Transglutaminases and their regulation: implications for polyamine metabolism

Polyamines: Α bioenergetic smart switch for plant protection and development

The present review highlights the bioenergetic role of polyamines in plant protection and development and proposes a universal model for describing polyamine-mediated stress responses. Any stress condition induces an excitation pressure on photosystem II by reforming the photosynthetic apparatus. To control this phenomenon, polyamines act directly on the molecular structure and function of the photosynthetic apparatus as well as on the components of the chemiosmotic proton-motive force (ΔpH/Δψ), thus regulating photochemical (qP) and non-photochemical quenching (NPQ) of energy. The review presents the mechanistic characteristics that underline the key role of polyamines in the structure, function, and bioenergetics of the photosynthetic apparatus upon light adaptation and/or under stress conditions. By following this mechanism, it is feasible to make stress-sensitive plants to be tolerant by simply altering their polyamine composition (especially the ratio of putrescine to spermine), either chemically or by light regulation.

Protein cross-linking by chlorinated polyamines and transglutamylation stabilizes neutrophil extracellular traps

Neutrophil extracellular trap (NET) ejected from activated dying neutrophils is a highly ordered structure of DNA and selected proteins capable to eliminate pathogenic microorganisms. Biochemical determinants of the non-randomly formed stable NETs have not been revealed so far. Studying the formation of human NETs we have observed that polyamines were incorporated into the NET. Inhibition of myeloperoxidase, which is essential for NET formation and can generate reactive chlorinated polyamines through hypochlorous acid, decreased polyamine incorporation. Addition of exogenous primary amines that similarly to polyamines inhibit reactions catalyzed by the protein cross-linker transglutaminases (TGases) has similar effect. Proteomic analysis of the highly reproducible pattern of NET components revealed cross-linking of NET proteins through chlorinated polyamines and ɛ(γ-glutamyl)lysine as well as bis-γ-glutamyl polyamine bonds catalyzed by the TGases detected in neutrophils. Competitive inhibition of protein cross-linking by monoamines disturbed the cross-linking pattern of NET proteins, which resulted in the loss of the ordered structure of the NET and significantly reduced capacity to trap bacteria. Our findings provide explanation of how NETs are formed in a reproducible and ordered manner to efficiently neutralize microorganisms at the first defense line of the innate immune system.

Phytochemicals and protein-polyamine conjugates by transglutaminase as chemopreventive and chemotherapeutic tools in cancer

Identifying novel chemopreventive and chemotherapeutic agents and targeting them to patients at high risk of developing cancer or following curative treatment may go some way towards improving prognosis. This review examines current knowledge regarding the chemopreventive and chemotherapeutic potential of phytochemicals in cancer. Both in vitro and animal studies demonstrate that several phytochemicals increase the activity of intracellular transglutaminases, a family of enzymes involved in cell differentiation, through the covalent conjugation of polyamine to cellular protein, with promising anti-neoplastic properties. The substantial data available on certain plant secondary metabolites makes a strong case for integrating these safe and well-tolerated agents into clinical practice.

Post-translational modification of glutamine and lysine residues of HIV-1 aspartyl protease by transglutaminase increases its catalytic activity

The human immunodeficiency virus type 1 aspartyl protease (HIV-1 PR) is a homodimeric aspartyl endopeptidase that is required for virus replication. HIV-1 PR was shown to act invitro as acyl-donor and -acceptor for both guinea pig liver transglutaminase (TG, EC 2.3.2.13) and human Factor XIIIa. These preliminary evidences suggested that the HIV-1 PR contains at least three TG-reactive glutaminyl and one lysyl residues. We report here that the incubation of HIV-1 PR with TG increases its catalytic activity. This increase is dependent upon the time of incubation, the concentration of TG and the presence of Ca2+. Identification of epsilon-(gamma-glutamyl)lysine in the proteolytic digest of the TG-modified HIV-1 PR suggested intramolecular covalent cross-linking of this protease which may promote a non-covalent dimerization and subsequent activation of this enzyme via a conformational change. This hypothesis is supported by the observation that the TG-catalyzed activation of HIV-1 PR was completely abolished by spermidine (SPD) which acts as a competitive inhibitor of epsilon-(gamma-glutamyl)lysine formation. Indeed, in the presence of 1mM SPD the formation of the isopeptide was decreased of about 80%. The main products of the TG-catalyzed modification of HIV-1 PR in the presence of SPD were N(1)-mono(gamma-glutamyl)SPD and N(8)-mono(gamma-glutamyl)SPD. Negligible amount of N(1),N(8)-bis(gamma-glutamyl)SPD were found. The significance of these results is discussed with respect to the activation of the protease by post-translational modification and design of potential inhibitors.

Arginine methylation provides epigenetic transcription memory for retinoid-induced differentiation in myeloid cells

Cellular differentiation is governed by changes in gene expression, but at the same time, a cell's identity needs to be maintained through multiple cell divisions during maturation. In myeloid cell lines, retinoids induce gene expression and a well-characterized two-step lineage-specific differentiation. To identify mechanisms that contribute to cellular transcriptional memory, we analyzed the epigenetic changes taking place on regulatory regions of tissue transglutaminase, a gene whose expression is tightly linked to retinoid-induced differentiation. Here we report that the induction of an intermediary or "primed" state of myeloid differentiation is associated with increased H4 arginine 3 and decreased H3 lysine 4 methylation. These modifications occur before transcription and appear to prime the chromatin for subsequent hormone-regulated transcription. Moreover, inhibition of methyltransferase activity, pre-acetylation, or activation of the enzyme PAD4 attenuated retinoid-regulated gene expression, while overexpression of PRMT1, a methyltransferase, enhanced retinoid responsiveness. Taken together, our results suggest that H4 arginine 3 methylation is a bona fide positive epigenetic marker and regulator of transcriptional responsiveness as well as a signal integration mechanism during cell differentiation and, as such, may provide epigenetic memory.

The chemopreventive agent alpha-difluoromethylornithine blocks Ki-ras-dependent tumor formation and specific gene expression in Caco-2 cells

Mutation of the Kirsten-ras (Ki-ras) proto-oncogene occurs frequently in colorectal cancers. alpha-Difluoromethylornithine (DFMO), an irreversible inhibitor of the polyamine biosynthetic enzyme, ornithine decarboxylase (ODC), inhibits Ki-ras transformation and colon tumorigenesis in carcinogen-treated animal models by mechanisms yet to be elucidated. Caco-2 cells transfected with an activated Ki-ras, but not parental cells, formed tumors in severe combined immunodeficient (SCID) mice. DFMO treatment (2% in drinking water) prevented tumor growth. Gene expression profiling was performed to identify Ki-ras-and DFMO-dependent patterns of gene expression. Microarray results were validated with real-time or semi-quantitative RT-PCR and/or Western blot analysis. Genes upregulated in Caco-2 cells expressing an activated Ki-ras encoded cytoskeletal-, transport-, protease-, and gap junction-associated proteins. These genes are important for normal development and maintenance of colonic epithelial tissue. Caco-2 cells transfected with an activated Ki-ras displayed increased expression of the integrin alpha 1 (INGA1) and enhanced cell migration on laminin. These parameters were unaffected by DFMO, but Ki-ras-dependent migration was inhibited by INGA1 antibodies. Other Ki-ras-dependent, but DFMO-independent, genes included transglutaminase (TGase) and kallikrein 6 (KLK6). Ki-ras-transfected cells also expressed increased levels of connexin43 (Cx43) (RNA and protein), tight junction protein, and endothelin 1. DFMO reversed these increases. The results indicated that the Ki-ras oncogene caused changes in experimental cell migration and cell-cell communication genes and that some of these changes could be reversed by DFMO.

Epoxyeicosatrienoic acids activate transglutaminases in situ and induce cornification of epidermal keratinocytes

The cytochrome P450 CYP2B19 is a keratinocyte-specific arachidonic acid epoxygenase expressed in the granular cell layer of mouse epidermis. In cultured keratinocytes, CYP2B19 mRNAs are up-regulated coordinately with those of profilaggrin, another granular cell-specific marker. We investigated effects of the CYP2B19 metabolites 11,12- and 14,15-epoxyeicosatrienoic acids (EETs) on keratinocyte transglutaminase activities and cornified cell envelope formation. Keratinocytes were differentiated in vitro in the presence of biotinylated cadaverine. Transglutaminases cross-linked this substrate into endogenous proteins in situ; an enzyme-linked immunosorbent assay was used to quantify the biotinylated proteins. Exogenously added or endogenously formed 14,15-EET increased transglutaminase cross-linking activities in cultured human and mouse epidermal keratinocytes in a modified in situ assay. Transglutaminase activities increased approximately 8-fold (p < or = 0.02 versus mock control) in human keratinocytes transduced with adenovirus particles expressing a 14S,15R-EET epoxygenase (P450 BM3v). The physiological transglutaminase substrate involucrin was preferentially biotinylated in situ, determined by immunoblotting and mass spectrometry. P450 BM3v-induced transglutaminase activation was associated with increased 14,15-EET formation (p = 0.002) and spontaneous cell cornification (p < or = 0.001). Preferential involucrin biotinylation and the increased cornified cell envelope formation provided evidence that transglutaminases mediated the P450 BM3v-induced cross-linking activities. These results support a physiological role for 14,15-EET epoxygenases in regulating epidermal cornification, and they have important implications for epidermal barrier functions in vivo.

Detection and characterization, using fluoresceincadaverine, of amine acceptor protein substrates accessible to active transglutaminase expressed by rabbit articular chondrocytes

The purpose of this study was to investigate the implication of transglutaminases in the biology of articular chondrocytes. Transglutaminase activity measurements performed on cell lysates showed that a transglutaminase was present in chondrocytes in primary culture and that it was strongly activated by limited proteolysis. In chondrocytes dedifferentiated by subculture or retinoic acid treatment, this transglutaminase appeared to be downregulated, while type II transglutaminase expression was induced. However, protein levels, mRNA steady-state levels or transglutaminase activity in whole-cell lysates do not necessarily reflect the activity present in living cells, as it is strongly regulated. Therefore, Fluoresceincadaverine, a fluorescent polyamine, was used for detecting amine acceptor protein substrates accessible to active transglutaminase in living cells. After incubation of chondrocytes with Fluoresceincadaverine, dedifferentiated cells exhibited an extracellular labelling, while chondrocytes in primary culture did not, unless thrombin was added to the culture medium. In contrast, Fluoresceincadaverine labelling was not detected in the cytosol, although the transglutaminases were also partly cytosolic. By confocal microscopy and Western blot analysis of labelled cells in culture, fibronectin was shown to be the main substrate for both transglutaminases. The transglutaminases present in articular chondrocytes may, therefore, contribute to the organization and the stabilization of their extracellular matrix.

Differences in transglutaminase mRNA after polyamine depletion in two cell lines

Polyamines serve as natural substrates for the transglutaminase that catalyzes covalent cross-linking of proteins and is involved in cellular adhesion and proliferation. This study tests the hypothesis that intracellular polyamines play a role in the regulation of transglutaminase expression in rat small intestinal crypt cells (IEC-6 cell line) and human colon carcinoma cells (Caco-2 cell line). Treatment with alpha-difluoromethylornithine (DFMO; a specific inhibitor of polyamine synthesis) significantly depleted the cellular polyamines putrescine, spermidine, and spermine in both cell lines. In IEC-6 cells, polyamine depletion was associated with a decrease in the levels of transglutaminase mRNA. In Caco-2 cells, however, polyamine depletion significantly increased the levels of transglutaminase mRNA and enzyme activity. In both cell lines, ornithine decarboxylase mRNA levels increased and protooncogene c-myc mRNA decreased in the presence of DFMO. Addition of polyamines to cells treated with DFMO reversed the effect of DFMO on the levels of mRNA for these genes in both lines. There was no significant change in the stability of transglutaminase mRNA between control and DFMO-treated IEC-6 cells. In contrast, the half-life of mRNA for transglutaminase in Caco-2 cells was dramatically increased after polyamine depletion. Spermidine, when given together with DFMO, completely prevented increased half-life of transglutaminase mRNA in Caco-2 cells. These results indicate that 1) expression of transglutaminase requires polyamines in IEC-6 cells but is inhibited by these agents in Caco-2 cells, 2) polyamines modulate transglutaminase expression at the level of mRNA through different pathways in these two cell lines, and 3) posttranscriptional regulation plays a major role in the induction of transglutaminase mRNA in polyamine-deficient Caco-2 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.

Response of intestinal transglutaminase activity to dietary phytohaemagglutinin

The behaviour of the activity of tissue transglutaminase, a calcium-dependent enzyme, and the levels of polyamines which are physiological substrates for the enzyme, were studied in rat small intestine induced to grow by lectin phytohaemagglutinin. Transglutaminase activity greatly increased in the homogenates and the cytosolic fractions of the intestinal mucosa of lectin-treated rats compared to that of untreated animals. The measurement of enzyme activity in the presence of monodansylcadaverine, a competitive inhibitor of transglutaminase, testified that the assayed enzyme activity was authentic transglutaminase. As regards polyamines, the level of spermine did not change, whereas putrescine and spermidine contents were enhanced. The activation of transglutaminase, which was probably due to Ca2+ accumulation in enterocytes, could have a role in maintaining enterocyte adhesion and intestinal cell homeostasis, and/or repairing lectin-induced damages of microvilli of the gut epithelium.

Type II transglutaminase expression in rabbit articular chondrocytes in culture: relation with cell differentiation, cell growth, cell adhesion and cell apoptosis

Depending on the cell type studied, the involvement of type II transglutaminase (TGase) has been proposed in almost any event of the cell life such as differentiation, apoptosis, growth, aging, cell morphology and adhesion, metastatic capacity or extracellular matrix stabilization. In order to define the field(s) where this enzyme may be implicated in chondrocytes, type II TGase expression was studied in chondrocytes at different passages which differentiated state was modulated by retinoic acid, dihydrocytochalasin B or staurosporin. Results showed that (i) type II TGase expression is not incompatible with type II collagen expression, a main marker of chondrocyte differentiation (ii) type II TGase expression is higher when cells are in the exponential phase of growth than when growth arrested (iii) a high type II TGase expression does not imply that cells are apoptotic although cell apoptosis correlates with increased type II TGase expression (iv) non-adherent cells do not express type II TGase whereas adherent cells do whatever their differentiation state as assessed by type II collagen synthesis. These results suggest that, in articular chondrocytes, type II TGase is specifically implicated in the cell adhesion capacity.

Transglutaminase activity in rabbit articular chondrocytes in culture

In vivo, articular chondrocytes produce an important amount of extracellular matrix (cartilage) whose quality is impaired upon inflammation or aging leading to arthritis or arthrosis. Transglutaminases (EC 2.3.2.13) are a family of enzymes which have been shown to be involved in extracellular matrix stabilization, cell differentiation and possibly in initiation and propagation of inflammatory diseases. It is therefore of interest to study transglutaminase activity in chondrocytes. Transglutaminase activity was studied in rabbit articular chondrocytes in primary culture, where cells are in a well-differentiated state as assessed by collagen-type synthesis, as well as in subculture and in retinoic acid-treated cells, where cells are in a dedifferentiated state. Results showed that two different TGases activities are expressed in chondrocytes. One, down-regulated upon retinoic acid treatment of cells, preferentially membrane bound and strongly activated upon trypsin treatment of cell lysates, is expressed at a high level in primary culture. The other one is up-regulated upon retinoic acid treatment, preferentially cytosolic and inactivated upon trypsin treatment of cell lysates. The rate of expression of the TGase down-regulated by RA seems to correlate with the differentiation state of the chondrocyte. This suggests that this TGase activity may have a physiological role in cartilage and merits further study.

Transglutaminase in azoxymethane-induced colon cancer in the rat

A widespread from of transglutaminase, tissue transglutaminase, has been identified in a number of mammalian cell types, both normal and transformed cells; its biological role is not well understood. We investigated the effect of experimentally induced colon cancer on transglutaminase activity in the rat. Azoxymethane (15 mg/kg for six weeks), given by a course of weekly intraperitoneal injections, produces tumors almost exclusively confined to the intestinal tract. Transglutaminase activity was assayed on tissue homogenates both during the period of treatment and, when the cancer had developed, on tumor tissue and on microscopically uninjured adjacent tissue. A transient proliferative phase was present in the intestine during azoxymethane treatment: in this phase we found a coincidentally increased transglutaminase levels. Transglutaminase activity in tumors of both small and large intestine was significantly higher than in adjacent tissue. Immunohistochemistry revealed higher levels of transglutaminase in tumors, mainly localized in the extracellular matrix, than in adjacent tissues, where it was widely distributed. The present study shows that transglutaminase, besides its potential role in intracellular process during early proliferative phase of carcinogenesis, may also play an important role in matrix processing during tumor growth and differentiation.

Polyamines influence transglutaminase activity and cell migration in two cell lines

Transglutaminases (TGAs) catalyze the cross-linking of proteins through formation of gamma-glutaminyl-epsilon-lysine bonds and incorporation of small-molecular-weight amines, including polyamines, into the gamma-glutamine sites of proteins. Tissue TGA has been shown to establish covalent cross-links between cytoskeletal proteins using polyamines as substrates, and protein-polyamine conjugates have been identified in a variety of cells. We have shown previously that polyamines are required for cell migration in IEC-6 cells [S. A. McCormack, M. J. Viar, and L. R. Johnson. Am. J. Physiol. 264 (Gastrointest. Liver Physiol. 27): G367-G374, 1993]. In this study, we explored the relationship between cell migration, polyamines, and tissue TGA activity in two cell lines and found that while both IEC-6 and Caco-2 cells required normal levels of polyamines to migrate across a denuded surface, tissue TGA activity responded differently to polyamine deficiency brought about by treatment with alpha-difluoromethylornithine (DFMO). DFMO is a specific and irreversible inhibitor of ornithine decarboxylase, a rate-limiting enzyme of polyamine biosynthesis. In IEC-6 cells, tissue TGA activity decreased significantly with DFMO treatment concurrent with a rise in inactive TGA protein as measured by Western blot analysis. On the other hand, in Caco-2 cells, tissue TGA activity and protein increased significantly with DFMO treatment. In both cell lines, addition of polyamines to the DFMO treatment restored cell migration, tissue TGA activity, and protein to control levels.(ABSTRACT TRUNCATED AT 250 WORDS)

High levels of transglutaminase expression in doxorubicin-resistant human breast carcinoma cells

Tissue type II transglutaminase (TGase) is a member of the TGase family that catalyzes Ca(2+)-dependent covalent cross-linking of several amines to the gamma-carboxamide group of protein-bound glutamine residues. The degree of therapeutic efficacy or toxicity of drugs may be related to their ability to serve as a substrate for TGase and their covalent linkage to glutamine residues of regulatory proteins through the catalytic action of this enzyme. Here, doxorubicin (adriamycin)-resistant human breast carcinoma MCF-7ADR cells exhibited 40- to 6C-fold higher TGase activity than control drug-sensitive MCF-7WT cells. The same was observed in vivo: a small proportion of tumor cells became positive for TGase after administration of adriamycin-based chemotherapy to patients with breast carcinoma. Similarly, continuous culture of MCF-7WT cells in the presence of adriamycin led to the appearance of the drug-resistant phenotype that was in turn associated with increased expression of TGase. This increase in TGase was specific for adriamycin resistance. Like most known TGase, MCF-7ADR TGase was completely dependent on the presence of Ca2+ for its catalytic activity. Based on its immunoreactivity, the TGase in MCF-7ADR cells was identified as an 85-kDa tissue-type TGase and was present only in the soluble form. Immunoblot analysis revealed that the increase in TGase activity was due to accumulation of the protein. Two cytosolic proteins of approximately 20 and 30 kDa in MCF-7 cells served as suitable acyl donor substrates in TGase-catalyzed reactions.

Some problems with the diamine oxidase (DAO) assay using putrescine as substrate in rat liver

Determination of diamine oxidase (DAO) activity in rat liver preparations by measuring the formation of radioactive delta 1-pyrroline from 14C-putrescine is complicated by the complexity of competing metabolic pathways. This can lead to complete masking of the DAO activity present when rat liver homogenates are used as the enzyme source. However, subcellular fractionation of rat liver homogenates makes it possible to detect some putrescine oxidizing activity in the microsomal fraction when assayed at pH 8.5. When 1 mM putrescine was used as the substrate, over 90% of this activity was inhibited by 6 x 10(-4) M selegiline (deprenyl), indicating that monoamine oxidase (MAO) rather than DAO activity was being measured. The observed activity was also interfered with by agents that reduced acetylation processes and polyamine synthesis. A different picture appears when microM concentrations of putrescine are used: in these conditions all interference is strongly reduced and DAO activity can be measured in rat liver microsomes. Furthermore, kinetic studies on deaminative oxidation of 14C-putrescine at concentrations from 1 microM to 5 mM confirm the existence of two enzymes: one with a high affinity for the substrate and similar to intestinal mucosa DAO in its sensitivity to alpha-aminoguanidine, and the other one with a low affinity and selegiline-sensitive.

Expression of tissue transglutaminase in Balb-C 3T3 fibroblasts: effects on cellular morphology and adhesion

Tissue transglutaminase is a cytosolic enzyme whose primary function is to catalyze the covalent cross-linking of proteins. To investigate the functions of this enzyme in physiological systems, we have established lines of Balb-C 3T3 fibroblasts stably transfected with a constitutive tissue transglutaminase expression plasmid. Several cell lines expressing high levels of catalytically active tissue transglutaminase have been isolated and characterized. Transglutaminase-transfected cells showed morphologic features quite distinct from their nontransfected counterparts. Many of the cells showed an extended and very flattened morphology that reflected increased adhesion of the cells to the substratum. Other cells, particularly those showing the highest levels of intracellular transglutaminase expression, showed extensive membrane blebbing and cellular fragmentation. The results of these experiments suggest that the induction and activation of tissue transglutaminase may contribute both to changes in cellular morphology and adhesiveness.

Regulation of extracellular phospholipase A2 activity: implications for inflammatory diseases

Phospholipases A2 (PLA2s; E.C.3.1.1.4) are a family of esterases that are involved in myriads of physiological and pathological processes. The involvement of these enzymes, especially the extracellular PLA2s, in the generation of proinflammatory lipid mediators makes them a very important target for investigation. These PLA2s have been suggested to be involved in the pathogenesis of several human inflammatory diseases. Thus, delineating the mechanism(s) of regulation of the activity of these enzymes may provide a better understanding of the pathophysiology of these diseases and allow the rational design and development of novel therapeutic agents. In this article, we provide a brief description of PLA2s in general with a special emphasis on extracellular enzymes, their mechanism(s) of action, and possible role in the pathogenesis of inflammatory diseases. Additionally, we describe: (i) a novel mechanism of activation of extracellular PLA2s by transglutaminases and (ii) the development of one class of antiinflammatory agents, antiflammins, derived from the active site structure of endogenous PLA2-inhibitory proteins.