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.
Regulated adhesion of T cells by the integrins LFA-1 (lymphocyte function-associated antigen-1) and VLA-4 (very late antigen-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 stromal cell-derived factor-1alpha (SDF-1alpha)-stimulated LFA-1-ICAM-1 (intercellular adhesion molecule-1) interactions and LFA-1 affinity modulation but unexpectedly did not significantly affect binding of VLA-4 to its ligand VCAM-1 (vascular cell adhesion molecule 1). Importantly, silencing of the Rap1 guanine exchange factor CalDAG-GEFI inhibited SDF-1alpha- and phorbol 12-myristate 13-acetate (PMA)-induced adhesion to ICAM-1 while having no effect on adhesion to VCAM-1. Pharmacologic 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, whereas 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, whereas alternate PLC- and PKC-dependent mechanisms are involved in the regulation of VLA-4.
Ghandour
Haifa
H
Center for Excellence in Vascular Biology, Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA.
Cullere
Xavier
X
Alvarez
Angeles
A
Luscinskas
Francis W
FW
Mayadas
Tanya N
TN
D002448:Cell Adhesion; D002478:Cells, Cultured; D020662:Guanine Nucleotide Exchange Factors / Q000502:physiology*; D006801:Humans; D039041:Integrin alpha4beta1 / Q000502:physiology*; D016169:Lymphocyte Function-Associated Antigen-1 / Q000502:physiology*; D008954:Models, Biological; D011493:Protein Kinase C / Q000502:physiology; D013601:T-Lymphocytes / Q000187:drug effects / Q000502:physiology*; D010738:Type C Phospholipases / Q000502:physiology; D020827:rap1 GTP-Binding Proteins / Q000502:physiology*
D020662:Guanine Nucleotide Exchange Factors; D039041:Integrin alpha4beta1; D016169:Lymphocyte Function-Associated Antigen-1; C115955:RAP1GDS1 protein, human; C415483:RASGRP2 protein, human; D011493:Protein Kinase C; D010738:Type C Phospholipases; D020827:rap1 GTP-Binding Proteins
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