Ultraviolet-B induces ERCC6 repression in lens epithelium cells of age-related nuclear cataract through coordinated DNA hypermethylation and histone deacetylation.

Yong Wang,Fei Li,Guowei Zhang,Huaijin Guan,Lihua Kang

doi:10.1186/s13148-016-0229-y

Abstract

BackgroundUltraviolet-B (UVB) exposure attributes to the formation of age-related nuclear cataract (ARNC), which is mediated with DNA damage. DNA damage, an important factor for pathogenesis of ARNC, is induced by UVB, and is generally resolved by the nucleotide excision repair (NER) repair mechanism. Cockayne syndrome complementation group B (CSB) protein coded by ERCC6 is a vital component for NER. However, we found no association between selected ERCC6 polymorphisms and ARNC. In this study, we investigated whether UVB exposure could alter ERCC6 expression and the process could involve epigenetic changes of DNA methylation and/or histone acetylation of ERCC6 in the lens epithelial cells (LECs). We also assessed the involvement of those coordinated changes in lens tissue from ARNC patients.ResultsmRNA and protein expression of ERCC6 in lens tissue (LECs) were lower in ARNCs than those in the controls. This reduction corresponded to methylation of a CpG site at the ERCC6 promoter and histone modifications (methylation and acetylation) nearby this site. UVB-treated human lens epithelium B3 (HLE-B3) and 239T cell presented (1) increased apoptosis, suggesting reduced UV-damage repair, (2) hypermethylation of the CpG site located at position -441 (relative to transcription start site) within the binding region for transcriptional factor Sp1 in the ERCC6 promoter, (3) the enhancement of histone H3K9 deacetylation, (4) induction in DNA methyltransferases 3b (DNMT3b) and histone deacetylase1 (HDAC1) associated to the CpG site of ERCC6 by CHIP assay.ConclusionsThese findings suggest an orchestrated mechanism triggered by UVB radiation where the concurrent association of specific hypermethylation CpG site, H3K9 deacetylation of ERCC6, and repression of ERCC6 gene expression. Taken together, with the similar changes in the lens tissue from ARNC patients, our data unveiled a possible mechanism of epigenetic modification of DNA repair gene in the pathogenesis of ARNC.Electronic supplementary materialThe online version of this article (doi:10.1186/s13148-016-0229-y) contains supplementary material, which is available to authorized users.

Highlights

Ultraviolet-B (UVB) exposure attributes to the formation of age-related nuclear cataract (ARNC), which is mediated with DNA damage
Results mRNA and protein expression of ERCC6 in lens tissue (LECs) of controls and Age-related nuclear cataract (ARNC) The transcript and protein expression of ERCC6 in lens epithelial cells (LECs) of controls and ARNCs were detected by quantitative reversetranscription polymerase chain reaction and Western blot analysis. mRNA expression of ERCC6 was 2.44-fold lower in LECs of ARNC than that of the controls (Fig. 1a, Additional file 1: Table S1)
ERCC6 mRNA levels and protein expression correlate with the methylation status of CpG site 8 in LECs of controls and ARNCs Bioinformatic analysis indicated a CpG island (from -603 to -396, transcription start site (TSS) as +1: chr10:49540952) located in the promoter of ERCC6, and a putative binding site for Sp1 was predicted in this region (Fig. 2a)

Summary

Introduction

Ultraviolet-B (UVB) exposure attributes to the formation of age-related nuclear cataract (ARNC), which is mediated with DNA damage. DNA damage, an important factor for pathogenesis of ARNC, is induced by UVB, and is generally resolved by the nucleotide excision repair (NER) repair mechanism. We investigated whether UVB exposure could alter ERCC6 expression and the process could involve epigenetic changes of DNA methylation and/or histone acetylation of ERCC6 in the lens epithelial cells (LECs). Age-related nuclear cataract (ARNC) ranks as the most common type of ARC [5]. Several studies suggested that ultraviolet (UV) radiation may be a cataractogenic factor [6,7,8,9,10]. Several studies showed a correlation between UVB exposure and nuclear cataract formation [14,15,16]. The exact mechanism is not completely understood in such cataractogenesis

Methods

Results

Discussion

Conclusion