Platelet-activating factor (PAF) stimulates the production of PAF acetylhydrolase by the human hepatoma cell line, HepG2.
The human hepatoma cell line, HepG2, secreted an activity that degrades platelet-activating factor (PAF) by the hydrolysis of the sn-2 acetyl group. This activity was Ca++ independent, inhibited by diisopropylfluorophosphate but not by p-bromophenacyl bromide, and resistant to treatment with trypsin or pronase. Separation of HepG2-conditioned medium by gel filtration disclosed that the activity was associated with lipoproteins. An antiserum against PAF acetylhydrolase immunoprecipitated this activity. It was not recognized by an antibody against lecithin:cholesterol acyltransferase (LCAT), which also is secreted by HepG2 cells. Therefore the phospholipase A2 activity of LCAT was excluded as a source of the observed activity. PAF added to the culture medium stimulated the secretion of the PAF-degrading activity by HepG2 cells, while lyso-PAF was inactive. Maximal stimulation was observed with 5 ng/ml PAF, which induced a fivefold increase. The presence of 5 ng/ml PAF, enhanced the secretion of [35S]methionine-labeled PAF acetylhydrolase and cycloheximide inhibited both the basal and PAF-stimulated secretion of the labeled enzyme. We conclude that HepG2 cells produce PAF acetylhydrolase. The liver may be a major source of plasma PAF acetylhydrolase, and PAF may induce the production of its inactivating enzyme by the liver.
Satoh
K
K
Department of Pathologic Physiology, Hirosaki University School of Medicine, Japan.
Imaizumi
T
T
Kawamura
Y
Y
Yoshida
H
H
Hiramoto
M
M
Takamatsu
S
S
Takamatsu
M
M
D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase; D000098:Acetophenones / Q000494:pharmacology; D006528:Carcinoma, Hepatocellular / Q000201:enzymology / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects; D002850:Chromatography, Gel; D003513:Cycloheximide / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases / Q000494:pharmacology; D006801:Humans; D006868:Hydrolysis; D007531:Isoflurophate / Q000494:pharmacology; D007770:L-Lactate Dehydrogenase / Q000032:analysis; D008113:Liver Neoplasms / Q000201:enzymology / Q000378:metabolism*; D008715:Methionine / Q000378:metabolism; D010741:Phospholipases A / Q000096:biosynthesis*; D054467:Phospholipases A2; D010743:Phospholipids / Q000494:pharmacology; D010972:Platelet Activating Factor / Q000494:pharmacology*; D011233:Precipitin Tests; D014407:Tumor Cells, Cultured
D000098:Acetophenones; D010743:Phospholipids; D010972:Platelet Activating Factor; D007531:Isoflurophate; D003513:Cycloheximide; D004492:Edetic Acid; D008715:Methionine; D007770:L-Lactate Dehydrogenase; D010741:Phospholipases A; D054467:Phospholipases A2; D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase; D010450:Endopeptidases; C006821:4-bromophenacyl bromide