Role of protein modifications mediated by transglutaminase 2 in human viral diseases

Viruses and celiac disease: what do we know ?

The aim of this review is to provide a comprehensive overview about the link between viruses and celiac disease. A systematic search on PubMed, Embase, and Scopus was conducted on March 07, 2023. The reviewers independently selected the articles and chose which articles to include. The review is a textual systemic review, and all relevant articles were included based on title and abstract. If there was a disagreement between the reviewers, they came to a consensus during deliberation sessions. A total of 178 articles were selected for the review and read in full; only part of them was retained. We found studies between celiac disease and 12 different viruses. Some of the studies were done only on small groups. Most studies were on pediatric population. Evidence for an association was found with several viruses (trigger or protective). It seems that only a part of the viruses could induce the disease. Several points are important to keep in mind: firstly, simple mimicry or that the virus induces a high level of TGA is not sufficient to promote the disease. Secondly, inflammatory background is necessary to induce CD with virus. Thirdly, IFN type 1 seems to have an important role. Some of the viruses are potential or known triggers like enteroviruses, rotaviruses, reoviruses, and influenza. Further studies are needed to better understand the role of viruses in celiac disease to better treat and prevent the disease.

Molecular Basis of Transglutaminase-2 and Muscarinic Cholinergic Receptors in Experimental Myopia: A Target for Myopia Treatment

Myopia, a prevalent refractive error disorder worldwide, is characterized by the elongation of the eye, leading to visual abnormalities. Understanding the genetic factors involved in myopia is crucial for developing therapeutic and preventive measures. Unfortunately, only a limited number of genes with well-defined functionality have been associated with myopia. In this study, we found that the homozygous TGM2-deleted gene in mice protected against the development of myopia by slowing down the elongation of the eye. The effectiveness of gene knockdown was confirmed by achieving a 60 percent reduction in TGM-2 transcript levels through the use of TGM-2-specific small interfering RNA (siRNA) in human scleral fibroblasts (SFs). Furthermore, treating normal mouse SFs with various transglutaminase inhibitors led to the down-regulation of TGM-2 expression, with the most significant reduction observed with specific TGM-2 inhibitors. Additionally, the study found that the pharmacological blockade of muscarinic receptors also slowed the progression of myopia in mice, and this effect was accompanied by a decrease in TGM-2 enzyme expression. Specifically, mice with homozygous mAChR5, mAChR1, and/or mAChR4 and knockout mice exhibited higher levels of TGM-2 mRNA compared to mice with homozygous mAChR2 and three knockout mice (fold changes of 5.8, 2.9, 2.4, -2.2, and -4.7, respectively; p < 0.05). These findings strongly suggest that both TGM-2 and muscarinic receptors play central roles in the development of myopia, and blocking these factors could potentially be useful in interfering with the progression of this condition. In conclusion, targeting TGM-2 may have a beneficial effect regarding myopia, and this may also be at least partially be the mechanism of anti-muscarinic drugs in myopia. Further studies should investigate the interaction between TGM-2 and muscarinic receptors, as well as the changes in other extracellular matrix genes associated with growth during the development of myopia.

Cell surface transglutaminase required for nodavirus entry into freshwater prawn hemocytes

To identify molecules involved in Macrobrachium rosenbergii nodavirus (MrNV) entry into hemocytes of the giant freshwater prawn M. rosenbergii, biotinylated prawn hemocyte membrane proteins were prepared, purified and separated by SDS-PAGE. The proteins were blotted on the nitrocellulose membrane before incubation with the MrNV capsid protein (MrNV-CP) by a VOPBA technique. Subsequent mass spectrometry and analysis of immune-reactive bands represent putative binding partners including transglutaminase (TG), actin, α2-macroglobulin, α1-tubulin, F₁-ATP synthase β-subunit and a currently uncharacterized protein. The sequence of TG has been characterized and found 5 amino acids differences to a previously reported MrTG (ADX99580), mainly at its N-terminal part and thus, we named it MrTGII (KM008611). Recombinant MrTGII was prepared to produce a polyclonal antibody against it, which was successfully revealed the presence of MrTGII (100 kDa) in prawn hemocyte lysates. Using the pentylamine-biotin incorporation assay, an acyl transfer reaction was observed when hemocyte lysates were added to solutions containing MrNV-CP, suggesting that hemocyte MrTG could use MrNV-CP as the substrate. The expression levels of MrTGII were changed during the course of MrNV infection. By using immunostaining technique, location of MrTGII on the hemocyte surface was confirmed. Specific interaction between MrTGII with MrNV-CP in a dose-dependent manner was confirmed by in vitro ELISA assay. The highest binding activity of MrNV-CP was found with the N-terminal portion of the protein. In vitro neutralization using anti-MrTGII antibody resulted in inhibition of MrNV attachment to the hemocyte surface, accompanied by a dramatic reduction in viral replication. This is the first time that crustacean TG has been shown to be involved in viral entry, in addition to its roles in blood clotting and haematopoiesis.

Novel and differentially abundant microRNAs in sperm cells, seminal plasma, and serum of boars due to porcine reproduction and respiratory syndrome virus infection

The objectives of this study were to identify and determine relative abundance of miRNAs in boar sperm, seminal plasma (SP), and serum pre- and post-viral infection. Functional enrichment analyses on predicted targets of miRNAs of interest were performed. Boars (n = 6) were inoculated with porcine reproductive and respiratory syndrome virus (PRRSv) strain 1-8-4 (Day 0). Semen and serum were collected on Day -2 and 6. Sperm and SP were separated and aliquots were flash frozen and stored at -80 °C. Serum was frozen and stored at -80 °C. Total RNA was isolated from sperm and SP samples and subjected to RNA sequencing. Microarray analysis was performed using the Day -2 and 6 RNA samples from serum, sperm and SP. Potential miRNA targets were predicted using miRanda 3.3a and targets were then analyzed for enrichment of Gene Ontology) and InterPro terms and were considered to be enriched if P <  0.01 using the Bonferroni correction. Microarray analyses resulted in 83, 13, and 10 miRNAs with differences in abundances in sperm, serum, and SP, respectively, when comparing Day -2 and 6. Results from enrichment analyses indicated that the predicted targets of 35, nine, and five miRNAs with differences in abundances for sperm, SP, and serum, respectively, that have functions and/or conserved protein domains that are enriched when compared to the pig genome. Enriched terms for P2X purinoceptors were identified for sperm, SP and serum. Enriched terms for cell adhesion were identified for sperm and serum transcripts. Enriched terms for cell signaling were identified for sperm and SP transcripts.

Senescence and programmed cell death in plants: polyamine action mediated by transglutaminase

Research on polyamines (PAs) in plants laps a long way of about 50 years and many roles have been discovered for these aliphatic cations. PAs regulate cell division, differentiation, organogenesis, reproduction, dormancy-break and senescence, homeostatic adjustments in response to external stimuli and stresses. Nevertheless, the molecular mechanisms of their multiple activities are still matter of research. PAs are present in free and bound forms and interact with several important cell molecules; some of these interactions may occur by covalent linkages catalyzed by transglutaminase (TGase), giving rise to "cationization" or cross-links among specific proteins. Senescence and programmed cell death (PCD) can be delayed by PAs; in order to re-interpret some of these effects and to obtain new insights into their molecular mechanisms, their conjugation has been revised here. The TGase-mediated interactions between proteins and PAs are the main target of this review. After an introduction on the characteristics of this enzyme, on its catalysis and role in PCD in animals, the plant senescence and PCD models in which TGase has been studied, are presented: the corolla of naturally senescing or excised flowers, the leaves senescing, either excised or not, the pollen during self-incompatible pollination, the hypersensitive response and the tuber storage parenchyma during dormancy release. In all the models examined, TGase appears to be involved by a similar molecular mechanism as described during apoptosis in animal cells, even though several substrates are different. Its effect is probably related to the type of PCD, but mostly to the substrate to be modified in order to achieve the specific PCD program. As a cross-linker of PAs and proteins, TGase is an important factor involved in multiple, sometimes controversial, roles of PAs during senescence and PCD.

Role and predictive strength of transglutaminase type 2 expression in premalignant lesions of the cervix

The demonstration that type 2 transglutaminase (TG2) can incorporate polyamine into the E7 oncoprotein of human papillomavirus (HPV) type 18 has led to the hypothesis that TG2 can have a role in the host cellular response to HPV infection. The aim of this study was to investigate whether HPV-related pathology, in infected human cervical epithelium, was associated with modulation of TG2 expression. Normal controls and HPV-infected cervical biopsies were analyzed for the expression of TG2, and the findings were compared with lesion grade. The correlation between TG2 expression and p16, a marker for HPV-induced dysplasia, and the retinoblastoma protein (Rb), a target of the E7 protein of HPV, was also investigated. Results obtained showed that TG2 was absent in normal squamous mucosa, whereas it was present in 100% CIN I lesions. Low-grade lesions showed significantly higher TG2 expression than high-grade lesions (P<0.0001). In 94% of CIN I more than 50% of the cells were positive for TG2, with a strong staining intensity (+3), whereas a decreased staining intensity and a low number of positive cells were found in CIN II/III. In CIN I cases, both nuclear and cytoplasmic staining were found in cells exhibiting classical morphological features of HPV infection. In addition, during progression from low-grade squamous intraepithelial lesions to severe dysplasia, TG2 expression was inversely correlated with p16 (Pearson: -0.930), whereas a positive correlation was observed between the expression of TG2 and pRb (Pearson: 0.997). TG2 is expressed in HPV infection as an early phenomenon, not restricted to high-risk genotypes. TG2 upregulation is probably part of host cell reaction against HPV-induced tissue modification. It may act as a cellular antioxidant defense factor, playing an important role in counteracting oxidative damage in neoplastic disease.

In situ detection of active transglutaminases for keratinocyte type (TGase 1) and tissue type (TGase 2) using fluorescence-labeled highly reactive substrate peptides

Transglutaminase is a calcium-dependent enzyme that posttranslationally modifies proteins by cross-linking between glutamine and lysine residues or attachment of a primary amine to specific polypeptide-bound glutamine residues. Eight isozymes play essential roles in various mammalian biological processes. The authors have recently identified 12–amino acid preferred substrate peptide sequences that are highly reactive and act in an isozyme-specific manner. In this study, a rapid, isozyme-specific, and sensitive detection of active keratinocyte type (TGase 1) and tissue type (TGase 2) was successful using fluorescence-labeled peptides. This procedure involved using whole-body sections of a mouse to extensively analyze the tissue distribution of both enzymes that revealed clearly distinct patterns. Strong active TGase 1 was observed in epithelial tissues such as tongue, developing teeth, forestomach, and skin epidermis. Significantly active TGase 2 was observed in various types of tissues as predicted and at particularly higher levels in the intestinal mucosa, muscle membrane, and whole veins in the liver. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.

Quantitative analysis of cellular proteome alterations in human influenza A virus-infected mammalian cell lines

Over the last years virus-host cell interactions were investigated in numerous studies. Viral strategies for evasion of innate immune response, inhibition of cellular protein synthesis and permission of viral RNA and protein production were disclosed. With quantitative proteome technology, comprehensive studies concerning the impact of viruses on the cellular machinery of their host cells at protein level are possible. Therefore, 2-D DIGE and nanoHPLC-nanoESI-MS/MS analysis were used to qualitatively and quantitatively determine the dynamic cellular proteome responses of two mammalian cell lines to human influenza A virus infection. A cell line used for vaccine production (MDCK) was compared with a human lung carcinoma cell line (A549) as a reference model. Analyzing 2-D gels of the proteomes of uninfected and influenza-infected host cells, 16 quantitatively altered protein spots (at least +/-1.7-fold change in relative abundance, p<0.001) were identified for both cell lines. Most significant changes were found for keratins, major components of the cytoskeleton system, and for Mx proteins, interferon-induced key components of the host cell defense. Time series analysis of infection processes allowed the identification of further proteins that are described to be involved in protein synthesis, signal transduction and apoptosis events. Most likely, these proteins are required for supporting functions during influenza viral life cycle or host cell stress response. Quantitative proteome-wide profiling of virus infection can provide insights into complexity and dynamics of virus-host cell interactions and may accelerate antiviral research and support optimization of vaccine manufacturing processes.

Transglutaminases in inflammation and fibrosis of the gastrointestinal tract and the liver

Transglutaminases are a family of eight currently known calcium-dependent enzymes that catalyze the cross-linking or deamidation of proteins. They are involved in important biological processes such as wound healing, tissue repair, fibrogenesis, apoptosis, inflammation and cell-cycle control. Therefore, they play important roles in the pathomechanisms of autoimmune, inflammatory and degenerative diseases, many of which affect the gastrointestinal system. Transglutaminase 2 is prominent, since it is central to the pathogenesis of celiac disease, and modulates inflammation and fibrosis in inflammatory bowel and chronic liver diseases. This review highlights our present understanding of transglutaminase function in gastrointestinal and liver diseases and therapeutic strategies that target transglutaminase activities.

Transglutaminases: widespread cross-linking enzymes in plants

BACKGROUND

Transglutaminases have been studied in plants since 1987 in investigations aimed at interpreting some of the molecular mechanisms by which polyamines affect growth and differentiation. Transglutaminases are a widely distributed enzyme family catalysing a myriad of biological reactions in animals. In plants, the post-translational modification of proteins by polyamines forming inter- or intra-molecular cross-links has been the main transglutaminase reaction studied.

CHARACTERISTICS OF PLANT TRANSGLUTAMINASES

The few plant transglutaminases sequenced so far have little sequence homology with the best-known animal enzymes, except for the catalytic triad; however, they share a possible structural homology. Proofs of their catalytic activity are: (a) their ability to produce glutamyl-polyamine derivatives; (b) their recognition by animal transglutaminase antibodies; and (c) biochemical features such as calcium-dependency, etc. However, many of their fundamental biochemical and physiological properties still remain elusive.

TRANSGLUTAMINASE ACTIVITY IS UBIQUITOUS

It has been detected in algae and in angiosperms in different organs and sub-cellular compartments, chloroplasts being the best-studied organelles.

POSSIBLE ROLES

Possible roles concern the structural modification of specific protein substrates. In chloroplasts, transglutaminases appear to stabilize the photosynthetic complexes and Rubisco, being regulated by light and other factors, and possibly exerting a positive effect on photosynthesis and photo-protection. In the cytosol, they modify cytoskeletal proteins. Preliminary reports suggest an involvement in the cell wall construction/organization. Other roles appear to be related to fertilization, abiotic and biotic stresses, senescence and programmed cell death, including the hypersensitive reaction.

CONCLUSIONS

The widespread occurrence of transglutaminases activity in all organs and cell compartments studied suggests a relevance for their still incompletely defined physiological roles. At present, it is not possible to classify this enzyme family in plants owing to the scarcity of information on genes encoding them.

Transglutaminase activity changes during the hypersensitive reaction, a typical defense response of tobacco NN plants to TMV

The occurrence of glutamyl polyamines (PAs) and changes in activity and levels of transglutaminase (TGase, EC 2.3.2.13), the enzyme responsible for their synthesis, are reported during the progression of the hypersensitive reaction (HR) of resistant NN tobacco plants (Nicotiana tabacum L. cv. Samsun) to tobacco mosaic virus (TMV). Mature leaves of tobacco were collected over 0-72 h after inoculation with TMV or phosphate buffer (mock). In vivo synthesis of polyamine glutamyl derivatives (glutamyl PAs), catalyzed by TGase activity, was evaluated after supplying labeled putrescine (Pu, a physiological substrate of TGase) to leaves. Results show that, starting from 24 h, mono-(gamma-glutamyl)-Pu and bis-(gamma-glutamyl)-Sd were recovered in TMV-inoculated samples but not in mock-inoculated ones; 2 days later, in the former, the amount of glutamyl derivatives further increased. An in vitro radiometric assay showed that, in TMV-inoculated leaves, TGase activity increased from 24 h onwards relative to mock controls. An immunoblot analysis with AtPng1p polyclonal antibody detected a 72-kDa protein whose amount increased at 72 h in TMV-inoculated leaves and in the lesion-enriched areas. A biotin-labeled cadaverine incorporation assay showed that TGase activity occurred in S1 (containing soluble proteins), S2 (proteins released by both cell walls and membranes) and S3 (membrane intrinsic proteins) fractions. In S3 fraction, where changes were the most relevant, TGase activity was enhanced in both mock-inoculated and TMV-inoculated samples, but the stimulation persisted only in the latter case. These data are discussed in the light of a possible role of TGase activity and glutamyl PAs in the defense against a viral plant pathogen.