RhoA and zeta PKC control distinct modalities of LFA-1 activation by chemokines: critical role of LFA-1 affinity triggering in lymphocyte in vivo homing.

Chemokines regulate rapid leukocyte adhesion by triggering a complex modality of integrin activation. We show that the small GTPase RhoA and the atypical zeta PKC differently control lymphocyte LFA-1 high-affinity state and rapid lateral mobility induced by chemokines. Activation of LFA-1 high-affinity state and lateral mobility is controlled by RhoA through the activity of distinct effector regions, demonstrating that RhoA is a central point of diversification of signaling pathways leading to both modalities of LFA-1 triggering. In contrast, zeta PKC controls LFA-1 lateral mobility but not affinity triggering. Blockade of the 23-40 RhoA effector region prevents induction of LFA-1 high-affinity state as well as lymphocyte arrest in Peyer's patch high endothelial venules. Thus, RhoA controls the induction of LFA-1 high-affinity state by chemokines independently of zeta PKC, and this is critical to support chemokine-regulated homing of circulating lymphocytes.