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

Abstract

In fibroblasts, the G protein α subunits Gα12 and Gα13 stimulate Rho-dependent stress fiber formation and focal adhesion assembly, whereas G protein βγ 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 β1 with γ2, γ5, γ7, and γ12 in quiescent HeLa cells induced stress fiber formation and focal adhesion assembly as did expression of the constitutively active Gα12. Co-expression of βγ with Gα(i2) and the C-terminal fragment of the β-adrenergic receptor kinase, both of which are known to bind and sequester free βγ, blocked βγ-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 βγ-induced stress fiber and focal adhesion assembly. These results indicate that G protein βγ subunits regulate Rho-dependent actin polymerization in HeLa cells.