Transglutaminase-mediated oligomerization of the fibrin(ogen) αC domains promotes integrin-dependent cell adhesion and signaling

Interactions of endothelial cells with fibrin(ogen) are implicated in inflammation, angiogenesis, and wound healing. Cross-linking of the fibrinogen alpha C domains with factor XIIIa generates ordered alpha C oligomers mimicking polymeric arrangement of the alpha C domains in fibrin. These oligomers and those prepared with tissue transglutaminase were used to establish a mechanism of the alpha C domain-mediated interaction of fibrin with endothelial cells. Cell adhesion and chemical cross-linking experiments revealed that oligomerization of the alpha C domains by both transglutaminases significantly increases their RGD (arginyl-glycyl-aspartate)dependent interaction with endothelial alpha V beta 3 and to a lesser extent with alpha V beta 5 and alpha 5 beta 1 integrins. The oligomerization promotes integrin clustering, thereby increasing cell adhesion, spreading, formation of prominent peripheral focal contacts, and integrin-mediated activation of focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK) signaling pathways. The enhanced integrin clustering is likely caused by ordered juxtaposition of RGD-containing integrin-binding sites upon oligomerization of the alpha C domains and increased affinity of these domains for integrins. Our findings provide new insights into the mechanism of the alpha C domain-mediated interaction of endothelial cells with fibrin and imply its potential involvement in cell migration. They also suggest a new role for transglutaminases in regulation of integrin-mediated adhesion and signaling via covalent modification of integrin ligands. (c) 2005 by The American Society of Hematology.