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Vol. 14, Issue 8, 3242-3253, August 2003

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SWAP-70 Identifies a Transitional Subset of Actin Filaments in Motile Cells

Pirta Hilpelä ^* , Pia Oberbanscheidt ^*, Penelope Hahne , Martin Hund ^*, Georg Kalhammer ^*, J. Victor Small , and Martin Bähler 

^* Institut für Allgemeine Zoologie und Genetik, Westfälische Wilhelms-Universität Münster, D-48149 Münster, Germany; Institute of Molecular Biology, Austrian Academy of Sciences, Salzburg, Austria

Submitted January 27, 2003; Revised March 21, 2003; Accepted March 21, 2003
Monitoring Editor: Paul Matsudaira

Functionally different subsets of actin filament arrays contribute to cellular organization and motility. We report the identification of a novel subset of loose actin filament arrays through regulated association with the widely expressed protein SWAP-70. These loose actin filament arrays were commonly located behind protruding lamellipodia and membrane ruffles. Visualization of these loose actin filament arrays was dependent on lamellipodial protrusion and the binding of the SWAP-70 PH-domain to a 3'-phosphoinositide. SWAP-70 with a functional pleckstrin homology-domain lacking the C-terminal 60 residues was targeted to the area of the loose actin filament arrays, but it did not associate with actin filaments. The C-terminal 60 residues were sufficient for actin filament association, but they provided no specificity for the subset of loose actin filament arrays. These results identify SWAP-70 as a phosphoinositide 3-kinase signaling-dependent marker for a distinct, hitherto unrecognized, array of actin filaments. Overexpression of SWAP-70 altered the actin organization and lamellipodial morphology. These alterations were dependent on a proper subcellular targeting of SWAP-70. We propose that SWAP-70 regulates the actincytoskeletonasaneffectororadaptorproteininresponsetoagoniststimulatedphosphatidylinositol (3,4)-bisphosphate production and cell protrusion.

Abbreviations used: 3'-phosphoinositide, refers to PI(3)P, PI(3,4)P₂, PI(3,5)P₂, and PI(3,4,5)P₃; GFP, green fluorescent protein; GST, glutathione S-transferase; HA, hemagglutinin; PH, pleckstrin homology; PI 3-kinase, phosphoinositide 3-kinase; PI(3,4)P₂, phosphatidylinositol 3,4-bisphosphate; PI(3,4,5)P₃, phosphatidylinositol 3,4,5-trisphosphate.

The online version of this article contains video material for some figures. Online version is available at www.molbiolcell.org.

Present address: Institute of Biotechnology, Viikki Biocenter, University of Helsinki, Helsinki FIN-00014, Finland.

Corresponding author. E-mail address: baehler{at}nwz.unimuenster.de.

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