Activity-independent cell adhesion to tissue-type transglutaminase is mediated by α4β1 integrin

Transglutaminases (TGases) are enzymes which catalyze cross-link formation between glutamine residues and lysine residues in substrate proteins. We have previously reported that one of the TGases, blood coagulation factor XIIIa (FXIIIa), is capable of mediating adhesion of various cells. In this paper, we report for the first time that tissue-type transglutaminase (TGc) also has cell adhesion activity. TGc-coated plastic surface promoted adhesion and spreading of cells in a TGc concentration-dependent manner. However, there are some obvious differences between cell adhesion mediated by TGc and FXIIIa. As was reported previously, the adhesion to FXIIIa is dependent on its TGase activity. In contrast, the TGc-mediated cell adhesion is independent of its TGase activity: 1) The modification of the active center cysteine with iodoacetamide blocked the enzyme activity without any effect on cell adhesion; 2) the addition of Mg²⁺ did not induce the enzyme activity but it was as effective as Ca²⁺ for cell adhesion; 3) the addition of NH₄⁺ inhibited the enzyme activity but did not affect the cell adhesion significantly. The integrins involved in these cell adhesions are quite different. In the case of FXIIIa, αvβ3 and α5β1 integrins are involved and consequently the RGD peptide substantially inhibited the adhesion. On the other hand, the cell adhesion to TGc is mediated by α4β1 integrin but not α5β1; a CS-1 peptide, which represents the binding site of fibronectin to α4β1 integrin, completely inhibited the cell adhesion to TGc. It is possible that TGc and FXIIIa may mediate cell adhesion under different physiological and pathological situations.