Scar1 and the related Wiskott-Aldrich syndrome protein, WASP, regulate the actin cytoskeleton through the Arp2/3 complex.
BACKGROUND
The actin-related proteins Arp2 and Arp3 are part of a seven-protein complex which is localized in the lamellipodia of a variety of cell types, and in actin-rich spots of unknown function. The Arp2/3 complex enhances actin nucleation and causes branching and crosslinking of actin filaments in vitro; in vivo it is thought to drive the formation of lamellipodia and to be a control center for actin-based motility. The Wiskott-Aldrich syndrome protein, WASP, is an adaptor protein implicated in the transmission of signals from tyrosine kinase receptors and small GTPases to the actin cytoskeleton. Scar1 is a member of a new family of proteins related to WASP, and it may also have a role in regulating the actin cytoskeleton. Scar1 is the human homologue of Dictyostelium Scar1, which is thought to connect G-protein-coupled receptors to the actin cytoskeleton. The mammalian Scar family contains at least four members. We have examined the relationships between WASP, Scar1, and the Arp2/3 complex.


RESULTS
We have identified WASP and its relative Scar1 as proteins that interact with the Arp2/3 complex. We have used deletion analysis to show that both WASP and Scar1 interact with the p21 subunit of the Arp2/3 complex through their carboxyl termini. Overexpression of carboxy-terminal fragments of Scar1 or WASP in cells caused a disruption in the localization of the Arp2/3 complex and, concomitantly, induced a complete loss of lamellipodia and actin spots. The induction of lamellipodia by platelet-derived growth factor was also suppressed by overexpression of the fragment of Scar1 that binds to the Arp2/3 complex.


CONCLUSIONS
We have identified a conserved sequence domain in proteins of the WASP family that binds to the Arp2/3 complex. Overexpression of this domain in cells disrupts the localization of the Arp2/3 complex and inhibits lamellipodia formation. Our data suggest that WASP-related proteins may regulate the actin cytoskeleton through the Arp2/3 complex.
Machesky
L M
LM
MRC-LMCB, Department of Molecular Medicine, University College London, Gower Street, London WC1E 6BT, UK. machesky@pugh.bip.bham
Insall
R H
RH
D016475:3T3 Cells; D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D000199:Actins / Q000378:metabolism*; D000818:Animals; D001923:Brain Chemistry; D019556:COS Cells; D003598:Cytoskeletal Proteins; D003599:Cytoskeleton / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D005786:Gene Expression Regulation; D006133:Growth Substances / Q000502:physiology; D051379:Mice; D008840:Microfilament Proteins; D011485:Protein Binding / Q000502:physiology; D014176:Protein Biosynthesis; D011506:Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011817:Rabbits; D013552:Swine; D051316:Wiskott-Aldrich Syndrome Protein; D051300:Wiskott-Aldrich Syndrome Protein Family
D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D000199:Actins; C495927:Actr2 protein, mouse; C495929:Actr3 protein, mouse; D003598:Cytoskeletal Proteins; D006133:Growth Substances; D008840:Microfilament Proteins; D011506:Proteins; C495768:Was protein, mouse; C495774:Wasf1 protein, mouse; D051316:Wiskott-Aldrich Syndrome Protein; D051300:Wiskott-Aldrich Syndrome Protein Family