct peaks of bone resorption-stimulating activity. One peak, KCMI, caused a significant increase in bone resorption at 2 micrograms protein/ml. KCMI did not increase medium PGE2, and inhibition of PGE2 synthesis in bone had no effect on KCMI-induced bone resorption. KCMI failed to increase cAMP production by human osteosarcoma SaOS-2 cells. Another peak, KCMII, caused a dose-dependent increase in bone resorption, and a significant increase in medium calcium was noted at a 20-fold lower concentration (0.1 microgram protein/ml) than with KCMI. In contrast to KCMI, the increase in bone resorption stimulated by KCMII was accompanied by a parallel increase in the production of PGE2, and inhibition of PGE2 synthesis completely inhibited the bone resorption-stimulating activity of KCMII. KCMII also caused an increase in cAMP production by SaOS-2 cells. We conclude that KCM contains at least two distinct bone resorption-stimulating factors, one of which acts via a PG-mediated mechanism and the other by a PG-independent pathway.
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PMID:Evidence for multiple bone resorption-stimulating factors produced by normal human keratinocytes in culture. 245 41

This study compares the metabolism of [14C]-arachidonic acid between PGE2 synthesizing (ROS 17/2.8) and nonsynthesizing (ROS 25/1) osteosarcoma cell lines. In both cell lines: (a) 90% of [14C]-arachidonic acid was taken up at 24 h. (b) More than 90% of the label was associated with phospholipids. (c) [14C]-arachidonic acid was rapidly taken up by phosphatidylcholine which reached the highest specific activity around 5 h while the labeling of other phospholipids was still increasing at 24 h. (d) Twenty-four hours after addition of [14C]-arachidonic acid only 4% of the label was associated with triacylglycerols in ROS 25/1 and 0.3% in ROS 17/2.8 cells. The calcium ionophore A23187 enhanced the release of [14C]-arachidonic acid from phospholipids in the PGE synthesizing osteoblastic cells (ROS 17/2.8 and 2/3) but had no effect in nonosteoblastic cells (ROS 24/1 and 25/1). ROS 17/2.8 and 2/3 cells converted the released arachidonic acid as well as exogeneously added arachidonic acid into PGE2. PGE2 synthesis depended on arachidonic acid concentration. Among bone resorbing agents, parathyroid hormone and 1,25(OH)2D3 had no effect on PGE synthesis, whereas thrombin and rabbit serum stimulated PGE2 production. The effect of rabbit serum was abolished by heat inactivation. The findings of this study indicate that the difference in PGE production between the osteoblastic and nonosteoblastic osteosarcoma cells are due mainly to differences in arachidonic acid conversion to PGE2.
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PMID:Clonal differences in prostaglandin synthesis among osteosarcoma cell lines. 245 9


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