title: Pointed-end capping by tropomodulin3 negatively regulates endothelial cell motility.
abstract: Actin filament pointed-end dynamics are thought to play a critical role in cell motility, yet regulation of this process remains poorly understood. We describe here a previously uncharacterized tropomodulin (Tmod) isoform, Tmod3, which is widely expressed in human tissues and is present in human microvascular endothelial cells (HMEC-1). Tmod3 is present in sufficient quantity to cap pointed ends of actin filaments, localizes to actin filament structures in HMEC-1 cells, and appears enriched in leading edge ruffles and lamellipodia. Transient overexpression of GFP-Tmod3 leads to a depolarized cell morphology and decreased cell motility. A fivefold increase in Tmod3 results in an equivalent decrease in free pointed ends in the cells. Unexpectedly, a decrease in the relative amounts of F-actin, free barbed ends, and actin-related protein 2/3 (Arp2/3) complex in lamellipodia are also observed. Conversely, decreased expression of Tmod3 by RNA interference leads to faster average cell migration, along with increases in free pointed and barbed ends in lamellipodial actin filaments. These data collectively demonstrate that capping of actin filament pointed ends by Tmod3 inhibits cell migration and reveal a novel control mechanism for regulation of actin filaments in lamellipodia.
authors.affiliation: Department of Cell Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, CB163, La Jolla, CA 92037, USA.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Fischer
authors.forename: Kimberly L
authors.initials: KL
authors.lastname: Fritz-Six
authors.forename: Velia M
authors.initials: VM
authors.lastname: Fowler
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D051377:Actin-Related Protein 2; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002465:Cell Movement / Q000235:genetics*; D016764:Cell Polarity / Q000235:genetics; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism; D015536:Down-Regulation / Q000235:genetics*; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D025461:Feedback, Physiological / Q000235:genetics*; D005786:Gene Expression Regulation / Q000235:genetics; D006801:Humans; D008840:Microfilament Proteins; D011554:Pseudopodia / Q000378:metabolism* / Q000648:ultrastructure; D011993:Recombinant Fusion Proteins; D051348:Tropomodulin
chemical_list: C495926:ACTR2 protein, human; D051377:Actin-Related Protein 2; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D008840:Microfilament Proteins; D011993:Recombinant Fusion Proteins; C495836:TMOD3 protein, human; D051348:Tropomodulin