Microtubule dynamics differentially regulates Rho and Rac activity and triggers Rho-independent stress fiber formation in macrophage polykaryons

Eur J Cell Biol. 2002 Jun;81(6):351-62. doi: 10.1078/0171-9335-00255.


Multinucleated giant cells (MNGC) derived from avian peripheral blood monocytes present a dense microtubular network emanating from peripherally located centrosomes. We were interested to study how microtubule and F-actin cytoskeletons cooperate in MNGC to maintain cell shape. Microtubule depolymerization by nocodazole triggered the reorganization of the F-actin cytoskeleton in MNGC that is normally organized into podosomes, cortical actin filaments and membrane ruffles. After nocodazole treatment, F-actin was redistributed into unusual transverse fibers associated with focal adhesion plaques. When microtubules were allowed to repolymerize after nocodazole removal, F-actin appeared transiently, together with the small GTPase Rac, in large membrane ruffles. Using affinity precipitation assays, we show that microtubule depolymerization leads to activation of Rho and inhibition of Rac, whereas microtubule repolymerization induces Rac activation and Rho inhibition. Thus, the level of microtubule polymerization inversely regulates Rho and Rac activity in MNGC. Moreover, using C3 exoenzyme, a known inhibitor of Rho, we demonstrate that both the F-actin fiber formation in response to microtubule depolymerization and the formation of membrane ruffles after microtubule repolymerization occur in C3-treated MNGC, indicating that Rho is not required for these events.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ADP Ribose Transferases / pharmacology
  • Actins / drug effects
  • Actins / metabolism*
  • Actins / ultrastructure
  • Animals
  • Botulinum Toxins / pharmacology
  • Cell Adhesion / drug effects
  • Cell Adhesion / physiology
  • Cell Membrane / drug effects
  • Cell Membrane / metabolism
  • Cell Membrane / ultrastructure
  • Cell Movement / drug effects
  • Cell Movement / physiology
  • Cell Size / drug effects
  • Cell Size / physiology
  • Cells, Cultured
  • Chickens
  • Cytochalasin D / pharmacology
  • Cytoskeletal Proteins / metabolism
  • Fluorescent Antibody Technique
  • Giant Cells / cytology
  • Giant Cells / drug effects
  • Giant Cells / metabolism*
  • Macrophages / cytology
  • Macrophages / drug effects
  • Macrophages / metabolism*
  • Microscopy, Confocal
  • Microtubules / drug effects
  • Microtubules / metabolism*
  • Microtubules / ultrastructure
  • Nocodazole / pharmacology
  • Polymers / metabolism
  • Ribose / metabolism
  • Stress Fibers / drug effects
  • Stress Fibers / metabolism*
  • Stress Fibers / ultrastructure
  • rac GTP-Binding Proteins / drug effects
  • rac GTP-Binding Proteins / metabolism*
  • rho GTP-Binding Proteins / drug effects
  • rho GTP-Binding Proteins / metabolism*


  • Actins
  • Cytoskeletal Proteins
  • Polymers
  • Cytochalasin D
  • Ribose
  • ADP Ribose Transferases
  • exoenzyme C3, Clostridium botulinum
  • Botulinum Toxins
  • rac GTP-Binding Proteins
  • rho GTP-Binding Proteins
  • Nocodazole