Enhanced production and extracellular deposition of the endothelial-type plasminogen activator inhibitor in cultured human lung fibroblasts by transforming growth factor-beta

Latent transforming growth factor-beta 1 associates to fibroblast extracellular matrix via latent TGF-beta binding protein

The role of latent transforming growth factor-beta (TGF-beta) binding protein (LTBP) in the association of TGF-beta 1 to the extracellular matrix of cultured fibroblasts and HT-1080 fibrosarcoma cells was studied by immunochemical methods. The matrices were isolated from the cells, and the levels of LTBP and TGF-beta 1 were estimated by immunoblotting and immunoprecipitation. LTBP, TGF-beta 1, and its propeptide (latency-associated peptide, LAP) were found to associate to the extracellular matrix. Immunoblotting analysis indicated that treatment of the cells with plasmin resulted in a concomitant time and dose dependent release of both LTBP and TGF-beta 1 from the extracellular matrix to the supernatant. Comparison of molecular weights suggested that plasmin treatment resulted in the cleavage of LTBP from the high molecular weight fibroblast form to a form resembling the low molecular weight LTBP found in platelets. Pulse-chase and immunoprecipitation analysis indicated that both the free form of LTBP and LTBP complexed to latent TGF-beta were efficiently incorporated in the extracellular matrix, from where both complexes were slowly released to the culture medium. Addition of plasmin to the chase solution resulted, however, in a rapid release of LTBP from the matrix. Fibroblast derived LTBP was found to associate to the matrix of HT-1080 cells in a plasmin sensitive manner as shown by immunoprecipitation analysis. These results suggest that the latent form of TGF-beta 1 associates with the extracellular matrix via LTBP, and that the release of latent TGF-beta 1 from the matrix is a consequence of proteolytic cleavage(s) of LTBP.

Activities, localizations, and roles of serine proteases and their inhibitors in human brain tumor progression

The plasminogen activation system consists of plasminogen activators and their inhibitors, serine proteases, and serpins. The proteases and inhibitors regulate a variety of processes in tissue morphogenesis, differentiation, cell migration, and cancer cell invasiveness and metastasis. One of the plasminogen activators, urokinase-type plasminogen activator (uPA), binds to a specific surface and provides a localized cell surface proteolytic activity required for the destruction of extracellular matrix, which is a vital step in tumor cell invasion. The proteolytic activity of uPA is modulated by its cell surface receptor, as well as by plasminogen activator inhibitor type-1 (PAI-1) and, to a lesser degree, by other inhibitors. The role of plasminogen activators and their inhibitors in cancer invasion can be demonstrated in the development and progression of malignant brain tumors. Our findings indicate that uPA and PAI-1 expression are dramatically upregulated in malignant brain tumors in parallel with the histological progression of the tumors. The results suggest that these molecules may contribute to tumor invasion in addition to their significant role in angiogenesis. An evaluation of the plasminogen activation system could add diagnostic and prognostic significance to the evaluation of individual patients.

Modulation of fibrinolysis by ionizing radiation

Radiation-induced damage to the central nervous system is believed to be targeted to glial or endothelial cells or both, although the pathophysiology of this process is still poorly understood. A series of experiments were, therefore, conducted, including irradiation to primary rat astrocytes (in vitro) and rat spinal cords (in vivo). The levels of plasminogen activators (uPA and tPA) and their inhibitors (PNI and PAI-1) were determined by fibrin zymography, ELISA, amidolytic activity assay, complex formation, and Western blot analysis. Fibrin zymography revealed the presence of M(r) 48,000 (uPA) and M(r) 68,000 (tPA) lytic bands that were increased in irradiated samples. Three- to four-fold higher levels of tPA and 8- to 10-fold higher levels of uPA were detected in irradiated samples. Western blot analysis confirmed the presence of a 51-kDa band (PAI-1) in irradiated samples. PAI-1 is undetectable in nonirradiated spinal cord. Serum-free medium and cell and spinal cord extracts of nonirradiated samples showed a 43-kDa band (PNI), the intensity of which is decreased in irradiated samples. Four- to five-fold decreased levels of PNI were detected in irradiated serum-free media and cell extracts, but no levels of PNI were detected in irradiated spinal cord extracts. This study provides additional information regarding the proposed roles of plasminogen activators and their inhibitors in the development of CNS damage after irradiation.

Cloning from a mouse osteoblastic cell line of a set of transforming-growth-factor-beta 1-regulated genes, one of which seems to encode a follistatin-related polypeptide

Transforming growth factor(TGF)beta 1 is a potent inhibitor of growth in mouse osteoblastic MC3T3-E1 cells. To isolate genes that are induced by TGF beta 1, the differential screening method was adopted using a cDNA library constructed from cells treated with TGF beta 1 for 4 h. Six independent cDNA clones were isolated (TGF beta-stimulated clone, TSC-5, TSC-36, TSC-115, TSC-128, TSC-160 and TSC-161), the expression of which was increased by TGF beta 1-treatment with maximal expression at 6-10 h. The steady-state levels of TSC-36, TSC-128 and TSC-160 increased almost tenfold, whereas those of TSC-5, TSC-115 and TSC-161 were elevated at most threefold. From partial nucleotide sequences, TSC-160 was found to be identical to rrg (ras-recision gene, lysyl oxidase), and TSC-115 had 80% similarity with tropomyosin cDNA, whereas other genes seemed novel. Expression of TSC-36 and TSC-160 was dramatically decreased in v-Ki-ras-transformed MC3T3 cells or in transformed NIH 3T3 cells (DT), and was recovered to normal levels in a flat revertant (C11). A nearly full-length copy of TSC-36 cDNA was isolated, and an open reading frame indicated that it encodes a protein of 35 kDa. An antiserum was raised against the C-terminal peptide predicted from the nucleotide sequence, and a polypeptide with an approximate molecular mass of 38 kDa was detected in cultured medium of MC3T3-E1 cells. The amino acid sequence of TSC-36 protein was found to have some similarity with follistatin, an activin-binding protein, and a limited similarity with the secreted protein rich in cysteine (SPARC).

Role of growth factors in cutaneous wound healing: a review

The well-orchestrated, complex series of events resulting in the repair of cutaneous wounds are, at least in part, regulated by polypeptide growth factors. This review provides a detailed overview of the known functions, interactions, and mechanisms of action of growth factors in the context of the overall repair process in cutaneous wounds. An overview of the cellular and molecular events involved in soft tissue repair is initially presented, followed by a review of widely studied growth factors and a discussion of commonly utilized preclinical animal models. The article concludes with a summary of the preliminary results from human clinical trials evaluating the effects of growth factors in the healing of chronic skin ulcers. Throughout, the interactions among the growth factors in the wound-healing process are emphasized.

Expression of cytokine genes in human cardiac allografts: correlation of IL-6 and transforming growth factor-beta (TGF-beta) with histological rejection

Cytokines may play critical roles in allograft rejection. Currently, a clear pattern of cytokine production that correlates with rejection has not emerged. Our preliminary studies suggested a trend toward increased IL-6 and TGF-beta gene expression in cardiac allografts during rejection. We have extended these studies using reverse transcriptase/polymerase chain reaction (RT/PCR) to detect the expression of IL-6, TGF-beta, and T cell receptor beta chain constant region (TCR-beta) genes in 21 additional consecutive myocardial biopsies obtained from six heart transplant patients and from five pre-transplant donor hearts. Cytokine gene expression was compared with histological diagnosis of rejection. There was strong correlation between IL-6 as well as TGF-beta gene expression, and histological rejection (6/8 biopsies with versus 0/7 without rejection (P = 0.006) and 7/9 biopsies with versus 0/7 without rejection (P = 0.003) respectively). Neither IL-6 nor TGF-beta transcripts were detected in any pre-transplant donor heart. TCR-beta chain mRNA was found in all allograft biopsies regardless of the presence of rejection, but was absent in pre-transplant donor hearts. Our results indicate that expression of IL-6 and TGF-beta is highly correlated with allograft rejection and thus may play an important role in regulation of cardiac allograft rejection. T cell infiltration of allografted myocardium is invariably detected by PCR regardless of histological rejection. The long-term functional significance of these cells in transplanted hearts needs further investigation.

Type 1 plasminogen activator inhibitor gene expression following partial hepatectomy

A murine model of partial hepatectomy (PH) was employed to investigate type 1 plasminogen activator inhibitor (PAI-1) gene expression in regenerating liver. Mice were anesthetized, and a portion of the left lobe of the liver was ligated and resected distal to the ligature, and at various times thereafter, total liver RNA was prepared and analyzed by Northern blotting. PH caused a transient increase in PAI-1 messenger (m)RNA that was apparent within 1 to 2 hours after surgery, was maximal at 8 hours (ninefold increase over sham-operated controls), and then slowly declined. Analysis of discrete liver segments demonstrated much greater induction of PAI-1 mRNA in the region adjacent to PH than in more distal regions. Further analysis of the adjacent tissue by in situ hybridization revealed that PAI-1 mRNA was induced primarily in hepatocytes in the transition zone created by the occluding hemostatic ligature between viable and necrotic tissue. Expression of PAI-1 mRNA could also be detected in this transition zone in capsular mesothelial cells, subcapsular hepatocytes, and venous endothelial cells bordering the area. A much weaker signal was evident in hepatocytes dispersed throughout the remaining intact lobes of PH mice, and no signal was detected in the livers of sham-operated mice. These observations suggest that PAI-1 may be of importance in local tissue remodeling events accompanying liver regeneration.

Cytokines in kidney disease: the role of transforming growth factor-beta

Cytokines such as transforming growth factor-beta (TGF-beta) are peptide factors that regulate embryogenesis, development, inflammation, tissue repair, and carcinogenesis. Growing evidence indicates that dysregulation of cytokine actions may underlie the pathogenesis of serious autoimmune, degenerative, and fibrotic diseases. Studies in a model of acute mesangial proliferative glomerulonephritis show that overproduction of TGF-beta is the cause of pathologic accumulation of extracellular matrix in the nephritic glomeruli. Transforming growth factor-beta acts to increase matrix production, inhibit matrix degradation, and modulate matrix receptors in the glomerulonephritic rats. It may also play a role in the glomerular matrix build-up that is a central feature of diabetic nephropathy. Elevated expression of TGF-beta mRNA and TGF-beta protein were found in the glomeruli of diabetic rats along with increased levels of proteoglycans and other matrix components that are known to be induced by TGF-beta. The study of human diabetic glomeruli has also showed markedly elevated levels of TGF-beta protein. Glomeruli from normal kidneys and nonprogressive kidney disorders were negative. The striking ability of TGF-beta to cause exuberant matrix formation may be due to the fact that TGF-beta can induce its own production by resident cells at a site of injury. Thus, the potential for TGF-beta to do harm may be due to this autoinduction mechanism whereby TGF-beta expression can become chronic, creating a vicious circle. As the role that TGF-beta plays in chronic fibrotic diseases becomes better understood, it is likely that TGF-beta inhibitors will become important future drugs for treating these conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming growth factor-beta 1 induces alpha-smooth muscle actin expression in granulation tissue myofibroblasts and in quiescent and growing cultured fibroblasts

Granulation tissue fibroblasts (myofibroblasts) develop several ultrastructural and biochemical features of smooth muscle (SM) cells, including the presence of microfilament bundles and the expression of alpha-SM actin, the actin isoform typical of vascular SM cells. Myofibroblasts have been proposed to play a role in wound contraction and in retractile phenomena observed during fibrotic diseases. We show here that the subcutaneous administration of transforming growth factor-beta 1 (TGF beta 1) to rats results in the formation of a granulation tissue in which alpha-SM actin expressing myofibroblasts are particularly abundant. Other cytokines and growth factors, such as platelet-derived growth factor and tumor necrosis factor-alpha, despite their profibrotic activity, do not induce alpha-SM actin in myofibroblasts. In situ hybridization with an alpha-SM actin probe shows a high level of alpha-SM actin mRNA expression in myofibroblasts of TGF beta 1-induced granulation tissue. Moreover, TGF beta 1 induces alpha-SM actin protein and mRNA expression in growing and quiescent cultured fibroblasts and preincubation of culture medium containing whole blood serum with neutralizing antibodies to TGF beta 1 results in a decrease of alpha-SM actin expression by fibroblasts in replicative and non-replicative conditions. These results suggest that TGF beta 1 plays an important role in myofibroblast differentiation during wound healing and fibrocontractive diseases by regulating the expression of alpha-SM actin in these cells.

Transforming growth factor-beta 1 stimulates macrophage urokinase expression and release of matrix-bound basic fibroblast growth factor

Macrophage expression of urokinase-type plasminogen activator (uPA) appears to play a role in their release of matrix-bound basic fibroblast growth factor (bFGF) and transforming growth factor-beta (TGF-beta). In experiments reported here, we have examined the potential regulatory effects of bFGF and TGF-beta 1 on macrophage uPA expression. TGF-beta 1 stimulated in a dose- and time-dependent manner the expression of secreted membrane and intracellular uPA activities by a macrophage cell line (RAW264.7). When examined at similar concentrations, bFGF had little effect, and interleukin-1 alpha, tumor necrosis factor-alpha, and monocyte colony stimulating factor had no effect on macrophage uPA expression. Exposure of macrophages to TGF-beta 1 led to a rapid and sustained increase in the steady-state levels of uPA mRNA that was independent of de novo protein synthesis and was completely inhibited by actinomycin D. However, the TGF-beta 1-induced increase in uPA mRNA was largely unaffected by subsequent incubation of cells with actinomycin D. The protein kinase C inhibitor H7 markedly reduced the ability of TGF-beta 1 to stimulate expression of uPA activity. Likewise, okadaic acid and microcystin, inhibitors of serine/threonine phosphatases, potentiated the ability of TGF-beta 1 to upregulate macrophage uPA expression. TGF-beta 1 primed cells converted nearly all added plasminogen to plasmin and expressed sixfold more membrane-bound plasmin than control cells. Preincubation of TGF-beta 1 with either serum or methylamine-modified alpha 2-macroglobulin did not affect its ability to induce macrophage uPA expression. When control and TGF-beta 1-primed macrophages were cultured on matrices containing bound 125I-bFGF, their release of 125I-bFGF was increased five and tenfold, respectively, in the presence of plasminogen. The ability of TGF-beta to induce macrophage uPA expression and the plasmin-dependent release of matrix-bound bFGF may provide an indirect mechanism by which TGF-beta stimulates angiogenesis.

Transforming growth factor-beta in neural embryogenesis and neoplasia

The transforming growth factor-beta (TGF-beta) family of polypeptides includes three structurally and functionally related mammalian isoforms that influence cell proliferation, differentiation, and extracellular matrix production. Recent identification of these isoforms in the embryonic murine central nervous system suggests that these factors may regulate proliferation and differentiation of meningeal and neuroepithelial cells during development. Predominant expression of TGF-beta 1 in the leptomeninges compared with the brain of the murine and human central nervous system implicates this isoform in regulation of that mesodermal tissue. Thus, defective TGF-beta regulation may contribute to neoplastic transformation. Failure to activate latent TGF-beta s may contribute to the loss of autocrine regulation seen in meningiomas. Expression of TGF-beta 2 and TGF-beta 3 primarily in embryonic murine radial glia and adult human astrocytes suggests other roles for these isoforms, including glioblast differentiation and guidance of neuroblast migration. Although inhibitory to "normal" astrocyte proliferation, TGF-beta s demonstrate autocrine growth stimulation in vitro among hyperdiploid malignant gliomas, medulloblastomas, primitive neuroectodermal tumors, and anaplastic ependymomas. Hence, synthesis and release of active TGF-beta s by malignant brain tumors may create aberrant stimulatory autocrine loops. The mechanism of TGF-beta-induced growth stimulation is poorly understood. Future studies will likely clarify and identify additional roles for the TGF-beta isoforms in neuro-embryogenesis and neoplasia.

Growth state-regulated expression of p52(PAI-1) in normal rat kidney cells

In normal rat kidney (NRK) cells, synthesis of the 52-kDa substrate-associated type 1 inhibitor of plasminogen activator [p52(PAI-1)] is linked to alterations in cell shape and substrate adhesion. Subconfluent NRK cells accumulated significantly more ventral undersurface-associated p52(PAI-1) compared to newly confluent or 1-to 2-day postconfluent cultures, suggesting that p52(PAI-1) expression was also growth state-modulated. Since cytoarchitectural constraints function in cell growth control, changes in p52(PAI-1) synthesis were assessed with respect to defined morphologic events that accompany growth activation of cultured NRK cells. Stimulation of low population density, quiescent NRK cells with 20% serum-containing medium resulted in a rapid increase in matrix p52(PAI-1) protein content (6- and 26-fold after 1 and 5 hr, respectively). Growth activation in response to serum reflected activations in p52(PAI-1) cytoplasmic mRNA abundance, which peaked at 2 hr (125-fold increase) and subsequently declined (100-fold increase) at 5 hr poststimulation. Morphologic analysis indicated that quiescent NRK cells were devoid of transcytoplasmic actin filaments and focal contact-associated vinculin. A marked increase in the fraction of cells that elaborated transcytoplasmic microfilaments and vinculin-containing focal adhesions was evident within 5 min of serum addition. Such cytoarchitectural restructuring preceded p52(PAI-1) induction. Morphologic reorganization and p52(PAI-1) induction occurred prior to progression of cells through the S-phase, indicating they are early events associated with serum stimulation in the NRK cell system. The relevance of p52(PAI-1) induction during this growth state transition is not clear but may influence the established cytoarchitectural changes observed prior to p52(PAI-1) induction by regulating pericellular proteolysis and, thereby, cell-to-substrate adhesion.

Regulation of chicken Hsp70 and Hsp90 family gene expression by transforming growth factor-beta 1

Transforming growth factor-beta 1 (TGF beta) is a regulator of protein synthesis in cultured chicken embryo cells (CEC). Preceding a gradual increase in overall protein synthesis, members of the Hsp70 family (Hsp70, Hsc70, and Grp78) and the Hsp90 family (90-2 and 90-3) of molecular chaperones are induced rapidly and represent a new class of TGF beta-inducible proteins (I.M. Takenaka and L.E. Hightower, J. Cell. Physiol., 152:568-577, 1992). Herein, 32P-labeled cDNA probes encoding Hsc70 and Hsp90 were used to show that levels of the corresponding mRNAs increased as a fraction of total RNA and in polysomes within five hours of treatment of CEC with TGF beta. This cytokine did not increase rates of hsc70 and hsp90 gene transcription as measured by run-on transcription assays of isolated nuclei. However, the Hsp RNA inductions were inhibited by dactinomycin, indicating a requirement for newly synthesized RNA. Both Hsc70 and Hsp90 mRNAs had relatively short half-lives, measured by Northern blot analyses of dactinomycin chases, which were not altered substantially in TGF beta-treated cells. In contrast, Hsp mRNA half-lives increased in heat shocked CEC exposed to dactinomycin during recovery, revealing a difference in regulation of these genes in stressed cells compared with TGF beta-treated cells. Our results support the conclusion that hsc70 and hsp90 gene expression is regulated posttranscriptionally in TGF beta-treated CEC, and the mechanism likely involves a nuclear event such as increasing the half-lives of nuclear RNA transcripts, processing, or transport into the cytoplasm.

Role of the latent TGF-beta binding protein in the activation of latent TGF-beta by co-cultures of endothelial and smooth muscle cells

Transforming growth factor beta (TGF-beta) is released from cells in a latent form consisting of the mature growth factor associated with an aminoterminal propeptide and latent TGF-beta binding protein (LTBP). The endogenous activation of latent TGF-beta has been described in co-cultures of endothelial and smooth muscle cells. However, the mechanism of this activation remains unknown. Antibodies to native platelet LTBP and to a peptide fragment of LTBP inhibit in a dose-dependent manner the activation of latent TGF-beta normally observed when endothelial cells are cocultured with smooth muscle cells. Inhibition of latent TGF-beta activation was also observed when cells were co-cultured in the presence of an excess of free LTBP. These data represent the first demonstration of a function for the LTBP in the extracellular regulation of TGF-beta activity and indicate that LTBP participates in the activation of latent TGF-beta, perhaps by concentrating the latent growth factor on the cell surface where activation occurs.

Transforming growth factor beta as a neuronoglial signal during peripheral nervous system response to injury

In contrast to the central nervous system (CNS), the peripheral nervous system (PNS) displays an important regenerative ability which is dependent, at least in part, on Schwann cell properties. The mechanisms which stimulate Schwann cells to adapt their behavior after a lesion to generate adequate conditions for PNS regeneration remain unknown. In this work, we report that adult rat dorsal root ganglion (DRG) neurons are able, after a lesion performed in vivo or when they are dissociated and cultured in vitro, to synthesize transforming growth factor beta (TGF beta), a pleiotropic growth factor implicated in wound healing processes and in carcinogenesis. This TGF beta is tentatively identified as the beta-1 isoform. Adult rat DRG neurons release a biologically active form of TGF beta which is able to elicit multiple Schwann cell responses including a stimulation to proliferate. Moreover, purified TGF beta-1 produces a Schwann cell morphology alteration and decreases the secretion of tissue-type plasminogen activator (tPA) and enhances the secretion of plasminogen activator inhibitor (PAI) by Schwann cells. This generates conditions which are thought to favor a successful neuritic regrowth. Furthermore, purified TGF beta-1 stimulates type IV collagen mRNA expression in Schwann cells. This subtype of collagen is associated with the process of myelinization. Finally, TGF beta-1 decreases nerve growth factor (NGF) mRNA expression by Schwann cells, an effect which could participate in the maintenance of a distoproximal NGF gradient during nerve regeneration. We propose that neuronal TGF beta plays an essential role as a neuronoglial signal that modulates the response of Schwann cells to injury and participates in the successful regeneration processes observed in the PNS.

Glomerular matrix accumulation is linked to inhibition of the plasmin protease system

TGF-beta plays a pivotal role in the pathological accumulation of extracellular matrix in experimental glomerulonephritis. Increased TGF-beta expression leads to increased synthesis and deposition of extracellular matrix components while administration of anti-serum to TGF-beta suppresses the major manifestations of the disease. We hypothesized that TGF-beta might also enhance matrix accumulation by decreasing matrix turnover via effects on protease/protease inhibitor balance. Plasmin is a potent protease capable of degrading a variety of matrix molecules. Plasmin generation from plasminogen is regulated by plasminogen activator(s) (PA) and plasminogen activator inhibitor(s) (PAI). In this study PA activity was markedly reduced and PAI-1 synthesis dramatically increased when TGF-beta was added to normal glomeruli. Diseased glomeruli also showed decreased PA activity, increased PAI-1 synthesis and increased PAI-1 deposition into matrix. Administration of anti-TGF-beta serum to glomerulonephritic rats blocked the expected increase in glomerular PAI-1 deposition. Thus changes in the PA/PAI balance favoring accumulation of matrix are induced by TGF-beta in normal glomeruli and are present in nephritic glomeruli when endogenous TGF-beta production is high. Our findings implicate the plasmin protease system in tissue repair following acute glomerular injury and suggest another mechanism by which TGF-beta enhances the matrix accumulation characteristic of many glomerular diseases.

Pattern of expression of transforming growth factor-beta 4 mRNA and protein in the developing chicken embryo

Expression of TGF-beta 4 mRNA and protein was studied in the developing chicken embryo using specific cDNA probes and antibodies for chicken TGF-beta 4. Expression of TGF-beta 4 mRNA was detected by day 4 of incubation (Hamburger and Hamilton stage 22, E4) by RNA Northern blot analysis and increased with developmental age until day 12 of incubation (stage 38, E12) where it was detected in every embryonic tissue examined, with expression being highest in smooth muscle and lowest in the kidney. The steady-state level of expression of TGF-beta 4 mRNA remained relatively constant in most embryonic tissues through day 19 (stage 45, E19). In situ hybridization analysis detected TGF-beta 4 mRNA as early as the "definitive primitive streak" stage (stage 4); during neurulation (stage 10), TGF-beta 4 mRNA was detected in all three germ layers, including neuroectoderm. Following neurulation, TGF-beta 4 mRNA was detected in the neural tube, notochord, ectoderm, endoderm, sclerotome, and myotome, but not dermotome at stage 16. By day 6 of incubation (stage 29, E6), TGF-beta 4 mRNA was localized in several tissues including heart, lung, and gizzard. Immunohistochemical staining analysis also showed expression of TGF-beta 4 protein in all three germ layers as early as stage 4 in various cell types in qualitatively similar locations as TGF-beta 4 mRNA. These results suggest that TGF-beta 4 may play an important role in the development of many tissues in the chicken.

Pericellular substrates of human mast cell tryptase: 72,000 dalton gelatinase and fibronectin

Migrating cells degrade pericellular matrices and basement membranes. For these purposes cells produce a number of proteolytic enzymes. Mast cells produce two major proteinases, chymase and tryptase, whose physiological functions are poorly known. In the present study we have analyzed the ability of purified human mast cell tryptase to digest pericellular matrices of human fibroblasts. Isolated matrices of human fibroblasts and fibroblast conditioned medium were treated with tryptase, and alterations in the radiolabeled polypeptides were observed in autoradiograms of sodium dodecyl sulphate polyacrylamide gels. It was found that an M(r) 72,000 protein was digested to an M(r) 62,000 form by human mast cell tryptase while the plasminogen activator inhibitor, PAI-1, was not affected. Cleavage of the M(r) 72,000 protein could be partially inhibited by known inhibitors of tryptase but not by aprotinin, soybean trypsin inhibitor, or EDTA. Fibroblastic cells secreted the M(r) 72,000 protein into their medium and it bound to gelatin as shown by analysis of the medium by affinity chromatography over gelatin-Sepharose. The soluble form of the M(r) 72,000 protein was also susceptible to cleavage by tryptase. Analysis using gelatin containing polyacrylamide gels showed that both the intact M(r) 72,000 and the M(r) 62,000 degraded form of the protein possess gelatinolytic activity after activation by sodium dodecyl sulphate. Immunoblotting analysis of the matrices revealed the cleavage of an immunoreactive protein of M(r) 72,000 indicating that the protein is related to type IV collagenase. Further analysis of the pericellular matrices indicated that the protease sensitive extracellular matrix protein fibronectin was removed from the matrix by tryptase in a dose-dependent manner. Fibronectin was also susceptible to proteolytic degradation by tryptase. The data suggest a role for mast cell tryptase in the degradation of pericellular matrices.

What's new in the role of cytokines on osteoblast proliferation and differentiation?

This review assesses recent data concerning the role of cytokines produced by a variety of cells in bone on osteoblast function. The following themes are presumed: (1) osteoblasts are mesenchymal cells which act as either the major cellular agents of bone formation or as modulators of bone resorption by osteoclasts. The regulation of osteoblast proliferation and differentiation may involve a negative feedback process resulting in phenotype suppression; (2) cytokines including platelet-derived growth factors (PDGF), parathyroid hormone-related proteins (PTHrP), bone morphogenic proteins (BMP), transforming growth factor beta (TGF beta), fibroblast growth factors (FGF), insulin-like growth factors (IGF), epidermal growth factors (EGF), interleukin-1 and 6, tumour necrosis factors (TNF), interferon and haematopoietic growth factors have effects on osteoblast differentiation and proliferation but their effectiveness may not be identical in vitro and in vivo; (3) finally, therapeutic strategies for cytokine use in clinical practice are considered.

Opposite and independent actions of cyclic AMP and transforming growth factor beta in the regulation of type 1 plasminogen activator inhibitor expression

We have investigated the mechanisms by which type 1 plasminogen activator inhibitor (PAI-1) is regulated by transforming growth factor beta (TGF-beta) and by epidermal growth factor (EGF) in CCL64 mink lung epithelial cells, BSC-1 monkey kidney epithelial cells, mouse embryo fibroblast (AKR-2B 84A) cells and normal rat kidney fibroblasts (NRK). TGF-beta increases PAI-1 expression in all four cell lines, and EGF acts synergistically with TGF-beta to increase PAI-1 expression in CCL64 cells but not in the other three cell lines. Here we show that PAI-1 expression can be regulated independently through two different signal transduction pathways. One pathway involves protein kinase C and is stimulated by the tumour promoter phorbol myristate acetate (PMA). Whereas preincubation with PMA completely eliminated PMA-induced PAI-1 synthesis and secretion in both CCL64 and BSC-1 cells, this treatment had no effect on TGF-beta- and EGF-induced PAI-1 levels. Therefore we conclude that protein kinase C does not mediate the effects of either EGF or TGF-beta on PAI-1 expression. The expression of PAI-1 was decreased by agents increasing intracellular cyclic AMP: (cAMP) cholera toxin, forskolin and dibutyryl cAMP lowered both the basal level and the TGF-beta- and PMA-induced levels of PAI-1 expression. These effects of cAMP-elevating agents and of TGF-beta on PAI-1 protein synthesis were also reflected in changes in TGF-beta-induced PAI-1 gene transcription, as measured by nuclear run-on. These results show that PAI-1 gene expression is sensitive to high levels of intracellular cAMP and that this effect occurs at the transcriptional level. Although increased intracellular cAMP concentrations decrease the absolute level of PAI-1 expression, the ability of TGF-beta and EGF to induce PAI-1 gene expression is unchanged. These results are discussed in relation to the observation that sensitivity to cAMP is a common feature of TGF-beta-regulated genes.

Proteolytic processing of the 72,000-Da type IV collagenase by urokinase plasminogen activator

Regulation of the activity of proteolytic enzymes is of major importance in the turnover of connective tissues. The search for physiologically relevant activation mechanisms of principal tissue-degrading enzymes, e.g., metalloproteinases, has therefore been of wide interest. We have now studied whether the initiating factor of the fibrinolytic system, urokinase plasminogen activator (u-PA), may also function in the early steps of activation of one of the metalloproteinases, the M(r) 72,000 gelatinase/type IV collagenase produced by cultured fibroblasts. Treatment of the secreted M(r) 72,000 proteinase by u-PA yielded a cleavage product of M(r) 62,000 as revealed by fluorography of radioactively labeled proteins as well as by gelatin zymography SDS-PAGE gels. The u-PA-catalyzed cleavage of the M(r) 72,000 proteinase was blocked by anti-u-PA antibodies, but was unaffected by the plasmin inhibitor aprotinin, thus indicating a specific action for the activator. On the contrary, the tissue activator of plasminogen, t-PA, did not cleave the type IV collagenase in similar assays. u-PA-catalyzed cleavage of recombinant type IV collagenase, produced in a baculovirus expression system, yielded a similar M(r) 62,000 activity in gelatinolysis assay. Zymograms of the isolated pericellular matrices of cultured fibroblasts also revealed M(r) 72,000 gelatinolytic polypeptide that was converted to an M(r) 62,000 form by u-PA. Both polypeptides were recognized in immunoblotting by antibodies against the gelatinase/type IV collagenase, suggesting immunological identity with the secreted enzyme. Thus the M(r) 72,000 gelatinase/type IV collagenase is not only secreted, but also deposited into the pericellular fibroblast matrix, and both forms are substrates for u-PA. The results suggest a new potential role for u-PA as a direct regulator of metalloproteinase-mediated extracellular proteolysis via the cleavage of the M(r) 72,000 gelatinase/type IV collagenase to an M(r) 62,000 form.

TGF-beta inhibits proliferation of and promotes differentiation of human promonocytic leukemia cells

Transforming growth factor-beta 1 (TGF-beta 1) has been implicated in a variety of responses associated with wound healing and inflammation. Thus, TGF-beta 1 enhances production of several extracellular matrix proteins both in vitro and in vivo, is chemotactic for monocytes, and alters the functioning of lymphocytes. We have examined the ability of TGF-beta 1 to affect the behavior of human THP-1 promonocytic leukemia cells, a cell line with the capacity to differentiate into macrophage-like cells. TGF-beta 1 reduces the growth rate of these cells, induces morphologic changes, and promotes adherence to culture surfaces. In addition, the adherent cell population expresses high levels of esterase activity, acquires the ability to ingest latex beads, and releases elevated levels of interleukin 1. TGF-beta 1-treated cells also express elevated levels of the beta 2 family of integrins. Taken together, these results suggest that TGF-beta 1 is capable of promoting the maturation of promonocytic cells into macrophages. This outcome has implications at wound sites where TGF-beta 1 and a myriad of other factors interact with many cell types to facilitate healing.

Basic fibroblast growth factor-induced activation of latent transforming growth factor beta in endothelial cells: regulation of plasminogen activator activity

Exposure of bovine aortic or capillary endothelial cells to basic FGF (bFGF) for 1 h resulted in an approximately sixfold increase in plasminogen activator (PA) activity by 18 h that returned nearly to basal levels by 36 h. We hypothesized that the decrease in PA activity following bFGF stimulation was mediated by transforming growth factor beta (TGF-beta) formed from its inactive precursor. Conditioned medium collected from endothelial cells 36 h after a 1-h exposure to bFGF, but not control medium, inhibited basal levels of PA activity when transferred to confluent monolayers of bovine aortic endothelial cells. Antibody to TGF-beta neutralized the inhibitory activity of this conditioned medium, indicating that the medium contained active TGF-beta. Northern blot analysis and quantitation of acid activatable latent TGF-beta in conditioned medium demonstrated that bFGF exposure did not increase the amount of transcription or secretion of latent TGF-beta by the endothelial cells. Both aprotinin, an inhibitor of plasmin, and anti-urokinase type PA IgG blocked the generation of active TGF-beta in cultures exposed to bFGF. These results demonstrated that plasmin generated by uPA activity is required for the activation of latent TGF-beta in endothelial cell cultures treated with bFGF. Activation of TGF-beta by endothelial cells exposed to bFGF appears to limit both the degree and duration of PA stimulation. Thus, in bFGF-stimulated endothelial cell cultures, PA levels are controlled by a negative feedback loop: PA, whose expression is stimulated by bFGF, contributes to the formation of TGF-beta, which in turn opposes the effects of bFGF by limiting PA synthesis and activity. These studies suggest a role for TGF-beta in reversing the invasive stage of angiogenesis and contributing to the formation of quiescent capillaries.

Transforming growth factor-beta 1 mRNA in neonatal ovine molars visualized by in situ hybridization: potential role for the stratum intermedium

Human dentine contains relatively large amounts of transforming growth factor-beta (TGF-beta), which might originate from odontoblasts. The expression of the TGF-beta 1 message in developing teeth was examined by in situ hybridization. The analysis was made on 5-microns serial sections of mandibular third molars of neonatal sheep cut from tissues that had been fixed in glutaraldehyde and paraffin-embedded. A 35S-labelled cRNA probe, complementary to TGF-beta 1 mRNA, was constructed from human TGF-beta 1 cDNA. Northern analysis of total RNA from sheep placenta and neonatal third molars demonstrated hybridization to a single 2.4 kb TGF-beta 1 transcript from both tissues, indicating cross-reactivity of the human probe in the sheep. In the neonatal molars, in situ hybridization was observed in cells of the inner enamel epithelium, mature ameloblasts and mature odontoblasts, but not within preodontoblasts before dentine matrix formation. TGF-beta 1 mRNA expression was also evident in the cells of the dental papilla but scarcely so in the stellate reticulum. The most striking feature was the appearance of hybridization signal in the cells of the stratum intermedium before hybridization was evident in the inner enamel epithelium. Control sections incubated with RNAase before incubation with probe did not show evidence of hybridization. These findings suggest that TGF-beta 1 may have an important regulatory role in the differentiation of ameloblasts and odontoblasts, perhaps by modulating matrix formation during amelogenesis or odontogenesis. They also suggest a potential novel regulatory role for the cells of the stratum intermedium.

Enhanced production of plasminogen activator activity in human and murine keratinocytes by transforming growth factor-beta 1

Transforming growth factor-beta (TGF beta) is the most potent known inhibitor of keratinocyte growth. Pericellular proteolytic activity is usually high in proliferating and malignant cells and decreased in resting or growth-arrested cells. We have therefore analyzed the effects of TGF beta 1 on the production of plasminogen activator activity by normal human keratinocytes and a mouse keratinocyte cell line under serum-free conditions. The plasminogen activator activity of the culture medium was analyzed using caseinolysis-in-agar and zymography assays, immunoblotting, and Northern hybridization analysis for the plasminogen activators (PA) and PA inhibitor-1 (PAI-1). Alterations of radiolabeled polypeptides were observed in fluorograms of gels. It was found that like in human epidermoid carcinoma cells picomolar concentrations of TGF beta 1 (0.2-20 ng/ml) enhanced total plasminogen activator activity in both keratinocyte cell systems. Zymographic and immunoblotting analyses of the medium indicated that the activator was of the urokinase type (u-PA). Immunoprecipitation and Concanavalin A affinity chromatography of the culture medium indicated that the cells also started to produce PAI-1. Analysis of the pericellular matrix preparations of the keratinocytes showed that PAI-1 is deposited to the pericellular space. Evidently due to elevated u-PA activity PAI-1 was removed from the extracellular matrix more rapidly in TGF beta 1-treated cells than from control cultures. Northern hybridization analysis of human keratinocytes showed that TGF beta 1 rapidly elevated both u-PA and PAI-1 mRNA levels. Comparison of the temporal induction profiles indicated that the mRNA for u-PA increased more slowly but was more persistent than that of PAI-1. Actinomycin D inhibited the induction of both u-PA and PAI-1 mRNA, suggesting that the induction was due to increased transcription. The results suggest that enhanced plasminogen activator activity can be associated with growth inhibition also in nonmalignant cells like cultured human or murine keratinocytes.

Cell density dependent effects of TGF-beta demonstrated by a plasminogen activator-based assay for TGF-beta

Transforming growth factor-beta 1 (TGF-beta 1) induces a decrease in plasminogen activator (PA) expression in confluent cultures of bovine aortic endothelial (BAE) cells. We describe an assay using the suppression of PA expression in confluent BAE cells by TGF-beta 1 which detects concentrations of the growth factor ranging from 5 to 200 pg/ml and has an ED50 of 15-20 pg/ml. The assay can be performed in 96-well plates and requires a minimum of 35 ul of solution per sample, thereby limiting the amount of reagents required and allowing many samples to be tested in a single assay. Here we demonstrate that the effect of TGF-beta 1 on PA expression in BAE cells depends on the length of time the cells are exposed to the growth factor and the density at which the cells are plated. In cells plated at a high density (3.5 x 10(5) cells/cm2), both 4 h and 24 h exposures to TGF-beta 1 suppress PA expression. However, with cells plated sparsely (3.5 x 10(4) cells/cm2), a 4 h exposure to TGF-beta 1 increases PA expression 2-fold, whereas a 24 h exposure results in an 85% inhibition of basal PA expression. The paradoxical stimulation of PA expression in cells at a sparse density upon 4 h exposure to TGF-beta 1 occurs in a dose-dependent manner with an ED50 of 15-20 pg/ml. This bifunctional response of PA production in cells exposed to TGF-beta 1 may have implications with regard to the role of TGF-beta 1 in angiogenesis.

Plasminogen activator inhibitor-1 deposition in the extracellular matrix of cultured human mesangial cells

Human mesangial cells secrete tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor 1 (PAI-1), the latter being secreted in large excess in vitro. We demonstrate that PAI-1 is a major component of the extracellular matrix of cultured human mesangial cells, where its deposition is dependent on cell density. By immunogold silver staining, epipolarization microscopy and dispersive X-ray spectrometry, we have shown that matrix-associated PAI-1 is synthesized by spreading human mesangial cells, as indicated by the time-dependent accumulation of PAI-1 and the inhibitory effect of cycloheximide. Furthermore, by in situ hybridization, PAI-1 mRNA was detected in cultured mesangial cells. t-PA is present inside the cells, or at the cell surface, but is never associated with the extracellular matrix. Exogenous t-PA can remove matrix-associated PAI-1 without affecting cell adhesion. A similar effect was obtained by addition of urokinase-type plasminogen activator (u-PA) but not with fibrinolysis unrelated enzymes. In conclusion, PAI-1 is synthesized by human cultured mesangial cells and is deposited in the extracellular matrix by nonconfluent cells, whereas less PAI-1 is seen between confluent cells. This can explain the absence of detectable PAI-1 in normal human kidney biopsies. t-PA released by mesangial cells can bind and detach matrix PAI-1.

Mitogenic, chemotactic, and synthetic responses of rat periodontal ligament fibroblastic cells to polypeptide growth factors in vitro

The mitogenic, chemotactic, and synthetic responses of rat periodontal ligament (PDL) fibroblastic cells to epidermal growth factor (EGF), transforming growth factor-beta (TGF-beta), recombinant human platelet-derived growth factor (rhPDGF)-AB, rhPDGF-BB, natural (n) PDGF-AB, and insulin-like growth factor-I (IGF-I) were examined in vitro using PDL cells obtained from the coagulum of healing tooth sockets. PDGFs and IGF-I have potent and comparable mitogenic effects on PDL fibroblastic cells. The maximum mitogenic effect of PDGFs was observed at the concentration of 10 ng/ml, whereas that of IGF-I was seen at concentrations higher than 100 ng/ml. In contrast, EGF induced moderate, and TGF-beta inhibitory mitogenic responses. The combination of rhPDGF-AB with either EGF or TGF-beta demonstrated comparable mitogenic potency, equivalent to the level of PDGF alone regardless of the mitogenic effect of other growth factors. The combination of rhPDGF-AB and IGF-I, however, showed a synergistic effect revealing the highest mitogenic effect among all individual growth factors as well as any combinations of the growth factors tested. Similarly, PDL fibroblastic cells demonstrated strong chemotactic responses to both IGF-I and PDGFs. The maximum effect was observed by IGF-I at concentrations higher than 10 ng/ml, followed by rhPDGF-BB at 0.1 ng/ml, rhPDGF-AB and nPDGF at concentrations ranging from 0.1 to 1 ng/ml. TGF-beta revealed no, and EGF slightly increased, chemotactic effects. IGF-I slightly enhanced the synthesis of total protein, whereas other factors had no significant effect. However, both rhPDGF-AB and TGF-beta stimulated collagen synthesis. On the other hand, IGF-I showed no effect on collagen synthesis, while EGF suppressed collagen synthesis. These findings suggest that rhPDGF-BB and IGF-I stimulate proliferation and chemotaxis of PDL fibroblastic cells. In addition, the combination of these growth factors further increases the mitogenic effect. rhPDGF-AB also stimulates collagen synthesis by PDL fibroblastic cells. Thus, rhPDGF-BB and IGF-I may have important roles in promotion of PDL healing, and consequently, may be useful for clinical application in periodontal regenerative procedures.

Ascorbic acid and transforming growth factor-beta 1 increase collagen biosynthesis via different mechanisms: coordinate regulation of pro alpha 1(I) and Pro alpha 1(III) collagens

The specific mechanisms of collagen induction in human dermal fibroblasts by ascorbic acid and transforming growth factor-beta 1 (TGF-beta 1) and their effect in combination are uncertain. Collagen synthesis and steady-state levels of pro alpha 1(I) and pro alpha 1(III) collagen RNA were examined in human dermal fibroblasts treated with 100 microM ascorbic acid, 2.5 ng/ml TGF-beta 1, or both. Within 72 h ascorbic acid and TGF-beta 1 had increased collagen synthesis by 2.55 +/- 0.32- and 1.98 +/- 0.13-fold, respectively; in the presence of both, collagen synthesis increased 4.51 +/- 0.74-fold, appearing additive. Ascorbic acid acts specifically by increasing relative collagen synthesis whereas TGF-beta 1 increases overall protein synthesis. Steady-state levels of the pro alpha 1(I) collagen (5.8 and 4.8 kb) and pro alpha 1(III) collagen (5.4 and 4.8 kb) mRNAs were examined independently. Under each condition the steady-state levels of the longer transcripts for pro alpha 1(I) and pro alpha 1(III) collagens appeared coordinately and preferentially elevated. In the presence of both ascorbic acid and TGF-beta 1 the steady-state RNA levels did not increase in an additive manner, suggesting that the additive increase in collagen synthesis results from additional post-transcriptional mechanisms.

Transforming growth factor beta 1-responsive element: closely associated binding sites for USF and CCAAT-binding transcription factor-nuclear factor I in the type 1 plasminogen activator inhibitor gene

Transforming growth factor beta (TGF-beta) is the name of a group of closely related polypeptides characterized by a multiplicity of effects, including regulation of extracellular proteolysis and turnover of the extracellular matrix. Its cellular mechanism of action is largely unknown. TGF-beta 1 is a strong and fast inducer of type 1 plasminogen activator inhibitor gene transcription. We have identified a TGF-beta 1-responsive element in the 5'-flanking region of the human type 1 plasminogen activator inhibitor gene and shown that it is functional both in its natural context and when fused to a heterologous nonresponsive promoter. Footprinting and gel retardation experiments showed that two different nuclear factors, present in extracts from both TGF-beta 1-treated and nontreated cells, bind to adjacent sequences contained in the responsive unit. A palindromic sequence binds a trans-acting factor(s) of the CCAAT-binding transcription factor-nuclear factor I family. A partially overlapping dyad symmetry interacts with a second protein that much evidence indicates to be USF. USF is a transactivator belonging to the basic helix-loop-helix family of transcription factors. Mutations which abolish the binding of either CCAAT-binding transcription factor-nuclear factor I or USF result in reduction of transcriptional activation upon exposure to TGF-beta 1, thus showing that both elements of the unit are necessary for the TGF-beta 1 response. We discuss the possible relationship of these findings to the complexity of the TGF-beta action.

Transforming growth factor beta 1-responsive element: closely associated binding sites for USF and CCAAT-binding transcription factor-nuclear factor I in the type 1 plasminogen activator inhibitor gene

Transforming growth factor beta (TGF-beta) is the name of a group of closely related polypeptides characterized by a multiplicity of effects, including regulation of extracellular proteolysis and turnover of the extracellular matrix. Its cellular mechanism of action is largely unknown. TGF-beta 1 is a strong and fast inducer of type 1 plasminogen activator inhibitor gene transcription. We have identified a TGF-beta 1-responsive element in the 5'-flanking region of the human type 1 plasminogen activator inhibitor gene and shown that it is functional both in its natural context and when fused to a heterologous nonresponsive promoter. Footprinting and gel retardation experiments showed that two different nuclear factors, present in extracts from both TGF-beta 1-treated and nontreated cells, bind to adjacent sequences contained in the responsive unit. A palindromic sequence binds a trans-acting factor(s) of the CCAAT-binding transcription factor-nuclear factor I family. A partially overlapping dyad symmetry interacts with a second protein that much evidence indicates to be USF. USF is a transactivator belonging to the basic helix-loop-helix family of transcription factors. Mutations which abolish the binding of either CCAAT-binding transcription factor-nuclear factor I or USF result in reduction of transcriptional activation upon exposure to TGF-beta 1, thus showing that both elements of the unit are necessary for the TGF-beta 1 response. We discuss the possible relationship of these findings to the complexity of the TGF-beta action.

Inhibition by methylprednisolone acetate suggests an indirect mechanism for TGF-B induced angiogenesis

Angiogenesis induced by transforming growth factor beta (TGFB) implanted in the rabbit cornea is accompanied by an influx of inflammatory cells. To determine if the inflammatory cells are the mediators of the neovascularization, they were depleted by local administration of methylprednisolone acetate (MPA). Subconjunctival injections of 16 mg of MPA immediately following implantation of 50 ng of TGFB in the cornea prevented the inflammation and subsequent formation of capillaries. If the injections of MPA were delayed by 48 hr and the inflammatory cells were allowed to enter the cornea, angiogenesis occurred, demonstrating that MPA had no adverse effects on the ability of endothelial cells to form capillaries. These results confirm the hypothesis that TGFB induces angiogenesis indirectly by recruiting inflammatory cells capable of stimulating direct angiogenesis.

Control of transforming growth factor-beta activity: latency vs. activation

Transforming growth factor-beta is a pluripotent regulator of cell growth and differentiation. The growth factor is expressed as a latent complex that must be converted to an active form before interacting with its ubiquitous high affinity receptors. This conversion involves the release of the mature growth factor through disruption of the non-covalent interactions with its pro-peptide or latency associated peptide. The mechanisms for this release in vivo have not been fully characterized but appear to be cell specific and might involve processes such as acidification or proteolysis. Although several factors including transcriptional regulation, receptor modulation and scavenging of the active growth factor have been implicated, the critical step controlling the biological effects of transforming growth factor-beta may be the activation of the latent molecule.

Thrombin neutralizes plasminogen activator inhibitor 1 (PAI-1) that is complexed with vitronectin in the endothelial cell matrix

Vitronectin endows plasminogen activator inhibitor 1 (PAI-1), the fast-acting inhibitor of both tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA), with additional thrombin inhibitory properties. In view of the apparent association between PAI-1 and vitronectin in the endothelial cell matrix (ECM), we analyzed the interaction between PAI-1 and thrombin in this environment. Upon incubating 125I-labeled alpha-thrombin with endothelial cell matrix (ECM), the protease formed SDS-stable complexes exclusively with PAI-1, with subsequent release of these complexes into the supernatant. Vitronectin was required as a cofactor for the association between PAI-1 and thrombin in ECM. Metabolic labeling of endothelial cell proteins, followed by incubation of ECM with t-PA, u-PA, or thrombin, indicated that all three proteases depleted PAI-1 from ECM by complex formation and proteolytic cleavage. Proteolytically inactive thrombin as well as anticoagulant thrombin, i.e., thrombin in complex with its endothelial cell surface receptor thrombomodulin, did not neutralize PAI-1, emphasizing that the procoagulant moiety of thrombin is required for a functional interaction with PAI-1. A physiological implication of our findings may be related to the mutual neutralization of both PAI-1 and thrombin, providing a new link between plasminogen activation and the coagulation system. Evidence is provided that in ECM, procoagulant thrombin may promote plasminogen activator activity by inactivating PAI-1.

Expression of transforming growth factor-beta 1, -beta 2, and -beta 3 mRNA and protein in the murine lung

Evidence has accumulated suggesting that the various isoforms of beta-type transforming growth factors (TGF-beta s) regulate important functions in the lung; however, the cellular source of these proteins is not well defined. Northern blot analysis of murine lung tissue demonstrates that mRNA transcripts for all three TGF-beta isoforms are found from birth through adulthood. Although the level of expression for each TGF-beta is variable during the first 2 wk post partum, all three isoforms are equal in the adult lung. Using in situ hybridization and immunohistochemical analysis, we have localized both mRNA and protein expression for all three isoforms of TGF-beta in the adult murine lung. At low magnification, immunohistochemical localization of TGF-beta proteins appears coincident in their pattern of expression with TGF-beta mRNAs in the large proximal conducting airways of the lung. However, on closer analysis, protein expression of all three TGF-beta isoforms is confined to the bronchiolar epithelium, while TGF-beta mRNA transcripts for each of the TGF-beta genes are found in smooth muscle cells and connective tissue fibroblasts lying subjacent to the epithelium. Although the levels of both TGF-beta mRNA and protein expression are high in the proximal bronchiolar tree, their signal intensities completely disappear as the terminal bronchioles progress to respiratory bronchioles. Additionally, in the lung vasculature, there is very high expression of all three TGF-beta mRNA transcripts in the smooth muscle cells of the large vessels. TGF-beta2 and TGF-beta but not TGF-beta1 proteins are expressed in these same smooth muscle cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of growth factors in the embryogenesis and differentiation of the eye

The vertebrate eye is composed of a variety of tissues that, embryonically, have their derivation from surface ectoderm, neural ectoderm, neural crest, and mesodermal mesenchyme. During development, these different types of cells are subjected to complex processes of induction and suppressive interactions that bring about their final differentiation and arrangement in the fully formed eye. With the changing concept of ocular development, we present a new perspective on the control of morphogenesis at the cellular and molecular levels by growth factors that include fibroblast growth factors, epidermal growth factor, nerve growth factor, platelet-derived growth factor, transforming growth factors, mesodermal growth factors, transferrin, tumor necrosis factor, neuronotrophic factors, angiogenic factors, and antiangiogenic factors. Growth factors, especially transforming growth factor-beta, have a crucial role in directing the migration and developmental patterns of the cranial neural-crest cells that contribute extensively to the structures of the eye. Some growth factors also exert an effect on the developing ocular tissues by influencing the synthesis and degradation of the extracellular matrix. The mRNAs for the growth factors that are involved in the earliest aspects of the growth and differentiation of the fertilized egg are supplied from maternal sources until embryonic tissues are able to synthesize them. Subsequently, the developing eye tissues are exposed to both endogenous and exogenous growth factors that are derived from nonocular tissues as well as from embryonic fluids and the systemic circulation. The early interaction between the surface head ectoderm and the underlying chordamesoderm confers a lens-forming bias on the ectoderm; later, the optic vesicle elicits the final phase of determination and enhances differentiation by the lens. After the blood-ocular barrier is established, the internal milieu of the eye is controlled by the interactions among the intraocular tissues; only those growth factors that selectively cross the barrier or that are synthesized by the ocular tissues can influence further development and differentiation of the cells. An understanding of the tissue interactions that are regulated by growth factors could clarify the precise mechanism of normal and abnormal ocular development.

The response to epidermal growth factor of human maxillary tumor cells in terms of tumor growth, invasion and expression of proteinase inhibitors

Three cancer cell lines, IMC-2, IMC-3 and IMC-4, were established from a single tumor of a patient with maxillary cancer. We examined responses to epidermal growth factor (EGF) of these 3 cell lines with regard to cell growth and tumor invasion. The growth rate of IMC-2 in nude mice was markedly faster than that of the IMC-3 and IMC-4 cell lines. Assay for invasion through fibrin gels showed significantly enhanced invasive capacity of IMC-2 cells in response to EGF, but no change for IMC-3 and IMC-4 cells. We examined response to EGF of IMC-2 cells with regard to expression of a growth-related oncogene (c-fos), proteinases and their inhibitors. Expression of c-fos was transiently increased in IMC-2 cells at rates comparable to those seen in the 2 other lines in the presence of EGF. There was no apparent effect of EGF on the expression of urokinase-type plasminogen activator and 72-kDa type-IV collagenase in IMC-2 cells. In contrast, EGF specifically enhanced the expression of plasminogen activator inhibitor-I (PAI-I) and tissue inhibitor of metalloproteinases-I (TIMP-I) in IMC-2 cells. Our data suggest that proteinase inhibitors or other related factors may play an important role in tumor growth and invasion in response to EGF.

Endothelial cell regulation by transforming growth factor-beta

Pronounced changes including growth inhibition, increased matrix deposition and suppression of cell-associated proteolytic activity, take place in endothelial cells (EC) upon the application of TGF-beta. Interrelationships between these effects have shed some light on the mechanism of action of TGF-beta and on its role in regulating EC function vis-a-vis angiogenesis. For instance, preliminary evidence has indicated that increased levels of certain matrix components may be partly responsible for the antiproliferative action of TGF-beta. In addition, TGF-beta and bFGF have opposing effects on cellular proteolytic balance which may contribute to the antagonistic effect that TGF-beta has on bFGF-induced EC growth and possibly to the anti-angiogenic effect exerted by TGF-beta under certain circumstances. Of particular interest in this regard is the fact that physical contact between EC and vascular mural cells in EC:mural cell cocultures has been found to generate active TGF-beta, thus further implicating TGF-beta in the maintenance of the quiescent, differentiated aggregation of EC as found in vascular structures in vivo. While more information is needed to define what, if any role TGF-beta plays in endothelial differentiation, it is to be noted that many of the cellular and biochemical processes affected by TGF-beta are linked to differentiation. It is therefore possible that the growth inhibition of EC by TGF-beta primes them for differentiation and/or is critical for the maintenance of a differentiated state.

Detection of mRNA for the transforming growth factor beta family in human articular chondrocytes by the polymerase chain reaction

The Transforming Growth Factor-beta (TGF beta) family of polypeptides elicits diverse biological actions on a wide range of cell types. There are known to be several isoforms of TGF beta coded for by different genes, with possibly differential expression and potencies. We have demonstrated that there is constitutive expression of three forms of transforming growth factor beta in adult human articular chondrocytes. The presence of 10% fetal calf serum in the culture medium may influence expression. The addition of transforming growth factor beta or interleukin 1 beta to the culture medium does not appear to consistently influence the expression of TGF beta by the cells.