Phosphorylation of the Arp2/3 complex is necessary to nucleate actin filaments.
The actin-related protein 2/3 (Arp2/3) complex is the primary nucleator of new actin filaments in most crawling cells. Nucleation-promoting factors (NPFs) of the Wiskott-Aldrich syndrome protein (WASP)/Scar family are the currently recognized activators of the Arp2/3 complex. We now report that the Arp2/3 complex must be phosphorylated on either threonine or tyrosine residues to be activated by NPFs. Phosphorylation of the Arp2/3 complex is not necessary to bind NPFs or the sides of actin filaments but is critical for binding the pointed end of actin filaments and nucleating actin filaments. Mass spectrometry revealed phosphorylated Thr237 and Thr238 in Arp2, which are evolutionarily conserved residues. In cells, phosphorylation of only the Arp2 subunit increases in response to growth factors, and alanine substitutions of Arp2 T237 and T238 or Y202 inhibits membrane protrusion. These findings reveal an additional level of regulation of actin filament assembly independent of WASP proteins, and show that phosphorylation of the Arp2/3 complex provides a logical "or gate" capable integrating diverse upstream signals.
LeClaire
Lawrence L
LL
Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, CA 94143, USA.
Baumgartner
Martin
M
Iwasa
Janet H
JH
Mullins
R Dyche
RD
Barber
Diane L
DL
D048248:Acanthamoeba castellanii / Q000378:metabolism; D008841:Actin Cytoskeleton / Q000378:metabolism*; D051376:Actin-Related Protein 2-3 Complex / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D017124:Conserved Sequence; D004331:Drosophila melanogaster / Q000166:cytology; D006801:Humans; D008969:Molecular Sequence Data; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D021122:Protein Subunits / Q000378:metabolism; D011554:Pseudopodia / Q000378:metabolism; D051381:Rats
D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D021122:Protein Subunits; D019000:Phosphotyrosine