RalB regulates contractility-driven cancer dissemination upon TGFβ stimulation via the RhoGEF GEF-H1

Sci Rep. 2015 Jul 8;5:11759. doi: 10.1038/srep11759.


RalA and RalB proteins are key mediators of oncogenic Ras signaling in human oncogenesis. Herein we investigated the mechanistic contribution of Ral proteins to invasion of lung cancer A549 cells after induction of epithelial-mesenchymal transition (EMT) with TGFβ. We show that TGFβ-induced EMT promotes dissemination of A549 cells in a 2/3D assay, independently of proteolysis, by activating the Rho/ROCK pathway which generates actomyosin-dependent contractility forces that actively remodel the extracellular matrix, as assessed by Traction Force microscopy. RalB, but not RalA, is required for matrix deformation and cell dissemination acting via the RhoGEF GEF-H1, which associates with the Exocyst complex, a major Ral effector. Indeed, uncoupling of the Exocyst subunit Sec5 from GEF-H1 impairs RhoA activation, generation of traction forces and cell dissemination. These results provide a novel molecular mechanism underlying the control of cell invasion by RalB via a cross-talk with the Rho pathway.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amides / pharmacology
  • Cell Line, Tumor
  • Epithelial-Mesenchymal Transition / drug effects*
  • Humans
  • Microscopy, Atomic Force
  • Pyridines / pharmacology
  • RNA Interference
  • RNA, Small Interfering / metabolism
  • Rho Guanine Nucleotide Exchange Factors / metabolism*
  • Signal Transduction / drug effects
  • Transforming Growth Factor beta / pharmacology*
  • rac1 GTP-Binding Protein / metabolism
  • ral GTP-Binding Proteins / antagonists & inhibitors
  • ral GTP-Binding Proteins / genetics
  • ral GTP-Binding Proteins / metabolism*
  • rho-Associated Kinases / antagonists & inhibitors
  • rho-Associated Kinases / metabolism


  • ARHGEF2 protein, human
  • Amides
  • Pyridines
  • RAC1 protein, human
  • RNA, Small Interfering
  • Ralb protein, human
  • Rho Guanine Nucleotide Exchange Factors
  • Transforming Growth Factor beta
  • Y 27632
  • rho-Associated Kinases
  • RALA protein, human
  • rac1 GTP-Binding Protein
  • ral GTP-Binding Proteins