Diacylglycerol generation in fluoride-treated neutrophils: involvement of
phospholipase D
D English, G Taylor and JG Garcia
Department of Medicine, Indiana University School of Medicine,
Indianapolis.
Neutrophils exposed to fluoride ion (F-) respond with a delayed and
sustained burst of superoxide anion release that is both preceded by and
dependent on the influx of Ca2+ from the extracellular medium. The results
of this study demonstrate a similarly delayed and sustained generation of
1,2-diglyceride in F(-)-treated neutrophils, over 90% of which was
1,2-diacylglycerol. Diacylglycerol generation was not dependent on the
presence of extracellular Ca2+. Conversely, in contrast to results obtained
with other agonists, removal of extracellular Ca2+ markedly potentiated
synthesis of diacylglycerol in F(-)-treated neutrophils. This effect was
accompanied by a corresponding decrease in the recovery of phosphatidic
acid. In either the presence or absence of extracellular Ca2+, phosphatidic
acid accumulated before diacylglycerol in F(-)-treated cells, suggesting
the latter was derived from the former. Consistent with this hypothesis,
the phosphatidic acid phosphohydrolase inhibitor, propranolol, suppressed
generation of diacylglycerol as it potentiated the accumulation of
phosphatidic acid in F(-)-treated neutrophils. This effect was observed
both in the presence and absence of extracellular Ca2+. Moreover, high
levels of propranolol (160 mumol/L) effected complete inhibition of
diacylglycerol generation in F(-)-treated neutrophils with a corresponding
increase in phosphatidic acid generation. Phosphatidylethanol accumulated
in neutrophils stimulated with F- in the presence of ethanol. The extent of
phosphatidylethanol accumulation at all time points after addition of F-
corresponded to decreased levels of both phosphatidic acid and
diacylglycerol, indicating that phosphatidylethanol was derived from the
phospholipase D-catalysed transphosphatidylation reaction. The results
indicate that F- activates a Ca(2+)-independent phospholipase D, which
appears to be the major, if not sole, catalyst for both phosphatidic acid
and diacylglycerol generation in F(-)-treated neutrophils. Ca2+, mobilized
as a result of F- stimulation and possibly as a consequence of
phospholipase D activation, exerts a profound effect on cellular second
messenger levels by modulating the conversion of phosphatidic acid to
diacylglycerol.
Volume 77,
Issue 12,
pp. 2746-2756,
06/15/1991
Copyright © 1991 by The American Society of Hematology
