Celiac Anti-Type 2 Transglutaminase Antibodies Induce Phosphoproteome Modification in Intestinal Epithelial Caco-2 Cells

Abstract

BackgroundCeliac disease is an inflammatory condition of the small intestine that affects genetically predisposed individuals after dietary wheat gliadin ingestion. Type 2-transglutaminase (TG2) activity seems to be responsible for a strong autoimmune response in celiac disease, TG2 being the main autoantigen. Several studies support the concept that celiac anti-TG2 antibodies may contribute to disease pathogenesis. Our recent findings on the ability of anti-TG2 antibodies to induce a rapid intracellular mobilization of calcium ions, as well as extracellular signal-regulated kinase phosphorylation, suggest that they potentially act as signaling molecules. In line with this concept, we have investigated whether anti-TG2 antibodies can induce phosphoproteome modification in an intestinal epithelial cell line.Methods and Principal FindingsWe studied phosphoproteome modification in Caco-2 cells treated with recombinant celiac anti-TG2 antibodies. We performed a two-dimensional electrophoresis followed by specific staining of phosphoproteins and mass spectrometry analysis of differentially phosphorylated proteins. Of 14 identified proteins (excluding two uncharacterized proteins), three were hypophosphorylated and nine were hyperphosphorylated. Bioinformatics analyses confirmed the presence of phosphorylation sites in all the identified proteins and highlighted their involvement in several fundamental biological processes, such as cell cycle progression, cell stress response, cytoskeletal organization and apoptosis.ConclusionsIdentification of differentially phosphorylated proteins downstream of TG2-antibody stimulation suggests that in Caco-2 cells these antibodies perturb cell homeostasis by behaving as signaling molecules. We hypothesize that anti-TG2 autoantibodies may destabilize the integrity of the intestinal mucosa in celiac individuals, thus contributing to celiac disease establishment and progression. Since several proteins here identified in this study were already known as TG2 substrates, we can also suppose that transamidating activity and differential phosphorylation of the same targets may represent a novel regulatory mechanism whose relevance in celiac disease pathogenesis is still unexplored.

Structural Basis for the Recognition in an Idiotype-Anti-Idiotype Antibody Complex Related to Celiac Disease

“…Indeed, several experimental evidences have highlighted the possible pathogenic role of anti-TG2 autoantibodies, as a consequence of their interaction with TG2 [68], [69]. Anti-idiotype antibodies have already been shown in vivo to be able to down-regulate autoantibodies, for instance in type-1 diabetes, by preventing them from binding to the autoantigen [23].…”

Transglutaminase 2 and Anti Transglutaminase 2 Autoantibodies in Celiac Disease and Beyond: Anti- Transglutaminase 2 Autoantibodies: Friends or Enemies

“…Since TG2 post translational deamidation of gliadin peptides is considered to be a cornerstone in the activation of the adaptive immune system, and since TG2 has multiple effects on major players in the intestinal innate immune system, and CD anti-TG2 antibodies were shown to inhibit TG2 enzymatic activity, those antibodies might be considered as pathogenic [22,27,[31][32][33][34]. They destabilize the integrity of the intestinal epithelium, thus may contribute to CD establishment and progression [35]. A CD total IgA was documented to increased transepithelial passage of gliadin peptides, in caco2 cellline.…”

Transglutaminase 2-specific coeliac disease autoantibodies induce morphological changes and signs of inflammation in the small-bowel mucosa of mice

“…Evidence shows that the TG2-autoantibodies are produced in the small-intestinal mucosa (Marzari et al 2001;Picarelli et al 1996), where they can bind TG2 present in the basement membrane and around blood vessels and form deposits characteristic of the disease (Di Niro et al 2012;Korponay-Szabó et al 2004;Koskinen et al 2008;Marzari et al 2001). The TG2-targeted autoantibodies have been demonstrated to mediate a wide spectrum of effects at in vitro, ex vivo and in vivo levels (Caja et al 2011;Caputo et al 2013;Kalliokoski et al 2013;Martucciello et al 2012;Paolella et al 2013), but their contribution to the disease pathogenesis remains as yet incompletely understood.…”