Phosphorylation and subcellular redistribution of pleckstrin in human neutrophils

Pleckstrin, originally described as a major substrate of protein kinase C (PKC) in platelets, was found to be highly expressed in human neutrophils (intracellular concentration, approximately 15 microM). As PKC isoforms play an important role in mediating neutrophil antimicrobial responses, we studied the regulation of pleckstrin phosphorylation in response to inflammatory stimuli. Following treatment of neutrophils with FMLP, 12-O-tetradecanoylphorbol-13-acetate, or opsonized zymosan, pleckstrin was rapidly phosphorylated, which resulted in a shift in its electrophoretic mobility. Several lines of evidence suggest that pleckstrin is phosphorylated in part by a nonconventional PKC following stimulation by FMLP: 1) chelation of intracellular Ca2+ had only a partial inhibitory effect; 2) diacylglycerol kinase inhibitors shortened the duration of phosphorylation, while the phosphatidic acid phosphohydrolase antagonist propranolol extended it; and 3) wortmannin and erbstatin blocked the phosphorylation of pleckstrin. These results suggest that nonconventional PKC isoforms, possibly delta or zeta, mediate the phosphorylation of pleckstrin. Both PKCdelta and -zeta are expressed in human neutrophils. Increased association of pleckstrin with both microsomes and with the cytoskeleton was observed in stimulated cells. These findings suggest that phosphorylation by nonconventional PKC isoforms induces a conformational change in pleckstrin that promotes its interaction with membranes and/or with the cytoskeleton. Such a translocation may serve to target proteins or lipids recognized by pleckstrin homology domains to sites where they can contribute to the microbicidal response.