Tissue plasminogen activator binds to human vascular smooth muscle cells by a novel mechanism. Evidence for a reciprocal linkage between inhibition of catalytic activity and cellular binding.

Human vascular smooth muscle cells (VSMC) bind tissue plasminogen activator (tPA) specifically, saturably, and with relatively high affinity (K(d) 25 nM), and this binding potentiates the activation of cell-associated plasminogen (Ellis, V., and Whawell, S. A. (1997) Blood 90, 2312-2322). We have observed that this binding can be efficiently competed by DFP-inactivated tPA and S478A-tPA but not by tPA inactivated with H-D-Phe-Pro-Arg-chloromethyl ketone (PPACK). VSMC-bound tPA also exhibited a markedly reduced inhibition by PPACK, displaying biphasic kinetics with second-order rate constants of 7. 5 x 10(3) M(-1) s(-1) and 0.48 x 10(3) M(-1) s(-1), compared with 7. 2 x 10(3) M(-1) s(-1) in the solution phase. By contrast, tPA binding to fibrin was competed equally well by all forms of tPA, and its inhibition was unaltered. These effects were shown to extend to the physiological tPA inhibitor, plasminogen activator inhibitor 1. tPA.plasminogen activator inhibitor 1 complex did not compete tPA binding to VSMC, and the inhibition of bound tPA was reduced by 30-fold. The behavior of the various forms of tPA bound to VSMC correlated with conformational changes in tPA detected by CD spectroscopy. These data suggest that tPA binds to its specific high affinity site on VSMC by a novel mechanism involving the serine protease domain of tPA and distinct from its binding to fibrin. Furthermore, reciprocally linked conformational changes in tPA appear to have functionally significant effects on both the interaction of tPA with its VSMC binding site and the susceptibility of bound tPA to inhibition.     

The Role of Tissue-type Plasminogen Activator in Rat Corpus Luteum

It is here reported for the first time that luteal cells are capable of secreting plasminogen activators(PA),(both tissue-type,tPA,and urokinase-type,uPA),and plasminogen activator inhibitor type-1(PAl-1).Using organ culture model,we have demonstrated that tPA,but not uPA,showed markedchange during luteolytic period in rat corpus luteum.A great amount oftPA was secreted in corpusluteum on D 14 and D 17 while very low level of tPA activity was detected before D 12.Correspondingly,the progesterone production in the corpus luteum increased gradually in a time-dependent manner from D 1 to D 12 but dropped abruptly to a very low level on D 14.Additionof exogenous tPA to the CL culture caused considerable decrease in progesterone secretion whileinclusion of purified monoclone tPA antibodies in the culture augmented progesterone productionof CL.It is therefore suggested that tPA may play an important role in luteolytic process.     

Purification and characterization of a stimulator of plasmin generation from the antiangiogenic agent Neovastat: identification as immunoglobulin kappa light chain

We have recently shown that Neovastat, an antiangiogenic extract from shark cartilage, stimulates the in vitro activation of plasminogen by facilitating the tissue-type plasminogen activator (tPA)-dependent conversion of plasminogen to plasmin. In this report, we describe the purification and characterization of the stimulatory molecules. Neovastat was subjected to a three-step purification procedure including gel filtration, preparative isoelectric focusing, and preparative SDS-PAGE. Two 28-kDa proteins with pIs of approximately 4.5 and 6.5 were purified to apparent homogeneity and identified as immunoglobulin (Ig) kappa light chains by N-terminal microsequencing. Ig light chains do not directly stimulate the activity of tPA or plasmin, suggesting a mechanism of action involving an interaction with plasminogen. Kinetic analysis showed that both Ig light chains accelerate the in vitro tPA-dependent conversion of plasminogen in plasmin by increasing the affinity of tPA for plasminogen by 32- and 38-fold (Km decrease from 456 nM to 12-14 nM). Shark Ig light chains also stimulated the degradation of fibrin by the tPA/plasminogen system in an in vitro assay. A direct interaction between Ig light chains and plasminogen (KA=4.0-5.5 x 10(7) M(-1); KD=18-25 nM) and with tPA (KA=2.8 x 10(7) M(-1); KD=36 nM) was demonstrated using real time binding measured by surface plasmon resonance. Ig light chain is the first molecule associated with the antiangiogenic activity of Neovastat to be purified and identified.     

Kinetic analysis of the interactions between plasminogen activator inhibitor 1 and both urokinase and tissue plasminogen activator

Plasminogen activator inhibitor 1 (PAI-1) was purified from medium conditioned by cultured bovine aortic endothelial cells by successive chromatography on concanavalin A Sepharose, Sephacryl S-200, Blue B agarose, and Bio-Gel P-60. As shown previously for conditioned media (C. M. Hekman and D. J. Loskutoff (1985) J. Biol. Chem. 260, 11581-11587) the purified PAI-1 preparation contained latent inhibitory activity which could be stimulated 9.4-fold by sodium dodecyl sulfate and 45-fold by guanidine-HCl. The specific activity of the preparation following treatment with 0.1% sodium dodecyl sulfate was 2.5 X 10(3) IU/mg. The reaction between purified, guanidine-activated PAI-1 and both urokinase and tissue plasminogen activator (tPA) was studied. The second-order rate constants (pH 7.2, 35 degrees C) for the interaction between guanidine-activated PAI-1 and urokinase (UK), and one- and two-chain tPA are 1.6 X 10(8), 4.0 X 10(7), and 1.5 X 10(8) M-1 S-1, respectively. The presence of CNBr fibrinogen fragments had no affect on the rate constants of either one- or two-chain tPA. Steady-state kinetic analysis of the effect of PAI-1 on the rate of plasminogen activation revealed that the initial UK/PAI-1 interaction can be competed with plasminogen suggesting that the UK/PAI-1 interaction may involve a competitive type of inhibition. In contrast, the initial tPA/PAI-1 interaction can be competed only partially with plasminogen, suggesting that the tPA/PAI-1 interaction may involve a mixed type of inhibition. The results indicate that PAI-1 interacts more rapidly with UK and tPA than any PAI reported to date and suggest that PAI-1 is the primary physiological inhibitor of single-chain tPA. Moreover, the interaction of PAI-1 with tPA differs from its interaction with UK, and may involve two sites on the tPA molecule.     

Regulation of tissue plasminogen activator activity by cells. Domains responsible for binding and mechanism of stimulation

A number of cell types have previously been shown to bind tissue plasminogen activator (tPA), which in some cases can remain active on the cell surface resulting in enhanced plasminogen activation kinetics. We have investigated several cultured cell lines, U937, THP1, K562, Molt4, and Nalm6 and shown that they bind both tPA and plasminogen and are able to act as promoters of plasminogen activation in kinetic assays. To understand what structural features of tPA are involved in cell surface interactions, we performed kinetic assays with a range of tPA domain deletion mutants consisting of full-length glycosylated and nonglycosylated tPA (F-G-K1-K2-P), DeltaFtPA (G-K1-K2-P), K2-P tPA (BM 06.022 or Reteplase), and protease domain (P). Deletion variants were made in Escherichia coli and were nonglycosylated. Plasminogen activation rates were compared with and without cells, over a range of cell densities at physiological tPA concentrations, and produced maximum levels of stimulation up to 80-fold with full-length, glycosylated tPA. Stimulation for nonglycosylated full-length tPA dropped to 45-60% of this value. Loss of N-terminal domains as in DeltaFtPA and K2P resulted in a further loss of stimulation to 15-30% of the full-length glycosylated value. The protease domain alone was stimulated at very low levels of up to 2-fold. Thus, a number of different sites are involved in cell interactions especially within finger and kringle domains, which is similar to the regulation of tPA activity by fibrin. A model was developed to explain the mechanism of stimulation and compared with actual data collected with varying cell, plasminogen, or tPA concentrations and different tPA variants. Experimental data and model predictions were generally in good agreement and suggest that stimulation is well explained by the concentration of reactants by cells.     

Characterization of monoclonal antibodies against human tissue plasminogen activator (tPA): quantitation of free tPA in human cell cultures by an ELISA.

Seven murine monoclonal antibodies produced against tissue plasminogen activator (tPA) were evaluated by means of enzyme-linked immunosorbent assays (ELISAs), and their effects on the enzymatic activities of tPA towards a synthetic substrate (S-2288) and plasminogen were investigated. One of the antibodies, TPA1-70, strongly inhibited the enzymatic activity of tPA in a fibrin agarose plate assay, while it did not affect the enzymatic activity towards the synthetic substrate or plasminogen. The antibody is directed to an epitope on the B-chain of tPA, which is necessary for the formation of a ternary complex of tPA, fibrin and plasminogen, but probably not to the active site. Another antibody, TPA2-14, partially inhibited the enzymatic activities of tPA towards the synthetic substrate and plasminogen, but it was not able to bind to the inactive tPA complexed with plasminogen activator inhibitor-1 (PAI-1). The antibody is directed to an epitope on the second kringle region, which is probably one of the PAI-1 binding sites. This property of the antibody enabled us to develop an ELISA for selective quantitation of free tPA in culture media conditioned with several human cell lines. The results indicate that tPA in these media exists either partially or almost entirely in a complex with PAI-1.     

Oncostatin M induces tissue-type plasminogen activator and plasminogen activator inhibitor-1 in Calu-1 lung carcinoma cells

Oncostatin M (OSM) is a glycoprotein cytokine that is produced by activated T-lymphocytes, monocytes, and macrophages. In a DNA synthesis assay, OSM reduced tritiated thymidine incorporation by 53% in Calu-1 lung carcinoma cells. Radiolabeled cDNAs from untreated Calu-1 cells and 30-h OSM-treated cells were used to probe duplicate nylon membrane cDNA expression arrays. This study revealed OSM-mediated expression of mRNAs encoding tissue-type plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1). Northern blot analysis showed that the steady-state level of tPA mRNA is nearly undetectable in Calu-1 cells. Exposure of these cells to OSM for 30 h increased tPA mRNA expression by 20-fold and PAI-1 mRNA expression by 5-fold. Exposure of these cells to other gp130 receptor family cytokines, including leukemia inhibitory factor (LIF), interleukin-6 (IL-6), and IL-11, do not significantly affect DNA synthesis or induction of tPA/PAI-1. Western blot studies demonstrated that OSM mediates a marked increase in secretion of the tPA protein. Secreted tPA was present in the conditioned medium almost exclusively as tPA/PAI-1 complexes. Inhibitor studies demonstrated that OSM-mediated induction of tPA and PAI-1 mRNAs is largely dependent upon activation of the MEK1/2 pathway. The JAK3/STAT3 pathway potentially serves a secondary role in these regulatory events.     

Zinc-triggered induction of tissue plasminogen activator by brain-derived neurotrophic factor and metalloproteinases

Tissue plasminogen activator (tPA) is necessary for hippocampal long-term potentiation. Synaptically released zinc also contributes to long-term potentiation, especially in the hippocampal CA3 region. Using cortical cultures, we examined whether zinc increased the concentration and/or activity of tPA. Two hours after a 10-min exposure to 300 μM zinc, expression of tPA and its substrate, plasminogen, were significantly increased, as was the proteolytic activity of tPA. In contrast, increasing extracellular or intracellular calcium levels did not affect the expression or secretion of tPA. Changing zinc influx or chelating intracellular zinc also failed to alter tPA/plasminogen induction by zinc, indicating that zinc acts extracellularly. Zinc-mediated extracellular activation of matrix metalloproteinase (MMP) underlies the up-regulation of brain-derived neurotrophic factor (BDNF) and tropomyosin receptor kinase (Trk) signaling. Consistent with these findings, co-treatment with a neutralizing antibody against BDNF or specific inhibitors of MMPs or Trk largely reversed tPA/plasminogen induction by zinc. Treatment of cortical cultures with p-aminophenylmercuric acetate, an MMP activator, MMP-2, or BDNF alone induced tPA/plasminogen expression. BDNF mRNA and protein expression was also increased by zinc and mediated by MMPs. Thus, an extracellular zinc-dependent, MMP- and BDNF-mediated synaptic mechanism may regulate the levels and activity of tPA.     

Expression, purification, and characterization of the recombinant kringle 1 domain from tissue-type plasminogen activator.

A novel fusion protein expression plasmid that allows ready purification and subsequent facile release of the target molecule has been constructed and employed to express in Escherichia coli and purify the tissue plasminogen activator kringle 1 domain ([K1tPA] residues C92-C173). The resulting plasmid encodes the tight lysine-binding kringle (K)1 domain of human plasminogen ([K1HPg]) followed by a peptide (PfXa) containing a factor Xa-sensitive bond, downstream of which [K1tPA] was inserted. The recombinant (r) [K1HPg]PfXa[K1tPA] fusion polypeptide was purified from various cell fractions in one step by Sepharose-lysine affinity chromatography. After cleavage with fXa, the mixture was repassaged over Sepharose-lysine, whereupon the r-[K1tPA]-containing polypeptide passed unretarded through the column. A homogeneous preparation of this material was then obtained after a simple step employing fast protein liquid chromatography. The purified r-[K1tPA], which contained the amino acid sequence SNAS[K1tPA]S, provided an amino-terminal amino acid sequence, through at least 20 amino acid residues, that was identical to that predicted from the cDNA sequence. The molecular mass of r-SNAS[K1tPA]S, determined by electrospray mass spectrometry, was 9621.9 +/- 4.0 (expected molecular mass, 9623.65). 1H-NMR spectroscopy and thermal stability studies of r-SNAS[K1tPA]S revealed that the purified material was properly folded and similar to other isolated kringle domains. Additionally, employment of this methodology revealed that only a very weak interaction between epsilon-aminocaproic acid and the isolated r-[K1tPA] domain occurred.     

Measuring plasminogen activator inhibitor activity in plasma by two enzymatic assays

We compared two methods that measure plasminogen activator inhibitor (PAI) activity in plasma based on the ability of PAI to inhibit tissue plasminogen activator (tPA) or urokinase (uPA) in order to determine which method most accurately measures plasma PAI activity after stressors, like hemorrhage. Plasma PAI activity was significantly elevated after hemorrhage in both assays. Using standard curves derived from rhPAI-1, we found that the tPA-PAI assay was more sensitive than the uPA-PAI assay. However, we measured a 10-fold difference in PAI activity as measured between assays, suggesting that some endogenous plasma constituents (tPA, uPA, plasminogen or plasmin) may interfere with the accurate determination of PAI activity. Increasing the amount of plasma in each assay led to a progressive increase in PAI activity. However, removing either tPA or plasminogen from the tPA-PAI assay unmasked the presence of some endogenous tPA and plasminogen. Furthermore, increasing plasma volume in either assay increases measured plasma tPA, but not uPA. Finally, plasma tPA is elevated after hemorrhage, whereas plasma uPA is not. These results suggest that endogenous tPA and plasminogen may interfere with the measurement of plasma PAI activity in the tPA-PAI assay after hemorrhage or other stresses. The uPA-PAI assay does not have this confounding problem because endogenous uPA does not interfere with the assay, nor does it rise during hemorrhage.     

Binding of tissue plasminogen activator to human aortic endothelial cells.

The experiments described in this paper were designed to examine the specific binding of tissue plasminogen activator (tPA) to cultured human aortic endothelial (HAE) cells. When 125I-labelled tPA was incubated with the cells at 4 degrees C, binding was found to plateau within 90 min after incubations were begun. Binding was saturable and the bound enzyme dissociated from the sites with a half-time of approx. 48 min. Scatchard analyses were performed using tPA molecules isolated from human melanoma and colon cells as well as from C127 and Chinese hamster ovary cells that had been transfected with the human tPA gene. These enzymes showed very similar binding characteristics in spite of the fact that they differ substantially in the types of sugars which comprise their side chains. Neither the chainedness of the molecules (one-chain or two-chain) nor the sites at which they are glycosylated (type I or type II) appear to affect their ability to interact with binding sites. The tPA molecules were found to have an average equilibrium dissociation constant of (1.15 +/- 0.10) x 10(-9) M and HAE cells appeared to have a single, homogeneous population of independent binding sites present at a concentration of (1.57 +/- 0.13) x 10(6) sites per cell. Lowering the pH of the binding buffer from 7.4 to 6.5 resulted in a reversible increase in specific binding of between 2-fold and 7-fold depending upon the particular preparation of cells. Preincubation of tPA with plasminogen activator inhibitor 1 (PAI-1) was found to have little effect on binding, suggesting that tPA interacts at sites distinct from surface-bound PAI-1. No evidence for either internalization or degradation of tPA was observed in assays run at 37 degrees C. This suggests that, like urokinase, tPA remains on cell surfaces for an extended period of time.     

Tissue plasminogen activator mediates amyloid-induced neurotoxicity via Erk1/2 activation

Tissue plasminogen activator (tPA) is the main activator of plasminogen into plasmin in the brain where it may have beneficial roles but also neurotoxic effects that could be plasmin dependent or not. Little is known about the substrates and pathways that mediate plasmin-independent tPA neurotoxicity. Here we show in primary hippocampal neurons that tPA promotes a catalytic-independent activation of the extracellular regulated kinase (Erk)1/2 signal transduction pathway through the N-methyl-D-aspartate receptor, G-proteins and protein kinase C. This results in GSK3 activation in a process that requires de novo synthesis of proteins, and leads to tau aberrant phosphorylation, microtubule destabilization and apoptosis. Similar effects are produced by amyloid aggregates in a tPA-dependent manner, as demonstrated by pharmacological treatments and in wt and tPA-/- mice neurons. Consistently, in Alzheimer's disease (AD) patients' brains, high levels of tPA colocalize with amyloid-rich areas, activated Erk1/2 and phosphorylated tau. This is the first demonstration of an intracellular pathway by which tPA triggers kinase activation, tau phosphorylation and neurotoxicity, suggesting a key role for this molecule in AD pathology.     

Extracellular matrix degradation by cultured mesangial cells: mediators and modulators

Decreased degradation of the glomerular extracellular matrix (ECM) is thought to contribute to the accumulation of glomerular ECM that occurs in diabetic nephropathy and other chronic renal diseases. Several lines of evidence indicate a key role for the plasminogen activator/plasminogen/plasmin system in glomerular ECM degradation. However, which of the two plasminogen activators (PAs) present in renal tissue, tissue plasminogen activator (tPA) or urokinase-type plasminogen activator (uPA), is responsible for plasmin generation and those factors that modulate the activity of this system remain unclear. This study utilized mesangial cells isolated from mice with gene deletions for tPA, uPA, and plasminogen activator inhibitor 1 (PAI-1) to further delineate the role of the PA/plasminogen/plasmin system in ECM accumulation. ECM degradation by uPA-null mesangial cells was not significantly different from controls (92% +/- 1%, n = 12). In contrast, ECM degradation by tPA-null mesangial cells was markedly reduced (-78 +/- 1%, n = 12, P < 0.05) compared with controls, whereas tPA/uPA double-null mesangial cells degraded virtually no ECM. Previous studies from this laboratory have established that transforming growth factor-beta1 (TGFbeta1) inhibits ECM degradation by cultured mesangial cells by increasing the production of PAI-1, the major physiological PA inhibitor. In keeping with this observation, TGFbeta1 (1 ng/ml) had no effect on ECM degradation by PAI-1-null MC. High glucose levels (30 mM) in the presence or absence of insulin (0.1 mM) caused a moderate increase in ECM degradation by normal human mesangial cells. In contrast, glycated albumin, whose concentration is known to increase in diabetes, produced a dose-dependent (0.2-0.5 mg/ml) inhibition of ECM degradation by normal human mesangial cells. Taken together, these results document the importance of tPA versus uPA in renal plasmin production and indicate that in contrast to elevated glucose, glycated albumin may contribute to ECM accumulation in diabetic nephropathy.     

Activators and inhibitors of the plasminogen system in Alzheimer's disease

Accumulation and deposition of Aβ is one of the main neuropathological hallmarks of Alzheimer's disease (AD) and impaired Aβ degradation may be one mechanism of accumulation. Plasmin is the key protease of the plasminogen system and can cleave Aβ. Plasmin is activated from plasminogen by tissue plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA). The activators are regulated by inhibitors which include plasminogen activator inhibitor-1 (PAI-1) and neuroserpin. Plasmin is also regulated by inhibitors including α2-antiplasmin and α2-macroglobulin. Here, we investigate the mRNA levels of the activators and inhibitors of the plasminogen system and the protein levels of tPA, neuroserpin and α2-antiplasmin in post-mortem AD and control brain tissue. Distribution of the activators and inhibitors in human brain sections was assessed by immunoperoxidase staining. mRNA measurements were made in 20 AD and 20 control brains by real-time PCR. In an expanded cohort of 38 AD and 38 control brains tPA, neuroserpin and α2-antiplasmin protein levels were measured by ELISA. The activators and inhibitors were present mainly in neurons and α2-antiplasmin was also associated with Aβ plaques in AD brain tissue. tPA, uPA, PAI-1 and α2-antiplasmin mRNA were all significantly increased in AD compared to controls, as were tPA and α2-antiplasmin protein, whereas neuroserpin mRNA and protein were significantly reduced. α2-macroglobulin mRNA was not significantly altered in AD. The increases in tPA, uPA, PAI-1 and α2-antiplasmin may counteract each other so that plasmin activity is not significantly altered in AD, but increased tPA may also affect synaptic plasticity, excitotoxic neuronal death and apoptosis.     

The effect of polymerised fibrin on the catalytic activities of one-chain tissue-type plasminogen activator as revealed by an analogue resistant to plasmin cleavage

A one-chain recombinant tissue-type plasminogen activator (EC 2.4.31.-) (tPA) analogue was constructed in which Arg-275 of the activation site was changed to Gly by site-directed mutagenesis. This analogue, tPA-Gly275, was very resistant to plasmin (EC 2.4.21.5) cleavage. It has been used to gain information about the activity of the uncleaved one-chain tPA form, also when plasmin is generated as a result of a plasminogen activation reaction. The amidolytic activity of tPA-Gly275 with less than Glu-Gly-Arg-pNA was investigated and compared to that of one-chain and two-chain wild-type recombinant tPA. A small but significant intrinsic amidolytic activity was observed with the analogue as well as the wild-type one-chain tPA form. However, it was much lower than that of two-chain tPA. Polymerised fibrin enhanced the amidolytic activity of both one-chain tPA forms but not of two-chain tPA. Measurements of the plasminogen activation kinetics in the absence of fibrin revealed that tPA-Gly275 possessed a significant intrinsic activity. However, it was 30-fold lower than that of two-chain tPA. Addition of polymerised fibrin profoundly enhanced the plasminogen activation rate of both tPA-Gly275 and wild-type one- and two-chain tPA to approximately the same maximal level. The results were interpreted to mean that fibrin binding can induce an activated state of the intact tPA one-chain form.     

Expression of plasminogen activator and plasminogen activator inhibitor mRNA in human fibroblasts grown on different substrates

mRNA levels for urokinase type plasminogen activator (uPA), tissue type plasminogen activator (tPA), plasminogen activator inhibitor-1 (PAI-1) and plasminogen activator inhibitor-2 (PAI-2) were examined in human diploid (neonatal foreskin) fibroblasts grown in 200-ml microcarrier suspension culture. Four different substrates were used. These included gelatin-coated polystyrene plastic, DEAE-dextran, glass-coated polystyrene plastic and uncoated polystyrene plastic. Our previous studies have shown that culture fluids from diploid fibroblasts grown on DEAE-dextran contained higher levels of plasminogen-dependent fibrinolytic activity than culture fluids from the same cells grown on other substrates. The increased plasminogen activator activity was due largely to elevated amounts of tPA (In Vitro Cell. Develop. Biol. 22: 575–582, 1986). The present study shows that there is a corresponding elevation of tPA mRNA in diploid fibroblasts cultured on DEAE-dextran relative to the other substrates. There does not appear to be any difference in uPA mRNA or in mRNA for PAI-1 or PAI-2 produced by the same cells on the four substrates. These data suggest that the influence of the substrate on plasminogen activator production is mediated at the genetic level.     

A single-step separation of the one- and two-chain forms of tissue plasminogen activator

Preparations of one-chain tissue plasminogen activator (tPA), usually a mixture of 65- and 63-kDa differentially glycosylated forms, contain variable amounts of two-chain tPA. There is no effective procedure currently available for removal of the two-chain contaminant from one-chain tPA preparations. In this report, affinity chromatography on benzamidine-Sepharose was investigated for the separation of two-chain from one-chain tPA. Activase, a preparation of recombinant tPA containing 80% one-chain tPA, a mixture of 65- and 63-kDa variants, and 20% two-chain tPA, was applied to a column of benzamidine-Sepharose, equilibrated with 1 M ammonium bicarbonate. Under this condition, both one-chain and two-chain forms of tPA were adsorbed by the column. Addition of 0.1 M arginine to the equilibration buffer led to elution of two-peaks, corresponding to the 65- and 63-kDa variants of one-chain tPA. Two-chain tPA remained bound to the column, but could be eluted with sodium acetate buffer, pH 4.0, containing 0.1 M arginine. The present procedure allows rapid and effective removal of two-chain tPA with concomitant separation of 65- and 63-kDa one-chain glycoforms from preparations of one-chain tPA. Kinetic analysis for the hydrolysis of D-Ile-Pro-Arg-p-nitroanilide (S-2288) by the highly purified molecular forms of tPA suggests that 63-kDa one-chain tPA possesses 30% higher catalytic efficiency than the 65-kDa variant, while two-chain tPA is 9- or 12-fold more efficient than 63- or 65-kDa one-chain tPA, respectively.     

Biphasic regulation of tissue plasminogen activator activity in ischemic rat brain and in cultured neural cells: essential role of astrocyte-derived plasminogen activator inhibitor-1

In brain, the serine protease tissue plasminogen activator (tPA) and its endogenous inhibitor plasminogen activator inhibitor-1 (PAI-1) have been implicated in the regulation of various neurophysiological and pathological responses. In this study, we investigated the differential role of neurons and astrocytes in the regulation of tPA/PAI-1 activity in ischemic brain. The activity of tPA peaked transiently and then decreased in cortex and striatum along with delayed induction of PAI-1 in the inflammatory stage after MCAO/reperfusion injury. In cultured primary cells, glutamate stimulation increased tPA activity in neurons but not in other cells such as microglia and astrocytes. With LPS stimulation, a model of neuroinflammatory insults, robust PAI-1 induction was observed in astrocytes but not in neurons and microglia. The upregulation of PAI-1 by LPS in astrocytes was also verified by RT-PCR analysis as well as PAI-1 promoter reporter assay. Lastly, we checked the effects of hypoxia on tPA/PAI-1 activity. Hypoxia increased tPA release from neurons without effects on microglia, while the activity of tPA in astrocyte was decreased consistent with increased PAI-1 activity in astrocyte. Taken together, the results from the present study suggest that neurons are the major source of tPA and that the glutamate-induced stimulated release is mainly governed by neurons in the acute phase. In contrast, the massive up-regulation of PAI-1 in astrocytes during subchronic and chronic inflammatory conditions, leads to decreased tPA activity in the later stages of MCAO. Differential regulation of tPA and PAI-1 in neurons, astrocytes and microglia suggest more attention is required to understand the role of local tPA activity in the vicinity of individual cell types.     

Pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates the expression and the release of tissue plasminogen activator (tPA) in neuronal cells: involvement of tPA in the neuroprotective effect of PACAP

Pituitary adenylate cyclase-activating polypeptide (PACAP) and tissue plasminogen activator (tPA) play important roles in neuronal migration and survival. However, a direct link between the neurotrophic effects of PACAP and tPA has never been investigated. In this study, we show that, in PC12 cells, PACAP induced a 9.85-fold increase in tPA gene expression through activation of the protein kinase A- and protein kinase C-dependent signaling pathways. In immature cerebellar granule neurons (CGN), PACAP stimulated tPA mRNA expression and release of proteolytically active tPA. Immunocytochemical labeling revealed the presence of tPA in the cytoplasm and processes of cultured CGN. The inhibitory effect of PACAP on CGN motility was not affected by the tPA substrate plasminogen or the tPA inhibitor plasminogen activator inhibitor-1. In contrast, plasminogen activator inhibitor-1 significantly reduced the stimulatory effect of PACAP on CGN survival. Altogether, these data indicate that tPA gene expression is activated by PACAP in both tumoral and normal neuronal cells. The present study also demonstrates that PACAP stimulates the release of tPA which promotes CGN survival by a mechanism dependent of its proteolytic activity.