COORDINATED REGULATION OF FIBRONECTIN FIBRIL ASSEMBLY AND ACTIN STRESS FIBER FORMATION

Assembly of a fibronectin (FN) matrix is a multistep process which inf luences a number of cellular functions including intracellular cytoske letal organization and signaling responses. We have previously reporte d on a recombinant FN (recFN), FN Delta III1-7, which differs from nat ive 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 matrice s by immunofluorescence at various time points. CHO alpha 5 cell cytos keleton was reorganized in response to both native and recFN matrix fo rmation. Assembly of native FN induced a rapid reorganization of actin into stress fibers and colocalization of alpha 5 beta 1 integrin, foc al adhesion kinase (FAK), vinculin, and paxillin to regions of cell-ma trix contact. alpha 5 beta 1 integrins and FAK are also clustered upon binding of FN Delta III1-7 to cells but actin reorganization and foca l adhesion formation are delayed and appear to be dependent on the for mation of FN Delta III1-7 fibrils. These results suggest that the stru ctural framework of the matrix plays an important role in the ability of FN to initiate intracellular responses.