Transglutaminase 2 programs differentiating acute promyelocytic leukemia cells in all-trans retinoic acid treatment to inflammatory stage through NF-κB activation

Metabolic characterisation of transglutaminase 2 inhibitor effects in breast cancer cell lines

Transglutaminase 2 (TG2), which mediates post-translational modifications of multiple intracellular enzymes, is involved in the pathogenesis and progression of cancer. We used 1 H-NMR metabolomics to study the effects of AA9, a novel TG2 inhibitor, on two breast cancer cell lines with distinct phenotypes, MCF-7 and MDA-MB-231. AA9 can promote apoptosis in both cell lines, but it is particularly effective in MD-MB-231, inhibiting transamidation reactions and decreasing cell migration and invasiveness. This metabolomics study provides evidence of a major effect of AA9 on MDA-MB-231 cells, impacting glutamate and aspartate metabolism, rather than on MCF-7 cells, characterised by choline and O-phosphocholine decrease. Interestingly, AA9 treatment induces myo-inositol alteration in both cell lines, indicating action on phosphatidylinositol metabolism, likely modulated by the G protein activity of TG2 on phospholipase C. Considering the metabolic deregulations that characterise various breast cancer subtypes, the existence of a metabolic pathway affected by AA9 further points to TG2 as a promising hot spot. The metabolomics approach provides a powerful tool to monitor the effectiveness of inhibitors and better understand the role of TG2 in cancer.

Transglutaminase 2 associated with PI3K and PTEN in a membrane-bound signalosome platform blunts cell death

Atypically expressed transglutaminase 2 (TG2) has been identified as a poor prognostic factor in a variety of cancers. In this study, we evaluated the contribution of TG2 to the prolonged cell survival of differentiated acute promyelocytic leukaemia (APL) cells in response to the standard treatment with combined retinoic acid (ATRA) and arsenic trioxide (ATO). We report that one advantage of ATRA + ATO treatment compared to ATRA alone diminishes the amount of activated and non-activated CD11b/CD18 and CD11c/CD18 cell surface integrin receptors. These changes suppress ATRA-induced TG2 docking on the cytosolic part of CD18 β2-integrin subunits and reduce cell survival. In addition, TG2 overexpresses and hyperactivates the phosphatidylinositol-3-kinase (PI3K), phospho-AKT S473, and phospho-mTOR S2481 signalling axis. mTORC2 acts as a functional switch between cell survival and death by promoting the full activation of AKT. We show that TG2 presumably triggers the formation of a signalosome platform, hyperactivates downstream mTORC2-AKT signalling, which in turn phosphorylates and inhibits the activity of FOXO3, a key pro-apoptotic transcription factor. In contrast, the absence of TG2 restores basic phospho-mTOR S2481, phospho-AKT S473, PI3K, and PTEN expression and activity, thereby sensitising APL cells to ATO-induced cell death. We conclude, that atypically expressed TG2 may serve as a hub, facilitating signal transduction via signalosome formation by the CD18 subunit with both PI3K hyperactivation and PTEN inactivation through the PI3K-PTEN cycle in ATRA-treated APL cells.

Roles of PADI4 in the expression of cytokines involved in inflammation and adhesion in differentiated NB4 cells treated with ATRA

Differentiation syndrome (DS) is a common complication in patients with acute promyelocytic leukemia (APL) treated with all-trans-retinoic acid (ATRA). However, the target of ATRA during DS in patients with APL remains to be elucidated. Therefore, the current study aimed to investigate the role of peptidylarginine deiminase 4 (PADI4) in the differentiation of ATRA-induced NB4 APL cells. The results showed that PADI4 was significantly upregulated in peripheral blood samples derived from patients with APL DS compared with patients with APL only. In addition, whether ATRA could enhance the expression levels of PADI4 in NB4 cells in vitro was subsequently investigated. The results also showed that PADI4 overexpression promoted the differentiation of NB4 cells treated with ATRA, which was reversed after PADI4 silencing. To uncover the potential mechanisms underlying the above process, PADI4 overexpression induced the secretion of inflammation-related cytokines, such as TNF-α, IL-1β, IL-8, C-C motif chemokine (CCL)2, CCL4, CCR1 and intercellular adhesion molecule-1 in ATRA-treated NB4 cells. However, PADI4 knockdown in the same cells had the opposite effect. The above findings indicated that PADI4 could be involved in the differentiation of ATRA-induced NB4 cells and upregulation of cytokines.

Effects of peripheral blood leukocyte count and tumor necrosis factor-alpha on early death in acute promyelocytic leukemia

BACKGROUND

Early death remains a major factor in survival in APL. We aimed to analyze the risk factors for differentiation syndrome and early death in acute promyelocytic leukemia (APL).

METHODS

The clinical data of APL patients who were newly diagnosed at Mianyang Central Hospital from January 2013 to January 2022 were retrospectively analyzed.

RESULTS

Eighty-six newly diagnosed APL patients (37 males and 49 females) were included in this study. The median age was 46 (17-75) years. Sixty-one patients (70.9%) had low/intermediate-risk APL, and 25 patients (29.1%) had high-risk APL. The incidence of differentiation syndrome (DS) was 62.4%. The multivariate analysis showed that a peak white blood cell (WBC) count ≥16 × 10^9/L was an independent risk factor (OR = 11.000, 95% CI: 2.830-42.756, P = 0.001) for DS in all APL patients, while a WBC count ≥10 × 10^9/L on Day 5 was an independent risk factor for DS in low-intermediate risk APL patients (OR = 9.114, 95% CI: 2.384-34.849, P = 0.001). There were 31 patients (36.5%) with mild DS and 22 patients (25.9%) with severe DS. The multivariate analysis showed that WBC count ≥23 × 10^9/L at chemotherapy was an independent risk factor for severe DS (OR = 10.500, 95% CI: 2.344-47.034, P = 0.002). The rate of early death (ED) was 24.4% (21/86). The multivariate analysis showed that male gender (OR = 7.578,95% CI:1.136-50.551, P = 0.036), HGB < 65 g/L (OR = 16.271,95% CI:2.012-131.594, P = 0.009) and WBC count ≥7 × 10^9/L on Day 3(OR = 23.359,95% CI:1.825-298.959, P = 0.015) were independent risk factors for ED. The WBC count at diagnosis, WBC count on Day 3 and WBC count on Day 5 had moderate positive correlations with tumor necrosis factor-α (TNF-α) at diagnosis, and the correlation coefficients were 0.648 (P = 0.012), 0.615 (P = 0.033), and 0.609 (P = 0.035), respectively. The WBC count had no correlation with IL-6.

CONCLUSION

During induction treatment, cytotoxic chemotherapy may need to be initiated to reduce the risk of DS for APL patients with a low-intermediate risk WBC count ≥10 × 10^9/L on Day 5 or for all patients with a peak WBC count ≥16 × 10^9/L. Patients with WBC > 7 × 10^9/L on Day 3 have a higher risk of ED. Leukocyte proliferation is associated with TNF-α rather than IL-6, and TNF-α may be a potential biomarker for predicting ED.

A Multidisciplinary Approach Establishes a Link between Transglutaminase 2 and the Kv10.1 Voltage-Dependent K+ Channel in Breast Cancer

Since the multifunctionality of transglutaminase 2 (TG2) includes extra- and intracellular functions, we investigated the effects of intracellular administration of TG2 inhibitors in three breast cancer cell lines, MDA-MB-231, MDA-MB-436 and MDA-MB-468, which are representative of different triple-negative phenotypes, using a patch-clamp technique. The first cell line has a highly voltage-dependent a membrane current, which is low in the second and almost absent in the third one. While applying a voltage protocol to responsive single cells, injection of TG2 inhibitors triggered a significant decrease of the current in MDA-MB-231 that we attributed to voltage-dependent K⁺ channels using the specific inhibitors 4-aminopyridine and astemizole. Since the Kv10.1 channel plays a dominant role as a marker of cell migration and survival in breast cancer, we investigated its relationship with TG2 by immunoprecipitation. Our data reveal their physical interaction affects membrane currents in MDA-MB-231 but not in the less sensitive MDA-MB-436 cells. We further correlated the efficacy of TG2 inhibition with metabolic changes in the supernatants of treated cells, resulting in increased concentration of methyl- and dimethylamines, representing possible response markers. In conclusion, our findings highlight the interference of TG2 inhibitors with the Kv10.1 channel as a potential therapeutic tool depending on the specific features of cancer cells.

Predictive values of plasma TNFα and IL-8 for intracranial hemorrhage in patients with acute promyelocytic leukemia

In patients with acute promyelocytic leukemia (APL), intracranial hemorrhage (ICH), if not identified promptly, could be fatal. It is the leading cause of failure of induction and early death. Thus, biomarkers that could promptly predict severe complications are critical. Here, cytokine differences between patients with APL with and without ICH were investigated to develop predictive models for this complication. The initial cytokine profiling using plasma samples from 39 patients and 18 healthy donors found a series of cytokines that were remarkedly different between patients with APL and healthy controls. The APL patients were subsequently divided into high and low white blood cell count groups. Results showed that tumor necrosis factor a and interleukin 8 (IL-8) were vital in distinguishing patients with APL who did or did not develop ICH. In addition, verification in 81 patients with APL demonstrated that the two cytokines were positively correlated with the cumulative incidence of ICH. Finally, in-vitro and in-vivo experimental evidence were provided to show that IL-8 influenced the migration of APL-derived NB4 cells and impaired the blood-brain barrier in PML/RARα positive blast-transplanted FVB/NJ mice. These assessments may facilitate the early warning of ICH and reduce future mortality levels in APL.

A Bioinformatics View on Acute Myeloid Leukemia Surface Molecules by Combined Bayesian and ABC Analysis

“Big omics data” provoke the challenge of extracting meaningful information with clinical benefit. Here, we propose a two-step approach, an initial unsupervised inspection of the structure of the high dimensional data followed by supervised analysis of gene expression levels, to reconstruct the surface patterns on different subtypes of acute myeloid leukemia (AML). First, Bayesian methodology was used, focusing on surface molecules encoded by cluster of differentiation (CD) genes to assess whether AML is a homogeneous group or segregates into clusters. Gene expressions of 390 patient samples measured using microarray technology and 150 samples measured via RNA-Seq were compared. Beyond acute promyelocytic leukemia (APL), a well-known AML subentity, the remaining AML samples were separated into two distinct subgroups. Next, we investigated which CD molecules would best distinguish each AML subgroup against APL, and validated discriminative molecules of both datasets by searching the scientific literature. Surprisingly, a comparison of both omics analyses revealed that CD339 was the only overlapping gene differentially regulated in APL and other AML subtypes. In summary, our two-step approach for gene expression analysis revealed two previously unknown subgroup distinctions in AML based on surface molecule expression, which may guide the differentiation of subentities in a given clinical–diagnostic context.

Quantitative proteomics and in-cell cross-linking reveal cellular reorganisation during early neuronal differentiation of SH-SY5Y cells

The neuroblastoma cell line SH-SY5Y is commonly employed to study neuronal function and disease. This includes cells grown under standard conditions or differentiated to neuron-like cells by administration of chemical reagents such as retinoic acid (RA) or phorbol-12-myristate-13-acetate (PMA). Even though SH-SY5Y cells are widely explored, a complete description of the resulting proteomes and cellular reorganisation during differentiation is still missing. Here, we relatively quantify the proteomes of cells grown under standard conditions and obtained from two differentiation protocols employing RA or a combination of RA and PMA. Relative quantification and KEGG pathway analysis of the proteins reveals the presence of early differentiating cells and provides a list of marker proteins for undifferentiated and differentiated cells. For characterisation of neuronal sub-types, we analyse expression of marker genes and find that RA-differentiated cells are acetylcholinergic and cholinergic, while RA/PMA-differentiated cells show high expression of acetylcholinergic and dopaminergic marker genes. In-cell cross-linking further allows capturing protein interactions in different cellular organelles. Specifically, we observe structural reorganisation upon differentiation involving regulating protein factors of the actin cytoskeleton.

Quantitative proteomic analyses are employed to explore the changes in the proteome that occur upon neuronal differentiation in the SH-SY5Y cell line.

Nuclear factor-kappa B and effector molecules in photoaging

Nuclear factor-kappa B (NF-κB) has important but complex functions in the photoaging of the human skin. This protein complex is activated upon UV irradiation and plays a key role in the signalling pathway of the inflammatory cascade. NF-κB induces the expression of various proinflammatory cytokines, such as tumour necrosis factor (TNF) and interleukin-1 (IL-1). These proinflammatory cytokines can in turn stimulate the activation of NF-κB, forming a vicious cycle. These processes cause chronic inflammation and contribute to skin ageing. In addition, the activation of NF-κB upregulates the expression of matrix metalloproteinases (MMPs) and leads to the degradation of structural proteins in the dermis. NF-κB disrupts the barrier function of the skin under prolonged and repeated UV stimulations in these ways. Such activity causes chronic skin damage, followed by the formation of wrinkles, dryness, roughness, laxity, and other photoaging manifestations. This study on the NF-κB signalling pathway and effector molecules provides a new perspective to understand and prevent photoaging.

ALDH1A1 overexpression in melanoma cells promotes tumor angiogenesis by activating the IL‑8/Notch signaling cascade

ALDH1A1 is a cytosolic enzyme upregulated in tumor cells, involved in detoxifying cells from reactive aldehydes and in acquiring resistance to chemotherapeutic drugs. Its expression correlates with poor clinical outcomes in a number of cancers, including melanoma. The present study hypothesized that the increased ALDH1A1 expression and activity upregulated the release of proangiogenic factors from melanoma cells, which regulate angiogenic features in endothelial cells (ECs) through a rearrangement of the Notch pathway. In vivo, when subcutaneously implanted in immunodeficient mice, ALDH1A1 overexpressing melanoma cells displayed a higher microvessel density. In a 3D multicellular system, obtained co‑culturing melanoma cancer cells with stromal cells, including ECs, melanoma ALDH1A1 overexpression induced the recruitment of ECs into the core of the tumorspheres. By using a genes array, overexpression of ALDH1A1 in tumor cells also promoted modulation of Notch cascade gene expression in ECs, suggesting an interaction between tumor cells and ECs mediated by enrichment of angiogenic factors in the tumor microenvironment. To confirm this hypothesis, inactivation of ALDH1A1 by the pharmacological inhibitor CM037 significantly affected the release of angiogenic factors, including IL‑8, from melanoma cells. High levels of ALDH1A1, through the retinoic acid pathway, regulated the activation of NF‑kB‑p65 and IL‑8. Further, in a 2D co‑culture system, the addition of an IL‑8 neutralizing antibody to ECs co‑cultured with melanoma cells forced to express ALDH1A1 dampened endothelial angiogenic features, both at the molecular (in terms of gene and protein expression of mediators of the Notch pathway) and at the functional level (proliferation, scratch assay, tube formation and permeability). In conclusion, these findings demonstrated the existence of a link between melanoma ALDH1A1 expression and EC Notch signaling modification that results in a pro‑angiogenic phenotype. Based on the crucial role of ALDH1A1 in melanoma control of the tumor microenvironment, the enzyme seems a promising target for the development of novel drugs able to interrupt the cross‑talk between cancer (stem) cells and endothelial cells.

[Regulatory Effect of All-Trans Retinoic Acid on the Expression of IL-1β in Macrophages and the Mechanisms Involved]

Objective

To investigate the regulatory effect of all-trans retinoic acid (ATRA) on the expression interleukin-1β (IL-1β) in macrophages and the mechanisms involved.

Methods

Macrophages were treated with 1 μmol/L ATRA for 24 h before RNA-Sequence. Differentially expressed genes (DEGs) were screened out and analyzed by Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis, gene ontology (GO) functional analysis, and protein-protein interaction networks (PPI) analysis. After treatment with different doses of ATRA for 24 h, the expression of IL-1β was examined with qRT-PCR and Western blot. The activation of NF-κB signaling and caspase-1 was observed by Western blot and immunofluorescence staining.

Results

Compared with the blank control group, a total of 71 DEGs of macrophages were upregulated in the ATRA treatment group. KEGG analysis showed that the up-regulated DEGs were involved in IL-17 signaling pathway, tumor necrosis factor (TNF) signaling pathway, etc. GO analysis indicated that the up-regulated DEGs were involved in the biological processes of the production of IL-1β, response to lipopolysaccharide, etc. PPI analysis revealed that inflammatory cytokines, adhesion molecules, and chemokines were the key genes that ATRA acted on. In vitro experiments showed that ATRA promoted IL-1β expression in macrophages in a concentration-dependent manner. The expression of p-NF-κB, NF-κB, and caspase-1 were significantly increased by ATRA compared with those of the control group ( P<0.05), and p-NF-κB translocated to the cell nucleus in the ATRA group.

Conclusion

ATRA may promote the expression of IL-1β by activating NF-κB signaling and caspase-1 in macrophages, this study may provide evidence for the immune regulatory function of ATRA on macrophages.

Dysregulation of Transglutaminase type 2 through GATA3 defines aggressiveness and Doxorubicin sensitivity in breast cancer

The role of transglutaminase type 2 in cell physiology is related to protein transamidation and signal transduction (affecting extracellular, intracellular and nuclear processes) aided by the expression of truncated isoforms and of two lncRNAs with regulatory functions. In breast cancer TG2 is associated with disease progression supporting motility, epithelial-mesenchymal transition, invasion and drug resistance. The aim of his work is to clarify these issues by emphasizing the interconnections among TGM2 variants and transcription factors associated with an aggressive phenotype, in which the truncated TGH isoform correlates with malignancy. TGM2 transcripts are upregulated by several drugs in MCF-7, but only Doxorubicin is effective in MDA-MB-231 cells. These differences reflect the expression of GATA3, as demonstrated by silencing, suggesting a link between this transcription factor and gene dysregulation. Of note, NC9, an irreversible inhibitor of enzymatic TG2 activities, emerges to control NF-ĸB and apoptosis in breast cancer cell lines, showing potential for combination therapies with Doxorubicin.

Role of Transglutaminase 2 in Cell Death, Survival, and Fibrosis

Transglutaminase 2 (TG2) is a ubiquitously expressed enzyme catalyzing the crosslinking between Gln and Lys residues and involved in various pathophysiological events. Besides this crosslinking activity, TG2 functions as a deamidase, GTPase, isopeptidase, adapter/scaffold, protein disulfide isomerase, and kinase. It also plays a role in the regulation of hypusination and serotonylation. Through these activities, TG2 is involved in cell growth, differentiation, cell death, inflammation, tissue repair, and fibrosis. Depending on the cell type and stimulus, TG2 changes its subcellular localization and biological activity, leading to cell death or survival. In normal unstressed cells, intracellular TG2 exhibits a GTP-bound closed conformation, exerting prosurvival functions. However, upon cell stimulation with Ca²⁺ or other factors, TG2 adopts a Ca²⁺-bound open conformation, demonstrating a transamidase activity involved in cell death or survival. These functional discrepancies of TG2 open form might be caused by its multifunctional nature, the existence of splicing variants, the cell type and stimulus, and the genetic backgrounds and variations of the mouse models used. TG2 is also involved in the phagocytosis of dead cells by macrophages and in fibrosis during tissue repair. Here, we summarize and discuss the multifunctional and controversial roles of TG2, focusing on cell death/survival and fibrosis.

The impact of ICAM-1, CCL2 and TGM2 gene polymorphisms on differentiation syndrome in acute promyelocytic leukemia

Background

Although arsenic trioxide (ATO) and all-trans retinoic acid (ATRA) are well-tolerated and effective treatments for Acute Promyelocytic Leukemia (APL), Differentiation Syndrome (DS) is a lethal side effect in some patients. The pathogenesis of DS is complex and not well understood; however, it is considered as an inflammatory response due to cytokines release of differentiated cells. Moreover, adhesion molecules that are widely expressed on the surface of differentiated cells and gene expression changes of transglutaminase2 (TGM2) are mechanisms involved in the development of DS. The purpose of this study was to assess the association of single nucleotide polymorphisms (SNP) of Intercellular Adhesion Molecule-1 (ICAM-1), chemokine (C-C motif) ligand 2 (CCL2) and TGM2 as inflammatory factors with differentiation syndrome susceptibility.

Methods

DNA was extracted from 133 APL patients and 100 normal controls. Assessment according to the PETHEMA criteria revealed that 13.5% of these patients experienced differentiation syndrome. Tetra-ARMS PCR and PCR-RFLP were done to amplify DNA fragments in APL patients with and without DS. Then DNA sequencing was done to validate the results. SNPStats, SPSS and Finch TV were used to analyze the results.

Results

A significant correlation was found between rs4811528 in the TGM2 gene and differentiation syndrome susceptibility (P = 0.002, 95% CI = 1.74–18.81, OR = 5.72) while rs5498 in ICAM-1, rs1024611 in CCL2, and rs7270785 in TGM2 genes showed no correlation with differentiation syndrome. The G allele of rs7270785 and rs4811528 showed a haplotypic association with differentiation syndrome (P = 0.03, 95% CI = 1.13–13.86, OR = 3.96).

Conclusions

AA genotype of the TGM2 SNP (rs4811528) may be a risk factor for development of DS in patients with APL following the use of ATRA/ATO.

Benefits of Combined All-Trans Retinoic Acid and Arsenic Trioxide Treatment of Acute Promyelocytic Leukemia Cells and Further Enhancement by Inhibition of Atypically Expressed Transglutaminase 2

Randomized trials in acute promyelocytic leukemia patients have shown that treatment with a combination of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) is superior in efficacy to monotherapy, with significantly decreased mortality. So far, there are little data available to explain the success of the ATRA and ATO combination treatment in molecular terms. We showed that ATRA- and ATO-treated cells had the same capacity for superoxide production, which was reduced by two-thirds in the combined treatment. Secreted inflammatory biomarkers (monocyte chemoattractant protein-1 [MCP-1], interleukin-1 beta [IL-1β] and tumor necrosis factor-α [TNF-α]) were significantly decreased and were further reduced in a transglutaminase 2 (TG2) expression-dependent manner. The amount of secreted TNF-α in the supernatant of NB4 TG2 knockout cells was close to 50 times lower than in ATRA-treated differentiated wild-type NB4 cells. The irreversible inhibitor of TG2 NC9 not only decreased reactive oxygen species production 28-fold, but decreased the concentration of MCP-1, IL-1β and TNF-α 8-, 15- and 61-fold, respectively in the combined ATRA + ATO-treated wild-type NB4 cell culture. We propose that atypical expression of TG2 leads to the generation of inflammation, which thereby serves as a potential target for the prevention of differentiation syndrome.

Neutrophil elastase-mediated proteolysis of the tumor suppressor p200 CUX1 promotes cell proliferation and inhibits cell differentiation in APL

AIMS

Neutrophil elastase (NE) is a critical proteolytic enzyme that is involved in cancer. We previously reported high NE expression in peripheral blood neutrophils from acute promyelocytic leukemia (APL) patients. The present study aimed to elucidate the specific role and mechanisms of NE in APL development.

MATERIALS AND METHODS

NE expression was detected in APL bone marrow samples and analyzed in the BloodSpot database. CCK-8 assay and flow cytometry were used to assess cell proliferation and cell cycle distribution, respectively. The expression levels of proliferation and differentiation markers were measured by Western blotting and quantitative real-time PCR. The co-expression and interaction of NE and p200 cut-like homeobox 1 (CUX1) were evaluated by indirect immunofluorescence, co-immunoprecipitation, and in situ proximity ligation assay.

KEY FINDINGS

NE was highly expressed in APL bone marrow and blood neutrophils. NE overexpression promoted the proliferation and inhibited the differentiation of NB4 cells, whereas NE downregulation achieved the opposite results in U937 cells. Mechanistically, NE interacted with and effectively hydrolyzed the tumor suppressor p200 CUX1. Rescue experiments revealed that p200 CUX1 upregulation reversed the functional influence of NE on APL cells.

SIGNIFICANCE

NE-mediated proteolysis of the tumor suppressor p200 CUX1 promotes APL progression. NE/p200 CUX1 axis is a novel and promising therapeutic target for APL treatment.

Overexpression of TG2 enhances the differentiation of ectomesenchymal stem cells into neuron‑like cells and promotes functional recovery in adult rats following spinal cord injury

Ectomesenchymal stem cells (EMSCs) represent a type of adult stem cells derived from the cranial neural crest. These cells are capable of self-renewal and have the potential for multidirectional differentiation. Tissue transglutaminase type 2 (TG2) is a ubiquitously expressed member of the transglutaminase family of Ca²⁺-dependent crosslinking enzymes. However, the effect of TG2 on neural differentiation and proliferation of EMSCs remains unknown. To determine whether TG2 improves EMSC proliferation and neurogenesis, a stable TG2-overexpressing EMSC cell line (TG2-EMSCs) was established by using an adenovirus system. Immunofluorescence staining and western blot analyses demonstrated that TG2 overexpression had beneficial effects on the rate of EMSC neurogenesis, and that the proliferative capacity of TG2-EMSCs was higher than that of controls. Furthermore, the results of western blotting revealed that extracellular matrix (ECM) and neurotrophic factors were upregulated during the differentiation of TG2-EMSCs. Notably, TG2-EMSC transplantation in an animal model of spinal cord injury (SCI), TG2-EMSCs differentiated into neuron-like cells and enhanced the repair of SCI. Taken together, these results demonstrated that TG2 gene transfection may offer a novel strategy to enhance EMSC proliferation and neurogenesis in vivo and in vitro, which may ultimately facilitate EMSC-based transplantation therapy in patients with SCI.

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.