Transglutaminase 2: a multi-tasking protein in the complex circuitry of inflammation and cancer

Monocyte/Macrophage: NK Cell Cooperation-Old Tools for New Functions

Monocyte/macrophage and natural killer (NK) cells are partners from a phylogenetic standpoint of innate immune system development and its evolutionary progressive interaction with adaptive immunity. The equally conservative ways of development and differentiation of both invertebrate hemocytes and vertebrate macrophages are reviewed. Evolutionary conserved molecules occurring in macrophage receptors and effectors have been inherited by vertebrates after their common ancestor with invertebrates. Cytolytic functions of mammalian NK cells, which are rooted in immune cells of invertebrates, although certain NK cell receptors (NKRs) are mammalian new events, are characterized. Broad heterogeneity of macrophage and NK cell phenotypes that depends on surrounding microenvironment conditions and expression profiles of specific receptors and activation mechanisms of both cell types are discussed. The particular tissue specificity of macrophages and NK cells, as well as their plasticity and mechanisms of their polarization to different functional subtypes have been underlined. The chapter summarized studies revealing the specific molecular mechanisms and regulation of NK cells and macrophages that enable their highly specific cross-cooperation. Attention is given to the evolving role of human monocyte/macrophage and NK cell interaction in pathogenesis of hypersensitivity reaction-based disorders, including autoimmunity, as well as in cancer surveillance and progression.

Tissue transglutaminase-2 promotes gastric cancer progression via the ERK1/2 pathway

Gastric cancer (GC) is one of the most common tumors worldwide and involves extensive local tumor invasion, metastasis, and poor prognosis. Understanding mechanisms regulating progression of GC is necessary for developing effective therapeutic strategies. Tissue transglutaminase-2 (TG2), a multifunctional member of the transglutaminase family, has been shown to be critical for tumor initiation and progression. However, how TG2 promotes the progression of GC is unknown. We report that TG2 was highly expressed in GC tissues and positively associated with depth of tumor invasion and late TNM stage. With gain- and loss-of-function approaches, we observed that TG2 promoted GC cell proliferation, migration, invasion, as well as tumorigenesis and peritoneal metastasis in vivo. These events were associated with the ERK1/2 pathway activation and an ERK1/2 inhibitor (U0126) inhibited cell proliferation, migration, and invasion induced by overexpression of TG2. In summary, TG2 contributes to tumorigenesis and progression of GC by activating the ERK1/2 signaling pathway and is a potential therapeutic target of metastatic gastric cancer.

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.

Tissue transglutaminase-1 promotes stemness and chemoresistance in gastric cancer cells by regulating Wnt/β-catenin signaling

Gastric cancer is a common malignancy, and is one of the most frequent causes of cancer deaths worldwide. Recently, members of the transglutaminases (TGM) family, especially TGM2, have been implicated in the progression and drug resistance of cancers, but the function of TGM1 in cancer development has been largely overlooked. In this study, we demonstrate the roles of TGM1 in development of gastric cancer. We found that expression levels of TGM1 were upregulated in both gastric cancer tissues and cultured gastric cancer cells, and that TGM1 expression levels were correlated with patient survival. In cultured gastric cancer cells, loss of TGM1 expression inhibited cell proliferation and promoted apoptosis, as well increased gastric cancer cell sensitivity to chemotherapeutic drugs and reducing stemness. These results strongly supported the participation of TGM1 in the regulation of gastric cancer development. In addition, we found evidence that the mechanism of action of TGM1 in regulating gastric cancer cell might involve the Wnt signaling pathway, as loss of TGM1 expression in gastric cancer cells led to a significant suppression of Wnt signaling activities.

Tumor macrophages are pivotal constructors of tumor collagenous matrix

Tumor-associated macrophages are pivotal constructors of the tumoral ECM structure and molecular composition. In particular, they orchestrate the buildup of the tumorigenic collagenous ECM niche.

Tumor-associated macrophages (TAMs) promote tumor development, invasion, and dissemination by various mechanisms. In this study, using an orthotopic colorectal cancer (CRC) model, we found that monocyte-derived TAMs advance tumor development by the remodeling of its extracellular matrix (ECM) composition and structure. Unbiased transcriptomic and proteomic analyses of (a) TAM-abundant and -deficient tumor tissues and (b) sorted tumor-associated and -resident colonic macrophage subpopulations defined a distinct TAM-induced ECM molecular signature composed of an ensemble of matricellular proteins and remodeling enzymes they provide to the tumor microenvironment. Remarkably, many of these ECM proteins are specifically increased in human CRC versus healthy colon. Specifically, we demonstrate that although differentiating into TAMs, monocytes up-regulate matrix-remodeling programs associated with the synthesis and assembly of collagenous ECM, specifically collagen types I, VI, and XIV. This finding was further established by advanced imaging showing that TAMs instruct the deposition, cross-linking, and linearization of collagen fibers during tumor development, especially at areas of tumor invasiveness. Finally, we show that cancer-associated fibroblasts are significantly outnumbered by TAMs in this model and that their expression of collagen XIV and I is reduced by TAM deficiency. Here, we outline a novel TAM protumoral function associated with building of the collagenous ECM niche.

Expression of Transglutaminase in Foreskin of Children with Balanitis Xerotica Obliterans

Balanitis xerotica obliterans (BXO) is a chronic inflammatory skin disorder of unclear etiology. The etiology and the exact molecular mechanisms underlying the disease are still unknown. The human transglutaminase (TG) family consists of several proteins with catalytic activity essential for biological processes. In the present research we investigated the transcript levels of three TGs in patients operated on for congenital phimosis without or with histologically confirmed BXO; Thirty children with acquired phimosis were enrolled. The removed foreskins were sent both for histological diagnosis and for quantitative real-time PCR to evaluate the transcript levels of keratinocyte (TG1), tissue (TG2), and epidermal (TG3) transglutaminase; We observed a decrease in TG1 and TG3 transcripts by about 70% (p < 0.001) in foreskins from patients with BXO (n = 15) in comparison with patients without BXO (n = 15) and an increase in TG2 mRNA levels by 2.9 folds (p < 0.001); Reduced expression of both TG1 and TG3 was associated with the altered structure of the foreskin in BXO and can be a consequence of damage to keratinocytes. Increased expression of TG2 can be the result of chronic inflammation. TG2 overexpression can play a pivotal role in triggering and maintaining the inflammatory response in BXO patients.

Prognostic role of tissue transglutaminase 2 in colon carcinoma

Tissue transglutaminase 2 (TG2) is involved in many biological processes, from wound healing to neurodegeneration. Recently, there has been an increasing interest in this enzyme as a potential prognostic marker or therapy target in human neoplasms. The aim of this study was to analyze expression of TG2 messenger RNA (mRNA) and protein in colon cancer samples and to evaluate the potential value of TG2 as prognostic marker. We investigated not only expression level but also location of the protein in a series of human tumors. In silico analysis using the GSE39582 dataset showed that TG2 mRNA expression is associated with earlier relapse. The results of qPCR in our cohort showed TG2 mRNA to be up-regulated in 25 out of 70 samples (34 %). Kaplan-Meier plots and log-rank test showed that patients with high TG2 mRNA expression have significantly worse prognosis in terms of overall survival (OS) and a trend to earlier recurrence. Immunohistochemical staining of tumor sections for TG2 revealed stromal staining in 152 cases (88 %) and epithelial cell staining in 105 cases (62 %). In stage II patients, stromal expression showed a significant association with disease-free survival (DFS). In patients with metastatic disease, TG2 expression was also associated with poor prognosis. Cox multivariate analysis showed that TG2 expression in epithelial cells is significantly and independently associated with OS, together with node involvement and presence of metastasis. Stromal TG2 expression was associated with DFS. In summary, in non-metastatic colorectal cancer patients, stromal TG2 expression is significantly associated with DFS and epithelial TG2 expression with OS, independently of node involvement and metastasis.

Transglutaminase-2: evolution from pedestrian protein to a promising therapeutic target

The ability of cancer cells to metastasize represents the most devastating feature of cancer. Currently, there are no specific biomarkers or therapeutic targets that can be used to predict the risk or to treat metastatic cancer. Many recent reports have demonstrated elevated expression of transglutaminase 2 (TG2) in multiple drug-resistant and metastatic cancer cells. TG2 is a multifunctional protein mostly known for catalyzing Ca²⁺-dependent -acyl transferase reaction to form protein crosslinks. Besides this transamidase activity, many Ca²⁺-independent and non-enzymatic activities of TG2 have been identified. Both, the enzymatic and non-enzymatic activities of TG2 have been implicated in diverse pathophysiological processes such as wound healing, cell growth, cell survival, extracellular matrix modification, apoptosis, and autophagy. Tumors have been frequently referred to as 'wounds that never heal'. Based on the observation that TG2 plays an important role in wound healing and inflammation is known to facilitate cancer growth and progression, we discuss the evidence that TG2 can reprogram inflammatory signaling networks that play fundamental roles in cancer progression. TG2-regulated signaling bestows on cancer cells the ability to proliferate, to resist cell death, to invade, to reprogram glucose metabolism and to metastasize, the attributes that are considered important hallmarks of cancer. Therefore, inhibiting TG2 may offer a novel therapeutic approach for managing and treatment of metastatic cancer. Strategies to inhibit TG2-regulated pathways will also be discussed.

TG2 and NF-κB Signaling Coordinates the Survival of Mantle Cell Lymphoma Cells via IL6-Mediated Autophagy

Expression of the transglutaminase TG2 has been linked to constitutive activation of NF-κB and chemotherapy resistance in mantle cell lymphoma (MCL) cells. TG2 forms complexes with NF-κB components, but mechanistic insights that could be used to leverage therapeutic responses has been lacking. In the current study, we address this issue with the discovery of an unexpected role for TG2 in triggering autophagy in drug-resistant MCL cells through induction of IL6. CRISPR-mediated silencing of TG2 delayed apoptosis while overexpressing TG2 enhanced tumor progression. Under stress, TG2 and IL6 mediate enhanced autophagy formation to promote MCL cell survival. Interestingly, the autophagy product ATG5 involved in autophagosome elongation positively regulated TG2/NF-κB/IL6 signaling, suggesting a positive feedback loop. Our results uncover an interconnected network of TG2/NF-κB and IL6/STAT3 signaling with autophagy regulation in MCL cells, the disruption of which may offer a promising therapeutic strategy. Cancer Res; 76(21); 6410-23. ©2016 AACR.

Gingival Crevicular Fluid and Plasma Levels of Transglutaminase-2 and Oxidative Stress Markers in Cyclosporin A-Induced Gingival Overgrowth

BACKGROUND

Transglutaminase (TGM)-2 has been shown to contribute to fibrosis by extracellular matrix accumulation in some organs and is activated by intracellular reactive oxygen species. The aim of this study is to investigate levels of gingival crevicular fluid (GCF) and plasma TGM-2 and oxidative stress markers (OSMs) in cyclosporin A (CsA)-induced gingival overgrowth (GO).

METHODS

The study enrolled 20 healthy (H) individuals; 20 patients with gingivitis (G); 20 CsA-medicated patients with GO (CsA GO+); and 20 CsA-medicated patients without GO (CsA GO-). GCF and plasma levels of TGM-2 were analyzed by enzyme-linked immunosorbent assay. Spectrofluorometry was used to analyze thiobarbituric acid reactive substance (TBARS); ferric-reducing antioxidant power (FRAP); total oxidant status (TOS); and total antioxidant capacity (TAC).

RESULTS

GCF TGM-2 level was elevated in CsA GO+ compared with G (P = 0.048) and H (P = 0.001) groups. GCF TBARS level was elevated in CsA GO+ compared with other groups (CsA GO- group: P = 0.003; G group: P <0.001; and H group: P <0.001) and was higher in CsA GO- than in H (P = 0.048). GCF FRAP level was lower in CsA GO- than in H (P = 0.04). Both CsA GO+ and CsA GO- groups had lower GCF TOS levels than H (P <0.001 and P = 0.002) and G (P = 0.003 and P = 0.04). GCF TAC was higher in CsA GO+ than in H (P = 0.02). Plasma TGM-2 level was elevated in CsA GO+ compared with G (P = 0.048) and H (P = 0.002). Plasma FRAP level was higher in H and CsA GO- than in CsA GO+ (P = 0.008 and P = 0.02).

CONCLUSIONS

CsA use significantly alters GCF and plasma levels of TGM-2 and OSMs. TGM-2 may contribute to CsA-induced GO in CsA-treated patients by changing GCF and plasma levels of OSMs. Further studies are needed to prove causality and its direction.

Transglutaminase 2 has opposing roles in the regulation of cellular functions as well as cell growth and death

Transglutaminase 2 (TG2) is primarily known as the most ubiquitously expressed member of the transglutaminase family with Ca²⁺-dependent protein crosslinking activity; however, this enzyme exhibits multiple additional functions through GTPase, cell adhesion, protein disulfide isomerase, kinase, and scaffold activities and is associated with cell growth, differentiation, and apoptosis. TG2 is found in the extracellular matrix, plasma membrane, cytosol, mitochondria, recycling endosomes, and nucleus, and its subcellular localization is an important determinant of its function. Depending upon the cell type and stimuli, TG2 changes its subcellular localization and biological activities, playing both anti- and pro-apoptotic roles. Increasing evidence indicates that the GTP-bound form of the enzyme (in its closed form) protects cells from apoptosis but that the transamidation activity of TG2 (in its open form) participates in both facilitating and inhibiting apoptosis. A difficulty in the study and understanding of this enigmatic protein is that opposing effects have been reported regarding its roles in the same physiological and/or pathological systems. These include neuroprotective or neurodegenerative effects, hepatic cell growth-promoting or hepatic cell death-inducing effects, exacerbating or having no effect on liver fibrosis, and anti- and pro-apoptotic effects on cancer cells. The reasons for these discrepancies have been ascribed to TG2's multifunctional activities, genetic variants, conformational changes induced by the immediate environment, and differences in the genetic background of the mice used in each of the experiments. In this article, we first report that TG2 has opposing roles like the protagonist in the novel Dr. Jekyll and Mr. Hyde, followed by a summary of the controversies reported, and finally discuss the possible reasons for these discrepancies.

Stromal Activation by Tumor Cells: An in Vitro Study in Breast Cancer

Background: The tumor microenvironment participates in the regulation of tumor progression and influences treatment sensitivity. In breast cancer, it also may play a role in determining the fate of non-invasive lesions such as ductal carcinoma in situ (DCIS), a non-obligate precursor of invasive diseases, which is aggressively treated despite its indolent nature in many patients since no biomarkers are available to predict the progression of DCIS to invasive disease. In vitro models of stromal activation by breast tumor cells might provide clues as to specific stromal genes crucial for the transition from DCIS to invasive disease. Methods: normal human dermal fibroblasts (NHDF) were treated under serum-free conditions with cell culture media conditioned by breast cancer cell lines (SkBr3, MDA-MB-468, T47D) for 72 h and subjected to gene expression profiling with Illumina platform. Results: TGM2, coding for a tissue transglutaminase, was identified as candidate gene for stromal activation. In public transcriptomic datasets of invasive breast tumors TGM2 expression proved to provide prognostic information. Conversely, its role as an early biosensor of tumor invasiveness needs to be further investigated by in situ analyses. Conclusion: Stromal TGM2 might probably be associated with precancerous evolution at earlier stages compared to DCIS.

Compensatory Increase of Transglutaminase 2 Is Responsible for Resistance to mTOR Inhibitor Treatment

The mechanistic target of rapamycin complex 1 (mTORC1) plays a crucial role in controlling cell growth and homeostasis. Deregulation of mTOR signaling is frequently observed in some cancers, making it an attractive drug target for cancer therapy. Although mTORC1 inhibitor rapalog-based therapy has shown positive results in various pre-clinical animal cancer studies, tumors rebound upon treatment discontinuation. Moreover, several recent clinical trials showed that the mTORC1 inhibitors rapamycin and rapalog only reduce the capacity for cell proliferation without promoting cell death, consistent with the concept that rapamycin is cytostatic and reduces disease progression but is not cytotoxic. It is imperative that rapamycin-regulated events and additional targets for more effective drug combinations be identified. Here, we report that rapamycin treatment promotes a compensatory increase in transglutaminase 2 (TGM2) levels in mTORC1-driven tumors. TGM2 inhibition potently sensitizes mTORC1-hyperactive cancer cells to rapamycin treatment, and a rapamycin-induced autophagy blockade inhibits the compensatory TGM2 upregulation. More importantly, tumor regression was observed in MCF-7-xenograft tumor-bearing mice treated with both mTORC1 and TGM2 inhibitors compared with those treated with either a single inhibitor or the vehicle control. These results demonstrate a critical role for the compensatory increase in transglutaminase 2 levels in promoting mTORC1 inhibitor resistance and suggest that rational combination therapy may potentially suppress cancer therapy resistance.

Transglutaminase 2 up-regulation is associated with RANKL/OPG pathway in cultured HPDL cells and THP-1-differentiated macrophages

Recent evidence emphasized that transglutaminase 2 (TG2), a protein cross-linking enzyme, may play a role in the early phase of inflammation. High levels of TG2 have been associated with the constitutive activation of nuclear factor-kappa B (NF-κB) that is considered the main regulator of inflammation. In this context, the receptor activator of NF-kappa B ligand (RANKL) and receptor activator of NF-κB have extensive functions in the regulation of cytokine secretion associated with different pathological conditions. The human periodontal ligament (HPDL) cells, which express and secrete osteoprotegerin (OPG) and RANKL, represent an useful "ex vivo" model for monitoring cell response in inflammatory microenvironments, such as periodontitis-dependent tissue response. Thus, we evaluated TG2 expression and alterations in RANKL/OPG ratio occurring in cultured HPDL cells. The HPDL cells were obtained from patients with chronic periodontitis (CP) and healthy subjects. We observed the up-regulation of some inflammatory markers, such as IL-6, TNF-α, and HMGB-1, and at the same time an increase in TG2 mRNA levels in HPDL cells from CP patients compared with healthy subjects. We found a positive correlation between RANKL/OPG ratio and TG2 mRNA levels in HPDL cells from CP patients. In the parallel experiments, we demonstrated that TG2 inhibition reduced RANKL expression in both HPDL cells from CP patients and monocytes differentiated to macrophages by tetradecanoyl phorbol acetate treatment. Given the RANKL key role in NF-κB pathway and the observed up-regulation of pro-inflammatory cytokines, our data suggest that TG2 may be involved in molecular mechanisms of inflammatory response occurring in periodontal disease.

Physiological, pathological, and structural implications of non-enzymatic protein-protein interactions of the multifunctional human transglutaminase 2

Transglutaminase 2 (TG2) is a ubiquitously expressed member of an enzyme family catalyzing Ca(2+)-dependent transamidation of proteins. It is a multifunctional protein having several well-defined enzymatic (GTP binding and hydrolysis, protein disulfide isomerase, and protein kinase activities) and non-enzymatic (multiple interactions in protein scaffolds) functions. Unlike its enzymatic interactions, the significance of TG2's non-enzymatic regulation of its activities has recently gained importance. In this review, we summarize all the partners that directly interact with TG2 in a non-enzymatic manner and analyze how these interactions could modulate the crosslinking activity and cellular functions of TG2 in different cell compartments. We have found that TG2 mostly acts as a scaffold to bridge various proteins, leading to different functional outcomes. We have also studied how specific structural features, such as intrinsically disordered regions and embedded short linear motifs contribute to multifunctionality of TG2. Conformational diversity of intrinsically disordered regions enables them to interact with multiple partners, which can result in different biological outcomes. Indeed, ID regions in TG2 were identified in functionally relevant locations, indicating that they could facilitate conformational transitions towards the catalytically competent form. We reason that these structural features contribute to modulating the physiological and pathological functions of TG2 and could provide a new direction for detecting unique regulatory partners. Additionally, we have assembled all known anti-TG2 antibodies and have discussed their significance as a toolbox for identifying and confirming novel TG2 regulatory functions.

CD49f Acts as an Inflammation Sensor to Regulate Differentiation, Adhesion, and Migration of Human Mesenchymal Stem Cells

The advent of mesenchymal stem cell (MSC)-based therapies has been an exciting innovation for the treatment of degenerative and inflammatory diseases. However, the surface markers that accurately reflect the self-renewal and differentiation potential of MSCs and their sensitivity to environmental cues remain poorly defined. Here, we studied the role of CD49f in bone marrow MSCs (BMSCs) and the mechanism by which it regulates the behavior of BMSCs under inflammatory conditions. We found that CD49f is preferentially expressed in fetal cells rather than adult cells, CD49f-positive BMSCs possess higher CFU-F formation ability and differentiation potential than CD49f negative cells, and the CD49f expression of BMSCs gradually decreases during in vitro passaging. CD49f knockdown dramatically decreased the differentiation of BMSCs and isoform A was demonstrated to be the main functional form that enhanced the differentiation ability of BMSCs. The influences of inflammatory cytokines on BMSCs revealed that TNF-α downregulated CD49f in BMSCs with impaired differentiation, decreased adhesion to laminins, and increased migration. Moreover, tissue transglutaminase was found to work together with CD49f to regulate the behavior of BMSCs. Finally, we showed that mTOR signaling rather than NF-κB activation mediated CD49f downregulation induced by TNF-α and maintained CD49f homeostasis in BMSCs. Our findings suggest that CD49f is a stemness marker of BMSCs and is tightly correlated with the behavioral changes of BMSCs under inflammatory conditions. These data demonstrate a novel role for CD49f in sensing inflammation through mTOR pathway to further modulate the behavior of MSCs to fulfill the requirements of the body.

Novel 3-arylethynyl-substituted thieno[3,4-b]pyrazine derivatives as human transglutaminase 2 inhibitors

In the process of optimization, we developed a novel core skeleton of thieno[3,4-b]pyrazine via GK-13. The derivatives synthesized were shown to inhibit TGase 2 activity in cancer cells. Some of the hit compounds such as the arylethynyl group-coupled thieno[3,4-b]pyrazine derivatives were shown to exhibit promising activity for use as potential therapeutic small-molecules in renal cancer by inhibiting TGase 2 activity.

Transglutaminase Is Required for Epidermal Squamous Cell Carcinoma Stem Cell Survival

Cancer stem cells are thought to be responsible for rapid tumor growth, metastasis, and enhanced tumor survival following drug treatment. For this reason, there is a major emphasis on identifying proteins that can be targeted to kill cancer stem cells or control their growth, and transglutaminase type II (TGM2/TG2) is such a target in epidermal squamous cell carcinoma. TG2 was originally described as a transamidase in the extracellular matrix that crosslinks proteins by catalyzing ε-(γ-glutamyl)lysine bonds. However, subsequent studies have shown that TG2 is a GTP-binding protein that plays an important role in cell signaling and survival. In the present study, TG2 shows promise as a target for anticancer stem cell therapy in human squamous cell carcinoma. TG2 was determined to be highly elevated in epidermal cancer stem cells (ECS cells), and TG2 knockdown or suppression of TG2 function with inhibitors reduced ECS cell survival, spheroid formation, Matrigel invasion, and migration. The reduction in survival is associated with activation of apoptosis. Mechanistic studies, using TG2 mutants, revealed that the GTP-binding activity is required for maintenance of ECS cell growth and survival, and that the action of TG2 in ECS cells is not mediated by NF-κB signaling.

IMPLICATIONS

This study suggests that TG2 has an important role in maintaining cancer stem cell survival, invasive, and metastatic behavior and is an important therapeutic target to reduce survival of cancer stem cells in epidermal squamous cell carcinoma.

Mesenchymal stromal cells derived from acute myeloid leukemia bone marrow exhibit aberrant cytogenetics and cytokine elaboration

Bone marrow-derived mesenchymal stromal cells (BM-MSCs) play a fundamental role in the BM microenvironment (BME) and abnormalities of these cells may contribute to acute myeloid leukemia (AML) pathogenesis. The aim of the study was to characterize the cytokine and gene expression profile, immunophenotype and cytogenetics of BM-MSCs from AML patients compared to normal BM-MSCs from healthy donors. AML BM-MSCs showed decreased monocyte chemoattractant protein-1 levels compared to normal BM-MSCs. AML BM-MSCs expressed similar β1 integrin, CD44, CD73, CD90 and E-cadherin compared to normal BM-MSCs. Cytogenetic analysis revealed chromosomal aberrations in AML BM-MSCs, some overlapping with and others distinct from their corresponding AML blasts. No significant difference in gene expression was detected between AML BM-MSCs compared to normal BM-MSCs; however, comparing the differences between AML and MSCs from AML patients with the differences between normal hematopoietic cells and normal MSCs by Ingenuity pathway analysis showed key distinctions of the AML setting: (1) upstream gene regulation by transforming growth factor beta 1, tumor necrosis factor, tissue transglutaminase 2, CCAAT/enhancer binding protein alpha and SWItch/Sucrose NonFermentable related, matrix associated, actin dependent regulator of chromatin, subfamily a, member 4; (2) integrin and interleukin 8 signaling as overrepresented canonical pathways; and (3) upregulation of transcription factors FBJ murine osteosarcoma viral oncogene homolog and v-myb avian myeloblastosis viral oncogene homolog. Thus, phenotypic abnormalities of AML BM-MSCs highlight a dysfunctional BME that may impact AML survival and proliferation.

Macrophages in diabetic gastroparesis--the missing link?

BACKGROUND

Diabetic gastroparesis results in significant morbidity for patients and major economic burden for society. Treatment options for diabetic gastroparesis are currently directed at symptom control rather than the underlying disease and are limited. The pathophysiology of diabetic gastroparesis includes damage to intrinsic and extrinsic neurons, smooth muscle, and interstitial cells of Cajal (ICC). Oxidative damage in diabetes appears to be one of the primary insults involved in the pathogenesis of several complications of diabetes, including gastroparesis. Recent studies have highlighted the potential role of macrophages as key cellular elements in the pathogenesis of diabetic gastroparesis. Macrophages are important for both homeostasis and defense against a variety of pathogens. Heme oxygenase 1 (HO1), an enzyme expressed in a subset of macrophages has emerged as a major protective mechanism against oxidative stress. Activation of macrophages with high levels of HO1 expression protects against development of delayed gastric emptying in animal models of diabetes, while activation of macrophages that do not express HO1 are linked to neuromuscular cell injury. Targeting macrophages and HO1 may therefore be a therapeutic option in diabetic gastroparesis.

PURPOSE

This report briefly reviews the pathophysiology of diabetic gastroparesis with a focus on oxidative damage and how activation and polarization of different subtypes of macrophages in the muscularis propria determines development of delay in gastric emptying or protects against its development.

Characterization of distinct sub-cellular location of transglutaminase type II: changes in intracellular distribution in physiological and pathological states

Transglutaminase type II (TG2) is a pleiotropic enzyme that exhibits various activities unrelated to its originally identified functions. Apart from post-translational modifications of proteins (peculiar to the transglutaminase family enzymes), TG2 is involved in diverse biological functions, including cell death, signaling, cytoskeleton rearrangements, displaying enzymatic activities, G-protein and non-enzymatic biological functions. It is involved in a variety of human diseases such as celiac disease, diabetes, neurodegenerative diseases, inflammatory disorders and cancer. Regulatory mechanisms might exist through which cells control multifunctional protein expression as a function of their sub-cellular localization. The definition of the tissue and cellular distribution of such proteins is important for the determination of their function(s). We investigate the sub-cellular localization of TG2 by confocal and immunoelectron microscopy techniques in order to gain an understanding of its properties. The culture conditions of human sarcoma cells (2fTGH cells), human embryonic kidney cells (HEK293^TG) and human neuroblastoma cells (SK-n-BE(2)) are modulated to induce various stimuli. Human tissue samples of myocardium and gut mucosa (diseased and healthy) are also analyzed. Immuno-gold labeling indicates that TG2 is localized in the nucleus, mitochondria and endoplasmic reticulum under physiological conditions but that this is not a stable association, since different locations or different amounts of TG2 can be observed depending on stress stimuli or the state of activity of the cell. We describe a possible unrecognized location of TG2. Our findings thus provide useful insights regarding the functions and regulation of this pleiotropic enzyme.

Differential expression of transglutaminase genes in patients with chronic periodontitis

OBJECTIVE

Gingival epithelium plays a key role in the protection of oral tissues from microbial challenge, especially during the periodontal disease. This study was aimed to evaluate levels of mRNA transcripts of different forms of transglutaminase in the human gingival tissues from patients with chronic periodontitis and relative controls.

SUBJECTS AND METHODS

This study included 22 patients with chronic periodontitis (CP) and 22 healthy controls. For each patient, the values of probing depth (PD), clinical attachment level (CAL), and bleeding on probing (BOP) were recorded. Gene expression of transglutaminase 1, transglutaminase 2, transglutaminase 3, and metalloprotease 2 was evaluated by real-time PCR, while that of Factor XIIIA and metalloprotease 9 by RT-PCR.

RESULTS

The values of all the clinical parameters were significantly higher in the CP group than in the healthy control group (P < 0.05). In the CP group, the mRNA expression of transglutaminase 1 and transglutaminase 3 was significantly decreased in comparison with healthy control group. A slight nonsignificant changes of transglutaminase 2 gene expression were observed in samples from CP patients in comparison with controls.

CONCLUSIONS

These observations suggest that transglutaminase gene expression may be modified in response to chronic injury in the damaged gingival and emphasizes the key role of these enzymes in gingival remodelling/healing and adaptive processes.

Tissue transglutaminase: an emerging target for therapy and imaging

Tissue transglutaminase (transglutaminase 2) is a multifunctional enzyme with many interesting properties resulting in versatile roles in both physiology and pathophysiology. Herein, the particular involvement of the enzyme in human diseases will be outlined with special emphasis on its role in cancer and in tissue interactions with biomaterials. Despite recent progress in unraveling the different cellular functions of transglutaminase 2, several questions remain. Transglutaminase 2 features in both confirmed and some still ambiguous roles within pathological conditions, raising interest in developing inhibitors and imaging probes which target this enzyme. One important prerequisite for identifying and characterizing such molecular tools are reliable assay methods to measure the enzymatic activity. This digest Letter will provide clarification about the various assay methods described to date, accompanied by a discussion of recent progress in the development of inhibitors and imaging probes targeting transglutaminase 2.

Transglutaminase regulation of cell function

Transglutaminases (TGs) are multifunctional proteins having enzymatic and scaffolding functions that participate in regulation of cell fate in a wide range of cellular systems and are implicated to have roles in development of disease. This review highlights the mechanism of action of these proteins with respect to their structure, impact on cell differentiation and survival, role in cancer development and progression, and function in signal transduction. We also discuss the mechanisms whereby TG level is controlled and how TGs control downstream targets. The studies described herein begin to clarify the physiological roles of TGs in both normal biology and disease states.

Transglutaminase-2 mediates calcium-regulated crosslinking of the Y-box 1 (YB-1) translation-regulatory protein in TGFβ1-activated myofibroblasts

Myofibroblast differentiation is required for wound healing and accompanied by activation of smooth muscle α-actin (SMαA) gene expression. The stress-response protein, Y-box binding protein-1 (YB-1) binds SMαA mRNA and regulates its translational activity. Activation of SMαA gene expression in human pulmonary myofibroblasts by TGFβ1 was associated with formation of denaturation-resistant YB-1 oligomers with selective affinity for a known translation-silencer sequence in SMαA mRNA. We have determined that YB-1 is a substrate for the protein-crosslinking enzyme transglutaminase 2 (TG2) that catalyzes calcium-dependent formation of covalent γ-glutamyl-isopeptide linkages in response to reactive oxygen signaling. TG2 transamidation reactions using intact cells, cell lysates, and recombinant YB-1 revealed covalent crosslinking of the 50 kDa YB-1 polypeptide into protein oligomers that were distributed during SDS-PAGE over a 75-250 kDa size range. In vitro YB-1 transamidation required nanomolar levels of calcium and was enhanced by the presence of SMαA mRNA. In human pulmonary fibroblasts, YB-1 crosslinking was inhibited by (a) anti-oxidant cystamine, (b) the reactive-oxygen antagonist, diphenyleneiodonium, (c) competitive inhibition of TG2 transamidation using the aminyl-surrogate substrate, monodansylcadaverine, and (d) transfection with small-interfering RNA specific for human TG2 mRNA. YB-1 crosslinking was partially reversible as a function of oligomer-substrate availability and TG2 enzyme concentration. Intracellular calcium accumulation and peroxidative stress in injury-activated myofibroblasts may govern SMαA mRNA translational activity during wound healing via TG2-mediated crosslinking of the YB-1 mRNA-binding protein.

Conformational changes and translocation of tissue-transglutaminase to the plasma membranes: role in cancer cell migration

BACKGROUND

Tissue-transglutaminase (TG2), a dual function G-protein, plays key roles in cell differentiation and migration. In our previous studies we reported the mechanism of TG2-induced cell differentiation. In present study, we explored the mechanism of how TG2 may be involved in cell migration.

METHODS

To study the mechanism of TG2-mediated cell migration, we used neuroblastoma cells (SH-SY5Y) which do not express TG2, neuroblastoma cells expressing exogenous TG2 (SHYTG2), and pancreatic cancer cells which express high levels of endogenous TG2. Resveratrol, a natural compound previously shown to inhibit neuroblastoma and pancreatic cancer in the animal models, was utilized to investigate the role of TG2 in cancer cell migration. Immunofluorescence assays were employed to detect expression and intracellular localization of TG2, and calcium levels in the migrating cells. Native gel electrophoresis was performed to analyze resveratrol-induced cellular distribution and conformational states of TG2 in migrating cells. Data are presented as the mean and standard deviation of at least 3 independent experiments. Comparisons were made among groups using one-way ANOVA followed by Tukey-Kramer ad hoc test.

RESULTS

TG2 containing cells (SHYTG2 and pancreatic cancer cells) exhibit increased cell migration and invasion in collagen-coated and matrigel-coated transwell plate assays, respectively. Resveratrol (1 μM-10 μM) prevented migration of TG2-expressing cells. During the course of migration, resveratrol increased the immunoreactivity of TG2 without affecting the total TG2 protein level in migrating cells. In these cells, resveratrol increased calcium levels, and depletion of intracellular calcium by a calcium chelator, BAPTA, attenuated resveratrol-enhanced TG2 immunoreactivity. In native-polyacrylamide gels, we detected an additional TG2 protein band with slower migration in total cell lysates of resveratrol treated cells. This TG2 form is non-phosphorylated, exclusively present in plasma membrane fractions and sensitive to intracellular Ca(2+) concentration suggesting a calcium requirement in TG2-regulated cell migration.

CONCLUSIONS

Taken together, we conclude that resveratrol induces conformational changes in TG2, and that Ca(2+)-mediated TG2 association with the plasma membrane is responsible for the inhibitory effects of resveratrol on cell migration.

Transglutaminase 2 reprogramming of glucose metabolism in mammary epithelial cells via activation of inflammatory signaling pathways

Aberrant glucose metabolism characterized by high levels of glycolysis, even in the presence of oxygen, is an important hallmark of cancer. This metabolic reprogramming referred to as the Warburg effect is essential to the survival of tumor cells and provides them with substrates required for biomass generation. Molecular mechanisms responsible for this shift in glucose metabolism remain elusive. As described herein, we found that aberrant expression of the proinflammatory protein transglutaminase 2 (TG2) is an important regulator of the Warburg effect in mammary epithelial cells. Mechanistically, TG2 regulated metabolic reprogramming by constitutively activating nuclear factor (NF)-κB, which binds to the hypoxia-inducible factor (HIF)-1α promoter and induces its expression even under normoxic conditions. TG2/NF-κB-induced increase in HIF-1α expression was associated with increased glucose uptake, increased lactate production and decreased oxygen consumption by mitochondria. Experimental suppression of TG2 attenuated HIF-1α expression and reversed downstream events in mammary epithelial cells. Moreover, downregulation of p65/RelA or HIF-1α expression in these cells restored normal glucose uptake, lactate production, mitochondrial respiration and glycolytic protein expression. Our results suggest that aberrant expression of TG2 is a master regulator of metabolic reprogramming and facilitates metabolic alterations in epithelial cells even under normoxic conditions. A TG2-induced shift in glucose metabolism helps breast cancer cells to survive under stressful conditions and promotes their metastatic competence.

Methylglyoxal in cells elicits a negative feedback loop entailing transglutaminase 2 and glyoxalase 1

Glyoxalase 1 (GlxI) is the key enzyme that converts the highly reactive α-oxo-aldehydes into the corresponding α-hydroxy acids using l-glutathione as a cofactor. In our preliminary data, GlxI was identified as a substrate of transglutaminase 2 (TG2), a ubiquitous enzyme with multiple functions. According to the catalytic properties of TG2, protein cross-linking, polyamine conjugation, and/or deamidation are potential post-translational modifications. In this article, we have demonstrated that TG2 catalyzes either polyamine conjugation or deamidation to GlxI depending on the presence of polyamines or not. Deamidation leads to activation of GlxI while polyamine conjugation results in activation of GlxI as well as stabilization of GlxI against denaturation treatment. In cultured HeLa cells, methylglyoxal challenge causes increase in intracellular levels of reactive oxygen species (ROS) and calcium leading to TG2 activation and subsequent transamidation and activation of GlxI. The inhibition of TG2 significantly weakens the cell resistance to the methylglyoxal challenge. Thus, GlxI is a novel substrate of TG2 and is activated by TG2 in vitro and in cellulo. Exposure to methylglyoxal elicits a negative feedback loop entailing ROS, calcium, TG2 and GlxI, thus leading to attenuation of the increase in the methylglyoxal level. The results imply that cancer cells highly express TG2 or GlxI can endure the oxidative stress derived from higher glycolytic flux and may gain extra growth advantage from the aerobic glycolysis.

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We have demonstrated novel modifications of glyoxalase I by transglutaminase 2.

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The modifications mediated by transglutaminse 2 modulate the glyoxalase I activities.

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Methylglyoxal treatment in cells induces increases in the levels of endogenous reactive oxygen species and activation transglutaminase 2 and glyoxalase I.

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Cells dispose the accumulated intracellular methylglyoxal by a negative feedback loop consisting of reactive oxygen species, calcium, transglutaminase 2 and glyoxalase I.

Transglutaminse 2 and EGGL, the protein cross-link formed by transglutaminse 2, as therapeutic targets for disabilities of old age

Aging of the extracellular matrix (ECM), the protein matrix that surrounds and penetrates the tissues and binds the body together, contributes significantly to functional aging of tissues. ECM proteins become increasingly cross-linked with age, and this cross-linking is probably important in the decline of the ECM's function. This article reviews the role of ε-(γ-glutamyl)-lysine (EGGL), a cross-link formed by transglutaminase enzymes, and particularly the widely expressed isozyme transglutaminase 2 (TG2), in the aging ECM. There is little direct data on EGGL accumulation with age, and no direct evidence of a role of EGGL in the aging of the ECM with pathology. However, several lines of circumstantial evidence suggest that EGGL accumulates with age, and its association with pathology suggests that this might reflect degradation of ECM function. TG activity increases with age in many circumstances. ECM protein turnover is such that some EGGL made by TG is likely to remain in place for years, if not decades, in healthy tissue, and both EGGL and TG levels are enhanced by age-related diseases. If further research shows EGGL does accumulate with age, removing it could be of therapeutic benefit. Also reviewed is the blockade of TG and active removal of EGGL as therapeutic strategies, with the conclusion that both have promise. EGGL removal may have benefit for acute fibrotic diseases, such as tendinopathy, and for treating generalized decline in ECM function with old age. Extracellular TG2 and EGGL are therefore therapeutic targets both for specific and more generalized diseases of aging.

Tissue transglutaminase mediates the pro-malignant effects of oncostatin M receptor over-expression in cervical squamous cell carcinoma

Oncostatin M receptor (OSMR) is commonly over-expressed in advanced cervical squamous cell carcinoma (SCC), producing a significantly worse clinical outcome. Cervical SCC cells that over-express OSMR show enhanced responsiveness to the major ligand OSM, which induces multiple pro-malignant effects, including increased cell migration and invasiveness. Here, we show that tissue transglutaminase (TGM2) is an important mediator of the ligand-dependent phenotypic effects of OSMR over-expression in SCC cells. TGM2 expression correlated with disease progression and with OSMR levels in clinical samples of cervical and oral SCC. TGM2 depletion in cervical SCC cells abrogated OSM-induced migration on fibronectin-coated surfaces and invasiveness through extracellular matrix, while ectopic expression of TGM2 increased cell motility and invasiveness. Confocal microscopy and co-immunoprecipitation assays showed that TGM2 interacted with integrin-α5β1 in the presence of fibronectin in cervical SCC cells, with OSM treatment strengthening the interaction. Importantly, integrin-α5β1 and fibronectin were also over-expressed in cervical and oral SCC, where levels correlated with those of OSMR and TGM2. This combined tissue and in vitro study demonstrates for the first time that stimulation of over-expressed OSMR in cervical SCC cells activates TGM2/integrin-α5β1 interactions and induces pro-malignant changes. We conclude that an OSMR/TGM2/integrin-α5β1/fibronectin pathway is of biological significance in cervical SCC and a candidate for therapeutic targeting.

Transglutaminase 2 overexpression in tumor stroma identifies invasive ductal carcinomas of breast at high risk of recurrence

Introduction

Molecular markers for predicting breast cancer patients at high risk of recurrence are urgently needed for more effective disease management. The impact of alterations in extracellular matrix components on tumor aggressiveness is under intense investigation. Overexpression of Transglutaminase 2 (TG2), a multifunctional enzyme, in cancer cells impacts epithelial mesenchymal transition, growth, invasion and interactions with tumor microenvironment. The objective of our study is to determine the clinical relevance of stromal TG2 overexpression and explore its potential to identify breast cancers at high risk of recurrence.

Methods

This retrospective study is based on immunohistochemical analysis of TG2 expression in normal breast tissues (n = 40) and breast cancers (n = 253) with clinical, pathological and follow-up data available for up to 12 years. TG2 expression was correlated with clinical and pathological parameters as well as disease free survival (DFS) of breast cancer patients.

Results

Stromal TG2 overexpression was observed in 114/253 (45.0%) breast cancer tissues as compared to breast normal tissues. Among invasive ductal carcinomas (IDC) of the breast, 97/168 (57.7%) showed strong TG2 expression in tumor stroma. Importantly, IDC patients showing stromal TG2 accumulation had significantly reduced DFS (mean DFS = 110 months) in comparison with patients showing low expression (mean DFS = 130 months) in Kaplan-Meier survival analysis (p<0.001). In Cox multivariate regression analysis, stromal TG2 accumulation was an independent risk factor for recurrence (p = 0.006, Hazard’s ratio, H.R. = 3.79). Notably, these breast cancer patients also showed immunostaining of N-epsilon gamma-glutamyl lysine amino residues in tumor stroma demonstrating the transamidating activity of TG2.

Conclusions

Accumulation of TG2 in tumor stroma is an independent risk factor for identifying breast cancer patients at high risk of recurrence. TG2 overexpression in tumor stroma may serve as a predictor of poor prognosis for IDC of the breast.

Suppression of Transglutaminase-2 is Involved in Anti-Inflammatory Actions of Glucosamine in 12-O-Tetradecanoylphorbol-13-Acetate-Induced Skin Inflammation

Glucosamine (GS) is well known for the treatment of inflam-mation. However, the mechanism and efficacy of GS for skin inflammation are unclear. The aim of this study was to evaluate the effects and mechanism of GS in the mouse 12-O-tetradecanoyl 13-acetate (TPA)-induced ear edema model. TPA-induced ear edema was evoked in ICR or transglutaminase 2 (Tgase-2) (-/-) mice. GS was administered orally (10-100 mg/kg) or topically (0.5-2.0 w/v %) prior to TPA treatment. Orally administered GS at 10 mg/kg showed a 76 or 57% reduction in ear weight or myeloperoxidase, respectively, and a decreased expression of cyclooxy-genase-2 (COX-2), NF-κB and Tgase-2 in TPA-induced ear edema by western blot and immunohistochemistry. Role of Tgase-2 in TPA ear edema is examined using Tgase-2 (-/-) mice and TPA did not induce COX-2 expression in ear of Tgase-2 (-/-) mice. These observations suggested that Tgase-2 is involved in TPA-induced COX-2 expression in the inflamed ear of mice and anti-inflammatory effects of glucosamine is mediated through suppression of Tgase-2 in TPA ear edema.

Comparison of gene expression profiles in primary and immortalized human pterygium fibroblast cells

PURPOSE

Pterygium is a fibrovascular growth on the ocular surface with corneal tissue destruction, matrix degradation and varying extents of chronic inflammation. To facilitate investigation of pterygium etiology, we immortalized pterygium fibroblast cells and profiled their global transcript levels compared to primary cultured cells.

METHODS

Fibroblast cells were cultured from surgically excised pterygium tissue using the explant method and propagated to passage number 2-4. We hypothesized that intervention with 3 critical molecular intermediates may be necessary to propage these cells. Primary fibroblast cells were immortalized sequentially by a retroviral construct containing the human telomerase reverse transcriptase gene and another retroviral expression vector expressing p53/p16 shRNAs. Primary and immortalized fibroblast cells were evaluated for differences in global gene transcript levels using an Agilent Genechip microarray.

RESULTS

Light microscopic morphology of immortalized cells was similar to primary pterygium fibroblast at passage 2-4. Telomerase reverse transcriptase was expressed, and p53 and p16 levels were reduced in immortalized pterygium fibroblast cells. There were 3308 significantly dysregulated genes showing at least 2 fold changes in transcript levels between immortalized and primary cultured cells (2005 genes were up-regulated and 1303 genes were down-regulated). Overall, 13.58% (95% CI: 13.08-14.10) of transcripts in immortalized cells were differentially expressed by at least 2 folds compared to primary cells.

CONCLUSION

Pterygium primary fibroblast cells were successfully immortalized to at least passage 11. Although a variety of genes are differentially expressed between immortalized and primary cells, only genes related to cell cycle are significantly changed, suggesting that the immortalized cells may be used as an in vitro model for pterygium pathology.

Transglutaminase 2 and phospholipase A₂ interactions in the inflammatory response in human Thp-1 monocytes

Several experimental approaches have demonstrated that transglutaminase 2 (TG2) increased activity is involved in monocyte activation and inflammatory response. Preliminary results also demonstrate a TG-mediated post-translational modification of phospholipase A2 (PLA2), which catalyzes the release of arachidonic acid from its lipid storage sites. The control of PLA2-mediated production of eicosanoids has been found to be of great benefit for inflammatory disease treatment. However, the identification of the mechanisms of PLA2 activation is a very complex issue, because of the presence of multiple PLA2 forms. The aim of this study was to characterize the interactions between TG2 and sPLA2 in LPS-stimulated THP-1 cells, which were treated with TPA to induce early differentiated macrophage-type model. We demonstrated that increases in TG2 enzyme activity and protein expression may be considered an early event in monocyte/macrophage activation by LPS. Under these conditions, TG2 protein was co-immunoprecipitated with PLA2 by monoclonal antibody directed against the secretory form of the enzyme (sPLA2-V). Concomitantly, the PLA2 enzyme activity increased in TPA-treated cells exposed to LPS; these high levels of enzyme activity were significant reduced by R283, a site-specific inhibitor of TG2. Moreover, confocal laser scanning microscopy analysis of double-immunostained cytochemical specimens confirmed a co-localization of BAPA-labeled proteins and sPLA2-V in LPS-treated cells. These findings give evidence of a complex TG2/sPLA2-V, suggesting the possibility that sPLA2-V is a substrate for TG2. These results demonstrated that TG2 increases produced a sustained activation of PLA2 activity, suggesting a functional interaction between these enzymes in the regulation of inflammatory response.

High-throughput screening for transglutaminase activities using recombinant fluorescent proteins

Since detailed evaluation of specific transglutaminases (TGs) from various species requires identification of their substrate specificities, rapid substrate screening method by measurement of their relative activities is in great demand. Here, a novel evaluation method of TG activity was developed using two recombinant fluorescent proteins (FPs), that is, eYFP and DsRed, tagged with TG substrate peptides. By cross-linking the two FPs based on the tagged target peptide sequences at their C-terminus, the expression of co-transformed TG allows quenching of the yellow fluorescence intensities. It was shown that the degree of in vivo fluorescent quenching by the TG activity agrees well with its in vitro reaction data, suggesting that this system can be used to identify relative substrate specificity of TGs for target peptide sequences. Using this method, the lysine substrates of TGs from Bacillus species (BTG) were evaluated, and the newly selected pentapeptide, KTKTN showed almost the same reactivity with the well-known hexa-lysine (K₆) substrate for BTG reaction.

Transglutaminase 2 expression predicts progression free survival in non-small cell lung cancer patients treated with epidermal growth factor receptor tyrosine kinase inhibitor

Transglutaminase 2 (TG2), a cross-linking enzyme, is involved in drug resistance and in the constitutive activation of nuclear factor kappa B (NF-κB). We investigated the association of non-small cell lung cancer (NSCLC) treatment efficacy with TG2 and NF-κB expression in 120 patients: 102 with adenocarcinoma and 18 with other histologic types. All patients underwent surgery; 88 received adjuvant chemotherapy, with 28 receiving platinum-based doublet chemotherapy as first-line treatment and 29 receiving epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor (TKI) therapy. Patients' TG2 and NF-κB expression values were calculated semiquantitatively. The median TG2 value was 50 (range, 0-300) and the median NF-κB value was 20 (range, 0-240). Disease-free survival did not differ between the low- and high-TG2 groups. Among patients who received palliative platinum-based doublet chemotherapy, progression free survival (PFS) was longer in the low-TG2 group than in the high-TG2 group (11.0 vs. 7.0 months; P=0.330). Among those who received EGFR-TKI therapy, PFS was also longer in the low-TG2 group than in the high-TG 2 group (11.0 vs. 2.0 months; P=0.013). Similarly, in EGFR wild-type patients treated with EGFR-TKI, PFS was longer in patients with low TG2 expression (9.0 vs. 2.0 months; P=0.013). TG2 expression levels can predict PFS in patients with NSCLC treated with EGFR-TKI.

Transglutaminase 2 inhibition found to induce p53 mediated apoptosis in renal cell carcinoma

Renal cell carcinoma (RCC), the predominant form of kidney cancer, is characterized by high resistance to radiation and chemotherapy. This study shows that expression of protein cross-linking enzyme transglutaminase 2 (TGase 2) is markedly increased in 7 renal cell carcinoma (RCC) cell lines in comparison to HEK293 and other cancer cell lines, such as NCI 60. However, the key role of TGase 2 in RCC was not clear. The down-regulation of TGase 2 was found to stabilize p53 expression, thereby inducing a 3- to 10-fold increase in apoptosis for 786-O, A498, CAKI-1, and ACHN cell lines by DAPI staining. MEF cells from TGase 2(-/-) mice showed stabilized p53 under apoptotic stress to compare to MEFs from wild-type mice. TGase 2 directly cross links the DNA binding domain of p53, leading to p53 depletion via autophagy in RCC. TGase 2 and p53 expression showed an inverse relationship in RCC cells. This finding implies that induced expression of TGase 2 promotes tumor cell survival through p53 depletion in RCC.

Tissue transglutaminase as a central mediator in inflammation-induced progression of breast cancer

TGM2 is a stress-responsive gene that encodes a multifunctional and structurally complex protein called tissue transglutaminase (abbreviated as TG2 or tTG). TGM2 expression is frequently upregulated during inflammation and wounding. Emerging evidence indicates that TGM2 expression is aberrantly upregulated in multiple cancer cell types, particularly those selected for resistance to chemotherapy and radiation therapy and those isolated from metastatic sites. It is becoming increasingly evident that chronic expression of TG2 in epithelial cancer cells initiates a complex series of signaling networks which contributes to the development of drug resistance and an invasive phenotype. For example, forced or basal high expression of TG2 in mammary epithelial cells is associated with activation of nuclear transcription factor-kappa B (NF-κB), Akt, focal adhesion kinase, and hypoxia-inducible factor. All of these changes are considered hallmarks of aggressive tumors. TG2 expression is able to induce the developmentally regulated program of epithelial-to-mesenchymal transition (EMT) and to confer cancer stem cell (CSC) traits in mammary epithelial cells; both EMT and CSCs have been implicated in cancer metastasis and resistance to standard therapies. Importantly, TG2 expression in tumor samples is associated with poor disease outcome, increased drug resistance, and increased incidence of metastasis. These observations imply that TG2 plays a crucial role in promoting an aggressive phenotype in mammary epithelial cells. In this review, we discuss recent evidence that TG2-regulated pathways contribute to the aggressive phenotype in breast cancer.

Genetic programs expressed in resting and IL-4 alternatively activated mouse and human macrophages: similarities and differences

The molecular repertoire of macrophages in health and disease can provide novel biomarkers for diagnosis, prognosis, and treatment. Th2-IL-4–activated macrophages (M2) have been associated with important diseases in mice, yet no specific markers are available for their detection in human tissues. Although mouse models are widely used for macrophage research, translation to the human can be problematic and the human macrophage system remains poorly described. In the present study, we analyzed and compared the transcriptome and proteome of human and murine macrophages under resting conditions (M0) and after IL-4 activation (M2). We provide a resource for tools enabling macrophage detection in human tissues by identifying a set of 87 macrophage-related genes. Furthermore, we extend current understanding of M2 activation in different species and identify Transglutaminase 2 as a conserved M2 marker that is highly expressed by human macrophages and monocytes in the prototypic Th2 pathology asthma.

Tissue transglutaminase constitutively activates HIF-1α promoter and nuclear factor-κB via a non-canonical pathway

Constitutive activation of nuclear factor kappa B (NF-κB) has been linked with carcinogenesis and cancer progression, including metastasis, chemoresistance, and radiation resistance. However, the molecular mechanisms that result in constitutive activation of NF-κB are poorly understood. Here we show that chronic expression of the pro-inflammatory protein tissue transglutaminase (TG2) reprograms the transcription regulatory network in epithelial cells via constitutive activation of NF-κB. TG2-induced NF-κB binds the functional NF-κB binding site in hypoxia-inducible factor-1 (HIF-1α) promoter and results in its increased expression at transcription and protein levels even under normoxic conditions. TG2/NF-κB-induced HIF-1 was deemed essential for increased expression of some transcription repressors, like Zeb1, Zeb2, Snail, and Twist. Unlike tumor necrosis factor-alpha (TNFα), TG2 did not require IκB kinase (IKK) for NF-κB activation. Our data suggest that TG2 binds with IκBα and results in its rapid degradation via a non-proteasomal pathway. Importantly, the catalytically inactive (C277S) mutant form of TG2 was as effective as was wild-type TG2 in activating NF-κB and inducing HIF-1 expression. We also found that TG2 interacted with p65/RelA protein, both in the cytosolic and the nuclear compartment. The TG2/p65(NF-κB) complex binds to the HIF-1 promoter and induced its transcriptional regulation. Inhibition of TG2 or p65/RelA also inhibited the HIF-1α expression and attenuated Zeb1, Zeb2, and Twist expression. To our knowledge, these findings show for the first time a direct link between TG2, NF-κB, and HIF-1α, demonstrating TG2's important role in cancer progression.

A comparison of epithelial-to-mesenchymal transition and re-epithelialization

Wound healing and cancer metastasis share a common starting point, namely, a change in the phenotype of some cells from stationary to motile. The term, epithelial-to-mesenchymal transition (EMT) describes the changes in molecular biology and cellular physiology that allow a cell to transition from a sedentary cell to a motile cell, a process that is relevant not only for cancer and regeneration, but also for normal development of multicellular organisms. The present review compares the similarities and differences in cellular response at the molecular level as tumor cells enter EMT or as keratinocytes begin the process of re-epithelialization of a wound. Looking toward clinical interventions that might modulate these processes, the mechanisms and outcomes of current and potential therapies are reviewed for both anti-cancer and pro-wound healing treatments related to the pathways that are central to EMT. Taken together, the comparison of re-epithelialization and tumor EMT serves as a starting point for the development of therapies that can selectively modulate different forms of EMT.

Tissue transglutaminase activity protects from cutaneous melanoma metastatic dissemination: an in vivo study

The role of tissue transglutaminase (TG-2, TGase-2) in cancer development is still a fascinating field of research. The available reports do not elucidate fully its mechanism of action, due to the limitations of in vitro approaches. Therefore, to understand TG-2 role in cancer, we carried out an in vivo study with a more direct approach. TG-2 was in vivo overexpressed in a murine model of melanoma (intravenous injection of B16 melanoma cells in C57BL/6N mice) by means of a plasmid carrying the TG-2 cDNA. The evaluation of the frequency and size of the metastases indicated that the number of melanoma lung foci was more markedly reduced by TG-2 overexpression than the metastatic size. Then, TG-2 overexpressing mice showed a prolonged survival with respect to control mice. Further analyses were carried by means of proteomic analysis of melanoma cell lysates and meta-analysis of published transcriptomic datasets. Proteomic analysis of cell lysates from a human melanoma cell line compared to human keratinocytes showed significant differences in the expression of TG-2 substrates known to be involved in proliferation/differentiation and cancer progression. Taken together, these findings indicate a protective role of TG-2 enzymatic activity in melanoma progression in vivo.

Transglutaminase 2 cross-linking activity is linked to invadopodia formation and cartilage breakdown in arthritis

Introduction

The microenvironment surrounding inflamed synovium leads to the activation of fibroblast-like synoviocytes (FLSs), which are important contributors to cartilage destruction in rheumatoid arthritic (RA) joints. Transglutaminase 2 (TG2), an enzyme involved in extracellular matrix (ECM) cross-linking and remodeling, is activated by inflammatory signals. This study was undertaken to assess the potential contribution of TG2 to FLS-induced cartilage degradation.

Methods

Transglutaminase (TGase) activity and collagen degradation were assessed with the immunohistochemistry of control, collagen-induced arthritic (CIA) or TG2 knockdown (shRNA)-treated joint tissues. TGase activity in control (C-FLS) and arthritic (A-FLS) rat FLSs was measured by in situ 5-(biotinamido)-pentylamine incorporation. Invadopodia formation and functions were measured in rat FLSs and cells from normal (control; C-FLS) and RA patients (RA-FLS) by in situ ECM degradation. Immunoblotting, enzyme-linked immunosorbent assay (ELISA), and p3TP-Lux reporter assays were used to assess transforming growth factor-β (TGF-β) production and activation.

Results

TG2 and TGase activity were associated with cartilage degradation in CIA joints. In contrast, TGase activity and cartilage degradation were reduced in joints by TG2 knockdown. A-FLSs displayed higher TGase activity and TG2 expression in ECM than did C-FLSs. TG2 knockdown or TGase inhibition resulted in reduced invadopodia formation in rat and human arthritic FLSs. In contrast, increased invadopodia formation was noted in response to TGase activity induced by TGF-β, dithiothreitol (DTT), or TG2 overexpression. TG2-induced increases in invadopodia formation were blocked by TGF-β neutralization or inhibition of TGF-βR1.

Conclusions

TG2, through its TGase activity, is required for ECM degradation in arthritic FLS and CIA joints. Our findings provide a potential target to prevent cartilage degradation in RA.

Phosphorylation of transglutaminase 2 (TG2) at serine-216 has a role in TG2 mediated activation of nuclear factor-kappa B and in the downregulation of PTEN

Background

Transglutaminase 2 (TG2) and its phosphorylation have been consistently found to be upregulated in a number of cancer cell types. At the molecular level, TG2 has been associated with the activation of nuclear factor-kappa B (NF-κB), protein kinase B (PKB/Akt) and in the downregulation of phosphatase and tensin homologue deleted on chromosome 10 (PTEN). However, the underlying mechanism involved is not known. We have reported that protein kinase A (PKA) induced phosphorylation of TG2 at serine-216 (Ser²¹⁶) regulates TG2 function and facilitates protein-protein interaction. However, the role of TG2 phosphorylation in the modulation of NF-κB, Akt and PTEN is not explored.

Methods

In this study we have investigated the effect of TG2 phosphorylation on NF-κB, Akt and PTEN using embryonic fibroblasts derived from TG2 null mice (MEF^tg2-/-) overexpressing native TG2 or mutant-TG2 (m-TG2) lacking Ser²¹⁶ phosphorylation site with and without dibutyryl cyclic-AMP (db-cAMP) stimulation. Functional consequences on cell cycle and cell motility were determined by fluorescence activated cell sorting (FACS) analysis and cell migration assay respectively.

Results

PKA activation in TG2 overexpressing MEF^tg2-/- cells resulted in an increased activation of NF-κB and Akt phosphorylation in comparison to empty vector transfected control cells as determined by the reporter-gene assay and immunoblot analysis respectively. These effects were not observed in MEF^tg2-/- cells overexpressing m-TG2. Similarly, a significant downregulation of PTEN at both, the mRNA and protein levels were found in cells overexpressing TG2 in comparison to empty vector control and m-TG2 transfected cells. Furthermore, Akt activation correlated with the simultaneous activation of NF-κB and a decrease in PTEN suggesting that the facilitatory effect of TG2 on Akt activation occurs in a PTEN-dependent manner. Similar results were found with MCF-7 and T-47D breast cancer cells overexpressing TG2 and m-TG2 further supporting the role of TG2 phosphorylation in NF-κB activation and in the downregulation of PTEN.

Conclusions

Collectively, these data suggest that phosphorylation of TG2 at Ser²¹⁶ plays a role in TG2 mediated activation of NF-κB, Akt and in the downregulation of PTEN. Blocking TG2 phosphorylation may provide a novel strategy to attenuate NF-κB activation and downregulation of PTEN in TG2 overexpressing cancers.

Fission yeast Cyk3p is a transglutaminase-like protein that participates in cytokinesis and cell morphogenesis

We have identified a fission yeast morphogenesis factor (Cyk3p) that functions with myosin II and chitin synthase during cytokinesis. Cyk3p possesses a novel transglutaminase domain that lacks an active site yet is essential for function. Our work demonstrates the physiological importance of such domains, which are found throughout eukaryotes.

Cell morphogenesis is a complex process that relies on a diverse array of proteins and pathways. We have identified a transglutaminase-like protein (Cyk3p) that functions in fission yeast morphogenesis. The phenotype of a cyk3 knockout strain indicates a primary role for Cyk3p in cytokinesis. Correspondingly, Cyk3p localizes both to the actomyosin contractile ring and the division septum, promoting ring constriction, septation, and subsequent cell separation following ring disassembly. In addition, Cyk3p localizes to polarized growth sites and plays a role in cell shape determination, and it also appears to contribute to cell integrity during stationary phase, given its accumulation as dynamic puncta at the cortex of such cells. Our results and the conservation of Cyk3p across fungi point to a role in cell wall synthesis and remodeling. Cyk3p possesses a transglutaminase domain that is essential for function, even though it lacks the catalytic active site. In a wider sense, our work illustrates the physiological importance of inactive members of the transglutaminase family, which are found throughout eukaryotes. We suggest that the proposed evolution of animal transglutaminase cross-linking activity from ancestral bacterial thiol proteases was accompanied by the emergence of a subclass whose function does not depend on enzymatic activity.