Transcriptional induction of urokinase in cultured human kidney carcinoma cells by tetradecanoyl-phorbol-acetate

IDENTIFICATION OF CELLS RESPONSIBLE FOR UROKINASE-TYPE PLASMINOGEN ACTIVATOR SYNTHESIS AND SECRETION IN HUMAN DIPLOID KIDNEY CELL CULTURES

Human urokinase-type plasminogen activator (uPA) is a serine protease that converts plasminogen to plasmin. It is produced and secreted by a variety of different human cells in vivo and in vitro. We have studied human diploid kidney cell (HKC) cultures prepared from neonatal kidney tissue and cultures of purified populations of HKC to determine which cells synthesize and secrete uPA into the culture medium. Antibodies against cell specific antigens and uPA were used to correlate specific kidney cell types with uPA synthesis. In addition, secretion of uPA activity into growth and uPA production media was determined for each cell type and cultures containing a mixture of cell types. The results of these studies demonstrated that glomerular visceral epithelial and kidney tubular epithelial cells synthesize and secrete uPA into the culture medium.

Nuclear pp64 is phosphorylated in both serine/threonine and tyrosine through complex pathways regulated by 12-O-tetradecanoylphorbol-13-acetate and platelet-derived growth factor

Platelet-derived growth factor (PDGF) induces the time and dose dependent serine/threonine phosphorylation of pp64, a nuclear protein in normal rat kidney (NRK) cells. pp64 is phosphorylated additionally on tyrosine in SSV-transformed NRK cells. To further characterize the regulation of phosphorylation of pp64, other mitogens and inhibitors were studied. 12-O-tetradecanoylphorbol-13-acetate (TPA) but not epidermal growth factor (EGF) or insulin induced the phosphorylation of nuclear pp64. Addition of the inhibitor H7 to TPA-treated NRK cells resulted in a striking further increase in phosphorylation of pp64 and, to a lesser extent, in NRK cells treated with PDGF and H7. When cells were treated with PDGF and H7, pp64 was recognized by anti-phosphotyrosine antisera. The increased phosphorylation induced by H7 was inhibited when forskolin was included. This loss of phosphorylation in pp64 with forskolin treatment paralleled a loss of immunoreactivity of pp64 to anti-phosphosphotyrosine. Complex and independent pathways thus appear to signal the growth factor dependent nuclear phosphorylation of pp64, involving phosphorylations both on serine/threonine and on tyrosine.

An upstream enhancer and a negative element in the 5' flanking region of the human urokinase plasminogen activator gene

The 5' flanking region of the human urokinase (uPA) gene has been fused to the reporter chloramphenicol acetyl transferase (CAT) gene and its activity assayed by transfection in two human cell lines. Progressive deletions of the uPA regulatory region from the 5' end maintain a high level of expression provided at least 1870 (in A1251 cells) or 1963 (in HFS10 cells) nucleotides of the 5' flanking region are retained. A DNA fragment from -2350 to -1824 has enhancer properties, stimulating transcription of an enhancerless SV40 early promoter independently of orientation and distance. Internal deletions that still retain the enhancer element reveal the presence of negative cis-acting sequences between -1824 and -1572. Their removal, in fact, increases uPA transcriptional activity. Differences of expression of the uPA-CAT fusion genes in the two cell lines are also observed, indicating the presence of cell-specific cis-acting sequences.

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.

Inhibition of protein synthesis in LLC-PK1 cells increases calcitonin-induced plasminogen-activator gene transcription and mRNA stability

The peptide hormone calcitonin induces the accumulation of urokinase-type plasminogen activator (uPA) mRNA in pig kidney LLC-PK1 cells. By itself, inhibition of protein synthesis had a negligible effect on uPA mRNA accumulation. Inhibition of protein synthesis led to two superinductive effects: an increase in calcitonin-induced uPA mRNA accumulation over time, and a shift in the dose-response curve so that lower calcitonin doses became more potent. To explain these two superinductive effects of protein-synthesis inhibition on calcitonin treatment, we demonstrated that the inhibition of protein synthesis increased both calcitonin-induced uPA-gene transcription and uPA-mRNA stability. Different protein-synthesis inhibitors had similar actions, arguing against the possibility that the results were attributable to an anomalous action of a particular inhibitor. The superinductive effects of protein-synthesis inhibition could not be mimicked when a tumour promoter, 12-O-tetradecanoylphorbol 13-acetate (TPA), was used instead of calcitonin as an inducer. Calcitonin and TPA exert their effects through different pathways, suggesting a clue to the mechanism of superinduction. Although inhibition of protein synthesis has been reported to increase transcription and mRNA stability in a number of other systems, the one described here appeared unique in combining both effects in the context of hormonal regulation.

Autocrine saturation of pro-urokinase receptors on human A431 cells

Single-chain pro-urokinase (pro-uPA) is present both in the medium and lysate of the A431 epidermoid carcinoma cell line. Most of the cell-associated pro-uPA is on the cell surface, as shown by indirect immunofluorescence and by surface iodination. Pro-uPA is not an integral membrane protein but is bound to a specific surface receptor that is completely saturated. A mild acid treatment uncovers the surface receptors by dissociating pro-uPA. Resaturation of uncovered receptors has been studied by reincubating cells in normal medium; within 40 min, 50% of the free sites are reoccupied. Excess uPA-specific antibodies prevent rebinding of ligand to the receptors. Thus, A431 cells first secrete uPA, which then binds to the surface receptor. We propose that the synthesis of uPA and uPA receptor by the same cell may provide a pathway for the activation of the metastatic potential of malignant cells.

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.

Increase in urokinase plasminogen activator mRNA synthesis in human carcinoma cells is a primary effect of the potent tumor promoter, phorbol myristate acetate

The effect of tumor promoters and growth factors on the synthesis of urokinase and urokinase mRNA in human carcinoma cells has been investigated. In urokinase-producing human carcinoma cells (A1251), a 20-40-fold increase in urokinase mRNA level is obtained after treatment with 10 nM phorbol myristate acetate (PMA), a smaller effect (two- to fourfold) with 2 ng/ml platelet-derived growth factor (PDGF) and no effect with epidermal growth factor (EGF) (up to 50 nM). After treatment with PMA, urokinase mRNA level increases already at 30 min peaking 2-4 h thereafter. Cell line A431, which has an abnormally high number of EGF receptors, shows the same response to PMA, but also responds to EGF (two- to fourfold increase in mRNA). The kinetics are similar to those of A1251. Nuclear transcription experiments show that the PMA-induced increase in urokinase mRNA is due to increased synthesis. The protein synthesis inhibitor, cycloheximide (10 micrograms/ml), also increases the level of urokinase mRNA. When both cycloheximide and PMA are used, super-induction is observed. This result may indicate that a short-lived protein negatively regulates the level of urokinase. The different efficiency of the effectors (PMA and PDGF better than EGF) and their kinetics, as well as the effect of cycloheximide on urokinase mRNA synthesis, (a) are reminiscent of the effect of PDGF and PMA on competence phase genes (Kelly, K., B.H. Cochran, C.D. Stiles, and P. Leder, 1983, Cell, 35: 603-610), (b) demonstrate that the synthesis of urokinase is part of the early cellular response to these factors, and (c) provide a preliminary insight in the overproduction of urokinase by primary malignant tumors and transformed cells in culture.

Characterization of plasminogen activator from two human renal carcinoma cell lines

Plasminogen activator (PA) activity was identified in the conditioned medium of two human renal carcinoma cell lines, Cur and Caki-1. PA activity of medium, following chromatography on Con A-Sepharose, was divided into effluent and eluate fractions, the latter obtained after elution with methyl mannoside. The ratio of PA activity in effluent:eluate was 90:10 for Caki-1 and 60:40 for Cur. The PA of both effluent fractions and the Caki-1 eluate fraction was of the urokinase (UK) type. Identification rested on molecular weight determination by zymography (major component with Mr 52,000 and a less prominent component of 93,000), lack of binding to fibrin, inhibition by anti-UK antibodies, and lack of inhibitory effect of anti-tissue type PA (TPA) antibodies or the Erythrina trypsin inhibitor, which inhibits TPA but not UK. PA of the Cur eluate fraction gave a more complex pattern in that it bound significantly to fibrin (like TPA), was completely inhibited by both anti-UK and anti-TPA antibodies, but was unaffected by Erythrina trypsin inhibitor. These results raise the possibility of an unusual PA-like enzyme that immunologically cross reacts with anti-UK and anti-TPA. Most of the PA of both cell lines was secreted in a latent form that could be activated by trypsin treatment. The latency appears to result largely from secretion of urokinase proenzyme, which is consistent with the Mr 52,000 of the major PA species and the insensitivity to diisopropyl fluorophosphate inhibition prior to trypsin activation. However, in addition, a UK binding component was found in the conditioned medium, which produced an Mr 93,000 component by reaction with UK.

The tumor promoter phorbol 12-myristate 13-acetate induces a program of altered gene expression similar to that induced by platelet-derived growth factor and transforming oncogenes

Treatment of mouse NIH 3T3 cells with the phorbol ester tumor promoter, phorbol 12-myristate 13-acetate, results in altered transcription of several genes as measured in nuclear run-off experiments. The first set of genes, whose altered transcription occurs rapidly in the absence of protein synthesis, is typified by induction of c-myc and c-fos and decreased transcription of alpha 2 type I procollagen. This work demonstrates the existence of a second class of genes whose rapidly increased transcription requires prior protein synthesis, which is represented by the gene encoding a secreted lysosomal protein, MEP. Similar induction of MEP RNA is seen after treatment with platelet-derived growth factor or transformation with Kirsten sarcoma virus.

Human urokinase gene is located on the long arm of chromosome 10

Urokinase is one of the two plasminogen activators that catalyze the conversion of inactive plasminogen to plasmin. By combining somatic cell genetics, in situ hybridization, and Southern hybridization, we localized the human urokinase gene on the distal third of the long arm (q24-qter) of chromosome 10.

The human urokinase-plasminogen activator gene and its promoter

The urokinase type of plasminogen activator (uPA) is subject to regulation by hormones, phorbol esters and oncogenic transformation. This enzyme has been suggested to play a key role in processes involving cell migration and tissue remodeling, and to be essential for tumor metastasis. In order to study these processes, we have isolated the human uPA gene, and have determined its entire nucleotide sequence. The gene is organized in 11 exons and is 6.4 kb long. The 5' end of uPA mRNA has been determined by both S1 mapping and primer extension experiments. A fragment of 800 bp containing the entire 5' flanking region shows promoter activity when introduced upstream of a bacterial chloramphenicol acetyltransferase gene and introduced into human cells. The hexanucleotide sequence GGCGGG, previously found at similar regions in several viral and eukaryotic promoters and shown to be essential for promoter activity (McKnight et al. (1984) Cell, 37, 253-262), is repeated three times between the CAAT and the TATA boxes.