Integrin and cAMP Metabolism

Clone A colon carcinoma cells develop fanshaped lamellae and exhibit random migration when plated on laminin, processes that depend on the ligation of the a 6 b 4 integrin. Here, we report that expression of a dominant negative RhoA (N19RhoA) in clone A cells inhibited a 6 b 4-dependent membrane ruffling, lamellae formation, and migration. In contrast, expression of a dominant negative Rac (N17Rac1) had no effect on these processes. Using the Rhotekin binding assay to assess RhoA activation, we observed that engagement of a 6 b 4 by either antibody-mediated clustering or laminin attachment resulted in a twoto threefold increase in RhoA activation, compared with cells maintained in suspension or plated on collagen. Antibody-mediated clustering of b 1 integrins, however, actually suppressed Rho A activation. The a 6 b 4-mediated interaction of clone A cells with laminin promoted the translocation of RhoA from the cytosol to membrane ruffles at the edges of lamellae and promoted its colocalization with b 1 integrins, as assessed by immunofluorescence microscopy. In addition, RhoA translocation was blocked by inhibiting phosphodiesterase activity and enhanced by inhibiting the activity of cAMP-dependent protein kinase. Together, these results establish a specific integrin-mediated pathway of RhoA activation that is regulated by cAMP and that functions in lamellae forma-