Inactivation of the type II receptor reveals two receptor pathways for the diverse TGF-beta activities

Inhibition of capillary morphogenesis and associated apoptosis by dominant negative mutant transforming growth factor-beta receptors

Transforming growth factor-beta 1 (TGF-beta 1) induces angiogenesis in vivo and capillary morphogenesis in vitro. Two receptor serine/threonine kinases (types I and II) have been identified as signal transducing TGF-beta receptors. We explored the possibility of inhibiting TGF-beta-mediated events in glomerular capillary endothelial cells using a TGF-beta type II receptor (T beta R-II) transdominant negative mutant. A mutant TGF-beta type II receptor (T beta R-IIM), lacking the cytoplasmic serine/threonine kinase domain, was produced by polymerase chain reaction using rat T beta R-II cDNA as template. Since T beta R-II and TGF-beta type I receptor (T beta R-I) heterodimerize for signal transduction, the mutant receptor competes for binding to wild-type T beta R-I, hence acting in a dominant negative fashion. Glomerular capillary endothelial cells were stably transfected with T beta R-IIM, and four independent clones were expanded. That the T beta R-IIM mRNA was expressed was shown by reverse transcriptase-polymerase chain reaction, RNase protection assay, and Northern analysis. Presence of cell surface T beta R-IIM protein was shown by affinity cross-linking with 125I-TGF-beta 1. In wild-type endothelial cells, TGF-beta 1 (2 ng/ml) significantly inhibited [3H]thymidine incorporation to 63 +/- 10% of control (n = 4). In transfected endothelial cells carrying T beta R-IIM, TGF-beta 1 stimulated [3H]thymidine incorporation to 131 +/- 9% of control (n = 4, p < 0.005). Also, in wild-type endothelial cells, endogenous and exogenous TGF-beta 1 induced apoptosis and associated capillary formation. Both apoptosis and capillary formation were uniformly and entirely absent in transfected endothelial cells carrying T beta R-IIM. This represents the first demonstration that capillary morphogenesis in vitro is associated with apoptosis, and that interference with T beta R-II signaling inhibits this process in glomerular capillary endothelial cells.

pRb is necessary for inhibition of N-myc expression by TGF-beta 1 in embryonic lung organ cultures

The beta type transforming growth factors (TGF-beta) are potent inhibitors of epithelial cell proliferation, and data suggest that growth inhibition by TGF-beta 1 is mediated through suppression of Myc family genes in certain cell types. Indirect evidence has indicated that the product of the retinoblastoma gene (pRb) may also be involved in this pathway. Previously, we have shown that TGF-beta 1 inhibits branching morphogenesis and N-myc expression in mouse embryonic lung cultures. The purpose of this study was to determine the role of pRb in the inhibition of branching morphogenesis and N-myc expression by TGF-beta 1. Treatment with TGF-beta 1 was shown to inhibit development of lungs from homozygous Rb null (Rb−/−) and heterozygous null (Rb+/−) mouse embryos to the same extent as lungs from wild-type (Rb+/+) embryos. However, TGF-beta 1 treatment did not suppress N-myc expression in Rb−/− as it did in Rb+/+ embryonic lung explants as determined by in situ hybridization and quantitative RT-PCR. The effect of TGF-beta 1 treatment on N-myc expression in lungs from Rb+/− embryos was intermediate between that seen in Rb+/+ and Rb−/− embryos. Embryonic lungs derived from transgenic mice expressing the SV40 large T-antigen in lung epithelium under the control of the surfactant protein C promoter also showed inhibition of development in response to TGF-beta 1 treatment. The data demonstrate that pRb is necessary for TGF-beta 1 suppression of N-myc expression but not for TGF-beta 1 inhibition of branching morphogenesis; therefore, suppression of N-myc is not necessary for inhibition of branching morphogenesis by TGF-beta 1.

Negative selection in hepatic tumor promotion in relation to cancer risk assessment

Mechanistic studies with phenobarbital (PB), 2,3,7,8,-tetrachlorodibenzo-p-dioxin (TCDD) and other liver tumor promoters support a general model of promotion involving negative selection where specifically-mutated cells derive a growth advantage in the presence of persistent mitosuppression. Exposure to these liver tumor promoters appears to transiently enhance hepatocyte replication, presumably via transcriptional activation of growth regulatory genes, leading to a homeostatic increase in mitoinhibitory growth factors in the liver to constrain proliferation. Transforming growth factor beta 1 (TGF-beta), a potent mitoinhibitory growth factor for hepatocytes, has been associated with the mitosuppression caused by PB and certain peroxisomal proliferators. Escape from TGF-beta mitosuppression may involve loss or alteration of function of the mannose 6-phosphate/insulin-like growth factor II (M6P/IGFII) receptor, which is required for TGF-beta 1 activation, or alterations of the TGF-beta types I, II and III signal transduction receptors. A risk assessment based on a negative selection mechanism could be conducted for tumor promotion endpoints with TCDD and compared with current approaches that implicitly regard TCDD as an initiator. Benchmark dose calculation using centrilobular induction of cytochromes P450 1A1 and 1A2 as a surrogate for periportal growth stimulation would provide a rational starting point for application of conventional safety factor approaches, similar to those used with non-cancer effects. In the future, tissue and plasma concentrations of specific growth factors, e.g. TGF-beta or hepatocyte growth factor, HGF, might be considered as more direct dose surrogates for tumor-promoting effects of xenobiotics. Uncertainty factor adjustments to a TCDD benchmark dose calculation should eventually rely on direct knowledge of regulation of specific growth regulatory genes and their receptors in relevant species and on species differences in TCDD pharmacokinetics, instead of application of default animal-to-human and interindividual uncertainty factors.

Restricted expression of type-II TGF beta receptor in murine embryonic development suggests a central role in tissue modeling and CNS patterning

The type-II TGF beta receptor mediates many of the biological responses to TGF beta. An examination of the expression of the type-II TGF beta receptor during mouse embryogenesis therefore provides specific information about the role of TGF beta during embryogenesis than has been available to date. We have isolated the genomic murine homologue of the human type-II TGF beta receptor corresponding to exon 2. The murine and human sequences show a high degree of homology. Using the murine probe, we found that type-II TGF beta receptor expression is regulated in both a spatial and a temporal fashion by using in situ hybridization and ribonuclease protection assays. Type-II TGF beta receptor expression is localized to the mesenchyme during critical interactions with adjacent epithelium such as developing hair follicles, whisker follicles and tooth anlage. In the central nervous system, type-II TGF beta receptor expression is highly restricted to the floor plate. Strong expression is also detected in migrating neural crest cells, meninges, and choroid plexus. Specific mesenchymal localization of type-II TGF beta receptor is also observed in lung, kidney, intestine, stomach, and bladder. The restricted expression of type-II TGF beta receptor in mesenchymal cells at sites of epithelial-mesenchymal interactions suggests that type-II TGF beta receptor plays a major role in mediating the establishment of embryonic organ systems. The highly restricted expression of type-II TGF beta receptor in the developing CNS suggests an important role for a serine/threonine kinase in patterning of the nervous system.

THP-1 macrophage membrane-bound plasmin activity is up-regulated by transforming growth factor-beta 1 via increased expression of urokinase and the urokinase receptor

Receptors for urokinase (uPA) and plasminogen provide a mechanism to direct the cellular activation of plasminogen. The regulation of these receptors is important for several macrophage functions. In these studies, the effect of transforming growth factor-beta 1 (TGF-beta 1) on uPA, uPA receptor, and plasminogen receptor expression by human THP-1 macrophage was examined. TGF-beta 1 induction of uPA expression by THP-1 cells was differentiation dependent. Suspension and adherent cultures expressed similar constitutive levels of uPA. Exposure of adherent cells to TGF-beta 1 led to a dose- and time-dependent increase in uPA activity which was paralleled by an increase in uPA antigen and uPA mRNA. In contrast, uPA expression by suspension cultures was unresponsive to TGF-beta 1. The differential response exhibited by suspension and adherent THP-1 cells may reflect differences in their expression of TGF-beta 1 receptors, since when assayed by crosslinking techniques, suspension cells primarily expressed a 65 kDa receptor; whereas, the adherent cells expressed 65 and 100 kDa receptors. TGF-beta 1-induced alterations in uPA receptor expression by adherent THP-1 cells were examined by quantitating membrane-bound uPA activity. Membrane-bound uPA activity increased three-fold when cells were incubated with TGF-beta 1. The increase in membrane-uPA activity expressed by TGF-beta 1-treated cells was not due to increased uPA receptor occupancy since incubation of either control or TGF-beta 1 primed cells with exogenous uPA did not lead to an increase in membrane-bound uPA activity. Furthermore, immunoreactive uPA receptor was increased in TGF-beta 1-treated cells. Following incubation with plasminogen, membrane-bound plasmin activity increased three-fold in TGF-beta 1-treated cells. However, no change in immunoreactive membrane-bound plasmin(ogen) was observed. In addition, binding of 125I-Lys-plasminogen to THP-1 cells was not affected by TGF-beta 1 treatment. We conclude that TGF-beta 1 stimulates membrane-bound plasmin activity, without affecting plasminogen receptor expression, through the up-regulation of uPA and the uPA receptor expression.

Trypanosome invasion of mammalian cells requires activation of the TGF beta signaling pathway

Trypanosoma cruzi invades most nucleated mammalian cells by as yet unknown mechanisms. We report here that while T. cruzi attaches to epithelial cells lacking signaling transforming growth factor beta (TGF beta) receptor I or II, the adherent parasites cannot penetrate and replicate inside the mutant cells, as they do in parental cells. Invasion of the mutants is restored by transfection with the TGF beta receptor genes, as are biological responses to TGF beta. Similar rescue of both TGF beta antiproliferative response and T. cruzi invasion was demonstrated in a hybrid of TGF beta-resistant bladder and colon carcinoma cells. In addition, T. cruzi did not efficiently invade epithelial cells with dysfunction of the intracellular signaling cascade caused by the constitutive expression of the cyclin-dependent kinase cdk4 or of the oncogene H-ras. Treatment with TGF beta, but not with other antiproliferative agents of non-phagocytic cells, greatly enhances T. cruzi invasion. Moreover, infective, but not noninfective, trypanosomes strongly induce a TGF beta-responsive reporter gene in TGF beta-sensitive, but not in TGF beta-insensitive, cell lines. Thus, T. cruzi itself may directly trigger activation of the TGF beta signaling pathway required for parasite entry into the mammalian cells.

Human type II receptor for bone morphogenic proteins (BMPs): extension of the two-kinase receptor model to the BMPs

Bone morphogenic proteins (BMPs) are universal regulators of animal development. We report the identification and cloning of the BMP type II receptor (BMPR-II), a missing component of this receptor system in vertebrates. BMPR-II is a transmembrane serine/threonine kinase that binds BMP-2 and BMP-7 in association with multiple type I receptors, including BMPR-IA/Brk1, BMPR-IB, and ActR-I, which is also an activin type I receptor. Cloning of BMPR-II resulted from a strong interaction of its cytoplasmic domain with diverse transforming growth factor beta family type I receptor cytoplasmic domains in a yeast two-hybrid system. In mammalian cells, however, the interaction of BMPR-II is restricted to BMP type I receptors and is ligand dependent. BMPR-II binds BMP-2 and -7 on its own, but binding is enhanced by coexpression of type I BMP receptors. BMP-2 and BMP-7 can induce a transcriptional response when added to cells coexpressing ActR-I and BMPR-II but not to cells expressing either receptor alone. The kinase activity of both receptors is essential for signaling. Thus, despite their ability to bind to type I and II receptors receptors separately, BMPs appear to require the cooperation of these two receptors for optimal binding and for signal transduction. The combinatorial nature of these receptors and their capacity to crosstalk with the activin receptor system may underlie the multifunctional nature of their ligands.

Expression of transforming growth factor type III receptor in vascular endothelial cells increases their responsiveness to transforming growth factor beta 2

Bovine aortic endothelial cells (BAECs) express both type I and type II receptors for transforming growth factor beta (TGF beta). These cells respond to TGF beta 1 but are relatively refractory to another isoform of TGF beta, termed TGF beta 2. TGF beta s are thought to signal through receptor complexes composed of type I and/or type II receptors, both of which appear to be functional serine-threonine kinases. The TGF beta type III receptor, on the other hand, does not seem to have any direct signaling capacity. We have now stably transfected BAECs with the type III receptor cDNA. These cells displayed surface expression of the type III receptor protein, as determined by cross-linking with iodinated TGF beta 1 and immunoprecipitation with antibodies to the type III receptor protein. Transfected BAECs exhibit increased responsiveness to TGF beta 2 by several different criteria including an increase in plasminogen activator inhibitor-1 protein and inhibition of migration and proliferation. Thus, the type III receptor protein may play a role in presenting TGF beta 2 to the type II receptor and increase responsiveness to TGF beta 2 to a level comparable to that of TGF beta 1.

Effect of TGF-beta on differentiated organoids of the colon carcinoma cell line LIM 1863

The LIM 1863 colon carcinoma cell line grows in suspension as morphologically and functionally organized organoids in serum-containing medium. Addition of TGF-beta caused the organoids to adhere and inhibited DNA synthesis. A 20 min incubation with TGF-beta was sufficient to induce adherence and this could be inhibited by cycloheximide. The adhesion and DNA synthesis inhibition were demonstrated to be separate events. We were not able to detect any changes in matrix or cell membrane antigens. Similarly there were no changes in synthesized proteins (by two-dimensional gel electrophoresis), and no upregulation of proteoglycan. When adhered organoids were lysed from the tissue culture plastic surface, untreated organoids adhered to this surface. This 'conditioned' surface was destroyed by trypsin but not collagenase or medium from normal LIM 1863 cultures. However, the adherent phenotype was prevented when organoids were treated with transforming growth factor-beta (TGF-beta) in the presence of medium conditioned by normal LIM 1863 cultures rather than in fresh medium. The adhesion process was inhibited by an antibody (QE2E5) against beta 1 integrin although no quantitative changes in integrins were observed (by immunoprecipitation or RNA analysis). A second anti-beta 1 integrin antibody (61.2C4) inhibited LIM 1863 adhesion to collagen but not TGF-beta induced adhesion, implying that TGF-beta induced a specific conformational change or interaction of a beta 1 integrin. In this morphologically structured system TGF-beta induced a number of subtle effects including formation of new extracellular matrix and conformational change of a beta 1 integrin, rather than the major quantitative changes in cell/matrix molecules reported previously.

Cytokines regulate the cellular phenotype of developing neural lineage species

The patterns and mechanisms of action of inductive signals that orchestrate neural lineage commitment and differentiation in the mammalian brain are incompletely understood. To examine these developmental issues, we have utilized several culture systems including conditionally immortalized cell lines, subventricular zone progenitor cells and primary neuronal cultures. A neural stem and progenitor cell line (MK31) was established from murine embryonic hippocampus by retroviral transduction of temperature-sensitive alleles of the simian virus 40 large tumor antigen. At the non-permissive temperature for antigen expression (39 degrees C) in serum-free media, the neural stem cells give rise to a series of increasingly mature neuronal progenitor and differentiated cellular forms under the influence of a subset of hematolymphopoietic cytokines (interleukins 5, 7, 9 and 11), when individually co-applied with transforming growth factor alpha, after pretreatment with basic fibroblast growth factor. These cellular forms elaborated a series of progressively more mature neurofilament proteins, a sequential pattern of ligand-gated channels, and inward currents and generation of action potentials with mature physiological properties. Because the factors regulating the development of central nervous system astrocytes have been so difficult to define, we have chosen to focus, in this manuscript, on the elaboration of this cell type. At 39 degrees C, application of a subfamily of bone morphogenetic proteins of the transforming growth factor beta superfamily of growth factors sanctioned the selective expression of astrocytic progenitor cells and mature astrocytes, as defined by sequential elaboration of the Yb subunit of glutathione-S-transferase and glial fibrillary acidic protein. These lineage-specific cytokine inductive relationships were verified using subventricular zone neural progenitor cells generated by the application of epidermal growth factor, alone or in combination with basic fibroblast growth factor, to dissociated cellular cultures derived from early embryonic murine brain, a normal non-transformed developmental population. Finally, application of a different series of cytokines from five distinct factor classes (basic fibroblast growth factor, platelet-derived growth factor-AA, insulin-like growth factor 1, neurotrophin 3 and representative gp130 receptor subunit-related ligands) caused the elaboration of oligodendroglial progenitor species and post-mitotic oligodendrocytes, defined by progressive morphological maturation and the expression of increasingly advanced oligodendroglial and oligodendrocyte lineage markers. In addition, seven different gp130-associated neuropoietic (ciliary neurotrophic factor, leukemia inhibitory factor, oncostatin-M) and hematopoietic (interleukins 6, 11, 12, granulocyte-colony stimulating factor) cytokines exhibited differential trophic effects on oligodendroglial lineage maturation and factor class interactions.(ABSTRACT TRUNCATED AT 400 WORDS)

Independent changes in type I and type II receptors for transforming growth factor beta induced by bone morphogenetic protein 2 parallel expression of the osteoblast phenotype

Transforming growth factor beta (TGF-beta), a potent regulator of bone formation, has bifunctional effects on osteoblast replication and biochemical activity that appear differentiation dependent. We now show that cell surface binding sites for TGF-beta vary markedly among fibroblasts, bone-derived cells, and highly differentiated osteosarcoma cultures from fetal rats. Expression of betaglycan and type II receptors decline relative to type I receptor expression in parallel with an increase in osteoblast-like activity, predicting that the ratio among various TGF-beta binding sites could influence how its signals are perceived. Bone morphogenetic protein 2 (BMP-2), which induces osteoblast function, does not alter TGF-beta binding or biochemical activity in fibroblasts and has only small effects in less differentiated bone cells. In contrast, BMP-2 rapidly reduces TGF-beta binding to betaglycan and type II receptors in osteoblast-enriched primary cell cultures and increases its relative binding to type I receptors in these cells and in ROS 17/2.8 cultures. Pretreatment with BMP-2 diminishes TGF-beta-induced DNA synthesis in osteoblast-enriched cultures but synergistically enhances its stimulatory effects on either collagen synthesis or alkaline phosphatase activity, depending on the present state of bone cell differentiation. Therefore, BMP-2 shifts the TGF-beta binding profile on bone cells in ways that are consistent with progressive expression of osteoblast phenotype, and these changes distinguish the biochemical effects mediated by each receptor. Our observations indicate specific stepwise actions by TGF-beta family members during osteoblast differentiation, developing in part from changes imprinted by BMP-2 on TGF-beta receptor stoichiometry.

Phosphorylation-dependent interaction of the cytoplasmic domains of the type I and type II transforming growth factor-beta receptors

Transforming growth factor-beta (TGF-beta) transduces signals through its type I and type II receptors. Both receptor types have previously been shown to interact in a heteromeric complex in the presence of TGF-beta. We have now characterized these interactions between both receptor types using a combination of yeast two-hybrid interaction assays and coimmunoprecipitation analyses. Our results indicate a direct association between the cytoplasmic domains of the two receptor types. Mutation analysis of these cytoplasmic domains reveals that this direct interaction requires kinase activity and, thus, depends on phosphorylation, probably via a transphosphorylation mechanism. Furthermore, the two receptor types already have an inherent affinity for each other in the absence of TGF-beta, and the heteromeric complex can be detected in coimmunoprecipitations under these conditions. Taken together, our results reveal a novel mechanism of receptor complex formation, whereby two different cytoplasmic domains directly associate with each other. This interaction may play a major role in activation of serine/threonine kinase receptors.

Early gene responses associated with transforming growth factor-beta 1 growth inhibition and autoinduction in MCF-7 breast adenocarcinoma cells

In the human breast carcinoma cell line (MCF-7), exogenous TGF-beta 1 induces a dose-dependent inhibition of cell proliferation. In a MCF-7 cell subline [MCF-7(-)], which has an undetectable level of type II TGF-beta receptor, exogenous TGF-beta 1 does not inhibit cell proliferation but is still able to induce its own message. In both cell lines, TGF-beta 1 stimulates expression of c-jun, whereas a rapid, transient and marked increase in c-fos mRNA is only observed in the MCF-7 cells sensitive to the growth inhibitory effect of TGF-beta 1. Depletion of protein kinase C abolishes the c-fos but not the c-jun response to TGF-beta 1. Our results suggest that growth inhibition and autoinduction by TGF-beta 1 are mediated by different signalling pathways. In addition, a PKC-dependent increase in c-fos expression seems to be associated with the growth inhibitory effect of TGF-beta 1.

Osteogenic growth peptide regulates proliferation and osteogenic maturation of human and rabbit bone marrow stromal cells

The recently discovered osteogenic growth peptide (OGP) has been shown to regulate proliferation in fibroblastic and osteoblastic cell lines derived from rats and mice and also alkaline phosphatase activity in the latter was found to be affected. In vivo the OGP enhances bone formation and trabecular bone density. The results of the current study indicate that the OGP is also a potent regulator of marrow stromal cells from man and rabbit, as well as rabbit muscle fibroblasts. The main OGP activity in both marrow systems is a marked stimulation of alkaline phosphatase activity and matrix mineralization. In the rabbit-derived cell culture this enhancement is accompanied by a reciprocal inhibition of proliferation. On the other hand, the human cells show a concomitant increase of both parameters. The proliferative effect of the OGP is similar to that of growth hormone (GH) and basic fibroblast growth factor (bFGF). The combined activity of the OGP with GH is smaller than that of each of the polypeptides alone. The OGP and bFGF potentiate each other. Of the three polypeptides tested, OGP is the most potent enhancer of alkaline phosphatase activity and mineralization. bFGF has no influence on these characteristics of osteogenic maturation. The OGP maturational activity is unaffected by either GH or bFGF. These data suggest that the marrow stromal cells serve as targets for the OGP that mediate the OGP-induced increase in osteogenesis. The effect on the human cells implies a role for the OGP in clinical situations where the osteogenic potential of bone marrow is involved.

Effects of TGF-beta 1 (transforming growth factor-beta 1) on the cell cycle regulation of human breast adenocarcinoma (MCF-7) cells

The antiproliferative effects of TGF-beta 1 were investigated in a human breast adenocarcinoma cell line (MCF-7). We report that TGF-beta 1 inhibits proliferation through cell cycle arrest in G1. A MCF-7 cell subline (MCF-7(-)), in which the type II TGF-beta receptor is not detected, was shown to be resistant to TGF-beta 1 growth inhibitory effect. Cdk2 kinase activity was inhibited in the MCF-7 sensitive cell subline in parallel with the inhibition of cell cycle progression. In both sensitive and resistant cell lines, TGF-beta 1 treatment did not affect cdk2, cdk4, cyclin E and cyclin D1 mRNA and protein levels. However, in the MCF-7 sensitive cell subline, a time-dependent increase in cells positive for p21WAF1/CIP1 nuclear localization was observed after TGF-beta 1 treatment. These findings suggest that TGF-beta 1 inhibition of MCF-7 cell proliferation is achieved through a type II receptor-dependent down-regulation of Cdk2 kinase activity without modification of Cdk and cyclin expression, but correlated with an increase in p21WAF1/CIP1 nuclear accumulation.

Inactive type II and type I receptors for TGF beta are dominant inhibitors of TGF beta-dependent transcription

Although transforming growth factor-beta (TGF beta) is implicated in differentiation and disease, proof of in vivo function requires specific inhibitors of the TGF beta cascade. TGF beta binds a family of type I and type II receptors (T beta RI, T beta RII), containing a cytoplasmic serine/threonine kinase domain. We previously reported that kinase-deficient T beta RII (delta kT beta RII) blocks TGF beta-dependent transcription in cardiac myocytes. It is controversial whether both receptors are needed in all cells for gene regulation by TGF beta or whether they mediate distinct subsets of TGF beta-dependent events. To resolve this uncertainty, TGF beta-dependent transcription was investigated in cardiac myocytes versus mink lung epithelial cells. 1) delta kT beta RII inhibits induction of a TGF beta-responsive reporter gene, in both cell backgrounds. 2) Charged-to-alanine mutations of key residues of the T beta RII kinase, including consensus ATP binding and amino acid recognition motifs, are competent for binding but not transcriptional activation. Each inactive receptor inhibits TGF beta-dependent transcription in both cell types. 3) Kinase-deficient T beta RI (delta kT beta RI) likewise impairs TGF beta-dependent transcription, less completely than delta kT beta RII; kinase-deficient activin type I receptor has no effect. 4) TGF beta-binding proteins in cardiac cells and Mv1Lu cells are comparable by affinity labeling and immunoprecipitation; however, Mv1Lu cells express up to 3-fold higher levels of T beta RII and T beta RI. Thus, the model inferred from TGF beta-resistant cell lines (that T beta RII and T beta RI are necessary in tandem for the TGF beta-signaling complex to regulate transcription) is valid for cardiac myocytes, the cell type most prominently affected in TGF beta-deficient animals.

Effect of transforming growth factor-beta 1 and -beta 2 on Schwann cell proliferation on neurites

Mechanisms regulating Schwann cell proliferation during development are unclear. Schwann cell division is known to be driven by an unidentified mitogen present on the surface of axons, but it is not known whether other molecules play a role in regulating this proliferation. Transforming growth factor-beta (TGF-beta) which is found in the developing peripheral nervous system (PNS) and is mitogenic for neuron-free Schwann cells in vitro could be involved. We have investigated the effects of TGF-beta 1, TGF-beta 2 and antibodies to TGF-beta 1 and TGF-beta 2 on axon driven Schwann cell proliferation. Rat embryonic dorsal root ganglion neurons (DRG) neurons and Schwann cells from the sciatic nerve were isolated, purified and recombined in vitro. Confirming earlier reports by others, we observed that TGF-beta 1 and TGF-beta 2 added to the culture medium stimulated the proliferation of Schwann cells in the absence of neurons. However, when added to neuron-Schwann cell co-cultures, TGF beta caused a variable response ranging from no effect to moderate inhibition of Schwann cell proliferation in different experiments. A stimulation of Schwann cell proliferation by TGF beta was never observed in neuron-Schwann cell co-cultures. Antibodies to TGF-beta 1 and TGF-beta 2 did not influence axon driven Schwann cell proliferation. To further determine the role of TGF-beta in Schwann cell proliferation and myelination, we studied Schwann cell proliferation in cultures from mice in which the TGF-beta 1 gene was delected by homologous recombination. Neuron-Schwann cell cultures from wild-type, heterozygous and homozygous mice were used. No differences were observed in either Schwann cell proliferation or myelination between cultures obtained from homozygous mutants and their heterozygous and wild-type controls. These findings suggest that TGF-beta does not function as a part of the mitogenic mechanism presented by neurons to Schwann cells, but that the presence of active TGF beta in the cellular environment might regulate the degree of proliferation induced by neuronal contact.

Regulation of fibroblast procollagen production. Transforming growth factor-beta 1 induces prostaglandin E2 but not procollagen synthesis via a pertussis toxin-sensitive G-protein

Transforming growth factor-beta 1 (TGF beta 1) initiates a series of signalling events resulting in diverse cellular responses including stimulation of extracellular matrix protein production. In this study we have investigated the role of pertussis toxin-sensitive G-proteins in mediating the effects of TGF beta 1 on fibroblast procollagen metabolism. TGF beta 1 stimulated human fetal lung fibroblast procollagen synthesis and production in a dose-dependent manner which was maximal at 0.5 ng/ml. TGF beta 1 also decreased the proportion of newly synthesized procollagen degraded intracellularly. Pertussis toxin, a G-protein inhibitor, further stimulated TGF beta 1-induced procollagen synthesis and production, but alone it had no effect on fibroblast procollagen metabolism. Addition of indomethacin also potentiated the TGF beta 1-induced increase in procollagen synthesis and production. The effects of pertussis toxin and indomethacin were not additive. Pertussis toxin and indomethacin did not affect the proportion of newly synthesized procollagen degraded intracellularly, either alone or in combination, by control cells. The TGF beta 1-induced decrease in intracellular procollagen degradation was maintained but not further affected by pertussis toxin or indomethacin. TGF beta 1 increased prostaglandin E2 (PGE2) compared with PGE2 production by control cells. Addition of pertussis toxin or indomethacin blocked the TGF beta 1-induced increase in PGE2 production. The TGF beta 1-induced increase in PGE2 preceded the increase in procollagen production. These results demonstrate that TGF beta 1-induced procollagen synthesis by lung fibroblasts is modulated by production of PGE2. Pertussis toxin and indomethacin block the production of PGE2 and enhance the effect of TGF beta 1 on procollagen synthesis. From these data we conclude that the effects of TGF beta 1 on PGE2 production but not procollagen synthesis are mediated via a receptor linked to a pertussis toxin-sensitive G-protein.

Transforming growth factor beta activation of p44mapk in proliferating cultures of epithelial cells

Transforming growth factor-beta (TGF-beta) is a potent growth inhibitor of a variety of epithelial cell types. The primary signaling mechanism involved in mediating this and other cellular effects of TGF-beta is still unknown. We report here that both TGF-beta 1 and TGF-beta 2 resulted in a rapid activation of mitogen-activated protein kinase (MAPK) p44mapk, occurring within 5-10 min of growth factor addition. This effect occurred in exponentially proliferating cultures of intestinal epithelial (IEC) 4-1 cells under conditions in which DNA synthesis was inhibited by 95% to 98%. Furthermore, TGF-beta 2 induced a sustained activation of p44mapk under these conditions, lasting for at least 90 min after initial growth factor treatment. Another TGF-beta-sensitive epithelial cell line (CCL 64) displayed a similar rapid increase in p44mapk activity when treated with TGF-beta 1. In contrast, in IEC 4-6 cells that are resistant to TGF-beta effects on growth and DNA synthesis, TGF-beta 2 treatment did not result in an activation of p44mapk. In contrast to the results in proliferating cultures, treatment of quiescent cultures of IEC 4-1 cells with TGF-beta 2 resulted in no significant change in either DNA synthesis or p44mapk activity within 15 min of TGF-beta addition. In contrast, addition of the growth-stimulatory combination of factors (epidermal growth factor + insulin + transferrin = EIT) to quiescent and proliferating IEC 4-1 cells stimulated DNA synthesis and resulted in a sustained activation of p44mapk. Together, our results suggest an association between activation of p44mapk and both TGF-beta-mediated growth inhibition and EIT-mediated growth stimulation. This suggests that the specificity for the cellular effects of growth factors may not occur at the level of MAPK activation per se, but rather at downstream events that include phosphorylation of distinct transcriptional complexes and activation of a select assortment of genes. With regard to TGF-beta specifically, we have proposed a model to explain how activation of p44mapk may be associated with a growth-inhibitory response.

Signaling activity of homologous and heterologous transforming growth factor-beta receptor kinase complexes

Transforming growth factor-beta (TGF-beta) signaling in Mv1Lu lung epithelial cells requires coexpression of TGF-beta receptors I (T beta R-I) and II (T beta R-II), two distantly related transmembrane serine/threonine kinases that form a heteromeric complex upon ligand binding. Here, we examine the formation of TGF-beta receptor homo-oligomers and their possible contribution to signaling. T beta R-I can contact ligand bound to T beta R-II, but not ligand free in the medium, and thus cannot form ligand-induced homo-oligomers. T beta R-II, which binds ligand on its own, formed oligomeric complexes when overexpressed in transfected COS cells. However, these complexes were largely ligand-independent and involved immature receptor protein. Since ligand-induced homo-oligomers could not be obtained with the wild-type TGF-beta receptors, we studied receptor cytoplasmic domain homo-oligomerization by using receptor chimeras. The extracellular domain of T beta R-II was fused to the transmembrane and cytoplasmic domains of T beta R-I, yielding T beta R-II/I, and the extracellular domain of T beta R-I was fused to the transmembrane and cytoplasmic domains of T beta R-II, yielding T beta R-I/II. When contransfected with wild-type receptors and exposed to ligand, T beta R-II/I formed a complex with T beta R-I, and T beta R-I/II formed a complex with T beta R-II, thus yielding complexes with homologous cytoplasmic domains. T beta R-II/I transfected alone or with T beta R-I did not restore TGF-beta responsiveness in T beta R-II-defective cell mutants. Furthermore, T beta R-II/I acted in a dominant negative fashion, inhibiting restoration of TGF-beta responsiveness by a cotransfected T beta R-II in T beta R-II-defective cells and by a cotransfected T beta R-I in T beta R-I-defective cells. Similarly, T beta R-I/II transfected alone or with T beta R-II did not restore TGF-beta responsiveness and acted in a dominant negative fashion against T beta R-I. Together with previous genetic and biochemical evidence, these results suggest that TGF-beta mediates transcriptional and antiproliferative responses through the heteromeric T beta R-I.T beta R-II complex and not through homo-oligomeric T beta R-I or T beta R-II complexes.

An absolute requirement for both the type II and type I receptors, punt and thick veins, for dpp signaling in vivo

TGF beta elicits diverse cellular responses by signaling through receptor complexes formed by two distantly related transmembrane serine/threonine kinases called type II and type I receptors. Previous studies have indicated that the product of the Drosophila thick veins (tkv) gene is a type I receptor for decapentaplegic (dpp). Here, we show that the Drosophila gene punt encodes a homolog of a vertebrate type II receptor, and we demonstrate that punt, like tkv, is essential in vivo for dpp-dependent patterning processes. Because no dpp-related signalling is apparent in the absence of either the punt or tkv receptor, we infer that both receptors act in concert to transduce the dpp signal and that their functions cannot be replaced by the other extant type II and I receptors.

Relationship between actions of transforming growth factor (TGF)-beta and cell surface expression of its receptors in clonal osteoblastic cells

Various osteoblastic cell lines were examined for the relationship between the presence of cell-surface transforming growth factor (TGF)-beta receptors and the synthesis of matrix proteins with their responsiveness to TGF-beta. Treatment with TGF-beta 1 inhibited proliferation and stimulated proteoglycan and fibronectin synthesis in MC3T3-E1 and MG 63 cells. The major proteoglycans synthesized by these cells were decorin and biglycan, and TGF-beta 1 markedly stimulated the synthesis of decorin in MC3T3-E1 and of biglycan in MG 63 cells. SaOS 2 and UMR 106 cells synthesized barely detectable amounts of decorin or biglycan, and TGF-beta 1 did not stimulate the synthesis of these proteoglycans. In SaOS 2 cells, however, TGF-beta 1 enhanced fibronectin synthesis. TGF-beta 1 did not show any of these effects in UMR 106 cells. Receptor cross-linking studies revealed that only MC3T3-E1 and MG 63 cells had both types I and II signal-transducing receptors for TGF-beta in addition to betaglycan. SaOS 2 cells possessed type I but no type II receptor on the cell surface. In contrast, SaOS 2 as well as MC3T3-E1 and MG 63 cells expressed type II receptor mRNA by Northern blot analysis, and cell lysates contained type II receptor by Western blot analysis. Thus, it appears that type II receptor present in SaOS 2 cells is not able to bind TGF-beta 1 under these conditions. UMR 106 cells with no response to TGF-beta 1 had neither of the signal-transducing receptors by any of the analyses. These observations using clonal osteoblastic cell lines demonstrate that the ability of osteoblastic cells to synthesize bone matrix proteoglycans is associated with the responsiveness of these cells to TGF-beta 1, that the responsiveness of osteoblastic cells to TGF-beta 1 in cell proliferation and proteoglycan synthesis correlates with the presence of both types I and II receptors, and that the effect of TGF-beta 1 on fibronectin synthesis can develop with little binding of TGF-beta 1 to type II receptor if type I receptor is present. It is suggested that the combination of cell-surface receptors for TGF-beta determines the responsiveness of osteoblastic cells to TGF-beta and that changes in cell-surface TGF-beta receptors may play a role in the regulation of matrix protein synthesis and bone formation in osteoblasts.

Collagen matrices attenuate the collagen-synthetic response of cultured fibroblasts to TGF-beta

Transforming growth factor-beta, a potent modulator of cell function, induces fibroblasts cultured on plastic to increase collagen synthesis. In 5- and 7-day porcine skin wounds, which have minimal to moderate collagen matrix, respectively, transforming growth factor-beta and type I procollagen were coordinately expressed throughout the granulation tissue. However, in 10-day collagen-rich granulation tissue type I procollagen expression diminished despite persistence of transforming growth factor-beta. To investigate whether collagen matrix attenuates the collagen-synthetic response of fibroblasts to transforming growth factor-beta, we cultured human dermal fibroblasts in conditions that simulate collagen-rich granulation tissue. Therefore, human dermal fibroblasts were suspended in attached collagen gels and collagen and noncollagen production was assayed in the absence and presence of transforming growth factor-beta. Although transforming growth factor-beta stimulated collagen synthesis by fibroblasts cultured in the collagen gels, these fibroblasts consistently produced less collagen than similarly treated fibroblasts cultured on plastic. This phenomenon was not secondary to nonspecific binding of transforming growth factor-beta to the collagen matrix. Fibroblasts cultured in a fibrin gel responded to transforming growth factor-beta similarly to fibroblasts cultured on plastic. Using immunofluorescence probes to type I procollagen, we observed that transforming growth factor-beta increased type I procollagen expression in most fibroblasts cultured on plastic, but only in occasional fibroblasts cultured in collagen gels. From these data we conclude that collagen matrices attenuate the collagen synthetic response of fibroblast to transforming growth factor-beta in vitro and possibly in vivo.

Neutralisation of TGF-beta 1 and TGF-beta 2 or exogenous addition of TGF-beta 3 to cutaneous rat wounds reduces scarring

Exogenous addition of neutralising antibody to transforming growth factor-beta 1,2 to cutaneous wounds in adult rodents reduces scarring. Three isoforms of transforming growth factor-beta (1, 2 and 3) have been identified in mammals. We investigated the isoform/isoforms of TGF-beta responsible for cutaneous scarring by: (i) reducing specific endogenous TGF-beta isoforms by exogenous injection of isoform specific neutralising antibodies; and (ii) increasing the level of specific TGF-beta isoforms by exogenous infiltration into the wound margins. Exogenous addition of neutralising antibody to TGF-beta 1 plus neutralising antibody to TGF-beta 2 reduced the monocyte and macrophage profile, neovascularisation, fibronectin, collagen III and collagen I deposition in the early stages of wound healing compared to control wounds. Treatment with neutralising antibodies to TGF-betas 1 and 2 markedly improved the architecture of the neodermis to resemble that of normal dermis and reduced scarring while the control wounds healed with scar formation. Exogenous addition of neutralising antibody to TGF-beta 1 alone also reduced the monocyte and macrophage profile, fibronectin, collagen III and collagen I deposition compared to control wounds. However, treatment with neutralising antibody to TGF-beta 1 alone only marginally reduced scarring. By contrast, wounds treated with neutralising antibody to TGF-beta 2 alone did not differ from control wounds. Interestingly, exogenous addition of the TGF-beta 3 peptide also reduced the monocyte and macrophage profile, fibronectin, collagen I and collagen III deposition in the early stages of wound healing and markedly improved the architecture of the neodermis and reduced scarring. By contrast, wounds treated with either TGF-beta 1 or with TGF-beta 2 had more extracellular matrix deposition in the early stages of wound healing but did not differ from control wounds in the final quality of scarring. This study clearly demonstrates isoform specific differences in the role of TGF-betas in wound healing and cutaneous scarring. TGF-beta 1 and TGF-beta 2 are implicated in cutaneous scarring. This study also suggests a novel therapeutic use of exogenous recombinant, TGF-beta 3 as an anti-scarring agent.

GH3 pituitary tumor cells contain heteromeric type I and type II receptor complexes for transforming growth factor beta and activin-A

Transforming growth factors beta (TGF-beta s) and activins induce and inhibins block secretion of follicle-stimulating hormone by rat GH3 pituitary tumor cells. Cheifetz et al. (Cheifetz, S., Ling, N., Guillemin, R., and Massagué, J. (1988) J. Biol. Chem. 263, 17225-17228) reported that GH3 cells express a approximately 50-kDa surface protein, termed the type IV TGF-beta receptor, that directly binds all of these peptide hormones. Here we show that GH3 cells express the previously identified type I and type II receptors for TGF-beta and activin-A. Immunoprecipitation of affinity-labeled surface binding proteins with antisera specific to known receptors demonstrated independent heteromeric complexes of TGF-beta types I and II receptors and of activin types I and II receptors. As judged by ligand-binding and cross-linking analysis, TGF-beta binding to the TGF-beta receptors is not inhibited by activin-A and activin-A binding to its receptors is not inhibited by TGF-beta. Screening of a cDNA library from GH3 cells for potential receptor serine-threonine kinases yielded the known types I and II TGF-beta and activin receptors. The presumed common intracellular signaling pathway for TGF-beta and activin in GH3 cells appears to be mediated by distinct cell-surface receptors.

Physical and biological characterization of a growth-inhibitory activity purified from the neuroepithelioma cell line A673

Epithelial- and haematopoietic-cell growth-inhibitory activities have been identified in the conditioned medium of the human peripheral neuroepithelioma cell line A673. An A673-cell-derived growth-inhibitory activity was previously fractionated into two distinct components which inhibited the proliferation of human carcinoma and leukaemia cells in culture. One inhibitory activity was shown to comprise interleukin-1 alpha (IL-1 alpha). Here, we have purified to homogeneity a distinct activity which inhibited the growth of the epithelial cells in vitro. Using a combination of protein-sequence analysis and mass spectrometry, we demonstrated that biological activity can be assigned to a dimeric protein with a molecular mass of 25,576 (+/- 4) Da and an N-terminal sequence identical with that of transforming growth factor-beta 1 (TGF-beta 1). Further characterization of the growth inhibitor with TGF-beta-isoform-specific antibodies showed that > 90% of the bioactivity consists of TGF-beta 1 and not TGF-beta 2 or TGF-beta 3. Although A673 cells were growth-inhibited by exogenous TGF-beta 1, we showed that TGF-beta 1 in A673-cell-conditioned media was present in the latent, biologically inactive, form which did not act as an autocrine growth modulator of A673 cells in vitro.

Characterization of a human hepatoma cell line with acquired resistance to growth inhibition by transforming growth factor beta 1 (TGF-beta 1)

A new cell line (Hep 3B-TR), which is resistant to growth-inhibition by transforming growth factor beta 1 (TGF-beta 1) up to 10 ng/ml (400 pM), was isolated from parental Hep 3B human hepatoma cells, which are sensitive to growth-inhibition by TGF-beta 1. In the presence of TGF-beta 1 (1 to 10 ng/ml), the growth of the parental cell line (Hep 3B-TS) was inhibited by more than 95%. Under the same conditions, the growth rate of the resistant clone (Hep 3B-TR) however, was identical in the presence or absence of TGF-beta 1 and was almost the same as that of the Hep 3B-TS cells in the absence of TGF-beta 1. Affinity crosslinking with 5 pM 125I-labeled TGF-beta 1 showed that the TGF-beta 1 receptors type I (TGF-beta RI) and type II (TGF-beta RII) were not present on the cell surface of the Hep 3B-TR cells, whereas they were present on the sensitive HEP 3B-TS cells. Hep 3B-TS cells had detectable TGF-beta RII mRNA, which was not found in Hep 3B-TR cells. RNA analysis showed different effects on the expression of TGF-beta 1, c-fos, c-myc, and protein disulfide isomerase (PDI) genes in the two cell lines in response to TGF-beta 1 protein. Addition of TGF-beta 1 (1 ng/ml) strongly increased the expression of TGF-beta 1 mRNA in Hep 3B-TS cells, but not in Hep 3B-TR cells.(ABSTRACT TRUNCATED AT 250 WORDS)

TGF-beta induced transdifferentiation of mammary epithelial cells to mesenchymal cells: involvement of type I receptors

The secreted polypeptide transforming growth factor-beta (TGF-beta) exerts its multiple activities through type I and II cell surface receptors. In epithelial cells, activation of the TGF-beta signal transduction pathways leads to inhibition of cell proliferation and an increase in extracellular matrix production. TGF-beta is widely expressed during development and its biological activity has been implicated in epithelial-mesenchymal interactions, e.g., in branching morphogenesis of the lung, kidney, and mammary gland, and in inductive events between mammary epithelium and stroma. In the present study, we investigated the effects of TGF-beta on mouse mammary epithelial cells in vitro. TGF-beta reversibly induced an alteration in the differentiation of normal mammary epithelial NMuMG cells from epithelial to fibroblastic phenotype. The change in cell morphology correlated with (a) decreased expression of the epithelial markers E-cadherin, ZO-1, and desmoplakin I and II; (b) increased expression of mesenchymal markers, such as fibronectin; and (c) a fibroblast-like reorganization of actin fibers. This phenotypic differentiation displays the hallmarks of an epithelial to mesenchymal transdifferentiation event. Since NMuMG cells make high levels of the type I TGF-beta receptor Tsk7L, yet lack expression of the ALK-5/R4 type I receptor which has been reported to mediate TGF-beta responsiveness, we evaluated the role of the Tsk7L receptor in TGF-beta-mediated transdifferentiation. We generated NMuMG cells that stably overexpress a truncated Tsk7L type I receptor that lacks most of the cytoplasmic kinase domain, thus function as a dominant negative mutant. These transfected cells no longer underwent epithelial to mesenchymal morphological change upon exposure to TGF-beta, yet still displayed some TGF-beta-mediated responses. We conclude that TGF-beta has the ability to modulate E-cadherin expression and induce a reversible epithelial to mesenchymal transdifferentiation in epithelial cells. Unlike other transdifferentiating growth factors, such as bFGF and HGF, these changes are accompanied by growth inhibition. Our results also implicate the Tsk7L type I receptor as mediating the TGF-beta-induced epithelial to mesenchymal transition.

TGF-beta-receptor-mediated signaling

Transforming growth factor beta (TGF-beta) and its many relatives are thought to play key roles in the control of cell proliferation and differentiation. In particular, the ability of TGF-beta to induce growth arrest in epithelial cells has drawn considerable attention. The recent cloning of TGF-beta receptors, which are considered to be prototypes of a new class of cell-surface receptors, has provided a first insight into how TGF-beta signaling induces a variety of intracellular changes. Furthermore, recent advances in the characterization of the cell-cycle machinery have stimulated studies aimed at understanding how TGF-beta signaling leads to growth arrest in the late G1 phase of the cell cycle.

A cDNA encoding the human transforming growth factor beta receptor suppresses the growth defect of a yeast mutant

Transforming growth factor beta (TGF-beta) is a multifunctional factor that regulates many aspects of cellular processes. TGF-beta signals through a heteromeric complex of type-I and type-II receptors, which both belong to the transmembrane (TM) receptor serine/threonine kinase family. Reported here is the isolation of a subtype of the human TGF-beta receptor type II from a cDNA library using a Saccharomyces cerevisiae mutant. This yeast mutant has a defect in the expression of the gene encoding inositol-1-phosphate synthase and requires myo-inositol for its growth. The cloned subtype of the TGF-beta receptor type II has a 25-amino-acid insertion relative to the reported receptor type-II sequence. In addition to that encoding the TGF-beta receptor, two more human genes were obtained using the same yeast mutant. They encode the protein phosphatase type 2A regulatory subunit A and a 14-3-3 protein which is known as a regulatory protein for protein kinases. These results clearly indicate that these human genes function in yeast cells. It is also suggested that yeast possesses a signal transduction mechanism resembling the human TGF-beta-mediated signaling pathway.

Inhibition of G1 phase cyclin dependent kinases by transforming growth factor beta 1

Transforming growth factor beta 1 (TGF beta 1) inhibits epithelial cell proliferation late in the G1 phase of the cell cycle. We examined the effect of TGF beta 1 on known late G1 cell cycle regulators in an attempt to determine the molecular mechanism of growth inhibition by this physiological inhibitor. The results demonstrate that TGF beta 1 inhibits the late G1 and S phase specific histone H1 kinase activity of p33cdk2. This inhibition is not due to TGF beta 1's effect on p33cdk2 synthesis, but rather due to its negative effects on the late G1 phosphorylation of p33cdk2. It is also shown that TGF beta inhibits both late G1 cyclin A and cyclin E associated histone H1 kinase activities. The inhibitor has no effects on the synthesis of cyclin E but is shown to inhibit the synthesis of cyclin A protein in a cell cycle dependent manner. If TGF beta 1 is added to cells which have progressed further than 8 hours into G1, then it is without inhibitory effect on cyclin A synthesis. These effects of TGF beta 1 on late G1 cell cycle regulators correlate well with its inhibitory effects on cellular growth and suggest that these G1 cyclin dependent kinases might serve as targets for TGF beta 1-mediated growth arrest.

Characterization of mutated transforming growth factor-beta s which possess unique biological properties

Transforming growth factor-beta (TGF-beta) is a potent regulator of cell growth and differentiation. On the basis of the crystal structure of TGF-beta 2, we have designed and synthesized two mutant TGF-beta s, TGF-beta 1 (71 Trp) and TGF-beta 1 (delta 69-73). Although both of these molecules inhibited the growth of Mv1Lu mink lung epithelial cells and LS1034 colorectal cancer cells, which are affected equally by TGF-beta 1 and TGF-beta 2, TGF-beta 1 (delta 69-73) was much less potent than TGF-beta 1 or TGF-beta 1 (71 Trp) at inhibiting the growth of LS513 colorectal cancer cells which are growth-inhibited by TGF-beta 1 but not TGF-beta 2. Both TGF-beta 1 (71 Trp) and TGF-beta 1 (delta 69-73) increased levels of mRNAs for fibronectin and plasminogen activator inhibitor with Mv1Lu cells, whereas only TGF-beta 1 (71 Trp) and not TGF-beta 1 (delta 69-73) up-regulated the mRNA level of carcinoembryonic antigen in LS513 cells. The expression level of carcinoembryonic antigen mRNA in LS1034 cells was not altered by either wild-type or mutant TGF-beta s. Receptor labeling experiments demonstrated that TGF-beta 1 (71 Trp) bound with high affinity to the cell-surface receptors of Mv1Lu, LS1034, and LS513 cells while TGF-beta 1 (delta 69-73) bound effectively to the receptors of Mv1Lu and LS1034 cells but much less to the receptors on LS513 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of transforming growth factor beta 1 on the regulation of osteocalcin synthesis in human MG-63 osteosarcoma cells

Treatment of human MG-63 osteosarcoma cells with human recombinant transforming growth factor beta 1 (TGF-beta 1) was found to inhibit cell proliferation. In addition, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]-induced osteocalcin synthesis was greatly influenced by TGF-beta 1. Dose- and time-dependent inhibition was seen both in medium osteocalcin and the corresponding mRNA concentrations. Furthermore, TGF-beta 1 decreased osteocalcin synthesis modulated negatively by dexamethasone or positively by retinoic acid. The stability of osteocalcin mRNA was not decreased by the TGF-beta 1 treatment, but in vitro transcription assays demonstrated diminished osteocalcin gene transcription caused by the TGF-beta 1 treatment. Binding of vitamin D receptor (VDR) to an oligonucleotide probe containing the osteocalcin vitamin D response element (VDRE) was not influenced by TGF-beta 1, however. Incubation of the cells with the serine/threonine kinase inhibitor H-7 did not block the ability of TGF-beta 1 to decrease osteocalcin synthesis but caused a further inhibition. Also, the 1,25(OH)2D3-induced osteocalcin synthesis was decreased by H-7 treatment, suggesting that phosphorylation as such is involved in the transcriptional activation mechanism of VDR. These results demonstrate that TGF-beta 1 is a strong inhibitor of the synthesis of osteocalcin, a calcium binding protein participating in bone mineralization, by counteracting the stimulatory effects of other hormones on its synthesis. We further suggest that TGF-beta 1 affects the synthesis of osteocalcin at the level of transcription through mechanism(s) different from the serine/threonine kinase pathway.

Genetic changes in the transforming growth factor beta (TGF-beta) type II receptor gene in human gastric cancer cells: correlation with sensitivity to growth inhibition by TGF-beta

We have found several genetic changes in the TGF-beta-type II receptor gene in human gastric cancer cell lines resistant to the growth inhibitory effect of TGF-beta. Southern blot analysis showed deletion of the type II receptor gene in two of eight cell lines and amplification in another two lines. The single cell line we studied that is sensitive to growth inhibition by TGF-beta showed no structural abnormalities of the type II receptor gene. Some of the gastric cancer cells resistant to the growth inhibitory effect of TGF-beta express either truncated or no detectable TGF-beta type II receptor mRNAs, whereas the one that retains responsiveness to the growth inhibitory effect of TGF-beta expresses a full-size type II receptor mRNA. Immunoprecipitation followed by Western blot analysis showed parallel changes in TGF-beta type II receptor expression. Our results suggest that one of the possible mechanisms of escape from autocrine or paracrine growth control by TGF-beta during carcinogenesis could involve genetic changes in the TGF-beta type II receptor gene itself or altered expression of its mRNA.

Interaction of the small interstitial proteoglycans biglycan, decorin and fibromodulin with transforming growth factor beta

We have analysed the interactions of three proteoglycans of the decorin family, decorin, biglycan and fibromodulin, with transforming growth factor beta (TGF-beta). The proteoglycan core proteins, expressed from human cDNAs as fusion proteins with Escherichia coli maltose-binding protein, each bound TGF-beta 1. They showed only negligible binding to several other growth factors. Intact decorin, biglycan and fibromodulin isolated from bovine tissues competed with the fusion proteins for the TGF-beta binding. Affinity measurements suggest a two-site binding model with Kd values ranging from 1 to 20 nM for a high-affinity binding site and 50 to 200 nM for the lower-affinity binding site. The stoichiometry indicated that the high-affinity binding site was present in one of ten proteoglycan core molecules and that each molecule contained a low-affinity binding site. Tissue-derived biglycan and decorin were less effective competitors for TGF-beta binding than fibromodulin or the non-glycosylated fusion proteins; removal of the chondroitin/dermatan sulphate chains of decorin and biglycan (fibromodulin is a keratan sulphate proteoglycan) increased the activities of decorin and biglycan, suggesting that the glycosaminoglycan chains may hinder the interaction of the core proteins with TGF-beta. The fusion proteins competed for the binding of radiolabelled TGF-beta to Mv 1 Lu cells and endothelial cells. Affinity labelling showed that the binding of TGF-beta to betaglycan and the type-I receptors in Mv 1 Lu cells and to endoglin in endothelial cells was reduced, but the binding to the type-II receptors was unaffected. TGF-beta 2 and 3 also bound to all three fusion proteins. Latent recombinant TGF-beta 1 precursor bound slightly to fibromodulin and not at all to decorin and biglycan. The results show that the three decorin-type proteoglycans each bind TGF-beta isoforms and that slight differences exist in their binding properties. They may regulate TGF-beta activities by sequestering TGF-beta into extracellular matrix.

Control of cardiac gene transcription by fibroblast growth factors

Skeletal alpha-actin (SkA) is representative of the cardiac genes that are expressed at high levels in embryonic myocardium, downregulated after birth, and reactivated by tropic signals including basic fibroblast growth factor (FGF-2) and type beta transforming growth factors (TGF beta). To investigate the molecular basis for cardiac-restricted and growth factor-induced SkA transcription, we have undertaken a mutational analysis of the SkA promoter in neonatal ventricular myocytes, with emphasis on the role of three nominal serum response elements. Serum response factor (SRF) and the bifunctional factor YY1 are the predominant cardiac proteins contacting the proximal SRE (SRE1). Mutations of SRE1 that prevent recognition by SRF and YY1. or SRF alone, virtually abolish SkA transcription; mutation of distal SREs was ineffective. A mutation which selectively abrogates YY1 binding increases expression, substantiating the predicted role of YY1 as an inhibitor of SRF effects. SkA transcription requires combinational action of SRE1 with consensus sites for Sp1 and the SV40 enhancer binding protein, TEF-1. As an isolated motif, SRE1 can confer responsiveness to both FGF-2 and TGF beta to a heterologous promoter. Whether TEF-1 binding sites likewise can function as FGF response elements is unknown. Molecular dissection of mechanisms that govern the differentiated cardiac phenotype has largely been undertaken to date in neonatal ventricular myocytes, as the adult ventricular myocyte has been refractory to conventional procedures for gene transfer. To circumvent expected limitations of other methods, we have used replication-deficient adenovirus to achieve efficient gene transfer to adult cardiac cells in culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming growth factor beta 1-mediated induction of junB is selectively inhibited by expression of Ad.12-E1A

Transforming growth factor beta (TGF-beta), a multifunctional polypeptide growth factor, regulates the expression of many genes critical to cell cycle progression, such as members of the jun gene family which encode components of the transcription factor complex AP-1. The transforming proteins encoded by the early region 1A of adenovirus12 (Ad.12-E1A) abrogate some of the cellular responses to TGF-beta as well as affecting, differentially, the expression of cellular jun genes. Our data demonstrate that expression of Ad.12-E1A in rat 3Y1 fibroblast cells inhibits induction of junB by TGF-beta 1 while not altering the regulation of junB by phorbol ester or serum. Regulation of c-jun gene expression by TGF-beta 1, phorbol ester, and serum is not appreciably altered by the expression of Ad.12-E1A. Inhibition of TGF-beta induced junB expression is not due to a defect in TGF-beta/receptor interaction on Ad.12-E1A transformed cells and is not observed in other isotypic fibroblast cells transformed by SV40 or polyomavirus. These data suggest that multiple, independent, intracellular signal transduction pathways exist which mediate genomic responses to TGF-beta. Cellular expression of Ad.12-E1A-12S gene products results in selective disruption of some TGF-beta 1 signaling cascades and not those activated by phorbol ester or serum. These data further suggest that some cellular targets which mediate TGF-beta 1 action may also be unique targets of action for the E1A-12S transforming protein of adenovirus12.

Genomic structure and cloned cDNAs predict that four variants in the kinase domain of serine/threonine kinase receptors arise by alternative splicing and poly(A) addition

Heterodimers of types I and II serine/threonine kinase receptor monomers compose the active receptor complex for ligands of the transforming growth factor beta family. Here we show that the genomic organization of coding sequences for the intracellular domain of a widely expressed type I serine/threonine kinase receptor is similar to that of the activin type II receptor gene. The genomic structure and cDNA clones indicate that poly(A) addition to alternative exons at each of three carboxyl-terminal coding exon-intron junctions may be a common feature of both type I and II receptor genes. The predicted products are monomers truncated at kinase subdomains VII, IX, and X which vary in kinase activity and potential serine, threonine, and tyrosine phosphorylation sites. These results suggest that combinations of variants that affect the signal-transducing intracellular kinase domain of both type I and II receptor monomers within the transforming growth factor beta ligand family may add to the heterogeneity of biological effects of individual ligands in the family.

Specific interaction of type I receptors of the TGF-beta family with the immunophilin FKBP-12

Transforming growth factor-beta (TGF-beta) family members bind to receptors that consist of heteromeric serine-threonine kinase subunits (type I and type II). In a yeast genetic screen, the immunophilin FKBP-12, a target of the macrolides FK506 and rapamycin, interacted with the type I receptor for TGF-beta and with other type I receptors. Deletion, point mutation, and co-immunoprecipitation studies further demonstrated the specificity of the interaction. Excess FK506 competed with type I receptors for binding to FKBP-12, which suggests that these receptors share or overlap the macrolide binding site on FKBP-12, and therefore they may represent its natural ligand. The specific interaction between the type I receptors and FKBP-12 suggests that FKBP-12 may play a role in type I receptor-mediated signaling.

The types II and III transforming growth factor-beta receptors form homo-oligomers

Affinity-labeling experiments have detected hetero-oligomers of the types I, II, and III transforming growth factor beta (TGF-beta) receptors which mediate intracellular signaling by TGF-beta, but the oligomeric state of the individual receptor types remains unknown. Here we use two types of experiments to show that a major portion of the receptor types II and III forms homo-oligomers both in the absence and presence of TGF-beta. Both experiments used COS-7 cells co-transfected with combinations of these receptors carrying different epitope tags at their extracellular termini. In immunoprecipitation experiments, radiolabeled TGF-beta was bound and cross-linked to cells co-expressing two differently tagged type II receptors. Sequential immunoprecipitations using anti-epitope monoclonal antibodies showed that type II TGF-beta receptors form homo-oligomers. In cells co-expressing epitope-tagged types II and III receptors, a low level of co-precipitation of the ligand-labeled receptors was observed, indicating that some hetero-oligomers of the types II and III receptors exist in the presence of ligand. Antibody-mediated cross-linking studies based on double-labeling immunofluorescence explored co-patching of the receptors at the cell surface on live cells. In cells co-expressing two differently tagged type II receptors or two differently tagged type III receptors, forcing one receptor into micropatches by IgG induced co-patching of the receptor carrying the other tag, labeled by noncross-linking monovalent Fab'. These studies showed that homo-oligomers of the types II and III receptors exist on the cell surface in the absence or presence of TGF-beta 1 or -beta 2. In cells co-expressing types II and III receptors, the amount of heterocomplexes at the cell surface was too low to be detected in the immunofluorescence co-patching experiments, confirming that hetero-oligomers of the types II and III receptors are minor and probably transient species.

Transforming growth factor beta 1 inhibits interleukin-1-induced but enhances ionomycin-induced interferon-gamma production in a T cell lymphoma: comparison with the effects of rapamycin

Transforming growth factor beta 1 (TGF-beta 1) is a multifunctional cytokine whose potent immunomodulatory activity is well documented. To explore the mechanisms of this activity we examined the effect of TGF-beta 1 on the production of IFN-gamma measured at the mRNA and protein levels in the YAC-1 T cell lymphoma. In previous studies, this model proved useful to characterize the mode of action of the immunosuppressant rapamycin (RAP). Here, we found that when induced by IL-1 or IL-1 + PMA, the production of IFN-gamma is suppressed by both TGF-beta 1 (ED50 = 1.9 pM) and RAP (ED50 = 0.2 nM). In contrast, when induced by the calcium ionophore ionomycin, in the absence or in the presence of PMA, this production is enhanced up to 10-fold by TGF-beta 1 (ED50 = 1.8 pM) and 1.5-3-fold by RAP. Therefore, in YAC-1 cells, TGF-beta 1 exerts opposite effects on IFN-gamma production depending on the mode of activation, and these effects parallel those of RAP. To further analyze the mode of action of TGF-beta 1 in this system, we used okadaic acid (OA), an inhibitor of serine/threonine protein phosphatases. Treatment with OA rendered the expression of IFN-gamma mRNA induced by IL-1 insensitive to TGF-beta 1 or RAP, indicating that activation of a phosphatase may play a role in the suppressive effect of both agents. However, OA did not prevent the augmentation of ionomycin-mediated induction of IFN-gamma mRNA by either TGF-beta 1 or RAP. Hence, the up-regulation of IFN-gamma production by TGF-beta 1 and RAP may involve a different biochemical mechanism than that mediating their suppressive action. These observations also favor the hypothesis that the two agents act on the same regulatory pathways. This was further supported by the finding that TGF-beta 1 and RAP modulate IFN-gamma production in an additive rather than synergistic fashion. However, their effects could be dissociated in mutants of YAC-1 cells selected for resistance to the inhibition of IL-1-mediated IFN-gamma induction by RAP. Moreover, the IFN-gamma modulatory action of RAP in YAC-1 cells was accompanied by an antiproliferative effect, whereas TGF-beta 1 failed to alter the growth of these cells. Therefore, the immunomodulatory action of TGF-beta 1 may result from the disruption of biochemical processes related to, although distinct from, those affected by RAP.

Type I receptors specify growth-inhibitory and transcriptional responses to transforming growth factor beta and activin

Transforming growth factor beta (TGF-beta) and activin bind to receptor complexes that contain two distantly related transmembrane serine/threonine kinases known as receptor types I and II. The type II receptors determine ligand binding specificity, and each interacts with a distinct repertoire of type I receptors. Here we identify a new type I receptor for activin, ActR-IB, whose kinase domain is nearly identical to that of the recently cloned TGF-beta type I receptor, T beta R-I. ActR-IB has the structural and binding properties of a type I receptor: it binds activin only in the presence of an activin type II receptor and forms a heteromeric noncovalent complex with activin type II receptors. In Mv1Lu lung epithelial cells, ActR-IB and T beta R-I signal a common set of growth-inhibitory and transcriptional responses in association with their corresponding ligands and type II receptors. The transcriptional responses include elevated expression of fibronectin and plasminogen activator inhibitor 1. Although T beta R-I and ActR-IB are nearly identical in their kinase domains (90% amino acid sequence identity), their corresponding type II receptor kinase domains are very different from each other (42% amino acid sequence identity). Therefore, signaling of a specific set of responses by TGF-beta and activin correlates with the presence of similar type I kinases in their complex. Indeed, other TGF-beta and activin type I receptors (TSR-I and ActR-I) whose kinase domains significantly diverge from those of T beta R-I and ActR-IB do not substitute as mediators of these growth-inhibitory and extracellular matrix transcriptional responses. Hence, we conclude that the type I receptor subunits are primary specifiers of signals sent by TGF-beta and activin receptor complexes.