Cellular receptors for type beta transforming growth factor. Ligand binding and affinity labeling in human and rodent cell lines

TGF-β signaling in health, disease, and therapeutics

Transforming growth factor (TGF)-β is a multifunctional cytokine expressed by almost every tissue and cell type. The signal transduction of TGF-β can stimulate diverse cellular responses and is particularly critical to embryonic development, wound healing, tissue homeostasis, and immune homeostasis in health. The dysfunction of TGF-β can play key roles in many diseases, and numerous targeted therapies have been developed to rectify its pathogenic activity. In the past decades, a large number of studies on TGF-β signaling have been carried out, covering a broad spectrum of topics in health, disease, and therapeutics. Thus, a comprehensive overview of TGF-β signaling is required for a general picture of the studies in this field. In this review, we retrace the research history of TGF-β and introduce the molecular mechanisms regarding its biosynthesis, activation, and signal transduction. We also provide deep insights into the functions of TGF-β signaling in physiological conditions as well as in pathological processes. TGF-β-targeting therapies which have brought fresh hope to the treatment of relevant diseases are highlighted. Through the summary of previous knowledge and recent updates, this review aims to provide a systematic understanding of TGF-β signaling and to attract more attention and interest to this research area.

Targeting cluster of differentiation 26 / dipeptidyl peptidase 4 (CD26/DPP4) in organ fibrosis

Cluster of differentiation 26 (CD26)/dipeptidyl peptidase 4 (DPP4) is an exopeptidase that is expressed as a transmembrane protein in many organs but also present in a circulating soluble form. Beyond its enzymatic and costimulatory activity, CD26/DPP4 is involved in the pathogenesis of chronic fibrotic diseases across many organ types, such as liver cirrhosis, kidney fibrosis and lung fibrosis. Organ fibrosis is associated with a high morbidity and mortality, and there are no causative therapies that can effectively attenuate the progress of the disease. Growing evidence suggests that inhibiting CD26/DPP4 can modulate the profibrotic tissue microenvironment and thus reduce fibrotic changes within affected organs. This review summarizes the role of CD26/DPP4 in fibroproliferative disorders and highlights new opportunities for an antifibrotic treatment by CD26/DPP4 inhibition. As a major advantage, CD26/DPP4 inhibitors have been in safe and routine clinical use in type 2 diabetes for many years and thus qualify for repurposing to repurpose as a promising therapeutic against fibrosis. LINKED ARTICLES: This article is part of a themed issue on Translational Advances in Fibrosis as a Therapeutic Target. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.22/issuetoc.

COVID-19-associated pulmonary aspergillosis in immunocompetent patients: a virtual patient cohort study

The opportunistic fungus Aspergillus fumigatus infects the lungs of immunocompromised hosts, including patients undergoing chemotherapy or organ transplantation. More recently however, immunocompetent patients with severe SARS-CoV2 have been reported to be affected by COVID-19 Associated Pulmonary Aspergillosis (CAPA), in the absence of the conventional risk factors for invasive aspergillosis. This paper explores the hypothesis that contributing causes are the destruction of the lung epithelium permitting colonization by opportunistic pathogens. At the same time, the exhaustion of the immune system, characterized by cytokine storms, apoptosis, and depletion of leukocytes may hinder the response to A. fumigatus infection. The combination of these factors may explain the onset of invasive aspergillosis in immunocompetent patients. We used a previously published computational model of the innate immune response to infection with Aspergillus fumigatus. Variation of model parameters was used to create a virtual patient population. A simulation study of this virtual patient population to test potential causes for co-infection in immunocompetent patients. The two most important factors determining the likelihood of CAPA were the inherent virulence of the fungus and the effectiveness of the neutrophil population, as measured by granule half-life and ability to kill fungal cells. Varying these parameters across the virtual patient population generated a realistic distribution of CAPA phenotypes observed in the literature. Computational models are an effective tool for hypothesis generation. Varying model parameters can be used to create a virtual patient population for identifying candidate mechanisms for phenomena observed in actual patient populations.

TGF-β at the crossroads of multiple prognosis in breast cancer, and beyond

Transforming growth factor β (TGF-β), a pluripotent cytokine and a multifunctional growth factor has a crucial role in varied biological mechanisms like invasion, migration, epithelial-mesenchymal transition, apoptosis, wound healing, and immunosuppression. Moreover, it also has an imperative role both in normal mammary gland development as well as breast carcinogenesis. TGF-β has shown to have a paradoxical role in breast carcinogenesis, by transitioning from a growth inhibitor to a growth promoter with the disease advancement. The inter-communication and crosstalk of TGF-β with different signaling pathways has strengthened the likelihood to explore it as a comprehensive biomarker. In the last two decades, TGF-β has been studied extensively and has been found to be a promising biomarker for early detection, disease monitoring, treatment selection, and tumor progression making it beneficial for disease management. In this review, we focus on the signaling pathways and biological activities of the TGF-β family in breast cancer pathogenesis and its role as a circulatory and independent biomarker for breast cancer progression and metastasis. Moreover, this review highlights TGF-β as a drug target, and the underlying mechanisms through which it is involved in tumorigenesis that will aid in the development of varied therapies targeting the different stages of breast cancer.

Transforming growth factor-β1 in regulatory T cell biology

Transforming growth factor-β1 (TGF-β1) is inextricably linked to regulatory T cell (Treg) biology. However, precisely untangling the role for TGF-β1 in Treg differentiation and function is complicated by the pleiotropic and context-dependent activity of this cytokine and the multifaceted biology of Tregs. Among CD4+ T cells, Tregs are the major producers of latent TGF-β1 and are uniquely able to activate this cytokine via expression of cell surface docking receptor glycoprotein A repetitions predominant (GARP) and αv integrins. Although a preponderance of evidence indicates no essential roles for Treg-derived TGF-β1 in Treg immunosuppression, TGF-β1 signaling is crucial for Treg development in the thymus and periphery. Furthermore, active TGF-β1 instructs the differentiation of other T cell subsets, including TH17 cells. Here, we will review TGF-β1 signaling in Treg development and function and discuss knowledge gaps, future research, and the TGF-β1/Treg axis in the context of cancer immunotherapy and fibrosis.

Xenogeneic Humoral Immune Responses to Human Mesenchymal Stem Cells in Mice

Background and Objectives

Many preclinical studies have been conducted using animal disease models to determine the effectiveness of human mesenchymal stem cells (hMSCs) for treating immune and inflammatory diseases based on the belief that hMSCs are not immunogenic across species. However, several researchers have suggested xenogeneic immune responses to hMSCs in animals, still without detailed features. This study aimed to investigate a xenogeneic humoral immune response to hMSCs in mice in detail.

Methods and Results

Balb/c mice were intraperitoneally injected with adipose tissue-derived or Wharton’s jelly-derived hMSCs. Sera from these mice were titrated for each isotype. To confirm specificity of the antibodies, hMSCs were stained with the sera and subjected to a flow cytometic analysis. Spleens were immunostained for proliferating cell nuclear antigen to verify the germinal center formation. Additionally, splenocytes were subjected to a flow cytometric analysis for surface markers including GL-7, B220, CD4, CD8, CD44, and CD62L. Similar experiments were repeated in C57BL/6 mice. The results showed increased IgG₁ and IgG_2a titers in the sera from Balb/c mice injected with hMSCs, and the titers were much higher in the secondary sera than in the primary sera. These antibodies were specifically stained the hMSCs. Germinal centers were observed in the spleen, and flow cytometric analysis of the splenocytes showed higher frequencies of centroblasts (B220^＋ GL7^＋) and memory T cells (CD62L^＋ CD44^＋) both in CD4^＋ and CD8^＋ subsets. Similar results were obtained for C57BL/6 mice.

Conclusions

hMSCs induced a humoral immune response in mice, with characters of T cell-dependent immunity.

Receptor binding competition: A paradigm for regulating TGF-β family action

The transforming growth factor (TGF)-β family is a group of structurally related, multifunctional growth factors, or ligands that are crucially involved in the development, regulation, and maintenance of animal tissues. In humans, the family counts over 33 members. These secreted ligands typically form multimeric complexes with two type I and two type II receptors to activate one of two distinct signal transduction branches. A striking feature of the family is its promiscuity, i.e., many ligands bind the same receptors and compete with each other for binding to these receptors. Although several explanations for this feature have been considered, its functional significance has remained puzzling. However, several recent reports have promoted the idea that ligand-receptor binding promiscuity and competition are critical features of the TGF-β family that provide an essential regulating function. Namely, they allow a cell to read and process multi-ligand inputs. This capability may be necessary for producing subtle, distinctive, or adaptive responses and, possibly, for facilitating developmental plasticity. Here, we review the molecular basis for ligand competition, with emphasis on molecular structures and binding affinities. We give an overview of methods that were used to establish experimentally ligand competition. Finally, we discuss how the concept of ligand competition may be fundamentally tied to human physiology, disease, and therapy.

Specification of BMP Signaling

Bone Morphogenetic Proteins (BMPs) together with the Growth and Differentiation Factors (GDFs) form the largest subgroup of the Transforming Growth Factor (TGF)β family and represent secreted growth factors, which play an essential role in many aspects of cell communication in higher organisms. As morphogens they exert crucial functions during embryonal development, but are also involved in tissue homeostasis and regeneration in the adult organism. Their involvement in maintenance and repair processes of various tissues and organs made these growth factors highly interesting targets for novel pharmaceutical applications in regenerative medicine. A hallmark of the TGFβ protein family is that all of the more than 30 growth factors identified to date signal by binding and hetero-oligomerization of a very limited set of transmembrane serine-threonine kinase receptors, which can be classified into two subgroups termed type I and type II. Only seven type I and five type II receptors exist for all 30plus TGFβ members suggesting a pronounced ligand-receptor promiscuity. Indeed, many TGFβ ligands can bind the same type I or type II receptor and a particular receptor of either subtype can usually interact with and bind various TGFβ ligands. The possible consequence of this ligand-receptor promiscuity is further aggravated by the finding that canonical TGFβ signaling of all family members seemingly results in the activation of just two distinct signaling pathways, that is either SMAD2/3 or SMAD1/5/8 activation. While this would implicate that different ligands can assemble seemingly identical receptor complexes that activate just either one of two distinct pathways, in vitro and in vivo analyses show that the different TGFβ members exert quite distinct biological functions with high specificity. This discrepancy indicates that our current view of TGFβ signaling initiation just by hetero-oligomerization of two receptor subtypes and transduction via two main pathways in an on-off switch manner is too simplified. Hence, the signals generated by the various TGFβ members are either quantitatively interpreted using the subtle differences in their receptor-binding properties leading to ligand-specific modulation of the downstream signaling cascade or additional components participating in the signaling activation complex allow diversification of the encoded signal in a ligand-dependent manner at all cellular levels. In this review we focus on signal specification of TGFβ members, particularly of BMPs and GDFs addressing the role of binding affinities, specificities, and kinetics of individual ligand-receptor interactions for the assembly of specific receptor complexes with potentially distinct signaling properties.

TGF-β receptors: In and beyond TGF-β signaling

Transforming growth factor β (TGF-β) plays an important role in normal development and homeostasis. Dysregulation of TGF-β responsiveness and its downstream signaling pathways contribute to many diseases, including cancer initiation, progression, and metastasis. TGF-β ligands bind to three isoforms of the TGF-β receptor (TGFBR) with different affinities. TGFBR1 and 2 are both serine/threonine and tyrosine kinases, but TGFBR3 does not have any kinase activity. They are necessary for activating canonical or noncanonical signaling pathways, as well as for regulating the activation of other signaling pathways. Another prominent feature of TGF-β signaling is its context-dependent effects, temporally and spatially. The diverse effects and context dependency are either achieved by fine-tuning the downstream components or by regulating the expressions and activities of the ligands or receptors. Focusing on the receptors in events in and beyond TGF-β signaling, we review the membrane trafficking of TGFBRs, the kinase activity of TGFBR1 and 2, the direct interactions between TGFBR2 and other receptors, and the novel roles of TGFBR3.

The predictive value of transforming growth factor-β in Wilms tumor immunopathogenesis

Wilms tumor is the most common kidney malignancy in children, especially in children aged less than 6 years. Although therapeutic approach has reached successful rates, there is still room for improvement. Considering the tumor microenvironment, cytokines represent important elements of interaction and communication between tumor cells, stroma, and immune cells. In this regard, the transforming growth factor beta (TGF-β) family members play significant functions in physiological and pathological conditions, particularly in cancer. By regulating cell growth, death, and immortalization, TGF-β signaling pathways exert tumor suppressor effects in normal and early tumor cells. Thus, it is not surprising that a high number of human tumors arise due to alterations in genes coding for various TGF-β signaling components. Understanding the ambiguous role of TGF-β in human cancer is of paramount importance for the development of new therapeutic strategies to specifically block the metastatic signaling pathway of TGF-β without affecting its tumor suppressive effect. In this context, this review attempt to summarize the involvement of TGF-β in Wilms tumor.

The Discovery and Early Days of TGF-β: A Historical Perspective

Transforming growth factors (TGFs) were discovered as activities that were secreted by cancer cells, and later by normal cells, and had the ability to phenotypically and reversibly transform immortalized fibroblasts. TGF-β distinguished itself from TGF-α because it did not bind to the same epidermal growth factor (EGF) receptor as TGF-α and, therefore, acted through different cell-surface receptors and signaling mediators. This review summarizes the discovery of TGF-β, the early developments in its molecular and biological characterization with its many biological activities in different cell and tissue contexts and its roles in disease, the realization that there is a family of secreted TGF-β-related proteins with many differentiation functions in development and activities in normal cell and tissue physiology, and the subsequent identification and characterization of the receptors and effectors that mediate TGF-β family signaling responses.

TGF-β is an inducer of ZEB1-dependent mesenchymal transdifferentiation in glioblastoma that is associated with tumor invasion

Different molecular subtypes of glioblastoma (GBM) have been recently identified, of which the mesenchymal subtype is associated with worst prognoses. Here, we report that transforming growth factor-β (TGF-β) is able to induce a mesenchymal phenotype in GBM that involves activation of SMAD2 and ZEB1, a known transcriptional inducer of mesenchymal transition in epithelial cancers. TGF-β exposure of established and newly generated GBM cell lines was associated with morphological changes, enhanced mesenchymal marker expression, migration and invasion in vitro and in an orthotopic mouse model. TGF-β-induced mesenchymal differentiation and invasive behavior was prevented by chemical inhibition of TGF-β signaling as well as small interfering RNA (siRNA)-dependent silencing of ZEB1. Furthermore, TGF-β-responding and -nonresponding GBM neurospheres were identified in vitro. Interestingly, nonresponding cells displayed already high levels of pSMAD2 and ZEB1 that could not be suppressed by inhibition of TGF-β signaling, suggesting the involvement of yet unknown mechanisms. These different GBM neurospheres formed invasive tumors in mice as well as revealed mesenchymal marker expression in immunohistochemical analyses. Moreover, we also detected distinct zones with overlapping pSMAD2, elevated ZEB1 and mesenchymal marker expression in GBM patient material, suggestive of the induction of local, microenvironment-dependent mesenchymal differentiation. Overall, our findings indicate that GBM cells can acquire mesenchymal features associated with enhanced invasive potential following stimulation by secretory cytokines, such as TGF-β. This property of GBM contributes to heterogeneity in this tumor type and may blur the boundaries between the proposed transcriptional subtypes. Targeting TGF-β or downstream targets like ZEB1 might be of potential benefit in reducing the invasive phenotype of GBM in a subpopulation of patients.

Transforming growth factor beta receptor type III is a tumor promoter in mesenchymal-stem like triple negative breast cancer

Introduction

There is a major need to better understand the molecular basis of triple negative breast cancer (TNBC) in order to develop effective therapeutic strategies. Using gene expression data from 587 TNBC patients we previously identified six subtypes of the disease, among which a mesenchymal-stem like (MSL) subtype. The MSL subtype has significantly higher expression of the transforming growth factor beta (TGF-β) pathway-associated genes relative to other subtypes, including the TGF-β receptor type III (TβRIII). We hypothesize that TβRIII is tumor promoter in mesenchymal-stem like TNBC cells.

Methods

Representative MSL cell lines SUM159, MDA-MB-231 and MDA-MB-157 were used to study the roles of TβRIII in the MSL subtype. We stably expressed short hairpin RNAs specific to TβRIII (TβRIII-KD). These cells were then used for xenograft tumor studies in vivo; and migration, invasion, proliferation and three dimensional culture studies in vitro. Furthermore, we utilized human gene expression datasets to examine TβRIII expression patterns across all TNBC subtypes.

Results

TβRIII was the most differentially expressed TGF-β signaling gene in the MSL subtype. Silencing TβRIII expression in MSL cell lines significantly decreased cell motility and invasion. In addition, when TβRIII-KD cells were grown in a three dimensional (3D) culture system or nude mice, there was a loss of invasive protrusions and a significant decrease in xenograft tumor growth, respectively. In pursuit of the mechanistic underpinnings for the observed TβRIII-dependent phenotypes, we discovered that integrin-α2 was expressed at higher level in MSL cells after TβRIII-KD. Stable knockdown of integrin-α2 in TβRIII-KD MSL cells rescued the ability of the MSL cells to migrate and invade at the same level as MSL control cells.

Conclusions

We have found that TβRIII is required for migration and invasion in vitro and xenograft growth in vivo. We also show that TβRIII-KD elevates expression of integrin-α2, which is required for the reduced migration and invasion, as determined by siRNA knockdown studies of both TβRIII and integrin-α2. Overall, our results indicate a potential mechanism in which TβRIII modulates integrin-α2 expression to effect MSL cell migration, invasion, and tumorigenicity.

A synthetic peptide from transforming growth factor-β₁ type III receptor inhibits NADPH oxidase and prevents oxidative stress in the kidney of spontaneously hypertensive rats

AIMS

The NADPH oxidases constitute a major source of superoxide anion (·O2(-)) in hypertension. Several studies suggest an important role of NADPH oxidases in different effects mediated by transforming growth factor-β₁ (TGF-β₁). We investigated whether a chronic treatment with P144, a peptide synthesized from type III TGF-β₁ receptor, inhibited NADPH oxidases in the renal cortex of spontaneously hypertensive rats (SHR).

RESULTS

Here, we show that chronic administration of P144 significantly reduced the NADPH oxidase expression and activity as well as the oxidative stress observed in control vehicle-treated SHR (V-SHR). In addition, P144 was also able to reduce the significant increase in the renal fibrosis and in mRNA expression of different components of collagen metabolism, as well as in the levels of connective tissue growth factor observed in V-SHR. Finally, TGF-β₁-stimulated NRK52E exhibited a significant increase in NADPH oxidase expression and activity as well as a TGF-β₁-dependent intracellular pathway that were inhibited in the presence of P144.

INNOVATION

Our experimental evidence suggests that reversing oxidative stress may be therapeutically useful in preventing fibrosis-associated renal damage. We show here that (i) the TGF-β₁-NADPH oxidases axis is crucial in the development of fibrosis in an experimental hypertensive renal disease animal model, and (ii) the use of P144 reverses TGF-β₁-dependent NADPH oxidase activity; thus, P144 may be considered a novel therapeutic tool in kidney disease associated with hypertension.

CONCLUSION

We demonstrate that P144 inhibits NADPH oxidases and prevents oxidative stress in kidneys from hypertensive rats. Our data also suggest that these effects are associated with the renal antifibrotic effect of P144.

Retromer maintains basolateral distribution of the type II TGF-β receptor via the recycling endosome

After basolateral (BL) cell surface delivery, retromer promotes type II TGF-β receptor exit and recycling to the BL plasma membrane. In the absence of retromer, however, type II receptors aberrantly sort and are mislocalized such that both BL and apical expression is observed independent of the Rab11-positive apical recycling endosome.

Transforming growth factor β (TGF-β) is critical for the development and maintenance of epithelial structures. Because receptor localization and trafficking affect the cellular and organismal response to TGF-β, the present study was designed to address how such homeostatic control is regulated. To that end, we identify a new role for the mammalian retromer complex in maintaining basolateral plasma membrane expression of the type II TGF-β receptor (TβRII). Retromer and TβRII associate in the presence or absence of TGF-β ligand. After retromer knockdown, although TβRII internalization and trafficking to a Rab5-positive compartment occur as in wild-type cells, receptor recycling is inhibited. This results in TβRII mislocalization from the basolateral to both the basolateral and apical plasma membranes independent of Golgi transit and the Rab11-positive apical recycling endosome. The data support a model in which, after initial basolateral TβRII delivery, steady-state polarized TβRII expression is maintained by retromer/TβRII binding and delivery to the common recycling endosome.

Prospective potency of TGF-β1 on maintenance and regeneration of periodontal tissue

Periodontal ligament (PDL) tissue, central in the periodontium, plays crucial roles in sustaining tooth in the bone socket. Irreparable damages of this tissue provoke tooth loss, causing a decreased quality of life. The question arises as to how PDL tissue is maintained or how the lost PDL tissue can be regenerated. Stem cells included in PDL tissue (PDLSCs) are widely accepted to have the potential to maintain or regenerate the periodontium, but PDLSCs are very few in number. In recent studies, undifferentiated clonal human PDL cell lines were developed to elucidate the applicable potentials of PDLSCs for the periodontal regenerative medicine based on cell-based tissue engineering. In addition, it has been suggested that transforming growth factor-beta 1 is an eligible factor for the maintenance and regeneration of PDL tissue.

The Dual Role of TGFβ in Human Cancer: From Tumor Suppression to Cancer Metastasis

The transforming growth factor-beta (TGFβ) superfamily encompasses widespread and evolutionarily conserved polypeptide growth factors that regulate and orchestrate growth and differentiation in all cell types and tissues. While they regulate asymmetric cell division and cell fate determination during early development and embryogenesis, TGFβ family members play a major regulatory role in hormonal and immune responses, cell growth, cell death and cell immortalization, bone formation, tissue remodeling and repair, and erythropoiesis throughout adult life. The biological and physiological functions of TGFβ, the founding member of this family, and its receptors are of central importance to human diseases, particularly cancer. By regulating cell growth, death, and immortalization, TGFβ signaling pathways exert tumor suppressor effects in normal cells and early carcinomas. Thus, it is not surprising that a high number of human tumors arise due to mutations or deletions in the genes coding for the various TGFβ signaling components. As tumors develop and progress, these protective and cytostatic effects of TGFβ are often lost. TGFβ signaling then switches to promote cancer progression, invasion, and tumor metastasis. The molecular mechanisms underlying this dual role of TGFβ in human cancer will be discussed in depth in this paper, and it will highlight the challenge and importance of developing novel therapeutic strategies specifically aimed at blocking the prometastatic arm of the TGFβ signaling pathway without affecting its tumor suppressive effects.

Blockade of TGF-β 1 signalling inhibits cardiac NADPH oxidase overactivity in hypertensive rats

NADPH oxidases constitute a major source of superoxide anion (·O(2)(-)) in hypertension. Several studies suggest an important role of NADPH oxidases in different effects mediated by TGF-β 1. In this study we show that chronic administration of P144, a peptide synthesized from type III TGF-β 1 receptor, significantly reduced the cardiac NADPH oxidase expression and activity as well as in the nitrotyrosine levels observed in control spontaneously hypertensive rats (V-SHR) to levels similar to control normotensive Wistar Kyoto rats. In addition, P144 was also able to reduce the significant increases in the expression of collagen type I protein and mRNA observed in hearts from V-SHR. In addition, positive correlations between collagen expression, NADPH oxidase activity, and nitrotyrosine levels were found in all animals. Finally, TGF-β 1-stimulated Rat-2 exhibited significant increases in NADPH oxidase activity that was inhibited in the presence of P144. It could be concluded that the blockade of TGF-β 1 with P144 inhibited cardiac NADPH oxidase in SHR, thus adding new data to elucidate the involvement of this enzyme in the profibrotic actions of TGF-β 1.

LY2109761 attenuates radiation-induced pulmonary murine fibrosis via reversal of TGF-β and BMP-associated proinflammatory and proangiogenic signals

PURPOSE

Radiotherapy is used for the treatment of lung cancer, but at the same time induces acute pneumonitis and subsequent pulmonary fibrosis, where TGF-β signaling is considered to play an important role.

EXPERIMENTAL DESIGN

We irradiated thoraces of C57BL/6 mice (single dose, 20 Gy) and administered them a novel small-molecule TGF-β receptor I serine/threonine kinase inhibitor (LY2109761) orally for 4 weeks before, during, or after radiation. Noninvasive lung imaging including volume computed tomography (VCT) and MRI was conducted 6, 16, and 20 weeks after irradiation and was correlated to histologic findings. Expression profiling analysis and protein analysis was conducted in human primary fibroblasts.

RESULTS

Radiation alone induced acute pulmonary inflammation and lung fibrosis after 16 weeks associated with reduced life span. VCT, MRI, and histology showed that LY2109761 markedly reduced inflammation and pulmonary fibrosis resulting in prolonged survival. Mechanistically, we found that LY2109761 reduced p-SMAD2 and p-SMAD1 expression, and transcriptomics revealed that LY2109761 suppressed expression of genes involved in canonical and noncanonical TGF-β signaling and downstream signaling of bone morphogenetic proteins (BMP). LY2109761 also suppressed radiation-induced inflammatory [e.g., interleukin (IL)-6, IL-7R, IL-8] and proangiogenic genes (e.g., ID1) indicating that LY2109761 achieves its antifibrotic effect by suppressing radiation-induced proinflammatory, proangiogenic, and profibrotic signals.

CONCLUSION

Small-molecule inhibitors of the TGF-β receptor I kinase may offer a promising approach to treat or attenuate radiation-induced lung toxicity or other diseases associated with fibrosis.

Stem cell antigen-1 enhances tumorigenicity by disruption of growth differentiation factor-10 (GDF10)-dependent TGF-beta signaling

Stem cell antigen (Sca)-1/Ly6A, a glycerophosphatidylinositol-linked surface protein, was found to be associated with murine stem cell- and progenitor cell-enriched populations, and also has been linked to the capacity of tumor-initiating cells. Despite these interesting associations, this protein's functional role in these processes remains largely unknown. To identify the mechanism underlying the protein's possible role in mammary tumorigenesis, Sca-1 expression was examined in Sca-1(+/EGFP) mice during carcinogenesis. Mammary tumor cells derived from these mice readily engrafted in syngeneic mice, and tumor growth was markedly inhibited on down-regulation of Sca-1 expression. The latter effect was associated with significantly elevated expression of the TGF-β ligand growth differentiation factor-10 (GDF10), which was found to selectively activate TGF-β receptor (TβRI/II)-dependent Smad3 phosphorylation. Overexpression of GDF10 attenuated tumor formation; conversely, silencing of GDF10 expression reversed these effects. Sca-1 attenuated GDF10-dependent TGF-β signaling by disrupting the heterodimerization of TβRI and TβRII receptors. These findings suggest a new functional role for Sca-1 in maintaining tumorigenicity, in part by acting as a potent suppressor of TGF-β signaling.

Modulation of transforming growth factor beta signalling pathway genes by transforming growth factor beta in human osteoarthritic chondrocytes: involvement of Sp1 in both early and late response cells to transforming growth factor beta

Introduction

Transforming growth factor beta (TGFβ) plays a central role in morphogenesis, growth, and cell differentiation. This cytokine is particularly important in cartilage where it regulates cell proliferation and extracellular matrix synthesis. While the action of TGFβ on chondrocyte metabolism has been extensively catalogued, the modulation of specific genes that function as mediators of TGFβ signalling is poorly defined. In the current study, elements of the Smad component of the TGFβ intracellular signalling system and TGFβ receptors were characterised in human chondrocytes upon TGFβ1 treatment.

Methods

Human articular chondrocytes were incubated with TGFβ1. Then, mRNA and protein levels of TGFβ receptors and Smads were analysed by RT-PCR and western blot analysis. The role of specific protein 1 (Sp1) was investigated by gain and loss of function (inhibitor, siRNA, expression vector).

Results

We showed that TGFβ1 regulates mRNA levels of its own receptors, and of Smad3 and Smad7. It modulates TGFβ receptors post-transcriptionally by affecting their mRNA stability, but does not change the Smad-3 and Smad-7 mRNA half-life span, suggesting a potential transcriptional effect on these genes. Moreover, the transcriptional factor Sp1, which is downregulated by TGFβ1, is involved in the repression of both TGFβ receptors but not in the modulation of Smad3 and Smad7. Interestingly, Sp1 ectopic expression permitted also to maintain a similar expression pattern to early response to TGFβ at 24 hours of treatment. It restored the induction of Sox9 and COL2A1 and blocked the late response (repression of aggrecan, induction of COL1A1 and COL10A1).

Conclusions

These data help to better understand the negative feedback loop in the TGFβ signalling system, and enlighten an interesting role of Sp1 to regulate TGFβ response.

Activin receptor-like kinase and the insulin gene

The biological responses of the transforming growth factor-β (TGF-β) superfamily, which includes Activins and Nodal, are induced by activation of a receptor complex and Smads. A type I receptor, which is a component of the complex, is known as an activin receptor-like kinase (ALK); currently seven ALKs (ALK1-ALK7) have been identified in humans. Activins signaling, which is mediated by ALK4 and 7 together with ActRIIA and IIB, plays a critical role in glucose-stimulated insulin secretion, development/neogenesis, and glucose homeostatic control of pancreatic endocrine cells; the insulin gene is regulated by these signaling pathways via ALK7, which is a receptor for Activins AB and B and Nodal. This review discusses signal transduction of ALKs in pancreatic endocrine cells and the role of ALKs in insulin gene regulation.

Type II transforming growth factor-beta receptor recycling is dependent upon the clathrin adaptor protein Dab2

Transforming growth factor-β receptor recycling is regulated by the clathrin adaptor Dab2 protein. In the absence of Dab2, receptors localize in a perinuclear locale because they are unable to transit from the early endosomal antigen 1-positive early endosome to the Rab11-positive endosomal recycling compartment.

Transforming growth factor (TGF)-β family proteins form heteromeric complexes with transmembrane serine/threonine kinases referred to as type I and type II receptors. Ligand binding initiates a signaling cascade that generates a variety of cell type-specific phenotypes. Whereas numerous studies have investigated the regulatory activities controlling TGF-β signaling, there is relatively little information addressing the endocytic and trafficking itinerary of TGF-β receptor subunits. In the current study we have investigated the role of the clathrin-associated sorting protein Disabled-2 (Dab2) in TGF-β receptor endocytosis. Although small interfering RNA-mediated Dab2 knockdown had no affect on the internalization of various clathrin-dependent (i.e., TGF-β, low-density lipoprotein, or transferrin) or -independent (i.e., LacCer) cargo, TGF-β receptor recycling was abrogated. Loss of Dab2 resulted in enlarged early endosomal antigen 1-positive endosomes, reflecting the inability of cargo to traffic from the early endosome to the endosomal recycling compartment and, as documented previously, diminished Smad2 phosphorylation. The results support a model whereby Dab2 acts as a multifunctional adaptor in mesenchymal cells required for TGF-β receptor recycling as well as Smad2 phosphorylation.

Roles for the type III TGF-beta receptor in human cancer

Transforming growth factor beta (TGF-beta) superfamily ligands have important roles in regulating cellular homeostasis, embryonic development, differentiation, proliferation, immune surveillance, angiogenesis, motility, and apoptosis in a cell type and context specific manner. TGF-beta superfamily signaling pathways also have diverse roles in human cancer, functioning to either suppress or promote cancer progression. The TGF-beta superfamily co-receptor, the type III TGF-beta receptor (TbetaRIII, also known as betaglycan) mediates TGF-beta superfamily ligand dependent as well as ligand independent signaling to both Smad and non-Smad signaling pathways. Loss of TbetaRIII expression during cancer progression and direct effects of TbetaRIII on regulating cell migration, invasion, proliferation, and angiogenesis support a role for TbetaRIII as a suppressor of cancer progression and/or as a metastasis suppressor. Defining the physiological function and mechanism of TbetaRIII action and alterations in TbetaRIII function during cancer progression should enable more effective targeting of TbetaRIII and TbetaRIII mediated functions for the diagnosis and treatment of human cancer.

Caenorhabditis elegans SMA-10/LRIG is a conserved transmembrane protein that enhances bone morphogenetic protein signaling

Bone morphogenetic protein (BMP) pathways control an array of developmental and homeostatic events, and must themselves be exquisitely controlled. Here, we identify Caenorhabditis elegans SMA-10 as a positive extracellular regulator of BMP-like receptor signaling. SMA-10 acts genetically in a BMP-like (Sma/Mab) pathway between the ligand DBL-1 and its receptors SMA-6 and DAF-4. We cloned sma-10 and show that it has fifteen leucine-rich repeats and three immunoglobulin-like domains, hallmarks of an LRIG subfamily of transmembrane proteins. SMA-10 is required in the hypodermis, where the core Sma/Mab signaling components function. We demonstrate functional conservation of LRIGs by rescuing sma-10(lf) animals with the Drosophila ortholog lambik, showing that SMA-10 physically binds the DBL-1 receptors SMA-6 and DAF-4 and enhances signaling in vitro. This interaction is evolutionarily conserved, evidenced by LRIG1 binding to vertebrate receptors. We propose a new role for LRIG family members: the positive regulation of BMP signaling by binding both Type I and Type II receptors.

A synthetic peptide from transforming growth factor-beta1 type III receptor prevents myocardial fibrosis in spontaneously hypertensive rats

AIM

We investigated whether P144, a synthetic peptide from transforming growth factor-beta(1) (TGF-beta(1)) type III receptor betaglycan, exhibits cardiac antifibrotic properties.

METHODS AND RESULTS

The study was carried out in one group of 10-week-old normotensive Wistar-Kyoto rats treated with vehicle (V-WKY), one group of 10-week-old spontaneously hypertensive rats treated with vehicle (V-SHR), and one group of 10-week-old SHR treated with P144 (P144-SHR) for 12 weeks. Two more groups of 10-week-old untreated WKY and SHR were used to assess baseline values of the parameters tested. In addition, the effects of P144 on rat cardiac fibroblasts stimulated with TGF-beta(1) were also studied. Compared with V-WKY, V-SHR exhibited significant increases in the myocardial expression of phosphorylated Smad2, 38 and 42 kDa connective tissue growth factor (CTGF) isoforms, procollagen alpha1 (I) mRNA, and collagen type I protein, as well as in the expression of lysyl oxidase (LOX) mRNA and protein, collagen cross-linking and deposition. P144 administration was associated with significant reduction in all these parameters in P144-SHR. TGF-beta(1)-stimulated fibroblasts exhibited significant increases in phosphorylated Smad2, 38 and 42 kDa CTGF proteins, and procollagen alpha(1) (I) mRNA compared with control fibroblasts. No significant differences were found in these parameters between fibroblasts incubated with TGF-beta(1) and P144 and control fibroblasts.

CONCLUSION

These results show that P144 inhibits TGF-beta(1)-dependent signalling pathway and collagen type I synthesis in cardiac fibroblasts. These effects may be involved in the ability of this peptide to prevent myocardial fibrosis in SHR.

The bone morphogenetic protein pathway is inactivated in the majority of sporadic colorectal cancers

BACKGROUND & AIMS

The finding of bone morphogenetic protein (BMP) receptor 1a mutations in juvenile polyposis suggests that BMPs are important in colorectal cancer (CRC). We investigated the BMP pathway in sporadic CRC.

METHODS

We investigated BMP receptor (BMPR) expression using immunoblotting and sequenced BMPR2 in CRC cell lines. We assessed the expression of BMPRs, SMAD4, and pSMAD1/5/8 in 72 sporadic CRCs using a tissue microarray and immunohistochemistry. We assessed the effect of reintroduction of wild-type BMPR2 on BMP pathway activity and the effect of wild-type or mutated BMPR2 3' untranslated region (UTR) sequences on protein expression by attachment to pCMV-Luc.

RESULTS

BMPR2 and SMAD4 protein expression is abrogated in microsatellite unstable (MSI) and microsatellite stable (MSS) cell lines, respectively. BMPR2 3'UTR is mutated in all MSI and in none of the MSS cell lines. Mutant BMPR2 3'UTR sequences reduced luciferase expression 10-fold compared with wild-type BMPR2 3'UTR. BMPR2 expression is impaired more frequently in MSI CRCs than MSS (85% vs 29%; P < .0001) and shows a mutually exclusive pattern of impaired expression compared with SMAD4. Nine of 11 MSI cancers with impaired expression of BMPR2 have microsatellite mutations. The BMP pathway is inactivated, as judged by nuclear pSMAD1/5/8 expression, in 70% of CRCs, and this correlates with BMPR and SMAD4 loss.

CONCLUSIONS

Our data suggest that the BMP pathway is inactivated in the majority of sporadic CRCs. In MSI CRC this is associated predominantly with impaired BMPR2 expression and in MSS CRC with impaired SMAD4 expression.

In vivo and in vitro effects of TGF-beta 1 on normal and neoplastic haemopoiesis

TGF-beta 1 and TGF-beta 2 are equipotent selective inhibitors of murine and human haemopoiesis in vitro. Primitive haemopoietic cells such as the high proliferative potential progenitor cell and the colony-forming unit (CFU)-GEMM are directly inhibited by TGF-beta whereas the more differentiated CFU-G, CFU-M and CFU-E are not. Recombinant TGF-beta 1 administered intraperitoneally or intravenously to mice selectively inhibits haemopoietic colony formation in a time- and dose-dependent manner to the same extent as seen in vitro. The progenitors are reversibly prevented from entering the cell cycle. This inhibitory action of TGF-beta functions on at least two levels: (1) down-modulation of the cell surface expression of receptors for growth stimulatory molecules and (2) interference with the intracellular signalling pathways of these molecules. In addition, expression of TGF-beta receptors is regulated during cytokine stimulation of haemopoiesis. Neoplastic B lymphocytes can proliferate by escaping from a TGF-beta-mediated autocrine inhibitory loop. Activation signals (e.g. phorbol esters) inhibit tumour cell growth by stimulating active TGF-beta production and inducing cell surface expression of TGF-beta receptors. These results indicate that TGF-beta may be useful as a bone marrow protective and/or an antitumour agent.

Ligand-dependent and -independent transforming growth factor-beta receptor recycling regulated by clathrin-mediated endocytosis and Rab11

Proteins in the transforming growth factor-beta (TGF-beta) family recognize transmembrane serine/threonine kinases known as type I and type II receptors. Binding of TGF-beta to receptors results in receptor down-regulation and signaling. Whereas previous work has focused on activities controlling TGF-beta signaling, more recent studies have begun to address the trafficking properties of TGF-beta receptors. In this report, it is shown that receptors undergo recycling both in the presence and absence of ligand activation, with the rates of internalization and recycling being unaffected by ligand binding. Recycling occurs as receptors are most likely internalized through clathrin-coated pits, and then returned to the plasma membrane via a rab11-dependent, rab4-independent mechanism. Together, the results suggest a mechanism wherein activated TGF-beta receptors are directed to a distinct endocytic pathway for down-regulation and clathrin-dependent degradation after one or more rounds of recycling.

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.

TGF-beta and the Smad signal transduction pathway

Transforming growth factor beta (TGF-beta) superfamily members are important regulators of many diverse developmental and homeostatic processes and disruption of their activity has been implicated in a variety of human diseases ranging from cancer to chondrodysplasias and pulmonary hypertension. TGF-beta family members signal through transmembrane Ser-Thr kinase receptors that directly regulate the intracellular Smad pathway. Smads are a unique family of signal transduction molecules that can transmit signals directly from the cell surface receptors to the nucleus, where they regulate transcription by interacting with DNA binding partners as well as transcriptional coactivators and corepressors. In addition, more recent evidence indicates that Smads can also function both as substrates and adaptors for ubiquitin protein ligases, which mediate the targeted destruction of intracellular proteins. Smads have thus emerged as multifunctional transmitters of TGF-beta family signals that play critical roles in the development and homeostasis of metazoans.

Transforming growth factor-beta expression is significantly lower in hearts preserved with blood/insulin versus crystalloid cardioplegia

The major cause of morbidity and mortality after cardiac transplantation is cardiac allograft vasculopathy (CAV). The purpose of this study was to examine the expression of markers of endothelial injury that may be affected by blood/insulin or crystalloid cardioplegia. After RNA-blot hybridization, the level of expression of tumor necrosis factor-alpha, transforming growth factor-beta (TGF-beta), intracellular adhesion molecule-1, platelet-endothelial cell adhesion molecule-1, endothelin-1, and E-selectin was increased in crystalloid cardioplegia as compared with normal and blood/insulin cardioplegia; TGF-beta was expressed at significantly lower levels in blood/insulin vs crystalloid cardioplegia (p < 0.05). Because increased expression of TGF-beta has been correlated with accelerated CAV, the use of blood/insulin cardioplegia may help to decrease the extent of endothelial damage and attenuate the progression of CAV.

Identification of receptors for prothymosin alpha on human lymphocytes

Prothymosin alpha (ProTalpha) is a highly conserved and widely distributed protein whose physiological functions remain elusive. In previous work we identified high and low affinity-binding sites for ProTalpha in lymphoid cells. Here we demonstrate, by affinity cross-linking and affinity chromatography, the existence of three binding partners (31, 29, and 19 kDa) for ProTalpha in the membrane of PHA-activated lymphoblasts. These surface molecules possess the expected affinity and specificity for a ProTalpha receptor. Examination of the expression of this complex of molecules by flow cytometry reveals that they bind ProTalpha in a specific and saturable way. In addition, the distribution of the receptor on the cell surface was studied by fluorescence microscopy; a cap-like structure at one of the poles of the cells was identified. These results represent a new and promising approach in the research on ProTalpha, opening the way toward the understanding of the molecular mechanism of action of this protein.

Expression of transforming growth factor (TGF)-beta1 and TGF-beta type II receptor in preneoplastic lesions during chemical hepatocarcinogenesis of rats

Transforming growth factor (TGF)-beta1 is an important apoptotic growth inhibitor of hepatocyte proliferation, and the expression of TGF-beta1, which regulates cell proliferation, is closely associated with the expression level of TGF-beta type II receptor (TGR2). Moreover, TGF-beta1 expression has been regarded to be an important change in hepatocarcinogenesis, We undertook this study to investigate the gene expression and protein localization of TGF-beta1 and TGR2 and their relationship with apoptosis in the chemically induced hepatocarcinogenesis of the rat, as produced using Solt and Farber's method, during the promotion stage (up to 56 days after partial hepatectomy). Northern blot analysis showed a slight, but not a significant, increase in TGF-beta1 transcripts, and a significant decrease in the TGR2 transcripts during the later stage of our experiments (42 days after partial hepatectomy). Immunohistochemical study showed that TGF-beta1-positive preneoplastic hepatocytes increased with time, and this correlated with an increase of TGR2 negative or reduced TGR2 expressed preneoplastic lesions. The TUNEL method revealed that apoptotic cells increased with time and were more numerous in the adjacent liver parenchyme than preneoplastic lesions. Our data suggest that the expressions of TGF-beta1 and TGR2 are significantly altered during the promotion stage of hepatocarcinogenesis of rat and that these changes might contribute to the development and progression of preneoplastic lesions.

Identification of soluble transforming growth factor-beta receptor III (sTbetaIII) in rat milk

Transforming growth factor-beta (TGF-beta) is present at high concentrations in maternal milk. In milk TGF-beta2 is the predominant isoform. For function TGF-beta2 requires TbetaRIII to facilitate efficient binding to the TGF-beta receptor types I and II signalling complex. We have shown that TGF-beta receptor types I (TbetaRI), II (TbetaRII) and III (TbetaRIII) are coexpressed in the suckling rat intestine. Immunostaining for TbetaRIII was also observed in the intestinal lumen prior to weaning. TbetaRIII (or betaglycan) has been reported in serum, cell culture medium and extracellular matrix. To determine whether a soluble form of TbetaRIII is present in milk, the rat milk aqueous phase was analysed by slot-blot and Western blot. Soluble TbetaRIII was detected in milk throughout lactation. Western blot analysis of rat milk revealed a high molecular weight band of glycosylated protein of >200 kDa, with a core protein of approximately 110-120 kDa that comigrated with recombinant TbetaRIII. Immunoabsorption of soluble TbetaRIII (sTbetaRIII) from milk resulted in partial depletion of active TGF-beta from milk, suggesting that the receptor may interact with ligand in milk. In addition rat pups suckled on mother's milk demonstrated an enhanced labelling of TbetaRIII in the gut, as compared with pups fed on a rat milk substitute (RMS). These findings suggest that milk sTbetaRIII is functional, and may modulate milk-derived TGF-beta function in the developing intestine.

Localization of specific binding sites for 125I-TGF-beta1 to fenestrated endothelium in bone and anastomosing capillary networks in enamel organ suggests a role for TGF-beta1 in angiogenesis

Previous studies have shown endothelial cells to be a major target for endocrine TGF-beta in several soft tissues in the normal growing rat. The potent effect of TGF-beta1 on bone formation prompted us to analyze in detail the localization of specific binding sites for endocrine TGF-beta in hard tissues. At 2.5 minutes after injection of 125I-TGF-beta1, specific binding, as demonstrated by quantitative radioautography, was localized to fenestrated endothelium participating in angiogenesis in the vascular invasion region of the growth plate in bone as well as to anatomizing capillary networks in the maturation zone of the enamel organ. At 15 minutes after injection, the bound ligand was internalized into endocytic vesicles of endothelial cells. In bone, quantitation revealed significant differences in receptor density between endothelia undergoing proliferation vs those in a state of elongation and anastomosis with neighboring endothelial cells. In the rat incisor, specific binding of 125I-TGF-beta1 to endothelium correlated with increased formation of anastomotic capillary networks. These studies identify differential specific binding sites of 125I-TGF-beta1 in angiogenically active endothelium, providing an important link between TGF-beta1, the endothelium, and hard tissue development.

Latency, activation, and binding proteins of TGF-beta

The TGF-beta superfamily of growth factors consists of an increasing number of different polypeptide modulators of cell growth, differentiation, and morphogenesis. Three mammalian isoforms have been molecularly cloned. Numerous ways to regulate the expression of the TGF-beta genes have been identified. TGF-betas are, for example, subject to regulation by retinoids, steroid hormones, and vitamin D. A characteristic feature in the biology of TGF-betas is that they are usually secreted from cells in latent forms. The large latent complex consists of the small latent complex (TGF-beta and its propeptide) and a high molecular weight protease resistant binding protein, latent TGF-beta binding protein (LTBP). LTBPs are required for the proper folding and secretion of TGF-beta. TGF-beta is not just secreted from cultured cells but is deposited via LTBPs to the pericellular space, namely to the extracellular matrix. Release of these complexes and activation by proteases is under tight regulation and provides a means to rapidly increase local concentrations of TGF-beta. Biological events, where enhanced or focal proteolysis and activation of latent TGF-beta takes place, include cell invasion, tissue remodeling, and wound healing.

Angiotensin II upregulates transforming growth factor-beta type I receptor on rat vascular smooth muscle cells

Angiotensin II (Ang II) and transforming growth factor-beta (TGF-beta) modulate cell growth and metabolism. Our objective was to evaluate the effect of Ang II on the characteristics and expression of TGF-beta receptors on vascular smooth muscle cells (VSMC) from Wistar-Kyoto rats. The addition of TGF-beta1 elicited a biphasic response on DNA synthesis in cultured VSMC in the absence of Ang II, but TGF-beta1 did not stimulate DNA synthesis in the presence of Ang II. TGF-beta binding data showed that Ang II increased the specific binding of 125I-TGF-beta1 by enhancing the expression of lower affinity receptors and increasing the number of binding sites. Ang II alone did not stimulate DNA synthesis in these cultures. However, Ang II significantly stimulated DNA synthesis after the inhibition of endogenous TGF-beta with a neutralizing antibody. The DNA synthesis stimulated by phorbol ester milisterol (PMA) was not affected by the TGF-beta neutralizing antibody. Affinity labeling data revealed receptor-ligand complexes of 280, 85, and 70 kDa, corresponding to TGF-beta type III, II, and I receptors, respectively. Incubation of VSMC with Ang II but not with PMA markedly increased the expression of the TGF-beta type I receptor. Reverse transcription and polymerase chain reaction data also indicated that Ang II, but not PMA, significantly increased the expression of TGF-beta type I receptor mRNA. Results suggest that Ang II increases the binding of TGF-beta with upregulation of TGF-beta type I receptor via a C-kinase-independent pathway. The enhanced expression of the TGF-beta type I receptor may counteract Ang II-promoted growth of VSMC.

Transforming growth factor beta1 enhances platelet aggregation through a non-transcriptional effect on the fibrinogen receptor

Upon activation, platelets store and release large amounts of the peptide transforming growth factor beta1 (TGFbeta1). The released TGFbeta1 can then act on nearby vascular cells to mediate subsequent vessel repair. In addition, TGFbeta1 may circulate to bone marrow and regulate megakaryocyte activity. It is not known what effect, if any, TGFbeta1 has on platelets. Adult TGFbeta1-deficient mice exhibit thrombocythemia and a mild bleeding disorder that is shown to result from faulty platelet aggregation. TGFbeta1-deficient platelets are shown to contain functional receptors, and preincubation with recombinant TGFbeta1 improves aggregation, demonstrating that TGFbeta1 plays an active role in platelet aggregation. TGFbeta1-deficient platelets fail to retain bound fibrinogen in response to aggregation agonists, but they possess normal levels of the alpha(IIb)/beta(3) fibrinogen receptor. Signaling from agonist receptors is normal because the platelets change shape, produce thromboxane A(2), and present P-selectin in response to stimulation. Consequently, activation and maintenance of alpha(IIb)/beta(3) into a fibrinogen-binding conformation is impaired in the absence of TGFbeta1. 4-Phorbol 12-myristate 13-acetate treatment and protein kinase C activity measurements suggest a defect downstream of protein kinase C in its activation cascade. Because platelets lack nuclei, these data demonstrate for the first time a non-transcriptionally mediated TGFbeta1 signaling pathway that enhances the activation and maintenance of integrin function.

Transforming growth factor-beta (TGF-beta) type I and type II receptors are both required for TGF-beta-mediated extracellular matrix production in lung fibroblasts

Transforming growth factor-beta (TGF-beta) regulates a variety of cellular activities including cell growth, differentiation and extracellular matrix production. The TGF-beta type I and type II serine/threonine kinase receptors (TbetaRI and TbetaRII) have been identified as signal-transducing TGF-beta receptors. This study was undertaken to examine the role of the type I and type II receptors in TGF-beta-induced extracellular matrix production of lung fibroblasts. We constructed expression plasmids containing truncated derivatives of TbetaRI and TbetaRII that lacked the cytoplasmic serine/threonine kinase domain (TbetaRI deltaK and TbetaRII deltaK), and transfected them into lung fibroblasts. TbetaRII deltaK expressed by lung fibroblasts was able to bind 125I-TGF-beta1, whereas TbetaRI deltaK was unable to bind ligand when expressed alone. Co-expression with TbetaRII was required for binding and cross-linking of TGF-beta1 to TbetaRI deltaK. Lung fibroblasts upregulate tenascin and fibronectin production when treated with TGF-beta1. The kinase-defective deletions of both TbetaRI and TbetaRII were dominant-acting inhibitors of TGF-beta signal transduction. Expression of either TbetaRI deltaK or TbetaRII deltaK alone was sufficient to block TGF-beta-induced tenascin and fibronectin production of lung fibroblasts. The results indicate that both TbetaRI and TbetaRII were required for TGF-beta signaling in regulation of extracellular matrix production by lung fibroblasts.

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.

Abrogation of betaglycan attenuates TGF-beta-mediated inhibition of embryonic murine lung branching morphogenesis in culture

Although betaglycan (TGF-beta type III receptor) is known to enhance TGF-beta ligand binding to its type II receptor in murine lung epithelial cell lines, the biological significance of this phenomenon in the process of lung organogenesis is not understood. Betaglycan gene expression was detected in embryonic murine lungs undergoing branching morphogenesis in ex vivo culture. Antisense betaglycan oligodeoxynucleotides (ODN) resulted in up to 56% stimulation of lung branching morphogenesis in culture, while betaglycan mRNA and protein expression levels were suppressed by 90 and 82%, respectively. Following abrogation of betaglycan expression with antisense oligodeoxynucleotide, embryonic lungs were relatively insensitive to TGF-beta: TGF-beta2 (0.5 ng/ml) and TGF-beta1 (20 ng/ml), respectively, down-regulated lung morphogenesis by 38 and 34% in control cultures, whereas TGF-beta-induced inhibition was attenuated to 13 and 26% respectively, in the presence of betaglycan antisense oligodeoxynucleotides. TGF-beta neutralizing antibodies also prevented TGF-beta-mediated inhibition of lung branching in culture, supporting the speculation that autocrine/paracrine TGF-beta signaling is minimal in the absence of betaglycan. Betaglycan was immunolocalized mainly to the epithelial cells in developing airways, a spatial distribution which overlaps with that of TGF-beta type II receptor. Furthermore, abrogation of endogenous betaglycan gene expression prevented the characteristic down-regulation of cyclin A and surfactant protein C (SP-C) mRNAs by exogenous TGF-beta ligands. These results show that betaglycan expression is essential for optimal TGF-beta signaling during embryonic lung development. We therefore conclude that the abrogation of endogenous betaglycan attenuates endogenous autocrine and/or paracrine TGF-beta-mediated negative regulation of lung organogenesis.

Role of transforming growth factor-beta1 in the suppressed allostimulatory function of AIDS patients

BACKGROUND

The T-cell stimulatory function of accessory cells isolated from peripheral blood lymphocytes of AIDS patients has been reported to be suppressed. These patients also have elevated levels of the immunosuppressive factor transforming growth factor (TGF)-beta1 in their serum and plasma.

OBJECTIVE

To explore the role of TGF-beta1 in the loss of accessory cell function of peripheral blood lymphocytes from AIDS patients.

METHODS

Fluorescent labeled anti-TGF-beta1 and confocal microscopy were used to detect the presence of TGF-beta1 on the cell membrane of dendritic cells. To assess the role of TGF-beta1 in the inhibition of accessory cell function in AIDS, antibodies against TGF-beta1 or the TGF-beta1 type III receptor, beta-glycan, were added to a mixed lymphocyte reaction.

RESULTS

TGF-beta1 was detected on the cell membrane of dendritic cells isolated from AIDS patients. The addition of blocking antibodies against either TGF-beta1 or beta-glycan restored the T-cell stimulatory function to accessory cells from these patients.

CONCLUSIONS

T-cell stimulatory function was not irreversibly lost in AIDS patients. Our data suggested that beta-glycan-TGF-beta1 immunosuppressive complexes may contribute to the suppression of accessory cell function in these patients.

Resistance to growth inhibition by transforming growth factor-beta in malignant glioma cells with functional receptors

OBJECT

The aim of this study was to investigate the mechanism by which malignant glioma cells escape from growth inhibition mediated by transforming growth factor-beta (TGF-beta), a ubiquitous cytokine that inhibits cell proliferation by causing growth arrest in the G1 phase of the cell cycle.

METHODS

The authors measured the response of eight malignant glioma cell lines to the growth-inhibiting activity of TGF-beta in vitro and the expression of TGF-beta Types I and II receptors in malignant glioma cells. The effect of TGF-beta on the expression of a p27Kip1 cyclin-dependent kinase inhibitor was also investigated to assess the downstream signal transmission from TGF-beta receptors. All malignant glioma cell lines were insensitive to growth inhibition by TGF-beta1 and TGF-beta2. Analyses of TGF-beta receptors by means of affinity labeling in which 125I-TGF-beta1 was used showed that six glioma lines had both TGF-beta Types I and II receptors on their cell surfaces, whereas two lines had very small amounts of TGF-beta Type I and/or Type II receptors. Northern blot analysis showed that all tumor lines expressed variable levels of messenger RNAs for both TGF-beta Types I and II receptors. Flow cytometric analyses revealed that treatment of malignant glioma cells with TGF-beta1 significantly downregulated the expression of p27Kip1 protein in all malignant glioma cell lines except one.

CONCLUSIONS

The authors suggest that most malignant glioma cells express TGF-beta Types I and II receptors, which can transmit some signals downstream and that the loss of response to TGF-beta growth inhibition may not be caused by an abnormality of the TGF-beta receptors.

Midkine induces tumor cell proliferation and binds to a high affinity signaling receptor associated with JAK tyrosine kinases

The G401 cell line derived from a rhabdoid tumor of the kidney secretes the heparin-binding growth factors midkine and pleiotrophin. Both proteins act as mitogens for diverse cells, but only midkine serves as an autocrine mitogen for G401 tumor cells. We show that midkine specifically binds a protein or complex of molecular mass greater than 200 kDa with high affinity (Kd = 0.07 +/- 0.01 nM). Midkine, but not pleiotrophin, stimulates tyrosine phosphorylation of several cellular proteins with molecular mass of 100, 130, and 200+ kDa. Upon midkine binding, the midkine-receptor complex associates with the Janus tyrosine kinases, JAK1 and JAK2. MK stimulates tyrosine phosphorylation of JAK1, JAK2, and STAT1alpha. Our initial characterization of the midkine receptor suggests that midkine autocrine stimulation of tumor cell proliferation is mediated by a cell-surface receptor which in turn might activate the JAK/STAT pathway.

Abnormal regulation of transforming growth factor-beta receptors on vascular smooth muscle cells from spontaneously hypertensive rats by angiotensin II

The effects of angiotensin II (Ang II) on the expression and characteristics of transforming growth factor-beta (TGF-beta) receptors on vascular smooth muscle cells (VSMC) from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) were investigated. TGF-beta-induced stimulation of DNA synthesis by VSMC from WKY rats was abolished with Ang II, whereas basal and TGF-beta-stimulated DNA synthesis by VSMC from SHR was increased with Ang II. Ang II stimulated DNA synthesis by VSMC from WKY rats in the presence but not in the absence of neutralizing antibody to TGF-beta1. Antibody to TGF-beta1 enhanced the stimulatory effect of Ang II on DNA synthesis by VSMC from SHR. Ang II increased the specific binding of TGF-beta to VSMC from WKY rats by increasing both the expression of the lower-affinity of TGF-beta receptors as well as the total number of TGF-beta binding sites. In contrast, VSMC from SHR showed a higher affinity and number of TGF-beta receptors in the absence of Ang II than did cells from WKY rats, and these parameters were not affected by Ang II. Ang II increased the expression of TGF-beta type I receptor mRNA in VSMC from WKY rats but had no effect of TGF-beta receptor type I or II mRNA in VSMC from SHR, which predominantly express the type II receptor. These results indicate that an increase in the expression of the TGF-beta type I receptor by Ang II may facilitate the ability of endogenous TGF-beta to counteract the stimulatory effect of Ang II on growth in VSMC from WKY rats, whereas endogenous TGF-beta induced by Ang II cannot counteract the growth-promoting action of Ang II in VSMC from SHR. The abnormal regulation of TGF-beta receptors by Ang II may be associated with the exaggerated growth of VSMC from SHR.

Mutational analysis of a transforming growth factor-beta receptor binding site

Transforming growth factor-beta s (TGF-beta 1, -beta 2, -beta 3) are important regulators of cell growth and differentiation which share approximately 70% identical amino acids. Using LS513 colorectal cells, which are growth inhibited by TGF-beta 1 (ED50 of 100 pM), but are refractory to TGF-beta 2 (ED50 of 50,000 to 100,000 pM), we have determined that amino acids 92-98 of TGF-beta specify growth inhibition. The chimeric protein TGF-beta 1/beta 2(92-98), in which amino acids 92-98 of TGF-beta 1 were exchanged for the corresponding amino acids of TGF-beta 2, was indistinguishable from TGF-beta 2 at inhibiting growth of LS513 cells. In contrast, both TGF-beta 1/beta 2(92-95) and TGF-beta 1/beta 2(94-98) inhibited the growth of LS513 cells with an ED50 of approximately 1000 pM. TGF-beta 1/beta 2(95-98), in which amino acids 95-98 of TGF-beta 1 have been replaced with the corresponding amino acids of TGF-beta 2, had full activity and was indistinguishable from TGF-beta 1. Receptor cross-linking experiments demonstrated that binding of the chimeras to the type I and type II receptors of LS513 cells was consistent with their biological activity. TGF-beta 1/beta 2(95-98), TGF-beta 1/beta 2(92-95) and TGF-beta 1/beta 2(94-98) were each similar to TGF-beta 2 in that they failed to bind to the soluble Type II receptor in a solid-phase assay. These results demonstrate that amino acids 92-98 are involved in the interaction between TGF-beta and its signaling receptors and they show that modest changes within this region can substantially alter biological response.

Distinct endocytic responses of heteromeric and homomeric transforming growth factor beta receptors

Transforming growth factor beta (TGF beta) family ligands initiate a cascade of events capable of modulating cellular growth and differentiation. The receptors responsible for transducing these cellular signals are referred to as the type I and type II TGF beta receptors. Ligand binding to the type II receptor results in the transphosphorylation and activation of the type I receptor. This heteromeric complex then propagates the signal(s) to downstream effectors. There is presently little data concerning the fate of TGF beta receptors after ligand binding, with conflicting reports indicating no change or decreasing cell surface receptor numbers. To address the fate of ligand-activated receptors, we have used our previously characterized chimeric receptors consisting of the ligand binding domain from the granulocyte/macrophage colony-stimulating factor alpha or beta receptor fused to the transmembrane and cytoplasmic domain of the type I or type II TGF beta receptor. This system not only provides the necessary sensitivity and specificity to address these types of questions but also permits the differentiation of endocytic responses to either homomeric or heteromeric intracellular TGF beta receptor oligomerization. Data are presented that show, within minutes of ligand binding, chimeric TGF beta receptors are internalized. However, although all the chimeric receptor combinations show similar internalization rates, receptor down-regulation occurs only after activation of heteromeric TGF beta receptors. These results indicate that effective receptor down-regulation requires cross-talk between the type I and type II TGF beta receptors and that TGF beta receptor heteromers and homomers show distinct trafficking behavior.