The M-Ras-RA-GEF-2-Rap1 pathway mediates tumor necrosis factor-alpha dependent regulation of integrin activation in splenocytes

Mol Biol Cell. 2007 Aug;18(8):2949-59. doi: 10.1091/mbc.e07-03-0250. Epub 2007 May 30.

Abstract

The Rap1 small GTPase has been implicated in regulation of integrin-mediated leukocyte adhesion downstream of various chemokines and cytokines in many aspects of inflammatory and immune responses. However, the mechanism for Rap1 regulation in the adhesion signaling remains unclear. RA-GEF-2 is a member of the multiple-member family of guanine nucleotide exchange factors (GEFs) for Rap1 and characterized by the possession of a Ras/Rap1-associating domain, interacting with M-Ras-GTP as an effector, in addition to the GEF catalytic domain. Here, we show that RA-GEF-2 is specifically responsible for the activation of Rap1 that mediates tumor necrosis factor-alpha (TNF-alpha)-triggered integrin activation. In BAF3 hematopoietic cells, activated M-Ras potently induced lymphocyte function-associated antigen 1 (LFA-1)-mediated cell aggregation. This activation was totally abrogated by knockdown of RA-GEF-2 or Rap1. TNF-alpha treatment activated LFA-1 in a manner dependent on M-Ras, RA-GEF-2, and Rap1 and induced activation of M-Ras and Rap1 in the plasma membrane, which was accompanied by recruitment of RA-GEF-2. Finally, we demonstrated that M-Ras and RA-GEF-2 were indeed involved in TNF-alpha-stimulated and Rap1-mediated LFA-1 activation in splenocytes by using mice deficient in RA-GEF-2. These findings proved a crucial role of the cross-talk between two Ras-family GTPases M-Ras and Rap1, mediated by RA-GEF-2, in adhesion signaling.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Adhesion / drug effects
  • Cell Aggregation / drug effects
  • Enzyme Activation / drug effects
  • Gene Targeting
  • Guanine Nucleotide Exchange Factors / metabolism*
  • Humans
  • Integrins / metabolism*
  • Intercellular Adhesion Molecule-1 / metabolism
  • Lymphocyte Function-Associated Antigen-1 / metabolism
  • Mice
  • Models, Biological
  • Monomeric GTP-Binding Proteins / metabolism*
  • Spleen / cytology*
  • Spleen / drug effects
  • Tumor Necrosis Factor-alpha / pharmacology*
  • rap1 GTP-Binding Proteins / metabolism*
  • ras Proteins / metabolism*

Substances

  • CNrasGEF protein, mouse
  • Guanine Nucleotide Exchange Factors
  • Integrins
  • Lymphocyte Function-Associated Antigen-1
  • MRAS protein, human
  • Tumor Necrosis Factor-alpha
  • Intercellular Adhesion Molecule-1
  • Mras protein, mouse
  • Monomeric GTP-Binding Proteins
  • rap1 GTP-Binding Proteins
  • ras Proteins