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

Vascular endothelial cells derived from rabbit vena cava and maintained in continuous culture exhibited properties characteristic of the intact endothelium. These cells were used as a model for characterizing the fibrinolytic components specified by the endothelium. Endothelial cells in culture digested radiolabeled fibrinogen. Digestion resulted from the synthesis and secretion of a plasminogen activator. Fibrinolysis was not detected when cells were grown in medium lacking plasminogen, indicating the absence of plasminogen-independent fibrinolytic enzymes. Phorbol-myristate-acetate increased extracellular plasminogen activator activity dramatically. This increase was prevented when actinomycin D or cycloheximide was included in the growth medium, indicating that new gene expression was required for it. Intracellular plasminogen activator could not be detected unless the cell extracts were exposed briefly to mildly acidic conditions. Mixing experiments between acid-treated and untreated extracts suggested that the cells contained a potent, acid-labile inhibitor of fibrinolysis. As little as 10 mug of protein from whole cell extracts inhibited both cell and urokinase-mediated fibrinolysis by more than 70%. Cell fractionation studies localized the inhibitor to the cytosol whereas plasminogen activator activity was restricted to the membrane-rich fraction. This membrane fraction did not require acidification for activity, suggesting that the inhibitor had been removed and that acidification did not activate a plasminogen proactivator. These observations demonstrate that regulation of endothelial fibrinolytic activity is far more complex than had been anticipated and raise several uncertainties in regard to detecting the presence of plasminogen activators in cells and tissues.
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PMID:Synthesis of a fibrinolytic activator and inhibitor by endothelial cells. 14 64

The carcinogenic process is usually multifactor in its causation and multistep in its evolution. It is likely that entirely different molecular mechanisms underlie the many steps in this process. In contrast to initiating carcinogens, the action of the tumor-promoting phorbol esters does not appear to involve covalent binding to cellular DNA and they are not mutagenic. Recent studies in cell culture have revealed two interesting biologic effects of the phorbol esters and related macrocyclic plant diterpenes. The first is that at nanomolar concentrations they induce several changes that resemble those seen in cells transformed by chemical carcinogens or tumor viruses. These include altered morphology and increased saturation density, altered cell surface fucose-glycopeptides, decrease in the LETS protein, increased transport of deoxyglucose, and increased levels of plasminogen activator and ornithine decarboxylase. In transformed cells exposed to phorbol esters the expression of these features is further accentuated. Phorbol esters do not induce normal cells to grow in agar but they do enhance the growth in agar of certain transformed cells. The second effect of the phorbol esters is inhibition of terminal differentiation. This effect extends to a variety of programs of differentiation and is reversible when the agent is removed. With certain cell culture systems induction of differentiation, rather than inhibition, is observed. Both the transformation mimetic and the differentiation effects are exerted by plant diterpenes that have tumor-promoting activity but not by congeners that lack such activity. The primary target of phorbol esters appears to be the cell membrane. Early membrane-related effects include enhanced uptake of 2-deoxyglucose and other nutrients, altered cell adhesion, induction of arachidonic acid release and prostaglandin synthesis, inhibition of the binding of epidermal growth factor to cell surface receptors, altered lipid metabolism, and modifications in the activities of other cell surface receptors. A model of "two stage" carcinogenesis encompassing the known molecular and cellular effects of initiating carcinogens and tumor promoters is presented. According to this model, initiating carcinogens induce stable alterations in the cellular genome but these are not manifested until tumor promoters modulate programs of gene expression and induce the clonal outgrowth of the initiated cell.
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PMID:Action of phorbol esters in cell culture: mimicry of transformation, altered differentiation, and effects on cell membranes. 39 70

Tumor-promoting phorbol esters are believed to affect ovarian granulosa cell progesterone and prostaglandin (PG) production and possibly ovulation by activating protein kinase-C (PKC). The effects of phorbol esters and PKC inhibitors on ovulation, progesterone, and PG production were examined in an in vitro perfused rabbit ovary. The effect of tranexamic acid, an inhibitor of the conversion of plasminogen activator to plasmin, on phorbol ester-induced ovulation was also examined. Phorbol 12,13-dibutyrate (PdBU), a PKC stimulator, induced ovulation in a dose-related manner in the absence of gonadotropins (56%, 200 nM PdBU; 0%, 0 nM PdBU; P < 0.05). Perfusate progesterone levels were increased only after 600 nM PdBU treatment, and perfusate PGF2 alpha, PGE2, and 6-keto-PGF1 alpha were increased in a dose-dependent fashion (P < 0.05). Staurosporine, a potent inhibitor of the catalytic domain of PKC, and calphostin-C, a specific inhibitor of the diacylglycerol-binding region, inhibited hCG-induced ovulation in a dose-related manner. Gonadotropin-induced ovulation decreased from 73% without staurosporine to 19% with 1.0 microM staurosporine (P < 0.01). Calphostin-C reduced ovulatory efficiency from 60% to 24% (P < 0.01). However, neither inhibitor decreased progesterone or PGF2 alpha production by ovaries exposed to hCG. hCG-induced oocyte maturation was also unaffected by exposure to either staurosporine or calphostin-C. Tranexamic acid reduced phorbol ester-induced ovulatory efficiency from 67% to 37% (P < 0.05). These findings demonstrate that the calcium-dependent PKC pathway is instrumental in gonadotropin-mediated follicular rupture in the rabbit. Although PGs may play an important role in ovulation, they do not appear to be directly responsible for PKC-mediated follicular rupture.
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PMID:The role of protein kinase-C in gonadotropin-induced ovulation in the in vitro perfused rabbit ovary. 139 26

Serum-free conditioned medium (CM) generated by human umbilical vein endothelial cell monolayers following pretreatment with 100 ng/ml of phorbol myristate acetate (PMA) promoted human polymorphonuclear leukocyte (PMNL) migration as assayed in blindwell chambers. Stimulation of PMNL migration in response to CM was dependent on the dose of PMA used to pretreat the endothelial cells as well as the duration of incubation time to generate CM. Phorbol esters have been previously shown to release plasminogen activators from vascular endothelial cells. In the present study, pretreatment of endothelial cells with PMA also increased plasminogen activator activity in CM at a time course similar to the generation of PMNL chemoattractant activity. Treatment of CM with a polyclonal antibody against human urokinase-type plasminogen activator (uPA) not only inhibited uPA activity, but also significantly reduced PMNL chemoattractant activity when compared with untreated CM. In contrast, treatment of CM with an antibody directed against tissue-type plasminogen activator (tPA) did not affect PMNL migratory activity. Furthermore, when CM was passed over an anti-uPA immunoaffinity column, plasminogen activator activity was reduced 90% and chemoattractant activities was reduced 68%. Both plasminogen activator and chemoattractant activities were reconstituted in the eluate from the anti-uPA column. These data demonstrate that uPA present in the CM from PMA-pretreated endothelial cells stimulates PMNL chemoattractant activity and suggests a possible role for endothelial cell-derived uPA in stimulating migration of peripheral blood leukocytes at an inflammatory locus.
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PMID:Urokinase in conditioned medium from phorbol ester-pretreated endothelial cells promotes polymorphonuclear leukocyte migration. 151 9

Using a perfused rat hindleg system, release of tissue-type plasminogen activator (t-PA) from endothelial cells could be induced by platelet-activating factor (PAF), bradykinin, substance P, thrombin, carbachol and A23187, while this release was inhibited by mepacrine and by nor-dihydroguaiaretic acid. The PAF-induced release of t-PA was inhibited by the cytochrome P-450 mono-oxygenase inhibitors, metyrapone, ketoconazole and SKF 525A and by eicosatetraynoic acid but not by indomethacin or BW 755C, suggesting the involvement of epoxygenase products. The PAF-induced release of von Willebrand factor (vWF) was also similarly inhibited by the cytochrome P-450 monooxygenase inhibitor, ketoconazole. Phorbol ester and phospholipase C induced the release of both t-PA and vWF, while phospholipase A2 did not. The release induced by PAF and bradykinin was not influenced by pretreatment with pertussis toxin.
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PMID:The involvement of products of the phospholipase pathway in the acute release of tissue-type plasminogen activator from perfused rat hindlegs. 152 62

Human mesangial cells in culture synthesize and secrete plasminogen activator inhibitor 1 (PAI-1) and tissue-type plasminogen activator (t-PA). Phorbol myristate acetate (PMA), a known activator of protein kinase C, induces a three to four-fold increase in t-PA and PAI-1 release over a period of 24 h, whereas cell-associated t-PA and PAI-1 levels remain relatively stable. A similar effect is obtained with oleylacetyl glycerol, a more physiologic protein kinase C activator. The effect of PMA is suppressed in the presence of H7, an inhibitor of cellular protein kinases, and by cycloheximide and actinomycin D, indicating a requirement for de novo protein and RNA synthesis, respectively. Northern blot analysis of PMA-treated cells reveals a rapid and transient increase in PAI-1 mRNA reaching a maximum after 4-8 h, whereas increase in t-PA mRNA levels requires 24 h. Activation of protein kinase A by addition of 8-bromocyclic AMP (8-bromo cAMP) has no significant effect on PAI-1 release but inhibits the PMA-mediated increases in PAI-1 antigen and mRNA. Addition of 8-bromo cAMP alone does not affect t-PA release. When added to PMA-stimulated cells, 8-bromo cAMP inhibits t-PA release in a dose-dependent manner, but causes a superinduction of t-PA mRNA. 8-bromo cAMP also induces a decrease in PMA-stimulated intracellular t-PA release. Similar inhibition is observed after stimulation of endogenous adenylate cyclase with prostaglandin E1 or isoproterenol. This indicates that protein kinase A activation may inhibit PMA-stimulated t-PA release via a post-transcriptional effect, e.g. inhibition of protein synthesis or activation of protein degradation. In conclusion, hormones or mediators which activate protein kinase C can stimulate t-PA and PAI-1 synthesis in human mesangial cells. Protein kinase A activation has no effect on the basal release of PAI-1 and t-PA by human mesangial cells, and, in contrast to endothelial cells, it inhibits both PMA-stimulated PAI-1 and t-PA releases. This cell-specific regulation of t-PA and PAI-1 seems to be mediated by differential transcriptional and post transcriptional mechanisms.
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PMID:Cell-specific regulation of plasminogen activator inhibitor 1 and tissue type plasminogen activator release by human kidney mesangial cells. 155 43

Phorbol myristate acetate (PMA) added to human synovial fibroblast cultures caused a dose-dependent increase in the production of plasminogen activator inhibitor-type 1 (PAI-1). In addition, PMA inhibited endogenous and interleukin-1 (IL-1) induced plasminogen activator (PA) activity, while increasing mRNA PAI-1 levels. Other protein kinase C (PKC) activators, mezerein and teleocidin B4, caused similar effects. The simultaneous addition of the PKC antagonists, H-7 or staurosporine, prevented the inhibition of PA activity by PMA. This study shows that activation of PKC inhibits PA and stimulates PAI production in human synovial fibroblasts. These results suggest that activation of PKC may play an important role in regulating increased PA production associated with joint destruction in rheumatoid arthritis (RA).
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PMID:Modulation of synovial fibroblast plasminogen activator and plasminogen activator inhibitor production by protein kinase C. 174 33

To investigate short-term activation and inhibition of fibrinolysis during shock, we studied plasma levels of tissue-type plasminogen activator (t-PA) and t-PA inhibition capacity (PAI) in anaesthetized pigs. t-PA in euglobulin fractions of plasma was measured by the conversion of plasminogen to plasmin in the presence of fibrin split products. Plasmin thus generated was measured in a chromogenic substrate assay. PAI was measured as plasma inhibition capacity for human melanoma t-PA. Controls (n = 8) had constant t-PA and PAI for 6 h. Lipopolysaccharide from Salmonella abortus equi in four different doses (n = 9 - 11), or live Escherichia coli (n = 3) induced a transient t-PA increase with peak values at 2 h. PAI decreased to 50% at 2 h and increased to 250% at 6 h. Phorbol myristate acetate (n = 7) induced no change of t-PA or PAI. Dextran sulphate (n = 4) produced a t-PA rise at 30 min, followed by a rapid decline. Endotoxin was an appropriate stimulus for activation and inhibition of fibrinolysis whereas phorbol ester failed to elicit this response.
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PMID:Time dependent release of tissue-type plasminogen activator and plasminogen activator inhibitor into the circulation of pigs during shock. 183 37

In perfused rat hindlegs, platelet-activating factor and bradykinin induced the acute release of both tissue-type plasminogen activator (t-PA) and von Willebrand Factor (vWF). The time course of release was similar for both proteins, and the amounts of t-PA and vWF released under various conditions were closely correlated. Release of both t-PA and vWF required extracellular calcium, and could be induced by the calcium ionophore A-23187. Protein synthesis was not required for release to occur. Phorbol myristate acetate also induced release of t-PA and vWF, though with a different time course; DDAVP was inactive. The results suggest that the release of t-PA, and that of vWF, are closely linked at the cellular level.
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PMID:The simultaneous acute release of tissue-type plasminogen activator and von Willebrand factor in the perfused rat hindleg region. 211 27

The hormonal regulation of the human urokinase type plasminogen activator (uPA) gene has been studied by introducing into mouse and rat Sertoli cell primary cultures a recombinant plasmid, in which the transcription regulatory elements of the cloned human uPA gene drive the expression of the bacterial chloramphenicol-acetyl-transferase gene. It was found to be expressed and regulated by FSH and (Bu)2cAMP in the mouse cells only, in agreement with data on the expression of the endogenous gene in rat and mouse gonads. The stimulation of transcription by FSH was evident in cultures from 13-day-old but not from 18-day-old mice, even though (Bu)2cAMP induction could be observed at both ages. Phorbol-myristate acetate was found to activate the human uPA promoter in Sertoli cell cultures from mice of both ages, even though the effect was less evident in cultures of 18-day-old animals. Deletion analysis of the human uPA 5'-flanking region showed that the distal enhancer element is not needed for (Bu)2cAMP induction, and that at least two promoter regions are involved in (Bu)2cAMP induced transcription. One of these cAMP responsive regions lies between nucleotides -72 and -29 from the CAP site. The sequence of this region would suggest the binding of transcription factor AP-2, a cell-specific mediator of both cAMP and phorbol esters action on gene expression. However, these sequences do not mediate phorbol ester activation of human uPA promoter in mouse Sertoli cells.
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PMID:Follicle-stimulating hormone and cyclic AMP induce transcription from the human urokinase promoter in primary cultures of mouse Sertoli cells. 217 96


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