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Vol. 18, Issue 5, 1609-1620, May 2007

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The N-Terminus of Dictyostelium Scar Interacts with Abi and HSPC300 and Is Essential for Proper Regulation and Function

Diana Caracino^*,,, Cheryl Jones^*, Mark Compton, and Charles L. Saxe, III^*,

*Department of Cell Biology and Graduate Program in Microbiology and Molecular Genetics, Emory University School of Medicine, Atlanta, GA 30322; and Department of Poultry Science, School of Agriculture, University of Georgia, Athens, GA 30602

Submitted June 13, 2006; Revised January 24, 2007; Accepted February 12, 2007
Monitoring Editor: Carole Parent

Scar/WAVE proteins, members of the conserved Wiskott-Aldrich syndrome (WAS) family, promote actin polymerization by activating the Arp2/3 complex. A number of proteins, including a complex containing Nap1, PIR121, Abi1/2, and HSPC300, interact with Scar/WAVE, though the role of this complex in regulating Scar function remains unclear. Here we identify a short N-terminal region of Dictyostelium Scar that is necessary and sufficient for interaction with HSPC300 and Abi in vitro. Cells expressing Scar lacking this N-terminal region show abnormalities in F-actin distribution, cell morphology, movement, and cytokinesis. This is true even in the presence of wild-type Scar. The data suggest that the first 96 amino acids of Scar are necessary for participation in a large-molecular-weight protein complex, and that this Scar-containing complex is responsible for the proper localization and regulation of Scar. The presence of mis-regulated or unregulated Scar has significant deleterious effects on cells and may explain the need to keep Scar activity tightly controlled in vivo either by assembly in a complex or by rapid degradation.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

Present address: Hunter Laboratory, Department of Molecular and Cellular Biology, Harvard University, 16 Divinity Avenue, Room 3050, Cambridge, MA 02138.

Address correspondence to: Charles L. Saxe (karl{at}cellbio.emory.edu)