Assessing the functional role of caspase-8 gene variants in breast cancer

Rationale and hypothesis

Mutations in high-penetrance genes such as BRCA1 and BRCA2 predispose to breast cancer, and recently a number of low-penetrance breast cancer genes have also been identified. We reported that a coding SNP in the caspase-8 gene (CASP8 D302H) is associated with a reduced risk of breast cancer. More recently we identified a CASP8 4-SNP haplotype associated with an increased risk of breast cancer [1]. A CASP8 promoter indel has been associated with breast cancer in an Asian population, although this has not been confirmed in Europeans. Our hypothesis is that these CASP8 variants may influence breast cancer susceptibility via effects on the apoptotic response.

Objective

Our objectives are to study the functional effects of six relevant CASP8 variants on caspase-8 activity and apoptosis induction in peripheral blood lymphocytes (PBLs).

Methods

We recruited 68 healthy women attending the Sheffield Mammography Screening Service and measured the ability of their PBLs to undergo drug-induced apoptosis. Levels of apoptosis and caspase-8 activity were determined by fluorescence-activated cell sorting analysis (Annexin V-FITC with PI and Red-IETD-FMK (Calbiochem), respectively). The six SNPs were genotyped using TaqMan assays (Applied Biosystems). Data were analysed using parametric and nonparametric analysis of variance.

Results

The median levels of induction of caspase-8 activity and apoptosis were 70.03% (28.19 to 94.65) and 78.11% (18.57 to 92.99), respectively. The rare alleles of rs3834129 (promoter indel), rs7608692 (intron 2) and rs1861269 (intron 4) were associated with reduced caspase-8 activity (P ANOVA = 0.03, 0.005 and 0.048, respectively). In addition, rs1861269 was significantly associated with reduced apoptosis (P ANOVA = 0.036). Although these results need to be confirmed, they suggest that SNPs in the caspase-8 gene may influence breast cancer susceptibility via effects on caspase-8 activity and apoptosis.