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 investigated the effects of PTH-induced desensitization on second messenger interactions in the rat osteosarcoma cell line ROS 17/2.8. Adenylate cyclase activation was assessed by accumulation of immunoassayable cAMP, and cytosolic calcium ion ([Ca2+]i) concentrations were measured in adherent perifused cells loaded with the Ca2(+)-sensitive bioluminescent protein aequorin. Preexposure to rat PTH-(1-34) [rPTH-(1-34); 10(-8) M for 48 h, then 10(-7) M for 24 h] dramatically reduced (by 85%) the cAMP response to fresh challenge [2 min; 10(-9)-10(-7) M rPTH-(1-34)], but the peak PTH-induced rise of [Ca2+]i was not diminished significantly (0-20%). Nevertheless, we did observe other changes in the PTH-induced [Ca2+]i response. Exposure of treated cells to (Bu)2cAMP nearly abolished the [Ca2+]i response to PTH (greater than 80% reduction), but had much less effect on the PTH-stimulated [Ca2+]i increment of the naive cells (less than 35% reduction). Treated cells also had a blunted [Ca2+]i response to PTH in the presence of low extracellular calcium (greater than 60% reduction), but in the naive cells, low extracellular Ca2+ did not significantly diminish the peak PTH-induced [Ca2+]i rise, although low extracellular Ca2+ dramatically reduced the area under this [Ca2+]i transient (greater than 50%). Low extracellular Ca2+ had no influence on the peak [Ca2+]i responses of treated cells to bradykinin or prostaglandin F2 alpha. Although the peak PTH-stimulated [Ca2+]i rise of treated cells in normal Ca2+ medium was not significantly attenuated, the time to half-maximum [Ca2+]i concentration was significantly increased (greater than 100%), and the area under the [Ca2+]i transient was diminished. These alterations in the [Ca2+]i response of treated cells were not observed upon challenge with bradykinin or prostaglandin F2 alpha. Thus, 1) the cAMP and [Ca2+]i responses of ROS 17/2.8 cells to rPTH-(1-34) are not obligatorily coupled; 2) the response of naive cells to PTH includes both the release of Ca2+ from intracellular stores and the entry of extracellular Ca2+; and 3) pretreatment of these cells with rPTH-(1-34) augments the dependence on Ca2+ entry during hormone rechallenge. We propose that the preserved PTH-stimulated [Ca2+]i rise in treated cells results partly from loss of cAMP-mediated inhibition of extracellular Ca2+ entry.
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PMID:Desensitization of rat osteoblast-like cells (ROS 17/2.8) to parathyroid hormone uncouples the adenosine 3',5'-monophosphate and cytosolic ionized calcium response limbs. 184 74

We showed recently that the initial peak cytosolic ionized calcium ([Ca2+]i) response to PTH (2-min exposure) is preserved relative to the cAMP response in osteoblast-like rat osteosarcoma cells (ROS 17/2.8) desensitized by 72-h exposure to PTH. We attempted in the present studies to determine the mechanisms for preservation of the [Ca2+]i response and to explore the effects of longer PTH rechallenges. The [Ca2+]i response to a 20-min perifusion with rat PTH [rPTH-(1-34)] was monitored by aequorin luminescence in both naive and PTH-desensitized ROS 17/2.8 cells. The responses of both naive and desensitized cells consisted of two phases: an initial peak, followed by an intermediate plateau that was sustained in the presence of PTH. We observed in the naive cell populations synchronous oscillations in [Ca2+]i concentration during this second phase (amplitude, 10-60 nM; frequency, 1-3/100 sec). These oscillations were maintained through extracellular calcium (EC Ca2+) entry; the initial peak was the result of Ca2+ release from intracellular stores. In desensitized cells, these two phases could not be clearly separated with respect to Ca2+ source, but, as we showed before, exhibited an enhanced dependence on EC Ca2+ entry for the response to PTH. Nevertheless, in the desensitized cells, the sustained [Ca2+]i response was diminished in magnitude and showed little oscillatory behavior. Brief exposure to neomycin sulfate, an inhibitor of phosphoinositide turnover, attenuated the PTH-induced [Ca2+]i rise in both naive and desensitized cells. Protein kinase-C activity did not appear to be required for either phase of the PTH-induced [Ca2+]i response. Exposure to cholera toxin attenuated the [Ca2+]i response to hormone in both naive and desensitized cells, more markedly in the latter. Cholera toxin treatment dramatically increased basal cAMP levels in both cell preparations; PTH-stimulated cAMP production was unchanged in naive cells, but increased nearly 4-fold in desensitized cells. We propose that the preserved PTH-induced peak [Ca2+]i rise in desensitized cells results primarily from the diminished regulation of EC Ca2+ entry by the cAMP response limb. The attenuated sustained oscillatory behavior observed in desensitized cells upon rechallenge with hormone may be the result of reduced phosphoinositide turnover and reduced Ca2+-stimulated Ca2+ release. Thus, the [Ca2+]i response to PTH in osteoblast-like cells is complex and modulable and seems to provide a number of ways to regulate intracellular metabolism under various conditions. We speculate that this plasticity of the [Ca2+]i response to PTH is related to the pleiotropic actions of the hormone on cells of the osteoblast lineage.
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PMID:Parathyroid hormone (PTH)-induced intracellular Ca2+ signalling in naive and PTH-desensitized osteoblast-like cells (ROS 17/2.8): pharmacological characterization and evidence for synchronous oscillation of intracellular Ca2+. 195 83

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

While the stimulatory effect of parathyroid hormone (PTH) on osteoblast-like cell adenylate cyclase is well known, the effect of PTH on cytosolic calcium ion ([Ca2+]i) mobilization is controversial, one group finding no effect but others reporting various increases. We investigated the effects on [Ca2+]i of synthetic rat PTH fragment 1-34 (rPTH(1-34)) and two bovine PTH analogues that inhibit PTH's stimulation of adenylate cyclase (bovine 8,18Nle, 34Tyr-PTH(3-34) and 34Tyr-PTH(7-34]. [Ca2+]i was measured before, during, and after exposure to PTH analogues in perifused, attached osteoblast-like rat osteosarcoma cells (ROS 17/2.8) that had been scrape-loaded with the luminescent photoprotein aequorin. Resting [Ca2+]i was 0.094 +/- 0.056 microM (mean +/- S.D., n = 103) and rose in a time- and dose-specific way after exposure to rPTH(1-34). At 10(-10) M rPTH(1-34), [Ca2+]i rose 100% within 30 s to a plateau; higher concentrations of PTH yielded increasing initial peaks of [Ca2+]i followed by lower plateaus. At 10(-6) M, the initial peak was 5-fold basal, or 0.64 +/- 0.07 microM. Both analogues of PTH were at least partial agonists for [Ca2+]i mobilization and did not reduce peak [Ca2+]i when co-perifused with rPTH(1-34). However, the analogues did reduce significantly rPTH(1-34)-induced cAMP accumulation and did not increase cAMP accumulation by themselves. Thus, rPTH(1-34) strongly mobilizes [Ca2+]i in ROS 17/2.8 cells, at near-physiologic concentrations. Failure of the PTH analogues to block the effect of PTH on [Ca2+]i while inhibiting the effect on cAMP accumulation suggests separate pathways for PTH activation of adenylate cyclase and mobilization of calcium.
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PMID:Differential effects of parathyroid hormone and its analogues on cytosolic calcium ion and cAMP levels in cultured rat osteoblast-like cells. 284 23

Rapid formation of high-Ca2+ perimitochondrial cytoplasmic microdomains has been shown to evoke mitochondrial Ca2+ signal and activate mitochondrial dehydrogenases, however, the significance of submicromolar cytoplasmic Ca2+ concentrations in the control of mitochondrial metabolism has not been sufficiently elucidated. Here we studied the mitochondrial response to application of Ca2+ at buffered concentrations in permeabilized rat adrenal glomerulosa cells, in an insulin-producing cell line (INS-1/EK-3) and in an osteosarcoma cell line (143BmA-13). Mitochondrial Ca2+ concentration was measured with the fluorescent dye rhod-2 and, using an in situ calibration method, with the mitochondrially targeted luminescent protein mt-aequorin. In both endocrine cell types, mitochondrial Ca2+ concentration increased in response to elevated cytoplasmic Ca2+ concentration (between 60 and 740 nM) and an increase in mitochondrial Ca2+ concentration could be revealed already at a cytoplasmic Ca2+ concentration step from 60-140 nM. Similar responses were observed in the osteosarcoma cell line, although a clearcut response was first observed at 280 nM extramitochondrial Ca2+ only. As examined in glomerulosa cells, graded increases in cytoplasmic Ca2+ concentration were associated with graded increases in the reduction of mitochondrial pyridine nucleotides, consistent with Ca2+-dependent activation of mitochondrial dehydrogenases. Our data indicate that in addition to the recognized role of high-Ca2+ cytoplasmic microdomains, also small Ca2+ signals may influence mitochondrial metabolism.
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PMID:Mitochondria respond to Ca2+ already in the submicromolar range: correlation with redox state. 1196 50