Cell-surface transglutaminase promotes fibronectin assembly via interaction with the gelatin-binding domain of fibronectin: a role in TGF beta-dependent matrix deposition

Assembly of fibronectin into a fibrillar matrix is critical for regulation of cell growth and migration, embryogenesis and wound healing. We have prev iously shown that cell-surface tissue transglutaminase serves as an integri n-binding adhesion coreceptor for fibronectin. Here we report that transglu taminase strongly promotes fibronectin assembly mediated by alpha5 beta1 in tegrin. This effect is independent from transglutaminase-mediated enzymatic crosslinking of fibronectin and separate from the ability of transglutamin ase to stimulate cell spreading. Surface transglutaminase increases the bin ding of fibronectin to cells via interaction with its gelatin-binding domai n that contains modules I6II1,2I7-9 and lacks integrin-binding motifs. The gelatin-binding fragment of fibronectin binds to surface transglutaminase o n cells in suspension but does not interact with cell monolayers where surf ace transglutaminase is occupied by fibronectin. Surface transglutaminase c olocalizes with growing fibronectin fibrils at early timepoints of matrix f ormation and remains codistributed with fibronectin matrices thereafter. Th e observed stimulation of matrix assembly by transglutaminase is blocked by the gelatin-binding fragment of fibronectin, but is not strongly perturbed by its N-terminal fragment consisting of modules I1-5. These results impli cate an interaction between transglutaminase and the gelatin-binding domain of fibronectin in matrix assembly and suggest its role in initiation of fi brillogenesis. However, blocking antibodies against alpha5 beta1 integrin o r the cell-binding fragment of fibronectin that contains modules III2-11 mo st strongly suppress matrix formation and abolish the effects of transgluta minase. Hence, transglutaminase cooperates with but can not substitute for alpha5 beta1 integrin in fibronectin assembly. Treatment of fibroblasts wit h transforming growth factor beta (TGF beta) significantly increases surfac e expression of transglutaminase and its association with beta1 integrins, but not with alphaV beta3 integrin. TGF beta enhances the binding of fibron ectin to the cell surface and elevates matrix formation, whereas antibody a gainst transglutaminase or the gelatin-binding fragment of fibronectin supp resses these effects, indicating an involvement of transglutaminase in TGF beta -dependent fibronectin assembly. Therefore, TGF beta -induced fibronec tin matrix deposition during normal wound healing or fibrotic disorders may depend on upregulation of integrin-associated surface transglutaminase.