title: Down-regulation of hepatic lipase expression by elevation of cAMP in human hepatoma but not adrenocortical cells.
abstract: Expression of hepatic lipase (HL) in the liver is reduced during prolonged fasting. This effect is mainly mediated via catecholamines, which signal through elevation of Ca(i)(2+) as well as cAMP. We have studied the effect of cAMP on HL expression in cell culture. Overnight incubation of HepG2 cells with 10-300microM 8-bromo-cyclic AMP resulted in a dose-dependent, up to 50% reduction in secretion of HL, but had no effect on secretion of alpha(1)-antitrypsin or overall protein synthesis. HL mRNA levels were decreased 1.5 fold, as determined by semi-quantitative and real-time RT-PCR. In HepG2 cells transiently transfected with human HL (-685/+13) or rat HL (-446/+9) promoter-reporter constructs, cAMP induced a similar dose-dependent suppression of HL promoter activity. cAMP responsiveness in HepG2 cells was mediated by a conserved 10-bp response element at -45/-36, that represents a potential binding site for CCAAT/enhancer-binding protein beta (C/EBPbeta). cAMP reduced expression of the 45kDa C/EBPbeta protein and binding of C/EBPbeta to the proximal promoter region of the human HL gene by 50%, as determined by immunoblotting and chromatin immunoprecipitation assay, respectively. In human H295R adrenocortical cells, cAMP failed to suppress HL promoter activity, and only slightly reduced C/EBPbeta expression. We conclude that the fall in HL expression during prolonged fasting may be mediated through elevation of cAMP and lowering of C/EBPbeta expression.
authors.affiliation: Department of Biochemistry, Erasmus MC, P.O. Box 2040, 3000 CA, Rotterdam, Netherlands.
authors.forename: Diederik
authors.initials: D
authors.lastname: van Deursen
authors.forename: Gert-Jan
authors.initials: GJ
authors.lastname: Botma
authors.forename: Hans
authors.initials: H
authors.lastname: Jansen
authors.forename: Adrie J M
authors.initials: AJ
authors.lastname: Verhoeven
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000302:Adrenal Cortex / Q000166:cytology* / Q000201:enzymology*; D000818:Animals; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000378:metabolism; D006528:Carcinoma, Hepatocellular / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D045744:Cell Line, Tumor; D000242:Cyclic AMP / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D008049:Lipase / Q000235:genetics* / Q000378:metabolism; D014176:Protein Biosynthesis / Q000187:drug effects; D051381:Rats; D020218:Response Elements; D014162:Transfection
chemical_list: D022782:CCAAT-Enhancer-Binding Protein-beta; C504173:LIPC protein, human; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000242:Cyclic AMP; D008049:Lipase; C502353:hepatic lipase, rat