Submitted on February 16, 2006
Revised on April 3, 2006
Accepted on April 6, 2006
Transcriptional regulation of the human hepatic lipase (LIPC) gene promoter
Laura E. Rufibach, Stephen A. Duncan, Michele Battle, and Samir S. Deeb
Medical Genetics and Genome Sciences, University of Washington, Seattle, WA 98195
Corresponding Author: lewarner{at}u.washington.edu
Hepatic lipase (HL) plays a key role in the metabolism of plasma lipoproteins and its level of activity requires tight regulation given the association of both low and high levels with atherosclerosis and coronary artery disease (CAD). However, little is know about the factors responsible for HL expression. Here we report that the human HL gene (LIPC) promoter is regulated by hepatocyte nuclear factor-4
(HNF4
), peroxisome proliferator-activated receptor
coactivator-1
(PGC-1
), apolipoprotein A-I regulatory protein-1 (ARP-1), and hepatocyte nuclear factor-1
(HNF1
). Reporter analysis showed that HNF4
directly regulates the LIPC promoter via two newly identified direct repeat elements, DR1 and DR4. The coactivator PGC-1
is capable of stimulating the HNF4
-dependent trans-activation of the LIPC promoter. ARP-1 displaces HNF4
from the DR1 site and blocks its ability to activate the LIPC promoter. Induction by HNF1
requires the HNF1 binding site and upon co-transfection with HNF4
leads to an additive effect. In addition, the in vivo relevance of HNF4
in LIPC expression is shown by the ability of the HNF4
antagonist Medica 16 to repress endogenous LIPC mRNA expression. Furthermore, disruption of Hnf4
in mice prevents expression of HL mRNA in liver. The overall effect these transcription factors have on HL expression will ultimately depend on the interplay between these various factors and their relative intracellular concentrations.