Rap1a activation by CalDAG-GEFI and p38 MAPK is involved in E-selectin-dependent slow leukocyte rolling

Eur J Immunol. 2011 Jul;41(7):2074-85. doi: 10.1002/eji.201041196. Epub 2011 Jun 7.


Rolling leukocytes are exposed to different adhesion molecules and chemokines. Neutrophils rolling on E-selectin induce integrin αLβ2-mediated slow rolling on ICAM-1 by activating a phospholipase C (PLC)γ2-dependent and a separate PI3Kγ-dependent pathway. E-selectin-signaling cooperates with chemokine signaling to recruit neutrophils into inflamed tissues. However, the distal signaling pathway linking PLCγ2 (Plcg2) to αLβ2-activation is unknown. To identify this pathway, we used different Tat-fusion-mutants and gene-deficient mice in intravital microscopy, autoperfused flow chamber, peritonitis, and biochemical studies. We found that the small GTPase Rap1 is activated following E-selectin engagement and that blocking Rap1a in Pik3cg-/- mice by a dominant-negative Tat-fusion mutant completely abolished E-selectin-mediated slow rolling. We identified CalDAG-GEFI (Rasgrp2) and p38 MAPK as key signaling intermediates between PLCγ2 and Rap1a. Gαi-independent leukocyte adhesion to and transmigration through endothelial cells in inflamed postcapillary venules of the cremaster muscle were completely abolished in Rasgrp2-/- mice. The physiological importance of CalDAG-GEFI in E-selectin-dependent integrin activation is shown by complete inhibition of neutrophil recruitment into the inflamed peritoneal cavity of Rasgrp2-/- leukocytes treated with pertussis toxin to block Gαi-signaling. Our data demonstrate that Rap1a activation by p38 MAPK and CalDAG-GEFI is involved in E-selectin-dependent slow rolling and leukocyte recruitment.

Publication types

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

MeSH terms

  • Animals
  • Class Ib Phosphatidylinositol 3-Kinase / genetics
  • Class Ib Phosphatidylinositol 3-Kinase / metabolism
  • E-Selectin / metabolism*
  • GTP-Binding Protein alpha Subunit, Gi2 / metabolism
  • Guanine Nucleotide Exchange Factors / genetics
  • Guanine Nucleotide Exchange Factors / metabolism*
  • Integrins / metabolism
  • Leukocyte Rolling*
  • Lymphocyte Function-Associated Antigen-1
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Neutrophil Infiltration / genetics
  • Neutrophils / physiology*
  • Peritonitis / immunology
  • Peritonitis / metabolism
  • Pertussis Toxin / pharmacology
  • Phospholipase C gamma
  • Signal Transduction
  • Transendothelial and Transepithelial Migration
  • p38 Mitogen-Activated Protein Kinases / metabolism*
  • rap1 GTP-Binding Proteins / metabolism*
  • tat Gene Products, Human Immunodeficiency Virus / genetics
  • tat Gene Products, Human Immunodeficiency Virus / metabolism


  • E-Selectin
  • Guanine Nucleotide Exchange Factors
  • Integrins
  • Lymphocyte Function-Associated Antigen-1
  • Rasgrp2 protein, mouse
  • tat Gene Products, Human Immunodeficiency Virus
  • Pertussis Toxin
  • Class Ib Phosphatidylinositol 3-Kinase
  • Pik3cg protein, mouse
  • p38 Mitogen-Activated Protein Kinases
  • Phospholipase C gamma
  • GTP-Binding Protein alpha Subunit, Gi2
  • rap1 GTP-Binding Proteins