Quantitative spectrophotometric assay of renal tissue plasminogen activator

Effect of Semecarpus anacardium nut extract on ECM and proteases in mammary carcinoma rats

The early stages of invasion are characterized by the extracellular proteolysis and the accumulation of specialized extracellular matrix (ECM) scaffold, that are responsible for the development of vascular bed, endothelial cell proliferation and invasion of tumour cells. The ground substance of provisional matrix consists of collagen, elastin, glycoaminoglycans and proteoglycans that facilitate the interaction of tumour cells with the host environment. In the present work, we have studied the influence of Semecarpus anacardium nut milk extract on localized differentials of ECM component and proteases involved in matrix metabolism of tumour tissue. Mammary carcinoma was induced in Sprague Dawley rats with 7,12, dimethyl benz(a)anthracene and treated with S. anacardium nut milk extract administered orally for 14 days. The altered amount of ECM components in tumour tissues was almost reverted back to normal level in the drug treated animals. The activities of reported proteases and glycohydrolases were also decreased on treatment with S. anacardium nut milk extract indicating decreased turnover of the matrix. Also, the factors associated with the matrix turnover and expression of MMP-1, MMP-2, MMP-3, TIMP-1 and TIMP-2 were restored back to near normal values. The stabilization of the ECM with the decreased activity of proteases might inhibit the epithelial-endothelial interaction and tumour cell migration thus, preventing the adjacent invasion and tumour growth and might be regarded as antineoplastic agent which demands further studies.

Stimulation of plasminogen activator and inhibitor in the lymphatic endothelium

Chromogenic assays, immunoblotting, and Northern blot hybridization methods were employed to assess the effects of various agonists on the production of tissue plasminogen activator (t-PA) and plasminogen activator inhibitor type 1 (PAI-1) by the lymphatic endothelium (LEC). Fibrin autography showed that plasminogen-dependent fibrinolytic activity occurred at M(r) of 110 kDa, which represents a complex of tPA with PAI-1, and 65- and 55-kDa bands corresponding to tPA and uPA, respectively. The fractionation of lymph collected from ovine lymphatic vessels also produced a prominent lytic band of approximately 110 kDa, suggesting the formation of PA/PAI complexes in lymph. The stimulation of various agonists produced large-scale increases in tPA mRNA, as shown by Northern blot hybridization analyses. The effects of ECGF, histamine, and LPS on the presence of tPA and on enhancing the levels of mRNA reached maximum activity at 4 h and declined to levels below that of controls by 8 h. However, phorbol-treated cells exhibited reduced levels of tPA mRNA at 4 h, but was significantly increased by 8 h. A large-scale increase in PAI-1 mRNA steady-state levels was also stimulated by the agonists used in these studies. Both the 3.4- and 2.4-kb species of PAI-1 mRNA were increased. These observations demonstrated that tPA and PAI-1 are produced and secreted by LEC monolayer cultures and are also present in lymph.

Characterization of 125I-tissue plasminogen activator binding to cerebellar granule neurons

Mouse cerebellar cells in culture secrete tissue plasminogen activator (tPA) into the culture medium. Fibrin overlays have shown tPA to be associated with granule neurons in these cultures. This cell associated tPA can be displaced by extensive washing of the cells or by a brief lowering of the pH (less than 4), which leads to a loss of fibrinolytic activity by the cells. Incubation of these fibrinolytically inactive cells with exogenously added murine tPA leads to the restoration of the fibrinolytic activity, indicating the presence of tPA binding sites on these granule neurons. Using 125I-tPA, the binding to cerebellar granule neurons is rapid, saturable, specific, high affinity (Kd = 50 pM) and reversible. Both murine and human tPA compete with 125I-tPA for binding, with both murine and human urokinase (uPA) as well as human thrombin and plasminogen fail to compete. Neither the catalytic site nor the carbohydrate moiety of tPA appear to be involved in the binding, since both diisopropyl-fluorophosphate-treated tPA and endoglycosidase-H-treated tPA compete with 12I-tPA for binding. Furthermore, epidermal growth factor does not compete well with tPA for binding even at a 10:1 molar excess, suggesting that the epidermal growth factor-like (EGF) domain of tPA may not be involved in the binding mechanism. Autoradiography and antibody immunofluorescence show the specific tPA binding is to granule neurons in these cultures. Thus, granule neurons possess tPA receptors on their surface, where this protease binds retaining is functional activity and may play a role in cell and axon migration.

Tissue plasminogen activator binding to mouse cerebellar granule neurons

Cultures of dissociated neonatal mouse cerebellar cells secrete primarily tissue plasminogen activator (tPA) and to a lesser extent urokinase plasminogen activator (uPA) into the culture medium. Fibrin overlays have localized plasminogen activator to granule neurons in these cultures; furthermore, this granule cell plasminogen activator activity is blocked by an antibody to tPA. Developmental studies indicate that maximal levels of soluble plasminogen activator in the culture medium preceed the peak of fibrinolytic activity by these cultures, suggesting that secreted PA may bind back to the surface of these granule neurons. Here we show that granule cell-associated tPA can be displaced by a brief pH shock. However, incubation of these fibrinolytically inactive cultures with exogenously added mouse tPA leads to a specific binding of active tPA to granule neurons as visualized by subsequent fibrin overlay. In similar studies mouse uPA, human uPa, and human tPA fail to show fibrinolytic activity associated with the cerebellar culture, whereas mouse tPA fails to bind to cerebellar glial cell cultures. These findings suggest that granule neurons possess binding sites for tPA on their surface, where this protease can retain its functional activity and may play an important role in cell migration or other cell activities.

Effect of proteases and their inhibitors on neurite outgrowth from neonatal mouse sensory ganglia in culture

Developing neurons and Schwann cells have been shown to secrete proteases. The influence of these proteases on neurite outgrowth by cultured sensory ganglia was examined by adding specific protease inhibitors. Neonatal mouse dorsal root ganglia were cultured directly on tissue-culture plastic dishes in serum-free N2 medium with different protease inhibitors. Soybean trypsin inhibitor was found to double the extent of neurite outgrowth by 4 days in vitro. Ovomucoid trypsin inhibitor and leupeptin also increased neurite outgrowth, while alpha 1-antitrypsin, antipain and phenylmethylsulfonyl fluoride elicited a smaller effect. Furthermore, added trypsin or thrombin inhibited neurite outgrowth and the inhibition could be reversed by soybean trypsin inhibitor, while exogenous plasminogen or urokinase were inhibitory only at high concentrations. Thus neurite outgrowth probably requires a closely regulated system of protease secretion and protease inhibitor production.

Normal and malignant cells, including neurons, deposit plasminogen activator on the growth substrata

The results of four different assay methods showed that both normal and malignant plasminogen activator-secreting cells deposited substantial amounts of this protease on tissue-culture substrata, including collagen coatings. The cells studied were Rous sarcoma virus (RSV)-transformed vole fibroblasts, a malignant neural cell line (NG108-15) capable of neurite formation, and normal mouse-regenerating sensory neurons. Deposited plasminogen activator was detected by a fibrin overlay assay at sites from which cells growing on coverslips had been gently dislodged, showing that active enzyme is left beneath cells and in the immediate pericellular area. For neuronal cells, fibrinolytic zones were detected not only at the previous positions of cell bodies but also along the terrain conditioned by neurite extension, suggesting that a trail of plasminogen activator is left behind during growth cone movement. Substratum-bound enzyme could be solubilized in buffers containing sodium dodecyl sulfate (SDS) or Triton X-100 and demonstrated by zymography following electrophoresis or assayed for amidolytic activity with a chromogenic substrate (Kabi S-2251). The results suggest that plasminogen activator may be considered a component of substrate-adhesion material. Secretory proteases deposited directly on matrix molecules would seem strategically positioned to participate in local degradation of components of the extracellular environment.

Photoaffinity labeling of functionally different lysine-binding sites in human plasminogen and plasmin

Photoaffinity labeling of human plasmin using 4-azidobenzoylglycyl-L-lysine inhibits clot lysis activity, while the activity toward the active-site titrant, p-nitrophenyl-p'-guanidinobenzoate, or alpha-casein are maintained. Photoaffinity labeling of native Glu-plasminogen with the same reagent causes incorporation of approximately 1.5 mol label per mol plasminogen. This labeled plasminogen can be activated to plasmin by either urokinase or streptokinase. The resulting plasmin has full clot lysis activity and can be subsequently photoaffinity labeled with a loss of clot lysis activity. The rate of activation of labeled plasminogen by urokinase is increased relative to that of native plasminogen. epsilon-Aminocaproic acid blocks incorporation of photoaffinity label into both plasminogen and plasmin, indicating that the labeling is specific to the lysine-binding sites. The labels are located in the kringle 1+2+3 fragment in either photoaffinity-labeled plasminogen or plasmin. These results indicate that the specific lysine-binding site blocked in plasmin acts in concert with the active-site in binding and using fibrin as a substrate. This clot lysis regulating site is not available for labeling in plasminogen, but is exposed or changed upon activation to plasmin. The different lysine-binding sites labeled in plasminogen may regulate the conformation of the molecule as evidence by an enhanced rate of activation to plasmin.

In situ effector pathways of allograft destruction. 3. Plasminogen activator activity in rat renal allografts

The question of which cell components in a rejecting rat renal allograft secrete plasminogen activator (PA) has been analyzed. Although normal renal parenchymal cells also secreted PA, most of the PA in a renal allograft (and to a lesser extent also in an autograft) was produced by the inflammatory leukocytes. Fractionation at 1 g demonstrated that the inflammatory cell population responsible for the PA production in the allograft sedimented together with the large mononuclear phagocytes (macrophages). Fractions purified for small blast cells and large lymphocytes did not contain any PA activity but they were able to induce resting peritoneal macrophages to produce PA when cocultured in vitro. The results demonstrate that the allograft-infiltrating mononuclear phagocytes are "activated" in the sense that they secrete PA and that the activation of mononuclear phagocytes at the site of inflammation may be partially regulated by the inflammatory lymphoid cells.

A simple spectrophotometric assay of plasminogen activator: comparison with the fibrinolytic method

We describe a simple assay of plasminogen activator in which the enzyme reacts with a mixture of plasminogen and H-D-valyl-L-leucyl-L-lysine-p-nitroanilide for 1 h at 37 degrees C after which the absorbance is measured at 405 nm. The method detects as little as 2 CTA milliunits of activator and is linear over a 100-fold range of enzyme concentration. The new procedure has been used successfully for the assay of activator in breast tumor cytosols, cell culture supernatants, and pleural or ascitic fluids. Thirty-two biological samples have been assayed for plasminogen activator activity with both the spectrophotometric method and a classical fibrinolytic technique using radiolabeled fibrin. Although the two series of results are significantly correlated, the activities measured with the former assay are significantly different from those determined with the latter. It is shown that the spectrophotometric method is, in many respects, superior to the fibrinolytic procedure.