Induction of lamellipodia by Kalirin does not require its guanine nucleotide exchange factor activity

Exp Cell Res. 2005 Jul 15;307(2):402-17. doi: 10.1016/j.yexcr.2005.03.024. Epub 2005 Apr 21.


Guanine nucleotide exchange factor (GEF) domains of the Dbl family occur in a variety of proteins that include multiple protein-protein and protein-lipid interaction domains. We used an epithelial-derived cell line to investigate the mechanisms by which the two GEF domains of Kalirin, a neuronal Rho GEF, influence morphology. As expected, Kal-GEF1, an efficient GEF for Rac1 and RhoG, induced the formation of lamellipodia resembling those induced by active Rac1. Although Kal-GEF1 activated Rac and Pak, its ability to induce formation of lamellipodia was not blocked by dominant negative Rho GTPases or by catalytically inactive Pak. Consistent with this, a catalytically inactive mutant of Kal-GEF1 induced formation of lamellipodia and activated Pak. Active Pak was required for the GEF-activity independent effect of Kal-GEF1 and the lamellipodia produced were filled with ribs of filamentous actin. Kal-GEF1 and a GEF-dead mutant co-immunoprecipitated with Pak. The interaction of Kal-GEF1 with Pak is indirect and requires the regulatory protein binding domain of Pak. Filamin A, which is known to interact with and activate Pak, binds to both catalytically active and inactive Kal-GEF1, providing a link by which catalytically inactive Kal-GEF1 can activate Pak and induce lamellipodia. Together, our results indicate that Kal-GEF1 induces lamellipodia through activation of Pak, where GEF activity is not required. GEF-activity-independent effects on downstream targets may be a general property of RhoGEFs.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Actins / metabolism
  • Cell Line
  • Cell Shape / physiology*
  • Contractile Proteins / metabolism
  • Filamins
  • GTP Phosphohydrolases / genetics
  • Guanine Nucleotide Exchange Factors / genetics
  • Guanine Nucleotide Exchange Factors / metabolism
  • Guanine Nucleotide Exchange Factors / physiology*
  • Histones / metabolism
  • Humans
  • Microfilament Proteins / metabolism
  • Models, Biological
  • Mutation / genetics
  • Nerve Tissue Proteins / metabolism
  • Peptide Fragments / genetics
  • Peptide Fragments / metabolism
  • Phosphorylation
  • Protein Binding
  • Protein Isoforms / genetics
  • Protein Isoforms / metabolism
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism
  • Protein-Serine-Threonine Kinases / physiology*
  • Pseudopodia / physiology*
  • Transfection
  • Wiskott-Aldrich Syndrome Protein Family
  • Wiskott-Aldrich Syndrome Protein, Neuronal
  • p21-Activated Kinases
  • rac1 GTP-Binding Protein / genetics
  • rac1 GTP-Binding Protein / metabolism
  • rho GTP-Binding Proteins


  • Actins
  • Contractile Proteins
  • Filamins
  • Guanine Nucleotide Exchange Factors
  • Histones
  • Microfilament Proteins
  • Nerve Tissue Proteins
  • Peptide Fragments
  • Protein Isoforms
  • WASF2 protein, human
  • WASL protein, human
  • Wiskott-Aldrich Syndrome Protein Family
  • Wiskott-Aldrich Syndrome Protein, Neuronal
  • RHOG protein, human
  • KALRN protein, human
  • PAK1 protein, human
  • Protein-Serine-Threonine Kinases
  • p21-Activated Kinases
  • GTP Phosphohydrolases
  • rac1 GTP-Binding Protein
  • rho GTP-Binding Proteins