Constitutively active Gα12, Gα13, and Gαq induce rho-dependent neurite retraction through different signaling pathways

In neuronal cells, activation of a certain heterotrimeric G protein-coupled receptor causes neurite retraction and cell rounding via the small GTPase Rho, However, the specific heterotrimeric G proteins that mediate Rho dependent neurite retraction and cell rounding have not yet been identified. Here we investigated the effects of expression of constitutively active G alpha subunits on the morphology of differentiated PC12 cells, Expression of GTPase-deficient G alpha(12), G alpha(13), and G alpha(q), but not G alpha(i2), caused neurite retraction and cell rounding in differentiated PC12 cells. These morphological changes induced by G alpha(12), G alpha(13), and G alpha(q) were completely inhibited by C3 exoenzyme, which specifically ADP-ribosylates and inactivates Rho, The tyrosine kinase inhibitor tyrphostin A25 blocked the neurite retraction and cell rounding induced by G alpha(13) and G alpha(q). However, tyrphostin A25 failed to inhibit the G alpha(12)-induced neuronal morphological changes. On the other hand, inhibition of protein kinase C or elimination of extracellular Ca2+ blocked the neurite retraction and cell rounding induced by G alpha q, whereas the morphological effects of G alpha(12) and G alpha(13) did not require activation of protein kinase C and extracellular Ca2+, These results demonstrate that activation of G alpha(12), G alpha(13), and G alpha(q) induces Rho-dependent morphological changes in PC12 cells through different signaling pathways.