Identification of the Flavonoid Luteolin as a Repressor of the Transcription Factor Hepatocyte Nuclear Factor 4α

Juan Li,Jun Inoue,Jung-Min Choi,Shugo Nakamura,Zhen Yan,Shinya Fushinobu,Haruhiko Kamada,Hisanori Kato,Tsutomu Hashidume,Makoto Shimizu,Ryuichiro Sato

doi:10.1074/jbc.m115.645200

Abstract

Hepatocyte nuclear factor 4α (HNF4α) is a nuclear receptor that regulates the expression of genes involved in the secretion of apolipoprotein B (apoB)-containing lipoproteins and in glucose metabolism. In the present study, we identified a naturally occurring flavonoid, luteolin, as a repressor of HNF4α by screening for effectors of the human microsomal triglyceride transfer protein (MTP) promoter. Luciferase reporter gene assays revealed that the activity of the MTP gene promoter was suppressed by luteolin and that the mutation of HNF4α-binding element abolished luteolin responsiveness. Luteolin treatment caused a significant decrease in the mRNA levels of HNF4α target genes in HepG2 cells and inhibited apoB-containing lipoprotein secretion in HepG2 and differentiated Caco2 cells. The interaction between luteolin and HNF4α was demonstrated using absorption spectrum analysis and luteolin-immobilized beads. Luteolin did not affect the DNA binding of HNF4α to the promoter region of its target genes but suppressed the acetylation level of histone H3 in the promoter region of certain HNF4α target genes. Short term treatment of mice with luteolin significantly suppressed the expression of HNF4α target genes in the liver. In addition, long term treatment of mice with luteolin significantly suppressed their diet-induced obesity and improved their serum glucose and lipid parameters. Importantly, long term luteolin treatment lowered serum VLDL and LDL cholesterol and serum apoB protein levels, which was not accompanied by fat accumulation in the liver. These results suggest that the flavonoid luteolin ameliorates an atherogenic lipid profile in vivo that is likely to be mediated through the inactivation of HNF4α.

Highlights

Flavonoids are naturally occurring compounds that can regulate certain transcription factors
The stimulated microsomal triglyceride transfer protein (MTP) promoter activity, due to the expression of exogenous HNF4␣, was significantly suppressed by treatment with luteolin (Fig. 2C). Consistent with this observation, luteolin suppressed the Gal4 DNA-binding domain (DBD)-fused HNF4␣ ligand-binding domain (LBD) (Fig. 2D). These results indicate that luteolin suppressed HNF4␣ activity by affecting HNF4␣ LBD
Our results demonstrate that the flavonoid luteolin suppressed HNF4␣ activity and the secretion of apolipoprotein B (apoB)-containing lipoproteins in cultured cells

Summary

Background

Flavonoids are naturally occurring compounds that can regulate certain transcription factors. Hepatocyte nuclear factor 4␣ (HNF4␣) is a nuclear receptor that regulates the expression of genes involved in the secretion of apolipoprotein B (apoB)-containing lipoproteins and in glucose metabolism. Short term treatment of mice with luteolin significantly suppressed the expression of HNF4␣ target genes in the liver. Tantly, long term luteolin treatment lowered serum VLDL and LDL cholesterol and serum apoB protein levels, which was not accompanied by fat accumulation in the liver. These results suggest that the flavonoid luteolin ameliorates an atherogenic lipid profile in vivo that is likely to be mediated through the inactivation of HNF4␣. HNF4␣ regulates the expression of genes involved in apoB-containing lipoprotein secretion, such as MTP and apoB; liver-specific HNF4␣-defi-

The abbreviations used are

Experimental Procedures

Results

Discussion