Gα12 and Gα13 stimulate Rho-dependent stress fiber formation and focal adhesion assembly

Abstract

Rho, a member of the Ras superfamily of GTP-binding proteins, regulates actin polymerization resulting in the formation of stress fibers and the assembly of focal adhesions. In Swiss 3T3 cells, heterotrimeric G protein-coupled receptors for lysophosphatidic acid and gastrin releasing peptide stimulate Rho-dependent stress fiber and focal adhesion formation. The specific heterotrimeric G protein subunits mediating Rho-dependent stress fiber and focal adhesion formation have not been defined previously. We have expressed GTPase-deficient, constitutively activated G protein α subunits and mixtures of β and γ subunits in Swiss 3T3 cells. Measurement of actin polymerization and focal adhesion formation indicated that GTPase-deficient α12 and α13, but not the activated forms of αi2 or αq stimulated stress fiber and focal adhesion assembly. Combinations of β and γ subunits were unable to stimulate stress fiber or focal adhesion formation. Gα12- and α13-mediated stress fiber and focal adhesion assembly was inhibited by botulinum C3 exoenzyme, which ADP-ribosylates and inactivates Rho, indicating that α12 and α13, but not other G protein α subunits or βγ complexes, regulate Rho-dependent responses. The results define the integration of G12 and G13 with the regulation of the actin cytoskeleton.