Abi, Sra1, and Kette control the stability and localization of SCAR/WAVE to regulate the formation of actin-based protrusions.
BACKGROUND
In animal cells, GTPase signaling pathways are thought to generate cellular protrusions by modulating the activity of downstream actin-regulatory proteins. Although the molecular events linking activation of a GTPase to the formation of an actin-based process with a characteristic morphology are incompletely understood, Rac-GTP is thought to promote the activation of SCAR/WAVE, whereas Cdc42 is thought to initiate the formation of filopodia through WASP. SCAR and WASP then activate the Arp2/3 complex to nucleate the formation of new actin filaments, which through polymerization exert a protrusive force on the membrane.


RESULTS
Using RNAi to screen for genes regulating cell form in an adherent Drosophila cell line, we identified a set of genes, including Abi/E3B1, that are absolutely required for the formation of dynamic protrusions. These genes delineate a pathway from Cdc42 and Rac to SCAR and the Arp2/3 complex. Efforts to place Abi in this signaling hierarchy revealed that Abi and two components of a recently identified SCAR complex, Sra1 (p140/PIR121/CYFIP) and Kette (Nap1/Hem), protect SCAR from proteasome-mediated degradation and are critical for SCAR localization and for the generation of Arp2/3-dependent protrusions.


CONCLUSIONS
In Drosophila cells, SCAR is regulated by Abi, Kette, and Sra1, components of a conserved regulatory SCAR complex. By controlling the stability, localization, and function of SCAR, these proteins may help to ensure that Arp2/3 activation and the generation of actin-based protrusions remain strictly dependant on local GTPase signaling.
Ludwig Institute for Cancer Research - University College Branch, London, UK.
Patricia
P
Kunda
Gavin
G
Craig
Veronica
V
Dominguez
Buzz
B
Baum
D000199:Actins / Q000378:metabolism*; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D004330:Drosophila / Q000502:physiology; D029721:Drosophila Proteins / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D008840:Microfilament Proteins / Q000378:metabolism*; D011554:Pseudopodia / Q000378:metabolism / Q000502:physiology*; D034622:RNA Interference; D015398:Signal Transduction; D051300:Wiskott-Aldrich Syndrome Protein Family
C121808:Abi protein, Drosophila; D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D029721:Drosophila Proteins; D008840:Microfilament Proteins; C449671:SCAR protein, Drosophila; C484666:Sra-1 protein, Drosophila; D051300:Wiskott-Aldrich Syndrome Protein Family; C478569:hem protein, Drosophila