Estrogen receptors genetic polymorphisms risk association and their functional roles in breast cancer risk: a study on Hong Kong Chinese women

Abstract

Estrogen receptor-alpha (ESR1) and -beta (ESR2) are known to play critical biological roles in estrogen signaling related to breast cancer progression. ESR1 polymorphism risk association has been conducted in different ethnic groups, but variable results have been observed. ESR2 is not as well-studied as ESR1. To investigate their role in the Chinese population, we re-sequenced the promoter and coding sequence regions of ESR1 and ESR2 in 90 local Chinese women and identified some novel single nucleotide polymorphisms (SNPs), not previously reported in the public database. After tagging-SNP analysis, all known and novel SNPs with minor allele frequency ≥0.05 were genotyped in 340 breast cancer cases and 325 age-matched controls by Sequenom and TaqMan assays. GeneScan analysis was used to genotype the TA dinucleotide tandem repeat (TAn) in the ESR1 promoter. Haplotype analysis (following the methodology of Gabriel et al) revealed that the cancer and control groups harbored different haplotype block patterns for ESR1. Haplotype block 1 (rs2071454-rs867239-rs2077647; haplotype G-G-C) and block 2 (rs2234693-rs9340799; haplotype C-A) were found to have significant association with lower breast cancer risk (OR=0.72, 95%CI=0.53-0.98, p=0.038; and OR=0.72, 95%CI=0.55-0.94, p=0.016). The five ESR1 SNPs in the haplotype blocks were also found independently associated with lower risk from genotype analysis. TA≤16 of ESR1 was found associated with increase of breast cancer risk (OR=1.47, 95%CI=1.18-1.84, p=0.0006). Functional role of the TAn repeat length of ESR1 in promoter activity was examined using luciferase reporter promoter activity assay. Results showed that TA16 had significant higher activity than TA22 and TA23. Shorter TAn repeat might form secondary DNA structures which may provide better binding sites for some transcriptional factors and/or with less hindering effect to nearby enhancer elements in ESR1. For ESR2, in contrast, no significant risk associated haplotype was found. The G-allele carrier of an ESR2 SNP (rs1256054) was found associated with higher breast cancer risk (OR=1.80 95%CI=1.01-3.20, p=0.046). Our results showed that ESR1 and ESR2 polymorphisms contributed to breast cancer susceptibility in Hong Kong Chinese women. Risk associated ESR1 SNPs and the haplotypes containing these SNPs were identified. The length of the ESR1 TAn repeat might have a role in regulating ESR1 promoter activity hence controlling gene expression. Further investigation of SNP-SNP interaction between the two genes will be performed using statistical models to identify SNPs with synergetic effect to breast cancer risk.