Tissue transglutaminase (tTG or TG2) is produced in excess in some diseases, such as cystic fibrosis, and contributes to inflammation and disease symptoms. tTG also readily moves in and out of cells by virtue of its basic triplet and when in the cytoplasm, tTG is ubiquinated and degraded by proteosomes. I have previously pointed out that internalization and proteosome degradation are also the initial steps in processing of proteins for presentation by the immune system and antibody production, i.e. turning a cellular protein into an autoantigen involved in autoimmune disease.
Here is an image of a computational protein model of tTG I drew with Chimera. I have highlighted the basic triplet to show its exposure to facilitate transport.
A recent article also links tTG intracellular chemical modifications (SUMOylation), which are linked to oxidative stress, to activation of NFkB and inflammation. Thus, tTG is a major player in controlling cell surface interactions with potentially toxic materials such as polyglutamine-rich gliadin, as well as triggering inflammation in response to oxidation stress.
Cystic Fibrosis Causes Overproduction of tTGWhen I read that cystic fibrosis results in an increase in the production of tTG in lungs, I immediately thought of the role of tTG as an autoantigen in celiac disease and the progression of celiac into Hashimoto’s thyroiditis, which has the same autoantigen, tTG. I suspected that the overproduction of tTG and inflammation in cystic fibrosis should increase tTG autoantibody production and tTG-mediated autoimmune diseases of celiac and Hashimoto’s thyroiditis.
Extra tTG Leads to Autoimmune CeliacA quick PubMed search of CF and celiac, revealed a study of comorbidity between CF and celiac in Norway. Just as expected, the two diseases occur together with a frequency three times higher than predicted by coincidence. CF stimulated tTG overproduction was driving the development of celiac.
references:
Luciani A, Villella VR, Vasaturo A, Giardino I, Raia V, Pettoello-Mantovani M, D'Apolito M, Guido S, Leal T, Quaratino S, Maiuri L. SUMOylation of tissue transglutaminase as link between oxidative stress and inflammation. J Immunol. 2009 Aug 15;183(4):2775-84.
Fluge G, Olesen HV, Gilljam M, Meyer P, Pressler T, Storrösten OT, Karpati F, Hjelte L. Co-morbidity of cystic fibrosis and celiac disease in Scandinavian cystic fibrosis patients. J Cyst Fibros. 2009 May;8(3):198-202.