Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:3.4.21.5 (thrombin)
33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Gallium nitrate is an effective antihypercalcemic and antiresorptive agent. Although its effects on osteoclasts are well documented, the mechanism of action of gallium nitrate on osteoblasts is still not established. To determine the effects of gallium nitrate on calcium signalling, we studied its effects on intracellular calcium concentration in UMR-106 rat osteoblastic osteosarcoma cell line. Cells were loaded with a calcium binding fluorescent dye, fluo-3. Changes in fluorescence reflected changes in cytosolic calcium. Gallium nitrate elicited a dose-dependent biphasic calcium transient with an initial decrease followed by an increase, and these changes were seen at high extracellular calcium concentration. Markedly altered signal was seen in nominal calcium-free medium, suggesting that gallium nitrate mobilized calcium only partly from intracellular stores. Gallium nitrate, at concentrations as low as 3 micrograms/ml, inhibited parathyroid hormone-stimulated calcium transients. High doses of parathyroid hormone could overcome this inhibition. This inhibitory effect appears to be selective, since gallium nitrate did not prevent calcium transients elicited by alpha-thrombin or prostaglandin F1 alpha. Failure of gallium nitrate to prevent calcium transients elicited by these agents, even after the inhibition of parathyroid hormone-induced signal, indicates that the inhibition is not a toxic effect. In conclusion, gallium nitrate has a marked effect on calcium signalling in UMR-106 cells that might be of major importance in modifying the effects of calcemic hormones or local factors on osteoblasts.
...
PMID:Effects of gallium nitrate on calcium transients in UMR-106 rat osteoblastic osteosarcoma cells. 141 79

The in vitro effects of parathyroid hormone on Ca2+ handling by fura-2 loaded rat platelets were studied. The incubation of these platelets with rat parathyroid hormone (1-34) for 10 min had no effect on intracellular fura-2 metabolism or [Ca2+]i in the resting state. The [Ca2+]i response to 0.1 U/mL thrombin was unaffected by preincubation with parathyroid hormone in the presence or absence of extracellular Ca2+. Furthermore, the recovery rate of [Ca2+]i after the thrombin-induced peak in Ca(2+)-depleted media was not altered with parathyroid hormone. These data indicate that parathyroid hormone may not have a significant effect on Ca2+ homeostasis in rat platelets in unstimulated and stimulated conditions.
...
PMID:Lack of effect of parathyroid hormone on calcium homeostasis in rat platelets. 145 84

Parathyroid hormone-related protein (PTHrP), which is responsible for producing hypercalcemia in patients with humoral hypercalcemia of malignancy, has recently been identified in several normal tissues. Because PTHrP, like parathyroid hormone (PTH), is known to exhibit vasodilatory properties, we investigated the expression and regulation of PTHrP mRNA in cultured rat aortic smooth muscle cells (SMC). We report here that PTHrP mRNA is expressed in SMC and is markedly induced by serum in a time- and concentration-dependent fashion. Addition of 10% fetal calf serum to serum-deprived, confluent cells, resulted in a marked induction of PTHrP mRNA by 2 h with a peak at 4-6 h. PTHrP was detected in SMC by immunocytochemistry and radioimmunoassay of conditioned medium, and was shown to be up-regulated within 24 h after the addition of serum. The serum induction of PTHrP mRNA was blocked by actinomycin D and by cycloheximide indicating the need for protein synthesis to evoke the serum effect on PTHrP gene transcription. In addition, treatment with dexamethasone, which has been previously shown to reduce the constitutive expression of PTHrP in human cancer cells, also blunted the serum induction of PTHrP mRNA in SMC. Treatment of quiescent cells with the serum mitogens platelet-derived growth factor or insulin-like growth factor-I had no effect on PTHrP, whereas the vasoactive peptides endothelin, norepinephrine and thrombin stimulated PTHrP expression. Exogenous addition of recombinant PTHrP-(1-141) had no significant effect on SMC DNA synthesis as measured by [3H]thymidine incorporation. In summary, the abundance of PTHrP mRNA and the characteristics of its regulation in SMC suggest a major role for PTHrP as a local modulator in vascular smooth muscle.
...
PMID:Abundant expression of parathyroid hormone-related protein in primary rat aortic smooth muscle cells accompanies serum-induced proliferation. 175 45

Human parathyroid hormone, hPTH, an 84 amino acid polypeptide, was produced intracellularly in Escherichia coli as a fusion protein, linked to the C-terminus of a 15 kD IgG-binding protein. Approximately 100 mg fusion protein was obtained per liter fermentation medium. To test the efficiency of two alternative enzymatic cleavage methods, two fusion proteins differing only in the linker region were constructed. Cleavage of a Phe-Phe-Pro-Arg linker was obtained with bovine thrombin and cleavage of a Phe-Ala-His-Tyr linker with recombinant H64A subtilisin. Both enzymes yielded the correct N-terminus and cleaved their respective linkers quantitatively, although additional internal cleavage sites in hPTH were detected and characterized. The linker cleavage conditions were optimized and hPTH was purified to homogeneity. Thrombin cleavage resulted in a final yield of 5 mg hPTH/L, while H64A subtilisin cleavage was more specific and gave 8 mg/L. The purified recombinant product was identical to native hPTH and exhibited full biological activity in an adenylate cyclase assay.
...
PMID:Thrombin and H64A subtilisin cleavage of fusion proteins for preparation of human recombinant parathyroid hormone. 179 10

Relations between platelet cytosolic calcium, parathyroid hormone, and blood pressure were investigated in 91 normotensive subjects: 47 men and 44 women ranging in age from 24 to 70 years. The men had higher mean arterial blood pressure, serum creatinine, and body mass index than the women. Serum total calcium, plasma ionized calcium, and parathyroid hormone (measured as both intact hormone and mid-molecule fragment) were not different between men and women; however, serum phosphate was higher in women than in men. Basal platelet cytosolic calcium was higher in men than in women (113.7 +/- 1.9 versus 105.9 +/- 1.7, respectively; p less than 0.01), but there was no difference in the peak platelet cytosolic calcium responses to thrombin between the two groups. In the combined group of male and female subjects, platelet cytosolic calcium correlated with diastolic blood pressure and mean arterial pressure (r = 0.37, p less than 0.001 and r = 0.32, p less than 0.01, respectively). Intact parathyroid hormone correlated with systolic and mean arterial blood pressure (r = 0.41, p less than 0.001 for both). Age correlated with both systolic blood pressure (r = 0.40, p less than 0.001) and intact parathyroid hormone (r = 0.51, p less than 0.001). When multiple regression analysis was performed using mean arterial pressure as the dependent variable, platelet cytosolic calcium and intact parathyroid hormone maintained significant correlations with mean arterial pressure. Platelet cytosolic calcium did not correlate with intact parathyroid hormone. These results suggest that both platelet cytosolic calcium and intact parathyroid hormone are associated with blood pressure regulation in normotensive subjects. However, the influences of these two factors on blood pressure are not interrelated.
...
PMID:Parathyroid hormone, platelet calcium, and blood pressure in normotensive subjects. 188 25

The influence of experimental conditions during long-time (72 h) incubations of neonatal mouse calvaria on the measurement of prostaglandins was investigated. Incubations of the cultured calvaria were carried out in the presence and absence of stimulating agents of bone resorption, such as thrombin and parathyroid hormone. It was found that during the first 24 h prostaglandin levels, estimated by gas chromatography negative ion chemical ionization mass spectrometry, did not correlate with calcium liberation, but were merely an artefact resulting from surgery by preparing the calvaria.
...
PMID:Experimental considerations on the measurement of prostaglandins during long-time incubations of neonatal mouse calvaria. 235 20

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.
...
PMID:Clonal differences in prostaglandin synthesis among osteosarcoma cell lines. 245 9

Agents that act as anion channel blockers (ACBs) and do not permeate cells appear to inhibit exocytosis in platelets, parathyroid cells, and neutrophils. Based in large part on these observations, anion influx through plasma membrane channels has been considered a factor controlling cellular secretion, but there have been no direct anion influx measurements in cells or granules to support this concept. We have found that ACBs inhibit only thrombin-induced platelet secretion, not secretion induced by ADP, collagen, or A23187. ACBs inhibit thrombin esterolytic activity, binding of thrombin to platelets, and thrombin-stimulated platelet production of malondialdehyde in proportion to the degree of inhibition of thrombin-induced platelet secretion. Thus inhibition of platelet secretion by ACBs is due to inactivation of the stimulatory agonist, thrombin, and not to interference with cellular secretion per se. We have also found that previously reported inhibition of secretion of parathyroid cells and neutrophils by ACBs can be explained by the ability of ACBs to interfere with detection of the cellular secretory products that were measured to assess exocytosis. Our measurements of parathyroid hormone and beta-glucuronidase in the presence of ACBs were reduced to the same degree as the reported reduction in apparent cellular secretion produced by these agents. We conclude that plasma membrane anion channels of the type that can be blocked by ACBs such as 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid, suramin, and probenecid do not participate in cellular secretory processes. Whether other types of anion channels exist that are not affected by these ACBs and whether there are mechanisms of anion flux during secretion not dependent on channels remain open questions.
...
PMID:Anion channel blockers cause apparent inhibition of exocytosis by reacting with agonist or secretory product, not with cell. 247 20

The effect of bradykinin on prostaglandin production in mouse calvarial bones and in isolated osteoblasts has been examined. Bradykinin (1 mumol/l) stimulated prostaglandin formation in neonatal mouse calvarial bones incubated for 30 min. In isolated osteoblast-like cells from neonatal mice calvarial bones and in a cloned mouse calvarial osteoblastic cell lineage (MC3T3-E1) bradykinin stimulated the production of prostaglandin E2 (PGE2) and 6-keto-prostaglandin F1 alpha (the stable breakdown product of prostacyclin). The stimulation of PGE2 production occurred rapidly (30 s) and reached its maximum after 5-10 min. The stimulatory effect of bradykinin on PGE2 production in isolated osteoblast-like cells and in MC3T3-E1 cells was dose dependent with apparent half maximal stimulation seen at 10 and 3 nmol/l, respectively. Bradykinin-induced prostaglandin production was totally reversible after withdrawal of the agonist. Pretreatment with bradykinin (1 mumol/l) resulted in desensitization to a subsequent challenge with bradykinin (1 mumol/l), while pretreatment with bradykinin had no effect upon arachidonic acid (30 mumol/l) induced prostaglandin formation. Bradykinin-induced production of PGE2 was abolished by several structurally unrelated, competitive and non-competitive inhibitors of arachidonic acid metabolism as well as by corticosteroids. The mouse calvarial osteoblast-like cells also showed a PGE2 and 6-keto-PGF1 alpha response to thrombin, but not to parathyroid hormone (PTH), calcitonin and 1 alpha(OH)D3. The formation of cyclic AMP in mouse calvarial osteoblasts was enhanced by PTH, bradykinin, thrombin and arachidonic acid but not by calcitonin and 1 alpha(OH)D3. The cyclic AMP response to bradykinin, thrombin and arachidonic acid, but not that to PTH, was abolished by indomethacin. The degree of confluency of the cell cultures greatly influenced the amount of prostaglandins being produced. At higher cell density the amount of prostanoids synthesized per cell was substantially decreased in untreated control cultures as well as in bradykinin- and arachidonic acid-treated cells. These data suggest that osteoblasts are equipped with receptors for bradykinin coupled to prostaglandin production.
...
PMID:Bradykinin stimulates production of prostaglandin E2 and prostacyclin in murine osteoblasts. 253 69

Auranofin (AF) in concentrations between 3 x 10(-7) and 3 x 10(-6) mol/l stimulated bone resorption in cultured neonatal mouse calvariae significantly with 1 x 10(-6) mol/l being most potent. Complete inhibition by 5 x 10(-7) mol/l indomethacin and increased medium concentrations of prostaglandin (PG) E2 and 6-keto-PGF1 alpha after 72 h indicate a PG mediated mechanism. Morphology revealed active osteoclasts. Cytotoxic effects were observed with 3 x 10(-6) and 1 x 10(-5) mol/l AF with osteocytes and osteoblasts being considerably more sensitive than osteoclasts. The latter concentrations inhibited bone resorption stimulated by parathyroid hormone (PTH) 1,25-dihydroxyvitamin D3, PGE2, thrombin and interleukin 1. The stimulatory effect of AF on PG production and subsequent bone resorption could limit its therapeutic usefulness.
...
PMID:Effect of auranofin on resorption, prostaglandin synthesis and ultrastructure of bone cells in cultured mouse calvaria. 277 56


1 2 3 4 Next >>

---