Investigating the functional significance of an FGFR2 intronic SNP in Breast Cancer

Abstract

Single nucleotide polymorphisms present in the second intron of the fibroblast growth factor receptor 2 (FGFR2) gene have been linked with increased risk of breast cancer in several genome wide association studies. The potential effect of those SNPs appeared to be mediated through the differential binding of cis-regulatory elements, such as transcription factors, since all the SNPs in linkage disequilibrium were located in a regulatory DNA region. Preliminary studies have shown that a Runx2 binding site is functional only in the minor, disease associated allele of rs2981578, resulting in increased expression of FGFR2 in cancers from patients homozygous for that allele. Moreover, the increased risk conferred by the minor FGFR2 allele is associated most strongly in oestrogen receptor alpha positive (ERα) breast tumours, suggesting a potential interaction between ERα and FGFR signalling. Here, we have developed a human cell line model system to study the effect of those SNPs on cell behaviour. In an ERα positive breast cancer cell line, rs2981578 was edited using Zinc Finger Nucleases. Unexpectedly, the acquisition of the single risk allele in MCF7 cells failed to affect proliferation or cell cycle progression. Binding of Runx2 to the risk allele was not observed. However FOXA1 binding, an important ERα partner, appeared decreased at the rs2981578 locus in the risk allele cells. Additionally, differences in allele specific expression (ASE) of FGFR2 were not observed in a panel of 72 ERα positive breast cancer samples. Thus, the apparent increased risk of developing ERα positive breast cancer is not caused by rs2981578 alone. Rather, the observed increased risk of developing breast cancer might be the result of a coordinated effect of multiple SNPs forming a risk haplotype in the second intron of FGFR2.