Effects of 12-O-tetradecanoylphorbol 13-acetate on the production of mRNAs for human tissue-type plasminogen activator

A novel organotypic model mimics the tumor microenvironment

Carcinoma cell invasion is traditionally studied in three-dimensional organotypic models composed of type I collagen and fibroblasts. However, carcinoma cell behavior is affected by the various cell types and the extracellular matrix (ECM) in the tumor microenvironment. In this study, a novel organotypic model based on human uterine leiomyoma tissue was established and characterized to create a more authentic environment for carcinoma cells. Human tongue squamous cell carcinoma cells (HSC-3) were cultured on top of either collagen or myoma. Organotypic sections were examined by immunohistochemistry and in situ hybridization. The maximal invasion depth of HSC-3 cells was markedly increased in myomas compared with collagen. In myomas, various cell types and ECM components were present, and the HSC-3 cells only expressed ECM molecules in the myoma model. Organotypic media were analyzed by radioimmunoassay, zymography, or Western blotting. During carcinoma cell invasion, matrix metalloprotease-9 production and collagen degradation were enhanced particularly in the myoma model. To evaluate the general applicability of the myoma model, several oral carcinoma, breast carcinoma, and melanoma cell lines were cultured on myomas and found to invade in highly distinct patterns. We conclude that myoma tissue mimics the native tumor microenvironment better than previous organotypic models and possibly enhances epithelial-to-mesenchymal transition. Thus, the myoma model provides a promising tool for analyzing the behavior of carcinoma cells.

Expression of collagenases-1 and -3 and their inhibitors TIMP-1 and -3 correlates with the level of invasion in malignant melanomas

Since proteolysis of the dermal collagenous matrix and basement membranes is required for local invasive growth and early metastasis formation of cutaneous melanomas, we have analysed the activities/expression levels of certain metalloproteinases in melanomas and cultured melanoma cells by in situ hybridization and Northern analysis. In addition to collagenases-1 and -3 that have been implicated in invasive growth behaviour of various malignant tumours, we analysed the levels of 72-kDa gelatinase and its activators MT1-MMP and TIMP-2 in cultured melanoma cells. The lesions examined included three cases of lentigo maligna and 28 cases of Clark grade I-V melanomas. The premalignant as well as the grade I tumours were consistently negative for collagenase-1 and -3 and TIMP-1 and -3. The collagenases were predominantly expressed in the cancer cells of Clark grade III and IV tumours. TIMP-1 and -3 were abundantly expressed in the cancer and/or stromal cells of grade III and IV melanomas, while TIMP-2 protein was detected also in melanomas representing lower invasive potential. Northern analysis of seven melanoma cell lines showed that the expression of collagenase-1 and TIMPs-1 and -3 was associated with 72-kDa gelatinase positivity. All melanoma cell lines were positive for MT1-MMP and TIMP-2 mRNAs. Our results suggest that overexpression of collagenases-1 and -3 and TIMPs-1 and -3 is induced during melanoma progression. Expression of TIMPs may reflect host response to tumour invasion in an effort to control MMP activity and preserve extracellular matrix integrity.

Thrombin regulation of tissue-type plasminogen activator synthesis in cultured human fetal lung fibroblasts

We examined the effects of thrombin on tissue-type plasminogen activator (t-PA) release and t-PA mRNA levels in cultured human fetal lung fibroblast cells, IMR-90. The secretion of t-PA was increased by thrombin in a dose- and time-dependent manner, but it was not affected by inactivated thrombin with diisopropylfluorophosphate (DFP). Both antithrombin III (ATIII) and heparin cofactor II (HCII), plasma inhibitors to thrombin, inhibited thrombin-induced t-PA release. The thrombin-induced t-PA secretion was preceded by an increase of the steady state level of t-PA-specific mRNA in the cells, suggesting that thrombin activates t-PA gene expression. The t-PA mRNA expression induced by thrombin was completely blocked by pretreatment of the cells with an inhibitor of translation, cycloheximide (CHX). These results suggest that the effect of thrombin on t-PA expression is mediated through its proteolytic activity and the biosynthesis of transcription factor(s).

Differential regulation of gelatinase B and tissue-type plasminogen activator expression in human Bowes melanoma cells

A comparison of the production of tissue-type plasminogen activator (t-PA) and gelatinases A and B was made at the mRNA and protein levels in human Bowes melanoma cells treated with phorbol myristate acetate (PMA). Immunocytochemical analysis confirmed previous quantitative data on PMA-mediated induction of t-PA. It also showed that t-PA immunoreactivity can be restrained to the local environment of the producing cell, most probably by interaction with extracellular matrix components. Zymographical analysis showed that gelatinase B protein was induced by PMA, whereas gelatinase A remained at the constitutive level. Protein kinase C (PKC) appeared to be involved in this regulation since, after PMA treatment (1) the PKC activity was found to be translocated from the cytosol to the particulate fraction of the cells and (2) addition of staurosporine and H-7 blocked the gelatinase B increase. Northern-blot hybridization showed a transient rise in t-PA and gelatinase B mRNA levels whereas gelatinase A mRNA levels remained unchanged. When c-fos and c-jun mRNAs were investigated, only that of c-fos was affected by PMA. Activation by PMA can be kinetically ordered as follows: translocation of PKC to the membrane fraction, transcription of the c-fos gene and eclipsing of gelatinase B mRNA, increase in steady-state mRNA levels of t-PA and gelatinase B and, finally, secretion of t-PA and gelatinase B glycoproteins. Our data also suggest that various proteases that are known to cooperate in the remodeling of the extracellular matrix can be differently regulated in one tumor-cell type.

Transcriptional regulation of the rat tissue type plasminogen activator gene: localization of DNA elements and nuclear factors mediating constitutive and cyclic AMP-induced expression

We have characterized tissue type plasminogen activator (tPA) promoter elements and nuclear factors required for follicle-stimulating hormone (FSH)-induced transcription of the rat tPA gene in granulosa cells and constitutive expression of the gene in the rat neuroblastoma cell line B103. Run-on transcription analysis of isolated nuclei revealed that B103 cells transcribe the tPA gene at a high and constitutive level, while FSH was found to induce tPA gene transcription in a rapid and transient manner in granulosa cells. The maximal FSH-induced transcription rate was obtained after 20 min and was similar in the absence or presence of the protein synthesis inhibitor cycloheximide. However, in the presence of cycloheximide, tPA transcription was not turned off but continued at a high rate for several hours. This phenomenon may at least partly explain the earlier finding that tPA mRNA is superinduced by FSH in the presence of cycloheximide. DNase I footprinting analysis of the first 621 bp of the tPA promoter revealed a total of six regions that interact with nuclear factors from B103 and granulosa cells. Deletion of the promoter region from positions -269 to -621, a region that includes the two most-upstream footprints, had no effect on constitutive or FSH-induced transcription in transient expression experiments. Nuclear extracts from both granulosa cells and B103 cells showed strong binding to a consensus cyclic AMP-responsive element (CRE) at positions -178 to -185 and a neighboring binding site for nuclear factor 1 (NF1) at positions -145 to -158. The factors binding to these two regions were identified as members of the CRE-binding protein and NF1 families of transcription factors, respectively. Footprints were also obtained over two GC boxes at positions -64 to -71 and -41 to -49. These footprints were more pronounced with nuclear extracts from B103 cells than with extracts from untreated or FSH-treated granulosa cells, but gel shift assays indicate that similar amounts of two distinct factors bind to the two GC boxes in both cell types. Transfection experiments using promoter constructs with inactivated promoter elements indicate that both the CRE and NF1 sites contribute to the FSH responsiveness of the rat tPA gene in granulosa cells, while only the NF1 site is important for constitutive expression in B103 cells. The two GC boxes were found to be necessary both for constitutive expression in B103 cells and for FSH-induced expression in granulosa cells, and inactivation of both GC boxes essentially eliminated the tPA promoter activity in both cell types.

Transcriptional regulation of the rat tissue type plasminogen activator gene: localization of DNA elements and nuclear factors mediating constitutive and cyclic AMP-induced expression

We have characterized tissue type plasminogen activator (tPA) promoter elements and nuclear factors required for follicle-stimulating hormone (FSH)-induced transcription of the rat tPA gene in granulosa cells and constitutive expression of the gene in the rat neuroblastoma cell line B103. Run-on transcription analysis of isolated nuclei revealed that B103 cells transcribe the tPA gene at a high and constitutive level, while FSH was found to induce tPA gene transcription in a rapid and transient manner in granulosa cells. The maximal FSH-induced transcription rate was obtained after 20 min and was similar in the absence or presence of the protein synthesis inhibitor cycloheximide. However, in the presence of cycloheximide, tPA transcription was not turned off but continued at a high rate for several hours. This phenomenon may at least partly explain the earlier finding that tPA mRNA is superinduced by FSH in the presence of cycloheximide. DNase I footprinting analysis of the first 621 bp of the tPA promoter revealed a total of six regions that interact with nuclear factors from B103 and granulosa cells. Deletion of the promoter region from positions -269 to -621, a region that includes the two most-upstream footprints, had no effect on constitutive or FSH-induced transcription in transient expression experiments. Nuclear extracts from both granulosa cells and B103 cells showed strong binding to a consensus cyclic AMP-responsive element (CRE) at positions -178 to -185 and a neighboring binding site for nuclear factor 1 (NF1) at positions -145 to -158. The factors binding to these two regions were identified as members of the CRE-binding protein and NF1 families of transcription factors, respectively. Footprints were also obtained over two GC boxes at positions -64 to -71 and -41 to -49. These footprints were more pronounced with nuclear extracts from B103 cells than with extracts from untreated or FSH-treated granulosa cells, but gel shift assays indicate that similar amounts of two distinct factors bind to the two GC boxes in both cell types. Transfection experiments using promoter constructs with inactivated promoter elements indicate that both the CRE and NF1 sites contribute to the FSH responsiveness of the rat tPA gene in granulosa cells, while only the NF1 site is important for constitutive expression in B103 cells. The two GC boxes were found to be necessary both for constitutive expression in B103 cells and for FSH-induced expression in granulosa cells, and inactivation of both GC boxes essentially eliminated the tPA promoter activity in both cell types.

Cytokines and proteases in invasive processes: molecular similarities between inflammation and cancer

Tumor-derived serine proteinases and metalloproteinases have been associated with invasion and metastasis of cancer cells. Leukocytes, particularly monocytes/macrophages and neutrophils, actively synthesize and store these proteolytic enzymes. The production by tumor cells of chemotactic factors that attract white blood cells raises questions that are important for the basic researcher as well as the clinical scientist. Are the proteinases, which have the capacity to dissolve the extracellular matrix and by this solubilization promote cell migration, the same in tumor cells as in normal cells? Is the production of chemotactic factors by tumor cells a coincident epiphenomenon of the malignant state or a selective way to parasitize the host? Does the early attraction of leukocytes to the tumor site contribute to early host defense against cancer? Does our knowledge about mechanisms of action of cytokines have implications for therapy of the cancer patient? Recent experimental data give hints to the answers to these questions and make it possible to deduce a fundamental model of cytokine mediated proteolysis in tissue remodelling.

Enhanced induction of tissue-type plasminogen activator in normal human cells compared to cancer-prone cells following ionizing radiation

Normal human fibroblast (i.e., GM2936B, GM2907A, and IMR-90) and cancer-prone human fibroblast (i.e., Fanconi's anemia, Bloom's syndrome, and Ataxia telangiectasia) cells demonstrated the induction of intracellular and extracellular levels of tissue-type plasminogen activator (t-PA) at 6 and 12 hr, respectively, following ionizing radiation. Induced t-PA enzymatic activities following ionizing radiation were blocked by actinomycin D treatments. t-PA enzymatic activities were induced over 14-fold in Ataxia telangiectasia cells, over 9-fold in Bloom's syndrome cells, and over 6-fold in Fanconi's anemia cells, as compared to normal human fibroblasts. Similarly, the induction of t-PA mRNA levels in cancer-prone cells were between 5- to 10-fold higher than those observed in normal cells following equitoxic doses of ionizing radiation. Temporal induction of t-PA mRNA levels for normal and cancer-prone human cells were consistent with quantifiable enzymatic activities. The elevated induction of an intracellular protease (i.e., t-PA) in cancer-prone human cells is reminiscent of an "SOS"-like response observed in yeast and bacteria.

Role of protein kinase C and cyclic adenosine monophosphate in the regulation of tissue-type plasminogen activator, plasminogen activator inhibitor-1, and platelet-derived growth factor mRNA levels in human endothelial cells. Possible involvement of proto-oncogenes c-jun and c-fos

Activation of protein kinase C leads to a strong induction of tissue-type plasminogen activator (t-PA) expression in endothelial cells. Using endothelial cells from human umbilical vein (HUVECs) and human aorta (HAECs), we have studied this regulation of t-PA and its inhibitor, plasminogen activator inhibitor-1 (PAI-1), at the mRNA level and have compared their induction with the expression of platelet-derived growth factors A and B (PDGF-A and PDGF-B) and the proto-oncogenes c-jun and c-fos. Treatment of HUVECs with exogenous bacterial phospholipase C or the synthetic diacylglycerol 1-oleoyl-2-acetylglycerol led to a threefold and a twofold increase, respectively, in t-PA concentrations in 24-hour-conditioned medium. Similarly, the more stable protein kinase C activator 4 beta-phorbol-12-myristate-13-acetate (PMA) caused about a 10-fold increase in t-PA antigen levels. This effect of PMA is maximal between 8 and 16 hours at a concentration of 10 nM and is fully accounted for by parallel increases in t-PA mRNA levels. An increase in intracellular cyclic adenosine monophosphate levels by forskolin (10 microM) slightly diminished t-PA expression but further enhanced the PMA-induced increases in t-PA synthesis and mRNA levels by at least twofold. PMA also enhanced the mRNA levels of two other important endothelium-expressed genes, PDGF-A and PDGF-B, with a time profile similar to that of t-PA, with peak values about fivefold higher than control values. Forskolin did not further stimulate this PMA-induced PDGF expression in HUVECs, which suggests a regulatory mechanism different from that of t-PA. Qualitatively very similar induction patterns of t-PA, PDGF-A, and PDGF-B were seen with HAECs. In contrast to t-PA and PDGF, PAI-1 mRNA and antigen levels increased only slightly after PMA treatment of HUVECs or HAECs; forskolin alone or in combination with PMA diminished the expression of PAI-1. The induction of t-PA mRNA by PMA was dependent on protein synthesis and was preceded by a strong transient increase in c-jun and c-fos mRNA levels; the induction of c-fos but not of c-jun was potentiated by forskolin. Because the products of these two proto-oncogenes form dimeric complexes for which specific binding sites are present in the t-PA promoter region, they may mediate the protein kinase C-dependent increase in t-PA gene expression, including the stimulating action of cyclic adenosine monophosphate.

Modulation of tissue plasminogen activator biosynthesis by phosphatidylinositol liposomes in human fetal lung fibroblasts

Phosphatidylinositol (PI) liposomes at 40 microM increased tissue plasminogen activator (t-PA) biosynthesis by human fetal lung fibroblasts IMR-90 (FLF), after 5 days of incubation by 7.4 +/- 1.4 times of the control level. Other phospholipid liposomes, such as phosphatidylserine (PS), phosphatidylcholine (PC), and phosphatidylglycerol (PG), had no effect on t-PA biosynthesis by FLF. The induction of t-PA biosynthesis by PI liposomes was inhibited by specific inhibitors of phosphoinositide pathway: gentamycin and lithium chloride. Thus, gentamycin inhibited the effect of PI liposomes on t-PA biosynthesis by 76% (P less than 0.001), while it had no effect on control FLF. Likewise, lithium chloride inhibited t-PA biosynthesis of both PI-treated and control FLF by greater than 84%. The induction of t-PA biosynthesis by PI liposomes was dependent on RNA transcription and independent of DNA biosynthesis.

Human hepatoma cells produce an 85 kDa gelatinase regulated by phorbol 12-myristate 13-acetate

Several human cell lines were studied for the production of gelatinases. Diploid fibroblasts, the melanoma cell line Bowes, the MG-63 osteosarcoma cell line and the human hepatoma cell line Malavu all constitutively produced a 67 kDa gelatinase. Gelatinolytic enzymes were quantified by a sensitive zymographic substrate conversion assay. Upon induction with phorbol 12-myristate 13-acetate (PMA), the human hepatoma cell line secreted considerable amounts of an 85 kDa gelatinase activity. The induction process was time- and dose-dependent. It represented a true increase in production per individual cell and was associated by a marked change of the cell morphology. The effect of various proteinase inhibitors and the maximal activity of the enzyme near neutral pH demonstrate that it is a neutral metalloproteinase. Characterization studies showed the 85 kDa gelatinase to be transformed to lower molecular weight, active forms by treatment with p-aminophenylmercuric acetate (APMA) or trypsin.

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.

A comparison of the effects of various stimulatory agents on t-PA secretion by normal and malignant cell lines

Succinyl con A and acetyl con A both stimulated epithelial cells to produce similar yields of tissue plasminogen activator (t-PA) to those previously obtained with native con A. However, unlike con A, the derivatized lectins did not adversely affect cell morphology and viability, and cells treated with succinyl con A could secrete t-PA for a prolonged period. Con A and the two derivatives produced similar morphological effects in Bowes melanoma cells, but t-PA production was not increased. Elevated cyclic nucleotide concentrations did not affect t-PA production from epithelial cells, but calcium ionophore treatment generated t-PA yields similar to those obtained with lectins. Azacytidine, which enhanced t-PA production from epithelial cells, did not increase yields from Bowes melanoma cells, and also sodium butyrate, reported to increase t-PA yields from human endothelial cells, had no effect on either cell line.

Simultaneous stimulation of urokinase and tissue-type plasminogen activators by phorbol esters in human ovarian carcinoma cells

OVCA 433 human ovarian carcinoma cells secrete both mammalian plasminogen activators (PAs) urokinase (UK) and tissue-type PA (tPA). Treatment of cells with 4 beta-phorbol-12-myristate-13-acetate (PMA), a stimulator of protein kinase C (PKC), leads to large increases in the secretion rates of both PA types. PA stimulation by PMA is time- and concentration-dependent, with maximal effects occurring between 12 and 24 h at PMA concentrations of 1-10 ng/ml. The PMA effect is mimicked by mezerein, another known PKC stimulator, but not by 4 alpha-phorbol or 4 alpha-phorbol-12,13-didecanoate, two phorbol compounds that do not stimulate PKC. PA activity is virtually unaffected by 1-oleoyl-2-acetylglycerol (OAG), a synthetic diacylglycerol that stimulates PKC in vitro but has variable effects on whole cells. PMA stimulation of PA activity is blocked by both actinomycin D and cycloheximide, indicating requirements for new RNA and protein synthesis. When analyzed individually, the relative PMA-induced increases in UK and tPA activities are identical. Increased UK activity is fully accounted for by increased UK antigen secretion, whereas increased tPA secretion accounts for only about one-half of the increased tPA activity. Similarly, PMA induces large increases in steady-state UK mRNA levels, while its effects on tPA mRNA levels are only modest. Thus, while increases in secretion rates and mRNA levels can completely account for UK stimulation, other mechanisms augmenting these processes must exist specifically for tPA. Since the relative increases in UK and tPA activities are identical despite the probable existence of multiple mechanisms contributing to tPA regulation, our data suggest the possibility of interrelationships between the two pathways such that equivalent degrees of UK and tPA activity stimulation are ultimately achieved.

Plasminogen activator inhibitor type 1: cell-specific and differentiation-induced expression and regulation in human cell lines, as determined by enzyme-linked immunosorbent assay

We have performed a comparative study of the regulation by glucocorticoids and phorbol 12-myristate 13-acetate (PMA) of the production of type 1 plasminogen activator inhibitor (PAI-1) by 12 human cell lines. A sandwich-type enzyme-linked immunosorbent assay (ELISA) for PAI-1 that measures free PAI-1 as well as complexes between PAI-1 and both types of plasminogen activators has been used. Basal PAI-1 accumulation varied more than 5000-fold between the cell lines. No correlation was found between the PAI-1 level and other characteristics of the cell lines, except that three lines of SV40-transformed fibroblasts produced more PAI-1 than two non-transformed fibroblast cell lines. Three out of the 12 cell lines responded to glucocorticoids by an increased PAI-1 production. Four cell lines responded to PMA by an increased PAI-1 production. In addition, PMA-induced differentiation of the monocyte cell line U937 and the promyelocytic cell line HL-60 into macrophage-like cells was found to be correlated with an up to 100-fold increase in PAI-1 accumulation. The PMA-dependent differentiation of HL-60 cells led to acquisition of glucocorticoid inducibility of PAI-1. These findings provide information for future studies of the molecular mechanism of cell-specific expression and regulation of PAI-1.

Heterogeneity of human tissue-type plasminogen activator

Tissue-type plasminogen activator (t-PA) from human melanoma cells (Bowes) was purified by immunosorbent chromatography on affinospecific polyclonal antibodies and gel filtration in the presence of KSCN. The immunosorbent eluate contained three major components of greater than 200, 85 and 65 kDa, respectively. The 65 kDa t-PA component could be separated by gel filtration on Ultrogel AcA44 in the presence of KSCN to a pure preparation yielding a unique N-terminal amino acid sequence. Immunoblot analysis, using affinospecific antibodies against t-PA, was a specific and sensitive method to identify different types of t-PA (I-IV), as well as t-PA-inhibitor complexes and degradation products in unstimulated melanoma cell culture fluids. Furthermore, the t-PA preparations, produced by phorbol ester-treated melanoma cells, were free of type IV and thus differed physiochemically from the constitutively produced t-PA preparations. The composition of t-PA from mammalian cell cultures is thus more complex than hitherto described.

Oncogenic potential in fibroblasts from individuals genetically predisposed to cancer

There is now considerable evidence to suggest that genetic factors can influence the incidence of cancer. Although expression of this susceptibility to cancer appears to be tissue-specific, the normal skin fibroblasts from individuals predisposed to cancer (predisposed fibroblasts) have also been shown to express the risk of the target cell in the development of cancer. In the context of the 2-stage theory of chemical carcinogenesis predisposed fibroblasts may, therefore, exist in a pre-neoplastic or initiated state. The purpose of the present study was to determine whether predisposed fibroblasts would be oncogenically transformed in vitro by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) alone. TPA treatment induced similar changes in cellular morphology, cytoskeleton, and epidermal growth-factor binding, in predisposed and normal cells. None of these cell lines acquired anchorage-independent growth or an unlimited growth potential in culture after chronic application of TPA. Fluorescent microscopy with an F-actin probe, in the absence of TPA, showed a disorganization of the microfilament and intermediate filament network in skin fibroblasts from individuals with familial polyposis coli, hereditary and sporadic retinoblastoma, basal cell nevus syndrome, and Gardner's syndrome, as compared to normal skin fibroblasts. Single and 2-dimensional electrophoresis also indicated that the incorporation of 35S-methionine into actin in predisposed fibroblasts was 2-fold greater than in normal fibroblasts, and the turnover rate of actin in predisposed fibroblasts was less than 5 h, compared to 48 h in normal fibroblasts. These observations clearly suggest that predisposed fibroblasts may not exist in a pre-neoplastic or initiated state, and that the mechanism of genetic susceptibility to cancer may be different from that of chemical carcinogenesis. In contrast, the results of this study indicate that genetic susceptibility to a variety of cancers may be associated with a rapid turnover of actin and a disorganization of the microfilament and intermediate filament networks.

Regulation of the synthesis and activity of urokinase plasminogen activator in A549 human lung carcinoma cells by transforming growth factor-beta

Transforming growth factor-beta (TGF beta) is a regulator of cellular proliferation which can alter the proteolytic activity of cultured cells by enhancing the secretion of endothelial type plasminogen activator inhibitor and affecting the secretion of plasminogen activators (PAs) in cultured fibroblastic cells. We used the TGF beta-responsive malignant human lung adenocarcinoma cell line A549 to study the relationships between the known TGF beta-induced growth inhibition and the effects of TGF beta on the secretion of PA activity by A549 cells. PA activity was quantitated by caseinolysis assays, and characterized by urokinase mRNA analysis, immunoprecipitation, and zymography assays. PA-inhibitor production was observed in autoradiograms of SDS-polyacrylamide gels and reverse zymography assays. It was found that TGF beta enhanced the production of PA activity by these cells, in accordance with an enhancement of urokinase mRNA levels. A concomitant stimulation of type 1 PA-inhibitor production was also observed in A549 cells in response to TGF beta. In contrast to the observations of A549 cells, TGF beta caused a decrease in the expression of both urokinase and the tissue-type PA mRNA in human embryonic WI-38 lung fibroblasts indicating opposite regulation of the expression of PAs in these cells. The results suggest that TGF beta may play a role in the regulation of the invasive, proteolytically active phenotype of certain lung carcinoma cells.

Role of plasminogen, plasmin, and plasminogen activators in the migration of fibroblasts into plasma clots

Human diploid fibroblasts were seeded onto or into plasma clots and different aspects of cell adhesion and migration were measured. The roles of plasminogen activators and plasmin were studied by either the removal of plasminogen from plasma prior to clotting or by the addition of 10 mM epsilon-aminocaproic acid, which brings about an inhibition of plasmin in this system. When cells were seeded onto the surface of plasma clots, rates of attachment, spreading, and migration were unaffected by plasminogen depletion or plasmin inhibition. In contrast, when cells were seeded into plasma clots, then, although the rates of cells spreading were unaffected, cell migration was abolished by plasminogen depletion or by plasmin inhibition. When cells were seeded onto the surface of plasma clots and the rate of migration into the clots was measured, there was an absolute requirement for plasmin activity; while fibroblasts migrated rapidly into the fibrin lattice of control clots, in the case of plasminogen-depleted clots, cells failed to penetrate the lattice. Focussing through a plasma clot revealed that fibroblasts do not migrate through the fibrin lattice but instead, localized areas of fibrinolysis are generated and cells migrate over the surface of the area of lysis.

Interleukin 1 preferentially stimulates the production of tissue-type plasminogen activator by human articular chondrocytes

Interleukin 1, derived from human placenta, stimulates plasminogen activator activity in human articular chondrocytes. The stimulation of plasminogen activator activity can be abolished by preincubation of placental interleukin 1 with an antiserum to homogeneous 22K factor, a species of interleukin 1 beta, indicating that the stimulation of plasminogen activator activity is due to interleukin 1 and not contaminating factors. Chondrocytes produce three species of plasminogen activator, with apparent Mr approximately 50,000, 65,000 and 100,000 as determined after sodium dodecyl sulphate (SDS)-polyacrylamide gel electrophoresis with gels containing casein and plasminogen. Both placental interleukin 1 and 22K factor enhance the production of the species of Mr approximately 65,000 and 100,000. Comparison of the mobility of the plasminogen activator species on SDS-polyacrylamide gel electrophoresis with human urokinase (u-PA) and human melanoma tissue-type plasminogen activator (t-PA) and studies with antibodies to these enzymes indicate that the Mr approximately 50,000 species is a u-PA and the Mr approximately 65,000 a t-PA. The Mr approximately 100,000 species is possibly an enzyme-inhibitor complex. Interleukin 1 therefore appears to enhance the production of t-PA and a putative enzyme-inhibitor complex. Abolition of plasminogen activator activity in the fibrin plate assay with antibodies to t-PA and u-PA also confirms enhanced t-PA production on interleukin 1 stimulation, though there is also evidence for increased cell-associated production of u-PA.

Human elongation factor 1 alpha: a polymorphic and conserved multigene family with multiple chromosomal localizations

One of the genes activated in human melanoma cells by the tumor-promoting phorbol ester is that of the elongation factor 1 alpha. A cDNA clone containing the complete 3'-end untranslated region and the nucleotide sequences coding for 227 carboxyterminal amino acids was isolated. Computer-assisted comparison with known sequences of elongation factors from other species revealed homologies up to 73% and 63% on amino acid and nucleotide sequences, respectively. Northern blot analysis of mRNA from unstimulated and phorbol ester-treated cells showed a 3- to 5-fold increase in cytoplasmic elongation factor 1 alpha mRNA after phorbol ester induction. When compared with the phorbol ester-inducible single-copy gene transcripts coding for the tissue-type plasminogen activator, the cellular mRNA content of elongation factor 1 alpha is 30 times higher. By Southern blot analysis experiments on human genomic DNA, a multi-gene family was found showing polymorphisms in restriction endonuclease fragment lengths (RFLP). Several polymorphisms were studied more extensively in the population on more than 100 DNA samples from normal individuals and in three-generation families. In situ hybridization of the cDNA probe to normal human metaphase chromosomes showed multiple chromosomal localizations of the elongation factor gene(s), with peak hybridization on the chromosomes 1, 2, 4, 5, 6, 7, and 15. The estimate of the gene copy number in humans is more than ten copies per (haploid) genome.

Phorbol ester stimulates the synthesis and phosphorylation of a 48 kDa-intracellular protein in plasminogen activator secreting melanoma cells

Phorbol ester (12-O-tetradecanoyl-phorbol 13-acetate) stimulates the secretion of tissue-type plasminogen activator by the melanoma cell line, Bowes. This effect is associated with increased levels of mRNAs for both tissue-type plasminogen activator and a 48 kDa-protein. Labelling of melanoma cells with L-[35S]methionine allowed to identify an intracellular protein which, by 3 criteria, was identical with the in vitro translation product of the 48kDa-protein mRNA: a Mr of 48,000 on electrophoresis in the presence of sodium dodecyl sulphate; inducibility by phorbol ester and failure of reducing agents to affect electrophoretic mobility. As detectable by L-[35S]methionine labelling, the protein was mainly localized in the cytosol. In vitro phosphorylation reactions, carried out on subcellular fractions revealed a membrane-associated protein which also had the three characteristics of the aforementioned 48 kDa-protein. Phosphorylation did not require Ca2+-ions. Addition of phorbol ester to the reaction mixtures increased the phosphorylation. Reconstitution experiments between membrane and cytosol fractions of phorbol ester-treated and untreated cells showed that the 48kDa protein occurs in a cytosolic, unphosphorylated and a membrane-bound, phosphorylated form and that the former is converted to the latter by a phorbol ester activated, membrane-associated protein kinase.

Hormonal regulation of extracellular plasminogen activators and Mr approximately 54,000 plasminogen activator inhibitor in human neoplastic cell lines, studied with monoclonal antibodies

We have studied the regulation by glucocorticoids and dibutyryl cAMP of the amounts of urokinase-type plasminogen activator (u-PA), tissue-type plasminogen activator (t-PA) and a Mr approximately 54000 plasminogen activator inhibitor accumulated in serum-free conditioned culture fluid by a human fibrosarcoma, a human glioblastoma and a human melanoma cell line (HT-1080, UCT/gl-1 and Bowes). For the quantitation of u-PA and t-PA, we used sandwich-type ELISA with a combination of polyclonal and monoclonal antibodies. For an estimation of variations in the amount of the inhibitor, we used sodium dodecyl sulphate-polyacrylamide gel electrophoresis followed by Coomassie blue staining of conditioned culture fluid proteins, the inhibitor protein band being identified by its selective removal by passage of the conditioned culture fluids through a column with monoclonal antibodies against the inhibitor. The modulation of the 3 proteins by the hormonal agents varied greatly between the cell lines. The proteins were independently regulated, in the sense that the hormonal agents did not concomitantly change their levels in the direction expected either to increase or decrease total extracellular plasminogen activator activity. In conditioned culture fluids containing both t-PA and inhibitor, the two were present in the medium as a Mr approximately 120 000 complex. In contrast, no u-PA inhibitor complexes were found in conditioned culture fluid from any of the cell lines; this is likely to be due to the occurrence of u-PA in the culture fluid in the one-chain proenzyme form, which, unlike active u-PA, does not react with the inhibitor. These findings illustrate the complexity of the regulation of extracellular plasminogen activator activity, and imply that the presumed functional diversity of u-PA and t-PA may be related to their independent regulation.

Messenger RNA for a phorbol-ester induced 48,000 dalton protein from human melanoma cells

Messenger RNA of the phorbol ester-induced 48kDa protein from human melanoma cells (Bowes) was isolated, characterized and used to study the protein processing. The 48kDa mRNA is induced simultaneously with that of tissue-type plasminogen activator. This induction is prominent as shown by sedimentation profiles on linear sucrose gradients. The mRNA can be isolated by classical phenol extractions, has a poly(A)-tail and sediments with a coefficient of 20 S. Translation in reticulocyte lysates yields a 48kDa protein whether the translation is modified with canine pancreas microsomal membranes or not. Analysis of 48kDa mRNA translation products by sodium dodecyl sulphate/polyacrylamide gel electrophoresis showed that the phorbol ester-induced 48kDa is a monomeric one-chain polypeptide. Glycosylation could not be detected, nor signal peptide cleaving, suggesting that it is a non-secreted intracellular protein.

Stimulation of tissue plasminogen activator production from epithelial cell lines

The aim of this study was to investigate the possibility of enhancing the yield of tissue plasminogen activator (tPA) from two epithelial cell lines of normal (non-malignant) derivation grown in tissue culture. The three agents used in this investigation were chosen because of their proven enhancing effect on analogous cells or products. The anabolic hormone stanozolol was found to have no significant stimulatory effect on these cell lines. A phorbol acetate (12-O-tetradecanoylphorbol 13-acetate) caused a twofold enhancement in tPA yield but the most significant results were obtained with 5-azacytidine. This agent increased the yield by up to fourfold in small stationary cultures and threefold in large-scale microcarrier cultures. A combination of azacytidine and phorbol acetate did not have an additive effect on total yield but did alter the kinetics of tPA expression with time. Indications were that the maximum yield with these types of potentiating agents was achieved as it could not be increased by using a combination of two different agents.

Plasminogen activator in mouse and rat oocytes: induction during meiotic maturation

We have found that ovulated mouse and rat oocytes contain tissue-type plasminogen activator (PA). Primary oocytes isolated from ovaries did not contain the enzyme. During spontaneous meiotic maturation in vitro, tissue-type PA became detectable 5 hr after germinal vesicle breakdown. Induction of tissue-type PA activity was blocked by dibutyryl-cAMP or isobutylmethyl-xanthine as well as by cycloheximide, but not by actinomycin D or alpha-amanitin. These results suggest that tissue-type PA mRNA is present in primary oocytes, and that translation of this mRNA is triggered upon resumption of meiotic maturation. Tissue-type PA catalyzed proteolysis around live secondary oocytes and fertilized eggs, indicating secretion of the enzyme. Unlike secondary oocytes, fertilized eggs denuded of their zona pellucida no longer contained the enzyme, suggesting that tissue-type PA production stops at or around fertilization, and that the bulk of the enzyme is secreted at this time.

Chromosomal locations of human tissue plasminogen activator and urokinase genes

A panel of human-mouse somatic cell hybrids and specific complementary DNA probes were used to map the human tissue plasminogen activator and urokinase genes to human chromosomes 8 and 10, respectively. This result is in contrast to a previous assignment of a plasminogen activator gene to chromosome 6. As neoplastic cells produce high levels of plasminogen activator, it is of interest that aberrations of chromosome 8 have been linked to various leukemias and lymphomas and that two human oncogenes, c-mos and c-myc, have also been mapped to chromosome 8.

Determination of tissue-type plasminogen-activator mRNA in human and non-human cell lines by dot-blot hybridization

A labelled cDNA clone was used in DNA-RNA hybridization on nitrocellulose filter paper (dot-blot technique) to detect and quantify mRNA for endogenous tissue plasminogen activator (PA) in cell extracts and samples of RNA purification runs. Although, for detection purposes, the assay was less sensitive than translation in Xenopus oocytes, it was at least as reliable and much more convenient for the purpose of quantitative determination. In particular, the technique was used to study the kinetics of PA mRNA formation in a human melanoma cell line (Bowes) after exposure to the tumour promoter 12-O-tetradecanoylphorbol 13-acetate (TPA). Incubation of the cells with TPA resulted in a 15-20-fold increase in cellular PA mRNA content. The effect was time- and dose-dependent: the increase in PA-specific mRNA was clearly visible as early as 4 h after initiation of TPA treatment in Bowes cells. It was blocked completely by pretreatment of the cells with actinomycin D, indicating that TPA caused enhancement of synthesis of PA mRNA rather than inhibition of PA mRNA degradation. The use of the nitrocellulose dot-blot technique also revealed that two non-human cell lines produce mRNAs which cross-react with the human PA mRNA, namely the mouse melanoma cell line B16 and the rat brain-tumour cell line, RT4-71-1. TPA was found to exert similar stimulatory effects on the synthesis of mRNAs in these cell lines as in Bowes cells.

In vivo induction of rat hepatic ornithine decarboxylase and plasminogen activator by 12-O-tetradecanoylphorbol 13-acetate

Rapid and substantial elevations in ornithine decarboxylase and plasminogen activator have been linked to tumor promotion in mouse epidermis and in vitro. Systemic administration of 12-O-tetradecanoylphorbol 13-acetate (TPA) rapidly increased both enzymic activities in rat liver. Pretreatment with either cycloheximide or actinomycin D attenuated both enzyme inductions. It is concluded that: (1) systemic TPA rapidly induces plasminogen activator and ornithine decarboxylase activities in rat liver; and (2) both inductions reflect de novo enzyme synthesis.

Cloning, nucleotide sequencing and expression of cDNAs encoding mouse urokinase-type plasminogen activator

Controlled extracellular proteolysis is catalyzed in part by the secretion of plasminogen activators. As a step in the study of the expression of these enzymes in mouse tissues, we have isolated five cDNAs encoding the mouse urokinase-type plasminogen activator from a cDNA library prepared with size-selected mRNA from MSV-transformed 3T3 cells. The longest cDNA insert contains the entire coding region of mouse urokinase, 58 base pairs of the 5' non-coding region, and the entire 3' non-coding region, which is 942 base pairs long. The deduced protein sequence, which starts with a signal peptide of 20 amino acids, shows extensive homology to that of human and porcine urokinase. However, in contrast to these enzymes, mouse urokinase contains no N-glycosylation site. Bacteria harbouring one of the recombinant plasmids synthesize and secrete into their periplasm a protease indistinguishable from mouse urokinase.

Isolation of a collagenase cDNA clone and measurement of changing collagenase mRNA levels during induction in rabbit synovial fibroblasts

To facilitate our studies on the mechanisms controlling collagenase production at a molecular level in rabbit synovial fibroblasts, we have constructed a cDNA library using mRNAs isolated from cells induced with crystals of monosodium urate monohydrate. We have screened this library with cDNA probes made from induced and control mRNA populations. From among 30 clones that hybridized preferentially to the induced-cell probe, 4 contained collagenase sequences. The largest, a clone of 650 base pairs, was identified by its ability to hybrid select a mRNA that could be translated in a cell-free system into a product that was precipitable with monospecific antibody to collagenase. Using this clone to probe blots of RNA from induced cells, we detected the appearance of a collagenase mRNA of 2.7 kilobases within 5 hr of addition of urate. The level of collagenase mRNA continued to increase for 35-40 hr, when it was 60 to 90 times more abundant in induced cells than in control cells. The increase in mRNA levels correlated with an increase in immunoreactive collagenase protein that was detectable in culture medium by 10 hr.

Induction of plasminogen activator in a human diploid fibroblast cell line (MRC-5) by conditions which cause induction of interferon: the role of calcium ions

The human diploid fibroblast cell line, MRC-5, derived from embryo lung tissue produced only small quantities of plasminogen activator (PA) when harvested using a standard nutrient medium (Eagle's Minimal Essential Medium, MEM). Use of a schedule designed to induce high concentrations of fibroblast interferon in these cells also resulted in production of considerably enhanced levels of PA. The kinetics of PA production differed from those of interferon production; specifically, PA was produced for at least 6 days following induction despite the toxicity of the inducers whereas interferon synthesis continued for only 1 day. Further investigation of the induction conditions for PA revealed that double-stranded RNA which was absolutely required for interferon production was not required for induction of PA. Indeed, the stimulus for enhancement of PA production appeared to be solely an elevated concentration of calcium ions in the extracellular medium. The possible physiological relevance of this induction of PA by elevated concentrations of calcium ions is discussed.