The essential role of profilin in the assembly of actin for microspike formation.
Profilin was first identified as an actin monomer binding protein; however, recent reports indicate its involvement in actin polymerization. To date, there is no direct evidence of a functional role in vivo for profilin in actin cytoskeletal reorganization. Here, we prepared a profilin mutant (H119E) defective in actin binding, but retaining the ability to bind to other proteins. This mutant profilin I suppresses actin polymerization in microspike formation induced by N-WASP, the essential factor in microspike formation. Profilin associates both in vivo and in vitro with N-WASP at proline-rich sites different from those to which Ash/Grb2 binds. This association between profilin and N-WASP is required for N-WASP-induced efficient microspike elongation. Moreover, we succeeded in reconstituting microspike formation in permeabilized cells using profilin I combined with N-WASP and its regulator, Cdc42. These findings provide the first evidence that profilin is a key molecule linking a signaling network to rapid actin polymerization in microspike formation.
Pubmed ID: 9822597 RIS Download
3T3 Cells | Actins | Amino Acid Sequence | Animals | Binding Sites | COS Cells | Contractile Proteins | Gene Expression Regulation | Mice | Microfilament Proteins | Molecular Sequence Data | Mutagenesis, Site-Directed | Nerve Tissue Proteins | Neurites | Profilins | Protein Binding | Wiskott-Aldrich Syndrome Protein, Neuronal