ABROGATION OF THE FC-GAMMA RECEPTOR IIA-MEDIATED PHAGOCYTIC SIGNAL BYSTEM-LOOP SYK ANTISENSE OLIGONUCLEOTIDES

The role of Syk kinase in Fc gamma receptor (Fc gamma R) IIA-mediated phagocytosis was examined with two forms of antisense oligodeoxynucleo tides (ODNs) designed to hybridize to human Syk mRNA. Monocytes were i ncubated with linear and stem-loop antisense ODNs targeted to Syk mRNA . When complexed with cationic liposomes, stem-loop Syk antisense ODN with phosphorothioate modification exhibited stability in fetal bovine and human serum. The stem-loop Syk antisense ODN at a concentration o f 0.2 mu M inhibited Fc gamma RIIA-mediated phagocytosis by 90% and co mpletely eliminated Syk mRNA and protein in monocytes, whereas scrambl ed-control ODNs had no effect. The Syk antisense ODNs did not change b eta-actin mRNA levels and Fc gamma RII cell-surface expression. In add ition, stem-loop Syk antisense ODN inhibited Fc gamma RI and Fc gamma RIIIA-mediated phagocytosis. These data indicate the efficacy of stem- loop Syk antisense ODN for targeting and degrading Syk mRNA and protei n and the importance of Syk kinase in Fc gamma receptor-mediated phago cytosis. Immunoblotting assay demonstrated that Fc gamma RII tyrosine phosphorylation after Fc gamma RII cross-linking did not change in the absence of Syk protein. These results indicate that Spk kinase is req uired for Fc gamma RIIA-mediated phagocytic signaling and that Fc gamm a RII cross-linking leads to tyrosine phosphorylation of Fc gamma RII independent of Syk kinase.