TGM2 and cystic fibrosis: Treharne et al. [53] found that RA could reduce the extent of the fibrotic lesions in cystic fibrosis, and could increase the expression of tissue transglutaminase (Tgase2); Tgase2 crosslinks proteins between ɛ-amino groups a lysine residues and γ-carboxamide groups of glutamine residues (increased stability and resistance to proteolysis) and also acts as a G-protein.