Altered arachidonic acid metabolism during differentiation of the human monoblastoid cell line U937

Abstract

The human cell line U937 was used as a model for differentiation along the mononuclear phagocyte lineage. Following treatment with the phorbol ester TPA, PGE 2 and TxB 2 secretion was induced 50–100-fold, and both PGF 2α and PGI 2 levels became detectable in the supernatant of TPA-differentiated U937 cells. The content of the prostaglandin precursor, arachidonic acid, remained unchanged in the cellular phospholipids of undifferentiated and TPA-differentiated U937 cells. Of the enzymes involved in the availability and metabolism of arachidonic acid, phospholipase A 2 activity was increased 2-fold in the membranes of TPA-differentiated U937 cells, whereas lysophosphatide acyltransferase activity remained unaltered. Cyclooxygenase activity, however, was enhanced 5–10-fold, which was due to enhanced expression of the enzyme as demonstrated by dot-blot analysis. The data suggest that the capacity to secrete prostaglandins is acquired during differentiation with TPA and results mainly from an increased Cyclooxygenase activity. Despite the capacity of TPA-differentiated U937 cells to synthesize prostaglandins, none of the known monocytic stimuli further stimulated prostaglandin secretion in TPA-differentiated U937 cells. Generation of leukotrienes appears to represent a later state in the differentiation along the monocyte-macrophage lineage, since neither LTB 4 nor cysteinyl-leukotrienes were detectable in the supernatant of either undifferentiated or TPA-differentiated U937 cells.