Plasmin cleaves betaglycan and releases a 60 kDa transforming growth factor-beta complex from the cell surface

The Role of TGFBR3 in the Development of Lung Cancer

The Transforming Growth Factor-β (TGF-β) mediates embryonic development, maintains cellular homeostasis, regulates immune function, and is involved in a wide range of other biological processes. TGF-β superfamily signaling pathways play an important role in cancer development and can promote or inhibit tumorigenesis. Type III TGF-β receptor (TGFBR3) is a co-receptor in the TGF-β signaling pathway, which often occurs with reduced or complete loss of expression in many cancer patients and can act as a tumor suppressor gene. The reduction or deletion of TGFBR3 is more pronounced compared to other elements in the TGF-β signaling pathway. In recent years, lung cancer is one of the major malignant tumors that endanger human health, and its prognosis is poor. Recent studies have reported that TGFBR3 expression decreases to varying degrees in different types of lung cancer, both at the tissue level and at the cellular level. The invasion, metastasis, angiogenesis, and apoptosis of lung cancer cells are closely related to the expression of TGFBR3, which strengthens the inhibitory function of TGFBR3 in the evolution of lung cancer. This article reviews the mechanism of TGFBR3 in lung cancer and the influencing factors associated with TGFBR3. Clarifying the physiological function of TGFBR3 and its molecular mechanism in lung cancer is conducive to the diagnosis and treatment of lung cancer.

Radiation-induced bystander effect and its clinical implications

For many years, targeted DNA damage caused by radiation has been considered the main cause of various biological effects. Based on this paradigm, any small amount of radiation is harmful to the organism. Epidemiological studies of Japanese atomic bomb survivors have proposed the linear-non-threshold model as the dominant standard in the field of radiation protection. However, there is increasing evidence that the linear-non-threshold model is not fully applicable to the biological effects caused by low dose radiation, and theories related to low dose radiation require further investigation. In addition to the cell damage caused by direct exposure, non-targeted effects, which are sometimes referred to as bystander effects, abscopal effects, genetic instability, etc., are another kind of significant effect related to low dose radiation. An understanding of this phenomenon is crucial for both basic biomedical research and clinical application. This article reviews recent studies on the bystander effect and summarizes the key findings in the field. Additionally, it offers a cross-sectional comparison of bystander effects caused by various radiation sources in different cell types, as well as an in-depth analysis of studies on the potential biological mechanisms of bystander effects. This review aims to present valuable information and provide new insights on the bystander effect to enlighten both radiobiologists and clinical radiologists searching for new ways to improve clinical treatments.

The Role of the Plasminogen/Plasmin System in Inflammation of the Oral Cavity

The oral cavity is a unique environment that consists of teeth surrounded by periodontal tissues, oral mucosae with minor salivary glands, and terminal parts of major salivary glands that open into the oral cavity. The cavity is constantly exposed to viral and microbial pathogens. Recent studies indicate that components of the plasminogen (Plg)/plasmin (Pm) system are expressed in tissues of the oral cavity, such as the salivary gland, and contribute to microbial infection and inflammation, such as periodontitis. The Plg/Pm system fulfills two major functions: (a) the destruction of fibrin deposits in the bloodstream or damaged tissues, a process called fibrinolysis, and (b) non-fibrinolytic actions that include the proteolytic modulation of proteins. One can observe both functions during inflammation. The virus that causes the coronavirus disease 2019 (COVID-19) exploits the fibrinolytic and non-fibrinolytic functions of the Plg/Pm system in the oral cavity. During COVID-19, well-established coagulopathy with the development of microthrombi requires constant activation of the fibrinolytic function. Furthermore, viral entry is modulated by receptors such as TMPRSS2, which is necessary in the oral cavity, leading to a derailed immune response that peaks in cytokine storm syndrome. This paper outlines the significance of the Plg/Pm system for infectious and inflammatory diseases that start in the oral cavity.

Proteolysis: a key post-translational modification regulating proteoglycans

Proteoglycans are composite molecules comprising a protein backbone, i.e., the core protein, with covalently attached glycosaminoglycan chains of distinct chemical types. Most proteoglycans are secreted or attached to the cell membrane. Their specialized structures, binding properties, and biophysical attributes underlie diverse biological roles, which include modulation of tissue mechanics, cell adhesion, and the sequestration and regulated release of morphogens, growth factors, and cytokines. As an irreversible post-translational modification, proteolysis has a profound impact on proteoglycan function, abundance, and localization. Proteolysis is required for molecular maturation of some proteoglycans, clearance of extracellular matrix proteoglycans during tissue remodeling, generation of bioactive fragments from proteoglycans, and ectodomain shedding of cell-surface proteoglycans. Genetic evidence shows that proteoglycan core protein proteolysis is essential for diverse morphogenetic events during embryonic development. In contrast, dysregulated proteoglycan proteolysis contributes to osteoarthritis, cardiovascular disorders, cancer, and inflammation. Proteolytic fragments of perlecan, versican, aggrecan, brevican, collagen XVIII, and other proteoglycans are associated with independent biological activities as so-called matrikines. Yet, proteoglycan proteolysis has been investigated to only a limited extent to date. Here, we review the actions of proteases on proteoglycans and illustrate their functional impact with several examples. We discuss the applications and limitations of strategies used to define cleavage sites in proteoglycans and explain how proteoglycanome-wide proteolytic mapping, which is desirable to fully understand the impact of proteolysis on proteoglycans, can be facilitated by integrating classical proteoglycan isolation methods with mass spectrometry-based proteomics.

Plasminogen activator receptor assemblies in cell signaling, innate immunity, and inflammation

Tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA) are serine proteases and major activators of fibrinolysis in mammalian systems. Because fibrinolysis is an essential component of the response to tissue injury, diverse cells, including cells that participate in the response to injury, have evolved receptor systems to detect tPA and uPA and initiate appropriate cell-signaling responses. Formation of functional receptor systems for the plasminogen activators requires assembly of diverse plasma membrane proteins, including but not limited to: the urokinase receptor (uPAR); integrins; N-formyl peptide receptor-2 (FPR2), receptor tyrosine kinases (RTKs), the N-methyl-d-aspartate receptor (NMDA-R), and low-density lipoprotein receptor-related protein-1 (LRP1). The cell-signaling responses elicited by tPA and uPA impact diverse aspects of cell physiology. This review describes rapidly evolving knowledge regarding the structure and function of plasminogen activator receptor assemblies. How these receptor assemblies regulate innate immunity and inflammation is then considered.

Priming the seed: Helicobacter pylori alters epithelial cell invasiveness in early gastric carcinogenesis

Helicobacter pylori (H. pylori) infection is a well-established risk factor for the development of gastric cancer (GC), one of the most common and deadliest neoplasms worldwide. H. pylori infection induces chronic inflammation in the gastric mucosa that, in the absence of treatment, may progress through a series of steps to GC. GC is only one of several clinical outcomes associated with this bacterial infection, which may be at least partially attributed to the high genetic variability of H. pylori. The biological mechanisms underlying how and under what circumstances H. pylori alters normal physiological processes remain enigmatic. A key aspect of carcinogenesis is the acquisition of traits that equip preneoplastic cells with the ability to invade. Accumulating evidence implicates H. pylori in the manipulation of cellular and molecular programs that are crucial for conferring cells with invasive capabilities. We present here an overview of the main findings about the involvement of H. pylori in the acquisition of cell invasive behavior, specifically focusing on the epithelial-to-mesenchymal transition, changes in cell polarity, and deregulation of molecules that control extracellular matrix remodeling.

Structural Biology and Evolution of the TGF-β Family

We review the evolution and structure of members of the transforming growth factor β (TGF-β) family, antagonistic or agonistic modulators, and receptors that regulate TGF-β signaling in extracellular environments. The growth factor (GF) domain common to all family members and many of their antagonists evolved from a common cystine knot growth factor (CKGF) domain. The CKGF superfamily comprises six distinct families in primitive metazoans, including the TGF-β and Dan families. Compared with Wnt/Frizzled and Notch/Delta families that also specify body axes, cell fate, tissues, and other families that contain CKGF domains that evolved in parallel, the TGF-β family was the most fruitful in evolution. Complexes between the prodomains and GFs of the TGF-β family suggest a new paradigm for regulating GF release by conversion from closed- to open-arm procomplex conformations. Ternary complexes of the final step in extracellular signaling show how TGF-β GF dimers bind type I and type II receptors on the cell surface, and enable understanding of much of the specificity and promiscuity in extracellular signaling. However, structures suggest that when GFs bind repulsive guidance molecule (RGM) family coreceptors, type I receptors do not bind until reaching an intracellular, membrane-enveloped compartment, blurring the line between extra- and intracellular signaling. Modulator protein structures show how structurally diverse antagonists including follistatins, noggin, and members of the chordin family bind GFs to regulate signaling; complexes with the Dan family remain elusive. Much work is needed to understand how these molecular components assemble to form signaling hubs in extracellular environments in vivo.

Proteolytic control of TGF-β co-receptor activity by BMP-1/tolloid-like proteases revealed by quantitative iTRAQ proteomics

The metalloproteinase BMP-1 (bone morphogenetic protein-1) plays a major role in the control of extracellular matrix (ECM) assembly and growth factor activation. Most of the growth factors activated by BMP-1 are members of the TGF-β superfamily known to regulate multiple biological processes including embryonic development, wound healing, inflammation and tumor progression. In this study, we used an iTRAQ (isobaric tags for relative and absolute quantification)-based quantitative proteomic approach to reveal the release of proteolytic fragments from the cell surface or the ECM by BMP-1. Thirty-eight extracellular proteins were found in significantly higher or lower amounts in the conditioned medium of HT1080 cells overexpressing BMP-1 and thus, could be considered as candidate substrates. Strikingly, three of these new candidates (betaglycan, CD109 and neuropilin-1) were TGF-β co-receptors, also acting as antagonists when released from the cell surface, and were chosen for further substrate validation. Betaglycan and CD109 proved to be directly cleaved by BMP-1 and the corresponding cleavage sites were extensively characterized using a new mass spectrometry approach. Furthermore, we could show that the ability of betaglycan and CD109 to interact with TGF-β was altered after cleavage by BMP-1, leading to increased and prolonged SMAD2 phosphorylation in BMP-1-overexpressing cells. Betaglycan processing was also observed in primary corneal keratocytes, indicating a general and novel mechanism by which BMP-1 directly affects signaling by controlling TGF-β co-receptor activity. The proteomic data have been submitted to ProteomeXchange with the identifier PXD000786 and doi: 10.6019/PXD000786 .

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.

Betaglycan has two independent domains required for high affinity TGF-beta binding: proteolytic cleavage separates the domains and inactivates the neutralizing activity of the soluble receptor

Betaglycan is a coreceptor for members of the transforming growth factor beta (TGF-beta) superfamily. Mutagenesis has identified two ligand binding regions, one at the membrane-distal and the other at the membrane-proximal half of the betaglycan ectodomain. Here we show that partial plasmin digestion of soluble betaglycan produces two proteolysis-resistant fragments of 45 and 55 kDa, consistent with the predicted secondary structure, which indicates an intervening nonstructured linker region separating the highly structured N- and C-terminal domains. Amino terminal sequencing indicates that the 45 and 55 kDa fragments correspond, respectively, to the membrane-distal and -proximal regions. Plasmin treatment of membrane betaglycan results in the production of equivalent proteolysis-resistant fragments. The 45 and 55 kDa fragments, as well as their recombinant soluble counterparts, Sol Delta10 and Sol Delta11, bind TGF-beta, but nonetheless, compared to intact soluble betaglycan, have a severely diminished ability to block TGF-beta activity. Surface plasmon resonance (SPR) analysis indicates that soluble betaglycan has K(d)'s in the low nanomolar range for the three TGF-beta isoforms, while those for Sol Delta10 and Sol Delta11 are 1-2 orders of magnitude higher. SPR analysis further shows that the K(d)'s of Sol Delta11 are not changed in the presence of Sol Delta10, indicating that the high affinity of soluble betaglycan is a consequence of tethering the domains together. Overall, these results suggest that betaglycan ectodomain exhibits a bilobular structure in which each lobule folds independently and binds TGF-beta through distinct nonoverlapping interfaces and that linker modification may be an approach to improve soluble betaglycan's TGF-beta neutralizing activity.

Cytokeratin 8 ectoplasmic domain binds urokinase-type plasminogen activator to breast tumor cells and modulates their adhesion, growth and invasiveness

Background

Generation of plasmin is a characteristic of tumor cells, promoting the degradation of extracellular matrix, tumor progression and metastasis. The process is accelerated if plasminogen and plasminogen activator are bound to their cell surface receptors.

Results

In this study we show that the monoclonal antibody that recognizes an epitope on the cytokeratin 8 (CK8) ectoplasmic domain (anti-CK MAb) inhibits plasminogen activation mediated by urokinase-type plasminogen activator (uPA) in MCF-7 and MCF-10A neoT cells. The ectoplasmic domain of CK8 acts as a binding site for plasminogen, however, by using confocal microscopy, we demonstrated that it is also co-localized with uPA. CK8, therefore, function also as a receptor for uPA on the cell surface, and the presence of anti-CK MAb may prevent the binding of uPA to a designated CK8 motif. The consequent inhibition of plasmin generation resulted in changed cell morphology, enhanced cell adhesion to fibronectin, reduced invasion potential, and an enhanced G1/S transition. Moreover, surface plasmon resonance analysis showed that the synthetic dodecapeptide corresponding to the epitope sequence (VKIALEVEIATY), binds uPA in the nanomolar range.

Conclusion

These novel findings suggest a model in which CK8, together with uPA, plasminogen and fibronectin, constitutes a signaling platform capable of modulating cell adhesion/growth-dependent signal transduction in breast tumor cells. Anti-CK MAb, which competes for the binding site for uPA, could be used as an agent to reduce the invasive potential of breast tumor cells.

Matrix metalloprotease inhibitors suppress initiation and progression of chondrogenic differentiation of mesenchymal stromal cells in vitro

Mesenchymal stromal cells (MSC) are an attractive source for cell therapy and tissue engineering of joint cartilage. Common chondrogenic in vitro protocols, however, induce hypertrophic markers like COL10A1, matrix metalloproteinase 13 (MMP13), and alkaline phosphatase (ALP) reminiscent of endochondral bone formation. To direct MSC toward articular chondrocytes more specifically, a better understanding of the regulatory steps is desirable. Proteases are important players in matrix remodeling, display inhibitory effects on growth plate development and MMP13 inhibition prevented hypertrophy of bovine chondrocytes. The aim of this study was to evaluate whether the activity of proteases and MMPs, especially MMP13, is crucial for the transition of MSC toward mature chondrocytes and could allow to selectively influence aspects of early and late chondrogenic differentiation. Protease inhibitors were added during MSC chondrogenesis and stage-specific markers were assessed by histology, qPCR, and ALP quantification. Chondrogenesis was little affected by leupeptin, pepstatin, or aprotinin. In contrast, broad spectrum pan-MMP inhibitors dose dependently suppressed proteoglycan deposition, collagen type II and type X staining, ALP activity, and reduced SOX9 and COL2A1 expression. A selective MMP13 inhibitor allowed chondrogenesis and showed only weak effects on ALP activity. In conclusion, transition of MSC toward mature chondrocytes in vitro depended on molecules suppressed by pan-MMP inhibitors identifying chondrogenic differentiation of MSC as a sophistically regulated process in which catabolic enzymes are capable to directly influence cellular fate. In future therapeutic applications of diseased joints, the tested MMP13-specific inhibitor promises suppression of collagen type II degradation without imposing a risk to impair MSC-driven regeneration processes.

Heart and liver defects and reduced transforming growth factor beta2 sensitivity in transforming growth factor beta type III receptor-deficient embryos

The type III transforming growth factor beta (TGFbeta) receptor (TbetaRIII) binds both TGFbeta and inhibin with high affinity and modulates the association of these ligands with their signaling receptors. However, the significance of TbetaRIII signaling in vivo is not known. In this study, we have sought to determine the role of TbetaRIII during development. We identified the predominant expression sites of TbetaRIII mRNA as liver and heart during midgestation and have disrupted the murine TbetaRIII gene by homologous recombination. Beginning at embryonic day 13.5, mice with mutations in TbetaRIII developed lethal proliferative defects in heart and apoptosis in liver, indicating that TbetaRIII is required during murine somatic development. To assess the effects of the absence of TbetaRIII on the function of its ligands, primary fibroblasts were generated from TbetaRIII-null and wild-type embryos. Our results indicate that TbetaRIII deficiency differentially affects the activities of TGFbeta ligands. Notably, TbetaRIII-null cells exhibited significantly reduced sensitivity to TGFbeta2 in terms of growth inhibition, reporter gene activation, and Smad2 nuclear localization, effects not observed with other ligands. These data indicate that TbetaRIII is an important modulator of TGFbeta2 function in embryonic fibroblasts and that reduced sensitivity to TGFbeta2 may underlie aspects of the TbetaRIII mutant phenotype.

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.

Stromal cells prevent apoptosis of AML cells by up-regulation of anti-apoptotic proteins

The aim of this study was to study interactions between stromal bone marrow microenvironment and leukemic cells. We tested the hypothesis that stromal cells prevent apoptosis of AML cells by up-regulating anti-apoptotic proteins in leukemic blasts. In HL-60 and NB-4 cells, serum deprivation- and ara-C-induced apoptosis was diminished when cells were cocultured with murine MS-5 stromal cells (P < 0.02). This effect was reproduced with conditioned medium from MS-5 cells. Cocultivation with stromal cells induced Bcl-2 expression levels, both by PCR analysis and flow cytometry. In primary AML (n = 14), ara-C-induced apoptosis was significantly lower in cells cocultured with MS-5 cells than in controls (P < 0.001). This effect was partially preserved when leukemic cells were separated from stromal cells by a microporous insert (in 5/9 samples, P = 0.04). In addition, Bcl-2 levels were significantly higher in stroma-supported than in control CD34(+) AML cells (P < 0.01). Bcl-X(L) levels were higher in 5/7 samples grown on stromal layers. Of note, in AML patients resistant to induction chemotherapy (n = 6), Bcl-2 increased significantly after cultivation with stromal cells, but no such increase was noted in cells from chemotherapy-sensitive patients. In conclusion, MS-5 stromal cells prevented apoptosis in HL-60 cells and in primary AML blasts via modulation of Bcl-2 family proteins. The observed association of high Bcl-2 expression in stroma-supported AML blasts in vitro with resistance to chemotherapy in vivo suggests that the same mechanisms may be operational in vivo.

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.

Do plasminogen activators play a role in lichen sclerosus?

The histological changes of lichen sclerosus suggest that significant remodelling of the extracellular matrix is occurring. As the proteases of the plasminogen activator system have been implicated in tissue remodelling, cell migration and tumour invasion, we performed an immunohistochemical study to look for evidence of alteration in the expression of plasminogen/plasmin, urokinase-type plasminogen activator, tissue-type plasminogen activator and alpha2-antiplasmin in biopsies of clinically typical vulval lichen sclerosus obtained from 11 untreated adult women. Normal vulva obtained from gynaecological procedures and samples of the patients' uninvolved thigh tissue were used as controls. No significant difference was seen in the staining pattern between the lichen sclerosus tissue and control tissue. However, although we found no immunohistochemical evidence that the plasminogen activator system is involved in the pathogenesis of vulval lichen sclerosus, it may be that other proteases are involved.

Angiostatin binds to smooth muscle cells in the coronary artery and inhibits smooth muscle cell proliferation and migration In vitro

Angiostatin is an inhibitor of angiogenesis that is known to reduce endothelial cell proliferation and consequently prevent the progression of tumor metastases. However, the modest effect of angiostatin on endothelial cell proliferation raises the possibility that angiostatin might exert its effects on other cells. To determine the cellular distribution of angiostatin binding in tissues with neovasculature (atherosclerotic coronary arteries), we developed a fusion protein consisting of placental alkaline phosphatase and the first 3 kringles of plasminogen. Angiostatin binding colocalized with smooth muscle cells and could be inhibited by a 50-fold molar excess of plasminogen and 10 mmol/L epsilon-amino-n-caproic acid. The fusion protein also bound to smooth muscle cells in culture. Angiostatin inhibited hepatocyte growth factor-induced proliferation and migration of smooth muscle cells, suggesting that they are a target for the antiangiogenic effect of angiostatin.

Latent transforming growth factor-beta binding proteins (LTBPs)--structural extracellular matrix proteins for targeting TGF-beta action

Growth factors of the transforming growth factor-beta family are potent regulators of the extracellular matrix formation, in addition to their immunomodulatory and regulatory roles for cell growth. TGF-beta s are secreted from cells as latent complexes containing TGF-beta and its propeptide, LAP (latency-associated peptide). In most cells LAP is covalently linked to an additional protein, latent TGF-beta binding protein (LTBP), forming the large latent complex. LTBPs are required for efficient secretion and correct folding of TGF-beta s. The secreted large latent complexes associate covalently with the extracellular matrix via the N-termini of the LTBPs. LTBPs belong to the fibrillin-LTBP family of extracellular matrix proteins, which have a typical repeated domain structure consisting mostly of epidermal growth factor (EGF)-like repeats and characteristic eight cysteine (8-Cys) repeats. Currently four different LTBPs and two fibrillins have been identified. LTBPs contain multiple proteinase sensitive sites, providing means to solubilize the large latent complex from the extracellular matrix structures. LTBPs are now known to exist both as soluble molecules and in association with the extracellular matrix. An important consequence of this is LTBP-mediated deposition and targeting of latent, activatable TGF-beta into extracellular matrices and connective tissues. LTBPs have a dual function, they are required both for the secretion of the small latent TGF-beta complex as well as directing bound latent TGF-beta to extracellular matrix microfibrils. However, it is not known at present whether LTBPs are capable of forming microfibrils independently, or whether they are a part of the fibrillin-containing fibrils. Most LTBPs possess RGD-sequences, which may have a role in their interactions with the cell surface. At least LTBP-1 is chemotactic to smooth muscle cells, and is involved in vascular remodelling. Analyses of the expressed LTBPs have revealed considerable variations throughout the molecules, generated both by alternative splicing and utilization of multiple promoter regions. The significance of this structural diversity is mostly unclear at present.

Serum immunoglobulin A from patients with celiac disease inhibits human T84 intestinal crypt epithelial cell differentiation

BACKGROUND & AIMS

Celiac disease is characterized by disturbed jejunal crypt-villus axis biology with immunoglobulin (Ig) A deposits underlining the epithelium. The aim of this study was to test whether celiac disease serum IgA (reticulin/endomysial autoantibodies) interferes with the mesenchymal-epithelial cell cross-talk.

METHODS

Differentiation of T84 epithelial cells was induced with IMR-90 fibroblasts or transforming growth factor beta in three-dimensional collagen gel cultures. The effects of purified celiac IgA and monoclonal tissue transglutaminase antibodies (CUB7402) were studied by adding the antibodies to the cocultures.

RESULTS

Active celiac disease IgA, reactive for tissue transglutaminase, significantly inhibited T84 epithelial cell differentiation (P < 0.001) and increased epithelial cell proliferation (P = 0.024). Similar effects were obtained with antibodies against tissue transglutaminase.

CONCLUSIONS

Celiac disease-associated IgA class antibodies disturb transforming growth factor beta-mediated fibroblast-epithelial cell cross-talk in this in vitro crypt-villus axis model. This primary finding indicates that celiac disease-specific autoantibodies may also contribute to the formation of the gluten-triggered jejunal mucosal lesion in celiac disease.

Characterization of the binding sites for plasminogen and tissue-type plasminogen activator in cytokeratin 8 and cytokeratin 18

Cytokeratin 8 (CK8) is an intermediate filament protein that penetrates to the external surfaces of breast cancer cells and is released from cells in the form of soluble heteropolymers. CK8 binds plasminogen and tissue-type plasminogen activator (t-PA) and accelerates plasminogen activation on cancer cell surfaces. The plasminogen-binding site is located at the C-terminus of CK8. In this study, we prepared GST-fusion proteins which contained either 174 amino acids from the C-terminus of CK8 (CK8f) or 134 amino acids from the C-terminus of CK18 (CK18f). A third GST-CK fusion protein was identical to CK8fexcept that the C-terminal lysine was mutated to glutamine (CK8fK483Q). CK8f bound plasminogen; the K(D) was 0.5 microM. Binding was completely inhibited by epsilonACA. CK8fK483Q also bound plasminogen, albeit with decreased affinity (K(D) approximately 1.5 microM). CK18f did not bind plasminogen at all. All three fusion proteins bound t-PA equivalently, providing the first evidence that CK18 may function as a t-PA receptor, t-PA and plasminogen cross-competed for binding to CK8f. Thus, t-PA and plasminogen cannot bind to the same CK8f monomer simultaneously. Nevertheless, CK8f still promoted plasminogen activation, probably reflecting the fact that CK8f was purified in dimeric or tetrameric form. These studies demonstrate that CK8 may promote plasminogen activation by t-PA only when present in an oligomerized state. CK18 may participate in the oligomer, together with CK8, based on its ability to bind t-PA.

Extracellular matrix-associated transforming growth factor-beta: role in cancer cell growth and invasion

Growth factors of the transforming growth factor-beta (TGF-beta) family inhibit the proliferation of epithelial, endothelial, and hematopoietic cells, and stimulate the synthesis of extracellular matrix components. TGF-beta s are secreted from cells in high-molecular-mass protein complexes that are composed of three proteins, the mature TGF-beta-dimer, the TGF-beta propeptide dimer, or latency-associated protein (LAP), and the latent TGF-beta binding protein (LTBP). Mature TGF-beta is cleaved from its propeptide during secretion, but the proteins remain associated by noncovalent interactions. LTBP is required for efficient secretion and processing of latent TGF-beta and it binds to LAP via disulfide bond(s). LTBP is a component of extracellular matrix microfibrils, and it targets the latent TGF-beta complex to the extracellular matrix. TGF-beta signaling is initiated by proteolytic cleavage of LTBP that results in the release of the latent TGF-beta complex from the extracellular matrix. TGF-beta is activated by dissociation of LAP from the mature TGF-beta. Subsequent signaling involves binding of active TGF-beta to its type II cell surface receptors, which phosphorylate and activate type I TGF-beta receptors. Type I receptors, in turn, phosphorylate cytoplasmic transcriptional activator proteins Smad2 and Smad3, inducing their translocation to the nucleus. Recent evidence suggests that acquisition of resistance to TGF-beta growth inhibition plays a major role in the progression of epithelial and hematopoietic cell malignancies. The role of secretion of TGF-beta in tumorigenesis is more complex. The secretion of TGF-beta s by tumor cells may contribute to autocrine growth inhibition, but on the other hand, it may also promote invasion, metastasis, angiogenesis, and even immunosuppression. Tumor cells may also fail to deposit LTBP:TGF-beta complexes to the extracellular matrix. The elucidation of the mechanisms of the release of TGF-beta from the matrix and its subsequent activation aids the understanding of the pathophysiologic roles of TGF-beta in malignant growth, and allows the development of therapeutic agents that regulate the activity of TGF-beta.

Binding ofEscherichia coliverotoxins to cell surface protein on wild-type and globotriaosylceramide-deficient Vero cells

We have examined verotoxin (VT) binding to cell surface proteins. When Vero or globotriaosylceramide (Gb3) deficient Vero (VRP) cells were incubated with125I-labelled verotoxin 2 (VT2) and disuccinimidyl suberate cross-linker, SDS-PAGE of cell lysates showed radiolabelled bands at 44, 50, 60, 86, 102, and 138 kDa. When125I-labelled verotoxin 1 (VT1) was cross-linked, radioactive bands occurred at 51, 67, 101, 160, 188, and 232 kDa. In contrast,125I-labelled VT1 B subunit produced a single radioactive band migrating at 50 kDa. CHO cells did not bind labelled VT. VT2 binding to VRP cells fit a rectangular hyperbola suggesting a single class of binding sites. In contrast, VT1 and VT1 B subunit binding to VRP cells was best fit by sigmoidal curves suggesting the presence of positive cooperativity between at least two binding sites. Scatchard analysis of VT2 binding data yielded 3.5 times 109molecules bound/ µg of cell protein with an equilibrium dissociation constant (KD) of 13 nM. The apparent KDwas 9.7 nM for VT1 and 73.2 nM for VT1 B subunit. These results indicate that VT binds to a protein, or proteins, on the surface of susceptible cells and that there appear to be differences between VT1 and VT2 binding. Interactions between VT1 or VT2 and the proteins demonstrated here may be important in the biological activity of VT.Key words: verotoxin, protein receptors, hemolytic uremic syndrome, Escherichia coli.

Proteoglycan synthesis in haematopoietic cells: isolation and characterization of heparan sulphate proteoglycans expressed by the bone-marrow stromal cell line MS-5

Proteoglycans of bone-marrow stromal cells and their extracellular matrix are important components of the haematopoietic microenvironment. Recently, several studies have indicated that they are involved in the interaction of haematopoietic stem and stromal cells. However, a detailed characterization of the heparan sulphate proteoglycans synthesized by bone-marrow stromal cells is still lacking. Here we report on the isolation and characterization of proteoglycans from the haematopoietic stromal cell line MS-5, that efficiently supports the growth and differentiation of human and murine haematopoietic progenitor cells. Biochemical characterization of purified proteoglycans revealed that the haematopoietic stromal cell line MS-5 synthesizes, in addition to chondroitin sulphate proteoglycans, several different heparan sulphate proteoglycans. Immunochemical analysis, using specific antibodies against the different members of the syndecan family, glypican, betaglycan and perlecan, showed that MS-5 cells synthesize all these different heparan sulphate proteoglycans. These data were further supported by reverse-transcriptase PCR and confirmed by sequence and Northern blot analysis. The relative abundance of the different heparan sulphate proteoglycans was estimated on the protein and mRNA levels.

TGF-beta-mediated hepatocellular apoptosis by rat and human hepatoma cells and primary rat hepatocytes

BACKGROUND/AIMS

Primary cultures of rat hepatocytes, rat (FAO) and human (HepG2) hepatoma cells were studied by immunocytochemistry for expression of transforming growth factor (TGF)-beta, for the release of TGF-beta into the medium, and generation of hepatocellular apoptosis by the respective cell-conditioned media.

METHODS/RESULTS

Using the alkaline-phosphatase anti-alkaline-phosphatase technique, intense TGF-beta immunostaining was shown in all cell types. The cytokine is released almost entirely in the latent form into the culture medium; only the FAO-cells had a substantial fraction of bioactive TGF-beta in the native (unacidified) culture fluid. Exposure of hepatocytes with the respective cell-conditioned media in the activated, but not in the native form (except for FAO-cell media), induced severe detrimental effects as evidenced by: (i) gross morphological alterations, (ii) functional impairment (reduction of WST-1 test, detachment of cells, lactate dehydrogenase increase in the medium), and (iii) generation of apoptosis. The latter phenomenon was confirmed by an increase of internucleosomal DNA fragments, positive TUNEL reaction, and intense binding of the fluorochrome Hoechst 33342 to fragmented nuclei. All these effects, which were mimicked by addition of recombinant human TGF-beta 1, were almost entirely antagonized by pre-incubation of the conditioned media with latency associated peptide. In contrast to hepatocytes, both types of hepatoma cells were completely resistant to the multiple actions of TGF-beta and activated conditioned media.

CONCLUSIONS

It is concluded that hepatocytes might have the ability to induce autocrine, TGF-beta-mediated apoptosis, whereas hepatoma cells, because of their TGF-beta resistance, might generate TGF-beta-mediated peritumorous apoptosis of hepatocytes in a paracrine way, which could facilitate their expansion in situ. Both mechanisms, however, are critically dependent on extracellular TGF-beta activation.

Role of laminin in matrix induction of macrophage urokinase-type plasminogen activator and 92-kDa metalloproteinase expression

Urokinase-type plasminogen activator (uPA) and 92-kDa matrix metalloproteinase (MMP-9) expression by RAW264.7 macrophages were up-regulated when plated on extracellular matrices. Collagen IV, fibronectin, and tenascin stimulated macrophages' MMP-9 expression. In contrast, laminin stimulated both uPA and MMP-9 expression in a dose- and time-dependent manner. The increase in macrophage uPA activity was preceded by an increase in their steady state levels of uPA mRNA. Laminin-induced uPA expression was most pronounced in RAW264.7 macrophages followed by THP-1 monocytes, J774A.1 macrophages, and bone marrow-derived macrophages. Neither laminin nor matrix induced alterations in THP-1 monocyte expression of plasminogen activator inhibitor, tissue inhibitor of metalloproteinase (TIMP)-1 or TIMP-2. Synthetic laminin peptides were utilized to identify the laminin domain(s) responsible for induction of uPA expression. Peptides derived from the beta1 chain of laminin had no effect on macrophage uPA expression, whereas SIKVAV, derived from alpha1 chain, stimulated uPA expression 20-fold. Preincubation of THP-1 monocytes with a monoclonal antibody directed against the alpha6 subunit of the alpha6beta1 laminin receptor blocked matrix induction of uPA without affecting the induction of MMP-9. These results demonstrate that macrophage binding to laminin plays an important role in the regulation of their degradative phenotype via the up-regulation of uPA and MMP-9.

Proteinases are isoform-specific regulators of the binding of transforming growth factor beta to alpha 2-macroglobulin

alpha 2-Macroglobulin (alpha 2M) regulates growth and gene expression in many cell types by binding and neutralizing transforming growth factor beta (TGF-beta). In this study we characterized the effects of the serine proteinase, plasmin, on the interaction of alpha 2M with TGF-beta 1 and TGF-beta 2. Binding of both TGF-beta isoforms to purified alpha 2M-plasmin complex was primarily non-covalent and reversible. The binding affinity of alpha 2M for TGF-beta 1 was increased by plasmin; the Kd values were 320 and 84 nM for native alpha 2M and alpha 2M-plasmin respectively. In contrast the affinity of alpha 2M for TGF-beta 2 was decreased by plasmin; the Kd values were 14 and 80 nM for native alpha 2M and alpha 2M-plasmin respectively. Thrombin decreased the affinity of alpha 2M for TGF-beta 2 in a similar manner to plasmin. In assays of DNA synthesis in fetal bovine heart endothelial cells, native alpha 2M neutralized the activity of exogenously added TGF-beta 2, whereas alpha 2M-plasmin, at equivalent concentrations, had almost no effect. Native alpha 2M and methylamine-modified alpha 2M increased platelet-derived growth factor alpha-receptor expression in vascular smooth-muscle cells, an activity attributed to the neutralization of autocrine TGF-beta activity, whereas alpha 2M-plasmin was less effective at the same concentration. These studies demonstrate that the effects of proteinases on the cytokine-binding and cytokine-neutralizing activities of alpha 2M are cytokine-dependent. By reacting with alpha 2M, proteinases might regulate not only the availability of cytokines in the extracellular spaces but also the composition of the cytokine milieu.

Murine alpha-macroglobulins demonstrate divergent activities as neutralizers of transforming growth factor-beta and as inducers of nitric oxide synthesis. A possible mechanism for the endotoxin insensitivity of the alpha2-macroglobulin gene knock-out mouse

alpha2-Macroglobulin null mice demonstrate increased resistance to endotoxin challenge (Umans, L., Serneels, L., Overbergh, L., Van Leuven, F., and Van den Berghe, H. (1995) J. Biol. Chem. 270, 19778-19785). We hypothesized that this phenotype might reflect the function of murine alpha2M (malpha2M) as a neutralizer of transforming growth factor-beta (TGF-beta) and inducer of nitric oxide synthesis in vivo. When incubated with wild-type mouse plasma, TGF-beta1 and TGF-beta2 bound only to malpha2M. Alternative TGF-beta-binding proteins were not detected in plasma from alpha2M(-/-) mice. Wild-type mouse plasma, but not plasma from alpha2M(-/-) mice, inhibited TGF-beta1 binding to TGF-beta receptors on fibroblasts. Purified malpha2M bound TGF-beta1 and TGF-beta2 with similar affinity; the KD values were 28 +/- 4 and 33 +/- 4 nM, respectively. Murinoglobulin, the second murine alpha-macroglobulin, bound both TGF-beta isoforms with 30-fold lower affinity. Malpha2M counteracted the activities of TGF-beta1 and TGF-beta2 in an endothelial cell growth assay. Malpha2M also induced NO synthesis when incubated with RAW 264.7 cells, an activity which probably results from the neutralization of autocrine TGF-beta activity. Human alpha2M induced NO synthesis comparably to malpha2M; however, MUG had no effect. These studies demonstrate that the ability to neutralize TGF-beta is a property of malpha2M, which is not redundant in the murine alpha-macroglobulin family or in murine plasma. Malpha2M is the only murine alpha-macroglobulin that promotes NO synthesis. The absence of malpha2M, in alpha2M(-/-) mice, may allow TGF-beta to more efficiently suppress excessive iNOS expression following endotoxin challenge.

Multiple forms of TGF-beta 1 in breast tissues: a biologically active form of the small latent complex of TGF-beta 1

The aim of this study was to investigate whether breast cancer growth in vivo could be due to a failure in the activation of TGF-beta 1, a growth factor which has been shown to affect the development of normal breast tissue. Tissue samples of 40 breast carcinomas and the normal adjacent tissue from 37 (henceforth referred to as 'adjacent tissue'), as well as 13 specimens of benign lesions, were included in this study. The specimens were used in vitro to produce conditioned medium (CM), and this was examined for TGF-beta 1 activity by measuring growth inhibition of the mink lung epithelial cell line CCL-64. Immunoblotting and electrophoresis were used to detect the presence of TGF-beta 1 in CM and homogenised tissue samples. We demonstrated that the majority of TGF-beta 1 in breast cancer conditioned medium was biologically active, in direct contrast to CM prepared from benign disease specimens. Furthermore, active TGF-beta 1 was also identified in CM prepared from adjacent tissue, suggesting an important early role for this growth factor in the spread of this disease. Three distinct breast cancer related (BCR) molecular weight species of TGF-beta 1 (12.5/25 kDa, 50 kDa and 95 kDa) were identified. Both the 50 kDa and 95 kDa bands immunoprecipitated by an anti-TGF-beta 1 antibody were also immunoreactive with anti-TGF-beta 1 binding protein antibodies suggesting that the 50 kDa band may comprise at least part of the previously described small latent complex of TGF-beta 1. However, using the CCL-64 cell assay, we were able to demonstrate that the 50 kDa TGF-beta 1 BCR protein was biologically active whereas the large (95 kDa) TGF-beta 1 BCR latent complex protein was not. Adjacent tissue was more likely to contain the 50 kDa form than the tumour tissues (P < 0.05). Similarly, the 50 kDa molecule was also more common in patients who had oestrogen receptor (ER) negative tumours (compared with ER positive patients; P < 0.05) and in those who had received tamoxifen treatment prior to surgery (P < 0.01). In all of these cases, the increase in the incidence of the small active complex form was accompanied by a decrease in the incidence of the high molecular weight complex (95 kDa). We confirmed that, in vitro, the 95 kDa TGF-beta 1 BCR can be proteolytically cleaved to yield a 50 kDa TGF-beta 1 BCR. Finally, we observed a correlation between the presence of the 50 kDa complex protein and reduced levels of plasminogen activator (PA), which was significant in ER negative patients (P < 0.05) and tamoxifen-pretreated patients (P < 0.01). This suggests that the secretion of this active TGF-beta 1 protein may provide breast tumours with a mechanism whereby they can escape oestrogen dependence, and may provide an explanation for the common problem of tamoxifen resistance.

A cytokeratin 8-like protein with plasminogen-binding activity is present on the external surfaces of hepatocytes, HepG2 cells and breast carcinoma cell lines

Plasminogen binding to cell surfaces may be important for tumor invasion and other processes that involve cellular migration. In this investigation, the principal plasminogen-binding protein was identified in the plasma membrane fraction of rat hepatocytes. The protein had an apparent mass of 59 kDa, was insoluble in a spectrum of detergents, and was identical to cytokeratin 8 (CK 8) as determined by sequence analysis of nine amino acids at the N terminus of two cyanogen bromide fragments. The 59 kDa protein bound CK 8-specific antibody in western blot analyses. These studies demonstrate that CK 8 or a CK 8-like protein binds plasminogen. Given this newly determined and potentially important CK 8 function, immunofluorescence and immunoelectron microscopy studies were performed to determine whether CK 8 may be present on the external surfaces of unpermeabilized, viable hepatocytes. All of the cells in each preparation were immunopositive with two separate CK 8-specific antibodies. A punctate pattern of immunofluorescence was detected on the cell surface with approximately even intensity from cell to cell. By immunoelectron microscopy, CK 8 was preferentially associated with microvilli. In order to determine whether other epithelial cells express cell-surface CK 8, immunofluorescence and immunoelectron microscopy studies were performed with HepG2 hepatocellular carcinoma cells and with BT20 and MCF-7 breast carcinoma cells. The pattern of antigen expression was equivalent with each cell type and comparable to that observed with hepatocytes. These studies support the hypothesis that CK 8 is associated with the external cell surface where it may express important proteinase receptor function.