Formation of extracellular matrix fibronectin fibrils localizes a high molecular weight gelatinase to the extracellular matrix and enhances cell spreading

Interactions between cells and their surrounding extracellular matrix mediate many cellular functions that are critical for physiological processes such as wound repair. Fibronectin is an extracellular matrix glycoprotein that exists in vivo in both a soluble and an insoluble, multimeric form. Soluble fibronectin is polymerized into insoluble fibrils within the extracellular matrix by a cell-dependent process. Recent studies indicate that the extracellular matrix form of fibronectin promotes cell growth and enhances cell migration. The goals of this dissertation were to investigate possible mechanisms by which extracellular matrix fibronectin promotes cell migration and growth.;Proteinases play an important role in cell migration. In this study, gelatin zymography was used to demonstrate that addition of fibronectin to collagen-adherent fibronectin-null myofibroblasts induces the expression of a high molecular weight gelatinase (HMWG) by a time- and dose-dependent mechanism. HMWG localized exclusively to extracellular matrices by a mechanism that required fibronectin matrix polymerization. In addition, small airway epithelial cells and IMR-90 fibroblasts were also capable of expressing HMWG in their extracellular matrices.;Cell spreading is a prerequisite for cell migration and is tightly coupled to cell proliferation. In this study, formation of extracellular matrix fibronectin by collagen-adherent cells increased cell area by a Src-dependent mechanism. Using a recombinant fibronectin construct engineered to mimic matrix fibronectin, my studies partially localized the effect of fibronectin matrix polymerization on cell spreading to the heparin-binding activity in the III-1 module of fibronectin. Fibronectin triggered a transient increase in Src kinase activity of collagen-adherent cells and a sustained increase in tyrosine phosphorylation of cortactin and caveolin. Fibronectin also stimulated the localization of phospho-cortactin and phospho-caveolin to the cell periphery. A positive correlation was established between cell area and cell growth of collagen-adherent cells in response to matrix fibronectin. However, an absolute change in cell area was not required for matrix fibronectin to enhance cell proliferation.;In summary, fibronectin matrix polymerization accumulates HMWG in extracellular matrices and increases cell spreading, thus providing possible mechanisms for matrix fibronectin-enhanced cell migration. A positive correlation between cell area and growth also provides insight into possible mechanism by which matrix fibronectin stimulates cell growth.