HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY Transglutaminase-mediated oligomerization of the fibrin(ogen) C 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 C domains with factor XIIIa generates ordered C oligomers mimicking polymeric arrangement of the C domains in fibrin. These oligomers and those prepared with tissue transglutaminase were used to establish a mechanism of the C domain– mediated interaction of fibrin with endothelial cells. Cell adhesion and chemical cross-linking experiments revealed that oligomerization of the C domains by both transglutaminases significantly increases their RGD (arginyl–glycyl–aspartate)– dependent interaction with endothelial V 3 and to a lesser extent with V 5 and 5 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 signalregulated kinase (ERK) signaling pathways. The enhanced integrin clustering is likely caused by ordered juxtaposition of RGDcontaining integrin-binding sites upon oligomerization of the C domains and increased affinity of these domains for integrins. Our findings provide new insights into the mechanism of the 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. (Blood. 2005;105:3561-3568)