WAVE2 belongs to a family of proteins that mediates actin reorganization by relaying signals from Rac to the Arp2/3 complex, resulting in lamellipodia protrusion. WAVE2 displays Arp2/3-dependent actin nucleation activity in vitro, and does not bind directly to Rac. Instead, it forms macromolecular complexes that have been reported to exert both positive and negative modes of regulation. How these complexes are assembled, localized and activated in vivo remains to be established. Here we use tandem mass spectrometry to identify an Abi1-based complex containing WAVE2, Nap1 (Nck-associated protein) and PIR121. Abi1 interacts directly with the WHD domain of WAVE2, increases WAVE2 actin polymerization activity and mediates the assembly of a WAVE2–Abi1–Nap1–PIR121 complex. The WAVE2–Abi1–Nap1–PIR121 complex is as active as the WAVE2–Abi1 sub-complex in stimulating Arp2/3, and after Rac activation it is re-localized to the leading edge of ruffles in vivo. Consistently, inhibition of Abi1 by RNA interference (RNAi) abrogates Rac-dependent lamellipodia protrusion. Thus, Abi1 orchestrates the proper assembly of the WAVE2 complex and mediates its activation at the leading edge in vivo.
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This work was supported by grants from AIRC (Associazione Italiana Ricerca sul Cancro) to G.S. and P.P.D.F.; Human Science Frontier Program to G.S. and M.F.C.; Telethon Foundation, the CNR (Target project Biotechnology) and the EC (V Framework) to P.P.D.F.; FIRC (Fondazione Italiana Ricerca sul Cancro) to M.I. from the Italian Ministry of Health to G.S. We would like to thank L. Cairns and S. Bossi for technical help, S. Polo for reading the manuscript, B. Baum for sharing unpublished materials, and G. Cesareni for helping with the generation of WAVE2 reagents.
The authors declare no competing financial interests.
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Innocenti, M., Zucconi, A., Disanza, A. et al. Abi1 is essential for the formation and activation of a WAVE2 signalling complex. Nat Cell Biol 6, 319–327 (2004). https://doi.org/10.1038/ncb1105
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