UMLS:C0029463 - FACTA Search

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

The pulsatile but not the continuous application of parathyroid hormone (PTH) increase bone mass in vivo. To study the effects of intermittent hormonal administration on bone-derived cells in vitro, we established a perifusion system using the human osteosarcoma cell line SaOS-2. Cells were grown in suspension culture attached to collagen beads and were then loaded into a 3 ml syringe for perifusion experiments. The application of PTH(1-34) resulted in a dose-dependent increase of cAMP release by SaOS-2 cells into the effluent medium. Cyclic AMP accumulation was rapidly desensitized by approx. 80% after 30 min of continuous exposure to PTH(1-34) (10(-7) M), while cells remained responsive to forskolin. The recovery of PTH responsiveness required at least 2 h of hormone-free perifusion. Desensitization in the experimental setting was dose-dependent (EC50 = 1 x 10(-10) M PTH(1-34)). Neither 8Br-cAMP (2 x 10(-4) M) nor PMA(1 x 10(-7) M) had an effect on the PTH(1-34)-induced desensitization of the adenylate cyclase. Radioreceptor assays showed that [125I]-[Tyr36]hPTHrP(1-36)amide binding to SaOS-2 cells was decreased by 60-70% by PTH(1-34) (1 x 10(-6) M), bPTH(1-84) (1.8 x 10(-6) M) and bPTH(3-34) (2 x 10(-6) M), whereas 8Br-cAMP (2 x 10(-4) M) had no effect on radioligand binding. PMA (1 x 10(-7) M) appeared to slightly increase [125I]PTHrP binding. This observation is consistent with a small (3-fold) increase in PTH-induced cAMP release as a result of PMA pre-treatment. Receptor internalization was dose-dependent EC50 = 3 x 10(-7) M PTH(1-34)). The maximal effect occurred after 10-30 min and was largely reversible within 2 h. Monensin (3 x 10(-5) M) inhibited the recovery from receptor internalization. We conclude that a perifusion system using SaOS-2 cells is a suitable model to study the effect of discontinuous application of PTH on cAMP release. A rapid, homologous desensitization of PTH(1-34) stimulated cAMP accumulation has been observed that does not appear to involve protein kinase A or C.
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PMID:Rapid desensitization of parathyroid hormone dependent adenylate cyclase in perifused human osteosarcoma cells (SaOS-2). 803 14

Parathyroid hormone/parathyroid-hormone-related peptide (PTH/PTHrP) receptors have been characterized with chicken parathyroid hormone related protein [Tyr36]chPTHrP(1-36)amide (chPTHrP(1-36)) as radioligand in rat UMR-106 osteosarcoma (UMR) cells and in rat renal cortical membranes (RCM). Binding of 125 pM [125I][Tyr36]chPTHrP(1-36) was displaced by chPTHrP(1-36) with ID50 values of 2.6 +/- 0.22 nM (mean +/- S.E.) and 0.9 +/- 0.03 nM in UMR cells and RCM, respectively. ID50 values in membranes from UMR cells and RCM were the same in the presence and absence of 10 microM guanosine-5'-O-(3-thiotriphosphate). Rat [Nle8,18] PTH(1-34) was 5-fold more potent than chPTHrP(1-36) in RCM, but not in UMR cells. Hill coefficients derived from binding inhibition were 0.93 and 0.35 in UMR and RCM, respectively. For affinity labeling, N-hydroxysuccinimidyl-4-azidobenzoate-modified [125I]chPTHrP(1-36) was used. Specifically-labeled PTH/PTHrP-binding proteins had a molecular mass of 83 kDa in UMR cells and RCM. Treatment with N-endoglycosidases lowered the molecular mass of chPTHrP binding proteins to 54 kDa in UMR and RCM. In conclusion, skeletal UMR-106 cells and renal cortical membranes of the rat reveal PTH/PTHrP receptors with no apparent tissue specific differences in molecular mass of the polypeptide backbone and polysaccharide chains. Higher affinity of rat PTH(1-34) binding and lower Hill coefficients in kidney compared to bone are consistent with tissue specific receptor-ligand interactions.
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PMID:Comparison of parathyroid hormone receptors in rat osteosarcoma cells and kidney. 821 61

Gene fusions have been widely used in heterologous expression systems as a technique to stabilize the recombinant product against proteolysis, increase the translational initiation efficiency or to serve as an affinity handle for the purification of the protein. A further advantage is the potential to generate an authentic amino terminus of the foreign protein when this is vital for its biological activity, such as for the ability of human parathyroid-hormone-related protein (hPTHrP) to mediate activation of adenylate cyclase. We report here the construction and utility of a ubiquitin fusion protein system for production of the otherwise short-lived hPTHrP(1-141) as a carboxyl extension to ubiquitin in yeast. A hybrid gene containing the hPTHrP(1-141) cDNA coding region fused in-frame to the 3' end of the yeast ubiquitin cDNA was constructed and expressed under the control of the regulatable yeast metallothionein promoter. The recombinant protein was purified to homogeneity and finally characterized by N-terminal amino acid sequencing and amino acid composition analysis, demonstrating that the fusion protein was cleaved correctly and quantitatively in vivo by an ubiquitin-specific yeast endoprotease to generate authentic hPTHrP(1-141). hPTHrP(1-141) stimulated adenylate cyclase in rat osteosarcoma cell membranes to the same extent as equimolar amounts of recombinant human parathyroid hormone(1-84) and [Tyr34]hPTHrP(1-34)amide. Thus, this expression cloning strategy permits the production of authentic, biologically active recombinant hPTHrP(1-141), and the procedure can easily be adapted to make PTHrP analogues for further studies of its domain-specific activities and biological roles.
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PMID:Synthesis of human parathyroid-hormone-related protein(1-141) in Saccharomyces cerevisiae. A correct amino-terminal processing vital for the hormone's biological activity is obtained by an ubiquitin fusion protein approach. 838 31

N-terminal fragments of PTH-related protein (PTHrP), PTHrP-(1-34), and PTHrP-(1-40) stimulated both adenylyl cyclase and a mechanism that increases membrane-associated protein kinase C (PKC) activity in ROS 17/2 rat osteosarcoma cells. There were two peaks in the PKC response to the N-terminal PTHrP fragments: one peak was obtained with picomolar and the other with nanomolar PTHrP concentrations. The PKC-stimulating picomolar concentrations of the PTHrP fragments did not detectably stimulate adenylyl cyclase, but the nanomolar concentrations did. Since a similar two-peak response of PKC activity was obtained with PTHrP-(28-34), the single, N-terminal PKC activation domain of the PTHrP is in the same 28-34 region of the molecule as that of PTH despite this region having different primary amino acid sequences in the two hormones. Unlike PTH, PTHrP has a second PKC activation domain, as indicated by the ability of picomolar concentrations of the PTHrP-(107-111) fragment to stimulate maximally membrane-associated PKC activity in the osteosarcoma cells.
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PMID:Protein kinase C-activating domains of parathyroid hormone-related protein. 847 99

The expression of parathyroid hormone-related protein (PTHrP) was studied in a range of cell cultures representative of the osteoblast lineage and in rat calvarial sections. Primary newborn rat calvarial cells, a rat preosteoblastic cell line (UMR 201), a mouse stromal cell line (ST 2), a mouse calvaria-derived osteoblastic cell line (KS 4), and rat osteosarcoma cell lines (UMR 106-01 and -06), all expressed PTHrP when examined by reverse transcription polymerase chain reaction (RT-PCR). Using a radioimmunoassay we also demonstrated PTHrP in the conditioned medium of the cultured cells, with the exception of UMR 106-01 and -06 cells. Treatment of UMR 201 cells with all-trans-retinoic acid which induces them to acquire a more differentiated phenotype, also led to a time-dependent decrease in PTHrP mRNA levels as determined by RT-PCR, Northern blot analysis, and in situ hybridization. Decreased PTHrP levels in the conditioned medium of the treated cells was also observed. These results suggested that PTHrP production might be greater in less mature osteoblasts. Examination of the populations obtained from newborn rat calvariae by sequential collagenase digestion revealed that the early digests exhibited low ALP activity, low expression of PTH/PTHrP receptor mRNA, and no adenylate cyclase response to PTHrP(1-34). These populations showed the highest level of mRNA and production of PTHrP. Cells from later digests, the "osteoblast-rich" populations, had reduced PTHrP expression. Immunohistochemistry and in situ hybridization in sections of newborn rat calvariae showed PTHrP expression in cuboidal osteoblasts located adjacent to bone and in spindle-shaped cells in the periosteal region. It is concluded that PTHrP is produced by cells of the osteoblast lineage, supporting the hypothesis that PTHrP may function physiologically as a paracrine factor in bone.
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PMID:Expression of parathyroid hormone-related protein in cells of osteoblast lineage. 855 80

The gene encoding PTH-related peptide (PTHrP), a protein that plays a primary role in the development of humoral hypercalcemia of malignancy, is widely expressed in normal and neoplastic tissues. This study demonstrates that expression of the PTHrP gene has features of early response genes, including up-regulation after serum repletion of serum-starved ROS 17/2.8 (rat osteosarcoma) cells. The PTHrP messenger RNA (mRNA) levels were induced within 30 min and peaked at 4 h. Elevated mRNA levels were accompanied by an increase in secreted PTHrP. The serum effects on PTHrP mRNA levels were blocked by actinomycin D, suggesting a requirement for gene transcription. Nuclear run-on assays revealed a 3-fold increase in PTHrP gene transcription 4 h after exposure to serum. Deletions of the 5' flanking sequence of the rat PTHrP gene fused to the chloramphenicol acetyltransferase gene and transfected into ROS 17/2.8 cells showed that the serum-responsive region is located between -1.05 kb and -0.3 kb upstream of the transcription start site. PTHrP mRNA levels were also induced by cycloheximide, another feature common to early response genes. The PTHrP mRNA half-life in serum-starved cells was 56 min. Serum treatment prolonged the half-life 2.7-fold, suggesting serum-induced stabilization of the mRNA. Insulin and epidermal growth factor also induced PTHrP mRNA expression in a time-dependent manner analogous to serum, indicating that the effects of serum may be mediated, at least partially, through these agents. In summary, serum up-regulated PTHrP mRNA expression through both transcriptional and posttranscriptional mechanisms. This rapid stimulation by growth factors suggests that PTHrP may contribute to the early cellular response after growth factor stimulation.
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PMID:Serum stimulation of parathyroid hormone-related peptide gene expression in ROS 17/2.8 osteosarcoma cells through transcriptional and posttranscriptional mechanisms. 875 33

Expression of the gene encoding PTH-related peptide (PTHrP), a protein that plays a primary role in the development of humoral hypercalcemia of malignancy, is down-regulated at the transcriptional level by 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Deletions of the 5'-flanking region of the rat PTHrP gene, when fused to the chloramphenicol acetyl-transferase gene and transfected into ROS 17/2.8 (rat osteosarcoma) cells, showed that the 1,25-(OH)2D3 responsive region is located between -1.05 and -0.71 kb upstream of the transcription start site. Further mapping of this region revealed that a 123-bp fragment is able to confer 1,25-(OH)2D3 responsiveness to a heterologous (SV40) promoter. This region contains two potential vitamin D response elements (VDREs). One of these motifs resembles the negative VDRE (nVDRE) from the PTH gene, which is also down-regulated by vitamin D3. The other element resembles the canonical VDRE (two hexanucleotide motifs separated by three nucleotides), which has been characterized in a number of genes whose expression is modulated by vitamin D3. Electrophoretic mobility shift assays using nuclear extracts from ROS 17/2,8 cells and from vitamin D receptor. (VDR)-enriched COS 1 cells revealed that both elements interact with the VDR. This protein-DNA interaction is disrupted by an anti-VDR antibody. Therefore, modulation of PTHrP gene transcription by 1,25-(OH)2D3 is mediated by the VDR interacting with one or both of the identified motifs in the 5'-flanking sequence of the gene.
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PMID:DNA sequences in the rat parathyroid hormone-related peptide gene responsible for 1,25-dihydroxyvitamin D3-mediated transcriptional repression. 877 27

We have previously shown that the response of osteoblasts to parathyroid hormone (PTH) can be influenced at the receptor level by growth on the physiological substrate, type I collagen, or by treatment with retinoic acid. We have also shown differential expression of genes when cells of the osteoblast lineage are grown on type I collagen. The aim of this study was therefore to examine the effect of retinoic acid and growth on type I collagen on PTH/PTH-related protein (PTHrP) receptor mRNA expression in the osteosarcoma osteoblast-like cell line UMR 106-06. PTH/PTHrP receptor mRNA levels, as assessed by Northern blot, of cells grown on collagen were increased up to 2-fold compared with cells on plastic and in a concentration-dependent manner with respect to collagen. An increase was seen as early as 6 h and was maintained over a 24 h period. This was not due to increased mRNA stability. Retinoic acid decreased the level of receptor mRNA on both plastic and collagen at each time but did not alter mRNA stability. For all treatments PTH/PTHrP receptor mRNA abundance, relative to glyceraldehyde-3-phosphate dehydrogenase, increased steadily over 24 h after subculture of cells. In contrast, PTHrP mRNA levels were reduced in cells on collagen, compared with plastic. PTH-stimulated cAMP levels of cells grown on collagen were increased compared with plastic at 24 h, but not earlier. Consistent with the mRNA data, retinoic acid decreased the amplitude of cAMP responses in cells on plastic and collagen. There was no evidence for changes in adenylate cyclase per se, since forskolin-induced cAMP levels did not change with either treatment. This study shows that known modulators of osteoblast maturation also affect signal transduction in these cells by regulating gene expression of the PTH/PTHrP receptor as well as the PTHrP ligand.
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PMID:A type I collagen substrate increases PTH/PTHrP receptor mRNA expression and suppresses PTHrP mRNA expression in UMR106-06 osteoblast-like cells. 886 96

A midregion fragment of PTH-related protein (PTHrP), which is intensively conserved across species, has been identified as a secretory product of several different cell types, including keratinocytes and squamous carcinomas. As recent data suggest that a midregion PTHrP fragment may be biologically active, we hypothesized that midregion PTHrPs interact with unique cell surface receptors that mediate autocrine or paracrine action. Dose-dependent transient elevations in intracellular calcium ([Ca2-]i) were observed in fura-2-loaded SqCC/Y1 squamous carcinoma cells exposed to human (h) PTHrP-(67-86)NH2, [Tyr36]hPTHrP-(1-36)NH2, and hPTHrP-(1-141) at concentrations ranging from 1 pM to 1 microM. The effects of maximal stimulatory concentrations of [Tyr36]PTHrP-(1-36)NH2 and PTHrP-(67-86)NH2 on [Ca2+]i were additive. The inhibitory PTH analog, [D-Trp12,Tyr34]bovine PTH-(7-34)NH2, attenuated the [Ca2+]i response to [Tyr36]hPTHrP-(1-36)NH2, but not that to PTHrP-(67-86)NH2. These data suggest that PTHrP-(67-86)NH2 activates a different receptor pathway in SqCC/Y1 cells from the one activated by [Tyr36]hPTHrP-(1-36)NH2. Radiolabeled PTHrP-(67-86)NH2 did not bind to SqCC/Y1 cells, and PTHrP-(67-86)NH2 did not compete for binding of 125I-labeled [Tyr36]PTHrP-(1-36)NH2 to PTH/PTHrP receptors on SaOS-2 osteosarcoma cells. Activation of the phospholipase C pathway by PTHrP-(67-86)NH2 was confirmed by exposing SqCC/Y1 cells to peptide for 1 min and measuring the accumulation of inositol trisphosphates. PTHrP-(67-86)NH2 treatment (100 nM) resulted in maximal stimulation of inositol trisphosphates of 3.1 +/- 0.1-fold over the control value, with an EC50 of 1.5 +/- 1.2 nm. In contrast, PTHrP-(67-86)NH2 (0.1 nM to 1 microM) did not stimulate adenylyl cyclase in SqCC/Y1 cells despite vigorous stimulation of cAMP formation by isoproterenol (1 microM) to 66-fold over the basal value. To determine whether messenger RNA (mRNA) prepared from SqCC/Y1 cells would direct the translation of a receptor protein that mediated a [Ca2+]i response to PTHrP-(67-86)NH2, we performed expression studies in Xenopus oocytes. Fluo-3 fluorescence in Xenopus oocytes expressing SqCC/Y1 mRNA was visualized by confocal video microscopy after exposure to 1 microM PTHrP-(67-86)NH2. Clear increases in [Ca2+]i were detected in mRNA-injected, but not in sham-injected, oocytes. Finally, we examined the effect of PTHrP-(67-86)NH2 treatment on fibronectin secretion from SqCC/YN1 cells. A significant 3.5-fold increase in fibronectin secretion into conditioned medium was observed when SqCC/Y1 cells were exposed to 100 nM PTHrP-(67-86)NH2, and this effect was dose dependent, with an EC50 of 0.1 nM. We conclude that PTHrP-(67-86)NH2 activates phospholipase C-dependent pathways in SqCC/Y1 cells through a receptor distinct from that activated by PTHrP-(1-36) in the same cells. As a midregion secretory fragment of PTHrP has been partially purified from several different cell types, this receptor may have broad biological significance.
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PMID:A midregion parathyroid hormone-related peptide mobilizes cytosolic calcium and stimulates formation of inositol trisphosphate in a squamous carcinoma cell line. 894 Mar 60

The C-terminal region of parathyroid hormone-related protein (PTHrP) containing the sequence (107-111) appears to be a potent inhibitor of osteoclastic bone resorption. In the present study, we have investigated the effect of human (h)PTHrP (107-139) and hPTHrP (107-111)NH2 on the proliferation of osteoblastic rat osteosarcoma UMR 106 cells. We found that both C-terminal PTHrP peptides, like hPTHrP (1-141), were antimitogenic for these cells, between 1 pM and 10 nM. [Tyr34]hPTHrP (1-34)NH2 was as potent as these peptides but less effective as growth inhibitor in these cells. UMR 106 cells were found to produce and secrete immunoreactive PTHrP. Addition of anti-PTHrP neutralizing antibodies to C- and N-terminal epitopes of PTHrP increased the growth of these cells. Our data suggest that the antiproliferative effect of these C-terminal PTHrP analogs may be independent of cyclic adenosine 3':5'-monophosphate (cAMP) and mediated by protein kinase C. These findings support an autocrine role of PTHrP in bone metabolism.
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PMID:Antiproliferative effect of the C-terminal fragments of parathyroid hormone-related protein, PTHrP-(107-111) and (107-139), on osteoblastic osteosarcoma cells. 900 50

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