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

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Query: EC:3.1.1.34 (lipoprotein lipase)
7,025 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To explore the possibility that protein kinase C (PKC) participates in desensitization to Ca(2+)-mobilizing hormones in MDCK cells, we measured intracellular free Ca2+ concentration ([Ca2+]i) using fura-2 and video microscopy. We first examined the response of MDCK cells grown on plastic dishes. Exposure of cells to bradykinin (BK) or to carbachol, followed by reexposure after washing off the hormone, revealed two features of hormone desensitization. First, the initial hormone-induced peak response of [Ca2+]i was transitory; [Ca2+]i returned to control levels despite continued presence of hormone. Second, cells remained refractory to hormone rechallenge for 5 min after washing off hormone; [Ca2+]i response on re-exposure was reduced 70% compared with initial hormone-stimulated peak. Subsequent experiments demonstrated involvement of PKC in both desensitization processes. Pretreatment with the phorbol ester, phorbol 12-myristate 13-acetate, significantly blunted initial response to BK and to carbachol by 70 and 86%, respectively. When hormone-stimulated C kinase activity was enhanced with the diglyceride lipase inhibitor, RG 80267, BK- and carbachol-induced increases in [Ca2+]i were blunted 50%. Pretreatment with sphingosine, an inhibitor of PKC, resulted in an amplification of initial hormone-stimulated increase in [Ca2+]i and restored the response to rechallenge. To examine the possible interaction between BK and carbachol,both of which use PKC to induce desensitization, we measured [Ca2+]i in cells grown as monolayers on permeable, collagen-coated supports. Both carbachol and BK induced desensitization to the other hormone (heterologous desensitization)provided that the two hormones were applied to the same side of the polarized monolayer (apical).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Participation of protein kinase C in desensitization to bradykinin and to carbachol in MDCK cells. 131 46

In order to study the role of collagens in the differentiation of TA1 preadipose cells in vitro, ethyl-3,4-dihydroxybenzoate (EDHB) was used as a specific inhibitor of collagen synthesis. The secretion of collagenous proteins only was severely decreased after exposure to EDHB, and this was accompanied by a decrease of differentiation as indicated by low activity levels of glycerophosphate dehydrogenase. The effect of EDHB was dose-dependent and also dependent upon the stage of cell differentiation. Northern-blot analysis show that EDHB addition to undifferentiated cells did not prevent the induction of A2COL6 gene, a marker of the preadipose state, but prevented the induction of the gene encoding for the adipocyte lipid binding protein and the modulation of the expression of the lipoprotein lipase gene which are both indicators of the adipose state. These results demonstrate that differentiation of preadipose cells into adipose cells requires active synthesis of collagens during the preadipose state.
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PMID:Essential role of collagens for terminal differentiation of preadipocytes. 141 7

We showed that the synthesis and secretion of type IV collagen, entactin, and laminin were enhanced when adipose conversion of 3T3-L1 cells at confluence was stimulated by hormones (Y. Aratani and Y. Kitagawa (1988) J. Biol. Chem. 263, 16163-16169). Ascorbic acid phosphate (Asc-P) stimulated the synthesis and secretion of type IV collagen and other collagens from both 3T3-L1 preadipocytes and adipocytes. The synthesis and secretion of laminin and entactin were not affected by Asc-P. The continuous addition of Asc-P stimulated cell growth and increased cell density at confluence 1.3-fold. Concomitantly, Asc-P remarkably accelerated the emergence of lipoprotein lipase, glycerophosphate dehydrogenase, and Oil Red O-stainable lipid droplets. These findings suggest an important role for type IV collagen in adipocyte differentiation.
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PMID:Ascorbic acid phosphate stimulates type IV collagen synthesis and accelerates adipose conversion of 3T3-L1 cells. 231 67

Stimulation of platelets with collagen results in the mobilization of arachidonic acid (AA) from phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI). In this study the effect of aspirin, indomethacin, BW755C and prostaglandin H2 (PGH2) on labelled AA release in response to varied concentrations of collagen was investigated. Our results indicate that aspirin (0.56 mM) and indomethacin (5.6 microM) not only inhibited the collagen-mediated formation of cyclo-oxygenase metabolites, but also caused a significant reduction in the accumulation of free labelled AA and 12-hydroxyeicosatetraenoic acid (12-HETE) (21-64%). Aspirin and indomethacin also inhibited the release of [3H]AA from PC (37-75%) and PI (33-63%). The inhibition of AA release caused by aspirin was reversed partially by PGH2 (1 microM). In contrast, a smaller/no inhibition of collagen-stimulated labelled AA and 12-HETE accumulation (0-11%) and of collagen-stimulated AA loss from PC and PI was observed in the presence of BW755C. The results obtained in the presence of aspirin, indomethacin and BW755C at lower concentrations of collagen further demonstrate that AA release from PI (45-61% inhibition at 10 micrograms of collagen), but not from PC, was affected by the inhibition of cyclo-oxygenase. The results obtained on the effect of PGH2 further support that deacylation of phospholipids occurs independently of cyclo-oxygenase metabolites, particularly at higher concentrations of collagen. These results also demonstrate that aspirin and indomethacin, but not BW755C, cause a direct inhibition of collagen-induced [3H]AA liberation from PC as well as from PI. We also conclude that the diacylglycerol lipase pathway is a minor, but important, route for AA release from PI in collagen-stimulated human platelets. The mechanisms underlying the regulation of AA release by collagen in the absence of cyclo-oxygenase metabolites are not clear.
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PMID:Mobilization of arachidonic acid in collagen-stimulated human platelets. 314 82

Temporal and spatial patterns of lipid deposition, vascularization and collagen deposition were described for subcutaneous adipose tissue in the fetal pig. Enzyme cytochemical changes were reported as they relate to the morphological differentiation of the subcutaneous depot. There are distinct temporal lags between the appearance of specific enzymes in adipocytes. For example, NADH-tetrazolium reductase activity appeared earliest whereas esterase activity appeared before lipoprotein lipase (LPL) activity. Adipose tissue primordia has been localized around specific tissue components in rat and pig tissues. These tissue components include hair follicles, sweat glands, large nerves, large blood vessels and mammary gland ducts. Lipid and enzyme cytochemistry demonstrates physical continuity between primordial cells and differentiated fat cell clusters. Alterations in maternal and/or fetal endocrine or metabolic profiles result in specific changes in fetal subcutaneous adipocytes. For example, maternal diabetes significantly increases cell size whereas genetic obesity has little effect on cell size but increases cellular LPL activity significantly. A comparison of subcutaneous and perirenal depots in the pig fetus indicated several depot specific anatomical and enzyme histochemical traits. Blood vessel architecture and vascular alkaline phosphatase activity clearly demarcated perirenal and subcutaneous depots in the fetus. These data indicate that site to site variations of adipose tissue characteristics may be reflecting intrinsic stromal-vascular aspects of specific locations.
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PMID:Anatomical and enzyme histochemical differentiation of adipose tissue. 393 90

The development of adipocytes was studied in primary cultures of rat adipose tissue stromal-vascular cells on collagen-coated glass coverslips. The effects of cell density and serum source on lipoprotein lipase (LPL), esterase and lipid histochemistry were evaluated. With a mixture of fetal calf serum (FCS; 2%), horse serum (2%) and pig serum (PS; 10%), large and loosely arranged clusters of adipocytes developed with time through an increase in cell number and size. An inverse relationship was observed between cell size and the number of adipocytes in a cluster. Lower cell densities were associated with large cells and the densest areas contained smaller cells. Unilocular adipocytes were observed by d 13 after plating and were generally absent from the densest area of the coverslips. Histochemically detectable LPL activity was demonstrable before lipid deposition in adipocyte clusters. A comparison of FCS (10%) and PS (10%) as the only serum sources indicated higher level of adipocyte esterase activity and lipid deposition in PS cultures. Cultures of cells from weanling (21 to 28 d old) and old (18 mo) rats were similar, whereas cells from younger rats (2 to 4 d old) formed denser cultures that contained fewer adipocytes. These adipocytes were small (less than 30 micron) and morphologically homogeneous (all multilocular). When cells from the very young rats (2 to 4 d old) were plated at low densities, an inverse relationship between cell size and number of cells in a cluster was also observed.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Adipocyte development in primary rat cell cultures, effect of cell density and serum source. 401 45

The diacylglycerol lipase inhibitor, RHC 80267, 1,6-di(O-(carbamoyl)cyclohexanone oxime)hexane, was tested for its ability to block the release of arachidonic acid from human platelets. At a concentration (10 microM) reported to completely inhibit diacylglycerol lipase in fractions of broken platelets, RHC 80267 had no effect on diacylglycerol lipase activity or the release of arachidonic acid from washed human platelets stimulated with collagen. At a high concentration (250 microM), the compound inhibited the formation of arachidonyl-monoacylglycerol by 70% and the release of arachidonate by 60%. However, at this concentration RHC 80267 was found to inhibit cyclooxygenase activity, phospholipase C activity and the hydrolysis of phosphatidylcholine (PC) (presumably by inhibiting phospholipase A2). The phospholipase C inhibition was attributed to the inhibition of prostaglandin H2 formation, as it was alleviated by the addition of the endoperoxide analog, U-46619. PC hydrolysis was only partially restored with U-46619, suggesting that RHC 80267 directly alters phospholipase A2 activity. The inhibition of arachidonate release observed was accounted for by the inhibition of PC hydrolysis. We conclude that RHC 80267, because of its lack of specificity at concentrations needed to inhibit diacylglycerol lipase, is an unsuitable inhibitor for studying the release of arachidonic acid in intact human platelets.
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PMID:The inhibition of arachidonic acid metabolism in human platelets by RHC 80267, a diacylglycerol lipase inhibitor. 642 15

Molecular mechanisms underlying the ability of heparin to enhance the platelet-aggregating effect of various agonists were studied. Heparin potentiates the aggregating effect of adenosine diphosphate (ADP) and epinephrine, but it is uneffective on the aggregation induced by ristocetin and collagen. Heparin inhibits aggregation induced by thrombin in the presence of plasma, but it is uneffective, or sometimes stimulates aggregation, in the absence of plasma. The effects on the platelet-activating factor- (PAF-acether) induced aggregation are very variable. The late phase of the ADP-induced aggregation is sensitive to proteinase inhibitors, but heparin overcomes this inhibitory effect. Drugs which inhibit remodeling of membrane phospholipids abolish the potentiating effect of heparin, while cyclooxygenase inhibitors do not. The proaggregating effect of heparin subfractions correlates with the lipoprotein lipase activity and, slightly, with the molecular weight, but it does not correlate with the anticoagulant activity. Platelets prelabelled with phosphatidyl[U14C]inositol show a very rapid effect of heparin in triggering phosphatidylinositor breakdown and a cooperative effect with ADP, a known agonist of the 'phosphatidylinositol cycle'. Heparin is also effective in stimulating the labelling of polyphosphoinositides in platelets prelabelled with 32Pi. These results, together with the selective sensitivity to drugs, lead to the conclusion that a stimulatory effect on the very early events of remodeling of membrane phospholipids is involved in the platelet proaggregating effect of heparin.
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PMID:Molecular events involved in the proaggregating effect of heparin on human platelets. 649 25

(1) The isolation and propagation of stromal cells from mature bovine subcutaneous white adipose tissue is described. The cells formed a homogenous population and synthesized collagen Types I and III in a ratio identical to that of bovine lung fibroblasts studied at the same stage of culture development. (2) Unlike lung fibroblasts the adipose tissue stromal cells (fibroblasts) accumulated lipid in the post confluence stage of culture development and lipoprotein lipase activity emerged. The emergence of lipoprotein lipase in these cells was not dependent on insulin in the medium unlike the 3T3-L1 mouse embryo pre-adipocytes studied in parallel. (3) Post-confluence the adipose tissue stromal cells preferentially incorporated more exogenous [14C]acetate into neutral lipids than a preconfluency. This was in distinction to the lung fibroblast cultures in which the ratio of acetate incorporated into neutral and polar lipids remained unchanged throughout. (4) From the data presented and by comparison with similar adipose tissue derived cells from other species it is proposed that mature bovine white adipose tissue contains cells which have the potential to differentiate from a fibroblast towards an adipocyte phenotype.
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PMID:The isolation and characterization of a proposed adipocyte precursor cell type from bovine subcutaneous white adipose tissue. 725 95

Chondroitin sulfate-dermatan sulfate proteoglycans (PG) were isolated from bovine aorta-intima by extraction with 4.0 M guanidinium chloride in the presence of protease inhibitors and purified through cetylpyridinium complexes. The PG were fractionated by CsCl isopyknic centrifugation into three fractions with different chemical composition. The anticoagulant activity of the PG fractions was studied by Stypven time, partial thromboplastin clotting time (PTT), and thrombin time assays. The three PG fractions delayed coagulation in the three assays. The PG fractions did not affect the ADP and collagen-induced platelet aggregation but inhibited the aggregation induced by 0.2 units per ml. of thrombin. The PG fractions released lipoprotein lipase in rabbits when injected, and the enzyme activity released by the major PG fraction was approximately 60 per cent of that of heparin. This PG fraction interacted with serum low density lipoproteins but not with high density lipoproteins. Certain biologic properties are probably due to the presence of dermatan sulfate in the PG fractions. These studies suggest important functional roles for PG in the arterial wall.
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PMID:Studies of biologic properties of proteoglycans from bovine aorta. 735 13


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