HL-60 cells are very sensitive to the cytotoxic action of ether lipids. Several hypotheses have been proposed to explain this cytotoxicity. We investigated the huluence of the alkylphosphoiipid ET-i8-OCHl on the activity of protein kinase C. HL-60 cel!s were incubated with ET-18-OCH; at a concentration of 20 pg/rnl for 4 h. After the incubation the membrane fraction of the HL-60 cells was isolated and the activity of protein kinase C was determined while it was still associated with the membrane, using the synthetic peptide substrate [SeP']-protein kinase C (19-S 1) as a protein kinase C specific substrate. The activity of the membrane-bound protein kinasc C was increased in HL-60 cells treated with ET-lg-OCHS compared to untreated HL-60 cells. The increase in protein kinase C activity was not a consequence of translocation and appeared to be additive to the effect of the phorbol ester 12myristate 13-acetate. In contrast, solubilized protein kinase C from HL-60 cells could be inhibited or stimulated in vitro by ET-18-OCH,, dependent on the mode of addition of ET-18OCHs and phospholipids.
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