Enhanced transglutaminase activity in transformed human lung fibroblast cells after exposure to sodium butyrate

Fluorescent probes of tissue transglutaminase reveal its association with arterial stiffening

Tissue transglutaminase (TG2) catalyzes the crosslinking of proteins. TG2 has been implicated in fibrosis and vascular calcification, both of which lead to a common feature of aging known as arterial stiffness. In order to probe the role of TG2 in arterial rigidification, we have prepared a fluorescent irreversible inhibitor as a probe for TG2 activity (RhodB-PGG-K(Acr)-LPF-OH). This probe was synthesized on solid support, characterized kinetically (k(inact) = 0.68 min⁻¹, K(I) = 79 μM), and then used to stain the aorta from rats used as a model of isolated systolic hypertension (ISH). Interestingly, TG2 activity was thus shown to increase over 4 weeks of the hypertension model, corresponding with the previously observed increase in arterial stiffness. These results clearly suggest an association between TG2 and the phenomenon of arterial rigidification.

Photolabeling of tissue transglutaminase reveals the binding mode of potent cinnamoyl inhibitors

We have recently developed a new class of cinnamoyl derivatives as potent tissue transglutaminase (TG2) inhibitors. Herein, we report the synthesis of a diazirine derivative of these inhibitors and its application to the photolabeling of its binding site on guinea pig liver transglutaminase. Two novel homology models were generated for this commonly studied TG2, which differ in the conformational state they represent. Tryptic digest and mass spectrometric analysis of the photolabeling experiment showed that only residue Cys230 was labeled, and our homology models were used to visualize these results. This visualization suggested that Cys230 is somewhat more solvent-exposed in the "closed" conformation of TG2, compared to the "open" conformation. Docking experiments suggested binding modes consistent with the labeling pattern that would block access to the tunnel leading to the active site, consistent with the observed mode of inhibition. However, while these modeling simulations favored the closed conformation as the target of our cinnamoyl inhibitors, native PAGE experiments indicated the open conformation of the enzyme in fact predominates in the presence of our photolabeling derivative. These results are important for understanding the binding modes of TG2 inhibitors in general and will be critical for the structure-based design of future inhibitors.

Synthesis of dipeptide-bound epoxides and alpha,beta-unsaturated amides as potential irreversible transglutaminase inhibitors

Herein we report the synthesis of 24 novel peptides as potential irreversible inactivators of transglutaminase (TGase). These peptides were designed to resemble Cbz-L-Gln-Gly, known to be a good TGase substrate, and to include either alpha,beta-unsaturated amide groups or the corresponding epoxide groups. The side chain length of the amino acid residue bearing the inhibitor group was also varied in order to permit investigation of this effect.

Synthesis and evaluation of novel dipeptide-bound 1,2,4-thiadiazoles as irreversible inhibitors of guinea pig liver transglutaminase

Herein we report the synthesis and evaluation of 14 novel peptides as potential irreversible inactivators of guinea pig liver transglutaminase (TGase). These peptides were designed to resemble Cbz-L-Gln-Gly, known to be a good TGase substrate, and to include a 1,2,4-thiadiazole group. The side chain length of the amino acid residue bearing the inhibitor group was also varied in order to permit investigation of this effect. Their inactivation rate constants were measured using a direct continuous spectrophotometric method and were found to vary between 0.330 to 0.89 microM(-1) min(-1).

Evaluation of novel dipeptide-bound alpha,beta-unsaturated amides and epoxides as irreversible inhibitors of guinea pig liver transglutaminase

Herein, we report the results of irreversible inhibition of guinea pig liver transglutaminase (TGase) by a series of 24 novel dipeptides containing either an alpha,beta-unsaturated amide or an epoxide functional group. Their inactivation rate constants were measured using a direct continuous spectrophotometric method and were found to vary between 421 x 10(3) and 3000 x 10(3)M(-1)min(-1).

Short-chain fatty acid in the human colon. Relation to inflammatory bowel diseases and colon cancer

Short chain fatty acids (SCFAs) are the end products of anaerobic bacteria break down of carbohydrates in the large bowel. This process, namely fermentation, is an important function of the large bowel; SCFAs, mainly acetate, propionate and butyrate account for approximately 80% of the colonic anion concentration and are produced in nearly constant molar ratio 60:25:15. Among their various properties, SCFAs are readily absorbed by intestinal mucosa, are relatively high in caloric content, are metabolized by colonocytes and epatocytes, stimulate sodium and water absorption in the colon and are trophic to the intestinal mucosa. While the fermentative production of SCFAs has been acknowledged as a principal mechanism of intestinal digestion in ruminants, the interest in the effects of SCFAs production on the human organism has been raising in the last ten years. SCFAs are of major importance in understanding the physiological function of dietary fibers and their possible role in intestinal neoplasia. SCFAs production and absorption are closely related to the nourishment of colonic mucosa, its production from dietary carbohydrates is a mechanism whereby considerable amounts of calories can be produced in short-bowel patients with remaining colonic function and kept on an appropriate dietary regimen. SCFAs enemas or oral probiotics are a new and promising treatment for ulcerative colitis. The effects have been attributed to the oxidation of SCFAs in the colonocytes and to the ability of butyrate to induce enzymes (i.e. transglutaminase) promoting mucosal restitution. Evidence is mounting regarding the effects of butyrate on various cell functions the significance of which needs further considerations. Up until now, attention has been related especially to cancer prophylaxis and treatment. This article briefly reviews the role of SCFAs, particularly butyrate, in intestinal mucosal growth and potential clinical applications in inflammatory and neoplastic processes of the large bowel.

Induction of tissue transglutaminase by dexamethasone: its correlation to receptor number and transglutaminase-mediated cell death in a series of malignant hamster fibrosarcomas

Treatment of the hamster fibrosarcoma cell lines (Met B, D and E) and BHK-21 hamster fibroblast cells with the glucocorticoid dexamethasone led to a powerful dose-dependent mRNA-synthesis-dependent increase in transglutaminase activity, which can be correlated with dexamethasone-responsive receptor numbers in each cell line. Increasing the number of dexamethasone-responsive receptors by transfection of cells with the HG1 glucocorticoid receptor protein caused an increase in transglutaminase activity that was proportional to the level of transfected receptor. In all experiments the levels of the tissue transglutaminase-mediated detergent-insoluble bodies was found to be comparable with increases in transglutaminase activity. Despite an increase in detergent-insoluble body formation, an increase in apoptosis as measured by DNA fragmentation was not found. Incubation of cells with the non-toxic competitive transglutaminase substrate fluorescein cadaverine led to the incorporation of this fluorescent amine into cellular proteins when cells were damaged after exposure to trypsin during cell passage. These cross-linked proteins containing fluorescein cadaverine were shown to be present in the detergent-insoluble bodies, indicating that the origin of these bodies is via activation of tissue transglutaminase after cell damage by trypsinization rather than apoptosis per se, since Met B cells expressing the bcl-2 cDNA were not protected from detergent-insoluble body formation. We describe a novel mechanism of cell death related to tissue transglutaminase expression and cell damage.

Enhanced apoptosis in transformed human lung fibroblasts after exposure to sodium butyrate

Simian virus-transformed human cells, WI-38 VA13A, showed a dose-dependent induction of apoptosis and reduction in cell numbers after exposure to sodium butyrate. Apoptosis was confirmed by ApopTag staining, isolation of apoptotic envelopes, and immunofluorescent staining with an antibody specific for apoptotic envelopes. Examination of the cell cultures by phase contrast and fluorescent microscopy revealed the presence of enlarged cells that displayed a more flattened morphology and morphological changes in the nucleus of cells exposed to sodium butyrate. Cell proliferation assays showed control and sodium butyrate cultures were synthesizing DNA and excluded any cytotoxic effects of sodium butyrate. Flow cytometry results indicated an increase in the number of aneuploid cells following sodium butyrate treatment. There was a decrease in the percentage of cells in G2/M in the diploid populations, but an increase in the percentage of cells in G2/ M in aneuploid populations. This human in vitro model system suggests a mode of action for the therapeutic effects of sodium butyrate, which have been observed in the topical treatment of neoplastic cells and reversal of symptom in ulcerative colitis, namely, the induction of apoptosis.

Immunochemical analyses of human plasma fibronectin-cytosolic transglutaminase interactions

Fibronectin is a glycoprotein involved in cell adhesion, tissue organization and wound healing. Transglutaminase binding and covalent cross-linking of fibronectin are physiologically important reactions. We describe microtiter plate-based immunochemical methods to analyze cytosolic transglutaminase-human plasma fibronectin interactions. The method was sensitive, specific, species-independent and capable of simultaneously analyzing 96 samples for binding. Binding was time-, temperature- and concentration-dependent and demonstrable with either protein immobilized to the plastic. The assay detected 1-5 ng transglutaminase or 50 pg fibronectin and was comparable in sensitivity to enzyme-linked immunosorbent assays. CaCl2 (8 mM) enhanced transglutaminase binding by two-fold. Molar concentrations of NaCl or millimolar concentrations of chloride salts of barium, copper or zinc inhibited binding by 50-60%. The binding was also competitively blocked by soluble fibronectin (IC50 = 2.3 nM) or by anti-fibronectin IgG (IC50 = 0.5 microM). Inclusion of dithiothreitol or 2-mercaptoethanol during binding resulted in a concentration-dependent inhibition of transglutaminase-fibronectin interactions (IC50 = 1.5 mM and 20 mM, respectively). A complex of [anti-transglutaminase IgG-transglutaminase-fibronectin-anti- fibronectin IgG] suggested that the binding sites and antibody epitopes could overlap, but are distinct and surface-exposed in the two proteins. Liver transglutaminase bound fibronectin 30-50% less compared to erythrocyte transglutaminase. Fibronectin-transglutaminase affinity was adequate for quantitating either antigen in lysates of lung fibroblasts, breast carcinomas or Escherichia coli. These immunochemical analyses will be useful for determining the affinity and mapping the domains involved in antibody recognition or protein-protein interactions using recombinant molecules of transglutaminase and fibronectin.

Butyrate, mesalamine, and factor XIII in experimental colitis in the rat: effects on transglutaminase activity

BACKGROUND/AIMS

Butyrate and factor XIII may improve ulcerative colitis; they also affect tissue and serum transglutaminase levels. We investigated the therapeutic potential of sodium butyrate and factor XIII and the role of transglutaminase during mucosal repair in experimental colitis.

METHODS

Rats with induced colitis were treated with sodium butyrate, mesalamine, sodium butyrate plus mesalamine, or saline enemas. Thromboxane B2 was monitored as index of inflammation. In a fifth group, the effectiveness of intravenous Factor XIII was assessed.

RESULTS

Sodium butyrate, alone or plus mesalamine, reduced histological activity from 13.7 +/- 1.7 (saline) to 2.5 +/- 1.3 and 2.3 +/- 1.1 (P < 0.01), respectively. Transglutaminase, reduced in the colons of the saline group (783 +/- 157 vs. normal 1800 +/- 192 mU/g; P < 0.01), returned toward normal values in the sodium butyrate or sodium butyrate plus mesalamine groups (1390 +/- 228 and 1226 +/- 172 mU/g, respectively; P < 0.01 vs. saline). Furthermore, sodium butyrate plus mesalamine reduced thromboxane B2 levels by day 5 (0.92 +/- 0.16 vs. saline 1.85 +/- 0.34 ng/mL; P < 0.05). Factor XIII therapy improved the histological picture (2.7 +/- 2.1 vs. saline 13.8 +/- 1.7; P < 0.01) and increased transglutaminase levels both in serum (2.81 +/- 0.11 vs. saline 1.45 +/- 0.09 mU/mL; P < 0.01) and in colon (1503 +/- 127 vs. saline 747 +/- 103).

CONCLUSIONS

Sodium butyrate and factor XIII improve colitis, sodium butyrate plus mesalamine reduce early thromboxane B2 synthesis, and transglutaminase(s) plays a role in ulcer healing.

Differential regulation of tissue transglutaminase in rat hepatoma cell lines McA-RH7777 and McA-RH8994: relation to growth rate and cell death

Close correlation between tissue transglutaminase (tTG) induction and growth regulation and/or cell death processes has been suggested in many cell lineages. In this study, the regulation of the tTG levels by various growth and differentiation factors and its relation to growth rate and cell death processes were investigated in two rat hepatoma cell lines, McA-RH7777 and McA-RH8994, using a monoclonal antibody against liver tTG. Transforming growth factor-beta 1 (TGF-beta 1) and retinoic acid (RA) each increased tTG to the level of 8- to 32-fold above that of control cultures in both cell lines after 72-h treatment. Dexamethasone (DEX) induced a 16- to 32-fold of tTG in McA-RH8994 cells while it did not change the enzyme level in McA-RH7777 cells. Simultaneous addition of DEX and RA increased the tTG level to more than 50-fold in McA-RH7777 cells as well as McA-RH8994 cells. Other factors, such as TGF-alpha, hepatocyte growth factor, dimethyl sulfoxide, and protein kinase C activator, did not show significant increases of the tTG levels. Although tTG induction by TGF-beta 1 or DEX appeared to be correlated with their growth suppressive effects, RA increased the tTG level without suppressing the growth rate of hepatoma cells. TGF-beta 1 was also shown to induce cell death in both cell lines. Our results demonstrate that RA and DEX are capable of modulating the TGF-beta 1-induced cell death processes independent of the tTG levels. We present evidence here that tTG induction by itself is not the direct cause of growth suppression and cell death in these hepatoma cells.

Site-directed mutagenesis of human tissue transglutaminase: Cys-277 is essential for transglutaminase activity but not for GTPase activity

Transglutaminases (EC 2.3.2.13) catalyze an acyl-transfer reaction between peptide-bound glutamine residues and primary amines, including the epsilon-amino group of lysine residues in protein. Purified human erythrocyte transglutaminase was found to have another activity, i.e., GTP hydrolysis. Treatment of the enzyme with iodoacetamide, a cysteine-directed reagent, caused a 94% loss of TGase activity within 8 min, but no significant loss of GTPase activity. Cys-277, a known residue which is selectively modified by iodoacetamide, was replaced with Ser by site-directed mutagenesis to assess the role of the Cys-277 in the transglutaminase/GTPase activities. Wild-type cDNA, coding for human endothelial cell transglutaminase, and its C277S-mutated cDNA were cloned into a plasmid vector that contained a promoter from phage T7, and then expressed in Escherichia coli. The wild-type recombinant enzyme was indistinguishable from human erythrocyte transglutaminase in mobility on a SDS-polyacrylamide gel, immunoreactivity and catalytic activities for transglutaminase and GTPase. However, the recombinant enzyme was not blocked at the N-terminal alanine residue, as is the case in the naturally occurring erythrocyte enzyme. The C277S mutant enzyme showed no transglutaminase activity, but had Km and kcat values for GTPase activity that were comparable to those of wild-type recombinant and natural erythrocyte enzymes. These results demonstrate that Cys-277 is essential for transglutaminase activity, but not for GTPase activity, and that N-terminal blocking of tissue-type transglutaminase is not critical for either transglutaminase or GTPase activities.

Retinoic acid-induced modulation of rat liver transglutaminase and total polyamines in vivo

The effect of a single intraperitoneal injection of retinoic acid on liver transglutaminase (EC 2.3.2.13) activity and total putrescine, spermidine and spermine was studied. The results demonstrate that: (1) transglutaminase activity is increased over control values as early as 4-6 h after treatment, reaching a maximum (2-fold increase) at 12 h and returning to control values at 36 h; (2) the retinoic acid-induced form of enzyme is the soluble tissue transglutaminase; (3) actinomycin D treatment does not completely inhibit the early (6 h) increase of activity, while suppressing that at 12 h; (4) the immunoassay of the soluble transglutaminase shows that, 6 h after treatment, there is no increase in the protein, whereas at 12 and 24 h a significant increase is observed; (5) putrescine, but not spermidine and spermine, increases (5-7-fold) 6 and 18 h after the retinoic acid treatment. The possibility also that the expression of soluble transglutaminase is modulated in vivo by retinoic acid and the relationship to polyamine levels are discussed.

Covalent incorporation of polyamines as gamma-glutamyl derivatives into CHO cell protein

The possible role of polyamines in the covalent modification of proteins in CHO cells was investigated by metabolic labeling with [3H]putrescine. A single radiolabeled protein band with an apparent relative molecular mass of 18,000 Da was observed by SDS-polyacrylamide gel electrophoresis. Almost all the radioactivity covalently linked to this protein was recovered as hypusine. The labeling of this protein was increased several-fold when cells were cultured with alpha-difluoromethylornithine (DFMO) or with this drug plus methylglyoxal bis(guanylhydrazone) (MGBG), as a result of increase in specific radioactivity of the hypusine immediate precursor, spermidine. Also labeled under the latter condition were other cellular proteins. These were aggregates on the top both of the stacking gel and of the running gel, and protein-like materials with relative molecular masses of 36 and 8 kDa. The radioactivity covalently associated with these proteins was recovered after acid hydrolysis as polyamines. The identification of gamma-glutamylputrescine and gamma-glutamylspermidines in proteolytic digests of the acid-insoluble fraction of treated cells indicates that polyamines are covalently linked to these cellular protein. Several possible cellular functions of gamma-glutamylpolyamine protein components are discussed.

Induction of cellular transglutaminase biosynthesis by sodium butyrate

Cellular transglutaminase activity was induced in simian virus-transformed human embryonic lung fibroblasts (WI-38 VA13A) by sodium butyrate. The level of enzyme activity approached a maximum by 6 days; 9-11-fold higher in the presence of sodium butyrate (1 mM) than in its absence. The observed increases in cellular transglutaminase activity could be entirely accounted for by equivalent increases in the levels of enzyme protein measured by inhibition enzyme-linked immunosorbent assay. Sodium butyrate also increased the rate of enzyme synthesis, but had no effect on the rate of cellular transglutaminase degradation. The increase in the rate of enzyme synthesis was matched by an increased level of translatable transglutaminase mRNA as measured in a cell-free translation system. Our results suggest that sodium butyrate regulates cellular transglutaminase at the pretranslational level.

Purification of human erythrocyte transglutaminase by immunoaffinity chromatography

Human erythrocyte transglutaminase was purified using a reusable immunoaffinity column prepared from a monoclonal antibody described previously (Birckbichler et al., Hybridoma, 4, 179-186, 1985). The purified TGase was catalytically active and exhibited a single band of apparent Mr = 85,000 on SDS-PAGE and Western blotting. The amino acid composition of the enzyme was determined. The amino terminus was blocked, and the carboxy-terminal residue appeared to be isoleucine.

Quantitation of tissue transglutaminase by a sandwich ELISA system

A sandwich ELISA system has been developed to quantitate transglutaminase in human cell extracts. It utilizes affinity-purified rabbit anti-human transglutaminase as the capture antibody and a mouse monoclonal anti-transglutaminase (Birckbichler et al., 1985) as the indicator antibody (together with peroxidase-labeled anti-mouse immunoglobulin). The sensitivity of the assay was less than 1.0 ng/mg cellular protein. Significantly higher concentrations of the enzyme were found in resting versus proliferating or transformed fibroblasts in good agreement with previous activity measurements. The levels of transglutaminase in normal T and B lymphocytes, malignant lymphoid cells and monocytes were also determined.

A monoclonal antibody to cellular transglutaminase

A cellular enzyme-linked immunosorbent assay was developed for estimating cellular transglutaminase in situ using a monoclonal antibody produced to tissue transglutaminase. The minimum level of detection of TGase was 2-5 ng. The enzyme was present in greater amounts in WI-38 and IMR90 cells than in their simian virus-transformed counterparts. The levels of TGase in the virus-transformed cells increased significantly when the cells were grown in the presence of sodium butyrate to induce enzyme activity. Staining of confluent WI-38 cells by indirect immunofluorescence using the monoclonal antibody showed microscopic fibers suggesting that the enzyme may be associated with detergent-insoluble components.

Effect of sodium butyrate on induction of ornithine decarboxylase activity in phytohemagglutinin-stimulated lymphocytes

Effect of sodium butyrate on DNA synthesis and the induction of ornithine decarboxylase (EC 4.1.1.17), a rate-limiting enzyme of polyamine biosynthesis, was studied in phytohemagglutinin (PHA)-stimulated bovine lymphocytes. Millimolar concentrations of butyrate completely inhibited the incorporation of [3H]thymidine into the acid-insoluble fraction and reversibly suppressed the induction of ornithine decarboxylase. Other short-chain fatty acids were much less active than butyrate. These results suggest that the suppression of ornithine decarboxylase activity may be one of the reasons for the inhibition of DNA synthesis with butyrate in bovine lymphocytes, because our previous experimental results have shown that the induction of ornithine decarboxylase closely correlates with the DNA synthesis in growth-stimulated cells.