CONSTITUTIVELY ACTIVE G-ALPHA(12), G-ALPHA(13), AND G-ALPHA(Q) INDUCERHO-DEPENDENT NEURITE RETRACTION THROUGH DIFFERENT SIGNALING PATHWAYS

In neuronal cells, activation of a certain heterotrimeric G protein-co upled receptor causes neurite retraction and cell rounding via the sma ll GTPase Rho, However, the specific heterotrimeric G proteins that me diate Rho dependent neurite retraction and cell rounding have not yet been identified. Here we investigated the effects of expression of con stitutively active G alpha subunits on the morphology of differentiate d 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 ce ll rounding in differentiated PC12 cells. These morphological changes induced by G alpha(12), G alpha(13), and G alpha(q) were completely in hibited by C3 exoenzyme, which specifically ADP-ribosylates and inacti vates Rho, The tyrosine kinase inhibitor tyrphostin A25 blocked the ne urite 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 prote in kinase C or elimination of extracellular Ca2+ blocked the neurite r etraction and cell rounding induced by G alpha q, whereas the morpholo gical effects of G alpha(12) and G alpha(13) did not require activatio n of protein kinase C and extracellular Ca2+, These results demonstrat e that activation of G alpha(12), G alpha(13), and G alpha(q) induces Rho-dependent morphological changes in PC12 cells through different si gnaling pathways.