title: Abi1 is essential for the formation and activation of a WAVE2 signalling complex.
abstract: 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.
authors.affiliation: IFOM Istituto FIRC di Oncologia Molecolare Via Adamello 16, 20134, Milan, Italy.
authors.forename: Metello
authors.initials: M
authors.lastname: Innocenti
authors.forename: Adriana
authors.initials: A
authors.lastname: Zucconi
authors.forename: Andrea
authors.initials: A
authors.lastname: Disanza
authors.forename: Emanuela
authors.initials: E
authors.lastname: Frittoli
authors.forename: Liliana B
authors.initials: LB
authors.lastname: Areces
authors.forename: Anika
authors.initials: A
authors.lastname: Steffen
authors.forename: Theresia E B
authors.initials: TE
authors.lastname: Stradal
authors.forename: Pier Paolo
authors.initials: PP
authors.lastname: Di Fiore
authors.forename: Marie-France
authors.initials: MF
authors.lastname: Carlier
authors.forename: Giorgio
authors.initials: G
authors.lastname: Scita
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D051377:Actin-Related Protein 2; D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins / Q000378:metabolism; D002465:Cell Movement / Q000502:physiology*; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D046911:Macromolecular Substances; D008840:Microfilament Proteins / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000502:physiology; D011554:Pseudopodia / Q000378:metabolism* / Q000648:ultrastructure; D034622:RNA Interference / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D051300:Wiskott-Aldrich Syndrome Protein Family; D020744:rac GTP-Binding Proteins / Q000378:metabolism
chemical_list: C513733:ABI1 protein, human; C495926:ACTR2 protein, human; D051377:Actin-Related Protein 2; D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D046911:Macromolecular Substances; D008840:Microfilament Proteins; C484362:NCKAP1 protein, human; C120152:WASF2 protein, human; D051300:Wiskott-Aldrich Syndrome Protein Family; D020744:rac GTP-Binding Proteins