title: Rac1-dependent phosphorylation and focal adhesion recruitment of myosin IIA regulates migration and mechanosensing.
abstract: BACKGROUND
  Cell migration requires coordinated formation of focal adhesions (FAs) and assembly and contraction of the actin cytoskeleton. Nonmuscle myosin II (MII) is a critical mediator of contractility and FA dynamics in cell migration. Signaling downstream of the small GTPase Rac1 also regulates FA and actin dynamics, but its role in regulation of MII during migration is less clear.
  
  
  RESULTS
  We found that Rac1 promotes association of MIIA with FA. Live-cell imaging showed that, whereas most MIIA at the leading edge assembled into dorsal contractile arcs, a substantial subset assembled in or was captured within maturing FA, and this behavior was promoted by active Rac1. Protein kinase C (PKC) activation was necessary and sufficient for integrin- and Rac1-dependent phosphorylation of MIIA heavy chain (HC) on serine1916 (S1916) and recruitment to FA. S1916 phosphorylation of MIIA HC and localization in FA was enhanced during cell spreading and ECM stiffness mechanosensing, suggesting upregulation of this pathway during physiological Rac1 activation. Phosphomimic and nonphosphorylatable MIIA HC mutants demonstrated that S1916 phosphorylation was necessary and sufficient for the capture and assembly of MIIA minifilaments in FA. S1916 phosphorylation was also sufficient to promote the rapid assembly of FAs to enhance cell migration and for the modulation of traction force, spreading, and migration by ECM stiffness.
  
  
  CONCLUSIONS
  Our study reveals for the first time that Rac1 and integrin activation regulates MIIA HC phosphorylation through a PKC-dependent mechanism that promotes MIIA association with FAs and acts as a critical modulator of cell migration and mechanosensing.
authors.affiliation: Cell Biology and Physiology Center, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Ana M
authors.initials: AM
authors.lastname: Pasapera
authors.affiliation: Cell Biology and Physiology Center, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA; Department of Cell and Systems Biology, University of Toronto, Toronto, ON M5S 3G5, Canada.
authors.forename: Sergey V
authors.initials: SV
authors.lastname: Plotnikov
authors.affiliation: Cell Biology and Physiology Center, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Fischer
authors.affiliation: Cell Biology and Physiology Center, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Lindsay B
authors.initials: LB
authors.lastname: Case
authors.affiliation: Department of Cellular and Molecular Medicine, Cleveland Clinic Lerner Research Institute, Cleveland, OH 44195, USA.
authors.forename: Thomas T
authors.initials: TT
authors.lastname: Egelhoff
authors.affiliation: Cell Biology and Physiology Center, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA. Electronic address: watermancm@nhlbi.nih.gov.
authors.forename: Clare M
authors.initials: CM
authors.lastname: Waterman
mesh_terms: D002460:Cell Line; D002465:Cell Movement; D022001:Focal Adhesions / Q000378:metabolism*; D006801:Humans; D040542:Mechanotransduction, Cellular / Q000502:physiology; D020409:Molecular Motor Proteins / Q000235:genetics* / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000235:genetics* / Q000378:metabolism; D010766:Phosphorylation; D015398:Signal Transduction; D020830:rac1 GTP-Binding Protein / Q000235:genetics* / Q000378:metabolism
chemical_list: C103814:MYH9 protein, human; D020409:Molecular Motor Proteins; C107953:RAC1 protein, human; D018995:Myosin Heavy Chains; D020830:rac1 GTP-Binding Protein