Tissue Transglutaminase Activation Modulates Inflammation in Cystic Fibrosis via PPARγ Down-Regulation

Abstract

Cystic fibrosis (CF), the most common life-threatening inherited disease in Caucasians, is due to mutations in the CF transmembrane conductance regulator (CFTR) gene and is characterized by airways chronic inflammation and pulmonary infections. The inflammatory response is not secondary to the pulmonary infections. Indeed, several studies have shown an increased proinflammatory activity in the CF tissues, regardless of bacterial infections, because inflammation is similarly observed in CFTR-defective cell lines kept in sterile conditions. Despite recent studies that have indicated that CF airway epithelial cells can spontaneously initiate the inflammatory cascade, we still do not have a clear insight of the molecular mechanisms involved in this increased inflammatory response. In this study, to understand these mechanisms, we investigated ex vivo cultures of nasal polyp mucosal explants of CF patients and controls, CFTR-defective IB3-1 bronchial epithelial cells, C38 isogenic CFTR corrected, and 16HBE normal bronchial epithelial cell lines. We have shown that a defective CFTR induces a remarkable up-regulation of tissue transglutaminase (TG2) in both tissues and cell lines. The increased TG2 activity leads to functional sequestration of the anti-inflammatory peroxisome proliferator-activated receptor γ and increase of the classic parameters of inflammation, such as TNF-α, tyrosine phosphorylation, and MAPKs. Specific inhibition of TG2 was able to reinstate normal levels of peroxisome proliferator-activated receptor-γ and dampen down inflammation both in CF tissues and CFTR-defective cells. Our results highlight an unpredicted central role of TG2 in the mechanistic pathway of CF inflammation, also opening a possible new wave of therapies for sufferers of chronic inflammatory diseases.

SUMOylation of Tissue Transglutaminase as Link between Oxidative Stress and Inflammation

“…We have shown that in CF airways high levels of reactive oxygen species (ROS) lead to an increase of TG2 activity, TG2-mediated PPAR␥ cross-linking, ubiquitination, and proteasome degradation, thus driving inflammation (22). Blocking TG2 through specific gene-silencing or TG2 inhibitors increases PPAR␥ protein and reverses inflammation (22). The mechanisms by which the genetic CF defect leads to TG2 up-regulation and inflammation, however, are still unknown.…”

“…We have previously investigated the molecular mechanisms that regulate this "intrinsic" proinflammatory profile and made a link between CFTR-defective function and inflammation (22). We have shown that nasal polyp mucosa from CF patients as well as human CFTR-defective cell lines constitutively up-regulate tissue transglutaminase (TG2), a multifunctional protein expressed in several tissues (25).…”

“…It catalyzes cross-links or deamidation of target proteins in the presence of high Ca 2ϩ levels (27), whereas at low Ca 2ϩ concentrations it may function as a G protein or a protein disulfide isomerase (27), thus contributing to the functionality of the mithocondrial respiratory chain complexes. We have shown that in CF airways high levels of reactive oxygen species (ROS) lead to an increase of TG2 activity, TG2-mediated PPAR␥ cross-linking, ubiquitination, and proteasome degradation, thus driving inflammation (22). Blocking TG2 through specific gene-silencing or TG2 inhibitors increases PPAR␥ protein and reverses inflammation (22).…”

“…IB3-1 cell lines were incubated for 24 h with EUK-134 (50 g/ml; Alexis Biochemicals), TG inhibitor R283 (250 M), KCC009 (250 M), or cystamine (400 M; Sigma-Aldrich) followed or not by rosiglitazone for 6 h (10 M; Alexis Biochemicals). A549 and 16HBE cell lines were incubated for 1 h with H 2 O 2 (33) (2 mM; Sigma-Aldrich) and for 24 h with rotenone (1 M; Sigma-Aldrich) or buthionine sulfoximine (10 M; Sigma-Aldrich) in the presence or absence of EUK-134 as well as with CFTR-inh172 (20,22) (20 M;Calbiochem). A549 and 16HBE cell lines were also cultured under hypoxic conditions in a humidified hypoxia chamber (Cop Laboratories) for 1 h at 1% O 2 (5% CO 2 balance N 2 ), and temperature was maintained at 37°C (34).…”

Cancer cells promote survival through depletion of the von Hippel–Lindau tumor suppressor by protein crosslinking

“…Increased TGase 2 expression correlates with increased NF-kB activity in breast cancer tissue ). Amplification of NF-kB-mediated signaling activity by TGase 2 appears to be mediated by the depletion of peroxisome proliferator-activated receptor-g, a known inhibitor of NF-kB (Maiuri et al, 2008). Either case of TGase-2-mediated downregulation of inhibitor of NF-kB or peroxisome proliferator-activated receptor-g presents reducing suppressor of inflammatory transcription factors.…”