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)

During continuous culture with serial passage, the human osteosarcoma cell line SaOS-2 showed a time-dependent decrease in skeletal alkaline phosphatase (ALP) activity. Because this was indicative of heterogeneity, subpopulations of SaOS-2 cells were isolated from replicate low-density cultures. The subpopulations were less heterogeneous and more stable (with respect to ALP) than the parent population. ALP specific activity in the subpopulations ranged from 0.05 to 2.3 U/mg protein, and cytochemical analyses indicated multiple steady-state levels of ALP activity per cell. The amount of ALP activity in SaOS-2 subpopulations was proportional to collagen production ([3H]proline incorporation into collagenase-digestible protein; r = .84, P less than .005), and to parathyroid hormone (PTH)-linked synthesis of cyclic adenosine monophosphate (cAMP) (r = .88, P less than .01). From these data, we inferred that ALP activity in SaOS-2 cells can provide a useful index of the osteoblastic phenotype, and that ALP activity, collagen production, and PTH-linked adenylate cyclase were coordinately regulated in these osteoblast-like osteosarcoma cells (ie, selection of subpopulations for ALP activity coselected for collagen synthesis and PTH-linked synthesis of cAMP). Further comparative studies showed that micromolar fluoride concentrations stimulated cell proliferation ([3H]thymidine incorporation into DNA) in low-ALP SaOS-2 subpopulations, but not in high-ALP cells (P less than .001), and that this differential sensitivity to fluoride was associated with an inverse correlation between fluoride-sensitive acid phosphatase and ALP activities (r = -.91, P less than .001).
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PMID:Skeletal alkaline phosphatase specific activity is an index of the osteoblastic phenotype in subpopulations of the human osteosarcoma cell line SaOS-2. 165 38

We present evidence that the regulation of osteocalcin secretion by PTH and PGE2 in normal human bone cells can be produced in the human osteoblast-like cell line MG-63. Both cell cultures showed time- and dose-dependent stimulation of osteocalcin secretion in response to 1,25(OH)2D3. Bovine parathyroid hormone (PTH) amino acid fragment 1-34 (40 nM) and prostaglandin E2 (PGE2, 5 nM) significantly inhibited 1,25(OH)2D3-induced osteocalcin secretion by these cells. The inhibition reached 20 and 36%, respectively. In contrast, PTH 3-34 had no effect on osteocalcin secretion. Both cell cultures produced cAMP in response to PTH. Dexamethasone (Dex) (100 nM) potentiated PTH-induced (40 nM) cAMP synthesis in subconfluent MG-63 cells (1.5-fold increase, P less than 0.05). This treatment with Dex resulted in a greater inhibition of 1,25(OH)2D3-induced osteocalcin secretion (-30%, P less than 0.005) by PTH in MG-63 cells as compared to cells exposed to PTH and 1,25(OH)2D3 alone. Pretreatment of subconfluent MG-63 cells with Dex (100 nM) for 48 h also increased 1,25(OH)2D3-induced osteocalcin secretion by 40% (P less than 0.025). In contrast, treatments of confluent MG-63 cells with Dex inhibited osteocalcin secretion regardless of the 1,25(OH)2D3 doses used. Forskolin (10(-7)-10(-5) M) and dibutyryl cAMP (10(-6)-(10(-3) M) both reproduced the effects observed with PTH and PGE2 in the two cell cultures. Forskolin's action was time-dependent: addition of forskolin (10(-6) M) 12 h after 1,25(OH)2D3 (50 nM) resulted in a progressively weaker inhibition of osteocalcin secretion. Increasing the extracellular calcium concentration of the incubation media resulted in a dose-dependent increase in osteocalcin secretion (P less than 0.01). These results indicate that PTH and PGE2 inhibit osteocalcin secretion by a mechanism involving cAMP production. In contrast, an increase in extracellular calcium stimulated osteocalcin release. Thus the human osteosarcoma cell line MG-63 is a useful osteoblast-like cell model to study the regulation of osteocalcin secretion. Furthermore, a factor (or factors) between hormone-receptor coupling and gene induction can regulate the expression of the osteocalcin gene or affect pre- or posttranslational mechanisms implicated in osteocalcin synthesis and secretion.
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PMID:Regulation of osteocalcin secretion by human primary bone cells and by the human osteosarcoma cell line MG-63. 165 56

The protein kinase C-(PKC) activating phorbol esters 12-O-tetradecanoylphorbol-13-acetate (TPA; 100 nmol/l) and phorbol 12,13-dibutyrate (PDBU; 100 nmol/l) enhanced basal cyclin AMP accumulation in cultured neonatal mouse calvaria. The cyclic AMP response to parathyroid hormone (PTH; 10 nmol/l) and the adenylate cyclase activators forskolin (1-3 mumol/l) and choleratoxin (0.1 mumg/ml) was potentiated in a more than additive manner by TPA and PDBU. In contrast, phorbol 13-monoacetate (phorb-13; 100 nmol/l), a related compound but inactive on PKC, had no effect on basal or stimulated cyclic AMP accumulation. In the presence of indomethacin (1 mumol/l), TPA and PDBU had no effect on cyclic AMP accumulation in calvarial bones per se, but were still able to cause a significant enhancement of the response to PTH, forskolin and choleratoxin. PTH-, forskolin- and choleratoxin-stimulated cyclic AMP accumulation in rat osteosarcoma cells UMR 106-01 was synergistically potentiated by TPA and PDBU, but not by phorb.-13. These data indicate that PKC enhances cyclic AMP formation and that the level of interaction may be at, or distal to, adenylate cyclase.
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PMID:Protein kinase C activating phorbolesters enhance the cyclic AMP response to parathyroid hormone, forskolin and choleratoxin in mouse calvarial bones and rat osteosarcoma cells. 166 87

Stanniocalcin (STC), a calcium-regulating glycoprotein hormone isolated from the corpuscles of Stannius of salmon, was tested for effects on bone and calcium metabolism in mammalian species (rats and mice). STC generally failed to alter serum calcium of parathyroidectomized rats at concentrations equimolar with effective concentrations of parathyroid hormone (PTH). STC did not increase cAMP in ROS 17/2.8 or UMR-108 osteosarcoma cells, OK kidney cells, fetal rat limb bones, or neonatal mouse calvariae, and similarly failed to increase urinary cAMP in rats. STC did not consistently stimulate resorption in any of the rodent bone culture systems, although variable resorptive responses were elicited in fetal mouse calvariae. The results indicate that this fish hormone has limited, if any, PTH-like activity on calcium metabolism in mammalian systems.
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PMID:Salmon stanniocalcin and bovine parathyroid hormone have dissimilar actions on mammalian bone. 166 5

Cytosolic calcium and its parathyroid hormone induced increase was evaluated in rat osteosarcoma cells by quin 2 fluorometry. Electron microscopic calcium detection in depot organelles (i.e. the recently defined calciosomes) is improved by a new precipitation method with hydroxylamine naphthoic acid and fluoride combined with X-ray microanalysis. As shown in submandibulary gland and pancreatic B cells, a new combination of GBHA staining with laser microprobe mass analysis (LAMMA) for the first time enables direct kinetical studies of calcium at the microscopical level using stable calcium isotopes (i.e. Ca44) as tracers.
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PMID:[Morphological demonstration of function-dependent cellular calcium redistributions in secretory cells by x-ray microanalysis, LAMMA and fluorescence cytometry]. 170 2

Uptake of 86Rb was used to follow the activity of Na-K-2Cl cotransport in the osteosarcoma cell line UMR-106-01. The ouabain-resistant fraction of 86Rb uptake was sensitive to bumetanide and furosemide. Furosemide-sensitive 86Rb uptake required the presence of Na+, K+, and Cl- in the incubation medium. These observations indicate the presence of a Na-K-2Cl cotransport system in osteoblasts. Cotransporter activity was stimulated by agonists which increase adenosine 3',5'-cyclic monophosphate (cAMP), cytosolic free Ca2+ ([Ca2+]i), and protein kinase C (PKC) activity such as parathyroid hormone (PTH) and prostaglandin E2 (PGE2). However, endothelin, which increases [Ca2+]i and PKC activity without affecting cellular levels of cAMP, was ineffective in stimulating the cotransporter. Accordingly, increasing cellular cAMP with forskolin was as effective as PTH and PGE2 in stimulating the cotransporter. Stimulation of PKC with TPA inhibited the cotransporter in a time- and concentration-dependent manner. No stimulation of cotransport could be demonstrated at any 12-O-tetradecanoyl-phorbol-13-acetate (TPA) concentration or incubation time. The Na-K-2Cl cotransporter was stimulated by cell shrinkage. Maximal stimulation was observed after swelling the cells in hypotonic medium and subsequent shrinkage in isotonic medium. Stimulation by cell shrinkage can be demonstrated in control, agonist-, cAMP-, and TPA-treated cells. These observations suggest that 1) the osteoblastic Na-K-2Cl cotransporter is activated by calciotropic hormones predominantly through an increase in cellular cAMP, and 2) in osteoblasts, the cotransporter is independently regulated by different biochemical pathways.
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PMID:Regulation of Na-K-2Cl cotransport in osteoblasts. 171 50

The effects of phorbol 12-myristate 13-acetate (PMA), a known activator of protein kinase C, on receptor-mediated stimulation of adenylate cyclase were evaluated in a rat osteosarcoma cell line (UMR-106) with the osteoblast phenotype. Pretreatment of UMR-106 cells with PMA increased parathyroid hormone (PTH)-stimulated adenylate cyclase activity and inhibited prostaglandin E2 (PGE2)-responsive enzyme activity. In addition, PMA enhanced enzyme activation by forskolin, which is thought to exert a direct stimulatory action on the catalytic subunit of adenylate cyclase. The regulatory effects of PMA were concentration dependent and of rapid onset (less than or equal to 1 min). Treatment with PMA also resulted in translocation of protein kinase C activity from the cytosol to the particulate cell fraction. Pertussis toxin, which attenuates inhibition of adenylate cyclase mediated by the inhibitory guanine nucleotide-binding regulatory protein (Gi), augmented PTH-sensitive adenylate cyclase activity and reduced the incremental increase in PTH response produced by PMA. The results suggest that activation of protein kinase C increases PTH-stimulated adenylate cyclase activity by actions on Gi and/or the catalytic subunit and decreases PGE2 responsiveness by a mechanism involving the PGE2 receptor.
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PMID:Protein kinase C differentially modulates PTH- and PGE2-sensitive adenylate cyclase in osteoblast-like cells. 173 55

Osteoblasts, the bone-forming cells, synthesize the macromolecules of the bone matrix including: type I collagen; osteocalcin; osteonectin; osteopontin; proteoglycan I and II; bone sialoprotein; matrix gla-protein; bone glycoprotein 75; several other proteins, which have not been extensively characterized; growth factors, including transforming growth factor beta and fibroblast growth factor. Osteoblasts also have high levels of the membrane-bound enzyme, alkaline phosphatase, which plays a role in matrix mineralization, and receptors for tissue-specific hormones, such as parathyroid hormone, as well as many other hormones, cytokines and growth factors, which regulate bone growth, differentiation and metabolism. The expression of these various proteins, most of which are not unique to bone but which together characterize the bone phenotype, is induced during osteoblastic differentiation in a stepwise fashion, suggestive of multiple regulatory factors. The detailed sequence of the expression of osteoblastic genes in situ has not been fully characterized. It appears that type I collagen and alkaline phosphatase are expressed early during the commitment to the osteoblastic phenotype, whereas osteopontin and osteocalcin appear late during osteoblastic differentiation. Diversity among "osteoblastic" cells is also apparent, probably not all osteoblastic cells express all the features. A large number of osteoblastic models are currently available to study the expression of osteoblast-related genes in vitro. These include primary cultures from calvaria or trabecular bone from several species, including humans, osteosarcoma-derived cell lines, and experimentally immortalized cells. Some of these in vitro models, especially the calvaria-derived cultures, undergo changes which mimic osteoblastic differentiation in vivo. The study of these and other cell models started providing insights into the regulation of gene expression in osteoblastic cells. In addition to a vast body of information on the conditions required for the expression of various proteins in culture and their regulation by hormones and growth factors, more detailed information on specific genes has recently been obtained. For example, regulation of type I collagen gene expression has been studied in osteosarcoma cell lines where 1,25(OH)2 vitamin D3 was shown to act via specific DNA segment(s) in the 5' flanking region of the gene, while parathyroid hormone affected gene expression by altering the stability of the transcripts. TGF beta 1, which stimulates osteogenesis, was shown to promote the transcription of osteopontin and type I collagen, the latter effect requiring the binding site for the transactivating protein, nuclear factor I.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Gene expression in osteoblastic cells. 180 5

Proteolytic enzymes acting at physiologic pH (neutral proteases) are involved in both the formation and modeling of new bone and the remodeling of mature bone. In endochondral ossification systems such as growth-plate calcification, fracture healing, osteophyte formation, and demineralized bone matrix-induced osteogenesis, neutral proteases are predominantly involved in modifying proteins and proteoglycans in the extracellular matrix in preparation for calcification. These enzymes are of low molecular weight (below 30,000 Mr), are poorly charged, metal ion dependent, and appear to become active only after being released from chondrocytes. These neutral proteases may be distributed to the extracellular matrix in association with matrix vesicles that are derived from chondrocyte plasma membranes. A similar mechanism of calcification may also exist during malignant osteogenesis in an osteosarcoma; however, the cell producing the neutral protease in this lesion is the osteoblast and the matrix being synthesized is osteoid. In remodeling bone, osteoblasts secrete neutral collagenase (as an inactive enzyme) and produce not only additional proteases capable of activating the collagenase but also a collagenase inhibitor. Osteoblast collagenase or neutral protease may act to remove unmineralized osteoid from bone surfaces, thus facilitating its subsequent degradation by osteoclasts. The production of all these factors by osteoblasts appears to be regulated by calciotropic hormones (e.g., parathyroid hormone, 1,25-dihydroxyvitamin D, and calcitonin), possibly in a concerted fashion. Other possible functions of neutral proteases involve direct actions on cells or on specific molecules (growth factors) residing in the extracellular matrix.
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PMID:Neutral proteases in regenerating bone. 184 59

Chicken parathyroid hormone (cPTH) has been reported to stimulate adrenal steroidogenesis and to have unusual potency on traditional PTH target tissues. To evaluate these properties, chicken PTH-(1-88) has been expressed in Escherichia coli using a plasmid encoding a fusion protein which links together growth hormone, a factor Xa recognition site, and chicken PTH-(1-88). The growth hormone-cPTH fusion protein required the presence of 0.02% sodium dodecyl sulfate to remain in solution and be cleaved by factor Xa. The high performance liquid chromatography-purified recombinant cPTH-(1-88) and chemically synthesized cPTH-(1-34) had similar potency in rat osteosarcoma (ROS 17/2.8) cells, opossum kidney (OK) cells, and dispersed primary chicken kidney cells. The biologic potencies of cPTH-(1-34) and cPTH-(1-88) in radioreceptor binding and cAMP generation in both bone- and kidney-derived cell lines were less than those of human (h)PTH-(1-34). In dispersed chicken kidney cells, cAMP production by cPTH-(1-34) and cPTH-(1-88) was similar to that stimulated by human PTH-(1-34). No stimulation of steroidogenesis could be detected when recombinant chicken PTH-(1-88) was added to dispersed chicken adrenal cells. The biologic activity of recombinant chicken PTH-(1-88) purified from E. coli was comparable with that of chicken PTH-(1-88) expressed by mammalian COS cells. Thus, the full-length chicken PTH did not exhibit enhanced potency, when compared with human PTH in ROS 17/2.8, OK cell lines, and dispersed chicken kidney cells and did not demonstrate the novel steroidogenic action previously reported in adrenal cells. The successful production of chicken PTH-(1-88) will enhance our understanding of the structure-activity relationships for PTH, particularly the sequence-dependent metabolism of the hormone.
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PMID:Full-length chicken parathyroid hormone. Biosynthesis in Escherichia coli and analysis of biologic activity. 184 86


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