Enhanced Peritoneal Ovarian Tumor Dissemination by Tissue Transglutaminase

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.

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.

Transglutaminase 2 has higher affinity for relaxed than for stretched fibronectin fibers

Transglutaminase 2 (TG2) plays a vital role in stabilizing extracellular matrix (ECM) proteins through enzymatic crosslinking during tissue growth, repair, and inflammation. TG2 also binds non-covalently to fibronectin (FN), an essential component of the ECM, facilitating cell adhesion, migration, proliferation, and survival. However, the interaction between TG2 and fibrillar FN remains poorly understood, as most studies have focused on soluble or surface-adsorbed FN or FN fragments, which differ in their conformations from insoluble FN fibers. Using a well-established in vitro FN fiber stretch assay, we discovered that the binding of a crosslinking enzyme to ECM fibers is mechano-regulated. TG2 binding to FN is tuned by the mechanical tension of FN fibers, whereby TG2 predominantly co-localizes to low-tension FN fibers, while fiber stretching reduces their affinity for TG2. This mechano-regulated binding relies on the proximity between the N-terminal β-sandwich and C-terminal β-barrels of TG2. Crosslinking mass spectrometry (XL-MS) revealed a novel TG2-FN synergy site within TG2's C-terminal β-barrels that interacts with FN regions located outside of the canonical gelatin binding domain, specifically FNI2 and FNIII14-15. Combining XL-MS distance restraints with molecular docking revealed the mechano-regulated binding mechanism between TG2 and modules FNI7-9 by which mechanical forces regulate TG2-FN interactions. This highlights a previously unrecognized role of TG2 as a tension sensor for FN fibers. This novel interaction mechanism has significant implications in physiology and mechanobiology, including how forces regulate cell adhesion, spreading, migration, phenotype modulation, depending on the tensional state of ECM fibers. Data are available via ProteomeXchange with identifier PXD043976.

Discovery and Characterization of PROTACs Targeting Tissue Transglutaminase (TG2)

Tissue transglutaminase (TG2) is a multifunctional enzyme involved in the cross-linking of extracellular matrix proteins, formation of complexes with fibronectin (FN) and integrins, and GTP hydrolysis. TG2 is activated in several pathological conditions, including cancer. We recently described a novel series of ligands that bind to TG2 and inhibit its interaction with FN. Because TG2 acts via multiple mechanisms, we set out to pursue a targeted protein degradation strategy to abolish TG2's myriad functions. Here, we report the synthesis and characterization of a series of VHL-based degraders that reduce TG2 in ovarian cancer cells in a proteasome-dependent manner. Degradation of TG2 resulted in significantly reduced cancer cell adhesion and migration in vitro in scratch-wound and migration assays. These results strongly indicate that further development of more potent and in vivo efficient TG2 degraders could be a new strategy for reducing the dissemination of ovarian and other cancers.

Canonical and truncated transglutaminase-2 regulate mucin-1 expression and androgen independency in prostate cancer cell lines

Androgen independency is associated with poor prostate cancer (PCa) survival. Here we report that silencing of transglutaminase-2 (TG2) expression by CRISPR-Cas9 is associated with upregulation of androgen receptor (AR) transcription in PCa cell lines. Knockout of TG2 reversed the migratory potential and anchorage independency of PC3 and DU145 cells and revealed a reduced level of mucin-1 (MUC1) RNA transcript through unbiased multi-omics profiling, which was restored by selective add-back of the truncated TG2 isoform (TGM2_v2). Silencing of AR resulted into increased MUC1 in TG2KO PC3 cells showing that TG2 affects transcriptional regulation of MUC1 via repressing AR expression. Treatment of PC3 WT cell line with TG2 inhibitor ZDON led to a significant increase in AR expression and decrease in MUC1. ZDON also blocked the formation of MUC1-multimers labelled with TG amine-donor substrates in reducing conditions, revealing for the first time a role for TG2, which we show to be externalised via extracellular vesicles, in MUC1 stabilisation via calcium-dependent transamidation. A specific antibody towards TGM2_v2 revealed its restricted nuclear location compared to the canonical long form of TG2 (TGM2_v1), which is predominantly cytosolic, suggesting that this form contributes to the previously suggested TG2-mediated NF-κB activation and AR transcriptional repression. As TGM2_v2 transcription was increased in biopsies of early-stage prostate adenocarcinoma (PRAD) patients compared to subjects presenting inflammatory prostatitis, and total TG2 protein expression significantly increased in PRAD versus normal tissue, the role of TG2 and its truncated form as a prostate malignancy marker is suggested. In conclusion, this investigation has provided the first unbiased discovery of a novel pathway mediated by TG2 via MUC1, which is shown to contribute to androgen insensitivity and malignancy of PCa cells and be upregulated in PCa biopsies, with potential relevance to cancer immune evasion.

Prognostic Value of Transglutaminase 2 in Patients with Solid Tumors: A Meta-analysis

Background: Transglutaminase 2 (TG2), a member of the transglutaminase family, also known as tissue transglutaminase, plays a fundamental role in cancer growth and progression. In this study, we aimed to comprehensively review the evidence of TG2 as a prognostic biomarker in solid tumors. Methods: PubMed, Embase, and Cochrane databases were searched for human studies with clearly described cancer types if they presented the relationship between TG2 expression and prognostic indicators from inception to February 2022. Two authors independently screened the eligible studies and extracted the relevant data. The association between TG2 and overall survival (OS), disease-free survival (DFS), and relapse-free survival (RFS) were described as hazard ratios (HR) and their corresponding 95% confidence intervals (CIs). Statistical heterogeneity was assessed using Cochrane Q-test and Higgins I-squared statistic. A sensitivity analysis was conducted by sequentially omitting the impact of each study. Publication bias was assessed by Egger's funnel plot. Results: A total of 2864 patients with various cancers from 11 individual studies were enrolled. Results showed that elevated TG2 protein expression and mRNA expression predicted a shorter OS, with a combined HR of 1.93 (95% CI: 1.41-2.63) or HR of 1.95 (95% CI: 1.27-2.99), respectively. Moreover, data suggested that elevated TG2 protein expression was correlated with a shorter DFS (HR = 1.76, 95% CI: 1.36-2.29); whereas elevated TG2 mRNA expression was associated with a shorter DFS (HR = 1.71, 95% CI: 1.30-2.24). Conclusions: Our meta-analysis indicated that TG2 might serve as a promising biomarker of cancer prognosis.

The transglutaminase 2 cancer cell survival factor maintains mTOR activity to drive an aggressive cancer phenotype

Transglutaminase 2 (TG2) is an important cancer stem-like cell survival protein that is highly expressed in epidermal squamous cell carcinoma and drives an aggressive cancer phenotype. In the present study, we show that TG2 knockdown or inactivation results in a reduction in mammalian target of rapamycin (mTOR) level and activity in epidermal cancer stem-like cells which are associated with reduced spheroid formation, invasion, and migration, and reduced cancer stem cell and epithelial-mesenchymal transition (EMT) marker expression. Similar changes were observed in both cultured cells and tumors. mTOR knockdown or treatment with rapamycin phenocopies the reduction in spheroid formation, invasion, and migration, and cancer stem cell and EMT marker expression. Moreover, mTOR appears to be a necessary mediator of TG2 action, as a forced expression of constitutively active mTOR in TG2 knockdown cells partially restores the aggressive cancer phenotype and cancer stem cell and EMT marker expression. Tumor studies show that rapamycin reduces tumor growth and cancer stem cell marker expression and EMT. These studies suggest that TG2 stimulates mTOR activity to stimulate cancer cell stemness and EMT and drive aggressive tumor growth.

TGM2 inhibits the proliferation, migration and tumorigenesis of MDCK cells

Madin-Darby canine kidney (MDCK) cells are one of the main cell lines used for influenza vaccine production due to their high virus yield and low mutation resistance. Due to their high tumorigenicity, the safety of vaccines produced from these cells is controversial. TGM2 is a multifunctional protein that plays an important role in the adhesion and migration of cells and is associated with tumor formation. We found that the expression level of TGM2 was significantly up-regulated in low tumorigenic MDCK cells. We first analyzed TGM2-overexpressed and knockout MDCK cells in vitro. Scratch-wound assay and Transwell chamber experiments showed that TGM2 overexpression significantly inhibited the migration and invasion of MDCK cells and significantly reduced their proliferation. TGM2 knockout significantly enhanced cell migration, invasion, and proliferation. The tumorigenesis results in nude mice were consistent with those in vitro. TGM2 knockout significantly enhanced the tumorigenesis rate of MDCK cells in nude mice. We also investigated the effects of TGM2 gene expression on the replication of the H1N1 influenza A virus in MDCK cells. The results showed that TGM2 induced the negative regulation of H1N1 replication. These findings contribute to a comprehensive understanding of the tumor regulation mechanism and biological functions of TGM2.

Tissue transglutaminase activates integrin-linked kinase and β-catenin in ovarian cancer

Ovarian cancer (OC) is the most lethal gynecological cancer. OC cells have high proliferative capacity, are invasive, resist apoptosis, and tumors often display rearrangement of extracellular matrix (ECM) components, contributing to accelerated tumor progression. The multifunctional protein tissue transglutaminase (TG2) is known to be secreted in the tumor microenvironment (TME), where it interacts with fibronectin (FN) and the cell surface receptor β1 integrin. However, the mechanistic role of TG2 in cancer cell proliferation is unknown. Here, we demonstrate TG2 directly interacts with and facilitates the phosphorylation and activation of the integrin effector protein integrin-linked kinase (ILK) at Ser246. We show TG2 and p-Ser246-ILK form a complex that is detectable in patient-derived OC primary cells grown on FN-coated slides. In addition, we show co-expression of TGM2 and ILK correlates with poor clinical outcome. Mechanistically, we demonstrate TG2-mediated ILK activation causes phosphorylation of glycogen synthase kinase-3α/β (GSK-3α/β), allowing β-catenin nuclear translocation and transcriptional activity. Furthermore, inhibition of TG2 and ILK using small molecules, neutralizing antibodies, or shRNA-mediated knockdown block cell adhesion to the FN matrix, as well as the Wnt receptor response to the Wnt-3A ligand, and ultimately, cell adhesion, growth, and migration. In conclusion, we demonstrate TG2 directly interacts with and activates ILK in OC cells and tumors, and define a new mechanism which links ECM cues with β-catenin signaling in OC. These results suggest a central role of TG2/FN/integrin clusters in ECM rearrangement and indicate downstream effector ILK may represent a potential new therapeutic target in OC.

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.

Metabolic Reprogramming of Ovarian Cancer Spheroids during Adhesion

Ovarian cancer remains a deadly disease and its recurrence disease is due in part to the presence of disseminating ovarian cancer aggregates not removed by debulking surgery. During dissemination in a dynamic ascitic environment, the spheroid cells' metabolism is characterized by low respiration and fragmented mitochondria, a metabolic phenotype that may not support secondary outgrowth after adhesion. Here, we investigated how adhesion affects cellular respiration and substrate utilization of spheroids mimicking early stages of secondary metastasis. Using different glucose and oxygen levels, we investigated cellular metabolism at early time points of adherence (24 h and less) comparing slow and fast-developing disease models. We found that adhesion over time showed changes in cellular energy metabolism and substrate utilization, with a switch in the utilization of mostly glutamine to glucose but no changes in fatty acid oxidation. Interestingly, low glucose levels had less of an impact on cellular metabolism than hypoxia. A resilience to culture conditions and the capacity to utilize a broader spectrum of substrates more efficiently distinguished the highly aggressive cells from the cells representing slow-developing disease, suggesting a flexible metabolism contributes to the stem-like properties. These results indicate that adhesion to secondary sites initiates a metabolic switch in the oxidation of substrates that could support outgrowth and successful metastasis.

Loss of host tissue transglutaminase boosts antitumor T cell immunity by altering STAT1/STAT3 phosphorylation in ovarian cancer

BACKGROUND

Tissue transglutaminase (TG2), an enzyme overexpressed in cancer cells, promotes metastasis and resistance to chemotherapy. Its distinct effects in cancer versus the host compartments have not been elucidated.

METHODS

Here, by using a TG2^-/- syngeneic ovarian cancer mouse model, we assessed the effects of TG2 deficiency in the host tissues on antitumor immunity and tumor progression. Multicolor flow cytometry was used to phenotype immune cell populations in the peritoneal environment. Cancer cells recovered from malignant ascites were characterized by RNA sequencing, proliferation, and apoptosis assays.

RESULTS

We observed that host TG2 loss delayed tumor growth and ascites accumulation and caused increased infiltration of CD8⁺ T cells and decreased numbers of myeloid cells in the peritoneal fluid. Tumor antigen-specific CD8⁺ T cell cytotoxic responses were enhanced in ascites from TG2^-/- versus TG2^+/+ mice and CD8⁺ T cell depletion caused accelerated ascites accumulation in TG2^-/- mice. CD8⁺ T cells from tumor-bearing TG2^-/- mice displayed an effector T cell phenotype, differentiated toward effector memory (T_em). Mechanistically, absence of TG2 augmented signals promoting T cell activation, such as increased cytokine-induced STAT1 and attenuated STAT3 phosphorylation in T cells. Additionally, immune-suppressive myeloid cell populations were reduced in the peritoneal milieu of TG2^-/- tumor-bearing mice. In response to the more robust immune response caused by loss of TG2, cancer cells growing intraperitoneally exhibited an interferon-γ(IFN-γ) responsive gene signature and underwent apoptosis. In human specimens, stromal, not tumor, TG2 expression correlated indirectly with numbers of tumor-infiltrating lymphocytes.

CONCLUSIONS

Collectively, our data demonstrate decreased tumor burden, increased activation and effector function of T cells, and loss of immunosuppressive signals in the tumor microenvironment of TG2^-/- mice. We propose that TG2 acts as an attenuator of antitumor T cell immunity and is a new immunomodulatory target.

The Multifaceted Role of HSF1 in Pathophysiology: Focus on Its Interplay with TG2

The cellular environment needs to be strongly regulated and the maintenance of protein homeostasis is crucial for cell function and survival. HSF1 is the main regulator of the heat shock response (HSR), the master pathway required to maintain proteostasis, as involved in the expression of the heat shock proteins (HSPs). HSF1 plays numerous physiological functions; however, the main role concerns the modulation of HSPs synthesis in response to stress. Alterations in HSF1 function impact protein homeostasis and are strongly linked to diseases, such as neurodegenerative disorders, metabolic diseases, and different types of cancers. In this context, type 2 Transglutaminase (TG2), a ubiquitous enzyme activated during stress condition has been shown to promote HSF1 activation. HSF1-TG2 axis regulates the HSR and its function is evolutionary conserved and implicated in pathological conditions. In this review, we discuss the role of HSF1 in the maintenance of proteostasis with regard to the HSF1-TG2 axis and we dissect the stress response pathways implicated in physiological and pathological conditions.

The Biological and Biomechanical Role of Transglutaminase-2 in the Tumour Microenvironment

Transglutaminase-2 (TG2) is the most highly and ubiquitously expressed member of the transglutaminase enzyme family and is primarily involved in protein cross-linking. TG2 has been implicated in the development and progression of numerous cancers, with a direct role in multiple cellular processes and pathways linked to apoptosis, chemoresistance, epithelial-mesenchymal transition, and stem cell phenotype. The tumour microenvironment (TME) is critical in the formation, progression, and eventual metastasis of cancer, and increasing evidence points to a role for TG2 in matrix remodelling, modulation of biomechanical properties, cell adhesion, motility, and invasion. There is growing interest in targeting the TME therapeutically in response to advances in the understanding of its critical role in disease progression, and a number of approaches targeting biophysical properties and biomechanical signalling are beginning to show clinical promise. In this review we aim to highlight the wide array of processes in which TG2 influences the TME, focussing on its potential role in the dynamic tissue remodelling and biomechanical events increasingly linked to invasive and aggressive behaviour. Drug development efforts have yielded a range of TG2 inhibitors, and ongoing clinical trials may inform strategies for targeting the biomolecular and biomechanical function of TG2 in the TME.

Role of Tissue Transglutaminase Catalytic and Guanosine Triphosphate-Binding Domains in Renal Cell Carcinoma Progression

Tissue transglutaminase (TG2) is a multifunctional protein that can act as a cross-linking enzyme, GTPase/ATPase, protein kinase, and protein disulfide isomerase. TG2 is involved in cell adhesion, migration, invasion, and growth, as well as epithelial-mesenchymal transition (EMT). Our previous findings indicate that the increased expression of TG2 in renal cell carcinoma (RCC) results in tumor metastasis with a significant decrease in disease- and cancer-specific survival outcome. Given the importance of the prometastatic activity of TG2 in RCC, in the present study, we aim to investigate the relative contribution of TG2's transamidase and guanosine triphosphate (GTP)-binding/GTPase activity in the cell migration, invasion, EMT, and cancer stemness of RCC. For this purpose, the mouse RCC cell line RenCa was transduced with wild-type-TG2 (wt-TG2), GTP-binding deficient-form TG2-R580A, transamidase-deficient form with low GTP-binding affinity TG2-C277S, and transamidase-inactive form TG2-W241A. Our results suggested that predominantly, GTP-binding activity of TG2 is responsible for cell migration and invasion. In addition, CD marker analysis and spheroid assay confirmed that GTP binding/GTPase activity of TG2 is important in the maintenance of mesenchymal character and the cancer stem cell profile. These findings support a prometastatic role for TG2 in RCC that is dependent on the GTP binding/GTPase activity of the enzyme.

RNA-seq reveals the diverse effects of substrate stiffness on epidermal ovarian cancer cells

Background: Increasing evidence has confirmed that ovarian cancer is a mechanically responsive tumor both in vivo and in vitro. However, an understanding of the complete molecular mechanism involved in the response to substrate stiffness is lacking, as the associated transcriptome-wide effects have not been mapped. This limited understanding has restricted the identification of potential mechanically responsive targets in ovarian cancer.

Results: To address these limitations, we used a polyacrylamide hydrogel system with a tunable Young’s modulus that broadly ranged from soft (1 kPa) to normal (6 kPa) and stiff (60 kPa) and investigated the effect of substrate rigidity on the morphology, spreading area, and cytoskeleton of SKOV-3 epidermal ovarian cancer (EOC) cells. RNA-seq analysis of these cells was then performed at appropriate timepoints to map the transcriptome-wide changes associated with stiffness sensing. We identified a large number of stiffness-sensing genes as well as many genes that were enriched in cancer-related pathways. Informed by these diverse expression results and based on bioinformatics analysis, we evaluated the hypothesis that PLEC and TNS2, which are located in focal adhesions and regulated by lnc-ZNF136, may play key roles in the EOC response to substrate stiffness.

Conclusion: Overall, the results of the present study reveal previously unknown features of the EOC stiffness response and provide new insights into EOC metastasis in the clinic.

The influence of secreted factors and extracellular vesicles in ovarian cancer metastasis

Ovarian cancer cells mainly metastasise within the peritoneal cavity, the lethal consequence of tumour progression in this cancer type. Classically, changes in tumour cells, such as epithelial to mesenchymal transition, involve the down-regulatinon of E-cadherin, activation of extracellular proteases and integrin-mediated adhesion. However, our current understanding of ovarian tumour progression suggests the implication of both intrinsic and extrinsic factors. It has been proposed that ovarian cancer metastases are a consequence of the crosstalk between cancer cells and the tumour microenvironment by soluble factors and extracellular vesicles. Characterisation of the alterations in both the tumour cells and the surrounding microenvironment has emerged as a new research field to understand ovarian cancer metastasis. In this mini review, we will summarise the most recent findings, focusing our attention on the role of secreted factors and extracellular vesicles in ovarian cancer metastasis.

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During ovarian cancer metastasis, tumour cells metastasise in the mesothelium as primarily ‘soil’ for ovarian cancer ‘seeds’.

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Soluble factors and extracellular vesicles secreted by tumor cells are involved in the generation of the pre-metastatic niche.

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Cancer-associated fibroblasts (CAFs) represent the majority of stromal cells in various types of human carcinoma, including ovarian cancer.

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Analysis of early metastasis to the omentum indicates that ovarian cancer cells rely on the interaction with immune cells such as macrophages.

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Liquid biopsy analyses in ovarian cancer may help to define novel biomarkers improving patient survival and reduce lethality.

Wnt/β-catenin signalling in ovarian cancer: Insights into its hyperactivation and function in tumorigenesis

Epithelial ovarian cancer (EOC) is the deadliest female malignancy. The Wnt/β-catenin pathway plays critical roles in regulating embryonic development and physiological processes. This pathway is tightly regulated to ensure its proper activity. In the absence of Wnt ligands, β-catenin is degraded by a destruction complex. When the pathway is stimulated by a Wnt ligand, β-catenin dissociates from the destruction complex and translocates into the nucleus where it interacts with TCF/LEF transcription factors to regulate target gene expression. Aberrant activation of this pathway, which leads to the hyperactivity of β-catenin, has been reported in ovarian cancer. Specifically, mutations of CTNNB1, AXIN, or APC, have been observed in the endometrioid and mucinous subtypes of EOC. In addition, upregulation of the ligands, abnormal activation of the receptors or intracellular mediators, disruption of the β-catenin destruction complex, inhibition of the association of β-catenin/E-cadherin on the cell membrane, and aberrant promotion of the β-catenin/TCF transcriptional activity, have all been reported in EOC, especially in the high grade serous subtype. Furthermore, several non-coding RNAs have been shown to regulate EOC development, in part, through the modulation of Wnt/β-catenin signalling. The Wnt/β-catenin pathway has been reported to promote cancer stem cell self-renewal, metastasis, and chemoresistance in all subtypes of EOC. Emerging evidence also suggests that the pathway induces ovarian tumor angiogenesis and immune evasion. Taken together, these studies demonstrate that the Wnt/β-catenin pathway plays critical roles in EOC development and is a strong candidate for the development of targeted therapies.

Integrins: Moonlighting Proteins in Invadosome Formation

Invadopodia are actin-rich protrusions developed by transformed cells in 2D/3D environments that are implicated in extracellular matrix (ECM) remodeling and degradation. These structures have an undoubted association with cancer invasion and metastasis because invadopodium formation in vivo is a key step for intra/extravasation of tumor cells. Invadopodia are closely related to other actin-rich structures known as podosomes, which are typical structures of normal cells necessary for different physiological processes during development and organogenesis. Invadopodia and podosomes are included in the general term 'invadosomes,' as they both appear as actin puncta on plasma membranes next to extracellular matrix metalloproteinases, although organization, regulation, and function are slightly different. Integrins are transmembrane proteins implicated in cell-cell and cell-matrix interactions and other important processes such as molecular signaling, mechano-transduction, and cell functions, e.g., adhesion, migration, or invasion. It is noteworthy that integrin expression is altered in many tumors, and other pathologies such as cardiovascular or immune dysfunctions. Over the last few years, growing evidence has suggested a role of integrins in the formation of invadopodia. However, their implication in invadopodia formation and adhesion to the ECM is still not well known. This review focuses on the role of integrins in invadopodium formation and provides a general overview of the involvement of these proteins in the mechanisms of metastasis, taking into account classic research through to the latest and most advanced work in the field.

Small Molecules Target the Interaction between Tissue Transglutaminase and Fibronectin

Tissue transglutaminase (TG2) is a multifunctional protein with enzymatic, GTP-ase, and scaffold properties. TG2 interacts with fibronectin (FN) through its N-terminus domain, stabilizing integrin complexes, which regulate cell adhesion to the matrix. Through this mechanism, TG2 participates in key steps involved in metastasis in ovarian and other cancers. High-throughput screening identified several small molecule inhibitors (SMI) for the TG2/FN complex. Rational medicinal chemistry optimization of the hit compound (TG53) led to second-generation analogues (MT1-6). ELISA demonstrated that these analogues blocked TG2/FN interaction, and bio-layer interferometry (BLI) showed that the SMIs bound to TG2. The compounds also potently inhibited cancer cell adhesion to FN and decreased outside-in signaling mediated through the focal adhesion kinase. Blockade of TG2/FN interaction by the small molecules caused membrane ruffling, delaying the formation of stable focal contacts and mature adhesions points and disrupted organization of the actin cytoskeleton. In an in vivo model measuring intraperitoneal dissemination, MT4 and MT6 inhibited the adhesion of ovarian cancer cells to the peritoneum. Pretreatment with MT4 also sensitized ovarian cancer cells to paclitaxel. The data support continued optimization of the new class of SMIs that block the TG2/FN complex at the interface between cancer cells and the tumor niche.

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.

The Role of Tissue Transglutaminase in Cancer Cell Initiation, Survival and Progression

Tissue transglutaminase (transglutaminase type 2; TG2) is the most ubiquitously expressed member of the transglutaminase family (EC 2.3.2.13) that catalyzes specific post-translational modifications of proteins through a calcium-dependent acyl-transfer reaction (transamidation). In addition, this enzyme displays multiple additional enzymatic activities, such as guanine nucleotide binding and hydrolysis, protein kinase, disulfide isomerase activities, and is involved in cell adhesion. Transglutaminase 2 has been reported as one of key enzymes that is involved in all stages of carcinogenesis; the molecular mechanisms of action and physiopathological effects depend on its expression or activities, cellular localization, and specific cancer model. Since it has been reported as both a potential tumor suppressor and a tumor-promoting factor, the role of this enzyme in cancer is still controversial. Indeed, TG2 overexpression has been frequently associated with cancer stem cells’ survival, inflammation, metastatic spread, and drug resistance. On the other hand, the use of inducers of TG2 transamidating activity seems to inhibit tumor cell plasticity and invasion. This review covers the extensive and rapidly growing field of the role of TG2 in cancer stem cells survival and epithelial–mesenchymal transition, apoptosis and differentiation, and formation of aggressive metastatic phenotypes.

siRNA Delivery Using Dithiocarbamate-Anchored Oligonucleotides on Gold Nanorods

We present a robust method for loading small interfering RNA (siRNA) duplexes onto the surfaces of gold nanorods (GNRs) at high density, using near-infrared laser irradiation to trigger their intracellular release with subsequent knockdown activity. Citrate-stabilized GNRs were first coated with oleylsulfobetaine, a zwitterionic amphiphile with low cytotoxicity, which produced stable dispersions at high ionic strength. Amine-modified siRNA duplexes were converted into dithiocarbamate (DTC) ligands and adsorbed onto GNR surfaces in a single incubation step at 0.5 M NaCl, simplifying the charge screening process. The DTC anchors were effective at minimizing premature siRNA desorption and release, a common but often overlooked problem in the use of gold nanoparticles as oligonucleotide carriers. The activity of GNR-siRNA complexes was evaluated systematically against an eGFP-producing ovarian cancer cell line (SKOV-3) using folate receptor-mediated uptake. Efficient knockdown was achieved by using a femtosecond-pulsed laser source to release DTC-anchored siRNA, with essentially no contributions from spontaneous (dark) RNA desorption. GNRs coated with thiol-anchored siRNA duplexes were less effective and also permitted low levels of knockdown activity without photothermal activation. Optimized siRNA delivery conditions were applied toward the targeted knockdown of transglutaminase 2, whose expression is associated with the progression of recurrent ovarian cancer, with a reduction in activity of >80% achieved after a single pulsed laser treatment.

Mapping the minimum domain of the fibronectin binding site on transglutaminase 2 (TG2) and its importance in mediating signaling, adhesion, and migration in TG2-expressing cells

The interaction between the enzyme transglutaminase 2 (TG2) and fibronectin (FN) is involved in the cell-matrix interactions that regulate cell signaling, adhesion, and migration and play central roles in pathologic conditions, particularly fibrosis and cancer. A precise definition of the exact interaction domains on both proteins could provide a tool to design novel molecules with potential therapeutic applications. Although specific residues involved in the interaction within TG2 have been analyzed, little is known regarding the TG2 binding site on FN. This site has been mapped to a large internal 45-kDa protein fragment coincident with the gelatin binding domain (GBD). With the goal of defining the minimal FN interacting domain for TG2, we produced several expression constructs encoding different portions or modules of the GBD and tested their binding and functional properties. The results demonstrate that the I₈ module is necessary and sufficient for TG2-binding in vitro, but does not have functional effects on TG2-expressing cells. Modules I₇ and I₉ increase the strength of the binding and are required for cell adhesion. A 15-kDa fragment encompassing modules I_7-9 behaves as the whole 45-kDa GBD and mediates signaling, adhesion, spreading, and migration of TG2⁺ cells. This study provides new insights into the mechanism for TG2 binding to FN.-Soluri, M. F., Boccafoschi, F., Cotella, D., Moro, L., Forestieri, G., Autiero, I., Cavallo, L., Oliva, R., Griffin, M., Wang, Z., Santoro, C., Sblattero, D. Mapping the minimum domain of the fibronectin binding site on transglutaminase 2 (TG2) and its importance in mediating signaling, adhesion, and migration in TG2-expressing cells.

Transglutaminase is a mesothelioma cancer stem cell survival protein that is required for tumor formation

Mesothelioma is a rare cancer of the mesothelial cell layer of the pleura, peritoneum, pericardium and tunica vaginalis. It is typically caused by asbestos, notoriously resistant to chemotherapy and generally considered incurable with a poor life expectancy. Transglutaminase 2 (TG2), a GTP binding regulatory protein, is an important cancer stem cell survival and therapy resistance factor. We show that TG2 is highly expressed in human mesothelioma tumors and in mesothelioma cancer stem cells (MCS cells). TG2 knockdown or TG2 inhibitor treatment reduces MCS cell spheroid formation, matrigel invasion, migration and tumor formation. Time to tumor first appearance is doubled in TG2 knockout cells as compared to wild-type. In addition, TG2 loss is associated with reduced expression of stemness, and epithelial mesenchymal transition markers, and enhanced apoptosis. These studies indicate that TG2 is an important MCS cell survival protein and suggest that TG2 may serve as a mesothelioma cancer stem cell therapy target.

Role of Transglutaminase 2 in Migration of Tumor Cells and How Mouse Models Fit

A search for the "magic bullet", a molecule, the targeting abilities of which could stop the migration of tumor cells, is currently underway, but remains in the early stages. There are still many unknowns regarding the cell migration. The main approach is the employment of mouse models, that are sources of valuable information, but still cannot answer all of the questions. One of the molecules of interest is Transglutaminase 2 (TG2). It is a well-described molecule involved in numerous pathways and elevated in metastatic tumors. The question remains whether mice and humans can give the same answer considering TG2.

Tissue transglutaminase 2 expression is epigenetically regulated in human lung cancer cells and prevents reactive oxygen species-induced apoptosis

Purpose

Tissue transglutaminase 2 (TG2) is a stress-regulated protein and associated with cancer cell survival. However, the effects of TG2 expression in human non-small-cell lung cancer (NSCLC) cells on reactive oxygen species (ROS) production and redox homeostasis have not been fully elucidated.

Materials and methods

We investigated the TG2 expression and activity in A549, H1299, H1355, and H460 lung cancer cells by Western blots and quantitative polymerase chain reaction assay. The enzyme-linked immunosorbent assay was used for transglutaminase activity. The epigenetic expression was characterized with histone deacetylase inhibitor trichostatin A and DNA methyltransferase inhibitor 5-Aza treatment. TG2 expression was inhibited by siRNA transfection and the intracellular calcium was measured by Flow-3AM assay, apoptosis was analyzed by Annexin V/propidium iodide assay, and intracellular ROS was detected by fluorescence-activated cell sorting analysis. The ROS scavenger N-acetyl-L-cysteine (NAC) was applied to reduce TG2-knockdown-induced oxidative stress.

Results

Only A549 cells expressing high levels of TG2 correlated with high TG2 activity. The expression of TG2 can be regulated by epigenetic regulation in A549, H1299, and H1355 cells. The data also show that TG2 reduction induces apoptosis in A549 and H1299 cells. Furthermore, increased intracellular ROS and calcium levels were both detected in TG2-reduced cells. Moreover, endoplasmic reticulum stress inhibitor (salubrinal) and antioxidant NAC were able to reduce ROS and calcium levels to recover cell viability. Interestingly, the extrinsic and intrinsic apoptosis pathways were activated with a p53 independence upon TG2 reduction. TG2 reduction not only attenuated AKT activation but also reduced superoxide dismutase 2 (SOD2) expression. Exogenous NAC partially recovered SOD2 expression, indicating that mitochondrial-mediated apoptosis accounts for a part of but not all of the TG2-reduction-related death.

Conclusion

TG2 plays a protection role in NSCLC cell lines. Regardless of the endogenous level of TG2 and p53 status, reduction of TG2 may result in oxidative stress that induces apop-tosis. Therefore, target TG2 expression represents a logical strategy for NSCLC management.

Targeting the Microenvironment in High Grade Serous Ovarian Cancer

Cancer⁻stroma interactions play a key role in cancer progression and response to standard chemotherapy. Here, we provide a summary of the mechanisms by which the major cellular components of the ovarian cancer (OC) tumor microenvironment (TME) including cancer-associated fibroblasts (CAFs), myeloid, immune, endothelial, and mesothelial cells potentiate cancer progression. High-grade serous ovarian cancer (HGSOC) is characterized by a pro-inflammatory and angiogenic signature. This profile is correlated with clinical outcomes and can be a target for therapy. Accumulation of malignant ascites in the peritoneal cavity allows for secreted factors to fuel paracrine and autocrine circuits that augment cancer cell proliferation and invasiveness. Adhesion of cancer cells to the mesothelial matrix promotes peritoneal tumor dissemination and represents another attractive target to prevent metastasis. The immunosuppressed tumor milieu of HGSOC is permissive for tumor growth and can be modulated therapeutically. Results of emerging preclinical and clinical trials testing TME-modulating therapeutics for the treatment of OC are highlighted.

The mechanical microenvironment regulates ovarian cancer cell morphology, migration, and spheroid disaggregation

There is growing appreciation of the importance of the mechanical properties of the tumor microenvironment on disease progression. However, the role of extracellular matrix (ECM) stiffness and cellular mechanotransduction in epithelial ovarian cancer (EOC) is largely unknown. Here, we investigated the effect of substrate rigidity on various aspects of SKOV3 human EOC cell morphology and migration. Young’s modulus values of normal mouse peritoneum, a principal target tissue for EOC metastasis, were determined by atomic force microscopy (AFM) and hydrogels were fabricated to mimic these values. We find that cell spreading, focal adhesion formation, myosin light chain phosphorylation, and cellular traction forces all increase on stiffer matrices. Substrate rigidity also positively regulates random cell migration and, importantly, directional increases in matrix tension promote SKOV3 cell durotaxis. Matrix rigidity also promotes nuclear translocation of YAP1, an oncogenic transcription factor associated with aggressive metastatic EOC. Furthermore, disaggregation of multicellular EOC spheroids, a behavior associated with dissemination and metastasis, is enhanced by matrix stiffness through a mechanotransduction pathway involving ROCK, actomyosin contractility, and FAK. Finally, this pattern of mechanosensitivity is maintained in highly metastatic SKOV3ip.1 cells. These results establish that the mechanical properties of the tumor microenvironment may play a role in EOC metastasis.

Tissue Tranglutaminase Regulates Interactions between Ovarian Cancer Stem Cells and the Tumor Niche

Cancer progression and recurrence are linked to a rare population of cancer stem cells (CSC). Here, we hypothesized that interactions with the extracellular matrix drive CSC proliferation and tumor-initiating capacity and investigated the functions of scaffold protein tissue transglutaminase (TG2) in ovarian CSC. Complexes formed by TG2, fibronectin (FN), and integrin β1 were enriched in ovarian CSC and detectable in tumors. A function-inhibiting antibody against the TG2 FN-binding domain suppressed complex formation, CSC proliferation as spheroids, tumor-initiating capacity, and stemness-associated Wnt/β-catenin signaling. Disruption of the interaction between TG2 and FN also blocked spheroid formation and the response to Wnt ligands. TG2 and the Wnt receptor Frizzled 7 (Fzd7) form a complex in cancer cells and tumors, leading to Wnt pathway activation. Protein docking and peptide inhibition demonstrate that the interaction between TG2 and Fzd7 overlaps with the FN-binding domain of TG2. These results support a new function of TG2 in ovarian CSC, linked to spheroid proliferation and tumor-initiating capacity and mediated through direct interactions with Fzd7. We propose this complex as a new stem cell target.Significance: These findings reveal a new mechanism by which ovarian CSCs interact with the tumor microenvironment, promoting cell proliferation and tumor initiation. Cancer Res; 78(11); 2990-3001. ©2018 AACR.

Repurposing disulfiram for cancer therapy via targeted nanotechnology through enhanced tumor mass penetration and disassembly

Disulfiram (DSF), an FDA approved drug for the treatment of alcoholism, degrades to therapeutically active diethyldithiocarbamate (DDTC) in the body by reduction. Hereby, we developed a redox sensitive DDTC-polymer conjugate for targeted cancer therapy. It was found that the DDTC-polymer conjugate modified with a β-d-galactose receptor targeting ligand can self-assemble into LDNP nanoparticle and efficiently enter cancer cells by receptor-mediated endocytosis. Upon cellular uptake, the LDNP nanoparticle degrades and releases DDTC due to the cleavage of disulfide bonds, and subsequently forms copper (II) DDTC complex to kill a broad spectrum of cancer cells. 3D cell culture revealed that this nanoparticle shows much stronger tumor mass penetrating and destructive capacity. Furthermore, LDNP nanoparticles exhibited much greater potency in inhibiting tumor growth in a peritoneal metastatic ovarian tumor model.

STATEMENT OF SIGNIFICANCE

The β-d-galactose receptor targeted disulfiram loaded nanoparticle (LDNP) is novel in the following aspects.

Transglutaminase 2 Promotes Migration and Invasion of Lung Cancer Cells

Lung cancer is the leading cause of cancer deaths worldwide. Given that the major threat of cancer is metastasis, delineation of the molecular mechanism underlying it would help devise therapeutic strategies. Transglutaminase 2 (TG2), belonging to the transglutaminase superfamily, is a versatile protein with enzymatic and nonenzymatic functions. It mainly localizes inside the cell, but also appears extracellularly. Recent findings have demonstrated the involvement of TG2 in cancer development. Here we examine the role of TG2 in metastasis of lung cancer using a lung cancer cell line CL1-0, which exhibits low invasiveness, and its invasive subline CL1-5. Our results show that CL1-5 cells express a higher amount of TG2 than CL1-0 cells. Overexpression of TG2 in CL1-0 enhances cell migration and invasion, and lowering TG2 expression in CL1-5 cells reduces their ability to do so. The transamidase activity of TG2 is not required since cells expressing the inactive TG2 mutant or treated with a TG2 inhibitor are still able to migrate and invade. TG2-stimulated migration and invasion are, at least in part, mediated by Rac, as inhibition of Rac activity suppresses cell migration and invasion. Lastly, exogenous application of recombinant TG2 protein to CL1-0 cells substantially augments cell migration and invasion, suggesting the significance of extracellular TG2 in promoting these events. Collectively, our results show that TG2 plays a positive role in cell migration and invasion, and this might help metastasis of lung cancer cells.

Transglutaminase 2 in human diseases

Transglutaminase 2 (TG2) is an inducible transamidating acyltransferase that catalyzes Ca(2+)-dependent protein modifications. In addition to being an enzyme, TG2 also serves as a G protein for several seven transmembrane receptors and acts as a co-receptor for integrin β1 and β3 integrins distinguishing it from other members of the transglutaminase family. TG2 is ubiquitously expressed in almost all cell types and all cell compartments, and is also present on the cell surface and gets secreted to the extracellular matrix via non-classical mechanisms. TG2 has been associated with various human diseases including inflammation, cancer, fibrosis, cardiovascular disease, neurodegenerative diseases, celiac disease in which it plays either a protective role, or contributes to the pathogenesis. Thus modulating the biological activities of TG2 in these diseases will have a therapeutic value.

Tissue transglutaminase expression is necessary for adhesion, metastatic potential and cancer stemness of renal cell carcinoma

Tissue transglutaminase (TG2) is the ubiquitously expressed member of transglutaminase family and shown to play a critical role in the development and progression of drug resistance malignancies. We have previously showed the association of TG2 upregulation with progression and metastasis of renal cell carcinoma (RCC) and low disease-free survival. In the present study we further investigate the role of TG2 in cell adhesion, migration and invasion of RCC by silencing TG2 expression in Caki-2 and A-498 primary site and Caki-1 and ACHN metastatic site RCC cell lines. Downregulation of TG2 expression led up to a 60% decrease in actin stress fiber formation and adhesion to β 1 integrin (ITGB1) substrates fibronectin, collagen type I and laminin in both primary and metastatic site RCC cell lines. In addition, treatment with siRNAs against TG2 impaired the migration capacity and cellular invasiveness of ITGB1 substrates in all 4 RCC cell lines. Lastly, the knockdown of TG2 in metastatic Caki-1 cells diminished the expression of CD44, CD73-and CD105 cancer stem cell-like markers. We conclude, for the first time, that TG2 expression is critical for cancer cell adhesion, migration, invasiveness and cancer cell-stemness during RCC progression and dissemination. Therefore, combined targeting of TG2 with drugs widely used in the treatment of RCC may be a promising therapeutic strategy for RCC.

The Gαh-PLCδ1 signaling axis drives metastatic progression in triple-negative breast cancer

BACKGROUND

Distant metastasis of triple-negative breast cancer (TNBC) to other organs, e.g., the lungs, has been correlated with poor survival rates among breast cancer patients. Therefore, the identification of useful therapeutic targets to prevent metastasis or even inhibit tumor growth of TNBC is urgently needed. Gαh is a novel GTP-binding protein and known as an inactive form of calcium-dependent tissue transglutaminase. However, the functional consequences of transamidating and G-protein activities of tissue transglutaminase in promoting cancer metastasis are still controversial.

METHODS

Kaplan-Meier analyses were performed to estimate the prognostic values of Gαh and PLCδ1 by utilizing public databases and performing immunohistochemical staining experiments. Cell-based invasion assays and in vivo lung colony-forming and orthotropic lung metastasis models were established to evaluate the effectiveness of interrupting the protein-protein interaction (PPI) between Gαh and PLCδ1 in inhibiting the invasive ability and metastatic potential of TNBC cells.

RESULTS

Here, we showed that the increased level of cytosolic, not extracellular, Gαh is a poor prognostic marker in breast cancer patients and correlates with the metastatic evolution of TNBC cells. Moreover, clinicopathological analyses revealed that the combined signature of high Gαh/PLCδ1 levels indicates worse prognosis in patients with breast cancer and correlates with lymph node metastasis of ER-negative breast cancer. Blocking the PPI of the Gαh/PLCδ1 complex by synthetically myristoylated PLCδ1 peptide corresponding to the Gαh-binding interface appeared to significantly suppress cellular invasiveness in vitro and inhibit lung metastatic colonies of TNBC cells in vivo.

CONCLUSIONS

This study establishes Gαh/PLCδ1 as a poor prognostic factor for patients with estrogen receptor-negative breast cancers, including TNBCs, and provides therapeutic value by targeting the PPI of the Gαh/PLCδ1 complex to combat the metastatic progression of TNBCs.

Tissue transglutaminase (TG2) is involved in the resistance of cancer cells to the histone deacetylase (HDAC) inhibitor vorinostat

Vorinostat demonstrated preclinical and clinical efficacy in human cancers and is the first histone deacetylase inhibitor (HDACi) approved for cancer treatment. Tissue transglutaminase (TG2) is a multifunctional enzyme that catalyzes a Ca²⁺ dependent transamidating reaction resulting in covalent cross-links between proteins. TG2 acts also as G-protein in trans-membrane signaling and as a cell surface adhesion mediator. TG2 up-regulation has been demonstrated in several cancers and its expression levels correlate with resistance to chemotherapy and metastatic potential. We demonstrated that the anti-proliferative effect of the HDACi vorinostat is paralleled by the induction of TG2 mRNA and protein expression in cancer cells but not in ex vivo treated peripheral blood lymphocytes. This effect was also shared by other pan-HDACi and resulted in increased TG2 transamidating activity. Notably, high TG2 basal levels in a panel of cancer cell lines correlated with lower vorinostat antiproliferative activity. Notably, in TG2-knockdown cancer cells vorinostat anti-proliferative and pro-apoptotic effects were enhanced, whereas in TG2-full-length transfected cells were impaired, suggesting that TG2 could represent a mechanism of intrinsic or acquired resistance to vorinostat. In fact, co-treatment of tumor cells with inhibitors of TG2 transamidating activity potentiated the antitumor effect of vorinostat. Moreover, vorinostat-resistant MCF7 cells selected by stepwise increasing concentrations of the drug, significantly overexpressed TG2 protein compared to parental cells, and co-treatment of these cells with TG2 inhibitors reversed vorinostat-resistance. Taken together, our data demonstrated that TG2 is involved in the resistance of cancer cells to vorinostat, as well as to other HDACi.

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.

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.

Niclosamide As a Potential Nonsteroidal Therapy for Endometriosis That Preserves Reproductive Function in an Experimental Mouse Model

Endometriosis causes severe chronic pelvic pain and infertility. Because the standard medication and surgical treatments of endometriosis show high recurrence of symptoms, it is necessary to improve current treatment options. In the initial study, we examined whether niclosamide can be a useful drug for endometriosis in a preclinical setting. Endometriotic implants were induced using an established mouse model involving transimplantation of mouse endometrial fragments to the peritoneal wall of recipient mice. When the recipient mice were treated with niclosamide for 3 weeks, niclosamide reduced the size of endometriotic implants with inhibition of cell proliferation, and inflammatory signaling including RELA (NFKB) and STAT3 activation, but did not alter expression of steroid hormone receptors. To identify genes whose expression is regulated by niclosamide in endometriotic implants, RNA-sequencing was performed, and several genes downregulated by niclosamide were related to inflammatory responses, WNT and MAPK signaling. In a second study designed to assess whether niclosamide affects reproductive function, the recipient mice started receiving niclosamide after the induction of endometriosis. Then, the recipient mice were mated with wild type males, and treatments continued until the pups were born. Niclosamide treated recipient mice became pregnant and produced normal size and number of pups. These results suggest that niclosamide could be an effective therapeutic drug, and acts as an inhibitor of inflammatory signaling without disrupting normal reproductive function.

Type II transglutaminase stimulates epidermal cancer stem cell epithelial-mesenchymal transition

Type II transglutaminase (TG2) is a multifunctional protein that has recently been implicated as having a role in ECS cell survival. In the present study we investigate the role of TG2 in regulating epithelial mesenchymal transition (EMT) in ECS cells. Our studies show that TG2 knockdown or treatment with TG2 inhibitor, results in a reduced EMT marker expression, and reduced cell migration and invasion. TG2 has several activities, but the most prominent are its transamidase and GTP binding activity. Analysis of a series of TG2 mutants reveals that TG2 GTP binding activity, but not the transamidase activity, is required for expression of EMT markers (Twist, Snail, Slug, vimentin, fibronectin, N-cadherin and HIF-1α), and increased ECS cell invasion and migration. This coupled with reduced expression of E-cadherin. Additional studies indicate that NF&#ξ03BA;B signaling, which has been implicated as mediating TG2 impact on EMT in breast cancer cells, is not involved in TG2 regulation of EMT in skin cancer. These studies suggest that TG2 is required for maintenance of ECS cell EMT, invasion and migration, and suggests that inhibiting TG2 GTP binding/G-protein related activity may reduce skin cancer tumor survival.

Strategies towards in vivo imaging of active transglutaminase type 2 using positron emission tomography

Transglutaminase type 2 (TG2) is increasingly linked to the pathogenesis of several diseases, such as celiac disease, cancer, and fibrotic and neurodegenerative diseases. In parallel with becoming an attractive target for therapy, interest in the development of compounds for in vivo imaging of TG2 is rising. Such imaging biomarkers might assist in clarifying the role of TG2 in pathology and in monitoring TG2 inhibition in vivo and thus assist in drug development. In this review, the latest results together with various strategies in TG2 PET tracer development are discussed, including radiolabelling of irreversible and reversible active-site inhibitors, as well as allosteric inhibitors, acyl-donor and acyl-acceptor substrates, and anti-TG2 monoclonal antibodies.

Tissue transglutaminase-interleukin-6 axis facilitates peritoneal tumor spreading and metastasis of human ovarian cancer cells

Inflammation has recently been implicated in cancer formation and progression. As tissue transglutaminase (TG2) has been associated with both inflammatory signaling and tumor cell behavior, we propose that TG2 may be an important link inducing interleukin-6 (IL-6)-mediated cancer cell aggressiveness, including cancer stem cell-like characteristics and distant hematogenous metastasis. We evaluated the effect of differential TG2 and IL-6 expression on in vivo distant metastasis of human ovarian cancer cells. IL-6 production in human ovarian cancer cells was dependent on their TG2 expression levels. The size and efficiency of tumor sphere formation were correlated with TG2 expression levels and were dependent on TG2-mediated IL-6 secretion in human ovarian cancer cells. Primary tumor growth and propagation in the peritoneum and distant hematogenous metastasis into the liver and lung were also dependent on TG2 and downstream IL-6 expression levels in human ovarian cancer cells. In this report, we provide evidence that TG2 is an important link in IL-6-mediated tumor cell aggressiveness, and that TG2 and downstream IL-6 could be important mediators of distant hematogenous metastasis of human ovarian cancer cells. Intervention specific to TG2 and/or downstream IL-6 in ovarian cancer cells could provide a promising means to control tumor metastasis.

Transglutaminase is a tumor cell and cancer stem cell survival factor

Recent studies indicate that cancer cells express elevated levels of type II transglutaminase (TG2), and that expression is further highly enriched in cancer stem cells derived from these cancers. Moreover, elevated TG2 expression is associated with enhanced cancer stem cell marker expression, survival signaling, proliferation, migration, invasion, integrin-mediated adhesion, epithelial-mesenchymal transition, and drug resistance. TG2 expression is also associated with formation of aggressive and metastatic tumors that are resistant to conventional therapeutic intervention. This review summarizes the role of TG2 as a cancer cell survival factor in a range of tumor types, and as a target for preventive and therapeutic intervention. The literature supports the idea that TG2, in the closed/GTP-binding/signaling conformation, drives cancer cell and cancer stem cell survival, and that TG2, in the open/crosslinking conformation, is associated with cell death.

Tissue Transglutaminase Mediated Tumor-Stroma Interaction Promotes Pancreatic Cancer Progression

PURPOSE

Aggressive pancreatic cancer is commonly associated with a dense desmoplastic stroma, which forms a protective niche for cancer cells. The objective of the study was to determine the functions of tissue transglutaminase (TG2), a Ca(2+)-dependent enzyme that cross-links proteins through transamidation and is abundantly expressed by pancreatic cancer cells in the pancreatic stroma.

EXPERIMENTAL DESIGN

Orthotopic pancreatic xenografts and coculture systems tested the mechanisms by which the enzyme modulates tumor-stroma interactions.

RESULTS

We show that TG2 secreted by cancer cells effectively molds the stroma by cross-linking collagen, which, in turn, activates fibroblasts and stimulates their proliferation. The stiff fibrotic stromal reaction conveys mechanical cues to cancer cells, leading to activation of the YAP/TAZ transcription factors, promoting cell proliferation and tumor growth. Stable knockdown of TG2 in pancreatic cancer cells leads to decreased size of pancreatic xenografts.

CONCLUSIONS

Taken together, our results demonstrate that TG2 secreted in the tumor microenvironment orchestrates the cross-talk between cancer cells and stroma fundamentally affecting tumor growth. Our study supports TG2 inhibition in the pancreatic stroma as a novel strategy to block pancreatic cancer progression.

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.

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.

Biological functionalities of transglutaminase 2 and the possibility of its compensation by other members of the transglutaminase family

Transglutaminase 2 (TG2) is the most widely distributed and most abundantly expressed member of the transglutaminase family of enzymes, a group of intracellular and extracellular proteins that catalyze the Ca²⁺-dependent posttranslational modification of proteins. It is a unique member of the transglutaminase family owing to its specialized biochemical, structural and functional elements, ubiquitous tissue distribution and subcellular localization, and substrate specificity. The broad substrate specificity of TG2 and its flexible interaction with numerous other gene products may account for its multiple biological functions. In addition to the classic Ca²⁺-dependent transamidation of proteins, which is a hallmark of transglutaminase enzymes, additional Ca²⁺-independent enzymatic and nonenzymatic activities of TG2 have been identified. Many such activities have been directly or indirectly implicated in diverse cellular physiological events, including cell growth and differentiation, cell adhesion and morphology, extracellular matrix stabilization, wound healing, cellular development, receptor-mediated endocytosis, apoptosis, and disease pathology. Given the wide range of activities of the transglutaminase gene family it has been suggested that, in the absence of active versions of TG2, its function could be compensated for by other members of the transglutaminase family. It is in the light of this assertion that we review, herein, TG2 activities and the possibilities and premises for compensation for its absence.

A novel mechanism by which tissue transglutaminase activates signaling events that promote cell survival

Tissue transglutaminase (tTG) functions as a GTPase and an acyl transferase that catalyzes the formation of protein cross-links. tTG expression is frequently up-regulated in human cancer, where it has been implicated in various aspects of cancer progression, including cell survival and chemo-resistance. However, the extent to which tTG cooperates with other proteins within the context of a cancer cell, versus its intrinsic ability to confer transformed characteristics to cells, is poorly understood. To address this question, we asked what effect the ectopic expression of tTG in a non-transformed cellular background would have on the behavior of the cells. Using NIH3T3 fibroblasts stably expressing a Myc-tagged form of tTG, we found that tTG strongly protected these cells from serum starvation-induced apoptosis and triggered the activation of the PI3-kinase/mTOR Complex 1 (mTORC1)/p70 S6-kinase pathway. We determined that tTG forms a complex with the non-receptor tyrosine kinase c-Src and PI3-kinase, and that treating cells with inhibitors to block tTG function (monodansylcadaverine; MDC) or c-Src kinase activity (PP2) disrupted the formation of this complex, and prevented tTG from activating the PI3-kinase pathway. Moreover, treatment of fibroblasts over-expressing tTG with PP2, or with inhibitors that inactivate components of the PI3-kinase pathway, including PI3-kinase (LY294002) and mTORC1 (rapamycin), ablated the tTG-promoted survival of the cells. These findings demonstrate that tTG has an intrinsic capability to stimulate cell survival through a novel mechanism that activates PI3-kinase signaling events, thus highlighting tTG as a potential target for the treatment of human cancer.

Small molecule inhibitors target the tissue transglutaminase and fibronectin interaction

Tissue transglutaminase (TG2) mediates protein crosslinking through generation of ε-(γ-glutamyl) lysine isopeptide bonds and promotes cell adhesion through interaction with fibronectin (FN) and integrins. Cell adhesion to the peritoneal matrix regulated by TG2 facilitates ovarian cancer dissemination. Therefore, disruption of the TG2-FN complex by small molecules may inhibit cell adhesion and metastasis. A novel high throughput screening (HTS) assay based on AlphaLISA™ technology was developed to measure the formation of a complex between His-TG2 and the biotinylated FN fragment that binds TG2 and to discover small molecules that inhibit this protein-protein interaction. Several hits were identified from 10,000 compounds screened. The top candidates selected based on >70% inhibition of the TG2/FN complex formation were confirmed by using ELISA and bioassays measuring cell adhesion, migration, invasion, and proliferation. In conclusion, the AlphaLISA bead format assay measuring the TG2-FN interaction is robust and suitable for HTS of small molecules. One compound identified from the screen (TG53) potently inhibited ovarian cancer cell adhesion to FN, cell migration, and invasion and could be further developed as a potential inhibitor for ovarian cancer dissemination.