Requirement for transglutaminase in the activation of latent transforming growth factor-beta in bovine endothelial cells

Effects of transforming growth factor-beta1 on renal extracellular matrix components and their regulating proteins

Transforming growth factor-beta1 (TGF-beta1) is widely regarded as a potent fibrogenic renal growth factor. In cell culture, TGF-beta1 has been shown to increase various extracellular matrix (ECM) proteins and tissue inhibitors of metalloproteinases (TIMP), while decreasing matrix metalloproteinases (MMP), providing the optimum environment for progressive ECM accumulation. This study, which uses the isolated perfused rat kidney (IPRK), describes for the first time in a whole kidney preparation the action of TGF-beta1 on factors associated with ECM processing. This model allows the study of the intact rat kidney with physiologic cell-cell interactions in the absence of confounding systemic influences. Left kidneys were removed from male Wistar rats by a nonischemic technique and perfused with a sterile, apyrogenic, endotoxin-free perfusate, based on the plasma volume expander Hemaccel (polygeline), at constant pressure in a recirculating IPRK system. Kidneys were perfused for 1 h either with (n = 3) or without (n = 3) recombinant human TGF-beta1 (20 ng/ml). The effects of perfusion were controlled by comparison with the nonperfused contralateral kidney (n = 6). TGF-beta1 was measured in the perfusate and urine, at the start and end of the experiment using an enzyme-linked immunosorbent assay to its biologically active form. After perfusion, sections of the kidneys were analyzed for changes in mRNA by Northern blotting. Significant increases in mRNA for fibronectin (7.5-fold, P < 0.01), heparan sulfate proteoglycan core protein (53-fold, P < 0.001), laminin beta1 (12-fold, P < 0.001), collagen alpha1(IV) (17-fold, P < 0.001), collagen alpha1(III) (fourfold, P < 0.001), and MMP9 (twofold, P < 0.05) were observed after perfusion with TGF-beta1. Measurement of TIMP1, TIMP2, TIMP3, MMP1, and MMP2 mRNA demonstrated no detectable change, whereas determination of mRNA for tissue transglutaminase, an enzyme capable of cross-linking many ECM components, showed an eightfold increase (P < 0.01). This study suggests that in the IPRK and in the absence of other exogenous growth factors, TGF-beta1 selectively increases the synthesis of ECM and tissue transglutaminase without changes that would result in the reduction of ECM degradation.

'Tissue' transglutaminase release from apoptotic cells into extracellular matrix during human liver fibrogenesis

Enhanced apoptosis characterizes several pathologies affecting human liver. This study sought to determine whether apoptosis is involved in the formation of fibrotic lesions occurring in hepatic disease. The expression of Bcl-2 was analysed, and of 'tissue' transglutaminase (tTG), a cross-linking enzyme which recent evidence suggests plays a role in the formation of fibrotic lesions in experimental settings. Regardless of the degree of liver injury, tTG abnormally accumulated in the liver cells adjacent to fibrotic tissue. Many cells showing DNA fragmentation and morphological features of apoptosis were also observed near fibrotic lesions. Bcl-2 was detected predominantly in infiltrating lymphocytes within the liver tissue. Marked staining for both tTG protein and chromatin was also observed in the acellular fibrotic tissue, which suggested an active release of intracellular macromolecules from the dying cells into the extracellular matrix. This study indicates that fibrogenesis in the liver is associated with the release of tTG from dying cells. By cross-linking extracellular matrix proteins, this enzyme might play a role in the formation of fibrotic lesions.

Cytokine regulation of hepatic stellate cells in liver fibrosis

Cytokines constitute a major class of mediators responsible for "activation" of hepatic stellate cells (HSCs) in vitro and in vivo. They are largely divided into mitogenic (transforming growth factor-alpha, platelet-derived growth factor, interleukin-1, tumor necrosis factor-alpha, and insulin-like growth factor) and fibrogenic (transforming growth factor-beta and interleukin-6) cytokines. In addition to their mitogenic (stimulation of cell proliferation) and fibrogenic (induction of matrix proteins) properties, they are also shown to confer in vitro unique cellular changes known to be the key features of HSC "activation," including loss of vitamin A, stimulation of migration, enhanced cellular contractility, and matrix metalloproteinase and tissue inhibitor of metalloproteinase induction. Potential cellular sources of the cytokines consist of hepatic macrophages, endothelial cells, biliary epithelial cells, lymphocytes, platelets, hepatocytes, and activated HSCs. To better understand the mode of actions and the pathogenetic significance of cytokines/chemokines involved in "activation" of HSCs, the following four questions need to be addressed: (1) What other cytokines are expressed by HSCs to establish critical autocrine stimulation? (2) What are endogenous or exogenous priming factors for HSC stimulation? (3) What is the mechanism of activation for transforming growth factor-beta, the pivotal fibrogenic cytokine? (4) How important are HSC-derived proinflammatory mediators in liver fibrosis? This review will discuss these questions, along with the current understanding of the role of cytokines in HSC activation.

Tissue transglutaminase: an enzyme with a split personality

Tissue transglutaminase (tTG) belongs to the family of transglutaminase enzymes that catalyze the posttranslational modification of proteins via Ca(2+)-dependent cross-linking reactions. The catalytic action of tTG results in the formation of an isopeptide bond that is of great physiological significance since it is highly resistant to proteolysis and denaturants. Although tTG-mediated cross-linking reactions have been implicated to play a role in diverse biological processes, the precise physiological function of the enzyme remains unclear. Recent data, however, suggest that the protein polymers resulting from tTG-catalyzed reactions may play a role in commitment of cells to undergo apoptosis. On the same token, tTG-mediated formation of insoluble protein aggregates may underlie the markers of numerous pathological conditions, such as the senile plaques in Alzheimer's disease and the Lewy bodies in Parkinson's disease. In addition to catalyzing Ca(2+)-dependent cross-linking reactions, tTG can also bind and hydrolyze guanosine triphosphate and adenosine triphosphate. By virtue of this ability, tTG has been identified as a novel G-protein that interacts and activates phospholipase C following stimulation of the alpha-adrenergic receptor. The ability of tTG to mediate signal transduction may contribute to its involvement in the regulation of cell cycle progression. The following review summarizes the important features of this multifunctional enzyme that have emerged as a result of recent work from different laboratories.

Cardiac specific overexpression of transglutaminase II (G(h)) results in a unique hypertrophy phenotype independent of phospholipase C activation

Tissue type transglutaminase (TGII, also known as G(h)) has been considered a multifunctional protein, with both transglutaminase and GTPase activity. The role of the latter function, which is proposed as a coupling mechanism between alpha(1)-adrenergic receptors and phospholipase C (PLC), is not well defined. TGII was overexpressed in transgenic mice in a cardiac specific manner to delineated relevant signaling pathways and their consequences in the heart. Cardiac transglutaminase activity in the highest expressing line was approximately 37-fold greater than in nontransgenic lines. However, in vivo signaling to PLC, as assessed by inositol phosphate turnover in [(3)H]myoinositol organ bath atrial preparations, was not increased in the TGII mice at base line or in response to alpha(1)-adrenergic receptor stimulation; nor was protein kinase Calpha (PKCalpha) or PKCepsilon activity enhanced in the TGII transgenic mice. This is in contrast to mice moderately (approximately 5-fold) overexpressing G(alphaq), where inositol phosphate turnover and PKC activity were found to be clearly enhanced. TGII overexpression resulted in a remodeling of the heart with mild hypertrophy, elevated expression of beta-myosin heavy chain and alpha-skeletal actin genes, and diffuse interstitial fibrosis. Resting ventricular function was depressed, but responsiveness to beta-agonist was not impaired. This set of pathophysiologic findings is distinct from that evoked by overexpression of G(alphaq). We conclude that TGII acts in the heart primarily as a transglutaminase, and modulation of this function results in unique pathologic sequelae. Evidence for TGII acting as a G-protein-like transducer of receptor signaling to PLC in the heart is not supported by these studies.

Expression of the wild-type insulin-like growth factor II receptor gene suppresses growth and causes death in colorectal carcinoma cells

The insulin-like growth factor II receptor (IGFIIR) has been implicated as a tumor suppressor gene in human malignancy. Frequent mutation, loss of heterozygosity, and microsatellite instability (MSI) directly affecting the IGFIIR gene have been reported in several primary human tumor types. However, to our knowledge, dynamic functional evidence of a growth-suppressive role for IGFIIR has not yet been provided. We identified one MSI-positive colorectal carcinoma cell line, SW48, with monoallelic mutation in IGFIIR identical to that seen in primary colorectal carcinomas. A zinc-inducible construct containing the wild-type IGFIIR cDNA was stably transfected into SW48 cells. Growth rate and apoptosis were compared between zinc-treated, untreated, and untransfected cells. A twofold increase in IGFIIR protein expression was detected after zinc treatment in discrete clonal isolates of transfected SW48 cells. Moreover, zinc induction of exogenous wild-type IGFIIR expression reproducibly decreased growth rate and increased apoptosis. These data prove that wild-type IGFIIR functions as a growth suppressor gene in colorectal cancer cells and provide dynamic in vitro functional support for the hypothesis that IGFIIR is a human growth suppressor gene.

Physical Interaction Between Retinoic Acid Receptor and Sp1: Mechanism for Induction of Urokinase by Retinoic Acid

Induction of urokinase plasminogen activator (uPA) by retinoic acid (RA) is the initial event preceding certain subsequent biological changes in vascular endothelial cells. We investigated the molecular mechanism by which RA stimulates the expression of uPA, which lacks a canonical RA receptor (RAR)-responsive element, in bovine and human aortic endothelial cells. Upon stimulation with RA, mRNA levels of RAR and β transiently increased in parallel with the induction of uPA, and this increase was inhibited by cycloheximide. Results of transient transfection of RAR/RXR cDNAs and experiments using specific agonists and antagonists suggested that uPA induction is dependent upon RAR (initially, RAR) with the help of RXR. Deletion analysis of the uPA promoter suggested that RAR/RXR acts on GC box region within the uPA promoter. This was further supported by inhibition of Sp1 binding to this region. Coimmunoprecipitation studies, glutathioneS-transferase pull-down experiment, and mammalian two-hybrid assays suggested a physical interaction between RAR/RXR and Sp1. Furthermore, gel shift studies showed that the binding of Sp1 to the uPA GC box is significantly potentiated in the presence of RARs/RXRs. Finally, Sp1 and RAR/RXR synergistically enhanced the transactivation activity of the uPA promoter. These results suggest that (1) RA induces RARs mainly via RAR and that (2) RAR/RXR physically and functionally interact with Sp1, resulting in a potentiation of uPA transcription.

Physical Interaction Between Retinoic Acid Receptor and Sp1: Mechanism for Induction of Urokinase by Retinoic Acid

Induction of urokinase plasminogen activator (uPA) by retinoic acid (RA) is the initial event preceding certain subsequent biological changes in vascular endothelial cells. We investigated the molecular mechanism by which RA stimulates the expression of uPA, which lacks a canonical RA receptor (RAR)-responsive element, in bovine and human aortic endothelial cells. Upon stimulation with RA, mRNA levels of RAR and β transiently increased in parallel with the induction of uPA, and this increase was inhibited by cycloheximide. Results of transient transfection of RAR/RXR cDNAs and experiments using specific agonists and antagonists suggested that uPA induction is dependent upon RAR (initially, RAR) with the help of RXR. Deletion analysis of the uPA promoter suggested that RAR/RXR acts on GC box region within the uPA promoter. This was further supported by inhibition of Sp1 binding to this region. Coimmunoprecipitation studies, glutathioneS-transferase pull-down experiment, and mammalian two-hybrid assays suggested a physical interaction between RAR/RXR and Sp1. Furthermore, gel shift studies showed that the binding of Sp1 to the uPA GC box is significantly potentiated in the presence of RARs/RXRs. Finally, Sp1 and RAR/RXR synergistically enhanced the transactivation activity of the uPA promoter. These results suggest that (1) RA induces RARs mainly via RAR and that (2) RAR/RXR physically and functionally interact with Sp1, resulting in a potentiation of uPA transcription.

Increased 9,13-di-cis-retinoic acid in rat hepatic fibrosis: implication for a potential link between retinoid loss and TGF-beta mediated fibrogenesis in vivo

BACKGROUND/AIMS

During hepatic fibrosis, hepatic stellate cells (HSCs) transform into myofibroblastic cells and lose their intracellular droplets of retinyl esters, the storage form of vitamin A. Recently, we have demonstrated that 9,13-di-cis-retinoic acid (RA), a geometric isomer identified as a stable and major metabolite of vitamin A in circulation, stimulates the synthesis of plasminogen activator (PA) and induces PA/plasmin-dependent latent transforming growth factor (TGF)-beta activation in HSC cultures, probably via induction and activation of RA receptor (RAR) alpha. The aim of the present study was to address a potential link between the loss of retinyl esters to increased formation of RA(s), which might play a role in facilitating TGF-beta-mediated liver fibrogenesis in vivo.

METHODS

We examined the effect of 9,13-di-cis-RA on transactivating activity of RARalpha in HeLa cells as well as its effect on PA- and TGF-beta-dependent collagen synthesis in rat and human HSC cultures. We measured the changes in 9,13-di-cis-RA levels both during activation of rat HSCs in vitro and during porcine serum-induced rat hepatic fibrosis in vivo and correlated this with RAR alpha/beta, PA, TGF-beta and type I procollagen mRNA expression in the fibrotic liver.

RESULTS

9,13-di-cis-RA transactivated RARalpha, and provoked PA/plasmin and TGF-beta-dependent procollagen synthesis in HSCs. 9,13-di-cis-RA levels were increased both in activated HSCs in vitro and in fibrotic liver accompanying the enhanced expression of RAR alpha/beta, PA, TGF-beta and procollagen in vivo.

CONCLUSIONS

These findings suggest a potential link between 9,13-di-cis RA formation and hepatic fibrosis via formation of TGF-beta in vivo, and thus provide further insight into the biologic role of retinoids during hepatic fibrogenesis.

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.

Immunocytochemical localization of latent transforming growth factor-beta1 activation by stimulated macrophages

Transforming growth factor-beta1 (TGF-beta) is secreted in a latent form consisting of mature TGF-beta noncovalently associated with its amino-terminal propeptide, which is called latency associated peptide (LAP). Biological activity depends upon the release of TGF-beta from the latent complex following extracellular activation, which appears to be the key regulatory mechanism controlling TGF-beta action. We have identified two events associated with latent TGF-beta (LTGF-beta) activation in vivo: increased immunoreactivity of certain antibodies that specifically detect TGF-beta concomitant with decreased immunoreactivity of antibodies to LAP. Macrophages stimulated in vitro with interferon-gamma and lipopolysaccharide reportedly activate LTGF-beta via cell membrane-bound protease activity. We show through dual immunostaining of paraformaldehyde-fixed macrophages that such physiological TGF-beta activation is accompanied by a loss of LAP immunoreactivity with concomitant revelation of TGF-beta epitopes. The induction of TGF-beta immunoreactivity colocalized with immunoreactive betaglycan/RIII in activated macrophages, suggesting that LTGF-beta activation occurs on the cell surface. Confocal microscopy of metabolically active macrophages incubated with antibodies to TGF-beta and betaglycan/RIII prior to fixation supported the localization of activation to the cell surface. The ability to specifically detect and localize LTGF-beta activation provides an important tool for studies of its regulation.

The integrin alpha v beta 6 binds and activates latent TGF beta 1: a mechanism for regulating pulmonary inflammation and fibrosis

Transforming growth factor beta (TGF beta) family members are secreted in inactive complexes with a latency-associated peptide (LAP), a protein derived from the N-terminal region of the TGF beta gene product. Extracellular activation of these complexes is a critical but incompletely understood step in regulation of TGF beta function in vivo. We show that TGF beta 1 LAP is a ligand for the integrin alpha v beta 6 and that alpha v beta 6-expressing cells induce spatially restricted activation of TGF beta 1. This finding explains why mice lacking this integrin develop exaggerated inflammation and, as we show, are protected from pulmonary fibrosis. These data identify a novel mechanism for locally regulating TGF beta 1 function in vivo by regulating expression of the alpha v beta 6 integrin.

Regulation of the transglutaminase I gene. Identification of DNA elements involved in its transcriptional control in tracheobronchial epithelial cells

The transglutaminase I (TGase I) gene encodes an enzyme that catalyzes the cross-linking of structural proteins involved in the formation of the cornified envelope during squamous cell differentiation. To identify DNA elements important for the transcriptional control of the TGase I gene, we analyzed the ability of a 2.9-kilobase pair (kb) upstream regulatory region to control the expression of a reporter gene in vivo and in vitro. Transgenic mice bearing the pTG(-2.9kb)CAT construct exhibited the same pattern of tissue-specific expression of CAT as reported for TGase I. Deletion analysis in transiently transfected rabbit tracheal epithelial cells indicated that two sequences from bp -490 to -470 and from -54 to -37 are involved in the activation of TGase I transcription. Point mutation analysis and mobility shift assays showed that the sequence located between -54 and -37 is a functional Sp1-like transcription element. Sp1 and Sp3, but not Sp2, are part of nuclear protein complexes from differentiated RbTE cells binding to this site. The element TGATGTCA between bp -490 and -470 is contained in a larger 22-bp palindrome and resembles the consensus cAMP response element-binding protein (CREB)/AP-1 element recognized by dimeric complexes of members of the CREB, ATF, Fos, and Jun families. Mutations in this sequence greatly reduced promoter activity. Supershift analysis identified CREB1, JunB, c-Fos, Fra-1, and c-Jun in protein complexes isolated from differentiated rabbit tracheal epithelial cells binding to this site. Our study shows that the Sp1- and CREB/AP-1-like sites act in concert to stimulate transcription of the TGase I gene. The 2.9-kb promoter region could guide expression of specific genes in the granular layer of the epidermis and could be useful in gene therapy.

Proteolytic control of growth factor availability

Most growth factors are released from cells in a form that does not permit immediate interaction with their high affinity receptors. An important mechanism for presentation of these released latent growth factors is activation by the plasminogen activator-plasmin system. The involvement of this system in the biology of Transforming Growth Factor-beta (TGF-beta) is reviewed.

Expression of transglutaminase K in normal cervix tissue and cervix carcinomas

The localization and expression of transglutaminase K has been investigated immunohistochemically in normal cervix tissue (n = 15) and in cervix carcinomas (n = 23). The distribution of the transglutaminase K was compared with the staining patterns of cytokeratin 10, Ki-67, p53, and oestrogen and progesterone receptors in these tumours. Weak to strong membrane-bound immunoreactivity for transglutaminase K was detected in almost all cervix carcinomas analyzed. The immunostaining was heterogeneous, with visual differences between individual tumour cells. 66.7% of normal cervix tissues revealed no immunoreactivity for the transglutaminase K. In normal cervix tissue, the immunoreactivity was confined to upper cervix layers, predominantly to the superficial and intermediate cell layers. The intensity of both the immunostaining and the number of transglutaminase K-positive cells were upregulated in cervix carcinomas as compared to normal cervix tissue. When the coexpressions of transglutaminase K with markers of proliferation and differentiation were analyzed, no statistically significant correlation was found. Our findings indicate that (1) transglutaminase K is upregulated at the protein level in cervix carcinomas as compared to normal cervix tissue; (2) upregulation of the transglutaminase K in cervix carcinoma is not exclusively induced by alterations of epithelial differentiation or proliferation, but by different, unknown mechanisms; and (3) upregulation of transglutaminase K in cervix carcinomas may play an important role for the regulation of tumour invasive properties by modulating cell-cell interactions.

Transforming growth factor-beta1 is an autocrine mediator of U937 cell growth arrest and differentiation induced by vitamin D3 and retinoids

Vitamin D and retinoids cooperate to inhibit the proliferation and induce the differentiation of human myelomonocytic U937 leukemia cells. In the present work, we investigated the role of TGF-beta as an endogenous mediator of this process. We found that the TGF-beta1 precursor began to accumulate in cell culture supernatants soon after the addition of 1alpha,25 dihydroxyvitamin D3 (VD) and retinoids. We used neutralizing antibodies (AbTGF-beta) and antisense oligonucleotide (AS Oligo) to inhibit its possible effects. Our data demonstrated that AbTGF-beta partially inhibit the expression of the differentiated phenotype, as assessed by measurement of phagocytic activity, response to the chemotactic peptide fMLP, and lysozyme secretion. AS Oligo was also inhibitory, and the effects of AS Oligo and AbTGF-beta were cumulative. Cell growth inhibition induced by VD and retinoids was completely reversed, and differentiation was reduced by about 75% when both inhibitors were associated. Time course experiments based on the delayed addition of AbTGF-beta and AS Oligo showed that TGF-beta1 was required for cell differentiation 24 h after the addition of inducers. Studies on TGF-beta receptors revealed that, while the expression of type II receptor was stable, the level of type I TGF-beta receptor mRNA and the expression of the protein began to decline early during the differentiation process. As a whole, these results support the notion that an autocrine TGF-beta pathway, activated by VD and retinoids in U937 cells, is involved in the early steps of the process leading to cell growth arrest and differentiation.

Cellular and extracellular biology of the latent transforming growth factor-beta binding proteins

The latent transforming growth factor-beta binding proteins (LTBP) are a recently identified family of widely expressed multidomain glycoproteins that range in size from 125 kDa to 240 kDa. Four LTBP genes have been described, and the homology of latent transforming growth factor-beta binding proteins molecules to the fibrillins has resulted in their inclusion in the so-called 'fibrillin superfamily'. They form intracellular covalent complexes with latent transforming growth factor-beta and target these growth factors to the extracellular matrix. This review describes their structure, summarizes current understanding of their dual roles as growth factor binding proteins and components of the extracellular matrix, and highlights their significance in tissue development and disease.

Autoantibodies to tissue transglutaminase as predictors of celiac disease

BACKGROUND & AIMS

Immunoglobulin A (IgA) autoantibodies to endomysium (EMA) are highly specific and sensitive markers for celiac disease. Recently, we identified tissue transglutaminase (tTG) as the major if not sole endomysial autoantigen.

METHODS

An enzyme-linked immunosorbent assay (ELISA) was established to measure IgA anti-tTG titers in serum samples from 106 celiac patients with partial or subtotal villous atrophy, 43 celiac patients on a gluten-free diet, and 114 diseased and healthy controls. Results were correlated with clinical and histological data and with EMA titers.

RESULTS

In patients with biopsy-proven celiac disease consuming a normal, gluten-containing diet, 98.1% of the serum samples had elevated IgA titers against tTG, whereas 94.7% of the control sera were negative. IgA anti-tTG correlated positively with semiquantitative IgA EMA titers (r = 0.862; P < 0.0001).

CONCLUSIONS

An ELISA based on tTG allows diagnosis of celiac disease with a high sensitivity and specificity. IgA anti-tTG and IgA EMA show an excellent correlation, further confirming the enzyme as the celiac disease autoantigen. Because the assay is quantitative, not subjected to interobserver variation, and easy to perform, it will be a useful tool for population screening of a hitherto underdiagnosed disease.

Differential expression and biological activity of retinoic acid-induced TGFbeta isoforms in embryonic palate mesenchymal cells

The effect of retinoic acid (RA) on TGF-beta mRNA expression and protein production in murine embryonic palate mesenchymal (MEPM) cells was examined by Northern blotting and TGF-beta bioassay in association with TGF-beta isoform-specific neutralizing antibodies. Heat or acid activation was used to distinguish between latent and active TGF-beta protein released into the culture medium. RA had little or no effect on TGF-beta1 mRNA expression and protein production. In contrast, RA increased TGF-beta2 and beta3 protein released into the culture medium, the protein being mostly in an inactive or latent form. The amount of active TGF-beta released was increased relative to the total increase in TGF-beta released, suggesting that RA treatment stimulated activation of latent TGF-beta. RA also increased TGF-beta2 mRNA expression; we have previously shown that RA upregulates TGF-beta3 mRNA in these cells. RA and TGF-beta individually inhibited 3H-thymidine incorporation into MEPM cell DNA, while, when administered simultaneously, they inhibited proliferative activity to a greater extent. Heat- or acid-activated conditioned medium (CM) from MEPM cells treated with RA was able to inhibit 3H-thymidine incorporation into MEPM cell DNA to an extent greater than seen with RA treatment alone. Coincubation of heat-activated CM from RA-treated MEPM cells with pan-specific or TGF-beta2 or beta3-specific neutralizing antibodies partially relieved the inhibitory effect on 3H-thymidine incorporation, suggesting that this proliferative response was due to RA-induced TGF-beta. Simultaneous treatment with RA and TGF-beta also stimulated gycosaminoglycan (GAG) synthesis to an extent greater than that seen with TGF-beta treatment alone, this despite the ability of RA to inhibit GAG synthesis. These data demonstrate a role for RA and RA-induced TGF-beta in the regulation of palate cell proliferation and GAG synthesis and suggest a role for TGF-beta in retinoid-induced cleft palate.

Interactions between growth factors and integrins: latent forms of transforming growth factor-beta are ligands for the integrin alphavbeta1

The multipotential cytokine transforming growth factor-beta (TGF-beta) is secreted in a latent form. Latency results from the noncovalent association of TGF-beta with its processed propeptide dimer, called the latency-associated peptide (LAP); the complex of the two proteins is termed the small latent complex. Disulfide bonding between LAP and latent TGF-beta-binding protein (LTBP) produces the most common form of latent TGF-beta, the large latent complex. The extracellular matrix (ECM) modulates the activity of TGF-beta. LTBP and the LAP propeptides of TGF-beta (isoforms 1 and 3), like many ECM proteins, contain the common integrin-binding sequence RGD. To increase our understanding of latent TGF-beta function in the ECM, we determined whether latent TGF-beta1 interacts with integrins. A549 cells adhered and spread on plastic coated with LAP, small latent complex, and large latent complex but not on LTBP-coated plastic. Adhesion was blocked by an RGD peptide, and cells were unable to attach to a mutant form of recombinant LAP lacking the RGD sequence. Adhesion was also blocked by mAbs to integrin subunits alphav and beta1. We purified LAP-binding integrins from extracts of A549 cells using LAP bound to Sepharose. alphavbeta1 eluted with EDTA. After purification in the presence of Mn2+, a small amount of alphavbeta5 was also detected. A549 cells migrated equally on fibronectin- and LAP-coated surfaces; migration on LAP was alphavbeta1 dependent. These results establish alphavbeta1 as a LAP-beta1 receptor. Interactions between latent TGF-beta and alphavbeta1 may localize latent TGF-beta to the surface of specific cells and may allow the TGF-beta1 gene product to initiate signals by both TGF-beta receptor and integrin pathways.

Retinoids potentiate transforming growth factor-beta activity in bovine endothelial cells through up-regulating the expression of transforming growth factor-beta receptors

Retinoic acid (RA) induces the activation of latent transforming growth factor-beta (TGF-beta) in bovine aortic endothelial cells (BAECs) via enhancement of cellular plasminogen activator (PA)/plasmin levels. The resultant TGF-beta suppresses the excessive fibrinolytic activity by decreasing PA expression and stimulating expression of the PA inhibitor, PA inhibitor-1 (PAI-1), and inhibits cell proliferation. Here, we report that, in this regulatory system, RA simultaneously up-regulates the expression of TGF-beta receptor types I and II, resulting in enhancement of TGF-beta activity in the cells. RA increased the numbers of high- and low-affinity binding sites for 125I-TGF-beta1 2.1-fold and 1.5-fold, respectively, without alteration of their Kd values. Affinity labeling and Western and Northern blotting studies showed that, following RA treatment, surface levels of both type I and type II receptors increased due to augmentation in their mRNA levels. The effect was dose- and time-dependent. Treatment with 1 microM RA for 15 hr increased mRNA levels of type I and II receptor threefold and eightfold, respectively. Pretreatment of BAECs with either RA or retinol lowered the concentration of TGF-beta1 required to suppress PA levels, to enhance PAI-1 levels, and to inhibit cell proliferation. Thus, retinoids may regulate cellular functions of BAECs not only by inducing the formation of active TGF-beta but also by stimulating TGF-beta receptor expression. This regulatory mechanism may sustain TGF-beta-mediated regulation of EC function at a focal site where RA is acting.

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.

Identification of a transforming growth factor-beta1/bone morphogenetic protein 4 (TGF-beta1/BMP4) response element within the mouse tissue transglutaminase gene promoter

Tissue transglutaminase is a calcium-dependent, protein cross-linking enzyme that is highly expressed in cells undergoing apoptosis. The expression of tissue transglutaminase is regulated by a variety of molecules including retinoids, interleukin-6, and transforming growth factor-beta1 (TGF-beta1). Retinoid and interleukin-6 inductions of tissue transglutaminase expression are mediated by specific cis-regulatory elements located within the first 4.0 kilobase pairs of the promoter of the gene. The present studies were designed to identify the molecular mechanisms mediating the regulation of tissue transglutaminase gene expression by TGF-beta family members. Transient transfection of Mv1Lu cells with transglutaminase promoter constructs demonstrated that 0.2 nM TGF-beta1 maximally induced the activation of the promoter through a 10-base pair TGF-beta1 response element (TRE; GAGTTGGTGC) located 868 base pairs upstream of the transcription start site. This same element mediated an inhibitory activity of TGF-beta1 on the transglutaminase promoter in MC3T3 E1 cells. The TRE through which TGF-beta1-regulated the activity of the transglutaminase promoter was necessary and sufficient for bone morphogenetic protein 2- (BMP) and BMP4-dependent inhibition of the tissue transglutaminase promoter. The TGF-beta1, BMP2, and BMP4 regulation of the transglutaminase promoter activity was similar to the responses we observed for the endogenous transglutaminase activity of Mv1Lu and MC3T3 E1 cells. For BMP2 and BMP4, this regulation was paralleled by a decrease in tissue transglutaminase mRNA in MC3T3 E1 cells. The results of these experiments suggest that TGF-beta1, BMP2, and BMP4 regulation of mouse tissue transglutaminase gene expression requires a composite TRE located in the 5'-flanking DNA.

Plasminogen/plasminogen activator and growth factor activation

The plasminogen/plasminogen activator system is widely used in extracellular proteolysis. In this review the involvement of this system in tumour invasion, cell migration, growth factor presentation and inhibition of angiogenesis are discussed.

Evidence for the Involvement of Both Retinoic Acid Receptor- and Retinoic X Receptor-Dependent Signaling Pathways in the Induction of Tissue Transglutaminase and Apoptosis in the Human Myeloma Cell Line RPMI 8226

In this study, we show that both all-trans-retinoic acid (atRA) and 9-cis-retinoic acid (9-cis-RA) are potent inducers of tissue transglutaminase (TGase II), an enzyme involved in apoptosis, at the level of both enzyme activity and mRNA in the human myeloma cell line RPMI 8226. RPMI 8226 cells were shown to express mRNAs for all the retinoid receptors subtypes, ie, RARα, RARβ, RARγ, RXRα, RXRβ, and RXRγ. To identify which of these receptors are involved in regulating TGase II expression, several receptor-selective synthetic retinoids were used. Neither CD367, a very potent retinoid that selectively binds and activates receptors of the RAR family, nor CD2425, an RXR-selective agonist, induced TGase II when used alone. However, combination of CD367 and CD2425 resulted in nearly full induction of the enzyme. Moreover, when used in combination with atRA, CD367 partially inhibited the atRA-dependent induction of TGase II, whereas CD2425 enhanced it. The effects of Am 580, CD417, and CD437, three synthetic retinoids selective for the RARs subtypes RARα, RARβ, and RARγ, respectively, were also investigated. None of these compounds was able to induce TGase II when used alone; however, the combination of each of them with CD2425 resulted in strong induction of the enzyme activity, reaching 30% to 50% of the values obtained in the presence of retinoic acid and suggesting functional redundancy between the RAR subtypes. Finally, treatment with atRA or the combination of CD367 and CD2425, but not with CD367 or CD2425 alone, was also shown to trigger apoptosis in RPMI 8226 cells, with prominent accumulation of TGase II immunoreactivity in apoptotic cells. Taken together these data suggest that the induction of TGase II expression and apoptosis in the RPMI 8226 myeloma cell line required ligand-dependent activation of both the RAR and RXR receptors.

Evidence for the Involvement of Both Retinoic Acid Receptor- and Retinoic X Receptor-Dependent Signaling Pathways in the Induction of Tissue Transglutaminase and Apoptosis in the Human Myeloma Cell Line RPMI 8226

In this study, we show that both all-trans-retinoic acid (atRA) and 9-cis-retinoic acid (9-cis-RA) are potent inducers of tissue transglutaminase (TGase II), an enzyme involved in apoptosis, at the level of both enzyme activity and mRNA in the human myeloma cell line RPMI 8226. RPMI 8226 cells were shown to express mRNAs for all the retinoid receptors subtypes, ie, RARα, RARβ, RARγ, RXRα, RXRβ, and RXRγ. To identify which of these receptors are involved in regulating TGase II expression, several receptor-selective synthetic retinoids were used. Neither CD367, a very potent retinoid that selectively binds and activates receptors of the RAR family, nor CD2425, an RXR-selective agonist, induced TGase II when used alone. However, combination of CD367 and CD2425 resulted in nearly full induction of the enzyme. Moreover, when used in combination with atRA, CD367 partially inhibited the atRA-dependent induction of TGase II, whereas CD2425 enhanced it. The effects of Am 580, CD417, and CD437, three synthetic retinoids selective for the RARs subtypes RARα, RARβ, and RARγ, respectively, were also investigated. None of these compounds was able to induce TGase II when used alone; however, the combination of each of them with CD2425 resulted in strong induction of the enzyme activity, reaching 30% to 50% of the values obtained in the presence of retinoic acid and suggesting functional redundancy between the RAR subtypes. Finally, treatment with atRA or the combination of CD367 and CD2425, but not with CD367 or CD2425 alone, was also shown to trigger apoptosis in RPMI 8226 cells, with prominent accumulation of TGase II immunoreactivity in apoptotic cells. Taken together these data suggest that the induction of TGase II expression and apoptosis in the RPMI 8226 myeloma cell line required ligand-dependent activation of both the RAR and RXR receptors.

Possible roles of transglutaminases in Alzheimer's disease

The localizations of two transglutaminases [factor XIIIa and tissue transglutaminase (tTG)] and their mRNAs were examined in human brain tissues from neurologically normal and Alzheimer disease (AD) cases, using immunohistochemical and in situ hybridization methods. In all cases, meningeal macrophages and ependymal macrophage/microglia were positive for factor XIIIa. The mRNA encoding factor XIIIa was detected in macrophages and microglia. As reported previously, intense staining with the antibody to factor XIIIa of a subset of microglia was seen in the parietal cortex in AD brains. Few or no microglia were found associated with classical senile plaques. In contrast, many labeled microglia were associated with primitive plaques. Further-more, most of these cells were mainly seen in the subpial cortical layer but were very rare in the hippocampus. On the other hand, few factor-XIIIa-positive microglia were found in the parietal cortices from non-neurological cases, but moderate numbers were found in their hippocampal tissues. TG and its mRNA were localized in astrocytes in all the cases. In AD, a few neurofibrillary tangles were positive to tTG. These results suggest that the subsets of microglia which express factor XIIIa may play some roles in the early phase of AD pathology.

Cell-associated activation of latent transforming growth factor-beta by calpain

Transforming growth factor-beta (TGF-beta) is normally secreted in a latent form, and plasmin-mediated proteolytic cleavage of latency-associated peptide (LAP), a component of latent TGF-beta complex that makes the complex inactive, activates latent TGF-beta. In the present study, we investigated the possible involvement of calpain, one of the cysteine proteases, in the activation of latent TGF-beta. When recombinant latent TGF-beta was incubated with calpain (1-10 u/ml) in a test tube, calpain cleaved LAP and released mature TGF-beta from the latent complex. When calpain was applied to cultured bovine capillary endothelial (BCE) cells, a low concentration of calpain (0.05-0.1 u/ml) inhibited the migration and proliferation of the cells, and these inhibitory effects were abrogated by anti-TGF-beta antibody as well as by calpain inhibitor peptide, but not by alpha2-antiplasmin, a specific inhibitor of plasmin. Active TGF-beta was detected in the conditioned medium of BCE cells collected in the presence of calpain. Chemical cross-linking of (125)I-calpain to BCE cells followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis indicated that calpain bound to the cell surface through chondroitinase ABC-sensitive proteoglycan. In addition, treatment of the BCE cells with chondroitinase ABC abrogated the inhibitory effect of calpain on the migration of these cells. Our data thus suggest that calpain is able to activate latent TGF-beta through a mechanism independent of plasmin. This activation is efficient in the presence of cells, and calpain binds to the cell surface via proteoglycan and activates latent TGF-beta, which is targeted to the same surface.

The mannose 6-phosphate/insulin-like growth factor 2 receptor (M6P/IGF2R), a putative breast tumor suppressor gene

Loss of heterozygosity (LOH) at the mannose 6-phosphate/insulin-like growth factor 2 receptor gene locus (M6P/IGF2R) on 6q26-27 has recently been demonstrated in approximately 30% of both invasive and in situ breast cancers. LOH was coupled with somatic point mutations in the remaining allele in several instances, leading to the proposition that M6P/IGF2R is a tumor suppressor gene. Somatic mutations in M6P/IGF2R have also been described in hepatoma and gastrointestinal cancers with the replication error positive (RER+) phenotype. These data indicate that M6P/IGF2R loss of function mutations may be involved in the pathogenesis of a wide spectrum of malignancies. Extensive data on the normal function of the M6P/IGF2R suggest that loss of M6P/IGF2R activity may contribute to multiple aspects of tumor pathophysiology, including deregulated growth, apoptosis, angiogenesis and invasion.

Coculture conditions alter endothelial modulation of TGF-beta 1 activation and smooth muscle growth morphology

We examined whether endothelial cells (ECs) inhibit smooth muscle cell (SMC) transforming growth factor-beta 1 (TGF-beta 1) activation in bilayer coculture. Western analysis showed that SMCs cocultured with ECs as a bilayer had lower amounts of active TGF-beta 1 protein compared with SMCs cultured alone and SMCs cocultured with ECs as a monolayer. EC inhibition of TGF-beta 1 activation could be blocked with plasminogen activator inhibitor-1 (PAI-1) antibody. Similarly, SMC hill-and-valley growth, a marker for TGF-beta 1 activity, was present in SMCs cultured alone and SMCs cocultured with ECs as a monolayer but was absent in SMCs cocultured as a bilayer. SMCs cocultured with ECs as a bilayer migrated at a greater rate than SMCs cultured either alone or cocultured as a monolayer. The EC effect on SMC migration was inhibited by the addition of 5 ng/ml TGF-beta 1. ECs had no effect on SMC RNA levels of TGF-beta 1. PAI-1 levels were increased in ECs and ECs cocultured with SMCs compared with SMCs cultured alone. ECs inhibit TGF-beta 1 activation in bilayer coculture. This appears to be mediated through an increase in EC PAI-1 release. Alterations in coculture conditions, in particular the degree of EC-SMC cell contact, have profound effects on this process.

Expression of tissue transglutaminase in human bladder carcinoma

The expression of cell adhesion proteins is frequently deranged in bladder carcinomas. Since tissue transglutaminase (tTG) can increase cellular adhesiveness, its expression was studied in both superficial and invasive transitional cell carcinomas. No expression of tTG was found in normal urothelium or in grade 1-3 papillary tumours without invasion. Expression of tTG was seen in the invasive processes of five grade 3 tumours with microinvasion and in 49 of 63 solid grade 3 and 4 tumours. In six cases, both primary tumours and biopsies from liver metastases were studied. In all these cases, the liver metastases were tTG-negative, while the primary tumours were tTG-negative in five cases and consisted of both tTG-positive and tTG-negative cells in one case. Analysis of tTG protein in tumour extracts by Western blotting showed expression of the 77 kD tTG, with no evidence for expression of the truncated form found in some cell types. It is suggested that tTG, when expressed, contributes to the deranged adhesive properties of the carcinoma cells and may influence the course of invasion. These results also raise the possibility that lack of tTG expression may increase the risk of developing blood-borne metastases.

Expression of transforming growth factor beta type III receptor suppresses tumorigenicity of human breast cancer MDA-MB-231 cells

Transforming growth factor beta (TGF-beta) promotes tumor progression in some model systems including human breast cancer cells. In this study, we report that human breast cancer cell lines express reduced amounts of TGF-beta type III receptor (RIII) when compared with untransformed human mammary epithelial cells. Consequently, we examined whether expression of RIII in human breast cancer MDA-MB-231 cells could reduce TGF-beta's tumor promoting activity by sequestering active TGF-beta isoforms produced by the cells. A tetracycline-repressible human RIII expression vector was stably transfected into the cell line. RIII expression in a pool of transfected clones and a single clone was found to be reversibly repressed by tetracycline treatment. Expression of RIII reduced the amount of active TGF-beta1 and TGF-beta2 in the conditioned medium. The medium conditioned by control cells showed a significantly higher growth inhibitory effect than that conditioned by RIII-transfected cells on the growth of the mink lung epithelial CCL64 cells. A conditioned medium collected from RIII-transfected cells treated with tetracycline significantly increased its growth inhibitory activity to that of control cells. Expression of RIII also reduced tumor incidence and growth rate in two separate experiments when the cells were inoculated in athymic nude mice. Treatment of the mice with tetracycline repressed RIII expression in the tumors generated by RIII-transfected cells and increased tumor incidence and growth rate. These results suggest that TGF-beta RIII can reduce tumorigenicity of MDA-MB-231 cells apparently by sequestering TGF-beta isoforms produced by these cells.

The use of Fluoresceincadaverine for detecting amine acceptor protein substrates accessible to active transglutaminase in living cells

The use of Fluoresceincadaverine as a primary amine donor for detecting the endogenous substrates for active transglutaminase in living cells was studied. Fluoresceincadaverine was found to be suitable for labelling cells in culture as it did not induce cytotoxicity when used at 0.5 mM in culture media and diffused throughout the cell. After appropriate fixation using methanol, Fluoresceincadaverine-labelled cells were observed by direct fluorescence microscopy, allowing visualization of the substrates for active transglutaminase. Simultaneous detection of transglutaminase and of Fluoresceincadaverine incorporated into proteins strongly suggested that cytosolic transglutaminase was inactive in these living cells. However, transglutaminase co-distributed with Fluoresceincadaverine-labelled structures, which resembled a lattice. Fluoresceincadaverine-labelled proteins detected by Western blotting using an anti-Fluorescein antibody showed that, in living cells, the major transglutaminase substrate migrated at an apparent molecular weight of 220 kDa, as does fibronectin. Fibronectin was found to co-distribute with Fluoresceincadaverine-labelled lattice. This confirmed that these lattice structures were extracellular and, therefore, that transglutaminase is in an active form in this compartment. This opportunity to perform morphological and biochemical analyses in the search for transglutaminase substrates in living cells should help in determining the specific function of transglutaminases in a particular cell type as well as in universal cellular events, such as apoptosis or cell growth.

Conjunctival fibrosis in ocular cicatricial pemphigoid--the role of cytokines

Ocular cicatricial pemphigoid (OCP) is a systemic, autoimmune disease characterised by conjunctival scarring that is often progressive. The pathophysiology of the fibrosis is unknown. This study aimed to determine which fibrogenic cytokines are present in the conjunctiva in patients with acute and chronic OCP as a first stage in determining the mechanisms of fibrosis. Conjunctival biopsies from patients with acute, subacute and chronic OCP (n=13) were compared to normal conjunctiva (n=10). Production of mRNA for, and expression of, transforming growth-beta1, 2 and 3 (TGF-beta), TGF-beta receptor, platelet derived growth factor (PDGF) and fibroblast growth factor (FGF) were assessed using in situ hybridisation and immunohistochemistry. Acute disease showed increased levels of mRNA for TGF-beta1 and 3, mainly in stromal fibroblasts and macrophages. In the stroma, there were concordant increases in latent and activated TGF-beta1 and 3 and TGF-beta receptor expression by fibroblasts. There were no significant increases in the expression of TGF-beta2, PDGF or FGF in acute disease. No cytokines or receptors were significantly increased in chronic disease. Acutely inflamed conjunctiva in OCP is associated with significant stromal levels of TGF-beta1 and 3 but not PDGF or FGF and none were increased in chronic disease. This suggests that TGF-beta may have a key role in the pathogenesis of the fibrosis. The absence of fibrogenic cytokines in chronic progressive OCP provides support for the proposal that fibroblasts in OCP conjunctiva may remain functionally and morphologically abnormal after the withdrawal of cytokine influences.

9,13-di-cis-Retinoic acid induces the production of tPA and activation of latent TGF-beta via RAR alpha in a human liver stellate cell line, LI90

We studied the mechanism by which 9,13-di-cis-retinoic acid (9,13dcRA), a novel and endogenous stereoisomer of all-trans-RA, induces TGF-beta formation in a human liver stellate cell line, LI90. 9,13dcRA induced the expression of RAR alpha and RARbeta, enhanced the production of tissue-type plasminogen activator (tPA), thereby, surface plasmin levels, and induced the activation of latent TGF-beta. Similar effects were obtained with RAR alpha-selective retinoid, but not with RARbeta- or RARgamma-selective retinoid, and the induction was inhibited by RAR alpha-selective antagonist. These results suggest that 9,13dcRA up-regulates tPA expression, resulting in the formation of TGF-beta by LI90 cells, at least in part, via induction and activation of RAR alpha.

Role of amphibian egg transglutaminase in the development of secondary cytostatic factor in vitro

Fresh cytosols extracted from unfertilized amphibian eggs contain a cytostatic factor (CSF) which arrests the cell cycle at metaphase when microinjected into cleaving blastomeres. This CSF is sensitive to Ca2+, and is designated primary CSF (1 degree CSF). During storage of Ca(2+)-containing cytosols at 2 degrees C, stable CSF activity appears, designated secondary CSF (2 degrees CSF). In Rana pipiens egg cytosols, the development of 2 degrees CSF coincides with the formation of a protein complex with a molecular weight above 2,000 kDa, and this large molecule exhibits a high 2 degrees CSF activity when purified (Shibuya and Masui, 1989: Development 106:799-808). The present study shows that both the formation of 2 degrees CSF protein complex and the development of its activity are inhibited by ethylamine and glycine-ethyl-ester (GEE), both known as potent transglutaminase (TGase) inhibitors. An affinity-purified polyclonal antibody raised against mammalian transglutaminase reacts with an approximately 68-kDa protein in fresh egg cytosols, as well as with the 2 degrees CSF protein complex. In cytosols deprived of transglutaminase by immunoprecipitation, neither the development of 2 degrees CSF activity nor the formation of its protein complex can occur. These results indicate that transglutaminase of Rana pipiens eggs is responsible or the formation of 2 degrees CSF, and that transglutaminase itself is incorporated into 2 degrees CSF molecules.

Analysis of small latent transforming growth factor-beta complex formation and dissociation by surface plasmon resonance. Absence of direct interaction with thrombospondins

Transforming growth factor-beta (TGFbeta) is a pluripotent regulator of cell growth and differentiation. The growth factor is expressed as a latent complex that must be converted to an active form before interacting with its ubiquitous high affinity receptors. This conversion involves the release of the mature TGFbeta through disruption of the noncovalent interactions with its propeptide or latency associated protein (LAP). Complex formation or dissociation between LAP and TGFbeta plays a very important role in TGFbeta biological activity at different steps. To further characterize the kinetic parameters of this interaction, we have employed surface plasmon resonance biosensor methodology. Using this technique, we observed real time association of LAP with mature TGFbeta1. The complex formation showed an equilibrium Kd around 3-7 nM. Furthermore, we observed dissociation of the complex in the presence of extreme pH, chaotropic agents, or plasmin, confirming their effects on TGFbeta activation. The same approach was used to examine whether latent TGFbeta1 could interact with thrombospondins, previously described as activators of latent TGFbeta. Using this method, we could not detect any direct interaction of thrombospondins with either LAP alone, TGFbeta1 alone, or the small latent TGFbeta1 complex. This suggests that activation of latent TGFbeta1 complex by thrombospondins is through an indirect mechanism.

The role of transglutaminase in the rat subtotal nephrectomy model of renal fibrosis

Tissue transglutaminase is a calcium-dependent enzyme that catalyzes the cross-linking of polypeptide chains, including those of extracellular matrix (ECM) proteins, through the formation of epsilon-(gamma-glutamyl) lysine bonds. This crosslinking leads to the formation of protein polymers that are highly resistant to degradation. As a consequence, the enzyme has been implicated in the deposition of ECM protein in fibrotic diseases such as pulmonary fibrosis and atherosclerosis. In this study, we have investigated the involvement of tissue transglutaminase in the development of kidney fibrosis in adult male Wistar rats submitted to subtotal nephrectomy (SNx). Groups of six rats were killed on days 7, 30, 90, and 120 after SNx. As previously described, these rats developed progressive glomerulosclerosis and tubulo-interstitial fibrosis. The tissue level of epsilon-(gamma-glutamyl) lysine cross-link (as determined by exhaustive proteolytic digestion followed by cation exchange chromatography) increased from 3.47+/- 0.94 (mean+/-SEM) in controls to 13.24+/-1.43 nmol/g protein 90 d after SNx, P </= 0.01. Levels of epsilon-(gamma-glutamyl) lysine cross-link correlated well with the renal fibrosis score throughout the 120 observation days (r = 0.78, P </= 0.01). Tissue homogenates showed no significant change in overall transglutaminase activity (14C putrescine incorporation assay) unless adjusted for the loss of viable tubule cells, when an increase from 5.77+/-0.35 to 13.93+/-4.21 U/mg DNA in cytosolic tissue transglutaminase activity was seen. This increase was supported by Western blot analysis, showing a parallel increase in renal tissue transglutaminase content. Immunohistochemistry demonstrated that this large increase in epsilon-(gamma-glutamyl) lysine cross-link and tissue transglutaminase took place predominantly in the cytoplasm of tubular cells, while immunofluorescence also showed low levels of the epsilon-(gamma-glutamyl) lysine cross-link in the extracellular renal interstitial space. The number of cells showing increases in tissue transglutaminase and its cross-link product, epsilon-(gamma-glutamyl) lysine appeared greater than those showing signs of typical apoptosis as determined by in situ end-labeling. This observed association between tissue transglutaminase, epsilon-(gamma-glutamyl) lysine cross-link, and renal tubulointerstitial scarring in rats submitted to SNx suggests that tissue transglutaminase may play an important role in the development of experimental renal fibrosis and the associated loss of tubule integrity.

Identification of human semaphorin E gene expression in rheumatoid synovial cells by mRNA differential display

Rheumatoid arthritis (RA) is characterised by chronic inflammation of synovial tissue with aggressive proliferation of synovial cells causing destruction of cartilage and bone. Immunopathological mechanisms, infectious causes and genetic factors have been discussed, but the etiology of the disease has not been understood until now. Especially, the mechanisms driving tumourlike growth and invasive behaviour of fibroblastoid synovial cells have not been identified yet. Our aim is to find cellular factors which are mediators for such pathways. One possibility to approach this, is searching for disease-relevant genes. We applied the mRNA-differential display technique to compare mRNA expression patterns of normal and rheumatic synovial fibroblasts. We identified an upregulation of the human semaphorin E gene in rheumatoid synovial fibroblastoid cells. Interestingly semaphorin E is a member of a protein-family described to play an immunosuppressive role via inhibition cytokines. A relevance of this finding towards the pathogenesis of RA is discussed.

TGF-beta and the endothelium during immune injury

During immune injury, activation of endothelial cells by inflammatory cytokines stimulates leukocyte adhesion to the endothelium, turns the endothelium from an anticoagulant surface to one that is frankly procoagulant, and results in the release of vasoactive mediators and growth factors. Cytokine activation of endothelial cells also results in increased endothelial cell TGF-beta 1 synthesis and enhanced activation of latent TGF-beta, the latter involving a shift of plasmin production from the apical to subendothelial surface. In cytokine-stimulated endothelial cells, TGF-beta hinders leukocyte adhesion and transmigration via inhibition of IL-8 and E-selectin expression. TGF-beta also profoundly diminishes cytokine-stimulated inducible nitric oxide synthase production and instead augments endothelial nitric oxide synthase expression. Thus, some of the TGF-beta actions on endothelium during immune activation can viewed as immunosuppressive. TGF-beta also influences mechanisms of vascular remodeling during the healing phase of immune injury. It stimulates PDGF-B synthesis by endothelial cells, causes bFGF release from subendothelial matrix, and promotes VEGF synthesis by non-endothelial cells. Together these mediators control angiogenesis, a critical component of the vascular repair phenomenon. Further, endothelial cell derived PDGF-B and bFGF influence the proliferation and migration of neighboring cells. Thus, endothelial cells and TGF-beta actions on the endothelium play important roles both during the initial phase of immune injury and during the later remodeling phase.

Latent transforming growth factor-beta: structural features and mechanisms of activation

Transforming growth factor-beta are cytokines with a wide range of biological effects. They play a pathologic role in inflammatory and fibrosing diseases such as nephrosclerosis. TGF-beta s are secreted in a latent form due to noncovalent association with latency associated peptide (LAP), which is a homodimer formed from the propeptide region of TGF-beta. LAP is disulfide linked to another protein, latent TGF-beta binding protein (LTBP). LTBP has features in common with extracellular matrix proteins, and targets latent TGF-beta to the matrix. Activation of latent TGF-beta can be accomplished in vitro by denaturing treatments, plasmin digestion, ionizing radiation and interaction with thrombospondin. The mechanisms by which latent TGF-beta is activated physiologically are not well understood. Results to date suggest an important role for proteases, particularly plasmin, although other mechanisms probably exist. A general model of activation is proposed in which latent TGF-beta is released from the extracellular matrix by proteases, localized to cell surfaces, and activated by cell-associated plasmin.

Transglutaminase activity in aging articular chondrocytes and articular cartilage vesicles

OBJECTIVE

Transglutaminases (TGases) (E.C. 2.3.2.13) catalyze a posttranslational modification of proteins and are associated with biomineralization in growth plate cartilage. Type II TGase participates in the activation of latent transforming growth factor beta (TGFbeta), a crucial factor for both normal cartilage mineralization and the pathologic mineralization that results in calcium pyrophosphate dihydrate (CPPD) crystal formation in aging articular cartilage. To explore a possible association between TGase levels and CPPD crystal formation in mature articular cartilage, TGase activity in articular chondrocytes from old and young pigs and in the articular cartilage vesicle (ACV) fraction of porcine articular cartilage was examined. In addition, the effects of TGase inhibitors on the production of inorganic pyrophosphate (PPi), a process necessary for CPPD crystallogenesis, were determined.

METHODS

TGase activity was measured with a radiometric assay in cultured articular chondrocytes from the knee joints of old (3-5 years old) and young (2-6 weeks old) pigs and in the ACVs. PPi levels were measured in chondrocyte-conditioned media in the presence of TGase inhibitors or control compounds.

RESULTS

Levels of TGase activity in the cytosolic fraction of old chondrocytes were 7-fold higher than those in identically cultured young chondrocytes. The mean +/- SD activity level in the membrane fraction of lysed chondrocytes was 6.0 +/- 0.6 units/mg protein in old articular chondrocytes and was undetectable in young chondrocytes. In ACVs, the mean +/- SD TGase activity level was 1.23 +/- 0.1 units/mg protein. Type II TGase protein was present in chondrocyte cytosol and in ACVs. TGase activity was increased by TGFbeta to 120% of control values (P < 0.01), and decreased by insulin-like growth factor 1 to 80% of control values (P < 0.01). TGase inhibitors blocked media accumulation of PPi, an essential precursor of CPPD crystal formation, and a sensitive marker of TGFbeta effect.

CONCLUSION

These data suggest a potential link between TGase activity and processes of pathologic biomineralization that result in CPPD crystal formation in aging articular cartilage.

Quantification of transforming growth factor-beta in biological material using cells transfected with a plasminogen activator inhibitor-1 promoter-luciferase construct

Transforming growth factor-beta (TGF-beta), a multifunctional cytokine, can be quantified by a variety of bioassays or immunoassays. One of the disadvantages of these techniques is that they require sample purification to remove components that interfere with the TGF-beta signal. In the current study the feasibility of quantifying TGF-beta in complex biological fluids directly with a recently developed bioassay was examined. This assay is based on the ability of TGF-beta to induce plasminogen activator inhibitor-1 (PAI-1) expression. Mature TGF-beta binds to the receptors of mink lung epithelial cells transfected with a plasminogen activator inhibitor-1 promoter-luciferase construct (PAI/L), resulting in a dose-dependent increase of luciferase activity. Specificity for TGF-beta was proven by treatment of the samples with neutralizing antibodies. The sensitivity and the intraassay precision are comparable to the ELISA. It is demonstrated, however, that, unlike the ELISA, a purification step by, e.g., acid-ethanol extraction prior to the PAI/L assay, is not required. This not only simplifies the assay but also reduces the minimal sample volume and allows to discriminate between latent and mature TGF-beta. The present study furthermore provides insight in the critical steps for accurate TGF-beta determination, which include careful blood collection and sample handling (storage and preparation). With this protocol TGF-beta has been quantified in human plasma, rat plasma, rat saliva, tissue extracts from rat lung, and in culture medium of TGF-beta-producing cells.

Dimerization of midkine by tissue transglutaminase and its functional implication

Midkine (MK), a retinoic acid-inducible growth/differentiation factor, serves as a substrate for tissue transglutaminase (Kojima, S. , Muramatsu, H., Amanuma, H., and Muramatsu, T. 1995. J. Biol. Chem. 270, 9590-9596). Upon incubation with transglutaminase MK forms multimers through cross-linkages. Here, we report the following results. 1) Heparin potentiated the multimer formation by MK. 2) The N- and C-terminal half domains each formed a dimer through the action of transglutaminase. 3) Gln42 or Gln44 in the N-terminal half and Gln95 in the C-terminal half served as amine acceptors in the cross-linking reaction, as judged from the incorporation of putrescine into whole MK or each half domain, and the competitive inhibition of the cross-linking by MK-derived peptides containing Gln residue(s). The strongest inhibition was obtained with Ala41-Pro51. 4) This peptide abolished the biological activity of MK to enhance the plasminogen activator activity in bovine aortic endothelial cells. The inhibition was limited against the MK monomer, and not seen against the MK dimer, separated by gel filtration chromatography. These results suggest that dimer formation through transglutaminase-mediated cross-linking is an important step as to the biological activity of MK.

Latent transforming growth factor-beta binding protein domains involved in activation and transglutaminase-dependent cross-linking of latent transforming growth factor-beta

Transforming growth factor-beta (TGF-beta) is secreted by many cell types as part of a large latent complex composed of three subunits: TGF-beta, the TGF-beta propeptide, and the latent TGF-beta binding protein (LTBP). To interact with its cell surface receptors, TGF-beta must be released from the latent complex by disrupting noncovalent interactions between mature TGF-beta and its propeptide. Previously, we identified LTBP-1 and transglutaminase, a cross-linking enzyme, as reactants involved in the formation of TGF-beta. In this study, we demonstrate that LTBP-1 and large latent complex are substrates for transglutaminase. Furthermore, we show that the covalent association between LTBP-1 and the extracellular matrix is transglutaminase dependent, as little LTBP-1 is recovered from matrix digests prepared from cultures treated with transglutaminase inhibitors. Three polyclonal antisera to glutathione S-transferase fusion proteins containing amino, middle, or carboxyl regions of LTBP-1S were used to identify domains of LTBP-1 involved in cross-linking and formation of TGF-beta by transglutaminase. Antibodies to the amino and carboxyl regions of LTBP-1S abrogate TGF-beta generation by vascular cell cocultures or macrophages. However, only antibodies to the amino-terminal region of LTBP-1 block transglutaminase-dependent cross-linking of large latent complex or LTBP-1. To further identify transglutaminase-reactive domains within the amino-terminal region of LTBP-1S, mutants of LTBP-1S with deletions of either the amino-terminal 293 (deltaN293) or 441 (deltaN441) amino acids were expressed transiently in CHO cells. Analysis of the LTBP-1S content in matrices of transfected CHO cultures revealed that deltaN293 LTBP-1S was matrix associated via a transglutaminase-dependent reaction, whereas deltaN441 LTBP-1S was not. This suggests that residues 294-441 are critical to the transglutaminase reactivity of LTBP-1S.

Colocalization of tissue transglutaminase and stress fibers in human vascular smooth muscle cells and human umbilical vein endothelial cells

The subcellular distribution of tissue transglutaminase in human umbilical vein endothelial cells and human arterial and venous smooth muscle cells was examined. Double-immunofluorescence staining of smooth muscle cells and endothelial cells with anti-transglutaminase antisera and rhodamine-tagged phalloidin revealed codistribution of transglutaminase with the stress fibers, with endothelial cells also containing a cytoplasmic pool. This pattern of distribution was confirmed by confocal microscopy. Immunoprecipitation experiments demonstrated that transglutaminase co-immunoprecipitated with myosin in high-molecular-weight complexes, but not with actin, suggesting that the association of transglutaminase with the stress fibers was due to its cross-linking to myosin. About 97% of endothelial cell transglutaminase activity was present in the cytosolic fraction and 3% in the particulate fraction. The detergent-insoluble fraction was practically devoid of activity as measured by the putrescine assay, but was active as evidenced by the covalent cross-linking of 125I-fibronectin. Western blotting with a polyclonal rabbit antiserum raised against human erythrocyte transglutaminase detected high levels of enzyme in endothelial cell cytosol and both detergent-soluble and detergent-insoluble membrane fractions. In contrast, smooth muscle cells contained much less cytosolic transglutaminase, as determined either functionally or antigenically. Furthermore, within the particulate fraction of the smooth muscle cells, most of the enzyme was located in the detergent-insoluble fraction, as assessed by Western blot analysis. Retinoic acid increased the levels of enzyme in the cytosol of all cell types and the increases were correlated with increases in mRNA. Thus, tissue transglutaminase is present in various particulate fractions of vascular smooth muscle cells and endothelial cells and may be present in this cellular fraction by virtue of autocross-linking of the enzyme itself to stress fiber-associated myosin.

A new biological glue for cartilage-cartilage interfaces: tissue transglutaminase

In this study, we used an in vitro model to test the capacity of tissue transglutaminase to increase the adhesive strength at a cartilage-cartilage interface. Full-thickness cartilage-bone cylinders were prepared from fresh adult bovine shoulder joints, and the superficial half of the hyaline cartilage was then removed to provide a plane surface. Tissue transglutaminase was applied to the freshly cut surface of one cylinder, and a calcium-chloride solution (to act as an activating agent) was applied to that of the other. The cartilage surfaces were immediately apposed, one on top of the other, and an eighty-gram weight was applied to the upper cylinder for ten minutes at 37 degrees Celsius under defined humidity conditions. A measured force was then applied transversely to the upper cylinder until it was displaced from the lower one (which was clamped in a holding device), and the force recorded at this point was taken as a measure of the adhesive strength achieved at the cartilage-cartilage interface. The adhesive strength increased linearly with an increasing concentration of tissue transglutaminase (0.25 to 2.75 milligrams per milliliter) and was enhanced by increasing the duration of incubation, but it was not influenced by the level of humidity. The adhesive strength was improved by as much as 40 per cent when the cartilage surfaces had been pretreated with chondroitinase AC or hyaluronidase to remove glycosaminoglycan chains of proteoglycans, which are largely responsible for the intrinsic anti-adhesive properties of cartilage.