Different roles for RhoA during neurite initiation, elongation, and regeneration in PC12 cells

The goal of the present study was to characterize the effects of RhoA at di fferent stages of nerve growth factor (NGF)-induced neuronal differentiatio n in the PC12 model. This comparative analysis was prompted by previous stu dies that reported apparently opposite effects for Rho in different models of neuronal differentiation and regeneration. PC12 cells were transfected w ith activated V14RhoA or dominant negative N19RhoA under the control of eit her a constitutive or a steroid-regulated promoter. Upon exposure to NGF, V 14RhoA cells continued to proliferate and did not extend neurites; however, they remained responsive to NGF, as indicated by the activation of extrace llular signal-regulated kinases. This inability to differentiate was revers ed by C3 toxin and activation of cyclic AMP signaling, which inactivate Rho A. N19RhoA expression led to an increase in neurite initiation and branchin g. In contrast, when the RhoA mutants were expressed after NGF priming, onl y the rate of neurite extension was altered; V14RhoA clones had neurites ap proximately twice as long, whereas neurites of N19RhoA cells were similar t o 50% shorter than those of appropriate controls. The effects of Rho in neu rite regeneration mimicked those observed during the initial stages of morp hogenesis; activation inhibited, whereas inactivation promoted, neurite out growth. Our results indicate that RhoA function changes at different stages of NGF-induced neuronal differentiation and neurite regeneration.