Phosphorylation of class I HLA antigens in U-937 monocyte-like cells: Role of protein kinase C

Abstract

Phorbol esters and 1-oleoyl-2-acetylglycerol induce an increase in phosphorylation of a series of 44-kD proteins in the U-937 human monocyte-like cell line. The phenomenon is rapid at 37 °C, starting 0.5 min after adding the inducer, increasing to a maximum of 5–10 min and decreasing to the basal level at 30 min. It is also observed at 4 °C, though much more slowly. Immunoprecipitation and two-dimensional electrophoresis demonstrated that these phosphorylated proteins belong to the class I HLA antigens.