Induction of macrophage-like differentiation of HL60 human myeloid leukemia cells by phorbol myristate acetate triggers an early decline in inositol lipid breakdown.

We have studied the metabolism and cellular levels of inositol lipids and their breakdown products, the inositol phosphates and diacylglycerol (DAG), in HL60 human myeloid leukemia cells. Changes in these species during phorbol myristate acetate (PMA)-induced differentiation to a macrophage-like phenotype were quantitated by isotopic labeling techniques. The slow, autonomous breakdown of inositol lipids detectable in uninduced cells was almost completely abolished between 3 and 6 h of PMA addition. The intracellular levels of the inositol phosphates were detectably reduced 1 h after PMA addition and continued to decline during the next 24 h. Also consistent with the reduced breakdown of inositol lipids, the molar ratio of these species showed a small but significant increase relative to other membrane lipids 24 h following PMA addition. However, the cellular DAG content increased gradually after PMA addition, presumably due to the cessation of cell proliferation and reduced utilization of DAG as a precursor for lipid synthesis. The results here suggest that the slow, autonomous generation of inositol lipid-derived second messengers may contribute to the stimulation of proliferation of HL60 cells and that the rapid PMA-induced inhibition of this pathway may precede the triggering of cellular differentiation in this system.