Human hepatic lipase (HL) is a glycoprotein with four N-linked oligosaccharide side chains. The importance of glycosylation for the secretion of catalytically active HL was studied in HepG2 cells by using inhibitors of intracellular trafficking, N-glycosylation and oligosaccharide processing. Secretion of HL was inhibited by carbonyl cyanide m-chlorophenylhydrazone (CCCP), monensin, brefeldin A (BFA), tunicamycin, castanospermine and N-methyldeoxynojirimycin, but not by 1-deoxymannojirimycin. Secretion of α1-antitrypsin, an unrelated N-glycoprotein, was also inhibited by monensin, BFA and tunicamycin, but not by CCCP, castanospermine or N-methyldeoxynojirimycin. Intracellular HL activity decreased with CCCP, tunicamycin, castanospermine and N-methyldeoxynojirimycin, but increased with monensin and BFA. In the absence of protein synthesis de novo, HL activity secreted into the medium was 7.8±2.1-fold higher (mean±S.D., n = 7) than the simultaneous fall in intracellular HL activity. In cells pretreated with monensin or BFA, this factor decreased to 1.3±0.5, indicating that the apparent increase in HL activity had already occurred within these cells. After chromatography on Sepharose–heparin, the specific triacylglycerol hydrolase activity of secreted HL was only 1.7±0.3-fold higher than that of intracellular HL, indicating that the secretion-coupled increase in HL activity is only partly explained by true activation. We conclude that oligosaccharide processing by glucosidases in the endoplasmic reticulum is necessary for the transport of newly synthesized human HL, but not α1-antitrypsin, to the Golgi, where the catalytic activity of HL is unmasked.
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Research Article|
December 17 1998
Secretion and apparent activation of human hepatic lipase requires proper oligosaccharide processing in the endoplasmic reticulum
Adrie J. M. VERHOEVEN;
Adrie J. M. VERHOEVEN
1
1Department of Biochemistry, Cardiovascular Research Institute (COEUR), Erasmus University Rotterdam, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands
1To whom correspondence should be addressed (e-mail Averhoev@bc1.fgg.eur.nl).
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Bernadette P. NEVE;
Bernadette P. NEVE
1Department of Biochemistry, Cardiovascular Research Institute (COEUR), Erasmus University Rotterdam, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands
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Hans JANSEN
Hans JANSEN
1Department of Biochemistry, Cardiovascular Research Institute (COEUR), Erasmus University Rotterdam, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands
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Publisher: Portland Press Ltd
Received:
August 10 1998
Accepted:
October 21 1998
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London © 1999
1999
Biochem J (1999) 337 (1): 133–140.
Article history
Received:
August 10 1998
Accepted:
October 21 1998
Citation
Adrie J. M. VERHOEVEN, Bernadette P. NEVE, Hans JANSEN; Secretion and apparent activation of human hepatic lipase requires proper oligosaccharide processing in the endoplasmic reticulum. Biochem J 1 January 1999; 337 (1): 133–140. doi: https://doi.org/10.1042/bj3370133
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