Epigallocatechin-3-Gallate Suppresses BMP-6-Mediated SMAD1/5/8 Transactivation of Hepcidin Gene by Inducing SMILE in Hepatocytes.

Yu-Ji Kim,Don-Kyu Kim,Woo-Ram Park,Byungyoon Choi,Hueng-Sik Choi

doi:10.3390/antiox10101590

Yu-Ji Kim, Don-Kyu Kim + Show 3 more

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https://doi.org/10.3390/antiox10101590

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Journal: Antioxidants	Publication Date: Oct 10, 2021
Citations: 4	License type: CC BY 4.0

Affiliation: Chonnam National University

Abstract

Hepcidin, a major regulator of systemic iron homeostasis, is mainly induced in hepatocytes by activating bone morphogenetic protein 6 (BMP-6) signaling in response to changes in the iron status. Small heterodimer partner-interacting leucine zipper protein (SMILE), a polyphenol-inducible transcriptional co-repressor, regulates hepatic gluconeogenesis and lipogenesis. Here, we examine the epigallocatechin-3-gallate (EGCG) effect on BMP-6-mediated SMAD1/5/8 transactivation of the hepcidin gene. EGCG treatment significantly decreased BMP-6-induced hepcidin gene expression and secretion in hepatocytes, which, in turn, abated ferroportin degradation. SMILE overexpression significantly decreased BMP receptor-induced hepcidin promoter activity. SMILE overexpression also significantly suppressed BMP-6-mediated induction of hepcidin mRNA and its secretion in HepG2 and AML12 cells. EGCG treatment inhibited BMP-6-mediated hepcidin gene expression and secretion, which were significantly reversed by SMILE knockdown in hepatocytes. Interestingly, SMILE physically interacted with SMAD1 in the nucleus and significantly blocked DNA binding of the SMAD complex to the BMP-response element on the hepcidin gene promoter. Taken together, these findings suggest that SMILE is a novel transcriptional repressor of BMP-6-mediated hepcidin gene expression, thus contributing to the control of iron homeostasis.

Highlights

Published: 10 October 2021Hepcidin, a hepatic circulating peptide, acts as a critical regulator of systemic iron homeostasis, which is the balance between the iron uptake into enterocytes, stored iron release from hepatocytes and iron recycling by macrophages [1]
To investigate whether EGCG could affect Bone morphogenetic protein-6 (BMP-6) receptor signaling in hepatocytes, we first examined the cytotoxic effects of EGCG on human (HepG2 and Huh7 cells) and mouse (AML12 cells) hepatocytes using the MTT assay
The reduction of FPN by BMP-6 was significantly reversed by EGCG (Figure 1d,e). These results suggest that EGCG could inhibit BMP-6 receptor signaling in hepatocytes

Summary

Introduction

A hepatic circulating peptide, acts as a critical regulator of systemic iron homeostasis, which is the balance between the iron uptake into enterocytes, stored iron release from hepatocytes and iron recycling by macrophages [1]. Hepcidin can bind to ferroportin (FPN, a mammalian iron exporter located mainly on the membrane of enterocytes, hepatocytes and macrophages) and induce its endocytosis and lysosomal degradation, thereby precluding iron efflux into plasma [2]. The BMP-6–hemojuvelin (HJV, a BMP co-receptor) complex can bind to heterodimeric BMP receptors (BMPRs) composed of type I (BMPRI; ALK1, ALK2, ALK3 and ALK6) and type II (BMPRII, ACTRIIA and ACTRIIB) serine threonine kinase receptors. Activated BMPR I can phosphorylate regulatory SMADs (R-SMADs; SMAD1, SMAD5 and SMAD8) [7,11]. Phosphorylated SMAD1/5/8 proteins form a heteromeric complex with co-mediator SMAD (co-SMAD; SMAD4). Translocation of the complex into the nucleus can activate hepcidin transcription [12,13]

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