Neurotrophin regulation of β-actin mRNA and protein localization within growth cones

Neurotrophins play an essential role in the regulation of actin- dependent changes in growth cone shape and motility. We have studied whether neurotrophin signaling can promote the localization of β-actin mRNA and protein within growth cones. The regulated localization of specific mRNAs within neuronal processes and growth cones could provide a mechanism to modulate cytoskeletal composition and growth cone dynamics during neuronal development. We have previously shown that β-actin mRNA is localized in granules that were distributed throughout processes and growth cones of cultured neurons. In this study, we demonstrate that the localization of β- actin mRNA and protein to growth cones of forebrain neurons is stimulated by neurotrophin-3 (NT-3). A similar response was observed when neurons were exposed to forskolin or db-cAMP, suggesting an involvement of a cAMP signaling pathway. NT-3 treatment resulted in a rapid and transient stimulation of PKA activity that preceded the localization of β-actin mRNA. Localization of β-actin mRNA was blocked by prior treatment of cells with Rp-cAMP, an inhibitor of cAMP-dependent protein kinase A. Depolymerization of microtubules, but not microfilaments, inhibited the NT-3-induced localization of β-actin mRNA. These results suggest that NT-3 activates a cAMP-dependent signaling mechanism to promote the microtubule-dependent localization of β- actin mRNA within growth cones.