Inhibition by drebrin of the actin-bundling activity of brain fascin, a protein localized in filopodia of growth cones.

The purification of drebrin, an actin-binding protein that is specifically expressed in embryonic rat brain, was described previously. During the purification of drebrin, we found that an actin-binding protein of 54 kDa was also expressed at high levels in embryonic brain, and this protein was identified by immunoblotting as fascin. To explore the roles of fascin in brain development, we purified fascin from brains of infant rats and characterized it. We found that the actin-binding activity of fascin was strongly inhibited by drebrin. Fascin caused formation of actin bundles, a process that was inhibited in the presence of drebrin, as confirmed by electron microscopy and a low-speed centrifugation assay. In PC12 cells, fascin was localized in the filopodia of growth cones, whereas drebrin was localized in the basal region of growth cones. Our results suggest that fascin might play an important role in the organization of actin in filopodia and that this organization might be regulated by drebrin.