β₂ integrin-dependent tyrosine phosphorylation of proline-rich tyrosine kinase 2 in platelet-activating factor-activated eosinophils

Platelet-activating factor (PAF) can activate various cellular functions, including degranulation in eosinophils. In the present study, we examined tyrosine phosphorylation of intracellular proteins induced by PAF in eosinophils derived from cord blood mononuclear cells. Platelet-activating factor induced tyrosine phosphorylation of many intracellular proteins, including 42, 123 and 150 kDa proteins. Immunoprecipitation studies showed that the 123 kDa phosphorylated protein was proline-rich tyrosine kinase 2 (PYK-2; also known as related adhesion focal tyrosine kinase (RAFTK), cell adhesion kinase β (CAKβ) and calcium-dependent tyrosine kinase (CADTK)). Furthermore, blocking of cellular adhesion through β₂ integrin by anti-CD18 monoclonal antibody inhibited tyrosine phosphorylation of PYK-2 as well as the degranulation response. These findings suggest that tyrosine phosphorylation of PYK-2 is involved in a signaling pathway mediated by cellular adhesion through β₂ integrin in PAF-activated eosinophils.