The Journal of Immunology, Vol 144, Issue 7 2678-2682, Copyright © 1990 by American Association of Immunologists
Effects of lipopolysaccharide on phospholipase A2 activity and tumor necrosis factor expression in HL-60 cells
M Mohri, DR Spriggs and D Kufe
Laboratory of Clinical Pharmacology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA 02115.
LPS has been identified as a potent activator of mononuclear phagocytes.
This activation is associated with TNF gene expression. The intracellular
signaling mechanisms responsible for this effect, however, are unknown. The
present studies demonstrate that LPS induces TNF transcripts in HL-60
promyelocytic leukemia cells. Because previous studies have demonstrated
that eicosanoids are involved in the regulation of TNF gene expression in
these cells, we examined the effects of LPS on activation of the
arachidonic acid cascade. The results demonstrate that LPS stimulates
phospholipase A2 activity and the hydrolysis of both 1,2-dipalmitoyl
phosphatidylcholine and 1- steroyl 2-arachidonoyl phosphatidylcholine. In
contrast, there was no detectable effect of LPS on activation of protein
kinase C. We also demonstrate that inhibition of phospholipase A2 activity
with bromophenacyl bromide or quinacrine blocks the induction of TNF
transcripts by LPS. These findings suggested that LPS induces TNF gene
expression through formation of arachidonic acid metabolites. Indeed,
similar results were obtained with mellitin, a known activator of
phospholipase A2 and eicosanoid production. Previous studies have also
suggested that TNF mRNA levels are increased in HL-60 cells by the 5-
lipoxygenase pathway and, in the present work inhibitors of this enzyme
blocked LPS-induced TNF expression. Moreover, the cyclooxygenase
metabolite, PGE2, as well as dibutyryl cAMP, inhibited the induction of TNF
transcripts by LPS. Taken together, these results suggest that LPS induces
TNF gene expression through activation of phospholipase A2 and that the
level of this induction is regulated by activity of the 5- lipoxygenase and
cyclooxygenase pathways.
