ECTOPROTEIN KINASE-ACTIVITIES ON NON-DIFFERENTIATED AND DIFFERENTIATED U-937 CELLS

Incubation of intact U-937 cells with 1 mu m [gamma-P-32] ATP resulted in rapid (10 min) incorporation of radioactivity into phosvitin, kemptide and protein kinase C (PKC)-peptide. The amount of incorporation was dependent on substrate type and concentration, and on incubation time. Staurosporine, H-7 and Mg2+-exclusion abolished phosphorylation of kemptide and PKC-peptide but not phosvitin. Cyclic AMP and phorbol ester enhanced kemptide and PKC-peptide phosphorylation. Protein kinase inhibitor (PKI) inhibits only kemptide phosphorylation. Cell differentiation enhanced 2-fold the phosphorylation of phosvitin and PKC-peptide without significant effect on kemptide phosphorylation. ATP concentrations sufficient to trigger changes in intracellular Ca2+ were sufficient to support extracellular phosphorylation reactions. The results suggest the presence of at least three ectokinase activities on U-937 cells that may play important roles in regulating membrane associated specific functions of developing and mature monocytes.