Rap1 translates chemokine signals to integrin activation, cell polarization, and motility across vascular endothelium under flow

TLDR

Chemokines arrest circulating lymphocytes by rapidly up‑regulating integrin adhesive activity, yet the key regulatory molecules mediating this process remain unknown. The study demonstrates that Rap1 is essential for chemokine‑induced integrin activation and lymphocyte migration. Rap1 is rapidly activated by SLC and CXCL4, driving shear‑resistant adhesion, polarized migration, and transendothelial migration of lymphocytes, while inhibition by Spa1 blocks these responses, indicating Rap1 controls chemokine‑mediated extravasation.

Abstract

Chemokines arrest circulating lymphocytes within the vasculature through the rapid up-regulation of leukocyte integrin adhesive activity, promoting subsequent lymphocyte transmigration. However, the key regulatory molecules regulating this process have remained elusive. Here, we demonstrate that Rap1 plays a pivotal role in chemokine-induced integrin activation and migration. Rap1 was activated by secondary lymphoid tissue chemokine (SLC; CCL21) and stromal-derived factor 1 (CXCL4) treatment in lymphocytes within seconds. Inhibition of Rap1 by Spa1, a Rap1-specific GTPase-activating protein, abrogated chemokine-stimulated lymphocyte rapid adhesion to endothelial cells under flow via intercellular adhesion molecule 1. Expression of a dominant active Rap1V12 in lymphocytes stimulated shear-resistant adhesion, robust cell migration on immobilized intercellular adhesion molecule 1 and vascular cell adhesion molecule 1, and transendothelial migration under flow. We also demonstrated that Rap1V12 expression in lymphocytes induced a polarized morphology, accompanied by the redistribution of CXCR4 and CD44 to the leading edge and uropod, respectively. Spa1 effectively suppressed this polarization after SLC treatment. This unique characteristic of Rap1 may control chemokine-induced lymphocyte extravasation.