Distinct bidirectional regulation of LFA1 and α4β7 by Rap1 and integrin adaptors in T cells under shear flow

Bidirectional control of integrin activation plays crucial roles in cell adhesive behaviors, but how integrins are specifically regulated by inside-out and outside-in signaling has not been fully understood. Here, we report distinct bidirectional regulation of major lymphocyte homing receptors LFA1 and α4β7 in primary T cells. A small increase of Rap1 activation in L-selectin-mediated tether/rolling was boosted by the outside-in signaling from ICAM1-interacting LFA1 through subsecond, simultaneous activation of Rap1 GTPase and talin1, but not kindlin-3, resulting in increased capture and slowing. In contrast, none of them were required for tether/rolling by α4β7 on MAdCAM1. High Rap1 activation with chemokines or the loss of Rap1-inactivating proteins Rasa3 and Sipa1 increased talin1/kindlin-3-dependent arrest with high-affinity binding of LFA1 to membrane-anchored ICAM1. However, despite increased affinity of α4β7, activated Rap1 severely suppressed adhesion on MAdCAM1 under shear flow, indicating the critical importance of a sequential outside-in/inside-out signaling for α4β7. [Display omitted] •Kindlin-3 is partially involved in attachment to high-density ICAM1 and HEV•Co-occupancy of LFA1 with ICAM1 and talin1 activates Rap1 and induces slow rolling•Distinct Rap1 impacts on affinity of integrins with different outcomes under flow Kamioka et al. reveal that Rap1 and integrin adaptors talin1 and kindlin-3 differently regulate two major homing integrins, LFA1 and α4β7, in T cells, resulting in distinct impacts by Rap1 on affinity of LFA1 and α4β7, generating promotion or inhibition of adhesion of T cells under flow conditions.