Abstract
The small GTPase CDC42 promotes axon growth through actin filament polymerization and this growth is driven by axonal localization of the mRNA encoding the prenylated CDC42 isoform (Prenyl-Cdc42). Here, we show that axonal Prenyl-Cdc42 mRNA levels and the mRNA's translation are decreased by growth-inhibiting stimulation and increased by growth-promoting stimulation. In contrast, axonal RhoA mRNA transport and translation are increased by growth-inhibiting but unaffected by growth-promoting stimuli. Localized increase in KHSRP in response to growth inhibitory stimulation, through elevation of intracellular Ca2+, promotes decrease in axonal levels of Prenyl-Cdc42 mRNA. Distinct 3'UTR motifs regulate transport and axonal levels of Prenyl-Cdc42 mRNA. KHSRP protein binds to a Prenyl-Cdc42 mRNA motif within nt 801-875 and the mRNA is remarkably increased in axons of Khsrp-/- mice. Depletion of the mRNA from sciatic nerve indicates that the increased axonal Prenyl-CDC42 contributes to the accelerated nerve regeneration when neuronal KHSRP is depleted.