DOCK2 is Required for Chemokine-Promoted Human T Lymphocyte Adhesion Under Shear Stress Mediated by the Integrin {alpha}4beta1.
The alpha(4)beta(1) integrin is an essential adhesion molecule for recruitment of circulating lymphocytes into lymphoid organs and peripheral sites of inflammation. Chemokines stimulate alpha(4)beta(1) adhesive activity allowing lymphocyte arrest on endothelium and subsequent diapedesis. Activation of the GTPase Rac by the guanine-nucleotide exchange factor Vav1 promoted by CXCL12 controls T lymphocyte adhesion mediated by alpha(4)beta(1). In this study, we investigated the role of DOCK2, a lymphocyte guanine-nucleotide exchange factor also involved in Rac activation, in CXCL12-stimulated human T lymphocyte adhesion mediated by alpha(4)beta(1). Using T cells transfected with DOCK2 mutant forms defective in Rac activation or with DOCK2 small interfering RNA, we demonstrate that DOCK2 is needed for efficient chemokine- stimulated lymphocyte attachment to VCAM-1 under shear stress. Flow chamber, soluble binding, and cell spreading assays identified the strengthening of alpha(4)beta(1)-VCAM-1 interaction, involving high affinity alpha(4)beta(1) conformations, as the adhesion step mainly controlled by DOCK2 activity. The comparison of DOCK2 and Vav1 involvement in CXCL12- promoted Rac activation and alpha(4)beta(1)-dependent human T cell adhesion indicated a more prominent role of Vav1 than DOCK2. These results suggest that DOCK2- mediated signaling regulates chemokine-stimulated human T lymphocyte alpha(4)beta(1) adhesive activity, and that cooperation with Vav1 might be required to induce sufficient Rac activation for efficient adhesion. In contrast, flow chamber experiments using lymph node and spleen T cells from DOCK2(-/-) mice revealed no significant alterations in CXCL12-promoted adhesion mediated by alpha(4)beta(1), indicating that DOCK2 activity is dispensable for triggering of this adhesion in mouse T cells, and suggesting that Rac activation plays minor roles in this process.[1]References
- DOCK2 is Required for Chemokine-Promoted Human T Lymphocyte Adhesion Under Shear Stress Mediated by the Integrin {alpha}4beta1. Garc??a-Bernal, D., Sotillo-Mallo, E., Nombela-Arrieta, C., Samaniego, R., Fukui, Y., Stein, J.V., Teixid??, J. J. Immunol. (2006) [Pubmed]
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