ADP-ribosylation of Rho enhances adhesion of U937 cells to fibronectin via the alpha 5 beta 1 integrin receptor

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 micrograms/ml, 24 h) increased adhesion to fibronectin 2-fold but had no effect on adhesion to collagen or huamn serum albumin. The increase in fibronectin adhesion was prevented by antibodies against the alpha 5 and beta 1 integrin subunits, but surface expression of beta 1 and alpha 5 was not altered. These results suggest that Rho proteins regulate the interaction of the monocyte alpha 5 beta 1 integrin receptor with fibronectin by post receptor mechanisms.