Differential involvement of Gα12 and Gα13 in receptor-mediated stress fiber formation.

Abstract The ubiquitously expressed heterotrimeric guanine nucleotide-binding proteins (G-proteins) G12 and G13 have been shown to activate the small GTPase Rho. Rho stimulation leads to a rapid remodeling of the actin cytoskeleton and subsequent stress fiber formation. We investigated the involvement of G12 or G13 in stress fiber formation induced through a variety of Gq/G11-coupled receptors. Using fibroblast cell lines derived from wild-type and Gαq/Gα11-deficient mice, we show that agonist-dependent activation of the endogenous receptors for thrombin or lysophosphatidic acid and of the heterologously expressed bradykinin B2, vasopressin V1A, endothelin ETA, and serotonin 5-HT2C receptors induced stress fiber formation in either the presence or absence of Gαq/Gα11. Stress fiber assembly induced through the muscarinic M1 and the metabotropic glutamate subtype 1α receptors was dependent on Gq/G11proteins. The activation of the Gq/G11-coupled endothelin ETB and angiotensin AT1A receptors failed to induce stress fiber formation. Lysophosphatidic acid, B2, and 5-HT2C receptor-mediated stress fiber formation was dependent on Gα13 and involved epidermal growth factor (EGF) receptors, whereas thrombin, ETA, and V1A receptors induced stress fiber accumulation via Gα12 in an EGF receptor-independent manner. Our data demonstrate that many Gq/G11-coupled receptors induce stress fiber assembly in the absence of Gαq and Gα11 and that this involves either a Gα12or a Gα13/EGF receptor-mediated pathway.