The small GTPase RalA targets filamin to induce filopodia.
The Ras-related small GTPases Rac, Rho, Cdc42, and RalA bind filamin, an actin filament-crosslinking protein that also links membrane and other intracellular proteins to actin. Of these GTPases only RalA binds filamin in a GTP-specific manner, and GTP-RalA elicits actin-rich filopods on surfaces of Swiss 3T3 cells and recruits filamin into the filopodial cytoskeleton. Either a dominant negative RalA construct or the RalA-binding domain of filamin 1 specifically block Cdc42-induced filopod formation, but a Cdc42 inhibitor does not impair RalA's effects, which, unlike Cdc42, are Rac independent. RalA does not generate filopodia in filamin-deficient human melanoma cells, whereas transfection of filamin 1 restores the functional response. RalA therefore is a downstream intermediate in Cdc42-mediated filopod production and uses filamin in this pathway.
Ohta
Y
Y
Division of Biochemistry and Cellular Biology, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Ogawahigashi, Kodaira, Tokyo 187, Japan. ohta@ncnaxp.ncnp.go.jp
Suzuki
N
N
Nakamura
S
S
Hartwig
J H
JH
Stossel
T P
TP
D016475:3T3 Cells; D000199:Actins / Q000378:metabolism; D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000378:metabolism; D003001:Cloning, Molecular; D003285:Contractile Proteins / Q000378:metabolism*; D003599:Cytoskeleton / Q000502:physiology / Q000648:ultrastructure; D004926:Escherichia coli; D064448:Filamins; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008840:Microfilament Proteins / Q000378:metabolism*; D018715:Microscopy, Video; D011554:Pseudopodia / Q000502:physiology* / Q000648:ultrastructure; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D020725:ral GTP-Binding Proteins
D000199:Actins; D002352:Carrier Proteins; D003285:Contractile Proteins; D064448:Filamins; D008565:Membrane Proteins; D008840:Microfilament Proteins; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D020558:GTP Phosphohydrolases; C492198:RALA protein, human; C118120:Rala protein, mouse; D020725:ral GTP-Binding Proteins