Antibody-induced engagement of beta2 integrins in human neutrophils causes a rapid redistribution of cytoskeletal proteins, Src-family tyrosine kinases, and p72syk that precedes de novo actin polymerization.

Beta2 integrins mediate rearrangement of the cytoskeleton and activation of selective cell functions in neutrophils. To elucidate early events following beta2 integrin ligation, we analyzed redistribution of cytoskeletal and signaling proteins as a consequence of antibody-induced integrin clustering. Incubation of neutrophils on surface-bound anti-beta2 subunit antibodies induced a very rapid (within 1 min) redistribution of the cytoskeletal proteins talin, alpha-actinin, and paxillin, and the tyrosine kinases p58(c-fgr), p53/56(lyn), and p72(syk) to a cell fraction insoluble in Triton X-100. Cytoskeletal and signaling proteins redistribution preceded de novo actin polymerization because cytochalasin B did not inhibit this redistribution. Antibody engagement of all the three distinct beta2 integrins (CD11a, CD11b, CD11c) expressed by neutrophils induced redistribution of cytoskeletal proteins and tyrosine kinases. Several tyrosine phosphorylated proteins were also rapidly redistributed as a consequence of beta2 integrin engagement and this was not affected by blocking de novo actin polymerization with cytochalasin B. In addition, genistein, an inhibitor of tyrosine kinase activities which strongly reduced protein tyrosine phosphorylation, had no effect on redistribution of cytoskeletal proteins, Src-family kinases, and p72(syk). These findings suggest that integrin-dependent cytoskeleton rearrangement in neutrophils occurs in at least two distinct steps and nucleation of some cytoskeletal proteins together with tyrosine kinases precedes rearrangement of the actin-based cytoskeleton and tyrosine kinases activation. On the basis of these and previous findings we propose a model explaining mechanisms of integrin signaling in neutrophils.