Abrogation of the Fcγ receptor IIA-mediated phagocytic signal by stem-loop Syk antisense oligonucleotides

Abstract

The role of Syk kinase in Fcγ receptor (FcγR) IIA-mediated phagocytosis was examined with two forms of antisense oligodeoxynucleotides (ODNs) designed to hybridize to human Syk mRNA. Monocytes were incubated 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 of 0.2 μM inhibited FcγRIIA- mediated phagocytosis by 90% and completely eliminated Syk mRNA and protein in monocytes, whereas scrambled-control ODNs had no effect. The Syk antisense ODNs did not change β-actin mRNA levels and FcγRII cell-surface expression. In addition, stem-loop Syk antisense ODN inhibited FcγRI and FcγRIIIA- mediated phagocytosis. These data indicate the efficacy of stem-loop Syk antisense ODN for targeting and degrading Syk mRNA and protein and the importance of Syk kinase in Fcγ receptor-mediated phagocytosis. Immunoblotting assay demonstrated that FcγRII tyrosine phosphorylation after FcγRII cross-linking did not change in the absence of Syk protein. These results indicate that Syk kinase is required for FcγRIIA-mediated phagocytic signaling and that FcγRII cross-linking leads to tyrosine phosphorylation of FcγRII independent of Syk kinase.