Protein kinase C controls Fcγ receptor‐mediated endocytosis in human neutrophils

Abstract
The aim of this study is to clarify which signaling mechanism operates in Fcγ receptor-mediated endocytosis in human neutrophils. Endocytosis of immune complexes was inhibited by antibodies directed to cell membrane phospholipase C (PLC) and A 2 (PLA 2 ) (maximal inhibition obtained was 57% and 28%, respectively), being almost abolished by these antibodies if used in combination (up to 91% inhibition). The protein kinase C (PKC) activator, phorbol 12,13-dibutyrate, reversed this inhibitory effect. Four different PKC inhibitors (H-7, palmitoylcarnitine, sphingosine. and tamoxifen) produced a dose-dependent inhibition of endocytosis, up to over 80% in each case. H-8 (1–10μM) which inhibits cyclic nucleotide protein kinases but not PKC had no effect upon endocytosis. It is concluded that Fcγ receptor-induced activation of PLC and PLA 2 triggers endocytosis by activation of PKC.