Transglutaminase 2: a new paradigm for NF-kappaB involvement in disease

Transglutaminase 2 Promotes Autophagy by LC3 Induction through p53 Depletion in Cancer Cell

Transglutaminase 2 (TGase 2) plays a key role in p53 regulation, depleting p53 tumor suppressor through autophagy in renal cell carcinoma. We found that microtubule-associated protein 1A/1B-light chain 3 (LC3), a hallmark of autophagy, were tightly associated with the level of TGase 2 in cancer cells. TGase 2 overexpression increased LC3 levels, and TGase 2 knockdown decreased LC3 levels in cancer cells. Transcript abundance of LC3 was inversely correlated with level of wild type p53. TGase 2 knockdown using siRNA, or TGase 2 inhibition using GK921 significantly reduced autophagy through reduction of LC3 transcription, which was followed by restoration of p53 levels in cancer cells. TGase 2 overexpression promoted the autophagy process by LC3 induction, which was correlated with p53 depletion in cancer cells. Rapamycin-resistant cancer cells also showed higher expression of LC3 compared to the rapamycin-sensitive cancer cells, which was tightly correlated with TGase 2 levels. TGase 2 knockdown or TGase 2 inhibition sensitized rapamycin-resistant cancer cells to drug treatment. In summary, TGase 2 induces drug resistance by potentiating autophagy through LC3 induction via p53 regulation in cancer.

Renal Cell Carcinoma Is Abrogated by p53 Stabilization through Transglutaminase 2 Inhibition

In general, expression of transglutaminase 2 (TGase 2) is upregulated in renal cell carcinoma (RCC), resulting in p53 instability. Previous studies show that TGase 2 binds to p53 and transports it to the autophagosome. Knockdown or inhibition of TGase 2 in RCC induces p53-mediated apoptosis. Here, we screened a chemical library for TGase 2 inhibitors and identified streptonigrin as a potential therapeutic compound for RCC. Surface plasmon resonance and mass spectroscopy were used to measure streptonigrin binding to TGase 2. Mass spectrometry analysis revealed that streptonigrin binds to the N-terminus of TGase 2 (amino acids 95–116), which is associated with inhibition of TGase 2 activity in vitro and with p53 stabilization in RCC. The anti-cancer effects of streptonigrin on RCC cell lines were demonstrated in cell proliferation and cell death assays. In addition, a single dose of streptonigrin (0.2 mg/kg) showed marked anti-tumor effects in a preclinical RCC model by stabilizing p53. Inhibition of TGase 2 using streptonigrin increased p53 stability, which resulted in p53-mediated apoptosis of RCC. Thus, targeting TGase 2 may be a new therapeutic approach to RCC.

New Insights into Development of Transglutaminase 2 Inhibitors as Pharmaceutical Lead Compounds

Transglutaminase 2 (EC 2.3.2.13; TG2 or TGase 2) plays important roles in the pathogenesis of many diseases, including cancers, neurodegeneration, and inflammatory disorders. Under normal conditions, however, mice lacking TGase 2 exhibit no obvious abnormal phenotype. TGase 2 expression is induced by chemical, physical, and viral stresses through tissue-protective signaling pathways. After stress dissipates, expression is normalized by feedback mechanisms. Dysregulation of TGase 2 expression under pathologic conditions, however, can potentiate pathogenesis and aggravate disease severity. Consistent with this, TGase 2 knockout mice exhibit reversal of disease phenotypes in neurodegenerative and chronic inflammatory disease models. Accordingly, TGase 2 is considered to be a potential therapeutic target. Based on structure–activity relationship assays performed over the past few decades, TGase 2 inhibitors have been developed that target the enzyme’s active site, but clinically applicable inhibitors are not yet available. The recently described the small molecule GK921, which lacks a group that can react with the active site of TGase 2, and efficiently inhibits the enzyme’s activity. Mechanistic studies revealed that GK921 binds at an allosteric binding site in the N-terminus of TGase 2 (amino acids (a.a.) 81–116), triggering a conformational change that inactivates the enzyme. Because the binding site of GK921 overlaps with the p53-binding site of TGase 2, the drug induces apoptosis in renal cell carcinoma by stabilizing p53. In this review, we discuss the possibility of developing TGase 2 inhibitors that target the allosteric binding site of TGase 2.

Prognostic role of tissue transglutaminase 2 in colon carcinoma

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

Transglutaminase 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.

Novel anti-nociceptive effects of cardamonin via blocking expression of cyclooxygenase-2 and transglutaminase-2

Recently, we reported that Alpinia katsumadai (AK) has anti-nociceptive activity in vivo and that cardamonin (CDN) from AK suppresses the activity and expression of transglutaminase-2 (Tgase-2). However, it remains unknown whether CDN contributes to the anti-nociceptive activities of AK in vivo. We examined the anti-inflammatory effects of CDN in MG63 osteoblast-like cells and Raw264.7 macrophage-like cells treated with interleukin-1β treatment. CDN suppressed the expression of Tgase-2, cyclooxygenase-2 (COX-2), and p65 (nuclear factor-κB) in a concentration-dependent manner, and restored the expression of IκB in MG63 and Raw264.7 cells. However, CDN did not inhibit the activity of COX-2. Gene silencing of Tgase-2 reduced the COX-2 expression in MG63 cells. Phenylbenzoquinone (PBQ)-induced writhing, carrageenan-induced hyperalgesia, and rota-rod test were used to evaluate the anti-nociceptive activity in vivo. CDN (3-30 mg/kg, orally administered) significantly inhibited PBQ-induced writhing. CDN also produced a significant, dose-dependent increase in the withdrawal response latencies in carrageenan-induced hyperalgesia. The effects of CDN on PBQ-induced writhing were not caused by impaired motor functions. These results suggest that CDN might be helpful in controlling the pain from inflammatory diseases.

Ethacrynic Acid Inhibits Sphingosylphosphorylcholine-Induced Keratin 8 Phosphorylation and Reorganization via Transglutaminase-2 Inhibition

Sphingosylphosphorylcholine (SPC) is significantly increased in the malicious ascites of tumor patients and induces perinuclear reorganization of keratin 8 (K8) filaments in PANC-1 cells. The reorganization contributes to the viscoelasticity of metastatic cancer cells resulting in increased migration. Recently, we reported that transglutaminase-2 (Tgase-2) is involved in SPC-induced K8 phosphorylation and reorganization. However, effects of Tgase-2 inhibitors on SPC-induced K8 phosphorylation and reorganization were not clearly studied. We found that ethacrynic acid (ECA) concentration-dependently inhibited Tgase-2. Therefore, we examined the effects of ECA on SPC-induced K8 phosphorylation and reorganization. ECA concentration-dependently suppressed the SPC-induced phosphorylation and perinuclear reorganization of K8. ECA also suppressed the SPC-induced migration and invasion. SPC induced JNK activation through Tgase-2 expression and ECA suppressed the activation and expression of JNK in PANC-1 cells. These results suggested that ECA might be useful to control Tgase-2 dependent metastasis of cancer cells such as pancreatic cancer and lung cancers.

Anti-cancer effect of a quinoxaline derivative GK13 as a transglutaminase 2 inhibitor

PURPOSE

Transglutaminase 2 (TGase 2), a cross-linking enzyme, plays an important role in both pro-survival and anti-apoptosis during oncogenesis. For instance, TGase 2 induces NF-κB activation through I-κBα polymerization, which leads to the increase of pro-survival factors such as BCl-2. TGase 2 also suppresses apoptosis via depletion of caspase 3 and cathepsin D. Therefore, a specific TGase 2 inhibitor may become a very useful treatment for cancer showing high levels of TGase 2 expression.

METHODS

By small-molecule library screening, we managed to locate a competitive TGase 2 inhibiting quinoxaline compound (GK13) from 50 other quinoxaline derivatives. The 50 compounds that were screened represent a thousand structurally diverse, potentially pharmaceutical heterocyclic compound libraries, including benzopyrans, oxadiazoles, thiadiazoles, and quinoxalines. By measuring GI50, TGI, and LC50 using SRB assay, GK13 was selected.

RESULTS

In vitro enzyme kinetics using guinea pig liver TGase 2 showed that IC50 value was about 16.4 E-6 M. GK13 inhibits TGase 2-mediated I-κBα polymerization in a dose-dependent manner. LC50 of GK13 showed greater efficacy as 4.3E-4 M than LC50 of doxorubicin that showed efficacy as 3.87E-3 M in NCC72 composing 11 tissue origins and 72 cancer cell lines.

CONCLUSION

GK13 showed a possibility that quinoxaline derivatives may be effective for anti-cancer activity via TGase 2 inhibition.

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

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

Transglutaminase-2 induces N-cadherin expression in TGF-β1-induced epithelial mesenchymal transition via c-Jun-N-terminal kinase activation by protein phosphatase 2A down-regulation

Epithelial-mesenchymal-transition (EMT) is a key event for tumour cells to initiate metastasis leading to switching of E-cadherin to N-cadherin. Transglutaminase-2 (Tgase-2) expression is increased in TGF-β1-induced EMT in A549 lung cancer cells or other lung cancer cells. The role and underlying mechanism of Tgase-2 in N-cadherin switching of TGF-β1-induced EMT are not known. The involvement and mechanisms of Tgase-2 were investigated in A549 cells using chemical inhibitors, gene silencing and over-expression. TGF-β1-induced EMT was suppressed by cystamine or gene silencing of Tgase-2. Suppression of Tgase-2 or the c-Jun-N-terminal kinase (JNK) inhibitor, SP600125, significantly reduced and over-expression of Tgase-2 increased the expression of N-cadherin. The relationship between Tgase-2 and JNK in the TGF-β1-induced EMT of A549 cells was examined using Tgase-2 over-expressed A549 cells (A549(TG2)) and Tgase-2 silenced A549 cells (A549(shTG2)). JNK activation was significantly increased in A549(TG2) cells and decreased in A549(shTG2) cells. In contrast, PP2A expression was decreased in A549(TG2) and A549 cells and increased in A549(shTG2) cells. The involvement of Tgase-2 in N-cadherin expression was also confirmed in an in vivo lung cancer orthotopic model by injection of A549(WT) and A549(shTG2) cells into SCID mice. Tgase-2 expressing A549(WT) cells-injected mice group showed increased expressions of N-cadherin and JNK activation, but decreased expression of PP2A in lung cancer tissue comparing with the A549(shTG2) cells-injected group. These results suggested that Tgase-2 induces N-cadherin expression of TGF-β1-induced EMT via JNK activation by PP2A down-regulation, and Tgase-2/PP2A/JNK might be a novel axis that affects N-cadherin switching in the EMT of A549 lung cancer cells.

Novel suppressive effects of cardamonin on the activity and expression of transglutaminase-2 lead to blocking the migration and invasion of cancer cells

AIMS

Alpinia katsumadai was recently found in our previous study to have anti-migratory and anti-invasion activities against HT-1080 cells. However, the study did not demonstrate the exact component of Alpinia katsumadai with anti-migratory and anti-invasive activities. We tested the effects and relevant mechanism of cardamonin (CDN) on the migration and invasion of cancer cells.

MAIN METHODS

Migration and invasion of cancer cells were measured using multi-well chambers. Zymography and Western blots were used to examine the effects of CDN on the activities of matrix metalloproteinases (MMPs) and expression of transglutaminase-2 (Tgase-2).

KEY FINDINGS

CDN, but not alpinetin, dose-dependently suppressed the migration and 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced invasion of HT-1080 sarcoma cells. CDN suppressed the expression of Tgase-2, MMP-2, NF-κB and MMP-9 in HT-1080 cells, and suppressed MMP-2 and MMP-9 activities. Gene silencing of Tgase-2 suppressed the migration and invasion of HT-1080 cells and suppressed the activities of MMP-2 and MMP-9. Migration of various cancer cells having high levels of Tgase-2 were also inhibited by CDN. CDN and Alpinia katsumadai extracts also directly inhibited the activity of Tgase-2.

SIGNIFICANCE

CDN inhibits migration of several cancer cell lines expressing Tgase-2 via suppression of Tgase-2 expression and inhibition of Tgase-2 activity. The finding that CDN has Tgase-2 inhibitory activity will give us a new scaffold or clue of pharmacophore for the development of more effective Tgase-2 inhibitors.

Divergent results induced by different types of septic shock in transglutaminase 2 knockout mice

Acute sepsis can be induced by cytokines such as TNF-α and biological products such as LPS. All of these agents cause systemic inflammation, which is characterized by hemodynamic shock and liver toxicity. However, the outcomes of different septic shock models were totally opposite in transglutaminase 2 knockout (TGase 2(-/-)) mice. The aim of our study was to clarify the role of TGase 2 in liver injury. Therefore, we explored the role of TGase 2 in liver damage using two different stress models: LPS-induced endotoxic shock and TNF-α/actinomycin D (ActD)-induced sepsis. TNF-α-dependent septic shock resulted in increased liver damage in TGase 2(-/-) mice compared with wild-type (WT) mice, and was accompanied by increased levels of caspase 3 and cathepsin D (CTSD) in the damaged liver. Conversely, LPS-induced septic shock resulted in ablation of inflammatory endotoxic shock in TGase 2(-/-) mice and decreased liver injury. We found that TGase 2 protected liver tissue from TNF-α-dependent septic shock by reducing the expression of caspase 3 and CTSD. However, TGase 2 differently participated in increased the hemodynamic shock in LPS-induced septic shock through macrophage activation rather than protecting direct liver damage. Therefore, these findings demonstrate that septic shock caused by different agents may induce different results in TGase 2(-/-) mice depending on the primary target organs affected.