Essential role for Rap1 GTPase and its guanine exchange factor CalDAG-GEFI in LFA-1 but not VLA-4 integrin-mediated human T cell adhesion

Ghandour H, Cullere X, Luscinskas FW, Mayadas TN
Source: Blood
Publication Date: (2007)
Issue: 110(10): 3682-90
Research Area:
Immunotherapy / Hematology
Cells used in publication:
T cell, human peripheral blood unstim.
Species: human
Tissue Origin: blood
Nucleofector® I/II/2b
Regulated adhesion of T cells by the integrins LFA-1 and VLA-4 is essential for T cell trafficking. The small GTPase Rap1 is a critical activator of both integrins in murine lymphocytes and T cell lines. Here we examined the contribution of the Rap1 regulatory pathway in integrin activation in primary CD3+ human T cells. We demonstrate that inactivation of Rap1 GTPase in human T cells by expression of SPA1 or Rap1GAP blocked SDF-1alpha-stimulated LFA-1-ICAM-1 interactions and LFA-1 affinity modulation but unexpectedly, did not significantly affect binding of VLA-4 to its ligand VCAM-1. Importantly, silencing of the Rap1 guanine exchange factor CalDAG-GEFI inhibited SDF-1alpha and PMA induced adhesion to ICAM-1, while having no effect on adhesion to VCAM-1. Pharmacological inhibition of Phospholipase C (PLC) blocked Rap1 activation and inhibited cell adhesion and polarization on ICAM-1 and VCAM-1. Protein kinase C (PKC) inhibition led to enhanced levels of active Rap1 concomitantly with increased T cell binding to ICAM-1, while adhesion to VCAM-1 was reduced. Thus, PLC/CalDAG-GEFI regulation of Rap1 is selectively required for chemokine and PMA induced LFA-1 activation in human T cells while alternate PLC and PKC dependent mechanisms are involved in the regulation of VLA-4.