Rac regulates phosphorylation of the myosin-II heavy chain, actinomyosin disassembly and cell spreading

F N van Leeuwen, S van Delft, H E Kain, R A van der Kammen, J G Collard

Research output: Contribution to journalArticlepeer-review

185 Citations (Scopus)


GTPases of the Rho family regulate actinomyosin-based contraction in non-muscle cells. Activation of Rho increases contractility, leading to cell rounding and neurite retraction in neuronal cell lines. Activation of Rac promotes cell spreading and interferes with Rho-mediated cell rounding. Here we show that activation of Rac may antagonize Rho by regulating phosphorylation of the myosin-II heavy chain. Stimulation of PC12 cells or N1E-115 neuroblastoma cells with bradykinin induces phosphorylation of threonine residues in the myosin-II heavy chain; this phosphorylation is Ca2+ dependent and regulated by Rac. Both bradykinin-mediated and constitutive activation of Rac promote cell spreading, accompanied by a loss of cortical myosin II. Our results identify the myosin-II heavy chain as a new target of Rac-regulated kinase pathways, and implicate Rac as a Rho antagonist during myosin-II-dependent cell-shape changes.

Original languageEnglish
Pages (from-to)242-8
Number of pages7
JournalNature cell biology
Issue number4
Publication statusPublished - Aug 1999
Externally publishedYes


  • Actomyosin/metabolism
  • Animals
  • Bradykinin/pharmacology
  • Calcium/metabolism
  • Cell Line
  • Cell Size/physiology
  • Mice
  • Myosin Heavy Chains/metabolism
  • PC12 Cells
  • Phosphorylation
  • Protein Serine-Threonine Kinases/metabolism
  • Rats
  • Signal Transduction
  • rac GTP-Binding Proteins/metabolism
  • rho GTP-Binding Proteins/metabolism


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