The Arf6 GAP centaurin α-1 is a neuronal actin-binding protein which also functions via GAP-independent activity to regulate the actin cytoskeleton

Abstract

Centaurin alpha-1 is a high-affinity PtdIns(3,4,5)P3-binding protein enriched in brain. Sequence analysis indicates centaurin alpha-1 contains two pleckstrin homology domains, ankyrin repeats and an Arf GAP homology domain, placing it in the AZAP family of phosphoinositide-regulated Arf GAPs. Other members of this family are involved in actin cytoskeletal and focal adhesion organization. Recently, it was reported that centaurin alpha-1 expression diminishes cortical actin and decreases Arf6GTP levels consistent with it functioning as an Arf6 GAP in vivo. In the current report, we show that centaurin alpha-1 binds Arfs in vitro and colocalizes with Arf6 and Arf5 in vivo, further supporting an interaction with Arfs. Centaurin alpha-1 expression produces dramatic effects on the actin cytoskeleton, decreasing stress fibers, diminishing cortical actin, and enhancing membrane ruffles and filopodia. Expression of centaurin alpha-1 also enhances cell spreading and disrupts focal adhesion protein localization. The effects of centaurin alpha-1 on stress fibers and cell spreading are reminiscent of those of Arf6GTP. Consistent with this, we show that many of the centaurin alpha-1-induced effects on the actin cytoskeleton and actin-dependent activities do not require GAP activity. Thus, centaurin alpha-1 likely functions via both GAP-dependent and GAP-independent mechanisms to regulate the actin cytoskeleton. Furthermore, we demonstrate that in vitro, centaurin alpha-1 binds F-actin directly, with actin binding activity localized to the PtdIns(3,4,5)P3-binding PH domain. Our data suggest that centaurin alpha-1 may be a component of the neuronal PI 3-kinase cascade that leads to regulation of the neuronal actin cytoskeleton.