Regulation of type II alveolar epithelial cell proliferation by TGF-beta during bleomycin-induced lung injury in rats

Three isoforms of transforming growth factor-beta (TGF-beta) are found in mammalian cells and are potent regulators of inflammation, connective tissue synthesis, cellular proliferation, and differentiation. To determine the distribution and regulation of TGF-beta isoforms during pulmonary injury, a rat model of bleomycin-induced lung inflammation and repair was used. Using immunohistochemistry, we demonstrate that TGF-beta 2 and TGF-beta 3 were localized to alveolar macrophages as well as epithelial and smooth muscle cells of both normal rat lungs and rat lungs obtained at all time intervals after bleomycin administration. Early in bleomycin-induced lung injury, when there is active proliferation of type II alveolar epithelial cells, there was an increase in the number of type II alveolar epithelial cells isolated per lung and an increase in DNA synthesis by explanted type II alveolar epithelial cells. At this time, the secretion of biologically active TGF-beta 1-3, which are potent inhibitors of epithelial cell proliferation, was decreased. However, the secretion of TGF-beta 1-3 activity was markedly increased later in the injury response and coincided with a reduction in the number of type II alveolar epithelial cells isolated per lung and DNA synthesis in vitro. Furthermore, the addition of TGF-beta 1, 2, and 3 to cultures of actively proliferating type II alveolar epithelial cells resulted in inhibition of [3H]thymidine incorporation, whereas, in the presence of anti-TGF-beta 1-3 antibody, there was an increase in [3H]thymidine incorporation. Our findings suggest that altered secretion of TGF-beta 1-3 activity by type II alveolar epithelial cells during bleomycin-induced lung injury may regulate pulmonary alveolar epithelial cell proliferation during injury and repair phases.

The univin gene encodes a member of the transforming growth factor-beta superfamily with restricted expression in the sea urchin embryo

We have identified a gene in the sea urchin Strongylocentrotus purpuratus that encodes a member of the transforming growth factor beta (TGF-beta) gene superfamily. We have named the gene univin, and it is the first member of this superfamily to be reported in echinoderms. The cDNA sequence predicts a 383-amino-acid residue protein with 7 cysteine residues characteristic of members of this superfamily and with a cluster of basic residues appropriately situated to signal proteolytic cleavage. Sequence comparisons place univin in the bone morphogenetic protein (BMP) group of the TGF-beta superfamily along with the vertebrate BMPs, decapentaplegic protein from Drosophila, and Vg-1 from Xenopus. Analyses of univin expression in early embryos by RNA blots and in situ hybridization revealed the highest levels of expression in the egg and prehatching blastula. During late cleavage stages, univin mRNA accumulation is progressively restricted to a circumequatorial band. Expression is further restricted during gastrulation when univin transcripts are detected primarily in the presumptive foregut and ciliated band. By pluteus stage, signals are detectable only in these cell types. The restricted temporal and spatial patterns of expression of univin during early blastula stages parallel those of SpAN, which encodes an astacin-like protease related to tolloid and BMP-1 (Reynolds et al., 1992). The fact that these proteases are thought to function in the proteolytic activation of TGF-beta-related proteins that, respectively, regulate Drosophila embryonic dorsal-ventral patterning and vertebrate bone development suggests that SpAN and univin could also have critical roles in early developmental decisions in the sea urchin embryo.

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)

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.

Formation of hetero-oligomeric complexes of type I and type II receptors for transforming growth factor-beta

Transforming growth factor-beta (TGF-beta) transduces signals through a heteromeric complex of type I (T beta R-I) and type II (T beta R-II) TGF-beta receptors. To determine the stoichiometry of this complex we used analysis by affinity labeling with 125I-TGF-beta 1 and covalent cross-linking with disuccinimidyl suberate and immunoprecipitation using T beta R-I- or T beta R-II-specific antisera, followed by two-dimensional gel electrophoresis under nonreducing (first dimension) and reducing (second dimension) conditions. Dimers composed of T beta R-I and/or T beta R-II were observed on mink lung epithelial cells as well as COS-1 cells transfected with T beta R-I and T beta R-II cDNAs. Homodimers of T beta R-I could be demonstrated on these cells after dissociation of T beta R-II by sodium dodecyl sulfate treatment. On the cell surface of mink lung epithelial cell mutants that express only T beta R-II and do not respond to TGF-beta, and on COS-1 cells transfected with only T beta R-II, only homodimers of T beta R-II were seen. The facts that T beta R-I does not bind TGF-beta in the absence of T beta R-II and that T beta R-II forms a signaling complex with T beta R-I, together with our observations that homodimers of T beta R-I and T beta R-II are seen on responsive cells, support the notion that TGF-beta induces the formation of hetero-oligomeric receptor complexes, most likely a heterotetramer containing two molecules each of T beta R-I and T beta R-II.

Expression of transforming growth factor-beta (TGF beta) isoforms and TGF beta type II receptor messenger ribonucleic acid and protein, and the effect of TGF beta s on endometrial stromal cell growth and protein degradation in vitro

Reverse transcription-polymerase chain reaction analysis of total RNA and immunocytochemical observations revealed that human endometrial glandular epithelial and stromal cells in primary culture express messenger RNAs and proteins for transforming growth factor-beta 1 (TGF beta 1), TGF beta 2, and TGF beta 3 as well as TGF beta type II receptor. The epithelial and stromal cells synthesize and secrete into their culture-conditioned medium 2.6 +/- 0.3 and 1.4 +/- 0.2 ng TGF beta 1/10(6) cells, respectively; after transient acidification of the medium, the TGF beta 1 levels were 18.1 +/- 0.4 and 7.8 +/- 0.7 ng/10(6) cells. These cells also contain specific binding sites for [125I]TGF beta 1, indicated by light microscope autoradiography. TGF beta s at 0.01-10 ng/ml neither stimulated or inhibited subconfluent quiescent stromal cells under serum-free condition nor altered the mitogenic action of 10% fetal bovine serum. However, in the presence of 2% fetal bovine serum, which induced half-maximal stimulation of [3H]thymidine incorporation, TGF beta 1 and TGF beta 2 at 0.1-0.5 ng/ml and TGF beta 3 at 0.1-2.5 ng/ml significantly stimulated the rate of [3H]thymidine incorporation into quiescent stromal cells (P < 0.005); they were ineffective at higher concentrations. TGF beta s did not have any effect on cell proliferation, as determined by cell counting; however, at 0.1 ng/ml and higher concentrations, TGF beta s significantly reduced the metabolic activity of stromal cells, as determined by colorimetric 3-(4,5-dimethylthiazol-2-yl)2, 5-diphenyltetrazolium bromide assay (P < 0.05). The stimulatory and inhibitory actions of TGF beta s in both assays were reversible using 5-10 micrograms/ml TGF beta 1- and TGF beta 2- and 3-6 micrograms/ml TGF beta 3-specific neutralizing antibodies. TGF beta 1 at 1 ng/ml had no significant effect on long-lived protein degradation, assayed by incorporation of [14C]valine into newly synthesized protein by stromal cells, and was similar to the effect of epidermal growth factor or platelet-derived growth factor-BB (10 ng/ml). The data suggest that the TGF beta expression by various endometrial cell types in an autocrine/paracrine manner acts as a negative regulator essential for restraining endometrial growth and transition from proliferation to differentiation stages during the secretory phase after mitogenic stimulation during the proliferative phase of the menstrual cycle.

Role of active and latent transforming growth factor beta in bone formation

At first reading the statement "TGF beta stimulates bone formation but inhibits mineralization" may appear to be an oxymoron. However, the bone formation process can take weeks to months to complete, and the unique properties of TGF beta allow this factor to be stored in bone matrix in a latent form, ready to be activated and inactivated at key, pivotal stages in this long process. TGF beta may act to trigger the cascade of events that ultimately leads to new bone formation. However, once this process is initiated, TGF beta must then be inactivated or removed because if present in the later stages of bone formation, mineralization will be inhibited. The unique properties of TGF beta and its role in bone remodeling are the subject of this review.

Inhibition of the chondrocyte phenotype by retinoic acid involves upregulation of metalloprotease genes independent of TGF-beta

Retinoic acid has been identified as a key morphogen governing pattern formation in the developing cartilaginous skeleton. Retinoids have also been implicated in the premature closure of the cartilage growth plate following vitamin A intoxication or administration of retinoids for dermatologic conditions. Previous studies of the mechanism of action of retinoids in non-chondrogenic cells have concluded that retinoic acid is a negative regulator of AP-1 responsive metalloprotease genes. We show that inhibition of expression of the cartilage phenotype by retinoic acid in epiphyseal chondrocytes is associated with positive regulation of AP-1 responsive metalloprotease genes, as well as induction of gene expression for the two components of the transcription factor AP-1, c-fos and c-jun. Despite the similar effects of TGF-beta 1 on expression of cartilage matrix proteins and metalloproteases in this culture system, no appreciable changes in the expression of TGF-beta isoforms were evident in response to retinoic acid treatment. The present investigation demonstrates that regulation of AP-1 responsive genes by retinoic acid can be either positive or negative, depending on the target cell type, and illuminates new mechanisms by which retinoic acid and other retinoids may exert control during development and growth of the limb.

Production of a bioactive high molecular weight transforming growth factor beta-like molecule by human malignant glioma cell lines

The present study describes identification and partial characterization of a glioma-derived high molecular weight transforming growth factor beta-like molecule (HMW-TGF beta) that requires no activation for biological activity. HMW-TGF beta, constitutively produced by the human glioma cell line, D54MG, is not acid- or heat-labile; is relatively resistant to denaturation, reduction, and high salt treatment. Monoclonal antibody 12A12.D7, produced against partially-purified HMW-TGF beta, was used both to deplete and to neutralize directly a > 158 kDa HMW-TGF beta activity from gel filtration fractions; the antibody also directly neutralized purified mature TGF beta 1. 12A12.D7 recognized a single protein species of 186 kDa from unlabeled glioma cell conditioned media and 35S-labeled lysates. HMW-TGF beta is not due to complex formation between TGF beta and any of the known carrier molecules. Production of HMW-TGF beta by glioma cells could facilitate tumor cell proliferation, and thus contribute to the inexorable and rapid progression that characterizes malignant gliomas.

Immunohistological demonstration of transforming growth factor-beta isoforms in the skin of patients with systemic sclerosis

We investigated the expression of transforming growth factor-beta (TGF-beta) isoforms in involved and uninvolved areas of skin from patients with systemic sclerosis (SSc) and normal controls. Paraffin-embedded skin specimens were stained for TGF-beta 1, TGF-beta 2, and TGF-beta 3 using the avidin-biotin-peroxidase technique. TGF-beta 2 was expressed intensely in the extracellular matrix of the skin biopsies obtained from involved areas of patients with SSc, in contrast to the uninvolved areas and normal individuals. TGF-beta 2 was deposited throughout the entire dermis and also in a linear fashion along the dermoepidermal junction and in the perivascular areas of SSc-involved skin. Although infiltrating mononuclear cells were not present in great numbers, they did not stain for TGF-beta 2. TGF-beta 1 and TGF-beta 3 were not expressed in the extracellular space in either patients or normal controls, except in rare cases. The cellular staining which was observed for all three isoforms did not differ between involved and uninvolved skin and normal controls. The finding of increased deposition of TGF-beta 2 in the involved skin of patients with SSc implies that it may be involved in the pathologic fibrotic process.

Topological similarities in TGF-beta 2, PDGF-BB and NGF define a superfamily of polypeptide growth factors

BACKGROUND

The development of functional diversity through gene duplication and subsequent divergent evolution can give rise to proteins that have little or no sequence similarity, but retain similar topologies.

RESULTS

The crystal structures of nerve growth factor, transforming growth factor-beta 2 and platelet-derived growth factor-BB show that all three are based on a cystine-knot plus beta-strands topology. There is very little sequence identity between the three proteins and the relationship between the structures had not been deduced from sequence comparisons. Each growth factor is usually active as a dimer; each exists as a dimer in the crystal, but the relative orientations of the protomers are different in each case.

CONCLUSION

The structural motif of disulphide bonds and hydrogen-bonded beta-strands unexpectedly found in these three growth factors acts as a stable framework for elaboration of loops of low sequence similarity that contain the specificity for receptor interaction.

Crystal structure of TGF-beta 2 refined at 1.8 A resolution

The crystal structure of TGF-beta 2 has been refined using data collected with synchrotron radiation (CHESS) to 1.8 A resolution with a residual R (= sigma magnitude of Fo-magnitude of Fc/sigma magnitude of Fo) factor of 17.3%. The model consists of 890 protein atoms from all 112 residues and 59 water molecules. The monomer of TGF-beta 2 assumes a rather extended conformation and lacks a well-defined hydrophobic core. Surface accessibility calculations show only 44% of the nonpolar surface is buried in the monomer. In contrast, 55.8% of the nonpolar surface area is buried when the two monomers form a dimer, a typical value for globular proteins. This includes a 1300 A2 buried interface area that is largely hydrophobic. Sequence comparisons using a profile derived from the refined TGF-beta 2 structure suggest that the cluster of four disulfides (three intramonomeric disulfide bonds 15-78, 44-109, 48-111 forming a disulfide knot, and one intermonomeric disulfide 77-77) together with the extended beta strand region constitutes the conserved structural motif for the TGF-beta superfamily. This structural motif, without the 77-77 disulfide bond, defines also the common fold for a general family of growth factors, including the nerve growth factor and platelet-derived growth factor families. The fold is conserved only at the monomer level, while the active forms are dimers, suggesting that dimerization plays an important role in regulating the binding of these cytokines to their receptors and in modulating the biological responses.

Refined crystal structure of human transforming growth factor beta 2 at 1.95 A resolution

Transforming growth factor beta 2 (TGF-beta 2), a homodimeric protein, is a member of a family of structurally related polypeptides that regulate various growth and differentiation processes in many cell types. The crystal structure of recombinant human TGF-beta 2 has been determined using a single heavy-atom derivative, anomalous scattering and by applying solvent flattening. The molecular model has been refined by a combination of simulated annealing and restrained least-squares refinement to a crystallographic R-factor of 0.194 including all data from 1.95 A to 8.0 A resolution. In the final structure, the root-mean-square deviation for bond lengths is 0.007 A and for bond angles 1.97 degrees. The final model includes 890 protein atoms (all 112 amino acid residues) as well as 84 water molecules. The new monomer fold consists of a separate alpha-helix and two pairs of antiparallel beta-sheet segments, which can be subdivided into nine individual beta-strands. The extended monomer lacks the typical hydrophobic core. A cluster of disulfide bridges, including the TGF-beta knot, connects the beta-strands with each other as well as the alpha-helix. Two monomers are covalently linked by a single disulfide bridge. In the dimer the alpha-helix of one subunit interacts with the beta-sheet of the other subunit forming two symmetrically related hydrophobic cores. The center of the dimer interaction is stabilized by a network of hydrogen bonds including several well-defined water molecules, which surround the central intersubunit disulfide bridge. The refined structure reveals the details of hydrogen bonding, electrostatic and hydrophobic interactions between intra- and intersubunit residues and allows the identification of possible receptor binding segments.

Isoform-specific effects of transforming growth factors-beta on degeneration of primary neuronal cultures induced by cytotoxic hypoxia or glutamate

The transforming growth factors-beta (TGFs-beta) are multifunctional peptide growth factors that have been localized in neuronal and glial cells of the CNS of mice, rats, and chick embryos. We tested the TGF-beta isoforms 1, 2, and 3 for their protective effects against neuronal degeneration caused by cytotoxic hypoxia or by the excitatory amino acid L-glutamate. A cytotoxic hypoxia was induced in cultured chick embryo telencephalic neurons by adding 1 mM sodium cyanide to the culture medium for a period of 30 min. Treatment with TGF-beta 1 (1-30 ng/ml) led to a statistically significant increase in cell viability, neuronal ATP levels, and protein content of the cultures assessed 72 h after the toxic insult. TGF-beta 3 was able to reduce the cyanide-induced neuronal damage at concentrations of 0.3 and 1 ng/ml, whereas TGF-beta 2 only showed neuroprotective activity at concentrations of 30 and 50 ng/ml. Both pre- and post-treatment with TGF-beta 1 also prevented the degeneration of cultured chick embryo telencephalic neurons that had been exposed to 1 mM L-glutamate in a buffered salt solution for a period of 60 min. Furthermore, TGF-beta 1 (0.3-3 ng/ml), and to a lesser extent TGF-beta 3 (0.1-1 ng/ml), significantly reduced excitotoxic injury of cultured neurons from rat cerebral cortex that had been exposed to serum-free culture medium supplemented with 1 mM L-glutamate. These results demonstrate that the TGFs-beta are able to prevent the degeneration of primary neuronal cultures, which was caused by energy depletion and activation of glutamate receptors, in an isoform-specific manner.

Transforming growth factor-beta 1 reduces infarct size after experimental cerebral ischemia in a rabbit model

BACKGROUND AND PURPOSE

The aim of this study was to examine the effect of transforming growth factor-beta 1, a cytokine shown to amelioriate cardiac ischemia, in a rabbit model of thromboembolic stroke.

METHODS

An autologous clot embolus was introduced intracranially through the right internal carotid artery in 21 New Zealand White rabbits, with seven in each group receiving either vehicle control (albumin) or 10 or 50 micrograms transforming growth factor-beta 1 administered as an intracarotid bolus immediately before autologous clot embolization. Multiple physiological parameters were monitored, including regional cerebral blood flow, arterial blood gases, hematocrit, glucose, core temperature, and mean arterial pressure. The brain was harvested 4 hours after embolization, and infarct size was determined planimetrically as a percentage of the entire hemisphere.

RESULTS

Brain infarct size was reduced in both the 10-microgram (16.7 +/- 4.0% [mean +/- SEM], p < 0.05) and 50-microgram (21.7 +/- 4.5%) transforming growth factor-beta 1-treated groups when compared with the control group (31.9 +/- 6.6%). Regional cerebral blood flow did not show any significant intergroup or intragroup variation over time, although the 10-microgram transforming growth factor-beta 1 group experienced a greater return of cerebral blood flow in the first 2 hours after embolization.

CONCLUSIONS

Transforming growth factor-beta 1 reduced brain infarct size in a rabbit model of thromboembolic stroke. This effect was not related to a direct effect on blood flow. Studies are ongoing to determine the mechanism by which transforming growth factor-beta 1 salvages ischemic brain.

Transforming growth factor beta 1: secondary structure as determined by heteronuclear magnetic resonance spectroscopy

Virtually complete backbone NMR signal assignments have been reported for transforming growth factor beta 1 (TGF-beta 1) [Archer et al. (1993) Biochemistry (preceding paper in this issue)]. Herein we report the secondary structure of the protein in solution on the basis of these assignments and proton NOE's observed in a variety of 2D and 3D heteronuclear NMR spectra. Regular elements of secondary structure derived from the NOE data consist of (a) three helices spanning residues Y58-H68, F24-G29, and N5-F8 and (b) several pairs of two-stranded antiparallel beta-sheets. The longest two-stranded sheet runs from residue L83 to V106 with a type II reverse turn at G93-R94 and a chain twist at residue N103-M104. These elements of regular structure were confirmed by hydrogen exchange, chemical shift, and coupling constant data. With the exception of residues G46-S53, which exhibit relatively few and weak intraresidue NOE's, residues in the rest of the protein adopt an irregular but well-defined structure. All peptide bonds are trans except for a cis peptide bond between Glu35 and Pro36. The structural characteristics observed for TGF-beta 1 in solution generally agree closely with the recently derived crystal structures of TGF-beta 2 [Daopin et al. (1992) Science 257, 369-374; Schlunegger & Grütter (1992) Nature 358, 430-434]. Several noteworthy differences were observed that may be related to function.

Transforming growth factor beta 1: NMR signal assignments of the recombinant protein expressed and isotopically enriched using Chinese hamster ovary cells

The transforming growth factor beta s are a homologous family of multifunctional cytokines that regulate cell growth and differentiation. As a prelude to studies of the solution structure and dynamics of TGF-beta 1, we report virtually complete assignment of 1H and 15N resonances for this 25-kDa homodimeric protein. Recombinant TGF-beta 1 was expressed in Chinese hamster ovary cells. The cells were grown either in a completely 15N-enriched medium or in a medium containing selectively 13C, 15N-labeled amino acids to obtain either uniformly or specifically labeled protein, respectively. Two- and three-dimensional heteronuclear edited magnetic resonance spectra of the uniformly 15N-labeled protein and three samples selectively labeled with 13C and 15N yielded assignments for 96% of the backbone amide and C alpha protons and 87% of the side chain protons. To our knowledge, this is the first report of the use of an animal cell expression system to obtain extensive isotopic enrichment in order to sequentially assign a protein. The methodology described herein for the isotopic enrichment and resonance assignments of TGF-beta 1 should be generally applicable to other eukaryotic proteins expressed by animal cells.

CDGF (chicken embryo fibroblast-derived growth factor) is mitogenically related to TGF-beta and modulates PDGF, bFGF, and IGF-I action on sparse NIH/3T3 cells

Chicken embryo fibroblast (CEF)-derived growth factor (CDGF), which was recently isolated from serum-free conditioned medium (SFCM) of confluent primary cultures of CEF (A. Geistlich and H. Gehring, Eur. J. Biochem. 207, 147-153, 1992), exhibited a strong mitogenic activity on sparse cultures of NIH/3T3 cells. The activity of CDGF was different from that of SFCM; i.e., the onset of DNA synthesis was delayed for about 7 h. CDGF induced maximally 25% of the activity of serum or SFCM if the activity was measured with a 2-h[3H]thymidine pulse starting 15 h after stimulation of the cells, indicating loss of a protein which modulated the mitogenic activity of CDGF. However, [3H]-thymidine incorporation of cells stimulated with approximately 50 pM CDGF reached serum values after prolongation of the thymidine pulse to 24 h. PDGF, at a concentration of approximately 300 pM, and bFGF (approximately 10 pM) exhibited strong activities in the 2-h pulse, whereas TGF-beta behaved like CDGF. IGF-I induced [3H]thymidine incorporation only weakly and only in the 2-h pulse. EGF did not induce any [3H]thymidine incorporation at all. CDGF together with small concentrations of bFGF (3.5 pM), higher concentrations of PDGF (300 pM), or IGF-I (1 nM) increased synergistically thymidine incorporation in the 2-h pulse, exceeding in the case of PDGF and bFGF the values obtained with 10% serum. Such a synergism could not be demonstrated with alpha-fetoprotein or fetuin, two serum proteins which have been reported to cooperate with growth factors. Regarding induction of cellular growth, only PDGF proved similar to serum, whereas cells stimulated with CDGF or TGF-beta showed a decreased rate of multiplication during the first day after stimulation. After this lag, however, CDGF- and TGF-beta-stimulated cells grew also with a rate similar to that obtained with serum, indicating the induction of an autocrine mitogen by CDGF or TGF-beta. FGF, IGF-I, and PDGF all enhanced CDGF-induced cell growth during the first day, whereas an additive stimulation over at least 2 days was observed with PDGF. CDGF behaved similar to TGF-beta in the synergism with IGF-I.

TGF beta signals through a heteromeric protein kinase receptor complex

Transforming growth factor beta (TGF beta) binds with high affinity to the type II receptor, a transmembrane protein with a cytoplasmic serine/threonine kinase domain. We show that the type II receptor requires both its kinase activity and association with another TGF beta-binding protein, the type I receptor, to signal growth inhibition and early gene responses. Receptors I and II associate as interdependent components of a heteromeric complex: receptor I requires receptor II to bind TGF beta, and receptor II requires receptor I to signal. This mode of operation points to fundamental differences between this receptor and the protein-tyrosine kinase cytokine receptors.

Transforming growth factor beta within fibrotic scleroderma lungs

PURPOSE, PATIENTS, AND METHODS

Since transforming growth factor beta (TGF beta) has been implicated as an important mediator of pulmonary fibrosis, we measured TGF beta protein and gene expression in alveolar epithelial lining fluid (ELF) of fibrotic scleroderma lungs sampled by bronchoalveolar lavage (BAL). TGF beta protein was qualitatively examined by Western blot analysis, and quantitatively by radioreceptor assays. Gene expression was evaluated in BAL mononuclear cells by Northern blot analysis with quantification of relative gene expression by densitometric analysis of the autoradiograms.

RESULTS

Normal and scleroderma subjects had a 24-kd protein that comigrated with defined human TGF beta 1 and immunoreacted with anti-TGF beta antibody. The normal population had a significantly higher average TGF beta concentration (705 pM) compared with the scleroderma subjects (177 pM). The TGF beta 1 gene was expressed in amounts that did not significantly differ between the scleroderma and normal groups. On an individual subject basis, the TGF beta concentration variability did not correlate with variations in BAL cellularity or TGF beta 1 gene expression within the recovered mononuclear cells.

CONCLUSIONS

It is concluded that both normal and fibrotic lungs have TGF beta 1 present at the alveolar epithelial surface. However, in the fibrotic scleroderma lungs, TGF beta protein content and gene expression were not increased at the alveolar epithelial surface. The simultaneous analysis of TGF beta protein content, gene expression, and cellular constituents within individual ELF specimens showed that the cellular components of the ELF do not appear to be major determinants of TGF beta protein concentration at the alveolar epithelial surface.

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.

Structure, function and possible clinical application of transforming growth factor-beta

Transforming growth factor-beta (TGF-beta) is a family of multifunctional 25 kDa proteins. TGF-beta was originally identified because of its ability to induce the growth of normal rodent fibroblasts in soft agar, but is now known as a potent growth inhibitor for many different cell types. In addition, TGF-beta is known to regulate the differentiation of cells, induce chemotaxis of cells, and to induce the accumulation of extracellular matrix proteins. In vivo, TGF-beta stimulates the repair of soft as well as hard tissues. It also acts as a potent immunosuppressant. TGF-beta is produced as latent high molecular weight complexes; since it is produced by many different cell types, and most cells have receptors for TGF-beta, the activation of latent TGF-beta is likely to be an important step in the regulation of its action. TGF-beta exerts its effects by binding to specific cell surface receptors. The type I and type II TGF-beta receptors are suggested to be the most important for signal transduction; a recent report has disclosed that the type II receptor has a serine/threonine kinase domain. Since TGF-beta is a potent growth regulator with multifunctional activity, it may be useful in the treatment of certain clinical disorders. Local application of TGF-beta is shown to accelerate wound healing. Since an increase in TGF-beta activity is often observed in various fibrotic disorders, antagonists for TGF-beta might be valuable in the treatment of such diseases.

Evolutionary origins of the transforming growth factor-beta gene family

A molecular phylogeny for the transforming growth factor-beta (TGF-beta) gene family based on a comparison of nucleotide sequences is proposed. A phylogenetic tree constructed from these sequences shows that the family evolved from a common ancestral gene that came into existence at about the time of arthropod and chordate divergence. This model suggests that the present day TGF-beta gene family consists of four members: TGF-beta 1 (= TGF-beta 4), TGF-beta 2, TGF-beta 3, and TGF-beta 5. The molecular phylogeny and Southern hybridization data also suggest that the proteins for mammalian TGF-beta 1 and chicken TGF-beta 4 are the products of homologous rather than duplicated genes. If the gene duplication event that produced the ancestral gene for TGF-beta 1 occurred before the divergence of birds and mammals, then sufficient time would have elapsed to generate these quite distinct avian and mammalian TGF-beta 1 proteins. Therefore, the TGF-beta family contains four distinct proteins, TGF-beta 1, 2, 3, and 5.

[Function, molecular structure and gene expression regulation of transforming growth factor-beta (TGF-beta)]

Transforming growth factor-beta (TGF-beta) is a multifunctional peptide growth factor widely distributed in vertebrates and represents a prototype of a large family of structurally related factors that regulate various cellular functions, ranging from amphibian embryonal development to hormone production in the human pituitary. TGF-beta is a disulfide-bonded homodimer of a subunit of 12.5 kD that is derived from a much larger precursor. The amino acid sequences of TGF-betas are highly conserved among species, suggesting their physiological importance. TGF-beta was originally isolated from human platelets as a factor that induces anchorage-independent growth of normal fibroblasts. However, later studies have revealed that its major biological activities include inhibition of cell proliferation, and regulation of differentiation, cell adhesion and extracellular matrix deposition. There are three types of cellular receptors that bind TGF-beta. Type II receptor, of which cDNA was recently cloned, is a functional serine/threonine kinase and is thought to be involved in the TGF-beta-mediated signal transduction pathway. The importance of TGF-beta in clinical medicine will increase not only as it is a promising therapeutic drug, but also as its excessive activity can be the cause of various human fibrotic diseases.

Transforming growth factor-beta 1 is a heparin-binding protein: identification of putative heparin-binding regions and isolation of heparins with varying affinity for TGF-beta 1

Previous studies indicated that a major factor in heparin's ability to suppress the proliferation of vascular smooth muscle cells is an interaction with transforming growth factor-beta 1 (TGF-beta 1). Heparin appeared to bind directly to TGF-beta 1 and to prevent the association of TGF-beta 1 with alpha 2-macroglobulin (alpha 2-M). The present studies indicate that 20-70% of iodinated TGF-beta 1 binds to heparin-Sepharose and the retained fraction is eluted with approximately 0.37 M NaCl. Native, unlabelled platelet TGF-beta 1, however, is completely retained by heparin-Sepharose and eluted with 0.9-1.2 M NaCl. Using synthetic peptides, the regions of TGF-beta 1 that might be involved in the binding of heparin and other polyanions were examined. Sequence analysis of TGF-beta 1 indicated three regions with a high concentration of basic residues. Two of these regions had the basic residues arranged in a pattern homologous to reported consensus heparin-binding regions of other proteins. The third constituted a structurally novel pattern of basic residues. Synthetic peptides homologous to these three regions, but not to other regions of TGF-beta 1, were found to bind to heparin-Sepharose and were eluted with 0.15 M-0.30 M NaCl. Only two of these regions were capable of blocking the binding of heparin to 125I-TGF-beta. Immobilization of these peptides, followed by affinity purification of heparin, indicated that one peptide was capable of isolating subspecies of heparin with high and low affinity for authentic TGF-beta 1. The ability of TGF-beta 1 to bind to heparin or related proteoglycans under physiological conditions may be useful in understanding the biology of this pluripotent growth and metabolic signal. Conversely, a subspecies of heparin molecules with high affinity for TGF-beta 1 may be a factor in some of the diverse biological actions of heparin.

An unusual feature revealed by the crystal structure at 2.2 A resolution of human transforming growth factor-beta 2

Transforming growth factor type beta 2 (TGF-beta 2) is a member of an expanding family of growth factors that regulate proliferation and differentiation of many different cell types. TGF-beta 2 binds to various receptors, one of which was shown to be a serine/threonine kinase. TGF-beta 2 is involved in wound healing, bone formation and modulation of immune functions. We report here the crystal structure of TGF-beta 2 at 2.2 A resolution, which reveals a novel monomer fold and dimer association. The monomer consists of two antiparallel pairs of beta-strands forming a flat curved surface and a separate, long alpha-helix. The disulphide-rich core has one disulphide bone pointing through a ring formed by the sequence motifs Cys-Ala-Gly-Ala-Cys and Cys-Lys-Cys, which are themselves connected through the cysteines. Two monomers are connected through a single disulphide bridge and associate such that the helix of one subunit interacts with the concave beta-sheet surface of the other. Four exposed loop regions might determine receptor specificity. The structure provides a suitable model for the TGF-beta s and other members of the super-family and is the basis for the analysis of the TGF-beta 2 interactions with the receptor.

Crystal structure of transforming growth factor-beta 2: an unusual fold for the superfamily

The transforming growth factors-beta (TGF-beta 1 through -beta 5) are a family of homodimeric cytokines that regulate proliferation and function in many cell types. Family members have 66 to 80% sequence identity and nine strictly conserved cysteines. A crystal structure of a member of this family, TGF-beta 2, has been determined at 2.1 angstrom (A) resolution and refined to an R factor of 0.172. The monomer lacks a well-defined hydrophobic core and displays an unusual elongated nonglobular fold with dimensions of approximately 60 A by 20 A by 15 A. Eight cysteines form four intrachain disulfide bonds, which are clustered in a core region forming a network complementary to the network of hydrogen bonds. The dimer is stabilized by the ninth cysteine, which forms an interchain disulfide bond, and by two identical hydrophobic interfaces. Sequence profile analysis of other members of the TGF-beta superfamily, including the activins, inhibins, and several developmental factors, imply that they also adopt the TGF-beta fold.

Identification of a structural domain that distinguishes the actions of the type 1 and 2 isoforms of transforming growth factor beta on endothelial cells

A chimeric transforming growth factor beta (TGF-beta) molecule has been synthesized to map the amino acids responsible for the substantially greater activity of TGF-beta 1 than TGF-beta 2 on growth and migration of endothelial cells. This chimera consists of a dimer of a monomeric unit composed of amino acids 1-39 of TGF-beta 2, 40-82 of TGF-beta 1, and 83-112 of TGF-beta 2. Structural identity of the purified recombinant protein has been confirmed by immunoblotting and NH2-terminal sequencing. The biological potency of the TGF-beta 2-1-2 chimera was equal to that of TGF-beta 1 in inhibition of growth of both fetal bovine heart endothelial cells and rat epididymal fat pad microvascular endothelial cells. Similarly, the TGF-beta 2-1-2 chimera was nearly equivalent to TGF-beta 1 and at least 10-fold more active than TGF-beta 2 in inhibiting migration of bovine aortic endothelial cells. These results identify the sequence between amino acids 40-82 as an important region within TGF-beta that functions to specify a TGF-beta 1- or TGF-beta 2-like activity.

Transforming growth factor beta 1-specific binding proteins on human vascular endothelial cells

Transforming growth factor beta (TGF beta) regulates the growth of human umbilical vein endothelial cells (HUVEC) differently depending on the isoform of TGF beta and the culture conditions. The cells are resistant to growth inhibition by TGF beta when the cells are cultured on substratum coated with gelatin. However, the proliferation of HUVEC cultured on substratum without a gelatin coating is inhibited by TGF beta, depending on the isoform and concentration of TGF beta. Binding assays with 125I-TGF beta 1 reveal that HUVEC contain a single class of high-affinity (Kd = 4.4 pM) TGF beta 1 binding sites with 8500 sites per cell. Affinity cross-linking studies demonstrate that HUVEC express 180 and 80 kDa TGF beta 1 binding sites that do not bind TGF beta 2. The reduction and the removal of glycosaminoglycans does not affect the electrophoretic mobility of the 180-kDa binding protein cross-linked with 125I-TGF beta 1. Therefore, the 180-kDa TGF beta 1 binding protein is not related to the type III TGF beta receptor, but might be a novel TGF beta 1-specific receptor/binding protein expressed on vascular endothelial cells. The expression of TGF beta 1 binding sites is not affected by the presence or absence of the gelatin coating on the culture substratum. The data suggest that a gelatin coating does not regulate the susceptibility of HUVEC to TGF beta 1 at the level of the receptor/binding proteins, and that growth inhibition of HUVEC by TGF beta 1 is linked to the regulation of extracellular matrices required for the interaction between the cells and the substratum.

Glucocorticoid regulation of transforming growth factor-beta activation in urogenital sinus mesenchymal cells

The transforming growth factors-beta (TGF-beta s) regulate many aspects of cell proliferation and differentiation. The TGF-beta isoforms are produced by most cell types in the biologically inactive, latent form. The physiological relevance of latent TGF-beta and the regulation of activation to the biologically active form are not well understood. Although expression of TGF-beta messenger RNA is regulated by the steroid hormone family, the mechanisms of hormonal regulation of TGF-beta activation have not been well studied. Fetal rat urogenital sinus organ cultures and derived mesenchymal cell lines (U4F, U4F1) have been established in order to analyze the expression of growth and differentiation regulatory factors which may function in mesenchymal induction of epithelial differentiation. The U4F1 cell line in chemically defined medium upon supplementation with dexamethasone (10 nM-1.4 microM), produced an activity which was growth inhibitory to PC-3 prostatic carcinoma epithelial cells. Analysis of physicochemical properties and purification of activity demonstrated a 25-kDa protein was responsible for activity. The activity cross-reacted to antisera specific for TGF-beta 1, beta 2 and for TGF-beta 2 exclusively, but not with antisera to rat interferon (alpha-beta) or rat interleukin 6. Acid treatment of control (unsupplemented) conditioned medium and cultures supplemented with other steroid hormones produced identical levels of activated TGF-beta as nonacid-treated conditioned medium from dexamethasone supplemented cultures which did not increase levels of activity upon acid activation. Activity from the acid-treated control conditioned medium was neutralized by TGF-beta antibodies. These data suggest latent TGF-beta is produced constitutively by U4F1 mesenchymal cultures in steroid unsupplemented medium and these cultures are induced by dexamethasone to activate identical levels of TGF-beta. These observations may be relevant to understanding diverse aspects of glucocorticoid regulation of tissue function and suggests that TGF-beta may be relevant to paracrine and autocrine growth regulation in the developing urogenital sinus.

Differential expression of TGF beta isoforms by human articular chondrocytes in response to growth factors

Transforming growth factor beta (TGF beta) is a family of important regulators of chondrocyte growth and differentiation. Although TGF beta has been detected in cartilage, the TGF beta isoforms expressed by chondrocytes and their regulation by growth factors are unknown. This study shows that human articular chondrocytes release TGF beta activity. Chondrocyte conditioned media contains active TGF beta and larger quantities in latent form. By neutralization with specific antibodies it is shown that all three isoforms (TGF beta 1, TGF beta 2, and TGF beta 3) are secreted by chondrocytes. Analysis of the inducers of TGF beta gene expression demonstrates complex regulation of TGF beta production by growth factors. Basic fibroblast growth factor (bFGF) stimulates the release of TGF beta activity but has no effect on steady state TGF beta mRNA levels while platelet-derived growth factor (PDGF) upregulates TGF beta 1 and TGF beta 3 mRNAs with a corresponding increase in protein secretion. The three TGF beta isoforms themselves differentially affect gene expression. While TGF beta 1 and TGF beta 2 show autoinduction, TGF beta 3 upregulates TGF beta 1 but does not affect TGF beta 2 mRNA levels. These results demonstrate that human articular chondrocytes produce all three TGF beta isoforms. Induction of TGF beta expression is differentially regulated by various growth factors and occurs at the mRNA level and/or posttranscriptionally. Chondrocyte expression and the differential regulation of TGF beta 1, TGF beta 2, and TGF beta 3 by growth factors suggest that all three isoforms of TGF beta are part of the network of cartilage regulatory factors.

A large domain common to sperm receptors (Zp2 and Zp3) and TGF-beta type III receptor

A new family of mosaic proteins is defined by sequence analysis. The family is characterized by a 260 residue domain common to proteins of apparently diverse function and tissue specificity: sperm receptors Zp2 and Zp3, betaglycan (also called TGF-beta type III receptor), uromodulin, as well as the major zymogen granule membrane protein (GP-2). The location of the common domain is similar with respect to putative transmembrane regions. The results lead to the hypothesis that this type of domain has a common tertiary structure and that there is a functional similarity in the recognition mechanism of the sperm receptor system and the TGF-beta receptor complex.

Neutralizing antibodies against transforming growth factor beta potentiate the proliferation of Ki-1 positive lymphoma cells. Further evidence for negative autocrine regulation by transforming growth factor beta

Activated lymphocytes and malignant lymphoma cells derived from them (Ki-1 positive lymphoma cells) share similar mechanisms of proliferation. To further examine the inhibitory role of endogenous transforming growth factor beta (TGF beta) in Ki-1 positive lymphoma cells, the authors studied anti-TGF beta antibodies and measured their effect on proliferation. A monoclonal antibody (T1A5) prepared against a unique antigenic epitope of high molecular weight Hodgkin's TGF beta and a polyclonal rabbit antibody prepared against highly purified 25,000 D porcine platelet TGF beta 1 were used. Both antibodies are shown here to inhibit the biological activity of Hodgkin's TGF beta and to crossreact with their respective antigens in immunoblotting. DNA synthesis by Ki-1 lymphoma cells was increased 138-fold by anti-TGF beta 1 antibody and 262-fold by anti-Hodgkin's TGF beta. Exogenous TGF beta 1 suppression was completely reversed by anti-TGF beta 1 antibody and IL-2-induced proliferation was markedly potentiated (41 fold). L-428 Reed-Sternberg cells secrete physiologically active TGF beta but have fewer than 500 TGF beta receptor sites per cell; no significant proliferative response was measured for either anti-TGF beta 1 or anti-Hodgkin's TGF beta. These results show the suppressive effect of exogenous TGF beta 1 on indolent Ki-1 lymphoma cells and suggest that the endogenous secretion of high molecular weight physiologically active TGF beta is important in maintaining the indolent nature of this low-grade Ki-1 positive lymphoma.

Purification and characterization of transforming growth factor-beta 2.3 and -beta 1.2 heterodimers from bovine bone

A unique form of transforming growth factor-beta (TGF-beta), TGF-beta 2.3 heterodimer, has been purified from bovine bone extract. TGF-beta 2.3 migrated as a single 25-kDa band by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, whereas under reducing conditions it migrated as a 12.5 kDa band. The TGF-beta 2.3 reacted positively with anti-TGF-beta 2 and anti-TGF-beta 3 antibodies on immunoblots. Equal levels of TGF-beta 2 and TGF-beta 3 sequences were detected by N-terminal sequencing. TGF-beta 2.3 eluted as a single sharp peak by reverse-phase high performance liquid chromatography. However, prior reduction of the protein with dithiothreitol resulted in the protein eluting in two peaks, one containing predominantly TGF-beta 3 and the other containing predominantly TGF-beta 2. TGF-beta 2.3 inhibited proliferation of mink lung epithelial cells and promoted the formation of colonies of normal rat kidney fibroblasts in culture with specific biological activity similar to those of TGF-beta 1 and TGF-beta 2. These results demonstrate that the protein is TGF-beta 2.3 heterodimer, consisting of one polypeptide chain each of TGF-beta 2 and TGF-beta 3 linked by one or more disulfide bonds. In addition, TGF-beta 1.2 heterodimer, previously found only in porcine platelets, has also been purified from bovine bone extract.

Isolation and characterization of transforming growth factor beta response variants from human prostatic tumor cell lines

In this study we examined the relation between the response to transforming growth factor beta (TGF beta 1) in vitro and the growth in vivo of 1-LN-PC3-1A (1-LN) human prostatic carcinoma cells. 1-LN cells resistant to the growth-inhibitory effects of TGF beta 1 were isolated after exposure to 2 ng/ml TGF beta 1 in an anchorage-independent growth assay. Cloning of TGF beta 1-resistant and -sensitive populations produced 2 clones (R2-6 and 1-LN clone 4), which maintained relatively stable resistance or sensitivity, respectively, in the absence of TGF beta 1 for up to 12 passages. Colony formation by the R2-6 cells in the presence of TGF beta 1 was 2-10 times greater than that of 1-LN clone 4, depending upon the TGF beta 1 concentration. Injection of 1 x 10(5) R2-6 cells into athymic nude mice produced tumors with a significantly shorter latency interval as compared with 1-LN clone 4 tumors (P < 0.0001). Western immunoblotting showed that higher levels of latent TGF beta 1 protein were secreted into the culture medium by 1-LN clone 4 cells. Acidified conditioned media from both clones inhibited mink lung epithelial cell DNA synthesis. Neutralizing monoclonal antibody to TGF beta 1 but not TGF beta 2 abrogated this inhibitory effect. Comparison of the different sensitive and resistant clones showed that in vitro sensitivity to TGF beta 1 and in vivo tumor latency interval were not invariably correlated. Thus, the TGF beta 1 response phenotype in vitro was not always predictive of growth delay in vivo.

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.

Regulation of expression of transforming growth factor-beta 2 by transforming growth factor-beta isoforms is dependent upon cell type

The effect of three different isoforms of transforming growth factor-beta (TGF-beta) on the expression of TGF-beta 2 mRNA was studied in several continuous tumor cell lines. As previously reported for the mouse fibroblast cell line AKR-2B, the expression of TGF-beta 2 mRNA transcripts of 5.4, 4.7, 3.7 and 3.0 kb was decreased after a 24 hr treatment with 5 ng/ml of TGF-beta 1, TGF-beta 2 or TGF-beta 3. In A549, HBL-100 and BSC-1 epithelial cell lines, five distinct TGF-beta 2 mRNA transcripts of 5.8, 5.1, 4.0, 3.8 and 2.8 kb were detected by Northern blot analysis. Treatment of these cells with TGF-beta 1, TGF-beta 2 or TGF-beta 3 for 24 hr resulted in a 2-3 fold increase in the 5.8, 4.0 and 3.8 kb transcripts, with little detectable change in abundance of the 5.1 and 2.8 kb transcripts. The effect of the TGF-beta proteins was dose (5 ng/ml) and time (3-6 hr) dependent. A similar 2-3 fold increase in the level of secreted TGF-beta 2 was observed following treatment of A549 cells with TGF-beta 1. Basal level and induced expression of TGF-beta 2 mRNA in response to TGF-beta isoforms was decreased in the presence of actinomycin D. In all cell lines studied, the expression of the 2.5 kb TGF-beta 1 mRNA was relatively unchanged or markedly increased in response to treatment with TGF-beta.(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming growth factors beta 1 and beta 2 are differentially expressed in fibrotic liver disease

Transforming growth factor (TGF) beta 1 has been implicated in the control of hepatocyte growth and stimulation of extracellular matrix synthesis in acute and chronic liver disease. The cellular localization of transforming growth factor (TGF) beta 1 and beta 2 RNA transcripts was determined in normal and fibrotic liver by in situ hybridization with [35S]-labeled RNA probes in combination with immunostaining for cell type characteristic markers. Fibrotic specimens were from patients with hepatitis B virus infection or alcohol abuse and rats with fibrosis secondary to bile duct ligation and scission. In normal liver, low levels of TGF beta 1 transcripts were found in some portal tract stromal cells, and TGF beta 2 RNA was not detectable. In fibrotic liver, high TGF beta 1 RNA levels were present in most mesenchymal liver cells, in most inflammatory cells, and in few bile duct epithelial cells. Hepatocytes did not express this cytokine with the exception of few limiting plate hepatocytes in cases of human cirrhosis with high activity. TGF beta 2 transcripts were detected at high levels in proliferating bile ducts of fibrotic livers, but were absent in all other cell types. TGF beta 1 expression in the liver is thus a function predominantly of mononuclear and mesenchymal cells as well as of some hepatocytes, whereas TGF beta 2 expression is a specific property of bile duct epithelial cells that may be related to the formation of specialized periductular connective tissue during bile duct proliferation.

Localization of transforming growth factor-beta 1, -beta 2 and -beta 3 gene expression in bovine mammary gland

We have studied the expression of transforming growth factor (TGF)-beta 1, -beta 2, and -beta 3 in the non-lactating and lactating bovine mammary gland by in situ hybridization. All three isoforms were expressed in the lobuloalveolar framework of the non-lactating and lactating gland although marked differences were apparent in their spatial distribution. TGF-beta 1 was expressed predominantly by the epithelial cells of the lobules although expression was also observed in the intralobular stroma cells lining the epithelium. In contrast, TGF-beta 2 expression was only observed in the epithelial cells. TGF-beta 3 transcripts were expressed at the highest levels and were observed in almost all cells of the lobule. No TGF-beta signals were found in the interlobular regions of the mammary gland. The possible regulatory functions of these molecules in development of the mammary gland and on differentiation processes in the neonate are discussed.

Separation, purification, and sequence identification of TGF-beta 1 and TGF-beta 2 from bovine milk

Cox and Bürk (Eur. J. Biochem., 1991) reported the partial characterization of Milk Growth Factor (MGF) which stimulated the migration of fibroblasts. We have fractionated the partially purified sample by RP-HPLC and obtained the separation of two peaks of activity. The two active components were isolated as pure MGF-a and MGF-b by RP-HPLC and preparative SDS-PAGE. The purified MGF-a, consisting of a single band by gel electrophoresis and a single peak on an HPLC reversed-phase C-4 column, has the same specific activity as TGF-beta 2 in the fibroblast migration assay. MGF-a was digested by endoprotease Asp-N and the cleaved peptides were analyzed by Edman degradation and plasma desorption mass spectrometry (PDMS). The whole sequence of MGF-a determined by automated sequenator and PDMS of S-pyridylethylated protein and selected fragments was found to be identical to that of TGF-beta 2. MGF-b protein mixture separated by SDS-PAGE was electrophoretically transferred onto a Biometra Glassybond membrane, and the blotted MGF-b protein was directly sequenced on an automated sequenator. The identified 29 amino acids sequence of MGF-b was identical to the amino-terminal sequence of TGF-beta 1. Our study demonstrates that MGF is composed of both TGF-beta 1 and TGF-beta 2. TGF-beta 2 (85%) is the predominant form.