CONTROL OF AKR FIBROBLAST PHENOTYPE BY FIBRONECTIN - REGULATION OF CELL-SURFACE FIBRONECTIN-BINDING RECEPTOR BY FIBRONECTIN

Results of previous studies show that the expression of fibronectin an d its cell-surface fibronectin binding receptor is coregulated in 3-me thylchloranthrene transformation of normal AKR-2B cells to form AKR-MC A cells and in N,N, dimethylformamide (DMF) induction of differentiati on of transformed AKR-MCA cells (1990, J. Cell. Physiol., 143:445). In this study, we tested the coregulation hypothesis by transfection exp eriments using an antisense fibronectin expression vector. We determin ed the effect of antisense fibronectin RNA expression on untransformed AKR-28 celIs, and on the responses of transformed AKR-MCA eel Is to D MF treatment. Expression of antisense fibronectin RNA in AKR-2B cells downmodulated fibronectin production, reduced adhesion to extracellula r fibronectin, and altered cellular morphology. Saturation binding and Scatchard analyses using radiolabelled fibronectin revealed a concurr ent down-modulation of cell-surface fibronectin binding sites, but the binding affinity of the receptor for the ligand was not affected. Imm unoblotting and immunostaining revealed down-modulation of the express ion of alpha 5 beta 1 integrins. Expression of antisense fibronectin R NA in AKR-MCA cells down-modulated the ability of DMF to restore norma l fibronectin production, cell-surface fibronectin binding receptor, a dhesion to extracellular fibronectin, and cellular morphology. These s tudies show that both fibronectin and its cell-surface fibronectin bin ding receptor were tightly regulated during transformation and inducti on of differentiation in these cells, that the ligand and its eell-sur face fibronectin binding receptor worked together to bring about pheno typic changes, and that fibronectin production regulated the expressio n of its cell-surface fibronectin binding receptor. (C) 1994 Wiley-Lis s, Inc.