MEMBRANE TARGETING OF P21-ACTIVATED KINASE-1 (PAK1) INDUCES NEURITE OUTGROWTH FROM PC12 CELLS

Rho-family GTPases regulate cytoskeletal dynamics in various cell type s. p21-activated kinase 1 (PAK1) is one of the downstream effecters of Rac and Cdc42 which has been implicated as a mediator of polarized cy toskeletal changes in fibroblasts. We show here that the extension of neurites induced by nerve growth factor (NGF) in the neuronal cell lin e PC12 is inhibited by dominant-negative Rac2 and Cdc42, indicating th at these GTPases are required components of the NGF signaling pathway, While cytoplasmically expressed PAK1 constructs do not cause efficien t neurite outgrowth from PC12 cells, targeting of these constructs to the plasma membrane via a C-terminal isoprenylation sequence induced P C12 cells to extend neurites similar to those stimulated by NGF, This effect was independent of PAK1 ser/thr kinase activity but was depende nt on structural domains within both the N- and C-terminal portions of the molecule, Using these regions of PAK1 as dominant-negative inhibi tors, we were able to effectively inhibit normal neurite outgrowth sti mulated by NGF, Taken together with the requirement for Rac and Cdc42 in neurite outgrowth, these data suggest that PAK(s) may be acting dow nstream of these GTPases in a signaling system which drives polarized outgrowth of the actin cytoskeleton in the developing neurite.