G protein βγ subunits induce stress fiber formation and focal adhesion assembly in a Rho-dependent manner in HeLa cells

In fibroblasts, the G protein alpha subunits G alpha(12) and G alpha(13) stimulate Rho-dependent stress fiber formation and focal adhesion assembly, whereas G protein beta gamma subunits instead exert a disruptive influence. We show here that the latter can, however, stimulate the formation of stress fibers and focal adhesions in epithelial-like HeLa cells. Transient expression of beta(1) with gamma(2), gamma(5), gamma(7), and gamma(12) in quiescent HeLa cells induced stress fiber formation and focal adhesion assembly as did expression of the constitutively active G alpha(12). Co-expression of beta gamma with G alpha(i2) and the C-terminal fragment of the beta-adrenergic receptor kinase, both of which are known to bind and sequester free beta gamma, blocked beta gamma-induced stress fiber and focal adhesion formation. Inhibition was also noted with co-expression of a dominant negative mutant of Rho. Botulinum C3 exoenzyme, which ADP-ribosylates and inactivates Rho, and a Rho-associated protein kinase inhibitor, Y-27632, similarly inhibited beta gamma-induced stress fiber and focal adhesion assembly. These results indicate that G protein beta gamma subunits regulate Rho-dependent actin polymerization in HeLa cells.