Collapsin response mediator protein switches RhoA and Rac1 morphology in N1E-115 neuroblastoma cells and is regulated by Rho kinase

The formation and directional guidance of neurites involves dynamic regulat ion of Rho family GTPases. Rac and Cdc42 promote neurite outgrowth, whereas Rho activation causes neurite retraction. Here we describe a role for coll apsin response mediator protein (Crmp-2), a neuronal protein implicated in axonal outgrowth and a component of the semaphorin 3A pathway, in switching GTPase signaling when expressed in combination with either dominant active Rac or Rho. In neuroblastoma N1E-115 cells, co-expression of Crmp-2 with d ominant active RhoA V14 induced Rac morphology, cell spreading and ruffling (and the formation of neurites). Conversely, co-expression of Crmp-2 with dominant active Rac1 V12 inhibited Rac morphology, and in cells already exp ressing Rac1 V12, Crmp-2 caused localized peripheral collapse, involving pi votal Rho (and Cdc42) activation. Rho kinase was a regulator of Crmp-2; Crm p-2 phosphorylation was required for Crmp-2/Rac1 V12 inhibition, but not Cr mp2/RhoA V14 induction, of Rac morphology. Thus Crmp-2, regulated by Rho ki nase, promotes outgrowth and collapse in response to active Rho and Rac, re spectively, reversing their usual morphological effects and providing a mec hanism for dynamic modulation of growth cone guidance.