Tc. Lee et al., DIFFERENTIATION-INDUCED INCREASE OF PLATELET-ACTIVATING-FACTOR ACETYLHYDROLASE IN HL-60 CELLS, Journal of lipid mediators and cell signalling, 9(3), 1994, pp. 267-283
Platelet-activating factor (PAF) acetylhydrolase catalyzes the convers
ion of PAF to lyso-PAF and acetate. In this study we show that induced
cellular differentiation of HL-60 cells grown in chemically defined m
edia by dimethylsulfoxide (DMSO) to granulocytic cells increases the a
cetylhydrolase activity with a concomitant increased secretion of the
enzyme into the media. This increase in acetylhydrolase activity is bl
ocked by the presence of actinomycin D (1 mu M) or cycloheximide (1-2
mu M) in the culture media. Acetylhydrolase is located both in the cyt
osolic and particulate fractions; the relative distribution of acetylh
ydrolase activity in the particulate fraction and cytosol increases an
d decreases respectively, as the differentiation progresses. The addit
ion of an intracellular protein transport inhibitor, monensin, causes
furl,her accumulation of acetylhydrolase activity in the particulate f
raction and a decrease in the media, with no effect on the acetylhydro
lase activity in the cytosol. Acetylhydrolase in differentiated HL-60
cells acquires properties similar to those of the plasma acetylhydrola
se in that it becomes less sensitive to 5,5'-dithiobis-2-nitrobenzoic
acid and p-bromophenacylbromide inhibition than the acetylhydrolase in
undifferentiated cells. The acetylhydrolase secreted into the media b
y the differentiated cells was almost totally insensitive to these inh
ibitors, whereas the acetylhydrolase from the particulate fraction gav
e an intermediate response; the cytosolic acetylhydrolase was sensitiv
e to bath inhibitors. However, the acetylhydrolase secreted by differe
ntiated HL-60 cells has a different electrophoretic mobility, temperat
ure sensitivity, and association with lipoproteins when compared to th
at of human plasma acetylhydrolase. Collectively, these results indica
te cellular differentiation induces intracellular acetylhydrolase acti
vity through a mechanism involving both transcriptional and translatio
nal events. Furthermore, the acetylhydrolase synthesized during the DM
SO-induced differentiation of HL-60 cells is then secreted into the me
dia via the intracellular membrane transport system for proteins. Base
d on results obtained with HL-60 cells as a cell model, it is likely t
hat more than one isoform of acetylhydrolase exists in the extracellul
ar milieu.