Increase in proliferative markers after inhibition of transglutaminase

Transglutaminase inhibition stimulates hematopoiesis and reduces aggressive behavior of crayfish, Pacifastacus leniusculus

Transglutaminase (TGase) is a Ca²⁺-dependent cross-linking enzyme, which has both enzymatic and nonenzymatic properties. TGase is involved in several cellular activities, including adhesion, migration, survival, apoptosis, and extracellular matrix (ECM) organization. In this study, we focused on the role of the TGase enzyme in controlling hematopoiesis in the crayfish, Pacifastacus leniusculus We hypothesized that a high TGase activity could mediate an interaction of progenitor cells with the ECM to maintain cells in an undifferentiated stage in the hematopoietic tissue (HPT). We found here that the reversible inhibitor cystamine decreases the enzymatic activity of TGase from crayfish HPT, as well as from guinea pig, in a concentration-dependent manner. Cystamine injection decreased TGase activity in HPT without affecting production of reactive oxygen species. Moreover, the decrease in TGase activity in the HPT increased the number of circulating hemocytes. Interestingly the cystamine-mediated TGase inhibition reduced aggressive behavior and movement in crayfish. In conclusion, we show that cystamine-mediated TGase inhibition directly releases HPT progenitor cells from the HPT into the peripheral circulation in the hemolymph and strongly reduces aggressive behavior in crayfish.

Transglutaminase 2-dependent deamidation of glyceraldehyde-3-phosphate dehydrogenase promotes trophoblastic cell fusion

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a multifunctional protein as well as a classic glycolytic enzyme, and its pleiotropic functions are achieved by various post-translational modifications and the resulting translocations to intracellular compartments. In the present study, GAPDH in the plasma membrane of BeWo choriocarcinoma cells displayed a striking acidic shift in two-dimensional electrophoresis after cell-cell fusion induction by forskolin. This post-translational modification was deamidation of multiple glutaminyl residues, as determined by molecular mass measurement and tandem mass spectrometry of acidic GAPDH isoforms. Transglutaminase (TG) inhibitors prevented this acidic shift and reduced cell fusion. Knockdown of the TG2 gene by short hairpin RNA reproduced these effects of TG inhibitors. Various GAPDH mutants with replacement of different numbers (one to seven) of Gln by Glu were expressed in BeWo cells. These deamidated mutants reversed the suppressive effect of wild-type GAPDH overexpression on cell fusion. Interestingly, the mutants accumulated in the plasma membrane, and this accumulation was increased according to the number of Gln/Glu substitutions. Considering that GAPDH binds F-actin via an electrostatic interaction and that the cytoskeleton is rearranged in trophoblastic cell fusion, TG2-dependent GAPDH deamidation was suggested to participate in actin cytoskeletal remodeling.

Transglutaminase 2: biology, relevance to neurodegenerative diseases and therapeutic implications

Neurodegenerative disorders are characterized by progressive neuronal loss and the aggregation of disease-specific pathogenic proteins in hallmark neuropathologic lesions. Many of these proteins, including amyloid Αβ, tau, α-synuclein and huntingtin, are cross-linked by the enzymatic activity of transglutaminase 2 (TG2). Additionally, the expression and activity of TG2 is increased in affected brain regions in these disorders. These observations along with experimental evidence in cellular and mouse models suggest that TG2 can contribute to the abnormal aggregation of disease causing proteins and consequently to neuronal damage. This accumulating evidence has provided the impetus to develop inhibitors of TG2 as possible neuroprotective agents. However, TG2 has other enzymatic activities in addition to its cross-linking function and can modulate multiple cellular processes including apoptosis, autophagy, energy production, synaptic function, signal transduction and transcription regulation. These diverse properties must be taken into consideration in designing TG2 inhibitors. In this review, we discuss the biochemistry of TG2, its various physiologic functions and our current understanding about its role in degenerative diseases of the brain. We also describe the different approaches to designing TG2 inhibitors that could be developed as potential disease-modifying therapies.

Tissue transglutaminase activity is involved in the differentiation of oligodendrocyte precursor cells into myelin-forming oligodendrocytes during CNS remyelination

During normal brain development, axons are myelinated by mature oligodendrocytes (OLGs). Under pathological, demyelinating conditions within the central nervous system (CNS), axonal remyelination is only partially successful because oligodendrocyte precursor cells (OPCs) largely remain in an undifferentiated state resulting in a failure to generate myelinating OLGs. Tissue Transglutaminase (TG2) is a multifunctional enzyme, which amongst other functions, is involved in cell differentiation. Therefore, we hypothesized that TG2 contributes to differentiation of OPCs into OLGs and thereby stimulates remyelination. In vivo studies, using the cuprizone model for de- and remyelination in TG2(-/-) and wild-type mice, showed that during remyelination expression of proteolipid protein mRNA, as a marker for remyelination, in the corpus callosum lags behind in TG2(-/-) mice resulting in less myelin formation and, moreover, impaired recovery of motor behavior. Subsequent in vitro studies showed that rat OPCs express TG2 protein and activity which reduces when the cells have matured into OLGs. Furthermore, when TG2 activity is pharmacologically inhibited, the differentiation of OPCs into myelin-forming OLGs is dramatically reduced. We conclude that TG2 plays a prominent role in remyelination of the CNS, probably through stimulating OPC differentiation into myelin-forming OLGs. Therefore, manipulating TG2 activity may represent an interesting new target for remyelination in demyelinating diseases.

Effect of retinoic acid on transglutaminase and ornithine decarboxylase activities during liver regeneration

Liver regeneration is regulated by several factors, including growth factors, cytokines, and post-translational modifications of several proteins. It is suggested that transglutaminase 2 (TG2) and ornithine decarboxylase (ODC) are involved in liver regeneration. To investigate the role of TG2 and ODC activities in regenerating liver, we used retinoic acid (RA), an inducer of TG2 and a suppressor of ODC. Regenerating rat liver was prepared by 70% partial hepatectomy (PH). Rats were sacrificed at 1, 2, 3, 4, and 6 days after surgery. RA was intraperitoneally injected immediately after PH. TG2 and ODC activities and products (epsilon-(gamma-glutamyl) lysine isopeptide (Gln-Lys) and polyamines, respectively) were examined at the indicated times. In RA-treated rat, DNA synthesis and ODC activity declined and the peak shifted to 2 days after PH, whereas TG2 activity increased at 1 day after PH. At that time, protein-polyamine, especially the protein-spermidine (SPD) bond, transiently decreased, whereas the formation of the Gln-Lys bond increased after PH. These results suggested that in regenerating liver, enhanced the formation of Gln-Lys bonds catalyzed by TG2 led to reduced DNA synthesis, whereas when ODC produced newly synthesized SPD, the inhibition of Gln-Lys bond production by the preferential formation of protein-SPD bonds led to an increase in DNA synthesis.

Transglutaminase 2 protects against ischemic insult, interacts with HIF1beta, and attenuates HIF1 signaling

Transglutaminase 2 (TG2) is a multifunctional enzyme that has been implicated in the pathogenesis of neurodegenerative diseases, ischemia, and stroke. The mechanism by which TG2 modulates disease progression have not been elucidated. In this study we investigate the role of TG2 in the cellular response to ischemia and hypoxia. TG2 is up-regulated in neurons exposed to oxygen and glucose deprivation (OGD), and increased TG2 expression protects neurons against OGD-induced cell death independent of its transamidating activity. We identified hypoxia inducible factor 1beta (HIF1beta) as a TG2 binding partner. HIF1beta and HIF1alpha together form the heterodimeric transcription factor hypoxia inducible factor 1 (HIF1). TG2 and the transaminase-inactive mutant C277S-TG2 inhibited a HIF-dependent transcription reporter assay under hypoxic conditions without affecting nuclear protein levels for HIF1alpha or HIF1beta, their ability to form the HIF1 heterodimeric transcription factor, or HIF1 binding to its DNA response element. Interestingly, TG2 attenuates the up-regulation of the HIF-dependent proapoptotic gene Bnip3 in response to OGD but had no effect on the expression of VEGF, which has been linked to prosurvival processes. This study demonstrates for the first time that TG2 protects against OGD, interacts with HIF1beta, and attenuates the HIF1 hypoxic response pathway. These results indicate that TG2 may play an important role in protecting against the delayed neuronal cell death in ischemia and stroke.

Proteomic analysis of high-molecular-weight protein polymers in a doxorubicin-resistant breast-cancer cell line

We recently reported that increased transglutaminase 2 (TGase 2) expression correlates with increased resistance to the cancer drug doxorubicin in breast-cancer cell lines. Interestingly, high-molecular-weight (HMW) proteins also increased with increased TGase 2 expression in the drug-resistant cell lines. TGase 2 is likely to be responsible for the formation of HMW proteins, because TGase 2 catalyzes cross-linking between proteins. Although the role of the HMW proteins is unclear, we demonstrated that TGase 2 inhibition increases drug sensitivity in breast-cancer cells. Herein we find that TGase 2 inhibition by cystamine dramatically reduces the level of HMW proteins. Identification of the HMW proteins may suggest the mechanism of cancer drug resistance associated with aberrant TGase 2 function. To explore the identities of HMW proteins, we performed in-gel tryptic digestions of unresolved HMW proteins and analyzed the resulting peptides using LC-MALDI-MS/MS. Most of the identified proteins were associated with gene regulation, such as polyadenylate-binding proteins, translation initiation factors, and ribonucleoproteins. This finding suggests that TGase 2 may participate in gene regulation, in addition to its role in cell adhesion.

The role of hypoxia inducible factor-1 in cell metabolism--a possible target in cancer therapy

In many cancer types, intratumoural hypoxia is linked to increased expression and activity of the transcription factor hypoxia-inducible factor (HIF-1alpha), which is associated with poor patient prognosis. This increased the interest in HIF-1alpha as a cancer drug target. Further, HIF-1alpha has also a central role in the adaptive cellular programme responding to hypoxia in normal tissues. Many of the HIF-1alpha-regulated genes encode enzymes of metabolic pathways. Therefore, studying the link and the feedback mechanisms between metabolism and HIF-1alpha is of major importance to find new and specific therapeutic strategies.

The protective effects of cystamine in the R6/2 Huntington's disease mouse involve mechanisms other than the inhibition of tissue transglutaminase

Tissue transglutaminase (tTG) is a multifunctional enzyme that contributes to disease progression in mouse models of Huntington's disease (HD), an inherited neurodegenerative disease that shows an age-related onset. Moreover, administration of the transglutaminase inhibitor cystamine delays the onset of pathology in the R6/2 HD mouse model. However, the contribution of tTG inhibition towards the therapeutic effects of cystamine has not been determined, as this compound likely has multiple mechanisms of action in the R6/2 mouse. In this study, we found that administration of cystamine in drinking water delayed the age of onset for motor dysfunction and extended lifespan to a similar extent in R6/2 mice that had a normal genetic complement of tTG compared with R6/2 mice that did not express tTG. Since the magnitude of cystamine's therapeutic effects was not affected by the genetic deletion of tTG, these results suggest that the mechanism of action for cystamine in this HD mouse model involves targets other than tTG inhibition.

Developmental regulation of tissue transglutaminase in the mouse forebrain

Tissue transglutaminase (tTG) is a multifunctional enzyme that catalyzes both transamidation and GTPase reactions. In cell culture models tTG-mediated transamidation positively regulates many processes that occur in vivo during the mammalian brain growth spurt (BGS), including neuronal differentiation, neurite outgrowth, synaptogenesis and cell death mechanisms. However, little is known about the levels of tTG expression and transglutaminase (TG) activity during mammalian brain development. In this study, C57BL/6 mouse forebrains were collected at embryonic day (E) 12, E14, E17, postnatal day (P) 0, P7 and P56 and analyzed for tTG expression and TG activity. RT-PCR analysis demonstrated that tTG mRNA content increases during mouse forebrain development, whereas immunoblot analysis demonstrated that tTG protein content decreases during this time. TG activity was low in prenatal mouse forebrain but increased fivefold to peak at P0, which corresponds with the beginning of the mouse BGS. Further analysis demonstrated that the lack of temporal correlation between tTG protein content and TG activity is the result of an endogenous inhibitor of tTG that is present in prenatal but not postnatal mouse forebrain. These results demonstrate for the first time that tTG enzymatic activity in the mammalian forebrain is developmentally regulated by post-translational mechanisms.

Metal-catalyzed oxidation of alpha-synuclein: helping to define the relationship between oligomers, protofibrils, and filaments

Oxidative stress is implicated in a number of neuro-degenerative diseases and is associated with the selective loss of dopaminergic neurons of the substantia nigra in Parkinson's disease. The role of alpha-synuclein as a potential target of intracellular oxidants has been demonstrated by the identification of posttranslational modifications of synuclein within intracellular aggregates that accumulate in Parkinson's disease brains, as well as the ability of a number of oxidative insults to induce synuclein oligomerization. The relationship between these relatively small soluble oligomers, potentially neurotoxic synuclein protofibrils, and synuclein filaments remains unclear. We have found that metal-catalyzed oxidation of alpha-synuclein inhibited formation of synuclein filaments with a concomitant accumulation of beta sheet-rich oligomers that may represent synuclein protofibrils. Similar results with a number of oxidative and enzymatic treatments suggest that the covalent association of synuclein into higher molecular mass oligomers/protofibrils represents an alternate pathway from filament formation and renders synuclein less prone to proteasomal degradation.

In vitro modification of betaine-homocysteine S-methyltransferase by tissue-type transglutaminase

Transglutaminases catalyze the cross-linking and amine incorporation of proteins, and are implicated in various biological phenomena. To elucidate the physiological roles of transglutaminase at the molecular level, we need to identify its physiological protein substrates and clarify the relationship between transglutaminase modification of protein substrates and biological responses. Here we examined whether betaine-homocysteine S-methyltransferase (BHMT: EC 2.1.1.5) can be a substrate of tissue-type transglutaminase by in vitro experiments using porcine liver BHMT and guinea pig liver transglutarninase. Guinea pig liver transglutaminase incorporated 5-(biotinamido) pentylamine and [3H] histamine into BHMT in a time-dependent manner. Putrescine and spermidine also seemed to be incorporated into BHMT by transglutaminase. In the absence of the primary amines, BHMT subunits were cross-linked intra- and intermolecularly. BHMT activity was decreased significantly through the cross-linking by transglutaminase. Histamine incorporation slightly reduced the BHMT activity. Peptide fragments of BHMT containing the glutamine residues reactive for transglutaminase reaction were isolated through biotin labelling, proteinase digestion, biotin-avidin a affinity separation, and reverse phase HPLC. The results of amino acid sequence analyses of these peptides and sequence homology alignment with other mammalian liver BHMT subunits showed that these reactive glutamine residues were located in the region near the carboxyl terminal of porcine BHMT subunit. These results suggested that the liver BHMT can be modified by tissue-type transglutaminase and its activity is regulated repressively by the modification, especially by the cross-linking. This regulatory reaction might be involved in the regulation of homocysteine metabolism in the liver.

Validity of mouse models for the study of tissue transglutaminase in neurodegenerative diseases

Tissue transglutaminase (tTG) is a multifunctional enzyme that catalyzes peptide cross-linking and polyamination reactions, and also is a signal-transducing GTPase. tTG protein content and enzymatic activity are upregulated in the brain in Huntington's disease and in other neurological diseases and conditions. Since mouse models are currently being used to study the role of tTG in Huntington's disease and other neurodegenerative diseases, it is critical that the level of its expression in the mouse forebrain be determined. In contrast to human forebrain where tTG is abundant, tTG can only be detected in mouse forebrain by immunoblotting a GTP-binding-enriched protein fraction. tTG mRNA content and transamidating activity are approximately 70% lower in mouse than in human forebrain. However, tTG contributes to the majority of transglutaminase activity within mouse forebrain. Thus, although tTG is expressed at lower levels in mouse compared with human forebrain, it likely plays important roles in neuronal function.

Tissue transglutaminase-induced aggregation of alpha-synuclein: Implications for Lewy body formation in Parkinson's disease and dementia with Lewy bodies

Proteinaceous aggregates containing alpha-synuclein represent a feature of neurodegenerative disorders such as Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. Despite extensive research, the mechanisms underlying alpha-synuclein aggregation remain elusive. Previously, tissue transglutaminase (tTGase) was found to contribute to the generation of aggregates by cross-linking pathogenic substrate proteins in Huntington's and Alzheimer's diseases. In this article, the role of tTGase in the formation of alpha-synuclein aggregates was investigated. Purified tTGase catalyzed alpha-synuclein cross-linking, leading to the formation of high molecular weight aggregates in vitro, and overexpression of tTGase resulted in the formation of detergent-insoluble alpha-synuclein aggregates in cellular models. Immunocytochemical studies demonstrated the presence of alpha-synuclein-positive cytoplasmic inclusions in 8% of tTGase-expressing cells. The formation of these aggregates was significantly augmented by the calcium ionophore and prevented by the inhibitor cystamine. Immunohistochemical studies on postmortem brain tissue confirmed the presence of transglutaminase-catalyzed epsilon (gamma-glutamyl)lysine cross-links in the halo of Lewy bodies in Parkinson's disease and dementia with Lewy bodies, colocalizing with alpha-synuclein. These findings, taken together, suggest that tTGase activity leads to alpha-synuclein aggregation to form Lewy bodies and perhaps contributes to neurodegeneration.

Transglutaminases: nature's biological glues

Transglutaminases (Tgases) are a widely distributed group of enzymes that catalyse the post-translational modification of proteins by the formation of isopeptide bonds. This occurs either through protein cross-linking via epsilon-(gamma-glutamyl)lysine bonds or through incorporation of primary amines at selected peptide-bound glutamine residues. The cross-linked products, often of high molecular mass, are highly resistant to mechanical challenge and proteolytic degradation, and their accumulation is found in a number of tissues and processes where such properties are important, including skin, hair, blood clotting and wound healing. However, deregulation of enzyme activity generally associated with major disruptions in cellular homoeostatic mechanisms has resulted in these enzymes contributing to a number of human diseases, including chronic neurodegeneration, neoplastic diseases, autoimmune diseases, diseases involving progressive tissue fibrosis and diseases related to the epidermis of the skin. In the present review we detail the structural and regulatory features important in mammalian Tgases, with particular focus on the ubiquitous type 2 tissue enzyme. Physiological roles and substrates are discussed with a view to increasing and understanding the pathogenesis of the diseases associated with transglutaminases. Moreover the ability of these enzymes to modify proteins and act as biological glues has not gone unnoticed by the commercial sector. As a consequence, we have included some of the present and future biotechnological applications of this increasingly important group of enzymes.

Apoptosis induction by S-allylcysteine, a garlic constituent, during 7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch carcinogenesis

The apoptosis-inducing capacity of S-allylcysteine (SAC), a water-soluble garlic constituent, during 7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch (HBP) carcinogenesis was investigated in male Syrian hamsters using DNA fragmentation and the apoptosis-associated proteins, tissue transglutaminase (tTG) and Bcl-2. Hamsters were divided into four groups of six animals each. Animals in group 1 were painted with a 0.5% solution of DMBA in liquid paraffin on the right buccal pouches three times a week for 14 weeks. Group 2 animals painted with DMBA as in group 1, in addition received 200 mg kg(-1) body weight SAC orally on days alternate to DMBA application. Group 3 animals received SAC as in group 2. Group 4 animals received neither DMBA nor SAC and served as the control. The experiment was terminated at the end of 14 weeks. Administration of SAC (200 mg kg(-1) body weight) to animals painted with DMBA inhibited DMBA-induced HBP carcinogenesis as revealed by the absence of neoplasms, induction of tTG and inhibition of Bcl-2 expression. The results of the present study suggest that SAC may exert its chemopreventive effect by inducing apoptosis.

Garlic induces apoptosis during 7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch carcinogenesis

The apoptosis-inducing capacity of aqueous garlic extract during 7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch (HBP) carcinogenesis was investigated in male Syrian hamsters using DNA fragmentation and the apoptosis-associated proteins, tissue transglutaminase (tTG) and Bcl-2. Hamsters were divided into four groups of six animals each. Animals in group 1 were painted with a 0.5% solution of DMBA in liquid paraffin on the right buccal pouches three times a week for 14 weeks. Group 2 animals painted with DMBA as in group 1, in addition received 250 mg/kg body weight aqueous garlic extract orally on days alternate to DMBA application. Group 3 animals received garlic extract as in group 2. Group 4 animals received neither DMBA nor garlic extract and served as the control. The experiment was terminated at the end of 14 weeks. Administration of aqueous garlic extract (250 mg/kg body weight) to animals painted with DMBA inhibited DMBA-induced oral carcinogenesis as revealed by the absence of neoplasms, induction of tTG and inhibition of Bcl-2 expression. The results of the present study suggest that garlic may exert its chemopreventive effect by inducing apoptosis.

Tissue transglutaminase differentially modulates apoptosis in a stimuli-dependent manner

Tissue transglutaminase is a unique member of the transglutaminase family as it not only catalyzes a transamidating reaction, but also binds and hydrolyzes GTP and ATP. Tissue transglutaminase has been reported to be pro-apoptotic, however, conclusive evidence is still lacking. To elucidate the role of tissue transglutaminase in the apoptotic process human neuroblastoma SH-SY5Y cells were stably transfected with vector only (SH/pcDNA), wild-type tissue transglutaminase (SH/tTG) and tissue transglutaminase that has no transamidating activity but retains its other functions (SH/C277S). In these studies three different apoptotic stimuli were used osmotic stress, staurosporine treatment and heat shock to delineate the role of tissue transglutaminase as a transamidating enzyme in the apoptotic process. In SH/tTG cells, osmotic stress and staurosporine treatments resulted in significantly greater caspase-3 activation and apoptotic nuclear changes then in SH/pcDNA or SH/C277S cells. This potentiation of apoptosis in SH/tTG cells was concomitant with a significant increase in the in situ transamidating activity of tissue transglutaminase. However, in the heat shock paradigm, which did not result in any increase in the transamidating activity in SH/tTG cells, there was a significant attenuation of caspase-3 activity, LDH release and apoptotic chromatin condensation in SH/tTG and SH/C277S cells compared with SH/pcDNA cells. These findings indicate for the first time that the effect of tissue transglutaminase on the apoptotic process is highly dependent on the type of the stimuli and how the transamidating activity of the enzyme is affected. Tissue transglutaminase facilitates apoptosis in response to stressors that result in an increase in the transamidating activity of the enzyme. However, when the stressors do not result in an increase in the transamidating activity of tissue transglutaminase, than tissue transglutaminase can ameliorate the apoptotic response through a mechanism that is independent of its transamidating function. Further, neither the phosphatidylinositol-3-kinase pathway nor the extracellular-regulated kinase pathway is downstream of the modulatory effects of wild-type tissue transglutaminase or C277S-tissue transglutaminase in the apoptotic cascade.

Co-overexpression of folding modulators improves the solubility of the recombinant guinea pig liver transglutaminase expressed in Escherichia coli

Transglutaminases (EC 2.3.2.13) catalyze the formation of epsilon-(gamma-glutamyl)lysine cross-links and the substitution of primary amines for the gamma-carboxamide groups of protein bound glutamine residues, and are involved in many biological phenomena. Transglutaminase reactions are also applicable in applied enzymology. Here, we established an expression system of recombinant mammalian tissue-type transglutaminase with high productivity. Overexpression of guinea pig liver transglutaminase in Escherichia coli, using a plasmid pET21-d, mostly resulted in the accumulation of insoluble and inactive enzyme protein. By the expression culture at lower temperatures (25 and 18 degrees C), however, a fraction of the soluble and active enzyme protein slightly increased. Co-overexpression of a molecular chaperone system (DnaK-DnaJ-GrpE) and/or a folding catalyst (trigger factor) improved the solubility of the recombinant enzyme produced in E. coli cells. The specific activity, the affinity to the amine substrate, and the sensitivity to the calcium activation and GTP inhibition of the purified soluble recombinant enzyme were lower than those of the natural liver enzyme. These results indicated that co-overexpression of folding modulators tested improved the solubility of the overproduced recombinant mammalian tissue-type transglutaminase, but the catalytic properties of the soluble recombinant enzyme were not exactly the same as those of the natural enzyme.

The metastasis gene osteopontin: a candidate target for cancer therapy

Malignant tumors are characterized by dysregulated growth control, overcoming of replicative senescence, and metastasis formation. Current therapeutic regimens mostly exert their effects through inhibition of cell cycle progression, leaving two major components of transformation untouched. The cytokine osteopontin is essential for the dissemination of various cancers. Past research has implied several modes in which osteopontin and its main receptors on tumor cells can be suppressed. Osteopontin expression is inhibitable on the levels of gene transcription and the RNA message, and the osteopontin protein can be blocked with antibodies or synthetic peptides. The osteopontin receptor CD44 has been targeted by diverse therapeutic strategies, including cytotoxic and immunotherapeutic approaches. The receptor integrin alpha(V)beta(3) contributes not only to tumor cell dissemination, but also to angiogenesis and osteolysis in bone metastases. Small molecule inhibitors of this receptor are under study as drug candidates. Because receptors and cytokine ligands that mediate metastasis formation are sparsely expressed in the adult healthy organism and are more readily reached by pharmaceuticals than intracellular drug targets they may represent a particularly suitable focus for therapeutic intervention.

Putative nucleotide binding sites of guinea pig liver transglutaminase

Three peptides corresponding to glycine-rich internal sequences of the guinea pig liver transglutaminase molecule were synthesized. These were peptide 1 (amino acid residues 520-544), peptide 2 (amino acid residues 345-367) and peptide 3 (amino acid residues 45-69). All of the synthetic peptides demonstrated significant binding ability for both ATP and GTP. Peptide 1 was the best protector of transglutaminase activity from both ATP and GTP inhibition, while peptides 2 and 3 protected the activity only from GTP inhibition. The data shown here lead us to propose putative binding site(s) for ATP and GTP guinea pig liver transglutaminase.

Tissue transglutaminase is essential for neurite outgrowth in human neuroblastoma SH-SY5Y cells

Tissue transglutaminase is a normal constituent of the central and peripheral nervous systems and in rats transglutaminase activity in brain and spinal cord is highest during fetal stages when axonal outgrowth is occurring. Further, treatment of human neuroblastoma SH-SY5Y cells with retinoic acid results in the cells withdrawing from the cell cycle and extending neurites, in the same time frame that tissue transglutaminase expression significantly increases. Considering these and other previous findings, this study was carried out to determine whether tissue transglutaminase is involved in neuronal differentiation of SH-SY5Y cells. For these studies SH-SY5Y cells stably overexpressing wild-type tissue transglutaminase, an inactive tissue transglutaminase mutant (C277S) or an antisense tissue transglutaminase construct (which decreased endogenous tissue transglutaminase below detectable levels) were used. SH-SY5Y cells overexpressing wild-type tissue transglutaminase spontaneously differentiated into a neuronal phenotype when grown in low-serum media. In contrast, cells overexpressing inactive tissue transglutaminase or the antisense tissue transglutaminase continued to proliferate and exhibit a flat polygenic morphology even when maintained in low-serum conditions. In addition, increased tissue transglutaminase expression in response to retinoic acid was abolished in the antisense tissue transglutaminase cells, and antisense and mutant tissue transglutaminase expressing cells did not extend neurites in response to retinoic acid. Moreover, wild-type and inactive tissue transglutaminase exhibited differential intracellular localization. These data indicate that tissue transglutaminase is necessary and sufficient for neuronal differentiation of human neuroblastoma SH-SY5Y cells.

A simple assay and histochemical localization of transglutaminase activity using a derivative of green fluorescent protein as substrate

Histidine-tagged green fluorescent protein (His(6)-Xpress-GFP), a widely used fluorescent probe, was found to be a good substrate for transglutaminase, an enzyme that catalyzes covalent crosslinking of proteins. GFP alone did not serve as a substrate but its derivative His(6)-Xpress-GFP was readily crosslinked through the Gln and Lys residues present in the short N-terminal extension (His(6)-Xpress). His(6)-Xpress-GFP was sensitive enough to detect the transglutaminase activity in guinea pig liver homogenates. The fluorescent substrate could also be used for activity staining of transglutaminase on histological tissue sections, and such applications revealed a surprisingly wide distribution of transglutaminase in the body, especially in the extracellular matrices of various tissues, suggesting an important role for transglutaminase in maintaining the integrity of the extracellular matrix and connective tissues by crosslinking its constituent proteins.(J Histochem Cytochem 49:247-258, 2001)

Loss of tissue transglutaminase as a biomarker for prostate adenocarcinoma

BACKGROUND

Additional molecular tissue biomarkers for prostate carcinoma are needed to stratify patients with clinically suspicious findings, such as an elevated prostate specific antigen (PSA) with a negative biopsy, according to risk.

METHODS

Prostate tissues from 43 cancer cases and 47 controls with no evidence of cancer were labeled for transglutaminase by immunohistochemistry. Immunoreactivity was quantified using the Autocyte Pathology Workstation. In addition, quantitative fluorescence image analysis was used to compare transglutaminase concentrations in cells obtained by fine-needle aspiration from excised prostates. Loss of gene expression was evaluated by reverse transcriptase-polymerase chain reaction and growth with 5-azacytidine.

RESULTS

Visually, benign glands from controls generally expressed tissue transglutaminase, whereas regions with adenocarcinoma generally were negative. With quantitative immunohistochemistry, 41 of 43 adenocarcinoma of the prostate (CaP) cases expressed lower mean percentage areas positive for transglutaminase than did 30 of 30 benign prostatic hyperplasia (BPH) and 17 of 17 prostatitis cases (P < 0.0001; odds ratio [OR], 1577; 95% confidence interval (CI), 74-33, 820; relative risk [RR], 25; 95% CI, 6-95). Quantitative immunofluorescence of 3277 cells collected by FNA from 19 CaP cases and 645 cells from 5 cases of BPH showed that the mean content of transglutaminase was 93 femtograms (fg) for the CaP-derived cells and 138 fg for the BPH cells (P < 0.0001). Receiver operating curve analysis of the immunohistochemistry data showed an optimized threshold produced 95% sensitivity with 100% specificity. Growth of LNCaP cells with 5-azacytidine failed to stimulate transglutaminase expression, suggesting that loss of expression was likely not attributable to promoter methylation.

CONCLUSIONS

Measurements of transglutaminase on tissue sections provides additional diagnostic information that is potentially useful for risk assessment of patients with suspicious clinical findings, such as nodules or positive PSA and negative biopsies, without overdetecting disease.

Inhibition of melanin synthesis by cystamine in human melanoma cells

In studies to determine whether pigmentation can be regulated physiologically by thiols, human melanoma cells (MM418c5) and melanocytes were found to become depigmented when cultured continuously in 50 microM cystamine. Cystamine was depleted from the culture medium and the treatment was nontoxic and reversible. Cysteamine, dithiothreitol, and phenylthiourea were less effective, and glutathione, cysteine, and cystine were inactive. Tyrosinase (dopa oxidase) activity was not greatly affected except for induction of a lag period. In contrast, tyrosinase activity in an amelanotic melanoma cell line (MM96L) was rapidly inhibited without consumption of cystamine/cysteamine, in association with the generation of free thiol in the culture medium, and could be enhanced by the cystine transport inhibitor, glutamate. Tyrosinase expressed by a recombinant vaccinia virus was inhibited by cystamine treatment of MM96L and HeLa cells. Cystamine treatment lowered the degree of cross-linking of the pigmentation antigen gp75/TRP-1 in MM418c5 cells. Tyrosinase protein and mRNA levels in MM418c5 cells were not affected by cystamine. The results show that cystamine at a concentration close to physiologic levels has multiple effects on the melanogenic pathway. In amelanotic cells, tyrosinase has a short half-life and is readily inhibited by cystamine/cysteamine whereas tyrosinase in the more mature melanosomes of the pigmented cell appears to be less accessible to proteolytic and thiol attack. Inhibition of melanin synthesis in the latter cell type may arise to a significant degree from reduction of cystamine to cysteamine, which sequesters quinones.

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.

Interaction of tissue transglutaminase with nuclear transport protein importin-alpha3

Tissue transglutaminase is a multifunctional enzyme which has been involved in the regulation of cell growth, differentiation, and apoptosis. Recently, nuclear localization of tTG has been reported indicating the potential of active nuclear transport. In this study we use the yeast two-hybrid assay and co-immunoprecipitation to show that tTG interacts with the nuclear transport protein importin-alpha3. Using electron microscopy we demonstrate that nuclear expression of tTG in a non-small cell lung cancer cell line is induced by retinoic acid (RA). These data suggest that importin-alpha3 could mediate active nuclear transport of tTG which may be important for the regulation of critical cellular processes.

Carcinoma cell lines resistant for growth inhibition and apoptosis to retinoic acid are responsive to 4-hydroxy-phenyl-retinamide: correlation with tissue transglutaminase

Retinoic acid (RA)-resistant cell lines are highly malignant. To inhibit the growth of the RA-resistant cells we used 4-HPR, a synthetic retinoid, which may act through alternative signal transduction pathways. 4-HPR induced cell growth inhibition and apoptosis in all RA-sensitive as well as -resistant cells, demonstrating a wider spectrum of potency over RA. 4-HPR induced tissue TGase activity. A tight correlation between the induction of tissue TGase, the inhibition of cell growth, and apoptosis was evident in all eight RA-sensitive cell lines. However, basal TGase differed in the different cells, suggesting inducibility rather than basal levels as the relevant parameter. In sharp contrast to the RA-sensitive cells, RA-resistant cells showed sporadic response to 4-HPR for tissue TGase. The wider spectrum of activity of 4-HPR in inhibiting cell growth and inducing apoptosis makes it a good candidate for the treatment of RA-resistant cancer cells.

Identification of amine acceptor protein substrates of transglutaminase in liver extracts: use of 5-(biotinamido) pentylamine as a probe

Transglutaminase is a calcium-dependent enzyme which catalyzes amine incorporation and cross-linking of proteins. To isolate the amine acceptor protein substrates of transglutaminase in mammalian livers, a biotin-labeled primary amine substrate of transglutaminase, 5-(biotinamido) pentylamine, was used for biotin labeling of proteins in the liver extracts by endogenous transglutaminase activity. The biotin-labeled proteins were isolated and recovered by biotin-avidin-affinity chromatography. The obtained proteins were separated by SDS-PAGE. Proteins with molecular masses of 15, 24, 35, 40, 44, 93, and 134 kDa were the main components of labeled proteins in mouse liver extract. In rat and guinea pig liver extracts, 32-, 38-, 40-, 44-, and 134-kDa proteins and28-, 40-, 44-, 55-, 60-, 91-, and 134-kDa proteins were the main components of labeled proteins, respectively.Using amino-terminal amino acid sequence analyses and sequence homology searches, the 38-kDa protein from rat liver was identified as a subunit of glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12), and the 28-kDa protein from guinea pig liver was identified as a subunit of glutathione S-transferase (class theta) (EC 2.5.1.18). Both the glyceraldehyde-3-phosphate dehydrogenase from rabbit muscle and glutathione S-transferase (class pi) from human placenta also could be amine acceptors in the amine incorporation catalyzed by guinea pig liver transglutaminase. These results suggest that these enzymes can be modified posttranslationally by cellular transglutaminase.

Identification of glycinin in vivo as a polyamine-conjugated protein via a gamma-glutamyl linkage

To identify a polyamine-conjugated protein by the action of transglutaminase in the absence of radiolabelled polyamine, extracts prepared from the leaves and developing soybean seeds were investigated for the specific activity of transglutaminase and the content of free polyamines. We identified the major storage protein, glycinin, as a polyamine-conjugated protein. This was established by the following procedures: (1) immunolocalization with antibody against putrescine prepared in rabbit against putrescine-BSA conjugate; (2) immunocross-reactivity on nitrocellulose transblot of the purified glycinin subunits by using antibody against putrescine; (3) identification of polyamines in acid hydrolysates of purified glycinin; (4) release of polyamines in proteolytic digests through the catalytic action of gamma-glutamylamine cyclotransferase, an enzyme specific for the disassembly of gamma-glutamylamines. The activity of gamma-glutamylamine cyclotransferase was also identified in soybean seeds.

Biologically active heteroarotinoids exhibiting anticancer activity and decreased toxicity

A series of retinoids, containing heteroatoms in a cyclic ring and called heteroarotinoids, were synthesized, and their biological activity was evaluated using tissue culture lines that have measurable responses to trans-retinoic acid (t-RA). Transglutaminase (TGase) was assessed in the human erythroleukemia cell line (GMO6141A) as an indicator of differentiation and apoptosis. Proliferation was evaluated in a human cervical cell line, CC-1, which exhibits dose-dependent alterations in growth rate in response to treatment with trans-retinoic acid. Activation of nuclear retinoic acid receptors was determined in a reporter cell line established from CC-1. The reporter line, called CC-B, contains a reporter gene controlled by a retinoic acid responsive element (RARE) and a thymidine kinase (tk) promoter. Treatment of the CC-B line with the heteroarotinoids resulted in a dose-responsive and retinoid-dependent regulation of reporter gene expression. The heteroarotinoids exhibited activity in all assays and correlated in a statistically significant manner between assays. RARE transactivation activity in CC-B cells correlated with induction of TGase in GMO6141A (R = 0.96) and with a decrease in the growth rate of CC-1 cells (R = -0.90). The ability of the selected heteroarotinoids to induce differentiation, inhibit proliferation, and activate nuclear receptors demonstrates the chemotherapeutic potential of these agents. In view of the biological activity cited, an in vivo toxicity study was conducted on male B6D2F1 mice with three heteroarotinoids, namely 8 [(2E,4E,6E)-3,7-dimethyl-7-(1,2,3,4-tetrahydro-4,4-dimeth ylthiochroman-6-yl)-2,4,6-heptatrienoic acid], 10 [(2E,4E,6E)-3,7-dimethyl-7-(1,2,3,4-tetrahydro-4,4-dimeth ylchroman-6-yl)-2, 4,6-heptatrienoic acid], and 13 [(E)-p-[2-(4,4-dimethylchroman-6-yl)propenyl]benzoic acid]. The mice were used with gavage of heteroarotinoids in corn oil [0.1, 0.2, 0.4, or 0.8 mg/kg] and with 0.01 or 0.05 mg/kg of TTNPB (5) [(E)-4-[2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)-1- propenyl]benzoic acid] as reference controls. The target organs affected in the mice by the three heteroarotinoids were those typically associated with t-RA (1) toxicity. The maximum tolerated dose (MTD) of 13 was 9.4 mg/kg/day, which was equal in toxicity to that of t-RA (1) and 1000-fold less toxic than TTNPB (5). The MTDs of 8 and 10 were 34 and 32 mg/kg/day, respectively, which is 3-fold less toxic than t-RA (1) and 3000-fold less toxic than TTNPB (5). The 3000-fold reduced toxicity, compared with only a 27% reduction biological activity of 8 and 10 with respect to that of TTNPB, observed in our assays indicates a good therapeutic ratio of these heteroarotinoids over the parent compound. The biological activity and reduced toxicity of these heteroartinoids demonstrate the potential efficacy as anticancer agents.

Novel transglutaminase inhibitors reduce the cornified cell envelope formation

Transglutaminase (TGase) is a calcium-dependent enzyme which catalyzes the iso-peptide cross-link between peptide-bound glutamine and lysine in vivo. Though the cross-link is developed as a barrier function in the skin system, overexpression of this could invoke skin hyperkeratosis in psoriasis and roughness in aged skin. In former research, many strong irreversible TGase inhibitors failed application because of high cytotoxicity. We selected one peptide after primary screening of six synthetic peptides designed from domains of known TGase substrates. Then we attempted to reduce the size and finally obtained two tetrameric peptides. When we treated keratinocyte with these TGase inhibitors under calcium-induced differentiation, the formation of a cornified cell envelope (CE) was decreased to the same level of CE under proliferating conditions without cytotoxic effect. Therefore, we propose that these TGase inhibitors may be useful for solving the physiological hypercross-linking problems for pharmaceutical or cosmetic purposes.

TPA induces transglutaminase C and inhibits cell growth in the colon carcinoma cell line SW620

In contrast to most other systems, TPA induced TGc activity and protein in SW620 human colon carcinoma cells. This induction was accompanied by cell growth inhibition and increased apoptosis. The general protein kinase-C inhibitor GF-109203X blocked the induction of TGc by TPA, whereas the specific inhibitor of the PKC alpha isoform, the indocarbazole Go6976, reduced it by 40%. These PKC inhibitors had similar inhibitory effects on TPA increased apoptosis and inhibition of cell growth, suggesting that the observed actions of TPA are mediated by PKC, and a close connection between TGc activity, increased apoptosis and cell growth inhibition. We conclude that TPA may offer new approaches in the management of colon cancer cell growth.

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.

Alpha 1-adrenergic receptor coupling with Gh in the failing human heart

BACKGROUND

We recently demonstrated that Gh, which transfers the signal from the alpha 1-adrenergic receptor to the 69-kD phospholipase C, is the previously identified tissue-type transglutaminase (TGase II). The alpha 1-adrenergic receptor mediates actions of the sympathetic nervous system, including cardiac, arteriolar, and smooth muscle contractions. In human cardiac tissue, the expression of the alpha 1-adrenergic receptor is increased under pathophysiological conditions, but changes in the physiological response are small. Therefore, it has been suggested that the other components involved in the alpha 1-adrenergic receptor-mediated signaling pathway are probably altered.

METHODS AND RESULTS

Immunological and biochemical studies with nonfailling and failing human heart tissues revealed that the GTP-binding and TGase activities of human heart TGase II (hhG alpha n) are downregulated in both ischemic and dilated cardiomyopathic human heart. In ischemic cardiomyopathy, the alpha 1-adrenergic receptor number increased twofold (27.0 fmol/mg) compared with the nonfailing (12.8 fmol/mg) and the dilated cardiomyopathic (15.6 fmol/mg) heart tissues, but the coupling of hhG alpha h with the alpha 1-adrenergic receptor did not increase. The intrinsic activity of hhG alpha h, was greatly decreased in membrane fractions, whereas the cytosolic TGase activity was not changed. In the dilated cardiomyopathic human heart, these intrinsic enzyme activities of hhG alpha h were also downregulated in the membrane fraction, whereas the amount of hhG alpha h protein was greatly increased (2.8-fold) compared with the nonfailing heart.

CONCLUSIONS

The results of the present study clearly demonstrate that the alpha 1-adrenergic receptor in human heart couples with Gh (TGase II) and indicate that downregulation of hhG alpha h activity is associated with human cardiac failure but that the mechanism differs between ischemic and dilated cardiomyopathies.

Transglutaminase induced by epidermal growth factor negatively regulates the growth signal in primary cultured hepatocytes

Transglutaminase (TGase) activity increased 2.5-fold at 6 h after treatment of rat hepatocytes with 17 nM epidermal growth factor (EGF). In the same manner, putrescine incorporation into the proteins of cells occurred in EGF-treated cells, but not in those pretreated with monodansylcadaverine (MDC), a TGase inhibitor, even in the presence of EGF. These results suggest that EGF-induced TGase was active and catalysed some cross-linkage reaction. Cycloheximide completely blocked the increase in TGase activity induced by EGF, suggesting that EGF stimulated de novo synthesis of TGase within 6 h. Furthermore, Northern blotting analysis indicated that EGF increased the expression of TGase mRNA. Pretreatment of cells with MDC additionally increased EGF-induced DNA-synthesis and the ratio of cells in S-phase. TGase antisense oligonucleotide inhibited de novo synthesis of TGase, resulting in increases in the ratios of S- and G2/M-phase cells in the presence of EGF. This effect was the result of inhibition of EGF-induced down-regulation of high-affinity receptor expression. These results suggest that the EGF-induced increase in TGase activity is a negative regulator of a growth signal in rat hepatocytes.

Interaction site of GTP binding Gh (transglutaminase II) with phospholipase C

The GTP binding G alpha h (transglutaminase II) mediates the alpha 1B-adrenoreceptor signal to a 69-kDa phospholipase C (PLC). Thus, G alpha h possesses both GTPase and transglutaminase activities with a signal transfer role. The recognition sites of this unique GTP binding protein for either the receptor or the effector are completely unknown. A site on human heart G alpha h (hhG alpha h) has been identified that interacts with and stimulates PLC. Expressed mutants of hhG alpha h with deleted C-terminal regions lost the response to (-)-epinephrine and GTP and failed to coimmunoprecipitate PLC by the specific Gh7 alpha antibody. The interaction regions were further defined by studies with synthetic peptides of hhG alpha h and a chimera in which residues Val665-Lys672 of hhG alpha h were substituted with Ile707-Ser714 residues of human coagulation factor XIIIa. Thus, eight amino acid residues near the C terminus of hhG alpha h are critical for recognition and stimulation of PLC.

Immunological characterization and activity of transglutaminases in human normal and malignant prostate and in prostate cancer cell lines

Using biochemical assays, we compared enzyme activities with the immunoreactivity of antibodies against rat seminal transglutaminase (TGase), human erythrocyte TGase and guinea pig liver TGase in human normal prostate, primary prostatic carcinomas and prostatic carcinoma cell lines. Glandular cells of the epithelium were only exceptionally positive with the antibody against (rat) secretory TGase. Using the antibodies against tissue-type TGase, most immunoreactive cells were found in the basal cell layer of prostatic epithelium as well as in stroma (fibroblasts, endothelial cells), whereas immunoreactive glandular cells were sparse. In the case of benign prostatic hyperplasia, few, irregularly distributed secretory cells along with a small number of stromal cells were also immunoreactive with the tissue-type TGase antibody. In dedifferentiated carcinomas, immunoreactive cells were nearly completely absent. Of the prostate cancer cell lines, the LNCaP line showed neither TGase enzyme activity nor immunoreactivity, whereas the PC-3 cell line displayed significant enzyme activity and immunoreactivity. No hormone-dependent changes in either enzyme activity or immunoreactivity were recorded after in vitro treatment of the respective cell lines with estrogens, androgens and antiandrogens. As there is no correlation between androgen deprivation and TGase expression in nonmalignant and malignant human prostatic epithelial cells, TGase activity more likely indicates cellular lesions and consecutive repair mechanisms.

Cross-linking of beta-amyloid protein precursor catalyzed by tissue transglutaminase

Alzheimer's disease is characterized by progressive dementia, cortical atrophy with synaptic loss, and the accumulation of neurofibrillary tangles and senile plaques containing beta-amyloid. The beta-amyloid protein precursor (beta-APP), may normally be involved in cell adhesion related to synaptic maintenance. Loss of synapses correlates with dementia, suggesting that synaptic deficits may underlie the disease. Synapse stability may depend on the action of tissue transglutaminase (tTG), an enzyme capable of crosslinking large, multi-domain extracellular glycoproteins, that is active and present at synapses. We now show that beta-APP is a substrate for tTG in vitro that results in dimers and multimers by silver staining and immunoblotting. This novel post-translational modification suggests further roles for beta-APP in synaptic function as well as in Alzheimer's disease.

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.

Effects of ionizing irradiation on endothelial cell transglutaminase

The activity of transglutaminase (TG) was measured in cultures of bovine aortic and capillary endothelial cells (EC) following exposure to gamma-irradiation. Resting confluent EC express significant TG activity which fluctuates in growing cells. This activity was increased by 2-fold following non-lethal irradiation. The increase in TG activity was dose dependent up to 20 Gy and reached a plateau at 24-36 h after irradiation. Immunohistochemical studies showed a prominent increase in cytoplasmic TG following irradiation. Western blot analysis of whole cell extracts showed no increase in total cellular TG. Kinetic studies demonstrated that the affinity of the enzyme to its substrate was not altered, but the Vmax was increased. TG has previously been shown to be stored in an inactive form in EC membranes. This activity could be recovered in normal EC, but not in irradiated EC, by the addition of potassium thiocyanate and dithiothreitol or 0.8 M NaCl. An inhibitor of TG was previously demonstrated in the 100,000 x g particulate fraction of EC. Following irradiation, a significant decrease in this inhibitory activity was demonstrated. These results imply that the post-irradiation enhancement of TG activity may be caused by activation of a latent cellular enzyme. This elevated TG activity may cross-link adjacent cytoplasmic and membrane proteins and may thus play an active role in the enhanced apoptosis observed following irradiation of EC.

Irreversible inhibition of transglutaminases by sulfonium methylketones: optimization of specificity and potency with omega-aminoacyl spacers

Sulfonium methylketones, of structure Cbz-Phe-NH(CH2)nCOCH2S+ (CH3)2, n > 2, are specific and potent inactivators of transglutaminases. The length of the -(CH2)n-spacer moiety, n = 1-5, is a critical determinant for both the specificity and potency of the inactivator. The dipeptidyl analog Cbz-Phe-Gly-(CH2)nS+ (CH3)2, n = 1, is a more powerful inactivator of the thiol proteinase cathepsin B, k/K > 3 x 10(5) M-1 min-1, than of transglutaminases, ki(app)/Ki(app) < 1.5 x 10(4) M-1 min-1. In contrast, the gamma-aminobutyryl analog, n = 3, is a very potent transglutaminase inactivator with ki(app)/Ki(app) = 3.1 x 10(6) M-1 min-1, but does not inactivate cathepsin B. In cell studies, the gamma-aminobutyryl and epsilon-aminohexyl analogs inhibited the transglutaminase-mediated process of ionophore-induced cross-linked envelope formation by human malignant keratinocytes and the order of potency was related to that found for enzyme inhibition. The sulfonium methylketones, in equilibrium with the resonance stabilized ylides, are chemically inert towards glutathione under ambient conditions demonstrating the potential utility of this novel class of transglutaminase inhibitors for the study of enzyme inhibition in cellular environments.

Inhibition of rat liver transglutaminase by nucleotides

Tissue-type transglutaminase (TGase) was purified from rat liver, and the effects of nucleotides on its activity were examined. The enzyme activity is inhibited by ATP in a concentration-dependent way, with complete inhibition by 3 mM ATP. Partially-purified TGase from human brain was inhibited by ATP in a manner similar to that observed with the rat liver enzyme. This suggests that the inhibition is a common phenomenon for tissue-type TGase in all species and tissues. The inhibition is reversible since full activity is restored by lowering the ATP concentration. CTP has a TGase-inhibitory potency equivalent to that of ATP, whereas GTP and UTP possess about 50% of the inhibitory activity of ATP. ADP inhibits TGase activity to the same extent as ATP, but AMP causes much less inhibition, and there is no inhibition by adenosine or adenine. The inhibition by ATP is insensitive to ionic strength and is non-competitive with the substrate putrescine. Since ATP levels in cells are of mM order, these results suggest that TGase activity is controlled by ATP in vivo.