Epac1-Rap1 signaling regulates monocyte adhesion and chemotaxis

J Leukoc Biol. 2006 Dec;80(6):1542-52. doi: 10.1189/jlb.0506357. Epub 2006 Aug 29.


Extravasation of leukocytes is a crucial process in the immunological defense. In response to a local concentration of chemokines, circulating leukocytes adhere to and migrate across the vascular endothelium toward the inflamed tissue. The small guanosinetriphosphatase Rap1 plays an important role in the regulation of leukocyte adhesion, polarization, and chemotaxis. We investigated the role of a guanine nucleotide exchange protein for Rap1 directly activated by cAMP (Epac1) in adhesion and chemotaxis in a promonocytic cell line and in primary monocytes. We found that Epac1 is expressed in primary leukocytes, platelets, CD34-positive hematopoietic cells, and the leukemic cell lines U937 and HL60. Epac activation with an Epac-specific cAMP analog induced Rap1 activation, beta1-integrin-dependent cell adhesion, and cell polarization. In addition, activated Epac1 enhanced chemotaxis of U937 cells and primary monocytes. Similar to activation of Epac1, stimulation of cells with serotonin to induce cAMP production resulted in Rap1 activation, increased cell adhesion and polarization, and enhanced chemotaxis. The effects of serotonin on U937 cell adhesion were dependent on cAMP production but could not be blocked by a protein kinase A inhibitor, implicating Epac in the regulation of serotonin-induced adhesion. In summary, our work reveals the existence of previously unrecognized cAMP-dependent signaling in leukocytes regulating cell adhesion and chemotaxis through the activation of Epac1.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • CHO Cells
  • Cell Adhesion / drug effects
  • Cell Adhesion / immunology
  • Cell Polarity / drug effects
  • Cell Polarity / immunology
  • Chemotaxis / drug effects
  • Chemotaxis / immunology*
  • Cricetinae
  • Cricetulus
  • Cyclic AMP / immunology
  • Cyclic AMP-Dependent Protein Kinases / antagonists & inhibitors
  • Cyclic AMP-Dependent Protein Kinases / immunology
  • Guanine Nucleotide Exchange Factors / immunology*
  • HL-60 Cells
  • Hematopoietic Stem Cells / immunology
  • Humans
  • Integrin beta1 / immunology
  • Macrophage Activation / drug effects
  • Macrophage Activation / immunology*
  • Protein Kinase Inhibitors / pharmacology
  • Serotonin / immunology
  • Serotonin / pharmacology
  • Signal Transduction / drug effects
  • Signal Transduction / immunology*
  • U937 Cells
  • rap1 GTP-Binding Proteins / immunology*


  • Guanine Nucleotide Exchange Factors
  • Integrin beta1
  • Protein Kinase Inhibitors
  • RAPGEF3 protein, human
  • Serotonin
  • Cyclic AMP
  • Cyclic AMP-Dependent Protein Kinases
  • rap1 GTP-Binding Proteins