Control of ACAT2 liver expression by HNF1

Camilla Pramfalk,Mats Eriksson,Matthew A. Davis,Lawrence L. Rudel,Paolo Parini

doi:10.1194/jlr.m400450-jlr200

Camilla Pramfalk, Mats Eriksson + Show 3 more

Open Access

https://doi.org/10.1194/jlr.m400450-jlr200

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Abstract

ACAT catalyzes the formation of cholesteryl esters from cholesterol and long-chain fatty acids. There are two known genes encoding the two ACAT enzymes, ACAT1 and ACAT2 (also known as Soat1 and Soat2). In adult humans, ACAT1 is present in most tissues, whereas ACAT2 is localized to enterocytes and hepatocytes. In this report, we elucidate the mechanisms that control the liver-specific expression of the human ACAT2 gene. We identified hepatic nuclear factor 1 (HNF1) as an important liver-specific trans-acting element for the human ACAT2 gene using the human hepatocellular carcinoma cell lines HuH7 and HepG2. Targeted deletion of the HNF1 binding site in the DNA sequence abolished not only the basal promoter function in HepG2 and HuH7 cells but also the induction of the ACAT2 promoter by HNF1. Electrophoretic mobility shift assay and chromatin immunoprecipitation assay demonstrated that the transcription factors HNF1alpha and HNF1beta interact with this region in the human ACAT2 gene in vitro and in vivo. These data indicate that a) the identified HNF1 binding site serves as a positive regulator sequence, b) the binding site is functionally active both in vivo and in vitro, and c) the transcription factors HNF1alpha and HNF1beta, which bind to this site, play an important part in the regulation of the human ACAT2 promoter.

Highlights

ACAT catalyzes the formation of cholesteryl esters from cholesterol and long-chain fatty acids
We recently showed that ACAT2 is the major ACAT isoenzyme in adult human liver and that it is located in hepatocytes, whereas ACAT1 is located in Kupffer cells [7]
To be able to identify regions that are important for human ACAT2 gene activity in liver, the ‫ف‬1.4 kb promoter region was used as template to create four deletion constructs, termed pϪ1196 (Ϫ1,196 to ϩ86), pϪ1044 (Ϫ1,044 to ϩ86), pϪ782 (Ϫ782 to ϩ86), and pϪ269 (Ϫ269 to ϩ86)

Summary

Introduction

ACAT catalyzes the formation of cholesteryl esters from cholesterol and long-chain fatty acids. We identify an important liver-specific cis-acting element in the promoter region of ACAT2 that acts as a putative binding site for the hepatic nuclear factor 1 (HNF1). By chromatin immunoprecipitation assay, we show that the transcription factors HNF1␣ and HNF1␤ bind to the identified promoter region of ACAT2 in vivo in human liver.

Results

Conclusion