High-density lipoprotein inhibits the production of platelet activating factor acetylhydrolase by HepG2 cells.
We previously demonstrated that HepG2 cells secrete platelet activating factor (PAF) acetylhydrolase, which is identical to human plasma PAF acetylhydrolase. PAF acetylhydrolase has been shown to be associated with high-density lipoproteins (HDLs) and low-density lipoproteins (LDLs) in plasma, and lipoprotein environment affects the enzyme activity. We examined the effects of HDL and LDL on the production of PAF acetylhydrolase by HepG2 cells. These lipoproteins were treated with diisopropylfluorophosphate (DFP) to inhibit completely the endogenous PAF acetylhydrolase. PAF acetylhydrolase activity in the control medium conditioned for 24 hours was 37 +/- 2.6 pmol/mg cell protein/min (mean +/- SD, n = 3). DFP-treated HDL markedly inhibited the production of PAF acetylhydrolase by HepG2 cells in a concentration-dependent manner, and 100 micrograms/ml of HDL inhibited the production by 82%. DFP-treated LDL had a slight inhibitory effect. Sulfur 35-labeled methionine-labeled PAF acetylhydrolase had a molecular weight of about 43 kd. In the presence of 100 micrograms/ml DFP-treated HDL, the labeling of PAF acetylhydrolase was decreased both in conditioned medium and in cell homogenate (to 62% and 42% of control values, respectively). DFP-treated HDL did not affect PAF acetylhydrolase activity of conditioned medium when they were mixed immediately before the assay. However, when conditioned medium was incubated for 24 hours with HDL, PAF acetylhydrolase activity was inhibited to 78% of the control value. Analysis with gel filtration chromatography disclosed that incubation with HDL resulted in the transfer of the LDL-associated enzyme to HDL fraction.(ABSTRACT TRUNCATED AT 250 WORDS)
Satoh
K
K
Department of Pathologic Physiology, Hirosaki University School of Medicine, Japan.
Imaizumi
T
T
Yoshida
H
H
Takamatsu
S
S
D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase; D016632:Apolipoprotein A-I / Q000494:pharmacology; D001053:Apolipoproteins / Q000494:pharmacology; D002784:Cholesterol / Q000378:metabolism; D002850:Chromatography, Gel; D017077:Culture Media, Conditioned; D006801:Humans; D007531:Isoflurophate / Q000494:pharmacology; D008075:Lipoproteins, HDL / Q000494:pharmacology*; D008077:Lipoproteins, LDL / Q000494:pharmacology; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D013462:Sulfur Radioisotopes
D016632:Apolipoprotein A-I; D001053:Apolipoproteins; D017077:Culture Media, Conditioned; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; D013462:Sulfur Radioisotopes; D007531:Isoflurophate; D002784:Cholesterol; D010741:Phospholipases A; D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase