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Abp1p and cortactin, new "hand-holds" for actin.

Olazabal IM, Machesky LM - J. Cell Biol. (2001)

Bottom Line: Recently, two new ligands of the Arp2/3 complex have been described that may shed light on the way cells organize complex networks of actin in response to signals.Abp1p, a yeast protein involved in endocytosis, and cortactin, a mammalian src substrate, both enhance the ability of the Arp2/3 complex to assemble branched actin filament networks.

View Article: PubMed Central - PubMed

Affiliation: School of Biosciences, Division of Molecular Cell Biology, University of Birmingham, Birmingham B15 2TT, United Kingdom.

ABSTRACT
Recently, two new ligands of the Arp2/3 complex have been described that may shed light on the way cells organize complex networks of actin in response to signals. Abp1p, a yeast protein involved in endocytosis, and cortactin, a mammalian src substrate, both enhance the ability of the Arp2/3 complex to assemble branched actin filament networks.

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Related in: MedlinePlus

Model depicting possible role of cortactin and Abp1p in the stabilization of actin networks during cell motility or membrane trafficking. (A) Events at the plasma membrane including receptor activation, small GTPase activation, and interaction with acidic phospholipids such as phosphatidylinositol 4,5-bisphosphate (PIP2) are thought to bring about the activation of WASP family proteins. Once active, a WASP family protein transiently binds to and activates the Arp2/3 complex. The Arp2/3 complex becomes stably incorporated into an actin filament branch, which elongates until capping protein blocks the polymerization at the barbed end. (B) For networks that will be remodelled, debranching may facilitate the formation of parallel filament bundles (by α-actinin, fascin, or another bundling protein) or depolymerization of filaments during filopodia formation or retraction of new pseudopodia. (C) If a branched network is to be maintained longer term, the activities of cortactin and Abp1p may be to stabilize branches and provide additional rigidity to the network.
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fig2: Model depicting possible role of cortactin and Abp1p in the stabilization of actin networks during cell motility or membrane trafficking. (A) Events at the plasma membrane including receptor activation, small GTPase activation, and interaction with acidic phospholipids such as phosphatidylinositol 4,5-bisphosphate (PIP2) are thought to bring about the activation of WASP family proteins. Once active, a WASP family protein transiently binds to and activates the Arp2/3 complex. The Arp2/3 complex becomes stably incorporated into an actin filament branch, which elongates until capping protein blocks the polymerization at the barbed end. (B) For networks that will be remodelled, debranching may facilitate the formation of parallel filament bundles (by α-actinin, fascin, or another bundling protein) or depolymerization of filaments during filopodia formation or retraction of new pseudopodia. (C) If a branched network is to be maintained longer term, the activities of cortactin and Abp1p may be to stabilize branches and provide additional rigidity to the network.

Mentions: Goode et al. (2001), Uruno et al. (2001), and Weaver et al. (2001) indicate that Abp1p and cortactin activate the Arp2/3 complex by stabilizing its interaction with actin filaments, acting as “hand-holds” for branching. One could imagine that Abp1p or cortactin could displace WASP family proteins by binding to the Arp2/3 complex, thus promoting stability of filament branches. Alternatively, WASP family proteins, Abp1p, or cortactin could be used in separate situations in which different types of actin networks are required (Fig. 2) . It is likely that WASP family proteins activate the Arp2/3 complex by a “hit and run” mechanism (Higgs and Pollard, 1999), requiring only transient interactions, whereas Abp1p binds more tightly to the complex. However, it is unclear whether Abp1p is localized purely via binding to the Arp2/3 complex, or whether other signals such as activated small GTPases could also direct it to the plasma membrane or to sites of actin assembly. The mechanism of cortactin localization to the membrane is also unknown. Notably, cortactin can only bind to actin filaments every 15 actin monomer subunits, thus inducing branch formation separated by a characteristic distance. With or without WASP, cortactin stabilizes actin branches and protects them from debranching. The importance of branching near the plasma membrane seems clear, but the role in endocytic trafficking is less obvious.


Abp1p and cortactin, new "hand-holds" for actin.

Olazabal IM, Machesky LM - J. Cell Biol. (2001)

Model depicting possible role of cortactin and Abp1p in the stabilization of actin networks during cell motility or membrane trafficking. (A) Events at the plasma membrane including receptor activation, small GTPase activation, and interaction with acidic phospholipids such as phosphatidylinositol 4,5-bisphosphate (PIP2) are thought to bring about the activation of WASP family proteins. Once active, a WASP family protein transiently binds to and activates the Arp2/3 complex. The Arp2/3 complex becomes stably incorporated into an actin filament branch, which elongates until capping protein blocks the polymerization at the barbed end. (B) For networks that will be remodelled, debranching may facilitate the formation of parallel filament bundles (by α-actinin, fascin, or another bundling protein) or depolymerization of filaments during filopodia formation or retraction of new pseudopodia. (C) If a branched network is to be maintained longer term, the activities of cortactin and Abp1p may be to stabilize branches and provide additional rigidity to the network.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2196464&req=5

fig2: Model depicting possible role of cortactin and Abp1p in the stabilization of actin networks during cell motility or membrane trafficking. (A) Events at the plasma membrane including receptor activation, small GTPase activation, and interaction with acidic phospholipids such as phosphatidylinositol 4,5-bisphosphate (PIP2) are thought to bring about the activation of WASP family proteins. Once active, a WASP family protein transiently binds to and activates the Arp2/3 complex. The Arp2/3 complex becomes stably incorporated into an actin filament branch, which elongates until capping protein blocks the polymerization at the barbed end. (B) For networks that will be remodelled, debranching may facilitate the formation of parallel filament bundles (by α-actinin, fascin, or another bundling protein) or depolymerization of filaments during filopodia formation or retraction of new pseudopodia. (C) If a branched network is to be maintained longer term, the activities of cortactin and Abp1p may be to stabilize branches and provide additional rigidity to the network.
Mentions: Goode et al. (2001), Uruno et al. (2001), and Weaver et al. (2001) indicate that Abp1p and cortactin activate the Arp2/3 complex by stabilizing its interaction with actin filaments, acting as “hand-holds” for branching. One could imagine that Abp1p or cortactin could displace WASP family proteins by binding to the Arp2/3 complex, thus promoting stability of filament branches. Alternatively, WASP family proteins, Abp1p, or cortactin could be used in separate situations in which different types of actin networks are required (Fig. 2) . It is likely that WASP family proteins activate the Arp2/3 complex by a “hit and run” mechanism (Higgs and Pollard, 1999), requiring only transient interactions, whereas Abp1p binds more tightly to the complex. However, it is unclear whether Abp1p is localized purely via binding to the Arp2/3 complex, or whether other signals such as activated small GTPases could also direct it to the plasma membrane or to sites of actin assembly. The mechanism of cortactin localization to the membrane is also unknown. Notably, cortactin can only bind to actin filaments every 15 actin monomer subunits, thus inducing branch formation separated by a characteristic distance. With or without WASP, cortactin stabilizes actin branches and protects them from debranching. The importance of branching near the plasma membrane seems clear, but the role in endocytic trafficking is less obvious.

Bottom Line: Recently, two new ligands of the Arp2/3 complex have been described that may shed light on the way cells organize complex networks of actin in response to signals.Abp1p, a yeast protein involved in endocytosis, and cortactin, a mammalian src substrate, both enhance the ability of the Arp2/3 complex to assemble branched actin filament networks.

View Article: PubMed Central - PubMed

Affiliation: School of Biosciences, Division of Molecular Cell Biology, University of Birmingham, Birmingham B15 2TT, United Kingdom.

ABSTRACT
Recently, two new ligands of the Arp2/3 complex have been described that may shed light on the way cells organize complex networks of actin in response to signals. Abp1p, a yeast protein involved in endocytosis, and cortactin, a mammalian src substrate, both enhance the ability of the Arp2/3 complex to assemble branched actin filament networks.

Show MeSH
Related in: MedlinePlus