A review of actin binding proteins: new perspectives

Actin binding proteins (ABPs) have been considered components of the cytoskeleton, which gives structure and allows mobility of the cell. The complex dynamic properties of the actin cytoskeleton are regulated at multiple levels by a variety of proteins that control actin polymerization, severing of actin filaments and cross-linking of actin filaments into networks, which may be used by molecular motors. Proteins that cross-link F-actin are important for the maintenance of the viscoelastic properties of the cytoplasm and for the integrity of plasma membrane-associated macromolecules. Most of these F-actin cross-linking proteins have an actin-binding domain homologous to calponin. In addition, some of them have been considered scaffolds. Through the years, several research groups have found different proteins that interact with ABPs; however, the effect of these interactions on ABPs remains mostly unknown. In addition to organize the cytoskeletal structure, recent data indicate that ABPs can also migrate to the nucleus. This fact is in agreement and could be relevant to the recently found role that actin might play in nuclear function. Recent data and analysis of published results have also indicated that scaffold proteins like filamin A (FLNa) may be processed by proteolysis and that the degradation products generated by this reaction may play a role as signaling molecules, integrating nuclear and cytosolic pathways. Some of the relevant information in this area is reviewed here.