title: Sra-1 and Nap1 link Rac to actin assembly driving lamellipodia formation.
abstract: The Rho-GTPase Rac1 stimulates actin remodelling at the cell periphery by relaying signals to Scar/WAVE proteins leading to activation of Arp2/3-mediated actin polymerization. Scar/WAVE proteins do not interact with Rac1 directly, but instead assemble into multiprotein complexes, which was shown to regulate their activity in vitro. However, little information is available on how these complexes function in vivo. Here we show that the specifically Rac1-associated protein-1 (Sra-1) and Nck-associated protein 1 (Nap1) interact with WAVE2 and Abi-1 (e3B1) in resting cells or upon Rac activation. Consistently, Sra-1, Nap1, WAVE2 and Abi-1 translocated to the tips of membrane protrusions after microinjection of constitutively active Rac. Moreover, removal of Sra-1 or Nap1 by RNA interference abrogated the formation of Rac-dependent lamellipodia induced by growth factor stimulation or aluminium fluoride treatment. Finally, microinjection of an activated Rac failed to restore lamellipodia protrusion in cells lacking either protein. Thus, Sra-1 and Nap1 are constitutive and essential components of a WAVE2- and Abi-1-containing complex linking Rac to site-directed actin assembly.
authors.affiliation: German Research Centre for Biotechnology, Department of Cell Biology, Braunschweig, Germany.
authors.forename: Anika
authors.initials: A
authors.lastname: Steffen
authors.forename: Klemens
authors.initials: K
authors.lastname: Rottner
authors.forename: Julia
authors.initials: J
authors.lastname: Ehinger
authors.forename: Metello
authors.initials: M
authors.lastname: Innocenti
authors.forename: Giorgio
authors.initials: G
authors.lastname: Scita
authors.forename: Jürgen
authors.initials: J
authors.lastname: Wehland
authors.forename: Theresia E B
authors.initials: TE
authors.lastname: Stradal
mesh_terms: D016475:3T3 Cells; D000199:Actins / Q000378:metabolism*; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D045744:Cell Line, Tumor; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008840:Microfilament Proteins / Q000096:biosynthesis / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000378:metabolism; D015513:Oncogene Proteins / Q000378:metabolism; D021381:Protein Transport; D011554:Pseudopodia / Q000378:metabolism*; D051300:Wiskott-Aldrich Syndrome Protein Family; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; D003598:Cytoskeletal Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D008840:Microfilament Proteins; D046912:Multiprotein Complexes; D015513:Oncogene Proteins; D051300:Wiskott-Aldrich Syndrome Protein Family; D020830:rac1 GTP-Binding Protein; C513734:Abi1 protein, mouse; C078332:Nck protein; C502089:Nckap1 protein, mouse; C495774:Wasf1 protein, mouse; C115472:Cyfip1 protein, mouse