Small GTPases and LFA-1 reciprocally modulate adhesion and signaling

Immunol Rev. 2007 Aug;218:114-25. doi: 10.1111/j.1600-065X.2007.00538.x.


Leukocyte-function-associated antigen-1 (LFA-1) is an integrin that is critical for T-cell adhesion and immunologic responses. As a transmembrane receptor and adhesion molecule, LFA-1 signals bidirectionally, whereby information about extracellular ligands is passed outside-in while cellular activation is transmitted inside-out to the adhesive ectodomain. Here, we review the role of small guanosine triphosphatases (GTPases) in LFA-1 signaling. Rap1, a Ras-related GTPase, appears to be central to LFA-1 function. Rap1 is regulated by receptor signaling [e.g. T-cell receptor (TCR), CD28, and cytotoxic T-lymphocyte antigen-4 (CTLA-4)] and by adapter proteins [e.g. adhesion and degranulation-promoting adapter protein (ADAP) and Src kinase-associated phosphoprotein of 55 kDa (SKAP-55)]. Inside-out signaling flows through Rap1 to regulator of adhesion and cell polarization enriched in lymphoid tissues (RAPL) and Rap1-GTP interacting adapter molecule (RIAM) that act in conjunction with the cytoskeleton on the cytosolic domain of LFA-1 to increase adhesion of the ectodomain. Outside-in signaling also relies on small GTPases such as Rho proteins. Vav-1, a guanine nucleotide exchange factor for Rho proteins, is activated as a consequence of LFA-1 engagement. Jun-activating binding protein-1 (JAB-1) and cytohesin-1 have been implicated as possible outside-in signaling intermediates. We have recently shown that Ras is also downstream of LFA-1 engagement: LFA-1 signaling through phospholipase D (PLD) to RasGRP1 was required for Ras activation on the plasma membrane following stimulation of TCR.

Publication types

  • Review

MeSH terms

  • Adaptor Proteins, Signal Transducing / metabolism
  • Animals
  • Cell Adhesion
  • Humans
  • Lymphocyte Function-Associated Antigen-1 / immunology*
  • Lymphocyte Function-Associated Antigen-1 / metabolism*
  • Models, Immunological
  • Monomeric GTP-Binding Proteins / immunology*
  • Monomeric GTP-Binding Proteins / metabolism*
  • Signal Transduction / immunology*


  • Adaptor Proteins, Signal Transducing
  • Lymphocyte Function-Associated Antigen-1
  • Monomeric GTP-Binding Proteins