p190-B, a new member of the Rho GAP family, and Rho are induced to cluster after integrin cross-linking

p120(GAP) forms distinct complexes with two phosphoproteins, p62 and p190, Here we have cloned a cDNA encoding a protein with 51% amino acid identity to p190 (hereafter designated p190-A) and have designated it p190-B. The N-terminal portion of p190-B contained several motifs characteristic of a GTPase domain, while its C terminus contained a Rho GAP domain, A recombinant Rho GAP domain polypeptide showed GAP activity for RhoA, Rac1, and G25K/CDC42Hs. Immunoprecipitation and immunofluorescence studies demonstrated that p190-B protein was expressed in a variety of cells and was localized diffusely in the cytoplasm and in fibrillar patterns that co-localized with the alpha(5) beta(1) integrin receptor for fibronectin, Adhesion of fibronectin-coated latex beads to cells resulted in recruitment of significant amounts of p190-B and Rho to the plasma membrane beneath the site of bead binding, In contrast, beads coated with polylysine or concanavalin A were unable to recruit p190-B or Rho, Additionally, anti-beta(1) or anti-alpha(5) integrin antibody-coated beads were also able to recruit large amounts of p190-B and Rho, These results identify a novel second member of the p190 family and establish the existence of a novel transmembrane link between integrins and a new protein p190-B and Rho.