DOCK2 is required for chemokine-promoted human T lymphocyte adhesion under shear stress mediated by the integrin α₄β₁

The α₄β₁ integrin is an essential adhesion molecule for recruitment of circulating lymphocytes into lymphoid organs and peripheral sites of inflammation. Chemokines stimulate α₄β 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 α₄β₁. 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 α₄β₁. 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 α₄β ₁-VCAM-1 interaction, involving high affinity α ₄β₁ conformations, as the adhesion step mainly controlled by DOCK2 activity. The comparison of DOCK2 and Vav1 involvement in CXCL12-promoted Rac activation and α₄β₁- 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 α₄β₁ adhesive activity, and that cooperation with Vav1 might be required to induce sufficient Rac activation for efficient adhesion. In contrast, low chamber experiments using lymph node and spleen T cells from DOCK2^-/- mice revealed no significant alterations in CXCL12-promoted adhesion mediated by α₄β₁, 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.