The mitogenic signaling pathway but not the plasminogen activator-inducing pathway of basic fibroblast growth factor is mediated through protein kinase C in fetal bovine aortic endothelial cells

Stability and biological activity evaluations of PEGylated human basic fibroblast growth factor

BACKGROUND

Human basic fibroblast growth factor (hBFGF) is a heparin-binding growth factor and stimulates the proliferation of a wide variety of cells and tissues causing survival properties and its stability and biological activity improvements have received much attention.

MATERIALS AND METHODS

In the present work, hBFGF produced by engineered Escherichia coli and purified by cation exchange and heparin affinity chromatography, was PEGylated under appropriate condition employing 10 kD polyethylene glycol. The PEGylated form was separated by size exclusion chromatography. Structural, biological activity, and stability evaluations were performed using Fourier transform infrared (FITR) spectroscopy, 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide (MTT) assay and effect denaturing agent, respectively.

RESULTS

FITR spectroscopy revealed that both PEGylated and native forms had the same structures. MTT assay showed that PEGyalated form had a 30% reduced biological activity. Fluorescence spectrophotometry indicated that the PEGylated form denatured at higher concentrations of guanidine HCl (1.2 M) compared with native, which denatured at 0.8 M guanidine HCl.

CONCLUSIONS

PEGylation of hBFGF makes it more stable against denaturing agent but reduces its bioactivity up to 30%.

Regulation of plasminogen activators in human thyroid follicular cells and their relationship to differentiated function

Human thyroid cells in culture take up and organify (125)I when cultured in TSH (acting through cAMP) and insulin. They also secrete urokinase (uPA) and tissue-type (tPA) plasminogen activators (5-100 IU/10(6)cells/day). TSH and insulin both decreased secreted PA activity (PAA), uPA and tPA protein and their mRNAs. Autocrine fibroblast growth factor increased secreted PAA and inhibited thyroid cell (125)I uptake. Epidermal growth factor (EGF) and the protein kinase C (PKC) activator, TPA significantly increased PAA and inhibited thyroid differentiated function, (TPA > EGF). For TPA, effects were rapid, increased PAA secretion and decreased (125)I uptake being seen at 4 h whereas for EGF, a 24 h incubation was required. qRT-PCR showed significantly increased mRNA expression of uPA with lesser effects on tPA. Aprotinin, which inhibits PAA, increased (125)I uptake but did not abrogate the effects of TPA and EGF. The MEKK inhibitor, PD98059 partially reversed the effects of EGF and TPA on PAA, and largely reversed the effects of EGF but not TPA on differentiated function. PKC inhibitors bisindoylmaleimide 1, and the specific PKCbeta inhibitor, LY379196 completely reversed the effects of TPA on (125)I uptake and PAA whereas EGF effects were unaffected. TPA inhibited follicle formation and this effect was blocked by LY379196 but not PD98059. We conclude that in thyroid cells, MAPK activation inversely correlates with (125)I uptake and directly correlates with PA expression, in contrast to the effects of cAMP. TPA effects on iodide metabolism, dissolution of follicles and uPA synthesis are mediated predominantly through PKCbeta whereas EGF exerts its effects through MAPK but not PKCbeta.

Nox1 mediates basic fibroblast growth factor-induced migration of vascular smooth muscle cells

OBJECTIVE

Basic fibroblast growth factor (bFGF) stimulates vascular smooth muscle cell (SMC) migration. We determined whether bFGF increases SMC reactive oxygen-species (ROS) and studied the role of ROS for SMC migration.

METHODS AND RESULTS

bFGF rapidly increased rat SMC ROS formation and migration through pathways sensitive to inhibition of NADPH oxidases, PI3-kinase, protein kinase C, and Rac-1. SiRNA directed against the NADPH oxidase Nox4 impaired basal but not bFGF-induced ROS formation and did not affect migration. In contrast, siRNA against Nox1 blocked the agonist-induced ROS generation as well as the bFGF-induced migration. Agonist-induced migration was also attenuated in SMC derived from Nox1 y/- mice and transduction of Nox1 restored normal migration. Likewise, SMC outgrowth in response to bFGF was attenuated in aortic segments from Nox1 y/- mice as compared with Nox1 y/+ mice. bFGF activated JNK but not Src in a Nox1-dependent manner. Consequently, phosphorylation of the adaptor protein paxillin, which is central for migration and secretion of matrix-metalloproteinases, were dependent on Nox1 as well as JNK but not Src.

CONCLUSIONS

These data demonstrate that bFGF activates the Nox1-containing NADPH oxidase and that bFGF through a pathway involving ROS and JNK stimulates SMC migration.

Bisindolylmaleimide I suppresses fibroblast growth factor-mediated activation of Erk MAP kinase in chondrocytes by preventing Shp2 association with the Frs2 and Gab1 adaptor proteins

Fibroblast growth factors (FGFs) inhibit chondrocyte proliferation via the Erk MAP kinase pathway. Here, we explored the role of protein kinase C in FGF signaling in chondrocytes. Erk activity in FGF2-treated RCS (rat chondrosarcoma) chondrocytes or human primary chondrocytes was abolished by the protein kinase C inhibitor bisindolylmaleimide I (Bis I). Bis I inhibited FGF2-induced activation of MEK, Raf-1, and Ras members of Erk signaling module but not the FGF2-induced tyrosine phosphorylation of Frs2 or the kinase activity of FGFR3, demonstrating that it targets the Erk cascade immediately upstream of Ras. Indeed, Bis I abolished the FGF2-mediated association of Shp2 tyrosine phosphatase with Frs2 and Gab1 adaptor proteins necessary for proper Ras activation. We also determined which PKC isoform is involved in FGF2-mediated activation of Erk. When both conventional and novel PKCs expressed by RCS chondrocytes (PKCalpha, -gamma, -delta, and -epsilon) were down-regulated by phorbol ester, cells remained responsive to FGF2 with Erk activation, and this activation was sensitive to Bis I. Moreover, treatment with PKClambda/zeta pseudosubstrate lead to significant reduction of FGF2-mediated activation of Erk, suggesting involvement of an atypical PKC.

Carboxyamido-triazole modulates retinal pigment epithelial and choroidal endothelial cell attachment, migration, proliferation, and MMP-2 secretion of choroidal endothelial cells

PURPOSE

To determine the effect of the calcium signaling modulating drug carboxyamido-triazole (CAI) on substeps of exudative age-related macular degeneration (AMD) in vitro.

MATERIALS AND METHODS

Zymography and ELISA determined the effect of CAI on MMP-2 production of choroidal endothelial cells (CECs) stimulated by bFGF and VEGF. The effects of CAI on attachment of retinal pigment endothelial (RPE) cells/CECs onto fibronectin, laminin, collagen IV, and migration toward fibronectin were investigated. Proliferation induced by serum and bFGF (10 microg/ml) with and without CAI (0.1-10 microM) was measured by cell counting and 3H-uptake. Viability and apoptosis of the exposed cells was assessed by an MTT and an apoptosis assay.

RESULTS

CAI inhibited serum- and bFGF-induced proliferation, cell attachment onto fibronectin and collagen IV, but only CEC attachment onto laminin. Inhibition of MMP-2 production was observed (10 microM CAI). CAI reduced the cellular viability by apoptosis induction.

CONCLUSIONS

CAI inhibits substeps of exudative macular degeneration and may be of value for the treatment of the disease.

[Carboxyamido-triazole inhibits substeps of choroidal neovascularization on retinal pigment epithelial cells and choroidal endothelial cells in vitro]

BACKGROUND

Retinal pigment epithelial cells (RPE cells) and choroidal endothelial cells (CECs) are important cell types in the process of choroidal neovascularization in exudative age-related macular degeneration (AMD). In this study, we evaluated the antiproliferative and antimigratory abilities of carboxyamido-triazole (CAI), a drug modulating calcium-dependent signal transduction on RPE cells and CECs.

METHODS

Human fetal RPE cells and bovine CECs were exposed to CAI in a concentration range of 0.1 to 10 microM. Cell proliferation was stimulated with 10% serum or 10 ng/ml bFGF. The effect of CAIs on cell proliferation was estimated. Furthermore, we evaluated CAI's effects on CEC and RPE cell migration induced by fibronectin.

RESULTS

CAI had a stronger inhibitory effect on serum-induced CEC proliferation than on RPE cell proliferation. A much stronger effect was seen on the proliferation of bFGF-stimulated RPE cells and CECs. Furthermore, the fibronectin-stimulated migration of RPE cells and CECs was inhibited by CAI. In this assay, a stronger inhibitory effect was seen on RPE cells than on CECs. CONCLUSION; CAI inhibits important substeps of choroidal neovascularization on RPR cells and CECs. Therefore, CAI may be of value for the treatment of choroidal neovascularization in exudative AMD.

High expression of PKC-MAPK pathway mRNAs correlates with glomerular lesions in human diabetic nephropathy

BACKGROUND

Activation of protein kinase C (PKC) is a major signaling pathway for transforming growth factor (TGF)-beta to induce extracellular matrix (ECM) production in diabetic nephropathy (DN). PKC also activates mitogen-activated protein kinase (MAPK), which is called the PKC-MAPK pathway. The PKC-MAPK pathway is probably responsible for PKC-related abnormalities in diabetic glomeruli. To confirm the involvement of this pathway, we determined the localization and expression of mRNAs in glomeruli by in situ hybridization method.

METHODS

In the present study, we examined expression of PKCbeta1, MAPK/ERK kinase (MEK) 1, MEK2, extracellular signal-regulated protein kinase (ERK) 1, ERK2, and TGF-beta1 mRNAs using renal tissue samples from kidneys affected by DN (N= 21) and from normal human kidney (NHK; N= 6). We also performed an immunohistochemical study using anti-phosphorylated MEK1/2 (P-MEK) and ERK1/2 (P-ERK) antibodies. The glomerular severity of DN was classified into three groups according to mesangial expansion: D1 (N= 4), D2 (N= 13), and D3 (N= 4). We analyzed differences and correlations between variables.

RESULTS

In the glomeruli, the number of cells that stained for these mRNAs in DN was significantly higher than in NHK. The expression of PKC-MAPK pathway mRNAs tended to be inversely proportional to the degree of mesangial expansion. The P-MEK and P-ERK signal intensity were parallel to its mRNA expression pattern. Furthermore, there were significant correlations among the P-MEK, P-ERK signal intensity, PKCbeta1 mRNA expression.

CONCLUSION

Our results suggest that high expression of PKC-MAPK pathway mRNAs plays an important role in the development and/or progression of early tissue damage in DN.

FGF2-mediated upregulation of urokinase-type plasminogen activator expression requires a MAP-kinase dependent activation of poly(ADP-ribose) polymerase

Poly(ADP-ribosyl)ation is a post-translational modification of protein occurring in the nucleus by poly(ADP-ribose) polymerase enzyme activity. The main role of poly(ADP-ribose) polymerase system as "nick sensor" and DNA breaks repair is based on its activation via DNA strand breaks. Furthermore, poly(ADP-ribose) polymerase modifies the binding to DNA of several transcriptional factors by poly(ADP-ribosyl)ation, thereby regulating also transcriptional gene expression. We have analyzed whether poly(ADP-ribose) polymerase activity is involved in basic fibroblast growth factor (FGF2)-mediated upregulation of urokinase-type plasminogen activator (uPA) mRNA. We demonstrated that specific inhibition of poly(ADP-ribose) polymerase activity via 3-aminobenzamide (3ABA) or NAD+ deprivation prevents FGF2-mediated uPA mRNA over-expression and cell-associated plasminogen activator (PA) production in GM7373 endothelial cell line. We verified that FGF2 stimulates poly(ADP-ribose) polymerase activity by a DNA strand breaks-independent manner which involves a mitogen-activated protein kinases (MAPK)-dependent pathway, as confirmed by using PD98059 inhibitor and anisomycin stimulation. Poly(ADP-ribose) polymerase involved in this mechanism is mainly the 60 kDa molecular mass isoform, that presents an increase in serine phosphorylation in the presence of FGF2.

Heparan sulfate proteoglycans as regulators of fibroblast growth factor-2 signaling in brain endothelial cells. Specific role for glypican-1 in glioma angiogenesis

Fibroblast growth factor-2 (FGF2) is a potent angiogenic factor in gliomas. Heparan sulfate promotes ligand binding to receptor tyrosine kinase and regulates signaling. The goal of this study was to examine the contribution of heparan sulfate proteoglycans (HSPGs) to glioma angiogenesis. Here we show that all brain endothelial cell HSPGs carry heparan sulfate chains similarly capable of forming a ternary complex with FGF2 and fibroblast growth factor receptor-1c and of promoting a mitogenic signal. Immunohistochemical analysis revealed that glypican-1 was overexpressed in glioma vessel endothelial cells, whereas this cell-surface HSPG was consistently undetectable in normal brain vessels. To determine the effect of increased glypican-1 expression on FGF2 signaling, we transfected normal brain endothelial cells, which express low base-line levels of glypican-1, with this proteoglycan. Glypican-1 expression enhanced growth of brain endothelial cells and sensitized them to FGF2-induced mitogenesis despite the fact that glypican-1 remained a minor proteoglycan. In contrast, overexpression of syndecan-1 had no effect on growth or FGF2 sensitivity. We conclude that the glypican-1 core protein has a specific role in FGF2 signaling. Glypican-1 overexpression may contribute to angiogenesis and the radiation resistance characteristic of this malignancy.

Anti-angiogenic activity of the purine analog 6-thioguanine

The antimetabolite 6-thioguanine (6-TG) is utilized in the management of acute myelogenous leukemia (AML). Angiogenesis is a possible therapeutic target in hematologic tumors. Thus, we addressed the possibility that 6-TG may also act as an anti-angiogenic molecule. 6-TG inhibited endothelial cell proliferation triggered by fibroblast growth factor-2 (FGF2) and vascular endothelial growth factor (VEGF) and delayed the repair of a mechanically wounded endothelial cell monolayer. Also, 6-TG inhibited sprouting within fibrin gel, morphogenesis on Matrigel, and collagen gel invasion by endothelial cells. 2-Aminopurine was ineffective. In vivo, 6-TG inhibited basal, VEGF-induced, and FGF2-induced vascularization in the chick embryo chorioallantoic membrane and prevented neovascularization triggered by leukemia LIK cells or their conditioned medium. Finally, bone marrow vascularization in AML patients was decreased to control values in the early remission phase and persisted unvaried after 8-12 months of maintenance therapy with 6-TG. Thus, 6-TG inhibits different steps of the angiogenesis process in vitro and exerts a potent anti-angiogenic activity in vivo. Its anti-angiogenic activity, together with its antimetabolite activity towards tumor cells, may contribute to its action during maintenance therapy in AML. These results suggest a new rationale for the use of purine analogs in the management of AML.

Docetaxel versus paclitaxel for antiangiogenesis

Cytoskeleton-toxic chemotherapeuticals, such as vinblastine and paclitaxel, display antiangiogenic activity. This study was designed to compare paclitaxel to its analog docetaxel and assess their doses still antiangiogenic in vitro and in vivo. Human endothelial cell functions involved in angiogenesis, namely proliferation, chemotaxis, morphogenesis, and secretion of matrix metalloproteinase-2 (MMP-2), MMP-9, and urokinase-type plasminogen activator (uPA) were studied in vitro upon exposure to docetaxel and paclitaxel, whereas their effect on angiogenesis was studied in vivo by using the chick embryo chorioallantoic membrane (CAM) model. Proliferation of mouse embryo fibroblasts and human Kaposi's sarcoma, breast and endometrial carcinoma, and lymphoid tumor cells was also studied. In vitro, 0.5, 0.75, and 1 nM docetaxel and 2, 3, and 4 nM paclitaxel, i.e., non-cytotoxic doses, impacted all endothelial cell functions, but not protease secretion, in a dose-dependent fashion, whereas they did not affect the proliferation of other cells, except those of Kaposi's sarcoma. No apoptosis was induced by 0.5 nM docetaxel and 2 nM paclitaxel, and moderate apoptosis was induced by 1 nM docetaxel and 4 nM paclitaxel. The antiangiogenic effect rapidly disappeared on drug suspension and was accompanied ultrastructurally by thin lesions of cytoskeleton in the form of slight and equally reversible depolymerization and accumulation of microfilaments. Massive endothelial cell apoptosis with evident cytotoxicity and irreversibility were associated with 2 nM docetaxel and 5 nM paclitaxel, although these higher doses were ineffective on other cells except Kaposi's sarcoma cells. In vivo, 1, 2, and 3 nM docetaxel and 4, 8, and 12 nM paclitaxel displayed a dose-dependent antiangiogenic activity. We suggest that very low docetaxel and paclitaxel doses selectively cause organic and functional damage of endothelial cells and that docetaxel is four times stronger. Their antiangiogenic activity could be applied to treat Kaposi's sarcoma and cancers.

Influence of gelatin complexation on cell proliferation activity and proteolytic resistance of basic fibroblast growth factor

The objective of this study is to investigate the influence of gelatin complexation on the biological activity of basic fibroblast growth factor (bFGF) and its resistance to trypsin digestion. When bFGF was mixed at 37 degrees C with acidic gelatin with an isoelectric point (IEP) of 5.0, the activity to promote in vitro proliferation of BHK cells became lower compared with that of free bFGF, in contrast to mixing with the basic gelatin with an IEP of 9.0. A maximum reduction in the bFGF activity was observed for the bFGF-gelatin complex prepared at a mixing molar ratio of 1/1. The bFGF activity of cell proliferation reduced at the initial period after mixing with the acidic gelatin at 37 degrees C, followed by no substantial change. Complexation with the acidic gelatin at 4 degrees C had no influence on the bFGF activity, irrespective of the bFGF/gelatin ratio and complexation time. The biological activity of bFGF was reduced by the trypsin treatment, but the reduced extent was suppressed through gelatin complexation at 37 degrees C. In an electrophoresis study, the protective effect of gelatin complexation on the trypsin digestion was also confirmed in terms of the molecular weight loss. It is possible that the complexing gelatin covers bFGF molecules, resulting in suppression of their interaction with the cell surface receptor as well as protection from their enzymatic attack.

FGF signals for cell proliferation and migration through different pathways

FGFs are pleiotropic growth factors that control cell proliferation, migration and differentiation. However, FGF transduction studies have so far focused primarily on the mitogenic effect of this growth factor family and it has been difficult to assess if the described intracellular signaling pathways are dedicated solely to cell proliferation, or whether they are equally important for the migratory activity often seen in responsive cells. We review here papers in which the migratory effects of this growth factor family were clearly discriminated from proliferative effects. In toto, these studies suggest that cells use different signaling pathways for migration, such as Src and p38 MAP kinase, from those for proliferation, which tend to upregulate the ERKs. Which signaling pathway a cell uses for proliferation or migration appears to depend on many factors, including the structure and the quantity of available FGF trapped in the basal lamina by heparan sulfate co-factors, the disposition of cognate high affinity receptors and the general environment of the cell. Thus the density of the cell population, the state of the cell cycle, the presence of other factors or receptors will modulate the migratory response of cells to FGF.

Interaction between endothelial differentiation-related factor-1 and calmodulin in vitro and in vivo

Calmodulin (CaM) is the principal Ca(2+) receptor protein inside the cell. When activated by Ca(2+), CaM binds and activates target proteins, thus altering the metabolism and physiology of the cell. Under basal conditions, calcium-free CaM binds to other proteins termed CaM-binding proteins. Recently, we described endothelial differentiation-related factor (EDF)-1 as a protein involved in the repression of endothelial cell differentiation (Dragoni, I., Mariotti, M., Consalez, G. G., Soria, M., and Maier, J. A. M. (1998) J. Biol. Chem. 273, 31119-31124). Here we report that (i) EDF-1 binds CaM in vitro and in vivo; (ii) EDF-1 is phosphorylated in vitro and in vivo by protein kinase C; and (iii) EDF-1-CaM interaction is modulated by the concentrations of Ca(2+) and by the phosphorylation of EDF-1 by protein kinase C both in vitro and in vivo. In addition, 12-O-tetradecanoylphorbol-13-acetate treatment of human umbilical vein endothelial cell stimulates the nuclear translocation of EDF-1. On the basis of the high homology of EDF-1 with multiprotein bridging factor-1, a transcriptional coactivator that binds TATA-binding protein (TBP), we also demonstrate that EDF-1 interacts with TBP in vitro and in human endothelial cells. We hypothesize that EDF-1 serves two main functions in endothelial cells as follows: (i) to bind CaM in the cytosol at physiologic concentrations of Ca(2+) and (ii) to act in the nucleus as a transcriptional coactivator through its binding to TBP.

Diabetes-induced metabolic abnormalities in myocardium: effect of antioxidant therapy

Effects of hyperglycemia (both diabetes and experimental galactosemia) on cardiac metabolism have been determined. In addition, the effect of supplemental antioxidants on these hyperglycemia-induced abnormalities of cardiac metabolism has been investigated. Diabetes or experimental galactosemia of 2 months duration in rats significantly increased oxidative stress in myocardium, as demonstrated by elevation of thiobarbituric acid reactive substances (TBARS) and lipid fluorescent products in left ventricle. Activity of protein kinase C (PKC) was elevated in the myocardium, and the activities of (Na,K)-ATPase and calcium ATPases were subnormal. Administration of supplemental antioxidants containing a mixture of ascorbic acid, Trolox; alpha-tocopherol acetate, N-acetyl cysteine, beta-carotene, and selenium prevented both the diabetes-induced and galactosemia-induced elevation of oxidative stress and PKC activity, and inhibited the decreases of myocardial (Na,K)-ATPase and calcium ATPases. The results show that these metabolic abnormalities are not unique to diabetes per se, but are secondary to elevated blood hexose levels, and supplemental antioxidants inhibit these metabolic abnormalities. Our findings suggest that antioxidants inhibit abnormal metabolic processes that may contribute to the development of cardiac disease in diabetes, and offer a potential clinical means to inhibit cardiac abnormalities in diabetes.

Effects of commonly used mitogens on the cytotoxicity of 4-tertiary butylphenol to human melanocytes

In the search for environmental compounds responsible for contact or occupational vitiligo, it was found that the most potent was 4-tertiary butylphenol (4-TBP). Exposure to 4-TBP is widespread both in industry and in consumer items including synthetic leather, plastic, glues, and germicidal phenolic detergents. How 4-TBP causes depigmentation and the death of melanocytes is currently unclear. Growth mitogens for human melanocytes include alpha-melanocyte stimulating hormone (alpha-MSH), basic fibroblast growth factor (bFGF) and 12-o-tetradecanoylphorbol-13-acetate (TPA). The former two mitogens are physiological growth factors for melanocytes. We have studied the effects of these mitogens on the cytotoxicity of 4-TBP in human melanocytes. Our results demonstrated that deprivation of alpha-MSH or bFGF from melanocyte cultures resulted in reduced cytotoxicity to 4-TBP. Similar results were obtained upon treatment of melanocytes with an inhibitor of cAMP-dependent protein kinase A (PKA), that is known to be activated by alpha-MSH, or with an inhibitor of the tyrosine kinase bFGF receptor. In contrast, removal of fetal bovine serum or TPA from the culture medium did not influence the susceptibility of melanocytes to 4-TBP. These results suggest that activation of the cAMP and tyrosine kinase signaling pathways, both of which are involved in the mitogenic response of melanocytes, increase the susceptibility of these cells to the cytotoxic effects of 4-TBP.

Dissociation of mesangial cell migration and proliferation in experimental glomerulonephritis

BACKGROUND

Recently, we documented that following in vivo mesangial cell (MC) ablation in the Thy1 model, reconstitution of the mesangium occurs by a coordinated proliferation and migration of Thy1 (OX-7)-positive cells originating from the hilus and extraglomerular mesangium. We investigated the role of basic fibroblast growth factor (bFGF) in the mediation of these events.

METHODS

Rats were injected with antithymocyte serum and 48 hours later were pulsed with 3H-thymidine to label proliferating cells. Ninety minutes later, a baseline renal biopsy was obtained, and rats were injected with neutralizing anti-bFGF antibodies or control IgG. Sacrificial biopsies were obtained at 96 hours of disease. Using computer image analysis, biopsies from both time points were quantitated for the number of radiolabeled MC (proliferation) and their mean distance from the hilus (migration). The effect of bFGF on the migration of MCs in culture was examined using a chemotactic assay.

RESULTS

At sacrifice, autoradiographs of rats receiving anti-bFGF had significantly fewer radiolabeled MCs as compared with rats receiving control IgG (8.7+/-1.9 vs. 14.7+/-3.5, P = 0.0001), yielding an overall 40% reduction in proliferation. There was no difference, however, in the final distance of radiolabeled MCs from the glomerular hilus in the two groups, indicating that the administration of anti-bFGF did not effect MC migration in this model. In an in vitro chemotactic assay, MCs migrated in response to platelet-derived growth factor (PDGF) BB (20 ng/ml), but did not migrate in response to bFGF at a wide range of concentrations (0.5 to 50 ng/ml).

CONCLUSIONS

These studies demonstrate that bFGF is an important mediator of MC proliferation but that it does not significantly influence MC migration. This is the first demonstration showing that the mediators effecting proliferation can be dissociated from those mediating migration in renal injury.

Role of endothelial cell extracellular signal-regulated kinase1/2 in urokinase-type plasminogen activator upregulation and in vitro angiogenesis by fibroblast growth factor-2

Downstream signaling triggered by the binding of fibroblast growth factor-2 (FGF2) to its tyrosine-kinase receptors involves the activation of mitogen-activated protein kinase kinase (MEK) with consequent phosphorylation of extracellular signal-regulated kinases (ERKs). Here we demonstrate that FGF2 induces ERK1/2 activation in bovine aortic endothelial (BAE) cells and that the continuous presence of the growth factor is required for sustained ERK1/2 phosphorylation. This is prevented by the MEK inhibitors PD 098059 and U0126, which also inhibit FGF2-mediated upregulation of urokinase-type plasminogen activator (uPA) and in vitro formation of capillary-like structures in three-dimensional type I collagen gel. Various FGF2 mutants originated by deletion or substitution of basic amino acid residues in the amino terminus or in the carboxyl terminus of FGF2 retained the capacity to induce a long-lasting activation of ERK1/2 in BAE cells. Among them, K128Q/R129Q-FGF2 was also able to stimulate uPA production and morphogenesis whereas R129Q/K134Q-FGF2 caused uPA upregulation only. In contrast, K27, 30Q/R31Q-FGF2, K128Q/K138Q-FGF2 and R118,129Q/K119,128Q-FGF2 exerted a significant uPA-inducing and morphogenic activity in an ERK1/2-dependent manner only in the presence of heparin. Furthermore, no uPA upregulation and morphogenesis was observed in BAE cells treated with the deletion mutant (delta)27-32-FGF2 even in the presence of soluble heparin. Thus, mutational analysis of FGF2 dissociates the capacity of the growth factor to induce a persistent activation of ERK1/2 from its ability to stimulate uPA upregulation and/or in vitro angiogenesis. In conclusion, the data indicate that ERK1/2 phosphorylation is a key step in the signal transduction pathway switched on by FGF2 in endothelial cells. Nevertheless, a sustained ERK1/2 activation is not sufficient to trigger uPA upregulation and morphogenesis. FGF2 mutants may represent useful tools to dissect the signal transduction pathway(s) mediating the complex response elicited by an angiogenic stimulus in endothelial cells.

Protein kinase C mediates basic fibroblast growth factor-induced proliferation through mitogen-activated protein kinase in coronary smooth muscle cells

Proliferation of coronary smooth muscle cells (cSMCs) contributes to the pathogenesis of arteriosclerosis and restenosis after angioplasty, and basic fibroblast growth factor (bFGF) is a powerful mitogen for cSMCs. In this study, we investigated the involvement of mitogen-activated protein kinase (MAPK), protein kinase C (PKC), and the transcription factor c-myc in bFGF-stimulated mitogenesis, as well as the functional relationship between these factors. cSMC stimulation with bFGF resulted in phosphorylation of p42 MAPK, as well as the phosphorylation and increased expression of c-myc. The MAPK kinase (MEK) inhibitor PD98059 blocked bFGF-stimulated MAPK phosphorylation and resulted in both a decrease of c-myc expression and inhibition of bFGF-stimulated DNA synthesis in cSMCs. bFGF also increased PKC activity in cSMCs in a time-dependent manner. The inhibition of PKC by chelerythrine or its downregulation by phorbol 12-myristate 13-acetate (PMA) inhibited bFGF-induced DNA synthesis and blocked the phosphorylation of MAPK and c-myc expression in response to bFGF. This indicates an involvement of phorbol ester-sensitive PKC isoforms in MAPK activation and mitogenic signaling by bFGF. Western blot analysis revealed the presence of the phorbol ester-sensitive isoforms PKC alpha, epsilon, and gamma as well as the PKC isoforms iota, lambda, micro, and zeta in cSMCs. In this study, we show that the MAPK cascade is required for bFGF-induced proliferation and that phorbol ester-sensitive PKC isoforms contribute to the bFGF-induced cSMC mitogenesis in cSMCs.

E-selectin gene expression is induced synergistically with the coexistence of activated classic protein kinase C and signals elicited by interleukin-1beta but not tumor necrosis factor-alpha

We have examined the effect of protein kinase C (PKC) on the expression of the E-selectin and intercellular adhesion molecule-1 (ICAM-1) mRNAs in human umbilical vein endothelial cells. The lower classic PKC activity on pretreatment with phorbol ester (phorbol 12-myristate 13-acetate (PMA)) for 24 h markedly decreased IL-1beta-induced E-selectin mRNA expression in the presence of fetal calf serum and basic fibroblast growth factor, although the induction of ICAM-1 mRNA expression was only influenced a little by the PKC down-regulation. On the other hand, tumor necrosis factor-alpha (TNFalpha)-induced gene expression of these adhesion molecules was unaffected by such PKC modulation. The intracellular signals generated by interleukin (IL)-1beta and TNFalpha themselves are not mediated through classic PKC activation, because the response to neither stimulant was inhibited by the PKC down-regulation in the absence of fetal calf serum and basic fibroblast growth factor. Simultaneous treatment with IL-1beta and PMA synergistically induced E-selectin gene expression but not when TNFalpha was substituted for IL-1beta. ICAM-1 mRNA expression was only additively induced on the cotreatment. The synergistic effect on E-selectin mRNA induction was independent of de novo protein synthesis and mediated by elevated transcriptional activity. Promoter analysis of E-selectin indicated that the NF-ELAM1/activating transcription factor element is critical for the synergistic effect of the cotreatment with IL-1beta and PMA.

Interaction of fibroblast growth factor-2 (FGF-2) with free gangliosides: biochemical characterization and biological consequences in endothelial cell cultures

Exogenous gangliosides affect the angiogenic activity of fibroblast growth factor-2 (FGF-2), but their mechanism of action has not been elucidated. Here, a possible direct interaction of sialo-glycolipids with FGF-2 has been investigated. Size exclusion chromatography demonstrates that native, but not heat-denatured, 125I-FGF-2 binds to micelles formed by gangliosides GT1b, GD1b, or GM1. Also, gangliosides protect native FGF-2 from trypsin digestion at micromolar concentrations, the order of relative potency being GT1b > GD1b > GM1 = GM2 = sulfatide > GM3 = galactosyl-ceramide, whereas asialo-GM1, neuraminic acid, and N-acetylneuramin-lactose were ineffective. Scatchard plot analysis of the binding data of fluorochrome-labeled GM1 to immobilized FGF-2 indicates that FGF-2/GM1 interaction occurs with a Kd equal to 6 microM. This interaction is inhibited by the sialic acid-binding peptide mastoparan and by the synthetic fragments FGF-2(112-129) and, to a lesser extent, FGF-2(130-155), whereas peptides FGF-2(10-33), FGF-2(39-59), FGF-2(86-96), and the basic peptide HIV-1 Tat(41-60) were ineffective. These data identify the COOH terminus of FGF-2 as a putative ganglioside-binding region. Exogenous gangliosides inhibit the binding of 125I-FGF-2 to high-affinity tyrosine-kinase FGF-receptors (FGFRs) of endothelial GM 7373 cells at micromolar concentrations. The order of relative potency was GT1b > GD1b > GM1 > sulfatide a = sialo-GM1. Accordingly, GT1b,GD1b, GM1, and GM2, but not GM3 and asialo-GM1, prevent the binding of 125I-FGF-2 to a soluble, recombinant form of extracellular FGFR-1. Conversely, the soluble receptor and free heparin inhibit the interaction of fluorochrome-labeled GM1 to immobilized FGF-2. In agreement with their FGFR antagonist activity, free gangliosides inhibit the mitogenic activity exerted by FGF-2 on endothelial cells in the same range of concentrations. Also in this case, GT1b was the most effective among the gangliosides tested while asialo-GM1, neuraminic acid, N-acetylneuramin-lactose, galactosyl-ceramide, and sulfatide were ineffective. In conclusion, the data demonstrate the capacity of exogenous gangliosides to interact with FGF-2. This interaction involves the COOH terminus of the FGF-2 molecule and depends on the structure of the oligosaccharide chain and on the presence of sialic acid residue(s) in the ganglioside molecule. Exogenous gangliosides act as FGF-2 antagonists when added to endothelial cell cultures. Since gangliosides are extensively shed by tumor cells and reach elevated levels in the serum of tumor-bearing patients, our data suggest that exogenous gangliosides may affect endothelial cell function by a direct interaction with FGF-2, thus modulating tumor neovascularization.

Different tyrosine autophosphorylation requirements in fibroblast growth factor receptor-1 mediate urokinase-type plasminogen activator induction and mitogenesis

Among the seven tyrosine autophosphorylation sites identified in the intracellular domain of tyrosine kinase fibroblast growth factor receptor-1 (FGFR1), five of them are dispensable for FGFR1-mediated mitogenic signaling. The possibility of dissociating the mitogenic activity of basic FGF (FGF2) from its urokinase-type plasminogen activator (uPA)-inducing capacity both at pharmacological and structural levels prompted us to evaluate the role of these autophosphorylation sites in transducing FGF2-mediated uPA upregulation. To this purpose, L6 myoblasts transfected with either wild-type (wt) or various FGFR1 mutants were evaluated for the capacity to upregulate uPA production by FGF2. uPA was induced in cells transfected with wt-FGFR1, FGFR1-Y463F, -Y585F, -Y730F, -Y766F, or -Y583/585F mutants. In contrast, uPA upregulation was prevented in L6 cells transfected with FGFR1-Y463/583/585/730F mutant (FGFR1-4F) or with FGFR1-Y463/583/585/730/766F mutant (FGFR1-5F) that retained instead a full mitogenic response to FGF2; however, preservation of residue Y730 in FGFR1-Y463/583/585F mutant (FGFR1-3F) and FGFR1-Y463/583/585/766F mutant (FGFR1-4Fbis) allows the receptor to transduce uPA upregulation. Wild-type FGFR1, FGFR1-3F, and FGFR1-4F similarly bind to a 90-kDa tyrosine-phosphorylated protein and activate Shc, extracellular signal-regulated kinase (ERK)2, and JunD after stimulation with FGF2. These data, together with the capacity of the ERK kinase inhibitor PD 098059 to prevent ERK2 activation and uPA upregulation in wt-FGFR1 cells, suggest that signaling through the Ras/Raf-1/ERK kinase/ERK/JunD pathway is necessary but not sufficient for uPA induction in L6 transfectants. Accordingly, FGF2 was able to stimulate ERK1/2 phosphorylation and cell proliferation, but not uPA upregulation, in L6 cells transfected with the FGFR1-Y463/730F mutant, whereas the FGFR1-Y583/585/730F mutant was fully active. We conclude that different tyrosine autophosphorylation requirements in FGFR1 mediate cell proliferation and uPA upregulation induced by FGF2 in L6 cells. In particular, phosphorylation of either Y463 or Y730, dispensable for mitogenic signaling, represents an absolute requirement for FGF2-mediated uPA induction.

Basic fibroblast growth factor release by human coronary artery endothelial cells is enhanced by matrix proteins, 17beta-estradiol, and a PKC signaling pathway

Endothelial cell function is regulated by interactions among cells, the extracellular matrix (ECM), and soluble mediators. We investigated this interaction by examining the effect of 17beta-estradiol (E2) on release of basic fibroblast growth factor (FGF-2) by human coronary artery endothelial cells (HCAEC) cultured on ECM proteins. After estrogen-depleted HCAEC were treated with E2 for 2 h, the conditioned media and cell layers were evaluated by immunoblot or ELISA for FGF-2. Release of FGF-2 into conditioned media was enhanced 10-fold compared to that on plastic and a further 2.4-fold by E2. As FGF-2 release from cells into the media increases, there is a corresponding decrease in the cellular content of FGF-2. By ELISA, FGF-2 release increased 406, 179, and 262%, on type IV collagen, laminin, or fibronectin, respectively. HCAEC cultured on type I collagen did not show E2-enhanced FGF-2 release by ELISA or immunoblot analysis. No changes were noted in HCAEC release of lactate dehydrogenase, tested as a control protein for cellular integrity. The estrogen receptor antagonist ICI182,780 blocked E2-induced, but not basal, FGF-2 release. Increased FGF-2 release occurred via a cycloheximide-insensitive pathway. Neither brefeldin-A nor genistein inhibited E2 enhancement of FGF-2 release by HCAEC cultured on fibronectin. However, the protein kinase C inhibitor calphostin C inhibited the E2-augmented FGF-2 release. These data show that E2 enhances FGF-2 release by HCAEC cultured on basement membrane proteins in the absence of wounding. This action requires the estrogen receptor and PKC activity, but does not require new protein synthesis, endoplasmic reticulum-to-Golgi-mediated secretion, or protein tyrosine phosphorylation. E2-enhanced FGF-2 release could contribute to the cardioprotective effects of estrogen.

Human lymphoblastoid cells produce extracellular matrix-degrading enzymes and induce endothelial cell proliferation, migration, morphogenesis, and angiogenesis

Human lymphoproliferative diseases can be hypothesized to invade locally and to metastatize via mechanisms similar to those developed by a variety of solid tumors, i.e., the secretion of extracellular matrix-degrading enzymes and stimulation of angiogenesis. To assess this hypothesis, Namalwa, Raji, and Daudi cell lines (Burkitt's lymphoma), LIK and SB cell lines (B-cell lymphoblastic leukemia), CEM and Jurkat cell lines (T-cell lymphoblastic leukemia), and U266 cell line (multiple myeloma) were evaluated for their capacity to produce matrix metalloproteinase-2 and -9, and urokinase-type plasminogen activator. These cell lines were also assessed for their ability: (1) to produce the angiogenic basic fibroblast growth factor and vascular endothelial growth factor; (2) to induce an angiogenic phenotype in cultured endothelial cells, represented by cell proliferation, chemotaxis, and morphogenesis; (3) to stimulate angiogenesis in different in vivo experimental models. All cell lines expressed the mRNA for one or both metalloproteinases. Namalwa, Raji, LIK, SB, and U266 cells secreted the active form of both metalloproteinases, while Daudi, CEM, and Jurkat cells produced metalloproteinase-2 but not-9. In contrast, urokinase-type plasminogen activator was secreted only by SB cells. While Raji, LIK, SB, CEM, and Jurkat cells secreted both basic fibroblast growth factor and vascular endothelial growth factor, Daudi and U266 cells produced only the former, and Namalwa cells only the latter. Accordingly, the conditioned medium of all cell lines stimulated cell proliferation and/or chemotaxis in cultured endothelial cells, with the exception of that of Namalwa cells which was ineffective. The conditioned medium of CEM and Jurkat cells induced morphogenesis in cultured endothelial cells grown on a reconstituted basement membrane (Matrigel). Lastly, Namalwa, Raji, LIK, SB, U266, CEM, and Jurkat cells induced angiogenesis and mononuclear cell recruitment in the murine Matrigel sponge model and in a chick embryo chorioallantoic membrane assay. The extent of angiogenesis in both models was strictly correlated with the density of the mononuclear cell infiltrate. The results indicate that human lymphoproliferative disease cells possess both local and remote invasive ability via the secretion of matrix-degrading enzymes and the induction of angiogenesis which is fostered by host inflammatory cells and by an intervening ensemble of angiogenic factors.

Noncompetitive, chemokine-mediated inhibition of basic fibroblast growth factor-induced endothelial cell proliferation

The proinflammatory and chemoattractant chemokine interleukin-8 (IL-8) inhibits cell proliferation induced by basic fibroblast growth factor (bFGF) in mouse endothelial cells isolated from subcutaneous sponge implant (sponge-induced mouse endothelial cells) and in bovine aortic endothelial GM 7373 cells. The mechanism of action of IL-8 was investigated in GM 7373 cells. IL-8 did not prevent the binding of bFGF to its tyrosine kinase FGF receptors (FGFRs) nor to cell surface heparan sulfate proteoglycans (HSPGs). A transient interaction of IL-8 with the cell before the addition of the growth factor was sufficient to prevent bFGF activity. The inhibitory activity of IL-8 was abolished by protein kinase C (PKC) inhibitors and was mimicked by the PKC activator 12-O-tetradecanoylphorbol-13-acetate. Accordingly, both IL-8 and 12-O-tetradecanoylphorbol-13-acetate caused a approximately 60% decrease of the binding capacity of GM 7373 cells due to the down-regulation of FGFRs. Several C-X-C and C-C chemokines exerted an inhibitory action on bFGF activity similar to IL-8. Soluble heparin, 6-O-desulfated heparin, N-desulfated heparin, and heparan sulfate but not 2-O-desulfated heparin, chondroitin-4-sulfate, hyaluronic acid, and K5 polysaccharide abrogated IL-8 inhibitory activity consistently with the presence of low affinity, high capacity HSPG-like chemokine-binding sites on GM 7373 cells. Finally, neovascularization induced by bFGF in murine subcutaneous sponge implants was reduced significantly by IL-8. In conclusion, IL-8 inhibits the mitogenic activity exerted by bFGF on cultured endothelial cells by a PKC-dependent, noncompetitive mechanism of action that causes FGFR down-regulation. This activity is shared by several chemokines and requires endothelial cell surface HSPGs. The endothelial cell line utilized in the present study may help to elucidate the complex interplay among chemokines, HSPGs, growth factors, and receptors in endothelial cells.

Clotrimazole, an imidazole antimycotic, is a potent inhibitor of angiogenesis

Clotrimazole, an imidazole antimycotic, interferes with the rise in cytosolic Ca2+ and inhibits cell proliferation in a reversible manner. Here we describe the effect of clotrimazole on vascular endothelial cells (ECs). Clotrimazole inhibited the proliferation of ECs stimulated with typical angiogenic growth factors; vascular endothelial growth factor and basic fibroblast growth factor (bFGF). This inhibitory effect of clotrimazole was dose-dependent and the maximal inhibition was observed at a concentration of 10 mM. We did not observe any increase in 51Cr release from ECs during treatment with 10 microM clotrimazole. Moreover, clotrimazole inhibited the basal and bFGF-stimulated migration of ECs. As clotrimazole inhibited two principle components of angiogenesis; the proliferation and migration of ECs, we examined whether clotrimazole inhibited angiogenesis. Tube formation by ECs in type 1 collagen gel was investigated, and clotrimazole was found to be significantly inhibitory. The inhibitory effect of clotrimazole on angiogenesis was further confirmed in an in vivo angiogenesis model of murine Matrigel plug assay. These results demonstrate that clotrimazole is a potent inhibitor of angiogenesis.

alphavbeta3 integrin mediates the cell-adhesive capacity and biological activity of basic fibroblast growth factor (FGF-2) in cultured endothelial cells

Fibroblast growth factor-2 (FGF-2) immobilized on non-tissue culture plastic promotes adhesion and spreading of bovine and human endothelial cells that are inhibited by anti-FGF-2 antibody. Heat-inactivated FGF-2 retains its cell-adhesive activity despite its incapacity to bind to tyrosine-kinase FGF receptors or to cell-surface heparan sulfate proteoglycans. Recombinant glutathione-S-transferase-FGF-2 chimeras and synthetic FGF-2 fragments identify two cell-adhesive domains in FGF-2 corresponding to amino acid sequences 38-61 and 82-101. Both regions are distinct from the FGF-receptor-binding domain of FGF-2 and contain a DGR sequence that is the inverse of the RGD cell-recognition sequence. Calcium deprivation, RGD-containing eptapeptides, soluble vitronectin (VN), but not fibronectin (FN), inhibit cell adhesion to FGF-2. Conversely, soluble FGF-2 prevents cell adhesion to VN but not FN, thus implicating VN receptor in the cell-adhesive activity of FGF-2. Accordingly, monoclonal and polyclonal anti-alphavbeta3 antibodies prevent cell adhesion to FGF-2. Also, purified human alphavbeta3 binds to immobilized FGF-2 in a cation-dependent manner, and this interaction is competed by soluble VN but not by soluble FN. Finally, anti-alphavbeta3 monoclonal and polyclonal antibodies specifically inhibit mitogenesis and urokinase-type plasminogen activator (uPA) up-regulation induced by free FGF-2 in endothelial cells adherent to tissue culture plastic. These data demonstrate that FGF-2 interacts with alphavbeta3 integrin and that this interaction mediates the capacity of the angiogenic growth factor to induce cell adhesion, mitogenesis, and uPA up-regulation in endothelial cells.

The differential effects of 12-O-tetradecanoylphorbol-13-acetate on the gap junctions and connexins of the developing mammalian lens

Epithelial cells in primary ovine lens cultures express the gap junction proteins connexin43 (Cx43) and connexin49 (Cx49; a.k.a. MP70), a homologue of mouse connexin50. In contrast, lens cultures of differentiated, fiber-like cells (termed lentoid cells) express Cx49 and connexin46 (Cx46), but not Cx43. To investigate the regulation of lens cell gap junctions by protein kinase C (PKC), differentiating lens cultures were treated with the PKC activator 12-O-tetradecanoylphorbol-13-acetate (beta-TPA). Within 10 min, beta-TPA significantly inhibited the transfer of Lucifer Yellow dye between epithelial, but not lentoid, cells. This inhibition was correlated with the phosphorylation of Cx43 and was followed by the gradual disappearance of Cx43 from cell interfaces. The protein kinase inhibitor staurosporine prevented Cx43 phosphorylation and the loss of Cx43 from intercellular junctions. Following treatment of cultures with beta-TPA for 2-6 hr, Cx49 disappeared from epithelial cell interfaces, and by 24 hr of beta-TPA treatment, levels of Cx49 detected on immunoblots of purified epithelial membrane fractions had also diminished significantly. The beta-TPA-induced loss of Cx49 both from regions of epithelial cell contact and from isolated membranes was correlated with the disappearance of Cx49 mRNA. In contrast to the epithelial connexins, the lentoid connexins Cx49 and Cx46 were unaffected by even extended beta-TPA treatment. In spite of lentoid dye transfer being refractory to beta-TPA, significant levels of PKC-alpha (a beta-TPA-sensitive isoform) were detected in the lentoid cell. The response of lens gap junctions to beta-TPA depends upon the stage of differentiation and the complement of connexins expressed. The contrasting effects of beta-TPA on Cx43 and Cx49 in lens epithelial cells indicate a fundamental difference in the regulation of these connexin proteins in the developing mammalian lens.

Nitric oxide promotes proliferation and plasminogen activator production by coronary venular endothelium through endogenous bFGF

We reported previously that NO is responsible for the angiogenesis produced by endothelium-dependent vasodilating peptides. To investigate the mechanisms by which NO controls angiogenesis, NO was assessed for the ability to affect cell proliferation and upregulation of urokinase-type plasminogen activator (uPA) induced by basic fibroblast growth factor (bFGF) when added exogenously to or when produced endogenously by coronary venular endothelial cells (CVECs). The treatment of the cells with the NO donor sodium nitroprusside (NaNp) induced uPA upregulation and cell proliferation, which were prevented by anti-bFGF antibodies. Similarly, the NO-dependent mitogenic activity of the vasodilating peptide substance P (SP) was blocked by anti-bFGF antibodies, thus implicating endogenous bFGF in the NO-induced response. NaNp and SP induced bFGF expression as measured by Western blot analysis of CVEC extracts and by differential reverse transcriptase-polymerase chain reaction of bFGF mRNA. SP-induced upregulation of bFGF was prevented by the NO synthase inhibitor N omega-monomethyl-L-arginine. We conclude that NO promotes cell proliferation and uPA upregulation in CVECs by inducing endogenous bFGF and that this pathway mediates the angiogenetic response to the vasoactive neuropeptide SP. This signaling paradigm may provide an important link between shear rate, NO, bFGF, and coronary angiogenesis.

Dynamic distribution of basic fibroblast growth factor during epulis formation: an immunohistochemical study in an enhanced healing process of the gingiva

Basic fibroblast growth factor (bFGF) is thought to play an important role in wound healing. However, its histological localization, both in normal and pathological conditions in the oral mucosa, has not been well documented. We have studied the immunolocalization of bFGF in normal gingiva and gingival epulis specimens corresponding to different organizing stages. In normal gingiva, bFGF was detected in subpopulations of macrophages, mast cells and most endothelial cells in the lamina propria. Granulation tissue in epulides was histopathologically classified into six organizing stages. In stages 1 and 2, a small number of bFGF-positive macrophages was seen at the periphery of ulcer bases. In stages 3 and 4, histologically characterized by prominent capillary proliferation, large numbers of bFGF-positive macrophages and mast cells were located within granulation tissue. A positive reaction for bFGF was also found in some endothelial cells and in myxoedematous stroma that was rich in heparan sulfate proteoglycan. In stages 5 and 6, when fibrosis was accelerated, bFGF-positive macrophages and mast cells decreased in number and were localized only at the periphery of the fibrous tissue. These findings suggest that maximum amounts of bFGF are synthesized and released from some macrophages and mast cells into the extracellular matrix during neovascularization of granulation tissue.

Role of fibrin and plasminogen activators in repair-associated angiogenesis: in vitro studies with human endothelial cells

Angiogenesis, the formation of new blood vessels from existing ones, plays a central role in development and in a number of pathological conditions. Tissue repair-associated angiogenesis usually involves cell invasion into a fibrin structure and the presence of inflammatory cells. In this chapter the role of plasminogen activators in the dissolution of fibrin and the invasion of endothelial cells into a fibrin matrix is described. Tissue-type plasminogen activator is stored in endothelial cells and can be released acutely into the vessel lumen upon stimulation of the endothelium to activate fibrinolysis and to prevent fibrin deposition. At the basolateral side of the cell, urokinase-type plasminogen activator (uPA) bound to a specific cellular receptor is involved in the proteolytic modulation of matrix proteins and cell-matrix interaction. The cytokine tumor necrosis factor-alpha (TNF-alpha) cooperates with the angiogenic factors basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) in inducing human microvascular endothelial cells in vitro to invade a three dimensional fibrin matrix and to form capillary-like tubular structures. The formation of these capillary-like tubules requires cell-bound uPA activity.

Induction of urokinase-type plasminogen activator by fibroblast growth factor (FGF)-2 is dependent on expression of FGF receptors and does not require activation of phospholipase Cgamma1

The roles of heparan sulfate proteoglycans and tyrosine kinase fibroblast growth factor (FGF) receptors in mediating the induction of plasminogen activator (PA) by FGF-2 were investigated using L6 myoblast cells that normally do not express detectable FGF receptors. PA was induced by FGF-2 in a dose-dependent manner in L6 cells expressing transfected FGF receptor-1 but not in nontransfected cells or cells transfected with the vector alone. The PA produced in these cells was characterized as urokinase-type PA (uPA). Thus, expression of a tyrosine kinase FGF receptor was required for induction of uPA. Internalization of FGF through heparan sulfates does not seem to be involved in this response as soluble heparin and suramin at concentrations which inhibited FGF-2 binding to heparan sulfates but not receptors did not affect the induction of uPA by FGF-2. Mutant receptors in which the tyrosine kinase was inactivated were not able to respond to FGF-2. In contrast, mutation of the site of phospholipase Cgamma1 (PLCgamma) binding in the receptor, which causes loss of PLCgamma activation, had no effect on uPA induction by FGF-2. These results suggest that PLCgamma activation is not required for induction of uPA by FGF-2.

Up-regulation of urokinase-type plasminogen activator in squamous cell carcinoma of human larynx

The expression of urokinase-type plasminogen activator (uPA) was investigated in squamous cell carcinoma of the human larynx. For this purpose, tissue extracts from 25 matched samples of normal mucosa and neoplastic larynx were compared for the levels of uPA activity as evaluated by a chromogenic PA assay and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) zymography. Also, uPA antigen was quantified by enzyme-linked immunosorbent assay (ELISA) in 19 cases. The results demonstrate a significant increase in the levels of uPA activity and protein in tumour tissue extracts, more pronounced in tumours with lymph node metastases. Immunohistochemistry performed on 70 biopsies showed that uPA positivity is present both in neoplastic cells and in fibroblast-like cells and macrophages. However, depending on the histological grading and invasive capacity of the tumour, a pronounced intra- and intertumoral heterogeneity in uPA staining was observed. In situ hybridisation confirmed the presence of uPA mRNA in both tumour and stromal cells. The present study provides experimental evidence for a role of uPA in the invasive growth of human laryngeal carcinoma.

Signal transduction by basic fibroblast growth factor in rat osteoblastic Py1a cells

Basic fibroblast growth factor (bFGF) is a potent mitogen for bone. In this study, we utilized the clonal rat osteoblastic cell line, Py1a, to examine signal transduction by bFGF and to determine the role of mitogen activated protein kinases (MAPK) and induction of c-fos mRNA in the mitogenic response to bFGF. Stimulation of [3H]thymidine incorporation (TDR) into DNA by bFGF was determined in the presence of phorbol myristate acetate of (PMA) to down-regulate the protein kinase C (PKC) pathway, genistein, an inhibitor of tyrosine kinase and H-7, a PKC inhibitor, bFGF 10(-8) M and PMA 10(-7) M increased TDR by 242 and 245%, respectively. Treatment with bFGF or PMA for 5 or 30 minutes increased tyrosine phosphorylation of multiple proteins, and immunoblotting with MAPK-specific antibody revealed that two of these bands were the 42 and 44 kD isoforms of MAPK. PMA and bFGF induced c-fos mRNA expression at 30 minutes. Genistein at 10 micrograms/ml blocked the mitogenic effect of bFGF and partially inhibited the mitogenic effect of PMA. Genistein at 100 micrograms/ml also blocked both bFGF- and PMA-induced increases in c-fos mRNA. A 24 h pretreatment with PMA at 10(-7) M inhibited the mitogenic response, tyrosine phosphorylation of MAPK, and induction of c-fos mRNA subsequent to the addition of PMA, but not bFGF. H-7 at 50 microM blocked bFGF-induced mitogenesis and c-fos induction, but did not inhibit bFGF-induced tyrosine phosphorylation of MAPK. In this study, we show that the signaling pathway of bFGF and PMA are similar in that they both induce tyrosine phosphorylation of MAP kinases and activate c-fos. However, the signaling pathways ultimately diverge in that once the PKC pathway is down-regulated by PMA pretreatment or blocked by the PKC inhibitor H-7, tyrosine phosphorylation of MAP kinase, c-fos induction, and the mitogenic effect of PMA is blocked. In contrast, down-regulation of the PKC pathway inhibits c-fos and the mitogenic response to bFGF, but not bFGF's effects on tyrosine phosphorylation of MAP kinase.

Basic fibroblast growth factor selectively regulates ornithine decarboxylase gene expression in malignant H-ras transformed cells

Cell growth regulation by fibroblast growth factors (FGFs) is highly complex. The present study demonstrates a novel link between alterations in bFGF regulation during malignant conversion and the expression of ornithine decarboxylase, a key rate-limiting and regulatory activity in the biosynthesis of polyamines. H-ras transformed mouse 10T 1/2 cell lines exhibiting increasing malignant potential were investigated for possible bFGF-mediated changes in ornithine decarboxylase gene expression. Selective induction of ornithine decarboxylase gene expression was observed, since, in contrast to nontransformed 10T 1/2 cells and cells capable of only benign tumor formation, H-ras transformed metastatic cells exhibited marked elevations in ornithine decarboxylase message levels. Evidence for regulation of ornithine decarboxylase gene expression by bFGF at both transcription and posttranscription was found. Actinomycin D pretreatment of malignant cells prior to bFGF exposure inhibited the increase in ornithine decarboxylase message. Furthermore, striking differences in the rates of ornithine decarboxylase message decay were observed when cells treated with bFGF were compared to untreated control cells, with the half-life of ornithine decarboxylase mRNA increasing from 2.4 h in untreated cells to 12.5 h in cells exposed to bFGF. Evidence was also obtained for a cycloheximide-sensitive regulator of ornithine decarboxylase gene expression whose effect, in combination with bFGF, resulted in a further augmentation of ornithine decarboxylase gene expression. Furthermore, evidence is presented to suggest a possible role for G-protein-coupled events in the bFGF-mediated regulation of ornithine decarboxylase gene expression. The bFGF regulation of ornithine decarboxylase expression in H-ras transformed malignant cells appeared to occur independent of protein kinase C-mediated events. These results show that bFGF can modulate ornithine decarboxylase gene expression in malignant H-ras transformed cells and further suggests a mechanism of growth factor stimulation of malignant cells wherein early alterations in the regulatory control of ornithine decarboxylase gene expression are critical.

A distinct basic fibroblast growth factor (FGF-2)/FGF receptor interaction distinguishes urokinase-type plasminogen activator induction from mitogenicity in endothelial cells

Basic fibroblast growth factor (FGF-2) induces cell proliferation and urokinase-type plasminogen activator (uPA) production in fetal bovine aortic endothelial GM 7373 cells. In the present paper we investigated the role of the interaction of FGF-2 with tyrosine-kinase (TK) FGF receptors (FGFRs) in mediating uPA up-regulation in these cells. The results show that FGF-2 antagonists suramin, protamine, heparin, the synthetic peptide FGF-2(112-155), and a soluble form of FGFR-1 do not inhibit FGF-2-mediated uPA up-regulation at concentrations that affect growth factor binding to cell surface receptors and mitogenic activity. In contrast, tyrosine phosphorylation inhibitors and overexpression of a dominant negative TK- mutant of FGFR-1 abolish the uPA-inducing activity of FGF-2, indicating that FGFR and its TK activity are essential in mediating uPA induction. Accordingly, FGF-2 induces uPA up-regulation in Chinese hamster ovary cells transfected with wild-type FGFR-1, -2, -3, or -4 but not with TK- FGFR-1 mutant. Small unilamellar phosphatidyl choline:cholesterol vesicles loaded with FGF-2 increased uPA production in GM 7373 cells in the absence of a mitogenic response. Liposome-encapsulated FGF-2 showed a limited but significant capacity, relative to free FGF-2, to interact with FGFR both at 4 degrees C and 37 degrees C and to be internalized within the cell. uPA up-regulation by liposome-encapsulated FGF-2 was quenched by neutralizing anti-FGF-2 antibodies, indicating that the activity of liposome-delivered FGF-2 is mediated by an extracellular action of the growth factor. Taken together, the data indicate that a distinct interaction of FGF-2 with FGFR, quantitatively and/or qualitatively different from the one that leads to mitogenicity, is responsible for the uPA-inducing activity of the growth factor.

Effects of fibrin on the secretion of plasminogen activator inhibitor-1 from endothelial cells and on protein kinase C

We previously demonstrated that cultured human umbilical vein endothelial cells (HUVECs) overlaid with a fibrin clot induced a slight increase in tissue-type plasminogen activator (t-PA) secretion and marked reduction in plasminogen activator inhibitor-1 (PAI-1) secretion. In this study, the intracellular signal transduction after fibrin stimulation was further investigated by analyzing cyclic AMP (cAMP) and protein kinase C (PK-C). When HUVECs were stimulated by fibrin clots, t-PA mRNA increased to 130% but PAI-1 mRNA decreased to 42%. These changes concurred with the data on the protein levels of t-PA and PAI-1 as previously reported. The effect of fibrin on t-PA production in HUVECs was not significantly altered after the elevation of cAMP by either forskolin or dibutyryl cAMP. Furthermore, an effect of fibrin on t-PA production did not appear when the cells were treated by phorbol 12-myristate 13-acetate (PMA) or 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7). The suppressive effect of fibrin on PAI-1 secretion from HUVECs was not altered by elevation of cAMP. Regarding the activation of PK-C by PMA, PAI-1 secretion was enhanced, but was suppressed by fibrin stimulation. H-7 suppressed PAI-1 secretion and further stimulation by fibrin almost completely abolished PAI-1 secretion. These changes were well associated with mRNA levels of t-PA and PAI-1. These results suggested that fibrin on HUVECs preferably down-regulates PK-C resulting in a decrease of PAI-1 in both the protein and mRNA levels and that effect of fibrin on t-PA secretion is neither involved in PK-C nor cAMP pathway.

Stimulation of zif/268 gene expression by basic fibroblast growth factor in primary rat striatal cultures

The presence of basic fibroblast growth factor (bFGF) in the basal ganglia, and its known neurotrophic activity, has created interest in its possible role as an agent to attenuate striatal neurodegeneration. However, little information is available on the mechanisms through which bFGF might exert a long-term influence on striatal function. Primary cultures of embryonic rat striatal neurones were used to ascertain whether bFGF can alter the pattern of striatal gene expression. Treatment of cultures with bFGF (500 pM) resulted in a dramatic increase in the levels of zif/268 mRNA within 45 min. This induction was attenuated by the tyrosine kinase inhibitor genistein (100 microM), but not by its inactive structural analogue genistin (100 microM). The induction of zif/268 mRNA was found to occur in non-neuronal cells, with no increase in mRNA levels being observed in neurones. A similar induction was noted for another putative transcription factor, jun B, although no induction of the related factor jun D could be detected. These results show that bFGF can induce immediate-early gene expression in striatal cultures, and therefore that this may provide a mechanism, mediated by non-neuronal cells, which allows bFGF to cause a long-term change in striatal neurochemistry.

High glucose concentrations and protein kinase C isoforms in vascular smooth muscle cells

High extracellular glucose activates protein kinase C (PKC), a family of kinases vital to intracellular signaling. However, which PKC isoforms are involved and where in the cell they operate is unclear. We tested the hypothesis that only those PKC isoforms binding to diacylglycerol (DAG) are activated by high glucose. We also reasoned that the isoforms would translocate to different parts of the cell, where they presumably serve different functions. The PKC isoforms alpha, beta, delta, epsilon, and zeta were studied. Twenty mM glucose caused an increase in total PKC activity at six hours, which was maintained at 24 hours. High glucose decreased the angiotensin II-induced calcium signal. This effect was reversed by preincubating the cells with the PKC inhibitor staurosporine. Glucose induced a translocation of all PKC isoforms except PKC zeta by Western blot. Confocal microscopy showed that PKC alpha, beta, and epsilon were translocated into the nucleus. PKC delta showed strong association with cytoskeletal structures. The effects were sustained at 24 hours for PKC isoform beta and to a lesser extent for PKC delta and epsilon, but not for PKC alpha. Thus, PKC isoforms differ in their propensity to be activated by high glucose. Those isoforms binding to DAG are activated. Both cytoskeletal and nuclear signaling may be involved.

Transcriptional and posttranscriptional regulation of urokinase-type plasminogen activator expression in endothelial cells by basic fibroblast growth factor

The mechanism of induction of urokinase-type plasminogen activator (uPA) by basic fibroblast growth factor (bFGF) was explored in fetal bovine aortic endothelial GM 7373 cells. A three- to four-fold increase in the steady-state levels of uPA mRNA was observed after 6 h of incubation of the cell cultures with bFGF. Accordingly, nuclear run-on experiments showed a 2-2.4-fold increase in the rate of uPA gene transcription during the first 4 h of treatment with the growth factor. bFGF did not affect uPA mRNA stability, as evaluated by chase experiments with the mRNA synthesis inhibitor actinomycin D. Upregulation of uPA mRNA was followed by a delayed increase in uPA protein synthesis paralleled by an increase in secreted and cell-associated uPA activity. Twelve h were required before accumulated uPA mRNA was translated into the corresponding protein. During this time interval, the continuous presence of biologically active bFGF in the extracellular environment represented an absolute requirement for uPA mRNA translation. Substitution of residues Lys-27, Lys-30, and Arg-31 to glutamine residues in the bFGF molecule resulted in a mutant (M1Q-bFGF) that caused uPA mRNA accumulation in the absence of a significant increase in cell-associated uPA activity. M1Q-bFGF also induced an increase in cell-associated uPA activity only when added to the cell cultures in the presence of soluble heparin. These results provide evidence that bFGF can affect uPA expression in endothelial GM 7373 cells both at transcriptional and posttranscriptional translational levels. They also show the possibility to dissociate upregulation of uPA mRNA from upregulation of uPA activity by mutagenesis of the bFGF molecule.

Angiogenesis: role of calcium-mediated signal transduction

During angiogenesis, endothelial cells react to stimulation with finely tuned signaling responses. The role of calcium-regulated signaling in angiogenesis has not been defined. This study investigated the calcium dependency of endothelial cell proliferation and invasion by using an inhibitor of ligand-stimulated calcium influx, CAI (carboxy-amidotriazole). Incubation with CAI significantly inhibited proliferation of human umbilical vein endothelial cells (HUVECs) in response to serum (IC50 = 1 microM) or basic fibroblast growth factor (FGF2; P2 < 0.005 at 10 microM). Statistically significant inhibition of HUVEC adhesion and motility to basement membrane proteins laminin, fibronectin, and type IV collagen was demonstrated (adhesion, P2 < 0.004-0.01; motility, P2 < 0.009-0.018). Marked inhibition of native and FGF2-induced gelatinase activity was shown by zymogram analysis and was confirmed by Northern blot analysis. CAI inhibited HUVEC tube formation on Matrigel and inhibited in vivo angiogenesis in the chicken chorioallantoic membrane assay, 67% at 20 microM and 56% at 10 microM compared with 16% for an inactive CAI analog or 9% for 0.1% dimethyl sulfoxide control. Incubation of HUVECs with CAI and/or FGF2 followed by immunoprecipitation with anti-phosphotyrosine antibody showed inhibition of FGF2-induced tyrosine phosphorylation of proteins in the range 110-150 kDa. These results suggest that calcium-regulated events are important in native and FGF2-stimulated HUVEC proliferation and invasion, perhaps through regulation of FGF2-induced phosphorylation events, and indicate a role for calcium in the regulation of angiogenesis in vivo.