Abstract
To examine the role of Rho GTP binding proteins in the adhesion of monocytic cells to fibronectin we used the C3 exoenzyme of Clostridium botulinum which ADP-ribosylates and inactivates Rho proteins in situ. Treatment of human monocytic U937 cells with C3 exoenzyme (10 μg/ml, 24 h) increased adhesion to fibronectin 2-fold but had no effect on adhesion to collagen or human serum albumin. The increase in fibronectin adhesion was prevented by antibodies against the α5 and β1 integrin subunits, but surface expression of β1 and α5 was not altered. These results suggest that Rho proteins regulate the interaction of the monocyte α5β1 integrin receptor with fibronectin by post receptor mechanisms

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