RhoA inhibits the nerve growth factor-induced Rac1 activation through Rho-associated kinase-dependent pathway

The Rho family of small GTPases has been shown to be involved in the regula tion of neuronal morphology, and Rac and Rho exert antagonistic actions in neurite formation. In this study, we have examined the cross-talk between R ac and Rho in relation to the nerve growth factor (NGF)-induced neurite out growth in PC12 cells. NGF induced a rapid activation of Pac 1 and suppressi on of RhoA activity. Constitutively active RhoA, RhoA(V14) or constitutivel y active G alpha (12)-induced endogenous RhoA activation inhibited the NGF- induced Rad activation without any effect on the NGF-induced extracellular signal-regulated kinase activation. Moreover, Y-27632, an inhibitor of Rho- associated kinase, completely abolished the RhoA-induced down-regulation of the NGF-induced Rad activation. We also revealed that NGF induced a rapid recruitment of Rad to the cell surface protrusion sites and formed filament ous actin-rich protrusions. Activation of RhoA and Rho-associated kinase fo rmed a thick ringlike structure of cortical actin filaments at the cell per iphery and then inhibited the NGF-induced recruitment of Rad to protrusions . These results indicate that RhoA down-regulates the NGF-induced Rad activ ation through Rho-associated kinase, inhibiting the neurite formation.