Drebrin particles: components in the ensemble of proteins regulating actindynamics of lamellipodia and filopodia

Drebrin, an actin-binding 70-kDa protein with an unusually slow SDS-PAGE mo bility corresponding to similar to 120 kDa, containing a proline-rich, prof ilin-binding motif, had originally been reported from neuronal cells, but r ecently has also been found in diverse other kinds of tissues and cell line s. In biochemical analyses of various cells and tissues, employing gel filt ration, sucrose gradient centrifugation, immunoprecipitation and -blotting, we have identified distinct states of soluble drebrin: a similar to 4S mon omer, an 8S, ca. 217-kDa putative trimer, a 13S and a > 20S oligomer. In th e 8S particles only [S-35]methionine-labelled drebrin but no other actin-bi nding protein has been detected in stoichiometric amounts. By immunofluores cence and immunoelectron microscopy, drebrin-positive material often appear ed as "granules" up to 400 urn in diameter, in some cell types clustered ne ar the Golgi apparatus or in lamellipodia, particularly at leading edges, o r in dense-packed submembranous masses at tips (acropodia) or ruffles of le ading edges, in filopodia and at plaques of adhering junctions. We conclude that these drebrin complexes and drebrin-rich structures allow the build-u p and maintenance of high local drebrin concentrations in strategic positio ns for the regulation of actin filament assembly, thereby contributing to c ell motility and morphology, in particular local changes of plasticity and the formation of protrusions.