Spatial regulation of β-actin translation by Src-dependent phosphorylation of ZBP1

Localization of beta-actin messenger RNA to sites of active actin polymerization modulates cell migration during embryogenesis, differentiation and possibly carcinogenesis(1-5). This localization requires the oncofetal protein ZBP1 (Zipcode binding protein 1), which binds to a conserved 54-nucleotide element in the 30 untranslated region of the beta-actin mRNA known as the 'zipcode'. ZBP1 promotes translocation of the beta-actin transcript to actin-rich protrusions in primary fibroblasts and neurons(6,7). It is not known how the ZBP1-RNA complex achieves asymmetric protein sorting by localizing beta-actin mRNA. Here we show that chicken ZBP1 modulates the translation of beta-actinmRNA. ZBP1 associates with the beta-actin transcript in the nucleus and prevents premature translation in the cytoplasm by blocking translation initiation. Translation only occurs when the ZBP1-RNA complex reaches its destination at the periphery of the cell. At the endpoint of mRNA transport, the protein kinase Src promotes translation by phosphorylating a key tyrosine residue in ZBP1 that is required for binding to RNA. These sequential events provide both temporal and spatial control over beta-actin mRNA translation, which is important for cell migration and neurite outgrowth.