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

Pretreatment of UMR-106 cells (rat osteoblast like osteosarcoma cell line) with the protein kinase C(PK-C) activating phorbol ester, phorbol 12-myristate 13-acetate (PMA) results in a time dependent (1-12h) desensitization of PTH-stimulated cAMP production. Compared to controls, PMA-treated cells showed 50% decrease of PTH-stimulated cAMP production. PK-C inhibitor, H-7 significantly blocked this PMA-induced desensitization. PTH receptor binding, assessed with 125I-[Nle8,Nle18,Tyr34]PTH-(1-34) as radioligand, was decreased by about 20% in PMA-treated cells. H-7 treatment completely restored receptor binding in PMA-treated cells. These data suggest that PK-C might act directly on PTH receptor which is coupling to adenylate cyclase, and induce desensitization.
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PMID:Phorbol ester induces desensitization of PTH-stimulated cyclic AMP production by decreasing the PTH receptor binding in UMR-106 cells. 185 Oct 4

The effect of alpha-tocopherol (vitamin E) on the proliferation of vascular smooth muscle cells (A7r5), human osteosarcoma cells (Saos-2), fibroblasts (Balb/3T3), and neuroblastoma cells (NB2A) has been studied. The proliferation of vascular smooth muscle cells was inhibited by physiologically relevant concentrations of alpha-tocopherol, neuroblastoma cells were only sensitive to higher alpha-tocopherol concentrations, and proliferation of the other cell lines was not inhibited. The inhibition of smooth muscle cell proliferation was specific for alpha-tocopherol. Trolox, phytol, and alpha-tocopherol esters had no effect. Proliferation of smooth muscle cells stimulated by platelet-derived growth factor or endothelin was completely sensitive to alpha-tocopherol. If smooth muscle cells were stimulated by fetal calf serum, proliferation was 50% inhibited by alpha-tocopherol. No effect of alpha-tocopherol was observed when proliferation of smooth muscle cells was stimulated by bombesin and lysophosphatidic acid. The possibility of an involvement of protein kinase C in the cell response to alpha-tocopherol was suggested by experiments with the isolated enzyme and supported by the 2- to 3-fold stimulation of phorbol ester binding induced by alpha-tocopherol in sensitive cells. Moreover, alpha-tocopherol also caused inhibition of protein kinase C translocation induced by phorbol esters and inhibition of the phosphorylation of its 80-kDa protein substrate in smooth muscle cells. A model is discussed by which alpha-tocopherol inhibits cell proliferation by interacting with the cytosolic protein kinase C, thus preventing its membrane translocation and activation.
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PMID:Inhibition of cell proliferation by alpha-tocopherol. Role of protein kinase C. 200 76

The parathyroid hormone (PTH) fragment [1-34] strongly stimulated both adenylate cyclase and membrane-associated PKC activities in rat 17/2 osteosarcoma cells. By contrast, the PTH [3-34] fragment, which was unable to stimulate adenylate cyclase, remained a potent stimulator of membrane-associated PKC activity in these cells. Both PTH fragments also strongly stimulated membrane-PKC activity in cyc-S49T-lymphoma cells possessing a defective adenylate cyclase system. This ability of PTH [3-34] to stimulate membrane-associated PKC activity could explain the residual bioactivity of this fragment.
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PMID:Parathyroid hormone fragment [3-34] stimulates protein kinase C (PKC) activity in rat osteosarcoma and murine T-lymphoma cells. 217 7

Previous work demonstrated that parathyroid hormone (PTH) activates the Ca2+/protein kinase C (PKC) system in addition to cAMP production. Therefore, the authors explored the role of cAMP-dependent and Ca2(+)-dependent signals in the regulation of osteoblastic growth and bone resorption. In exponentially growing UMR 106-01 osteogenic sarcoma cells, PTH (10(-7) M) inhibited [3H] thymidine incorporation by 80%. This effect was reproduced by maximal doses of both dibutyryl-cAMP (dbcAMP) and forskolin. The Ca2+ ionophore ionomycin (10(-7) M) had no effect, whereas phorbol 12-myristate 13-acetate (PMA) was slightly mitogenic. The antimitogenic action of dbcAMP was dose-dependent, with ED0.5 at about 3 X 10(-5) M. Ionomycin enhanced this dbcAMP effect at submaximal doses of the cAMP analog. PMA used in combination with both dbcAMP and ionomycin induced further depression of cell proliferation, indicating synergism with cAMP. Both dbcAMP (10(-4) M) and ionomycin (10(-7) M) stimulated 45Ca release from fetal rat limb bones after five days in culture, although the Ca2+ ionophore was less potent. 1-Oleoyl 2-acetyl-glycerol (2 X 10(-6) M) was ineffective alone, and slightly inhibited the 45Ca release produced by the other second messenger analogs in all combinations. The combination of dbcAMP and ionomycin showed a synergistic effect, and fully reproduced PTH effect. In conclusion, PTH signal transduction for control of cell proliferation and bone resorption is mediated mainly by cAMP. Activation of the Ca2+/PKC message system is nevertheless necessary to express a full hormonal response in both cell and organ culture systems.
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PMID:Cyclic AMP-dependent and calcium-dependent signals in parathyroid hormone function. 217 68

A 180-kilodalton (kDa) protein (p180) was identified among the antigens for a panel of monoclonal antibodies raised against human fibroblast cell surface proteins. Binding studies with 125I-Fab' fragments of an anti-p180 monoclonal antibody demonstrated that 10 to 30% of p180 was located on the plasma membrane and that the remaining 70 to 90% was on intracellular membranes. p180 was rapidly internalized from the cell surface at 37 degrees C, and kinetic analyses indicated that this was a constitutive process followed by the recycling of p180 back to the plasma membrane. Morphological studies demonstrated that on the cell surface p180 was concentrated in coated pits, whereas inside the cell it was found in endosomes as suggested by its colocalization with the transferrin receptor. Immunoblot analysis with a polyclonal antiserum raised against purified human protein showed that p180 has a restricted distribution with expression at high levels in fibroblast cultures and in tissues containing cells of mesodermal origin. A biochemical characterization of p180 showed it to be a transmembrane glycoprotein with an extracellular domain, which consists of approximately 30 kDa of complex oligosaccharides attached to at least 45 kDa of the protein core. The cytoplasmic domain of p180 was found to contain a serine residue(s) that was phosphorylated both in vivo and in vitro by activated protein kinase C. p180 was purified by subjecting solubilized membrane proteins from a human osteosarcoma cell line to immunoaffinity chromatography and gel filtration. The N-terminal sequence information obtained from the purified protein showed no homology to other known proteins. It was concluded that p180 may be a novel recycling receptor which is highly restricted in its expression to fibroblastlike cells.
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PMID:p180, a novel recycling transmembrane glycoprotein with restricted cell type expression. 218 94

Measurements of cytosolic pH (pHi) 36Cl fluxes and free cytosolic Ca2+ concentration ([Ca2+]i) were performed in the clonal osteosarcoma cell line UMR-106 to characterize the kinetic properties of Cl-/HCO3- (OH-) exchange and its regulation by pHi and [Ca2+]i. Suspending cells in Cl(-)-free medium resulted in rapid cytosolic alkalinization from pHi 7.05 to approximately 7.42. Subsequently, the cytosol acidified to pHi 7.31. Extracellular HCO3- increased the rate and extent of cytosolic alkalinization and prevented the secondary acidification. Suspending alkalinized and Cl(-)-depleted cells in Cl(-)-containing solutions resulted in cytosolic acidification. All these pHi changes were inhibited by 4',4',-diisothiocyano-2,2'-stilbene disulfonic acid (DIDS) and H2DIDS, and were not affected by manipulation of the membrane potential. The pattern of extracellular Cl- dependency of the exchange process suggests that Cl- ions interact with a single saturable external site and HCO3- (OH-) complete with Cl- for binding to this site. The dependencies of both net anion exchange and Cl- self-exchange fluxes on pHi did not follow simple saturation kinetics. These findings suggest that the anion exchanger is regulated by intracellular HCO3- (OH-). A rise in [Ca2+]i, whether induced by stimulation of protein kinase C-activated Ca2+ channels, Ca2+ ionophore, or depolarization of the plasma membrane, resulted in cytosolic acidification with subsequent recovery from acidification. The Ca2+-activated acidification required the presence of Cl- in the medium, could be blocked by DIDS, and H2DIDS and was independent of the membrane potential. The subsequent recovery from acidification was absolutely dependent on the initial acidification, required the presence of Na+ in the medium, and was blocked by amiloride. Activation of protein kinase C without a change in [Ca2+]i did not alter pHi. Likewise, in H2DIDS-treated cells and in the absence of Cl-, an increase in [Ca2+]i did not activate the Na+/H+ exchanger in UMR-106 cells. These findings indicate that an increase in [Ca2+]i was sufficient to activate the Cl-/HCO3- exchanger, which results in the acidification of the cytosol. The accumulated H+ in the cytosol activated the Na+/H+ exchanger. Kinetic analysis of the anion exchange showed that at saturating intracellular OH-, a [Ca2+]i increase did not modify the properties of the extracellular site. A rise in [Ca2+]i increased the apparent affinity for intracellular OH- (or HCO3-) of both net anion and Cl- self exchange. These results indicate that [Ca2+]i modifies the interaction of intracellular OH- (or HCO3-) with the proposed regulatory site of the anion exchanger in UMR-106 cells.
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PMID:Cytosolic pH regulation in osteoblasts. Regulation of anion exchange by intracellular pH and Ca2+ ions. 229 28

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

We demonstrate that a novel integrin beta subunit is present in association with the vitronectin receptor (VNR) alpha subunit on the surface of MG-63 human osteosarcoma cells. This beta subunit and the glycoprotein IIIa beta subunit (beta 3) were both found complexed with VNR alpha on MG-63 cells and in at least two other human cell types we examined. Tryptic peptide mapping indicated that the two beta subunits are related but distinct. The novel beta chain, referred to here as beta s, was not recognized by the monoclonal antibody AP3, which recognizes GPIIIa, nor by an antiserum raised against a peptide from the COOH-terminal cytoplasmic domain of beta 3. Both receptor complexes bound to and were specifically eluted from a column containing the cell adhesion peptide GRGDSP. The unique beta subunit became phosphorylated at high stoichiometry when MG-63 cells or AG1523 human fibroblasts were treated with the phorbol-ester tumor promoter phorbol 12-myristate 13-acetate. This phosphorylation occurred mainly on serine and probably at one major site, as determined by phosphotryptic peptide mapping. Protein kinase C phosphorylated the beta s subunit of intact receptor in vitro, at the same site phosphorylated in treated cells, indicating that protein kinase C is likely to be responsible for this phosphorylation in vivo.
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PMID:A novel integrin beta subunit is associated with the vitronectin receptor alpha subunit (alpha v) in a human osteosarcoma cell line and is a substrate for protein kinase C. 247 39

The calcium and phospholipid-dependent protein kinase C (PKC) system appears to play an important role in mediating hormonal effects in various tissues including bone. Accordingly, we characterized PKC activity in the UMR-106-01 rat osteosarcoma osteoblastlike cell line and examined its hormonal regulation. UMR-106-01 cells were found to possess a classic, phorbol ester-activated PKC system, which was highly calcium and phospholipid dependent. A 30 s exposure to 10 nM bovine parathyroid hormone (PTH) (1-34) increased cytosolic and membrane-bound PKC activity by 12 and 157%, respectively, resulting in a 2.2-fold increase in the membrane-bound to cytosolic (MB/C) activity ratio (all p less than 0.01). The MB/C activity ratio was highest at 20 min, exhibiting a 2.8-fold increase over the control values (p less than 0.01). In contrast, 10 nM insulin increased cytosolic PKC activity but decreased membrane-bound activity, resulting in a 61% decrease in the MB/C activity ratio at 20 min (p less than 0.02). Moreover, insulin reduced PTH stimulation of the PKC activity ratio by 42 and 62% at 30 s and 20 min, respectively (p less than 0.02). Thus, PTH and insulin have opposing effects on the PKC activity ratio in UMR-106-01 cells.
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PMID:Protein kinase C activity in UMR-106-01 cells: effects of parathyroid hormone and insulin. 268 93

A clonal cell line (Saos-2/B-10) derived from human osteosarcoma Saos-2 cells had the same osteoblastic characteristics as the mother line, but lacked sensitivity to parathyroid hormone (PTH) at early passages. At later passages (greater than 70) the cells became very sensitive to PTH (0.1 nmol/l). The absence of PTH-stimulatable adenylate cyclase correlated with the secretion of an adenylate cyclase-stimulatory activity which had the properties of the recently characterized PTH-like peptide (PTH-LP). This activity was inhibited by the PTH antagonist [8norleucyl,18norleucyl,34tyrosinyl]bovine PTH-(3-34)amide and could be neutralized by an antiserum raised against the synthetic PTH-LP-(1-34). Hybridization with a human PTH-LP cDNA showed that these cells produce two PTH-LP mRNAs of approximately 1.5 and 1.8 kb. The production of PTH-LP was stimulated by 12-O-tetradecanoyl-phorbol-13-acetate (TPA; 150 nmol/l) and epidermal growth factor (EGF; 10 ng/ml). The increased accumulation of PTH-LP in conditioned media in response to TPA was seen after 1 h and levelled off at 6 h. In contrast, EGF stimulation was lower at 3 and 6 h but continued for 24 h. Both agents increased PTH-LP mRNA levels in Saos-2/B-10 cells. A TPA analogue which does not stimulate protein kinase C had no effect on PTH-LP production. Cycloheximide blocked the stimulatory effect of both TPA and EGF and the TPA effect was blocked by actinomycin D, suggesting transcriptional control. The regulation of PTH-LP by these agents may offer clues regarding the association of this protein with malignancy.
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PMID:Production of parathyroid hormone-like peptide in a human osteosarcoma cell line: stimulation by phorbol esters and epidermal growth factor. 278 97


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