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

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.

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.

18F-labeling and initial in vivo evaluation of a Hitomi peptide for imaging tissue transglutaminase 2

INTRODUCTION

Tissue transglutaminase 2 (TG2) is a calcium-dependent enzyme which cross-links proteins. It is overexpressed in many diseases and plays a key role in tissue remodeling, including cell adhesion and migration. Overexpression of TG2 in breast cancer is a marker for patients at risk of recurrence. Non-invasive imaging of TG2 can therefore play an important role in patient management. TG2 probes labeled with the positron emitters ¹¹C and ¹⁸F have thus far not found widespread application due to purity and metabolism issues. Our approach was to radiolabel a TG2 selective, 13-mer amino acid peptide, which was modified with a 5-azidopentanoic acid group at the N-terminus via a copper free click chemistry approach.

METHODS

Radiochemistry was performed and fully automated using an iPhase FlexLab module. We produced the radiolabeling synthon [¹⁸F]FBz-DBCO from [¹⁸F]SFB and DBCO-amine. After HPLC purification, [¹⁸F]FBz-DBCO was reacted with the modified peptide and the putative radiotracer purified by HPLC. In vivo imaging using the radiolabeled amine was performed in mice bearing either TG2 expressing MDA-MB-231 or non-TG2 expressing MCF-7 xenografts as negative control. Expression of the target was confirmed using immunohistochemistry and western blot techniques.

RESULTS

We obtained 9 ± 2 GBq of the radiolabeled peptide from 55 ± 5 GBq of fluorine-18 in an overall synthesis time of 160 min from end of bombardment (EOB), including HPLC purification and reformulation. Small animal PET/MR imaging showed that visualization of MDA-MB-231 tumors using the radiolabeled peptide could only be achieved due to differences in clearance between tumor and surrounding tissue. In the MCF-7 xenograft model, radiotracer clearance from tumor and surrounding tissue occurred at a similar rate, thus making it impossible to visualize MCF-7 tumors. The presence of TG2 in MDA-MB-231 tumors and absence in MCF-7 tumors was confirmed by immunohistochemistry staining and western blot analysis.

CONCLUSION

A fully automated synthesis of a TG2 selective, 13-amino-acid peptide modified with 5-azido pentynoic acid at the N-terminal was established using [¹⁸F]FBzDBCO as a prosthetic group. Although our results show that radiolabeled peptides have potential as imaging agents for TG2, more research needs to be performed to improve radiotracer kinetics.

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.

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.

Transglutaminase 2 crosslinks the glutathione S-transferase tag, impeding protein-protein interactions of the fused protein

Glutathione S-transferase (GST) from Schistosoma japonicum has been widely used as a tag for affinity purification and pulldown of fusion proteins to detect protein-protein interactions. However, the reliability of this technique is undermined by the formation of GST-fused protein aggregates after incubation with cell lysates. It remains unknown why this aggregation occurs. Here, we demonstrate that the GST tag is a substrate of transglutaminase 2 (TG2), which is a calcium-dependent enzyme that polyaminates or crosslinks substrate proteins. Mutation analysis identified four glutamine residues in the GST tag as polyamination sites. TG2-mediated modification of the GST tag caused aggregate formation but did not affect its glutathione binding affinity. When incubated with cell lysates, GST tag aggregation was dependent on cellular TG2 expression levels. A GST mutant in which four glutamine residues were replaced with asparagine (GST^4QN) exhibited a glutathione binding affinity similar to that of wild-type GST and could be purified by glutathione affinity chromatography. Moreover, the use of GST^4QN as a tag reduced fused p53 aggregation and enhanced the induction of p21 transcription and apoptosis in cells treated with 5-fluorouracil (5-FU). These results indicated that TG2 interferes with the protein-protein interactions of GST-fused proteins by crosslinking the GST tag; therefore, a GST^4QN tag could improve the reproducibility and reliability of GST pulldown experiments.

Transglutaminase 2 induces intrinsic EGFR-TKI resistance in NSCLC harboring EGFR sensitive mutations

The non-small cell lung cancer (NSCLC) patients with EGFR-sensitive mutations can be therapeutically treated by EGFR-TKI such as erlotinib and gefitinib. However, about 40% of individuals harboring EGFR-TKI sensitive mutations are still resistant to EGFR-TKI. And, it has been reported that both PTEN loss and NF-κB activation contribute to intrinsic EGFR-TKI resistance in EGFR-mutant lung cancer. Transglutaminse 2 (TG2) is post-translational modification enzyme and known to induce degradation of tumor suppressors including PTEN and IκBα with peptide cross-linking activity. Because TG2 was known as a regulator of PTEN and IκBα (NF-κB inhibitor) level in cytosol, we have explored if TG2 can be another key regulator to the intrinsic resistance of EGFR-TKI in the intrinsic EGFR-TKI resistant NSCLC cell. We first found that higher TG2 expression level and lower PTEN and IκBα expression levels in the intrinsic EGFR-TKI resistant NSCLC compare with EGFR-TKI sensitive NSCLC. TG2 stably expressing EGFR-TKI sensitive NSCLC cells harboring EGFR mutations showed reduction of both PTEN and IκBα and exhibited EGFR-TKI resistance. In reverse, When TG2 is downregulated by TG2 inhibitor in H1650, intrinsic EGFR-TKI resistant NSCLC cell harboring EGFR sensitive mutation, reversed EGFR-TKI resistance via IκBα restoration. Moreover, combination treatment of TG2 inhibitor and EGFR-TKI decreased the tumor growth in mouse xenograft models of EGFR mutant NSCLCs. Therefore, we have demonstrated that TG2 elicits the intrinsic EGFR-TKI resistance via PTEN loss and activation of NF-κB pathway. These results suggest that TG2 may be a useful predictive marker and also be a target for overcoming the resistance.

Transglutaminase 2 takes center stage as a cancer cell survival factor and therapy target

Transglutaminase 2 (TG2) has emerged as a key cancer cell survival factor that drives epithelial to mesenchymal transition, angiogenesis, metastasis, inflammation, drug resistance, cancer stem cell survival and stemness, and invasion and migration. TG2 can exist in a GTP-bound signaling-active conformation or in a transamidase-active conformation. The GTP bound conformation of TG2 contributes to cell survival and the transamidase conformation can contribute to cell survival or death. We present evidence suggesting that TG2 has a role in human cancer, summarize what is known about the TG2 mechanism of action in a range of cancer types, and discuss TG2 as a cancer therapy target.

Prognostic value of Transglutaminase 2 in non-small cell lung cancer patients

Transglutaminase 2 (TG2) plays important roles in cell survival and cancer progression. In this study, we examined TG2 expression in specimen of 194 patients diagnosed with non-small cell lung cancer (NSCLC), and found that the TG2 gene expression was significantly higher in lung cancer tissues as compared to paired incisal marginal tissues or normal tissues. Our data revealed that patients with lower level of TG2 expression detected in cancer tissues had longer disease free survival and overall survival as compared to the patients with higher TG2 expression. We also found that TG2 expression level correlated to NSCLC recurrence. These results suggest a potential prognosis impact of TG2 for NSCLC patients.

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.

Association between tumor heterogeneity and progression-free survival in non-small cell lung cancer patients with EGFR mutations undergoing tyrosine kinase inhibitors therapy

For non-small cell lung cancer (NSCLC) patients with epidermal growth factor receptor (EGFR) mutations, current staging methods do not accurately predict the risk of disease recurrence after tyrosine kinase inhibitors (TKI) therapy. Developing a noninvasive method to predict whether individual could benefit from TKI therapy has great clinical significance. In this research, a radiomics approach was proposed to determine whether the tumor heterogeneity of NSCLC, which was measured by the texture on computed tomography (CT), could make an independent prediction of progression-free survival (PFS). A primary dataset contained 80 patients (median PFS, 9.5 months) with positive EGFR mutations and a validation dataset contained 72 NSCLC (median PFS, 10.2 months) patients were used for prognosis trial. The experiment results indicated that the features: "Cluster Prominence of Gray Level Co-occurrence" (hazard ratio [HR]: 2.13, 95% confidence interval [CI]: (1.33, 3.40), P = 0.010) and "Short Run High Gray Level Emphasis of Run Length" (HR: 2.43, 95%CI: (1.46, 4.05), P = 0.005) were significantly associated with PFS in the primary dataset, and these two texture features also make a consistent performance on the validation cohort. Our study further supported that the quantitative measurement of tumor heterogeneity can be associated with prognosis of NSCLC patients with EGFR mutation.

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

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

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-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.

Transglutaminase 2 in cancer

The significant influence of tumor microenvironment on malignant cells has been investigated with enthusiasm in this era of targeted therapy. Transglutaminase 2 (TG2, EC 2.3.2.13), a multi-functional enzyme that catalyzes the formation of intermolecular isopeptide bonds between glutamine and lysine side-chains, has been reported to exert important pathophysiological functions. The aim of this review was to investigate the correlation between TG2 and malignant behaviors, which could provide the rationale for novel approaches in anti-cancer therapy. We performed a systematic and electronic search on Medline, Scopus, and Web of Science for relevant publications from inception to April 2015. The bibliographic references of retrieved articles were further reviewed for additional relevant studies. TG2 exerts important physiological functions and plays vital roles in inflammation mainly through its modulation on the structure and stability of extracellular matrix (ECM). It also regulates EMT of diverse malignant cells through various intracellular and extracellular pathways. TG2 also plays an important role in tumor progression and may serve as a novel prognostic biomarker and therapeutic target in various cancer types. TG2 promotes malignant cell mobility, invasion, and metastasis, and induces chemo-resistance of cancer cells, mainly through its pro-crosslink and signaling transduction mediation propensities. In conclusion, TG2 plays vital roles in malignancy progression, and may have important prognostic and therapeutic significances.

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.

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.