17\u03b2-estradiol regulates the expression of apolipoprotein M through estrogen receptor \u03b1-specific binding motif in its promoter

Jiang Wei,Li-Li Pan,Miao-Mei Yu,Yang Yu,Peter Nilsson-Ehle,Yue-Hua Feng,Qin-Feng Mu,Ning Xu,Jun Zhang,Maria Berggren-Söderlund,Yuan-Ping Shi,Guang-Hua Luo,Xiao-Ying Zhang

doi:10.1186/s12944-017-0458-x

Abstract

BackgroundWe have previously demonstrated that estrogen could significantly enhance expression of apolipoprotein M (apoM), whereas the molecular basis of its mechanism is not fully elucidated yet. To further investigate the mechanism behind the estrogen induced up-regulation of apoM expression.ResultsOur results demonstrated either free 17β-estradiol (E2) or membrane-impermeable bovine serum albumin-conjugated E2 (E2-BSA) could modulate human apoM gene expression via the estrogen receptor alpha (ER-α) pathway in the HepG2 cells. Moreover, experiments with the luciferase activity analysis of truncated apoM promoters could demonstrate that a regulatory region (from-1580 to −1575 bp (−GGTCA-)) upstream of the transcriptional start site of apoM gene was essential for the basal transcriptional activity that regulated by the ER-α. With the applications of an electrophoresis mobility shift assay and a chromatin immunoprecipitation assay, we could successfully identify a specific ER-α binding element in the apoM promoter region.ConculsionIn summary, the present study indicates that 17β-estradiol induced up-regulation of apoM in HepG2 cells is through an ER-α-dependent pathway involving ER-α binding element in the promoter of the apoM gene.

Highlights

We have previously demonstrated that estrogen could significantly enhance expression of apolipoprotein M, whereas the molecular basis of its mechanism is not fully elucidated yet
Estrogen induced up-regulation of apolipoprotein M (apoM) expression is via the Estrogen receptor alpha (ER-α) As shown in Fig. 1a and Fig. 1b, 100 nM BSA-E2 significantly upregulated mRNA and protein levels of apoM (p < 0.05)
P3 mutant construct showed an approximately 1300% lower luciferase activity in MCF-7 compared with the P3 WT construct, which suggest that this DNA motif plays a positive role toward apoM promoter activity (Fig. 2b)

Summary

Introduction

We have previously demonstrated that estrogen could significantly enhance expression of apolipoprotein M (apoM), whereas the molecular basis of its mechanism is not fully elucidated yet. Apolipoprotein M (apoM) is mainly located in high density lipoprotein (HDL) in human plasma, with only a small proportion presented in low density lipoprotein (LDL) and very low density lipoprotein (VLDL) particles [1]. The apoM-containing lipoproteins were predominantly of HDL size, and about 5% of the total HDL population contained apoM in human plasma [4]. Wolfrum and his colleagues, by using apoM-deficient mice, demonstrated that apoM is important for preβHDL formation and cholesterol efflux from macrophages; apoM-deficient HDL was markedly less efficient in facilitating cholesterol efflux from macrophages in vitro than normal HDL [5].

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