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 Gα subunits on the morphology of differentiated PC12 cells. Expression of GTPase-deficient Gα 12 , Gα 13 , and Gα q , but not Gα i2 , caused neurite retraction and cell rounding in differentiated PC12 cells. These morphological changes induced by Gα 12 , Gα 13 , and Gα 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 Gα 13 and Gα q . However, tyrphostin A25 failed to inhibit the Gα 12 -induced neuronal morphological changes. On the other hand, inhibition of protein kinase C or elimination of extracellular Ca 2+ blocked the neurite retraction and cell rounding induced by Gαq, whereas the morphological effects of Gα 12 and Gα 13 did not require activation of protein kinase C and extracellular Ca 2+ . These results demonstrate that activation of Gα 12 , Gα 13 , and Gα q induces Rho-dependent morphological changes in PC12 cells through different signaling pathways.