Detection of an unusually stable fibrinolytic inhibitor produced by bovine endothelial cells

Activation of coagulation and fibrinolysis during dengue virus infection

Dengue virus infection can induce mild dengue fever (DF) or severe dengue hemorrhagic fever and dengue shock syndrome (DHF/DSS) in human. The pathogenesis of hemorrhage in dengue virus infection is not fully understood. Since hemostasis depends on the balance between coagulation and fibrinolysis, alternation of some coagulation parameters (platelet count and activated partial thromoboplastin time, APTT) as well as fibrinolytic parameters (tissue plasminogen activator, tPA and plasminogen activator inhibitor-1, PAI-1) were compared in 8 DHF/DSS and 17 DF patients. Patients showed thrombocytopenia, APTT prolongation, and tPA increase in the acute stage of disease, indicating activation of coagulation and fibrinolysis. The activation of coagulation and fibrinolysis in DHF/DSS patients was much more severe than DF patients. In the convalescent stage, a rise of PAI-1 level and platelet count with concomitant decline of tPA level and APTT returned to normal in both DHF/DSS and DF patients. Therefore, the activation of coagulation and fibrinolysis during the acute stage of dengue virus infection is offset by the increase of platelet and PAI-1 during convalescent stage. Taken together, these results suggest that the degree of coagulation and fibrinolysis activation induced by dengue virus infection is associated with the disease severity.

Biologic responses to IFN-alpha administration in humans

Although interferon-alpha (IFN-alpha) was discovered over 40 years ago, it was many years before it was registered as a therapeutic agent. Because of its unique qualities, it has been registered for both antiviral and antitumor indications. In addition to its therapeutic effects in viral diseases and cancer, IFN-alpha interferes with several important physiologic systems. It interacts with the immune system and affects several neuroendocrine and metabolic circuits. The specific mechanisms by which IFN-alpha exerts its therapeutic effects are complex, and it is very difficult to tie the biologic actions of IFN-alpha to specific clinical effects.

Effects of HMG-CoA reductase inhibitor on hemostasis

Clinical trials of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor (statin) therapy have demonstrated improvement in coronary atherosclerosis progression and reduction in risk of cardiovascular events. However, improvement in cardiovascular end-points is incompletely explained by the baseline or treated LDL cholesterol level. The beneficial effects of statins on clinical events may involve nonlipid mechanisms that modify hemostasis. Local activation of platelets and thrombus formation adjacent to atheromatous plaques, especially where ruptured or eroded, are now recognized to be of pathophysiological importance in the acute and chronic clinical expression of coronary heart disease. Thus, favorable effects of statins on hemostasis may be relevant to decreasing or delaying the progression and clinical manifestations of atherosclerosis.

The fibrinolytic enzyme system. Basic principles and links to venous and arterial thrombosis

This article briefly describes some important aspects of the fibrinolytic system, its regulation, and possible disturbances of this system in connection with deep vein thrombosis and myocardial infarction.

Different Effects of Lipopolysaccharide on Plasminogen Activator Inhibitor-1 Production in Aortic Media in Vivo and in Culture

Background: Lipopolysaccharide (endotoxin) has been shown to increase the expression of plasminogen activator inhibitor type-1 (PAI-1) in the vessel wall. Endotoxin is known to increase PAI-1 production in endothelial cells, but its action on smooth muscle cells (SMCs) is presently not clear. In this study we determined the effect of endotoxin on PAI-1 and tissue plasminogen activator (t-PA) production by aortic SMCs in vivo in two animal species, and in culture. Methods: The aortas of Sprague Dawley rats and of New Zealand White rabbits were rapidly excised after parenteral administration of endotoxin. Total RNA was extracted from the aortic media, and PAI-1 and t-PA mRNA levels were quantified after Northern blotting. In addition, cultured rat aortic SMCs were treated with endotoxin. PAI activity in the conditioned medium was determined with a spectrophotometric assay, and total RNA was extracted from the cells and analyzed. Results: A rapid and strong induction in the aortic medi a of PAI-1 mRNA was observed by endotoxin in both rat (50 mg/kg) and rabbit (1 mg/kg). t-PA mRNA was barely detectable and was not increased by endotoxin. Studies in cultured SMCs showed low expression of PAI-1 mRNA under serum-free conditions and little PAI activity in the cell-conditioned medium. Endotoxin did not increase the levels of PAI-1 mRNA nor PAI activity under serum-free conditions. The effect of endotoxin (10 mg/ml) in the presence of 10% (v/v) newborn calf serum on PAI-1 mRNA was negligible; PAI activity, however, increased by 50.3 +/- 7.3% compared with controls. mRNA levels of t-PA and low-density lipoprotein/receptor-related protein/alpha2-macroglobulin receptor also increased after endotoxin administration. PAI activity was identified as PAI-1 by immunoblotting. Fibrin zymography showed that t-PA was present only in complex with PAI-1. Conclusions: A strong increase in PAI-1 gene expression by endotoxin was observed in aortic SMCs in vivo but not in culture. Th is suggests that the effect of endotoxin on SMCs is indirect. The fibrinolytic/proteolytic potential of the SMCs in the vessel wall is likely to have important implications for the migration of cells during vessel wall remodeling, such as neointima formation, during tumor cell metastasis, and for the fate of intramural thrombi.

The role of His(143) for the pH-dependent stability of plasminogen activator inhibitor-1

Using site-directed mutagenesis, His(143) on the alpha-helix F of PAI-1 was substituted by Lys, Asp, Phe and Thr, respectively. The generated single-site changed plasminogen activator inhibitor-1 (PAI-1) mutants were expressed in Escherichia coli and purified by heparin-Sepharose and anhydrotrypsin agarose chromatographies. When compared with wild-type (wtPAI-1), the PAI-1 mutants His143Asp and His143Phe had shorter half-lives at pH 7.5 (1.1 and 1.4 h, respectively, vs. 2 h for wtPAI-1). They also exhibited less pH dependency of their stability, with half-lives at pH 5.5 of 2.5 and 2.2 h, respectively, vs. 18 h for wtPAI-1. However, the PAI-1 mutants His143Lys and His143Thr had similar properties as wtPAI-1 in this respect. In conclusion, our results suggest that His(143) in one way or another might be involved in the pH-dependent stability of PAI-1. However, it seems that the protonation of this particular residue is of less importance. The PAI-1 mutants His143Asp and His143Phe only displayed about 20% of the specific activity obtained for wtPAI-1, because they, to a large extent, act as substrates for tissue-type plasminogen activator.

Regulation of tissue-type plasminogen activator and its inhibitor (PAI-1) by lipopolysaccharide-induced phagocytosis in a Sertoli cell line

The plasminogen activator (PA) system is thought to play a major role in the proteolytic events associated with spermatogenesis. The mechanisms controlling the expression of PA and of its major physiological inhibitor, plasminogen activator inhibitor type-1 (PAI-1), in the seminiferous epithelium are still unknown. In the present study we analyzed the expression of PA and PAI-1 in a murine Sertoli cell line (42GPA9) in response to stimulation by lipopolysaccharides (LPS) used to activate the phagocytic activity of these cells. Immortalized Sertoli cells cultured under basal conditions secreted predominantly tissue-type PA (tPA) as demonstrated by zymographic analysis and the presence of tPA transcripts. In zymographic experiments a larger molecular weight proteolytic band corresponding to the formation of PA-PAI-1 complex was also observed. The stimulation of immortalized Sertoli cells by LPS resulted in both alteration of the apparent tPA molecular weight to a higher form and transient increase in PAI-1 biosynthesis. The phorbol ester TPA stimulates similarly PAI-1 synthesis in the Sertoli cell line, while 8-bromo-cAMP has no effect. These results suggest for the first time the existence of a direct linkage between molecular events triggered by phagocytosis and regulation of tPA and PAI-1 in Sertoli cells.

Cutaneous small-vessel vasculitis

Cutaneous small-vessel vasculitis (CSVV) refers to a group of disorders usually characterized by palpable purpura; it is caused by leukocytoclastic vasculitis of postcapillary venules. CSVV can be idiopathic or can be associated with a drug, infection, or underlying systemic disease. Initially, the pathogenesis of CSVV is immune complex related, but in its later stages different pathogenetic mechanisms may intensify the reaction and lymphocytes may predominate in the infiltrate. Cure requires elimination of the cause (ie, drugs, chemicals, infections, food allergens) when possible, as well as therapy with nonsteroidal antiinflammatory agents, corticosteroids, dapsone, potassium iodide, fibrinolytic agents, aminocaproic acid, immunosuppressive agents (ie, cyclophosphamide, azathioprine, methotrexate, cyclosporine) or even monoclonal antibodies, depending on disease severity.

Expression of extracellular matrix proteins accompanies lesion growth in a model of intimal reinjury

Reinjury of rat arterial lesions induces an increase in lesion size that is not associated with an increase in cell number. In this study, matrix volume was examined after reinjury to preexisting lesions, and the kinetics of matrix gene expression and activity of proteolytic enzymes in the lesion were evaluated. Volume densitometry in intima showed a significant increase in matrix volume 28 days after the reinjury, although no change was observed at 14 days. Three common vascular matrix molecules, alpha1(I)procollagen, tropoelastin, and fibronectin, were expressed highly at 7 days after the reinjury. Expression of tropoelastin remained upregulated for the entire 28 days after the reinjury, whereas alpha1(I)procollagen and fibronectin returned to the control level by 28 days. Protease activity was also increased after reinjury. Within days, a marked increase in urokinase plasminogen activator activity was observed in intima, and this activity decreased to control level by 14 days. The activity of tissue plasminogen activator did not change. The 95-kDa gelatinolytic activity was increased 1 to 2 days after the reinjury, but no change in other gelatinolytic activities was observed. These findings demonstrate that the accumulation of extracellular matrix is important in the increase in lesion size after reinjury and that a balance of matrix synthesis and degradation may explain why no change in matrix volume was detected until 28 days after the reinjury.

Thrombolytic therapy in the treatment of stroke

Approximately 80 to 90% of cerebral ischaemic events that occur within 24 hours of symptom onset are due to atherothrombotic or thromboembolic occlusions. This forms the rationale for the use of thrombolytic agents in patients with acute ischaemic stroke. Early studies determined that recanalisation occurred in approximately 21 to 72% of patients with occluded cerebral arteries after intra-arterial or intravenous administration of streptokinase, urokinase, alteplase (recombinant tissue-type plasminogen activator; rt-PA) or duteplase (a 2-chain rt-PA). Initial reports suggested that frequencies of haemorrhagic transformation and parenchymatous haematoma in the carotid territory were similar whether patients with middle cerebral artery stroke received thrombolysis via intra-arterial or intravenous administration. The Multicentre Acute Stroke Trial-Europe (MAST-E), the Australia Streptokinase (ASK), and the Multicentre Acute Stroke Trial-Italy (MAST-I) trials, which evaluated intravenous streptokinase 1.5 x 10(6) IU in patients with acute ischaemic stroke, were terminated prematurely because of excessive early mortality and symptomatic intracranial haemorrhage in streptokinase recipients compared with those treated with placebo. However, those studies had not been preceded by dose-ranging trials. Intravenous administration of alteplase 0.9 mg/kg within 3 hours [National Institute of Neurological Disorders and Stroke (NINDS) trial], or 1.1 mg/kg within 6 hours [European Cooperative Acute Stroke Study (ECASS)], of symptom onset in patients with acute ischaemic stroke resulted in an absolute 11 to 13% treatment-associated improvement in clinical measurement scales; such as the modified Rankin scale and Barthel index, compared with placebo recipients. In the ECASS trial, those results were limited to a 'target population' restricted to those who satisfied all entry criteria. In both trials, the frequency of symptomatic haemorrhage was greater in patients treated with alteplase than with placebo and reinforced the importance of careful patient selection. Strict patient selection remains central to the success of this approach.

Trends and future developments in the pharmacological treatment of acute ischaemic stroke

Stroke stands as the third leading cause of death. It makes great demands on patients, who must not only survive the complications of the acute stages, but must cope then with the great physical and economic costs of long-term disabilities. Therefore, there is urgent need to establish generally useful regimens for the acute treatment of ischaemic stroke. Three treatment approaches are based upon pathophysiologic concepts derived from experimental work with focal cerebral ischaemia. These include pharmacologic strategies for arterial recanalisation, inhibition of inflammatory processes and neural protection. Focal cerebral ischaemia secondary to occlusion of a brain-supplying artery initiates neuronal and microvascular events, and the simultaneous processes of inflammation which further injure tissue. The use of plasminogen activators to mediate thrombus and lysis in the acute setting has been shown to be clinically beneficial. Further work with arterial reperfusion strategies is under way. Early clinical studies with polymorphonuclear leukocyte-dependent endothelial adhesion receptor antagonists are being completed, but a strategy has yet to emerge. A large effort examining the potential efficacy of agents which may stabilise or protect neurons from ischaemic injury has shown promise in experimental models, and has been translated into clinical trials. Experimental work, and limited clinical experience, have indicated that: (a) the time window for intervention is important in limiting ischaemic and inflammatory injury, and for reducing the risk of haemorrhagic transformation; (b) putative neuroprotective strategies may potentially elongate the time interval for treatment; and (c) limitations from the adverse effects of plasminogen activators and of agents which beneficially affect neuronal dysfunction during ischaemia must yet be overcome. This review surveys pharmacological approaches currently undergoing evaluation which provide the goal of establishing effective strategies for the treatment of patients with acute cerebral ischaemia.

Calcium spirulan as an inducer of tissue-type plasminogen activator in human fetal lung fibroblasts

Calcium spirulan (Ca-SP), a novel sulfated polysaccharide isolated from the blue-green alga Spirulina platensis, has been found to have antiviral and heparin cofactor II-dependent antithrombin activities. We have obtained evidence that Ca-SP is a potent inducer of tissue-type plasminogen activator (t-PA) production. The addition of Ca-SP to a culture of IMR-90 human fetal lung fibroblasts increased t-PA concentrations in the conditioned medium, in a dose- and time-dependent manner, but in the cell lysate, t-PA concentrations were unchanged, suggesting that t-PA induced by Ca-SP is easily secreted into the conditioned medium. The amount of newly synthesized t-PA in IMR-90 cells, as measured by labeling with [35S]methionine and subsequent immunoprecipitation of t-PA from conditioned medium, was significantly increased by Ca-SP-stimulation. However, Ca-SP did not increase the t-PA mRNA levels. As previously reported, thrombin stimulated t-PA gene transcription in IMR-90 cells, and the simultaneous treatment with Ca-SP and thrombin caused further enhancement of t-PA production, in a synergistic manner. It would thus appear that Ca-SP increases t-PA production through post-transcriptional processes. IMR-90 cells also produce plasminogen activator inhibitor type-1 (PAI-1), but Ca-SP showed little effect on the PAI-1 production. H-SP, which was obtained by removing the calcium from Ca-SP, had no effect on the t-PA production. Na-SP, which was prepared by replacement of the calcium with sodium, stimulated the t-PA production similarly to Ca-SP. Thus, Ca-SP specifically induces t-PA production, and the molecular conformation of Ca-SP maintained by Ca or Na may be essential for the stimulation of t-PA synthesis.

Different expression of the plasminogen activation system in renal thrombotic microangiopathy and the normal human kidney

Renal thrombotic microangiopathy is characterized by glomerular and vascular thrombosis. The persistancy of fibrin deposits may result from imbalance between plasminogen activation and inhibition. In the present study, we used immunohistochemistry and in situ hybridization techniques to determine the localization of urokinase-type (u-PA) and tissue-type (t-PA) plasminogen activators, type 1 plasminogen activator inhibitor (PAI-1) and membrane receptor for u-PA (uPA-R) antigen and their sites of synthesis in renal thrombotic microangiopathy (N = 10) as compared to acute tubular necrosis (N = 5) and normal human kidneys (N = 7). We found an induction of PAI-1 and uPA-R expression in glomeruli and in arterial walls in renal thrombotic microangiopathy. In addition, the induction of uPA-R expression was also found in some tubular epithelial cells. In most case, local synthesis of PAI-1 and uPA-R was confirmed by in situ hybridization with the corresponding cDNA probes. In contrast, using similar techniques PAI-1 and uPA-R antigens and messenger RNAs could not be detected in normal kidneys. In both renal thrombotic microangiopathy and normal kidneys, t-PA mRNA was detected in large amounts in all glomeruli and in vascular endothelial cells, but t-PA antigen was only detected in a limited number of glomerular and arterial endothelial cells, whereas it was strongly expressed by all venous endothelial cells. Although u-PA antigen was found in almost all tubular sections, u-PA mRNA was only found in tubular epithelial cells in the deep cortex and the outer medulla. Our results indicate that there is an up-regulation of PAI-1 and u-PA-R expression in the glomeruli and in the arterial walls of thrombotic microangiopathy. The local release of PAI-1 could play a role in the persistancy of fibrin deposition and the further development of fibrotic lesions. Whether uPA-R plays a pathogenic role in the development of glomerular and vascular lesions, or is involved in the repair process of these lesion, remains to be elucidated.

Significance of serine proteinase and matrix metalloproteinase systems in the destruction of human articular cartilage

1. During the destruction of articular cartilage, fibrinolytic enzymes and matrix metalloproteinases (MMP) may contribute to the related pathology. The activities, antigens and messenger RNA (mRNA) levels of urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor-1 (PAI-1) in articular cartilage were measured in patients with no history of joint diseases (control), those with osteoarthritis (OA) classified into osteophyte-formed site (OS) and weight-bearing site (WS), and in patients with rheumatoid arthritis (RA). 2. The uPA content was higher in WS and RA compared to normal. The PAI-1 content was higher in OS and RA compared to normal. Weight-bearing site patients expressed a high uPA mRNA level but a low PAI-1 mRNA level. Osteophyte-formed site patients expressed a low uPA mRNA level but a high PAI-1 mRNA level. 3. The levels of the MMP and mRNA of tissue inhibitors of metalloproteinases (TIMP) were measured in WS, OS, and RA. In WS, the levels of MMP were high and levels of TIMP mRNA expression low. In OS, the levels of TIMP were high and levels of MMP mRNA were low. In RA, the levels of MMP and TIMP mRNA were high. 4. These findings suggest that regulation of fibrinolysis may play an important role in the matrix of articular cartilage with arthropathy.

Biochemical and biophysical studies of reactive center cleaved plasminogen activator inhibitor type 1. The distance between P3 and P1' determined by donor-donor fluorescence energy transfer

Plasminogen activator inhibitor type 1 (PAI-1) is a fast acting inhibitor of plasminogen activators (PAs). In accordance with other serpins, PAI-1 is thought to undergo a conformational change upon reactive center cleavage. In this study we have developed methods to produce and purify reactive center cleaved wild-type PAI-1 and characterized this molecular form of PAI-1 by biochemical and biophysical methods. Incubation with Sepharose-bound trypsin caused cleavage only at the P1-P1' bond in the reactive center and resulted in 39- and 4-kDa polypeptides, strongly held together by noncovalent interactions. Circular dichroism measurements suggest that the reactive center cleavage triggers larger conformational changes than the conversion from the active to the latent form. Cleaved PAI-1 did not bind to either PAs or vitronectin but retained the heparin-binding capacity. To study the structure of cleaved PAI-1 by polarized fluorescence spectroscopy and to measure intramolecular distances, we used cysteine substitution mutants to which extrinsic fluorescence probes were attached. These studies revealed increasing orientational freedom of probes in the P3 and P1' positions upon cleavage. Distance measurements based on fluorescence energy transfer between probes in positions P3 and P1' indicate that these residues are separated by at least 68 +/- 10 A in cleaved PAI-1.

Plasminogen activator system in human coronary atherosclerosis

Altered coronary artery expression of plasminogen activator (PA) system components may predispose to thrombosis and modulate the vascular response to injury. By immunohistochemistry, we studied the expression of PAs (tPA and uPA), their major physiological inhibitor (PAI-1), and a receptor for uPA (uPAR) in human coronary arteries with either pure fibrointimal proliferation (n = 15) or developed atherosclerotic plaques (n = 10). Overall, the degree of staining showed the following rank order: PAI-1 > tPA > uPAR > uPA. A similar pattern was seen in two normal coronary arteries. There were no significant differences in the extent of staining in any vascular compartment between atherosclerotic arteries and those with only fibrointimal proliferation. However, the ratio of intimal to medial expression of tPA (P = .001) and uPAR (P = .004) was significantly increased in atherosclerotic arteries, with a similar trend for uPA (P = .069) but not for PAI-1 (P = .73). Four of 10 atherosclerotic arteries had higher uPAR expression in the intima than in the media, whereas none of the 15 arteries with only fibrointimal proliferation had this pattern (P < .01). Dual labeling studies demonstrated colocalization of all four PA system components in endothelial cells, smooth muscle cells, and macrophages, with a predominance of PAI-1. Thus, coronary arteries with a wide range of vascular pathology express an abundance of antifibrinolytic potential with enhanced local expression of profibrinolytic proteins, mainly within atherosclerotic plaques.

Angiotensin II regulates the expression of plasminogen activator inhibitor-1 in cultured endothelial cells. A potential link between the renin-angiotensin system and thrombosis

Plasminogen activator-inhibitor C-1 (PAI-1) plays a critical role in the regulation of fibrinolysis, serving as the primary inhibitor of tissue-type plasminogen activator. Elevated levels of PAI-1 are a risk factor for recurrent myocardial infarction, and locally increased PAI-1 expression has been described in atherosclerotic human arteries. Recent studies have shown that the administration of angiotensin converting enzyme inhibitors reduces the risk of recurrent myocardial infarction in selected patients. Since angiotensin II (Ang II) has been reported to induce PAI-1 production in cultured astrocytes, we have hypothesized that one mechanism that may contribute to the beneficial effect of angiotensin converting enzyme inhibitors is an effect on fibrinolytic balance. In the present study, we examined the interaction of Ang II with cultured bovine aortic endothelial cells (BAECs) and the effects of this peptide on the production of PAI-1. 125I-Ang II was found to bind to BAECs in a saturable and specific manner, with an apparent Kd of 1.4 nM and Bmax of 74 fmol per mg of protein. Exposure of BAECs to Ang II induced dose-dependent increases in PAI-1 antigen in the media and in PAI-1 mRNA levels. Induction of PAI-1 mRNA expression by Ang II was not inhibited by pretreating BAECs with either Dup 753 or [Sar1, Ile8]-Ang II, agents that are known to compete effectively for binding to the two major angiotensin receptor subtypes. These data indicate that Ang II regulates the expression of PAI-1 in cultured endothelial cells and that this response is mediated via a pharmacologically distinct form of the angiotensin receptor.

Induction of plasminogen activator inhibitor type-1 (PAI-1) by proinsulin and insulin in vivo

BACKGROUND

Fasting hyperinsulinemia (reflected by elevations in immunoreactive "insulin") is typical of patients with non-insulin-dependent diabetes mellitus (NIDDM) and is often associated with obesity and hypertension. The elevated concentrations detected are indicative not only of insulin but also of its immunologically cross-reactive precursors, including proinsulin. Fasting hyperinsulinemia appears to be associated with decreased fibrinolytic activity in blood, which results from increased activity of plasminogen activator inhibitor type-1 (PAI-1), a potential independent risk factor for coronary artery disease. Patients who were given proinsulin in a previous clinical study by others exhibited an increased incidence of cardiovascular events. Thus, a "proinsulin-PAI-1 axis" may predispose to coronary thrombosis. To define the possible presence of such an axis, this study was designed to determine whether insulin, its precursors, or both increase the concentrations of PAI-1 in rabbits in vivo.

METHODS AND RESULTS

Equimolar proinsulin (n = 10), insulin (n = 11), C-peptide (n = 4), or vehicle alone (n = 10) was administered intravenously over 1 hour to euglycemic, conscious rabbits. Plasma PAI-1 activity increased 3.8-fold with proinsulin (P = .002) and 3.6-fold with insulin (P = .002). By contrast, no increase occurred after C-peptide or vehicle was administered. The increased PAI-1 activity was shown to be attributable to PAI-1 protein by reverse fibrin autography. As judged from changes in mRNA in tissues, proinsulin and insulin increased PAI-1 gene expression within 3 hours by 2.1- and 2.1-fold, respectively, in aorta (P = .025 each) and by 1.9- and 2.4-fold in liver (P = .015 and P = .001), with return of values to baseline within 24 hours (n = 4 experiments in each case).

CONCLUSIONS

These results extend our previous observations from studies in vitro and suggest that hyperinsulinemia attributable to augmented concentrations of proinsulin and insulin in plasma increase plasma PAI-1 activity and may contribute to acceleration of atherosclerosis and impairment of coronary thrombolysis in patients with NIDDM.

Overexpression of plasminogen activator inhibitor 2 in human melanoma cells inhibits spontaneous metastasis in scid/scid mice

A metastatic human melanoma cell line that produces urokinase-type plasminogen activator was stably transfected with cDNA encoding human plasminogen activator inhibitor 2 (PAI-2). Transfected clones expressed PAI-2 at levels two to nine times higher than both the parental cell line and mock transfectants, as detected by ELISA of cell lysates and conditioned medium. The clone with the highest PAI-2 expression exhibited complete inhibition of soluble and cell-surface-bound plasminogen activator activity. The level of PAI-2 overexpression in these clonal cell lines correlated positively with the inhibition of their ability to degrade extracellular matrix in vitro. Parental, mock-transfected, and PAI-2-transfected cell lines produced rapidly growing tumors when injected s.c. into the skin of mice with severe combined immunodeficiency. The tumors producing the highest levels of PAI-2 were surrounded by a dense tumor capsule. Both parental cells and mock-transfected cells invariably metastasized from s.c. tumors to lymph nodes and lungs of mice. PAI-2-transfected cell lines produced significantly less or no metastases. Taken together, these data indicate a critical role for plasminogen activator activity in melanoma invasion and metastasis.

Insulin sensitivity is not an independent determinant of plasma plasminogen activator inhibitor-1 activity

It recently has been hypothesized that increased plasma plasminogen activator inhibitor-1 (PAI-1) activity could be a possible link between insulin resistance and coronary heart disease. However, it is not known whether insulin sensitivity per se is a determinant of plasma PAI-1 activity or whether other intermediates could explain this association. We investigated the relationship between plasma PAI-1 activity and insulin sensitivity, obesity, distribution of body fat, blood pressure, plasma insulin concentration, and serum lipid levels in normoglycemic men (n = 61) and women (n = 77) 53 to 61 years old who participated in a previous population-based study. Insulin sensitivity was estimated by the minimal model from a frequently sampled intravenous glucose tolerance test. In univariate analyses, PAI-1 correlated positively with body mass index, waist-to-hip ratio (WHR), fasting and 2-hour insulin levels, and triglyceride level in both men and women. Furthermore, in women PAI-1 correlated inversely with high-density lipoprotein (HDL) cholesterol level. There was an inverse relationship between PAI-1 and insulin sensitivity (r = -.39, P < .01 in men; r = -.38, P < .001 in women). In multivariate analyses in men, insulin sensitivity failed to show any significant association with PAI-1. In contrast, triglyceride level and body mass index were independently associated with PAI-1. Also in women, insulin sensitivity was not independently associated with PAI-1. In women, WHR and HDL cholesterol concentration or WHR and 2-hour insulin concentration were independently related to PAI-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Activities, localizations, and roles of serine proteases and their inhibitors in human brain tumor progression

The plasminogen activation system consists of plasminogen activators and their inhibitors, serine proteases, and serpins. The proteases and inhibitors regulate a variety of processes in tissue morphogenesis, differentiation, cell migration, and cancer cell invasiveness and metastasis. One of the plasminogen activators, urokinase-type plasminogen activator (uPA), binds to a specific surface and provides a localized cell surface proteolytic activity required for the destruction of extracellular matrix, which is a vital step in tumor cell invasion. The proteolytic activity of uPA is modulated by its cell surface receptor, as well as by plasminogen activator inhibitor type-1 (PAI-1) and, to a lesser degree, by other inhibitors. The role of plasminogen activators and their inhibitors in cancer invasion can be demonstrated in the development and progression of malignant brain tumors. Our findings indicate that uPA and PAI-1 expression are dramatically upregulated in malignant brain tumors in parallel with the histological progression of the tumors. The results suggest that these molecules may contribute to tumor invasion in addition to their significant role in angiogenesis. An evaluation of the plasminogen activation system could add diagnostic and prognostic significance to the evaluation of individual patients.

Inhibition of the effects of rheumatoid synovial fluid cells on chondrogenesis and cartilage breakdown in vitro: possible therapeutical conclusions. A morphological--biochemical study

Short-term co-cultivation of blastemal cells from 12-day-old mouse limb buds and human rheumatoid synovial fluid cells in high density cultures (Trowell culture system) resulted, depending on when co-cultivation started, either in (1) an inhibition of chondrogenesis (co-cultivation right from the start) or in (2) an extensive breakdown of cartilaginous matrix (co-cultivation after formation of embryonic cartilage). These synovial effects were markedly impeded if Avarol (a dioxygenase inhibitor) was applied singly or in combination with PAI-2 (a u-PA-inhibitor). PAI-2 alone, however, had no effect on the synovial-induced inhibition of chondrogenesis, but produced a pronounced inhibitory effect on matrix breakdown. The effects of both inhibitors were studied electron microscopically and biochemically (determination of sulfated-glycosaminoglycans in the high density cultures by Alcian Blue binding assay). The results of this study are consistent with the presumption that rheumatoid synovial cells are capable of inhibiting chondrogenesis and enhancing the breakdown of the cartilaginous matrix. Amongst others, the possible mediators involved are prostaglandins and plasminogen activators. The response to the inhibitors Avarol and PAI-2 is compatible with their mode of action. The chondroprotective action of these substances may be useful in developing potential antirheumatic drugs.

Glomerular fibrinolytic activity in anti-GBM glomerulonephritis in rabbits

Fibrin is an important mediator of injury in severe proliferative forms of glomerulonephritis (GN). Normal glomeruli express fibrinolytic activity, which may protect against the injurious effects of fibrin deposition. Changes in glomerular fibrinolytic activity (GFA) may play an important role in modulating fibrin accumulation in GN. To study the changes in GFA associated with fibrin deposition in GN, autologous phase anti-glomerular basement antibody initiated GN (anti-GBM GN) was studied in rabbits. Net GFA was significantly reduced in association with glomerular fibrin deposition (1.3 +/- 0.8 ng fibrin lysed/10(3) glomeruli/2 hr, normal 57.1 +/- 25.4 ng fibrin lysed/10(3) glomeruli/2 hr, P < 0.02). Reduced GFA in fibrin associated GN was associated with decreased expression of tissue type plasminogen activator (tPA) and increased expression of plasminogen activator inhibitor type-1 (PAI-1) and glomerular macrophage infiltration. In a fibrin independent model of anti-GBM induced GN (heterologous phase), with equivalent injury (proteinuria), net GFA was increased (174 +/- 64 ng fibrin lysed/10(3) glomeruli/2 hr). This was associated with increased tPA and uPA, and decreased PAI-1 in the absence of significant macrophage infiltration. These studies demonstrate that fibrin deposition in GN is associated with a net reduction of GFA, attributable to reduced expression of plasminogen activators and augmentation of PAI-1. Reduction of GFA may potentiate glomerular fibrin deposition and consequent glomerular injury. The association between glomerular macrophage influx and reduction in GFA suggests that this change may be directed by macrophages.

Differential expression of plasminogen activators and their inhibitors in an organotypic skin coculture system

Using immunohistochemistry and in situ hybridization, we have characterized the expression and localization of components of the plasminogen activator proteolytic cascade in an organotypic coculture system which consists of a “dermal” portion (human dermal fibroblasts throughout a collagen matrix) and a stratified, well-differentiated epidermal portion. Specifically, the following components were examined: the enzymes urokinase-type plasminogen activator and tissue-type plasminogen activator and their type 1 and type 2 inhibitors. Urokinase plasminogen activator mRNA and antigen were found predominantly in the least differentiated, basal keratinocytes; in some fields there was also faint deposition of antigen beneath the basal cells. The distribution of plasminogen activator inhibitor type 1 was similar to that of urokinase, except that inhibitor type 1 antigen deposition beneath the basal cells appeared more intense and uniform. In contrast to the results with urokinase plasminogen activator and inhibitor type 1, tissue plasminogen activator mRNA and antigen were localized focally in the suprabasal, i.e. more differentiated, keratinocytes. Plasminogen activator inhibitor type 2 mRNA and antigen were detected in most epidermal layers, but were more intense suprabasally and often spared the basal layer. These studies demonstrate that the same type of cell, i.e. the keratinocyte, can express different components of the plasminogen activator cascade depending on its state of differentiation. The change in expression of plasminogen activator cascade components with keratinocyte differentiation suggests distinct epidermal functions for these components, related to cell-matrix interaction and epidermal differentiation.

Plasminogen activator in human tears

Measurements were made of the nature and levels of plasminogen activator in human tears using, as a model of inflammation, patients undergoing cataract surgery. Tissue plasminogen activator (t-PA) but not urokinase plasminogen activator (u-PA) was found in tears. A wide variation in the range of t-PA in pre-operative tears was found. In those patients not receiving per-operative subconjunctival betamethasone a significant rise in t-PA was found in tears on the first post-operative day over pre-operative levels. A significant fall was noted in those receiving per-operative subconjunctival betamethasone.

A substrate-like form of plasminogen-activator-inhibitor type 1. Conversions between different forms by sodium dodecyl sulphate

Recombinant plasminogen-activator-inhibitor type 1 (PAI-1) purified in an active form from Escherichia coli and eucaryotic cells was found to contain a mixture of three functionally distinct forms: an active form that forms complexes with plasminogen activators (PAs), an inactive (latent) form that remains intact after incubation with PAs, and a substrate-like form which is easily cleaved by PAs. Since active PAI-1 purified from bacteria (rpPAI-1) contains only trace amounts of the inactive latent and the substrate-like forms, this material was used to study the effect of sodium dodecyl sulphate (SDS) on the structure and function of active PAI-1. After treatment with 0.01% SDS, active rpPAI-1 was converted to an inactive form that did not form complexes with PAs, but exhibited characteristics similar to those of latent PAI-1. After treatment with 0.1% SDS, PAI-1 lost its inhibitory activity and was cleaved as a substrate in the reactive center. Circular dichroism spectral analysis reveals that SDS changed the conformation of PAI-1 dramatically, mainly by increasing its alpha-helical content.

Opposite and independent actions of cyclic AMP and transforming growth factor beta in the regulation of type 1 plasminogen activator inhibitor expression

We have investigated the mechanisms by which type 1 plasminogen activator inhibitor (PAI-1) is regulated by transforming growth factor beta (TGF-beta) and by epidermal growth factor (EGF) in CCL64 mink lung epithelial cells, BSC-1 monkey kidney epithelial cells, mouse embryo fibroblast (AKR-2B 84A) cells and normal rat kidney fibroblasts (NRK). TGF-beta increases PAI-1 expression in all four cell lines, and EGF acts synergistically with TGF-beta to increase PAI-1 expression in CCL64 cells but not in the other three cell lines. Here we show that PAI-1 expression can be regulated independently through two different signal transduction pathways. One pathway involves protein kinase C and is stimulated by the tumour promoter phorbol myristate acetate (PMA). Whereas preincubation with PMA completely eliminated PMA-induced PAI-1 synthesis and secretion in both CCL64 and BSC-1 cells, this treatment had no effect on TGF-beta- and EGF-induced PAI-1 levels. Therefore we conclude that protein kinase C does not mediate the effects of either EGF or TGF-beta on PAI-1 expression. The expression of PAI-1 was decreased by agents increasing intracellular cyclic AMP: (cAMP) cholera toxin, forskolin and dibutyryl cAMP lowered both the basal level and the TGF-beta- and PMA-induced levels of PAI-1 expression. These effects of cAMP-elevating agents and of TGF-beta on PAI-1 protein synthesis were also reflected in changes in TGF-beta-induced PAI-1 gene transcription, as measured by nuclear run-on. These results show that PAI-1 gene expression is sensitive to high levels of intracellular cAMP and that this effect occurs at the transcriptional level. Although increased intracellular cAMP concentrations decrease the absolute level of PAI-1 expression, the ability of TGF-beta and EGF to induce PAI-1 gene expression is unchanged. These results are discussed in relation to the observation that sensitivity to cAMP is a common feature of TGF-beta-regulated genes.

Clonal variation of expression of the genes coding for plasminogen activators, their inhibitors and the urokinase receptor in HT1080 sarcoma cells

The human sarcoma cell line HT1080 was found, by in situ hybridization, to consist of cells expressing various levels of urokinase (uPA) and tissue type (tPA) plasminogen activator (PA) suggesting clonal variation of expression of these genes. Colonies originating from single HT1080 cells were, therefore, established and screened for PA activity using a fibrin agarose overlay. Colonies inducing lysis (clone C+ and H+) or no lysis (clones B- and M-) were isolated and tested for mRNA levels of uPA, tPA, uPA receptor (uPAR) and the 3 PA inhibitors (PAI), PAI-1, PAI-2 and protease-nexin I. The different clones revealed considerable variation of expression of the different PA and PAI genes, with lysis-inducing clones expressing mainly the PA genes, whereas non-lysing clones demonstrated higher expression of the PAI genes. Amplification or loss of specific genes was excluded by Southern blotting. The protein levels of cellular and secreted PA and PAI determined by ELISA and Western blots demonstrated a pattern similar to that observed for PA and PAI mRNA concentrations, suggesting clonal differences either on the level of transcription or in RNA processing and/or stability. Due to complex interactions between PA and PAI, neither mRNA nor protein levels of the different genes were predictive for the amount of functional PA activity present in the supernatant or on the cell surface of the different clones. Receptor-bound uPA activity was found to be considerably higher in lysis-inducing than in non-lysing clones and the activity was dependent on neutralization by PAI-1 rather than on the level of uPAR mRNA.

Cultured rat aortic vascular smooth muscle cells digest naturally produced extracellular matrix. Involvement of plasminogen-dependent and plasminogen-independent pathways

Vascular smooth muscle (VSM) cell migration and proliferation play a major role in the development of atherosclerotic lesions, graft occlusion, and restenosis after angioplasty. Cell migration implies the digestion of the surrounding extracellular matrix. Cell-associated proteolysis has been extensively studied in neoplastic and inflammatory cells, but very little is known about the proteolytic properties of VSM. We have evaluated the ability of rat cultured VSM cells to solubilize [3H]amino acid-labeled extracellular matrices produced by bovine VSM. When plated at a density of 30,000 cells per well in 24 multiwell plates, VSM cells were able to solubilize 63.3 +/- 7.0% of the extracellular matrix after 10 days in culture. Extracellular matrix digestion occurred also when the cells were cultured in plasminogen-depleted serum but was higher in the presence of 10 micrograms/ml purified plasminogen (net percent digestion after the subtraction of the appropriate control, 8.6 +/- 3.0% versus 21.2 +/- 3.5% after 3 days in culture, p less than 0.005, respectively). The involvement of other enzymes in addition to plasmin is confirmed by the ability of VSM cells to degrade extracellular matrices from which the plasmin-sensitive component was removed with plasmin pretreatment. Rat VSM cells were able to solubilize 52.3 +/- 2.0% of this residual extracellular matrix-associated radioactivity after 6 days in culture versus 26.1 +/- 1.5% in the control dishes (p less than 0.01, n = 5). Cell contact was required for extracellular matrix degradation: cell-conditioned medium did not have any effect on extracellular matrix digestion.(ABSTRACT TRUNCATED AT 250 WORDS)

Tumor necrosis factor alpha increases antifibrinolytic activity of cultured human mesangial cells

Tumor necrosis factor alpha (TNF alpha) is likely to exert a major influence in the pathogenesis of glomerulopathies. Besides its proinflammatory properties. TNF alpha interacts with cell growth and synthesis of components of the fibrinolytic system. In this study, we report the effects of recombinant human TNF alpha on the synthesis of tissue-type plasminogen activator (t-PA) and its inhibitor (PAI-1) by human mesangial cells in culture. We first demonstrate that TNF alpha binds specifically to a single class of high affinity receptors (Kd 5.10(-11) M; 1500 receptors/cell). TNF alpha has an antimitogenic effect on human mesangial cells since it decreased DNA synthesis, measured by 3H-thymidine incorporation, in a dose-dependent manner. Release of cytosolic LDH and incorporated 51Cr was not increased by 100 ng/ml TNF alpha as compared with control, indicating that this monokine is not cytotoxic for cultured human mesangial cells. Zymographic analysis and reverse fibrin autography disclosed a 120 kD t-PA-PAI-1 complex and a 50 kD free form of PAI-1 in the supernatants of both unstimulated and TNF-stimulated cells; PAI-1 was released in excess and free t-PA was not observed. TNF alpha (0 to 100 ng/ml) had no effect on t-PA synthesis, but enhanced PAI-1 release in a time- and dose-dependent manner (97% increase of PAI-1 synthesis after a 24 hour incubation). This effect was abolished by cycloheximide, suggesting that protein synthesis was required. Northern blot analysis showed that TNF alpha increased the steady-state PAI-1 mRNA levels in a time-dependent manner, with a maximal effect at two hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma t-PA and PAl-1 antigen concentrations in non-insulin dependent diabetic patients: effects of treatment modality on fibrinolysis

Basal plasma tissue type plasminogen activator (t-PA) and plasminogen activator inhibitor type 1 (PAl-1) antigen levels were studied in 49 non-insulin dependent diabetic patients (23 men, 26 women: ages 51.3 +/- 14.9 years) and 16 age matched non-diabetic subjects (9 men, 7 women: ages 49.8 +/- 12.2 years) as a control group. Compared to a control group, the diabetic patients had a significantly higher mean t-PA antigen (5.15 +/- 3.02 vs 3.20 +/- 2.30 ng/ml) and PAl-1 antigen (35.89 +/- 18.59 vs 17.60 +/- 15.36 ng/ml) levels (p < 0.05). Plasma t-PA antigen level was not influenced by each treatment modality. There was a significant decrease of plasma PAl-1 antigen level after Metformin administration compared to that of before Metformin administration (39.74 +/- 19.39 vs 25.14 +/- 16.18 ng/ml) (p < 0.05), and the insulin-treated group showed a tendency for a decrease of plasma PAl-1 antigen levels after insulin administration but this did not reach statistical significance (29.93 +/- 15.37 vs 17.32 +/- 10.60 ng/ml). Sulfonylurea did not change both plasma t-PA and PAl-1 antigen levels. In conclusion, diabetic patients have high t-PA and PAl-1 antigen levels. Biguanide reduced plasma PAl-1 antigen levels, which might play some helpful role in the improvement of chronic complications in NIDDM.

Plasminogen activator inhibitor type 1 production by rat type II pneumocytes in culture

Co-secretion of plasminogen activator inhibitor type 1 (PAI-1) and urokinase-type plasminogen activator was identified in short-term cultures of primary type II pneumocytes isolated from adult rats. After separation by sodium dodecyl sulfate (SDS)-PAGE and reverse fibrin autography (reverse FA) of serum-free conditioned medium (SFCM), cellular lysate, and extracellular matrix (ECM), the inhibitor was seen as a zone of spared lysis at an apparent molecular mass of 46 to 48 kD. The plasminogen activator (PA) activity could only be visualized when human instead of bovine fibrin was used in the indicator gel. It presented as a single band of lysis at an apparent molecular mass of 45 kD when tested by regular FA and was found adjacent to PAI-1 when examined by reverse FA. Immunoblot analysis of type II pneumocyte SFCM, cellular lysate, and ECM revealed two bands at 46 and 48 kD, consistent with the apparent molecular masses (Mr) reported for rat PAI-1 from HTC hepatoma cells. Type II pneumocyte PAI-1 formed SDS-resistant complexes with tissue-type and urokinase-type plasminogen activator and was found to be stable to acid, to short-term exposure to heat, and to the denaturants guanidine HCl and SDS, while being sensitive to treatment with alkali and urea. When levels of type II pneumocyte PAI-1 activity were monitored over time during short-term culture conditions, the level of PAI-1 in SFCM remained stable, whereas activity in the lysate accumulated and activity in the ECM declined.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical properties of vascular endothelial cells

Present knowledge in the field of vascular endothelial cells is reviewed. The role of endothelial cells in the synthesis of matrix proteins and glycosaminoglycans is described. Endothelial cells play a considerable role in the processes of coagulation and fibrinolysis. They also interact with neurotransmitters and vasomotoric substances, and participate in inflammation and immunological responses. They produce several different growth factors. Their role in lipoprotein metabolism is of special importance to research into atherosclerosis.

Stimulating effect of oxidized low density lipoproteins on plasminogen activator inhibitor-1 synthesis by endothelial cells

Oxidized low density lipoproteins (ox-LDL) are thought to accelerate atherogenesis. It was recently demonstrated that patients with coronary heart disease have defects in plasma fibrinolysis due to increased plasminogen activator inhibitor-1 (PAI-1) levels. Investigation of PAI-1 synthesis by endothelial cells may allow insight into the effect of native LDL (N-LDL) and ox-LDL on endothelial cells. In the present study, secretion of PAI-1 by human umbilical vein endothelial cells (HUVEC) in culture was evaluated after incubation with N-LDL and ox-LDL. Ox-LDL were obtained by peroxidation under ultraviolet radiation, which induced compositional changes in LDL, namely, a decrease in the levels of arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid, and alpha-tocopherol and an increase in the malondialdehyde content. Ox-LDL induced a dose-dependent increase in PAI-1 secretion by HUVEC as assayed by an enzyme-linked immunosorbent assay. After a 24-hour incubation, a twofold increase in the PAI-1 content was observed with 50 micrograms/ml ox-LDL protein. Studies with inhibitors of protein synthesis and metabolic labeling with [35S]methionine confirmed that PAI-1 synthesis was stimulated by ox-LDL. N-LDL had no detectable effect on PAI-1 secretion. Binding studies with radiolabeled lipoproteins showed that the effect of ox-LDL was independent of the B/E receptor. Our experiments indicate that ox-LDL stimulate PAI-1 secretion from HUVEC and that this effect may involve a scavenger receptor.

Differential expression of urokinase-type plasminogen activator and its type-1 inhibitor during healing of mouse skin wounds

The expression of urokinase-type plasminogen activator (u-PA) and its type-1 inhibitor (PAI-1) was examined in vivo in mouse wounds by in situ hybridization and immunohistochemistry. u-PA mRNA was present in both basal and suprabasal keratinocytes in the regenerative epithelial outgrowths at the edge of the wounds. In the same area, PAI-1 mRNA was only present in the basal keratinocytes. u-PA protein was detected in keratinocytes in several layers of the epithelial outgrowth, whereas PAI-1 protein was confined to the basal keratinocytes and to the area of the basal membrane. The two proteins and their mRNA were not detected in normal epidermis or in normal-looking epidermis adjacent to the wounds. Fibroblast-like cells and fairly large stellate cells (possibly macrophages) in the granulation tissue underneath the wound contained both the two proteins and their mRNA. The large stellate cells, showing a strong hybridization signal for PAI-1 mRNA, were especially abundant at the border between the necrotic wound and the newly formed granulation tissue. The specificity of these results was supported by the use of two different non-overlapping antisense probes, sense mRNA probes, antibody preparations preabsorbed with purified proteins, and Northern analysis of tissue extracts. The localized and regulated expression of u-PA and PAI-1 seen in this study may reflect that plasminogen activation plays a role in the migration of keratinocytes and connective tissue cells during reepithelialization and tissue remodeling in wound healing.

Stable cell line of T-SV40 immortalized human glomerular visceral epithelial cells

Human subcultures (third passage) of glomerular visceral epithelial cells (VEC) isolated from one month old kidney were successfully transfected by two recombinant plasmids containing the cloned oncogenes from the simian virus 40 large T antigen and H-ras gene. One postcrisis cell clone (56/10 A1) was selected, propagated and characterized. One hundred percent of the 56/10 A1 cells (current passage greater than 100th; doubling time 30 hrs) expressed the nuclear T-SV40 antigen assayed by IF; the cells failed to express H-ras (RNA blot analysis). Immortalized cells were morphologically and phenotypically compared to parental cell type (third passage). Phenotypic characterization of the 56/10 A1 cells was achieved using indirect immunofluorescence (IF) and immunogold silver staining coupled to bright field and epipolarization microscopy. Both parental and 56/10 A1 cells displayed positivity for cytokeratin, CALLA and PHM5, whereas von Willebrand factor was not detected in the two cell types. Since we have previously shown that human glomerular epithelial cells in culture synthetize plaminogen activator (PA) related compounds, we investigated the secretion pattern of these products in parental and transfected cells. Zymographic analysis of secreted PA related compounds revealed production of free urokinase (u-PA) and type 1 plasminogen activator inhibitor (PAI-1) complexed to tissular plasminogen activator (t-PA). Finally, in the transfected cells, increased cGMP generation under atrial natriuretic factor (ANF) stimulation agreed with previous work performed on nontransfected human VEC. In conclusion, the establishment of a human permanent cell line which retains most of the phenotypic features of parental glomerular visceral epithelial cells should represent a new tool to study human glomerular cell functions.

Regulation of murine type 1 plasminogen activator inhibitor gene expression in vivo. Tissue specificity and induction by lipopolysaccharide, tumor necrosis factor-alpha, and transforming growth factor-beta

The regulation of type 1 plasminogen activator inhibitor (PAI-1) gene expression was studied in vivo employing a murine model system. Nuclease protection analysis revealed relatively high concentrations of PAI-1 mRNA in the aorta, adipose tissue, heart, and lungs of untreated CB6 (BalbC X C57B16) mice. Treatment of CB6 mice with LPS, TNF-alpha, or transforming growth factor-beta (TGF-beta) increased the steady-state levels of PAI-1 mRNA within 3 h in all tissues examined. However, the greatest responses to TGF-beta were observed in adipose tissue and the kidney, while LPS and TNF-alpha strongly stimulated PAI-1 gene expression in the liver, kidney, lung, and adrenals. In C3H/HeJ mice, which exhibit defective TNF-alpha release in response to LPS, the response of the PAI-1 gene to LPS was severely attenuated. However, injection of these mice with TNF-alpha increased PAI-1 mRNA in a tissue-specific pattern strikingly similar to that observed in LPS-treated CB6 mice. These results demonstrate that the PAI-1 gene is regulated in a complex and tissue-specific manner in vivo, and suggest a role for TNF-alpha in the response of the PAI-1 gene to sepsis.

Differential protease expression by cutaneous squamous and basal cell carcinomas

To assess the postulated role of plasminogen activation in tumor invasion, we have investigated the cellular sites of synthesis for urokinase-type (uPA) and tissue-type (tPA) plasminogen activators and their inhibitors (PAI-1 and PAI-2) in two human cutaneous neoplasia that differ in their metastatic potential. The combined use of zymography on tissue sections and in situ hybridization demonstrates that uPA is produced by malignant cells of squamous cell carcinomas (SCC) but not by basal cell carcinomas (BCC), whereas tPA is detected exclusively in nonmalignant dermal tissue. In addition, we show that SCC neoplastic cells simultaneously produce variable amounts of PAI-1, and that PAI-1 production correlates inversely with uPA enzymatic activity. These observations establish that invasive human malignant cells in vivo can activate plasminogen through uPA production during the early phases of tumor growth; they also demonstrate that the proteolytic activity of tumor cells can be modulated by the concomitant production of PAI-1. Because SCC have a higher invasive and metastatic potential than BCC, our findings lend further support to the involvement of plasminogen activation in malignant behavior.

Role of tissue remodeling in mammary epithelial cell proliferation and morphogenesis

Lactation is a physiological process characterized by the secretion of large quantities of protein, carbohydrate, and lipid. To achieve the production, the mammary gland must grow and then differentiate; both processes require extensive tissue remodeling. Remodeling begins with a carefully controlled proteolysis of the extracellular matrix and cell-cell adhesion proteins. Plasmin is a serine protease that has been implicated in the tissue remodeling associated with the declining phase of lactation and mammary involution. As lactation progresses, the quantity of plasmin activity increases within the mammary tissue and milk. This has led to the hypothesis that gradual involution results from progressive tissue remodeling. Hormonal attenuation of gradual involution by bST would slow tissue remodeling and would be permissive for lactation. In vitro results indicate that insulin-like growth factor-I impairs the secretion of plasminogen activator by bovine mammary epithelial cells. As such, a mechanism of action for bST exists.