Binding of urokinase to specific receptor sites on human breast cancer membranes

Breast Cancer Metastasis Suppressor 1 Inhibits Gene Expression by Targeting Nuclear Factor-κB Activity

Breast cancer metastasis suppressor 1 (BRMS1) functions as a metastasis suppressor gene in breast cancer and melanoma cell lines, but the mechanism of BRMS1 suppression remains unclear. We determined that BRMS1 expression was inversely correlated with that of urokinase-type plasminogen activator (uPA), a prometastatic gene that is regulated at least in part by nuclear factor-kappaB (NF-kappaB). To further investigate the role of NF-kappaB in BRMS1-regulated gene expression, we examined NF-kappaB binding activity and found an inverse correlation between BRMS1 expression and NF-kappaB binding activity in MDA-MB-231 breast cancer and C8161.9 melanoma cells stably expressing BRMS1. In contrast, BRMS1 expression had no effect on activation of the activator protein-1 transcription factor. Further, we showed that suppression of both constitutive and tumor necrosis factor-alpha-induced NF-kappaB activation by BRMS1 may be due to inhibition of IkappaBalpha phosphorylation and degradation. To examine the relationship between BRMS1 and uPA expression in primary breast tumors, we screened a breast cancer dot blot array of normalized cDNA from 50 breast tumors and corresponding normal breast tissues. There was a significant reduction in BRMS1 mRNA expression in breast tumors compared with matched normal breast tissues (paired t test, P < 0.0001) and a general inverse correlation with uPA gene expression (P < 0.01). These results suggest that at least one of the underlying mechanisms of BRMS1-dependent suppression of tumor metastasis includes inhibition of NF-kappaB activity and subsequent suppression of uPA expression in breast cancer and melanoma cells.

Clinical significance of urokinase-type plasminogen activator receptor (uPAR) expression in cancer

The involvement of the urokinase-type plasminogen activator (uPA) system in particular has been extensively studied in the pathogenesis of cancer. The molecular role of the uPA receptor (uPAR) is well characterized with its participation in cell migration and extracellular matrix (ECM) degradation. Over-expression of uPAR in cancer has been demonstrated in many studies and is considered an attractive target for anticancer agents. We and others have down-regulated uPAR expression in an attempt to inhibit cancer metastasis based on its molecular role. Uniquely, uPAR which is a glycosyl phosphatidylinositol anchored protein is not only bound to the cell surface but also has a soluble form, suPAR. There is now accumulated clinical and experimental evidence supporting the significant role of uPAR and its soluble counterpart in a number of solid cancers. The expression of uPAR can be associated with tumor cells or stromal cells or both. Differences observed in the expression of uPAR using immunohistochemistry (IHC) are likely explained by the use of different antibodies and techniques rather than true cellular differences and are reviewed here. This review summarizes the clinical relevance of uPAR and its soluble form in the prognosis and diagnosis of different cancers.

Reduced β3-endonexin levels are associated with enhanced urokinase-type plasminogen activator receptor expression in ApoE−/− mice

Proteolysis of extracellular matrix components is required for cell migration occurring in atherosclerotic lesion formation. In the present study, gene expression of the urokinase plasmingen activator receptor (uPAR) and underlying mechanisms were analyzed during the development of atherosclerosis in the aorta of apolipoprotein E-deficient mice (apoE(-/-)). A significant increase of uPAR expression was detected in the atherosclerotic tissue with advancing plaque-dimension. As uPAR gene transcription involves the transcription factor nuclear factor-kappaB (NF-kappaB), we analyzed nuclear NF-kappaB activity in vascular tissue of apoE-deficient mice. Congruent to uPAR, we could detect an increase in NF-kappaB activity, which underlines the chronic inflammatory component of the disease. Recently we reported that beta(3)-endonexin, a protein that modulates beta(3)-integrins, regulates uPAR expression through direct interaction with subunits of the NF-kappaB-complex. Herein we could show that beta(3)-endonexin protein is expressed in aortic tissue of mice. Moreover, in contrast to uPAR or NF-kappaB, the expression of beta(3)-endonexin was reduced in extracts of advanced atherosclerotic aortic tissue. The cytoplasmic protein beta(3)-endonexin regulates function of beta(3)-integrins. We revealed that integrin stimulation of endothelial cells led to an enhanced NF-kappaB activity and secretion of the NF-kappaB dependent chemokine monocyte chemoattractant protein-1 (MCP-1). The beta(3)-integrin dependent increase in MCP-1 was notedly reduced in cells that overexpressed beta(3)-endonexin. These results provide strong evidence that beta(3)-endonexin acts as a regulating factor in the integrin-mediated signal transduction and the present findings imply a pathophysiological role of beta(3)-endonexin in atherogenesis.

Growth factor-dependent activation of the MAPK pathway in human pancreatic cancer: MEK/ERK and p38 MAP kinase interaction in uPA synthesis

Increased expression of the hepatocyte growth factor (HGF) receptor (c-met) and urokinase type plasminogen (uPA) correlated with the development and metastasis of cancers. To investigate the role of HGF/c-met signaling on metastasis in cancer cells stimulated with HGF, we examined the effects of a specific MEK1 inhibitor (PD98059) and a p38 MAP kinase inhibitor (SB203580) on HGF-induced uPA expression in pancreatic cancer cell lines, L3.6PL and IMIM-PC2. Pretreatment of PD98059 decreased HGF-mediated phosphorylation of extracellular receptor kinase (ERK), uPA secretion and expression of matrix metalloproteinases (MMP-2 and MMP-9) in a dose-dependent manner. In contrast, SB203580 pretreatment increased HGF-stimulated ERK phosphorylation, uPA secretion and expression of MMPs. SB203580 also reversed the inhibition of HGF-mediated ERK activation and uPA secretion in the PD98059-pretreated cells. These results suggest that ERK activation by HGF might play important roles in the metastasis of pancreatic cancer and the p38 MAPK pathway also involved in the HGF-mediated uPA secretion and metastasis by regulation of ERK pathway.

Prognostic significance of tissue-type plasminogen activator (tPA) content in gastric cancer and surrounding mucosa

AIMS

We analyzed the tPA content in primary gastric carcinomas and surrounding mucosa in order to assess the relationship between tPA content, clinicopathological tumor characteristics, and estrogen and progesterone receptor content. We evaluated the prognostic value of this serine protease in gastric cancer patients.

PATIENTS AND METHODS

122 resected gastric neoplasms and 95 adjacent mucosa samples were studied. The tPA content was measured in cytosol by an ELISA method. Cytosolic ER and PgR were measured with a solid phase enzyme immunoassay.

RESULTS

Cytosolic tPA levels in neoplastic tissues (median 1.0 ng/mg prot) were significantly lower (p=0.002) than those found in paired mucosa samples (median 2.3 ng/mg prot). There was no significant association between tPA levels and clinicopathological parameters or PgR content, but tPA levels were significantly correlated with ER content. The intermediate-tPA-content group, corresponding to samples with between 0.3 and 1.70 ng/mg protein, proved to have a significantly high risk of relapse.

CONCLUSIONS

We found a wide variability in tPA levels in gastric carcinoma and adjacent mucosa samples, with significantly decreased levels in tumors and a significantly positive relationship between tPA levels and ER status. There was a non-monotonic relationship between tPA levels and prognosis in patients with gastric cancer.

beta(3)A-integrin downregulates the urokinase-type plasminogen activator receptor (u-PAR) through a PEA3/ets transcriptional silencing element in the u-PAR promoter

Migration of cells requires interactions with the extracellular matrix mediated, in part, by integrins, proteases, and their receptors. Previous studies have shown that beta(3)-integrin interacts with the urokinase-type plasminogen activator receptor (u-PAR) at the cell surface. Since integrins mediate signaling into the cell, the current study was undertaken to determine if in addition beta(3)-integrin regulates u-PAR expression. Overexpression of beta(3)-integrin in CHO cells, which are avid expressers of the receptor, downregulated u-PAR protein and mRNA expression. The u-PAR promoter (-1,469 bp) that is normally constitutively active in CHO cells was downregulated by induced beta(3)-integrin expression. A region between -398 and -197 bp of the u-PAR promoter was critical for beta(3)-integrin-induced downregulation of u-PAR promoter activity. Deletion of the PEA3/ets motif at -248 bp substantially impaired the ability of beta(3)-integrin to downregulate the u-PAR promoter, suggesting that the PEA3/ets site acts as a silencing element. An expression vector encoding the transcription factor PEA3 caused inhibition of the wild-type but not the PEA3/ets-deleted u-PAR promoter. The PEA3/ets site bound nuclear factors from CHO cells specifically, but binding was enhanced when beta(3)-integrin was overexpressed. A PEA3 antibody inhibited DNA-protein complex formation, indicating the presence of PEA3. Downregulation of the u-PAR promoter was achieved by the beta(3)A-integrin isoform but not by other beta(3)-integrin isoforms and required the cytoplasmic membrane NITY(759) motif. Moreover, overexpression of the short but not the long isoform of the beta(3)-integrin adapter protein beta(3)-endonexin blocked u-PAR promoter activity through the PEA3/ets binding site. Thus, besides the physical interaction of beta(3)-integrin and u-PAR at the cell surface, beta(3) signaling is implicated in the regulation of u-PAR gene transcription, suggesting a mutual regulation of adhesion and proteolysis receptors.

Oestradiol regulation of the components of the plasminogen-plasmin system in MDA-MB-231 human breast cancer cells stably expressing the oestrogen receptor

To understand the hormonal regulation of the components of the plasminogen-plasmin system in human breast cancer, we examined the oestradiol (E2) regulation of plasminogen activators (PAs), namely urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA), plasminogen activator inhibitor type 1 (PAI-1) and uPA receptor (uPAR), in our model system. We used stable transfectants of the MDA-MB-231 human breast cancer cells that express either the wild-type (S30 cells) or the mutant 351asp-->tyr oestrogen receptor (ER) (BC-2 cells). Northern blot analysis showed that there was a concentration-dependent down-regulation of uPA, tPA and PAI-1 mRNAs by E2. In contrast, uPAR mRNA was not modulated by E2. The pure anti-oestrogen ICI 182,780 was able to block E2 action, indicating that the regulation of these genes is ER mediated. The E2 also inhibited the expression and secretion of uPA, tPA and PAI-1 proteins as determined by enzyme-linked immunosorbent assay (ELISA) in cell extracts (CEs) and conditioned media (CM). Zymography of the CM confirmed the inhibitory effect of E2 on uPA activity. Thus, we now report the regulation of uPA, PAI-1 and tPA by E2 in both mRNA and protein levels in ER transfectants. The association between down-regulation of the uPA by E2 and known E2-mediated growth inhibition of these cells was also explored. Our findings indicate that down-regulation of uPA by E2 is an upstream event of inhibitory effects of E2 on growth of these cells as the addition of exogenous uPA did not block the growth inhibition by E2.

The influence of antiestrogens on the release of plasminogen activator (uPA) by MDA-MB-231 and MCF-7 breast cancer cells

Plasminogen activators are known to be involved in the metastatic spread of breast cancer. In the present study we examined the effects of antiestrogens [Analog II (1,1-dichloro-cis-2,3-diphenyl cyclopropane) (AII), ICI-182,780 (ICI) and tamoxifen (TAM)], on the in vitro release of uPA from estrogen receptor (ER)-positive MCF-7 (MCF) and ER-negative MDA-MB-231 (MDA) human breast cancer cell lines. Using a solid-phase radioassay, uPA activity was found to be higher in the culture medium from MDA cells compared to MCF cells. Aminocaproic acid, a specific plasmin inhibitor, produced a 50-60% reduction in the degradation of labeled substrate, in the solid phase assay, using culture medium from both cell lines, thus indicating that most of the proteolysis observed was due to uPA-mediated plasmin generation from plasminogen. In the absence of plasminogen, the enzyme activity was not detected in either the quantitative assay or by zymography. In MDA cells, uPA release was not altered by any of the antiestrogens used alone or in the presence of estradiol. In contrast, in MCF cells, ICI alone produced maximal inhibition (40%) of enzyme release, while estradiol alone produced a 120% increase in enzyme activity. When co-administered with estradiol, in MCF cultures, each antiestrogen reduced enzyme activity to control levels. Substrate gel zymography revealed that the urokinase-type PA is the predominant form of PA released by both cell lines. Comparison of the activity of all three antiestrogens used in this study indicates that ICI is the most potent inhibitor of enzyme activity in ER-positive MCF cells.

In vitro anti-proliferative and anti-invasive role of aminoterminal fragment of urokinase-type plasminogen activator on 8701-BC breast cancer cells

8701-BC cells, derived from a primary carcinoma of the breast, constitutively express mRNA for urokinase-type plasminogen activator (uPA). In this paper, we demonstrated the presence of uPA in the conditioned medium, and of uPA-receptor (uPAR) on the cell surface of 8701-BC cells, which therefore have the potential for an autocrine mechanism of uPA-mediated stimulation. We examined whether exogenous addition of either intact uPA, or its amino-terminal fragment (uPA-ATF), which lacks catalytic activity but retains the uPAR binding site and a growth factor-like domain, or immunoneutralisation of endogenous uPA-uPAR interactions could exert any effect on the proliferative and invasive behaviour of 8701-BC cells. The data demonstrate that, while uPA promotes growth and invasion of 8701-BC cells, its effect reversed by blocking uPA-uPAR interactions, uPA-ATF not only fails to impart growth factor-like signals, but also restrains cell invasion in vitro. In the light of these and other data, an active participation of ATF in the complex cell-ECM network of interactions underlying cancer progression can be postulated. In addition, it appears worth considering the possibility of testing the effect of this uPA fragment in vivo for the therapy of breast (and possibly other) human invasive carcinomas.

Urokinase plasminogen activator and urokinase plasminogen activator receptor in breast cancer

Urokinase plasminogen activator (uPA) is a serine protease involved in cancer invasion and metastasis. uPA mediates its action while attached to a membrane-bound receptor (uPAR). In this investigation we show that uPAR levels correlate with uPA levels in human breast cancers. uPAR levels, however, do not correlate with other components of the plasminogen activator system such as tissue-type plasminogen activator (t-PA), PAI-I or PAI-2. In addition, uPAR levels showed no correlation with tumor size, axillary-node status or estrogen-receptor status. On the basis of an optimum cut-off point, patients with breast cancers containing high levels of uPAR had a worse prognosis than patients with low levels of the receptor. However, as a prognostic marker in breast cancer, uPAR was not as strong as uPA. Our results are consistent with data from model systems suggesting that both uPA and uPAR are necessary for metastasis.

Urokinase receptor in breast cancer tissue extracts. Enzyme-linked immunosorbent assay with a combination of mono- and polyclonal antibodies

Urokinase plasminogen activator (uPA) is a proteolytic enzyme involved in degradation of the extracellular matrix during cancer invasion. The levels of uPA and its inhibitor PAI-1 in tumor extracts have previously been demonstrated to be of prognostic value in breast cancer as well as other types of cancer. We have previously characterized a specific cell surface receptor for uPA (uPAR) which strongly enhances the catalytic activity of uPA and is expressed during mammary cancer invasion. In order to quantitate uPAR in breast cancer tissue, we have now developed a sensitive enzyme-linked immunosorbent assay (ELISA), with polyclonal catching antibodies and three monoclonal detecting antibodies. The detection limit of the assay is approximately 0.16 fmol of uPAR in a volume of 100 microliters (1.6 pM). There is a linear relationship between signal and uPAR concentration up to at least 6.6 fmol per 100 microliters (66 pM). Both free uPAR and uPAR in complex with uPA is detected. The recovery of an internal uPAR standard in breast cancer tissue extracts is above 87%. The intra-assay and inter-assay variation coefficients are 7% and 13%. In order to find a suitable buffer for extraction of various components of the uPA-system from breast cancer tissue, we tested buffers which previously have been used for optimal extraction of estrogen receptor (A), uPA (B), and uPAR (C). Buffer A and B extracted approximately 30% and 50%, respectively, of the amount of uPAR extracted with buffer C.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro receptor imaging for characterization of human solid tumors

Since many of the factors involved in tumor growth and progression act through a receptor-mediated mechanism, we applied in vitro receptor imaging techniques to study the intratumoral distribution and concentration of receptor-molecules having experimental biological relevance in such processes. Here we summarize the results of a study concerning the role of urokinase receptor (uPAR) in the acquisition of an invasive phenotype by tumor cells. Independently of the system studied, we demonstrated that in vitro receptor imaging techniques can be used to define the biological characteristics of human solid tumors and can contribute to clarify the complex network of ligand/receptor interactions leading to tumor spread.

Plasminogen activators and plasminogen activator inhibitors in blood and tumour fluids of patients with ovarian cancer

We quantitated urokinase and tissue plasminogen activator (u-PA, t-PA), plasminogen activator inhibitor 1 and 2 (PAI-1, PAI-2), and fibrinolytic activity in peripheral blood (PB), tumour blood (TB), peritoneal/ascitic fluid (PAF) and cystic fluid (CF) from 104 patients with benign and 36 patients with malignant ovarian tumours, and in peripheral blood from 62 healthy controls. PB levels of u-PA were higher in patients with benign and malignant tumours than in controls. High concentrations of u-PA were found in CF, but not in TB, suggesting that u-PA is released by the tumour tissue, but not by the tumour vasculature. PB levels of t-PA were higher in both tumour groups than in controls. Increased levels of t-PA were found in TB, but not in CF, indicating that t-PA is released by the tumour vasculature, but not by the tumour tissue. PB levels of PAI-1 were higher in patients with both benign and malignant tumours than in controls. High levels of PAI-1 were present in both TB and CF from malignant tumours, suggesting that PAI-1 is released from the tumour vasculature as well as the tumour tissue. Elevated concentrations of PAI-2 were found in CF, but not in TB, indicating release from the tumour tissue, but not from the vasculature. High levels of t-PA, PAI-1 and PAI-2 were found in PAF of malignant tumours, and resorption from this compartment may explain elevated PB levels in patients with ascites. None of the PAs/PAIs proved useful as a PB marker for detection of early stage ovarian cancer. However, an index based on PAF levels of t-PA and PAI-1 discriminated between malignant and benign ovarian cysts in the absence of ascites. In addition, our study stresses the importance of including patients with benign tumours as well as healthy controls when markers for malignant tumours are evaluated.

The Na+/H+ antiporter in oncology in the light of the spontaneous regression of cancer and cell metabolism

Multiple metabolic and biochemical interrelationships, as well as the most recent views on mechanisms of malignant cell growth, proliferation, and oncogen activity mediated by the Na+/H+ antiporter, can be integrated from the unitarian point of view of the dynamics of the hydrogen ion to parallel pH-related mechanisms involved in the Spontaneous Regression (SR) of some malignant tumors. Also, pH-related growth inhibitors of the amiloride series are considered as possible agents to be used in the adjuvant and co-adjuvant treatment of some human tumors as well as in the control of the metastatic process and in overcoming cancer multidrug resistance (MDR).

Cell membrane receptors for urokinase plasminogen activator are increased in malignant ovarian tumours

The binding of 125I-labelled urokinase plasminogen activator (uPA) to cell membranes of ovarian tumours was characterised. Binding was fast, specific to HMW-uPA, and saturated at low concentration [1.5 (range 1.2-1.6) nmol/l]. Scatchard analysis suggested a single class of binding sites with Kd 1.1 (0.9-1.3) nmol/l. These data indicate the presence of a specific cell membrane receptor for uPA in ovarian tumours, whose characteristics are similar to those reported for uPA receptors in other tissues. Endogenously occupied receptors were uncovered by exposing the membranes to acid conditions (pH 2) before assay, thereby allowing quantitation of the total amount of receptor. uPA receptors were assayed in 10 malignant and 6 benign epithelial ovarian tumours. The total number of receptors was higher in the malignant tumours. This was secondary to increases of both free and occupied receptors. We conclude that this reflects the biological function of cell surface bound plasminogen activation in tumour growth and spread.

Increase in levels of plasminogen activator and type-1 plasminogen activator inhibitor in human breast cancer: possible roles in tumor progression and metastasis

We measured antigen levels of two kinds of plasminogen activators, tissue type plasminogen activator (t-PA) and urokinase type plasminogen activator (UK), as well as their primary inhibitor, type-1 plasminogen activator inhibitor (PAI-1) in the tissue extracts of benign and malignant breast tumors. Tumor tissues of 36 fibroadenomas and 39 breast cancers were examined. t-PA levels were not different in both groups. Malignant tumors contained the significantly higher levels of UK than benign tumors (p less than 0.001). Furthermore in breast cancer tissues, UK antigen levels of tumors with axillary lymph node involvements were significantly higher than those of tumors without lymph node involvements (p less than 0.05). PAI-1 antigen levels of breast cancer tissues were dramatically higher than those of fibroadenoma (p less than 0.001). PAI-1 levels of node positive carcinomas showed also values significantly higher than node negative ones (p less than 0.01). When we divided cancer tissues into three groups as node negative tumors, tumors with positive axillary nodes fewer than four and tumors with four or more positive nodes, PAI-1 levels increased corresponding to the progression of lymph node involvements (p less than 0.05). Immunohistochemical studies, using mouse monoclonal antibodies to human UK and PAI-1, showed that those immunoreactivities were diffusely distributed in the cytoplasm of human breast cancer cells. Their staining patterns were very similar to each other.

Immunohistochemical analysis of plasminogen activator expression in human colorectal carcinomas: correlation with CEA distribution and tumor cell kinetics

Fifty cases of colorectal adenocarcinoma were immunohistochemically examined for the relationship between distribution of plasminogen activators (PAs) and the degree of differentiation of cancer cells as reflected by carcinoembryonic antigen (CEA) expression as well as tumor cell kinetics. The A chain of urokinase-type PA (u-PA-A) was mainly observed in the apical portions of highly differentiated cancer cells. Increased expression and change in localization to the cytoplasm were found with progressive dedifferentiation. The numbers of DNA polymerase alpha (pol. alpha) positive cancer cells also increased in line with u-PA-A expression. The B chain of u-PA (u-PA-B), and the A and B chains of tissue-type PA (t-PA-A and -B) did not show similar alteration. The present findings suggest that the distribution of u-PA-A in colorectal carcinoma tissues, the degree of tumor differentiation, and the proliferation kinetics of cancer cells are closely related.

Enhanced production of tissue-type plasminogen activator by estradiol in a novel type variant of human breast cancer MCF-7 cell line

ES-1 cells, which showed a higher sensitivity to the cytocidal action of estradiol were isolated from a human breast cancer MCF-7 cell line. Growth of ES-1 cells was inhibited by a dose of 17-beta estradiol that stimulated the growth of the parental MCF-7 cells. Proteins secreted from MCF-7 and ES-1 cells when cultured with 17-beta estradiol were compared by sodium dodecyl sulfate-containing polyacrylamide gel electrophoresis (SDS-PAGE). Addition of estradiol to culture medium enhanced secretion of a protein of molecular mass of 52 kDa in media for both MCF-7 and ES-1 cell lines, but the secretion of a second 67 kDa protein was enhanced about 10-fold only in ES-1 cells. The analysis by SDS-PAGE of culture medium immunoprecipitated with anti-tissue-type plasminogen activator (t-PA) antibody demonstrated that the band of 67 kDa protein specifically secreted from estradiol-treated ES-1 cells contained t-PA. Zymography assays, quantitative immunoreactive assays, and Northern analysis showed about 5-fold specific increase by estradiol of t-PA with molecular mass of 65-70 kDa in ES-1 but not in its parental MCF-7 cells. Cellular level of the plasminogen activity was also specifically enhanced in ES-1 cells by estradiol, but only a slightly in MCF-7 cells. By contrast, another urokinase-type PA (u-PA) with molecular weight of 55 kDa showed very low level activity in both MCF-7 and ES-1 cell lines in the presence of estradiol. Formation of t-PA mRNA was specifically enhanced in ES-1 cells when ES-1 cells were treated for more than 12 h with 10(-8) M 17-beta estradiol. Estradiol did not elongate the lifetime of t-PA mRNA in ES-1 cells. A unique phenotype of ES-1 cells in response to estradiol is discussed in relation to activating expression of the t-PA gene.

Regulation of urokinase receptors in monocytelike U937 cells by phorbol ester phorbol myristate acetate

A specific surface receptor for urokinase plasminogen activator (uPA) recognizes the amino-terminal growth factor-like sequence of uPA, a region independent from and not required for the catalytic activity of this enzyme. The properties of the uPA receptor (uPAR) and the localization and distribution of uPA in tumor cells and tissues suggest that the uPA/uPAR interaction may be important in regulating extracellular proteolysis-dependent processes (e.g., invasion, tissue destruction). Phorbol myristate acetate (PMA), an inducer of U937 cell differentiation to macrophage-like cells, elicits a time- and concentration-dependent increase in the number of uPAR molecules as shown by binding, cross-linking, and immunoprecipitation studies. The effect of PMA is blocked by cycloheximide. Overall, the data indicate that PMA increases the synthesis of uPA. PMA treatment also causes a decrease in the affinity of the uPAR for uPA, thus uncovering another way of regulating the interaction between uPA and uPAR. In addition, the PMA treatment causes a modification of migration of the cross-linked receptor in mono- and bidimensional gel electrophoresis.

Modulation of the urokinase receptor in human colon cell lines by N,N-dimethylformamide

The present study documents the effect of the planar, polar differentiation promoter N,N-dimethylformamide (DMF) on urokinase binding to colon carcinoma cells. Exposure of the colon carcinoma cell lines to the agent resulted in enhanced specific binding of radioactive urokinase to all cells tested. Insulin binding to the cells was, however, unaffected by DMF. A DMF exposure period of 45 h was required to observe maximum urokinase binding to two representative cell lines FET and RKO. Optimal stimulation of both cell lines occurred with 0.8% DMF. Scatchard analysis revealed the dissociation constants to be unchanged by the agent with the increased binding of radioactive plasminogen activator reflecting an up-regulation of binding sites. In this regard, the cell line RKO upon exposure to DMF, displayed approx. 700,000 receptors/cell, the highest value published, to date, for any cell line.

In vitro effect of mercury and vanadium on superoxide anion production and plasminogen activator activity of mouse peritoneal macrophages

The in vitro effects of mercuric chloride and vanadate were examined on two functions of mouse peritoneal macrophages, i.e., the superoxide anion production and the plasminogen activator (PA) activity. Vanadate, at concentrations which do not affect the viability of the cells, does not seriously alter any of these functions. High concentrations of mercury depress the respiratory burst; this effect results from loss of the reducing properties of cellular NADPH. Low concentrations of mercury stimulate the effect of phorbol 12-myristate 13-acetate on PA activity. The mechanism of this stimulation does not involve the protein kinase C system. It is hypothesized that mercury could enhance the synthesis of PA, its translocation to the cell surface, or its binding to the membrane receptors.