Effects of antiflammins on transglutaminase and phospholipase A2 activation by transglutaminase

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.

Transglutaminase 2 and neuroinflammation

Neuroinflammatory processes seem to play a pivotal role in various chronic neurodegenerative diseases, characterized also by the pathogenetic accumulation of specific protein aggregates. Several of these proteins have been shown to be substrates of transglutaminases, calcium-dependent enzymes that catalyze protein crosslinking reactions. However, it has recently been demonstrated that transglutaminase 2 (TG2) may also be involved in molecular mechanisms underlying inflammation. In the central nervous system, astrocytes and microglia are the cell types mainly involved in the inflammatory process. This review is focused on the increases of TG2 protein expression and enzyme activity that occur in astroglial, microglial and monocyte cell models in response to inflammatory stimuli. The transcription factor NF-κB is considered the main regulator of inflammation, being activated by a variety of stimuli including calcium influx, oxidative stress and inflammatory cytokines. Under these conditions, the over-expression of TG2 results in the sustained activation of NF-κB. Several findings emphasize the possible role of the TG2/NF-κB activation pathway in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, multiple sclerosis and amyotrophic lateral sclerosis. Although further studies are needed to characterize the TG2/NF-κB cross-talk in monocytes/macrophages/microglia within the central nervous system, some results show that TG2 and NF-κB are co-localized in cell compartments. Together, evidence suggests that TG2 plays a role in neuroinflammation and contributes to the production of compounds that are potentially deleterious to neuronal cells.

Uteroglobin, a possible ligand of the lipoxin receptor inhibits serum amyloid A-driven inflammation

Serum amyloid A (SAA) production is increased by inflamed arthritic synovial tissue, where it acts as a cytokine/chemoattractant for inflammatory and immune cells and as an inducer of matrix degrading enzymes. SAA has been shown to bind lipoxin A4 receptor, a member of the formyl-peptide related 2 G-protein coupled receptor family (ALX) and elicit proinflammatory activities in human primary fibroblast-like synoviocytes (FLS). We report on the identification of uteroglobin, a small globular protein with potent anti-inflammatory activities, as a possible ligand of ALX. Uteroglobin-specific association with ALX was demonstrated by an enzyme immunoassay experiment employing a cell line engineered to express the human ALX receptor. Uteroglobin's interaction with ALX resulted in the inhibition of SAA responses, such as attenuation of phospholipase A2 activation and cellular chemotaxis. In FLS, uteroglobin showed an antagonism against SAA-induced interleukin-8 release and decreased cell migration. These novel roles described for uteroglobin via ALX may help elucidate genetic and clinical observations indicating that a polymorphism in the uteroglobin promoter is linked to disease outcome, specifically prediction of bone erosion in patients with rheumatoid arthritis or severity of IgA glomerulonephritis and sarcoidosis.

Antiflammin-1 attenuates bleomycin-induced pulmonary fibrosis in mice

BACKGROUND

Antiflammin-1 (AF-1), a derivative of uteroglobin (UG), is a synthetic nonapeptide with diverse biological functions. In the present study, we investigated whether AF-1 has a protective effect against bleomycin-induced pulmonary fibrosis.

METHODS

C57BL/6 mice were injected with bleomycin intratracheally to create an animal model of bleomycin-induced pulmonary fibrosis. On Day 7 and Day 28, we examined the anti-inflammatory effect and antifibrotic effect, respectively, of AF-1 on the bleomycin-treated mice. The effects of AF-1 on the transforming growth factor-beta 1 (TGF-β1)-induced proliferation of murine lung fibroblasts (NIH3T3) were examined by a bromodeoxycytidine (BrdU) incorporation assay and cell cycle analysis.

RESULTS

Severe lung inflammation and fibrosis were observed in the bleomycin-treated mice on Day 7 and Day 28, respectively. Administration of AF-1 significantly reduced the number of neutrophils in the bronchoalveolar lavage fluid (BALF) and the levels of tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) in the lung homogenates on Day 7. Histological examination revealed that AF-1 markedly reduced the number of infiltrating cells on Day 7 and attenuated the collagen deposition and destruction of lung architecture on Day 28. The hydroxyproline (HYP) content was significantly decreased in the AF-1-treated mice. In vitro, AF-1 inhibited the TGF-β1-induced proliferation of NIH3T3 cells, which was mediated by the UG receptor.

CONCLUSIONS

AF-1 has anti-inflammatory and antifibrotic actions in bleomycin-induced lung injury. We propose that the antifibrotic effect of AF-1 might be related to its suppression of fibroblast growth in bleomycin-treated lungs and that AF-1 has potential as a new therapeutic tool for pulmonary fibrosis.

Transglutaminase 2 and phospholipase A₂ interactions in the inflammatory response in human Thp-1 monocytes

Several experimental approaches have demonstrated that transglutaminase 2 (TG2) increased activity is involved in monocyte activation and inflammatory response. Preliminary results also demonstrate a TG-mediated post-translational modification of phospholipase A2 (PLA2), which catalyzes the release of arachidonic acid from its lipid storage sites. The control of PLA2-mediated production of eicosanoids has been found to be of great benefit for inflammatory disease treatment. However, the identification of the mechanisms of PLA2 activation is a very complex issue, because of the presence of multiple PLA2 forms. The aim of this study was to characterize the interactions between TG2 and sPLA2 in LPS-stimulated THP-1 cells, which were treated with TPA to induce early differentiated macrophage-type model. We demonstrated that increases in TG2 enzyme activity and protein expression may be considered an early event in monocyte/macrophage activation by LPS. Under these conditions, TG2 protein was co-immunoprecipitated with PLA2 by monoclonal antibody directed against the secretory form of the enzyme (sPLA2-V). Concomitantly, the PLA2 enzyme activity increased in TPA-treated cells exposed to LPS; these high levels of enzyme activity were significant reduced by R283, a site-specific inhibitor of TG2. Moreover, confocal laser scanning microscopy analysis of double-immunostained cytochemical specimens confirmed a co-localization of BAPA-labeled proteins and sPLA2-V in LPS-treated cells. These findings give evidence of a complex TG2/sPLA2-V, suggesting the possibility that sPLA2-V is a substrate for TG2. These results demonstrated that TG2 increases produced a sustained activation of PLA2 activity, suggesting a functional interaction between these enzymes in the regulation of inflammatory response.

The protective role of uteroglobin through the modulation of tissue transglutaminase in the experimental crescentic glomerulonephritis

BACKGROUND AND METHODS

Tissue transglutaminase (tTG) may induce pro-inflammatory cytokines and produce irreversible end-products, thus promoting renal scarring. It has recently been confirmed that the crescent formation in murine experimental crescentic glomerulonephritis (ecGN) has been inhibited by the administration of recombinant uteroglobin (rUG). However, the ability of UG on tTG modulation has not been thoroughly assessed. In this study, we investigated the feasible protective role of UG in murine ecGN through the modulation of tTG and TGF-beta1 expressions. ecGN was induced by the administration of anti-GBM Ab into C57BL/6 mice.

RESULTS

Both proteinuria and BUN levels were distinctively lower in rUG-treated mice compared to those of disease control mice. Glomerular injuries such as mesangial proliferation, matrix production and crescent formation were lessened with the rUG treatment, and these findings were parallel with the attenuated expression of tTG and TGF-beta1. tTG and TGF-beta1 were expressed mainly on mesangial areas by the induction of ecGN and rUG treatment markedly attenuated the expressions of these proteins in glomeruli without spatial changes. With the addition of LPS to mesangial cells, the expressions of tTG and TGF-beta1 were up-regulated, whilst the addition of cysteamine, tTG inhibitor, attenuated the expression of tTG and TGF-beta1 as well as the cellular proliferation which was further induced by LPS.

CONCLUSION

We demonstrate for the first time that rUG is able to attenuate the renal injury through the modulation of expressions of tTG and TGF-beta1 in ecGN and further suggest a wide range of feasible molecular targets to reduce the severity of human glomerulonephritis.

Uteroglobin: a steroid-inducible immunomodulatory protein that founded the Secretoglobin superfamily

Blastokinin or uteroglobin (UG) is a steroid-inducible, evolutionarily conserved, secreted protein that has been extensively studied from the standpoint of its structure and molecular biology. However, the physiological function(s) of UG still remains elusive. Isolated from the uterus of rabbits during early pregnancy, UG is the founding member of a growing superfamily of proteins called Secretoglobin (Scgb). Numerous studies demonstrated that UG is a multifunctional protein with antiinflammatory/ immunomodulatory properties. It inhibits soluble phospholipase A(2) activity and binds and perhaps sequesters hydrophobic ligands such as progesterone, retinols, polychlorinated biphenyls, phospholipids, and prostaglandins. In addition to its antiinflammatory activities, UG manifests antichemotactic, antiallergic, antitumorigenic, and embryonic growth-stimulatory activities. The tissue-specific expression of the UG gene is regulated by several steroid hormones, although a nonsteroid hormone, prolactin, further augments its expression in the uterus. The mucosal epithelia of virtually all organs that communicate with the external environment express UG, and it is present in the blood, urine, and other body fluids. Although the physiological functions of this protein are still under investigation, a single nucleotide polymorphism in the UG gene appears to be associated with several inflammatory/autoimmune diseases. Investigations with UG-knockout mice revealed that the absence of this protein leads to phenotypes that suggest its critical homeostatic role(s) against oxidative damage, inflammation, autoimmunity, and cancer. Recent studies on UG-binding proteins (receptors) provide further insight into the multifunctional nature of this protein. Based on its antiinflammatory and antiallergic properties, UG is a potential drug target.

A Peptide with anti-transglutaminase activity decreases lipopolysaccharide-induced lung inflammation in mice

Octapeptide R2 (KVLDGQDP), which has anti-transglutaminas (TGase) activity, decreases inflammation in allergic conjunctivitis model in guinea pigs. The authors examined the effect of R2 on lipopolysaccharide (LPS)-induced lung injury in BALB/c mice. R2 inhalation significantly decreased neutrophil count and cytokine mRNA expression in the lungs of LPS (25 mg/kg)-treated mice (P < .05). It also showed a tendency for decreased tumor necrosis factor (TNF)-alpha-immunoreactive protein in lung homogenates and significantly decreased TNF-alpha-immunoreactive protein in the serum of LPS-injected mice (P < .05). These results indicate that TGase may be a new therapeutic target in LPS-induced lung inflammation.