Coordinated Regulation of Fibronectin Fibril Assembly and Actin Stress Fiber Formation

Assembly of a fibronectin (FN) matrix is a multistep process which influences a number of cellular functions including intracellular cytoskeletal organization and signaling responses. We have previously reported on a recombinant FN (recFN), FNΔIII_1-7, which differs from native FN in its rate of fibril formation. To determine the intracellular consequences of a delay in assembly, we compared the distribution of cytoskeletal proteins during the formation of native and recFN matrices by immunofluorescence at various time points. CHOα5 cell cytoskeleton was reorganized in response to both native and recFN matrix formation. Assembly of native FN induced a rapid reorganization of actin into stress fibers and colocalization of α5β1 integrin, focal adhesion kinase (FAK), vinculin, and paxillin to regions of cell-matrix contact. α5β1 integrins and FAK are also clustered upon binding of FNΔIII_1-7 to cells but actin reorganization and focal adhesion formation are delayed and appear to be dependent on the formation of FNΔIII_1-7 fibrils. These results suggest that the structural framework of the matrix plays an important role in the ability of FN to initiate intracellular responses.