Regulation of apoA-I gene expression: mechanism of action of estrogen and genistein

Stefania Lamon-Fava,Dale Micherone

doi:10.1194/jlr.m300179-jlr200

Abstract

We have previously shown that 17-beta-estradiol (E2) and genistein increase the expression of apolipoprotein A-I (apoA-I), the major protein component of HDL, in Hep G2 cells. To elucidate the mechanism mediating the increase in apoA-I gene expression by these compounds, plasmid constructs containing serial deletions of the apoA-I promoter region were generated. The smallest region maintaining response to E2 and genistein spanned the -220 to -148 sequence, and the estrogen antagonist ICI182,780 completely inhibited the E2 and genistein effect. Nuclear extracts from cells treated with E2 and genistein showed increased binding to site B oligonucleotide (-169 to -146), and nuclear extracts from genistein-treated cells showed increased binding to an early growth response factor 1 (Egr-1) oligonucleotide compared to control cells. An increase in the concentrations of Egr-1 and hepatocyte nuclear factor-3beta was observed in nuclear extracts of cells treated with both compounds compared to control cells. Treatment with a specific inhibitor of mitogen-activated protein (MAP) kinase, but not with other inhibitors, abolished the stimulation of apoA-I gene expression by E2 and genistein. These results indicate that the MAP kinase pathway is involved in the regulation of apoA-I gene expression by genistein and E2, possibly through downstream regulation of transcription factors binding to the promoter region.

Highlights

We have previously shown that 17-␤-estradiol (E2) and genistein increase the expression of apolipoprotein A-I, the major protein component of HDL, in Hep G2 cells
Two estrogen response element (ERE) half-palidromic sites are located within site A, but previous work has shown that the estrogen receptor (ER) does not bind to this sequence, suggesting that other transcription factors may be involved in the estrogen-mediated increase in apolipoprotein A-I (apoA-I) expression [24]
Our study shows that both estrogen and genistein activate the expression of the apoA-I gene in liver cells, leading to increased production of apoA-I protein

Summary

Introduction

We have previously shown that 17-␤-estradiol (E2) and genistein increase the expression of apolipoprotein A-I (apoA-I), the major protein component of HDL, in Hep G2 cells. Treatment with a specific inhibitor of mitogen-activated protein (MAP) kinase, but not with other inhibitors, abolished the stimulation of apoA-I gene expression by E2 and genistein These results indicate that the MAP kinase pathway is involved in the regulation of apoA-I gene expression by genistein and E2, possibly through downstream regulation of transcription factors binding to the promoter region.—Lamon-Fava, S., and D. Two ERE half-palidromic sites are located within site A, but previous work has shown that the estrogen receptor (ER) does not bind to this sequence, suggesting that other transcription factors may be involved in the estrogen-mediated increase in apoA-I expression [24]

Methods

Results

Conclusion