Hypoxia-Dependent Expression of TG2 Isoforms in Neuroblastoma Cells as Consequence of Different MYCN Amplification Status

Biological Implications and Functional Significance of Transglutaminase Type 2 in Nervous System Tumors

Transglutaminase type 2 (TG2) is the most ubiquitously expressed member of the transglutaminase family. TG2 catalyzes the transamidation reaction leading to several protein post-translational modifications and it is also implicated in signal transduction thanks to its GTP binding/hydrolyzing activity. In the nervous system, TG2 regulates multiple physiological processes, such as development, neuronal cell death and differentiation, and synaptic plasticity. Given its different enzymatic activities, aberrant expression or activity of TG2 can contribute to tumorigenesis, including in peripheral and central nervous system tumors. Indeed, TG2 dysregulation has been reported in meningiomas, medulloblastomas, neuroblastomas, glioblastomas, and other adult-type diffuse gliomas. The aim of this review is to provide an overview of the biological and functional relevance of TG2 in the pathogenesis of nervous system tumors, highlighting its involvement in survival, tumor inflammation, differentiation, and in the resistance to standard therapies.

Hypoxia and inflammation conditions differentially affect the expression of tissue transglutaminase spliced variants and functional properties of extravillous trophoblast cells

PROBLEM

Persistent hypoxia and inflammation beyond early pregnancy are involved in a bad outcome because of defective trophoblast invasiveness. Tissue transglutaminase (TG2) coregulates several cell functions. An aberrant expression and/or transamidation activity could contribute to placental dysfunction.

METHOD OF STUDY

The first-trimester trophoblast cell line (Swan-71) was used to study TG2 expression and cell functions in the absence or presence of inflammatory cytokines (TNF-α, IL-1β) or chemical hypoxia (CoCl₂ ). We analyzed The concentration of cytokines in the supernatant by ELISA; Cell migration by scratch assay; NF-κB activation by detection of nuclear p65 by immunofluorescence or flow cytometry using a Swan-71 NF-κB-hrGFP reporter cell line. Tissue transglutaminase expression was analyzed by immunoblot and confocal microscopy. Expression of spliced mRNA variants of tissue transglutaminase was analyzed by RT-PCR. Transamidation activity was assessed by flow cytometry using 5-(biotinamido)-pentylamine substrate.

RESULTS

Chemical hypoxia and TGase inhibition, but not inflammatory stimuli, decreased Swan-71 migration. IL-6 production was also decreased by chemical hypoxia, but increased by inflammation. Intracellular TGase activity was increased by all stimuli, but NF-κB activation was observed only in the presence of proinflammatory cytokines. TG2 expression was decreased by CoCl₂ and TNF-α. Translocation of TG2 and p65 to nuclei was observed only with TNF-α, without colocalization. Differential relative expression of spliced variants of mRNA was observed between CoCl₂ and inflammatory stimuli.

CONCLUSION

The observed decrease in total TG2 expression and relative increase in short variants under hypoxia conditions could contribute to impaired trophoblast invasion and impact on pregnancy outcome.

CO2 pneumoperitoneum effects on proliferation and apoptosis in two different neuroblastoma cell lines

PURPOSE

The proto-oncogene MYCN is considered a transcription factor involved in the regulation of neuroblastoma (NB) cell biology. Since minimally invasive-surgery represents a debated treatment of NB, we investigated CO₂ effects on proliferative activity and apoptotic pathway in two NB cell lines, SH-SY5Y (MYCN-non-amplified) and IMR-32 (MYCN-amplified).

METHODS

SH-SY5Y and IMR-32 were exposed to CO₂ (100%) at a pressure of 15 mmHg for 4 h and then moved to normal condition for 24 h. Cell proliferation, caspase 3 activity and transcript levels of BAX, BCL-2, cyclin B, cyclin D and MMP-2 were evaluated.

RESULTS

CO₂ exposure caused a decrease in cell proliferation associated to increases in BAX/BCL-2 ratio and caspase 3 activity in SH-SY5Y, while opposite effects have been found in IMR-32. CO₂ exposure induced a decrease of cyclin B1 in SH-SY5Y, while an increase in cyclin B1 and D1 was observed in IMR-32. A slight up-regulation of MMP-2 expression in SH-SY5Y and a significant increase of 2.2 folds in IMR-32 was observed (p < 0.05).

CONCLUSIONS

Our results suggest that CO₂ exposure may cause different effects on various NB cell lines, likely due to MYCN amplification status. Further in vitro and in vivo studies are needed to highlight the role of laparoscopy on NB behaviour.

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.

Baicalin-Induced Autophagy Preserved LPS-Stimulated Intestinal Cells from Inflammation and Alterations of Paracellular Permeability

Several studies have demonstrated a relevant role of intestinal epithelial cells in the immune response and in chronic inflammatory conditions, including ulcers, colitis, and Crohn's disease. Baicalin (BA), extracted from the root of Scutellaria baicalensis, has various beneficial healthy effects, including anti-inflammatory activity. However, few studies have evaluated BA effects on autophagic signaling in epithelial cell response to inflammatory stimuli. To explore possible beneficial effects of BA, HT-29 cells were exposed to lipopolysaccharide (LPS), in presence or absence of BA, for 4 h. We evaluated mRNA levels of autophagy-related genes and cytokines, triggering inflammatory response. Furthermore, the expression of claudin 1, involved in the regulation of paracellular permeability was analyzed. BA treatment repressed LPS-induced expression of TNF-α and IL-1β. The down-regulation of autophagy-related genes induced by LPS was counteracted by cell pretreatment with BA. Under these conditions, BA reduced the NF-κB activation caused by LPS. Also, BA restored mRNA and protein levels of claudin 1, which were reduced by LPS. In conclusion, in intestinal epithelial cells BA regulates the NF-κB activation and modulates both autophagic and inflammatory processes, leading to an improvement of paracellular permeability. These results suggest that the anti-inflammatory effects of BA can be associated to the regulation of autophagic flux.