Studies on differentiation‐dependent expression and activity of distinct transglutaminases by specific substrate peptides using three‐dimensional reconstituted epidermis

During skin formation, particularly during differentiation of keratinocytes, unique post‐translational modifications play a role in forming a proteinaceous supermolecule called the cornified envelope (CE), which is necessary for barrier function. Transglutaminases (TGs) are essential enzymes involved in the cross‐linking of various keratinocyte structural proteins to complete CE formation. The TG family consists of eight isozymes, with two members, TG1 and TG3, located mainly in the epidermis. In an in vitro three‐dimensional (3D) culture system, reconstruction of the epidermis allows cornification of the terminally differentiated keratinocytes. In this study, using isozyme‐specific substrate peptides that enable detection of TG activity, we investigated the expression and the activation pattern of each isozyme during differentiation in this culture system. In the differentiating cells, the protein levels, enzymatic activities, as well as localization of TG1 and TG3 exhibited distinct patterns. Specific knockdown of these enzymes by siRNA revealed less cornification, suggesting that each TG contributes to the epidermal formation. In conclusion, we demonstrate the efficiency of the 3D system for studying differentiation‐dependent expression and activity of distinct TGs by specific substrate peptides. Enzyme Transglutaminase, EC2.3.2.13. Transglutaminase (TG) is a cross‐linking enzyme polymerizing several structural proteins in keratinocytes. Expressions and activities of the two TG isozymes, TG1 and TG3, were investigated using three‐dimensional reconstituted human epidermis. Fluorescent‐labeled isozyme‐specific substrate peptide enabled to detect the distinct activity during keratinocyte differentiation.