Down-regulation of hepatic lipase expression by elevation of cAMP in human hepatoma but not adrenocortical cells

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 10-300 mu M 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/EBP beta). cAMP reduced expression of the 45 kDa C/EBP beta protein and binding of C/EBP beta to the proximal promoter region of the human HL gene by 50%, as determined by immunoblotting and chromatin immunoprecipitation assay, respectively. In human H295R adrenocorticall cells, cAMP failed to suppress HL promoter activity, and only slightly reduced C/EBP beta expression. We conclude that the fall in HL expression during prolonged fasting may be mediated through elevation of cAMP and lowering of C/EBP beta expression. (C) 2008 Elsevier Ireland Ltd. All rights reserved.