ACTIN POLYMERIZATION REGULATES INTEGRIN-MEDIATED ADHESION AS WELL AS RIGIDITY OF NEUTROPHILS

Activation of adherent neutrophils causes them to convert from selecti n-mediated rolling to integrin-mediated immobilisation and migration, Migration is known to depend on formation and redistribution of filame ntous (F) actin, but although immobilisation in seconds parallels earl y cortical actin polymerisation, no link has been proven. We tested th e effect. of the actin-polymerising agent jasplakinolide (10 mu M) on adhesive and mechanical properties of neutrophils. Pretreated cells we re able to adhere and roll on immobilised platelets in a how-based adh esion assay, but whereas untreated rolling cells became immobilised in seconds when chemo tactic formyl peptide (fMLP, 0.1 mu M) was superfu sed over them, the cells treated with jasplakinolide continued rolling . Pretreatment with jasplakinolide also blocked de novo expression of integrin CD11b and shape change which otherwise occurred in minutes af ter treatment with fMLP. Jasplakinolide directly caused actin polymeri sation within neutrophils, evidenced by a marked increase in rigidity (resistance to aspiration into a 5 mu m micropipette) and increase in association of actin with the Triton-insoluble cytoskeleton. These res ults indicate that rearrangement of the actin cytoskeleton regulates i ntegrin-mediated adhesion of activated neutrophils, as well as their m igration and mechanical properties. (C) 1997 Academic Press.