Transforming growth factor beta peptide antagonists and their conversion to partial agonists

Bioreactors for Vocal Fold Tissue Engineering

It is estimated that almost one-third of the United States population will be affected by a vocal fold (VF) disorder during their lifespan. Promising therapies to treat VF injury and scarring are mostly centered on VF tissue engineering strategies such as the injection of engineered biomaterials and cell therapy. VF tissue engineering, however, is a challenging field as the biomechanical properties, structure, and composition of the VF tissue change upon exposure to mechanical stimulation. As a result, the development of long-term VF treatment strategies relies on the characterization of engineered tissues under a controlled mechanical environment. In this review, we highlight the importance of bioreactors as a powerful tool for VF tissue engineering with a focus on the current state of the art of bioreactors designed to mimic phonation in vitro. We discuss the influence of the phonatory environment on the development, function, injury, and healing of the VF tissue and its importance for the development of efficient therapeutic strategies. A concise and comprehensive overview of bioreactor designs, principles, operating parameters, and scalability are presented. An in-depth analysis of VF bioreactor data to date reveals that mechanical stimulation significantly influences cell viability and the expression of proinflammatory and profibrotic genes in vitro. Although the precision and accuracy of bioreactors contribute to generating reliable results, diverse gene expression profiles across the literature suggest that future efforts should focus on the standardization of bioreactor parameters to enable direct comparisons between studies. Impact statement We present a comprehensive review of bioreactors for vocal fold (VF) tissue engineering with a focus on the influence of the phonatory environment on the development, function, injury, and healing of the VFs and the importance of mimicking phonation on engineered VF tissues in vitro. Furthermore, we put forward a strong argument for the continued development of bioreactors in this area with an emphasis on the standardization of bioreactor designs, principles, operating parameters, and oscillatory regimes to enable comparisons between studies.

IGFBP-3 and TGF-β inhibit growth in epithelial cells by stimulating type V TGF-β receptor (TβR-V)-mediated tumor suppressor signaling

The TGF-β type V receptor (TβR-V) mediates growth inhibition by IGFBP-3 and TGF-β in epithelial cells and loss of TβR-V expression in these cells leads to development of carcinoma. The mechanisms by which TβR-V mediates growth inhibition (tumor suppressor) signaling remain elusive. Previous studies revealed that IGFBP-3 and TGF-β inhibit growth in epithelial cells by stimulating TβR-V-mediated IRS-1/2-dependent activation and cytoplasm-to-nucleus translocation of IGFBP-3- or TGF-β-stimulated protein phosphatase (PPase), resulting in dephosphorylation of pRb-related proteins (p107, p130) or pRb, and growth arrest. To define the signaling, we characterized/identified the IGFBP-3- and TGF-β-stimulated PPases in cell lysates and nucleus fractions in Mv1Lu cells treated with IGFBP-3 and TGF-β, using a cell-free assay with 32P-labeled casein as a substrate. Both IGFBP-3- and TGF-β-stimulated PPase activities in cell lysates are abolished when cells are co-treated with TGF-β/IGFBP-3 antagonist or RAP (LRP-1/TβR-V antagonist). However, the IGFBP-3-stimulated PPase activity, but not TGF-β-stimulated PPase activity, is sensitive to inhibition by okadaic acid (OA). In addition, OA or PP2Ac siRNA reverses IGFBP-3 growth inhibition, but not TGF-β growth inhibition, in Mv1Lu and 32D cells. These suggest that IGFBP-3- and TGF-β-stimulated PPases are identical to PP2A and PP1, respectively. By Western blot/phosphorimager/immunofluorescence-microscopy analyses, IGFBP-3 and TGF-β stimulate TβR-V-mediated IRS-2-dependent activation and cytoplasm-to-nucleus translocation of PP2Ac and PP1c, resulting in dephosphorylation of p130/p107 and pRb, respectively, and growth arrest. Small molecule TGF-β enhancers, which potentiate TGF-β growth inhibition by enhancing TβR-I-TβR-II-mediated canonical signaling and thus activating TβR-V-mediated tumor suppressor signaling cascade (TβR-V/IRS-2/PP1/pRb), could be used to prevent and treat carcinoma.

Inhibitory Effect of the LY2109761 on the Development of Human Keloid Fibroblasts

Keloids are scars characterized by abnormal proliferation of fibroblasts and overproduction of extracellular matrix components including collagen. We previously showed that LY2109761, a transforming growth factor- (TGF-) β receptor inhibitor, suppressed the secretion of matrix components and slowed the proliferation of fibroblasts derived from human hypertrophic scar tissue. However, the exact mechanism underlying this effect remains unclear. Here, we replicated the above results in keloid-derived fibroblasts and show that LY2109761 promoted apoptosis, decreased the phosphorylation of Smad2 and Smad3, and suppressed TGF-β1. These results suggest that the development and pathogenesis of keloids are positively regulated by the Smad2/3 signaling pathway and the upregulation of TGF-β1 receptors. LY2109761 and other inhibitors of these processes may therefore serve as therapeutic targets to limit excessive scarring after injury.

Emerging evidence for the roles of peptide in hypertrophic scar

Hypertrophic scar is a dermal fibroproliferative disorder characterized by excess collagen deposition. There are many existing treatment modalities, but none works perfectly in all individuals. Recently, evidence is increasing that peptides can play crucial roles in the prevention or treatment of hypertrophic scar. The peptides may be derived from growth factors, hormones, and intracellular products of proteolysis. In vitro and in vivo studies have revealed that a number of peptides, usually topically applied, have beneficial effects on fibroblasts in rat, mouse, hamster, pig and rabbit scar models. The length of such peptides typically ranges between 10 and 15 amino acids (aa). Peptides may reduce scar progenitors, prevent excessive scarring, decrease scar growth, speed re-epithelialization and promote scar maturation through multiple mechanisms. They may target TGF-β signaling, fibroblast function or collagen modulation, inflammation, renin angiotensin system, gap junction and other pathways. However, there is a paucity of evidence regarding specific binding sites for these peptides in scar models. Here, we review current research progress on the roles of peptides and underlying mechanisms in hypertrophic scar. We also discuss the clinical potential of peptides as therapeutic agents in scarring. Finally, the functions of several peptide-related compounds in hypertrophic scar are summarized.

Sorafenib suppresses TGF-β responses by inducing caveolae/lipid raft-mediated internalization/degradation of cell-surface type II TGF-β receptors: Implications in development of effective adjunctive therapy for hepatocellular carcinoma

Sorafenib is the only FDA approved drug for the treatment of advanced hepatocellular carcinoma (HCC) and other malignancies. Studies indicate that TGF-β signalling is associated with tumour progression in HCC. Autocrine and paracrine TGF-β promotes tumour growth and malignancy by inducing epithelial-mesenchymal transition (EMT). Sorafenib is believed to antagonize tumour progression by inhibiting TGF-β-induced EMT. It improves survival of patients but HCC later develops resistance and relapses. The underlying mechanism of resistance is unknown. Understanding of the molecular mechanism of sorafenib inhibition of TGF-β-induced signalling or responses in HCC may lead to development of adjunctive effective therapy for HCC. In this study, we demonstrate that sorafenib suppresses TGF-β responsiveness in hepatoma cells, hepatocytes, and animal liver, mainly by downregulating cell-surface type II TGF-β receptors (TβRII) localized in caveolae/lipid rafts and non-lipid raft microdomains via caveolae/lipid rafts-mediated internalization and degradation. Furthermore, sorafenib-induced downregulation and degradation of cell-surface TβRII is prevented by simultaneous treatment with a caveolae disruptor or lysosomal inhibitors. On the other hand, sorafenib only downregulates cell-surface TβRII localized in caveolae/lipid rafts but not localized in non-lipid raft microdomains in hepatic stellate cells. These results suggest that sorafenib inhibits TGF-β signalling mainly by inducing caveolae/lipid raft-mediated internalization and degradation of cell-surface TβR-II in target cells. They may also imply that treatment with agents which promote formation of caveolae/lipid rafts, TGF-β receptor kinase inhibitors (e.g., LY2157299) or TGF-β peptide antagonists (by liver-targeting delivery) may be considered as effective adjunct therapy with sorafenib for HCC.

Inhibitory effect of TGF-β peptide antagonist on the fibrotic phenotype of human hypertrophic scar fibroblasts

CONTEXT

TGF-β plays a central role in hypertrophic scar (HS) formation and development.

OBJECTIVE

This study investigated the role of a TGF-β antagonist peptide in inhibiting fibrotic behavior of human HS-derived fibroblasts (HSFs).

MATERIALS AND METHODS

HSFs were seeded at a density of 3.1 × 10(4)/cm(2) and were subjected to treatment of peptide antagonist (30 μM) or TGF-β receptor inhibitor LY2109761 (10 μM) or without treatment followed by the analyses of quantitative PCR, Elisa, in vitro wounding and fibroblast-populated collagen lattice (FPCL) assays.

RESULTS

qPCR and Elisa analyses showed that the peptide could, respectively, reduce the gene (at 48 h) and protein (at 72 h) expression levels of collagen I (86 ± 4.8%; 56.6 ± 7.3%), collagen III (73 ± 10.7%; 43.7 ± 7.2%), fibronectin (90 ± 8.9%; 21.1 ± 2.8%), and TGF-β1 (85 ± 9.3%; 25.0 ± 9.4%) as opposed to the non-treated group (p < 0.05), as the LY2109761 group similarly did. Cell proliferation was also significantly inhibited at day 5 (CCK-8 assay) by both peptide and LY2109761 treatments compared with the non-treated group (p < 0.05). The peptide also significantly inhibited cell migration as opposed to blank control at 24 h (43 ± 6.7% versus 60 ± 2.1%, p < 0.05) and at 48 h (63.9 ± 3.1% versus 95 ± 4.1%, p < 0.05). Similar to LY2109761, the peptide antagonist significantly reduced HS FPCL contraction compared with the non-treated group with significant differences in surface area at 48 h (0.71 ± 0.06 cm(2) versus 0.51 ± 0.06 cm(2), p < 0.05) and at 72 h (0.65 ± 0.02 cm(2) versus 0.42 ± 0.01 cm(2), p < 0.05).

CONCLUSION

The TGF-β antagonist peptide may serve as an important drug for HS prevention and reduction given the obvious benefits of good biosafety, low cost, and easy manufacture and delivery.

DMSO Enhances TGF-β Activity by Recruiting the Type II TGF-β Receptor From Intracellular Vesicles to the Plasma Membrane

Dimethyl sulfoxide (DMSO) is used to treat many diseases/symptoms. The molecular basis of the pharmacological actions of DMSO has been unclear. We hypothesized that DMSO exerts some of these actions by enhancing TGF-β activity. Here we show that DMSO enhances TGF-β activity by ∼3-4-fold in Mv1Lu and NMuMG cells expressing Smad-dependent luciferase reporters. In Mv1Lu cells, DMSO enhances TGF-β-stimulated expression of P-Smad2 and PAI-1. It increases cell-surface expression of TGF-β receptors (TβR-I and/or TβR-II) by ∼3-4-fold without altering their cellular levels as determined by (125) I-labeled TGF-β-cross-linking/Western blot analysis, suggesting the presence of large intracellular pools in these cells. Sucrose density gradient ultracentrifugation/Western blot analysis reveals that DMSO induces recruitment of TβR-II (but not TβR-I) from its intracellular pool to plasma-membrane microdomains. It induces more recruitment of TβR-II to non-lipid raft microdomains than to lipid rafts/caveolae. Mv1Lu cells transiently transfected with TβR-II-HA plasmid were treated with DMSO and analyzed by indirect immunofluoresence staining using anti-HA antibody. In these cells, TβR-II-HA is present as a vesicle-like network in the cytoplasm as well as in the plasma membrane. DMSO causes depletion of TβR-II-HA-containing vesicles from the cytoplasm and co-localization of TβR-II-HA and cveolin-1 at the plasma membrane. These results suggest that DMSO, a fusogenic substance, enhances TGF-β activity presumably by inducing fusion of cytoplasmic vesicles (containing TβR-II) and the plasma membrane, resulting in increased localization of TβR-II to non-lipid raft microdomains where canonical signaling occurs. Fusogenic activity of DMSO may play a pivotal role in its pharmacological actions involving membrane proteins with large cytoplasmic pools. J. Cell. Biochem. 117: 1568-1579, 2016. © 2015 Wiley Periodicals, Inc.

Hexon modification to improve the activity of oncolytic adenovirus vectors against neoplastic and stromal cells in pancreatic cancer

Primary pancreatic carcinoma has an unfavourable prognosis and standard treatment strategies mostly fail in advanced cases. Virotherapy might overcome this resistance to current treatment modalities. However, data from clinical studies with oncolytic viruses, including replicating adenoviral (Ad) vectors, have shown only limited activity against pancreatic cancer and other carcinomas. Since pancreatic carcinomas have a complex tumor architecture and frequently a strong stromal compartment consisting of non-neoplastic cell types (mainly pancreatic stellate cells = hPSCs) and extracellular matrix, it is not surprising that Ad vectors replicating in neoplastic cells will likely fail to eradicate this aggressive tumor type. Because the TGFβ receptor (TGFBR) is expressed on both neoplastic cells and hPSCs we inserted the TGFBR targeting peptide CKS17 into the hypervariable region 5 (HVR5) of the capsid protein hexon with the aim to generate a replicating Ad vector with improved activity in complex tumors. We demonstrated increased transduction of both pancreatic cancer cell lines and of hPSCs and enhanced cytotoxicity in co-cultures of both cell types. Surface plasmon resonance analysis demonstrated decreased binding of coagulation factor X to CKS17-modified Ad particles and in vivo biodistribution studies performed in mice indicated decreased transduction of hepatocytes. Thus, to increase activity of replicating Ad vectors we propose to relax tumor cell selectivity by genetic hexon-mediated targeting to the TGFBR (or other receptors present on both neoplastic and non-neoplastic cells within the tumor) to enable replication also in the stromal cell compartment of tumors, while abolishing hepatocyte transduction, and thereby increasing safety.

Nonsteroidal anti-inflammatory drugs for wounds: pain relief or excessive scar formation?

The inflammatory process has direct effects on normal and abnormal wound healing. Hypertrophic scar formation is an aberrant form of wound healing and is an indication of an exaggerated function of fibroblasts and excess accumulation of extracellular matrix during wound healing. Two cytokines--transforming growth factor-beta (TGF-beta) and prostaglandin E2 (PGE2)--are lipid mediators of inflammation involving wound healing. Overproduction of TGF-beta and suppression of PGE2 are found in excessive wound scarring compared with normal wound healing. Nonsteroidal anti-inflammatory drugs (NSAIDs) or their selective cyclooxygenase-2 (COX-2) inhibitors are frequently used as a pain-killer. However, both NSAIDs and COX-2 inhibitors inhibit PGE2 production, which might exacerbate excessive scar formation, especially when used during the later proliferative phase. Therefore, a balance between cytokines and medication in the pathogenesis of wound healing is needed. This report is a literature review pertaining to wound healing and is focused on TGF-beta and PGE2.

Inhalation of TGF-beta1 antibody: a new method to inhibit the airway stenosis induced by the endobronchial tuberculosis

Tuberculous tracheobronchial stenosis is a serious clinical problem because it can cause obstructive pneumonia, dyspnea on exertion even pulmonary atelectasis of the whole lung. More than 90% of the patients with EBTB have some degree of bronchial stenosis. The interventional therapy through bronchoscopy has been used as standard treatment to deal with the scar stenosis of EBTB routinely, which have showed significant effects to keep airway open. However the scar rapid growing and restenosis can often be seen in many patients. TGF-beta1 has been demonstrated to play a very important role in scar formation. Some agents against TGF-beta1 have been proved to inhibit the scar growing effectively. The level of TGF-beta elevated in the BALF of EBTB patients suggests TGF-beta be related to the pathogenesis of stenosis induced by EBTB. We hypothesize that inhalation of TGF-beta1 antibody can neutralize the local TGF-beta and reduce the level of this kind of cytokine so as to prevent the scar formation partially, and find a new pathway to deal with this tough clinical problem.

A novel TGF-beta antagonist speeds reepithelialization and reduces scarring of partial thickness porcine burns

Scar formation after thermal injury is common and results in significant aesthetic and functional impairment. Transforming growth factor beta (TGF-beta) plays a significant role in scar formation. We tested the hypothesis that a novel TGF-beta peptantagonist would reduce scar formation and wound contraction in partial thickness burns by using a randomized controlled experiment. The subjects include two domestic pigs (20-25 kg). Forty burns were created on the animal's dorsum using an aluminum bar preheated to 80 degrees C and applied for 20 seconds resulting in a partial thickness thermal burn extending half way down the dermis. Burns were treated every other day for 1 week, then twice weekly for 3 weeks with a topical TGF-beta antagonist or its vehicle. Full thickness biopsies were obtained from all burns at 7, 10, and 14 days after injury. The wounds were completely excised after 28 days for histological assessment. Wound sections were stained with H&&E and evaluated by a dermatopathologist masked to treatment assignment for reepithelialization and depth of scar formation. We also determined the number of wounds at 28 days that healed with contracted, hour-glass shaped scars. Data were compared with chi and t-tests. Twenty burns were treated with TGF-beta antagonist and 20 with control vehicle. TGF-beta antagonist increased the percentage of completely reepithelialized wounds at 14 days (90 vs 45%, P = .002) and reduced the percentage of contracted wounds (35 vs 65%, P = .02) and full thickness scars (10 vs 60%, P = .002) at 28 days. Treatment of partial thickness porcine burns with the TGF-beta antagonist speeds reepithelialization and reduces scar formation and wound contraction in partial thickness porcine burns.

TGF-beta-like transcriptional effects of thyroglobulin (Tg) in mouse mesangial cells

TGF-beta-like activities of proteins unrelated to the cytokine could mimic its actions in fibrosis and cell proliferation. Thyroglobulin (Tg) has been identified as having a TGF-beta receptor (TGFbetaR)-binding activity and is deposited in the glomerulus in certain immune-complex diseases. The aim of the present study is to determine whether Tg can reproduce the transcriptional activity of TGF-beta1 in the mouse glomerular mesangial cell (MC), and to examine whether such activity is manifested through TGFbetaR. Real-time RT-PCR was employed to examine the effects of TGF-beta1 and bovine Tg on the expression of three genes (TGF-beta1, plasminogen activator inhibitor 1 [PAI-1], and Pax-8) regulated by TGF-beta1 in other cell types. In addition, a pentacosapeptide TGF-beta1 antagonist, beta(1)(25) (41-65) was employed to determine whether the transcriptional activity of Tg was mediated through the TGF-beta binding site on the TGFbetaR. A 6h exposure to TGF-beta1 resulted in increased TGF-beta1 and PAI-1 transcript, and a decrease in Pax-8. Similarly, a 6h exposure to Tg resulted in increases of about 5-fold in TGF-beta1 and PAI-1 mRNA and a decrease of 53% in Pax-8. In comparison with other proteins, Tg had the greatest positive effect on TGF-beta1 transcript levels. beta(1)(25) (41-65) significantly reduced the TGF-beta1-, but not the Tg-induced changes in TGF-beta1, PAI-1 and Pax-8 transcript levels. We conclude from these studies that Tg possesses a TGF-beta-mimetic transcriptional activity in the MC that is not mediated by its binding to TGFbetaR. These results suggest that Tg and other proteins could initiate glomerular injury by reproducing the actions of TGF-beta1 in the mesangial cell.

TGF-beta control of cell proliferation

This article focuses on recent findings that the type V TGF-beta receptor (TbetaR-V), which co-expresses with other TGF-beta receptors (TbetaR-I, TbetaR-II, and TbetaR-III) in all normal cell types studied, is involved in growth inhibition by IGFBP-3 and TGF-beta and that TGF-beta activity is regulated by two distinct endocytic pathways (clathrin- and caveolar/lipid-raft-mediated). TGF-beta is a potent growth inhibitor for most cell types, including epithelial and endothelial cells. The signaling by which TGF-beta controls cell proliferation is not well understood. Many lines of evidence indicate that other signaling pathways, in addition to the prominent TbetaR-I/TbetaR-II/Smad2/3/4 signaling cascade, are required for mediating TGF-beta-induced growth inhibition. Recent studies revealed that TbetaR-V, which is identical to LRP-1, mediates IGF-independent growth inhibition by IGFBP-3 and mediates TGF-beta-induced growth inhibition in concert with TbetaR-I and TbetaR-II. In addition, IRS proteins and a Ser/Thr-specific protein phosphatase(s) are involved in the TbetaR-V-mediated growth inhibitory signaling cascade. The TbetaR-V signaling cascade appears to cross-talk with the TbetaR-I/TbetaR-II, insulin receptor (IR), IGF-I receptor (IGF-IR), integrin and c-Met signaling cascades. Attenuation or loss of the TbetaR-V signaling cascade may enable carcinoma cells to escape from TGF-beta growth control and may contribute to the aggressiveness and invasiveness of these cells via promoting epithelial-to-mesenchymal transdifferentiation (EMT). Finally, the ratio of TGF-beta binding to TbetaR-II and TbetaR-I is a signal controlling TGF-beta partitioning between two distinct endocytosis pathways and resultant TGF-beta responsiveness. These recent studies have provided new insights into the molecular mechanisms underlying TGF-beta-induced cellular growth inhibition, cross-talk between the TbetaR-V and other signaling cascades, the signal that controls TGF-beta responsiveness and the role of TbetaR-V in tumorigenesis.

Identification of insulin receptor substrate proteins as key molecules for the TβR‐V/LRP‐1‐mediated growth inhibitory signaling cascade in epithelial and myeloid cells

The type V TGF-beta receptor (TbetaR-V) mediates IGF-independent growth inhibition by IGFBP-3 and mediates growth inhibition by TGF-beta1 in concert with the other TGF-beta receptor types. TbetaR-V was recently found to be identical to LRP-1. Here we find that insulin and (Q3A4Y15L16) IGF-I (an IGF-I analog that has a low affinity for IGFBP-3) antagonize growth inhibition by IGFBP-3 in mink lung epithelial cells (Mv1Lu cells) stimulated by serum. In these cells, IGFBP-3 induces serine-specific dephosphorylation of IRS-1 and IRS-2. The IGFBP-3-induced dephosphorylation of IRS-2 is prevented by cotreatment of cells with insulin, (Q3A4Y15L16) IGF-I, or TbetaR-V/LRP-1 antagonists. The magnitude of the IRS-2 dephosphorylation induced by IGFBP-3 positively correlates with the degree of growth inhibition by IGFBP-3 in Mv1Lu cells and mutant cells derived from Mv1Lu cells. Stable transfection of murine 32D myeloid cells (which lack endogenous IRS proteins and are insensitive to growth inhibition by IGFBP-3) with IRS-1 or IRS-2 cDNA confers sensitivity to growth inhibition by IGFBP-3; this IRS-mediated growth inhibition can be completely reversed by insulin in 32D cells stably expressing IRS-2 and the insulin receptor. These results suggest that IRS-1 and IRS-2 are key molecules for the TbetaR-V/LRP-1-mediated growth inhibitory signaling cascade.

Molecular recognition in bone morphogenetic protein (BMP)/receptor interaction

Bone morphogenetic proteins (BMPs) and other members of the TGF-β superfamily are secreted signalling proteins determining the development, maintenance and regeneration of tissues and organs. These dimeric proteins bind, via multiple epitopes, two types of signalling receptor chains and numerous extracellular modulator proteins that stringently control their activity. Crystal structures of free ligands and of complexes with type I and type II receptor extracellular domains and with the modulator protein Noggin reveal structural epitopes that determine the affinity and specificity of the interactions. Modelling of a ternary complex BMP/(BMPR-IAEC)2/(ActR-IIEC)2suggests a mechanism of receptor activation that does not rely on direct contacts between extracellular domains of the receptors. Mutational and interaction analyses indicate that the large hydrophobic core of the interface of BMP-2 (wrist epitope) with the type I receptor does not provide a hydrophobic hot spot for binding. Instead, main chain amide and carbonyl groups that are completely buried in the contact region represent major binding determinants. The affinity between ligand and receptor chains is probably strongly increased by two-fold interactions of the dimeric ligand and receptor chains that exist as homodimers in the membrane (avidity effects). BMP muteins with disrupted epitopes for receptor chains or modulator proteins provide clues for drug design and development.

Ursolic acid, an antagonist for transforming growth factor (TGF)-beta1

Transforming growth factor-beta (TGF-beta), a multifunctional cytokine which is involved in extracellular matrix modulation, has a major role in the pathogenesis and progression of fibrotic diseases. We now report the effects of ursolic acid on TGF-beta1 receptor binding and TGF-beta1-induced cellular functions in vitro. Ursolic acid inhibited [(125)I]-TGF-beta1 receptor binding to Balb/c 3T3 mouse fibroblasts with an IC(50) value of 6.9+/-0.8 microM. Ursolic acid dose-dependently recovered reduced proliferation of Minc Mv1Lu cells in the presence of 5 nM of TGF-beta1 and attenuated TGF-beta1-induced collagen synthesis and production in human fibroblasts. Molecular dynamics simulations suggest that ursolic acid may interact with the hydrophobic region of the dimeric interface and thereby inhibit the binding of TGF-beta1 to its receptor. All these findings taken together show that ursolic acid functions as an antagonist for TGF-beta1. This is the first report to show that a small molecule can inhibit TGF-beta1 receptor binding and influence functions of TGF-beta1.

Cellular growth inhibition by TGF-β1involves IRS proteins

In Mv1Lu cells, insulin partially reverses transforming growth factor-beta1 (TGF-beta1) growth inhibition in the presence of alpha5beta1 integrin antagonists. TGF-beta1 appears to induce phosphorylation of IRS-2 in these cells; this is inhibited by a TGF-beta antagonist known to reverse TGF-beta growth inhibition. Stable transfection of 32D myeloid cells (which lack endogenous IRS proteins and are insensitive to growth inhibition by TGF-beta1) with IRS-1 or IRS-2 cDNA confers sensitivity to growth inhibition by TGF-beta1; this IRS-mediated growth inhibition can be partially reversed by insulin in 32D cells stably expressing IRS-2 and the insulin receptor (IR). These results suggest that growth inhibition by TGF-beta1 involves IRS proteins.

Molecular recognition of BMP-2 and BMP receptor IA

Bone morphogenetic protein-2 (BMP-2) and other members of the TGF-beta superfamily regulate the development, maintenance and regeneration of tissues and organs. Binding epitopes for these extracellular signaling proteins have been defined, but hot spots specifying binding affinity and specificity have so far not been identified. In this study, mutational and structural analyses show that epitopes of BMP-2 and the BRIA receptor form a new type of protein-protein interface. The main chain atoms of Leu 51 and Asp53 of BMP-2 represent a hot spot of binding to BRIA. The BMP-2 variant L51P was deficient in type I receptor binding only, whereas its overall structure and its binding to type II receptors and modulator proteins, such as noggin, were unchanged. Thus, the L51P substitution converts BMP-2 into a receptor-inactive inhibitor of noggin. These results are relevant for other proteins of the TGF-beta superfamily and provide useful clues for structure-based drug design.

Cellular growth inhibition by IGFBP‐3 and TGF‐β1requires LRP‐1

The type V TGF-beta receptor (TbetaR-V)/IGFBP-3 receptor mediates the IGF-independent growth inhibition induced by IGFBP-3. It also mediates the growth inhibitory response to TGF-beta1 in concert with other TGF-beta receptor types, and its loss may contribute to the malignant phenotype of human carcinoma cells. Here we demonstrate that TbetaR-V is identical to LRP-1/alpha2M receptor as shown by MALDI-TOF analysis of tryptic peptides of TbetaR-V purified from bovine liver. In addition, 125I-IGFBP-3 affinity-labeled TbetaR-V in Mv1Lu cells is immunoprecipitated by antibodies to LRP-1 and TbetaR-V. RAP, an LRP-1 antagonist, inhibits binding of 125I-TGF-beta1 and 125I-IGFBP-3 to TbetaR-V and diminishes IGFBP-3-induced growth inhibition in Mv1Lu cells. Absent or low levels of LRP-1, as with TbetaR-V, have been linked to the malignant phenotype of carcinoma cells. Mutagenized Mv1Lu cells selected for reduced expression of LRP-1 have an attenuated growth inhibitory response to TGF-beta1 and IGFBP-3. LRP-1-deficient mouse embryonic fibroblasts lack a growth inhibitory response to TGF-beta1 and IGFBP-3. On the other hand, stable transfection of H1299 human lung carcinoma cells with LRP-1 cDNA restores the growth inhibitory response. These results suggest that the LRP-1/TbetaR-V/IGFBP-3 receptor is required for the growth inhibitory response to IGFBP-3 and TGF-beta1.

A synthetic peptide from transforming growth factor beta type III receptor inhibits liver fibrogenesis in rats with carbon tetrachloride liver injury

Transforming growth factor beta1 (TGF-beta1) is a pleiotropic cytokine, which displays potent profibrogenic effects and is highly expressed in fibrotic livers. For this reason, development of TGF-B1 inhibitors might be of great importance to control liver fibrogenesis as well as other undesired side effects due to this cytokine. Potential peptide inhibitors of TGF-beta1 (derived from TGF-beta1 and from its type III receptor) were tested in vitro and in vivo using different assays. Peptides P11 and P12, derived from TGF-beta1, and P54 and P144, derived from its type III receptor, prevented TGF-beta1-dependent inhibition of MV1Lu proliferation in vitro and markedly reduced binding of TGF-beta1 to its receptors. P144 blocked TGF-beta1-dependent stimulation of a reporter gene under the control of human alpha2(I) collagen promoter. Intraperitoneal administration of P144 also showed potent antifibrogenic activity in vivo in the liver of rats receiving CCl4. These rats also showed a significant decrease in the number of activated hepatic stellate cells as compared with those treated with saline only. These results suggest that short synthetic peptides derived from TGF-beta1 type III receptor may be of value in reducing liver fibrosis in chronic liver injury.

Synthetic TGF-beta antagonist accelerates wound healing and reduces scarring

Wound healing consists of re-epithelialization, contraction and formation of granulation and scar tissue. TGF-b is involved in these events, but its exact roles are not well understood. Here we demonstrate that topical application of a synthetic TGF-b antagonist accelerates re-epithelialization in pig burn wounds (100% re-epithelialization in antagonist-treated wounds vs. approximately 70% re-epithelialization in control wounds on postburn day 26) and reduces wound contraction and scarring in standard pig skin burn, pig skin excision and rabbit skin excision wounds. These results support the distinct roles of TGF-b in the complex process of wound healing and demonstrate the feasibility of manipulating wound healing by TGF-b antagonist.

The effect of TGF-beta receptor binding peptides on smooth muscle cells

TGF-beta1 is a potent regulator of vascular smooth muscle cell (VSMC) proliferation, migration, and extracellular matrix (ECM) synthesis. In this study, we selected two peptides, IM-1 and IM-2, that bind to the TGF-beta type II receptor (TGF-beta RII) using phage display. IM-1 and IM-2 bind to the TGF-beta RII, with a K(d) of 1 microM. Like TGF-beta, IM-1 induced VSMC chemotaxis and PAI-1 mRNA expression, as determined using Boyden chambers and real time quantitative PCR. In contrast, IM-2 had no effect on VSMC chemotaxis or PAI-1 induction. Induction of ECM synthesis, involving proteins such as osteopontin and alpha-smooth muscle actin, was determined by ELISA. Osteopontin expression was inhibited by both peptides, but TGF-beta-induced alpha-smooth muscle actin expression could only be inhibited by IM-1. In conclusion, IM-1 activity on VSMC is agonistic with TGF-beta, except for ECM synthesis, whereas the IM-2 peptide is antagonistic for some examined TGF-beta functions.

Identification of the high affinity binding site in transforming growth factor-beta involved in complex formation with alpha 2-macroglobulin. Implications regarding the molecular mechanisms of complex formation between alpha 2-macroglobulin and growth factors, cytokines, and hormones

The biological activities of transforming growth factor-beta isoforms (TGF-beta(1,2)) are known to be modulated by alpha(2)-macroglobulin (alpha(2)M). alpha(2)M forms complexes with numerous growth factors, cytokines, and hormones, including TGF-beta. Identification of the binding sites in TGF-beta isoforms responsible for high affinity interaction with alpha(2)M many unravel the molecular basis of the complex formation. Here we demonstrate that among nine synthetic pentacosapeptides with overlapping amino acid sequences spanning the entire TGF-beta(1) molecule, the peptide (residues 41-65) containing Trp-52 exhibited the most potent activity in inhibiting the formation of complexes between (125)I-TGF-beta(1) and activated alpha(2)M (alpha(2)M*) as determined by nondenaturing polyacrylamide gel electrophoresis and by plasma clearance in mice. TGF-beta(2) peptide containing the homologous sequence and Trp-52 was as active as the TGF-beta(1) peptide, whereas the corresponding TGF-beta(3) peptide lacking Trp-52, was inactive. The replacement of the Trp-52 with alanine abolished the inhibitory activities of these peptides. (125)I-TGF-beta(3), which lacks Trp-52, bound to alpha(2)M* with an affinity lower than that of (125)I-TGF-beta(1). Furthermore, unlabeled TGF-beta(3) and the mutant TGF-beta(1)W52A, in which Trp-52 was replaced with alanine, were less potent than unlabeled TGF-beta(1) in blocking I(125)-TGF-beta(1) binding to alpha(2)M*. TGF-beta(1) and TGF-beta(2) peptides containing Trp-52 were also effective in inhibiting I(125)-nerve growth factor binding to alpha(2)M*. Tauhese results suggest that Trp-52 is involved in high affinity binding of TGF-beta to alpha(2)M*. They also imply that TGF-beta and other growth factors/cytokines/hormones may form complexes with alpha(2)M* via a common mechanism involving the interactions between topologically exposed Trp and/or other hydrophobic residues and a hydrophobic region in alpha(2)M*.

Characterization of the inhibition of DNA synthesis in proliferating mink lung epithelial cells by insulin-like growth factor binding protein-3

Insulin-like growth factor binding protein-3 (IGFBP-3) can inhibit cell growth by directly interacting with cells, as well as by forming complexes with IGF-I and IGF-II that prevent their growth-promoting activity. The present study examines the mechanism of inhibition of DNA synthesis by IGFBP-3 in CCL64 mink lung epithelial cells. DNA synthesis was measured by the incorporation of 5-bromo-2'-deoxyuridine, using an immunocolorimetric assay. Recombinant human IGFBP-3 (rh[N109D,N172D]IGFBP-3) inhibited DNA synthesis in proliferating and quiescent CCL64 cells. Inhibition was abolished by co-incubation of IGFBP-3 with a 20% molar excess of Leu(60)-IGF-I, a biologically inactive IGF-I analogue that binds to IGFBP-3 but not to IGF-I receptors. DNA synthesis was not inhibited by incubation with a preformed 1:1 molar complex of Leu(60)-IGF-I and IGFBP-3, indicating that only free IGFBP-3 inhibits CCL64 DNA synthesis. Inhibition by IGFBP-3 is not due to the formation of biologically inactive complexes with free IGF, since endogenous IGFs could not be detected in CCL64 conditioned media; any IGFs that might have been present could only have existed in inactive complexes, since endogenous IGFBPs were present in excess; and biologically active IGFs were not displaced from endogenous IGFBP complexes by Leu(60)-IGF-I. After incubation with CCL64 cells, (125)I-IGFBP-3 was covalently cross-linked to a major thick similar400-kDa complex. This complex co-migrated with a complex formed after incubation with (125)I-labeled transforming growth factor-beta (TGF-beta) that has been designated the type V TGF-beta receptor. (125)I-IGFBP-3 binding to the thick similar400-kDa receptor was inhibited by co-incubation with unlabeled IGF-I or Leu(60)-IGF-I. The ability of Leu(60)-IGF-I to decrease both the inhibition of DNA synthesis by IGFBP-3 and IGFBP-3 binding to the thick similar400-kDa receptor is consistent with the hypothesis that the thick similar400-kDa IGFBP-3 receptor mediates the inhibition of CCL64 DNA synthesis by IGFBP-3.

An active site of transforming growth factor-beta(1) for growth inhibition and stimulation

Transforming growth factor-beta (TGF-beta) is a bifunctional growth regulator. It inhibits growth of many cell types, including epithelial cells, but stimulates growth of others (e.g. fibroblasts). The active site on the TGF-beta molecule, which mediates its growth regulatory activity, has not been defined. Here, we show that antibody to a TGF-beta(1) peptide containing the motif WSLD (52nd to 55th amino acid residues) completely blocked both (125)I-TGF-beta(1) binding to TGF-beta receptors and TGF-beta(1)-induced growth inhibition in mink lung epithelial cells. Site-directed mutagenesis analysis revealed that the replacement of Trp(52) and Asp(55) by alanine residues diminished the growth inhibitory activity of TGF-beta(1) by approximately 90%. Finally, while wild-type TGF-beta(1) was able to stimulate growth of transfected NIH 3T3 cells, the double mutant TGF-beta(1) W52A/D55A was much less active. These results support the hypothesis that the WSLD motif is an active site of TGF-beta(1), which is important for growth inhibition of epithelial cells and growth stimulation of fibroblasts.

Identification of two amino acids in activin A that are important for biological activity and binding to the activin type II receptors

Activins are members of the transforming growth factor-beta family of growth and differentiation factors. In this paper, we report the results of a structure-function analysis of activin A. The primary targets for directed mutagenesis were charged, individual amino acids located in accessible domains of the protein, concentrating on those that differ from transforming growth factor-beta2, the x-ray crystal structure of which is known. Based on the activities of the recombinant activin mutants in two bioassays, 4 out of 39 mutant proteins (D27K, K102A, K102E, and K102R) produced in a vaccinia virus system were selected for further investigation. After production in insect cells and purification of these four mutants to homogeneity, they were studied in bioassays and in cross-linking experiments involving transfected receptor combinations. Mutant D27K has a 2-fold higher specific bio-activity and binding affinity to an ActRIIA/ALK-4 activin receptor complex than wild type activin, whereas mutant K102E had no detectable biological activity and did not bind to any of the activin receptors. Mutant K102R and wild type activin bound to all the activin receptor combinations tested and were equipotent in bioassays. Our results with the Lys-102 mutants indicate that the positive charge of amino acid 102 is important for biological activity and type II receptor binding of activins.

Interactions of high affinity insulin-like growth factor-binding proteins with the type V transforming growth factor-beta receptor in mink lung epithelial cells

High affinity insulin-like growth factor-binding proteins (IGFBP-1 to -6) are a family of structurally homologous proteins that induce cellular responses by insulin-like growth factor (IGF)-dependent and -independent mechanisms. The IGFBP-3 receptor, which mediates the IGF-independent growth inhibitory response, has recently been identified as the type V transforming growth factor-beta receptor (TbetaR-V) (Leal, S. M., Liu, Q. L., Huang, S. S., and Huang, J. S. (1997) J. Biol. Chem. 272, 20572-20576). To characterize the interactions of high affinity IGFBPs with TbetaR-V, mink lung epithelial cells (Mv1Lu cells) were incubated with 125I-labeled recombinant human IGFBPs (125I-IGFBP-1 to -6) in the presence of the cross-linking agent disuccinimidyl suberate and analyzed by 5% SDS-polyacrylamide gel electrophoresis and autoradiography. 125I-IGFBP-3, -4, and -5 but not 125I-IGFBP-1, -2, and -6 bound to TbetaR-V as demonstrated by the detection of the approximately 400-kDa 125I-IGFBP.TbetaR-V cross-linked complex in the cell lysates and immunoprecipitates. The analyses of 125I-labeled ligand binding competition and DNA synthesis inhibition revealed that IGFBP-3 was a more potent ligand for TbetaR-V than IGFBP-4 or -5. Most of the high affinity 125I-IGFBPs formed dimers at the cell surface. The cell-surface dimer of 125I-IGFBP-3 preferentially bound to and was cross-linked to TbetaR-V in the presence of disuccinimidyl suberate. IGFBP-3 did not stimulate the cellular phosphorylation of Smad2 and Smad3, key transducers of the transforming growth factor-beta type I/type II receptor (TbetaR-I.TbetaR-II) heterocomplex-mediated signaling. These results suggest that IGFBP-3, -4, and -5 are specific ligands for TbetaR-V, which mediates the growth inhibitory response through a signaling pathway(s) distinct from that mediated by the TbetaR-I and TbetaR-II heterocomplex.

Distinct functional domains of TGF-beta bind receptors on endothelial cells

Transforming growth factor-beta (TGF-beta) is a multi-functional regulator of cell growth and differentiation. Three distinct isoforms of TGF-beta exist having similar, but not identical actions. TGF-beta 1, but not TGF-beta 2, binds to T beta RII and also to endoglin, a cell surface protein abundant on endothelial cells. In contrast, the affinity constant of TGF-beta 2 for alpha 2-macroglobulin is 10-fold greater than that of TGF-beta 1. TGF-beta 2 also binds better than TGF-beta 1 to a glycosyl phosphatidylinositol (GPI)-linked binding protein expressed on vascular endothelial cells. Using chimeric TGF-beta molecules, in which selected regions of TGF-beta 1 have been exchanged for the corresponding region of TGF-beta 2, we demonstrate here that amino acids 92-95 or 94-98 of TGF-beta determine isoform specific binding to endoglin. In contrast, exchange of only amino acids 95 and 98 did not alter TGF-beta specificity. Isoform specific binding to a GPI-linked protein on EJG endothelial cells was modulated by a region containing amino acids 40-68, although exchange of only amino acids 40-47 did not confer isoform specific binding. Significantly, the 92-98 region also modulates binding of TGF-beta to the type II receptor whereas isoform specific binding to alpha 2-macroglobulin requires concerted exchange of amino acids 45 and 47. Taken together, these results show that at least three different functional domains are important modulators of TGF-beta interaction with binding proteins and receptors.

Amyloid beta-peptide possesses a transforming growth factor-beta activity

Amyloid beta-peptide (Abeta) of 39-42 amino acid residues is a major constituent of Alzheimer's disease neurite plaques. Abeta aggregates (fibrils) are believed to be responsible for neuronal damage and dysfunction, as well as microglia and astrocyte activation in disease lesions by multiple mechanisms. Since Abeta aggregates possess the multiple valencies of an FAED motif (20th to 23rd amino acid residues), which resembles the putative transforming growth factor-beta (TGF-beta) active site motif, we hypothesize that Abeta monomers and Abeta aggregates may function as TGF-beta antagonists and partial agonists, analogous to previously described monovalent and multivalent TGF-beta peptide antagonists and agonists (Huang, S. S., Liu, Q., Johnson, F. E., Konish, Y., and Huang, J. S. (1997) J. Biol. Chem. 272, 27155-27159). Here, we report that the Abeta monomer, Abeta-(1-40) and its fragment, containing the motif inhibit radiolabeled TGF-beta binding to cell-surface TGF-beta receptors in mink lung epithelial cells (Mv1Lu cells). Abeta-(1-40)-bovine serum albumin conjugate (Abeta-(1-40)-BSA), a multivalent synthetic analogue of Abeta aggregates, exhibited cytotoxicity toward bovine cerebral endothelial cells and rat post-mitotic differentiated hippocampal neuronal cells (H19-7 cells) and inhibitory activities of radiolabeled TGF-beta binding to TGF-beta receptors and TGF-beta-induced plasminogen activator inhibitor-1 expression, that were approximately 100-670 times more potent than those of Abeta-(1-40) monomers. At less than micromolar concentrations, Abeta-(1-40)-BSA but not Abeta-(1-40) monomers inhibited proliferation of Mv1Lu cells. Since TGF-beta is an organizer of responses to neurodegeneration and is also found in neurite plaques, the TGF-beta antagonist and partial agonist activities of Abeta monomers and aggregates may play an important role in the pathogenesis of the disease.

Activated thyroglobulin possesses a transforming growth factor-beta activity

Thyroglobulin (Tg), the thyroid hormone precursor, is a major protein component in the thyroid gland and may have other important functions. Here, we show that bovine Tg inhibited 125I-labeled transforming growth factor-beta1 (125I-TGF-beta1) binding to cell-surface TGF-beta receptors in mink lung epithelial cells with an IC50 of approximately 300 nM. After disuccinimidyl suberate (DSS) modification, reduction/alkylation, treatment with 8 M urea, 0. 1% SDS, or acidic pH (pH 4-5), Tg exhibited a approximately 5-10-fold increase of 125I-TGF-beta1 binding inhibitory activity with IC50 of approximately 30-60 nM. This inhibitory activity was an intrinsic property of the Tg and could not be segregated from Tg protein by 5% SDS-polyacrylamide gel electrophoresis or by immunoprecipitation using antiserum to Tg. Untreated Tg did not affect DNA synthesis but blocked the TGF-beta-induced inhibition of DNA synthesis in mink lung epithelial cells. After DSS activation, Tg possessed TGF-beta agonist activity and inhibited DNA synthesis of mink lung epithelial cells and rat thyroid cells. The activated Tg also exerted a small but significant TGF-beta agonist activity in transcriptional activation of plasminogen activator inhibitor-1. These results suggest that Tg possesses an authentic TGF-beta activity which can be induced by chemical modifications and treatments with denaturing agents and acidic pH.

A pentacosapeptide (CKS-25) homologous to retroviral envelope proteins possesses a transforming growth factor-beta activity

CKS-17, a synthetic heptadecapeptide homologous to a conserved domain in retroviral envelope protein p15E, mimics the immunosuppressive properties of p15E in vitro and in vivo, but the mechanisms are not understood. Here we report that a synthetic pentacosapeptide designated CKS-25, a longer version of CKS-17 that contains a functional transforming growth factor-beta3 (TGF-beta3) active-site motif (RXXD), inhibits 125I-labeled TGF-beta1 (125I-TGF-beta1) binding to cell-surface TGF-beta receptors in cultured epithelial cells. Multiple conjugation of CKS-25 to bovine serum albumin and carbonic anhydrase enhances the 125I-TGF-beta1 binding inhibitory activity and confers a partial TGF-beta agonist activity (growth inhibition but not transcriptional activation). Since TGF-beta is a potent immunosuppressive factor, these results suggest that the immunosuppressive properties of CKS-17-bovine serum albumin conjugate and p15E are mediated at least in part by their TGF-beta agonist activities.

The type V transforming growth factor beta receptor is the putative insulin-like growth factor-binding protein 3 receptor

Insulin-like growth factor-binding protein 3 (IGFBP-3) has been shown to inhibit cell growth by IGF-dependent and -independent mechanisms. The putative cell-surface IGFBP-3 receptor that mediates the IGF-independent growth inhibition has not been identified. Here we show that recombinant human IGFBP-3 inhibits 125I-transforming growth factor (TGF)-beta1 binding to the type V TGF-beta receptor (Mr 400,000) in mink lung epithelial cells. We also demonstrate that the approximately 400-kDa 125I-IGFBP-3 affinity-labeled putative IGFBP-3 receptor is immunoprecipitated by specific antiserum to the type V TGF-beta receptor. The 125I-IGFBP-3 affinity labeling of the putative receptor and IGFBP-3-induced growth inhibition as measured by DNA synthesis in these cells is blocked by a TGF-beta1 peptide antagonist. The 125I-IGFBP-3 affinity-labeled putative receptor can only be detected in cells expressing the type V TGF-beta receptor, but not in cells lacking the type V TGF-beta receptor. These results indicate that the type V TGF-beta receptor is the putative IGFBP-3 receptor and that IGFBP-3 is a functional ligand for the type V TGF-beta receptor.