Physiological actions and clinical applications of transforming growth factor-beta (TGF-beta)

Structure and expression of the promoter for the R4/ALK5 human type I transforming growth factor-beta receptor: regulation by TGF-beta

The type I transforming growth factor-beta (TGF-beta) receptors are serine/threonine kinases that are essential for the action of TGF-beta. In this paper, we describe the molecular cloning and expression of the R4/ALK5 human type I TGF-beta receptor promoter. DNA sequence analysis indicates that the promoter lacks a TATA and CAAT box but is highly GC-rich and contains putative Sp1 binding sites. The transcriptional start site is approx. 232 base pairs upstream of the AUG start codon. In human lung fibroblasts, TGF-beta induced a 3-fold increase in steady-state level for type I receptor mRNA. Exposure of cells transfected with a 618 bp promoter fragment to TGF-beta 1 up-regulated transcriptional activity indicating that a TGF-beta response element is contained within this region.

Mad-related genes in the human

Resistance to the growth inhibitory effects of TGF-beta is common in human cancers. However, the mechanism(s) by which tumour cells become resistant to TGF-beta are generally unknown. We have identified five novel human genes related to a Drosophila gene called Mad which is thought to transduce signals from TGF-beta family members. One of these genes was found to be somatically mutated in two of eighteen colorectal cancers, and three of the other genes were located at chromosomal positions previously suspected to harbor tumour suppressor genes. These data suggest that this gene family may prove to be important in the suppression of neoplasia, imparting the growth inhibitory effects of TGF-beta-like ligands.

The role of growth factors in wound healing

Growth factors have many activities that make them attractive agents for stimulating tissue repair. Growth factors attract cells into the wound, stimulate their proliferation, and have profound influence on extracellular matrix deposition. Since developing the ability to mass-produce these cytokines by recombinant techniques, hundreds of studies have demonstrated that growth factors can augment all aspects of tissue repair in normal and impaired healing models. After demonstrating that growth factors augment healing, investigators have started to detect and measure growth factors in wounds and have found that wounding initiates the expression of various growth factors. Impaired healing has also been linked to altered growth factor production. These findings have prompted great interest in the use of growth factors to augment clinical healing. Preliminary clinical trials have not produced the results expected. Growth factor treatment has occasionally led to statistically significant improvements in tissue repair, but whether the results are clinically significant can be debated. It appears that to be cost effective, clinical trials must focus on targeting growth factors for specific types of impaired healing. Although growth factors have not been the panacea that was originally expected, they have the potential for making significant clinical improvements when targeted for specific problem wounds.

The recombinant proregion of transforming growth factor beta1 (latency-associated peptide) inhibits active transforming growth factor beta1 in transgenic mice

All three isoforms of transforming growth factors beta (TGF-betal, TGF-beta2, and TGF-beta3) are secreted as latent complexes and activated extracellularly, leading to the release of the mature cytokines from their noncovalently associated proregions, also known as latency-associated peptides (LAPs). The LAP region of TGF-beta1 was expressed in a baculovirus expression system and purified to homogeneity. In vitro assays of growth inhibition and gene induction mediated by TGF-beta3 demonstrate that recombinant TGF-beta1 LAP is a potent inhibitor of the activities of TGF-betal, -beta2, and -beta3. Effective dosages of LAP for 50% neutralization of TGF-beta activities range from 4.7- to 80-fold molar excess depending on the TGF-beta isoform and activity examined. Using 125I-labeled LAP, we show that the intraperitoneal application route is effective for systemic administration of LAP. Comparison of concentrations of LAP in tissues shows a homogenous pattern in most organs with the exception of heart and muscle, in which levels of LAP are 4- to 8-fold lower. In transgenic mice with elevated hepatic levels of bioactive TGF-betal, treatment with recombinant LAP completely reverses suppression of the early proliferative response induced by TGF-beta1 in remnant livers after partial hepatectomy. The results suggest that recombinant LAP is a potent inhibitor of bioactive TGF-beta both in vitro and in vivo, after intraperitoneal administration. Recombinant LAP should be a useful tool for novel approaches to study and therapeutically modulate pathophysiological processes mediated by TGF-beta3.

Endoglin modulates cellular responses to TGF-beta 1

Endoglin is a homodimeric membrane glycoprotein which can bind the beta 1 and beta 3 isoforms of transforming growth factor-beta (TGF-beta). We reported previously that endoglin is upregulated during monocyte differentiation. We have now observed that TGF-beta itself can stimulate the expression of endoglin in cultured human monocytes and in the U-937 monocytic line. To study the functional role of endoglin, stable transfectants of U-937 cells were generated which overexpress L- or S- endoglin isoforms, differing in their cytoplasmic domain. Inhibition of cellular proliferation and downregulation of c-myc mRNA which are normally induced by TGF-beta 1 in U-937 cells were totally abrogated in L-endoglin transfectants and much reduced in the S-endoglin transfectants. Inhibition of proliferation by TGF-beta 2 was not altered in the transfectants, in agreement with the isoform specificity of endoglin. Additional responses of U-937 cells to TGF-beta 1, including stimulation of fibronectin synthesis, cellular adhesion, platelet/endothelial cell adhesion molecule 1 (PECAM-1) phosphorylation, and homotypic aggregation were also inhibited in the endoglin transfectants. However, modulation of integrin and PECAM-1 levels and stimulation of mRNA levels for TGF-beta 1 and its receptors R-I, R-II, and betaglycan occurred normally in the endoglin transfectants. No changes in total ligand binding were observed in L-endoglin transfectants relative to mock, while a 1.5-fold increase was seen in S-endoglin transfectants. The degradation rate of the ligand was the same in all transfectants. Elucidating the mechanism by which endoglin modulates several cellular responses to TGF-beta 1 without interfering with ligand binding or degradation should increase our understanding of the complex pathways which mediate the effects of this factor.

Altered CD3 chain and cytokine gene expression in tumor infiltrating T lymphocytes during the development of mesothelioma

The mechanisms whereby tumors escape immunosurveillance remain poorly understood. De-activation or deviation of T lymphocyte responses may occur following exposure to tumor-associated or -derived signals. In the present study it is demonstrated that during development of syngeneic malignant mesothelioma in mice, the relative CD3 delta, CD3 gamma and CD3 zeta mRNA levels expressed by tumor infiltrating lymphocytes (TIL) decrease, while CD3 epsilon mRNA levels remain relatively constant. Expression of IFN gamma mRNA by TIL decreased during tumor development, while IL-2 mRNA levels showed slight increases. IL-3 mRNA was not detected at any time during tumor development and IL-4 transcripts were detected in the later stages of tumor development. In the spleens of tumor-bearing mice, IL-2 transcripts were detected throughout the time course from days 1 to 22(24), while IFN gamma mRNA was only detected at early times from days 0-13. Previous work demonstrated a role for tumor cell-derived TGF beta in the immunobiology of mesothelioma. Here it is shown that the suppression of CD3-subunit expression by TIL was ameliorated in tumors where TGF beta -expression was reduced by inducible TGF beta-specific antisense-RNA, thus, suggesting that lymphocytes may become de-activated upon infiltration of the tumor micro-environment.

Intragraft TGF-beta 1 mRNA: a correlate of interstitial fibrosis and chronic allograft nephropathy

Chronic allograft nephropathy is a relentlessly progressive process and a major cause of long-term graft dysfunction and ultimate failure. Interstitial fibrosis, tubular atrophy, and glomerular and vascular lesions characterize this mechanistically unresolved disorder. Given the prominent role of TGF-beta 1 in tissue repair and in fibrosis, we have explored the hypothesis that fibrosis and chronic allograft nephropathy would be distinguished by intragraft TGF-beta 1 mRNA expression. This postulate was tested by mRNA phenotyping of RNA isolated from 127 human renal allograft biopsies. Reverse transcription assisted polymerase chain reaction was used to amplify and identify ingraft gene expression. Our investigation demonstrated a significant correlation between intragraft TGF-beta 1 mRNA display and renal allograft interstitial fibrosis and chronic allograft nephropathy. In contrast, intragraft expression of mRNA encoding immunoregulatory cytokines, IL-2, IFN-gamma, IL-4, IL-10, or cytotoxic attack molecules, granzyme B and perforin was not a correlate of interstitial fibrosis or chronic allograft nephropathy. Our studies identify, for the first time, a significant association between intragraft TGF-beta 1 mRNA expression and renal allograft interstitial fibrosis, and advance a candidate molecular mechanism for chronic allograft nephropathy.

Vascular endothelial growth factor production is stimulated by gangliosides and TGF-beta isoforms in human glioma cells in vitro

Vascular endothelial growth factor (VEGF) is an angiogenic factor which is known to be expressed in several malignancies including glioma. The effect of transforming growth factor-beta (TGF-beta) isoforms as well as gangliosides on VEGF production was investigated in human glioma cell lines. TGF-beta isoforms and gangliosides were found to differentially stimulate VEGF production by these cells. The ganglioside GD3 enhanced this release to the greatest extent and the stimulation was more marked in a glioblastoma cell line than in the two other anaplastic astrocytoma cell lines. These results suggest that both TGF-betas and gangliosides may act as indirect angiogenic factors by stimulating VEGF secretion.

Regulation and interactions of transforming growth factor-beta with cardiovascular cells: implications for development and disease

1. Transforming growth factors-beta (TGF-beta) are multifunctional proteins that regulate cell growth, differentiation, migration and extracellular matrix production and have an important role in embryonic development and tissue remodelling. 2. The diverse biological actions of TGF-beta are elicited following their interaction with type I and type II TGF-beta receptors, both of which are transmembrane serine/threonine kinases, suggesting an important role for protein phosphorylation in the mechanism of action of these cytokines on the growth of cells and their extracellular environment. 3. Alterations in TGF-beta gene expression and action in various cell types associated with the cardiovascular system may contribute to the pathophysiology of a number of diseases, such as hypertension, atherosclerosis and restenosis, as well as the development of cardiac abnormalities.

Serum levels of the TGF-beta receptor are increased in atherosclerosis

Murine monoclonal antibody E9 recognises a transforming growth factor (TGF) beta receptor, which is expressed in increased amounts by activated endothelial cells. In order to examine the biological role of this molecule in atherosclerosis, we have measured levels of the TGF-beta receptor alongside those of two other endothelial cell products (von Willebrand factor and soluble E-selectin) in the serum of 55 patients with atherosclerosis (29 with ischaemic heart disease and 26 with peripheral vascular disease), and in a cohort of 26 age- and sex-matched asymptomatic controls. There were increased levels of the TGF-beta receptor (P = 0.0079) and von Willebrand factor (P = 0.0001), but not soluble E-selection in patients' serum relative to the controls. In multivariate analysis of the endothelial cell products against total cholesterol, high density lipoprotein cholesterol and low density lipoprotein cholesterol, triglycerides, systolic and diastolic blood pressures, age, sex and smoking, both the TGF-beta receptor and von Willebrand factor correlated with total cholesterol (Spearman's r = 0.37 and r = 0.35, respectively, both P < 0.001). Lack of a correlation with a coarse endothelial damage marker von Willebrand factor or soluble E-selectin (produced by immunologically stimulated endothelial cells) implies other mechanisms are responsible for increased levels of the TGF-beta receptor in serum of patients with atherosclerosis.

Caenorhabditis elegans genes sma-2, sma-3, and sma-4 define a conserved family of transforming growth factor beta pathway components

Although transforming growth factor beta (TGF-beta) superfamily ligands play critical roles in diverse developmental processes, how cells transduce signals from these ligands is still poorly understood. Cell surface receptors for these ligands have been identified, but their cytoplasmic targets are unknown. We have identified three Caenorhabditis elegans genes, sma-2, sma-3, and sma-4, that have mutant phenotypes similar to those of the TGF-beta-like receptor gene daf-4, indicating that they are required for daf-4-mediated developmental processes. We show that sma-2 functions in the same cells as daf-4, consistent with a role in transducing signals from the receptor. These three genes define a protein family, the dwarfins, that includes the Mad gene product, which participates in the decapentaplegic TGF-beta-like pathway in Drosophila [Sekelsky, J. J., Newfeld, S. J., Raftery, L. A., Chartoff, E. H. & Gelbart, W. M. (1995) Genetics 139, 1347-1358]. The identification of homologous components of these pathways in distantly related organisms suggests that dwarfins may be universally required for TGF-beta-like signal transduction. In fact, we have isolated highly conserved dwarfins from vertebrates, indicating that these components are not idiosyncratic to invertebrates. These analyses suggest that dwarfins are conserved cytoplasmic signal transducers.

Effects of exogenous transforming growth factor-beta 1 on spinal cord injury in rats

This study was undertaken to examine the effect of transforming growth factor-beta 1 (TGF-beta 1) administered into the subarachnoid space after spinal cord injury (SCI) on the increased production of inducible-nitric oxide synthase (i-NOS) in the injured spinal cord in rats. The expression of i-NOS mRNA after SCI was remarkably down-regulated by TGF-beta 1 in vivo. Rats treated with TGF-beta 1 showed a better outcome regarding hindlimb motor dysfunction in the first 5 days after injury compared to the saline-treated rats. However, the final outcome was not better and fibrous scar formation in the injured spinal cord was more evident, which was demonstrated as increased immunoreactivity of fibronectin in the later stage after SCI. These results provide evidence of both positive and negative contributions of TGF-beta 1 to the pathology associated with SCI.

Engineering, expression and renaturation of targeted TGF-beta fusion proteins

This study reports the expression, purification, and renaturation of biologically active Transforming Growth Factor-beta 1 (TGF-beta 1) fusion proteins from Escherichia coli (E. coli). A prokaryotic expression vector was engineered to produce tripartite fusion proteins consisting of (i) a purification tag, (ii) a protease-sensitive linker/collagen binding domain, and (iii) a cDNA sequence encoding the active fragment of human TGF-beta 1. The expressed fusion proteins TGF-B1-F1 and TGF-B1-F2, located in inclusion bodies, were solubilized with 8 M urea and renatured using a glutathione redox-coupled system and protracted dialysis under several experimental conditions. The purification of the recombinant proteins was achieved by binding the His-tag of the fusion proteins on a Ni-NTA metal chelate column. The biological activity of the recombinant growth factor was demonstrated by its ability to inhibit mink lung (Mv1Lu) cell proliferation and/or to stimulate proliferation of NIH-3T3 mouse fibroblasts, where purified human platelet TGF-beta 1 served as a positive control. Purified TGF-B1-F1 and TGF-B1-F2 (collagen-binding) constructs exhibited anti-proliferative activities comparable to purified platelet TGF-beta 1, but at lower specific activities. Binding of the renatured TGF-B1-F2 fusion protein to collagen was demonstrated by stable binding on a collagen-conjugated Sephadex-G15 column. The high affinity binding was also demonstrated by the binding of 3H-collagen to the TGF-B1-F2 protein immobilized on a Ni-NTA column. The TGF-B1-F2 fusion protein bound to collagen coated surfaces with high affinity but exhibited comparatively lower biological activity than the fusion protein in solution, suggesting a potentially latent configuration. Taken together, these results demonstrate that biologically active TGF-beta 1 fusion proteins can be recovered from transformed bacteria by oxidative refolding; thus, providing a means for its high-yield production, purification, and renaturation from microorganisms. Furthermore, these results support the concept that auxiliary domains may be used to modulate and/or target TGF-beta 1 for specific applications.

Human albumin solder supplemented with TGF-beta 1 accelerates healing following laser welded wound closure

BACKGROUND AND OBJECTIVE

We examined the possibility that human albumin solder can be used as a vehicle for site specific delivery of growth factors for the purpose of accelerating tissue repair following laser welded wound closure. Certain human recombinant growth factors have been shown to accelerate wound healing in model systems. Pilot in vitro studies have established that several growth factors, including TGF-beta 1, maintain bioactivity following exposure to temperatures achieved during laser tissue welding. Using a temperature controlled laser delivery system (TCL) to precisely maintain welding temperatures, it is now possible to avoid thermal denaturation of exogenous bioactive molecules such as growth factors.

STUDY DESIGN/MATERIALS AND METHODS

HB-EGF, bFGF, and TGF-beta 1 were tested in vitro for maintenance of bioactivity after exposure to 80 degrees C. In vivo experiments using porcine skin determined the efficacy of solders augmented with growth factors. Incisions were repaired using human albumin alone or supplemented with HB-EGF (2 micrograms), bFGF (10 micrograms), or TGF-beta 1 (1 microgram). Wounds were excised at 3, 5, and 7 days post-operatively. Tensile strength, total collagen content, and histology were performed.

RESULTS

At 3 days, tensile strength (TS) of TGF-beta 1 wounds were 36% (P < 0.05) and 20% (n.s.) stronger than laser alone and suture closures, respectively. By 5 days the TS of the TGF-beta 1 group increased by 50% (P < 0.05) and 59% (P < 0.02) over laser alone and suture groups, respectively. At 7 days the TGF-beta 1 group was 50% (P < 0.05) and 79% (P < 0.01) stronger than laser solder alone or suture, respectively. The HB-EGF and bFGF groups were equivalent to the laser solder group at all time points. Total collagen TGF-beta 1 Accelerates Healing Following Laser Welding content at 7 days increased in the TGF-beta 1 group by 7% (n.s.) over the suture group and 21% (P < 0.05) in the laser group.

CONCLUSION

Human albumin solder supplemented with TGF-beta 1 increases the early post-operative strength of laser welded wounds. This novel application of laser tissue soldering augmented with a growth factor has the potential to bring about immediate fluid tight seals while providing site specific delivery of biological modifiers. This may lead to an overall improvement in post-operative convalescence, wound infections, and hospital costs.

Embryonic expression of glial cell-line derived neurotrophic factor (GDNF) suggests multiple developmental roles in neural differentiation and epithelial-mesenchymal interactions

We describe the cloning of the mouse glial cell line-derived neurotrophic factor (GDNF) gene and its expression during embryogenesis. GDNF is a distant member of the superfamily of TGF-beta related genes that was originally identified on the basis of its striking neurotrophic activity. GDNF is expressed in a highly dynamic pattern in the anterior neuroectoderm during early stages of neurogenesis between E7.5 and E10.5. Beginning at E10.5 GDNF is also expressed in several organs that develop through inductive epithelial-mesenchymal interactions. In those organs, GDNF expression is strictly confined to mesenchymal tissues and is not found in epithelia. Our results suggest multiple roles for GDNF during early stages of neuronal development and in epithelial-mesenchymal interactions.

Activation of a serine/threonine kinase signaling pathway by transforming growth factor type beta

Transforming growth factor type beta (TGF-beta) is a multifunctional factor that regulates proliferation and differentiation of many cell types. TGF-beta mediates its effects by binding to and activating cell surface receptors that possess serine/threonine kinase activity. However, the intracellular signaling pathways through which TGF-beta receptors act remain largely unknown. Here we show that TGF-beta activates a 78-kDa protein (p78) serine/threonine kinase as evidenced by an in-gel kinase assay. Ligand-induced activation of the kinase was near-maximal 5 min after TGF-beta addition to the cells and occurred exclusively on serine and threonine residues. This kinase is distinct from TGF-beta receptor type II, as well as several cytoplasmic serine/threonine kinases of similar size, including protein kinase C, Raf, mitogen-activated protein kinase kinase kinase, and ribosomal S6 kinase. Indeed, these kinases can be separated almost completely from p78 kinase by immunoprecipitation with specific antibodies. Furthermore, using different cell lines, we demonstrate that p78 kinase is activated only in cells for which TGF-beta can act as a growth inhibitory factor. These data raise the interesting possibility that protein serine/threonine kinases contribute to the intracellular relay of biological signals originating from receptor serine/threonine kinases such as the TGF-beta receptors.

Identification of a novel TGF-beta-regulated gene encoding a putative zinc finger protein in human osteoblasts

The TGF-beta family of growth factors has been extensively studied and found to play major roles in bone physiology and disease. A novel, TGF-beta-inducible early gene (TIEG) in normal human fetal osteoblasts (hFOB) has been identified using differential-display PCR. Using this differentially expressed cDNA fragment of TIEG to screen a hOB cDNA library, a near full-length cDNA for this gene was isolated. Northern analyses indicated that the steady-state levels of the 3.5 kb TIEG mRNA increased within 30 min of TGF-beta treatment of human osteoblasts and reached a maximum of 10-fold above control levels at 120 min post-treatment. This regulation was independent of new protein synthesis. Computer sequence analyses indicates that TIEG mRNA encodes for a 480 amino-acid protein. The TIEG protein contains three zinc finger motifs, several proline-rich src homology-3 (SH3) binding domains at the C-terminal end, and is homologous in this region to the zinc finger-containing transcription factor family of genes. A growth factor/cytokine-specific induction of TIEG has been shown. TIEG expression in hFOB cells was highly induced by TGF-beta and bone morphogenetic protein-2 (BMP-2), with a moderate induction by epidermal growth factor (EGF), but no induction by other growth factors/cytokines was observed. In addition to osteoblastic cells, high levels of TIEG expression were detected in skeletal muscle tissue, while low or no detectable levels were found in brain, lung, liver or kidney. Because TIEG is an early induced putative transcription factor gene, and shows a growth factor induction and tissue specificity, its protein product might play an important role as a signalling molecule in osteoblastic cells.

Angiostatic role of astrocytes: suppression of vascular endothelial cell growth by TGF-beta and other inhibitory factor(s)

Our previous in vivo analyses have suggested that astrocytes play a key role in retinal vascularization by inducing endothelial cell differentiation. Here we demonstrate that medium conditioned by cultured rat brain astrocytes (ACM) contains factors, including transforming growth factor-beta (TGF-beta), that inhibit endothelial cell growth. Serum-free medium conditioned for 1-3 days was tested on exponentially growing bovine retinal microvascular endothelial, aortic endothelial, mink lung epithelial CCL-64, and Swiss mouse 3T3 fibroblast cells. The growth of all four cell types was inhibited in a dose- and time-dependent manner. CCL cells, which are used as a model for assaying TGF-beta activity, were more sensitive than the endothelial cells, suggesting that ACM contains TGF-beta. Moreover, acid treatment significantly increased the inhibitory activity of ACM, indicating that TGF-beta in ACM is predominantly in the latent form. Mouse fibroblasts, which are not affected by TGF-beta treatment under the same conditions, were also inhibited by ACM. This suggests that other inhibitory factors in addition to TGF-beta may be involved. Adsorption by an anti-TGF-beta polyclonal antibody column substantially reduced but did not eliminate the inhibitory activity of ACM for CCL and endothelial cells. Western blot analysis of ACM and proteins eluted from the affinity column revealed a 25 kDa band that co-migrates with TGF-beta. Comparative densitometry of the 25 kDa bands on Western blot indicated that the amount of TGF-beta in ACM is not sufficient to account for the total growth-inhibitory activity. These experiments demonstrate directly that rat brain astrocytes express TGF-beta. They also indicate that astrocytes may produce other growth-inhibitory factor(s) yet to be identified.

Inhibitors of haemopoiesis and their potential clinical relevance

Current cytotoxic treatment regimens are most frequently dose-limited by the problem of myelotoxicity, and this could theoretically be prevented or reduced by the use of stem-cell inhibitors, since protection of this compartment during treatment could result in a more favourable outcome in terms of bone-marrow regeneration. Several negative stem-cell regulators have been identified, including macrophage inflammatory protein-1 alpha, transforming growth factor-beta, tumour necrosis factor-alpha, tetrapeptide and pentapeptide. All of these molecules have been shown to inhibit the proliferation of normal haemopoietic progenitors in bone marrow, and stem-cell protection from cytotoxic agents both in vitro and in vivo has been demonstrated. The potential use of inhibitors for the purging of tumour cells from stem-cell grafts is suggested by the observation that there is a differential response between normal and leukaemic progenitors to some inhibitors.

Irradiation induces up-regulation of E9 protein (CD105) in human vascular endothelial cells

The use of MAb E-9 raised against tissue-cultured endothelial cells (EC) has shown marked heterogeneity in vascular EC lining the blood vessels of normal and tumour tissues. MAb E-9 is human EC-specific and the protein recognized by it is a homodimer with a molecular mass of 97 kDa. The E-9 protein is resistant to treatment by 3 mM sodium periodate, but is sensitive to 10% trichloroacetic acid and 70% ethanol. E-9 protein has been assigned to a new cluster, CD105, and mapped to human chromosome 9q3. It has approximately 70% homology with type-III cell-surface receptor for transforming growth factor beta (TGF-beta). Recently CD105 has been reported to be the gene in patients with hereditary haemorrhagic telangiectasia. We have examined the effects of radiation on its expression in normal human umbilical-vein endothelial cells (HUVEC) and brain-tumour-derived endothelial cells (BTEC). Irradiation induced dose- and time-dependent up-regulation in the expression of the E-9 protein on the plasma membranes of EC, and also resulted in greater increase in the expression of the E-9 protein in semi-confluent (proliferating) as compared with confluent (non-proliferating) EC. It may well be that, following radiotherapy in cancer patients, E-9 protein is also up-regulated. The presence of increased amounts of E-9 protein in EC makes it an attractive target in the control of angiogenesis, especially after radiotherapy in cancer patients. The time scale involved in the up-regulation of E-9 protein following irradiation has led us to suggest that it may be a secondary event, the primary being the production and release of mitogenic factors (such as basic fibroblast growth factor) from irradiated EC.

Expression of transforming growth factor-beta 1 in mouse skin during the acute phase of radiation damage

Transforming growth factor-beta (TGF beta 1) plays a central role in wound healing, so its perturbation by radiation may contribute to the acute and late effects seen in irradiated skin. TGF beta 1 mRNA expression was measured by PCR, in the skin of the CD1 and CBA mouse, exposed to Sr-90 beta from an 11-mm diameter source. TGF beta 1 mRNA expression increased sharply after doses between 1 and 10 Gy and plateaued at approximately 200% above controls after doses between 20 and 50 Gy. Immunohistochemistry showed that the TGF beta 1 protein was confined to the dermis and suprabasal cells with none in basal cells. A dose of 50 Gy produces an acute desquamative reaction in 100% of mice that is resolved in 30 days. After the same dose, TGF beta 1 mRNA expression fell below the controls at 3 h (-9.4% in the CD1 and -44% in the CBA mouse); rose sharply at 6-12 h (+124% CD1, +230% CBA), returned to control levels by 24-48 h, then rose progressively to approximately 200% above the controls between days 7 and 14. TGF beta 1 mRNA expression remained elevated at 100-200% above controls until the end of the experiment at 55 days. The significance of these changes in TGF beta 1 is discussed in the context of the early stress response reaction to radiation, the acute inflammatory and the later chronic fibrosis of the skin.

Stimulation and inhibition of proliferation in the small intestinal crypts of the mouse after in vivo administration of growth factors

The effects of epidermal growth factor (EGF), transforming growth factor alpha (TGF alpha), insulin-like growth factor (IGF) I and II, acidic fibroblast growth factor (FGF), tumour necrosis factor alpha (TNF alpha), macrophage inhibitory protein 1 alpha (MIP-1 alpha) (LD78), and TGF beta-1 on cell proliferation in the crypts of the small intestine of mice were investigated. Various doses and dosing regimens were tested. Three in vivo assays were developed, in each case involving detailed cell positional analysis of methyl tritiated thymidine labelling and mitotic activity. These allowed deductions to be made about the regions of the crypt and hence regions of the proliferative hierarchy (stem cells versus dividing transit cells) that are affected by treatment with growth factors. The assays involved: (1) normal untreated mice (an assay most likely to be effective for detecting inhibitors); (2) mice shortly after whole body irradiation when compensatory proliferation has been endogenously triggered (another assay for inhibitory factors, possibly ones associated specifically with the regenerative process); and (3) mice at late times (96 hours) after irradiation in the regression phase after a proliferative overshoot (an assay designed to detect stimulators). Little effect was seen after treatment with acidic FGF, TNF alpha, or MIP-1 alpha but EGF, IGF-I and II, and TGF alpha can all be seen to exert some stimulatory effects on labelling or mitosis. EGF and IGF-I stimulate both unirradiated mice and 96 hour recipients, while TGF alpha had a greater effect on the 96 hour animals. In all cases, multiple doses were used. TGF beta-1 was an effective inhibitor of proliferation in unirradiated and early regenerating (18 hour) animals. EGF was the most effective of the stimulators, raising the levels of proliferation at all positions in the crypt, but particularly in the upper crypt. IGF-I also exerted its effect predominantly in the upper crypt, while TGF alpha raised proliferation at all cell positions. TGF beta-1 tended to have its strongest inhibitory effects in the lower (stem cell) regions of the crypt.

Regulation of platelet-derived growth factor A and B chain gene expression in bone marrow stromal cells

MBA-2, bone marrow-derived endothelial stromal cells, express platelet-derived growth factor (PDGF) A and B chain mRNAs and secrete PDGF activity that is induced by TGF-beta. Either chain of the PDGF molecule could modulate hematopoiesis and stromal cell growth. Intracellular pathways that regulate PDGF expression in the marrow microenvironment are unknown. In the present study, we examined the mechanisms that mediate PDGF A and B chain mRNA induction by TGF-beta and the role of protein kinase C (PKC) and cyclic AMP in PDGF regulation. TGF-beta was tested in parallel with PMA, an activator of phorbol ester-dependent PKC isoforms. Both PMA (10(-7)M) and TGF-beta (2.5 ng/ml) increased PDGF A and B chain mRNA levels. The serine/threonine protein kinase inhibitor, H7, blocked PDGF A and B chain mRNA induction in response to TGF-beta. However, down-regulation of PKC by prolonged incubation with PMA failed to abolish TGF-beta induction of PDGF A and B chain mRNAs. These findings indicate that induction of PDGF A and B chain mRNAs can be mediated via phorbol ester-dependent PKC pathway. In contrast, H7-sensitive protein kinase(s) other than phorbol ester-sensitive protein kinase C mediate the effect of TGF-beta. Agents that increase cAMP were also tested for their effect on PDGF gene expression. TGF-beta-mediated induction of PDGF A and B chain mRNAs was markedly inhibited by cAMP. cAMP also blocked stimulation of PDGF A chain mRNA by PMA. The positive and negative signaling mechanisms involved in modulating PDGF in the microenvironment may be important for determining hematopoietic and stromal cell responses in vivo.

Immunobiology and immunopharmacology of organ allograft rejection

Much has been learned regarding immunobiological mechanisms responsible for the rejection of histoincompatible allografts. There has also been considerable progress in our understanding of mechanisms responsible for tolerance. The new knowledge gained regarding graft destructive alloimmunity process and the mechanisms of action of immunosuppressants have resulted in solid organ graft survival rates that are in excess of 80% at one year posttransplantation. The principles of tolerance mechanism are yet to be successfully applied in the clinic. In this review, molecular and cellular mechanisms of action of clinically useful immunosuppressive drugs are reviewed from the perspective of regulation of the anti-allograft repertory.

Transforming growth factor-beta 1 levels are elevated in the striatum and in ventricular cerebrospinal fluid in Parkinson's disease

Transforming growth factor (TGF)-beta 1 content was measured for the first time in the brain (caudate nucleus, putamen, and cerebral cortex) and in ventricular cerebrospinal fluid (VCSF) from control and parkinsonian patients by a sandwich enzyme immunoassay. The concentrations of TGF-beta 1 were significantly higher in the dopaminergic striatal regions in parkinsonian patients than those in controls, but were not significantly different in the cerebral cortex between parkinsonian and control patients. Furthermore, the concentrations of TGF-beta 1 in VCSF were significantly higher in parkinsonian patients than those in non-parkinsonian control patients. Since TGF-beta 1 has potent regulatory activity on cell growth, these results suggest that TGF-beta 1 may have some significant modulatory role in the process of neurodegeneration in Parkinson's disease.

Complex flexibility of the transforming growth factor beta superfamily

The transforming growth factors beta (TGF-beta s) are important modulators of growth and differentiation. They are intermolecular disulfide-bonded homodimeric molecules. The monomer fold has a conserved cystine knot and lacks a hydrophobic core. The biological specificity of a given member of the family is believed to be determined by the conformational flexibility of the variable loop regions of the monomer. The monomer subunit assembly in the dimer is stabilized mainly by hydrophobic contacts and a few hydrogen bonds. Since these interactions are nondirectional, we examined subunit assemblies of TGF-beta by using conformational analysis. The different subunit assemblies in TGF-beta 2 dimer were characterized in terms of the intersubunit disulfide torsion. Our analyses show that the subunit assemblies fall into two states: the crystallographically observed gauche+conformation and the previously not reported gauche--conformation, both having almost identical interaction energies. Furthermore, there is significant flexibility in the subunit assembly within the gauche+ and the gauche- states of the disulfide bond. The monomer subunit assembly is independent of the variations about the loop regions. The variations in the loop regions, coupled with flexibility in the monomer assembly, lead to a complex flexibility in the dimer of the TGF-beta superfamily. For the TGF-beta superfamily, the cystine knot acts as a scaffold and complex flexibility provides for biological selectivity. Complex flexibility might provide an explanation for the diverse range of biological activities that these important molecules display.

Schnurri is required for Drosophila Dpp signaling and encodes a zinc finger protein similar to the mammalian transcription factor PRDII-BF1

Cytokines of the TGF beta superfamily regulate many aspects of cellular function by activating receptor complexes consisting of two distantly related serine/threonine kinases. Previous studies have indicated that Drosophila dpp uses similar signaling complexes and strictly requires the punt and thick veins receptors to transduce the signal across the membrane. Here, we show that the schnurri (shn) gene is required for many aspects of dpp signaling. Genetic epistasis experiments indicate that shn functions downstream of the dpp signal and its receptors. The shn gene encodes a large protein similar to a family of mammalian zinc finger transcription factors. The shn protein might therefore act as a nuclear target in the dpp signaling pathway directly regulating the expression of dpp-responsive genes.

Stimulation and inhibition of proliferation in the small intestinal crypts of the mouse after in vivo administration of growth factors

The effects of epidermal growth factor (EGF), transforming growth factor alpha (TGF alpha), insulin-like growth factor (IGF) I and II, acidic fibroblast growth factor (FGF), tumour necrosis factor alpha (TNF alpha), macrophage inhibitory protein 1 alpha (MIP-1 alpha) (LD78), and TGF beta-1 on cell proliferation in the crypts of the small intestine of mice were investigated. Various doses and dosing regimens were tested. Three in vivo assays were developed, in each case involving detailed cell positional analysis of methyl tritiated thymidine labelling and mitotic activity. These allowed deductions to be made about the regions of the crypt and hence regions of the proliferative hierarchy (stem cells versus dividing transit cells) that are affected by treatment with growth factors. The assays involved: (1) normal untreated mice (an assay most likely to be effective for detecting inhibitors); (2) mice shortly after whole body irradiation when compensatory proliferation has been endogenously triggered (another assay for inhibitory factors, possibly ones associated specifically with the regenerative process); and (3) mice at late times (96 hours) after irradiation in the regression phase after a proliferative overshoot (an assay designed to detect stimulators). Little effect was seen after treatment with acidic FGF, TNF alpha, or MIP-1 alpha but EGF, IGF-I and II, and TGF alpha can all be seen to exert some stimulatory effects on labelling or mitosis. EGF and IGF-I stimulate both unirradiated mice and 96 hour recipients, while TGF alpha had a greater effect on the 96 hour animals. In all cases, multiple doses were used. TGF beta-1 was an effective inhibitor of proliferation in unirradiated and early regenerating (18 hour) animals. EGF was the most effective of the stimulators, raising the levels of proliferation at all positions in the crypt, but particularly in the upper crypt. IGF-I also exerted its effect predominantly in the upper crypt, while TGF alpha raised proliferation at all cell positions. TGF beta-1 tended to have its strongest inhibitory effects in the lower (stem cell) regions of the crypt.

Specific binding of endocrine transforming growth factor-beta 1 to vascular endothelium

The presentation of recombinant biologically active 125I-TGF-beta 1 via the bloodstream to potential target cells in mice and rats was evaluated by quantitative light and electron microscope radioautography. Specificity was evaluated by in vivo competition with excess unlabeled TGF-beta 1, and integrity of the ligand at the binding site was demonstrated by trichloroacetic acid precipitation after extraction from tissues. The distribution of radiolabel at 2.5, 15, 30, 45, and 60 min after 125I-TGF-beta 1 injection revealed radiolabel principally over microvasculature endothelium but at times > 2.5 min over endothelial endocytic components indicative of internalization. Nonspecific binding of 125I-TGF-beta 1 to the apex of the proximal convoluted tubule of the kidney indicated it as the likely site of rapid clearance of TGF-beta 1 from the circulation, while a comparison of the binding of 125I-TGF-beta 1 (endothelial) to that of 125I-TGF-beta 1 complexed with alpha 2-macroglobulin-methylamine (liver parenchyma) indicated that clearance of TGF-beta 1 complexed alpha 2-macroglobulin was likely via the hepatic alpha 2-macroglobulin receptor. The endothelial TGF-beta receptors uncovered here are likely involved in the local regulatory mechanism of leukocyte and monocyte adhesion and tissue infiltration regulated by endocrine TGF-beta 1.

Basic aspects of neuroimmunology as they relate to immunotherapeutic targets: present and future prospects

The neurological diseases with definite or putative immune pathogenesis include myasthenia gravis; Lambert-Eaton myasthenic syndrome; IgM monoclonal anti-myelin-associated glycoprotein-associated demyelinating polyneuropathy; Guillain-Barré syndrome; chronic inflammatory demyelinating polyneuropathy; multifocal motor neuropathy with or without GM1 antibodies; multiple sclerosis; inflammatory myopathies; stiff-man syndrome; autoimmune neuromyotonia; paraneoplastic neuronopathies and cerebellar degeneration; and neurological diseases associated with systemic autoimmune conditions, vasculitis, or viral infections. The events that lead to these autoimmune diseases are not clear but the following sequential steps are critical: (a) the breaking of tolerance, a process in which cytokines, molecular mimicry, or superantigens may play a role in rendering previously anergic T cells to recognize neural autoantigens; (b) antigen recognition by the T-cell receptor complex and processing of the antigen via the major histocompatibility complex class I or II; (c) costimulatory factors especially B7 and B7-binding proteins (CD28, CTLA-4) and intercellular adhesion molecule (ICAM)-1 and its leukocyte function-associated (LFA)-1 ligand; (d) traffic of the activated T cells across the blood-brain or blood-nerve barrier via a series of adhesion molecules that include selectins, leukocyte integrins (LFA-1, Mac-1, very late activating antigen [VLA]-4) and their counterreceptors (ICAM-1, vascular cell adhesion molecule [VCAM]) on the endothelial cells; and (e) tissue injury when the activated T cells, macrophages, or specific autoantibodies find their antigenic targets on glial cells, myelin, axon, calcium channels, or muscle. In designing specific immunotherapy, the main players involved in every step of the immune response need to be considered. Targets for specific therapy in neurological diseases include agents that (a) interfere or compete with antigen recognition or stimulation, (b) inhibit costimulatory signals or cytokines, (c) inhibit the traffic of the activated cells to tissues, and (d) intervene at the antigen recognition sites in the targeted organ. The various immunomodulating procedures and immunosuppressive drugs currently used for nonselective neuroimmunotherapy are discussed in the context of their interference with the above-described immune mediators.

Transforming growth factor-beta receptors on human endometrial cells: identification of the type I, II, and III receptors and glycosyl-phosphatidylinositol anchored TGF-beta binding proteins

In the present study, we have characterized the cell surface receptors for transforming growth factor-beta (TGF-beta) on monolayer cultures of stromal cells prepared from human endometrial biopsies, and on a human endometrial epithelial cell line (RL95-2) using affinity cross-link labeling techniques. On the stromal cells, five TGF-beta binding proteins were identified. Analysis of the sensitivity of these proteins to dithiothreitol and phosphatidylinositol-specific phospholipase C, together with results from immunoprecipitations with antibodies against the type II and III TGF-beta receptors, confirmed that three of these binding proteins correspond to the cloned type I, II, and III TGF-beta receptors. The other two binding proteins observed exhibit the characteristics of isoform-specific GPI-anchored TGF-beta binding proteins. On RL95-2 cells, three TGF-beta binding proteins, corresponding to the type I, II, and III TGF-beta receptors, were identified. The receptors which we have characterized on endometrial cells are responsive to physiological concentrations of TGF-beta as demonstrated by the effect of TGF-beta on endometrial cell proliferation. Accordingly, these receptors have the potential to respond to the TGF-beta isoforms which have recently been detected in the endometrium in an autocrine and/or paracrine manner.

Hepatic expression of mature transforming growth factor beta 1 in transgenic mice results in multiple tissue lesions

Aberrant expression of transforming growth factor beta 1 (TGF-beta 1) has been implicated in a number of disease processes, particularly those involving fibrotic and inflammatory lesions. To determine the in vivo effects of overexpression of TGF-beta 1 on the function and structure of hepatic as well as extrahepatic tissues, transgenic mice were generated containing a fusion gene (Alb/TGF-beta 1) consisting of modified porcine TGF-beta 1 cDNA under the control of the regulatory elements of the mouse albumin gene. Five transgenic lines were developed, all of which expressed the Alb/TGF-beta 1 transgene selectively in hepatocytes. The transgenic line 25 expressing the highest level of the transgene in the liver also had high (> 10-fold over control) plasma levels of TGF-beta 1. Hepatic fibrosis and apoptotic death of hepatocytes developed in all the transgenic lines but was more pronounced in line 25. The fibrotic process was characterized by deposition of collagen around individual hepatocytes and within the space of Disse in a radiating linear pattern. Several extrahepatic lesions developed in line 25, including glomerulonephritis and renal failure, arteritis and myocarditis, as well as atrophic changes in pancreas and testis. The results from this transgenic model strongly support the proposed etiological role for TGF-beta 1 in a variety of fibrotic and inflammatory disorders. The transgenic model may also provide an appropriate paradigm for testing therapeutic interventions aimed at neutralizing the detrimental effects of this important cytokine.

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.

Biochemical evidence for the autophosphorylation and transphosphorylation of transforming growth factor beta receptor kinases

Transforming growth factor beta (TGF-beta) signals through a receptor complex containing the type I (TGF-beta RI) and type II (TGF-beta RII) receptors. We describe here biochemical studies on early events in the TGF-beta signaling pathways. TGF-beta RII is highly phosphorylated when expressed alone in COS-1 cells; its autophosphorylation occurs via an intramolecular (cis) mechanism that is independent of ligand binding. TGF-beta RI is also highly phosphorylated when expressed alone in COS-1 cells. Both wild-type TGF-beta RI and a kinase-deficient mutant thereof are transphosphorylated by the coexpressed TGF-beta RII kinase in a ligand-independent fashion in these cells. We propose that the association of TGF-beta RI and TGF-beta RII, induced by ligand binding or over-expression, leads to transphosphorylation of the TGF-beta RI by the TGF-beta RII kinase. This represents a mechanism of activation of receptors distinct from that of tyrosine kinase receptors and may apply to other serine/threonine kinase receptors.

Pharmacologic enhancement of wound healing

The field of pharmacologic modulation of soft tissue repair is in its infancy. Although the soluble, cellular, and insoluble mediators that govern repair have not been elucidated, the application of pharmacologic concentrations of purified polypeptide growth factors, cytokines, and matrix molecules has nonetheless resulted in the acceleration of normal repair and the reversal of deficient repair in a wide variety of dermal wound models in animals. However, early clinical results using these factors have been less than encouraging, and their potential roles in the armamentarium of chronic wound therapies remain to be established.

Mammalian antiproliferative signals and their targets

The effect of mitogens on the mammalian cell cycle is opposed by the action of antimitogens, such as TGF-beta, cAMP agonists, and various antiproliferative drugs. The recent identification of TGF-beta receptors that initiate antimitogenic signals and of cell cycle kinase inhibitors that respond to these signals has provided new insights into this process. The evidence argues that mitogenic and antimitogenic signals confront each other by regulating in opposite ways the activity of cyclin-dependent kinases that control cell commitment to DNA replication.

Stimulation of transforming growth factor-beta 1 transcription by cyclosporine

In searching for a candidate mechanism for the immunosuppressive as well as fibrogenic consequences of cyclosporine usage, we have explored the hypothesis that cyclosporine stimulates transcription of transforming growth factor-beta 1 (TGF-beta 1), a multifunctional cytokine endowed with immunosuppressive and fibrogenic properties. Our results demonstrate that cyclosporine (i) stimulates TGF-beta 1 promoter-dependent transcription of chloramphenicol acetyl transferase gene in transiently transfected human A-549 cells, (ii) stimulates the synthesis of TGF-beta 1 RNA transcripts in human T cells, and (iii) permits the expression/emergence of DNA regulatory proteins (retinoblastoma control factor-1 (RCF-1) and RCF-2) that bind and regulate TGF-beta 1 promoter activity. Our studies demonstrate for the first time that cyclosporine stimulates TGF-beta 1 gene transcription and suggest a novel mechanism of action of cyclosporine.

Regulation of mRNA transcripts and DNA synthesis in the rat heart following intravenous injection of transforming growth factor beta 1

Transforming Growth Factor-beta 1 (TGF-beta 1) is expressed in the heart by muscle and non-muscle cardiac cells. In vitro, cardiac myocytes and non-muscle cells including cardiac fibroblasts and endothelial cells respond to regulatory effects of TGF-beta 1. Expression of TGF-beta 1 in the heart is subject to regulation by hemodynamic stimuli. Increased expression of mRNA transcripts for TGF-beta 1 has been reported in several models of cardiac hypertrophy. The objective of this study was to determine the effect of TGF-beta 1 in the myocardium. TGF-beta 1 was injected intravenously. Expression of mRNA transcripts for functional and structural proteins was determined by Northern hybridization analysis. DNA synthesis was determined by measurement of 3H-thymidine incorporation into ventricular DNA. The results showed differential regulation of mRNAs for myocyte- and non-myocyte-specific proteins in the heart of TGF-beta 1 treated rats. Moderate but statistically significant decrease in DNA synthesis was observed in the heart of TGF-beta 1 treated rats (37.5%, P < 0.025). Together, these data point to a physiological role for TGF-beta 1 in the heart. They further suggest that similar to its diverse in vitro cell-specific regulatory effects, TGF-beta 1 may have multicellular targets in the heart. Effect of TGF-beta 1 alone or combined with those of other cytokines/hormones that come into play, as the result of its administration, may be responsible for altered gene expression and DNA synthesis in the myocardium.(ABSTRACT TRUNCATED AT 250 WORDS)

Sequence and chromosomal localisation of the gene encoding ovine latent transforming growth factor-beta 1

Transforming growth factor-beta 1 (TGF-beta 1) plays important roles in pathologic processes. To further investigate the actions of this cytokine in sheep, the entire 1170-bp ovine TGF-beta 1 pro-protein-encoding sequence has been determined by the cloning and sequencing of specific polymerase-chain-reaction amplification products of TGF-beta 1 cDNA sequences. In addition, these sequences have been used to estimate the length of the TGF-beta 1 mRNA as 1.5-1.7 kb by Northern blot hybridization and determine that the ovine TGF-beta 1 gene occupies a single locus in the sheep genome by chromosomal in situ hybridization.

Transforming growth factor beta 1, insulin and prostaglandin E1 enhance prostaglandin F2 alpha mitogenic action in Swiss 3T3 cells via separate events

Transforming growth factor beta 1 (TGF beta 1) had no mitogenic effect in Swiss 3T3 cells, but could increase prostaglandin F2 alpha (PGF2 alpha)-induced DNA synthesis. Insulin, but not prostaglandin E1 (PGE1), further enhanced PGF2 alpha action at low TGF beta 1 concentrations. TGF beta 1 also acted concertedly with the protein kinase C (PKC) activator 1-oleoyl-2-acetylglycerol to induce mitogenesis. Thus, it appears that TGF beta 1 and insulin act via separate signals, while TGF beta 1 and PGE1 might share a common pathway not involving TGF beta 1-mediated prostaglandin synthesis. These results suggest that TGF beta 1 might elicit various signalling mechanisms to enhance PGF2 alpha-triggered events.