Abstract
As transcriptional regulators, circadian genes have the potential to influence a variety of biological pathways, including many cancer-related processes. Cryptochrome 2 (CRY2) is essential for proper circadian timing and is a key component of the circadian regulatory feedback loop. Here, we report findings from genetic, epigenetic, loss-of-function, and transcriptional profiling analyses of CRY2 in breast cancer. Six single-nucleotide polymorphisms in CRY2 were identified for genotyping in a case-control population (n = 441 cases and n = 479 controls), and three single-nucleotide polymorphisms (rs11038689, rs7123390, and rs1401417) were significantly associated with postmenopausal breast cancer risk, with significant effect modification by menopausal status [dominant model for rs11038689: odds ratio (OR), 0.71; 95% confidence interval (95% CI), 0.51-0.99; P for trend = 0.028; homozygous variants for rs7123390: OR, 0.44; 95% CI, 0.22-0.86; P for trend = 0.028; and rs1401417: OR, 0.44; 95% CI, 0.21-0.92; P for trend = 0.017]. Interestingly, this association was only evident in women with estrogen and progesterone receptor (ER/PR)-negative breast tumors but not with ER/PR-positive tumors. Breast cancer patients also had significantly higher levels of CRY2 promoter methylation relative to controls, which is consistent with tissue array data showing lower levels of CRY2 expression in tumor tissue relative to adjacent normal tissue. Furthermore, in vitro analyses identified several breast cancer-relevant genes that displayed altered expression following CRY2 knockdown. These findings suggest a role for CRY2 in breast tumorigenesis and provide further evidence that the circadian system may be an important modulator of hormone-related cancer susceptibility.