THE G-PROTEIN G(13) BUT NOT G(12) MEDIATES SIGNALING FROM LYSOPHOSPHATIDIC ACID RECEPTOR VIA EPIDERMAL GROWTH-FACTOR RECEPTOR TO RHO

Lysophosphatidic acid (LPA) utilizes a G-protein-coupled receptor to a ctivate the small GTP-binding protein Rho and to induce rapid remodeli ng of the actin cytoskeleton, We studied the signal transduction from LPA receptors to Rho activation, Analysis of the G-protein-coupling pa ttern 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, expressi on of GTPase-deficient mutants of G alpha(12) and G alpha(13) triggere d 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 str ess fibers and assembly of focal adhesions in a Rho-dependent manner, Interestingly, the LPA dependent cytoskeletal reorganization was suppr essed by microinjected antibodies directed against G alpha(13), wherea s G alpha(12)-specific antibodies showed no inhibition, The tyrosine k inase inhibitor tyrphostin A 25 and the epidermal growth factor (EGF) receptor-specific tyrphostin AG 1478 completely blocked actin stress f iber formation caused by LPA or activated G alpha(13) but not the effe cts of activated G alpha(12). Also, expression of the dominant negativ e EGF receptor mutant EGFR-CD533 markedly prevented the LPA- and G alp ha(13)-induced actin polymerization, Coexpression of EGFR CD533 and ac tivated G alpha(13) in COS-7 cells resulted in decreased Rho-GTP level s 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 t he LPA-induced activation of Rho, Moreover, our results suggest an inv olvement of the EGF receptor in this pathway.