Disruption of β₂-integrin-cytoskeleton coupling abolishes the signaling capacity of these integrins on granulocytes

Integrin dependent adhesion and dynamic modulations of the actin network are prerequisites for normal cell locomotion. To investigate whether the actin microfilamentous system does play a role in regulation of β₂-integrin-induced signalling, we pretreated granulocytes with staurosporine, a well-known protein kinase inhibitor that has also been shown to disrupt the cytoskeleton of intact cells. Pretreatment with staurosporine completely inhibited the β₂-integrin-induced Ca²⁺ signal and also its ability to trigger actin polymerisation. This inhibition was not related to phosphorylation of the CD18-chain of the β₂-integrin, nor to inhibition of protein kinases. Instead, association of β₂-integrins with the cortical cytoskeleton, which was observed in untreated cells, was abolished after exposure to staurosporine, indicating that β₂-integrin signalling depends on integrin-cytoskeleton interaction. These results suggest not only that the actin network provides an adhesive link to the extracellular matrix and a driving force for the locomotory response, but also that it participates in regulation of β₂-integrin signalling during granulocyte locomotion.