title: V-1 regulates capping protein activity in vivo.
abstract: Capping Protein (CP) plays a central role in the creation of the Arp2/3-generated branched actin networks comprising lamellipodia and pseudopodia by virtue of its ability to cap the actin filament barbed end, which promotes Arp2/3-dependent filament nucleation and optimal branching. The highly conserved protein V-1/Myotrophin binds CP tightly in vitro to render it incapable of binding the barbed end. Here we addressed the physiological significance of this CP antagonist in Dictyostelium, which expresses a V-1 homolog that we show is very similar biochemically to mouse V-1. Consistent with previous studies of CP knockdown, overexpression of V-1 in Dictyostelium reduced the size of pseudopodia and the cortical content of Arp2/3 and induced the formation of filopodia. Importantly, these effects scaled positively with the degree of V-1 overexpression and were not seen with a V-1 mutant that cannot bind CP. V-1 is present in molar excess over CP, suggesting that it suppresses CP activity in the cytoplasm at steady state. Consistently, cells devoid of V-1, like cells overexpressing CP described previously, exhibited a significant decrease in cellular F-actin content. Moreover, V-1-null cells exhibited pronounced defects in macropinocytosis and chemotactic aggregation that were rescued by V-1, but not by the V-1 mutant. Together, these observations demonstrate that V-1 exerts significant influence in vivo on major actin-based processes via its ability to sequester CP. Finally, we present evidence that V-1's ability to sequester CP is regulated by phosphorylation, suggesting that cells may manipulate the level of active CP to tune their "actin phenotype."
authors: Cell Biology and Physiology Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892.
authors: Goeh
authors: G
authors: Jung
authors: Cell Biology and Physiology Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892.
authors: Christopher J
authors: 0000-0002-4803-6542
authors: CJ
authors: Alexander
authors: Light Microscopy Core, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892.
authors: Xufeng S
authors: XS
authors: Wu
authors: Biophysics Core, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892.
authors: Grzegorz
authors: G
authors: Piszczek
authors: Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA 20147.
authors: Bi-Chang
authors: BC
authors: Chen
authors: Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA 20147.
authors: Eric
authors: E
authors: Betzig
authors: Cell Biology and Physiology Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892; hammerj@nhlbi.nih.gov.
authors: John A
authors: JA
authors: Hammer
mesh_terms: D051344:Actin Capping Proteins / Q000235:genetics* / Q000378:metabolism; D051377:Actin-Related Protein 2 / Q000235:genetics / Q000378:metabolism; D051376:Actin-Related Protein 2-3 Complex / Q000235:genetics* / Q000378:metabolism; D051378:Actin-Related Protein 3 / Q000235:genetics / Q000378:metabolism; D000199:Actins / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002633:Chemotaxis / Q000235:genetics; D017124:Conserved Sequence; D004023:Dictyostelium / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D005786:Gene Expression Regulation; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics* / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D009154:Mutation; D010766:Phosphorylation; D010873:Pinocytosis / Q000235:genetics; D011485:Protein Binding; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D015800:Protozoan Proteins / Q000235:genetics* / Q000378:metabolism; D011554:Pseudopodia / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D016415:Sequence Alignment; D015398:Signal Transduction
chemical_list: D051344:Actin Capping Proteins; D051377:Actin-Related Protein 2; D051376:Actin-Related Protein 2-3 Complex; D051378:Actin-Related Protein 3; D000199:Actins; D036341:Intercellular Signaling Peptides and Proteins; D021122:Protein Subunits; D015800:Protozoan Proteins; C065700:myotrophin
keywords: CARMIL; V-1; actin; capping protein; myotrophin