The effect of cyclin D1 (CCND1) G870A-polymorphism on breast cancer risk is modified by oxidative stress among Chinese women in Singapore

Cyclin D1 (CCND1), an intracellular cell-cycle regulatory protein with checkpoint function, can promote cell proliferation or induce growth arrest and apoptosis depending on the cellular context. We hypothesized that the direction of the association between the (CCND1) G870A-polymorphism and breast cancer risk may be modified by dietary and genetic factors influencing the oxidant-antioxidant balance, such as a dietary pattern with a high intake of n-6 fatty acids and a low intake of n-3 fatty acids, or a genetic profile that is deficient in glutathione S-transferases. We tested our hypothesis in a case-control study nested into the Singapore Chinese Health Study, a prospective investigation of diet and cancer in 63,000 Chinese men and women. Genomic DNA collected from 258 incident cases of breast cancer and 670 female cohort controls was examined for CCND1, GSTM1, GSTT1 and GSTP1 genes using fluorogenic 5'-nuclease assay. Unconditional logistic regression models were used to assess the effects with adjustment for potential confounders. All statistical tests were two-sided. The heterozygous CCND1 GA genotype significantly reduced the breast cancer risk in all subjects (OR=0.67, 95% CI 0.45-0.99) when compared with the GG genotype. The association was restricted to women with a high (above median value) intake level of n-6 fatty acids (OR=0.51, 95% CI 0.30-0.87), a low (below median value) intake level of the antagonistic marine n-3 fatty acids (OR=0.54, 95% CI 0.32-0.93) or a total lack of the antioxidative GSTM1 (OR=0.44, 95% CI 0.25-0.80) or GSTT1 genes (OR=0.46, 95% CI 0.24-0.87). The effects were consistently stronger in cases with advanced disease. The AA genotype did not affect breast cancer risk. The results of this study are compatible with the hypothesis that the oxidant-antioxidant balance in cells is an important determinant of the direction of the cyclin D1 effect, leading either to cell proliferation or cell death.