Effect of differentiation on platelet-activating factor metabolism in HL-60 cells

Abstract

The formation and metabolism of 1-O-alkyl-2-acetyl-sn-glycerol (AAG), a protein kinase C (PKC) activator formed from platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3- phosphocholine; PAF), was studied in HL-60 cells to determine whether differentiation may influence this process. HL-60 cells differentiated to macrophages (HL-60/M phi) with a phorbol ester convert added [3H]PAF to AAG; 22% of the incorporated radioactivity is converted to AAG within 15s. By contrast, neither undifferentiated HL-60 cells (HL-60/U) nor HL-60 cells differentiated to granulocytes (HL-60/GN) with retinoic acid produce AAG from PAF. The HL-60/M phi rapidly convert radiolabeled AAG to 1-O-alkyl-sn-glycerol and, subsequently, to two other unidentified metabolites. However, some apparently unmodified AAG persists in the cell lipids for at least 6 h. The HL-60 subtypes which do not convert PAF to AAG can nevertheless catabolize AAG; HL-60/U and HL-60/GN produce alkylglycerol and the other AAG metabolites. These findings demonstrate that differentiation can alter the processing of PAF in a human leukocyte cell line. Furthermore, they suggest that PAF may produce at least some of its biological effects in macrophages by conversion to AAG.

Low- and High-Affinity Phorbol Ester and Diglyceride Interactions with Protein Kinase C: 1-O-Alkyl-2-acyl-sn-glycerol Enhances Phorbol Ester- and Diacylglycerol-Induced Activity but Alone Does Not Induce Activity

“…A number of biological properties of HAG have been described. For example, it stimulates Ca 2+ influx into human bronchial epithelial HBE-16 cells (44), activates human neutrophil cytosolic phospholipase A 2 (45), accumulates during myocardial ischemia (46), and has effects on vascular smooth muscle cell proliferation (47). In HL-60 promyeloid leukemia cells, HAG was shown to attenuate stimulus-response coupling in tumor cells, thereby contributing to the mechanism by which the ether lipid 1-O-hexadecyl-2-O-methylsn-glycero-3-phosphocholine exerts its anticancer effects (48).…”