Distinct bidirectional regulation of LFA1 and or4137 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 or4137 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 ta-lin1, but not kindlin-3, resulting in increased capture and slowing. In contrast, none of them were required for tether/rolling by or4137 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 or4137, activated Rap1 severely suppressed adhesion on MAdCAM1 under shear flow, indicating the critical importance of a sequential outside-in/inside-out signaling for or4137.

Automated summary

Bidirectional control of integrin activation plays crucial roles in cell adhesive behaviors. In this study, distinct bidirectional regulation of LFA1 and Or4137 in primary T cells was observed. Outside-in signaling from ICAM1-interacting LFA1 activated Rap1 GTPase and talin1, leading to increased capture and slowing. However, activated Rap1 severely suppressed adhesion of Or4137 on MAdCAM1 under shear flow.