HSP90 cross-links branched actin filaments induced by N-WASP and the Arp2/3 complex.

N-WASP induces filopodial actin cytoskeleton through activation of the Arp2/3 complex. Here, we show that heat shock protein 90 (HSP90) regulates the structure of actin filaments induced by N-WASP and the Arp2/3 complex. HSP90 binds to N-WASP and to F-actin and bundles actin filaments. Bundling activity of HSP90 does not affect actin filament nucleation induced by N-WASP and the Arp2/3 complex. HSP90 is co-localized with N-WASP at branching points of actin filaments produced by the Arp2/3 complex and thereby bundles branched filaments; this bundled actin structure is inhibited by blocking direct binding between HSP90 and N-WASP. Furthermore, HSP90 converts branched actin filaments on N-WASP-coated beads to filopodia-like star-shaped bundles. These findings indicate that HSP90 promotes the formation of N-WASP/Arp2/3 complex-induced unbranched filopodial actin structures.