β-Arrestin 2 is required for the induction and strengthening of integrin-mediated leukocyte adhesion during CXCR2-driven extravasation

Leukocyte extravasation involves interdependent signaling pathways underlying the complex dynamics of firm adhesion, crawling, and diapedesis. While signal transduction by agonist-bound chemokine receptors plays a central role in the above responses, it is unclear how it contributes to the sustained and concurrent nature of such responses, given the rapid kinetics of chemokine-induced trimeric G protein coupling and homologous desensitization. Our findings unveil a novel role of beta-arrestins in regulating the activation of signaling pathways underlying discrete integrin-mediated steps in CXCR2-driven leukocyte extravasation. By combining in vivo approaches in beta-arrestin knockout mice with in vitro studies in engineered cellular models, we show that membrane-recruited beta-arrestin 2 is required for the onset and maintenance of shear stress-resistant leukocyte adhesion mediated by both beta(1) and beta(2) integrins. While both beta-arrestin isoforms are required for rapid keratinocyte-derived chemokine (KC)-induced arrest onto limiting amounts of vascular cell adhesion molecule-1 (VCAM-1), adhesion strengthening under shear is selectively dependent on beta-arrestin 2. The latter synergizes with phospholipase C in promoting activation of Rap1A and B, both of which cooperatively control subsecond adhesion as well as postarrest adhesion stabilization. Thus, receptor-induced G alpha(i) and beta-arrestins act sequentially and in spatially distinct compartments to promote optimal KC-induced integrin-dependent adhesion during leukocyte extravasation. (Blood. 2009; 114: 1073-1082)