The effect of cyclic AMP and prostaglandins on the fibrinolytic activity of mouse neuroblastoma cells

Induction of morphological differentiation of human neuroblastoma cells is accompanied by induction of tissue-type plasminogen activator

Human SH-SY5Y neuroblastoma cells treated with retinoic acid, 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or nerve growth factor differentiated morphologically to neuronlike cells with increased amounts of neurofilament protein and mRNA. All three effectors induced an increase in the amount of relative molecular weight (Mr) 70,000 tissue-type plasminogen activator (t-PA) and its mRNA, as determined by immunocapture, enzyme activity, and Northern blotting analyses. About 90% of the t-PA activity was secreted to the culture medium. In contrast, of the three effectors studied, only TPA induced transcription of the proto-oncogene c-fos, studied as a control gene responsive to various stimuli, and induced a rapid increase in urokinase-type PA (u-PA). Most of the u-PA activity induced by TPA remained cell-associated. Because induction of differentiation correlated closely with induction of t-PA, and not u-PA, the authors propose that t-PA may have a functional role in the morphological differentiation of neuronal cells.

Effect of retinoic acid on human neuroblastoma: correlation between morphological differentiation and changes in plasminogen activator and inhibitor activity

The relationship between plasminogen activator (PA)/plasminogen activator inhibitor (PAI) activity and morphological differentiation was investigated in human neuroblastoma (NB) cells treated with retinoic acid (RA). Conditioned medium from nine NB cell lines and one closely related neuroepithelioma line was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and zymography. All NB cell lines were shown to secrete urokinase (UK)-type PA (mol. wt., 52 kDa), and all except two produced tissue PA (mol. wt., 65 kDa). Identification of the PAs was made based on molecular weight and sensitivity to inhibition by anti-UK and anti-tPA antibodies. Several cell lines expressed PA inhibitory molecules; two molecular-weight forms were observed (35 and 40 kDa) in different cell lines. Complex formation with [125]I-labelled proteases revealed specific binding with UK and trypsin but not thrombin, plasmin, or kallikrein. After treatment for 6 days with 1 microM RA, six of the cell lines exhibited an increase in cell-associated and/or secreted tPA activity, corresponding to morphological differentiation of the cells as manifested by extensive neurite outgrowth. A decrease in UK and UK-complex secretion was observed in several of these cell lines. Three cell lines exhibiting no detectable morphological alterations with RA treatment also showed no dramatic changes in PA/PAI activity. These results suggest that morphological differentiation of NB cells may be associated with alterations in the regulation of PA activity.

Secretion of plasminogen activator by cerebral astrocytes and its modulation

Plasminogen activator (PA) has been related to the neuron migration during brain development. PA has also been shown to degrade myelin basic protein. We present data to show that neonatal Balb/c astrocytes show PA activity on 125I-fibrin coated plates. Secreted and cell associated fibrinolytic activity is detected only in the presence of plasminogen. Modulants like concanavalin A and phorbol myristate acetate enhance PA production and this function involves a transcriptional event. Dexamethasone inhibits baseline as well as concanavalin A induced enhancement of PA activity. These results raise the possibility that astrocytes may have an active role in myelinoclastic disorders and CNS developmental defects.

Calcium regulation of tissue plasminogen activator and prostaglandin biosynthesis in HeLa cells

Phorbol 12-myristate 13-acetate, 1-20 nM, induced the synthesis in HeLa cells of a 65 200 Mr tissue-type plasminogen activator, and of prostaglandin E2. Omission of Ca2+ from the incubation medium inhibited the induction of plasminogen activator synthesis by 40-60% and abolished the induction of prostaglandin E2 synthesis. Maximal plasminogen activator synthesis could be maintained at extracellular Ca2+ concentrations of approx. 0.1 mM, while maximal prostaglandin synthesis required at least 0.45-0.9 mM Ca2+. The induction of each factor was inhibited by 10-100 microM 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8), an inhibitor of intracellular C2+ mobilization. Prostaglandin synthesis, but not plasminogen activator synthesis, was also inhibited by 10-100 microM verapamil and nifedipine, which inhibit intracellular Ca2+ uptake via the so-called 'slow-channels' and by 0.5-10 microM trifluoperazine, an inhibitor of calmodulin. Neither plasminogen activator synthesis nor prostaglandin synthesis were stimulated by 5-50 microM 1-oleoyl-2-acetylglycerol or 1-250 microM 1,2-dioctanoylglycerol, alone and in combination with 50 nM-1 microM ionophore A23187. These results indicate that the synthesis of plasminogen activator and prostaglandins in HeLa cells is Ca2+-dependent, and that the Ca2+ requirements for each process are not identical. Thus, Ca2+ regulation of the production of tissue plasminogen activator and prostaglandin E2 occurs at multiple points in their biosynthetic pathways.

Differentiation characteristics of human neuroblastoma cells in the presence of growth modulators and antimitotic drugs

Morphological characteristics of undifferentiated and differentiated human neuroblastoma cells were studied. Monolayer cultures of a human neuroblastoma, IMR-32 clone, were grown in Eagle's minimum essential medium with fetal calf serum in tissue culture dishes with polystyrene film liners. After 48 h, cultures were treated with either mitomycin C and 5-bromodeoxyuridine or prostaglandin E1 (PGE1) and dibutyryl adenosine 3',5'-cyclophosphate (cAMP). A third dish was untreated to study as an undifferentiated control. Three days later, all cultures were processed for acetylcholinesterase staining, scanning and transmission electron microscopy and high performance liquid chromatography. Treatment with mitomycin/5-bromodeoxyuridine and PGE1/cAMP inhibited growth as seen by the growth curves and caused morphological differentiation as seen by the extension of long neurites. The treated cells showed increased acetylcholinesterase staining compared to the controls. With the scanning electron microscope, the differentiated cells showed long neurites, processes with beaded varicosities and growth cones. By transmission electron microscopy, these cells contained a large number of neurosecretory granules in their cytoplasm and neurites. Specialized cell contacts were also observed between the treated cells. This is the first study demonstrating that both the treated and control cells of IMR-32 clone contain large quantities of serotonin and comparatively small amounts of norepinephrine and dopamine.

The effects of serine protease inhibitors on morphological differentiation of murine neuroblastoma cells (NB15)

Morphological differentiation of neuroblastoma cells (NB15) was induced by cAMP effectors in the presence and absence of serine protease inhibitors. In all conditions tested, the percent differentiation was inhibited by protease inhibitors antipain, diisopropylfluorophosphate (DFP), leupeptin, and soybean trypsin inhibitor (SBTI). The level of morphological differentiation obtained in medium containing fetal calf serum was significantly less than the percent differentiation obtained with serum-free medium alone, so serum-free medium was the principal method of induction and comparisons were made to control uninduced cultures or cultures induced with the phosphodiesterase inhibitor R020-1724. Secreted or cell surface caseinolytic protease activity was higher in differentiating cells than in control cultures and was inhibited by the serine protease inhibitors. The effects of the protease inhibitors on growth and differentiation are discussed.

Hormonal regulation of plasminogen activator in rat hepatoma cells

Plasminogen activators are membrane-associated, arginine-specific serine proteases which convert the inactive plasma zymogen plasminogen to plasmin, an active, broad-spectrum serine protease. Plasmin, the major fibrinolytic enzyme in blood, also participates in a number of physiologic functions involving protein processing and tissue remodelling, and may play an important role in tumor invasion and metastasis. In HTC rat hepatoma cells in tissue culture, glucocorticoids rapidly decrease plasminogen activator (PA) activity. We have shown that this decrease is mediated by induction of a soluble inhibitor of PA activity rather than modulation of the amount of PA. The hormonally-induced inhibitor is a cellular product which specifically inhibits PA but not plasmin. We have isolated variant lines of HTC cells which are selectively resistant to the glucocorticoid inhibition of PA but retain other glucocorticoid responses. These variants lack the hormonally-induced inhibitor; PA from these variants is fully sensitive to inhibition by inhibitor from steroid-treated wild-type cells. Cyclic nucleotides dramatically stimulate PA activity in HTC cells in a time- and concentration-dependent manner. Paradoxically, glucocorticoids further enhance this stimulation. Thus glucocorticoids exert two separate and opposite effects on PA activity. The availability of glucocorticoid-resistant variant cell lines, together with the unique regulatory interactions of steroids and cyclic nucleotides, make HTC cells a useful experimental system in which to study the multihormonal regulation of plasminogen activator.

Paradoxical effects of glucocorticoids on regulation of plasminogen activator activity of rat hepatoma cells

Incubation of rat hepatoma cells with cAMP derivatives stimulates cell-associated plasminogen activator activity 8- to 22-fold and extracellular plasminogen activator activity 30- to 1300-fold. This time- and concentration-dependent increase is enhanced by phosphodiesterase inhibitors. Dexamethasone, a synthetic glucocorticoid, decreases the plasminogen activator activity of these cells, probably through induction of an inhibitor. Paradoxically, dexamethasone, added simultaneously with cAMP derivatives causes a further 4-fold enhancement of the cAMP-mediated stimulation of plasminogen activator activity. Dexamethasone also alters the time course of cAMP-mediated enhancement of plasminogen activator activity: increased protease activity is detected at 4 hr in cells incubated with 8-bromoadenosine-3':5'-cyclic monophosphoric acid and 1-methyl-3-isobutylxanthine but not until 12 hr in cells incubated with dexamethasone as well. Glucocorticoids thus exert two separate and opposite effects on plasminogen activator activity: induction of an inhibitor and amplification of cyclic nucleotide action. Although permissive and synergistic effects of dexamethasone on cyclic nucleotide action have been reported previously, glucocorticoid regulation of plasminogen activator activity is unique in that the amplification of cyclic nucleotide effects by dexamethasone opposes its regulatory action toward a specific enzyme.

Effect of sodium butyrate on the hepatoma cell cycle: possible use for cell synchronization

Exposure of HTC cells to sodium butyrate caused inhibition of growth. The site of growth inhibition was studied by time-lapse cinematography and [3H]thymidine incorporation studies. Evidence is presented that sodium butyrate affected the cell cycle at a specific point immediately after mitosis. Inasmuch as it does not modify the interphase duration after its removal, butyrate may be used for HTC synchronization.

Plasminogen activator release at the neuronal growth cone

The site of plasminogen activator release by differentiated neuroblastoma clonal cell lines was determined with a fibrin overlay assay. Release of plasminogen activator was seen at the growth cone in 72 percent of the cells bearing neurites. For 21 percent of these cells the growth cone was the predominant or exclusive site of this enzyme activity. Selective release of protease at the "trailblazing" tip of the neurite may be important in neuron migration and neurite growth in vivo.