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

Component levels of the fibrinolysin system in the plasma and ascitic fluid of Swiss mice bearing Ehrlich ascites tumor cells were determined during a 15-day tumor growth time phase. During tumor growth, the concentration of plasminogen in the ascitic fluid decreased inversely to the total packed cell volume. Free plasmin was not present in the ascitic fluid nor was there any measurable plasminogen activator activity. Both antiplasmin activity and fibrinogen levels present in the fluid decreased during tumor growth. The nuclear and mitochondrial-microsomal subcellular fractions of the tumor cell exhibited plasminogen activator activity. No significant changes in the above parameters occurred in the plasma during the tumor growth period we studied.
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PMID:Proteases during the growth of Ehrlich ascites tumor. I. The fibrinolysin system. 12 66

Tissue-type plasminogen activator (t-PA) is synthesized in mammalian cells as a mixture of two forms that differ in their extent of N-linked glycosylation. We have investigated the mechanism underlying this variation in glycosylation, using a cell-free system that consists of a rabbit reticulocyte lysate optimized for the formation of disulphide bonds and supplemented with dog pancreas microsomal membranes. Molecules of human t-PA synthesized in vitro are enzymically active and responsive to natural activators and inhibitors, and are glycosylated in a pattern identical with that of the protein produced in vivo. This demonstrates that t-PA synthesized in vitro folds into the same conformation as the protein synthesized in vivo. We show that the extent of glycosylation of individual t-PA molecules is dependent on the state of folding of the polypeptide chain, since the probability of addition of an oligosaccharide side chain at Asn-184 is decreased under conditions that promote the formation of enzymically active molecules. This variation in glycosylation is independent of the rate of protein synthesis.
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PMID:Cell-free synthesis of enzymically active tissue-type plasminogen activator. Protein folding determines the extent of N-linked glycosylation. 152 Feb 79

The effects of Ca and other agents on secretion of plasminogen activator (PA) and PTH have been examined and compared, using parathyroid cells obtained from the glands of chronic renal patients. During 2 weeks culture at different [Ca], the secretory rates of PA activity and PTH were parallel; steady-state secretion over 24-h periods was maximal at 0.5-0.9 mM Ca, minimal at 1.5-2.5 mM Ca, and the [Ca] at 50% suppression was 1.1 mM. At 2.5 mM Ca, two inhibitors of cellular proteolysis, 3-methyladenine and chloroquine, stimulated secretion of both PA activity and PTH. The results indicated that secretion of PA from human parathyroid cells is regulated similarly to that of PTH. The characteristics of human parathyroid PA were also examined using human parathyroid adenoma tissue. In homogenates, the highest specific activity of PA was in microsomal fractions. The Mr of PA from tissue and from culture media was 70 kilodalton by sodium dodecyl sulfate gel electrophoresis followed by zymography, or by Western blotting using antisera to human tissue PA (tPA). Enzyme activity was inhibited by incubation with antisera to tPA but not to urokinase. In contrast to bovine parathyroid cells that secrete a urokinase, human parathyroids apparently contain and secrete tPA.
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PMID:Calcium-regulated secretion of tissue plasminogen activator and parathyroid hormone from human parathyroid cells. 173 Aug 6

The characteristics and secretion of plasminogen activator (PA) were examined in fresh and cultured bovine parathyroid cells. Release of PA activity was maximal at low Ca concentrations ([Ca]) and suppressed at physiological [Ca]. PA secretion at high [Ca], like that of PTH, was increased by treatment of cells with chloroquine and/or 3-methyladenine. Secretion from organoids was not affected by hydrocortisone hemisuccinate, but was strongly increased by 1,25-dihydroxyvitamin D3. In cell homogenates, PA specific activity was highest in microsomes, from which less than 50% could be solubilized by Triton X-100. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of microsomes and media followed by zymography on fibrin-agarose gels showed that PA from both sources had an apparent mol wt of 44,000. No inhibitors of PA were detected by reverse zymography. PA activity was inhibited by placental urokinase (uPA) inhibitor and amiloride, which indicated that it was a uPA, but the secreted form required tissue-type PA stimulator (fibrin peptides) or denatured microsomes for full activity. Neither the microsomal nor the secreted forms of PA were active with S-2444, a substrate specific for active uPA. By comparison with the characteristics of human activators, the results suggested that parathyroid cells secrete uPA that is primarily in the precursor form single chain urokinase or scuPA.
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PMID:Secretion of plasminogen activator from bovine parathyroid cells. 210 81

When messenger RNA (mRNA) from both untreated and phorbol ester-treated melanoma cells is translated in simple reticulocyte lysates, tissue-type plasminogen activator can be immunoprecipitated by an affinity-purified antibody as a approximately 52,000 mol wt protein, with no detectable biological (plasminogen activating) activity. When the reticulocyte lysate system is supplemented with a preparation of microsomal membranes, biological activity becomes detectable and a 63,000 mol wt protein can be immunoprecipitated with the same antibody. Furthermore, when natural tissue-type plasminogen activator (mol wt approximately equal to 70,000) is incubated with different glycosidases, distinct alterations in the electrophoretic mobility of the molecules are observed, together with alterations in the level of biological activity. While treatment with neuraminidase and beta-galactosidase caused decreases in activity, alpha-mannosidase caused an increase. These results suggest that the carbohydrate part of the molecule can influence its biological behavior.
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PMID:Influence of carbohydrate side chains on activity of tissue-type plasminogen activator. 308 8

Messenger RNA of the phorbol ester-induced 48kDa protein from human melanoma cells (Bowes) was isolated, characterized and used to study the protein processing. The 48kDa mRNA is induced simultaneously with that of tissue-type plasminogen activator. This induction is prominent as shown by sedimentation profiles on linear sucrose gradients. The mRNA can be isolated by classical phenol extractions, has a poly(A)-tail and sediments with a coefficient of 20 S. Translation in reticulocyte lysates yields a 48kDa protein whether the translation is modified with canine pancreas microsomal membranes or not. Analysis of 48kDa mRNA translation products by sodium dodecyl sulphate/polyacrylamide gel electrophoresis showed that the phorbol ester-induced 48kDa is a monomeric one-chain polypeptide. Glycosylation could not be detected, nor signal peptide cleaving, suggesting that it is a non-secreted intracellular protein.
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PMID:Messenger RNA for a phorbol-ester induced 48,000 dalton protein from human melanoma cells. 308 63

Antiestrogens have proven to be effective in controlling the growth of hormone-responsive breast cancers. At the concentrations of antiestrogens achieved in the blood of breast cancer patients taking antiestrogens (up to 2 X 10(-6) M), antiestrogens selectively inhibit the proliferation of estrogen receptor-containing breast cancer cells, and this inhibition is reversible by estradiol. Antiestrogens also inhibit estrogen-stimulation of several specific protein synthetic activities in breast cancer cells, including increases in plasminogen activator activity, progesterone receptor levels and production of several secreted glycoproteins and intracellular proteins. Antiestrogens bind with high affinity to the estrogen receptor and to additional microsomal binding sites to which estrogens do not bind. These latter sites, called antiestrogen binding sites (AEBS), are present in equal concentrations in estrogen receptor-positive and -negative breast cancer cells and are present in a wide variety of tissues, with highest concentrations being found in the liver. The antiestrogenic and growth suppressive potencies of a variety of antiestrogens correlate best with their affinity for estrogen receptor and not with affinity for AEBS. Antiestrogens undergo bioactivation and metabolism in vivo and hydroxylated forms of the antiestrogen have markedly enhanced affinities for the estrogen receptor. Detailed studies with high affinity radiolabelled antiestrogens indicate that antiestrogens induce important conformational changes in receptor that are reflected in the enhanced maintenance of a 5 S form of the estrogen receptor complex; reduced interaction with DNA; and altered activation and dissociation kinetics of the antiestrogen-estrogen receptor complex. These conformational changes effected by antiestrogens likely result in different interactions with chromatin, causing altered cell proliferation and protein synthesis. Analyses of the rates of synthesis and turnover of the estrogen receptor through pulse-chase experiments utilizing the covalently attaching antiestrogen, tamoxifen aziridine, and studies employing dense amino acid labeling of estrogen receptor reveal that the antiestrogen-occupied receptor is degraded at a rate (t 1/2 = 4 h) similar to that of the control unoccupied receptor. Hence, antiestrogens do not prevent estrogen receptor synthesis and they do not either accelerate or block estrogen receptor degradation.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Antiestrogen action in breast cancer cells: modulation of proliferation and protein synthesis, and interaction with estrogen receptors and additional antiestrogen binding sites. 402 93

We describe here a semi-permeabilized cell-system which reconstitutes the efficient synthesis, translocation, folding, assembly and degradation of membrane and secretory proteins. Cells grown in culture were treated with the detergent digitonin which selectively permeabilized the plasma membrane leaving the cellular organelles, such as the endoplasmic reticulum (ER) and trans-Golgi network intact. These permeabilized cells were added to an in vitro translation system, either wheatgerm or reticulocyte lysate, supplemented with RNA coding for either membrane or secretory proteins. Efficient translocation and modification of proteins by these cells was demonstrated by protease protection, photocross-linking of nascent chains to components of the translocation apparatus and by post-translational modifications such as glycosylation or hydroxylation. A comparison was made between the ability of semi-permeabilized cells and microsomal vesicles to fold and assemble proteins. The results show that the intact ER within these cells can assemble proteins much more efficiently than vesicularized ER. Furthermore, the semi-permeabilized cells carried out the redox-dependent degradation of tissue-type plasminogen activator. This system has all the advantages of conventional cell-free systems, including speed and, importantly, the ability to manipulate the components of the assay, while retaining intracellular organelles and, therefore, allowing cellular processes to occur as they would in the intact cell.
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PMID:The translocation, folding, assembly and redox-dependent degradation of secretory and membrane proteins in semi-permeabilized mammalian cells. 774 97

The activities of microsomal phospholipase A(2) (PLA(2)) and C (PLC) from mouse brain, heart and liver were determined using the substrate 1-palmitoyl-2-N-(4-nitrobenzo-2-oxa-1,3-diazole amino caproyl-phosphatidylcholine (NBD-PC), and the effects of chronic ethanol treatment (ethanol) as well as in vitro addition of various n-alcohols including ethanol on these activities were evaluated. Microsomal membrane fluidity was estimated by diphenylhexatriene anisotropy (gamma). The microsomes from the brain and heart of ethanol-treated mice showed significantly higher PLA(2) activity than those from controls. The brains of ethanol group showed significantly higher PLC activity, while the heart showed significantly lower PLC activity than those of controls. The microsomes from the brain and heart of ethanol-treated mice showed significantly reduced gamma values compared to those of controls. The addition of ethanol in vitro to microsomes was found to increase PLC activity in these tissues, while it decreased PLA(2) activity in a dose-dependent manner. The other n-alcohols showed similar effects on PLA(2) and PLC activity in the live microsomes, while decreases were observed the gamma values in a dose-dependent manner. These results suggest that the change in the membrane fluidity associated with addition of alcohols is a prerequisite for the changes in PLA(2) and PLC activities. In addition, our findings suggest that these changes may play a major role in the cellular injury associated with chronic ethanol treatment in the mouse.
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PMID:Effects of ethanol on phospholipases in the mouse brain, heart and liver. 886 Sep 51

Vitamin A and its active metabolite retinoic acid (RA) modulate host-pathogen interactions by interfering with the host immune and inflammatory response including prostaglandin (PG) biosynthesis. The effects of RA on phospholipase A(2) (PLA(2)) and cyclooxygenase (COX) isoforms in vitro are controversial, and few in vivo studies exist. We investigated the in vivo effects of RA on PG biosynthesis in the presence or absence of lipopolysaccharide (LPS) in rats. RA alone [10 mg/(kg. d) for 5 d] increased plasma and liver PG concentrations by increasing COX-1 protein expression (twofold that of control rats). RA acted synergistically with LPS to increase plasma (400-fold) and liver (15-fold) concentrations of prostaglandin E(2) (PGE(2)) and significantly, but to a lesser extent, other PG compared with RA rats, in the absence of major differences in PLA(2) expression or activity or COX-1 and COX-2 mRNA or protein expression. The RA + LPS-mediated increase in PGE(2) was significantly attenuated (97%) by aminoguanidine (AG), a relatively specific inhibitor of the inducible nitric oxide synthase (NOS2), consistent with the previously reported synergistic effect of RA and LPS on NOS2 expression and activity. In addition, RA and LPS induced the expression of the microsomal isoform of PGE synthase (mPGES). In conclusion, in vivo, RA and LPS increased PG and especially PGE(2) concentrations. The PGE(2) increase was associated with NOS2-mediated activation of COX and induction of mPGES. These results contribute to the characterization of the effects of vitamin A on the host inflammatory response.
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PMID:Retinoic acid and lipopolysaccharide act synergistically to increase prostanoid concentrations in rats in vivo. 1158 82


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