ADHESION OF CHO CELLS TO FIBRONECTIN IS MEDIATED BY FUNCTIONALLY AND STRUCTURALLY DISTINCT ADHESION PLAQUES

We have investigated the dynamics between free fibronectin receptors a nd clusters of them organized into adhesion plaques on CHO cells using the ability of these free integrins to be endocytosed and recycled to the plasma membrane. Indirect inhibition of the endocytic cycle by mo nensin resulted in the subsequent internalization of free receptors, w hich we followed by indirect immunostaining and confocal microscopy. C onsequently, all the adhesive structures that were in equilibrium with free integrins became progessively disorganized. The cellular morphol ogical changes were analyzed and correlated with the distribution of c ell-substratum contacts viewed by confocal images obtained after immun ostaining with antibodies raised against the fibronectin receptor, tal in, vinculin and actin. After cell adhesion to fibronectin, blockage o f the endocytic cycle induced disruption of the adhesion plaques that were mainly localized at the cell periphery, and disappearance of the stress fibers. However, the cells remained firmly attached to the subs tratum through focal contacts localized in the central part of the cel l. These central focal contacts, but not the peripheral adhesion plaqu es, could form when the vesicular traffic was blocked prior to adhesio n and they allowed the cells to attach and flatten onto the substratum . Whereas both adhesive structures contained the same receptors linked to talin and vinculin, the central adhesive structures were attached to a short stretch of actin but never permitted the organization of st ress fibers.