beta(2) Integrin (CD11/CD18)-mediated signaling involves tyrosine phosphorylation of c-Cbl in human neutrophils

Leukocyte adhesion molecules of the beta(2) integrin (CD11/CD18) family med iate cell-cell and cell-substrate interactions of human polymorphonuclear n eutrophils (PMN) during their recruitment to sites of inflammation. To eluc idate the molecular events that follow extracellular ligand interactions of beta(2) integrins, protein tyrosine signaling was studied subsequent to in tegrin engagement by Western blotting technique. Upon adhesion to immobiliz ed fibrinogen, a native ligand of the beta(2) integrins Mac-1 (CD11b/CD18) and gp150/95 (CD11c/CD18), tyrosine phosphorylation of several proteins inc luding a 120-kDa protein was observed in human PMN. This effect was specifi c for beta(2) integrins because it was absent in PMN derived from CD18-defi cient mice, which lack any beta(2) integrin expression. Moreover, no signal ing was detectable upon engagement of CD29 and CD61, the beta-subunits of t he beta(1) and beta(3) integrins, respectively, revealing the unique functi on of the beta(2) integrins in PMN. By means of immunoprecipitation, the mo st prominent protein that became tyrosine phosphorylated upon beta(2) integ rin engagement was identified as the 120-kDa protein c-Cbl. The observed si gnaling was independent of both pertussis toxin-sensitive heterotrimeric G- proteins as well as the small G-protein ras. Inhibition of beta(2) integrin -mediated signaling by herbimycin A prevented adhesion, shape change, and s preading of PMN to immobilized fibrinogen, demonstrating the biological sig nificance of the observed effect, Together, the present data suggest that t he beta(2) integrins fulfill a unique function among the leukocyte integrin s in human PMN by activating an intracellular signal transduction cascade t hat leads to tyrosine phosphorylation of c-Cbl and allows subsequent adhesi on, shape change, and spreading.