Fibronectin Polymerization Regulates the Composition and Stability of Extracellular Matrix Fibrils and Cell-Matrix Adhesions

Abstract

Remodeling of extracellular matrices occurs during development, wound healing, and in a variety of pathological processes including atherosclerosis, ischemic injury, and angiogenesis. Thus, identifying factors that control the balance between matrix deposition and degradation during tissue remodeling is essential for understanding mechanisms that regulate a variety of normal and pathological processes. Using fibronectin-null cells, we found that fibronectin polymerization into the extracellular matrix is required for the deposition of collagen-I and thrombospondin-1 and that the maintenance of extracellular matrix fibronectin fibrils requires the continual polymerization of a fibronectin matrix. Further, integrin ligation alone is not sufficient to maintain extracellular matrix fibronectin in the absence of fibronectin deposition. Our data also demonstrate that the retention of thrombospondin-1 and collagen I into fibrillar structures within the extracellular matrix depends on an intact fibronectin matrix. An intact fibronectin matrix is also critical for maintaining the composition of cell-matrix adhesion sites; in the absence of fibronectin and fibronectin polymerization, neither ␣5␤1 integrin nor tensin localize to fibrillar cell-matrix adhesion sites. These data indicate that fibronectin polymerization is a critical regulator of extracellular matrix organization and stability. The ability of fibronectin polymerization to act as a switch that controls the organization and composition of the extracellular matrix and cell-matrix adhesion sites provides cells with a means of precisely controlling cell-extracellular matrix signaling events that regulate many aspects of cell behavior including cell proliferation, migration, and differentiation. INTRODUCTIONExtracellular matrix remodeling plays an important role during development, wound healing, atherosclerosis, ischemic injury, and angiogenesis. Perturbing matrix remodeling by preventing the turnover of collagen I or by altering the levels of matrix-degrading proteases or protease inhibitors has been shown to result in fibrosis, arthritis, reduced angiogenesis, and developmental abnormalities (Liu et al., 1995;Vu et al., 1998;Holmbeck et al., 1999;Ducharme et al., 2000). In normal adult tissue, some extracellular matrix components such as elastin and fibrillar collagen have half lives of months to years (Krane, 1985;Debelle and Tamburro, 1999). Other extracellular matrix components, such as proteoglycans, thrombospondin-1 and -2, and vitronectin, can be endocytosed and degraded in the lysosomes (McKeownLongo et al., 1984;Yanagishita and Hascall, 1984; MurphyUllrich and Mosher, 1987;Hausser et al., 1992;Godyna et al., 1995a;Pijuan-Thompson and Gladson, 1997;Memmo and McKeown-Longo, 1998). Extracellular matrix molecules can also be degraded extracellularly by proteases such as matrix metalloproteinases (MMPs), plasminogen activators, and plasmin (Hynes, 1990;Marchina and Barlati, 1996;Shapiro, 1998).Recent data indicate that polymerized forms of extracellular matri...

Syndecan-1 in Breast Cancer Stroma Fibroblasts Regulates Extracellular Matrix Fiber Organization and Carcinoma Cell Motility

“…An intact FN matrix is essential for the formation and stability of a mature collagen-containing ECM. 39,40 Therefore, the regulation of FN fibril assembly may hold the key to understanding matrix organization. Fibronectin fibrillogenesis is a complex cell-mediated process that involves FN binding to cell surface receptors, FN-FN self-association, and interaction with the actin cytoskeleton.…”

Fibrillin Assembly Requires Fibronectin

“…The assembly of a few extracellular matrix proteins have been demonstrated to be dependent on the presence of fibronectin, including collagen types I and III and thrombospondin-1 (McDonald et al, 1982;Sottile and Hocking, 2002;Velling et al, 2002;Li et al, 2003), fibulin-1 (Roman and McDonald, 1993;Godyna et al, 1995), fibrinogen (Pereira et al, 2002), and LTBP-1 (Dallas et al, 2005). Further studies established for collagen type I, thrombospondin-1, and LTBP-1 that a continuous assembly and supply of fibronectin is a prerequisite for matrix stability of these proteins Dallas et al, 2005).…”

“…This portion of the molecule is directly followed by the binding site for collagen/gelatin, which is located between FNI 6 and FNI 9 (Engvall et al, 1978;Balian et al, 1979;Shimizu et al, 1997). Although a plethora of reports have been published on the initial assembly mechanisms for fibronectin, virtually nothing is known about how individual fibronectin molecules are spatially oriented and organized in early and fully assembled fibronectin networks.The assembly of a few extracellular matrix proteins have been demonstrated to be dependent on the presence of fibronectin, including collagen types I and III and thrombospondin-1 (McDonald et al, 1982;Sottile and Hocking, 2002;Velling et al, 2002; Li et al, 2003), fibulin-1 (Roman andMcDonald, 1993;Godyna et al, 1995), fibrinogen (Pereira et al, 2002), and LTBP-1 (Dallas et al, 2005). Further studies established for collagen type I, thrombospondin-1, and LTBP-1 that a continuous assembly and supply of fibronectin is a prerequisite for matrix stability of these proteins Dallas et al, 2005).…”

The N-terminal 70-kDa fragment of fibronectin binds to cell surface fibronectin assembly sites in the absence of intact fibronectin

“…The fibrillar form of fibronectin (FN) provides information important for cell adhesion, migration, survival and proliferation, and for connective tissue remodeling (Pankov and Yamada, 2002;Sottile and Hocking, 2002). Much is known about the transformation of soluble FN into its fibrillar form (Magnusson and Mosher, 1998;Mao and Schwarzbauer, 2005;Wierzbicka-Patynowski and Schwarzbauer, 2003), but the precise mechanism is yet to be elucidated.…”