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Query: UNIPROT:P00750 (PLA)
16,800 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Sertoli cells in primary cultures produce plasminogen activator activity, and release it into the medium at rates greatly influenced by a variety of factors, including cell density, the presence of hormones, incubation temperature and duration of culture. In Sertoli cells maintained in culture in the presence of dibutyryl cAMP, the amounts of plasminogen activator activity secreted per cells were maximal at cell densities up to 2.5 microgram DNA/cm2 (350 units/microgram cell DNA), and declined to 40 units/microgran cell DNA at a density of 22 micrograms DNA/cm2. Concentrations of follicle-stimulating hormone (FSH) required to elicit half-maximal stimulation of the production of plasminogen activator activity were 0.37 micrograms/ml for oFSH-NIH S12 and 8 ng/ml for the more purified of SH-S1528C2. The ED50 for dibutyryl cAMP was found to be 0.08 mM. Addition of an inhibitor of phosphodiesterase (3-isobutyl-l-methylxanthine) enhanced the formation of plasminogen activator by cells cultured in the presence of FSH. Addition to the culture medium of testosterone, epidermal growth factor, insulin, human chorionic gonadotropin or prostaglandins (E1, E2 or F1 alpha) did not result in increased production of PA activity by Sertoli cells. Cells in culture for as long as 14 days remained responsive to FSH or dibutyryl cAMP. Increases in cellular levels of plasminogen activator became evident within 2-4 after addition of either FSH or dibutyryl cAMP to the medium. The stimulation of FSH or dibutyryl cAMP of the production of plasminogen activator activity was shown to be dependent upon de novo synthesis of RNA and protein. Levels of enzyme activity released by Sertoli cells maintained in culture for 48 h at 37 degrees C were approx. 50% higher than plasminogen activator released by cells cultured at 32 degrees C. The control of the production of plasminogen activator activity by Sertoli cells was discussed in relation to the control of plasminogen activator production by granulose cells, and the possible role of plasminogen activator in gonadal functions.
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PMID:The control of the synthesis and secretion of plasminogen activator by rat sertoli cells in culture. 617 77

Incubation of rat hepatoma cells with cAMP derivatives stimulates cell-associated plasminogen activator activity 8- to 22-fold and extracellular plasminogen activator activity 30- to 1300-fold. This time- and concentration-dependent increase is enhanced by phosphodiesterase inhibitors. Dexamethasone, a synthetic glucocorticoid, decreases the plasminogen activator activity of these cells, probably through induction of an inhibitor. Paradoxically, dexamethasone, added simultaneously with cAMP derivatives causes a further 4-fold enhancement of the cAMP-mediated stimulation of plasminogen activator activity. Dexamethasone also alters the time course of cAMP-mediated enhancement of plasminogen activator activity: increased protease activity is detected at 4 hr in cells incubated with 8-bromoadenosine-3':5'-cyclic monophosphoric acid and 1-methyl-3-isobutylxanthine but not until 12 hr in cells incubated with dexamethasone as well. Glucocorticoids thus exert two separate and opposite effects on plasminogen activator activity: induction of an inhibitor and amplification of cyclic nucleotide action. Although permissive and synergistic effects of dexamethasone on cyclic nucleotide action have been reported previously, glucocorticoid regulation of plasminogen activator activity is unique in that the amplification of cyclic nucleotide effects by dexamethasone opposes its regulatory action toward a specific enzyme.
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PMID:Paradoxical effects of glucocorticoids on regulation of plasminogen activator activity of rat hepatoma cells. 617 95

Macrophages from various sources can be stimulated by a variety of substances to secrete a range of inflammatory mediators and degradative enzymes. The mechanisms involved in the activation and secretory processes are unknown, However, recent evidence suggests that cyclic AMP may play a role in the regulation of neutral protease secretion. Thus, it has been shown that agents known to increase intracellular cyclic AMP levels (cyclic AMP analogues, phosphodiesterase inhibitors, prostaglandin E1 and E2, catecholamines, cholera toxin and, indirectly, glucocorticosteroids) inhibit the secretion of the neutral protease plasminogen activator. It is speculated that macrophage activation may also initiated by changes in the steady-state levels of cyclic nucleotides. A decrease in intracellular cyclic AMP and/or an increase in cyclic GMP levels would favour secretion. It is possible that these changes could be brought about by the action of various stimuli to modify the capacity of the macrophage to synthetize or degrade cyclic nucleotides.
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PMID:Cyclic nucleotides, possible intracellular mediators of macrophage activation and secretory processes. 626 14

Plasminogen activators are highly selective proteases that activate the proenzyme plasminogen to the general protease, plasmin. We studied a porcine kidney cell line, originally isolated as a high producer of plasminogen activator, in which activities of cellular adenylate cyclase and cAMP-dependent protein kinase are increased in response to calcitonin. We found that salmon calcitonin, in the concentration range 0.03-300 nM, increased plasminogen activator production up to approximately 1,000-fold and concurrently inhibited cell multiplication; both of these effects were reversible. Human calcitonin was approximately 0.01 times as potent as salmon calcitonin, corresponding to potency differences observed in other biological systems. Plasminogen activator production was also stimulated by other agents that raise cellular cAMP levels such as cholera toxin, phosphodiesterase inhibitors, and vasopressin, but not to the same extent as by calcitonins. The rapidity and sensitivity of the plasminogen activator determination and other cellular responses may make it possible in the future to use this cell stain in a convenient bioassay for calcitonins and their analogues.
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PMID:Calcitonin stimulates plasminogen activator in porcine renal tubular cells: LLC-PK1. 627 91

We confirm that basal rates of formation of plasminogen activator by cells in cultured tubule segments at stages of the cycle associated with spermiation (stages VII and VIII) are higher than those by cells in tubule segments at any other stages of the cycle of the seminiferous epithelium. We demonstrate that addition of cAMP derivatives or follicle-stimulating hormone in the presence of a phosphodiesterase inhibitor results in a large stimulation of plasminogen activator formation by tubule segments at all stages of the cycle. The greatest percentage increase (approximately 100-fold) is observed in cells in tubule segments having lowest basal rates of plasminogen activator formation (stages IX-VI). Even under stimulated conditions, however, the amounts of plasminogen activator produced by cultured tubule segments at stages VII and VIII remain greater than those produced by cultured tubule segments at other stages of the cycle, and these differences persist during organ culture for 48 h. Insulin and testosterone do not alter rates of formation of plasminogen activator. We conclude that Sertoli cells, the primary source of formation of plasminogen activator in the testis, are metabolically heterogeneous in the seminiferous tubule and that the germ cell association patterns in various stages of the cycle modulate Sertoli cell functions. We discuss the data in relation to the tissue restructuring within the seminiferous tubule which occurs during spermatogenesis and the possible role of plasminogen activator in these processes.
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PMID:Hormonal influences on formation of plasminogen activator by cultured testis tubule segments at defined stages of the cycle of the seminiferous epithelium. 631 51

Synovial activator (SA) from peripheral blood mononuclear cells stimulates the plasminogen activator (PA) levels of human synovial fibroblasts. Using the sensitive technique of transcriptional inhibition followed by a prolonged translation period, data suggested that the first synthesis of mRNA needed for the increase in PA activity began within 40-60 min; this increase in protease activity was reversible on removal of SA from the cultures and also declined after about 3 days even if SA was not withdrawn. The RNA dependent events necessary for the synovial cell activation were to a large extent completed by about 4-8 h while those dependent on protein synthesis lasted for about 12 h. The effectiveness of suboptimal concentrations of SA could be potentiated by all-trans retinoic acid. A similar potentiation was effected by phosphodiesterase inhibitors, 3-isobutyl-1-methylxanthine and theophylline, by 8-bromo-cAMP, and by prostaglandins of the E and F series; these last observations suggest cyclic nucleotide involvement in the SA-mediated elevation of synovial fibroblast PA activity.
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PMID:Synovial cell activation. Studies on the mechanism of action of synovial activator activity. 642 May 60

The effects of prostaglandins on the fibrinolytic activity of cultured human foreskin fibroblasts have been measured by a [125I]fibrin dish assay. Prostaglandin (PG) E1, added to fibroblasts in serum-containing medium, produced dose-dependent increases in the fibrinolytic activity of both cellular extracts and conditioned medium. PGE2 and PGI2, but not PGD2 or 6-keto-PGF1 alpha, also stimulated fibrinolytic activity. In each case, activity was due to the protease plasminogen activator because it was abolished by omitting plasminogen from the fibrinolytic assays. The effects of PGE1 were observed at 10 ng/ml and maximal stimulation occurred at 1 microgram/ml. Levels of both intra- and extracellular plasminogen activator increased, indicating that PGE1 stimulated the overall synthesis and release of the protease. The effects of PGE1 were slow in onset and persistent (greater than 48 hr) and were abolished by cycloheximide and actinomycin D. Cellular plasminogen activator was stimulated by 10 microM isoproterenol and 250 microM dibutyryl cyclic AMP; the effects of PGE1, isoproterenol and dibutyryl cyclic AMP were potentiated by the phosphodiesterase inhibitors 1-methyl-3-isobutylxanthine (100 microM) and dipyridamole (20 microM). The induction of plasminogen activator by PGE1 may therefore be initiated by stimulation of cellular adenylate cyclase. Increased fibrinolytic stimulation of cellular adenylate cyclase. Increased fibrinolytic activity could contribute to the prolonged beneficial effects which have been reported after the administration of PGE1 and PGI2 in the treatment of occlusive vascular disease.
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PMID:Stimulation of fibrinolytic activity in human skin fibroblasts by prostaglandins E1, E2 and I2. 705 Mar 42

Osteoblasts have been reported to produce tissue-type (t) plasminogen activator (PA), which may be involved in the initiation of bone resorption via plasmin-metalloproteinase degradation of adjacent extracellular matrix. To investigate this cAMP-activated gene, we characterized the PTH regulation of tPA messenger RNA (mRNA) in neonatal rat osteoblast cultures before and after differentiation in vitro. RNA was purified from cultures at confluence or after treatment with glucocorticoid for 1 week and BGJ/ascorbic acid/beta-glycerophosphate for a second week. Northern blots of total or poly(A)+ RNA were hybridized simultaneously with an oligonucleotide or complementary RNA probe for rat tPA and an oligomeric DNA probe for cyclophilin (CYP), an abundant control gene. Differentiation was monitored by expression of rat osteocalcin mRNA and protein. Both bovine PTH1-34 and forskolin caused an increase in tPA/CYP ratio in the presence of phosphodiesterase inhibitor (IBMX) and cycloheximide (CHX). The effect was maximal (16- to 21-fold increase in tPA mRNA and 6- to 8-fold increase in tPA/CYP ratio) with 25 nM hormone for 6 h and was half-maximally stimulated by 0.75-2.5 nM PTH. The tPA response to PTH was present in first passage osteoblast cultures at confluence and after 1 to 2 weeks of glucocorticoid treatment. Exposure of the differentiated cultures of 1,25-dihydroxyvitamin D (10 nM) for 2 days markedly stimulated osteocalcin mRNA while having no effect on tPA. In Northern blots of poly(A)+ RNA from cultures not treated with CHX, IBMX and PTH (2.5 h) independently stimulated tPA mRNA with no significant effect on CYP mRNA levels. The tPA/CYP ratio increased in five consecutive experiments and the effect of IBMX and PTH were additive. These data indicate that PTH acts via cAMP to stimulate tPA expression by a mechanism that is independent of protein synthesis. The enhancement of PTH action by CHX is compatible with feedback inhibition of tPA transcription by a hormone-activated repressor (which has been proposed to occur in granulosa cells) but effects of CHX on tPA mRNA stability may also occur. Expression of tPA mRNA before and after differentiation may indicate that the enzyme has more than one function.
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PMID:Increased expression of tissue plasminogen activator messenger ribonucleic acid is an immediate response to parathyroid hormone in neonatal rat osteoblasts. 811 83

Inhibitors of cyclic nucleotide phosphodiesterase hydrolysis of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate are known to inhibit platelet aggregation, which plays an important role in acute reocclusion after thrombolysis in acute myocardial infarction. In the present study of a canine preparation of coronary artery thrombosis superimposed on high-grade stenosis, we tested whether the antithrombotic agent cilostazol, an inhibitor of cAMP phosphodiesterase, could prevent acute reocclusion or sustain coronary blood flow after thrombolysis when used with recombinant tissue-type plasminogen activator (rt-PA) and heparin. Intravenous infusion of rt-PA (0.5 mg/kg body wt for 30 minutes) and heparin (a 150 IU/kg body wt i.v. bolus and then 25 IU/kg body wt per hour i.v.) was combined with cilostazol (0.6 or 1.8 mg/kg body wt for 60 minutes). Without cilostazol, reperfusion was observed in seven of eight dogs, but reocclusion occurred in six of these seven dogs after 9 +/- 2 minutes. After administration of 1.8 mg/kg body wt cilostazol (group B-2; a 120-minute observation after the start of rt-PA infusion), reperfusion occurred in all seven dogs (p < 0.05 versus control group), and brief cyclic reocclusion was observed in only one dog 63 minutes after reperfusion. At the same dose of cilostazol (group B-2L; a 240-minute observation after the start of rt-PA infusion), reperfusion occurred in all five dogs (p < 0.05 versus control group), and coronary blood flow was well maintained except for one short reocclusion in one dog. Cilostazol inhibited cyclic flow reduction in a dose-dependent fashion.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Cilostazol, a novel cyclic AMP phosphodiesterase inhibitor, prevents reocclusion after coronary arterial thrombolysis with recombinant tissue-type plasminogen activator. 838 80

The effect of compounds increasing intracellular adenosine 3':5'-cyclic monophosphate [cAMP]i levels (prostacyclin, isoproterenol, forskolin, cholera toxin), and of the cAMP analogs 8-bromo-cAMP and dibutyryl-cAMP, on the regulated secretion (acute release) of tissue-type plasminogen activator (tPA) and von Willebrand factor (vWF) was studied in cultured human umbilical vein endothelial cells (HUVEC). Prostacyclin, isoproterenol and forskolin, which increased [cAMP]i in HUVEC, and the cell-permeant cAMP analog 8-bromo-cAMP induced dose- and time-dependent secretion of tPA and vWF. The extent of vWF and tPA release correlated with [cAMP]i, and was increased by the phosphodiesterase inhibitor isobutylmethylxanthine. In contrast to thrombin, the cAMP-elevating agents did not increase the intracellular calcium concentration [Ca2+]i in HUVEC. At submaximal concentrations, the effects of thrombin and prostacyclin were additive. Our results show that an increase in [cAMP]i resulted in regulated secretion (acute release) of tPA and vWF from HUVEC, without the concomitant increase in [Ca2+]i which is, in HUVEC, essential for thrombin-induced regulated secretion to occur. cAMP-induced secretion represents a novel mechanism for causing regulated secretion of tPA and vWF from endothelial cells.
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PMID:Adenosine 3':5'-cyclic monophosphate induces regulated secretion of tissue-type plasminogen activator and von Willebrand factor from cultured human endothelial cells. 956 4

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