Enhanced osteoblast adhesion on transglutaminase 2-crosslinked fibronectin

Abstract

Fibronectin (FN) is a cell adhesion protein that binds integrins in a process also involving the protein-crosslinking enzyme transglutaminase 2 (TG2) as a co-receptor. The cell-adhesive property of TG2 has been linked to a complex formation with FN and to its ability to crosslink and polymerize FN on the cell surface. We tested here the effects of extracellular FN, before and after in vitro crosslinking and polymerization by TG2, on MC3T3-E1 osteoblast adhesion. We show that TG2-mediated crosslinking creates large, compacted chain-like protein clusters that include both TG2 and FN molecules as analyzed by Western blotting and atomic force microscopy. Crosslinking of FN significantly promotes osteoblast adhesion as measured by crystal violet staining, and enhances beta(1)-integrin clustering on the cell surface as visualized by immunofluorescence microscopy. We hypothesize that TG2-mediated crosslinking enhances the cell-adhesive properties of FN by increasing the molecular rigidity of FN in the extracellular matrix.

Transglutaminase-mediated oligomerization promotes osteoblast adhesive properties of osteopontin and bone sialoprotein

“…22 In this study, we show that two other matricellular proteins that are substrates for TG2, OPN and BSP, have increased cell adhesion properties after oligomerization by TG2. Furthermore, the oligomerization appears to promote the formation of cellular extensions indicating that the cells are in better contact with this surface than when plated onto monomer-bound surfaces.…”

“…A recent report suggests that oligomerization of OPN promotes endothelial and carcinoma cell line attachment to the protein complex. 40 Furthermore, we have shown that FN exhibits enhanced osteoblast adhesion properties after oligomerization by TG2, 22 and that TG-activity in osteoblast cultures is required for osteoblast differentiation. 38 The purpose of this study is to ascertain whether oligomerization of OPN and BSP also enhances cell adhesion function.…”

“…4 We have recently demonstrated that TG2-mediated polymerization/oligomerization of FN significantly increases its osteoblast adhesive properties and enhances β1-integrin clustering, which further underscores the importance of a functional relationship between TG2 and FN. 22 We and others have demonstrated that in addition to FN, TG2 can also mediate oligomerization of certain members ©2 0 1 1 L a n d e s B i o s c i e n c e .…”

“…[13][14][15][16][17][18][19][20][21] Integrin clustering by TG2 promotes RhoA activation. TG2 also incorporates itself into the protein oligomers that it creates, 22 and high-molecular weight TG2 have been observed on cell surfaces. 4 We have recently demonstrated that TG2-mediated polymerization/oligomerization of FN significantly increases its osteoblast adhesive properties and enhances β1-integrin clustering, which further underscores the importance of a functional relationship between TG2 and FN.…”

Transglutaminases and Disease: Lessons From Genetically Engineered Mouse Models and Inherited Disorders

“…7). First, TG2 stabilizes ECM proteins by enhancing the initial phase of fibronectin matrix formation (15) and by crosslinking ECM proteins (8,93,109). Second, cell-surface TG2 promotes fibroblast adhesion to fibronectin (10,16,283,299,311) by interacting directly with ␤1/␤3/␤5 integrins (16,97,311), with heparan sulfate chains of the heparan sulfate proteoglycan receptor syndecan-4 (283,299), and with the orphan G protein-coupled cell-adhesion receptor GPR56 (303).…”