The G-protein G13 but not G12 mediates signaling from lysophosphatidic acid receptor via epidermal growth factor receptor to Rho

Lysophosphatidic acid (LPA) utilizes a G-protein-coupled receptor to activate the small GTP-binding protein Rho and to induce rapid remodeling of the actin cytoskeleton, We studied the signal transduction from LPA receptors to Rho activation, Analysis of the G-protein-coupling pattern of LPA receptors by labeling activated G-proteins with [alpha-P-32]GTP azidoanilide revealed interaction with proteins of the G(q), G(i), and G(12) subfamilies, We could show that in COS 7 cells, expression of GTPase-deficient mutants of G alpha(12) and G alpha(13) triggered Rho activation as measured by increased Rho-GTP levels. In Swiss 3T3 cells, incubation with LPA or microinjection of constitutively active mutants of G alpha(12) and G alpha(13) induced formation of actin stress fibers and assembly of focal adhesions in a Rho-dependent manner, Interestingly, the LPA dependent cytoskeletal reorganization was suppressed by microinjected antibodies directed against G alpha(13), whereas G alpha(12)-specific antibodies showed no inhibition, The tyrosine kinase inhibitor tyrphostin A 25 and the epidermal growth factor (EGF) receptor-specific tyrphostin AG 1478 completely blocked actin stress fiber formation caused by LPA or activated G alpha(13) but not the effects of activated G alpha(12). Also, expression of the dominant negative EGF receptor mutant EGFR-CD533 markedly prevented the LPA- and G alpha(13)-induced actin polymerization, Coexpression of EGFR CD533 and activated G alpha(13) in COS-7 cells resulted in decreased Rho-GTP levels compared with expression of activated G alpha(13) alone, These data indicate that in Swiss 3T3 cells, G(13) but not G(12) is involved in the LPA-induced activation of Rho, Moreover, our results suggest an involvement of the EGF receptor in this pathway.