TG2, a novel extracellular protein with multiple functions

PROTACs in gynecological cancers: Current knowledge and future potential as a treatment strategy

Cancer continues to threaten human health regardless of novel therapeutic options. Over the last two decades, targeted therapy has emerged as a significant advancement in treating malignancies, surpassing standard chemoradiotherapy and surgical procedures. Gynecological malignancies, including cervical, endometrial, and ovarian carcinoma, have a bad prognosis in advanced or metastatic stages and are difficult to treat. The advancements in understanding the molecular pathways behind cancer development offer valuable insights into promising targeted medicines, and researchers have always searched for a superior and safe technique to target cancer-related oncoproteins because of the limited therapeutic benefit, drug resistance, and off-target effects of current targeted treatments. Recently, proteolysis-targeting chimeras (PROTACs) have been developed to selectively degrade proteins using the natural ubiquitin-proteasome system (UPS). These approaches have garnered significant attention in the field of cancer research. The rapid progress in PROTACs has also eased the targeting of various oncoproteins in gynecological cancer. Therefore, this review aims to elucidate the mechanism and research advancements of PROTACs and provide a comprehensive overview of their use in gynecological tumors.

PROTACs in Ovarian Cancer: Current Advancements and Future Perspectives

Ovarian cancer is the deadliest gynecologic malignancy. The majority of patients diagnosed with advanced ovarian cancer will relapse, at which point additional therapies can be administered but, for the most part, these are not curative. As such, a need exists for the development of novel therapeutic options for ovarian cancer patients. Research in the field of targeted protein degradation (TPD) through the use of proteolysis-targeting chimeras (PROTACs) has significantly increased in recent years. The ability of PROTACs to target proteins of interest (POI) for degradation, overcoming limitations such as the incomplete inhibition of POI function and the development of resistance seen with other inhibitors, is of particular interest in cancer research, including ovarian cancer research. This review provides a synopsis of PROTACs tested in ovarian cancer models and highlights PROTACs characterized in other types of cancers with potential high utility in ovarian cancer. Finally, we discuss methods that will help to enable the selective delivery of PROTACs to ovarian cancer and improve the pharmacodynamic properties of these agents.

Molecular analysis of the extracellular microenvironment: from form to function

The extracellular matrix (ECM) proteome represents an important component of the tissue microenvironment that controls chemical flux and induces cell signaling through encoded structure. The analysis of the ECM represents an analytical challenge through high levels of post-translational modifications, protease-resistant structures, and crosslinked, insoluble proteins. This review provides a comprehensive overview of the analytical challenges involved in addressing the complexities of spatially profiling the extracellular matrix proteome. A synopsis of the process of synthesizing the ECM structure, detailing inherent chemical complexity, is included to present the scope of the analytical challenge. Current chromatographic and spatial techniques addressing these challenges are detailed. Capabilities for multimodal multiplexing with cellular populations are discussed with a perspective on developing a holistic view of disease processes that includes both the cellular and extracellular microenvironment.

Tissue transglutaminase: a multifunctional and multisite regulator in health and disease

Tissue transglutaminase (TG2) is a widely distributed multifunctional protein involved in a broad range of cellular and metabolic functions carried out in a variety of cellular compartments. In addition to transamidation, TG2 also functions as a Gα signaling protein, a protein disulfide isomerase (PDI), a protein kinase, and a scaffolding protein. In the nucleus, TG2 modifies histones and transcription factors. The PDI function catalyzes the trimerization and activation of heat shock factor-1 in the nucleus and regulates the oxidation state of several mitochondrial complexes. Cytosolic TG2 modifies proteins by the addition of serotonin or other primary amines and in this way affects cell signaling. Modification of protein-bound glutamines reduces ubiquitin-dependent proteasomal degradation. At the cell membrane, TG2 is associated with G protein-coupled receptors (GPCRs), where it functions in transmembrane signaling. TG2 is also found in the extracellular space, where it functions in protein cross-linking and extracellular matrix stabilization. Of particular importance in transglutaminase research are recent findings concerning the role of TG2 in gene expression, protein homeostasis, cell signaling, autoimmunity, inflammation, and hypoxia. Thus, TG2 performs a multitude of functions in multiple cellular compartments, making it one of the most versatile cellular proteins. Additional evidence links TG2 with multiple human diseases including preeclampsia, hypertension, cardiovascular disease, organ fibrosis, cancer, neurodegenerative diseases, and celiac disease. In conclusion, TG2 provides a multifunctional and multisite response to physiological stress.

An emerging view on vascular fibrosis molecular mediators and relevant disorders: from bench to bed

Vascular fibrosis is a widespread pathologic condition that arises during vascular remodeling in cardiovascular dysfunctions. According to previous studies, vascular fibrosis is characterized by endothelial matrix deposition and vascular wall thickening. The RAAS and TGF-β/Smad signaling pathways have been frequently highlighted. It is, however, far from explicit in terms of understanding the cause and progression of vascular fibrosis. In this review, we collected and categorized a large number of molecules which influence the fibrosing process, in order to acquire a better understanding of vascular fibrosis, particularly of pathologic dysfunction. Furthermore, several mediators that prevent vascular fibrosis are discussed in depth in this review, with the aim that this will contribute to the future prevention and treatment of related conditions.

Colon-targeted EMSCs conditional medium hydrogel for treatment of ulcerative colitis in mice

Oral ecto-mesenchymal stem cells-conditional medium (EMSCs-CM) is a promising strategy for treating ulcerative colitis (UC). However, this therapy is currently limited by the harsh gastrointestinal environment and poor colonic targeting ability. Herein, a glutamine transaminase 2 (TG2) crosslinked EMSCs-CM hydrogel (EMSCs-CM-Gel) was fabricated by combining EMSCs-CM with negatively chargedγ-polyglutamic acid (γ-PGA) hydrogel. Intestinal epithelial cell 6 (IEC-6) was applied to construct a cell model with lipopolysaccharide to evaluate the anti-inflammatory potential of EMSCs-CMin vitro. The crosslinked gel was orally administered to mice in liquid form to access the effects of EMSCs-CM-Gelin vivo. This study was based on the fact that the hydrogel containing EMSCs-CM has negative charges, which ensure it remains at the positively charged inflamed colon tissue. The EMSCs-CM could continuously be released in the damaged colon mucosa along with the degradation of theγ-PGA hydrogel. Immunofluorescence and western blot were performed to assess the effects of EMSCs-CM-Gel on mice. The resultsin vivoshowed that EMSCs-CM-Gel could significantly suppress the expression of inflammatory cytokines, prevent the shortening of the length of the intestine and repair the intestinal barrier. Collectively, our findings provided a novel colon-targeted strategy, hoping to benefit UC patients a lot.

Human nasal mucosa ectomesenchymal stem cells derived extracellular vesicles loaded omentum/chitosan composite scaffolds enhance skull defects regeneration

Engineered bone tissue that can promote osteogenic differentiation is considered an ideal substitute for materials to heal bone defects. Extracellular vesicle (EV)-based cell-free regenerative therapies represent an emerging promising alternative for bone tissue engineering. We hypothesized that EVs derived from human nasal mucosa-derived ectomesenchymal stem cells (hEMSCs) can promote bone tissue regeneration. Herein, hEMSCs were cultured with osteogenic induction medium or normal medium to generate two types of EVs. We first demonstrated that the two EVs exhibited strong potential to promote rat suture mesenchymal stem cell (SMSC) osteogenesis by transferring TG2 to SMSCs and regulating extracellular matrix (ECM) synthesis. Next, we developed a composite hydrogel made of porcine omentum and chitosan into which EVs were adsorbed to enable the effective delivery of EVs with sustained release kinetics. Implantation of the EV-loaded hydrogels in a critical-size rat cranial defect model significantly promoted bone regeneration. Therefore, we suggest that our hEMSC-derived EV-loading system can serve as a new therapeutic paradigm for promoting bone tissue regeneration in the clinic.

The Post-Translational Modifications of Human Salivary Peptides and Proteins Evidenced by Top-Down Platforms

In this review, we extensively describe the main post-translational modifications that give rise to the multiple proteoforms characterized to date in the human salivary proteome and their potential role. Most of the data reported were obtained by our group in over twenty-five years of research carried out on human saliva mainly by applying a top-down strategy. In the beginning, we describe the products generated by proteolytic cleavages, which can occur before and after secretion. In this section, the most relevant families of salivary proteins are also described. Next, we report the current information concerning the human salivary phospho-proteome and the limited news available on sulfo-proteomes. Three sections are dedicated to the description of glycation and enzymatic glycosylation. Citrullination and N- and C-terminal post-translational modifications (PTMs) and miscellaneous other modifications are described in the last two sections. Results highlighting the variation in the level of some proteoforms in local or systemic pathologies are also reviewed throughout the sections of the manuscript to underline the impact and relevance of this information for the development of new diagnostic biomarkers useful in clinical practice.

Biochemical and Functional Characterization of the Three Zebrafish Transglutaminases 2

Transglutaminase 2 (TG2) is a multifunctional protein widely distributed in various tissues and involved in many physiological and pathological processes. However, its actual role in biological processes is often controversial as TG2 shows different effects in these processes depending on its localization, cell type, or experimental conditions. We characterized the enzymatic and functional properties of TG2 proteins expressed in Danio rerio (zebrafish) to provide the basis for using this established animal model as a reliable tool to characterize TG2 functions in vivo. We confirmed the existence of three genes orthologous to human TG2 (zTGs2) in the zebrafish genome and their expression and function during embryonic development. We produced and purified the zTGs2s as recombinant proteins and showed that, like the human enzyme, zTGs2 catalyzes a Ca2+ dependent transamidation reaction that can be inhibited with TG2-specific inhibitors. In a cell model of human fibroblasts, we also demonstrated that zTGs2 can mediate RGD-independent cell adhesion in the extracellular environment. Finally, we transfected and selected zTGs2-overexpressing HEK293 cells and demonstrated that intracellular zTGs2 plays a very comparable protective/damaging role in the apoptotic process, as hTG2. Overall, our results suggest that zTGs2 proteins behave very similarly to the human ortholog and pave the way for future in vivo studies of TG2 functions in zebrafish.

Involvement and possible role of transglutaminases 1 and 2 in mediating fibrotic signalling, collagen cross-linking and cell proliferation in neonatal rat ventricular fibroblasts

Transglutaminase (TG) isoforms control diverse normal and pathophysiologic processes through their capacity to cross-link extracellular matrix (ECM) proteins. Their functional and signalling roles in cardiac fibrosis remain poorly understood, despite some evidence of TG2 involvement in abnormal ECM remodelling in heart diseases. In this study, we investigated the role of TG1 and TG2 in mediating fibrotic signalling, collagen cross-linking, and cell proliferation in healthy fibroblasts by siRNA-mediated knockdown. siRNA for TG1, TG2 or negative control was transfected into cultured neonatal rat ventricular fibroblasts and cardiomyocytes. mRNA expression of TGs and profibrotic, proliferation and apoptotic markers was assessed by qPCR. Cell proliferation and soluble and insoluble collagen were determined by ELISA and LC-MS/MS, respectively. TG1 and TG2 were both expressed in neonatal rat cardiomyocytes and fibroblasts before transfection. Other TGs were not detected before and after transfection. TG2 was predominantly expressed and more effectively silenced than TG1. Knocking down TG1 or TG2 significantly modified profibrotic markers mRNA expression in fibroblasts, decreasing connective tissue growth factor (CTGF) and increasing transforming growth factor-β1 compared to the negative siRNA control. Reduced expression of collagen 3A1 was found upon TG1 knockdown, while TG2 knockdown raised α-smooth muscle actin expression. TG2 knockdown further increased fibroblast proliferation and the expression of proliferation marker cyclin D1. Lower insoluble collagen content and collagen cross-linking were evidenced upon silencing TG1 or TG2. Transcript levels of collagen 1A1, fibronectin 1, matrix metalloproteinase-2, cyclin E2, and BCL-2-associated X protein/B-cell lymphoma 2 ratio were strongly correlated with TG1 mRNA expression, whereas TG2 expression correlated strongly with CTGF mRNA abundance. These findings support a functional and signalling role for TG1 and TG2 from fibroblasts in regulating key processes underlying myocardial ECM homeostasis and dysregulation, suggesting that these isoforms could be potential and promising targets for the development of cardiac fibrosis therapies.

Tumour microenvironment in pheochromocytoma and paraganglioma

Pheochromocytomas and Paragangliomas (Pheo/PGL) are rare catecholamine-producing tumours derived from adrenal medulla or from the extra-adrenal paraganglia respectively. Around 10-15% of Pheo/PGL develop metastatic forms and have a poor prognosis with a 37% of mortality rate at 5 years. These tumours have a strong genetic determinism, and the presence of succinate dehydrogenase B (SDHB) mutations are highly associated with metastatic forms. To date, no effective treatment is present for metastatic forms. In addition to cancer cells, the tumour microenvironment (TME) is also composed of non-neoplastic cells and non-cellular components, which are essential for tumour initiation and progression in multiple cancers, including Pheo/PGL. This review, for the first time, provides an overview of the roles of TME cells such as cancer-associated fibroblasts (CAFs) and tumour-associated macrophages (TAMs) on Pheo/PGL growth and progression. Moreover, the functions of the non-cellular components of the TME, among which the most representatives are growth factors, extracellular vesicles and extracellular matrix (ECM) are explored. The importance of succinate as an oncometabolite is emerging and since Pheo/PGL SDH mutated accumulate high levels of succinate, the role of succinate and of its receptor (SUCNR1) in the modulation of the carcinogenesis process is also analysed. Further understanding of the mechanism behind the complicated effects of TME on Pheo/PGL growth and spread could suggest novel therapeutic targets for further clinical treatments.

The Outside-In Journey of Tissue Transglutaminase in Cancer

Tissue transglutaminase (TG2) is a member of the transglutaminase family that catalyzes Ca²⁺-dependent protein crosslinks and hydrolyzes guanosine 5′-triphosphate (GTP). The conformation and functions of TG2 are regulated by Ca²⁺ and GTP levels; the TG2 enzymatically active open conformation is modulated by high Ca²⁺ concentrations, while high intracellular GTP promotes the closed conformation, with inhibition of the TG-ase activity. TG2’s unique characteristics and its ubiquitous distribution in the intracellular compartment, coupled with its secretion in the extracellular matrix, contribute to modulate the functions of the protein. Its aberrant expression has been observed in several cancer types where it was linked to metastatic progression, resistance to chemotherapy, stemness, and worse clinical outcomes. The N-terminal domain of TG2 binds to the 42 kDa gelatin-binding domain of fibronectin with high affinity, facilitating the formation of a complex with β-integrins, essential for cellular adhesion to the matrix. This mechanism allows TG2 to interact with key matrix proteins and to regulate epithelial to mesenchymal transition and stemness. Here, we highlight the current knowledge on TG2 involvement in cancer, focusing on its roles translating extracellular cues into activation of oncogenic programs. Improved understanding of these mechanisms could lead to new therapeutic strategies targeting this multi-functional protein.

Implications of enigmatic transglutaminase 2 (TG2) in cardiac diseases and therapeutic developments

Cardiac diseases are the leading cause of mortality and morbidity worldwide. Mounting evidence suggests that transglutaminases (TGs), tissue TG (TG2) in particular, are involved in numerous molecular responses underlying the pathogenesis of cardiac diseases. The TG family has several intra- and extracellular functions in the human body, including collagen cross-linking, angiogenesis, cell growth, differentiation, migration, adhesion as well as survival. TGs are thiol- and calcium-dependent acyl transferases that catalyze the formation of a covalent bond between the γ-carboxamide group of a glutamine residue and an amine group, thus increasing the stability, rigidity, and stiffness of the myocardial extracellular matrix (ECM). Excessive accumulation of cross-linked collagen leads to increase myocardial stiffness and fibrosis. Beyond TG2 extracellular protein cross-linking action, mounting evidence suggests that this pleiotropic TG isozyme may also promote fibrotic diseases through cell survival and profibrotic pathway activation at the signaling, transcriptional and translational levels. Due to its multiple functions and localizations, TG2 fulfils critical yet incompletely understood roles in myocardial fibrosis and associated heart diseases, such as cardiac hypertrophy, heart failure, and age-related myocardial stiffness under several conditions. This review summarizes current knowledge and existing gaps regarding the ECM-dependent and ECM-independent roles of TG2 and highlights the therapeutic prospects of targeting TG2 to treat cardiac diseases.

Mapping the metabolomic and lipidomic changes in the Bleomycin model of pulmonary fibrosis in young and aged mice

Alterations in metabolic pathways were recently recognized as potential underlying drivers of idiopathic pulmonary fibrosis (IPF), translating into novel therapeutic targets. However, knowledge of metabolic and lipid regulation in fibrotic lungs is limited. To comprehensively characterize metabolic perturbations in the bleomycin mouse model of IPF, we analyzed the metabolome and lipidome by mass spectrometry. We identified increased tissue turnover and repair, evident by enhanced breakdown of proteins, nucleic acids and lipids and extracellular matrix turnover. Energy production was upregulated, including glycolysis, the tricarboxylic acid cycle, glutaminolysis, lactate production and fatty acid oxidation. Higher eicosanoid synthesis indicated inflammatory processes. Because the risk of IPF increases with age, we investigated how age influences metabolomic and lipidomic changes in the bleomycin-induced pulmonary fibrosis model. Surprisingly, except for cytidine, we did not detect any significantly differential metabolites or lipids between old and young bleomycin-treated lungs. Together, we identified metabolomic and lipidomic changes in fibrosis that reflect higher energy demand, proliferation, tissue remodeling, collagen deposition and inflammation, which might serve to improve diagnostic and therapeutic options for fibrotic lung diseases in the future.

Editor's choice: Using bleomycin-induced lung injury as a mouse model for idiopathic pulmonary fibrosis, this study identifies metabolomic and lipidomic changes in fibrosis reflecting higher energy demand, proliferation, tissue remodeling, collagen deposition and inflammation.

Black Phosphorus Nanoparticles Promote Osteogenic Differentiation of EMSCs Through Upregulated TG2 Expression

At bio-safe concentrations, black phosphorus nanoparticles activated TG2, and promote the expression of ECM, which further promoted osteogenic differentiation of EMSCs. From these results, we can conclude that black phosphorus nanoparticles are suitable as biological factors in bone tissue engineering. Black phosphorus nanoparticles (BPs) present excellent biocompatibility and good biodegradability, which have been rigorously studied and proven. However, its utilization in bone tissue engineering fields is still in its infancy. Thus, the main purpose of the present study was to investigate the effects of BPs on osteogenic differentiation of ectodermal mesenchymal stem cell (EMSC) in vitro. Biocompatible BPs with high yield were prepared with a simple and efficient ultrasonication technique. EMSCs were isolated from adult rat nasal respiratory mucosa. Then, we treated EMSCs with BPs at different concentrations in vitro and examined the effect of BPs on osteogenic differentiation of EMSCs. In addition, inhibitor of transglutaminase 2 (TG2) and western blot were used to clarify the mechanism of the promoting effect of BPs on osteogenesis. Our results indicated that BPs could significantly enhance osteogenic differentiation of EMSCs in vitro. Nevertheless, BPs had no effect on EMSCs proliferation. Mechanistically, BPs promoted osteogenesis differentiation of EMSCs through upregulating TG2 expression. These results highlight the advantage of using chemical materials for novel engineering strategies of these highly promising small molecules for bone-tissue regeneration.

Transglutaminase 2 moderates the expansion of mouse abdominal aortic aneurysms

Objective

Previously published work has indicated that transcripts encoding transglutaminase 2 (TG2) increase markedly in a rat model of abdominal aortic aneurysm. This study determines whether TG2 and the related TG, factor XIII-A (FXIII-A), protect against aortic aneurysm development in mice.

Methods

C57BL/6J wild-type, Tgm2 ^-/- knockout, F13a1 ^-/- knockout, and Tgm2 ^-/- /F13a1 ^-/- double knockout mice were subjected to laparotomy and periaortic application of CaCl₂.

Results

Tgm2 ^-/- mice showed slightly greater aortic dilatation at 6 weeks after treatment when compared with wild type. However, vessels from Tgm2 ^-/- mice, but not wild-type mice, continued to dilate up to 6 months after injury and by 24 weeks, a greater number of Tgm2 ^-/- mice had developed aneurysms (16/17 vs 10/19; P = .008). Laparotomy resulted in a high death rate in F13a1 ^-/- knockout mice, more frequently from cardiac complications than from hemorrhage, but among F13a1 ^-/- mice that survived for 6 weeks after CaCl₂ treatment, abdominal aortic aneurysm diameter was unaltered relative to wild-type mice. Laparotomy resulted in a higher death rate among Tgm2 ^-/- /F13a1 ^-/- double knockout mice, owing to an increased frequency of delayed bleeding. Surprisingly, Tgm2 ^-/- /F13a1 ^-/- double knockout mice showed a trend toward decreased dilatation of the aorta 6 weeks after injury, and this finding was replicated in Tgm2 ^-/- /F13a1 ^-/- mice subjected to carotid artery injury. Levels of transcripts encoding TG2 were not increased in the aortas of injured wild-type or F13a1 ^-/- knockout mice relative to uninjured mice, although changes in the levels of other transcripts accorded with previous descriptions of the CaCl₂ aneurysm model in mice.

Conclusions

Knockout of Tgm2, but not F13a1 exacerbates aortic dilatation, suggesting that TG2 confers protection. However, levels of TG2 messenger RNA are not acutely elevated after injury. FXIII-A plays a role in preventing postoperative damage after laparotomy, confirming previous reports that it prevents distal organ damage after trauma. TG2 promotes wound healing after surgery and, in its absence, the bleeding diathesis associated with FXIII-A deficiency is further exposed.

Probing tissue transglutaminase mediated vascular smooth muscle cell aging using a novel transamidation-deficient Tgm2-C277S mouse model

Tissue transglutaminase (TG2), a multifunctional protein of the transglutaminase family, has putative transamidation-independent functions in aging-associated vascular stiffening and dysfunction. Developing preclinical models will be critical to fully understand the physiologic relevance of TG2's transamidation-independent activity and to identify the specific function of TG2 for therapeutic targeting. Therefore, in this study, we harnessed CRISPR-Cas9 gene editing technology to introduce a mutation at cysteine 277 in the active site of the mouse Tgm2 gene. Heterozygous and homozygous Tgm2-C277S mice were phenotypically normal and were born at the expected Mendelian frequency. TG2 protein was ubiquitously expressed in the Tgm2-C277S mice at levels similar to those of wild-type (WT) mice. In the Tgm2-C277S mice, TG2 transglutaminase function was successfully obliterated, but the transamidation-independent functions ascribed to GTP, fibronectin, and integrin binding were preserved. In vitro, a remodeling stimulus led to the significant loss of vascular compliance in WT mice, but not in the Tgm2-C277S or TG2^-/- mice. Vascular stiffness increased with age in WT mice, as measured by pulse-wave velocity and tensile testing. Tgm2-C277S mice were protected from age-associated vascular stiffening, and TG2 knockout yielded further protection. Together, these studies show that TG2 contributes significantly to overall vascular modulus and vasoreactivity independent of its transamidation function, but that transamidation activity is a significant cause of vascular matrix stiffening during aging. Finally, the Tgm2-C277S mice can be used for in vivo studies to explore the transamidation-independent roles of TG2 in physiology and pathophysiology.

Transglutaminase 2: a novel therapeutic target for idiopathic pulmonary fibrosis using selective small molecule inhibitors

This study investigates the effects of a site-directed TG2-selective inhibitor on the lung myofibroblast phenotype and ECM deposition to elucidate TG2 as a novel therapeutic target in idiopathic pulmonary fibrosis (IPF)-an incurable progressive fibrotic disease. IPF fibroblasts showed increased expression of TG2, α smooth muscle actin (αSMA) and fibronectin (FN) with increased extracellular TG2 and transforming growth factor β1 (TGFβ1) compared to normal human lung fibroblasts (NHLFs) which do not express αSMA and express lower levels of FN. The myofibroblast phenotype shown by IPF fibroblasts could be reversed by selective TG2 inhibition with a reduction in matrix FN and TGFβ1 deposition. TG2 transduction or TGFβ1 treatment of NHLFs led to a comparable phenotype to that of IPF fibroblasts which was reversible following selective TG2 inhibition. Addition of exogenous TG2 to NHLFs also induced the myofibroblast phenotype by a mechanism involving TGFβ1 activation which could be ameliorated by selective TG2 inhibition. SMAD3-deleted IPF fibroblasts via CRISPR-cas9 genome editing, showed reduced TG2 protein levels following TGFβ1 stimulation. This study demonstrates a key role for TG2 in the induction of the myofibroblast phenotype and shows the potential for TG2-selective inhibitors as therapeutic agents for the treatment of fibrotic lung diseases like IPF.

Epithelial cell dysfunction in coeliac disease

The intestinal epithelium limits host-luminal interactions and maintains gut homeostasis. Breakdown of the epithelial barrier and villous atrophy are hallmarks of coeliac disease. Besides the well characterized immune-mediated epithelial damage induced in coeliac mucosa, constitutional changes and early gluten direct effects disturb intestinal epithelial cells. The subsequent modifications in key epithelial signaling pathways leads to outnumbered immature epithelial cells that, in turn, facilitate epithelial dysfunction, promote crypt hyperplasia, and increase intestinal permeability. Consequently, underlying immune cells have a greater access to gluten, which boosts the proinflammatory immune response against gluten and positively feedback the epithelial damage loop. Gluten-free diet is an indispensable treatment for coeliac disease patients, but additional therapies are under development, including those that reinforce intestinal epithelial healing. In this chapter, we provide an overview of intestinal epithelial cell disturbances that develop during gluten intake in coeliac disease mucosa.

Specific and direct modulation of the interaction between adhesion GPCR GPR56/ADGRG1 and tissue transglutaminase 2 using synthetic ligands

Blocking the interaction between cell-surface receptors and their ligands is a proven therapeutic strategy. Adhesion G protein-coupled receptors (aGPCRs) are key cell-surface receptors that regulate numerous pathophysiological processes, and their large extracellular regions (ECRs) mediate ligand binding and function. The aGPCR GPR56/ADGRG1 regulates central nervous system myelination and melanoma progression by interacting with its ligand, tissue transglutaminase 2 (TG2), but the molecular basis for this interaction is largely undefined. Here, we show that the C-terminal portion of TG2 directly interacted with the GPR56 ECR with high-nanomolar affinity, and used site-directed mutagenesis to identify a patch of conserved residues on the pentraxin/laminin-neurexin-sex-hormone-binding-globulin-like (PLL) domain of GPR56 as the TG2 binding site. Importantly, we also show that the GPR56-TG2 interaction was blocked by previously-reported synthetic proteins, termed monobodies, that bind the GPR56 ECR in a domain- and species-specific manner. This work provides unique tools to modulate aGPCR-ligand binding and establishes a foundation for the development of aGPCR-targeted therapeutics.

Transglutaminase 3: The Involvement in Epithelial Differentiation and Cancer

Transglutaminases (TGMs) contribute to the formation of rigid, insoluble macromolecular complexes, which are essential for the epidermis and hair follicles to perform protective and barrier functions against the environment. During differentiation, epidermal keratinocytes undergo structural alterations being transformed into cornified cells, which constitute a highly tough outermost layer of the epidermis, the stratum corneum. Similar processes occur during the hardening of the hair follicle and the hair shaft, which is provided by the enzymatic cross-linking of the structural proteins and keratin intermediate filaments. TGM3, also known as epidermal TGM, is one of the pivotal enzymes responsible for the formation of protein polymers in the epidermis and the hair follicle. Numerous studies have shown that TGM3 is extensively involved in epidermal and hair follicle physiology and pathology. However, the roles of TGM3, its substrates, and its importance for the integument system are not fully understood. Here, we summarize the main advances that have recently been achieved in TGM3 analyses in skin and hair follicle biology and also in understanding the functional role of TGM3 in human tumor pathology as well as the reliability of its prognostic clinical usage as a cancer diagnosis biomarker. This review also focuses on human and murine hair follicle abnormalities connected with TGM3 mutations.

Metformin attenuates TGF-β1-induced pulmonary fibrosis through inhibition of transglutaminase 2 and subsequent TGF-β pathways

The purpose of this study was to confirm whether metformin can attenuate TGF-β1-induced pulmonary fibrosis through inhibition of transglutaminase 2 (TG2) and subsequent TGF-β pathways. In vitro, MTT assay and Annexin V-FITC/PI staining assay were performed to determine the effect of metformin on the proliferation and apoptosis of human fetal lung fibroblasts (HFL-1 cell). Protein expression of TG2, Collagen I (Col I) and α-smooth muscle actin (α-SMA) were determined by western blot. To further confirm the relationship between TG2 and the anti-fibrotic effect of metformin, TG2 siRNA and TG2 overexpression plasmid were used to interfere the expression of TG2. A bleomycin-induced pulmonary fibrosis model was employed to determine the in vivo inhibitory effect of metformin. The concentrations of TG2, both in supernatants of cells and serum of rats, were determined by ELISA assay. Our results showed that metformin concentration-dependently inhibited the proliferation and promoted the apoptosis of TGF-β1-stimulated HFL-1 cells. The protein expressions of TG2, Col I and α-SMA stimulated by TGF-β1 were decreased after metformin intervention, which was confirmed in both siRNAs and plasmids treatment conditions. In vivo, metformin attenuated bleomycin-induced pulmonary fibrosis as demonstrated by H&E and Masson staining, as well as the protein expressions of Col I and α-SMA. Besides, phosphorylated SMAD2, phosphorylated SMAD3, phosphorylated Akt and phosphorylated ERK1/2 were all significantly increased after bleomycin treatment and decreased to normal levels after metformin intervention. Taken together, our results demonstrated that metformin can attenuate TGF-β1-induced pulmonary fibrosis, at least partly, through inhibition of TG2 and subsequent TGF-β pathways.

Oláh A, Fésüs L, Mádi A. Transglutaminase 2 Has Metabolic and Vascular Regulatory Functions Revealed by In Vivo Activation of Alpha1-Adrenergic Receptor

The multifunctional tissue transglutaminase has been demonstrated to act as α1-adrenergic receptor-coupled G protein with GTPase activity in several cell types. To explore further the pathophysiological significance of this function we investigated the in vivo effects of the α1-adrenergic receptor agonist phenylephrine comparing responses in wild type and TG2-/- mice. Injection of phenylephrine, but not a beta3-adrenergic agonist (CL-316,243), resulted in the long-term decline of the respiratory exchange ratio and lower lactate concentration in TG2-/- mice indicating they preferred to utilize fatty acids instead of glucose as fuels. Measurement of tail blood pressure revealed that the vasoconstrictive effect of phenylephrine was milder in TG2-/- mice leading to lower levels of lactate dehydrogenase (LDH) isoenzymes in blood. LDH isoenzyme patterns indicated more damage in lung, liver, kidney, skeletal, and cardiac muscle of wild type mice; the latter was confirmed by a higher level of heart-specific CK-MB. Our data suggest that TG2 as an α1-adrenergic receptor-coupled G protein has important regulatory functions in alpha1-adrenergic receptor-mediated metabolic processes and vascular functions.

Transglutaminase 3 Reduces the Severity of Psoriasis in Imiquimod-Treated Mouse Skin

Four transglutaminase (TG) isoforms have been detected in epidermal keratinocytes: TG1, TG2, TG3, and TG5. Except for TG1 and TG3, their contribution to keratinocyte development and structure remains undefined. In this paper, we focused on the roles of TG2 and TG3 in imiquimod-induced psoriasis in mouse skin. We evaluated the severity of psoriasis markers in the skin of imiquimod-treated TG3 null and TG2 null mice. Our results showed that compromised TG3KO mouse skin was more responsive than WT or TG2KO mouse skin to the action of the pro-inflammatory drug imiquimod.

Mapping of Transglutaminase-2 Sites of Human Salivary Small Basic Proline-Rich Proteins by HPLC-High-Resolution ESI-MS/MS

Because of the distinctive features of the oral cavity, the determination of the proteins involved in the formation of the "oral protein pellicle" is demanding. The present study investigated the susceptibility of several human basic proline-rich peptides, named P-H, P-D, P-F, P-J, and II-2, as substrates of transglutaminase-2. The reactivity of the P-C peptide and statherin was also investigated. Peptides purified from human whole saliva were incubated with the enzyme in the presence or in the absence of monodansyl-cadaverine. Mass spectrometry analyses of the reaction products highlighted that P-H and P-D (P₃₂ and A₃₂ variants) were active substrates, II-2 was less reactive, and P-F and P-J showed very low reactivity. P-C and statherin were highly reactive. All of the peptides formed cyclo derivatives, and only specific glutamine residues were involved in the cycle formation and reacted with monodansyl-cadaverine: Q₂₉ of P-H, Q₃₇ of P-D, Q₂₁ of II-2, Q₄₁ of P-C, and Q₃₇ of statherin were the principal reactive residues. One or two secondary glutamine residues of only P-H, P-D P₃₂, P-C, and statherin were hierarchically susceptible to the reaction with monodansyl-cadaverine. MS and MS/MS data were deposited to the ProteomeXchange Consortium ( http://www.ebi.ac.uk/pride ) via the PRIDE partner repository with the data set identifier PXD014658.

Transglutaminase 2 limits the extravasation and the resultant myocardial fibrosis associated with factor XIII-A deficiency

Background and aims

Transglutaminase (TG) 2 and Factor (F) XIII-A have both been implicated in cardiovascular protection and repair. This study was designed to differentiate between two competing hypotheses: that TG2 and FXIII-A mediate these functions in mice by fulfilling separate roles, or that they act redundantly in this respect.

Methods

Atherosclerosis was assessed in brachiocephalic artery plaques of fat-fed mixed strain apolipoprotein (Apo)e deficient mice that lacked either or both transglutaminases. Cardiac fibrosis was assessed both in the mixed strain mice and also in C57BL/6J Apoe expressing mice lacking either or both transglutaminases.

Results

No difference was found in the density of buried fibrous caps within brachiocephalic plaques from mice expressing or lacking these transglutaminases. Cardiac fibrosis developed in both Apoe/F13a1 double knockout and F13a1 single knockout mice, but not in Tgm2 knockout mice. However, concomitant Tgm2 knockout markedly increased fibrosis, as apparent in both Apoe/Tgm2/F13a1 knockout and Tgm2/F13a1 knockout mice. Amongst F13a1 knockout and Tgm2/F13a1 knockout mice, the extent of fibrosis correlated with hemosiderin deposition, suggesting that TG2 limits the extravasation of blood in the myocardium, which in turn reduces the pro-fibrotic stimulus. The resulting fibrosis was interstitial in nature and caused only minor changes in cardiac function.

Conclusions

These studies confirm that FXIII-A and TG2 fulfil different roles in the mouse myocardium. FXIII-A protects against vascular leakage while TG2 contributes to the stability or repair of the vasculature. The protective function of TG2 must be considered when designing clinical anti-fibrotic therapies based upon FXIII-A or TG2 inhibition.

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Double transglutaminase 2 and Factor XIII-A knockout exacerbates cardiac fibrosis.

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Double knockout does not promote the growth of, or destabilise, brachiocephalic plaques.

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FXIII-A in resident cardiac macrophages does not protect against cardiac fibrosis.

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FXIII-A in inflammatory macrophages may contribute to protection against fibrosis.

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Transglutaminase 2 and Factor XIII-A protect against extravasation of blood.

Integrins expressed on the surface of human endometrial stromal cells derived from a female patient experiencing spontaneous abortion

Here, as a basic study in revealing the correlation between extracellular matrix components and spontaneous abortion, we defined the types of integrins expressed on the surface of endometrial stromal (ES) cells retrieved from the uterus of a patient experiencing spontaneous abortion. For these, the types of integrin subunits in the ES cells retrieved from a woman with spontaneous abortion were identified at the transcriptional and translational levels, and functional assay was conducted for confirming the combinations of integrin α and β subunits. Among the genes encoding 25 integrin subunits, significantly high transcription was seen in integrins α₁, α₂, α₃, α₄, α₅, α_V, β₁, β₃, and β₅. Translation of integrins α₁, α₃, α₅, α_V, and β₁ on the cell surface was detected in almost all ES cells, whereas integrins α₂, α₄, β₃, and β₄ were expressed translationally only in some ES cells. Subsequently, ES cells showed significantly increased adhesion to collagen I, laminin, fibronectin, and vitronectin, and functional blocking of integrin α₁, α₃, α₅, and α_V significantly inhibited adhesion to these molecules. These results demonstrated that active heterodimers composed of integrins α₁β₁, α₃β₁, α₅β₁, and α_Vβ₁ were co-localized on the surface of ES cells derived from a patient experiencing spontaneous abortion.

Characterization of Tissue Transglutaminase as a Potential Biomarker for Tissue Response toward Biomaterials

Tissue transglutaminase (TGase 2) is proposed to be important for biomaterial-tissue interactions due to its presence and versatile functions in the extracellular environment. TGase 2 catalyzes the cross-linking of proteins through its Ca²⁺-dependent acyltransferase activity. Moreover, it enhances the interactions between fibronectin and integrins, which in turn mediates the adhesion, migration, and motility of the cells. TGase 2 is also a key player in the pathogenesis of fibrosis. In this study, we investigated whether TGase 2 is present at the biomaterial-tissue interface and might serve as an informative biomarker for the visualization of tissue response toward gelatin-based biomaterials. Two differently cross-linked hydrogels were used, which were obtained by the reaction of gelatin with lysine diisocyanate ethyl ester. The overall expression of TGase 2 by endothelial cells, macrophages, and granulocytes was partly influenced by contact to the hydrogels or their degradation products, although no clear correlation was evidenced. In contrast, the secretion of TGase 2 differed remarkably between the different cells, indicating that it might be involved in the cellular reaction toward gelatin-based hydrogels. The hydrogels were implanted subcutaneously in immunocompetent, hairless SKH1-Elite mice. Ex vivo immunohistochemical analysis of tissue sections over 112 days revealed enhanced expression of TGase 2 around the hydrogels, in particular at days 14 and 21 post-implantation. The incorporation of fluorescently labeled cadaverine derivatives for the detection of active TGase 2 was in accordance with the results of the expression analysis. The presence of an irreversible inhibitor of TGase 2 led to attenuated incorporation of the cadaverines, which verified the catalytic action of TGase 2. Our in vitro and ex vivo results verified TGase 2 as a potential biomarker for tissue response toward gelatin-based hydrogels. In vivo, no TGase 2 activity was detectable, which is mainly attributed to the unfavorable physicochemical properties of the cadaverine probe used.

Transglutaminase 2 maintains a colorectal cancer stem phenotype by regulating epithelial-mesenchymal transition

Transglutaminase 2 (TG2), a multifunctional protein, is reported in regulating the cancer stem cell (CSC) phenotype in various cancers. Our previous work suggested the link between TG2 and Epithelial-Mesenchymal Transition (EMT) in colorectal cancer (CRC). Here we demonstrate the importance of TG2 in CSC development in human CRC cell lines HCT116 and SW620. CRC spheroid cells showed increased CSC characteristics over their monolayer cells with increased expression of CD44 and over expression of Oct3/4, Sox2 and Nanog. They also showed increased EMT and invasiveness, and enhanced expression of TG2. TG2 inhibition by its selective inhibitor 1-155 reduced both spheroid formation and invasive potential of the spheroid cells. β-catenin, a mediator of stem cell maintenance, was overexpressed in the spheroid cells and could be attenuated by TG2 inhibition. Spheroid cells possessed increased angiogenesis stimulating ability via overexpression of Vascular Endothelial Growth Factor (VEGF). Increased VEGF was present in the culture media from spheroid cells when compared to monolayer cultures which could be reduced by selective inhibition by 1-155. Stemness and malignancy in the colorectal spheroid cells was associated with increased TG2, EMT, β-catenin and VEGF. Here we demonstrate that inhibiting TG2 reduces both stemness and angiogenic stimulating activity in CRC.

Pathogenesis of fibrostenosing Crohn's disease

Crohn's disease (CD) is a chronic inflammatory disease, which could affect any part of the gastrointestinal tract. A severe complication of CD is fibrosis-associated strictures, which can cause bowel obstruction. Unfortunately, there is no specific antifibrotic therapy available. More than 80% of the patients with CD will have to undergo at least 1 surgery in their life and recurrence of strictures after surgery is common. Investigations on the mechanism of fibrostenosing CD have revealed that fibrosis is mainly driven by expansion of mesenchymal cells including fibroblasts, myofibroblasts, and smooth muscle cells. Being exposed to a pro-fibrotic milieu, these cells increase the secretion of extracellular matrix, as well as crosslinking enzymes, which drive tissue stiffness and remodeling. Fibrogenesis can become independent of inflammation in later stages of disease, which offers unique therapeutic potential. Exciting new evidence suggests smooth muscle cell hyperplasia as a strong contributor to luminal narrowing in fibrostenotic CD. Approval of new drugs in other fibrotic diseases, such as idiopathic pulmonary fibrosis, as well as new targets associated with fibrosis found in CD, such as cadherins or specific integrins, shed light on the development of novel antifibrotic approaches in CD.

Transglutaminase 2: The Maestro of the Oncogenic Mediators in Renal Cell Carcinoma

Transglutaminase 2 (TG2) is a multifunctional crosslinking enzyme that displays transamidation, protein disulfide isomerase, protein kinase, as well as GTPase and ATPase activities. TG2 can also act as an adhesion molecule involved in the syndecan and integrin receptor signaling. In recent years, TG2 was implicated in cancer progression, survival, invasion, migration, and stemness of many cancer types, including renal cell carcinoma (RCC). Von Hippel-Lindau mutations leading to the subsequent activation of Hypoxia Inducible Factor (HIF)-1-mediated signaling pathways, survival signaling via the PI3K/Akt pathway resulting in Epithelial Mesenchymal Transition (EMT) metastasis and angiogenesis are the main factors in RCC progression. A number of studies have shown that TG2 was important in HIF-1- and PI3K-mediated signaling, VHL and p53 stabilization, glycolytic metabolism and migratory phenotype in RCC. This review focuses on the role of TG2 in the regulation of molecular pathways nurturing not only the development and propagation of RCC, but also drug-resistance and metastatic potential.

Notch ligand Delta-like 4 induces epigenetic regulation of Treg cell differentiation and function in viral infection

Notch ligand Delta-like ligand 4 (DLL4) has been shown to regulate CD4 T-cell differentiation, including regulatory T cells (T_reg). Epigenetic alterations, which include histone modifications, are critical in cell differentiation decisions. Recent genome-wide studies demonstrated that T_reg have increased trimethylation on histone H3 at lysine 4 (H3K4me3) around the T_reg master transcription factor, Foxp3 loci. Here we report that DLL4 dynamically increased H3K4 methylation around the Foxp3 locus that was dependent upon upregulated SET and MYDN domain containing protein 3 (SMYD3). DLL4 promoted Smyd3 through the canonical Notch pathway in iT_reg differentiation. DLL4 inhibition during pulmonary respiratory syncytial virus (RSV) infection decreased Smyd3 expression and Foxp3 expression in T_reg leading to increased Il17a. On the other hand, DLL4 supported Il10 expression in vitro and in vivo, which was also partially dependent upon SMYD3. Using genome-wide unbiased mRNA sequencing, novel sets of DLL4- and Smyd3-dependent differentially expressed genes were discovered, including lymphocyte-activation gene 3 (Lag3), a checkpoint inhibitor that has been identified for modulating Th cell activation. Together, our data demonstrate a novel mechanism of DLL4/Notch-induced Smyd3 epigenetic pathways that maintain regulatory CD4 T cells in viral infections.

Tissue transglutaminase induction in the pressure-overloaded myocardium regulates matrix remodelling

Aims

Tissue transglutaminase (tTG) is induced in injured and remodelling tissues, and modulates cellular phenotype, while contributing to matrix cross-linking. Our study tested the hypothesis that tTG may be expressed in the pressure-overloaded myocardium, and may regulate cardiac function, myocardial fibrosis and chamber remodelling.

Methods and results

In order to test the hypothesis, wild-type and tTG null mice were subjected to pressure overload induced through transverse aortic constriction. Moreover, we used isolated cardiac fibroblasts and macrophages to dissect the mechanisms of tTG-mediated actions. tTG expression was upregulated in the pressure-overloaded mouse heart and was localized in cardiomyocytes, interstitial cells, and in the extracellular matrix. In contrast, expression of transglutaminases 1, 3, 4, 5, 6, 7 and FXIII was not induced in the remodelling myocardium. In vitro, transforming growth factor (TGF)-β1 stimulated tTG synthesis in cardiac fibroblasts and in macrophages through distinct signalling pathways. tTG null mice had increased mortality and enhanced ventricular dilation following pressure overload, but were protected from diastolic dysfunction. tTG loss was associated with a hypercellular cardiac interstitium, reduced collagen cross-linking, and with accentuated matrix metalloproteinase (MMP)2 activity in the pressure-overloaded myocardium. In vitro, tTG did not modulate TGF-β-mediated responses in cardiac fibroblasts; however, tTG loss was associated with accentuated proliferative activity. Moreover, when bound to the matrix, recombinant tTG induced synthesis of tissue inhibitor of metalloproteinases (TIMP)-1 through transamidase-independent actions.

Conclusions

Following pressure overload, endogenous tTG mediates matrix cross-linking, while protecting the remodelling myocardium from dilation by exerting matrix-preserving actions.

Spotlight on the transglutaminase 2 gene: a focus on genomic and transcriptional aspects

The type 2 isoenzyme is the most widely expressed transglutaminase in mammals displaying several intra- and extracellular activities depending on its location (protein modification, modulation of gene expression, membrane signalling and stabilization of cellular interactions with the extracellular matrix) in relation to cell death, survival and differentiation. In contrast with the appreciable knowledge about the regulation of the enzymatic activities, much less is known concerning its inducible expression, which is altered in inflammatory and neoplastic diseases. In this context, we first summarize the gene's basic features including single-nucleotide polymorphism characterization, epigenetic DNA methylation and identification of regulatory regions and of transcription factor-binding sites at the gene promoter, which could concur to direct gene expression. Further aspects related to alternative splicing events and to ncRNAs (microRNAs and lncRNAs) are involved in the modulation of its expression. Notably, this important gene displays transcriptional variants relevant for the protein's function with the occurrence of at least seven transcripts which support the synthesis of five isoforms with modified catalytic activities. The different expression of the TG2 (type 2 transglutaminase) variants might be useful for dictating the multiple biological features of the protein and their alterations in pathology, as well as from a therapeutic perspective.

Pharmacologic inhibition of the enzymatic effects of tissue transglutaminase reduces cardiac fibrosis and attenuates cardiomyocyte hypertrophy following pressure overload

Tissue transglutaminase (tTG) is a multifunctional protein with a wide range of enzymatic and non-enzymatic functions. We have recently demonstrated that tTG expression is upregulated in the pressure-overloaded myocardium and exerts fibrogenic actions promoting diastolic dysfunction, while preventing chamber dilation. Our current investigation dissects the in vivo and in vitro roles of the enzymatic effects of tTG on fibrotic remodeling in pressure-overloaded myocardium. Using a mouse model of transverse aortic constriction, we demonstrated perivascular and interstitial tTG activation in the remodeling pressure-overloaded heart. tTG inhibition through administration of the selective small molecule tTG inhibitor ERW1041E attenuated left ventricular diastolic dysfunction and reduced cardiomyocyte hypertrophy and interstitial fibrosis in the pressure-overloaded heart, without affecting chamber dimensions and ejection fraction. In vivo, tTG inhibition markedly reduced myocardial collagen mRNA and protein levels and attenuated transcription of fibrosis-associated genes. In contrast, addition of exogenous recombinant tTG to fibroblast-populated collagen pads had no significant effects on collagen transcription, and instead increased synthesis of matrix metalloproteinase (MMP)3 and tissue inhibitor of metalloproteinases (TIMP)1 through transamidase-independent actions. However, enzymatic effects of matrix-bound tTG increased the thickness of pericellular collagen in fibroblast-populated pads. tTG exerts distinct enzymatic and non-enzymatic functions in the remodeling pressure-overloaded heart. The enzymatic effects of tTG are fibrogenic and promote diastolic dysfunction, but do not directly modulate the pro-fibrotic transcriptional program of fibroblasts. Targeting transamidase-dependent actions of tTG may be a promising therapeutic strategy in patients with heart failure and fibrosis-associated diastolic dysfunction.

Cancer Associated Fibroblasts: The Architects of Stroma Remodeling

Fibroblasts have exceptional phenotypic plasticity and capability to secrete vast amount of soluble factors, extracellular matrix components and extracellular vesicles. While in physiological conditions this makes fibroblasts master regulators of tissue homeostasis and healing of injured tissues, in solid tumors cancer associated fibroblasts (CAFs) co-evolve with the disease, and alter the biochemical and physical structure of the tumor microenvironment, as well as the behavior of the surrounding stromal and cancer cells. Thus CAFs are fundamental regulators of tumor progression and influence response to therapeutic treatments. Increasing efforts are devoted to better understand the biology of CAFs to bring insights to develop complementary strategies to target this cell type in cancer. Here we highlight components of the tumor microenvironment that play key roles in cancer progression and invasion, and provide an extensive overview of past and emerging understanding of CAF biology as well as the contribution that MS-based proteomics has made to this field.

Screening pathogenic genes in oral squamous cell carcinoma based on the mRNA expression microarray data

Oral squamous cell carcinoma (OSCC) is one of the most common malignancies and its survival rate has barely improved over the past few decades. The purpose of this study was to screen pathogenic genes of OSCC via microarray analysis. The mRNA expression microarray datasets (GSE2280 and GSE3524) were downloaded from the Gene Expression Omnibus (GEO) database. In GSE2280, there were 22 OSCC samples without metastasis and 5 OSCC samples with lymph node metastasis. In GSE3524, there were 16 OSCC samples and 4 normal tissue samples. The differentially expressed genes (DEGs) in OSCC samples with lymph node metastasis compared with those without metastasis (named as DEGs-1), and the DEGs in OSCC samples compared with normal tissue samples (named as DEGs-2), were obtained via limma package. The Database for Annotation, Visualization and Integrated Discovery (DAVID) was used to perform the functional enrichment analyses of DEGs-1 and DEGs-2. The miRNA-gene pairs of overlaps among DEGs were screened out with the TargetScan database, and the miRNA-gene regulated network was constructed by Cytoscape software. A total of 233 and 410 DEGs were identified in the sets of DEGs-1 and DEGs-2, respectively. DEGs-1 were enriched in 188 Gene Ontology (GO) terms and 8 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, and DEGs-2 were enriched in 228 GO terms and 6 KEGG pathways. In total, 126 nodes and 135 regulated pairs were involved in the miRNA-gene regulated network. Our study indicated that transglutaminase 2 (TGM2) and Islet 1 (ISL1) may be biomarkers of OSCC and their metastases. Moreover, it provided some potential pathogenic genes (e.g. P2RY2 and RAPGEFL1) in OSCC.

Biomimetic tumor microenvironments based on collagen matrices

This review provides an overview of the current approaches to engineer defined 3D matrices for the investigation of tumor cell behaviorin vitro, with a focus on collagen-based fibrillar systems.

Tissue transglutaminase induces Epithelial-Mesenchymal-Transition and the acquisition of stem cell like characteristics in colorectal cancer cells

Human colon cancer cell lines (CRCs) RKO, SW480 and SW620 were investigated for TG2 involvement in tumour advancement and aggression. TG2 expression correlated with tumour advancement and expression of markers of epithelial-mesenchymal transition (EMT). The metastatic cell line SW620 showed high TG2 expression compared to the primary tumour cell lines SW480 and RKO and could form tumour spheroids under non- adherent conditions. TG2 manipulation in the CRCs by shRNA or TG2 transduction confirmed the relationship between TG2 and EMT. TGFβ1 expression in CRC cells, and its level in the cell medium and extracellular matrix was increased in primary tumour CRCs overexpressing TG2 and could regulate TG2 expression and EMT by both canonical (RKO) and non-canonical (RKO and SW480) signalling. TGFβ1 regulation was not observed in the metastatic SW620 cell line, but TG2 knockdown or inhibition in SW620 reversed EMT. In SW620, TG2 expression and EMT was associated with increased presence of nuclear β-catenin which could be mediated by association of TG2 with the Wnt signalling co-receptor LRP5. TG2 inhibition/knockdown increased interaction between β-catenin and ubiquitin shown by co-immunoprecipitation, suggesting that TG2 could be important in β-catenin regulation. β-Catenin and TG2 was also upregulated in SW620 spheroid cells enriched with cancer stem cell marker CD44 and TG2 inhibition/knockdown reduced the spheroid forming potential of SW620 cells. Our data suggests that TG2 could hold both prognostic and therapeutic significance in colon cancer.

Thioredoxin-Interact ing-Pro t e in [TXNIP] and Transglutaminase 2 [TGM2] Expression in Meningiomas of Different Grades and the Role of Their Expression in Meningioma Recurrence and Prognosis

Background: Meningiomas are common central nervous system (CNS) tumors that account for thirty percent of primary intracranial tumors.. The accuracy of predicting meningioma recurrence and progression is not enough. So, there is a real need for discovering recent factors for identification of the relapse risk, progression rates, which patients will need aggressive treatment and predicting and improving patients’ survival. Thioredoxin-interacting-protein [TXNIP] is an alpha-arrestin-protein family member that is mapped on chromosome 1-q21–22 and is found to participate in cellular redox reactions regulations and control. Transglutaminase 2 (TGM2) is a transglutaminase enzyme family member that is found in many human cells, it may act as an enzyme, a structural protein and also has multiple roles in many cellular activities. Aim of our study: It was to explore the expression of TXNIP, TGM2 and Ki-67 using immunohistochemistry in different pathological grades of meningiomas, and to investigate the relevance between their expressions, clinicopathological criteria, disease recurrence and prognosis of meningioma patients. Methods: we included 50 cases of meningioma of different pathological grades; all patients were managed according to their grade by surgery alone, with radiotherapy or combined modalities. Sections from paraffin blocks prepared from samples of all patients stained by TXNIP, TGM2 and Ki-67 using immunohistochemistry. Results: high expression of TXNIP in 28 out of 50 (56%) cases of meningioma of different pathological grades and was positively correlated with meningioma lower grade, low KI labeling index (p=0.000), adequacy of resection, negatively correlated with high incidence of recurrence after surgery and it was negatively correlated with meningioma higher pathological grades (p=0.000). We detected high expression of TGM2 in 21 out of 50 (42%) cases of meningioma and it was positively correlated with meningioma higher grade (p= 0.002), high KI labeling index (p=0.000), high incidence of recurrence after surgery, progression to higher pathological grades and was negatively correlated with adequacy of resection of meningioma (p=0.000). Conclusion: There is inverse relation between both [TXNIP and TGM2 expression in meningiomas and the combination of decreased expression of TXNIP and increased expression of TGM2 could predict risk of meningioma recurrence and progression in to higher pathological grades.

Browning deficiency and low mobilization of fatty acids in gonadal white adipose tissue leads to decreased cold-tolerance of transglutaminase 2 knock-out mice

During cold-exposure 'beige' adipocytes with increased mitochondrial content are activated in white adipose tissue (WAT). These cells, similarly to brown adipose tissue (BAT), dissipate stored chemical energy in the form of heat with the help of uncoupling protein 1 (UCP1). We investigated the effect of tissue transglutaminase (TG2) ablation on the function of ATs in mice. Although TG2^+/+ and TG2^-/- mice had the same amount of WAT and BAT, we found that TG2^+/+ animals could tolerate acute cold exposure for 4h, whereas TG2^-/- mice only for 3h. Both TG2^-/- and TG2^+/+ animals used up half of the triacylglycerol content of subcutaneous WAT (SCAT) after 3h treatment; however, TG2^-/- mice still possessed markedly whiter and higher amount of gonadal WAT (GONAT) as reflected in the larger size of adipocytes and lower free fatty acid levels in serum. Furthermore, lower expression of 'beige' marker genes such as UCP1, TBX1 and TNFRFS9 was observed after cold exposure in GONAT of TG2^-/- mice, paralleled with a lower level of UCP1 protein and a decreased mitochondrial content. The detected changes in gene expression of Resistin and Adiponectin did not provoke glucose intolerance in the investigated TG2^-/- mice, and TG2 deletion did not influence adrenaline, noradrenaline, glucagon and insulin production. Our data suggest that TG2 has a tissue-specific role in GONAT function and browning, which becomes apparent under acute cold exposure.

The proteomic profile of a mouse model of proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) develops as a complication of retinal detachment surgery and represents a devastating condition leading to serious vision loss. A good animal model that permits extensive functional studies and drug testing is crucial in finding better therapeutic modalities for PVR. A previously established mouse model, using dispase injection, was analyzed from the proteomic point of view, examining global protein profile changes by 2D electrophoresis, image analysis and HPLC–tandem mass spectrometry‐based protein identification. The easy applicability of the mouse model was used to study the role of transglutaminase 2 (TG2) in PVR formation by proteomic examination of dispase‐induced TG2 knockout vitreous samples. Our data demonstrate that, despite the altered appearance of crystallin proteins, the lack of TG2 did not prevent the development of PVR.

Secreted CLIC3 drives cancer progression through its glutathione-dependent oxidoreductase activity

The secretome of cancer and stromal cells generates a microenvironment that contributes to tumour cell invasion and angiogenesis. Here we compare the secretome of human mammary normal and cancer-associated fibroblasts (CAFs). We discover that the chloride intracellular channel protein 3 (CLIC3) is an abundant component of the CAF secretome. Secreted CLIC3 promotes invasive behaviour of endothelial cells to drive angiogenesis and increases invasiveness of cancer cells both in vivo and in 3D cell culture models, and this requires active transglutaminase-2 (TGM2). CLIC3 acts as a glutathione-dependent oxidoreductase that reduces TGM2 and regulates TGM2 binding to its cofactors. Finally, CLIC3 is also secreted by cancer cells, is abundant in the stromal and tumour compartments of aggressive ovarian cancers and its levels correlate with poor clinical outcome. This work reveals a previously undescribed invasive mechanism whereby the secretion of a glutathione-dependent oxidoreductase drives angiogenesis and cancer progression by promoting TGM2-dependent invasion.

Dermatan sulfate is a player in the transglutaminase 2 interaction network

Transglutaminase 2 (TG2) is a multifunctional protein that is primarily engaged in cell adhesion/signaling or shows Ca2+-dependent transglutaminase activity in the extracellular space of tissues. This latter action leads to the cross-linking of the extracellular matrix (ECM) proteins. The enhanced extracellular expression of TG2 is associated with processes such as wound healing, fibrosis or vascular remodeling that are also characterized by a high deposition of dermatan sulfate (DS) proteoglycans in the ECM. However, it is unknown whether DS may bind to TG2 or affect its function. Using the plasmon surface resonance method, we showed that DS chains, especially those of biglycan, are good binding partners for TG2. The interaction has some requirements as to the DS structure. The competitive effect of heparin on DS binding to TG2 suggests that both glycosaminoglycans occupy the same binding site(s) on the protein molecule. An occurrence of the DS-TG2 interaction was confirmed by the co-immunoprecipitation of this protein with native decorin that is a DS-bearing proteoglycan rather than with the decorin core protein. Moreover, in vivo DS is responsible for both TG2 binding and the regulation of the location of this protein in the ECM as can be suggested from an increased extraction of TG2 from the human fascia only when an enzymatic degradation of the tissue DS was conducted in the presence of the anti-collagen type I antiserum. In addition, DS with a low affinity for TG2 exerted an inhibitory effect on the protein transamidating activity most probably via the control of the accessibility of a substrate. Our data show that DS can affect several aspects of TG2 biology in both physiological and pathological conditions.

Tissue transglutaminase (TG2) enables survival of human malignant pleural mesothelioma cells in hypoxia

Malignant pleural mesothelioma (MPM) is an aggressive tumor linked to environmental/occupational exposure to asbestos, characterized by the presence of significant areas of hypoxia. In this study, we firstly explored the expression and the role of transglutaminase 2 (TG2) in MPM cell adaptation to hypoxia. We demonstrated that cells derived from biphasic MPM express the full-length TG2 variant at higher levels than cells derived from epithelioid MPM and normal mesothelium. We observed a significant induction of TG2 expression and activity when cells from biphasic MPM were grown as a monolayer in chronic hypoxia or packed in spheroids, where the presence of a hypoxic core was demonstrated. We described that the hypoxic induction of TG2 was HIF-2 dependent. Importantly, TGM2-v1 silencing caused a marked and significant reduction of MPM cell viability in hypoxic conditions when compared with normoxia. Notably, a TG2-selective irreversible inhibitor that reacts with the intracellular active form of TG2, but not a non-cell-permeable inhibitor, significantly compromised cell viability in MPM spheroids. Understanding the expression and function of TG2 in the adaptation to the hypoxic environment may provide useful information for novel promising therapeutic options for MPM treatment.

Transglutaminase Interaction with α6/β4-Integrin Stimulates YAP1-Dependent ΔNp63α Stabilization and Leads to Enhanced Cancer Stem Cell Survival and Tumor Formation

Transglutaminase 2 (TG2) expression is required for epidermal squamous cell carcinoma cancer stem cell survival. However, the molecular signaling mechanisms triggered by TG2 that mediate this survival action are not well understood. Here we show that TG2 is constitutively expressed in ECS cells, where it interacts with α6/β4 integrin to stimulate FAK and Src signaling, leading to PI3K activation of phosphoinositide-dependent kinase 1 (PDK1). PDK1 inhibits Hippo signaling, leading to enhanced nuclear accumulation of YAP1, which interacted with and stabilized ΔNp63α to enhance epidermal squamous cell carcinoma spheroid formation, invasion, and migration. Overall, these findings suggest that constitutive TG2 expression results in stabilization of ΔNp63α, leading to maintenance of cancer stem cell properties and enhanced tumor formation. Cancer Res; 76(24); 7265-76. ©2016 AACR.