Studies on the control of plasminogen activator production by cultured human embryonic lung cells: requirements for inhibition by corticosteroids

Variable response of tissue parameters of the fibrinolytic system to unilateral or bilateral adrenalectomy and unilateral or bilateral adrenal demedullation

The effect of unilateral and bilateral adrenalectomy, unilateral and bilateral demedullation or unilateral adrenalectomy/unilateral demedullation on tissue plasminogen activator activity (PAA), plasminogen activator inhibition (PAI) and plasmin inhibition (PI) was studied in the rat. All the above treatments induced an increase of PAA in lungs. Increased PAA was also noted in brain after bilateral adrenalectomy or demedullation, as well as unilateral adrenalectomy/unilateral demedullation. In kidneys the PAA was decreased after bilateral adrenalectomy or demedullation and unilateral adrenalectomy/unilateral demedullation. In aorta only after bilateral adrenalectomy a decreased PAA was induced. In heart and liver no changes in PAA were noted. A decreased PAI expressed against tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA) was found in lungs of all treated rats compared to controls. However, an increased PAI was noted in heart, liver and aorta against t-PA or u-PA after bilateral adrenalectomy and in liver after bilateral demedullation as well as after unilateral adrenalectomy/unilateral demedullation (rats with only one adrenal cortex). A dissociation between anti-t-PA and anti-u-PA response was seen in heart, liver and aorta. A variable change in PI was induced in kidneys, aorta, lungs and brain in all treatments except unilateral demedullation or unilateral adrenalectomy. Therefore, the effect of adrenalectomy or demedullation on tissue PAA, PAI and PI was variable and dependent on the extent of the treatment (unilateral or bilateral), the organ as well as the time after the treatment.

Medroxyprogesterone acetate, an anti-cancer and anti-angiogenic steroid, inhibits the plasminogen activator in bovine endothelial cells

Medroxyprogesterone acetate (MPA) is an anti-cancer drug for mammary carcinomas and an angiostatic steroid. The effects of MPA on the growth and plasminogen activator (PA) activity of bovine endothelial cells were investigated to elucidate the inhibitory mechanism observed in angiogenesis. MPA did not suppress the growth of capillary endothelial cells, even at high concentrations. On the other hand, in bovine endothelial cells of 3 types (adrenal cortical capillary, aortic and pulmonary artery endothelial cells), MPA inhibited extracellular and cell-associated activity of PA, which might be a protease involved in the neovascular response. MPA also greatly inhibited the high level of PA induced by basic fibroblast growth factor (FGF). The same result was obtained when PA production was induced by 4 beta-phorbol-12-myristate-13-acetate (PMA) in endothelial cells. These findings suggest that one of the points of inhibitory action of MPA in the process of angiogenesis may be the suppression of PA activity, and that inhibition of this protease might be useful for reduction of tumorigenic or excessive angiogenesis in vivo.

Down-regulation of epidermal growth factor receptor correlates with plasminogen activator activity in human A431 epidermoid carcinoma cells

Human A431 epidermoid carcinoma cells in culture exhibit epidermal growth factor (EGF)-induced "down-regulation" of cell-surface and total cellular (Triton X-100 extractable) EGF receptors caused entirely by an enhanced rate (4-fold) of receptor inactivation [Krupp, M. N., Connolly, D. T. & Lane, M. D. (1982) J. Biol. Chem. 257, 11489-11496]. The following observations show that this enhanced rate of EGF receptor inactivation is closely correlated with an increased cellular activity of plasminogen activator (PA), a serine protease. First, EGF-induced down-regulation of cell-surface and total cellular EGF receptors and the concomitant increase in cellular PA activity occur with identical kinetics, the t 1/2 for both processes being 3-3.5 hr. Second, the EGF dose-response curves for down-regulation of total cellular EGF receptor and increased PA activity are similar. The EGF concentrations for half-maximal responses of both processes are 10-15 nM and 20 nM, respectively. Third, the removal of EGF from previously down-regulated cells results in the recovery of total cellular EGF binding activity with a concurrent loss of cellular PA activity. Fourth, blocking PA synthesis or activity with cycloheximide or dexamethasone prevents down-regulation of the EGF receptor. Fifth, the addition of leupeptin, an inhibitor of PA and plasmin action, blocks EGF-induced receptor down-regulation as well as the increase of PA activity. That EGF receptor down-regulation is independent of plasminogen per se in the culture medium suggests that PA-mediated events may initiate the rapid inactivation of the EGF receptor that occurs during down-regulation.

Comparison of fibrin clot retraction with other transformation parameters after hydridization of normal and established cell lines

The expression of transformation parameters (inhibition of cell division during cell crowding, anchorage dependence, loss of fibrin clot retractile activity and secretion of plasminogen activator) was studied in a heterospecific cellular hybrid, made between established L(TK-) cells and the normal human MRC-5 cells. The hybrid nature of the cross was confirmed by the ability to incorporate [3H]-thymidine, by growth in selective HAT medium, by the identification of human chromosomes and by the expression on the surface of 100% of hybrid cells of a human glycoprotein, which is recognized by the 4F2 monoclonal antibody. The hybrid cultures showed cell cycle inhibition which became less stringent with increasing population doublings and the loss of human chromosomes. Fibrin clot retraction and anchorage dependence were absent in spite of the presence of many human chromosomes. The two properties were present or lost simultaneously in the normal parent cells and in the transformed parent or hybrid cells respectively. The human type of plasminogen activator was secreted even with very little human genetic material left, and a complete dissociation between fibrin clot retraction and production of plasminogen activator was observed. The data strengthen the hypothesis that transformation is a multistep process that involves complex genetic control and where cells progressively express different phenotypes and escape growth control.

Isolation of the major serine protease inhibitor from the 5-day serum-free conditioned medium of human embryonic lung cells and demonstration that it is fetuin

Human embryonic lung (HuEL) cells in culture produce large amounts of the enzyme, plasminogen activator, and thus generate substantial amounts of active plasmin. Despite the presence of plasmin, however, HuEL cells grow in ordered, flattened, adherent sheets. It seemed of interest to characterize protease inhibitors that might be present in HuEL cultures and which might account for this apparent contradiction. This paper reports the isolation and purification of the major serine protease inhibitor in 5-day serum-free conditioned medium (CM) from HuEL cells, and the purification of an identical molecule from fetal bovine serum (FBS). Both the CM-derived inhibitor and the FBS-derived inhibitor are identical with fetuin, the major glycoprotein of FBS. The CM-derived inhibitor is apparently derived from the FBS used to supplement the growth medium of HuEL cells between serum-free CM collection periods. It is not labeled metabolically with 3H-leucine. Its electrophoretic behavior is indistinguishable from that of standard fetuin in SDS-PAGE, non-SDS basic pH,PAGE, and isoelectric focusing. The CM-derived inhibitor and standard fetuin inhibit trypsin and plasmin with similar efficiencies, but neither inhibits chymotrypsin, pancreatic elastase, or plasminogen activator. They are immunologically indistinguishable. The suggestion is made that fetuin, and possibly other protease inhibitors present in HuEL cell cultures, may be concentrated locally by HuEL cells and gradually released back into the medium in the absence of serum. These molecules may serve to protect HuEL cells against proteases they generate.